763 research outputs found
Power Spectrum of Velocity Fluctuations in the Universe
We investigate the power spectrum of velocity fluctuations in the universe,
, starting from four different measures of velocity: (1) the power
spectrum of velocity fluctuations from peculiar velocities of galaxies; (2) the
rms peculiar velocity of galaxy clusters; (3) the power spectrum of velocity
fluctuations from the power spectrum of density fluctuations in the galaxy
distribution; (4) and the bulk velocity from peculiar velocities of galaxies.
We show that measures (1) and (2) are not consistent with each other and either
the power spectrum from peculiar velocities of galaxies is overestimated or the
rms cluster peculiar velocity is underestimated. The amplitude of velocity
fluctuations derived from the galaxy distribution (measure 3) depends on the
parameter . We estimate the parameter on the basis of measures
(2) and (4). The power spectrum of velocity fluctuations from the galaxy
distribution in the Stromlo-APM redshift survey is consistent with the observed
rms cluster velocity and with the observed large-scale bulk flow when the
parameter is in the range 0.4-0.5. In this case the value of the
function at wavelength Mpc is km s
and the rms amplitude of the bulk flow at the radius Mpc is km s. The velocity dispersion of galaxy systems originates mostly
from the large-scale velocity fluctuations with wavelengths Mpc.Comment: Astrophysical Journal, Vol. 493, in press: 23 pages, uses AAS Latex,
and 14 separate postscript figure
Helping babies breathe: Building capacity and sustainability through education and training of Ethiopian healthcare workers in neonatal resuscitation to decrease neonatal mortality
CIRCULAR DICHROISM OF LIGHT-HARVESTING COMPLEXES FROM PURPLE PHOTOSYNTHETIC BACTERIA
The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of α-helix (50%) and very little 0-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b)
The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system
The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO2) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO2 systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption
Role of Magnetic Resonance Spectroscopy in Follow up Brain Tumors after Treatment
Background: 1 H magnetic resonance spectroscopy (MRS) is an analytical method that enables the identification and quantification of metabolites in samples. It differs from conventional Magnetic Resonance Imaging (MRI) in that spectra provide physiological and chemical information instead of anatomy. MRS imaging allows a valuable insights into brain tumors characteristics, grads, and progression then follow up during treatments. Typically in MRS a single spectrum is acquired by averaging enough spectra over a long acquisition time. Averaging is necessary because of the complex spectral structures and relatively low concentrations of many brain metabolites, which result in a low signal-to-noise ratio (SNR) in MRS of a living brain. Objective: In this paper, acquiring and analyzing multivoxel MRS data are reviewed by calculating the areas under different peaks then compared with that obtained directly from 1H-MRS machine. 1H-MRS measurements of amounts of Choline (Cho), creatine (Cr) and Nacetylaspartate (NAA) relative to Cho, NAA and Cr in healthy brain tissue of a normal control brain tissue, and in the tissue of tumor of patient who had taken radiation therapy sessions. Results: The obtained results show a good agreement between the data obtained directly from MRS machine and that calculated from their spectra. This method is now used for to insure that these obtained spectra are calibrated with that obtained directly from MRS machine. So these may reflect the small changes in metabolites during treatment and follow up. Conclusion: The MRS data are seen to provide unique information that when combined with high-quality anatomical MR images has implications for defining tumor type and grade, directing biopsy or surgical resection, planning focal radiation or biological therapies, and understanding the mechanisms of success and failure of new treatments
Cosmological constraints from COMBO-17 using 3D weak lensing
We present the first application of the 3D cosmic shear method developed in
Heavens et al. (2006) and the geometric shear-ratio analysis developed in
Taylor et al. (2006), to the COMBO-17 data set. 3D cosmic shear has been used
to analyse galaxies with redshift estimates from two random COMBO-17 fields
covering 0.52 square degrees in total, providing a conditional constraint in
the (sigma_8, Omega_m) plane as well as a conditional constraint on the
equation of state of dark energy, parameterised by a constant w= p/rho c^2. The
(sigma_8, Omega_m) plane analysis constrained the relation between sigma_8 and
Omega_m to be sigma_8(Omega_m/0.3)^{0.57 +- 0.19}=1.06 +0.17 -0.16, in
agreement with a 2D cosmic shear analysis of COMBO-17. The 3D cosmic shear
conditional constraint on w using the two random fields is w=-1.27 +0.64 -0.70.
The geometric shear-ratio analysis has been applied to the A901/2 field, which
contains three small galaxy clusters. Combining the analysis from the A901/2
field, using the geometric shear-ratio analysis, and the two random fields,
using 3D cosmic shear, w is conditionally constrained to w=-1.08 +0.63 -0.58.
