6,502 research outputs found
Our Commitment to Economic Development
When I arrived at UNLV, I gave considerable thought to how the university could better embrace the identity of our city. What I didn’t quite anticipate at the time was just how much the city wanted to embrace UNLV
Dial It In: Rotating RF Sensors to Enhance Radio Tomography
A radio tomographic imaging (RTI) system uses the received signal strength
(RSS) measured by RF sensors in a static wireless network to localize people in
the deployment area, without having them to carry or wear an electronic device.
This paper addresses the fact that small-scale changes in the position and
orientation of the antenna of each RF sensor can dramatically affect imaging
and localization performance of an RTI system. However, the best placement for
a sensor is unknown at the time of deployment. Improving performance in a
deployed RTI system requires the deployer to iteratively "guess-and-retest",
i.e., pick a sensor to move and then re-run a calibration experiment to
determine if the localization performance had improved or degraded. We present
an RTI system of servo-nodes, RF sensors equipped with servo motors which
autonomously "dial it in", i.e., change position and orientation to optimize
the RSS on links of the network. By doing so, the localization accuracy of the
RTI system is quickly improved, without requiring any calibration experiment
from the deployer. Experiments conducted in three indoor environments
demonstrate that the servo-nodes system reduces localization error on average
by 32% compared to a standard RTI system composed of static RF sensors.Comment: 9 page
A note on stratification errors in the analysis of clinical trials
Stratification in both the design and analysis of randomized clinical trials
is common. Despite features in automated randomization systems to re-confirm
the stratifying variables, incorrect values of these variables may be entered.
These errors are often detected during subsequent data collection and
verification. Questions remain about whether to use the mis-reported initial
stratification or the corrected values in subsequent analyses. It is shown that
the likelihood function resulting from the design of randomized clinical trials
supports the use of the corrected values. New definitions are proposed that
characterize misclassification errors as `ignorable' and `non-ignorable'.
Ignorable errors may depend on the correct strata and any other modeled
baseline covariates, but they are otherwise unrelated to potential treatment
outcomes. Data management review suggests most misclassification errors are
arbitrarily produced by distracted investigators, so they are ignorable or at
most weakly dependent on measured and unmeasured baseline covariates. Ignorable
misclassification errors may produce a small increase in standard errors, but
other properties of the planned analyses are unchanged (e.g., unbiasedness,
confidence interval coverage). It is shown that unbiased linear estimation in
the absence of misclassification errors remains unbiased when there are
non-ignorable misclassification errors, and the corresponding confidence
intervals based on the corrected strata values are conservative.Comment: 15 page
Magnetized Accretion and Dead Zones in Protostellar Disks
The edges of magnetically-dead zones in protostellar disks have been proposed
as locations where density bumps may arise, trapping planetesimals and helping
form planets. Magneto-rotational turbulence in magnetically-active zones
provides both accretion of gas on the star and transport of mass to the dead
zone. We investigate the location of the magnetically-active regions in a
protostellar disk around a solar-type star, varying the disk temperature,
surface density profile, and dust-to-gas ratio. We also consider stellar masses
between 0.4 and 2 , with corresponding adjustments in the disk mass
and temperature. The dead zone's size and shape are found using the Elsasser
number criterion with conductivities including the contributions from ions,
electrons, and charged fractal dust aggregates. The charged species' abundances
are found using the approach proposed by S. Okuzumi. The dead zone is in most
cases defined by the ambipolar diffusion. In our maps, the dead zone takes a
variety of shapes, including a fish-tail pointing away from the star and
islands located on and off the midplane. The corresponding accretion rates vary
with radius, indicating locations where the surface density will increase over
time, and others where it will decrease. We show that density bumps do not
readily grow near the dead zone's outer edge, independently of the disk
parameters and the dust properties. Instead, the accretion rate peaks at the
radius where the gas-phase metals freeze out. This could lead to clearing a
valley in the surface density, and to a trap for pebbles located just outside
the metal freeze-out line.Comment: 58 pages, 25 figures, 2 tables, accepted to Ap
Woman\u27s Work: Female Lighthouse Keepers in the Early Republic, 1820–1859
During the Early Republic between 1820 and 1859, women, on average, comprised about five percent of the principal lighthouse keepers in the United States. These women represent a unique exception to the experience of the majority of working women during the Early Republic. They received equal pay to men, and some supervised lower-paid male assistants. They filled these predominately male positions because lighthouse work had much in common with stereotypical woman\u27s work, they were most often related to the previous keeper, and they fit within cultural ideals of gender roles. Inquiry beyond the romantic image crafted for these light keepers reveals real woman struggling to survive in a turbulent period of American history. The history of female lighthouse keepers from 1820 to 1859 thus broadens our understanding of American women\u27s occupational history as well as the interplay of cultural constraints on women\u27s employment
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