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排序方式: 共有335条查询结果,搜索用时 203 毫秒
131.
Haller J Jenderka KV Durando G Shaw A 《The Journal of the Acoustical Society of America》2012,131(2):1121-1130
The pressure fields of two different high intensity focused ultrasound (HIFU) transducers operated in burst mode were measured at acoustical power levels of 25 and 50 W (continuous wave equivalent) with three different hydrophones: A fiber-optic displacement sensor, a commercial HIFU needle hydrophone, and a prototype of a membrane hydrophone with a protective coating against cavitation effects. Additionally, the fields were modeled using a freely available simulations software package. The measured waveforms, the peak pressure profiles, as well as the spatial-peak temporal-average intensities from the different devices and from the modeling are compared and possible reasons for differences are discussed. The results clearly show that reliable pressure measurements in HIFU fields remain a difficult task concerning both the reliability of the measured values and the robustness of the sensors used: Only the fiber-optic hydrophone survived all four exposure regimes and the measured spatial-peak temporal-average intensities varied by a factor of up to 1.5 between the measurements and the modeling and between the measurements among themselves. 相似文献
132.
Kirk Haller Audrey Lee-St.John Meera Sitharam Ileana Streinu Neil White 《Computational Geometry》2012,45(8):385-405
Motivated by constraint-based CAD software, we develop the foundation for the rigidity theory of a very general model: the body-and-cad structure, composed of rigid bodies in 3D constrained by pairwise coincidence, angular and distance constraints. We identify 21 relevant geometric constraints and develop the corresponding infinitesimal rigidity theory for these structures. The classical body-and-bar rigidity model can be viewed as a body-and-cad structure that uses only one constraint from this new class.As a consequence, we identify a new, necessary, but not sufficient, counting condition for minimal rigidity of body-and-cad structures: nested sparsity. This is a slight generalization of the well-known sparsity condition of Maxwell. 相似文献
133.
M. Baak M. Goebel J. Haller A. Hoecker D. Kennedy K. M?nig M. Schott J. Stelzer 《The European Physical Journal C - Particles and Fields》2012,72(5):1-35
We present an update of the Standard Model fit to electroweak precision data. We include newest experimental results on the top-quark mass, the W mass and width, and the Higgs-boson mass bounds from LEP, Tevatron and the LHC. We also include a new determination of the electromagnetic coupling strength at the Z pole. We find for the Higgs-boson mass $91^{+30}_{-23}~\mbox{GeV}$ and $120^{+12}_{-5}~\mbox{GeV}$ when not including and including the direct Higgs searches, respectively. From the latter fit we indirectly determine the W mass to be $(80.360^{+0.014}_{-0.013})~\mbox{GeV}$ . We exploit the data to determine experimental constraints on the oblique vacuum polarisation parameters, and confront these with predictions from the Standard Model (SM) and selected SM extensions. By fitting the oblique parameters to the electroweak data we derive allowed regions in the BSM parameter spaces. We revisit and consistently update these constraints for a fourth fermion generation, two Higgs doublet, inert Higgs and littlest Higgs models, models with large, universal or warped extra dimensions and technicolour. In most of the models studied a heavy Higgs boson can be made compatible with the electroweak precision data. 相似文献
134.
We show how the recently developed theory of geodesic transport barriers for fluid flows can be used to uncover key invariant manifolds in externally forced, one-degree-of-freedom mechanical systems. Specifically, invariant sets in such systems turn out to be shadowed by least-stretching geodesics of the Cauchy–Green strain tensor computed from the flow map of the forced mechanical system. This approach enables the finite-time visualization of generalized stable and unstable manifolds, attractors and generalized KAM curves under arbitrary forcing, when Poincaré maps are not available. We illustrate these results by detailed visualizations of the key finite-time invariant sets of conservatively and dissipatively forced Duffing oscillators. 相似文献
135.
Heng Pan Nipun Misra Seung H. Ko Costas P. Grigoropoulos Nate Miller Eugene E. Haller Oscar Dubon 《Applied Physics A: Materials Science & Processing》2009,94(1):111-115
Nanoparticle solutions are considered promising for realizing low cost printable high performance flexible electronics. In
this letter, excimer laser annealing (ELA) was employed to induce melting of solution-deposited ZnO nanoparticles and form
electrically conductive porous films. The properties of the films were characterized by scanning electron microscopy, high-resolution
transmission electron microscopy, DC conductance, and photoluminescence measurements. Thin-film field-effect transistors have
been fabricated by ELA without the use of conventional vacuum or any high temperature thermal annealing processes. The transistors
show n-type accumulation mode behavior with mobility greater than 0.1 cm2/V s and current on/off ratios of more than 104. Optimization and control of the laser processing parameters minimized thermal impact on the substrate. This technique can
be beneficial in the fabrication of metal oxide based electronics on heat sensitive flexible plastic substrates using low-cost,
large-area solution processing combined with direct printing techniques. 相似文献
136.
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139.
MRI-guided biopsy in inflammatory myopathy: Initial results 总被引:3,自引:0,他引:3
Alan M. Pitt James L. Fleckenstein Ralph G. Greenlee Jr. Dennis K. Burns Wilson W. Bryan Ronald Haller 《Magnetic resonance imaging》1993,11(8):1093-1099
The purpose of this report is to describe our initial experience with techniques employing magnetic resonance imaging (MRI) to guide the choice of muscle to be biopsied in patients suspected of having inflammatory myopathy. Five patients with a clinical diagnosis of inflammatory myopathy (IM) were studied. Four were imaged prior to biopsy. Four had repeated examinations, either immediately following biopsy or to evaluate disease progression. Use of MRI to localize muscle lesions was associated with abnormal pathologic findings in all cases, including histopathologic demonstration of lymphocyte infiltration in three cases of idiopathic polymyositis; nonspecific myopathic changes were seen in one patient with probable dermatomyositis and in one patient with chronic inflammatory polyneuropathy and high serum creatine kinase levels (>45,000 IU/ml). The precise location of the area sampled by biopsy was visible in only one of four postbiopsy images. MRI shows promise in identifying pathologic muscle in patients suspected of having one of the inflammatory myopathies; however, further refinement of localization techniques may be needed to optimize histopathologic diagnoses. 相似文献
140.
E. Silveira W. Dondl G. Abstreiter E. E. Haller 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
Raman scattering by optical phonons is used to study the interface intermixing in isotopic (
Ge)
(
Ge)
thin superlattices, with
and
equal to 8, 12, 16 and 24 atomic monolayers, for annealling at
C and various times. The experimental results compares very well with theoretical calculations within the planar force constant model and the bond polarizability approach. The diffusion is simulated by a combination of the virtual crystal approximation and the solution of the Fick’s diffusion equation for the superlattice geometry. 相似文献