2,589 research outputs found
Variations in subcuticular acid phosphatase activity during the molting cycle of the euphausiid crustacean, Thysanoessa raschii (M. Sars) Hansen
A histochemical technique, applicable to intact euphausiids, has been used in the laboratory to demonstrate variations in the level of subcuticular acid phosphatase activity during the molting cycle of Thysanoessa raschii; it shows that there is a marked increase in such activity during the 24 hours in which ecdysis occurs. We suggest that the technique could form a useful tool in future studies on euphausiid biology since it would allow, for example, assessments of the numbers of individuals in any one collection or population that is passing through this particular 24-hour period at the time of sampling
Cosmological Parameter Extraction from the First Season of Observations with DASI
The Degree Angular Scale Interferometer (\dasi) has measured the power
spectrum of the Cosmic Microwave Background anisotropy over the range of
spherical harmonic multipoles 100<l<900. We compare this data, in combination
with the COBE-DMR results, to a seven dimensional grid of adiabatic CDM models.
Adopting the priors h>0.45 and 0.0<=tau_c<=0.4, we find that the total density
of the Universe Omega_tot=1.04+/-0.06, and the spectral index of the initial
scalar fluctuations n_s=1.01+0.08-0.06, in accordance with the predictions of
inflationary theory. In addition we find that the physical density of baryons
Omega_b.h^2=0.022+0.004-0.003, and the physical density of cold dark matter
Omega_cdm.h^2=0.14+/-0.04. This value of Omega_b.h^2 is consistent with that
derived from measurements of the primordial abundance ratios of the light
elements combined with big bang nucleosynthesis theory. Using the result of the
HST Key Project h=0.72+/-0.08 we find that Omega_t=1.00+/-0.04, the matter
density Omega_m=0.40+/-0.15, and the vacuum energy density
Omega_lambda=0.60+/-0.15. (All 68% confidence limits.)Comment: 7 pages, 4 figures, minor changes in response to referee comment
Generic construction of the Standard Model gauge group and matter representations in F-theory
We describe general classes of 6D and 4D F-theory models with gauge group
. We prove that this set of constructions gives all possible
consistent 6D supergravity theories with no tensor multiplets having this gauge
group and the corresponding generic matter representations, which include those
of the MSSM. We expect, though do not prove, that these models are similarly
generic for 6D theories with tensor multiplets and for 4D
supergravity theories. The largest class of these constructions comes from
deforming an underlying geometry with gauge symmetry .Comment: 10 pages, LaTeX; references added, minor edit
DASI Three-Year Cosmic Microwave Background Polarization Results
We present the analysis of the complete 3-year data set obtained with the
Degree Angular Scale Interferometer (DASI) polarization experiment, operating
from the Amundsen-Scott South Pole research station. Additional data obtained
at the end of the 2002 Austral winter and throughout the 2003 season were added
to the data from which the first detection of polarization of the cosmic
microwave background radiation was reported. The analysis of the combined data
supports, with increased statistical power, all of the conclusions drawn from
the initial data set. In particular, the detection of E-mode polarization is
increased to 6.3 sigma confidence level, TE cross-polarization is detected at
2.9 sigma, and B-mode polarization is consistent with zero, with an upper limit
well below the level of the detected E-mode polarization. The results are in
excellent agreement with the predictions of the cosmological model that has
emerged from CMB temperature measurements. The analysis also demonstrates that
contamination of the data by known sources of foreground emission is
insignificant.Comment: 13 pages Latex, 10 figures, submitted to Ap
The shape of the CMB power spectrum
The recent WMAP data represents a milestone in cosmology and helps constrain
cosmological parameters with unprecedented accuracy. In this work we combine
the WMAP data with previous CMB anisotropy measurements at smaller angular
scales to characterize the shape of the CMB anisotropy power spectrum. We carry
out a phenomenological analysis of the data. By allowing non-physical shapes of
the power spectrum we analyse high and low frequency experiments separately and
together. We find that WMAP dramatically constrains the power spectrum up to l
\~ 700. On smaller scales, the data show discrepancies that can be associated
with experimental systematics. If we combine all types of experiments, the
observable features in the power spectrum are in excellent agreement with the
WMAP cosmological parameter estimation. This work illustrates the advantages of
a model-independent approach to understanding experimental systematics that
might affect CMB observations.Comment: 7 pages, to appear in New Astronomy Reviews, Proceedings of the
CMBNET Meeting, 20-21 February 2003, Oxford, U
- …