Soft Clamp Research Articles

On the link between mechanics and thermal properties: mechanothermics

We report on the theoretical derivation of macroscopic thermal properties (specific heat, thermal conductivity) of an electrically insulating rod connected to two reservoirs, from the linear superposition of its mechanical mode Brownian motions. The calculation is performed for a weak thermal gradient, in the classical limit (high temperature). The development is kept basic as far as geometry and experimental conditions are concerned, enabling an almost fully analytic treatment. In the modeling, each of the modes is subject to a specific Langevin force, which enables to produce the required temperature profile along the rod. The theory is predictive: the temperature gradient (and therefore energy transport) is linked to motion amplitude cross-correlations between nearby mechanical modes. This arises because energy transport is actually mediated by mixing between the modal waves, and not by the modes themselves. This result can be tested on experiments, and shall extend the concepts underlying equipartition and fluctuation–dissipation theorems. The theory links intimately the macroscopic size of the clamping region where the mixing occurs to the microscopic lengthscale of the problem at hand: the phonon mean-free-path. This clamping region, which is key, has received recently a renewed attention in the field of nanomechanics with topical works on ‘phonon shields’ and ‘soft clamping’. We believe that our work should impact the domain of thermal transport in nanostructures, with future developments of the theory toward the quantum regime.

Nano-beam clamping revisited

Within recent years, the field of nano-mechanics has diversified in a variety of applications, ranging from quantum information processing to biological molecules recognition. Among the diversity of devices produced these days, the simplest (but versatile) element remains the doubly clamped beam: it can store very large tensile stresses (producing high resonance frequencies f0 and quality factors Q), is interfaceable with electric setups (by means of conductive layers), and can be produced easily in clean rooms (with scalable designs, including multiplexing). Besides, its mechanical properties are the simplest to describe. Resonance frequencies and Qs are being modeled, with as specific achievement the ultrahigh quality resonances based on “soft clamping” and “phonon shields.” Here, we demonstrate that the fabrication undercut of the clamping regions of basic nano-beams produces “natural soft clamping,” given for free. We present the analytic theory that enables to fit experimental data, which can be used for {Q,f0} design: beyond finite element modeling validation, the presented expressions provide a profound understanding of the phenomenon, with both Q enhancement and a downward frequency shift.

Hierarchical tensile structures with ultralow mechanical dissipation

Structural hierarchy is found in myriad biological systems and has improved man-made structures ranging from the Eiffel tower to optical cavities. In mechanical resonators whose rigidity is provided by static tension, structural hierarchy can reduce the dissipation of the fundamental mode to ultralow levels due to an unconventional form of soft clamping. Here, we apply hierarchical design to silicon nitride nanomechanical resonators and realize binary tree-shaped resonators with room temperature quality factors as high as 7.8 × 108 at 107 kHz frequency (1.1 × 109 at T = 6 K). The resonators’ thermal-noise-limited force sensitivities reach 740 zN/Hz1/2 at room temperature and 90 zN/Hz1/2 at 6 K, surpassing state-of-the-art cantilevers currently used for force microscopy. Moreover, we demonstrate hierarchically structured, ultralow dissipation membranes suitable for interferometric position measurements in Fabry-Pérot cavities. Hierarchical nanomechanical resonators open new avenues in force sensing, signal transduction and quantum optomechanics, where low dissipation is paramount and operation with the fundamental mode is often advantageous.

Perimeter Modes of Nanomechanical Resonators Exhibit Quality Factors Exceeding 109 at Room Temperature

Systems with low mechanical dissipation are extensively used in precision measurements such as gravitational wave detection, atomic force microscopy and quantum control of mechanical oscillators via opto- and electromechanics. The mechanical quality factor ($Q$) of these systems determines the thermomechanical force noise and the thermal decoherence rate of mechanical quantum states. While the dissipation rate is typically set by the bulk acoustic properties of the material, by exploiting dissipation dilution, mechanical $Q$ can be engineered through geometry and increased by many orders of magnitude. Recently, soft clamping in combination with strain engineering has enabled room temperature quality factors approaching one billion ($10^9$) in millimeter-scale resonators. Here we demonstrate a new approach to soft clamping which exploits vibrations in the perimeter of polygon-shaped resonators tethered at their vertices. In contrast to previous approaches, which rely on cascaded elements to achieve soft clamping, perimeter modes are soft clamped due to symmetry and the boundary conditions at the polygon vertices. Perimeter modes reach $Q$ of 3.6 billion at room temperature while spanning only two acoustic wavelengths -- a 4-fold improvement over the state-of-the-art mechanical $Q$ with 10-fold smaller devices. The small size of our devices makes them well-suited for near-field integration with microcavities for quantum optomechanical experiments. Moreover, their compactness allows the realization of phononic lattices. We demonstrate a one-dimensional Su-Schrieffer-Heeger chain of high-$Q$ perimeter modes coupled via nearest-neighbour interaction and characterize the localized edge modes.

