Body Worn Research Articles

Maternal Physical Activity Is Associated With Improved Blood Pressure Regulation During Late Pregnancy

BackgroundCardiovagal baroreflex gain (cBRG) reflects an individual's ability to buffer swings in blood pressure. It is not well understood how this mechanism is influenced by physical activity in pregnancy. Because pregnant women tend to engage in low levels of moderate-to-vigorous physical activity (MVPA) and high levels of sedentary behaviour, we sought to determine the influence of MVPA and sedentary behaviour on cBRG and mean arterial pressure (MAP) in pregnancy. MethodsFifty-eight third trimester (31.9 ± 3.0 weeks) normotensive pregnant women (31.2 ± 2.8 years) were tested. Heart rate (electrocardiogram) and blood pressure (systolic blood pressure and MAP; finger photoplethysmography) were collected on a beat-by-beat basis, and averaged over 3 minutes of rest. Spontaneous cBRG was calculated as the slope of the relationship between fluctuations in systolic blood pressure and heart rate. Objective measures of MVPA and sedentary behaviour were collected over a 7-day period using an ActiGraph accelerometer (model wGTX3-BT; ActiGraph LLC, Pensacola, FL). ResultsParticipants spent 67.5 ± 7.9% of waking hours engaged in sedentary behaviour, and performed 68.6 ± 91.9 minutes of MVPA per week. Sedentary behaviour was not related to cBRG (r = −0.035; P = 0.793) or MAP (r = −0.033; P = 0.803). However, MVPA was positively associated with cBRG (r = 0.315; P = 0.016), but not MAP (r = −0.115; P = 0.389). The association between MVPA and cBRG remained significant after controlling for age, pre-pregnancy body mass index, gestational age, and wear time (r = 0.338; P = 0.013), indicating that women who engaged in greater amounts of MVPA showed increased cBRG. ConclusionsOur data suggest that increased MVPA, but not necessarily reduced sedentary behaviour, might be beneficial for reflex control of blood pressure during pregnancy.

Long-term survival of Stanmore total hip replacements inserted with radiolucent bone cement.

Radio-opacifiers in bone cements are an accepted part of every-day practice. They have, however, been shown to be a potential cause of an increase in third body wear and to excite bone resorption in in vitro and in vivo studies. We reviewed the results of 228 consecutive Stanmore total hip replacements performed between 1981 and 1985 in 211 patients. All were inserted with radiolucent bone cement. Information regarding whether the prosthesis had been revised was available for all patients. Seventy-three patients (83 hips) were still alive and 41 patients (44 hips) were sufficiently healthy to attend clinic. Information regarding pain level was obtained from the remaining 32 patients. When revision of the implant was taken as the end-point, there was 95% ten-year survival, 91% fifteen-year survival and 75% eighteen-year survival. These long-term results of Stanmore THRs, performed in a district general hospital, with radiolucent bone cement, compare favourably with the other published series for this implant. We did not find the inability to see the bone cement a particular disadvantage when reviewing radiographs for signs of loosening. (Hip International 2002; 12: 274-80).

Experimental investigation of bearing wear of a gear unit DMGH 25.4 of horizontal cement mill

PurposeRotating machines play a strategic role in the process; it is the case of a gear unit of a cement mill. These machines are composed of tribo-pairs (bearings and gears, etc.) subjected to mechanical stress and harsh industrial environments. This study aims to make an experimental investigation of bearing wear of a gear unit DMGH 25.4 of a horizontal cement mill.Design/methodology/approachSeveral tests were carried out in collaboration with industrial Algerian companies, for example, spectroscopy, micro hardness, X-Ray diffraction analysis and microscopic examination of wear-characterized QJ1244 N2MA bearing.FindingsExperimental results reveal that there are two types of bearing wear: the first is a continuous mode of damage. The second mode is the wear by a third body (wear debris in suspension in oil). The spalling results from the propagation of cracks through the thickness of the material generally give rise to cracks in the sub-layer depth hertz. An unusual hardening observed suggests that the damage was caused by the dissipation of a large surge of frictional energy lasting several milliseconds. It is found also that heating due to insufficient lubrication of the bearing led to the formation of high-density fine carbides in the microstructure of 100Cr6, which tends to decelerate the movement of dislocations during plastic deformation.Practical implicationsThis study allowed the characterization of bearings wear in industrial mechanical systems.Originality/valueCharacterization of the bearings showed that the unusual hardening observed suggests that the damage was caused by the dissipation of a large surge of frictional energy lasting several milliseconds. The microhardness of the worn bearing is very high compared to the beginning wear bearing, which is due to the quantity of carbides formed. The thermo-mechanical stresses do not affect the main phases such as martensite, but they accelerate the fracture propagation at the surface.

