Simulating star clusters with the AMUSE software framework. I. Dependence of cluster lifetimes on model assumptions and cluster dissolution modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitehead, Alfred J.; McMillan, Stephen L. W.; Vesperini, Enrico

2013-12-01

We perform a series of simulations of evolving star clusters using the Astrophysical Multipurpose Software Environment (AMUSE), a new community-based multi-physics simulation package, and compare our results to existing work. These simulations model a star cluster beginning with a King model distribution and a selection of power-law initial mass functions and contain a tidal cutoff. They are evolved using collisional stellar dynamics and include mass loss due to stellar evolution. After studying and understanding that the differences between AMUSE results and results from previous studies are understood, we explored the variation in cluster lifetimes due to the random realization noisemore » introduced by transforming a King model to specific initial conditions. This random realization noise can affect the lifetime of a simulated star cluster by up to 30%. Two modes of star cluster dissolution were identified: a mass evolution curve that contains a runaway cluster dissolution with a sudden loss of mass, and a dissolution mode that does not contain this feature. We refer to these dissolution modes as 'dynamical' and 'relaxation' dominated, respectively. For Salpeter-like initial mass functions, we determined the boundary between these two modes in terms of the dynamical and relaxation timescales.« less

Galacti chemical evolution: Hygrogen through zinc

NASA Technical Reports Server (NTRS)

Timmes, F. X.; Woosley, S. E.; Weaver, Thomas A.

1995-01-01

Using the output from a grid of 60 Type II supernova models (Woosley & Weaver 1995) of varying mass (11 approx. less than (M/solar mass) approx. less than 40) and metallicity (0, 10(exp -4), 0.01, and 1 solar metallicity), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 Gyr e-folding timescale onto a exponential dsk and 1/r(exp 2) bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 approx. less than (Fe/H) approx. less than 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernova rates, an intrinsically Galactic quality, are also discussed.

NGC 1614: A Laboratory for Starburst Evolution

NASA Technical Reports Server (NTRS)

Alonso-Herrero, A.; Engelbracht, C. W.; Rieke, M. J.; Rieke, G. H.; Quillen, A. C.

2000-01-01

The modest extinction and reasonably face-on viewing geometry make the luminous infrared galaxy NGC 1614 an ideal laboratory for study of a powerful starburst. HST/NICMOS observations show: (1) deep CO stellar absorption, tracing a starburst nucleus about 45 pc in diameter; (2) surrounded by an approx. 600 pc diameter ring of supergiant H II regions revealed in Pa-alpha line emission; (3) lying within a molecular ring indicated by its extinction shadow in H - K; and (4) all at the center of a disturbed spiral galaxy. The luminosities of the giant H II regions in the ring axe extremely high, an order of magnitude brighter than 30 Doradus; very luminous H II regions, comparable with 30 Dor, are also found in the spiral arms of the galaxy. Luminous stellar clusters surround the nucleus and lie in the spiral arms, similar to clusters observed in other infrared luminous and ultraluminous galaxies. The star forming activity may have been initiated by a merger between a disk galaxy and a companion satellite, whose nucleus appears in projection about 300 pc to the NE of the nucleus of the primary galaxy. The relation of deep stellar CO bands to surrounding ionized gas ring to molecular gas indicates that the luminous starburst started in the nucleus and is propagating outward into the surrounding molecular ring. This hypothesis is supported by evolutionary starburst modeling that shows that the properties of NGC 1614 can be fitted with two short-lived bursts of star formation separated by 5 Myr (and by inference by a variety of models with a similar duration of star formation). The total dynamical mass of the starburst region of 1.3 x 10(exp 9) solar masses is mostly accounted for by the old pre-starburst stellar population. Although our starburst models use a modified Salpeter initial mass function (turning over near one solar mass), the tight mass budget suggests that the IMF may contain relatively more 10 - 30 solar masses stars and fewer low mass stars than the Salpeter function. The dynamical mass is nearly four times smaller than the mass of molecular gas estimated from the standard ratio of (C-12)O (1 - 0) to H2. A number of arguments place the mass of gas in the starburst region at approx. 25% of the dynamical mass, nominally about 1/15 and with an upper limit of 1/10 of the amount estimated from (C-12)O and the standard ratio.

Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies

NASA Astrophysics Data System (ADS)

Salimbeni, S.; Fontana, A.; Giallongo, E.; Grazian, A.; Menci, N.; Pentericci, L.; Santini, P.

2009-05-01

We discuss the uncertainties and the systematic effects that exist in the estimates of the stellar masses of high redshift galaxies, using broad band photometry, and how they affect the deduced galaxy stellar mass function. We use at this purpose the latest version of the GOODS-MUSIC catalog. In particular, we discuss the impact of different synthetic models, of the assumed initial mass function and of the selection band. Using Chariot & Bruzual 2007 and Maraston 2005 models we find masses lower than those obtained from Bruzual & Chariot 2003 models. In addition, we find a slight trend as a function of the mass itself comparing these two mass determinations with that from Bruzual & Chariot 2003 models. As consequence, the derived galaxy stellar mass functions show diverse shapes, and their slope depends on the assumed models. Despite these differences, the overall results and scenario is observed in all these cases. The masses obtained with the assumption of the Chabrier initial mass function are in average 0.24 dex lower than those from the Salpeter assumption, at all redshifts, causing a shift of galaxy stellar mass function of the same amount. Finally, using a 4.5 μm-selected sample instead of a Ks-selected one, we add a new population of highly absorbed, dusty galaxies at z~=2-3 of relatively low masses, yielding stronger constraints on the slope of the galaxy stellar mass function at lower masses.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.

Here, we investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We also perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. Furthermore, we found that the dark matter mass projected within the innermore » 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.« less

Mapping the core mass function to the initial mass function

NASA Astrophysics Data System (ADS)

Guszejnov, Dávid; Hopkins, Philip F.

2015-07-01

It has been shown that fragmentation within self-gravitating, turbulent molecular clouds (`turbulent fragmentation') can naturally explain the observed properties of protostellar cores, including the core mass function (CMF). Here, we extend recently developed analytic models for turbulent fragmentation to follow the time-dependent hierarchical fragmentation of self-gravitating cores, until they reach effectively infinite density (and form stars). We show that turbulent fragmentation robustly predicts two key features of the initial mass function (IMF). First, a high-mass power-law scaling very close to the Salpeter slope, which is a generic consequence of the scale-free nature of turbulence and self-gravity. We predict the IMF slope (-2.3) is slightly steeper than the CMF slope (-2.1), owing to the slower collapse and easier fragmentation of large cores. Secondly, a turnover mass, which is set by a combination of the CMF turnover mass (a couple solar masses, determined by the `sonic scale' of galactic turbulence, and so weakly dependent on galaxy properties), and the equation of state (EOS). A `soft' EOS with polytropic index γ < 1.0 predicts that the IMF slope becomes `shallow' below the sonic scale, but fails to produce the full turnover observed. An EOS, which becomes `stiff' at sufficiently low surface densities Σgas ˜ 5000 M⊙ pc-2, and/or models, where each collapsing core is able to heat and effectively stiffen the EOS of a modest mass (˜0.02 M⊙) of surrounding gas, are able to reproduce the observed turnover. Such features are likely a consequence of more detailed chemistry and radiative feedback.

Merger-driven evolution of the effective stellar initial mass function of massive early-type galaxies

NASA Astrophysics Data System (ADS)

Sonnenfeld, Alessandro; Nipoti, Carlo; Treu, Tommaso

2017-02-01

The stellar initial mass function (IMF) of early-type galaxies is the combination of the IMF of the stellar population formed in situ and that of accreted stellar populations. Using as an observable the effective IMF αIMF, defined as the ratio between the true stellar mass of a galaxy and the stellar mass inferred assuming a Salpeter IMF, we present a theoretical model for its evolution as a result of dry mergers. We use a simple dry-merger evolution model, based on cosmological N-body simulations, together with empirically motivated prescriptions for the IMF to make predictions on how the effective IMF of massive early-type galaxies changes from z = 2 to z = 0. We find that the IMF normalization of individual galaxies becomes lighter with time. At fixed velocity dispersion, αIMF is predicted to be constant with redshift. Current dynamical constraints on the evolution of the IMF are in slight tension with this prediction, even though systematic uncertainties, including the effect of radial gradients in the IMF, prevent a conclusive statement. The correlation of αIMF with stellar mass becomes shallower with time, while the correlation between αIMF and velocity dispersion is mostly preserved by dry mergers. We also find that dry mergers can mix the dependence of the IMF on stellar mass and velocity dispersion, making it challenging to infer, from z = 0 observations of global galactic properties, what is the quantity that is originally coupled with the IMF.

Matrix algorithms for solving (in)homogeneous bound state equations

PubMed Central

Blank, M.; Krassnigg, A.

2011-01-01

In the functional approach to quantum chromodynamics, the properties of hadronic bound states are accessible via covariant integral equations, e.g. the Bethe–Salpeter equation for mesons. In particular, one has to deal with linear, homogeneous integral equations which, in sophisticated model setups, use numerical representations of the solutions of other integral equations as part of their input. Analogously, inhomogeneous equations can be constructed to obtain off-shell information in addition to bound-state masses and other properties obtained from the covariant analogue to a wave function of the bound state. These can be solved very efficiently using well-known matrix algorithms for eigenvalues (in the homogeneous case) and the solution of linear systems (in the inhomogeneous case). We demonstrate this by solving the homogeneous and inhomogeneous Bethe–Salpeter equations and find, e.g. that for the calculation of the mass spectrum it is as efficient or even advantageous to use the inhomogeneous equation as compared to the homogeneous. This is valuable insight, in particular for the study of baryons in a three-quark setup and more involved systems. PMID:21760640

Structure preserving parallel algorithms for solving the Bethe–Salpeter eigenvalue problem

DOE PAGES

Shao, Meiyue; da Jornada, Felipe H.; Yang, Chao; ...

2015-10-02

The Bethe–Salpeter eigenvalue problem is a dense structured eigenvalue problem arising from discretized Bethe–Salpeter equation in the context of computing exciton energies and states. A computational challenge is that at least half of the eigenvalues and the associated eigenvectors are desired in practice. In this paper, we establish the equivalence between Bethe–Salpeter eigenvalue problems and real Hamiltonian eigenvalue problems. Based on theoretical analysis, structure preserving algorithms for a class of Bethe–Salpeter eigenvalue problems are proposed. We also show that for this class of problems all eigenvalues obtained from the Tamm–Dancoff approximation are overestimated. In order to solve large scale problemsmore » of practical interest, we discuss parallel implementations of our algorithms targeting distributed memory systems. Finally, several numerical examples are presented to demonstrate the efficiency and accuracy of our algorithms.« less

Initial mass functions from ultraviolet stellar photometry: A comparison of Lucke and Hodge OB associations near 30 Doradus with the nearby field

NASA Technical Reports Server (NTRS)

Hill, Jesse K.; Isensee, Joan E.; Cornett, Robert H.; Bohlin, Ralph C.; O'Connell, Robert W.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

1994-01-01

UV stellar photometry is presented for 1563 stars within a 40 minutes circular field in the Large Magellanic Cloud (LMC), excluding the 10 min x 10 min field centered on R136 investigated earlier by Hill et al. (1993). Magnitudes are computed from images obtained by the Ultraviolet Imaging Telescope (UIT) in bands centered at 1615 A and 2558 A. Stellar masses and extinctions are estimated for the stars in associations using the evolutionary models of Schaerer et al. (1993), assuming the age is 4 Myr and that the local LMC extinction follows the Fitzpatrick (1985) 30 Dor extinction curve. The estimated slope of the initial mass function (IMF) for massive stars (greater than 15 solar mass) within the Lucke and Hodge (LH) associations is Gamma = -1.08 +/- 0.2. Initial masses and extinctions for stars not within LH associations are estimated assuming that the stellar age is either 4 Myr or half the stellar lifetime, whichever is larger. The estimated slope of the IMF for massive stars not within LH associations is Gamma = -1.74 +/- 0.3 (assuming continuous star formation), compared with Gamma = -1.35, and Gamma = -1.7 +/- 0.5, obtained for the Galaxy by Salpeter (1955) and Scalo (1986), respectively, and Gamma = -1.6 obtained for massive stars in the Galaxy by Garmany, Conti, & Chiosi (1982). The shallower slope of the association IMF suggests that not only is the star formation rate higher in associations, but that the local conditions favor the formation of higher mass stars there. We make no corrections for binaries or incompleteness.

Evidence of ghost suppression in gluon mass scale dynamics

NASA Astrophysics Data System (ADS)

Aguilar, A. C.; Binosi, D.; Figueiredo, C. T.; Papavassiliou, J.

2018-03-01

In this work we study the impact that the ghost sector of pure Yang-Mills theories may have on the generation of a dynamical gauge boson mass scale, which hinges on the appearance of massless poles in the fundamental vertices of the theory, and the subsequent realization of the well-known Schwinger mechanism. The process responsible for the formation of such structures is itself dynamical in nature, and is governed by a set of Bethe-Salpeter type of integral equations. While in previous studies the presence of massless poles was assumed to be exclusively associated with the background-gauge three-gluon vertex, in the present analysis we allow them to appear also in the corresponding ghost-gluon vertex. The full analysis of the resulting Bethe-Salpeter system reveals that the contribution of the poles associated with the ghost-gluon vertex are particularly suppressed, their sole discernible effect being a slight modification in the running of the gluon mass scale, for momenta larger than a few GeV. In addition, we examine the behavior of the (background-gauge) ghost-gluon vertex in the limit of vanishing ghost momentum, and derive the corresponding version of Taylor's theorem. These considerations, together with a suitable Ansatz, permit us the full reconstruction of the pole sector of the two vertices involved.

Impact of Stellar Convection Criteria on the Nucleosynthetic Yields of Population III Supernovae.

NASA Astrophysics Data System (ADS)

Teffs, Jacob; Young, Tim; Lawlor, Tim

2018-01-01

A grid of 15-80 solar mass Z=0 stellar models are evolved to pre-core collapse using the stellar evolution code BRAHAMA. Each initial zero-age main sequence mass model star is evolved with two different convection criteria, Ledoux and Schwarzchild. The choice of convection produces significant changes in the evolutionary model tracks on the HR diagram, mass loss, and interior core and envelope structures. At onset of core collapse, a SNe explosion is initiated using a one-dimensional radiation-hydrodynamics code and followed for 400 days. The explosion energy is varied between 1-10 foes depending on the model as there are no observationally determined energies for population III supernovae. Due to structure differences, the Schwarzchild models resemble Type II-P SNe in their lightcurve while the Ledoux models resemble SN1987a, a Type IIpec. The nucleosynthesis is calculated using TORCH, a 3,208 isotope network, in a post process method using the hydrodynamic history. The Ledoux models have, on average, higher yields for elements above Fe compared to the Schwarzchild. Using a Salpeter IMF and other recently published population III IMF’s, the net integrated yields per solar mass are calculated and compared to published theoretical results and to published observations of extremely metal poor halo stars of [Fe/H] < -3. Preliminary results show the lower mass models of both criteria show similar trends to the extremely metal poor halo stars but more work and analysis is required.

FRAGMENTATION AND EVOLUTION OF MOLECULAR CLOUDS. II. THE EFFECT OF DUST HEATING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urban, Andrea; Evans, Neal J.; Martel, Hugo

2010-02-20

We investigate the effect of heating by luminosity sources in a simulation of clustered star formation. Our heating method involves a simplified continuum radiative transfer method that calculates the dust temperature. The gas temperature is set by the dust temperature. We present the results of four simulations; two simulations assume an isothermal equation of state and the two other simulations include dust heating. We investigate two mass regimes, i.e., 84 M{sub sun} and 671 M{sub sun}, using these two different energetics algorithms. The mass functions for the isothermal simulations and simulations that include dust heating are drastically different. In themore » isothermal simulation, we do not form any objects with masses above 1 M{sub sun}. However, the simulation with dust heating, while missing some of the low-mass objects, forms high-mass objects ({approx}20 M{sub sun}) which have a distribution similar to the Salpeter initial mass function. The envelope density profiles around the stars formed in our simulation match observed values around isolated, low-mass star-forming cores. We find the accretion rates to be highly variable and, on average, increasing with final stellar mass. By including radiative feedback from stars in a cluster-scale simulation, we have determined that it is a very important effect which drastically affects the mass function and yields important insights into the formation of massive stars.« less

Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schleife, A; Bechstedt, F

2012-02-15

Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparentmore » conducting oxides in good agreement with experiment.« less

Lattice QCD studies on baryon interactions in the strangeness -2 sector with physical quark masses

NASA Astrophysics Data System (ADS)

Sasaki, Kenji; Aoki, Sinya; Doi, Takumi; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Iritani, Takumi; Ishii, Noriyoshi; Miyamoto, Takaya

2018-03-01

We investigate baryon-baryon (BB) interactions in the strangeness S = -2 sector via the coupled-channel HAL QCD method which enables us to extract the scattering observables from Nambu-Bethe-Salpeter (NBS) wave function on the lattice. The simulations are performed with (almost) physical quark masses (mπ = 146MeV) and a huge lattice volume of La = 8.1fm. We discuss the fate of H-dibaryon state through the ΛΛ and NΞ coupled-channel scatterings

The pion form factor from first principles

NASA Astrophysics Data System (ADS)

van der Heide, J.

2004-08-01

We calculate the electromagnetic form factor of the pion in quenched lattice QCD. The non-perturbatively improved Sheikoleslami-Wohlert lattice action is used together with the O(a) improved current. We calculate form factor for pion masses down to mπ = 380 MeV. We compare the mean square radius for the pion extracted from our form factors to the value obtained from the `Bethe Salpeter amplitude'. Using (quenched) chiral perturbation theory, we extrapolate our results towards the physical pion mass.

Golden gravitational lensing systems from the Sloan Lens ACS Survey - II. SDSS J1430+4105: a precise inner total mass profile from lensing alone

NASA Astrophysics Data System (ADS)

Eichner, Thomas; Seitz, Stella; Bauer, Anne

2012-12-01

We study the Sloan Lens ACS (SLACS) survey strong-lensing system SDSS J1430+4105 at zl = 0.285. The lensed source (zs = 0.575) of this system has a complex morphology with several subcomponents. Its subcomponents span a radial range from 4 to 10 kpc in the plane of the lens. Therefore, we can constrain the slope of the total projected mass profile around the Einstein radius from lensing alone. We measure a density profile that is slightly but not significantly shallower than isothermal at the Einstein radius. We decompose the mass of the lensing galaxy into a de Vaucouleurs component to trace the stars and an additional dark component. The spread of multiple-image components over a large radial range also allows us to determine the amplitude of the de Vaucouleurs and dark matter components separately. We get a mass-to-light ratio of M de Vauc LB ≈ (5.5±1.5) M⊙L⊙,B and a dark matter fraction within the Einstein radius of ≈20 to 40 per cent. Modelling the star formation history assuming composite stellar populations at solar metallicity to the galaxy's photometry yields a mass-to-light ratio of M, salp LB ≈ 4.0-1.3+0.6 M⊙L⊙,B and M, chab LB ≈ 2.3-0.8+0.3 M⊙L⊙,B for Salpeter and Chabrier initial mass functions, respectively. Hence, the mass-to-light ratio derived from lensing is more Salpeter like, in agreement with results for massive Coma galaxies and other nearby massive early-type galaxies. We examine the consequences of the galaxy group in which the lensing galaxy is embedded, showing that it has little influence on the mass-to-light ratio obtained for the de Vaucouleurs component of the lensing galaxy. Finally, we decompose the projected, azimuthally averaged 2D density distribution of the de Vaucouleurs and dark matter components of the lensing signal into spherically averaged 3D density profiles. We can show that the 3D dark and luminous matter density within the Einstein radius (REin ≈ 0.6 Reff) of this SLACS galaxy is similar to the values of Coma galaxies with the same velocity dispersions.

THE SL2S GALAXY-SCALE LENS SAMPLE. V. DARK MATTER HALOS AND STELLAR IMF OF MASSIVE EARLY-TYPE GALAXIES OUT TO REDSHIFT 0.8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.

2015-02-20

We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increasesmore » for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M {sub *} = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.« less

The SL2S galaxy-scale lens sample. V. dark matter halos and stellar IMF of massive early-type galaxies out to redshift 0.8

DOE PAGES

Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; ...

2015-02-17

Here, we investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We also perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. Furthermore, we found that the dark matter mass projected within the innermore » 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.« less

The bulge-halo conspiracy in massive elliptical galaxies: implications for the stellar initial mass function and halo response to baryonic processes

NASA Astrophysics Data System (ADS)

Dutton, Aaron A.; Treu, Tommaso

2014-03-01

Recent studies have shown that massive elliptical galaxies have total mass density profiles within an effective radius that can be approximated as ρ_tot∝ r^{-γ^', with mean slope <γ'> = 2.08 ± 0.03 and scatter σ _{γ ^' } }=0.16± 0.02. The small scatter of the slope (known as the bulge-halo conspiracy) is not generic in Λ cold dark matter (ΛCDM) based models and therefore contains information about the galaxy formation process. We compute the distribution of γ' for ΛCDM-based models that reproduce the observed correlations between stellar mass, velocity dispersion, and effective radius of early-type galaxies in the Sloan Digital Sky Survey. The models have a range of stellar initial mass functions (IMFs) and dark halo responses to galaxy formation. The observed distribution of γ' is well reproduced by a model with cosmologically motivated but uncontracted dark matter haloes, and a Salpeter-type IMF. Other models are on average ruled out by the data, even though they may happen in individual cases. Models with adiabatic halo contraction (and lighter IMFs) predict too small values of γ'. Models with halo expansion, or mass-follows-light predict too high values of γ'. Our study shows that the non-homologous structure of massive early-type galaxies can be precisely reproduced by ΛCDM models if the IMF is not universal and if mechanisms, such as feedback from active galactic nuclei, or dynamical friction, effectively on average counterbalance the contraction of the halo expected as a result of baryonic cooling.

Is the Link Between the Observed Velocities of Neutron Stars and their Progenitors a Simple Mass Relationship?

NASA Astrophysics Data System (ADS)

Bray, J. C.

2017-11-01

While the imparting of velocity `kicks' to compact remnants from supernovae is widely accepted, the relationship of the `kick' to the progenitor is not. We propose the `kick' is predominantly a result of conservation of momentum between the ejected and compact remnant masses. We propose the `kick' velocity is given by v kick = α(M ejecta/M remnant)+β, where α and β are constants we wish to determine. To test this we use the BPASS v2 (Binary Population and Spectral Synthesis) code to create stellar populations from both single star and binary star evolutionary pathways. We then use our Remnant Ejecta and Progenitor Explosion Relationship (REAPER) code to apply `kicks' to neutron stars from supernovae in these models using a grid of α and β values, (from 0 to 200 km s-1 in steps of 10 km s-1), in three different `kick' orientations, (isotropic, spin-axis aligned and orthogonal to spin-axis) and weighted by three different Salpeter initial mass functions (IMF's), with slopes of -2.0, -2.35 and -2.70. We compare our synthetic 2D and 3D velocity probability distributions to the distributions provided by Hobbs et al. (1995).

The Low-mass Population in the Young Cluster Stock 8: Stellar Properties and Initial Mass Function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jose, Jessy; Herczeg, Gregory J.; Fang, Qiliang

The evolution of H ii regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution, and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6 and 4.5 μ m photometry from UKIDSS and Spitzer -IRAC. We use multicolor criteria to identify the candidate young stellar objects in the region. Using evolutionary models,more » we obtain a median log(age) of ∼6.5 (∼3.0 Myr) with an observed age spread of ∼0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ∼0.15 dex. The intrinsic age spread in the cluster is ∼0.2 dex. The fraction of young stellar objects surrounded by disks is ∼35%. The K -band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The initial mass function (IMF) of Stock 8 has a Salpeter-like slope at >0.5 M {sub ⊙} and flattens and peaks at ∼0.4 M {sub ⊙}, below which it declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of the IMF due to the proximity of massive stars around the cluster.« less

Probing the stellar initial mass function with high-z supernovae

NASA Astrophysics Data System (ADS)

de Souza, R. S.; Ishida, E. E. O.; Whalen, D. J.; Johnson, J. L.; Ferrara, A.

2014-08-01

The first supernovae (SNe) will soon be visible at the edge of the observable universe, revealing the birthplaces of Population III stars. With upcoming near-infrared missions, a broad analysis of the detectability of high-z SNe is paramount. We combine cosmological and radiation transport simulations, instrument specifications and survey strategies to create synthetic observations of primeval core-collapse (CC), Type IIn and pair-instability (PI) SNe with the James Webb Space Telescope (JWST). We show that a dedicated observational campaign with the JWST can detect up to ˜15 PI explosions, ˜300 CC SNe, but less than one Type IIn explosion per year, depending on the Population III star formation history. Our synthetic survey also shows that ≈1-2 × 102 SNe detections, depending on the accuracy of the classification, are sufficient to discriminate between a Salpeter and flat mass distribution for high-redshift stars with a confidence level greater than 99.5 per cent. We discuss how the purity of the sample affects our results and how supervised learning methods may help to discriminate between CC and PI SNe.

BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association

NASA Astrophysics Data System (ADS)

Gagné, Jonathan; Faherty, Jacqueline K.; Mamajek, Eric E.; Malo, Lison; Doyon, René; Filippazzo, Joseph C.; Weinberger, Alycia J.; Donaldson, Jessica K.; Lépine, Sébastien; Lafrenière, David; Artigau, Étienne; Burgasser, Adam J.; Looper, Dagny; Boucher, Anne; Beletsky, Yuri; Camnasio, Sara; Brunette, Charles; Arboit, Geneviève

2017-02-01

A determination of the initial mass function (IMF) of the current, incomplete census of the 10 Myr-old TW Hya association (TWA) is presented. This census is built from a literature compilation supplemented with new spectra and 17 new radial velocities from ongoing membership surveys, as well as a reanalysis of Hipparcos data that confirmed HR 4334 (A2 Vn) as a member. Although the dominant uncertainty in the IMF remains census incompleteness, a detailed statistical treatment is carried out to make the IMF determination independent of binning while accounting for small number statistics. The currently known high-likelihood members are fitted by a log-normal distribution with a central mass of {0.21}-0.06+0.11 M ⊙ and a characteristic width of {0.8}-0.1+0.2 dex in the 12 M Jup-2 M ⊙ range, whereas a Salpeter power law with α ={2.2}-0.5+1.1 best describes the IMF slope in the 0.1-2 M ⊙ range. This characteristic width is higher than other young associations, which may be due to incompleteness in the current census of low-mass TWA stars. A tentative overpopulation of isolated planetary-mass members similar to 2MASS J11472421-2040204 and 2MASS J11193254-1137466 is identified: this indicates that there might be as many as {10}-5+13 similar members of TWA with hot-start model-dependent masses estimated at ˜5-7 M Jup, most of which would be too faint to be detected in 2MASS. Our new radial velocity measurements corroborate the membership of 2MASS J11472421-2040204, and secure TWA 28 (M8.5 γ), TWA 29 (M9.5 γ), and TWA 33 (M4.5 e) as members. The discovery of 2MASS J09553336-0208403, a young L7-type interloper unrelated to TWA, is also presented.

Bayesian extraction of the parton distribution amplitude from the Bethe-Salpeter wave function

NASA Astrophysics Data System (ADS)

Gao, Fei; Chang, Lei; Liu, Yu-xin

2017-07-01

We propose a new numerical method to compute the parton distribution amplitude (PDA) from the Euclidean Bethe-Salpeter wave function. The essential step is to extract the weight function in the Nakanishi representation of the Bethe-Salpeter wave function in Euclidean space, which is an ill-posed inversion problem, via the maximum entropy method (MEM). The Nakanishi weight function as well as the corresponding light-front parton distribution amplitude (PDA) can be well determined. We confirm prior work on PDA computations, which was based on different methods.

The stellar population and initial mass function of NGC 1399 with MUSE

NASA Astrophysics Data System (ADS)

Vaughan, Sam P.; Davies, Roger L.; Zieleniewski, Simon; Houghton, Ryan C. W.

2018-06-01

We present spatially resolved measurements of the stellar initial mass function (IMF) in NGC 1399, the largest elliptical galaxy in the Fornax Cluster. Using data from the Multi Unit Spectroscopic Explorer (MUSE) and updated state-of-the-art stellar population synthesis models from Conroy et al. (2018), we use full spectral fitting to measure the low-mass IMF, as well as a number of individual elemental abundances, as a function of radius in this object. We find that the IMF in NGC 1399 is heavier than the Milky Way in its centre and remains radially constant at a super-salpeter slope out to 0.7 Re. At radii larger than this, the IMF slope decreases to become marginally consistent with a Milky Way IMF just beyond Re. The inferred central V-band M/L ratio is in excellent agreement with the previously reported dynamical M/L measurement from Houghton et al. (2006). The measured radial form of the M/L ratio may be evidence for a two-phase formation in this object, with the central regions forming differently to the outskirts. We also report measurements of a spatially resolved filament of ionised gas extending 4"(404 pc at DL = 21.1 Mpc) from the centre of NGC 1399, with very narrow equivalent width and low velocity dispersion (65 ± 14 kms-1). The location of the emission, combined with an analysis of the emission line ratios, leads us to conclude that NGC 1399's AGN is the source of ionising radiation.

An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

NASA Astrophysics Data System (ADS)

Cowie, L. L.; Barger, A. J.

2008-10-01

We present an integrated study of star formation and galactic stellar mass assembly from z = 0.05 to 1.5 and galactic metallicity evolution from z = 0.05 to 0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 M⊙). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24 μm sources, but after correcting for extinction, the bulk of the 24 μm sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21 +/- 0.03 dex between the local value and the value at z = 0.77 in the 1010-1011 M⊙ range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (gtrsim1011 M⊙) ceases at z < 1.5 because of gas starvation. Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

Constraints for the Progenitor Masses of Historic Core-collapse Supernovae

NASA Astrophysics Data System (ADS)

Williams, Benjamin F.; Hillis, Tristan J.; Murphy, Jeremiah W.; Gilbert, Karoline; Dalcanton, Julianne J.; Dolphin, Andrew E.

2018-06-01

We age-date the stellar populations associated with 12 historic nearby core-collapse supernovae (CCSNe) and two supernova impostors; from these ages, we infer their initial masses and associated uncertainties. To do this, we have obtained new Hubble Space Telescope imaging covering these CCSNe. Using these images, we measure resolved stellar photometry for the stars surrounding the locations of the SNe. We then fit the color–magnitude distributions of this photometry with stellar evolution models to determine the ages of any young existing populations present. From these age distributions, we infer the most likely progenitor masses for all of the SNe in our sample. We find ages between 4 and 50 Myr, corresponding to masses from 7.5 to 59 solar masses. There were no SNe that lacked a local young population. Our sample contains four SNe Ib/c; their masses have a wide range of values, suggesting that the progenitors of stripped-envelope SNe are binary systems. Both impostors have masses constrained to be ≲7.5 solar masses. In cases with precursor imaging measurements, we find that age-dating and precursor imaging give consistent progenitor masses. This consistency implies that, although the uncertainties for each technique are significantly different, the results of both are reliable to the measured uncertainties. We combine these new measurements with those from our previous work and find that the distribution of 25 core-collapse SNe progenitor masses is consistent with a standard Salpeter power-law mass function, no upper mass cutoff, and an assumed minimum mass for core-collapse of 7.5 M⊙. The distribution is consistent with a minimum mass <9.5 M⊙.

The Core Mass Function in the Massive Protocluster G286.21+0.17 Revealed by ALMA

NASA Astrophysics Data System (ADS)

Cheng, Yu; Tan, Jonathan C.; Liu, Mengyao; Kong, Shuo; Lim, Wanggi; Andersen, Morten; Da Rio, Nicola

2018-02-01

We study the core mass function (CMF) of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3 mm continuum emission at a resolution of 1.″0 (2500 au). We have mapped a field of 5.‧3 × 5.‧3 centered on the protocluster clump. We measure the CMF in the central region, exploring various core detection algorithms, which give source numbers ranging from 60 to 125, depending on parameter selection. We estimate completeness corrections due to imperfect flux recovery and core identification via artificial core insertion experiments. For masses M ≳ 1 M ⊙, the fiducial dendrogram-identified CMF can be fit with a power law of the form dN/dlog M ∝ M ‑α with α ≃ 1.24 ± 0.17, slightly shallower than, but still consistent with, the index of the Salpeter stellar initial mass function of 1.35. Clumpfind-identified CMFs are significantly shallower with α ≃ 0.64 ± 0.13. While raw CMFs show a peak near 1 M ⊙, completeness-corrected CMFs are consistent with a single power law extending down to ∼0.5 M ⊙, with only a tentative indication of a shallowing of the slope around ∼1 M ⊙. We discuss the implications of these results for star and star cluster formation theories.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conroy, Charlie; Van Dokkum, Pieter G.; Villaume, Alexa

It is now well-established that the stellar initial mass function (IMF) can be determined from the absorption line spectra of old stellar systems, and this has been used to measure the IMF and its variation across the early-type galaxy population. Previous work focused on measuring the slope of the IMF over one or more stellar mass intervals, implicitly assuming that this is a good description of the IMF and that the IMF has a universal low-mass cutoff. In this work we consider more flexible IMFs, including two-component power laws with a variable low-mass cutoff and a general non-parametric model. Wemore » demonstrate with mock spectra that the detailed shape of the IMF can be accurately recovered as long as the data quality is high (S/N ≳ 300 Å{sup −1}) and cover a wide wavelength range (0.4–1.0 μ m). We apply these flexible IMF models to a high S/N spectrum of the center of the massive elliptical galaxy NGC 1407. Fitting the spectrum with non-parametric IMFs, we find that the IMF in the center shows a continuous rise extending toward the hydrogen-burning limit, with a behavior that is well-approximated by a power law with an index of −2.7. These results provide strong evidence for the existence of extreme (super-Salpeter) IMFs in the cores of massive galaxies.« less

Study of molecular N D bound states in the Bethe-Salpeter equation approach

NASA Astrophysics Data System (ADS)

Wang, Zhen-Yang; Qi, Jing-Juan; Guo, Xin-Heng; Wei, Ke-Wei

2018-05-01

We study the Λc(2595 )+ and Σc(2800 )0 states as the N D bound systems in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. With the kernel induced by ρ , ω and σ exchanges, we solve the Bethe-Salpeter equations for the N D bound systems numerically and find that the bound states may exist. We assume that the observed states Λc(2595 )+ and Σc(2800 )0 are S -wave N D molecular bound states and calculate the decay widths of Λc(2595 )+→Σc0π+ and Σc(2800 )0→Λc+π-.

Benchmarking the Bethe–Salpeter Formalism on a Standard Organic Molecular Set

PubMed Central

2015-01-01

We perform benchmark calculations of the Bethe–Salpeter vertical excitation energies for the set of 28 molecules constituting the well-known Thiel’s set, complemented by a series of small molecules representative of the dye chemistry field. We show that Bethe–Salpeter calculations based on a molecular orbital energy spectrum obtained with non-self-consistent G0W0 calculations starting from semilocal DFT functionals dramatically underestimate the transition energies. Starting from the popular PBE0 hybrid functional significantly improves the results even though this leads to an average −0.59 eV redshift compared to reference calculations for Thiel’s set. It is shown, however, that a simple self-consistent scheme at the GW level, with an update of the quasiparticle energies, not only leads to a much better agreement with reference values, but also significantly reduces the impact of the starting DFT functional. On average, the Bethe–Salpeter scheme based on self-consistent GW calculations comes close to the best time-dependent DFT calculations with the PBE0 functional with a 0.98 correlation coefficient and a 0.18 (0.25) eV mean absolute deviation compared to TD-PBE0 (theoretical best estimates) with a tendency to be red-shifted. We also observe that TD-DFT and the standard adiabatic Bethe–Salpeter implementation may differ significantly for states implying a large multiple excitation character. PMID:26207104

Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites

NASA Astrophysics Data System (ADS)

Gennaro, Mario; Tchernyshyov, Kirill; Brown, Thomas M.; Geha, Marla; Avila, Roberto J.; Guhathakurta, Puragra; Kalirai, Jason S.; Kirby, Evan N.; Renzini, Alvio; Simon, Joshua D.; Tumlinson, Jason; Vargas, Luis C.

2018-03-01

Using deep observations obtained with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST), we demonstrate that the sub-solar stellar initial mass function (IMF) of six ultra-faint dwarf Milky Way satellites (UFDs) is more bottom light than the IMF of the Milky Way disk. Our data have a lower-mass limit of ∼0.45 M ⊙, while the upper limit is ∼0.8 M ⊙, set by the turnoff mass of these old, metal-poor systems. If formulated as a single power law, we obtain a shallower IMF slope than the Salpeter value of ‑2.3, ranging from ‑1.01 for Leo IV to ‑1.87 for Boötes I. The significance of these deviations depends on the galaxy and is typically 95% or more. When modeled as a log-normal, the IMF fit results in a higher peak mass than in the Milky Way disk, but a Milky Way disk value for the characteristic system mass (∼0.22 M ⊙) is excluded at only 68% significance, and only for some UFDs in the sample. We find that the IMF slope correlates well with the galaxy mean metallicity, and to a lesser degree, with the velocity dispersion and the total mass. The strength of the observed correlations is limited by shot noise in the number of observed stars, but future space-based missions like the James Webb Space Telescope (JWST) and the Wide-Field Infrared Survey Telescope ( WFIRST) will enhance both the number of dwarf Milky Way satellites that can be studied in such detail and the observation depth for individual galaxies. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-12549.

Mosfire Spectroscopy Of Galaxies In Cosmic Noon

NASA Astrophysics Data System (ADS)

Nanayakkara, Themiya

2017-07-01

The recent development of sensitive, multiplexed near infra-red instruments has presented astronomers the unique opportunity to survey mass/magnitude complete samples of galaxies at Cosmic Noon, a time period where ˜ 80% of the observed baryonic mass is generated and galaxies are actively star-forming and evolving rapidly. This thesis takes advantage of the recently commissioned MOSFIRE spectrograph on Keck, to conduct a survey (ZFIRE) of galaxies at 1.5 < z < 2.5 to measure accurate spectroscopic redshifts and basic galaxy properties derived from multiple emission lines. The majority of the thesis work involved survey planning, observing, data reduction, and catalogue preparation of the ZFIRE survey and is described in detail in this thesis. Using the ZFIRE spectroscopic redshifts, I show why spectroscopy is instrumental to determine fundamental galaxy properties via SED fitting techniques and to probe gravitationally bound structures in the early universe. The thesis further presents basic properties of the ZFIRE data products publicly released for the benefit of the astronomy community. The high mass-completeness of the ZFIRE spectroscopic data at z ˜ 2 makes it ideal to study fundamental galaxy properties such as, star formation rates, metallicities, interstellar medium properties, galaxy kinematics, and the stellar initial mass functions in unbiased star-forming galaxies. This thesis focuses on one such aspect, the IMF. By using a mass-complete (log10(M∗/M) ˜ 9.3) sample of 102 galaxies at z = 2.1 in the COSMOS field from ZFIRE, I investigate the IMF of star-forming galaxies by revisiting the classical Kennicutt (1983) technique of using the Hα equivalent widths and rest-frame optical colours. I present a thorough analysis of stellar population properties of the ZFIRE sample via multiple synthetic stellar population models and stellar libraries. Due to an excess of high Hα-EW galaxies that are up to 0.3-0.5 dex above the Salpeter locus, the Hα-EW distribution is much broader (10-500˚A) than can be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. This result is robust against uncertainties in dust correction and observational bias, and no single IMF (i.e. non-Salpeter slope) can explain the distribution. Starburst models cannot explain the Hα-EW distribution because: 1) spectral stacking still shows an excess Hα-EW in composite populations and 2) Monte Carlo burst models show that the timescale for high Hα-EW is too short to explain their abundance in the ZFIRE sample. Other possible physical mechanisms that could produce excess ionising photons for a given star-formation rate, and hence high equivalent widths, including models with variations in stellar rotation, binary star evolution, metallicity, and upper mass cutoff of the IMF are investigated and ruled out. IMF variation is one possible explanation for the high Hα-EWs. However, the highest Hα-EW values would require very shallow slopes (Γ > -1.0) and no single IMF change can explain the large variation in Hα-EWs. Instead the IMF would have to vary stochastically. Therefore, currently there is no simple physical model to explain the large variation in Hα-EWs at z ˜ 2, but the distinct differences of the z ˜ 2 sample with that of local galaxies are found to be intriguing. Further study is required to fully constrain the stellar population parameters of actively star-forming galaxies at the epoch of maximum star-formation. Probing multiple rest-frame UV and optical features of galaxies simultaneously along with galaxy dynamical studies via integral field spectroscopy will be vital to understand stellar and ionized gas properties of these galaxies. Furthermore, low-z analogues of galaxies at z ˜ 2 will provide vital clues to constrain galaxy evolution models aided by the ability to probe galaxies in high resolution to low surface brightness limits.

Numerical studies of the Bethe-Salpeter equation for a two-fermion bound state

NASA Astrophysics Data System (ADS)

de Paula, W.; Frederico, T.; Salmè, G.; Viviani, M.

2018-03-01

Some recent advances on the solution of the Bethe-Salpeter equation (BSE) for a two-fermion bound system directly in Minkowski space are presented. The calculations are based on the expression of the Bethe-Salpeter amplitude in terms of the so-called Nakanishi integral representation and on the light-front projection (i.e. the integration of the light-front variable k - = k 0 - k 3). The latter technique allows for the analytically exact treatment of the singularities plaguing the two-fermion BSE in Minkowski space. The good agreement observed between our results and those obtained using other existing numerical methods, based on both Minkowski and Euclidean space techniques, fully corroborate our analytical treatment.

THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geha, Marla; Brown, Thomas M.; Tumlinson, Jason

2013-07-01

We present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. The Hercules and Leo IV galaxies are extremely low luminosity (M{sub V} = -6.2, -5.5), metal-poor (([Fe/H]) = -2.4, -2.5) systems that have old stellar populations (>11 Gyr). Because they have long relaxation times, we can directly measure the low-mass stellar IMF by counting stars below the main-sequence turnoff without correcting for dynamical evolution. Over the stellar mass range probed by our data, 0.52-0.77 M{sub Sun }, the IMFmore » is best fit by a power-law slope of {alpha}= 1.2{sub -0.5}{sup +0.4} for Hercules and {alpha} = 1.3 {+-} 0.8 for Leo IV. For Hercules, the IMF slope is more shallow than a Salpeter ({alpha} = 2.35) IMF at the 5.8{sigma} level, and a Kroupa ({alpha} = 2.3 above 0.5 M{sub Sun }) IMF slope at 5.4{sigma} level. We simultaneously fit for the binary fraction, f{sub binary}, finding f{sub binary}= 0.47{sup +0.16}{sub -0.14} for Hercules, and 0.47{sup +0.37}{sub -0.17} for Leo IV. The UFD binary fractions are consistent with that inferred for Milky Way stars in the same mass range, despite very different metallicities. In contrast, the IMF slopes in the UFDs are shallower than other galactic environments. In the mass range 0.5-0.8 M{sub Sun }, we see a trend across the handful of galaxies with directly measured IMFs such that the power-law slopes become shallower (more bottom-light) with decreasing galactic velocity dispersion and metallicity. This trend is qualitatively consistent with results in elliptical galaxies inferred via indirect methods and is direct evidence for IMF variations with galactic environment.« less

A systematic approach to sketch Bethe-Salpeter equation

NASA Astrophysics Data System (ADS)

Qin, Si-xue

2016-03-01

To study meson properties, one needs to solve the gap equation for the quark propagator and the Bethe-Salpeter (BS) equation for the meson wavefunction, self-consistently. The gluon propagator, the quark-gluon vertex, and the quark-anti-quark scattering kernel are key pieces to solve those equations. Predicted by lattice-QCD and Dyson-Schwinger analyses of QCD's gauge sector, gluons are non-perturbatively massive. In the matter sector, the modeled gluon propagator which can produce a veracious description of meson properties needs to possess a mass scale, accordingly. Solving the well-known longitudinal Ward-Green-Takahashi identities (WGTIs) and the less-known transverse counterparts together, one obtains a nontrivial solution which can shed light on the structure of the quark-gluon vertex. It is highlighted that the phenomenologically proposed anomalous chromomagnetic moment (ACM) vertex originates from the QCD Lagrangian symmetries and its strength is proportional to the magnitude of dynamical chiral symmetry breaking (DCSB). The color-singlet vector and axial-vector WGTIs can relate the BS kernel and the dressed quark-gluon vertex to each other. Using the relation, one can truncate the gap equation and the BS equation, systematically, without violating crucial symmetries, e.g., gauge symmetry and chiral symmetry.

Bethe-Salpeter wave functions of ηc(1S, 2S) and ψ(1S, 2S) states: local-potential description of the charmonium system revisited

NASA Astrophysics Data System (ADS)

Nochi, Kazuki; Kawanai, Taichi; Sasaki, Shoichi

2018-03-01

The quark potential models with an energy-independent central potential have been successful for understanding the conventional charmonium states especially below the open charm threshold. As one might consider, however, the interquark potential is in general energy-dependent, and its tendency gets stronger in higher lying states. Confirmation of whether the interquark potential is energy-independent is also important to verify the validity of the quark potential models. In this talk, we examine the energy dependence of the charmonium potential, which can be determined from the Bethe-Salpeter (BS) amplitudes of cc̅ mesons in lattice QCD.We first calculate the BS amplitudes of radially excited charmonium states, the ηc(2S) and ψ(2S) states, using the variational method and then determine both the quark kinetic mass and the charmonium potential within the HAL QCD method. Through a direct comparison of charmonium potentials determined from both the 1S and 2S states, we confirm that neither the central nor spin-spin potential shows visible energy dependence at least up to 2S state.

Young Cluster Berkeley 59: Properties, Evolution, and Star Formation

NASA Astrophysics Data System (ADS)

Panwar, Neelam; Pandey, A. K.; Samal, Manash R.; Battinelli, Paolo; Ogura, K.; Ojha, D. K.; Chen, W. P.; Singh, H. P.

2018-01-01

Berkeley 59 is a nearby (∼1 kpc) young cluster associated with the Sh2-171 H II region. We present deep optical observations of the central ∼2.5 × 2.5 pc2 area of the cluster, obtained with the 3.58 m Telescopio Nazionale Galileo. The V/(V–I) color–magnitude diagram manifests a clear pre-main-sequence (PMS) population down to ∼0.2 M ⊙. Using the near-infrared and optical colors of the low-mass PMS members, we derive a global extinction of A V = 4 mag and a mean age of ∼1.8 Myr, respectively, for the cluster. We constructed the initial mass function and found that its global slopes in the mass ranges of 0.2–28 M ⊙ and 0.2–1.5 M ⊙ are ‑1.33 and ‑1.23, respectively, in good agreement with the Salpeter value in the solar neighborhood. We looked for the radial variation of the mass function and found that the slope is flatter in the inner region than in the outer region, indicating mass segregation. The dynamical status of the cluster suggests that the mass segregation is likely primordial. The age distribution of the PMS sources reveals that the younger sources appear to concentrate close to the inner region compared to the outer region of the cluster, a phenomenon possibly linked to the time evolution of star-forming clouds. Within the observed area, we derive a total mass of ∼103 M ⊙ for the cluster. Comparing the properties of Berkeley 59 with other young clusters, we suggest it resembles more closely the Trapezium cluster.

The Low End of the Initial Mass Function in Young Clusters. II. Evidence for Primordial Mass Segregation in NGC 330 in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Sirianni, Marco; Nota, Antonella; De Marchi, Guido; Leitherer, Claus; Clampin, Mark

2002-11-01

As part of a larger program aimed at investigating the universality of the initial mass function (IMF) at low masses in a number of young clusters in the LMC and SMC, we present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the SMC, from deep broadband V and I images obtained with HST/WFPC2. We detect stars down to a limiting magnitude of m555=24.9, which corresponds to stellar masses of ~0.8Msolar at the distance of the SMC. A comparison of the cluster color-magnitude diagram with theoretical evolutionary tracks indicates an age of ~30 Myr for NGC 330, in agreement with previous published results. We derive the cluster luminosity function, which we correct for background contamination using an adjacent SMC field, and construct the mass function in the 1-7Msolar mass range. Given the young cluster age, the MF can well approximate the IMF. We find that the IMF in the central cluster regions (within 30") is well reproduced by a power law with a slope consistent with Salpeter's. In addition, the richness of the cluster allows us to investigate the IMF as a function of radial distance from the center. We find that the IMF becomes steeper at increasing distances from the cluster center (between 30" and 90"), with the number of massive stars (>5Msolar) decreasing from the core to the outskirts of the cluster 5 times more rapidly than the less-massive objects (~=1Msolar). We believe the observed mass segregation to be of a primordial nature rather than dynamical since the age of NGC 330 is 10 times shorter than the expected relaxation time of the cluster. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS5-26555.

Relativistic proton-nucleus scattering and one-boson-exchange models

NASA Technical Reports Server (NTRS)

Maung, Khin Maung; Gross, Franz; Tjon, J. A.; Townsend, L. W.; Wallace, S. J.

1993-01-01

Relativistic p-(Ca-40) elastic scattering observables are calculated using four sets of relativistic NN amplitudes obtained from different one-boson-exchange (OBE) models. The first two sets are based upon a relativistic equation in which one particle is on mass shell and the other two sets are obtained from a quasipotential reduction of the Bethe-Salpeter equation. Results at 200, 300, and 500 MeV are presented for these amplitudes. Differences between the predictions of these models provide a study of the uncertainty in constructing Dirac optical potentials from OBE-based NN amplitudes.

Re-derived overclosure bound for the inert doublet model

NASA Astrophysics Data System (ADS)

Biondini, S.; Laine, M.

2017-08-01

We apply a formalism accounting for thermal effects (such as modified Sommerfeld effect; Salpeter correction; decohering scatterings; dissociation of bound states), to one of the simplest WIMP-like dark matter models, associated with an "inert" Higgs doublet. A broad temperature range T ˜ M/20 . . . M/104 is considered, stressing the importance and less-understood nature of late annihilation stages. Even though only weak interactions play a role, we find that resummed real and virtual corrections increase the tree-level overclosure bound by 1 . . . 18%, depending on quartic couplings and mass splittings.

Observing stellar mass and supermassive black holes

NASA Astrophysics Data System (ADS)

Cherepashchuk, A. M.

2016-07-01

During the last 50 years, great progress has been made in observing stellar-mass black holes (BHs) in binary systems and supermassive BHs in galactic nuclei. In 1964, Zeldovich and Salpeter showed that in the case of nonspherical accretion of matter onto a BH, huge energy releases occur. The theory of disk accretion of matter onto BHs was developed in 1972-1973 by Shakura and Sunyaev, Pringle and Rees, and Novikov and Thorne. Up to now, 100 years after the creation of Albert Einstein's General Theory of Relativity, which predicts the existence of BHs, the masses of tens of stellar-mass BHs ( M_BH=(4-35) M_⊙) and many hundreds of supermassive BHs ( M_BH=(10^6-1010) M_⊙) have been determined. A new field of astrophysics, so-called BH demography, is developing. The recent discovery of gravitational waves from BH mergers in binary systems opens a new era in BH studies.

Radial measurements of IMF-sensitive absorption features in two massive ETGs

NASA Astrophysics Data System (ADS)

Vaughan, Sam P.; Davies, Roger L.; Zieleniewski, Simon; Houghton, Ryan C. W.

2018-03-01

We make radial measurements of stellar initial mass function (IMF) sensitive absorption features in the two massive early-type galaxies NGC 1277 and IC 843. Using the Oxford Short Wavelength Integral Field specTrogaph (SWIFT), we obtain resolved measurements of the Na I 0.82 and FeH 0.99 indices, amongst others, finding both galaxies show strong gradients in Na I absorption combined with flat FeH profiles at ˜0.4 Å. We find these measurements may be explained by radial gradients in the IMF, appropriate abundance gradients in [Na/Fe] and [Fe/H], or a combination of the two, and our data are unable to break this degeneracy. We also use full spectral fitting to infer global properties from an integrated spectrum of each object, deriving a unimodal IMF slope consistent with Salpeter in IC 843 (x = 2.27 ± 0.17) but steeper than Salpeter in NGC 1277 (x = 2.69 ± 0.11), despite their similar FeH equivalent widths. Independently, we fit the strength of the FeH feature and compare to the E-MILES and CvD12 stellar population libraries, finding agreement between the models. The IMF values derived in this way are in close agreement with those from spectral fitting in NGC 1277 (x_{CvD}=2.59^{+0.25}_{-0.48}, x_{E-MILES}=2.77± 0.31), but are less consistent in IC 843, with the IMF derived from FeH alone leading to steeper slopes than when fitting the full spectrum (x_{CvD}=2.57^{+0.30}_{-0.41}, x_{E-MILES}=2.72± 0.25). This work highlights the importance of a large wavelength coverage for breaking the degeneracy between abundance and IMF variations, and may bring into doubt the use of the Wing-Ford band as an IMF index if used without other spectral information.

Mass spectrum and decay constants of radially excited vector mesons

NASA Astrophysics Data System (ADS)

Mojica, Fredy F.; Vera, Carlos E.; Rojas, Eduardo; El-Bennich, Bruno

2017-07-01

We calculate the masses and weak decay constants of flavorless and flavored ground and radially excited JP=1- mesons within a Poincaré covariant continuum framework based on the Bethe-Salpeter equation. We use in both the quark's gap equation and the meson bound-state equation an infrared massive and finite interaction in the leading symmetry-preserving truncation. While our numerical results are in rather good agreement with experimental values where they are available, no single parametrization of the QCD inspired interaction reproduces simultaneously the ground and excited mass spectrum, which confirms earlier work on pseudoscalar mesons. This feature being a consequence of the lowest truncation, we pin down the range and strength of the interaction in both cases to identify common qualitative features that may help to tune future interaction models beyond the rainbow-ladder approximation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mor, Rivay; Netzer, Hagai; Trakhtenbrot, Benny

We report new Herschel observations of 25 z {approx_equal} 4.8 extremely luminous optically selected active galactic nuclei (AGNs). Five of the sources have extremely large star-forming (SF) luminosities, L{sub SF}, corresponding to SF rates (SFRs) of 2800-5600 M{sub Sun} yr{sup -1} assuming a Salpeter initial mass function. The remaining sources have only upper limits on their SFRs, but stacking their Herschel images results in a mean SFR of 700 {+-} 150 M{sub Sun} yr{sup -1}. The higher SFRs in our sample are comparable to the highest observed values so far at any redshift. Our sample does not contain obscured AGNs,more » which enables us to investigate several evolutionary scenarios connecting supermassive black holes and SF activity in the early universe. The most probable scenario is that we are witnessing the peak of SF activity in some sources and the beginning of the post-starburst decline in others. We suggest that all 25 sources, which are at their peak AGN activity, are in large mergers. AGN feedback may be responsible for diminishing the SF activity in 20 of them, but is not operating efficiently in 5 others.« less

X (3872 ) as a molecular D D\\xAF * state in the Bethe-Salpeter equation approach

NASA Astrophysics Data System (ADS)

Wang, Zhen-Yang; Qi, Jing-Juan; Guo, Xin-Heng; Wang, Chao

2018-01-01

We discuss the possibility that the X (3872 ) can be a D D¯* molecular bound state in the Bethe-Salpeter equation approach in the ladder and instantaneous approximations. We show that the D D¯ * bound state with quantum numbers JP C=1++ exists. We also calculate the decay width of X (3872 )→γ J /ψ channel and compare our result with those from previous calculations.

EXTREMELY METAL-POOR STARS AND A HIERARCHICAL CHEMICAL EVOLUTION MODEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Komiya, Yutaka

2011-07-20

Early phases of the chemical evolution of the Galaxy and formation history of extremely metal-poor (EMP) stars are investigated using hierarchical galaxy formation models. We build a merger tree of the Galaxy according to the extended Press-Schechter theory. We follow the chemical evolution along the tree and compare the model results to the metallicity distribution function and abundance ratio distribution of the Milky Way halo. We adopt three different initial mass functions (IMFs). In a previous study, we argued that the typical mass, M{sub md}, of EMP stars should be high, M{sub md} {approx} 10 M{sub sun}, based on studiesmore » of binary origin carbon-rich EMP stars. In this study, we show that only the high-mass IMF can explain an observed small number of EMP stars. For relative element abundances, the high-mass IMF and the Salpeter IMF predict similar distributions. We also investigate dependence on nucleosynthetic yields of supernovae (SNe). The theoretical SN yields by Kobayashi et al. and Chieffi and Limongi show reasonable agreement with observations for {alpha}-elements. Our model predicts a significant scatter of element abundances at [Fe/H] < -3. We adopted the stellar yields derived in the work of Francois et al., which produce the best agreement between the observational data and the one-zone chemical evolution model. Their yields well reproduce a trend of the averaged abundances of EMP stars but predict much larger scatter than do the observations. The model with hypernovae predicts Zn abundance, in agreement with the observations, but other models predict lower [Zn/Fe]. Ejecta from the hypernovae with large explosion energy is mixed in large mass and decreases the scatter of the element abundances.« less

Equation for the Nakanishi Weight Function Using the Inverse Stieltjes Transform

NASA Astrophysics Data System (ADS)

Karmanov, V. A.; Carbonell, J.; Frederico, T.

2018-05-01

The bound state Bethe-Salpeter amplitude was expressed by Nakanishi in terms of a smooth weight function g. By using the generalized Stieltjes transform, we derive an integral equation for the Nakanishi function g for a bound state case. It has the standard form g= \\hat{V} g, where \\hat{V} is a two-dimensional integral operator. The prescription for obtaining the kernel V starting with the kernel K of the Bethe-Salpeter equation is given.

Symmetry preserving truncations of the gap and Bethe-Salpeter equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binosi, Daniele; Chang, Lei; Papavassiliou, Joannis

2016-05-01

Ward-Green-Takahashi (WGT) identities play a crucial role in hadron physics, e.g. imposing stringent relationships between the kernels of the one-and two-body problems, which must be preserved in any veracious treatment of mesons as bound states. In this connection, one may view the dressed gluon-quark vertex, Gamma(alpha)(mu), as fundamental. We use a novel representation of Gamma(alpha)(mu), in terms of the gluon-quark scattering matrix, to develop a method capable of elucidating the unique quark-antiquark Bethe-Salpeter kernel, K, that is symmetry consistent with a given quark gap equation. A strength of the scheme is its ability to expose and capitalize on graphic symmetriesmore » within the kernels. This is displayed in an analysis that reveals the origin of H-diagrams in K, which are two-particle-irreducible contributions, generated as two-loop diagrams involving the three-gluon vertex, that cannot be absorbed as a dressing of Gamma(alpha)(mu) in a Bethe-Salpeter kernel nor expressed as a member of the class of crossed-box diagrams. Thus, there are no general circumstances under which the WGT identities essential for a valid description of mesons can be preserved by a Bethe-Salpeter kernel obtained simply by dressing both gluon-quark vertices in a ladderlike truncation; and, moreover, adding any number of similarly dressed crossed-box diagrams cannot improve the situation.« less

GW and Bethe-Salpeter study of small water clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blase, Xavier, E-mail: xavier.blase@neel.cnrs.fr; Boulanger, Paul; Bruneval, Fabien

We study within the GW and Bethe-Salpeter many-body perturbation theories the electronic and optical properties of small (H{sub 2}O){sub n} water clusters (n = 1-6). Comparison with high-level CCSD(T) Coupled-Cluster at the Single Double (Triple) levels and ADC(3) Green’s function third order algebraic diagrammatic construction calculations indicates that the standard non-self-consistent G{sub 0}W{sub 0}@PBE or G{sub 0}W{sub 0}@PBE0 approaches significantly underestimate the ionization energy by about 1.1 eV and 0.5 eV, respectively. Consequently, the related Bethe-Salpeter lowest optical excitations are found to be located much too low in energy when building transitions from a non-self-consistent G{sub 0}W{sub 0} description ofmore » the quasiparticle spectrum. Simple self-consistent schemes, with update of the eigenvalues only, are shown to provide a weak dependence on the Kohn-Sham starting point and a much better agreement with reference calculations. The present findings rationalize the theory to experiment possible discrepancies observed in previous G{sub 0}W{sub 0} and Bethe-Salpeter studies of bulk water. The increase of the optical gap with increasing cluster size is consistent with the evolution from gas to dense ice or water phases and results from an enhanced screening of the electron-hole interaction.« less

Lattice QCD studies of s-wave meson-baryon interactions

NASA Astrophysics Data System (ADS)

Ikeda, Yoichi

2011-10-01

We study the s-wave KN interactions in the isospin I = 0, 1 channels and associated exotic state Θ+ from 2+1 flavor full lattice QCD simulation for relatively heavy quark mass corresponding to mπ = 871 MeV. The s-wave KN potentials are obtained from the Bethe-Salpeter amplitudes. Potentials in both channels reveal short range repulsions: Strength of the repulsion is stronger in the I = 1 potential. The I = 0 potential is found to have attractive well at mid range. The KN scattering phase shifts are calculated and compared with the experimental data.

Origin of the fundamental plane of elliptical galaxies in the Coma cluster without fine-tuning

NASA Astrophysics Data System (ADS)

Chiu, Mu-Chen; Ko, Chung-Ming; Shu, Chenggang

2017-03-01

Thirty years after the discovery of the fundamental plane, explanations of the tilt of the fundamental plane with respect to the virial plane are still in need of fine-tuning. In this paper, we try to explore the origin of this tilt from the perspective of modified Newtonian dynamics (MOND) by applying the 16 Coma galaxies available in J. Thomas et al. [Mon. Not. R. Astron. Soc. 415, 545 (2011), 10.1111/j.1365-2966.2011.18725.x]. Based on the mass models that can reproduce de Vaucouleurs' law closely, we find that the tilt of the traditional fundamental plane is naturally explained by the simple form of the MONDian interpolating function, if we assume a well motivated choice of anisotropic velocity distribution, and adopt the Kroupa or Salpeter stellar mass-to-light ratio. Our analysis does not necessarily rule out a varying stellar mass-to-light ratio.

Massive Stars in the MCs: What They Tell Us about the IMF, Stellar Evolution, and Upper Mass "Cutoffs"

NASA Astrophysics Data System (ADS)

Massey, P.

Massive stars in the Magellanic Clouds provide an instantaneous "snapshot" of star-formation. In this talk I will review what we have learned both about star formation, and stellar evolution. Studies over the past decade have shown that the initial mass function (IMF) is the same for massive stars born in OB associations in the LMC and SMC as in associations and clusters in the Milky Way; the slope of the IMF is essentially Salpeter (Gamma ~ -1.3), despite the factor of 10 difference in metallicity between these systems. Recent work on the R136 cluster (described in Hunter's review talk) suggest that there is no such thing as an upper mass cutoff to the IMF, at least not one that has been found observationally: for the youngest clusters (2 Myr and younger), the mass of the highest mass star present is simply dependent upon how populous the cluster is; i.e., the IMF is truncated by statistics, not physics. There does appear to be a significant population of massive stars that are born in the "field" (not part of a large OB association or cluster); the IMF of these stars is quite a bit steeper (Gamma ~ -4), although stars as massive as those found in associations are also found in the field. The mixed-age population of the MCs as a whole can be used to test stellar evolutionary models; the agreement with the work of the Geneva group is found to be excellent, for stars with masses >25 Mo, although the youngest stars may be missing in the HRD. The discovery that clusters born in associations are quite coeval (Delta tau <1-2 Myr) allows us to use the "turn-off masses" to determine what mass objects become Wolf-Rayet stars of various types, and new results will be reviewed.

Large Binocular Telescope/LUCIFER spectroscopy: kinematics of a compact early-type galaxy at z ≃ 1.4

NASA Astrophysics Data System (ADS)

Longhetti, M.; Saracco, P.; Gargiulo, A.; Tamburri, S.; Lonoce, I.

2014-04-01

We present a high signal-to-noise ratio (S/N > 10) medium-resolution (R = 2000) Large Binocular Telescope/LUCIFER spectrum of the early-type galaxy (ETG) S2F1-142 at z ≃ 1.4. By means of the CaT line at 8662 Å, we measured its redshift z = 1.386 ± 0.001 and we estimated its velocity dispersion σ v=340^{-60}_{+120} km s-1. Its corresponding virial mass is 3.9 × 1011 M⊙, compatible with the stellar mass estimates obtained assuming initial mass functions (IMFs) less dwarf rich than the Salpeter one. S2F1-142 is a compact galaxy with Re = 3.1 ± 0.2 kpc, i.e. an effective radius more than three times smaller than the average Re of ETGs with the same mass in the local Universe. At the same time, we found local and high-redshift galaxies with a similar mass content and similar effective radius confirming that it is fully consistent with the already available measures of Re and σv both in the local and in the distant Universe. Considering the distribution of Re and σv as a function of the stellar mass content of ETGs, both in the local and in the distant Universe, we noticed that the measured velocity dispersions of the more compact galaxies are on average slightly lower than expected on the basis of their compactness and the virial theorem, suggesting that (i) their dark matter content is lower than in the more diffuse galaxies and/or (ii) their luminosity profiles are steeper than in the more diffuse galaxies and/or (iii) their larger compactness is an apparent effect caused by the overestimate of their stellar mass content (due to bottom lighter IMF and/or systematic affecting the stellar mass estimates).

