1,413 research outputs found
SOCIOECONOMIC DETERMINANTS OF FOOD EXPENDITURE PATTERNS AMONG RACIALLY DIFFERENT LOW-INCOME HOUSEHOLDS: AN EMPIRICAL ANALYSIS
This paper examines the impact of selected socioeconomic characteristics on aggregate and group food expenditure patterns of racially different low-income households. A double logarithmic functional form was used to explain responses in household food expenditures to socioeconomic factors. Household income, family size, and Food Stamp Program participation were found to exert a strong positive impact on food expenditures. The general educational level of the homemaker registered no significant impact on household food expenditures. However, the nutritional knowledge of the homemaker increased the efficiency of food purchasing activities.Food Consumption/Nutrition/Food Safety,
Spawning characteristics of the South African mudcrab <i>Scylla serrata</i> (Forskål) in captivity
Scylla serrata is a potential aquaculture species in Southern Africa. Information about its reproductive biology is required as a prerequisite to establishing hatchery technology. Adult female S. serrata were caught in the Umlalazi estuary on the subtropical east coast of South Africa and kept in captivity to observe and record spawning characteristics. Data collected included crab size and mass, time in captivity prior to spawning, fecundity per batch, relative fecundity, individual egg mass and size, size of zoea 1 larvae, incubation time, and hatch success rate. Of the 119 crabs kept in captivity 83% spawned in the maturation system— most within 40 d of capture. The crabs were highly fecund (mean relative fecundity per batch = 10,655 ± 4,069 eggs/g female) and the majority of the batches hatched within 288 h (12 d) at 27 C. Spawning in captivity occurred throughout the year, with a peak in late winter/early spring. This differs slightly from records of ovarian maturity stages of the crabs in the wild. A pattern of synchronous spawning was recorded where the females were observed to extrude their eggs in groups, commonly within 3 d of one another, separated by long periods of inactivity, suggesting an exogenous spawning cue. A total of 1,374,488 zoea larvae were obtained per kg of female per month. This means that if sufficient mature females can be caught from the wild, these could be used for stocking hatchery operations. The crabs were easy to maintain, mature, and spawn in captivity. This will facilitate future domestication which will eventually reduce the need for wild caught broodstock. The spawning characteristics of South African S. serrata fit in well with those observed for the genus throughout its distribution implying that ecological and fisheries management could be similar
Weak force detection using a double Bose-Einstein condensate
A Bose-Einstein condensate may be used to make precise measurements of weak
forces, utilizing the macroscopic occupation of a single quantum state. We
present a scheme which uses a condensate in a double well potential to do this.
The required initial state of the condensate is discussed, and the limitations
on the sensitivity due to atom collisions and external coupling are analyzed.Comment: 12 pages, 2 figures, Eq.(41) has been correcte
Bridging the gap between stellar-mass black holes and ultraluminous X-ray sources
The X-ray spectral and timing properties of ultraluminous X-ray sources
(ULXs) have many similarities with the very high state of stellar-mass black
holes (power-law dominated, at accretion rates greater than the Eddington
rate). On the other hand, their cool disk components, large characteristic
inner-disk radii and low characteristic timescales have been interpreted as
evidence of black hole masses ~ 1000 Msun (intermediate-mass black holes). Here
we re-examine the physical interpretation of the cool disk model, in the
context of accretion states of stellar-mass black holes. In particular, XTE
J1550-564 can be considered the missing link between ULXs and stellar-mass
black holes, because it exhibits a high-accretion-rate, low-disk-temperature
state (ultraluminous branch). On the ultraluminous branch, the accretion rate
is positively correlated with the disk truncation radius and the bolometric
disk luminosity, while it is anti-correlated with the peak temperature and the
frequency of quasi-periodic-oscillations. Two prototypical ULXs (NGC1313 X-1
and X-2) also seem to move along that branch. We use a phenomenological model
to show how the different range of spectral and timing parameters found in the
two classes of accreting black holes depends on both their masses and accretion
rates. We suggest that ULXs are consistent with black hole masses ~ 50-100
Msun, moderately inefficiently accreting at ~20 times Eddington.Comment: 11 pages, accepted for publication in Astrophysics and Space Science.
