ShantanuT01/DACTYL-Pretraining huggingface dataset:
This paper presents a new defect model for the mixed mobile ion effect. The essential physical concept involved is that simultaneous migration of two unlike mobile ions in mixed ionic glass is accompanied by expansion or contraction of the guest-occupied sites with distortion of surrounding glass matrix; in many cases, an intensity of the local stresses in glass matrix surrounding ionic sites occupied by foreign ions is much greater than, or at least comparable to the glass network binding energy. Hence, when the stress exceeds the breaking threshold, relaxation occurs almost immediately via the rupture of the bonds in the nearest glass matrix with generation of pairs of intrinsic structural defects. The specificity of the mechanism of defect generation leads to the clustering of negatively charged defects, so that rearranged sites act as high energy anion traps in glass matrix. This results in the immobilization of almost all minority mobile species and part of majority mobile species, so mixed mobile ion glass behaves as single mobile ion glass of much lower concentration of charge carriers. Generation of defects leads also to the depolymerization of glass network, which in turn results in the reduction of the glass viscosity and Tg as well as in the compaction of glass structure (thermometer effect). The magnitude of the mixed mobile ion effect is defined by the size mismatch of unlike mobile ions, their total and relative concentrations, the binding energy of the glass-forming network, and temperature. Although the proposed model is based upon the exploration of alkali silicate glass-forming system, the approach developed here can be easily adopted to other mixed ionic systems such as crystalline and even liquid ionic conductors.
The radio emission in radio loud quasars originates in a jet carrying relativistic electrons. In radio quiet quasars (RQQs) the relative radio emission is ~10^3 times weaker, and its origin is not established yet. We show here that there is a strong correlation between the radio luminosity (L_R) and X-ray luminosity (L_X) with L_R~10^-5L_X, for the radio quiet Palomar-Green (PG) quasar sample. The sample is optically selected, with nearly complete radio and X-ray detections, and thus this correlation cannot be due to direct selection biases. The PG quasars lie on an extension of a similar correlation noted by Panessa et al., for a small sample of nearby low luminosity type 1 AGN. A remarkably similar correlation, known as the Guedel-Benz relation, where L_R/L_X~10^-5, holds for coronally active stars. The Guedel-Benz relation, together with correlated stellar X-ray and radio variability, implies that the coronae are magnetically heated. We therefore raise the possibility that AGN coronae are also magnetically heated, and that the radio emission in RQQ also originates in coronal activity. If correct, then RQQ should generally display compact flat cores at a few GHz due to synchrotron self-absorption, while at a few hundred GHz we should be able to see directly the X-ray emitting corona, and relatively rapid and large amplitude variability, correlated with the X-ray variability, is likely to be seen. We also discuss possible evidence that the radio and X-ray emission in ultra luminous X-ray sources and Galactic black holes may be of coronal origin as well.
In this paper we work out collapsing conditions for a spherical star in the weak field limit of the $R+\mu^4/R$ gravity and discuss the importance of the parameter $\mu$ to generate different criteria in the theory. Such criteria are proved to be resulting in a variety of different fates for the evolution of the outer shells of stars. Furthermore, we investigate the special case of violating the first junction condition and point out corresponding contradictions to the normal cases. These results show that the consistency of the $R+\mu^4/R$ theory of gravity with the common astrophysical predictions relies highly on the adoption of the parameter $\mu$ and satisfaction/violation of the first junction condition. For those anomalous results, further observational attempts are mandatory.
We discuss, in this review, the existing models for the production of QGP in Relativistic Heavy Ion Collisions. We shall try to give a brief description of the models available for the pre-equilibrium production of QGP, ranging from soft process dominated QCD regime to the pQCD dominated regime. We also present the estimates for the initial energy density, the temperature and the thermalisation time -- available from each of these studies. Finally, we shall address the questions regarding thermalisation, color equilibration and chemical equilibration of the produced QGP in different experimental facilities.
We combine a number of recent studies of the extended main sequence turn-off (eMSTO) phenomenon in intermediate age stellar ($1-2$ Gyr) clusters in the Large Magellanic Cloud (LMC) in order to investigate its origin. By employing the largest sample of eMSTO LMC clusters so far used, we show that cluster core radii, masses, and dynamical state are not related to the genesis of eMSTOs. Indeed, clusters in our sample have core radii, masses and age-relaxation time ratios in the range $\approx$ 2--6 pc, 3.35- 5.50 (log($M_{cls}$/$M_\odot$) and 0.2-8.0, respectively. These results imply that the eMSTO phenomenon is not caused by actual age spreads within the clusters. Furthermore, we confirm from a larger cluster sample recent results including young eMSTO LMC clusters, that the FWHM at the MSTOs correlates most strongly with cluster age, suggesting that a stellar evolutionary effect is the underlying cause.
