An Edge-specific Scheme For Equation-of-motion Coupled-cluster Calculations Of X-ray Absorption Spectra

We present an edge-specific scheme for calculating near edge x-ray absorption fine structure (NEXAFS) spectra using core-valence separated equation-of-motion coupled-cluster (CVS-EOM-CC) theory. [1,2] Standard correlation-consistent basis set for the atom where targeted core excitation takes place is systematically augmented with diffuse s-, p-, and d-type functions to accurately describe Rydberg-type core excitations with diffuse character. It is also shown that triple excitations in CVS-EOM-CC methods not only are important for obtaining accurate absolute values of core excitation energies, but also make significant contributions to relative shifts between local and Rydberg core excitations. Quadruples excitations are shown to be relevant when aiming at high-accuracy calculations of absolute values.\\ \Large{\textbf{Reference}}\\ \small [1] L. S. Cederbaum, W. Domcke, J. Schirmer, and W. von Niessen, Phys. Scripta 21, 481 (1980). [2] S. Coriani, and H. Koch, J. Chem. Phys. 143, 181103 (2015)

DELTA-COUPLED-CLUSTER METHODS FOR ACCURATE CALCULATIONS OF CORE IONIZATION ENERGIES

While scalar-relativistic core-valence separated equation-of-motion coupled-cluster [1] methods can provide quantitative description of core ionization energies [2,3], the necessity of including higher excitations (full triples and quadruples) limits the applicability to small molecules. Here we explore the use of delta-coupled-cluster ($\Delta$CC) methods as an efficient alternative that is applicable to larger molecules. The $\Delta$CC methods perform CC calculations separately for the neutral and core ionized states and thus fully account for the orbital relaxation induced by the core hole in the core ionized state. The convergence difficulty in $\Delta$CC equations [4] is solved by adapting the generic idea of core-valence separation (CVS) [5] to $\Delta$CC. In benchmark calculations of chemical shifts for the core ionization energies for second-row elements, $\Delta$CCSD(T) is shown to be as accurate as EOM-CCSDTQ, which is by far a more expensive method. It is also shown that the errors introduced by CVS within $\Delta$CC for the absolute values of core ionization energies is around 0.5 eV and should be taken care of when aming at high-accuracy calculations of the absolute values. \begin{thebibliography}{comment} \bibitem{Sonia2015} S. Coriani, and H. Koch, J. Chem. Phys. \textbf{143}, 181103 (2015). \bibitem{Lan2018} R. H. Myhre, T. J. A. Wolf, L. Cheng, S. Nandi, S. Coriani, M. G{\"u}hr and H. Koch, J. Chem. Phys. \textbf{148}, 064106 (2018). \bibitem{LiuCVS} J. Liu, D. Matthews, S. Coriani, and L. Cheng, J. Chem. Theory Comp. (2019). DOI:10.1021/acs.jctc.8b01160. \bibitem{DCCbesley} N. A. Besley, Chem. Phys. Lett. \textbf{542}, 42 (2012). \bibitem{CVS} L. S. Cederbaum, W. Domcke, J. Schirmer, and W. von Niessen, Phys. Scripta \textbf{21}, 481 (1980). \end{thebibliography

MaNGA integral-field stellar kinematics of LoTSS radio galaxies: Luminous radio galaxies tend to be slow rotators

