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1.
Nano Lett ; 20(1): 158-165, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31756115

RESUMO

Fascinating optical properties governed by extremely confined excitons have been so far observed in 2D crystals like monolayers of transition metal dichalcogenides. These materials, however, are limited for production by epitaxial methods. Besides, they are not suitable for the development of optoelectronics for the challenging deep-ultraviolet spectral range. Here, we present a single monolayer of GaN in AlN as a heterostructure fabricated by molecular beam epitaxy, which provides extreme 2D confinement of excitons, being ideally suited for light generation in the deep-ultraviolet. Optical studies in the samples, supplemented by a group-theory analysis and first-principle calculations, make evident a giant enhancement of the splitting between the dark and bright excitons due to short-range electron-hole exchange interaction that is a fingerprint of the strongly confined excitons. The practical significance of our results is in the observation of the internal quantum yield of the room-temperature excitonic emission as high as ∼75% at 235 nm.

2.
Sci Rep ; 9(1): 8066, 2019 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-31147575

RESUMO

Atomic, electronic structure and composition of top-down metal-assisted wet-chemically etched silicon nanowires were studied by synchrotron radiation based X-ray absorption near edge structure technique. Local surrounding of the silicon and oxygen atoms in silicon nanowires array was studied on as-prepared nanostructured surfaces (atop part of nanowires) and their bulk part after, first time applied, in-situ mechanical removal atop part of the formed silicon nanowires. Silicon suboxides together with disturbed silicon dioxide were found in the composition of the formed arrays that affects the electronic structure of silicon nanowires. The results obtained by us convincingly testify to the homogeneity of the phase composition of the side walls of silicon nanowires and the electronic structure in the entire length of the nanowire. The controlled formation of the silicon nanowires array may lead to smart engineering of its atomic and electronic structure that influences the exploiting strategy of metal-assisted wet-chemically etched silicon nanowires as universal matrices for different applications.

3.
Artigo em Inglês | MEDLINE | ID: mdl-26955051

RESUMO

Phylogenetic tree reconciliation is an important technique for reconstructing the evolutionary histories of species and genes and other dependent entities. Reconciliation is typically performed in a maximum parsimony framework and the number of optimal reconciliations can grow exponentially with the size of the trees, making it difficult to understand the solution space. This paper demonstrates how a small number of reconciliations can be found that collectively contain the most highly supported events in the solution space. While we show that the formal problem is NP-complete, we give a approximation algorithm, experimental results that indicate its effectiveness, and the new DTL-RnB software tool that uses our algorithms to summarize the space of optimal reconciliations (www.cs.hmc.edu/dtlrnb).


Assuntos
Algoritmos , Biologia Computacional/métodos , Modelos Genéticos , Filogenia , Software
4.
J Appl Phys ; 1242018.
Artigo em Inglês | MEDLINE | ID: mdl-31274882

RESUMO

The Zeeman splitting and degree of circular polarization (DCP) of photoluminescence (PL) from type-II submonolayer ZnTe/ZnSe quantum dots (QDs) have been investigated in magnetic fields up to 18 T. To explain the observed relative intensities and energy positions of the σ+ and the σ- PL, a non-Boltzmann distribution for holes with ultra-long spin-flip time, confined to submonolayer QDs, is proposed. The g-factor of electrons, located in the ZnSe barriers, was obtained from fitting the temperature dependence of the DCP, and its value is in excellent agreement with that of bulk ZnSe. The g-factor of type-II excitons was extracted by analyzing the Zeeman splitting, from which the g-factor of holes confined within submonolayer ZnTe QDs was found to be ~2.65 ± 0.40. This value is considerably larger than that in bulk ZnTe. Tight-binding calculations using an sp 3 s* model were employed to understand the origin of such an increase. The results of the simulation match the experiment and show that the enhancement of the hole g-factor is mostly caused by a reduced orbital contribution to Zeeman splitting arising from the submonolayer thickness of these QDs.

5.
Vestn Otorinolaringol ; 82(6): 52-59, 2017.
Artigo em Russo | MEDLINE | ID: mdl-29260783

RESUMO

There is considered modern classification of rhinitis and the accents in diagnostic and therapeutic approaches to patients with this disease are indicated, as well as the possibilities of using topical intranasal antihistamines in the treatment of allergic, vasomotor and medicamentous rhinitis.


