Direct Contact Force Research Articles

Simulation of finite-size fibers in turbulent channel flows

The dynamical behavior of almost neutrally buoyant finite-size rigid fibers or rods in turbulent channel flow is studied by direct numerical simulations. The time evolution of the fiber orientation and translational and rotational motions in a statistically steady channel flow is obtained for three different fiber lengths. The turbulent flow is modeled by an entropy lattice Boltzmann method, and the interaction between fibers and carrier fluid is modeled through an external boundary force method. Direct contact and lubrication force models for fiber-fiber interactions and fiber-wall interaction are taken into account to allow for a full four-way interaction. The density ratio is chosen to mimic cellulose fibers in water. It is shown that the finite size leads to fiber-turbulence interactions that are significantly different from earlier reported results for pointlike particles (e.g., elongated ellipsoids smaller than the Kolmogorov scale). An effect that becomes increasingly accentuated with fiber length is an accumulation in high-speed regions near the wall, resulting in a mean fiber velocity that is higher than the mean fluid velocity. The simulation results indicate that the finite-size fibers tend to stay in the high-speed streaks due to collisions with the wall. In the central region of the channel, long fibers tend to align in the spanwise direction. Closer to the wall the long fibers instead tend to toward to a rotation in the shear plane, while very close to the wall they become predominantly aligned in the streamwise direction.

Catheter-tissue contact force for pulmonary veins isolation: a pilot multicentre study on effect on procedure and fluoroscopy time

AimsCatheter–tissue contact is critical for effective lesion creation in radiofrequency catheter ablation (RFCA). In a multicentre prospective study, we assessed the effect of direct contact force (CF) measurement on acute procedural parameters during RFCA of atrial fibrillation (AF).Methods and resultsA new open-irrigated tip catheter with CF sensing (SmartTouch™, Biosense Webster Inc.) was used. All the patients underwent the first ablation procedure for paroxysmal AF with antral pulmonary vein (PV) isolation, aiming at entry and exit conduction block in all PVs. Ninety-five patients were enroled in nine centres and successfully underwent ablation. Overall procedure time, fluoroscopy time, and ablation time were 138.0 ± 67.0, 14.3 ± 11.2, and 33.8 ± 19.4 min, respectively. The mean CF value during ablation was 12.2 ± 3.9 g. Force time integral (FTI) analysis showed that patients achieving a value below the median of 543.0gs required longer procedural (158.0 ± 74.0 vs. 117.0 ± 52.0 min, P = 0.004) and fluoroscopy (17.5 ± 13.0 vs. 11.0 ± 7.7 min, P = 0.007) times as compared with those in whom FTI was above this value. Patients in whom the mean CF during ablation was >20 g required shorter procedural time (92.0 ± 23.0 vs. 160.0 ± 67.0 min, P = 0.01) as compared with patients in whom this value was <10 g. Four groin haematomas were the only complications observed.ConclusionContact force during RFCA for PV isolation affects procedural parameters, in particular procedural and fluoroscopy times, without increasing complications.

Providing haptic feedback in robot-assisted minimally invasive surgery: A direct optical force-sensing solution for haptic rendering of deformable bodies

This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system with the optical force sensor, and (b) study human haptic perception during the identification of remote object deformability. The first experiment was carried out to discriminate deformability of objects when human subjects were in direct contact with deformable objects by means of a laparoscopic tool. The control parameters were then tuned based on the results of this experiment using a gain-scheduling method. The second experiment was conducted to study the effectiveness of the force feedback provided through the enhanced teleoperation system. The results show that the force feedback increased the ability of subjects to correctly identify materials of different deformable types. In addition, the virtual force feedback provided by the teleoperation system comes close to the real force feedback experienced in direct MIS. The experimental results provide design guidelines for choosing and validating the control architecture and the optical force sensor.

Benign Anterior Temporal Epidural Hematoma: Indolent Lesion with a Characteristic CT Imaging Appearance after Blunt Head Trauma

Epidural hematomas (EDHs) occur in 0.9–12% of patients with head trauma and most often result from direct contact forces to the head leading to laceration of the middle meningeal artery. This study sought to evaluate the pathogenesis and clinical importance of a subgroup of EDHs isolated to the anterior middle cranial fossa as these may have a more benign natural history. The authors retrospectively evaluated 200 patients with acute traumatic supratentorial EDHs at a single hospital center. A subset of 21 patients in whom the EDH was located at the anterior aspect of the middle cranial fossa was identified.

Multiple dynamic regimes in concentrated microgel systems

We investigate dynamical heterogeneities in the collective relaxation of a concentrated microgel system, for which the packing fraction can be conveniently varied by changing the temperature. The packing fraction-dependent mechanical properties are characterized by a fluid-solid transition, where the system properties switch from a viscous to an elastic low-frequency behaviour. Approaching this transition from below, we find that the range xi of spatial correlations in the dynamics increases. Beyond this transition, xi reaches a maximum, extending over the entire observable system size of approximately 5 mm. Increasing the packing fraction even further leads to a second transition, which is characterized by the development of large zones of lower and higher dynamical activity that are well separated from each other; the range of correlation decreases at this point. This striking non-monotonic dependence of xi on volume fraction is reminiscent of the behaviour recently observed at the jamming/rigidity transition in granular systems. We identify this second transition as the transition to 'squeezed' states, where the constituents of the system start to exert direct contact forces on each other, such that the dynamics becomes increasingly determined by imbalanced stresses. Evidence of this transition is also found in the frequency dependence of the storage and loss moduli, which become increasingly coupled as direct friction between the particles starts to contribute to the dissipative losses within the system. To our knowledge, our data provide the first observation of a qualitative change in dynamical heterogeneity as the dynamics switches from purely thermally driven to stress driven.

