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  • Springer  (394,840)
  • 1990-1994  (232,620)
  • 1970-1974  (115,206)
  • 1955-1959  (47,014)
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Year
  • 1
    Keywords: Leukemia / therapy ; Prognosis
    Notes: Last volumes with varying subtitle and editor.
    ISSN: 0949-7021
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  • 2
    Keywords: Hazardous Substances / toxicity
    Notes: Ceased with vol. 15(1999).
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  • 3
    ISSN: 1432-0932
    Keywords: Intervertebral disc ; Nd-YAG laser ; Lumbosacral region
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In a prospective study on 50 patients, the 1064-nm Nd-YAG laser was used to denaturate protruding lumbar discs. The method of Ascher [1] was modified using a saline pressure infusion system. Early results show a very good decompressive effect with 48 out of 50 patients in the categories very good and good. At follow-up (mean 184 days postoperation) 31 out of 46 were in these categories, indicating a longer lasting retrieval of the protruded mass. A marked reduction of clinical nerve compression signs was noted. No severe complications occurred. Due to the irrigation system less low back pain was reported. The method seems promising in the standard neurosurgical setting
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  • 4
    ISSN: 1432-0932
    Keywords: Intervertebral disc degeneration ; Discomanometry ; Minipig ; Hyaluronic acid ; Viscosupplementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In an experimental study with 18 minipigs, we have tried to establish a model for the standardized evaluation of mechanical, histological and radiological phenomena of degenerative and reparative processes within the lumbar motion segment. Comparing different operative techniques revealed that the intradiscal application of hyaluronic acid into the nuclear defect is likely to enhance the regeneration process. Using the measurement of disc compliance, a semiautomatic picture analyzer and a new semiquantitative disc score could make future studies more comparable. From this basis, the intradiscal application of hyaluronic acid deserves further evaluation.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 28-31 
    ISSN: 1432-0932
    Keywords: Discography ; Delayed pain onset ; Incomplete annular tears ; Anterior spinal tenderness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The delayed onset of symptomatic pain following lumbar discography (with no immediate pain response) is described in six patients, five with a minimum 2-year follow-up. It is usually seen in patients with nearly normal disc morphology who have incomplete or discrete annular tears that are not filled at the time of injection. Later (2–12 h in this study), dye leakage occurs through these lesions, thereby precipitating the discogenic pain This phenomenon may be missed and is probably more common than previously believed due to early discharge from the hospital, the patient expecting discomfort after the invasive study (hence no complaint is made), and the clinician being unaware of this delayed symptom, thereby not asking about it in follow-up. Close patient questioning regarding a delayed onset of symptomatic pain after discography is, therefore, an essential element in diagnostic information following this study.
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  • 6
    ISSN: 1432-0932
    Keywords: Spinal fusion ; Thoracolumbar fractures ; Transpedicular bone graft
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Fifty patients with thoracolumbar fractures were treated by internal fixation using the Dick fixator. In the first 22 patients (group 1) this was accompanied by posterior intertransverse grafting. The technique was then modified in the following 28 patients (group 2) to include transpedicular elevation of the depressed vertebral end plate and grafting of the vertebral body, in an attempt to reduce the postoperative loss of correction of the kyphotic deformity. The clinical records and X-rays were reviewed to determine whether the change in technique had achieved this objective and whether it affected operative time, blood loss, postoperative recovery and complications. The mean operating time and blood loss in group 1 were 2 h, 38 min and 650 ml, respectively, and in group 2 2 h, 59 min and 783 ml. These differences were not statistically significant. Time from operation to mobilisation and discharge from hospital were related to neurological deficit, but there was no significant difference between group 1 and group 2 in this regard. There was no difference in the complication rate between the two groups and no complication attributable to transpedicular bone grafting. The radiological results postoperatively and at a mean follow-up period of 9 months were assessed by measurement of the kyphosis angle, anterior vertebral height, anterior displacement, scoliosis, and reduction in cross-sectional area of the spinal canal. In group 1 the mean preoperative kyphosis angle and anterior vertebral height were 8° and 21 mm; postoperatively these values were −12° (lordosis) and 27 mm; and at follow-up they were −4° and 24 mm. In group 2 the mean preoperative kyphosis angle and anterior vertebral height were 9.7° and 16 mm; postoperatively these values were −11° and 31 mm; and at follow-up they were −6° and 30 mm. The difference in the restoration and maintenance of anterior vertebral height between the two groups was statistically significant. The mean reduction of canal cross-sectional area for all patients preoperatively was 56%. The mean postoperative reduction of canal cross-sectional area was 23%. It is concluded that use of the Dick fixator for thoracolumbar fractures produces marked correction of the kyphosis angle and restoration of anterior vertebral height and a moderate restoration of canal cross-sectional area. The correction of the kyphosis angle and anterior vertebral height is greater and maintained better in the postoperative period if transpedicular bone grafting of the vertebral body is also performed.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 294-294 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 8
    ISSN: 1432-0932
    Keywords: Sciatic nerve ; Compressive neuropathy ; Bone graft ; Piriformis muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A 27-year-old woman developed a haematoma-related compressive neuropathy of the right sciatic nerve following the harvesting of a bone graft from the posterior aspect of the right iliac crest. The nerve was compressed in an enclosed compartment between the sciatic notch and the piriformis muscle, which is thought to be involved in the piriformis syndrome. The symptoms improved once the haematoma was evacuated, and this complication stresses the importance of adequate haemostasis of the area from which the bone graft is taken.
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  • 9
    ISSN: 1432-0932
    Keywords: Thoracolumbar spine trauma ; Burst fracture ; Spinal canal encroachment ; Bone fragment resorption ; Computed tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Spinal canal areas were measured prospectively in 22 consecutive burst fractures of the thoracolumbar junction, preoperatively, within 1 week postoperatively and 1 year after operation. Preoperative canal encroachment averaged 38% (range 10%–70%) of the estimated original area. The 11 patients with neurological impairment had a significantly more severe initial canal encroachment (mean 48%) than those who were neurologically intact (mean 33%). Postoperatively, canal encroachment had decreased to a mean of 18% (range 0%–62%). Within 12 to 15 months postoperatively, canal encroachment was further reduced by resorption of bone fragments to a mean of 2%. The largest observed remaining encroachment was 29%. The amount of bone resorption correlated significantly with the persistent postoperative encroachment. A critical appraisal of the methods used to assess the pre-fracture canal area revealed that reconstructing the vertebral foramen of the fractured vertebra on CT scans substantially overrated the original area as compared with averaging the canal area of the two adjacent vertebrae.
