Showing papers on "Absorption (logic) published in 2017"

Discovery of water at high spectral resolution in the atmosphere of 51 Peg b

Abstract: We report the detection of water absorption features in the day side spectrum of the first-known hot Jupiter, 51 Peg b, confirming the star–planet system to be a double-lined spectroscopic binary. We use high-resolution ($R\approx $ 100,000), $3.2\,\mu {\rm{m}}$ spectra taken with CRIRES/VLT to trace the radial-velocity shift of the water features in the planet's day side atmosphere during 4 hr of its 4.23 day orbit after superior conjunction. We detect the signature of molecular absorption by water at a significance of $5.6\sigma $ at a systemic velocity of ${V}_{\mathrm{sys}}=-33\pm 2$ km s−1, coincident with the 51 Peg host star, with a corresponding orbital velocity ${K}_{{\rm{P}}}={133}_{-3.5}^{+4.3}$ km s−1. This translates directly to a planet mass of ${M}_{{\rm{p}}}={0.476}_{-0.031}^{+0.032}\,{M}_{{\rm{J}}}$, placing it at the transition boundary between Jovian and Neptunian worlds. We determine upper and lower limits on the orbital inclination of the system of $70^\circ \lt i\lt 82\buildrel{\circ}\over{.} 2$. We also provide an updated orbital solution for 51 Peg b, using an extensive set of 639 stellar radial velocities measured between 1994 and 2013, finding no significant evidence of an eccentric orbit. We find no evidence of significant absorption or emission from other major carbon-bearing molecules of the planet, including methane and carbon dioxide. The atmosphere is non-inverted in the temperature–pressure region probed by these observations. The deepest absorption lines reach an observed relative contrast of $0.9\times {10}^{-3}$ with respect to the host star continuum flux at an angular separation of 3 milliarcseconds. This work is consistent with a previous tentative report of K-band molecular absorption for 51 Peg b by Brogi et al.

Massive warm/hot galaxy coronae as probed by uv/x-ray oxygen absorption and emission. i. basic model

Abstract: We construct an analytic phenomenological model for extended warm/hot gaseous coronae of $L_*$ galaxies. We consider UV OVI COS-Halos absorption line data in combination with Milky Way X-ray OVII and OVIII absorption and emission. We fit these data with a single model representing the COS-Halos galaxies and a Galactic corona. Our model is multi-phased, with hot and warm gas components, each with a (turbulent) log-normal distribution of temperatures and densities. The hot gas, traced by the X-ray absorption and emission, is in hydrostatic equilibrium in a Milky Way gravitational potential. The median temperature of the hot gas is $1.5 \times 10^6$~K and the mean hydrogen density is $\sim 5 \times 10^{-5}~{\rm cm^{-3}}$. The warm component as traced by the OVI, is gas that has cooled out of the high density tail of the hot component. The total warm/hot gas mass is high and is $1.2 \times 10^{11}~{\rm M_{\odot}}$. The gas metallicity we require to reproduce the oxygen ion column densities is $0.5$ solar. The warm OVI component has a short cooling time ($\sim 2 \times 10^8$ years), as hinted by observations. The hot component, however, is $\sim 80\%$ of the total gas mass and is relatively long-lived, with $t_{cool} \sim 7 \times 10^{9}$ years. Our model supports suggestions that hot galactic coronae can contain significant amounts of gas. These reservoirs may enable galaxies to continue forming stars steadily for long periods of time and account for "missing baryons" in galaxies in the local universe.

Optical levitation of 10-ng spheres with nano-g acceleration sensitivity

Abstract: We demonstrate optical levitation of ${\mathrm{SiO}}_{2}$ spheres with masses ranging from 0.1 to 30 ng. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of $0.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{4pt}{0ex}}g/\sqrt{\mathrm{Hz}}$ for a 12-ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of $(\ensuremath{-}0.7\ifmmode\pm\else\textpm\fi{}2.4\phantom{\rule{0.16em}{0ex}}[\text{stat}]\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.16em}{0ex}}[\text{syst}])\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.16em}{0ex}}g$ is measured in $1.4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.

Antiferromagnetic Resonance and Terahertz Continuum in α-RuCl_{3}.

Abstract: We report measurements of optical absorption in the zigzag antiferromagnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ as a function of temperature $T$, magnetic field $B$, and photon energy $\ensuremath{\hbar}\ensuremath{\omega}$ in the range $\ensuremath{\sim}0.3$--8.3 meV, using time-domain terahertz spectroscopy. Polarized measurements show that threefold rotational symmetry is broken in the honeycomb plane from 2 to 300 K. We find a sharp absorption peak at 2.56 meV upon cooling below the N\'eel temperature of 7 K at $B=0$ that we identify as the magnetic-dipole excitation of a zero-wave-vector magnon, or antiferromagnetic resonance (AFMR). With the application of $B$, the AFMR broadens and shifts to a lower frequency as long-range magnetic order is lost in a manner consistent with transitioning to a spin-disordered phase. From a direct, internally calibrated measurement of the AFMR spectral weight, we place an upper bound on the contribution to the dc susceptibility from a magnetic excitation continuum.

