Brightness enhancement limits in pulsed cladding pumped fiber Raman amplifiers

We analyze theoretically limitations on the brightness enhancement of a multimode pump beam, to be efficiently converted into a diffraction-limited Stokes beam in a cladding-pumped fiber Raman amplifier. For a given minimum Raman pump absorption, parasitic 2nd Stokes generation limits the cladding-to-core area ratio, and thus the brightness enhancement. A W-type fiber acting as a spectral waveguide filter allows for nearly five times larger inner-cladding areas by suppressing the 2nd Stokes. We further analyze limits set by glass damage and indirectly propagation loss, as well as pulse walk-off. A well-designed fiber with 3.5 dB/km propagation loss allows for a pump-to-signal brightness improvement of up to 3600 times both in the pulsed and the cw regime

100W CW cladding-pumped Raman fiber last at 1120nm

In recent years, rare-earth doped silica fiber lasers have become a popular medium to generate very high-power laser source, in particular in the 1 µm range where up to 10 kW single-mode ytterbium doped fiber (YDF) laser source has been reported and up to 0.9 kW from Tm doped fiber. The powers from other wavelengths are much lower typically between 10 to 100 W. An alternative to produce gain and power in optical fiber is to use nonlinear effect such as stimulated Raman scattering (SRS). SRS is wavelength agile, limited only by the transparency range of the fiber and the pump power wavelength. In addition, SRS sources benefit from low quantum defect, in particular at shorter wavelengths making them extremely efficient. However, because these effects rely on strong optical intensities to take place, fibers with small core size are typically used with core pumping scheme, limiting the scope for power scaling. Therefore, no very high power Raman fiber laser (RFL) has been reported and little progress has been made to increase the output power of those. As far as we are aware, the highest reported power from a core pumped RFL is about 68 W. There are several challenges in power scaling core-pumped Raman fiber laser, mainly the power handling capacity of single-mode fiber and the careful adjustment of the fiber length to avoid spurious 2nd order Stokes generation in the laser cavity

Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzburgites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0·5121 (close to the host minette values) to 0·5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd/144Nd values (0·5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf) as in the host minettes, and their Sr–Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere

Tandem-pumped ytterbium-doped aluminosilicate fiber amplifier with low quantum defect

We show theoretically that a quantum-defect below 1% is possible in tandem-pumped Yb-doped aluminosilicate fibers operating off the gain peak. Experimentally, we reach a quantum defect of 2% and a slope efficiency of 90% or more

Virtual Drive Testing Over-The-Air for Vehicular Communications

Multiple-input multiple-output (MIMO) over-the-air (OTA) testing is a standardized procedure to evaluate the performance of MIMO-capable devices such as mobile phones and laptops. With the growth of the vehicle-to-everything (V2X) service, the need for vehicular communication testing is expected to increase significantly. The so-called multi-probe anechoic chamber (MPAC) setup is standardized for MIMO OTA testing. Typically, a test zone of 0.85 wavelength in diameter can be achieved with an 8-probe MPAC setup, which can encompass device-under-test (DUT) of small form factors. However, a test zone of this size may not be large enough to encompass DUTs such as cars. In this article, the sufficient number of OTA probes for the MPAC setup for car testing is investigated with respect to the emulation accuracy. Our investigation shows that the effective antenna distance of the DUT is more critical than its physical dimensions to determine the required number of OTA probes. In addition, throughput measurements are performed under the standard SCME UMa and UMi channel models with the 8-probe MPAC setup and the wireless cable setup, i.e. another standardized testing setup. The results show reasonably good agreement between the two setups for MIMO OTA testing with cars under the standard channel models

Characteristics of healthy vascular ageing in pooled population-based cohort studies: the global Metabolic syndrome and Artery REsearch Consortium

