Pinning and depinning of a classic quasi-one-dimensional Wigner crystal in the presence of a constriction

We studied the dynamics of a quasi-one-dimensional chain-like system of charged particles at low temperature, interacting through a screened Coulomb potential in the presence of a local constriction. The response of the system when an external electric field is applied was investigated. We performed Langevin molecular dynamics simulations for different values of the driving force and for different temperatures. We found that the friction together with the constriction pins the particles up to a critical value of the driving force. The system can depin \emph{elastically} or \emph{quasi-elastically} depending on the strength of the constriction. The elastic (quasi-elastic) depinning is characterized by a critical exponent $\beta\sim0.66$ ($\beta\sim0.95$). The dc conductivity is zero in the pinned regime, it has non-ohmic characteristics after the activation of the motion and then it is constant. Furthermore, the dependence of the conductivity with temperature and strength of the constriction was investigated in detail. We found interesting differences between the single and the multi-chain regimes as the temperature is increased.Comment: 18 pages, 16 figures, accepted for publication in PR

A Hippocratic Oath for geologists?

We argue here that the introduction of an ethical code of conduct that follows the example of the Hippocratic Oath of physicians will help geologists to acquire binding awareness of their professional and social responsibilities. The ethical behavior and obligations of modern geologists involve, but are not limited to, the following issues: correct land/ environment use and management; respect of truth and science; and protection of the Earth systems, on both the local and global scales, and therefore, of our well-being. We believe that for geoligists, the explicit acceptance of an ethical code will help to promote: (i) an awareness of their social role, expertise and sense of belonging to a professional community; (ii) an understanding of the expectations of citizens and society; and (iii) cultural growth, with better use of research and implementation of scientific and professional skills. All this should enhance the public recognition of the social mission of geologists, which is essential for the well-being of society. Therefore, we suggest that like in the majority of medical schools, ethical training should be a part of the university curriculum for students in geology

Generic properties of a quasi-one dimensional classical Wigner crystal

We studied the structural, dynamical properties and melting of a quasi-one-dimensional system of charged particles, interacting through a screened Coulomb potential. The ground state energy was calculated and, depending on the density and the screening length, the system crystallizes in a number of chains. As a function of the density (or the confining potential), the ground state configurations and the structural transitions between them were analyzed both by analytical and Monte Carlo calculations. The system exhibits a rich phase diagram at zero temperature with continuous and discontinuous structural transitions. We calculated the normal modes of the Wigner crystal and the magneto-phonons when an external constant magnetic field $B$ is applied. At finite temperature the melting of the system was studied via Monte Carlo simulations using the $modified$ $Lindemann$ $criterion$ (MLC). The melting temperature as a function of the density was obtained for different screening parameters. Reentrant melting as a function of the density was found as well as evidence of directional dependent melting. The single chain regime exhibits anomalous melting temperatures according to the MLC and as a check we study the pair correlation function at different densities and different temperatures, formulating a different criterion. Possible connection with recent theoretical and experimental results are discussed and experiments are proposed.Comment: 13 pages text, 21 picture

Tumores óseos de la pelvis

Se presenta la experiencia del Servicio de Ortopedia del Adulto del Hospital «Ramón y Cajal», en neoplasias de la pelvis, desde su creación hasta la actualidad, siendo 61 los pacientes recogidos y no se hace un trabajo estadístico, sino más bien se muestran las peculiaridades recogidas con la experiencia, que abarca desde la abstención en algunos casos de tumores secundarios, y el simple curetage hasta las grandes sustituciones con homoinjertos de banco, relacionándolo a su vez con publicaciones de aparición más o menos moderna sobre este tema, para concluir que se trata de una cirugía no exenta de complicaciones y problemas, pero necesaria a la hora de proporcionar a los enfermos curaciones, que le ofrezcan una salida a este difícil problema.The experience of Adult Orthopaedics Unit at the Hospital «Ramón y Cajal», Madrid, treating patients with malignant tumors of the pelvic bons is presented. In this paper, the results after surgery are not reported in terms of statistical analysis. The aún of this work is to comment the surgical experience covering from simple curettage to great bone replacement using bank allografts. The message is that surgical treatment of pelvic tumors is not exent of complications, but it seems to be worth in order to offer a better quality of Ufe for patients

Impaired bone remodeling in children with osteogenesis imperfecta treated and untreated with bisphosphonates: the role of DKK1, RANKL, and TNF-α

