110 research outputs found
On supersymmetry breaking and the Dijkgraaf-Vafa conjecture
We investigate the Dijkgraaf-Vafa proposal when supersymmetry is broken. We
consider U(N) SYM with chiral adjoint matter where the coupling constants in
the tree-level superpotential are promoted to chiral spurions. The holomorphic
part of the low-energy glueball superpotential can still be analyzed. We
compute the holomorphic supersymmetry breaking contributions using methods of
the geometry underlying the N=1 effective gauge theory viewed as a Whitham
system. We also study the change in the effective glueball superpotential using
perturbative supergraph techniques in the presence of spurions.Comment: 24 pages, LaTeX; minor changes, one reference added, version to
appear in JHE
Superspace calculation of the four-loop spectrum in N=6 supersymmetric Chern-Simons theories
Using N=2 superspace techniques we compute the four-loop spectrum of single
trace operators in the SU(2) x SU(2) sector of ABJM and ABJ supersymmetric
Chern-Simons theories. Our computation yields a four-loop contribution to the
function h^2(\lambda) (and its ABJ generalization) in the magnon dispersion
relation which has fixed maximum transcendentality and coincides with the
findings in components given in the revised versions of arXiv:0908.2463 and
arXiv:0912.3460. We also discuss possible scenarios for an all-loop function
h^2(\lambda) that interpolates between weak and strong couplings.Comment: LaTeX, feynmp, 34 pages; v2: typos corrected, formulations improved,
references adde
Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?
Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted
by their own melt at the triple point. We present extensive simulations for
NaCl, followed by calculations of the solid-vapor, solid-liquid, and
liquid-vapor free energies showing that solid NaCl(100) is a nonmelting
surface, and that its full behavior can quantitatively be accounted for within
a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting
is traced to the conspiracy of three factors: surface anharmonicities
stabilizing the solid surface; a large density jump causing bad liquid-solid
adhesion; incipient NaCl molecular correlations destabilizing the liquid
surface. The latter is pursued in detail, and it is shown that surface
short-range charge order acts to raise the surface tension because incipient
NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl
much below that of solid NaCl(100).Comment: 4 pages, 3 figure
Ectoplasm & Superspace Integration Measure for 2D Supergravity with Four Spinorial Supercurrents
Building on a previous derivation of the local chiral projector for a two
dimensional superspace with eight real supercharges, we provide the complete
density projection formula required for locally supersymmetrical theories in
this context. The derivation of this result is shown to be very efficient using
techniques based on the Ectoplasmic construction of local measures in
superspace.Comment: 18 pages, LaTeX; V2: minor changes, typos corrected, references
added; V3: version to appear in J. Phys. A: Math. Theor., some comments and
references added to address a referee reques
Rubber friction on smooth surfaces
We study the sliding friction for viscoelastic solids, e.g., rubber, on hard
flat substrate surfaces. We consider first the fluctuating shear stress inside
a viscoelastic solid which results from the thermal motion of the atoms or
molecules in the solid. At the nanoscale the thermal fluctuations are very
strong and give rise to stress fluctuations in the MPa-range, which is similar
to the depinning stresses which typically occur at solid-rubber interfaces,
indicating the crucial importance of thermal fluctuations for rubber friction
on smooth surfaces. We develop a detailed model which takes into account the
influence of thermal fluctuations on the depinning of small contact patches
(stress domains) at the rubber-substrate interface. The theory predicts that
the velocity dependence of the macroscopic shear stress has a bell-shaped f
orm, and that the low-velocity side exhibits the same temperature dependence as
the bulk viscoelastic modulus, in qualitative agreement with experimental data.
