Lateral Interface Research Articles

Drebrin-induced Stabilization of Actin Filaments

Drebrin is a mammalian neuronal protein that binds to and organizes filamentous actin (F-actin) in dendritic spines, the receptive regions of most excitatory synapses that play a crucial role in higher brain functions. Here, the structural effects of drebrin on F-actin were examined in solution. Depolymerization and differential scanning calorimetry assays show that F-actin is stabilized by the binding of drebrin. Drebrin inhibits depolymerization mainly at the barbed end of F-actin. Full-length drebrin and its C-terminal truncated constructs were used to clarify the domain requirements for these effects. The actin binding domain of drebrin decreases the intrastrand disulfide cross-linking of Cys-41 (in the DNase I binding loop) to Cys-374 (C-terminal) but increases the interstrand disulfide cross-linking of Cys-265 (hydrophobic loop) to Cys-374 in the yeast mutants Q41C and S265C, respectively. We also demonstrate, using solution biochemistry methods and EM, the rescue of filament formation by drebrin in different cases of longitudinal interprotomer contact perturbation: the T203C/C374S yeast actin mutant and grimelysin-cleaved skeletal actin (between Gly-42 and Val-43). Additionally, we show that drebrin rescues the polymerization of V266G/L267G, a hydrophobic loop yeast actin mutant with an impaired lateral interface formation between the two filament strands. Overall, our data suggest that drebrin stabilizes actin filaments through its effect on their interstrand and intrastrand contacts.

Post-Operative Cyst Formation after Autologous Osteochondral Transplanation in the Talus: An MRI Evaluation (SS-45)

Post-Operative Cyst Formation after Autologous Osteochondral Transplanation in the Talus: An MRI Evaluation (SS-45)

Numerical simulations of complex fluid-fluid interface dynamics

Interfaces between two fluids are ubiquitous and of special importance for industrial applications, e.g., stabilisation of emulsions. The dynamics of fluid-fluid interfaces is difficult to study because these interfaces are usually deformable and their shapes are not known a priori. Since experiments do not provide access to all observables of interest, computer simulations pose attractive alternatives to gain insight into the physics of interfaces. In the present article, we restrict ourselves to systems with dimensions comparable to the lateral interface extensions. We provide a critical discussion of three numerical schemes coupled to the lattice Boltzmann method as a solver for the hydrodynamics of the problem: (a) the immersed boundary method for the simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for multi-component fluids in combination with (b) an additional advection-diffusion component for surfactant modelling and (c) a molecular dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.

A New Design of Hip Prosthesis Coating using Functionally Graded Material

Abstract Titanium and its alloys which have been widely used in many prostheses carry the major joint load and cause stress shielding. Thus, the bone might become osteoporotic due to lack of physiological stress flow in common hip replacement. Therefore, the optimization of hip joint materials is one of the most challenging tasks in prosthetic design. It is found in the literature that there is a great contradiction regarding the use of hydroxyapatite (HAP) coating. In this study a finite element analysis (FEA) and optimization techniques have been carried out in order to find a new design of hip stem coating using functionally graded material (FGM) to reduce stress shielding at the proximal medial part of the femur, as well as reducing the interface shear stress at the interface between the coating and the bone which directly affects the implantation and long-term stability. This work is divided into two parts: in the first part, the gradation of the elastic modulus of the coating material has been changed in the vertical direction, while the second part changes the elastic modulus in the horizontal direction. The optimal design of the first and second models was compared with HAP coating and with homogenous uncoated titanium stem. The design optimization of the first model revealed, using a coating material consisting of HAP at the upper layer of the coating graded to collagen at the lower layer, increases the maximum von Mises stress in bone at the proximal medial part of the femur by 65% and 19% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress in the bone at the bone/coating interface is reduced by 23% and 12%, respectively. However, the maximum medial interface shear stress in the bone at the bone/coating interface is reduced by 39% and 14% compared to titanium stem and titanium coated with HAP, respectively. The design optimization of the second model revealed, using a coating material consisting of collagen at the inner layer adjacent to stem graded to HAP at the outer layer adjacent to bone, increases the maximum von Mises stress at the proximal medial part of the femur by 60% and 15% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress is reduced by 18% and 6%, respectively. However, the maximum medial interface shear stress is reduced by 35% and 8% compared to titanium stem and titanium coated with HAP, respectively.