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  • 10
    ISSN: 1432-0932
    Keywords: Disc herniation ; Macrophage ; Blood vessel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Twenty disc herniations (DH) were studied immunocytochemically for macrophages and blood vessels. Serial thin frozen sections were immunostained with an antibody specific for tissue macrophages (monoclonal antibody to CD68 antigen) and the endothelium of blood vessels (polyclonal antibody to von Willebrand factor). With this method, blood vessels, often abundant, were observed in as many as 16/20 (80%) of the DH studied, 12 disc extrusions and 8 sequestrated discs, whereas abundant macrophages were noted in 11/20 (55%) of the DH. Macrophages were present only in areas with blood vessels and had presumably infiltrated the tissue from them. As has been noted previously, some blood vessels are apparently newly formed as a result of tissue injury, whereas others were present in the disc prior to herniation. This is suggested by the lack of a clear correlation between the presence or absence of blood vessels and the preoperative duration of radicular pain. In areas of the DH where cartilage fragments occurred, both macrophages and blood vessels were particularly abundant.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 353-353 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 354-354 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 13
    ISSN: 1432-0932
    Keywords: Low-back pain ; Bony vibration ; Discography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Fifty-seven patients with low-back pain were evaluated immediately prior to a discography examination by means of an electrical tool which produced bony vibration to the lumbar spinal processes. The vibrator was composed of a standard electric toothbrush shaft (Braun) with a blunt head instead of the brush. The lumbar spinal processes were compressed one by one for a few seconds with this blunt, vibrating tool. The patient's pain experience provoked by vibration was compared with that from injections during discography. A good correlation was found between these two examinations when patients with previously operated backs and painful, prolapsed discs were excluded: sensitivity was 0.96 and specificity 0.72. Prolapsed, but discographically painful discs were always painless in the vibration examination. The local, non-invasive bony vibration stimulation test is an easy, quick, safe, inexpensive and reliable method for examining intradiscal pain.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 239-239 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 15
    ISSN: 1432-0932
    Keywords: Lumbar nerve root sheath infiltration ; CT-guided infiltration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To determine the reliability of lumbar nerve root sheath infiltration, a prospective study was performed. Ninety-four patients were randomized into three groups. In the first group of 33 patients, 0.5 cc of dye (Telebrix N, 30 g) was applied at nerve root L4, in the second group of 30 patients, 1.0 cc, and in the third group of 31 patients, 2.0 cc. The infiltration was quided by computer tomography. The diffusion of the dye was documented with computed tomography of the affected segment L4-5. The images were evaluated by an unbiased observer. The results showed that in the first group the dye diffused to the adjacent ipsilateral nerve roots L3 and/or L5 in nine patients. In the second and third groups this diffusion was seen in 9 and 11 patients, respectively. A diffusion into the psoas muscle was documented in 4, 10 and 22 patients, respectively. These latter differences were statistically significant (P 〈 0.01). Diffusion into the psoas muscle is especially important because the nerve roots converge in this muscle to become a plexus, and they are no longer surrounded by their dural sheaths. Diagnostic lumbar nerve root sheath infiltration should be performed by an experienced examiner. To guarantee high reliability, the tip of the needle should be placed as near as possible to the affected nerve root. The amount of local anaesthetic should be as small as possible, 0.5 cc or preferably less.
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  • 16
    ISSN: 1432-0932
    Keywords: Low-back pain ; Sciatica ; Spinous hypertrophy ; Spina bifida occulta ; Spinous impingement syndrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We report on a rare disease called to Anquin's disease or spinous engagement or impingement syndrome. Low-back pain in this specific syndrome probably combined with sciatica is caused by a hypertrophic spinous process along with a spina bifida occulta of the underlying vertebra. Mostly, the enlarged spinous process is seen at L5 and the spina bifida occulta at S I. Conservative therapy consists of physiotherapy with postural exercises including improvement of lumbar flexion. If conservative treatment is unsuccessful, surgical treatment is indicated. Surgical therapy should include resection of the hypertrophic spinous process, probably combined with revision of the nerve roots and division of adhesions. Between 1981 and 1993 six patients were treated surgically after long-lasting periods of conservative therapy. All patients were re-examined clinically and radiologically after a mean follow-up period of 2.9 years. In all but one patient a distinct release from lumbar back pain and/or sciatica was observed. Regarding this, the most important fact in de Anquin's disease is to be aware of this specific syndrome. If low-back pain can be traced to a hypertrophic spinous process the first choice of therapy should be conservative. In unsuccessful cases simple surgical resection probably combined with division of the adhesion can lead to significant release from pain and is recommended.
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  • 17
    ISSN: 1432-0932
    Keywords: Osteoporosis ; Burst fracture ; Paraplegia ; Harrington fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This is a report of seven patients suffering from osteoporosis, who sustained unstable burst fractures in the thoracolumbar spine associated with neurological impairment, without trauma. The manner of presentation, the neurological involvement, the radiological findings, as well as the surgical treatment with respect to functional and neurological recovery are discussed.
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 289-290 
    ISSN: 1432-0932
    Keywords: Fetal alcohol syndrome ; Klippel-Feil anomaly ; Alcohol abuse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Alcohol is the most frequent and most important teratogenic noxa for the embryo and fetus. It may lead to deformation of all cells and organs. A case of Klippel-Feil anomaly associated with fetal alcohol syndrome is described. The diagnosis of Klippel-Feil anomaly, even a late diagnosis made on the basis of rare deformities, is very important as the affected patients are at a high risk of alcoholism. The combination of Klippel-Feil anomaly with numerous other syndromes and deformities suggests a basic general disorder of skeletal maturation. Diverse cases of Klippel-Feil anomaly possibly originate., in reality, in an unrecognzied fetal alcohol syndrome.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 236-236 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 20
    ISSN: 1432-0932
    Keywords: Spine surgery ; Magnetic resonance imaging ; (MRI) ; Artifacts ; Orthopaedic devices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Magnetic resonance (MR) imaging is often disturbed after spine surgical procedures with or without an implant. Artifacts are induced by ferromagnetic or nonferromagnetic implants and devices and by small metallic particles left by surgical instruments. All metallic artifacts can affect the quality and usefulness of postoperative spine MR examinations. The physical effects caused by the introduction of metal or other conductive materials into a magnetic field and their consequences are presented. The application to postoperative spine MR examinations and solutions to reduce artifacts are discussed.
