403 research outputs found
Book Reviews
We develop a first-principles approach based on many-body perturbation theory to investigate the effects of the interaction between electrons and carrier plasmons on the electronic properties of highly doped semiconductors and oxides. Through the evaluation of the electron self-energy, we account simultaneously for electron-plasmon and electron-phonon coupling in theoretical calculations of angle-resolved photoemission spectra, electron linewidths, and relaxation times. We apply this methodology to electron-doped anatase TiO2 as an illustrative example. The simulated spectra indicate that electron-plasmon coupling in TiO2 underpins the formation of satellites at energies comparable to those of polaronic spectral features. At variance with phonons, however, the energy of plasmons and their spectral fingerprints depends strongly on the carrier concentration, revealing a complex interplay between plasmon and phonon satellites. The electron-plasmon interaction accounts for approximately 40% of the total electron-boson interaction strength, and it is key to improve the agreement with measured quasiparticle spectra
First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field
We present a first-principles study on the dielectric properties of an NaCl
crystal and ultrathin NaCl films under a finite external electric field. Our
results show that the high-frequency dielectric constant of the films is not
affected by the finite size effect from crystal surfaces and is close to that
of the crystal, whereas the static one is sensitive to the thickness of the
film due to the difference in the atomic configurations between the surface and
inside of the film.Comment: 11 pages and 4 figure
Thrust distribution for 3-jet production from e+e 12 annihilation within the QCD conformal window and in QED
We investigate the theoretical predictions for thrust distribution in the electron positron annihilation to three-jets process at NNLO for different values of the number of flavors, Nf. To determine the distribution along the entire renormalization group flow from the highest energies to zero energy we consider the number of flavors near the upper boundary of the conformal window. In this regime of number of flavors the theory develops a perturbative infrared interacting fixed point. We then consider also the QED thrust obtained as the limit Nc\u21920 of the number of colors. In this case the low energy limit is governed by an infrared free theory. Using these quantum field theories limits as theoretical laboratories we arrive at an interesting comparison between the Conventional Scale Setting - (CSS) and the Principle of Maximum Conformality (PMC 1e) methods. We show that within the perturbative regime of the conformal window and also out of the conformal window the PMC 1e leads to a higher precision, and that reducing the number of flavors, from the upper boundary to the lower boundary, through the phase transition the curves given by the PMC 1e method preserve with continuity the position of the peak, showing perfect agreement with the experimental data already at NNLO
Saddle Pressures Factors in Road and Off-Road Cyclists of Both Genders: A Narrative Review
: The contact point of the pelvis with the saddle of the bicycle could generate abnormal pressure, which could lead to injuries to the perineum in cyclists. The aim of this review was to summarize in a narrative way the current literature on the saddle pressures and to present the factors that influence saddle pressures in order to prevent injury risk in road and off-road cyclists of both genders. We searched the PubMed database to identify English-language sources, using the following terms: "saddle pressures", "pressure mapping", "saddle design" AND "cycling". We also searched the bibliographies of the retrieved articles. Saddle pressures are influenced by factors such as sitting time on the bike, pedaling intensity, pedaling frequency, trunk and hand position, handlebars position, saddle design, saddle height, padded shorts, and gender. The jolts of the perineum on the saddle, especially on mountain bikes, generate intermittent pressures, which represent a risk factor for various pathologies of the urogenital system. This review highlights the importance of considering these factors that influence saddle pressures in order to prevent urogenital system injuries in cyclists
Physical fitness assessment in Goalball: A scoping review of the literature
Background: Goalball is a Paralympic sport for visually impaired athletes. Although it is widely practiced, a great variety of tests are adopted to evaluate athletes' physical fitness. Therefore, the objective was to identify the physical fitness tests adopted in this sport to find the common aspects between them and, eventually, to propose a standard operating procedure. Methods: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) guidelines were adopted. The studies were extracted from PubMed, Web of Science, and Scopus. A selection process by title, abstract, and full-text, according to the inclusion and exclusion criteria, was performed. The results were discussed with narrative synthesis. Results: A total of 7 papers and 222 participants were included. A wide variety of tests were adopted and the Brockport Physical Fitness Test (BPFT) was the only battery included to evaluate general athletes' well-being. Conclusions: Although few literature exists on Goalball, the BPFT could be the battery for evaluating Goalball athletes though the test battery should be standardized to the characteristics of this sport
Setting the Renormalization Scale in QCD: The Principle of Maximum Conformality
A key problem in making precise perturbative QCD predictions is the
uncertainty in determining the renormalization scale of the running
coupling The purpose of the running coupling in any gauge
theory is to sum all terms involving the function; in fact, when the
renormalization scale is set properly, all non-conformal terms in
a perturbative expansion arising from renormalization are summed into the
running coupling. The remaining terms in the perturbative series are then
identical to that of a conformal theory; i.e., the corresponding theory with
. The resulting scale-fixed predictions using the "principle of
maximum conformality" (PMC) are independent of the choice of renormalization
scheme -- a key requirement of renormalization group invariance. The results
avoid renormalon resummation and agree with QED scale-setting in the Abelian
limit. The PMC is also the theoretical principle underlying the BLM procedure,
commensurate scale relations between observables, and the scale-setting method
used in lattice gauge theory. The number of active flavors in the QCD
function is also correctly determined. We discuss several methods for
determining the PMC scale for QCD processes. We show that a single global PMC
scale, valid at leading order, can be derived from basic properties of the
perturbative QCD cross section. The elimination of the renormalization scale
ambiguity and the scheme dependence using the PMC will not only increase the
precision of QCD tests, but it will also increase the sensitivity of collider
experiments to new physics beyond the Standard Model.Comment: 13 pages,2 figure
Angle-resolved photoemission spectra of graphene from first-principles calculations
Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental
technique for directly probing electron dynamics in solids. The energy vs.
momentum dispersion relations and the associated spectral broadenings measured
by ARPES provide a wealth of information on quantum many-body interaction
effects. In particular, ARPES allows studies of the Coulomb interaction among
electrons (electron-electron interactions) and the interaction between
electrons and lattice vibrations (electron-phonon interactions). Here, we
report ab initio simulations of the ARPES spectra of graphene including both
electron-electron and electron-phonon interactions on the same footing. Our
calculations reproduce some of the key experimental observations related to
many-body effects, including the indication of a mismatch between the upper and
lower halves of the Dirac cone
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