Pinning Forces Research Articles

Aqueous films limit bacterial cell motility and colony expansion on partially saturated rough surfaces

Bacterial motility is a key mechanism for survival in a patchy environment and is important for ecosystem biodiversity maintenance. Quantitative description of bacterial motility in soils is hindered by inherent heterogeneity, pore-space complexity and dynamics of microhydrological conditions. Unsaturated conditions result in fragmented aquatic habitats often too small to support full bacterial immersion thereby forcing strong interactions with mineral and air interfaces that significantly restrict motility. A new hybrid model was developed to study hydration effects on bacterial motility. Simulation results using literature parameter values illustrate sensitivity of colony expansion rates to hydration conditions and are in general agreement with measured values. Under matric potentials greater than -0.5 kPa (wet), bacterial colonies grew fast at colony expansion rates exceeding 421 +/- 94 microm h(-1); rates dropped significantly to 31 +/- 10 microm h(-1) at -2 kPa; as expected, no significant colony expansion was observed at -5 kPa because of the dominance of capillary pinning forces in the submicrometric water film. Quantification of hydration-related constraints on bacterial motion provides insights into optimal conditions for bacterial dispersion and spatial ranges of resource accessibility important for bioremediation and biogeochemical cycles. Results define surprisingly narrow range of hydration conditions where motility confers ecological advantage on natural surfaces.

A mechanical model for surface layer formation on self-lubricating ceramic composites

To predict the thickness of a self-lubricating layer on the contact surface of ceramic composite material containing a soft phase during dry sliding test, a mechanical model was built to calculate the material transfer of the soft second phase in the composite to the surface. The tribological test, as a case, the contact situation of a composite disk sliding against a loaded pin was studied in the model. The macroscopic deformation of the composite was supposed to be elastic. Subsurface stresses were calculated by the Hamilton's formulae. Further, the squeezed second phase material of inclusions was analyzed microscopically based on the Hashin's equations of inelastic inclusions. Based on the mechanical model, the thickness of the transferred layer during the multi sliding passes was predicted. The influence of material parameters and loading conditions such as inclusion (second phase) concentration in the composite, yield strength of the inclusion material, normal load on the pin and friction force were studied. The model can be used to design and optimize self-lubricating ceramic composites for applications and resulting contact conditions.

Effects of Novel Disk-type Furrow Opener Used in No-Tillage System on Micro Environment of Seed

Problem statement: Offset Double-Disk Opener (DDO) is a popular furrow opener in conservation tillage. It has some limitations such as negative suction to penetrate in the soil, hair pinning and mixing seed and fertilizer in the slot. Because of importance of separation of seed and fertilizer in the slot, by adding two horizontal mi ni disks to DDO a modified opener was made (MDO) which placed the fertilizer between and under two r ows of seed. Approach: To consider performance of novel opener an indoor comparison test between DDO and MDO was performed at soil bin. The experiment was conducted with three working speeds (3, 6 and 8 km h -1 ), two bulk densities of soil (1.1 and 1.4 Mg m -3 ) and two levels of residues (1 and 2 ton ha -1 ). The experimental design consisted in a (3◊2◊2) complete randomized factorial with three re plicates for each test. Moisture of seed furrow, separation of seed and fertilizer, hair pinning and resultant forces acting on the openers were used a s assessing indexes. Results: There was no significant difference between soil m oisture content in slots created by DDO and MDO at 0-4 cm depth, but at 4-8 cm the in the slot created by MDO moisture content was higher about 9%. Horizontal force for b oth openers increased with increasing speed and soil bulk density. Vertical force for DDO was negat ive so it needed additional weight for penetrating in the soil, but vertical force for MDO was positive a nd, which can solve the challenge of penetration in the soil in DDO. In soft soil with heavy residues s ome trash was pushed by DDO into seed furrow (hair pinning) but at MDO seed were placed at clean groove. Lateral and vertical separation of seed and fertilizer was performed effectively by MDO (4. 5 and 5 cm, respectively) while DDO put seed and fertilizer close to each other. Conclusion: Overall, the Modified Offset Double-disks (MDO) had better performance. So by adapting this opener with no-tillage drillers it would possible to have higher yield in conservation tillage where the most appropriate opener is disk type.

