Loss Of Curvature Research Articles

Bending Actuators with Maximum Curvature and Force and Zero Interfacial Stress

Stress at the interface of a bilayer actuator can lead to delamination, and this stress increases with the difference in the Young’s moduli of the two layers. In this study, an actuator that includes a third ‘buffer’ layer is modeled, and it is shown how optimization of the thickness and modulus of this layer can reduce stress at that interface to zero, with no loss of curvature and only a small loss in force. A polypyrrole (PPy)/conducting polymer/gold trilayer is used as a model system, with the aim of reducing stress at the weak polymer/gold interface. For a 450 nm thick PPy layer with a Young’s modulus of 0.2 GPa, an intermediate layer of 150 nm thickness with a modulus of 5 GPa reduces the stress to zero with no loss of curvature and only a 7% loss in force compared to the bilayer case.

First aid and treatment for cervical spinal cord injury with fracture and dislocation

Background:Traumatic cervical spinal cord injury with subaxial fracture and dislocation not only indicates a highly unstable spine but can also induce life-threatening complications. This makes first aid critically important before any definitive operative procedure is undertaken. The present study analyzes the various first aid measures and operative procedures for such injury.Materials and Methods:Two hundred and ninety-five patients suffered from cervical spinal cord injury with fracture and dislocation. The average period between injury and admission was 4.5 days (range 5 h-12 weeks). The injury includes burst fractures (n = 90), compression fractures with herniated discs (n = 50), fractures and dislocation (n = 88) and pure dislocation (n = 36). Other injuries including developmental spinal canal stenosis and/or multi-segment spinal cord compression associated with trauma (n = 12), lamina fractures compressing the spinal cord (n = 6), ligament injuries (n = 7) and hematoma (n = 6) were observed in the present study. The injury level was C4 (n = 17), C5 (n = 29), C6 (n = 39), C7 (n = 35), C4-5 (n = 38), C5-6 (n = 58), C6-7 (n = 49), C4-6 (n = 16) and C5-7 (n = 14). According to the Frankel grading system, grade A was observed in 20 cases, grade B in 91, grade C in 124 and grade D in 60. One hundred and eighteen (40%) patients had a high fever and difficulty in breathing on presentation. First aid measures included early reduction and immobilization of the injured cervical spine, controlling the temperature, breathing support, and administration of high-dose methylprednisolone within eight hours of the injury (n = 12) and administration of dehydration and neurotrophy medicine. Oxygen support was given and tracheotomy was performed for patients with serious difficulty in breathing. Measures were taken to prevent bedsores and infections of the respiratory and urological systems. Two hundred and thirty six patients were treated with anterior decompression, 31 patients were treated by posterior approach surgery and combined anterior and posterior approach surgery was performed in a single sitting on 28 patients.Results:All patients were followed for 0.5-18 years (mean 11.8 years). At least one Frankel grade improvement was observed in 178 (60.3%) patients. In the anterior surgery group, the best results were observed in the cases with slight compressive fracture with disc herniation (44/50 patients, 88.0%). In the posterior surgery group, one Frankel grade improvement was observed in the cases with developmental spinal canal stenosis with trauma, lamina fractures, ligament injuries and hematoma (27/31, 87.1%). Most of the patients in the Frankel D group recovered normal neurological function after surgery. The majority of the patients with Frankel C neurological deficit (102/124) had the ability to walk postoperatively, while most of the seriously injured patients (Frankel A and B) had no improvement in their neurological function. Radiolographic fusion of the operated segments occurred in most patients within three months. Loss of intervertebral height and cervical physiological curvature was observed to varying degrees in 30.1% (71/236) of the cases in the anterior surgery group.Conclusion:First aid measures of early closed reduction or realignment and immobilization of the cervical spine, breathing support and high-dose methylprednisolone were most important in the treatment for traumatic spinal cord injury. Surgery should be performed as soon as the indications of spinal injury appear. The choice of the approach—anterior, posterior or both, should be based on the type of the injury and the surgeon's experience. Any complications should be actively prevented and treated.

Congenital Absence of Pericardium and Straight Back Syndrome: Do They Have Similarities?

