Clumps of material orbiting a black hole and the QPOs

Clumps of material orbiting a black hole may be disturbed, somewhat like comets in the Kuiper belt, to relatively small periastron orbits. Each periastron passage changes the orbital parameters in such a way that the orbit becomes more and more eccentric and the angular momentum approaches the critical value for tidal capture. When this value is reached, the body is suddenly caught by the relativistic potential to the last periastron (occurring at two Schwarzschild radii for a non rotating black hole). In this process the transfer of orbital into internal energy heats the body before it makes a few more turns toward the horizon of the black hole. Because of strong relativistic effects this last bright message from the object is seen as a quasi-periodic flare. Assuming that a black hole may be fed by a large number of such small debris we calculate light curves expected from such events. We investigate the resemblance of the Fourier spectra of such light curves with those of observed QPOs.Comment: 3 pages, 6 figure

Do flares in Sagittarius A* reflect the last stage of tidal capture?

In recent years the case for the presence of 3-4 10^6 M_sun black hole in our Galactic Center has gained strength from results of stellar dynamics observations and from the detection of several rapid X-ray and IR flares observed in the Sagittarius A* from 2000 to 2004. Here we explore the idea that such flares are produced when the central black hole tidally captures and disrupts a small body - e.g. a comet or an asteroid.Comment: 6 pages, 9 figures, acknowledgments added, to appear in the Proceedings of the Albert Einstein's Century International Conference, Paris 200

A revised synthesis of the cationic lipids DMRI and MLRI

Lipid nanoparticles (LNPs) are an increasingly utilized method of intracellular delivery for nucleic acids. The COVID-19 vaccines from Moderna and Pfizer-BioNTech have used LNP technology to combat the recent global SARS-CoV-2 pandemic, saving millions of lives.1,2 These vaccines consist of a lipid formulation that binds to the anionic phosphate groups of mRNAs and serves as an effective way to transport the nucleic acid across membranes into cells.9The mRNA encodes a viral protein. When introduced to cells, the viral protein is produced so that the immune system then can generate an appropriate antibody response.3 However, this approach — genetic immunization, a type of gene therapy — is still developing and needs improvement, with new lipids continually being discovered to better help transport nucleic acids into target cells. One such group of state-of-the-art, ‘third-generation’ lipids are hydroxylated oxime ether lipids (OELs), with emphasis on lipid OEL4.4 Although OEL4 formulations have been proven to be an effective transport agent for small interfering RNA (siRNA) in animal model experiments, there are still questions of whether OEL lipids are superior to previous lipid-based delivery systems, such as the efficacious second-generation lipids DMRI (dimyristoyl Rosenthal inhibitor) and MLRI (dissymmetric myristoyl and lauroyl Rosenthal inhibitor), especially in tissue systems not yet well studied.5,6As a result, our long-range goal is to directly compare synthesized OEL4 to both MLRI and DMRI in order to further analyze their respective abilities to deliver genes to the central nervous system (CNS), an area of study in which ortho ester lipids have not been examined. However, what is of particular interest to the present thesis work is the refinement of a synthetic route to both MLRI and DMRI. By circumventing multiple steps in the known synthesis of MLRI and DMRI, there is the possibility of developing a better way for synthesizing these molecules that would reduce both time and cost, which is of great interest for obvious reasons. Thus, the immediate goal of this work is to examine a new synthesis of MLRI and DMRI to make these lipids available for the key comparative study with OEL4. In this project, the quaternary ammonium moiety (R4N+ portion of molecule responsible for the characteristic RNA-binding properties of the molecule) of OEL4, MLRI, and DMRI will also be assessed, and their effectiveness will be hypothesized in comparison to newer LNP formulations, such as those using eiOEL4. The key difference between eiOEL4 and OEL4, MLRI, and DMRI is that eiOEL4 has a tertiary amine core instead of a quaternary ammonium salt. eiOEL4 is also different from OEL4 in that the carbon chain between the oxime ether linkage and the tertiary amine is longer, having been increased from two carbons to five, hence the designation eiOEL4 (extended, ionizable OEL4). The hypothesis of this thesis is that the protection group strategy (i.e., trityl-group protection of a primary alcohol) used in the literature synthesis of MLRI is unnecessary and can be circumvented. Eliminating this step has the potential to save two linear steps in the synthesis sequence and thereby lower the cost of overall lipid production. The lipids will also be assessed in comparison to the “newer generation” lipids in future studies and whether the newer formulation of this LNP is better than the classical molecules for gene delivery. We confirmed that the trityl-group strategy employed in the synthesis of MLRI is not needed. Along with this refinement, we examined the synthesis of DMRI by using an excess of acid chloride in the first acylation step, further reducing a step in the synthesis of this lipid. However, due to small scale reactions, and novice level mistakes, some reaction steps lost yield, which can be minimized in future applications

Cross-Border Investment, Conflict of Laws, and the Privatization of Securities Law

The rapid acceleration of transnational investing is occurring in an environment in which emerging markets, and foreign interest in these markets, are exploding. The issues involved with cross-border investment, conflict of laws and the privatization of securities law are examined

Quantification of the early pupillary dilation kinetic to assess rod and cone activity.

