Pinching Conditions Research Articles

Effects of different loading conditions on the stress features of hyperextension injury to the cervical spinal cord

Objective To investigate the mechanical responses by the cervical spinal cord to the hyperextension injury under different loading conditions. Methods A three dimensional finite element model of the cervical spinal cord was built and imported into the preprocessor of the Ansys software for assigning boundary and different loading conditions. Then the extension and pinching conditions were simulated after the solution module was entered. The stress results of 9 different anatomical regions in the cross-section of the cervical spinal cord were read and analyzed in the postprocessor of the Ansys software. Results The localized stress mainly occurred at the anterior horn and posterior horn in the gray matter, the anterior funiculus, the medial part of the lateral funiculus, and the lateral part of the posterior funiculus, with the average magnitude decreasing successively. The magnitude of the stress increased with the severity of the cervical spine injury. The maximum stress increment occurrred at the anterior horn. Significant differences in the stress increment were observed between the anterior horn and the lateral funiculus( P 0. 05). Conclusions The cervical hyperextension injury mainly leads to injury to the motor neuron of the anterior horn. More damage to the motor neuron dominating the intrinsic muscle of hand can lead to poorer prognosis. A greater injury load may cause stress to distribute onto more adjacent white matter. Key words: Spinal cord injuries; Finite element analysis; Biomechanics

The volume-preserving mean curvature flow in Euclidean space

We study the convergence of the volume-preserving mean curvature flow of hypersurfaces in Euclidean space under some initial integral pinching conditions. We prove that if the traceless second fundamental form is sufficiently small, the flow will exist for all time and converge exponentially fast to a round sphere.

GaN‐on‐Si HEMT stress under high electric field condition

AbstractNowadays, GaN‐on‐Si HEMTs (High Electron Mobility transistors) are receiving a lot of attention thanks to their impressive performance in terms of high current and voltage capabilities combined with a low production cost. Since the technology has matured, the reliability aspects have been initially investigated in order to prove the performances of these devices in the long term. In this work GaN‐on‐Si HEMTs were electrically stressed in pinched off condition while high voltages were applied on the drain side (high electric field condition). Transistors with and without in‐situ Si3N4 layer underneath the gate were tested, as well as a transistor with 1 μm field plate on each side, due to a T shaped gate.Both type of devices with and without Si3N4 under the gate showed the same failure mode: a sudden increase of the gate and drain leakage current. This excludes, in principle, the role of Si3N4 layer on the degradation mechanism involved. Possible explanations about the failure mechanism are compared and discussed. Finally, a preliminary test on the T‐shape gate technology showed no degradation after more than 500 hours under high electric field condition of stress, which include 282 hours in pinched off condition with the drain voltage fixed as high as 60 V. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Space-like hypersurfaces in locally symmetric Lorentz space

Let M be an n-dimensional space-like hypersurface in a locally symmetric Lorentz space, with n(n−1)R=κH(κ>0) and satisfying certain additional conditions on the sectional curvature. Denote by S and H the squared norm of the second fundamental form and the mean curvature of M, respectively. We show that if the mean curvature is nonnegative and attains its maximum on M, then: (1) if H2<4(n−1)c/n2, M is totally umbilical; (2) if H2=4(n−1)c/n2, M is totally umbilical or is an isoparametric hypersurface; (3) if H2>4(n−1)c/n2 and S satisfies some pinching conditions, M is totally umbilical or is an isoparametric hypersurface. doi:10.1017/S1446181108000254

SPACE-LIKE HYPERSURFACES IN LOCALLY SYMMETRIC LORENTZ SPACE

Let M be an n-dimensional space-like hypersurface in a locally symmetric Lorentz space, with n(n−1)R=κH(κ>0) and satisfying certain additional conditions on the sectional curvature. Denote by S and H the squared norm of the second fundamental form and the mean curvature of M, respectively. We show that if the mean curvature is nonnegative and attains its maximum on M, then: (1) if H2<4(n−1)c/n2, M is totally umbilical; (2) if H2=4(n−1)c/n2, M is totally umbilical or is an isoparametric hypersurface; (3) if H2>4(n−1)c/n2 and S satisfies some pinching conditions, M is totally umbilical or is an isoparametric hypersurface. doi:10.1017/S1446181108000254

The Brake Orbits of Hamiltonian Systems on Positive-type Hypersurfaces

This paper deals with the brake orbits of Hamiltonian system Open image in new window on given energy hypersurfaces Σ = H −1(1). We introduce a class of contact type but not necessarily star-shaped hypersurfaces in ℝ2n and call them normalized positive-type hypersurfaces. By using of the critical point theory, we prove that if Σ is a partially symmetric normalized positive-type hypersurface, it must carries a brake orbit of (HS). Furthermore, we obtain some multiplicity results under certain pinching conditions. Our results include the earlier works on this subject given by P. Rabinowitz and A. Szulkin in star-shaped case. An example of partially symmetric normalized positive-type hypersurface in ℝ4 that is not star-shaped is also presented

