Loss Of Tension Research Articles

Loss of wire tension in the wire web during the slurry based multi wire sawing process

In the multi wire sawing process the wire tension is an important parameter for reliability and wafer quality. Changes of wire quality and wire tension from one end of a wire web in a multi wire saw to the other are investigated by several methods: wire tension measurements in the wire saw, wire elongation during an industrial process and material testing of representative wires. Two mechanisms for the loss of wire tension are identified. Firstly, the decrease of wire diameter due to abrasion causes a slow loss of wire tension along the whole wire web. Secondly, plastic deformation of the wire due to random overloading leads to a fast decrease of the wire tension within the first few centimeters of the wire web. Both effects are confirmed by modeling and calculations.

Mechanism of mitotic arrest induced by dolastatin 15 involves loss of tension across kinetochore pairs

Dolastatin 15 (DL15) is a potent, tubulin-targeted, vinca-site binding, anticancer agent that induces mitotic arrest and inhibit cell proliferation in a variety of cell types. Several analogs of DL15, including LU 103793 and tasidotin, have been progressed to clinical trials for different types of cancer. DL15 has been known to interfere with cellular microtubules and purified tubulin in vitro. However, the molecular mechanism with which the peptide arrests cells in mitosis is poorly understood. This study reports a possible antimitotic mechanism of action of DL15. DL15 inhibited HeLa cell proliferation in a concentration-dependent manner with a half-maximal inhibitory concentration (IC50) of 2.8 ± 0.3 nM, induced mitotic arrest, disrupted cellular microtubules near its IC50 for cell proliferation, and inhibited the re-polymerization of cellular microtubules. By staining the centrosomes of DL15-treated cells with anti-γ tubulin antibodies, the study found a significant reduction in interpolar distances in mitotic HeLa cells, indicating a disruption in the normal assembly dynamics of the microtubules. The study further found that DL15 induced a loss of tension across the kinetochore pairs as indicated by a reduction in interkinetochore distance. In response to this loss of tension, the tension-sensing checkpoint protein BuBR1 accumulated at the kinetochores, promoting mitotic arrest. In vitro, DL15 promoted formation of curved and fragmented polymers of microtubule proteins and inhibited tubulin decay in a manner similar to vinca-site binding agents such as phomopsin A. Together, the data indicate that the mitotic arrest induced by DL15 involves a loss of tension across the kinetochore pairs due to disruption of normal assembly dynamics of microtubules.

Novel anterior cruciate ligament graft fixation device reduces slippage

Clinically significant laxity occurs in 10%–30% of knees after anterior cruciate ligament reconstruction. Graft slippage and tension loss at the hamstring graft tibial fixation site during and after reconstruction surgery contribute to postoperative joint laxity and are detrimental to long-term knee stability and graft properties. Limiting graft slippage will reduce associated complications. We sought to compare the in vitro mechanical properties and in vivo joint stabilization, postoperative limb use, and graft incorporation of the novel GraftGrab™ (GG) device designed to reduce hamstring graft tibial fixation slippage with the commercially available bioabsorbable Bio-Post™ and spiked washer (BP). Mechanical testing was performed on canine tibia-hamstring graft constructs to quantify initial fixation properties. In vivo joint stabilization, postoperative limb use and graft incorporation of hamstring graft reconstructions were determined in a canine model. Outcomes included tibial translation and ground reaction forces preoperatively and 4 and 8 weeks postoperatively, three-dimensional graft and bone tunnel dimensions at the latter two time points, and graft-bone microstructure, as well as mechanical properties 8 weeks after implantation. Immediately after fixation, all grafts slipped from the BP constructs versus about 30% of GG constructs. In vivo limb use remained low, and tibial translation increased with time in the BP cohort. These results together confirm that initial graft slippage is lower with GG versus BP extracortical hamstring graft tibial fixation. In addition, postoperative recovery and joint stability are more consistent with the GG. This information supports the GG as an alternative to extracortical tibial hamstring graft fixation that has procedural advantages over current implants and reduces graft failure from slippage.

Release of cellular tension signals self-restorative ventral lamellipodia to heal barrier micro-wounds

Basic mechanisms by which cellular barriers sense and respond to integrity disruptions remain poorly understood. Despite its tenuous structure and constitutive exposure to disruptive strains, the vascular endothelium exhibits robust barrier function. We show that in response to micrometer-scale disruptions induced by transmigrating leukocytes, endothelial cells generate unique ventral lamellipodia that propagate via integrins toward and across these "micro-wounds" to close them. This novel actin remodeling activity progressively healed multiple micro-wounds in succession and changed direction during this process. Mechanical probe-induced micro-wounding of both endothelia and epithelia suggests that ventral lamellipodia formed as a response to force imbalance and specifically loss of isometric tension. Ventral lamellipodia were enriched in the Rac1 effectors cortactin, IQGAP, and p47Phox and exhibited localized production of hydrogen peroxide. Together with Apr2/3, these were functionally required for effective micro-wound healing. We propose that barrier disruptions are detected as local release of isometric tension/force unloading, which is directly coupled to reactive oxygen species-dependent self-restorative actin remodeling dynamics.

