Evidence of vacuum birefringence from the polarisation of the optical emission from an Isolated Neutron Star

Isolated Neutron Stars are some of the most exciting stellar objects known to astronomers: they have the most extreme magnetic fields, with values up to $10^{15}$ G, and, with the exception of stellar-mass black holes, they are the most dense stars, with densities of $\approx 10^{14}$ g cm$^{-3}$. As such, they are perfect laboratories to test theories of electromagnetism and nuclear physics under conditions of magnetic field and density unattainable on Earth. In particular, the interaction of radiation with strong magnetic fields is the cause of the {\em vacuum birefringence}, an effect predicted by quantum electrodynamics in 1936 but that lacked an observational evidence until now. Here, we show how the study of the polarisation of the optical radiation from the surface of an isolated neutron star yielded such an observational evidence, opening exciting perspectives for similar studies at other wavelengths.Comment: 5 pages, 1 figure, Contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 201

A Comment on "A note on polarized light from Magnetars: QED effects and axion-like particles" by L.M. Capparelli, L. Maiani and A.D. Polosa

The recent detection of a large polarization degree in the optical emission of an isolated neutron star led to the suggestion that this has been the first evidence of vacuum polarization in a strong magnetic field, an effect predicted by quantum electrodynamics but never observed before. This claim was challanged in a paper by Capparelli, Maiani & Polosa (2017), according to whom a much higher polarization degree would be necessary to positively identify vacuum polarization. Here we show that their conclusions are biased by several inadequate assumptions and have no impact on the original claim.Comment: 10 pages, 2 figure

Finite size effects on thermal denaturation of globular proteins

Finite size effects on the cooperative thermal denaturation of proteins are considered. A dimensionless measure of cooperativity, Omega, scales as N^zeta, where N is the number of amino acids. Surprisingly, we find that zeta is universal with zeta = 1 + gamma, where the exponent gamma characterizes the divergence of the susceptibility for a self-avoiding walk. Our lattice model simulations and experimental data are consistent with the theory. Our finding rationalizes the marginal stability of proteins and substantiates the earlier predictions that the efficient folding of two-state proteins requires the folding transition temperature to be close to the collapse temperature.Comment: 3 figures. Physical Review Letters (in press

Evidence of vacuum birefringence from the polarisation of the optical emission from an Isolated Neutron Star

Isolated Neutron Stars are some of the most exciting stellar objects known to astronomers: they have the most extreme magnetic fields, with values up to 1015 G, and, with the exception of stellar-mass black holes, they are the most dense stars, with densities of ≈ 1014 g cm−3 . As such, they are perfect laboratories to test theories of electromagnetism and nuclear physics under conditions of magnetic field and density unattainable on Earth. In particular, the interaction of radiation with strong magnetic fields is the cause of the vacuum birefringence, an effect predicted by quantum electrodynamics in 1936 but that lacked an observational evidence until now. Here, we show how the study of the polarisation of the optical radiation from the surface of an isolated neutron star yielded such an observational evidence, opening exciting perspectives for similar studies at other wavelengths

Electron localization and possible phase separation in the absence of a charge density wave in single-phase 1T-VS2_2

We report on a systematic study of the structural, magnetic and transport properties of high-purity 1T-VS$_2$ powder samples prepared under high pressure. The results differ notably from those previously obtained by de-intercalating Li from LiVS$_2$. First, no Charge Density Wave (CDW) is found by transmission electron microscopy down to 94 K. Though, \textit{ab initio} phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector ${\bf q}_{CDW} \approx$ (0.21,0.21,0) previously reported in de-intercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature. Second, infrared optical absorption and electrical resistivity measurements give evidence of non metallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with \textit{ab initio} band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and non-metallic domains in the nm scale. We conclude that 1T-VS$_2$ is at the verge of a CDW transition and suggest that residual electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase with metallic properties.Comment: 22 pages, 10 Figures. Full resolution pictures available at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.23512

Vacuum birefringence and X-ray polarimetry in transient magnetars

Recent optical polarimetry observations of an X-ray dim isolated neutron star, RX J1856.5-3754, showed a first evidence for QED vacuum birefringence induced by a strong magnetic field. This important result can be confirmed by performing systematically polarimetry observations in the X-ray band for other strongly magnetized neutron stars, such as transient or persistent magnetars. We computed the phase averaged polarization fraction (PF) and polarization angle (PA) expected in the thermal emission from transient magnetars in the soft X-ray energy band. We found that the detection of a PF higher than 60% is a strong evidence for vacuum birefringence. We also found that a steady change in the PA measured from transient magnetars during their outburst decay (up to 23 degrees for a magnetospheric untwisting of 0.5 rad) is a strong signature of vacuum birefringence. This latter detection would also provide an independent check of the magnetospheric untwisting model for these sources. Simulations show that these measurements are achievable by future polarimetric missions such as XIPE and IXPE with 20-380 ks of observational time, and with eXTP with 3-60 ks

