2,421 research outputs found
Packing defects and the width of biopolymer bundles
The formation of bundles composed of actin filaments and cross-linking
proteins is an essential process in the maintenance of the cells' cytoskeleton.
It has also been recreated by in-vitro experiments, where actin networks are
routinely produced to mimic and study the cellular structures. It has long been
observed that these bundles seem to have a well defined width distribution,
which has not been adequately described theoretically. We propose here that
packing defects of the filaments, quenched and random, contribute an effective
repulsion that counters the cross-linking adhesion energy and leads to a well
defined bundle width. This is a two-dimensional strain-field version of the
classic Rayleigh instability of charged droplets
Probing Supersymmetric Flavor Models with
We discuss the supersymmetric contribution to in various
supersymmetric flavor models. We find that in alignment models the
supersymmetric contribution could be significant while in heavy squark models
it is expected to be small. The situation is particularly interesting in models
that solve the flavor problems by either of the above mechanisms and the
remaining CP problems by means of approximate CP, that is, all CP violating
phases are small. In such models, the standard model contributions cannot
account for and a failure of the supersymmetric
contributions to do so would exclude the model. In models of alignment and
approximate CP, the supersymmetric contributions can account for
only if both the supersymmetric model parameters and the
hadronic parameters assume rather extreme values. Such models are then strongly
disfavored by the measurements. Models of heavy squarks
and approximate CP are excluded.Comment: 16 pages, harvmac. v2: We added a discussion of the intriguing
implications that would follow if a recent lattice result is confirme
Superheavy Supersymmetry from Scalar Mass--A Parameter Fixed Points
In supersymmetric models, the well-known tension between naturalness and
experimental constraints is relieved if the squarks and sleptons of the first
two generations are superheavy, with masses of order 10 TeV, and all other
superpartners are light, with masses of order 1 TeV. We show that even if all
scalar masses and trilinear A parameters are of order 10 TeV at some high
scale, a mass-squared hierarchy of order 400 may be generated dynamically
through renormalization group evolution. The required high energy relations are
consistent with grand unification, or, alternatively, may be realized in
moduli-dominated supersymmetry-breaking scenarios.Comment: 12 pages, 3 figure
Self-Improving Algorithms
We investigate ways in which an algorithm can improve its expected
performance by fine-tuning itself automatically with respect to an unknown
input distribution D. We assume here that D is of product type. More precisely,
suppose that we need to process a sequence I_1, I_2, ... of inputs I = (x_1,
x_2, ..., x_n) of some fixed length n, where each x_i is drawn independently
from some arbitrary, unknown distribution D_i. The goal is to design an
algorithm for these inputs so that eventually the expected running time will be
optimal for the input distribution D = D_1 * D_2 * ... * D_n.
We give such self-improving algorithms for two problems: (i) sorting a
sequence of numbers and (ii) computing the Delaunay triangulation of a planar
point set. Both algorithms achieve optimal expected limiting complexity. The
algorithms begin with a training phase during which they collect information
about the input distribution, followed by a stationary regime in which the
algorithms settle to their optimized incarnations.Comment: 26 pages, 8 figures, preliminary versions appeared at SODA 2006 and
SoCG 2008. Thorough revision to improve the presentation of the pape
Sequestering CP Violation and GIM-Violation with Warped Extra Dimensions
We propose a model of spontaneous CP violation to address the strong CP
problem in warped extra dimensions that relies on sequestering flavor and CP
violation. We assume that brane-localized Higgs Yukawa interactions respect a
U(3) flavor symmetry that is broken only by bulk fermion mass and Yukawa terms.
All CP violation arises from the vev of a CP-odd scalar field localized in the
bulk. To suppress radiative corrections to theta-bar, the doublet quarks in
this model are localized on the IR brane. We calculate constraints from
flavor-changing neutral currents (FCNCs), precision electroweak measurements,
CKM unitarity, and the electric dipole moments in this model and predict
theta-bar to be at least about 10^-12.Comment: 38 page
A possible supersymmetric solution to the discrepancy between B -> \phi K_S and B -> \eta' K_S CP asymmetries
We present a possible supersymmetric solution to the discrepancy between the
observed mixing CP asymmetries in B -> \phi K_S and B -> \eta' K_S. We show
that due to the different parity in the final states of these processes, their
supersymmetric contributions from the R-sector have an opposite sign, which
naturally explain the large deviation between S_{\phi K_S} and S_{\eta' K_S}.
