Aging is associated with an earlier arrival of reflected waves without a distal shift in reflection sites

Background-Despite pronounced increases in central pulse wave velocity (PWV) with aging, reflected wave transit time (RWTT), traditionally defined as the timing of the inflection point (T-INF) in the central pressure waveform, does not appreciably decrease, leading to the controversial proposition of a "distal-shift" of reflection sites. T-INF, however, is exceptionally prone to measurement error and is also affected by ejection pattern and not only by wave reflection. We assessed whether RWTT, assessed by advanced pressure-flow analysis, demonstrates the expected decline with aging. Methods and Results-We studied a sample of unselected adults without cardiovascular disease (n=48; median age 48 years) and a clinical population of older adults with suspected/established cardiovascular disease (n=164; 61 years). We measured central pressure and flow with carotid tonometry and phase-contrast MRI, respectively. We assessed RWTT using wave-separation analysis (RWTTWSA) and partially distributed tube-load (TL) modeling (RWTTTL). Consistent with previous reports, T-INF did not appreciably decrease with age despite pronounced increases in PWV in both populations. However, aging was associated with pronounced decreases in RWTTWSA (general population -15.0 ms/decade, P<0.001; clinical population -9.07 ms/decade, P=0.003) and RWTTTL (general -15.8 ms/decade, P<0.001; clinical -11.8 ms/decade, P<0.001). There was no evidence of an increased effective reflecting distance by either method. TINF was shown to reliably represent RWTT only under highly unrealistic assumptions about input impedance. Conclusions-RWTT declines with age in parallel with increased PWV, with earlier effects of wave reflections and without a distal shift in reflecting sites. These findings have important implications for our understanding of the role of wave reflections with aging

Parametrizations of density matrices

This article gives a brief overview of some recent progress in the characterization and parametrization of density matrices of finite dimensional systems. We discuss in some detail the Bloch-vector and Jarlskog parametrizations and mention briefly the coset parametrization. As applications of the Bloch parametrization we discuss the trace invariants for the case of time dependent Hamiltonians and in some detail the dynamics of three-level systems. Furthermore, the Bloch vector of two-qubit systems as well as the use of the polarization operator basis is indicated. As the main application of the Jarlskog parametrization we construct density matrices for composite systems. In addition, some recent related articles are mentioned without further discussion.Comment: 31 pages. v2: 32 pages, Abstract and Introduction rewritten and Conclusion section added, references adde

Von Neumann equations with time-dependent Hamiltonians and supersymmetric quantum mechanics

Starting with a time-independent Hamiltonian $h$ and an appropriately chosen solution of the von Neumann equation $i\dot\rho(t)=[ h,\rho(t)]$ we construct its binary-Darboux partner $h_1(t)$ and an exact scattering solution of $i\dot\rho_1(t)=[h_1(t),\rho_1(t)]$ where $h_1(t)$ is time-dependent and not isospectral to $h$. The method is analogous to supersymmetric quantum mechanics but is based on a different version of a Darboux transformation. We illustrate the technique by the example where $h$ corresponds to a 1-D harmonic oscillator. The resulting $h_1(t)$ represents a scattering of a soliton-like pulse on a three-level system.Comment: revtex, 3 eps file

Saccadic eye movements estimate prolonged time awake

Prolonged time awake increases the need to sleep. Sleep pressure increases sleepiness, impairs human alertness and performance and increases the probability of human errors and accidents. Human performance and alertness during waking hours are influenced by homeostatic sleep drive and the circadian rhythm. Cognitive functions, especially attentional ones, are vulnerable to circadian rhythm and increasing sleep drive. A reliable, objective and practical metrics for estimating sleepiness could therefore be valuable. Our aim is to study whether saccades measured with electro-oculography (EOG) outside the laboratory could be used to estimate the overall time awake without sleep of a person. The number of executed saccades was measured in 11 participants during an 8-min saccade task. The saccades were recorded outside the laboratory (Naval Academy, Bergen) using EOG every sixth hour until 54 hr of time awake. Measurements were carried out on two occasions separated by 10 weeks. Five participants participated in both measurement weeks. The number of saccades decreased during sustained wakefulness. The data correlated with the three-process model of alertness; performance differed between participants but was stable within individual participants. A mathematically monotonous relation between performance in the saccade task and time awake was seen after removing the circadian rhythm component from measured eye movement data. The results imply that saccades measured with EOG can be used as a time-awake metric outside the laboratory.Peer reviewe

