Mechanical Tolerance Research Articles

Lack of Neuromuscular Origins of Adaptation After a Long-Term Stretching Program

Static stretching is commonly used during the treatment and rehabilitation of orthopedic injuries to increase joint range of motion (ROM) and muscle flexibility. Understanding the physiological adaptations that occur in the neuromuscular system as a result of long-term stretching may provide insight into the mechanisms responsible for changes in flexibility. To examine possible neurological origins and adaptations in the Ia-reflex pathway that allow for increases in flexibility in ankle ROM, by evaluating the reduction in the synaptic transmission of Ia afferents to the motoneuron pool. Repeated-measures, case-controlled study. Sports medicine research laboratory. 40 healthy volunteers with no history of cognitive impairment, neurological impairment, or lower extremity surgery or injury within the previous 12 mo. Presynaptic and postsynaptic mechanisms were evaluated with a chronic stretching pro- tocol. Twenty subjects stretched 5 times a wk for 6 wk. All subjects were measured at baseline, 3 wk, and 6 wk. Ankle-dorsiflexion ROM, Hmax:Mmax, presynaptic inhibition, and disynaptic reciprocal inhibition. Only ROM had a significant interaction between group and time, whereas the other dependent variables did not show significant differences. The experimental group had significantly improved ROM from baseline to 3 wk (mean 6.2 ± 0.9, P < .001), 3 wk to 6 wk (mean 5.0 ± 0.8, P < .001), and baseline to 6 wk (mean 11.2 ±0.9, P < .001). Ankle dorsiflexion increased by 42.25% after 6 wk of static stretching, but no significant neurological changes resulted at any point of the study, contrasting current literature. Significant neuromuscular origins of adaptation do not exist in the Ia-reflex-pathway components after a long-term stretching program as currently understood. Thus, any increases in flexibility are the result of other factors, potentially mechanical changes or stretch tolerance.

Investigation of Source Grating Stepping for Differential Phase-contrast Cone Beam CT (DPC-CBCT) System.

Differential phase contrast (DPC) imaging, which utilizes phase shift information of X-ray, has the potential of dramatically increasing the contrast in biological sample imaging compared to attenuation-based method that relies on X-ray absorption information, since the X-ray phase is much more sensitive than the attenuation during transmission. In a DPC imaging system, the phase stepping method is widely used to obtain DPC images: at each angle the phase grating is shifted incrementally to produce a set of images and then the so obtained images are used to retrieve DPC image. However, DPC imaging requires a high mechanical precision to perform phase stepping, which is generally one order higher than the period of phase grating. Given that phase grating period is generally 2-4 um, the requirement of mechanical accuracy and stability are very demanding (<0.5um) and difficult to meet in a system with rotating gantry. In this paper, we present a method that is able to greatly relax the requirement of mechanical accuracy and stability by stepping the source grating rather than the analyzer grating. This method is able to increase the system's mechanical tolerance without compromising image quality and make it feasible to install the system on a rotating gantry to perform differential phase-contrast cone beam CT (DPC-CBCT). It is also able to increase the grating shifting precision and as a result improve the reconstructed image quality. Mechanical tolerance investigation and image quality investigation at different phase stepping schemes and different dose levels will be carried out on both the original modality and the new modality, the results will be evaluated and compared. We will deliberately create random mechanical errors in phase stepping and evaluate the resulting DPC images and DPC-CBCT reconstructions. The contrast, noise level and sharpness will be evaluated to assess the influence of mechanical errors. By stepping the source grating, the system is expected to tolerate an error of 6-7 times bigger than that with analyzer grating stepping.

Benchmarking of Direct and Indirect Friction Tests in Micro Forming

In this study the application of a simulative sliding friction test at micro scale is suggested. Two work piece specimens are upset against opposing sides of a flat tool element. The tool element is then pulled out while the resulting friction force F is measured. The test principle offers several advantages when compared against the DEC-test, including easy visual inspection of tool and work piece surfaces, continuous measurement of friction coefficient over the complete sliding length and less sensitivity to mechanical tolerance deviations of work piece and tool elements.