We also consider the proposed mechanisms to solve the puzzle of the observed
large branching ratio of B -> \eta' K and study their impact on S_{eta' K_S}.Comment: 4 pages, 2 figure
Solid-state electronic spin coherence time approaching one second
Solid-state electronic spin systems such as nitrogen-vacancy (NV) color
centers in diamond are promising for applications of quantum information,
sensing, and metrology. However, a key challenge for such solid-state systems
is to realize a spin coherence time that is much longer than the time for
quantum spin manipulation protocols. Here we demonstrate an improvement of more
than two orders of magnitude in the spin coherence time () of NV centers
compared to previous measurements: s at 77 K, which enables
coherent NV spin manipulations before decoherence. We employed
dynamical decoupling pulse sequences to suppress NV spin decoherence due to
magnetic noise, and found that is limited to approximately half of the
longitudinal spin relaxation time () over a wide range of temperatures,
which we attribute to phonon-induced decoherence. Our results apply to
ensembles of NV spins and do not depend on the optimal choice of a specific NV,
which could advance quantum sensing, enable squeezing and many-body
entanglement in solid-state spin ensembles, and open a path to simulating a
wide range of driven, interaction-dominated quantum many-body Hamiltonians
Environmental market factors associated with electronic health record adoption among cancer hospitals
Background: Although recent literature has explored the relationship between various environmental market characteristics and the adoption of electronic health records (EHRs) among general, acute care hospitals, no such research currently exists for specialty hospitals, including those providing cancer care.
Purpose: The aim of the study was to examine the relationship between market characteristics and the adoption of EHRs among Commission on Cancer (CoC)-accredited hospitals.
Methods/Approach: Secondary data on EHR adoption combined with hospital and environmental market characteristics were analyzed using logistic regression. Using the resource dependence theory, we examined how measures of munificence, complexity, and dynamism are related to the adoption of EHRs among CoC-accredited hospitals and, separately, hospitals not CoC-accredited.
Findings: In a sample of 2,670 hospitals, 141 (0.05%) were academic-based CoC-accredited hospitals and 562 (21%) were community-based CoC-accredited hospitals. Measures of munificence such as cancer incidence rates (OR = 0.99, CI [0.99, 1.00], p = .020) and percentage population aged 65+ (OR = 0.99, CI [0.99, 1.00], p = .001) were negatively associated with basic EHR adoption, whereas urban location was positively associated with comprehensive EHR adoption (OR = 3.07, CI [0.89, 10.61], p = .076) for community-based CoC-accredited hospitals. Measures of complexity such as hospitals in areas with less competition were less likely to adopt a basic EHR (OR = 0.33, CI [0.19, 0.96], p = .005), whereas Medicare Managed Care penetration was positively associated with comprehensive EHR adoption (OR = 1.02, CI [1.00, 1.05], p = .070) among community-based CoC-accredited hospitals. Lastly, dynamism, measured as population change, was negatively associated with the adoption of comprehensive EHRs (OR = 0.99, CI [0.99, 1.00], p = .070) among academic-based CoC-accredited hospitals.
Practice implications: A greater understanding of the environment’s relationship to health information technology adoption in cancer hospitals will help stakeholders in these institutions make informed strategic decisions about information technology investments guided by their facilities’ respective environmental factors. The results of this study may also be useful to hospital chief information officers and chief executive officers seeking to either improve their quality of care or achieve and maintain accreditation in providing cancer care
CP Violation in Mixing
The existence of mixing at a detectable level requires
new physics, which effectively yields a superweak interaction.
In general this interaction may involve significant CP violation. For small
values of the mixing it may be much easier to detect the CP-violating part of
the mixing than the CP-conserving part.Comment: 3 pages, latex, no figure
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