Abrasive Wear Trends of Non-Conforming Contact Surfaces

Abrasive wear is found to decrease the efficiency of any equipment where three body wear takes place. The abrasive wear is found to increase the down time of the equipment, decrease the efficiency of operation, and in extreme condition total failure of the equipment. The abrasive wear is found to depend on operating parameter like hardness of contacting surfaces, abrasive grain size etc. The abrasive wear was found to increase with decrease in hardness and increase with abrasive grain size until grain size reaches a critical value. Once grain size reaches the critical value abrasive wear was found insensitive to the grain size. Different test in laboratory have been designed to simulate the abrasive wear. The one which is very popular is a dry abrasion test rig TR-53. It was found that wear rate increases with increase in rubber hardness of the wheel. The rubber hardness was also found to be dependent on temperature. In the present work a wear model abrasive test is done on cast iron, EN 31 and ceramics. Samples were accompanied at loads of 53.22N and 102.46N. The wear model predicted ploughing mode of wear and was found that the wear characterized in terms of volume loss increased with decrease in hardness. Scanning electron microscope study was carried out on wear scar to identify the wear mechanism which reveal basically cutting and ploughing mode type of wear.

Experimentation and Analysis of Granite Super-Finishing Process for Flatness Testing

Granites are used in high precision machines and metrological applications. Final finishing operation on granite is done by means of manual lapping operation based on three body wear principle. Traditional granite lapping is time consuming process and requires high skill of operator which may lead to variation in process parameters. Taguchi method is applied to optimize the lapping process to reduce variation based on process parameters such as abrasive size, load applied and time of lapping.For this purpose three process parameters with three levels are considered and accordingly L9 orthogonal array is used for experimentation. Analysis of variance (ANOVA) is performed to study the effect of these process parameters on the surface flatness as response variable. For final finishing operation of 630 X 630 X 80 surface plate optimum parameters for surface flatness are found to be 14 µm abrasive size, 8kg load applied and 40 minutes of cycle time and they are ranked based on significance to process. Abrasive size is most significant than other parameters for flatness response of granite surface plate.Thus this experimentation and analysis is useful toobtain optimum parameters for maximum flatness value lapped results in reduction of operation cycle time for finishing of granite surface plates manufactured by reputed industry for various applications.

Evaluation of wear resistance of opposed recent types of dental composites

Background: A wide use of light-activated resin composites, in clinics, has increased recently due to the increased needs for esthetics teeth fillings. This in vitro study evaluated the wear resistance of various direct resin composites with different compositions. Methodology: Composite samples were divided into three main groups: group A representing 20 discs of Filtek Z350 XT, group B representing 20 discs of Bio active restorative and group C (as antagonist composite) representing 40 discs of Filtek Z250 XT. A programmable logic controlled equipment was used to record the two body wear of tested composites. Images analysis software evaluated the tested samples surface topography. Statistical analysis was performed using studentÂ’s t-test and Aasistat 7.6 statistics software. Results: It was found that group B composite recorded statistically significant higher weight loss mean value; and in antagonistic composite groups, non-significant higher weight loss mean value than group A composite mean value. Also, it was found that group B composite recorded statistically non-significant higher roughness change mean value than group A composite mean value. It was found that group A antagonistic composite recorded statistically non-significant higher roughness change mean value. Conclusion: A different wear resistance is observed for the two-body wear test, combining the results confirmed that the use of nanoparticles filled resin composites of value reduces abrasion of opposing surface especially with hard fillers like zirconia. A higher filler load in excess of 60 (vol %) results in increasing wear resistance although that softer glass particles filler was used.