E-평면 프로브를 이용한 Ka 대역 마이크로스트립-도파관 변환기의 설계 및 제작

본 논문에서는 K-커넥터를 사용하지 않고 다수의 전력증폭기를 WR-28 도파관에서 전력 합성하기 위해 마이크로스트립 전송 선로를 도파관으로 직접 변환하는 2가지 형태의 개방형 E-평면 프로브를 최적 설계하고, 이를 활용한 변환기를 제작, 평가하였다. 중심 주파수 35 GHz에서 <TEX>${\pm}500MHz$</TEX>의 대역폭을 가지며, 0.1 dB의 삽입 손실과 20 dB 이상의 반사 손실을 목표로 변환기 설계가 진행되었으며, 제작 시 발생할 수 있는 지그 가공 및 조립오차에 대한 특성도 3차원 전자기 시뮬레이션을 통해 고려하였다. 16 mm와 26.57 mm의 마이크로스트립 선로를 가지는 back-to-back 변환기 구조를 제작하였으며, 35 GHz에서 변환기 당 약 0.1 dB의 우수한 삽입 손실을 얻었고, Ka 대역 전체 주파수 영역에서 평균 0.2 dB의 삽입 손실 특성을 보였다. 반사 손실의 경우, back-to-back 구조가 Ka 대역에서 15 dB 이상의 특성을 보여 변환기 자체로는 20 dB 이상의 값을 가지는 것으로 파악되었다. In this paper, two kinds of E-plane microstrip-to-waveguide transitions are optimally designed and fabricated for combining output power from multiple small-power amplifiers in a WR-28 waveguide because conventional K connectors cause unnecessary insertion loss and adaptor loss. The transition design is based on target specifications such as a center frequency of 35 GHz, bandwidth of <TEX>${\pm}500MHz$</TEX>, 0.1 dB insertion loss and 20 dB return loss. Performance variation caused by mechanical tolerance and assembly deviation is fully evaluated by three dimensional electromagnetic simulation. The fabricated back-to-back transitions with 16 mm and 26.57 mm interstage microstrip lines show insertion loss per transition of ~0.1 dB at 35 GHz and average 0.2 dB over full Ka band. Also the back-to-back transition shows return loss greater than 15 dB, which implies that the transition itself has return loss better than 20 dB.

MAX phase carbides and nitrides: Properties for future nuclear power plant in-core applications and neutron transmutation analysis

Abstract A family of ternary carbides and nitrides, known as MAX phases, combine attractive properties of both ceramics and metals, and has been suggested for potential nuclear reactor applications. The unirradiated materials properties of importance for in-core structural materials and as fuel pellet coatings for several leading MAX phase materials have been summarized from literature. The materials show high mechanical damage tolerance in terms of creep, thermal/mechanical fatigue and fracture resistance, and very good chemical compatibility with select coolants such as molten lead and sodium. Neutron activation has been calculated for commercial purity materials exposed to both idealized fast and thermal reactor neutron spectra for 10, 30, and 60 years of exposure. The specific activities of Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC were compared to those of SiC and Alloy 617, two leading candidate materials for next generation reactor components. The specific activities of MAX phases were similar to SiC and three orders of magnitude less than Alloy 617 after 10–60 years decay for all three activation times in both the fast and thermal spectra. As with SiC, the main radioisotopes after a decay period of 10 years for all three activation times in the MAX phases are tritium and C 14 . Neutron irradiation results of Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC experimentally confirmed the neutron transmutation analysis.

Present Status and Future Perspective of Bismuth-Based High-Temperature Superconducting Wires Realizing Application Systems

Among a series of high-temperature superconducting materials that have been discovered to date, (Bi,Pb)2Sr2Ca2Cu3O10-x is the best candidate for superconducting wires that are long with commercial productivity, and critical current performance. In particular, the controlled overpressure (CT-OP) sintering technique gave us a 100% density of (Bi,Pb)2Sr2Ca2Cu3O10-x portion, which leads to robustness, increase in critical current, and mechanical tolerance. Many application prototypes are already verified and are being evaluated worldwide. Current leads for large magnets and magnetic billet heaters are already commercial products. Commercial applications for power cables, motors for ship propulsion and electric vehicles, and many kinds of magnets are promising in the near future.

Soft Magnetic Composite Switched Reluctance Generator - Fabrication and Analysis

The main objective of this paper is to investigate the suitability of Soft Magnetic Composite (SMC) material SOMOLOY1000 for a Switched Reluctance Generator (SRG) through electromagnetic, thermal and vibration characteristics employing extensive Finite Element Analysis. The fabrication aspects of Soft Magnetic Composite Switched Reluctance Generator (SMC-SRG) using preform material blanks utilizing indigenous machining process have been delineated. The static and transient electromagnetic characteristics have been obtained through the electromagnetic finite element analysis software MagNet6.22.1 while the thermal and vibration aspects have been studied through coupled field Finite Element Analysis employing the multi physics software ANSYS10 while the Impulse hammers excitation - free vibration test using RT Pro Photon data acquisition system facilitated the experimental determination of vibration characteristics. The study concludes that the advantages of less weight , low torque ripple, low eddy current losses, reduction in vibration level of stator structure coupled with the ability to maintain precise mechanical dimensional tolerance may present SMC-SRG a viable candidate in standalone wind energy conversion systems meant for rural and remote area electrification scheme.

