2,119 research outputs found
Calcium-Rich Gap Transients: Tidal Detonations of White Dwarfs?
We hypothesize that at least some of the recently discovered class of
calcium-rich gap transients are tidal detonation events of white dwarfs (WDs)
by black holes (BHs) or possibly neutron stars. We show that the properties of
the calcium-rich gap transients agree well with the predictions of the tidal
detonation model. Under the predictions of this model, we use a follow-up X-ray
observation of one of these transients, SN 2012hn, to place weak upper limits
on the detonator mass of this system that include all intermediate-mass BHs
(IMBHs). As these transients are preferentially in the stellar haloes of
galaxies, we discuss the possibility that these transients are tidal
detonations of WDs caused by random flyby encounters with IMBHs in dwarf
galaxies or globular clusters. This possibility has been already suggested in
the literature but without connection to the calcium-rich gap transients. In
order for the random flyby cross-section to be high enough, these events would
have to be occurring inside these dense stellar associations. However, there is
a lack of evidence for IMBHs in these systems, and recent observations have
ruled out all but the very faintest dwarf galaxies and globular clusters for a
few of these transients. Another possibility is that these are tidal
detonations caused by three-body interactions, where a WD is perturbed toward
the detonator in isolated multiple star systems. We highlight a number of ways
this could occur, even in lower-mass systems with stellar-mass BHs or neutron
stars. Finally, we outline several new observational tests of this scenario,
which are feasible with current instrumentation.Comment: 10 pages, 1 figure, accepted for publication in MNRA
Processing time shifts affects the execution of motor responses
a b s t r a c t We explore whether time shifts in text comprehension are represented spatially. Participants read sentences involving past or future events and made sensibility judgment responses in one of two ways: (1) moving toward or away from their body and (2) pressing the toward or away buttons without moving. Previous work suggests that spatial compatibility effects should be observed, where the future is mapped onto responses away from the body, and the past is mapped onto responses toward the body. These effects were observed, but only when participants were moving to make their responses, and only for larger time shifts (e.g., a month)
The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
The carrier of the dust-associated photoluminescence process causing the
extended red emission (ERE) in many dusty interstellar environments remains
unidentified. Several competing models are more or less able to match the
observed broad, unstructured ERE band. We now constrain the character of the
ERE carrier further by determining the wavelengths of the radiation that
initiates the ERE. Using the imaging capabilities of the Hubble Space
Telescope, we have resolved the width of narrow ERE filaments appearing on the
surfaces of externally illuminated molecular clouds in the bright reflection
nebula NGC 7023 and compared them with the depth of penetration of radiation of
known wavelengths into the same cloud surfaces. We identify photons with
wavelengths shortward of 118 nm as the source of ERE initiation, not to be
confused with ERE excitation, however. There are strong indications from the
well-studied ERE in the Red Rectangle nebula and in the high-|b| Galactic
cirrus that the photon flux with wavelengths shortward of 118 nm is too small
to actually excite the observed ERE, even with 100% quantum efficiency. We
conclude, therefore, that ERE excitation results from a two-step process. While
none of the previously proposed ERE models can match these new constraints, we
note that under interstellar conditions most polycyclic aromatic hydrocarbon
(PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV
and that the electronic energy level structure of PAH di-cations is consistent
with fluorescence in the wavelength band of the ERE. Therefore, PAH di-cations
deserve further study as potential carriers of the ERE. (abridged)Comment: Accepted for Publication in the Ap
Normative Data for the NeuroCom Sensory Organization Test in US Military Special Operations Forces.
CONTEXT: Postural stability is the ability to control the center of mass in relation to a person\u27s base of support and can be affected by both musculoskeletal injury and traumatic brain injury. The NeuroCom Sensory Organization Test (SOT) can be used to objectively quantify impairments to postural stability. The ability of postural stability to predict injury and be used as an acute injury-evaluation tool makes it essential to the screening and rehabilitation process. To our knowledge, no published normative data for the SOT from a healthy, highly active population are available for use as a reference for clinical decision making.
OBJECTIVE: To present a normative database of SOT scores from a US Military Special Operations population that can be used for future comparison.
DESIGN: Cross-sectional study.
SETTING: Human performance research laboratory.