The straight back syndrome, consisting of loss of normal upper thoracic spinal curvature is not an uncommon entity. In contrary congenital defects of the pericardium is a rare disease (1/10000 autopsies).In this report we present a case presented with chest pain whom after initial work up was presumed to have congenital absence of pericardium but further investigation uncovered the diagnosis as straight back syndrome. Here in we review the literature for the possible similarities between these two entities and the possible reason for our first misdiagnosis.

Polarization-Dependent Curvature Loss in Silicon Rib Waveguides

We show that the quasi-TM mode in silicon rib waveguides can experience significantly less curvature loss at the same bend radius than does the quasi-TE mode. Photonic devices making use only of the TM mode and a polarization-diversity scheme can, thus, profit from smaller possible bend radii and the resulting circuit-size reduction. The main loss mechanism for the quasi-TM rib mode can be coupling to the orthogonally polarized TE slab mode, which radiates power away from the waveguide. This is possible due to the slight hybridicity of the quasi-TM rib mode. Neglecting this hybridicity would lead to a significant underestimation of the curvature losses. Thus, accurate simulation of waveguides with low quasi-TM-mode curvature loss requires full-vectorial simulation models

The Gauss–Bonnet defect of complex affine hypersurfaces

We study the loss of curvature at the “ends” of a hypersurface in the affine space and we express it in terms of singularities at infinity.

COMPARACION DE LOS EFECTOS DE PRESERVANTES EN POSTCOSECHA DE LISIANTHUS (Eustroma grandiflorum L.)

Lisianthus is a crop that has been acquiring importance as a cut flower in Central Southern Chile. However, a number of preservation problems, related to its distribution in the local market, have been identified. The present study had the aim of increasing its preservation time as a cut flower, through the use of chemical preservatives, such as: Sucrose, sodium hypoclorite and organic preservatives such as Ethylene control which works as an ethylene absorbent. A pure water control was also included. A total of five variables were measured: Geotropism and stem curvature, petal and foliage colour loss, petal and floral bud abscission, pedicel stability or firmness and open flower weight variation. The complete random design was analysed using the Kruskal Wallis test and average means separation, using multiple separations. The use of Ethylene control was found to reduce the deterioration effects on cut flowers more effectively than sucrose and sodium hipoclorine application and water alone. After 15 days of storage at 4 o C and 85 % relative humidity, no significant difference was observed among the 3 treatments and the 5 quality parameters measured. The treatment using Ethylene control (T2) was more effective in reducing the Botrytis cinerea incidence and cold provoked damage than treatments T0 with pure water and T1 with sodium hypoclorite.

Dynamical and statistical effects of the intrinsic curvature of internal space of molecules

The Hamilton dynamics of a molecule in a translationally and/or rotationally symmetric field is kept rigorously constrained in its phase space. The relevant dynamical laws should therefore be extracted from these constrained motions. An internal space that is induced by a projection of such a limited phase space onto configuration space is an intrinsically curved space even for a system of zero total angular momentum. In this paper we discuss the general effects of this curvedness on dynamics and structures of molecules in such a manner that is invariant with respect to the selection of coordinates. It is shown that the regular coordinate originally defined by Riemann is particularly useful to expose the curvature correction to the dynamics and statistical properties of molecules. These effects are significant both qualitatively and quantitatively and are studied in two aspects. One is the direct effect on dynamics: A trajectory receives a Lorentz-like force from the curved space as though it was placed in a magnetic field. The well-known problem of the trapping phenomenon at the transition state is analyzed from this point of view. By showing that the trapping force is explicitly described in terms of the curvature of the internal space, we clarify that the physical origin of the trapped motion is indeed originated from the curvature of the internal space and hence is not dependent of the selection of coordinate system. The other aspect is the effect of phase space volume arising from the curvedness: We formulate a general expression of the curvature correction of the classical density of states and extract its physical significance in the molecular geometry along with reaction rate in terms of the scalar curvature and volume loss (gain) due to the curvature. The transition state theory is reformulated from this point of view and it is applied to the structural transition of linear chain molecules in the so-called dihedral angle model. It is shown that the curvature effect becomes large roughly linearly with the size of molecule.