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  • 21
    ISSN: 1432-0932
    Keywords: Lumbar spinal stenosis ; Low back pain ; Oswestry questionnaire ; Decompressive surgery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A total of 439 patients operated on for lumbar spinal stenosis during the period 1974–1987 was re-examinated and evaluated for working and functional capacity approximately 4 years after the decompressive surgery. The assessment of subjective disability was based on the Oswestry low-back pain questionnaire. The proportion of excellent-to-good outcomes was 62% (women 57%, men 65%). The ability to work before or after the operation and a history of no prior back surgery were variables predictive of a good outcome. Before the operation 86 patients were working, 223 patients were on sick leave, and 130 patients were retired. After the operation 52 of the employed patients and 70 of the unemployed patients returned to work. None of the retired patients returned to work. In logistic regression analysis the ability to work preoperatively, age under 50 years at the time of operation and the absence of prior back surgery predicted a postoperative ability to work. Our results suggest that more attention should be focussed on the diagnosis of spinal stenosis and on the timing of the operative intervention.
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  • 22
    ISSN: 1432-0932
    Keywords: Back pain ; Pregnancy ; Pain provocation test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study was done to evaluate a new, simple, non-invasive pain provocation test as an aid to differentiate between low-back and posterior pelvic pain in pregnant women. The test was performed on 72 pregnant women at various stages of pregnancy with or without low-back or posterior pelvic pain. The study was conducted by two physiotherapists with special interest in back pain in pregnancy at a normal antenatal clinic. The test was easy to learn, perform and interpret and was applicable throughout pregnancy. There was a strong correlation between a positive test answer and a history of posterior pelvic pain (P 〈 0.01, chi-square). There were no side-effects. The test was highly specific and had a high positive prediction value for posterior pelvic pain and a high negative prediction value for low-back pain among pregnant women.
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 282-285 
    ISSN: 1432-0932
    Keywords: Odontoid fracture ; Anterior screw fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A total of 150 odontoid fractures was treated over a 12-year period, 43 by anterior screw fixation. The rate of pseudarthrosis dropped from 20% to 5% in type II unstable fractures. Thus, anterior screw fixation seems to be safe and efficient, and may be more widely used to treat all type 11 and some type III fractures. Odontoid pseudarthrosis is usually tolerated quite well and therefore requires no correction. If necessary, anterior grafting with fixation can be proposed as an alternative for posterior fusion.
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  • 24
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 3 (1994), S. 347-352 
    ISSN: 1432-0932
    Keywords: Spinal instrumentation ; Internal fixation ; Scoliosis ; Spinal deformity ; Spinal trauma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this paper is to describe the concepts and use of a new, versatile instrumentation system, the universal spine system (USS), that has been designed to have wide application for pathology of the thoracolumbar spine. Many instrumentation systems for thoracolumbar spinal surgery now exist that were each originally designed to address specific areas of spinal pathology. For example, the recent systems designed to treat scoliosis deformities do not provide the instrumentation and implant support to adequately address other spinal disorders, such as fractures. In addition, most posterior implant systems were not designed for use anteriorly, and vice versa. As a result, surgeons have been required to become familiar with several different instrumentation systems in order to meet the varied needs of a spinal surgery practice. The objective of designing a new system was to simplify the surgical treatment of the commonly encountered spinal disorders by providing the surgeon with a single set of instruments and implants that could be used to treat tumors, trauma, deformities, and degnerative conditions affecting the thoracolumbar spine, via either an anterior or a posterior approach. This paper describes the development of the concepts, instruments, and implants of the USS and provides examples of its application in several case illustrations.
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  • 25
    ISSN: 1432-0932
    Keywords: Human lumbar muscle ; Muscle biopsy ; Myofiber
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The macroanatomy of the clinically important lumbar muscles has recently been investigated in detail, whereas the information about their microscopic structure in healthy persons is still scanty. In this study we have analysed lumbar multifidus and erector spinae muscles from 21 previously healthy persons who died suddenly and were of working age (range 23–65 years, mean 44.7 years). The microscopic structure of myofibers within the lumbar muscles was found to be regionally uniform, which renders in vivo biopsies representative of the whole muscle bulk. Somewhat surprisingly, age did not significantly influence fiber type composition, fiber size, or proportion of nonmuscular tissue. There was a slight predominance of type 1 fibers. The size of type 1 fibers (mean lesser diameter 54.0 μm) corresponded to that in other skeletal muscles, with no significant sex difference (55.1/51.6 μm male/female). Selective type 2 fiber atrophy was a common finding in both sexes, but significantly less so in men (mean diameter 38.8/28.4 μm male/female). We suggest that the values of fiber type proportions and fiber size in the deep multifidus presented in this study can be used as reference values for healthy adults in the present society with limited physical activity.
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  • 26
    ISSN: 1432-0932
    Keywords: Thoracolumbar fractures ; Harrington rods ; Zielke device
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thirty consecutive patients who had suffered unstable fractures and dislocations of the thoracolumbar spine mostly associated with neurologic impairment and bony encroachment on the spinal canal were treated either with Harrington distraction rods combined with sublaminar wires or with the Zielke-VDS device. These patients were subsequently assessed for neurologic outcome, spinal canal clearance, sagittal and coronal spinal deformity correction preoperatively and postoperatively with a minimum follow-up of 26 months. In the follow-up evaluation, the patients who underwent surgery with Harrington rods showed an overall improvement of their neurologic function of 90.9%, whereas all patients who underwent the Zielke operation improved. Preoperatively, positive correlations were found between the level of injury and Frankel grades; the cord lesion tended to demonstrate more severe neurologic deficit when compared with cauda equina ones (P 〈 0.001). Furthermore, dislocation accompanying the injury resulted in a more severe neurological deficit (P 〈 0.05). Harrington rods and Zielke device offer sufficient initial correction of the frontal spinal deformity but did not significantly either restore or maintain sagittal plane alignment. The Harrington series showed an overallimprovement of the segmental kyphosis of 26% (NS), with a subsequent loss of correction of 7.38% (NS) on the follow-up observation. The Zielke device produced an immediate, much better correction of the segmental posttraumatic kyphosis of 45% (NS), but a loss of correction of 22.9% (NS) was measured in the follow-up evaluation. Correction of the anterior and posterior vertebral height was shown to be better for the Zielke patient group. The coronal deformity was completely corrected equally well by the Harrington and Zielke devices. There was no statistically significant correlation between the degree of bony encroachment of the spinal canal and the initial Frankel grade. Additionally, no statistically significant correlation was found between correction of the sagittal deformity, restoration of anterior and posterior vertebral height, coronal deformity correction, and clearance of the vertebral canal. Concerning neurological status, no patient in either group was worse in the follow-up evaluation. A significant correlation was found between the age of the patient and the neurological improvement favoring young patients (P 〈 0.001).
