15,492 research outputs found
Low Temperature Kinetics as a Probe of Protein Structure and Dynamics
The recombination kinetics of flash-photolyzed carbon monoxy
heme proteins has been studied as a function of temperature over
the range of 2 K-350 K. Low temperature kinetics (< 200 K) reveal
that internal activation energy barriers to recombination (a) control
the room temperature kinetics, (b) are of a distributed nature, forming
an ensemble of activation energies, (c) are specific to the
protein studied and are sensitive to the presence of substrates
bound to the protein.
Cytochrome P450 from camphor induced Pseudomonas putida
reveals low temperature kinetics which are highly dependent on the
presence or absence of the camphor substrate
Control of large space structures
The control of large space structures was studied to determine what, if any, limitations are imposed on the size of spacecraft which may be controlled using current control system design technology. Using a typical structure in the 35 to 70 meter size category, a control system design that used actuators that are currently available was designed. The amount of control power required to maintain the vehicle in a stabilized gravity gradient pointing orientation that also damped various structural motions was determined. The moment of inertia and mass properties of this structure were varied to verify that stability and performance were maintained. The study concludes that the structure's size is required to change by at least a factor of two before any stability problems arise. The stability margin that is lost is due to the scaling of the gravity gradient torques (the rigid body control) and as such can easily be corrected by changing the control gains associated with the rigid body control. A secondary conclusion from the study is that the control design that accommodates the structural motions (to damp them) is a little more sensitive than the design that works on attitude control of the rigid body only
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Lamina-specific AMPA receptor dynamics following visual deprivation in vivo.
Regulation of AMPA receptor (AMPAR) expression is central to synaptic plasticity and brain function, but how these changes occur in vivo remains elusive. Here, we developed a method to longitudinally monitor the expression of synaptic AMPARs across multiple cortical layers in awake mice using two-photon imaging. We observed that baseline AMPAR expression in individual spines is highly dynamic with more dynamics in primary visual cortex (V1) layer 2/3 (L2/3) neurons than V1 L5 neurons. Visual deprivation through binocular enucleation induces a synapse-specific and depth-dependent change of synaptic AMPARs in V1 L2/3 neurons, wherein deep synapses are potentiated more than superficial synapses. The increase is specific to L2/3 neurons and absent on apical dendrites of L5 neurons, and is dependent on expression of the AMPAR-binding protein GRIP1. Our study demonstrates that specific neuronal connections, across cortical layers and even within individual neurons, respond uniquely to changes in sensory experience
Time-resolved measurement of single pulse femtosecond laser-induced periodic surface structure formation
Time-resolved diffraction microscopy technique has been used to observe the
formation of laser-induced periodic surface structures (LIPSS) from the
interaction of a single femtosecond laser pulse (pump) with a nano-scale groove
mechanically formed on a single-crystal Cu substrate. The interaction dynamics
(0-1200 ps) was captured by diffracting a time-delayed, frequency-doubled pulse
from nascent LIPSS formation induced by the pump with an infinity-conjugate
microscopy setup. The LIPSS ripples are observed to form sequentially outward
from the groove edge, with the first one forming after 50 ps. A 1-D analytical
model of electron heating and surface plasmon polariton (SPP) excitation
induced by the interaction of incoming laser pulse with the groove edge
qualitatively explains the time-evloution of LIPSS formation.Comment: 4 pages, 5 figure
ANS hard X-ray experiment development program
The hard X-ray (HXX) experiment is one of three experiments included in the Dutch Astronomical Netherlands Satellite, which was launched into orbit on 30 August 1974. The overall objective of the HXX experiment is the detailed study of the emission from known X-ray sources over the energy range 1.5-30keV. The instrument is capable of the following measurements: (1) spectral content over the full energy range with an energy resolution of approximately 20% and time resolution down to 4 seconds; (2) source time variability down to 4 milliseconds; (3) silicon emission lines at 1.86 and 2.00keV; (4) source location to a limit of one arc minute in ecliptic latitude; and (5) spatial structure with angular resolution of the arc minutes. Scientific aspects of experiment, engineering design and implementation of the experiment, and program history are included
Experiments on Visual Acuity and the Visibility of Markings on the Ground in Long-duration Earth-Orbital Space Flight
Visual acuity and visibility of markings on ground in long duration earth orbital space fligh
Reply to ``Comment on `Insulating Behavior of -DNA on the Micron Scale' "
In our experiment, we found that the resistance of vacuum-dried -DNA
exceeds at 295 K. Bechhoefer and Sen have raised a number of
objections to our conclusion. We provide counter arguments to support our
original conclusion.Comment: 1 page reply to comment, 1 figur
Near-infrared optical properties and proposed phase-change usefulness of transition metal disulfides
The development of photonic integrated circuits would benefit from a wider
selection of materials that can strongly-control near-infrared (NIR) light.
Transition metal dichalcogenides (TMDs) have been explored extensively for
visible spectrum opto-electronics, but the NIR properties of these layered
materials have been less-studied. The measurement of optical constants is the
foremost step to qualify TMDs for use in NIR photonics. Here we measure the
complex optical constants for select sulfide TMDs (bulk crystals of MoS2, TiS2
and ZrS2) via spectroscopic ellipsometry in the visible-to-NIR range. Through
Mueller matrix measurements and generalized ellipsometry, we explicitly measure
the direction of the ordinary optical axis. We support our measurements with
density functional theory (DFT) calculations, which agree with our measurements
and predict giant birefringence. We further propose that TMDs could find use as
photonic phase-change materials, by designing alloys that are thermodynamically
adjacent to phase boundaries between competing crystal structures, to realize
martensitic (i.e. displacive, order-order) switching.Comment: supplementary at end of document. 6 main figure
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