Connector Length Research Articles

Polymer–polymer adhesion with mobile promoters: Connector length dependence

The adhesion between two immiscible polymers stitched together via mobile chains is studied with large scale molecular simulations employing a coarse-grained bead-spring model. An adhesion model is presented that incorporates both connector molecular slipping out viscously and bulk dissipation in two dissimilar glassy polymers, in which one is dense melt and another is loose. The contributions to the separation work from thermodynamics and chain suction are studied in dependence of the connector length, at constant temperature, and at fixed basic molecular parameters. It is shown that connector length relative to its entanglement length can enhance the adhesion toughness and interfacial strength. Bulk dissipation is not considerable with low connector areal density in mushroom regime, while becomes more evident in the loose melt with increasing connector length when the coverage density is increased up to overlapping brush regime. The results provide insight into the structure evolution of adhesion interface with mobile promoter molecular, which are useful for future developments of continuum cohesive models for fracture of polymer–polymer interfaces.

Polymer-polymer adhesion with mobile promoters: Connector areal density dependence

The adhesion between two immiscible polymers stitched together via mobile promoters is studied with large scale molecular simulations employing a coarse-grained bead-spring model. An adhesion model is presented that enables both connector molecular slipping out viscously and bulk dissipation in two dissimilar glassy polymers, in which one is dense melt and another is loose. The contributions to the separation work from thermodynamics and chain suction are studied in dependence of the connector areal density, at constant temperature, and at fixed basic molecular parameters. It is shown that high connector coverage, but below saturation areal density, can enhance the adhesion toughness and interfacial strength. Bulk dissipation is not considerable with low connector areal density in mushroom regime, while becomes more evident in the loose block when the coverage density is increased up to overlapping brush regime. With increasing connector length, both bulk melts are enhanced by the segments of connector chains that penetrated in. The results provide insight into the structure evolution of adhesion interface coupled with promoter molecular, which are useful for future developments of continuum cohesive models for fracture of polymer- polymer interfaces.

Locked Intramedullary Total Wrist Arthrodesis

Total wrist arthrodesis is commonly performed using fixation plates, which can produce soft tissue irritation, often require removal, and limit the ability to position the hand in space. The Skeletal Dynamics IMPLATE is an intramedullary total wrist fusion device designed to provide stable fixation while avoiding the problems associated with plates. Radial and metacarpal locked intramedullary nails are inserted and joined by a connector. Desired hand placement is achieved by selecting the proper connector length and angle, then orienting it appropriately. Fusion mass compression is obtained by virtue of longitudinal threads on the radial nail that allow for length adjustment. Seven wrists in three men and four women were treated with this device and followed for a minimum of 24 weeks. In all cases, local cancellous bone graft was used and the third carpometacarpal (CMC) joint incorporated into the fusion. The median age was 49 (range, 28-71) years. Indications for fusion were two posttraumatic arthritides, three rheumatoid arthritides, one spastic deformity, and one infection. Patients were evaluated before surgery and at final follow-up using the Fernandez pain score and grip strength measurements using a hand-held dynamometer. All patients improved their grip strength and decreased their pain scores. All fusions united, and none of the patients presented dorsal soft tissue problems or required implant removal. One rheumatoid patient required secondary surgery for removal of a retained palmar osteophyte. This device delivers stable fixation, facilitates hand placement, and does not require removal.

Potential errors in fiber length measurements resulting from lever arm rotation during mechanical testing of muscle cells

In single muscle cell preparations fibers are often suspended between connectors, extending perpendicularly from a force transducer, and the lever arm of a torque motor. The fiber does not move along a horizontal plane when shortened or lengthened by lever arm rotation. An error from the true length (TL) is introduced if the expected length (EL) is calibrated along this horizontal optical plane. Lever arm length (LAL), initial fiber length (FLi), connector length (CL), and the magnitude of EL all contribute to this error. A mathematical model was used to determine the TL during shortening (0.96–0.80FLi) and lengthening (1.10–1.50FLi) at a constant LAL of 13.6mm. CL had the greatest impact on error. For FLi=2mm at the longest CL modeled (15mm), an expected shortening of 0.20FLi produced a true shortening of ∼0.17FLi, and an expected stretch to 1.50FLi resulted in a true stretch to almost 1.60FLi. Under these conditions, the true sarcomere length would be 4% and 6% longer than expected during shortening and lengthening, respectively. Because of their non-linear nature, length errors at long CL's may result in an over-estimation of unloaded shortening velocity during slack tests and a left-ward shift in the passive tension-fiber length relationship at long fiber lengths. Measurement errors decreased dramatically with shorter CL's, becoming negligible (<1%) at CL=3mm. We recommend that investigators keep CL as short as possible. Alternatively, we provide a method for adjusting the magnitude of the EL to yield a desired TL.

