Formation and stability of a two-dimensional nickel silicide on Ni (111) an Auger, LEED, STM, and high-resolution photoemission Study

Using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunnelling microscopy (STM) and high resolution photo-electron spectroscopy (HR-PES) techniques we have studied the annealing effect of one silicon monolayer deposited at room temperature onto a Ni (111) substrate. The variations of the Si surface concentration, recorded by AES at 300{\deg}C and 400{\deg}C, show at the beginning a rapid Si decreasing followed by a slowing down up to a plateau equivalent to about 1/3 silicon monolayer. STM images and LEED patterns, both recorded at room temperature just after annealing, reveal the formation of an ordered hexagonal superstructure(rot3xrot3)R30{\deg}-type. From these observations and from a quantitative analysis of HR-PES data, recorded before and after annealing, we propose that the (rot3 x rot3)R30{\deg}superstructure corresponds to a two dimensional (2D) Ni2Si surface silicide.Comment: Journal Physical Review B (2012

Photopolarimetric Retrievals of Snow Properties

Polarimetric observations of snow surfaces, obtained in the 410-2264 nm range with the Research Scanning Polarimeter onboard the NASA ER-2 high-altitude aircraft, are analyzed and presented. These novel measurements are of interest to the remote sensing community because the overwhelming brightness of snow plagues aerosol and cloud retrievals based on airborne and spaceborne total reflection measurements. The spectral signatures of the polarized reflectance of snow are therefore worthwhile investigating in order to provide guidance for the adaptation of algorithms currently employed for the retrieval of aerosol properties over soil and vegetated surfaces. At the same time, the increased information content of polarimetric measurements allows for a meaningful characterization of the snow medium. In our case, the grains are modeled as hexagonal prisms of variable aspect ratios and microscale roughness, yielding retrievals of the grains' scattering asymmetry parameter, shape and size. The results agree with our previous findings based on a more limited data set, with the majority of retrievals leading to moderately rough crystals of extreme aspect ratios, for each scene corresponding to a single value of the asymmetry parameter

Fel Oscillators with Tapered Undulators: Inclusion of Harmonic Generation and Pulse Propagation

We review the theory of FEL oscillators operating with tapered undulators. We consider the case of a uniform tapering and introduce a parameter which characterizes the effect of the tapering on the gain and on the saturation intensity. We analyze the effect of the tapering on the FEL dynamics by including the pulse propagation effects too. We analyze the importance of tapering as a tool to model the optical pulse shapes and to control the higher harmonic intensities

Topoisomerase IB: a relaxing enzyme for stressed DNA

DNA topoisomerase I enzymes relieve the torsional strain in DNA; they are essential for fundamental molecular processes such as DNA replication, transcription, recombination, and chromosome condensation; and act by cleaving and then religating DNA strands. Over the past few decades, scientists have focused on the DNA topoisomerases biological functions and established a unique role of Type I DNA topoisomerases in regulating gene expression and DNA chromosome condensation. Moreover, the human enzyme is being investigated as a target for cancer chemotherapy. The active site tyrosine is responsible for initiating two transesterification reactions to cleave and then religate the DNA backbone, allowing the release of superhelical tension. The different steps of the catalytic mechanism are affected by various inhibitors; some of them prevent the interaction between the enzyme and the DNA while others act as poisons, leading to TopI-D NA lesions, breakage of DNA, and eventually cellular death. In this review, our goal is to provide an overview of mechanism of human topoisomerase IB action together with the different types of inhibitors and their effect on the enzyme functionality

Cerebral plasticity in acute vestibular deficit

The aim of this study was to analyze the effect of acute vestibular deficit on the cerebral cortex and its correlation with clinical signs and symptoms. Eight right-handed patients affected by vestibular neuritis, a purely peripheral vestibular lesion, underwent two brain single photon emission computed tomography (SPECT) in 1 month. The first SPECT analysis revealed reduced blood flow in the temporal frontal area of the right hemisphere in seven of eight patients, independent of the right/left location of the lesion. The alteration was present always in the right, non-dominant hemisphere and was reversible in some patients 1 month after the onset, together with attenuation of signs and symptoms. It may be hypothesized that the transient reduction of cortical blood flow and subsequently of cortical activity in the non-dominant hemisphere, also the expression of cerebral plasticity, may serve as a defense mechanism aimed to attenuate the vertigo symptom

Polarization phase gate with a tripod atomic system

We analyze the nonlinear optical response of a four-level atomic system driven into a tripod configuration. The large cross-Kerr nonlinearities that occurr in such a system are shown to produce nonlinear phase shift of order $\pi$. Such a substantial shift may be observed in a cold atomic gas in a magneto-optical trap where it coupl be fasibly exploited towards the realization of a polarization quantum phase gate. The experimental feasibility of such a gate is here examined in detail.Comment: Corrected versio

