4,110 research outputs found
Gravitational Instantons and Fluxes from M/F-theory on Calabi-Yau fourfolds
We compactify four-dimensional N=1 gauged supergravity theories on a circle
including fluxes for shift-symmetric scalars. Four-dimensional Taub-NUT
gravitational instantons universally correct the three-dimensional
superpotential in the absence of fluxes. In the presence of fluxes these
Taub-NUT instanton contributions are no longer gauge-invariant. Invariance can
be restored by gauge instantons on top of Taub-NUT instantons. We establish the
embedding of this scenario into M-theory. Circle fluxes and gaugings arise from
a restricted class of M-theory four-form fluxes on a resolved Calabi-Yau
fourfold. The M5-brane on the base of the elliptic fourfold dualizes into the
universal Taub-NUT instanton. In the presence of fluxes this M5-brane is
anomalous. We argue that anomaly free contributions arise from involved
M5-brane geometries dual to gauge-instantons on top of Taub-NUT instantons.
Adding a four-dimensional superpotential to the gravitational instanton
corrections leads to three-dimensional Anti-de Sitter vacua at stabilized
compactification radius. We comment on the possibility to uplift these M-theory
vacua, and to tunnel to four-dimensional F-theory vacua.Comment: 47 pages, 2 figure
Polarization fluctuations in insulators and metals: New and old theories merge
The ground-state fluctuation of polarization P is finite in insulators and
divergent in metals, owing to the SWM sum rule [I. Souza, T. Wilkens, and R. M.
Martin, Phys. Rev. B 62, 1666 (2000)]. This is a virtue of periodic (i.e.
transverse) BCs. I show that within any other boundary conditions the P
fluctuation is finite even in metals, and a generalized sum rule applies. The
boundary-condition dependence is a pure correlation effect, not present at the
independent-particle level. In the longitudinal case div P = -rho, and one
equivalently addresses charge fluctuations: the generalized sum rule reduces
then to a well known result of many-body theory.Comment: 4 pages, no figur
Inductive Reasoning Games as Influenza Vaccination Models: Mean Field Analysis
We define and analyze an inductive reasoning game of voluntary yearly
vaccination in order to establish whether or not a population of individuals
acting in their own self-interest would be able to prevent influenza epidemics.
We find that epidemics are rarely prevented. We also find that severe epidemics
may occur without the introduction of pandemic strains. We further address the
situation where market incentives are introduced to help ameliorating
epidemics. Surprisingly, we find that vaccinating families exacerbates
epidemics. However, a public health program requesting prepayment of
vaccinations may significantly ameliorate influenza epidemics.Comment: 20 pages, 7 figure
Relaxation to equilibrium driven via indirect control in Markovian dynamics
We characterize to what extent it is possible to modify the stationary states
of a quantum dynamical semigroup, that describes the irreversible evolution of
a two-level system, by means of an auxiliary two-level system. We consider
systems that can be initially entangled or uncorrelated. We find that the
indirect control of the stationary states is possible, even if there are not
initial correlations, under suitable conditions on the dynamical parameters
characterizing the evolution of the joint system.Comment: revtex4, 7 page
Theory of Boundary Effects in Invasion Percolation
We study the boundary effects in invasion percolation with and without
trapping. We find that the presence of boundaries introduces a new set of
surface critical exponents, as in the case of standard percolation. Numerical
simulations show a fractal dimension, for the region of the percolating cluster
near the boundary, remarkably different from the bulk one. We find a
logarithmic cross-over from surface to bulk fractal properties, as one would
expect from the finite-size theory of critical systems. The distribution of the
quenched variables on the growing interface near the boundary self-organises
into an asymptotic shape characterized by a discontinuity at a value ,
which coincides with the bulk critical threshold. The exponent of
the boundary avalanche distribution for IP without trapping is
; this value is very near to the bulk one. Then we
conclude that only the geometrical properties (fractal dimension) of the model
are affected by the presence of a boundary, while other statistical and
dynamical properties are unchanged. Furthermore, we are able to present a
theoretical computation of the relevant critical exponents near the boundary.
