5,661 research outputs found
Lithium Ionization by a Strong Laser Field
We study ab initio computations of the interaction of Lithium with a strong
laser field. Numerical solutions of the time-dependent fully-correlated
three-particle Schroedinger equation restricted to the one-dimensional
soft-core approximation are presented. Our results show a clear transition from
non-sequential to sequential double ionization for increasing intensities. Non
sequential double ionization is found to be sensitive to the spin configuration
of the ionized pair. This asymmetry, also found in experiments of
photoionization of Li with synchrotron radiation, shows the evidence of the
influence of the exclusion principle in the underlying rescattering mechanism
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles
We study, by means of magnetic susceptibility and magnetic aging experiments,
the nature of the glassy magnetic dynamics in arrays of Co nanoparticles,
self-organized in N layers from N=1 (two-dimensional limit) up to N=20
(three-dimensional limit). We find no qualitative differences between the
magnetic responses measured in these two limits, in spite of the fact that no
spin-glass phase is expected above T=0 in two dimensions. More specifically,
all the phenomena (critical slowing down, flattening of the field-cooled
magnetization below the blocking temperature and the magnetic memory induced by
aging) that are usually associated with this phase look qualitatively the same
for two-dimensional and three-dimensional arrays. The activated scaling law
that is typical of systems undergoing a phase transition at zero temperature
accounts well for the critical slowing down of the dc and ac susceptibilities
of all samples. Our data show also that dynamical magnetic correlations
achieved by aging a nanoparticle array below its superparamagnetic blocking
temperature extend mainly to nearest neighbors. Our experiments suggest that
the glassy magnetic dynamics of these nanoparticle arrays is associated with a
zero-temperature spin-glass transition.Comment: 6 pages 6 figure
TeV gamma-rays from photo-disintegration/de-excitation of cosmic-ray nuclei
It is commonly assumed that high-energy gamma-rays are made via either purely
electromagnetic processes or the hadronic process of pion production, followed
by decay. We investigate astrophysical contexts where a third process (A*) may
dominate, namely the photo-disintegration of highly boosted nuclei followed by
daughter de-excitation. Starbust regions such as Cygnus OB2 appear to be
promising sites for TeV gamma-ray emission via this mechanism. A unique feature
of the A* process is a sharp energy minimum ~ 10 TeV/(T/eV) for gamma-ray
emission from a thermal region of temperature T. We also check that a diffuse
gamma-ray component resulting from the interaction of a possible extreme-energy
cosmic-ray nuclei with background radiation is well below the observed EGRET
data. The A* mechanism described herein offers an important contribution to
gamma-ray astronomy in the era of intense observational activity.Comment: To be published in Phys. Rev. Let
Large quantum nonlinear dynamic susceptibility of single-molecule magnets
The nonlinear dynamical response of Mn single-molecule magnets is
experimentally found to be very large, quite insensitive to the spin-lattice
coupling constant, and displaying peaks reversed with respect to classical
superparamagnets. It is shown that these features are caused by the strong
field dependence of the relaxation rate due to the detuning of energy levels
between which tunneling takes place. The nonlinear susceptibility technique,
previously overlooked, is thus proposed as a privileged probe to ascertain the
occurrence of quantum effects in mesoscopic magnetic systems.Comment: 4 pages, 4 figure
Review of the “state of the art” and possibilities of the most significant approaches to the specific delivery of chemotherapy agents to tumor cells
Los principales problemas de la quimioterapia proceden esencialmente de la relativa falta de
especificidad derivada de la extensa biodistribución de los agentes antitumorales y de los efectos
secundarios generados por la acción inespecífica de éstos en tejidos y órganos sanos. La necesidad de
encontrar tratamientos eficaces contra el cáncer ha hecho que se incrementen las líneas de
investigación en esta materia. Una de las aproximaciones más prometedoras en este sentido es el
desarrollo de sistemas coloidales biodegradables para el transporte de fármacos antitumorales.
