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 X1Σg+X^1\Sigma_g^+ state

This review outlines the main results which show the dual nature of the chemical bond in diatomic beryllium molecule in the ground $X^1\Sigma_g^+$ 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$_2$ 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$_2$ 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 μm and 500 μm 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 μm. B1-bN is clearly detected between 100 μm and 250 μm. 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