1,036 research outputs found
Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities
We analyze the signal processing required for the optimal detection of a
stochastic background of gravitational radiation using laser interferometric
detectors. Starting with basic assumptions about the statistical properties of
a stochastic gravity-wave background, we derive expressions for the optimal
filter function and signal-to-noise ratio for the cross-correlation of the
outputs of two gravity-wave detectors. Sensitivity levels required for
detection are then calculated. Issues related to: (i) calculating the
signal-to-noise ratio for arbitrarily large stochastic backgrounds, (ii)
performing the data analysis in the presence of nonstationary detector noise,
(iii) combining data from multiple detector pairs to increase the sensitivity
of a stochastic background search, (iv) correlating the outputs of 4 or more
detectors, and (v) allowing for the possibility of correlated noise in the
outputs of two detectors are discussed. We briefly describe a computer
simulation which mimics the generation and detection of a simulated stochastic
gravity-wave signal in the presence of simulated detector noise. Numerous
graphs and tables of numerical data for the five major interferometers
(LIGO-WA, LIGO-LA, VIRGO, GEO-600, and TAMA-300) are also given. The treatment
given in this paper should be accessible to both theorists involved in data
analysis and experimentalists involved in detector design and data acquisition.Comment: 81 pages, 30 postscript figures, REVTE
The Effect Of Preventative Drills On Stability Of The Knee In Female Basketball Players
The purpose of this investigation was to study the effect of incorporating three preventative mechanical principles into the practice sessions of an eighth grade girls' basketball team over the duration of one season on the players' knee stability. Three mechanical principles were utilized by 17 females (age=13.7 yrs, mass=52.2 kg, ht=166.8 cm) during each practice: (a) bent knee landings, (b) accelerated rounded turns, and (c) two-three step stops.
Knee stability was assessed prior to and at the conclusion of the season by measuring three variables:
(a) knee range of motion in extension and flexion tested by a goniometer,
(b) comparative strength of the hamstrings and quadriceps muscles tested by an Orthotron at 60 and 180 deg/s, and
(c) end of the season joint laxity as an indicator of anterior cruciate ligament displacement tested by a KT-2000 at 28 deg of flexion. A control group of 9 female basketball players (age=12.8 yrs, mass=52.8 kg, ht=160.7 cm) were used for comparison. No significant differences were revealed between groups for knee ROM or joint laxity (L ROM = 145 deg, R ROM = 144 deg; L ACL d = 5.7 mm, R ACL d = 6.5 mm). Significant increases were revealed between pre- and post-season testing for flexion/ extension ratios in both legs at both speeds for experimental subjects (L 60 deg/s = 14%, L 180 deg/s = 15%, R 60 deg/s = 13%, and R 180 deg/s = 8%). A significant decrease was revealed between preand post-season testing for flexion/ extension ratios in the right leg at 180 deg/s for control subjects (7%). Significant increases were revealed between preand post-season testing for p~ak torque of L flexion (6%) at 60 deg/s, L flexion (7%) and extension (13%) at 180 .deg/s, and R flexion (6%) and extension (6%) at 180 deg/s for experimental subjects. A significant increase (
White sorghum grain (Funk\u27s G766W) and elevator-run red sorghum grain compared for fattening cattle
An new white variety of sorghum grain (Funk\u27s G766W) has been reported to be higher in digestible dry matter and protein than elevator-run, rod sorghum grain. A 120-day field trial was conducted on the George and Vernon Miller farm near Great Bend to compare the two sorghum grain types under feed-lot conditions
Large Angle CMB Fluctuations from Cosmic Strings with a Comological Constant
In this paper, we present results for large-angle CMB anisotropies generated
from high resolution simulations of cosmic string networks in a range of flat
FRW universes with a cosmological constant. Using an ensemble of all-sky maps,
we compare with the COBE data to infer a normalization (or upper bound) on the
string linear energy density . For a flat matter-dominated model
() we find , which is lower
than previous constraints probably because of the more accurate inclusion of
string small-scale structure. For a cosmological constant within an
observationally acceptable range, we find a relatively weak dependence with
less than 10% higher.Comment: 5 pages, 5 figures; replaced with version to appear in Physical
Review
Evaluative Conditioning: Arti-fact or -fiction?âA Reply to Baeyens, De Houwer, Vansteenwegen, and Eelen (1998)
Baeyens et al.(1998) claim that Field and Davey's (1997) controversial study of conceptual conditioning offers little threat to current conceptions of evaluative conditioning. This article addresses some of the questions posed by Baeyenset al.First, some criticisms of the conceptual conditioning study appear to be based on a misunderstanding of the procedure. Second, we address the issues surrounding the so-called Type-X procedure. Specifically, we begin by reviewing the status of studies that have used a procedure different from the Type-X procedure. It is then argued that, although the Type-X procedure has been used in only a portion of EC research, it has been used primarily in those studies whose outcome has been used to argue that evaluative conditioning (EC) is functionally distinct from autonomic conditioning. We then review the evidence from non-Type-X procedures that EC is a distinct form of learning. Finally, an attempt is made to explain why between-subject controls should be used as a matter of course in this field of research
