6,739 research outputs found

    Direct imaging of a digital-micromirror device for configurable microscopic optical potentials

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    Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.Comment: 9 page

    On the Hausdorff volume in sub-Riemannian geometry

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    For a regular sub-Riemannian manifold we study the Radon-Nikodym derivative of the spherical Hausdorff measure with respect to a smooth volume. We prove that this is the volume of the unit ball in the nilpotent approximation and it is always a continuous function. We then prove that up to dimension 4 it is smooth, while starting from dimension 5, in corank 1 case, it is C^3 (and C^4 on every smooth curve) but in general not C^5. These results answer to a question addressed by Montgomery about the relation between two intrinsic volumes that can be defined in a sub-Riemannian manifold, namely the Popp and the Hausdorff volume. If the nilpotent approximation depends on the point (that may happen starting from dimension 5), then they are not proportional, in general.Comment: Accepted on Calculus and Variations and PD

    Towards a monolithic optical cavity for atom detection and manipulation

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    We study a Fabry-Perot cavity formed from a ridge waveguide on a AlGaAs substrate. We experimentally determined the propagation losses in the waveguide at 780 nm, the wavelength of Rb atoms. We have also made a numerical and analytical estimate of the losses induced by the presence of the gap which would allow the interaction of cold atoms with the cavity field. We found that the intrinsic finesse of the gapped cavity can be on the order of F ~ 30, which, when one takes into account the losses due to mirror transmission, corresponds to a cooperativity parameter for our system C ~ 1

    Nesterov Meets Optimism: Rate-Optimal Separable Minimax Optimization

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    We propose a new first-order optimization algorithm -- AcceleratedGradient-OptimisticGradient (AG-OG) Descent Ascent -- for separable convex-concave minimax optimization. The main idea of our algorithm is to carefully leverage the structure of the minimax problem, performing Nesterov acceleration on the individual component and optimistic gradient on the coupling component. Equipped with proper restarting, we show that AG-OG achieves the optimal convergence rate (up to a constant) for a variety of settings, including bilinearly coupled strongly convex-strongly concave minimax optimization (bi-SC-SC), bilinearly coupled convex-strongly concave minimax optimization (bi-C-SC), and bilinear games. We also extend our algorithm to the stochastic setting and achieve the optimal convergence rate in both bi-SC-SC and bi-C-SC settings. AG-OG is the first single-call algorithm with optimal convergence rates in both deterministic and stochastic settings for bilinearly coupled minimax optimization problems.Comment: 44 pages. This version matches the camera-ready that appeared at ICML 2023 under the same titl

    A myoelectric digital twin for fast and realistic modelling in deep learning

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    Muscle electrophysiology has emerged as a powerful tool to drive human machine interfaces, with many new recent applications outside the traditional clinical domains, such as robotics and virtual reality. However, more sophisticated, functional, and robust decoding algorithms are required to meet the fine control requirements of these applications. Deep learning has shown high potential in meeting these demands, but requires a large amount of high-quality annotated data, which is expensive and time-consuming to acquire. Data augmentation using simulations, a strategy applied in other deep learning applications, has never been attempted in electromyography due to the absence of computationally efficient models. We introduce a concept of Myoelectric Digital Twin - highly realistic and fast computational model tailored for the training of deep learning algorithms. It enables simulation of arbitrary large and perfectly annotated datasets of realistic electromyography signals, allowing new approaches to muscular signal decoding, accelerating the development of human-machine interfaces

    Characterization of the "diabesity" gene HMG20A in pancreatic islets

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    Motivation: Type 2 Diabetes (T2D) accounts for 90-95% of diagnosed diabetic patients, which tendency in the next years is also expected to increase. Recent genomic wide association studies showed a correlation of an allelic variation of HMG20A with T2D in some ethnic groups. Up to date, there is no scientific evidence of the role of this gene in pancreatic tissue. But, in central nervous system, HMG20A regulates the expression of NeuroD, common in pancreas and nervous system morphogenesis. Here, our group makes an approach to characterize HMG20A in pancreatic islets, focusing on its involvement in glucose-stimulated insulin secretion (GSIS) and pancreatic islets development. We want to demonstrate that: 1) HMG20A is expressed in endocrine pancreas 2) HMG20A modifies expression of genes involved in pancreas development 3) silencing HMG20A affects expression levels of insulin secretion related genes and functionality.Methods: Qualitative expression of HMG20A is tested out in slides of pancreatic sections obtained from control mice. Co-localization with őĪ or ő≤ cells is analyzed by immunofluorescence using anti-HMG20A, anti-insulin/glucagon antibodies and Dapi for nuclei. INS-1E cells are cultured and treated with a specific siRNA against HMG20A or a non-specific siRNA control during 72h. Genes involved in insulin secretion and endocrine pancreas development are assayed via qRT-PCR in INS1-E cells after siRNA treatment. Pdx1, Pax4, MafA and HMG20A expression levels are assessed following 2-őĒőĒCt method. Finally, HMG20A silenced mouse islets and INS-1E are cultured at low glucose (2.8 mM) and high glucose medium (22 mM) following quantification of insulin secretion by ELISA.Results: Immunofluorescence confirmed co-localization of HMG20A with insulin (ő≤-cell) and with glucagon (őĪ-cells) producing cells in mouse pancreas. HMG20A expression diminished a 60% after treating INS1-E cells with a specific siRNA for HMG20A. Insulin secretion regulator gene, MafA, is downregulated significantly (50-60%) after HMG20A silencing. Pax4 expression significantly increased meanwhile Pdx1 showed a tendency to decrease. A 40% drop in insulin secretion is obtained in siHMG20A treated mouse islets compared to control.Conclusions: This data confirms HMG20A expression in pancreatic islets and impairment of insulin secretion when it is knocked down. Hence, concluding that HMG20A plays an important role in physiological GSIS and regulating pancreatic development related genes

