96 research outputs found
Control of Length and Spatial Functionality of Single-Wall Carbon Nanotube AFM Nanoprobes
Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto conductive
atomic force microscopy (AFM) probes with the help of dielectrophoresis (DEP).
This process involved the application of a 10 V, 2 MHz, AC bias between a
metal-coated AFM probe and a dilute suspension of SWNTs. This exerted a
positive dielectrophoretic force onto the nanotubes that caused them to align
while precipitating out onto the probe. The gradual removal of the AFM probe
away from the SWNT suspension consolidated these nanotubes into nanofibrils
with a high degree of alignment as demonstrated with polarization Raman
experiments. By varying the pulling speed, immersion time, and concentration of
the SWNT suspension, one can tailor the diameter and thus the stiffness of
these probes. Precise length trimming of these nanofibrils was also performed
by their gradual immersion and dissolution into a liquid that strongly
interacted with nanotubes, (i.e., sodium dodecyl sulfate (SDS) solution).
Vacuum annealing these nanoprobes at temperature up to 450 degree C further
increased their stiffness and rendered them insoluble to SDS and all other
aqueous media. Regrowth of a new SWNT nanofibril from the side or at the end of
a previously grown SWNT nanofibril was also demonstrated by a repeated
dielectrophoretic assembly at the desired immersion depth. These SWNT
nanofibril-equipped AFM probes are electrically conductive and mechanically
robust for use as high-aspect-ratio electrochemical nanoprobes
Characterisation of Laser Wakefield Acceleration Efficiency with Octave Spanning Near-IR Spectrum Measurements
We report on high efficiency energy transfer in a GeV-class laser wakefield
accelerator. Both the transfer of energy from the laser to the plasma
wakefield, and from the plasma to the accelerated electron beam were diagnosed
experimentally by simultaneous measurement of the deceleration of laser photons
and the accelerated electrons as a function of acceleration length. The
extraction efficiency, which we define as the ratio of the energy gained by the
electron beam to the energy lost by the self-guided laser mode, was maximised
at % by tuning of the plasma density, plasma length and incident laser
pulse compression. At higher densities, the laser was observed to fully
redshift over an entire octave, from 800~nm to 1600~nm.Comment: 7 pages, 5 figure
Response-based selection of barley cultivars and legume species for complementarity:root morphology and exudation in relation to nutrient source
Phosphorus (P) and nitrogen (N) use efficiency may be improved through increased biodiversity in agroecosystems. Phenotypic variation in plants’ response to nutrient deficiency may influence positive complementarity in intercropping systems. A multicomponent screening approach was used to assess the influence of P supply and N source on the phenotypic plasticity of nutrient foraging traits in barley (H. vulgare L.) and legume species. Root morphology and exudation were determined in six plant nutrient treatments. A clear divergence in the response of barley and legumes to the nutrient treatments was observed. Root morphology varied most among legumes, whereas exudate citrate and phytase activity were most variable in barley. Changes in root morphology were minimized in plants provided with ammonium in comparison to nitrate but increased under P deficiency. Exudate phytase activity and pH varied with legume species, whereas citrate efflux, specific root length, and root diameter lengths were more variable among barley cultivars. Three legume species and four barley cultivars were identified as the most responsive to P deficiency and the most contrasting of the cultivars and species tested. Phenotypic response to nutrient availability may be a promising approach for the selection of plant combinations for minimal input cropping systems
Generation of electron high energy beams with a ring-like structure by a dual stage laser wakefield accelerator
The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 – 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process
Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures
Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA, we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 µm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from LWFA can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures
A three-step numerical approximant based on block hybrid backward differentiation formula for stiff system of ordinary differential equation
We present results of an analysis of the reaction in the two-photon process in the untagged mode. The cross section is largely compatible with previous determinations; however, we do not confirm the enhancement claimed at 1.9 GeV. All observed ω's are accompanied by ϱ's in the recoiling ππ spectrum. An angular correlation analysis shows that the data is not dominated by a single spin-parity state, thus establishing severe constraints on models which predict
Алгоритм сжатия на основе вычисления скорости изменения ультразвукового сигнала
The intermittency structure of multihadronic e+e- annihilation is analyzed by evaluating the factorial moments F2-F5 in three-dimensional Lorentz invariant phase space as a function of the resolution scale. We interpret our data in the language of fractal objects. It turns out that the fractal dimension depends on the resolution scale in a way that can be attributed to geometrical resolution effects and dynamical effects, such as the pi-O Dalitz decay. The LUND 7.2 hadronization model provides an excellent description of the data. There is no indication of unexplained multiplicity fluctuations in small phase space regions
Разработка модульного стенда физического подобия для изучения гидротехнических систем
В рамках данной работы проведен обзор и анализ образовательных стендов, сформулирована концепция модульного стенда физического подобия, разработаны функциональные схемы двух модулей, в соответствии с которыми подобраны основные элементы. Для первого модуля предоставлены принципиальная схема и демонстрационный алгоритм работы.In this work, a review and analysis of educational booths, formulated the concept of modular stand physical similarity, developed functional diagrams of the two modules, in accordance with which the selected basic elements. For the first module, a schematic diagram and a demonstration algorithm are provided
Накопление газообразных продуктов деления и соединений в микрокапсулированном топливе в сверхдлинных кампаниях
The production of b and c quarks in annihilation has been studied with the CELLO detector in the range from 35 GeV up to the highest PETRA energies. The heavy quarks have been tagged by their semileptonic decays. The charge asymmetries for b quarks at 35 and 43 GeV have been found to be , respectively, using a method incorporating jet variables and their correlations for the separation of the heavy quarks from the back ground of the lighter quarks. For c quarks we obtain and , respectively. The axial vector coupling constants of the heavy quarks c and b are found to be and taking mixing into account. The results are in agreement with the expectations from the standard model
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