The radio jets of an active galactic nucleus (AGN) can heat up the gas around a host galaxy and quench star formation activity. The presence of a radio jet could be related to the evolutionary path of the host galaxy and may be imprinted in the morphology and kinematics of the galaxy. In this work, we use data from the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory survey and the Low Frequency Array (LOFAR) Two-Metre Sky Survey as well as the National Radio Astronomy Observatory (NRAO) the Karl G. Jansky Very Large Array (VLA) Sky Survey and the Faint Images of the Radio Sky at Twenty Centimeter survey. We combine these integral field spectroscopic data and radio data to study the link between stellar kinematics and radio AGNs. We find that the luminosity-weighted stellar angular momentum $\lambda_{Re}$ is tightly related to the range of radio luminosity and the fraction of radio AGNs F radio present in galaxies, as high-luminosity radio AGNs are only in galaxies with a small $\lambda_{Re}$, and the $F_{radio}$ at a fixed stellar mass decreases with $\lambda_{Re}$. These results indicate that galaxies with stronger random stellar motions with respect to the ordered motions might be better breeding grounds for powerful radio AGNs. This would also imply that the merger events of galaxies are important in the triggering of powerful radio jets in our sample.Comment: 10 pages,7 figures. Accepted in A&

Can softer junctions lead to stiffer gels? Understanding the role of stereochemistry in associative polymer gels

The ability to create synthetic materials that mimic the structural and mechanical properties of soft biological tissues remains a significant challenge. In this presentation, we focus on creating stiff hydrogels and novel nanoscale and microscale structure by engineering crystalline domains into associative hydrogels of poly(lactic acid)-poly(ethylene oxide)-poly(lactic acid) (PLA-PEO-PLA) triblock copolymers. In aqueous media, these materials form associative gels of micelles with PLA cores that serve as network junctions. We extend previous studies from our group and others by varying the stereochemistry of the PLA block to create polymers with PLA blocks with ratios of L/D lactide units varying from 100/0 to 50/50. We had previously found that the 100/0 systems (triblocks with poly(L-lactide) blocks) formed gels with nanoscale crystalline domains, and these gels displayed a high value of the elastic modulus which was strongly dependent on PLA block length. Interestingly, our most recent results show that the storage modulus of these gels does not vary monotonically with L/D ratio. Rather, systems at intermediate L/D values are stiffer than the 100/0 systems, displaying higher storage moduli in spite of the fact that the PLA domains are expected to have a lower degree of crystallinity than in the 100/0 systems. Small-angle neutron scattering (SANS) results also indicate that the strongest interactions between micelles occurs for systems with intermediate L/D ratios, and ultra-small angle neutron scattering (USANS) shows evidence of larger structures in these gels, reminiscent of the hierarchical structures observed in biological gels. Collectively, our work shows that stereochemistry can be used in unexpected ways to access novel structures and properties in relatively simple synthetic polymers, giving insight into new routes for creating complex soft materials

Softer Junctions Can Result In Stiffer Gels: Associative Polymer Gels With Crystalline And Semicrystalline Domains

The ability to create synthetic materials that mimic the structural and mechanical properties of soft biological tissues remains a significant challenge. In this presentation, we discuss rheology and structural studies of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer gels with various ratios of L-lactide and D-lactide in the PLA blocks (Figure 1). These materials form associative micellar gels in water, and previous work has shown that stereoregular triblocks with a L/D ratio of 100/0 form much stiffer gels than triblocks with a 50/50 L/D ratio. Our systems display an unexpected maximum in the storage modulus, G’, of the hydrogels at intermediate L/D ratio. The impact of stereochemistry on the rheology is very striking; gels with an L/D ratio of 85/15 have storage moduli that are ~1-2 orders of magnitude higher than hydrogels with L/D ratios of 100/0. No stereocomplexation is observed in the gels, although PLLA crystals are found for gels with L/D ratios of 95/5 and 90/10, and SANS results show a decrease in the intermicellar spacing for intermediate L/D ratios. We expect the dominant contribution to the elasticity of the gels to be intermicellar brdging chains and attribute the rheology to a competition between an increase in the time for PLA endblocks to pull out of micelles as the L/D ratio is increased and PLLA crystallization occurs, and a decrease in the number of bridging chains for micelles with crystalline PLA domains, as formation of bridges may be hindered by crowded crystalline PLA domains. Ultra-small angle neutron scattering (USANS) and confocal microscopy shows evidence of larger structures in these gels, reminiscent of the hierarchical structures observed in biological gels. These results provide a new strategy for controlling the rheology of PLA-based hydrogels for potential applications in biomaterials, as well as fundamental insights into how intermicellar interactions can be tuned via stereochemistry. Collectively, our work shows that stereochemistry can be used in unexpected ways to access novel structures and properties in relatively simple synthetic polymers, giving insight into new routes for creating complex soft materials. Please click Additional Files below to see the full abstract