    Polarization instabilities in a two-photon laser

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    We describe the operating characteristics of a new type of quantum oscillator that is based on a two-photon stimulated emission process. This two-photon laser consists of spin-polarized and laser-driven 39^{39}K atoms placed in a high-finesse transverse-mode-degenerate optical resonator, and produces a beam with a power of ‚ąľ\sim 0.2 őľ\mu W at a wavelength of 770 nm. We observe complex dynamical instabilities of the state of polarization of the two-photon laser, which are made possible by the atomic Zeeman degeneracy. We conjecture that the laser could emit polarization-entangled twin beams if this degeneracy is lifted.Comment: Accepted by Physical Review Letters. REVTeX 4 pages, 4 EPS figure

    PAX4 preserves endoplasmic reticulum integrity preventing beta cell degeneration in a mouse model of type 1 diabetes mellitus

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    [Aims/hypothesis]: A strategy to enhance pancreatic islet functional beta cell mass (BCM) while restraining inflammation, through the manipulation of molecular and cellular targets, would provide a means to counteract the deteriorating glycaemic control associated with diabetes mellitus. The aims of the current study were to investigate the therapeutic potential of such a target, the islet-enriched and diabetes-linked transcription factor paired box 4 (PAX4), to restrain experimental autoimmune diabetes (EAD) in the RIP-B7.1 mouse model background and to characterise putative cellular mechanisms associated with preserved BCM. [Methods]: Two groups of RIP-B7.1 mice were genetically engineered to: (1) conditionally express either PAX4 (BPTL) or its diabetes-linked mutant variant R129W (mutBPTL) using doxycycline (DOX); and (2) constitutively express luciferase in beta cells through the use of RIP. Mice were treated or not with DOX, and EAD was induced by immunisation with a murine preproinsulin II cDNA expression plasmid. The development of hyperglycaemia was monitored for up to 4 weeks following immunisation and alterations in the BCM were assessed weekly by non-invasive in vivo bioluminescence intensity (BLI). In parallel, BCM, islet cell proliferation and apoptosis were evaluated by immunocytochemistry. Alterations in PAX4- and PAX4R129W-mediated islet gene expression were investigated by microarray profiling. PAX4 preservation of endoplasmic reticulum (ER) homeostasis was assessed using thapsigargin, electron microscopy and intracellular calcium measurements. [Results]: PAX4 overexpression blunted EAD, whereas the diabetes-linked mutant variant PAX4R129W did not convey protection. PAX4-expressing islets exhibited reduced insulitis and decreased beta cell apoptosis, correlating with diminished DNA damage and increased islet cell proliferation. Microarray profiling revealed that PAX4 but not PAX4R129W targeted expression of genes implicated in cell cycle and ER homeostasis. Consistent with the latter, islets overexpressing PAX4 were protected against thapsigargin-mediated ER-stress-related apoptosis. Luminal swelling associated with ER stress induced by thapsigargin was rescued in PAX4-overexpressing beta cells, correlating with preserved cytosolic calcium oscillations in response to glucose. In contrast, RNA interference mediated repression of PAX4-sensitised MIN6 cells to thapsigargin cell death. [Conclusions/interpretation]: The coordinated regulation of distinct cellular pathways particularly related to ER homeostasis by PAX4 not achieved by the mutant variant PAX4R129W alleviates beta cell degeneration and protects against diabetes mellitus. The raw data for the RNA microarray described herein are accessible in the Gene Expression Omnibus database under accession number GSE62846

    Serum dioxin and PCB levels among PCB waste processing plant workers

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    peer reviewedA clinical investigation and a biological monitoring were carried out to evaluate the occupational exposure of workers in contact with pyralen in a PCB-transformer and capacitor decontamination plant in France. The aim of this study was to assess the body burden of polychlorinated dibenzo-p- dioxin (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like (DL) PCBs and marker PCBs for those workers. We examined 8 representative workers (34-44 years old). The subjects of this study worked from 5 years to 19 years at the plant. All workers reported daily multiple contacts with various metal and wood parts of dismantled transformers during working hours. On a yearly basis, the exposed subjects were examined by the occupational health physician for a check-up. Basic parameters such as liver function and lipid statement were performed
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