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  • 27
    ISSN: 1432-0940
    Keywords: Primary 28A65 ; Secondary 58F11 ; Invariant measures ; Higher-dimensional transformations ; Approximations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let τ be a piecewiseC 2 transformation on a rectangular partition of then-dimensional cube which has a unique absolutely continuous invariant measure. An approximation to τ by a sequence of Jablonski transformations is presented and it is shown that the associated sequence of invariant density functions converges to the density function invariant under τ. An example is presented.
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  • 28
    ISSN: 1432-0940
    Keywords: 41A10 ; 41A15 ; 41A25 ; 41A29 ; Polynomial and spline approximation ; Degree of convex approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We prove that a convex functionf ∈ C[−1, 1] can be approximated by convex polynomialsp n of degreen at the rate of ω3(f, 1/n). We show this by proving that the error in approximatingf by C2 convex cubic splines withn knots is bounded by ω3(f, 1/n) and that such a spline approximant has anL ∞ third derivative which is bounded by n3ω3(f, 1/n). Also we prove that iff ∈ C2[−1, 1], then it is approximable at the rate ofn −2 ω(f″, 1/n) and the two estimates yield the desired result.
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  • 29
    ISSN: 1432-0940
    Keywords: Primary 42C10 ; Secondary 44A05 ; Bessel functions ; Fourier series ; Hankel transform ; A p -theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract LetJ μ denote the Bessel function of order μ. For α〉−1, the system x−α/2−1/2Jα+2n+1(x1/2, n=0, 1, 2,..., is orthogonal onL 2((0, ∞),x α dx). In this paper we study the mean convergence of Fourier series with respect to this system for functions whose Hankel transform is supported on [0, 1].
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  • 30
    ISSN: 1432-0940
    Keywords: Primary 41A50, 41A63 ; Secondary 31A05 ; Best approximation ; Harmonic function ; Riemannian manifold ; Density theorem ; Kolmogorov criterion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We investigate best uniform approximations to bounded, continuous functions by harmonic functions on precompact subsets of Riemannian manifolds. Applications to approximation on unbounded subsets ofR 2 are given.
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  • 31
    ISSN: 1432-0940
    Keywords: 41A05 ; 41A28 ; Simultaneous approximation ; Lagrange interpolation ; Pairwise distinct nodes ; Chebyshev polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Recently, several publications have been devoted to investigation of simultaneous Lagrange interpolating approximation. In this paper we carefully construct a counterexample with a system of nodes showing that the simultaneous Lagrange interpolating approximation need not always be convergent. It is especially interesting to note that the system of nodes behaving “badly” in this case is exactly the “near optimal choice” in the ordinary Lagrange interpolating case, the zeros of the Chebyshev polynomials.
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  • 32
    Electronic Resource
    Electronic Resource
    Springer
    Constructive approximation 10 (1994), S. 95-106 
    ISSN: 1432-0940
    Keywords: 41A27 ; 41A40 ; Inverse inequality ; Kantorovich operators
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract For the Kantorovich polynomial approximationK n (f, t), 1〈p≤∞, we prove that, for somem, This equivalence includes a strong converse inequality of type B.
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  • 33
    ISSN: 1432-0940
    Keywords: 30D10 ; 30D15 ; Riemann Hypothesis ; de Bruijn-Newman constant ; Lehmer pairs of zeros
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We give here a rigorous formulation for a pair of consecutive simple positive zeros of the functionH 0 (which is closely related to the Riemann ξ-function) to be a “Lehmer pair” of zeros ofH 0. With this formulation, we establish that each such pair of zeros gives a lower bound for the de Bruijn-Newman constant Λ (where the Riemann Hypothesis is equivalent to the assertion that Λ≤0). We also numerically obtain the following new lower bound for Λ: $$ - 4.379 \cdot 10^{ - 6}〈 \Lambda $$
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  • 34
    Electronic Resource
    Electronic Resource
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    Constructive approximation 10 (1994), S. 145-152 
    ISSN: 1432-0940
    Keywords: 30E10 ; 41A10 ; Key words and phrases ; Polynomial approximation ; Complex domain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We investigate the possibility of approximating a function on a compact setK of the complex plane in such a way that the rate of approximation is almost optimal onK, and the rate inside the interior ofK is faster than on the whole ofK. We show that ifK has an external angle smaller than π at some point zo∈δK, then geometric convergence insideK is possible only for functions that are analytic at zo. We also consider the possibility of approximation rates of the form exp(−cn β), for approximation insideK, where β is related to the largest external angle ofK. It is also shown that no matter how slowly the sequence {γ n } tends to zero, there is aK and a Lip β, β〈1, functionf such that approximation insideK cannot have order {γ n }.
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  • 35
    Electronic Resource
    Electronic Resource
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    Constructive approximation 10 (1994), S. 179-186 
    ISSN: 1432-0940
    Keywords: 30C35 ; 30E10 ; Conformal mapping ; Crowding ; Distortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Letf be a function analytic in the unit diskD. If the rangef(D) off is contained in a rectangleR with sidesa andb withb≤a such thatf(D) touches both small sides ofR, then the supremum norm of the derivative satisfies ‖f′‖ ≥b·ψ(b/a). We derive tight bounds for the best possible function ψ in this estimate. In particular, we show that $$\psi (\tau ) \sim (2\pi \sqrt e )^{ - 1} \cdot \exp (\pi /2\tau )$$ for small τ.
