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At least 199 records · Page 11Linked to original sources
PubMed2005

The influence of the rigidity of geosorbent organic matter on non-ideal sorption behaviors of chlorinated benzenes.

This study focused on evaluating the influence of the rigidity of natural organic matter (NOM) associated with four natural geosorbents in controlling the non-ideal sorption behaviors of five chlorinated benzenes. Single solute sorption isotherms for each sorbate/sorbent combination were modeled and interpreted by the Freundlich sorption isotherm and the adsorption-partitioning model based on Polanyi-Manes theory (PM model). "Rigid" organic matter was operationally quantified as the fraction of carbon resistant to wet chemical oxidation (hard carbon) or thermal oxidation (soot carbon); atomic H/O ratios indicated a close correlation between the degree of reduction of the NOM and its rigidity. Sorbents with larger rigid carbon fractions had more non-linear sorption isotherms and higher organic carbon (OC) normalized sorption affinities. The size of the PM hole filling domain for a given sorbent was closely correlated with the extent to which the sorbent's affinity for chlorobenzenes exceeded predictions from a linear free energy relationship. Loss of some portions of the rigid character of the NOM domain due to the penetration of sorbate molecules (plasticization) was discussed as a possible contributor to the non-ideal sorption behaviors observed in this study. The existence of a permanently rigid NOM domain, not subject to plasticization under environmental conditions, was postulated as an additional factor determining the observed sorption behavior.

Adsorption↗
PubMed2003

Rigidity in children's drawings and its relation with representational change.

Four studies tested the application of to the drawing domain. In particular, we tested her claim that young children are inhibited in their attempts at changing their graphic representations (representational change) due to being constrained by the order in which the elements of the representation are drawn (procedural rigidity). The first study required 60 children (4- to 6-year-olds and an older comparison group of 8-year-olds) to make three drawings of a familiar and novel topic. From these drawings each child was measured for procedural rigidity. In a further drawing the child was asked to modify their usual representation of each topic. Regression analyses revealed procedural rigidity levels were not predictive of manipulation performance. A second study, testing 75 4- to 6-year-olds and a third study, testing 30 3- to 4-year-olds, revealed that when young children were specifically asked to manipulate rigid sub-procedures on a familiar topic they were indeed able to do so. Finally, a fourth study (testing 40 5-year-olds and 40 8-year-olds) removed the notational trace in drawing (a possible aid for procedural interruption) but this still produced no evidence of a relation between procedural rigidity and representational change. We suggest how the concept of procedural rigidity might be re-interpreted for the drawing domain so that the RR model can remain as a domain-general theory of cognitive development. We also suggest the development of information processing may be crucial for flexibility in drawing.

Child↗
PubMed1992

Reproducibility in monitoring nocturnal penile tumescence and rigidity.

The evaluation of sexual dysfunction has improved with the advent of methods to test nocturnal penile tumescence that also monitor penile rigidity. Earlier techniques may not have recorded abnormal rigidity despite normal tumescence. To test the reproducibility of penile tumescence and rigidity, the results of initial and repeat tracings performed a mean of 39 days apart were compared in 17 patients (median age 62 years). Three nocturnal patterns were identified. 1) Among the 17 patients the initial penile tumescence and rigidity pattern was reproduced on repeat testing in 15. 2) Patterns that were not reproduced in the other 2 patients were explained by the ingestion of alcohol or because of a febrile illness during the period monitored. 3) Nocturnal penile rigidity and tumescence tracings from these patients reproduced previous patterns. Monitoring of nocturnal penile tumescence and rigidity is a useful and reproducible tool in the evaluation of male sexual dysfunction.

Adult↗
PubMed1997

Cost advantages of two-level anterior cervical fusion with rigid internal fixation for radiculopathy and degenerative disease.