Design and control of a novel linear wire bonding head

Wire bonding has been one of the standard operations in plastic integrated circuit (IC) package assembly for a long time. With the development of IC assembly technology, the equipment of wire bonding should be improved for even higher performance. Thus, a novel linear wire bonding head driven by a permanent magnet linear motor (PMLM), instead of the rotary bonding structure, is designed to optimize the system structure and improve the performance of wire bonding. Based on two different wire bonding states, the switching control scheme corresponding to this linear structure is presented. In free motion, the position tracking control suppressing the vibration of flexible parts of the structure is performed at high speed and acceleration. In constrained motion, the active force control with direct contact force feedback is adopted for more precise bonding force compared with the indirect current feedback control in previous rotary structure. The experiment results show higher performance of wire bonding because of the combination of novel linear structure and control scheme.

Effects of applied contact force and volume control setting on output force levels of the BAHA® Softband

The BAHA® Softband has been developed to provide a transcutaneous anchor for a BAHA® until a child is a surgical candidate for the percutaneous BAHA® implant. We tested the objective output force level of the BAHA® Classic 300 and Compact connected to a Softband on an artificial mastoid to determine: (1) the effects of direct contact force on output force levels (dB); and (2) the required volume control setting to ensure audibility of speech (assuming an average adult reference equivalent threshold force level).Direct contact force was varied from 2 to 5 N in 1 N steps. Output force level increased with increasing contact force. However, the average increase was 3 dB or lower, suggesting that the contact force is of minor importance. Volume control setting appears to be of much greater importance. It is suggested that the volume setting of either device be set to at least 2.5 to ensure audibility of conversational speech. Data from normal-hearing adults with simulated conductive hearing losses are presented to validate this conclusion.

Three-Dimensionality of direct contact forces in chiropractic spinal manipulative therapy

Objective To perform three-dimensional (3-D) manual contact force measurements of chiropractic adjustments at the patient-chiropractor interface. Methods A new hand/palm-held computerized 3-D force measuring system was used to collect 3-D force data at the doctor-patient interface (direct measurement) during cervical, thoracic, and sacroiliac adjustments by 2 chiropractors on 10 healthy subjects. Results 3-D components of force were significantly greater than matching 1-dimensional (1-D) perpendicular force components, which have been the standard in direct measurement up until now. As well, 3-D components of force were significantly different between adjustment levels, suggesting different dynamics (kinetics) of adjustment techniques. Force magnitudes and statistically significant differences between loading rates and adjustment levels fit in the existing body of knowledge of chiropractic adjustment forces. Conclusion To our knowledge, this is the first study which presents 3-D force-time histories of chiropractic adjustments recorded at the doctor-subject interface. Direct 3-D contact force data seem to have the potential to contribute to chiropractic research because of a more complete description of this biomechanical aspect of daily practice. Results can be used to study novice and experienced chiropractors' techniques and permit the development of training and evaluation protocols in teaching institutions.

Three-dimensionality of contact forces during clinical manual examination and treatment: A new measuring system

Objective. Three-dimensionality (3D) of manual contact forces at the patient–practitioner interface. Design. Description of a new hand/palm-held computerized 3D force measuring system. Background. Up until now instrumented direct manual contact force measurement has been one-dimensional (1D). Methods. The system is built for interface (direct) measurement of 3D manual contact force with real-time data presentation. Static calibration was performed of the 3D force sensor with variable preloads to study their effect as well of the prototype system adapted for clinical manual examination and treatment. Results. Calibration validity and reliability of the 3D force sensor under all but the 5 kN preload and of the new system showed systematic respective random errors in the order or smaller than one newton. Conclusions. The new system enables, for the first time, recording and presenting of 3D manual contact forces at the patient–practitioner interface. 3D direct manual contact force measures have the potential to give a more complete and differentiated characterization of patient and practitioner forces than 1D forces. Clinical validity of the prototype system will have to be investigated, and for studying specific clinical manual handling techniques, obvious limitations require further development. Relevance Manual techniques play a prominent role in chiropractic, manual-therapy and -medicine, massage therapy and osteopathy. The more complete 3D manual contact force description also can help practitioners and students to improve both manual force perception and delivery skills by providing higher standardization and real-time objective feedback about performance.

The use of padding in rugby union. An overview.

In any contact sport where impact and collision are an accepted feature, the use of various forms of external padding has become more common. Rugby union players experience a combination of characteristic extrinsic forces through the acts of tackling and scrummaging. The laws which are part of the international regulation of rugby union only permit the wearing of certain, clearly delineated forms of padding. Only then is such padding permitted on medical recommendation, provided that this padding is attached to the body or sewn into the jersey. This article discusses the padding of the shoulders, shins and thighs of rugby union players and highlights the need to address these issues with respect to the increasing number of women who are now playing this sport, particularly in the Southern hemisphere. There is little evidence to show that shoulder pads decrease the incidence of severe shoulder injuries. However, well-fitting shoulder pads constructed of materials that effectively disperse the force of impact appear to reduce the effect of direct contact and reduce the potential for soft tissue damage. Shin guards that are made of light, soft, compliant materials are effective in reducing impact to the shin and thereby reduce the risk of bruising injuries which are common to the pretibial region. Similarly, thigh pads are considered to be able to modify the effects of direct contact forces to the anterior thigh where deep contusional injuries with the potential for myositis ossificans are well reported. Informed advice for women rugby players regarding the use of specific padding is unavailable at present. Current information is anecdotal and not confirmed by statistical studies or well-conducted research. In these circumstances, women rugby players should observe the same recommendations that apply to their male counterparts.