137 research outputs found

    Bird Community Responses to Rest-Rotation Grazing in Western Canada\u27s Grasslands

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    Western Canada’s native grasslands support high levels of avian diversity including both resident and migrant species. Many grassland specialist bird populations, however, are in serious decline due to widespread habitat loss resulting from agricultural conversion and adverse land management. As the primary use on remaining grasslands, cattle grazing largely determines the availability and quality of bird species’ habitat, depending on the timing, intensity, and frequency of livestock use. While adaptive multi-paddock grazing (AMP, a short duration, high-intensity grazing system that prioritises plant recovery between grazing events) is growing in popularity, comprehensive assessments of bird diversity in relation to AMP grazing practices are largely lacking. As part of a larger grazing management study, we examined how AMP grazing practices influence the taxonomic and phylogenetic diversity of bird species, compared to neighbouring (n-AMP) properties managed with more conventional grazing practices. In addition to the AMP/n-AMP contrast, we used rancher survey information to test for the influence of specific grazing practices over and above biophysical effects. Bird communities were surveyed at 309 point count locations across 38 ranches (set up as matched pairs) using visual and acoustic detection. Overall, we identified 96 bird species, of which 81 species were recorded on AMP-grazed ranches compared to 84 species on grasslands under n-AMP grazing, ranging from 10-32 species per ranch. We observed a considerable grazing management signal on species abundance and diversity including significant associations between some threatened species and n-AMP grazing. Moreover, AMP grazing, and specifically the use of higher rest-to-grazing ratios early in the growing season (prior to August 1), was associated with phylogenetically more clustered bird communities. Overall, this study highlights the potential of specialized rotational grazing systems to alter the composition and phylogenetic diversity of grassland bird communities. In conclusion, we stress the importance for prioritisation of strategic management plans to safeguard and restore North America’s grassland bird communities

    CLIC High-Gradient Test Results

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    The CLIC (Compact Linear Collider) high-gradient RF structure testing program has been carried out in order to gain insight into the physical processes involved in RF breakdown, determine the mechanisms that limit gradient and produce damage so that technical concepts can be developed which allow higher accelerating gradients. Two main paths towards higher gradients have emerged from this program, and the performances of two new structures which incorporate them are presented

    High Power Test on an x-Band Slotted-Iris Accelerator Structure at NLCTA

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    The CLIC study group at CERN has built two X-band HDS (Hybrid Damped Structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf-design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design. INTRODUCTIO

    High-Gradient Test of a Tungsten-Iris X-Band Accelerator Structure at NLCTA

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    The CLIC study group at CERN has built two X-band accelerating structures to be tested at SLAC in NLCTA. The structures consist of copper cells with insert irises made out of molybdenum and tungsten, clamped together and installed in a vacuum tank. These structures are exactly scaled versions from structures tested previously at 30 GHz and with short pulses (16 ns) in the CLIC Test Facility at CERN. At 30 GHz these structures reached gradients of 150 MV/m for tungsten and 195 MV/m for molybdenum. These experiments were designed to provide data on the dependence of rf breakdown on pulse length and frequency. This paper reports in particular on the high-gradient test of the tungsten-iris structure. At the shortest possible pulse length of 22 ns a gradient of 125 MV/m was reached at X-band, 20 % lower than the 150 MV/m measured at 30 GHz in the CLIC Test Facility. The pulse length dependence and the dependence of the break down rate as a function of gradient were measured in detail. The results are compared to data obtained from the molybdenum-iris experiment at X-band which took place earlier as well as to 30 GHz data

    Commissioning Status of the CTF3 Delay Loop

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    The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the linear collider by 2010. In particular, one of the main goals is to study the generation of high-current electron pulses by interleaving bunch trains in delay lines and rings using transverse RF deflectors. This will be done in the 42 m long delay loop, built under the responsibility of INFN/LNF, and the 84 m long combiner ring that will follow it. The delay loop installation was completed and its commissioning started at the end of 2005. In this paper the commissioning results are presented, including the first tests of beam recombination

