ShantanuT01/DACTYL-Pretraining huggingface dataset:
The characteristic double-bumped spectral energy distribution (SED) of blazars is explained by either leptonic or hadronic models. In the former, Inverse Compton emission dominates the emission of the high energy bump, while proton synchrotron emission and proton-gamma interactions dominate it in the latter. We present a new stationary lepto-hadronic code that evaluates both the leptonic and the hadronic interactions. Apart from the modelling of the SED produced in a leptonic or hadronic model, the code permits the study of interesting mixed lepto-hadronic scenarios, where both processes contribute significantly to the high energy bump. A first application to data from the high frequency peaked BL Lac object PKS 2155-304 is discussed.
We report the observation of an unpredicted behavior of interfering 2D electrons in the integer quantum Hall effect (IQHE) regime via a utilization of an electronic analog of the well-known Mach-Zehnder interferometer (MZI). The beauty of this experiment lies in the simplicity of two path interference. Electrons that travel the two paths via edge channels, feel only the edge potential and the strong magnetic field; both typical in the IQHE regime. Yet, the interference of these electrons via the Aharonov-Bohm (AB) effect, behaves surprisingly in a most uncommon way.   We found, at filling factors 1 and 2, high visibility interference oscillations, which were strongly modulated by a lobe-type structure as we increased the electron injection voltage. The visibility went through a few maxima and zeros in between, with the phase of the AB oscillations staying constant throughout each lobe and slipping abruptly by at each zero. The lobe pattern and the 'stick-slip' behavior of the phase were insensitive to details of the interferometer structure; but highly sensitive to magnetic field. The observed periodicity defines a 'new energy scale' with an unclear origin. The phase rigidity, on the other hand, is surprising since Onsager relations are not relevant here.
We compute the class of the classifying stack of the exceptional algebraic group $G_2$ and of the spin groups $\mathrm{Spin}_7$ and $\mathrm{Spin}_8$ in the Grothendieck ring of stacks, and show that they are equal to the inverse of the class of the corresponding group. Furthermore, we show that the computation of the motivic classes of the stacks $\mathscr{B}\mathrm{Spin}_n$ can be reduced to the computation of the classes of $\mathscr{B} \Delta_n$, where $\Delta_n\subset \mathrm{Pin}_n$ is the "extraspecial $2$-group", the preimage of the diagonal matrices under the projection $\mathrm{Pin}_n\to \mathrm{O}_n$ to the orthogonal group.
We examine observational signatures of the asymptotically de Sitter branch of static spherically symmetric Horndeski/Galileon solutions. Our analysis reveales that possible deviations of the photon sphere size from those of the GR Schwarzshild solution are vanishing compared to the resolution of modern radio-interferometric observations. These deviations are heavily suppressed by the bounds coming from the weak-field observation. We conclude that shadow size would not be a useful characteristic to distinguish the Horndeski/Galileon static spherically symmetric spacetimes in the foreseeable future.
This paper presents a principal components analysis of rotation curves from a sample of low surface brightness galaxies. The physical meaning of the principal components is investigated, and related to the intrinsic properties of the galaxies. The rotation curves are re-scaled using the optical disk scale, the resulting principal component decomposition demonstrates that the whole sample is properly approximated using two components. The ratio of the second to the first component is related to the halo steepness in the central region, is correlated to the gas fraction in the galaxy, and is un-correlated to other parameters. As a consequence the gas fraction appear as a fundamental variable with respect to the galaxies rotation curves, and its correlation with the halo steepness is especially important. Since the gas fraction is related to the degree of galaxy evolution, it is very likely that the steepness of the halo at the center is a consequence of galaxy evolution. More evolved galaxies have shallower central profile and statistically less gas, most likely as a consequence of more star formation and supernovae. The differences in evolution, gas fractions and halo central steepness of the galaxies could be due to the influence of different environments.
