Variation In Rigidity Research Articles

Variations in Membrane Rigidity Induced by the Vesicle Trafficking Protein Sar1

Understanding how specific proteins manipulate the shape and form of membranes is crucial to understanding key biological functions. Membrane curvature generation enables the creation of structures such as intracellular transport vesicles, and also guides geometry-dependent protein localization. We focus on Sar1, a roughly 21.5 kDa GTPase of the COPII family of coat proteins, which initiates the assembly of coated vesicles at the endoplasmic reticulum. Our recent work has shown that the yeast (S. cerevisiae) Sar1p dramatically lowers membrane rigidity, and has an energetic preference for concave curvature (Settles et. al. Biophysical Journal, 99(5) pp. 1539 - 1545). Exploring the structurally similar mammalian Sar1 paralogs Sar1a and Sar1b, using both optical-trap based assays involving dynamic membrane deformation and microfabricated surfaces that present controlled curvatures to the proteins, we quantify the mechanical properties of Sar1-membrane interactions and delineate differences in the abilities of these proteins to lower the membrane bending modulus.

Effect of Point Source, Self-Reinforcement and Heterogeneity on the Propagation of Magnetoelastic Shear Wave

This paper investigates the propagation of horizontally polarised shear waves due to a point source in a magnetoelastic self-reinforced layer lying over a heterogeneous self-reinforced half-space. The heterogeneity is caused by consideration of quadratic variation in rigidity. The methodology employed combines an efficient derivation for Green’s functions based on algebraic transformations with the perturbation approach. Dispersion equation has been obtained in the closed form. The dispersion curves are compared for different values of magnetoelastic coupling parameters and inhomogeneity parameters. Also, the comparative study is being made through graphs to find the effect of reinforcement over the reinforced-free case on the phase velocity. It is observed that the dispersion equation is in assertion with the classical Love-type wave equation in the absence of reinforcement, magnetic field and heterogeneity. Moreover, some important peculiarities have been observed in graphs.

Variations in the geomagnetic cutoff rigidity of cosmic rays at individual points of the Asian region during the extreme events of 2003

The variations in the geomagnetic cutoff rigidity in Irkutsk, Alma-Ata, and Beijing in October–November 2003 were calculated using ground-based measurements of cosmic ray intensity from the worldwide network of stations and GOES spacecraft. The calculated variations in geomagnetic cutoff rigidity are presented together with D st variations of the geomagnetic field. The obtained results are compared to calculations performed using the Tsyganenko model of the magnetosphere.

Propagation of torsional surface wave in anisotropic poroelastic medium under initial stress

The present work deals with the possibility of propagation of torsional surface wave in fluid saturated poroelastic layer lying over nonhomogeneous elastic half space. Both the media are assumed to be under compressive initial stress. The half space has two types of inhomogeneity, viz; hyperbolic and quadratic. The dispersion equation for torsional wave in porous layer has been derived and observed that the presence of fluid in pores increases the velocity of the torsional surface wave but the phase velocity diminishes due to the presence of compressive initial stress in the porous layer. It is also observed that the velocity of the torsional surface wave increases due to the increase of initial stress in inhomogeneous half space. The inhomogeneity factor due to quadratic and hyperbolic variations in rigidity, density and initial stress of the medium decreases the phase velocity as it increases.

Reviewer’s comment on “The ‘X-Factor’ Index: a new parameter for the assessment of the adolescent idiopathic scoliosis correction” by Yuqing Sun et al. (ESJO-D-09-00493 R1)

