Degree Of Twist Research Articles

Perforator flaps in hand reconstruction: the effect of blood vessel twisting.

Background and aimsPerforator flaps increasingly find acceptance and use in hand reconstructive surgery. A propeller flap is an island flap that moves from one orientation to another by rotating around its vascular pedicle. It is now possible to design propeller flaps based on a single perforator, so-called “perforator-based propeller flaps,” but they are more prone to vascular impairment when twisted more than 90°.MethodsWe present a prospective study conducted in the Plastic and Reconstructive Surgery Department of the Rehabilitation Hospital over 17 months. All perforator-based propeller flaps that were used for hand reconstruction were analyzed. The parameters studied included the size and location of the defect, the size and shape of the flap, the perforator (length and location) that was used, the degree of twisting of the perforator, the degree of perforator dissection, the management of the donor site, and flap survival area.ResultsIn this study we investigated the circulatory impairment induced by twisting of the pedicle on a true perforator flap. All flaps survived completely with the exception of partial skin necrosis in few cases. Some of these cases required debridement and skin grafting.ConclusionsPerforator-based propeller flaps provide a reliable option for covering small- to medium-size hand complex tissue defects. They have the advantages of using similar tissues in reconstruction, not damaging another area, they do not require main vessels sacrifice, and the donor site can be generally directly closed.

Influence of GA-BP Artificial Neural Network Based on PCA Dimension Reduction in Yarn Tenacity Prediction

The fiber characteristics directly affecting the yarn tensile properties are analyzed and the features of GA-BP artificial neural network are presented. Based on the interrelationship among the fiber characteristics, which could led to a worse predicting result, Principal component analysis (PCA) is adopted to solve this problem. 12 characteristics of cotton fiber tested by HVI or AFIS and yarn process parameters, such as combing, degree of twist, yarn count, was preprocessed by this method and 10 independent comprehensive indexes are induced and substituted into GA-BP artificial neural network as input factors. For further comparison, the 10 dimension reduced indexes and the 15 initial variables are respectively introduced into the GA-BP and BP artificial neural network to develop 4 prediction models. By comparing the accuracy in predicting yarn tenacity, it is concluded that GA-BP model has higher accuracy than BP model, and the dimension reduced indexes based on PCA would decrease the accuracy in prediction instead. So, blindly using PCA method for reducing the complex correlation among input variables was not helpful for the prediction accuracy.

Large Area Plan-View Transmission Electron Microscopy Sample Preparation for Direct-Bonded Interfaces

A focused ion beam (FIB) sample preparation technique is developed to produce large areas of electron transparent material for plan-view transmission electron microscopy measurements from direct-bonded interfaces without thinning the bonded wafers. A FIB cut allows plan-view sample creation from the bonded interface region, and therefore rapid characterization of the defect density as a function of bonding conditions, substrate miscut, or pre-bonding surface treatments. Uniform electron transparent plan-view areas are extracted from the interface region to facilitate observation of the interface reconfiguration. To demonstrate the technique, the electrically active interfaces of a series of bonded III-V structures is studied as a function of substrate miscut as well as in-plane misorientation. Distinct differences in the interface reconstruction are observed and the interface reconstruction produces screw and edge dislocation networks at the III-V interfaces. The degree of twist and tilt is confirmed with both cross section electron microscopy measurements as well as in-plane x-ray diffraction measurements.

Crystal structure of 4-meth-oxy-N-phenyl-benzamide.

In the title mol­ecule, C14H13NO2, the dihedral angle between the planes of the benzene rings is 65.18 (4)°. The central amide group has about the same degree of twist with respect to both ring planes, as indicated by the dihedral angles of 34.70 (8) and 30.62 (8)° between its plane and that of the phenyl and 4-meth­oxy­benzene rings, respectively. The C atom of the meth­oxy group is close to being coplanar with its attached ring [deviation = −0.112 (2) Å]. In the crystal, mol­ecules are linked by inter-amide N—H⋯O hydrogen bonds, which generate C(4) chains propagating in the [100] direction. Adajcent mol­ecules in the chain are related by translational symmetry.