First Data Release of the COSMOS Lyman-Alpha Mapping And Tomography Observations: 3D Lyman-$\alpha$ Forest Tomography at 2.05 < z < 2.55

Abstract: Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-$\alpha$ forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck-I telescope. Over an observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we used 240 galaxies and quasars at $2.17

First-principles study on the electronic, optical, and transport properties of monolayer α - and β -GeSe

Abstract: The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-GeSe, revealing a direct band gap of 1.61 eV for monolayer $\ensuremath{\alpha}$-GeSe and an indirect band gap of 2.47 eV for monolayer $\ensuremath{\beta}$-GeSe. For monolayer $\ensuremath{\beta}$-GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of $2.93\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{2}/\text{V}\phantom{\rule{0.16em}{0ex}}\text{s}$ along the armchair direction, comparable to that of black phosphorene. Furthermore, for $\ensuremath{\beta}$-GeSe, robust band gaps nearly independent of the applied tensile strain along the armchair direction are observed. Both monolayer $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-GeSe exhibit anisotropic optical absorption in the visible spectrum.

Evidence for a radiatively driven disc-wind in PDS 456?

Abstract: We present a newly discovered correlation between the wind outflow velocity and the X-ray luminosity in the luminous ($L_{\rm bol}\sim10^{47}\,\rm erg\,s^{-1}$) nearby ($z=0.184$) quasar PDS\,456. All the contemporary XMM-Newton, NuSTAR and Suzaku observations from 2001--2014 were revisited and we find that the centroid energy of the blueshifted Fe\,K absorption profile increases with luminosity. This translates into a correlation between the wind outflow velocity and the hard X-ray luminosity (between 7--30\,keV) where we find that $v_{\rm w}/c \propto L_{7-30}^{\gamma}$ where $\gamma=0.22\pm0.04$. We also show that this is consistent with a wind that is predominately radiatively driven, possibly resulting from the high Eddington ratio of PDS\,456.

The Chandra COSMOS Legacy Survey: Energy Spectrum of the Cosmic X-Ray Background and Constraints on Undetected Populations

Abstract: Using {\em Chandra} observations in the 2.15 deg$^{2}$ COSMOS legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT$\sim$0.27 and 0.07 keV and an extragalactic power-law with photon spectral index $\Gamma$=1.45$\pm{0.02}$. The 1 keV normalization of the extragalactic component is 10.91$\pm{0.16}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. Removing all X-ray detected sources, the remaining unresolved CXB is best-fit by a power-law with normalization 4.18$\pm{0.26}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$ and photon spectral index $\Gamma$=1.57$\pm{0.10}$. Removing faint galaxies down to i$_{AB}\sim$27-28 leaves a hard spectrum with $\Gamma\sim$1.25 and a 1 keV normalization of $\sim$1.37 keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. This means that $\sim$91\% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute $\sim 8-9\%$ of the total CXB show a marginal evidence of being harder and possibly more obscured than resolved sources. Another $\sim$1\% of the CXB can be attributed to still undetected star forming galaxies and absorbed AGN. According to these limits, we investigate a scenario where early black holes totally account for non source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the $z\sim$6 accreted mass density, such a population of black holes must grow in Compton-thick envelopes with N$_{H}>$1.6$\times$10$^{25}$ cm$^{-2}$ and form in extremely low metallicity environments $(Z_\odot)\sim10^{-3}$.

Optical potential from first principles

Abstract: We develop a method to construct a microscopic optical potential from chiral interactions for nucleon-nucleus scattering. The optical potential is constructed by combining the Green's function approach with the coupled-cluster method. To deal with the poles of the Green's function along the real energy axis we employ a Berggren basis in the complex energy plane combined with the Lanczos method. Using this approach, we perform a proof-of-principle calculation of the optical potential for the elastic neutron scattering on $^{16}\mathrm{O}$. For the computation of the ground state of $^{16}\mathrm{O}$, we use the coupled-cluster method in the singles-and-doubles approximation, while for the $A\ifmmode\pm\else\textpm\fi{}1$ nuclei we use particle-attached/removed equation-of-motion method truncated at two-particle--one-hole and one-particle--two-hole excitations, respectively. We verify the convergence of the optical potential and scattering phase shifts with respect to the model-space size and the number of discretized complex continuum states. We also investigate the absorptive component of the optical potential (which reflects the opening of inelastic channels) by computing its imaginary volume integral and find an almost negligible absorptive component at low energies. To shed light on this result, we computed excited states of $^{16}\mathrm{O}$ using the equation-of-motion coupled-cluster method with singles-and-doubles excitations and we found no low-lying excited states below 10 MeV. Furthermore, most excited states have a dominant two-particle--two-hole component, making higher-order particle-hole excitations necessary to achieve a precise description of these core-excited states. We conclude that the reduced absorption at low energies can be attributed to the lack of correlations coming from the low-order cluster truncation in the employed coupled-cluster method.