S stars are late-type giants with overabundances of s-process elements. They come in two flavours depending on the presence or not of technetium (Tc), an element without stable isotopes. Intrinsic S stars are Tc-rich and genuine asymptotic giant branch (AGB)stars while extrinsic S stars owe their s-process overabundances to the pollution from a former AGB companion, now a white dwarf(WD). In addition to Tc, another distinctive feature between intrinsic and extrinsic S stars is the overabundance of niobium (Nb) in the latter class. We discuss the case of the S stars BD+79 156 and o1Ori whose specificity is to share the distinctive features of both intrinsic and extrinsic S stars, namely the presence of Tc along with a Nb overabundance. BD+79 156 is the first clear case of a bitrinsic star, i.e. a doubly s-process-enriched object, first through mass transfer in a binary system, and then through internal nucleosynthesis (responsible for the Tc-enrichment in BD+79 156 which must therefore have reached the AGB phase of its evolution). This hybrid nature of the s-process pattern in BD+79 156 is supported by its binary nature and its location in the HR diagram just beyond the onset of the third dredge-up on the AGB. The Tc-rich, binary S-star o1Ori with a WD companion was another long-standing candidate for a similar hybrid s-process enrichment. However the marginal overabundance of Nb derived ino1Ori does not allow to trace unambiguously the evidence of a large pollution coming from the AGB progenitor of its current WD companion. As a side product, the current study offers a new way of detecting binary AGB stars with WD companions by identifying their Tc-rich nature along with a Nb overabundance.
We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy fields in (Ga,Mn)As results in a magnetization reorientation transition and an anisotropic AC susceptibility which is fully consistent with a simple single domain model. The uniaxial and biaxial anisotropy constants vary respectively as the square and fourth power of the spontaneous magnetization across the whole temperature range up to T_C. The weakening of the anisotropy at the transition may be of technological importance for applications involving thermally-assisted magnetization switching.
We analyze theoretically a superlattice structure proposed by A. Andronov et al. [JETP Lett 102, 207 (2015)] to give Terahertz gain for an operation point with positive differential conductivity. Here we confirm the existence of gain and show that an optimized structure displays gain above 20 cm$^{-1}$ at low temperatures, so that lasing may be observable. Comparing a variety of simulations, this gain is found to be strongly affected by elastic scattering. It is shown that the dephasing modifies the nature of the relevant states, so that the common analysis based on Wannier-Stark states is not reliable for a quantitative description of the gain in structures with extremely diagonal transitions.
Recently, a microscopically motivated nuclear energy density functional was derived by applying the density matrix expansion to the Hartree-Fock (HF) energy obtained from long-range chiral effective field theory two- and three-nucleon interactions. However, the HF approach cannot account for all many-body correlations. One class of correlations is included by Brueckner-Hartree-Fock (BHF) theory, which gives an improved definition of the one-body HF potential by replacing the interaction by a reaction matrix $G$. In this paper, we find that the difference between the $G$-matrix and the nucleon-nucleon potential $V_{\mathrm{NN}}$ can be well accounted for by a truncated series of contact terms. This is consistent with renormalization group decoupling generating a series of counterterms as short-distance physics is integrated out. The coefficients $C_{n}$ of the power series expansion $\sum C_{n}q^{n}$ for the counterterms are examined for two potentials at different renormalization group resolutions and at a range of densities. The success of this expansion for $G-V_{\mathrm{NN}}$ means we can apply the density matrix expansion at the HF level with low-momentum interactions and density-dependent zero-range interactions to model BHF correlations.
In this thesis we presented a detailed spectroscopic study in a sample of Giant HII Regions in galaxies visible from Southern Hemisphere.
An eight stage balanced modulation scheme for dual beam polarimetry is presented in this paper. The four Stokes parameters are weighted equally in all the eight stages of modulation resulting in total polarimetric efficiency of unity. The gain table error inherent in dual beam system is reduced by using the well known beam swapping technique. The wavelength dependent polarimetric efficiencies of Stokes parameters due to the chromatic nature of the waveplates are presented. The proposed modulation scheme produces better Stokes $Q$ and $V$ efficiencies for wavelengths larger than the design wavelength whereas Stokes $U$ has better efficiency in the shorter wavelength region. Calibration of the polarimeter installed as a backend instrument of the Kodaikanal Tower Telescope is presented. It is found through computer simulation that a 14% sky transparency variation during calibration of the polarimeter can introduce $\approx 1.8%$ uncertainty in the determination of its response matrix.
