1,020 research outputs found
An Analysis of the Relationship between Price and Variance for Homogeneous Housing Stock
This study examines the structure of price variance for homogeneous residential housing stock, where homogeneous is defined as economically equivalent, not necessarily physically identical. Assessed values, obtained from ad valorem tax rolls, are used as the basis for identifying properties considered to be economically equivalent. From these data an investigation of the distribution of sale price and variance for housing in selected value ranges is conducted. Subsequently, ANOVA is performed to determine the composition of variance through time and across cities within one metropolitan housing market. In line with conventional wisdom, we find that variance increases with price over the entire data set. The increase, however, is not constant nor does it exhibit a simple proportional relationship to price. Variance increases at an increasing rate in the lower to mid-price ranges and continues to increase but at a decreasing rate in the upper price ranges. From this it was determined that the functional relationship between price and variance is best approximated by a quadratic function in the lower to mid-price ranges and a cubic function when higher price properties are included. ANOVA results indicate that variance is significantly different through time and across location. The interactive term was also significant. The findings of this study would appear to have implications for fee appraisers, assessors, investors, and mortgage lenders.
Assets and Barriers to Infection Control on a College Campus
An abstract about a photovoice done concerning infection control on college campus
Measurements of the methane relaxation times for application to the infrared emission models of the upper atmospheres of outer planets and Titan
The 7.8 micrometer emission from the nu(sub 4) band of methane (CH4) is a regularly observed feature in the stratosphere of all the giant planets and Titan. On Jupiter, enhancements in this emission are associated with the infrared hot spots in the auroral zone. Attempts to model this phenomenon in particular, and to understand the role of methane in general, have been hampered in part by a lack of adequate laboratory measurements of the collisional relaxation times for the nu(sub 3) and nu(sub 4) levels over the appropriate temperature range. To provide this needed data, a series of laboratory experiments were initiated. In the experimental arrangement the nu(sub3) band of methane is pumped at 3.3 micrometers using a pulsed infrared source (Nd:YAG/dye laser system equipped with a wave-length extender). The radiative lifetime of the nu(sub 3) level (approximately 37 ms) is much shorter than the nu(sub 4) lifetime (approximately 390 ms); however, a rapid V-V energy transfer rate ensures that the nu(sub 4) level is substantially populated. The photoacoustic technique is used to acquire relaxation rate information. The experiments are performed using a low-temperature, low-pressure cell. Experimental apparatus and technique are described. In addition some of the experimental difficulties associated with making these measurements are discussed and some preliminary results are presented
Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta
Recent discovery of the year-scale variability in the synchrotron X-ray
emission of the supernova remnant (SNR) RX J1713.7-3946 has initiated our study
of multi-epoch X-ray images and spectra of the young SNR Cassiopeia A based on
the Chandra archive data taken in 2000, 2002, and 2004. We have found
year-scale time variations in the X-ray intensity for a number of X-ray
filaments or knots associated with the reverse-shocked regions. The X-ray
spectra of the variable filaments are characterized by a featureless continuum,
and described by a power law with a photon index within 1.9-2.3. The upper
limits on the iron K-line equivalent width are 110 eV, which favors a
synchrotron origin of the X-ray emission. The characteristic variability
timescale of 4 yr can be explained by the effects of fast synchrotron cooling
and diffusive shock acceleration with a plausible magnetic field of 1 mG. The
X-ray variability provides a new effective way of studying particle
acceleration at supernova shocks.Comment: 4 pages, 4 figures, accepted for publication in ApJ Lette
Probing Shock Properties with Non-thermal X-ray Filaments in Cas A
Thin non-thermal X-ray filaments are often seen in young supernova remnants.
We used data from the 1 Ms Chandra observation of Cassiopeia A to study
spectral properties of some of the filaments in this remnant. For all the cases
that we examined, the X-ray spectrum across the filaments hardens, at about 10%
level, going outward, while observed filament widths depend only weakly on the
photon energy. Using a model that includes radiative cooling, advection and
diffusion of accelerated particles behind the shock, we estimated the magnetic
field, turbulence level and shock obliquity.Comment: 21 pages, 5 figure
The Three-Dimensional Structure of Cassiopeia A
We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the
entire extent of Cassiopeia A between 5-40 micron. Using infrared and Chandra
X-ray Doppler velocity measurements, along with the locations of optical ejecta
beyond the forward shock, we constructed a 3-D model of the remnant. The
structure of Cas A can be characterized into a spherical component, a tilted
thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all
populating the thick disk plane. The Bright Ring in Cas A identifies the
intersection between the thick plane/pistons and a roughly spherical reverse
shock. The ejecta pistons indicate a radial velocity gradient in the explosion.
