Proposal of an extended t-J Hamiltonian for high-Tc cuprates from ab initio calculations on embedded clusters

A series of accurate ab initio calculations on Cu_pO-q finite clusters, properly embedded on the Madelung potential of the infinite lattice, have been performed in order to determine the local effective interactions in the CuO_2 planes of La_{2-x}Sr_xCuO_4 compounds. The values of the first-neighbor interactions, magnetic coupling (J_{NN}=125 meV) and hopping integral (t_{NN}=-555 meV), have been confirmed. Important additional effects are evidenced, concerning essentially the second-neighbor hopping integral t_{NNN}=+110meV, the displacement of a singlet toward an adjacent colinear hole, h_{SD}^{abc}=-80 meV, a non-negligible hole-hole repulsion V_{NN}-V_{NNN}=0.8 eV and a strong anisotropic effect of the presence of an adjacent hole on the values of the first-neighbor interactions. The dependence of J_{NN} and t_{NN} on the position of neighbor hole(s) has been rationalized from the two-band model and checked from a series of additional ab initio calculations. An extended t-J model Hamiltonian has been proposed on the basis of these results. It is argued that the here-proposed three-body effects may play a role in the charge/spin separation observed in these compounds, that is, in the formation and dynamic of stripes.Comment: 24 pages, 4 figures, submitted to Phys. Rev.

Measurement of the refractive index profile of an optical fiber by Fresnel diffraction

In this work we present a non-destructive technique based on Fresnel diffraction to obtain the refractive index profile of a fiber grating. The system has been firstly calibrated by using the experimental data of the diffraction pattern of rectangular slits at different distances.This work was supported by the Ministerio de Economía y Competitividad (Spain) (FIS2015-66570-P and FIS2017-82919-R) and by Generalitat Valenciana (Spain) (PROMETEOII/2015/015)

Direct generation of local orbitals for multireference treatment and subsequent uses for the calculation of the correlation energy

We present a method that uses the one-particle density matrix to generate directly localized orbitals dedicated to multireference wave functions. On one hand, it is shown that the definition of local orbitals making possible physically justified truncations of the CAS ~complete active space! is particularly adequate for the treatment of multireference problems. On the other hand, as it will be shown in the case of bond breaking, the control of the spatial location of the active orbitals may permit description of the desired physics with a smaller number of active orbitals than when starting from canonical molecular orbitals. The subsequent calculation of the dynamical correlation energy can be achieved with a lower computational effort either due to this reduction of the active space, or by truncation of the CAS to a shorter set of references. The ground- and excited-state energies are very close to the current complete active space self-consistent field ones and several examples of multireference singles and doubles calculations illustrate the interest of the procedur

Computational split-field finite-difference time-domain evaluation of simplified tilt-angle models for parallel-aligned liquid-crystal devices

Simplified analytical models with predictive capability enable simpler and faster optimization of the performance in applications of complex photonic devices. We recently demonstrated the most simplified analytical model still showing predictive capability for parallel aligned liquid crystal on silicon devices (PA-LCoS), which provides the voltage dependent retardance for a very wide range of incidence angles and any wavelength in the visible. In this work we further show that the proposed model is not only phenomenological but it is also physically meaningful, since two of its parameters provide the correct values for important internal properties of these devices related with the birefringence, cell gap and director profile. Therefore, the proposed model can be used as a means to inspect internal physical properties of the cell. Also as a novelty, we also show the applicability of the split-field finite difference time domain (SF-FDTD) technique for phase-shift and retardance evaluation of PA-LCoS devices under oblique incidence. As simplified model for PA-LCoS devices we also consider the exact description of homogeneous birefringent slabs. However, we show that despite its higher degree of simplification the proposed model is more robust, providing unambiguous and physically meaningful solutions when fitting its parameters.Work supported by Ministerio de Economía, Industria y Competitividad (Spain) (FIS2014-56100-C2-1-P and FIS2015-66570-P) and by Generalitat Valenciana (Spain) (PROMETEO II/2015/015)

Analytical evaluation of normalization criteria for the diffraction efficiency of blazed gratings on LCoS devices

Through analytical expressions, three experimental-based normalizations are evaluated for the diffraction efficiency of blazed gratings on LCoS devices. We find that non-inclusion of the fill factor, usually the case, leads to wrong conclusions.Ministerio de Ciencia e Innovación, Spain (FIS2017-82919-R (MINECO/AEI/FEDER, UE)); Generalitat Valenciana, Spain (IDIFEDER/2021/014, potential FEDER funding); Universidad de Alicante, Spain (UATALENTO18-10)

Comparison between methodologies and evaluations in core Physic subjects in Engineering and Architecture Bachelors