Bethe-Salpeter Eigenvalue Solver Package (BSEPACK) v0.1

DOE Office of Scientific and Technical Information (OSTI.GOV)

SHAO, MEIYEU; YANG, CHAO

2017-04-25

The BSEPACK contains a set of subroutines for solving the Bethe-Salpeter Eigenvalue (BSE) problem. This type of problem arises in this study of optical excitation of nanoscale materials. The BSE problem is a structured non-Hermitian eigenvalue problem. The BSEPACK software can be used to compute all or subset of eigenpairs of a BSE Hamiltonian. It can also be used to compute the optical absorption spectrum without computing BSE eigenvalues and eigenvectors explicitly. The package makes use of the ScaLAPACK, LAPACK and BLAS.

Evolution of Optical Binary Fraction in Sparse Stellar Systems

NASA Astrophysics Data System (ADS)

Li, Zhongmu; Mao, Caiyan

2018-05-01

This work studies the evolution of the fraction of optical binary stars (OBF; not including components such as neutron stars and black holes), which is caused by stellar evolution, and the contributions of various binaries to OBF via the stellar population synthesis technique. It is shown that OBF decreases from 1 to about 0.81 for stellar populations with the Salpeter initial mass function (IMF), and to about 0.85 for the case of the Kroupa IMF, on a timescale of 15 Gyr. This result depends on metallicity, slightly. The contributions of binaries varying with mass ratio, orbital period, separation, spectral types of primary and secondary, contact degree, and pair type to OBF are calculated for stellar populations with different ages and metallicities. The contribution of different kinds of binaries to OBF depends on age and metallicity. The results can be used for estimating the global OBF of star clusters or galaxies from the fraction of a kind of binary. It is also helpful for estimating the primordial and future binary fractions of sparse stellar systems from the present observations. Our results are suitable for studying field stars, open clusters, and the outer part of globular clusters, because the OBF of such objects is affected by dynamical processes, relatively slightly, but they can also be used for giving some limits for other populations.

Potential description of the charmonium from lattice QCD

NASA Astrophysics Data System (ADS)

Kawanai, Taichi; Sasaki, Shoichi

2016-01-01

We present spin-independent and spin-spin interquark potentials for charmonium states, that are calculated using a relativistic heavy quark action for charm quarks on the PACS-CS gauge configurations generated with the Iwasaki gauge action and 2+1 flavors of Wilson clover quark. The interquark potential with finite quark masses is defined through the equal-time Bethe-Salpeter amplitude. The light and strange quark masses are close to the physical point where the pion mass corresponds to Mπ ≈ 156(7) MeV, and charm quark mass is tuned to reproduce the experimental values of ηc and J/ψ states. Our simulations are performed with a lattice cutoff of a-1 ≈ 2.2 GeV and a spatial volume of (3 fm)3. We solve the nonrelativistic Schrödinger equation with resulting charmonium potentials as theoretical inputs. The resultant charmonium spectrum below the open charm threshold shows a fairly good agreement with experimental data of well-established charmonium states.

The binary Feige 24 - The mass, radius, and gravitational redshift of the DA white dwarf

NASA Technical Reports Server (NTRS)

Vennes, Stephane; Shipman, Harry L.; Thorstensen, John R.; Thejll, Peter

1991-01-01

Observations are reported which refine the binary ephemeris of the Feige 24 system, which contains a peculiar hot DA white dwarf and an M dwarf with an atmosphere illuminated by extreme ultraviolet radiation from the white dwarf. With the new ephemeris and a set of IUE high-dispersion spectra, showing phase-dependent redshifted C IV, N V, and Si IV resonance lines, the orbital velocity, and hence the mass (0.54 + or - 0.20 solar masses), and the gravitational redshift of the white dwarf (14.1 + or - 5.2 km/s) are determined independently. It is shown that the measured Einstein redshift is consistent with an estimated radius for the white dwarf obtained from a model atmosphere solid angle and a parallax measurement. This radius is twice the Hamada-Salpeter radius for the given mass and offers a prospect to investigate the presence of a massive hydrogen envelope in that white dwarf star.

Biases on Initial Mass Function Determinations. II. Real Multiple Systems and Chance Superpositions

NASA Astrophysics Data System (ADS)

Maíz Apellániz, J.

2008-04-01

When calculating stellar initial mass functions (IMFs) for young clusters, one has to take into account that (1) most massive stars are born in multiple systems, (2) most IMFs are derived from data that cannot resolve such systems, and (3) multiple chance superpositions between members are expected to happen if the cluster is too distant. In this article I use numerical experiments to model the consequences of those phenomena on the observed color-magnitude diagrams and the IMFs derived from them. Real multiple systems affect the observed or apparent massive-star MF slope little but can create a significant population of apparently ultramassive stars. Chance superpositions produce only small biases when the number of superimposed stars is low but, once a certain number threshold is reached, they can affect both the observed slope and the apparent stellar upper mass limit. I apply these experiments to two well known massive young clusters in the Local Group, NGC 3603 and R136. In both cases I show that the observed population of stars with masses above 120 M⊙ can be explained by the effects of unresolved objects, mostly real multiple systems for NGC 3603 and a combination of real and chance-alignment multiple systems for R136. Therefore, the case for the reality of a stellar upper mass limit at solar or near-solar metallicities is strengthened, with a possible value even lower than 150 M⊙. An IMF slope somewhat flatter than Salpeter or Kroupa with γ between -1.6 and -2.0 is derived for the central region of NGC 3603, with a significant contribution to the uncertainty arising from the imprecise knowledge of the distance to the cluster. The IMF at the very center of R136 cannot be measured with the currently available data but the situation could change with new HST observations. This article is partially based on observations made with the NASA/ESA Hubble Space Telescope (HST), some of them associated with GO program 10602 and the rest gathered from the archive, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

KINETyS II: Constraints on spatial variations of the stellar initial mass function from K-band spectroscopy

NASA Astrophysics Data System (ADS)

Alton, P. D.; Smith, R. J.; Lucey, J. R.

2018-05-01

We investigate the spatially resolved stellar populations of a sample of seven nearby massive Early-type galaxies (ETGs), using optical and near infrared data, including K-band spectroscopy. This data offers good prospects for mitigating the uncertainties inherent in stellar population modelling by making a wide variety of strong spectroscopic features available. We report new VLT-KMOS measurements of the average empirical radial gradients out to the effective radius in the strengths of the Ca I 1.98 μm and 2.26 μm features, the Na I 2.21 μm line, and the CO 2.30 μm bandhead. Following previous work, which has indicated an excess of dwarf stars in the cores of massive ETGs, we pay specific attention to radial variations in the stellar initial mass function (IMF) as well as modelling the chemical abundance patterns and stellar population ages in our sample. Using state-of-the-art stellar population models we infer an [Fe/H] gradient of -0.16±0.05 per dex in fractional radius and an average [Na/Fe] gradient of -0.35±0.09. We find a large but radially-constant enhancement to [Mg/Fe] of ˜ 0.4 and a much lower [Ca/Fe] enhancement of ˜ 0.1. Finally, we find no significant IMF radial gradient in our sample on average and find that most galaxies in our sample are consistent with having a Milky Way-like IMF, or at most a modestly bottom heavy IMF (e.g. less dwarf enriched than a single power law IMF with the Salpeter slope).

Interquark potential with finite quark mass from lattice QCD.

PubMed

Kawanai, Taichi; Sasaki, Shoichi

2011-08-26

We present an investigation of the interquark potential determined from the q ̄q Bethe-Salpeter (BS) amplitude for heavy quarkonia in lattice QCD. The q ̄q potential at finite quark mass m(q) can be calculated from the equal-time and Coulomb gauge BS amplitude through the effective Schrödinger equation. The definition of the potential itself requires information about a kinetic mass of the quark. We then propose a self-consistent determination of the quark kinetic mass on the same footing. To verify the proposed method, we perform quenched lattice QCD simulations with a relativistic heavy-quark action at a lattice cutoff of 1/a≈2.1  GeV in a range 1.0≤m(q)≤3.6 GeV. Our numerical results show that the q ̄q potential in the m(q)→∞ limit is fairly consistent with the conventional one obtained from Wilson loops. The quark-mass dependence of the q ̄q potential and the spin-spin potential are also examined. © 2011 American Physical Society

The Puzzlingly Small Ca II Triplet Absorption in Elliptical Galaxies

NASA Astrophysics Data System (ADS)

Saglia, R. P.; Maraston, Claudia; Thomas, Daniel; Bender, Ralf; Colless, Matthew

2002-11-01

We measure the central values (within Re/8) of the Ca II triplet line indices CaT* and CaT and the Paschen index PaT at 8600 Å for a 93% complete sample of 75 nearby early-type galaxies with BT<12 mag and Vgal<2490 km s-1. We find that the values of CaT* are constant to within 5% over the range of central velocity dispersions 100 km s-1<=σ<=340 km s-1, while the PaT (and CaT) values are mildly anticorrelated with σ. Using simple and composite stellar population models, we show the following: (1) The measured CaT* and CaT are lower than expected from simple stellar population (SSP) models with Salpeter initial mass functions (IMFs) and with metallicities and ages derived from optical Lick (Fe, Mg, and Hβ) indices. Uncertainties in the calibration, the fitting functions, and the SSP modeling taken separately cannot explain the discrepancy. On average, the observed PaT values are within the range allowed by the models and the large uncertainties in the fitting functions. (2) The steepening of the IMF at low masses required to lower the CaT* and CaT indices to the observed values is incompatible with the measured FeH index at 9916 Å and the dynamical mass-to-light ratios of elliptical galaxies. (3) Composite stellar populations with a low-metallicity component reduce the disagreement, but rather artificial metallicity distributions are needed. Another explanation may be that calcium is indeed underabundant in elliptical galaxies.

Asymptotic behavior of Nambu-Bethe-Salpeter wave functions for multiparticles in quantum field theories

NASA Astrophysics Data System (ADS)

Aoki, Sinya; Ishii, Noriyoshi; Doi, Takumi; Ikeda, Yoichi; Inoue, Takashi

2013-07-01

We derive asymptotic behaviors of the Nambu-Bethe-Salpeter (NBS) wave function at large space separations for systems with more than two particles in quantum field theories. To deal with n particles in the center-of-mass frame coherently, we introduce the Jacobi coordinates of n particles and then combine their 3(n-1) coordinates into the one spherical coordinate in D=3(n-1) dimensions. We parametrize the on-shell T matrix for n scalar particles at low energy using the unitarity constraint of the S matrix. We then express asymptotic behaviors of the NBS wave function for n particles at low energy in terms of parameters of the T matrix and show that the NBS wave function carries information of the T matrix such as phase shifts and mixing angles of the n-particle system in its own asymptotic behavior, so that the NBS wave function can be considered as the scattering wave of n particles in quantum mechanics. This property is one of the essential ingredients of the HAL QCD scheme to define “potential” from the NBS wave function in quantum field theories such as QCD. Our results, together with an extension to systems with spin 1/2 particles, justify the HAL QCD’s definition of potentials for three or more nucleons (or baryons) in terms of the NBS wave functions.

Bound H dibaryon in flavor SU(3) limit of lattice QCD.

PubMed

Inoue, Takashi; Ishii, Noriyoshi; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji

2011-04-22

The flavor-singlet H dibaryon, which has strangeness -2 and baryon number 2, is studied by the approach recently developed for the baryon-baryon interactions in lattice QCD. The flavor-singlet central potential is derived from the spatial and imaginary-time dependence of the Nambu-Bethe-Salpeter wave function measured in N(f)=3 full QCD simulations with the lattice size of L≃2,3,4  fm. The potential is found to be insensitive to the volume, and it leads to a bound H dibaryon with the binding energy of 30-40 MeV for the pseudoscalar meson mass of 673-1015 MeV.

Coupled-channel approach to strangeness S = -2 baryon-bayron interactions in lattice QCD

NASA Astrophysics Data System (ADS)

Sasaki, Kenji; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Ishii, Noriyoshi; Murano, Keiko

2015-11-01

Baryon-baryon interactions with strangeness S=-2 with flavor SU(3) breaking are calculated for the first time by using the HAL QCD method extended to the coupled-channel system in lattice QCD. The potential matrices are extracted from the Nambu-Bethe-Salpeter wave functions obtained by the 2+1-flavor gauge configurations of the CP-PACS/JLQCD Collaborations with a physical volume of (1.93 fm)^3 and with m_{π }/m_K=0.96, 0.90, 0.86. The spatial structure and the quark mass dependence of the potential matrix in the baryon basis and in the SU(3) basis are investigated.

Is the Bethe–Salpeter Formalism Accurate for Excitation Energies? Comparisons with TD-DFT, CASPT2, and EOM-CCSD

PubMed Central

2017-01-01

Developing ab initio approaches able to provide accurate excited-state energies at a reasonable computational cost is one of the biggest challenges in theoretical chemistry. In that framework, the Bethe–Salpeter equation approach, combined with the GW exchange-correlation self-energy, which maintains the same scaling with system size as TD-DFT, has recently been the focus of a rapidly increasing number of applications in molecular chemistry. Using a recently proposed set encompassing excitation energies of many kinds [J. Phys. Chem. Lett.2016, 7, 586–591], we investigate here the performances of BSE/GW. We compare these results to CASPT2, EOM-CCSD, and TD-DFT data and show that BSE/GW provides an accuracy comparable to the two wave function methods. It is particularly remarkable that the BSE/GW is equally efficient for valence, Rydberg, and charge-transfer excitations. In contrast, it provides a poor description of triplet excited states, for which EOM-CCSD and CASPT2 clearly outperform BSE/GW. This contribution therefore supports the use of the Bethe–Salpeter approach for spin-conserving transitions. PMID:28301726

A structure preserving Lanczos algorithm for computing the optical absorption spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Meiyue; Jornada, Felipe H. da; Lin, Lin

2016-11-16

We present a new structure preserving Lanczos algorithm for approximating the optical absorption spectrum in the context of solving full Bethe-Salpeter equation without Tamm-Dancoff approximation. The new algorithm is based on a structure preserving Lanczos procedure, which exploits the special block structure of Bethe-Salpeter Hamiltonian matrices. A recently developed technique of generalized averaged Gauss quadrature is incorporated to accelerate the convergence. We also establish the connection between our structure preserving Lanczos procedure with several existing Lanczos procedures developed in different contexts. Numerical examples are presented to demonstrate the effectiveness of our Lanczos algorithm.

Omega-Omega interaction from 2+1-flavor lattice quantum chromodynamics

NASA Astrophysics Data System (ADS)

Yamada, Masanori; Sasaki, Kenji; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Ishii, Noriyoshi; Murano, Keiko; Nemura, Hidekatsu

2015-07-01

We investigate the interaction between Ω baryons in the {^{1}S}_0 channel from 2{+ }1-flavor lattice quantum chromodynamics (QCD) simulations. On the basis of the HAL QCD method, the Ω Ω potential is extracted from the Nambu-Bethe-Salpeter wave function calculated on the lattice by using the PACS-CS gauge configurations with a lattice spacing of a˜eq 0.09fm, a lattice volume of L˜eq 2.9fm, and quark masses corresponding to m_π ˜eq 700MeV and m_Ω ˜eq 1970MeV. The Ω Ω potential has a repulsive core at short distances and an attractive well at intermediate distances. Accordingly, the phase shift obtained from the potential shows moderate attraction at low energies. Our data indicate that the Ω Ω system with the present quark masses may appear close to the unitary limit where the scattering length diverges.

Dark matter and MOND dynamical models of the massive spiral galaxy NGC 2841

NASA Astrophysics Data System (ADS)

Samurović, S.; Vudragović, A.; Jovanović, M.

2015-08-01

We study dynamical models of the massive spiral galaxy NGC 2841 using both the Newtonian models with Navarro-Frenk-White (NFW) and isothermal dark haloes, as well as various MOND (MOdified Newtonian Dynamics) models. We use the observations coming from several publicly available data bases: we use radio data, near-infrared photometry as well as spectroscopic observations. In our models, we find that both tested Newtonian dark matter approaches can successfully fit the observed rotational curve of NGC 2841. The three tested MOND models (standard, simple and, for the first time applied to another spiral galaxy than the Milky Way, Bekenstein's toy model) provide fits of the observed rotational curve with various degrees of success: the best result was obtained with the standard MOND model. For both approaches, Newtonian and MOND, the values of the mass-to-light ratios of the bulge are consistent with the predictions from the stellar population synthesis (SPS) based on the Salpeter initial mass function (IMF). Also, for Newtonian and simple and standard MOND models, the estimated stellar mass-to-light ratios of the disc agree with the predictions from the SPS models based on the Kroupa IMF, whereas the toy MOND model provides too low a value of the stellar mass-to-light ratio, incompatible with the predictions of the tested SPS models. In all our MOND models, we vary the distance to NGC 2841, and our best-fitting standard and toy models use the values higher than the Cepheid-based distance to the galaxy NGC 2841, and the best-fitting simple MOND model is based on the lower value of the distance. The best-fitting NFW model is inconsistent with the predictions of the Λ cold dark matter cosmology, because the inferred concentration index is too high for the established virial mass.

Discovery of a Strong Lensing Galaxy Embedded in a Cluster at z = 1.62

NASA Astrophysics Data System (ADS)

Wong, Kenneth C.; Tran, Kim-Vy H.; Suyu, Sherry H.; Momcheva, Ivelina G.; Brammer, Gabriel B.; Brodwin, Mark; Gonzalez, Anthony H.; Halkola, Aleksi; Kacprzak, Glenn G.; Koekemoer, Anton M.; Papovich, Casey J.; Rudnick, Gregory H.

2014-07-01

We identify a strong lensing galaxy in the cluster IRC 0218 (also known as XMM-LSS J02182-05102) that is spectroscopically confirmed to be at z = 1.62, making it the highest-redshift strong lens galaxy known. The lens is one of the two brightest cluster galaxies and lenses a background source galaxy into an arc and a counterimage. With Hubble Space Telescope (HST) grism and Keck/LRIS spectroscopy, we measure the source redshift to be z S = 2.26. Using HST imaging in ACS/F475W, ACS/F814W, WFC3/F125W, and WFC3/F160W, we model the lens mass distribution with an elliptical power-law profile and account for the effects of the cluster halo and nearby galaxies. The Einstein radius is θ _E=0.38+0.02-0.01 arcsec (3.2-0.1+0.2 kpc) and the total enclosed mass is M _tot (< θ _E)=1.8+0.2-0.1× 1011 M⊙ . We estimate that the cluster environment contributes ~10% of this total mass. Assuming a Chabrier initial mass function (IMF), the dark matter fraction within θE is f_DMChab = 0.3-0.3+0.1, while a Salpeter IMF is marginally inconsistent with the enclosed mass (f_DMSalp = -0.3-0.5+0.2). The total magnification of the source is μ _tot=2.1-0.3+0.4. The source has at least one bright compact region offset from the source center. Emission from Lyα and [O III] are likely to probe different regions in the source. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program No. 12590.

Towards a model of pion generalized parton distributions from Dyson-Schwinger equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moutarde, H.

2015-04-10

We compute the pion quark Generalized Parton Distribution H{sup q} and Double Distributions F{sup q} and G{sup q} in a coupled Bethe-Salpeter and Dyson-Schwinger approach. We use simple algebraic expressions inspired by the numerical resolution of Dyson-Schwinger and Bethe-Salpeter equations. We explicitly check the support and polynomiality properties, and the behavior under charge conjugation or time invariance of our model. We derive analytic expressions for the pion Double Distributions and Generalized Parton Distribution at vanishing pion momentum transfer at a low scale. Our model compares very well to experimental pion form factor or parton distribution function data.

Regge trajectories for heavy quarkonia from the quadratic form of the spinless Salpeter-type equation

NASA Astrophysics Data System (ADS)

Chen, Jiao-Kai

2018-03-01

In this paper, we present one new form of the Regge trajectories for heavy quarkonia which is obtained from the quadratic form of the spinless Salpeter-type equation (QSSE) by employing the Bohr-Sommerfeld quantization approach. The obtained Regge trajectories take the parameterized form M^2={β }({c_l}l+{π }n_r+c_0)^{2/3}+c_1, which are different from the present Regge trajectories. Then we apply the obtained Regge trajectories to fit the spectra of charmonia and bottomonia. The fitted Regge trajectories are in good agreement with the experimental data and the theoretical predictions.

Efficient implementation of core-excitation Bethe-Salpeter equation calculations

NASA Astrophysics Data System (ADS)

Gilmore, K.; Vinson, John; Shirley, E. L.; Prendergast, D.; Pemmaraju, C. D.; Kas, J. J.; Vila, F. D.; Rehr, J. J.

2015-12-01

We present an efficient implementation of the Bethe-Salpeter equation (BSE) method for obtaining core-level spectra including X-ray absorption (XAS), X-ray emission (XES), and both resonant and non-resonant inelastic X-ray scattering spectra (N/RIXS). Calculations are based on density functional theory (DFT) electronic structures generated either by ABINIT or QuantumESPRESSO, both plane-wave basis, pseudopotential codes. This electronic structure is improved through the inclusion of a GW self energy. The projector augmented wave technique is used to evaluate transition matrix elements between core-level and band states. Final two-particle scattering states are obtained with the NIST core-level BSE solver (NBSE). We have previously reported this implementation, which we refer to as OCEAN (Obtaining Core Excitations from Ab initio electronic structure and NBSE) (Vinson et al., 2011). Here, we present additional efficiencies that enable us to evaluate spectra for systems ten times larger than previously possible; containing up to a few thousand electrons. These improvements include the implementation of optimal basis functions that reduce the cost of the initial DFT calculations, more complete parallelization of the screening calculation and of the action of the BSE Hamiltonian, and various memory reductions. Scaling is demonstrated on supercells of SrTiO3 and example spectra for the organic light emitting molecule Tris-(8-hydroxyquinoline)aluminum (Alq3) are presented. The ability to perform large-scale spectral calculations is particularly advantageous for investigating dilute or non-periodic systems such as doped materials, amorphous systems, or complex nano-structures.

Towards a comprehensive knowledge of the open cluster Haffner 9

NASA Astrophysics Data System (ADS)

Piatti, Andrés E.

2017-03-01

We turn our attention to Haffner 9, a Milky Way open cluster whose previous fundamental parameter estimates are far from being in agreement. In order to provide with accurate estimates, we present high-quality Washington CT1 and Johnson BVI photometry of the cluster field. We put particular care in statistically cleaning the colour-magnitude diagrams (CMDs) from field star contamination, which was found a common source in previous works for the discordant fundamental parameter estimates. The resulting cluster CMD fiducial features were confirmed from a proper motion membership analysis. Haffner 9 is a moderately young object (age ∼350 Myr), placed in the Perseus arm - at a heliocentric distance of ∼3.2 kpc - , with a lower limit for its present mass of ∼160 M⊙ and of nearly metal solar content. The combination of the cluster structural and fundamental parameters suggest that it is in an advanced stage of internal dynamical evolution, possibly in the phase typical of those with mass segregation in their core regions. However, the cluster still keeps its mass function close to that of the Salpeter's law.

Testing modified gravity at large distances with the HI Nearby Galaxy Survey's rotation curves

NASA Astrophysics Data System (ADS)

Mastache, Jorge; Cervantes-Cota, Jorge L.; de la Macorra, Axel

2013-03-01

Recently a new—quantum motivated—theory of gravity has been proposed that modifies the standard Newtonian potential at large distances when spherical symmetry is considered. Accordingly, Newtonian gravity is altered by adding an extra Rindler acceleration term that has to be phenomenologically determined. Here we consider a standard and a power-law generalization of the Rindler modified Newtonian potential. The new terms in the gravitational potential are hypothesized to play the role of dark matter in galaxies. Our galactic model includes the mass of the integrated gas, and stars for which we consider three stellar mass functions (Kroupa, diet-Salpeter, and free mass model). We test this idea by fitting rotation curves of seventeen low surface brightness galaxies from the HI Nearby Galaxy Survey (THINGS). We find that the Rindler parameters do not perform a suitable fit to the rotation curves in comparison to standard dark matter profiles (Navarro-Frenk-White and Burkert) and, in addition, the computed parameters of the Rindler gravity show a high spread, posing the model as a nonacceptable alternative to dark matter.

Perspectives: Black Holes

NASA Technical Reports Server (NTRS)

Dolan, Joseph F.; Fisher, Richard R. (Technical Monitor)

2001-01-01

When asked to discuss Cyg XR-1, E. E. Salpeter once concluded, 'A black hole in Cyg X(R)-1 is the most conservative hypothesis.' Recent observations now make it likely that a black hole in Cyg XR-1 is the only hypothesis tenable. Chandrasekhar first showed that compact stars - those with the inward force of gravity on their outer layers balanced by the pressure generated by the Pauli exclusion principle acting on its electrons (in white dwarfs) or nucleons (in neutron stars) - have a maximum mass. Equilibrium is achieved at a minimum of the total energy of the star, which is the sum of the positive Fermi energy and the negative gravitational energy. The maximum mass attainable in equilibrium is found by setting E = 0: M(max) = 1.5 M(Sun). If the mass of the star is larger than this, then E can be decreased without bound by decreasing the star's radius and increasing its (negative) gravitational energy. No equilibrium value of the radius exist, and general relativity predicts that gravitational collapse to a point occurs. This point singularity is a black hole.

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

NASA Astrophysics Data System (ADS)

Piskunov, A. E.; Belikov, A. N.; Kharchenko, N. V.; Sagar, R.; Subramaniam, A.

2004-04-01

We construct the observed luminosity functions of the remote young open clusters NGC 2383, 2384, 4103, 4755, 7510 and Hogg 15 from CCD observations of them. The observed LFs are corrected for field star contamination determined with the help of a Galactic star count model. In the case of Hogg 15 and NGC 2383 we also consider the additional contamination from neighbouring clusters NGC 4609 and 2384, respectively. These corrections provide a realistic pattern of cluster LF in the vicinity of the main-sequence (MS) turn-on point and at fainter magnitudes reveal the so-called H-feature arising as a result of the transition of the pre-MS phase to the MS, which is dependent on the cluster age. The theoretical LFs are constructed representing a cluster population model with continuous star formation for a short time-scale and a power-law initial mass function (IMF), and these are fitted to the observed LF. As a result, we are able to determine for each cluster a set of parameters describing the cluster population (the age, duration of star formation, IMF slope and percentage of field star contamination). It is found that in spite of the non-monotonic behaviour of observed LFs, cluster IMFs can be described as power-law functions with slopes similar to Salpeter's value. The present main-sequence turn-on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to the turn-off region of the upper main sequences.

Cas A and the Crab were not stellar binaries at death

NASA Astrophysics Data System (ADS)

Kochanek, C. S.

2018-01-01

The majority of massive stars are in binaries, which implies that many core collapse supernovae should be binaries at the time of the explosion. Here we show that the three most recent, local (visual) SNe (the Crab, Cas A and SN 1987A) were not stellar binaries at death, with limits on the initial mass ratios of q = M2/M1 ≲ 0.1. No quantitative limits have previously been set for Cas A and the Crab, while for SN 1987A we merely updated existing limits in view of new estimates of the dust content. The lack of stellar companions to these three ccSNe implies a 90 per cent confidence upper limit on the q ≳ 0.1 binary fraction at death of fb < 44 per cent. In a passively evolving binary model (meaning no binary interactions), with a flat mass ratio distribution and a Salpeter IMF, the resulting 90 per cent confidence upper limit on the initial binary fraction of F < 63 per cent is in tension with observed massive binary statistics. Allowing a significant fraction fM ≃ 25 per cent of stellar binaries to merge reduces the tension, with F < 63({1-f}M)^{-1}{ per cent} ˜eq 81{ per cent}, but allowing for the significant fraction in higher order systems (triples, etc.) reintroduces the tension. That Cas A was not a stellar binary at death also shows that a surviving massive binary companion at the time of the explosion is not necessary for producing a Type IIb SNe. Much larger surveys for binary companions to Galactic SNe will become feasible with the release of the full Gaia proper motion and parallax catalogues providing a powerful probe of the statistics of such binaries and their role in massive star evolution, neutron star velocity distributions and runaway stars.

Can comet clouds around neutron stars explain gamma-ray bursts?

NASA Technical Reports Server (NTRS)

Tremaine, S.; Zytkow, A. N.

1986-01-01

The proposal of Harwit and Salpeter (1973) that gamma-ray bursts are due to impacts of comets onto neutron stars is examined further. It is assumed that most stars are formed with comet clouds similar to the Oort comet cloud which surrounds the sun, and it is suggested that there are at least four mechanisms by wich neutron stars may be formed while retaining their comet clouds: a spherically symmetric supernova explosion in an isolated star, accretion-induced collapse of a white dwarf in a cataclysmic variable with a very low mass secondary, accretion-induced collapse of a white dwarf in a wide binary with a low-mass giant companion, and coalescence of a close binary composed of two white dwarfs. Estimates are given of the cometary impact rates for such systems. It is suggested that if the wide binary scenario is correct, optical bursts may arise from the impact of comets onto the white dwarf remnant of the giant companion.

White dwarfs and revelations

NASA Astrophysics Data System (ADS)

Saltas, Ippocratis D.; Sawicki, Ignacy; Lopes, Ilidio

2018-05-01

We use the most recent, complete and independent measurements of masses and radii of white dwarfs in binaries to bound the class of non-trivial modified gravity theories, viable after GW170817/GRB170817, using its effect on the mass-radius relation of the stars. We show that the uncertainty in the latest data is sufficiently small that residual evolutionary effects, most notably the effect of core composition, finite temperature and envelope structure, must now accounted for if correct conclusions about the nature of gravity are to be made. We model corrections resulting from finite temperature and envelopes to a base Hamada-Salpeter cold equation of state and derive consistent bounds on the possible modifications of gravity in the stars' interiors, finding that the parameter quantifying the strength of the modification Y< 0.14 at 95% confidence, an improvement of a factor of three with respect to previous bounds. Finally, our analysis reveals some fundamental degeneracies between the theory of gravity and the precise chemical makeup of white dwarfs.

Origins of Singlet Fission in Solid Pentacene from an ab initio Green's Function Approach

NASA Astrophysics Data System (ADS)

Refaely-Abramson, Sivan; da Jornada, Felipe H.; Louie, Steven G.; Neaton, Jeffrey B.

2017-12-01

We develop a new first-principles approach to predict and understand rates of singlet fission with an ab initio Green's-function formalism based on many-body perturbation theory. Starting with singlet and triplet excitons computed from a G W plus Bethe-Salpeter equation approach, we calculate the exciton-biexciton coupling to lowest order in the Coulomb interaction, assuming a final state consisting of two noninteracting spin-correlated triplets with finite center-of-mass momentum. For crystalline pentacene, symmetries dictate that the only purely Coulombic fission decay process from a bright singlet state requires a final state consisting of two inequivalent nearly degenerate triplets of nonzero, equal and opposite, center-of-mass momenta. For such a process, we predict a singlet lifetime of 30-70 fs, in very good agreement with experimental data, indicating that this process can dominate singlet fission in crystalline pentacene. Our approach is general and provides a framework for predicting and understanding multiexciton interactions in solids.

Baryon interactions from lattice QCD with physical masses —S = -3 sector: Ξ∑ and Ξ∑-Λ∑—

NASA Astrophysics Data System (ADS)

Ishii, Noriyoshi; Aoki, Sinya; Doi, Takumi; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Iritani, Takumi; Miyamoto, Takaya; Nemura, Hidekatsu; Sasaki, Kenji

2018-03-01

Hyperon-nucleon and hyperon-hyperon interactions are important in studying the properties of hypernuclei in hypernuclear physics. However, unlike the nucleons which are quite stable, hyperons are unstable so that the direct scattering experiments are difficult, which leads to the large uncertainty in the phenomenological determination of hyperon potentials. In this talk, we use the gauge configurations generated at the (almost) physical point (mπ = 146 MeV) on a huge spatial volume (8:1fm)4 to present our latest result on the hyperon-hyperon potentials in S = -3 sector (Ξ∑ single channel and Ξ∑- ΞΛ; coupled channel) from the Nambu-Bethe-Salpeter wave functions based on the HAL QCD method with improved statistics.

Three-body spectrum in a finite volume: The role of cubic symmetry

DOE PAGES

Doring, M.; Hammer, H. -W.; Mai, M.; ...

2018-06-15

The three-particle quantization condition is partially diagonalized in the center-of-mass frame by using cubic symmetry on the lattice. To this end, instead of spherical harmonics, the kernel of the Bethe-Salpeter equation for particle-dimer scattering is expanded in the basis functions of different irreducible representations of the octahedral group. Such a projection is of particular importance for the three-body problem in the finite volume due to the occurrence of three-body singularities above breakup. Additionally, we study the numerical solution and properties of such a projected quantization condition in a simple model. It is shown that, for large volumes, these solutions allowmore » for an instructive interpretation of the energy eigenvalues in terms of bound and scattering states.« less

Three-body spectrum in a finite volume: The role of cubic symmetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doring, M.; Hammer, H. -W.; Mai, M.

The three-particle quantization condition is partially diagonalized in the center-of-mass frame by using cubic symmetry on the lattice. To this end, instead of spherical harmonics, the kernel of the Bethe-Salpeter equation for particle-dimer scattering is expanded in the basis functions of different irreducible representations of the octahedral group. Such a projection is of particular importance for the three-body problem in the finite volume due to the occurrence of three-body singularities above breakup. Additionally, we study the numerical solution and properties of such a projected quantization condition in a simple model. It is shown that, for large volumes, these solutions allowmore » for an instructive interpretation of the energy eigenvalues in terms of bound and scattering states.« less

Kaon-Nucleon potential from lattice QCD

NASA Astrophysics Data System (ADS)

Ikeda, Y.; Aoki, S.; Doi, T.; Hatsuda, T.; Inoue, T.; Ishii, N.; Murano, K.; Nemura, H.; Sasaki, K.

2010-04-01

We study the K N interactions in the I(Jπ) = 0(1/2-) and 1(1/2-) channels and associated exotic state Θ+ from 2+1 flavor full lattice QCD simulation for relatively heavy quark mass corresponding to mπ = 871 MeV. The s-wave K N potentials are obtained from the Bethe-Salpeter wave function by using the method recently developed by HAL QCD (Hadrons to Atomic nuclei from Lattice QCD) Collaboration. Potentials in both channels reveal short range repulsions: Strength of the repulsion is stronger in the I = 1 potential, which is consistent with the prediction of the Tomozawa-Weinberg term. The I = 0 potential is found to have attractive well at mid range. From these potentials, the K N scattering phase shifts are calculated and compared with the experimental data.

Features and flaws of a contact interaction treatment of the kaon

NASA Astrophysics Data System (ADS)

Chen, Chen; Chang, Lei; Roberts, Craig D.; Schmidt, Sebastian M.; Wan, Shaolong; Wilson, David J.

2013-04-01

Elastic and semileptonic transition form factors for the kaon and pion are calculated using the leading order in a global-symmetry-preserving truncation of the Dyson-Schwinger equations and a momentum-independent form for the associated kernels in the gap and Bethe-Salpeter equations. The computed form factors are compared both with those obtained using the same truncation but an interaction that preserves the one-loop renormalization-group behavior of QCD and with data. The comparisons show that in connection with observables revealed by probes with |Q2|≲M2, where M≈0.4GeV is an infrared value of the dressed-quark mass, results obtained using a symmetry-preserving regularization of the contact interaction are not realistically distinguishable from those produced by more sophisticated kernels, and available data on kaon form factors do not extend into the domain whereupon one could distinguish among the interactions. The situation differs if one includes the domain Q2>M2. Thereupon, a fully consistent treatment of the contact interaction produces form factors that are typically harder than those obtained with QCD renormalization-group-improved kernels. Among other things also described are a Ward identity for the inhomogeneous scalar vertex, similarity between the charge distribution of a dressed u quark in the K+ and that of the dressed u quark in the π+, and reflections upon the point whereat one might begin to see perturbative behavior in the pion form factor. Interpolations of the form factors are provided, which should assist in working to chart the interaction between light quarks by explicating the impact on hadron properties of differing assumptions about the behavior of the Bethe-Salpeter kernel.

CLASH: Extending galaxy strong lensing to small physical scales with distant sources highly magnified by galaxy cluster members

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grillo, C.; Christensen, L.; Gobat, R.

2014-05-01

We present a complex strong lensing system in which a double source is imaged five times by two early-type galaxies. We take advantage in this target of the extraordinary multi-band photometric data set obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program, complemented by the spectroscopic measurements of the VLT/VIMOS and FORS2 follow-up campaign. We use a photometric redshift value of 3.7 for the source and confirm spectroscopically the membership of the two lenses to the galaxy cluster MACS J1206.2–0847 at redshift 0.44. We exploit the excellent angular resolution of the HST/ACS images to modelmore » the two lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersion values of 97 ± 3 and 240 ± 6 km s{sup –1}. Interestingly, the total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, which is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to our best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of approximately (1.0 ± 0.5) × 10{sup 9} M {sub ☉} (assuming a Salpeter stellar initial mass function). By combining the total and luminous mass estimates of the two lenses, we measure luminous over total mass fractions projected within the effective radii of 0.51 ± 0.21 and 0.80 ± 0.32. Remarkably, with these lenses we can extend the analysis of the mass properties of lens early-type galaxies by factors that are approximately two and three times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of our lenses with those of astrophysical objects with different physical scales, like massive early-type galaxies and dwarf spheroidals, reveals the potential of studies of this kind for improving our knowledge about the internal structure of galaxies. These studies, made possible thanks to the CLASH survey, will allow us to go beyond the current limits posed by the available lens samples in the field.« less

Symmetry-preserving contact interaction model for heavy-light mesons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serna, F. E.; Brito, M. A.; Krein, G.

2016-01-22

We use a symmetry-preserving regularization method of ultraviolet divergences in a vector-vector contact interaction model for low-energy QCD. The contact interaction is a representation of nonperturbative kernels used Dyson-Schwinger and Bethe-Salpeter equations. The regularization method is based on a subtraction scheme that avoids standard steps in the evaluation of divergent integrals that invariably lead to symmetry violation. Aiming at the study of heavy-light mesons, we have implemented the method to the pseudoscalar π and K mesons. We have solved the Dyson-Schwinger equation for the u, d and s quark propagators, and obtained the bound-state Bethe-Salpeter amplitudes in a way thatmore » the Ward-Green-Takahashi identities reflecting global symmetries of the model are satisfied for arbitrary routing of the momenta running in loop integrals.« less

Decay width of hadronic molecule structure for quarks

NASA Astrophysics Data System (ADS)

Chen, Xiaozhao; Lü, Xiaofu

2018-06-01

Based on the general form of the Bethe-Salpeter wave functions for the bound states consisting of two vector fields, we obtain the general formulas for the decay widths of molecular states composed of two heavy vector mesons with arbitrary spin and parity into a heavy meson plus a light meson. In this approach, our attention is still focused on the internal structure of heavy vector mesons in the molecular state. According to the molecule state model of exotic meson, we give the generalized Bethe-Salpeter wave function of molecular state as a four-quark state. Then the observed Y (3940 ) state is considered as a molecular state consisting of two heavy vector mesons D*0D¯*0 and the strong Y (3940 )→J /ψ ω decay width is calculated. The numerical result is consistent with the experimental values.

Effect of ladder diagrams on optical absorption spectra in a quasiparticle self-consistent GW framework

NASA Astrophysics Data System (ADS)

Cunningham, Brian; Grüning, Myrta; Azarhoosh, Pooya; Pashov, Dimitar; van Schilfgaarde, Mark

2018-03-01

We present an approach to calculate the optical absorption spectra that combines the quasiparticle self-consistent GW method [Phys. Rev. B 76, 165106 (2007), 10.1103/PhysRevB.76.165106] for the electronic structure with the solution of the ladder approximation to the Bethe-Salpeter equation for the macroscopic dielectric function. The solution of the Bethe-Salpeter equation has been implemented within an all-electron framework, using a linear muffin-tin orbital basis set, with the contribution from the nonlocal self-energy to the transition dipole moments (in the optical limit) evaluated explicitly. This approach addresses those systems whose electronic structure is poorly described within the standard perturbative GW approaches with density-functional theory calculations as a starting point. The merits of this approach have been exemplified by calculating optical absorption spectra of a strongly correlated transition metal oxide, NiO, and a narrow gap semiconductor, Ge. In both cases, the calculated spectrum is in good agreement with the experiment. It is also shown that for systems whose electronic structure is well-described within the standard perturbative GW , such as Si, LiF, and h -BN , the performance of the present approach is in general comparable to the standard GW plus Bethe-Salpeter equation. It is argued that both vertex corrections to the electronic screening and the electron-phonon interaction are responsible for the observed systematic overestimation of the fundamental band gap and spectrum onset.

Environmentally sensitive theory of electronic and optical transitions in atomically thin semiconductors

NASA Astrophysics Data System (ADS)

Cho, Yeongsu; Berkelbach, Timothy C.

2018-01-01

We present an electrostatic theory of band-gap renormalization in atomically thin semiconductors that captures the strong sensitivity to the surrounding dielectric environment. In particular, our theory aims to correct known band gaps, such as that of the three-dimensional bulk crystal. Combining our quasiparticle band gaps with an effective-mass theory of excitons yields environmentally sensitive optical gaps as would be observed in absorption or photoluminescence. For an isolated monolayer of MoS2, the presented theory is in good agreement with ab initio results based on the G W approximation and the Bethe-Salpeter equation. We find that changes in the electronic band gap are almost exactly offset by changes in the exciton binding energy such that the energy of the first optical transition is nearly independent of the electrostatic environment, rationalizing experimental observations.

Color-suppression of non-planar diagrams in bosonic bound states

NASA Astrophysics Data System (ADS)

Alvarenga Nogueira, J. H.; Ji, Chueng-Ryong; Ydrefors, E.; Frederico, T.

2018-02-01

We study the suppression of non-planar diagrams in a scalar QCD model of a meson system in 3 + 1 space-time dimensions due to the inclusion of the color degrees of freedom. As a prototype of the color-singlet meson, we consider a flavor-nonsinglet system consisting of a scalar-quark and a scalar-antiquark with equal masses exchanging a scalar-gluon of a different mass, which is investigated within the framework of the homogeneous Bethe-Salpeter equation. The equation is solved by using the Nakanishi representation for the manifestly covariant bound-state amplitude and its light-front projection. The resulting non-singular integral equation is solved numerically. The damping of the impact of the cross-ladder kernel on the binding energies are studied in detail. The color-suppression of the cross-ladder effects on the light-front wave function and the elastic electromagnetic form factor are also discussed. As our results show, the suppression appears significantly large for Nc = 3, which supports the use of rainbow-ladder truncations in practical non-perturbative calculations within QCD.

Baryon interactions from lattice QCD with physical masses — strangeness S = -1 sector —

NASA Astrophysics Data System (ADS)

Nemura, Hidekatsu; Aoki, Sinya; Doi, Takumi; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Iritani, Takumi; Ishii, Noriyoshi; Miyamoto, Takaya; Sasaki, Kenji

2018-03-01

We present our recent results of baryon interactions with strangeness S = -1 based on Nambu-Bethe-Salpeter (NBS) correlation functions calculated fromlattice QCD with almost physical quark masses corresponding to (mk,mk) ≈ (146, 525) MeV and large volume (La)4 ≈ (96a)4 ≈ (8.1 fm)4. In order to perform a comprehensive study of baryon interactions, a large number of NBS correlation functions from NN to ΞΞ are calculated simultaneously by using large scale computer resources. In this contribution, we focus on the strangeness S = -1 channels of the hyperon interactions by means of HAL QCD method. Four sets of three potentials (the 3S1 - 3 D1 central, 3S1 - 3 D1 tensor, and the 1S0 central potentials) are presented for the ∑N - ∑N (the isospin I = 3/2) diagonal, the ∧N - ∧N diagonal, the ∧N → ∑N transition, and the ∑N - ∑N (I = 1/2) diagonal interactions. Scattering phase shifts for ∑N (I = 3/2) system are presented.

General relativistic calculations for white dwarfs

NASA Astrophysics Data System (ADS)

Mathew, Arun; Nandy, Malay K.

2017-05-01

The mass-radius relations for white dwarfs are investigated by solving the Newtonian as well as Tolman-Oppenheimer-Volkoff (TOV) equations for hydrostatic equilibrium assuming the electron gas to be non-interacting. We find that the Newtonian limiting mass of 1.4562{M}⊙ is modified to 1.4166{M}⊙ in the general relativistic case for {}_2^4{{He}} (and {}_612{{C}}) white dwarfs. Using the same general relativistic treatment, the critical mass for {}2656{{Fe}} white dwarfs is obtained as 1.2230{M}⊙ . In addition, departure from the ideal degenerate equation of state (EoS) is accounted for by considering Salpeter’s EoS along with the TOV equation, yielding slightly lower values for the critical masses, namely 1.4081{M}⊙ for {}_2^4{{He}}, 1.3916{M}⊙ for {}_612{{C}} and 1.1565{M}⊙ for {}2656{{Fe}} white dwarfs. We also compare the critical densities for gravitational instability with the neutronization threshold densities to find that {}_2^4{{He}} and {}_612{{C}} white dwarfs are stable against neutronization with the critical values of 1.4081{M}⊙ and 1.3916{M}⊙ , respectively. However, the critical masses for {}_816{{O}}, {}1020{{Ne}}, {}1224{{Mg}}, {}1428{{Si}}, {}1632{{S}} and {}2656{{Fe}} white dwarfs are lower due to neutronization. Corresponding to their central densities for neutronization thresholds, we obtain their maximum stable masses due to neutronization by solving the TOV equation coupled with the Salpeter EoS.

Measuring the Progenitor Masses and Dense Circumstellar Material of Type II Supernovae

NASA Astrophysics Data System (ADS)

Morozova, Viktoriya; Piro, Anthony L.; Valenti, Stefano

2018-05-01

Recent modeling of hydrogen-rich Type II supernova (SN II) light curves suggests the presence of dense circumstellar material (CSM) surrounding the exploding progenitor stars. This has important implications for the activity and structure of massive stars near the end of their lives. Since previous work focused on just a few events, here we expand to a larger sample of 20 well-observed SNe II. For each event we are able to constrain the progenitor zero-age main-sequence (ZAMS) mass, explosion energy, and the mass and radial extent of the dense CSM. We then study the distribution of each of these properties across the full sample of SNe. The inferred ZAMS masses are found to be largely consistent with a Salpeter distribution with minimum and maximum masses of 10.4 and 22.9 M ⊙, respectively. We also compare the individual ZAMS masses we measure with specific SNe II that have pre-explosion imaging to check their consistency. Our masses are generally comparable to or higher than the pre-explosion imaging masses, potentially helping ease the red supergiant problem. The explosion energies vary from (0.1–1.3) × 1051 erg, and for ∼70% of the SNe we obtain CSM masses in the range between 0.18 and 0.83 M ⊙. We see a potential correlation between the CSM mass and explosion energy, which suggests that pre-explosion activity has a strong impact on the structure of the star. This may be important to take into account in future studies of the ability of the neutrino mechanism to explode stars. We also see a possible correlation between the CSM radial extent and ZAMS mass, which could be related to the time with respect to explosion when the CSM is first generated.

Potential description of charmonium and charmed-strange mesons from lattice QCD

NASA Astrophysics Data System (ADS)

Kawanai, Taichi; Sasaki, Shoichi

2015-11-01

We present spin-independent and spin-spin interquark potentials for the charmonium and charmed-strange mesons, which are calculated in 2 +1 flavor lattice QCD simulations using the PACS-CS gauge configurations generated at the lightest pion mass (Mπ≈156 (7 ) MeV ) with a lattice cutoff of a-1≈2.2 GeV and a spatial volume of (3 fm )3 . For the charm quark, we use a relativistic heavy quark (RHQ) action with fine tuned RHQ parameters, which closely reproduce both the experimental spin-averaged mass and hyperfine splitting of the 1 S charmonium. The interquark potential and the quark kinetic mass, both of which are key ingredients within the potential description of heavy-heavy and heavy-light mesons, are determined from the equal-time Bethe-Salpeter (BS) amplitude. The charmonium potentials are obtained from the BS wave function of 1 S charmonia (ηc and J /ψ mesons), while the charmed-strange potential are calculated from the Ds and Ds* heavy-light mesons. We then use resulting potentials and quark masses as purely theoretical inputs so as to solve the nonrelativistic Schrödinger equation for calculating accessible energy levels of charmonium and charmed-strange mesons without unknown parameters. The resultant spectra below the D D ¯ and D K thresholds excellently agree with well-established experimental data.

Strong Coupling Continuum QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pennington, M. R.

2011-05-23

The Schwinger-Dyson, Bethe-Salpeter system of equations are the link between coloured quarks and gluons, and colourless hadrons and their properties. This talk reviews some aspects of these studies from the infrared behaviour of ghosts to the prediction of electromagnetic form-factors.

Strong Coupling Continuum QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael Pennington

2011-05-01

The Schwinger-Dyson, Bethe-Salpeter system of equations are the link between coloured quarks and gluons, and colourless hadrons and their properties. This talk reviews some aspects of these studies from the infrared behaviour of ghosts to the prediction of electromagnetic form-factors.

THE O- AND B-TYPE STELLAR POPULATION IN W3: BEYOND THE HIGH-DENSITY LAYER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiminki, Megan M.; Kim, Jinyoung Serena; Bagley, Micaela B.

2015-11-01

We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R{sub V} of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecularmore » cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8–10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.« less

Quantitative evaluation of first-order retardation corrections to the quarkonium spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brambilla, N.; Prosperi, G.M.

1992-08-01

We evaluate numerically first-order retardation corrections for some charmonium and bottomonium masses under the usual assumption of a Bethe-Salpeter purely scalar confinement kernel. The result depends strictly on the use of an additional effective potential to express the corrections (rather than to resort to Kato perturbation theory) and on an appropriate regularization prescription. The kernel has been chosen in order to reproduce in the instantaneous approximation a semirelativistic potential suggested by the Wilson loop method. The calculations are performed for two sets of parameters determined by fits in potential theory. The corrections turn out to be typically of the ordermore » of a few hundred MeV and depend on an additional scale parameter introduced in the regularization. A conjecture existing in the literature on the origin of the constant term in the potential is also discussed.« less

Annihilation rates of 3D2(2--) and 3D3(3--) heavy quarkonia

NASA Astrophysics Data System (ADS)

Wang, Tianhong; Fu, Hui-Feng; Jiang, Yue; Li, Qiang; Wang, Guo-Li

2017-03-01

We calculate the annihilation decay rates of the 3D 2(2--) and 3D 3(3--) charmonia and bottomonia by using the instantaneous Bethe-Salpeter (BS) method. The wave functions of states with quantum numbers JPC = 2-- and 3-- are constructed. By solving the corresponding instantaneous BS equations, we obtain the mass spectra and wave functions of the quarkonia. The annihilation amplitude is written within Mandelstam formalism and the relativistic corrections are taken into account properly. This is important, especially for high excited states, since their relativistic corrections are large. The results for the 3g channel are as follows: Γ13D2(cc¯)→ggg = 9.24 keV, Γ13D3(cc¯)→ggg = 25.0 keV, Γ13D2(bb¯)→ggg = 1.87 keV and Γ13D3(bb¯)→ggg = 0.815 keV.

Charge symmetry breaking effects in pion and kaon structure

NASA Astrophysics Data System (ADS)

Hutauruk, Parada T. P.; Bentz, Wolfgang; Cloët, Ian C.; Thomas, Anthony W.

2018-05-01

Charge symmetry breaking (CSB) effects associated with the u and d quark mass difference are investigated in the quark distribution functions and spacelike electromagnetic form factors of the pion and kaon. We use a confining version of the Nambu-Jona-Lasinio model, where CSB effects at the infrared scale associated with the model are driven by the dressed u and d quark mass ratio, which because of dynamical chiral symmetry breaking is much closer to unity than the associated current quark mass ratio. The pion and kaon are given as bound states of a dressed quark and a dressed antiquark governed by the Bethe-Salpeter equation, and exhibit the properties of Goldstone bosons, with a pion mass difference given by mπ+2-mπ0 2∝(mu-md)2 as demanded by dynamical chiral symmetry breaking. We find significant CSB effects for realistic current quark mass ratios (mu/md˜0.5 ) in the quark flavor-sector electromagnetic form factors of both the pion and kaon. For example, the difference between the u and d quark contributions to the π+ electromagnetic form factors is about 8% at a momentum transfer of Q2≃10 GeV2 , while the analogous effect for the light quark sector form factors in the K+ and K0 is about twice as large. For the parton distribution functions we find CSB effects which are considerably smaller than those found in the electromagnetic form factors.

Nova Scorpii and Coalescing Low-Mass Black Hole Binaries as LIGO Sources

NASA Astrophysics Data System (ADS)

Sipior, Michael S.; Sigurdsson, Steinn

2002-06-01

Double neutron star (NS-NS) binaries, analogous to the well-known Hulse-Taylor pulsar PSR 1913+16 (documented by Hulse & Taylor in 1974), are guaranteed-to-exist sources of high-frequency gravitational radiation detectable by LIGO. There is considerable uncertainty in the estimated rate of coalescence of such systems (see the work of Phinney in 1991, Narayan and coworkers in 1991, and Kalogera and coworkers in 2001), with conservative estimates of ~1 per 106 yr per galaxy, and optimistic theoretical estimates 1 or more mag larger. Formation rates of low-mass black hole (BH)-neutron star binaries may be higher than those of NS-NS binaries and may dominate the detectable LIGO signal rate. Rate estimates for such binaries are plagued by severe model uncertainties. Recent estimates by Portegies Zwart & Yungelson in 1998 and De Donder & Vanbeveren in 1998 suggest that BH-BH binaries do not coalesce at significant rates despite being formed at high rates. We estimate the enhanced coalescence rate for BH-BH binaries due to weak asymmetric kicks during the formation of low-mass black holes like Nova Sco (see the work of Brandt, Podsiadlowski, & Sigurdsson in 1995) and find they may contribute significantly to the LIGO signal rate, possibly dominating the phase I detectable signals if the range of black hole masses for which there is significant kick is broad enough. For a standard Salpeter initial mass function, assuming mild natal kicks, we project that the R6 merger rate (the rate of mergers per 106 yr in a Milky Way-like galaxy) of BH-BH systems is ~0.5, smaller than that of NS-NS systems. However, the higher chirp mass of these systems produces a signal nearly 4 times greater, on average, with a commensurate increase in search volume, hence, our claim that BH-BH mergers (and, to a lesser extent, BH-NS coalescence) should comprise a significant fraction of the signal seen by LIGO. The BH-BH coalescence channel considered here also predicts that a substantial fraction of BH-BH systems should have at least one component with near-maximal spin (a/M~1). This is from the spin-up provided by the fallback material after a supernova. If no mass transfer occurs between the two supernovae, both components could be spinning rapidly. The waveforms produced by the coalescence of such a system should produce a clear spin signature, so this hypothesis could be directly tested by LIGO.

Fast iterative solution of the Bethe-Salpeter eigenvalue problem using low-rank and QTT tensor approximation

NASA Astrophysics Data System (ADS)

Benner, Peter; Dolgov, Sergey; Khoromskaia, Venera; Khoromskij, Boris N.

2017-04-01

In this paper, we propose and study two approaches to approximate the solution of the Bethe-Salpeter equation (BSE) by using structured iterative eigenvalue solvers. Both approaches are based on the reduced basis method and low-rank factorizations of the generating matrices. We also propose to represent the static screen interaction part in the BSE matrix by a small active sub-block, with a size balancing the storage for rank-structured representations of other matrix blocks. We demonstrate by various numerical tests that the combination of the diagonal plus low-rank plus reduced-block approximation exhibits higher precision with low numerical cost, providing as well a distinct two-sided error estimate for the smallest eigenvalues of the Bethe-Salpeter operator. The complexity is reduced to O (Nb2) in the size of the atomic orbitals basis set, Nb, instead of the practically intractable O (Nb6) scaling for the direct diagonalization. In the second approach, we apply the quantized-TT (QTT) tensor representation to both, the long eigenvectors and the column vectors in the rank-structured BSE matrix blocks, and combine this with the ALS-type iteration in block QTT format. The QTT-rank of the matrix entities possesses almost the same magnitude as the number of occupied orbitals in the molecular systems, No

The {{\\rm{D}}\\bar{{\\rm{D}}}}^{{\\rm{* }}} interaction with isospin zero in an extended hidden gauge symmetry approach

NASA Astrophysics Data System (ADS)

Sun, Bao-Xi; Wan, Da-Ming; Zhao, Si-Yu

2018-05-01

The {{{D}}\\bar{{{D}}}}{{* }} interaction via a ρ or ω exchange is constructed within an extended hidden gauge symmetry approach, where the strange quark is replaced by the charm quark in the SU(3) flavor space. With this {{{D}}\\bar{{{D}}}}{{* }} interaction, a bound state slightly lower than the {{{D}}\\bar{{{D}}}}{{* }} threshold is generated dynamically in the isospin zero sector by solving the Bethe-Salpeter equation in the coupled-channel approximation, which might correspond to the X(3872) particle announced by many collaborations. This formulism is also used to study the {{{B}}\\bar{{{B}}}}{{* }} interaction, and a {{{B}}\\bar{{{B}}}}{{* }} bound state with isospin zero is generated dynamically, which has no counterpart listed in the review of the Particle Data Group. Furthermore, the one-pion exchange between the D meson and the {\\bar{{{D}}}}{{* }} is analyzed precisely, and we do not think the one-pion exchange potential need be considered when the Bethe-Salpeter equation is solved.

Optical properties of body-centered tetragonal C4: Insights from many-body perturbation and time-dependent density functional theories

NASA Astrophysics Data System (ADS)

Tarighi Ahmadpour, Mahdi; Rostamnejadi, Ali; Hashemifar, S. Javad

2018-04-01

We study the electronic structure and optical properties of a body-centered tetragonal phase of carbon (bct-C4) within the framework of time-dependent density functional theory and Bethe-Salpeter equation. The results indicate that the optical properties of bct-C4 are strongly affected by the electron-hole interaction. It is demonstrated that the long-range corrected exchange-correlation kernels could fairly reproduce the Bethe-Salpeter equation results. The effective carrier number reveals that at energies above 30 eV, the excitonic effects are not dominant any more and that the optical transitions originate mainly from electronic excitations. The emerged peaks in the calculated electron energy loss spectra are discussed in terms of plasmon excitations and interband transitions. The results of the research indicate that bct-C4 is an indirect wide-band-gap semiconductor, which is transparent in the visible region and opaque in the ultraviolet spectral range.

G W (Γ ) method without the Bethe-Salpeter equation for photoabsorption energies of spin-polarized systems

NASA Astrophysics Data System (ADS)

Isobe, Tomoharu; Kuwahara, Riichi; Ohno, Kaoru

2018-06-01

The one-shot G W method, beginning with the local density approximation (LDA), enables one to calculate photoemission and inverse photoemission spectra. In order to calculate photoabsorption spectra, one had to additionally solve the Bethe-Salpeter equation (BSE) for the two-particle (electron-hole) Green's function, which doubly induces evaluation errors. It has been recently reported that the G W +BSE method significantly underestimates the experimental photoabsorption energies (PAEs) of small molecules. In order to avoid these problems, we propose to apply the G W (Γ ) method not to the neutral ground state but to the cationic state to calculate PAEs without solving the BSE, which allows a rigorous one-to-one correspondence between the photoabsorption peak and the "extended" quasiparticle level. We applied the self-consistent linearized G W Γ method including the vertex correction Γ to our method, and found that this method gives the PAEs of B, Na3, and Li3 to within 0.1 eV accuracy.

White dwarfs in the building blocks of the Galactic spheroid

NASA Astrophysics Data System (ADS)

van Oirschot, Pim; Nelemans, Gijs; Starkenburg, Else; Toonen, Silvia; Helmi, Amina; Zwart, Simon Portegies

2017-11-01

Aims: The Galactic halo likely grew over time in part by assembling smaller galaxies, the so-called building blocks (BBs). We investigate if the properties of these BBs are reflected in the halo white dwarf (WD) population in the solar neighbourhood. Furthermore, we compute the halo WD luminosity functions (WDLFs for four major BBs of five cosmologically motivated stellar haloes). We compare the sum of these to the observed WDLF of the Galactic halo, derived from selected halo WDs in the SuperCOSMOS Sky Survey, aiming to investigate if they match better than the WDLFs predicted by simpler models. Methods: We couple the SeBa binary population synthesis model to the Munich-Groningen semi-analytic galaxy formation model applied to the high-resolution Aquarius dark matter simulations. Although the semi-analytic model assumes an instantaneous recycling approximation, we model the evolution of zero-age main sequence stars to WDs, taking age and metallicity variations of the population into account. To be consistent with the observed stellar halo mass density in the solar neighbourhood (ρ0), we simulate the mass in WDs corresponding to this density, assuming a Chabrier initial mass function (IMF) and a binary fraction of 50%. We also normalize our WDLFs to ρ0. Results: Although the majority of halo stars are old and metal-poor and therefore the WDs in the different BBs have similar properties (including present-day luminosity), we find in our models that the WDs originating from BBs that have young and/or metal-rich stars can be distinguished from WDs that were born in other BBs. In practice, however, it will be hard to prove that these WDs really originate from different BBs, as the variations in the halo WD population due to binary WD mergers result in similar effects. The five joined stellar halo WD populations that we modelled result in WDLFs that are very similar to each other. We find that simple models with a Kroupa or Salpeter IMF fit the observed luminosity function slightly better, since the Chabrier IMF is more top-heavy, although this result is dependent on our choice of ρ0.

CONSTRAINING VERY HIGH MASS POPULATION III STARS THROUGH He II EMISSION IN GALAXY BDF-521 AT z = 7.01

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Zheng; Fan, Xiaohui; Davé, Romeel

2015-01-30

Numerous theoretical models have long proposed that a strong He II λ1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high-redshift galaxies. The He II λ1640 line strength can constrain the mass and initial mass function (IMF) of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 to look for strong He II λ1640 emission in the galaxy BDF-521 at z = 7.01, one of the most distant spectroscopically confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125Wmore » and F160W filters, we do not detect He II emission from this galaxy, but place a 2σ upper limit on the flux of 5.3×10{sup −19} erg s{sup −1} cm{sup −2}. This measurement corresponds to a 2σ upper limit on the Pop III star formation rate (SFR{sub PopIII}) of ∼0.2 M {sub ☉} yr{sup –1}, assuming a Salpeter IMF with 50 ≲ M/M {sub ☉} ≲ 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The spectral flux density is ∼3.6×10{sup −11}×λ{sup −2.32} erg s{sup −1} cm{sup −2} Å{sup –1}, which corresponds to an overall unobscured SFR of ∼5 M {sub ☉} yr{sup –1}. Our upper limit on SFR{sub PopIII} suggests that massive Pop III stars represent ≲ 4% of the total star formation. Further, the HST high-resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.« less

An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H II Region W4 †

NASA Astrophysics Data System (ADS)

Sung, Hwankyung; Bessell, Michael S.; Chun, Moo-Young; Yi, Jonghyuk; Nazé, Y.; Lim, Beomdu; Karimov, R.; Rauw, G.; Park, Byeong-Gon; Hur, Hyeonoh

2017-05-01

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 μm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color-color and color-magnitude diagrams, and the presence of Hα emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R V = 3.05 ± 0.06). However, the distance modulus of the cluster is estimated to be 11.9 ± 0.2 mag (d=2.4+/- 0.2 kpc) from the reddening-free color-magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 ({τ }{MSTO}=3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Γ = -1.3 ± 0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700 ± 200 {M}⊙ . Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions. The optical imaging data in this article were gathered with two facilities: the AZT-22 1.5 m telescope at Maidanak Astronomical Observatory in Uzbekistan and the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Globules and pillars in Cygnus X. II. Massive star formation in the globule IRAS 20319+3958

NASA Astrophysics Data System (ADS)

Djupvik, A. A.; Comerón, F.; Schneider, N.