Piercing Through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields: I. X-ray Spectral and Long-term Variability Analyses

We present a detailed X-ray spectral analysis of 1152 AGNs selected in the Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs ($N_{\rm H} > 10^{23}\ \rm cm^{-2}$). By fitting spectra with physical models, 436 (38%) sources with $L_{\rm X} > 10^{42}\ \rm erg\ s^{-1}$ are confirmed to be highly obscured, including 102 Compton-thick (CT) candidates. We propose a new hardness-ratio measure of the obscuration level which can be used to select highly obscured AGN candidates. The completeness and accuracy of applying this method to our AGNs are 88% and 80%, respectively. The observed logN-logS relation favors cosmic X-ray background models that predict moderate (i.e., between optimistic and pessimistic) CT number counts. 19% (6/31) of our highly obscured AGNs that have optical classifications are labeled as broad-line AGNs, suggesting that, at least for part of the AGN population, the heavy X-ray obscuration is largely a line-of-sight effect, i.e., some high-column-density clouds on various scales (but not necessarily a dust-enshrouded torus) along our sightline may obscure the compact X-ray emitter. After correcting for several observational biases, we obtain the intrinsic NH distribution and its evolution. The CT-to-highly-obscured fraction is roughly 52% and is consistent with no evident redshift evolution. We also perform long-term (~17 years in the observed frame) variability analyses for 31 sources with the largest number of counts available. Among them, 17 sources show flux variabilities: 31% (5/17) are caused by the change of NH, 53% (9/17) are caused by the intrinsic luminosity variability, 6% (1/17) are driven by both effects, and 2 are not classified due to large spectral fitting errors.Comment: 32 pages, 21 figures, 9 tables, accepted for publication in Ap

UIAI System for Short-Duration Speaker Verification Challenge 2020

International audienceIn this work, we present the system description of the UIAI entry for the short-duration speaker verification (SdSV) challenge 2020. Our focus is on Task 1 dedicated to text-dependent speaker verification. We investigate different feature extraction and modeling approaches for automatic speaker verification (ASV) and utterance verification (UV). We have also studied different fusion strategies for combining UV and ASV modules. Our primary submission to the challenge is the fusion of seven subsystems which yields a normalized minimum detection cost function (minDCF) of 0.072 and an equal error rate (EER) of 2.14% on the evaluation set. The single system consisting of a pass-phrase identification based model with phone-discriminative bottleneck features gives a normalized minDCF of 0.118 and achieves 19% relative improvement over the state-of-the-art challenge baseline

X-ray induced electron and ion fragmentation dynamics in IBr

Characterization of the inner-shell decay processes in molecules containing heavy elements is key to understanding x-ray damage of molecules and materials and for medical applications with Auger-electron-emitting radionuclides. The 1s hole states of heavy atoms can be produced by absorption of tunable x-rays and the resulting vacancy decays characterized by recording emitted photons, electrons, and ions. The 1s hole states in heavy elements have large x-ray fluorescence yields that transfer the hole to intermediate electron shells that then decay by sequential Auger-electron transitions that increase the ion's charge state until the final state is reached. In molecules the charge is spread across the atomic sites, resulting in dissociation to energetic atomic ions. We have used x-ray/ion coincidence spectroscopy to measure charge states and energies of I$^{q+}$ and Br$^{q'+}$ atomic ions following 1s ionization at the I and Br \textit{K}-edges of IBr. We present the charge states and kinetic energies of the two correlated fragment ions associated with core-excited states produced during the various steps of the cascades. To understand the dynamics leading to the ion data, we develop a computational model that combines Monte-Carlo/Molecular Dynamics simulations with a classical over-the-barrier model to track inner-shell cascades and redistribution of electrons in valence orbitals and nuclear motion of fragments

Piercing through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields. II. Are Highly Obscured AGNs the Missing Link in the Merger-Triggered AGN-Galaxy Coevolution Models?