The Effect of Second Phase Additions on the Microstructure and Bulk Pinning Force in ${\rm Nb}_{3}{\rm Sn}$ PIT Wire

The effect of second phase gadolinium and yttrium additions on the microstructure and the bulk pinning force are reported for PIT Nb3Sn mono-wires. High resolution SEM of the grain morphology show smaller grain size for mono-wires with the second phase additions after 750degC and 850degC heat treatment compared to control samples. The bulk pinning force properties are determined from magnetization measurements at 9 K which allow the whole pinning force curve to be seen.

Systematic study of BaSnO 3 doped YBa 2Cu 3O 7−x films

YBa 2Cu 3O 7− x + BaSnO 3 (YBCO + BSO) mixed films with increased BSO content were prepared on SrTiO 3 substrates by pulsed-laser deposition of YBCO + x wt% BSO mixed targets ( x = 2, 4, 6 and 8 wt%). TEM images reveal that BSO is incorporated into the YBCO matrix in form of nanorods, whose density and size increase with the BSO content. The pinning properties for the mixed YBCO + BSO film were systematically studied. The 4 wt% BSO sample exhibited the maximum global pinning forces F P at all temperatures: 28.3 GN/m 3 near 3 T at 77 K, 103 GN/m 3 near 5 T at 65 K, and >241 GN/m 3 near 9 T at 40 K.

Magnetic flux penetration into high-temperature superconductors in the vortex liquid state under the blow-up conditions

The problem of magnetic field penetration into a type-II high-temperature superconductor that is in the weakly pinned vortex-liquid phase is considered. A magnetic field on the superconductor boundary rises with time in the blow-up regime. A model hydrodynamic equation describing the magnetic induction distribu- tion in the vortex-liquid phase for thermomagnetic motion of the flux is derived. Analytical expressions for the depth and rate of magnetic field penetration into the superconductor are found. It is demonstrated that these quantities depend on parameters of the problem: index of power n in the boundary regime characterizing the penetration rate of vortices into the superconducting half-space and a parameter describing the effect of random pinning forces and thermal fluctuations on the magnetic flux distribution.

Three‐dimensional vibration characteristics of the permanent magnet–HTSC magnetic bearing

AbstractThe three‐dimensional vibration of the rotor in a permanent magnet– HTSC magnetic bearing system is studied. We have developed a magnetic bearing system which can revolve at up to 12,000 rpm, and three‐dimensional vibration of the rotor is measured with laser displacement sensors. To consider the rotor vibration in a mechanical resonance state, the static lateral and vertical pinning forces of the magnetic bearing are measured. The results are used to obtain the resonant frequency. There are two factors in the mechanical resonance caused by the magnetic bearing. One is the lateral equivalent spring coefficient and the other is the vertical equivalent spring coefficient. The influence of mechanical resonance caused by the lateral spring coefficient is large, and that of the vertical one is small. The three‐dimensional vibration of the rotor position around the mechanical resonant frequency is measured. Because the revolution of the rotor increases the lateral force to the center, the resonant frequency obtained in a free revolution experiment is larger than that obtained from pinning force measurement. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 58–64, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20586

How to make sticky surfaces slippery: Contact angle hysteresis in electrowetting with alternating voltage

Contact angle hysteresis caused by random pinning forces is a major obstacle in moving small quantities of liquid on solid surfaces. Here, we demonstrate that the contact angle hysteresis for sessile drops in electrowetting almost disappears with increasing alternating voltage, whereas for direct voltage it remains constant. This observation is explained in terms of a balance of surface tension, pinning, and (time-dependent) electrostatic forces at the contact line.

