724 research outputs found
Industrial High Voltage: 4. Coordinating, 5. Testing, 6. Measuring
No full textThis book is based on the lectures of Prof.dr.ir. F.H. Kreuger at the Delft University of Technology.Electrical Engineering, Mathematics and Computer Scienc
Internal shock model for microquasars
No full textWe present a model for the radio outbursts of microquasars based on the assumption of quasi-continuous jet ejection. The jets are 'lit up' by shock fronts traveling along the jets during outbursts. The shocks accelerate relativistic particles which emit the observed synchrotron radiation. The observed comparatively flat decay light curves combined with gradually steepening spectral slopes are explained by a superposition of the radiation of the aging relativistic particle population left behind by the shocks. This scenario is the low energy, time-resolved equivalent to the internal shock model for GRBs. We show that this model predicts energy contents of the radiating plasma similar to the plasmon model. At the same time, the jet model relaxes the severe requirements on the central source in terms of the rate at which this energy must be supplied to the jet. Observations of 'mini-bursts' with flat spectral slopes and of infrared emission far from the source centre suggest two different states of jet ejections: (i) A 'mini-burst' mode with relatively stable jet production and weak radio emission with flat spectra and (ii) an outburst mode with strong variations in the jet bulk velocities coupled with strong radio emission with steeper spectra. We also show that the continuous jets in microquasars should terminate in strong shocks and possibly inflate radio lobes similar to extragalactic jet sources. We investigate the possibility of testing the predictions of this model with resolved radio observations. Finally, we suggest that Doppler-shifted X-ray iron lines, and possibly H-alpha lines, may be emitted by the jet flow of microquasars if thermal instabilities analogous to those in SS433 exist in their jets
Industrial High DC Voltage: 1. Fields, 2. Breakdowns, 3. Tests
No full textThis book is based on the lectures of Prof.dr.ir. F.H. Kreuger at the Delft University of Technology.Electrical Engineering, Mathematics and Computer Scienc
Geology of Northeastern British Columbia:
Get PDFby F.H. McLearn and E.D. KindleMemoir (Geological Survey of Canada) ; 25
Industrial High Voltage: 1. Electric fields, 2. Dielectrics, 3. Constructions
No full textThis book is based on the lectures of Prof.dr.ir. F.H. Kreuger at the Delft University of Technology.Electrical Engineering, Mathematics and Computer Scienc
ON THE DENSITY-WAVE THEORY OF GALACTIC SPIRALS .2. PROPAGATION OF DENSITY OF WAVE ACTION
No full text[[abstract]]The properties of galactic density waves are studied in the WKBJ approximation. In the lowest order of approximation, we reproduce the dispersion relation reported by Lin and Shu in an earlier communication. In the next order, we demonstrate explicitly that the density of “wave action” is transported with the group velocity derived by Toomre. Some general implications are drawn for mechanisms proposed for the origin of spiral structure.[[fileno]]2010118010135[[department]]物理
Self-similar collapse of an isopedic isothermal disk
Get PDF[[abstract]]We study the gravitational collapse of an isothermal disk which is isopedically magnetized (i.e., with a mass-to-flux ratio that is spatially constant). The two theorems concerning magnetic forces in such a disk proven in a companion paper (Shu & Li 1997), plus the self-similar nature of the overall problem, allow a semianalytical treatment. The inflow occurs in an inside-out manner similar to that which applies in the collapse of the unmagnetized singular isothermal sphere (Shu 1977). These two cases (singular sphere and disk) bracket the range of possible collapse behaviors expected for the family of isopedic singular isothermal toroids described by Li & Shu (1996b). Although the strong magnetic fields dilute the effects of self-gravity in the isopedic isothermal disk, they do not prevent its outer parts (envelope) from falling onto the central condensed object (protostar) at a fixed infall rate M, even when the held is perfectly frozen to the matter. Indeed, the higher densities supported by the fields in the equilibrium state increase M during collapse in comparison with the unmagnetized case. The larger effective speed of sound due to magnetization produces a smaller effect. The flattened geometry enforced by the strong magnetic fields introduces a complication: the appearance of an outwardly propagating shock wave that runs ahead of the region of infall (also studied by Tsai & Hsu 1995 in a different context). We discuss the implications of our results for the magnetic-flux problem and for the formation of centrifugally supported disks in the presence of rotation.[[fileno]]2010118010048[[department]]物理
South Dakota
Get PDFCorrespondence from 1902 to James P. Bree, the National Secretary of the Ancient Order of Hibernians, New Haven, Connecticut. The correspondence, concerning South Dakota AOH business, includes a letter from a D. O\u27Connor, on Depot Hotel, F.H. Kent, Prop., Huron, S.D. stationery.https://digitalcommons.sacredheart.edu/irish_hiberus/1042/thumbnail.jp
Magnetic forces in an isopedic disk
Get PDF[[abstract]]We consider the magnetic forces in electrically conducting thin disks threaded by magnetic fields originating in the external (interstellar) medium. We focus on disks that have dimensionless ratios a of the mass to flux that are spatially constant, a condition that we term isopedic. For arbitrary distributions of the surface density Sigma (which can be nonaxisymmetric and time dependent), we show that the magnetic tension exerts a force in the plane of the disk equal to -1/lambda(2) times the self-gravitational force. In addition, if the disk maintains magnetostatic equilibrium in the vertical direction, the magnetic pressure, integrated over the z-height of the disk, may be approximated as (1 + eta(2))/(lambda(2) + eta(2)) times the gas pressure integrated over z, where eta = f(parallel to)/2 pi G Sigma and f(parallel to) is the component of the local gravitational held parallel to the plane of the disk. We apply these results to the problem of the stability of magnetized isothermal disks to gravitational fragmentation into subcondensations of a size comparable to the vertical scale height of the disk. Contrary to common belief, such dynamical fragmentation probably does not occur. In particular, the case of the magnetized singular isothermal disk. undergoes not dynamical fragmentation into many subcondensations, but inside-out collapse into a single compact object, a self similar problem that is studied in a companion paper (Li & Shu 1997).[[fileno]]2010118010049[[department]]物理
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