BACKGROUND: Conventional anterior cervical discectomy with fusion is thought to require postoperative neck immobilization for the promotion of bony fusion. Rigid internal fixation with anterior cervical plates may decrease graft-related complications and provide immediate stability. This stability may obviate postoperative external immobilization. METHODS: This report reviews one surgeon's experience with the use of rigid internal fixation for two-level anterior cervical discectomy and fusion for radiculopathy to promote early mobilization without external bracing. It compares outcomes and costs with a similar population of patients treated with anterior cervical discectomy and fusion who did not undergo rigid internal fixation. We compared patients who underwent two-level allograft anterior cervical discectomy and fusion with or without rigid internal fixation between 1989 and 1994 performed by a single surgeon (FJP) to evaluate the cost advantages and outcome of each procedure. All patients had clinical evidence of cervical radiculopathy unresponsive to medical therapy with magnetic resonance imaging confirmation of the appropriate nerve root impingement. Thirty-nine patients underwent two-level Cloward allograft fusion using Synthes anterior cervical locking plates, 25 underwent identical fusion without plating. Follow-up was 6 months to 4 years (mean, 31 months). RESULTS: Twenty-three of 25 patients in the nonplated group and 36 of 39 patients in the plated group achieved excellent or good outcomes using the Odom criteria. There were six complications (two major and four minor) in each group. Patients who underwent plating returned to light activities (mean, 17 vs. 29 days), driving (28 vs. 57 days), and unrestricted work (66 vs. 136 days) sooner than non-plated patients (p < 0.05, paired t test). No patient with plates was given external immobilization. CONCLUSIONS: Two-level anterior cervical discectomy and fusion with anterior plating for radiculopathy is safe, effective, and seems to provide shorter convalescence compared with conventional anterior cervical discectomy and fusion. Patients returned to unrestricted work sooner, thus reducing short-term disability. Rigid internal fixation may provide cost advantages to patients and insurance disability providers. The authors conclude that the increased cost of treatment for rigid internal fixation is more than offset by the benefits of earlier mobilization.

Bone Plates↗
PubMed1992

Effect of buckling material on ocular rigidity.

Enucleated human eyes were banded with metal and silicone bands to produce reductions in their diameter of 2 mm and 4 mm. The ocular rigidity produced by each banding material at each diameter was measured in the pressure range of 10 mmHg to 40 mmHg. Metal bands produced mild reductions in ocular rigidity that were significantly (P less than 0.05 to 0.01) lower than the control ocular rigidities in some pressure ranges. Silicone bands produced large reductions in ocular rigidity that were significantly (P less than 0.01) lower than ocular rigidities observed in metal-banded or control conditions in all pressure ranges. The influence of the elastic silicone banding material on ocular rigidity was greater than the influence of altered shape and wall stress that occurred with metal banding.

Aged↗
PubMed1996

A comparative review of 266 mandibular fractures with internal fixation using rigid (AO/ASIF) plates or mini-plates.

This study compares the internal fixation of mandibular fractures using either rigid 2.7 mm AO/ASIF plates or mini-plates. In the rigid plate group, 88 fractures were fixed with 88 plates. In the mini-plate group, 116 fractures were fixed with 170 plates. All the cases were consecutive and were treated in two South Wales hospitals during a 3-year period from 1988 to 1991. The aetiology of injury, timing of surgery, site of fracture, antibiotic policy and demographic features were evenly distributed between the two groups but there was a higher incidence of females in the mini-plate group. Both plating systems were successful in restoring functional occlusion. Rigid plates avoided the use of postoperative elastics better than mini-plates but the difference was not significant. There was a significantly higher incidence (P = 0.013) of infection in the mini-plate (12.9%) compared with the rigid plate (2.3%) group but 7.9% of the rigid group developed facial nerve weakness. A significantly higher proportion of mini-plates needed to be removed (P = 0.00019). A better treatment outcome for angle and comminuted fractures was noted with rigid plates.

Adolescent↗
PubMed2003

The space-developed dynamic vertical cutoff rigidity model and its applicability to aircraft radiation dose.

We have developed a dynamic geomagnetic vertical cutoff rigidity model that predicts the energetic charged particle transmission through the magnetosphere. Initially developed for space applications, we demonstrate the applicability of this library of cutoff rigidity models for computing aircraft radiation dose. The world grids of vertical cutoff rigidities were obtained by particle trajectory tracing in a magnetospheric model. This reference set of world grids of vertical cutoff rigidities calculated for satellite altitudes covers all magnetic activity levels from super quiet to extremely disturbed (i.e., Kp indices ranging from 0 to 9+) for every three hours in universal time. We utilize the McIlwain "L" parameter as the basis of the interpolation technique to reduce these initial satellite altitude vertical cutoff rigidities to cutoff rigidity values at aircraft altitudes.

Aircraft↗
PubMed2002

Rates and causes of intraoperative removal of foldable and rigid intraocular lenses: clinicopathological analysis of 100 cases.