Initial Tension Loss in Cerclage Cables

Cerclage cables, frequently used in the management of fractures and osteotomies, are associated with a high failure rate and significant loosening during surgery. This study compared the capacity to maintain tension of different types of orthopaedic cable systems. Multifilament Cobalt-Chrome (CoCr) cables with four different crimp/clamp devices (DePuy, Stryker, Zimmer and Smith&Nephew) and one non-metallic Nylon (Ny) cable from Kinamed were instrumented with a load cell to measure tension during insertion. Significant tension loss was observed with crimping for all cables (P<0.05). Removing the tensioner led to an additional unexpected tension loss (CoCr-DePuy: 18%, CoCr-Stryker: 29%, CoCr-Smith&Nephew: 33%, Ny: 46%, and CoCr-Zimmer: 52%). The simple CoCr (DePuy) cable system outperformed the more sophisticated locking devices due to its significantly better ability to prevent tension loss.

Improved electromechanical behavior in castable dielectric elastomer actuators

Non-viscoelastic castable elastomers are replacing the polyacrylate VHB films in the new generations of dielectric elastomer actuators (DEAs) to achieve fast and reliable actuation. We introduce the optimum prestretch conditions to enhance the electromechanical behavior of the castable DEAs resulting in large actuation strain. For castable actuator in which the thickness is selected independent of the prestretch, uniaxial prestretch mode offers the highest actuation strain in the transverse direction compared to biaxial and pure shear. We experimentally demonstrate that miniaturization hinders the loss of tension and up to 85% linear actuation strain is generated with a 300 × 300 μm2 polydimethylsiloxanes-based DEA.

Subbrachial approach to humeral shaft fractures: new surgical technique and retrospective case series study

There are few surgical approaches for treating humeral shaft fractures. Here we present our results using a subbrachial approach. We conducted a retrospective case series involving patients who had surgery for a humeral shaft fracture between January 1994 and January 2008. We divided patients into 4 groups based on the surgical approach (anterior, anterolateral, posterior, subbrachial). In all patients, an AO 4.5 mm dynamic compression plate was used. During our study period, 280 patients aged 30-36 years underwent surgery for a humeral shaft fracture. The average duration of surgery was shortest using the subbrachial approach (40 min). The average loss of muscle strength was 40% for the anterolateral, 48% for the posterior, 42% for the anterior and 20% for the subbrachial approaches. The average loss of tension in the brachialis muscle after 4 months was 61% for the anterolateral, 48% for the anterior and 11% for the subbrachial approaches. Sixteen patients in the anterolateral and anterior groups and 6 patients in the posterior group experienced intraoperative lesions of the radial nerve. No postoperative complications were observed in the subbrachial group. The subbrachial approach is practical and effective. The average duration of the surgery is shortened by half, loss of the muscle strength is minimal, and patients can resume everyday activities within 4 months. No patients in the subbrachial group experienced injuries to the radial or musculocutaneous nerves.

Crossbridge Properties during Fatigue and Recovery in Mouse Skeletal Muscle Fibres

Fatigue occurring during exercise can be defined as the inability to maintain the initial force or power output. We showed recently that fatigue during repetitive tetanic stimulation at 24 °C of fibre bundles dissected from FDB mouse (C57BL/6) muscle, occurs in two phases: an initial one during which individual crossbridge force decreases, and a later phase during which also crossbridge number decrease (Nocella et al.,2011 J Physiol 589).The present experiments were made on the same preparation to compare the fatigue mechanism at 24°C and at physiological temperature of 35 °C and to investigate the mechanism of force recovery from fatigue at 24°C. Fatigue was induced with 105 consecutive isometric tetani evoked every 1.5 s. Force recovery was followed by tetani evoked every 90s until force recovered to 90-100% of pre-fatigue value. Stiffness was measured with small sinusoidal length oscillations at 6.5 kHz. At both temperatures fatigue occurred initially through the decrease of the individual crossbridge force followed by the reduction of crossbridge number. However the initial phase lasted for ∼40 tetani at 35°C and ∼20 tetani at 24°C. This suggests a greater resistance to fatigue of this mechanism at high temperature. In contrast, during the second phase the tension loss was faster at 35°C than at 24°C so that after 105 tetani tension was similar at both temperatures. Force recovery also occurred in two phases. The initial phase lasted from ∼1.5-4 min and recovered 40-90% of tension loss. The second phase lasted for ∼60 min and its amplitude was well correlated with tension decrease during the second phase of fatigue. Thus the mechanism of tension recovery after fatigue seems symmetrical to tension loss during fatigue.

