1,536 research outputs found
Design of a 3 GHz Accelerator Structure for the CLIC Test Facility (CTF 3) Drive Beam
For the CLIC two-beam scheme, a high-current, long-pulse drive beam is
required for RF power generation. Taking advantage of the 3 GHz klystrons
available at the LEP injector once LEP stops, a 180 MeV electron accelerator is
being constructed for a nominal beam current of 3.5 A and 1.5 microsecond pulse
length. The high current requires highly effective suppression of dipolar
wakes. Two concepts are investigated for the accelerating structure design: the
"Tapered Damped Structure" developed for the CLIC main beam, and the "Slotted
Iris - Constant Aperture" structure. Both use 4 SiC loads per cell for
effective higher-order mode damping. A full-size prototype of the TDS structure
has been built and tested successfully at full power. A first prototype of the
SICA structure is being built.Comment: Contribution to Linac 2000 Conference, TUA16 (Poster
Giant Spin Seebeck Effect through an Interface Organic Semiconductor
Interfacing an organic semiconductor C60 with a non-magnetic metallic thin
film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at
ambient temperature, while its interface with a magnetic metal (Fe or Co) can
tune the anisotropic magnetic surface property of the material. Here, we
demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12:
YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient
spin current transport via the thermally driven spin Seebeck effect (SSE).
Experiments and first principles calculations consistently show that the
presence of C60 reduces significantly the conductivity mismatch between YIG and
Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to
enhanced spin mixing conductance across YIG/C60/Pt interfaces. As a result, a
600% increase in the SSE voltage (VLSSE) has been realized in YIG/C60/Pt
relative to YIG/Pt. Temperature-dependent SSE voltage measurements on
YIG/C60/Pt with varying C60 layer thicknesses also show an exponential increase
in VLSSE at low temperatures below 200 K, resembling the temperature evolution
of spin diffusion length of C60. Our study emphasizes the important roles of
the magnetic anisotropy and the spin diffusion length of the intermediate layer
in the SSE in YIG/C60/Pt structures, providing a new pathway for developing
novel spin-caloric materials
Unusual chemical bond and spectrum of beryllium dimer in ground state
This review outlines the main results which show the dual nature of the
chemical bond in diatomic beryllium molecule in the ground
state. It has been shown that the beryllium atoms are covalently bound at
low-lying vibrational energy levels ({\nu}=0-4), while at higher ones
({\nu}=5-11) they are bound by van der Waals forces near the right turning
points. High precision ab initio quantum calculations of Be resulted in the
development of the modified expanded Morse oscillator potential function which
contains all twelve vibrational energy levels [A.V. Mitin, Chem. Phys. Lett.
682, 30 (2017)]. The dual nature of chemical bond in Be is evidenced as a
sharp corner on the attractive branch of the ground state potential curve.
Moreover, it has been found that the Douglas-Kroll-Hess relativistic
corrections also show a sharp corner when presented in dependence on the
internuclear separation. The difference in energy between the extrapolated and
calculated multi-reference configuration interaction energies in dependence on
the internuclear separation also exhibits singular point in the same region.
The other problems of ab initio quantum calculations of the beryllium dimer are
also discussed. Calculated spectrum of vibrational-rotational bound states and
new metastable states of the beryllium dimer in the ground state important for
laser spectroscopy are presented. The vibration problem was solved for the
modified expanded Morse oscillator potential function and for the potential
function obtained with Slater-type orbitals [M. Lesiuk et al, Chem. Theory
Comput. 15, 2470 (2019)]. The theoretical upper and lower estimates of the
spectrum of vibrational-rotational bound states and the spectrum of
rotational-vibrational metastable states with complex-valued energy eigenvalues
and the scattering length in the beryllium dimer are presented
GPU-based Approaches for Multiobjective Local Search Algorithms. A Case Study: the Flowshop Scheduling Problem
International audienceMultiobjective local search algorithms are efficient methods to solve complex problems in science and industry. Even if these heuristics allow to significantly reduce the computational time of the solution search space exploration, this latter cost remains exorbitant when very large problem instances are to be solved. As a result, the use of GPU computing has been recently revealed as an efficient way to accelerate the search process. This paper presents a new methodology to design and implement efficiently GPU-based multiobjective local search algorithms. The experimental results show that the approach is promising especially for large problem instances
Predicting wet age-related macular degeneration (AMD) using DARC (detecting apoptosing retinal cells) AI (artificial intelligence) technology
Objectives:
To assess a recently described CNN (convolutional neural network) DARC (Detection of Apoptosing Retinal Cells) algorithm in predicting new Subretinal Fluid (SRF) formation in Age-related-Macular-Degeneration (AMD).
Methods:
Anonymized DARC, baseline and serial OCT images (n = 427) from 29 AMD eyes of Phase 2 clinical trial (ISRCTN10751859) were assessed with CNN algorithms, enabling the location of each DARC spot on corresponding OCT slices (n = 20,629). Assessment of DARC in a rabbit model of angiogenesis was performed in parallel.
