Dynamics of Coherent States in Regular and Chaotic Regimes of the Non-integrable Dicke Model

The quantum dynamics of initial coherent states is studied in the Dicke model and correlated with the dynamics, regular or chaotic, of their classical limit. Analytical expressions for the survival probability, i.e. the probability of finding the system in its initial state at time $t$, are provided in the regular regions of the model. The results for regular regimes are compared with those of the chaotic ones. It is found that initial coherent states in regular regions have a much longer equilibration time than those located in chaotic regions. The properties of the distributions for the initial coherent states in the Hamiltonian eigenbasis are also studied. It is found that for regular states the components with no negligible contribution are organized in sequences of energy levels distributed according to Gaussian functions. In the case of chaotic coherent states, the energy components do not have a simple structure and the number of participating energy levels is larger than in the regular cases.Comment: Contribution to the proceedings of the Escuela Latinoamericana de F\'isica (ELAF) Marcos Moshinsky 2017. (9 pages, 4 figures

Secure Metric-Based Index for Similarity Cloud

We propose a similarity index that ensures data privacy and thus is suitable for search systems outsourced in a cloud. The proposed solution can exploit existing efficient metric indexes based on a fixed set of reference points. The method has been fully implemented as a security extension of an existing established approach called M-Index. This Encrypted M-Index supports evaluation of standard range and nearest neighbors queries both in precise and approximate manner. In the first part of this work, we analyze various levels of privacy in existing or future similarity search systems; the proposed solution tries to keep a reasonable privacy level while relocating only the necessary amount of work from server to an authorized client. The Encrypted M-Index has been tested on three real data sets with focus on various cost components

Direct evidence for efficient ultrafast charge separation in epitaxial WS2_2/graphene heterostructure

We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS$_2$ and graphene. This heterostructure combines the benefits of a direct gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS$_2$, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS$_2$ layer. The resulting charge transfer state is found to have a lifetime of $\sim1$\,ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS$_2$ and graphene bands as revealed by high resolution ARPES. In combination with spin-selective excitation using circularly polarized light the investigated WS$_2$/graphene heterostructure might provide a new platform for efficient optical spin injection into graphene.Comment: 28 pages, 14 figure

A possible origin of superconducting currents in cosmic strings

The scattering and capture of right-handed neutrinos by an Abelian cosmic string in the SO(10) grand unification model are considered. The scattering cross-section of neutrinos per unit length due to the interaction with the gauge and Higgs fields of the string is much larger in its scaling regime than in the friction one because of the larger infrared cutoff of the former.The probability of capture in a zero mode of the string accompanied by the emission of a gauge or Higgs boson shows a resonant peak for neutrino momentum of the order of its mass. Considering the decrease of number of strings per unit comoving volume in the scaling epoch the cosmological consequences of the superconducting strings formed in this regime will be much smaller than those which could be produced already in the friction one.Comment: 14 pages Latex, 4 figues/ep

Analysis of educational trajectories of students with disabilities at the Universidad Nacional del Tucumán

En el marco del proyecto de investigación "Los alumnos con discapacidad en la Universidad Nacional del Tucumán: prácticas inclusivas y condiciones de accesibilidad"; aprobado y financiado por el Consejo de Ciencia y Técnica de la mencionada universidad, se analizaron las trayectorias educativas de un colectivo de alumnos universitarios con discapacidad. La muestra se conformó por estudiantes de las facultades de Filosofía y Letras; Artes y Derecho y Ciencias Sociales. Se administró una encuesta semiestructurada a fin de conocer los obstáculos físicos y las condiciones de accesibilidad académicas de los alumnos. La cual permitió identificar los tipos de discapacidad de los estudiantes y las condiciones necesarias para garantizar su ingreso, permanencia y egreso. Los encuestados identificaron como principales obstáculos la falta de: formación de los docentes, materiales adecuados (braille y digitalización), intérpretes y accesibilidad en las condiciones edilicias. Este trabajo plantea analizar las trayectorias educativas reales de cada alumno en particular y dar respuestas concretas, desde un modelo social de discapacidad y una educación inclusiva.Under the research project "Students with disabilities in the UNT: inclusive practices and accessibility"; approved and funded by the Council of Science and Technology of the UNT (CIUNT) educational trajectories of a group of university students with disabilities was analyzed. The sample was composed by students from the Faculty of Philosophy and Letters; Arts; Law and Social Sciences. A semi-structured survey was administered in order to know the physical obstacles and the academic accessibility conditions of the students. This allowed to identify the types of students' disabilities and the necessary conditions to guarantee their entrance, permanence and graduation. Respondents identified as main obstacles the lack of: teacher training, adequate materials (braille and digitization), interpreters and accessibility in the building conditions. This work aims to analyze the real educational trajectories of each student in particular and give concrete answers, from a social model of disability and an inclusive education.Fil: Esterking, Ana Elena. Universidad Nacional de TucumánFil: González, Juana B.. Universidad Nacional de TucumánFil: Chávez, María Gabriela. Universidad Nacional de Tucumá

Análisis estadístico para un arreglo factorial con un factor no aleatorizable.

El análisis estadístico de un experimento en bloques completos al azar con dos factores, uno aleatorizado y otro no aleatorizado, fue propuesto por Johnson en 1983. En este escrito se presenta el diseño y análisis de un experimento en bloques completos al azar con tres factores, dos factores aleatorizados en arreglo factorial y uno no aleatorizado. A través del análisis de perfiles, técnica multivariada, se establecieron pruebas de hipótesis válidas para el análisis de resultados. El análisis propuesto se aplica a experimentos donde se realizan varias lecturas sobre una misma unidad experimental. La información dada a través del análisis propuesto es de gran importancia debido a que se pueden involucrar varios factores e interacciones de interés para el investigador. La metodología se muestra en un experimento hipotético de riego por aspersión para un diseño de bloques al azar con arreglo factoria