155,589 research outputs found
Plasmons in topological insulator cylindrical nanowires
No full textWe present a theoretical analysis of Dirac magnetoplasmons in topological insulator nanowires. We discuss
a cylindrical geometry where Berry phase effects induce the opening of a gap at the neutrality point. By
taking into account surface electron wave functions introduced in previous papers and within the random phase
approximation, we provide an analytical form of the dynamic structure factor. Dispersions and spectral weights
of Dirac plasmons are studied with varying the radius of the cylinder, the surface doping, and the strength of an
external magnetic field. We show that, at zero surface doping, interband damped plasmonlike excitations form
at the surface and survive at low electron surface dopings (∼1010 cm−2). Then, we point out that the plasmon
excitations are sensitive to the Berry phase gap closure when an external magnetic field close to half quantum flux
is introduced. Indeed, a well-defined magnetoplasmon peak is observed at lower energies upon the application
of the magnetic field. Finally, the increase of the surface doping induces a crossover from damped interband to
sharp intraband magnetoplasmons, which, as expected for large radii and dopings (∼1012 cm−2), approach the
proper limit of a two-dimensional surface
Strain-induced topological phase transition at (111) SrTiO3-based heterostructures
No full textThe quasi-two-dimensional electronic gas at the (111) SrTiO3-based heterostructure interfaces is described by a multiband tight-binding model providing electronic bands in agreement at low energies with photoemission experiments. We analyze both the roles of the spin-orbit coupling and of the trigonal crystal-field effects. We point out the presence of a regime with sizable strain where the band structure exhibits a Dirac cone whose features are consistent with ab initio approaches. The combined effect of spin-orbit coupling and trigonal strain gives rise to nontrivial spin and orbital angular momenta patterns in the Brillouin zone and to quantum spin Hall effect by opening a gap at the Dirac cone. The system can switch from a conducting to a topological insulating state via modification of trigonal strain within a parameter range which is estimated to be experimentally achievable
Strain-induced topological phase transition at (111) SrTiO3-based heterostructures
No full textThe quasi-two-dimensional electronic gas at the (111) -based heterostructure interfaces is described by a multiband tight-binding model providing electronic bands in agreement at low energies with photoemission experiments. We analyze both the roles of the spin-orbit coupling and of the trigonal crystal-field effects. We point out the presence of a regime with sizable strain where the band structure exhibits a Dirac cone whose features are consistent with ab initio approaches. The combined effect of spin-orbit coupling and trigonal strain gives rise to nontrivial spin and orbital angular momenta patterns in the Brillouin zone and to quantum spin Hall effect by opening a gap at the Dirac cone. The system can switch from a conducting to a topological insulating state via modification of trigonal strain within a parameter range which is estimated to be experimentally achievable
Time-consistent policy and politics: does voting matter when individuals are identical?
No full textWe consider the implications of a lack of policy commitment when policies are chosen through a political process and individuals are ex-ante identical. We show that politics, by allowing ex-post distributional tensions to shape policy, can make it possible to sustain non-trivial equilibria in which the commitment problem is alleviated or fully eliminated. How effective politics can be at countering collective commitment problems in homogeneous groups depends on the nature of the political process and on the extent to which private choices are public information
Theoretical approaches for nanoscale thermoelectric phenomena
No full textWe focus on the theoretical approaches aimed to analyze thermoelectric properties at the nanoscale. We discuss several relevant theoretical approaches for different set-ups of nano-devices providing estimations of the thermoelectric parameters in the linear and non-linear regime, in particular the thermoelectric figure of merit and the power-efficiency trade-off. Moreover, we analyze the role of not only electronic, but also of vibrational degrees of freedom. First, nanoscale thermoelectric phenomena are considered in the quantum coherent regime using the Landauer-Büttiker method and focusing on effects of energy filtering. Then, we analyze the effects of many-body couplings between nanostructure degrees of freedom, such as electron-electron and electron-vibration interactions, which can strongly affect the thermoelectric conversion. In particular, we discuss the enhancement of the thermoelectric figure of merit in the Coulomb blockade regime for a quantum dot model starting from the master equation for charge state probabilities and the tunneling rates through the electrodes. Finally, within the non-equilibrium Green function formalism, we quantify the reduction of the thermoelectric performance in simple models of molecular junctions due to the effects of the electron-vibration coupling and phonon transport at room temperature
Relationship among explosive power, body fat, fat free mass, and pubertal development in youth soccer players. A preliminary study
No full textPurpose Changes in body size and functional capacities
are highly individual during puberty, and the performance
of a soccer player is often closely related to their maturity
status. The aim of the study was to evaluate the relationships
among explosive power, body fat, fat free mass and
pubertal development in young soccer players.
Methods Explosive power (countermovement jump—
CMJ), body mass index (BMI), percentage of body fat
(%BF), fat free mass (FFM) and a Self-Administered
Rating Scale for pubertal development (PDS) values of 11
‘‘Giovanissimi’’ (age 13 year), 13 ‘‘Allievi’’ (age 15 year)
and 10 ‘‘Juniores’’ (age [17 year) male soccer players
were compared. The statistical analysis was performed
using an analysis of variance among categories with
Fisher’s post hoc as appropriate. Furthermore, Pearson
correlations among variables were calculated considering
all subjects and also within categories.