A Möbius characterization of submanifolds

In this paper, we study Mobius characterizations of submanifolds without umbilical points in a unit sphere S n + p ( 1 ) . First of all, we proved that, for an n -dimensional ( n ≥ 2 ) submanifold x : M ↦ S n + p ( 1 ) without umbilical points and with vanishing Mobius form Φ , if ( n - 2 ) | | A ˜ | | ≤ n - 1 n n R - 1 n [ ( n - 1 ) 2 - 1 p - 1 ] is satisfied, then, x is Mobius equivalent to an open part of either the Riemannian product S n - 1 ( r ) × S 1 1 - r 2 in S n + 1 ( 1 ) , or the image of the conformal diffeomorphism σ of the standard cylinder S n - 1 ( 1 ) × R in R n + 1 , or the image of the conformal diffeomorphism τ of the Riemannian product S n - 1 ( r ) × H 1 1 + r 2 in H n + 1 , or x is locally Mobius equivalent to the Veronese surface in S 4 ( 1 ) . When p = 1 , our pinching condition is the same as in Main Theorem of Hu and Li [6], in which they assumed that M is compact and the Mobius scalar curvature n ( n - 1 ) R is constant. Secondly, we consider the Mobius sectional curvature of the immersion x . We obtained that, for an n -dimensional compact submanifold x : M ↦ S n + p ( 1 ) without umbilical points and with vanishing form Φ , if the Mobius scalar curvature n ( n - 1 ) R of the immersion x is constant and the Mobius sectional curvature K of the immersion x satisfies K ≥ 0 when p = 1 and K > 0 when p > 1 . Then, x is Mobius equivalent to either the Riemannian product S k ( r ) × S n - k 1 - r 2 , for k = 1 , 2 , ⋯ , n - 1 , in S n + 1 ( 1 ) ; or x is Mobius equivalent to a compact minimal submanifold with constant scalar curvature in S n + p ( 1 ) .

Open manifolds with asymptotically nonnegative curvature

In this paper we establish a generalization of Toponogov's theorem for manifolds with asymptotically nonnegative sectional curvature, and we give a pinching condition under which asymptotically nonnegative curved manifolds are diffeomorphic to $\mathbb{R}^{n}$.

Multiple brake orbits on convex hypersurfaces under asymmetric pinch conditions

In this paper, we give an example of an asymmetric convex compact hypersurface possessing precisely n brake orbits. For H ∈ C 1 ( R 2 n , R ) satisfying H ( - p , q ) = H ( p , q ) for all ( p , q ) ∈ R n × R n , we prove multiplicity result of the brake orbits on H - 1 ( 1 ) pinched by not necessarily symmetric hypersurfaces.

Periodic orbits of Hamiltonian systems on symmetric positive-type hypersurfaces

This paper discusses the existence and multiplicity of periodic orbits of Hamiltonian systems on symmetric positive-type hypersurfaces. We prove that each such energy hypersurface carries at least one symmetric periodic orbit. Under some suitable pinching conditions, we also get an existence result of multiple symmetric periodic orbits.

Periodic orbits of Hamiltonian systems on symmetric positive-type hypersurfaces

This paper discusses the existence and multiplicity of periodic orbits of Hamiltonian systems on symmetric positive-type hypersurfaces. We prove that each such energy hypersurface carries at least one symmetric periodic orbit. Under some suitable pinching conditions, we also get an existence result of multiple symmetric periodic orbits.

EXCESS FUNCTIONS OF RAYS ON COMPLETE NONCOMPACT MANIFOLDS

This paper gives an estimate of excess functions of rays on complete noncompact manifolds. By using this estimation, the authors can get the results in [3] as corollaries, which asserts that a complete manifold is diffeomorphic to Rn under some curvature and pinching conditions. At last, they obtain a refinement of them with extra Ricci condition.

Thermodynamic analysis of multicomponent distillation columns: identifying optimal feed conditions

A new methodology for the optimisation of feed conditions as well as the calculation of minimum reflux ratio of distillation columns is presented. The reversible profile approach used for saturated liquid feeds is extended to consider other feed conditions. For flashed feed, the liquid fraction of the feed stream is used to compute the column pinch conditions and the minimum reflux ratio. The modifications required for subcooled liquid and superheated vapor feed are discussed, and a procedure to estimate the minimum reflux for those conditions is proposed. The methodology presented allows the identification of the optimal feed condition, without having to resort to a full stage-by-stage procedure.

Open manifolds with sectional curvature bounded from below

In this paper, we study complete open manifolds with sectional curvature bounded from below. We obtain some pinching conditions to insure that such manifolds are diffeomorphic to a Euclidean space.

