Slow Light amplification in a non-inverted gain medium

We investigate the propagation of a coherent probe light pulse through a three-level atomic medium (in the $\Lambda$--configuration) in the presence of a pump laser under the conditions for gain without inversion. When the carrier frequency of the probe pulse and the pump laser are in a Raman configuration, we show that it is possible to amplify a slow propagating pulse. We also analyze the regime in which the probe pulse is slightly detuned from resonance where we observe anomalous light propagation.Comment: 7 pages, 10 figures. To be published in Europhysics Letter

Active primate simulator Final report

Systems engineering data and design specifications for Biosatellite active primate simulato

Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient $\beta$ on the excited state ($2^3P_2$) and metastable state ($2^3S_1$) populations is also investigated. From these results we infer a rather uniform rate constant $K_{sp}=(1{\pm}0.4)\times10^{-7}$ cm$^3$/s.Comment: 8 pages, 9 figures, Revte

Optical mapping of neuronal activity during seizures in zebrafish

Mapping neuronal activity during the onset and propagation of epileptic seizures can provide a better understanding of the mechanisms underlying this pathology and improve our approaches to the development of new drugs. Recently, zebrafish has become an important model for studying epilepsy both in basic research and in drug discovery. Here, we employed a transgenic line with pan-neuronal expression of the genetically-encoded calcium indicator GCaMP6s to measure neuronal activity in zebrafish larvae during seizures induced by pentylenetretrazole (PTZ). With this approach, we mapped neuronal activity in different areas of the larval brain, demonstrating the high sensitivity of this method to different levels of alteration, as induced by increasing PTZ concentrations, and the rescuing effect of an anti-epileptic drug. We also present simultaneous measurements of brain and locomotor activity, as well as a high-throughput assay, demonstrating that GCaMP measurements can complement behavioural assays for the detection of subclinical epileptic seizures, thus enabling future investigations on human hypomorphic mutations and more effective drug screening methods. Notably, the methodology described here can be easily applied to the study of many human neuropathologies modelled in zebrafish, allowing a simple and yet detailed investigation of brain activity alterations associated with the pathological phenotype

Efficient magneto-optical trapping of a metastable helium gas

This article presents a new experiment aiming at BEC of metastable helium atoms. It describes the design of a high flux discharge source of atoms and a robust laser system using a DBR diode coupled with a high power Yb doped fiber amplifier for manipulating the beam of metastable atoms. The atoms are trapped in a small quartz cell in an extreme high vacuum. The trapping design uses an additional laser (repumper) and allows the capture of a large number of metastable helium atoms (approximately $10^9$) in a geometry favorable for loading a tight magnetostatic trap.Comment: 12 pages, 7 figures, Late

Bimodal Spectroscopy of Formalin Fixed Samples to Discriminate Dysplastic and Tumor Brain Tissues

Biomedical spectroscopy has gained attention in the past few years for disease diagnosis. Fluorescence and Raman spectroscopies provide finger-print information related to biochemical and morphological alterations when tissues progress from the normal to a malignant stage. Usually, freshly excised tissue specimens are preferred for bio-spectroscopic studies. However, ethical issues, sample availability and distance between the surgery room and the laboratory provide an impelling restriction for in-vitro spectroscopic studies using freshly excised samples. After surgical resection tissues are fixed in 4% formalin for histological studies under a light microscope. The process of fixation prevents degradation of tissues. In this study, we probe the use of formalin fixed sample for differentiating normal and dysplastic brain tissues using fluorescence and Raman spectroscopies. It was found that fluorescence spectral profile changes in the wavelength range from 550-750 nm between dysplastic and tumor samples. Also, significant differences were found in the Raman spectral profiles of such samples. The results indicate a potential diagnostic application of spectroscopy in formalin fixed brain samples for differentiating dysplastic and tumor brain tissues

Multidimensional clustering of EU regions. A contribution to orient public policies in reducing regional disparities

This paper applies multidimensional clustering of EU-28 regions with regard to their specialisation strategies and socioeconomic characteristics. It builds on an original dataset. Several academic studies discuss the relevant issues to be addressed by innovation and regional development policies, but so far no systematic analysis has linked the different aspects of EU regions research and innovation strategies (RIS3) and their socio-economic characteristics. This paper intends to fill this gap, with the aim to provide clues for more effective regional and innovation policies. In the data set analysed in this paper, the socioeconomic and demographic classification associates each region to one categorical variable (with 19 categories), while the classification of the RIS3 priorities clustering was performed separately on “descriptions” (21 Boolean categories) and “codes” (11 Boolean Categories) of regions’ RIS3. The cluster analysis, implemented on the results of the correspondence analysis on the three sets of categories, returns 9 groups of regions that are similar in terms of priorities and socioeconomic characteristics. Each group has different characteristics that revolve mainly around the concepts of selectivity (group’s ability to represent a category) and homogeneity (similarity in the group with respect to one category) with respect to the different classifications on which the analysis is based. Policy implications showed in this paper are discussed as a contribution to the current debate on post-2020 European Cohesion Policy, which aims at orienting public policies toward the reduction of regional disparities and to the enhance complementarities and synergies within macro-regions

Detecting multidimensional clustering across EU regions. Focus on R&I smart specialisation strategies and on socio-economic and demographic conditions

This paper applies multidimensional clustering of EU-28 regions to identify similar specialisation strategies and socioeconomic characteristics. It builds on an original dataset where the EU-28 regions are classified according to their socioeconomic and demographic features and to the strategic priorities outlined in their research and innovation smart specialisations strategy (RIS3). The socioeconomic and demographic classification associates each region to one categorical variable (with 19 modalities), while the classification of the RIS3 priorities clustering was performed separately on “descriptions” (21 Boolean categories) and “codes” (11 Boolean Categories) of regions’ RIS3. Three techniques of clustering have been applied: Infomap multilayer algorithm, Correspondence Analysis plus Cluster Analysis and cross tabulation. The most effective clustering, in terms of both the characteristics of the data and the emerging results, is that obtained on the results of the Correspondence Analysis. By contrast, due to the very dense network induced by the data characteristics, the Infomap algorithm does not produce significant results. Finally, cross tabulation is the most detailed tool to identify groups of regions with similar characteristics. In particular, in the paper we present an application of cross tabulation to focus on the regions investing in sustainable development priorities. Policy implications of methods implemented in this paper are discussed as a contribution to the current debate on post-2020 European Cohesion Policy, which aims at orienting public policies toward the reduction of regional disparities and the enhancement of complementarities and synergies within macroregions

Calibration of optical tweezers with positional detection in the back-focal-plane

We explain and demonstrate a new method of force- and position-calibration for optical tweezers with back-focal-plane photo detection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped ob ject as an input. Thus, neither the viscosity, nor the size of the trapped ob ject, nor its distance to nearby surfaces need to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error-bars. We tested this experimentally, near and far from surfaces. Both position- and force-calibration were accurate to within 3%. To calibrate, we moved the sample with a piezo-electric translation stage, but the laser beam could be moved instead, e.g. by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a micro-sphere in non-constant motion parallel to it. We give such a formula.Comment: Submitted to: Review of Scientific Instruments. 13 pages, 5 figures. Appendix added (hydrodynamically correct calibration