The Fermi Large Area Telescope (LAT) collaboration recently released the updated results of the measurement of the cosmic ray electron (CRE) spectrum and published its first constraints on the CRE anisotropy. With respect to the previous Fermi-LAT results, the CRE spectrum measurement was extended down from 20 to 7 GeV, thus providing a better lever arm to discriminate theoretical models. Here we show that the new data strengthen the evidence for the presence of two distinct electron and positron spectral components. Furthermore, we show that under such hypothesis most relevant CRE and positron data sets are remarkably well reproduced. Consistent fits of cosmic-ray nuclei and antiproton data, which are crucial to validate the adopted propagation setup(s) and to fix the solar modulation potential, are obtained for the Kraichnan and plain-diffusion propagation setups, while the Kolmogorov one is disfavored. We then confirm that nearby pulsars are viable source candidates of the required $e^\pm$ extra-component. In that case, we show that the predicted CRE anisotropy is compatible with Fermi-LAT constraints and that a positive detection should be at hand of that observatory. Models assuming that only nearby supernova remnants contribute to the high energy tail of the observed CRE spectrum are in contrast with anisotropy limits.
We continue a sequence of recent works studying Ramsey functions for semialgebraic predicates in $\mathbb{R}^d$. A $k$-ary semialgebraic predicate $\Phi(x_1,\ldots,x_k)$ on $\mathbb{R}^d$ is a Boolean combination of polynomial equations and inequalities in the $kd$ coordinates of $k$ points $x_1,\ldots,x_k\in\mathbb{R}^d$. A sequence $P=(p_1,\ldots,p_n)$ of points in $\mathbb{R}^d$ is called $\Phi$-homogeneous if either $\Phi(p_{i_1}, \ldots,p_{i_k})$ holds for all choices $1\le i_1 < \cdots < i_k\le n$, or it holds for no such choice. The Ramsey function $R_\Phi(n)$ is the smallest $N$ such that every point sequence of length $N$ contains a $\Phi$-homogeneous subsequence of length $n$.   Conlon, Fox, Pach, Sudakov, and Suk constructed the first examples of semialgebraic predicates with the Ramsey function bounded from below by a tower function of arbitrary height: for every $k\ge 4$, they exhibit a $k$-ary $\Phi$ in dimension $2^{k-4}$ with $R_\Phi$ bounded below by a tower of height $k-1$. We reduce the dimension in their construction, obtaining a $k$-ary semialgebraic predicate $\Phi$ on $\mathbb{R}^{k-3}$ with $R_\Phi$ bounded below by a tower of height $k-1$.   We also provide a natural geometric Ramsey-type theorem with a large Ramsey function. We call a point sequence $P$ in $\mathbb{R}^d$ order-type homogeneous if all $(d+1)$-tuples in $P$ have the same orientation. Every sufficiently long point sequence in general position in $\mathbb{R}^d$ contains an order-type homogeneous subsequence of length $n$, and the corresponding Ramsey function has recently been studied in several papers. Together with a recent work of B\'ar\'any, Matou\v{s}ek, and P\'or, our results imply a tower function of $\Omega(n)$ of height $d$ as a lower bound, matching an upper bound by Suk up to the constant in front of $n$.
A smooth compactification X<n> of the configuration space of n distinct labeled points in a smooth algebraic variety X is constructed by a natural sequence of blowups, with the full symmetry of the permutation group S_n manifest at each stage of the construction. The strata of the normal crossing divisor at infinity are labeled by trees with levels and their structure is studied. This is the maximal wonderful compactification in the sense of DeConcini-Procesi, and it has a strata-compatible surjection onto the Fulton-MacPherson compactification. The degenerate configurations added in the compactification are geometrically described by `polyscreens' similar to screens of Fulton and MacPherson. In characteristic 0, isotropy subgroups of the action of S_n on X<n> are abelian, thus X<n> may be a step toward an explicit resolution of singularities of the symmetric products X^n/S_n.