High Resolution Imaging of Living Cells with Microsecond Force Spectroscopy

Mapping cell mechanical properties down to molecular level can both refine our knowledge about cellular structures and reveal information about biological functions like cell adhesion, proliferation and survival. Atomic force microscopy (AFM) is a powerful method to probe materials at the nanoscale. Although AFM has been used to image live cells and probe their mechanical properties1, its resolution on cells is much lower than on stiffer materials. To address this, we adapted Microsecond Force Spectroscopy2 to rapidly image mechanical properties of live and cross-linked fibroblasts, neurons and Human Umbilical Vein Endothelial Cells in culture media or buffer.Mechanical properties images showed cellular features as small as 50nm, representing an unprecedented resolution over a wide variation of cell types. The enhanced resolution and speed of our method allowed the identification of dynamic changes in elastic modulus of fine cellular structures, which did not appear to be reflected in optical images of fluorescently-labeled actin, acquired from the same cells. These changes might reflect a loss of tension in the actin network underneath the cell membrane. Preliminary data further suggest that our platform might allow the label-free recognition of stress fibers, retraction fibers, Weibel-Palade bodies and microvilli solely based on nanomechanical contrast. These developments extend the cell imaging capabilities of AFM and highlight the value of mechanics in the delineation of cellular physiological states. The compatibility of our method with human cells suggests that it can be further developed as a diagnostic tool for the detection of disease-specific cellular mechanical responses.1-Casuso et al. J.Mol.Recogn. 2011; 24:406-413.2-Dong et al. Nature Nanotechnology 2009; 4:514-517.

Paper 69: The Effect of Pullout Suture For the Radial tear of Posterior Horn of Medial Meniscus in Porcine Knee

PurposeThe radial tear of the meniscus results in the loss of hoop tension which may lead to the premature degenerative changes of knee joint. The effect of current pullout suture techniques on radial tear of posterior horn of medial meniscus(PHMM) is unknown. The aim of this study is to measure the contact pressures of medial compartment of the knee joint after pullout suture in radial tear of PHMM.

Electromechanical and dynamic analyses of tunable dielectric elastomer resonator

When used as resonators, dielectric elastomers are subjected to high frequencies and nonlinear oscillation. The present study is focused on a dielectric elastomer resonator whose dielectric membrane is subject to combined loads of tensile forces and voltages. When the loads are static, the resonator may reach a state of equilibrium. The stability and the natural frequency of the resonator with small-amplitude oscillation around the equilibrium state are analyzed. When a periodic voltage is applied, the device resonates at multiple frequencies of excitation. Pre-stretches and applied static voltages tune the natural frequency and modify the dynamic behavior of the resonator. The membrane may suffer loss of tension and electromechanical instability, causing the failure of the resonator. Safe operation range is identified for failure prevention while actuating the resonator.

Performance of Unpretensioned Wind Stabilizing Cables in the Construction of a Cable-Stayed Bridge

AbstractA stabilizing cable (SC), used for mitigating buffeting vibration in a cantilevered structure of a cable-stayed bridge during construction, is normally installed with pretension. When a situation arises where only SCs are allowed in side spans, heavy counterweights in the center span are required to satisfy the force balance. The mitigating effect of unpretensioned cables was investigated using a wind tunnel in an attempt to eliminate the need for counterweights. An elastic wind tunnel test at a scale of 1/125 was prepared, and a series of comparative wind tunnel tests were performed. The vertical displacement at the cantilever tip of the center span and the horizontal displacement at the top of the pylon were measured, and stabilizing effects were then estimated. An unpretensioned cable produces a nonlinear motion because of a loss of tension. A quantitative evaluation of the stabilizing effect of an unpretensioned stabilizing situation indicated that the counterweight could be removed only when ...

