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  • Polymer and Materials Science  (4)
  • Analytical Chemistry and Spectroscopy  (1)
  • Biochemistry and Biotechnology  (1)
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  • 1
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A general expression for the energy and angular distribution of Auger/photoelectrons emitted from a specimen with an arbitrary depth profile is presented. The central quantities in this expression are the so-called partial escape distributions, which describe the probability that a signal electron generated in a certain depth interval escapes from the surface with a direction in a certain angular interval after experiencing a certain number of inelastic scattering processes. The partial escape distributions accounting for elastic scattering are calculated in the transport approximation. Comparison of analytical calculations with Monte Carlo data based on the more relastic Mott crosssection for elastic scattering yields excellent agreement. As an illustration of the general approach, the energy/angular spectrum of a sample with a model depth profile has been evaluated using analytical calculations and Monte Carlo data. The results obtained show that the proposed formalism properly accounts for elastic and inelastic processes and correctly predicts the shape of the energy distribution in the vicinity of the peak. It is, moreover, shown that the true intrinsic spectrum and depth profile may be reconstructed simultaneously from the measured energy/angular distribution of emitted electrons.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Reflection electron energy loss spectroscopy (REELS) spectra for Al, Ni, Pt and Au were measured in the energy range 300-1500 eV for different scattering geometries. The energy dependence of the loss spectra was found to depend strongly on the shape and the magnitude of the elastic scattering cross-section. This effect is extremely pronounced in the angle-resolved spectra, but also persists in the angle-integrated case. It was moreover observed that the relative intensities of the surface excitations in REELS spectra exhibit a similar dependence on the elastic scattering properties. These experimental observations are in good agreement with MC calculations accounting for elastic scattering through the differential Mott cross-section and demonstrate that quantitative information regarding the inelastic scattering probability can only be extracted from REELS spectra if the exact shape of the elastic scattering cross-section is accounted for and a quantitative description of surface excitations is available.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0006-3592
    Keywords: biocompatibility ; microfabrication ; biohybrid organs ; immunoisolation ; Islets of Langerhans ; silicon ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A microfabricated silicon-based biocapsule for the immunoisolation of cell transplants is presented. The biocapsule-forming process employs bulk micromachining to define cell-containing chambers within single crystalline silicon wafers. These chambers interface with the surrounding biological environment through polycrystalline silicon filter membranes. The membranes are surface micromachined to present a high density of uniform pores, thus affording sufficient permeability to oxygen, glucose, and insulin. The pore dimensions, as small as 20 nm, are designed to impede the passage of immune molecules and graft-borne viruses. The underlying filter-membrane nanotechnology has been successfully applied in controlled cell culture systems (Ferrari et al., 1995), and is under study for viral elimination in plasma fractionation protocols. Here we report the encouraging results of in vitro experiments investigating the biocompatibility of the microfabricated biocapsule, and demonstrate that encapsulated rat neonatal pancreatic islets significantly outlive and outperform controls in terms of insulin-secretion capability over periods of several weeks. These results appear to warrant further investigations on the potential of cell xenografts encapsulated within microfabricated, immunoisolating environments for the treatment of insulin-dependent diabetes. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 118-120, 1998.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: New methods are presented for the evaluation of ion structures and fragmentation pathways using tandem mass spectrometry (MS/MS) with low energy collision-induced dissociation. As an aid for mass spectroscopists, they incorporate a PC software package (named PDNL, written in Turbo-PASCAL 5.5 (Borland), running under DOS (Microsoft) with mouse-control). A database of almost 300 low energy MS/MS spetra is available for library searches. It utilizes a new, intensity-based matching algorithm fitting to the demand of MS/MS data. Computational methods have been developed for (i) the separation of the spectra of unresolved isobaric ions and evaluation of the ratio of the ion abundances, (ii) the evaluation of single-collision spectra using the multi-collisional data map, and (iii) the elucidation of collision-induced dissociation fragmentation pathways. Principal component analyses of sets of at least eight MS/MS spectra were used for a quick comparison of these spectra and for a summary of inter-ion relationships.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Human fibroblasts cultured for 10 days in a collagen sponge migrated through the pores of the sponge and expressed a moderate mitotic activity, which stabilized after 10 days, and a high collagen and protein synthesis. Between 10 and 27 days, the newly synthesized collagen filled the pores of the sponge. This matrix accumulation induced a delayed decrease of collagen and protein synthesis. Finally, after 27 days of culture, the fibroblasts expressed low bio-synthetic activities similar to the ones exhibited in vivo. The newly synthesized matrix was highly differentiated, as shown by the presence of a dense network of quarter-staggered collagen fibrils (42 nm ± 6 nm in diameter) surrounding the cells. The size and the shape of these fibrils demonstrated that the newly synthesized procollagen was fully processed in collagen by removal of their N- and C-terminal propeptides. Moreover, these fibrils were packed in bundles organized into an interwoven network that mimics the pattern of the papillary dermis. These findings show that fibroblasts cultured for one month in a collagen sponge construct large amounts of a highly differentiated connective tissue. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 6
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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