Renormalization of spin-orbit coupling in quantum dots due to Zeeman interaction

We derive analitycally a partial diagonalization of the Hamiltonian representing a quantum dot including spin-orbit interaction and Zeeman energy on an equal footing. It is shown that the interplay between these two terms results in a renormalization of the spin-orbit intensity. The relation between this feature and experimental observations on conductance fluctuations is discussed, finding a good agreement between the model predictions and the experimental behavior.Comment: 4 pages, no figures. To appear in Phys. Rev. B (Brief Report) (2004

Efficient management of backtracking in and-parallelism

A backtracking algorithm for AND-Parallelism and its implementation at the Abstract Machine level are presented: first, a class of AND-Parallelism models based on goal independence is defined, and a generalized version of Restricted AND-Parallelism (RAP) introduced as characteristic of this class. A simple and efficient backtracking algorithm for R A P is then discussed. An implementation scheme is presented for this algorithm which offers minimum overhead, while retaining the performance and storage economy of sequent ial implementations and taking advantage of goal independence to avoid unnecessary backtracking ("restricted intelligent backtracking"). Finally, the implementation of backtracking in sequential and AND-Parallcl systems is explained through a number of examples

State Law, the Westfall Act, and the Nature of the \u3ci\u3eBivens\u3c/i\u3e Question

In a number of recent cases touching to varying degrees on national security, different courts of appeals have applied a strong presumption against recognition of a Bivens cause of action. In each of these cases, the courts’ approach was based on the belief that the creation of a cause of action is a legislative function and that the courts would be usurping Congress’s role if they recognized a Bivens action without legislative authorization. Thus, faced with a scenario where they believed that the remedial possibilities were either Bivens or nothing, these courts of appeals chose nothing. The concerns that led these courts to decline to recognize a Bivens action, if truly implicated by these cases, would be reasons to bar the suits from the courts altogether. In contrast, as we explain in this essay, the Bivens question was at least initially understood as whether a federal cause of action should supplement existing state law remedies. Thus, these recent lower-court decisions reveal a fundamental misapprehension about the intended relationship between Bivens and state law. So understood, and as courts have already recognized in other contexts, the very concerns relied upon in these recent national security cases would, if anything, have traditionally supported a federal remedial regime rather than one under state law. As the Supreme Court\u27s recent decision in Minneci v. Pollard illustrates, the principal reason to disfavor recognition of Bivens remedies should be the availability of adequate remedies under state law, and not a desire to immunize the relevant officers from any liability whatsoever. Thus, unlike these recent cases, decisions not to recognize a Bivens remedy should leave the plaintiff free to pursue whatever recourse state law may provide. Although this view of Bivens was generally shared by both its supporters and detractors when it was decided, it has receded from view largely thanks to the Westfall Act, which most courts and commentators today read as preempting all state-law tort claims against federal officers acting within the scope of their employment. In our view, this conclusion reflects a surprising misreading of the Act, which specifically exempts from its preemption provision any claim which is brought for a violation of the Constitution of the United States, presumably including non-federal tort claims grounded on federal constitutional violations. Indeed, given that the legislative history of the Westfall Act suggests that Congress merely sought to preserve the status quo, it is odd to read the statute as dramatically altering the nature and consequences of the Bivens question. Nevertheless, if the Westfall Act does indeed have this effect, we conclude that it should therefore significantly strengthen the argument for recognizing Bivens claims, since the Act takes away the main alternative remedial scheme that previously existed. Indeed, an (incorrect) interpretation of the Westfall Act as preempting non-federal remedies but not authorizing equivalent federal remedies may well raise significant constitutional questions--questions that have thus far been dramatically under-appreciated by the lower courts, but that must be taken seriously going forward. And if courts conclude that, in appropriate cases, the question really should be Bivens or nothing, they must recognize that either answer requires judicial lawmaking--and not just recognition of a federal cause of action

Two-dimensional wave propagation in layered periodic media

We study two-dimensional wave propagation in materials whose properties vary periodically in one direction only. High order homogenization is carried out to derive a dispersive effective medium approximation. One-dimensional materials with constant impedance exhibit no effective dispersion. We show that a new kind of effective dispersion may arise in two dimensions, even in materials with constant impedance. This dispersion is a macroscopic effect of microscopic diffraction caused by spatial variation in the sound speed. We analyze this dispersive effect by using high-order homogenization to derive an anisotropic, dispersive effective medium. We generalize to two dimensions a homogenization approach that has been used previously for one-dimensional problems. Pseudospectral solutions of the effective medium equations agree to high accuracy with finite volume direct numerical simulations of the variable-coefficient equations

Systematic Differential Renormalization to All Orders

We present a systematic implementation of differential renormalization to all orders in perturbation theory. The method is applied to individual Feynamn graphs written in coordinate space. After isolating every singularity. which appears in a bare diagram, we define a subtraction procedure which consists in replacing the core of the singularity by its renormalized form givenby a differential formula. The organizationof subtractions in subgraphs relies in Bogoliubov's formula, fulfilling the requirements of locality, unitarity and Lorentz invariance. Our method bypasses the use of an intermediate regularization andautomatically delivers renormalized amplitudes which obey renormalization group equations.Comment: TEX, 20 pages, UB-ECM-PF 93/4, 1 figureavailable upon reques

Flexibility at the margin and labor market volatility in OECD countries

We argue that segmented labor markets with flexibility at the margin (e.g., just affecting fixed-term employees) may achieve similar volatility than fully deregulated labor markets. Flexibility at the margin produces a gap in separation costs among matched workers that cause fixed-term employment to be the main workforce adjustment device. Moreover, in the presence of limitations in the duration and number of renewals of fixed-term contracts, firms respond by fostering labor turnover which further raises the volatility of the labor market. We present a matching model with temporary and permanent jobs where (i) the gap in firing costs and (ii) restrictions in the use of fixedterm contracts play the central role to explain the similar volatility observed in many regulated labor markets with flexibility at the margin vis-à-vis the fully deregulated ones