Magnetic Tweezers for the Measurement of Twist and Torque

Single-molecule techniques make it possible to investigate the behavior of individual biological molecules in solution in real time. These techniques include so-called force spectroscopy approaches such as atomic force microscopy, optical tweezers, flow stretching, and magnetic tweezers. Amongst these approaches, magnetic tweezers have distinguished themselves by their ability to apply torque while maintaining a constant stretching force. Here, it is illustrated how such a “conventional” magnetic tweezers experimental configuration can, through a straightforward modification of its field configuration to minimize the magnitude of the transverse field, be adapted to measure the degree of twist in a biological molecule. The resulting configuration is termed the freely-orbiting magnetic tweezers. Additionally, it is shown how further modification of the field configuration can yield a transverse field with a magnitude intermediate between that of the “conventional” magnetic tweezers and the freely-orbiting magnetic tweezers, which makes it possible to directly measure the torque stored in a biological molecule. This configuration is termed the magnetic torque tweezers. The accompanying video explains in detail how the conversion of conventional magnetic tweezers into freely-orbiting magnetic tweezers and magnetic torque tweezers can be accomplished, and demonstrates the use of these techniques. These adaptations maintain all the strengths of conventional magnetic tweezers while greatly expanding the versatility of this powerful instrument.

Magnetic tweezers for the measurement of twist and torque.

Single-molecule techniques make it possible to investigate the behavior of individual biological molecules in solution in real time. These techniques include so-called force spectroscopy approaches such as atomic force microscopy, optical tweezers, flow stretching, and magnetic tweezers. Amongst these approaches, magnetic tweezers have distinguished themselves by their ability to apply torque while maintaining a constant stretching force. Here, it is illustrated how such a “conventional” magnetic tweezers experimental configuration can, through a straightforward modification of its field configuration to minimize the magnitude of the transverse field, be adapted to measure the degree of twist in a biological molecule. The resulting configuration is termed the freely-orbiting magnetic tweezers. Additionally, it is shown how further modification of the field configuration can yield a transverse field with a magnitude intermediate between that of the “conventional” magnetic tweezers and the freely-orbiting magnetic tweezers, which makes it possible to directly measure the torque stored in a biological molecule. This configuration is termed the magnetic torque tweezers. The accompanying video explains in detail how the conversion of conventional magnetic tweezers into freely-orbiting magnetic tweezers and magnetic torque tweezers can be accomplished, and demonstrates the use of these techniques. These adaptations maintain all the strengths of conventional magnetic tweezers while greatly expanding the versatility of this powerful instrument.

A Rare Case of Testicular Torsion in a 75 Year Old

Background: Testicular torsion occurs when a testicle torts on the spermatic cord resulting in the cutting off of blood supply. The most common symptom is acute testicular pain and the most common underlying cause, a bell-clapper deformity. Testicular torsion implies obstruction of first venous, and later, arterial flow. The extent of testicular ischemia will depend on the degree of twisting (180°-720°) and the duration of the torsion. Testicular salvage is more likely in patients treated within 4-6 hours after the onset of torsion. Case Presentation: We came across an unusual case of testicular torsion in a 75 years old man,who presented to our emergency department with a 7 days history of right-sided testicular pain with no pyrexia,urinary symptoms and negative urine routine ,initially treated with antibiotics elsewhere as torsion amongst the elderly population is rarely described. This case presents the oldest surgically confirmed case of testicular torsion, in a 75-year-old male, documented in a journal so far .There was no pyrexia or urinary symptoms and negative urine routine. In adults above the age of 40, likely diagnoses include epididymo-orchitis, epididymitis, neoplasm or hydrocele. Clinical differentiation with epididymo-orchitis can be difficult in any age range. Clinical signs such as fever, elevated C-reactive protein and positive urine test are suggestive of epididymo-orchitis/orchitis. Conclusion: This case study demonstrates that testicular torsion can occur at any age, and clinical suspicion should always be high in patients presenting with testicular pain and a negative urine tests, regardless of age. Although risk in this subgroup is low, the identification of a potentially reversible testicular abnormality should be of high priority.

