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Notizen: The planar radius and the binding energy of excitons in extremely shallow quantum well (ESQW) structures are calculated theoretically. As the strength of an applied electric field increases, the exciton planar radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures. We also calculate the energy difference between heavy hole and light hole exciton transitions in quantum wells with various barrier heights. Due to the small energy difference in ESQW structures, the light hole peak is not clearly resolved from heavy hole peak by room-temperature photocurrent experiments. © 1996 American Institute of Physics.

Notizen: It is proposed that the nucleation and growth of the amorphous phase through the solid-state amorphizing reaction in thin-film diffusion couples can be predicted by using the concept of effective driving force. The effective driving force consists of two factors: (i) the thermodynamic driving force given by maximum free-energy difference between the physical mixture of binary elements and the amorphous phase (ΔGmax), and (ii) the kinetic factor given by a ratio of the effective radius of the interstitial site in the host matrix to the atomic radius of the diffusing species (Rm/d). From the comparison of reported experimental results, it is shown that the criterion of effective driving force holds well for predicting the nucleation of the amorphous phase in metal/silicon systems as well as that of metal/metal systems. In addition, the concept of effective driving force holds well for predicting the growth tendency of the amorphous phase in metal/silicon systems. © 1995 American Institute of Physics.

Notizen: Edge-defined film-fed-growth (EFG) Si is investigated using deep-level transient spectroscopy and surface photovoltage. An impurity energy level of CrB was found at 0.27 eV above the valence band in EFG Si contaminated with Cr. The Cr diffusion coefficient in EFG Si was obtained as 2×10−17 cm2/s at room temperature using association and dissociation of CrB pairs after a 210 °C dissociation anneal. Most of the deep-level transient spectroscopy (DLTS) spectra are not analyzable with conventional methods due to abnormally broad peaks. DLTS spectra of as-grown EFG Si are modeled using a Gaussian distribution of impurity energy states. The simulated DLTS peaks agree well with measured data explaining the origin of the deep-level impurities of EFG Si. © 1995 American Institute of Physics.

Notizen: Upon reversal of the external magnetic field H during any hysteretic cycling of a type-II superconductor in its vortex state, the rate at which the magnetic flux density B varies with H is typically seen to start from zero and then change gradually. Measurements have now been made of the time dependence of B (the vortex flux creep) at many fixed-H points on several hysteresis loops of a grain-oriented YBa2Cu3O7 sample at 4.2 K (with H and B along the c axis), and it is observed that the size of the logarithmic dB/dt drops abruptly to zero, before proceeding to change in sign, whenever H is reversed. This curious similarity between the hysteretic behavior of dB/dt at fixed H and that of the nearly instantaneously measured dB/dH can be understood qualitatively in terms of the vortex pinning. As rotational magnetization measurements have recently shown,1 the unpinning and repinning of moving vortices is manifested macroscopically as a frictional process. Thus, the reversal of vortex motion involves the reversal of frictional forces, during which the vortex population in the superconducting sample (which is proportional to B) does not change with time or field.