Development of an Ultra-Wideband Suspended Stripline to Shielded Microstrip Transition

A novel ultra-wideband suspended stripline to shielded microstrip transition is presented here with measurement results. The novel transition has less than 0.2 dB insertion loss and better than 15 dB return loss over dc to 40 GHz. This transition design addresses the interconnection challenge between suspended stripline and shielded microstrip circuits, such as in assemblies where the active circuitry is in MS environment, and the passive circuitry is in low-loss SS environment. The described design allows for less critical mechanical tolerance and is less sensitive to misalignment.

Inhibition of β‐catenin signaling in chondrocytes induces delayed fracture healing in mice

Appropriate and controlled chondrogenesis and endochondral ossification play fundamental roles in the fracture healing cascade, a regenerative process involved in highly coordinated biological events, including the Wnt/β-catenin signaling pathway. To examine the role and importance of this pathway in chondrocytes, we studied bone repair of closed tibias fractures in Col2a1-ICAT transgenic mice, in which the Wnt/β-catenin signaling pathway is specially inhibited in chondrocytes. Radiological, histological, and histomorphometric analyses at 7, 9, 12, 14, 21, and 28 days after fracture demonstrated the bone repairs were retarded in Col2a1-ICAT transgenic mice, due to reduced and delayed cartilage formation, chondrocyte hypertrophy, and bone generation. In addition, at 5 weeks, Col2a1-ICAT transgenic mice exhibited a weak mechanical tolerance to four-point bending. Furthermore, quantitative-PCR analysis revealed that the expression of genes associated specifically with cartilage extracellular matrix formation (collagen II, collagen X, and mmp13), bone remodeling (alp, collagen I, and osteocalcin), and vascular extravagation (vegf), and transcriptional activators involved in cartilage generation and ossification (sox9 and runx2) was decreased and delayed in the fracture sites of Col2a1-ICAT transgenic mice during healing. Collectively, these results suggest that Wnt/β-catenin signaling is critical for fracture healing, especially with respect to chondrogenesis and endochondral ossification. Thus, our study provides insight into the possible mechanisms of and therapeutic targets for improving normal facture repair and the healing of non-union fractures.

Mechanical stress tolerance of two microalgae

Aim of the present work is quantifying the mechanical stress generated by some major process equipment used in massive microalgae culturing plants (centrifugal and air-lift pumps, and nozzles) and highlighting its effects on the microalgal population. Two microalgal species were used as test cases: Chlorella vulgaris (unicellular) and Scenedesmus dimorphus 1237 (colonial). The evaluation of the shear effect on algal growth was carried out through measurement of absorbance, photosynthetic activity (oxygen evolution) and variable chlorophyll fluorescence. Cell aggregate development/breakage was effectuated by visual inspection and light scattering. The use of centrifugal pumps for culture recycling strongly affected the growth of C. vulgaris, while nozzles effects were confined to aggregate breakage of S. dimorphus. The analysis of experimental data is supported by the consideration of hydrodynamic stress calculated by: shear rate, shear stress, stress volumes/times, energy dissipation rates, and turbulence microscale size.

Mechanical requirement and influence on the design and manufacturing of beam position monitor of Taiwan photon source

The beam position monitors (BPMs) with submicron-level resolution act as the major eyes of storage ring in detecting the position of electron beams and are used for feedback system to guide the beam orbit to the desired track. Compared to major improvements on backend electronics, the physical devices generate and transmit signals had little improvement due to the lack of control on manufacturing processes including all mechanical tolerance requirements. The design started with ANSYS to simulate mechanical deformation. Due to the small size (submillimetre) and complicated assembly of feedthrough structure, it is difficult to achieve 1 % tolerance (submicron) in all aspects including machining and brazing. The smallest tolerance for machining is 5 µ and the overall tolerance will be 30 µm. The influence of the tolerance on mechanical will be shown on time-domain reflectometry measurement. The resulted heat-related issue will also be discussed and addressed since the problem happened at SLAC (private communication with Albert Sheng at Stanford Linear Accelerator Center) and DIAMOND (presented at the RF Button Heating Mini-Workshop at EPAC 2008). Manufacturing steps will be described. The consequence of mismatch on manufacturing will be discussed. All related measurement and simulation data are presented in this paper.

