6,623 research outputs found
Laser radiation pressure slowing of a molecular beam
There is substantial interest in producing samples of ultracold molecules for
possible applications in quantum computation, quantum simulation of condensed
matter systems, precision measurements, controlled chemistry, and high
precision spectroscopy. A crucial step to obtaining large samples of ultracold,
trapped molecules is developing a means to bridge the gap between typical
molecular source velocities (~150-600 m/s) and velocities for which trap
loading or confinement is possible (~5-20 m/s). Here we show deceleration of a
beam of neutral strontium monofluoride (SrF) molecules using radiative force.
Under certain conditions, the deceleration results in a substantial flux of
molecules with velocities <50 m/s. The observed slowing, from ~140 m/s,
corresponds to scattering ~10000 photons. We also observe longitudinal velocity
compression under different conditions. Combined with molecular laser cooling
techniques, this lays the groundwork to create slow and cold molecular beams
suitable for trap loading.Comment: 7 pages, 7 figures. Supplementary material updated
Evaluation of the potential of the Stirling engine for heavy duty application
A 150 hp four cylinder heavy duty Stirling engine was evaluated. The engine uses a variable stroke power control system, swashplate drive and ceramic insulation. The sensitivity of the design to engine size and heater temperature is investigated. Optimization shows that, with porous ceramics, indicated efficiencies as high as 52% can be achieved. It is shown that the gain in engine efficiency becomes insignificant when the heater temperature is raised above 200 degrees F
Can Polymer Coils be modeled as "Soft Colloids"?
We map dilute or semi-dilute solutions of non-intersecting polymer chains
onto a fluid of ``soft'' particles interacting via a concentration dependent
effective pair potential, by inverting the pair distribution function of the
centers of mass of the initial polymer chains. A similar inversion is used to
derive an effective wall-polymer potential; these potentials are combined to
successfully reproduce the calculated exact depletion interaction induced by
non-intersecting polymers between two walls. The mapping opens up the
possibility of large-scale simulations of polymer solutions in complex
geometries.Comment: 4 pages, 3 figures ReVTeX[epsfig,multicol,amssymb] references update
Adjusting the melting point of a model system via Gibbs-Duhem integration: application to a model of Aluminum
Model interaction potentials for real materials are generally optimized with
respect to only those experimental properties that are easily evaluated as
mechanical averages (e.g., elastic constants (at T=0 K), static lattice
energies and liquid structure). For such potentials, agreement with experiment
for the non-mechanical properties, such as the melting point, is not guaranteed
and such values can deviate significantly from experiment. We present a method
for re-parameterizing any model interaction potential of a real material to
adjust its melting temperature to a value that is closer to its experimental
melting temperature. This is done without significantly affecting the
mechanical properties for which the potential was modeled. This method is an
application of Gibbs-Duhem integration [D. Kofke, Mol. Phys.78, 1331 (1993)].
As a test we apply the method to an embedded atom model of aluminum [J. Mei and
J.W. Davenport, Phys. Rev. B 46, 21 (1992)] for which the melting temperature
for the thermodynamic limit is 826.4 +/- 1.3K - somewhat below the experimental
value of 933K. After re-parameterization, the melting temperature of the
modified potential is found to be 931.5K +/- 1.5K.Comment: 9 pages, 5 figures, 4 table
Slowing heavy, ground-state molecules using an alternating gradient decelerator
Cold supersonic beams of molecules can be slowed down using a switched
sequence of electrostatic field gradients. The energy to be removed is
proportional to the mass of the molecules. Here we report deceleration of YbF,
which is 7 times heavier than any molecule previously decelerated. We use an
alternating gradient structure to decelerate and focus the molecules in their
ground state. We show that the decelerator exhibits the axial and transverse
stability required to bring these molecules to rest. Our work significantly
extends the range of molecules amenable to this powerful method of cooling and
trapping.Comment: 4 pages, 5 figure
Paradigm of biased PAR1 (protease-activated receptor-1) activation and inhibition in endothelial cells dissected by phosphoproteomics
Thrombin is the key serine protease of the coagulation cascade and mediates cellular responses by activation of PARs (protease-activated receptors). The predominant thrombin receptor is PAR1, and in endothelial cells (ECs), thrombin dynamically regulates a plethora of phosphorylation events. However, it has remained unclear whether thrombin signaling is exclusively mediated through PAR1. Furthermore, mechanistic insight into activation and inhibition of PAR1-mediated EC signaling is lacking. In addition, signaling networks of biased PAR1 activation after differential cleavage of the PAR1 N terminus have remained an unresolved issue. Here, we used a quantitative phosphoproteomics approach to show that classical and peptide activation of PAR1 induce highly similar signaling, that low thrombin concentrations initiate only limited phosphoregulation, and that the PAR1 inhibitors vorapaxar and parmodulin-2 demonstrate distinct antagonistic properties. Subsequent analysis of the thrombin-regulated phosphosites in the presence of PAR1 inhibitors revealed that biased activation of PAR1 is not solely linked to a specific G-protein downstream of PAR1. In addition, we showed that only the canonical thrombin PAR1 tethered ligand induces extensive early phosphoregulation in ECs. Our study provides detailed insight in the signaling mechanisms downstream of PAR1. Our data demonstrate that thrombin-induced EC phosphoregulation is mediated exclusively through PAR1, that thrombin and thrombin-tethered ligand peptide induce similar phosphoregulation, and that only canonical PAR1 cleavage by thrombin generates a tethered ligand that potently induces early signaling. Furthermore, platelet PAR1 inhibitors directly affect EC signaling, indicating that it will be a challenge to design a PAR1 antagonist that will target only those pathways responsible for tissue pathology
Post-silicon tuning capabilities of 45nm low-power CMOS digital circuits
Adaptive circuit techniques enable modification of power-performance efficient circuit operation. Yet it is unclear if such techniques remain effective in modern deep-submicron CMOS. In this paper we examine the technological boundaries of supply voltage scaling and body biasing in 45nm low-power CMOS. We demonstrate that there exists an effective tuning range for power-performance and performance variability control. Our analysis is supported by ring oscillator test-chip measurements
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