2017-03-01

Globules and pillars, impressively revealed by the Spitzer and Herschel satellites, for example, are pervasive features found in regions of massive star formation. Studying their embedded stellar populations can provide an excellent laboratory to test theories of triggered star formation and the features that it may imprint on the stellar aggregates resulting from it. We studied the globule IRAS 20319+3958 in Cygnus X by means of visible and near-infrared imaging and spectroscopy, complemented with mid-infrared Spitzer/IRAC imaging, in order to obtain a census of its stellar content and the nature of its embedded sources. Our observations show that the globule contains an embedded aggregate of about 30 very young (≲1 Myr) stellar objects, for which we estimate a total mass of 90 M⊙. The most massive members are three systems containing early B-type stars. Two of them most likely produced very compact H II regions, one of them being still highly embedded and coinciding with a peak seen in emission lines characterising the photon dominated region (PDR). Two of these three systems are resolved binaries, and one of those contains a visible Herbig Be star. An approximate derivation of the mass function of the members of the aggregate gives hints of a slope at high masses shallower than the classical Salpeter slope, and a peak of the mass distribution at a mass higher than that at which the widely adopted log-normal initial mass function peaks. The emission distribution of H2 and Brγ, tracing the PDR and the ionised gas phase, respectively, suggests that molecular gas is distributed as a shell around the embedded aggregate, filled with centrally-condensed ionised gas. Both, the morphology and the low excitation of the H II region, indicate that the sources of ionisation are the B stars of the embedded aggregate, rather than the external UV field caused by the O stars of Cygnus OB2. The youth of the embedded cluster, combined with the isolation of the globule, suggests that star formation in the globule was triggered by the passage of the ionisation front. Based on observations from the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, the Nordic Optical Telescope, La Palma, and the IAC80 telescope, Tenerife.Full Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A37

General relativistic effects in the structure of massive white dwarfs

NASA Astrophysics Data System (ADS)

Carvalho, G. A.; Marinho, R. M.; Malheiro, M.

2018-04-01

In this work we investigate the structure of white dwarfs using the Tolman-Oppenheimer-Volkoff equations and compare our results with those obtained from Newtonian equations of gravitation in order to put in evidence the importance of general relativity (GR) for the structure of such stars. We consider in this work for the matter inside white dwarfs two equations of state, frequently found in the literature, namely, the Chandrasekhar and Salpeter equations of state. We find that using Newtonian equilibrium equations, the radii of massive white dwarfs (M>1.3M_{⊙ }) are overestimated in comparison with GR outcomes. For a mass of 1.415M_{⊙ } the white dwarf radius predicted by GR is about 33% smaller than the Newtonian one. Hence, in this case, for the surface gravity the difference between the general relativistic and Newtonian outcomes is about 65%. We depict the general relativistic mass-radius diagrams as M/M_{⊙ }=R/(a+bR+cR^2+dR^3+kR^4), where a, b, c and d are parameters obtained from a fitting procedure of the numerical results and k=(2.08× 10^{-6}R_{⊙ })^{-1}, being R_{⊙ } the radius of the Sun in km. Lastly, we point out that GR plays an important role to determine any physical quantity that depends, simultaneously, on the mass and radius of massive white dwarfs.

THE JCMT GOULD BELT SURVEY: A FIRST LOOK AT DENSE CORES IN ORION B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, H.; Francesco, J. Di; Johnstone, D.

2016-02-01

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 μm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 μm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found inmore » previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1–2 × 10{sup 23} cm{sup −2}, most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 10{sup 23} cm{sup −2}, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.« less

The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B

NASA Astrophysics Data System (ADS)

Kirk, H.; Di Francesco, J.; Johnstone, D.; Duarte-Cabral, A.; Sadavoy, S.; Hatchell, J.; Mottram, J. C.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Jenness, T.; Nutter, D.; Pattle, K.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coude, S.; Davis, C. J.; Drabek-Maunder, E.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

2016-02-01

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 μm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 μm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1-2 × 1023 cm-2, most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 1023 cm-2, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.

Simple many-body based screening mixing ansatz for improvement of G W /Bethe-Salpeter equation excitation energies of molecular systems

NASA Astrophysics Data System (ADS)

Ziaei, Vafa; Bredow, Thomas

2017-11-01

We propose a simple many-body based screening mixing strategy to considerably enhance the performance of the Bethe-Salpeter equation (BSE) approach for prediction of excitation energies of molecular systems. This strategy enables us to closely reproduce results of highly correlated equation of motion coupled cluster singles and doubles (EOM-CCSD) through optimal use of cancellation effects. We start from the Hartree-Fock (HF) reference state and take advantage of local density approximation (LDA) based random phase approximation (RPA) screening, denoted as W0-RPA@LDA with W0 as the dynamically screened interaction built upon LDA wave functions and energies. We further use this W0-RPA@LDA screening as an initial screening guess for calculation of quasiparticle energies in the framework of G0W0 @HF. The W0-RPA@LDA screening is further injected into the BSE. By applying such an approach on a set of 22 molecules for which the traditional G W /BSE approaches fail, we observe good agreement with respect to EOM-CCSD references. The reason for the observed good accuracy of this mixing ansatz (scheme A) lies in an optimal damping of HF exchange effect through the W0-RPA@LDA strong screening, leading to substantial decrease of typically overestimated HF electronic gap, and hence to better excitation energies. Further, we present a second multiscreening ansatz (scheme B), which is similar to scheme A with the exception that now the W0-RPA@HF screening is used in the BSE in order to further improve the overestimated excitation energies of carbonyl sulfide (COS) and disilane (Si2H6 ). The reason for improvement of the excitation energies in scheme B lies in the fact that W0-RPA@HF screening is less effective (and weaker than W0-RPA@LDA), which gives rise to stronger electron-hole effects in the BSE.

VizieR Online Data Catalog: Metal enrichment in semi-analytical model (Cousin+, 2016)

NASA Astrophysics Data System (ADS)

Cousin, M.; Buat, V.; Boissier, S.; Bethermin, M.; Roehlly, Y. Genois M.

2016-04-01

The repository contains outputs from the different models: - m1: Classical (only hot gas) isotropic accretion scenario + Standard Shmidt Kennicutt law - m2: Bimodal accretion (cold streams) + Standard Shmidt Kennicutt law - m3: Classical (only hot gas) isotropic accretion scenario + ad-hoc non-star forming gas reservoir - m4: Bimodal accretion (cold streams) + ad-hoc non-star forming gas reservoir For each model of these models dada are saved in eGalICS_m*.fits file. All these fits-formated files are compatible with the TOPCAT software available on: http://www.star.bris.ac.uk/~mbt/topcat/ We also provide, for each Initial Mass Function available, a set of two fits-formated files associated to the chemodynamical library presented in the paper. For these two files, data are available for all metallicity bins used. - masslossrates_IMF.fits: The instantaneous total ejecta rate associated to a SSP for the six different main-ISM elements. - SNratesIMF.fits: The total SN rate (SNII+SNIa [nb/Gyr]) associated to a SSP, individual contribution of SNII and SNIa are also given. These files are available for four different IMFs: Salpeter+55 (1955ApJ...121..161S), Chabrier+03 (2003PASP..115..763C), Kroupa+93 (2001MNRAS.322..231K) and Scalo+98 (1998ASPC..142..201S. Both ejecta rates and SN rates are computed for the complete list of stellar ages provided in the BC03 spectra library. They are saved in fits-formated files and structured with different extensions corresponding to the different initial stellar metallicity bins. We finally provide the median star formation history, the median gas accretion history and the metal enrichment histories associated to our MW-sisters sample: MWsistershistories.dat If you used data associated to eGalICS semi-analytic model, please cite the following paper: Cousin et al., 2015A&A...575A..33C, "Toward a new modelling of gas flows in a semi-analytical model of galaxy formation and evolution" (3 data files).

GW/Bethe-Salpeter calculations for charged and model systems from real-space DFT

NASA Astrophysics Data System (ADS)

Strubbe, David A.

GW and Bethe-Salpeter (GW/BSE) calculations use mean-field input from density-functional theory (DFT) calculations to compute excited states of a condensed-matter system. Many parts of a GW/BSE calculation are efficiently performed in a plane-wave basis, and extensive effort has gone into optimizing and parallelizing plane-wave GW/BSE codes for large-scale computations. Most straightforwardly, plane-wave DFT can be used as a starting point, but real-space DFT is also an attractive starting point: it is systematically convergeable like plane waves, can take advantage of efficient domain parallelization for large systems, and is well suited physically for finite and especially charged systems. The flexibility of a real-space grid also allows convenient calculations on non-atomic model systems. I will discuss the interfacing of a real-space (TD)DFT code (Octopus, www.tddft.org/programs/octopus) with a plane-wave GW/BSE code (BerkeleyGW, www.berkeleygw.org), consider performance issues and accuracy, and present some applications to simple and paradigmatic systems that illuminate fundamental properties of these approximations in many-body perturbation theory.

molgw 1: Many-body perturbation theory software for atoms, molecules, and clusters

DOE PAGES

Bruneval, Fabien; Rangel, Tonatiuh; Hamed, Samia M.; ...

2016-07-12

Here, we summarize the MOLGW code that implements density-functional theory and many-body perturbation theory in a Gaussian basis set. The code is dedicated to the calculation of the many-body self-energy within the GW approximation and the solution of the Bethe–Salpeter equation. These two types of calculations allow the user to evaluate physical quantities that can be compared to spectroscopic experiments. Quasiparticle energies, obtained through the calculation of the GW self-energy, can be compared to photoemission or transport experiments, and neutral excitation energies and oscillator strengths, obtained via solution of the Bethe–Salpeter equation, are measurable by optical absorption. The implementation choicesmore » outlined here have aimed at the accuracy and robustness of calculated quantities with respect to measurements. Furthermore, the algorithms implemented in MOLGW allow users to consider molecules or clusters containing up to 100 atoms with rather accurate basis sets, and to choose whether or not to apply the resolution-of-the-identity approximation. Finally, we demonstrate the parallelization efficacy of the MOLGW code over several hundreds of processors.« less

Exciton self-trapping and Stark effect in the optical response of pentacene crystals from first principles

NASA Astrophysics Data System (ADS)

Strubbe, David A.; Sharifzadeh, Sahar; Neaton, Jeffrey B.; Louie, Steven G.

2012-02-01

Pentacene is a prototypical organic semiconductor with optoelectronic and photovoltaic applications. It is known that the lowest-energy singlet excitation has a Stokes shift between absorption and emission of about 0.14 eV, but the deformation associated with this self-trapped exciton remains unknown. We begin with a calculation of the optical properties via the first-principles GW/Bethe-Salpeter (BSE) theory [ML Tiago, JE Northrup, and SG Louie, Phys. Rev. B 67, 115212 (2003); S Sharifzadeh, A Biller, L Kronik, and JB Neaton, arXiv:1110.4928 (2011)]. We then study the self-trapping phenomenon via our reformulation of the Bethe-Salpeter excited-state forces approximation of Ismail-Beigi and Louie [Phys. Rev. Lett. 90, 076401 (2003)], which can describe the structural relaxation after optical excitation. Whether excitons in pentacene have charge-transfer character has been controversial in electro-absorption experiments. We use the same BSE analytic derivatives approach to calculate the changes in excitation energies due to an applied electric field to understand this experimental controversy.

Spatially associated clump populations in Rosette from CO and dust maps

NASA Astrophysics Data System (ADS)

Veltchev, Todor V.; Ossenkopf-Okada, Volker; Stanchev, Orlin; Schneider, Nicola; Donkov, Sava; Klessen, Ralf S.

2018-04-01

Spatial association of clumps from different tracers turns out to be a valuable tool to determine the physical properties of molecular clouds. It provides a reliable estimate for the X-factors, serves to trace the density of clumps seen in column densities only, and allows one to measure the velocity dispersion of clumps identified in dust emission. We study the spatial association between clump populations, extracted by use of the GAUSSCLUMPS technique from 12CO (1-0), 13CO (1-0) line maps and Herschel dust-emission maps of the star-forming region Rosette, and analyse their physical properties. All CO clumps that overlap with another CO or dust counterpart are found to be gravitationally bound and located in the massive star-forming filaments of the molecular cloud. They obey a single mass-size relation M_cl∝ R_cl^γ with γ ≃ 3 (implying constant mean density) and display virtually no velocity-size relation. We interpret their population as low-density structures formed through compression by converging flows and still not evolved under the influence of self-gravity. The high-mass parts of their clump mass functions are fitted by a power law dN_cl/d log M_cl∝ M_cl^{Γ } and display a nearly Salpeter slope Γ ˜ -1.3. On the other hand, clumps extracted from the dust-emission map exhibit a shallower mass-size relation with γ = 2.5 and mass functions with very steep slopes Γ ˜ -2.3 even if associated with CO clumps. They trace density peaks of the associated CO clumps at scales of a few tenths of pc where no single density scaling law should be expected.

Time Series Spectroscopic and Photometric Observations of the Massive DAV BPM 37093

NASA Astrophysics Data System (ADS)

Nitta, Atsuko; Kepler, S. O.; Chene, Andre–Nicolas; Koester, D.; Provencal, J. L.; Sullivan, D. J.; Chote, Paul; Safeko, Ramotholo; Kanaan, Antonio; Romero, Alejandra; Corti, Mariela; Corti, Mariela; Kilic, Mukremin; Winget, D. E.

2015-06-01

BPM 37093 was the first of only a handful of massive (1.05+/-0.05 M⊙; Bergeron 2004;Koester & Allard 2000) white dwarf pulsators discovered (Kanaan et al. 1992). These stars are particularly interesting because the crystallized mass-fraction as a function of mass and temperature is poorly constrained by observation, yet this process adds 1-2 Gyr uncertainty in ages of the oldest white dwarf stars observed and hence, in the ages of associations that contain them (Abrikosov 1960; Kirzhnits 1960; Salpeter 1961). Last year, we discovered that ESO uses BPM 37093 as a standard star and extracted corresponding spectra from the public archive. The data suggested a large variation in the observed hydrogen line profiles that could potentially be due to pulsations, but the measurement did not reach a detection-quality threshold. To further explore this possibility, though, we obtained 4hrs of continuous time series spectroscopy of BPM 37093 with Gemini in the Northern Spring of 2014. We present our preliminary results from these data along with those from the accompanying time series photometric observations we gathered from Mt. John (New Zealand), South African Astronomical Observatory (SAAO), Panchromatic Robotic optical Monitoring and Polarimetry Telescopes (PROMPT) in Chile, and Complejo Astronomico El Leoncito (Argentina) to support the Gemini observations.

Galactic Stellar and Substellar Initial Mass Function

NASA Astrophysics Data System (ADS)

Chabrier, Gilles

2003-07-01

We review recent determinations of the present-day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy-disk, spheroid, young, and globular clusters-and in conditions characteristic of early star formation. As a general feature, the IMF is found to depend weakly on the environment and to be well described by a power-law form for m>~1 Msolar and a lognormal form below, except possibly for early star formation conditions. The disk IMF for single objects has a characteristic mass around mc~0.08 Msolar and a variance in logarithmic mass σ~0.7, whereas the IMF for multiple systems has mc~0.2 Msolar and σ~0.6. The extension of the single MF into the brown dwarf regime is in good agreement with present estimates of L- and T-dwarf densities and yields a disk brown dwarf number density comparable to the stellar one, nBD~n*~0.1 pc-3. The IMF of young clusters is found to be consistent with the disk field IMF, providing the same correction for unresolved binaries, confirming the fact that young star clusters and disk field stars represent the same stellar population. Dynamical effects, yielding depletion of the lowest mass objects, are found to become consequential for ages >~130 Myr. The spheroid IMF relies on much less robust grounds. The large metallicity spread in the local subdwarf photometric sample, in particular, remains puzzling. Recent observations suggest that there is a continuous kinematic shear between the thick-disk population, present in local samples, and the genuine spheroid one. This enables us to derive only an upper limit for the spheroid mass density and IMF. Within all the uncertainties, the latter is found to be similar to the one derived for globular clusters and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk, mc~0.2-0.3 Msolar, excluding a significant population of brown dwarfs in globular clusters and in the spheroid. The IMF characteristic of early star formation at large redshift remains undetermined, but different observational constraints suggest that it does not extend below ~1 Msolar. These results suggest a characteristic mass for star formation that decreases with time, from conditions prevailing at large redshift to conditions characteristic of the spheroid (or thick disk) to present-day conditions. These conclusions, however, remain speculative, given the large uncertainties in the spheroid and early star IMF determinations. These IMFs allow a reasonably robust determination of the Galactic present-day and initial stellar and brown dwarf contents. They also have important galactic implications beyond the Milky Way in yielding more accurate mass-to-light ratio determinations. The mass-to-light ratios obtained with the disk and the spheroid IMF yield values 1.8-1.4 times smaller than for a Salpeter IMF, respectively, in agreement with various recent dynamical determinations. This general IMF determination is examined in the context of star formation theory. None of the theories based on a Jeans-type mechanism, where fragmentation is due only to gravity, can fulfill all the observational constraints on star formation and predict a large number of substellar objects. On the other hand, recent numerical simulations of compressible turbulence, in particular in super-Alfvénic conditions, seem to reproduce both qualitatively and quantitatively the stellar and substellar IMF and thus provide an appealing theoretical foundation. In this picture, star formation is induced by the dissipation of large-scale turbulence to smaller scales through radiative MHD shocks, producing filamentary structures. These shocks produce local nonequilibrium structures with large density contrasts, which collapse eventually in gravitationally bound objects under the combined influence of turbulence and gravity. The concept of a single Jeans mass is replaced by a distribution of local Jeans masses, representative of the lognormal probability density function of the turbulent gas. Objects below the mean thermal Jeans mass still have a possibility to collapse, although with a decreasing probability. The page charges for this Review were partially covered by a generous gift from a PASP supporter.

Existence of diproton-like particles in 3+1 lattice QCD with two flavors and strong coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faria da Veiga, Paulo A.; O'Carroll, Michael; Neto, A. Francisco

2011-02-01

Starting from quarks, gluons, and their dynamics, we consider the existence of two-baryon bound states of total isospin I=1 in an imaginary-time formulation of a strongly coupled 3+1-dimensional SU(3){sub c} lattice QCD with two flavors and 4x4 spin matrices, defined using the Wilson action. For a small hopping parameter {kappa}>0 and a much smaller gauge coupling 0<{beta}<<{kappa}<<1 (heavy quarks and large glueball mass), using a ladder approximation to a lattice Bethe-Salpeter equation, diproton-like bound states are found in the I=1 isospin sector, with asymptotic masses -6ln{kappa} and binding energies of order {kappa}{sup 2}. By isospin symmetry, for each diproton theremore » is also a dineutron bound state with the same mass and binding energy. The dominant two-baryon interaction is an energy-independent spatial range-one potential with an O({kappa}{sup 2}) strength. There is also an attraction arising from gauge field correlations associated with six overlapping bonds, but it is subdominant. The overall range-one potential results from a quark-antiquark exchange with no meson exchange interpretation (wrong spin indices). The repulsive or attractive nature of the interaction does depend on the isospin and spin of the two-baryon states. A novel representation in term of permanents is obtained for the spin, isospin interaction between the baryons, which is valid for any isospin sector.« less

On the Relativistic Separable Functions for the Breakup Reactions

NASA Astrophysics Data System (ADS)

Bondarenko, Serge G.; Burov, Valery V.; Rogochaya, Elena P.

2018-02-01

In the paper the so-called modified Yamaguchi function for the Bethe-Salpeter equation with a separable kernel is discussed. The type of the functions is defined by the analytic stucture of the hadron current with breakup - the reactions with interacting nucleon-nucleon pair in the final state (electro-, photo-, and nucleon-disintegration of the deuteron).

Extraction of hadron interactions above inelastic threshold in lattice QCD.

PubMed

Aoki, Sinya; Ishii, Noriyoshi; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji

2011-01-01

We propose a new method to extract hadron interactions above inelastic threshold from the Nambu-Bethe-Salpeter amplitude in lattice QCD. We consider the scattering such as A + B → C + D, where A, B, C, D are names of different 1-particle states. An extension to cases where particle productions occur during scatterings is also discussed.

Contemporary continuum QCD approaches to excited hadrons

NASA Astrophysics Data System (ADS)

El-Bennich, Bruno; Rojas, Eduardo

2016-03-01

Amongst the bound states produced by the strong interaction, radially excited meson and nucleon states offer an important phenomenological window into the long-range behavior of the coupling constant in Quantum Chromodynamics. We here report on some technical details related to the computation of the bound state's eigenvalue spectrum in the framework of Bethe-Salpeter and Faddeev equations.

Extraction of hadron interactions above inelastic threshold in lattice QCD

PubMed Central

AOKI, Sinya; ISHII, Noriyoshi; DOI, Takumi; HATSUDA, Tetsuo; IKEDA, Yoichi; INOUE, Takashi; MURANO, Keiko; NEMURA, Hidekatsu; SASAKI, Kenji

2011-01-01

We propose a new method to extract hadron interactions above inelastic threshold from the Nambu–Bethe–Salpeter amplitude in lattice QCD. We consider the scattering such as A + B → C + D, where A, B, C, D are names of different 1-particle states. An extension to cases where particle productions occur during scatterings is also discussed. PMID:21986314

Benchmark of Ab Initio Bethe-Salpeter Equation Approach with Numeric Atom-Centered Orbitals

NASA Astrophysics Data System (ADS)

Liu, Chi; Kloppenburg, Jan; Kanai, Yosuke; Blum, Volker

The Bethe-Salpeter equation (BSE) approach based on the GW approximation has been shown to be successful for optical spectra prediction of solids and recently also for small molecules. We here present an all-electron implementation of the BSE using numeric atom-centered orbital (NAO) basis sets. In this work, we present benchmark of BSE implemented in FHI-aims for low-lying excitation energies for a set of small organic molecules, the well-known Thiel's set. The difference between our implementation (using an analytic continuation of the GW self-energy on the real axis) and the results generated by a fully frequency dependent GW treatment on the real axis is on the order of 0.07 eV for the benchmark molecular set. We study the convergence behavior to the complete basis set limit for excitation spectra, using a group of valence correlation consistent NAO basis sets (NAO-VCC-nZ), as well as for standard NAO basis sets for ground state DFT with extended augmentation functions (NAO+aug). The BSE results and convergence behavior are compared to linear-response time-dependent DFT, where excellent numerical convergence is shown for NAO+aug basis sets.

Macroscopic and microscopic components of exchange-correlation interactions

NASA Astrophysics Data System (ADS)

Sottile, F.; Karlsson, K.; Reining, L.; Aryasetiawan, F.

2003-11-01

We consider two commonly used approaches for the ab initio calculation of optical-absorption spectra, namely, many-body perturbation theory based on Green’s functions and time-dependent density-functional theory (TDDFT). The former leads to the two-particle Bethe-Salpeter equation that contains a screened electron-hole interaction. We approximate this interaction in various ways, and discuss in particular the results obtained for a local contact potential. This, in fact, allows us to straightforwardly make the link to the TDDFT approach, and to discuss the exchange-correlation kernel fxc that corresponds to the contact exciton. Our main results, illustrated in the examples of bulk silicon, GaAs, argon, and LiF, are the following. (i) The simple contact exciton model, used on top of an ab initio calculated band structure, yields reasonable absorption spectra. (ii) Qualitatively extremely different fxc can be derived approximatively from the same Bethe-Salpeter equation. These kernels can however yield very similar spectra. (iii) A static fxc, both with or without a long-range component, can create transitions in the quasiparticle gap. To the best of our knowledge, this is the first time that TDDFT has been shown to be able to reproduce bound excitons.

Dynamics of Proton Spin: Role of qqq Force

NASA Astrophysics Data System (ADS)

Mitra, A. N.

The analytic structure of the qqq wave function, obtained recently in the high momentum regime of QCD, is employed for the formulation of baryonic transition amplitudes via quark loops. A new aspect of this study is the role of a direct (Y -shaped, Mercedes-Benz type) qqq force in generating the qqq wave function The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. The dynamics of this 3-body force shows up through a characteristic singularity in the hypergeometric differential equation for the 3D wave function ϕ, corresponding to a negative eigenvalue of the spin operator iσ1·σ2 × σ3 which is an integral part of the qqq force. As a first application of this wave function to the problem of the proton spin anomaly, the two-gluon contribution to the anomaly yields an estimate of the right sign, although somewhat smaller in magnitude.

Symmetric and anti-symmetric LS hyperon potentials from lattice QCD

NASA Astrophysics Data System (ADS)

Ishii, Noriyoshi; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji; Inoue, Takashi; HAL QCD Collaboration

2014-09-01

We present recent results of odd-parity hyperon-hyperon potentials from lattice QCD. By using HAL QCD method, we generate hyperon-hyperon potentials from Nambu-Bethe-Salpeter (NBS) wave functions generated by lattice QCD simulation in the flavor SU(3) limit. Potentials in the irreducible flavor SU(3) representations are combined to make a Lambda-N potential which has a strong symmetric LS potential and a weak anti-symmetric LS potential. We discuss a possible cancellation between symmetric and anti-symmetric LS (Lambda-N) potentials after the coupled Sigma-N sector is integrated out. We present recent results of odd-parity hyperon-hyperon potentials from lattice QCD. By using HAL QCD method, we generate hyperon-hyperon potentials from Nambu-Bethe-Salpeter (NBS) wave functions generated by lattice QCD simulation in the flavor SU(3) limit. Potentials in the irreducible flavor SU(3) representations are combined to make a Lambda-N potential which has a strong symmetric LS potential and a weak anti-symmetric LS potential. We discuss a possible cancellation between symmetric and anti-symmetric LS (Lambda-N) potentials after the coupled Sigma-N sector is integrated out. This work is supported by JSPS KAKENHI Grant Number 25400244.

Yunnan-III models for evolutionary population synthesis

NASA Astrophysics Data System (ADS)

Zhang, F.; Li, L.; Han, Z.; Zhuang, Y.; Kang, X.

2013-02-01

We build the Yunnan-III evolutionary population synthesis (EPS) models by using the mesa stellar evolution code, BaSeL stellar spectra library and the initial mass functions (IMFs) of Kroupa and Salpeter, and present colours and integrated spectral energy distributions (ISEDs) of solar-metallicity stellar populations (SPs) in the range of 1 Myr to 15 Gyr. The main characteristic of the Yunnan-III EPS models is the usage of a set of self-consistent solar-metallicity stellar evolutionary tracks (the masses of stars are from 0.1 to 100 M⊙). This set of tracks is obtained by using the state-of-the-art mesa code. mesa code can evolve stellar models through thermally pulsing asymptotic giant branch (TP-AGB) phase for low- and intermediate-mass stars. By comparisons, we confirm that the inclusion of TP-AGB stars makes the V - K, V - J and V - R colours of SPs redder and the infrared flux larger at ages log(t/yr) ≳ 7.6 [the differences reach the maximum at log(t/yr) ˜ 8.6, ˜0.5-0.2 mag for colours, approximately two times for K-band flux]. We also find that the colour-evolution trends of Model with-TPAGB at intermediate and large ages are similar to those from the starburst99 code, which employs the Padova-AGB stellar library, BaSeL spectral library and the Kroupa IMF. At last, we compare the colours with the other EPS models comprising TP-AGB stars (such as CB07, M05, V10 and POPSTAR), and find that the B - V colour agrees with each other but the V-K colour shows a larger discrepancy among these EPS models [˜1 mag when 8 ≲ log(t/yr) ≲ 9]. The stellar evolutionary tracks, isochrones, colours and ISEDs can be obtained on request from the first author or from our website (http://www1.ynao.ac.cn/~zhangfh/). Using the isochrones, you can build your EPS models. Now the format of stellar evolutionary tracks is the same as that in the starburst99 code; you can put them into the starburst99 code and get the SP's results. Moreover, the colours involving other passbands or on other systems (e.g. HST F439W - F555W colour on AB system) can also be obtained on request.

Starburst clusters in the Galactic center

NASA Astrophysics Data System (ADS)

Habibi, Maryam

2014-09-01

The central region of the Galaxy is the most active site of star formation in the Milky Way, where massive stars have formed very recently and are still forming today. The rich population of massive stars in the Galactic center provide a unique opportunity to study massive stars in their birth environment and probe their initial mass function, which is the spectrum of stellar masses at their birth. The Arches cluster is the youngest among the three massive clusters in the Galactic center, providing a collection of high-mass stars and a very dense core which makes this cluster an excellent site to address questions about massive star formation, the stellar mass function and the dynamical evolution of massive clusters in the Galactic center. In this thesis, I perform an observational study of the Arches cluster using K_{s}-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/Cisco J-band data to gain a full understanding of the cluster mass distribution out to its tidal radius for the first time. Since the light from the Galactic center reaches us through the Galactic disc, the extinction correction is crucial when studying this region. I use a Bayesian method to construct a realistic extinction map of the cluster. It is shown in this study that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, I show that the difference can reach up to 30% for individually derived stellar masses and Δ A_{Ks}˜ 1 magnitude in acquired K_{s}-band extinction, while the present-day mass function slope changes by ˜ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law, which suggests a steeper wavelength dependence for the infrared extinction law, reveals an overpopulation of massive stars in the core (r<0.2 pc) with a flat slope of α_{Nishi}=-1.50 ±0.35 in comparison to the Salpeter slope of α=-2.3. The slope of the mass function increases to α_{Nishi}=-2.21 ±0.27 in the intermediate annulus (0.2

Low-mass young stellar population and star formation history of the cluster IC 1805 in the W4 H II region

NASA Astrophysics Data System (ADS)

Panwar, Neelam; Samal, M. R.; Pandey, A. K.; Jose, J.; Chen, W. P.; Ojha, D. K.; Ogura, K.; Singh, H. P.; Yadav, R. K.

2017-07-01

W4 is a giant H II region ionized by the OB stars of the cluster IC 1805. The H II region/cluster complex has been a subject of numerous investigations as it is an excellent laboratory for studying the feedback effect of massive stars on the surrounding region. However, the low-mass stellar content of the cluster IC 1805 remains poorly studied till now. With the aim to unravel the low-mass stellar population of the cluster, we present the results of a multiwavelength study based on deep optical data obtained with the Canada-France-Hawaii Telescope, infrared data from Two Micron All Sky Survey and Spitzer Space Telescope and X-ray data from Chandra Space Telescope. The present optical data set is complete enough to detect stars down to 0.2 M⊙, which is the deepest optical observation so far for the cluster. We identified 384 candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within the cluster using various colour-colour and colour-magnitude diagrams. We inferred the mean age of the identified YSOs to be ˜2.5 Myr and mass in the range 0.3-2.5 M⊙. The mass function of our YSO sample has a power-law index of -1.23 ± 0.23, close to the Salpeter value (-1.35), and consistent with those of other star-forming complexes. We explored the disc evolution of the cluster members and found that the disc-less sources are relatively older compared to the disc bearing YSO candidates. We examined the effect of high-mass stars on the circumstellar discs and within uncertainties, the influence of massive stars on the disc fraction seems to be insignificant. We also studied the spatial correlation of the YSOs with the distribution of gas and dust of the complex to conclude that IC 1805 would have formed in a large filamentary cloud.

Mesons in strong magnetic fields: (I) General analyses

DOE PAGES

Hattori, Koichi; Kojo, Toru; Su, Nan

2016-03-21

Here, we study properties of neutral and charged mesons in strong magnetic fields |eB| >> Λ 2 QCD with Λ QCD being the QCD renormalization scale. Assuming long-range interactions, we examine magnetic-field dependences of various quantities such as the constituent quark mass, chiral condensate, meson spectra, and meson wavefunctions by analyzing the Schwinger–Dyson and Bethe–Salpeter equations. Based on the density of states obtained from these analyses, we extend the hadron resonance gas (HRG) model to investigate thermodynamics at large B. As B increases the meson energy behaves as a slowly growing function of the meson's transverse momenta, and thus amore » large number of meson states is accommodated in the low energy domain; the density of states at low temperature is proportional to B 2. This extended transverse phase space in the infrared regime significantly enhances the HRG pressure at finite temperature, so that the system reaches the percolation or chiral restoration regime at lower temperature compared to the case without a magnetic field; this simple picture would offer a gauge invariant and intuitive explanation of the inverse magnetic catalysis.« less

Extension of the HAL QCD approach to inelastic and multi-particle scatterings in lattice QCD

NASA Astrophysics Data System (ADS)

Aoki, S.

We extend the HAL QCD approach, with which potentials between two hadrons can be obtained in QCD at energy below inelastic thresholds, to inelastic and multi-particle scatterings. We first derive asymptotic behaviors of the Nambu-Bethe-Salpeter (NBS) wave function at large space separations for systems with more than 2 particles, in terms of the one-shell $T$-matrix consrainted by the unitarity of quantum field theories. We show that its asymptotic behavior contains phase shifts and mixing angles of $n$ particle scatterings. This property is one of the essential ingredients of the HAL QCD scheme to define "potential" from the NBS wave function in quantum field theories such as QCD. We next construct energy independent but non-local potentials above inelastic thresholds, in terms of these NBS wave functions. We demonstrate an existence of energy-independent coupled channel potentials with a non-relativistic approximation, where momenta of all particles are small compared with their own masses. Combining these two results, we can employ the HAL QCD approach also to investigate inelastic and multi-particle scatterings.

Pion and kaon valence-quark parton quasidistributions

NASA Astrophysics Data System (ADS)

Xu, Shu-Sheng; Chang, Lei; Roberts, Craig D.; Zong, Hong-Shi

2018-05-01

Algebraic Ansätze for the Poincaré-covariant Bethe-Salpeter wave functions of the pion and kaon are used to calculate their light-front wave functions, parton distribution amplitudes, parton quasidistribution amplitudes, valence parton distribution functions, and parton quasidistribution functions (PqDFs). The light-front wave functions are broad, concave functions, and the scale of flavor-symmetry violation in the kaon is roughly 15%, being set by the ratio of emergent masses in the s - and u -quark sectors. Parton quasidistribution amplitudes computed with longitudinal momentum Pz=1.75 GeV provide a semiquantitatively accurate representation of the objective parton distribution amplitude, but even with Pz=3 GeV , they cannot provide information about this amplitude's end point behavior. On the valence-quark domain, similar outcomes characterize PqDFs. In this connection, however, the ratio of kaon-to-pion u -quark PqDFs is found to provide a good approximation to the true parton distribution function ratio on 0.4 ≲x ≲0.8 , suggesting that with existing resources computations of ratios of parton quasidistributions can yield results that support empirical comparison.

Reddening and Extinction toward the Galactic Bulge from OGLE-III: The Inner Milky Way's RV ~ 2.5 Extinction Curve

NASA Astrophysics Data System (ADS)

Nataf, David M.; Gould, Andrew; Fouqué, Pascal; Gonzalez, Oscar A.; Johnson, Jennifer A.; Skowron, Jan; Udalski, Andrzej; Szymański, Michał K.; Kubiak, Marcin; Pietrzyński, Grzegorz; Soszyński, Igor; Ulaczyk, Krzysztof; Wyrzykowski, Łukasz; Poleski, Radosław

2013-06-01

We combine VI photometry from OGLE-III with VISTA Variables in The Via Lactea survey and Two Micron All Sky Survey measurements of E(J - Ks ) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well fit by the relation AI = 0.7465 × E(V - I) + 1.3700 × E(J - Ks ), or, equivalently, AI = 1.217 × E(V - I)(1 + 1.126 × (E(J - Ks )/E(V - I) - 0.3433)). The optical and near-IR reddening law toward the inner Galaxy approximately follows an RV ≈ 2.5 extinction curve with a dispersion {\\sigma }_{R_{V}} \\approx 0.2, consistent with extragalactic investigations of the hosts of Type Ia SNe. Differential reddening is shown to be significant on scales as small as our mean field size of 6'. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (M_{I,RC}, \\sigma _{I,RC,0}, (V-I)_{RC,0}, \\sigma _{(V-I)_{RC}}, (J-K_{s})_{RC,0}) = (-0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion, and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc. We measure an upper bound on the tilt α ≈ 40° between the bulge's major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at α ≈ 25°. The number of RC stars suggests a total stellar mass for the Galactic bulge of ~2.3 × 1010 M ⊙ if one assumes a canonical Salpeter initial mass function (IMF), or ~1.6 × 1010 M ⊙ if one assumes a bottom-light Zoccali IMF. Based on observations obtained with the 1.3 m Warsaw telescope at the Las Campanas Observatory of the Carnegie Institution for Science.

The ATLAS3D project - XX. Mass-size and mass-σ distributions of early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio, molecular gas fraction and stellar initial mass function

NASA Astrophysics Data System (ADS)

Cappellari, Michele; McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Bureau, M.; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

2013-07-01

In the companion Paper XV of this series, we derive accurate total mass-to-light ratios (M/L)_JAM≈ (M/L)({r}= {R_e}) within a sphere of radius r= {R_e} centred on the galaxy, as well as stellar (M/L)stars (with the dark matter removed) for the volume-limited and nearly mass-selected (stellar mass M_star ≳ 6× 10^9 { M_{⊙}}) ATLAS3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). Here, we use those parameters to study the two orthogonal projections ({M_JAM}, {σ _e}) and ({M_JAM}, {R_e^maj}) of the thin Mass Plane (MP) ({M_JAM}, {σ _e}, {R_e^maj}) which describes the distribution of the galaxy population, where {M_JAM}≡ L× (M/L)_JAM≈ M_star. The distribution of galaxy properties on both projections of the MP is characterized by: (i) the same zone of exclusion (ZOE), which can be transformed from one projection to the other using the scalar virial equation. The ZOE is roughly described by two power laws, joined by a break at a characteristic mass {M_JAM}≈ 3× 10^{10} { M_{⊙}}, which corresponds to the minimum Re and maximum stellar density. This results in a break in the mean {M_JAM}-{σ _e} relation with trends {M_JAM}∝ σ _e^{2.3} and {M_JAM}∝ σ _e^{4.7} at small and large σe, respectively; (ii) a characteristic mass {M_JAM}≈ 2× 10^{11} { M_{⊙}} which separates a population dominated by flat fast rotator with discs and spiral galaxies at lower masses, from one dominated by quite round slow rotators at larger masses; (iii) below that mass the distribution of ETGs' properties on the two projections of the MP tends to be constant along lines of roughly constant σe, or equivalently along lines with {R_e^maj}∝ {M_JAM}, respectively (or even better parallel to the ZOE: {R_e^maj}∝ M_JAM^{0.75}); (iv) it forms a continuous and parallel sequence with the distribution of spiral galaxies; (v) at even lower masses, the distribution of fast-rotator ETGs and late spirals naturally extends to that of dwarf ETGs (Sph) and dwarf irregulars (Im), respectively. We use dynamical models to analyse our kinematic maps. We show that σe traces the bulge fraction, which appears to be the main driver for the observed trends in the dynamical (M/L)JAM and in indicators of the (M/L)pop of the stellar population like Hβ and colour, as well as in the molecular gas fraction. A similar variation along contours of σe is also observed for the mass normalization of the stellar initial mass function (IMF), which was recently shown to vary systematically within the ETGs' population. Our preferred relation has the form log _{10} [(M/L)_stars/(M/L)_Salp]=a+b× log _{10}({σ _e}/130 {km s^{-1}}) with a = -0.12 ± 0.01 and b = 0.35 ± 0.06. Unless there are major flaws in all stellar population models, this trend implies a transition of the mean IMF from Kroupa to Salpeter in the interval log _{10}({σ _e}/{km s}^{-1})≈ 1.9-2.5 (or {σ _e}≈ 90-290 km s-1), with a smooth variation in between, consistently with what was shown in Cappellari et al. The observed distribution of galaxy properties on the MP provides a clean and novel view for a number of previously reported trends, which constitute special two-dimensional projections of the more general four-dimensional parameters trends on the MP. We interpret it as due to a combination of two main effects: (i) an increase of the bulge fraction, which increases σe, decreases Re, and greatly enhance the likelihood for a galaxy to have its star formation quenched, and (ii) dry merging, increasing galaxy mass and Re by moving galaxies along lines of roughly constant σe (or steeper), while leaving the population nearly unchanged.

The Wigner function in the relativistic quantum mechanics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kowalski, K., E-mail: kowalski@uni.lodz.pl; Rembieliński, J.

2016-12-15

A detailed study is presented of the relativistic Wigner function for a quantum spinless particle evolving in time according to the Salpeter equation. - Highlights: • We study the Wigner function for a quantum spinless relativistic particle. • We discuss the relativistic Wigner function introduced by Zavialov and Malokostov. • We introduce relativistic Wigner function based on the standard definition. • We find analytic expressions for relativistic Wigner functions.

Benchmarking the GW Approximation and Bethe–Salpeter Equation for Groups IB and IIB Atoms and Monoxides

DOE PAGES

Hung, Linda; Bruneval, Fabien; Baishya, Kopinjol; ...

2017-04-07

Energies from the GW approximation and the Bethe–Salpeter equation (BSE) are benchmarked against the excitation energies of transition-metal (Cu, Zn, Ag, and Cd) single atoms and monoxide anions. We demonstrate that best estimates of GW quasiparticle energies at the complete basis set limit should be obtained via extrapolation or closure relations, while numerically converged GW-BSE eigenvalues can be obtained on a finite basis set. Calculations using real-space wave functions and pseudopotentials are shown to give best-estimate GW energies that agree (up to the extrapolation error) with calculations using all-electron Gaussian basis sets. We benchmark the effects of a vertex approximationmore » (ΓLDA) and the mean-field starting point in GW and the BSE, performing computations using a real-space, transition-space basis and scalar-relativistic pseudopotentials. Here, while no variant of GW improves on perturbative G0W0 at predicting ionization energies, G0W0Γ LDA-BSE computations give excellent agreement with experimental absorption spectra as long as off-diagonal self-energy terms are included. We also present G0W0 quasiparticle energies for the CuO –, ZnO –, AgO –, and CdO – anions, in comparison to available anion photoelectron spectra.« less

Benchmarking the GW Approximation and Bethe–Salpeter Equation for Groups IB and IIB Atoms and Monoxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hung, Linda; Bruneval, Fabien; Baishya, Kopinjol

Energies from the GW approximation and the Bethe–Salpeter equation (BSE) are benchmarked against the excitation energies of transition-metal (Cu, Zn, Ag, and Cd) single atoms and monoxide anions. We demonstrate that best estimates of GW quasiparticle energies at the complete basis set limit should be obtained via extrapolation or closure relations, while numerically converged GW-BSE eigenvalues can be obtained on a finite basis set. Calculations using real-space wave functions and pseudopotentials are shown to give best-estimate GW energies that agree (up to the extrapolation error) with calculations using all-electron Gaussian basis sets. We benchmark the effects of a vertex approximationmore » (ΓLDA) and the mean-field starting point in GW and the BSE, performing computations using a real-space, transition-space basis and scalar-relativistic pseudopotentials. Here, while no variant of GW improves on perturbative G0W0 at predicting ionization energies, G0W0Γ LDA-BSE computations give excellent agreement with experimental absorption spectra as long as off-diagonal self-energy terms are included. We also present G0W0 quasiparticle energies for the CuO –, ZnO –, AgO –, and CdO – anions, in comparison to available anion photoelectron spectra.« less

A systematic benchmark of the ab initio Bethe-Salpeter equation approach for low-lying optical excitations of small organic molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruneval, Fabien; Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Department of Physics, University of California, Berkeley, California 94720

2015-06-28

The predictive power of the ab initio Bethe-Salpeter equation (BSE) approach, rigorously based on many-body Green’s function theory but incorporating information from density functional theory, has already been demonstrated for the optical gaps and spectra of solid-state systems. Interest in photoactive hybrid organic/inorganic systems has recently increased and so has the use of the BSE for computing neutral excitations of organic molecules. However, no systematic benchmarks of the BSE for neutral electronic excitations of organic molecules exist. Here, we study the performance of the BSE for the 28 small molecules in Thiel’s widely used time-dependent density functional theory benchmark setmore » [Schreiber et al., J. Chem. Phys. 128, 134110 (2008)]. We observe that the BSE produces results that depend critically on the mean-field starting point employed in the perturbative approach. We find that this starting point dependence is mainly introduced through the quasiparticle energies obtained at the intermediate GW step and that with a judicious choice of starting mean-field, singlet excitation energies obtained from BSE are in excellent quantitative agreement with higher-level wavefunction methods. The quality of the triplet excitations is slightly less satisfactory.« less

The Intermediate Stellar Population in R136 Determined from Hubble Space Telescope Images

NASA Astrophysics Data System (ADS)

Hunter, D. A.; WFPC1 IDT; WFPC2 IDT

1994-12-01

We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01 pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_{555,o} of 0.9 or a mass of 2.8 cal Msolar . Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8 cal Msolar , and stars with M_{555,o}>=0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3--4 Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8--15 cal Msolar in three annuli from 0.5--4.7 pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5 pc. Furthermore, the combined IMF slope, -1.2+/-0.1, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <=2.8 cal Msolar beyond 0.5 pc and <=7 cal Msolar within 0.1 pc. This is contrary to some predictions that the lower mass limit could be as high as 10 cal Msolar in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136.

Quasiparticle Lifetime Broadening in Resonant X-ray Scattering of NH4NO3.

PubMed

Vinson, John; Jach, Terrence; Müller, Matthias; Unterumsberger, Rainer; Beckhoff, Burkhard

2016-07-15

It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectra from the N K edge of the insulating crystal ammonium nitrate. First, vibrational disorder causes major changes in the absorption spectrum, originating not only from the thermal population of phonons, but, significantly, from zero-point motion as well. Second, the anomalously large broadening ( ~ 4 eV) of the emission originating from nitrate σ states is due to unusually short lifetimes of quasiparticles in an otherwise extremely narrow band. In this work we investigate the coupling of these effects to core and valence excitons that are created as the initial x-ray excitation energy is progressively reduced toward the N edge. Using a GW /Bethe-Salpeter approach, we show the extent to which this anomalous broadening is captured by the GW approximation. The data and calculations demonstrate the importance that the complex self-energies (finite lifetimes) of valence bands have on the interpretation of emission spectra. We produce a scheme to explain why extreme lifetimes should appear in σ states of other similar compounds.

Recent development in lattice QCD studies for three-nucleon forces

NASA Astrophysics Data System (ADS)

Doi, Takumi; HAL QCD Collaboration

2014-09-01

The direct determination of nuclear forces from QCD has been one of the most desirable challenges in nuclear physics. Recently, a first-principles lattice QCD determination is becoming possible by a novel theoretical method, HAL QCD method, in which Nambu-Bethe-Salpeter (NBS) wave functions are utilized. In this talk, I will focus on the study of three-nucleon forces in HAL QCD method by presenting the recent theoretical/numerical development.

OPTICAL PHOTOMETRIC AND POLARIMETRIC INVESTIGATION OF NGC 1931

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, A. K.; Eswaraiah, C.; Sharma, Saurabh

We present optical photometric and polarimetric observations of stars toward NGC 1931 with the aim of deriving cluster parameters such as distance, reddening, age, and luminosity/mass function as well as understanding dust properties and star formation in the region. The distance to the cluster is found to be 2.3 {+-} 0.3 kpc and the reddening E(B - V) in the region is found to be variable. The stellar density contours reveal two clusters in the region. The observations suggest a differing reddening law within the cluster region. Polarization efficiency of the dust grains toward the direction of the cluster ismore » found to be less than that for the general diffuse interstellar medium (ISM). The slope of the mass function (-0.98 {+-} 0.22) in the southern region in the mass range of 0.8 < M/M {sub Sun} < 9.8 is found to be shallower in comparison to that in the northern region (-1.26 {+-} 0.23), which is comparable to the Salpeter value (-1.35). The K-band luminosity function (KLF) of the region is found to be comparable to the average value of the slope ({approx}0.4) for young clusters obtained by Lada and Lada; however, the slope of the KLF is steeper in the northern region as compared to the southern region. The region is probably ionized by two B2 main-sequence-type stars. The mean age of the young stellar objects (YSOs) is found to be 2 {+-} 1 Myr, which suggests that the identified YSOs could be younger than the ionizing sources of the region. The morphology of the region, the distribution and ages of the YSOs, and ionizing sources indicate a triggered star formation in the region.« less

Flavor dependence of the pion and kaon form factors and parton distribution functions

DOE PAGES

Hutauruk, Parada T. P.; Cloët, Ian C.; Thomas, Anthony W.

2016-09-01

The separate quark flavor contributions to the pion and kaon valence quark distribution functions are studied, along with the corresponding electromagnetic form factors in the space-like region. The calculations are made using the solution of the Bethe-Salpeter equation for the model of Nambu and Jona-Lasinio with proper-time regularization. Both the pion and kaon form factors and the valence quark distribution functions reproduce many features of the available empirical data. The larger mass of the strange quark naturally explains the empirical fact that the ratio u(K) + (x)/u(pi) + (x) drops below unity at large x, with a value of approximately Mmore » $$2\\atop{u}$$/Ms$$2\\atop{s}$$ as x → 1. With regard to the elastic form factors we report a large flavor dependence, with the u-quark contribution to the kaon form factor being an order of magnitude smaller than that of the s-quark at large Q 2, which may be a sensitive measure of confinement effects in QCD. Surprisingly though, the total K + and π + form factors differ by only 10%. Lastly, in general we find that flavor breaking effects are typically around 20%.« less

Flavor dependence of the pion and kaon form factors and parton distribution functions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hutauruk, Parada T. P.; Cloët, Ian C.; Thomas, Anthony W.

The separate quark flavor contributions to the pion and kaon valence quark distribution functions are studied, along with the corresponding electromagnetic form factors in the space-like region. The calculations are made using the solution of the Bethe-Salpeter equation for the model of Nambu and Jona-Lasinio with proper-time regularization. Both the pion and kaon form factors and the valence quark distribution functions reproduce many features of the available empirical data. The larger mass of the strange quark naturally explains the empirical fact that the ratio u(K) + (x)/u(pi) + (x) drops below unity at large x, with a value of approximately Mmore » $$2\\atop{u}$$/Ms$$2\\atop{s}$$ as x → 1. With regard to the elastic form factors we report a large flavor dependence, with the u-quark contribution to the kaon form factor being an order of magnitude smaller than that of the s-quark at large Q 2, which may be a sensitive measure of confinement effects in QCD. Surprisingly though, the total K + and π + form factors differ by only 10%. Lastly, in general we find that flavor breaking effects are typically around 20%.« less

In-Medium K^+ Electromagnetic Form Factor with a Symmetric Vertex in a Light Front Approach

NASA Astrophysics Data System (ADS)

Yabusaki, George H. S.; de Melo, J. P. B. C.; de Paula, Wayne; Tsushima, K.; Frederico, T.

2018-05-01

Using the light-front K^ +-Meson wave function based on a Bethe-Salpeter amplitude model for the Quark-Antiquark bound state, we study the Electromagnetic Form Factor (EMFF) of the K^ +-Meson in nuclear medium within the framework of light-front field theory. The K^ +-Meson model we adopt is well constrained by previous and recent studies to explain its properties in vacuum. The in-medium K^ +-Meson EMFF is evaluated for the plus-component of the electromagnetic current, J^+, in the Breit frame. In order to consistently incorporate the constituent up and antistrange Quarks of the K^ +-Meson immersed in symmetric nuclear matter, we use the Quark-Meson coupling model, which has been widely applied to various hadronic and nuclear phenomena in a nuclear medium with success. We predict the in-medium modification of the K^ +-Meson EMFF in symmetric nuclear matter. It is found that, after a fine tuning of the regulator mass, i.e. m_R = 0.600 GeV, the model is suitable to fit the available experimental data in vacuum within the theoretical uncertainties, and based on this we predict the in-medium modification of the K^ +-Meson EMFF.

Light-front Ward-Takahashi identity for two-fermion systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marinho, J. A. O.; Frederico, T.; Pace, E.

We propose a three-dimensional electromagnetic current operator within light-front dynamics that satisfies a light-front Ward-Takahashi identity for two-fermion systems. The light-front current operator is obtained by a quasipotential reduction of the four-dimensional current operator and acts on the light-front valence component of bound or scattering states. A relation between the light-front valence wave function and the four-dimensional Bethe-Salpeter amplitude both for bound or scattering states is also derived, such that the matrix elements of the four-dimensional current operator can be fully recovered from the corresponding light-front ones. The light-front current operator can be perturbatively calculated through a quasipotential expansion, andmore » the divergence of the proposed current satisfies a Ward-Takahashi identity at any given order of the expansion. In the quasipotential expansion the instantaneous terms of the fermion propagator are accounted for by the effective interaction and two-body currents. We exemplify our theoretical construction in the Yukawa model in the ladder approximation, investigating in detail the current operator at the lowest nontrivial order of the quasipotential expansion of the Bethe-Salpeter equation. The explicit realization of the light-front form of the Ward-Takahashi identity is verified. We also show the relevance of instantaneous terms and of the pair contribution to the two-body current and the Ward-Takahashi identity.« less

Star Formation Histories of the LEGUS Dwarf Galaxies. I. Recent History of NGC 1705, NGC 4449, and Holmberg II

NASA Astrophysics Data System (ADS)

Cignoni, M.; Sacchi, E.; Aloisi, A.; Tosi, M.; Calzetti, D.; Lee, J. C.; Sabbi, E.; Adamo, A.; Cook, D. O.; Dale, D. A.; Elmegreen, B. G.; Gallagher, J. S., III; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Hunter, D. A.; Johnson, K. E.; Messa, M.; Smith, L. J.; Thilker, D. A.; Ubeda, L.; Whitmore, B. C.

2018-03-01

We use Hubble Space Telescope observations from the Legacy Extragalactic UV Survey to reconstruct the recent star formation histories (SFHs) of three actively star-forming dwarf galaxies, NGC 4449, Holmberg II, and NGC 1705, from their UV color–magnitude diagrams (CMDs). We apply a CMD fitting technique using two independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the uncertainties related to stellar evolution modeling. Irrespective of the adopted stellar models, all three dwarfs are found to have had almost constant star formation rates (SFRs) in the last 100–200 Myr, with modest enhancements (a factor of ∼2) above the 100 Myr averaged SFR. Significant differences among the three dwarfs are found in terms of the overall SFR, the timing of the most recent peak, and the SFR/area. The initial mass function of NGC 1705 and Holmberg II is consistent with a Salpeter slope down to ≈5 M ⊙, whereas it is slightly flatter, s = ‑2.0, in NGC 4449. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. They also share the drawback that all synthetic diagrams predict a clear separation in color between the upper main-sequence and helium-burning stars, which is not apparent in the data. Since neither differential reddening, which is significant in NGC 4449, nor unresolved binaries appear to be sufficient to fill the gap, we suggest this calls for a revision of both sets of stellar evolutionary tracks. Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

An isochrone data base and a rapid model for stellar population synthesis

NASA Astrophysics Data System (ADS)

Li, Zhongmu; Han, Zhanwen

2008-06-01

We first presented an isochrone data base that can be widely used for stellar population synthesis studies and colour-magnitude diagram (CMD) fitting. The data base consists of the isochrones of both single-star and binary-star simple stellar populations (ss-SSPs and bs-SSPs). The ranges for the age and metallicity of populations are 0-15 Gyr and 0.0001-0.03, respectively. All data are available for populations with two widely used initial mass functions (IMFs), that is, Salpeter IMF and Chabrier IMF. The uncertainty caused by the data base (about 0.81 per cent) is designed to be smaller than those caused by the Hurley code and widely used stellar spectra libraries (e.g. BaSeL 3.1) when it is used for stellar population synthesis. Based on the isochrone data base, we then built a rapid stellar population synthesis (RPS) model and calculated the high-resolution (0.3-Å) integrated spectral energy distributions, Lick indices and colour indices for bs-SSPs and ss-SSPs. In particular, we calculated the UBVRIJHKLM colours, ugriz colours and some composite colours that consist of magnitudes on different systems. These colours are useful for disentangling the well-known stellar age-metallicity degeneracy according to our previous work. As an example for applying the isochrone data base for CMD fitting, we fitted the CMDs of two star clusters (M67 and NGC1868) and obtained their distance moduli, colour excesses, stellar metallicities and ages. The results showed that the isochrones of bs-SSPs are closer to those of real star clusters. It suggests that we should take the effects of binary interactions into account in stellar population synthesis. We also discussed on the limitations of the application of the isochrone data base and the results of the RPS model. All the data are available at the CDS or on request to the authors. E-mail: zhongmu.li@gmail.com

The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function

NASA Astrophysics Data System (ADS)

Habibi, M.; Stolte, A.; Brandner, W.; Hußmann, B.; Motohara, K.

2013-08-01

The Galactic center is the most active site of star formation in the Milky Way, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the Galactic disk, knowledge of extinction is crucial when studying this region. The Arches cluster is a young, massive starburst cluster near the Galactic center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/CISCO J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ΔAKs ~ 1 magnitude in acquired Ks-band extinction, while the present-day mass function slope changes by ~ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law increases from a flat slope of αNishi = -1.50 ± 0.35 in the core (r < 0.2 pc) to αNishi = -2.21 ± 0.27 in the intermediate annulus (0.2 < r < 0.4 pc), where the Salpeter slope is -2.3. The mass function steepens to αNishi = -3.21 ± 0.30 in the outer annulus (0.4 < r < 1.5 pc), indicating that the outer cluster region is depleted of high-mass stars. This picture is consistent with mass segregation owing to the dynamical evolution of the cluster. Based on observations collected at the ESO/VLT under Program ID 081.D-0572(B) (PI: Brandner) and ID 71.C-0344(A) (PI: Eisenhauer, retrieved from the ESO archive). Also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.Full Table 5 is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A26

REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S R{sub V} {approx} 2.5 EXTINCTION CURVE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nataf, David M.; Gould, Andrew; Johnson, Jennifer A.

We combine VI photometry from OGLE-III with VISTA Variables in The Via Lactea survey and Two Micron All Sky Survey measurements of E(J - K{sub s} ) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well fit by the relation A{sub I} = 0.7465 Multiplication-Sign E(V - I) + 1.3700 Multiplication-Sign E(J - K{sub s} ), or, equivalently, A{sub I} = 1.217 Multiplication-Sign E(V - I)(1 + 1.126 Multiplication-Sign (E(J - K{sub s} )/E(V - I) - 0.3433)). The optical and near-IR reddening law toward the inner Galaxymore » approximately follows an R{sub V} Almost-Equal-To 2.5 extinction curve with a dispersion {sigma}{sub R{sub V}}{approx}0.2, consistent with extragalactic investigations of the hosts of Type Ia SNe. Differential reddening is shown to be significant on scales as small as our mean field size of 6'. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (M{sub I,RC},{sigma}{sub I,RC,0}, (V-I){sub RC,0},{sigma}{sub (V-I){sub R{sub C}}}, (J-K{sub s}){sub RC,0}) = (-0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion, and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc. We measure an upper bound on the tilt {alpha} Almost-Equal-To 40 Degree-Sign between the bulge's major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at {alpha} Almost-Equal-To 25 Degree-Sign . The number of RC stars suggests a total stellar mass for the Galactic bulge of {approx}2.3 Multiplication-Sign 10{sup 10} M{sub Sun} if one assumes a canonical Salpeter initial mass function (IMF), or {approx}1.6 Multiplication-Sign 10{sup 10} M{sub Sun} if one assumes a bottom-light Zoccali IMF.« less

Three-body unitarity with isobars revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mai, M.; Hu, B.; Döring, M.

The particle exchange model of hadron interactions can be used to describe three-body scattering under the isobar assumption. Here, we start from the 3->3 scattering amplitude for spinless particles, which contains an isobar-spectator scattering amplitude. Using a Bethe-Salpeter Ansatz for the latter, we derive a relativistic three-dimensional scattering equation that manifestly fulfills three-body unitarity and two-body unitarity for the sub-amplitudes. Furthermore, this property holds for energies above breakup and also in the presence of resonances in the sub-amplitudes.

Three-body unitarity with isobars revisited

DOE PAGES

Mai, M.; Hu, B.; Döring, M.; ...

2017-09-08

The particle exchange model of hadron interactions can be used to describe three-body scattering under the isobar assumption. Here, we start from the 3->3 scattering amplitude for spinless particles, which contains an isobar-spectator scattering amplitude. Using a Bethe-Salpeter Ansatz for the latter, we derive a relativistic three-dimensional scattering equation that manifestly fulfills three-body unitarity and two-body unitarity for the sub-amplitudes. Furthermore, this property holds for energies above breakup and also in the presence of resonances in the sub-amplitudes.

Pycnonuclear reaction rates for binary ionic mixtures

NASA Technical Reports Server (NTRS)

Ichimaru, S.; Ogata, S.; Van Horn, H. M.

1992-01-01

Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

STELLAR POPULATIONS AND EVOLUTION OF EARLY-TYPE CLUSTER GALAXIES: CONSTRAINTS FROM OPTICAL IMAGING AND SPECTROSCOPY OF z = 0.5-0.9 GALAXY CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jorgensen, Inger; Chiboucas, Kristin, E-mail: ijorgensen@gemini.edu, E-mail: kchiboucas@gemini.edu

2013-03-15

We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z = 0.54), RXJ0152.7-1357 (z = 0.83), and RXJ1226.9+3332 (z = 0.89). Our analysis is based on high signal-to-noise ground-based optical spectroscopy and Hubble Space Telescope imaging for a total of 17-34 members in each cluster. Using the dynamical masses together with the effective radii and the velocity dispersions, we find no indication of evolution of sizes or velocity dispersions with redshift at a given galaxy mass. We establish the Fundamental Plane (FP) and scaling relations between absorption line indices andmore » velocity dispersions. We confirm that the FP is steeper at z Almost-Equal-To 0.86 compared to the low-redshift FP, indicating that under the assumption of passive evolution the formation redshift, z{sub form}, depends on the galaxy velocity dispersion (or alternatively mass). At a velocity dispersion of {sigma} = 125 km s{sup -1} (Mass = 10{sup 10.55} M{sub Sun }) we find z{sub form} = 1.24 {+-} 0.05, while at {sigma} = 225 km s{sup -1} (Mass = 10{sup 11.36} M{sub Sun }) the formation redshift is z{sub form} = 1.95{sup +0.3}{sub -0.2}, for a Salpeter initial mass function. The three clusters follow similar scaling relations between absorption line indices and velocity dispersions as those found for low-redshift galaxies. The zero point offsets for the Balmer lines depend on cluster redshifts. However, the offsets indicate a slower evolution, and therefore higher formation redshift, than the zero point differences found from the FP, if interpreting the data using a passive evolution model. Specifically, the strength of the higher order Balmer lines H{delta} and H{gamma} implies z{sub form} > 2.8. The scaling relations for the metal indices in general show small and in some cases insignificant zero point offsets, favoring high formation redshifts for a passive evolution model. Based on the absorption line indices and recent stellar population models from Thomas et al., we find that MS0451.6-0305 has a mean metallicity [M/H] approximately 0.2 dex below that of the other clusters and our low-redshift sample. We confirm our previous result that RXJ0152.7-1357 has a mean abundance ratio [{alpha}/Fe] approximately 0.3 dex higher than that of the other clusters. The differences in [M/H] and [{alpha}/Fe] between the high-redshift clusters and the low-redshift sample are inconsistent with a passive evolution scenario for early-type cluster galaxies over the redshift interval studied. Low-level star formation may be able to bring the metallicity of MS0451.6-0305 in agreement with the low-redshift sample, while we speculate whether galaxy mergers can lead to sufficiently large changes in the abundance ratios for the RXJ0152.7-1357 galaxies to allow them to reach the low-redshift sample values in the time available.« less

Quasiparticle lifetime broadening in resonant x-ray scattering of NH4NO3

NASA Astrophysics Data System (ADS)

Vinson, John; Jach, Terrence; Müller, Matthias; Unterumsberger, Rainer; Beckhoff, Burkhard

2016-07-01

It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectra from the N K edge of the insulating crystal ammonium nitrate. First, vibrational disorder causes major changes in the absorption spectrum, originating not only from the thermal population of phonons, but, significantly, from zero-point motion as well. Second, the anomalously large broadening (˜4 eV) of the emission originating from nitrate σ states is due to the unusually short lifetimes of quasiparticles in an otherwise extremely narrow band. In this work, we investigate the coupling of these effects to core and valence excitons that are created as the initial x-ray excitation energy is progressively reduced toward the N edge. Using a G W /Bethe-Salpeter approach, we show the extent to which this anomalous broadening is captured by the G W approximation. The data and calculations demonstrate the importance that the complex self-energies (finite lifetimes) of the valence bands have on the interpretation of emission spectra. We produce a scheme to explain why extreme lifetimes should appear in σ states of other similar compounds.

Quantification of soil erosion rates related to ancient Maya deforestation

NASA Astrophysics Data System (ADS)

Anselmetti, Flavio S.; Hodell, David A.; Ariztegui, Daniel; Brenner, Mark; Rosenmeier, Michael F.

2007-10-01

We used seismic and sediment core data to quantify soil erosion rates for the past ˜6000 yr in the closed catchment of Lake Salpetén, in the tropical lowlands of northern Guatemala. The region was affected by ancient Maya land use from before ca. 1000 B.C. to A.D. 900. This period of human impact coincided with deposition in the lake of a detrital unit (Maya Clay) as much as 7 m thick that contrasts sharply with the relatively organic-rich gyttja deposited both before and after Maya occupation of the watershed. The greatest soil loss, with mean sustained values of ˜1000 t/km2yr-1, occurred in the Middle and Late Preclassic Periods (700 B.C. to A.D. 250), associated with relatively low Maya population densities. Soil erosion slowed during the period of maximum population density in the Late Classic Period (A.D. 550-830), indicating a decoupling between human population density and soil erosion rate. The most rapid soil loss occurred early during initial land clearance, suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes.