High-precision limit on variation in the fine-structure constant from a single quasar absorption system

Abstract: The brightest southern quasar above redshift $z=1$, HE 0515$-$4414, with its strong intervening metal absorption-line system at $z_{abs}=1.1508$, provides a unique opportunity to precisely measure or limit relative variations in the fine-structure constant ($\Delta\alpha/\alpha$). A variation of just $\sim$3 parts per million (ppm) would produce detectable velocity shifts between its many strong metal transitions. Using new and archival observations from the Ultraviolet and Visual Echelle Spectrograph (UVES) we obtain an extremely high signal-to-noise ratio spectrum (peaking at S/N $\approx250$ pix$^{-1}$). This provides the most precise measurement of $\Delta\alpha/\alpha$ from a single absorption system to date, $\Delta\alpha/\alpha=-1.42\pm0.55_{\rm stat}\pm0.65_{\rm sys}$ ppm, comparable with the precision from previous, large samples of $\sim$150 absorbers. The largest systematic error in all (but one) previous similar measurements, including the large samples, was long-range distortions in the wavelength calibration. These would add a $\sim$2 ppm systematic error to our measurement and up to $\sim$10 ppm to other measurements using Mg and Fe transitions. However, we corrected the UVES spectra using well-calibrated spectra of the same quasar from the High Accuracy Radial velocity Planet Searcher (HARPS), leaving a residual 0.59 ppm systematic uncertainty, the largest contribution to our total systematic error. A similar approach, using short observations on future, well-calibrated spectrographs to correct existing, high S/N spectra, would efficiently enable a large sample of reliable $\Delta\alpha/\alpha$ measurements. The high S/N UVES spectrum also provides insights into analysis difficulties, detector artifacts and systematic errors likely to arise from 25-40-m telescopes.

The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV

Abstract: We identify sources with extremely hard X-ray spectra (i.e., with photon indices of ${\rm{\Gamma }}\lesssim 0.6$) in the 13 deg2 NuSTAR serendipitous survey, to search for the most highly obscured active galactic nuclei (AGNs) detected at $\gt 10\,\mathrm{keV}$. Eight extreme NuSTAR sources are identified, and we use the NuSTAR data in combination with lower-energy X-ray observations (from Chandra, Swift XRT, and XMM-Newton) to characterize the broadband (0.5–24 keV) X-ray spectra. We find that all of the extreme sources are highly obscured AGNs, including three robust Compton-thick (CT; ${N}_{{\rm{H}}}\gt 1.5\times {10}^{24}$ cm−2) AGNs at low redshift ($z\lt 0.1$) and a likely CT AGN at higher redshift (z = 0.16). Most of the extreme sources would not have been identified as highly obscured based on the low-energy ($\lt 10$ keV) X-ray coverage alone. The multiwavelength properties (e.g., optical spectra and X-ray–mid-IR luminosity ratios) provide further support for the eight sources being significantly obscured. Correcting for absorption, the intrinsic rest-frame 10–40 keV luminosities of the extreme sources cover a broad range, from $\approx 5\times {10}^{42}$ to 1045 erg s−1. The estimated number counts of CT AGNs in the NuSTAR serendipitous survey are in broad agreement with model expectations based on previous X-ray surveys, except for the lowest redshifts ($z\lt 0.07$), where we measure a high CT fraction of ${f}_{\mathrm{CT}}^{\mathrm{obs}}={30}_{-12}^{+16} \% $. For the small sample of CT AGNs, we find a high fraction of galaxy major mergers (50% ± 33%) compared to control samples of "normal" AGNs.

CO-dark molecular gas at high redshift: very large H2 content and high pressure in a low-metallicity damped Lyman alpha system

Abstract: We present a detailed analysis of a H$_2$-rich, extremely strong intervening Damped Ly-$\alpha$ Absorption system (DLA) at $z_{\rm abs}=2.786$ towards the quasar J$\,$0843+0221, observed with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. The total column density of molecular (resp. atomic) hydrogen is $\log N$(H$_2$)=$21.21\pm0.02$ (resp. $\log N$(H$\,$I)=$21.82\pm0.11$), making it to be the first case in quasar absorption lines studies with H$_2$ column density as high as what is seen in $^{13}$CO-selected clouds in the Milky-Way. We find that this system has one of the lowest metallicity detected among H$_2$-bearing DLAs, with $\rm [Zn/H]=-1.52^{+0.08}_{-0.10}$. This can be the reason for the marked differences compared to systems with similar H$_2$ column densities in the local Universe: $(i)$ the kinetic temperature, $T\sim$120~K, derived from the $J=0,1$ H$_2$ rotational levels is at least twice higher than expected; $(ii)$ there is little dust extinction with A$_V 2\times 10^{23} $ cm$^{-2}$/(km/s\,K), in the very low metallicity gas. Low CO and high H$_2$ contents indicate that this system represents "CO-dark/faint" gas. We investigate the physical conditions in the H$_2$-bearing gas using the fine-structure levels of C$\,$I, C$\,$II, Si$\,$II and the rotational levels of HD and H$_2$. We find the number density to be about $n \sim 260-380\,$cm$^{-3}$, implying a high thermal pressure of $(3-5) \times 10^4\,$cm$^{-3}\,$K. We further identify a trend of increasing pressure with increasing total hydrogen column density. This independently supports the suggestion that extremely strong DLAs (with $\log\,$N(H) $\sim 22$) probe high-z galaxies at low impact parameters.