Rods, cones and melanopsin contribute in various proportions, depending on the stimulus light, to the pupil light response. This study used a first derivative analysis to focus on the quantification of the dynamics of pupillary dilation that immediately follows light-induced pupilloconstriction in order to identify novel parameters that reflect rod and cone activity. In 18 healthy adults, the pupil response to a 1 s blue light stimulus ranging from - 6.0 to 2.65 log cd/m <sup>2</sup> in dark-adapted conditions and to a 1 s blue light stimulus (2.65 log cd/m <sup>2</sup> ) in light-adapted conditions was recorded on a customized pupillometer. Three derivative parameters which describe the 2.75 s following the light onset were quantified: dAMP (maximal amplitude of the positive peak), dLAT (latency of the positive peak), dAUC (area under the curve of the positive peak). We found that dAMP and dAUC but not dLAT have graded responses over a range of light intensities. The maximal positive value of dAMP, representing maximal rate of change of early pupillary dilation phase, occurs at - 1.0 log cd/m <sup>2</sup> and this stimulus intensity appears useful for activating rods and cones. From - 0.5 log cd/m <sup>2</sup> to brighter intensities dAMP and dAUC progressively decrease, reaching negligible values at 2.65 log cd/m <sup>2</sup> indicative of a melanopsin-driven pupil response that masks the contribution from rods and cones to the early phase of pupillary dilation

Estimating Koopman operators with sketching to provably learn large scale dynamical systems

The theory of Koopman operators allows to deploy non-parametric machine learning algorithms to predict and analyze complex dynamical systems. Estimators such as principal component regression (PCR) or reduced rank regression (RRR) in kernel spaces can be shown to provably learn Koopman operators from finite empirical observations of the system's time evolution. Scaling these approaches to very long trajectories is a challenge and requires introducing suitable approximations to make computations feasible. In this paper, we boost the efficiency of different kernel-based Koopman operator estimators using random projections (sketching). We derive, implement and test the new “sketched” estimators with extensive experiments on synthetic and large-scale molecular dynamics datasets. Further, we establish non asymptotic error bounds giving a sharp characterization of the trade-offs between statistical learning rates and computational efficiency. Our empirical and theoretical analysis shows that the proposed estimators provide a sound and efficient way to learn large scale dynamical systems. In particular our experiments indicate that the proposed estimators retain the same accuracy of PCR or RRR, while being much faster. Code is available at https://github.com/Giodiro/NystromKoopman

Compression and strength behaviour of viscose/polypropylene nonwoven fabrics

Compression and strength properties of viscose/polypropylene nonwoven fabrics has been studied. Compressionbehavior of the nonwoven samples (sample compressibility, sample thickness loss & sample compressive resilience) havebeen analyzed considering the magnitude of applied pressure, fabric weight, fabric thickness, and the porosity of thesamples. Based on the calculated porosity of the samples, pore compression behavior (pore compressibility, porosity loss &pore compressive resilience) are determined. Equations for the determination of pore compressibility, porosity loss, and porecompressive resilience, are established. Tensile strength and elongation as well as bursting strength and ball traverseelongation are also determined. The results show that the sample compression behavior as well as pore compressionbehavior depend on the magnitude of applied pressure. At the high level of applied pressure, a sample with highercompressibility has the lower sample compressive resilience. Differences in pore compressibility and porosity loss betweeninvestigated samples have also been registered, except in pore compressive resilience. Sample with the higher fabric weight,higher thickness, and lower porosity shows the lower sample compressibility, pore compressibility, sample thickness loss,porosity loss, and tensile elongation, but the higher tensile strength, bursting strength, and ball traverse elongation

Design of Proportional-Resonant Control for Current Harmonic Compliance in Electric Railway Power Systems

This paper presents the process of designing proportional-resonant controller for a four-quadrant rectifier in electric railway traction system. In the context of ever-stricter power quality and electromagnetic compatibility standards in electric railway power systems, developers of electric locomotives need to adapt with new ways to comply. This paper develops on the process of designing a four-quadrant rectifier proportional-resonant control for mitigation of low frequency current harmonic distortion, a novel method in the field of railway EMC. The control parameters are determined through analytical modeling of the rectifier through transfer functions. For the purpose of studying the harmonic distortion mitigation effects, only the current control loop was modeled and designed. The modeling starts with simplification of the model via large-signal modeling of the power converter. The parameters of the circuit then were used to develop the transfer functions, and select the appropriate parameter values of the current loop plant. The control loop and parameters were evaluated on test locomotive to validate the control, with results confirming the improved impact on the electromagnetic compatibility and conformity to regulation

Paramagnetic Meissner Effect in Multiply-Connected Superconductors

We have measured a paramagnetic Meissner effect in Nb-Al2O3-Nb Josephson junction arrays using a scanning SQUID microscope. The arrays exhibit diamagnetism for some cooling fields and paramagnetism for other cooling fields. The measured mean magnetization is always less than 0.3 flux quantum (in terms of flux per unit cell of the array) for the range of cooling fields investigated. We demonstrate that a new model of magnetic screening, valid for multiply-connected superconductors, reproduces all of the essential features of paramagnetism that we observe and that no exotic mechanism, such as d-wave superconductivity, is needed for paramagnetism.Comment: 4 pages, 3 figures, LaTe