2,607 research outputs found
The ATLAS discovery potential for a heavy charged Higgs boson in gg->tbH^{+-} with H^{+-}->tb
The feasibility of detecting a heavy charged Higgs boson,
m(H^{+-})>m(t)+m(b), decaying in the H^{+-}->tb channel is studied with the
fast simulation of the ATLAS detector. We study the gg->H^{+-}tb production
process at the LHC which together with the aforementioned decay channel leads
to four b-quarks in the final state. The whole production and decay chain reads
gg->H^{+-}tb->t\bar{t}b\bar{b}->b\bar{b}b\bar{b}l\nu\bar{q}q'. Combinatorial
background is a major difficulty in this multi-jet environment but can be
overcome by employing multivariate techniques in the event reconstruction.
Requiring four b-tagged jets in the event helps to effectively suppress the
Standard Model backgrounds but leads to no significant improvement in the
discovery potential compared to analyses requiring only three b-tagged jets.
This study indicates that charged Higgs bosons can be discovered at the LHC up
to high masses (m(H^{+-})>400 GeV) in the case of large tan(beta)
Inverting Chaos: Extracting System Parameters from Experimental Data
Given a set of experimental or numerical chaotic data and a set of model differential equations with several parameters, is it possible to determine the numerical values for these parameters using a least-squares approach, and thereby to test the model against the data? We explore this question (a) with simulated data from model equations for the Rossler, Lorenz, and pendulum attractors, and (b) with experimental data produced by a physical chaotic pendulum. For the systems considered in this paper, the least-squares approach provides values of model parameters that agree well with values obtained in other ways, even in the presence of modest amounts of added noise. For experimental data, the “fitted” and experimental attractors are found to have the same correlation dimension and the same positive Lyapunov exponent
Predicting the progress of diffusively limited chemical reactions in the presence of chaotic advection
The effects of chaotic advection and diffusion on fast chemical reactions in
two-dimensional fluid flows are investigated using experimentally measured
stretching fields and fluorescent monitoring of the local concentration. Flow
symmetry, Reynolds number, and mean path length affect the spatial distribution
and time dependence of the reaction product. A single parameter \lambda*N,
where \lambda is the mean Lyapunov exponent and N is the number of mixing
cycles, can be used to predict the time-dependent total product for flows
having different dynamical features.Comment: 4 pages, 4 figures, updated reference
Curvature Fields, Topology, and the Dynamics of Spatiotemporal Chaos
The curvature field is measured from tracer particle trajectories in a
two-dimensional fluid flow that exhibits spatiotemporal chaos, and is used to
extract the hyperbolic and elliptic points of the flow. These special points
are pinned to the forcing when the driving is weak, but wander over the domain
and interact in pairs at stronger driving, changing the local topology of the
flow. Their behavior reveals a two-stage transition to spatiotemporal chaos: a
gradual loss of spatial and temporal order followed by an abrupt onset of
topological changes.Comment: 5 pages, 5 figure
Dynamical heterogeneity in soft particle suspensions under shear
We present experimental measurements of dynamical heterogeneities in a dense
system of microgel spheres, sheared at different rates and at different packing
fractions in a microfluidic channel, and visualized with high speed digital
video microscopy. A four-point dynamic susceptibility is deduced from video
correlations, and is found to exhibit a peak that grows in height and shifts to
longer times as the jamming transition is approached from two different
directions. In particular, the time for particle-size root-mean square relative
displacements is found to scale as where is the strain rate and
is the distance from the random close packing volume
fraction. The typical number of particles in a dynamical heterogeneity is
deduced from the susceptibility peak height and found to scale as . Exponent uncertainties are less than ten
percent. We emphasize that the same power-law behavior is found at packing
fractions above and below . Thus, our results considerably extend a
previous observation of for granular heap flow at
fixed packing below . Furthermore, the implied result compares well with expectation from mode-coupling theory and
with prior observations for driven granular systems
Hydrodynamic Irreversibility in Particle Suspensions with Non-Uniform Strain
A dynamical phase transition from reversible to irreversible behavior occurs
when particle suspensions are subjected to uniform oscillatory shear, even in
the Stokes flow limit. We consider a more general situation with non-uniform
strain (e.g. oscillatory channel flow), which is observed to exhibit markedly
different dynamics. Self-organization and shear-induced migration only
partially explain the delayed, simultaneous onset of irreversibility across the
channel. The onset of irreversibility is accompanied by long-range correlated
particle motion. This motion leads to particle activity even at the channel
center, where the strain is negligible, and prevents the system from evolving
into a reversible state
Charge migration in organic materials: Can propagating charges affect the key physical quantities controlling their motion?
