5,142 research outputs found
Sound speed of a Bose-Einstein condensate in an optical lattice
The speed of sound of a Bose-Einstein condensate in an optical lattice is
studied both analytically and numerically in all three dimensions. Our
investigation shows that the sound speed depends strongly on the strength of
the lattice. In the one-dimensional case, the speed of sound falls
monotonically with increasing lattice strength. The dependence on lattice
strength becomes much richer in two and three dimensions. In the
two-dimensional case, when the interaction is weak, the sound speed first
increases then decreases as the lattice strength increases. For the three
dimensional lattice, the sound speed can even oscillate with the lattice
strength. These rich behaviors can be understood in terms of compressibility
and effective mass. Our analytical results at the limit of weak lattices also
offer an interesting perspective to the understanding: they show the lattice
component perpendicular to the sound propagation increases the sound speed
while the lattice components parallel to the propagation decreases the sound
speed. The various dependence of the sound speed on the lattice strength is the
result of this competition.Comment: 15pages 6 figure
Derivation of Electroweak Chiral Lagrangian from One Family Technicolor Model
Based on previous studies deriving the chiral Lagrangian for pseudo scalar
mesons from the first principle of QCD in the path integral formalism, we
derive the electroweak chiral Lagrangian and dynamically compute all its
coefficients from the one family technicolor model. The numerical results of
the order coefficients obtained in this paper are proportional to the
technicolor number and the technifermion number ,
which agrees with the arguments in previous works, and which confirms the
reliability of this dynamical computation.Comment: 6 page
Probing the topcolor-assisted technicolor model via the single t-quark production at Hadron colliders
In this paper, we systematically study the contribution of the TC2 model to
the single t-quark production at the Hadron colliders, specially at the LHC.
The TC2 model can contribute to the cross section of the single t-quark
production in two different ways. First, the existence of the top-pions and
top-higgs can modify the coupling via their loop contributions, and such
modification can cause the correction to the cross sections of all three
production modes. Our study shows that this kind of correction is negative and
very small in all cases. Thus it is difficult to observe such correction even
at the LHC. On the other hand, there exist the tree-level FC couplings in the
TC2 model which can also contribute to the cross sections of the and
production processes. The resonant effect can greatly enhance the
cross sections of the and productions. The first evidence of
the single t-quark production has been reported by the collaboration and
the measured cross section for the single t-quark production of
is compatible at the 10% level with the
standard model prediction. Because the light top-pion can make great
contribution to the production, the top-pion mass should be very
large in order to make the predicted cross section in the TC2 model be
consistent with the Tevatron experiments. More detailed information about the
top-pion mass and the FC couplings in the TC2 model should be obtained with the
running of the LHC.Comment: 30 pages, 3 tables, 10 figure
Experimental study of flashing LNG jet fires following horizontal releases
A horizontally oriented jet fire could occur if the leaking liquefied natural gas (LNG) from the side surface of a pipe or storage tank was ignited. Previous work with LNG mostly focused on pool fires. In the present study, horizontally oriented LNG jet fires were studied through 10 open field full scale tests. The flames were visualized by both infrared and video cameras. The recorded flame shapes are compared and analysed. Peak temperatures and heat fluxes at various flow rates were measured and recorded. For relatively low reservoir pressure, a small amount of LNG was found to spray through the fire and rainout onto the ground, forming an LNG pool. A correlation was established to calculate the flame length from the mass flow rate
Dynamics Simulation of the Risk Coupling Effect between Maritime Pilotage Human Factors under the HFACS Framework
Maritime pilotage is an important guarantee for the safety of water traffic in port. The pilot is affected by the complex port environment, the differences of crew and equipment of different ships, the physical and psychological pressure of the pilot himself, as well as the management factors from the pilot station and maritime safety administration. In order to avoid pilotage accidents (PAs), it is necessary to study the coupling effect of humanorganizational factors (HOFs) on PAs. In this paper, from the perspective of HOF risk coupling in pilotage, the problem of HOF risk coupling in maritime pilotage is studied by using the hierarchical classification idea of the human factors analysis and classification system (HFACS) and the method of system dynamics (SD). First of all, HFACS is used to analyse the HOF risk causal elements (RCEs) in pilotage, and 70 RCEs are summed up in four layers; secondly, the SD coupling model of RCEs is constructed; finally, based on a dataset of PAs collected by the Shanghai Harbour Pilot Association, the coupling simulation of RCEs in pilotage is carried out, and the volatility is evaluated. In general, the safety situation of maritime pilotage has been improving in the Shanghai port. However, four RCEs (negligence, habit, pilotage experience, and violations) in unsafe acts and two RCEs (teamwork and personal safety awareness) in precondition for unsafe acts contribute the most to maritime PAs and need to be paid attention to.</jats:p
Coherent population trapping in a dressed two-level atom via a bichromatic field
We show theoretically that by applying a bichromatic electromagnetic field,
the dressed states of a monochromatically driven two-level atom can be pumped
into a coherent superposition termed as dressed-state coherent population
trapping. Such effect can be viewed as a new doorknob to manipulate a two-level
system via its control over dressed-state populations. Application of this
effect in the precision measurement of Rabi frequency, the unexpected
population inversion and lasing without inversion are discussed to demonstrate
such controllability.Comment: 14 pages, 6 figure
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