6,518 research outputs found
Irradiation of Sperm Tails by Laser Microbeam
1. Sea-urchin and starfish sperm tails were irradiated at pre-selected points along the flagellum and at pre-selected phases of the beat cycle by means of a pulsed ruby laser microbeam. Multiple-exposure dark-field photomicrographs were taken immediately before and after irradiation. The flagellum usually appeared to be broken at the irradiated point.
2. The portion of a flagellum between the head and the irradiated point continued for at least a few beats if its length was at least 25% of the length of the tail, and stopped immediately if it was shorter.
3. Bends already established beyond the irradiated point continued to propagate to the tip of the flagellum. Their propagation velocity generally decreased, and there were usually changes in other bend parameters.
4. No new bends ever developed beyond the irradiated point.
5. Irradiation within a bent region often completely eliminated that region
Investigation of Systematic Bias in Radiometric Diameter Determination of Near-Earth Asteroids: the Night Emission Simulated Thermal Model (NESTM)
The Near-Earth Asteroid Thermal Model (NEATM, Harris, 1998) has proven to be
a reliable simple thermal model for radiometric diameter determination. However
NEATM assumes zero thermal emission on the night side of an asteroid. We
investigate how this assumption affects the best-fit beaming parameter,
overestimates the effective diameter and underestimates the albedo at large
phase angles, by testing NEATM on thermal IR fluxes generated from simulated
asteroid surfaces with different thermal inertia. We compare NEATM to radar
diameters and find that NEATM overestimates the diameter when the beaming
parameter is fitted to multi-wavelength observations and underestimates the
diameter when the default beaming parameter is used. The Night Emission
Simulated Thermal Model (NESTM) is introduced. NESTM models the night side
temperature as an iso-latitudinal fraction (f) of the maximum day side
temperature (Maximum temperature calculated for NEATM with beaming parameter =
1). A range of f is found for different thermal parameters, which depend on the
thermal inertia. NESTM diameters are compared with NEATM and radar diameters,
and it is shown that NESTM may reduce the systematic bias in overestimating
diameters. It is suggested that a version of the NESTM which assumes the
thermal inertia = 200 S.I. units is adopted as a default model when the solar
phase angle is greater than 45 degrees.Comment: 48 pages, 10 Figures, 5 Table
Volumetric parcellation methodology of the human hypothalamus in neuroimaging: Normative data and sex differences
There is increasing evidence regarding the importance of the hypothalamus for understanding sex differences in relation to neurological, psychiatric, endocrine and sleep disorders. Although different in histology, physiology, connections and function, multiple hypothalamic nuclei subserve non-voluntary functions and are nodal points for the purpose of maintaining homeostasis of the organism. Thus, given the critical importance of hypothalamic nuclei and their key multiple roles in regulating basic functions, it is important to develop the ability to conduct in vivo human studies of anatomic structure, volume, connectivity, and function of hypothalamic regions represented at the level of its nuclei. The goals of the present study were to develop a novel method of semi-automated volumetric parcellation for the human hypothalamus that could be used to investigate clinical conditions using MRI and to demonstrate its applicability. The proposed new method subdivides the hypothalamus into five parcels based on visible anatomic landmarks associated with specific nuclear groupings and was confirmed using two ex vivo hypothalami that were imaged in a 7 T (7 T) scanner and processed histologically. Imaging results were compared with histology from the same brain. Further, the method was applied to 44 healthy adults (26 men; 18 women, comparable on age, handedness, ethnicity, SES) to derive normative volumes and assess sex differences in hypothalamic regions using 1.5 T MRI. Men compared to women had a significantly larger total hypothalamus, relative to cerebrum size, similar for both hemispheres, a difference that was primarily driven by the tuberal region, with the sex effect size being largest in the superior tuberal region and, to a lesser extent, inferior tuberal region. Given the critical role of hypothalamic nuclei in multiple chronic diseases and the importance of sex differences, we argue that the use of the novel methodology presented here will allow for critical investigations of these disorders and further delineation of potential treatments, particularly sex-specific approaches to gene and drug discoveries that involve hypothalamic nuclei
P Pbar to T Tbar H: A Discovery mode for the Higgs boson at the Tevatron
The production of a Standard Model Higgs boson in association with a top
quark pair at the upcoming high luminosity run (15 inverse fb integrated
luminosity) of the Fermilab Tevatron (root s = 2.0 TeV) is revisited. For Higgs
masses below 140 GeV we demonstrate that the production cross section times
branching ratio for H->B Bbar decays yields a significant number of events and
that this mode is competitive with and complementary to the searches using P
Pbar -> WH, ZH associated production. For higher mass Higgs bosons the H -> W+
W- decays are more difficult but have the potential to provide a few
spectacular events.Comment: 10 pages, Latex, RevTex, 3 ps figures: Updated reconstruction
efficiency and figure
The influence of tennis court surfaces on player perceptions and biomechanical response.