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  • 36
    ISSN: 1432-0940
    Keywords: Primary ; 41A10 ; 41A25 ; 41A29 ; Degree of convex approximation by polynomals ; Averaged moduli of smoothness ; Ditzian-Totik moduli of smoothness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let Δ q be the set of functionsf for which theqth difference, is nonnegative on the interval [− 1,1],P n is the set of algebraic polynomials of degree not exceedingn, τ k (f, δ) p is the averaged Sendov-Popov modulus of smoothness in theL p [−1,1] metric for 1≦p≦∞, ω k (f, δ) and $$\omega _\phi ^k (f,\delta ),\phi (x): = \sqrt {1 - x^2 } ,$$ , are the usual modulus and the Ditzian-Totik modulus of smoothness in the uniform metric, respectively. For a functionf∈C[−1,1]⋂Δ2 we construct a polynomialp n ∈P n ⋂Δ2 such that $$\begin{gathered} \left| {f(x) - p_n (x)} \right| \leqslant C\omega _3 (f,n^{ - 1} \sqrt {1 - x^2 } + n^{ - 2} ),x \in [ - 1,1]; \hfill \\ \left\| {f - p_n } \right\|_\infty \leqslant C\omega _\phi ^3 (f,n^{ - 1} ); \hfill \\ \left\| {f - p_n } \right\|_p \leqslant C\tau _3 (f,n^{ - 1} )_p . \hfill \\ \end{gathered}$$ As a consequence, for a functionf∈C 2[−1,1]⋂Δ3 a polynomialp n * ∈P n ⋂Δ3 exists such that $$\left\| {f - p_n^* } \right\|_\infty \leqslant Cn^{ - 1} \omega _2 (f\prime ,n^{ - 1} ),$$ wheren≥2 andC is an absolute constant.
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  • 37
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    Constructive approximation 10 (1994), S. 187-196 
    ISSN: 1432-0940
    Keywords: Primary 65D10 ; Secondary 41A50 ; 90C30 ; Chebyshev approximation ; Optimality conditions ; Lipschitz optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The problem of calculating the best approximating straight line—in the sense of Chebyshev—to a finite set of points inR n is considered. First-and second-order optimality conditions are derived and analysed. Lipschitz optimization techniques can be used to find a global minimizer.
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  • 38
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    Constructive approximation 10 (1994), S. 197-206 
    ISSN: 1432-0940
    Keywords: 41A10 ; Müntz polynomials ; Incomplete polynomials ; Bernstein polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we prove that given certain convex domains Δ on the plane, ε〉0, andf∈C(Δ) such thatf=0 on θ2Δ={(θ2 x,θ2 y):(x,y)∉Δ} (0〈θ〈1), a polynomialp(x, y) of the form $$p(x,y) = \sum\limits_{\theta n \leqslant k + l \leqslant n} {a_{kl} x^k y^l }$$ exists such that ∥f−p∥ C(Δ) ≤ε. The admissible convex domains include triangles and parallelograms with a vertex at the origin and sections of unit disk.
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  • 39
    ISSN: 1432-0940
    Keywords: 65D07 ; 41A20 ; 41A29 ; Rational splines ; Data interpolation and approximation ; Convexity-preserving data fitting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A discussion and algorithm for combined interpolation and approximation by convexity-preserving rational splines is given.
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  • 40
    ISSN: 1432-0940
    Keywords: Primary 39A10 ; 40A15 ; 30B70 ; 30B40 ; Secondary 40A05 ; 11B37 ; Explicit solutions to linear difference equations and their asymptotic behavior ; Convergence of continued fractions ; Analytic continuation ; Convergence of recurrent sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract For any system of linear difference equations of arbitrary order, a family of solution formulas is constructed explicitly by way of relating the given system to simpler neighboring systems. These formulas are then used to investigate the asymptotic behavior of the solutions. When applying this difference equation method to second-order equations that belong to neighboring continued fractions, new results concerning convergence of continued fractions as well as meromorphic extension of analytic continued fractions beyond their convergence region are provided. This is demonstrated for analytic continued fractions whose elements tend to infinity. Finally, a recent result on the existence of limits of solutions to real difference equations having infinite order is extended to complex equations.
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  • 41
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    Constructive approximation 10 (1994), S. 285-299 
    ISSN: 1432-0940
    Keywords: 41A15 ; 41A50 ; 41A52 ; Best uniform approximation ; Splines with free knots ; Uniqueness of best approximations ; Strong uniqueness of best approximations ; Suns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We derive a necessary alternation condition for unique local best approximations fromS m, k , the set of splines of degreem withk free knots. This result is related to a conjecture of L. L. Schumaker. Moreover, we give a complete description of functions from the interior of the strong unicity set forS m,k 1 the set of splines of degreem withk free simple knots, and show that this set is dense in the unicity set forS m,k 1 . Finally, we prove a general characterization of suns for strong unicity and show thatS m,k 1 is a set of this type, although, it is not a sun.
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  • 42
    ISSN: 1432-0940
    Keywords: 41A20 ; 30C85 ; 30E10 ; 31C15 ; Rational functions ; Ray sequences ; Zolotarev problem ; Logarithmic potential ; Sylvester's equation ; ADI iterative method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Given two compact disjoint subsetsE 1,E 2 of the complex plane, the third problem of Zolotarev concerns estimates for the ratio $$\mathop {\sup }\limits_{z \in E_1 } |r(z)|/\mathop {\inf }\limits_{z \in E_2 } |r(z)|,$$ wherer is a rational function of degreen. We consider, more generally, the infimumZ mn of such ratios taken over the class of all rational functionsr with numerator degreem and denominator degreen. For any “ray sequence” of integers (m, n); that is,m/n→λ,m+n→∞, we show thatZ mn /1/(m+n) approaches a limitL(λ) that can be described in terms of the solution to a certain minimum energy problem with respect to the logarithmic potential. For example, we prove thatL(λ)-exp(−F(τ)), where τ=λ/(λ+1) andF(τ) is a concave function on [0,1] and we give a formula forF(τ) in terms of the equilibrium measures forE 1 * ∪E 2 * and the condenser (E 1 * ,E 2 * ), whereE 1 * ,E 2 * are suitable subsets ofE 1,E 2. Of particular interest is the choice for λ that yields the smallest value forL(λ). In the case whenE 1,E 2, are real intervals, we provide for this purpose a simple algorithm for directly computingF(τ) and for the determination of near optimal rational functionsr mn . Furthermore, we discuss applications of our results to the approximation of the characteristic function and to the generalized alternating direction iteration method for solving Sylvester's equation.
