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Symmetry breaking in binary Bose-Einstein condensates in the presence of an inhomogeneous artificial gauge field
Get PDFWe study a twocomponent Bose-Einstein condensate in the presence of an inhomogeneous artificial gauge field. In response to this field, the condensate forms a localized vortex lattice structure that leads to a nontrivial symmetry breaking in the phase separated regime. The underlying physical mechanism can be understood by considering the energy landscape and we present a simplified model that is capable of reproducing the main features of the phase separation transition. The intuition gained by numerically solving this simplified model is then corroborated using an analytical solution found within the Thomas-Fermi limit.journal articl
Total stochastic gradient algorithms and applications to model-based reinforcement learning
Get PDFOkinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyOptimizing via stochastic gradients is a powerful and exible technique ubiquitously used in machine learning, reinforcement learning, control, operations research, etc. In many of these applications, the gradients are estimated through a stochastic sampling process, and the learning performance hinges on the accuracy of the estimated gradients. This thesis develops a collection of several novel statistical algorithms to acquire improved gradient estimation accuracy. The need to develop such algorithms was motivated from a model-based reinforcement learning (MBRL) scenario, where I observed that chaotic properties of the dynamics caused the gradient variance to explode when using standard gradient estimation techniques, such as reparameterization gradients. The new techniques sometimes improve the accuracy by 10⁶ times and more. The methods rely on both new gradient estimators, as well as clever algorithms to take advantage of the graph structure of the computations to combine estimators in a statistically principled way. While the work started by trying to solve a specific problem related to MBRL, the proposed solutions are general and applicable to any other stochastic computation graph. The problems with chaos have recently been also observed in other tasks, such as meta-learning or protein folding software, and the solutions may prove useful in those domains as well. The main contributions are 1) an MBRL framework called PIPPS, which is similar to the PILCO algorithm, but lifts all of its restrictions by swapping the cumbersome moment-matching computations with a particle sampling approach while achieving the same learning performance with no down-sides, 2) the total propagation algorithm, which is a replacement for backpropagation that prevents the exploding gradient problem by combining gradient estimators in the backwards pass, 3) the probabilistic computation graph framework, which is an intuitive visual method to reason about total gradients on graphs, 4) new policy gradient estimators derived by using the probabilistic computation graph framework, 5) some theoretical discussion about control variates for gradients, a unified theory of reparameterization and likelihood ratio gradient estimators, and an optimal importance sampling scheme for reducing likelihood ratio gradient variance. I hope this work may lead towards new software frameworks that go beyond backpropagation, and implement more advanced methods for estimating gradients.doctoral thesi
Imaging and time-resolved study of laser-induced fluorescence of dysprosium atoms injected into superfluid helium
Get PDFWe study the time evolution of the cloud of Dy atoms dispersed in superfluid helium and investigate the possibility of using these atoms as tracers for the imaging of superfluid-helium flows. The atoms are produced by pulsed laser ablation and are visualized via their laser-induced fluorescence. It turns out that the observation time is limited by the optical pumping of the atomic population into a nonabsorbing metastable state which is also responsible for the saturation of the fluorescence yield observed earlier.journal articl
Varroa mite evolution: a neglected aspect of worldwide bee collapses?
Get PDFWhile ectoparasitic Varroa mites cause minimal damage to their co-evolved ancestral host, the eastern honey bee (Apis cerana), they devastate their novel host, the western honey bee (Apis mellifera). Over several decades, the host switch caused worldwide population collapses, threatening global food security. Varroa management strategies have focused on breeding bees for tolerance. But, can Varroa overcome these counter-adaptations in a classic coevolutionary arms race? Despite increasing evidence for Varroa genetic diversity and evolvability, this eventuality has largely been neglected. We therefore suggest a more holistic paradigm for studying this host-parasite interaction, one in which 'Varroa-tolerant' bee traits should be viewed as a shared phenotype resulting from Varroa and honey bee interaction.journal articl
A holistic approach to interface stabilization for efficient perovskite solar modules with over 2,000-hour operational stability