PURPOSE: To analyze the rates of and reasons for intraoperative explantation of foldable and rigid intraocular lenses (IOLs) to determine the complication profile of each IOL design. SETTING: Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. METHODS: The study comprised data analysis of foldable (n = 85) and rigid (n = 15) IOL specimens that were explanted immediately after primary implantation. RESULTS: Eighty-five foldable intraoperative explants were accessioned. These comprised 14.5% of the 586 foldable IOL explants received between January 1988 and September 2000. There were 15 rigid poly(methyl methacrylate) (PMMA) intraoperative explants out of 2077 rigid explant specimens (0.7%). Fifty-one (60%) of the foldable IOLs requiring intraoperative explantation were the 1-piece silicone plate-haptic large-hole design, and 29 (34.1%) were the 3-piece silicone polyimide-haptic design. The most frequent reason for explantation of both designs was optic damage, 37.3% in the large-hole design and 55.2% in the polyimide design. Optic damage did not occur in rigid PMMA IOLs. CONCLUSION: Some foldable IOL designs have a higher risk of damage during surgical insertion than rigid designs. Two modern foldable IOLs, the silicone plate-haptic large-hole and the silicone polyimide-haptic, appear to be more prone to damage during folding, loading, and implantation than other IOLs.

Device Removal↗
PubMed2005

Rigid-rod molecules in biomembrane models: from hydrogen-bonded chains to synthetic multifunctional pores.

Synthetic ion channels and pores formed by rigid-rod molecules are summarized. This includes work on hydrogen-bonded chains installed along membrane-spanning rigid-rod scaffolds to transport protons. As a second topic, programmed assembly of p-septiphenyls with terminal iminodiacetate-copper complexes for potassium transport by cation-pi interactions is described. The third topic concerns rigid push-pull rods as fluorescent alpha-helix mimics to probe the importance of dipole-potential interactions for voltage gating, both on the functional and the structural level. Topic number four deals with p-octiphenyl staves as key scaffolds for the synthesis of rigid-rod beta-barrel pores. The description of internal and external design strategies for these rigid-rod beta-barrels covers a rich collection of pH-, pM-, voltage-, ligand-, and enzyme-gated synthetic multifunctional pores that can act as hosts, sensors, and catalysts. As far as practical applications are concerned, the possibility to detect chemical reactions with synthetic multifunctional pores appears most attractive. Recent molecular mechanics simulations are presented as a valuable approach to insights on the elusive suprastructures of multifunctional pores made from rigid rods.

Hydrogen Bonding↗
PubMed2006

Role of rigidity on the activity of proteinase inhibitors and their peptide mimics.

The Bowman-Birk inhibitors (BBIs) are a family of proteins that share a canonical loop structure whose presence in a conserved conformation is linked to their inhibitory activity. We study the conformational properties of the canonical loop using a graph theoretical approach as implemented in the floppy inclusions and rigid substructure topography (FIRST). We find that the canonical loop is an independent rigid cluster in the natural inhibitors. We have further used this technique to identify residues that play an important role in the structural rigidity of the protein by quantifying their contribution to the overall rigidity of the inhibitor. We find that the conserved elements among the natural and synthetic peptides are the ones that contribute the most to rigidity, even if they are located far from the active site, as rigidity effects are nonlinear and hence nonlocal. The results help to elucidate why certain mutations in the loop of the BBI produce peptides that fail to have the designed inhibitory activity.

Amino Acid Sequence↗
PubMed2001

The correlation between penile tumescence measured by the erectometer and penile rigidity by the RigiScan.

BACKGROUND: The goal of this study was to evaluate the correlation between increments of penile tumescence and penile rigidity measured by the erectometer and the RigiScan, respectively. METHODS: Nocturnal penile tumescence (NPT) was measured in 25 volunteers (mean age, 49.5 years). The erectometer and the RigiScan were used simultaneously for a total of 47 nights. We studied the correlation between maximum penile circumferential changes determined by the erectometer and penile rigidity patterns measured by the RigiScan. RESULTS: Maximum circumferential changes during NPT measured by the erectometer were well correlated to those determined by the RigiScan (correlation coefficient, 0.719). In addition, penile circumferential changes measured by the erectometer corresponded well to the penile rigidity pattern determined by the RigiScan (P=0.0001). Specifically, maximum penile circumferential changes of more than 30 mm and less than 10 mm had 70% positive predictive value and 100% negative predictive value for predicting the normal rigidity pattern, respectively. CONCLUSIONS: Penile circumferential changes measured by the erectometer were well correlated to penile rigidity measured by the RigiScan, particularly when the increments were larger than 30 mm or less than 10 mm. These results suggested that the erectometer was a useful tool to estimate the penile rigidity patterns of the RigiScan.

Adult↗
PubMed2007

[Results after lidloading with rigid gold weights--a meta-analysis].