PATIENTS OR OTHER PARTICIPANTS: A total of 542 active military operators from Naval Special Warfare Combatant-Craft Crewmen (n = 149), Naval Special Warfare Command, Sea, Air, and Land (n = 101), US Army Special Operations Command (n = 171), and Air Force Special Operations Command (n = 121).
MAIN OUTCOME MEASURE(S): Participants performed each of the 6 SOT conditions 3 times. Scores for each condition, total equilibrium composite score, and ratio scores for the somatosensory, visual, and vestibular systems were recorded.
RESULTS: Differences were present across all groups for SOT conditions 1 (P \u3c .001), 2 (P = .001), 4 (P \u3e .001), 5 (P \u3e .001), and 6 (P = .001) and total equilibrium composite (P = .000), visual (P \u3e .001), vestibular (P = .002), and preference (P \u3e .001) NeuroCom scores.
CONCLUSIONS: Statistical differences were evident in the distribution of postural stability across US Special Operations Forces personnel. This normative database for postural stability, as assessed by the NeuroCom SOT, can provide context when clinicians assess a Special Operations Forces population or any other groups that maintain a high level of conditioning and training
The first resolved imaging of milliarcsecond-scale jets in Circinus X-1
We present the first resolved imaging of the milliarcsecond-scale jets in the
neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline
Array. The angular extent of the resolved jets is ~20 milliarcseconds,
corresponding to a physical scale of ~150 au at the assumed distance of 7.8
kpc. The jet position angle is relatively consistent with previous
arcsecond-scale imaging with the Australia Telescope Compact Array. The radio
emission is symmetric about the peak, and is unresolved along the minor axis,
constraining the opening angle to be less than 20 degrees. We observe evidence
for outward motion of the components between the two halves of the observation.
Constraints on the proper motion of the radio-emitting components suggest that
they are only mildly relativistic, although we cannot definitively rule out the
presence of the unseen, ultra-relativistic (Lorentz factor >15) flow previously
inferred to exist in this system.Comment: Accepted for publication in MNRAS Letters. 6 pages, 4 figure
Shell-Shocked: The Interstellar Medium Near Cygnus X-1
We conduct a detailed case-study of the interstellar shell near the high-mass
X-ray binary, Cygnus X-1. We present new WIYN optical spectroscopic and Chandra
X-ray observations of this region, which we compare with detailed MAPPINGS III
shock models, to investigate the outflow powering the shell. Our analysis
places improved, physically motivated constraints on the nature of the
shockwave and the interstellar medium (ISM) it is plowing through. We find that
the shock is traveling at less than a few hundred km/s through a low-density
ISM (< 5 cm^-3). We calculate a robust, 3 sigma upper limit to the total,
time-averaged power needed to drive the shockwave and inflate the bubble, < 2 x
10^38 erg/s. We then review possible origins of the shockwave. We find that a
supernova origin to the shockwave is unlikely and that the black hole jet
and/or O-star wind can both be central drivers of the shockwave. We conclude
that the source of the Cygnus X-1 shockwave is far from solved.Comment: 16 pages, 8 figures, accepted for publication in MNRA
A Longitudinal Analysis of Moving Desires, Expectations and Actual Moving Behaviour
Residential mobility theory proposes that moves are often preceded by the expression of moving desires and expectations. Much research has investigated how individuals form these premove thoughts, with a largely separate literature examining actual mobility. Although a growing number of studies link premove thoughts to subsequent moving behaviour, these often do not distinguish explicitly between different types and combinations of premove thoughts. Using 1998â2006 British Household Panel Survey data, this study investigates whether moving desires and expectations are empirically distinct premove thoughts. Using multinomial regression models we demonstrate that moving desires and expectations have different meanings, and are often held in combination: the factors associated with expecting to move differ depending upon whether the move is also desired (and vice versa). Next, using panel logistic regression models, we show that different desireâexpectation combinations have different effects on the probability of subsequent moving behaviour. The study identified two important groups generally overlooked in the literature: those who expect undesired moves and those who desire to move without expecting this to happen.The definitive, peer reviewed and edited version of this article is published in Environment and Planning A, 2011, 43(11), pp. 2742-2760, doi:10.1068/a44105
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