Force Fp Research Articles

Lifetime of Membrane-Cytoskeleton Bonds is Mediated by RHO-GTPases in a Cancer Cell

Cells especially cancer cells are capable of rapid cytoskeleton remodeling and often membrane reorganization in response to environmental cues. The propensity to remodel is reflected in part by the lifetime τ of the membrane-cytoskeleton bonds at the edges of cells; τ increases as their number density and on-rate increases. We measure τ by monitoring the time-course of the membrane peeling force Fp at the edge of a cancer cell. Experiments are conducted at the near-equilibrium region (cf. irreversible), where an optical tweezers is used to apply a load with a handle which is bound to a slowly moving cell, and the handle displacement is detected at a resolution of 500 μs after averaging.Under constant load, Fp increases monotonically with time; at force fR and time tR this slope abruptly changes indicating membrane-cytoskeleton bond rupture. Repeating for many cells we find fR is not constant but increases with tR. We propose it represents the rupture of a cluster of bonds with larger clusters demonstrating greater rupture forces and lifetimes. This is in agreement with theory that calculates the lifetime of a cluster of bonds between two bodies (J.Chem.Phys.121:8997). Comparing experimental data with this theory, we find that molecular parameters are within expected ranges reported for biomolecular bonds in vitro withevidence that the bonds can re-bind. Cells treated with Rho-GTPase inhibitors possess membrane-cytoskeleton bonds with lower stiffness that show no rebinding on the timescale of the measurements (zero on-rate). This is predictable since active Rho-GTPases form linkages between the membrane and actin-effector proteins of the cytoskeleton. This measurable change in bond properties provides a quantitative method for evaluating the role of Rho-GTPases in dynamic cytoskeleton remodeling. This is relevant as Rho-GTPases are upregulated in many human cancers including the HN-31 cell line used in this study.

Modulation of lipid membrane structural and mechanical properties by a peptidomimetic derived from reduced amide scaffold

Understanding how antimicrobial peptidomimetics interact with lipid membranes is important in battling multidrug resistant bacterial pathogens. We study the effects of a recently reported peptidomimetic on lipid bilayer structural and mechanical properties. The compound referred to as E107-3 is synthesized based on the acylated reduced amide scaffold and has been shown to exhibit good antimicrobial potency. Our vesicle leakage assay indicates that the compound increases lipid bilayer permeability. We use micropipette aspiration to explore the kinetic response of giant unilamellar vesicles (GUVs). Exposure to the compound causes the GUV protrusion length LP to spontaneously increase and then decrease, followed by GUV rupture. Solution atomic force microscopy (AFM) is used to visualize lipid bilayer structural modulation within a nanoscopic regime. Unlike melittin, which produces pore-like structures, the peptidomimetic compound is found to induce nanoscopic heterogeneous structures. Finally, we use AFM-based force spectroscopy to study the impact of the compound on lipid bilayer mechanical properties. We find that incremental addition of the compound to planar lipid bilayers results in a moderate decrease of the bilayer puncture force FP and a 39% decrease of the bilayer area compressibility modulus KA. To explain our experimental data, we propose a membrane interaction model encompassing disruption of lipid chain packing and extraction of lipid molecules. The later action mode is supported by our observation of a double-bilayer structure in the presence of fusogenic calcium ions.

Scaling of pinning forces in BaSnO3-added GdBa2Cu3O7 − x superconducting thin films

We have investigated the flux pinning force Fp in pure and 2wt.% BaSnO3 (BSO)-added GdBa2Cu3O7−x (GdBCO) superconducting films. Both pure and BSO-added GdBCO films with the thicknesses varying from 0.2μm to 1.5μm were prepared by using a pulsed laser deposition (PLD) technique. As BSO is added to the GdBCO films, two changes were observed in the field dependence of the pinning forces. First, the magnitude of the pinning force was greatly enhanced at each corresponding thickness. Second, the pinning forces exhibited an interesting plateau-like behavior. As a result, a universal scaling law of the pinning forces can be applied to the BSO-added GdBCO films which accounts for all variation in thickness. These results suggest an existence of an extra pinning mechanism through the film thickness which is induced by the formation of the BSO nanostructures. PACS numbers74.25.Sv74.25.Qt74.62.Dh74.72.Jt