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  • 43
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    Constructive approximation 10 (1994), S. 301-315 
    ISSN: 1432-0940
    Keywords: 41A25 ; 42C05 ; Exponential weights ; Weighted polynomial approximation ; Bernstein's problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We show that ifw(x)=exp(−|x|λ), then in the case λ=1 for every continuousf that vanishes outside the support of the corresponding extremal measure there are polynomialsP n of degree at mostn such thatw n P n uniformly tends tof, and this is not true when λ〈1. These are the missing cases concerning approximation by weighted polynomials of the formw n P n wherew is a Freud weight. Our second theorem shows that even if we are only interested in approximation off on the extremal support, the functionf must still vanish at the endpoints, and we actually determine the (sequence of) largest possible intervals where approximation is possible. We also briefly discuss approximation by weighted polynomials of the formW(anx)P n (x).
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  • 44
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    Constructive approximation 10 (1994), S. 339-376 
    ISSN: 1432-0940
    Keywords: Primary 42A99 ; Secondary 30E20 ; 46A99 ; Weights ; Lipschitz ; Special atoms ; Besov space ; Muckenhoupt weights ; Dini growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Weighted Lipschitz spaces are studied where the growth function varies, i.e., $$|f(x + h) - f(x)| \leqslant C\rho (h)$$ and where the growth function may also depend on x. Connections between a functionf defined on the complex unit circle and its analytic extensionF to the inside are given. In particular, theory relating the Lipschitz growth of the boundary function and derivative growth of the analytic function is developed. An atomic decomposition of the boundary values of a weighted Besov space is also obtained.
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  • 45
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    Constructive approximation 10 (1994), S. 317-338 
    ISSN: 1432-0940
    Keywords: Primary 33C45 ; 33D45 ; 42C10 ; 43A62 ; Secondary 39A12 ; Linearization formula ; Polynomial hypergroup ; Orthogonal polynomials Associated Hermite polynomials ; Associated ultraspherical polynomials ; q-analogues ; Basic hypergeometric function ; Partial difference equation ; Discrete Reimann function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A new constructive approach is given to the linearization formulas of symmetric orthogonal polynomials. We use the monic three-term recurrence relation of an orthogonal polynomial system to set up a partial difference equation problem for the product of two polynomials and solve it in terms of the initial data. To this end, an auxiliary function of four integer variables is introduced, which may be seen as a discrete analogue of Riemann's function. As an application, we derive the linearization formulas for the associated Hermite polynomials and for their continuousq-analogues. The linearization coefficients are represented here in terms of3 F 2 and3Φ2 (basic) hypergeometric functions, respectively. We also give some partial results in the case of the associated continuousq-ultraspherical polynomials.
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  • 46
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    Constructive approximation 10 (1994), S. 377-409 
    ISSN: 1432-0940
    Keywords: Primary 41A52 ; 42A10 ; 41A10 ; Secondary 42A05 ; MinimalL α-deviation ; Oscillating polynomials ; Extremal problems ; Monictrigonometric polynomials ; Trigonometric polynomial of half-integer degree ; Topological degree of mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let π n−1 be the linear space of algebraic polynomials of degreen−1. We prove that the extremal problem $$\mathop {\min }\limits_{p_{n - 1} \in \pi _{n - 1} } \int_{ - 1}^1 {(1 + x)^\beta (1 - x)^\gamma |x^n + p_{n - 1} (x)|^\alpha dx} $$ has a unique solution for β〉-−1/2, γ〉-−1/2, and α〉0. From the result of A. Kroó and E. B. Saff [5] uniqueness follows only for β, γ〉-0 but the Kroó-Saff result applies to a general class of weights while we consider only Jacobi weights. Various other results of the same kind for trigonometric and algebraic polynomials have been obtained. Our approach is based on the concept of topological degree. Let −1〈−x1(α)〈...〈x[n/2](α)〈...〈x1(α)〈1 be the zeros of the algebraic polynomial of minimalL α-deviation for β=γ=0. We prove that 0〈xi(α)〈xi(1) for 0〈α〈1 and i=1,..., [n/2]. It is shown in [4] that xi(1)〈xi(α)〈xi(∞) for 1〈α〈∞ and i=1,..., [n/2].
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  • 47
    ISSN: 1432-0940
    Keywords: 41A17 ; Markov-type inequality ; Bernstein-type inequality ; Polynomials with restricted zeros
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We prove that an absolute constantc〉0 exists such that $$|p'(y)| \leqslant c\min \left\{ {n(k + 1),\left( {\frac{{n(k + 1)}}{{1 - y^2 }}} \right)^{1/2} } \right\}\mathop {\max }\limits_{ - 1 \leqslant x \leqslant 1} |p(x)|, - 1 \leqslant y \leqslant 1,$$ for every real algebraic polynomial of degree at mostn having at mostk zeros in the open unit disk {z∈C:|z|〈1}. This inequality, which has been conjectured for at least a decade, improves and generalizes several earlier results. Up to the multiplicative absolute constantc, it is a sharp generalization of both Markov's and Bernstein's inequalities.
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  • 48
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    Constructive approximation 10 (1994), S. 427-438 
    ISSN: 1432-0940
    Keywords: 41A10 ; 30E10 ; Faber set ; Faber operator ; Maximal convergence ; Polynomial approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we study various problems concerning Faber sets and polynomial approximation on Faber sets. We give various conditions for a compact setK to be a Faber set and we characterize (for a certain class of Faber sets) the range of the Faber operator. Furthermore, we study the convergence behavior of Faber expansions and more general sequences of polynomials which approximate functions that are holomorphic onK and continuous on a level curve of the normalized conformal mapping from ......-...... onto ......-K.
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  • 49
    ISSN: 1432-0940
    Keywords: 41A05 ; Hermite-Fejér interpolation of higher order ; Convergence ; Strong normality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we give a theorem of Grünwald-type for (0, 1,...,m-1) Hermite-Fejér interpolation (m=2, 4,...), which extends the famous result for a strongly normal system of nodes in the casem=2 given by Grünwald in [1].
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  • 50
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
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  • 51
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present numerical computations for the dynamics of the development of twinned martensitic microstructure and for the propagation of the austeniticfinely twinned martensitic interface. Our computations approximated a threedimensional model for the dynamics of the In-20.7 at% T1 alloy which used the stress tensor derived from the Ericksen-James energy density.
