4,622 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
Coexistence of multi-photon processes and longitudinal couplings in superconducting flux qubits
In contrast to natural atoms, the potential energies for superconducting flux
qubit (SFQ) circuits can be artificially controlled. When the inversion
symmetry of the potential energy is broken, we find that the multi-photon
processes can coexist in the multi-level SFQ circuits. Moreover, there are not
only transverse but also longitudinal couplings between the external magnetic
fields and the SFQs when the inversion symmetry of potential energy is broken.
The longitudinal coupling would induce some new phenomena in the SFQs. Here we
will show how the longitudinal coupling can result in the coexistence of
multi-photon processes in a two-level system formed by a SFQ circuit. We also
show that the SFQs can become transparent to the transverse coupling fields
when the longitudinal coupling fields satisfy the certain conditions. We
further show that the quantum Zeno effect can also be induced by the
longitudinal coupling in the SFQs. Finally we clarify why the longitudinal
coupling can induce coexistence and disappearance of single- and two-photon
processes for a driven SFQ, which is coupled to a single-mode quantized field.Comment: 11 pages, 6 figure
Object Picture of Quasinormal Modes for Stringy Black Holes
We study the quasinormal modes (QNMs) for stringy black holes. By using
numerical calculation, the relations between the QNMs and the parameters of
black holes are minutely shown. For (1+1)-dimensional stringy black hole, the
real part of the quasinormal frequency increases and the imaginary part of the
quasinormal frequency decreases as the mass of the black hole increases.
Furthermore, the dependence of the QNMs on the charge of the black hole and the
flatness parameter is also illustrated. For (1+3)-dimensional stringy black
hole, increasing either the event horizon or the multipole index, the real part
of the quasinormal frequency decreases. The imaginary part of the quasinormal
frequency increases no matter whether the event horizon is increased or the
multipole index is decreased.Comment: 4 pages, 5 figure
Broad-spectrum antimicrobial activity and improved stability of a D-Amino acid enantiomer of DMPC-10A, the designed derivative of dermaseptin truncates
DMPC-10A (ALWKKLLKK-Cha-NH2) is a 10-mer peptide derivative from the N-terminal domain of Dermaseptin-PC which has shown broad-spectrum antimicrobial activity as well as a considerable hemolytic effect. In order to reduce hemolytic activity and improve stability to endogenous enzymes, a D-amino acid enantiomer (DMPC-10B) was designed by substituting all L-Lys and L-Leu with their respective D-form amino acid residues, while the Ala1 and Trp3 remained unchanged. The D-amino acid enantiomer exhibited similar antimicrobial potency to the parent peptide but exerted lower cytotoxicity and hemolytic activity. Meanwhile, DMPC-10B exhibited remarkable resistance to hydrolysis by trypsin and chymotrypsin. In addition to these advantages, DMPC-10B exhibited an outstanding antibacterial effect against Methicillin-resistant Staphylococcus aureus (MRSA) and Klebsiella pneumoniae using the Galleria mellonella larva model and displayed synergistic activities with gentamicin against carbapenem-resistant K. pneumoniae strains. This indicates that DMPC-10B would be a promising alternative for treating antibiotic-resistant pathogens
Hole Doping Dependence of the Coherence Length in Thin Films
By measuring the field and temperature dependence of magnetization on
systematically doped thin films, the critical current
density and the collective pinning energy are determined in
single vortex creep regime. Together with the published data of superfluid
density, condensation energy and anisotropy, for the first time we derive the
doping dependence of the coherence length or vortex core size in wide doping
regime directly from the low temperature data. It is found that the coherence
length drops in the underdoped region and increases in the overdoped side with
the increase of hole concentration. The result in underdoped region clearly
deviates from what expected by the pre-formed pairing model if one simply
associates the pseudogap with the upper-critical field.Comment: 4 pages, 4 figure
Structural phase transitions in epitaxial perovskite films
Three different film systems have been systematically investigated to
understand the effects of strain and substrate constraint on the phase
transitions of perovskite films. In SrTiO films, the phase transition
temperature T was determined by monitoring the superlattice peaks
associated with rotations of TiO octahedra. It is found that T depends
on both SrTiO film thickness and SrRuO buffer layer thickness. However,
lattice parameter measurements showed no sign of the phase transitions,
indicating that the tetragonality of the SrTiO unit cells was no longer a
good order parameter. This signals a change in the nature of this phase
transition, the internal degree of freedom is decoupled from the external
degree of freedom. The phase transitions occur even without lattice relaxation
through domain formation. In NdNiO thin films, it is found that the
in-plane lattice parameters were clamped by the substrate, while out-of-plane
lattice constant varied to accommodate the volume change across the phase
transition. This shows that substrate constraint is an important parameter for
epitaxial film systems, and is responsible for the suppression of external
structural change in SrTiO and NdNiO films. However, in SrRuO films
we observed domain formation at elevated temperature through x-ray reciprocal
space mapping. This indicated that internal strain energy within films also
played an important role, and may dominate in some film systems. The final
strain states within epitaxial films were the result of competition between
multiple mechanisms and may not be described by a single parameter.Comment: REVTeX4, 14 figure
Study on the structure-activity relationship of an antimicrobial peptide, Brevinin-2GUb, from the skin secretion of Hylarana guentheri
Antimicrobial peptides (AMPs) are considered potential alternatives to antibiotics due to their advantages in solving antibiotic resistance. Brevinin-2GUb, which was extracted from the skin secretion of Hylarana guentheri, is a peptide with modest antimicrobial activity. Several analogues were designed to explore the structure–activity relationship and enhance its activity. In general, the Rana box is not an indispensable motif for the bioactivity of Brevinin-2GUb, and the first to the 19th amino acids at the N-terminal end are active fragments, such that shortening the peptide while maintaining its bioactivity is a promising strategy for the optimisation of peptides. Keeping a complete hydrophobic face and increasing the net charges are key factors for antimicrobial activity. With the increase of cationic charges, α-helical proportion, and amphipathicity, the activity of t-Brevinin-2GUb-6K (tB2U-6K), in combatting bacteria, drastically improved, especially against Gram-negative bacteria, and the peptide attained the capacity to kill clinical isolates and fungi as well, which made it possible to address some aspects of antibiotic resistance. Thus, peptide tB2U-6K, with potent antimicrobial activity against antibiotic-resistant bacteria, the capacity to inhibit the growth of biofilm, and low toxicity against normal cells, is of value to be further developed into an antimicrobial agent
Entanglement distillation using particle statistics
We extend the idea of entanglement concentration for pure states(Phys. Rev.
Lett. {\bf 88}, 187903) to the case of mixed states. The scheme works only with
particle statistics and local operations, without the need of any other
interactions. We show that the maximally entangled state can be distilled out
when the initial state is pure, otherwise the entanglement of the final state
is less than one. The distillation efficiency is a product of the diagonal
elements of the initial state, it takes the maximum 50%, the same as the case
for pure states.Comment: 3 pages, 1 figur
Brevinin-2GHk from Sylvirana guentheri and the design of truncated analogs exhibiting the enhancement of antimicrobial activity
Brevinins are an important antimicrobial peptide (AMP) family discovered in the skin secretions of Ranidae frogs. The members demonstrate a typical C-terminal ranabox, as well as a diverse range of other structural characteristics. In this study, we identified a novel brevinin-2 peptide from the skin secretion of Sylvirana guentheri, via cloning transcripts, and identifying the expressed mature peptide, in the skin secretion. The confirmed amino acid sequence of the mature peptide was designated brevinin-2GHk (BR2GK). Moreover, as a previous study had demonstrated that the N-terminus of brevinin-2 is responsible for exerting antimicrobial activity, we also designed a series of truncated derivatives of BR2GK. The results show that the truncated derivatives exhibit significantly improved antimicrobial activity and cytotoxicity compared to the parent peptide, except a Pro14 substituted analog. The circular dichroism (CD) analysis of this analog revealed that it did not fold into a helical conformation in the presence of either lipopolysaccharides (LPS) or TFE, indicating that position 14 is involved in the formation of the α-helix. Furthermore, three more analogs with the substitutions of Ala, Lys and Arg at the position 14, respectively, revealed the influence on the membrane disruption potency on bacteria and mammalian cells by the structural changes at this position. Overall, the N-terminal 25-mer truncates demonstrated the potent antimicrobial activity with low cytotoxicity
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