1,084 research outputs found
Charge neutralization in vacuum for non-conducting and isolated objects using directed low-energy electron and ion beams
We propose using ions and electrons of energy 1 eV–10 eV for neutralizing the charges on the non-conducting or isolated surfaces of high-sensitivity experiments. The mirror surfaces of the test masses of the laser interferometer gravitational observatory are used as an example of the implementation of this method. By alternatively directing beams of positive and negative charges towards the mirror surfaces, we ensure the neutralization of the total charge as well as the equalization of the surface charge distribution to within a few eV of the potential of the ground reference of the vacuum system. This method is compatible with operation in high vacuum, does not require measuring the potential of the mirrors and is expected not to damage sensitive optical surfaces
Improved outer boundary conditions for Einstein's field equations
In a recent article, we constructed a hierarchy B_L of outer boundary
conditions for Einstein's field equations with the property that, for a
spherical outer boundary, it is perfectly absorbing for linearized
gravitational radiation up to a given angular momentum number L. In this
article, we generalize B_2 so that it can be applied to fairly general
foliations of spacetime by space-like hypersurfaces and general outer boundary
shapes and further, we improve B_2 in two steps: (i) we give a local boundary
condition C_2 which is perfectly absorbing including first order contributions
in 2M/R of curvature corrections for quadrupolar waves (where M is the mass of
the spacetime and R is a typical radius of the outer boundary) and which
significantly reduces spurious reflections due to backscatter, and (ii) we give
a non-local boundary condition D_2 which is exact when first order corrections
in 2M/R for both curvature and backscatter are considered, for quadrupolar
radiation.Comment: accepted Class. Quant. Grav. numerical relativity special issue; 17
pages and 1 figur
OPTIS - a satellite-based test of Special and General Relativity
A new satellite based test of Special and General Relativity is proposed. For
the Michelson-Morley experiment we expect an improvement of at least three
orders of magnitude, and for the Kennedy-Thorndike experiment an improvement of
more than one order of magnitude. Furthermore, an improvement by two orders of
the test of the universality of the gravitational red shift by comparison of an
atomic clock with an optical clock is projected.
The tests are based on ultrastable optical cavities, an atomic clock and a
comb generator.Comment: To appear in Class. Quantum Gra
Design Evaluation of High Reliability Lithium Batteries
Within one year, a lithium battery design can be qualified for device use through the application of accelerated discharge testing, calorimetry measurements, real time tests and other supplemental testing. Materials and corrosion testing verify that the battery components remain functional during expected battery life. By combining these various methods, a high reliability lithium battery can be manufactured for applications which require zero defect battery performance
Electrostatic Patch Effect in Cylindrical Geometry. III. Torques
We continue to study the effect of uneven voltage distribution on two close
cylindrical conductors with parallel axes started in our papers [1] and [2],
now to find the electrostatic torques. We calculate the electrostatic potential
and energy to lowest order in the gap to cylinder radius ratio for an arbitrary
relative rotation of the cylinders about their symmetry axis. By energy
conservation, the axial torque, independent of the uniform voltage difference,
is found as a derivative of the energy in the rotation angle. We also derive
both the axial and slanting torques by the surface integration method: the
torque vector is the integral over the cylinder surface of the cross product of
the electrostatic force on a surface element and its position vector. The
slanting torque consists of two parts: one coming from the interaction between
the patch and the uniform voltages, and the other due to the patch interaction.
