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  • 1
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Chinstrap penguins (Pygoscelis antarctica) normally lay two eggs, but brood size is often reduced by mortality during incubation or after hatching. We hypothesized that this variation in brood size would affect the parents’ foraging behavior and their chick provisioning performance. We studied patterns of adult foraging trip duration and frequency, food load delivery, and chick growth rates in relation to brood size during the guard phase in four breeding seasons (1991–1994) on Seal Island, Antarctica. Within a given year, parents with two chicks made more frequent foraging trips to sea and may have transported larger food loads to the nest; however, the duration of foraging trips was unrelated to brood size. Overall, parents with two chicks spent ∼15% more time at sea than parents with only one chick. Both the frequency and duration of foraging trips varied between years. Foraging trip duration may partly reflect the birds’ foraging radius, which probably varies with time in response to shifts in krill distribution. Chick growth rate varied betwen years, but was related to brood size only in 1992, when chicks from two-chick broods grew significantly more slowly than chicks from one-chick broods. Food loads transported to chicks, as well as chick growth rates, were highest in 1994, when concurrent hydroacoustic studies indicated that regional krill biomass was severely depressed. This apparent anomaly suggests that the spatial scale of the krill survey may have been too coarse to detect some high-density krill aggregations within the penguins’ foraging range.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular dynamics of amorphous and liquid-crystalline (LC) side-chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10-2 to 106 Hz and at temperatures from -160 to 180°C. ‘Model’ compounds containing no mesogenic side-groups showed two relaxations, which originate from the carbonate group (α, βm-relaxation). By contrast, in LC-polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature Tg up to three relaxation modes were distinguished (α-, λ1-, λ2-process); below Tg four secondary relaxations (γ-, βm-, βs-, βsc-relaxation) were observed. The γ-relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from βm-, two additional β-processes were identified as relaxations associated with the mesogenic unit in the glassy (βs) or in the crystalline state (βsc).
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  • 3
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of new side-chain liquid crystalline polymers was prepared with a polycarbonate backbone, bearing (E)-4′-nitrostilbene mesogenic groups, connected to the backbone by spacers of different length. The polymers were synthesized in 1,4-dioxane by polycondensation of diphosgene and diol monomers with the general structure 2-[ω-(4′-nitrostilben-4-ylcxy)alkyloxy]-1,3-propanediol in the presence of pyridine as a proton trap and catalyst. The mesomorphic properties of all monomers, polymers and intermediates were studied by polarized optical microscopy and differential scanning calorimetry (DSC). The polymers were also studied by X-ray diffraction of non-oriented and oriented samples (fibres). All monomers were liquid crystalline with nematic and/or smectic phases. For the polymers a clear relation was found between spacer length and glass transition temperature (Tg), which decreases with increasing spacer length and between spacer length and clearing temperature, which increases with increasing spacer length. X-ray diffraction measurements indicated the presence of a smectic A double layer structure (SAd) for all polymers at room temperature, with an antiparallel of overlapping mesogenic groups. A distinct difference in the orientation of the mesogens was found when fibres were drawn from the smectic phase or from the nematic or isotropic phase. In the first case the mesogenic groups were oriented perpendicular to the fibre axis and in the second case the mesogenic groups were oriented parallel to the fibre axis. By gel-permeation chromatography (GPC) measurements of heated samples and by thermogravimetric analysis (TGA) and DSC the polymers were found to be thermally stable up to temperatures well above their clearing point.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Previous studies suggested that surface topographic configurations of 1-3 μm influence cellular behavior and tissue response. They did not address which specific aspect of the configurations elicits the cellular response. We therefore investigated the effect of the orientation of several surface configurations. Seven different textures on polydimethyl siloxane (silicone; Dow Corning Silastic®) specimens were used to test the question of whether orientation into (down) or out of the surface (up) affected cellular response to a material. The textures were smooth and photoetched configurations of 2 μm up, 2 μm down, 5 μm up, 5 μm down, 10 μm up, and 10 μm down. The response of cultured fibroblasts on these surfaces was compared with that of a standard tissue culture