Updating the orbital ephemeris of the dipping source XB 1254–690 and the distance to the source

XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254-690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254-690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M2 = 0.42 ± 0.04 M for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 Mo. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.

Detailed characterization of a laboratory magnetized supercritical collisionless shock and of the associated proton energization

Collisionless shocks are ubiquitous in the Universe and are held responsible for the production of nonthermal particles and high-energy radiation.In the absence of particle collisions in the system,theory shows that the interaction of an expanding plasma with a pre-existing electromagnetic structure(as in our case)is able to induce energy dissipation and allow shock formation.Shock formation can alternatively take place when two plasmas interact,through microscopic instabilities inducing electromagnetic fields that are able in turn to mediate energy dissipation and shock formation.Using our platform in which we couple a rapidly expanding plasma induced by high-power lasers(JLF/Titan at LLNL and LULI2000)with high-strength magnetic fields,we have investigated the generation of a magnetized collisionless shock and the associated particle energization.We have characterized the shock as being collisionless and supercritical.We report here on measurements of the plasma density and temperature,the electromagnetic field structures,and the particle energization in the experiments,under various conditions of ambient plasma and magnetic field.We have also modeled the formation of the shocks using macroscopic hydrodynamic simulations and the associated particle acceleration using kinetic particle-in-cell simulations.As a companion paper to Yao et al.[Nat.Phys.17,1177–1182(2021)],here we show additional results of the experiments and simulations,providing more information to allow their reproduction and to demonstrate the robustness of our interpretation of the proton energization mechanism as being shock surfing acceleration.

Comparison of Proton Shower Developments in the BGO Calorimeter of the Dark Matter Particle Explorer between GEANT4 and FLUKA Simulations

The DArk Matter Particle Explorer(DAMPE)is a satellite-borne detector for high-energy cosmic rays and y-rays.To fully understand the detector performance and obtain reliable physical results,extensive simulations of the detector are necessary.The simulations are particularly important for the data analysis of cosmic ray nuclei,which relies closely on the hadronic and nuclear interactions of particles in the detector material.Widely adopted simulation softwares include the GEANT4 and FLUKA,both of which have been implemented for the DAMPE simulation tool.Here we describe the simulation tool of DAMPE and compare the results of proton shower properties in the calorimeter from the two simulation softwares.Such a comparison gives an estimate of the most significant uncertainties of our proton spectral analysis.

A New Approach to Investigate Students’ Behavior by Using Cluster Analysis as an Unsupervised Methodology in the Field of Education

The problem of taking a set of data and separating it into subgroups where the elements of each subgroup are more similar to each other than they are to elements not in the subgroup has been extensively studied through the statistical method of cluster analysis. In this paper we want to discuss the application of this method to the field of education: particularly, we want to present the use of cluster analysis to separate students into groups that can be recognized and characterized by common traits in their answers to a questionnaire, without any prior knowledge of what form those groups would take (unsupervised classification). We start from a detailed study of the data processing needed by cluster analysis. Then two methods commonly used in cluster analysis are before described only from a theoretical point a view and after in the Section 4 through an example of application to data coming from an open-ended questionnaire administered to a sample of university students. In particular we describe and criticize the variables and parameters used to show the results of the cluster analysis methods.

Three X-ray flares near primary eclipse of the RS CVn binary XY UMa

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa （Porb≈0.48 d）. In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly （〈 0.125 Porb） after a primary eclipse, and the other two happening shortly （〈 0.05/9orb） before a primary eclipse. Two flares occurred within roughly one orbital period （△Ф≈ 1.024 Porb） of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.

Modelling Bacterial Dynamics in Food Products: Role of Environmental Noise and Interspecific Competition

In this paper we review some results obtained within the context of the predictive microbiology, which is a specific field of the population dynamics. In particular we discuss three models, which exploit tools of statistical mechanics, for bacterial dynamics in food of animal origin. In the first model, the random fluctuating behaviour, experimentally measured, of the temperature is considered. In the second model stochastic differential equations are introduced to take into account the influence of physical and chemical variables, such as temperature, pH and activity water, subject to deterministic and random variations. The third model, which is an extended version of the second one, neglects the environmental fluctuations, and concentrates on the role of the interspecific bacterial interactions. The comparison between expected results and observed data indicates that the presence of noise sources and interspecific bacterial interactions improves the predictive features of the models analyzed.

