827 research outputs found
Extreme laser pulses for possible development of boron fusion power reactors for clean and lasting energy
Extreme laser pulses driving non-equilibrium processes in high density
plasmas permit an increase of the fusion of hydrogen with the boron isotope 11
by nine orders of magnitude of the energy gains above the classical values.
This is the result of initiating the reaction by non-thermal ultrahigh
acceleration of plasma blocks by the nonlinear (ponderomotive) force of the
laser field, in addition to the avalanche reaction that has now been
experimentally and theoretically manifested. The design of a very compact
fusion power reactor is scheduled to produce then environmentally fully clean
and inexhaustible generation of energy at profitably low costs. The reaction
within a volume of cubic millimetres during a nanosecond can only be used for
controlled power generation.Comment: 10 pages, 5 fugure
Modelling of Dynamic Strain Aging with a Dislocation-Based Isotropic Hardening Model and Investigation of Orthogonal Loading
Based on experimental results, a dislocation material model describing the dynamic strain aging\ud
effect at different temperatures is presented. One and two stage loading tests were performed in\ud
order to investigate the influence of the loading direction as well as the temperature influence due\ud
to the hardening mechanism. Bergstrƶmās theory of work hardening was used as a basis for the\ud
model development regarding the thermal isotropic behavior as well as the Chaboche model to\ud
describe the kinematic hardening. Both models were implemented in an in-house FE-Code in\ud
order to simulate the real processes. The present paper discusses two hardening mechanisms,\ud
where the first part deals with the pure isotropic hardening including dynamic strain aging and the\ud
second part involves the influence of the loading direction regarding combined (isotropic and\ud
kinematic) hardening behavior
Accounting for material scatter in sheet metal forming simulations
Robust design of forming processes is gaining attention throughout the industry. To analyze the robustness of a sheet metal forming process using Finite Element (FE) simulations, an accurate input in terms of parameter variation is required. This paper presents a pragmatic, accurate and economic approach for measuring and modeling one of the main inputs, i.e. material properties and its associated scattering. For the purpose of this research, samples of 41 coils of a forming steel DX54D+Z (EN 10327:2004) from multiple batches have been collected. Fully determining the stochastic material behavior to the required accuracy for precise modeling in FE simulations would involve performing many mechanical experiments. Instead, the present work combines mechanical testing and texture analysis to limit the required effort. Moreover, use is made of the correlations between the material parameters to efficiently model the material property scatter for use in the numerical robustness analysis. The proposed approach is validated by the forming of a series of cup products using the collected material. The observed experimental scatter can be reproduced efficiently using FE simulations, demonstrating the potential of the modeling approach and robustness analysis in general
Material Induced Anisotropic Damage
The anisotropy in damage can be driven by two different phenomena; anisotropic defor-mation state named Load Induced Anisotropic Damage (LIAD) and anisotropic (shape and/or distribution) second phase particles named Material Induced Anisotropic Damage (MIAD). Most anisotropic damage models are based on LIAD. This work puts emphasis on the presence of MIAD in DP600 steel. Scanning Electron Microscopic (SEM) analysis was carried out on undeformed and deformed tensile specimens. The martensite morphology showed anisotropy in size and orientation. Consequently, significant MIAD was observed in the deformed tensile specimens. A through thickness shear failure is observed in the tensile specimen, which is pulled along the rolling direction (RD), whereas a dominant ductile fracture is observed when pulled perpendicular to RD. The Modified Lemaitreās (ML) anisotropic damage model is improved to account for MIAD in a phenomenological manner. The MIAD parameters are determined from tensile tests carried out in 0o, 45o and 90o to the RD. The formability of DP600 is lower in the RD compared to that in 90o to the RD, due to the phenomenon of MIAD
Compactlike kinks and vortices in generalized models
This work deals with the presence of topological defects in k-field models,
where the dynamics is generalized to include higher order power in the kinetic
term. We investigate kinks in (1,1) dimensions and vortices in (2,1)
dimensions, focusing on some specific features of the solutions. In particular,
we show how the kinks and vortices change to compactlike solutions, controlled
by the parameter used to introduce the generalized models.Comment: 7 pages, 7 figures. Version to be published in PR
Cascaded acceleration of proton beams in ultrashort laser-irradiated microtubes
A cascaded ion acceleration scheme is proposed by use of ultrashort
laser-irradiated microtubes. When the electrons of a microtube are blown away
by intense laser pulses, strong charge-separation electric fields are formed in
the microtube both along the axial and along the radial directions. By
controlling the time delay between the laser pulses and a pre-accelerated
proton beam injected along the microtube axis, we demonstrate that this proton
beam can be further accelerated by the transient axial electric field in the
laser-irradiated microtube. Moreover, the collimation of the injected proton
beam can be enhanced by the inward radial electric field. Numerical simulations
show that this cascaded ion acceleration scheme works efficiently even at
non-relativistic laser intensities, and it can be applied to injected proton
beams in the energy range from 1 to 100 MeV. Therefore, it is particularly
suitable for cascading acceleration of protons to higher energy.Comment: 13 pages, 4 figure
Oreoglanis infulatus , a new species of glyptosternine catfish (Siluriformes: Sisoridae) from central Vietnam
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72781/1/j.1095-8649.2001.tb00183.x.pd
Chirped pulse Raman amplification in plasma
Raman amplification in plasma has been proposed to be a promising method of amplifying short radiation pulses. Here, we investigate chirped pulse Raman amplification (CPRA) where the pump pulse is chirped and leads to spatiotemporal distributed gain, which exhibits superradiant scaling in the linear regime, usually associated with the nonlinear pump depletion and Compton amplification regimes. CPRA has the potential to serve as a high-efficiency high-fidelity amplifier/compressor stage
Physical Properties of Near-Earth Asteroid 2011 MD
We report on observations of near-Earth asteroid 2011 MD with the Spitzer
Space Telescope. We have spent 19.9 h of observing time with channel 2 (4.5
{\mu}m) of the Infrared Array Camera and detected the target within the
2{\sigma} positional uncertainty ellipse. Using an asteroid thermophysical
model and a model of nongravitational forces acting upon the object we
constrain the physical properties of 2011 MD, based on the measured flux
density and available astrometry data. We estimate 2011 MD to be 6 (+4/-2) m in
diameter with a geometric albedo of 0.3 (+0.4/-0.2) (uncertainties are
1{\sigma}). We find the asteroid's most probable bulk density to be 1.1
(+0.7/-0.5) g cm^{-3}, which implies a total mass of (50-350) t and a
macroporosity of >=65%, assuming a material bulk density typical of
non-primitive meteorite materials. A high degree of macroporosity suggests 2011
MD to be a rubble-pile asteroid, the rotation of which is more likely to be
retrograde than prograde.Comment: 20 pages, 4 figure
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