This analysis combines two recently introduced theoretical tools, the Fixed
Scale Transformation (FST) and the Run Time Statistics (RTS), which are
particularly suited for the study of irreversible self-organised growth models
with quenched disorder. Our theoretical results are in rather good agreement
with numerical data.Comment: 11 pages, 13 figures, revte
Cloud Capacity Spectrum Method: Accounting for record-to-record variability in fragility analysis using nonlinear static procedures
This paper investigates a number of computational issues related to the use of nonlinear static procedures in fragility analysis of structures. Such approaches can be used to complement nonlinear dynamic procedures, reducing the computational and modelling effort. Specifically, this study assesses the performance of the Capacity Spectrum Method (CSM) with real (i.e. recorded) ground motions (as opposed to code-based conventional spectra) to explicitly account for record-to-record variability in fragility analysis. The study focuses on single-degree-of-freedom systems, providing a basis for future multi-degree-of-freedom system applications. A case-study database of 2160 inelastic oscillators is defined through parametric backbones with different elastic periods, (yield) base shear coefficients, values of the ductility capacity, hardening ratios, residual strength values and hysteresis rules. These case studies are analysed using 100 real ground motions. An efficient algorithm to perform the CSM with real spectra is proposed, combined with a cloud-based approach (Cloud-CSM) to derive fragility relationships. Simple criteria to solve the issue of multiple CSM solutions (i.e. two or more points on the backbone satisfying the CSM procedure) are proposed and tested. It is demonstrated that the performance point selection can be carried out based on a particularly efficient intensity measure detected via optimal intensity measure analysis. The effectiveness of the proposed Cloud-CSM in fragility analysis is discussed through extensive comparisons with nonlinear time-history analyses, the code-based N2 method, and a simple method involving an intensity measure as a direct proxy for the performance displacement. The Cloud-CSM provides errors lower than ±20% in predicting the median of the fragility curves in most of the analysed cases and outperforms the other considered methodologies in calculating the fragility dispersion
Wage Posting or Wage Bargaining? A Test Using Dual Jobholders
This paper examines the behavior of dual jobholders to test a simple model of wage bargaining and wage posting. We estimate the sensitivity of wages and separation rates to wage shocks in a worker’s secondary job to assess the degree of bargaining versus wage posting in the labor market. We interpret the evidence within a model where workers facing hours constraints in their primary job may take a second, flexible-hours job for additional income. When a secondary job offers a sufficiently high wage, a worker either bargains with the primary employer for a wage increase or separates. The model provides a number of predictions that we test using matched employer-employee administrative data from Washington State. In the aggregate, wage bargaining appears to be a limited determinant of wage setting. The estimated wage response to improved outside options, which we interpret as bargaining, is precisely estimated, but qualitatively small. Wage posting appears to be more important than bargaining for wage determination overall, and especially in lower parts of the wage distribution. Observed wage bargaining takes place mainly among workers in the highest wage quartile. For this group, improved outside options translate to higher wages, but not higher separation rates. In contrast, for workers in the lowest wage quartile, wage increases in the secondary job lead to higher separation rates but no significant wage increase in the primary job, consistent with wage posting. We also find evidence in support of the hours-constraint model for dual jobholding. In particular, work hours in the primary job do not respond to wages in the secondary job, but hours and separations in the secondary job are sensitive to wages in the primary job due to income effects
Caveolin-1 Modulates Mechanotransduction Responses to Substrate Stiffness through Actin-Dependent Control of YAP
The transcriptional regulator YAP orchestrates many cellular functions, including tissue homeostasis, organ growth control, and tumorigenesis. Mechanical stimuli are a key input to YAP activity, but the mechanisms controlling this regulation remain largely uncharacterized. We show that CAV1 positively modulates the YAP mechanoresponse to substrate stiffness through actin-cytoskeleton-dependent and Hippo-kinase-independent mechanisms. RHO activity is necessary, but not sufficient, for CAV1-dependent mechanoregulation of YAP activity. Systematic quantitative interactomic studies and image-based small interfering RNA (siRNA) screens provide evidence that this actin-dependent regulation is determined by YAP interaction with the 14-3-3 protein YWHAH. Constitutive YAP activation rescued phenotypes associated with CAV1 loss, including defective extracellular matrix (ECM) remodeling. CAV1-mediated control of YAP activity was validated in vivo in a model of pancreatitis-driven acinar-to-ductal metaplasia. We propose that this CAV1-YAP mechanotransduction system controls a significant share of cell programs linked to these two pivotal regulators, with potentially broad physiological and pathological implications. Moreno-Vicente et al. report that CAV1, a key component of PM mechanosensing caveolae, mediates adaptation to ECM rigidity by modulating YAP activity through the control of actin dynamics and phosphorylation-dependent interaction of YAP with the 14-3-3-domain protein YWHAH. Cav1-dependent YAP regulation drives two pathophysiological processes: ECM remodeling and pancreatic ADM. © 2018 The Author
Dynamical-charge neutrality at a crystal surface
For both molecules and periodic solids, the ionic dynamical charge tensors
which govern the infrared activity are known to obey a dynamical neutrality
condition. This condition enforces their sum to vanish (over the whole finite
system, or over the crystal cell, respectively). We extend this sum rule to the
non trivial case of the surface of a semiinfinite solid and show that, in the
case of a polar surface of an insulator, the surface ions cannot have the same
dynamical charges as in the bulk. The sum rule is demonstrated through
calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include
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