material, polyethylene terephalate (ThermanoxTM). The cell density was measured over a 12-day period with the use of a colorimetric assay. The uptake of methylene blue was measured daily and compared as an absorbance in a destaining agent. Cells on the 2 and 5 μm up arrays showed increased rates of proliferation and cell density as compared with their down counterparts. This would indicate that textures of 2 and 5 μm have a significant influence on cell growth, and that the surface with hills has a greater effect than the surface with wells. In contrast, the 10 μm up and 10 μm down arrays did not prove to be statistically different from smooth ones. This indicates that the orientation effect is related to the configuration size and that this configuration size is not viewed differently from smooth silicone by the cells. The presented data are in agreement with results of this laboratory and others that fibroblasts recognize the dimensions of surface configurations and react accordingly. Specifically, they appear to react to the uppermost surface area presented to them, but conclusive data can only be obtained from a study of the focal adhesions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The bone response to different calcium phosphate (Ca-P) coated and non-coated titanium implants was evaluated in a goat animal model. Two types of Ca-P coatings have been investigated: an experimental plasma-spray bi-layered Ca-P coating (FA-HA) and an amorphous RF magnetron sputter coating (Ca-P-a). Fifty-four conical screw shaped implants were inserted in the lateral and medial femoral condyles of 18 Saanen goats. After implantation periods of 3, 12 and 24 days, the bone-implant interface was evaluated histologically and histomorphometrically. Light microscopical evaluation revealed that bone formation on the Ca-P coated implants proceeded faster. At 24 days higher percentages of bone contact were measured for both Ca-P coated implants than for non-coated implants. However, this difference was only significant for the FA-HA coated implants. On basis of these findings. we concluded that Ca-P coatings show improved bone response due to an initial difference in bone cell response.
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  • 6
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We analysed the effect of three portion sizes Optocal Plus (small, medium and large) on swallowing thresholds in subjects with either conventional complete dentures or mandibular implant-retained overdentures (transmandibular and permucosal cylindric implants). Tests were carried out in 52 women and 15 men (mean age 59 years) 4 years after treatment in a randomised controlled clinical trial. The results indicated that the degree of mucosal support for the mandibular denture did not affect the number of chewing strokes, time till swallowing or swallowed particle size. Only the chewing rate differed: subjects wearing mandibular implant-retained overdentures chewed the food at a higher rate than complete-denture wearers. With larger portion sizes, subjects needed significantly more chewing strokes and time until swallowing and they would have swallowed larger particles. Men chewed their food more efficiently than women, as they used the same number of chewing strokes and time, but achieved a greater particle size reduction at the swallowing moment.
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  • 7
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The aim of this study was to determine the cell characteristics that regulate implant osseointegration. The heterogeneity of bone marrow stromal cells obtained from 11 donors was assessed by measuring the expression of a large panel of adhesion molecules. Large differences in expression of adhesion molecules were detected depending on the culture conditions used. Cells cultured in fetal bovine serum induced the expression of different adhesion molecules from cells cultured in human serum. Donor-to-donor variation was determined by measuring the expression of adhesion molecules for stromal cells obtained from different donors that were processed identically. Fat adherent cells but also loose bone marrow cells showed large differences in expression of some but not all adhesion molecules. The flow cytometric data demonstrated large heterogeneity in expression of adhesion molecules, and this heterogeneity was influenced by culture conditions and varied from donor to donor. This demonstrates that the implant encounters different cell types, which could lead to different levels of integration. Surprisingly, in vitro only a subfraction of bone marrow stromal cells attached to titanium coated with ceramic hydroxyapatite. Adaptation of all cell types present in heterogeneous bone marrow to a coated surface is apparently not possible. Differential binding was not caused by aberrant staining of the stromal cells as the results were confirmed with bone marrow cells obtained from transgenic GFP mice. These results demonstrate that hydroxyapatite ceramics are selective in cell recruitment from the bone marrow, explaining the differences found in vivo for these coatings compared with titanium.