Tension-dependent nucleosome remodeling at the pericentromere in yeast

Nucleosome positioning is important for the structural integrity of chromosomes. During metaphase the mitotic spindle exerts physical force on pericentromeric chromatin. The cell must adjust the pericentromeric chromatin to accommodate the changing tension resulting from microtubule dynamics to maintain a stable metaphase spindle. Here we examine the effects of spindle-based tension on nucleosome dynamics by measuring the histone turnover of the chromosome arm and the pericentromere during metaphase in the budding yeast Saccharomyces cerevisiae. We find that both histones H2B and H4 exhibit greater turnover in the pericentromere during metaphase. Loss of spindle-based tension by treatment with the microtubule-depolymerizing drug nocodazole or compromising kinetochore function results in reduced histone turnover in the pericentromere. Pericentromeric histone dynamics are influenced by the chromatin-remodeling activities of STH1/NPS1 and ISW2. Sth1p is the ATPase component of the Remodels the Structure of Chromatin (RSC) complex, and Isw2p is an ATP-dependent DNA translocase member of the Imitation Switch (ISWI) subfamily of chromatin-remodeling factors. The balance between displacement and insertion of pericentromeric histones provides a mechanism to accommodate spindle-based tension while maintaining proper chromatin packaging during mitosis.

Re‐establishment of cytoskeletal tensional homeostasis in lax tendons occurs through an actin‐mediated cellular contraction of the extracellular matrix

Cytoskeletal tensional homeostasis is known to be an important factor in controlling catabolic gene expression in tendon cells. Loss of cell tension in lax rat tail tendon fascicles (RTTfs) has been associated with an upregulation of MMP-13 gene expression and protein synthesis. To determine the role of the actin cytoskeleton in re-establishing tensional homeostasis in lax tendons, RTTfs were allowed to freely contract in vitro for 8 days. The cultured RTTfs contracted rapidly, reaching 50% of their initial length by 3 days. This contraction was associated with the presence of α-smooth muscle actin positive cells within the tendon. Disruption of the actin network by cytochalasian D caused an immediate and significant elongation of the contracted RTTfs. Subsequent removal of the cytochalasian D re-initiated the contraction process. When lax RTTfs were allowed to contract between fixed clamps in culture and become taut, they demonstrated a marked decrease in MMP-13 staining intensity when compared to freely contracting RTTfs. The ability of native tendon cells to contract lax tendons and re-establish their homeostatic "set point" with respect to collagenase production may be an important mechanism in the recovery of tendons elongated by injury, surgical positioning, or cyclic, viscoelastic creep secondary to repetitive exercise.

Anaphase B Precedes Anaphase A in the Mouse Egg

Segregation of chromosomes at the time of cell division is achieved by the microtubules and associated molecules of the spindle. Chromosomes attach to kinetochore microtubules (kMTs), which extend from the spindle pole region to kinetochores assembled upon centromeric DNA. In most animal cells studied, chromosome segregation occurs as a result of kMT shortening, which causes chromosomes to move toward the spindle poles (anaphase A). Anaphase A is typically followed by a spindle elongation that further separates the chromosomes (anaphase B). The experiments presented here provide the first detailed analysis of anaphase in a live vertebrate oocyte and show that chromosome segregation is initially driven by a significant spindle elongation (anaphase B), which is followed by a shortening of kMTs to fully segregate the chromosomes (anaphase A). Loss of tension across kMTs at anaphase onset produces a force imbalance, allowing the bipolar motor kinesin-5 to drive early anaphase B spindle elongation and chromosome segregation. Early anaphase B spindle elongation determines the extent of chromosome segregation and the size of the resulting cells. The vertebrate egg therefore employs a novel mode of anaphase wherein spindle elongation caused by loss of k-fiber tension is harnessed to kick-start chromosome segregation prior to anaphase A.

Unidirectional barbed suture versus standard monofilament for urethrovesical anastomosis during robotic assisted laparoscopic radical prostatectomy

V-Loc™180 (Covidien Healthcare, Mansfield, MA) is a new unidirectional barbed suture that may reduce loss of tension during a running closure. We evaluated the use of the barbed suture for urethrovesical anastomosis (UVA) during robotic assisted laparoscopic prostatectomy (RALP). Time to completion of UVA, post-operative anastomotic leak rate, and urinary incontinence were compared in patients undergoing UVA with 3-0 unidirectional-barbed suture vs. 3-0 Monocryl™ (Ethicon, Somerville, NJ). Data were prospectively collected for 70 consecutive patients undergoing RALP for prostate cancer between November 2009 and October 2010. In the first 35 patients, the UVA was performed using a modified running van Velthoven anastomosis technique using two separate 3-0 monofilament sutures. In the subsequent 35 patients, the UVA was performed using two running novel unidirectional barbed sutures. At 7-12 days postoperatively, all patients were evaluated with a cystogram to determine anastomotic integrity. Urinary incontinence was assessed at two months and five months by total daily pad usage. Clinical symptoms suggestive of bladder neck contracture were elicited. Age, PSA, Gleason score, prostate size, estimated blood loss, body mass index, and clinical and pathologic stage between the 2 groups were similar. Comparing the monofilament group and V-Loc™180 cohorts, average time to complete the anastomosis was similar (27.4 vs. 26.4 minutes, p = 0.73) as was the rate of urinary extravasation on cystogram (5.7 % vs. 8.6%, p = 0.65). There were no symptomatic bladder neck contractures noted at 5 months of follow-up. At 2 months, the percentage of patients using 2 or more pads per day was lower in the V-Loc™180 cohort (24% vs. 44%, p < 0.02). At 5 months, this difference was no longer evident. Time to complete the UVA was similar in the intervention and control groups. Rates of urine leak were also comparable. While the V-Loc™180 was associated with improved early continence, this difference was transient.

