On the occurrence and detectability of Bose-Einstein condensation in helium white dwarfs

It has been recently proposed that helium white dwarfs may provide promising conditions for the occurrence of the Bose-Einstein condensation. The argument supporting this expectation is that in some conditions attained in the core of these objects, the typical De Broglie wavelength associated with helium nuclei is of the order of the mean distance between neighboring nuclei. In these conditions the system should depart from classical behavior showing quantum effects. As helium nuclei are bosons, they are expected to condense. In order to explore the possibility of detecting the Bose-Einstein condensation in the evolution of helium white dwarfs we have computed a set of models for a variety of stellar masses and values of the condensation temperature. We do not perform a detailed treatment of the condensation process but mimic it by suppressing the nuclei contribution to the equation of state by applying an adequate function. As the cooling of white dwarfs depends on average properties of the whole stellar interior, this procedure should be suitable for exploring the departure of the cooling process from that predicted by the standard treatment. We find that the Bose-Einstein condensation has noticeable, but not dramatic effects on the cooling process only for the most massive white dwarfs compatible with a helium dominated interior (\approx 0.50 M_\odot) and very low luminosities (say, Log(L/L_\odot) < -4.0). These facts lead us to conclude that it seems extremely difficult to find observable signals of the Bose-Einstein condensation. Recently, it has been suggested that the population of helium white dwarfs detected in the globular cluster NGC 6397 is a good candidate for detecting signals of the Bose-Einstein condensation. We find that these stars have masses too low and are too bright to have an already condensed interior.Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the Journal of Cosmology and Astroparticle Physics (JCAP

Adhesive contact of model randomly rough rubber surfaces

We study experimentally and theoretically the equilibrium adhesive contact between a smooth glass lens and a rough rubber surface textured with spherical microasperities with controlled height and spatial distributions. Measurements of the real contact area $A$ versus load $P$ are performed under compression by imaging the light transmitted at the microcontacts. $A(P)$ is found to be non-linear and to strongly depend on the standard deviation of the asperity height distribution. Experimental results are discussed in the light of a discrete version of Fuller and Tabor's (FT) original model (\textit{Proceedings of the Royal Society A} \textbf{345} (1975) 327), which allows to take into account the elastic coupling arising from both microasperities interactions and curvature of the glass lens. Our experimental data on microcontact size distributions are well captured by our discrete extended model. We show that the elastic coupling arising from the lens curvature has a significant contribution to the $A(P)$ relationship. Our discrete model also clearly shows that the adhesion-induced effect on $A$ remains significant even for vanishingly small pull-off forces. Last, at the local asperity length scale, our measurements show that the pressure dependence of the microcontacts density can be simply described by the original FT model

An evolutionary model for the gamma-ray system PSR J1311-3430 and its companion

The most recent member of the millisecond pulsar with very low-mass companions and short orbital periods class, PSR J1311-3430 (Pletsch et al. 2012) is a remarkable object in various senses. Besides being the first discovered in gamma-rays, its measured features include the very low or absent hydrogen content. We show in this Letter that this important piece of information leads to a very restricted range of initial periods for a given donor mass. For that purpose, we calculate in detail the evolution of the binary system self-consistently, including mass transfer and evaporation, finding the features of the new evolutionary path leading to the observed configuration. It is also important to remark that the detailed evolutionary history of the system naturally leads to a high final pulsar mass, as it seems to be demanded by observations.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in MNRAS Letter

Microstructure and chemical composition of Roman orichalcum coins emitted after the monetary reform of Augustus (23 B.C.)

A collection of ancient Roman orichalcum coins, i.e., a copper-zinc alloy, minted under the reigns from Caesar to Domitianus, have been characterised using scanning electron microscopy (SEM-EDS) and electron microprobe analysis (EMPA). We studied, for the first time, coins emitted by Romans after the reforms of Augustus (23 B.C.) and Nero (63-64 A.D). These coins, consisting of asses, sestertii, dupondii and semisses, were analysed using non- and invasive analyses, aiming to explore microstructure, corrosive process and to acquire quantitative chemical analysis. The results revealed that the coins are characterized by porous external layers, which are affected by dezincification and decuprification processes. As pictured by the X-ray maps, the elemental distribution of Cu and Zn shows patterns of depletion that in some cases penetrate in deep up to 1 mm. The composition of the un-corroded nucleus is a Cu-Zn alloy containing up to 30% of Zn, typical of coins produced via cementation process

Vulnerability and Protection of Critical Infrastructures

Critical infrastructure networks are a key ingredient of modern society. We discuss a general method to spot the critical components of a critical infrastructure network, i.e. the nodes and the links fundamental to the perfect functioning of the network. Such nodes, and not the most connected ones, are the targets to protect from terrorist attacks. The method, used as an improvement analysis, can also help to better shape a planned expansion of the network.Comment: 4 pages, 1 figure, 3 table

Group Theoretical Quantum Tomography

The paper is devoted to the mathematical foundation of the quantum tomography using the theory of square-integrable representations of unimodular Lie groups.Comment: 13 pages, no figure, Latex2e. Submitted to J.Math.Phy

The Limits of Permissible Judicial Campaign Speech in New York

(Excerpt) In December 2018, New York’s Advisory Committee on Judicial Ethics (“ACJE”), which I proudly served on for ten years, issued Opinion 17-28, concerning an inquiry by a judicial candidate as to whether he or she could respond to a candidate questionnaire prepared by the New York State Right to Life Committee (“RTL questionnaire”). In the RTL questionnaire, the candidate is asked a series of questions concerning the candidate’s personal beliefs on abortion, the beginning of life, Roe v. Wade, the definition of personhood, the New York and United States Constitutions, and so on. Each question asking for the candidate’s personal beliefs is preceded by a prefatory acknowledgment of “the judicial obligation to follow binding precedents of higher courts and applicable constitutional and statutory provisions, to honor stare decisis, and to decide any future case based on the law and facts of that case.” Concluding that the RTL questionnaire, “when viewed as a whole, is clearly designed to elicit a series of implied pledges, promises, and commitments, touching on a wide variety of closely interrelated issues that may come before judges at every level of the judiciary” and that “a candidate’s impartiality” could “ ‘reasonably be questioned’ in a wide variety of cases . . . if he/she agreed to the bold-faced statements on the questionnaire,” the candidate was advised to decline responding to it. As I strongly disagree with the ACJE’s opinion, I write this Article to express my personal views on the subject. Let me emphasize that this Article reflects my attempt to engage in a reasoned analysis of an admittedly difficult topic which, in my opinion, has not been sufficiently explored or discussed by academics, ethics committees, or judges since the Supreme Court of the United States decided Republican Party of Minnesota v. White (occasionally abbreviated herein as “White”)

Implementing Adult Learning Principles to Overcome Barriers Of Learning in Continuing Higher Education Programs

A fundamental aspect to continuing higher education is overcoming of barriers of learning when dealing with non-traditional students. With non-traditional student enrollment on the rise, continuing higher education programs have an obligation to address issues of accessibility, affordability and accountability in higher education. The purpose of the study was to identify the relationship between adult learning principles and overcoming barriers of adult learning in continuing higher education at higher education institutions based on published literature