HST/WFC3 OBSERVATIONS OF LOW-MASS GLOBULAR CLUSTERS AM 4 AND PALOMAR 13: PHYSICAL PROPERTIES AND IMPLICATIONS FOR MASS LOSS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamren, Katherine M.; Smith, Graeme H.; Guhathakurta, Puragra

2013-11-01

We investigate the loss of low-mass stars in two of the faintest globular clusters known, AM 4 and Palomar 13 (Pal 13), using HST/WFC3 F606W and F814W photometry. To determine the physical properties of each cluster—age, mass, metallicity, extinction, and present day mass function (MF)—we use the maximum likelihood color-magnitude diagram (CMD) fitting program MATCH and the Dartmouth, Padova, and BaSTI stellar evolution models. For AM 4, the Dartmouth models provide the best match to the CMD and yield an age of >13 Gyr, metallicity log Z/Z {sub ☉} = –1.68 ± 0.08, a distance modulus (m – M) {submore » V} = 17.47 ± 0.03, and reddening A{sub V} = 0.19 ± 0.02. For Pal 13 the Dartmouth models give an age of 13.4 ± 0.5 Gyr, log Z/Z {sub ☉} = –1.55 ± 0.06, (m – M) {sub V} = 17.17 ± 0.02, and A{sub V} = 0.43 ± 0.01. We find that the systematic uncertainties due to choice in assumed stellar model greatly exceed the random uncertainties, highlighting the importance of using multiple stellar models when analyzing stellar populations. Assuming a single-sloped power-law MF, we find that AM 4 and Pal 13 have spectral indices α = +0.68 ± 0.34 and α = –1.67 ± 0.25 (where a Salpeter MF has α = +1.35), respectively. Comparing our derived slopes with literature measurements of cluster integrated magnitude (M{sub V} ) and MF slope indicates that AM 4 is an outlier. Its MF slope is substantially steeper than clusters of comparable luminosity, while Pal 13 has an MF in line with the general trend. We discuss both primordial and dynamical origins for the unusual MF slope of AM 4 and tentatively favor the dynamical scenario. However, MF slopes of more low luminosity clusters are needed to verify this hypothesis.« less

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

NASA Astrophysics Data System (ADS)

Pattle, K.; Ward-Thompson, D.; Kirk, J. M.; Di Francesco, J.; Kirk, H.; Mottram, J. C.; Keown, J.; Buckle, J.; Beaulieu, S. F.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Hatchell, J.; Jenness, T.; Johnstone, D.; Nutter, D.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Walker-Smith, S.; Hogerheijde, M. R.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coudé, S.; Davis, C. J.; Drabek-Maunder, E.; Duarte-Cabral, A.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Sadavoy, S.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

2017-02-01

We present observations of the Cepheus Flare obtained as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2 instrument. We produce a catalogue of sources found by SCUBA-2, and separate these into starless cores and protostars. We determine masses and densities for each of our sources, using source temperatures determined by the Herschel Gould Belt Survey. We compare the properties of starless cores in four different molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core mass functions for each region typically show shallower-than-Salpeter behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores to Class II protostars, while L1251 and L1174 have a low ratio, consistent with the latter regions being more active sites of current star formation, while the former are forming stars less actively. We determine that if modelled as thermally supported Bonnor-Ebert spheres, most of our cores have stable configurations accessible to them. We estimate the external pressures on our cores using archival 13CO velocity dispersion measurements and find that our cores are typically pressure confined, rather than gravitationally bound. We perform a virial analysis on our cores, and find that they typically cannot be supported against collapse by internal thermal energy alone, due primarily to the measured external pressures. This suggests that the dominant mode of internal support in starless cores in the Cepheus Flare is either non-thermal motions or internal magnetic fields.

An Application of Gröbner Basis in Differential Equations of Physics

NASA Astrophysics Data System (ADS)

Chaharbashloo, Mohammad Saleh; Basiri, Abdolali; Rahmany, Sajjad; Zarrinkamar, Saber

2013-11-01

We apply the Gröbner basis to the ansatz method in quantum mechanics to obtain the energy eigenvalues and the wave functions in a very simple manner. There are important physical potentials such as the Cornell interaction which play significant roles in particle physics and can be treated via this technique. As a typical example, the algorithm is applied to the semi-relativistic spinless Salpeter equation under the Cornell interaction. Many other applications of the idea in a wide range of physical fields are listed as well.

Frenkel versus charge-transfer exciton dispersion in molecular crystals

NASA Astrophysics Data System (ADS)

Cudazzo, Pierluigi; Gatti, Matteo; Rubio, Angel; Sottile, Francesco

2013-11-01

By solving the many-body Bethe-Salpeter equation at finite momentum transfer, we characterize the exciton dispersion in two prototypical molecular crystals, picene and pentacene, in which localized Frenkel excitons compete with delocalized charge-transfer excitons. We explain the exciton dispersion on the basis of the interplay between electron and hole hopping and electron-hole exchange interaction, unraveling a simple microscopic description to distinguish Frenkel and charge-transfer excitons. This analysis is general and can be applied to other systems in which the electron wave functions are strongly localized, as in strongly correlated insulators.

Is the black hole in NGC 1277 really overmassive?

NASA Astrophysics Data System (ADS)

Emsellem, Eric

2013-08-01

A recent claim has been made by van den Bosch et al. that the fast-rotator galaxy NGC 1277 hosts an overmassive black hole with a mass (1.7 × 1010 M⊙) larger than half its (central) stellar spheroid mass. We revisit this claim here by examining the predictions from simple dynamical realizations based on new multi-Gaussian expansion (MGE) models of NGC 1277, using the same inclination i = 75°, and constant mass-to-light ratios. We present realizations which fit well the observed photometry taking into account an approximation for the extinction due to the central dust ring. The mass-to-light ratio M/L is fixed following scaling relations which predict a Salpeter-like initial mass function for such a luminous early-type fast rotator, 60 per cent higher than the one of the previously derived best-fitting model. A model without a black hole provides a surprisingly good fit of the observed kinematics outside the unresolved central region, but not, as expected, of the central dispersion and Gauss-Hermite h4 values. A model with a black hole mass of 5 × 109 M⊙ allows us to fit the central dispersion profile, consistently with models of the same mass and M/L in van den Bosch et al. It departs from the central h4 values by only about twice the given uncertainty. A slightly varying M/L or the addition of high-velocity stars in the central spatially unresolved region would further lower the need for a very massive black hole in the central region of NGC 1277. These results do not, by themselves, rule out the presence of a presumed overmassive black hole at the centre of NGC 1277. However, they lead us to advocate the use of 3σ (as opposed to 1σ) confidence intervals for derived MBH as better, more conservative, guidelines for such studies. We also caution for the use of ill-defined spheroidal components as an input for scaling relations, and emphasize the fact that a MBH in the range 2-5 × 109 M⊙ would represent less than 5 per cent of the spheroid bulge-like mass of our models and less than 2.5 per cent of its total stellar mass. This would make the black hole in NGC 1277 consistent or just twice as large as what a recent version of the MBH-σ predicts, well within the observed scatter. We examine the impact of the presence of an inner bar by running simulations from the same MGE model but with extreme anisotropies. An inner small (600 pc diameter) bar forms, and an end-on view does get closer to fitting the central dispersion profile (and fits the h3 amplitude) without the need for a central dark mass, while adding a black hole of 2.5 × 109 M⊙, in line with the prediction from scaling relations, allows us to fit the dispersion peak and h3 profiles. Both models, however, still fail to fit the central h4 value (overpredicting the mean velocity). The claimed large mass of the presumed black hole therefore mostly relies on the measured positive high central h4 (at high dispersion), which can be associated with broad wings in the line-of-sight velocity distribution (high-velocity stars). This emphasizes the need to go beyond medium-resolution long-slit kinematics, with e.g. high-resolution integral-field spectroscopic data. In the specific case of NGC 1277, molecular or ionized gas kinematics (if present) within the central arcsecond (or at large scale) may provide a strong discriminant between these various models. We finally briefly discuss the fact that NGC 1277 resembles a scaled-up version of e.g. NGC 4342, another nearly edge-on fast rotator with a potentially large (but not overmassive) black hole.

A comprehensive study of the rich open star cluster NGC 2099 based on deep BVI CCD observations

NASA Astrophysics Data System (ADS)

Nilakshi,; Sagar, R.

2002-01-01

The CCD observations of the rich open star cluster NGC 2099 and its surrounding field region have been carried out up to a limiting magnitude of V ~ 22 mag in B, V and I passbands for the first time. A total of ~ 12 000 stars have been observed in the area of about 24arcmin x 34arcmin in the cluster region, as well as ~ 2180 stars in the ~ 12arcmin x 12arcmin area of the field region located ~ 45arcmin away from the cluster center. The cluster parameters determined by fitting the convective core overshoot isochrones in the V, (B-V) and V, (V-I) diagrams are E(B-V) = 0.30+/-0.04 mag, distance = 1360+/- 100 pc, age = 400 Myr and metallicity Z = 0.008. A well-defined cluster main sequence spread over about 8 mag in range is observed for the first time. Its intrinsic spread amounting to ~ 0.06 mag in colour is almost the same over the entire brightness and can be understood in terms of the presence of physical/optical binaries. The core and cluster radii determined from the radial stellar density profiles are 185 arcsec and 1000 arcsec respectively. Only about 22% of cluster members are present in the core region. The effects of mass segregation, most probably due to dynamical evolution, have been observed in the cluster. The mass function slope of the entire cluster is ~ -0.67+/-0.12. It becomes closer to the Salpeter value of -1.35, if flattening in the cluster mass function due to presence of both binaries and a much more extended corona is considered. Full Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/65

Black holes in binary stellar systems and galactic nuclei

NASA Astrophysics Data System (ADS)

Cherepashchuk, A. M.

2014-04-01

In the last 40 years, following pioneering papers by Ya B Zeldovich and E E Salpeter, in which a powerful energy release from nonspherical accretion of matter onto a black hole (BH) was predicted, many observational studies of black holes in the Universe have been carried out. To date, the masses of several dozen stellar-mass black holes (M_BH = (4{-}20) M_\\odot) in X-ray binary systems and of several hundred supermassive black holes (M_BH = (10^{6}{-}10^{10}) M_\\odot) in galactic nuclei have been measured. The estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozen supermassive black holes, the values of the dimensionless angular momentum a_* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a_* = 0.998. A new field of astrophysics, so-called black hole demography, which studies the birth and growth of black holes and their evolutionary connection to other objects in the Universe, namely stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. The evolutionary relations between supermassive black holes in galactic centers and spheroidal stellar components (bulges) of galaxies, as well as dark-matter galactic haloes are brought out. The launch into Earth's orbit of the space radio interferometer RadioAstron opened up the real possibility of finally proving that numerous discovered massive and highly compact objects with properties very similar to those of black holes make up real black holes in the sense of Albert Einstein's General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths \\lambda \\lesssim 1 mm (the international program, Event Horizon Telescope).

The Intermediate Stellar Mass Population in R136 Determined from Hubble Space Telescope Planetary Camera 2 Images

NASA Astrophysics Data System (ADS)

Hunter, Deidre A.; Shaya, Edward J.; Holtzman, Jon A.; Light, Robert M.; O'Neil, Earl J., Jr.; Lynds, Roger

1995-07-01

We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01 pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M555,0 of 0.9 or a mass of 2.8 Msun. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8 Msun, and stars with M555,0 ≥ 0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4 Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15 Msun in three annuli from 0.5-4.7 pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5 pc. Furthermore, the combined IMF slope, -122±006 is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: ≤ 2.8 Msun beyond 0.5 pc and ≤ 7 Msun within 0.1 pc. This is contrary to some predictions that the lower mass limit could be as high as 10 Msun in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for the core radius of 0.02 pc is set. Within a radius of 0.4 pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5 pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M555,0 = -5 and of a deficit in the highest mass stars between 0.6 pc and 1.2 pc. This would be consistent with dynamical segregation.

Spin dynamics of qqq wave function on light front in high momentum limit of QCD: Role of qqq force

NASA Astrophysics Data System (ADS)

Mitra, A. N.

2008-04-01

The contribution of a spin-rich qqq force (in conjunction with pairwise qq forces) to the analytical structure of the qqq wave function is worked out in the high momentum regime of QCD where the confining interaction may be ignored, so that the dominant effect is Coulombic. A distinctive feature of this study is that the spin-rich qqq force is generated by a ggg vertex (a genuine part of the QCD Lagrangian) wherein the 3 radiating gluon lines end on as many quark lines, giving rise to a (Mercedes-Benz type) Y-shaped diagram. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. With these ingredients, the differential equation for the 3D wave function ϕ receives well-defined contributions from the qq and qqq forces. In particular a negative eigenvalue of the spin operator iσ1 · σ2 × σ3 which is an integral part of the qqq force, causes a characteristic singularity in the differential equation, signalling the dynamical effect of a spin-rich qqq force not yet considered in the literature. The potentially crucial role of this interesting effect vis-a-vis the so-called 'spin anomaly' of the proton, is a subject of considerable physical interest.

VizieR Online Data Catalog: HST photometry in R136 (Hunter+ 1995)

NASA Astrophysics Data System (ADS)

Hunter, D. A.; Shaya, E. J.; Holtzman, J. A.; Light, R. M.; Oneil, Earl J., Jr.

1996-01-01

We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_555.0 of 0.9 or a mass of 2.8M⊙. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8M⊙, and stars with M_555.0>=0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15M⊙ in three annuli from 0.5-4.7pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5pc. Furthermore, the combined IMF slope, -1.22+/-0.06, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <=2.8M⊙ beyond 0.5pc and <=7M⊙ within 0.1pc. This is contrary to some predictions that the lower mass limit could be as high as 10M⊙ in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for core radius of 0.02pc is set. Within a radius of 0.4pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M_555.0=-5 and of a deficit in the highest mass stars between 0.6pc and 1.2pc. This would be consistent with dynamical segregation. (1 data file).

Effects of phonon broadening on x-ray near-edge spectra in molecular crystals

NASA Astrophysics Data System (ADS)

Vinson, John; Jach, Terrence; Elam, Tim; Denlinger, Jonathon

2014-03-01

Calculations of near-edge x-ray spectra are often carried out using the average atomic coordinates from x-ray or neutron scattering experiments or from density functional theory (DFT) energy minimization. This neglects disorder from thermal and zero-point vibrations. Here we look at the nitrogen K-edge of ammonium chloride and ammonium nitrate, comparing Bethe-Salpeter calculations of absorption and fluorescence to experiment. We find that intra-molecular vibrational effects lead to significant, non-uniform broadening of the spectra, and that for some features zero-point motion is the primary source of the observed shape.

Relativistic bound states in three space-time dimensions in Minkowski space

NASA Astrophysics Data System (ADS)

Gutierrez, C.; Gigante, V.; Frederico, T.; Tomio, Lauro

2016-01-01

With the aim to derive a workable framework for bound states in Minkowski space, we have investigated the Nakanishi perturbative integral representation of the Bethe-Salpeter (BS) amplitude in two-dimensions (2D) in space and time (2+1). The homogeneous BS amplitude, projected onto the light-front plane, is used to derive an equation for the Nakanishi weight function. The formal development is illustrated in detail and applied to the bound system composed by two scalar particles interacting through the exchange of a massive scalar. The explicit forms of the integral equations are obtained in ladder approximation.

Chempy: A flexible chemical evolution model for abundance fitting. Do the Sun's abundances alone constrain chemical evolution models?

NASA Astrophysics Data System (ADS)

Rybizki, Jan; Just, Andreas; Rix, Hans-Walter

2017-09-01

Elemental abundances of stars are the result of the complex enrichment history of their galaxy. Interpretation of observed abundances requires flexible modeling tools to explore and quantify the information about Galactic chemical evolution (GCE) stored in such data. Here we present Chempy, a newly developed code for GCE modeling, representing a parametrized open one-zone model within a Bayesian framework. A Chempy model is specified by a set of five to ten parameters that describe the effective galaxy evolution along with the stellar and star-formation physics: for example, the star-formation history (SFH), the feedback efficiency, the stellar initial mass function (IMF), and the incidence of supernova of type Ia (SN Ia). Unlike established approaches, Chempy can sample the posterior probability distribution in the full model parameter space and test data-model matches for different nucleosynthetic yield sets. It is essentially a chemical evolution fitting tool. We straightforwardly extend Chempy to a multi-zone scheme. As an illustrative application, we show that interesting parameter constraints result from only the ages and elemental abundances of the Sun, Arcturus, and the present-day interstellar medium (ISM). For the first time, we use such information to infer the IMF parameter via GCE modeling, where we properly marginalize over nuisance parameters and account for different yield sets. We find that 11.6+ 2.1-1.6% of the IMF explodes as core-collapse supernova (CC-SN), compatible with Salpeter (1955, ApJ, 121, 161). We also constrain the incidence of SN Ia per 103M⊙ to 0.5-1.4. At the same time, this Chempy application shows persistent discrepancies between predicted and observed abundances for some elements, irrespective of the chosen yield set. These cannot be remedied by any variations of Chempy's parameters and could be an indication of missing nucleosynthetic channels. Chempy could be a powerful tool to confront predictions from stellar nucleosynthesis with far more complex abundance data sets and to refine the physical processes governing the chemical evolution of stellar systems.

Flavour symmetry breaking in the kaon parton distribution amplitude

DOE PAGES

none,

2014-11-01

We compute the kaon's valence-quark (twist-two parton) distribution amplitude (PDA) by projecting its Poincaré-covariant Bethe–Salpeter wave-function onto the light-front. At a scale ζ = 2 GeV, the PDA is a broad, concave and asymmetric function, whose peak is shifted 12–16% away from its position in QCD's conformal limit. These features are a clear expression of SU(3)-flavour-symmetry breaking. They show that the heavier quark in the kaon carries more of the bound-state's momentum than the lighter quark and also that emergent phenomena in QCD modulate the magnitude of flavour-symmetry breaking: it is markedly smaller than one might expect based on themore » difference between light-quark current masses. Our results add to a body of evidence which indicates that at any energy scale accessible with existing or foreseeable facilities, a reliable guide to the interpretation of experiment requires the use of such nonperturbatively broadened PDAs in leading-order, leading-twist formulae for hard exclusive processes instead of the asymptotic PDA associated with QCD's conformal limit. We illustrate this via the ratio of kaon and pion electromagnetic form factors: using our nonperturbative PDAs in the appropriate formulae, F K/F π=1.23 at spacelike-Q 2=17 GeV 2, which compares satisfactorily with the value of 0.92(5) inferred in e +e - annihilation at s=17 GeV 2.« less

Probing ionization potential, electron affinity and self-energy effect on the spectral shape and exciton binding energy of quantum liquid water with self-consistent many-body perturbation theory and the Bethe-Salpeter equation.

PubMed

Ziaei, Vafa; Bredow, Thomas

2018-05-31

An accurate theoretical prediction of ionization potential (IP) and electron affinity (EA) is key in understanding complex photochemical processes in aqueous environments. There have been numerous efforts in literature to accurately predict IP and EA of liquid water, however with often conflicting results depending on the level of theory and the underlying water structures. In a recent study based on hybrid-non-self-consistent many-body perturbation theory (MBPT) Gaiduk et al (2018 Nat. Commun. 9 247) predicted an IP of 10.2 eV and EA of 0.2 eV, resulting in an electronic band gap (i.e. electronic gap (IP-EA) as measured by photoelectron spectroscopy) of about 10 eV, redefining the widely cited experimental gap of 8.7 eV in literature. In the present work, we show that GW self-consistency and an implicit vertex correction in MBPT considerably affect recently reported EA values by Gaiduk et al (2018 Nat. Commun. 9 247) by about 1 eV. Furthermore, the choice of pseudo-potential is critical for an accurate determination of the absolute band positions. Consequently, the self-consistent GW approach with an implicit vertex correction based on projector augmented wave (PAW) method on top of quantum water structures predicts an IP of 10.2, an EA of 1.1, a fundamental gap of 9.1 eV and an exciton binding (Eb) energy of 0.9 eV for the first absorption band of liquid water via the Bethe-Salpeter equation (BSE). Only within such a self-consistent approach a simultanously accurate prediction of IP, EA, Eg, Eb is possible.

Probing ionization potential, electron affinity and self-energy effect on the spectral shape and exciton binding energy of quantum liquid water with self-consistent many-body perturbation theory and the Bethe–Salpeter equation

NASA Astrophysics Data System (ADS)

Ziaei, Vafa; Bredow, Thomas

2018-05-01

An accurate theoretical prediction of ionization potential (IP) and electron affinity (EA) is key in understanding complex photochemical processes in aqueous environments. There have been numerous efforts in literature to accurately predict IP and EA of liquid water, however with often conflicting results depending on the level of theory and the underlying water structures. In a recent study based on hybrid-non-self-consistent many-body perturbation theory (MBPT) Gaiduk et al (2018 Nat. Commun. 9 247) predicted an IP of 10.2 eV and EA of 0.2 eV, resulting in an electronic band gap (i.e. electronic gap (IP-EA) as measured by photoelectron spectroscopy) of about 10 eV, redefining the widely cited experimental gap of 8.7 eV in literature. In the present work, we show that GW self-consistency and an implicit vertex correction in MBPT considerably affect recently reported EA values by Gaiduk et al (2018 Nat. Commun. 9 247) by about 1 eV. Furthermore, the choice of pseudo-potential is critical for an accurate determination of the absolute band positions. Consequently, the self-consistent GW approach with an implicit vertex correction based on projector augmented wave (PAW) method on top of quantum water structures predicts an IP of 10.2, an EA of 1.1, a fundamental gap of 9.1 eV and an exciton binding (Eb) energy of 0.9 eV for the first absorption band of liquid water via the Bethe–Salpeter equation (BSE). Only within such a self-consistent approach a simultanously accurate prediction of IP, EA, Eg, Eb is possible.

A Nakanishi-based model illustrating the covariant extension of the pion GPD overlap representation and its ambiguities

NASA Astrophysics Data System (ADS)

Chouika, N.; Mezrag, C.; Moutarde, H.; Rodríguez-Quintero, J.

2018-05-01

A systematic approach for the model building of Generalized Parton Distributions (GPDs), based on their overlap representation within the DGLAP kinematic region and a further covariant extension to the ERBL one, is applied to the valence-quark pion's case, using light-front wave functions inspired by the Nakanishi representation of the pion Bethe-Salpeter amplitudes (BSA). This simple but fruitful pion GPD model illustrates the general model building technique and, in addition, allows for the ambiguities related to the covariant extension, grounded on the Double Distribution (DD) representation, to be constrained by requiring a soft-pion theorem to be properly observed.

Nonequilibrium itinerant-electron magnetism: A time-dependent mean-field theory

NASA Astrophysics Data System (ADS)

Secchi, A.; Lichtenstein, A. I.; Katsnelson, M. I.

2016-08-01

We study the dynamical magnetic susceptibility of a strongly correlated electronic system in the presence of a time-dependent hopping field, deriving a generalized Bethe-Salpeter equation that is valid also out of equilibrium. Focusing on the single-orbital Hubbard model within the time-dependent Hartree-Fock approximation, we solve the equation in the nonequilibrium adiabatic regime, obtaining a closed expression for the transverse magnetic susceptibility. From this, we provide a rigorous definition of nonequilibrium (time-dependent) magnon frequencies and exchange parameters, expressed in terms of nonequilibrium single-electron Green's functions and self-energies. In the particular case of equilibrium, we recover previously known results.

The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

NASA Astrophysics Data System (ADS)

Davies, Ben; Clark, J. S.; Trombley, Christine; Figer, Donald F.; Najarro, Francisco; Crowther, Paul A.; Kudritzki, Rolf-Peter; Thompson, Mark; Urquhart, James S.; Hindson, Luke

2012-01-01

The G305 H II complex (G305.4+0.1) is one of the most massive star-forming structures yet identified within the Galaxy. It is host to many massive stars at all stages of formation and evolution, from embedded molecular cores to post-main-sequence stars. Here, we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2, using Hubble Space Telescope+NICMOS imaging and Very Large Telescope+ISAAC spectroscopy. We find that the spectrophotometric distance to the clusters is consistent with the kinematic distance to the G305 complex, an average of all measurements giving a distance of 3.8 ± 0.6 kpc. From analysis of the stellar populations and the pre-main-sequence stars, we find that Danks 2 is the elder of the two clusters, with an age of 3+3- 1 Myr. Danks 1 is clearly younger with an age of 1.5+1.5- 0.5 Myr, and is dominated by three very luminous H-rich Wolf-Rayet stars which may have masses ≳100 M⊙. The two clusters have mass functions consistent with the Salpeter slope, and total cluster masses of 8000 ± 1500 and 3000 ± 800 M⊙ for Danks 1 and Danks 2, respectively. Danks 1 is significantly the more compact cluster of the two, and is one of the densest clusters in the Galaxy with log (ρ/M⊙ pc-3) = 5.5+0.5- 0.4. In addition to the clusters, there is a population of apparently isolated Wolf-Rayet stars within the molecular cloud's cavity. Our results suggest that the star-forming history of G305 began with the formation of Danks 2, and subsequently Danks 1, with the origin of the diffuse evolved population currently uncertain. Together, the massive stars at the centre of the G305 region appear to be clearing away what is left of the natal cloud, triggering a further generation of star formation at the cloud's periphery.

Optical and near-infrared survey of the stellar contents associated with the star-forming complex Sh2-252

NASA Astrophysics Data System (ADS)

Jose, Jessy; Pandey, A. K.; Ogura, K.; Samal, M. R.; Ojha, D. K.; Bhatt, B. C.; Chauhan, N.; Eswaraiah, C.; Mito, H.; Kobayashi, N.; Yadav, R. K.

2012-08-01

We present the analyses of the stellar contents associated with the extended H II region Sh2-252 using deep optical UBVRI photometry, slit and slitless spectroscopy along with the near-infrared (NIR) data from Two-Micron All-Sky Survey (2MASS) for an area ˜ 1 × 1 deg2. We have studied the sub-regions of Sh2-252, which includes four compact-H II (CH II ) regions, namely A, B, C and E, and two clusters, NGC 2175s and Teutsch 136 (Teu 136). Of the 15 spectroscopically observed bright stars, eight have been identified as massive members of spectral class earlier than B3. From the spectrophotometric analyses, we derived the average distance of the region as 2.4 ± 0.2 kpc, and the reddening E(B - V) of the massive members is found to vary between 0.35 and 2.1 mag. We found that NGC 2175s and Teu 136, located towards the eastern edge of the complex, are the sub-clusters of Sh2-252. The stellar surface density distribution in K band shows clustering associated with the regions A, C, E, NGC 2175s and Teu 136. We have also identified the candidate ionizing sources of the CH II regions. 61 Hα emission sources are identified using slitless spectroscopy. The distribution of the Hα emission sources and candidate young stellar objects (YSOs) with IR excess on the V/(V - I) colour-magnitude diagram (CMD) shows that a majority of them have approximate ages between 0.1 and 5 Myr and masses in the range of 0.3-2.5 M⊙. The optical CMDs of the candidate pre-main-sequence (PMS) sources in the individual regions also show an age spread of 0.1-5 Myr for each of them. We calculated the K-band luminosity functions (KLFs) for the sub-regions A, C, E, NGC 2175s and Teu 136. Within errors, the KLFs for all the sub-regions are found to be similar and comparable to that of young clusters of age <5 Myr. We also estimated the mass function of the PMS sample of the individual regions in the mass range of 0.3-2.5 M⊙. In general, the slopes of the MFs of all the sub-regions are found comparable to the Salpeter value.

Prediction of a two-dimensional S3N2 solid for optoelectronic applications

NASA Astrophysics Data System (ADS)

Xiao, Hang; Shi, Xiaoyang; Liao, Xiangbiao; Zhang, Yayun; Chen, Xi

2018-02-01

Two-dimensional materials have attracted tremendous attention for their fascinating electronic, optical, chemical, and mechanical properties. However, the band gaps of most reported two-dimensional (2D) materials are smaller than 2.0 eV, which has greatly restricted their optoelectronic applications in the blue and ultraviolet range of the spectrum. Here, we propose a stable trisulfur dinitride (S3N2 ) 2D crystal that is a covalent network composed solely of S-N σ bonds. The S3N2 crystal is dynamically, thermally, and chemically stable, as confirmed by the computed phonon spectrum and ab initio molecular dynamics simulations. GW calculations show that the S3N2 crystal is a wide, direct band-gap (3.92 eV) semiconductor with a small-hole effective mass. In addition, the band gap of S3N2 structures can be tuned by forming multilayer S3N2 crystals, S3N2 nanoribbons, and S3N2 nanotubes, expanding its potential applications. The anisotropic optical response of the 2D S3N2 crystal is revealed by GW-Bethe-Salpeter-equation calculations. The optical band gap of S3N2 is 2.73 eV and the exciton binding energy of S3N2 is 1.19 eV, showing a strong excitonic effect. Our result not only marks the prediction of a 2D crystal composed of nitrogen and sulfur, but also underpins potential innovations in 2D electronics and optoelectronics.

Against Laplacian Reduction of Newtonian Mass to Spatiotemporal Quantities

NASA Astrophysics Data System (ADS)

Martens, Niels C. M.

2018-05-01

Laplace wondered about the minimal choice of initial variables and parameters corresponding to a well-posed initial value problem. Discussions of Laplace's problem in the literature have focused on choosing between spatiotemporal variables relative to absolute space (i.e. substantivalism) or merely relative to other material bodies (i.e. relationalism) and between absolute masses (i.e. absolutism) or merely mass ratios (i.e. comparativism). This paper extends these discussions of Laplace's problem, in the context of Newtonian Gravity, by asking whether mass needs to be included in the initial state at all, or whether a purely spatiotemporal initial state suffices. It is argued that mass indeed needs to be included; removing mass from the initial state drastically reduces the predictive and explanatory power of Newtonian Gravity.

Against Laplacian Reduction of Newtonian Mass to Spatiotemporal Quantities

NASA Astrophysics Data System (ADS)

Martens, Niels C. M.

2018-03-01

Laplace wondered about the minimal choice of initial variables and parameters corresponding to a well-posed initial value problem. Discussions of Laplace's problem in the literature have focused on choosing between spatiotemporal variables relative to absolute space (i.e. substantivalism) or merely relative to other material bodies (i.e. relationalism) and between absolute masses (i.e. absolutism) or merely mass ratios (i.e. comparativism). This paper extends these discussions of Laplace's problem, in the context of Newtonian Gravity, by asking whether mass needs to be included in the initial state at all, or whether a purely spatiotemporal initial state suffices. It is argued that mass indeed needs to be included; removing mass from the initial state drastically reduces the predictive and explanatory power of Newtonian Gravity.

From Bethe–Salpeter Wave functions to Generalised Parton Distributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mezrag, C.; Moutarde, H.; Rodríguez-Quintero, J.

2016-06-06

We review recent works on the modelling of Generalised Parton Distributions within the Dyson-Schwinger formalism. We highlight how covariant computations, using the impulse approximation, allows one to fulfil most of the theoretical constraints of the GPDs. A specific attention is brought to chiral properties and especially the so-called soft pion theorem, and its link with the Axial-Vector Ward-Takahashi identity. The limitation of the impulse approximation are also explained. Beyond impulse approximation computations are reviewed in the forward case. Finally, we stress the advantages of the overlap of lightcone wave functions, and possible ways to construct covariant GPD models within thismore » framework, in a two-body approximation« less

Quasi-particle energies and optical excitations of hydrogenated and fluorinated germanene.

PubMed

Shu, Huabing; Li, Yunhai; Wang, Shudong; Wang, Jinlan

2015-02-14

Using density functional theory, the G0W0 method and Bethe-Salpeter equation calculations, we systematically explore the structural, electronic and optical properties of hydrogenated and fluorinated germanene. The hydrogenated/fluorinated germanene tends to form chair and zigzag-line configurations and its electronic and optical properties show close geometry dependence. The chair hydrogenated/fluorinated and zigzag-line fluorinated germanene are direct band-gap semiconductors, while the zigzag-line hydrogenated germanene owns an indirect band-gap. Moreover, the quasi-particle corrections are significant and strong excitonic effects with large exciton binding energies are observed. Moreover, the zigzag-line hydrogenated/fluorinated germanene shows highly anisotropic optical responses, which may be used as a good optical linear polarizer.

The infrared behaviour of QCD Green's functions. Confinement, dynamical symmetry breaking, and hadrons as relativistic bound states

NASA Astrophysics Data System (ADS)

Alkofer, Reinhard; von Smekal, Lorenz

2001-11-01

Recent studies of QCD Green's functions and their applications in hadronic physics are reviewed. We discuss the definition of the generating functional in gauge theories, in particular, the rôle of redundant degrees of freedom, possibilities of a complete gauge fixing versus gauge fixing in presence of Gribov copies, BRS invariance and positivity. The apparent contradiction between positivity and colour antiscreening in combination with BRS invariance in QCD is considered. Evidence for the violation of positivity by quarks and transverse gluons in the covariant gauge is collected, and it is argued that this is one manifestation of confinement. We summarise the derivation of the Dyson-Schwinger equations (DSEs) of QED and QCD. For the latter, the implications of BRS invariance on the Green's functions are explored. The possible influence of instantons on DSEs is discussed in a two-dimensional model. In QED in (2+1) and (3+1) dimensions, the solutions for Green's functions provide tests of truncation schemes which can under certain circumstances be extended to the DSEs of QCD. We discuss some limitations of such extensions and assess the validity of assumptions for QCD as motivated from studies in QED. Truncation schemes for DSEs are discussed in axial and related gauges, as well as in the Landau gauge. Furthermore, we review the available results from a systematic non-perturbative expansion scheme established for Landau gauge QCD. Comparisons to related lattice results, where available, are presented. The applications of QCD Green's functions to hadron physics are summarised. Properties of ground state mesons are discussed on the basis of the ladder Bethe-Salpeter equation for quarks and antiquarks. The Goldstone nature of pseudoscalar mesons and a mechanism for diquark confinement beyond the ladder approximation are reviewed. We discuss some properties of ground state baryons based on their description as Bethe-Salpeter/Faddeev bound states of quark-diquark correlations in the quantum field theory of confined quarks and gluons.

Early efficacy of the ketogenic diet is not affected by initial body mass index percentile.

PubMed

Shull, Shastin; Diaz-Medina, Gloria; Wong-Kisiel, Lily; Nickels, Katherine; Eckert, Susan; Wirrell, Elaine

2014-05-01

Predictors of the ketogenic diet's success in treating pediatric intractable epilepsy are not well understood. The aim of this study was to determine whether initial body mass index and weight percentile impact early efficacy of the traditional ketogenic diet in children initiating therapy for intractable epilepsy. This retrospective study included all children initiating the ketogenic diet at Mayo Clinic, Rochester from January 2001 to December 2010 who had body mass index (children ≥2 years of age) or weight percentile (those <2 years of age) documented at diet initiation and seizure frequency recorded at diet initiation and one month. Responders were defined as achieving a >50% seizure reduction from baseline. Our cohort consisted of 48 patients (20 male) with a median age of 3.1 years. There was no significant correlation between initial body mass index or weight percentile and seizure frequency reduction at one month (P = 0.72, r = 0.26 and P = 0.91, r = 0.03). There was no significant association between body mass index or weight percentile quartile and responder rates (P = 0.21 and P = 0.57). Children considered overweight or obese at diet initiation (body mass index or weight percentile ≥85) did not have lower responder rates than those with body mass index or weight percentiles <85 (6/14 vs 19/34, respectively, P = 0.41). Greater initial body mass index and weight-for-age percentiles do not adversely affect the efficacy of the ketogenic diet. Copyright © 2014 Elsevier Inc. All rights reserved.

EVOLUTIONARY MODELS OF SUPER-EARTHS AND MINI-NEPTUNES INCORPORATING COOLING AND MASS LOSS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howe, Alex R.; Burrows, Adam, E-mail: arhowe@astro.princeton.edu, E-mail: burrows@astro.princeton.edu

We construct models of the structural evolution of super-Earth- and mini-Neptune-type exoplanets with H{sub 2}–He envelopes, incorporating radiative cooling and XUV-driven mass loss. We conduct a parameter study of these models, focusing on initial mass, radius, and envelope mass fractions, as well as orbital distance, metallicity, and the specific prescription for mass loss. From these calculations, we investigate how the observed masses and radii of exoplanets today relate to the distribution of their initial conditions. Orbital distance and the initial envelope mass fraction are the most important factors determining planetary evolution, particularly radius evolution. Initial mass also becomes important belowmore » a “turnoff mass,” which varies with orbital distance, with mass–radius curves being approximately flat for higher masses. Initial radius is the least important parameter we study, with very little difference between the hot start and cold start limits after an age of 100 Myr. Model sets with no mass loss fail to produce results consistent with observations, but a plausible range of mass-loss scenarios is allowed. In addition, we present scenarios for the formation of the Kepler-11 planets. Our best fit to observations of Kepler-11b and Kepler-11c involves formation beyond the snow line, after which they moved inward, circularized, and underwent a reduced degree of mass loss.« less

Impact of nearest-neighbor repulsion on superconducting pairing in 2D extended Hubbard model

NASA Astrophysics Data System (ADS)

Jiang, Mi; Hahner, U. R.; Maier, T. A.; Schulthess, T. C.

Using dynamical cluster approximation (DCA) with an continuous-time QMC solver for the two-dimensional extended Hubbard model, we studied the impact of nearest-neighbor Coulomb repulsion V on d-wave superconducting pairing dynamics. By solving Bethe-Salpeter equation for particle-particle superconducting channel, we focused on the evolution of leading d-wave eigenvalue with V and the momentum and frequency dependence of the corresponding eigenfunction. The comparison with the evolution of both spin and charge susceptibilities versus V is presented showing the competition between spin and charge fluctuations. This research received generous support from the MARVEL NCCR and used resources of the Swiss National Supercomputing Center, as well as (INCITE) program in Oak Ridge Leadership Computing Facility.

Effects of a spin-flavour-dependent interaction on light-flavoured baryon helicity amplitudes

NASA Astrophysics Data System (ADS)

Ronniger, Michael; Metsch, Bernard Ch.

2013-01-01

This paper is a continuation of a previous work about the effects of a phenomenological flavour-dependent force in a relativistically covariant constituent quark model based on the Salpeter equation on the structure of light-flavoured baryon resonances. Here the longitudinal and transverse helicity amplitudes as studied experimentally in the electro-excitation of nucleon- and Δ-resonances are calculated. In particular the amplitudes for the excitation of three- and four-star resonances as calculated in a previous model A are compared to those of the novel model C as well as to existing and partially new experimental data such as, e.g., determined by the CB-ELSA Collaboration. A brief discussion on some improvements to model C is given after the introduction.

Chiral dynamics of the p wave in K-p and coupled states

NASA Astrophysics Data System (ADS)

Jido, D.; Oset, E.; Ramos, A.

2002-11-01

We perform an evaluation of the p-wave amplitudes of meson-baryon scattering in the strangeness S=-1 sector starting from the lowest order chiral Lagrangians and introducing explicitly the Σ* field with couplings to the meson-baryon states obtained using SU(6) symmetry. The N/D method of unitarization is used, equivalent, in practice, to the use of the Bethe-Salpeter equation with a cutoff. The procedure leaves no freedom for the p-waves once the s-waves are fixed and thus one obtains genuine predictions for the p-wave scattering amplitudes, which are in good agreement with experimental results for differential cross sections, as well as for the width and partial decay widths of the Σ*(1385).

Manipulating Light with Transition Metal Clusters, Organic Dyes, and Metal Organic Frameworks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogut, Serdar

The primary goals of our research program is to develop and apply state-of-the-art first-principles methods to predict electronic and optical properties of three systems of significant scientific and technological interest: transition metal clusters, organic dyes, and metal-organic frameworks. These systems offer great opportunities to manipulate light for a wide ranging list of energy-related scientific problems and applications. During this grant period, we focused our investigations on the development, implementation, and benchmarking of many-body Green’s function methods (GW approximation and the Bethe-Salpeter equation) to examine excited-state properties of transition metal/transition-metal-oxide clusters and organic molecules that comprise the building blocks of dyesmore » and metal-organic frameworks.« less

Nuclear force from lattice QCD.

PubMed

Ishii, N; Aoki, S; Hatsuda, T

2007-07-13

The nucleon-nucleon (NN) potential is studied by lattice QCD simulations in the quenched approximation, using the plaquette gauge action and the Wilson quark action on a 32(4) [approximately (4.4 fm)(4)] lattice. A NN potential V(NN)(r) is defined from the equal-time Bethe-Salpeter amplitude with a local interpolating operator for the nucleon. By studying the NN interaction in the (1)S(0) and (3)S(1) channels, we show that the central part of V(NN)(r) has a strong repulsive core of a few hundred MeV at short distances (r approximately < 0.5 fm) surrounded by an attractive well at medium and long distances. These features are consistent with the known phenomenological features of the nuclear force.

Derivative expansion of wave function equivalent potentials

NASA Astrophysics Data System (ADS)

Sugiura, Takuya; Ishii, Noriyoshi; Oka, Makoto

2017-04-01

Properties of the wave function equivalent potentials introduced by the HAL QCD collaboration are studied in a nonrelativistic coupled-channel model. The derivative expansion is generalized, and then applied to the energy-independent and nonlocal potentials. The expansion coefficients are determined from analytic solutions to the Nambu-Bethe-Salpeter wave functions. The scattering phase shifts computed from these potentials are compared with the exact values to examine the convergence of the expansion. It is confirmed that the generalized derivative expansion converges in terms of the scattering phase shift rather than the functional structure of the non-local potentials. It is also found that the convergence can be improved by tuning either the choice of interpolating fields or expansion scale in the generalized derivative expansion.

I -Love- Q relations for white dwarf stars

NASA Astrophysics Data System (ADS)

Boshkayev, K.; Quevedo, H.; Zhami, B.

2017-02-01

We investigate the equilibrium configurations of uniformly rotating white dwarfs, using Chandrasekhar and Salpeter equations of state in the framework of Newtonian physics. The Hartle formalism is applied to integrate the field equation together with the hydrostatic equilibrium condition. We consider the equations of structure up to the second order in the angular velocity, and compute all basic parameters of rotating white dwarfs to test the so-called moment of inertia, rotational Love number, and quadrupole moment (I-Love-Q) relations. We found that the I-Love-Q relations are also valid for white dwarfs regardless of the equation of state and nuclear composition. In addition, we show that the moment of inertia, quadrupole moment, and eccentricity (I-Q-e) relations are valid as well.

Quasiparticle and optical properties of strained stanene and stanane.

PubMed

Lu, Pengfei; Wu, Liyuan; Yang, Chuanghua; Liang, Dan; Quhe, Ruge; Guan, Pengfei; Wang, Shumin

2017-06-20

Quasiparticle band structures and optical properties of two dimensional stanene and stanane (fully hydrogenated stanene) are studied by the GW and GW plus Bethe-Salpeter equation (GW-BSE) approaches, with inclusion of the spin-orbit coupling (SOC). The SOC effect is significant for the electronic and optical properties in both stanene and stanane, compared with their group IV-enes and IV-anes counterparts. Stanene is a semiconductor with a quasiparticle band gap of 0.10 eV. Stanane has a sizable band gap of 1.63 eV and strongly binding exciton with binding energy of 0.10 eV. Under strain, the quasiparticle band gap and optical spectrum of both stanene and stanane are tunable.

The Initial Physical Conditions of Kepler-36 b and c

NASA Astrophysics Data System (ADS)

Owen, James E.; Morton, Timothy. D.

2016-03-01

The Kepler-36 planetary system consists of two exoplanets at similar separations (0.115 and 0.128 au), which have dramatically different densities. The inner planet has a density consistent with an Earth-like composition, while the outer planet is extremely low density, such that it must contain a voluminous H/He envelope. Such a density difference would pose a problem for any formation mechanism if their current densities were representative of their composition at formation. However, both planets are at close enough separations to have undergone significant evaporation in the past. We constrain the core mass, core composition, initial envelope mass, and initial cooling time of each planet using evaporation models conditioned on their present-day masses and radii, as inferred from Kepler photometry and transit timing analysis. The inner planet is consistent with being an evaporatively stripped core, while the outer planet has retained some of its initial envelope due to its higher core mass. Therefore, both planets could have had a similar formation pathway, with the inner planet having an initial envelope-mass fraction of ≲10% and core mass of ˜4.4 M⊕, while the outer had an initial envelope-mass fraction of the order of 15%-30% and core mass ˜7.3 M⊕. Finally, our results indicate that the outer planet had a long (≳30 Myr) initial cooling time, much longer than would naively be predicted from simple timescale arguments. The long initial cooling time could be evidence for a dramatic early cooling episode such as the recently proposed “boil-off” process.

The mass function and dynamical mass of young star clusters: why their initial crossing-time matters crucially

NASA Astrophysics Data System (ADS)

Parmentier, Geneviève; Baumgardt, Holger

2012-12-01

We highlight the impact of cluster-mass-dependent evolutionary rates upon the evolution of the cluster mass function during violent relaxation, that is, while clusters dynamically respond to the expulsion of their residual star-forming gas. Mass-dependent evolutionary rates arise when the mean volume density of cluster-forming regions is mass-dependent. In that case, even if the initial conditions are such that the cluster mass function at the end of violent relaxation has the same shape as the embedded-cluster mass function (i.e. infant weight-loss is mass-independent), the shape of the cluster mass function does change transiently during violent relaxation. In contrast, for cluster-forming regions of constant mean volume density, the cluster mass function shape is preserved all through violent relaxation since all clusters then evolve at the same mass-independent rate. On the scale of individual clusters, we model the evolution of the ratio of the dynamical mass to luminous mass of a cluster after gas expulsion. Specifically, we map the radial dependence of the time-scale for a star cluster to return to equilibrium. We stress that fields of view a few pc in size only, typical of compact clusters with rapid evolutionary rates, are likely to reveal cluster regions which have returned to equilibrium even if the cluster experienced a major gas expulsion episode a few Myr earlier. We provide models with the aperture and time expressed in units of the initial half-mass radius and initial crossing-time, respectively, so that our results can be applied to clusters with initial densities, sizes, and apertures different from ours.

Estimating initial contaminant mass based on fitting mass-depletion functions to contaminant mass discharge data: Testing method efficacy with SVE operations data

NASA Astrophysics Data System (ADS)

Mainhagu, J.; Brusseau, M. L.

2016-09-01

The mass of contaminant present at a site, particularly in the source zones, is one of the key parameters for assessing the risk posed by contaminated sites, and for setting and evaluating remediation goals and objectives. This quantity is rarely known and is challenging to estimate accurately. This work investigated the efficacy of fitting mass-depletion functions to temporal contaminant mass discharge (CMD) data as a means of estimating initial mass. Two common mass-depletion functions, exponential and power functions, were applied to historic soil vapor extraction (SVE) CMD data collected from 11 contaminated sites for which the SVE operations are considered to be at or close to essentially complete mass removal. The functions were applied to the entire available data set for each site, as well as to the early-time data (the initial 1/3 of the data available). Additionally, a complete differential-time analysis was conducted. The latter two analyses were conducted to investigate the impact of limited data on method performance, given that the primary mode of application would be to use the method during the early stages of a remediation effort. The estimated initial masses were compared to the total masses removed for the SVE operations. The mass estimates obtained from application to the full data sets were reasonably similar to the measured masses removed for both functions (13 and 15% mean error). The use of the early-time data resulted in a minimally higher variation for the exponential function (17%) but a much higher error (51%) for the power function. These results suggest that the method can produce reasonable estimates of initial mass useful for planning and assessing remediation efforts.

Determining the Stellar Initial Mass by Means of the 17O/18O Ratio on the AGB

NASA Astrophysics Data System (ADS)

De Nutte, Rutger; Decin, Leen; Olofsson, Hans; de Koter, Alex; Karakas, Amanda; Lombaert, Robin; Milam, Stefanie; Ramstedt, Sofia; Stancliffe, Richard; Homan, Ward; Van de Sande, Marie

2016-07-01

This poster presentsnewly obtainedcircumstellar 12C17O and 12C18O line observations, from which theline intensity are then related directly tothe 17O/18O surface abundance ratiofor a sample of nine AGB stars covering the three spectral types ().These ratios are evaluated in relation to a fundamental stellar evolution parameters: the stellar initial mass. The17O/18O ratio is shown to function as an effective method of determining the initial stellar mass. Through comparison with predictions bystellar evolution models, accurate initial mass estimates are calculated for all nine sources.

The Core Mass Growth and Stellar Lifetime of Thermally Pulsing Asymptotic Giant Branch Stars

NASA Astrophysics Data System (ADS)

Kalirai, Jason S.; Marigo, Paola; Tremblay, Pier-Emmanuel

2014-02-01

We establish new constraints on the intermediate-mass range of the initial-final mass relation, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). These constraints derive from newly discovered (bright) white dwarfs in the nearby Hyades and Praesepe star clusters, including a total of 18 high signal-to-noise ratio measurements with progenitor masses of M initial = 2.8-3.8 M ⊙. We also include a new analysis of existing white dwarfs in the older NGC 6819 and NGC 7789 star clusters, M initial = 1.6 and 2.0 M ⊙. Over this range of initial masses, stellar evolutionary models for metallicity Z initial = 0.02 predict the maximum growth of the core of TP-AGB stars. By comparing the newly measured remnant masses to the robust prediction of the core mass at the first thermal pulse on the AGB (i.e., from stellar interior models), we establish several findings. First, we show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with M initial = 1.6 to 2.0 M ⊙. At larger masses, the core-mass growth decreases steadily to ~10% at M initial = 3.4 M ⊙, after which there is a small hint of a upturn out to M initial = 3.8 M ⊙. These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the literature, as well as of the third dredge-up efficiency as a function of the stellar mass. Finally, we estimate the lifetime and the integrated luminosity of stars on the TP-AGB to peak at t ~ 3 Myr and E = 1.2 × 1010 L ⊙ yr for M initial ~ 2 M ⊙ (t ~ 2 Myr for luminosities brighter than the red giant branch tip at log (L/L ⊙) > 3.4), decreasing to t = 0.4 Myr and E = 6.1 × 109 L ⊙ yr for stars with M initial ~ 3.5 M ⊙. The implications of these results are discussed, especially with respect to general studies aimed at characterizing the integrated light output of TP-AGB stars in population synthesis models.

The initial masses of the red supergiant progenitors to Type II supernovae

NASA Astrophysics Data System (ADS)

Davies, Ben; Beasor, Emma R.

2018-02-01

There are a growing number of nearby supernovae (SNe) for which the progenitor star is detected in archival pre-explosion imaging. From these images it is possible to measure the progenitor's brightness a few years before explosion, and ultimately estimate its initial mass. Previous work has shown that II-P and II-L SNe have red supergiant (RSG) progenitors, and that the range of initial masses for these progenitors seems to be limited to ≲ 17 M⊙. This is in contrast with the cut-off of 25-30 M⊙ predicted by evolutionary models, a result that is termed the `red supergiant problem'. Here we investigate one particular source of systematic error present in converting pre-explosion photometry into an initial mass, which of the bolometric correction (BC) used to convert a single-band flux into a bolometric luminosity. We show, using star clusters, that RSGs evolve to later spectral types as they approach SN, which in turn causes the BC to become larger. Failure to account for this results in a systematic underestimate of a star's luminosity, and hence its initial mass. Using our empirically motivated BCs we reappraise the II-P and II-L SNe that have their progenitors detected in pre-explosion imaging. Fitting an initial mass function to these updated masses results in an increased upper mass cut-off of Mhi = 19.0^{+2.5}_{-1.3} M⊙, with a 95 per cent upper confidence limit of <27 M⊙. Accounting for finite sample size effects and systematic uncertainties in the mass-luminosity relationship raises the cut-off to Mhi = 25 M⊙ (<33 M⊙, 95 per cent confidence). We therefore conclude that there is currently no strong evidence for `missing' high-mass progenitors to core-collapse SNe.

Effects of molecular packing in organic crystals on singlet fission with ab initio many body perturbation theory

NASA Astrophysics Data System (ADS)

Haber, Jonah; Refaely-Abramson, Sivan; da Jornada, Felipe H.; Louie, Steven G.; Neaton, Jeffrey B.

Multi-exciton generation processes, in which multiple charge carriers are generated from a single photon, are mechanisms of significant interest for achieving efficiencies beyond the Shockley-Queisser limit of conventional p-n junction solar cells. One well-studied multiexciton process is singlet fission, whereby a singlet decays into two spin-correlated triplet excitons. Here, we use a newly developed computational approach to calculate singlet-fission coupling terms and rates with an ab initio Green's function formalism based on many-body perturbation theory (MBPT) within the GW approximation and the Bethe-Salpeter equation approach. We compare results for crystalline pentacene and TIPS-pentacene and explore the effect of molecular packing on the singlet fission mechanism. This work is supported by the Department of Energy.

Two-peak structure in the K-edge RIXS spectra of a spatially frustrated Heisenberg antiferromagnet

NASA Astrophysics Data System (ADS)

Datta, Trinanjan; Luo, Cheng; Yao, Dao-Xin

2014-03-01

Quantum fluctuations due to spatial anisotropy and strong magnetic frustration lead to the formation of a two-peak structure in the K-edge bimagnon RIXS intensity spectra of a Jx-Jy-J2 Heisenberg model on a square lattice. We compute the RIXS intensity, including up to first order 1/S spin wave expansion correction, using the Bethe-Salpeter equation within the ladder approximation scheme. The two-peak feature occurs in both the antiferromagnetic phase and the collinear antiferromagnetic phase. A knowledge of the peak splitting energy from both magnetically ordered regime can provide experimentalists with an alternative means to measure and study the effects of local microscopic exchange constants. Cottrell Research Corporation, NSFC-11074310, NSFC-11275279, Specialized Research Fund for the Doctoral Program of Higher Education.

Combining the GW formalism with the polarizable continuum model: A state-specific non-equilibrium approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duchemin, Ivan, E-mail: ivan.duchemin@cea.fr; Jacquemin, Denis; Institut Universitaire de France, 1 rue Descartes, 75005 Paris Cedex 5

We have implemented the polarizable continuum model within the framework of the many-body Green’s function GW formalism for the calculation of electron addition and removal energies in solution. The present formalism includes both ground-state and non-equilibrium polarization effects. In addition, the polarization energies are state-specific, allowing to obtain the bath-induced renormalisation energy of all occupied and virtual energy levels. Our implementation is validated by comparisons with ΔSCF calculations performed at both the density functional theory and coupled-cluster single and double levels for solvated nucleobases. The present study opens the way to GW and Bethe-Salpeter calculations in disordered condensed phases ofmore » interest in organic optoelectronics, wet chemistry, and biology.« less

Chiral symmetry and π - π scattering in the Covariant Spectator Theory

DOE PAGES

Biernat, Elmar P.; Peña, M. T.; Ribeiro, J. E.; ...

2014-11-14

The π-π scattering amplitude calculated with a model for the quark-antiquark interaction in the framework of the Covariant Spectator Theory (CST) is shown to satisfy the Adler zero constraint imposed by chiral symmetry. The CST formalism is established in Minkowski space and our calculations are performed in momentum space. We prove that the axial-vector Ward-Takahashi identity is satisfied by our model. Then we show that, similarly to what happens within the Bethe-Salpeter formalism, application of the axial-vector Ward Takahashi identity to the CST π-π scattering amplitude allows us to sum the intermediate quark-quark interactions to all orders. Thus, the Adlermore » self-consistency zero for π-π scattering in the chiral limit emerges as the result for this sum.« less

First Principles Optical Absorption Spectra of Organic Molecules Adsorbed on Titania Nanoparticles

NASA Astrophysics Data System (ADS)

Baishya, Kopinjol; Ogut, Serdar; Mete, Ersen; Gulseren, Oguz; Ellialtioglu, Sinasi

2012-02-01

We present results from first principles computations on passivated rutile TiO2 nanoparticles in both free-standing and dye-sensitized configurations to investigate the size dependence of their optical absorption spectra. The computations are performed using time-dependent density functional theory (TDDFT) as well as GW-Bethe-Salpeter-Equation (GWBSE) methods and compared with each other. We interpret the first principles spectra for free-standing TiO2 nanoparticles within the framework of the classical Mie-Gans theory using the bulk dielectric function of TiO2. We investigate the effects of the titania support on the absorption spectra of a particular set of perylene-diimide (PDI) derived dye molecules, namely brominated PDI (Br2C24H8N2O4) and its glycine and aspartine derivatives.

Zn-VI quasiparticle gaps and optical spectra from many-body calculations.

PubMed

Riefer, A; Weber, N; Mund, J; Yakovlev, D R; Bayer, M; Schindlmayr, Arno; Meier, C; Schmidt, W G

2017-06-01

The electronic band structures of hexagonal ZnO and cubic ZnS, ZnSe, and ZnTe compounds are determined within hybrid-density-functional theory and quasiparticle calculations. It is found that the band-edge energies calculated on the [Formula: see text] (Zn chalcogenides) or GW (ZnO) level of theory agree well with experiment, while fully self-consistent QSGW calculations are required for the correct description of the Zn 3d bands. The quasiparticle band structures are used to calculate the linear response and second-harmonic-generation (SHG) spectra of the Zn-VI compounds. Excitonic effects in the optical absorption are accounted for within the Bethe-Salpeter approach. The calculated spectra are discussed in the context of previous experimental data and present SHG measurements for ZnO.

Comparison of Vegetation Change Inferred From Palynology and Compound-Specific Carbon Isotopes of Lipid Biomarkers in the Maya Lowlands of Peten, Guatemala

NASA Astrophysics Data System (ADS)

Newell, S. D.; Hodell, D. A.; Curtis, J. H.; Brenner, M.; Venz-Curtis, K.

2005-12-01

The Petén region of northern Guatemala has been occupied by humans for more than 3000 years. Expansion of the Maya civilization during the Preclassic (~1000 BC to AD 250) and Classic (AD 250 to AD 900) Periods was accompanied by increasing deforestation of Petén watersheds and accelerated rates of soil erosion. Palynological data from Petén lake cores illustrate the near elimination of high forest taxa and prevalence of disturbance taxa (grasses, weeds) during the height of Classic Maya occupation (~AD 500 to AD 800). After flourishing during the Classic Period between AD 250 and 800, Maya population densities declined significantly in the Petén, thereby curtailing human pressures on the landscape. This cycle of population expansion and decline in the Petén provides a natural historical experiment that has been used to study the response of tropical vegetation to long-term changes in land-use by humans. We measured the carbon isotopic composition of long-chain n-alkanes of leaf waxes in two cores from Lakes Sacnab and Salpetén in the Petén Lake District of the southern Maya Lowlands. The carbon isotopic composition of leaf waxes has been shown to be a reliable indicator of the relative proportion of C3 to C4 biomass in a watershed. Biomarker results were compared directly to a pollen profile from Lake Salpetén. Although the general pattern of increased C4 abundance inferred from δ13C of long-chain n-alkanes and increased disturbance taxa from pollen studies agree during the period of Maya occupation, the two proxies differ in detail suggesting they are recording different characteristics of watershed vegetation. For example, the highest long-chain δ13C values (representing greatest C4 biomass) occurred during early settlement of the basins in the early to middle Preclassic Period (1300 to 500 BC) when Maya population densities were relatively low. This period also corresponded to the time of greatest erosion rates in the Salpetén basin (Anselmetti et al., in prep.). In contrast, pollen profiles indicate the highest percentages of disturbance taxa and lowest high forest taxa from 250 BC to AD 700 in the late Preclassic and Classic Periods, when both the δ13C of long-chain n-alkanes and erosion rates declined. The high compound-specific δ13C values in the early to middle Preclassic Period may be greatly influenced by the early cultivation of maize (a C4 plant) along the shoreline. In contrast, maize is generally under-represented in pollen profiles because of its large size and difficulty of transport. Pollen may be more representative of vegetation over a larger area than the lipid biomarkers, but is biased towards tropical vegetation that is pollinated by wind and does not reflect those plants that depend on pollination by insects or self-fertilization. The δ13C of long-chain n-alkanes, on the other hand, may provide a reliable proxy for estimating the relative changes in C3 to C4 biomass, but it cannot be used to interpret changes in forest structure and composition. We conclude that the δ13C of long-chain n-alkanes and pollen are recording different aspects of watershed vegetation in Petén, and should be used in tandem to infer the response of tropical vegetation to past changes in Maya land-use.

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time.

PubMed

Zhang, Zhi-Yu; Romano, D; Ivison, R J; Papadopoulos, Padelis P; Matteucci, F

2018-06-01

All measurements of cosmic star formation must assume an initial distribution of stellar masses-the stellar initial mass function-in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum 1 . The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time 2 . Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies 2,3 , especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths 4,5 . The 13 C/ 18 O isotope abundance ratio in the cold molecular gas-which can be probed via the rotational transitions of the 13 CO and C 18 O isotopologues-is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of 13 CO and C 18 O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low 13 CO/C 18 O ratio for all our targets-alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way 6 -implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the 'main sequence' of star-forming galaxies 7 , although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.

Electron Capture Supernovae from Close Binary Systems

NASA Astrophysics Data System (ADS)

Poelarends, Arend J. T.; Wurtz, Scott; Tarka, James; Cole Adams, L.; Hills, Spencer T.

2017-12-01

We present the first detailed study of the Electron Capture Supernova Channel (ECSN Channel) for a primary star in a close binary star system. Progenitors of ECSN occupy the lower end of the mass spectrum of supernova progenitors and are thought to form the transition between white dwarf progenitors and core-collapse progenitors. The mass range for ECSN from close binary systems is thought to be wider than the range for single stars, because of the effects of mass transfer on the helium core. Using the MESA stellar evolution code, we explored the parameter space of initial primary masses between 8 and 17 {M}⊙ , using a large grid of models. We find that the initial primary mass and the mass transfer evolution are important factors in the final fate of stars in this mass range. Mass transfer due to Roche lobe overflow during and after carbon burning causes the core to cool down so that it avoids neon ignition, even in helium-free cores with masses up to 1.52 {M}⊙ , which in single stars would ignite neon. If the core is able to contract to high enough densities for electron captures to commence, we find that, for the adopted Ledoux convection criterion, the initial mass range for the primary to evolve into an ECSN is between 13.5 and 17.6 {M}⊙ . The mass ratio, initial period, and mass-loss efficiency only marginally affect the predicted ranges.

A Dual Power Law Distribution for the Stellar Initial Mass Function

NASA Astrophysics Data System (ADS)

Hoffmann, Karl Heinz; Essex, Christopher; Basu, Shantanu; Prehl, Janett

2018-05-01

We introduce a new dual power law (DPL) probability distribution function for the mass distribution of stellar and substellar objects at birth, otherwise known as the initial mass function (IMF). The model contains both deterministic and stochastic elements, and provides a unified framework within which to view the formation of brown dwarfs and stars resulting from an accretion process that starts from extremely low mass seeds. It does not depend upon a top down scenario of collapsing (Jeans) masses or an initial lognormal or otherwise IMF-like distribution of seed masses. Like the modified lognormal power law (MLP) distribution, the DPL distribution has a power law at the high mass end, as a result of exponential growth of mass coupled with equally likely stopping of accretion at any time interval. Unlike the MLP, a power law decay also appears at the low mass end of the IMF. This feature is closely connected to the accretion stopping probability rising from an initially low value up to a high value. This might be associated with physical effects of ejections sometimes (i.e., rarely) stopping accretion at early times followed by outflow driven accretion stopping at later times, with the transition happening at a critical time (therefore mass). Comparing the DPL to empirical data, the critical mass is close to the substellar mass limit, suggesting that the onset of nuclear fusion plays an important role in the subsequent accretion history of a young stellar object.

Dynamical Formation Signatures of Black Hole Binaries in the First Detected Mergers by LIGO

NASA Astrophysics Data System (ADS)

O'Leary, Ryan M.; Meiron, Yohai; Kocsis, Bence

2016-06-01

The dynamical formation of stellar-mass black hole-black hole binaries has long been a promising source of gravitational waves for the Laser Interferometer Gravitational-Wave Observatory (LIGO). Mass segregation, gravitational focusing, and multibody dynamical interactions naturally increase the interaction rate between the most massive black holes in dense stellar systems, eventually leading them to merge. We find that dynamical interactions, particularly three-body binary formation, enhance the merger rate of black hole binaries with total mass M tot roughly as \\propto {M}{{tot}}β , with β ≳ 4. We find that this relation holds mostly independently of the initial mass function, but the exact value depends on the degree of mass segregation. The detection rate of such massive black hole binaries is only further enhanced by LIGO’s greater sensitivity to massive black hole binaries with M tot ≲ 80 {M}⊙ . We find that for power-law BH mass functions dN/dM ∝ M -α with α ≤ 2, LIGO is most likely to detect black hole binaries with a mass twice that of the maximum initial black hole mass and a mass ratio near one. Repeated mergers of black holes inside the cluster result in about ˜5% of mergers being observed between two and three times the maximum initial black hole mass. Using these relations, one may be able to invert the observed distribution to the initial mass function with multiple detections of merging black hole binaries.

