5,853 research outputs found
Dark energy, Ricci-nonflat spaces, and the Swampland
It was recently pointed out that the existence of dark energy imposes highly
restrictive constraints on effective field theories that satisfy the Swampland
conjectures. We provide a critical confrontation of these constraints with the
cosmological framework emerging from the Salam-Sezgin model and its string
realization by Cvetic, Gibbons, and Pope. We also discuss the implication of
the constraints for string model building.Comment: Matching version to be published in PL
Hydrogenated Graphene Nanoribbons for Spintronics
We show how hydrogenation of graphene nanoribbons at small concentrations can
open new venues towards carbon-based spintronics applications regardless of any
especific edge termination or passivation of the nanoribbons. Density
functional theory calculations show that an adsorbed H atom induces a spin
density on the surrounding orbitals whose symmetry and degree of
localization depends on the distance to the edges of the nanoribbon. As
expected for graphene-based systems, these induced magnetic moments interact
ferromagnetically or antiferromagnetically depending on the relative adsorption
graphene sublattice, but the magnitude of the interactions are found to
strongly vary with the position of the H atoms relative to the edges. We also
calculate, with the help of the Hubbard model, the transport properties of
hydrogenated armchair semiconducting graphene nanoribbons in the diluted regime
and show how the exchange coupling between H atoms can be exploited in the
design of novel magnetoresistive devices
Probing QCD approach to thermal equilibrium with ultrahigh energy cosmic rays
The Pierre Auger Collaboration has reported an excess in the number of muons
of a few tens of percent over expectations computed using extrapolation of
hadronic interaction models tuned to accommodate LHC data. Very recently, we
proposed an explanation for the muon excess assuming the formation of a
deconfined quark matter (fireball) state in central collisions of
ultrarelativistic cosmic rays with air nuclei. At the first stage of its
evolution the fireball contains gluons as well as and quarks. The very
high baryochemical potential inhibits gluons from fragmenting into
and , and so they fragment predominantly into pairs. In
the hadronization which follows this leads to the strong suppression of pions
and hence photons, but allows heavy hadrons to be emitted carrying away
strangeness. In this manner, the extreme imbalance of hadron to photon content
provides a way to enhance the muon content of the air shower. In this
communication we study theoretical systematics from hadronic interaction models
used to describe the cascades of secondary particles produced in the fireball
explosion. We study the predictions of one of the leading LHC-tuned models
QGSJET II-04 considered in the Auger analysis.Comment: 7 pages LaTeX, 6 .pdf figure
Tobacco use in the third trimester of pregnancy and its relationship to birth weight. A prospective study in Spain
Background Few studies have been carried out in Spain examining the use of tobacco amongst expectant mothers and its effect on birth weight. Aims To observe the proportion of expectant mothers who smoke during their pregnancy, and the impact of tobacco consumption on maternal and birth weight. We also aimed to identify the trimester of pregnancy in which tobacco use produced the greatest reduction in birth weight. Methods Prospective observational study in Spain. A random sampling strategy was used to select health centres and participant women. A total of 137 individuals were enrolled in the study. Exposure to tobacco was measured through a self-reported questionnaire. Regressions were performed to obtain a predictive model for birth weight related to smoking. Findings Overall, 35% of study participants were smokers during the pre-gestational period (27% in the first trimester, 21.9% in the second and 21.2% in the third). 38.7% of smoking cessation attempts took place in the third-trimester. Pregnant women who smoked up to the third trimester had a higher risk of giving birth to a baby under 3000 g, compared to non-smokers (OR = 5.94, CI 95%: 1.94–18.16). Each additional unit of tobacco consumed daily in the 3rd trimester led to a 32 g reduction in birth weight. Conclusion An important proportion of pregnant women in Spain smoke during pregnancy. Pregnant women exposed to tobacco have newborns with lower birth weight. Smoking during the 3rd trimester of pregnancy is associated with the greatest risk of lower birth weight
Isotropic charged cosmologies in infrared-modified electrodynamics
It has long been known that the covariant formulation of quantum
electrodynamics conflicts with the local description of states in the charged
sector. Some of the solutions to this problem amount to modifications of the
subsidiary conditions below some arbitrarily low photon frequency. Such
infrared modified theories have been shown to be equivalent to standard Maxwell
electrodynamics with an additional classical electromagnetic current induced by
the quantum charges. The induced current only has support for very small
frequencies and cancels the effects of the physical charges on large scales. In
this work we explore the possibility that this de-electrification effect could
allow for the existence of isotropic charged cosmologies, thus evading the
stringent limits on the electric charge asymmetry of the universe. We consider
a simple model of infrared-modified scalar electrodynamics in the cosmological
context and find that the charged sector generates a new contribution to the
energy-momentum tensor whose dominant contribution at late times is a
cosmological constant-like term. If the charge asymmetry was generated during
inflation, the limits on the asymmetry parameter in order not to produce a
too-large cosmological constant are very stringent for a number of e-folds in typical models. However if the
charge imbalance is produced after inflation, the limits are relaxed in such a
way that \eta_Q<10^{-43}(100 \,\mbox{GeV}/T_Q), with the temperature at
which the asymmetry was generated. If the charge asymmetry has ever existed and
the associated electromagnetic fields vanish in the asymptotic future, the
limit can be further reduced to .Comment: 10 pages, 6 figure
Editorial: Functional fitness/high intensity functional training for health and performance
Functional fitness training (FFT) is an emerging fitness trend that emphasizes functional, multi-joint movements, including aerobic (e.g., cycling, rowing, running) and strength exercises (e.g., weightlifting and derivatives: squat, snatch, clean and jerk, bench press, deadlift; bodyweight exercises: air squat, push-up, pull-up, muscle-up; plyometrics: box jumps, tuck ups) (Claudino et al., 2018; Feito et al., 2018). Researchers have shown that FFT may be not only suitable for professional athletes but also for populations with different fitness levels. Indeed, it is suggested that FFT elicits greater muscle recruitment than aerobic exercises alone, thereby improving both endurance and muscular strength and power (Bergeron et al., 2011; Claudino et al., 2018; Feito et al., 2018; Schlegel, 2020; Sharp et al., 2022). However, FFT units (i.e., workouts) are highly varied daily, and more research is needed to clarify its acute effects and its associated chronic training adaptations (Bergeron et al., 2011; Claudino et al., 2018; Feito et al., 2018; Schlegel, 2020; Sharp et al., 2022). Therefore, the aim of this Research Topic is to increase the knowledge of the evidence-based effects and adaptations of implementing FFT on health and performance in individuals with different biological conditions
- …