Based on work presented at the Fifth Stromlo Symposium, Australian National
University, Dec 200
Interference between the halves of a double-well trap containing a Bose-Einstein condensate
Interference between the halves of a double-well trap containing a
Bose-Einstein condensate is studied. It is found that when the atoms in the two
wells are initially in the coherent state, the intensity exhibits collapses and
revivals, but it does not for the initial Fock states. Whether the initial
states are in the coherent states or in a Fock states, the fidelity time has
nothing to do with collision. We point out that interference and its fidelity
can be adjusted experimentally by properly preparing the number and initial
states of the system.Comment: 10 pages, 3 figures, accepted by Phy. rev.
Dissipative Dynamics of a Josephson Junction In the Bose-Gases
The dissipative dynamics of a Josephson junction in the Bose-gases is
considered within the framework of the model of a tunneling Hamiltonian. The
effective action which describes the dynamics of the phase difference across
the junction is derived using functional integration method. The dynamic
equation obtained for the phase difference across the junction is analyzed for
the finite temperatures in the low frequency limit involving the radiation
terms. The asymmetric case of the Bose-gases with the different order
parameters is calculated as well
Arsenite sorption and co-precipitation with calcite
Sorption of As(III) by calcite was investigated as a function of As(III)
concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log
[As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended
version of the surface precipitation model. At low concentrations, As(OH)3
degrees is adsorbed by complexation to surface Ca surface sites, as previously
described by the X-ray standing wave technique. The inflexion point of the
isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST),
yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this
value, the amount of sorbed arsenic increases linearly with solution
concentration, up to the saturation of arsenic with respect to the
precipitation of CaHAsO3(s). The solid solutions formed in this concentration
range were examined by X-ray and neutron diffraction. The doped calcite lattice
parameters increase with arsenic content while c/a ratio remains constant. Our
results made on bulk calcite on the atomic displacement of As atoms along
[0001] direction extend those published by Cheng et al., (1999) on calcite
surface. This study provides a molecular-level explanation for why As(III) is
trapped by calcite in industrial treatments.Comment: 9 page
Optimizing tuning masses for helicopter rotor blade vibration reduction including computed airloads and comparison with test data
The development and validation of an optimization procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads are described. The masses and their corresponding locations are the design variables that are manipulated to reduce the harmonics of hub shear for a four-bladed rotor system without adding a large mass penalty. The procedure incorporates a comprehensive helicopter analysis to calculate the airloads. Predicting changes in airloads due to changes in design variables is an important feature of this research. The procedure was applied to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses. In both cases the added mass was able to achieve significant reductions in the hub shear. In addition, the procedure was applied to place a single mass of fixed value on a blade model to reduce the hub shear for three flight conditions. The analytical results were compared to experimental data from a wind tunnel test performed in the Langley Transonic Dynamics Tunnel. The correlation of the mass location was good and the trend of the mass location with respect to flight speed was predicted fairly well. However, it was noted that the analysis was not entirely successful at predicting the absolute magnitudes of the fixed system loads
Testing Broken U(1) Symmetry in a Two-Component Atomic Bose-Einstein Condensate
We present a scheme for determining if the quantum state of a small trapped
Bose-Einstein condensate is a state with well defined number of atoms, a Fock
state, or a state with a broken U(1) gauge symmetry, a coherent state. The
proposal is based on the observation of Ramsey fringes. The population
difference observed in a Ramsey fringe experiment will exhibit collapse and
revivals due to the mean-field interactions. The collapse and revival times
depend on the relative strength of the mean-field interactions for the two
components and the initial quantum state of the condensate.Comment: 20 Pages RevTex, 3 Figure
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