Some ejecta pistons are bipolar with oppositely-directed flows about the
expansion center while some ejecta pistons show no such symmetry. Some ejecta
pistons appear to maintain the integrity of the nuclear burning layers while
others appear to have punched through the outer layers. The ejecta pistons
indicate a radial velocity gradient in the explosion. In 3-D, the Fe jet in the
southeast occupies a "hole" in the Si-group emission and does not represent
"overturning", as previously thought. Although interaction with the
circumstellar medium affects the detailed appearance of the remnant and may
affect the visibility of the southeast Fe jet, the bulk of the symmetries and
asymmetries in Cas A are intrinsic to the explosion.Comment: Accepted to ApJ. 54 pages, 21 figures. For high resolution figures
and associated mpeg movie and 3D PDF files, see
http://homepages.spa.umn.edu/~tdelaney/pape
Priority setting partnership to identify the top 10 research priorities for the management of Parkinson’s disease
Objectives: This priority setting partnership was commissioned by Parkinson’s UK to encourage people with direct and personal experience of the condition to work together to identify and prioritise the top 10 evidential uncertainties that impact on everyday clinical practice for the management of Parkinson’s disease (PD). Setting: The UK. Participants: Anyone with experience of PD including: people with Parkinson’s (PwP), carers, family and friends, healthcare and social care professionals. Non-clinical researchers and employees of pharmaceutical or medical devices companies were excluded. 1000 participants (60% PwP) provided ideas on research uncertainties, 475 (72% PwP) initially prioritised them and 27 (37% PwP) stakeholders agreed a final top 10. Methods: Using a modified nominal group technique, participants were surveyed to identify what issues for the management of PD needed research. Unique research questions unanswered by current evidence were identified and participants were asked to identify their top 10 research priorities from this list. The top 26 uncertainties were presented to a consensus meeting with key stakeholders to agree the top 10 research priorities. Results: 1000 participants provided 4100 responses, which contained 94 unique unanswered research questions that were initially prioritised by 475 participants. A consensus meeting with 27 stakeholders agreed the top 10 research priorities. The overarching research aspiration was an effective cure for PD. The top 10 research priorities for PD management included the need to address motor symptoms (balance and falls, and fine motor control), non-motor symptoms (sleep and urinary dysfunction), mental health issues (stress and anxiety, dementia and mild cognitive impairments), side effects of medications (dyskinesia) and the need to develop interventions specific to the phenotypes of PD and better monitoring methods. Conclusions: These research priorities identify crucial gaps in the existing evidence to address everyday practicalities in the management of the complexities of PD
Sequence biases in large scale gene expression profiling data
We present the results of a simple, statistical assay that measures the G+C content sensitivity bias of gene expression experiments without the requirement of a duplicate experiment. We analyse five gene expression profiling methods: Affymetrix GeneChip, Long Serial Analysis of Gene Expression (LongSAGE), LongSAGELite, ‘Classic’ Massively Parallel Signature Sequencing (MPSS) and ‘Signature’ MPSS. We demonstrate the methods have systematic and random errors leading to a different G+C content sensitivity. The relationship between this experimental error and the G+C content of the probe set or tag that identifies each gene influences whether the gene is detected and, if detected, the level of gene expression measured. LongSAGE has the least bias, while Signature MPSS shows a strong bias to G+C rich tags and Affymetrix data show different bias depending on the data processing method (MAS 5.0, RMA or GC-RMA). The bias in the Affymetrix data primarily impacts genes expressed at lower levels. Despite the larger sampling of the MPSS library, SAGE identifies significantly more genes (60% more RefSeq genes in a single comparison)
On the Expansion Rate, Age, and Distance of the Supernova Remnant G266.2-1.2 (Vela Jr.)
An analysis of Chandra ACIS data for two relatively bright and narrow
portions of the northwestern rim of G266.2-1.2 (a.k.a. RX J0852.0-4622 or Vela
Jr.) reveal evidence of a radial displacement of 2.40 +/- 0.56 arcsec between
2003 and 2008. The corresponding expansion rate (0.42 +/- 0.10 arcsec/yr or
13.6 +/- 4.2%/kyr) is about half the rate reported for an analysis of
XMM-Newton data from a similar, but not identical, portion of the rim over a
similar, but not identical, time interval (0.84 +/- 0.23 arcsec/yr, Katsuda et
al. 2008a). If the Chandra rate is representative of the remnant as a whole,
then the results of a hydrodynamic analysis suggest that G266.2-1.2 is between
2.4 and 5.1 kyr old if it is expanding into a uniform ambient medium (whether
or not it was produced by a Type Ia or Type II event). If the remnant is
expanding into the material shed by a steady stellar wind, then the age could
be as much as 50% higher. The Chandra expansion rate and a requirement that the
shock speed be greater than or equal to 1000 km/s yields a lower limit on the
distance of 0.5 kpc. An analysis of previously-published distance estimates and
constraints suggests G266.2-1.2 is no further than 1.0 kpc. This range of
distances is consistent with the distance to the nearer of two groups of
material in the Vela Molecular Ridge (0.7 +/- 0.2 kpc, Liseau et al. 1992) and
to the Vel OB1 association (0.8 kpc, Eggen 1982).Comment: 30 pages, 7 figure
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