Exosomes from metastatic cancer cells transfer amoeboid phenotype to non-metastatic cells and increase endothelial permeability: their emerging role in tumor heterogeneity

The goal of this study was to understand if exosomes derived from high-metastatic cells may influence the behavior of less aggressive cancer cells and the properties of the endothelium. We found that metastatic colon cancer cells are able to transfer their amoeboid phenotype to isogenic primary cancer cells through exosomes, and that this morphological transition is associated with the acquisition of a more aggressive behavior. Moreover, exosomes from the metastatic line (SW620Exos) exhibited higher ability to cause endothelial hyperpermeability than exosomes from the non metastatic line (SW480Exos). SWATH-based quantitative proteomic analysis highlighted that SW620Exos are significantly enriched in cytoskeletal-associated proteins including proteins activating the RhoA/ROCK pathway, known to induce amoeboid properties and destabilization of endothelial junctions. In particular, thrombin was identified as a key mediator of the effects induced by SW620Exos in target cells, in which we also found a significant increase of RhoA activity. Overall, our results demonstrate that in a heterogeneous context exosomes released by aggressive sub-clones can contribute to accelerate tumor progression by spreading malignant properties that affect both the tumor cell plasticity and the endothelial cell behavior

Rituximab-EPOCH, an effective salvage therapy for relapsed, refractory or transformed B-cell lymphomas: results of a phase II study

Background: Relapsed or refractory diffuse large B-cell and mantle-cell lymphoma have a poor prognosis. The EPOCH regimen and rituximab monotherapy have demonstrated activity as salvage therapies. Because of their non-overlapping toxicity, we evaluated their combination as salvage therapy in a phase II study. Patients and methods: Patients with relapsed or refractory CD20-positive large B-cell and mantle-cell lymphoma were offered treatment with rituximab 375 mg/m2 intravenously (i.v.) on day 1, doxorubicin 15 mg/m2 as a continuous i.v. infusion on days 2-4, etoposide 65 mg/m2 as a continuous i.v. infusion on days 2-4, vincristine 0.5 mg as a continuous i.v. infusion on days 2-4, cyclophosphamide 750 mg/m2 i.v. on day 5 and prednisone 60 mg/m2 orally on days 1-14. Results: Fifty patients, with a median age of 56 years (range 23-72), entered the study. Twenty-five had primary diffuse large B-cell lymphoma, 18 transformed large B-cell lymphoma and seven mantle-cell lymphoma. The median number of prior chemotherapy regimens was 1.7 (range one to four). The median number of treatment cycles was four (range one to six). Possible treatment-related death occurred in two patients. Objective responses were obtained in 68% of patients (28% complete responses, 40% partial responses). Nineteen patients received consolidating high-dose chemotherapy with autologous stem-cell transplantation. The median follow-up was 33 months. Three patients developed a secondary myelodysplastic syndrome. The median overall survival was 17.9 months; the projected overall survival at 1, 2 and 3 years was 66, 42 and 35%, respectively. The median event-free survival was 11.8 months; the projected event-free survival at 1, 2 and 3 years was 50, 30 and 26%, respectively. Conclusion: The rituximab-EPOCH regimen is effective and well tolerated, even in extensively pretreated patients with relapsed or refractory large B-cell lymphoma and mantle-cell lymphom

Evolution favors protein mutational robustness in sufficiently large populations

BACKGROUND: An important question is whether evolution favors properties such as mutational robustness or evolvability that do not directly benefit any individual, but can influence the course of future evolution. Functionally similar proteins can differ substantially in their robustness to mutations and capacity to evolve new functions, but it has remained unclear whether any of these differences might be due to evolutionary selection for these properties. RESULTS: Here we use laboratory experiments to demonstrate that evolution favors protein mutational robustness if the evolving population is sufficiently large. We neutrally evolve cytochrome P450 proteins under identical selection pressures and mutation rates in populations of different sizes, and show that proteins from the larger and thus more polymorphic population tend towards higher mutational robustness. Proteins from the larger population also evolve greater stability, a biophysical property that is known to enhance both mutational robustness and evolvability. The excess mutational robustness and stability is well described by existing mathematical theories, and can be quantitatively related to the way that the proteins occupy their neutral network. CONCLUSIONS: Our work is the first experimental demonstration of the general tendency of evolution to favor mutational robustness and protein stability in highly polymorphic populations. We suggest that this phenomenon may contribute to the mutational robustness and evolvability of viruses and bacteria that exist in large populations