Indium(111) pentetreotide single photon emission computed tomography (In-111 pentetreotide SPECT): a new technique to evaluate somatostatin receptors in chordomas

Chordomas are rare neoplasms originating along the neuraxis. Although they do not usually show cytological atypia, metastases have been reported in 30 per cent of cases. Survival rates in cases of skull base locations are low, and local recurrence is common after local excision. Radiation therapy is used in post-operative treatment and proton radiation therapy as the primary treatment. In the present paper we present the case of a 50-year-old Caucasian man affected by chordoma of the clivus, with liver and chest metastases, relapsed after several surgical local excisions, to discuss improvements in therapeutic and imaging techniques. Indium(III) (In-III) pentetreotide single photon emission computed tomography (SPECT) was employed to assess the presence of somatostatin receptors and to treat the tumour with radiolabelled Y-90-DOTA-lanreotide. Imaging, performed 2 months afterwards, showed stable disease in the lungs but a local progression in the metastases, in comparison with pre-treatment uptake. These data suggest the usefulness of radiolabelled somatostatin analogues in the diagnosis and therapy of chordomas

Vestibulo-Ocular Reflex Modification after Virtual Environment Exposure

Immersion in an illusory world is possible by means of virtual reality (VR), where environmental perception is modi bff c1c ed by artificial sensorial stimulation. The application of VR for the assessment and rehabilitation of pathologies affecting the vestibular system, in terms of both diagnosis and care, could represent an interesting new line of research. Our perception of reality is in fact based on static and dynamic spatial information perceived by our senses. During head movements in a virtual environment the images on the display and the labyrinthine information relative to the head angular accelerations differ and therefore a visuo-vestibular conflict is present. It is known that mismatches between visual and labyrinthine information may modify the vestibulo-oculomotor reflex (VOR) gain. We studied the post-immersion modifications in 20 healthy subjects (mean age 25 years) exposed to a virtual environment for 20 min by wearing a head-mounted display. VOR gain and phase were measured by means of harmonic sinusoidal stimulation in the dark before, at the end of and 30 min after VR exposure. A VOR gain reduction was observed in all subjects at the end of VR exposure which disappeared after 30 min. Our data show that exposure to a virtual environment can induce a temporary modi bff c1c cation of the VOR gain. This bff c1c nding can be employed to enable an artificial, instrumental modification of the VOR gain and therefore opens up new perspectives in the assessment and rehabilitation of vestibular diseases

Gaussian two-mode attacks in one-way quantum cryptography

We investigate the asymptotic security of one-way continuous variable quantum key distribution against Gaussian two-mode coherent attacks. The one-way protocol is implemented by arranging the channel uses in two-mode blocks. By applying symmetric random permutations over these blocks, the security analysis is in fact reduced to study two-mode coherent attacks and, in particular, Gaussian ones, due to the extremality of Gaussian states. We explicitly show that the use of two-mode Gaussian correlations by an eavesdropper leads to asymptotic secret key rates which are strictly larger than the rate obtained under standard single-mode Gaussian attacks.Comment: 9 pages, 2 figure

Socioeconomic risk, parenting during the preschool years and child health age 6 years

Parent–child relationships and parenting processes are emerging as potential life course determinants of health. Parenting is socially patterned and could be one of the factors responsible for the negative effects of social inequalities on health, both in childhood and adulthood. This study tests the hypothesis that some of the effect of socioeconomic risk on health in mid childhood is transmitted via early parenting. Methods: Prospective cohort study in 10 USA communities involving 1041 mother/ child pairs, selected at birth at random with conditional sampling. Exposures: income, maternal education, maternal age, lone parenthood, ethnic status and objective assessments of mother child interaction in the first 4 years of life covering warmth, negativity and positive control. Outcomes: mother’s report of child’s health in general at 6 years. Modelling: multiple regression analyses with statistical testing of mediational processes. Results: All five indicators of socioeconomic status (SES) were correlated with all three measures of parenting, such that low SES was associated with poor parenting. Among the measures of parenting maternal warmth was independently predictive of future health, and among the socioeconomic variables maternal education, partner presence and ‘other ethnic group’ proved predictive. Measures of parenting significantly mediated the impact of measures of SES on child health. Conclusions: Parenting mediates some, but not all of the detectable effects of socioeconomic risk on health in childhood. As part of a package of measures that address other determinants, interventions to support parenting are likely to make a useful contribution to reducing childhood inequalities in health