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At least 721 records · Page 40Linked to original sources
PubMed1983

The surgeon's use of the rigid and flexible bronchoscopes in the diagnosis of bronchial carcinoma.

The results of a prospective study comparing the rigid and flexible fibreoptic bronchoscopic techniques in the diagnosis and assessment of bronchial carcinoma are reported. One hundred and nine patients underwent fibreoptic bronchoscopy and these were compared with a similar group of 111 patients in whom the rigid bronchoscope was used. Bronchoscopic diagnosis of malignancy was achieved in 73.4% of patients in the fibreoptic group and in 73% using the rigid bronchoscope.

Biopsy↗
PubMed1995

[Capnography for bronchoscopy with rigid technique using high frequency jet ventilation (HFJV)].

OBJECTIVES AND METHODS: Rapid bronchoscopy in general anaesthesia still has its precise indications, where the high frequency jet ventilation technique offers several advantages. The monitoring of ventilation, however, has been rather unsatisfactory up to date. We therefore studied capnography in 60 bronchoscopies during HFJV (rate: 100/min; I:E = 0.33; driving pressure: 0.08-0.14 MPa) using a rigid bronchoscope with a distally located sampling port. Continuous capnograms were recorded. End-tidal partial pressures of carbon dioxide (petCO2), however, were obtained from 2-3 single breaths by intermittently reducing the jet-frequency to 10-12/min. After 6 min (MP1: whole group; n = 60) and 18 min of HFJV (MP2: n = 34 of this group) petCO2 values were regularly obtained and compared to pCO2 in synchronously drawn capillary blood samples (pcCO2). The jet driving pressure initially adjusted to body weight, however, was only corrected according to petCO2, aiming at 34 mmHg. RESULTS: During HFJV, sinusoidal capnograms permitted the identification of every single jet impulse. With instruments being passed through the bronchoscope, however, these curves were substantially distorted. Mean pcCO2 at MP1 (37.8 +/- 6.7 mmHg) and MP2 (37.2 +/- 6.7 mmHg) demonstrated normal ventilation to light hyperventilation. Differences from mean petCO2 obtained during low frequency breathing were 3.3 mmHg at MP1 and 4.4 mmHg at MP2 (p < 0.05). There were strong correlations between the individual pairs of pcCO2 and petCO2 from MP1 (r = 0.80) and MP2 (r = 0.75) as well as between the pairs of dpcCO2 and dpetCO2 from both MPs (r = 0.77). The accuracy of the ventilator setting according to petCO2 with reference to pcCO2 was 73% for MP1 and 74% for MP2 (sensitivity: 75%/79%; specificity: 72%/67%). CONCLUSIONS: Capnography in rigid bronchoscopy during HFJV proved a clinically applicable addition to monitoring. Its routine use is strongly recommended in interventional bronchoscopy. The true petCO2 values obtained by intermittent single low frequency jet breathing permit estimates of gas exchange sufficiently exact for clinical purposes and for adjustment of the ventilator setting. Wave forms of the continuously recorded capnogram during HFJV are a warning of impeded ventilation or airway obstruction and, thus, of the danger of barotrauma or hypoventilation. Besides contributing to patient safety, this monitoring method might improve the acceptance of HFJV for bronchoscopy. Furthermore, it can also be applied to rigid bronchoscopy with common ventilation.

Adult↗
PubMed1985

[Rectoscopy: rigid or flexible? A comparative study].

The customary rigid rectoscope was compared prospectively, with a new, flexible one (prototypes of Olympus Opt. and Fuji) in each of 114 patients selected at random. Maximal depth of introduction was reached on average after 1 min with the rigid instruments, after 1 min 40 sec with the flexible one. Mean depth of introduction was 16 cm for the rigid and 33 cm for the flexible one. In 21 patients (18.4%) additional information was obtained with the flexible rectoscope. 80% of patients reported that the flexible instrument caused them no or only slight discomfort. Skill in using the flexible instrument can be quickly acquired.