Effects of Mechanical Tolerances on QMF Performance for Operation in the Third Stability Zone

Our previously reported method of accurately simulating the performance of a quadrupole mass filter (QMF) has been applied to the investigation of the effects of electrode positional tolerance on the performance of a QMF when operated in stability zone 3 ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ≈ 3.16 and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> ≈ 3.23). Simulations for single- and dual-electrode positional errors have been undertaken. Single-axis errors produced changes in mass peak shape that are similar to those previously reported for zone 1. Compound errors produce changes in mass peak shape that are approximately a summation of the effects obtained from individual single-axis errors. Our results show that the direction of the electrode displacement, not the electrode, is the important factor in determining the effect on QMF performance. We also show that the effects of an individual electrode radius tolerance result in changes to the mass peak shape that are similar to those produced by individual electrode positional errors. Simulations also show the suitability of unbalanced excitation voltages as a method of compensating for mechanical tolerance when operating in zone 3. From these results, we are able to provide suitable limits for the voltage accuracy and stability when employing this method of compensation.

Surface Thiolation of MCMB to Support Sn Nanoparticles for Anode Materials of Lithium Ion Batteries

Abstract In this study, we suggest a unique approach with which it is possible to enhance the capacity and cycle performance of composite anode materials for lithium ion batteries. We introduced surface thiol groups onto mesocarbon microbeads (MCMB), and these functional groups efficiently obstructed the agglomeration between Sn nanoparticles in the composite formation. This resulted in the high dispersion of Sn nanoparticles with very small size. Half-cell tests showed that highly dispersed Sn nanoparticles enabled us to enhance the capacity by improvement of mechanical stress tolerance in the charge/discharge process.

Analysis of the impacts of mechanical errors on the RF performance of a single spoke cavity

Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.

Kinematics Based Knee Moment Prediction for Video Analysis of Anterior Cruciate Ligament Injury

BACKGROUND: Anterior cruciate ligament (ACL) is frequently injured during sports activities with abducted and rotated knee position, indicating that huge external force is causing such out of plane knee kinematics. For ethical reason, it is impossible to measure knee dynamics in injury situation. However, if we predict the knee moment based only on kinematic information, we may be able to quantify the knee loadings by analyzing ACL video sequence. We had proposed a kinematics-based model for knee moment calculation at last ACSM's meeting and experimentally confirmed its accuracy (2009). In this study, we then apply this model to injury video analysis. PURPOSE: To determine the knee loadings at ACL injury from previously filmed injury video. METHODS: A video of an ACL injury situation, that a handball player suffered her ACL at a landing from a jump, was utilized. A written permission was obtained from both the player and Japanese Handball Association for the use of this video. A three dimensional Cartesian coordinate was reconstructed based on the known geometries, e.g., court lines and goal posts, filmed in background. The positions and the orientations of the player's body segments were obtained by fitting a skeletal figure to the player's silhouette. The ground reaction force and its acting point were calculated with the acceleration of body center of mass. The segmental masses and those positions were estimated from Chandler et al.(1975). The knee moment was then calculated using the kinematics-based model. RESULTS: A peak knee abduction moment of 460 Nm was observed at about 100 ms after foot impact. Previous cadaveric data supported that the peak value of knee abduction moment exceeded the knee mechanical tolerance. CONCLUSIONS: Findings suggest that the knee experienced an increased abduction moment at the time of ACL injury. This study showed a possibility to quantify the direct mechanism of ACL injury that cannot be evaluated in lab study. Future work is required to understand how we decrease knee loadings for injury prevention. Supported by the Ministry of ESCST Japan, Grant-in-Aid, 21700667,2009.

Inspection of Mechanical Tolerance by Using the Virtual Gauge on a Coordinate Measuring Machine

The function to obtain associated surfaces on coordinate measuring machines (CMM's) is based on the minimization of the distance between measured points and the ideal surface. This function is non-linear for usual surfaces. In many works, to accelerate iterative calculations, the problem is linearized. The aim of this work is to reduce scraps using a transcription optimization of the fitting functionality of mechanical parts in maximum state of matter. An adaptive verification method is suggested. It takes account of the interface properties. A control by a virtual gauge and verification a process is developed to validate the tolerancing according to the previously suggested methodology.

