Orientation dependent molecular friction on organic layer compound crystals

High resolution friction force maps of the benzylammonium terminated crystalline surface of a layer compound are presented. The lateral force map acquired with an atomic force microscope, reveals a significant contrast between different molecular orientations yielding molecular rows which differ from their neighboring ones. The single crystals are formed by stacks of copper oxalate sheets sandwiched between stereoregular organic cations, resulting in highly organized surface structures. Single molecular defects are observed at small loads. The experimental results are compared with numerical calculations which indicate a transition from an unperturbed state at small loads to a distorted state at higher loads. (C) 2011 American Institute of Physics.

Driving and emergency braking may be impaired after tibiotalar joint arthrodesis: conclusions after a case series.

PURPOSE To assess whether reaction time (RT) and movement time (MT), as the two components of the total brake response time (TBRT) and brake force (BF) are different in patients with a foot joint arthrodesis in comparison to controls. METHODS The study was a comparative case series in a driving simulator under realistic driving conditions. Mobile patients without a walker, ≥6 months after surgery who were driving a car and had no neurological co-morbidity, knee or hip joint prosthesis were included in the study. The selection criteria resulted in 12 patients with right tibiotalar joint arthrodesis (TTJA) and 12 patients with another right foot joint arthrodesis (OFJA), who were compared to 17 individuals without any ankle-joint pathology. For TBRT, an empirical safe driving threshold of 700 ms was used. The outcome measures were RT, MT, TBRT, BF and McGuire score. RESULTS MT (p = 0.034) and TBRT (p = 0.026) were longer in TTJA patients in comparison with the controls. Also, more patients with TTJA than patients with OFJA and controls exceeded the safe driving threshold (p = 0.028). The outcomes in OFJA patients and in controls were comparable. The McGuire score was similar between the TTJA and OFJA patients (p = 0.26). CONCLUSIONS Significantly slower MT and TBRT, and significantly more patients exceeding the safe driving threshold, were observed after a tibiotalar-joint arthrodesis in comparison to the controls. Patients with OFJAs were not significantly different from the controls. Driving and emergency braking may be impaired after tibiotalar-joint arthrodesis.

Cost of low back pain in Switzerland in 2005

Low back pain (LBP) is the most prevalent health problem in Switzerland and a leading cause of reduced work performance and disability. This study estimated the total cost of LBP in Switzerland in 2005 from a societal perspective using a bottom-up prevalence-based cost-of-illness approach. The study considers more cost categories than are typically investigated and includes the costs associated with a multitude of LBP sufferers who are not under medical care. The findings are based on a questionnaire completed by a sample of 2,507 German-speaking respondents, of whom 1,253 suffered from LBP in the last 4 weeks; 346 of them were receiving medical treatment for their LBP. Direct costs of LBP were estimated at 2.6 billion and direct medical costs at 6.1% of the total healthcare expenditure in Switzerland. Productivity losses were estimated at 4.1 billion with the human capital approach and 2.2 billion with the friction cost approach. Presenteeism was the single most prominent cost category. The total economic burden of LBP to Swiss society was between 1.6 and 2.3% of GDP.

An intraoperatively moulded PMMA prostheses like spacer for two-stage revision of infected total knee arthroplasty

We report a series of 16 consecutive total knee arthroplasty (TKA) revision procedures for deep infection, treated with a newly developed intraoperatively moulded PMMA cement-prostheses-like spacer (CPLS). The standard treatment consisted of a two-stage protocol with initial explantation of the infected components combined with radical debridement, followed by implantation of a temporary cement spacer and final reimplantation of a new TKA. A sterilizeable Teflon tapered aluminium mould was developed for production of a custom made CPLS during the intervention. Stable implantation of the CPLS was achieved with a second cementation, allowing for correct alignment and ligament balancing. The spacer remained 3.5 months on average until reimplantation of a TKA occurred. At time of reimplantation, patients had an average KSS score of 84.44 points with an average flexion capacity of 102°. There was no recurrent infection during the study period of minimum 2 years. With this new technique, a low friction articulation with good stability, high comfort and a better range of motion compared to handcrafted spacers was achieved. The use of this spacer is a time sparing, cheap and convenient option in 2-stage TKA revision.

