898 research outputs found
Complete description of polarization effects in emission of a photon by an electron in the field of a strong laser wave
We consider emission of a photon by an electron in the field of a strong
laser wave. Polarization effects in this process are important for a number of
physical problems. A probability of this process for circularly or linearly
polarized laser photons and for arbitrary polarization of all other particles
is calculated. We obtain the complete set of functions which describe such a
probability in a compact invariant form. Besides, we discuss in some detail the
polarization effects in the kinematics relevant to the problem of electron to
photon conversion at photon-photon and photon-electron colliders.Comment: 18 pages, minor changes, published versio
The Electroweak Standard Model in the Axial Gauge
We derive the Feynman rules of the standard model in the axial gauge. After
this we prove that the fields and do not correspond to
physical particles. As a consequence, these fields cannot appear as incoming or
outgoing lines in Feynman graphs. We then calculate the contribution of these
fields in the case of a particular decay mode of the top quark.Comment: 16 pages, no figures. Added derivation of polarization su
Recursive actions for scalar theories
We introduce a class of self-interacting scalar theories in which the various
coupling contants obey a recursive relation. These imply a particularly simple
form for the generating function of the Feynman amplitudes with vanishing
external momenta, as well as for the effective potential. In addition we
discuss an interesting duality inherent in these models. Specializing to the
case of zero spacetime dimensions we find intriguing nullification properties
for the amplitudes.Comment: 28 pages, 2 figures Replaced contract numbe
Moiré flat bands in strongly coupled atomic arrays
Moiré effects arise from stacking periodic structures with a specific geometrical mismatch and promise unique possibilities. However, their full potential for photonic applications has yet to be explored. Here, we investigate the photonic band structure for an atomic stack of strongly coupled linear arrays in the dipolar regime. A moiré parameter θ is used to parameterize a relative lattice constant mismatch between the two arrays that plays the role of a 1D twist angle. The system’s interaction matrix is analytically diagonalized and reveals the presence of localized excitations which strongly enhance the density of optical states in spectral regions that can be controlled via the moiré parameter. We also confirm our findings by numerical simulations of finite systems. Our work provides a better understanding of photonic moiré effects and their potential use in photonic devices such as optical sensors and light traps
Environmental Determinants of Malaria Transmission Around the Koka Reservoir in Ethiopia
New dam construction is known to exacerbate malaria transmission in Africa as the vectors of malaria—Anopheles mosquitoes—use bodies of water as breeding sites. Precise environmental mechanisms of how reservoirs exacerbate malaria transmission are yet to be identified. Understanding of these mechanisms should lead to a better assessment of the impacts of dam construction and to new prevention strategies. Combining extensive multiyear field surveys around the Koka Reservoir in
Ethiopia and rigorous model development and simulation studies, environmental mechanisms of malaria transmission around the reservoir were examined. Most comprehensive and detailed malaria transmission model, Hydrology, Entomology, and Malaria Transmission Simulator, was applied to a village adjacent to the reservoir. Significant contributions to the dynamics of malaria transmission are shaped by wind profile, marginal pools, temperature, and shoreline locations. Wind speed and wind direction influence Anopheles populations and malaria transmission during the major and secondary mosquito seasons. During the secondary mosquito season, a noticeable influence was also attributed to marginal pools. Temperature was found to play an important role, not so much in Anopheles population dynamics, but in malaria transmission dynamics. Change in shoreline locations drives malaria transmission dynamics, with closer shoreline locations to the village making malaria transmission more likely. Identified environmental mechanisms help in predicting malaria transmission seasons and in developing village relocation strategies upon dam construction to minimize the risk of malaria
Optimization of Precursor Injection in an Atmospheric Pressure Plasma Jet System
Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP PECVD) of thin films is a recently emerged technology, showing important advantages in comparison with the traditional and well established low pressure plasma enhanced deposition methods. The main benefit of AP-PECVD is the potential of cost efficient in-line production without expensive and bulky vacuum equipment. In this work, an innovative AP plasma jet system is investigated which serves as a pilot system for industrial scale equipment, the VITO PlasmaLine®. Applications include moisture/oxygen diffusion barriers as well as grease barriers, UV curing of coatings or chemical activation of a surface. For industrial application a high throughput (~ 100-1000 m/min) is critical in order to compete with conventional techniques, such as wet chemical coating. Barrier coating deposition by AP-PECVD on polymer substrates has been demonstrated to be superior to wet chemical coating, with less consumption of precursor material [1], though many technical challenges remain to obtain the desired (dynamic) growth rates. The pilot equipment utilizes a 0.5 mm double slit configuration with 1000-2000 W power input at a frequency of 40-50 kHz with N2 as the primary carrier gas. By utilizing the plasma afterglow remote from the source, uniform surface treatment can be achieved despite the filamentary discharge in the slits. Deposition on the electrodes is prevented by injection of precursor into the jet and because of the remote nature of the plasma source the thermal load on the substrate is minimized, making it ideally suited for treatment of polymers and paper. A key area for improvement and upscaling of the pilot system for industrial application is optimization of gaseous and liquid (aerosol) precursor injection. To this end, extensive characterization of the plasma jet is undertaken, including current-voltage, fast imaging and optical emission and absorption measurements, with focus on the dynamics of gaseous and aerosol precursor particles in the jet. For optimum control over the gas distribution and precursor injection, Computational Fluid Dynamic models are presented in conjunction with the experimental work
Alzheimer's Disease-Related Dementias Summit 2019: National research priorities for the investigation of traumatic brain injury as a risk factor for Alzheimer's Disease and Related Dementias
TBI is a risk factor for later life dementia. Clinical and preclinical studies have elucidated multiple mechanisms through which TBI may influence or exacerbate multiple pathological processes underlying Alzheimer’s Disease and Alzheimer’s Disease Related Dementias (AD/ADRD). The National Institutes of Health hosts triennial ADRD Summits to inform a national research agenda, and the 2019 ADRD Summit was the first to highlight ‘TBI and AD/ADRD Risk’ as an emerging topic in the field. A multidisciplinary committee of TBI researchers with relevant expertise reviewed extant literature, identified research gaps and opportunities, and proposed draft research recommendations at the 2019 ADRD Summit. These research recommendations, further refined after broad stakeholder input at the Summit, cover four overall areas: (1) Encourage crosstalk and interdisciplinary collaboration between TBI and dementia researchers, (2) Establish infrastructure to study TBI as a risk factor for AD/ADRD, (3) Promote basic and clinical research examining the development and progression of TBI AD/ADRD neuropathologies and associated clinical symptoms, and (4) Characterize the clinical phenotype of progressive dementia associated with TBI and develop non-invasive diagnostic approaches. These recommendations recognize a need to strengthen communication and build frameworks to connect the complexity of TBI with rapidly evolving AD/ADRD research. Recommendations acknowledge TBI as a clinically and pathologically heterogeneous disease whose associations with AD/ADRDs remain incompletely understood. The recommendations highlight the scientific advantage of investigating AD/ADRD in the context of a known TBI exposure, the study of which can directly inform on disease mechanisms and treatment targets for AD/ADRDs with shared common pathways
A Stochastic Fluid Model Approach to the Stationary Distribution of the Maximum Priority Process
In traditional priority queues, we assume that every customer upon arrival
has a fixed, class-dependent priority, and that a customer may not commence
service if a customer with a higher priority is present in the queue. However,
in situations where a performance target in terms of the tails of the
class-dependent waiting time distributions has to be met, such models of
priority queueing may not be satisfactory. In fact, there could be situations
where high priority classes easily meet their performance target for the
maximum waiting time, while lower classes do not.
Here, we are interested in the stationary distribution at the times of
commencement of service of this maximum priority process. Until now, there has
been no explicit expression for this distribution. We construct a mapping of
the maximum priority process to a tandem fluid queue, which enables us to find
expressions for this stationary distribution. We derive the results for the
stationary distribution of the maximum priority process at the times of the
commencement of service.Comment: The Eleventh International Conference on Matrix-Analytic Methods in
Stochastic Models (MAM11), 2022, Seoul, Republic of Kore
Almost Linear B\"uchi Automata
We introduce a new fragment of Linear temporal logic (LTL) called LIO and a
new class of Buechi automata (BA) called Almost linear Buechi automata (ALBA).
We provide effective translations between LIO and ALBA showing that the two
formalisms are expressively equivalent. While standard translations of LTL into
BA use some intermediate formalisms, the presented translation of LIO into ALBA
is direct. As we expect applications of ALBA in model checking, we compare the
expressiveness of ALBA with other classes of Buechi automata studied in this
context and we indicate possible applications
- …