Strained crystalline nanomechanical resonators with quality factors above 10 billion

In strained mechanical resonators, the concurrence of tensile stress and geometric nonlinearity dramatically reduces dissipation. This phenomenon, called dissipation dilution, is employed in mirror suspensions of gravitational-wave interferometers and at the nanoscale, where soft clamping and strain engineering have allowed extremely high quality factors. However, these techniques have so far been applied only to amorphous materials, specifically Si3N4. Crystalline materials exhibit substantially lower intrinsic damping at cryogenic temperatures. Applying dissipation dilution engineering to strained crystalline materials could, therefore, enable extremely low loss nanomechanical resonators, as they combine low internal friction, high intrinsic strain and high yield strength. This potential has not yet been fully exploited. Here we demonstrate that single-crystal strained silicon—a material developed for high-mobility transistors—can be used to realize mechanical resonators with ultralow dissipation. We fabricate strained silicon nanostrings with high aspect ratios supporting megahertz mechanical modes with quality factors exceeding 1010 at 7 K, a tenfold improvement over values reported in Si3N4. We estimate a thermal-noise-limited force sensitivity of (5 ± 2) × 10–20 N Hz–1/2 at 7 K—approaching that of carbon nanotubes—and a heating rate of only 60 quanta per second. The low mass and high quality factors of our nanomechanical resonators make them particularly promising for quantum sensing and transduction. Soft clamping reduces the dissipation of nanomechanical resonators, but this method has been limited to amorphous materials. When applied in crystalline silicon, it enables resonators with quality factors beyond ten billion.

Experimental measurement of force, torque control and vibration absorber system for intraoperative tele-operated robotic-assisted femoral shaft drilling using air-controlled soft balloon damper

The use of closed intramedullary nailing fixation and drilling technique is a very common, safe and standard method for treating diaphyseal femoral fractures. However, it has several demerits such as high cutting forces and torque during drilling and this could cause high vibration and result in cracks, tool breakage and necrosis of the already fractured bone. This paper presents the measure of force, torque control and vibration absorber system for intra-operative tele-operated robotic-assisted femoral shaft drilling using air-controlled balloon damper experimentally, since bone is surrounded by soft tissues that can cause more severe injury to the tissue due to high traction force. Simulated femur bone and tissue are used for this experiment. A sensor-based model clamping system embedded with controlled pressurized air balloon to damp drilling vibration was developed; the drilling forces were monitored by the force sensor attached to the end robot effector, while the resulted vibration was measured by contact sensor during the entire surgical drilling. Forces and vibration caused by drilling forces acting on the bone at varying damper pressure at varying spindle drill speed were obtained using (EMS 309 data acquisition and then the data were processed using MATLAB R2015b. The vibration results were processed with wavelet packet transform (WPT) using Fast Fourier transform to analyze the vibration signals, frequencies and amplitude of the vibration. This modeled control system is a good concept, results clearly justify that soft clamping fixation system can be employed to reduce force, torque and vibration without causing harm to the delicate surrounding tissues. This control measures can provide surgeons with real-time information which can assist them in repositioning and repair of fracture bone within control and safe margins. It is believed that this idea will have greater future developmental prospect.

Analysis of Membrane Phononic Crystals with Wide Band Gaps and Low-Mass Defects

We present techniques to model and design membrane phononic crystals with low-mass defects, optimized for force sensing. Further, we identify the importance of the phononic crystal mass contrast as it pertains to the size of acoustic bandgaps and to the dissipation properties of defect modes. In particular, we quantify the tradeoff between high mass contrast phononic crystals with their associated robust acoustic isolation, and a reduction of soft clamping of the defect mode. We fabricate a set of phononic crystals with a variety of defect geometries out of high stress stoichiometric silicon nitride membranes, and measured at both room temperature and 4 K in order to characterize the dissipative pathways across a variety of geometries. Analysis of these devices highlights a number of design principles integral to the implementation of low-mass, low-dissipation mechanical modes into optomechanical systems.