According to Luk et al. [1] the fulcrum bending radiograph can predict the magnitude of correction of idiopathic scoliosis. The fulcrum bending is a measure of the intrinsic properties of the scoliotic spine like fixed bony deformity of vertebrae, as well as flexibility of discs, thoracic cage, muscles, and ligaments. Correction depends on extrinsic factors: on instrumentation pattern, mobilisation technique, magnitude and sequence of applied forces and moments, as well as on positioning of the patient. Furthermore, we can expect some random variation between fulcrum bending Cobb angles and postoperative Cobb angles. According to equation 7 the authors have defined the X-Factor Index as the difference between the fulcrum bending angle and the postoperative Cobb angle, divided by a factor indicating flexibility of the curve. The dividend (fulcrum bending angle minus the postoperative Cobb angle) depends on the extrinsic factors as well as on random variation, the divisor (equation 4) is an expression of the intrinsic factors (and of the performance of the fulcrum bending radiograph). An example will demonstrate how the X-Factor Index (XFI) is responding to variation of the fulcrum angle. Let us assume the preoperative Cobb angle be 50°, and the postoperative Cobb angle be 20°. The resulting X-Factor is 0%, if the fulcrum bending is 20° (same correction obtained by fulcrum bending and postoperatively), 25% with a fulcrum bending angle of 30°, 100% with 40°, and 250% with 45°, respectively. With a 50° fulcrum bending angle, no X-factor can be obtained because of division by zero. If the preoperative angle be 50°, the postoperative 20°, and the fulcrum angle 10° (final correction worse than fulcrum bending), the X-Factor Index will get negative and would be −12.5%, and with a fulcrum angle of 0° −20%. Therefore, in a typical range of pre- and postoperative angles as well as fulcrum angles, the X-Factor Index provides reasonable results, but not in a linear correlation. If no correction can be obtained, the X-Factor Index will be infinite. If rigid and flexible curves are mixed in a sample of patients, the average may tend to extreme values. The X-Factor Index is a quotient of extrinsic factors divided by intrinsic factors, with the intention to create a parameter to measure extrinsic factors. The original construct of Luk et al. to measure extrinsic factors, the Fulcrum Bending Correction Index (FBCI, equation 6), is comparable to the XFI, with a different dividend and the same divisor, the dividend being fulcrum bending angle minus the postoperative Cobb angle in the XFI, and the correction rate (preop − postop)/preop in the FBCI. In Luk et al. [2] the FBCI was almost the same for four different instrumentations. We do not know, whether the XFI reacts more than the FBCI to particular surgical techniques such as mobilisation of ribs, or the use of pedicle screws in every pedicle versus in “strategic” pedicles. The authors recommend the X-Factor Index in order to compare between different surgical techniques. These extrinsic factors may be associated with the X-Factor Index in different and varying proportions. An analysis of variance can demonstrate the varying degree of impact of different techniques, but will need a much higher number of patients, bearing in mind the considerable variation in curve magnitude, curve extension and rigidity of idiopathic scoliotic curves. Such an analysis could not be addressed in the current study due to an entire sample of only 30 patients. The X-Factor Index is presumably not a good indicator for surgical skill, but may be valuable as a construct to measure the impact of different surgical techniques. As the techniques vary often in a way, which is not communicated, because surgeons consider their personal technique as a matter of course, differences in reported X-Factor Index values may induce a search for the reasons explaining differences. Furthermore, the proportion of the effect of a surgical measure can be expressed as a proportion of the X-Factor.

Three-Dimensional Analysis of Tall Reinforced Concrete Buildings with Nonlinear Cracking Effects#

In this study, a computer program based on the iterative analytical procedure has been developed for the three-dimensional analysis of reinforced concrete frames with beam, column and shear-wall elements in cracked state. ACI and probability-based effective stiffness models are used for the effective moment of inertia of the cracked members. In the analysis, shear deformation effects are also taken into account, and the variation of the shear rigidity due to cracking is considered by employing the reduced shear stiffness models available in the literature. The computer program is based on an iterative procedure which is subsequently verified experimentally through a reinforced concrete wall-frame test. The effectiveness of the analytical procedure is also illustrated through a practical three-dimensional reinforced concrete shear wall frame example. The iterative analytical procedure can provide an accurate and efficient prediction of deflections of reinforced concrete structures due to cracking under service loads. The main advantage of the proposed procedure is that the variations in the flexural stiffness of each member in the reinforced concrete structures can be observed explicitly.