By using a large highly obscured ($N_{\rm H} > 10^{23}\ \rm cm^{-2}$) AGN sample (294 sources at $z \sim 0-5$) selected from detailed X-ray spectral analyses in the deepest Chandra surveys, we explore distributions of these X-ray sources in various optical/IR/X-ray color-color diagrams and their host-galaxy properties, aiming at characterizing the nuclear obscuration environment and the triggering mechanism of highly obscured AGNs. We find that the refined IRAC color-color diagram fails to identify the majority of X-ray selected highly obscured AGNs, even for the most luminous sources with ${\rm log}\,L_{\rm X}\, \rm (erg\ s^{-1}) > 44$. Over 80% of our sources will not be selected as heavily obscured candidates using the flux ratio of $f_{\rm 24 \mu m}\, /\,f_R > 1000$ and $R - K > 4.5$ criteria, implying complex origins and conditions for the obscuring materials that are responsible for the heavy X-ray obscuration. The average star formation rate of highly obscured AGNs is similar to that of stellar mass- ($M_*$-) and $z$-controlled normal galaxies, while the lack of quiescent hosts is observed for the former. Partial correlation analyses imply that highly obscured AGN activity (traced by $L_{\rm X}$) appears to be more fundamentally related to $M_*$, and no dependence of $N_{\rm H}$ on either $M_*$ or SFR is detected. Morphology analyses reveal that 61% of our sources have a significant disk component, while only 27% of them exhibit irregular morphological signatures. These findings together point toward a scenario where secular processes (e.g., galactic-disk instabilities), instead of mergers, are most probable to be the leading mechanism that triggers accretion activities of X-ray-selected highly obscured AGNs.Comment: 23 pages, 12 figures, 3 tables, resubmitted to ApJ after addressing referee's comment

DEVELOPMENT OF RELATIVISTIC COUPLED-CLUSTER TECHNIQUES FOR X-RAY SPECTROSCOPY

The dissertation is focused on development of relativistic coupled-cluster (CC) techniques aiming to accurately calculate x-ray photoelectron and absorption spectroscopy. The hierarchy of CC methods provide a unique computational framework to ensure a systematic convergence of computed results. I have developed relativistic core-valence separated delta-coupled-cluster (CVS-$\Delta$CC) methods for calculations of core-ionization energies aiming at high accuracy. High-level relativistic (HLR) corrections beyond the spin-free exact two-component theory in its one-electron variant (SFX2C-1e), including the contributions from two-electron picture-change effects, spin-orbit coupling, the Breit term, and quantum electrodynamics effects, have been taken into account and demonstrated to play an important role in calculations of core-ionization energies for third-row elements. I have also extended the applicability of CVS equation-of-motion CC (CVS-EOM-CC) methods for calculations of x-ray absorption spectra. With systematic extension of regular basis sets to capture the diffuse character of core-excited Rydberg states, CVS-EOM-CCSD can provide accurate description for near-edge x-ray absorption fine structure (NEXAFS) spectral features of complex molecules. A first development of analytic gradients for spinor-based relativistic coupled-cluster singles and doubles augumented with noniterative triples [CCSD(T)] method using an all-electron exact two-component Hamiltonian has also been reported. This analytic gradient approach improves the efficiency of accurate calculations of properties for molecules containing heavy atoms. It has the potential to significantly impact computational heavy-element chemistry and physics, including computational x-ray spectroscopy for molecules containing heavy atoms