Relic Gravitational Waves and Their Detection
The range of expected amplitudes and spectral slopes of relic (squeezed)
gravitational waves, predicted by theory and partially supported by
observations, is within the reach of sensitive gravity-wave detectors. In the
most favorable case, the detection of relic gravitational waves can be achieved
by the cross-correlation of outputs of the initial laser interferometers in
LIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advanced
ground-based and space-based laser interferometers will be needed. The specific
statistical signature of relic gravitational waves, associated with the
phenomenon of squeezing, is a potential reserve for further improvement of the
signal to noise ratio.Comment: 25 pages, 9 figures included, revtex. Based on a talk given at
"Gyros, Clocks, and Interferometers: Testing General Relativity in Space"
(Germany, August 99
Assembly of a Three-Dimensional Multitype Bronchiole Coculture Model Using Magnetic Levitation
A longstanding goal in biomedical research has been to create organotypic cocultures that faithfully represent
native tissue environments. There is presently great interest in representative culture models of the lung, which
is a particularly challenging tissue to recreate in vitro. This study used magnetic levitation in conjunction with
magnetic nanoparticles as a means of creating an organized three-dimensional (3D) coculture of the bronchiole
that sequentially layers cells in a manner similar to native tissue architecture. The 3D coculture model was
assembled from four human cell types in the bronchiole: endothelial cells, smooth muscle cells (SMCs), fibroblasts,
and epithelial cells (EpiCs). This study represents the first effort to combine these particular cell types into
an organized bronchiole coculture. These cell layers were first cultured in 3D by magnetic levitation, and then
manipulated into contact with a custom-made magnetic pen, and again cultured for 48 h. Hematoxylin and eosin
staining of the resulting coculture showed four distinct layers within the 3D coculture. Immunohistochemistry
confirmed the phenotype of each of the four cell types and showed organized extracellular matrix formation,
particularly, with collagen type I. Positive stains for CD31, von Willebrand factor, smooth muscle a-actin,
vimentin, and fibronectin demonstrate the maintenance of the phenotype for endothelial cells, SMCs, and
fibroblasts. Positive stains for mucin-5AC, cytokeratin, and E-cadherin after 7 days with and without 1% fetal
bovine serum showed that EpiCs maintained the phenotype and function. This study validates magnetic levitation
as a method for the rapid creation of organized 3D cocultures that maintain the phenotype and induce
extracellular matrix formation
Studying the anisotropy of the gravitational wave stochastic background with LISA
A plethora of gravitational wave stochastic backgrounds populate the
sensitivity window of the Laser Interferometer Space Antenna. We show that LISA
can detect the anisotropy of the background corresponding to the multipole
moments of order l=2 and 4. The signal-to-noise ratio generated by galactic
white dwarf binary systems could be as high as 60 for 3 yrs of integration, and
LISA could provide valuable information on the spatial distribution of a
variety of galactic sources. We also show that the cross-correlation of the
data sets from two interferometers could marginally lead to meaningful
upper-limits on the degree of isotropy of the primordial gravitational wave
background.Comment: 4 pages, uses RevTe
Multicomponent theory of buoyancy instabilities in magnetized plasmas: The case of magnetic field parallel to gravity
We investigate electromagnetic buoyancy instabilities of the electron-ion
plasma with the heat flux based on not the magnetohydrodynamic (MHD) equations,
but using the multicomponent plasma approach when the momentum equations are
solved for each species. We consider a geometry in which the background
magnetic field, gravity, and stratification are directed along one axis. The
nonzero background electron thermal flux is taken into account. Collisions
between electrons and ions are included in the momentum equations. No
simplifications usual for the one-fluid MHD-approach in studying these
instabilities are used. We derive a simple dispersion relation, which shows
that the thermal flux perturbation generally stabilizes an instability for the
geometry under consideration. This result contradicts to conclusion obtained in
the MHD-approach. We show that the reason of this contradiction is the
simplified assumptions used in the MHD analysis of buoyancy instabilities and
the role of the longitudinal electric field perturbation which is not captured
by the ideal MHD equations. Our dispersion relation also shows that the medium
with the electron thermal flux can be unstable, if the temperature gradients of
ions and electrons have the opposite signs. The results obtained can be applied
to the weakly collisional magnetized plasma objects in laboratory and
astrophysics.Comment: Accepted for publication in Astrophysics & Space Scienc
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