Get PDFThe upscaling of perovskite solar cells to module scale and long-term stability have been recognized as the most important challenges for the commercialization of this emerging photovoltaic technology. In a perovskite solar module, each interface within the device contributes to the efficiency and stability of the module. Here, we employed a holistic interface stabilization strategy by modifying all the relevant layers and interfaces, namely the perovskite layer, charge transporting layers and device encapsulation, to improve the efficiency and stability of perovskite solar modules. The treatments were selected for their compatibility with low-temperature scalable processing and the module scribing steps. Our unencapsulated perovskite solar modules achieved a reverse-scan efficiency of 16.6% for a designated area of 22.4 cm². The encapsulated perovskite solar modules, which show efficiencies similar to the unencapsulated one, retained approximately 86% of the initial performance after continuous operation for 2,000 h under AM1.5G light illumination, which translates into a T₉₀ lifetime (the time over which the device efficiency reduces to 90% of its initial value) of 1,570 h and an estimated T80 lifetime (the time over which the device efficiency reduces to 80% of its initial value) of 2,680 h.journal articl
The complex viscosity of Möbius macromolecules
Get PDFUsing general rigid bead–rod theory, we explore the effect of twisting a macromolecule on its rheological properties in suspensions. We thus focus on macromolecules having the form of Möbius bands so that the number of twists can be incremented. We call these Möbius macromolecules. When represented in general rigid bead–rod theory, these macromolecules comprise beads whose centers all fall on a Möbius band. From first principles, we calculate the complex viscosity of twisted rings with zero to seven twists. We find that the zero-shear values of the viscosity and first normal stress coefficient increase with twisting. Furthermore, we find that the real part of the complex viscosity descends more rapidly, with frequency, with extent of twist. For the imaginary part of the complex viscosity, the more twisted, the higher the peak. For each part of the dimensionless complex viscosity and the first normal stress coefficient, the results fall on one of just three curves corresponding to zero, even, or odd numbers of twists. We also explore the effects of the length and the aspect ratio of twisted macromolecular suspensions. We close with a worked example for a suspension of triply twisted Möbius annulene.journal articl
A multimodal treatment of carbon ions irradiation, miRNA-34 and mTOR inhibitor specifically control high-grade chondrosarcoma cancer stem cells
Get PDFBackground and purpose
High-grade chondrosarcomas are chemo- and radio-resistant cartilage-forming tumors of bone that often relapse and metastase. Thus, new therapeutic strategies are urgently needed.
Material and methods
Chondrosarcoma cells (CH-2879) were exposed to carbon-ion irradiation, combined with miR-34 mimic and/or rapamycin administration. The effects of treatment on cancer stem cells, stemness-associated phenotype, radioresistance and tumor-initiating properties were evaluated.
Results
We show that high-grade chondrosarcoma cells contain a population of radioresistant cancer stem cells that can be targeted by a combination of carbon-ion therapy, miR-34 mimic administration and/or rapamycin treatment that triggers FOXO3 and miR-34 over-expression. mTOR inhibition by rapamycin triggered FOXO3 and miR-34, leading to KLF4 repression.
Conclusion
Our results show that particle therapy combined with molecular treatments effectively controls cancer stem cells and may overcome treatment resistance of high-grade chondrosarcoma.journal articl
Versatile optical fiber feedthroughs for ultra-high vacuum applications
Get PDFIn this article we present an investigation of three different fiber optic vacuum feedthroughs. Using Swageloktype tube fittings, metal tubings containing the optical fibers are sealed into a vacuum flange. This allows for easy replacement of the feedthrough without replacing the entire flange. Employing only epoxy resin for sealing the optical fiber into the feedthough we have measured a helium diffusion rate of 2:5.10(-10) mbar . l/s, whereas with a combination of a solderglass and epoxy resin seal we have obtained a diffusion rate below 1.10(-2) mbar . l/s. In a third approach, using small tolerance fiber optic ferrules in our feedthroughs, we have obtained helium diffusion rates of below 1.10(-12) mbar . l/s, making these feedthroughs well suited for ultra-high vacuum applications.journal articl
Altered Response to Total Body Irradiation of C57BL/6-Tg (CAG-EGFP) Mice
Get PDFApplication of green fluorescent protein (GFP) in a variety of biosystems as a unique bioindicator or biomarker has revolutionized biological research and made groundbreaking achievements, while increasing evidence has shown alterations in biological properties and physiological functions of the cells and animals overexpressing transgenic GFP. In this work, response to total body irradiation (TBI) was comparatively studied in GFP transgenic C57BL/6-Tg (CAG-EGFP) mice and C57BL/6 N wild type mice. It was demonstrated that GFP transgenic mice were more sensitive to radiation-induced bone marrow death, and no adaptive response could be induced. In the nucleated bone marrow cells of GFP transgenic mice exposed to a middle dose, there was a significant increase in both the percentage of cells expressing pro-apoptotic gene Bax and apoptotic cell death. While in wild type cells, lower expression of pro-apoptotic gene Bax and higher expression of anti-apoptotic gene Bcl-2, and significant lower induction of apoptosis were observed compared to GFP transgenic cells. Results suggest that presence of GFP could alter response to TBI at whole body, cellular and molecular levels in mice. These findings indicate that there could be a major influence on the interpretation of the results obtained in GFP transgenic mice.journal articl