25,940 research outputs found
Tunable negative refraction without absorption via electromagnetically induced chirality
We show that negative refraction with minimal absorption can be obtained by
means of quantum interference effects similar to electromagnetically induced
transparency. Coupling a magnetic dipole transition coherently with an electric
dipole transition leads to electromagnetically induced chirality, which can
provide negative refraction without requiring negative permeability, and also
suppresses absorption. This technique allows negative refraction in the optical
regime at densities where the magnetic susceptibility is still small and with
refraction/absorption ratios that are orders of magnitude larger than those
achievable previously. Furthermore, the value of the refractive index can be
fine-tuned via external laser fields, which is essential for practical
realization of sub-diffraction-limit imaging.Comment: 4 pages, 5 figures (shortened version, submitted to PRL
Oncogenic K-Ras suppresses IP<sub>3</sub>-dependent Ca<sup>2+</sup> release through remodeling of IP<sub>3</sub>Rs isoform composition and ER luminal Ca<sup>2+</sup> levels in colorectal cancer cell lines
The GTPase Ras is a molecular switch engaged downstream of G-protein coupled receptors and receptor tyrosine inases that controls multiple cell fate-determining signalling athways. Ras signalling is frequently deregulated in cancer underlying associated changes in cell phenotype. Although Ca2+ signalling pathways control some overlapping functions with Ras, and altered Ca2+ signalling pathways are emerging as important players in oncogenic transformation, how Ca2+ signalling is remodelled during transformation and whether it has a causal role remains unclear. We have investigated Ca2+ signalling in two human colorectal cancer cell lines and their isogenic derivatives in which the mutated K-Ras allele (G13D) has been deleted by homologous recombination. We show that agonist-induced Ca2+ release from intracellular stores is enhanced by loss of K-RasG13D through an increase in the ER store content and a modification of IP3R subtype abundance. Consistently, uptake of Ca2+ into mitochondria and sensitivity to apoptosis was enhanced as a result of KRasG13D loss. These results suggest that suppression of Ca2+ signalling is a common response to naturally occurring levels of K-RasG13D that contributes to a survival
advantage during oncogenic transformation
Innermost stable circular orbits around relativistic rotating stars
We investigate the innermost stable circular orbit (ISCO) of a test particle
moving on the equatorial plane around rotating relativistic stars such as
neutron stars. First, we derive approximate analytic formulas for the angular
velocity and circumferential radius at the ISCO making use of an approximate
relativistic solution which is characterized by arbitrary mass, spin, mass
quadrupole, current octapole and mass -pole moments. Then, we show that
the analytic formulas are accurate enough by comparing them with numerical
results, which are obtained by analyzing the vacuum exterior around numerically
computed geometries for rotating stars of polytropic equation of state. We
demonstrate that contribution of mass quadrupole moment for determining the
angular velocity and, in particular, the circumferential radius at the ISCO
around a rapidly rotating star is as important as that of spin.Comment: 12 pages, 2 figures, accepted for publication in Phys. Rev.
Fragmentation of Nuclei at Intermediate and High Energies in Modified Cascade Model
The process of nuclear multifragmentation has been implemented, together with
evaporation and fission channels of the disintegration of excited remnants in
nucleus-nucleus collisions using percolation theory and the intranuclear
cascade model. Colliding nuclei are treated as face--centered--cubic lattices
with nucleons occupying the nodes of the lattice. The site--bond percolation
model is used. The code can be applied for calculation of the fragmentation of
nuclei in spallation and multifragmentation reactions.Comment: 19 pages, 10 figure
Fragile phase stability in (1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 crystals: A comparisons of [001] and [110] field-cooled phase diagrams
Phase diagrams of [001] and [110] field-cooled (FC)
(1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 or PMN-xPT crystals have been constructed, based
on high-resolution x-ray diffraction data. Comparisons reveal several
interesting findings. First, a region of abnormal thermal expansion above the
dielectric maximum was found, whose stability range extended to higher
temperatures by application of electric field (E). Second, the rhombohedral (R)
phase of the ZFC state was replaced by a monoclinic MA in the [001] FC diagram,
but with monoclinic MB in the [110] FC. Third, the monoclinic MC phase in ZFC
and [001] FC diagram was replaced by an orthorhombic (O) phase in the [110] FC.