Fiber Optic Technology↗
PubMed2005

Coarse-grained rigid blob model for soft matter simulations.

We have developed a coarse-grained multiscale molecular simulation method for soft matter systems that directly incorporates stereochemical information. We divide the material into disjoint groups of atoms or particles that move as separate rigid bodies; we call these groups "rigid blobs," hence the name coarse-grained rigid blob model. The method is enabled by the construction of transferable interblob potentials that approximate the net intermolecular interactions, as obtained from ab initio electronic structure calculations, other all-atom empirical potentials, experimental data, or any combination of the above. We utilize a multipolar expansion to obtain the interblob potential-energy functions. The series, which contains controllable approximations that allow us to estimate the errors, approaches the original intermolecular potential as the number of terms increases. Using a novel numerical algorithm, we can calculate the interblob potentials very efficiently in terms of a few interaction moment tensors. This reduces the labor well beyond what is required in standard molecular-dynamics calculations and allows large-scale simulations for temporal scales commensurate with characteristic times of nano- and mesoscale systems. A detailed derivation of the formulas is presented, followed by illustrative applications to several systems showing that the method can effectively capture realistic microscopic details and can easily extend to large-scale simulations.

Journal Article↗
PubMed2005

Simulations of concentrated suspensions of rigid fibers: relationship between short-time diffusivities and the long-time rotational diffusion.

Brownian dynamics simulations of the behavior of suspensions of fibers demonstrate that the scaling of the rotational diffusivity with respect to the number density (nL3) is a sensitive function of the thickness and the parameter L2D(R0)/D(T0), where D(R0) is the rotational diffusivity at infinite dilution, D(T0) is the average center-of-mass diffusivity at infinite dilution, and L is the fiber length. Existing theories for the long-time rotational diffusivities of rigid fibers in the semidilute and concentrated regimes fail to accurately account for the relationship with the dilute values of the rotational and translational diffusivities of the various physical models used to simulate the fibers. The concentration regime studied in this work ranges from a number density of nL3 approximately 0-150, which is below the transition from an isotropic to nematic state. The effect of the fiber thickness was studied by performing simulations of rods with aspect ratios (fiber length over diameter) of 25, 50, and 500, as well as performing projections for infinitely thin fibers. The excluded volume of the rods was enforced through the use of short-range potentials. For a rod with an aspect ratio of 50 with a parameter of L2D(R0)/D(T0)=9, which corresponds to a slender-body model of the individual fibers, the rotational diffusivity (D(R)) scales as D(R)/D(R0) approximately (nL3)(-1.9) in the concentration regime of 70 < or = nL3 < or = 150. Similarly with a parameter of L2D(R0)/D(T0)=4, corresponding to a rigid-dumbbell model, the rotational diffusivity scales as D(R)/D(R0) approximately (nL3)(-1.1) over the same range of concentrations. For rods with aspect ratios of 25, it is observed that a difference in the scaling is seen for L2D(R0)/D(T0) approximately < 8, with higher values of this ratio exhibiting essentially the same scaling. Additional values of the ratio L2D(R0)/D(T0) were investigated to determine the overall behavior of the suspension dynamics with respect to this parameter. These findings resolve discrepancies between simulation results for rotational diffusivities reported by previous investigators and provide new insights for the development of an accurate theory for the diffusivity of rigid rods suspended in solution.

Journal Article↗
PubMed2005

Effect of bending and torsion rigidity on self-diffusion in polymer melts: a molecular-dynamics study.