This study aimed to examine player perceptions and biomechanical responses to tennis surfaces and to evaluate the influence of prior clay court experience. Two groups with different clay experiences (experience group, n = 5 and low-experience group, n = 5) performed a 180° turning movement. Three-dimensional ankle and knee movements (50 Hz), plantar pressure of the turning step (100 Hz) and perception data (visual analogue scale questionnaire) were collected for two tennis courts (acrylic and clay). Greater initial knee flexion (acrylic 20. 8 ± 11.2° and clay 32.5 ± 9.4°) and a more upright position were reported on the clay compared to the acrylic court (P < 0.05). This suggests adaptations to increase player stability on clay. Greater hallux pressures and lower midfoot pressures were observed on the clay court, allowing for sliding whilst providing grip at the forefoot. Players with prior clay court experience exhibited later peak knee flexion compared to those with low experience. All participants perceived the differences in surface properties between courts and thus responded appropriately to these differences. The level of previous clay court experience did not influence players' perceptions of the surfaces; however, those with greater clay court experience may reduce injury risk as a result of reduced loading through later peak knee flexion
Nutrition aspects in children receiving maintenance hemodialysis: impact on outcome
Children with end-stage renal disease (ESRD) have rates of mortality estimated to be 30-times higher than expected for age compared with those of healthy children. Physical manifestations of under-nutrition, such as body mass index (BMI) and low height standard deviation score (SDS), have been associated with increased risk of mortality. Traditional measures, such as height, weight and serum albumin concentration, may not be accurate indicators to assess the nutritional status of children receiving maintenance hemodialysis. Normalized protein catabolic rate (nPCR) has emerged as a better marker of nutritional status of such children. Meeting the special nutritional needs of these children often requires nutritional supplementation, by either the enteral or the parenteral route. Recently, in children receiving maintenance hemodialysis who are malnourished, intradialytic parenteral nutrition (IDPN) has been utilized as a means to provide additional protein and calories. This article is a state-of-the-art review of malnutrition in children receiving maintenance hemodialysis, with special focus on outcome, nPCR and IDPN
Coalescing Binary Neutron Stars
Coalescing compact binaries with neutron star or black hole components
provide the most promising sources of gravitational radiation for detection by
the LIGO/VIRGO/GEO/TAMA laser interferometers now under construction. This fact
has motivated several different theoretical studies of the inspiral and
hydrodynamic merging of compact binaries. Analytic analyses of the inspiral
waveforms have been performed in the Post-Newtonian approximation. Analytic and
numerical treatments of the coalescence waveforms from binary neutron stars
have been performed using Newtonian hydrodynamics and the quadrupole radiation
approximation. Numerical simulations of coalescing black hole and neutron star
binaries are also underway in full general relativity. Recent results from each
of these approaches will be described and their virtues and limitations
summarized.Comment: Invited Topical Review paper to appear in Classical and Quantum
Gravity, 35 pages, including 5 figure
Sensitivity to millicharged particles in future proton-proton collisions at the LHC with the milliQan detector
We report on the expected sensitivity of dedicated scintillator-based
detectors at the LHC for elementary particles with charges much smaller than
the electron charge. The dataset provided by a prototype scintillator-based
detector is used to characterise the performance of the detector and provide an
accurate background projection. Detector designs, including a novel slab
detector configuration, are considered for the data taking period of the LHC to
start in 2022 (Run 3) and for the high luminosity LHC. With the Run 3 dataset,
the existence of new particles with masses between 10 MeV and 45 GeV could be
excluded at 95% confidence level for charges between 0.003e and 0.3e, depending
on their mass. With the high luminosity LHC dataset, the expected limits would
reach between 10 MeV and 80 GeV for charges between 0.0018e and 0.3e, depending
on their mas
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
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