Ground reaction force profiles after partial and pancarpal arthrodesis in dogs

OBJECTIVES: To evaluate and compare long-term functional outcome after partial carpal arthrodesis and pancarpal arthrodesis in dogs using kinetic gait analysis. METHODS: Fourteen dogs with 19 partial carpal or pancarpal arthrodeses were retrospectively examined and underwent force-plate gait analysis. Mean times since surgery were 29.4 and 24.4 months for pancarpal and partial carpal arthrodesis respectively. Vertical and braking-propulsive ground reaction force profiles were compared between treatment groups, and to those of normal dogs (control group) using Kruskal-Wallis one-way analysis of variance. RESULTS: With the exception of time to vertical peak that occurred earlier in dogs with pancarpal than in dogs with partial carpal arthrodesis (p <0.01), there was no difference between the two treatment groups. Several parameters differed significantly between operated and healthy dogs (p <0.01): vertical impulses were significantly lower in both treatment groups, braking forces and impulses were also reduced after both techniques. Propulsive forces and impulses were only reduced in dogs with pancarpal arthrodesis. When comparing gait parameters of sound limbs of unilateral operated dogs to those of control dogs, braking forces and impulses (p <0.01; p <0.05) were significantly higher in the sound legs of unilateral operated dogs. CLINICAL SIGNIFICANCE: Long-term outcome after partial carpal and pancarpal arthrodesis is good and comparable to each other. Propulsive action may be altered more in dogs with pancarpal arthrodesis.

A treatment method for Class II Division 1 patients with extraction of permanent maxillary first molars

Throughout the years, various treatment modalities have been presented for the treatment of Class II Division 1 malocclusions. The goal of this paper is to present a treatment approach that involves the extraction of the maxillary first molars followed by use of fixed appliances with low-friction brackets. This treatment approach has proven to be an efficient treatment modality for Class II Division 1 malocclusions, especially with noncompliant patients.

Toxic effects of brake wear particles on epithelial lung cells in vitro

ABSTRACT: BACKGROUND: Fine particulate matter originating from traffic correlates with increased morbidity and mortality. An important source of traffic particles is brake wear of cars which contributes up to 20% of the total traffic emissions. The aim of this study was to evaluate potential toxicological effects of human epithelial lung cells exposed to freshly generated brake wear particles. RESULTS: An exposure box was mounted around a car's braking system. Lung cells cultured at the air-liquid interface were then exposed to particles emitted from two typical braking behaviours ("full stop" and "normal deceleration"). The particle size distribution as well as the brake emission components like metals and carbons was measured on-line, and the particles deposited on grids for transmission electron microscopy were counted. The tight junction arrangement was observed by laser scanning microscopy. Cellular responses were assessed by measurement of lactate dehydrogenase (cytotoxicity), by investigating the production of reactive oxidative species and the release of the pro-inflammatory mediator interleukin-8. The tight junction protein occludin density decreased significantly (p < 0.05) with increasing concentrations of metals on the particles (iron, copper and manganese, which were all strongly correlated with each other). Occludin was also negatively correlated with the intensity of reactive oxidative species. The concentrations of interleukin-8 were significantly correlated with increasing organic carbon concentrations. No correlation was observed between occludin and interleukin-8, nor between reactive oxidative species and interleukin-8. CONCLUSION: These findings suggest that the metals on brake wear particles damage tight junctions with a mechanism involving oxidative stress. Brake wear particles also increase pro-inflammatory responses. However, this might be due to another mechanism than via oxidative stress.