Results:
A CNN DARC count >5 at baseline was significantly (p = 0.0156) related to development of new SRF throughout 36 months. Prediction rate of eyes using unique DARC spots overlying new SRF had positive predictive values, sensitivities and specificities >70%, with DARC count significantly (p < 0.005) related to the magnitude of SRF accumulation at all time points. DARC identified earliest stages of angiogenesis in-vivo.
Conclusions:
DARC was able to predict new wet-AMD activity. Using only an OCT-CNN definition of new SRF, we demonstrate that DARC can identify early endothelial neovascular activity, as confirmed by rabbit studies. Although larger validation studies are required, this shows the potential of DARC as a biomarker of wet AMD, and potentially saving vision-loss
Etiology and Severity of Liver Disease in HIV-Positive Patients With Suspected NAFLD: Lessons From a Cohort With Available Liver Biopsies
BACKGROUND: Spectrum of liver injury among HIV-positive people is wide; in particular, prevalence of nonalcoholic fatty liver disease (NAFLD) seems to be higher compared with HIV-negative people. METHODS: We retrospectively evaluated all liver biopsies performed at Royal Free Hospital from 2000 to 2017 in HIV monoinfected patients with abnormal transaminases, to assess the underlying cause of liver disease and to characterize the extent of fibrosis. We furthermore evaluated the diagnostic accuracy of FIB4 and FibroScan as noninvasive tools for fibrosis assessment. RESULTS: Ninety-seven patients were included. Most common histological findings were NAFLD (28%), nonspecific changes (26%), and normal histology (13%). Twenty percent of the patients had significant fibrosis and 11% had advanced fibrosis. FIB4, at a cutoff of 1.3, had a specificity of 82% and negative predictive value (NPV) of 95% for exclusion of advanced fibrosis. FibroScan was available in 28% patients and 33% had a liver stiffness ≥7.5 kPa. FibroScan showed a specificity of 77% and NPV of 94% for exclusion of significant fibrosis. Among patients with NAFLD (n = 27), 18% had advanced fibrosis, whereas the majority (56%) did not have any fibrosis. The NPV of FIB4 for advanced fibrosis in these patients was 93%. CONCLUSIONS: Among HIV-positive patients with elevated transaminases, a surprisingly high number of patients had nonsignificant changes or even normal histological findings. The prevalence of NAFLD was lower than reported in other series. Use of noninvasive tools with a high NPV for significant fibrosis can help reduce the number of required biopsies
Herschel Observations of the W43 "mini-starburst"
Aims: To explore the infrared and radio properties of one of the closest
Galactic starburst regions. Methods: Images obtained with the Herschel Space
Observatory at wavelengths of 70, 160, 250, 350, and 500 microns using the PACS
and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8
micron images from the Spitzer Space Telescope. The morphology of the
far-infrared emission is combined with radial velocity measurements of
millimeter and centimeter wavelength transitions to identify features likely to
be associated with the W43 complex. Results: The W43 star-forming complex is
resolved into a dense cluster of protostars, infrared dark clouds, and ridges
of warm dust heated by massive stars. The 4 brightest compact sources with L >
1.5 x 10^4 Lsun embedded within the Z-shaped ridge of bright dust emission in
W43 remain single at 4" (0.1 pc) resolution. These objects, likely to be
massive protostars or compact clusters in early stages of evolution are
embedded in clumps with masses of 10^3 to 10^4 Msun, but contribute only 2% to
the 3.6 x 10^6 Lsun far-IR luminosity of W43 measured in a 16 by 16 pc box. The
total mass of gas derived from the far-IR dust emission inside this region is
~10^6 Msun. Cometary dust clouds, compact 6 cm radio sources, and warm dust
mark the locations of older populations of massive stars. Energy release has
created a cavity blowing-out below the Galactic plane. Compression of molecular
gas in the plane by the older HII region near G30.684-0.260 and the bipolar
structure of the resulting younger W43 HII region may have triggered the
current mini-star burst.Comment: 5 pages, 3 figures, accepted for A&A Special Issu
<i>Herschel</i> observations of B1-bS and B1-bN: two first hydrostatic core candidates in the Perseus star-forming cloud
We report far-infrared Herschel observations obtained between 70 ÎĽm and 500 ÎĽm of two star-forming dusty condensations, [HKM99] B1-bS and [HKM99] B1-bN, in the B1 region of the Perseus star-forming cloud. In the western part of the Perseus cloud, B1-bS is the only source detected in all six PACS and SPIRE photometric bands, but it is not visible in the Spitzer map at 24 ÎĽm. B1-bN is clearly detected between 100 ÎĽm and 250 ÎĽm. We have fitted the spectral energy distributions of these sources to derive their physical properties, and find that a simple greybody model fails to reproduce the observed spectral energy distributions. At least a two-component model is required, consisting of a central source surrounded by a dusty envelope. The properties derived from the fit, however, suggest that the central source is not a Class 0 object. We then conclude that while B1-bS and B1-bN appear to be more evolved than a pre-stellar core, the best-fit models suggest that their central objects are younger than a Class 0 source. Hence, they may be good candidates to be examples of the first hydrostatic core phase. The projected distance between B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close to this value, this pair would allow studying the mutual interactions between two forming stars at a very early stage of their evolution
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