Size quantization of Dirac fermions in graphene constrictions

Quantum point contacts (QPCs) are cornerstones of mesoscopic physics and central building blocks for quantum electronics. Although the Fermi wave-length in high-quality bulk graphene can be tuned up to hundreds of nanometers, the observation of quantum confinement of Dirac electrons in nanostructured graphene systems has proven surprisingly challenging. Here we show ballistic transport and quantized conductance of size-confined Dirac fermions in lithographically-defined graphene constrictions. At high charge carrier densities, the observed conductance agrees excellently with the Landauer theory of ballistic transport without any adjustable parameter. Experimental data and simulations for the evolution of the conductance with magnetic field unambiguously confirm the identification of size quantization in the constriction. Close to the charge neutrality point, bias voltage spectroscopy reveals a renormalized Fermi velocity ($v_F \approx 1.5 \times 10^6 m/s$) in our graphene constrictions. Moreover, at low carrier density transport measurements allow probing the density of localized states at edges, thus offering a unique handle on edge physics in graphene devices.Comment: 24 pages including 20 figures and 1 table. Corrected typos. To appear in Nature Communication

Electrostatically Confined Monolayer Graphene Quantum Dots with Orbital and Valley Splittings

The electrostatic confinement of massless charge carriers is hampered by Klein tunneling. Circumventing this problem in graphene mainly relies on carving out nanostructures or applying electric displacement fields to open a band gap in bilayer graphene. So far, these approaches suffer from edge disorder or insufficiently controlled localization of electrons. Here we realize an alternative strategy in monolayer graphene, by combining a homogeneous magnetic field and electrostatic confinement. Using the tip of a scanning tunneling microscope, we induce a confining potential in the Landau gaps of bulk graphene without the need for physical edges. Gating the localized states toward the Fermi energy leads to regular charging sequences with more than 40 Coulomb peaks exhibiting typical addition energies of 7-20 meV. Orbital splittings of 4-10 meV and a valley splitting of about 3 meV for the first orbital state can be deduced. These experimental observations are quantitatively reproduced by tight binding calculations, which include the interactions of the graphene with the aligned hexagonal boron nitride substrate. The demonstrated confinement approach appears suitable to create quantum dots with well-defined wave function properties beyond the reach of traditional techniques

Expert Assessment of a Ratio of Expenses at Construction of Oil Transport Infrastructure in the Arctic

When assessing the cost of construction and operation of transport infrastructure in the early stages of the investment process, there is a problem in the formalization of some indicators of the factors influencing decision-making. The temporary impossibility to express them in monetary or comparable natural quantities leads to uncertainty in the ratio between these two groups of factors. On the example of one of the discussed objects of oil transport infrastructure in the territory of the Russian Arctic, quantitative estimates of such uncertainties are obtained, the value of which was very weighty and variable depending on the considered alternative. The authors propose an approach based on the vector representation of factors, fuzzy set theory and expert estimates, which allows developing a criterion of the limit value of uncertainty, allowing making management decisions in the problems of choice. The corresponding model giving the possibility of calculation of such criterion is constructed

Разработка композиции на основе полимочевины с увеличенным сроком жизни

Objectives. Improvement of the technology for obtaining polymer-sprayed coatings based on polycarbodiimides (polyureas) with high chemical, hydrolytic, and abrasive resistance and improved physical and mechanical properties, as well as obtainment of polyurea compositions with a lifetime of at least 5 min without loss performance characteristics (i.e., “hand-applied” polyureas) suitable for repair of coatings already in use.Methods. The reaction rate between isocyanate and amino groups is almost a hundred times higher than that between isocyanate and hydroxyl groups, necessitating the use of special highperformance and high-pressure installations equipped with self-cleaning mixing chambers and heating of components. The following are determined from the obtained materials: strength, elongation at break according to the standard method, Taber abrasion, and Shore hardness.Results. Three methods of slowing down the reaction are investigated: 1) the synthesis of prepolymers with the content of NCO groups from 10.5% to 18%; 2) the addition of a plasticizer into the prepolymer in the amount of 1–10 mass parts; and 3) the introduction of polyesters into the composition and radiation of the so-called “hybrid” systems. When using 14% polyesters with a molecular weight of 2000 Da, only “hybrid” systems make it possible to obtain compositions with a lifetime of more than 5 min. At the same time, the tensile strength decreases by 20%, and the abrasion increases by 40%; however, such “hybrid” systems have a higher adhesion force and are cheaper than pure polyureas, allowing them to be used as “repair” systems.Conclusions. The developed composition and technology of applying “hybrid” systems allow for the repair of existing coatings without using specialized devices. “Manual” polyurea is easy to use and does not require special training. Цели. Совершенствование технологии получения полимерных напыляемых покрытий на основе поликарбодиимидов (полимочевин), с высокой химической, гидролитической и абразивной стойкостью и улучшенными физико-механическими показателями, а также, получение полимочевинных композиций с временем жизни не менее 5 мин без потери эксплуатационных характеристик (полимочевин «ручного» нанесения), пригодных для ремонта уже эксплуатирующихся покрытий.Методы. Скорость реакции между изоцианатными и аминогруппами практически в сто раз превышает скорость реакции между изоцианатными и гидроксильными группами, что вызывает необходимость использовать специальные высокопроизводительные установки высокого давления, оснащенные самоочищающимися смесительными камерами и обогревом компонентов. У полученных материалов определяли прочность, удлинение на разрыв по стандартной методике, истираемость по Таберу и твердость по Шору.Результаты. Исследованы три способа замедления реакции: во-первых, синтез предполимеров с содержанием NCO-групп от 10.5% до 18%; во-вторых, введение в предполимер пластификатора в количестве 1–10 масс.ч.; в-третьих, введение в композицию полиэфиров и получения «гибридных» систем. Показано, что только «гибридные» системы при использовании полиэфиров с молекулярной массой 2000 Да, в количестве 14% позволяют получить композиции с временем жизни более 5 мин. При этом прочность на разрыв снижается на 20%, истираемость увеличивается на 40%, но такие «гибридные» системы имеют более высокую силу адгезии и дешевле по сравнению с чистыми полимочевинами, что позволяет использовать их в качестве «ремонтных» систем.Выводы. Разработанный состав и технология нанесения «гибридных» систем позволяют производить ремонтные работы существующих покрытий без применения специализированных устройств. Полимочевина «ручного» нанесения удобна в эксплуатации и не требует специальной подготовки.

