A generic circuit, the charge controlled analog synapse (CCAS) is presented. The CCAS is designed to be the basic building block in microelectronic realizations of large scale artificial neural networks. It is based on representing the synaptic strength as a charge packet which controls the junction capacitance of a reverse biased diode. The CCAS is a synapse with three main features: (i) a small cell with few components per cell; (ii) a short term dynamic memory, and (iii) a variable accuracy which depends on the cell size. The principle of operation of the CCAS is explained. Details of the design of a first prototype are given. Experimental results which substantiate the theoretical predictions are presented. Finally, the basic properties of the CCAS are discussed. Copyright (C) 1996 Elsevier Science Ltd
Chemiluminescence (CL) reactions were studied in a model system based on a phase diagram which was composed of Triton X-100, 2-butanol, toluene, and H2O. The CL reaction was achieved by using trichlorophenyl oxalate, H2O2, and perylene as the fluorophore. The intensity of light (I0) and t1/2 depend on both reactant concns. and phase compn. The CL reaction was conducted in W/O microemulsions, and an inverse relation between I0 and t1/2 was found. These two parameters could also indicate the transition from a W/O (water-in-oil) emulsion to a W/O microemulsion. The effect of medium polarity was evaluated by fluorescence, absorbance, and chemiluminescence spectra. [on SciFinder(R)]
Molecular dynamics simulations of the dissociation of I-2 embedded in large Ar-n (n = 319, 553) clusters, which impact at high velocities (upsilon = 7-15 km s(-1)) on Pt surfaces, result in information on heterogeneous and homogeneous dissociation mechanisms. A broad distribution of dissociation lifetimes is exhibited, which can be attributed to prompt and retarded heterogeneous dissociation and to prompt, retarded and outbound homogeneous dissociation events. The propagation of a microshock wave within a large cluster can be interrogated by the homogeneous dissociation of a chemical probe, with the velocity of the propagation of the dissociation front being close to the cluster impact velocity.
The unique amplitude obtained by an inversion of an observed Raman excitation profile is one of minimal phase. As the frequency varies, the phase of such an amplitude can span a range larger than 2 pi. Therefore such an inversion can yield an amplitude that accurately reproduces the input profile. It is possible to add to the minimal phase additional terms but such modifications of the phase of the Raman amplitude cannot change the corresponding Raman excitation profile. Hence such terms cannot be determined from the profile and introducing them does not constitute an inversion procedure.
An electronically or optically addressed compact optical bypass–exchange switch is investigated and experimentally demonstrated. The switch is polarization based and consists of a controllable λ/2 plate sandwiched between two polarizing beam displacers. The input and the output signals propagate normal to the switching array, which makes the switch extremely attractive for cascading switching arrays, as found in multistage interconnect networks. A complete, all-optical interconnection network is suggested.
Modern Dead Sea cosmetics have developed in order to meet the demands of new regulations, technical opportunities, and today's consumer expectations for higher quality standards and proven performance. As an example of the application of this approach, the authors describe the development of a new cosmetic formulation, based on "Osmoter", a special Dead Sea mineral composition, and the evaluation of this formulation's effect on the depth of skin wrinkles, by a controlled assay. Possible mode of action is discussed.[on SciFinder (R)]
The article discusses the possession and exorcism of sixteen-year-old Nicole Obry (1565-1566). It offers a three-layer interpretation of the case and argues that a combination of psychological, political, and gender issues brought about the woman's possession. I first suggest that possession by either good or evil spirits was a culturally recognized syndrome that allowed laypeople, mostly women, to express religious concern in a society that did not permit laywomen to address spiritual issues in more normative ways. Indeed, in her own perception prior to the clerical intervention, Nicole regarded herself as a visionary and not as a demoniac. The complexity of spirit possession as a psychological and psychopathological behavior also necessitates a personal (sub)conscious motivation, and I suggest that metaphors of penetration and possessions were directly related to Nicole's personal experiences and anxieties as a young woman. The social/cultural and the personal contexts are then conn
The coupling of a Rydberg electron to the vibrational motion is discussed in the intermediate regime in which the orbital period is long on the scale of the vibrational motion but is still considerably faster than the rotation of the core. Two dimensionless variables characterize the dynamics: the ratio of time scales and the action exchanged between the electron and the core, per one revolution. The classical dynamics are reduced to a map which provides a realistic approximation in the limit when the action exchanged is larger than h. There are two distinguishable time regimes, that of prompt processes where the corresponding spectrum is so broad that individual Rydberg states cannot be resolved and a much slower process, where the electron revolves many times around the core before it ionizes. The overall spectrum is that of a Rydberg series, where the lines are broadened by (the delayed) vibrational autoionization superimposed on a broad background. The semiclassical dynamics is quantitatively more accurate in the typical situation when the action exchanged is comparable or smaller than h. Explicit analytical expressions are obtained for the width for vibrational autoionization including for the case when resonances are possible. The presence of resonances is evident in Rydberg lines which are broader. For low Rydberg states the present approach recovers the Herzberg-Jungen approximation in the weak coupling limit. (C) 1996 American Institute of Physics.