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  • 8
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The aim of this study was to evaluate the clinical applicability and biological behavior of a newly developed injectable calcium phosphate (Ca-P) cement as bone filler for gaps around oral implants. Twenty-four step-like implants, creating gaps of 1 and 2 mm, were inserted into the trabecular bone of the medial femoral condyles of six goats. Four different situations were tested: (1) implant + gaps; (2) implant + gaps, but covered with a polylactic acid membrane; (3) implant + gaps that were filled with Ca-P cement; and (4) implant + gaps that were filled with Ca-P cement and covered with a membrane. All implants were left in place for 12 weeks. Histological and quantitative histomorphometrical measurements demonstrated that implants + gaps had generally poor bone contact at the implant base. Furthermore, fibrous encapsulation was observed in the gap part. In contrast, the presence of a membrane promoted bone ingrowth into the gap and also the bone contact at the implant base. Injection of Ca-P cement resulted in an almost complete filling of the gaps around the implant. The cement surface was completely covered by bone. Active resorption and remodeling of cement particles was observed, suggesting a pattern of slow resorption associated with full replacement with newly formed bone. Additional use of a membrane did not result in adjunctive benefits. Bone-to-implant contact at the implant base was comparable with the implants provided only with a membrane. In conclusion, the Ca-P cement used here showed excellent clinical handling properties combined with a superior bone behavior. On the other hand, the degradation rate of the material was still very slow. This current characteristic can hamper the final clinical applicability of the material as gap filler for periimplant or periodontal defects.
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  • 9
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The influence of surface roughness and calcium phosphate (Ca-P) coating on the bone response of titanium implants was investigated. Four types of titanium implants, i.e. as-machined, grit blasted, as-machined with Ca-P sputter coating, and grit blasted with Ca-P sputter coating, were prepared. The Ca-P sputter-coating, produced by using the RF magnetron sputter technique, was rapid heat-treated with infrared radiation at 600°C. These implants were inserted into the left and right femoral condyles and the left and right tibial diaphyses of the rabbits. After implantation periods of 2 and 12 weeks, the bone–implant interface was evaluated histologically and histomorphometrically. Histological evaluation revealed no new bone formation around different implant materials after 2 weeks of implantation. After 12 weeks, bone healing was almost completed. For both tibial and femoral implants, Ca-P coated implants always showed a higher amount of bone contact than either of the non-coated implants. On the other hand, surface roughness improved only the response to implants inserted into the tibial diaphysis. On the basis of these findings, we concluded that 1) deposition of a sputtered Ca-P coating on an implant has a beneficial effect on the bone response to this implant during the healing phase, and 2) besides implant surface conditions the bone response is also determined by local implant site conditions.
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  • 10
    ISSN: 1600-0501
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The influence of Ca-P magnetron sputter coated implants on the mechanical anchorage was evaluated in a goat model. Therefore, uncoated and coated screw designed commercially pure titanium TiO2-blasted implants were inserted into the trabecular bone of the femoral condyles of 12 goats. The thicknesses of the coatings were 0.1 μm (CaP-0.1), 1.0 μm (CaP-1) and 4.0 μm (CaP-4). In addition, uncoated TiO2-blasted implants (Ti) were used as control. Evaluation of the interface strength and appearance, using torque test and scanning electron microscopy, was done at implantation periods of 6 and 12 weeks. Although, especially at 6 weeks of implantation, the Ca-P coated implants showed higher failure torque values than the TiO2 blasted implants, the observed differences for type of implant and evaluation period were not significant (P〉0.1). SEM evaluation showed that all implants with failure values of more than 100 N conducted bone growth into their screw threads. In addition, we observed that the fracture plane for the CaP-4 implants was situated at the coating–implant interface or inside the coating. For the CaP-1 and CaP-0.1 the fracture line could not be determined definitely. For the Ti implants, the fracture torque testing resulted in failure at the bone–implant interface. Therefore, we conclude that all implants resulted in a good bonding strength with the surrounding bone. The sputtered Ca-P coatings seemed to improve the initial fixation of the TiO2 blasted implants.
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