1,880 research outputs found
Nanomechanics of a Hydrogen Molecule Suspended between Two Equally Charged Tips
Geometric configuration and energy of a hydrogen molecule centered between
two point-shaped tips of equal charge are calculated with the variational
quantum Monte-Carlo (QMC) method without the restriction of the
Born-Oppenheimer (BO) approximation. Ground state nuclear distribution,
stability, and low vibrational excitation are investigated. Ground state
results predict significant deviations from the BO treatment that is based on a
potential energy surface (PES) obtained with the same QMC accuracy. The quantum
mechanical distribution of molecular axis direction and bond length at a
sub-nanometer level is fundamental for understanding nanomechanical dynamics
with embedded hydrogen. Because of the tips' arrangement, cylindrical symmetry
yields a uniform azimuthal distribution of the molecular axis vector relative
to the tip-tip axis. With approaching tips towards each other, the QMC sampling
shows an increasing loss of spherical symmetry with the molecular axis still
uniformly distributed over the azimuthal angle but peaked at the tip-tip
direction for negative tip charge while peaked at the equatorial plane for
positive charge. This directional behavior can be switched between both stable
configurations by changing the sign of the tip charge and by controlling the
tip-tip distance. This suggests an application in the field of molecular
machines.Comment: 20 pages, 10 figure
Pathogenic variability in monoconidial isolates of the sorghum anthracnose fungus Colletotrichum graminicola from single lesions and from monoconidial cultures.
A patogenidade de culturas c sub-culturas monospóricas de Colletotrichum graminicola obtidas de uma única lesão c de isolamentos monospóricos das cultivares de sorgo Tx623 e SC748-5 foi avaliada em 5 cultivares diferenciadoras. Isolados foram separados em diferentes fenótipos de virulência, indicando a ocorrência de instabilidade patogenica em isolados deste patógeno. Reversão de um estado de virulência para um de virulência foi observada para alguns isolados
Efficient UC Commitment Extension with Homomorphism for Free (and Applications)
Homomorphic universally composable (UC) commitments allow for the sender to reveal the result of additions and multiplications of values contained in commitments without revealing the values themselves while assuring the receiver of the correctness of such computation on committed values.
In this work, we construct essentially optimal additively homomorphic UC commitments from any (not necessarily UC or homomorphic) extractable commitment. We obtain amortized linear computational complexity in the length of the input messages and rate 1.
Next, we show how to extend our scheme to also obtain multiplicative homomorphism at the cost of asymptotic optimality but retaining low concrete complexity for practical parameters.
While the previously best constructions use UC oblivious transfer as the main building block, our constructions only require extractable commitments and PRGs, achieving better concrete efficiency and offering new insights into the sufficient conditions for obtaining homomorphic UC commitments.
Moreover, our techniques yield public coin protocols, which are compatible with the Fiat-Shamir heuristic.
These results come at the cost of realizing a restricted version of the homomorphic commitment functionality where the sender is allowed to perform any number of commitments and operations on committed messages but is only allowed to perform a single batch opening of a number of commitments.
Although this functionality seems restrictive, we show that it can be used as a building block for more efficient instantiations of recent protocols for secure multiparty computation and zero knowledge non-interactive arguments of knowledge
Effects of Self-field and Low Magnetic Fields on the Normal-Superconducting Phase Transition
Researchers have studied the normal-superconducting phase transition in the
high- cuprates in a magnetic field (the vortex-glass or Bose-glass
transition) and in zero field. Often, transport measurements in "zero field"
are taken in the Earth's ambient field or in the remnant field of a magnet. We
show that fields as small as the Earth's field will alter the shape of the
current vs. voltage curves and will result in inaccurate values for the
critical temperature and the critical exponents and , and can
even destroy the phase transition. This indicates that without proper screening
of the magnetic field it is impossible to determine the true zero-field
critical parameters, making correct scaling and other data analysis impossible.
