29 research outputs found
Problems of transhipment development in Ukraine: decision ways
У статті розглядаються основні проблеми, що постали перед розвитком контейнерних перевезень в режимі трансшипмента в Україні та шляхи їх вирішення з огляду на зростаючий рівень конкуренції контейнерних терміналів сусідніх країн на ринку фідерних перевезень Чорного моря. Здійснити трансшипмент в Україні вдалося завдяки змінам до Закону України «Про транзит вантажів» і наданню Міністерством транспорту та зв'язку України знижки у розмірі 50% на навантажувально-розвантажувальні роботи для цього виду транспорту. Запропоновано ряд організаційних заходів щодо сприяння розвитку цього виду перевезень в Україні, який, в свою чергу, сприяє реалізації транзитного потенціалу держави
Half-quantum vortex state in a spin-orbit coupled Bose-Einstein condensate
We investigate theoretically the condensate state and collective excitations
of a two-component Bose gas in two-dimensional harmonic traps subject to
isotropic Rashba spin-orbit coupling. In the weakly interacting regime when the
inter-species interaction is larger than the intra-species interaction
(), we find that the condensate ground state has a
half-quantum-angular-momentum vortex configuration with spatial rotational
symmetry and skyrmion-type spin texture. Upon increasing the interatomic
interaction beyond a threshold , the ground state starts to involve
higher-order angular momentum components and thus breaks the rotational
symmetry. In the case of , the condensate becomes
unstable towards the superposition of two degenerate half-quantum vortex
states. Both instabilities (at and ) can be
determined by solving the Bogoliubov equations for collective density
oscillations of the half-quantum vortex state, and by analyzing the softening
of mode frequencies. We present the phase diagram as functions of the
interatomic interactions and the spin-orbit coupling. In addition, we directly
simulate the time-dependent Gross-Pitaevskii equation to examine the dynamical
properties of the system. Finally, we investigate the stability of the
half-quantum vortex state against both the trap anisotropy and anisotropy in
the spin-orbit coupling term.Comment: 13 pages, 18 figure
Precision measurements of s-wave scattering lengths in a two-component Bose-Einstein condensate
We use collective oscillations of a two-component Bose-Einstein condensate
(2CBEC) of \Rb atoms prepared in the internal states and for the precision measurement of
the interspecies scattering length with a relative uncertainty of
. We show that in a cigar-shaped trap the three-dimensional
(3D) dynamics of a component with a small relative population can be
conveniently described by a one-dimensional (1D) Schr\"{o}dinger equation for
an effective harmonic oscillator. The frequency of the collective oscillations
is defined by the axial trap frequency and the ratio , where
is the intra-species scattering length of a highly populated component
1, and is largely decoupled from the scattering length , the total atom
number and loss terms. By fitting numerical simulations of the coupled
Gross-Pitaevskii equations to the recorded temporal evolution of the axial
width we obtain the value , where is the Bohr
radius. Our reported value is in a reasonable agreement with the theoretical
prediction but deviates significantly from the
previously measured value \cite{Mertes07} which is commonly
used in the characterisation of spin dynamics in degenerate \Rb atoms. Using
Ramsey interferometry of the 2CBEC we measure the scattering length
which also deviates from the previously reported value
\cite{Mertes07}. We characterise two-body losses for the
component 2 and obtain the loss coefficients
and
.Comment: 11 pages, 8 figure
Strategic direction of development of container transport technological system of Ukraine
Участь у міжнародній морській торгівлі дедалі все більше розглядається як провідний засіб ефективного використання геостратегічного розташування України, визначення та проведення нею ефективної міжнародної транспортної політики, інтеграції України до світового та європейського економічного простору. За своїм розташуванням Україна є природним «хабом», якій має обслуговувати територію суміжних країн, забезпечуючи створення умов ефективного розвитку власної економіки, оскільки контейнерні перевезення грають важливу роль у розвитку міжнародної торгівлі і є головним сегментом зовнішньоекономічної діяльності
Dynamical preparation of EPR entanglement in two-well Bose-Einstein condensates
We propose to generate Einstein-Podolsky-Rosen (EPR) entanglement between
groups of atoms in a two-well Bose-Einstein condensate using a dynamical
process similar to that employed in quantum optics. The local nonlinear S-wave
scattering interaction has the effect of creating a spin squeezing at each
well, while the tunneling, analogous to a beam splitter in optics, introduces
an interference between these fields that results in an inter-well
entanglement. We consider two internal modes at each well, so that the
entanglement can be detected by measuring a reduction in the variances of the
sums of local Schwinger spin observables. As is typical of continuous variable
(CV) entanglement, the entanglement is predicted to increase with atom number,
and becomes sufficiently strong at higher numbers of atoms that the EPR paradox
and steering non-locality can be realized. The entanglement is predicted using
an analytical approach and, for larger atom numbers, stochastic simulations
based on truncated Wigner function. We find generally that strong tunnelling is
favourable, and that entanglement persists and is even enhanced in the presence
of realistic nonlinear losses.Comment: 15 pages, 19 figure
Mean-field dynamics of two-mode Bose-Einstein condensates in highly anisotropic potentials: Interference, dimensionality, and entanglement
We study the mean-field dynamics and the reduced-dimension character of
two-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means
of perturbative techniques, we show that the tightly confined (transverse)
degrees of freedom can be decoupled from the dynamical equations at the expense
of introducing additional effective three-body, attractive, intra- and
inter-mode interactions into the dynamics of the loosely confined
(longitudinal) degrees of freedom. These effective interactions are mediated by
changes in the transverse wave function. The perturbation theory is valid as
long as the nonlinear scattering energy is small compared to the transverse
energy scales. This approach leads to reduced-dimension mean-field equations
that optimally describe the evolution of a two-mode condensate in general
quasi-1D and quasi-2D geometries. We use this model to investigate the relative
phase and density dynamics of a two-mode, cigar-shaped Rb BEC. We study
the relative-phase dynamics in the context of a nonlinear Ramsey interferometry
scheme, which has recently been proposed as a novel platform for high-precision
interferometry. Numerical integration of the coupled, time-dependent,
three-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers
shows that this model gives a considerably more refined analytical account of
the mean-field evolution than an idealized quasi-1D description.Comment: 35 pages, 10 figures. Current version is as publishe