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Search Results: 1 - 10 of 2849 matches for " Matteo Mitrano "
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Anisotropic compression in the high pressure regime of pure and Cr-doped vanadium dioxide
Matteo Mitrano,Beatrice Maroni,Carlo Marini,Michael Hanfland,Boby Joseph,Paolo Postorino,Lorenzo Malavasi
Physics , 2011, DOI: 10.1103/PhysRevB.85.184108
Abstract: We present structural studies of V$_{1-x}$Cr$_x$O$_2$ (pure, 0.7% and 2.5% Cr doped) compounds at room temperature in a diamond anvil cell for pressures up to 20 GPa using synchrotron x-ray powder diffraction. All the samples studied show a persistence of the monoclinic $M_1$ symmetry between 4 and 12 GPa. Above 12 GPa, the monoclinic $M_1$ symmetry changes to isostructural $M_x$ phase (space group $P2_1/c$) with a significant anisotropy in lattice compression of the $b$-$c$ plane of the $M_{1}$ phase. This behavior can be reconciled invoking the pressure induced charge-delocalization.
Population Inversion in Monolayer and Bilayer Graphene
Isabella Gierz,Matteo Mitrano,Jesse C. Petersen,Cephise Cacho,I. C. Edmond Turcu,Emma Springate,Alexander St?hr,Axel K?hler,Ulrich Starke,Andrea Cavalleri
Physics , 2014, DOI: 10.1088/0953-8984/27/16/164204
Abstract: The recent demonstration of saturable absorption and negative optical conductivity in the Terahertz range in graphene has opened up new opportunities for optoelectronic applications based on this and other low dimensional materials. Recently, population inversion across the Dirac point has been observed directly by time- and angle-resolved photoemission spectroscopy (tr-ARPES), revealing a relaxation time of only ~ 130 femtoseconds. This severely limits the applicability of single layer graphene to, for example, Terahertz light amplification. Here we use tr-ARPES to demonstrate long-lived population inversion in bilayer graphene. The effect is attributed to the small band gap found in this compound. We propose a microscopic model for these observations and speculate that an enhancement of both the pump photon energy and the pump fluence may further increase this lifetime.
Snapshots of non-equilibrium Dirac carrier distributions in graphene
Isabella Gierz,Jesse C. Petersen,Matteo Mitrano,Cephise Cacho,Edmond Turcu,Emma Springate,Alexander St?hr,Axel K?hler,Ulrich Starke,Andrea Cavalleri
Physics , 2013, DOI: 10.1038/nmat3757
Abstract: The optical properties of graphene are made unique by the linear band structure and the vanishing density of states at the Dirac point. It has been proposed that even in the absence of a semiconducting bandgap, a relaxation bottleneck at the Dirac point may allow for population inversion and lasing at arbitrarily long wavelengths. Furthermore, efficient carrier multiplication by impact ionization has been discussed in the context of light harvesting applications. However, all these effects are difficult to test quantitatively by measuring the transient optical properties alone, as these only indirectly reflect the energy and momentum dependent carrier distributions. Here, we use time- and angle-resolved photoemission spectroscopy with femtosecond extreme ultra-violet (EUV) pulses at 31.5 eV photon energy to directly probe the non-equilibrium response of Dirac electrons near the K-point of the Brillouin zone. In lightly hole-doped epitaxial graphene samples, we explore excitation in the mid- and near-infrared, both below and above the minimum photon energy for direct interband transitions. While excitation in the mid-infrared results only in heating of the equilibrium carrier distribution, interband excitations give rise to population inversion, suggesting that terahertz lasing may be possible. However, in neither excitation regime do we find indication for carrier multiplication, questioning the applicability of graphene for light harvesting. Time-resolved photoemission spectroscopy in the EUV emerges as the technique of choice to assess the suitability of new materials for optoelectronics, providing quantitatively accurate measurements of non-equilibrium carriers at all energies and wavevectors.
DELTA: Documenta??o de Estudos em Lingüística Teórica e Aplicada , 1997, DOI: 10.1590/S0102-44501997000100003
Abstract: this paper reviews the notions of illocutionary transparency and pragmatic markedness from a cross-linguistic perspective. such a review is carried out in the light of the role they play in indirect behaviour in brazilian portuguese, british english and in the brazilian advanced efl(english as a foreign language) learners? pragmatic production. on the basis of three empirical studies, it is claimed that the inference-based pragmatic model, commonly used to explain indirect directive behaviour, can only be accepted cross-linguistically if the notion of pragmatic markedness is also taken into account. in addition, it is argued here that such a notion plays a crucial role in accounting for the occurrence of cross-linguistic influence in the interlanguage production of directives.
DELTA: Documenta??o de Estudos em Lingüística Teórica e Aplicada , 1997,
Abstract: Este trabalho pretende abordar, sob perspectiva interlingüística, as no es de transparência ilocucionária e marca o pragmática à luz do papel que desempenham na configura o do comportamento indireto no português do Brasil, no inglês britanico e na produ o pragmática de alunos brasileiros de inglês de nível adiantado. Com base em três estudos empíricos, argumenta-se que o modelo pragmático de base referencial, comumente usado na explica o do comportamento diretivo indireto, só poderá ser aceito em conjunto com a no o de marca o pragmática. Argumenta-se, ainda, que tal no o é crucial para se explicar a ocorrência da influência interlingüística na produ o de diretivos na interlíngua.