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time

NASA Astrophysics Data System (ADS)

Zhang, Zhi-Yu; Romano, D.; Ivison, R. J.; Papadopoulos, Padelis P.; Matteucci, F.

2018-06-01

All measurements of cosmic star formation must assume an initial distribution of stellar masses—the stellar initial mass function—in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum1. The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time2. Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies2,3, especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths4,5. The 13C/18O isotope abundance ratio in the cold molecular gas—which can be probed via the rotational transitions of the 13CO and C18O isotopologues—is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of 13CO and C18O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low 13CO/C18O ratio for all our targets—alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way6—implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the `main sequence' of star-forming galaxies7, although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.

B^+→ K^-π ^+π ^+: Three-Body Final State Interactions and Kπ Isospin States

NASA Astrophysics Data System (ADS)

Nogueira, J. H. Alvarenga; Frederico, T.; Lourenço, O.

2017-03-01

In this exploratory study, final state interactions are considered to formulate the B meson decay amplitude for the Kπ π channel. The Faddeev decomposition of the Bethe-Salpeter equation is used in order to build a relativistic three-body model within the light-front framework. The S-wave scattering amplitude for the Kπ system is considered in the 1/2 and 3/2 isospin channels with the set of inhomogeneous integral equations solved perturbatively. In comparison with previous results for the D meson decay in the same channel, one has to consider the different partonic processes, which build the source amplitudes, and the larger absorption to other decay channels appears, that are important features to be addressed. As in the D decay case, the convergence of the rescattering perturbative series is also achieved with two-loop contributions.

Astronomical observations of solid phase carbon

NASA Technical Reports Server (NTRS)

Jura, M.

1990-01-01

In the outer envelopes of red giants, when the gas cools sufficiently, molecules and solids form. Thermodynamically, the most stable molecule is CO, and it is usually assumed that all the available carbon and oxygen are consumed in the formation of this molecule (Salpeter 1977). If the carbon abundance is greater than the oxygen abundance, then the carbon left over after the formation of CO is available for solid grains. Because carbon is by far the most abundant species available for making solids in these environments, researchers anticipate that the grains are composed of nearly pure carbon in some form. The observations which can be used to infer the nature of this solid phase carbon are discussed. The observations of the dust around carbon-rich red giants are discussed. These results are then placed into their broader astrophysical context.

Nonperturbative dynamics of scalar field theories through the Feynman-Schwinger representation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cetin Savkli; Franz Gross; John Tjon

2004-04-01

In this paper we present a summary of results obtained for scalar field theories using the Feynman-Schwinger (FSR) approach. Specifically, scalar QED and {chi}{sup 2}{phi} theories are considered. The motivation behind the applications discussed in this paper is to use the FSR method as a rigorous tool for testing the quality of commonly used approximations in field theory. Exact calculations in a quenched theory are presented for one-, two-, and three-body bound states. Results obtained indicate that some of the commonly used approximations, such as Bethe-Salpeter ladder summation for bound states and the rainbow summation for one body problems, producemore » significantly different results from those obtained from the FSR approach. We find that more accurate results can be obtained using other, simpler, approximation schemes.« less

First-Principle Calculation of Quasiparticle Excitations and Optical Absorption in NiO

NASA Astrophysics Data System (ADS)

Li, Je-Luen; Rignanese, Gian-Marco; Louie, Steven G.

2001-03-01

We present a first-principle study of the quasiparticle excitations and optical absorption spectrum in NiO. The ground state electronic structure is calculated with the generalized gradient approximation in density functional theory and ab initio pseudopotential. The quasiparticle energies are then computed employing the GW approximation. In addition to comparing to photoemisson result, comparison between the measured and calculated complex dielectric function helps to identify the onset of excitations in this system. We illustrate some subtleties of pseudopotential calculations: the effect of including 3 s and 3p electrons in Ni pseudopotential; the difference between using velocity and momentum operators in the RPA dielectric function. Finally, we discuss a recent effort to solve the Bethe-Salpeter equation for the optical spectrum in this spin polarized system to address the remaining discrepancy between theory and experiment.

Excitons in molecular crystals from first-principles many-body perturbation theory: Picene versus pentacene

NASA Astrophysics Data System (ADS)

Cudazzo, Pierluigi; Gatti, Matteo; Rubio, Angel

2012-11-01

By solving the first-principles many-body Bethe-Salpeter equation, we compare the optical properties of two prototype and technological relevant organic molecular crystals: picene and pentacene. Albeit very similar for the structural and electronic properties, picene and pentacene show remarkable differences in their optical spectra. While for pentacene the absorption onset is due to a charge-transfer exciton, in picene it is related to a strongly localized Frenkel exciton. The detailed comparison between the two materials allows us to discuss, on general grounds, how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. It represents a clear example of the relevance of the competition between localization and delocalization in the description of two-particle electronic correlation.

Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li

2014-05-01

Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10'more » northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and higher interstellar medium metallicities. For the merging cluster A2319, local surface density is a better environmental indicator rather than the cluster-centric distance. Compared with the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is found in A2319, indicating that the galaxy-scale turbulence stimulated by the subcluster merger might have played a role in triggering the star formation activity.« less

Committees

NASA Astrophysics Data System (ADS)

2003-08-01

Born in Buenos Aires, Argentina, in 1930, Alberto Sirlin studied at the University of Buenos Aires from 1948-52, where he carried out research work in classical nonlinear physics, under the guidance of Richard Gans, and in 1953 received the degree of doctor in Physical-Mathematical Sciences. In 1953 he held a fellowship at the Centro Brasileiro de Pesquisas Fisicas in Rio de Janeiro, Brazil, where he did research work and attended some graduate courses, including a memorable and highly influential one taught by Richard Feynman. He spent the academic year 1954-55 at UCLA, where he initiated his work on electroweak physics in collaboration with Robert Finkelstein and Ralph Behrends. His next move was to Cornell University in 1955, earning his PhD there in 1958 for research in electroweak physics in collaboration with Toichiro Kinoshita. Sirlin spent 1957-59 as a research associate at Columbia University, becoming an Assistant Professor of Physics at New York University in 1959, an Associate Professor in 1961, and a full Professor in 1968. It is a remarkable coincidence that one of his fellow post-docs, Steven Weinberg, was to become one of the founders of the Standard Model, which in turn has provided the natural setting for Sirlin's work. During his formative years, he was extremely fortunate to receive guidance and advice from an extraordinary group of distinguished scientists, including R Gans, R P Feynman, R J Finkelstein, H A Bethe and E E Salpeter. He also enjoyed close and fruitful long-term collaborations with a number of brilliant theorists, including R E Behrends, T Kinoshita, T D Lee, M A B Beg, W J Marciano, P Langacker, G Degrassi, P Gambino and B A Kniehl, and has had fourteen excellent, interesting, and highly enterprising graduate students, who have remained close friends. Sirlin's main research interests have been in precision electroweak physics, other topics in weak interaction theory, the search for higher symmetries of the strong interactions, non-topological solitons, theorems on symmetry breaking, some aspects of QCD, dimensional regularization of infrared divergences, the study of mass singularities, and the theoretical treatment of unstable particles. Sirlin is a fellow of the American Physical Society. In 1983 he was awarded a Guggenheim fellowship and in 1997 received an Alexander von Humboldt Award. In 2002, he shared with William J Marciano the J J Sakurai Prize for Theoretical Particle Physics, awarded by the American Physical Society. M Porrati Professor of Physics, New York University, USA Alberto Sirlin

Rehydration Capacities and Rates for Various Porcine Tissues after Dehydration

PubMed Central

Meyer, Jacob P.; McAvoy, Kieran E.; Jiang, Jack

2013-01-01

The biphasic effects of liquid on tissue biomechanics are well known in cartilage and vocal folds, yet not extensively in other tissue types. Past studies have shown that tissue dehydration significantly impacts biomechanical properties and that rehydration can restore these properties in certain tissue types. However, these studies failed to consider how temporal exposure to dehydrating or rehydrating agents may alter tissue rehydration capacity, as overexposure to dehydration may permanently prevent rehydration to the initial liquid volume. Select porcine tissues were dehydrated until they reached between 100% and 40% of their initial mass. Each sample was allowed to rehydrate for 5 hours in a 0.9% saline solution, and the percent change between the initial and rehydrated mass values was calculated. Spearman correlation tests indicated a greater loss in mass despite rehydration when tissues were previously exposed to greater levels of dehydration. Additionally, Pearson correlation tests indicated the total liquid mass of samples after complete rehydration decreased when previously exposed to higher levels of dehydration. Rehydration rates were found by dehydrating tissues to 40% of their initial mass followed by rehydration in a 0.9% saline solution for 60 minutes, with mass measurements occurring in 15 minute intervals. All tissues rehydrated nonlinearly, most increasing significantly in mass up to 30 minutes after initial soaking. This study suggests the ability for tissues to rehydrate is dependent on the level of initial dehydration exposure. In vitro rehydration experiments therefore require controlled dosage and temporal exposure to dehydrating and rehydrating agents to avoid incomplete rehydration, and caution should be taken when combining different tissue types in models of hydration. PMID:24023753

Mass functional for initial data in 4 +1 -dimensional spacetime

NASA Astrophysics Data System (ADS)

Alaee, Aghil; Kunduri, Hari K.

2014-12-01

We consider a broad class of asymptotically flat, maximal initial data sets satisfying the vacuum constraint equations, admitting two commuting rotational symmetries. We construct a mass functional for "t -ϕi"-symmetric data which evaluates to the Arnowitt-Deser-Misner mass. We then show that R ×U (1 )2 -invariant solutions of the vacuum Einstein equations are critical points of this functional amongst this class of data. We demonstrate the positivity of this functional for a class of rod structures which include the Myers-Perry initial data. The construction is a natural extension of Dain's mass functional to D =5 , although several new features arise.

Binary Systems and the Initial Mass Function

NASA Astrophysics Data System (ADS)

Malkov, O. Yu.

2017-07-01

In the present paper we discuss advantages and disadvantages of binary stars, which are important for star formation history determination. We show that to make definite conclusions of the initial mass function shape, it is necessary to study binary population well enough to correct the luminosity function for unresolved binaries; to construct the mass-luminosity relation based on wide binaries data, and to separate observational mass functions of primaries, of secondaries, and of unresolved binaries.

The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models

NASA Astrophysics Data System (ADS)

Dull, J. D.; Cohn, H. N.; Lugger, P. M.; Murphy, B. W.; Seitzer, P. O.; Callanan, P. J.; Rutten, R. G. M.; Charles, P. A.

1997-05-01

We report a new measurement of the velocity dispersion profile within 1' (3 pc) of the center of the globular cluster M15 (NGC 7078), using long-slit spectra from the 4.2 m William Herschel Telescope at La Palma Observatory. We obtained spatially resolved spectra for a total of 23 slit positions during two observing runs. During each run, a set of parallel slit positions was used to map out the central region of the cluster; the position angle used during the second run was orthogonal to that used for the first. The spectra are centered in wavelength near the Ca II infrared triplet at 8650 Å, with a spectral range of about 450 Å. We determined radial velocities by cross-correlation techniques for 131 cluster members. A total of 32 stars were observed more than once. Internal and external comparisons indicate a velocity accuracy of about 4 km s-1. The velocity dispersion profile rises from about σ = 7.2 +/- 1.4 km s-1 near 1' from the center of the cluster to σ = 13.9 +/- 1.8 km s-1 at 20". Inside of 20", the dispersion remains approximately constant at about 10.2 +/- 1.4 km s-1 with no evidence for a sharp rise near the center. This last result stands in contrast with that of Peterson, Seitzer, & Cudworth who found a central velocity dispersion of 25 +/- 7 km s-1, based on a line-broadening measurement. Our velocity dispersion profile is in good agreement with those determined in the recent studies of Gebhardt et al. and Dubath & Meylan. We have developed a new set of Fokker-Planck models and have fitted these to the surface brightness and velocity dispersion profiles of M15. We also use the two measured millisecond pulsar accelerations as constraints. The best-fitting model has a mass function slope of x = 0.9 (where 1.35 is the slope of the Salpeter mass function) and a total mass of 4.9 × 105 M⊙. This model contains approximately 104 neutron stars (3% of the total mass), the majority of which lie within 6" (0.2 pc) of the cluster center. Since the velocity dispersion profile of M15 is well fitted by this postcollapse model in which the most massive objects are neutron stars, there appears to be no need to invoke the presence of a massive central black hole in M15. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

Stellar populations in the Carina region. The Galactic plane at l = 291°

NASA Astrophysics Data System (ADS)

Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

2016-08-01

Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the mass distributions of the covered clusters and several others in the region (which we took form the literature). They consistently show a canonical IMF slope (the Salpeter one). We discover and characterise an abnormally reddened massive stellar population, scattered between 6.6 and 11 kpc. Spectroscopic observations of ten stars of this latter population show that all selected targets were massive OB stars. Their location is consistent with the position of the Carina-Sagittarius spiral arm. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A149

Energy and momentum analysis of the deployment dynamics of nets in space

NASA Astrophysics Data System (ADS)

Botta, Eleonora M.; Sharf, Inna; Misra, Arun K.

2017-11-01

In this paper, the deployment dynamics of nets in space is investigated through a combination of analysis and numerical simulations. The considered net is deployed by ejecting several corner masses and thanks to momentum and energy transfer from those to the innermost threads of the net. In this study, the net is modeled with a lumped-parameter approach, and assumed to be symmetrical, subject to symmetrical initial conditions, and initially slack. The work-energy and momentum conservation principles are employed to carry out centroidal analysis of the net, by conceptually partitioning the net into a system of corner masses and the net proper and applying the aforementioned principles to the corresponding centers of mass. The analysis provides bounds on the values that the velocity of the center of mass of the corner masses and the velocity of the center of mass of the net proper can individually attain, as well as relationships between these and different energy contributions. The analytical results allow to identify key parameters characterizing the deployment dynamics of nets in space, which include the ratio between the mass of the corner masses and the total mass, the initial linear momentum, and the direction of the initial velocity vectors. Numerical tools are employed to validate and interpret further the analytical observations. Comparison of deployment results with and without initial velocity of the net proper suggests that more complete and lasting deployment can be achieved if the corner masses alone are ejected. A sensitivity study is performed for the key parameters identified from the energy/momentum analysis, and the outcome establishes that more lasting deployment and safer capture (i.e., characterized by higher traveled distance) can be achieved by employing reasonably lightweight corner masses, moderate shooting angles, and low shooting velocities. A comparison with current literature on tether-nets for space debris capture confirms overall agreement on the importance and effect of the relevant inertial and ejection parameters on the deployment dynamics.

How Constant Momentum Acceleration Decouples Energy and Space Focusing in Distance-of-Flight and Time-of-Flight Mass Spectrometries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dennis, Elise; Gundlach-Graham, Alexander W.; Enke, Chris

2013-05-01

Time-of-flight (TOF) and distance-of-flight (DOF) mass spectrometers require means for focusing ions at the detector(s) because of initial dispersions of position and energy at the time of their acceleration. Time-of-flight mass spectrometers ordinarily employ constant energy acceleration (CEA), which creates a space-focus plane at which the initial spatial dispersion is corrected. In contrast, constant-momentum acceleration (CMA), in conjunction with an ion mirror, provides focus of the initial energy dispersion at the energy focus time for ions of all m/z at their respective positions along the flight path. With CEA, the initial energy dispersion is not simultaneously correctable as its effectmore » on ion velocity is convoluted with that of the spatial dispersion. The initial spatial dispersion with CMA remains unchanged throughout the field-free region of the flight path, so spatial dispersion can be reduced before acceleration. Improved focus is possible when each dispersion can be addressed independently. With minor modification, a TOF mass spectrometer can be operated in CMA mode by treating the TOF detector as though it were a single element in the array of detectors that would be used in a DOF mass spectrometer. Significant improvement in mass resolution is thereby achieved, albeit over a narrow range of m/z values. In this paper, experimental and theoretical results are presented that illustrate the energy-focusing capabilities of both DOF and TOF mass spectrometry.« less

Massive Infrared-Quiet Dense Cores: Unveiling the Initial Conditions of High-Mass Star Formation

NASA Astrophysics Data System (ADS)

Motte, F.; Bontemps, S.; Schneider, N.; Schilke, P.; Menten, K. M.

2008-05-01

As Th. Henning said at the conference, cold precursors of high-mass stars are now ``hot topics''. We here propose some observational criteria to identify massive infrared-quiet dense cores which can host the high-mass analogs of Class~0 protostars and pre-stellar condensations. We also show how far-infrared to millimeter imaging surveys of entire complexes forming OB stars are starting to unveil the initial conditions of high-mass star formation.

Constructing binary black hole initial data with high mass ratios and spins

NASA Astrophysics Data System (ADS)

Ossokine, Serguei; Foucart, Francois; Pfeiffer, Harald; Szilagyi, Bela; Simulating Extreme Spacetimes Collaboration

2015-04-01

Binary black hole systems have now been successfully modelled in full numerical relativity by many groups. In order to explore high-mass-ratio (larger than 1:10), high-spin systems (above 0.9 of the maximal BH spin), we revisit the initial-data problem for binary black holes. The initial-data solver in the Spectral Einstein Code (SpEC) was not able to solve for such initial data reliably and robustly. I will present recent improvements to this solver, among them adaptive mesh refinement and control of motion of the center of mass of the binary, and will discuss the much larger region of parameter space this code can now address.

On the adiabatic limit of Hadamard states

NASA Astrophysics Data System (ADS)

Drago, Nicolò; Gérard, Christian

2017-08-01

We consider the adiabatic limit of Hadamard states for free quantum Klein-Gordon fields, when the background metric and the field mass are slowly varied from their initial to final values. If the Klein-Gordon field stays massive, we prove that the adiabatic limit of the initial vacuum state is the (final) vacuum state, by extending to the symplectic framework the adiabatic theorem of Avron-Seiler-Yaffe. In cases when only the field mass is varied, using an abstract version of the mode decomposition method we can also consider the case when the initial or final mass vanishes, and the initial state is either a thermal state or a more general Hadamard state.

Mass Medication Clinic (MMC) Patient Medical Assistant (PMA) System Training Initiative

DTIC Science & Technology

2007-06-01

AD_________________ Award Number: W81XWH-06-2-0045 TITLE: Mass Medication Clinic (MMC) Patient ...SUBTITLE 5a. CONTRACT NUMBER Mass Medication Clinic (MMC) Patient Medical Assistant (PMA) System Training Initiative 5b. GRANT NUMBER W81XWH-06-2...sections will describe the events, results, and accomplishments of this study. With validation through this project the Patient Medical Assistant

Anticipatory Postural Control of Stability during Gait Initiation Over Obstacles of Different Height and Distance Made Under Reaction-Time and Self-Initiated Instructions.

PubMed

Yiou, Eric; Artico, Romain; Teyssedre, Claudine A; Labaune, Ombeline; Fourcade, Paul

2016-01-01

Despite the abundant literature on obstacle crossing in humans, the question of how the central nervous system (CNS) controls postural stability during gait initiation with the goal to clear an obstacle remains unclear. Stabilizing features of gait initiation include anticipatory postural adjustments (APAs) and lateral swing foot placement. To answer the above question, 14 participants initiated gait as fast as possible in three conditions of obstacle height, three conditions of obstacle distance and one obstacle-free (control) condition. Each of these conditions was performed with two levels of temporal pressure: reaction-time (high-pressure) and self-initiated (low-pressure) movements. A mechanical model of the body falling laterally under the influence of gravity and submitted to an elastic restoring force is proposed to assess the effect of initial (foot-off) center-of-mass position and velocity (or "initial center-of-mass set") on the stability at foot-contact. Results showed that the anticipatory peak of mediolateral (ML) center-of-pressure shift, the initial ML center-of-mass velocity and the duration of the swing phase, of gait initiation increased with obstacle height, but not with obstacle distance. These results suggest that ML APAs are scaled with swing duration in order to maintain an equivalent stability across experimental conditions. This statement is strengthened by the results obtained with the mechanical model, which showed how stability would be degraded if there was no adaptation of the initial center-of-mass set to swing duration. The anteroposterior (AP) component of APAs varied also according to obstacle height and distance, but in an opposite way to the ML component. Indeed, results showed that the anticipatory peak of backward center-of-pressure shift and the initial forward center-of-mass set decreased with obstacle height, probably in order to limit the risk to trip over the obstacle, while the forward center-of-mass velocity at foot-off increased with obstacle distance, allowing a further step to be taken. These effects of obstacle height and distance were globally similar under low and high-temporal pressure. Collectively, these findings imply that the CNS is able to predict the potential instability elicited by the obstacle clearance and that it scales the spatiotemporal parameters of APAs accordingly.

Anticipatory Postural Control of Stability during Gait Initiation Over Obstacles of Different Height and Distance Made Under Reaction-Time and Self-Initiated Instructions

PubMed Central

Yiou, Eric; Artico, Romain; Teyssedre, Claudine A.; Labaune, Ombeline; Fourcade, Paul

2016-01-01

Despite the abundant literature on obstacle crossing in humans, the question of how the central nervous system (CNS) controls postural stability during gait initiation with the goal to clear an obstacle remains unclear. Stabilizing features of gait initiation include anticipatory postural adjustments (APAs) and lateral swing foot placement. To answer the above question, 14 participants initiated gait as fast as possible in three conditions of obstacle height, three conditions of obstacle distance and one obstacle-free (control) condition. Each of these conditions was performed with two levels of temporal pressure: reaction-time (high-pressure) and self-initiated (low-pressure) movements. A mechanical model of the body falling laterally under the influence of gravity and submitted to an elastic restoring force is proposed to assess the effect of initial (foot-off) center-of-mass position and velocity (or “initial center-of-mass set”) on the stability at foot-contact. Results showed that the anticipatory peak of mediolateral (ML) center-of-pressure shift, the initial ML center-of-mass velocity and the duration of the swing phase, of gait initiation increased with obstacle height, but not with obstacle distance. These results suggest that ML APAs are scaled with swing duration in order to maintain an equivalent stability across experimental conditions. This statement is strengthened by the results obtained with the mechanical model, which showed how stability would be degraded if there was no adaptation of the initial center-of-mass set to swing duration. The anteroposterior (AP) component of APAs varied also according to obstacle height and distance, but in an opposite way to the ML component. Indeed, results showed that the anticipatory peak of backward center-of-pressure shift and the initial forward center-of-mass set decreased with obstacle height, probably in order to limit the risk to trip over the obstacle, while the forward center-of-mass velocity at foot-off increased with obstacle distance, allowing a further step to be taken. These effects of obstacle height and distance were globally similar under low and high-temporal pressure. Collectively, these findings imply that the CNS is able to predict the potential instability elicited by the obstacle clearance and that it scales the spatiotemporal parameters of APAs accordingly. PMID:27656138

From star-disc encounters to numerical solutions for a subset of the restricted three-body problem

NASA Astrophysics Data System (ADS)

Breslau, Andreas; Vincke, Kirsten; Pfalzner, Susanne

2017-03-01

Various astrophysical processes exist, where the fly-by of a massive object affects matter that is initially supported against gravity by rotation. Examples are perturbations of galaxies, protoplanetary discs, or planetary systems. We approximate such events as a subset of the restricted three-body problem by considering only perturbations of non-interacting low-mass objects that are initially on circular Keplerian orbits. In this paper, we present a new parametrisation of the initial conditions of this problem. Under certain conditions, the initial positions of the low-mass objects can be specified as being largely independent of the initial position of the perturber. In addition, exploiting the known scalings of the problem reduces the parameter space of initial conditions for one specific perturbation to two dimensions. To this two-dimensional initial condition space, we have related the final properties of the perturbed trajectories of the low-mass objects from our numerical simulations. In this way, maps showing the effect of the perturbation on the low-mass objects were created, which provide a new view on the perturbation process. Comparing the maps for different mass-ratios reveals that the perturbations by low- and high-mass perturbers are dominated by different physical processes. The equal-mass case is a complicated mixture of the other two cases. Since the final properties of trajectories with similar initial conditions are also usually similar, the results of the limited number of integrated trajectories can be generalised to the full presented parameter space by interpolation. Since our results are also unique within the accuracy strived for, they constitute general numerical solutions for this subset of the restricted three-body problem. As such, they can be used to predict the evolution of real physical problems by simple transformations, such as scaling, without further simulations. Possible applications are the perturbation of protoplanetary discs or planetary systems by the fly-by of another star. Here, the maps enable us, for example, to quantify the portion of unbound material for any periastron distance without the need for further simulations.

Variation in body mass dynamics among sites in Black Brant Branta bernicla nigricans supports adaptivity of mass loss during moult

USGS Publications Warehouse

Fondell, Thomas F.; Flint, Paul L.; Schmutz, Joel A.; Schamber, Jason L.; Nicolai, Christopher A.

2013-01-01

Birds employ varying strategies to accommodate the energetic demands of moult, one important example being changes in body mass. To understand better their physiological and ecological significance, we tested three hypotheses concerning body mass dynamics during moult. We studied Black Brant in 2006 and 2007 moulting at three sites in Alaska which varied in food availability, breeding status and whether geese undertook a moult migration. First we predicted that if mass loss during moult were simply the result of inadequate food resources then mass loss would be highest where food was least available. Secondly, we predicted that if mass loss during moult were adaptive, allowing birds to reduce activity during moult, then birds would gain mass prior to moult where feeding conditions allowed and mass loss would be positively related to mass at moult initiation. Thirdly, we predicted that if mass loss during moult were adaptive, allowing birds to regain flight sooner, then across sites and groups, mass at the end of the flightless period would converge on a theoretical optimum, i.e. the mass that permits the earliest possible return to flight. Mass loss was greatest where food was most available and thus our results did not support the prediction that mass loss resulted from inadequate food availability. Mass at moult initiation was positively related to both food availability and mass loss. In addition, among sites and years, variation in mass was high at moult initiation but greatly reduced at the end of the flightless period, appearing to converge. Thus, our results supported multiple predictions that mass loss during moult was adaptive and that the optimal moulting strategy was to gain mass prior to the flightless period, then through behavioural modifications use these body reserves to reduce activity and in so doing also reduce wing loading. Geese that undertook a moult migration initiated moult at the highest mass, indicating that they were more than able to compensate for the energetic cost of the migration. Because Brant frequently change moult sites between years in relation to breeding success, the site-specific variation in body mass dynamics we observed suggests individual plasticity in moult body mass dynamics.

RIXS of Ammonium Nitrate using OCEAN

NASA Astrophysics Data System (ADS)

Vinson, John; Jach, Terrence; Mueller, Matthias; Unterumsberger, Rainer; Beckhoff, Burkhard

The ocean code allows for calculations of near-edge x-ray spectroscopies using a GW/Bethe-Salpeter equation (BSE) approach. Here we present an extension of the code for calculating resonant inelastic x-ray scattering (RIXS). Recent work has shown that peak-specific broadening of nitrogen K α emission in nitrates is due to a valence-band lifetime that is an order of magnitude shorter than that of the nitrogen 1s hole, an inversion of the usual assumption that valence holes have longer lifetimes than core-level holes. Using the BSE, including GW corrections to the DFT energies, as implemented in ocean we are able to compare calculations of RIXS with measured spectra of the same. By utilizing an approach free from fitting parameters we are able to identify the origins of various broadening effects observed in experiment.

Excitonic structure of the optical conductivity in MoS2 monolayers

NASA Astrophysics Data System (ADS)

Ridolfi, Emilia; Lewenkopf, Caio H.; Pereira, Vitor M.

2018-05-01

We investigate the excitonic spectrum of MoS2 monolayers and calculate its optical absorption properties over a wide range of energies. Our approach takes into account the anomalous screening in two dimensions and the presence of a substrate, both cast by a suitable effective Keldysh potential. We solve the Bethe-Salpeter equation using as a basis a Slater-Koster tight-binding model parameterized to fit the ab initio MoS2 band structure calculations. The resulting optical conductivity is in good quantitative agreement with existing measurements up to ultraviolet energies. We establish that the electronic contributions to the C excitons arise not from states at the Γ point, but from a set of k points over extended portions of the Brillouin zone. Our results reinforce the advantages of approaches based on effective models to expeditiously explore the properties and tunability of excitons in TMD systems.

Strong excitonic interactions in the oxygen K-edge of perovskite oxides.

PubMed

Tomita, Kota; Miyata, Tomohiro; Olovsson, Weine; Mizoguchi, Teruyasu

2017-07-01

Excitonic interactions of the oxygen K-edge electron energy-loss near-edge structure (ELNES) of perovskite oxides, CaTiO 3 , SrTiO 3 , and BaTiO 3 , together with reference oxides, MgO, CaO, SrO, BaO, and TiO 2 , were investigated using a first-principles Bethe-Salpeter equation calculation. Although the transition energy of oxygen K-edge is high, strong excitonic interactions were present in the oxygen K-edge ELNES of the perovskite oxides, whereas the excitonic interactions were negligible in the oxygen K-edge ELNES of the reference compounds. Detailed investigation of the electronic structure suggests that the strong excitonic interaction in the oxygen K-edge ELNES of the perovskite oxides is caused by the directionally confined, low-dimensional electronic structure at the Ti-O-Ti bonds. Copyright © 2016 Elsevier B.V. All rights reserved.

Competition between pressure and gravity confinement in Lyman Alpha forest observations

NASA Technical Reports Server (NTRS)

Charlton, Jane C.; Salpeter, Edwin E.; Linder, Suzanne M.

1994-01-01

A break in the distribution function of Lyman Alpha clouds (at a typical redshift of 2.5) has been reported by Petit-jean et al. (1993). This feature is what would be expected from a transition between pressure confinement and gravity confinement (as predicted in Charlton, Salpeter & Hogan 1993). The column density at which the feature occurs has been used to determine the external confining pressure approximately 10 per cu cm K, which could be due to a hot, intergalactic medium. For models that provide a good fit to the data, the contribution of the gas in clouds to omega is small. The specific shape of the distribution function at the transition (predicted by models to have a nonmonotonic slope) can serve as a diagnostic of the distribution of dark matter around Lyman Alpha forest clouds, and the present data already eliminate certain models.

Defect properties of Sn- and Ge-doped ZnTe: suitability for intermediate-band solar cells

NASA Astrophysics Data System (ADS)

Flores, Mauricio A.

2018-01-01

We investigate the electronic structure and defect properties of Sn- and Ge- doped ZnTe by first-principles calculations within the DFT+GW formalism. We find that ({{{Sn}}}{{Zn}}) and ({{{Ge}}}{{Zn}}) introduce isolated energy levels deep in the band gap of ZnTe, derived from Sn-5s and Ge-4s states, respectively. Moreover, the incorporation of Sn and Ge on the Zn site is favored in p-type ZnTe, in both Zn-rich and Te-rich environments. The optical absorption spectra obtained by solving the Bethe-Salpeter equation reveals that sub-bandgap absorptance is greatly enhanced due to the formation of the intermediate band. Our results suggest that Sn- and Ge-doped ZnTe would be a suitable material for the development of intermediate-band solar cells, which have the potential to achieve efficiencies beyond the single-junction limit.

Understanding Singlet and Triplet Excitons in Acene Crystals from First Principles

NASA Astrophysics Data System (ADS)

Rangel Gordillo, Tonatiuh; Sharifzadeh, Sahar; Kronik, Leeor; Neaton, Jeffrey

2014-03-01

Singlet fission, a process in which two triplet excitons are formed from a singlet exciton, has the potential to increase the solar cell efficiencies above 100%. Efficient singlet fission has been reported in larger acene crystals, such as tetracene and pentacene, in part attributable to their low-lying triplet energies. In this work, we use many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach to compute quasiparticle gaps, low-lying singlet and and triplet excitations, and optical absorption spectra across the entire acene family of crystals, from benzene to hexacene. We closely examine the degree of localization and charge-transfer character of the low-lying singlets and triplets, and their sensitivity to crystal environment, and discuss implications for the efficiency of singlet fission in this systems. This work supported by DOE and computational resources provided by NERSC.

Theory of Raman scattering in coupled electron-phonon systems

NASA Astrophysics Data System (ADS)

Itai, K.

1992-01-01

The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.

Many-body effects and excitonic features in 2D biphenylene carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lüder, Johann, E-mail: johann.luder@physics.uu.se; Puglia, Carla; Eriksson, Olle

2016-01-14

The remarkable excitonic effects in low dimensional materials in connection to large binding energies of excitons are of great importance for research and technological applications such as in solar energy and quantum information processing as well as for fundamental investigations. In this study, the unique electronic and excitonic properties of the two dimensional carbon network biphenylene carbon were investigated with GW approach and the Bethe-Salpeter equation accounting for electron correlation effects and electron-hole interactions, respectively. Biphenylene carbon exhibits characteristic features including bright and dark excitons populating the optical gap of 0.52 eV and exciton binding energies of 530 meV asmore » well as a technologically relevant intrinsic band gap of 1.05 eV. Biphenylene carbon’s excitonic features, possibly tuned, suggest possible applications in the field of solar energy and quantum information technology in the future.« less

Many-body Green’s function theory for electron-phonon interactions: The Kadanoff-Baym approach to spectral properties of the Holstein dimer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Säkkinen, Niko; Peng, Yang; Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin-Dahlem

2015-12-21

We present a Kadanoff-Baym formalism to study time-dependent phenomena for systems of interacting electrons and phonons in the framework of many-body perturbation theory. The formalism takes correctly into account effects of the initial preparation of an equilibrium state and allows for an explicit time-dependence of both the electronic and phononic degrees of freedom. The method is applied to investigate the charge neutral and non-neutral excitation spectra of a homogeneous, two-site, two-electron Holstein model. This is an extension of a previous study of the ground state properties in the Hartree (H), partially self-consistent Born (Gd) and fully self-consistent Born (GD) approximationsmore » published in Säkkinen et al. [J. Chem. Phys. 143, 234101 (2015)]. Here, the homogeneous ground state solution is shown to become unstable for a sufficiently strong interaction while a symmetry-broken ground state solution is shown to be stable in the Hartree approximation. Signatures of this instability are observed for the partially self-consistent Born approximation but are not found for the fully self-consistent Born approximation. By understanding the stability properties, we are able to study the linear response regime by calculating the density-density response function by time-propagation. This amounts to a solution of the Bethe-Salpeter equation with a sophisticated kernel. The results indicate that none of the approximations is able to describe the response function during or beyond the bipolaronic crossover for the parameters investigated. Overall, we provide an extensive discussion on when the approximations are valid and how they fail to describe the studied exact properties of the chosen model system.« less

Rapid profiling of laser-induced photochemistry in single microdroplets using mass spectrometry.

PubMed

Tracey, Phillip J; Vaughn, Bartholomew S; Roberts, Brendon J; Poad, Berwyck L J; Trevitt, Adam J

2014-03-18

Rapid assessment of laser-induced photochemistry in single microdroplets is afforded by on-demand microdroplet generation coupled to a commercial ion-trap mass spectrometer. Single microdroplets (diameter ∼50 μm, 65 pL) fall on a steel needle held at +2 kV where they subsequently form a spray that is directed toward the inlet of an ion-trap mass spectrometer. It is demonstrated that single microdroplet mass spectra are recordable, one at a time, for methanol droplets containing 100 μM 4-iodoaniline. Extending on this, to probe laser-initiated photochemistry in single picoliter volumes, a UV laser pulse is timed to intercept the droplet before hitting the needle. Comparison of laser-on and laser-off mass spectra reveals the laser-initiated photochemical products. We demonstrate the technique by following UV laser initiated chemistry in methanol droplets containing 4-iodoaniline and 3-(iodomethyl)-N,N,N-trimethylbenzenamine and reveal numerous products within a few hundred single droplet experiments over several minutes. This technique allows for rapid detection of laser-initiated photochemistry in single picoliter volumes.

On the link between energy equipartition and radial variation in the stellar mass function of star clusters

NASA Astrophysics Data System (ADS)

Webb, Jeremy J.; Vesperini, Enrico

2017-01-01

We make use of N-body simulations to determine the relationship between two observable parameters that are used to quantify mass segregation and energy equipartition in star clusters. Mass segregation can be quantified by measuring how the slope of a cluster's stellar mass function α changes with clustercentric distance r, and then calculating δ _α = d α (r)/d ln(r/r_m), where rm is the cluster's half-mass radius. The degree of energy equipartition in a cluster is quantified by η, which is a measure of how stellar velocity dispersion σ depends on stellar mass m via σ(m) ∝ m-η. Through a suite of N-body star cluster simulations with a range of initial sizes, binary fractions, orbits, black hole retention fractions, and initial mass functions, we present the co-evolution of δα and η. We find that measurements of the global η are strongly affected by the radial dependence of σ and mean stellar mass and the relationship between η and δα depends mainly on the cluster's initial conditions and the tidal field. Within rm, where these effects are minimized, we find that η and δα initially share a linear relationship. However, once the degree of mass segregation increases such that the radial dependence of σ and mean stellar mass become a factor within rm, or the cluster undergoes core collapse, the relationship breaks down. We propose a method for determining η within rm from an observational measurement of δα. In cases where η and δα can be measured independently, this new method offers a way of measuring the cluster's dynamical state.

The necessity of feedback physics in setting the peak of the initial mass function

NASA Astrophysics Data System (ADS)

Guszejnov, Dávid; Krumholz, Mark R.; Hopkins, Philip F.

2016-05-01

A popular theory of star formation is gravito-turbulent fragmentation, in which self-gravitating structures are created by turbulence-driven density fluctuations. Simple theories of isothermal fragmentation successfully reproduce the core mass function (CMF) which has a very similar shape to the initial mass function (IMF) of stars. However, numerical simulations of isothermal turbulent fragmentation thus far have not succeeded in identifying a fragment mass scale that is independent of the simulation resolution. Moreover, the fluid equations for magnetized, self-gravitating, isothermal turbulence are scale-free, and do not predict any characteristic mass. In this paper we show that, although an isothermal self-gravitating flow does produce a CMF with a mass scale imposed by the initial conditions, this scale changes as the parent cloud evolves. In addition, the cores that form undergo further fragmentation and after sufficient time forget about their initial conditions, yielding a scale-free pure power-law distribution dN/dM ∝ M-2 for the stellar IMF. We show that this problem can be alleviated by introducing additional physics that provides a termination scale for the cascade. Our candidate for such physics is a simple model for stellar radiation feedback. Radiative heating, powered by accretion on to forming stars, arrests the fragmentation cascade and imposes a characteristic mass scale that is nearly independent of the time-evolution or initial conditions in the star-forming cloud, and that agrees well with the peak of the observed IMF. In contrast, models that introduce a stiff equation of state for denser clouds but that do not explicitly include the effects of feedback do not yield an invariant IMF.

Centrifugal Compressor Surge Controlled

NASA Technical Reports Server (NTRS)

Skoch, Gary J.

2003-01-01

It shows the variation in compressor mass flow with time as the mass flow is throttled to drive the compressor into surge. Surge begins where wide variations in mass flow occur. Air injection is then turned on to bring about a recovery from the initial surge condition and stabilize the compressor. The throttle is closed further until surge is again initiated. Air injection is increased to again recover from the surge condition and stabilize the compressor.

Degradation mechanisms of bioresorbable polyesters. Part 2. Effects of initial molecular weight and residual monomer.

PubMed

Gleadall, Andrew; Pan, Jingzhe; Kruft, Marc-Anton; Kellomäki, Minna

2014-05-01

This paper presents an understanding of how initial molecular weight and initial monomer fraction affect the degradation of bioresorbable polymers in terms of the underlying hydrolysis mechanisms. A mathematical model was used to analyse the effects of initial molecular weight for various hydrolysis mechanisms including noncatalytic random scission, autocatalytic random scission, noncatalytic end scission or autocatalytic end scission. Different behaviours were identified to relate initial molecular weight to the molecular weight half-life and to the time until the onset of mass loss. The behaviours were validated by fitting the model to experimental data for molecular weight reduction and mass loss of samples with different initial molecular weights. Several publications that consider initial molecular weight were reviewed. The effect of residual monomer on degradation was also analysed, and shown to accelerate the reduction of molecular weight and mass loss. An inverse square root law relationship was found between molecular weight half-life and initial monomer fraction for autocatalytic hydrolysis. The relationship was tested by fitting the model to experimental data with various residual monomer contents. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Impact of uneven sample morphology on mass resolving power in linear MALDI-TOF mass spectrometry: A comprehensive theoretical investigation.

PubMed

Cai, Yi-Hong; Wang, Yi-Sheng

2018-04-01

This work discusses the correlation between the mass resolving power of matrix-assisted laser desorption/ionization time-of-flight mass analyzers and extraction condition with an uneven sample morphology. Previous theoretical calculations show that the optimum extraction condition for flat samples involves an ideal ion source design and extraction delay. A general expression of spectral feature takes into account ion initial velocity, and extraction delay is derived in the current study. The new expression extends the comprehensive calculation to uneven sample surfaces and above 90% Maxell-Boltzmann initial velocity distribution of ions to account for imperfect ionization condition. Calculation shows that the impact of uneven sample surface or initial spatial spread of ions is negligible when the extraction delay is away from the ideal value. When the extraction delay approaches the optimum value, the flight-time topology shows a characteristic curve shape, and the time-domain mass spectral feature broadens with an increase in initial spatial spread of ions. For protonated 2,5-dihydroxybenzoic acid, the mass resolving power obtained from a sample of 3-μm surface roughness is approximately 3.3 times lower than that of flat samples. For ions of m/z 3000 coexpanded with 2,5-dihydroxybenzoic acid, the mass resolving power in the 3-μm surface roughness case only reduces roughly 7%. Comprehensive calculations also show that the mass resolving power of lighter ions is more sensitive to the accuracy of the extraction delay than heavier ions. Copyright © 2018 John Wiley & Sons, Ltd.

Biomechanical Analysis of Defensive Cutting Actions During Game Situations: Six Cases in Collegiate Soccer Competitions

PubMed Central

Sasaki, Shogo; Koga, Hideyuki; Krosshaug, Tron; Kaneko, Satoshi; Fukubayashi, Toru

2015-01-01

The strengths of interpersonal dyads formed by the attacker and defender in one-on-one situations are crucial for performance in team ball sports such as soccer. The purpose of this study was to analyze the kinematics of one-on-one defensive movements in soccer competitions, and determine the relationships between lower limb kinematics and the center of mass translation during cutting actions. Six defensive scenes in which a player was responding to an offender’s dribble attack were selected for analysis. To reconstruct the three-dimensional kinematics of the players, we used a photogrammetric model-based image-matching technique. The hip and knee kinematics were calculated from the matched skeleton model. In addition, the center of mass height was expressed as a ratio of each participant’s body height. The relationships between the center of mass height and the kinematics were determined by the Pearson’s product-moment correlation coefficient. The normalized center of mass height at initial contact was correlated with the vertical center of mass displacement (r = 0.832, p = 0.040) and hip flexion angle at initial contact (r = −0.823, p = 0.044). This suggests that the lower center of mass at initial contact is an important factor to reduce the downwards vertical center of mass translation during defensive cutting actions, and that this is executed primarily through hip flexion. It is therefore recommended that players land with an adequately flexed hip at initial contact during one-on-one cutting actions to minimize the vertical center of mass excursion. PMID:26240644

78 FR 29131 - Electricity MASS, LLC; Supplemental Notice that Initial Market-Based Rate Filing Includes Request...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-17

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. ER13-1440-000] Electricity MASS, LLC; Supplemental Notice that Initial Market- Based Rate Filing Includes Request for Blanket Section 204 Authorization This is a supplemental notice in the above-referenced proceeding, of Electricity...

Nuclear and Non-Nuclear Airblast Effects.

DTIC Science & Technology

1984-02-14

algorithms. 2 The above methodologr has been applied to a series of test prorlems initiated by a spherical high- explosive (HE) detonation In air . An...used, together with a real- air equation of state, to follow the development of an explosion initialized with the 1-kton standard as it reflects from the...interior. Stage (1) is not contained in our model; since the weapon mass greatly exceeds the ,mass of air contained within the initial explosion radius

Adiabatic invariants in stellar dynamics, 3: Application to globular cluster evolution

NASA Technical Reports Server (NTRS)

Weinberg, Martin D.

1994-01-01

The previous two companion papers demonstrate that slowly varying perturbations may not result in adiabatic cutoffs and provide a formalism for computing the long-term effects of time-dependent perturbations on stellar systems. Here, the theory is implemented in a Fokker-Planck code and a suite of runs illustrating the effects of shock heating on globular cluster evolution are described. Shock heating alone results in considerable mass loss for clusters with R(sub g) less than or approximately 8 kpc: a concentration c = 1.5 cluster with R(sub g) kpc loses up to 95% of its initial mass in 15 Gyr. Only those with concentration c greater than or approximately 1.3 survive disk shocks inside of this radius. Other effects, such as mass loss by stellar evolution, will decrease this survival bound. Loss of the initial halo together with mass segregation leads to mass spectral indices, x, which may be considerably larger than their initial values.

Effects of Main-Sequence Mass Loss on Stellar and Galactic Chemical Evolution.

NASA Astrophysics Data System (ADS)

Guzik, Joyce Ann

1988-06-01

L. A. Willson, G. H. Bowen and C. Struck -Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10^{-9}M o/yr, diminishing over several times 10^8 years. We attempted to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M o, and mass-loss rates decreasing exponentially over 2-3 times 10^8 years. Compared to a constant -mass model, these models require a reduced initial ^4He abundance, have deeper envelope convection zones and higher ^8B neutrino fluxes. Early processing of present surface layers at higher interior temperatures increases the surface ^3He abundance, destroys Li, Be and B, and decreases the surface C/N ratio following first dredge-up. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 Mo and mass loss timescales 0.2 to 2.0 Gyr. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M o and a metallicity -dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus -remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main sequence to the present. The ratio of stars to stellar remnants and the white dwarf age distribution may prove valuable in distinguishing between explanations for the observed bimodal present-day stellar mass function.

Patient Characteristics and Comorbidities Influence Walking Distances in Symptomatic Peripheral Arterial Disease: A Large One-Year Physiotherapy Cohort Study.

PubMed

Dörenkamp, Sarah; Mesters, Ilse; de Bie, Rob; Teijink, Joep; van Breukelen, Gerard

2016-01-01

The aim of this study is to investigate the association between age, gender, body-mass index, smoking behavior, orthopedic comorbidity, neurologic comorbidity, cardiac comorbidity, vascular comorbidity, pulmonic comorbidity, internal comorbidity and Initial Claudication Distance during and after Supervised Exercise Therapy at 1, 3, 6 and 12 months in a large sample of patients with Intermittent Claudication. Data was prospectively collected in standard physiotherapy care. Patients received Supervised Exercise Therapy according to the guideline Intermittent Claudication of the Royal Dutch Society for Physiotherapy. Three-level mixed linear regression analysis was carried out to analyze the association between patient characteristics, comorbidities and Initial Claudication Distance at 1, 3, 6 and 12 months. Data from 2995 patients was analyzed. Results showed that being female, advanced age and a high body-mass index were associated with lower Initial Claudication Distance at all-time points (p = 0.000). Besides, a negative association between cardiac comorbidity and Initial Claudication Distance was revealed (p = 0.011). The interaction time by age, time by body-mass index and time by vascular comorbidity were significantly associated with Initial Claudication Distance (p≤ 0.05). Per year increase in age (range: 33-93 years), the reduction in Initial Claudication Distance was 8m after 12 months of Supervised Exercise Therapy. One unit increase in body-mass index (range: 16-44 kg/m2) led to 10 m less improvement in Initial Claudication Distance after 12 months and for vascular comorbidity the reduction in improvement was 85 m after 12 months. This study reveals that females, patients at advanced age, patients with a high body-mass index and cardiac comorbidity are more likely to show less improvement in Initial Claudication Distances (ICD) after 1, 3, 6 and 12 months of Supervised Exercise Therapy. Further research should elucidate treatment adaptations that optimize treatment outcomes for these subgroups.

The History and Rate of Star Formation within the G305 Complex

NASA Astrophysics Data System (ADS)

Faimali, Alessandro Daniele

2013-07-01

Within this thesis, we present an extended multiwavelength analysis of the rich massive Galactic star-forming complex G305. We have focused our attention on studying the both the embedded massive star-forming population within G305, while also identifying the intermediate-, to lowmass content of the region also. Though massive stars play an important role in the shaping and evolution of their host galaxies, the physics of their formation still remains unclear. We have therefore set out to studying the nature of star formation within this complex, and also identify the impact that such a population has on the evolution of G305. We firstly present a Herschel far-infrared study towards G305, utilising PACS 70, 160 micron and SPIRE 250, 350, and 500 micron observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS, and Red MSX Source survey data available from previous studies. From this sample we identify some 16 candidate associations are identified as embedded massive star-forming regions, and derive a two-selection colour criterion from this sample of log(F70/F500) >= 1 and log(F160/F350) >= 1.6 to identify an additional 31 embedded massive star candidates with no associated star-formation tracers. Using this result, we are able to derive a star formation rate (SFR) of 0.01 - 0.02 Msun/yr. Comparing this resolved star formation rate, to extragalactic star formation rate tracers (based on the Kennicutt-Schmidt relation), we find the star formation activity is underestimated by a factor of >=2 in comparison to the SFR derived from the YSO population. By next combining data available from 2MASS and VVV, Spitzer GLIMPSE and MIPSGAL, MSX, and Herschel Hi-GAL, we are able to identify the low-, to intermediate-mass YSOs present within the complex. Employing a series of stringent colour selection criteria and fitting reddened stellar atmosphere models, we are able remove a significant amount of contaminating sources from our sample, leaving us with a highly reliable sample of some 599 candidate YSOs. From this sample, we derive a present-day SFR of 0.005±0.001 Msun/yr, and find the YSO mass function (YMF) of G305 to be significantly steeper than the standard Salpeter-Kroupa IMF. We find evidence of mass segregation towards G305, with a significant variation of the YMF both with the active star-forming region, and the outer region. The spatial distribution, and age gradient, of our 601 candidate YSOs also seem to rule out the scenario of propagating star formation within G305, with a more likely scenario of punctuated star formation over the lifetime of the complex.

Black hole genesis of dark matter

NASA Astrophysics Data System (ADS)

Lennon, Olivier; March-Russell, John; Petrossian-Byrne, Rudin; Tillim, Hannah

2018-04-01

We present a purely gravitational infra-red-calculable production mechanism for dark matter (DM) . The source of both the DM relic abundance and the hot Standard Model (SM) plasma is a primordial density of micro black holes (BHs), which evaporate via Hawking emission into both the dark and SM sectors. The mechanism has four qualitatively different regimes depending upon whether the BH evaporation is 'fast' or 'slow' relative to the initial Hubble rate, and whether the mass of the DM particle is 'light' or 'heavy' compared to the initial BH temperature. For each of these regimes we calculate the DM yield, Y, as a function of the initial state and DM mass and spin. In the 'slow' regime Y depends on only the initial BH mass over a wide range of initial conditions, including scenarios where the BHs are a small fraction of the initial energy density. The DM is produced with a highly non-thermal energy spectrum, leading in the 'light' DM mass regime (~260 eV and above depending on DM spin) to a strong constraint from free-streaming, but also possible observational signatures in structure formation in the spin 3/2 and 2 cases. The 'heavy' regime (~1.2 × 108 GeV to MPl depending on spin) is free of these constraints and provides new possibilities for DM detection. In all cases there is a dark radiation component predicted.

Numerical black hole initial data with low eccentricity based on post-Newtonian orbital parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walther, Benny; Bruegmann, Bernd; Mueller, Doreen

2009-06-15

Black hole binaries on noneccentric orbits form an important subclass of gravitational wave sources, but it is a nontrivial issue to construct numerical initial data with minimal initial eccentricity for numerical simulations. We compute post-Newtonian orbital parameters for quasispherical orbits using the method of Buonanno, Chen and Damour, (2006) and examine the resulting eccentricity in numerical simulations. Four different methods are studied resulting from the choice of Taylor-expanded or effective-one-body Hamiltonians, and from two choices for the energy flux. For equal-mass, nonspinning binaries the approach succeeds in obtaining low-eccentricity numerical initial data with an eccentricity of about e=0.002 for rathermore » small initial separations of D > or approx. 10M. The eccentricity increases for unequal masses and for spinning black holes, but remains smaller than that obtained from previous post-Newtonian approaches. The effective-one-body Hamiltonian offers advantages for decreasing initial separation as expected, but in the context of this study also performs significantly better than the Taylor-expanded Hamiltonian for binaries with spin. For mass ratio 4 ratio 1 and vanishing spin, the eccentricity reaches e=0.004. For mass ratio 1 ratio 1 and aligned spins of size 0.85M{sup 2} the eccentricity is about e=0.07 for the Taylor method and e=0.014 for the effective-one-body method.« less

29 CFR 4219.11 - Withdrawal liability upon mass withdrawal.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 29 Labor 9 2010-07-01 2010-07-01 false Withdrawal liability upon mass withdrawal. 4219.11 Section... Redetermination of Withdrawal Liability Upon Mass Withdrawal § 4219.11 Withdrawal liability upon mass withdrawal. (a) Initial withdrawal liability. The plan sponsor of a multiemployer plan that experiences a mass...

29 CFR 4219.11 - Withdrawal liability upon mass withdrawal.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 29 Labor 9 2011-07-01 2011-07-01 false Withdrawal liability upon mass withdrawal. 4219.11 Section... Redetermination of Withdrawal Liability Upon Mass Withdrawal § 4219.11 Withdrawal liability upon mass withdrawal. (a) Initial withdrawal liability. The plan sponsor of a multiemployer plan that experiences a mass...

40 CFR 86.156-98 - Calculations; refueling test.

Code of Federal Regulations, 2010 CFR

2010-07-01

... standard shall be computed by dividing the total refueling mass emissions by the total gallons of fuel... of the net hydrocarbon mass change and methanol mass change (if applicable) in the enclosure is used to determine refueling mass emissions. The mass is calculated from initial and final hydrocarbon and...

40 CFR 86.156-98 - Calculations; refueling test.

Code of Federal Regulations, 2012 CFR

2012-07-01

... standard shall be computed by dividing the total refueling mass emissions by the total gallons of fuel... of the net hydrocarbon mass change and methanol mass change (if applicable) in the enclosure is used to determine refueling mass emissions. The mass is calculated from initial and final hydrocarbon and...

40 CFR 86.156-98 - Calculations; refueling test.

Code of Federal Regulations, 2014 CFR

2014-07-01

... standard shall be computed by dividing the total refueling mass emissions by the total gallons of fuel... of the net hydrocarbon mass change and methanol mass change (if applicable) in the enclosure is used to determine refueling mass emissions. The mass is calculated from initial and final hydrocarbon and...

Nanostructure-initiator mass spectrometry biometrics

DOEpatents

Leclerc, Marion; Bowen, Benjamin; Northen, Trent

2015-09-08

Several embodiments described herein are drawn to methods of identifying an analyte on a subject's skin, methods of generating a fingerprint, methods of determining a physiological change in a subject, methods of diagnosing health status of a subject, and assay systems for detecting an analyte and generating a fingerprint, by nanostructure-initiator mass spectrometry (NIMS).

Selective Transcatheter Arterial Embolization for Treatment of Bleeding Complications or Reduction of Tumor Mass of Hepatocellular Adenomas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erdogan, Deha; Delden, Otto M. van; Busch, Olivier R. C.

2007-11-15

Hepatocellular adenomas (HCAs) are benign liver lesions which may be complicated by spontaneous intratumoral bleeding, with or without rupture into the abdominal cavity, or malignant degeneration. Recent advances in radiological interventional techniques now offer selective transcatheter arterial embolization (TAE) as an alternative approach to surgery as the initial treatment to stop the bleeding or as an elective treatment to reduce the tumor mass of the HCA. Herein, we report our initial experience using TAE in the management of HCA. Five female patients and one male patient presented with spontaneous hemorrhage of HCA. Four patients were initially treated with selective TAEmore » to stop the bleeding. In two patients in whom the bleeding stopped spontaneously, TAE was electively undertaken 1 year after presentation to reduce the tumor mass of HCAs >5 cm. Selective TAE as initial treatment in patients with spontaneous bleeding of HCA with or without rupture is effective and will change the need for urgent laparotomy to control bleeding. Selective TAE may also be used as an elective treatment to reduce the tumor mass of larger HCAs.« less

Excursion set mass functions for hierarchical Gaussian fluctuations

NASA Technical Reports Server (NTRS)

Bond, J. R.; Kaiser, N.; Cole, S.; Efstathiou, G.

1991-01-01

It is pointed out that most schemes for determining the mass function of virialized objects from the statistics of the initial density perturbation field suffer from the cloud-in-cloud problem of miscounting the number of low-mass clumps, many of which would have been subsumed into larger objects. The paper proposes a solution based on the theory of the excursion sets of F(r, R sub f), the four-dimensional initial density perturbation field smoothed with a continuous hierarchy of filters of radii R sub f.

Mass retention efficiencies of He accretion onto carbon-oxygen white dwarfs and type Ia supernovae

NASA Astrophysics Data System (ADS)

Wu, C.; Wang, B.; Liu, D.; Han, Z.

2017-07-01

Context. Type Ia supernovae (SNe Ia) play a crucial role in studying cosmology and galactic chemical evolution. They are thought to be thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs) when their masses reach the Chandrasekar mass limit in binaries. Previous studies have suggested that He novae may be progenitor candidates of SNe Ia. However, the mass retention efficiencies during He nova outbursts are still uncertain. Aims: In this article, we aim to study the mass retention efficiencies of He nova outbursts and to investigate whether SNe Ia can be produced through He nova outbursts. Methods: Using the stellar evolution code Modules for Experiments in Stellar Astrophysics, we simulated a series of multicycle He-layer flashes, in which the initial WD masses range from 0.7 to 1.35 M⊙ with various accretion rates. Results: We obtained the mass retention efficiencies of He nova outbursts for various initial WD masses, which can be used in the binary population synthesis studies. In our simulations, He nova outbursts can increase the mass of the WD to the Chandrasekar mass limit and the explosive carbon burning can be triggered in the center of the WD; this suggests that He nova outbursts can produce SNe Ia. Meanwhile, the mass retention efficiencies in the present work are lower than those of previous studies, which leads to a lower birthrates of SNe Ia through the WD + He star channel. Furthermore, we obtained the elemental abundances distribution at the moment of explosive carbon burning, which can be used as the initial input parameters in studying explosion models of SNe Ia.

Star formation in a hierarchical model for Cloud Complexes

NASA Astrophysics Data System (ADS)

Sanchez, N.; Parravano, A.

The effects of the external and initial conditions on the star formation processes in Molecular Cloud Complexes are examined in the context of a schematic model. The model considers a hierarchical system with five predefined phases: warm gas, neutral gas, low density molecular gas, high density molecular gas and protostars. The model follows the mass evolution of each substructure by computing its mass exchange with their parent and children. The parent-child mass exchange depends on the radiation density at the interphase, which is produced by the radiation coming from the stars that form at the end of the hierarchical structure, and by the external radiation field. The system is chaotic in the sense that its temporal evolution is very sensitive to small changes in the initial or external conditions. However, global features such as the star formation efficience and the Initial Mass Function are less affected by those variations.

Galaxy Evolution Insights from Spectral Modeling of Large Data Sets from the Sloan Digital Sky Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoversten, Erik A.

This thesis centers on the use of spectral modeling techniques on data from the Sloan Digital Sky Survey (SDSS) to gain new insights into current questions in galaxy evolution. The SDSS provides a large, uniform, high quality data set which can be exploited in a number of ways. One avenue pursued here is to use the large sample size to measure precisely the mean properties of galaxies of increasingly narrow parameter ranges. The other route taken is to look for rare objects which open up for exploration new areas in galaxy parameter space. The crux of this thesis is revisitingmore » the classical Kennicutt method for inferring the stellar initial mass function (IMF) from the integrated light properties of galaxies. A large data set (~ 10 5 galaxies) from the SDSS DR4 is combined with more in-depth modeling and quantitative statistical analysis to search for systematic IMF variations as a function of galaxy luminosity. Galaxy Hα equivalent widths are compared to a broadband color index to constrain the IMF. It is found that for the sample as a whole the best fitting IMF power law slope above 0.5 M ⊙ is Γ = 1.5 ± 0.1 with the error dominated by systematics. Galaxies brighter than around M r,0.1 = -20 (including galaxies like the Milky Way which has M r,0.1 ~ -21) are well fit by a universal Γ ~ 1.4 IMF, similar to the classical Salpeter slope, and smooth, exponential star formation histories (SFH). Fainter galaxies prefer steeper IMFs and the quality of the fits reveal that for these galaxies a universal IMF with smooth SFHs is actually a poor assumption. Related projects are also pursued. A targeted photometric search is conducted for strongly lensed Lyman break galaxies (LBG) similar to MS1512-cB58. The evolution of the photometric selection technique is described as are the results of spectroscopic follow-up of the best targets. The serendipitous discovery of two interesting blue compact dwarf galaxies is reported. These galaxies were identified by their extremely weak (< 150) [N π] Γ6584 to Hα emission line ratios. Abundance analysis from emission line fluxes reveals that these galaxies have gas phase oxygen abundances 12 + log(O/H) ~ 7.7 to 7.9, not remarkably low, and near infrared imaging detects an old stellar population. However, the measured nitrogen to oxygen ratios log(N/O) < 1.7 are anomalously low for blue compact dwarf galaxies. These objects may be useful for understanding the chemical evolution of nitrogen.« less

Transformations of asymptotically AdS hyperbolic initial data and associated geometric inequalities

NASA Astrophysics Data System (ADS)

Cha, Ye Sle; Khuri, Marcus

2018-01-01

We construct transformations which take asymptotically AdS hyperbolic initial data into asymptotically flat initial data, and which preserve relevant physical quantities. This is used to derive geometric inequalities in the asymptotically AdS hyperbolic setting from counterparts in the asymptotically flat realm, whenever a geometrically motivated system of elliptic equations admits a solution. The inequalities treated here relate mass, angular momentum, charge, and horizon area. Furthermore, new mass-angular momentum inequalities in this setting are conjectured and discussed.

Sizes of Black Holes Throughout the Universe

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-05-01

What is the distribution of sizes of black holes in our universe? Can black holes of any mass exist, or are there gaps in their possible sizes? The shape of this black-hole mass function has been debated for decades and the dawn of gravitational-wave astronomy has only spurred further questions.Mind the GapsThe starting point for the black-hole mass function lies in the initial mass function (IMF) for stellar black holes the beginning size distribution of black holes after they are born from stars. Instead of allowing for the formation of stellar black holes of any mass, theoretical models propose two gaps in the black-hole IMF:An upper mass gap at 50130 solar masses, due to the fact that stellar progenitors of black holes in this mass range are destroyed by pair-instability supernovae.A lower mass gap below 5 solar masses, which is argued to arise naturally from the mechanics of supernova explosions.Missing black-hole (BH) formation channels due to the existence of the lower gap (LG) and the upper gap (UG) in the initial mass function. a) The number of BHs at all scales are lowered because no BH can merge with BHs in the LG to form a larger BH. b) The missing channel responsible for the break at 10 solar masses, resulting from the LG. c) The missing channel responsible for the break at 60 solar masses, due to the interaction between the LG and the UG. [Christian et al. 2018]We can estimate the IMF for black holes by scaling a typical IMF for stars and then adding in these theorized gaps. But is this initial distribution of black-hole masses the same as the distribution that we observe in the universe today?The Influence of MergersBased on recent events, the answer appears to be no! Since the first detections of gravitational waves in September 2015, we now know that black holes can merge to form bigger black holes. An initial distribution of black-hole masses must therefore evolve over time, as mergers cause the depletion of low-mass black holes and an increase in higher-mass black holes.A team of scientists led by Pierre Christian, an Einstein Fellow at Harvard University, has now looked into characterizing this shift. In particular, Christian and collaborators explore how black-hole mergers in the centers of dense star clustersultimately shape the black-hole mass function of the universe.Black Holes TodayChristian and collaborators use analytical models of coagulation mergers of particles to form larger particles to estimate the impact of mergers in star clusters on resulting black-hole sizes. They find that, over an evolution of 10 billion years, mergers can appreciably fill in the upper mass gap of the black-hole IMF.An example of the black-hole mass function that can result from evolving the initial mass function complete with gaps over time. Two breaks appear as a result of the initial gaps: one at 10 (LB) and one at 60 solar masses (UB). [Christian et al. 2018]The lower mass gap, on the other hand, leaves observable signatures in the final black-hole mass function: a break at 10 solar masses (since black holes below this mass cant be created by mergers) and one at 60 solar masses (caused by the interaction of the upper and lower gaps). As we build up black-hole statistics in the future (thanks, gravitational-wave detectors!), searching for these breaks will help us to test our models.Lastly, the authors find that their models can only be consistent with observations if ejection is efficient black holes must be regularly ousted from star clusters through interactions with other bodies or as a result of kicks when they merge. This idea is consistent with many recent studies supporting a large population of free-floating stellar-mass black holes.CitationPierre Christian et al 2018 ApJL 858 L8. doi:10.3847/2041-8213/aabf88

Mass-losing M supergiants in the solar neighborhood

NASA Technical Reports Server (NTRS)

Jura, M.; Kleinmann, S. G.

