530 research outputs found
Weak Gravitational Lensing by Voids
We consider the prospects for detecting weak gravitational lensing by
underdensities (voids) in the large-scale matter distribution. We derive the
basic expressions for magnification and distortion by spherical voids.
Clustering of the background sources and cosmic variance are the main factors
which limit in principle the detection of lensing by voids. We conclude that
only voids with radii larger than \hm have lensing signal to noise
larger than unity.Comment: 12 pages, 7 figures, uses mn-1_4.sty file, submitted to MNRA
Phase Transition in Sexual Reproduction and Biological Evolution
Using Monte Carlo model of biological evolution we have discovered that
populations can switch between two different strategies of their genomes'
evolution; Darwinian purifying selection and complementing the haplotypes. The
first one is exploited in the large panmictic populations while the second one
in the small highly inbred populations. The choice depends on the crossover
frequency. There is a power law relation between the critical value of
crossover frequency and the size of panmictic population. Under the constant
inbreeding this critical value of crossover does not depend on the population
size and has a character of phase transition. Close to this value sympatric
speciation is observed.Comment: 13 pages, 8 figure
Dark Energy and the Statistical Study of the Observed Image Separations of the Multiply Imaged Systems in the CLASS Statistical Sample
The present day observations favour a universe which is flat, accelerated and
composed of matter (baryonic + dark) and of a negative
pressure component, usually referred to as dark energy or quintessence. The
Cosmic Lens All Sky Survey (CLASS), the largest radio-selected galactic mass
scale gravitational lens search project to date, has resulted in the largest
sample suitable for statistical analyses. In the work presented here, we
exploit observed image separations of the multiply imaged lensed radio sources
in the sample. We use two different tests: (1) image separation distribution
function of the lensed radio sources and (2)
{\dtheta}_{\mathrm{pred}} vs {\dtheta}_{\mathrm{obs}} as observational
tools to constrain the cosmological parameters and \Om. The results are
in concordance with the bounds imposed by other cosmological tests.Comment: 20 pages latex; Modified " Results and Discussion " section, new
references adde
Selection of DNA aptamers that bind to influenza A viruses with high affinity and broad subtype specificity
AbstractMany cases of influenza are reported worldwide every year. The influenza virus often acquires new antigenicity, which is known as antigenic shift; this results in the emergence of new virus strains, for which preexisting immunity is not found in the population resulting in influenza pandemics. In the event a new strain emerges, diagnostic tools must be developed rapidly to detect the novel influenza strain. The generation of high affinity antibodies is costly and takes time; therefore, an alternative detection system, aptamer detection, provides a viable alternative to antibodies as a diagnostic tool. In this study, we developed DNA aptamers that bind to HA1 proteins of multiple influenza A virus subtypes by the SELEX procedure. To evaluate the binding properties of these aptamers using colorimetric methods, we developed a novel aptamer-based sandwich detection method employing our newly identified aptamers. This novel sandwich enzyme-linked aptamer assay successfully detected the H5N1, H1N1, and H3N2 subtypes of influenza A virus with almost equal sensitivities. These findings suggest that our aptamers are attractive candidates for use as simple and sensitive diagnostic tools that need sandwich system for detecting the influenza A virus with broad subtype specificities
Inhibition of CDK activity and PCNA-dependent DNA replication by p21 is blocked by interaction with the HPV-16 E7Â oncoprotein
p21 inhibits cyclin-dependent kinase (CDK) activity and proliferating cell nuclear antigen (PCNA)-dependent DNA replication by binding to CDK/cyclin complexes and to PCNA through distinct domains. The human papillomavirus (HPV)-16 E7 oncoprotein (16E7) abrogated a DNA damage-induced cell cycle arrest in vivo, despite high levels of p21. Using cell lysates and purified proteins we show that 16E7 prevented p21 both from inhibiting CDK2/cyclin E activity and PCNA-dependent DNA replication, whereas the nononcogenic HPV-6 E7 had reduced effects. Inactivation of both inhibitory functions of p21 was attained through binding between 16E7 and sequences in the carboxy-terminal end of p21 that overlap with the PCNA-binding site and the second p21 cyclin-binding motif. These data imply that the carboxyl terminus of p21 simultaneously modulates both CDK activity and PCNA-dependent DNA replication and that a single protein, 16E7, can override this modulation to disrupt normal cell cycle control
An analysis of cosmological perturbations in hydrodynamical and field representations
Density fluctuations of fluids with negative pressure exhibit decreasing time
behaviour in the long wavelength limit, but are strongly unstable in the small
wavelength limit when a hydrodynamical approach is used. On the other hand, the
corresponding gravitational waves are well behaved. We verify that the
instabilities present in density fluctuations are due essentially to the
hydrodynamical representation; if we turn to a field representation that lead
to the same background behaviour, the instabilities are no more present. In the
long wavelength limit, both approachs give the same results. We show also that
this inequivalence between background and perturbative level is a feature of
negative pressure fluid. When the fluid has positive pressure, the
hydrodynamical representation leads to the same behaviour as the field
representation both at the background and perturbative levels.Comment: Latex file, 18 page
Inhomogeneous Universe Models with Varying Cosmological Term
The evolution of a class of inhomogeneous spherically symmetric universe
models possessing a varying cosmological term and a material fluid, with an
adiabatic index either constant or not, is studied.Comment: 11 pages Latex. No figures. To be published in the GRG Journa
The late Vistulian and Holocene evolution of Jezioro Lake : a record of environmental change in southern Poland found in deposits and landforms
Jezioro Lake is the only natural lake in
southern Poland outside mountainous areas to have
existed continuously since the Pleistocene. The record
of environmental change in the Late Vistulian
(Weichselian) and Holocene is preserved in the
deposits and landforms around the lake. This paper
presents the results of paleogeographical and paleoecological
research that emabled us to reconstruct the
history of the Jezioro Lake. At the end of the Vistulian
period, the outlet of the lake was blocked by a
parabolic dune moving in from the west. Limnic
sedimentation was evident in the sediment core at all
levels from the Holocene, with remains of Cladocera,
Chironomidae larvae, and aquatic plants. The lake did
not disappear at that time, although its area decreased
by a factor of 12 by the end of the period. Paleobotanical
research permitted the reconstruction of
sequences of plant communities and changes in
nutrient status and water level. An initial oligotrophic
lake, as indicated by the presence of Isoeštes lacustris
L., changed to a eutrophic lake, as indicated by the
presence of Potamogeton natans L. and Nuphar sp.,
then the lake progressed to the present-day dystrophic
lake that is surrounded by a swamp. The profile of organic deposits contains a record of environmental
change at least since the Younger Dryas in southern
Poland
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