    Latest Developments from the S-DALINAC*

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    The S-DALINAC is a 130 MeV superconducting recirculating electron accelerator serving several nuclear and radiation physics experiments as well as driving an infrared free-electron laser. A system of normal conducting rf resonators for noninvasive beam position and current measurement was established. For the measurement of gamma-radiation inside the accelerator cave a system of Compton diodes has been developed and tested. Detailed investigations of the transverse phasespace were carried out with a tomographical reconstruction method of optical transition radiation spots. The method can be applied also to non-Gaussian phasespace distributions. The results are in good accordance with simulations. To improve the quality factor of the superconducting 3 GHz cavities, an external 2K testcryostat was commissioned. The influence of electro-chemical polishing and magnetic shielding is currently under investigation. A digital rf-feedback-system for the accelerator cavities is being developed in order to improve the energy spread of the beam of the S-DALINAC. * Supported by the BMBF under contract no. 06 DA 820, the DFG under contract no. Ri 242/12-1 and -2 and the DFG Graduiertenkolleg 'Physik und Technik von Beschleunigern

    Discussion on Research and Development of Local Documents Exchange Platform

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    地方文献是一个地方政治、经济、文化和社会事业发展以及历史、风俗、资源等方面的文献资料.它具有区域性、史料性、广泛性和时代性等特点,地方文献与一般文献的最主要区别在于其具有地方特色。因此,它是目前国内外图书馆界公认的重要文献资源之一。但是由于各地方图书馆在地方文献的收集标准、范围上并没有达成共识,收集重点也不明确。在地方文献保管上,除少数图书馆是设专库集中收藏外,绝大多数馆是分散在各个书库之中;在数据库建设方面缺乏统筹规划,处于一种无序的、各自为政的状态。因此,必须加强地方文献信息资源共享建设,使之更好的促进社会的发展,而传统的地方文献资源共享的方式主要有:建立联合目录与进行合作编目、馆际互借、...Local documents are a local political, economic, cultural and social undertakings development and the history, customs, resources and other aspects of documents. It has the characteristics of regional, historical data, universality and times. The most important differences between local documents and general documents is that local documents has its local characteristics. Therefore, it is one of t...学位:工学硕士院系专业:图书馆_计算机技术学号:X200822102

    Instrumentation for Longitudinal Beam Gymnastics in FEL's and at the CLIC Test Facility 3

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    Built at CERN by an international collaboration, the CLIC Test Facility 3 (CTF3) aims at demonstrating the feasibility of a high luminosity 3 TeV e+-e- collider by the year 2010. One of the main issues to be demonstrated is the generation of a high average current (30 A) high frequency (12 GHz) bunched beam by means of RF manipulation. At the same time, Free Electron Lasers (FEL) are developed in several places all over the world with the aim of providing high brilliance photon sources. These machines rely on the production of high peak current electron bunches. The required performances put high demands on the diagnostic equipment and innovative longitudinal monitors have been developed during the past years. This paper gives an overview of the longitudinal instrumentation developed at ELETTRA and CTF3, where a special effort was made in order to implement at the same time non-intercepting devices for online monitoring, and destructive diagnostics which have the advantage of providing more detailed information

    Competing electric and magnetic excitations in backward electron scattering from heavy deformed nuclei

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    Important E2E2 contributions to the (e,e)(e,e^{\prime}) cross sections of low-lying orbital M1M1 excitations are found in heavy deformed nuclei, arising from the small energy separation between the two excitations with IπK=2+1I^{\pi}K = 2^+1 and 1+1^+1, respectively. They are studied microscopically in QRPA using DWBA. The accompanying E2E2 response is negligible at small momentum transfer qq but contributes substantially to the cross sections measured at θ=165\theta = 165 ^{\circ} for 0.6<qeff<0.90.6 < q_{\rm eff} < 0.9 fm1^{-1} (40Ei7040 \le E_i \le 70 MeV) and leads to a very good agreement with experiment. The electric response is of longitudinal C2C2 type for θ175\theta \le 175 ^{\circ} but becomes almost purely transverse E2E2 for larger backward angles. The transverse E2E2 response remains comparable with the M1M1 response for qeff>1.2q_{\rm eff} > 1.2 fm1^{-1} (Ei>100E_i > 100 MeV) and even dominant for Ei>200E_i > 200 MeV. This happens even at large backward angles θ>175\theta > 175 ^{\circ}, where the M1M1 dominance is limited to the lower qq region.Comment: RevTeX, 19 pages, 8 figures included Accepted for publication in Phys Rev
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