Assuntos
Glucocorticoides/administração & dosagem , Ftalazinas , Qualidade de Vida , Rinite Alérgica Perene , Administração Intranasal , Antialérgicos/administração & dosagem , Antialérgicos/farmacocinética , Disponibilidade Biológica , Diagnóstico Diferencial , Humanos , Ftalazinas/administração & dosagem , Ftalazinas/farmacocinética , Rinite Alérgica Perene/diagnóstico , Rinite Alérgica Perene/imunologia , Rinite Alérgica Perene/psicologia , Rinite Alérgica Perene/terapia , Resultado do Tratamento
6.
Sci Rep ; 7(1): 11131, 2017 09 11.
Artigo em Inglês | MEDLINE | ID: mdl-28894162

RESUMO

Understanding the influence of changes in solar activity on Earth's climate and distinguishing it from other forcings, such as volcanic activity, remains a major challenge for palaeoclimatology. This problem is best approached by investigating how these variables influenced past climate conditions as recorded in high precision paleoclimate archives. In particular, determining if the climate system response to these forcings changes through time is critical. Here we use the Wiener-Granger causality approach along with well-established cross-correlation analysis to investigate the causal relationship between solar activity, volcanic forcing, and climate as reflected in well-established Intertropical Convergence Zone (ITCZ) rainfall proxy records from Yok Balum Cave, southern Belize. Our analysis reveals a consistent influence of volcanic activity on regional Central American climate over the last two millennia. However, the coupling between solar variability and local climate varied with time, with a regime shift around 1000-1300 CE after which the solar-climate coupling weakened considerably.

7.
Phys Rev Lett ; 118(11): 116801, 2017 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-28368634

RESUMO

In disordered systems, the hopping conductivity regime is usually realized at low temperatures where spin-related phenomena differ strongly from the cases of delocalized carriers. We develop the unified microscopic theory of current-induced spin orientation, spin-galvanic, and spin-Hall effects for the two-dimensional hopping regime. We show that the corresponding susceptibilities are proportional to each other and determined by the interplay between the drift and the diffusion spin currents. Estimations are made for realistic semiconductor heterostructures using the percolation theory. We show that the electrical spin polarization in the hopping regime increases exponentially with the increase of the concentration of localization sites and may reach a few percent at the crossover from the hopping to the diffusion conductivity regime.

8.
Nat Commun ; 7: 12576, 2016 08 30.
Artigo em Inglês | MEDLINE | ID: mdl-27573209

RESUMO

It has recently been shown that electronic states in bulk gapless HgCdTe offer another realization of pseudo-relativistic three-dimensional particles in condensed matter systems. These single valley relativistic states, massless Kane fermions, cannot be described by any other relativistic particles. Furthermore, the HgCdTe band structure can be continuously tailored by modifying cadmium content or temperature. At critical concentration or temperature, the bandgap collapses as the system undergoes a semimetal-to-semiconductor topological phase transition between the inverted and normal alignments. Here, using far-infrared magneto-spectroscopy we explore the continuous evolution of band structure of bulk HgCdTe as temperature is tuned across the topological phase transition. We demonstrate that the rest mass of Kane fermions changes sign at critical temperature, whereas their velocity remains constant. The velocity universal value of (1.07±0.05) × 10(6) m s(-1) remains valid in a broad range of temperatures and Cd concentrations, indicating a striking universality of the pseudo-relativistic description of the Kane fermions in HgCdTe.

9.
J Phys Condens Matter ; 28(5): 055503, 2016 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-26766872

RESUMO

This work aims to investigate the effects of magnetic field strength and direction on the electronic properties and optical response of GaAs/AlGaAs-based heterostructures. An investigation of the excitonic spin-splitting of a disordered multiple quantum well embedded in a wide parabolic quantum well is presented. The results for polarization-resolved photoluminescence show that the magnetic field dependencies of the excitonic spin-splitting and photoluminescence linewidth are crucially sensitive to magnetic field orientation. Our experimental results are in good agreement with the calculated Zeeman splitting obtained by the Luttinger model, which predicts a hybridization of the spin character of states in the valence band under tilted magnetic fields.