Charge migration is a ubiquitous phenomenon with profound implications
throughout many areas of chemistry, physics, biology and materials science. The
long-term vision of designing functional materials with tailored molecular
scale properties has triggered an increasing quest to identify prototypical
systems where truly molecular conduction pathways play a fundamental role. Such
pathways can be formed due to the molecular organization of various organic
materials and are widely used to discuss electronic properties at the nanometer
scale. Here, we present a computational methodology to study charge propagation
in organic molecular stacks at nano and sub-nanoscales and exploit this
methodology to demonstrate that moving charge carriers strongly affect the
values of the physical quantities controlling their motion. The approach is
also expected to find broad application in the field of charge migration in
soft matter systems.Comment: 18 pages, 6 figures, accepted for publication in the Israel Journal
of Chemistr
Tracing the History of Racial Injustice in Policing and Working Towards Justice through Data Analysis
There is an extensive history of racial disparity in the criminal justice system that has influenced the issue of racial bias in policing which continues to be a prominent issue even up to this day. The Sentencing Project (2008) explains that racial disparity “exists when the proportion of a racial or ethnic group within the control of the system is greater than the proportion of such groups in the general population” (1). It is important to note that there is a difference between the modern use of “disparity” and the historic subjugation and control. Back in the 1600s to the 1900s, Black people were put under control by laws whereas today, they suffer an unjust disparity. Starting with slavery in the 1600s to Jim Crow laws in the 1800s to disproportionately targeting minority communities in today’s policing, it is evident that there is a long and ongoing issue of racial disparity. This racial disparity is so prevalent that several scholars have asserted that “the whole criminal justice system has historically been used to maintain racial hierarchies” (Soto, 2018, 2; Alexander, 2010). To better understand why systemic racial injustice occurs it would be beneficial to draw upon the ethnic competition theory.
The ethnic competition theory is helpful for understanding why systemic racial injustice occurs because it provides an explanation for intergroup conflict. Cunningham (2012) explains that the “ethnic competition theory builds on Barth’s (1969) emphasis on the socially constructed boundaries through which ethnic groups ascribe difference” (3). Cunningham (2012) goes on to share, “Competition, stemming from overlap in the economic or political activities of multiple 5 ethnic groups, becomes a key mechanism through which particular boundaries are reinforced. This enhanced salience of ethnic divisions, in turn, can contribute to the emergence of ethnic conflict” (3). Keeping the framework of the ethnic competition theory in mind will help make sense of the history that will be discussed in this paper. Davenport, Soule and Armstrong II (2011) explains that it is valuable to understand the historical context of racial disparity in the criminal justice system to see how history has shaped today’s policing practices. The purpose of this paper is to outline the history of racial disparity in the criminal justice system and how it has influenced today’s policing practices
Phaseless computational imaging with a radiating metasurface
Computational imaging modalities support a simplification of the active
architectures required in an imaging system and these approaches have been
validated across the electromagnetic spectrum. Recent implementations have
utilized pseudo-orthogonal radiation patterns to illuminate an object of
interest---notably, frequency-diverse metasurfaces have been exploited as fast
and low-cost alternative to conventional coherent imaging systems. However,
accurately measuring the complex-valued signals in the frequency domain can be
burdensome, particularly for sub-centimeter wavelengths. Here, computational
imaging is studied under the relaxed constraint of intensity-only measurements.
A novel 3D imaging system is conceived based on 'phaseless' and compressed
measurements, with benefits from recent advances in the field of phase
retrieval. In this paper, the methodology associated with this novel principle
is described, studied, and experimentally demonstrated in the microwave range.
A comparison of the estimated images from both complex valued and phaseless
measurements are presented, verifying the fidelity of phaseless computational
imaging.Comment: 18 pages, 18 figures, articl
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