Low-Energy Magnetic Dipole Radiation in Open-Shell Nuclei

Abstract: Low-energy $M1$ strength functions of $^{60,64,68}\mathrm{Fe}$ are determined on the basis of large-scale shell-model calculations with the goal to study their development from the bottom to the middle of the neutron shell. We find that the zero-energy spike, which characterizes nuclei near closed shells, develops toward the middle of the shell into a bimodal structure composed of a weaker zero-energy spike and a scissorslike resonance around 3 MeV, where the summed strengths of the two structures change within only 8% around a value of $9.8\text{ }\text{ }{\ensuremath{\mu}}_{N}^{2}$. The summed strength of the scissors region exceeds the total $\ensuremath{\gamma}$ absorption strength from the ground state by a factor of about three, which explains the discrepancy between total strengths of the scissors resonance derived from ($\ensuremath{\gamma}$, ${\ensuremath{\gamma}}^{\ensuremath{'}}$) experiments and from experiments using light-ion induced reactions.

Modeling Day-to-Day Variability of Glucose–Insulin Regulation Over 12-Week Home Use of Closed-Loop Insulin Delivery

Abstract: Parameters of physiological models of glucose–insulin regulation in type 1 diabetes have previously been estimated using data collected over short periods of time and lack the quantification of day-to-day variability. We developed a new hierarchical model to relate subcutaneous insulin delivery and carbohydrate intake to continuous glucose monitoring over 12 weeks while describing day-to-day variability. Sensor glucose data sampled every 10-min, insulin aspart delivery and meal intake were analyzed from eight adults with type 1 diabetes (male/female 5/3, age ${\text{39.9}\,\pm \,\text{9.5}}$ years, BMI $\text{25.4}\,\pm \,\text{4.4 kg/ m}^{2}$ , HbA1c ${\text{8.4}\,\pm \,\text{0.6}}$ %) who underwent a 12-week home study of closed-loop insulin delivery. A compartment model comprised of five linear differential equations; model parameters were estimated using the Markov chain Monte Carlo approach within a hierarchical Bayesian model framework. Physiologically, plausible a posteriori distributions of model parameters including insulin sensitivity, time-to-peak insulin action, time-to-peak gut absorption, and carbohydrate bioavailability, and good model fit were observed. Day-to-day variability of model parameters was estimated in the range of 38–79% for insulin sensitivity and 27–48% for time-to-peak of insulin action. In conclusion, a linear Bayesian hierarchical approach is feasible to describe a 12-week glucose–insulin relationship using conventional clinical data. The model may facilitate in silico testing to aid the development of closed-loop insulin delivery systems.

Single-layer group IV-V and group V-IV-III-VI semiconductors: Structural stability, electronic structures, optical properties, and photocatalysis

Abstract: Recently, single-layer group III monochalcogenides have attracted both theoretical and experimental interest at their potential applications in photonic devices, electronic devices, and solar energy conversion. Excited by this, we theoretically design two kinds of highly stable single-layer group IV-V ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P) and group V-IV-III-VI ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P; $\mathrm{III}=\mathrm{Al},\mathrm{Ga}$, and In; $\mathrm{VI}=\mathrm{O}$ and S) compounds with the same structures with single-layer group III monochalcogenides via first-principles simulations. By using accurate hybrid functional and quasiparticle methods, we show the single-layer group IV-V and group V-IV-III-VI are indirect bandgap semiconductors with their bandgaps and band edge positions conforming to the criteria of photocatalysts for water splitting. By applying a biaxial strain on single-layer group IV-V, single-layer group IV nitrides show a potential on mechanical sensors due to their bandgaps showing an almost linear response for strain. Furthermore, our calculations show that both single-layer group IV-V and group V-IV-III-VI have absorption from the visible light region to far-ultraviolet region, especially for single-layer SiN-AlO and SnN-InO, which have strong absorption in the visible light region, resulting in excellent potential for solar energy conversion and visible light photocatalytic water splitting. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting.

Estimation of Colored Dissolved Organic Matter From Landsat-8 Imagery for Complex Inland Water: Case Study of Lake Huron