1990-01-01

A list of the 21 mass-losing red supergiants (20 M type, one G type; L greater than 100,000 solar luminosities) within 2.5 kpc of the sun is compiled. These supergiants are highly evolved descendants of main-sequence stars with initial masses larger than 20 solar masses. The surface density is between about 1 and 2/sq kpc. As found previously, these stars are much less concentrated toward the Galactic center than W-R stars, which are also highly evolved massive stars. Although with considerable uncertainty, it is estimated that the mass return by the M supergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpc yr. In the hemisphere facing the Galactic center there is much less mass loss from M supergiants than from W-R stars, but, in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 200,000 and 400,000 yr. During this phase, a star of initially at least 20 solar masses returns perhaps 3-10 solar masses into the interstellar medium.

Improvements to the construction of binary black hole initial data

NASA Astrophysics Data System (ADS)

Ossokine, Serguei; Foucart, Francois; Pfeiffer, Harald P.; Boyle, Michael; Szilágyi, Béla

2015-12-01

Construction of binary black hole initial data is a prerequisite for numerical evolutions of binary black holes. This paper reports improvements to the binary black hole initial data solver in the spectral Einstein code, to allow robust construction of initial data for mass-ratio above 10:1, and for dimensionless black hole spins above 0.9, while improving efficiency for lower mass-ratios and spins. We implement a more flexible domain decomposition, adaptive mesh refinement and an updated method for choosing free parameters. We also introduce a new method to control and eliminate residual linear momentum in initial data for precessing systems, and demonstrate that it eliminates gravitational mode mixing during the evolution. Finally, the new code is applied to construct initial data for hyperbolic scattering and for binaries with very small separation.

Quantum Chromodynamics and Color Confinement (confinement 2000) - Proceedings of the International Symposium

NASA Astrophysics Data System (ADS)

Suganuma, H.; Fukushima, M.; Toki, H.

The Table of Contents for the book is as follows: * Preface * Opening Address * Monopole Condensation and Quark Confinement * Dual QCD, Effective String Theory, and Regge Trajectories * Abelian Dominance and Monopole Condensation * Non-Abelian Stokes Theorem and Quark Confinement in QCD * Infrared Region of QCD and Confining Configurations * BRS Quartet Mechanism for Color Confinement * Color Confinement and Quartet Mechanism * Numerical Tests of the Kugo-Ojima Color Confinement Criterion * Monopoles and Confinement in Lattice QCD * SU(2) Lattice Gauge Theory at T > 0 in a Finite Box with Fixed Holonomy * Confining and Dirac Strings in Gluodynamics * Cooling, Monopoles, and Vortices in SU(2) Lattice Gauge Theory * Quark Confinement Physics from Lattice QCD * An (Almost) Perfect Lattice Action for SU(2) and SU(3) Gluodynamics * Vortices and Confinement in Lattice QCD * P-Vortices, Nexuses and Effects of Gribov Copies in the Center Gauges * Laplacian Center Vortices * Center Vortices at Strong Couplings and All Couplings * Simulations in SO(3) × Z(2) Lattice Gauge Theory * Exciting a Vortex - the Cost of Confinement * Instantons in QCD * Deformation of Instanton in External Color Fields * Field Strength Correlators in the Instanton Liquid * Instanton and Meron Physics in Lattice QCD * The Dual Ginzburg-Landau Theory for Confinement and the Role of Instantons * Lattice QCD for Quarks, Gluons and Hadrons * Hadronic Spectral Functions in QCD * Universality and Chaos in Quantum Field Theories * Lattice QCD Study of Three Quark Potential * Probing the QCD Vacuum with Flavour Singlet Objects : η' on the Lattice * Lattice Studies of Quarks and Gluons * Quarks and Hadrons in QCD * Supersymmetric Nonlinear Sigma Models * Chiral Transition and Baryon-number Susceptibility * Light Quark Masses in QCD * Chiral Symmetry of Baryons and Baryon Resonances * Confinement and Bound States in QCD * Parallel Session * Off-diagonal Gluon Mass Generation and Strong Randomness of Off-diagonal Gluon Phase in the Maximally Abelian Gauge * On the Colour Confinement and the Minimal Surface * Glueball Mass and String Tension of SU(2) Gluodynamics from Abelian Monopoles and Strings * Application of the Non-Perturbative Renormalization Group to the Nambu-Jona-Lasinio Model at Finite Temperature and Density * Confining Flux-Tube and Hadrons in QCD * Gauge Symmetry Breakdown due to Dynamical Higgs Scalar * Spatial Structure of Quark Cooper Pairs * New Approach to Axial Coupling Constants in the QCD Sum Rule and Instanton Effects * String Breaking on a Lattice * Bethe-Salpeter Approach for Mesons within the Dual Ginzburg-Landau Theory * Gauge Dependence and Matching Procedure of a Nonrelativistic QCD Boundstate Formalism * A Mathematical Approach to the SU(2)-Quark Confinement * Simulations of Odd Flavors QCD by Hybrid Monte Carlo * Non-Perturbative Renormalization Group Analysis of Dynamical Chiral Symmetry Breaking with Beyond Ladder Contributions * Charmonium Physics in Finite Temperature Lattice QCD * From Meson-Nucleon Scattering to Vector Mesons in Nuclear Matter * Symposium Program * List of Participants

Origins of extreme broadening mechanisms in near-edge x-ray spectra of nitrogen compounds

NASA Astrophysics Data System (ADS)

Vinson, John; Jach, Terrence; Elam, W. T.; Denlinger, J. D.

2014-11-01

We demonstrate the observation of many-body lifetime effects in valence-band x-ray emission. A comparison of the N K α emission of crystalline ammonium nitrate to molecular-orbital calculations revealed an unexpected, extreme broadening of the NO σ recombination—so extensively as to virtually disappear. GW calculations establish that this disappearance is due to a large imaginary component of the self-energy associated with the NO σ orbitals. Building upon density-functional theory, we have calculated radiative transitions from the nitrogen 1 s level of ammonium nitrate and ammonium chloride using a Bethe-Salpeter method to include electron-hole interactions. The absorption and emission spectra of both crystals evince large, orbital-dependent sensitivity to molecular dynamics. We demonstrate that many-body effects as well as thermal and zero-point motion are vital for understanding observed spectra. A computational approach using average atomic positions and uniform broadening to account for lifetime and phonon effects is unsatisfactory.

Final Technical Report [Scalable methods for electronic excitations and optical responses of nanostructures: mathematics to algorithms to observables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saad, Yousef

2014-03-19

The master project under which this work is funded had as its main objective to develop computational methods for modeling electronic excited-state and optical properties of various nanostructures. The specific goals of the computer science group were primarily to develop effective numerical algorithms in Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT). There were essentially four distinct stated objectives. The first objective was to study and develop effective numerical algorithms for solving large eigenvalue problems such as those that arise in Density Functional Theory (DFT) methods. The second objective was to explore so-called linear scaling methods ormore » Methods that avoid diagonalization. The third was to develop effective approaches for Time-Dependent DFT (TDDFT). Our fourth and final objective was to examine effective solution strategies for other problems in electronic excitations, such as the GW/Bethe-Salpeter method, and quantum transport problems.« less

Excitonic Effects and Optical Absorption Spectrum of Doped Graphene

NASA Astrophysics Data System (ADS)

Jornada, Felipe; Deslippe, Jack; Louie, Steven

2012-02-01

First-principles calculations based on the GW-Bethe-Salpeter Equation (GW-BSE) approach and subsequent experiments have shown large excitonic effects in the optical absorbance of graphene. Here we employ the GW-BSE formalism to probe the effects of charge carrier doping and of having an external electric field on the absorption spectrum of graphene. We show that the absorbance peak due to the resonant exciton exhibits systematic changes in both its position and profile when graphene is gate doped by carriers, in excellent agreement to very recent measurementsootnotetextTony F. Heinz, private communications.. We analyze the various contributions to these changes in the absorption spectrum, such as the effects of screening by carriers to the quasiparticle energies and electron-hole interactions. This work was supported by National Science Foundation Grant No. DMR10-1006184, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and the U.S. DOD - Office of Naval Research under RTC Grant No. N00014-09-1-1066. Computer time was provided by NERSC.

Accurate X-Ray Spectral Predictions: An Advanced Self-Consistent-Field Approach Inspired by Many-Body Perturbation Theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Yufeng; Vinson, John; Pemmaraju, Sri

Constrained-occupancy delta-self-consistent-field (ΔSCF) methods and many-body perturbation theories (MBPT) are two strategies for obtaining electronic excitations from first principles. Using the two distinct approaches, we study the O 1s core excitations that have become increasingly important for characterizing transition-metal oxides and understanding strong electronic correlation. The ΔSCF approach, in its current single-particle form, systematically underestimates the pre-edge intensity for chosen oxides, despite its success in weakly correlated systems. By contrast, the Bethe-Salpeter equation within MBPT predicts much better line shapes. This motivates one to reexamine the many-electron dynamics of x-ray excitations. We find that the single-particle ΔSCF approach can bemore » rectified by explicitly calculating many-electron transition amplitudes, producing x-ray spectra in excellent agreement with experiments. This study paves the way to accurately predict x-ray near-edge spectral fingerprints for physics and materials science beyond the Bethe-Salpether equation.« less

Excitation spectrum and staggering transformations in lattice quantum models.

PubMed

Faria da Veiga, Paulo A; O'Carroll, Michael; Schor, Ricardo

2002-08-01

We consider the energy-momentum excitation spectrum of diverse lattice Hamiltonian operators: the generator of the Markov semigroup of Ginzburg-Landau models with Langevin stochastic dynamics, the Hamiltonian of a scalar quantum field theory, and the Hamiltonian associated with the transfer matrix of a classical ferromagnetic spin system at high temperature. The low-lying spectrum consists of a one-particle state and a two-particle band. The two-particle spectrum is determined using a lattice version of the Bethe-Salpeter equation. In addition to the two-particle band, depending on the lattice dimension and on the attractive or repulsive character of the interaction between the particles of the system, there is, respectively, a bound state below or above the two-particle band. We show how the existence or nonexistence of these bound states can be understood in terms of a nonrelativistic single-particle lattice Schrödinger Hamiltonian with a delta potential. A staggering transformation relates the spectra of the attractive and the repulsive cases.

First-principles study of excitonic effects in Raman intensities

NASA Astrophysics Data System (ADS)

Gillet, Yannick; Giantomassi, Matteo; Gonze, Xavier

2013-09-01

The ab initio prediction of Raman intensities for bulk solids usually relies on the hypothesis that the frequency of the incident laser light is much smaller than the band gap. However, when the photon frequency is a sizable fraction of the energy gap, or higher, resonance effects appear. In the case of silicon, when excitonic effects are neglected, the response of the solid to light increases by nearly three orders of magnitude in the range of frequencies between the static limit and the gap. When excitonic effects are taken into account, an additional tenfold increase in the intensity is observed. We include these effects using a finite-difference scheme applied on the dielectric function obtained by solving the Bethe-Salpeter equation. Our results for the Raman susceptibility of silicon show stronger agreement with experimental data compared with previous theoretical studies. For the sampling of the Brillouin zone, a double-grid technique is proposed, resulting in a significant reduction in computational effort.

Bright and dark singlet excitons via linear and two-photon spectroscopy in monolayer transition metal dichalcogenides

DOE PAGES

Berkelbach, Timothy C.; Hybertsen, Mark S.; Reichmann, David R.

2015-08-10

We discuss the linear and two-photon spectroscopic selection rules for spin-singlet excitons in monolayer transition-metal dichalcogenides. Our microscopic formalism combines a fully k-dependent few-orbital band structure with a many-body Bethe-Salpeter equation treatment of the electron-hole interaction, using a model dielectric function. We show analytically and numerically that the single-particle, valley-dependent selection rules are preserved in the presence of excitonic effects. Furthermore, we definitively demonstrate that the bright (one-photon allowed) excitons have s-type azimuthal symmetry and that dark p-type excitons can be probed via two-photon spectroscopy. Thus, the screened Coulomb interaction in these materials substantially deviates from the 1/ε₀r form; thismore » breaks the “accidental” angular momentum degeneracy in the exciton spectrum, such that the 2p exciton has a lower energy than the 2s exciton by at least 50 meV. We compare our calculated two-photon absorption spectra to recent experimental measurements.« less

Linear Scaling of the Exciton Binding Energy versus the Band Gap of Two-Dimensional Materials

NASA Astrophysics Data System (ADS)

Choi, Jin-Ho; Cui, Ping; Lan, Haiping; Zhang, Zhenyu

2015-08-01

The exciton is one of the most crucial physical entities in the performance of optoelectronic and photonic devices, and widely varying exciton binding energies have been reported in different classes of materials. Using first-principles calculations within the G W -Bethe-Salpeter equation approach, here we investigate the excitonic properties of two recently discovered layered materials: phosphorene and graphene fluoride. We first confirm large exciton binding energies of, respectively, 0.85 and 2.03 eV in these systems. Next, by comparing these systems with several other representative two-dimensional materials, we discover a striking linear relationship between the exciton binding energy and the band gap and interpret the existence of the linear scaling law within a simple hydrogenic picture. The broad applicability of this novel scaling law is further demonstrated by using strained graphene fluoride. These findings are expected to stimulate related studies in higher and lower dimensions, potentially resulting in a deeper understanding of excitonic effects in materials of all dimensionalities.

Resonant-Raman Intensities of N-layer Transition Metal Dichalcogenides from First Principles

NASA Astrophysics Data System (ADS)

Miranda, Henrique; Froehlicher, Guillaume; Lorchat, Ettienne; Fernique, François; Molina-Sánchez, Alejandro; Berciaud, Stéphane; Wirtz, Ludger

Transition metal dichalcogenides (TMDs) have interesting optical and electronic properties that make them good candidates for nano-engineering applications. Raman spectroscopy provides information about the vibrational modes and optical spectrum at the same time: when the laser energy is close to an electronic transition, the intensity is increased due to resonance. We investigate these effects combining different ab initio methods: we obtain ground-state and vibrational properties from density functional theory and the optical absorption spectrum using GW corrections and the Bethe-Salpeter equation to account for the excitonic effects which are known to play an important role in TMDs. Using a quasi-static finite differences approach, we calculate the dielectric susceptibility for different light polarizations and different phonon modes in order to determine the Raman tensor of TMDs, in particular of multi-layer and bulk MoTe2. We explain recent experimental results for the splitting of high-frequency modes and deviations from the non-resonant Raman model. We also give a brief outlook on possible improvements of the methodology.

Solution of two-body relativistic bound state equations with confining plus Coulomb interactions

NASA Technical Reports Server (NTRS)

Maung, Khin Maung; Kahana, David E.; Norbury, John W.

1992-01-01

Studies of meson spectroscopy have often employed a nonrelativistic Coulomb plus Linear Confining potential in position space. However, because the quarks in mesons move at an appreciable fraction of the speed of light, it is necessary to use a relativistic treatment of the bound state problem. Such a treatment is most easily carried out in momentum space. However, the position space Linear and Coulomb potentials lead to singular kernels in momentum space. Using a subtraction procedure we show how to remove these singularities exactly and thereby solve the Schroedinger equation in momentum space for all partial waves. Furthermore, we generalize the Linear and Coulomb potentials to relativistic kernels in four dimensional momentum space. Again we use a subtraction procedure to remove the relativistic singularities exactly for all partial waves. This enables us to solve three dimensional reductions of the Bethe-Salpeter equation. We solve six such equations for Coulomb plus Confining interactions for all partial waves.

Accurate X-Ray Spectral Predictions: An Advanced Self-Consistent-Field Approach Inspired by Many-Body Perturbation Theory

DOE PAGES

Liang, Yufeng; Vinson, John; Pemmaraju, Sri; ...

2017-03-03

Constrained-occupancy delta-self-consistent-field (ΔSCF) methods and many-body perturbation theories (MBPT) are two strategies for obtaining electronic excitations from first principles. Using the two distinct approaches, we study the O 1s core excitations that have become increasingly important for characterizing transition-metal oxides and understanding strong electronic correlation. The ΔSCF approach, in its current single-particle form, systematically underestimates the pre-edge intensity for chosen oxides, despite its success in weakly correlated systems. By contrast, the Bethe-Salpeter equation within MBPT predicts much better line shapes. This motivates one to reexamine the many-electron dynamics of x-ray excitations. We find that the single-particle ΔSCF approach can bemore » rectified by explicitly calculating many-electron transition amplitudes, producing x-ray spectra in excellent agreement with experiments. This study paves the way to accurately predict x-ray near-edge spectral fingerprints for physics and materials science beyond the Bethe-Salpether equation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trevisanutto, Paolo E.; Vignale, Giovanni, E-mail: vignaleg@missouri.edu

Ab initio electronic structure calculations of two-dimensional layered structures are typically performed using codes that were developed for three-dimensional structures, which are periodic in all three directions. The introduction of a periodicity in the third direction (perpendicular to the layer) is completely artificial and may lead in some cases to spurious results and to difficulties in treating the action of external fields. In this paper we develop a new approach, which is “native” to quasi-2D materials, making use of basis function that are periodic in the plane, but atomic-like in the perpendicular direction. We show how some of the basicmore » tools of ab initio electronic structure theory — density functional theory, GW approximation and Bethe-Salpeter equation — are implemented in the new basis. We argue that the new approach will be preferable to the conventional one in treating the peculiarities of layered materials, including the long range of the unscreened Coulomb interaction in insulators, and the effects of strain, corrugations, and external fields.« less

Exploring the Influence of Dynamic Disorder on Excitons in Solid Pentacene

NASA Astrophysics Data System (ADS)

Wang, Zhiping; Sharifzadeh, Sahar; Doak, Peter; Lu, Zhenfei; Neaton, Jeffrey

2014-03-01

A complete understanding of the spectroscopic and charge transport properties of organic semiconductors requires knowledge of the role of thermal fluctuations and dynamic disorder. We present a first-principles theoretical study aimed at understanding the degree to which dynamic disorder at room temperature results in energy level broadening and excited-state localization within bulk crystalline pentacene. Ab initio molecular dynamics simulations are well-equilibrated for 7-9 ps and tens of thousands of structural snapshots, taken at 0.5 fs intervals, provide input for many-body perturbation theory within the GW approximation and Bethe-Salpeter equation (BSE) approach. The GW-corrected density of states, including thousands of snapshots, indicates that thermal fluctuations significantly broaden the valence and conduction states by >0.2 eV. Additionally, we investigate the nature and energy of the lowest energy singlet and triplet excitons, computed for a set of uncorrelated and energetically preferred structures. This work supported by DOE; computational resources provided by NERSC.

Exciton dispersion in molecular solids

NASA Astrophysics Data System (ADS)

Cudazzo, Pierluigi; Sottile, Francesco; Rubio, Angel; Gatti, Matteo

2015-03-01

The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.

Accurate X-Ray Spectral Predictions: An Advanced Self-Consistent-Field Approach Inspired by Many-Body Perturbation Theory.

PubMed

Liang, Yufeng; Vinson, John; Pemmaraju, Sri; Drisdell, Walter S; Shirley, Eric L; Prendergast, David

2017-03-03

Constrained-occupancy delta-self-consistent-field (ΔSCF) methods and many-body perturbation theories (MBPT) are two strategies for obtaining electronic excitations from first principles. Using the two distinct approaches, we study the O 1s core excitations that have become increasingly important for characterizing transition-metal oxides and understanding strong electronic correlation. The ΔSCF approach, in its current single-particle form, systematically underestimates the pre-edge intensity for chosen oxides, despite its success in weakly correlated systems. By contrast, the Bethe-Salpeter equation within MBPT predicts much better line shapes. This motivates one to reexamine the many-electron dynamics of x-ray excitations. We find that the single-particle ΔSCF approach can be rectified by explicitly calculating many-electron transition amplitudes, producing x-ray spectra in excellent agreement with experiments. This study paves the way to accurately predict x-ray near-edge spectral fingerprints for physics and materials science beyond the Bethe-Salpether equation.

Optical properties of single and bilayer arsenene phases

NASA Astrophysics Data System (ADS)

Kecik, Deniz; Ciraci, Salim; Durgun, Engin

An extensive investigation of the optical properties of single-layer buckled and washboard arsenene and their bilayers was performed, starting from layered three-dimensional (3D) crystalline phase of arsenic using density functional and many-body perturbation theories combined with Random Phase Approximation. Electron-hole interactions were taken into account by solving the Bethe-Salpeter equation, suggesting first bound exciton energies on the order of 0.7 eV. Thus, many-body effects were found to be crucial for altering the optical properties of arsenene. The light absorption of single layer and bilayer arsenene structures in general falls within the visible-ultraviolet (UV) spectral regime. Moreover, directional anisotropy, varying the number of layers and applying homogeneous or uniaxial in-plane tensile strain were found to modify the optical properties of two-dimensional (2D) arsenene phases, which could be useful for diverse photovoltaic and optoelectronic applications. This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No 115F088.

Adsorption of basic dyes on granular activated carbon and natural zeolite.

PubMed

Meshko, V; Markovska, L; Mincheva, M; Rodrigues, A E

2001-10-01

The adsorption of basic dyes from aqueous solution onto granular activated carbon and natural zeolite has been studied using an agitated batch adsorber. The influence of agitation, initial dye concentration and adsorbent mass has been studied. The parameters of Langmuir and Freundlich adsorption isotherms have been determined using the adsorption data. Homogeneous diffusion model (solid diffusion) combined with external mass transfer resistance is proposed for the kinetic investigation. The dependence of solid diffusion coefficient on initial concentration and mass adsorbent is represented by the simple empirical equations.

Evaluation of Mass Filtered, Time Dilated, Time-of-Flight Mass Spectrometry

DTIC Science & Technology

2010-01-01

Figure 4.4: Mass resolution dependence on field for selected actinides and surrogates...45 Figure 4.7: Mass resolution dependence on field for selected actinides and actinide surrogates, modeled with no initial...system. A somewhat better mass resolution would need to be achieved in order to separate hydride molecules in the actinide region. However, the

Two Massive White Dwarfs from NGC 2323 and the Initial-Final Mass Relation for Progenitors of 4 to 6.5 M

NASA Astrophysics Data System (ADS)

Cummings, Jeffrey D.; Kalirai, Jason S.; Tremblay, P.-E.; Ramirez-Ruiz, Enrico

2016-02-01

We observed a sample of 10 white dwarf candidates in the rich open cluster NGC 2323 (M50) with the Keck Low-Resolution Imaging Spectrometer. The spectroscopy shows eight to be DA white dwarfs, with six of these having high signal-to-noise ratio appropriate for our analysis. Two of these white dwarfs are consistent with singly evolved cluster membership, and both are high mass ˜1.07 M⊙, and give equivalent progenitor masses of 4.69 M⊙. To supplement these new high-mass white dwarfs and analyze the initial-final mass relation (IFMR), we also looked at 30 white dwarfs from publicly available data that are mostly all high-mass (≳ 0.9 M⊙). These original published data exhibited significant scatter, and to test if this scatter is true or simply the result of systematics, we have uniformly analyzed the white dwarf spectra and have adopted thorough photometric techniques to derive uniform cluster parameters for their parent clusters. The resulting IFMR scatter is significantly reduced, arguing that mass-loss rates are not stochastic in nature and that within the ranges of metallicity and mass analyzed in this work mass loss is not highly sensitive to variations in metallicity. Lastly, when adopting cluster ages based on Y2 isochrones, the slope of the high-mass IFMR remains steep and consistent with that found from intermediate-mass white dwarfs, giving a linear IFMR from progenitor masses between 3 and 6.5 M⊙. In contrast, when adopting the slightly younger cluster ages based on PARSEC isochrones, the high-mass IFMR has a moderate turnover near an initial mass of 4 M⊙. Based on observations with the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, was made possible by the generous financial support of the W.M. Keck Foundation.

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-07-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star-forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-04-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜ 600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜ 200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

Journal: A Review of Some Tracer-Test Design Equations for Tracer-Mass Estimation and Sample Collection Frequency

EPA Science Inventory

Determination of necessary tracer mass, initial sample-collection time, and subsequent sample-collection frequency are the three most difficult aspects to estimate for a proposed tracer test prior to conducting the tracer test. To facilitate tracer-mass estimation, 33 mass-estima...

VizieR Online Data Catalog: GalIMF version 1.0.0 (Yan+, 2017)

NASA Astrophysics Data System (ADS)

Yan, Z.; Jerabkova, T.; Kroupa, P.

2017-08-01

GalIMF stands for the Galaxy-wide Initial Mass Function. It is a Python 3 module that allows users to compute galaxy-wide initial stellar mass functions based on locally derived empirical constraints following the IGIMF theory. See the GalIMF homepage https://sites.google.com/view/galimf/home for more information. (1 data file).

E-Standards For Mass Properties Engineering

NASA Technical Reports Server (NTRS)

Cerro, Jeffrey A.

2008-01-01

A proposal is put forth to promote the concept of a Society of Allied Weight Engineers developed voluntary consensus standard for mass properties engineering. This standard would be an e-standard, and would encompass data, data manipulation, and reporting functionality. The standard would be implemented via an open-source SAWE distribution site with full SAWE member body access. Engineering societies and global standards initiatives are progressing toward modern engineering standards, which become functioning deliverable data sets. These data sets, if properly standardized, will integrate easily between supplier and customer enabling technically precise mass properties data exchange. The concepts of object-oriented programming support all of these requirements, and the use of a JavaTx based open-source development initiative is proposed. Results are reported for activity sponsored by the NASA Langley Research Center Innovation Institute to scope out requirements for developing a mass properties engineering e-standard. An initial software distribution is proposed. Upon completion, an open-source application programming interface will be available to SAWE members for the development of more specific programming requirements that are tailored to company and project requirements. A fully functioning application programming interface will permit code extension via company proprietary techniques, as well as through continued open-source initiatives.

Velocity-induced collapses of stable neutron stars

NASA Astrophysics Data System (ADS)

Novak, J.

2001-09-01

The collapse of spherical neutron stars is studied in General Relativity. The initial state is a stable neutron star to which an inward radial kinetic energy has been added through some velocity profile. For two different equations of state and two different shapes of velocity profiles, it is found that neutron stars can collapse to black holes for high enough inward velocities, provided that their masses are higher than some minimal value, depending on the equation of state. For a polytropic equation of state of the form p=Krho gamma, with gamma = 2 it is found to be 1.16 ( (K)/(0.1) right )0.5 Msun, whereas for a more realistic one (described in Pons et al. \\cite{PonREPL00}), it is 0.36 Msun . In some cases of collapse forming a black hole, part of the matter composing the initial neutron star can be ejected through a shock, leaving only a fraction of the initial mass to form a black hole. Therefore, black holes of very small masses can be formed and, in particular, the mass scaling relation, as a function of initial velocity, takes the form discovered by Choptuik (\\cite{Cho93}) for critical collapses.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mink, S. E. de; Belczynski, K., E-mail: S.E.deMink@uva.nl, E-mail: kbelczyn@astrouw.edu.pl

The initial mass function (IMF), binary fraction, and distributions of binary parameters (mass ratios, separations, and eccentricities) are indispensable inputs for simulations of stellar populations. It is often claimed that these are poorly constrained, significantly affecting evolutionary predictions. Recently, dedicated observing campaigns have provided new constraints on the initial conditions for massive stars. Findings include a larger close binary fraction and a stronger preference for very tight systems. We investigate the impact on the predicted merger rates of neutron stars and black holes. Despite the changes with previous assumptions, we only find an increase of less than a factor ofmore » 2 (insignificant compared with evolutionary uncertainties of typically a factor of 10–100). We further show that the uncertainties in the new initial binary properties do not significantly affect (within a factor of 2) our predictions of double compact object merger rates. An exception is the uncertainty in IMF (variations by a factor of 6 up and down). No significant changes in the distributions of final component masses, mass ratios, chirp masses, and delay times are found. We conclude that the predictions are, for practical purposes, robust against uncertainties in the initial conditions concerning binary parameters, with the exception of the IMF. This eliminates an important layer of the many uncertain assumptions affecting the predictions of merger detection rates with the gravitational wave detectors aLIGO/aVirgo.« less

Multimegawatt electric propulsion system design considerations

NASA Technical Reports Server (NTRS)

Gilland, J. H.; Myers, Roger M.; Patterson, Michael J.

1991-01-01

Piloted Mars Mission Requirements of relatively short trip times and low initial mass in Earth orbit as identified by the NASA Space Exploration Initiative, indicate the need for multimegawatt electric propulsion systems. The design considerations and results for two thruster types, the argon ion, and hydrogen magnetoplasmadynamic thrusters, are addressed in terms of configuration, performance, and mass projections. Preliminary estimates of power management and distribution for these systems are given. Some assessment of these systems' performance in a reference Space Exploration Initiative piloted mission are discussed. Research and development requirements of these systems are also described.

Areal Mass Oscillations in Planar Targets Due to Feedout: Theory and Simulations.

NASA Astrophysics Data System (ADS)

Velikovich, A. L.; Schmitt, A. J.; Karasik, M.; Obenschain, S. P.; Serlin, V.; Pawley, C. J.; Gardner, J. H.; Aglitskiy, Y.; Metzler, N.

2001-10-01

When a planar shock wave breaks out at a rippled rear surface of a laser-driven target, the lateral pressure gradient in a rippled rarefaction wave propagating back to the front surface causes a lateral mass redistribution that reverses the phase of mass variation. If the driving laser pulse has no foot, then the RT growth, starting when the rarefaction wave reaches the front surface, causes the second phase reversal of mass variation, and continues at the initial phase, as consistently observed in feedout experiments on Nike. A foot of the laser pulse can cause an early phase reversal of mass variation, making the strong shock wave driven by the main pulse interact with a density variation in a rippled rarefaction wave rather than with static rear surface ripples. Theory and simulations predict that this interaction can make the phase of mass variation reverse one or three times. Then the phase of the RT growing mode would be opposite to that of the initial mass variation.

White Dwarfs in Star Clusters: The Initial-Final Mass Relation for Stars from 0.85 to 8 M$_\\odot$

NASA Astrophysics Data System (ADS)

Cummings, Jeffrey; Kalirai, Jason; Tremblay, P.-E.; Ramírez-Ruiz, Enrico

2018-01-01

The spectroscopic study of white dwarfs provides both their mass, cooling age, and intrinsic photometric properties. For white dwarfs in the field of well-studied star clusters, this intrinsic photometry can be used to determine if they are members of that star cluster. Comparison of a member white dwarf's cooling age to its total cluster's age provides the evolutionary timescale of its progenitor star, and hence the mass. This is the initial-final mass relation (IFMR) for stars, which gives critical information on how a progenitor star evolves and loses mass throughout its lifetime, and how this changes with progenitor mass. Our work, for the first time, presents a uniform analysis of 85 white dwarf cluster members spanning from progenitor masses of 0.85 to 8 M$_\\odot$. Comparison of our work to theoretical IFMRs shows remarkable consistency in their shape but differences remain. We will discuss possible explanations for these differences, including the effects of stellar rotation.

Effects of a statewide antismoking campaign on mass media messages and smoking beliefs.

PubMed

Murray, D M; Prokhorov, A V; Harty, K C

1994-01-01

BACKGROUND. In 1985, The Minnesota Legislature initiated a long-term and broad-based program to deter adolescent tobacco use. The initiative was funded by higher taxes on tobacco products and combined school-based programming, mass-media campaigns, and local community grants. The Minnesota-Wisconsin Adolescent Tobacco-Use Research Project was designed to evaluate this effort by monitoring adolescent tobacco use and related factors in Minnesota and Wisconsin from 1986 to 1990. The results presented in this paper indicate that the Minnesota initiative dramatically increased Minnesota schoolchildren's reported exposure to the anti-smoking messages in the mass media but had little effect on smoking-related beliefs or smoking behaviors. CONCLUSIONS. These results, together with the findings from other recent studies, suggest that even dramatic increases in exposure to anti-tobacco messages in the mass-media, in the absence of a substantial and sustained school-based tobacco prevention measures, may be insufficient to generate reductions in adolescent tobacco use.

Breast mass as the initial presentation of esophageal carcinoma: a case report

PubMed Central

Norooz, Mohammad Tayefeh; Ahmadi, Hamed; Zavarei, Mansour Jamali; Daryaei, Parviz

2009-01-01

Introduction Esophageal cancer is considered as a fatal malignancy. It mostly metastasizes to lung, liver, and bone while breast metastasis has been rarely reported. This is the fifth report of metastatic breast cancer from esophageal cancer, which differs from previous reported cases in terms of initial presentation with metastatic breast mass and no metastatic involvement of other organs. Case presentation We present a 35-year-old Caucasian woman who initially complained of a painful breast mass. Squamous pearls on cytologic evaluation suggested a metastatic lesion. Two months history of dysphagia was extracted through detailed interview with patient and further investigation revealed a stage IV esophageal squamous cell carcinoma. Conclusion In this case, breast lesion as an unusual presentation of esophageal carcinoma emphasizes the great role of thorough medical history taking and cytologic study in evaluating an accidentally detected breast mass. The increasing reports of breast metastasis in patients with esophageal carcinoma necessitate the careful breast examination in visits after treatment of the primary tumor. PMID:19829901

Multiple populations within globular clusters in Early-type galaxies Exploring their effect on stellar initial mass function estimates

NASA Astrophysics Data System (ADS)

Chantereau, W.; Usher, C.; Bastian, N.

2018-05-01

It is now well-established that most (if not all) ancient globular clusters host multiple populations, that are characterised by distinct chemical features such as helium abundance variations along with N-C and Na-O anti-correlations, at fixed [Fe/H]. These very distinct chemical features are similar to what is found in the centres of the massive early-type galaxies and may influence measurements of the global properties of the galaxies. Additionally, recent results have suggested that M/L variations found in the centres of massive early-type galaxies might be due to a bottom-heavy stellar initial mass function. We present an analysis of the effects of globular cluster-like multiple populations on the integrated properties of early-type galaxies. In particular, we focus on spectral features in the integrated optical spectrum and the global mass-to-light ratio that have been used to infer variations in the stellar initial mass function. To achieve this we develop appropriate stellar population synthesis models and take into account, for the first time, an initial-final mass relation which takes into consideration a varying He abundance. We conclude that while the multiple populations may be present in massive early-type galaxies, they are likely not responsible for the observed variations in the mass-to-light ratio and IMF sensitive line strengths. Finally, we estimate the fraction of stars with multiple populations chemistry that come from disrupted globular clusters within massive ellipticals and find that they may explain some of the observed chemical patterns in the centres of these galaxies.

Towards an initial mass function for giant planets

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Davies, Melvyn B.; Johansen, Anders

2018-07-01

The distribution of exoplanet masses is not primordial. After the initial stage of planet formation, gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. In this report we demonstrate how the present-day eccentricities of the observed exoplanet population can be used to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the mass of the planets that were ejected or collided in the past. Integrating across the exoplanet population, one can estimate the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn-type planets. While the present-day distribution appears to be bimodal, with peaks around ˜1MJ and ˜20M⊕, this bimodality does not seem to be primordial. Instead, planets around ˜60M⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population may have been depleted of sub-Saturn-mass planets. Future observations may reveal that young giant planets have a more continuous size distribution with lower eccentricities and more sub-Saturn-type planets. Lastly, there is a need for additional data and for more research on how the system architecture and multiplicity might alter our results.

Toward an initial mass function for giant planets

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Davies, Melvyn B.; Johansen, Anders

2018-05-01

The distribution of exoplanet masses is not primordial. After the initial stage of planet formation, gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. In this report we demonstrate how the present-day eccentricities of the observed exoplanet population can be used to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the mass of the planets that were ejected or collided in the past. Integrating across the exoplanet population, one can estimate the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn type planets. While the present-day distribution appears to be bimodal, with peaks around ˜1MJ and ˜20M⊕, this bimodality does not seem to be primordial. Instead, planets around ˜60M⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population may have been been depleted of sub-Saturn-mass planets. Future observations may reveal that young giant planets have a more continuous size distribution with lower eccentricities and more sub-Saturn type planets. Lastly, there is a need for additional data and for more research on how the system architecture and multiplicity might alter our results.

40 CFR 63.3521 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2013 CFR

2013-07-01

.... (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified... to be 0.5 percent of the material by mass, you do not have to count it. Express the mass fraction of...

40 CFR 63.3521 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

.... (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified... to be 0.5 percent of the material by mass, you do not have to count it. Express the mass fraction of...

40 CFR 63.3521 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

.... (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified... to be 0.5 percent of the material by mass, you do not have to count it. Express the mass fraction of...

Comprehensive characterization of C-glycosyl flavones in wheat (Triticum aestivum L.) germ using UPLC-PDA-ESI/HRMSn and mass defect filtering

USDA-ARS?s Scientific Manuscript database

A comprehensive characterization of C-glycosyl flavones in wheat germ has been conducted using multi-stage high resolution mass spectrometry (HRMS) combined with mass defect filter (MDF). MDF performed the initial search of raw data with defined mass ranges and mass defect windows to generate the n...

On the mass function of stars growing in a flocculent medium

NASA Astrophysics Data System (ADS)

Maschberger, Th.

2013-12-01

Stars form in regions of very inhomogeneous densities and may have chaotic orbital motions. This leads to a time variation of the accretion rate, which will spread the masses over some mass range. We investigate the mass distribution functions that arise from fluctuating accretion rates in non-linear accretion, ṁ ∝ mα. The distribution functions evolve in time and develop a power-law tail attached to a lognormal body, like in numerical simulations of star formation. Small fluctuations may be modelled by a Gaussian and develop a power-law tail ∝ m-α at the high-mass side for α > 1 and at the low-mass side for α < 1. Large fluctuations require that their distribution is strictly positive, for example, lognormal. For positive fluctuations the mass distribution function develops the power-law tail always at the high-mass hand side, independent of α larger or smaller than unity. Furthermore, we discuss Bondi-Hoyle accretion in a supersonically turbulent medium, the range of parameters for which non-linear stochastic growth could shape the stellar initial mass function, as well as the effects of a distribution of initial masses and growth times.

Mass-energy and momentum extraction by gravitational wave emission in the merger of two colliding black holes: The non-head-on case

NASA Astrophysics Data System (ADS)

Aranha, R. F.; Soares, I. Damião; Tonini, E. V.

2012-01-01

We examine numerically the post-merger regime of two nonspining holes in non-head-on collisions in the realm of nonaxisymmetric Robinson-Trautman spacetimes. Characteristic initial data for the system are constructed and evolved via the Robinson-Trautman equation. The numerical integration is performed using a Galerkin spectral method which is sufficiently stable to reach the final configuration of the remnant black hole, when the gravitational wave emission ceases. The initial data contains three independent parameters, the ratio mass α of the individual colliding black holes, their initial premerger infalling velocity and the incidence angle of collision ρ0. The remnant black hole is characterized by its final boost parameter, rest mass and scattering angle. The motion of the remnant black hole is restricted to the plane determined by the directions of the two initial colliding black holes, characterizing a planar collision. The net momentum fluxes carried out by gravitational waves are confined to this plane. We evaluate the efficiency of mass-energy extraction, the total energy and momentum carried out by gravitational waves and the momentum distribution of the remnant black hole for a large domain of initial data parameters. Our analysis is based on the Bondi-Sachs four-momentum conservation laws. The process of mass-energy extraction is shown to be less efficient as the initial data departs from the head-on configuration. Head-on collisions (ρ0=0o) and orthogonal collisions (ρ0=90°) constitute, respectively, upper and lower bounds to the power emission and to the efficiency of mass-energy extraction. On the contrary, head-on collisions and orthogonal collisions constitute, respectively, lower and upper bounds for the momentum of the remnant. Distinct regimes of gravitational wave emission (bursts or quiescent emission) are characterized by the analysis of the time behavior of the gravitational wave power as a function of α. In particular, the net gravitational wave flux is nonzero for equal-mass colliding black holes in non-head-on collisions. The momentum extraction and the patterns of the momentum fluxes, as a function of the incidence angle, are examined. The relation between the incidence angle and the scattering angle closely approximates a relation for the inelastic collision of classical particles in Newtonian dynamics.

Evolution and fate of very massive stars

NASA Astrophysics Data System (ADS)

Yusof, Norhasliza; Hirschi, Raphael; Meynet, Georges; Crowther, Paul A.; Ekström, Sylvia; Frischknecht, Urs; Georgy, Cyril; Abu Kassim, Hasan; Schnurr, Olivier

2013-08-01

There is observational evidence that supports the existence of very massive stars (VMS) in the local universe. First, VMS (Mini ≲ 320 M⊙) have been observed in the Large Magellanic Clouds (LMC). Secondly, there are observed supernovae (SNe) that bear the characteristics of pair creation supernovae (PCSNe, also referred to as pair instability SN) which have VMS as progenitors. The most promising candidate to date is SN 2007bi. In order to investigate the evolution and fate of nearby VMS, we calculated a new grid of models for such objects, for solar, LMC and Small Magellanic Clouds (SMC) metallicities, which covers the initial mass range from 120 to 500 M⊙. Both rotating and non-rotating models were calculated using the GENEVA stellar evolution code and evolved until at least the end of helium burning and for most models until oxygen burning. Since VMS have very large convective cores during the main-sequence phase, their evolution is not so much affected by rotational mixing, but more by mass loss through stellar winds. Their evolution is never far from a homogeneous evolution even without rotational mixing. All the VMS, at all the metallicities studied here, end their life as WC(WO)-type Wolf-Rayet stars. Because of very important mass losses through stellar winds, these stars may have luminosities during the advanced phases of their evolution similar to stars with initial masses between 60 and 120 M⊙. A distinctive feature which may be used to disentangle Wolf-Rayet stars originating from VMS from those originating from lower initial masses would be the enhanced abundances of Ne and Mg at the surface of WC stars. This feature is however not always apparent depending on the history of mass loss. At solar metallicity, none of our models is expected to explode as a PCSN. At the metallicity of the LMC, only stars more massive than 300 M⊙ are expected to explode as PCSNe. At the SMC metallicity, the mass range for the PCSN progenitors is much larger and comprises stars with initial masses between about 100 and 290 M⊙. All VMS in the metallicity range studied here produce either a Type Ib SN or a Type Ic SN but not a Type II SN. We estimate that the progenitor of SN 2007bi, assuming a SMC metallicity, had an initial mass between 160 and 175 M⊙. None of models presented in this grid produces gamma-ray bursts or magnetars. They lose too much angular momentum by mass loss or avoid the formation of a black hole by producing a completely disruptive PCSN.

DEVELOPMENT OF A CONTAMINANT TRANSPORT AND FATE MASS BALANCE CALIBRATION MODEL FOR LAKE MICHIGAN MASS BALANCE PROJECT (LMMBP)

EPA Science Inventory

Lake Michigan Mass Balance Project (LMMBP) was initiated to directly support the development of a lakewide management plan (LaMP) for Lake Michigan. A mass balance modeling approach is proposed for the project to addrss the realtionship between sources of toxic chemicals and thei...

Volume, Mass, And Nutrients Of Down Woody Debris Following Initial Shortleaf Pine-Bluestem Grass Restoration Activities In The Ouachita Mountains Of Arkansas

Treesearch

Jessica C. Seifert; Hal O. Liechty; Martin A. Spetich; Daniel A. Marion

2004-01-01

Abstract - The Ouachita National Forest is restoring pine-mixed hardwood forests to a shortleaf pine-bluestem grass ecosystem through harvesting, midstory control, and the application of prescribed fire. Mean mass and volume of downed woody debris (DWD) in plots following initial harvesting and midstory-control were respectively 335 percent and 253...

A model for the formation of the Local Group

NASA Technical Reports Server (NTRS)

Peebles, P. J. E.; Melott, A. L.; Holmes, M. R.; Jiang, L. R.

1989-01-01

Observational tests of a model for the formation of the Local Group are presented and analyzed in which the mass concentration grows by gravitational accretion of local-pressure matter onto two seed masses in an otherwise homogeneous initial mass distribution. The evolution of the mass distribution is studied in an analytic approximation and a numerical computation. The initial seed mass and separation are adjusted to produce the observed present separation and relative velocity of the Andromeda Nebula and the Galaxy. If H(0) is adjusted to about 80 km/s/Mpc with density parameter Omega = 1, then the model gives a good fit to the motions of the outer members of the Local Group. The same model gives particle orbits at radius of about 100 kpc that reasonably approximate the observed distribution of redshifts of the Galactic satellites.

Effects of Planetesimal Accretion on the Structural Evolution of Sub-Neptunes

NASA Astrophysics Data System (ADS)

Chatterjee, Sourav; Chen, Howard

2018-01-01

A remarkable discovery of NASA's Kepler mission is the wide diversity in the average densities of planets even when they are of similar mass. After gas disk dissipation, fully formed planets could accrete nearby planetesimals from a remnant planetesimal disk. We present calculations using the open-source stellar evolution toolkit Modules for Experiments in Stellar Astrophysics (MESA) modified to include the deposition of planetesimals into the H/He envelopes of sub-Neptunes. We show that planetesimal accretion can alter the mass-radius isochrones for these planets. The additional energy deposited via planetesimal accretion puffs up the envelopes leading to enhanced gas loss during the phase of rapid accretion. As a result, the same initial planet can evolve to contain very different final envelope-mass fractions. This manifest as differences in the average planet densities long after accretion stops. Differences in the accretion history, total accreted mass, and the inherent stochasticity of the accretion process can bring wide diversity in final average densities even when the initial planets are very similar. These effects are particularly important for planets initially less massive than ~10 MEarth and with envelope mass fraction less than ~10%, thought to be the most common type of planets discovered by Kepler.

The galaxy-wide initial mass function of dwarf late-type to massive early-type galaxies

NASA Astrophysics Data System (ADS)

Weidner, C.; Kroupa, P.; Pflamm-Altenburg, J.; Vazdekis, A.

2013-12-01

Observational studies are showing that the galaxy-wide stellar initial mass function (IMF) is top-heavy in galaxies with high star formation rates (SFRs). Calculating the integrated galactic stellar initial mass function (IGIMF) as a function of the SFR of a galaxy, it follows that galaxies which have or which formed with SFRs >10 M⊙ yr-1 would have a top-heavy IGIMF in excellent consistency with the observations. Consequently and in agreement with observations, elliptical galaxies would have higher mass-to-light ratios as a result of the overabundance of stellar remnants compared to a stellar population that formed with an invariant canonical stellar IMF. For the Milky Way, the IGIMF yields very good agreement with the disc- and the bulge IMF determinations. Our conclusions are that purely stochastic descriptions of star formation on the scales of a parsec and above are falsified. Instead, star formation follows the laws, stated here as axioms, which define the IGIMF theory. We also find evidence that the power-law index β of the embedded cluster mass function decreases with increasing SFR. We propose further tests of the IGIMF theory through counting massive stars in dwarf galaxies.

Observed Luminosity Spread in Young Clusters and FU Ori Stars: A Unified Picture

NASA Astrophysics Data System (ADS)

Baraffe, I.; Vorobyov, E.; Chabrier, G.

2012-09-01

The idea that non-steady accretion during the embedded phase of protostar evolution can produce the observed luminosity spread in the Herzsprung-Russell diagram (HRD) of young clusters has recently been called into question. Observations of FU Ori, for instance, suggest an expansion of the star during strong accretion events, whereas the luminosity spread implies a contraction of the accreting objects, decreasing their radiating surface. In this paper, we present a global scenario based on calculations coupling episodic accretion histories derived from numerical simulations of collapsing cloud prestellar cores of various masses and subsequent protostar evolution. Our calculations show that, assuming an initial protostar mass Mi ~ 1 M Jup, typical of the second Larson's core, both the luminosity spread in the HRD and the inferred properties of FU Ori events (mass, radius, accretion rate) can be explained by this scenario, providing two conditions. First, there must be some variation within the fraction of accretion energy absorbed by the protostar during the accretion process. Second, the range of this variation should increase with increasing accretion burst intensity and thus with the initial core mass and final star mass. The numerical hydrodynamics simulations of collapsing cloud prestellar cores indeed show that the intensity of the accretion bursts correlates with the mass and initial angular momentum of the prestellar core. Massive prestellar cores with high initial angular momentum are found to produce intense bursts characteristic of FU Ori-like events. Our results thus suggest a link between the burst intensities and the fraction of accretion energy absorbed by the protostar, with some threshold in the accretion rate, of the order of 10-5 M ⊙ yr-1, delimitating the transition from "cold" to "hot" accretion. Such a transition might reflect a change in the accretion geometry with increasing accretion rate, i.e., a transition from magnetospheric or thin-disk to thick-disk accretion, or in the magnetospheric interaction between the star and the disk. Conversely, the luminosity spread can also be explained by a variation of the initial protostar mass within the ~1-5 M Jup range, although it is unclear for now whether such a spread among the second Larson's core can be produced during the prestellar core second collapse. This unified picture confirms the idea that early accretion during protostar and proto-brown dwarf formation/evolution can explain the observed luminosity spread in young clusters without invoking any significant age spread, and that the concept of a well-defined birthline does not apply for low-mass objects. Finally, we examine the impact of accretion on the determination of the initial mass function in young clusters.

The role of external and internal mass transfer in the process of Cu2+ removal by natural mineral sorbents.

PubMed

Sljivić, M; Smiciklas, I; Plećas, I; Pejanović, S

2011-07-01

The kinetics of Cu2+ sorption on to zeolite, clay and diatomite was investigated as a function of initial metal concentrations. For consideration of the mass transfer phenomena, single resistance models based on both film and intraparticle diffusion were tested and compared. The obtained results suggested that the rate-limiting step in Cu2+ sorption strongly depended on the sorbent type, as well as on initial cation concentration. The decrease in external mass transfer coefficients with the increase in initial metal concentrations was in excellent agreement with expressions based on Sherwood and Schmidt dimensionless numbers. The internal diffusivities through zeolite particles were in the range 1.0 x 10(-11) to 1.0 x 10(-13) m2/min, depending on the Cu2+ concentration and the applied theoretical model.

Alterations of Body Mass Gain of Neonates (P7&P14) During Certrifugation AT 2G

NASA Technical Reports Server (NTRS)

Baer, L. A.; Corbin, B. J.; Wade, C. E.; Hargens, Alan R. (Technical Monitor)

1996-01-01

Previous research has shown animal body mass to be significantly affected by centrifugation. At the onset of centrifugation, animals have a selective loss of fat, causing an initial body mass loss. Body mass gain will resume at the same rate as uncentrifuged animals, but this subsequent gain will be lower. For this study, two different ages of Sprague Hawley neonate families were observed during centrifugation. Eight litters (dam with eight neonates) of postnatal day (PN) seven and four litters (dam with ten neonates) of PN 14 were separated into two separate groups each, centrifuge (+2G(sub z)) and environmental controls (EC) and placed into either the centrifuge or an animal holding unit in the centrifuge rotunda for a total of 16 days. P7: Total litter start mass of +2G(sub z) litter = 138.90 g/end = 311.0 g EC litter = 150.85 g/end = 516.9 g. P14: Total litter start mass of +2G(sub z) litter = 287.70 g/end = 762.5g; EC litter = 245 g/end = 942.9 g. An initial body mass loss was observed in both groups of +2G(sub z) animals for two days after the onset of centrifugation, but then an increase began to occur. Literature suggests adult animals at +2G(sub z), will have an initial loss, but will resume similar growth rates over time as compared to control animals. The P7 +2G(sub z) animals began to gain body mass, but showed a significantly slower growth rate than their EC animals for the duration of the test (pace). The P14 +2G(sub z) animals began to show similar growth rates to their EC after day nine. At day 16, both groups of +2Gz animals were significantly smaller than the EC animals (pace). At +2Gz, animals experience an initial body mass loss. Older animals are able to resume similar growth rates as their controls, but younger animals showed growth rates to be significantly reduced.

Collapse of primordial gas clouds and the formation of quasar black holes

NASA Technical Reports Server (NTRS)

Loeb, Abraham; Rasio, Frederic A.

1994-01-01

The formation of quasar black holes during the hydrodynamic collapse of protogalactic gas clouds is discussed. The dissipational collapse and long-term dynamical evolution of these systems is analyzed using three-dimensional numerical simulations. The calculations focus on the final collapse stages of the inner baryonic component and therefore ignore the presence of dark matter. Two types of initial conditions are considered: uniformly rotating spherical clouds, and iirotational ellipsoidal clouds. In both cases the clouds are initially cold, homogeneous, and not far from rotational support (T/(absolute value of W) approximately equals 0.1). Although the details of the dynamical evolution depend sensitively on the initial conditions, the qualitative features of the final configurations do not. Most of the gas is found to fragment into small dense clumps, that eventually make up a spheroidal component resembling a galactic bulge. About 5% of the initial mass remains in the form of a smooth disk of gas supported by rotation in the gravitational potential potential well of the outer spheroid. If a central seed black hole of mass approximately greater than 10(exp 6) solar mass forms, it can grow by steady accretion from the disk and reach a typical quasar black hole mass approximately 10(exp 8) solar mass in less than 5 x 10(exp 8) yr. In the absence of a sufficiently massive seed, dynamical instabilities in a strongly self-gravitating inner region of the disk will inhibit steady accretion of gas and may prevent the immediate formation of quasar.

Remediation of Chlorinated Solvent Plumes Using In-Situ Air Sparging—A 2-D Laboratory Study

PubMed Central

Adams, Jeffrey A.; Reddy, Krishna R.; Tekola, Lue

2011-01-01

In-situ air sparging has evolved as an innovative technique for soil and groundwater remediation impacted with volatile organic compounds (VOCs), including chlorinated solvents. These may exist as non-aqueous phase liquid (NAPL) or dissolved in groundwater. This study assessed: (1) how air injection rate affects the mass removal of dissolved phase contamination, (2) the effect of induced groundwater flow on mass removal and air distribution during air injection, and (3) the effect of initial contaminant concentration on mass removal. Dissolved-phase chlorinated solvents can be effectively removed through the use of air sparging; however, rapid initial rates of contaminant removal are followed by a protracted period of lower removal rates, or a tailing effect. As the air flow rate increases, the rate of contaminant removal also increases, especially during the initial stages of air injection. Increased air injection rates will increase the density of air channel formation, resulting in a larger interfacial mass transfer area through which the dissolved contaminant can partition into the vapor phase. In cases of groundwater flow, increased rates of air injection lessened observed downward contaminant migration effect. The air channel network and increased air saturation reduced relative hydraulic conductivity, resulting in reduced groundwater flow and subsequent downgradient contaminant migration. Finally, when a higher initial TCE concentration was present, a slightly higher mass removal rate was observed due to higher volatilization-induced concentration gradients and subsequent diffusive flux. Once concentrations are reduced, a similar tailing effect occurs. PMID:21776228

Remediation of chlorinated solvent plumes using in-situ air sparging--a 2-D laboratory study.

PubMed

Adams, Jeffrey A; Reddy, Krishna R; Tekola, Lue

2011-06-01

In-situ air sparging has evolved as an innovative technique for soil and groundwater remediation impacted with volatile organic compounds (VOCs), including chlorinated solvents. These may exist as non-aqueous phase liquid (NAPL) or dissolved in groundwater. This study assessed: (1) how air injection rate affects the mass removal of dissolved phase contamination, (2) the effect of induced groundwater flow on mass removal and air distribution during air injection, and (3) the effect of initial contaminant concentration on mass removal. Dissolved-phase chlorinated solvents can be effectively removed through the use of air sparging; however, rapid initial rates of contaminant removal are followed by a protracted period of lower removal rates, or a tailing effect. As the air flow rate increases, the rate of contaminant removal also increases, especially during the initial stages of air injection. Increased air injection rates will increase the density of air channel formation, resulting in a larger interfacial mass transfer area through which the dissolved contaminant can partition into the vapor phase. In cases of groundwater flow, increased rates of air injection lessened observed downward contaminant migration effect. The air channel network and increased air saturation reduced relative hydraulic conductivity, resulting in reduced groundwater flow and subsequent downgradient contaminant migration. Finally, when a higher initial TCE concentration was present, a slightly higher mass removal rate was observed due to higher volatilization-induced concentration gradients and subsequent diffusive flux. Once concentrations are reduced, a similar tailing effect occurs.

[Copper recovery from artificial bioleaching lixivium of waste printed circuit boards].

PubMed

Cheng, Dan; Zhu, Neng-Wu; Wu, Ping-Xiao; Zou, Ding-Hui; Xing, Yi-Jia

2014-04-01

The key step to realize metal recovery from bioleaching solutions is the recovery of copper from bioleaching lixivium of waste printed circuit boards in high-grade form. The influences of cathode material, current density, initial pH and initial copper ion concentration on the efficiency and energy consumption of copper recovery from artificial bioleaching lixivium under condition of constant current were investigated using an electro-deposition approach. The results showed that the larger specific surface area of the cathode material (carbon felt) led to the higher copper recovery efficiency (the recovery efficiencies of the anode and the cathode chambers were 96.56% and 99.25%, respectively) and the smaller the total and unit mass product energy consumption (the total and unit mass product energy consumptions were 0.022 kW x h and 15.71 kW x h x kg(-1), respectively). The copper recovery efficiency and energy consumption increased with the increase of current density. When the current density was 155.56 mA x cm(-2), the highest copper recovery efficiencies in the anode and cathode chambers reached 98.51% and 99.37%, respectively. Accordingly, the highest total and unit mass product energy consumptions were 0.037 kW x h and 24.34 kW x h x kg(-1), respectively. The copper recovery efficiency was also significantly affected by the initial copper ion concentration. The increase of the initial copper ion concentration would lead to faster decrease of copper ion concentration, higher total energy consumption, and lower unit mass product consumption. However, the initial pH had no significant effect on the copper recovery efficiency. Under the optimal conditions (carbon felt for cathode materials, current density of 111.11 mA x cm(-2), initial pH of 2.0, and initial copper ion concentration of 10 g x L(-1)), the copper recovery efficiencies of the anode and cathode chambers were 96.75% and 99.35%, and the total and unit mass product energy consumptions were 0.021 kW x h and 14.61 kW x h x kg(-1), respectively. The deposited copper on the cathode material was fascicularly distributed and no oxygen was detected.

Supernova 2007bi as a pair-instability explosion.

PubMed

Gal-Yam, A; Mazzali, P; Ofek, E O; Nugent, P E; Kulkarni, S R; Kasliwal, M M; Quimby, R M; Filippenko, A V; Cenko, S B; Chornock, R; Waldman, R; Kasen, D; Sullivan, M; Beshore, E C; Drake, A J; Thomas, R C; Bloom, J S; Poznanski, D; Miller, A A; Foley, R J; Silverman, J M; Arcavi, I; Ellis, R S; Deng, J

2009-12-03

Stars with initial masses such that 10M[symbol: see text] or= 140M[symbol: see text] (if such exist) develop oxygen cores with masses, M(core), that exceed 50M[symbol: see text], where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion that unbinds the star in a pair-instability supernova. Transitional objects with 100M[symbol: see text] < M(initial) < 140M[symbol: see text] may end up as iron-core-collapse supernovae following violent mass ejections, perhaps as a result of brief episodes of pair instability, and may already have been identified. Here we report observations of supernova SN 2007bi, a luminous, slowly evolving object located within a dwarf galaxy. We estimate the exploding core mass to be M(core) approximately 100M[symbol: see text], in which case theory unambiguously predicts a pair-instability supernova. We show that >3M[symbol: see text] of radioactive (56)Ni was synthesized during the explosion and that our observations are well fitted by models of pair-instability supernovae. This indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic stellar mass limit, which perhaps result from processes similar to those that created the first stars in the Universe.

The Initial-Final Mass Relationship: Spectroscopy of White Dwarfs in NGC 2099 (M37)

NASA Astrophysics Data System (ADS)

Kalirai, Jasonjot Singh; Richer, Harvey B.; Reitzel, David; Hansen, Brad M. S.; Rich, R. Michael; Fahlman, Gregory G.; Gibson, Brad K.; von Hippel, Ted

2005-01-01

We present new observations of very faint white dwarfs (WDs) in the rich open star cluster NGC 2099 (M37). Following deep, wide-field imaging of the cluster using the Canada-France-Hawaii Telescope, we have now obtained spectroscopic observations of candidate WDs using both the Gemini Multi-Object Spectrograph on Gemini North and the Low-Resolution Imaging Spectrometer on Keck. Of our 24 WD candidates (all fainter than V=22.4), 21 are spectroscopically confirmed to be bona fide WDs, four or five of which are most likely field objects. Fitting 18 of the 21 WD spectra with model atmospheres, we find that most WDs in this cluster are quite massive (0.7-0.9 Msolar), as expected given the cluster's young age (650 Myr) and, hence, high turnoff mass (~2.4 Msolar). We determine a new initial-final mass relationship and almost double the number of existing data points from previous studies. The results indicate that stars with initial masses between 2.8 and 3.4 Msolar lose 70%-75% of their mass through stellar evolution. For the first time, we find some evidence of a metallicity dependence on the initial-final mass relationship. Based on observations with Gemini (run ID GN-2002B-Q-11) and Keck. Gemini is an international partnership managed by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation. The W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, was made possible by the generous financial support of the W. M. Keck Foundation.

The stellar population of the Lupus clouds

NASA Technical Reports Server (NTRS)

Hughes, Joanne; Hartigan, Patrick; Krautter, Joachim; Kelemen, Janos

1994-01-01

We present photometric and spectroscopic observations of the H alpha emission stars in the Lupus dark cloud complex. We estimate the effective temperatures of the stars from their spectral types and calculate the reddening towards each object from the (R-I) colors. From these data, we derive mass and age distributions for the Lupus stars using a new set of pre-main sequence evolutionar tracks. We compare the results for the Lupus stars with those for a similar population of young stellar objects in Taurus-Auriga and Chamaeleon and with the initial mass function for field stars in the solar neighborhood. From the H-R diagrams, Lupus appears to contain older stars than Taurus. The Lupus dark clouds form a greater proportion of low mass stars than the Taurus complex. Also, the proportion of low mass stars in Lupus is higher than that predicted by the Miller-Scalo initial mass function, and the lowest mass stars in Lupus are less active than similar T Tauri stars in other regions.

TEMPO-Assisted Free Radical-Initiated Peptide Sequencing Mass Spectrometry (FRIPS MS) in Q-TOF and Orbitrap Mass Spectrometers: Single-Step Peptide Backbone Dissociations in Positive Ion Mode

NASA Astrophysics Data System (ADS)

Jang, Inae; Lee, Sun Young; Hwangbo, Song; Kang, Dukjin; Lee, Hookeun; Kim, Hugh I.; Moon, Bongjin; Oh, Han Bin

2017-01-01

The present study demonstrates that one-step peptide backbone fragmentations can be achieved using the TEMPO [2-(2,2,6,6-tetramethyl piperidine-1-oxyl)]-assisted free radical-initiated peptide sequencing (FRIPS) mass spectrometry in a hybrid quadrupole time-of-flight (Q-TOF) mass spectrometer and a Q-Exactive Orbitrap instrument in positive ion mode, in contrast to two-step peptide fragmentation in an ion-trap mass spectrometer (reference Anal. Chem. 85, 7044-7051 (30)). In the hybrid Q-TOF and Q-Exactive instruments, higher collisional energies can be applied to the target peptides, compared with the low collisional energies applied by the ion-trap instrument. The higher energy deposition and the additional multiple collisions in the collision cell in both instruments appear to result in one-step peptide backbone dissociations in positive ion mode. This new finding clearly demonstrates that the TEMPO-assisted FRIPS approach is a very useful tool in peptide mass spectrometry research.

Sampling methods for stellar masses and the mmax-Mecl relation in the starburst dwarf galaxy NGC 4214

NASA Astrophysics Data System (ADS)

Weidner, Carsten; Kroupa, Pavel; Pflamm-Altenburg, Jan

2014-07-01

It has been claimed in the recent literature that a non-trivial relation between the mass of the most-massive star, mmax, in a star cluster and its embedded star cluster mass (the mmax - Mecl relation) is falsified by observations of the most-massive stars and the Hα luminosity of young star clusters in the starburst dwarf galaxy NGC 4214. Here, it is shown by comparing the NGC 4214 results with observations from the Milky Way that NGC 4214 agrees very well with the predictions of the mmax - Mecl relation and with the integrated galactic stellar initial mass function theory. The difference in conclusions is based on a high degree of degeneracy between expectations from random sampling and those from the mmax - Mecl relation, but are also due to interpreting mmax as a truncation mass in a randomly sampled initial mass function. Additional analysis of galaxies with lower SFRs than those currently presented in the literature will be required to break this degeneracy.

Lunar PMAD technology assessment

NASA Technical Reports Server (NTRS)

Metcalf, Kenneth J.

1992-01-01

This report documents an initial set of power conditioning models created to generate 'ballpark' power management and distribution (PMAD) component mass and size estimates. It contains converter, rectifier, inverter, transformer, remote bus isolator (RBI), and remote power controller (RPC) models. These models allow certain studies to be performed; however, additional models are required to assess a full range of PMAD alternatives. The intent is to eventually form a library of PMAD models that will allow system designers to evaluate various power system architectures and distribution techniques quickly and consistently. The models in this report are designed primarily for space exploration initiative (SEI) missions requiring continuous power and supporting manned operations. The mass estimates were developed by identifying the stages in a component and obtaining mass breakdowns for these stages from near term electronic hardware elements. Technology advances were then incorporated to generate hardware masses consistent with the 2000 to 2010 time period. The mass of a complete component is computed by algorithms that calculate the masses of the component stages, control and monitoring, enclosure, and thermal management subsystem.

