72,743 research outputs found
The Sensitivity of Consumption to Transitory Income: Estimates from Panel Data on Households
We investigate the stochastic relation between income and consumption (specifically, consumption of food) within a panel of about 2,000 households. Our major findings are: 1. Consumption responds much more strongly to permanent than to transitory movements of income. 2. The response to transitory income is nonetheless clearly positive. 3. A simple test, independent of our model of consumption, rejects a central implication of the pure life cycle-permanent income hypothesis. The observed covariation of income and consumption is compatible with pure life cycle-permanent income behavior on the part of80 percent of families and simple proportionality of consumption and income among the remaining 20 percent. As a general matter, our findings support the view that families respond differently to different sources of income variations. In particular, temporary income tax policies have smaller effects on consumption than do other, more permanent changes in income of the same magnitude.
2MASS 1315-2649: A High Proper Motion L Dwarf with Strong H-alpha Emission
In Hall (2002) I reported that 2MASSI J1315309-264951 is an L dwarf with
strong H-alpha emission. Two spectroscopic epochs appeared to show that the
H-alpha was variable, decreasing from 121 Angstroms to 25 Angstroms EW, which I
interpreted as a flare during the first observation. Gizis (2002) independently
discovered this object, and his intermediate spectroscopic epoch shows H-alpha
with 97 Angstroms EW. A new fourth epoch of spectroscopy again shows a very
large H-alpha EW (124 Angstroms), confirming this object to be a persistent,
strong H-alpha emitter. Whether the H-alpha is steady (like 2MASS 1237+6526) or
from continuous strong flaring (like PC0025+0447) remains unclear. Imaging
confirms that 2MASS 1315-2649 has a high proper motion (0.71"/year),
corresponding to a transverse velocity of ~76 km/s at its distance of ~23 pc.
Thus 2MASS 1315-2649 is consistent with being >~2 Gyr old and therefore
relatively massive. If that is so, the correlation of H-alph activity with mass
found by Gizis et al. (2000) would seem to support the continuous strong
flaring scenario, though it does not rule out a brown dwarf binary accretion
scenario.Comment: 2 pages, ApJL accepte
Modeling quasar accretion disc temperature profiles
Microlensing observations indicate that quasar accretion discs have
half-light radii larger than expected from standard theoretical predictions
based on quasar fluxes or black hole masses. Blackburne and colleagues have
also found a very weak wavelength dependence of these half-light radii. We
consider disc temperature profile models that might match these observations.
Nixon and colleagues have suggested that misaligned accretion discs around
spinning black holes will be disrupted at radii small enough for the
Lense-Thirring torque to overcome the disc's viscous torque. Gas in precessing
annuli torn off a disc will spread radially and intersect with the remaining
disc, heating the disc at potentially large radii. However, if the intersection
occurs at an angle of more than a degree or so, highly supersonic collisions
will shock-heat the gas to a Compton temperature of T~10^7 K, and the spectral
energy distributions (SEDs) of discs with such shock-heated regions are poor
fits to observations of quasar SEDs. Torn discs where heating occurs in
intermittent weak shocks that occur whenever the intersection angle reaches a
tenth of a degree pose less of a conflict with observations, but do not have
significantly larger half-light radii than standard discs. We also study two
phenomenological disc temperature profile models. We find that discs with a
temperature spike at relatively large radii and lowered temperatures at radii
inside the spike yield improved and acceptable fits to microlensing sizes in
most cases. Such temperature profiles could in principle occur in sub-Keplerian
discs partially supported by magnetic pressure. However, such discs overpredict
the fluxes from quasars studied with microlensing except in the limit of
negligible continuum emission from radii inside the temperature spike.Comment: Submitted to MNRAS. Comments welcome. 20 pages, 5 figure
Spoken words
Chiefly tablesIncludes bibliographical referencesSupported in part by the National Institute of Education under contract no. US-NIE-C-400-76-011
Fish -- More Than Just Another Commodity
This brief highlights the contribution of wild capture fisheries to nutritional security in fish dependent developing countries. It is intended to stimulate debate around two broad themes: (1) when should the focus of fisheries policies be on local food security and human well-being as opposed to revenue generation, and (2) how does the current research agenda, with its emphasis on environmental and economic issues, assist or impair decision making processes
The evaluation of failure detection and isolation algorithms for restructurable control
Three failure detection and identification techniques were compared to determine their usefulness in detecting and isolating failures in an aircraft flight control system; excluding sensor and flight control computer failures. The algorithms considered were the detection filter, the Generalized Likelihood Ratio test and the Orthogonal Series Generalized Likelihood Ratio test. A modification to the basic detection filter is also considered which uses secondary filtering of the residuals to produce unidirectional failure signals. The algorithms were evaluated by testing their ability to detect and isolate control surface failures in a nonlinear simulation of a C-130 aircraft. It was found that failures of some aircraft controls are difficult to distinguish because they have a similar effect on the dynamics of the vehicle. Quantitative measures for evaluating the distinguishability of failures are considered. A system monitoring strategy for implementing the failure detection and identification techniques was considered. This strategy identified the mix of direct measurement of failures versus the computation of failure necessary for implementation of the technology in an aircraft system
A possible supersymmetric solution to the discrepancy between B -> \phi K_S and B -> \eta' K_S CP asymmetries
We present a possible supersymmetric solution to the discrepancy between the
observed mixing CP asymmetries in B -> \phi K_S and B -> \eta' K_S. We show
that due to the different parity in the final states of these processes, their
supersymmetric contributions from the R-sector have an opposite sign, which
naturally explain the large deviation between S_{\phi K_S} and S_{\eta' K_S}.
We also consider the proposed mechanisms to solve the puzzle of the observed
large branching ratio of B -> \eta' K and study their impact on S_{eta' K_S}.Comment: 4 pages, 2 figure
Gravitating semirelativistic N-boson systems
Analytic energy bounds for N-boson systems governed by semirelativistic
Hamiltonians of the form H=\sum_{i=1}^N(p_i^2 + m^2)^{1/2} - sum_{1=i<j}^N
v/r_{ij}, with v>0, are derived by use of Jacobi relative coordinates. For
gravity v=c/N, these bounds are substantially tighter than earlier bounds and
they are shown to coincide with known results in the nonrelativistic limit.Comment: 7 pages, 2 figures It is now proved that the reduced Hamiltonian is
bounded below by the simple N/2 Hamiltonia
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