We study the optical and near-infrared luminosities and detectability of radioactively powered electromagnetic transients ('macronovae') occuring in the aftermath of binary neutron star and neutron star black hole mergers. We explore the transients that result from the dynamic ejecta and those from different types of wind outflows. Based on full nuclear network simulations we calculate the resulting light curves in different wavelength bands. We scrutinize the robustness of the results by comparing a) two different nuclear reaction networks and b) two macronova models. We explore in particular how sensitive the results are to the production of alpha-decaying trans-lead nuclei. We compare two frequently used mass models: the Finite-Range Droplet Model (FRDM) and the nuclear mass model of Duflo and Zuker (DZ31). We find that the abundance of alpha-decaying trans-lead nuclei has a significant impact on the observability of the resulting macronovae. For example, the DZ31 model yields considerably larger abundances resulting in larger heating rates and thermalization efficiencies and therefore predicts substantially brighter macronova transients. We find that the dynamic ejecta from NSNS models can reach peak K-band magnitudes in excess of -15 while those from NSBH cases can reach beyond -16. Similar values can be reached by some of our wind models. Several of our models (both wind and dynamic ejecta) yield properties that are similar to the transient that was observed in the aftermath of the short GRB 130603B. We further explore the expected macronova detection frequencies for current and future instruments such as VISTA, ZTF and LSST.
We present the first results from our population synthesis models of elliptical galaxies. In this paper, we concentrate upon the near-infrared region of the spectrum (0.7-3 um). We model elliptical galaxies as coeval, single-metallicity stellar populations. Integrated spectra are constructed from synthetic spectra of the stars which lie along 6, 10 and 16 Gyr isochrones having [Fe/H]=+0.39, 0.00 and -0.47. The V-K and H-K colors and CO indices measured from our synthetic, integrated spectra are found to agree well with E/S0 galaxy photometry, but the J-K colors of the models are redder than the galaxies at a given V-K. We attribute this discrepancy to the oscillator strengths we employ for spectral lines in the phi system of TiO. We have probably overestimated the strengths of these lines, causing our J-band magnitudes to be too faint and our model J-K colors too red.
We present an analysis of the average spectral properties of 12,000 SDSS quasars as a function of accretion disc inclination, as measured from the equivalent width of the [O III] 5007{\AA} line. The use of this indicator on a large sample of quasars from the SDSS DR7 has proven the presence of orientation effects on the features of UV/optical spectra, confirming the presence of outflows in the NLR gas and that the geometry of the BLR is disc-like. Relying on the goodness of this indicator, we are now using it to investigate other bands/components of AGN. Specifically, the study of the UV/optical/IR SED of the same sample provides information on the obscuring "torus". The SED shows a decrease of the IR fraction moving from face-on to edge-on sources, in agreement with models where the torus is co-axial with the accretion disc. Moreover, the fact we are able to observe the broad emission lines also in sources in an edge-on position, suggests that the torus is rather clumpy than smooth as in the Unified Model. The behaviour of the SED as a function of EW[OIII] is in agreement with the predictions of the clumpy torus models as well.
We present optical and near-infrared (NIR) surface brightness and colour profiles,in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 degrees. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk.
Extremal problems for $3$-uniform hypergraphs are known to be very difficult and despite considerable effort the progress has been slow. We suggest a more systematic study of extremal problems in the context of quasirandom hypergraphs. We say that a $3$-uniform hypergraph $H=(V,E)$ is weakly $(d,\eta)$-quasirandom if for any subset $U\subseteq V$ the number of hyperedges of $H$ contained in $U$ is in the interval $d\binom{|U|}{3}\pm\eta|V|^3$. We show that for any $\varepsilon>0$ there exists $\eta>0$ such that every sufficiently large weakly $(1/4+\varepsilon,\eta)$-quasirandom hypergraph contains four vertices spanning at least three hyperedges. This was conjectured by Erd\H{o}s and S\'os and it is known that the density $1/4$ is best possible.   Recently, a computer assisted proof of this result based on the flag-algebra method was established by Glebov, Kr\'al', and Volec. In contrast to their work our proof presented here is based on the regularity method of hypergraphs and requires no heavy computations. In addition we obtain an ordered version of this result. The method of our proof allows us to study extremal problems of this type in a more systematic way and we discuss a few extensions and open problems here.
Nucleonic matter displays a quantum liquid structure, but in some cases finite nuclei behave like molecules composed of clusters of protons and neutrons. Clustering is a recurrent feature in light nuclei, from beryllium to nickel. For instance, in $^{12}$C the Hoyle state, crucial for stellar nucleosynthesis, can be described as a nuclear molecule consisting of three alpha-particles. The mechanism of cluster formation, however, has not yet been fully understood. We show that the origin of clustering can be traced back to the depth of the confining nuclear potential. By employing the theoretical framework of energy density functionals that encompasses both cluster and quantum liquid-drop aspects of nuclei, it is shown that the depth of the potential determines the energy spacings between single-nucleon orbitals, the localization of the corresponding wave functions and, therefore, the degree of nucleonic density clustering. Relativistic functionals, in particular, are characterized by deep single-nucleon potentials. When compared to non-relativistic functionals that yield similar ground-state properties (binding energy, deformation, radii), they predict the occurrence of much more pronounced cluster structures. More generally, clustering is considered as a transitional phenomenon between crystalline and quantum liquid phases of fermionic systems.
