Double Inverse Stochastic Resonance with Dynamic Synapses

We investigate the behavior of a model neuron that receives a biophysically-realistic noisy post-synaptic current based on uncorrelated spiking activity from a large number of afferents. We show that, with static synapses, such noise can give rise to inverse stochastic resonance (ISR) as a function of the presynaptic firing rate. We compare this to the case with dynamic synapses that feature short-term synaptic plasticity, and show that the interval of presynaptic firing rate over which ISR exists can be extended or diminished. We consider both short-term depression and facilitation. Interestingly, we find that a double inverse stochastic resonance (DISR), with two distinct wells centered at different presynaptic firing rates, can appear.Comment: 12 pages, 7 figure

Fate of the Universe, Age of the Universe, Dark Matter, and the Decaying Vacuum Energy

It is shown that in the cosmological models based on a vacuum energy decaying as a^{-2}, where a is the scale factor of the universe, the fate of the universe in regard to whether it will collapse in future or expand forever is determined not by the curvature constant k but by an effective curvature constant k_{eff}. It is argued that a closed universe with k=1 may expand forever, in other words simulate the expansion dynamics of a flat or an open universe because of the possibility that k_{eff}=0 or -1, respectively. Two such models, in one of which the vacuum does not interact with matter and in another of which it does, are studied. It is shown that the vacuum equation of state p_{vac}= -\rho_{vac} may be realized in a decaying vacuum cosmology provided the vacuum interacts wuth matter. The optical depths for gravitational lensing as a function of the matter density and other parameters in the models are calculated at a source redshift of 2. The age of the universe is discussed and shown to be compatible with the new Hipparcos lower limit of 11Gyr. The possibility that a time-varying vacuum energy may serve as dark matter is suggested.Comment: AAS LaTex, 29 pages, published in the Astrophysical Journal, 520, 45, 199

Proceedings of the Conference on Human and Economic Resources

Recent studies about estimating half-lives of purchasing power parity argues that heterogeneity bias resulting from aggregating the real exchange rate across sectors is important and should be taken into account. However, they do not use appropriate techniques to measure persistence. In this paper we use the extended median-unbiased estimation method in panel context for each sector separately and calculate both point estimates and confidence intervals. We conclude that controlling for sectoral heterogeneity bias and small sample bias will not solve the PPP puzzle.PPP persistence, real exchange rate, heterogeneity bias extended median-unbiased estimation, panel data

SURF -A simulation model for the behaviour of oil slicks at sea

This report describes the SURF model, one of the basic models of the OPERA software package, which predicts the fate of oil spilled at sea. SURF is a fully operational computer model for describing the behaviour of oil slicks at sea. With necessary information, it may be used to simulate or to forecast the transport, the spreading and the aging of oil slicks. The model aims mainly at forecasting the behaviour of a pollution in case of an accident at sea. The information provided by the model (position and extent of the polluted area, oil characteristics) can efficiently help the authorities and the combating teams in making decisions on how to wrestle the pollution. But other model applications can be faced. For instance, knowing the zones where oil is extracted, carried or trans-shiped, the model can be used to investigate, a priori, the high risk areas

Intersectional Discrimination Is Associated with Housing Instability among Trans Women Living in the San Francisco Bay Area.

Trans women face numerous structural barriers to health due to discrimination. Housing instability is an important structural determinant of poor health outcomes among trans women. The purpose of this study was to determine if experiences of intersectional anti-trans and racial discrimination are associated with poor housing outcomes among trans women in the San Francisco Bay Area. A secondary analysis of baseline data from the Trans *National study (n = 629) at the San Francisco Department of Public Health (2016-2018) was conducted. Multivariable logistic regression was used to analyze the association between discrimination as an ordered categorical variable (zero, one to two, or three or more experiences) and housing status adjusting for age, years lived in the Bay Area, and gender identity. We found that the odds of housing instability increased by 1.25 for every categorical unit increase (1-2, or 3+) in reported experiences of intersectional (both anti-trans and racial) discrimination for trans women (95% CI = 1.01-1.54, p-value < 0.05). Intersectional anti-trans and racial discrimination is associated with increased housing instability among trans women, giving some insight that policies and programs are needed to identify and address racism and anti-trans stigma towards trans women. Efforts to address intersectional discrimination may positively impact housing stability, with potential for ancillary effects on increasing the health and wellness of trans women who face multiple disparities

Creating a computational tool to simulate vibration control for piezoelectric devices

Piezoelectric materials have the unique ability to convert electrical energy to mechanical vibrations and vice versa. This project takes a stab to develop a reliable computational tool to simulate the vibration control of a novel “partial differential equation” model for a piezoelectric device, which is designed by integrating electric conducting piezoelectric layers constraining a viscoelastic layer to provide an active and lightweight intelligent structure. Controlling unwanted vibrations on piezoelectric devices (or harvesting energy from ambient vibrations) through piezoelectric layers has been the major focus in cutting-edge engineering applications such as ultrasonic welders and inchworms. The corresponding mathematical models for piezoelectric devices are either heuristic or mathematically oversimplified differential equations. Moreover, their “unjustified” approximated reductions consider only the first several vibrations on these devices. In this project, a novel partial differential equation model, accounting for all vibrational modes, is analyzed to provide new insights for a cost-efficient sensor feedback design. Therefore, the sensor feedback signals are not allowed to be contaminated by the residual modes. Our primary goal is to develop reproducible computational tools by an emerging stable approximation technique, so-called filtered Finite Difference Method, which is proved to provide faster and reliable computation. Filtering in the approximation is necessary since the spurious vibrations, due to the blind application of the Finite Difference Method, provide a false stability result. To see the efficiency of the algorithm, we compare the approximation to the one obtained by the Finite Element Method based on the Galerkin\u27s approximation, which is a common technique being used in the engineering literature. The mathematical techniques and computational tools developed in this project are essential to provide new insights into the active controlling of piezoelectric devices. Improving the efficiency of active controlling enables us to take better advantage of piezoelectric technology change since one-time design and fabrication may be unavoidable for many applications such as cardiac pacemakers or NASA/commercially-operated inflatable space antennas. Our state-of-the-art partial differential equation model and its stable approximations will be adaptable for a large class of piezoelectric devices

Simulation of ecological impacts of the new outer-harbour development in Zeebrugge

The new outer-harbour in Zeebrugge is to be protected by jetties extending 1,750 m seaward, This development will alter the local distribution of tidal and residual currents. Such hydrodynamic changes will, in turn, affect the dispersion pattern of dissolved and particular matters in the vicinity of Zeebrugge. A mathematical model is presented, which simulates the dispersion - before and after outer harbour development - of dissolved organic matters, faecal bacteria and heavy metals, which are indicative of, respectively domestic, human, and industrial pollutions