841 research outputs found
Density of states and zero Landau level probed through capacitance of graphene
We report capacitors in which a finite electronic compressibility of graphene
dominates the electrostatics, resulting in pronounced changes in capacitance as
a function of magnetic field and carrier concentration. The capacitance
measurements have allowed us to accurately map the density of states D, and
compare it against theoretical predictions. Landau oscillations in D are robust
and zero Landau level (LL) can easily be seen at room temperature in moderate
fields. The broadening of LLs is strongly affected by charge inhomogeneity that
leads to zero LL being broader than other levels
ABOUT COMMON AND THEORETICAL INFORMATICS
In this article are considered the integrant importance of informatics and informational technologys includes the sciences and the humanities.There are a differences between scientifi c grounds of the various information orientations, which include physical informatics, bioinfomatics, technical and social informatics. Creation of a united theoretical base for these orientations is very problematical. The metodologically important issue of classifi cation different informatics is a part of the general informatics, the example of which are considered here
CLASSIFICATION OF INFORMATICS AND INFORMATION TECHNOLOGIES
The article considers the actual question about informatics and information technologies classifi cation. There are the hegemony information technologies over the information sciences and two modern methods of classifi cation: “habitatual” and “conceptual-criterial” method. On the basis of the last the article calls attention to example for classifi cation of science’s nomenclature of VAK
How close can one approach the Dirac point in graphene experimentally?
The above question is frequently asked by theorists who are interested in
graphene as a model system, especially in context of relativistic quantum
physics. We offer an experimental answer by describing electron transport in
suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with
the onset of Landau quantization occurring in fields below 5 mT. The observed
charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state
with a few charge carriers per entire micron-scale device. Above liquid helium
temperatures, the electronic properties of such devices are intrinsic, being
governed by thermal excitations only. This yields that the Dirac point can be
approached within 1 meV, a limit currently set by the remaining charge
inhomogeneity. No sign of an insulating state is observed down to 1 K, which
establishes the upper limit on a possible bandgap
Prospects for the discovery of the next new element: Influence of projectiles with Z > 20
The possibility of forming new superheavy elements with projectiles having Z
> 20 is discussed. Current research has focused on the fusion of 48Ca with
actinides targets, but these reactions cannot be used for new element
discoveries in the future due to a lack of available target material. The
influence on reaction cross sections of projectiles with Z > 20 have been
studied in so-called analog reactions, which utilize lanthanide targets
carefully chosen to create compound nuclei with energetics similar to those
found in superheavy element production. The reactions 48Ca, 45Sc, 50Ti, 54Cr +
159Tb, 162Dy have been studied at the Cyclotron Institute at Texas A&M
University using the Momentum Achromat Recoil Spectrometer. The results of
these experimental studies are discussed in terms of the influence of
collective enhancements to level density for compound nuclei near closed
shells, and the implications for the production of superheavy elements. We have
observed no evidence to contradict theoretical predictions that the maximum
cross section for the 249Cf(50Ti, 4n)295120 and 248Cm(54Cr, 4n)298120 reactions
should be in the range of 10-100 fb.Comment: An invited talk given by Charles M. Folden III at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. Also contains information presented by
Dmitriy A. Mayorov and Tyler A. Werke in separate contributions to the
conference. This contribution will appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Cosmic ray tests of the D0 preshower detector
The D0 preshower detector consists of scintillator strips with embedded
wavelength-shifting fibers, and a readout using Visible Light Photon Counters.
The response to minimum ionizing particles has been tested with cosmic ray
muons. We report results on the gain calibration and light-yield distributions.
The spatial resolution is investigated taking into account the light sharing
between strips, the effects of multiple scattering and various systematic
uncertainties. The detection efficiency and noise contamination are also
investigated.Comment: 27 pages, 24 figures, submitted to NIM
Intermediate result of negative consequences of the epidemic of the new coronavirus infection for the global economy
The epidemic of the new SARS-CoV-2 coronavirus infection slowed global economic growth and became the main threat for the global economy and financial markets in 2020. Authorities in many countries around the world have declared a health emergency. Without the experience of state quarantine, countries have faced negative consequences for citizens, the economy and financial market participants. The introduction of temporary regulatory easing in the context of the spread of a new coronavirus infection assisted to partially limit the negative consequences. The next few months will, probably, have a particularly strong impact on small business, as government support schemes are reduced or ceased. The article reveals the main consequences of the new coronavirus infection for the global economy
Quantum electrodynamics with anisotropic scaling: Heisenberg-Euler action and Schwinger pair production in the bilayer graphene
We discuss quantum electrodynamics emerging in the vacua with anisotropic
scaling. Systems with anisotropic scaling were suggested by Horava in relation
to the quantum theory of gravity. In such vacua the space and time are not
equivalent, and moreover they obey different scaling laws, called the
anisotropic scaling. Such anisotropic scaling takes place for fermions in
bilayer graphene, where if one neglects the trigonal warping effects the
massless Dirac fermions have quadratic dispersion. This results in the
anisotropic quantum electrodynamics, in which electric and magnetic fields obey
different scaling laws. Here we discuss the Heisenberg-Euler action and
Schwinger pair production in such anisotropic QEDComment: 5 pages, no figures, JETP Letters style, version accepted in JETP
Letter
Graphene nanoribbons with zigzag and armchair edges prepared by scanning tunneling microscope lithography on gold substrates
The properties of graphene nanoribbons are dependent on both the nanoribbon width and the crystallographic orientation of the edges. Scanning tunneling microscope lithography is a method which is able to create graphene nanoribbons with well defined edge orientation, having a width of a few nanometers. However, it has only been demonstrated on the top layer of graphite. In order to allow practical applications of this powerful lithography technique, it needs to be implemented on single layer graphene. We demonstrate the preparation of graphene nanoribbons with well defined crystallographic orientation on top of gold substrates. Our transfer and lithography approach brings one step closer the preparation of well defined graphene nanoribbons on arbitrary substrates for nanoelectronic applications
PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy
The satellite-borne experiment PAMELA has been used to make a new measurement
of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which
extends previously published measurements down to 60 MeV and up to 180 GeV in
kinetic energy. During 850 days of data acquisition approximately 1500
antiprotons were observed. The measurements are consistent with purely
secondary production of antiprotons in the galaxy. More precise secondary
production models are required for a complete interpretation of the results.Comment: 11 pages, 3 figures, 1 table. Accepted for publication in Physical
Review Letter
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