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  • 1
    Electronic Resource
    Electronic Resource
    Rapid collapse of Wannier–Stark localization caused by space charge electric field screening in short-period superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5094-5105 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A rapid optical absorption change is observed in a GaAs/AlAs short-period superlattice having Wannier–Stark localization. This phenomenon is clearly explained by a rapid collapse of Wannier–Stark localization due to electric field screening by photogenerated space charges. The screening causes a positive feedback loop between restoration of the blue-shifted wavelength of the absorption band-edge towards the red and an increase in optical absorption, which causes an additional field screening. The experimental bias voltage dependence of the intensity of photoluminescence and photocurrent under high optical excitation, agree well with a model applying Fowler–Nordheim tunneling at the heterointerface cladding layer. It is concluded that the space charges are stopped near the cladding layer and that the superlattice region is almost fully screened to near the flat-band bias condition. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363489
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  • 2
    Electronic Resource
    Electronic Resource
    Pseudo-negative photocurrent spectroscopy in GaAs-AlAs superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4197-4202 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pseudo-negative photocurrent spectra, i.e., the appearance of a minimum in photocurrent at an absorption maximum, are experimentally studied at different temperatures and excitation intensities in GaAs-AlAs superlattices on GaAs substrates. Superlattice and substrate are isolated by a thick Al0.3Ga0.7As barrier, but electrically connected through penetrating contacts. A simple model is proposed for the analysis of the conditions which can lead to pseudo-negative photocurrent in this sample configuration. The radiative recombination of the carriers in the superlattice was found to be the main process determining the sign of the photocurrent at an absorption maximum. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361877
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  • 3
    Electronic Resource
    Electronic Resource
    Wannier–Stark localization in strained barrier GaAs/InXAl1−XAs superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2285-2290 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of the Wannier–Stark localization effect in short period GaAs/ InXAl1−XAs superlattices with strained barriers. The superlattices, each of which is contained in the intrinsic region of a p-i-n diode structure, consist of GaAs (3.0 nm) wells and strained shallow InXAl1−XAs (0.9 nm) barriers (X=0, 0.1, 0.2, and 0.3) grown on GaAs by molecular beam epitaxy. In spite of the use of strained barriers, the Wannier–Stark localization effect is clearly observed for all samples at room temperature. Even the superlattice sample with the highest In content of X=0.3 exhibits distinct photocurrent spectra showing several peaks associated with Wannier–Stark ladder transitions as well as Franz–Keldysh oscillations. It is found that the transition intensities are consistent with theoretically calculated oscillator strengths based on the simplified tight-binding model. By increasing the In content X, the miniband width increases and the absorption peak energy due to the zeroth order ladder (e1-hh1 and e1-lh1) transitions decreases because of the reduced barrier height. The transition energies are consistently explained by taking modulation effects into account on the valence subbands due to the compressively strained barriers. The above results show that the use of a large strain effect on the barriers is possible in Wannier–Stark localization effect type devices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363057
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  • 4
    Electronic Resource
    Electronic Resource
    Structural and optical investigations of high quality InGaAs/InAlAs short period superlattices grown on an InGaAs quasisubstrate (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5915-5920 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Unstrained InGaAs (4.5 nm)/InAlAs (1.0 nm) short-period superlattices grown on a (100) GaAs substrate were studied. To achieve this growth, an In-composition-graded buffer layer and a thick InGaAs buffer layer were adopted. Structural properties were investigated by x-ray diffraction, atomic force microscopy, and a compositional analysis by the thickness fringe method. X-ray diffraction patterns showed clear periodicity in the superlattices and atomic force spectroscopy images showed cross-hatch morphology for the main ridge along the (011¯) direction. Clear thickness fringes in the bright-field electron microscope images for the superlattice region and ambiguous fringes for the graded buffer layer indicate that misfit dislocation due to lattice mismatch concentrates in the graded buffer and a high-quality superlattice is successfully grown in spite of the large lattice mismatch between the superlattice and the substrate. Optical characteristics measured by photocurrent spectroscopy reveal a clear Wannier–Stark localization effect at room temperature. The experimental absorption energies agree well with calculated values by a transfer matrix method using parameters for bulk InGaAs and InAlAs. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363587
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  • 5
    Electronic Resource
    Electronic Resource
    Current self-oscillations in photoexcited type-II GaAs-AlAs superlattices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 500-502 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-oscillations of the photocurrent have been observed in type-II GaAs-AlAs superlattices. In addition to the fundamental frequency, several higher harmonics are present. The frequency of the oscillations can be tuned for a fixed carrier density from 15 to 120 MHz by simply changing the applied bias. The frequency distribution within a certain voltage range can be varied by changing the density of photoexcited carriers. For larger carrier densities, higher frequencies are observed in a different voltage range. This system could therefore be used as a high-frequency oscillator, which can be controlled by two external parameters, the applied voltage and the light intensity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117766
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  • 6
    Electronic Resource
    Electronic Resource
    Oral mucosal lesions in experimental graft-versus-host disease: morphological and immunohistochemical characterization of infiltrating cells (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral pathology & medicine 25 (1996), S. 0 
    Details
    ISSN: 1600-0714