10.
Nano Lett ; 16(1): 227-31, 2016 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26636471

RESUMO

Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG) in which the real spin, orbital pseudospin, and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate QH plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only in the presence of an interlayer potential U⊥. In the phase space of U⊥ and filling factor ν, we observe an intriguing "hexagon" pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.

11.
Sci Rep ; 5: 8979, 2015 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-25759288

RESUMO

Here, we present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. Without dielectric engineering and beyond a T-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm(2)/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm(2)/Vs as T is lowered below ~150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe2 and SiO2. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe2-based FETs displaying higher room temperature mobilities, i.e. approaching those of p-doped Si, which would make it a suitable candidate for high performance opto-electronics.

12.
Izv Akad Nauk Ser Biol ; (6): 605-16, 2015.
Artigo em Russo | MEDLINE | ID: mdl-26852480

RESUMO

Shell variability of the steppe mollusk Chondrula tridens from 18 micropopulations in the forest-steppe zone of the Volga Upland was studied. It was found that larger specimens of Ch. tridens with well-developed teeth inhabit the central and eastern parts of the territory. Specimens in the northwestern part of the upland are characterized by small shells, the highest degree of roundness, and mostly reduced teeth in the mouth. The main factors that determine variability in the size and proportions of shells are the average daily temperatures increasing from the northwest to the south, the reduction in the total precipitation, the decrease in the soil moisture content, and, possibly, the increased content of carbonates in the soil.


Assuntos
Exoesqueleto/anatomia & histologia , Gastrópodes/anatomia & histologia , Fenótipo , Animais , Ecossistema , Variação Genética
13.
Nat Commun ; 5: 5656, 2014 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-25502210

RESUMO

Many physical phenomena can be understood by single-particle physics; that is, treating particles as non-interacting entities. When this fails, many-body interactions lead to spontaneous symmetry breaking and phenomena such as fundamental particles' mass generation, superconductivity and magnetism. Competition between single-particle and many-body physics leads to rich phase diagrams. Here we show that rhombohedral-stacked trilayer graphene offers an exciting platform for studying such interplay, in which we observe a giant intrinsic gap ~42 meV that can be partially suppressed by an interlayer potential, a parallel magnetic field or a critical temperature ~36 K. Among the proposed correlated phases with spatial uniformity, our results are most consistent with a layer antiferromagnetic state with broken time reversal symmetry. These results reflect the interplay between externally induced and spontaneous symmetry breaking whose relative strengths are tunable by external fields, and provide insight into other low-dimensional systems.

14.
Nat Commun ; 5: 4550, 2014 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-25078144

RESUMO

The quantum Hall effect, in which a two-dimensional sample's Hall conductivities become quantized, is a remarkable transport anomaly commonly observed at strong magnetic fields. However, it may also appear at zero magnetic field if time-reversal symmetry is broken. Charge-neutral bilayer graphene is unstable to a variety of competing and closely related broken symmetry states, some of which have non-zero quantized Hall conductivities. Here we explore those states by stabilizing them with external fields. Transport spectroscopy measurements reveal two distinct states that have two quantum units of Hall conductivity, stabilized by large magnetic and electric fields, respectively. The majority spins of both phases form a quantum anomalous Hall state, and the minority spins constitute a Kekulé state with spontaneous valley coherence for phase I and a quantum valley Hall state for phase II. Our results shed light on the rich set of competing ordered states in bilayer graphene.

15.
Phys Chem Chem Phys ; 16(36): 19394-401, 2014 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-25101924

RESUMO

The arrays of metallic nanowires are considered as promising precursors for 1D semiconductor nanostructures after appropriate treatment at temperatures close to the melting point. Therefore the melting behaviour of the metallic structures in oxide templates is a key parameter for the subsequent conversion process. The present paper focuses on understanding of the effect of mechanical stress generated during heating on the melting point of the metal nanowires deposited into the pores of anodic alumina. Extremely high local compressive stress appears due to the difference in the thermal coefficients of the oxide template and nanowires inside the pores. The effect of the composite structural parameter that may be related to the concentration of nanowires on the melting temperature has been investigated. A numerical model predicting the melting point has been developed for composites with indium, tin, and zinc nanowires. The simulation results obtained using the suggested model were compared with the experimental data.

