3,257 research outputs found
Simulation and visualization of face seal motion stability by means of computer generated movies
A computer aided design method for mechanical face seals is described. Based on computer simulation, the actual motion of the flexibly mounted element of the seal can be visualized. This is achieved by solving the equations of motion of this element, calculating the displacements in its various degrees of freedom vs. time, and displaying the transient behavior in the form of a motion picture. Incorporating such a method in the design phase allows one to detect instabilities and to correct undesirable behavior of the seal. A theoretical background is presented. Details of the motion display technique are described, and the usefulness of the method is demonstrated by an example of a noncontacting conical face seal
Analysis and design of a flat central finned-tube radiator
Computer program based on fixed conductance parameter yields minimum weight design. Second program employs variable conductance parameter and variable ratio of fin length to tube outside radius, and is used for radiator designs with geometric limitations. Major outputs of the two programs are given
Analysis of low-temperature direct-condensing vapor-chamber fin and conducting fin radiators
Analysis of flat, direct-condensing finned-tube space radiator with vapor chamber, and central fin tube geometries for low temperature Rankine space power electric generating syste
Computer program for preliminary design and analysis of V/STOL tip-turbine fans
Computer program for design and analysis of V/STOL tip turbine fan
Entangled photons from the polariton vacuum in a switchable optical cavity
We study theoretically the entanglement of two-photon states in the ground
state of the intersubband cavity system, the so-called polariton vacuum. The
system consists of a sequence of doped quantum wells located inside a
microcavity and the photons can interact with intersubband excitations inside
the quantum wells. Using an explicit solution for the ground state of the
system, operated in the ultrastrong coupling regime, a post-selection is
introduced, where only certain two-photon states are considered and analyzed
for mode entanglement. We find that a fast quench of the coupling creates
entangled photons and that the degree of entanglement depends on the absolute
values of the in-plane wave vectors of the photons. Maximally entangled states
can be generated by choosing the appropriate modes in the post-selection.Comment: 9+ pages, 7 figure
Differential effects of food availability on minimum and maximum rates of metabolism
Metabolic rates reflect the energetic cost of living but exhibit remarkable variation among conspecifics, partly as a result of the constraints imposed by environmental conditions. Metabolic rates are sensitive to changes in temperature and oxygen availability, but effects of food availability, particularly on maximum metabolic rates, are not well understood. Here, we show in brown trout (Salmo trutta) that maximum metabolic rates are immutable but minimum metabolic rates increase as a positive function of food availability. As a result, aerobic scope (i.e. the capacity to elevate metabolism above baseline requirements) declines as food availability increases. These differential changes in metabolic rates likely have important consequences for how organisms partition available metabolic power to different functions under the constraints imposed by food availability
Direct Visualization of Single Nuclear Pore Complex Proteins Using Genetically-Encoded Probes for DNA-PAINT
The nuclear pore complex (NPC) is one of the largest and most complex protein assemblies in the cell and, among other functions, serves as the gatekeeper of nucleocytoplasmic transport. Unraveling its molecular architecture and functioning has been an active research topic for decades with recent cryogenic electron microscopy and super-resolution studies advancing our understanding of the architecture of the NPC complex. However, the specific and direct visualization of single copies of NPC proteins is thus far elusive. Herein, we combine genetically-encoded self-labeling enzymes such as SNAP-tag and HaloTag with DNA-PAINT microscopy. We resolve single copies of nucleoporins in the human Y-complex in three dimensions with a precision of circa 3 nm, enabling studies of multicomponent complexes on the level of single proteins in cells using optical fluorescence microscopy
Generic Mechanism of Emergence of Amyloid Protofilaments from Disordered Oligomeric aggregates
The presence of oligomeric aggregates, which is often observed during the
process of amyloid formation, has recently attracted much attention since it
has been associated with neurodegenerative conditions such as Alzheimer's and
Parkinson's diseases. We provide a description of a sequence-indepedent
mechanism by which polypeptide chains aggregate by forming metastable
oligomeric intermediate states prior to converting into fibrillar structures.
Our results illustrate how the formation of ordered arrays of hydrogen bonds
drives the formation of beta-sheets within the disordered oligomeric aggregates
that form early under the effect of hydrophobic forces. Initially individual
beta-sheets form with random orientations, which subsequently tend to align
into protofilaments as their lengths increases. Our results suggest that
amyloid aggregation represents an example of the Ostwald step rule of first
order phase transitions by showing that ordered cross-beta structures emerge
preferentially from disordered compact dynamical intermediate assemblies.Comment: 14 pages, 4 figure
Thermal emission from low-field neutron stars
We present a new grid of LTE model atmospheres for weakly magnetic
(B<=10e10G) neutron stars, using opacity and equation of state data from the
OPAL project and employing a fully frequency- and angle-dependent radiation
transfer. We discuss the differences from earlier models, including a
comparison with a detailed NLTE calculation. We suggest heating of the outer
layers of the neutron star atmosphere as an explanation for the featureless
X-ray spectra of RX J1856.5-3754 and RX J0720.4-3125 recently observed with
Chandra and XMM.Comment: 8 pages A&A(5)-Latex, 6 Figures, A&A in press. The model spectra
presented here are available as XSPEC tables at
http://www.astro.soton.ac.uk/~btg/outgoing/nsspec
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