648 research outputs found
Automated beam builder
Requirements for the space fabrication of large space structures are considered with emphasis on the design, development, manufacture, and testing of a machine which automatically produces a basic building block aluminum beam. Particular problems discussed include those associated with beam cap forming; brace storage, dispensing, and transporting; beam component fastening; and beam cut-off. Various critical process tests conducted to develop technology for a machine to produce composite beams are also discussed
Acceleration-Induced Nonlocal Electrodynamics in Minkowski Spacetime
We discuss two nonlocal models of electrodynamics in which the nonlocality is
induced by the acceleration of the observer. Such an observer actually measures
an electromagnetic field that exhibits persistent memory effects. We compare
Mashhoon's model with a new ansatz developed here in the framework of charge &
flux electrodynamics with a constitutive law involving the Levi-Civita
connection as seen from the observer's local frame and conclude that they are
in partial agreement only for the case of constant acceleration.Comment: LaTeX file, 3 figures, 14 page
Molecular basis for resistance of acanthamoeba tubulins to all major classes of antitubulin compounds
Tubulin is essential to eukaryotic cells and is targeted by several antineoplastics, herbicides, and antimicrobials. We demonstrate that Acanthamoeba spp. are resistant to five antimicrotubule compounds, unlike any other eukaryote studied so far. Resistance correlates with critical amino acid differences within the inhibitor binding sites of the tubulin heterodimers
The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
In this paper we present the results of a systematic investigation of an
entire population of starless dust cores within a single molecular cloud.
Analysis of extinction data shows the cores to be dense objects characterized
by a narrow range of density. Analysis of C18O and NH3 molecular-line
observations reveals very narrow lines. The non-thermal velocity dispersions
measured in both these tracers are found to be subsonic for the large majority
of the cores and show no correlation with core mass (or size). Thermal pressure
is thus the dominate source of internal gas pressure and support for most of
the core population. The total internal gas pressures of the cores are found to
be roughly independent of core mass over the entire range of the core mass
function (CMF) indicating that the cores are in pressure equilibrium with an
external source of pressure. This external pressure is most likely provided by
the weight of the surrounding Pipe cloud within which the cores are embedded.
Most of the cores appear to be pressure confined, gravitationally unbound
entities whose nature, structure and future evolution are determined by only a
few physical factors which include self-gravity, the fundamental processes of
thermal physics and the simple requirement of pressure equilibrium with the
surrounding environment. The observed core properties likely constitute the
initial conditions for star formation in dense gas. The entire core population
is found to be characterized by a single critical Bonnor-Ebert mass. This mass
coincides with the characteristic mass of the Pipe CMF indicating that most
cores formed in the cloud are near critical stability. This suggests that the
mass function of cores (and the IMF) has its origin in the physical process of
thermal fragmentation in a pressurized medium.Comment: To appear in the Astrophysical Journa
Phase-Field Simulation and Design of a Ferroelectric Nano-Generator
We study the behavior of ferroelectric material (BaTiO3) for the design of a nano-generator to convert mechanical
into electrical energy. The investigations consider an electro-mechanical phase-field model with polarization as
state variable. This widely accepted model has its origins in the work of and is fully developed by Landis and
coworkers. We use a finite element model to simulate tetragonal regions of ferroelectric material sputtered on
substrate. Different geometries as well as various mechanical and electrical boundary conditions are considered.
The model parameters are normalized to achieve better computational conditions within the stiffness matrix.
The major objective of this contribution is the fundamental understanding of domain switching caused by a
cyclic electrical field. The corresponding hysteresis loops of the overall polarization cannot be achieved by using
a two-dimensional model because the domain topologies evolve in three dimensions. The three-dimensional
nature of the domain structure evolution is even true for flat regions or thin films. We show some examples of
three-dimensional domain topologies, which are able to break energetically unfavorable symmetries. Finally, the
computational model of a tetragonal nano-generator with dimensions 10 x 60 x 10 nm is presented. The specific
ratio of height to width and the mounting on substrate is essential for its performance and principle of energy
harvesting. We discuss the challenges and scopes of such a system.Aerospace Engineerin
The Initial Mass Function as given by the fragmentation
The dichotomy between a universal mass function (IMF) and a variable IMF
which depends on local physical parameters characterises observational and
theoretical stellar astronomy. In this contribution the available distributions
of probability are briefly reviewed. The physical nature of two of them, gamma
variate and lognormal, is then explained once the framework of the
fragmentation is introduced. Interpolating techniques are then applied to the
sample of the first 10 pc and to the open cluster NGC6649: in both cases
lognormal distribution produces the best fit. The three power law function has
also been investigated and visual comparison with an artificially generated
sample of 100000 stars suggests that the variations in the spectral index are
simply due to the small number of stars available in the observational sample.
In order to derive the sample of masses, a new formula that allows us to
express the mass as a function of the absolute magnitude and (B-V) for MAIN V,
GIANTS III and SUPERGIANTS I is derived.Comment: 6 pages 9 figure
DNA methylation age is accelerated in alcohol dependence.
Alcohol dependence (ALC) is a chronic, relapsing disorder that increases the burden of chronic disease and significantly contributes to numerous premature deaths each year. Previous research suggests that chronic, heavy alcohol consumption is associated with differential DNA methylation patterns. In addition, DNA methylation levels at certain CpG sites have been correlated with age. We used an epigenetic clock to investigate the potential role of excessive alcohol consumption in epigenetic aging. We explored this question in five independent cohorts, including DNA methylation data derived from datasets from blood (n = 129, n = 329), liver (n = 92, n = 49), and postmortem prefrontal cortex (n = 46). One blood dataset and one liver tissue dataset of individuals with ALC exhibited positive age acceleration (p < 0.0001 and p = 0.0069, respectively), whereas the other blood and liver tissue datasets both exhibited trends of positive age acceleration that were not significant (p = 0.83 and p = 0.57, respectively). Prefrontal cortex tissue exhibited a trend of negative age acceleration (p = 0.19). These results suggest that excessive alcohol consumption may be associated with epigenetic aging in a tissue-specific manner and warrants further investigation using multiple tissue samples from the same individuals
The Core of the Participatory Budgeting Problem
In participatory budgeting, communities collectively decide on the allocation
of public tax dollars for local public projects. In this work, we consider the
question of fairly aggregating the preferences of community members to
determine an allocation of funds to projects. This problem is different from
standard fair resource allocation because of public goods: The allocated goods
benefit all users simultaneously. Fairness is crucial in participatory decision
making, since generating equitable outcomes is an important goal of these
processes. We argue that the classic game theoretic notion of core captures
fairness in the setting. To compute the core, we first develop a novel
characterization of a public goods market equilibrium called the Lindahl
equilibrium, which is always a core solution. We then provide the first (to our
knowledge) polynomial time algorithm for computing such an equilibrium for a
broad set of utility functions; our algorithm also generalizes (in a
non-trivial way) the well-known concept of proportional fairness. We use our
theoretical insights to perform experiments on real participatory budgeting
voting data. We empirically show that the core can be efficiently computed for
utility functions that naturally model our practical setting, and examine the
relation of the core with the familiar welfare objective. Finally, we address
concerns of incentives and mechanism design by developing a randomized
approximately dominant-strategy truthful mechanism building on the exponential
mechanism from differential privacy
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