Effect of microfibril twisting on theoretical powder diffraction patterns of cellulose Iβ

Previous studies of calculated diffraction patterns for cellulose crystallites suggest that distortions that arise once models have been subjected to MD simulation are the result of both microfibril twisting and changes in unit cell dimensions induced by the empirical force field; to date, it has not been possible to separate the individual contributions of these effects. To provide a better understanding of how twisting manifests in diffraction data, the present study demonstrates a method for generating twisted and linear cellulose structures that can be compared without the bias of dimensional changes, allowing assessment of the impact of twisting alone. Analysis of unit cell dimensions, microfibril volume, hydrogen bond patterns, glycosidic torsion angles, and hydroxymethyl group orientations confirmed that the twisted and linear structures collected with this method were internally consistent, and theoretical powder diffraction patterns for the two were shown to be effectively indistinguishable. These results indicate that differences between calculated patterns for the crystal coordinates and twisted structures from MD simulation can result entirely from changes in unit cell dimensions, and not from microfibril twisting alone. Although powder diffraction patterns for models in the 81-chain size regime were shown to be unaffected by twisting, suggesting that a modest degree of twist is not inconsistent with experimental data, it may be that other diffraction techniques are capable of detecting this structural difference. Until such time as definitive experimental evidence comes to light, the results of this study suggest that both twisted and linear microfibrils may represent an appropriate model for cellulose Iβ.

Мультиспецифичные промоторные островки как участки генома с необычными структурными и функциональными свойствами

The study is aimed at unusual genomic regions of E. coli - mixed promoter islands, which possess high density of potential transcription initiation points. They were predicted by promoter finder PlatPromU, without the consideration of conservative elements, recognized by σ-subunits of RNA polymerase, thus they are supposed to interact with polymerase, which has different σ-factors. We found that the structural and functional properties of mixed promoter islands are very similar to those of promoter islands, previously revealed by the algorithm PlatProm, which was adjusted to the search for σ 70 -specific promoters of E. coli. Thus, both types of islands are preferentially located in the regulatory regions of genes acquired by horizontal transfer. Their double helix is characterized by a higher degree of curvature and twisting, compared to normal promoters. Both types of islands have a higher capacity to form complexes with RNAP, than normal promoters, but lower ability to initiate productive transcription. This suppression can be largely explained by the advanced ability of islands to interact with the histone-like inhibitory protein H-NS. However, RNA synthesis from the promoter island associated with the gene appY, increased upon its transfer into the plasmid pET28b-eGFP and showed dependence not only from the presence of H-NS binding sites, but also from the spatial configuration of the neighboring areas. That means that conformational changes in the genome can increase the transcriptional activity from the islands, delivering the products of adjacent genes for metabolic needs of the bacterial cell.

Peripartum Cardiomyopathy Associated With Left Ventricular Noncompaction Phenotype and Reversible Rigid Body Rotation

A 30-year-old woman presented 1-month postpartum with new-onset biventricular heart failure for which no other contributing cause could be found clinically or on laboratory investigations. Her 2 previous pregnancies were uncomplicated. She was HIV-positive for the preceding 3 years, but had never been on antiretroviral therapy. Initial echocardiography revealed a left ventricular (LV) end-diastolic diameter of 59 mm and LV ejection fraction of 32% (online-only Data Supplement Movies 1 and 2). There was evidence of LV noncompaction involving the apex and midinferior and midlateral walls of the LV that satisfied the Jenni criteria (Figure 1). There was no echocardiographic evidence of other congenital or organic valvular disease. Speckle tracking revealed rigid body rotation (ie, rotation at both the basal and apical levels of the LV occurred in a counterclockwise direction during systole; Figure 2). The patient was treated with furosemide, carvedilol, an angiotensin-converting enzyme inhibitor, and spironolactone. On reevaluation 6 months later, her functional status was New York Heart Association Class 1. Echocardiography revealed that LV ejection fraction was now 48% …

Helical graphite

One-handed helical graphite films with a structure controlled by that of the original iodine-doped helical polyacetylene (H-PA) films were prepared using the recently developed morphology-retaining carbonization method. The fibrillar structure of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10–29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same structure as that of the precursor films. The screw direction, degree of twist, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the sense and pitch of the helix, and the orientation of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. The important potential of these graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an increase in electrical conductivity compared to the nonaligned one. The aligned helical graphite film also shows an electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis. [TANSO 2013 (No. 258) 201–9.]