Spin detection with a micromechanical trampoline: towards magnetic resonance microscopy harnessing cavity optomechanics

We explore the prospects and benefits of combining the techniques of cavity optomechanics with efforts to image spins using magnetic resonance force microscopy (MRFM). In particular, we focus on a common mechanical resonator used in cavity optomechanics—high-stress stoichiometric silicon nitride (Si3N4) membranes. We present experimental work with a ‘trampoline’ membrane resonator that has a quality factor above 106 and an order of magnitude lower mass than a comparable standard membrane resonators. Such high-stress resonators are on a trajectory to reach 0.1 force sensitivities at MHz frequencies by using techniques such as soft clamping and phononic-crystal control of acoustic radiation in combination with cryogenic cooling. We present a demonstration of force-detected electron spin resonance of an ensemble at room temperature using the trampoline resonators functionalized with a magnetic grain. We discuss prospects for combining such a resonator with an integrated Fabry–Perot cavity readout at cryogenic temperatures, and provide ideas for future impacts of membrane cavity optomechanical devices on MRFM of nuclear spins.

Generalized dissipation dilution in strained mechanical resonators

Mechanical resonators with high quality factors are of relevance in precision experiments, ranging from gravitational wave detection and force sensing to quantum optomechanics. Beams and membranes are well known to exhibit flexural modes with enhanced quality factors when subjected to tensile stress. The mechanism for this enhancement has been a subject of debate, but is typically attributed to elastic energy being "diluted" by a lossless potential. Here we clarify the origin of the lossless potential to be the combination of tension and geometric nonlinearity of strain. We present a general theory of dissipation dilution that is applicable to arbitrary resonator geometries and discuss why this effect is particularly strong for flexural modes of nanomechanical structures with high aspect ratios. Applying the theory to a non-uniform doubly clamped beam, we show analytically how dissipation dilution can be enhanced by modifying the beam shape to implement "soft clamping", thin clamping and geometric strain engineering, and derive the ultimate limit for dissipation dilution.

Giant, Voltage Tuned, Quality Factors of Single Wall Carbon Nanotubes and Graphene at Room Temperature.

Mastering dissipation in graphene-based nanostructures is still the major challenge in most fundamental and technological exploitations of these ultimate mechanical nanoresonators. Although high quality factors have been measured for carbon nanotubes (>106) and graphene (>105) at cryogenic temperatures, room-temperature values are orders of magnitude lower (≃102). We present here a controlled quality factor increase of up to ×103 for these basic carbon nanostructures when externally stressed like a guitar string. Quantitative agreement is found with theory attributing this decrease in dissipation to the decrease in viscoelastic losses inside the material, an effect enhanced by tunable "soft clamping". Quality factors exceeding 25 000 for SWCNTs and 5000 for graphene were obtained on several samples, reaching the limits of the graphene material itself. The combination of ultralow size and mass with high quality factors opens new perspectives for atomically localized force sensing and quantum computing as the coherence time exceeds state-of-the-art cryogenic devices.

RETRACTED: Decision making in junctional trauma care

Paul Parker, Decision making in junctional trauma care. Trauma. Published online ahead of print 4 June 2013. DOI: 10.1177/1460408613489088. This article was published in error and is therefore retracted. Improvised explosive devices cause 60% of all UK military fatalities. The signature injury produced is that of a bilateral above-knee amputation, significant perineal trauma and an open-book pelvic fracture. Shorter timelines deliver these patients to hospital at the very edge of the physiological envelope of survivability. The available time period for their haemorrhage control and initial wound surgery is short – often of the order of 75 min. The concepts and practise of ‘right turn resuscitation’, damage control surgery and orthopaedics, on-table ‘ITU’ pause/catch-up and then further resuscitative surgery are now commonplace. In Helmand in 2013, multiple-team operating is now the norm on these casualties with up to seven surgeons and three anaesthetists contemporaneously involved in the operative care of one patient. This usually involves one consultant orthopaedic surgeon and trainee per lower limb, a plastic surgeon on the upper limb or face/eyes and two general surgeons obtaining proximal vascular control or in-cavity haemorrhage control. A series of consensus statements were issued by the UK Military Limb Trauma Working Group and Torso Trauma Working Group of the UK Academic Department of Military Surgery and Trauma. Twenty-five clear and didactic statements were produced to provide advice to the newly qualified consultant team dealing with significant junctional or terrorist-related trauma. The fundamental message is that bleeding is always a surgical problem. Some adjuncts are available; massive transfusion, pressure (direct and indirect), compressive bandaging, haemostatic dressings and tourniquets. However, only formal surgical control, whether by the surgeon’s finger, soft clamp or tie, is definitive. Early proximal control is mandatory: In all cases, we state, ‘rapidly obtain the most distally appropriate proximal control – above the zone of injury.’