The errors presented in this paper are shown to agree with Fisher matrix
predictions made in Heavens et al. (2006) and Taylor et al. (2006). When these
methods are applied to large datasets, as expected soon from surveys such as
Pan-STARRS and VST-KIDS, the dark energy equation of state could be constrained
to an unprecedented degree of accuracy.Comment: 10 pages, 4 figures. Accepted to MNRA
Origin and evolution of halo bias in linear and non-linear regimes
We present results from a study of bias and its evolution for galaxy-size
halos in a large, high-resolution simulation of a LCDM model. We consider the
evolution of bias estimated using two-point correlation function (b_xi), power
spectrum (b_P), and a direct correlation of smoothed halo and matter
overdensity fields (b_d). We present accurate estimates of the evolution of the
matter power spectrum probed deep into the stable clustering regime
(k~[0.1-200]h/Mpc at z=0). The halo power spectrum evolves much slower than the
power spectrum of matter and has a different shape which indicates that the
bias is time- and scale-dependent. At z=0, the halo power spectrum is
anti-biased with respect to the matter power spectrum at wavenumbers
k~[0.15-30]h/Mpc, and provides an excellent match to the power spectrum of the
APM galaxies at all probed k. In particular, it nicely matches the inflection
observed in the APM power spectrum at k~0.15h/Mpc. We complement the power
spectrum analysis with a direct estimate of bias using smoothed halo and matter
overdensity fields and show that the evolution observed in the simulation in
linear and mildly non-linear regimes can be well described by the analytical
model of Mo & White (1996), if the distinction between formation redshift of
halos and observation epoch is introduced into the model. We present arguments
and evidence that at higher overdensities, the evolution of bias is
significantly affected by dynamical friction and tidal stripping operating on
the satellite halos in high-density regions of clusters and groups; we
attribute the strong anti-bias observed in the halo correlation function and
power spectrum to these effects. (Abridged)Comment: submitted to the Astrophys.Journal; 19 pages, 9 figures LaTeX (uses
emulateapj.sty
Formation and characteristics of ions and charged aerosol particles in a native Australian Eucalypt forest
International audienceBiogenic aerosol formation is likely to contribute significantly to the global aerosol load. In recent years, new-particle formation has been observed in various ecosystems around the world but hardly any measurements have taken place in the terrestrial Southern Hemisphere. Here, we report the first results of atmospheric ion and charged particle concentrations as well as of new-particle formation in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measurements were carried out with an Air Ion Spectrometer (AIS) with a size range from 0.34 to 40 nm. The Eucalypt forest was a very strong source of new aerosol particles. Daytime aerosol formation took place on 52% of days with acceptable data, which is 2?3 times as often as in the Nordic boreal zone. Average growth rates for negative/positive 1.5?3 nm particles during these formation events were 2.89/2.68 nmh?1, respectively; for 3-7 nm particles 4.26/4.03, and for 7?20 nm particles 8.90/7.58 nmh?1, respectively. The growth rates for large ions were highest when the air was coming from the native forest which suggests that the Eucalypts were a strong source of condensable vapours. Average concentrations of cluster ions (0.34?1.8 nm) were 2400/1700 cm?3 for negative/positive ions, very high compared to most other measurements around the world. One reason behind these high concentrations could be the strong radon efflux from the soils around the Tumbarumba field site. Furthermore, comparison between night-time and daytime concentrations supported the view that cluster ions are produced close to the surface within the boundary layer also at night but that large ions are mostly produced in daytime. Finally, a previously unreported phenomenon, nocturnal aerosol formation, appeared in 32% of the analysed nights but was clustered almost entirely within six months from summer to autumn in 2006. From January to May, nocturnal formation was 2.5 times as frequent as daytime formation. Therefore, it appears that in summer and autumn, nocturnal production was the major mechanism for aerosol formation in Tumbarumba
Double Inflation in Supergravity and the Large Scale Structure
The cosmological implication of a double inflation model with hybrid + new
inflations in supergravity is studied. The hybrid inflation drives an inflaton
for new inflation close to the origin through supergravity effects and new
inflation naturally occurs. If the total e-fold number of new inflation is
smaller than , both inflations produce cosmologically relevant density
fluctuations. Both cluster abundances and galaxy distributions provide strong
constraints on the parameters in the double inflation model assuming
standard cold dark matter scenario. The future satellite
experiments to measure the angular power spectrum of the cosmic microwave
background will make a precise determination of the model parameters possible.Comment: 19 pages (RevTeX file
Breast MRI and tumour biology predict axillary lymph node response to neoadjuvant chemotherapy for breast cancer
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