The impact of interface/border defect on performance and reliability of high-k/metal-gate CMOSFET

The impact of interface/border defect on performance and reliability was investigated for gate-first and gate-last high-k/metal-gate CMOSFET. For high-k/metal-gate CMOSFET, VFB roll-off is critical as effective oxide thickness (EOT) scales below 15 angstrom (Å) especially for metal gate-first device with an extra capping layer to adjust VTH. By proposing a model of metal-gate process induced interface trap releasing oxygen, the vertical and lateral interface trap distribution and the dependence of interfacial layer (IL) on VFB roll-off phenomena can be well interpreted. In this work, we found that VFB roll-off can be improved by reducing oxygen vacancy (VO) at the HfO2/IL interface with suppression of oxygen diffusion from high-k to IL. By the way, a metal gate-last process with lower interface trap was proposed to minimize VO formation by suppress oxygen releasing, thus optimize a 28nm 15Å EOT HfO2/metal-gate CMOSFET with low VFB–EOT roll-off, it can be a reference for sub 22nm CMOSFET with thin EOT (<15Å) design.

Potential Steps at C60–TiOPc–Ag(111) Interfaces: Ultrahigh-Vacuum–Noncontact Scanning Probe Metrology

Nanoscale structure-electric potential relations in films of the organic molecular semiconductors C(60) and titanyl phthalocyanine (TiOPc) on Ag(111) have been measured under UHV conditions. Noncontact force methods were utilized to image domain structures and boundaries with molecular resolution, while simultaneously quantifying the local surface electric potential. Sensitivity and spatial resolution for the local potential measurement were first established on Ag(111) through direct observation of the electrical dipole and potential step, φ(step) = 10 ± 3 mV, of monatomic crystallographic steps. A local surface potential increase of 27 ± 11 mV occurs upon crossing the boundary between the neat Ag(111) surface and C(60) islands. Potential steps in binary C(60)-TiOPc films, nanophase-separated into crystalline C(60) and TiOPc domains, were then mapped quantitatively. The 207 ± 66 mV potential step across the C(60)-to-TiOPc domain boundary exhibits a 3.6 nm width that reflects the spatial resolution for electric potential across a material interface. The absence of potential asymmetry across this lateral interface sets the upper bound for the C(60)-TiOPc interface dipole moment as 0.012 e nm.

Kelvin probe microscopic visualization of charge storage at polystyrene interfaces with pentacene and gold

Charge carriers trapped in polystyrene (PS) were investigated with Kelvin probe microscopy (KPM) and thermally stimulated discharge current (TSDC). Lateral heterojunctions of pentacene/PS were scanned using KPM, effectively observing polarization along a side view of a lateral nonvolatile organic field-effect transistor dielectric interface. TSDC was used to observe charge migration out of PS films and to estimate the trap energy level inside the PS, using the initial rise method.

Analytical study of the horizontal ducting of sound by an oceanic front over a slope

The horizontal ducting of sound by an oceanic temperature front over a sloping bottom is studied with an idealized wedge model consisting of a lateral interface across the slope. The water outside the frontal interface has higher temperature, hence faster sound speed, and it will produce inshore reflection/refraction of the sound. Combining the offshore refraction caused by the sloping bottom, propagating sound can be ducted along the front. An analytical solution to the sound pressure field in the idealized model is derived, and an example is presented to demonstrate and discuss the ducting effect.

Ground-Liner Interaction Analysis in Underground Opening

The ground-liner interaction research has important engineering value for the underground engineering design optimization and evaluation of construction safety. The interface between ground and liner is considered. In this paper, the effect of different ground-liner stiffness ratio, lateral pressure coefficient, thickness and different interface stiffness ratio and other factors on the support structure for internal forces and interface stress is analyzed. The analysis results show that liner internal force and interface stress increase with the increase of stiffness ratio between liner and ground, and the impact is very significant. Effect of lateral pressure coefficient on liner internal force and interface stress mainly reflects on laws around the cavern, where 1 is the limitation of lateral pressure coefficient. It presents symmetrical distribution. With the increase of liner thickness, the liner internal force and interface normal stress increase, but it make no difference to the contact interface tangential stress.

