Computational Study of Tunneling Transistor Based on Graphene Nanoribbon

Tunneling field-effect transistors (FETs) have been intensely explored recently due to its potential to address power concerns in nanoelectronics. The recently discovered graphene nanoribbon (GNR) is ideal for tunneling FETs due to its symmetric bandstructure, light effective mass, and monolayer-thin body. In this work, we examine the device physics of p-i-n GNR tunneling FETs using atomistic quantum transport simulations. The important role of the edge bond relaxation in the device characteristics is identified. The device, however, has ambipolar I-V characteristics, which are not preferred for digital electronics applications. We suggest that using either an asymmetric source-drain doping or a properly designed gate underlap can effectively suppress the ambipolar I-V. A subthreshold slope of 14mV/dec and a significantly improved on-off ratio can be obtained by the p-i-n GNR tunneling FETs

Confined Phase In The Real Time Formalism And The Fate Of The World Behind The Horizon

In the real time formulation of finite temperature field theories, one introduces an additional set of fields (type-2 fields) associated to each field in the original theory (type-1 field). In hep-th/0106112, in the context of the AdS-CFT correspondence, Maldacena interpreted type-2 fields as living on a boundary behind the black hole horizon. However, below the Hawking-Page transition temperature, the thermodynamically preferred configuration is the thermal AdS without a black hole, and hence there are no horizon and boundary behind it. This means that when the dual gauge theory is in confined phase, the type-2 fields cannot be associated with the degrees of freedom behind the black hole horizon. I argue that in this case the role of the type-2 fields is to make up bulk type-2 fields of classical closed string field theory on AdS at finite temperature in the real time formalism.Comment: v2: cases divided into sections with more detailed explanations. considerably enlarged with examples and a lot of figures. sec 4.1.2 for general closed cut-out circuits and appendix A for a sample calculation newly added. many minor corrections and clarifying comments. refs added. v3: refs and related discussion added. 1+46 pages, 26 figures. published versio

A Phenomenological Description of the Non-Fermi-Liquid Phase of MnSi

In order to understand the non-Fermi-liquid behavior of MnSi under pressure we propose a scenario on the basis of the multispiral state of the magnetic moment. This state can describe the recent critical experiment of the Bragg sphere in the neutron scattering which is the key ingredient of the non-Fermi-liquid behavior.Comment: 3 page

Exact 4-point Scattering Amplitude of the Superconformal Schrodinger Chern-Simons Theory

We consider the non-relativistic superconformal U(N) X U(N) Chern-Simons theory with level (k,-k) possessing fourteen supersymmetries. We obtain an exact four-point scattering amplitude of the theory to all orders in 1/N and 1/k and prove that the scattering amplitude becomes trivial when k=1 and 2. We confirm this amplitude to one-loop order by using an explicit field theoretic computation and show that the beta function for the contact interaction vanishes to the one-loop order, which is consistent with the quantum conformal invariance of the underlying theory.Comment: 16 page

Bogoliubov-de Gennes study of trapped spin-imbalanced unitary Fermi gases

It is quite common that several different phases exist simultaneously in a system of trapped quantum gases of ultra-cold atoms. One such example is the strongly-interacting Fermi gas with two imbalanced spin species, which has received a great amount of attention due to the possible presence of exotic superfluid phases. By employing novel numerical techniques and algorithms, we self-consistently solve the Bogoliubov de-Gennes equations, which describe Fermi superfluids in the mean-field framework. From this study, we investigate the novel phases of spin-imbalanced Fermi gases and examine the validity of the local density approximation (LDA), which is often invoked in the extraction of bulk properties from experimental measurements within trapped systems. We show how the validity of the LDA is affected by the trapping geometry, number of atoms and spin imbalance.Comment: 15 pages, 5 figures, to be published in New J. Phys. (focus issue on "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas"