We argue that, at finite temperature, parity invariant non-compact electrodynamics with massive electrons in 2+1 dimensions can exist in both confined and deconfined phases. We show that an order parameter for the confinement-deconfinement phase transition is the Polyakov loop operator whose average measures the free energy of a test charge that is not an integral multiple of the electron charge. The effective field theory for the Polyakov loop operator is a 2-dimensional Euclidean scalar field theory with a global discrete symmetry $Z$, the additive group of the integers. We argue that the realization of this symmetry governs confinement and that the confinement-deconfinement phase transition is of Berezinskii-Kosterlitz-Thouless type. We compute the effective action to one-loop order and argue that when the electron mass $m$ is much greater than the temperature $T$ and dimensional coupling $e^2$, the effective field theory is the Sine-Gordon model. In this limit, we estimate the critical temperature, $T_{\rm crit.}=e^2/8\pi(1-e^2/12\pi m+\ldots)$.
In this paper, eit is shown for a single-$j$ shell that the intrinsic excitations induced by the quadrupole-quadrupole interaction can be viewed as that due to the inverted surface-delta interaction whose multipole-pairing component with the largest spin is the dominant term and is attractive. This allow us to trace the origin of the recently introduced optimum pair description of rotation and leads naturally to analytical expressions for the rotational energies for the various bands in a single $j$-shell with the quadrupole-quadrupole interaction.
We report an extension of the source imaging method for imaging full three-dimensional sources from three-dimensional like-pair correlations. Our technique consists of expanding the correlation data and the underlying source function in spherical harmonics and inverting the resulting system of one-dimensional integral equations. With this method of attack, we can image the source function quickly, even with the extremely large data sets common in three-dimensional analyses. We apply our method to the recently measured E859 un-Coulomb corrected data.
We present predictions for numerous statistics related to the presence of voids in the distribution of galaxies in a cold dark matter model of structure formation using a semi-analytic model of galaxy formation. Our study is able to probe galaxies with masses as low as 10^9Msun/h corresponding to absolute magnitudes of M_bJ-5log(h)=-18.1 and M_r-5log(h)=-18.7. We quantify the void and underdense probability functions, distributions of nearest neighbour distances and void sizes and compute the density profiles of voids. These results are contrasted with the expectations for dark matter (and the difference examined in terms of the galaxy/dark matter biasing relation) and are compared to analytic predictions and observational data where available. The predicted void probability functions are consistent with those measured from the Center for Astrophysics redshift surveys given the rather large uncertainties in this relatively small (for studies of voids) observational sample. The size of the observational sample is too small to probe the bias between galaxies and dark matter that we predict. We also examine the predicted properties of galaxies living within voids and contrast these with the general galaxy population. Our predictions are aimed at forthcoming large galaxy redshift surveys which should for the first time provide statistically accurate measures of the void population.
Fast radio bursts (FRBs) are bright flashes observed typically at GHz frequencies with millisecond duration, whose origin is likely extragalactic. Their nature remains mysterious, motivating searches for counterparts at other wavelengths. FRB 121102 is so far the only source known to repeatedly emit FRBs and is associated with a host galaxy at redshift $z \simeq 0.193$. We conducted simultaneous observations of FRB 121102 with the Arecibo and MAGIC telescopes during several epochs in 2016--2017. This allowed searches for millisecond-timescale burst emission in very-high-energy (VHE) gamma rays as well as the optical band. While a total of five FRBs were detected during these observations, no VHE emission was detected, neither of a persistent nature nor burst-like associated with the FRBs. The average integral flux upper limits above 100 GeV at 95% confidence level are $6.6 \times 10^{-12}~\mathrm{photons\ cm^{-2}\ s^{-1}}$ (corresponding to luminosity $L_{\rm VHE} \lesssim 10^{45}~\mathrm{erg\ s^{-1}}$) over the entire observation period, and $1.2 \times 10^{-7}~ \mathrm{photons\ cm^{-2}\ s^{-1}}$ ($L_{\rm VHE} \lesssim 10^{49}~\mathrm{erg\ s^{-1}}$) over the total duration of the five FRBs. We constrain the optical U-band flux to be below 8.6 mJy at 5-$\sigma$ level for 1-ms intervals around the FRB arrival times. A bright burst with U-band flux $29~\mathrm{mJy}$ and duration $\sim 12$ ms was detected 4.3 s before the arrival of one FRB. However, the probability of spuriously detecting such a signal within the sampled time space is 1.5% (2.2 $\sigma$, post-trial), i.e. consistent with the expected background. We discuss the implications of the obtained upper limits for constraining FRB models.