Constraining the binarity of black hole candidates: a proof-of-concept study of Gaia BH1 and Gaia BH2

Nearly a hundred of binary black holes (BBHs) have been discovered with gravitational-wave signals emitted at their merging events. Thus, it is quite natural to expect that significantly more abundant BBHs with wider separations remain undetected in the universe, or even in our Galaxy. We consider a possibility that star-BH binary candidates may indeed host an inner BBH, instead of a single BH. We present a detailed feasibility study of constraining the binarity of the currently available two targets, Gaia BH1 and Gaia BH2. Specifically, we examine three types of radial velocity (RV) modulations of a tertiary star in star-BBH triple systems; short-term RV modulations induced by the inner BBH, long-term RV modulations induced by the nodal precession, and long-term RV modulations induced by the von Zeipel-Kozai-Lidov oscillations. Direct three-body simulations combined with approximate analytic models reveal that Gaia BH1 system may exhibit observable signatures of the hidden inner BBH if it exists at all. The methodology that we examine here is quite generic, and is expected to be readily applicable to future star-BH binary candidates in a straightforward manner.Comment: 19 pages, 10 figures, 1 table, submitted to Ap

Regeneration of Retinotectal Projections After Optic Tectum Removal in Adult Newts

Purpose: When injured, the adult newt possesses the remarkable capability to regenerate tissues and organs with return of function and physiology. One example is the newt eye, in which regeneration can restore normal vision if the retina or lens has been removed. We wanted to examine how the retinotectal projections regenerate after removal of the brain’s optic tectum and establish this animal as a model for retinal projection as well as a central nervous system regeneration model

Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET

We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in the Galactic ridge environment. The calculation includes the diffractive pp interaction and incorporates the Feynman scaling violation for the first time. Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the prediction based on experimental pp->pi^0 cross-sections and the Feynman scaling hypothesis. We show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in power-law index, and, that the scaling violation produces 30-80% more pi^0 than the scaling model for incident proton energies above 100GeV. Combination of the two can explain about a half of the "GeV Excess" with the local cosmic proton (power-law index ~2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder (~0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e^+ over e^- and the scaling violation gives 50-100% higher p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa

Use of imaging plates at near saturation for high energy density particles

Copyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 79(10), 10E910, 2008 and may be found at http://dx.doi.org/10.1063/1.298767

Evolution of superconductivity in isovalent Te-substituted KxFe2-ySe2 crystals

We report the evolution of superconductivity and the phase diagram of the KxFe2-ySe2-zTez (z=0-0.6) crystals grown by a simple one-step synthesis. No structural transition is observed in any crystals, while lattice parameters exhibit a systematic expansion with Te content. The Tc exhibits a gradual decrease with increasing Te content from Tconset = 32.9 K at z = 0 to Tconset = 27.9 K at z = 0.5, followed by a sudden suppression of superconductivity at z = 0.6. Upon approaching a Te concentration of 0.6, the shielding volume fraction decreases and eventually drops to zero. Simultaneously, hump positions in r-T curve shift to lower temperatures. These results suggest that isovalent substitution of Te for Se in KxFe2-ySe2 crystals suppresses the superconductivity in this system.Comment: 10 pages, 1 table, 8 figure

Calibration of imaging plate for high energy electron spectrometer

Copyright 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 76(1), 013507_1-013507_5, 2005 and may be found at http://dx.doi.org/10.1063/1.182437

Large-Eddy / Reynolds-Averaged Navier-Stokes Simulations of a Dual-Mode Scramjet Combustor

Numerical simulations of reacting and non-reacting flows within a scramjet combustor configuration experimentally mapped at the University of Virginia s Scramjet Combustion Facility (operating with Configuration A ) are described in this paper. Reynolds-Averaged Navier-Stokes (RANS) and hybrid Large Eddy Simulation / Reynolds-Averaged Navier-Stokes (LES / RANS) methods are utilized, with the intent of comparing essentially blind predictions with results from non-intrusive flow-field measurement methods including coherent anti-Stokes Raman spectroscopy (CARS), hydroxyl radical planar laser-induced fluorescence (OH-PLIF), stereoscopic particle image velocimetry (SPIV), wavelength modulation spectroscopy (WMS), and focusing Schlieren. NC State's REACTMB solver was used both for RANS and LES / RANS, along with a 9-species, 19- reaction H2-air kinetics mechanism by Jachimowski. Inviscid fluxes were evaluated using Edwards LDFSS flux-splitting scheme, and the Menter BSL turbulence model was utilized in both full-domain RANS simulations and as the unsteady RANS portion of the LES / RANS closure. Simulations were executed and compared with experiment at two equivalence ratios, PHI = 0.17 and PHI = 0.34. Results show that the PHI = 0.17 flame is hotter near the injector while the PHI = 0.34 flame is displaced further downstream in the combustor, though it is still anchored to the injector. Reactant mixing was predicted to be much better at the lower equivalence ratio. The LES / RANS model appears to predict lower overall heat release compared to RANS (at least for PHI = 0.17), and its capability to capture the direct effects of larger turbulent eddies leads to much better predictions of reactant mixing and combustion in the flame stabilization region downstream of the fuel injector. Numerical results from the LES/RANS model also show very good agreement with OH-PLIF and SPIV measurements. An un-damped long-wave oscillation of the pre-combustion shock train, which caused convergence problems in some RANS simulations, was also captured in LES / RANS simulations, which were able to accommodate its effects accurately

Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered

Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime “workhorse” aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr–CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νN≡C, νC≡O, kC≡O} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kC≡O,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3

Bmi1 facilitates primitive endoderm formation by stabilizing Gata6 during early mouse development

International audienceThe transcription factors Nanog and Gata6 are critical to specify the epiblast versus primitive endoderm (PrE) lineages. However, little is known about the mechanisms that regulate the protein stability and activity of these factors in the developing embryo. Here we uncover an early developmental function for the Polycomb group member Bmi1 in supporting PrE lineage formation through Gata6 protein stabilization. We show that Bmi1 is enriched in the extraembryonic (endoderm [XEN] and trophectodermal stem [TS]) compartment and repressed by Nanog in pluripotent embryonic stem (ES) cells. In vivo, Bmi1 overlaps with the nascent Gata6 and Nanog protein from the eight-cell stage onward before it preferentially cosegregates with Gata6 in PrE progenitors. Mechanistically, we demonstrate that Bmi1 interacts with Gata6 in a Ring finger-dependent manner to confer protection against Gata6 ubiquitination and proteasomal degradation. A direct role for Bmi1 in cell fate allocation is established by loss-of-function experiments in chimeric embryoid bodies. We thus propose a novel regulatory pathway by which Bmi1 action on Gata6 stability could alter the balance between Gata6 and Nanog protein levels to introduce a bias toward a PrE identity in a cell-autonomous manner

Femtosecond X-ray emission study of the spin cross-over dynamics in haem proteins

In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from the haem by photodissociation, while its recombination was monitored using time-resolved infrared to ultraviolet spectroscopic tools. However, these are neither element- nor spin-sensitive. Here we investigate the transition state in the case of Myoglobin-NO (MbNO) using femtosecond Fe Kalpha and Kbeta non-resonant X-ray emission spectroscopy (XES) at an X-ray free-electron laser upon photolysis of the Fe-NO bond. We find that the photoinduced change from the LS (S = 1/2) MbNO to the HS (S = 2) deoxy-myoglobin (deoxyMb) haem occurs in ca. 800 fs, and that it proceeds via an intermediate (S = 1) spin state. The XES observables also show that upon NO recombination to deoxyMb, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in ca. 30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process