The Memory Properties of Cold-Worked Titanium Rods in Scoliosis Constructs

Time series monitoring changes in titanium and stainless steel rod curvature kept at a constant temperature of 37 C as a function of time. To assess the possibility of loss of curvature in titanium rods after scoliosis surgery. Titanium rods have gained use in scoliosis surgery due to their excellent biocompatibility, while allowing medical personnel to obtain undistorted magnetic resonance imaging scans following surgery. However, the impression of several clinicians has been that when screw pullout and/or loss of sagittal balance occurs, it may be due to the rods losing some of their curvature. Five 6-mm rods of differing compositions and lengths (titanium 300 and 100 mm, stainless steel 300 and 100 mm, prebent titanium 85 mm) were bent at room temperature with a 3-point rod bender, then placed in an incubator at 37 C. Digital photographs were taken every 2 weeks and analyzed to extract the radius of curvature of each rod. The Ti rods had a significantly decreasing curvature with time. The prebent Ti and stainless steel rods did not exhibit significant change in curvature. Titanium rods bent at room temperature and then exposed to body temperature over time tend to exhibit "metal memory"; they gradually revert to their original shape. This may result in loss of sagittal balance and/or proximal screw pullout.

Loss of cervical spinal curvature during radiotherapy for head-and-neck cancers: the neck moves, too

Purpose We became concerned about our observation of the loss of the normal lordotic cervical spinal curvature during the course of radiotherapy (RT) for head-and-neck tumors. Our goal was to evaluate formally the cervical lordotic curve in 50 random patients by comparing the cervical spinal angles (CSAs) measured at the initiation of RT with the CSAs measured during the last week of RT. Methods and materials Fifty patients treated mono-isocentrically for head-and-neck cancer were selected randomly for review. All patients had custom-made masks, shoulder pulls, and multiple tattoos to ensure reproducibility. The CSA was defined as the angle formed by the line projected parallel to the posterior surface of C2 and the line projected parallel to C6. The measurements were done on the simulation film and the first and last port films. Results The average decrease in the CSA was 2.26° (SD ±2.19°). In patients with the isocenter placed as low as possible, the change was significantly more compared with the remaining population. (3.8° vs. 1.7°, p = 0.004). Conclusion Despite customized immobilization, the neck position changes during the course of RT for head-and-neck tumors. Patients with the isocenter placed very low have the least long-term reproducibility and a comfortable position may be best suited to intensity-modulated RT for such head-and-neck cancer patients.

Performance of clinical referral criteria for bone densitometry in patients under 65 years of age assessed by spine bone mineral density

Background: A case finding strategy based on a number of established risk factors has been suggested by Royal College of Physicians’ (RCP) guidelines to optimise bone densitometry referrals for assessment...

Design Optimisation Of The Head Of A HighprecisionOptical Polishing Machine

A highly deformable polishng tool has been specified for a revolutionary aspheric polishing system. This rubber tool is required to retain a spherical outer surface with minimal change in shape when subjected to internal pressure. It is proposed here that using a variable wall thickness around the tool will reduce deviations from the spherical shape. This paper describes a theoretical study carried out using finite element analysis to determine the optimum wall thickness variation. The component performance was judged against the three criteria of change in radius, center of curvature drift and loss of sphericity. A multi-criteria optimization code llnked to a parametric finite element model was used to analyze the problem and generate a set of Pareto optimal solutions. The characteristics of this Pareto set are described in this paper and used to explain the various deformation modes of the tool. It is concluded that varying the wall hckness will achieve the desired objective.

Optical time-domain reflectometry of bent plastic optical fibers

Optical time-domain reflectometry (OTDR) signals of step-index plastic optical fibers (POF's) and graded-index POF's were measured with a laser diode and an avalanche photodiode. When bent step-index and graded-index POF's were used, the OTDR signal behavior differed. The OTDR signal of the bent graded-index POF's had a step that corresponds to a curvature loss, but the step-index POF's had a spike signal at a bend, which indicated the occurrence of backscattering. The peak intensity was proportional to the square of the curvature. The refractive-index variation of the bent step-index POF's was measured, and the dependence of the peak intensity on the curvature was shown to agree with that predicted by the scattering from the refractive-index perturbation.

Autonomic straightening of gravitropically curved cress roots in microgravity.

The typical response of plant organs to gravistimulation is differential growth that leads to organ bending. If the gravitropic stimulus is withdrawn, endogenous compensation of the graviresponse and subsequent straightening occur in some plants. For instance, autonomic straightening of Lepidium roots occurs when gravitropically-curved rootsare rotated on a clinostat (Stankovi et al., 1998a). To determine whether endogenous compensation of the graviresponse also occurs in space, microgravity-grown cress roots were laterally centrifuged in-flight and then returned to microgravity using Biorack hardware on a shuttle mission (STS-81). The cress roots were centrifuged at 4 different g-doses (0.1 x g and 1 x g for 15 or 75 min). All four treatments yielded varying degrees of root curvature. Upon removal from the centrifuge, roots in all four treatments underwent subsequent straightening in microgravity. This straightening resulted from a loss of gravitropic curvature in older regions of the root and the coordinated alignment of new growth. These results show that both microgravity and clinostat rotation on Earth are equivalent in stimulus withdrawal with respect to the induction of endogenous compensation of the curvature. Cress roots are the only plant organ shown to undergo compensation of the curvature in both microgravity and on a clinostat. The compensation of graviresponse in space rules out the hypothesis that the endogenous root straightening ("autotropism") represents a commitment to a pre-stimulus orientation with respect to gravity and instead suggests that there is a default tendency towards axiality following a withdrawal of a g-stimulus.

A large targeted deletion of Hoxb1-Hoxb9 produces a series single-segment anterior homeotic transformations

Hox genes regulate axial regional specification during animal embryonic development and are grouped into four clusters. The mouse HoxB cluster contains 10 genes, Hoxb1 to Hoxb9 and Hoxb13, which are transcribed in the same direction. We have generated a mouse strain with a targeted 90-kb deletion within the HoxB cluster from Hoxb1 to Hoxb9. Surprisingly, heterozygous mice show no detectable abnormalities. Homozygous mutant embryos survive to term and exhibit an ordered series of one-segment anterior homeotic transformations along the cervical and thoracic vertebral column and defects in sternum morphogenesis. Neurofilament staining indicates abnormalities in the IXth cranial nerve. Notably, simultaneous deletion of Hoxb1 to Hoxb9 resulted in the sum of phenotypes of single HoxB gene mutants. Although a higher penetrance is observed, no synergistic or new phenotypes were observed, except for the loss of ventral curvature at the cervicothoracic boundary of the vertebral column. Although Hoxb13, the most 5' gene, is separated from the rest by 70 kb, it has been suggested to be expressed with temporal and spatial colinearity. Here, we show that the expression pattern of Hoxb13 is not affected by the targeted deletion of the other 9 genes. Thus, Hoxb13 expression seems to be independent of the deleted region, suggesting that its expression pattern could be achieved independent of the colinear pattern of the cluster or by a regulatory element located 5' of Hoxb9.

A SAXS Study of Microstructure Ordering Transitions in Liquid Crystalline Side-Chain Diblock Copolymers

For a series of side-chain liquid crystalline (LC) diblock copolymers we have investigated the overlap of liquid crystalline and morphological phase behaviors. LC thermal transitions were identified using polarized optical microscopy combined with calorimetry. Order−disorder and order−order transitions (ODT's and OOT's) associated with the diblock copolymer morphology were located using elevated temperature SAXS and TEM microscopy. At low LC fractions, samples exhibit pure lamellar morphologies, and the ODT temperature, TODT, is correlated to the LC isotropization temperature, Tiso. For samples with higher LC volume fractions, morphologies were found to have curvature at room temperatures, and the TODT was found to exceed Tiso. In one sample, we observed a thermoreversible OOT transition between a predominately lamellar morphology with cylindrical defects and a completely lamellar morphology. The loss of curvature occurs upon heating, which is unusual for a block copolymer OOT and may be related to the co...

Septation and differentiation of the embryonic human cloaca

Background/Purpose: Limitations in methodologies have fostered controversy regarding the septation of the human embryonic cloaca. The aim of this study was to evaluate the septation of the human embryonic cloaca.Methods: Using the Carnegie Embryological Collection and specimens at Johns Hopkins, Baltimore, MD, the authors studied 12 embryos and five fetuses. Embryo photomicrographs were reconstructed using three-dimensional modeling.Results: In Carnegie stage 13 the authors observed a cloaca, distinct primitive urogenital sinus, and anorectum separated by the urorectal septum. The primitive urogenital sinus and anorectum enter the cloaca separated from the amniotic space by the cloacal membrane. As the embryo becomes a fetus it lengthens, grows, expands and rotates through a process called transformation. Transformation gives rise to a loss of caudal curvature and a decrease in distance between the septum and membrane, but these structures do not fuse. Disintegration of the cloacal membrane produces openings for the urogenital sinus and anorectum.Conclusions: The observations suggest that the urogenital sinus and anorectum form early and are separated by the urorectal septum as a passive structure. There does not appear to be septation or differentiation of the cloaca itself.

