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Search Results: 1 - 10 of 350365 matches for " E. C. Hunter "
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Axisymmetric galaxy models wth central BHs, with an application to M32
E. E. Qian,P. T. de Zeeuw,R. P. van der Marel,C. Hunter
Physics , 1994, DOI: 10.1093/mnras/274.2.602
Abstract: The contour integral method of Hunter & Qian is applied to axisymmetric galaxy models in which the distribution function (DF) is of the form f=f(E,L_z), where E and L_z are the classical integrals of motion in an axisymmetric potential. A practical way to construct the unique even part of the DF for such systems is presented. It is applied to models, both oblate and prolate, in which the mass density is stratified on similar concentric spheroids. The spheroids with scale-free densities are discussed in detail. These provide useful approximations to the behaviour of more realistic models in the limit of small and large radii. The self-consistent case is treated, as well as the case in which there are additional contributions to the potential from a central black hole or dark halo. The range of axis ratios and density profile slopes is determined for which spheroidal power--law cusps with a central black hole have a physical two--integral DF. More generally, the f(E,L_z) DFs are discussed for a set of spheroidal `(alpha,beta)-models', characterized by a power-law density cusp with slope alpha at small radii, and a power-law density fall-off with slope [alpha + 2 beta] at large radii. As an application, the DF is constructed for the (alpha,beta) model with a 1.8 x 10^6 solar mass black hole used by van der Marel et al. to interpret their high spatial resolution spectroscopic data for M32. The results confirm that the model fits the observed line-of-sight velocity profiles remarkably well. The model is used to calculate predictions for future spectroscopic observations with the HST.
A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
C. J. Cyganowski,C. L. Brogan,T. R. Hunter,E. Churchwell
Physics , 2009, DOI: 10.1088/0004-637X/702/2/1615
Abstract: We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz methanol maser survey of a sample of ~20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 micron emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) images. These 4.5 micron-selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color IRAC images. The detection rate of 6.7 GHz Class II methanol masers, which are associated exclusively with massive YSOs, towards EGOs is greater than ~64%--nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz methanol masers, which trace molecular outflows, is ~89% towards EGOs associated with 6.7 GHz methanol masers. The two types of methanol masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 micron emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 micron features. We also present results of a complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular line survey of EGOs in the outflow tracers HCO+(3-2) and SiO(5-4). The HCO+ line profiles and high SiO detection rate (90%) are indicative of the presence of active outflows. No 44 GHz continuum emission is detected at the 5 mJy/beam (5 sigma) level towards 95% of EGOs surveyed, excluding bright ultracompact HII regions as powering sources for the 4.5 micron outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.
Deep Very Large Array Radio Continuum Surveys of GLIMPSE Extended Green Objects (EGOs)
C. J. Cyganowski,C. L. Brogan,T. R. Hunter,E. Churchwell
Physics , 2011, DOI: 10.1088/0004-637X/743/1/56
Abstract: We present the results of deep, high angular resolution Very Large Array (VLA) surveys for radio continuum emission towards a sample of 14 GLIMPSE Extended Green Objects (EGOs). Identified as massive young stellar object (MYSO) outflow candidates based on their extended 4.5 micron emission in Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz Class II and/or 44 GHz Class I methanol masers. No continuum is detected at 3.6 or 1.3 cm towards the majority (57%) of our targets (median rms ~0.03 and 0.25 mJy/beam). Only two EGOs are associated with optically thin emission consistent with ultracompact/compact HII regions. Both of these sources exhibit cm-wavelength multiplicity, with evidence that one of the less-evolved members may be driving the 4.5 micron outflow. Most of the other cm-wavelength EGO counterparts are weak (< 1 mJy), unresolved, undetected at 1.3 cm, and characterized by intermediate spectral indices consistent with hypercompact (HC) HII regions or ionized winds or jets. One EGO cm counterpart, likely an optically thick HC HII region, is detected only at 1.3 cm and is associated with hot core line emission and water and 6.7 GHz methanol masers. The results of our exceptionally sensitive survey indicate that EGOs signify an early stage of massive star formation, before photoionizing feedback from the central MYSO significantly influences the (proto)cluster environment. Actively driving outflows (and so, presumably, actively accreting), the surveyed EGOs are associated with significant clump-scale gas reservoirs, providing sufficient material for sustained, rapid accretion.