Solar photospheric magnetic field plays a dominant role in the variability of total solar irradiance (TSI). The modulation of magnetic flux at six specific ranges on TSI is characterized for the first time. The daily flux values of magnetic field at four ranges are extracted from MDI/{\sl SOHO}, together with daily flux of active regions (MF$_{\text{ar}}$) and quiet regions (MF$_{\text{qr}}$); the first four ranges (MF$_{1-4}$) are: 1.5--2.9, 2.9--32.0, 32.0--42.7, and 42.7--380.1 ($\times 10^{18}$ Mx per element), respectively. Cross-correlograms show that MF$_4$, MF$_{\text{qr}}$, and MF$_{\text{ar}}$ are positively correlated with TSI, while MF$_2$ is negatively correlated with TSI; the correlations between MF$_1$, MF$_3$ and TSI are insignificant. The bootstrapping tests confirm that the impact of MF$_4$ on TSI is more significant than that of MF$_{\text{ar}}$ and MF$_{\text{qr}}$, and MF$_{\text{ar}}$ leads TSI by one rotational period. By extracting the rotational variations in the MFs and TSI, the modulations of the former on the latter at the solar rotational timescale are clearly illustrated and compared during solar maximum and minimum times, respectively. Comparison of the relative amplitudes of the long-term variation show that TSI is in good agreement with the variation of MF$_4$ and MF$_{\text{ar}}$; besides, MF$_2$ is in antiphase with TSI, and it lags the latter by about 1.5 years.
We present an analysis of stellar populations in passive galaxies in seven massive X-ray clusters at z=0.19-0.89. Based on absorption line strengths measured from our high signal-to-noise spectra, the data support primarily passive evolution of the galaxies. We use the scaling relations between velocity dispersions and the absorption line strengths to determine representative mean line strengths for the clusters. From the age determinations based on the line strengths (and stellar population models), we find a formation redshift of z_form=1.96(-0.19,+0.24). Based on line strength measurements from high signal-to-noise composite spectra of our data, we establish the relations between velocity dispersion, ages, metallicities [M/H] and abundance ratios [alpha/Fe] as a function of redshift. The [M/H]-velocity dispersion and [alpha/Fe]-velocity dispersion relations are steep and tight. The age-velocity dispersion relation is flat, with zero point changes reflecting passive evolution. The scatter in all three parameters are within 0.08-0.15 dex at fixed velocity dispersions, indicating a large degree of synchronization in the evolution of the galaxies. We find indication of cluster-to-cluster differences in metallicities and abundance ratios. However, variations in stellar populations with the cluster environment can only account for a very small fraction of the intrinsic scatter in the scaling relations. Thus, within these very massive clusters the main driver of the properties of the stellar populations in passive galaxies appears to be the galaxy velocity dispersion.
One classical theory, as determined by an equation of motion or set of classical trajectories, can correspond to many unitarily {\em in}equivalent quantum theories upon canonical quantization. This arises from a remarkable ambiguity, not previously investigated, in the construction of the classical (and hence the quantized) Hamiltonian or Lagrangian. This ambiguity is illustrated for systems with one degree of freedom: An arbitrary function of the constants of motion can be introduced into this construction. For example, the nonrelativistic and relativistic free particles follow identical classical trajectories, but the Hamiltonians or Lagrangians, and the canonically quantized versions of these descriptions, are inequivalent. Inequivalent descriptions of other systems, such as the harmonic oscillator, are also readily obtained.