Remote Sensing with a Twist

Physics Our eyes sense light that has bounced off objects, with our brain then making sense of the input flowing through the optic nerve. In this case, the photons that hit our eyes must interact with the object. However, it is possible to get information about an object using photons that have not actually hit the object. This counterintuitive process of ghost imaging follows from the quantum-mechanical properties of photons and the ability to find correlations between specially generated pairs of photons. Uribe-Patarroyo et al. use such correlations between beams of light that have been imprinted with specific values of optical angular momentum: The light beam is effectively twisted, with the photons mapping out a spiral as they propagate. Using correlated photons produced by parametric downconversion, whereby a high-energy photon is converted into a pair of correlated photons of lower energy, they send one of the photons to the object and hold on to the other. When the photon hits the object, the process of that interaction changes its degree of twist and in turn affects the correlation between the pair. The object can then be determined by looking at changes in the correlations between the two photons. With a modification of the experimental setup, it should be possible to remotely sense reflective targets at large distances, with the target unaware that it is being watched. Phys. Rev. Lett. 110 , 043601 (2013).

The Relative Biologic Effectiveness versus Linear Energy Transfer Curve as a Cell Trait

The magnitude of biological response varies with different radiation types. Using Linear Energy Transfer (LET) to differentiate types of incident radiation beam, the Relative Biologic Effectiveness (RBE) as a function of LET (RBE-LET) was found to have a characteristic shape with a peak around LET values 100 - 200 eV/nm. This general feature is believed to be a property of the incident beam. Our systems engineering model, however, suggests that the shape of the RBE-LET curve is a cell trait, a property of the cell. Like any other trait, phenotypic variations result from interactions of the genes and their context. State-space block diagram of the differential equation model suggests the genes are those in the DNA double strand break (dsb) repair pathway; and the context is cellular stress responsing to DNA damage by both external stimuli and internal redox state. At a deeper level, the block diagram suggests cell using mathematical calculations in its decision-making when facing a stress signal. The MRN protein complex, in particular, may perform addition to count the degree of DNA twisting for the homeostatic regulation of DNA supercoiling. The ATM protein may act as a feedback amplifier.

Transverse kink oscillations in the presence of twist

Magnetic twist is thought to play an important role in coronal loops. The effects of magnetic twist on stable magnetohydrodynamic (MHD) waves is poorly understood because they are seldom studied for relevant cases. The goal of this work is to study the fingerprints of magnetic twist on stable transverse kink oscillations. We numerically calculated the eigenmodes of propagating and standing MHD waves for a model of a loop with magnetic twist. The azimuthal component of the magnetic field was assumed to be small in comparison to the longitudinal component. We did not consider resonantly damped modes or kink instabilities in our analysis. For a nonconstant twist the frequencies of the MHD wave modes are split, which has important consequences for standing waves. This is different from the degenerated situation for equilibrium models with constant twist, which are characterised by an azimuthal component of the magnetic field that linearly increases with the radial coordinate. In the presence of twist standing kink solutions are characterised by a change in polarisation of the transverse displacement along the tube. For weak twist, and in the thin tube approximation, the frequency of standing modes is unaltered and the tube oscillates at the kink speed of the corresponding straight tube. The change in polarisation is linearly proportional to the degree of twist. This has implications with regard to observations of kink modes, since the detection of this variation in polarisation can be used as an indirect method to estimate the twist in oscillating loops.

Structural origin of polymorphism of Alzheimer's amyloid β-fibrils

Formation of senile plaques containing amyloid fibrils of Aβ (amyloid β-peptide) is a pathological hallmark of Alzheimer's disease. Unlike globular proteins, which fold into unique structures, the fibrils of Aβ and other amyloid proteins often contain multiple polymorphs. Polymorphism of amyloid fibrils leads to different toxicity in amyloid diseases and may be the basis for prion strains, but the structural origin for fibril polymorphism is still elusive. In the present study we investigate the structural origin of two major fibril polymorphs of Aβ40: an untwisted polymorph formed under agitated conditions and a twisted polymorph formed under quiescent conditions. Using electron paramagnetic resonance spectroscopy, we studied the inter-strand side-chain interactions at 14 spin-labelled positions in the Aβ40 sequence. The results of the present study show that the agitated fibrils have stronger inter-strand spin-spin interactions at most of the residue positions investigated. The two hydrophobic regions at residues 17-20 and 31-36 have the strongest interactions in agitated fibrils. Distance estimates on the basis of the spin exchange frequencies suggest that inter-strand distances at residues 17, 20, 32, 34 and 36 in agitated fibrils are approximately 0.2 Å (1 Å=0.1 nm) closer than in quiescent fibrils. We propose that the strength of inter-strand side-chain interactions determines the degree of β-sheet twist, which then leads to the different association patterns between different cross β-units and thus distinct fibril morphologies. Therefore the inter-strand side-chain interaction may be a structural origin for fibril polymorphism in Aβ and other amyloid proteins.

