389 research outputs found
Decision making modeling in port operation management
Сформулированы новые подходы к улучшению системы управления и организации работы портовой инфраструктуры с применением моделирования процессов управления работы порта, направленных на повышение уровня организации и эффективности функционирования систем управления и обработки транспортных средств в морских портах
Estimating the First-year Corrosion Losses of Structural Metals for Continental Regions of the World
The knowledge of the first-year corrosion losses of metals (K1) in various regions of the world is of great importance in engineering applications. The K1 values are used to determine the categories of atmospheric corrosivity, and K1 is also the main parameter in models for the prediction of long-term corrosion losses of metals. In the absence of experimental values of K1, their values can be predicted on the basis of meteorological and aerochemical parameters of the atmosphere using the dose-response functions (DRF). Currently, the DRFs presented in ISO 9223:2012(E) /1/ standard are used for predicting K1 in any region of the world, along with the unified DRFs /2/ and the new DRFs /3/. The predicted values of corrosion losses (K1pr) of carbon steel, zinc, copper and aluminum obtained by various DRFs for various continental regions of the world are presented. In this work we used the atmosphere corrosivity parameters and experimental data on the corrosion losses of metals for the first year of exposure (K1exp) for the locations of the tests performed under the international UN/ECE program, the MICAT project, and the Russian program. For the first time, a comparative assessment of the reliability of various DRFs is given by comparing the values of K1pr and K1ex using graphical and statistical methods. The statistical indicators of reliability of predicting the corrosion losses of metals are calculated for various categories of atmosphere corrosivity. It is shown that the new dose-response functions offer the highest reliability for all categories of atmosphere corrosivity
Thermoelectric prospects of nanomaterials with spin-orbit surface bands
Nanostructured composites and nanowire arrays of traditional thermoelectrics
like Bi, Bi(1-x)Sb(x) and Bi(2)Te(3) have metallic Rashba surface spin-orbit
bands featuring high mobilities rivaling that of the bulk for which topological
insulator behavior has been proposed. Nearly pure surface electronic transport
has been observed at low temperatures in Bi nanowires with diameter around the
critical diameter, 50 nm, for the semimetal-to semiconductor transition. The
surface contributes strongly to the thermopower, actually dominating for
temperatures T < 100 K in these nanowires. The surface thermopower was found to
be -1 T microvolt/(K^2), a value that is consistent with theory. We show that
surface electronic transport together with boundary phonon scattering leads to
enhanced thermoelectric performance at low temperatures of Bi nanowire arrays.
We compare with bulk n-BiSb alloys, optimized CsBi(4)Te(6) and optimized
Bi(2)Te(3). Surface dominated electronic transport can be expected in
nanomaterials of the other traditional thermoelectrics.Comment: 18 pages, 3 figure
Surface state band mobility and thermopower in semiconducting bismuth nanowires
Many thermoelectrics like Bi exhibit Rashba spin-orbit surface bands for
which topological insulator behavior consisting of ultrahigh mobilities and
enhanced thermopower has been predicted. Bi nanowires realize surface-only
electronic transport since they become bulk insulators when they undergo the
bulk semimetal-semiconductor transition as a result of quantum confinement for
diameters close to 50 nm. We studied 20-, 30-, 50- and 200-nm trigonal Bi
wires. Shubnikov-de Haas magnetoresistance oscillations caused by surface
electrons and bulklike holes enable the determination of their densities and
mobilities. Surface electrons have high mobilities exceeding 2(m^2)/(Vsec) and
contribute strongly to the thermopower, dominating for temperatures T< 100 K.
The surface thermopower is - 1.2 T microvolt/(K^2), a value that is consistent
with theory, raising the prospect of developing nanoscale thermoelectrics based
on surface bands.Comment: 19 pages. 3 figure
Observation of three-dimensional behavior in surface states of bismuth nanowires and the evidence for bulk Bi charge fractionalization
Whereas bulk bismuth supports very-high mobility, light, Dirac electrons and
holes in its interior, its boundaries support a layer of heavy electrons in
surface states formed by spin orbit interaction in the presence of the surface
electric field. Small diameter d trigonal Bi nanowires (30 nm < d < 200 nm)
were studied via magnetotransport at low temperatures and for fields up to 14 T
in order to investigate the role of surfaces in electronic transport. A
two-dimensional behavior was expected for surface charges; however we found
instead a three-dimensional behavior, with a rich spectrum of Landau levels in
a nearly spherical Fermi surface. This is associated with the long penetration
length of surface states of trigonal wires. The prospect of the participation
of surface transport and surface-induced relaxation of bulk carriers in the
electronic properties of macroscopic samples is evaluated. We show that recent
observations of magnetoquantum peaks in the Nernst thermopower coefficient,
attributed to two-dimensional electron gas charge fractionalization, can be
more plausibly interpreted in terms of these surface states.Comment: 14 pages, 3 figure
Quantum interference of surface states in bismuth nanowires probed by the Aharonov-Bohm oscillatory behavior of the magnetoresistance
We report the observation of a dependence of the low temperature resistance
of individual single-crystal bismuth nanowires on the Aharonov-Bohm phase of
the magnetic flux threading the wire. 55 and 75-nm wires were investigated in
magnetic fields of up to 14 T. For 55 nm nanowires, longitudinal
magnetoresistance periods of 0.8 and 1.6 T that were observed at magnetic
fields over 4 T are assigned to h/2e to h/e magnetic flux modulation. The same
modes of oscillation were observed in 75-nm wires. The observed effects are
consistent with models of the Bi surface where surface states give rise to a
significant population of charge carriers of high effective mass that form a
highly conducting tube around the nanowire. In the 55-nm nanowires, the Fermi
energy of the surface band is estimated to be 15 meV. An interpretation of the
magnetoresistance oscillations in terms of a subband structure in the surface
states band due to quantum interference in the tube is presented.Comment: 30 pages, 9 figure
Experimental study of a possible role of the scrape off layer radial electric field in determining H-mode confinement properties on ASDEX Upgrade
Optoelectronic Inactivity of Dislocations in Cu In,Ga Se2 Thin Films
High efficiency Cu In,Ga Se2 CIGS thin film solar cells are based on poly crystalline CIGS absorber layers, which contain grain boundaries, stacking faults, and dislocations. While planar defects in CIGS layers have been investigated extensively, little is still known about the impact of dislocations on optoelectronic properties of CIGS absorbers. Herein, evidence for an optoelectronic inactivity of dislocations in these thin films is given, in contrast to the situation at grain boundaries. This unique behavior is explained by the extensive elemental redis tribution detected around dislocation cores, which is connected with the dislocation strain field, probably leading to a shift of defect states toward the band edge
Observation of
Based on a sample of \etapr mesons produced in the radiative decay
in events collected
with the BESIII detector, the decay is
observed for the first time, with a statistical significance of . The
branching fraction is measured to be , which is
in agreement with theoretical predictions. The branching fraction of
is also measured to be
, which is the
most precise measurement to date, and the relative branching fraction
is determined to be
.Comment: 8 pages, 10 figure
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