3,149 research outputs found
Has the "Farm Problem" Disappeared? A Comparison of Household and Self-Employment Income Levels of the Farm and Nonfarm Self-Employed
This study tests the impact of household and demographic factors on the economic well-being of the farm and nonfarm self-employed using data from the Integrated Public Use Microdata Series. Parametric and nonparametric techniques are used to test for statistical differences in self-employment and household income levels. Further, household and demographic factors are tested for their effect on self-employment income using a censored tobit regression model. The farm self-employed report significantly higher levels of self-employment income. Results reveal that several household and demographic factors significantly impact self-employment income levels for the farm and nonfarm self-employed, with key differences in impacts.self-employment, farm households, Community/Rural/Urban Development,
Mark 3 real-time fringe detection system
A RAM memory built into the Mark 3 decoder module allows the capture of 1 Megabit of data. Data may be collected either in real time or from a pre-recorded tape. Once collected, the data may be retrieved using a standard EIA serial data link. The data may be transmitted to a remote computer for cross correlation processing with similar data from other stations to verify fringes in real time. The data may also be analyzed by a local computer to verify phase calibration, bandpass, format, etc., during a Mark 3 observing session
Does Experience Determine Performance? A Meta-Analysis on the Experience-Performance Relationship
The impact of experience on entrepreneurial performance has been widely tested. Although experience is expected to positively impact performance, results are varied. This research synthesizes the current literature by determining systematic sources of variation through both exploratory and ordered probit analyses. Results reveal that start date for data collection and form of experience tested pose a major impact on the probability of obtaining a positive estimate for the experience-performance relationship. This research further emphasizes the need for tightened standards across the experience-performance literature in order to equip both academics and practitioners with better information.Entrepreneurship, Experience, Performance, Meta-Analysis, Agribusiness, Labor and Human Capital,
Am I missing something? Experiences of using social media by blind and partially sighted users
People with a visual impairment are more likely to experience social isolation as an effect of their vision loss. Social media can particularly benefit these users, but it is of concern if it cannot be fully and successfully used. This study was instigated at the request of an advisory group of visual impaired users and experts. The aim of the study was to investigate potential accessibility issues visually impaired users could encounter when using social media. A major concern was over missing content embedded in images on social media sites. A subsequent evaluation of Facebook posts carried out by a group of student participants demonstrated that nearly half of images considered contained embedded text, which would be inaccessible to visually impaired users. Despite efforts by social media companies to improve accessibility, any text present in images is not presented in an accessible way to visually impaired users. This research demonstrated the inequality that can arise from partial accessibility and the requirement to consider accessibility at all stages of design and development
Spin bath interactions effects on the geometric phase
We calculate the geometric phase of a spin-1/2 particle coupled to an
external environment comprising N spin-1/2 particle in the framework of open
quantum systems. We analyze the decoherence factor and the deviation of the
geometric phase under a nonunitary evolution from the one gained under an
unitary one. We show the dependence upon the system's and bath's parameter and
analyze the range of validity of the perturbative approximation. Finally, we
discuss the implications of our results.Comment: 8 pages, 5 figures. Version to appear in Phys. Lett.
