Commentary

Ronald J. Tabak, Chair of the Committee on the Death Penalty for the American Bar Association\u27s Section of Individual Rights and Responsibilities, discusses the Section\u27s purpose in organizing Forhdam University School of Law\u27s panel discussion on Politics and the Death Penalty. The goal was to illuminate the variety of effects of a widespread perception that the belief of legislators, governors, prosecutors, judges, clemency boards, political candidates and others that the public is overwhelmingly in support of capital punishment. The Section aimed to bring together knowledgeable people from a variety of perspectives to discuss (a) how the capital punishment system and the political process have been affected by the perceived overwhelming popular support for the death penalty, (b) the role that reportage - or the lack thereof - has had on public attitudes about the death penalty and (c) whether opponents of capital punishment can survive politically. Taback then gives an overview of what was discussed by each panelist, which included Norman Redlich, former Dean of New York University Law School, James Coleman, Shabata Sundiata Waglini, Attorney General Ernest Preate, Jr., Bryan Stevenson, Executive Director of the Alabama Capital Representation Resource Center, journalist Nat Hentoff, New York State Assemblywoman Susan John, and Chief Justice Exum of the North Carolina Supreme Court discuss the issue of the death penalty in America

Trapped Modes in Linear Quantum Stochastic Networks with Delays

Networks of open quantum systems with feedback have become an active area of research for applications such as quantum control, quantum communication and coherent information processing. A canonical formalism for the interconnection of open quantum systems using quantum stochastic differential equations (QSDEs) has been developed by Gough, James and co-workers and has been used to develop practical modeling approaches for complex quantum optical, microwave and optomechanical circuits/networks. In this paper we fill a significant gap in existing methodology by showing how trapped modes resulting from feedback via coupled channels with finite propagation delays can be identified systematically in a given passive linear network. Our method is based on the Blaschke-Potapov multiplicative factorization theorem for inner matrix-valued functions, which has been applied in the past to analog electronic networks. Our results provide a basis for extending the Quantum Hardware Description Language (QHDL) framework for automated quantum network model construction (Tezak \textit{et al.} in Philos. Trans. R. Soc. A, Math. Phys. Eng. Sci. 370(1979):5270-5290, to efficiently treat scenarios in which each interconnection of components has an associated signal propagation time delay

The Dynamic Relationship between Stock Prices and Exchange Rates: evidence for Brazil

This paper studies the dynamic relationship between stock prices and exchange rates in the Brazilian economy. We use recently developed unit root and cointegration tests, which allow endogenous breaks, to test for a long run relationship between these variables. We performed linear, and nonlinear causality tests after considering both volatility and linear dependence. We found that there is no long-run relationship, but there is linear Granger causality from stock prices to exchange rates, in line with the portfolio approach: stock prices lead exchange rates with a negative correlation. Furthermore, we found evidence of nonlinear Granger causality from exchange rates to stock prices, in line with the traditional approach: exchange rates lead stock prices. We believe these findings have practical applications for international investors

Decentralized Portfolio Management

Within a mean-variance model we analyze the problem of decentralized portfolio management. We find the solution for the optimal portfolio allocation for a head trader operating in n different markets, which is called the optimal centralized portfolio. However, as there are many traders specialized in different markets, the solution to the problem of optimal decentralized allocation should be different from the centralized case. In this paper we derive conditions for the solutions to be equivalent. We use multivariate normal returns and a negative exponential function to solve the problem analytically. We generate the equivalence of solutions by assuming that different traders face different interest rates for borrowing and lending. This interest rate is dependent on the ratio of the degrees of risk aversion of the trader and the head trader, on the excess return, and on the correlation between asset returns.

Numerical analysis of the 3D flow induced by propagation of plane-wave deformations on thin membranes inside microchannels

Propulsion mechanisms of microorganisms are based on either beating or screw-like motion of thin elastic biopolymers. Arguably, this motion is optimal for propulsion at very low Reynolds numbers. Similar actuation mechanisms can be utilized in the design of an autonomous microswimmer or even a micropump. In principle, propagation of plane-wave deformations on a thin-membrane placed inside a channel can lead to a net flow in the direction of the wave propagation. In this study we present effects of the amplitude, frequency, and the width of the membrane on the time-averaged flow rate and the rate of work done on the fluid by the membrane by means of threedimensional transient simulations of flows induced by plane-wave deformations on membranes. Navier- Stokes and continuity equations are used to model the flow on a time-varying domain, which is prescribed with respect to the motion of the membrane. Third party commercial software, COMSOL, is used in to solve the finite-element representation of the 3D time-dependent flow on moving mesh. Numerical simulations show that the flow inside the microchannel depend on the square of the amplitude and is proportional to the excitation frequency. Lastly, characteristic flow rate vs. pressure head curve and efficiency of a typical pump are obtained from 3D transient simulations, and presented here