Recently an air-stable layered semiconductor Bi2O2Se was discovered to exhibit an ultrahigh mobility in transistors fabricated with its thin layers. In this work, we explored the mechanism that induces the high mobility and distinguishes Bi2O2Se from other semiconductors. We found that the electron donor states lie above the lowest conduction band. Thus, electrons get spontaneously ionized from donor sites (e.g., Se vacancies) without involving the thermal activation, different from the donor ionization in conventional semiconductors. Consequently, the resistance decreases as reducing the temperature as observed in our measurement, which is similar to a metal but contrasts to a usual semiconductor. Furthermore, the electron conduction channels locate spatially away from ionized donor defects (Se vacancies) in different van der Waals layers. Such a spatial separation can strongly suppress the scattering caused by donor sites and subsequently increase the electron mobility, especially at the low temperature. We call this high-mobility mechanism self-modulation doping, i.e. the modulation doping spontaneously happening in a single-phase material without requiring a heterojunction. Our work paves a way to design novel high-mobility semiconductors with layered materials.
We generalize Werner's defect formula for nodal hypersurfaces in $\mathbb P^{4}$ to the case of a nodal complete intersection threefold.
Generalizations of GL(n) abelian Toda and $\widetilde{GL}(n)$ abelian affine Toda field theories to the noncommutative plane are constructed. Our proposal relies on the noncommutative extension of a zero-curvature condition satisfied by algebra-valued gauge potentials dependent on the fields. This condition can be expressed as noncommutative Leznov-Saveliev equations which make possible to define the noncommutative generalizations as systems of second order differential equations, with an infinite chain of conserved currents. The actions corresponding to these field theories are also provided. The special cases of GL(2) Liouville and $\widetilde{GL}(2)$ sinh/sine-Gordon are explicitly studied. It is also shown that from the noncommutative (anti-)self-dual Yang-Mills equations in four dimensions it is possible to obtain by dimensional reduction the equations of motion of the two-dimensional models constructed. This fact supports the validity of the noncommutative version of the Ward conjecture. The relation of our proposal to previous versions of some specific Toda field theories reported in the literature is presented as well.
Context. Binary evolution can result in fast-rotating stars, predicted to be observable as Be stars, through accretion of angular momentum during mass-transfer phases. Despite numerous observational evidence pointing to this possibly being the dominant Be formation channel, current models struggle to produce a satisfactory description of Be star populations.   Aims. Given distinct uncertainties in detailed binary evolution calculations, we investigate a rigorous and model independent upper limit for the production of Be stars through binary interaction and aim to confront this limit with observations of Be stars in young star clusters.   Methods. Using extreme assumptions, we calculate the number ratio of post-interaction to pre-interaction binary systems in a coeval population, which describes an upper limit to Be star formation through mass-transfer. A detailed comparison is made between our derived upper limit and relevant observations of Be stars, which allows us to probe several aspects of binary star physics.   Results. We find that in coeval populations, binary interaction can at most account for one third of all main-sequence stars being Be stars. Near the cluster turn-off region, this limit appears to be realised in the clusters studied. Away from the turn-off, applying simple assumptions about which systems undergo unstable mass-transfer produces a good fit to the observed Be fraction as a function of mass.   Conclusions. We find that assuming distinct physics, binary evolution alone can in principle match the high numbers of Be stars observed in open clusters. Whether the required binary physics is realised in nature remains to be investigated.
We report the discovery of a ~100 kpc ionized nebula associated with the radio quiet type 2 quasar (QSO2) nicknamed the "Teacup" (z=0.085). The giant nebula is among the largest known around active galaxies at any z. We propose that it is part of the circumgalactic medium (CGM) of the QSO2 host, which has been populated with tidal debris by galactic interactions. This rich gaseous medium has been rendered visible due to the illumination by the powerful active nucleus (AGN). Subsolar abundances (~0.5Z(sun)) are tentatively favored by AGN photoionization models. We also report the detection of coronal emission (Fe+6) from the NE bubble, at ~9 kpc from the AGN. The detection of coronal lines at such large distances from the AGN and the [NII]/Halpha, [SII]/Halpha, [OI]/Halpha optical emission line ratios of the giant nebula are consistent with the fading quasar scenario proposed by Gagne et al. (2014). The fading rate appears to have been faster in the last ~46,000 yr. Deep wide field integral field spectroscopy of giant nebulae around powerful AGN such as the "Teacup's" with instruments such as MUSE on VLT opens up a way to detect and study the elusive material from the CGM around massive active galaxies thanks to the illumination by the luminous AGN.