Computer package for design/rating of thermal desalination processes

A computer package has been developed for design and simulation of thermal desalination processes. This was motivated by unavailability of such packages in the literature or on a commercial scale. The package includes models for various systems of the single effect evaporation (SEE), the multistage flash (MSF), and the multi effect evaporation (MEE). The MSF systems include brine circulation, brine mixing, once through, and thermal vapor compression. The MEE configurations include parallel and forward feed systems. The SEE and MEE systems include the stand-alone and the vapor compression units. Vapor compression systems include mechanical, thermal, absorption, and adsorption heat pumps. All models are based on a well-developed set of material and energy balance equations as well as correlations for evaluation of physical properties, heat transfer coefficient, and thermo-dynamic losses. All mathematical models have been developed and previously tested and validated by authors against available industrial and literature data. All models generate the design and simulation variables, which have the strongest effect on the unit product cost. These include the thermal performance ratio, the specific heat transfer area, the conversion ratio, the specific power consumption, and the specific flow rate of cooling water. The computer package includes displays for process design, rating, flow charting, performance calculations, help files, and graphing of process schematics and performance curves. The package allows for parameter selection, printing of forms and data files, and selection of parameters for performance charts. The package performs checks on parameter range and prevents pinch conditions in various heat exchange processes. The package have been tested in a number of undergraduate, graduate, and training classes and found simple to use and providing fast and accurate results. © 2000 John Wiley & Sons, Inc. Comput Appl Eng Educ 8: 80–103, 2000

A simulator for thermal desalination processes

A computer package has been developed for design and simulation of thermal desalination processes. This was motivated by the unavailability of such packages in the literature or on a commercial scale. The package includes models for various systems of single effect evaporation (SEE), multistage flash (MSF), and multi effect evaporation (MEE). The MSF systems include brine circulation, brine mixing, once through, and thermal vapor compression. The MEE configurations include parallel and forward feed systems. The SEE and MEE systems include stand-alone and vapor compression units. Vapor compression systems include mechanical, thermal, absorption, and adsorption heat pumps. All models are based on a well developed set of materials and energy balance equations as well as correlations for evaluation of physical properties, heat transfer coefficient, and thermodynamic losses. All mathematical models have been developed and previously tested and validated by the authors against available industrial and literature data. All models generate the design and simulation variables which have the strongest effect on the unit product cost. These include the thermal performance ratio, the specific heat transfer area, the conversion ratio, the specific power consumption, and the specific flow rate of cooling water. The computer package includes displays for process design, rating, flow charting, performance calculations, help files, and graphing of process schematics and performance curves. The package allows for parameter selection, printing of forms and data files, and selection of parameters for performance charts. The package performs checks on parameter range and prevents pinch conditions in various heat exchange processes. The package has been tested in a number of undergraduate, graduate, and training classes and is found simple to use and provides fast and accurate results.

Bounded and L 2 harmonic forms on universal covers

We relate the positivity of the curvature term in the Weitzenbock formula for the Laplacian on p-forms on a complete manifold to the existence of bounded and $L^2$ harmonic forms. In the case where the manifold is the universal cover of a compact manifold, we obtain topological and geometric information about the compact manifold. For example, we show that a compact manifold cannot admit one metric with pinched negative curvature and another metric with positive Weitzenbock term on two-forms. Many of these results can be thought of as differential form analogues of Myers' theorem. We also give pinching conditions on certain sums of sectional curvatures which imply the positivity of the curvature term, and hence yield vanishing theorems. In particular, we construct a compact manifold with planes of negative sectional curvature at each point and which satisfies the hypothesis of our vanishing theorems.

The effects of pinch width on pinch strengths of adult males using realistic pinch-handle coupling

This study examined the effects of pinch width on pinch strengths, using more realistic pinching conditions — larger contact area, worktable height pinching level, and freedom to hyperextend the thumb when gripping. Chuck, pulp-2 and lateral pinches were tested at widths within the range of 2.0–14.0 cm among 17 right-handed male volunteers, using the right hand while standing. The results showed that (1) pinch strength was not significantly different between 2.0–5.6 cm for chuck and lateral pinches, nor between 2.0–9.2 cm for pulp-2 pinch, but decreased significantly at wider widths, (2) strength differences between different types of pinches depended on the width of the pinch, (3) chuck pinch was greater than lateral or pulp-2 pinch at all widths, and lateral pinch was greater than pulp-2 pinch from 2.0–5.6 cm width but weaker at greater widths, and (4) pinch strength was much greater under these test conditions compared to the traditional standardized testing conditions, for similar pinch widths. These data may be more relevant to industrial tasks than those in previously published studies.

Analytic intrinsic model based parasitic extraction method for HEMTs

The parasitic elements for HEMTs are extracted using an iterative technique based on the analytic intrinsic model instead of the equivalent circuit. Only two point S-parameter measurements under the pinched FET condition and zero gate bias are needed. The S-parameter simulation shows the validity of the proposed method.

3-dimensional submanifolds of spheres with parallel mean curvature vector

In this paper, for a 3-dimensional complete submanlfold $M$ with parallel mean curvature vector in $S^{3+p}(c)$ , we give a pinching condition of the Ricci curvature under which $M$ is a 3-dimensional small sphere.