683 research outputs found
The Fresh Start Policy in Consumer Bankruptcy: A Historical Inventory and An Interpretive Theory
In part II, the article traces the historical development of the idea of providing relief to troubled debtors in bankruptcy, an idea usually summarized as the fresh start policy of bankruptcy law. The article catalogs and describes the empirical assumptions and normative judgments underlying the various explanations offered for the availability of a discharge or fresh start in bankruptcy. In part II, the article examines the existing Bankruptcy Code in the light of these various theories. The article concludes that the Code\u27s debtor relief provisions are best understood as a form of compulsory insurance for debtors. The nature of insurance and the grounds for compelling it are employed to provide a detailed framework both for understanding and for interpreting specific aspects of the Code\u27s discharge provisions
Space station WP-04 power system. Volume 2: Study results
Results of the phase B study contract for the definition of the space station Electric Power System (EPS) are presented in detail along with backup information and supporting data. Systems analysis and trades, preliminary design, advanced development, customer accommodations, operations planning, product assurance, and design and development phase planning are addressed. The station design is a hybrid approach which provides user power of 25 kWe from the photovoltaic subsystem and 50 kWe from the solar dynamic subsystem. The electric power is distributed to users as a utility service; single phase at a frequency of 20 kHz and voltage of 440VAC. The solar array NiH2 batteries of the photovoltaic subsystem are based on commonality to those used on the co-orbiting and solar platforms
Space station WP-04 power system. Volume 1: Executive summary
Major study activities and results of the phase B study contract for the preliminary design of the space station Electrical Power System (EPS) are summarized. The areas addressed include the general system design, man-tended option, automation and robotics, evolutionary growth, software development environment, advanced development, customer accommodations, operations planning, product assurance, and design and development phase planning. The EPS consists of a combination photovoltaic and solar dynamic power generation subsystem and a power management and distribution (PMAD) subsystem. System trade studies and costing activities are also summarized
Electron beam induced radio emission from ultracool dwarfs
We present the numerical simulations for an electron-beam-driven and
loss-cone-driven electron-cyclotron maser (ECM) with different plasma
parameters and different magnetic field strengths for a relatively small region
and short time-scale in an attempt to interpret the recent discovered intense
radio emission from ultracool dwarfs. We find that a large amount of
electromagnetic field energy can be effectively released from the beam-driven
ECM, which rapidly heats the surrounding plasma. A rapidly developed
high-energy tail of electrons in velocity space (resulting from the heating
process of the ECM) may produce the radio continuum depending on the initial
strength of the external magnetic field and the electron beam current. Both
significant linear polarization and circular polarization of electromagnetic
waves can be obtained from the simulations. The spectral energy distributions
of the simulated radio waves show that harmonics may appear from 10 to
70 ( is the electron plasma frequency) in the
non-relativistic case and from 10 to 600 in the relativistic
case, which makes it difficult to find the fundamental cyclotron frequency in
the observed radio frequencies. A wide frequency band should therefore be
covered by future radio observations.Comment: 10 pages, 19 figures, accepted for publication in the Astrophysical
Journa
Constraints on the Growth and Spin of the Supermassive Black Hole in M32 From High Cadence Visible Light Observations
We present 1-second cadence observations of M32 (NGC221) with the CHIMERA
instrument at the Hale 200-inch telescope of the Palomar Observatory. Using
field stars as a baseline for relative photometry, we are able to construct a
light curve of the nucleus in the g-prime and r-prime band with 1sigma=36
milli-mag photometric stability. We derive a temporal power spectrum for the
nucleus and find no evidence for a time-variable signal above the noise as
would be expected if the nuclear black hole were accreting gas. Thus, we are
unable to constrain the spin of the black hole although future work will use
this powerful instrument to target more actively accreting black holes. Given
the black hole mass of (2.5+/-0.5)*10^6 Msun inferred from stellar kinematics,
the absence of a contribution from a nuclear time-variable signal places an
upper limit on the accretion rate which is 4.6*10^{-8} of the Eddington rate, a
factor of two more stringent than past upper limits from HST. The low mass of
the black hole despite the high stellar density suggests that the gas liberated
by stellar interactions was primarily at early cosmic times when the low-mass
black hole had a small Eddington luminosity. This is at least partly driven by
a top-heavy stellar initial mass function at early cosmic times which is an