Incorporation of double artificial pinning centers in YBa 2Cu 3O 7−δ films

YBa 2Cu 3O 7−x + BaZrO 3 + Y 2O 3 (YBCO + BaZrO 3 + Y 2O 3) mixed films were prepared on SrTiO 3/MgO substrates by pulsed-laser deposition from an YBCO + BaZrO 3 target with a thin Y 2O 3 sector stuck on the top. The pinning properties for the double-doped YBCO + BaZrO 3 + Y 2O 3 thin film were enhanced in comparison with a pure YBCO sample prepared in the same experimental conditions. The maximum global pinning forces F P for the double-doped sample are 12.8 GN/m 3 at 77K, 46.3 GN/m 3 at 65K, and 122 GN/m 3 at 40K. In the double-doped sample, the angular dependence of J c showed a broad peak at B//c due to the flux pinning by c-axis correlated defects, combined with a plateau, due to the flux pinning by isotropic pinning centres. Consistently, both BaZrO 3 nanorods parallel to the c-axis and Y 2O 3 nanoparticles randomly dispersed inside the YBCO matrix were observed in TEM images.

A Novel Halo Orthosis to Reduce Pin Loosening

Pin loosening is a frequent complication associated with the use of halo orthoses. Efforts to reduce pin loosening incidence include increasing the number of halo pins, increasing the torque specification, and proactively retightening the halo pins. Although these approaches lower pin loosening incidence rates, none addresses the cause of pin loosening, which is the inability of current halo ring designs to accommodate changes in geometry of the skull. A novel four-pin adaptive halo ring is introduced that can accommodate changes in geometry of the skull and provide a nearly constant pin force. To quantify pin loosening in a halo ring, tests were performed using a fixture that was capable of simulating the changes in skull geometry that are responsible for pin loosening. Both the four-pin adaptive halo and a conventional halo were tested. After 1.1mm of radial recession of the skull at the pin site, the average halo pin force in the conventional halo decreased by 78% while the average halo pin force in the four-pin adaptive halo decreased by 12%. In addition, the four-pin adaptive halo had significantly less variation in initial halo pin force (p-value <0.0001) than that of the four-pin adaptive halo.

Experimental Measurements of Load Distributions on Friction Stir Weld Pin Tools

An understanding of the forces acting on the pin of friction stir weld tools is critical to appropriate design, especially in materials with limited toughness such as polycrystalline cubic boron nitride. This article describes a study to measure the longitudinal force distribution on a friction stir weld pin tool. Total longitudinal forces were recorded on a dynamometer while welding 6061 aluminum with pins that varied in length and diameter. A model was developed that characterizes the pin force as a function of pin length and diameter. As the pin length approaches zero, the longitudinal force reaches an asymptote, which is apparently the longitudinal force due to the shoulder. The force due to the pin increases with pin length, but appears not to vary significantly with pin diameter. The force distribution on the pin appears to increase linearly with distance from the shoulder. Unexpected force variation was found at large pin lengths, a result which has yet to be explained.

Material Flow Around a Friction Stir Welding Tool: Development of a Thermo-Fluid Code

In Friction Stir Welding the heat generated through friction and plastic deformation softens the materials and allows them to be joined. The tool consists of two features, a pin and the shoulder. Several pin geometries have been proposed, for example a threaded cylinder, a cylinder with flattened sides, etc. The rotating pin forces the materials to flow around the pin and to mix. The shoulder applies a pressure to the material to constrain the plasticized material around the pin, and generates heat through friction and plastic deformation in a relatively thin layer under the shoulder surface. The material flow around the tool is very complex, and to date not fully understood. However one can distinguish two main parts: an extrusion of material around the rotating cylinder, and a vortex flow field near the probe due to the downward flow induced by the probe thread. The correct prediction of the resulting temperature field during welding is very important if the process is used industrially, as this would allow the evolution of the metallurgy, as well as the residual stresses to be predicted. A model which is able to predict the temperature field can also be used to optimise the operating parameters (tool rotating and advancing speed). Currently most numerical models rely on the measurement of the heat flux to be used as input data into the numerical model. This means that these models are not predictive. This paper presents a finite element model which does not require the heat input to be measured. The MORFEO (Manufacturing Oriented Finite Element toOI) finite element code developed at CENAERO is used for all simulations. The simulation results of the flow around simple tool geometries are presented. The predicted flow fields are compared to a first weld experiment conducted at INSTITUT DE SOUDURE. The first results are encouraging as a reasonable correlation between the experiment and the simulation is obtained.

