12,881 research outputs found
The effects of optically induced non-Abelian gauge field in cold atoms
We show that degenerate dark states can be generated by coupling
-fold degenerate ground states and a common excited state with laser
fields. Interferences between light waves with different frequencies can
produce laser fields with time-dependent amplitudes, which can induce not only
U(N) non-Abelian vector fields but also the scalar ones for the adiabatic
motion of atoms in such laser fields. As an example, a time-periodic gauge
potential is produced by applying specific laser fields to a tripod system.
Some features of the Landau levels and the ground-state phase diagram of a
rotating Bose-Einstein condensate for a concrete gauge field are also
discussed.Comment: Revtex 6 pages, 2 figures, version to be published in PR
Kinetic Ballooning Mode Under Steep Gradient: High Order Eigenstates and Mode Structure Parity Transition
The existence of kinetic ballooning mode (KBM) high order (non-ground)
eigenstates for tokamak plasmas with steep gradient is demonstrated via
gyrokinetic electromagnetic eigenvalue solutions, which reveals that eigenmode
parity transition is an intrinsic property of electromagnetic plasmas. The
eigenstates with quantum number for ground state and for
non-ground states are found to coexist and the most unstable one can be the
high order states (). The conventional KBM is the state. It is
shown that the KBM has the same mode structure parity as the
micro-tearing mode (MTM). In contrast to the MTM, the KBM can be driven
by pressure gradient even without collisions and electron temperature gradient.
The relevance between various eigenstates of KBM under steep gradient and edge
plasma physics is discussed.Comment: 6 pages, 6 figure
Conversion of K-Rb mixtures into stable molecules
We study the conversion of K and Rb atoms into stable molecules
through the stimulated Raman adiabatic passage (STIRAP) in photoassociation
assisted with Feshbach resonance. Starting with the mean-field Langrange
density, we show that the atom-to-molecule conversion efficiency by STIRAP
aided by Feshbach resonance is much larger than that by bare Feshbach
resonance. We also study the influence of the population imbalance on the
atom-to-molecule conversion.Comment: Revtex, 5 pages, 3 figures; version to appear in PRA (some content
changed
The role of inter-well tunneling strength on coherence dynamics of two-species Bose-Einstein condensates
Coherence dynamics of two-species Bose-Einstein condensates in double wells
is investigated in mean field approximation. We show that the system can
exhibit decoherence phenomena even without the condensate-environment coupling
and the variation tendency of the degree of coherence depends on not only the
parameters of the system but also the initial states. We also investigate the
time evolution of the degree of coherence for a Rosen-Zener form of tunneling
strength, and propose a method to get a condensate system with certain degree
of coherence through a time-dependent tunneling strength
Boron Nitride Nanosheets for Metal Protection
Although the high impermeability of graphene makes it an excellent barrier to
inhibit metal oxidation and corrosion, graphene can form a galvanic cell with
the underlying metal that promotes corrosion of the metal in the long term.
Boron nitride (BN) nanosheets which have a similar impermeability could be a
better choice as protective barrier, because they are more thermally and
chemically stable than graphene and, more importantly, do not cause galvanic
corrosion due to their electrical insulation. In this study, the performance of
commercially available BN nanosheets grown by chemical vapor deposition as a
protective coating on metal has been investigated. The heating of the copper
foil covered with the BN nanosheet at 250 {\deg}C in air over 100 h results in
dramatically less oxidation than the bare copper foil heated for 2 h under the
same conditions. The electrochemical analyses reveal that the BN nanosheet
coating can increase open circuit potential and possibly reduce oxidation of
the underlying copper foil in sodium chloride solution. These results indicate
that BN nanosheets are a good candidate for oxidation and corrosion protection,
although conductive atomic force microscopy analyses show that the
effectiveness of the protection relies on the quality of BN nanosheets.Comment: With Supporting Informatio
Ideias de governança em Kong-Zi Jiayu e seus valores contemporùneos
Kong-Zi Jia Yu is a book that recorded many Confucius and his disciplesâ conversations and thoughts, making it an indispensable source to explore traditional Chinese culture and ideas. In particular, the governance ideas presented in the book are still highly relevant today. People-oriented thoughts were the core of governance wisdom, paradigmatic kingcraft and virtuous courtiers were a sensible part of governance, and the penological ideas further ensured the robust operations of it. In the new era, new ideas like âputting the people as the top priorityâ, Xi Jinpingâs thoughts on building cadre teams and governing China by the rule of law have successively proposed as creative converts and innovative development of Chinese culture that has been carried forward over thousands of years. Inheriting and promoting these cultural "genes", refining their ideological essence, are of great reference value for cultivating the current political landscape, enriching the connotation of the construction of the cadre team in the new era, adhering to the rule of law and providing ideas for the formulation of current rural governance policies.Kong-Zi Jia Yu Ă© um livro que registrou muitas conversas e pensamentos de ConfĂșcio e de seus discĂpulos, tornando-o uma fonte indispensĂĄvel para explorar a cultura e as ideias tradicionais chinesas. Em particular, as ideias de governança apresentadas no livro ainda sĂŁo altamente relevantes hoje. Os pensamentos orientados para as pessoas eram o nĂșcleo da sabedoria da governação, a realeza paradigmĂĄtica e os cortesĂŁos virtuosos eram uma parte sensata da governança, e as ideias penolĂłgicas asseguravam ainda mais as operaçÔes robustas da mesma. Na nova era, novas ideias como âcolocar o povo como prioridade mĂĄximaâ, os pensamentos de Xi Jinping sobre a construção de equipas de quadros e governar a China pelo Estado de direito foram sucessivamente propostos como conversĂ”es criativas e desenvolvimento inovador da cultura chinesa que foi levado adiante ao longo de milhares de anos. Herdar e promover estes âgenesâ culturais, refinando a sua essĂȘncia ideolĂłgica, sĂŁo de grande valor de referĂȘncia para cultivar o panorama polĂtico atual, enriquecendo a conotação da construção da equipa de quadros na nova era, aderindo ao Estado de direito e fornecendo ideias para a formulação das actuais polĂticas de governação rural
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