Abstract: Spectral reflectance data, including irradiance reflectance $(R_{t})$ and remote sensing reflectance $(R_{\mathrm {rs}}$ , sr $^{-1})$ , and colored dissolved organic matter (CDOM) absorption coefficients $a_{\mathrm {CDOM}}$ (440), were collected in the Saginaw River and Kawkawlin River plume regions of Lake Huron. We developed an empirical band ratio algorithm to derive $a_{\mathrm {CDOM}}$ (440) that could be directly applicable to Landsat-8 imagery. A model ranking method is used to determine the best band ratios as well as their empirical functions. One problem of previous CDOM estimations from Landsat imagery is that they usually use $R_{t}$ or $R_{t}/\pi $ rather than the real $R_{\mathrm {rs}}$ as the input data, but as a result of our study, algorithms derived using $R_{\mathrm {rs}}$ performed much better than using $R_{t}$ . The green/red band ratio gave the best accuracies by fitting with power and exponential models (power model: $R^{{2}} = 0.819$ and RMSE $=0.889~\text{m}^{-1}$ and exponential model: $R^{2} = 0.829$ and RMSE $=0.863~\text{m}^{-1})$ . The power and exponential models were further validated using an independent data group, achieving excellent results with the RMSE of 0.642 and 0.504 $\text{m}^{-1}$ , respectively. The application of the exponential model $a_{\mathrm {CDOM}}$ (440) = 40.75e−2.463 x , $x = R_{\mathrm {rs}}$ (B3)/ $R_{\mathrm {rs}}$ (B4) on two Landsat-8 images demonstrated that estimating CDOM from to Landsat-8 imagery has potential applications for monitoring water quality in long term and large scale.

Subaru Telescope limits on cosmological variations in the fine-structure constant

Abstract: Previous, large samples of quasar absorption spectra have indicated some evidence for relative variations in the fine-structure constant ($\Delta\alpha/\alpha$) across the sky. However, they were likely affected by long-range distortions of the wavelength calibration, so it is important to establish a statistical sample of more reliable results, from multiple telescopes. Here we triple the sample of $\Delta\alpha/\alpha$ measurements from the Subaru Telescope which have been `supercalibrated' to correct for long-range distortions. A blinded analysis of the metallic ions in 6 intervening absorption systems in two Subaru quasar spectra provides no evidence for $\alpha$ variation, with a weighted mean of $\Delta\alpha/\alpha=3.0\pm2.8_{\rm stat}\pm2.0_{\rm sys}$ parts per million (1$\sigma$ statistical and systematic uncertainties). The main remaining systematic effects are uncertainties in the long-range distortion corrections, absorption profile models, and errors from redispersing multiple quasar exposures onto a common wavelength grid. The results also assume that terrestrial isotopic abundances prevail in the absorbers; assuming only the dominant terrestrial isotope is present significantly lowers $\Delta\alpha/\alpha$, though it is still consistent with zero. Given the location of the two quasars on the sky, our results do not support the evidence for spatial $\alpha$ variation, especially when combined with the 21 other recent measurements which were corrected for, or resistant to, long-range distortions. Our spectra and absorption profile fits are publicly available.

First-principles study of the luminescence of Eu 2 + -doped phosphors

Abstract: The luminescence of fifteen representative ${\mathrm{Eu}}^{2+}$-doped phosphors used for white-LED and scintillation applications is studied through a constrained density functional theory. Transition energies and Stokes shift are deduced from differences of total energies between the ground and excited states of the systems, in the absorption and emission geometries. The general applicability of such methodology is first assessed: for this representative set, the calculated absolute error with respect to experiment on absorption and emission energies is within 0.3 eV. This set of compounds covers a wide range of transition energies that extents from 1.7 to 3.5 eV. The information gained from the relaxed geometries and total energies is further used to evaluate the thermal barrier for the $4f\text{\ensuremath{-}}5d$ crossover, the full width at half maximum of the emission spectrum and the temperature shift of the emission peak, using a one-dimensional configuration-coordinate model. The former results indicate that the $4f\text{\ensuremath{-}}5d$ crossover cannot be the dominant mechanism for the thermal quenching behavior of ${\mathrm{Eu}}^{2+}$-doped phosphors and the latter results are compared to available experimental data and yield a $30%$ mean absolute relative error. Finally, a semiempirical model used previously for ${\mathrm{Ce}}^{3+}$-doped hosts is adapted to ${\mathrm{Eu}}^{2+}$-doped hosts and gives the absorption and emission energies within 0.9 eV of experiment, underperforming compared to the first-principles calculation.

Addressing electron-hole correlation in core excitations of solids: An all-electron many-body approach from first principles

Abstract: We present an ab initio study of core excitations of solid-state materials focusing on the role of electron-hole correlation. In the framework of an all-electron implementation of many-body perturbation theory into the $\mathtt{exciting}$ code, we investigate three different absorption edges of three materials, spanning a broad energy window, with transition energies between a few hundred to thousands of eV. Specifically, we consider excitations from the Ti $K$ edge in rutile and anatase ${\mathrm{TiO}}_{2}$, from the Pb ${M}_{4}$ edge in ${\mathrm{PbI}}_{2}$, and from the Ca ${L}_{2,3}$ edge in CaO. We show that the electron-hole attraction rules x-ray absorption for deep core states when local fields play a minor role. On the other hand, the local-field effects introduced by the exchange interaction between the excited electron and the hole dominate excitation processes from shallower core levels, separated by a spin-orbit splitting of a few eV. Our approach yields absorption spectra in good agreement with available experimental data and allows for an in-depth analysis of the results, revealing the electronic contributions to the excitations, as well as their spatial distribution.