Determination of the texturing gradient in ex situ MgB2∕Fe tapes examined by x-ray diffraction and its effects on the pinning force

We found that the reduced pinning forces of ex situ MgB2∕Fe monofilamentary tapes do not scale with temperature if the external magnetic field is applied parallel to the tape surface. A model is proposed to explain the behavior of the volume pinning forces in parallel and perpendicular orientations of the magnetic field, accounting for the observed texturing gradient between the center of the filament and the MgB2∕Fe interface. The degree of texturing of the sample, as determined by x-ray diffraction, is confirmed by modeling the pinning force in parallel field as the superposition of two components, the first one due to a highly textured region on the external part of the filament and the latter due to a low texturing region in the core.

Line vortex pinning and spacing in a three-dimensional ordered Josephson medium

A method of calculating the configuration of two line vortices interacting in a three-dimensional ordered Josephson medium and a minimal distance between them at a given pinning parameter is proposed. The axes of the vortices lie in the middle row of an infinite slab 9 or 13 cells thick with different conditions at the boundaries of the slab. Away from the centers of the vortices, the system of finite-difference equations becomes linear. Fluxoid quantization conditions in cells near the centers of the vortices serve as boundary conditions. An exact solution is approached by iterations in those phase discontinuities which cannot be considered small. This technique provides a much higher calculation accuracy and offers a wider domain of applicability than the earlier methods. Critical values I d of the pinning parameter at which two initial vortices keep given spacing d between them are calculated. For various vortex configurations, maximal pinning forces are calculated as functions of the pinning parameter and the distance to the nearest vortices. It is shown that the pinning force decreases near parallel vortices and increases near antiparallel ones.

Ti/Al Interaction and Austenite Grain Control in Crankshaft Manufacturing with 38MnSiVS5 Steel

38MnSiVS5 steel is similar to 38MnVS6 steel (EN), the difference being the addition of a small Ti content. Typical Ti and Al contents in the chemical composition of 38MnSiVS5 steel are Ti=0.020 and Al=0.035 mass%. Both elements combine easily with nitrogen, especially Ti, and it has been observed that relatively high Al levels are harmful for austenite grain size control at reheating temperatures. In this work 38MnSiVS5 steel is used to manufacture a large number of castings, varying only the Ti and Al contents and obtaining ingots with a different Ti/Al ratio in each case. The results show that abnormal growth of the austenitic grain occurs irrespective of the Ti and Al contents, due fundamentally to the partial dissolution and coarsening of TiN precipitates. However, the steels with high Al contents present worse behaviour due to the formation of a second type of precipitates, namely AIN, which quickly dissolve between 1000 and 1100°C, causing a drastic decline in local pinning forces that gives rise to more pronounced abnormal growth of the affected grains.

Increase of critical currents and peak effect in Mo-substitutedYBa2Cu3O7

Superconducting critical currents $j_{c} > 10^{5}$ A/cm$^{2}$ at temperatures $T \sim 50$ K and magnetic fields $B \sim 6$ T are reported for the YBa$_{2}$Cu$_{3-x}$Mo$_{x}$O$_{7+d}$ compound with $x = 0.02$. Clear evidence for the increased pinning force $F_p$ was found from a peak effect present for $j_{c}(B)$. The pinning force was analyzed by a scaling procedure using Kramer's approach. For a wide range of fields and temperatures, we were able to express all $F_p$ data as a single function of a reduced field $b = B/B_k$, where the scaling field $B_{k} << H_{c2}$ was related to the irreversibility filed $B_{irr}$. Analyses of the field dependence of $j_{c}(B,T)$ and $F_{p}(b)$ show that the effective pinning centers act as weakly interacting extended point-like defects. We propose that the pinning centers are randomly distributed small defects, most likely the dimers of MoO$_6$ octahedra in the CuO chains.