In the framework created by the new graduate in European higher education, this work focuses on the foundations of the system of teaching and learning: methodology and evaluation. The comparative study of the methodology and evaluation was performed for the core subjects of Physics, of the degrees in engineering and architecture from the Polytechnic School (EPS) of the University of Alicante (UA) over four years. The work allows comparing the subjects of physics in terms of credits, methodology, evaluation, success rates in percentage, and compared cutting-off marks for each particular degree.The authors wish to acknowledge the support and funding of the University of Alicante via GITE-09006-UA, GITE-09014-UA projects

65. Physical and clinical dosimetry by means of Monte Carlo using a process distribution tool

The choice of the most appropriate strategy in a Radiotherapy treatment is mainly based on the use of a planning system. With the introduction of new techniques (conformal and/or small fields, asymmetrical and non coplanar beams, true 3D calculations, IMRT) the trustworthiness of the algorithms is being questioned. An alternative verification procedure is every time more necessary to warranty a treatment delivery. The reliability of Monte Carlo is generally accepted. However, its clinical use has not been operative due to the high CPU times needed. During the last few years our objective has been focussed to reduce this time by means of new process distribution techniques. Tnis drop has made it feasible, not only the physical dosimetry under special conditions, but also a numerous variety of clinical cases: photon and electron conformal fields, Radiosurgery and IMRT. The carried out procedure is presented. Furthermore, experimental dosimetry data as well as conventional TPS calculations are compared with Monte Carlo simulations

SF-FDTD analysis of a predictive physical model for parallel aligned liquid crystal devices

Recently we demonstrated a novel and simplified model enabling to calculate the voltage dependent retardance provided by parallel aligned liquid crystal devices (PA-LCoS) for a very wide range of incidence angles and any wavelength in the visible. To our knowledge it represents the most simplified approach still showing predictive capability. Deeper insight into the physics behind the simplified model is necessary to understand if the parameters in the model are physically meaningful. Since the PA-LCoS is a black-box where we do not have information about the physical parameters of the device, we cannot perform this kind of analysis using the experimental retardance measurements. In this work we develop realistic simulations for the non-linear tilt of the liquid crystal director across the thickness of the liquid crystal layer in the PA devices. We consider these profiles to have a sine-like shape, which is a good approximation for typical ranges of applied voltage in commercial PA-LCoS microdisplays. For these simulations we develop a rigorous method based on the split-field finite difference time domain (SF-FDTD) technique which provides realistic retardance values. These values are used as the experimental measurements to which the simplified model is fitted. From this analysis we learn that the simplified model is very robust, providing unambiguous solutions when fitting its parameters. We also learn that two of the parameters in the model are physically meaningful, proving a useful reverse-engineering approach, with predictive capability, to probe into internal characteristics of the PA-LCoS device.Work supported by Ministerio de Economía, Industria y Competitividad (Spain) (FIS2014-56100-C2-1-P and FIS2015- 66570-P) and by Generalitat Valenciana (Spain) (PROMETEO II/2015/015)

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure

Targeting Hypoxia in Cancer Cells by Restoring Homeodomain Interacting Protein-Kinase 2 and p53 Activity and Suppressing HIF-1α

BACKGROUND:The tumor suppressor homeodomain-interacting protein kinase-2 (HIPK2) by phosphorylating serine 46 (Ser46) is a crucial regulator of p53 apoptotic function. HIPK2 is also a transcriptional co-repressor of hypoxia-inducible factor-1alpha (HIF-1alpha) restraining tumor angiogenesis and chemoresistance. HIPK2 can be deregulated in tumors by several mechanisms including hypoxia. Here, we sought to target hypoxia by restoring HIPK2 function and suppressing HIF-1alpha, in order to provide evidence for the involvement of both HIPK2 and p53 in counteracting hypoxia-induced chemoresistance. METHODOLOGY/PRINCIPAL FINDINGS:Upon exposure of colon and lung cancer cells to hypoxia, by either low oxygen or cobalt, HIPK2 function was impaired allowing for increased HIF-1alpha expression and inhibiting the p53-apoptotic response to drug. Cobalt suppressed HIPK2 recruitment onto HIF-1alpha promoter. Hypoxia induced expression of the p53 target MDM2 that downregulates HIPK2, thus MDM2 inhibition by siRNA restored the HIPK2/p53Ser46 response to drug. Zinc supplementation to hypoxia-treated cells increased HIPK2 protein stability and nuclear accumulation, leading to restoration of HIPK2 binding to HIF-1alpha promoter, repression of MDR1, Bcl2, and VEGF genes, and activation of the p53 apoptotic response to drug. Combination of zinc and ADR strongly suppressed tumor growth in vivo by inhibiting HIF-1 pathway and upregulating p53 apoptotic target genes. CONCLUSIONS/SIGNIFICANCE:We show here for the first time that hypoxia-induced HIPK2 deregulation was counteracted by zinc that restored HIPK2 suppression of HIF-1 pathway and reactivated p53 apoptotic response to drug, underscoring the potential use of zinc supplementation in combination with chemotherapy to address hypoxia and improve tumor treatment