Holiday Price Rigidity and Cost of Price Adjustment

The Thanksgiving–Christmas holiday period is a major sales period for US retailers. Due to higher store traffic, tasks, such as restocking shelves, handling customers' questions and inquiries, running cash registers, cleaning and bagging, become more urgent during holidays. As a result, the holiday‐period opportunity cost of price adjustment may increase dramatically for retail stores, which should lead to greater price rigidity during holidays. We test this prediction using weekly retail scanner price data from a major Midwestern supermarket chain. We find that, indeed, prices are more rigid during holiday periods than non‐holiday periods. For example, the econometric model we estimate suggests that the probability of a price change is lower during holiday periods, even after accounting for cost changes. Moreover, we find that the probability of a price change increases with the size of the cost change, during both the holiday as well as non‐holiday periods. We argue that these findings are best explained by higher price adjustment costs (menu cost) the retailers face during the holiday periods. Our data provides a natural experiment for studying variation in price rigidity because most aspects of market environment such as market structure, industry concentration, the nature of long‐term relationships, contractual arrangements, etc. do not vary between holiday and non‐holiday periods. We, therefore, are able to rule out these commonly used alternative explanations for the price rigidity, and conclude that the menu cost theory offers the best explanation for the holiday period price rigidity.

Multipole borehole acoustic theory: Source imbalances and the effects of an elastic logging tool

In recent years the emphasis in acoustic logging has been shifting from the wireline to the Logging While Drilling (LWD) environment, the latter being far different from the former in that both tool rigidity and tool radius are considerably greater. In this paper we present a generic mathematical formulation for the multipole borehole acoustic measurement (alternate and equal polarity case), including a detailed analysis on the effects of multipole source amplitude imbalances. It is shown that source imbalance induced mode contaminants have excitation amplitudes that are scaled by the sum of the relative source imbalances between diametrically opposed sources. Furthermore it is shown that for mode contaminants with odd modal number there can be a significant offset in the associated directivity pattern, even at low levels of source imbalance. However, it is also shown that source imbalance induced mode contaminants can be completely eliminated if the multipole source is accompanied with a ‘vertically’ (but not azimuthally) offset multipole receiver. Mathematically, it is demonstrated (for a centered tool) that a polarity weighted stack of these multipole receivers completely eliminates the source imbalance induced mode contaminants. Excitation amplitudes and phase slowness of borehole guided modes are presented for the most common excitation regimes, i.e., monopole, dipole, quadrupole and the hexapole excitation, the latter one showing to have the advantage of a higher formation shear cut-off frequency than the quadrupole mode. Special emphasis will be on the analysis of the dipole excitation and the differences that occur due to variations in tool rigidity, tool diameter and (isotropic) formation properties with the resulting conclusion that a formation flexural mode is not observable as a result of a LWD dipole excitation (this opposed to its dipole wireline counterpart). The guided mode excitation amplitudes are calculated as residues using a Laurent series expansion. This (unconventional) way of calculating the residue has the advantage that it is independent of the pole order, does not require the numerical evaluation of derivatives with respect to the vertical wavenumber and allows for an accurate and efficient FFT implementation.

Optimization of matching section of an accelerator with a spatially uniform quadrupole focusing

A new approach is proposed for determining the matching section profile in an accelerator with spatially uniform quadrupole focusing. The approach based on mathematically formalized optimization problem and considerably extends the class of possible profiles since it is primarily independent of specific laws of variation of rigidity in the matching section and makes it possible to find the values of the aperture at the boundaries and in the cells directly as a solution.

