1,263 research outputs found
Free Space Optical Link Utilizing a Modulated Retro-Reflector Intended for Planetary Duplex Communication Links Between an Orbiter and Surface Unit
Presented are simulation and experimental results that provide duplex optical-free space communication links with minimal power and pointing requirements by using a modulated retro-reflector (MRR) for planetary communications. The design is the MRR resides on the surface of a planet or moon, where energy is scarce, while the source of the communication laser resides on an orbiter to achieve satellite-to-ground communications. Also, a simulated scenario using the Mars Reconnaissance Orbiter (MRO) is provided for real world potential results. The information sent through this communication path can range from raw scientific data to multimedia files such as videos and pictures. Bidirectional communications is established with the MRR by using a nested pulse position modulation (PPM) structure. This modulation scheme is then evaluated for its validity in a proof-of-concept experiment. Initial results indicate a promising return-link performance of at least 300 kbps in the nested arrangement
Intensity of Brillouin light scattering from spin waves in magnetic multilayers with noncollinear spin configurations: Theory and experiment
The scattering of photons from spin waves (Brillouin light scattering -- BLS)
is a well-established technique for the study of layered magnetic systems. The
information about the magnetic state and properties of the sample is contained
in the frequency position, width, and intensity of the BLS peaks. Previously
[Phys. Rev. B 67, 184404 (2003)], we have shown that spin wave frequencies can
be conveniently calculated within the ultrathin film approach, treating the
intralayer exchange as an effective bilinear interlayer coupling between thin
virtual sheets of the ferromagnetic layers. Here we give the consequent
extension of this approach to the calculation of the Brillouin light scattering
(BLS) peak intensities. Given the very close relation of the BLS cross-section
to the magneto-optic Kerr effect (MOKE), the depth-resolved longitudinal and
polar MOKE coefficients calculated numerically via the usual magneto-optic
formalism can be employed in combination with the spin wave precessional
amplitudes to calculate full BLS spectra for a given magnetic system. This
approach allows an easy calculation of BLS intensities even for noncollinear
spin configurations including the exchange modes. The formalism is applied to a
Fe/Cr/Fe/Ag/Fe trilayer system with one antiferromagnetically coupling spacer
(Cr). Good agreement with the experimental spectra is found for a wide variety
of spin configurations.Comment: 19 pages, 5 figure
Eukaryotic initiation factor-4E in superficial and muscle invasive bladder cancer and its correlation with vascular endothelial growth factor expression and tumour progression
Vascular endothelial growth factor (VEGF) is an important factor mediating tumour angiogenesis. VEGF mRNA is differentially expressed in bladder cancer with high expression in superficial tumours (stage pTaand pT1) contrasting with low expression in muscle invasive tumours (stage ≥ pT2). To investigate mechanisms regulating VEGF expression in bladder cancer, VEGF mRNA and protein were measured in normal bladder (n = 12) and primary bladder cancers (n = 57). VEGF protein levels correlated with mRNA expression in normal bladder (r = 0.68, P = 0.02) and bladder cancer (r = 0.46, P = 0.0007). Whilst VEGF mRNA expression was threefold higher in superficial compared to muscle invasive bladder cancers (P = 0.0001) there was no difference in VEGF protein (P = 0.81). Accordingly, the median protein:mRNA ratios increased more than 15-fold with increasing tumour stage (P< 0.0001) suggesting translational regulation. Expression of the eukaryotic initiation factor-4E (eIF-4E), a factor implicated in the translational regulation of VEGF, was greater in tumours than normal bladder (P< 0.0001) and correlated with VEGF protein:mRNA ratios (n = 43, r = 0.54, P = 0.0004) pointing to its role in the regulation of VEGF. In superficial tumours (n = 37) high expression of eIF-4E was associated with a poor prognosis and reduced stage progression-free survival (P = 0.04, Cox proportional hazards model). The study demonstrates that eIF-4E may be involved in translational regulation of VEGF in bladder cancer and might have a role as a prognostic factor in bladder cancer. © 2000 Cancer Research Campaig
Evolving outer heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer
The first all-sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow ribbon of enhanced ENA emissions. In this study we compare the second set of sky maps to the first in order to assess the possibility of temporal changes over the 6 months between views of each portion of the sky. While the large-scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale. In particular, we find that (1) the overall ENA emissions coming from the outer heliosphere appear to be slightly lower in the second set of maps compared to the first, (2) both the north and south poles have significantly lower (similar to 10-15%) ENA emissions in the second set of maps compared to the first across the energy range from 0.5 to 6 keV, and (3) the knot in the northern portion of the ribbon in the first maps is less bright and appears to have spread and/or dissipated by the time the second set was acquired. Finally, the spatial distribution of fluxes in the southernmost portion of the ribbon has evolved slightly, perhaps moving as much as 6 degrees (one map pixel) equatorward on average. The observed large-scale stability and these systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy and help inform possible mechanisms for producing the IBEX ribbon
In flight performance and first results of FREGATE
The gamma-ray detector of HETE-2, called FREGATE, has been designed to detect
gamma-ray bursts in the energy range [6-400] keV. Its main task is to alert the
other instruments of the occurrence of a gamma-ray burst (GRB) and to provide
the spectral coverage of the GRB prompt emission in hard X-rays and soft
gamma-rays. FREGATE was switched on on October 16, 2000, one week after the
successful launch of HETE-2, and has been continuously working since then. We
describe here the main characteristics of the instrument, its in-flight
performance and we briefly discuss the first GRB observations.Comment: Invited lecture at the Woods Hole 2001 GRB Conference, 8 pages, 15
figure
Bermuda grass latent virus in Australia: genome sequence, sequence variation, and new hosts
Bermuda grass latent virus (BGLV; genus Panicovirus) is identified for the first time in Australia and in only the second country after the USA. A full-length genome sequence was obtained, which has 97% nucleotide sequence identity to that of the species exemplar isolate. Surveys for BGLV, utilising a newly designed universal panicovirus RT-PCR assay for diagnosis, demonstrated widespread infection by this virus in a broad variety of Bermuda grass cultivars (Cynodon dactylon and C. dactylon × C. transvaalensis) grown in both New South Wales and Queensland. The virus was also detected in Rhodes grass (Chloris gayana) and Kikuyu grass (Cenchrus clandestinus), which are both important pasture grasses in subtropical Australia, and the latter is also grown as turf. Furthermore, the Rhodes grass plant, which had strong mosaic symptoms, was also infected with sugarcane mosaic virus, warranting further investigations as to whether synergistic interactions occur between these two viruses
HETE-II and the Interplanetary Network
The FREGATE experiment aboard HETE-II has been successfully integrated into
the Third Interplanetary Network (IPN) of gamma-ray burst detectors. We show
how HETE's timing has been verified in flight, and discuss what HETE can do for
the IPN and vice-versa.Comment: To appear in the proceedings of the conference on Gamma-Ray Burst and
Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE
Mission, to be published by AIP. Figures must be downloaded and printed
separatel
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