Morphometric characteristics of effects induced by <i>Ensifer meliloti</i> lipopolysaccharide fractions on parenchymatous organs in laboratory rats with secondary immunodeficiency

Introduction. Gram-negative bacteria-derived lipopolysaccharides (LPS) are better known as bacterial endotoxins. However, an increasing body of evidence has been accumulated regarding a whole range of LPS-bound physiological effects also observed in normal settings. In particular, LPS derived from some bacterial species was shown to exhibit an immunomodulating activity.Study objective — to characterize physiological effects of Ensifer meliloti lipopolysaccharides in modelled rat induced immunodeficiency.Materials and methods. Biological activity of intraperitoneally administered E. meliloti LPS fractions was studied for 21 days in 60 outbred male rats after induction of a minimal immunodeficiency state 24 hours later after inoculating cytostatic agent cyclophosphamide (CF). Animals were euthanized on day 22 followed by conducting an autopsy and morphometric study of internal organs. Later, paraffin-embedded sections of parenchymal organs were stained with hematoxylin-eosin and examined histologically by light microscopy.Results. It was found that at the end of the experiment cyclophosphamide applied to laboratory animals insignificantly decreased weight of liver and kidney, but not that of heart and spleen (compared to intact animals). In contrast, lung weight was solely significantly increased in immunodeficient rats compared to control. Intraperitoneally administered LPS fractions during secondary immunodeficiency affected weight parameters in the liver and kidney as the most intensively blood supplied organs suggesting its systemic effects. Quantity of follicles with large germinal centers as well as secondary follicles and lymphatic sheath formation in splenic stroma was increased that features activated immune response. Moreover, hepatic lymphoid infiltration in the portal tracts and reversal to normal vascular pattern were found as well. In contrast, LPS and Licopid administered to rats resulted in marked lung hyperplasia of lymphoid tissue containing large germinal centers.Conclusion. The data obtained indicate that E. meliloti-derived LPS fractions administered to rats with secondary immunodeficiency positively affected immunoreactivity

Pecularities of infringements of behaviour with runaways and vagrancy at children with the of attention-deficit and hyperactivity disorder

The presented study includes 122 teenagers with runaway and vagrancy syndrome by clinical-psychopathological and clinical-dynamic methods. It was defined that children with the socialized behavior disorder, accompanied with vagrancy at preschool age, revealed the signs of Attention-Deficit/Hyperactivity Disorder (ADHD). Two variants of behavioral features of ADHD were allocated. The first variant is affective-behavioral, with the prevalence of affective reactions and oppositional disorder. The second one is infantile-behavioral with the domination of personal immaturity, hyperactivity and neuropathic symptoms. The characteristic of vagrancy at children with affective-behavioral variant reflected their reactive type, and at children with infantile-behavioral - a group one, with propensity to unmotivated runaways, connected with pathology. It was find out that the combination of oppositional behavior and hyperactivity turned to be a risk factor of the development of personal dissocial disorder. And a combination of infantility signs with hyperactivity and neuropathic symptoms formed a disharmonious type of the person with unstable characteristics. Allocation of the presented features of ADHD current allows to predict the development of the socialized behavior disorder and to optimize medical rehabilitation actions already at preschool age.Изучено 284 подростка с уходами и бродяжничеством клинико-психопатологическим, клинико-динамическим и клинико­анамнестическим методами. Определено, что у детей с социализированным расстройством поведения, сопровождающимся уходами и бродяжничеством в дошкольном возрасте выявлены признаки СДВГ. Выделено два типа поведенческих особенностей СДВГ в дошкольном возрасте. Первый вариант аффективно-поведенческий, с преобладанием аффективных реакций и оппозиционного расстройства. Второй вариант - инфантильно-поведенческий с превалированием личностной незрелости, гиперактивности и симптомов невропатии. Характеристика уходов у детей с аффективно-поведенческим вариантом отражала их реактивный тип, а у детей с инфантильно-поведенческим, групповой, со склонностью к «безмотивным» уходам, связанных с патологией влечений. Установлено, что сочетание оппозиционного поведения с гиперактивностью является фактором риска развития диссоциального расстройства личности. А сочетание признаков инфантилизма с гиперактивностью и невропатической симптоматикой формируют дисгармоничный тип личности с неустойчивыми чертами. Выделение представленных особенностей течения СДВГ позволяет прогнозировать развитие социализированного расстройства поведения и оптимизировать лечебно-реабилитационные мероприятия уже в дошкольном возрасте

Large tunable valley splitting in edge-free graphene quantum dots on boron nitride

Coherent manipulation of binary degrees of freedom is at the heart of modern quantum technologies. Graphene offers two binary degrees: the electron spin and the valley. Efficient spin control has been demonstrated in many solid state systems, while exploitation of the valley has only recently been started, yet without control on the single electron level. Here, we show that van-der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control. We use a graphene quantum dot induced by the tip of a scanning tunneling microscope and demonstrate valley splitting that is tunable from -5 to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts the range of controlled valley splitting by about one order of magnitude. The tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits