1,820 research outputs found
Statics, Dynamics and Manipulations of Bright Matter-Wave Solitons in Optical Lattices
Motivated by recent experimental achievement in the work with Bose-Einstein
condensates (BECs), we consider bright matter-wave solitons, in the presence of
a parabolic magnetic trap and a spatially periodic optical lattice (OL), in the
attractive BEC. We examine pinned states of the soliton and their stability by
means of perturbation theory. The analytical predictions are found to be in
good agreement with numerical simulations. We then explore possibilities to use
a time-modulated OL as a means of stopping and trapping a moving soliton, and
of transferring an initially stationary soliton to a prescribed position by a
moving OL. We also study the emission of radiation from the soliton moving
across the combined magnetic trap and OL. We find that the soliton moves freely
(without radiation) across a weak lattice, but suffers strong loss for stronger
OLs.Comment: 7 pages, 5 figs, Phys Rev A in Press (2005
Obesity-induced changes in lipid mediators persist after weight loss.
BackgroundObesity induces significant changes in lipid mediators, however, the extent to which these changes persist after weight loss has not been investigated.Subjects/methodsWe fed C57BL6 mice a high-fat diet to generate obesity and then switched the diet to a lower-fat diet to induce weight loss. We performed a comprehensive metabolic profiling of lipid mediators including oxylipins, endocannabinoids, sphingosines and ceramides in key metabolic tissues (including adipose, liver, muscle and hypothalamus) and plasma.ResultsWe found that changes induced by obesity were largely reversible in most metabolic tissues but the adipose tissue retained a persistent obese metabolic signature. Prostaglandin signaling was perturbed in the obese state and lasting increases in PGD2, and downstream metabolites 15-deoxy PGJ2 and delta-12-PGJ2 were observed after weight loss. Furthermore expression of the enzyme responsible for PGD2 synthesis (hematopoietic prostaglandin D synthase, HPGDS) was increased in obese adipose tissues and remained high after weight loss. We found that inhibition of HPGDS over the course of 5 days resulted in decreased food intake in mice. Increased HPGDS expression was also observed in human adipose tissues obtained from obese compared with lean individuals. We then measured circulating levels of PGD2 in obese patients before and after weight loss and found that while elevated relative to lean subjects, levels of this metabolite did not decrease after significant weight loss.ConclusionsThese results suggest that lasting changes in lipid mediators induced by obesity, still present after weight loss, may play a role in the biological drive to regain weight
Mobility of Discrete Solitons in Quadratically Nonlinear Media
We study the mobility of solitons in second-harmonic-generating lattices.
Contrary to what is known for their cubic counterparts, discrete quadratic
solitons are mobile not only in the one-dimensional (1D) setting, but also in
two dimensions (2D). We identify parametric regions where an initial kick
applied to a soliton leads to three possible outcomes, namely, staying put,
persistent motion, or destruction. For the 2D lattice, it is found that, for
the solitary waves, the direction along which they can sustain the largest kick
and can attain the largest speed is the diagonal. Basic dynamical properties of
the discrete solitons are also discussed in the context of an analytical
approximation, in terms of an effective Peierls-Nabarro potential in the
lattice setting.Comment: 4 page
Flavonoides presentes en extractos hexánicos de especies del género Sideritis
In continuation to the studies of the Genus Sideritis that this Pharmacology Department has done, we have isolated and identificated the flavonoid compounds in the hexanic extracts of ten species of this Genus by an HPLC method. We have to remark the presence of Isoscutellarein-7-0-(allosyl-glucoside), in all the studied extracts.Continuando con los trabajos llevados a cabo en el Dep. de FarmacologĂa, sobre el gĂ©nero Sideri tis, hemos separado e identificado los flavonoides presentes en los extractos hexánicos correspondientes a 10 especies de dicho gĂ©nero, por tĂ©cnicas de HPLC y con ayuda de patrones. Entre los compuestos aislados, cabe destacar la isoscutelareina 7-0-(alosil-glucĂłsido), presente en todos los extractos
Towards two-dimensional metallic behavior at LaAlO3/SrTiO3 interfaces
Using a low-temperature conductive-tip atomic force microscope in
cross-section geometry we have characterized the local transport properties of
the metallic electron gas that forms at the interface between LaAlO3 and
SrTiO3. At low temperature, we find that the carriers do not spread away from
the interface but are confined within ~10 nm, just like at room temperature.
Simulations taking into account both the large temperature and electric-field
dependence of the permittivity of SrTiO3 predict a confinement over a few nm
for sheet carrier densities larger than ~6 10^13 cm-2. We discuss the
experimental and simulations results in terms of a multi-band carrier system.
Remarkably, the Fermi wavelength estimated from Hall measurements is ~16 nm,
indicating that the electron gas in on the verge of two-dimensionality.Comment: Accepted for publication in Physical Review Letter
Vortices in a Bose-Einstein condensate confined by an optical lattice
We investigate the dynamics of vortices in repulsive Bose-Einstein
condensates in the presence of an optical lattice (OL) and a parabolic magnetic
trap. The dynamics is sensitive to the phase of the OL potential relative to
the magnetic trap, and depends less on the OL strength. For the cosinusoidal OL
potential, a local minimum is generated at the trap's center, creating a stable
equilibrium for the vortex, while in the case of the sinusoidal potential, the
vortex is expelled from the center, demonstrating spiral motion. Cases where
the vortex is created far from the trap's center are also studied, revealing
slow outward-spiraling drift. Numerical results are explained in an analytical
form by means of a variational approximation. Finally, motivated by a discrete
model (which is tantamount to the case of the strong OL lattice), we present a
novel type of vortex consisting of two pairs of anti-phase solitons.Comment: 10 pages, 6 figure
Point defect distribution in high-mobility conductive SrTiO3 crystals
We have carried out positron annihilation spectroscopy to characterize the spatial distribution and the nature of vacancy defects in insulating as-received as well as in reduced SrTiO3 substrates exhibiting high-mobility conduction. The substrates were reduced either by ion etching the substrate surfaces or by doping with vacancies during thin film deposition at low pressure and high temperature. We show that Ti-vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects are the same both in ion-etched and substrates reduced during the film growth, and they consist of non-homogeneous distributions of cation-oxygen vacancy complexes. Their spatial extension is tuned from a few microns in ion-etched samples to the whole substrate in specimens reduced during film deposition. Our results shed light on the transport mechanisms of conductive SrTiO3 crystals and on strategies for defect-engineered oxide quantum wells, wires and dots
The teaching of recent and violent conflicts as challenges for history education
This paper has been written with the support of Projects EDU2015-65088P from the DGICYT (Ministry of Education, Spain) and also the Project PICT2012-1594 from the ANPCYT (Argentina) coordinated by the autho
Lysine-PEGylated Cytochrome C with Enhanced Shelf-Life Stability
Cytochrome c (Cyt-c), a small mitochondrial electron transport heme protein, has been employed in bioelectrochemical and therapeutic applications. However, its potential as both a biosensor and anticancer drug is significantly impaired due to poor long-term and thermal stability. To overcome these drawbacks, we developed a site-specific PEGylation protocol for Cyt-c. The PEG derivative used was a 5 kDa mPEG-NHS, and a site-directed PEGylation at the lysine amino-acids was performed. The effects of the pH of the reaction media, molar ratio (Cyt-c:mPEG-NHS) and reaction time were evaluated. The best conditions were defined as pH 7, 1:25 Cyt-c:mPEG-NHS and 15 min reaction time, resulting in PEGylation yield of 45% for Cyt-c-PEG-4 and 34% for Cyt-c-PEG-8 (PEGylated cytochrome c with 4 and 8 PEG molecules, respectively). Circular dichroism spectra demonstrated that PEGylation did not cause significant changes to the secondary and tertiary structures of the Cyt-c. The long-term stability of native and PEGylated Cyt-c forms was also investigated in terms of peroxidative activity. The results demonstrated that both Cyt-c-PEG-4 and Cyt-c-PEG-8 were more stable, presenting higher half-life than unPEGylated protein. In particular, Cyt-c-PEG-8 presented great potential for biomedical applications, since it retained 30-40% more residual activity than Cyt-c over 60-days of storage, at both studied temperatures of 4 °C and 25 °C.publishe
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