212 research outputs found
Large-Scale Integration of Nanoelectromechanical Systems for Gas Sensing Applications
We have developed arrays of nanomechanical systems (NEMS) by large-scale integration, comprising thousands of individual nanoresonators with densities of up to 6 million NEMS per square centimeter. The individual NEMS devices are electrically coupled using a combined series-parallel configuration that is extremely robust with respect to lithographical defects and mechanical or electrostatic-discharge damage. Given the large number of connected nanoresonators, the arrays are able to handle extremely high input powers (>1 W per array, corresponding to <1 mW per nanoresonator) without excessive heating or deterioration of resonance response. We demonstrate the utility of integrated NEMS arrays as high-performance chemical vapor sensors, detecting a part-per-billion concentration of a chemical warfare simulant within only a 2 s exposure period
Tensor Product and Permutation Branes on the Torus
We consider B-type D-branes in the Gepner model consisting of two minimal
models at k=2. This Gepner model is mirror to a torus theory. We establish the
dictionary identifying the B-type D-branes of the Gepner model with A-type
Neumann and Dirichlet branes on the torus.Comment: 26 page
Matrix Factorizations and Homological Mirror Symmetry on the Torus
We consider matrix factorizations and homological mirror symmetry on the
torus T^2 using a Landau-Ginzburg description. We identify the basic matrix
factorizations of the Landau-Ginzburg superpotential and compute the full
spectrum, taking into account the explicit dependence on bulk and boundary
moduli. We verify homological mirror symmetry by comparing three-point
functions in the A-model and the B-model.Comment: 41 pages, 9 figures, v2: reference added, minor corrections and
clarifications, version published in JHE
Bounds for State Degeneracies in 2D Conformal Field Theory
In this note we explore the application of modular invariance in
2-dimensional CFT to derive universal bounds for quantities describing certain
state degeneracies, such as the thermodynamic entropy, or the number of
marginal operators. We show that the entropy at inverse temperature 2 pi
satisfies a universal lower bound, and we enumerate the principal obstacles to
deriving upper bounds on entropies or quantum mechanical degeneracies for fully
general CFTs. We then restrict our attention to infrared stable CFT with
moderately low central charge, in addition to the usual assumptions of modular
invariance, unitarity and discrete operator spectrum. For CFT in the range
c_left + c_right < 48 with no relevant operators, we are able to prove an upper
bound on the thermodynamic entropy at inverse temperature 2 pi. Under the same
conditions we also prove that a CFT can have a number of marginal deformations
no greater than ((c_left + c_right) / (48 - c_left - c_right)) e^(4 Pi) - 2.Comment: 23 pages, LaTeX, minor change
Bulk flows in Virasoro minimal models with boundaries
The behaviour of boundary conditions under relevant bulk perturbations is
studied for the Virasoro minimal models. In particular, we consider the bulk
deformation by the least relevant bulk field which interpolates between the mth
and (m-1)st unitary minimal model. In the presence of a boundary this bulk flow
induces an RG flow on the boundary, which ensures that the resulting boundary
condition is conformal in the (m-1)st model. By combining perturbative RG
techniques with insights from defects and results about non-perturbative
boundary flows, we determine the endpoint of the flow, i.e. the boundary
condition to which an arbitrary boundary condition of the mth theory flows to.Comment: 34 pages, 6 figures. v4: Typo in fig. 2 correcte
Matrix factorisations and D-branes on K3
D-branes on K3 are analysed from three different points of view. For
deformations of hypersurfaces in weighted projected space we use geometrical
methods as well as matrix factorisation techniques. Furthermore, we study the
D-branes on the T^4/\Z_4 orbifold line in conformal field theory. The behaviour
of the D-branes under deformations of the bulk theory are studied in detail,
and good agreement between the different descriptions is found.Comment: 35 pages, no figure
Systematic first-principles study of impurity hybridization in NiAl
We have performed a systematic first-principles computational study of the
effects of impurity atoms (boron, carbon, nitrogen, oxygen, silicon, phosporus,
and sulfur) on the orbital hybridization and bonding properties in the
intermetallic alloy NiAl using a full-potential linear muffin-tin orbital
method. The matrix elements in momentum space were used to calculate real-space
properties: onsite parameters, partial densities of states, and local charges.