Ab initio dynamics on more than one electronic state is reported for the NaI system. This requires both a method for computing the electronic energy curves and their coupling and a matched method for propagating the equations of motion for the atoms. The long-range electron transfer (a `harpoon' process) requires a particularly accurate electronic computation and many configurations are employed in a novel method which combines the advantages of the molecular orbital and valence bond approaches. The computation is performed `on the fly' with the required electronic input being generated at each nuclear separation reached by the system.
Activation energies for desorption and for diffusion were experimentally determined as a function of surface coverage for the system of ammonia on Re(001) utilizing optical second harmonic generation techniques, For the first time coverage grating with up to 5th order SH-diffraction is reported for K atoms on Re(001). Preliminary diffusion measurements were performed on this system as well. These systems may be considered as ideal model to study the effect of very strong lateral repulsion on the kinetics of desorption and diffusion. A MC study on the ammonia-Re(001) system is presented, which examines the significance of long range repulsive dipole-dipole interactions on the outcome desorption and diffusion kinetics, We found that a single set of parameters, within the dipole-dipole like (1/r(3)) dependence on adsorbates separation distance, explains qualitatively and in certain cases quantitatively the experimental observations. Interaction range up to 4th order neighbors must be computed in order to properly account for the results.
The effects of adsorbate lateral interactions on the kinetics of surface diffusion and desorption are studied by means of kinetic and thermodynamic Monte Carlo simulations. This study is motivated by recent diffusion and desorption experiments on the NH3/Re(001) system, which show that the activation energies of these processes decrease (in different fashions) with increasing surface coverage, the interactions between the adsorbates are thus assumed to be repulsive. A long range dipole-dipole-like potential is used to simulate both the diffusion and desorption processes. Most calculations are carried out with the interaction range extending up to fourth-order neighbors. Longer ranges are found to barely affect the kinetic behavior. On the other hand, shorter ranges of interaction result in qualitatively and quantitatively different structural (thermodynamic phase) behaviors and, consequently, in very different kinetics of diffusion and desorption. The model used to calculate diffusion kinetics assumes that the activation barrier to particle diffusion depends, simultaneously, on the local environments of both the initial and the final sites involved in the elementary event of particle jumps. The chemical diffusion coefficient is evaluated based on thermodynamic and kinetic Monte Carlo simulations. It is found to increase with surface coverage, reflecting the repulsive nature of the interactions. Yet, unlike the experimental results, the increase is nonmonotonic but rather, somewhat oscillatory-reflecting the structural phase transitions of the adsorbed layer. The activation energy of desorption is found to decrease by about 15 kcal/mole as the coverage increases from 0 to 1, showing steeper slopes around the coverages corresponding to a perfectly ordered adlayer phase. These results are in satisfactory qualitative and quantitative agreement with experiment. Finally, it is shown that the coverage dependence of the activation barrier to diffusion can be reasonably well evaluated from equilibrium thermodynamic desorption data. (C) 1996 American Institute of Physics.
We investigate the influence of an internal barrier on an exothermic adiabatic reaction model between diatomic ions and molecules. Reaction cross-sections are calculated from quasi-classical trajectories for different initial vibrational and rotational states of the reactants and for relative collision energies in the range from 0.01 to 3 eV. It is shown that the height of a late internal barrier strongly influences both the characteristics of the state-selected cross-sections and the energy distributions of the products. In contrast to complex formation in the entrance region according to the Langevin model our analysis emphasizes the role of the full potential energy surface for an understanding of the dynamics of ion-molecule reactions. (C) 1996 American Institute of Physics.
Since the beginning of the century, feedback interventions (FIs) produced negative-but largely ignored-effects on performance. A meta-analysis (607 effect sizes; 23,663 observations) suggests that FIs improved performance on average (d=.41) but that over 1/3 of the FIs decreased performance. This finding cannot be explained by sampling error, feedback sign, or existing theories. The authors proposed a preliminary FI theory (FIT) and tested it with moderator analyses. The central assumption of FIT is that FIs change the locus of attention among 3 general and hierarchically organized levels of control: task learning, task motivation, and meta-tasks (including self-related) processes. The results suggest that FI effectiveness decreases as attention moves up the hierarchy closer to the self and away from the task. These findings are further moderated by task characteristics that are still poorly understood.
During the annual life cycle of the bumble bee Bombus terrestris (L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) release in vitro, ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.
