Hot electron relaxation dynamics in semiconductors: assessing the strength of the electron-phonon coupling from the theoretical and experimental viewpoints.

The rapid development of the computational methods based on density functional theory, on the one hand, and of time-, energy-, and momentum-resolved spectroscopy, on the other hand, allows today an unprecedently detailed insight into the processes governing hot-electron relaxation dynamics, and, in particular, into the role of the electron-phonon coupling. Instead of focusing on the development of a particular method, theoretical or experimental, this review aims to treat the progress in the understanding of the electron-phonon coupling which can be gained from both, on the basis of recently obtained results. We start by defining several regimes of hot electron relaxation via electron-phonon coupling, with respect to the electron excitation energy. We distinguish between energy and momentum relaxation of hot electrons, and summarize, for several semiconductors of the IV and III-V groups, the orders of magnitude of different relaxation times in different regimes, on the basis of known experimental and numerical data. Momentum relaxation times of hot electrons become very short around 1 eV above the bottom of the conduction band, and such ultrafast relaxation mechanisms are measurable only in the most recent pump-probe experiments. Then, we give an overview of the recent progress in the experimental techniques allowing to obtain detailed information on the hot-electron relaxation dynamics, with the main focus on time-, energy-, and momentum-resolved photoemission experiments. The particularities of the experimental approach developed by one of us, which allows to capture time-, energy-, and momentum-resolved hot-electron distributions, as well as to measure momentum relaxation times of the order of 10 fs, are discussed. We further discuss the main advances in the calculation of the electron-phonon scattering times from first principles over the past ten years, in semiconducting materials. Ab initio techniques and efficient interpolation methods provide the possibility to calculate electron-phonon scattering times with high precision at reasonable numerical cost. We highlight the methods of analysis of the obtained numerical results, which allow to give insight into the details of the electron-phonon scattering mechanisms. Finally, we discuss the concept of hot electron ensemble which has been proposed recently to describe the hot-electron relaxation dynamics in GaAs, the applicability of this concept to other materials, and its limitations. We also mention some open problems.

Time Dependence of the Electron and Positron Components of the Cosmic Radiation Measured by the PAMELA Experiment between July 2006 and December 2015.

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.

New upper limit on strange quark matter abundance in cosmic rays with the PAMELA space experiment.

In this work we present results of a direct search for strange quark matter (SQM) in cosmic rays with the PAMELA space spectrometer. If this state of matter exists it may be present in cosmic rays as particles, called strangelets, having a high density and an anomalously high mass-to-charge (A/Z) ratio. A direct search in space is complementary to those from ground-based spectrometers. Furthermore, it has the advantage of being potentially capable of directly identifying these particles, without any assumption on their interaction model with Earth's atmosphere and the long-term stability in terrestrial and lunar rocks. In the rigidity range from 1.0 to ∼1.0×10^{3} GV, no such particles were found in the data collected by PAMELA between 2006 and 2009. An upper limit on the strangelet flux in cosmic rays was therefore set for particles with charge 1≤Z≤8 and mass 4≤A≤1.2×10^{5}. This limit as a function of mass and as a function of magnetic rigidity allows us to constrain models of SQM production and propagation in the Galaxy.

Cosmic-ray positron energy spectrum measured by PAMELA.

Precision measurements of the positron component in the cosmic radiation provide important information about the propagation of cosmic rays and the nature of particle sources in our Galaxy. The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray positron flux and fraction that extends previously published measurements up to 300 GeV in kinetic energy. The combined measurements of the cosmic-ray positron energy spectrum and fraction provide a unique tool to constrain interpretation models. During the recent solar minimum activity period from July 2006 to December 2009, approximately 24,500 positrons were observed. The results cannot be easily reconciled with purely secondary production, and additional sources of either astrophysical or exotic origin may be required.

A field survey on the presence of prednisolone and prednisone in urine samples from untreated cows.

Prednisolone is a synthetic glucocorticoid widely employed in bovine clinical practice that may also be used illegally as a growth promoter. Recent in vitro and in vivo studies lend support to the hypothesis that prednisolone could be synthesised from cortisol in untreated cattle subjected to stressful events. To verify such a hypothesis, a field survey was conducted on urine samples collected from 131 guaranteed untreated cows and analysed for the presence of prednisolone and prednisone - in some instances also for cortisol and cortisone - with a validated LC/MS-MS method. None of the examined samples exhibited either prednisolone levels higher than the CCα limit (around 0.70 µg l⁻¹) or prednisone, being therefore officially compliant for both analytes. Trace amounts of prednisolone, approximately estimated in the range 0.1-0.3 µg l⁻¹ were found in only seven samples from cows also showing urinary cortisol and cortisone levels higher than those detected in negative specimens, as the result of a probable stress condition.

Cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV.

Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy. Here we present new results regarding negatively charged electrons between 1 and 625 GeV performed by the satellite-borne experiment PAMELA. This is the first time that cosmic-ray e⁻ have been identified above 50 GeV. The electron spectrum can be described with a single power-law energy dependence with spectral index -3.18 ± 0.05 above the energy region influenced by the solar wind (> 30 GeV). No significant spectral features are observed and the data can be interpreted in terms of conventional diffusive propagation models. However, the data are also consistent with models including new cosmic-ray sources that could explain the rise in the positron fraction.

PAMELA measurements of cosmic-ray proton and helium spectra.

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 1.2 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics). We find that the spectral shapes of these two species are different and cannot be described well by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data.

PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy.

The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy. During 850 days of data acquisition approximately 1500 antiprotons were observed. The measurements are consistent with purely secondary production of antiprotons in the Galaxy. More precise secondary production models are required for a complete interpretation of the results.

Progesterone receptor gene expression in the accessory sex glands of veal calves.

This study investigated progesterone receptor (PR) cDNA expression in the testes, prostate and bulbourethral glands of prepubertal calves treated experimentally with high and low doses of 17beta-oestradiol and with testosterone. Tissue samples were examined histologically and immunohistochemically for PR. Western blot analysis and quantitative PCR against PR was performed on cDNA and protein extracted from the same tissues. Bulbourethral glands from animals treated with low and high dosages of 17beta-oestradiol had 39- and 429-fold increases of PR transcript, respectively, compared with controls. In the prostate there were 7.5- and 16-fold increases, respectively. Animals treated with testosterone showed no increases in PR transcript. The results demonstrate that 17beta-oestradiol specifically induces marked overexpression of the PR gene and protein, particularly in the bulbourethral gland.

An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV.

Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a 'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5-100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.

17beta-oestradiol-induced gene expression in cattle prostate: biomarkers to detect illegal use of growth promoters.

The effects of 17beta-oestradiol (E2) on gene expression in cultures of bovine primary prostate stromal cells (BPSCs) and prostate gland tissue were studied. In the first part of the study, BPSCs were grown in the presence of E2 from the first passage to the end of the experiment; a second group was treated in the same way but the treatment was suspended for 48 hours before the end of the experiment; a third group of BPSCs served as a control. In the second part of the study, five male veal calves, aged 130 days, were treated four times intramuscularly with 10 mg of E2 at intervals of two weeks and then euthanased two weeks after the last treatment. Quantitative PCR and immunohistochemistry were used to evaluate the expression of fibroblast growth factor (FGF) receptors (FGFRs), FGFs, progesterone receptor, androgen receptor and oestrogen receptor in BPSCs and prostate tissue. E2 induced a significant over-expression of progesterone receptor in both BPSCs and prostate tissue. There was also a marked up-regulation of FGFR types 1, 2 and 3 genes observed in the BPSCs.

Development and validation of a three-dimensional finite element model of the face.

A detailed three-dimensional finite element model of the face is presented in this paper. Bones, muscles, skin, fat, and superficial muscoloaponeurotic system were reconstructed from magnetic resonance images and modeled according to anatomical, plastic, and reconstructive surgery literature. The finite element mesh, composed of hexahedron elements, was generated through a semi-automatic procedure with an effective compromise between the detailed representation of anatomical parts and the limitation of the computational time. Nonlinear constitutive equations are implemented in the finite element model. The corresponding model parameters were selected according to previous work with mechanical measurements on soft facial tissue, or based on reasonable assumptions. Model assumptions concerning tissue geometry, interactions, mechanical properties, and the boundary conditions were validated through comparison with experiments. The calculated response of facial tissues to gravity loads, to the application of a pressure inside the oral cavity and to the application of an imposed displacement was shown to be in good agreement with the data from corresponding magnetic resonance images and holographic measurements. As a first application, gravimetric soft tissue descent was calculated from the long time action of gravity on the face in the erect position, with tissue aging leading to a loss of stiffness. Aging predictions are compared with the observations from an "aging database" with frontal photos of volunteers at different age ranges (i.e., 20-40 years and 50-70 years).

New measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation.

A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-Earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a tenfold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g., dark matter particle annihilations.

Effects of anabolic and therapeutic doses of dexamethasone on thymus morphology and apoptosis in veal calves.

Three groups of 10 veal calves were treated, respectively, with 5 mg of dexamethasone-21-isonicotinate administered intramuscularly on days 0 and 7 (group A); 0.4 mg/day of dexamethasone-21-phosphate administered orally for 20 days (group B); or left untreated as controls (group C). Two animals from each group were slaughtered on day 3, 7, 14, 32 and 52. The size and weight of the thymus decreased progressively in both treated groups until day 32. On day 14, in comparison with the controls, there was a mean reduction of 76 per cent in the thymus weight of group A and 35 per cent in group B. On day 32, the reductions were 13 per cent in group A and 50 per cent in group B, but the thymus weight of both groups had recovered completely by day 52. Dexamethasone-induced changes in thymus weight associated with lymphoid depletion and fat replacement, and there were clear correlations between these changes and apoptosis of thymocytes.

Effects of low-dose dexamethasone on thymus morphology and immunological parameters in veal calves.

Glucocorticoids are often illegally used in association with anabolic steroids as growth promoters in veal calves and beef production. An experimental administration of dexamethasone was carried out in veal calves in order to assess the role of low doses of exogenous glucocorticoids on induction of thymus atrophy and on the immune response. Three groups of five veal calves each were included in this study: group D was administered 0.4 mg/day of dexamethasone-21-phosphate per os for 25 days; group V was administered 2 mg of dexamethasone-21-isonicotinate i.m. at days 14 and 21, and group K served as control. At slaughter, the weight of the thymus was severely reduced in group D and in group V, compared with control animals. Lesions included severe lymphoid depletion and hyperplasia of adipose tissue. In situ evaluation of apoptosis in thymus, showed a reduction of the percentage of positive nuclear areas of animals belonging to group V in comparison with control animals. An overall decrease of lymphocyte proliferative response was detected after treatment with short acting dexamethasone, while antibody response was not affected by treatments.