Extensive molecular-dynamics simulations have been performed to study the effect of chain conformational rigidity, controlled by bending and torsion potentials, on self-diffusion in polymer melts. The polymer model employs a novel torsion potential that avoids computational singularities without the need to impose rigid constraints on the bending angles. Two power laws are traditionally used to characterize the dependence of the self-diffusion coefficient on polymer length: D proportional to N(-nu) with nu=1 for N Ne (reptation regime), Ne being the entanglement length. Our simulations, at constant temperature and density, up to N=250 reveal that, as the chain rigidity increases, the exponent nu gradually increases towards nu=2.0 for N Ne. The value of Ne is slightly increased from 70 for flexible chains, up to the point where the crossover becomes undefined. This behavior is confirmed also by an analysis of the bead mean-square displacement. Subsequent investigations of the Rouse modes, dynamical structure factor, and chain trajectories indicate that the pre-reptation regime, for short stiff chains, is a modified Rouse regime rather than reptation.

Biopolymers↗
PubMed2005

Sulfur hexafluoride's liquid-vapor coexistence curve, interfacial properties, and diffusion coefficients as predicted by a simple rigid model.

We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case.

Journal Article↗
PubMed2006

A rigid-body Newtonian propagation scheme based on instantaneous decomposition into rotation and translation blocks.

The rotation and translation block (RTB) method of Durand et al. [Biopolymers 34, 759 (1994)] and Tama et al. [Proteins 41, 1 (2000)] provides an appealing way to calculate low-frequency normal modes of large biomolecules by restricting the space of motions to exclude internal motions of preselected rigid fragments within the molecule. These fragments are modeled essentially as rigid bodies and the need to calculate high-frequency relative motions of the atoms that form them is obviated in a natural way. Here we extend the RTB approach into a method for computing the classical (Newtonian) dynamics of a biomolecule, or any large molecule, with effective rigid-body constraints applied to a prechosen set of internal molecular fragments. This method, to be termed RTB dynamics, is easy to implement, conserves the total energy of the system, does not require the construction of the matrix of second spatial derivatives of the potential-energy function (Hessian matrix), and can be used to compute the classical dynamics of a system moving in an arbitrary anharmonic force field. An elementary numerical application to signal propagation in the small membrane-bound polypeptide gramicidin-A is presented for illustration purposes.

Journal Article↗
PubMed2006

HF in clusters of molecular hydrogen: II. Quantum solvation by H2 isotopomers, cluster rigidity, and comparison with CO-doped parahydrogen clusters.

We present a comprehensive theoretical study of the quantum solvation of the HF molecule by small clusters of the H2 isotopomers, p-H2, HD, and o-D2, with up to 13 hydrogen solvent molecules. This complements our earlier work on the HF-doped parahydrogen clusters [H. Jiang and Z. Bacic, J. Chem. Phys. 122, 244306 (2005)]. The ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. Detailed information is obtained regarding the size and isotopomer dependences of the energetics, vibrationally averaged structures, and their rigidity. The rigidity of these clusters is investigated further by analyzing the distributions of their principal moments of inertia from the diffusion Monte Carlo simulations. The clusters are found to be rather rigid, especially when compared with the pure parahydrogen clusters of the same size. Extensive comparison is made with the quantum Monte Carlo results for the CO-doped parahydrogen clusters and significant differences are observed in the size evolution of certain properties, notably the chemical potential.

Journal Article↗
PubMed2001

Mandibular range of motion after bilateral sagittal split ramus osteotomy with wire osteosynthesis or rigid fixation.

OBJECTIVES: An analysis was conducted to compare mandibular range of motion among Class II patients treated with wire osteosynthesis or rigid internal fixation after surgical mandibular advancement. STUDY DESIGN: Patients randomly received wire osteosynthesis and 8 weeks of maxillomandibular fixation (n = 49) or rigid internal fixation (n = 78). Mandibular range of motion was measured 2 weeks before surgery and 8 weeks, 6 months, and 1, 2, and 5 years after surgery. RESULTS: Both groups showed decreased mobility in all movement dimensions that progressively recovered to near presurgical levels over the 5-year follow-up period. The difference in range of motion between treatment groups was not statistically significant. Changes in proximal and distal segment position could not explain decreased mobility. CONCLUSIONS: Similar decreases in mandibular mobility occurred with wire and rigid fixation of a bilateral sagittal split ramus osteotomy after surgery. Long-term changes were statistically, but not clinically, significant.