Heat treated twin wire arc spray AISI 420 coatings under dry and wet abrasive wear

The influence of applying two different heat treatments such as: deep cryogenic and tempering on dry/wet abrasive wear resistance of twin wire arc spray martensitic AISI 420 coatings was evaluated by using a modified rubber wheel type test apparatus. A load dependency was observed on the abrasive wear rate behavior of both; dry and wet tests. Three body (rolling) and two body (sliding) wear mechanisms were identified in dry conditions, prevailing rolling at lower and higher loads. However, at higher loads, more presence of grooving and pits formation was observed. Coatings tempered at 205 °C/1 h displayed better wear resistance than cryogenic treated ones. A change in wear mechanism between dry and wet conditions was observed; two body wear mechanism predominated respect to three body. In both; dry and wet conditions the microstructure (several inter-splat oxides) as well as strain and residual stress promotes brittle material removal which was more evident in cryogenic and as-sprayed samples during dry test and at higher loads in wet conditions.

Dry Sliding Wear Behavior of 2218 Al-Alloy-Al2O3(TiO2) Hybrid Composites

AA2218–Al2O3(TiO2) composites are synthesized by stirring 2, 5, and 7 wt % of 1:2 mixture of Al2O3:TiO2 powders in molten AA2218 alloy. T61 heat-treated composites characterized for microstructure and hardness. Dry sliding wear tests conducted on pin-on-disk setup at available loads 4.91–13.24 N, sliding speed of 1.26 m/s up to sliding distance of 3770 m. Stir cast AA2218 alloy (unreinforced, 0 wt % composite) wears quickly by adhesion, following Archard's law. Aged alloy exhibits lesser wear rate than unaged (solutionized). Mathematical relationship between wear rate and load proposed for solutionized and peak aged alloy. Volume loss in wear increases linearly with sliding distance but drops with the increase in particle wt % at a given load, attributed to the increase in hardness due to matrix reinforcement. Minimum wear rate is recorded in 5 wt % composite due to increased particles retention, lesser porosity, and uniform particle distribution. In composites, wear phenomenon is complex, combination of adhesive and abrasive wear which includes the effect of shear rate, due to sliding action in composite, and abrasive effect (three body wear) of particles. General mathematical relationship for wear rate of T61 aged composite as a function of particle wt % load is suggested. Fe content on worn surface increases with the increase in particle content and counterface temperature increases with the increase in load. Coefficient of friction decreases with particle addition but increases in 7 wt % composite due to change in microstructure.

Biomaterials for hip implants – important considerations relating to the choice of materials

Abstract This article is a review of important material requirements for hip biomaterials including their response to the body environment (biocompatibility), mechanical properties, wear resistance, fretting corrosion and availability as well as the price. The application of proper biomaterials for hip implants is one of the major focal points in this article. Background information is also provided on metals used in other prosthetic devices and implant components. Titanium and its alloys, cobalt base alloys and stainless steels (bio-steels) are used for load-bearing hip implants. These three groups of metallic materials will be introduced and discussed in detail. Metals and their alloys are crystalline materials since their properties depend on the crystal lattice, chemical and phase compositions, grain size, lattice defects, crystalline texture and residual micro- and macro-stresses. All these features of biomaterials are formed during technological manufacturing, such as metallurgical process, solidification, plastic deformation (rolling and forging), machining, heat treatment and coating. All these technological processes work in optimal conditions in order to achieve the optimal microstructure and mechanical, chemical and biological properties. Amongst the above-mentioned particular properties of biomaterials, fretting is a major concern as regards hip implants at the femoral head and neck taper interface. Additional important mechanisms of interaction between the implant and the human body must be taken into account, i.e. diffusion stream of foreign particles and atoms from the implant to body fluids, to the tissue and to the bone. These foreign particles and atoms are released from the implant to the body fluid, to the tissue and to the bone as wear product during use. All together they contribute to the wear, i.e. loss of weight, strength or volume of hip components. Wear rates of ultrahigh molecular weight polyethylene mated against Ti-6Al-4V are significantly greater than the ones for Co-Cr-Mo alloys. Therefore, thermochemical surface treatments like diffusion ion nitriding should be applied to increase the resistance of titanium alloys to wear. Austenitic stainless steels are also used for temporary applications, but they have lower resistance to pitting corrosion than titanium and cobalt alloys. The purpose of the paper is to introduce a group of metallic materials, which is often chosen for surgical hip implants. Conclusions of the paper refer to information which support important medical and patient decisions on hip implants. Also, the development of biomaterials, their treatments, properties, surface layers and coatings are considered. All these features develop over time and need synergy and experience in the progress of the biomedical, mechanical and materials science.

