On a random walk with memory and its relation to Markovian processes

We study a one-dimensional random walk with memory in which the step lengths to the left and to the right evolve at each step in order to reduce the wandering of the walker. The feedback is quite efficient and lead to a non-diffusive walk. The time evolution of the displacement is given by an equivalent Markovian dynamical process. The probability density for the position of the walker is the same at any time as for a random walk with shrinking steps, although the two-time correlation functions are quite different.Comment: 10 pages, 4 figure

Prospectus, April 10, 2008

https://spark.parkland.edu/prospectus_2008/1009/thumbnail.jp

Prospectus, April 24, 2008

https://spark.parkland.edu/prospectus_2008/1011/thumbnail.jp

Acute stress affects peripersonal space representation in cortisol stress responders.

Peripersonal space is the representation of the space near the body. It is implemented by a dedicated multisensory-motor network, whose purpose is to predict and plan interactions with the environment, and which can vary depending on environmental circumstances. Here, we investigated the effect on the PPS representation of an experimentally induced stress response and compared it to a control, non-stressful, manipulation. We assessed PPS representation in healthy humans, before and after a stressful manipulation, by quantifying visuotactile interactions as a function of the distance from the body, while monitoring salivary cortisol concentration. While PPS representation was not significantly different between the control and experimental group, a relation between cortisol response and changes in PPS emerged within the experimental group. Participants who showed a cortisol stress response presented enhanced visuotactile integration for stimuli close to the body and reduced for far stimuli. Conversely, individuals with a less pronounced cortisol response showed a reduced difference in visuotactile integration between the near and the far space. In our interpretation, physiological stress resulted in a freezing-like response, where multisensory-motor resources are allocated only to the area immediately surrounding the body

Prospectus, February 7, 2008

https://spark.parkland.edu/prospectus_2008/1002/thumbnail.jp

MILIARY TUBERCULOSIS IN THE XXI CENTURY – A CASE REPORT

Introdução: Atualmente, a tuberculose ainda representa um sério problema de saúde pública. A idade precoce e a infeção VIH constituem importantes fatores de risco para doença grave ou disseminada. Caso clínico: Apresentamos o caso de uma menina de três anos de idade observada por febre prolongada sem foco infecioso evidente ao exame físico. O estudo analítico inicial foi sugestivo de infeção urinária, pelo que iniciou antibioticoterapia empírica. A urocultura confirmou esse diagnóstico, mas a febre persistiu. Na investigação complementar, a radiografia torácica revelou um infiltrado pulmonar com padrão miliar. O Mycobacterium tuberculosis foi isolado no aspirado gástrico, líquor e urina. Iniciou tratamento com antituberculosos e corticóide, com melhoria clínica significativa. Conclusões: Nesta era de tecnologia médica avançada, a tuberculose ainda é um desafio diagnóstico, especialmente quando a apresentação clínica é atípica e extrapulmonar. Um elevado índice de suspeição clínica é fundamental, pois a instituição precoce do tratamento é decisiva para o prognóstico

X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143

Thermonuclear X-ray bursts from accreting neutron stars power brief but strong irradiation of their surroundings, providing a unique way to study accretion physics. We analyze MAXI/Gas Slit Camera and Swift/XRT spectra of a day-long flash observed from IGR J17062-6143 in 2015. It is a rare case of recurring bursts at a low accretion luminosity of 0.15% Eddington. Spectra from MAXI, Chandra, and NuSTAR observations taken between the 2015 burst and the previous one in 2012 are used to determine the accretion column. We find it to be consistent with the burst ignition column of 5 × 10^(10) g cm^(−2), which indicates that it is likely powered by burning in a deep helium layer. The burst flux is observed for over a day, and decays as a straight power law: F ∝ t^(-1.15). The burst and persistent spectra are well described by thermal emission from the neutron star, Comptonization of this emission in a hot optically thin medium surrounding the star, and reflection off the photoionized accretion disk. At the burst peak, the Comptonized component disappears, when the burst may dissipate the Comptonizing gas, and it returns in the burst tail. The reflection signal suggests that the inner disk is truncated at ~102 gravitational radii before the burst, but may move closer to the star during the burst. At the end of the burst, the flux drops below the burst cooling trend for 2 days, before returning to the pre-burst level

Prospectus, February 28, 2008

https://spark.parkland.edu/prospectus_2008/1004/thumbnail.jp

Dilaton Interactions and the Anomalous Breaking of Scale Invariance of the Standard Model

We discuss the main features of dilaton interactions for fundamental and effective dilaton fields. In particular, we elaborate on the various ways in which dilatons can couple to the Standard Model and on the role played by the conformal anomaly as a way to characterize their interactions. In the case of a dilaton derived from a metric compactification (graviscalar), we present the structure of the radiative corrections to its decay into two photons, a photon and a $Z$, two $Z$ gauge bosons and two gluons, together with their renormalization properties. We prove that, in the electroweak sector, the renormalization of the theory is guaranteed only if the Higgs is conformally coupled. For such a dilaton, its coupling to the trace anomaly is quite general, and determines, for instance, an enhancement of its decay rates into two photons and two gluons. We then turn our attention to theories containing a non-gravitational (effective) dilaton, which, in our perturbative analysis, manifests as a pseudo-Nambu Goldstone mode of the dilatation current ($J_D$). The infrared coupling of such a state to the two-photons and to the two-gluons sector, and the corresponding anomaly enhancements of its decay rates in these channels, is critically analyzed.Comment: Revised version, 42 pages, 5 figure