Influence of experimental setups on the apparent uniaxial tensile load-bearing capacity of Textile Reinforced Concrete specimens

An important parameter for dimensioning of Textile Reinforced Concrete (TRC) structures and structural elements is the tensile load-bearing capacity of the composite. Respective values are usually derived from uniaxial tensile tests with overcritically reinforced TRC specimens. In this paper, influences from specimen geometry, e.g. plane and waisted specimens, and load application design, e.g. stiff glued steel plates or soft clamping constructions are investigated. Therefore, experimental results regarding the load-bearing capacity of the composite are statistically evaluated. The experimental observations are supported by results of numerical simulations with a one-dimensional model based on the Finite Element Method. These simulations provide stress distributions in concrete and reinforcing fibres as well as the tensile load-bearing capacity. Based on these results existing test setups for the derivation of the load-bearing capacity of the composite for dimensioning are assessed. As a result, plane plate specimens with a load application by means of friction is recommended for experimental determination.

Structural basis for the enhancement of eIF4A helicase activity by eIF4G

The eukaryotic translation initiation factors 4A (eIF4A) and 4G (eIF4G) are crucial for the assembly of the translationally active ribosome. Together with eIF4E, they form the eIF4F complex, which recruits the 40S subunit to the 5' cap of mRNA. The two-domain RNA helicase eIF4A is a very weak helicase by itself, but the activity is enhanced upon interaction with the scaffolding protein eIF4G. Here we show that, albeit both eIF4A domains play a role in binding the middle domain of eIF4G (eIF4G-m, amino acids 745-1003), the main interaction surface is located on the C-terminal domain. We use NMR spectroscopy to define the binding site and find that the contact surface is adjacent to the RNA-, ATP-, and eIF4A-NTD-interacting regions. Mutations of interface residues abrogated binding, confirmed the interface, and showed that the N-terminal end of eIF4G-m interacts with the C-terminal domain of eIF4A. The data suggest that eIF4G-m forms a soft clamp to stabilize the closed interdomain orientation of eIF4A. This model can explain the cooperativity between all binding partners of eIF4A (eIF4G, RNA, ATP) and stimulation of eIF4A activity in the eIF4F complex.

Cord Monitoring Changes and Segmental Vessel Ligation in the “At Risk” Cord During Anterior Spinal Deformity Surgery

Retrospective analysis of all cases of anterior spinal deformity surgery that had intraoperative spinal cord monitoring (somatosensory-evoked potentials, SSEPs). The prime purpose of this study was to determine the incidence of significant SSEP changes in patients undergoing anterior spinal deformity surgery. A secondary objective was to ascertain if patients with "cords at risk" were more likely to produce significant intraoperative SSEP changes and what proportion of these changes resulted in postoperative neurological deficit. There is anecdotal evidence to suggest that patients with intraspinal abnormalities are at greater risk of postoperative neurological deficit after spinal deformity surgery. To date, there have been no studies detailing this risk and how it relates to the type of surgery performed. This is a question of increasing relevance with the modern trend towards more anterior scoliosis correction and instrumentation. Recent reports have suggested a low incidence of neurological complication with anterior deformity procedures. There is controversy as to whether SSEP monitoring is required for these anterior procedures and whether soft clamping of segmental vessels before their division is a necessary precaution. This study is a chart review of all patients who had an anterior deformity operation between 1990 and 2001. Those patients who had a complete data set (preoperative magnetic resonance imaging scan, patient and procedural documentation, and adequate intraoperative SSEP traces) were included in this study. A significant SSEP change was correlated with the type of procedure performed, whether that patient had a "cord at risk" (CAR) and the degree of postoperative neurological deficit if present. During the study period, 871 patients underwent elective anterior spinal deformity surgery. Ninety five (11%) patients had intraspinal abnormalities on magnetic resonance imaging. From this group, 27 (3%) were termed CAR. Twenty six (3%) patients had significant change in the intraoperative SSEP monitoring. Seventeen (2% total) occurred in the CAR group and nine (1% of total) in the normal cord group. There were five patients (0.6%) with significant postoperative neurological deficits, four (0.5%) in the CAR group, and one (0.1%) in the normal cord group. These patients had also demonstrated changes in their SSEPs. The sensitivity of SSEP monitoring for the whole series was 100%, specificity 97.5%, the positive predictive value was 19% and the negative predictive value was 100%. The CAR group was significantly more likely to have significant SSEP changes during any operation and was more likely to have postoperative paresis. Patients with identified cords at risk should undergo spinal cord monitoring (SSEP) if they undergo anterior spinal deformity surgery. Soft clamping of segmental vessels is indicated with cord monitoring to prevent the risk of postoperative neurological sequelae.