Determination of Minimum Required Halo Pin Force

The motivation for this study is to provide design guidance for a new halo system that minimizes pin loosening. If halo pin loosening can be substantially decreased with a new halo system, then the current standard of care of overtightening halo pins will not be necessary. Accordingly, there is a need to determine the halo pin force that should be applied to ensure adequate fixation. A biomechanical test was performed using cadaver head constructs, a custom halo fixture, and a tensile testing machine in an attempt to determine the relationship between the force required to dislodge a halo ring and the initial halo pin force. Three cadaver head constructs were tested at initial pin forces of 120, 240, and 360 N. For each test, the halo was pulled from a cadaver head with a displacement rate of 2.5 mm/min until the halo ring disengaged from the head. The vertical force that caused disengagement of the halo from the head was determined from the resulting load-displacement curves. A linear regression of the data predicts disengagement forces of 80, 320, and 570 N, respectively, for initial pin forces of 120, 240, and 360 N. The 95% prediction interval of disengagement forces for initial pin forces of 120, 240, and 360 N were +/-130, 120, and 130 N, respectively. A previously published study reported the maximum vertical load on a halo orthosis during patient usage to be 186 N. The lower 95% prediction interval from this study indicates that an average initial pin force of 230 N is necessary to prevent halo pin disengagement from a 186-N vertical load.

Micro wetting system by controlling pinning and capillary forces

In the recent years, wetting micro systems acting in liquid environment have been recognized as one important technology in chemical, bio and relative fields. In this regard, the micro wetting behaviors become major factors in controlling the liquid flow artificially in the micro tube, which are mainly affected by the pinning effect, capillary force, Laplace force, convection and so on. The purpose of our study is to realize the drastic control method of the wetting processes based on pinning effect and capillary forces. In this study, in order to analyze the wetting behavior precisely, we observed the spontaneous wetting processes depending on the micro pattern arrangement. From the results, the wetting phenomena can be clearly observed due to the pinning effect and capillary force. Moreover, we also found that the deionized water (DI-water) is more likely to spread on a hydrophilic surface compared with that on a hydrophobic surface. Therefore, we discuss the wetting behavior in this investigation on thermodynamics. We can control the wetting behavior practically by designing the surface energy of the resist patterns and its arrangements.

Recrystallisation Driving and Pinning Forces during Hot Rolling of a Low Nb-Microalloyed Steel

The values of recrystallisation driving (FR) and pinning forces (FP) during the hot rolling of a low Nb-microalloyed steel were calculated using several expressions found in the literature. A comparative study of the hypothesis into the interaction between precipitates and migrating grain boundaries was carried out, and the methods for estimating volume fractions of precipitates and dislocation density were assessed. Though the criterion selected greatly influences the values obtained for both forces, FP grows faster than FR as the rolling temperature drops.

Surface flux density distribution characteristics of bulk high- Tc superconductor in external magnetic field

This paper describes the measured results of the two-dimensional flux density distribution of a YBCO bulk under applied AC magnetic fields with various frequency. Melt-processed oxide superconductors have been developed in order to obtain strong pinning forces. Various electric mechanical systems or magnetic levitation systems use those superconductors. The major problem is that cracks occur because the bulk superconductors are brittle. The bulk may break in magnetizing process after cracks make superconducting state instable. The trapped flux density and the permanent current characteristics of bulk superconductors have been analyzed, so as to examine the magnetizing processes or superconducting states of the bulk. In those studies, the two-dimensional surface flux density distributions of the bulk in static fields are discussed. On the other hand, the distributions in dynamic fields are little discussed. We attempted to examine the states of the bulk in the dynamic fields, and made a unique experimental device which has movable sensors synchronized with AC applied fields. As a result, the two-dimensional distributions in the dynamic fields are acquired by recombining the one-dimensional distributions. The dynamic states of the flux of the bulk and the influences of directions of cracks are observed from the distributions. In addition, a new method for measuring two-dimensional flux density distribution under dynamic magnetic fields is suggested.