Notizen: The scientific view of aging is still rather fragmented, because no sound unifying aging theory yet exists. Most hypotheses are rather limited, in the sense that they describe only the some aspect of the aging phenomenon, summarized in the aspect theory of aging. But it cannot be denied that the majority of hypotheses are based on a deterministic view of aging. This kind of concept presents a single strategy of aging control wholly dependent on the replacement principle, which purports the substitution of all possible tools, such as genes, cells, tissues and organs. But, recently a novel aging concept has been proposed, based on the possible control of aged cells. Therefore, the new concept of aging and a novel approach for the development of a strategic pathway to aging control are introduced, which may hopefully result in functional longevity.The concept that aging is an irreversible, inevitable, universal process of an organism provides the basis of the deterministic view of aging. The underlying view of aging as a determined irresistible fate has conjured many hypothesis on the aging process such as aging clock hypothesis, genetic determinism, telomere hypothesis, wearing hypothesis, disposable soma hypothesis and error catastrophe hypothesis, etc. Although these hypotheses are under debates, the majority of scientists and the public are inclined to accept these ideas, preoccupied by the view that aging is a natural irresistible process leading to death. Based on the deterministic view on aging, it would be natural to adopt the replacement principle as the ultimate strategy for counteracting the aging process.In other words, if the aging process were irreversible, inevitable, irresistible and universal, only the replacement principle provides a solution, that is, just substitute the aged material with new fresh material. Many replacement principles have been developed at various levels from genes to organs. However, when we examine the replacement principle, many gloomy aspects of its approaches can be identified. At the gene level, the fundamental question of existence of gerontogene has not been resolved, though many virtual gerontogenes have been suggested. In terms of the cell therapy approach, stem cell have recently attracted a great deal of attention, but still the problem of the stem cell niche and the mode of regulating stem cell development have not been unveiled. At the tissue or organ level, tissue patches, artificial organs and the transplantation approach have been elaborately pursued. However, it is well known that these methods are restricted because of our limited knowledge on the complex of coordinated development, bionanotechnology and immuno-compatibility, etc. This reality encourages to depend on camouflage transient strategies such as plastic surgery or hormonal supplementation.The complex nature of aging, denying the consensus explanation of aging, has led us to pursue historic views of aging. The core problem in understanding the aging process is the traditional prejudice concerning aging as a one-way phenomenon based on the deterministic view. However, the aging process has now been revealed to be a reactive phenomenon based on adaptive response and designed to maintain the purpose of an organism, its LIFE. Aging-related complicated changes in metabolism, signal transduction, stress response, cytoskeletal modulation, and in genetic control are adaptive and responsive, as opposed to the deterministic programmed systems, presumed to be operating in the aging process. Therefore, it is natural that large differences in the aging process are observed not only at the individual level but also at the interorgan level in the same individuals.In our previous papers, we have reported that increased levels of caveolin are mainly responsible for the hyporesponsiveness of senescent cells through the modulation of receptor-mediated endocytosis. And we have shown that the senescent phenotype of growth factor response loss can be resumed by simply reducing the caveolin status. Moreover, the adjustment of the caveolin status of old cells restored not only their functional efficiencies by adjusting the signal transduction apparatus but also their structural features, probably by modulating focal adhesion complex activities.Therefore, it can be tentatively concluded that the fundamental notion of aging as a process of functional deterioration and morphological alteration are affected by caveolin status. Such data suggest that caveolin plays the role of gatekeeper in the aging process, for if increased, aging results, but if decreased, the senescent phenotype disappears. In addition to caveolins, there seem to be several other tentative gatekeeper molecules, such as amphiphysin and some G proteins.If the existence of a molecular gatekeeper for aging were assumed, it would be natural to suppose that an aging field could be generated inside a cell, as regulated by the gatekeeper. This novel concept would explain the aging phenotype as an adaptive responsive phenomenon toward environmental stress. Since caveolin is one of the candidate gatekeepers, its simple increase or decrease might be responsible for many aspects of the aging phenotype. Therefore, we suggest that the aging phenotype can be explained in terms of a new aging hypothesis, namely the gate theory of aging. The characteristic features of this novel view of aging are its focus upon flexibility rather than irreversibility, manageability rather than inevitability, and individuality rather than generality.The gate theory of aging implies the possibility of adjusting the aging phenotype. Based on this theory, the restoration principle can be proposed as a novel approach to aging control. For example, the effect of nutrition and exercise, which result in changes in cellular cholesterol content and promoter methylation status, would profoundly influence the cellular caveolin status. Therefore, it can be presumed that the aging phenotype can be adjusted to induce restoration by modulating gatekeeper molecules, illustrated by caveolin. There may be many other tools, which can be used to augment the actions of aging-related gatekeepers.As society enters a new era of longevity, never before experienced problems concerning the elderly are generated at the social, economic, environmental, medical and cultural levels. However, most problems are based on the traditional concept of aging; that is the deterministic view on aging as an irreversible, inevitable, inefficient status. But, now it is clear that the aging process can be explained in a totally different way, as an adaptive response to age, which implies the possibility of restoration by adjusting the cellular apparatus. Actually, this new aspect of aging is readily illustrated by the superlongevity of people like centenarians. There are now many centenarians in good shape with a good status, and sound social skills.The active attitude and the positive way of life shown by centenarians present the longlive community with a new concept; functional longevity. The adoption of this approach to life marks revolutionary conversion of the view of aging from simple longevity to functional longevity. The concept of functional longevity incorporates active participation, positive thinking, and responsible behavior. It may be concluded that the concept of functional longevity based on the gate theory of aging may be used to solve the emerging problems associated with aging and aged societies.〈section xml:id="abs1-1"〉〈title type="main"〉References 1. Cho, K.A., Ryu, S.J., Oh, Y.S., Park, J.H., Lee, J.W., Kim, K.T., Jang, I.S. and Park, S.C. Morphological adjustment of senescent cells by modulating caveolin-1 status. J. Biol. Chem. (2004) (epublication ahead of print).2. Cho, K.A., Ryu, S.J., Park, J.S., Jang, I.S., Ahn, J.S., Kim, K.T. and Park, S.C. Senescent phenotype can be reversed by reduction of caveolin status. J. Biol. Chem.278, 27789–27795 (2