Adult↗
PubMed1984

A counterexample to the rigidity assumption in the visual perception of structure from motion.

It has been proposed that the human visual system prefers perceptions of objects that are rigid or undergo minimum form change. A counterexample is presented in which a rigid two-dimensional figure rotating in the frontal plane is perceived as a distorting three-dimensional shape. It is argued that this perception results from the stimulation of automatic processes for perceiving size change, and that these processes are not subject to a general rigidity assumption.

Depth Perception↗
PubMed1993

Perceived rigidity and nonrigidity in the kinetic depth effect.

Stroboscopic simulations of three-dimensional rotating rigid structures can be perceived as highly nonrigid. To investigate this nonrigidity effect a sequence of either three (experiment 2 and 3) or thirty six frames (experiment 4) was used, each consisting of a set of dots with location on the horizontal axis corresponding to the parallel projection of a nominally defined helix. Observers were asked to judge the angle of rotation of eighty helices defined by the factorial combination of eight phase (phi) values (ie difference between the sinusoidal path of one dot and its neighbours) and ten different angular displacement values (alpha). When in each static frame the dots can be organized into curved dotted line (small values of phi), the perceived 3-D helices are highly nonrigid. But when shape information is not available in each static frame (high values of phi), the helices are perceived as rigid and rotation judgement is possible providing that alpha < 15 degrees. It appears that at small values of phi observers fail to recover the rigid structure of the helices since the input to the structure from the motion process may be distorted.

Adult↗
PubMed2006

The bar-cross-ellipse illusion: alternating percepts of rigid and nonrigid motion based on contour ownership and trackable feature assignment.

We present a new multistable stimulus generated by continuously rotating an ellipse behind four fixed occluders. Despite the stimulus remaining constant, observers can alternate between one of four percepts: (1) a continuously morphing cross; (2) two independent perpendicular bars oscillating in depth; (3) a rigidly rotating ellipse observed behind the occluders; (4) a fixed cross observed through a continuously rotating, elliptical aperture. Interestingly, the initial percept naive observers tend to see is percept 1, which is the only nonrigid motion percept. This appears to be a violation of the hypothesized 'rigidity heuristic' in which rigid motion percepts tend to be perceived over retinally equivalent nonrigid ones. Here, we describe the relationships between each of the percepts and the assignment of contour ownership and figure/ground segmentation.

Form Perception↗
PubMed1996

Torsional rigidity of single actin filaments and actin-actin bond breaking force under torsion measured directly by in vitro micromanipulation.

Knowledge of the elastic properties of actin filaments is crucial for considering its role in muscle contraction, cellular motile events, and formation of cell shape. The stiffness of actin filaments in the directions of stretching and bending has been determined. In this study, we have directly determined the torsional rigidity and breaking force of single actin filaments by measuring the rotational Brownian motion and tensile strength using optical tweezers and microneedles, respectively. Rotational angular fluctuations of filaments supplied the torsional rigidity as (8.0 +/- 1.2) x 10(-26) Nm2. This value is similar to that deduced from the longitudinal rigidity, assuming the actin filament to be a homogeneous rod. The breaking force of the actin-actin bond was measured while twisting a filament through various angles using microneedles. The breaking force decreased greatly under twist, e.g., from 600-320 pN when filaments were turned through 90 degrees, independent of the rotational direction. Our results indicate that an actin filament exhibits comparable flexibility in the rotational and longitudinal directions, but breaks more easily under torsional load.

Actins↗
PubMed2003

Tryptophan phosphorescence spectroscopy reveals that a domain in the NAD(H)-binding component (dI) of transhydrogenase from Rhodospirillum rubrum has an extremely rigid and conformationally homogeneous protein core.

