Control of trunk movement: Perturbations in cart pushing

Dieen, J.H. van [Promotor]Hoozemans, M.J.M. [Copromotor

Characterization of interfacial strength of syntactic foam by unit cell finite element model

The interfacial strength between glass hollow microspheres and epoxy in epoxy-based syntactic foam was investigated using finite element method. The stiffness of the foam in tension and compression was studied by unit cell type finite element model containing a microsphere and an epoxy matrix. The changes in the stiffness of the foams having different interfacial strength were analyzed by introducing interfacial elements between the microsphere and the matrix in the model. The tension and compression moduli of the foam was studied by the model, in terms of the stiffness of the interfacial elements. Finally, the moduli of the foam having different volume fractions of the microspheres were evaluated by experiments and compared to the results of the model to characterize the interfacial strength between the microsphere and the matrix. Please click Additional Files below to see the full abstract

Orthogonal polynomials in two variables and second-order partial differential equations

AbstractWe study the second-order partial differential equations L[u] = Auxx +22Buxy + Cuyy + Dux + Euy = λnu, which have orthogonal polynomials in two variables as solutions. By using formal functional calculus on moment functionals, we first give new simpler proofs and improvements of the results by Krall and Sheffer and Littlejohn. We then give a two-variable version of Al-Salam and Chihara's characterization of classical orthogonal polynomials in one variable. We also study in detail the case when L[·] belongs to the basic class, that is, Ay = Cx = 0. In particular, we characterize all such differential equations which have a product of two classical orthogonal polynomials in one variable as solutions

Handle height and expectation of cart movement affect the control of trunk motion at movement onset in cart pushing

As unexpected sudden unloading of the trunk may cause low-back injury, the objective of the present study was to investigate whether handle height and the expectation of cart movement in pushing affect trunk control at movement onset. Eleven healthy male participants pushed a 200-kg cart with handles at shoulder and hip heights. The cart would suddenly move when externally released (externally triggered condition) or when static friction was overcome (self-initiated condition). Before self-initiated cart movement, trunk stiffness and muscle activity were significantly higher than before an externally triggered onset at comparable pushing force. Lower muscle activity and trunk stiffness at shoulder height compared with the hip height before the onset resulted in higher trunk inclination after the onset. In conclusion, higher preparatory activation of trunk muscles serves to increase trunk stiffness in anticipation of cart movement and may reduce the impact of the perturbation associated with the onset of cart movement. Statement of Relevance: Sudden cart movement in pushing causes an unexpected unloading perturbation to the trunk. This perturbation was shown to cause uncontrolled trunk movement, which may explain how pushing tasks can be associated with low-back injury. Effects of handle height and awareness of the subjects of the possible cart movement suggest directions for prevention. © 2011 Taylor & Francis

Microfluidics for simultaneous quantification of platelet adhesion and blood viscosity

Platelet functions, including adhesion, activation, and aggregation have an influence on thrombosis and the progression of atherosclerosis. In the present study, a new microfluidic-based method is proposed to estimate platelet adhesion and blood viscosity simultaneously. Blood sample flows into an H-shaped microfluidic device with a peristaltic pump. Since platelet aggregation may be initiated by the compression of rotors inside the peristaltic pump, platelet aggregates may adhere to the H-shaped channel. Through correlation mapping, which visualizes decorrelation of the streaming blood flow, the area of adhered platelets (A(Platelet)) can be estimated without labeling platelets. The platelet function is estimated by determining the representative index I-A.T based on A(Platelet) and contact time. Blood viscosity is measured by monitoring the flow conditions in the one side channel of the H-shaped device. Based on the relation between interfacial width (W) and pressure ratio of sample flows to the reference, blood sample viscosity (mu) can be estimated by measuring W. Biophysical parameters (IA.T, mu) are compared for normal and diabetic rats using an ex vivo extracorporeal model. This microfluidic-based method can be used for evaluating variations in the platelet adhesion and blood viscosity of animal models with cardiovascular diseases under ex vivo conditions.119Ysciescopu

High-throughput and label-free blood-on-a-chip for malaria diagnosis

The malaria parasite Plasmodium falciparum (Pf) changes the structure and mechanical properties of red blood cells (RBCs). These changes decrease deformability and increase cytoadherence of Pf-infected RBCs to the vascular endothelium, eventually leading to flow occlusions in capillary vessels. In this study, to detect Pf-infected RBCs effectively, deformability and viscosity of blood sample are measured simultaneously and indirectly by quantifying blood flow in a microfluidic device. The microfluidic device is designed by mimicking a Wheatstone-bridge electric circuit. To measure RBC deformability, a deformability assessment chamber (DAC) at the left lower side channel has parallel microfluidic filters. After delivering blood sample and 1x PBS solution at the same flow rate, hemodynamic properties are measured using a time-resolved microparticle image velocimetry technique. Blood volume delivered into the DAC for 200 s is evaluated as a deformability index. Subsequently, blood viscosity is quantified by monitoring blood-filled width of parallel flows in the microfluidic device. The proposed method is applied to evaluate variations in biophysical properties of blood samples partially mixed with normal RBCs and hardened RBCs. As a result, RBC deformability is more effective than blood viscosity in the detection of blood samples with hardened RBC volume fraction of 5%. The microfluidic device is also applied to detect Pf-infected RBCs. When parasitemia is greater than 0.515% for ring stage, 0.0544% for trophozoite stage, and 0.0054% for schizont stage, the measured velocity fields show unstable behavior because of cytoadherence of Pf-infected RBCs. Blood volume delivered into the DAC significantly decreases with increasing parasitemia. The experimental method proposed in this study can detect Pf-infected RBCs with good accuracy.1113Ysciescopu

Influence of glass hollow microsphere fillers on the Rheological behavior of Epoxy resin

The rheological behavior of epoxy resin filled with glass hollow microspheres was studied using three types of microspheres with different particle size distributions. The shear-rate dependence on viscosity, as well as relative apparent viscosity, of the suspensions were investigated at different microsphere filler loadings. The change in relative viscosity with different types of microsphere loads was investigated using the established semi empirical model to estimate the critical filler load. It was found that the critical filler load for all kangspecific surface area of the filler. Please click Additional Files below to see the full abstract

Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4 La2_{2}CuO4.11_{4.11} and La1.88_{1.88}Sr0.12_{0.12}CuO4_{4}

This paper reports muon spin relaxation (MuSR) measurements of two single crystals of the title high-Tc cuprate systems where static incommensurate magnetism and superconductivity coexist. By zero-field MuSR measurements and subsequent analyses with simulations, we show that (1) the maximum ordered Cu moment size (0.36 Bohr magneton) and local spin structure are identical to those in prototypical stripe spin systems with the 1/8 hole concentration; (2) the static magnetism is confined to less than a half of the volume of the sample, and (3) regions with static magnetism form nano-scale islands with the size comparable to the in-plane superconducting coherence length. By transverse-field MuSR measurements, we show that Tc of these systems is related to the superfluid density, in the same way as observed in cuprate systems without static magnetism. We discuss a heuristic model involving percolation of these nanoscale islands with static magnetism as a possible picture to reconcile heterogeneity found by the present MuSR study and long-range spin correlations found by neutron scattering.Comment: 19 pages, 15 figures, submitted to Phys. Rev. B. E-mail: [email protected]