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  • Springer  (298)
  • 1
    ISSN: 0025-5874
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract. We consider the Burgers equation with a periodic force $\frac{\partial}{\partial t}u+u\cdot\nabla u=\frac12\Delta u+\nabla V(x)$ which presents a simplified model for turbulence. We are interested in the asymptotic behaviour of solutions for $t\to\infty$ . This problem has been studied by Sinai who uses a probabilistic and very technical approach. Using methods from spectral theory we get similar results. This functional analytic approach gives an easier proof. For certain initial data (periodic or some random perturbations of those) we show time-convergence towards a deterministic periodic limit solution related to the ground state of a certain Schrödinger operator.
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  • 2
    ISSN: 1573-904X
    Keywords: near-IR spectroscopy ; film coating ; chemometrics ; pharmaceutical analysis ; process monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purpose of this study was to investigate the potential of near-infrared (near-IR) spectroscopy for non-destructive at-line determination of the amount of polymer coat applied to tablet cores in a Wurster column. Methods. The effects of coating composition on the near-IR spectroscopic determination of ethylcellulose (Aquacoat ECD-30) or hydroxypropylmethylcellulose (HPMC)-based (Spectrablend) coating were evaluated, as were the performance of several chemometric techniques. Results. Tablets were coated with up to 30% ethylcellulose or 22% HPMC, and samples were pulled at regular intervals during each coating run. Near-IR reflectance spectra of the intact tablets were then collected. The spectra were preprocessed by multiplicative scatter correction (MSC) or second derivative (D2) calculations, and calibrations developed using either principal components (PCs) or multiple spectral wavelengths. The near-IR method provided predictions of film applied with standard errors of 1.07% w/w or less. Conclusions. Near-IR spectroscopy can be profitably employed in a rapid and non-destructive determination of the amount of polymer film applied to tablets, and offers a simple means to monitor the film coating process.
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  • 3
    ISSN: 1573-7055
    Keywords: molecular systematics ; phylogeny ; placental mammals ; mitochondrial rDNA ; Paenungulata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Part of the 12S rDNA gene was amplified and sequenced for 11 placental mammals, 3 marsupials, and 2 monotremes. Multiple alignments for these sequences and nine additional placental sequences taken from GenBank were obtained using CLUSTAL. Phylogenetic analyses were performed using standard parsimony, transversion parsimony, and Lake's method of invariants. All of our analyses uniteLoxodontia withDugong. Procavia, in turn, is a sister group to these taxa, thus supporting the monophyly of the Paenungulata. Perissodactyls are a sister group to paenungulates when transitions and transversions are both included but not when transitions are omitted. Likewise, cetaceans are a sister group to artiodactyls on minimum length trees under standard parsimony but not under transversion parsimony. Rodent monophyly and bat monophyly also receive mixed support, as does a putative alliance between primates and lagomorphs. Interestingly, the percentage divergence between the echidna and the platypus is less than for the rat and mouse.
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  • 4
    ISSN: 1573-7373
    Keywords: Angiogenesis ; brain tumor ; glioma ; clinical trials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of angiogenesis inhibitors may offer novel strategies in brain tumor therapy. In contrast to traditional cancer treatments that attack tumor cells directly, angiogenesis inhibitors target at the formation of tumor-feeding blood vessels that provide continuous supply of nutrients and oxygen. With respect to brain tumor therapy, inhibitors of angiogenesis display unique features that are unknown to conventional chemotherapeutic agents. The most important features are independence of the blood–brain barrier, cell type specificity, and reduced resistance. Malignant brain tumors, especially malignant gliomas, are among the most vascularized tumors known. Despite multimodal therapeutic approaches, the prognosis remains dismal. Thus, angiogenesis inhibitors may be highly effective drugs against these tumors. In a clinical setting, they could be applied in the treatment of multiple tumors or postsurgically as an adjuvant therapy to prevent recurrence. This article provides an overview of current anti-angiogenic treatment strategies with emphasis on substances already in clinical trials or candidate substances for clinical trials. The cellular and molecular basis of these substances is reviewed.
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  • 5
    ISSN: 1573-7373
    Keywords: Angiogenesis ; brain tumor ; glioma ; clinical trials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neovascularization. Removal of inhibiting anti-angiogenic factors led to growth of dormant metastases. A number of endogenous inhibitors have been identified and have shown success in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.
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  • 6
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In electrophysiological experiments involving intracellular recording from horizontal cells in the isolated retina of the roach, light adaptation of the retina has been shown to result in potentiation both of (1) the depolarizing component of biphasic chromaticity type S-potentials, and (2) the temporal frequency transfer functions of photopic luminosity type horizontal cells. Under identical light adaptation conditions, the number of spinules on horizontal cell dendrites positioned laterally at cone pedicle ribbon synapses, increase by some threefold. The latter effect occurs equally in pedicles of red- and green-sensitive cones. Thus, horizontal cells are ‘plastic’ in both structural and electrophysiological respects. Furthermore, since the two electrophysiological parameters studied depend on negative feedback from horizontal cells onto cones, the results suggest that it is the inhibitory synapses that are plastic and that spinules may be sites of the negative feedback interaction. Physiological and behavioural aspects of light-dependent horizontal cell plasticity are also discussed.
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  • 7
    ISSN: 1573-904X
    Keywords: aspartyl transpeptidation ; peptide degradation pathway ; pH–rate profiles ; daptomycin ; lipopeptide antibiotic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two degradation products of the lipopeptide antibiotic, daptomycin, were identified and the reaction pathway and kinetics were delineated in aqueous solution at 60°C, pH range 3 to 8 and ionic strength 0.01. The degradation products were 1) a succinimido intermediate (anhydro-daptomycin) formed by attack of side-chain carbonyl on the peptide-bond nitrogen in the asp–gly sequence and 2) a β-asp daptomycin isomer formed by rehydration of the anhydrodaptomycin succinimide. This aspartyl transpeptidation pathway was found to be reversible. Formation of the anhydrodaptomycin from either daptomycin or β-asp daptomycin was pH dependent but the pH–rate profiles for anhydrodaptomycin formation were not mechanistically interpretable. The pH–rate profiles for the formation of daptomycin or β-asp daptomycin from the anhydrodaptomycin were linear with slopes = 1, which is consistent with nucleophilic hydroxide ion attack of the succinimido intermediate at either the α-carbonyl, giving rise to the β-asp daptomycin, or the β-carbonyl, giving rise to daptomycin.
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  • 8
    ISSN: 1424-0661
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract. We consider the three-dimensional Schrödinger operator with constant magnetic field and bounded random electric potential. We investigate the asymptotic behaviour of the integrated density of states for this operator as the norm of the magnetic field tends to infinity.
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  • 9
    ISSN: 1432-0878
    Keywords: Shanny ; Fish skin ; Chloride cells ; Chloride exchange ; Outfluxes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fine structure of the skin and its importance in chloride outfluxes were investigated in a sea-water teleost, the shanny (Blennius pholis L.). The epidermis is composed of three cells types: epithelial cells, mucous cells and chloride cells. These chloride cells typically contain a great number of mitochondria and an extensive agranular reticulum extending through the whole cell body. They open at the surface of the epidermis into an apical pit. An undifferentiated small cell is often observed near these chloride cells and probably corresponds to the “adjacent chloride cell”. The values of chloride outfluxes through the skin and the gills are respectively 5333±884 μEq·h−1·kg−1 and 4479±2521 μEq·h−1·kg −1; n=6; t∘=13±0.5°C. Thus the ratio between skin chloride outflux and total chloride outflux is 64.7±9.3%.
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  • 10
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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