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: To facilitate recognition of the oral mucosal lesion that develops in rats with graft-versus-host disease (GVHD) induced by injecting spleen cells of parental strain rats (Brown Norway) into non-irradiated (Brown Nonvay×Lewis) F1 hybrid rats, we followed the development of the tongue lesion histologically and immunohistochemically. This assessment revealed an increase in the number of MHC class II+ cells with dendritic shape in the lamina propria to be the earliest stage of the tongue lesions in GVHD rats. The subsequent mononuclear cell infiltration with epithelial cell destruction, characteristic of GVHD. consisted of CD8+ cells and macrophages. Our findings seem to indicate that MHC class II+ cells with dendritic shape may provide antigen presentation in the induction of local immunological responses, including tissue destruction, by CD8+ cells and macrophages in the tongue of GVHD rats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0714.1996.tb00269.x
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  • 7
    Electronic Resource
    Electronic Resource
    Management of subarachnoid fluid collection in infants based on a long-term follow-up study (1996)
    Springer
    Acta neurochirurgica 138 (1996), S. 179-184 
    Details
    ISSN: 0942-0940
    Keywords: Subarachnoid fluid collection ; subdural fluid collection ; subdural haematoma ; infant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We report the natural history and management of subarachnoid fluid collections in infants and their management based on a longterm follow-up study in 20 cases. These subarachnoid fluid collections were resolved spontaneously in 17 of 20 patients and only 3 by surgical intervention at the age of 2. In our 20 patients the natural history of subarachnoid fluid collection in infants was benign unless the patients sustained head trauma. Surgical treatment was performed in the cases where a subarachnoid fluid collection developed into a subdural haematoma. Head trauma may precipitate subdural haematoma in patients with subarachnoid fluid collection. All patients except one who underwent the placement of subdural-peritoneal shunt, attained normal psychomotor development in time. During the follow-up period of 3 to 10 years after resolution of the fluid collection, no patient has had a recurrence once it resolved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01411358
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of the exposure dose of etoposide on the cell growth and cell kinetics of human ovarian cancer cells (1996)
    Springer
    Cancer chemotherapy and pharmacology 38 (1996), S. 141-146 
    Details
    ISSN: 1432-0843
    Keywords: Key words Etoposide ; Cell kinetics ; Exposure dose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Although schedule-dependent cytotoxicity of etoposide has been reported, its mechanisms have not been elucidated fully. In this study, we attempted to clarify what concentration, time or exposure dose (ED, concentration of drug×time) of etoposide result in the antitumor effect on human ovarian cancer cells from the standpoint of cell cycle perturbation. The different ED were produced by different drug treatment schedules: 10 μg/ml×4 h (ED 40), 1.66 μg/ml×24 h (ED 40), 5 μg/ml×4 h (ED 20), 0.83 μg/ml×24 h (ED 20), 10 μg/ml×0.8 h (ED 8), 5 μg/ml×1.6 h (ED 8), 2 μg/ml×4 h (ED 8), 0.33 μg/ml×24 h (ED 8). Cell cycle perturbation on day 5 and the suppression of cell growth were dependent on the drug concentration at the lowest exposure dose (ED 8), but were dependent on ED at the higher EDs (20 or 40). The percentage of cells in the G2/M fraction significantly decreased from day 5 to day 7 in BG-1 cells treated at ED 20 or treated with higher concentrations (10 and 5 μg/ml) at ED 8, but not in those treated at ED 40 or treated with lower concentrations (2 and 0.33 μg/ml) at ED 8. Therefore, the cytotoxic mechanism of etoposide may not be explained by simple schedule dependency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002800050462
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  • 9
    Electronic Resource
    Electronic Resource
    Immunocytochemical localization of polyamines in the gastrointestinal tracts of rats and mice (1996)
    Springer
    Histochemistry and cell biology 106 (1996), S. 465-471 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  An immunocytochemical method using a recently produced monoclonal antibody (ASPM-29) with an antibody specificity to spermine (Spm) and spermidine (Spd) fixed in situ, was used to demonstrate an immunocytochemical localization of polyamine (PA) pools in the gastrointestinal tracts of rats and mice. High PA immunoreactivity was always found in the cytoplasm of cells not only at the cell proliferative zone or the precursor cell zone but also at the neighboring non-proliferative premature cell zone of the epithelium, and a gradient of decreasing PA levels was noticed from these cells to the fully mature differentiated gastric surface mucous cells and absorptive cells of the small and large intestines. Also, strong staining for PAs was seen in the cytoplasm of fully differentiated gastric chief cells and neurons of both the myenteric and submucous plexuses, whereas the nuclei of the cells remained virtually unstained. These results may suggest that PAs are closely associated with the high biosynthetic activity in the cells of the gastrointestinal mucosa of normal rats and mice. This seems to be consistent with the PA imunocytochemical results previously obtained for neoplastic cells and active protein- or peptide-secreting cells, including exocrine or endocrine cell types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004180050065
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  • 10
    Electronic Resource
    Electronic Resource
    Immunocytochemical localization of polyamines in the gastrointestinal tracts of rats and mice (1996)
    Springer
    Histochemistry and cell biology 106 (1996), S. 465-471 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract An immunocytochemical method using a recently produced monoclonal antibody (ASPM-29) with an antibody specificity to spermine (Spm) and spermidine (Spd) fixed in situ, was used to demonstrate an immunocytochemical localization of polyamine (PA) pools in the gastrointestinal tracts of rats and mice. High PA immunoreactivity was always found in the cytoplasm of cells not only at the cell proliferative zone or the precursor cell zone but also at the neighboring non-proliferative premature cell zone of the epithelium, and a gradient of decreasing PA levels was noticed from these cells to the fully mature differentiated gastric surface mucous cells and absorptive cells of the small and large intestines. Also, strong staining for PAs was seen in the cytoplasm of fully differentiated gastric chief cells and neurons of both the myenteric and submucous plexuses, whereas the nuclei of the cells remained virtually unstained. These results may suggest that PAs are closely associated with the high biosynthetic activity in the cells of the gastrointestinal mucosa of normal rats and mice. This seems to be consistent with the PA imunocytochemical results previously obtained for neoplastic cells and active protein- or peptide-secreting cells, including exocrine or endocrine cell types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02473308
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