Anomalies and the chiral magnetic effect in the Sakai-Sugimoto model

In the chiral magnetic effect an imbalance in the number of left- and right-handed quarks gives rise to an electromagnetic current parallel to the magnetic field produced in noncentral heavy-ion collisions. The chiral imbalance may be induced by topologically nontrivial gluon configurations via the QCD axial anomaly, while the resulting electromagnetic current itself is a consequence of the QED anomaly. In the Sakai-Sugimoto model, which in a certain limit is dual to large-N_c QCD, we discuss the proper implementation of the QED axial anomaly, the (ambiguous) definition of chiral currents, and the calculation of the chiral magnetic effect. We show that this model correctly contains the so-called consistent anomaly, but requires the introduction of a (holographic) finite counterterm to yield the correct covariant anomaly. Introducing net chirality through an axial chemical potential, we find a nonvanishing vector current only before including this counterterm. This seems to imply the absence of the chiral magnetic effect in this model. On the other hand, for a conventional quark chemical potential and large magnetic field, which is of interest in the physics of compact stars, we obtain a nontrivial result for the axial current that is in agreement with previous calculations and known exact results for QCD.Comment: 35 pages, 4 figures, v2: added comments about frequency-dependent conductivity at the end of section 4; references added; version to appear in JHE

Holographic zero sound at finite temperature in the Sakai-Sugimoto model

In this paper, we study the fate of the holographic zero sound mode at finite temperature and non-zero baryon density in the deconfined phase of the Sakai-Sugimoto model of holographic QCD. We establish the existence of such a mode for a wide range of temperatures and investigate the dispersion relation, quasi-normal modes, and spectral functions of the collective excitations in four different regimes, namely, the collisionless quantum, collisionless thermal, and two distinct hydrodynamic regimes. For sufficiently high temperatures, the zero sound completely disappears, and the low energy physics is dominated by an emergent diffusive mode. We compare our findings to Landau-Fermi liquid theory and to other holographic models.Comment: 1+24 pages, 19 figures, PDFTeX, v2: some comments and references added, v3: some clarifications relating to the different regimes added, matches version accepted for publication in JHEP, v4: corrected typo in eq. (3.18

ВИКОРИСТАННЯ НЕЙРОКІНЕМАТОГРАФА В ПІСЛЯДИПЛОМНІЙ ОСВІТІ В УМОВАХ ДИСТАНЦІЙНОГО НАВЧАННЯ

In the face of COVID-19 pandemic, the postgraduate education has been changed due to distance learning. Using Microsoft Teams program, the interns and students of the Department of Neurology and Neurosurgery of Odesa National Medical University continue to study neurology. Analysis of case studies after watching a neurocinema, training in making the diagnosis and administration of treatment are in complement to the forced lacking of clinical practice. Neurocinema provides the opportunity for addressing a broad range of diseases, for instance, stroke, traumatic brain injury, traumatic spinal cord injury, multiple sclerosis, amyotrophic lateral sclerosis, epilepsy, Parkinson’s disease, Alzheimer’s disease etc. A modern approach with the watchful guidance of teachers and the possibility of a discussion in real-time increases the activity and interest of interns and students.В умовах пандемії COVID-19 отримання післядипломної освіти змінилося завдяки дистанційному навчанню. Використовуючи програму відеоконференц-звʼязку Microsoft Teams, на кафедрі неврології та нейрохірургії Одеського національного медичного університету інтерни-невропатологи й студенти активно продовжують вивчення неврології. Розбір клінічних випадків після перегляду фільмів, що присвячені неврологічним хворим, тренування у виставленні функціонального та клінічного діагнозів й призначенні лікування доповнюють вимушену нестачу практики з пацієнтами. Нейрокінематограф дозволяє широко охопити такі хвороби, як інсульт, черепно-мозкова травма, хребетно-спинномозкова травма, розсіяний склероз, боковий аміотрофічний склероз, епілепсія, хвороба Паркінсона, хвороба Альцгеймера та ін. Такий сучасний підхід з пильним керівництвом викладачів і можливістю дискусії у режимі реального часу збільшує активність, зацікавленість лікарів-інтернів та студентів

Electronic and Magnetic Properties of Partially-Open Carbon Nanotubes

On the basis of the spin-polarized density functional theory calculations, we demonstrate that partially-open carbon nanotubes (CNTs) observed in recent experiments have rich electronic and magnetic properties which depend on the degree of the opening. A partially-open armchair CNT is converted from a metal to a semiconductor, and then to a spin-polarized semiconductor by increasing the length of the opening on the wall. Spin-polarized states become increasingly more stable than nonmagnetic states as the length of the opening is further increased. In addition, external electric fields or chemical modifications are usable to control the electronic and magnetic properties of the system. We show that half-metallicity may be achieved and the spin current may be controlled by external electric fields or by asymmetric functionalization of the edges of the opening. Our findings suggest that partially-open CNTs may offer unique opportunities for the future development of nanoscale electronics and spintronics.Comment: 6 figures, to appear in J. Am. Chem. So