Transition curvature analysis

On-track recording losses associated with transition curvature in a merged magnetoresistive-read/inductive-write recording system were investigated. Variations in write head design resulted in a wide variation of reproduced pulse width. Magnetic force microscope (MFM) observation of written tracks revealed that transition curvature was related to the pulse width variation. The effect of transition curvature is modeled as a separable loss function by convolving a reader cross-track sensitivity function with a cross-track phase delay profile. Curvature loss has a different spectral content than transition broadening, allowing us to separate the two effects by comparing discrete Fourier transforms of isolated pulses. Results of such an analysis agree satisfactorily with MFM measurements. Planarization of mid-shields had minimal impact on the pulse width, but a notched write head design mitigated the effect. Transition curvature must be taken into account during write head design and in decisions regarding relative read and write widths.

Combined effects of radiation, flame curvature, and stretch on the extinction and bifurcations of cylindrical CH 4/air premixed flame

The combined effects of flame radiation, stretch, and curvature on the extinction and flame bifurcations of the cylindrical premixed CH 4/air flames are numerically investigated with a detailed chemistry. The interaction between radiation heat loss and flame curvature is emphasized. The results show that a mixture below the standard limit can burn in the cylindrical flame configuration by imposing a moderate stretch rate. This flame is quenched either by radiation heat loss at low stretch rate or by incomplete combustion with an excessive stretch. As the fuel concentration increases, it is found that two kinds of flames, normal flame and weak flame, can exist at the same boundary conditions. A G-shaped extinction curve showing the flammable regions of these two flame regimes is obtained. The relation between the flammability limit of the cylindrical flame and the standard limit is discussed. Furthermore, comparisons between the cylindrical flame and the counterflow flame are made. The results show that the interaction of flame curvature and radiation heat loss greatly affects the flame strength and extinction. It is shown that flame curvature extends the radiation extinction limit and accelerates the opening up of the sublimit flame branch. Comparisons between the predicted results with the experimental data show good agreements both in the extinction limit and in the extinction flame diameter.

Autonomic straightening after gravitropic curvature of cress roots.

Few studies have documented the response of gravitropically curved organs to a withdrawal of a constant gravitational stimulus. The effects of stimulus withdrawal on gravitropic curvature were studied by following individual roots of cress (Lepidium sativum L.) through reorientation and clinostat rotation. Roots turned to the horizontal curved down 62 degrees and 88 degrees after 1 and 5 h, respectively. Subsequent rotation on a clinostat for 6 h resulted in root straightening through a loss of gravitropic curvature in older regions and through new growth becoming aligned closer to the prestimulus vertical. However, these roots did not return completely to the prestimulus vertical, indicating the retention of some gravitropic response. Clinostat rotation shifted the mean root angle -36 degrees closer to the prestimulus vertical, regardless of the duration of prior horizontal stimulation. Control roots (no horizontal stimulation) were slanted at various angles after clinostat rotation. These findings indicate that gravitropic curvature is not necessarily permanent, and that the root retains some commitment to its equilibrium orientation prior to gravitropic stimulation.

Analysis of curved bends in arbitrary optical devices using cylindrical coordinates

An extension of the beam propagation algorithm based on the method of lines (MoL–BPM) is proposed and substantiated for analysis of curved bends–constituent parts of complicated optical devices, connecting waveguides with different orientation. Cylindrical coordinates are introduced. The formulas are compatible with those in Cartesian coordinates for analysis of straight waveguides. So, in combination concatenations of curved bends and straight waveguides can be examined in a uniform way. For the purpose of analysis in cylindrical coordinates a suitable set of wave equations without any approximation and valid for a general hybrid case is derived. To prove the accuracy of the MoL–BPM in cylindrical coordinates applying the derived formulas, the curvature loss of a rib waveguide was computed and compared with other methods showing very good agreement. As an application of the method two straight waveguides are connected by a curved bend and the power flow is determined.