The characteristics of tryptophan phosphorescence from the NAD(H)-binding component (dI) component of Rhodospirillum rubrum transhydrogenase are described. This enzyme couples hydride transfer between NAD(H) and NADP(H) to proton translocation across a membrane and is only active as a dimer. Tryptophan phosphorescence spectroscopy is a sensitive technique for the detection of protein conformational changes and was used here to characterize dI under mechanistically relevant conditions. Our results indicate that the single tryptophan in dI, Trp-72, is embedded in a rigid, compact, and homogeneous protein matrix that efficiently suppresses collisional quenching processes and results in the longest triplet lifetime for Trp ever reported in a protein at ambient temperature (2.9 s). The protein matrix surrounding Trp-72 is extraordinarily rigid up to 50 degrees C. In all previous studies on Trp-containing proteins, changes in structure were reflected in a different triplet lifetime. In dI, the lifetime of Trp-72 phosphorescence was barely affected by protein dimerization, cofactor binding, complexation with the NADP(H)-binding component (dIII), or by the introduction of two amino acid substitutions at the hydride-transfer site. It is suggested that the rigidity and structural invariance of the protein domain (dI.1) housing this Trp residue are important to the mechanism of transhydrogenase: movement of dI.1 affects the width of a cleft which, in turn, regulates the positioning of bound nucleotides ready for hydride transfer. The unique protein core in dI may be a paradigm for the design of compact and stable de novo proteins.

Acrylamide↗
PubMedDate not supplied

The use of the Circadian Type Inventory as a measure of the circadian constructs of vigour and rigidity.

The Circadian Type Inventory (Folkard 1987) was administered to 191 students (150 females and 41 males). Corrected item to total correlations for both the Vigour and Rigidity scales were low to moderate. The internal reliabilities of the scales indicate that Vigour is statistically more homogeneous (0.74) than Rigidity (0.58). In the absence of the original CTI correlation matrix, replication using a 2-factor principal component varimax solution was undertaken. It explained only 26.7% of the variance. Post hoc factor analyses yielded 3 factors which explained 33.4% of the variance. The relatively low amounts of variance explained and the inadequate transfer of the circadian constructs of Rigidity and Vigour into question items does not recommend the use of the CTI to measure circadian rhythm characteristics in order to predict tolerance to shiftwork.

Adolescent↗
PubMed1977

Problem-solving rigidity of children on perceptual tasks as a function of parental authoritarianism.

The effect of parental authoritarianism on the rigid problem-solving behavior of 25 10- to 12-year-old children was examined. Children were tested on three perceptually ambiguous tasks in an experimentally induced ego-involving situation. Authoritarianism in one parent was associated with authoritarianism in the other. Children's greater difficulty on all three tasks was associated with higher parental authoritarianism; opposite sex correlations betweens sons' and mothers' and between daughters' and fathers' scores are stronger than same sex correlations. Children were consistent across all three tasks on rigid problem-solving behavior. It is suggested that rigid problem-solving behavior may mediate the transmission of authoritarianism from parent to child.

Anxiety↗
PubMed1985

Torsional and bending rigidity of the double helix from data on small DNA rings.

We have calculated the variance of equilibrium distribution of a circular wormlike polymer chain over the writhing number, [Wr)2), as a function of the number of Kuhn statistical segments, n. For large n these data splice well with our earlier results obtained for a circular freely jointed polymer chain. Assuming that [delta Lk)2) = [delta Tw)2) we have compared our results with experimental data on the chain length dependence of the [delta Lk)2) value recently obtained by Horowitz and Wang for small DNA rings. This comparison has shown an excellent agreement between theory and experiment and yielded a reliable estimate of the torsional and bending rigidity parameters. Namely, the torsional rigidity constant is C = 3.0.10(-19) erg cm, and the bending rigidity as expressed in terms of the DNA persistence length is a = 500 A. The obtained value of C agrees well with earlier estimates by Shore and Baldwin as well as by Horowitz and Wang whereas the a value is in accord with the data of Hagerman. We have found the data of Shore and Baldwin on the chain length dependence of the [delta Lk)2) value to be entirely inconsistent with our theorectical results.

Chemical Phenomena↗