A Method for Determining Optimum Re-entry Trajectories

Determining optimum atmospheric reentry trajectories using Pontryagin maximum principl

Two Cell-Bound Keratinases of Trichophyton Mentagrophytes

Two cell-bound keratinases, II and III, of Trichophyton mentagrophytes were extracted from mycelium and purified. The purified keratinases, II and III, had a specific keratinolytic activity of 36.4 and 39.4 KU/mg respectively. The molecular weights of keratinases II and III were 440,000 and 20,300 respectively. Immunodiffusion analysis showed that these two cell-bound keratinases, II and III, were not identical to each other nor to extracellular keratinase I of the same species

Power-law population heterogeneity governs epidemic waves

We generalize the Susceptible-Infected-Removed (SIR) model for epidemics to take into account generic effects of heterogeneity in the degree of susceptibility to infection in the population. We introduce a single new parameter corresponding to a power-law exponent of the susceptibility distribution at small susceptibilities. We find that for this class of distributions the gamma distribution is the attractor of the dynamics. This allows us to identify generic effects of population heterogeneity in a model as simple as the original SIR model which is contained as a limiting case. Because of this simplicity, numerical solutions can be generated easily and key properties of the epidemic wave can still be obtained exactly. In particular, we present exact expressions for the herd immunity level, the final size of the epidemic, as well as for the shape of the wave and for observables that can be quantified during an epidemic. In strongly heterogeneous populations, the herd immunity level can be much lower than in models with homogeneous populations as commonly used for example to discuss effects of mitigation. Using our model to analyze data for the SARS-CoV-2 epidemic in Germany shows that the reported time course is consistent with several scenarios characterized by different levels of immunity. These scenarios differ in population heterogeneity and in the time course of the infection rate, for example due to mitigation efforts or seasonality. Our analysis reveals that quantifying the effects of mitigation requires knowledge on the degree of heterogeneity in the population. Our work shows that key effects of population heterogeneity can be captured without increasing the complexity of the model. We show that information about population heterogeneity will be key to understand how far an epidemic has progressed and what can be expected for its future course

Dynamical control of electron spin coherence in a quantum dot

We investigate the performance of dynamical decoupling methods at suppressing electron spin decoherence from a low-temperature nuclear spin reservoir in a quantum dot. The controlled dynamics is studied through exact numerical simulation, with emphasis on realistic pulse delays and long-time limit. Our results show that optimal performance for this system is attained by a periodic protocol exploiting concatenated design, with control rates substantially slower than expected from the upper spectral cutoff of the bath. For a known initial electron spin state, coherence can saturate at long times, signaling the creation of a stable ``spin-locked'' decoherence-free subspace. Analytical insight on saturation is obtained for a simple echo protocol, in good agreement with numerical results.Comment: 4 pages, 4 figures with 3 of them in colo

The Burst and Transient Source Experiment Earth Occultation Technique

An Earth orbiting detector sensitive to gamma ray photons will see step-like occultation features in its counting rate when a gamma ray point source crosses the Earth's limb. This is due to the change in atmospheric attenuation of the gamma rays along the line of sight. In an uncollimated detector, these occultation features can be used to locate and monitor astrophysical sources provided their signals can be individually separated from the detector background. We show that the Earth occultation technique applied to the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) is a viable and flexible all-sky monitor in the low energy gamma ray and hard X-ray energy range (20 keV - 1 MeV). The method is an alternative to more sophisticated photon imaging devices for astronomy, and can serve well as a cost-effective science capability for monitoring the high energy sky. Here we describe the Earth occultation technique for locating new sources and for measuring source intensity and spectra without the use of complex background models. Examples of transform imaging, step searches, spectra, and light curves are presented. Systematic uncertainties due to source confusion, detector response, and contamination from rapid background fluctuations are discussed and analyzed for their effect on intensity measurements. A sky location-dependent average systematic error is derived as a function of galactic coordinates. The sensitivity of the technique is derived as a function of incident photon energy and also as a function of angle between the source and the normal to the detector entrance window. Occultations of the Crab Nebula by the Moon are used to calibrate Earth occultation flux measurements independent of possible atmospheric scattering effects.Comment: 39 pages, 24 figures. Accepted for publication in the Astrophysical Journal Supplement

Development and evaluation of an evaporation model for predicting sprinkler interval time

Heat stress in swine causes decreased productivity and economic losses; hence, heat stress mitigation techniques must be developed to be economically and resource efficient. Current cooling strategies for livestock facilities, such as evaporative coolers or sprinklers, are governed by the Water Vapor Pressure (WVP) concentration gradient between the air (a function of dry-bulb temperature; tdb, Relative Humidity; RH, and atmospheric pressure) and the saturated WVP at the wet surface. Traditional sprinkler control systems operate at fixed ‘off’ intervals (i.e., drying) regardless if the thermal environment (TE) has the capacity or not to evaporate the dispersed water. Therefore, the objectives were to develop and simulate a novel Variable Interval Sprinkler Control System (VISCoS) that dynamically changes the ‘off’ interval based on tdb, RH, and airspeed feedback. A theoretical simplified pig evaporation model estimated water evaporation rate as a function of the TE, pig surface area and skin temperature, and mass of water applied. To evaluate the model in controlled conditions, a cylinder (assumed geometry of a pig) was placed inside an insulated enclosure where different combinations of tdb, RH, and airspeed could be simulated across the cylinder. The inside surface of the cylinder was heated and controlled to replicate the skin temperature of an animal, while the outer surface was wrapped in a thin chamois. Water was applied to the cylinder via a sprinkler where approximately 40% of the top portion of the cylinder was wetted. Comparison of modeled with measured evaporation time showed reasonable agreement with a root-mean-square error of 7.9 min for evaporation times ranging from 5 to 25 min

A k-shell decomposition method for weighted networks

We present a generalized method for calculating the k-shell structure of weighted networks. The method takes into account both the weight and the degree of a network, in such a way that in the absence of weights we resume the shell structure obtained by the classic k-shell decomposition. In the presence of weights, we show that the method is able to partition the network in a more refined way, without the need of any arbitrary threshold on the weight values. Furthermore, by simulating spreading processes using the susceptible-infectious-recovered model in four different weighted real-world networks, we show that the weighted k-shell decomposition method ranks the nodes more accurately, by placing nodes with higher spreading potential into shells closer to the core. In addition, we demonstrate our new method on a real economic network and show that the core calculated using the weighted k-shell method is more meaningful from an economic perspective when compared with the unweighted one.Comment: 17 pages, 6 figure

Decoherence by a chaotic many-spin bath

We numerically investigate decoherence of a two-spin system (central system) by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical regime of the bath has been varied from quantum chaos to regular, while all other dynamical characteristics have been kept practically intact. We explicitly demonstrate that for a many-body quantum bath, the onset of quantum chaos leads to significantly faster and stronger decoherence compared to an equivalent non-chaotic bath. Moreover, the non-diagonal elements of the system's density matrix decay differently for chaotic and non-chaotic baths. Therefore, knowledge of the basic parameters of the bath (strength of the system-bath interaction, bath's spectral density of states) is not always sufficient, and much finer details of the bath's dynamics can strongly affect the decoherence process.Comment: 4 pages, RevTeX, 5 eps figure