Finally, in the [001] FC diagram, the phase boundary between tetragonal (T) and
MA was extended to lower PT contents (x=0.25); whereas in the [110] FC diagram,
this extended region was entirely replaced by the O phase. These results
clearly demonstrate that the phase stability of PMN-xPT crystals is quite
fragile, depending not only on modest changes in E, but also on the direction
along which that E is applied.Comment: 13 pages, 8 figures, 1 tabl
A Search for Stellar Obscuration Events due to Dark Clouds
The recent detections of a large population of faint submillimetre sources,
an excess halo gamma-ray background, and the extreme scattering events observed
for extragalactic radio sources have been explained as being due to baryonic
dark matter in the form of small, dark, gas clouds. In this paper we present
the results of a search for the transient stellar obscurations such clouds are
expected to cause. We examine the Macho project light curves of 48 x 10^6 stars
toward the Galactic bulge, LMC and SMC for the presence of dark cloud
extinction events. We find no evidence for the existence of a population of
dark gas clouds with Av > 0.2 and masses between ~ 10^-4 and 10^-2 M_solar in
the Galactic disk or halo. However, it is possible that such dark cloud
populations could exist if they are clustered in regions away from the observed
lines of sight.Comment: 13 pages, 9 figures, submitted to Ap
Correspondence between solar fine-scale structures in the corona, transition region, and lower atmosphere from collaborative observations
The Soft X-Ray Imaging Payload and the High Resolution Telescope and Spectrograph (HRTS) instrument were launched from White Sands on 11 December 1987 in coordinated sounding rocket flights to investigate the correspondence of coronal and transition region structures, especially the relationship between X-ray bright points (XBPs) and transition region small spatial scale energetic events. The coaligned data from X-ray images are presented along with maps of sites of transition region energetic events observed in C IV (100,000 K), HRTS 1600 A spectroheliograms of the T sub min region and ground based magnetogram and He I 10830 A images
Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages
The effects of different polyphenol-containing beverages on Fe absorption from a bread meal were estimated in adult human subjects from the erythrocyte incorporation of radio-Fe. The test beverages contained different polyphenol structures and were rich in either phenolic acids (chlorogenic acid in coffee), monomeric flavonoids (herb teas, camomile (Matricaria recutita L.)), vervain (Verbena officinalis L.), lime flower (Tilia cordata Mill.), pennyroyal (Mentha pulegium L.) and peppermint (Mentha piperita L.), or complex polyphenol polymerization products (black tea and cocoa). All beverages were potent inhibitors of Fe absorption and reduced absorption in a dose-dependent fashion depending on the content of total polyphenols. Compared with a water control meal, beverages containing 20-50 mg total polyphenols/serving reduced Fe absorption from the bread meal by 50-70 %, whereas beverages containing 100-400 mg total polyphenols/serving reduced Fe absorption by 60-90 %. Inhibition by black tea was 79-94 %, peppermint tea 84 %, pennyroyal 73 %, cocoa 71 %, vervain 59 %, lime flower 52 % and camomile 47 %. At an identical concentration of total polyphenols, black tea was more inhibitory than cocoa, and more inhibitory than herb teas camomile, vervain, lime flower and pennyroyal, but was of equal inhibition to peppermint tea. Adding milk to coffee and tea had little or no influence on their inhibitory nature. Our findings demonstrate that herb teas, as well as black tea, coffee and cocoa can be potent inhibitors of Fe absorption. This property should be considered when giving dietary advice in relation to Fe nutritio
- …