Bipolar Molecular Outflows and Hot Cores in GLIMPSE Extended Green Objects (EGOs)
C. J. Cyganowski,C. L. Brogan,T. R. Hunter,E. Churchwell,Q. Zhang
Physics , 2010, DOI: 10.1088/0004-637X/729/2/124
Abstract: We present high angular resolution Submillimeter Array (SMA) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of two GLIMPSE Extended Green Objects (EGOs)--massive young stellar object (MYSO) outflow candidates identified based on their extended 4.5 micron emission in Spitzer images. The mm observations reveal bipolar molecular outflows, traced by high-velocity 12CO(2-1) and HCO+(1-0) emission, coincident with the 4.5 micron lobes in both sources. SiO(2-1) emission confirms that the extended 4.5 micron emission traces active outflows. A single dominant outflow is identified in each EGO, with tentative evidence for multiple flows in one source (G11.92-0.61). The outflow driving sources are compact millimeter continuum cores, which exhibit hot-core spectral line emission and are associated with 6.7 GHz Class II methanol masers. G11.92-0.61 is associated with at least three compact cores: the outflow driving source, and two cores that are largely devoid of line emission. In contrast, G19.01-0.03 appears as a single MYSO. The difference in multiplicity, the comparative weakness of its hot core emission, and the dominance of its extended envelope of molecular gas all suggest that G19.01-0.03 may be in an earlier evolutionary stage than G11.92-0.61. Modeling of the G19.01-0.03 spectral energy distribution suggests that a central (proto)star (M ~10 Msun) has formed in the compact mm core (Mgas ~ 12-16 Msun), and that accretion is ongoing at a rate of ~10^-3 solar masses per year. Our observations confirm that these EGOs are young MYSOs driving massive bipolar molecular outflows, and demonstrate that considerable chemical and evolutionary diversity are present within the EGO sample.
Trophic Cascades Induced by Lobster Fishing Are Not Ubiquitous in Southern California Kelp Forests
Carla M. Guenther, Hunter S. Lenihan, Laura E. Grant, David Lopez-Carr, Daniel C. Reed
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0049396
Abstract: Fishing can trigger trophic cascades that alter community structure and dynamics and thus modify ecosystem attributes. We combined ecological data of sea urchin and macroalgal abundance with fishery data of spiny lobster (Panulirus interruptus) landings to evaluate whether: (1) patterns in the abundance and biomass among lobster (predator), sea urchins (grazer), and macroalgae (primary producer) in giant kelp forest communities indicated the presence of top-down control on urchins and macroalgae, and (2) lobster fishing triggers a trophic cascade leading to increased sea urchin densities and decreased macroalgal biomass. Eight years of data from eight rocky subtidal reefs known to support giant kelp forests near Santa Barbara, CA, USA, were analyzed in three-tiered least-squares regression models to evaluate the relationships between: (1) lobster abundance and sea urchin density, and (2) sea urchin density and macroalgal biomass. The models included reef physical structure and water depth. Results revealed a trend towards decreasing urchin density with increasing lobster abundance but little evidence that urchins control the biomass of macroalgae. Urchin density was highly correlated with habitat structure, although not water depth. To evaluate whether fishing triggered a trophic cascade we pooled data across all treatments to examine the extent to which sea urchin density and macroalgal biomass were related to the intensity of lobster fishing (as indicated by the density of traps pulled). We found that, with one exception, sea urchins remained more abundant at heavily fished sites, supporting the idea that fishing for lobsters releases top-down control on urchin grazers. Macroalgal biomass, however, was positively correlated with lobster fishing intensity, which contradicts the trophic cascade model. Collectively, our results suggest that factors other than urchin grazing play a major role in controlling macroalgal biomass in southern California kelp forests, and that lobster fishing does not always catalyze a top-down trophic cascade.
Public Health Response Systems In-Action: Learning from Local Health Departments’ Experiences with Acute and Emergency Incidents
Jennifer C. Hunter, Jane E. Yang, Adam W. Crawley, Laura Biesiadecki, Tomás J. Aragón
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079457
Abstract: As part of their core mission, public health agencies attend to a wide range of disease and health threats, including those that require routine, acute, and emergency responses. While each incident is unique, the number and type of response activities are finite; therefore, through comparative analysis, we can learn about commonalities in the response patterns that could improve predictions and expectations regarding the resources and capabilities required to respond to future acute events. In this study, we interviewed representatives from more than 120 local health departments regarding their recent experiences with real-world acute public health incidents, such as infectious disease outbreaks, severe weather events, chemical spills, and bioterrorism threats. We collected highly structured data on key aspects of the incident and the public health response, particularly focusing on the public health activities initiated and community partners engaged in the response efforts. As a result, we are able to make comparisons across event types, create response profiles, and identify functional and structural response patterns that have import for future public health preparedness and response. Our study contributes to clarifying the complexity of public health response systems and our analysis reveals the ways in which these systems are adaptive to the character of the threat, resulting in differential activation of functions and partners based on the type of incident. Continued and rigorous examination of the experiences of health departments throughout the nation will refine our very understanding of what the public health response system is, will enable the identification of organizational and event inputs to performance, and will allow for the construction of rich, relevant, and practical models of response operations that can be employed to strengthen public health systems.