Shear resistance of channel shear connectors in plain, reinforced and lightweight concrete

This paper presents an experimental study on determining shear resistance of channel shear connectors in a solid concrete material slab under monotonic loading. The solid concrete slab is of different types of concrete including plain, reinforced and lightweight concrete. The channel shear connector length is varied as well. A series of push-out specimens were tested for this study. The results verified using channel shear connectors embedded in lightweight concrete in composite structures and shows that lightweight concrete has a slight effect on the ductility and load-displacement performance of the specimens. However, using reinforcement in concrete causes considerable increase in ultimate strength and ductility of channel shear connectors and using channels embedded in unconfined normal concrete has a brittle performance of them. In general, the channel shear connector showed a ductile behaviour.

Correction of Error in Fiber Length Due to Lever Arm Rotation During Mechanical Tests of Single Muscle Fibers

The single muscle fiber preparation is a popular technique to assess mechanical properties at the cellular level and how these properties change with aging, disease, exercise, etc. Fibers are usually attached to wires extending perpendicularly from the lever arm of a high speed motor and force transducer that are then mounted to the stage of a microscope. Because of lever arm rotation, the fiber does not move along the optical plane, introducing a length measurement error if length is measured along the optical plane. The purpose of this study was to 1) calculate the error of lever arm movement and 2) provide a correction equation. The error was calculated assuming 2 mm fiber length at up to 50% displacement, because this is a commonly used stretch or slack magnitude (∼15% slacking with unloaded shortening velocity, ∼30% lengthening response to eccentric contraction, ∼50% stretch with passive tension). The range of error was hyperbolically enlarged as either lever arm length or optical plane stretch magnitude increased, and this error was exacerbated with the increase of both factors. For example, with a 5 mm connector attached to the lever arm, the relative error [100×(actual displacement-target displacement)/target displacement] was 0.59%, 1.36%, and 1.78% with 10, 30, and 50% of stretch or slacking, respectively. However, with a 10 mm connector, the relative error was 2.38%, 5.66%, and 7.64%, and in the case of a 15 mm connector, the relative error increased dramatically up to 5.36%, 12.69%, and 17.10%. We suggest the following correction equation to eliminate potential errors; q=b+f−r|mT+1|/(m2T2+m2+T2+1)1/2, where q = observed fiber length, b=connector length, f=fiber length, h=lever arm length, r=(b2+h2)1/2, m=-h/(b+f), T=[p2-(d-r)1/2/(d2+r2-p2)]1/2, p=target fiber length, and d=[(b+f)2+h2]1/2.

Investigation of a Special 6-6 Parallel Platform for Contour Milling

Recently, companies have been experimenting with parallel-mechanism based approaches for milling machines. This research presents an investigation into the development of a special 6-6 parallel mechanism for application to contour milling. The idea behind this approach is that existing non-CNC milling equipment can be augmented to increase its capability at a lower cost than purchasing traditional 5-axis machining centers. This paper presents the phase of research associated with developing a parametric kinestatic design methodology for a special 6-6 parallel mechanism (Kinestatic Platform, KP). This methodology was applied to the design specifications associated with 5-axis contour milling. The resulting kinestatic design’s dynamics were evaluated to determine the actuation requirements of each connector. A prototype connector was built to allow the evaluation of actuator response under simulated loading conditions. Joint stiffness and control strategy were of primary concern in evaluating the performance of the prototype connector. The parametric kinestatic design and control strategy results are presented. Several observations are evidenced from the research. Joint deflection is an obvious critical issue and the most difficult to quantify. A scheme is proposed detailing the concept of using a separate metrology frame to overcome difficulties associated with accurate connector length determination. [S1087-1357(00)70101-8]

High-resolution transmission electron microscopy of the nanostructure of melamine-formaldehyde aerogels

The transparency of melamine-formaldehyde (MF) aerogels strongly depends on the solution pH during polymerization. Two MF aerogels were studied. MF #1 was transparent and was formed at pH ⋍ 2 with a bulk density of 160 kg/m 3 and a Brunauer, Emmett and Teller (BET) surface area of 970 m 2/gm. MF #2 was an opaque aerogel formed at pH ⋍ 0.5 with a bulk density of 130 kg/m 3 and a surface area of 850 m 2/gm. Both MF aerogels have a polymeric nanostructure. Melamine and formaldehyde formed single polymeric chains of ⋍ 0.95 nm in diameter. The MF #1 aerogel connectors were frequently composed of two or three polymeric chains with the connector diameter averaging ⋍ 2.0 and ⋍ 2.8 nm which usually showed branching every 12.6 ± 4.5 nm thereby defining the connector length. The side chains along the connectors in MF #1 formed a reticular MF matrix. The MF #1 matrix pores averaged 10.4 ± 5.5 nm and pores between sections of the MF matrix averaged 28.8 ± 19 nm. In MF #2, the connectors also formed side chains but these side chains did not form a reticular matrix. As a consequence, the connector diameter, 8.8 ± 5.8 nm, includes the side chains projecting from a core chain of 1.9 ± 0.7 nm. In addition to the average pore size of 47.7 ± 30 nm, MF #2 contained cavities or voids within the aerogel with length dimensions averaging 328 ± 130 nm, responsible for its opacity. The high BET surface areas of both MF aerogels correlate with their polymeric structure.