Vulnerability Screening and Capacity Assessment of Reinforced Concrete Columns Subjected to Blast

In this study, a nonlinear model is developed to study the response of blast-loaded reinforced concrete (RC) columns. The strain rate dependency and the axial load and P−Δ effects on the flexural rigidity variation along the column heights were implemented in the model. Strain rate and axial load effects on a typical RC column cross section were investigated by developing strain-rate-dependent moment-curvature relationships and force-moment interaction diagrams. Analysis results showed that the column cross section strength and deformation capacity are highly dependent on the level of strain rates. Pressure-impulse diagrams were developed for two different column heights with two different end connection details (ductile and nonductile) and the effects of the axial load on the column midheight deflection and end rotation at failure were evaluated for both connection types. Based on the results of this study, a pressure-impulse band (PIB) technique is proposed. The PIB technique presents a useful tool that...

Specific features of the structure, magnetic properties, and heat capacity of intercalated compounds Cr x TiSe2

Structural features, magnetic properties, and heat capacity of CrxTiSe2 intercalated compounds with a layered structure have been studied experimentally for 0 ≤ x ≤ 0.5. It is shown that, at high chromium concentrations (x > 0.25), the magnetic properties of the compounds are strongly affected by the degree of ordering and distribution pattern of the intercalated atoms. Depending on the cooling rate of samples of the same composition (x = 0.5), an antiferromagnetic or a cluster-glass-type state can be obtained. Heat capacity measurements have revealed a nonmonotonic variation in the lattice rigidity with increasing concentration of intercalated atoms.

Distribution of filipin-sterol complexes in sperm membranes from hypercholesterolaemic rabbits.

The distribution of membrane filipin-sterol complexes (FSC) was examined ultrastructurally in cauda epididymal sperm from normal and hypercholesterolaemic rabbits. Membrane FSC were quantitatively analysed on replicas of filipin-treated cells. We determined a significant difference in FSC concentration in the plasma membrane of the acrosome region (PMAR) of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.56 +/- 0.05 FSC complex per micron 2 (enriched Cholesterol diet: Diet 2) in the marginal segment of PMAR; 0.62 +/- 0.05 FSC complex per micron 2 (enriched Cholesterol and fish oil diet: Diet 3) and only 0.28 +/- 0.01 FSC complex per micron 2 for normal animals (Control Diet 1). In the principal (anterior) segment we found 0.54 +/- 0.10 FSC complex per micron 2 (Diet 2), 0.56 +/- 0.03 FSC complex per micron 2 (Diet 3) and 0.30 +/- 0.04 FSC complex per micron 2 (Control Diet 1). We also counted 0.47 +/- 0.1 FSC complex per micron 2 in the equatorial segment of PMAR for Diet 2, 0.27 +/- 0.05 and 0.28 +/- 0.04 FSC complex per micron 2 in Diet 1 and Diet 3 respectively. Diet 4 (fish oil) did not differ from the control. An increase in the Cholesterol (Chol) level in biological membranes or a difference in the Chol membrane domains could cause a variation in the membrane rigidity that could modify the sperm membrane fusion capacity and functionality. The results presented in this paper are in agreement and could explain the decrease in the kinetic of the sperm acrosome reaction that we have observed in experimentally hypercholesterolaemic rabbits (Díaz-Fontdevila & Bustos-Obregón, 1992).

Intensity, repetitiveness, and directionality of habitual adolescent mobility patterns influence the tibial diaphysis morphology of athletes

