25 research outputs found
Theory of magnetically powered jets
The magnetic theory for the production of jets by accreting objects is
reviewed with emphasis on outstanding problem areas. An effort is made to show
the connections behind the occasionally diverging nomenclature in the
literature, to contrast the different points of view about basic mechanisms,
and to highlight concepts for interpreting the results of numerical
simulations. The role of dissipation of magnetic energy in accelerating the
flow is discussed, and its importance for explaining high Lorentz factors. The
collimation of jets to the observed narrow angles is discussed, including a
critical discussion of the role of `hoop stress'. The transition between disk
and outflow is one of the least understood parts of the magnetic theory; its
role in setting the mass flux in the wind, in possible modulations of the mass
flux, and the uncertainties in treating it realistically are discussed. Current
views on most of these problems are still strongly influenced by the
restriction to 2 dimensions (axisymmetry) in previous analytical and numerical
work; 3-D effects likely to be important are suggested. An interesting problem
area is the nature and origin of the strong, preferably highly ordered magnetic
fields known to work best for jet production. The observational evidence for
such fields and their behavior in numerical simulations is discussed. I argue
that the presence or absence of such fields may well be the `second parameter'
governing not only the presence of jets but also the X-ray spectra and timing
behavior of X-ray binaries.Comment: 29 pages. Publication delays offered the opportunity for further
corrections, an expansion of sect 4.2, and one more Fig. To appear in
Belloni, T. (ed.): The Jet Paradigm - From Microquasars to Quasars, Lect.
Notes Phys. 794 (2009
Observation of jet structure in high transverse energy events at the CERN intersecting storage rings
The Protective Effects of Sense of Community, Multigroup Ethnic Identity, and Self-Esteem Against Internalizing Problems Among Dominican Youth: Implications for Social Workers
This study examined the risk and protective factors associated with internalizing problems among Dominican adolescents (N = 500; 58% female) attending high school (grades 9-12) in a Northeastern, high poverty, urban community. Using a path analysis, this study found that depression and anxiety are complex mental health constructs and there are many factors that contribute to their developmental trajectory. Findings revealed that greater disorganization in one\u27s neighborhood, perception of availability of drugs and handguns in one\u27s community, and overall drug use and violent behaviors were linked with depression and anxiety. Conversely, higher levels of sense of community, which was linked to positive multigroup ethnic identity, and higher levels of self-esteem had a protective effect against depression and anxiety. Implications for social workers are discussed