Effect of Conical Angle and Thread Pitch on the Self-Loosening Performance of Preloaded Countersunk-Head Bolts

This paper investigates the effect of the countersunk conical angle and thread pitch on the loosening performance of preloaded countersunk-head bolts that are subjected to harmonic transverse loading. A nonlinear mathematical model is used to predict the loosening performance. Cumulative differential loosening rotation of the bolt head is converted to a gradual loss in the bolt tension and joint clamp load. Model prediction of the self-loosening behavior is experimentally validated.

Tension Monitoring Devices Development for Bolted Joints

The present paper reviews recent patents disclosing various ways to monitor the variation of the bolt tension in order to timely readjust the torque to initial specifications. The recent advances related to bolted joints have seen tremendous developments to ease inspection of the fastening tension in both visual and remote inspections. Precision of bolt tightening is one of the major issues noted in industrial plants where accurate preload is questioned whether it is achieved or not. Insufficient preload, caused by an inaccurate tightening method, is a frequent cause of bolted joint failure which may lead to potentially catastrophic structural failures. The loss of tension may occur due to vibration, thermal effects, change in the material characteristics and so on. Reviews of recent related developments are discussed in this paper with proposal of intended features for smart bolts.

Urocortins Improve Dystrophic Skeletal Muscle Structure and Function through Both PKA- and Epac-Dependent Pathways

In Duchenne muscular dystrophy, the absence of dystrophin causes progressive muscle wasting and premature death. Excessive calcium influx is thought to initiate the pathogenic cascade, resulting in muscle cell death. Urocortins (Ucns) have protected muscle in several experimental paradigms. Herein, we demonstrate that daily s.c. injections of either Ucn 1 or Ucn 2 to 3-week-old dystrophic mdx(5Cv) mice for 2 weeks increased skeletal muscle mass and normalized plasma creatine kinase activity. Histological examination showed that Ucns remarkably reduced necrosis in the diaphragm and slow- and fast-twitch muscles. Ucns improved muscle resistance to mechanical stress provoked by repetitive tetanizations. Ucn 2 treatment resulted in faster kinetics of contraction and relaxation and a rightward shift of the force-frequency curve, suggesting improved calcium homeostasis. Ucn 2 decreased calcium influx into freshly isolated dystrophic muscles. Pharmacological manipulation demonstrated that the mechanism involved the corticotropin-releasing factor type 2 receptor, cAMP elevation, and activation of both protein kinase A and the cAMP-binding protein Epac. Moreover, both STIM1, the calcium sensor that initiates the assembly of store-operated channels, and the calcium-independent phospholipase A(2) that activates these channels were reduced in dystrophic muscle by Ucn 2. Altogether, our results demonstrate the high potency of Ucns for improving dystrophic muscle structure and function, suggesting that these peptides may be considered for treatment of Duchenne muscular dystrophy.

Dynamics and Control of Hose-Drogue Refueling Systems During Coupling

Dynamic analyses and control system design for aerial refueling hose―drogue systems during receiver―probe coupling are studied. When a receiver plane approaches to couple with a refueling drogue, the hose―drogue system to undergoes transient motion due to the receiver forebody aerodynamic effect in addition to the tanker motion and downwash, and atmospheric turbulence. As a receiver probe comes into contact with the drogue, loss of tension in the refueling hose may cause it to exhibit erratic motion without hose-tension control. In this paper, a previously developed hose―drogue dynamic model is extended to study 1) the receiver forebody aerodynamic effect on the drogue transient motion before coupling and possible active stabilization and control methods, and 2) the wave motion of the hose―drogue system due to the tension change in the hose upon the receiver coupling and possible hose-tension control methods.