Mobility patterns affect the loads placed on the lower limbs during locomotion and may influence variation in lower limb diaphyseal robusticity and shape. This relationship commonly forms the basis for inferring mobility patterns from hominin fossil and skeletal remains. This study assesses the correspondence between athletic histories, varying by loading intensity, repetition and directionality, measured using a recall questionnaire, and peripheral quantitative computed tomography-derived measurements of tibial diaphysis rigidity and shape. Participants included male university varsity cross-country runners (n = 15), field hockey players (n = 15), and controls (n = 20) [mean age: 22.1 (SD +/- 2.6) years]. Measurements of tibial rigidity (including J, %CA, Imax, Imin, and average cortical thickness) of both runners and field hockey players were greater than controls (P < or = 0.05). Differences in tibial shape (Imax/Imin, P < or = 0.05) between runners and hockey players reflect pronounced maximum plane (Imax) rigidity in runners, and more symmetrical hypertrophy (Imax, Imin) among hockey players. This corresponds with the generally unidirectional locomotor patterns of runners, and the multidirectional patterns of hockey players. These results support the relationship between mobility and tibial diaphysis morphology as it is generally interpreted in the anthropological literature, with greater levels of mobility associated with increased diaphyseal robusticity and shape variation. Although exercise intensity may be the primary influence on these properties, the repetitiveness of the activity also deserves consideration. In conclusion, bone morphological patterns can reflect habitual behaviors, with adaptation to locomotor activities likely contributing to variation in tibial rigidity and shape properties in archaeological and fossil samples.

Variations of cut-off rigidity in Irkutsk

According to the ground-based measurements of cosmic ray intensity on the worldwide network of stations and GOES spacecrafts, variations in cut-off rigidity in Irkutsk for the period 2004–2005 have been calculated. The calculated variations in cut-off rigidity are presented along with the Dst variations of the geomagnetic field.

Reflection of the solar wind parameters in the CR geomagnetic cutoff rigidity before a strong magnetic storm in November 2003

The time variations in the CR geomagnetic cutoff rigidity and their relation to the interplanetary parameters and the Dst index during a strong magnetic storm of November 18–24, 2003, have been analyzed. The Tsyganenko (Ts03) model of a strongly disturbed magnetosphere [Tsyganenko, 2002a, 2002b; Tsyganenko et al., 2003] have been used to calculate effective geomagnetic thresholds with the help of the method for tracing CR particle trajectories in the magnetospheric magnetic field. The geomagnetic thresholds have been calculated using the method of global spectrographic survey (GSS), based on the data from the global network of CR stations, and the results have been compared with the effective geomagnetic cutoff rigidities. The daily anisotropy of effective geomagnetic thresholds during the Dst variation minimum have been estimated. The relation of the theoretical and experimental geomagnetic thresholds, obtained using the GSS method, to the interplanetary parameters and Dst variation is analyzed. The Dst variations, IMF B z , and solar wind density are most clearly defined in the geomagnetic thresholds during this storm. The correlation between B y and experimental geomagnetic thresholds is higher than such a correlation between this parameter and theoretical thresholds by a factor 2–3, which suggests that a real dawn-dusk asymmetry during this storm was stronger than such an asymmetry represented by the Ts03 model.

Body tides of a convecting, laterally heterogeneous, and aspherical Earth

Precise knowledge of Earth's body tides is crucial for correcting geodetic positioning measurements, satellite gravity surveys, and superconducting gravimeters with nanogal precision. With this aim, body tides are generally computed assuming a radially (or elliptically) stratified Earth. However, seismic tomography surveys and fluid dynamic studies show that thermal convection within Earth's mantle produces significant lateral heterogeneity exemplified by superplumes, superswells, and subducting slabs. To determine the influence of this heterogeneity on body tides, we used a tomographic model to constrain lateral variations in mantle density and rigidity. This heterogeneity drives convective flow that deflects Earth's surface and core‐mantle boundaries by a few kilometers; we used a viscous flow model to constrain this dynamically supported asphericity. After verifying this complete Earth model using geoid observations, we used the spectral element method to determine how Earth's body tides are perturbed compared to a spherical Earth. We find maximum radial perturbations of surface and geoid displacements of 0.3 and 0.1 mm, respectively, and tidal gravity variations of 150 nGal. The amplitude of tidal gravity perturbations depends strongly on location and is greatest above large mantle density anomalies: e.g., large dense slabs (South America, Indonesia, Marianas), hot spots (Hawaii, Iceland), and the East African Rift. Predicted gravity perturbations are 100 times larger than the present precision of superconducting gravimeters and are comparable in magnitude to the unexplained residue observed at some gravimeter stations after tidal corrections. While this residue has been attributed to unmodeled loading from ocean tides, body tide perturbations caused by convection‐induced mantle heterogeneity may contribute to this observed residue.