Kinetic energy and radial momentum distribution of hydrogen and oxygen atoms of water confined in silica hydrogel in the temperature interval 170-325 K

Water is an ubiquitous liquid and it is necessary for life;studies on water are therefore of obvious scientific and technological relevance.In view of its peculiar physical properties(the so-called water anomalies,particularly relevant at low temperatures[1]),studies on water structure and dynamics in ample temperature intervals,covering also the supercooling region,have attracted much interest in recent years.In particular,studies focused on the supercooled phase are important in order to test theories and hypotheses[2,3],including the liquid-liquid phase transition hypothesis[4-6]and the related fragile-to-strong crossover observed in water confined in silica matrices and in the hydration water of proteins[7,8].In this context,water confined within nanometer-sized porous hydrophilic/hydrophobic matrices has been investigated both to extend the supercooling temperature range accessible to experiment and to mimic the crowding/confined conditions experienced by water molecules in biological systems relevant to biophysics,bio-preservation,and pharmaceutics.In view of the above arguments,studies on the short-time dynamics of hydrogen and oxygen atoms of supercooled water(bulk or confined)are of great relevance.

Dynamics of supercooled confined water measured by deep inelastic neutron scattering

In this paper, we present the results of deep inelastic neutron scattering （DINS） measurements on supercooled water confined within the pores （average pore diameter - 20A） of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl- Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures （250 K and 210 K, i.e., before and after the putative liquid-liquid transition of supercooled confined water） on a ＂wet＂ sample with hydration h -40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually ＂dry＂ sample at h - 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As ：is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semi-empirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid-liquid transition hypothesis.

The enhanced X-ray Timing and Polarimetry mission—eXTP

In this paper we present the enhanced X-ray Timing and Polarimetry mission—eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources.The paper provides a detailed description of:(1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload;(2) the elements and functions of the mission, from the spacecraft to the ground segment.

Reply to "Comment to ‘Dynamics of supercooled confined water measured by deep inelastic neutron scattering’ by Y.Finkelstein and R.Moreh"

We reply to the comment [Front.Phys.14(5),53G05 (2019)] by Y.Finkelstein and R.Moreh on our article Front.Phys.13(1).138205 (2018).We agree with some of their criticisms about our calculation of the temperature effect on the kinetic energy of hydrogen atoms of supercooled confined water;we also agree with their statoincnt that ,in view of the current sensitivity of the technique,possible effects of the liquid liquid water transition are hardly detected with deep inelastic neutron scattering (DINS).However,we disagree with tlieir use of the translational mass ratio of a single water molecule and,in general,with their underostimation of collective effects.

Attosecond magnetization dynamics in non-magnetic materials driven by intense femtosecond lasers

Irradiating solids with ultrashort laser pulses is known to initiate femtosecond timescale magnetization dynamics.However,sub-femtosecond spin dynamics have not yet been observed or predicted.Here,we explore ultrafast light-driven spin dynamics in a highly nonresonant strong-field regime.Through state-of-the-art ab initio calculations,we predict that a nonmagnetic material can transiently transform into a magnetic one via dynamical extremely nonlinear spin-flipping processes,which occur on attosecond timescales and are mediated by cascaded multi-photon and spin–orbit interactions.These are nonperturbative nonresonant analogs to the inverse Faraday effect,allowing the magnetization to evolve in very high harmonics of the laser frequency(e.g.here up to the 42nd,oscillating at~100 attoseconds),and providing control over the speed of magnetization by tuning the laser power and wavelength.Remarkably,we show that even for linearly polarized driving,where one does not intuitively expect the onset of an induced magnetization,the magnetization transiently oscillates as the system interacts with light.This response is enabled by transverse light-driven currents in the solid,and typically occurs on timescales of~500 attoseconds(with the slower femtosecond response suppressed).An experimental setup capable of measuring these dynamics through pump–probe transient absorption spectroscopy is simulated.Our results pave the way for attosecond regimes of manipulation of magnetism.

Dense matter with eXTP

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry(eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020 s.

Accretion in strong field gravity with eXTP

In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

进行中的弗洛凯能带工程

In a recent article in Nature,Zhou et al.[1]reported an impressive demonstration of Floquet materials engineering.In this field researchers aim at creating properties in materials that they do not usually exhibit in their equilibrium state.The scope ranges from inducing phase transitions in out-of-equilibrium that can otherwise only be achieved by pressure or doping.