511 research outputs found
A monostrain test apparatus
Test apparatus is designed for determining tensile strength, modulus of elasticity, elongation, and thermal coefficient of contraction or expansion of uniformly shaped plastics, adhesives, and foam materials over temperature range of 700 to 90 K (800 to -300). Tests may be used in design quality control, and in evaluation of new adhesives and plastic materials
Adaptation dynamics in densely clustered chemoreceptors
In many sensory systems, transmembrane receptors are spatially organized in
large clusters. Such arrangement may facilitate signal amplification and the
integration of multiple stimuli. However, this organization likely also affects
the kinetics of signaling since the cytoplasmic enzymes that modulate the
activity of the receptors must localize to the cluster prior to receptor
modification. Here we examine how these spatial considerations shape signaling
dynamics at rest and in response to stimuli. As a model, we use the chemotaxis
pathway of Escherichia coli, a canonical system for the study of how organisms
sense, respond, and adapt to environmental stimuli. In bacterial chemotaxis,
adaptation is mediated by two enzymes that localize to the clustered receptors
and modulate their activity through methylation-demethylation. Using a novel
stochastic simulation, we show that distributive receptor methylation is
necessary for successful adaptation to stimulus and also leads to large
fluctuations in receptor activity in the steady state. These fluctuations arise
from noise in the number of localized enzymes combined with saturated
modification kinetics between localized enzymes and receptor substrate. An
analytical model explains how saturated enzyme kinetics and large fluctuations
can coexist with an adapted state robust to variation in the expression level
of the pathway constituents, a key requirement to ensure the functionality of
individual cells within a population. This contrasts with the well-mixed
covalent modification system studied by Goldbeter and Koshland in which mean
activity becomes ultrasensitive to protein abundances when the enzymes operate
at saturation. Large fluctuations in receptor activity have been quantified
experimentally. Here we clarify their mechanistic relationship with
well-studied aspects of the chemotaxis system, precise adaptation and
functional robustness.Comment: Pontius W, Sneddon MW, Emonet T (2013) Adaptation Dynamics in Densely
Clustered Chemoreceptors. PLoS Comput Biol 9(9): e1003230.
doi:10.1371/journal.pcbi.100323
CONDITIONING PLOTS AND DESIGNED EXPERIMENTS
Conditioning plots (coplots) are useful graphics for displaying values of response variables conditional on the values of given (conditioning) variables. We present a principles guide for construction of coplots when the data or statistics come from studies based on designed experiments, and illustrate the usefulness of these coplots in interpreting results. We have found coplots to be useful in our statistical consulting work, and illustrate our approach so that others may find them useful. Coplots in traditional and in trellis displays are provided
Ultrafast relaxation dynamics of optically excited electrons in Ni3-
Photon-induced ultrafast energy dissipation in small isolated Ni-3(-) has been studied by two-color pump-probe photoelectron spectroscopy. The time-resolved photoelectron spectra clearly trace the path from a single-electron excitation to a thermalized cluster via both inelastic electron-electron scattering and electron-vibrational coupling. The relatively short electron-electron-scattering time of 215 fs results from the narrow energy spread of the partially filled d levels in this transition-metal cluster. The relaxation dynamics is discussed in view of the cluster size and in comparison to the totally different relaxation behavior of s/p-metal clusters
Ultrafast Optically Induced Ferromagnetic State in an Elemental Antiferromagnet
We present evidence for an ultrafast optically induced ferromagnetic alignment of antiferromagnetic Mn in Co/Mn multilayers. We observe the transient ferromagnetic signal at the arrival of the pump pulse at the Mn L3 resonance using x-ray magnetic circular dichroism in reflectivity. The timescale of the effect is comparable to the duration of the excitation and occurs before the magnetization in Co is quenched. Theoretical calculations point to the imbalanced population of Mn unoccupied states caused by the Co interface for the emergence of this transient ferromagnetic state
1961 Ruby Yearbook
A digitized copy of the 1961 Ruby, the Ursinus College yearbook.https://digitalcommons.ursinus.edu/ruby/1064/thumbnail.jp
Biophysical suitability, economic pressure and land-cover change: a global probabilistic approach and insights for REDD+
There has been a concerted effort by the international scientific community to understand the multiple causes and patterns of land-cover change to support sustainable land management. Here, we examined biophysical suitability, and a novel integrated index of “Economic Pressure on Land” (EPL) to explain land cover in the year 2000, and estimated the likelihood of future land-cover change through 2050, including protected area effectiveness. Biophysical suitability and EPL explained almost half of the global pattern of land cover (R 2 = 0.45), increasing to almost two-thirds in areas where a long-term equilibrium is likely to have been reached (e.g. R 2 = 0.64 in Europe). We identify a high likelihood of future land-cover change in vast areas with relatively lower current and past deforestation (e.g. the Congo Basin). Further, we simulated emissions arising from a “business as usual” and two reducing emissions from deforestation and forest degradation (REDD) scenarios by incorporating data on biomass carbon. As our model incorporates all biome types, it highlights a crucial aspect of the ongoing REDD + debate: if restricted to forests, “cross-biome leakage” would severely reduce REDD + effectiveness for climate change mitigation. If forests were protected from deforestation yet without measures to tackle the drivers of land-cover change, REDD + would only reduce 30 % of total emissions from land-cover change. Fifty-five percent of emissions reductions from forests would be compensated by increased emissions in other biomes. These results suggest that, although REDD + remains a very promising mitigation tool, implementation of complementary measures to reduce land demand is necessary to prevent this leakage
Ultrafast and Distinct Spin Dynamics in Magnetic Alloys
Controlling magnetic order on ultrashort timescales is crucial for engineering the next-generation magnetic devices that combine ultrafast data processing with ultrahigh-density data storage. An appealing scenario in this context is the use of femtosecond (fs) laser pulses as an ultrafast, external stimulus to fully set the orientation and the magnetization magnitude of a spin ensemble. Achieving such control on ultrashort timescales, e.g., comparable to the excitation event itself, remains however a challenge due to the lack of understanding the dynamical behavior of the key parameters governing magnetism: The elemental magnetic moments and the exchange interaction. Here, we investigate the fs laser-induced spin dynamics in a variety of multi-component alloys and reveal a dissimilar dynamics of the constituent magnetic moments on ultrashort timescales. Moreover, we show that such distinct dynamics is a general phenomenon that can be exploited to engineer new magnetic media with tailor-made, optimized dynamic properties. Using phenomenological considerations, atomistic modeling and time-resolved X-ray magnetic circular dichroism (XMCD), we demonstrate demagnetization of the constituent sub-lattices on significantly different timescales that depend on their magnetic moments and the sign of the exchange interaction. These results can be used as a “recipe” for manipulation and control of magnetization dynamics in a large class of magnetic materials
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