Covariance systems

We introduce new definitions of states and of representations of covariance systems. The GNS-construction is generalized to this context. It associates a representation with each state of the covariance system. Next, states are extended to states of an appropriate covariance algebra. Two applications are given. We describe a nonrelativistic quantum particle, and we give a simple description of the quantum spacetime model introduced by Doplicher et al.Comment: latex with ams-latex, 23 page

Desambiguación de autores para un sistema de recuperación de expertos en un contexto académico

La identificación de un autor y sus obras es un componente importante en los sistemas que administran información de publicaciones científicas. Dicha tarea es determinante para identificar expertos y conocer sus obras. El presente trabajo es una investigación para el relevamiento y desarrollo de estrategias de desambiguación de autores para un sistema de recuperación de información del área de las Ciencias de la Computación.Sociedad Argentina de Informática e Investigación Operativ

Clasificación de autores para un proceso de recomendación integrado a un metabuscador científico

La búsqueda de producción científica en la web se ha convertido en un desafío, tanto por volumen, variedad y velocidad de actualización. Se requiere de herramientas que ayuden al usuario a obtener resultados relevantes ante la ejecución de una consulta. Dentro de estas herramientas, este equipo ha desarrollado un metabuscador específico para el área de ciencias de la computación. En su evolución se pretende incorporar recomendaciones de autores para cada consulta de sus usuarios. La generación de tales recomendaciones requiere de un método que cuente con la capacidad de clasificar a los autores para definir su inclusión y posición en un listado de sugerencias para el usuario final. En este trabajo se presenta un método que cumple con este objetivo, habiendo sido evaluado y habiendo obtenido resultados que permiten plantear su inclusión en un posterior desarrollo del sistema recomendador.XV Workshop Bases de Datos y Minería de Datos (WBDDM)Red de Universidades con Carreras en Informática (RedUNCI

Clasificación de autores para un proceso de recomendación integrado a un metabuscador científico

La búsqueda de producción científica en la web se ha convertido en un desafío, tanto por volumen, variedad y velocidad de actualización. Se requiere de herramientas que ayuden al usuario a obtener resultados relevantes ante la ejecución de una consulta. Dentro de estas herramientas, este equipo ha desarrollado un metabuscador específico para el área de ciencias de la computación. En su evolución se pretende incorporar recomendaciones de autores para cada consulta de sus usuarios. La generación de tales recomendaciones requiere de un método que cuente con la capacidad de clasificar a los autores para definir su inclusión y posición en un listado de sugerencias para el usuario final. En este trabajo se presenta un método que cumple con este objetivo, habiendo sido evaluado y habiendo obtenido resultados que permiten plantear su inclusión en un posterior desarrollo del sistema recomendador.XV Workshop Bases de Datos y Minería de Datos (WBDDM)Red de Universidades con Carreras en Informática (RedUNCI

Mechanochemical Synthesis of TiO2 Nanocomposites as Photocatalysts for Benzyl Alcohol Photo-Oxidation

TiO2 (anatase phase) has excellent photocatalytic performance and different methods have been reported to overcome its main limitation of high band gap energy. In this work, TiO2-magnetically-separable nanocomposites (MAGSNC) photocatalysts with different TiO2 loading were synthesized using a simple one-pot mechanochemical method. Photocatalysts were characterized by a number of techniques and their photocatalytic activity was tested in the selective oxidation of benzyl alcohol to benzaldehyde. Extension of light absorption into the visible region was achieved upon titania incorporation. Results indicated that the photocatalytic activity increased with TiO2 loading on the catalysts, with moderate conversion (20%) at high benzaldehyde selectivity (84%) achieved for 5% TiO2-MAGSNC. These findings pointed out a potential strategy for the valorization of lignocellulosic-based biomass under visible light irradiation using designer photocatalytic nanomaterial