General properties of the torques are described. A convenient model of a
localized patch suggested in [2] is used to calculate the torques explicitly in
terms of elementary functions. Based on this, we analyze in detail patch
interaction for one pair of patches, namely, the torque dependence on the patch
parameters (width and strength) and their mutual positions. The effect of the
axial torque is then studied for the experimental conditions of the STEP
mission.Comment: 28 pages, 6 Figures. Submitted to Classical Quantum Gravit
Monomeric alpha-synuclein exerts a physiological role in brain ATP synthase
Misfolded α-synuclein is a key factor in the pathogenesis of Parkinson's disease (PD). However, knowledge about a physiological role for the native, unfolded α-synuclein is limited. Using brains of mice lacking α-, β-, and γ-synuclein, we report that extracellular monomeric α-synuclein enters neurons and localizes to mitochondria, interacts with ATP synthase subunit α, and modulates ATP synthase function. Using a combination of biochemical, live-cell imaging and mitochondrial respiration analysis, we found that brain mitochondria of α-, β-, and γ-synuclein knock-out mice are uncoupled, as characterized by increased mitochondrial respiration and reduced mitochondrial membrane potential. Furthermore, synuclein deficiency results in reduced ATP synthase efficiency and lower ATP levels. Exogenous application of low unfolded α-synuclein concentrations is able to increase the ATP synthase activity that rescues the mitochondrial phenotypes observed in synuclein deficiency. Overall, the data suggest that α-synuclein is a previously unrecognized physiological regulator of mitochondrial bioenergetics through its ability to interact with ATP synthase and increase its efficiency. This may be of particular importance in times of stress or PD mutations leading to energy depletion and neuronal cell toxicity
The effects of high dose and highly fractionated radiation on distraction osteogenesis in the murine mandible
Abstract
The ability of irradiated tissue to support bony growth remains poorly defined, although there are anecdotal cases reported showing mixed results for the use of mandibular distraction osteogenesis after radiation for head and neck cancer. Many of these reports lack objective measures that would allow adequate analysis of outcomes or efficacy. The purpose of this experiment was to utilize a rat model of mandibular distraction osteogenesis after high dose and highly fractionated radiation therapy and to evaluate and quantify distracted bone formation under these conditions. Male Sprague–Dawley rats underwent 12 fractions of external beam radiation (48 Gray) of the left mandible. Following a two week recovery period, an external frame distractor was applied and gradual distraction of the mandible was performed. Tissue was harvested after a twenty-eight day consolidation period. Gross, radiologic and histological evaluations were undertaken. Those animals subjected to pre-operative radiation showed severe attenuation of bone formation including bone atrophy, incomplete bridging of the distraction gap, and gross bony defects or non-union. Although physical lengthening was achieved, the irradiated bone consistently demonstrated marked damaging effects on the normal process of distraction osteogenesis. This murine model has provided reliable evidence of the injurious effects of high dose radiation on bone repair and regeneration in distraction osteogenesis utilizing accurate and reproducible metrics. These results can now be used to assist in the development of therapies directed at mitigating the adverse consequences of radiation on the regeneration of bone and to optimize distraction osteogenesis so it can be successfully applied to post-oncologic reconstruction.http://deepblue.lib.umich.edu/bitstream/2027.42/112356/1/13014_2012_Article_656.pd
Testing outer boundary treatments for the Einstein equations
Various methods of treating outer boundaries in numerical relativity are
compared using a simple test problem: a Schwarzschild black hole with an
outgoing gravitational wave perturbation. Numerical solutions computed using
different boundary treatments are compared to a `reference' numerical solution
obtained by placing the outer boundary at a very large radius. For each
boundary treatment, the full solutions including constraint violations and
extracted gravitational waves are compared to those of the reference solution,
thereby assessing the reflections caused by the artificial boundary. These
tests use a first-order generalized harmonic formulation of the Einstein
equations. Constraint-preserving boundary conditions for this system are
reviewed, and an improved boundary condition on the gauge degrees of freedom is
presented. Alternate boundary conditions evaluated here include freezing the
incoming characteristic fields, Sommerfeld boundary conditions, and the
constraint-preserving boundary conditions of Kreiss and Winicour. Rather
different approaches to boundary treatments, such as sponge layers and spatial
compactification, are also tested. Overall the best treatment found here
combines boundary conditions that preserve the constraints, freeze the
Newman-Penrose scalar Psi_0, and control gauge reflections.Comment: Modified to agree with version accepted for publication in Class.
Quantum Gra
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