INTRODUCTION: For the surgical therapy of lagophthalmos rigid gold implants were used. There are a lot of studies using rigid gold implants with widely different complications. In the primary study the small amount of patients is often a problem. The aim of our study was to survey the postoperative results and complications after insertion of rigid gold implants and to statistically compare the results with a meta-analysis. MATERIAL AND METHODS: 38 publications on 1000 rigid gold implants were analyzed in the context of a meta-analysis of the postoperative results. RESULTS: Complete lid closure can be obtained in 84.5 % with the rigid gold implants. The postoperative complication rates were 13.4 % for bulging, 6.4 % for migration, 6.8 % for extrusion, 11.5 % for corneal astigmatism and 7.0 % postoperative infections. DISCUSSION: Lidloading is a very simple and reversible procedure for the surgical treatment of lagophthalmos. The statistical analysis in using rigid gold implants showed a significant rate of postoperative complications. To increase the effectivity of the treatment method these results should be taken into account for alternative implants.

Eyelid Diseases↗
PubMed2004

Computer simulation study of the global phase behavior of linear rigid Lennard-Jones chain molecules: comparison with flexible models.

The global phase behavior (i.e., vapor-liquid and fluid-solid equilibria) of rigid linear Lennard-Jones (LJ) chain molecules is studied. The phase diagrams for three-center and five-center rigid model molecules are obtained by computer simulation. The segment-segment bond lengths are L = sigma, so that models of tangent monomers are considered in this study. The vapor-liquid equilibrium conditions are obtained using the Gibbs ensemble Monte Carlo method and by performing isobaric-isothermal NPT calculations at zero pressure. The phase envelopes and critical conditions are compared with those of flexible LJ molecules of tangent segments. An increase in the critical temperature of linear rigid chains with respect to their flexible counterparts is observed. In the limit of infinitely long chains the critical temperature of linear rigid LJ chains of tangent segments seems to be higher than that of flexible LJ chains. The solid-fluid equilibrium is obtained by Gibbs-Duhem integration, and by performing NPT simulations at zero pressure. A stabilization of the solid phase, an increase in the triple-point temperature, and a widening of the transition region are observed for linear rigid chains when compared to flexible chains with the same number of segments. The triple-point temperature of linear rigid LJ chains increases dramatically with chain length. The results of this work suggest that the fluid-vapor transition could be metastable with respect to the fluid-solid transition for chains with more than six LJ monomer units.

Journal Article↗
PubMed1990

Perception of structure from two-, four-, or eight-dot oscillatory motion: restoration of rigidity with the aid of structural information.

The motion of two dots corresponding to the two endpoints of an oscillating rigid pendulum produces the perception of an elastic rod, not a rigid one. The possibility that structural information about a rigid object whose motion is simulated plays an important role in the perceptual restoration of the rigidity is examined. Two experiments are reported in which the motion of the endpoints of rigid objects (two endpoints for a rod, four for a sheet, and eight for a board) was displayed. Rigid structure was restored whenever structural information could be used to activate a knowledge data-base on the properties of the objects.

Adult↗
PubMed1997

Protein-lipid interaction on the surface of a rigid gas-permeable contact lens in vitro.

PURPOSE: To investigate the mechanism of protein-lipid interactions responsible for biofilm formation on the surface of rigid gas-permeable contact lenses in vitro. METHODS: Two types of new, never-worn rigid gas-permeable contact lenses (siloxanyl alkyl acrylate and fluorosiloxanyl alkyl acrylate) were individually incubated in a protein only, lipid only, or combination protein-lipid artificial tear solution for 24 h at 37 degrees C with constant stirring. Deposited lipids were removed with a methanol based extraction procedure, separated using high performance thin layer chromatography and quantitatively analyzed densitometrically. Deposited proteins were extracted with 4M urea, separated using gel electrophoresis and quantitatively analyzed densitometrically. RESULTS: Lipid deposition on rigid gas-permeable contact lenses is dependent on lens matrix hydrophobicity while protein deposition is minimal and not material-dependent. The presence of lipid in the artificial tear solution enhances protein deposition on both types of rigid gas-permeable materials examined. The presence of protein in the artificial tear solution decreases lipid deposition on a siloxanyl alkyl acrylate lens. CONCLUSIONS: The hydrophobic nature of rigid gas-permeable contact lenses causes them to be more prone to lipid than to protein deposition. When both types of molecule are present in an artificial tear solution, the hydrophobic sites of the lipid molecules are attracted to the lens matrix while the more hydrophilic sites are repelled by the matrix and, thereby, exposed to the aqueous surroundings. Thus, lipid binding to rigid gas-permeable contact lenses reduces the hydrophobicity of the lens surface allowing protein to bind. The bound deposited hydrophilic protein then alters subsequent binding of both protein and lipid.