Convex hulls of random walks, hyperplane arrangements, and Weyl chambers

Abstract: We give an explicit formula for the probability that the convex hull of an n-step random walk in $${\mathbb{R}^d}$$ does not contain the origin, under the assumption that the distribution of increments of the walk is centrally symmetric and puts no mass on affine hyperplanes. This extends the formula by Sparre Andersen (Skand Aktuarietidskr 32:27–36, 1949) for the probability that such random walk in dimension one stays positive. Our result is distribution-free, that is, the probability does not depend on the distribution of increments. This probabilistic problem is shown to be equivalent to either of the two geometric ones: (1) Find the number of Weyl chambers of type B n intersected by a generic linear subspace of $${\mathbb{R}^n}$$ of codimension d; (2) Find the conic intrinsic volumes of a Weyl chamber of type B n . We solve the first geometric problem using the theory of hyperplane arrangements. A by-product of our method is a new simple proof of the general formula by Klivans and Swartz (Discrete Comput Geom 46(3):417–426, 2011) relating the coefficients of the characteristic polynomial of a linear hyperplane arrangement to the conic intrinsic volumes of the chambers constituting its complement. We obtain analogous distribution-free results for Weyl chambers of type $${A_{n-1}}$$ (yielding the probability of absorption of the origin by the convex hull of a generic random walk bridge), type D n , and direct products of Weyl chambers (yielding the absorption probability for the joint convex hull of several random walks or bridges). The simplest case of products of the form $${B_1\times \cdots \times B_1}$$ recovers the Wendel formula (Math Scand 11:109–111, 1962) for the probability that the convex hull of an i.i.d. multidimensional sample chosen from a centrally symmetric distribution does not contain the origin. We also give an asymptotic analysis of the obtained absorption probabilities as $${n \to \infty}$$ , in both cases of fixed and increasing dimension d.

Nonperturbative quasiclassical theory of the nonlinear electrodynamic response of graphene

Abstract: An electromagnetic response of a single graphene layer to a uniform, arbitrarily strong electric field $\mathbit{E}(t)$ is calculated by solving the kinetic Boltzmann equation within the relaxation-time approximation. The theory is valid at low (microwave, terahertz, infrared) frequencies satisfying the condition $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\lesssim}2{E}_{F}$, where ${E}_{F}$ is the Fermi energy. We investigate the saturable absorption and higher harmonics generation effects, as well as the transmission, reflection, and absorption of radiation incident on the graphene layer, as a function of the frequency and power of the incident radiation and of the ratio of the radiative to scattering damping rates. We show that the optical bistability effect, predicted in Phys. Rev. B 90, 125425 (2014) on the basis of a perturbative approach, disappears when the problem is solved exactly. We show that under the action of a high-power radiation $(\ensuremath{\gtrsim}100\phantom{\rule{4pt}{0ex}}\mathrm{kW}/{\mathrm{cm}}^{2})$ both the reflection and absorption coefficients strongly decrease and the layer becomes transparent.

Cosmological constant, fine structure constant and beyond

Abstract: In the present work, we consider the cosmological constant model $$\Lambda \propto \alpha ^{-6}$$ , which is well motivated from three independent approaches. As is well known, the hint of varying fine structure constant $$\alpha $$ was found in 1998. If $$\Lambda \propto \alpha ^{-6}$$ is right, it means that the cosmological constant $$\Lambda $$ should also be varying. Here, we try to develop a suitable framework to model this varying cosmological constant $$\Lambda \propto \alpha ^{-6}$$ , in which we view it from an interacting vacuum energy perspective. Then we consider the observational constraints on these models by using the 293 $$\Delta \alpha /\alpha $$ data from the absorption systems in the spectra of distant quasars. We find that the model parameters can be tightly constrained to the very narrow ranges of $$\mathcal{O}(10^{-5})$$ typically. On the other hand, we can also view the varying cosmological constant model $$\Lambda \propto \alpha ^{-6}$$ from another perspective, namely it can be equivalent to a model containing “dark energy” and “warm dark matter”, but there is no interaction between them. We find that this is also fully consistent with the observational constraints on warm dark matter.

C60+ and the Diffuse Interstellar Bands: An Independent Laboratory Check

Abstract: In 2015, Campbell et al. presented spectroscopic laboratory gas phase data for the fullerene cation, ${{{\rm{C}}}_{60}}^{+}$, that coincide with the reported astronomical spectra of two diffuse interstellar band (DIB) features at 9633 and 9578 A. In the following year, additional laboratory spectra were linked to three other and weaker DIBs at 9428, 9366, and 9349 A. The laboratory data were obtained using wavelength-dependent photodissociation spectroscopy of small (up to three) He-tagged ${{{\rm{C}}}_{60}}^{+}\mbox{--}{\mathrm{He}}_{n}$ ion complexes, yielding rest wavelengths for the bare ${{{\rm{C}}}_{60}}^{+}$ cation by correcting for the He-induced wavelength shifts. Here we present an alternative approach to derive the rest wavelengths of the four most prominent ${{{\rm{C}}}_{60}}^{+}$ absorption features, using high-resolution laser dissociation spectroscopy of ${{{\rm{C}}}_{60}}^{+}$ embedded in ultracold He droplets. Accurate wavelengths of the bare fullerene cation are derived from linear wavelength shifts recorded for ${\mathrm{He}}_{n}$ ${{{\rm{C}}}_{60}}^{+}$ species with n up to 32. A careful analysis of all of the available data results in precise rest wavelengths (in air) for the four most prominent ${{{\rm{C}}}_{60}}^{+}$ bands: 9631.9(1) A, 9576.7(1) A, 9427.5(1) A, and 9364.9(1) A. The corresponding bandwidths have been derived and the relative band intensity ratios are discussed.