Field behaviour of stiffened deep cement mixing piles

Full-scale pile load tests were performed on soft Bangkok clay improved by stiffened deep cement mixing (SDCM) piles and deep cement mixing (DCM) piles installed by jet-mixing to compare their performance. The SDCM pile is a DCM pile with a precast reinforced concrete core pile inserted in the middle. A series of full-scale tests consisting of axial compression, lateral and pullout interface between the concrete core pile and surrounding DCM material were performed. The length of the concrete core pile influenced both the ultimate axial bearing capacity and the settlement of the SDCM piles more than its section area. Furthermore, the section area of the concrete core pile affected both the lateral ultimate bearing capacity and the lateral displacements of SDCM piles significantly. Moreover, the SDCM piles with area ratio (Acore/ADCM) of 0·17 and length ratio (Lcore/LDCM) of 0·85 increased the axial and lateral ultimate bearing capacities so that they were as much as 2·2 and 15 times higher than the corresponding values of DCM piles, respectively. The flexural strength of the DCM pile obtained from the laboratory was 16% of its unconfined compressive strength whereas that obtained from full-scale lateral load tests was much lower at 4–7% of its unconfined compressive strength. The strength reduction factor, Rinter, at the interface between the concrete core pile and DCM pile in the field averaged 0·40, which agreed with the data from laboratory tests of 0·38–0·46.

Lateral air cavities for microfluidic pumping with the use of acoustic energy

An acoustically activated micropump is fabricated and demonstrated using a single step lithography process and an off-chip acoustic energy source. Using angled lateral cavities with trapped air bubbles, acoustic energy is used to oscillate the liquid–air interface to create a fluidic driving force. The angled lateral cavity design allows for fluid rectification from the first-order pulsatile flow of the oscillating bubbles. The fluid rectification is achieved through the asymmetrical flow produced by the oscillating interface generating fluid flow away from the lateral cavity interface. Simulation and experimental results are used to develop a pumping mechanism that is capable of driving fluid at pressures of 350 Pa. This pumping system is then integrated into a stand-alone battery operated system to drive fluid from one chip to another.

Dual Action of ATP Hydrolysis Couples Lid Closure to Substrate Release into the Group II Chaperonin Chamber

Group II chaperonins are ATP-dependent ring-shaped complexes that bind nonnative polypeptides and facilitate protein folding in archaea and eukaryotes. A built-in lid encapsulates substrate proteins within the central chaperonin chamber. Here, we describe the fate of the substrate during the nucleotide cycle of group II chaperonins. The chaperonin substrate-binding sites are exposed, and the lid is open in both the ATP-free and ATP-bound prehydrolysis states. ATP hydrolysis has a dual function in the folding cycle, triggering both lid closure and substrate release into the central chamber. Notably, substrate release can occur in the absence of a lid, and lid closure can occur without substrate release. However, productive folding requires both events, so that the polypeptide is released into the confined space of the closed chamber where it folds. Our results show that ATP hydrolysis coordinates the structural and functional determinants that trigger productive folding.

E93R Substitution of Escherichia coli FtsZ Induces Bundling of Protofilaments, Reduces GTPase Activity, and Impairs Bacterial Cytokinesis

Recently, we found that divalent calcium has no detectable effect on the assembly of Mycobacterium tuberculosis FtsZ (MtbFtsZ), whereas it strongly promoted the assembly of Escherichia coli FtsZ (EcFtsZ). While looking for potential calcium binding residues in EcFtsZ, we found a mutation (E93R) that strongly promoted the assembly of EcFtsZ. The mutation increased the stability and bundling of the FtsZ protofilaments and produced a dominating effect on the assembly of the wild type FtsZ (WT-FtsZ). Although E93R-FtsZ was found to bind to GTP similarly to the WT-FtsZ, it displayed lower GTPase activity than the WT-FtsZ. E93R-FtsZ complemented for its wild type counterpart as observed by a complementation test using JKD7-1/pKD3 cells. However, the bacterial cells became elongated upon overexpression of the mutant allele. We modeled the structure of E93R-FtsZ using the structures of MtbFtsZ/Methanococcus jannaschi FtsZ (MjFtsZ) dimers as templates. The MtbFtsZ-based structure suggests that the Arg(93)-Glu(138) salt bridge provides the additional stability, whereas the effect of mutation appears to be indirect (allosteric) if the EcFtsZ dimer is similar to that of MjFtsZ. The data presented in this study suggest that an increase in the stability of the FtsZ protofilaments is detrimental for the bacterial cytokinesis.