Critical current and flux dynamics in Ag-doped FeSe superconductor

The measurements of DC magnetization as a function of the temperature M(T), magnetic field M(H), and time M(t) have been performed in order to compare the superconducting and pinning properties of an undoped FeSe0.94 sample and a silver doped FeSe0.94 + 6 wt% Ag sample. The M(T) curves indicate an improvement of the superconducting critical temperature and a reduction of the non-superconducting phase Fe7Se8 due to the silver doping. This is confirmed by the field and temperature dependent critical current density Jc(H,T) extracted from the superconducting hysteresis loops at different temperatures within the Bean critical state model. Moreover, the combined analysis of the Jc(T) and of the pinning force Fp(H/Hirr) indicate that the pinning mechanisms in both samples can be described in the framework of the collective pinning theory. The U*(T, J) curves show a pinning crossover from an elastic creep regime of intermediate size flux bundles, for low temperatures, to a plastic creep regime at higher temperatures for both the samples. Finally, the vortex hopping attempt time has been evaluated for both samples and the results are comparable with the values reported in the literature for high Tc materials.

Stiffness of uncured resin-composites assessed via cavity-packing forces

ObjectivesTo evaluate the stiffness and packability of unset resin-composites at different temperatures, taking into account the cavity wall effect. Materials and MethodsSix representative commercial resin-composites were selected. Each material was placed in mould of different sizes for example (φ=7, depth=5mm; or φ=3, depth=5mm) held at 26 or 37°C. Maximum packing force (Fp) of the resin-composite was measured. A flat-ended stainless-steel probe with a diameter of either 6mm or 3mm was mechanically lowered onto and into the surface of each unset sample with a speed of 0.50mm/s to a depth of 2mm, which was held constant for 10s. The compressive force produced on the probe by the unset resin-composites was plotted against time and the maximum value was identified (Fp). Peak stress Sp was calculated by dividing the Fp by area of the probe used. Data were analyzed by univariate ANOVA and multiple pair wise comparisons were performed using a Tukey post-hoc test to establish homogenous subsets (at p=0.05). ResultsSp was taken as potential measure of stiffness. It ranged from 0.12 to 4.21MPa and from 0.07 to 3.08MPa at 26 and 37°C, respectively. Univariate ANOVA showed significant influence of the plunger cavity ratios, temperature and materials on Sp (p<0.001). A strong interaction was also found between plunger cavity ratios, temperature and materials for Sp (p<0.05). ConclusionPeak stress Sp is a useful parameter for characterizing the stiffness of uncured resin-composite materials, additionally resin-composite formulation, temperature and wall effect did effect the packability of resin-composite.

The influence of HIP process on critical parameters of MgB2/Fe wires with big boron grains and without barriers

We show transport results of the critical temperature (Tc), irreversible magnetic field (Birr), upper critical field (Bc2), critical current density (Jc) and the pinning force (Fp) for undoped MgB2 wires without barriers. The results of SEM show that the hot isostatic pressure process increases the density and uniformity of MgB2 materials. Hot isostatic pressure allows for obtaining small grains and increasing the number of connections between the grains, accelerated reaction rate and limits the diffusion of Fe atoms into MgB2 material from the adjacent sheath. The pressure of 1.1 GPa increases Tc quite significantly in high magnetic field range of 6–12 T, improves the Birr and Bc2 and increase the Jc at 4.2 K and 20 K of about three times. Our results may be important for this field since many MgB2 wires are made from big grains of boron greater than 1 μm. Moreover, our research can be important for the production of MgB2 wires for the International Thermonuclear Experimental Reactor with boron 11B.