Results Statistical differences emerged among categories
in CMJ (F(2,30) = 28.3, p\0.01), body fat weight (F(2,31) =
29.2, p\0.01) and PDS (F(2,29) = 18.5, p\0.01), while
%BF values showed statistical differences only for ‘‘Giovanissimi’’
and ‘‘Juniores’’ (F(2,31) = 3.4, p = 0.01). CMJ
showed significant correlations with FFM (r = 0.68) and
PDS (r = 0.63), PDS with FFM (r = 0.66) and BMI with
%BF(r = 0.71) and FFM (r = 0.71).A high correlation was
found within categories.
Conclusion Since we found differences between categories
and no correlation between chronological age and
pubertal status, this study highlights the importance of
assessing of puberty in youth soccer team
Magnetization dynamics in dysprosium orthoferrites via the inverse Faraday effect
No full textThe ultrafast nonthermal control of magnetization has recently become feasible in canted antiferromagnets through photomagnetic instantaneous pulses [A. V. Kimel , Nature 435, 655 (2005)]. In this experiment, circularly polarized femtosecond laser pulses set up a strong magnetic field along the wave vector of the radiation through the inverse Faraday effect, thereby exciting nonthermally the spin dynamics of dysprosium orthoferrites. A theoretical study is performed by using a model for orthoferrites based on a general form of free energy whose parameters are extracted from experimental measurements. The magnetization dynamics is described by solving coupled sublattice Landau-Lifshitz-Gilbert equations whose damping term is associated with the scattering rate due to magnon-magnon interaction. Due to the inverse Faraday effect and the nonthermal excitation, the effect of the laser is simulated by magnetic-field Gaussian pulses with temporal width of the order of 100 fs. When the field is along the z axis, a single resonance mode of the magnetization is excited. The amplitude of the magnetization and out-of-phase behavior of the oscillations for fields in the z and -z directions are in good agreement with the cited experiment. The analysis of the effect of the temperature shows that the magnon-magnon scattering mechanism affects the decay of the oscillations on the picosecond scale. Finally, when the field pulse is along the x axis, another mode is excited, as observed in experiments. In this case, a comparison between theoretical and experimental results shows some discrepancies, the origin of which is related to the role played by anisotropies in orthoferrites
Editorial: innovative quantum materials
No full textQuantum Materials are materials where the manifestation of the quantum mechanical nature of matter constituents, which comes into evidence at the macroscopic scale, is used to obtain new functionalities. The study of quantum materials is relevant both on the fundamental and on the applied side. Indeed, this class of materials provides a common thread between physics, materials science and engineering. The focus is on emergent excitations, such as Dirac and Majorana fermions. In particular, it analyzes their sensitivity to external perturbations, such as electric and magnetic fields, and boundary conditions that can be controlled by surface/edge terminations, defect states and nanostructuring. The topical issue provides a broad description of innovative quantum materials discussing a variety of different phenomena: (1) interference phenomena in quantum devices made up of a topological insulator, (2) bound states in finite length nanowires with an inhomogeneous spin–orbit coupling profile relevant for Majorana physics, (3) sensitivity of graphene transport properties to defect states and edge functionalization, (4) role of Moiré phonons on the energy properties of twisted bilayer graphene at the magic angle important for van der Waals materials, (5) emergent spin excitations and anisotropic magnetotransport properties in iridates, (6) magnetoelectric couplings and improper magnetoelectric behavior in manganites significant for the realization of novel spintronic devices
Energy cost and energy sources of an elite female soccer player to Repeated Sprint Ability Test: a case study
No full textBackground: Intense physical efforts performed at maximal or near-maximal speeds and the ability to recover among sprint are important characteristics of a soccer player. In the last years, women's soccer has become a rapidly and markedly growing sport (+34% of new players from 2000). Objective: The aim of this case study was to analyse the performance (total time –TT; fatigue index percentage-IF%) and physiological (aerobic and anaerobic) responses to Repeated Sprint Ability test (RSAt) of an elite female player. Methods: To identify the contribution of the 3 energy sources at the beginning, middle, and at the end of the different sprint of RSAt performance in a female player (age: 30 years; BMI: 20.3 kg/m 2 ), which requested 7x30 m sprints (25 s active recovery among sprints) with a change of direction, a portable metabolimeter and software dedicated were used. A repeated measure MANOVA over the 7 sprints time series was applied (p< 0.05). Results: Results showed that TT was 58.71 s (Ideal Time: 56.98 s) with IF% of 3.0%. Energy contributions were given for 80.3% by aerobic, 19.2% by anaerobic lactid, and 0.5% by anaerobic alactid sources. We have found different kinetics in the heart rate (HR) and maximum oxygen uptake with the oxygen uptake that reached the peak when HR was still rising. Conclusion: Considering that the energy consumption during intermittent exercises requires different metabolism as a result of physiological stimuli proposed, the present findings substantiate the need to choose specific and adequate training methods for female soccer players that aim at increasing their RSA performances. © 2019 Perroni et al
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