Excitation of Orbital Angular Momentum Resonances in Helically Twisted Photonic Crystal Fiber

Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.

Defects in crystalline packings of twisted filament bundles. II. Dislocations and grain boundaries

Twisted and ropelike assemblies of filamentous molecules are common and vital structural elements in cells and tissues of living organisms. We study the intrinsic frustration occurring in these materials between the two-dimensional organization of filaments in cross section and out-of-plane interfilament twist in bundles. Using nonlinear continuum elasticity theory of columnar materials, we study the favorable coupling of twist-induced stresses to the presence of edge dislocations in the lattice packing of bundles, which leads to a restructuring of the ground-state order of these materials at intermediate twist. The stability of dislocations increases as both the degree of twist and lateral bundle size grow. We show that in ground states of large bundles, multiple dislocations pile up into linear arrays, radial grain boundaries, whose number and length grows with bundle twist, giving rise to a rich class of "polycrystalline" packings.

Defects in crystalline packings of twisted filament bundles. I. Continuum theory of disclinations

We develop the theory of the coupling between in-plane order and out-of-plane geometry in twisted, two-dimensionally ordered filament bundles based on the nonlinear continuum elasticity theory of columnar materials. We show that twisted textures of filament backbones necessarily introduce stresses into the cross-sectional packing of bundles and that these stresses are formally equivalent to the geometrically induced stresses generated in thin elastic sheets that are forced to adopt spherical curvature. As in the case of crystalline order on curved membranes, geometrically induced stresses couple elastically to the presence of topological defects in the in-plane order. We derive the effective theory of multiple disclination defects in the cross section of bundle with a fixed twist and show that above a critical degree of twist, one or more fivefold disclinations is favored in the elastic energy ground state. We study the structure and energetics of multidisclination packings based on models of equilibrium and nonequilibrium cross-sectional order.

Controlled Conjugated Backbone Twisting for an Increased Open-Circuit Voltage while Having a High Short-Circuit Current in Poly(hexylthiophene) Derivatives

Conjugated polymers with nearly planar backbones have been the most commonly investigated materials for organic-based electronic devices. More twisted polymer backbones have been shown to achieve larger open-circuit voltages in solar cells, though with decreased short-circuit current densities. We systematically impose twists within a family of poly(hexylthiophene)s and examine their influence on the performance of polymer:fullerene bulk heterojunction (BHJ) solar cells. A simple chemical modification concerning the number and placement of alkyl side chains along the conjugated backbone is used to control the degree of backbone twisting. Density functional theory calculations were carried out on a series of oligothiophene structures to provide insights on how the sterically induced twisting influences the geometric, electronic, and optical properties. Grazing incidence X-ray scattering measurements were performed to investigate how the thin-film packing structure was affected. The open-circuit voltage and charge-transfer state energy of the polymer:fullerene BHJ solar cells increased substantially with the degree of twist induced within the conjugated backbone--due to an increase in the polymer ionization potential--while the short-circuit current decreased as a result of a larger optical gap and lower hole mobility. A controlled, moderate degree of twist along the poly(3,4-dihexyl-2,2':5',2''-terthiophene) (PDHTT) conjugated backbone led to a 19% enhancement in the open-circuit voltage (0.735 V) vs poly(3-hexylthiophene)-based devices, while similar short-circuit current densities, fill factors, and hole-carrier mobilities were maintained. These factors resulted in a power conversion efficiency of 4.2% for a PDHTT:[6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) blend solar cell without thermal annealing. This simple approach reveals a molecular design avenue to increase open-circuit voltage while retaining the short-circuit current.

Manufacture of knit products from silica and carbon fibers

This article describes the properties of silica and carbon fibers that affect their conversion into knit products: degree of twist, stiffness in bending, drag coefficients, etc. Optimizing the processing of non-traditional fibers on knitting machinery makes it possible to balance the forces that act on the fibers during the stitching operation. The phenomena that lead to damage and breakage of the fibers are described, and recommendations are presented on reducing the values of the coefficients that characterize the tangential drag of fibers of the given type and the drag associated with their movement through the needles.