Relativistic Two-stream Instability

We study the (local) propagation of plane waves in a relativistic, non-dissipative, two-fluid system, allowing for a relative velocity in the "background" configuration. The main aim is to analyze relativistic two-stream instability. This instability requires a relative flow -- either across an interface or when two or more fluids interpenetrate -- and can be triggered, for example, when one-dimensional plane-waves appear to be left-moving with respect to one fluid, but right-moving with respect to another. The dispersion relation of the two-fluid system is studied for different two-fluid equations of state: (i) the "free" (where there is no direct coupling between the fluid densities), (ii) coupled, and (iii) entrained (where the fluid momenta are linear combinations of the velocities) cases are considered in a frame-independent fashion (eg. no restriction to the rest-frame of either fluid). As a by-product of our analysis we determine the necessary conditions for a two-fluid system to be causal and absolutely stable and establish a new constraint on the entrainment.Comment: 15 pages, 2 eps-figure

Gravitational-wave astronomy: the high-frequency window

This contribution is divided in two parts. The first part provides a text-book level introduction to gravitational radiation. The key concepts required for a discussion of gravitational-wave physics are introduced. In particular, the quadrupole formula is applied to the anticipated ``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300: inspiralling compact binaries. The second part provides a brief review of high frequency gravitational waves. In the frequency range above (say) 100Hz, gravitational collapse, rotational instabilities and oscillations of the remnant compact objects are potentially important sources of gravitational waves. Significant and unique information concerning the various stages of collapse, the evolution of protoneutron stars and the details of the supranuclear equation of state of such objects can be drawn from careful study of the gravitational-wave signal. As the amount of exciting physics one may be able to study via the detections of gravitational waves from these sources is truly inspiring, there is strong motivation for the development of future generations of ground based detectors sensitive in the range from hundreds of Hz to several kHz.Comment: 21 pages, 5 figures, Lectures presented at the 2nd Aegean Summer School on the Early Universe, Syros, Greece, September 200

Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/Al2_2O3_3

The magnetization and magnetic ac susceptibility, $\chi = \chi' - i \chi''$, of superferromagnetic systems are studied by numerical simulations. The Cole-Cole plot, $\chi''$ vs. $\chi'$, is used as a tool for classifying magnetic systems by their dynamical behavior. The simulations of the magnetization hysteresis and the ac susceptibility are performed with two approaches for a driven domain wall in random media. The studies are motivated by recent experimental results on the interacting nanoparticle system Co$_{80}$Fe$_{20}$/Al$_{2}$O$_{3}$ showing superferromagnetic behavior. Its Cole-Cole plot indicates domain wall motion dynamics similarly to a disordered ferromagnet, including pinning and sliding motion. With our models we can successfully reproduce the features found in the experimental Cole-Cole plots.Comment: 8 pages, 6 figure

r-modes in Relativistic Superfluid Stars

We discuss the modal properties of the $r$-modes of relativistic superfluid neutron stars, taking account of the entrainment effects between superfluids. In this paper, the neutron stars are assumed to be filled with neutron and proton superfluids and the strength of the entrainment effects between the superfluids are represented by a single parameter $\eta$. We find that the basic properties of the $r$-modes in a relativistic superfluid star are very similar to those found for a Newtonian superfluid star. The $r$-modes of a relativistic superfluid star are split into two families, ordinary fluid-like $r$-modes ($r^o$-mode) and superfluid-like $r$-modes ($r^s$-mode). The two superfluids counter-move for the $r^s$-modes, while they co-move for the $r^o$-modes. For the $r^o$-modes, the quantity $\kappa\equiv\sigma/\Omega+m$ is almost independent of the entrainment parameter $\eta$, where $m$ and $\sigma$ are the azimuthal wave number and the oscillation frequency observed by an inertial observer at spatial infinity, respectively. For the $r^s$-modes, on the other hand, $\kappa$ almost linearly increases with increasing $\eta$. It is also found that the radiation driven instability due to the $r^s$-modes is much weaker than that of the $r^o$-modes because the matter current associated with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review

NA0D – The new traumatic dental injury classification of the world health organization