$\eta$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity

Abstract: Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable $\eta$ Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the Great Eruption. We present the 2.4 - 670 $\mu$m spectral energy distribution, constructed from legacy ISO observations and new spectroscopy obtained with the {\em{Herschel Space Observatory}}. Using radiative transfer modeling, we find that the two best-fit dust models yield compositions which are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2 $\mu$m feature. Our preferred model contains nitrides AlN and Si$_3$N$_4$ in low abundances. Dust masses range from 0.25 to 0.44 $M_\odot$ but $M_{\rm{tot}} \ge$ 45 $M_\odot$ in both cases due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5$"$ $\times$ 7$"$ central region. An additional compact feature is detected at 390 $\mu$m. We obtain $L_{\rm{IR}}$ = 2.96 $\times$ 10$^6$ $L_\odot$, a 25\% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25-40\% of optical and UV radiation to escape from the central source. We also present an analysis of $^{12}$CO and $^{13}$CO $J = 5-4$ through $9-8$ lines, showing that the abundances are consistent with expectations for CNO-processed material. The [$^{12}$C~{\sc{ii}}] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures.

Planar Wideband Differential-Mode Bandpass Filter With Common-Mode Noise Absorption

Abstract: In this letter, a planar differential-mode (DM) four-port circuit is proposed to design a balanced-to-balanced bandpass filter (BPF) with common-mode noise absorption add-on feature. By using the matrix transformation between the mixed and the single-ended scattering parameters, even- (odd-) mode equivalent circuit and the closed-form solutions of the proposed circuit structure are obtained based on the constraint rules. Finally, a microstrip DM BPF is designed and fabricated. The measured (simulated) results show that the relative bandwidth is 55.5% (57.5%) under the conditions of $\vert S_{\mathbf {ddBA}}\vert > -1$ dB and $\vert S_{\mathbf {ddAA}}\vert $ , $\vert S_{\mathbf {ccAA}}\vert $ , and $\vert S_{\mathbf {ccBA}}\vert dB. Good agreements between the simulated and measured results verify the correctness of the design theory.

Analysis of the intermediate-band absorption properties of type-II GaSb/GaAs quantum-dot photovoltaics

Abstract: Quantum-dot (QD) intermediate-band (IB) materials are regarded as promising candidates for high-efficiency photovoltaics. The sequential two-step two-photon absorption processes that take place in these materials have been proposed to develop high-efficiency solar cells and infrared (IR) photodetectors. In this work, we experimentally and theoretically study the interrelation of the absorptivity with transitions of carriers to and from the IB in type-II GaSb/GaAs QD devices. Our devices exhibit three optical band gaps with: ${E}_{\mathrm{L}}=0.49\phantom{\rule{0.16em}{0ex}}\mathrm{eV},{E}_{\mathrm{H}}=1.02\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, and ${E}_{\mathrm{G}}=1.52\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, with the IB located 0.49 eV above the valence band. These values are well supported by semiempirical calculations of the QDs electronic structure. Through intensity-dependent two-photon photocurrent experiments, we are able to vary the filling state of the IB, thus modifying the absorptivity of the transitions to and from this band. By filling the IB with holes via $E=1.32\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ or $E=1.93\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ monochromatic illumination, we demonstrate an increase in the ${E}_{\mathrm{L}}$-related absorptivity of more than two orders of magnitude and a decrease in the ${E}_{\mathrm{H}}$-related absorptivity of one order of magnitude. The antisymmetrical evolution of those absorptivities is quantitatively explained by a photoinduced shift of the quasi-Fermi level of the IB. Furthermore, we report the observation of a two-photon photovoltage, i.e., the contribution of subband gap two-photon absorption to increase the open-circuit voltage of solar cells. We find that the generation of the two-photon photovoltage is related, in general, to the production of a two-photon photocurrent. However, while photons with energy close to ${E}_{\mathrm{L}}$ participate in the production of the two-photon photocurrent, they are not effective in the production of a two-photon photovoltage. We also report the responsivity of GaSb/GaAs QD devices performing as optically triggered photodetectors. These devices exhibit an amplification factor of almost 400 in the IR spectral region. This high value is achieved by minimizing---via doping---the absorptivity in the IR range of the QDs under equilibrium conditions.