Towards a dephasing diode: asymmetric and geometric dephasing
We study the effect of a noisy environment on spin and charge transport in
ballistic quantum wires with spin-orbit coupling (Rashba coupling). We find
that the wire then acts as a ``dephasing diode'', inducing very different
dephasing of the spins of right and left movers. We also show how Berry phase
(geometric phase) in a curved wire can induce such asymmetric dephasing, in
addition to purely geometric dephasing. We propose ways to measure these
effects through spin detectors, spin-echo techniques, and Aharanov-Bohm
interferometry.Comment: 4 pages (2 fig) v2: extensive improvements to "readability" &
references adde
Controlling the Sign of Magnetoconductance in Andreev Quantum Dots
We construct a theory of coherent transport through a ballistic quantum dot
coupled to a superconductor. We show that the leading-order quantum correction
to the two-terminal conductance of these Andreev quantum dots may change sign
depending on (i) the number of channels carried by the normal leads or (ii) the
magnetic flux threading the dot. In contrast, spin-orbit interaction may affect
the magnitude of the correction, but not always its sign. Experimental
signatures of the effect include a non-monotonic magnetoconductance curve and a
transition from an insulator-like to a metal-like temperature dependence of the
conductance. Our results are applicable to ballistic or disordered dots.Comment: Final version (4pages 3figs)- improved presentation and fig 3, and
updated reference
Mid-Infrared Variability of protostars in IC 1396A
We have used Spitzer/IRAC to conduct a photometric monitoring program of the
IC1396A dark globule in order to study the mid-IR (3.6 - 8 micron) variability
of the heavily embedded Young Stellar Objects (YSOs) present in that area. We
obtained light curves covering a 14 day timespan with a twice daily cadence for
69 YSOs, and continuous light curves with approximately 12 second cadence over
7 hours for 38 YSOs. Typical accuracies for our relative photometry were 1-2%
for the long timespan data and a few mmag, corresponding to less than 0.5%, for
the 7 hour continuous "staring-mode" data. More than half of the YSOs showed
detectable variability, with amplitudes from ~0.05 mag to ~0.2 mag. About
thirty percent of the YSOs showed quasi-sinusoidal light curve shapes with
apparent periods from 5-12 days and light curve amplitudes approximately
independent of wavelength over the IRAC bandpasses. We have constructed models
which simulate the time dependent spectral energy distributions of Class I and
I I YSOs in order to attempt to explain these light curves. Based on these
models, the apparently periodic light curves are best explained by YSO models
where one or two high latitude photospheric spots heat the inner wall of the
circumstellar disk, and where we view the disk at fairly large inclination
angle. Disk inhomogeneities, such as increasing the height where the accretion
funnel flows to the stellar hotspot, enhances the light curve modulations. The
other YSOs in our sample show a range of light curve shapes, some of which are
probably due to varying accretion rate or disk shadowing events. One star,
IC1396A-47, shows a 3.5 hour periodic light curve; this object may be a PMS
Delta Scuti star
2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence
We present model spectral energy distributions, colors, polarization, and
images for an evolutionary sequence of a low-mass protostar from the early
collapse stage (Class 0) to the remnant disk stage (Class III). We find a
substantial overlap in colors and SEDs between protostars embedded in envelopes
(Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths.
Edge-on Class I-II sources show double-peaked spectral energy distributions,
with a short-wavelength hump due to scattered light and the long-wavelength
hump due to thermal emission. These are the bluest sources in mid-IR
color-color diagrams.
Since Class 0 and I sources are diffuse, the size of the aperture over which
fluxes are integrated has a substantial effect on the computed colors, with
larger aperture results showing significantly bluer colors. This causes overlap
in color-color diagrams between all evolutionary states, especially in the
mid-IR. However the near-IR polarization of the Class 0 sources is much higher
than the Class I-II sources, providing a means to separate these evolutionary
states.
We varied the grain properties in the circumstellar envelope, allowing for
larger grains in the disk midplane and smaller in the envelope. We find that
grain growth in disks of Class I sources can be detected at wavelengths greater
than 100 m.
Our image calculations predict that the diffuse emission from edge-on Class I
and II sources should be detectable in the mid-IR with the Space Infrared
Telescope Facility (SIRTF) in nearby star forming regions (out to several
hundred parsecs).Comment: A version with high-resolution images is available at
http://www.astro.wisc.edu/glimpse/glimpsepubs.htm
Applied regional monitoring of the vernal advancement and retrogradation (Green wave effect) of natural vegetation in the Great Plains corridor
The author has identified the following significant results. LANDSAT 2 has shown that digital data products can be effectively employed on a regional basis to monitor changes in vegetation conditions. The TV16 was successfully applied to an extended test site and the Great Plains Corridor in tests of the ability to assess green forage biomass on rangelands as an index to vegetation condition. A strategy for using TV16 on a regional basis was developed and tested. These studies have shown that: (1) for rangelands with good vegetative cover, such as most of the Great Plains, and which are not heavily infested with brush or undesirable weed species, the LANDSAT digital data can provide a good estimate (within 250 kg/ha) of the quantity of green forage biomass, and (2) at least five levels of pasture and range feed conditions can be adequately mapped for extended regions
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