49,600 research outputs found
Schwinger Effect in Non-parallel D1-branes: A Path Integral Approach
We study the Schwinger effect in a system of non-parallel D1-branes for the
bosonic strings using the path integral formalism. We drive the string pair
creation rate by calculating the one loop vacuum amplitude of the setup in
presence of the background electric filed defined along one of the D1-branes.
We find an angle dependent minimum value for the background field and show that
the decaying of vacuum into string pairs takes place for the field above this
value. It is shown that in limit the vacuum
becomes stable and thus no pair creation occurs
In Situ Nanomechanical Measurements of Interfacial Strength in Membrane-Embedded Chemically Functionalized Si Microwires for Flexible Solar Cells
Arrays of vertically aligned Si microwires embedded in polydimethylsiloxane (PDMS) have emerged as a promising candidate for use in solar energy conversion devices. Such structures are lightweight and concurrently demonstrate competitive efficiency and mechanical flexibility. To ensure reliable functioning under bending and flexing, strong interfacial adhesion between the nanowire and the matrix is needed. In situ uniaxial tensile tests of individual, chemically functionalized, Si microwires embedded in a compliant PDMS matrix reveal that chemical functionality on Si microwire surfaces is directly correlated with interfacial adhesion strength. Chemical functionalization can therefore serve as an effective methodology for accessing a wide range of interfacial adhesion between the rigid constituents and the soft polymer matrix; the adhesion can be quantified by measuring the mechanical strength of such systems
Generation of graph-state streams
We propose a protocol to generate a stream of mobile qubits in a graph state
through a single stationary parent qubit and discuss two types of its physical
implementation, namely, the generation of photonic graph states through an
atom-like qubit and those of flying atoms through a cavity-mode photonic qubit.
The generated graph states fall into an important class that can hugely reduce
the resource requirement of fault-tolerant linear optics quantum computation,
which was previously known to be far from realistic. In regard to the flying
atoms, we also propose a heralded generation scheme, which allows for
high-fidelity graph states even under the photon loss.Comment: Accepted for publication at PRA Rapid Communication
High-Contrast Interference in a Thermal Cloud of Atoms
The coherence properties of a gas of bosonic atoms above the BEC transition
temperature were studied. Bragg diffraction was used to create two spatially
separated wave packets, which interfere during expansion. Given sufficient
expansion time, high fringe contrast could be observed in a cloud of arbitrary
temperature. Fringe visibility greater than 90% was observed, which decreased
with increasing temperature, in agreement with a simple model. When the sample
was "filtered" in momentum space using long, velocity-selective Bragg pulses,
the contrast was significantly enhanced in contrast to predictions
Gravitational field of vacuumless defects
It has been recently shown that topological defects can arise in symmetry
breaking models where the scalar field potential has no minima and is
a monotonically decreasing function of . Here we study the
gravitational fields produced by such vacuumless defects in the cases of both
global and gauge symmetry breaking. We find that a global monopole has a
strongly repulsive gravitational field, and its spacetime has an event horizon
similar to that in de Sitter space. A gauge monopole spacetime is essentially
that of a magnetically charged black hole. The gravitational field of a global
string is repulsive and that of a gauge string is attractive at small distances
and repulsive at large distances. Both gauge and global string spacetimes have
singularities at a finite distance from the string core.Comment: 19 pages, REVTeX, 6 Postscript figure
Recommended from our members
Emergency Medicine Palliative Care Access (EMPallA): Protocol for a multicentre randomised controlled trial comparing the effectiveness of specialty outpatient versus nurse-led telephonic palliative care of older adults with advanced illness
Introduction Emergency department (ED)-initiated palliative care has been shown to improve patient-centred outcomes in older adults with serious, life-limiting illnesses. However, the optimal modality for providing such interventions is unknown. This study aims to compare nurse-led telephonic case management to specialty outpatient palliative care for older adults with serious, life-limiting illness on: (1) quality of life in patients; (2) healthcare utilisation; (3) loneliness and symptom burden and (4) caregiver strain, caregiver quality of life and bereavement. Methods and analysis This is a protocol for a pragmatic, multicentre, parallel, two-arm randomised controlled trial in ED patients comparing two established models of palliative care: nurse-led telephonic case management and specialty, outpatient palliative care. We will enrol 1350 patients aged 50+ years and 675 of their caregivers across nine EDs. Eligible patients: (1) have advanced cancer (metastatic solid tumour) or end-stage organ failure (New York Heart Association class III or IV heart failure, end-stage renal disease with glomerular filtration rate /min/m2, or global initiative for chronic obstructive lung disease stage III, IV or oxygen-dependent chronic obstructive pulmonary disease); (2) speak English; (3) are scheduled for ED discharge or observation status; (4) reside locally; (5) have a working telephone and (6) are insured. Patients will be excluded if they: (1) have dementia; (2) have received hospice care or two or more palliative care visits in the last 6 months or (3) reside in a long-term care facility. We will use patient-level block randomisation, stratified by ED site and disease. Effectiveness will be compared by measuring the impact of each intervention on the specified outcomes. The primary outcome will measure change in patient quality of life. Ethics and dissemination Institutional Review Board approval was obtained at all study sites. Trial results will be submitted for publication in a peer-reviewed journal
- …