Memory effects in nanoparticle dynamics and transport

NASA Astrophysics Data System (ADS)

Sanghi, Tarun; Bhadauria, Ravi; Aluru, N. R.

2016-10-01

In this work, we use the generalized Langevin equation (GLE) to characterize and understand memory effects in nanoparticle dynamics and transport. Using the GLE formulation, we compute the memory function and investigate its scaling with the mass, shape, and size of the nanoparticle. It is observed that changing the mass of the nanoparticle leads to a rescaling of the memory function with the reduced mass of the system. Further, we show that for different mass nanoparticles it is the initial value of the memory function and not its relaxation time that determines the "memory" or "memoryless" dynamics. The size and the shape of the nanoparticle are found to influence both the functional-form and the initial value of the memory function. For a fixed mass nanoparticle, increasing its size enhances the memory effects. Using GLE simulations we also investigate and highlight the role of memory in nanoparticle dynamics and transport.

The He I 2.06 microns/Br-gamma ratio in starburst galaxies - An objective constraint on the upper mass limit to the initial mass function

NASA Technical Reports Server (NTRS)

Doyon, Rene; Puxley, P. J.; Joseph, R. D.

1992-01-01

The use of the He I 2.06 microns/Br-gamma ratio as a constraint on the massive stellar population in star-forming galaxies is developed. A theoretical relationship between the He I 2.06 microns/Br-gamma ratio and the effective temperature of the exciting star in H II regions is derived. The effects of collisional excitation and dust within the nebula on the ratio are also considered. It is shown that the He I 2.06 microns/Br-gamma ratio is a steep function of the effective temperature, a property which can be used to determine the upper mass limit of the initial mass function (IMF) in galaxies. This technique is reliable for upper mass limits less than about 40 solar masses. New near-infrared spectra of starburst galaxies are presented. The He I 2.06 microns/Br-gamma ratios observed imply a range of upper mass limits from 27 to over 40 solar masses. There is also evidence that the upper mass limit is spatially dependent within a given galaxy. These results suggest that the upper mass limit is not a uniquely defined parameter of the IMF and probably varies with local physical conditions.

The Low-Mass Stellar Initial Mass Function: Ultra-Faint Dwarf Galaxies Revisited

NASA Astrophysics Data System (ADS)

Platais, Imants

2017-08-01

The stellar Initial Mass Function plays a critical role in the evolution of the baryonic content of the Universe. The form of the low-mass IMF - stars of mass less than the solar mass - determines the fraction of baryons locked up for a Hubble time, and thus indicates how gas and metals are cycled through galaxies. Inferences from resolved stellar populations, where the low-mass luminosity function and associated IMF can be derived from direct star counts, generally favor an invariant and universal IMF. However, a recent study of ultra-faint dwarf galaxies Hercules and Leo IV indicates a bottom-lite IMF, over a narrow range of stellar mass (only 0.55-0.75 M_sun), correlated with the internal velocity dispersion and/or metallicity. We propose to obtain ultra-deep imaging for a significantly closer ultra-faint dwarf, Bootes I, which will allow us to construct the luminosity function down to M_v=+10 (equivalent to 0.35 solar mass). We will also re-analyze the HST archival observations for the Hercules and Leo IV dwarfs using the same updated techniques as for Bootes I. The combined datasets should provide a reliable answer to the question of how variable is the low-mass stellar IMF.

A two-step initial mass function:. Consequences of clustered star formation for binary properties

NASA Astrophysics Data System (ADS)

Durisen, R. H.; Sterzik, M. F.; Pickett, B. K.

2001-06-01

If stars originate in transient bound clusters of moderate size, these clusters will decay due to dynamic interactions in which a hard binary forms and ejects most or all the other stars. When the cluster members are chosen at random from a reasonable initial mass function (IMF), the resulting binary characteristics do not match current observations. We find a significant improvement in the trends of binary properties from this scenario when an additional constraint is taken into account, namely that there is a distribution of total cluster masses set by the masses of the cloud cores from which the clusters form. Two distinct steps then determine final stellar masses - the choice of a cluster mass and the formation of the individual stars. We refer to this as a ``two-step'' IMF. Simple statistical arguments are used in this paper to show that a two-step IMF, combined with typical results from dynamic few-body system decay, tends to give better agreement between computed binary characteristics and observations than a one-step mass selection process.

Galaxy and Mass Assembly (GAMA): the star formation rate dependence of the stellar initial mass function

NASA Astrophysics Data System (ADS)

Gunawardhana, M. L. P.; Hopkins, A. M.; Sharp, R. G.; Brough, S.; Taylor, E.; Bland-Hawthorn, J.; Maraston, C.; Tuffs, R. J.; Popescu, C. C.; Wijesinghe, D.; Jones, D. H.; Croom, S.; Sadler, E.; Wilkins, S.; Driver, S. P.; Liske, J.; Norberg, P.; Baldry, I. K.; Bamford, S. P.; Loveday, J.; Peacock, J. A.; Robotham, A. S. G.; Zucker, D. B.; Parker, Q. A.; Conselice, C. J.; Cameron, E.; Frenk, C. S.; Hill, D. T.; Kelvin, L. S.; Kuijken, K.; Madore, B. F.; Nichol, B.; Parkinson, H. R.; Pimbblet, K. A.; Prescott, M.; Sutherland, W. J.; Thomas, D.; van Kampen, E.

2011-08-01

The stellar initial mass function (IMF) describes the distribution in stellar masses produced from a burst of star formation. For more than 50 yr, the implicit assumption underpinning most areas of research involving the IMF has been that it is universal, regardless of time and environment. We measure the high-mass IMF slope for a sample of low-to-moderate redshift galaxies from the Galaxy and Mass Assembly survey. The large range in luminosities and galaxy masses of the sample permits the exploration of underlying IMF dependencies. A strong IMF-star formation rate dependency is discovered, which shows that highly star-forming galaxies form proportionally more massive stars (they have IMFs with flatter power-law slopes) than galaxies with low star formation rates. This has a significant impact on a wide variety of galaxy evolution studies, all of which rely on assumptions about the slope of the IMF. Our result is supported by, and provides an explanation for, the results of numerous recent explorations suggesting a variation of or evolution in the IMF.

A New Mass Criterium for Electron Capture Supernovae

NASA Astrophysics Data System (ADS)

Poelarends, Arend

2016-06-01

Electron capture supernovae (ECSN) are thought to populate the mass range between massive white dwarf progenitors and core collapse supernovae. It is generally believed that the initial stellar mass range for ECSN from single stars is about 0.5-1.0 M⊙ wide and centered around a value of 8.5 or 9 M⊙, depending on the specifics of the physics of convection and mass loss one applies. Since mass loss in a binary system is able to delay or cancel the second dredge-up, it is also believed that the initial mass range for ECSN in binary systems is wider than in single stars, but an initial mass range has not been defined yet.The last phase of stars in this particular mass range, however, is challenging to compute, either due to recurring Helium shell flashes, or due to convectively bound flames in the degenerate interior of the star. It would be helpful, nevertheless, to know before we enter these computationally intensive phases whether a star will explode as an ECSN or not. The mass of the helium core after helium core burning is one such criterium (Nomoto, 1984), which predicts that ECSN will occur if the helium core mass is between 2.0 M⊙ and 2.5 M⊙. However, since helium cores can be subject to erosion due to mass loss — even during helium core burning, this criterium will not yield accurate predictions for stars in binary systems.We present a dense grid of stellar evolution models that allow us to put constraints on the final fate of their cores, based on a combination of Carbon/Oxygen core mass, the mass of the surrounding Helium layer and C/O abundance. We find that CO cores with masses between 1.365 and 1.420 M⊙ at the end of Carbon burning will result in ECSN, with some minor adjustments of these ranges due to the mass of the Helium layer and the C/O ratio. While detailed models of stars within the ECSN mass range remain necessary to understand the details of pre-ECSN evolution, our research refines the Helium core criterion and provides a useful way to determine the final fate of stars in this complicated mass range early on.

The minimal SUSY B - L model: from the unification scale to the LHC

DOE PAGES

Ovrut, Burt A.; Purves, Austin; Spinner, Sogee

2015-06-26

Here, this paper introduces a random statistical scan over the high-energy initial parameter space of the minimal SUSY B - L model — denoted as the B - L MSSM. Each initial set of points is renormalization group evolved to the electroweak scale — being subjected, sequentially, to the requirement of radiative B - L and electroweak symmetry breaking, the present experimental lower bounds on the B - L vector boson and sparticle masses, as well as the lightest neutral Higgs mass of ~125 GeV. The subspace of initial parameters that satisfies all such constraints is presented, shown to bemore » robust and to contain a wide range of different configurations of soft supersymmetry breaking masses. The low-energy predictions of each such “valid” point — such as the sparticle mass spectrum and, in particular, the LSP — are computed and then statistically analyzed over the full subspace of valid points. Finally, the amount of fine-tuning required is quantified and compared to the MSSM computed using an identical random scan. The B - L MSSM is shown to generically require less fine-tuninng.« less

Evidence for Universality in the Initial Planetesimal Mass Function

NASA Astrophysics Data System (ADS)

Simon, Jacob B.; Armitage, Philip J.; Youdin, Andrew N.; Li, Rixin

2017-10-01

Planetesimals may form from the gravitational collapse of dense particle clumps initiated by the streaming instability. We use simulations of aerodynamically coupled gas-particle mixtures to investigate whether the properties of planetesimals formed in this way depend upon the sizes of the particles that participate in the instability. Based on three high-resolution simulations that span a range of dimensionless stopping times 6× {10}-3≤slant τ ≤slant 2, no statistically significant differences in the initial planetesimal mass function are found. The mass functions are fit by a power law, {dN}/{{dM}}p\\propto {M}p-p, with p = 1.5-1.7 and errors of {{Δ }}p≈ 0.1. Comparing the particle density fields prior to collapse, we find that the high-wavenumber power spectra are similarly indistinguishable, though the large-scale geometry of structures induced via the streaming instability is significantly different between all three cases. We interpret the results as evidence for a near-universal slope to the mass function, arising from the small-scale structure of streaming-induced turbulence.

40 CFR 86.156-98 - Calculations; refueling test.

Code of Federal Regulations, 2011 CFR

2011-07-01

... of the net hydrocarbon mass change and methanol mass change (if applicable) in the enclosure is used... methanol (if applicable) concentrations in ppm carbon, initial and final enclosure ambient temperatures... standard shall be computed by dividing the total refueling mass emissions by the total gallons of fuel...

Pre-ESRD Changes in Body Weight and Survival in Nursing Home Residents Starting Dialysis

PubMed Central

Stack, Shobha; Chertow, Glenn M.; Johansen, Kirsten L.; Si, Yan

2013-01-01

Summary Background and objectives Among patients receiving maintenance dialysis, weight loss at any body mass index is associated with mortality. However, it is not known whether weight changes before dialysis initiation are associated with mortality and if so, what risks are associated with weight gain or loss. Design, setting, participants, and measurements Linking data from the US Renal Data System to a national registry of nursing home residents, this study identified 11,090 patients who started dialysis between January of 2000 and December of 2006. Patients were categorized according to weight measured between 3 and 6 months before dialysis initiation and the percentage change in body weight before dialysis initiation (divided into quintiles). The outcome was mortality within 1 year of starting dialysis. Results There were 361 patients (3.3%) who were underweight (Quételet’s [body mass] index<18.5 kg/m2) and 4046 patients (36.5%) who were obese (body mass index≥30 kg/m2) before dialysis initiation. The median percentage change in body weight before dialysis initiation was −6% (interquartile range=−13% to 1%). There were 6063 deaths (54.7%) over 1 year of follow-up. Compared with patients with minimal weight changes (−3% to 3%, quintile 4), patients with weight loss ≥15% (quintile 1) had 35% higher risk for mortality (95% confidence interval, 1.25 to 1.47), whereas those patients with weight gain≥4% (quintile 5) had a 24% higher risk for mortality (95% confidence interval, 1.14 to 1.35) adjusted for baseline body mass index and other confounders. Conclusions Among nursing home residents, changes in body weight in advance of dialysis initiation are associated with significantly higher 1-year mortality. PMID:24009221

Factors which modulate the rates of skeletal muscle mass loss in non-small cell lung cancer patients: a pilot study.

PubMed

Atlan, Philippe; Bayar, Mohamed Amine; Lanoy, Emilie; Besse, Benjamin; Planchard, David; Ramon, Jordy; Raynard, Bruno; Antoun, Sami

2017-11-01

Advanced non-small cell lung cancer (NSCLC) is associated with weight loss which may reflect skeletal muscle mass (SMM) and/or total adipose tissue (TAT) depletion. This study aimed to describe changes in body composition (BC) parameters and to identify the factors unrelated to the tumor which modulate them. SMM, TAT, and the proportion of SMM to SMM + TAT were assessed with computed tomography. Estimates of each BC parameter at follow-up initiation and across time were derived from a mixed linear model of repeated measurements with a random intercept and a random slope. The same models were used to assess the independent effect of gender, age, body mass index (BMI), and initial values on changes in each BC parameter. Sixty-four patients with stage III or IV NSCLC were reviewed. The mean ± SD decreases in body weight and SMM were respectively 59 ± 3 g/week (P < 0.03) and 7 mm 2 /m 2 /week (P = 0.0003). During follow-up, no changes were identified in TAT nor in muscle density or in the proportion of SMM to SMM + TAT, estimated at 37 ± 2% at baseline. SMM loss was influenced by initial BMI (P < 0.0001) and SMM values (P = 0.0002): the higher the initial BMI or SMM values, the greater the loss observed. Weight loss was greater when the initial weight was heavier (P < 0.0001). Our results demonstrate that SMM wasting in NSCLC is lower when initial SMM and BMI values are low. These exploratory findings after our attempt to better understand the intrinsic factors associated with muscle mass depletion need to be confirmed in larger studies.

Smoking and the New Health Education in Britain 1950s–1970s

PubMed Central

Berridge, Virginia; Loughlin, Kelly

2005-01-01

Advertising has a dual function for British public health. Control or prohibition of mass advertising detrimental to health is a central objective for public health in Britain. Use of mass advertising has also been a more general public health strategy, such as during the initial government responses to HIV/AIDS in the 1980s. We trace the initial significance of mass advertising in public health in Britain in the postwar decades up to the 1970s, identifying smoking as the key issue that helped to define this new approach. This approach drew from road safety and drink driving models, US advertising theory, relocation of health education within the central government, the arrival of mass consumption, and the rise of the “new public health” agenda. PMID:15914816

Smoking and the new health education in Britain 1950s-1970s.

PubMed

Berridge, Virginia; Loughlin, Kelly

2005-06-01

Advertising has a dual function for British public health. Control or prohibition of mass advertising detrimental to health is a central objective for public health in Britain. Use of mass advertising has also been a more general public health strategy, such as during the initial government responses to HIV/AIDS in the 1980s. We trace the initial significance of mass advertising in public health in Britain in the postwar decades up to the 1970s, identifying smoking as the key issue that helped to define this new approach. This approach drew from road safety and drink driving models, US advertising theory, relocation of health education within the central government, the arrival of mass consumption, and the rise of the "new public health" agenda.

40 CFR 63.3951 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... reclaimed. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of... coating per liter coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. For reactive adhesives as defined in § 63.3981, use the mass fraction of organic HAP that is...

40 CFR 63.4151 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... option. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of... coating per liter coating. Wc,i = mass fraction of organic HAP in coating, i, kg organic HAP per kg... thinner per liter thinner. Wt,j = mass fraction of organic HAP in thinner, j, kg organic HAP per kg...

40 CFR 63.3951 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2013 CFR

2013-07-01

... reclaimed. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of... coating per liter coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. For reactive adhesives as defined in § 63.3981, use the mass fraction of organic HAP that is...

40 CFR 63.3951 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... reclaimed. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of... coating per liter coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. For reactive adhesives as defined in § 63.3981, use the mass fraction of organic HAP that is...

40 CFR 63.4151 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... option. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of... coating per liter coating. Wc,i = mass fraction of organic HAP in coating, i, kg organic HAP per kg... thinner per liter thinner. Wt,j = mass fraction of organic HAP in thinner, j, kg organic HAP per kg...

A System of ODEs for a Perturbation of a Minimal Mass Soliton

NASA Astrophysics Data System (ADS)

Marzuola, Jeremy L.; Raynor, Sarah; Simpson, Gideon

2010-08-01

We study soliton solutions to the nonlinear Schrödinger equation (NLS) with a saturated nonlinearity. NLS with such a nonlinearity is known to possess a minimal mass soliton. We consider a small perturbation of a minimal mass soliton and identify a system of ODEs extending the work of Comech and Pelinovsky (Commun. Pure Appl. Math. 56:1565-1607, 2003), which models the behavior of the perturbation for short times. We then provide numerical evidence that under this system of ODEs there are two possible dynamical outcomes, in accord with the conclusions of Pelinovsky et al. (Phys. Rev. E 53(2):1940-1953, 1996). Generically, initial data which supports a soliton structure appears to oscillate, with oscillations centered on a stable soliton. For initial data which is expected to disperse, the finite dimensional dynamics initially follow the unstable portion of the soliton curve.

Mass Ordering of Spectra from Fragmentation of Saturated Gluon States in High-Multiplicity Proton-Proton Collisions

DOE PAGES

Schenke, Björn; Schlichting, Sören; Tribedy, Prithwish; ...

2016-10-14

The mass ordering of mean transverse momentummore » $$\\langle$$p T$$\\rangle$$ and of the Fourier harmonic coefficient v 2 (p T) of azimuthally anisotropic particle distributions in high energy hadron collisions is often interpreted as evidence for the hydrodynamic flow of the matter produced. We investigate an alternative initial state interpretation of this pattern in high-multiplicity proton-proton collisions at the LHC. The QCD Yang-Mills equations describing the dynamics of saturated gluons are solved numerically with initial conditions obtained from the color-glass-condensate-based impact-parameter-dependent glasma model. The gluons are subsequently fragmented into various hadron species employing the well established Lund string fragmentation algorithm of the pythia event generator. Lastly, we find that this initial state approach reproduces characteristic features of bulk spectra, in particular, the particle mass dependence of $$\\langle$$p T$$\\rangle$$ and v 2 (p T).« less

Wind-driven angular momentum loss in binary systems. I - Ballistic case

NASA Technical Reports Server (NTRS)

Brookshaw, Leigh; Tavani, Marco

1993-01-01

We study numerically the average loss of specific angular momentum from binary systems due to mass outflow from one of the two stars for a variety of initial injection geometries and wind velocities. We present results of ballistic calculations in three dimensions for initial mass ratios q of the mass-losing star to primary star in the range q between 10 exp -5 and 10. We consider injection surfaces close to the Roche lobe equipotential surface of the mass-losing star, and also cases with the mass-losing star underfilling its Roche lobe. We obtain that the orbital period is expected to have a negative time derivative for wind-driven secular evolution of binaries with q greater than about 3 and with the mass-losing star near filling its Roche lobe. We also study the effect of the presence of an absorbing surface approximating an accretion disk on the average final value of the specific angular momentum loss. We find that the effect of an accretion disk is to increase the wind-driven angular momentum loss. Our results are relevant for evolutionary models of high-mass binaries and low-mass X-ray binaries.

Using mass media within health-promoting practice: a nursing perspective.

PubMed

Whitehead, D

2000-10-01

For some time health professionals have recognized the growing importance of utilizing mass media strategies as part of their health-promoting practice. The ever-evolving climate of technology and increasing reliance on mass communications has further reinforced the position of mass media initiatives. The enormous potential for mass media resources to reach certain audiences and influence their health-related behaviours has become particularly well established. Despite these facts, however, it is argued that the nursing profession has been less than pro-active in acknowledging, accommodating and adopting such practices. Consequently, the incorporation of health-related mass media initiatives into nursing's health-promotional role remains an elusive exercise. The maintenance of such a position, it is claimed, is potentially damaging for the profession as a whole. In light of this state of affairs, this paper seeks to review the literature surrounding the nature and processes of mass media strategies, their relevance to health promotion and nursing, how they are currently utilized and how they can be incorporated further into nursing practice. In conclusion, it is argued that nursing should seek to become a more active user of mass communication/media technology--especially in relation to its health-promotional practices.

Cervical lung herniation complicating a case of acute asphyxial asthma in a child.

PubMed

Martchek, Melissa A; Padilla, Benjamin E; Zonfrillo, Mark R; Friedlaender, Eron Y

2015-04-01

The abrupt onset of respiratory failure secondary to asthma, known as acute asphyxial asthma (AAA) in adults, is uncommonly reported in children. Here, we report a case of a child with the acute onset of respiratory failure consistent with AAA complicated by the finding of a neck mass during resuscitation. This 11-year-old boy with a history of asthma initially presented in respiratory failure with altered mental status after the complaint of difficulty in breathing minutes before collapsing at home. Initially, his respiratory failure was thought to be secondary to status asthmaticus, and treatment was initiated accordingly. However, a neck mass noted during the resuscitation was cause for concern, and other etiologies for his respiratory failure were considered, including an airway obstructing neck mass. After pediatric surgery and anesthesia consultation for intubation and possible tracheostomy placement, general anesthesia was induced in the operating room with an inhaled anesthetic, with prompt resolution of the bronchspasm and decompression of the neck mass. Review of the imaging and clinical course ultimately yielded a diagnosis of cervical lung herniation as the etiology of his neck mass. We report this case of AAA and cervical lung herniation and a review of the literature of these 2 uncommon phenomena in children.

Women and Society: The Mass Media.

ERIC Educational Resources Information Center

Busby, Linda J.

Males and females have become vitally concerned with sex-role images in the mass media because of the ubiquitous nature of the media. Mass media, which have heavily penetrated Americans' lives, have the potential for initiating, reinforcing, or denying certain social values. In studies of various media, including magazine advertising, magazine…

Dispersion and Lifetime of the SO2 Cloud from the August 2008 Kasatochi Eruption

NASA Technical Reports Server (NTRS)

Krotkov, N. A.; Schoeberl, M. R.; Morris, G. A.; Carn, S.; Yang, K.

2010-01-01

Hemispherical dispersion of the SO2 cloud from the August 2008 Kasatochi eruption is analyzed using satellite data from the Ozone Monitoring Instrument (OMI) and the Goddard Trajectory Model (GTM). The operational OMI retrievals underestimate the total SO2 mass by 20-30% on 8-11 August, as compared with more accurate offline Extended Iterative Spectral Fit (EISF) retrievals, but the error decreases with time due to plume dispersion and a drop in peak SO2 column densities. The GTM runs were initialized with and compared to the operational OMI SO2 data during early plume dispersion to constrain SO2 plume heights and eruption times. The most probable SO2 heights during initial dispersion are estimated to be 10-12 km, in agreement with direct height retrievals using EISF algorithm and IR measurements. Using these height constraints a forward GTM run was initialized on 11 August to compare with the month-long Kasatochi SO2 cloud dispersion patterns. Predicted volcanic cloud locations generally agree with OMI observations, although some discrepancies were observed. Operational OMI SO2 burdens were refined using GTM-predicted mass-weighted probability density height distributions. The total refined SO2 mass was integrated over the Northern Hemisphere to place empirical constraints on the SO2 chemical decay rate. The resulting lower limit of the Kasatochi SO2 e-folding time is approx.8-9 days. Extrapolation of the exponential decay back in time yields an initial erupted SO2 mass of approx.2.2 Tg on 8 August, twice as much as the measured mass on that day.

Extreme isolation of WN3/O3 stars and implications for their evolutionary origin as the elusive stripped binaries

NASA Astrophysics Data System (ADS)

Smith, Nathan; Götberg, Ylva; de Mink, Selma E.

2018-03-01

Recent surveys of the Magellanic Clouds have revealed a subtype of Wolf-Rayet (WR) star with peculiar properties. WN3/O3 spectra exhibit both WR-like emission and O3 V-like absorption - but at lower luminosity than O3 V or WN stars. We examine the projected spatial distribution of WN3/O3 stars in the Large Magellanic Cloud as compared to O-type stars. Surprisingly, WN3/O3 stars are among the most isolated of all classes of massive stars; they have a distribution similar to red supergiants dominated by initial masses of 10-15 M⊙, and are far more dispersed than classical WR stars or luminous blue variables. Their lack of association with clusters of O-type stars suggests strongly that WN3/O3 stars are not the descendants of single massive stars (30 M⊙ or above). Instead, they are likely products of interacting binaries at lower initial mass (10-18 M⊙). Comparison with binary models suggests a probable origin with primaries in this mass range that were stripped of their H envelopes through non-conservative mass transfer by a low-mass secondary. We show that model spectra and positions on the Hertzsprung-Russell diagram for binary-stripped stars are consistent with WN3/O3 stars. Monitoring radial velocities with high-resolution spectra can test for low-mass companions or runaway velocities. With lower initial mass and environments that avoid very massive stars, the WN3/O3 stars fit expectations for progenitors of Type Ib and possibly Type Ibn supernovae.

Acceleration switch

DOEpatents

Abbin, Jr., Joseph P.; Devaney, Howard F.; Hake, Lewis W.

1982-08-17

The disclosure relates to an improved integrating acceleration switch of the type having a mass suspended within a fluid filled chamber, with the motion of the mass initially opposed by a spring and subsequently not so opposed.

Acceleration switch

DOEpatents

Abbin, J.P. Jr.; Devaney, H.F.; Hake, L.W.

1979-08-29

The disclosure relates to an improved integrating acceleration switch of the type having a mass suspended within a fluid filled chamber, with the motion of the mass initially opposed by a spring and subsequently not so opposed.

Protective Effectiveness of Porous Shields Under the Influence of High-Speed Impact Loading

NASA Astrophysics Data System (ADS)

Kramshonkov, E. N.; Krainov, A. V.; Shorohov, P. V.

2016-02-01

The results of numerical simulations of a compact steel impactor with the aluminum porous shields under high-speed shock loading are presented. The porosity of barrier varies in wide range provided that its mass stays the same, but the impactor has always equal (identical) mass. Here presented the final assessment of the barrier perforation speed depending on its porosity and initial shock speed. The range of initial impact speed varies from 1 to 10 km/s. Physical phenomena such as: destruction, melting, vaporization of a interacting objects are taken into account. The analysis of a shield porosity estimation disclosed that the protection effectiveness of porous shield reveals at the initial impact speed grater then 1.5 km/s, and it increases when initial impact speed growth.

Secuencias evolutivas e isocronas para estrellas de baja masa e intermedia

NASA Astrophysics Data System (ADS)

Panei, J.; Baume, G.

2016-08-01

We present theoretical evolutionary sequences for low- and intermediate-mass stars. The masses calculated range from 1.7 to 10 M. The initial chemical composition is . In addition, we have taken into account a nuclear network with 17 isotopes and 34 nuclear reactions. With respect to the mix, we considered overshooting with a parameter . The evolutionary calculations were initialized from the region of instability of Hayashi, in order to calculate isochrones of pre-sequence, too.

Simultaneous effect of initial moisture content and airflow rate on biodrying of sewage sludge.

PubMed

Huiliñir, Cesar; Villegas, Manuel

2015-10-01

The simultaneous effect of initial moisture content (initial Mc) and air-flow rate (AFR) on biodrying performance was evaluated. For the study, a 3(2) factorial design, whose factors were AFR (1, 2 and 3 L/min kg(TS)) and initial Mc (59, 68 and 78% w.b.), was used. Using energy and water mass balance the main routes of water removal, energy use and efficiencies were determined. The results show that initial Mc has a stronger effect on the biodrying than the AFR, affecting the air outlet temperature and improving the water removal, with higher maximum temperatures obtained around 68% and the lowest maximum matrix temperature obtained at initial Mc = 78%.Through the water mass balance it was found that the main mechanism for water removal was the aeration, with higher water removal at intermediate initial Mc (68%) and high AFR (3 L/min kg(TS)). The energy balance indicated that bioreaction is the main energy source for water evaporation, with higher energy produced at intermediate initial Mc (68%). Finally, it was found that low values of initial Mc (59%) improve biodrying efficiency. Copyright © 2015 Elsevier Ltd. All rights reserved.

An Analytical Approach to the Evolution and Death of AGB Stars

NASA Astrophysics Data System (ADS)

Prager, Henry Alexander; Willson, Lee Anne M.; Marengo, Massimo; Creech-Eakman, Michelle J.

2017-01-01

Pop. I and II stars have a significant amount of metals throughout their structure, In the final stages of their evolution, intermediate mass stars (between 0.7 and 2 solar masses) ascend the Asymptotic Giant Branch (AGB). During their last few hundred thousand years on the AGB, these stars quickly lose their envelopes, recycling their metals as dust into the interstellar medium. The rate at which this happens consequently impacts the formation rate of stars, stellar systems, and the wider distribution of s-process isotopes.At the end of their life cycles, AGB stars experience a steep increase in mass loss rate. We can define the death line in two steps. First we define the critical mass loss rate to be where the mass loss rate equals the initial mass divided by the evolution time. Then the death line is where the rate of change of logMdot equals the rate of change of logL. Most of the stars we observe to be rapidly losing mass appear in the death zone between 0.1 and 10 times the critical mass loss rate.Assuming the mass loss rate increases exponentially with time, or, equivalently, the luminosity increases as a power of a characteristic exponent b, then the width of the death zone is the change in logL. This directly implies time is inversely proportional to b. This can be found for any mass-loss rate formula near the death line. By combining this with what we know about the initial-final mass relation and the core mass-luminosity relation, we can test for b with three observables — duration (width) of the death zone, the amplitude of mass loss variations (when L varies on an observable time scale such as a shell flash), and distributions of luminosity and pulsation period.By applying the initial mass function (IMF) and star formation rate (SFR) of an observed region, we can relate these observables to the characteristic exponent. We will need to look at nearby regions where we can see large numbers of AGB stars, such as the Magellanic clouds. We will show that by fixing the death line and the characteristic exponent that intermediate changes in the mass loss rate better fit observations than extreme values. This is consistent with dust-driven as opposed to pulsation-driven processes.

Modular space station mass properties

NASA Technical Reports Server (NTRS)

1972-01-01

An update of the space station mass properties is presented. Included are the final status update of the Initial Space Station (ISS) modules and logistic module plus incorporation of the Growth Space Station (GSS) module additions.

Where can a Trappist-1 planetary system be produced?

NASA Astrophysics Data System (ADS)

Haworth, Thomas J.; Facchini, Stefano; Clarke, Cathie J.; Mohanty, Subhanjoy

2018-04-01

We study the evolution of protoplanetary discs that would have been precursors of a Trappist-1-like system under the action of accretion and external photoevaporation in different radiation environments. Dust grains swiftly grow above the critical size below which they are entrained in the photoevaporative wind, so although gas is continually depleted, dust is resilient to photoevaporation after only a short time. This means that the ratio of the mass in solids (dust plus planetary) to the mass in gas rises steadily over time. Dust is still stripped early on, and the initial disc mass required to produce the observed 4 M⊕ of Trappist-1 planets is high. For example, assuming a Fatuzzo & Adams distribution of UV fields, typical initial disc masses have to be >30 per cent the stellar (which are still Toomre Q stable) for the majority of similar mass M dwarfs to be viable hosts of the Trappist-1 planets. Even in the case of the lowest UV environments observed, there is a strong loss of dust due to photoevaporation at early times from the weakly bound outer regions of the disc. This minimum level of dust loss is a factor of 2 higher than that which would be lost by accretion on to the star during 10 Myr of evolution. Consequently, even in these least irradiated environments, discs that are viable Trappist-1 precursors need to be initially massive (>10 per cent of the stellar mass).

[Correlation of molecular weight and nanofiltration mass transfer coefficient of phenolic acid composition from Salvia miltiorrhiza].

PubMed

Li, Cun-Yu; Wu, Xin; Gu, Jia-Mei; Li, Hong-Yang; Peng, Guo-Ping

2018-04-01

Based on the molecular sieving and solution-diffusion effect in nanofiltration separation, the correlation between initial concentration and mass transfer coefficient of three typical phenolic acids from Salvia miltiorrhiza was fitted to analyze the relationship among mass transfer coefficient, molecular weight and concentration. The experiment showed a linear relationship between operation pressure and membrane flux. Meanwhile, the membrane flux was gradually decayed with the increase of solute concentration. On the basis of the molecular sieving and solution-diffusion effect, the mass transfer coefficient and initial concentration of three phenolic acids showed a power function relationship, and the regression coefficients were all greater than 0.9. The mass transfer coefficient and molecular weight of three phenolic acids were negatively correlated with each other, and the order from high to low is protocatechualdehyde >rosmarinic acid> salvianolic acid B. The separation mechanism of nanofiltration for phenolic acids was further clarified through the analysis of the correlation of molecular weight and nanofiltration mass transfer coefficient. The findings provide references for nanofiltration separation, especially for traditional Chinese medicine with phenolic acids. Copyright© by the Chinese Pharmaceutical Association.

Risks of nuclear waste disposal in space. III - Long-term orbital evolution of small particle distribution

NASA Technical Reports Server (NTRS)

Friedlander, A. L.; Wells, W. C.

1980-01-01

A study of long term risks is presented that treats an additional pathway that could result in earth reentry, namely, small radioactive particles released in solar orbit due to payload fragmentation by accidental explosion or meteoroid impact. A characterization of such an event and of the initial mass size distribution of particles is given for two extremes of waste form strength. Attention is given to numerical results showing the mass-time distribution of material and the fraction of initial mass intercepted by earth. It is concluded that it appears that program planners need not be to concerned about the risks of this particular failure mechanism and return pathway.

Optical absorption in disordered monolayer molybdenum disulfide

NASA Astrophysics Data System (ADS)

Ekuma, C. E.; Gunlycke, D.

2018-05-01

We explore the combined impact of sulfur vacancies and electronic interactions on the optical properties of monolayer MoS2. First, we present a generalized Anderson-Hubbard Hamiltonian that accounts for both randomly distributed sulfur vacancies and the presence of dielectric screening within the material. Second, we parametrize this energy-dependent Hamiltonian from first-principles calculations based on density functional theory and the Green's function and screened Coulomb (GW) method. Third, we apply a first-principles-based many-body typical medium method to determine the single-particle electronic structure. Fourth, we solve the Bethe-Salpeter equation to obtain the charge susceptibility χ with its imaginary part being related to the absorbance A . Our results show that an increased vacancy concentration leads to decreased absorption both in the band continuum and from exciton states within the band gap. We also observe increased absorption below the band-gap threshold and present an expression, which describes Lifshitz tails, in excellent qualitative agreement with our numerical calculations. This latter increased absorption in the 1.0 -2.5 eV range makes defect engineering of potential interest for solar cell applications.

Infrared Dielectric Screening Determines the Low Exciton Binding Energy of Metal-Halide Perovskites.

PubMed

Umari, Paolo; Mosconi, Edoardo; De Angelis, Filippo

2018-02-01

The performance of lead-halide perovskites in optoelectronic devices is due to a unique combination of factors, including highly efficient generation, transport, and collection of photogenerated charge carriers. The mechanism behind efficient charge generation in lead-halide perovskites is still largely unknown. Here, we investigate the factors that influence the exciton binding energy (E b ) in a series of metal-halide perovskites using accurate first-principles calculations based on solution of the Bethe-Salpeter equation, coupled to ab initio molecular dynamics simulations. We find that E b is strongly modulated by screening from low-energy phonons, which account for a factor ∼2 E b reduction, while dynamic disorder and rotational motion of the organic cations play a minor role. We calculate E b = 15 meV for MAPbI 3 , in excellent agreement with recent experimental estimates. We then explore how different material combinations (e.g., replacing Pb → Pb:Sn→ Sn; and MA → FA → Cs) may lead to different E b values and highlight the mechanisms underlying E b tuning.

Stochastic Optimally Tuned Range-Separated Hybrid Density Functional Theory.

PubMed

Neuhauser, Daniel; Rabani, Eran; Cytter, Yael; Baer, Roi

2016-05-19

We develop a stochastic formulation of the optimally tuned range-separated hybrid density functional theory that enables significant reduction of the computational effort and scaling of the nonlocal exchange operator at the price of introducing a controllable statistical error. Our method is based on stochastic representations of the Coulomb convolution integral and of the generalized Kohn-Sham density matrix. The computational cost of the approach is similar to that of usual Kohn-Sham density functional theory, yet it provides a much more accurate description of the quasiparticle energies for the frontier orbitals. This is illustrated for a series of silicon nanocrystals up to sizes exceeding 3000 electrons. Comparison with the stochastic GW many-body perturbation technique indicates excellent agreement for the fundamental band gap energies, good agreement for the band edge quasiparticle excitations, and very low statistical errors in the total energy for large systems. The present approach has a major advantage over one-shot GW by providing a self-consistent Hamiltonian that is central for additional postprocessing, for example, in the stochastic Bethe-Salpeter approach.

Strong decays of DJ(3000 ) and Ds J(3040 )

NASA Astrophysics Data System (ADS)

Li, Si-Chen; Wang, Tianhong; Jiang, Yue; Tan, Xiao-Ze; Li, Qiang; Wang, Guo-Li; Chang, Chao-Hsi

2018-03-01

In this paper, we systematically calculate two-body strong decays of newly observed DJ(3000 ) and Ds J(3040 ) with 2 P (1+) and 2 P (1+') assignments in an instantaneous approximation of the Bethe-Salpeter equation method. Our results show that both resonances can be explained as the 2 P (1+') with broad width via 3P1 and 1P1 mixing in D and Ds families. For DJ(3000 ), the total width is 229.6 MeV in our calculation, close to the upper limit of experimental data, and the dominant decay channels are D2*π , D*π , and D*(2600 )π . For Ds J(3040 ), the total width is 157.4 MeV in our calculation, close to the lower limit of experimental data, and the dominant channels are D*K and D*K*. These results are consistent with observed channels in experiments. Given the very little information that has been obtained from experiments and the large error bars of the total decay widths, we recommend the detection of dominant channels in our calculation.

Assessment of the Accuracy of the Bethe-Salpeter (BSE/GW) Oscillator Strengths.

PubMed

Jacquemin, Denis; Duchemin, Ivan; Blondel, Aymeric; Blase, Xavier

2016-08-09

Aiming to assess the accuracy of the oscillator strengths determined at the BSE/GW level, we performed benchmark calculations using three complementary sets of molecules. In the first, we considered ∼80 states in Thiel's set of compounds and compared the BSE/GW oscillator strengths to recently determined ADC(3/2) and CC3 reference values. The second set includes the oscillator strengths of the low-lying states of 80 medium to large dyes for which we have determined CC2/aug-cc-pVTZ values. The third set contains 30 anthraquinones for which experimental oscillator strengths are available. We find that BSE/GW accurately reproduces the trends for all series with excellent correlation coefficients to the benchmark data and generally very small errors. Indeed, for Thiel's sets, the BSE/GW values are more accurate (using CC3 references) than both CC2 and ADC(3/2) values on both absolute and relative scales. For all three sets, BSE/GW errors also tend to be nicely spread with almost equal numbers of positive and negative deviations as compared to reference values.

Frenkel and Charge-Transfer Excitations in Donor-acceptor Complexes from Many-Body Green's Functions Theory.

PubMed

Baumeier, Björn; Andrienko, Denis; Rohlfing, Michael

2012-08-14

Excited states of donor-acceptor dimers are studied using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. For a series of prototypical small-molecule based pairs, this method predicts energies of local Frenkel and intermolecular charge-transfer excitations with the accuracy of tens of meV. Application to larger systems is possible and allowed us to analyze energy levels and binding energies of excitons in representative dimers of dicyanovinyl-substituted quarterthiophene and fullerene, a donor-acceptor pair used in state of the art organic solar cells. In these dimers, the transition from Frenkel to charge transfer excitons is endothermic and the binding energy of charge transfer excitons is still of the order of 1.5-2 eV. Hence, even such an accurate dimer-based description does not yield internal energetics favorable for the generation of free charges either by thermal energy or an external electric field. These results confirm that, for qualitative predictions of solar cell functionality, accounting for the explicit molecular environment is as important as the accurate knowledge of internal dimer energies.

Neutral and charged excitations in carbon fullerenes from first-principles many-body theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiago, Murilo L; Kent, Paul R; Hood, Randolph Q.

2008-01-01

We use first-principles many-body theories to investigate the low energy excitations of the carbon fullerenes C_20, C_24, C_50, C_60, C_70, and C_80. Properties are calculated via the GW-Bethe-Salpeter Equation (GW-BSE) and diffusion Quantum Monte Carlo (QMC) methods. At a lower level of theoretical complexity, we also calculate these properties using static and time-dependent density-functional theory. We critically compare these theories and assess their accuracy against available experimental data. The first ionization potentials are consistently well reproduced and are similar for all the fullerenes and methods studied. The electron affinities and first triplet excitation energies show substantial method and geometry dependence.more » Compared to available experiment, GW-BSE underestimates excitation energies by approximately 0.3 eV while QMC overestimates them by approximately 0.5 eV. We show the GW-BSE errors result primarily from a systematic overestimation of the electron affinities, while the QMC errors likely result from nodal error in both ground and excited state calculations.« less

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr 3, BaI 2, and SrI 2

DOE PAGES

Schleife, Andre; Zhang, Xiao; Li, Qi; ...

2016-11-03

In this paper, materials for scintillator radiation detectors need to fulfill a diverse set of requirements such as radiation hardness and highly specific response to incoming radiation, rendering them a target of current materials design efforts. Even though they are amenable to cutting-edge theoretical spectroscopy techniques, surprisingly many fundamental properties of scintillator materials are still unknown or not well explored. In this work, we use first-principles approaches to thoroughly study the optical properties of four scintillator materials: NaI, LaBr 3, BaI 2, and SrI 2. By solving the Bethe–Salpeter equation for the optical polarization function we study the influence ofmore » excitonic effects on dielectric and electron-energy loss functions. This work sheds light into fundamental optical properties of these four scintillator materials and lays the ground-work for future work that is geared toward accurate modeling and computational materials design of advanced radiation detectors with unprecedented energy resolution.« less

Ionisation in turbulent magnetic molecular clouds. I. Effect on density and mass-to-flux ratio structures

NASA Astrophysics Data System (ADS)

Bailey, Nicole D.; Basu, Shantanu; Caselli, Paola

2017-05-01

Context. Previous studies show that the physical structures and kinematics of a region depend significantly on the ionisation fraction. These studies have only considered these effects in non-ideal magnetohydrodynamic simulations with microturbulence. The next logical step is to explore the effects of turbulence on ionised magnetic molecular clouds and then compare model predictions with observations to assess the importance of turbulence in the dynamical evolution of molecular clouds. Aims: In this paper, we extend our previous studies of the effect of ionisation fractions on star formation to clouds that include both non-ideal magnetohydrodynamics and turbulence. We aim to quantify the importance of a treatment of the ionisation fraction in turbulent magnetised media and investigate the effect of the turbulence on shaping the clouds and filaments before star formation sets in. In particular, here we investigate how the structure, mass and width of filamentary structures depend on the amount of turbulence in ionised media and the initial mass-to-flux ratio. Methods: To determine the effects of turbulence and mass-to-flux ratio on the evolution of non-ideal magnetised clouds with varying ionisation profiles, we have run two sets of simulations. The first set assumes different initial turbulent Mach values for a fixed initial mass-to-flux ratio. The second set assumes different initial mass-to-flux ratio values for a fixed initial turbulent Mach number. Both sets explore the effect of using one of two ionisation profiles: step-like (SL) or cosmic ray only (CR-only). We compare the resulting density and mass-to-flux ratio structures both qualitatively and quantitatively via filament and core masses and filament fitting techniques (Gaussian and Plummer profiles). Results: We find that even with almost no turbulence, filamentary structure still exists although at lower density contours. Comparison of simulations shows that for turbulent Mach numbers above 2, there is little structural difference between the SL and CR-only models, while below this threshold the ionisation structure significantly affects the formation of filaments. This holds true for both sets of models. Analysis of the mass within cores and filaments shows that the mass decreases as the degree of turbulence increases. Finally, observed filaments within the Taurus L1495/B213 complex are best reproduced by models with supercritical mass-to-flux ratios and/or at least mildly supersonic turbulence, however, our models show that the sterile fibres observed within Taurus may occur in highly ionised, subcritical environments. Conclusions: From the analysis of the simulations, we conclude that in the presence of low turbulent velocities, the ionisation structure of the medium still plays a role in shaping the structure of the cloud, however, above Mach 2, the differences between the two profiles become indistinguishable. However, differences may be present in the underlying velocity structure. Kinematics studies will be the focus of the next paper in this series. Regions with fertile fibres likely indicate a trans- or supercritical mass-to-flux ratio within the region while sterile fibres are likely subcritical and transient.

Constraints from Dust Mass and Mass Accretion Rate Measurements on Angular Momentum Transport in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Mulders, Gijs D.; Pascucci, Ilaria; Manara, Carlo F.; Testi, Leonardo; Herczeg, Gregory J.; Henning, Thomas; Mohanty, Subhanjoy; Lodato, Giuseppe

2017-09-01

In this paper, we investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in protoplanetary disks. We find a correlation between dust disk mass and mass accretion rate in Chamaeleon I with a slope that is close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit {M}{dust}-{M}\\star and {\\dot{M}}{acc}-{M}\\star relations is uncorrelated. We simulate synthetic observations of an ensemble of evolving disks using a Monte Carlo approach and find that disks with a constant α viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass but overpredict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. In the first one, the observed scatter in {M}{dust} and {\\dot{M}}{acc} is not primordial, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large timescales affects the mass accretion rates. In the second scenario, the observed scatter is primordial, but disks have not evolved substantially at the age of Lupus and Chamaeleon I owing to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of protoplanetary disks, through either direct observations of the gas or spatially resolved multiwavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.

Use of Interrupted Helium Flow in the Analysis of Vapor Samples with Flowing Atmospheric-Pressure Afterglow-Mass Spectrometry

NASA Astrophysics Data System (ADS)

Storey, Andrew P.; Zeiri, Offer M.; Ray, Steven J.; Hieftje, Gary M.

2017-02-01

The flowing atmospheric-pressure afterglow (FAPA) source was used for the mass-spectrometric analysis of vapor samples introduced between the source and mass spectrometer inlet. Through interrupted operation of the plasma-supporting helium flow, helium consumption is greatly reduced and dynamic gas behavior occurs that was characterized by schlieren imaging. Moreover, mass spectra acquired immediately after the onset of helium flow exhibit a signal spike before declining and ultimately reaching a steady level. This initial signal appears to be due to greater interaction of sample vapor with the afterglow of the source when helium flow resumes. In part, the initial spike in signal can be attributed to a pooling of analyte vapor in the absence of helium flow from the source. Time-resolved schlieren imaging of the helium flow during on and off cycles provided insight into gas-flow patterns between the FAPA source and the MS inlet that were correlated with mass-spectral data.

Stellar evolution of high mass based on the Ledoux criterion for convection

NASA Technical Reports Server (NTRS)

Stothers, R.; Chin, C.

1972-01-01

Theoretical evolutionary sequences of models for stars of 15 and 30 solar masses were computed from the zero-age main sequence to the end of core helium burning. During the earliest stages of core helium depletion, the envelope rapidly expands into the red-supergiant configuration. At 15 solar mass, a blue loop on the H-R diagram ensues if the initial metals abundance, initial helium abundance, or C-12 + alpha particle reaction rate is sufficiently large, or if the 3-alpha reaction rate is sufficiently small. These quantities affect the opacity of the base of the outer convection zone, the mass of the core, and the thermal properties of the core. The blue loop occurs abruptly and fully developed when the critical value of any of these quantities is exceeded, and the effective temperature range and fraction of the lifetime of core helium burning during the slow phase of the blue loop vary surprisingly little. At 30 solar mass no blue loop occurs for any reasonable set of input parameters.

Sorption of atmospheric gases by bulk lithium metal

DOE PAGES

Hart, C. A.; Skinner, C. H.; Capece, A. M.; ...

2016-01-01

Lithium conditioning of plasma facing components has enhanced the performance of several fusion devices. Elemental lithium will react with air during maintenance activities and with residual gases (H 2O, CO, CO 2) in the vacuum vessel during operations. We have used a mass balance (microgram sensitivity) to measure the mass gain of lithium samples during exposure of a ~1 cm 2 surface to ambient and dry synthetic air. For ambient air, we found an initial mass gain of several mg/h declining to less than 1 mg/h after an hour and decreasing by an order of magnitude after 24 h. Amore » 9 mg sample achieved a final mass gain corresponding to complete conversion to Li 2CO 3 after 5 days. Exposure to dry air resulted in a 30 times lower initial rate of mass gain. The results have implications for the chemical state of lithium plasma facing surfaces and for safe handling of lithium coated components.« less

Use of Interrupted Helium Flow in the Analysis of Vapor Samples with Flowing Atmospheric-Pressure Afterglow-Mass Spectrometry.

PubMed

Storey, Andrew P; Zeiri, Offer M; Ray, Steven J; Hieftje, Gary M

2017-02-01

The flowing atmospheric-pressure afterglow (FAPA) source was used for the mass-spectrometric analysis of vapor samples introduced between the source and mass spectrometer inlet. Through interrupted operation of the plasma-supporting helium flow, helium consumption is greatly reduced and dynamic gas behavior occurs that was characterized by schlieren imaging. Moreover, mass spectra acquired immediately after the onset of helium flow exhibit a signal spike before declining and ultimately reaching a steady level. This initial signal appears to be due to greater interaction of sample vapor with the afterglow of the source when helium flow resumes. In part, the initial spike in signal can be attributed to a pooling of analyte vapor in the absence of helium flow from the source. Time-resolved schlieren imaging of the helium flow during on and off cycles provided insight into gas-flow patterns between the FAPA source and the MS inlet that were correlated with mass-spectral data. Graphical Abstract ᅟ.

The Initial Mass Function of the First Stars Inferred from Extremely Metal-poor Stars

NASA Astrophysics Data System (ADS)

Ishigaki, Miho N.; Tominaga, Nozomu; Kobayashi, Chiaki; Nomoto, Ken’ichi

2018-04-01

We compare the elemental abundance patterns of ∼200 extremely metal-poor (EMP; [Fe/H] < ‑3) stars to the supernova yields of metal-free stars, in order to obtain insights into the characteristic masses of the first (Population III or Pop III) stars in the universe. The supernova yields are prepared with nucleosynthesis calculations of metal-free stars with various initial masses (M = 13, 15, 25, 40 and 100 M ⊙) and explosion energies (E 51 = E/1051[erg] = 0.5–60), to include low-energy, normal-energy, and high-energy explosions. We adopt the mixing-fallback model, to take into account possible asymmetry in the supernova explosions, and the yields that best fit the observed abundance patterns of the EMP stars are searched by varying the model parameters. We find that the abundance patterns of the EMP stars are predominantly best-fitted by the supernova yields with initial masses M < 40 M ⊙, and that more than than half of the stars are best-fitted by the M = 25 M ⊙ hypernova (E 51 = 10) models. The results also indicate that the majority of the primordial supernovae have ejected 10‑2–10‑1 M ⊙ of 56Ni, leaving behind a compact remnant (either a neutron star or a black hole), with a mass in the range of ∼1.5–5 M ⊙. These results suggest that the masses of the first stars responsible for the first metal enrichment are predominantly <40 M ⊙. This implies that the higher-mass first stars were either less abundant, directly collapsed into a black hole without ejecting heavy elements, or a supernova explosion of a higher-mass first star inhibits the formation of the next generation of low-mass stars at [Fe/H] < ‑3.

Rapid mass segregation in small stellar clusters

NASA Astrophysics Data System (ADS)

Spera, Mario; Capuzzo-Dolcetta, Roberto

2017-12-01

In this paper we focus our attention on small-to-intermediate N-body systems that are, initially, distributed uniformly in space and dynamically `cool' (virial ratios Q=2T/|Ω| below ˜0.3). In this work, we study the mass segregation that emerges after the initial violent dynamical evolution. At this scope, we ran a set of high precision N-body simulations of isolated clusters by means of HiGPUs, our direct summation N-body code. After the collapse, the system shows a clear mass segregation. This (quick) mass segregation occurs in two phases: the first shows up in clumps originated by sub-fragmentation before the deep overall collapse; this segregation is partly erased during the deep collapse to re-emerge, abruptly, during the second phase, that follows the first bounce of the system. In this second stage, the proper clock to measure the rate of segregation is the dynamical time after virialization, which (for cold and cool systems) may be significantly different from the crossing time evaluated from initial conditions. This result is obtained for isolated clusters composed of stars of two different masses (in the ratio mh/ml=2), at varying their number ratio, and is confirmed also in presence of a massive central object (simulating a black hole of stellar size). Actually, in stellar systems starting their dynamical evolution from cool conditions, the fast mass segregation adds to the following, slow, secular segregation which is collisionally induced. The violent mass segregation is an effect persistent over the whole range of N (128 ≤ N ≤1,024) investigated, and is an interesting feature on the astronomical-observational side, too. The semi-steady state reached after virialization corresponds to a mass segregated distribution function rather than that of equipartition of kinetic energy per unit mass as it should result from violent relaxation.

Mass sensing based on deterministic and stochastic responses of elastically coupled nanocantilevers.

PubMed

Gil-Santos, Eduardo; Ramos, Daniel; Jana, Anirban; Calleja, Montserrat; Raman, Arvind; Tamayo, Javier

2009-12-01

Coupled nanomechanical systems and their entangled eigenstates offer unique opportunities for the detection of ultrasmall masses. In this paper we show theoretically and experimentally that the stochastic and deterministic responses of a pair of coupled nanocantilevers provide different and complementary information about the added mass of an analyte and its location. This method allows the sensitive detection of minute quantities of mass even in the presence of large initial differences in the active masses of the two cantilevers. Finally, we show the fundamental limits in mass detection of this sensing paradigm.

VizieR Online Data Catalog: Evolution of rotating very massive LC stars (Kohler, 2015)

NASA Astrophysics Data System (ADS)

Kohler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Grafener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2014-11-01

A dense model grid with chemical composition appropriate for the Large Magellanic Cloud is presented. A one-dimensional hydrodynamic stellar evolution code was used to compute our models on the main sequence, taking into account rotation, transport of angular momentum by magnetic fields and stellar wind mass loss. We present stellar evolution models with initial masses of 70-500M⊙ and with initial surface rotational velocities of 0-550km/s. (2 data files).

Seizure as an initial presentation of human immunodeficiency virus: acute toxoplasmosis mimicking glioblastoma multiforme.

PubMed

Parekh, Parth; Boggs, Jody P; Silverberg, Marc; Marik, Paul

2013-11-14

We present a case of a 46-year-old man with a history significant only for hypertension and depression that presented with a new onset seizure resulting from a right parietal lobe mass. Further evaluation determined the parietal mass to be central nervous system toxoplasmosis, which was the initial presentation of his underlying HIV/AIDS. This case provided a diagnostic challenge and demonstrates the importance of a thorough evaluation as it pertains to a newly diagnosed brain lesion.

Measuring the High-Mass IMF in Low-Metallicity Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Weisz, Daniel

2017-08-01

We propose to measure the stellar initial mass function above >1-2 Msun in 46 nearby dwarf galaxies with archival HST observations. This novel approach leverages the redundant age information provided by the main sequence and blue core helium burning stars <500 years old to break the well-known degeneracy between the IMF and star formation history (SFH), enabling a direct measurement of the high-mass IMF in dwarf galaxies. We will be able to constrain the high-mass IMF slope to a precision better than 0.1 to 0.3 dex in each galaxy. Our sample spans a factor of 6 in metallicity ( 5-30% Zsun), 4 decades in star formation rate, and 3 decades in both stellar and gas mass, allowing us to explore the IMF over a wide range of extreme environments.Current observational evidence suggests that nearby dwarf galaxies are the most likely candidates to host significant and systematic variations in the high-mass IMF (e.g., Halpha/UV ratios). However, to date there have been no direct measurements of the high-mass IMF in environments with lower star formation rates and/or more metal poor than the Magellanic Clouds. Our program remedies this shortcoming allowing us to (1) make the first-ever measurement of the high-mass IMF in extremely metal-poor environments; (2) empirically quantify environmental the (lack of) variations in the high-mass IMF; (3) directly test the integrated galactic mass initial mass function (IGIMF), which predicts environmental sensitivity of the IMF in dwarf galaxies.

VizieR Online Data Catalog: Post-merger cluster A2255 membership (Tyler+, 2014)

NASA Astrophysics Data System (ADS)

Tyler, K. D.; Bai, L.; Rieke, G. H.

2017-04-01

A2255 was initially chosen from the Popesso et al. (2007, J/A+A/461/397) sample because it is a large cluster with complete SDSS photometric and spectroscopic coverage out to ~3 r200. It has incomplete areal spectroscopic coverage from 3 r200<~rproj<~5 r200 - about half of this region is covered. The SDSS photometric survey provides a uniform data set to study galaxy properties in the cluster. The model magnitudes are the linear combinations of best-fit exponential and de Vaucouleurs profiles and are recommended as the best estimates of magnitude by SDSS. As such, we use the model magnitudes (except where explicitly stated otherwise) and correct them for Galactic extinction (O'Donnell, 1994ApJ...422..158O). We used these photometric data to estimate galactic stellar masses with the SDSS_KCORRECT routine within KCORRECT (v. 4.2; Blanton & Roweis 2007AJ....133..734B). KCORRECT uses different cosmological values and initial mass function, so we corrected the original stellar mass output to the cosmology and initial mass function (Kroupa, 2001MNRAS.322..231K) adopted in this paper. (1 data file).

Summary of Part 75 Administrative Processes: Table 1

EPA Pesticide Factsheets

Learn how to submit your initial certification, recertification, monitoring plans, routine quality assurance tests, diagnostic tests and DAHS verifications, low mass emissions units and other notification requirements. Table 1, initial certification.

Two black hole initial data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leski, Szymon

2005-06-15

The Misner initial data are a standard example of time-symmetric initial data with two apparent horizons. Compact formulae describing such data are presented in the cases of equal or nonequal masses (i.e. isometric or nonisometric horizons). The interaction energy in the 'Schwarzschild + test-particle' limit of the Misner data is analyzed.

20 CFR 408.1004 - Which administrative actions are not initial determinations?

Code of Federal Regulations, 2010 CFR

2010-04-01

... 20 Employees' Benefits 2 2010-04-01 2010-04-01 false Which administrative actions are not initial determinations? 408.1004 Section 408.1004 Employees' Benefits SOCIAL SECURITY ADMINISTRATION SPECIAL BENEFITS FOR... federally administered State recognition payments due to a State-initiated mass change, as defined in § 408...

Smoke emissions due to burning of green waste in the Mediterranean area: Influence of fuel moisture content and fuel mass

NASA Astrophysics Data System (ADS)

Tihay-Felicelli, V.; Santoni, P. A.; Gerandi, G.; Barboni, T.

2017-06-01

The aim of this study was to investigate emission characteristics in relation to differences in fuel moisture content (FMC) and initial dry mass. For this purpose, branches and twigs with leaves of Cistus monspeliensis were burned in a Large Scale Heat Release apparatus coupled to a Fourier Transform Infrared Spectrometer. A smoke analysis was conducted and the results highlighted the presence of CO2, H2O, CO, CH4, NO, NO2, NH3, SO2, and non-methane organic compounds (NMOC). CO2, NO, and NO2 species are mainly released during flaming combustion, whereas CO, CH4, NH3, and NMOC are emitted during both flaming and smoldering combustion. The emission of these compounds during flaming combustion is due to a rich fuel to air mixture, leading to incomplete combustion. The fuel moisture content and initial dry mass influence the flame residence time, the duration of smoldering combustion, the combustion efficiency, and the emission factors. By increasing the initial dry mass, the emission factors of NO, NO2, and CO2 decrease, whereas those of CO and CH4 increase. The increase of FMC induces an increase of the emission factors of CO, CH4, NH3, NMOC, and aerosols, and a decrease of those of CO2, NO, and NO2. Increasing fuel moisture content reduces fuel consumption, duration of smoldering, and peak heat release rate, but simultaneously increases the duration of propagation within the packed bed, and the flame residence time. Increasing the initial dry mass, causes all the previous combustion parameters to increase. These findings have implications for modeling biomass burning emissions and impacts.

Nucleosynthesis in the Innermost Ejecta of Neutrino-driven Supernova Explosions in Two Dimensions

NASA Astrophysics Data System (ADS)

Wanajo, Shinya; Müller, Bernhard; Janka, Hans-Thomas; Heger, Alexander

2018-01-01

We examine nucleosynthesis in the innermost neutrino-processed ejecta (a few {10}-3 {M}ȯ ) of self-consistent two-dimensional explosion models of core-collapse supernovae (CCSNe) for six progenitor stars with different initial masses. Three models have initial masses near the low-mass end of the SN range of 8.8 {M}ȯ (e8.8; electron-capture SN), 9.6 {M}ȯ (z9.6), and 8.1 {M}ȯ (u8.1), with initial metallicities of 1, 0, and 10‑4 times the solar metallicity, respectively. The other three are solar-metallicity models with initial masses of 11.2 {M}ȯ (s11), 15 {M}ȯ (s15), and 27 {M}ȯ (s27). The low-mass models e8.8, z9.6, and u8.1 exhibit high production factors (nucleosynthetic abundances relative to the solar abundances) of 100–200 for light trans-Fe elements from Zn to Zr. This is associated with an appreciable ejection of neutron-rich matter in these models. Remarkably, the nucleosynthetic outcomes for the progenitors e8.8 and z9.6 are almost identical, including interesting productions of 48Ca and 60Fe, irrespective of their quite different (O–Ne–Mg and Fe) cores prior to collapse. In the more massive models s11, s15, and s27, several proton-rich isotopes of light trans-Fe elements including the p-isotope 92Mo (for s27) are made, up to production factors of ∼30. Both electron-capture SNe and CCSNe near the low-mass end can therefore be dominant contributors to the Galactic inventory of light trans-Fe elements from Zn to Zr and probably 48Ca and live 60Fe. The innermost ejecta of more massive SNe may have only subdominant contributions to the chemical enrichment of the Galaxy except for 92Mo.

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

PubMed Central

Leitzinger, M.; Odert, P.; Kulikov, Yu.N.; Lammer, H.; Wuchterl, G.; Penz, T.; Guarcello, M.G.; Micela, G.; Khodachenko, M.L.; Weingrill, J.; Hanslmeier, A.; Biernat, H.K.; Schneider, J.

2011-01-01

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68REarth) and Kepler-10b (∼1.416REarth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects. PMID:21969736

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

PubMed

Leitzinger, M; Odert, P; Kulikov, Yu N; Lammer, H; Wuchterl, G; Penz, T; Guarcello, M G; Micela, G; Khodachenko, M L; Weingrill, J; Hanslmeier, A; Biernat, H K; Schneider, J

2011-10-01

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68REarth) and Kepler-10b (∼1.416REarth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a "Hot Neptune" nor a "Hot Uranus"-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.

Restoration of the covariant gauge α in the initial field of gravity in de Sitter spacetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheong, Lee Yen; Yan, Chew Xiao

2014-03-05

The gravitational field generated by a mass term and the initial surface through covariant retarded Green's function for linearized gravity in de Sitter spacetime was studied recently [4, 5] with the covariant gauges set to β = 2/3 and α = 5/3. In this paper we extend the work to restore the gauge parameter α in the field coming from the initial data using the method of shifting the parameter. The α terms in the initial field cancels exactly with the one coming from the source term. Consequently, the correct field configuration, with two equal mass points moving in itsmore » geodesic, one located at the North pole and another one located at the South pole, is reproduced in the whole manifold of de Sitter spacetime.« less

Reconstructing the Initial Relaxation Time of Young Star Clusters in the Large Magellanic Cloud: The Evolution of Star Clusters

NASA Astrophysics Data System (ADS)

Portegies Zwart, S. F.; Chen, H.-C.

2008-06-01

We reconstruct the initial two-body relaxation time at the half mass radius for a sample of young ⪉ 300 Myr star clusters in the Large Magellanic cloud. We achieve this by simulating star clusters with 12288 to 131072 stars using direct N-body integration. The equations of motion of all stars are calculated with high precision direct N-body simulations which include the effects of the evolution of single stars and binaries. We find that the initial relaxation times of the sample of observed clusters in the Large Magellanic Cloud ranges from about 200 Myr to about 2 Gyr. The reconstructed initial half-mass relaxation times for these clusters have a much narrower distribution than the currently observed distribution, which ranges over more than two orders of magnitude.

40 CFR 63.4751 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... rate without add-on controls option. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating, thinner, and cleaning material used during each... of coating, i, grams coating per liter coating. Wc,i = Mass fraction of organic HAP in coating, i...