Modulation of KvAP Unitary Conductance and Gating by 1-Alkanols and Other Surface Active Agents

The actions of alcohols and anesthetics on ion channels are poorly understood. Controversy continues about whether bilayer restructuring is relevant to the modulatory effects of these surface active agents (SAAs). Some voltage-gated K channels (Kv), but not KvAP, have putative low affinity alcohol-binding sites, and because KvAP structures have been determined in bilayers, KvAP could offer insights into the contribution of bilayer mechanics to SAA actions. We monitored KvAP unitary conductance and macroscopic activation and inactivation kinetics in PE:PG/decane bilayers with and without exposure to classic SAAs (short-chain 1-alkanols, cholesterol, and selected anesthetics: halothane, isoflurane, chloroform). At levels that did not measurably alter membrane specific capacitance, alkanols caused functional changes in KvAP behavior including lowered unitary conductance, modified kinetics, and shifted voltage dependence for activation. A simple explanation is that the site of SAA action on KvAP is its entire lateral interface with the PE:PG/decane bilayer, with SAA-induced changes in surface tension and bilayer packing order combining to modulate the shape and stability of various conformations. The KvAP structural adjustment to diverse bilayer pressure profiles has implications for understanding desirable and undesirable actions of SAA-like drugs and, broadly, predicts that channel gating, conductance and pharmacology may differ when membrane packing order differs, as in raft versus nonraft domains.

Competing magnetic interactions in exchange-bias-modulated films

The magnetization reversal in stripelike exchange-bias-patterned ${\text{Ni}}_{81}{\text{Fe}}_{19}/\text{IrMn}$ thin films was investigated by complementary inductive and high-resolution magneto-optical magnetometry, magneto-optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange-bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange-bias direction. Due to the interaction of interfacial coupling, exchange, and magnetostatic energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micropatterned exchange-bias films.

Decoupled pelvis adjustment to induce lumbar motion: A technique that controls low back load in sitting

Static sitting in confined settings have been associated with low back pain in sedentary occupations such as office works and car driving. To prevent lumbar discomfort in prolonged static sitting, periodic motion of the lumbar spine is needed. Because the pelvis forms the basis for lumbar spine curvature, a passive motion technique was developed, which adjusts pelvis orientation independent from the trunk. This study uses a computer-aided simulator chair instrumented with a mechanism for decoupled pelvis adjustment and investigates the effects on low back load in eighteen healthy male individuals. Experiments involved measurement of body segments orientation, interface back pressure distribution and seat reaction forces during quasi-static actuated pelvis rotation in the sagittal and frontal plane. Joint forces and torques were estimated in the lumbosacral spine region. In sagittal pelvis adjustment, the pelvis rotated 19 ± 3 degrees and strong relations (r 2 > 0.8) were found with centre of back pressure in upward direction (cp z, r 2 = 0.90), lumbosacral shear force in forward direction (F ly, r 2 = 0.91), lumbosacral normal force in axial direction (F lz, r 2 = 0.80), lumbosacral torque around lateral direction (T lx, r 2 = 0.87) and interface pressure at the lower back (P lb, r 2 = 0.88). In frontal pelvis adjustment, the pelvis rotated 9 ± 1 degrees and strong relations were found with centre of back pressure in lateral direction (cp x, r 2 = 0.96), lumbosacral torque around forward direction (T ly, r 2 = 0.98) and lumbosacral torque around axial direction (T lz, r 2 = 0.95). These findings indicate that decoupled pelvis adjustment could be an applicable intervention to control low back load in prolonged static sitting. Relevance to industry Decoupled pelvis adjustment might be an applicable technique to induce periodic lumbar motion which potentially improves tolerance for prolonged static sitting.