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  • 52
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We derive the field energy of micromagnetics by computing the limiting energy of a lattice of dipoles as a typical lattice parameter goes to zero. Different limiting energies are obtained, depending upon whether the dipoles do not oscillate (strong convergence), oscillate on a scale much larger than the scale of the lattice (weak-long) or oscillate on the scale of the lattice (weak-short). The analysis suggests a framework and some methods for the direct derivation of continuum theory from molecular theory.
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  • 53
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract X-radiography was used to study annual linear skeletal extension rates of the reef-building scleractinian corals Diploria strigosa and Diploria labyrinthiformis from the high-latitude reefs of Bermuda. Coral samples for X-radiography were collected from seven localities of varying biotopes and depths around the Bermuda platform and band couplets were measured. Mean extension rates of both species were highest on inshore and nearshore reefs, gradually decreasing towards the edge of the Bermuda platform and onto the fore-reef slope. Extension rates of D. labyrinthiformis were statistically higher than those of D. strigosa at three localities, while at the other four, the rates of both species were not statistically separable. extension rates of d. labyrinthiformis were statistically higher than D. strigosa within depths of 20 m and 32 m but not statistically separable at 3 m and 6 m depths. Extension rates of both species decreased significantly with increasing depth (r 2=0.92, P〈0.03 for D. labyrinthiformis and r 2=0.95, P〈0.02 for D. strigosa). Each species showed an inverse curvilinear relationship between extension rate and depth, the rate of change (i.e. slope) being the same for each species. Comparison of extension rates of each species from Berumuda with published rates of these species from lower latitudes showed an inverse relationship between extension rate and latitude.
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  • 54
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A flight of six major coral reef terraces, up to 700 m in altitude, occurs along the eastern and northern sides of Kabola Peninsula, Alor Island, Indonesia. Some radiometric dates have been obtained from unrecrystallized coral samples collected in growth position by three different methods (14C, 230Th/234U, ESR). This enabled the identification of the terraces corresponding to the Holocene and to oxygen-isotope stages 5c, 5e and 7. According to the present elevation of the dated terraces, a 1.0–1.2 mm/y mean rate of uplift can be discerned. Extrapolation of this trend to the whole sequence of terraces reveals a good correlation between the development of major terraces and interglacial or interstadial stages corresponding to astronomically calibrated oxygen isotope records, up to stage 13. The relatively rapid uplift rate in this region minimized the possibility of polycyclic sea-level stands at the same levels and contributed to the good preservation of some morphological reef features. Two superimposed marine notches are visible near the present shoreline, with retreat points at about 5.0 m and 8.6 m respectively above the present MLWST level. They can be interpreted as corresponding to a glacial interstadial (the upper notch) and to the Holocene sea-level peak (the lower one). As Holocene emergence has been less than what could be expected from a 1 mm/y rate of uplift, a major coseismic vertical displacement may occur in the future.
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  • 55
    ISSN: 1432-0983
    Keywords: Yeast ; Yarrowia lipolytica ; Lysine acetyl transferase ; Lysine catabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the yeastYarrowia lipolytica, theLYC1 locus controls the first step of the lysine degradation pathway which is catalyzed by lysine N-6-acetyl transferase (LAT). This gene was cloned by complementation of thelyc1-100 mutation. Its position in the cloned insert was determined by conversion mapping and by complementation. TheLYC1 gene encodes a 391 amino-acid polypeptide which has no homolog in protein databases. The required upstream region extends over 960 bp. When placed under the control of theGAL10 promoter inSaccharomyces cerevisiae, LYC1 drives the expression of lysine acetyl transferase activity, thus providing strong evidence that it is the structural gene encoding this enzyme.
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  • 56
    ISSN: 1432-0983
    Keywords: Plasmid exchange ; ras/Ras gene ; Basidiomycete ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It was shown by a plasmid exchange procedure that the Ras-encoding cDNA of the basidiomyceteLentinus edodes (namedLeras cDNA) can functionally replace its homolog genes (ScRAS1 andScRAS2) in the yeastSaccharomyces cerevisiae to maintain the viability of an yeast strain containing genetic disruptions of bothRAS genes. The strain replaced by aLeras−cDNA-carrying plasmid, however, grew slower than the strains replaced by aScRAS1− or aScRAS2−carrying plasmid. The intracellular level of cAMP in the strain harboring theLeras−cDNA-carrying plasmid was clearly higher than that of a parental strain which maintains a plasmid carrying theS. cerevisiae cAMP-dependent protein kinase catalytic subunit C1 gene,TPK1, but was lower than that in a strain harboring anScRAS2−carrying plasmid. These results suggest that theLeras cDNA can complement theras1 − ras2− mutation of yeast by virture of the stimulation of adenylate cyclase activity, although the complementation is not as efficient as that obtained by expressing theScRAS2 gene.
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  • 57
    ISSN: 1432-0983
    Keywords: Psoralen ; DNA repair mutants ; Gene conversion ; Recombination ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of the DNA repair genePSO3 on photoactivated psoralen-induced meiotic recombination, gene conversion, reverse mutation, and on survival, was assayed in diploid strains ofSaccharomyces cerevisiae homozygous for the wild-type or thepso3-1 mutant allele. Sporulation was normal in thepso3-1 diploid. Wild-type and mutant strains had the same sensitivity to photoactivated monofunctional psoralen (3-CPs+UVA) in meiosis-uncommitted and meiosis-committed stages. The mutant showed higher sensitivity to photoactivated bifunctional psoralen (8-MOP+UVA) during all stages of the meiotic cycle. Mutation induction by 3-CPs+UVA or 8-MOP+UVA in meiosis-committed cells revealed no significant differences between wild-type and thepso3-1 mutant. The status of thePSO3 gene has no influence on the kinetics of induction of gene conversion and crossing-over after 3-CPs+UVA treatment in meiosis-committed cells: gene conversion was blocked while recombination was induced. After treatment with 8-MOP+UVA gene conversion was also blocked in both strains while crossing-over could only be observed in meiosis-committed wild-type cells.