Sliding wear of spark plasma sintered CrFeCoNiCu high entropy alloy coatings with MoS2 and WC additions

Using spark plasma sintering (SPS), the coatings of CrFeCoNiCu high entropy alloy (HEA) and its composites with MoS2 and WC additions were sintered on carbon steel substrate, respectively. The dry sliding wear behavior of the HEA coatings was investigated using a ball-on-disk sliding tribometer with a silicon nitride ball. The wear mass loss and the coefficient of friction (COF) increased greatly with the normal load increased. 2 wt.% MoS2 addition is beneficial to decrease the COF as well as the wear rate of HEA coatings. However, adding more MoS2 induce to larger wear rate though the COF decreases continually. On the other hand, adding 50 wt.% WC, the mass loss and COF of this HEA coating decreased obviously. So WC addition is also beneficial to decrease wear rate as well as the COF. The composite coating with 80 wt.% WC has the lowest wear rate 0.7 mg under 30 N normal load, which is more than 16 times lower than that of HEA coating without additions. The worn surface observation for the HEA coatings shows MoS2 addition leads to the wear mechanism evolution from two-body wear to three body wear and delamination wear is the domain wear mechanism of WC/HEA. Therefore, SPS sintered CrFeCoNiCu HEA coating possesses outstanding wear resistance, and the wear rate and COF can be extremely decreased by adding MoS2 and WC.

Modelling, fabrication and experimental testing of an heat sink free wearable thermoelectric generator

Thermoelectric pastes of stoichiometric Sb2Te3 and Bi2Te3 were prepared, characterized and used as active materials to fabricate a flexible heat sink free thermoelectric generator (TEG). The module was designed to be coupled to a 80mV start-up input voltage fully electrical DC-DC converter. Although practical aspects and technological limitations led to a not optimal dimensioning of the device, an improvement of its thermoelectric performance might be obtained by including an additional thick film metal layer on the two sides of TEG, as demonstrated by Finite Element Analysis (FEA) results. The designed thermopile consists of 450 thermocouples realized by blade coating of p- and n-type materials into 2mm tall vertical cavities of a pre-patterned Polydimethylsiloxane (PDMS) through-holes layer of total area 98×98mm2.For a first functional investigation, a prototype of 45 thermocouples into a footprint area of about 2.2×10−3m2 was fabricated and tested to evaluate its thermoelectric performance stand-alone and coupled with the DC-DC converter. A mean Seebeck coefficient of about 60μV/K for pn couple was calculated from experimental data, and a power of about 27nW was measured at 10K on matched load of about 6.8kΩ. A temperature difference of about 1.8°C was achieved between the junctions in working conditions next to those typical of human body wearing in indoors (quiescent air at room temperature, constant temperature of 34.8°C applied on the TEG hot side). The investigation shown that a thermopile of 450 couples requires a minimum thermal gradient of about 2°C between junctions to be able to switch on the custom voltage boost DC-DC converter.

Reprint of ‘‘Modeling of surface roughness in ball end magnetorheological finishing (BEMRF) process’’