Interaction of multichip module substrates with high-density connectors

The stresses and strains in substrate-connector systems in multichip modules (MCMs) are discussed. Simultaneous stresses were applied as structural loads in combined stress models. Modeling results show that definite relations exist between connector pitch, length, substrate thickness and material, and stresses in a connector body. >

The domino billiard

We study one-dimensional chains of billiards, where it is possible to switch between order and disorder in two respects: regular versus chaotic scattering in the billiards, and periodic versus random length sequence of the connecting pipes. Classically, the dynamics is largely dominated by the type of the scatterers. Quantum mechanically, the connector length sequence is also decisive: there are extended states and a band spectrum if it is periodic, whereas if it is random, states are localized and the spectrum is discrete. In this case, the spectral statistics forms a transition between GOE (for short chains, compared to the localization length) and Poissonian (for very long chains) and can be related to the way a corresponding classical ensemble explores phase space.

Bond-length and bond-angle distributions in coarse-grained polymer chains

The joint distribution pN(ω,R1,R2) of the lengths of the vectors (R1,R2) and the angle ω between the vectors joining the center of mass of a block or bead in a chain with the centers of mass of the preceding and succeeding beads of a coarse-grained chain is investigated. Somewhat unexpectedly, the a priori and the conditional distributions for the connector length pRN(R1) and for the interconnector angle pωN(ω) can be determined in closed form for the Gaussian random walk for any number of monomers N per bead. Additionally, pωN(ω) is also obtained for an unperturbed polymethylene chain by a Monte Carlo scheme. In general, pωN(ω) is asymmetric and shifted to values greater than π/2 for all bead sizes, implying that the chain made up of the centers of mass of the beads tends to be locally more extended or spread out than a random walk. Convergence to the (analytically known) asymptotic distribution pω∞(ω) for the Gaussian random walk is given analytically and turns out to be very nearly quadratic in 1/N. For the polymethylene chain convergence is linear. The a priori and the conditional distributions are used to formulate a Monte Carlo scheme for the generation of the coarse-grained chain. The bias of pωN(ω) to angles greater than π/2 should be taken into account by any model that attempts to represent a linear chain polymer by lumping its detailed structural information in coarser units at a larger length scale.

スタッドコネクタのせん断耐力と合成ばりの挙動に関する実験的研究

This paper proposes the shear strength of stud connectors and behaviors of composite beams. The experimental work of the investigation reported herein is consisted of tests of 26 solid Push-out specimens, 24 Deck Push-out specimens and 15 composite beams. From this study, we could find out the following conclusions. 1. The shear strength of stud connectors in solid slab is also concerned with exponent function of cross-sectional areas of stud connectors. 2. The shear strength of stud connectors with Deck is concerned with Deck ribs ratio and stud connector length above ribs. 3. Effective moment of inertia and effective section modulus of partial composite beams are concerned with exponent function α=1/3 of composite degrees.

25—ANALYSES OF SPRING-UNDERMOTION SUB-MECHANISMS

The spring parameters that affect the form of the undermotion-force-lift characteristic are discussed. The method of analysis previously described is then applied to specific undermotion submechanisms. The usual form of spring-side mechanism is analysed in terms of two geometrical parameters, and the ways in which both the theoretical working range and the form of the force-angular-position characteristic depend on these parameters are determined. For springs with initial tension, this requires that the spring index and material and the effective lengths of the rigid spring connectors be assumed. The general effects of changes in this index and connector length are indicated. The contributions to the characteristic of two common types of connexion from heald frame to undermotion are also determined and shown to be small. Finally, the results of a comparison of the proposed method of analysis with a direct analysis of a complete undermotion are given.

Natural frequencies of two cantilevers joined by a rigid connector at their free ends

The derivation of the equations of motion is given for a system consisting of two identical parallel cantilevers joined by a rigid connector at their free ends. Elementary beam theory is employed, and it is observed that the longitudinal and flexural deformations of the system are coupled through the boundary conditions but not through the differential equations. The associated free vibration problem is solved, and it is shown that the frequency determinant can be factored, yielding two independent frequency equations. One of these corresponds to the pure, free longitudinal motion of a pair of rods connected by a rigid body at their tips (both rods being equally stretched or compressed simultaneously), whereas the second and more complicated frequency equation is pertinent for the system undergoing flexural deformations in both rods, stretching in one rod, and compression in the other. This latter frequency equation is solved numerically, and the variations of the first six natural frequencies with connector thickness and length parameters are displayed graphically. Two orthogonality conditions for the eigenfunctions are derived, and a relatively simple form for the normalizing factor is presented.