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  • 58
    ISSN: 1432-0983
    Keywords: Acremonium chrysogenum ; β-tubulin gene ; Homologous transformation system ; Benomyl resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Theβ−tubulin gene was isolated from the filamentous fungusAcremonium chrysogenum using a heterologous gene probe to screen anA. chrysogenum lambda library. Sequencing of theA. chrysogenum gene revealed a mosaic gene which contains five exons and four intervening sequences. The exons encode for a polypeptide of 447 amino-acid residues which showed a high degree of similarity when compared with amino-acid sequences from β-tubulins of other eukaryotes. The introns are characterized by typical consensus sequences found in intervening sequences from other filamentous fungi. In-vitro mutagenesis of codon 167 of the β-tubulin gene resulted in the substitution of a phenylalanine by a tyrosine in the corresponding polypeptide sequence. The mutated gene was used successfully in the transformation and co-transformation ofA. chrysogenum to benomyl resistance. The molecular analysis of transformants provided evidence that they contain the mutated β-tubulin gene in addition to the wild-type gene, as was proved by Southern-hybridization analysis and direct sequencing of PCR amplification products.
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  • 59
    ISSN: 1432-0983
    Keywords: Aspergillus nidulans ; Acetate ; Propionate metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Propionate medium is normally toxic for the growth ofAspergillus nidulans. Spontaneous mutations relieving the toxicity to propionate, which arose on propionate medium, have been shown to be mutations in acetate metabolism. Oneacu − mutant is allelic withacuA (the structural gene for acetyl-CoA synthetase), another withacuB (the regulatory gene involved in the induction of enzymes concerned with acetate metabolism, including acetyl-CoA synthetase), and a third mutants,acuO, represents a newacu − locus that maps on likage group V.
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  • 60
    ISSN: 1432-0983
    Keywords: ψ-RNA polymerase I ; 3-μm circles ; Translation fidelity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The extrachromosomal element ψ affects translation fidelity in the yeastSaccharomyces cerevisiae by increasing the efficiency of tRNA-mediated ochre suppression. The nature of the ψ factor is unknown, although there is evidence that 3-μm circles from ψ+ strains can be used to transform ψ− cells to ψ+. The 3-μm circles are extrachromosomal copies of the repeating ribosomal DNA unit, which is organized into two transcription units: the 35s rRNA precursor transcribed by RNA polymerase I, and the 5s rRNA transcribed by RNA polymerase III. We used a strain containing a mutation in RNA polymerase I to test whether ψ expression and inheritance depended on RNA polI. Neither expression nor inheritance of ψ requires intact RNA polI.
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  • 61
    ISSN: 1432-0983
    Keywords: Fungal transformation ; Colletotrichum lagenarium ; Penetration peg formation ; DNA complementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Infection byColletotrichum lagenarium requires formation of an appressorium and of a penetration peg. A mutant, 83 348, defective in morphogenesis of the penetration peg was unable to penetrate into cellulose membranes or infect cucumber leaves. DNA transformation using a wild-type genomic library constructed in pKVB resulted in two transformants, Ppr1 and Ppr2, with restored penetration peg formation, from 2,000 benomylresistant transformants. However, penetration into cellulose membranes by these transformats ranged from 30 to 40% compared to greater than 90% by wild-type. Southern-blot hybridization showed that a single copy of a cosmid clone had integrated into the genome of the transformants. A 12.0-kbp fragment of the cosmid vector with the flanking region of wild-type genomic DNA was recovered by plasmid rescue from Ppr1. Using the flanking DNA sequences as a probe for colony blot hybridization, a genomic clone was identified and designated pRP46. Transformants obtained following transformation with pRP46 were able to penetrate cellulose membranes. The penetration frequency of pRP46 transformants ranged from 25 to 65%. Transformants were also pathogenic on cucumber.
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  • 62
    ISSN: 1432-0983
    Keywords: Secale cereale ; mtDNA ; DNA polymerase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondrial (mt)DNA ofSecale cereale contains an open reading frame (pol-r), the potential translation product of which shows significant homology to the type-B DNA polymerase encoded by theS1 plasmid ofZea mays; it contains the highly-conserved domains IIa to V of family B polymerases. Thepol-r ORF is transcribed, as proven by RT-PCR, but the transcript is not edited. Upstream of the putative start codon a potential promoter motif was detected, fitting well into the postulated consensus sequence of the transcription initiation regions ofZ. mays andTriticum aestivum. Thepol-r ORF occurs in mtDNA of the fertile rye variety “Halo” and the cytoplasmic male-sterile (CMS) line “Pampa”. Both ORFs are almost identical, apart from the 3′ terminus;pol-r from Halo can code for 289 amino acids,pol-r from Pampa for 312 amino acids. Based on codon usage and the lack of editing,pol-r is considered to be a “young” gene, probably introduced in the mtDNA of rye by recombination with an mt plasmid.
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  • 63
    ISSN: 1432-0983
    Keywords: PRPP amidotransferase ; ade4 gene ; Adenine ; Schizosaccharomyces pombe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the isolation and sequence of the Schizosaccharomyces pombe ade4 gene which encodes the glutamine phosphoribosylpyrophosphate amidotransferase, the first enzyme of the purine nucleotide de-novo biosynthetic pathway. The enzyme contains 533 amino acids and its sequence exhibits homologies to the corresponding enzymes of Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, chicken, rat, and human. In contrast to the situation in S. cerevisiae, adenine does not repress ade4 expression at the mRNA level and also other nutritional signals seem not to affect its expression.
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  • 64
    ISSN: 1432-0983
    Keywords: tRNA processing ; Saccharomyces cerevisiae ; Mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We used a genetic approach to study the nuclear factors involved in the biogenesis of mitochondrial tRNAs. A point mutation in the mitochondrial tRNAAsp gene of Saccharomyces cerevisiae had previously been shown to result in a temperature-sensitive respiratory-deficient phenotype as a result of the absence of 3′ end-processing of the tRNAAsp. Analysis of mitochondrial revertants has shown that all revertants sequenced have a G-A compensatory change at position 53, which restores the hydrogen-bond with the mutated nucleotide. We then searched for nuclear suppressors to identify the nuclear gene(s) involved in mitochondrial tRNA 3′ end-processing. One such suppressor mutation was further characterized: it restores tRNAAsp maturation and growth at 36°C on glycerol medium in heterozygous diploids, but leads to a defective growth phenotype in haploids.
    Type of Medium: Electronic Resource
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  • 65
    ISSN: 1432-0983
    Keywords: Reciprocal recombination ; Mitochondrial genome ; Chondriome variability ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mitochondrial genome of the selfed progeny of a plant regenerated from long-term somatic tissue culture displays specific structural rearrangements characterized by the appearance of novel restriction fragments. A mitochondrial DNA library was constructed from this selfed progeny in the SalI site of cosmid pHC79 and the nov