We also show, theoretically and experimentally, that the self-field generated
by the current flowing in the sample has no effect on the current vs. voltage
isotherms.Comment: 4 pages, 4 figure
Normal-Superconducting Phase Transition Mimicked by Current Noise
As a superconductor goes from the normal state into the superconducting
state, the voltage vs. current characteristics at low currents change from
linear to non-linear. We show theoretically and experimentally that the
addition of current noise to non-linear voltage vs. current curves will create
ohmic behavior. Ohmic response at low currents for temperatures below the
critical temperature mimics the phase transition and leads to incorrect
values for and the critical exponents and . The ohmic response
occurs at low currents, when the applied current is smaller than the
width of the probability distribution , and will occur in both the
zero-field transition and the vortex-glass transition. Our results indicate
that the transition temperature and critical exponents extracted from the
conventional scaling analysis are inaccurate if current noise is not filtered
out. This is a possible explanation for the wide range of critical exponents
found in the literature.Comment: 4 pages, 2 figure
The Dwarf Starburst Host Galaxy of a Type Ia SN at z = 1.55 from CANDELS
We present VLT/X-shooter observations of a high redshift, type Ia supernova
host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project.
The galaxy exhibits strong emission lines of Ly{\alpha}, [O II], H{\beta}, [O
III], and H{\alpha} at z = 1.54992(+0.00008-0.00004). From the emission-line
fluxes and SED fitting of broad-band photometry we rule out AGN activity and
characterize the host galaxy as a young, low mass, metal poor, starburst galaxy
with low intrinsic extinction and high Ly{\alpha} escape fraction. The host
galaxy stands out in terms of the star formation, stellar mass, and metallicity
compared to its lower redshift counterparts, mainly because of its high
specific star-formation rate. If valid for a larger sample of high-redshift SN
Ia host galaxies, such changes in the host galaxy properties with redshift are
of interest because of the potential impact on the use of SN Ia as standard
candles in cosmology.Comment: 25 pages, 8 figures. Accepted for publication in Ap
Contemporary Global Movement of Emerging Plant Diseases
Plant diseases are a significant constraint to agricultural productivity. Exotic plant diseases pose a continued threat to profitable agriculture in the United States. The extent of this threat has increased dramatically in the 1980s and 1990s due to the expansion of international trade in agricultural products and frequent movement of massive volume of people and goods across national boundaries. Introduction of new diseases has not only caused farm losses, but has also diminished export revenue since phytosanitary issues are linked to international commerce. Plant pathogens and their vectors have also moved across national boundaries, sometimes naturally and at other times influenced by the recent changes in trade practices. Sorghum ergot, Karnal bunt of wheat, potato late blight, and citrus tristeza are some of the most recent examples of enhanced importance of diseases due to the introduction of plant pathogens or vectors
Radiation from relativistic jets
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic
nuclei (AGNs), and Galactic microquasar systems usually have power-law emission
spectra. Recent PIC simulations of relativistic electron-ion
(electron-positron) jets injected into a stationary medium show that particle
acceleration occurs within the downstream jet. In the presence of relativistic
jets, instabilities such as the Buneman instability, other two-streaming
instability, and the Weibel (filamentation) instability create collisionless
shocks, which are responsible for particle (electron, positron, and ion)
acceleration. The simulation results show that the Weibel instability is
responsible for generating and amplifying highly nonuniform, small-scale
magnetic fields. These magnetic fields contribute to the electron's transverse
deflection behind the jet head. The ``jitter'' radiation from deflected
electrons in small-scale magnetic fields has different properties than
synchrotron radiation which is calculated in a uniform magnetic field. This
jitter radiation, a case of diffusive synchrotron radiation, may be important
to understand the complex time evolution and/or spectral structure in gamma-ray
bursts, relativistic jets, and supernova remnants.Comment: 8 pages,3 figures, accepted for the Proceedings of Science of the
Workshop on Blazar Variability across the Electromagnetic Spectrum, April 22
to 25, 200
Ion dynamics and acceleration in relativistic shocks
Ab-initio numerical study of collisionless shocks in electron-ion
unmagnetized plasmas is performed with fully relativistic particle in cell
simulations. The main properties of the shock are shown, focusing on the
implications for particle acceleration. Results from previous works with a
distinct numerical framework are recovered, including the shock structure and
the overall acceleration features. Particle tracking is then used to analyze in
detail the particle dynamics and the acceleration process. We observe an energy
growth in time that can be reproduced by a Fermi-like mechanism with a reduced
number of scatterings, in which the time between collisions increases as the
particle gains energy, and the average acceleration efficiency is not ideal.
The in depth analysis of the underlying physics is relevant to understand the
generation of high energy cosmic rays, the impact on the astrophysical shock
dynamics, and the consequent emission of radiation.Comment: 5 pages, 3 figure
Flax diseases
1 online resource (PDF, 2 pages)This archival publication may not reflect current scientific knowledge or recommendations. Current information available from the University of Minnesota Extension: https://www.extension.umn.edu
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