940 research outputs found
Factorization for generic jet production
Factorization is the central ingredient in any theoretical prediction for
collider experiments. We introduce a factorization formalism that can be
applied to any desired observable, like event shapes or jet observables, for
any number of jets and a wide range of jet algorithms in leptonic or hadronic
collisions. This is achieved by using soft-collinear effective theory to prove
the formal factorization of a generic fully-differential cross section in terms
of a hard coefficient, and generic jet and soft functions. In this formalism,
whether a given observable factorizes in the usual sense, depends on whether it
is inclusive enough, so the jet functions can be calculated perturbatively. The
factorization formula for any such observable immediately follows from our
general result, including the precise definition of the jet and soft functions
appropriate for the observable in question. As examples of our formalism, we
work out several results in two-jet production for both e+e- and pp collisions.
For the latter, we also comment on how our formalism allows one to treat
underlying events and beam remnants.Comment: 33 pages, v2: minor typos corrected, journal versio
Postbuckling of a Circular Plate - Comparing Different Solutions
Azisymmetric problems have been often investigated in the past. Since the problem is one-dimensional, the boundary problem is suitable for analytical investigations and acts as a benchmark for numerical methods. The postbuckling of an elastic circular plate under azisymmetric loading is investigated. An analytical description is given. Solutions by means of the perturbation method and the finite element method (axisymmetric shell element) are introduced. Numerical results are presented
Remarks on Raasch’s Hook
Finite Element’s designers have always been seeking for benchmarks to judge the capability and potentiality of a numerical method. Considering shell elements many benchmark tests have been established over the years. The Raasch challenge problem, a clamped curved hook with a tip in-plane shear load, acts as a very interesting benchmark of shell elements. The structure consists of two cylindrical shells with different curvatures. In this paper the problem is also modelled as a curved beam with a rectangular cross-section. The beam model is investigated analytically. Thus an analytical expression for the tip deflection can be obtained. Further on numerical calculations with 4-node-shell elements based on a director theory are carried out and verify the elements applicability
Observation of thermal acoustic modes of a droplet coupled to an optomechanical sensor
The bulk acoustic modes of liquid droplets, well understood from a
theoretical perspective, have rarely been observed experimentally. Here, we
report the direct observation of acoustic vibrational modes in a
picoliter-scale droplet, extending up to ~ 40 MHz. This was achieved by
coupling the droplet to an ultra-sensitive optomechanical sensor, which
operates in a thermal-noise limited regime and with a substantial contribution
from acoustic noise in the ambient medium. The droplet vibrational modes
manifest as Fano resonances in the thermal noise spectrum of the sensor. This
is amongst the few reported observations of droplet acoustic modes, and of Fano
interactions in a coupled mechanical oscillator system driven only by thermal
Brownian motion.Comment: 11 pages, 3 figure
Braided magnetic fields:equilibria, relaxation and heating
We examine the dynamics of magnetic flux tubes containing non-trivial field
line braiding (or linkage), using mathematical and computational modelling, in
the context of testable predictions for the laboratory and their significance
for solar coronal heating. We investigate the existence of braided force-free
equilibria, and demonstrate that for a field anchored at perfectly-conducting
plates, these equilibria exist and contain current sheets whose thickness
scales inversely with the braid complexity - as measured for example by the
topological entropy. By contrast, for a periodic domain braided exact
equilibria typically do not exist, while approximate equilibria contain thin
current sheets. In the presence of resistivity, reconnection is triggered at
the current sheets and a turbulent relaxation ensues. We finish by discussing
the properties of the turbulent relaxation and the existence of constraints
that may mean that the final state is not the linear force-free field predicted
by Taylor's hypothesis.Comment: To appear in Plasma Physics and Controlled Fusio
Ultrasonic spectroscopy of sessile droplets coupled to optomechanical sensors
We describe a system for interrogating the acoustic properties of
sub-nanoliter liquid samples within an open microfluidics platform. Sessile
droplets were deposited onto integrated optomechanical sensors, which possess
ambient-medium-noise-limited sensitivity and can thus passively sense the
thermally driven acoustic spectrum of the droplets. The droplet acoustic
breathing modes manifest as resonant features in the thermomechanical noise
spectrum of the sensor, in some cases hybridized with the sensor's own
vibrational modes. Excellent agreement is found between experimental
observations and theoretical predictions, over the entire ~ 0 - 40 MHz
operating range of our sensors. With suitable control over droplet size and
morphology, this technique has the potential for precision acoustic sensing of
small-volume biological and chemical samples
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A murine model for neuropsychiatric disorders associated with group A β-hemolytic streptococcal infection
A syndrome of motoric and neuropsychiatric symptoms comprising various elements, including chorea, hyperactivity, tics, emotional lability, and obsessive-compulsive symptoms, can occur in association with group A β-hemolytic streptococcal (GABHS) infection. We tested the hypothesis that an immune response to GABHS can result in behavioral abnormalities. Female SJL/J mice were immunized and boosted with a GABHS homogenate in Freund's adjuvant, whereas controls received Freund's adjuvant alone. When sera from GABHS-immunized mice were tested for immunoreactivity to mouse brain, a subset was found to be immunoreactive to several brain regions, including deep cerebellar nuclei (DCN), globus pallidus, and thalamus. GABHS-immunized mice having serum immunoreactivity to DCN also had increased IgG deposits in DCN and exhibited increased rearing behavior in open-field and hole-board tests compared with controls and with GABHS-immunized mice lacking serum anti-DCN antibodies. Rearing and ambulatory behavior were correlated with IgG deposits in the DCN and with serum immunoreactivity to GABHS proteins in Western blot. In addition, serum from a GABHS mouse reacted with normal mouse cerebellum in nondenaturing Western blots and immunoprecipitated C4 complement protein and α-2-macroglobulin. These results are consistent with the hypothesis that immune response to GABHS can result in motoric and behavioral disturbances and suggest that anti-GABHS antibodies cross-reactive with brain components may play a role in their pathophysiology
Pattern formation and selection in quasi-static fracture
Fracture in quasi-statically driven systems is studied by means of a discrete
spring-block model. Developed from close comparison with desiccation
experiments, it describes crack formation induced by friction on a substrate.
The model produces cellular, hierarchical patterns of cracks, characterized by
a mean fragment size linear in the layer thickness, in agreement with
experiments. The selection of a stationary fragment size is explained by
exploiting the correlations prior to cracking. A scaling behavior associated
with the thickness and substrate coupling, derived and confirmed by
simulations, suggests why patterns have similar morphology despite their
disparity in scales.Comment: 4 pages, RevTeX, two-column, 5 PS figures include
Pure Samples of Quark and Gluon Jets at the LHC
Having pure samples of quark and gluon jets would greatly facilitate the
study of jet properties and substructure, with many potential standard model
and new physics applications. To this end, we consider multijet and jets+X
samples, to determine the purity that can be achieved by simple kinematic cuts
leaving reasonable production cross sections. We find, for example, that at the
7 TeV LHC, the pp {\to} {\gamma}+2jets sample can provide 98% pure quark jets
with 200 GeV of transverse momentum and a cross section of 5 pb. To get 10 pb
of 200 GeV jets with 90% gluon purity, the pp {\to} 3jets sample can be used.
b+2jets is also useful for gluons, but only if the b-tagging is very efficient.Comment: 19 pages, 16 figures; v2 section on formally defining quark and gluon
jets has been adde
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