16.
Sci Rep ; 4: 4215, 2014 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-24572993

RESUMO

Although the main Raman features of semiconducting transition metal dichalcogenides are well known for the monolayer and bulk, there are important differences exhibited by few layered systems which have not been fully addressed. WSe2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe2, MoSe2, WS2 and MoS2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E', E″ and E2g modes shift to lower frequencies, and the A'1 and A1g modes shift to higher frequencies. Second, new high frequency first order A'1 and A1g modes appear, explaining recently reported experimental data for WSe2, MoSe2 and MoS2. Third, splitting of modes around A'1 and A1g is found which explains those observed in MoSe2. Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD.

17.
Izv Akad Nauk Ser Biol ; (1): 53-64, 2014.
Artigo em Russo | MEDLINE | ID: mdl-25735157

RESUMO

A complex analysis of the food range of 15 bat species inhabiting floodplain ecosystems of the Samara Bend has been performed. It is shown that, in bats, an important component of the structuring of their communities is the division of food resources. The guild structure and position of species in the trophic space are described. Seven food guilds consisting of nonspecialized and specialized species are distinguished. It is noted that most species are characterized by a wide overlapping of their trophic niches, which may be a consequence of their weak competition in an environment that is rich in food resources.


Assuntos
Quirópteros , Ecologia , Ecossistema , Animais , Meio Ambiente , Cadeia Alimentar , Federação Russa , Especificidade da Espécie
18.
Eksp Klin Gastroenterol ; (11): 25-9, 2014.
Artigo em Russo | MEDLINE | ID: mdl-25842659

RESUMO

AIM: To perform the analysis of correlation of clinical symptoms and laboratory sings in patients of elderly and senile age with coronary heart disease depending on a blood flow condition in the pool of abdominal aorta. MATERIAL AND METHODS: Longitudinal clinical research was conducted. The register was made by 132 patients of elderly and senile age with coronary heart disease being on treatment during the period since 2013-2014. RESULTS: Results of the research of correlation of clinical symptoms and indexes of lipidemia in patients of elderly and senile age with coronary heart disease depending on a blood flow condition in the pool of abdominal aorta are performed. CONCLUSION: Specific features of the cardiovascular pathology and a course of coronary heart disease in combination with atherosclerosis of the abdominal aorta and its visceral branches are revealed.


Assuntos
Envelhecimento/patologia , Aorta Abdominal/patologia , Aorta Abdominal/fisiopatologia , Velocidade do Fluxo Sanguíneo/fisiologia , Doença das Coronárias/patologia , Doença das Coronárias/fisiopatologia , Aterosclerose/etiologia , Aterosclerose/metabolismo , Aterosclerose/patologia , Aterosclerose/fisiopatologia , Estudos de Casos e Controles , Colesterol/sangue , Doença das Coronárias/complicações , Doença das Coronárias/metabolismo , Humanos , Lipoproteínas/sangue , Triglicerídeos/sangue , Ultrassonografia Doppler
19.
Phys Rev Lett ; 111(4): 047202, 2013 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-23931402

RESUMO

We combined Raman and infrared vibrational spectroscopies with complementary lattice dynamics calculations and magnetization measurements to reveal the dynamic aspects of charge-lattice-spin coupling in Co[N(CN)2]2. Our work uncovers electron-phonon coupling as a magnetic field-driven avoided crossing of the low-lying Co2+ electronic excitation with two ligand phonons and a magnetoelastic effect that signals a flexible local CoN6 environment. Their simultaneous presence indicates the ease with which energy is transferred over multiple length and time scales in this system.

20.
Stomatologiia (Mosk) ; 92(3): 112-3, 2013.
Artigo em Russo | MEDLINE | ID: mdl-23752855

RESUMO

Dental implantation is a widespread method of oral rehabilitation by teeth loss. The purpose of the study was to evaluate patients need and awareness of dental implantation. 486 respondents were included in survey. The low level of knowledge about dental implantation was identified among patients in Saratov.


Assuntos
Implantação Dentária , Determinação de Necessidades de Cuidados de Saúde , Perda de Dente/cirurgia , Feminino , Humanos , Masculino , Pacientes , Federação Russa , Inquéritos e Questionários
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