efficient producer of stellar mass black holes. The implication is that
supermassive black holes likely arise from seeds formed through the coalescence
of 3-100 Msun mass black holes that then accrete gas produced through stellar
interaction processes.Comment: 8 pages, 3 figures, submitted to the Astrophysical Journal, comments
welcom
On associating Fast Radio Bursts with afterglows
A radio source that faded over six days, with a redshift of
host, has been identified by Keane et al. (2016) as the transient afterglow to
a fast radio burst (FRB 150418). We report follow-up radio and optical
observations of the afterglow candidate and find a source that is consistent
with an active galactic nucleus. If the afterglow candidate is nonetheless a
prototypical FRB afterglow, existing slow-transient surveys limit the fraction
of FRBs that produce afterglows to 0.25 for afterglows with fractional
variation, , and 0.07 for , at 95%
confidence. In anticipation of a barrage of bursts expected from future FRB
surveys, we provide a simple framework for statistical association of FRBs with
afterglows. Our framework properly accounts for statistical uncertainties, and
ensures consistency with limits set by slow-transient surveys.Comment: Accepted version (ApJL
Sporadic Long-term Variability in Radio Activity from a Brown Dwarf
Radio activity has been observed in a large variety of stellar objects,
including in the last few years, ultra-cool dwarfs. To explore the extent of
long-term radio activity in ultra-cool dwarfs, we use data taken over an
extended period of 9 hr from the Very Large Array of the source 2MASS
J05233822-1403022 in September 2006, plus data taken in 2004. The observation
taken in September 2006 failed to detect any radio activity at 8.46 GHz. A
closer inspection of earlier data reveals that the source varied from a null
detection on 3 May 2004, to 95 Jy on 17 May 2004, to 230 Jy
on 18 June 2004. The lack of detection in September 2006 suggests at least a
factor of ten flux variability at 8.46 GHz. Three short photometric runs did
not reveal any optical variability. In addition to the observed pulsing nature
of the radio flux from another ultra-cool source, the present observations
suggests that ultra-cool dwarfs may not just be pulsing but can also display
long-term sporadic variability in their levels of quiescent radio emission. The
lack of optical photometric variability suggests an absence of large-scale
spots at the time of the latest VLA observations, although small very high
latitude spots combined with a low inclination could cause very low amplitude
rotational modulation which may not be measurable. We discuss this large
variability in the radio emission within the context of both gyrosynchrotron
emission and the electron-cyclotron maser, favoring the latter mechanism.Comment: 7 pages, 2 figures, 1 table, accepted for publication in A&A Letter
A Mini-survey of Ultracool Dwarfs at 4.9 GHz
A selection of ultracool dwarfs are known to be radio active, with both
gyrosynchrotron emission and the electron cyclotron maser instability being
given as likely emission mechanisms. To explore whether ultracool dwarfs
previously undetected at 8.5 GHz may be detectable at a lower frequency. We
select a sample of fast rotating ultracool dwarfs with no detectable radio
activity at 8.5 GHz, observing each of them at 4.9 GHz. From the 8 dwarfs in
our sample, we detect emission from 2MASS J07464256+2000321, with a mean flux
level of 286 24 . The light-curve of 2MASS J07464256+2000321, is
dominated towards the end of the observation by a very bright, 100 %
left circularly polarized burst during which the flux reached 2.4 mJy. The
burst was preceded by a raise in the level of activity, with the average flux
being 160 in the first hour of observation rising to
400 in the 40 minutes before the burst. During both periods,
there is significant variability. The detection of 100% circular polarization
in the emission at 4.9 GHz points towards the electron cyclotron maser as the
emission mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not
simultaneous, thus the actual fraction of dwarfs capable of producing radio
emission, as well as the fraction of those that show periodic pulsations is
still unclear, as indeed are the relative roles played by the electron
cyclotron maser instability versus gyrosynchrotron emission, therefore we
cannot assert if the previous non-detection at 8.5 GHz was due to a cut-off in
emission between 4.9 and 8.4 GHz, or due to long term variability
Mapping radio emitting-region on low-mass stars and brown dwarfs
Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) have emerged from a number of radio observations, including the periodic beams. The highly (up to 100%) circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM) instability. Several anisotropic velocity distibution models of electrons, including the horseshoe distribution, ring shell distribution and the loss-cone distribution, are able to generate the ECM instability. A magnetic-field-aligned electric potential would play an significant role in the ECM process. We are developing a theoretical model in order to simulate ECM and apply this model to map the radio-emitting region on low-mass stars and brown dwarfs
- …