43,664 research outputs found
Investigation of the Problems of Lunar and Planetary Exploration Annual Report, 1 Dec. 1964 - 30 Nov. 1965
Problems of lunar and planetary exploratio
Irrigation system performance assessment and diagnosis
Performance evaluation / Irrigation programs / Irrigation management / Irrigation systems / Case studies / Hydraulics / Management / Environmental effects / Asia / Africa / South America
DNA nano-mechanics: how proteins deform the double helix
It is a standard exercise in mechanical engineering to infer the external
forces and torques on a body from its static shape and known elastic
properties. Here we apply this kind of analysis to distorted double-helical DNA
in complexes with proteins. We extract the local mean forces and torques acting
on each base-pair of bound DNA from high-resolution complex structures. Our
method relies on known elastic potentials and a careful choice of coordinates
of the well-established rigid base-pair model of DNA. The results are robust
with respect to parameter and conformation uncertainty. They reveal the complex
nano-mechanical patterns of interaction between proteins and DNA. Being
non-trivially and non-locally related to observed DNA conformations, base-pair
forces and torques provide a new view on DNA-protein binding that complements
structural analysis.Comment: accepted for publication in JCP; some minor changes in response to
review 18 pages, 5 figure + supplement: 4 pages, 3 figure
Probabilistic computing with future deep sub-micrometer devices: a modelling approach
An approach is described that investigates the potential of probabilistic "neural" architectures for computation with deep sub-micrometer (DSM) MOSFETs. Initially, noisy MOSFET models are based upon those for a 0.35 /spl mu/m MOS technology with an exaggerated 1/f characteristic. We explore the manifestation of the 1/f characteristic at the output of a 2-quadrant multiplier when the key n-channel MOSFETs are replaced by "noisy" MOSFETs. The stochastic behavior of this noisy multiplier has been mapped on to a software (Matlab) model of a continuous restricted Boltzmann machine (CRBM) - an analogue-input stochastic computing structure. Simulation of this DSM CRBM implementation shows little degradation from that of a "perfect" CRBM. This paper thus introduces a methodology for a form of "technology-downstreaming" and highlights the potential of probabilistic architectures for DSM computation
Thermal studies of Martian channels and valleys using Termoskan data: New results
The Termoskan instrument onboard the Phobos '88 spacecraft acquired the highest-spatial-resolution thermal data ever obtained for Mars. Included in the thermal images are 2 km/pixel midday observations of several major channel and valley systems, including significant portions of Shalbatana Vallis, Ravi Vallis, Al-Qahira Vallis, Ma'adim Vallis, the channel connecting Valles Marineris with Hydraotes Chaos, and channel material in Eos Chasma. Termoskan also observed small portions of the southern beginnings of Simud, Tiu, and Ares Valles and some channel material in Gangis Chasma. Simultaneous broad band visible data were obtained for all but Ma'adim Vallis. We find that most of the channels and valleys have higher inertias than their surroundings, consistent with Viking IRTM-based thermal studies of Martian channels. We see for the first time that thermal inertia boundaries closely match all flat channel floor boundaries. Combining Termoskan thermal data, relative observations from Termoskan visible channel data, Viking absolute bolometric albedos, and a thermal model of the Mars surface, we have derived lower bounds on channel thermal inertias. Lower bounds on typical channel thermal inertias range from 8.4 to 12.5 (10(exp -3) cal cm(exp -2) s(exp -1/2)K(exp -1)) (352 to 523 in SI units). Lower bounds on inertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5 (46 to 147 in SI units). Atmospheric and geometric effects are not sufficient to cause the inertia enhancements. We agree with previous researchers that localized, dark, high inertia areas within channels are likely eolian in nature. However, the Temloskan data show that eolian deposits do not fill the channels, nor are they responsible for the overall thermal inertia enhancement. Thermal homogeneity and strong correlation of thermal boundaries with the channel floor boundaries lead us to favor noneolian overall explanations
Preliminary Report on High-Silica Sand in Indiana
In the past few years, largely because of increased freight rates,
a keen interest in finding sources of high-silica sand has developed.