Low-energy nuclear structure is not sensitive enough to resolve fine details of nucleon-nucleon (NN) interaction. Insensitivity of infrared physics to the details of short-range strong interaction allows for consistent, free of ultraviolet divergences, formulation of local theory at the level of local energy density functional (LEDF) including, on the same footing, both particle-hole as well as particle-particle channels. Major difficulty is related to parameterization of the nuclear LEDF and its density dependence. It is argued that structural simplicity of terminating or isomeric states offers invaluable source of informations that can be used for fine-tuning of the NN interaction in general and the nuclear LEDF parameters in particular. Practical applications of terminating states at the level of LEDF and nuclear shell-model are discussed.
Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature and detailed structure can affect the excitation process of various stellar pulsation modes, and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, and its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection, and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (2013), and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. (2013) prescription in the Toulouse-Geneva Evolution code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Th\'eado et al. (2009), that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases ultimately triggers dynamical convection.
We present a generalization of a version of the Kruskal-Katona theorem due to Lovasz. A shadow of a d-tuple (S_1,...,S_d) in binom{X}{r}^d consists of d-tuples (S_1',...,S_d') in binom{X}{r-1}^d obtained by removing one element from each of S_i. We show that if a family F in binom{X}{r}^d has size |F|=binom{x}{r}^d for a real number x>=r, then the shadow of F has size at least binom{x}{r-1}^d.
We study the interplay of electric and magnetic order in the one dimensional Heisenberg spin-1/2 XXZ chain with large Ising anisotropy in the presence of the Dzyaloshinskii-Moriya (D-M) interaction and with longitudinal and transverse magnetic fields, interpreting the D-M interaction as a coupling between the local electric polarization and an external electric field. We obtain the ground state phase diagram using the density matrix renormalization group method and compute various ground state quantities like the magnetization, staggered magnetization, electric polarization and spin correlation functions, etc. In the presence of both longitudinal and transverse magnetic fields, there are three different phases corresponding to a gapped N\'{e}el phase with antiferromagnetic (AF) order, gapped saturated phase and a critical incommensurate gapless phase. The external electric field modifies the phase boundaries but does not lead to any new phases. Both external magnetic fields and electric fields can be used to tune between the phases. We also show that the transverse magnetic field induces a vector chiral order in the N\'{e}el phase (even in the absence of an electric field) which can be interpreted as an electric polarization in a direction parallel to the AF order.
A number of studies have shown that the visibility of scattered broad emission lines in Seyfert 2 galaxies is strongly dependent on the IRAS f_60/f_25 flux ratio, where those Seyfert 2s with `warm' IRAS colours show polarised broad line emission. It is now clear that this effect is due to the increasing dominance of the galactic rather than the AGN emission at 60um in less luminous `cool' Seyfert 2s. However, we present evidence that the 25um emission is a good measure of the AGN luminosity for most Seyfert 2s. Using this result, we show that the visibility of scattered broad line emission has a dependence on the AGN luminosity. The observations can be interpreted self-consistently if the scale height of the scattering zone varies with central source luminosity whilst the scale height of the obscuring torus is approximately constant.
In the present work we investigate the photocatalytic hydrogen production (water splitting) activity of different Pt loaded TiO2 nanotube layers. Therefore, we fabricate free standing membranes and fix them in four different configurations: top up (with initiation layer grass or without) and bottom up (bottom closed or open), then decorate the tubes with various amounts of Pt and measure the open-circuit photocatalytic H2 production rate. We find a strong influence of the configuration with the open top morphology showing the highest photocatalytic hydrogen production efficiency, these nanotubes yield 3.5 times more H2 than the least efficient structure (bottom closed). The work therefore provides valuable guidelines for optimizing TiO2 nanotube layers for photocatalytic applications.