40 CFR 63.4741 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... compliant material option. If the mass fraction of organic HAP of a coating equals zero, determined... fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified...

40 CFR 63.4941 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... material option. (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for each coating, thinner, and cleaning material used during the... 311 (appendix A to 40 CFR part 63). You may use Method 311 for determining the mass fraction of...

40 CFR 63.4941 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2013 CFR

2013-07-01

... material option. (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for each coating, thinner, and cleaning material used during the... 311 (appendix A to 40 CFR part 63). You may use Method 311 for determining the mass fraction of...

40 CFR 63.4141 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... the compliant material option. If the mass fraction of organic HAP of a coating equals zero... fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified...

40 CFR 63.4751 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... rate without add-on controls option. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating, thinner, and cleaning material used during each... of coating, i, grams coating per liter coating. Wc,i = Mass fraction of organic HAP in coating, i...

40 CFR 63.4141 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... the compliant material option. If the mass fraction of organic HAP of a coating equals zero... fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified...

40 CFR 63.4741 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... compliant material option. If the mass fraction of organic HAP of a coating equals zero, determined... fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for...). You may use Method 311 for determining the mass fraction of organic HAP. Use the procedures specified...

40 CFR 63.4941 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... material option. (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for each coating, thinner, and cleaning material used during the... 311 (appendix A to 40 CFR part 63). You may use Method 311 for determining the mass fraction of...

40 CFR 63.4161 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2014 CFR

2014-07-01

... compliance period, kg. AI = total mass of organic HAP in the coatings used in the controlled coating... this section: ER23JY02.007 Where: AI = mass of organic HAP in the coatings used in the controlled... recovery system using a liquid-liquid material balance during the compliance period, kg. AI = total mass of...

40 CFR 63.4161 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2012 CFR

2012-07-01

... compliance period, kg. AI = total mass of organic HAP in the coatings used in the controlled coating... this section: ER23JY02.007 Where: AI = mass of organic HAP in the coatings used in the controlled... recovery system using a liquid-liquid material balance during the compliance period, kg. AI = total mass of...

40 CFR 63.4161 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2010 CFR

2010-07-01

... compliance period, kg. AI = total mass of organic HAP in the coatings used in the controlled coating... this section: ER23JY02.007 Where: AI = mass of organic HAP in the coatings used in the controlled... recovery system using a liquid-liquid material balance during the compliance period, kg. AI = total mass of...

40 CFR 1065.650 - Emission calculations.

Code of Federal Regulations, 2012 CFR

2012-07-01

... for performing the drift validation according to § 1065.550(b). When applying the initial THC and CH4...-corrected set of calculations as described in § 1065.520(g)(7). (ii) Correct all THC and CH4 concentrations... § 1065.667. (5) Mass of NMHC. Compare the corrected mass of NMHC to corrected mass of THC. If the...

Massive, wide binaries as tracers of massive star formation

NASA Astrophysics Data System (ADS)

Griffiths, Daniel W.; Goodwin, Simon P.; Caballero-Nieves, Saida M.

2018-05-01

Massive stars can be found in wide (hundreds to thousands au) binaries with other massive stars. We use N-body simulations to show that any bound cluster should always have approximately one massive wide binary: one will probably form if none are present initially, and probably only one will survive if more than one is present initially. Therefore, any region that contains many massive wide binaries must have been composed of many individual subregions. Observations of Cyg OB2 show that the massive wide binary fraction is at least a half (38/74), which suggests that Cyg OB2 had at least 30 distinct massive star formation sites. This is further evidence that Cyg OB2 has always been a large, low-density association. That Cyg OB2 has a normal high-mass initial mass function (IMF) for its total mass suggests that however massive stars form, they `randomly sample' the IMF (as the massive stars did not `know' about each other).

The Effect of Upper Body Mass and Initial Knee Flexion on the Injury Outcome of Post Mortem Human Subject Pedestrian Isolated Legs.

PubMed

Petit, Philippe; Trosseille, Xavier; Dufaure, Nicolas; Dubois, Denis; Potier, Pascal; Vallancien, Guy

2014-11-01

In the ECE 127 Regulation on pedestrian leg protection, as well as in the Euro NCAP test protocol, a legform impactor hits the vehicle at the speed of 40 kph. In these tests, the knee is fully extended and the leg is not coupled to the upper body. However, the typical configuration of a pedestrian impact differs since the knee is flexed during most of the gait cycle and the hip joint applies an unknown force to the femur. This study aimed at investigating the influence of the inertia of the upper body (modelled using an upper body mass fixed at the proximal end of the femur) and the initial knee flexion angle on the lower limb injury outcome. In total, 18 tests were conducted on 18 legs from 9 Post Mortem Human Subjects (PMHS). The principle of these tests was to impact the leg at 40 kph using a sled equipped with 3 crushing steel tubes, the stiffness of which were representative of the front face of a European sedan (bonnet leading edge, bumper and spoiler). The mass of the equipped sled was 74.5 kg. The test matrix was designed to perform 4 tests in 4 configurations combining two upper body masses (either 0 or 3 kg) and two knee angles (0 or 20 degrees) at 40 kph (11 m/s) plus 2 tests at 9 m/s. Autopsies were performed on the lower limbs and an injury assessment was established. The findings of this study were first that the increase of the upper body mass resulted in more severe injuries, second that an initial flexion of the knee, corresponding to its natural position during the gait cycle, decreased the severity of the injuries, and third that based on the injury outcome, a test conducted with no upper body mass and the knee fully extended was as severe as a test conducted with a 3 kg upper body mass and an initial knee flexion of 20°.

Effect of Initial FeO Content and CaO:SiO2 Ratio on the Reduction Smelting Kinetics of the CaO-SiO2-MgOsatd.-FeO Slag System

NASA Astrophysics Data System (ADS)

Kim, Jong Bae; Sohn, Il

2018-02-01

The effect of the initial FeO content and CaO:SiO2 ratio (CaO mass pct/SiO2 mass pct) on the reduction smelting of FeO with carbon flake addition is investigated in the CaO-MgOsatd.-SiO2-FeO slag system at 1823 K (1550 °C). Carbon rapidly reacted with FeO in the molten slag, causing both foaming and compositional changes in the slag. As FeO is reduced, the MgO saturation is modified, and solid precipitants, including MgO and other complex oxides, were observed, which significantly affected the slag properties, including the viscosity and foaming behavior. The solid-phase fraction and viscosity were estimated from changes in the measured FeO content over time using the thermochemical software FactSage. The iron recovery, which is distinguished from the amount of reduced Fe droplets, showed opposite behavior to the measured maximum foaming height and modified foaming index. According to the FeO mass transfer coefficient considering slag foaming at various initial FeO contents and CaO:SiO2 ratios, the reduction rate was optimal at higher initial FeO contents and a CaO:SiO2 ratio of 2.0, which did not correspond to the optimal iron recovery at an initial FeO content of 44 mass pct and above and a CaO:SiO2 ratio of 1.2. The results showed that slag foaming may increase the reduction kinetics, but the slag composition needs to be optimized for greater iron recovery.

Four new iron meteorite finds

NASA Technical Reports Server (NTRS)

Scott, E. R. D.; Wasson, J. T.; Bild, R. W.

1977-01-01

Four new iron meteorites are described: Buenaventura (IIIB) from Chihuahua, Mexico: mass 114 kg; Denver City (anomalous) from Texas, USA: mass 26.1 kg; Kinsella (IIIB) from Alberta, Canada: mass 3.7 kg; and Tacoma (IA) from Washington, USA: mass 17 g. Denver City is unique - i.e., not related to any other known iron. Tacoma is the smallest iron meteorite recorded. The meteorites were initially discovered in 1969, 1975, 1946, and between 1925 and 1932, respectively.

The Application of an Emerging Technique for Protein–Protein Interaction Interface Mapping: The Combination of Photo-Initiated Cross-Linking Protein Nanoprobes with Mass Spectrometry

PubMed Central

Ptáčková, Renata; Ječmen, Tomáš; Novák, Petr; Hudeček, Jiří; Stiborová, Marie; Šulc, Miroslav

2014-01-01

Protein–protein interaction was investigated using a protein nanoprobe capable of photo-initiated cross-linking in combination with high-resolution and tandem mass spectrometry. This emerging experimental approach introduces photo-analogs of amino acids within a protein sequence during its recombinant expression, preserves native protein structure and is suitable for mapping the contact between two proteins. The contact surface regions involved in the well-characterized interaction between two molecules of human 14-3-3ζ regulatory protein were used as a model. The employed photo-initiated cross-linking techniques extend the number of residues shown to be within interaction distance in the contact surface of the 14-3-3ζ dimer (Gln8–Met78). The results of this study are in agreement with our previously published data from molecular dynamic calculations based on high-resolution chemical cross-linking data and Hydrogen/Deuterium exchange mass spectrometry. The observed contact is also in accord with the 14-3-3ζ X-ray crystal structure (PDB 3dhr). The results of the present work are relevant to the structural biology of transient interaction in the 14-3-3ζ protein, and demonstrate the ability of the chosen methodology (the combination of photo-initiated cross-linking protein nanoprobes and mass spectrometry analysis) to map the protein-protein interface or regions with a flexible structure. PMID:24865487

The effects of the initial mass function on the chemical evolution of elliptical galaxies

NASA Astrophysics Data System (ADS)

De Masi, Carlo; Matteucci, F.; Vincenzo, F.

2018-03-01

We describe the use of our chemical evolution model to reproduce the abundance patterns observed in a catalogue of elliptical galaxies from the Sloan Digital Sky Survey Data Release 4. The model assumes ellipticals form by fast gas accretion, and suffer a strong burst of star formation followed by a galactic wind, which quenches star formation. Models with fixed initial mass function (IMF) failed in simultaneously reproducing the observed trends with the galactic mass. So, we tested a varying IMF; contrary to the diffused claim that the IMF should become bottom heavier in more massive galaxies, we find a better agreement with data by assuming an inverse trend, where the IMF goes from being bottom heavy in less massive galaxies to top heavy in more massive ones. This naturally produces a downsizing in star formation, favouring massive stars in largest galaxies. Finally, we tested the use of the integrated Galactic IMF, obtained by averaging the canonical IMF over the mass distribution function of the clusters where star formation is assumed to take place. We combined two prescriptions, valid for different SFR regimes, to obtain the Integrated Initial Mass Function values along the whole evolution of the galaxies in our models. Predicted abundance trends reproduce the observed slopes, but they have an offset relative to the data. We conclude that bottom-heavier IMFs do not reproduce the properties of the most massive ellipticals, at variance with previous suggestions. On the other hand, an IMF varying with galactic mass from bottom heavier to top heavier should be preferred.

Period of an Interrupted Pendulum

NASA Astrophysics Data System (ADS)

Miller, Bradley E.

2002-11-01

While demonstrating a classic conservation-of-energy problem to my AP Physics students, I became curious about the periodic motion that ensued for certain initial conditions. The original problem consists of releasing a mass at the end of a string from an initial position horizontal to the plane of a table. The string comes in contact with a peg some distance below the point where the string is attached at the top. One is asked to find what minimum fraction of the string's length should the peg be placed to have the mass complete a circle about the peg. However, when the mass is released from much lower heights, the system undergoes periodic motion that can be thought of as an interrupted pendulum.

VizieR Online Data Catalog: Stellar yields and the initial mass function (Molla+, 2015)

NASA Astrophysics Data System (ADS)

Molla, M.; Cavichia, O.; Gavilan, M.; Gibson, B. K.

2017-10-01

These tables give the theoretical chemical evolution models applied for the Milky Way Galaxy (MWG) from the cited paper. Basically give tables 2, 4 of stellar yields used and results of table 6 for the 144 models computed that work. Tables 2 and 4 give the stellar yields q_i(m) and remmnant mass for low and intermediate stars and massive stars, respectively, in a similar format for all authors. Table 6 gives the value of Chi2 for the 144 models computed for MWG using those stellar yields and different Initial Mass Function (see paper). Moreover, we give the table with results of the present time state of the Galactic disk for these 144 models. (12 data files).

40 CFR 63.4961 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2014 CFR

2014-07-01

... controlled coating operation during the compliance period, kg. AI = Total mass of organic HAP in the coatings... the controlled coating operation in Equation 1D of this section. ER23MY03.028 Where: AI = Total mass...

40 CFR 63.4961 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2012 CFR

2012-07-01

... controlled coating operation during the compliance period, kg. AI = Total mass of organic HAP in the coatings... the controlled coating operation in Equation 1D of this section. ER23MY03.028 Where: AI = Total mass...

The evolution of rotating very massive stars with LMC composition

NASA Astrophysics Data System (ADS)

Köhler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Gräfener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2015-01-01

Context. With growing evidence for the existence of very massive stars at subsolar metallicity, there is an increased need for corresponding stellar evolution models. Aims: We present a dense model grid with a tailored input chemical composition appropriate for the Large Magellanic Cloud (LMC). Methods: We use a one-dimensional hydrodynamic stellar evolution code, which accounts for rotation, transport of angular momentum by magnetic fields, and stellar wind mass loss to compute our detailed models. We calculate stellar evolution models with initial masses from 70 to 500 M⊙ and with initial surface rotational velocities from 0 to 550 km s-1, covering the core-hydrogen burning phase of evolution. Results: We find our rapid rotators to be strongly influenced by rotationally induced mixing of helium, with quasi-chemically homogeneous evolution occurring for the fastest rotating models. Above 160 M⊙, homogeneous evolution is also established through mass loss, producing pure helium stars at core hydrogen exhaustion independent of the initial rotation rate. Surface nitrogen enrichment is also found for slower rotators, even for stars that lose only a small fraction of their initial mass. For models above ~150 M⊙ at zero age, and for models in the whole considered mass range later on, we find a considerable envelope inflation due to the proximity of these models to their Eddington limit. This leads to a maximum ZAMS surface temperature of ~56 000 K, at ~180 M⊙, and to an evolution of stars in the mass range 50 M⊙...100 M⊙ to the regime of luminous blue variables in the Hertzsprung-Russell diagram with high internal Eddington factors. Inflation also leads to decreasing surface temperatures during the chemically homogeneous evolution of stars above ~180 M⊙. Conclusions: The cool surface temperatures due to the envelope inflation in our models lead to an enhanced mass loss, which prevents stars at LMC metallicity from evolving into pair-instability supernovae. The corresponding spin-down will also prevent very massive LMC stars to produce long-duration gamma-ray bursts, which might, however, originate from lower masses. The dataset of the presented stellar evolution models is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A71Appendices are available in electronic form at http://www.aanda.org

Mathematical modeling of forest fire initiation in three dimensional setting

Treesearch

Valeriy Perminov

2007-01-01

In this study, the assignment and theoretical investigations of the problems of forest fire initiation were carried out, including development of a mathematical model for description of heat and mass transfer processes in overterrestrial layer of atmosphere at crown forest fire initiation, taking into account their mutual influence. Mathematical model of forest fire...

Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

NASA Astrophysics Data System (ADS)

Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

2017-04-01

The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

Mass-Luminosity Relations for Rapid and Slow Rotators.

NASA Astrophysics Data System (ADS)

Malkov, O. Yu.

2006-08-01

Comparing the radii of eclipsing binaries components and single stars we have found a noticeable difference between observational parameters of B0V-G0V components of eclipsing binaries and those of single stars of the corresponding spectral type. This difference was confirmed by re-analysing the results of independent investigations published in the literature. Larger radii and higher temperatures of A-F eclipsing binaries can be explained by synchronization of such stars in close systems that prevents them to rotate rapidly. So, we have found that the mass-luminosity relation based on eclipsing binary data cannot be used to derive the initial mass function of single stars. While our current knowledge of the empirical mass-luminosity relation for intermediate-mass (1.5 to 10 m[*]) stars is based exclusively on data from eclipsing binaries, knowledge of the mass-luminosity relation should come from dynamical mass determinations of visual binaries, combined with spatially resolved precise photometry. Then the initial mass function should be revised for m>1.5m[*]. Data were collected on fundamental parameters of stars with masses m > 1.5.m [*]). They are components of binaries with P > 15^d and consequently are not synchronised with the orbital periods and presumably are rapid rotators. These stars are believed to evolve similarly with single stars, so these data allow us to construct mass-luminosity and other relations that can more confidently be used for statistical and astrophysical investigations of single stars than so called standard relations, based on data on detached main-sequence double-lined short-period eclipsing binaries. Mass-luminosity, mass-temperature and mass-radius relations of single stars are presented, as well as their HR diagram.

Formation of a black hole in the dark.

PubMed

Mirabel, I Félix; Rodrigues, Irapuan

2003-05-16

We show that the black hole in the x-ray binary Cygnus X-1 was formed in situ and did not receive an energetic trigger from a nearby supernova. The progenitor of the black hole had an initial mass greater than 40 solar masses, and during the collapse to form the approximately 10-solar mass black hole of Cygnus X-1, the upper limit for the mass that could have been suddenly ejected is approximately 1 solar mass, much less than the mass ejected in a supernova. The observations suggest that high-mass stellar black holes may form promptly, when massive stars disappear silently.

No energy equipartition in globular clusters

NASA Astrophysics Data System (ADS)

Trenti, Michele; van der Marel, Roeland

2013-11-01

It is widely believed that globular clusters evolve over many two-body relaxation times towards a state of energy equipartition, so that velocity dispersion scales with stellar mass as σ ∝ m-η with η = 0.5. We show here that this is incorrect, using a suite of direct N-body simulations with a variety of realistic initial mass functions and initial conditions. No simulated system ever reaches a state close to equipartition. Near the centre, the luminous main-sequence stars reach a maximum ηmax ≈ 0.15 ± 0.03. At large times, all radial bins convergence on an asymptotic value η∞ ≈ 0.08 ± 0.02. The development of this `partial equipartition' is strikingly similar across our simulations, despite the range of different initial conditions employed. Compact remnants tend to have higher η than main-sequence stars (but still η < 0.5), due to their steeper (evolved) mass function. The presence of an intermediate-mass black hole (IMBH) decreases η, consistent with our previous findings of a quenching of mass segregation under these conditions. All these results can be understood as a consequence of the Spitzer instability for two-component systems, extended by Vishniac to a continuous mass spectrum. Mass segregation (the tendency of heavier stars to sink towards the core) has often been studied observationally, but energy equipartition has not. Due to the advent of high-quality proper motion data sets from the Hubble Space Telescope, it is now possible to measure η for real clusters. Detailed data-model comparisons open up a new observational window on globular cluster dynamics and evolution. A first comparison of our simulations to observations of Omega Cen yields good agreement, supporting the view that globular clusters are not generally in energy equipartition. Modelling techniques that assume equipartition by construction (e.g. multi-mass Michie-King models) are approximate at best.

The optimally sampled galaxy-wide stellar initial mass function. Observational tests and the publicly available GalIMF code

NASA Astrophysics Data System (ADS)

Yan, Zhiqiang; Jerabkova, Tereza; Kroupa, Pavel

2017-11-01

Here we present a full description of the integrated galaxy-wide initial mass function (IGIMF) theory in terms of the optimal sampling and compare it with available observations. Optimal sampling is the method we use to discretize the IMF deterministically into stellar masses. Evidence indicates that nature may be closer to deterministic sampling as observations suggest a smaller scatter of various relevant observables than random sampling would give, which may result from a high level of self-regulation during the star formation process. We document the variation of IGIMFs under various assumptions. The results of the IGIMF theory are consistent with the empirical relation between the total mass of a star cluster and the mass of its most massive star, and the empirical relation between the star formation rate (SFR) of a galaxy and the mass of its most massive cluster. Particularly, we note a natural agreement with the empirical relation between the IMF power-law index and the SFR of a galaxy. The IGIMF also results in a relation between the SFR of a galaxy and the mass of its most massive star such that, if there were no binaries, galaxies with SFR < 10-4M⊙/yr should host no Type II supernova events. In addition, a specific list of initial stellar masses can be useful in numerical simulations of stellar systems. For the first time, we show optimally sampled galaxy-wide IMFs (OSGIMF) that mimic the IGIMF with an additional serrated feature. Finally, a Python module, GalIMF, is provided allowing the calculation of the IGIMF and OSGIMF dependent on the galaxy-wide SFR and metallicity. A copy of the python code model is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A126

Initial mass function of planetesimals formed by the streaming instability

NASA Astrophysics Data System (ADS)

Schäfer, Urs; Yang, Chao-Chin; Johansen, Anders

2017-01-01

The streaming instability is a mechanism to concentrate solid particles into overdense filaments that undergo gravitational collapse and form planetesimals. However, it remains unclear how the initial mass function of these planetesimals depends on the box dimensions of numerical simulations. To resolve this, we perform simulations of planetesimal formation with the largest box dimensions to date, allowing planetesimals to form simultaneously in multiple filaments that can only emerge within such large simulation boxes. In our simulations, planetesimals with sizes between 80 km and several hundred kilometers form. We find that a power law with a rather shallow exponential cutoff at the high-mass end represents the cumulative birth mass function better than an integrated power law. The steepness of the exponential cutoff is largely independent of box dimensions and resolution, while the exponent of the power law is not constrained at the resolutions we employ. Moreover, we find that the characteristic mass scale of the exponential cutoff correlates with the mass budget in each filament. Together with previous studies of high-resolution simulations with small box domains, our results therefore imply that the cumulative birth mass function of planetesimals is consistent with an exponentially tapered power law with a power-law exponent of approximately -1.6 and a steepness of the exponential cutoff in the range of 0.3-0.4.

Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity

NASA Astrophysics Data System (ADS)

Marks, Michael; Kroupa, Pavel; Dabringhausen, Jörg; Pawlowski, Marcel S.

2012-05-01

Residual-gas expulsion after cluster formation has recently been shown to leave an imprint in the low-mass present-day stellar mass function (PDMF) which allowed the estimation of birth conditions of some Galactic globular clusters (GCs) such as mass, radius and star formation efficiency. We show that in order to explain their characteristics (masses, radii, metallicity and PDMF) their stellar initial mass function (IMF) must have been top heavy. It is found that the IMF is required to become more top heavy the lower the cluster metallicity and the larger the pre-GC cloud-core density are. The deduced trends are in qualitative agreement with theoretical expectation. The results are consistent with estimates of the shape of the high-mass end of the IMF in the Arches cluster, Westerlund 1, R136 and NGC 3603, as well as with the IMF independently constrained for ultra-compact dwarf galaxies (UCDs). The latter suggests that GCs and UCDs might have formed along the same channel or that UCDs formed via mergers of GCs. A Fundamental Plane is found which describes the variation of the IMF with density and metallicity of the pre-GC cloud cores. The implications for the evolution of galaxies and chemical enrichment over cosmological times are expected to be major.

Enhancement of the Accretion of Jupiters Core by a Voluminous Low-Mass Envelope

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; D'angelo, Gennaro; Weidenschilling, Stuart John; Bodenheimer, Peter; Hubickyj, Olenka

2013-01-01

We present calculations of the early stages of the formation of Jupiter via core nucleated accretion and gas capture. The core begins as a seed body of about 350 kilometers in radius and orbits in a swarm of planetesimals whose initial radii range from 15 meters to 100 kilometers. We follow the evolution of the swarm by accounting for growth and fragmentation, viscous and gravitational stirring, and for drag-induced migration and velocity damping. Gas capture by the core substantially enhances the cross-section of the planet for accretion of small planetesimals. The dust opacity within the atmosphere surrounding the planetary core is computed self-consistently, accounting for coagulation and sedimentation of dust particles released in the envelope as passing planetesimals are ablated. The calculation is carried out at an orbital semi-major axis of 5.2 AU and an initial solids' surface density of 10/g/cm^2 at that distance. The results give a core mass of 7 Earth masses and an envelope mass of approximately 0.1 Earth mass after 500,000 years, at which point the envelope growth rate surpasses that of the core. The same calculation without the envelope gives a core mass of only 4 Earth masses.

40 CFR 63.3151 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... paragraph (d) of this section. (a) Determine the mass fraction of organic HAP for each material used. You must determine the mass fraction of organic HAP for each material used during the compliance period by... 40 CFR part 63). You may use Method 311 for determining the mass fraction of organic HAP. Use the...

40 CFR 63.4321 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... dyeing or finishing material with a mass fraction of organic HAP that exceeds the applicable emission... fraction of organic HAP for each material. You must determine the mass fraction of organic HAP for each... (appendix A to 40 CFR part 63). You may use Method 311 for determining the mass fraction of organic HAP. Use...

40 CFR 63.3531 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating and... coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. m = Number of...,j = Density of thinner, j, kg per liter. Wt,j = Mass fraction of organic HAP in thinner, j, kg...

40 CFR 63.4321 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2012 CFR

2012-07-01

... dyeing or finishing material with a mass fraction of organic HAP that exceeds the applicable emission... fraction of organic HAP for each material. You must determine the mass fraction of organic HAP for each... (appendix A to 40 CFR part 63). You may use Method 311 for determining the mass fraction of organic HAP. Use...

40 CFR 63.3531 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2014 CFR

2014-07-01

... fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating and... coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. m = Number of...,j = Density of thinner, j, kg per liter. Wt,j = Mass fraction of organic HAP in thinner, j, kg...

40 CFR 63.3531 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2013 CFR

2013-07-01

... fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating and... coating. Wc,i = Mass fraction of organic HAP in coating, i, kg organic HAP per kg coating. m = Number of...,j = Density of thinner, j, kg per liter. Wt,j = Mass fraction of organic HAP in thinner, j, kg...

40 CFR 63.3531 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2011 CFR

2011-07-01

... be performed with either metric or English units. (a) Determine the mass fraction of organic HAP for each material. Determine the mass fraction of organic HAP for each coating and thinner used during each... thinner, j, kg per liter. Wt,j = Mass fraction of organic HAP in thinner, j, kg organic HAP per kg thinner...

Initial fungal colonizer affects mass loss and fungal community development in Picea abies logs 6 yr after inoculation

Treesearch

Daniel L. Lindner; Rimvydas Vasaitis; Ariana Kubartova; Johan Allmer; Hanna Johannesson; Mark T. Banik; Jan. Stenlid

2011-01-01

Picea abies logs were inoculated with Resinicium bicolor, Fomitopsis pinicola or left un-inoculated and placed in an old-growth boreal forest. Mass loss and fungal community data were collected after 6 yr to test whether simplification of the fungal community via inoculation affects mass loss and fungal community development. Three...

40 CFR 63.4751 - How do I demonstrate initial compliance with the emission limitations?

Code of Federal Regulations, 2013 CFR

2013-07-01

... mass of organic HAP emissions during the month, grams. A = Total mass of organic HAP in the coatings used during the month, grams, as calculated in Equation 1A of this section. B = Total mass of organic HAP in the thinners used during the month, grams, as calculated in Equation 1B of this section. C...

Initiatives and Challenges in Consequence Management after a WMD Attack

DTIC Science & Technology

2004-08-01

Challenges in Consequence Management people to seek shelter or other protection when possible, to avoid exposure to weapons of mass destruction effects . The...Potential Effects .........................................9 V. Methods for Managing the Consequences of WMD Use.................14 VI. Toward a...mass destruction (WMD). Consequence management1 is a process to mitigate the effects of the use of weapons of mass destruction, including

Incidence Rates of Sexual Harassment in Mass Communications Internship Programs: An Initial Study Comparing Intern, Student, and Professional Rates.

ERIC Educational Resources Information Center

Bowen, Michelle; Laurion, Suzanne

A study documented, using a telephone survey, the incidence rates of sexual harassment of mass communication interns, and compared those rates to student and professional rates. A probability sample of 44 male and 52 female mass communications professionals was generated using several random sampling techniques from among professionals who work in…

Star Formation in NGC 4631

NASA Astrophysics Data System (ADS)

Smith, A. M.; Collins, N. R.; Bohlin, R.; Fanelli, M. N.; Neff, S. G.; O'Connell, R. W.; Roberts, M. S.; Stecher, T. P.; Waller, W. H.

1997-12-01

The group of galaxies including NGC 4631 provides an outstanding example of a galaxy interaction accompanied by intensive star formation. FUV imagery, recorded by the Ultraviolet Imaging Telescope (UIT), exhibits very bright far- ultraviolet (FUV) emission corresponding to the H II regions cataloged by Crillon and Monet (1969). This data is, in our experience, extraordinary in that NCG 4631 is observed nearly edge-on and strong attenuation of FUV light could be anticipated. Analysis of the ultraviolet imagery together with ground-based data leads to the following conclusions. The average extinction internal to the bright FUV regions is low [E(B--V) = 0.31], which combined with the optical morphology implies that the FUV bright regions are close to the edge of the galactic disk. The FUV luminosity of that part of the galaxy which can be observed is 8.2 x 10(40) ergs/s and is about a factor 6 less than the FUV luminosities of M101 and M83. FUV colors, M152-U, M152-B and M152-V, when compared to the predicted colors from cluster formation models utilizing a Salpeter IMF imply an internal extinction like that of a non-30Dor LMC extinction curve (Fitzpatrick 1985). Instantaneous burst models indicate an average age of the FUV bright regions of about 6 Myr and a total created stellar mass of 2.8 x 10(7) Msun . If the measured colors are compared to continuous star formation models, star formation beginning about 100 Myr in the past and continuing to the present with a total star formation rate in the FUV bright regions of 0.026 Msun /yr is implied. The total number of OB stars in the H II regions comprising the large ring in the eastern part of the galaxy (Rand's Shell #1, 1993) is inferred to be 20,000. This number can be compared to Rand's estimate of 10,000 to 35,000 supernova-producing OB stars which are required to impart momentum to an expanding shell of hydrogen gas.

CO outflows from high-mass Class 0 protostars in Cygnus-X

NASA Astrophysics Data System (ADS)

Duarte-Cabral, A.; Bontemps, S.; Motte, F.; Hennemann, M.; Schneider, N.; André, Ph.

2013-10-01

Context. The earliest phases of the formation of high-mass stars are not well known. It is unclear whether high-mass cores in monolithic collapse exist or not, and what the accretion process and origin of the material feeding the precursors of high-mass stars are. As outflows are natural consequences of the accretion process, they represent one of the few (indirect) tracers of accretion. Aims: We aim to search for individual outflows from high-mass cores in Cygnus X and to study the characteristics of the detected ejections. We compare these to what has been found for the low-mass protostars, to understand how ejection and accretion change and behave with final stellar mass. Methods: We used CO (2-1) PdBI observations towards six massive dense clumps, containing a total of 9 high-mass cores. We estimated the bolometric luminosities and masses of the 9 high-mass cores and measured the energetics of outflows. We compared our sample to low-mass objects studied in the literature and developed simple evolutionary models to reproduce the observables. Results: We find that 8 out of 9 high-mass cores are driving clear individual outflows. They are therefore true equivalents of Class 0 protostars in the high-mass regime. The remaining core, CygX-N53 MM2, has only a tentative outflow detection. It could be one of the first examples of a true individual high-mass prestellar core. We also find that the momentum flux of high-mass objects has a linear relation to the reservoir of mass in the envelope, as a scale up of the relations previously found for low-mass protostars. This suggests a fundamental proportionality between accretion rates and envelope masses. The linear dependency implies that the timescale for accretion is similar for high- and low-mass stars. Conclusions: The existence of strong outflows driven by high-mass cores in Cygnus X clearly indicates that high-mass Class 0 protostars exist. The collapsing envelopes of these Class 0 objects have similar sizes and a similar fragmentation scale to the low-mass equivalents, and have enough mass to directly form high-mass stars from a monolithic collapse. If the pre-collapse evolution is quasi-static, the fragmentation scale is expected to limit the size of the initial mass reservoirs for all masses leading to higher densities at birth and therefore shorter free-fall times for higher mass stars. However, we find the collapse timescales to be similar for both low- and high-mass objects. This implies that in a quasi-static view, we would require significant turbulent/magnetic support to slow down the collapse of the more massive envelopes. But with this support still to be discovered, and based on independent indications of large dynamics in pre-collapse gas for high-mass star formation, we propose that such an identical collapse timescale implies that the initial densities, which should set the duration of the collapse, should be similar for all masses. Since the fragmentation scale is identical for all masses, a lower initial density requires that the mass that incorporates massive stars has to have been accreted from larger scales than those of low-mass stars and in a dynamical way. Appendices are available in electronic form at http://www.aanda.org

20 CFR 416.1401 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-04-01

... Employees' Benefits SOCIAL SECURITY ADMINISTRATION SUPPLEMENTAL SECURITY INCOME FOR THE AGED, BLIND, AND... Council. Determination means the initial determination or the reconsidered determination. Mass change means a State-initiated change in the level(s) of federally administered State supplementary payments...

Clumps in the outer disk by disk instability: Why they are initially gas giants and the legacy of disruption

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Hayfield, Tristen; Mayer, Lucio; Durisen, Richard H.

2010-06-01

We explore the initial conditions for fragments in the extended regions (r≳50AU) of gravitationally unstable disks. We combine analytic estimates for the fragmentation of spiral arms with 3D SPH simulations to show that initial fragment masses are in the gas giant regime. These initial fragments will have substantial angular momentum, and should form disks with radii of a few AU. We show that clumps will survive for multiple orbits before they undergo a second, rapid collapse due to H 2 dissociation and that it is possible to destroy bound clumps by transporting them into the inner disk. The consequences of disrupted clumps for planet formation, dust processing, and disk evolution are discussed. We argue that it is possible to produce Earth-mass cores in the outer disk during the earliest phases of disk evolution.

Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

NASA Astrophysics Data System (ADS)

McGuire, Luke A.; Rengers, Francis K.; Kean, Jason W.; Staley, Dennis M.

2017-07-01

Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

USGS Publications Warehouse

McGuire, Luke; Rengers, Francis K.; Kean, Jason W.; Staley, Dennis M.

2017-01-01

Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

Stochasticity and predictability in terrestrial planet formation

NASA Astrophysics Data System (ADS)

Hoffmann, Volker; Grimm, Simon L.; Moore, Ben; Stadel, Joachim

2017-02-01

Terrestrial planets are thought to be the result of a vast number of gravitational interactions and collisions between smaller bodies. We use numerical simulations to show that practically identical initial conditions result in a wide array of final planetary configurations. This is a result of the chaotic evolution of trajectories which are highly sensitive to minuscule displacements. We determine that differences between systems evolved from virtually identical initial conditions can be larger than the differences between systems evolved from very different initial conditions. This implies that individual simulations lack predictive power. For example, there is not a reproducible mapping between the initial and final surface density profiles. However, some key global properties can still be extracted if the statistical spread across many simulations is considered. Based on these spreads, we explore the collisional growth and orbital properties of terrestrial planets, which assemble from different initial conditions (we vary the initial planetesimal distribution, planetesimal masses, and giant planet orbits.). Confirming past work, we find that the resulting planetary systems are sculpted by sweeping secular resonances. Configurations with giant planets on eccentric orbits produce fewer and more massive terrestrial planets on tighter orbits than those with giants on circular orbits. This is further enhanced if the initial mass distribution is biased to the inner regions. In all cases, the outer edge of the system is set by the final location of the ν6 resonance and we find that the mass distribution peaks at the ν5 resonance. Using existing observations, we find that extrasolar systems follow similar trends. Although differences between our numerical modelling and exoplanetary systems remain, we suggest that CoRoT-7, HD 20003 and HD 20781 may host undetected giant planets.

Sites in Mass. and Conn. are on EPA's Superfund Redevelopment Focus List

EPA Pesticide Factsheets

Today, the US EPA released its initial list of Superfund National Priorities List sites with the greatest expected redevelopment & commercial potential including two sites in New England: New Bedford Harbor in New Bedford, Mass. & Raymark Industries Inc.

40 CFR 63.4961 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2010 CFR

2010-07-01

... the compliance period, kg. AI = Total mass of organic HAP in the coatings used in the controlled... coating operation in Equation 1D of this section. ER23MY03.028 Where: AI = Total mass of organic HAP in...

Nano Icy Moons Propellant Harvester

NASA Technical Reports Server (NTRS)

VanWoerkom, Michael (Principal Investigator)

2017-01-01

As one of just a few bodies identified in the solar system with a liquid ocean, Europa has become a top priority in the search for life outside of Earth. However, cost estimates for exploring Europa have been prohibitively expensive, with estimates of a NASA Flagship class orbiter and lander approaching $5 billion. ExoTerra's NIMPH offers an affordable solution that can not only land, but return a sample from the surface to Earth. NIMPH combines solar electric propulsion (SEP) technologies being developed for the asteroid redirect mission and microsatellite electronics to reduce the cost of a full sample return mission below $500 million. A key to achieving this order-of-magnitude cost reduction is minimizing the initial mass of the system. The cost of any mission is directly proportional to its mass. By keeping the mission within the constraints of an Atlas V 551 launch vehicle versus an SLS, we can significantly reduce launch costs. To achieve this we reduce the landed mass of the sample return lander, which is the largest multiplier of mission mass, and shrink propellant mass through high efficiency SEP and gravity assists. The NIMPH projects first step in reducing landed mass focuses on development of a micro-In Situ Resource Utilization (micro-ISRU) system. ISRU allows us to minimize landed mass of a sample return mission by converting local ice into propellants. The project reduces the ISRU system to a CubeSat-scale package that weighs just 1.74 kg and consumes just 242 W of power. We estimate that use of this ISRU vs. an identical micro-lander without ISRU reduces fuel mass by 45 kg. As the dry mass of the lander grows for larger missions, these savings scale exponentially. Taking full advantage of the micro-ISRU system requires the development of a micro-liquid oxygen-liquid hydrogen engine. The micro-liquid oxygen-liquid hydrogen engine is tailored for the mission by scaling it to match the scale of the micro-lander and the low gravity of the target moon. We also tailor the engine for a near stoichiometric mixture ratio of 7.5. Most high-performance liquid oxygen-liquid hydrogen engines inject extra liquid hydrogen to lower the average molecular weight of the exhaust, which improves specific impulse. However, this extra liquid hydroden requires additional power and processing time on the surface for the ISRU to create. This increases mission cost, and on missions within high radiation environments such as Europa, increases radiation shielding mass. The resulting engine weighs just 1.36 kg and produces 71.5 newton of thrust at 364 s specific impulse. Finally, the mission reduces landed mass by taking advantage of the SEP modules solar power to beam energy to the surface using a collimated laser. This allows us to replace an 45 kg MMRTG with a 2.5 kg resonant array. By using the combination of ISRU, a liquid oxygen-liquid hydrogen engine, and beamed power, we reduce the initial mass of the lander to just 51.5 kg. When combined with an SEP module to ferry the lander to Europa the initial mission mass is just 6397 kg - low enough to be placed on an Earth escape trajectory using an Atlas V 551 launch vehicle. By comparison, we estimate a duplicate lander using an MMRTG and semi-storable propellants such as liquid oxygen-methane would result in an order of magnitude increase in initial lander mass to 445 kg. Attempting to perform the trajectory with a 450 s liquid oxygen-liquid hydrogen engine would increase initial mass to approximately 135,000 kg. Using an Atlas V 1 U.S. Dollar per kg rate to Earth escape value of $27.7k per kg, just the launch savings are over $3.5 billion.

Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy

NASA Astrophysics Data System (ADS)

Kuncarayakti, H.; Anderson, J. P.; Galbany, L.; Maeda, K.; Hamuy, M.; Aldering, G.; Arimoto, N.; Doi, M.; Morokuma, T.; Usuda, T.

2018-05-01

Context. Observationally, supernovae (SNe) are divided into subclasses according to their distinct characteristics. This diversity naturally reflects the diversity in the progenitor stars. It is not entirely clear, however, how different evolutionary paths leading massive stars to become an SN are governed by fundamental parameters such as progenitor initial mass and metallicity. Aims: This paper places constraints on progenitor initial mass and metallicity in distinct core-collapse SN subclasses through a study of the parent stellar populations at the explosion sites. Methods: Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a median distance of 18 Mpc has been collected and analysed, enabling detection and spectral extraction of the parent stellar population of SN progenitors. From the parent stellar population spectrum, the initial mass and metallicity of the coeval progenitor are derived by means of comparison to simple stellar population models and strong-line methods. Additionally, near-infrared IFS was employed to characterise the star formation history at the explosion sites. Results: No significant metallicity differences are observed among distinct SN types. The typical progenitor mass is found to be highest for SN type Ic, followed by type Ib, then types IIb and II. Type IIn is the least associated with young stellar populations and thus massive progenitors. However, statistically significant differences in progenitor initial mass are observed only when comparing SNe IIn with other subclasses. Stripped-envelope SN progenitors with initial mass estimates lower than 25 M⊙ are found; they are thought to be the result of binary progenitors. Confirming previous studies, these results support the notion that core-collapse SN progenitors cannot arise from single-star channels only, and both single and binary channels are at play in the production of core-collapse SNe. Near-infrared IFS suggests that multiple stellar populations with different ages may be present in some of the SN sites. As a consequence, there could be a non-negligible amount of contamination from old populations, and therefore the individual age estimates are effectively lower limits. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 089.D-0367, 091.D-0482, 093.D-0318, 094.D-0290, and 095.D-0172

Application of the double paddle oscillator for quantifying environmental, surface mass variation

NASA Astrophysics Data System (ADS)

Wei, Haoyan; Pomeroy, Joshua

2016-04-01

Sub-monolayer sensitivity to controlled gas adsorption and desorption is demonstrated using a double paddle oscillator (DPO) installed within an ultra-high vacuum (UHV) environmental chamber equipped with in situ film deposition, (multi)gas admission and temperature control. This effort is intended to establish a robust framework for quantitatively comparing mass changes due to gas loading and unloading on different materials systems selected or considered for use as mass artefacts. Our apparatus is composed of a UHV chamber with gas introduction and temperature control and in situ materials deposition for future materials testing enabling in situ preparation of virgin surfaces that can be monitored during initial exposure to gasses of interest. These tools are designed to allow us to comparatively evaluate how different materials gain or lose mass due to precisely controlled environmental excursions, with a long term goal of measuring changes in absolute mass. Herein, we provide a detailed experimental description of the apparatus, an evaluation of the initial performance, and demonstration measurements using nitrogen adsorption and desorption directly on the DPO.

Application of the double paddle oscillator for quantifying environmental, surface mass variation

PubMed Central

Wei, Haoyan; Pomeroy, Joshua

2016-01-01

Sub-monolayer sensitivity to controlled gas adsorption and desorption is demonstrated using a double paddle oscillator (DPO) installed within an UHV (ultra-high vacuum) environmental chamber equipped with in situ film deposition, (multi)gas admission and temperature control. This effort is intended to establish a robust framework for quantitatively comparing mass changes due to gas loading and unloading on different materials systems selected or considered for use as mass artifacts. Our apparatus is composed of a UHV chamber with gas introduction and temperature control and in-situ materials deposition for future materials testing enabling in situ preparation of virgin surfaces that can be monitored during initial exposure to gasses of interest. These tools are designed to allow us to comparatively evaluate how different materials gain or lose mass due to precisely controlled environmental excursions, with a long term goal of measuring changes in absolute mass. Herein, we provide a detailed experimental description of the apparatus, an evaluation of the initial performance, and demonstration measurements using nitrogen adsorption and desorption directly on the DPO. PMID:27212736

Journal: Efficient Hydrologic Tracer-Test Design for Tracer ...

EPA Pesticide Factsheets

Hydrological tracer testing is the most reliable diagnostic technique available for the determination of basic hydraulic and geometric parameters necessary for establishing operative solute-transport processes. Tracer-test design can be difficult because of a lack of prior knowledge of the basic hydraulic and geometric parameters desired and the appropriate tracer mass to release. A new efficient hydrologic tracer-test design (EHTD) methodology has been developed to facilitate the design of tracer tests by root determination of the one-dimensional advection-dispersion equation (ADE) using a preset average tracer concentration which provides a theoretical basis for an estimate of necessary tracer mass. The method uses basic measured field parameters (e.g., discharge, distance, cross-sectional area) that are combined in functional relatipnships that descrive solute-transport processes related to flow velocity and time of travel. These initial estimates for time of travel and velocity are then applied to a hypothetical continuous stirred tank reactor (CSTR) as an analog for the hydrological-flow system to develop initial estimates for tracer concentration, tracer mass, and axial dispersion. Application of the predicted tracer mass with the hydraulic and geometric parameters in the ADE allows for an approximation of initial sample-collection time and subsequent sample-collection frequency where a maximum of 65 samples were determined to be necessary for descri

Fall-Back Disks in Long and Short GRBS

NASA Technical Reports Server (NTRS)

Cannizo, John K.; Troja, E.; Gehrels, N.

2011-01-01

We present numerical time-dependent calculations for fall-back disks relevant for GRBs in which the disk of material surrounding the black hole (BH) powering the GRB jet modulates the mass flow, and hence the strength of the jet. Given the initial existence of a small mass appr oximately less than 10(exp -4) M(solar) near the progenitor with a circularization radius approximately 10(exp 10) - 10(exp 11) cm, an una voidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution in the initial fall-back disk traces the progenitor envelope, then a radius approximates 10(exp 11) cm gives a time scale app roximately 10(exp 4) s for the X-ray plateau. For late times t > 10(exp 7) s a steepening due to a cooling front in the disk may have obser vational support in GRB 060729. For short GRBs, one expects most of t he mass initially to lie at small radii < 10(exp 8) cm; however the presence of even a trace amount approximately 10(exp -9) M(solar) of hi gh angular material can give a brief plateau in the light curve.

Predictors of Energy Compensation during Exercise Interventions: A Systematic Review

PubMed Central

Riou, Marie-Ève; Jomphe-Tremblay, Simon; Lamothe, Gilles; Stacey, Dawn; Szczotka, Agnieszka; Doucet, Éric

2015-01-01

Weight loss from exercise-induced energy deficits is usually less than expected. The objective of this systematic review was to investigate predictors of energy compensation, which is defined as body energy changes (fat mass and fat-free mass) over the total amount of exercise energy expenditure. A search was conducted in multiple databases without date limits. Of 4745 studies found, 61 were included in this systematic review with a total of 928 subjects. The overall mean energy compensation was 18% ± 93%. The analyses indicated that 48% of the variance of energy compensation is explained by the interaction between initial fat mass, age and duration of exercise interventions. Sex, frequency, intensity and dose of exercise energy expenditure were not significant predictors of energy compensation. The fitted model suggested that for a shorter study duration, lower energy compensation was observed in younger individuals with higher initial fat mass (FM). In contrast, higher energy compensation was noted for younger individuals with lower initial FM. From 25 weeks onward, energy compensation was no longer different for these predictors. For studies of longer duration (about 80 weeks), the energy compensation approached 84%. Lower energy compensation occurs with short-term exercise, and a much higher level of energy compensation accompanies long-term exercise interventions. PMID:25988763

3-D MHD disk wind simulations of protostellar jets

NASA Astrophysics Data System (ADS)

Staff, Jan E.; Koning, Nico; Ouyed, Rachid; Tanaka, Kei; Tan, Jonathan C.

2016-01-01

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disk winds for different initial magnetic field configurations. The jets are followed from the source to distances, which are resolvable by HST and ALMA observations. Our simulations show that jets are heated along their length by many shocks. The mass of the protostar is a free parameter that can be inserted in the post processing of the data, and we apply the simulations to both low mass and high mass protostars. For the latter we also compute the expected diagnostics when the outflow is photoionized by the protostar. We compute the emission lines that are produced, and find excellent agreement with observations. For a one solar mass protostar, we find the jet width to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be 100 km s-1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. For the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disk (counter-rotating). This is not seen in the less open field configurations.

Preoperative fat-free mass: a predictive factor of weight loss after gastric bypass.

PubMed

Robert, Maud; Pelascini, Elise; Disse, Emmanuel; Espalieu, Philippe; Poncet, Gilles; Laville, Martine; Gouillat, Christian

2013-04-01

Weight loss failure occurs in 8% to 40% of patients after gastric bypass (GBP). The aim of our study was to analyse the predictive factors of weight loss at 1 year so as to select the best candidates for this surgery and reduce the failures. We included 73 patients treated by laparoscopic GBP. We retrospectively analysed the predictive factors of weight loss in kilograms as well as excess weight loss in percentage (EWL%) at 1 year. The population was divided into tertiles so as to compare the sub-group with the highest weight loss with the sub-group with the least satisfactory results. The significantly predictive factors of a better weight loss in kilograms were male, higher initial weight (144 versus 118 kg, p = 0.002), a significant early weight loss and a higher preoperative percentage of fat-free mass (FFM%; p = 0.03). A higher FFM% was also associated with a better EWL% (p = 0.004). The preoperative FFM (in kilograms) was the principal factor accounting for the weight loss at 1 year regardless of age, gender, height and initial body mass index (BMI; p < 0.0001). There was a better correlation between FFM and weight loss (Spearman test, p = 0.0001) than between initial BMI and weight loss (p = 0.016). We estimated weight loss at 1 year according to initial FFM using the formula: 0.5 kg of lost weight per kilogram of initial FFM. The initial FFM appears to be a decisive factor in the success of GBP. Thus, the sarcopoenic patients would appear to be less suitable candidates for this surgery.

Effect of hormone therapy on lean body mass, falls, and fractures: Six-year results from the Women’s Health Initiative Hormone Trials

PubMed Central

Bea, Jennifer W.; Zhao, Qiuhong; Cauley, Jane A.; LaCroix, Andrea Z.; Bassford, Tamsen; Lewis, Cora E.; Jackson, Rebecca D.; Tylavsky, Frances A.; Chen, Zhao

2010-01-01

Objective Loss of lean body mass with aging may contribute to falls and fractures. The objective of this analysis was to determine if taking postmenopausal hormone therapy (HT: estrogen plus progestogen therapy, EPT or estrogen therapy alone, ET) favorably affects age-related changes in lean body mass and if these changes partially account for decreased falls or fractures with HT. Methods Participants randomly assigned to either EPT (n=543) or control (n=471) and ET (n= 453) or control (n= 474) and receiving dual-energy X-ray absorptiometry (DXA) scans to estimate body composition during the Women’s Health Initiative (WHI) were evaluated. Falls and fracture occurrence were obtained by annual self-report. Fractures were confirmed by clinical chart review. Results At 6yrs post-randomization, lean body mass was not different between HT and control groups. Although lean body mass positively influenced BMD, independent of HT status, the preserved lean body mass observed in the HT arms in the first 3 years did not significantly contribute to models evaluating HT influence on falls and fractures between years 3 and 6. Women taking at least 80% of their medication in the HT arms demonstrated fewer falls compared to placebo; this difference was not attributable to change in lean body mass. Conclusions Despite early preservation of lean body mass with HT (3years), HT did not ameliorate long-term (6 years) loss in lean body mass with aging. PMID:20689466

Effect of hormone therapy on lean body mass, falls, and fractures: 6-year results from the Women's Health Initiative hormone trials.

PubMed

Bea, Jennifer W; Zhao, Qiuhong; Cauley, Jane A; LaCroix, Andrea Z; Bassford, Tamsen; Lewis, Cora E; Jackson, Rebecca D; Tylavsky, Frances A; Chen, Zhao

2011-01-01

Loss of lean body mass with aging may contribute to falls and fractures. The objective of this analysis was to determine if taking postmenopausal hormone therapy (or HT: estrogen plus progestogen therapy or estrogen therapy alone) favorably affects age-related changes in lean body mass and if these changes partially account for decreased falls or fractures with HT. Participants randomly assigned to either estrogen plus progestogen therapy (n = 543) or control (n = 471) and estrogen therapy alone (n = 453) or control (n = 474) and receiving dual-energy x-ray absorptiometry scans to estimate body composition during the Women's Health Initiative were evaluated. Falls and fracture occurrence were obtained by annual self-report. Fractures were confirmed by a clinical chart review. At 6 years postrandomization, lean body mass was not different between HT and control groups. Although lean body mass positively influenced bone mineral density, independent of HT status, the preserved lean body mass observed in the HT arms in the first 3 years did not significantly contribute to models evaluating HT influence on falls and fractures between years 3 and 6. Women taking at least 80% of their medication in the HT arms demonstrated fewer falls compared with placebo; this difference was not attributable to change in lean body mass. Despite early preservation of lean body mass with HT (3 y), HT did not ameliorate long-term (6 y) loss in lean body mass with aging.

Asymptotic analysis of quasilinear parabolic-hyperbolic equations describing the large longitudinal motion of a light viscoelastic bar with a heavy attachment

NASA Astrophysics Data System (ADS)

Yip, Shui Cheung

We study the longitudinal motion of a nonlinearly viscoelastic bar with one end fixed and the other end attached to a heavy tip mass. This problem is a precise continuum mechanical analog of the basic discrete mechanical problem of the motion of a mass point on a (massless) spring. This motion is governed by an initial-boundary-value problem for a class of third-order quasilinear parabolic-hyperbolic partial differential equations subject to a nonstandard boundary condition, which is the equation of motion of the tip mass. The ratio of the mass of the bar to that of the tip mass is taken to be a small parameter varepsilon. We prove that this problem has a unique regular solution that admits a valid asymptotic expansion, including an initial-layer expansion, in powers of varepsilon for varepsilon near 0. The fundamental constitutive hypothesis that the tension be a uniformly monotone function of the strain rate plays a critical role in a delicate proof that each term of the initial layer expansion decays exponentially in time. These results depend on new decay estimates for the solution of quasilinear parabolic equations. The constitutive hypothesis that the viscosity become large where the bar nears total compression leads to important uniform bounds for the strain and the strain rate. Higher-order energy estimates support the proof by the Schauder Fixed-Point Theorem of the existence of solutions having a level of regularity appropriate for the asymptotics.

Development of a quadrupole-based Secondary-Ion Mass Spectrometry (SIMS) system at Lewis Research Center

NASA Technical Reports Server (NTRS)

Vargas-Aburto, Carlos; Aron, Paul R.; Liff, Dale R.

1990-01-01

The design, construction, and initial use of an ion microprobe to carry out secondary ion mass spectrometry (SIMS) of solid samples is reported. The system is composed of a differentially pumped custom-made UHV (Ultra High Vacuum) chamber, a quadrupole mass spectrometer and a telefocus A-DIDA ion gun with the capability of producing beams of Cesium, as well as inert and reactive gases. The computer control and acquisition of the data were designed and implemented using a personal computer with plug-in boards, and external circuitry built as required to suit the system needs. The software is being developed by using a FORTH-like language. Initial tests aimed at characterizing the system, as well as preliminary surface and depth-profiling studies are presently underway.

The magnetic field inside a protoplanetary disc gap opened by planets of different masses

NASA Astrophysics Data System (ADS)

Carballido, Augusto; Matthews, Lorin S.; Hyde, Truell W.

2017-12-01

We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets of various masses, with the aim of calculating the strength of the vertical magnetic field threading such gaps. We introduce a gravitational potential at the centre of a shearing box to compute the tidal interaction between the planets and the disc gas, which is turbulent due to the magnetorotational instability. Two types of simulations are executed: 1) In type 'Z', the initial magnetic field has only a uniform, vertical component, and ten planet masses between 0.66 and 6.64 thermal masses are used; 2) In type 'YZ', the initial magnetic field has both toroidal and vertical components, and five planet masses covering the same mass range are used. Our results show that, for low planet masses, higher values of the vertical magnetic field occur inside the gaps than outside, in agreement with the previous work. However, for massive planets, we find that the radial profiles of the field show dips near the gap centre. The interior of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values (i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one Hill radius from each planet show a moderate decrease with planet mass. These results are relevant for the magnetic structure of circumplanetary discs and their possible outflows, and may be refined to aid future observational efforts to infer planet masses from high-resolution polarimetric observations of discs with gaps.

The complex fluid dynamics of simple diffusion

NASA Astrophysics Data System (ADS)

Vold, Erik

2017-11-01

Diffusion as the mass transport process responsible for mixing fluids at the atomic level is often underestimated in its complexity. An initial discontinuity between two species of different atomic masses exhibits a mass density discontinuity under isothermal pressure equilibrium implying equal species molar densities. The self-consistent kinetic transport processes across such an interface leads to a zero sum of mass flux relative to the center of mass and so diffusion alone cannot relax an initially stationary mass discontinuity nor broaden the density profile at the interface. The diffusive mixing leads to a molar imbalance which drives a center of mass velocity which moves the heavier species toward the lighter species leading to the interfacial density relaxation. Simultaneously, the species non-zero molar flux modifies the pressure profile in a transient wave and in a local perturbation. The resulting center of mass velocity has two components; one, associated with the divergence of the flow, persists in the diffusive mixing region throughout the diffusive mixing process, and two, travelling waves at the front of the pressure perturbations propagate away from the mixing region. The momentum in these waves is necessary to maintain momentum conservation in the center of mass frame. Thus, in a number of ways, the diffusive mixing provides feedback into the small scale advective motions. Numerical methods which diffuse all species assuming P-T equilibrium may not recover the subtle dynamics of mass transport at an interface. Work performed by the LANS, LLC, under USDOE Contract No. DE-AC52-06NA25396, funded by the (ASC) Program.

Accuracy of Estimating Highly Eccentric Binary Black Hole Parameters with Gravitational-wave Detections

NASA Astrophysics Data System (ADS)

Gondán, László; Kocsis, Bence; Raffai, Péter; Frei, Zsolt

2018-03-01

Mergers of stellar-mass black holes on highly eccentric orbits are among the targets for ground-based gravitational-wave detectors, including LIGO, VIRGO, and KAGRA. These sources may commonly form through gravitational-wave emission in high-velocity dispersion systems or through the secular Kozai–Lidov mechanism in triple systems. Gravitational waves carry information about the binaries’ orbital parameters and source location. Using the Fisher matrix technique, we determine the measurement accuracy with which the LIGO–VIRGO–KAGRA network could measure the source parameters of eccentric binaries using a matched filtering search of the repeated burst and eccentric inspiral phases of the waveform. We account for general relativistic precession and the evolution of the orbital eccentricity and frequency during the inspiral. We find that the signal-to-noise ratio and the parameter measurement accuracy may be significantly higher for eccentric sources than for circular sources. This increase is sensitive to the initial pericenter distance, the initial eccentricity, and the component masses. For instance, compared to a 30 {M}ȯ –30 {M}ȯ non-spinning circular binary, the chirp mass and sky-localization accuracy can improve by a factor of ∼129 (38) and ∼2 (11) for an initially highly eccentric binary assuming an initial pericenter distance of 20 M tot (10 M tot).

40 CFR 63.7941 - How do I conduct a performance test, design evaluation, or other type of initial compliance...

Code of Federal Regulations, 2010 CFR

2010-07-01

... vent; Ei, Eo = Mass rate of total organic compounds (TOC) (minus methane and ethane) or total HAP, from... reduction for all affected process vents, percent Ei = Mass rate of TOC (minus methane and ethane) or total... uncontrolled vents, as calculated in this section, kilograms TOC per hour or kilograms HAP per hour; Eo = Mass...

Features of neutrino mixing

NASA Astrophysics Data System (ADS)

Chiu, S. H.; Kuo, T. K.

2018-03-01

The elements (squared) of the neutrino mixing matrix are found to satisfy, as functions of the induced mass, a set of differential equations. They show clearly the dominance of pole terms when the neutrino masses "cross." Using the known vacuum mixing parameters as initial conditions, it is found that these equations have very good approximate solutions, for all values of the induced mass. The results are applicable to long baseline experiments.

Low-mass stars in globular clusters. III. The mass function of 47 Tucanae.

NASA Astrophysics Data System (ADS)

de Marchi, G.; Paresce, F.

1995-12-01

We have used the WFPC2 on board HST to investigate the stellar population in a field located 4'6 E of the center of the globular cluster 47 Tuc (NGC 104), close to the half-mass radius, through wide band imaging at 606 and 812nm. A total of ~3000 stars are accurately classified by two-color photometry to form a color-magnitude diagram extending down to a limiting magnitude m_814_=~m_I_=~24. A rich cluster main sequence is detected spanning the range from m_814_=~18 through m_814_=~23, where it spreads considerably due to the increasing photometric uncertainty and galaxy contamination. A secondary sequence of objects is also detected, parallel to the main sequence, as expected for a population of binary stars. The measured binary fraction in the range 195%. The main sequence luminosity function obtained from the observed CMD increases with decreasing luminosity following a power-law trend with index α=~0.15 in the range 5

A High-Mass Cold Core in the Auriga-California Giant Molecular Cloud

NASA Astrophysics Data System (ADS)

Magnus McGehee, Peregrine; Paladini, Roberta; Pelkonen, Veli-Matti; Toth, Viktor; Sayers, Jack

2015-08-01

The Auriga-California Giant Molecular Cloud is noted for its relatively low star formation rate, especially at the high-mass end of the Initial Mass Function. We combine maps acquired by the Caltech Submillimeter Observatory's Multiwavelength Submillimeter Inductance Camera [MUSIC] in the wavelength range 0.86 to 2.00 millimeters with Planck and publicly-available Herschel PACS and SPIRE data in order to characterize the mass, dust properties, and environment of the bright core PGCC G163.32-8.41.

Ruprecht 106: The first single population globular cluster?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villanova, S.; Geisler, D.; Muñoz, C.

2013-12-01

All old Galactic globular clusters (GCs) studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars of the first. This process can happen if the initial mass of the cluster exceeds a threshold above which ejecta are retained and a second generation is formed. A determination of this mass threshold is mandatory in order to understand how GCs form. We analyzed nine red giant branch stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES@VLT2 spectrograph. Spectra cover a widemore » range and allowed us to measure abundances for light (O, Na, Mg, Al), α (Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and neutron-capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb) elements. Based on these abundances, we show that Ruprecht 106 is the first convincing example of a single-population GC (i.e., a true simple stellar population), although the sample is relatively small. This result is supported also by an independent photometric test and by the horizontal branch morphology and the dynamical state. It is old (∼12 Gyr) and, at odds with other GCs, has no α-enhancement. The material it formed from was contaminated by both s- and r-process elements. The abundance pattern points toward an extragalactic origin. Its present-day mass (M = 10{sup 4.83} M {sub ☉}) can be assumed as a strong lower limit for the initial mass threshold below which no second generation is formed. Clearly, its initial mass must have been significantly greater, but we have no current constraints on the amount of mass loss during its evolution.« less

The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

NASA Astrophysics Data System (ADS)

Capuzzo-Dolcetta, Roberto

1993-10-01

Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

A single-degenerate channel for the progenitors of Type Ia supernovae with different metallicities

NASA Astrophysics Data System (ADS)

Meng, X.; Chen, X.; Han, Z.

2009-06-01

A single-degenerate channel for the progenitors of Type Ia supernovae (SNe Ia) is currently accepted, in which a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit and then explodes as a SN Ia. Incorporating the prescription of Hachisu et al. for the accretion efficiency into Eggleton's stellar evolution code, and assuming that the prescription is valid for all metallicities, we performed binary stellar evolution calculations for more than 25000 close WD binaries with metallicities Z = 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.004, 0.001, 0.0003 and 0.0001. For our calculations, the companions are assumed to be unevolved or slightly evolved stars (WD + MS). As a result, the initial parameter spaces for SNe Ia at various Z are presented in the orbital period-secondary mass (logPi, Mi2) plane. Our study shows that both the initial mass of the secondary and the initial orbital period increase with metallicity. Thus, the minimum mass of the CO WD for SNe Ia decreases with metallicity Z. The difference in the minimum mass may be as large as 0.24Msolar for different Z. Adopting the results above, we studied the birth rate of SNe Ia for various Z via a binary population synthesis approach. If a single starburst is assumed, SNe Ia occur systemically earlier and the peak value of the birth rate is larger for a high Z. The Galactic birth rate from the WD + MS channel is lower than (but comparable to) that inferred from observations. Our study indicates that supernovae like SN2002ic will not occur in extremely low-metallicity environments, if the delayed dynamical-instability model is appropriate.

Mass selectivity of dipolar resonant excitation in a linear quadrupole ion trap.

PubMed

Douglas, D J; Konenkov, N V

2014-03-15

For mass analysis, linear quadrupole ion traps operate with dipolar excitation of ions for either axial or radial ejection. There have been comparatively few computer simulations of this process. We introduce a new concept, the excitation contour, S(q), the fraction of the excited ions that reach the trap electrodes when trapped at q values near that corresponding to the excitation frequency. Ion trajectory calculations are used to calculate S(q). Ions are given Gaussian distributions of initial positions in x and y, and thermal initial velocity distributions. To model gas damping, a drag force is added to the equations of motion. The effects of the initial conditions, ejection Mathieu parameter q, scan speed, excitation voltage and collisional damping, are modeled. We find that, with no buffer gas, the mass resolution is mostly determined by the excitation time and is given by R~dβ/dq qn, where β(q) determines the oscillation frequency, and n is the number of cycles of the trapping radio frequency during the excitation or ejection time. The highest resolution at a given scan speed is reached with the lowest excitation amplitude that gives ejection. The addition of a buffer gas can increase the mass resolution. The simulation results are in broad agreement with experiments. The excitation contour, S(q), introduced here, is a useful tool for studying the ejection process. The excitation strength, excitation time and buffer gas pressure interact in a complex way but, when set properly, a mass resolution R0.5 of at least 10,000 can be obtained at a mass-to-charge ratio of 609. Copyright © 2014 John Wiley & Sons, Ltd.