Gracias a éstos, se logra acumular específicamente la cantidad de fármaco administrada en el lugar de
acción, logrando así un aumento significativo de la eficacia clínica, junto con una minimización de
las reacciones adversas asociadas. En este trabajo, pretendemos analizar el estado actual en el diseño
de coloides como transportadores de fármacos antitumorales, junto con la aplicación de las novedosas estrategias de transporte pasivo y activo de fármacos.The main problems related to chemotherapy mainly come from a relative lack of selectivity, that is
associated to the extensive biodistribution of antitumor molecules, and to the severe side effects
generated by the unspecific drug action on healthy tissues and organs. The need of finding out
efficient treatments against cancer has led to an enhancement in the number of research lines in the
field. In this way, one of the most promising approaches is the development of biodegradable colloids
for the delivery of antitumor drugs. Thanks to them, it is possible to specifically concentrate the drug
into the site of action. Therefore, a significant improvement of the chemotherapy effect is obtained
along with a minimization of the related adverse side effects. In this review, we analyze the current
“state of the art” in the development of colloidal systems for the efficient delivery of anticancer
drugs. The possibilities of novel drug delivery strategies based on passive and active targeting mechanisms are also discussed
Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical
We present an experimental study of the {\em nonlinear} susceptibility of
Mn single-molecule magnets. We investigate both their
thermal-equilibrium and dynamical nonlinear responses. The equilibrium results
show the sensitivity of the nonlinear susceptibility to the magnetic
anisotropy, which is nearly absent in the linear response for axes distributed
at random. The nonlinear dynamic response of Mn was recently found to be
very large and displaying peaks reversed with respect to classical
superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201
(2004)]. Here we corroborate the proposed explanation -- strong field
dependence of the relaxation rate due to the detuning of tunnel energy levels.
This is done by studying the orientational dependence of the nonlinear
susceptibility, which permits to isolate the quantum detuning contribution.
Besides, from the analysis of the longitudinal and transverse contributions we
estimate a bound for the decoherence time due to the coupling to the phonon
bath.Comment: 13 pages, 8 figures, resubmitted to Phys. Rev. B with minor change
Optimal growth under endogenous depreciation, capital utilization and maintenance costs
This paper analyzes the equilibrium dynamics of an optimal growth model that incorporates endogenous depreciation, variable capital utilization, and expenditures on the maintenance of physical capital. Maintenance acts as a substitute for investment, since it reduces the depreciation of capital. Investment is subject to adjustment costs, and capital is not fully utilized, the degree of capital utilization affecting the activity of maintaining. We establish a set of sufficient conditions for the existence and uniqueness of a steady state equilibrium. Also, we define a “delta golden rule” consistent with the proposed economic environment and we analyze the dynamic efficiency of this economy. Finally, the steady state is found locally saddle-path stable. These results provide a framework for the analysis of comparative dynamics in general equilibrium with these features
A Pea (Pisum sativum L.) Seed Vicilins Hydrolysate Exhibits PPARγ Ligand Activity and Modulates Adipocyte Differentiation in a 3T3-L1 Cell Culture Model
© 2020 by the authors.Legume consumption has been reported to induce beneficial effects on obesity-associated metabolic disorders, but the underlying mechanisms have not been fully clarified. In the current work, pea (Pisum sativum L.) seed meal proteins (albumins, legumins and vicilins) were isolated, submitted to a simulated gastrointestinal digestion, and the effects of their hydrolysates (pea albumins hydrolysates (PAH), pea legumins hydrolysates (PLH) and pea vicilin hydrolysates (PVH), respectively) on 3T3-L1 murine pre-adipocytes were investigated. The pea vicilin hydrolysate (PVH), but not native pea vicilins, increased lipid accumulation during adipocyte differentiation. PVH also increased the mRNA expression levels of the adipocyte fatty acid-binding protein (aP2) and decreased that of pre-adipocyte factor-1 (Pref-1) (a pre-adipocyte marker gene), suggesting that PVH promotes adipocyte differentiation. Moreover, PVH induced adiponectin and insulin-responsive glucose transporter 4 (GLUT4) and stimulated glucose uptake. The expression levels of peroxisome proliferator-activated receptor γ (PPARγ), a key regulator of adipocyte differentiation, were up-regulated in 3T3-L1 cells treated with PVH during adipocyte differentiation. Finally, PVH exhibited PPARγ ligand activity. Lactalbumin or other pea hydrolysates (PAH, PLH) did not exhibit such effects. These findings show that PVH stimulates adipocyte differentiation via, at least in part, the up-regulation of PPARγ expression levels and ligand activity. These effects of PVH might be relevant in the context of the beneficial health effects of legume consumption in obesity-associated metabolic disorders.This work was carried out with financial support from the Spanish MICIIN (PET2008-0311 and
AGL2017-83772-R). This research has been also partially supported by the FEDER and FSE funds from the European Union.Peer reviewe
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