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$_{12}$ 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$_{12}$ 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$_{12}$ 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