Arterial ageing is characterized by increasing arterial stiffness as measured by pulse wave velocity (PWV). This process is enhanced in participants with early vascular ageing (EVA), but slowed in participants with healthy vascular ageing (HVA). We aimed to describe characteristics of EVA and HVA in a transcontinental study including 11 cohorts.The Asklepios Study is supported by the Fund for Scientific Research – Flanders (FWO research grants G042703 and G083810N). The Rotterdam Study is supported by the Erasmus Medical Center and Erasmus University Rotterdam; the Netherlands Organization for Scientific Research; the Netherlands Organization for Health Research and Devel- opment (ZonMw); the Research Institute for Diseases in the Elderly (RIDE); the Netherlands Heart Foundation; the Ministry of Education, Culture and Science; the Ministry of Health Welfare and Sports; the European Commission; and the Municipality of Rotterdam. The SardiNIA team was supported by Contract NO1-AG- 1–2109 from the NIA. This research was supported in part by the Intramural Research Program of the NIH, National Institute on Aging (USA). The Baltimore Longitudinal Study of Aging (BLSA) is supported in part by the Intramural Research Program of the NIH, National Institute on Aging. The Kingmen Aging Study was supported, in part, by a grant from the National Science Council (NSC 99-2314-B- 010-034-MY3), an intramural grant from the Taipei Veterans General Hospital (grant V102C-119), Research and Devel- opment contract NO1-AG-1–2118, and the Intramural Research Program of the National Institute on Aging, National Institutes of Health. The Malmoe Diet Cancer – Cardiovascular Study was supported by grants from the Swedish Research Council (K2008-65X-20752-01-3, K2011-65X-20752-04-6), the Lund- stroms Foundation, the Swedish Heart-Lung Foundation (2010-0244; 2013-0249) and ALF government grants (Dnr: 2012/1789)info:eu-repo/semantics/publishedVersio

Multiple Parton Scattering in Nuclei: Parton Energy Loss

Multiple parton scattering and induced parton energy loss is studied in deeply inelastic scattering (DIS) off nuclei. The effect of multiple scattering of a highly off-shell quark and the induced parton energy loss is expressed in terms of the modification to the quark fragmentation functions. We derive such modified quark fragmentation functions and their QCD evolution equations in DIS using generalized factorization of higher twist parton distributions. We consider double-hard, hard-soft parton scattering as well as their interferences in the same framework. The final result, which depends on both the diagonal and off-diagonal twist-four parton distributions in nuclei, demonstrates clearly the Landau-Pomeranchuk-Migdal interference features and predicts a unique nuclear modification of the quark fragmentation functions.Comment: Final version published in Nucl. Phys. A. 40 pages in RevTex with 15 postscript figure

Widespread forest vertebrate extinctions induced by a mega hydroelectric dam in lowland Amazonia

Mega hydropower projects in tropical forests pose a major emergent threat to terrestrial and freshwater biodiversity worldwide. Despite the unprecedented number of existing, underconstruction and planned hydroelectric dams in lowland tropical forests, long-term effects on biodiversity have yet to be evaluated. We examine how medium and large-bodied assemblages of terrestrial and arboreal vertebrates (including 35 mammal, bird and tortoise species) responded to the drastic 26-year post-isolation history of archipelagic alteration in landscape structure and habitat quality in a major hydroelectric reservoir of Central Amazonia. The Balbina Hydroelectric Dam inundated 3,129 km2 of primary forests, simultaneously isolating 3,546 land-bridge islands. We conducted intensive biodiversity surveys at 37 of those islands and three adjacent continuous forests using a combination of four survey techniques, and detected strong forest habitat area effects in explaining patterns of vertebrate extinction. Beyond clear area effects, edge-mediated surface fire disturbance was the most important additional driver of species loss, particularly in islands smaller than 10 ha. Based on species-area models, we predict that only 0.7% of all islands now harbor a species-rich vertebrate assemblage consisting of ≥80% of all species. We highlight the colossal erosion in vertebrate diversity driven by a man-made dam and show that the biodiversity impacts of mega dams in lowland tropical forest regions have been severely overlooked. The geopolitical strategy to deploy many more large hydropower infrastructure projects in regions like lowland Amazonia should be urgently reassessed, and we strongly advise that long-term biodiversity impacts should be explicitly included in pre-approval environmental impact assessments