The Southern Hemisphere at glacial terminations: insights from the Dome C ice core

The many different proxy records from the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core allow for the first time a comparison of nine glacial terminations in great detail. Despite the fact that all terminations cover the transition from a glacial maximum into an interglacial, there are large differences between single terminations. For some terminations, Antarctic temperature increased only moderately, while for others, the amplitude of change at the termination was much larger. For the different terminations, the rate of change in temperature is more similar than the magnitude or duration of change. These temperature changes were accompanied by vast changes in dust and sea salt deposition all over Antarctica. Here we investigate the phasing between a South American dust proxy (non-sea-salt calcium flux, nssCa2+), a sea ice proxy (sea salt sodium flux, ssNa+) and a proxy for Antarctic temperature (deuterium, δD). In particular, we look into whether a similar sequence of events applies to all terminations, despite their different characteristics. All proxies are derived from the EPICA Dome C ice core, resulting in a relative dating uncertainty between the proxies of less than 20 years. At the start of the terminations, the temperature (δD) increase and dust (nssCa2+ flux) decrease start synchronously. The sea ice proxy (ssNa+ flux), however, only changes once the temperature has reached a particular threshold, approximately 5°C below present day temperatures (corresponding to a δD value of −420‰). This reflects to a large extent the limited sensitivity of the sea ice proxy during very cold periods with large sea ice extent. At terminations where this threshold is not reached (TVI, TVIII), ssNa+ flux shows no changes. Above this threshold, the sea ice proxy is closely coupled to the Antarctic temperature, and interglacial levels are reached at the same time for both ssNa+ and δD. On the other hand, once another threshold at approximately 2°C below present day temperature is passed (corresponding to a δD value of −402‰), nssCa2+ flux has reached interglacial levels and does not change any more, despite further warming. This threshold behaviour most likely results from a combination of changes to the threshold friction velocity for dust entrainment and to the distribution of surface wind speeds in the dust source region.

Strong Down-Valley Low-Level Jets over the Atacama Desert: Observational Characterization

The near-surface wind and temperature regime at three points in the Atacama Desert of northern Chile is described using two-year multi-level measurements from 80-m towers located in an altitude range between 2100 and 2700 m ASL. The data reveal the frequent development of strong nocturnal drainage flows at all sites. Down-valley nose-shaped wind speed profiles are observed with maximum values occurring at heights between 20 m and 60 m AGL. The flow intensity shows considerable inter-daily variability and a seasonal modulation of maximum speeds, which in the cold season can attain hourly average values larger than 20 m s−1. Turbulent mixing appears significant over the full tower layer, affecting the curvature of the nighttime temperature profile and possibly explaining the observed increase of surface temperatures in the down-valley direction. Nocturnal valley winds and temperatures are weakly controlled by upper-air conditions observed at the nearest aerological station. Estimates of terms in the momentum budget for the development and the quasi-stationary phases of the down-valley flows suggest that the pressure gradient force due to the near-surface cooling along the sloping valley axes plays an important role in these drainage flows. A scale for the jet nose height of equilibrium turbulent down-slope jets is proposed, based on surface friction velocity and surface inversion intensity. At one of the sites this scale explains about 70% of the case-to-case observed variance of jet nose heights. Further modeling and observational work is needed, however, in order to better define the dynamics, extent and turbulence structure of this flow system, which has significant wind-energy, climatic and environmental implications.

A centrifugal ice microtome for measurements of atmospheric CO₂ on air trapped in polar ice cores

For atmospheric CO2 reconstructions using ice cores, the technique to release the trapped air from the ice samples is essential for the precision and accuracy of the measurements. We present here a new dry extraction technique in combination with a new gas analytical system that together show significant improvements with respect to current systems. Ice samples (3–15 g) are pulverised using a novel centrifugal ice microtome (CIM) by shaving the ice in a cooled vacuum chamber (−27 °C) in which no friction occurs due to the use of magnetic bearings. Both, the shaving principle of the CIM and the use of magnetic bearings have not been applied so far in this field. Shaving the ice samples produces finer ice powder and releases a minimum of 90% of the trapped air compared to 50%–70% when needle crushing is employed. In addition, the friction-free motion with an optimized design to reduce contaminations of the inner surfaces of the device result in a reduced system offset of about 2.0 ppmv compared to 4.9 ppmv. The gas analytical part shows a higher precision than the corresponding part of our previous system by a factor of two, and all processes except the loading and cleaning of the CIM now run automatically. Compared to our previous system, the complete system shows a 3 times better measurement reproducibility of about 1.1 ppmv (1 σ) which is similar to the best reproducibility of other systems applied in this field. With this high reproducibility, no replicate measurements are required anymore for most future measurement campaigns resulting in a possible output of 12–20 measurements per day compared to a maximum of 6 with other systems.