Experimental study on a novel minimization method of top burr formation in micro-end milling of Ti-6Al-4V

This paper investigates the top burr formation mechanism and minimization method in the micro-end milling of titanium alloy Ti-6Al-4V. The top burr formation procedure has been systematically deduced to reveal the reason for the occurrence of a top burr considering the cutting trajectory of the micro-milling tool, the chip thickness h, and the variation in the micro-milling force Fp. A new method to minimize the top burr in micro-end milling of Ti-6Al-4V is proposed in this study: resin coating is fabricated to control and reduce the top burr size by absorbing the Wp energy. A series of micro-end milling experiments were performed to test this new method. The experimental measurement results prove that the method in this study significantly reduces the top burr size in the micro-end milling of Ti-6Al-4V. Two different top burr formation modes during micro-end milling have been found, and the effect of the minimum chip thickness hm on the top burr size is revealed. When h is below hm, large squeezing and tearing result in a poor surface and large top burrs; when h is above hm, the top burr size suddenly decreases. The relations between the top burr size variation bl, bw, and the cutting-force work Wp are determined and discussed. Based on the new technology that this study develops, a series of micro-milling surfaces with the smallest top burr size to date worldwide are achieved. The knowledge obtained from this study is expected to be an important contribution to top burr minimization in micro-machining.

Crash performance and multi-objective optimization of a gradual energy-absorbing structure for subway vehicles

To improve the crash performance of subway vehicles, this study presents an investigation of a newly designed gradual energy-absorbing structure subjected to impact loads using a test trolley for experimental and numerical simulations, as referenced in EN15227:2008. The structure is composed of a front-end beam, rear-end plate, outer-side beams, inner-side beams, cross beams and longitudinal beams. In this work, a finite element model (FEM) was established and effectively verified using experimental data. To evaluate the effect of the thicknesses of the longitudinal beams (t1), outer-side beams (t2) and inner-side beams (t3) on the energy absorption (EA) and peak crushing force (Fp), sensitivity study was performed using extreme difference (R) analysis. Then, a polynomial response surface method (PRSM) was employed to formulate the output responses of EA and Fp with the input parameters of t1, t2 and t3. In order to optimize the crash performance of the structure, a Non-dominated Sorting Genetic Algorithm (NSGA) was used in a multi-objective optimization to achieve the maximum EA and minimum Fp values. The optimal EA and Fp with the associated thickness parameters (t1, t2, and t3) of the gradual energy-absorbing structure were obtained in the form of Pareto fronts. Additionally, the Pareto solutions derived from the surrogate models of the quadratic, cubic and quartic polynomials eventually converge at intersection D (i.e., Fp=7.2940×103kN, EA=1.3511×103kJ).

Evidence of Point Pinning Centers in Un-Doped Mgb2 Wires at 20 K after HIP Process

In this paper we present results of transport critical current density (Jc) at 20 K and 4.2 K, irreversible magnetic field (Birr), upper critical field (Bc2), critical temperature (Tc), pinning force (Fp), scanning pinning force scaling results (Fp/Fpmax and B/Birr) and electron microscope (SEM) images of un-doped MgB2 wires of 0.63 mm diameter. All wires were annealed at pressures ranging from 0.1 MPa to 1 GPa for 15 min between 680°C to 740°C. SEM images show that 1 GPa pressure yields small grains, higher MgB2 material density, and small voids. The results obtained by a physical properties measurement system (PPMS) show that high pressure (1 GPa) and 700°C annealing slightly decreases Tc above 27 K and increases Tc and Birr below 25 K. Un-doped MgB2 wire annealed in 1 GPa for 15 min at 680°C at has a 20 K, 4.5 T Jc of 100 A/mm2 in and a Birr of 7 T. At 4.2 K, this wire has Jc of 100 A/mm2 at 10.5 T. Scaling results show that the dominant pinning mechanism is point pinning for undoped MgB2 wires under 1 GPa pressure and annealed at 680°C (at 20 K).

Energy consumption characterization in precision hard machining using CBN cutting tools

In this paper, the contribution of tool wear to the energy balance was determined for precision hard turning using chamfered CBN cutting tools. The tool nose wear VBC and the corresponding changes of component forces F c, F f and F p resulting from tool wear evolution were continuously measured during wear tests. Based on the cutting mechanics, specific cutting and ploughing energies were calculated for a number of tool wear states. In particular, changes of energy balance due to tool wear under variable feed rate, depth of cut and tool nose radius were discussed. A distinction between material removal conditions resulting from precision cutting and grinding at a very low uncut chip thickness is considered.