The Geological Survey has received many inquiries about possible
sources of high-silica sand in the state. Although published information
on the geology of the formations that may contain high-silica
sand has been available, economic information, such as quality, distribution,
extent, and accessibility, has not been available
Regulatory activity revealed by dynamic correlations in gene expression noise
Gene regulatory interactions are context dependent, active in some cellular states but not in others. Stochastic fluctuations, or 'noise', in gene expression propagate through active, but not inactive, regulatory links^(1,2). Thus, correlations in gene expression noise could provide a noninvasive means to probe the activity states of regulatory links. However, global, 'extrinsic', noise sources generate correlations even without direct regulatory links. Here we show that single-cell time-lapse microscopy, by revealing time lags due to regulation, can discriminate between active regulatory connections and extrinsic noise. We demonstrate this principle mathematically, using stochastic modeling, and experimentally, using simple synthetic gene circuits. We then use this approach to analyze dynamic noise correlations in the galactose metabolism genes of Escherichia coli. We find that the CRP-GalS-GalE feed-forward loop is inactive in standard conditions but can become active in a GalR mutant. These results show how noise can help analyze the context dependence of regulatory interactions in endogenous gene circuits
Hopping Conduction and Bacteria: Transport in Disordered Reaction-Diffusion Systems
We report some basic results regarding transport in disordered
reaction-diffusion systems with birth (A->2A), death (A->0), and binary
competition (2A->A) processes. We consider a model in which the growth process
is only allowed to take place in certain areas--"oases"--while the rest of
space--the "desert"--is hostile to growth. In the limit of low oasis density,
transport is mediated through rare "hopping" events, necessitating the
inclusion of discreteness effects in the model. By first considering transport
between two oases, we are able to derive an approximate expression for the
average time taken for a population to traverse a disordered medium.Comment: 4 pages, 2 figure
Far infrared absorption by acoustic phonons in titanium dioxide nanopowders
We report spectral features of far infrared electromagnetic radiation
absorption in anatase TiO2 nanopowders which we attribute to absorption by
acoustic phonon modes of nanoparticles. The frequency of peak excess absorption
above the background level corresponds to the predicted frequency of the
dipolar acoustic phonon from continuum elastic theory. The intensity of the
absorption cannot be accounted for in a continuum elastic dielectric
description of the nanoparticle material. Quantum mechanical scale dependent
effects must be considered. The absorption cross section is estimated from a
simple mechanical phenomenological model. The results are in plausible
agreement with the absorption being due to a sparse layer of charge on the
nanoparticle surface.Comment: 8 pages, 5 figures, submitted to Journal of Nanoelectronics and
Optoelectronic
Biologically Inspired Feedback Design for Drosophila Flight
We use a biologically motivated model of the Drosophila's flight mechanics and sensor processing to design a feedback control scheme to regulate forward flight. The model used for insect flight is the grand unified fly (GUF) [3] simulation consisting of rigid body kinematics, aerodynamic forces and moments, sensory systems, and a 3D environment model. We seek to design a control algorithm that will convert the sensory signals into proper wing beat commands to regulate forward flight. Modulating the wing beat frequency and mean stroke angle produces changes in the flight envelope. The sensory signals consist of estimates of rotational velocity from the haltere organs and translational velocity estimates from visual elementary motion detectors (EMD's) and matched retinal velocity filters. The controller is designed based on a longitudinal model of the flight dynamics. Feedforward commands are generated based on a desired forward velocity. The dynamics are linearized around this operating point and a feedback controller designed to correct deviations from the operating point. The control algorithm is implemented in the GUF simulator and achieves the desired tracking of the forward reference velocities and exhibits biologically realistic responses
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