Improving backdrivability in geared rehabilitation robots

Many rehabilitation robots use electric motors with gears. The backdrivability of geared drives is poor due to friction. While it is common practice to use velocity measurements to compensate for kinetic friction, breakaway friction usually cannot be compensated for without the use of an additional force sensor that directly measures the interaction force between the human and the robot. Therefore, in robots without force sensors, subjects must overcome a large breakaway torque to initiate user-driven movements, which are important for motor learning. In this technical note, a new methodology to compensate for both kinetic and breakaway friction is presented. The basic strategy is to take advantage of the fact that, for rehabilitation exercises, the direction of the desired motion is often known. By applying the new method to three implementation examples, including drives with gear reduction ratios 100-435, the peak breakaway torque could be reduced by 60-80%.

Performance analysis of a miniature turbine generator for intracorporeal energy harvesting

Replacement intervals of implantable medical devices are commonly dictated by battery life. Therefore, intracorporeal energy harvesting has the potential to reduce the number of surgical interventions by extending the life cycle of active devices. Given the accumulated experience with intravascular devices such as stents, heart valves, and cardiac assist devices, the idea to harvest a small fraction of the hydraulic energy available in the cardiovascular circulation is revisited. The aim of this article is to explore the technical feasibility of harvesting 1 mW electric power using a miniature hydrodynamic turbine powered by about 1% of the cardiac output flow in a peripheral artery. To this end, numerical modelling of the fluid mechanics and experimental verification of the overall performance of a 1:1 scale friction turbine are performed in vitro. The numerical flow model is validated for a range of turbine configurations and flow conditions (up to 250 mL/min) in terms of hydromechanic efficiency; up to 15% could be achieved with the nonoptimized configurations of the study. Although this article does not entail the clinical feasibility of intravascular turbines in terms of hemocompatibility and impact on the circulatory system, the numerical model does provide first estimates of the mechanical shear forces relevant to blood trauma and platelet activation. It is concluded that the time-integrated shear stress exposure is significantly lower than in cardiac assist devices due to lower flow velocities and predominantly laminar flow.

ANALYTICAL MODELS OF EXOPLANETARY ATMOSPHERES. I. ATMOSPHERIC DYNAMICS VIA THE SHALLOW WATER SYSTEM

Within the context of exoplanetary atmospheres, we present a comprehensive linear analysis of forced, damped, magnetized shallow water systems, exploring the effects of dimensionality, geometry (Cartesian, pseudo-spherical, and spherical), rotation, magnetic tension, and hydrodynamic and magnetic sources of friction. Across a broad range of conditions, we find that the key governing equation for atmospheres and quantum harmonic oscillators are identical, even when forcing (stellar irradiation), sources of friction (molecular viscosity, Rayleigh drag, and magnetic drag), and magnetic tension are included. The global atmospheric structure is largely controlled by a single key parameter that involves the Rossby and Prandtl numbers. This near-universality breaks down when either molecular viscosity or magnetic drag acts non-uniformly across latitude or a poloidal magnetic field is present, suggesting that these effects will introduce qualitative changes to the familiar chevron-shaped feature witnessed in simulations of atmospheric circulation. We also find that hydrodynamic and magnetic sources of friction have dissimilar phase signatures and affect the flow in fundamentally different ways, implying that using Rayleigh drag to mimic magnetic drag is inaccurate. We exhaustively lay down the theoretical formalism (dispersion relations, governing equations, and time-dependent wave solutions) for a broad suite of models. In all situations, we derive the steady state of an atmosphere, which is relevant to interpreting infrared phase and eclipse maps of exoplanetary atmospheres. We elucidate a pinching effect that confines the atmospheric structure to be near the equator. Our suite of analytical models may be used to develop decisively physical intuition and as a reference point for three-dimensional magnetohydrodynamic simulations of atmospheric circulation.