7,210 research outputs found
Pioneer Venus polarimetry and haze optical thickness
The Pioneer Venus mission provided us with high-resolution measurements at four wavelengths of the linear polarization of sunlight reflected by the Venus atmosphere. These measurements span the complete phase angle range and cover a period of more than a decade. A first analysis of these data by Kawabata et al. confirmed earlier suggestions of a haze layer above and partially mixed with the cloud layer. They found that the haze exhibits large spatial and temporal variations. The haze optical thickness at a wavelength of 365 nm was about 0.06 at low latitudes, but approximately 0.8 at latitudes from 55 deg poleward. Differences between morning and evening terminator have also been reported by the same authors. Using an existing cloud/haze model of Venus, we study the relationship between the haze optical thickness and the degree of linear polarization. Variations over the visible disk and phase angle dependence are investigated. For that purpose, exact multiple scattering computations are compared with Pioneer Venus measurements. To get an impression of the variations over the visible disk, we have first studied scans of the polarization parallel to the intensity equator. After investigating a small subset of the available data we have the following results. Adopting the haze particle characteristics given by Kawabata et al., we find a thickening of the haze at increasing latitudes. Further, we see a difference in haze optical thickness between the northern and southern hemispheres that is of the same order of magnitude as the longitudinal variation of haze thickness along a scan line. These effects are most pronounced at a wavelength of 935 nm. We must emphasize the tentative nature of the results, because there is still an enormous amount of data to be analyzed. We intend to combine further polarimetric research of Venus with constraints on the haze parameters imposed by physical and chemical processes in the atmosphere
Synthetic control of a fitness tradeoff in yeast nitrogen metabolism
Background:
Microbial communities are involved in many processes relevant to industrial and medical biotechnology, such as the formation of biofilms, lignocellulosic degradation, and hydrogen production. The manipulation of synthetic and natural microbial communities and their underlying ecological parameters, such as fitness, evolvability, and variation, is an increasingly important area of research for synthetic biology.
Results:
Here, we explored how synthetic control of an endogenous circuit can be used to regulate a tradeoff between fitness in resource abundant and resource limited environments in a population of Saccharomyces cerevisiae. We found that noise in the expression of a key enzyme in ammonia assimilation, Gdh1p, mediated a tradeoff between growth in low nitrogen environments and stress resistance in high ammonia environments. We implemented synthetic control of an endogenous Gdh1p regulatory network to construct an engineered strain in which the fitness of the population was tunable in response to an exogenously-added small molecule across a range of ammonia environments.
Conclusion:
The ability to tune fitness and biological tradeoffs will be important components of future efforts to engineer microbial communities
Agent Based Modeling for Low-cost Counter UAS Protocol in Prisons
Technological advances have led to the prevalence of small unmanned aerial systems (sUAS) which has proven to be a security concern for fixed facilities to include prisons, airports, and forward operating bases. This study explores if agent-based simulation modeling can serve as a useful tool for developing counter unmanned aerial system (C-UAS) parameters for a fixed facility. The relationship between threat speed and a hypothetical C-UAS is explored in an AnyLogic model designed to represent a prison and general sUAS smuggling threats that prisons have experienced in recent years. The data suggests there is a critical threat sUAS speed in which C-UAS failures occur at a much higher frequency and that the relationship is non-linear
Zero Entropy Interval Maps And MMLS-MMA Property
We prove that the flow generated by any interval map with zero topological
entropy is minimally mean-attractable (MMA) and minimally mean-L-stable (MMLS).
One of the consequences is that any oscillating sequence is linearly disjoint
with all flows generated by interval maps with zero topological entropy. In
particular, the M\"obius function is orthogonal to all flows generated by
interval maps with zero topological entropy (Sarnak's conjecture for interval
maps). Another consequence is a non-trivial example of a flow having the
discrete spectrum.Comment: 12 page
Visualizing genetic constraints
Principal Components Analysis (PCA) is a common way to study the sources of
variation in a high-dimensional data set. Typically, the leading principal
components are used to understand the variation in the data or to reduce the
dimension of the data for subsequent analysis. The remaining principal
components are ignored since they explain little of the variation in the data.
However, evolutionary biologists gain important insights from these low
variation directions. Specifically, they are interested in directions of low
genetic variability that are biologically interpretable. These directions are
called genetic constraints and indicate directions in which a trait cannot
evolve through selection. Here, we propose studying the subspace spanned by low
variance principal components by determining vectors in this subspace that are
simplest. Our method and accompanying graphical displays enhance the
biologist's ability to visualize the subspace and identify interpretable
directions of low genetic variability that align with simple directions.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS603 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Kalinia, a New North American Genus for a Species Long Misplaced in Eragrostis (Poaceae, Chloridoideae)
Eragrostis obtusiflora (Poaceae, Chloridoideae), a species distributed from the southwestern United States to central Mexico, has long been recognized for exhibiting morphological and anatomical features atypical of Eragrostis. Phylogenetic analyses of nuclear internal transcribed spacer sequences and plastid sequences demonstrate that E. obtusiflora should be excluded from Eragrostis (Eragrostideae) and instead be placed in Cynodonteae, although its position within this tribe was unresolved. Additional data, including anatomical and micromorphological characters, suggest a close relationship with Distichlis. However, differences in spikelet and rhizome characters prevent its inclusion in Distichlis. Therefore, the species is transferred to a newly described genus, Kalinia, as K. obtusiflora
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