General solution of the Jeans equations for triaxial galaxies with separable potentials
G. van de Ven,C. Hunter,E. K. Verolme,P. T. de Zeeuw
Physics , 2003, DOI: 10.1046/j.1365-8711.2003.06501.x
Abstract: The Jeans equations relate the second-order velocity moments to the density and potential of a stellar system. For general three-dimensional stellar systems, there are three equations and six independent moments. By assuming that the potential is triaxial and of separable Staeckel form, the mixed moments vanish in confocal ellipsoidal coordinates. Consequently, the three Jeans equations and three remaining non-vanishing moments form a closed system of three highly-symmetric coupled first-order partial differential equations in three variables. These equations were first derived by Lynden-Bell, over 40 years ago, but have resisted solution by standard methods. We present the general solution here. We consider the two-dimensional limiting cases first. We solve their Jeans equations by a new method which superposes singular solutions. The singular solutions, which are new, are standard Riemann-Green functions. The two-dimensional solutions are applied to non-axisymmetric discs, oblate and prolate spheroids, and also to the scale-free triaxial limit. We then extend the method of singular solutions to the triaxial case, and obtain a full solution. The general solution can be expressed in terms of complete (hyper)elliptic integrals which can be evaluated in a straightforward way, and provides the full set of second moments which can support a triaxial density distribution in a separable triaxial potential. (abridged)
The Stellar and Gas Kinematics of Several Irregular Galaxies
Deidre A. Hunter,Vera C. Rubin,Rob A. Swaters,Linda S. Sparke,Stephen E. Levine
Physics , 2002, DOI: 10.1086/343080
Abstract: We present long-slit spectra of three irregular galaxies from which we determinethe stellar kinematics in two of the galaxies (NGC 1156 and NGC 4449) and ionized-gas kinematics in all three (including NGC 2366). We compare this to the optical morphology and to the HI kinematics of the galaxies. In the ionized gas, we see a linear velocity gradient in all three galaxies. In NGC 1156 we also detect a weak linear velocity gradient in the stars of (5+/-1/sin i) km/s/kpc to a radius of 1.6 kpc. The stars and gas are rotating about the same axis, but this is different from the major axis of the stellar bar which dominates the optical light of the galaxy. In NGC 4449 we do not detect organized rotation of the stars and place an upper limit of (3/sin i) km/s/kpc to a radius of 1.2 kpc. For NGC 4449, which has signs of a past interaction with another galaxy, we develop a model to fit the observed kinematics of the stars and gas. In this model the stellar component is in a rotating disk seen nearly face-on while the gas is in a tilted disk with orbits whose planes precess in the gravitational potential. This model reproduces the apparent counter-rotation of the inner gas of the galaxy. The peculiar orbits of the gas are presumed due to acquisition of gas in the past interaction.
Electron elastic scattering and low-frequency bremsstrahlung on A@$C_{60}$: A model static approximation
V. K. Dolmatov,C. Bayens,M. B. Cooper,M. E. Hunter
Physics , 2015,
Abstract: Electron elastic-scattering phase shifts and cross sections along with the differential and total cross sections and polarization of low-frequency bremsstrahlung upon low-energy electron collision with endohedral fullerenes $A$@C$_{60}$ are theoretically scrutinized versus the nature, size and spin of the encapsulated atom $A$. The case-study-atoms $A$ are N, Ar, Cr, Mn, Mo, Tc, Xe, Ba, and Eu. They are thoughtfully picked out of different rows of the periodic table. The study is performed in the framework of a model static approximation. There, both the encapsulated atom $A$ and C$_{60}$ cage are regarded as non-polarizable targets. The C$_{60}$ cage is modeled by an attractive spherical annular potential well. The study provides the most complete initial understanding of how the processes of interest might evolve upon electron collision with various $A$@C$_{60}$. Calculated results identify the most interesting and/or useful future measurements or more rigorous calculations to perform.
Characteristics of Sleep in a Pediatric Population Seeking Mental Health Services  [PDF]
Kimberly E. Hunter, Michele S. Knox
Psychology (PSYCH) , 2017, DOI: 10.4236/psych.2017.814160
Abstract: This study explored characteristics of sleep and other presenting problems in children and adolescents seeking mental health services within an outpatient clinic. Primary caregivers seeking outpatient mental health services for their children between the ages of 2 - 18 completed a measure assessing various aspects of their children’s sleep, emotional and behavioral problems, and use of electronics at bedtime. Results showed reduced sleep durations compared to recommended guidelines. Results also indicated that sleep duration was negatively associated with the total number of problems listed for both the youngest and school aged groups. Children and adolescents with worries and fears, irritability, and mood swings had significantly less sleep, and participants with sadness had longer sleep latencies. Regarding use of electronics, participants with televisions in the bedroom reported significantly less hours of sleep than those without. The average number of hours of television watched per week was positively correlated with the number of minutes of sleep latency, while videogame usage was negatively correlated with sleep duration. The study results indicated that sleep disturbances are significant issues impacting youth who are experiencing mental health issues. These results also emphasize the importance of a thorough sleep assessment for children who present for mental health services.
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