Correlation Between Friction and Wear of Cubic Borone Nitride Cutting Tools in Precision Hard Machining

In this paper, the contribution of tool wear to friction was determined for precision hard turning using Cubic Borone Nitride (CBN) cutting tools. The tool nose wear VBC and the corresponding changes of component forces Fc, Ff, and Fp resulting from tool wear evolution were continuously measured during wear tests. Based on the mechanics of nonorthogonal cutting, the normal and friction forces acting on rake and flank faces were calculated for all measuring points, and as a result, relevant changes of the friction coefficient were determined. Additionally, friction changes resulting from tool wear under different feed rate, depth of cut, and tool nose radius were discussed in terms of the plowing energy produced by the tool nose.

The electric field jump—detection of damaged Nb barrier in MgB2 wires annealed under pressure

In this paper we present the results of critical current (Ic) measurements of MgB2 wires made with two different set-ups of the four-point probe method: current sweep type—constant magnetic field and increasing current, and field sweep type—constant current and rapidly increasing magnetic field. Results from magnet field sweep type measurements can be interpreted by a new physical concept—a jump of the electric field in low magnetic fields. This physical concept can be correlated with damages in the Nb-barrier existing in the MgB2 wire and be employed as a detection scheme. The damage in Nb barrier reduces critical current density (Jc) and complicates the study on critical temperature (Tc), upper critical field (Bc2), irreversible magnetic field (Birr), pinning force (Fp), and pinning centers in superconducting MgB2 wires. Our proposed method to detect damages in Nb barrier would benefit efforts in development and applications of MgB2 wires.

Influence of YBa2HfO5.5 – ‘derived secondary phase’ on the critical current density and flux-Pinning force of YBa2Cu3O7−δ thick films

Enhancement in critical current density (Jc) and flux pinning force (Fp) in superconducting thick films of YBa2Cu3O7−δ (YBCO) added with small quantities of nanopowders of HfO2, BaHfO3 and YBa2HfO5.5, coated on YBa2ZrO5.5 substrate by dip-coating technique is reported. Critical current density measurements were done over an applied magnetic field using standard four probe technique and the results are compared with that of pure YBCO. High critical current density (Jc) of ∼4.84MA/cm2 at 77K in self-field was obtained for 2wt% of YBa2HfO5.5 added YBCO. A systematic increase in Jc observed in YBCO films prepared by the addition of nano HfO2, BaHfO3 and YBa2HfO5.5, attributed to the formation of a non-reacting ‘derived secondary phase’ YBa2HfO5.5 (YBHO) in the YBCO matrix. YBCO–YBa2HfO5.5 composite thick films have showed eightfold increases in Jc (3.29MA/cm2) at 77K and 0.4T compared to pure YBa2Cu3O7−δ film (0.37MA/cm2), while maintaining a high transition temperature (Tc). The development of effective pinning centers in nano particle added YBCO thick film have enhanced the flux pinning force from 1.8GN/m3 for pure YBCO to a maximum value of 13.15GN/m3 for YBCO–YBa2HfO5.5. X-ray diffraction and energy dispersive spectroscopic analysis confirmed the presence of secondary phase, derived in the matrix.

The critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping

MgB2 precursor wires were prepared using powder in tube technique by Institute of High Pressure PAS in Warsaw. All samples were annealed under isostatic pressure generated by liquid Argon in the range from 0.3 GPa to 1 GPa. In this paper, we show the effects of different processing routes, namely, cold drawing (CD), cold rolling (CR), hot isostatic pressure (HIP) and doping on critical current density (Jc), pinning force (Fp), irreversible magnetic-field (Birr), critical temperature (Tc), n value, and dominant pinning mechanism in MgB2/Fe wires with ex situ MgB2 barrier. The results show that medium pressures (∼0.35 GPa) lead to high Jc in low and medium magnetic fields (0 T – 9 T). On the other hand, higher pressures (∼1 GPa) lead to enhanced Jc in high magnetic fields (above 9 T). Transport measurements show that CD, CR, and HIP have small effects on Birr and Tc, but CD, CR, HIP, and doping enhance Jc and Fp in in situ MgB2 wires with ex situ MgB2 barrier. Transport measurements on in situ undoped MgB2 wire with ex situ MgB2 barrier yield a Jc of about 100 A/mm2 at 4.2 K in 6 T, at 10 K in 4 T and at 20 K in 2 T. The results also show that cold drawing causes increase of n value.