Finally, we discuss the influence of small-amplitude substrate roughness on
rubber sliding friction.Comment: 14 pages, 16 figure
Determinants of inappropriate acute pain management in old people unable to communicate verbally in the emergency department
Objectives: Poor pain management is relevant among individuals unable to communicate verbally (UCV). Analgesia may be due to three determinants: patients' status, physician's characteristics and pain etiology. Our aim is to investigate the association between prescription of ED pain treatment and these determinants. Materials and Methods: An observational prospective study including UCV patients was conducted. Severity of pain was evaluated by ALGOPLUS Scale and a score P â¥Â 2 out of 5 on the pain scale was retained as the threshold for the presence of acute pain in elderly UCV patients. Results: Our data showed that only 31,9% of UCV patients received a pharmacological treatment. The presence of the caregiver would influence the rate of therapy administration [OR 6,19 (95% CI 2,6â14,75)]. The presence of leg pain [OR 0,32 (95% CI 0,12â0,86)] and head pain [OR 0,29 (95% CI 0,10â0,84)] were less likely associated to receive analgesia. Pain related to trauma [OR 4.82 (95% CI 1.17 to 19.78)] and youngest physicians [OR 1.08 (95% CI 1.001 to 1.18)] were variables associated with the administration of drugs opiates. Discussion: Older UCV patients presenting to the ED with pain are at high risk of inadequate analgesia. Providers should always suspect presence of pain and an increasing need for behavioural pain evaluation is necessary for a complete assessment. Conclusions: Presence of a caregiver influences a more appropriate pain management in these patients. Staff training on pain management could result in better assessment, treatment, and interaction with caregivers. Keywords: Emergency department, Pain, Oligoanalgesi
Rubber friction on wet and dry road surfaces: the sealing effect
Rubber friction on wet rough substrates at low velocities is typically 20-30%
smaller than for the corresponding dry surfaces. We show that this cannot be
due to hydrodynamics and propose a novel explanation based on a sealing effect
exerted by rubber on substrate "pools" filled with water. Water effectively
smoothens the substrate, reducing the major friction contribution due to
induced viscoelastic deformations of the rubber by surface asperities. The
theory is illustrated with applications related to tire-road friction.Comment: Format Revtex 4; 8 pages, 11 figures (no color); Published on Phys.
Rev. B (http://link.aps.org/abstract/PRB/v71/e035428); previous work on the
same topic: cond-mat/041204
Feedback Loops Between Fields and Underlying Space Curvature: an Augmented Lagrangian Approach
We demonstrate a systematic implementation of coupling between a scalar field
and the geometry of the space (curve, surface, etc.) which carries the field.
This naturally gives rise to a feedback mechanism between the field and the
geometry. We develop a systematic model for the feedback in a general form,
inspired by a specific implementation in the context of molecular dynamics (the
so-called Rahman-Parrinello molecular dynamics, or RP-MD). We use a generalized
Lagrangian that allows for the coupling of the space's metric tensor (the first
fundamental form) to the scalar field, and add terms motivated by RP-MD. We
present two implementations of the scheme: one in which the metric is only
time-dependent [which gives rise to ordinary differential equation (ODE) for
its temporal evolution], and one with spatio-temporal dependence [wherein the
metric's evolution is governed by a partial differential equation (PDE)].
Numerical results are reported for the (1+1)-dimensional model with a
nonlinearity of the sine-Gordon type.Comment: 5 pages, 3 figures, Phys. Rev. E in pres
Three-dimensional (p,q) AdS superspaces and matter couplings
We introduce N-extended (p,q) AdS superspaces in three space-time dimensions,
with p+q=N and p>=q, and analyse their geometry. We show that all (p,q) AdS
superspaces with X^{IJKL}=0 are conformally flat. Nonlinear sigma-models with
(p,q) AdS supersymmetry exist for p+q4 the target space geometries
are highly restricted). Here we concentrate on studying off-shell N=3
supersymmetric sigma-models in AdS_3. For each of the cases (3,0) and (2,1), we
give three different realisations of the supersymmetric action. We show that
(3,0) AdS supersymmetry requires the sigma-model to be superconformal, and
hence the corresponding target space is a hyperkahler cone. In the case of
(2,1) AdS supersymmetry, the sigma-model target space must be a non-compact
hyperkahler manifold endowed with a Killing vector field which generates an
SO(2) group of rotations of the two-sphere of complex structures.Comment: 52 pages; V3: minor corrections, version published in JHE
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