Studying Diquark Structure of Heavy Baryons in Relativistic Heavy Ion Collisions

We propose the enhancement of $\Lambda_c$ yield in heavy ion collisions at RHIC and LHC as a novel signal for the existence of diquarks in the strongly coupled quark-gluon plasma produced in these collisions as well as in the $\Lambda_c$. Assuming that stable bound diquarks can exist in the quark-gluon plasma, we argue that the yield of $\Lambda_c$ would be increased by two-body collisions between $ud$ diquarks and $c$ quarks, in addition to normal three-body collisions among $u$, $d$ and $c$ quarks. A quantitative study of this effect based on the coalescence model shows that including the contribution of diquarks to $\Lambda_c$ production indeed leads to a substantial enhancement of the $\Lambda_c/D$ ratio in heavy ion collisions.Comment: Prepared for Chiral Symmetry in Hadron and Nuclear Physics (Chiral07), Nov. 13-16, 2007, Osaka, Japa

Optical Response of Solid CO2_2 as a Tool for the Determination of the High Pressure Phase

We report first-principles calculations of the frequency dependent linear and second-order optical properties of the two probable extended-solid phases of CO$_2$--V, i.e. $I\bar42d$ and $P2_12_12_1$. Compared to the parent $Cmca$ phase the linear optical susceptibility of both phases is much smaller. We find that $I\bar42d$ and $P2_12_12_1$ differ substantially in their linear optical response in the higher energy regime. The nonlinear optical responses of the two possible crystal structures differ by roughly a factor of five. Since the differences in the nonlinear optical spectra are pronounced in the low energy regime, i.e. below the band gap of diamond, measurements with the sample inside the diamond anvil cell are feasible. We therefore suggest optical experiments in comparison with our calculated data as a tool for the unambiguous identification of the high pressure phase of CO$_2$.Comment: 4 pages 2 fig

Optimizing Cybersecurity Risk in Medical Cyber-Physical Devices

Medical devices are increasingly connected, both to cyber networks and to sensors collecting data from physical stimuli. These cyber-physical systems pose a new host of deadly security risks that traditional notions of cybersecurity struggle to take into account. Previously, we could predict how algorithms would function as they drew on defined inputs. But cyber-physical systems draw on unbounded inputs from the real world. Moreover, with wide networks of cyber-physical medical devices, a single cybersecurity breach could pose lethal dangers to masses of patients. The U.S. Food and Drug Administration (FDA) is tasked with regulating medical devices to ensure safety and effectiveness, but its regulatory approach—designed decades ago to regulate traditional medical hardware—is ill-suited to the unique problems of cybersecurity. Because perfect cybersecurity is impossible and every cybersecurity improvement entails costs to affordability and health, designers need standards that balance costs and benefits to inform the optimal level of risk. The FDA, however, conducts limited cost-benefit analyses, believing that its authorizing statute forbids consideration of economic costs. We draw on statutory text and case law to show that this belief is mistaken and that the FDA can and should conduct cost-benefit analyses to ensure safety and effectiveness, especially in the context of cybersecurity. We describe three approaches the FDA could take to implement this analysis as a practical matter. Of these three, we recommend an approach modeled after the Federal Trade Commission’s cost-benefit test. Regardless of the specific approach the FDA chooses, however, the critical point is that the agency must weigh costs and benefits to ensure the right level of cybersecurity. Until then, medical device designers will face continued uncertainty as cybersecurity threats become increasingly dangerous

Stochastic Path Planning for Autonomous Underwater Gliders with Safety Constraints

© 2019 IEEE. Autonomous underwater gliders frequently execute extensive missions with high levels of uncertainty due to limitations of sensing, control and oceanic forecasting. Glider path planning seeks an optimal path with respect to conflicting objectives, such as travel cost and safety, that must be explicitly balanced subject to these uncertainties. In this paper, we derive a set of recursive equations for state probability and expected travel cost conditional on safety, and use them to implement a new stochastic variant of FMT-{ast } in the context of two types of objective functions that allow a glider to reach a destination region with minimum cost or maximum probability of arrival given a safety threshold. We demonstrate the framework using three simulated examples that illustrate how user-prescribed safety constraints affect the results

Depressed clad hollow optical fiber with fundamental LP01 mode cut-off

We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm

Electroweak phase transition in a nonminimal supersymmetric model

The Higgs potential of the minimal nonminimal supersymmetric standard model (MNMSSM) is investigated within the context of electroweak phase transition. We investigate the allowed parameter space yielding correct electroweak phase transitoin employing a high temperature approximation. We devote to phenomenological consequences for the Higgs sector of the MNMSSM for electron-positron colliders. It is observed that a future $e^+ e^-$ linear collider with $\sqrt{s} = 1000$ GeV will be able to test the model with regard to electroweak baryogenesis.Comment: 28 pages, 5 tables, 12 figure

New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects

We present a general relativistic description of galaxy clustering in a FLRW universe. The observed redshift and position of galaxies are affected by the matter fluctuations and the gravity waves between the source galaxies and the observer, and the volume element constructed by using the observables differs from the physical volume occupied by the observed galaxies. Therefore, the observed galaxy fluctuation field contains additional contributions arising from the distortion in observable quantities and these include tensor contributions as well as numerous scalar contributions. We generalize the linear bias approximation to relate the observed galaxy fluctuation field to the underlying matter distribution in a gauge-invariant way. Our full formalism is essential for the consistency of theoretical predictions. As our first application, we compute the angular auto correlation of large-scale structure and its cross correlation with CMB temperature anisotropies. We comment on the possibility of detecting primordial gravity waves using galaxy clustering and discuss further applications of our formalism.Comment: 10 pages, 2 figures, accepted for publication in Physical Review