Comparison of Earth’s magnetospheric magnetic field models in the context of cosmic ray physics

Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000. For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages and drawbacks of the different models in the context of space weather.

Micro-computed tomography assessment of fracture healing: Relationships among callus structure, composition, and mechanical function

Non-invasive characterization of fracture callus structure and composition may facilitate development of surrogate measures of the regain of mechanical function. As such, quantitative computed tomography- (CT-) based analyses of fracture calluses could enable more reliable clinical assessments of bone healing. Although previous studies have used CT to quantify and predict fracture healing, it is unclear which of the many CT-derived metrics of callus structure and composition are the most predictive of callus mechanical properties. The goal of this study was to identify the changes in fracture callus structure and composition that occur over time and that are most closely related to the regain of mechanical function. Micro-computed tomography (μCT) imaging and torsion testing were performed on murine fracture calluses ( n = 188) at multiple post-fracture timepoints and under different experimental conditions that alter fracture healing. Total callus volume (TV), mineralized callus volume (BV), callus mineralized volume fraction (BV/TV), bone mineral content (BMC), tissue mineral density (TMD), standard deviation of mineral density ( σ TMD), effective polar moment of inertia ( J eff ), torsional strength, and torsional rigidity were quantified. Multivariate statistical analyses, including multivariate analysis of variance, principal components analysis, and stepwise regression were used to identify differences in callus structure and composition among experimental groups and to determine which of the μCT outcome measures were the strongest predictors of mechanical properties. Although calluses varied greatly in the absolute and relative amounts of mineralized tissue (BV, BMC, and BV/TV), differences among timepoints were most strongly associated with changes in tissue mineral density. Torsional strength and rigidity were dependent on mineral density as well as the amount of mineralized tissue: TMD, BV, and σ TMD explained 62% of the variation in torsional strength ( p < 0.001); and TMD, BMC, BV/TV, and σ TMD explained 70% of the variation in torsional rigidity ( p < 0.001). These results indicate that fracture callus mechanical properties can be predicted by several μCT-derived measures of callus structure and composition. These findings form the basis for developing non-invasive assessments of fracture healing and for identifying biological and biomechanical mechanisms that lead to impaired or enhanced healing.

Pseudolinear equivalent constant rigidity concept for analyzing welding residual deformation

To ascertain the extent of deformation due to the thermal cycles caused by welding it calls for solving a complex thermal elasto-plastic problem, which is non-linear and involves plastic deformation of the medium at high temperature varying in both time and space. Analytical solutions turned out to be inadequate. At the same time conventional numerical techniques proved to be highly time consuming and thereby prohibitively expensive in real life situations. The concept of pseudolinear equivalent constant rigidity system was developed in this investigation for thermo-mechanical analysis of plates undergoing variation of rigidity due to a continuously changing temperature profile as is encountered in welding situations. The initial non-linear problem with modulus varying with temperature was transformed into a pseudolinear equivalent system of constant rigidity that was solved by applying linear analysis. The numerical results compared very well with those of the experimental ones. The present method was found to be computationally more efficient and simpler to model compared to FEM for solving similar thermo-elasto-plastic nonlinear problems. The analysis procedure presented in this work and the results thus obtained, holds a great promise for analyzing the complicated thermo-elasto-plastic problems as encountered in real life situations.

Dislocation models of interseismic deformation in the western United States

The GPS‐derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ∼2500‐km‐long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ∼1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ∼100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth‐averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ∼1000 km from the major plate boundaries.