8,262 research outputs found
Search for long lived charged massive particles in pp collisions at s-hat = 1.8TeV
We report a search for the production of long-lived charged massive particles in a data sample of 90 pb-1 of √s=1.8 TeV pp̅ collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton
Energy-level ordering and ground-state quantum numbers for frustrated two-leg spin-1/2 ladder model
The Lieb-Mattis theorem about antiferromagnetic ordering of energy levels on
bipartite lattices is generalized to finite-size two-leg spin-1/2 ladder model
frustrated by diagonal interactions. For reflection-symmetric model with
site-dependent interactions we prove exactly that the lowest energies in
sectors with fixed total spin and reflection quantum numbers are monotone
increasing functions of total spin. The nondegeneracy of most levels is proved
also. We also establish the uniqueness and obtain the spin value of the
lowest-level multiplet in the whole sector formed by reflection-symmetric
(antisymmetric) states. For a wide range of coupling constants, we prove that
the ground state is a unique spin singlet. For other values of couplings, it
may be also a unique spin triplet or may consist of both multiplets. Similar
results have been obtained for the ladder with arbitrary boundary impurity
spin. Some partial results have also been obtained in the case of periodical
boundary conditions.Comment: 17 page
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Rapid Response of an Academic Surgical Department to the COVID-19 Pandemic: Implications for Patients, Surgeons, and the Community.
BackgroundAs the coronavirus disease 2019 (COVID-19) pandemic continues to spread, swift actions and preparation are critical for ensuring the best outcomes for patients and providers. We aim to describe our hospital and Department of Surgery's experience in preparing for the COVID-19 pandemic and caring for surgical patients during this unprecedented time.Study designThis is a descriptive study outlining the strategy of a single academic health system for addressing the following 4 critical issues facing surgical departments during the COVID-19 pandemic: developing a cohesive leadership team and system for frequent communication throughout the department; ensuring adequate hospital capacity to care for an anticipated influx of COVID-19 patients; safeguarding supplies of blood products and personal protective equipment to protect patients and providers; and preparing for an unstable workforce due to illness and competing personal priorities, such as childcare.ResultsThrough collaborative efforts within the Department of Surgery and hospital, we provided concise and regular communication, reduced operating room volume by 80%, secured a 4-week supply of personal protective equipment, and created reduced staffing protocols with back-up staffing plans.ConclusionsBy developing an enabling infrastructure, a department can nimbly respond to crises like COVID-19 by promoting trust among colleagues and emphasizing an unwavering commitment to excellent patient care. Sharing principles and practical applications of these changes is important to optimize responses across the country and the world
Precision Measurement of a Particle Mass at the Linear Collider
Precision measurement of the stop mass at the ILC is done in a method based
on cross-sections measurements at two different center-of-mass energies. This
allows to minimize both the statistical and systematic errors. In the framework
of the MSSM, a light stop, compatible with electro-weak baryogenesis, is
studied in its decay into a charm jet and neutralino, the Lightest
Supersymmetric Particle(LSP), as a candidate of dark matter. This takes place
for a small stop-neutralino mass difference.Comment: 6 pages, 4 figures, 3tables,
Conference(Workshop)-LCWS/ILC2007-June,2,200
Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers
Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging
Diffusion on a hypercubic lattice with pinning potential: exact results for the error-catastrophe problem in biological evolution
In the theoretical biology framework one fundamental problem is the so-called
error catastrophe in Darwinian evolution models. We reexamine Eigen's
fundamental equations by mapping them into a polymer depinning transition
problem in a ``genotype'' space represented by a unitary hypercubic lattice.
The exact solution of the model shows that error catastrophe arises as a direct
consequence of the equations involved and confirms some previous qualitative
results. The physically relevant consequence is that such equations are not
adequate to properly describe evolution of complex life on the Earth.Comment: 10 pages in LaTeX. Figures are available from the authors.
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Magnetic order in the quasi-one-dimensional spin 1/2 chain, copper pyrazine dinitrate
We present the first evidence of magnetic order in the quasi-one-dimensional
spin 1/2 molecular chain compound, copper pyrazine dinitrate Cu(C4H4N2)(NO3)2}.
Zero field muon-spin relaxation measurements made at dilution refrigerator
temperatures show oscillations in the measured asymmetry, characteristic of a
quasistatic magnetic field at the muon sites. Our measurements provide
convincing evidence for long range magnetic order below a temperature
T_N=107(1) mK. This leads to an estimate of the interchain coupling constant of
|J'|/k_B=0.046 K and to a ratio |J'/J| = 4.4 x 10^-3.Comment: 4 pages, 3 figures. Submitted to Physical Review Letter
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