In impurity atoms that are empirically known to be embrittler (N and O) we
found that the 2s orbital is bound to the impurity and therefore does not
participate in the covalent bonding. In contrast, the corresponding 2s orbital
is found to be delocalized in the cohesion enhancers (B and C). Each of these
impurity atoms is found to acquire a net negative local charge in NiAl
irrespective of whether they sit in the Ni or Al site. The embrittler therefore
reduces the total number of electrons available for covalent bonding by
removing some of the electrons from the neighboring Ni or Al atoms and
localizing them at the impurity site. We show that these correlations also hold
for silicon, phosporus, and sulfur.Comment: Revtex, 8 pages, 7 eps figures, to appear in Phys. Rev.
Whirling Hexagons and Defect Chaos in Hexagonal Non-Boussinesq Convection
We study hexagon patterns in non-Boussinesq convection of a thin rotating
layer of water. For realistic parameters and boundary conditions we identify
various linear instabilities of the pattern. We focus on the dynamics arising
from an oscillatory side-band instability that leads to a spatially disordered
chaotic state characterized by oscillating (whirling) hexagons. Using
triangulation we obtain the distribution functions for the number of pentagonal
and heptagonal convection cells. In contrast to the results found for defect
chaos in the complex Ginzburg-Landau equation and in inclined-layer convection,
the distribution functions can show deviations from a squared Poisson
distribution that suggest non-trivial correlations between the defects.Comment: 4 mpg-movies are available at
http://www.esam.northwestern.edu/~riecke/lit/lit.html submitted to New J.
Physic
Boundary and defect CFT: Open problems and applications
A review of Boundary and defect conformal field theory: open problems and applications, following a workshop held at Chicheley Hall, Buckinghamshire, UK, 7–8 Sept. 2017. We attempt to provide a broad, bird’s-eye view of the latest progress in boundary and defect conformal field theory in various sub-fields of theoretical physics, including the renormalization group, integrability, conformal bootstrap, topological field theory, supersymmetry, holographic duality, and more. We also discuss open questions and promising research directions in each of these sub-fields, and combinations thereof
Rapid Growth Reduces Cold Resistance: Evidence from Latitudinal Variation in Growth Rate, Cold Resistance and Stress Proteins
Background: Physiological costs of rapid growth may contribute to the observation that organisms typically grow at submaximal rates. Although, it has been hypothesized that faster growing individuals would do worse in dealing with suboptimal temperatures, this type of cost has never been explored empirically. Furthermore, the mechanistic basis of the physiological costs of rapid growth is largely unexplored. Methodology/Principal Finding: Larvae of the damselfly Ischnura elegans from two univoltine northern and two multivoltine southern populations were reared at three temperatures and after emergence given a cold shock. Cold resistance, measured by chill coma recovery times in the adult stage, was lower in the southern populations. The faster larval growth rates in the southern populations contributed to this latitudinal pattern in cold resistance. In accordance with their assumed role in cold resistance, Hsp70 levels were lower in the southern populations, and faster growing larvae had lower Hsp70 levels. Yet, individual variation in Hsp70 levels did not explain variation in cold resistance. Conclusions/Significance: We provide evidence for a novel cost of rapid growth: reduced cold resistance. Our results indicate that the reduced cold resistance in southern populations of animals that change voltinism along the latitudinal gradient may not entirely be explained by thermal selection per se but also by the costs of time constraint-induced higher growth rates. This also illustrates that stressors imposed in the larval stage may carry over and shape fitness in the adul
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