63 research outputs found
The Formation of Molecular Clouds
In a recent paper, Elmegreen (2000) has made a cogent case, from an
observational point of view, that the lifetimes of molecular clouds are
comparable to their dynamical timescales. If so, this has important
implications for the mechanisms by which molecular clouds form. In particular
we consider the hypothesis that molecular clouds may form not by {\it in situ}
cooling of atomic gas, but rather by the agglomeration of the dense phase of
the interstellar medium (ISM), much, if not most, of which is already in
molecular form.Comment: 6 pages, no figures, accepted on 20 June 2001 for publication in
MNRA
The kinetic power of jets magnetically accelerated from advection dominated accretion flows in radio galaxies
There is a significant nonlinear correlation between the Eddington ratio
(L_bol=L_Edd) and the Eddington-scaled kinetic power (L_kin=L_Edd) of jets in
low luminosity active galactic nuclei (AGNs) (Merloni & Heinz). It is believed
that these low luminosity AGNs contain advection dominated accretion flows
(ADAFs). We adopt the ADAF model developed by Li & Cao, in which the global
dynamics of ADAFs with magnetically driven outflows is derived numerically, to
explore the relation between bolometric luminosity and kinetic power of jets.
We find that the observed relation, L_kin/L_Edd ~ (L_bol=L_Edd)^0.49, can be
well reproduced by the model calculations with reasonable parameters for ADAFs
with magnetically driven outflows. Our model calculations is always consistent
with the slope of the correlation independent of the values of the parameters
adopted. Compared with the observations, our results show that over 60% of the
accreted gas at the outer radius escapes from the accretion disc in a wind
before the gas falls into the black holes. The observed correlation between
Eddington-scaled kinetic power and Bondi power can also be qualitatively
reproduced by our model calculations. Our results show that the mechanical
efficiency varies from 10^-2 ~ 10^-3, which is roughly consistent with that
required in AGN feedback simulations.Comment: 5 pages, 5 figures, accepted by MN Letter
Time and Encoding Effects in the Concealed Knowledge Test
Although the traditional âlie detectorâ test is used frequently in forensic contexts, it has (like most test of deception) some limitations. The concealed knowledge test (CKT) focuses on participantsâ recognition of privileged knowledge rather than lying per-se and has been studied extensively using a variety of measures. A âguiltyâ suspectâs interaction with and memory of crimescene items may vary. Furthermore, memory for crimescene items may diminish over time. The interaction of encoding quality and test delay on CKT efficiency has been previously implied, but not yet demonstrated. We used a response-time based CKT to detect concealed knowledge from shallow and deep study procedures after 10-min, 24-h, and 1-week delays. Results show that more elaborately encoded information afforded higher detection accuracy than poorly encoded items. Although classification accuracy following deep study was unaffected by delay, detection of poorly elaborated information was initially high, but compromised after 1Â week. Thus, choosing optimal test items requires considering both test delay and initial encoding level
Gravitational Collapse and Disk Formation in Magnetized Cores
We discuss the effects of the magnetic field observed in molecular clouds on
the process of star formation, concentrating on the phase of gravitational
collapse of low-mass dense cores, cradles of sunlike stars. We summarize recent
analytic work and numerical simulations showing that a substantial level of
magnetic field diffusion at high densities has to occur in order to form
rotationally supported disks. Furthermore, newly formed accretion disks are
threaded by the magnetic field dragged from the parent core during the
gravitational collapse. These disks are expected to rotate with a sub-Keplerian
speed because they are partially supported by magnetic tension against the
gravity of the central star. We discuss how sub-Keplerian rotation makes it
difficult to eject disk winds and accelerates the process of planet migration.
Moreover, magnetic fields modify the Toomre criterion for gravitational
instability via two opposing effects: magnetic tension and pressure increase
the disk local stability, but sub-Keplerian rotation makes the disk more
unstable. In general, magnetized disks are more stable than their nonmagnetic
counterparts; thus, they can be more massive and less prone to the formation of
giant planets by gravitational instability.Comment: Chapter 16 in "Magnetic Fields in Diffuse Media", Springer-Verlag,
eds. de Gouveia Dal Pino, E., Lazarian, A., Melioli,
Helioseismology and Solar Abundances
Helioseismology has allowed us to study the structure of the Sun in
unprecedented detail. One of the triumphs of the theory of stellar evolution
was that helioseismic studies had shown that the structure of solar models is
very similar to that of the Sun. However, this agreement has been spoiled by
recent revisions of the solar heavy-element abundances. Heavy element
abundances determine the opacity of the stellar material and hence, are an
important input to stellar model calculations. The models with the new, low
abundances do not satisfy helioseismic constraints. We review here how
heavy-element abundances affect solar models, how these models are tested with
helioseismology, and the impact of the new abundances on standard solar models.
We also discuss the attempts made to improve the agreement of the low-abundance
models with the Sun and discuss how helioseismology is being used to determine
the solar heavy-element abundance. A review of current literature shows that
attempts to improve agreement between solar models with low heavy-element
abundances and seismic inference have been unsuccessful so far. The
low-metallicity models that have the least disagreement with seismic data
require changing all input physics to stellar models beyond their acceptable
ranges. Seismic determinations of the solar heavy-element abundance yield
results that are consistent with the older, higher values of the solar
abundance, and hence, no major changes to the inputs to solar models are
required to make higher-metallicity solar models consistent with helioseismic
data.Comment: To appear in Physics Reports. Large file (1.6M PDF, 3.4M PS), 27
figure
Innate lymphoid cells at the human maternalĂą fetal interface in spontaneous preterm labor
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143766/1/aji12820.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143766/2/aji12820_am.pd
An Overview of the association between schizotypy and dopamine
Schizotypy refers to a constellation of personality traits that are believed to mirror the subclinical
expression of schizophrenia in the general population. Evidence from pharmacological studies indicates that dopamine is involved in the aetiology of schizophrenia. Based on the assumption of a continuum between schizophrenia and schizotypy, researchers have begun investigating the association between dopamine and schizotypy using a wide range of methods. In this article, we review published studies on this association from the following areas of work: (1) Experimental investigations of the interactive effects of dopaminergic challenges and schizotypy on cognition, motor control and behaviour, (2) dopaminergically supported cognitive functions, (3) studies of associations between schizotypy and polymorphisms in genes involved in dopaminergic neurotransmission, and (4) molecular imaging studies of the association between schizotypy and markers of the dopamine system. Together, data from these lines of evidence suggest that dopamine is important to the expression and experience of schizotypy and associated behavioural biases. An important observation is that the experimental designs, methods, and manipulations used in this research are highly heterogeneous. Future studies are required to replicate individual observations, to enlighten the link between dopamine and different schizotypy dimensions (positive, negative, cognitive disorganisation), and to guide the search for solid dopamine-sensitive behavioural markers. Such studies are important in order to clarify inconsistencies between studies. More work is also needed to identify differences between dopaminergic alterations in schizotypy compared to the dysfunctions observed in schizophrenia
Determining crystal structures through crowdsourcing and coursework
We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit players achieved the most accurate structure. Analysing the target protein of the competition, YPL067C, uncovered a new family of histidine triad proteins apparently involved in the prevention of amyloid toxicity. From this study, we conclude that crystallographers can utilize crowdsourcing to interpret electron density information and to produce structure solutions of the highest quality
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