In this study, we investigated the bone cell activity in patients with osteogenesis imperfecta (OI) treated and untreated with neridronate. We demonstrated the key role of Dickkopf-1 (DKK1), receptor activator of nuclear factor-κB ligand (RANKL), and tumor necrosis factor alpha (TNF-α) in regulating bone cell of untreated and treated OI subjects. These cytokines could represent new pharmacological targets for OI. Introduction: Bisphosphonates are widely used in the treatment of children with osteogenesis imperfecta (OI) with the objective of reducing the risk of fractures. Although bisphosphonates increase bone mineral density in OI subjects, the effects on fracture incidence are conflicting. The aim of this study was to investigate the mechanisms underlying bone cell activity in subjects with mild untreated forms of OI and in a group of subjects with severe OI treated with cycles of intravenous neridronate. Methods: Sclerostin, DKK1, TNF-α, RANKL, osteoprotegerin (OPG), and bone turnover markers were quantified in serum of 18 OI patients (12 females, mean age 8.86 ± 3.90), 8 of which were receiving cyclic intravenous neridronate, and 21 sex- and age-matched controls. The effects on osteoblastogenesis and OPG expression of media conditioned by the serum of OI patients and anti-DKK1 neutralizing antibody were evaluated. Osteoclastogenesis was assessed in cultures from patients and controls. Results: DKK1 and RANKL levels were significantly increased both in untreated and in treated OI subjects with respect to controls. The serum from patients with high DKK1 levels inhibited both osteoblast differentiation and OPG expression in vitro. High RANKL and low OPG messenger RNA (mRNA) levels were found in lymphomonocytes from patients. High amounts of TNF-α were expressed by monocytes, and an elevated percentage of circulating CD11b-CD51/CD61+ osteoclast precursors was observed in patients. Conclusions: Our study demonstrated the key role of DKK1, RANKL, and TNF-α in regulating bone cell activity of subjects with OI untreated and treated with bisphosphonates. These cytokines could represent new pharmacological targets for OI patients

Triterpene Saponins from the Aerial Parts of Trifolium medium L. var. sarosiense

Seven previously unreported triterpene glycosides (1−7) were isolated from methanol extract of the aerial parts of Trifolium medium var. sarosiense (zigzag clover). Their structures were established by the extensive use of 1D and 2D NMR experiments along with ESI-MS and HRMS analyses. Compounds 1−7 are oleanane derivatives characterized by the presence of a keto group at C-22 of an aglycone and a primary alcoholic function at C-24 and differing functions at C-30. Among these, compounds 1−3 and 6 showed a secondary alcoholic function at C-11, which is methoxylated in compounds 4 and 7. Compound 5 was shown to possess a known aglycone, wistariasapogenol A; however, it is described here for the first time as a saponin constituent of the Trifolium genus. Some aspects of taxonomic classification of zigzag clover are also discussed

Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease

Background: Experimental and clinical data suggest that reducing inflammation without affecting lipid levels may reduce the risk of cardiovascular disease. Yet, the inflammatory hypothesis of atherothrombosis has remained unproved. Methods: We conducted a randomized, double-blind trial of canakinumab, a therapeutic monoclonal antibody targeting interleukin-1β, involving 10,061 patients with previous myocardial infarction and a high-sensitivity C-reactive protein level of 2 mg or more per liter. The trial compared three doses of canakinumab (50 mg, 150 mg, and 300 mg, administered subcutaneously every 3 months) with placebo. The primary efficacy end point was nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death. RESULTS: At 48 months, the median reduction from baseline in the high-sensitivity C-reactive protein level was 26 percentage points greater in the group that received the 50-mg dose of canakinumab, 37 percentage points greater in the 150-mg group, and 41 percentage points greater in the 300-mg group than in the placebo group. Canakinumab did not reduce lipid levels from baseline. At a median follow-up of 3.7 years, the incidence rate for the primary end point was 4.50 events per 100 person-years in the placebo group, 4.11 events per 100 person-years in the 50-mg group, 3.86 events per 100 person-years in the 150-mg group, and 3.90 events per 100 person-years in the 300-mg group. The hazard ratios as compared with placebo were as follows: in the 50-mg group, 0.93 (95% confidence interval [CI], 0.80 to 1.07; P = 0.30); in the 150-mg group, 0.85 (95% CI, 0.74 to 0.98; P = 0.021); and in the 300-mg group, 0.86 (95% CI, 0.75 to 0.99; P = 0.031). The 150-mg dose, but not the other doses, met the prespecified multiplicity-adjusted threshold for statistical significance for the primary end point and the secondary end point that additionally included hospitalization for unstable angina that led to urgent revascularization (hazard ratio vs. placebo, 0.83; 95% CI, 0.73 to 0.95; P = 0.005). Canakinumab was associated with a higher incidence of fatal infection than was placebo. There was no significant difference in all-cause mortality (hazard ratio for all canakinumab doses vs. placebo, 0.94; 95% CI, 0.83 to 1.06; P = 0.31). Conclusions: Antiinflammatory therapy targeting the interleukin-1β innate immunity pathway with canakinumab at a dose of 150 mg every 3 months led to a significantly lower rate of recurrent cardiovascular events than placebo, independent of lipid-level lowering. (Funded by Novartis; CANTOS ClinicalTrials.gov number, NCT01327846.

Phase stability of the earth-abundant tin sulfides SnS, SnS2, and Sn2S3

The various phases of tin sulfide have been studied as semiconductors since the 1960s and are now being investigated as potential earth-abundant photovoltaic and photocatalytic materials. Of particular note is the recent isolation of zincblende SnS in particles and thin-films. Herein, first-principles calculations are employed to better understand this novel geometry and its place within the tin sulfide multiphasic system. We report the enthalpies of formation for the known phases of SnS, SnS2, and Sn2S3, with good agreement between theory and experiment for the ground-state structures of each. While theoretical X-ray diffraction patterns do agree with the assignment of the zincblende phase demonstrated in the literature, the structure is not stable close to the lattice parameters observed experimentally, exhibiting an unfeasibly large pressure and a formation enthalpy much higher than any other phase. Ab initio molecular dynamics simulations reveal spontaneous degradation to an amorphous phase much lower in energy, as Sn(II) is inherently unstable in a regular tetrahedral environment. We conclude that the known rocksalt phase of SnS has been mis-assigned as zincblende in the recent literature