Quantum transport thermometry for electrons in graphene

We propose a method of measuring the electron temperature $T_e$ in mesoscopic conductors and demonstrate experimentally its applicability to micron-size graphene devices in the linear-response regime ($T_e\approx T$, the bath temperature). The method can be {especially useful} in case of overheating, $T_e>T$. It is based on analysis of the correlation function of mesoscopic conductance fluctuations. Although the fluctuation amplitude strongly depends on the details of electron scattering in graphene, we show that $T_e$ extracted from the correlation function is insensitive to these details.Comment: 4 pages, 4 figures; final version, as publishe

Dirac fermions in a power-law-correlated random vector potential

We study localization properties of two-dimensional Dirac fermions subject to a power-law-correlated random vector potential describing, e.g., the effect of "ripples" in graphene. By using a variety of techniques (low-order perturbation theory, self-consistent Born approximation, replicas, and supersymmetry) we make a case for a possible complete localization of all the electronic states and compute the density of states.Comment: Latex, 4+ page

Observation of dipole-mode vector solitons

We report on the first experimental observation of a novel type of optical vector soliton, a {\em dipole-mode soliton}, recently predicted theoretically. We show that these vector solitons can be generated in a photorefractive medium employing two different processes: a phase imprinting, and a symmetry-breaking instability of a vortex-mode vector soliton. The experimental results display remarkable agreement with the theory, and confirm the robust nature of these radially asymmetric two-component solitary waves.Comment: 4 pages, 8 figures; pictures in the PRL version are better qualit

Instabilities of Higher-Order Parametric Solitons. Filamentation versus Coalescence

We investigate stability and dynamics of higher-order solitary waves in quadratic media, which have a central peak and one or more surrounding rings. We show existence of two qualitatively different behaviours. For positive phase mismatch the rings break up into filaments which move radially to initial ring. For sufficient negative mismatches rings are found to coalesce with central peak, forming a single oscillating filament.Comment: 5 pages, 7 figure

Tunable metal-insulator transition in double-layer graphene heterostructures

We report a double-layer electronic system made of two closely-spaced but electrically isolated graphene monolayers sandwiched in boron nitride. For large carrier densities in one of the layers, the adjacent layer no longer exhibits a minimum metallic conductivity at the neutrality point, and its resistivity diverges at low temperatures. This divergence can be suppressed by magnetic field or by reducing the carrier density in the adjacent layer. We believe that the observed localization is intrinsic for neutral graphene with generic disorder if metallic electron-hole puddles are screened out

Факторы риска и механизмы развития частой респираторной заболеваемости у детей

Summary. The aim of the study was to investigate risk factors of high respiratory morbidity in preschool children with frequent respiratory infection episodes. Medical records of 95 children with frequent respiratory infections and of 30 healthy children and questioning of their parents were retrospectively analyzed. The results demonstrated that most significant risk factors of frequent respiratory infection episodes were obstetric and gynecological morbidity of the child's mother, metabolic and dystrophic disorders in children, presence of smokers in the family. Investigation of local and systemic defensive mechanisms revealed decreased serum immunoglobulin A and INF-γ levels and elevated concentrations of IL-4 and TNF-α. Increased concentration of nitrates / nitrites in exhaled breath condensate was also found. A direct correlation was found between concentration of nitric oxide metabolites in exhaled breath condensate and IL-4 level in the serum; an inverse relationship was found between the former parameter and INF-γ level in the blood serum.Резюме. С целью изучения анамнестических факторов риска у детей дошкольного возраста с частой респираторной заболеваемостью проведены ретроспективный анализ амбулаторных карт, анкетирование родителей. Всего проанализирован анамнез 95 часто болеющих и 30 здоровых детей. Показано, что наиболее значимыми факторами риска развития частой респираторной заболеваемости являются отягощенный акушерский и генеалогический анамнез, обменно-дистрофические нарушения у ребенка, наличие курения в семье. При исследовании особенностей местных и системных реакций защиты установлено уменьшение количества иммуноглобулина А, увеличение концентрации интерлейкина-4 (IL-4), фактора некроза опухоли-α и снижение интерферона-γ (INF-γ) в сыворотке крови, увеличение концентрации нитратов / нитритов в конденсате выдыхаемого воздуха. Установлено, что концентрация метаболитов оксида азота в конденсате выдыхаемого воздуха имеет прямую зависимость с содержанием IL-4 и обратную связь с уровнем INF-γ в сыворотке крови

Nonlinear Waves in Bose-Einstein Condensates: Physical Relevance and Mathematical Techniques

The aim of the present review is to introduce the reader to some of the physical notions and of the mathematical methods that are relevant to the study of nonlinear waves in Bose-Einstein Condensates (BECs). Upon introducing the general framework, we discuss the prototypical models that are relevant to this setting for different dimensions and different potentials confining the atoms. We analyze some of the model properties and explore their typical wave solutions (plane wave solutions, bright, dark, gap solitons, as well as vortices). We then offer a collection of mathematical methods that can be used to understand the existence, stability and dynamics of nonlinear waves in such BECs, either directly or starting from different types of limits (e.g., the linear or the nonlinear limit, or the discrete limit of the corresponding equation). Finally, we consider some special topics involving more recent developments, and experimental setups in which there is still considerable need for developing mathematical as well as computational tools.Comment: 69 pages, 10 figures, to appear in Nonlinearity, 2008. V2: new references added, fixed typo

Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineering

Among many remarkable qualities of graphene, its electronic properties attract particular interest due to a massless chiral character of charge carriers, which leads to such unusual phenomena as metallic conductivity in the limit of no carriers and the half-integer quantum Hall effect (QHE) observable even at room temperature [1-3]. Because graphene is only one atom thick, it is also amenable to external influences including mechanical deformation. The latter offers a tempting prospect of controlling graphene's properties by strain and, recently, several reports have examined graphene under uniaxial deformation [4-8]. Although the strain can induce additional Raman features [7,8], no significant changes in graphene's band structure have been either observed or expected for realistic strains of approx. 10% [9-11]. Here we show that a designed strain aligned along three main crystallographic directions induces strong gauge fields [12-14] that effectively act as a uniform magnetic field exceeding 10 T. For a finite doping, the quantizing field results in an insulating bulk and a pair of countercirculating edge states, similar to the case of a topological insulator [15-20]. We suggest realistic ways of creating this quantum state and observing the pseudo-magnetic QHE. We also show that strained superlattices can be used to open significant energy gaps in graphene's electronic spectrum