Experimental evaluation of the buckling phenomena in the new joint design for upper deck structure of a bridge

This paper is concerned with the experimental mechanical analysis of a new design of a joint for a main components of a upper deck of a road bridge. These components are subject to the compression state stress induced by the weight and the load acting on the road. Each upper deck of a bridge (positioned on each side of the bridge) is composed by four tubular structures that must be joint each together. The joint must to take in to account many aspects, for example that the length of each component is not the same (because, obviously, there is a mechanical tolerance). This phenomena induce different compression stress on each component and so is very important non only the critical buckling load but also the post buckling behaviour of the structure. It is very important that if a single tubular structure reaches the critical load of instability, it still has load capacity . This is to avoid that, in the case where a column reaches the instability, the entire load acting on a column increase the load on the remaining three. For this purpose many different geometrical solutions have been designed (elaborated by fem analyses and successively tested experimentally). This work reports the main experimental results on the best joint solution and how this increase the load capacity and the displacement respect to the solution without this flange.

Differentiation of human bone marrow mesenchymal stem cells grown in terpolyesters of 3-hydroxyalkanoates scaffolds into nerve cells

Polyhydroxyalkanoates, abbreviated as PHA, have been studied for medical applications due to their suitable mechanical properties, blood and tissue tolerance and in vivo biodegradability. As a new member of PHA family, terpolyester of 3-hydroxybutyrate, 3-hydroxyvalerate and 3-hydroxyhexanoate, abbreviated as PHBVHHx, was compared with polylactic acid (PLA), copolyester of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx) for their respective functions leading to differentiation of human bone marrow mesenchymal stem cell (hBMSC) into nerve cells. Results indicated that 3D scaffolds promoted the differentiation of hBMSC into nerve cells more intensively compared with 2D films. Smaller pore sizes of scaffolds increased differentiation of hBMSC into nerve cells, whereas decreased cell proliferation. PHBVHHx scaffolds with pore sizes of 30–60 μm could be used in nerve tissue engineering for treatment of nerve injury. The above results were supported by scanning electron microscope (SEM) and confocal microscopy observation on attachment and growth of hBMSCs on PLA, PHBHHx and PHBVHHx, and by CCK-8 evaluation of cell proliferation. In addition, expressions of nerve markers nestin, GFAP and β-III tubulin of nerve cells differentiated from hBMSC grown in PHBVHHx scaffolds were confirmed by real-time PCR.

Experimental Mild Traumatic Brain Injury Induces Functional Alteration of the Developing Hippocampus

It is estimated that approximately 1.5 million Americans suffer a traumatic brain injury (TBI) every year, of which approximately 80% are considered mild injuries. Because symptoms caused by mild TBI last less than half an hour by definition and apparently resolve without treatment, the study of mild TBI is often neglected resulting in a significant knowledge gap for this wide-spread problem. In this work, we studied functional (electrophysiological) alterations of the neonatal/juvenile hippocampus after experimental mild TBI. Our previous work reported significant cell death after in vitro injury >10% biaxial deformation. Here we report that biaxial deformation as low as 5% affected neuronal function during the first week after in vitro mild injury of hippocampal slice cultures. These results suggest that even very mild mechanical events may lead to a quantifiable neuronal network dysfunction. Furthermore, our results highlight that safe limits of mechanical deformation or tolerance criteria may be specific to a particular outcome measure and that neuronal function is a more sensitive measure of injury than cell death. In addition, the age of the tissue at injury was found to be an important factor affecting posttraumatic deficits in electrophysiological function, indicating a relationship between developmental status and vulnerability to mild injury. Our findings suggest that mild pediatric TBI could result in functional deficits that are more serious than currently appreciated.

VCM 액추에이터의 전자기력을 이용한 HDD 래치 설계

Various types of latch designs for hard disk drives using load/unload mechanism have been introduced to protect undesired release motions of a voice coil motor(VCM) actuator from sudden disturbances. Recently, various inertia-type latches have been widely used because locking performance is better than that of other types of latch. However there has been a limit in the inertia type in order to guarantee perfect latch and unlatch operations because of changes in latch/unlatch conditions due to mechanical tolerance and temperature-dependent friction. In this paper, a reliable and robust magnetic latch mechanism is proposed through only simple modifications of coil and yoke shapes in order to overcome the mechanical limit of current inertia-type latches. This new magnetic latch does not have only a simple structure but it also ensures reliable operations and anti-shock performance. The operating mechanism of the proposed latch is theoretically analyzed and optimally designed using an electromagnetic simulation.