Phonon-pump XUV-photoemission-probe in graphene: evidence for non-adiabatic heating of Dirac carriers by lattice deformation
Isabella Gierz,Matteo Mitrano,Hubertus Bromberger,Cephise Cacho,Richard Chapman,Emma Springate,Stefan Link,Ulrich Starke,Burkhard Sachs,Martin Eckstein,Tim O. Wehling,Mikhail I. Katsnelson,Alexander Lichtenstein,Andrea Cavalleri
Physics , 2014, DOI: 10.1103/PhysRevLett.114.125503
Abstract: We modulate the atomic structure of bilayer graphene by driving its lattice at resonance with the in-plane E1u lattice vibration at 6.3um. Using time- and angle-resolved photoemission spectroscopy (tr-ARPES) with extreme ultra-violet (XUV) pulses, we measure the response of the Dirac electrons near the K-point. We observe that lattice modulation causes anomalous carrier dynamics, with the Dirac electrons reaching lower peak temperatures and relaxing at faster rate compared to when the excitation is applied away from the phonon resonance or in monolayer samples. Frozen phonon calculations predict dramatic band structure changes when the E1u vibration is driven, which we use to explain the anomalous dynamics observed in the experiment.
Instabilities in moderately dense granular binary mixtures
Peter P. Mitrano,Vicente Garzó,Christine M. Hrenya
Physics , 2013, DOI: 10.1103/PhysRevE.89.020201
Abstract: A linear stability analysis of the Navier-Stokes (NS) granular hydrodynamic equations is performed to determine the critical length scale for the onset of vortices and clusters instabilities in granular dense binary mixtures. In contrast to previous attempts, our results (which are based on the solution to the inelastic Enskog equation to NS order) are not restricted to nearly elastic systems since they take into account the complete nonlinear dependence of the NS transport coefficients on the coefficients of restitution $\alpha_{ij}$. The theoretical predictions for the critical length scales are compared to molecular dynamics (MD) simulations in flows of strong dissipation ($\alpha_{ij}\geq 0.7$) and moderate solid volume fractions ($\phi\leq 0.2$). We find excellent agreement between MD and kinetic theory for the onset of velocity vortices, indicating the applicability of NS hydrodynamics to polydisperse flows even for strong inelasticity, finite density, and particle dissimilarity.
Comment on "Terahertz time-domain spectroscopy of transient metallic and superconducting states" (arXiv:1506.06758)
D. Nicoletti,M. Mitrano,A. Cantaluppi,A. Cavalleri
Physics , 2015,
Abstract: We comment on the model proposed by Orenstein and Dodge in arXiv:1506.06758v1, which describes time-domain terahertz measurements of transiently generated, high-electron-mobility (or superconducting) phases of solids. The authors' main conclusion is that time-domain terahertz spectroscopy does not measure a response function that is mathematically identical to the transient optical conductivity. We show that although this is correct, the difference between the measured response function and the microscopic optical conductivity is small for realistic experimental parameters. We also show that for the experiments reported by our group on light-induced superconducting-like phases in cuprates and in organic conductors, the time-domain terahertz yields a very good estimate for the optical conductivity.
Somatic cell mutations in cerebral tissue of cattle affected by bovine spongiform encephalopathy  [PDF]
Matteo Busconi, Corrado Fogher
Agricultural Sciences (AS) , 2010, DOI: 10.4236/as.2010.11005
Abstract: In animals the prion disease includes sheep and goat scrapie and the bovine spongiform encephalopathy (BSE). While several polymorphisms of the prion (PRNP) gene have been identified in sheep and some of them have been associated with susceptibility to scrapie, few mutations are reported in cattle and no correlation with BSE have been demonstrated. Genetic screening for mutants in the PRNP gene of 21 BSE positive animals by direct sequencing of the amplified gene, using DNA extracted from brain as template, confirmed that only few polymorphisms are present. However DNA molecules cloned and sequenced from the population of fragments considering a total of 90 clones from 9 BSE positive and 70 clones from 7 BSE negative animals, gave a highly significant differences in the frequency of mutations (p = 0.01). The high frequency and type of variants found cannot be explained only with misincorporation error of the Taq polymerase. Interestingly one of the mutations found in the BSE positive animals (F209S) corresponds to a mutant that causes a familiar form of prion disease in humans (F198S). These data can be explained with the presence of somatic mutations modifying the PRNP gene in single brain cells.
Related Party Transactions and Financial Performance: Is There a Correlation? Empirical Evidence from Italian Listed Companies  [PDF]
Matteo Pozzoli, Marco Venuti
Open Journal of Accounting (OJAcct) , 2014, DOI: 10.4236/ojacct.2014.31004
Abstract: Related party transactions (RPTs) can have a dual nature. On one hand, these transactions may be considered sound business exchanges, fulfilling the economic needs of the company. On the other hand, RPTs may be considered a mechanism to exploit company resources as a consequence of existing conflicting interests. This study takes into account both aspects. Specifically, this paper investigates the relation between RPTs and companies’ financial performance, and thus verifies whether there is an association between these kinds of transactions and earnings management. This study examines the existence of this relation as regards the universe of Italian listed companies for the period of 2008-2011. According to the related data analysis, the research concludes that related party transactions and companies’ financial performance results are not correlated and that there is no evidence of a cause-effect relation. Therefore, related party transactions do not appear—thanks also to the existence of control mechanisms—a means used by Italian listed companies to realize earnings management, especially earnings smoothing.
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