An accurate, clear, and easy-to- use traumatic dental injury (TDI) classification and definition system is a prerequisite for proper diagnosis, study, and treatment. However, more than 50 classifications have been used in the past. The ideal solution would be that TDIs are adequately classified within the International Classification of Diseases (ICD), endorsed by the World Health Organization (WHO). TDI classification provided by the 11th Revision of the ICD (ICD-11), released in 2018, and previous Revisions, failed to classify TDIs satisfactorily. Therefore, in December 2018, a proposal was submitted by Dr's Stefano Petti, Jens Ove Andreasen, Ulf Glendor, and Lars Andersson, to the ICD-11, asking for a change of the existing TDI classification. Proposal #2130 highlighted the TDI paradox, the fifth most frequent disease/condition neglected by most public health agencies in the world, and the limits of ICD-11 classification. Namely, injuries of teeth and periodontal tissues were located in two separate blocks that did not mention dental/periodontal tissues; infraction, concussion, and subluxation were not coded; most TDIs lacked description; and tooth fractures were described through bone fracture descriptions (e.g., comminuted, compression, and fissured fractures). These limitations led to TDI mis-reporting, under-reporting, and non-specific reporting by untrained non-dental healthcare providers. In addition, no scientific articles on TDIs, present in PubMed, Scopus, and Web-of- Science, used the ICD classification. Proposal #2130 suggested to adopt the Andreasen classification, the most widely acknowledged classification used in dental traumatology. The Proposal was reviewed by two WHO teams, two scientific Committees, one WHO Collaborating Center, and the Department of Non-Communicable Disease Prevention at WHO headquarters, and it underwent two voting sessions. In March 2022, the Andreasen classification was accepted integrally. A new entity was generated, called NA0D, “Injury of teeth or supporting structures” (https://icd.who.int/brows e11/l-m/ en#/http://id. who.int/icd /ent ity/141 3338122). Hopefully, this will contribute to increasing the public awareness, and the dental profession's management, of TDIs

Genetic polymorphisms of glutathione S-transferase genes GSTP1, GSTM1, and GSTT1 and risk of esophageal and gastric cardia cancers

Glutathione S-transferase (GST) enzymes are known to metabolize tobacco-related carcinogens. Previous studies on the association of functional polymorphisms of GST genes with esophageal squamous cell carcinoma have yielded conflicting but overall null results. A few studies of esophageal adenocarcinoma were likewise conflicting, but the scarcity of data is striking. We aimed to study associations of the GSTM1 and GSTT1 null deletion polymorphisms as well as the GSTP1 Ile105Val polymorphism with risks for esophageal and gastric cardia cancers. DNA was prepared from 96 and 79 cases of esophageal adenocarcinoma and squamous cell carcinoma, respectively, 126 cardia cancer cases, and 471 population-based controls. Pyrosequencing typed the GSTP1 Ile105Val polymorphism, while multiplex PCR detected GSTM1 and GSTT1 deletions. Logistic regression modeling estimated odds ratios (ORs) with 95% confidence intervals (CIs). None of the studied polymorphisms were related to the risk of esophageal adenocarcinoma, but the variant GSTP1 Val 105 allele was associated with an increased risk of esophageal squamous cell carcinoma (OR = 1.7; 95% CI 1.0-2.9) and tended to be weakly, positively linked to cardia cancer (OR = 1.4; 95% CI 0.9-2.1). Finally, we performed a meta-analysis and found that GSTP1 polymorphism seems to be associated with the risk of esophageal squamous cell carcinoma among Caucasian population (OR = 1.4; 95% CI 1.0-2.2; p value for heterogeneity test 0.34). © 2009 Springer Science+Business Media B.V

Extinction in Lotka-Volterra model

Competitive birth-death processes often exhibit an oscillatory behavior. We investigate a particular case where the oscillation cycles are marginally stable on the mean-field level. An iconic example of such a system is the Lotka-Volterra model of predator-prey competition. Fluctuation effects due to discreteness of the populations destroy the mean-field stability and eventually drive the system toward extinction of one or both species. We show that the corresponding extinction time scales as a certain power-law of the population sizes. This behavior should be contrasted with the extinction of models stable in the mean-field approximation. In the latter case the extinction time scales exponentially with size.Comment: 11 pages, 17 figure