Prevention of Air Leakage by Spraying Vivostat Fibrin Sealant After Lung Resection in Pigs

To evaluate Vivostat fibrin sealant in the prevention of air leakage after experimental lung resection in pigs. Randomized study. University laboratory. Six Landrace pigs were operated on in both lungs through a median sternotomy. Five different resection sites were created in each lung. Randomization was performed to either application of Vivostat fibrin sealant (ConvaTec; Skillman NJ) or human albumin 20% (control) at the resection sites. The lung parenchyma was occluded with a soft clamp for either 1, 2, 5, or 10 min in the treatment group and 10 min in the control group. After removal of the clamp, the lung was ventilated with an increasing intrabronchial pressure of 20, 30, and 45 cm H(2)O for 2 min at each step. At inspiratory pressures of 20 and 30 cm H(2)O air leaks were found in the control group but not in the Vivostat group (p < 0.001). At an inspiratory pressure of 45 cm H(2)O, there were two small air leaks in the Vivostat group at each clamping time (four at 5 min), compared with five small and seven large leaks in the control group. Analysis of the data after 10 min of clamping showed that the Vivostat group was superior to the human albumin group (p = 0.002). This randomized study shows that Vivostat fibrin sealant is effective in preventing air leakage after small lung resections in pigs, even at high inspiratory pressures.

Paraplegia resulting from vessel ligation.

This is a retrospective review of clinical records for evidence of paraplegia specifically resulting from segmental vessel ligation during anterior spinal surgery. To determine the precise risk rate, and to potentially identify risk factors. Although many authors have alluded to this risk, the exact risk rate and risk factors have never been identified. All patients having an anterior approach involving T1-L3 were reviewed. The two reviewers were not involved in any of the surgeries. The 1197 cases were consecutive from 1967 to 1991. There were no paralyses. There would appear to be virtually no risk to segmental vessel ligation provided: 1) vessel ligation is unilateral, 2) done on the convexity of a scoliosis, 3) ligated at midvertebral body level, and 4) hypotensive anesthesia is avoided. Soft clamping with somatosensory-evoked potential monitoring does not appear justified.

Internal Thoracic Artery Flow in Diabetic Patients

Patients with diabetes mellitus have an increased frequency of atherosclerotic coronary artery disease, plus abnormalities of vascular tone that could be contributed to autonomic, platelet, and endothelial dysfunction. The purpose of this prospective study was to compare the internal thoracic artery (ITA) flow of diabetic and nondiabetic patients, to determine whether any pathophysiologic changes occur that have any bearing on vascular tone and the adequacy of flow of the ITA. In a consecutive group of patients undergoing coronary artery bypass graft (CABG) surgery, 117 patients (group I) were nondiabetic (ND), 18 patients (group II) were noninsulin dependent (NIDDM), and 20 patients (group III) were insulin dependent (IDDM) diabetics. The ITA was mobilized, and following systemic heparinization it was divided and trimmed for the subsequent anastomoses. The first ITA flow measurement was recorded (flow 1). This was followed by an intraluminal injection of 2 mL of dilute papaverine solution (30 mg in 20 mL N/saline), which was enclosed in the artery for fifteen minutes by applying a soft clamp to the distal end. At the end of this period, a second flow measurement was taken (flow 2). Percent increase in flow and flow reserve (flow 2/flow 1) were recorded for each patient. The median values for flow 1 were 48, 46, and 58 mL/minute for groups I, II, and III respectively. For flow 2 the values were 132, 118, and 126 for groups I, II, and III, respectively, with a median percent increase in flow being 138% (47-380%), 179% (100-380%), and 115% (35-470%) for groups I, II, and III respectively (P &lt; 0.0001). ITA flow reserve was similar among the three groups and was 2.4, 2.8, and 2.2 for groups I, II, and III respectively. The ITA exhibits the same degree of initial spasm, similar relaxation to intraluminal papaverine, and similar flow reserve. No physiologic abnormalities of ITA flow and reactivity are specific to diabetes. The ITA should be used with the same indications or contraindications as in nondiabetic patients.