Contact Lenses↗
PubMed2000

Dynamics of a double stranded DNA oligomer: mode-coupling diffusion approach and reduced rigid fragment models.

The local dynamics of a double stranded DNA fragment [d(CpGpCpApApApTpTpTpGpCpG)]2 of twelve base pairs is obtained to second order in the mode-coupling expansion of the Smoluchowski diffusion theory. The DNA is considered a fluctuating three-dimensional (3D) structure undergoing rotational diffusion. The starting structure for the calculations is the B canonical structure of the fragment, while the fluctuations are evaluated using molecular dynamics simulations, with the ensemble averages approximated by time averages along a trajectory of length 1.5 ns. The rotational dynamics of the bonds along the double strands are calculated and compared to experimental NMR relaxation rates of different 13C along the sequence: R(Cz), R(Cxy) and R(Hz-->Cz). For a fluctuating 3D structure the mode-coupling diffusion theory is found to be in good agreement with several relative characteristics of the experimental relaxation parameters, while motivations are given for the few differences which are due mainly to poor statistics or to inaccuracies in the diffusion model. With a view to application to larger DNA fragments, discussion is dedicated to the validity of reducing the number of degrees of freedom in the double helix statistics by grouping the atoms in rigid fragments (e.g. the backbone atoms, the sugar atoms and the base atoms of each nucleotide). Consideration is given to the effect on local dynamics properties of reduced descriptions that include only three or four rigid bodies per nucleotide as well as five rigid bodies per base pair. It is found that in general these approximations almost uniformly produce slight increase in the correlation time pattern, which grows as the rigidity in the model increases. The relative effects on the dynamic pattern for the most accurate rigid body models are modest. The errors in C1' and C5' mobilities are more significant if C5' is included in the backbone rigid body. These results offer new tools to analyse NMR relaxation behaviour and new perspectives in studying the role of dynamics in biological macromolecules.

Algorithms↗
PubMed2002

The creation of a database of odorous compounds focused on molecular rigidity and analysis of the molecular features of the compounds in the database.

It is important to select odorous molecules for experiments on olfaction and for the development of an electronic nose. Odorous molecules having a small number of conformers, namely structurally rigid molecules, are assumed to interact with a small number of types of olfactory receptor proteins or to interact with the proteins in a simpler manner than that of fairly flexible molecules. Focusing on the rigidity of molecular structures, we collected 287 odorous molecules from data sources, which included 1205 chemicals in total and a database of the 287 odorous molecules (DB_odMOL) was created using CS ChemFinder Pro (version 5.0). The logarithmic value of the octanol/water partition coefficient (log P) and melting point, boiling point and vapour pressure of the molecules were estimated using CS Chem3D Pro. The database DB_odMOL accumulates these estimated data in addition to literature values for odour quality, odour detection thresholds and the safety of molecules. The rigidity of the 287 molecules was further analysed by conformational analysis performed by molecular mechanics using Conformer in CS Chem3D Pro (version 5) and 72 rigid odorous molecules were selected. The 287 molecules were also analysed based on atomic composition, substructure and molecular size. Sixty-two odorous molecules among the 72 rigid odorous molecules were further selected based on their atomic composition. The 62 rigid molecules with simple atomic composition that were finally selected should be useful for researchers in choosing odorous molecules for the study of olfaction, including the fields of molecular biology, physiology, structure-odour relationships and other fields of the study concerning odour.

Algorithms↗
PubMed2000

A pilot study of short- and long-term sequelae to rigid fixation across metacarpal physes in a baboon model.

The use of rigid fixation for fractures of the extremities has become commonplace. The short- and long-term effects of rigid fixation on the growing hand, however, have not been studied thoroughly. In this project, the use of rigid fixation across metacarpal growth plates (physes) in growing primate hands was examined. The hypothesis to be tested was that long-term placement of rigid fixation devices across physes during stabilization of mid-shaft osteotomies will cause the physes to close prematurely. Fixation devices with screws placed in the epiphysis and left in place for 4 months or 1 year resulted in open physes, in support of the null hypothesis. However, in physes plated for 1 year, biochemical changes associated with increased bone differentiation were apparent. Findings suggest that rigid fixation across physes for as long as 1 year can be used appropriately in growing individuals when necessary. However, until additional investigation establishes whether the open physes are still capable of producing bone-lengthening hypertrophic chondrocytes, caution should be used in long-term placement of rigid fixation devices.

Animals↗