Notizen: It was demonstrated that the trans-activating transcriptional activator (TAT) protein from HIV-1 could enter cells when added to the surrounding media. TAT peptide chemically attached to various proteins was able to deliver these proteins to various cells and even at high levels in heart and spleen tissues in mice. In this study, the tri-peptide GKH (glycine–lysine–histidine) derived from the parathyroid hormone, which is known as a lipolytic peptide, was attached to 9-poly lysine (TAT) to be used as a cosmetic ingredient for eye-bag care product. When glycerol is released, expressed as the extracellular glycerol concentration (the so-called lipolysis index), TAT–GKH at 10−5m induces a maximal lipolytic effect of approximately 41.5% in epididymal adipocytes isolated from rats, compared with basal lipolysis. In a microdialysis study, TAT–GKH was perfused into epididymal adipose tissues of anaesthetized rats in increasing concentrations in a Ringer solution. The glycerol concentration in each dialysate was measured using an ultra-sensitive radiometric method. The perfusion of TAT–GKH induced a lipolytic effect. A penetration study showed that TAT–GKH resulted in a sevenfold higher penetration into excised hairless mice skin than GKH. An in vivo study showed that a TAT–GKH containing emulsion had a better effect upon the relative volume reduction of eye bag after 28 days of application on 22 healthy female volunteers than the placebo.It was therefore concluded that TAT–GKH increased skin penetration, which resulted in enhanced lipolytic effects in in vitro, ex vivo and in volume reduction of eye-bags in in vivo studies.

Notizen: A human Cu,Zn-superoxide dismutase was fused with a transcriptional transactivator protein transduction domain of HIV-1 to produce a novel anti-aging ingredient for cosmeceuticals, transcriptional transactivator superoxide dismutase (Tat-SOD). Stability tests and evaluation of the transduction efficacy and enzymatic activity suggest Tat-SOD is an effective active ingredient for anti-aging treatment.

Notizen: The effects of several natural products on in vitro MMP-1 activity and UVA-induced MMP-1 synthesis in human dermal fibroblast (HDF) cultures were studied with the aim of developing novel anti-aging agents from natural sources. We measured MMP-1 activities by fluorescence assay using gelatin as substrates. In addition, UVA-induced MMP-1 expression was analyzed by enzyme-linked immunosorbent assay (ELISA) and gelatin-based zymography in HDF cultures, and RT-PCR techniques were used. The results showed a strong inhibitory effect of the extracts of Dicentra spectabilis and of the flower buds of Tussilago farfara. In a concentration of 0.05% (w/v), the extracts of the flower buds of Tussilago farfara and of Dicentra spectabilis inhibited MMP-1 activity by 92 and 87% respectively. At 0.1% (w/v), the extracts of the flower buds of Tussilago farfara and of Dicentra spectabilis suppressed the UVA-induced expression of MMP-1 by an amount similar to that with Vitamin C 200 μm. These results suggest that the extracts of Dicentra spectabilis and of the flower buds of Tussilago farfara effectively protect skin from UV-induced photoaging. Therefore, the extracts are thought to have potential as effective raw materials for anti-aging cosmetics.

Notizen: The electrical and optical properties of amphoteric Si-doped GaAs diodes prepared by a single-step liquid-phase-epitaxy technique have been studied. These diodes have a P-P0-N structure and their current-voltage characteristics exhibit a negative resistance near 77 K. Existence of a recombination barrier is confirmed near the P0-P boundary by the spatial distribution of light emission, and a typical onset voltage of the negative resistance is 3 V at a current of 30 mA at 77 K. This low value can be interpreted as due to the relatively high density of thermally generated holes contributed by the shallow acceptors with activation energy of ∼30 meV. The deep acceptor level of ∼100 meV above the valence band edge is considered to be the origin for the negative resistance.

Notizen: The failure behavior of mortar under dynamic impact loading is characterized through a series of plate impact experiments. The analysis focuses on the spall strength and the shear stress carrying capacity in different regions of the specimen under normal impact loading. Special attention is paid to the possible existence of a failure wave phenomenon that has been widely recognized as an important failure mechanism for glasses during plate impact. The experiments are designed to allow the strengths of the medium at locations behind and ahead of a possible failure wave front to be analyzed. The diagnostics used include velocity interferometer system for any reflector (VISAR) recording of the free surface velocities of targets and monitoring of the internal stresses via polyvinylidene fluoride (PVDF) gauges embedded in the specimen. Experiments conducted do not provide evidence for the existence of a failure wave phenomenon for mortar under plate normal impact loading. While the study suggests that a threshold impact stress must be exceeded for failure to occur, a clearly defined failure wave that propagates behind the loading wave is not observed. Instead, a gradual failure process that initiates upon the arrival of the loading wave and progresses thereafter is observed. This gradual failure process in mortar is in contrast to the well-defined failure front and complete loss of tensile strength associated with the failure wave phenomenon reported for glasses. The study also indicates that, under impact involving high levels of input stresses, attenuation of the loading wave occurs as it propagates through the failed medium. © 2001 American Institute of Physics.