A new precision finishing process called the ball end magnetorheological finishing (BEMRF) process was developed for super finishing of complex 3D surfaces. This process is based on magnetorheological polishing (MRP) fluid whose rheological behaviour varies with the magnitude of the applied magnetic field. The magnetically energized MRP fluid is used at the tip of a rotating tool to finish workpiece of different materials and shapes. The MRP fluid is a mixture of abrasives and magnetizable carbonyl iron particles (CIP) in a carrier medium. To improve the in-depth understanding of the BEMRF process, this work deals with the theoretical investigations into modeling of surface roughness and mechanism of material removal associated with ferromagnetic workpiece. Since it is very difficult to understand the complex structure of the magnetically energized MRP fluid during finishing operation, microstructure of the constituents of the MRP fluid has been proposed. A theoretical model of magnetically induced normal and shear forces acting on the abrasive is also proposed in the present study. Based on these forces, the material removal process and wear behaviour during finishing operation have been analyzed. While the normal force model explains the penetration of abrasives into the workpiece surface, the shear force model aids in the understanding of three body wear mechanism between the abrasives and the workpiece surface. A mathematical model has been developed to evaluate the surface roughness. Using the developed model, the theoretical value of surface roughness is computed. The close agreement of theoretical and experimental results validates the proposed model.

Effect of debris size on the reciprocating sliding wear of aluminium

The literature is controversial in relation to the influence of wear debris on tribological behaviour. Some works have shown that the presence of debris is fundamental to the formation of a protective tribolayer, thus reducing friction, whereas others showed that the presence of wear debris could contribute to increase friction coefficient due to the energy spent dragging them into the contact. This work aims to study the influence of the presence of wear debris, simulated by Al2O3 particles, on the tribological behaviour of an aluminium-steel pair under reciprocating sliding contact. Special emphasis is given to the particle size (0.05 µm, 0.1 µm, 1 µm and 10 µm). The particles were dispersed in distilled water (2 wt.%) as the source of debris. Reference tests were carried out solely in the presence of distilled water. The addition of alumina particles contributed to a significant reduction in friction coefficient, in particular for the largest particles (diameter ϕ=10 µm). When the larger particles were added, it was possible to observe the formation of a tribolayer on the sample surface leading to a gain of mass. In opposition, the wear rate of the counter body increased when large particles were added and the wear tracks showed strong evidence of abrasive wear. This suggests that hard and large wear debris, incorporated in the tribolayer formed on the samples, can act as hard protuberances, leading to abrasive wear of the counterbodies. When small particles were added, friction was still reduced when compared with the reference test, but the reduction of the friction coefficient was less significant. Small particles reduced the steel counter body wear rate and did not affect significantly the wear rate of the aluminium samples. It is proposed that small debris can get entrapped in the surface irregularities of the specimens and therefore participate less in the formation of the tribolayers.

The Feasibility of Using Body Worn Cameras in an Inpatient Mental Health Setting

The Feasibility of Using Body Worn Cameras in an Inpatient Mental Health Setting

Modeling of surface roughness in ball end magnetorheological finishing (BEMRF) process

A new precision finishing process called the ball end magnetorheological finishing (BEMRF) process was developed for super finishing of complex 3D surfaces. This process is based on magnetorheological polishing (MRP) fluid whose rheological behaviour varies with the magnitude of the applied magnetic field. The magnetically energized MRP fluid is used at the tip of a rotating tool to finish workpiece of different materials and shapes. The MRP fluid is a mixture of abrasives and magnetizable carbonyl iron particles (CIP) in a carrier medium. To improve the in-depth understanding of the BEMRF process, this work deals with the theoretical investigations into modeling of surface roughness and mechanism of material removal associated with ferromagnetic workpiece. Since it is very difficult to understand the complex structure of the magnetically energized MRP fluid during finishing operation, microstructure of the constituents of the MRP fluid has been proposed. A theoretical model of magnetically induced normal and shear forces acting on the abrasive is also proposed in the present study. Based on these forces, the material removal process and wear behaviour during finishing operation have been analyzed. While the normal force model explains the penetration of abrasives into the workpiece surface, the shear force model aids in the understanding of three body wear mechanism between the abrasives and the workpiece surface. A mathematical model has been developed to evaluate the surface roughness. Using the developed model, the theoretical value of surface roughness is computed. The close agreement of theoretical and experimental results validates the proposed model.