Spin-orbit coupling, optical transitions, and spin pumping in monolayer and few-layer InSe

Abstract: We show that spin-orbit coupling (SOC) in InSe enables the optical transition across the principal band gap to couple with in-plane polarized light. This transition, enabled by ${p}_{x,y}\ensuremath{\leftrightarrow}{p}_{z}$ hybridization due to intra-atomic SOC in both In and Se, can be viewed as a transition between two dominantly $s$- and ${p}_{z}$-orbital based bands, accompanied by an electron spin-flip. Having parametrized $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory using first-principles density functional theory we estimate the absorption for ${\ensuremath{\sigma}}^{\ifmmode\pm\else\textpm\fi{}}$ circularly polarized photons in the monolayer as $\ensuremath{\sim}1.5$%, which saturates to $\ensuremath{\sim}0.3$% in thicker films (3--5 layers). Circularly polarized light can be used to selectively excite electrons into spin-polarized states in the conduction band, which permits optical pumping of the spin polarization of In nuclei through the hyperfine interaction.

ipole - semianalytic scheme for relativistic polarized radiative transport

Abstract: We describe ${\tt ipole}$, a new public ray-tracing code for covariant, polarized radiative transport. The code extends the ${\tt ibothros}$ scheme for covariant, unpolarized transport using two representations of the polarized radiation field: in the coordinate frame, it parallel transports the coherency tensor; in the frame of the plasma it evolves the Stokes parameters under emission, absorption, and Faraday conversion. The transport step is implemented to be as spacetime- and coordinate- independent as possible. The emission, absorption, and Faraday conversion step is implemented using an analytic solution to the polarized transport equation with constant coefficients. As a result, ${\tt ipole}$ is stable, efficient, and produces a physically reasonable solution even for a step with high optical depth and Faraday depth. We show that the code matches analytic results in flat space, and that it produces results that converge to those produced by Dexter's ${\tt grtrans}$ polarized transport code on a complicated model problem. We expect ${\tt ipole}$ will mainly find applications in modeling Event Horizon Telescope sources, but it may also be useful in other relativistic transport problems such as modeling for the IXPE mission.

Control of photoemission delay in resonant two-photon transitions

Abstract: The photoelectron emission time delay $\ensuremath{\tau}$ associated with one-photon absorption, which coincides with half the Wigner delay ${\ensuremath{\tau}}_{\mathrm{W}}$ experienced by an electron scattered off the ionic potential, is a fundamental descriptor of the photoelectric effect. Although it is hard to access directly from experiment, it is possible to infer it from the time delay of two-photon transitions, ${\ensuremath{\tau}}^{(2)}$, measured with attosecond pump-probe schemes, provided that the contribution of the probe stage can be factored out. In the absence of resonances, $\ensuremath{\tau}$ can be expressed as the energy derivative of the one-photon ionization amplitude phase, $\ensuremath{\tau}={\ensuremath{\partial}}_{E}arg{D}_{Eg}$, and, to a good approximation, $\ensuremath{\tau}={\ensuremath{\tau}}^{(2)}\ensuremath{-}{\ensuremath{\tau}}_{\mathrm{cc}}$, where ${\ensuremath{\tau}}_{\mathrm{cc}}$ is associated with the dipole transition between Coulomb functions. Here we show that, in the presence of a resonance, the correspondence between $\ensuremath{\tau}$ and ${\ensuremath{\partial}}_{E}arg{D}_{Eg}$ is lost. Furthermore, while ${\ensuremath{\tau}}^{(2)}$ can still be written as the energy derivative of the two-photon ionization amplitude phase, ${\ensuremath{\partial}}_{E}arg{D}_{Eg}^{(2)}$, it does not have any scattering counterpart. Indeed, ${\ensuremath{\tau}}^{(2)}$ can be much larger than the lifetime of an intermediate resonance in the two-photon process or more negative than the lower bound imposed on scattering delays by causality. Finally, we show that ${\ensuremath{\tau}}^{(2)}$ is controlled by the frequency of the probe pulse, ${\ensuremath{\omega}}_{\mathrm{IR}}$, so that by varying ${\ensuremath{\omega}}_{\mathrm{IR}}$, it is possible to radically alter the photoelectron group delay.

K - nuclear states: Binding energies and widths

Abstract: ${K}^{\ensuremath{-}}$ optical potentials relevant to calculations of ${K}^{\ensuremath{-}}$ nuclear quasibound states were developed within several chiral meson-baryon coupled-channels interaction models. The applied models yield quite different ${K}^{\ensuremath{-}}$ binding energies and widths. Then the ${K}^{\ensuremath{-}}$ multinucleon interactions were incorporated by a phenomenological optical potential fitted recently to kaonic atom data. Though the applied ${K}^{\ensuremath{-}}$ interaction models differ significantly in the ${K}^{\ensuremath{-}}N$ subthreshold region, our self-consistent calculations of kaonic nuclei across the periodic table lead to conclusions valid quite generally. Due to ${K}^{\ensuremath{-}}$ multinucleon absorption in the nuclear medium, the calculated widths of ${K}^{\ensuremath{-}}$ nuclear states are sizable, ${\mathrm{\ensuremath{\Gamma}}}_{{K}^{\ensuremath{-}}}\ensuremath{\ge}90$ MeV, and exceed substantially their binding energies in all considered nuclei.