Characteristics of high-performance BaHfO3-doped SmBa2Cu3Oy superconducting films fabricated with a seed layer and low-temperature growth

BaHfO3(BHO)-doped SmBa2Cu3Oy (SmBCO) superconducting films were fabricated with a seed layer and low-temperature growth (LTG technique) via pulsed laser deposition. The LTG technique enables the fabrication of high-quality SmBCO films even at a low substrate temperature during the deposition, and also greatly increases the number density of BHO nano-rods. Transmission electron microscopy observations showed that the 5.6 vol% BHO-doped sample had a high number density [(4.8 ± 0.3) × 103 μm−2] of small (5.4 ± 0.7 nm) BHO nano-rods. This sample exhibits maximum flux pinning forces (Fp) of 405 GN m−3 in 9.0 T at 40 K and 105 GN m−3 in 9.0 T at 65 K. The high density and small size of the nano-rods in a REBa2Cu3Oy matrix (where RE is a rare earth element) is considered to be very effective for enhancing Fp at low temperatures under a high field.

Effect of contact angle hysteresis on breakage of a liquid bridge

In this paper, the importance of considering contact angle hysteresis (CAH) during the process of stretching and breaking a liquid bridge between two solid surfaces is addressed. We clearly show that due to the pinning of contact line at the end of the stretching stage, the contact angle between liquid bridge and surfaces cannot be simply assumed to have a constant value (e.g. receding contact angle, θ r ). Simulation results for stretching a liquid bridge with and without CAH, showed that the contact line pinning can lead to breakage at a larger surface separation and smaller value of pull-off force (F p ). A systematic study about the effect of CAH and contact line pinning on the value of F p is provided. It is found that when one of the surfaces has a θ r larger than 90∘, F p decreases with the increase of θ r on either surface delimiting the bridge. For the cases where θ r of both surfaces are smaller than 90∘, significantly smaller F p is seen when contact line pinning occurs on both surfaces, as compared to F p when contact line pinning occurs only on one surface. This smaller F p is caused by more curved profile and later breakage of liquid bridge.

Effect of addition of BaTiO3 nano particles on the electrical transport properties of YBCO superconductor

The flux pinning properties of YBCO bulk superconductors synthesized by conventional solid state route and are added with different weight% (x=0, 0.5, 1, 2, 3, 5) of nano BaTiO3 which are prepared by a modified combustion route are studied systematically. The phase analysis of the samples was done by using X-ray diffraction and scanning electron microscopy. Temperature-resistivity measurements, magnetic field dependence of critical current density (Jc-B Characteristics) and flux pinning force calculations were done at 77 K. From the SEM images the microstructure of the sample showed a relative uniform distribution of the nano-particles within the specimen. We found that, even though the transition temperature (Tc) does not change considerably with the BaTiO3 addition, both the critical current density (Jc) and flux pinning force (Fp) increased systematically up to 2 wt% BaTiO3 in the composite, in the presence of magnetic field ranging between 0 and 0.6 T. The Jc value in 2 wt% BaTiO3 added sample showed at least 250% larger than that of the pure YBCO. Also the flux pinning force calculated for the 2 wt% BaTiO3 added is found to be enhanced more than 9 times that of pure YBCO. These observations suggest that the BaTiO3 addition to the Y-123- compounds improve the electrical connection between superconducting grains to result in the increase in Jc.

