Theory for a Hanbury Brown Twiss experiment with a ballistically expanding cloud of cold atoms

We have studied one-body and two-body correlation functions in a ballistically expanding, non-interacting atomic cloud in the presence of gravity. We find that the correlation functions are equivalent to those at thermal equilibrium in the trap with an appropriate rescaling of the coordinates. We derive simple expressions for the correlation lengths and give some physical interpretations. Finally a simple model to take into account finite detector resolution is discussed

Synthesis, structure and non-linear optical properties of L-argininium perrhenate crystal

A new hybrid organic–inorganic non-linear optical crystalline material, L-argininium perrhenate has been synthesized. The crystal belongs to P212121 space group, has a good optical quality and high transmission in the visible and near infra-red spectral regions. L-argininium perrhenate has high birefringence and is more than four times as efficient as KDP in second harmonic generation, making it a potentially attractive material for non-linear optical applicationsThis work was financially supported by the European Regional Development Fund (ERDF) through Programa Operacional Factores de Competitividade (COMPETE: FCOMP-01-0124-FEDER-014628) and the Portugal Fundacao para a Ciencia e Tecnologia (PTDC/CTM-NAN/114269/2009, PTDC/CTM/105597/2008 and Pest-C/FIS/UI0036/2011)

High nonlinear optical anisotropy of urea nanofibers

Nanofibers consisting of the optically nonlinear organic molecule urea embedded in both poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) polymers were produced by the electrospinning technique. The second-harmonic generation produced by aligned fiber mats of these materials displays a strong dependence on the polarization of the incident light. In PVA-urea nanofibers the effectiveness in generating of the second-harmonic light is as high as that of a pure urea powder with an average grain size of 110 μm. The results suggest that single crystalline urea nanofibers were achieved with a long-range crystalline order extending into the range of 2–4 μm with PVA as the host polymer.This work was carried out in the frame of CIENCIA-2007 program (reference UMINHO-CF06) and financially supported by Fundacao para a Ciencia e Tecnologia, PTDC/CTM/105597/2008

Quantitative investigations of quantum coherence for a light-harvesting protein at conditions simulating photosynthesis

Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the initial dynamic response of photosynthetic proteins can involve quantum coherence. We show how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of PC645 at increasing levels of acidity to determine if the change in pH affects the quantum coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change.We acknowledge financial support from DARPA under the QuBE program, the United States Air Force Office of Scientific Research under contract number FA9550-10-1-0260, and the Natural Sciences and Engineering Research Council of Canada. We thank Min-Duk Seo and Mitsuhiko Ikura for assistance with the CD measurements and Philip Johnson, Alexei Halpin, and Jurgen Hauer for helpful conversations regarding the 2D ES apparatus

Laser-Evoked Vertex Potentials Predict Defensive Motor Actions

The vertex potential is the largest response that can be recorded in the electroencephalogram of an awake, healthy human. It is elicited by sudden and intense stimuli, and is composed by a negative-positive deflection. The stimulus properties that determine the vertex potential amplitude have been well characterized. Nonetheless, its functional significance remains elusive. The dominant interpretation is that it reflects neural activities related to the detection of salient stimuli. However, given that threatening stimuli elicit both vertex potentials and defensive movements, we hypothesized that the vertex potential is related to the execution of defensive actions. Here, we directly compared the salience and motoric interpretations by investigating the relationship between the amplitude of laser-evoked potentials (LEPs) and the response time of movements with different defensive values. First, we show that a larger LEP negative wave (N2 wave) predicts faster motor response times. Second, this prediction is significantly stronger when the motor response is defensive in nature. Third, the relation between the N2 wave and motor response time depends not only on the kinematic form of the movement, but also on whether that kinematic form serves as a functional defense of the body. Therefore, the N2 wave of the LEP encodes key defensive reactions to threats

Ferroelectric characterization of aligned barium titanate nanofibres

We report the synthesis, structural and ferroelectric characterization of continuous well-aligned nanofibres of barium titanate produced by the electrospinning technique. The fibres with average diameter of 150–400 nm consist of connected nanoparticles of BaTiO 3 stacked together to form the shape of a long filament. The tetragonal phase in the obtained nanofibres was revealed by the x-ray diffraction and Raman spectroscopy and has been also confirmed by the second harmonic generation (SHG) and piezoresponse force microscopy (PFM). The temperature dependence of the SHG in the vicinity of the paraelectric–ferroelectric phase transition suggests that barium titanate nanofibres are indeed ferroelectric with an apparent glass-like state caused by metastable polar nanoregions. The existence of domain structure and local switching studied by PFM present clear evidence of the polar phase at room temperature.Fundação para a Ciência e a Tecnologia (FCT

Predicting the Position of Attributive Adjectives in the French NP

Cet article est une version révisée de l'article paru dans Student session of the European Summer School for Logic, Language and Information, Copenhague : Danemark (2010)International audienceThis article proposes a quantitative study of the placement alternation for the adjective within the noun phrase in French. Taking the hypothesis that position constraints are mostly preferential as a starting point, we develop a methodology based on statistical inference in order to provide a formal account of the relative importance of different groups of constraints. Results show the relative importance of lexical constraints and that frequency-based and length constraints are the best predictors. This suggests that the placement of adjectives not only depends on our knowledge of lexical items but also on the knowledge of the way in which we use them in discourse, i.e. on usage

Fishing for complementarities : competitive research funding and research productivity

This paper empirically investigates complementarities between different sources of research funding with regard to academic publishing. We find for a sample of UK engineering academics that competitive funding is associated with an increase in ex-post publications but that industry funding decreases the marginal utility of public funding by lowering the publication and citation rate increases associated with public grants. However, when holding all other explanatory variables at their mean, the negative effect of the interaction does not translate into an effective decrease in publication and citation numbers. The paper also shows that the positive effect of public funding is driven by UK research council and charity grants and that EU funding has no significant effect on publication outcomes