Different Mechanisms of Translational Symmetry Breaking in Liquid-Crystal Coil–Rod–Coil Triblock Copolymers

A molecular-statistical theory of coil–rod–coil triblock copolymers with orientationally ordered rod-like fragments has been developed using the density functional approach. An explicit expression for the free energy has been obtained in terms of the direct correlation functions of the reference disordered phase, the Flory–Huggins parameter and the potential of anisotropic interaction between rigid rods. The theory has been used to derive several phase diagrams and to calculate numerically orientational and translational order parameter profiles for different polymer architecture as a function of the Flory–Huggins parameter, which specifies the short-range repulsion and as functions of temperature. In triblock copolymers, the nematic–lamellar transition is accompanied by the translational symmetry breaking, which can be caused by two different microscopic mechanisms. The first mechanism resembles a low dimensional crystallization and is typical for conventional smectic liquid crystals. The second mechanism is related to the repulsion between rod and coil segments and is typical for block copolymers. Both mechanisms are analyzed in detail as well as the effects of temperature, coil fraction and the triblock asymmetry on the transition into the lamellar phase.

Failure Analysis of a Fractured Leaf Spring as the Suspension System Applied on the Dump Truck

A spring is a component which is designed to have relatively low stiffness compared to normal rigid rods, thereby making it possible to accept certain forces that are charged. A leaf spring is an important suspension component for heavy vehicles, as a failure of the leaf spring can cause severe if not fatal accidents. This study aims to investigate the factors that cause leaf spring failure in the form of a 125 PS dump truck vehicle suspension system. The method employed incorporated experimental and finite element analyses. The experimental work included visual observations, observation using a scanning electron microscope (SEM), hardness testing, and microstructure testing. Leaf spring modelling was conducted using Autodesk Inventor 2017 software, and the finite element analysis (FEA) was performed using Siemens ™ FEMAP V12.0.1 application software to calculate the maximum stress and strain that occurred near the crack tip of the leaf spring. The results from the analysis indicated that the cause of the fracture that occurred in leaf spring No. 3 was due to a defect discovered on the surface of the leaf spring. Based on the observations of the fracture surface, it is revealed that the cause of failure was due to the cyclic load experienced by the components during operation which caused crack propagation beginning from micro-cracks until reaching a significant dimension to cause a final fracture. In addition, the overload imposed on the leaf springs also caused maximum stress on the springs to increase, thus accelerating the failure of the leaf springs. Further results also showed that the value of the stress intensity factor, KI = 29.15 MPa.m1/2 was greater than the value of fracture toughness, KIC = 23 MPa.m1/2 of the spring material.

DNA topology dictates strength and flocculation in DNA-microtubule composites

Polymer composites are ubiquitous in biology and industry alike, owing to their emergent desirable mechanical properties not attainable in single-species systems. At the same time, polymer topology has been shown to play a key role in tuning the rheology of polymeric fluids. However, how topology impacts the rheology of composites remains poorly understood. Here, we create composites of rigid rods (microtubules) polymerized within entangled solutions of flexible linear and ring polymers (DNA). We couple linear and nonlinear optical tweezers microrheology with confocal microscopy and scaled particle theory to show that composites of linear DNA and microtubules exhibit a strongly non-monotonic dependence of elasticity and stiffness on microtubule concentration due to depletion-driven polymerization and flocculation of microtubules. In contrast, composites of ring DNA and microtubules show a much more modest monotonic increase in elastic strength with microtubule concentration, which we demonstrate arises from the increased ability of rings to mix with microtubules.

ICTV Virus Taxonomy Profile: Plectroviridae

Members of the family Plectroviridae produce particles that are non-enveloped rigid rods (70–280×10–16 nm). The supercoiled, circular, single-stranded DNA genome of about 4.5–8.3 kb, encodes 4–13 proteins. Viruses of this family infect cell wall-less bacteria, adsorbing to the bacterial surface, replicating their DNA by a rolling-circle mechanism or transposition, and releasing progeny from cells by extrusion, without killing the host. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Plectroviridae which is available at ictv.global/report/plectroviridae.

Evaluation of correction rates for titanium-alloy and cobalt-chrome-alloy rods in adolescent idiopathic scoliosis

<p><strong>Background: </strong>The customary treatment of AIS is spinal fusion with instrumentation using rigid rods. In parallel, agents such as, curve magnitude, points of fixation, level instrument selection, curve flexibility, kind of anchor rods used for patients and post-operative care are the main factors affecting the outcome of surgery.</p><p><strong>Methods: </strong>A total 50 patients was included in the study. The control group, which included 31 patients treated with Ti rods, was compared with an experimental group of 19 patients treated with CCM rods. Correction surgery was performed through posterior approach using rod-rotation maneuver after inserting a pedicle screw in each vertebrae within the fusion. Six-millimeter CCM and six-millimeter Ti rods were used in experimental and control groups, respectively. Pre and postoperative indices of coronal alignment and sagittal alignment were measured.</p><p><strong>Results: </strong>There was no statistical difference between the two groups for age, sex, Risser’s stage, preoperative Cobb’s angle, type and flexibility of curvature. The correction rate of thoracic curve was 71.4±10.2% for the CCM group and 71.8±6.1% for the Ti group. There were no statistical differences between the two groups for all coronal and sagittal factors (p&gt;0.05).</p><p><strong>Conclusions: </strong>AIS cases with double curvature, there was no statistically significant difference between Ti and CCM rods for coronal and sagittal plane correction rates. The derivations from biomechanical studies do not translate into clinical situations.</p>

Draping woven sheets

Motivated by the manufacture of carbon fibre components, this paper considers the smooth draping of loosely woven fabric over rigid obstacles, both smooth and nonsmooth. The draped fabric is modelled as the continuum limit of a Chebyshev net of two families of short rigid rods that are freely pivoted at their joints. This approach results in a system of nonlinear hyperbolic partial differential equations whose characteristics are the fibres in the fabric. The analysis of this system gives useful information about the drapability of obstacles of many shapes and also poses interesting theoretical questions concerning well-posedness, smoothness and computability of the solutions. doi:10.1017/S144618112000019X

Allosteric linkages that emulate a molecular motor enzyme

Allosteric mechanisms are fundamental to the operation of biomolecular motors. Recreating the molecular phenomena associated with allostery, from first principles, would help advance the design and construction of synthetic molecular motors, which remain quite simple compared natural motors. In this study, I present a model for generating allosteric interactions using mechanical linkages, which are devices in which flexible nodes are connected by rigid rods. I describe how allosteric information can be communicated between multivalent binding sites on an enzyme when linkages bind or dissociate in a stepwise fashion, which takes place stochastically according to assigned binding rates and partitioned binding energies. This design allows geometric competitions to autonomously push a linkage enzyme through a desired sequence of states, driven by consumption of a fuel. I use the model to emulate the chemical and conformational cycle of a myosin monomer, which is demonstrated by simulating chemical reaction networks of the linkage structures, and by describing how two linkage monomers can be connected together to construct a motor that walks on a track. This work shows how the complex behavior of biomolecular motors can be recapitulated with simple geometric and chemical principles that encode allosteric mechanisms. Because the concepts are material-agnostic, they can potentially be used to design and construct allosteric machines using various chemistries.