1,322 research outputs found
Microscopic laser-driven high-energy colliders
The concept of a laser-guided collider in the high-energy regime is
presented and its feasibility discussed. Ultra-intense laser pulses and strong
static magnetic fields are employed to unite in one stage the electron and
positron acceleration and their head-on-head collision. We show that the
resulting coherent collisions in the GeV regime yield an enormous enhancement
of the luminosity with regard to conventional incoherent colliders
Constant Resistance During Proportional Speed Provoked Higher Lower Limb Proximal Musculature Recruitment than Distal Musculature in Young Healthy Adults
The lack of exercise in society today often leads to severe muscle loss and poor physical performance. Training methods targeting specific weakened muscle groups can help prevent or counteract muscle loss. This study aimed to analyze how the lower extremity muscles are activated when pushing a sled with constant resistance at two different speeds. Twenty-six participants with an average age of 23.77 years consented to having electromyography surface electrodes placed along the gluteus maximus (GMax), gluteus medius (GMed), tibialis anterior (TA), and gastrocnemius (GA) of their dominant leg. Muscle activation levels were then measured while the participant walked and ran with and without sled resistance. The study results showed that muscle activation was comparable during all trials and was not influenced by speed or constant resistance. However, the muscle activation for GMax and GMed was significantly higher than the activation levels exhibited by GA and TA. While pushing a sled has been shown to impact all studied musculature similarly, adding resistance to the movement can affect gait parameters such as stride length and cadence. Our findings support the use of sled training in patients with hip pathologies who are seeking to strengthen their GMax and GMed
Collective coherent population trapping in a thermal field
We analyzed the efficiency of coherent population trapping (CPT) in a
superposition of the ground states of three-level atoms under the influence of
the decoherence process induced by a broadband thermal field. We showed that in
a single atom there is no perfect CPT when the atomic transitions are affected
by the thermal field. The perfect CPT may occur when only one of the two atomic
transitions is affected by the thermal field. In the case when both atomic
transitions are affected by the thermal field, we demonstrated that regardless
of the intensity of the thermal field the destructive effect on the CPT can be
circumvented by the collective behavior of the atoms. An analytic expression
was obtained for the populations of the upper atomic levels which can be
considered as a measure of the level of thermal decoherence. The results show
that the collective interaction between the atoms can significantly enhance the
population trapping in that the population of the upper state decreases with
increased number of atoms. The physical origin of this feature was explained by
the semiclassical dressed atom model of the system. We introduced the concept
of multiatom collective coherent population trapping by demonstrating the
existence of collective (entangled) states whose storage capacity is larger
than that of the equivalent states of independent atoms.Comment: Accepted for publication in Phys. Rev.
Extraction of the electron mass from factor measurements on light hydrogenlike ions
The determination of the electron mass from Penning-trap measurements with
C ions and from theoretical results for the bound-electron
factor is described in detail. Some recently calculated contributions slightly
shift the extracted mass value. Prospects of a further improvement of the
electron mass are discussed both from the experimental and from the theoretical
point of view. Measurements with He ions will enable a consistency
check of the electron mass value, and in future an improvement of the He
nuclear mass and a determination of the fine-structure constant
PyFstat: a Python package for continuous gravitational-wave data analysis
Gravitational waves in the sensitivity band of ground-based detectors can be emitted by a number of astrophysical sources, including not only binary coalescences, but also individual spinning neutron stars. The most promising signals from such sources, although not yet detected, are long-lasting, quasi-monochromatic Continuous Waves (CWs). The PyFstat package provides tools to perform a range of CW data-analysis tasks. It revolves around the F-statistic, a matched-filter detection statistic for CW signals that has been one of the standard methods for LIGO-Virgo CW searches for two decades. PyFstat is built on top of established routines in LALSuite but through its more modern Python interface it enables a flexible approach to designing new search strategies. Hence, it serves a dual function of (i) making LALSuite CW functionality more easily accessible through a Python interface, thus facilitating the new user experience and, for developers, the exploratory implementation of novel methods; and (ii) providing a set of production-ready search classes for use cases not yet covered by LALSuite itself, most notably for MCMC-based followup of promising candidates from wide-parameter-space searches
Proportionality of gravitational and electromagnetic radiation by an electron in an intense plane wave
Accelerated charges emit both electromagnetic and gravitational radiation.
Classically, it was found that the electromagnetic energy spectrum radiated by
an electron in a monochromatic plane wave is proportional to the corresponding
gravitational one. Quantum mechanically, it was shown that the amplitudes of
graviton photoproduction and Compton scattering are proportional to each other
at tree level. Here, by combining strong-field QED and quantum gravity, we
demonstrate that the amplitude of nonlinear graviton photoproduction in an
arbitrary plane wave is proportional to the corresponding amplitude of
nonlinear Compton scattering at tree level. Also, introducing classical
amplitudes and taking into account exactly the effects of the plane wave into
the electron dynamics, we prove that the proportionality only relies on the
symmetries of a plane wave and on energy-momentum conservation laws, leading to
the same proportionality constant in the classical and quantum case. These
results deepen the intertwine between gravity and electromagnetism into both a
nonlinear and a quantum level.Comment: 7 pages (one of supplemental material), 1 figur
Spontaneous emission interference in negative-refractive-index waveguides
The spontaneous decay of a V-type three-level atom placed in a
negative-refractive-index waveguide is analyzed. We find that in thin
waveguides, highly efficient surface guided modes are supported, which do not
occur in positive index waveguides. In addition, at low absorption, the mode
density and thus spontaneous emission into particular regular guided modes is
enhanced by several orders of magnitude as compared to regular dielectric
waveguides. The asymmetries between emission into the different modes and the
enhancement of particular guided modes allow to induce strong
spontaneous-emission interference between transitions with orthogonal
transition dipole moments.Comment: 7 pages, 7 figure
Nonspreading relativistic electron wavepacket in a strong laser field
A solution of the Dirac equation in a strong laser field presenting a
nonspreading wave packet in the rest frame of the electron is derived. It
consists of a generalization of the self-accelerating free electron wave packet
[Kaminer et al. Nature Phys. 11, 261 (2015)] to the case with the background of
a strong laser field. Built upon the notion of nonspreading for an extended
relativistic wavepacket, the concept of Born rigidity for accelerated motion in
relativity is the key ingredient of the solution. At its core, the solution
comes from the connection between the self-accelerated free electron wave
packet and the eigenstate of a Dirac electron in a constant and homogeneous
gravitational field via the equivalence principle. The solution is an essential
step towards the realization of the laser-driven relativistic collider [Meuren
et al. PRL 114, 143201 (2015)], where the large spreading of a common Gaussian
wave packet during the excursion in a strong laser field strongly limits the
expectable yields.Comment: 12 pages, 2 figure
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