322,874 research outputs found
Theory and Computation of Hall Scattering Factor in Graphene
No full textThe Hall scattering factor, r, is a key quantity for establishing carrier concentration and drift mobility from Hall measurements; in experiments, it is usually assumed to be 1. In this paper, we use a combination of analytical and ab initio modeling to determine r in graphene. Although at high carrier densities r ~ 1 in a wide temperature range, at low doping the temperature dependence of r is very strong with values as high as 4 below 300 K. These high values are due to the linear bands around the Dirac cone and the carrier scattering rates due to acoustic phonons. At higher temperatures, r can instead become as low as 0.5 due to the contribution of both holes and electrons and the role of optical phonons. Finally, we provide a simple analytical model to compute accurately r in graphene in a wide range of temperatures and carrier densities
First-principles study of electronic transport and structural properties of Cu12Sb4 S13 in its high-temperature phase
No full textWe present an ab initio study of the structural and electronic transport properties of tetrahedrite, Cu12Sb4S13, in its high-temperature phase. We show how this complex compound can be seen as the outcome of an ordered arrangement of S-vacancies in a semiconducting fematinite-like structure (Cu3SbS4). Our calculations confirm that the S-vacancies are the natural doping mechanism in this thermoelectric compound and reveal a similar local chemical environment around crystallographically inequivalent Cu atoms, shedding light on the debate on X-ray photoelectron spectroscopy measurements in this compound. To access the electrical transport properties as a function of temperature we use the Kubo-Greenwood formula applied to snapshots of first-principles molecular dynamics simulations. This approach is essential to effectively account for the interaction between electrons and lattice vibrations in such a complex crystal structure where a strong anharmonicity plays a key role in stabilizing the high-temperature phase. Our results show that the Seebeck coefficient is in good agreement with experiments and the phonon-limited electrical resistivity displays a temperature trend that compares well with a wide range of experimental data. The predicted lower bound for the resistivity turns out to be remarkably low for a pristine mineral in the Cu-Sb-S system but not too far from the lowest experimental data reported in literature. The Lorenz number turns out to be substantially lower than what is expected from the free-electron value in the Wiedemann-Franz law, thus providing an accurate way to estimate the electronic and lattice contributions to the thermal conductivity in experiments, of great significance in this very low thermal conductivity crystalline material
Olfactory memory is impaired in a triple transgenic model of Alzheimer disease
No full textOlfactory memory dysfunctions were investigated in the triple-transgenic murine model of Alzheimer's disease (3x Tg-AD). In the social transmission of food preference test, 3x Tg-AD mice presented severe deficits in odor-based memory, without gross changes in general odor-ability. A beta and tau immunoreactivity was not observed in the primary processing regions for odor, the olfactory bulbs (OBs), whereas marked immunostaining was present in the piriform, entorhinal, and orbitofrontal cortex, as well as in the hippocampus. Our results suggest that the impairment in olfactory-based information processing might arise from degenerative mechanisms mostly affecting higher cortical regions and limbic areas, such as the hippocampus. (C) 2011 Elsevier B.V. All rights reserved
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Effects of perinatal exposure to Delta-9-tetrahydrocannabinol on the emotional reactivity of the offspring: a longitudinal behavioral study in Wistar rats.
No full textRATIONALE:
The endocannabinoid system plays a crucial role in the control of emotionality and recent clinical findings have shown that heavy prenatal exposure to cannabis is significantly associated with self-reported anxiety symptoms in exposed children. However, the long-term neurobehavioral consequences of in utero exposure to low-moderate doses of cannabinoid compounds have never been investigated.
OBJECTIVE:
The objective of this study was to investigate whether perinatal exposure to moderate doses of the active constituent of cannabis, the CB(1) cannabinoid receptor agonist delta-9-tetrahydrocannabinol (THC), influences the emotional reactivity of rat offspring.
METHODS:
Primiparous Wistar rats were treated during pregnancy and lactation with doses of THC equivalent to the current estimates of moderate cannabis consumption in humans (2.5-5 mg kg(-1), per os, from gestational day 15 to postnatal day 9). The emotional reactivity of infant, adolescent, and adult offspring was investigated using the isolation-induced ultrasonic vocalization, social interaction, and elevated plus-maze tests, respectively.
RESULTS:
Perinatal THC treatment did not affect parameters of reproduction; however, at the dose of 5 mg kg(-1), it increased the number of ultrasounds emitted by rat pups removed from the nest, inhibited social interaction and play behavior in the adolescent offspring, and induced an anxiogenic-like profile in the adult offspring tested in the elevated plus-maze test.
CONCLUSION:
These results suggest that the endocannabinoid system is involved in the control of emotionality since early developmental stages. Thus, even moderate doses of cannabinoid compounds, when administered during the perinatal period, can have profound consequences for brain maturation, leading to long-lasting neurodevelopmental alterations
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Raman scattering with infrared excitation resonant with the MoSe2 indirect band gap
No full textResonance Raman scattering, which probes electrons, phonons, and their interplay in crystals, is extensively used in two-dimensional materials. Here we investigate Raman modes in MoSe2 at different laser excitation energies from 2.33 eV down to the near infrared 1.16 eV. The Raman spectrum at 1.16 eV excitation energy shows that the intensity of high-order modes is strongly enhanced if compared to the first-order phonon modes' intensity due to resonance effects with the MoSe2 indirect band gap. By comparing the experimental results with the two-phonon density of states calculated with density functional theory, we show that the high-order modes originate mostly from two-phonon modes with opposite momenta. In particular, we identify the momenta of the phonon modes that couple strongly with the electrons to produce the resonance process at 1.16 eV, while we verify that at 2.33 eV the two-phonon modes' line shape compares well with the two-phonon density of states calculated over the entire Brillouin zone. We also show that by lowering the crystal temperature, we actively suppress the intensity of the resonant two-phonon modes and we interpret this as the result of the increase of the indirect band gap at low temperature that moves our excitation energy out of the resonance condition
First-principles predictions of Hall and drift mobilities in semiconductors
No full textCarrier mobility is at the root of our understanding of electronic devices. We present a unified methodology for the parameter-free calculations of phonon-limited drift and Hall carrier mobilities in real materials within the framework of the Boltzmann transport equation. This approach enables accurate and parameter-free calculations of the intrinsic mobility and will find applications in the design of electronic devices under realistic conditions of strain and temperature. The methodology exploits a novel approach for incorporating the effect of long-range quadrupole fields in the electron-phonon scattering rates and capitalizes on a rigorous and efficient procedure for numerical convergence. The accuracy reached in this work allows us to assess the impact of common approximations employed in transport calculations, including the role of exchange and correlation functionals, spin-orbit coupling, pseudopotentials, Wannier interpolation, Brillouin-zone sampling, dipole and quadrupole corrections, and the relaxation-time approximation. We study diamond, silicon, GaAs, 3C-SiC, AlP, GaP, c-BN, AlAs, AlSb, and SrO, and find that our most accurate calculations predict Hall mobilities significantly larger than the experimental data in the case of SiC, AlAs, and GaP. We identify possible improvements to the theoretical and computational frameworks to reduce this discrepancy, and we argue that new experimental data are needed to perform a meaningful comparison, since almost all existing data are more than two decades old. By setting tight standards for reliability and reproducibility, the present work aims to facilitate validation and verification of data and software towards predictive calculations of transport phenomena in semiconductors
Mice lacking fatty acid amide hydrolase (FAAH-/-) showed increased serotonergic neurotransmission and reduced emotional reactivity
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