Effect of Number of Saw Blade Teeth on Noise Level and Wear of Blade Edges during Cutting of Wood

The effect of varying the number of saw blade teeth while transversally cutting beech (Fagus sylvatica L.) wood on the noise level and saw blade lifetime between two sharpenings was tested. The experiment was carried out with raw beech wood samples with dimensions of 25 x 100 x 1000 mm and circular saw blades with cemented carbide tips (24, 40, and 60 teeth). The saw blade diameters were identical (D = 250 mm), as were the cutting wedge angle geometries (α = 15°, β = 60°, γ = 15°). The saw blades were selected based on commonly used blades (in the Czech Republic and Slovakia) for the transversal cutting of the given wood species. Neither the cutting speed (vc = 62 m/s) nor the feed force (Fp = 75 N) were changed during the cutting process. The results suggest that the number of saw blade teeth is an important factor that affects the noise level of saw blade during sawing as well as the wear of cutting edge.

Analysis of Laser Assisted Milling (LAM) of Inconel 718 with Ceramic Tools

Laser Assisted Milling (LAM) is a hybrid machining technology which combines conventional milling with a localized laser beam. The laser spot heats the uncut workpiece material in front of the cutting edge. The aim of this technology is to improve the machinability of difficult to cut alloys, like Inconel 718. Hence, the material strength is reduced by high temperatures in the hot cutting process. Indeed, Inconel 718 is widely used in aerospace industry due to its excellent mechanical strength and corrosion resistance at high temperatures. These properties result in poor machinability and high tool wear. In this paper experiments of LAM and conventional milling of Inconel 718 were performed by using ceramic inserts. Methods from the Design of Experiment (DoE) were adopted in order to investigate the influence of laser and milling parameters in the hybrid process. The response variables were measured as tool wear, tool deflection, active machining force Fa and passive force Fp. The results showed that machining forces, tool deflection and also tool wear could be reduced by laser heating, especially using enhanced cutting data.

Pore size and pore shape – but not mesh density – alter the mechanical strength of tissue ingrowth and host tissue response to synthetic mesh materials in a porcine model of ventral hernia repair

BackgroundOver 100 types of soft tissue repair materials are commercially available for hernia repair applications. These materials vary in characteristics such as mesh density, pore size, and pore shape. It is difficult to determine the impact of a single variable of interest due to other compounding variables in a particular design. Thus, the current study utilized prototype meshes designed to evaluate each of these mesh parameters individually. MethodsFive prototype meshes composed of planar, monofilament polyethylene terephthalate (PET) were evaluated in this study. The meshes were designed to focus on three key parameters, namely mesh density, pore size, and pore shape. The prototype meshes were implanted in the preperitoneal, retrorectus space in a porcine model of ventral incisional hernia repair, and tissue ingrowth characteristics were evaluated after 90 days. Mesh-tissue composite specimens were obtained from each repair site and evaluated via T-peel mechanical testing. Force–displacement data for each T-peel test were analyzed and five characteristics of tissue ingrowth reported: peak force (fp), critical force (fc), fracture energy (Γc), work (W), and work density (Wden). Hematoxylin and eosin (H&E) stained sections of explanted mesh-tissue composites were also assessed for characteristics of tissue response including cellular infiltration, cell types, inflammatory response, extracellular matrix deposition, neovascularization, and fibrosis, with a composite score assigned to represent overall tissue response. ResultsThe medium-weight, very large pore, hexagonal (MWVLH) mesh performed significantly better than the light-weight, medium pore, diamond (LWMD) mesh for all parameters evaluated (fp, fc, Γc, W, Wden) and trended toward better results than the medium-weight, medium pore, diamond (MWMD) mesh for the majority of the parameters evaluated. When the data for the five meshes was grouped to evaluate mesh density, pore size, and pore shape, differences were more pronounced. No significant differences were observed with respect to mesh density, however significant improvement in mechanical strength of tissue ingrowth occurred as pore size increased from medium to very large. In addition, the hexagonal pores resulted in the strongest tissue ingrowth, followed by the square pores, and finally the diamond pores. Scores for several histological parameters were significantly different for these prototype meshes. For example, the MWVLH mesh showed significantly greater tissue ingrowth by neovascularization histological score than MWMD and MWVLS meshes (p<0.05) and significantly less fibrosis than LWMD and MWVLS meshes (p<0.05). ConclusionPore shape and pore size significantly altered the mechanical strength of tissue ingrowth and host-site integration in a porcine model of ventral hernia repair, while mesh density had no effect.