SU-FF-T-626: Dynamic Splitting of Gaussian Pencil Beams in Heterogeneity-Correction Algorithms for Radiotherapy with Heavy Charged Particles

Purpose: To develop an algorithm to resolve intrinsic problems with dose calculations using pencil beams when particles involved in each beam are overreaching a lateral density interface or when they are detouring in a laterally heterogeneous medium. Method and Materials: A finding on a Gaussian distribution, such that it can be approximately decomposed into multiple narrower, shifted, and scaled ones, was applied to dynamic splitting of pencil beams implemented in a dose calculation algorithm for proton and ion beams. The method was tested in an experiment with a range-compensated carbon-ion beam. Its effectiveness and efficiency were evaluated for carbon-ion and proton beams in a heterogeneous phantom model. Results: The splitting dose calculation reproduced the detour effect observed in the experiment, which amounted to about 10% at a maximum or as large as the lateral particle-disequilibrium effect. The proton-beam dose generally showed large scattering effects including the overreach and detour effects. The overall computational times were 9 s and 45 s for non-splitting and splitting carbon-ion beams and 15 s and 66 s for non-splitting and splitting proton beams. Conclusions: The beam-splitting method was developed and verified to resolve the intrinsic size limitation of the Gaussian pencil-beam model in dose calculation algorithms. The computational speed slowed down by factor of 5, which would be tolerable for dose accuracy improvement at a maximum of 10%, in our test case.

Thermal resistance between low-dimensional nanostructures and semi-infinite media

Nanostructured electronic and photonic devices include a high density of material interfaces, which can strongly impede heat conduction and influence performance and reliability. Thermal conduction through interfaces is a very mature discipline for the traditional geometry, in which the lateral interface dimensions are large compared to the phonon wavelength. In nanostructures, however, the localization of phonons in the directions parallel to the interface may strongly influence the effective thermal resistance. The present work investigates model problems of abrupt junctions between a harmonic one-dimensional (1D) and a three-dimensional (3D) fcc lattice and between a 1D and a two-dimensional square lattice. The abrupt change in geometry modifies the phonon modes participating in energy transmission and creates an additional thermal resistance that is comparable with that occurring due to the acoustic mismatch at the interface of bulk media. For both cases, varying the impedance mismatch at the junction suggests that engineering an intentional impedance mismatch at a nanostructured interface may enhance the transmission of energy. The lattice dynamics calculations are used to develop qualitative arguments for the interface resistances in the practical geometries involving carbon nanotubes, silicon nanopillars, and graphene. This research provides foundations for detailed investigations of the impact of localized phonon modes on the acoustic mismatch resistance.

Tire Force and Terrain Disturbance Measurements During Turning Maneuvers

A proof-of-concept study to link vehicle performance measures to associated terrain disturbance was performed with the intent to improve terrain impact prediction methods. Field tests to assess terrain disturbance during turning maneuvers were completed on dry and wet, grassy fields and slopes in northern Vermont. The vehicle tests consisted of a series of spiral maneuvers at two speeds, and serpentine maneuvers on slopes, to comprise a range of turning radii, upslope and downslope turns, and velocity. The CRREL instrumented vehicle (CIV) and a military high-mobility multipurpose wheeled vehicle (HMMWV) were instrumented to measure linear accelerations, angular and linear velocity, wheel forces, speeds, and location. The terrain was fully characterized for soil type, wetness, shear strength, and vegetation cover prior to testing. The disturbance created by the vehicle was measured using the cumulative impact width method based on disturbed width and impact severity. Results show increased disturbance for the wetter soil, but generally the impacts were low because of sufficient terrain strength for these two vehicles. Nonetheless, correlations were found between the measured horizontal forces, accelerations and yaw rates, and the terrain disturbance; most significantly, increased lateral tire-terrain interface forces resulted in increased cumulative impact width. Additionally, the vehicle lateral force, accerlation, and yaw rate that were directly measured are comparable with those calculated from the global positioning system (GPS) data, illustrating the potential of the much simpler measurements for this purpose.

The initial surface composition and topography modulate sphingomyelinase-driven sphingomyelin to ceramide conversion in lipid monolayers

Changes of the initial composition and topography of mixed monolayers of Sphingomyelin and Ceramide modulate the degradation of Sphingomyelin by Bacillus cereus Sphingomyelinase. The presence of initial lateral phase boundary due to coexisting condensed and expanded phase domains favors the precatalytic steps of the reaction. The amount and quality of the domain lateral interface, defined by the type of boundary undulation, appears as a modulatory supramolecular code which regulates the catalytic efficiency of the enzyme. The long range domain lattice structuring is determined by the Sphingomyelinase activity.