Numerical simulations of a traveling plane-wave actuator for microfluidic applications

Continuous forming and propagation of large planar deformations on a thin solid elastic film can create propulsion when the film is immersed in a fluid. Microscopic organisms such as spermatozoa use similar mechanisms to propel themselves. In this work, we present a numerical analysis of the effect of traveling plane-wave deformations on an elastic-film actuator within a fluid medium inside a channel. In particular, we analyzed a micropump that consists of a wave actuator, which is placed in a channel to pump the fluid in the direction of the planedeformation waves. The unsteady flow over the moving boundary between the parallel plates has very low Reynolds number, and, hence, is modeled using the two-dimensional time-dependent Stokes equations. The fluid-structure interaction due to moving boundary is modeled with the arbitrary Lagrangian Eulerian (ALE) method incorporating the Winslow smoothing. COMSOL is used to solve two-dimensional timedependent Stokes equations on a deforming mesh, and to carry out simulations of the flow. Effects of the deformation amplitude, wavelength, frequency and channel height on the flow rate are presented

Experiment-based kinematic validation of numeric modeling and simulated control of an untethered biomimetic microrobot in channel

Modeling and control of swimming untethered microrobots are important for future therapeutic medical applications. Bio-inspired propulsion methods emerge as realistic substitutes for hydrodynamic thrust generation in micro realm. Accurate modeling, power supply, and propulsion-means directly affect microrobot motility and maneuverability. In this work, motility of bacteria-like untethered helical microrobots in channels is modeled with the resistive force theory coupled with motor dynamics. Results are validated with private experiments conducted on cm-scale prototypes fully submerged in Si-oil filled glass channel. Li-Po battery is utilized as the onboard power supply. Helical tail rotation is triggered by an IR remote control. It is observed that time-averaged velocities calculated by the model agree well with experimental results. Finally, time-dependent performance of a hypothetical model-based position control scheme is simulated with upstream flow as disturbance

Validated reduced order models for simulating trajectories of bio-inspired artificial micro-swimmers

Autonomous micro-swimming robots can be utilized to perform specialized procedures such as in vitro or in vivo medical tasks as well as chemical surveillance or micro manipulation. Maneuverability of the robot is one of the requirements that ensure successful completion of its task. In micro fluidic environments, dynamic trajectories of active micro-swimming robots must be predicted reliably and the response of control inputs must be well-understood. In this work, a reduced-order model, which is based on the resistive force theory, is used to predict the transient, coupled rigid body dynamics and hydrodynamic behavior of bio-inspired artificial micro-swimmers. Conceptual design of the micro-swimmer is biologically inspired: it is composed of a body that carries a payload, control and actuation mechanisms, and a long flagellum either such as an inextensible whip like tail-actuator that deforms and propagates sinusoidal planar waves similar to spermatozoa, or of a rotating rigid helix similar to many bacteria, such as E. Coli. In the reduced-order model of the microswimmer, fluid’s resistance to the motion of the body and the tail are computed from resistive force theory, which breaks up the resistance coefficients to local normal and tangential components. Using rotational transformations between a fixed world frame, body frame and the local Frenet-Serret coordinates on the helical tail we obtain the full 6 degrees-of-freedom relationship between the resistive forces and torques and the linear and rotational motions of the swimmer. In the model, only the tail’s frequency (angular velocity for helical tail) is used as a control input in the dynamic equations of the micro-swimming robot. The reduced-order model is validated by means of direct observations of natural micro swimmers presented earlier in the literature and against; results show very good agreement. Three-dimensional, transient CFD simulations of a single degree of freedom swimmer is used to predict resistive force coefficients of a micro-swimmer with a spherical body and flexible tail actuator that uses traveling plane wave deformations for propulsion. Modified coefficients show a very good agreement between the predicted and actual time-dependent swimming speeds, as well as forces and torques along all axes

On the thermal behaviour of small iron grains

The optical properties of small spherical iron grains are derived using a Kramers-Kronig-consistent model of the dielectric function including its dependence on temperature and size. Especially discussed is the effect of the size dependence, which results from the limitation of the free path of the free electrons in the metal by the size of the grain, on the absorption behaviour of small iron spheres and spheroids. The estimated absorption properties are applied to study the temperature behaviour of spherical and spheroidal grains which are heated by the interstellar radiation field.Comment: 12 pages, 16 figure