Research of the influence of abrasive wear of grinding bodies in the rotational vibration mill

Research of the influence of abrasive wear of grinding bodies in the rotational vibration mill

Influence of Mn Content on Tribological Wear Behaviour of ZA-27 Alloy

The impact of Mn content on tribological wear behaviour of ZA-27 alloy which is used in an Industrial engineering and tribological applications has been studied. Wear test were conducted under the operational conditions of varying in Nr. pressures and sliding speeds using pin-on-disc wear testing machine. To peruse the wear mechanisms of worn out surface of samples were investigate by SEM images. Result shows 1.5 m/s sliding speed and 0.2498 MPa is observed as critical sliding speed and critical Nr. pressure. Also, minimum vol. wear rate and frictional force for 0.5% Mn content ZA-27 alloy. Laminative wear mechanism for 0.2% Mn, three body wear mechanism for 0.5% Mn and abrasive wear mechanism for 1% Mn is observed.

Effect of Nanocrystalline Diamond Films Deflection on Wear Observed in Reciprocating Sliding Tests

The present study deals with the tribological behavior of nanocrystalline diamond (NCD) films. The diamond films were deposited by microwave plasma enhanced chemical vapor deposition (MPCVD) in methane/hydrogen/air plasma on the Si(100) substrates. The tribological properties were studied by reciprocal sliding tests against Si3N4 balls. The depth profiles and surface morphology of the wear scars were investigated by means of mechanical profilometry and scanning electron microscopy (SEM). Various adaptation processes occur between contacting surfaces including asperity polishing, formation of carbonaceous tribolayer and ripple patterns on the wear scar surfaces. The film deflection is the specific form of adaptation decreasing contact pressure and, therefore, the damage (including wear) of both counter bodies. The deflection of NCD films in sliding tests can be related with the effect of fatigue.

MotionLab@Home: Complementary Measurement of Gait Characteristics Using Wearable Technology and Markerless Video Tracking - A Study Protocol

Background: While treatment monitoring of healthcare interventions is mainly conducted at the hospital, most information on a patient’s health status could be obtained from his everyday life activities. Therefore, there is a great interest in methods for long term (home) monitoring applications. However, there is still a lack of quantitative methods allowing everyday life activities monitoring such as gait analysis at home. While video-based systems have been employed given their high accuracy, they remain expensive and obtrusive with the range of motion of a patient limited to the set up measurement volume. Body worn sensors on the other hand present as an excellent opportunity to remotely and unobtrusively monitor gait characteristics not only at home, but during activities of everyday life. Technical limitations as well as changes in the patient’s gait patterns challenge the extraction of specific gait parameters. Methods: We propose a hybrid system comprising of a markerless video-based motion capturing system and a wearable sensor system with foot worn sensors. A study protocol is presented that will be used to validate the systems against each other. Discussion: This study will evaluate whether a markerless motion capturing system is feasible as a complementary tool for everyday gait analysis. Further, we will validate the accuracy of the sensor system using the video-based system as a gold standard. In the future, the combination might allow a recalibration of algorithmic sensor parameters based on deviations from the reference video-based system, and the combination of both modalities may enhance gait analysis in home monitoring.

Effect of niobium onto the tribological behavior of cathodic arc deposited Nb–Ti–N coatings

This investigation addresses a need for higher quality surfaces and wear resistance of coatings used on load bearing medical implants. Multilayered cathodic arc deposited coatings are candidates for such applications and were the subject of this study. Nb–Ti–N coatings were deposited by cathodic arc using TiNb compound cathodes. The microstructure and properties of the coatings were characterized using XRD, TEM/STEM, EDS, nanoindentation, scratch tests and pin-on-disc testing. Throughout the coating, macroparticles consisting of a Nb rich core and a nitrided titanium porous shell were evidenced by STEM and EDS. It was shown that inhomogeneities related with the soft and malleable metallic Nb inclusions alter the tribological behavior of the coatings. The underlying mechanism of wear in hip-simulator test liquid against UHMWPE was investigated. During pin-on-disc tests, the top layers of the coatings were removed and the embedded niobium droplets became visible. The wear of UHMWPE during pin-on-disks tests was increased on Nb–Ti–N counter surfaces compared to the wear of UHMWPE on TiN itself. It is inferred that the wear of the coatings is initiated by the growth discontinuities and pores around the Nb droplets. The debris released from the coating acts as third body wear particles, grinds the remaining coating and causes the wear of UHMWPE pins.