Changes In Geometric Parameters Research Articles

Why is N···Be distance of NH3H+···DBeH shorter than that of NH3D+···HBeH? paradoxical geometrical isotope effects for partially isotope‐substituted dihydrogen‐bonded isotopomers

The partial isotope substitution for the change of geometrical parameters, interaction energies, and nuclear magnetic shielding tensors (σ) of dihydrogen-bonded NH3X(+)···YBeH (X, Y = H, D, and T) systems is analyzed. Based on the theoretical calculation, the distance between heavy atoms RN···Be of NH3H(+) ···DBeH is clearly found to be shorter than that in NH3D(+)···HBeH. Such apparently paradoxical geometrical isotope effect (GIE) on RN···Be is revealed by the cooperative effect of two kinds of (1) primary covalent-bonded GIE and (2) secondary dihydrogen-bonded one. We have demonstrated that (1) the covalent bond lengths become shorter by heavier isotope-substitution and (2) the dihydrogen-bonded distance RX···Y becomes shorter by heavier Y and lighter X isotope-substitution due to the difference of electronic structure reflected by the nuclear distribution. We have also found that interaction energy of NH3H(+)···DBeH is stronger than that of NH3D(+)···HBeH and isotopic deshielding effect of magnetic shielding becomes large in lighter isotope.

Retinal vascular changes and immune restoration in a cohort of HIV/AIDS patients on highly active antiretroviral therapy

BackgroundRetinal microvascular changes have been shown to reflect systemic inflammation in vivo. We aimed to investigate whether retinal microvascular changes are correlated with, and predictive of, CD4 and CD8 cell count changes in patients with HIV/AIDS being treated with highly active antiretroviral therapy (HAART). MethodsWe did a longitudinal hospital-based study. 50 HIV/AIDS patients being treated with HAART were sequentially recruited from March, 2011, to September, 2011, from the Communicable Disease Center, Singapore, and then followed up at a 9 month visit. Demographic and socioeconomic information and history of HIV infection were collected at baseline. Blood pressure and anthropometric measurements, blood tests for immune status assessment (CD4 and CD8 cell counts), and retinal photography were done at baseline and at 9 months. Retinal vascular parameters (calibre, tortuosity, branching angle, and fractal dimension) were assessed by a semiautomated computer-based programme (Singapore I vessel assessment [SIVA], version 3.0, Singapore Eye Research Institute, Singapore). Changes of retinal vascular parameters and CD4 and CD8 cell counts were defined as the difference between baseline and 9 months. FindingsThe mean age of the 50 participants was 46·36 years (SD 8·67). Participants were ethnically Chinese, Malay, and Indian; most (82%) were Chinese and most male (96%). 35 of 50 patients had CD4 counts of fewer than 200 cells per μL at baseline. Years of HAART ranged from 0 to 11 years. There were significant increments in CD4 cell counts (153·42 vs 227·74 cells per μL; p<0·0001) and CD8 cell counts (819·90 vs 1014·1 cells per μL; p=0·012) between baseline and the 9 month visit, respectively. There were no temporal changes in retinal vascular parameters during this period. After adjustment for age, sex, ethnicity, and years of HAART, each 10 μm reduction in retinal venular calibre at baseline was associated with a 191·08 cells per μL increase in CD8 count (SE 63·54; p=0·004), but not in CD4 cell count, during the 9 month period. Changes of retinal arteriolar calibre and other retinal vascular geometric parameters were not associated with CD4 or CD8 cell count changes. InterpretationRetinal venular narrowing was associated with an increase in CD8 cell counts over time. Our findings suggest that improved retinal venular health was predictive of immune restoration in HIV/AIDS patients who had been on HAART for at least 9 months. Longer follow-up is warranted to monitor the retinal vascular calibre changes in response to HAART treatment. FundingSingapore Medical Research Counsel SIG/11016.

Resonance properties of low-energy electron beams radiation in a two-layer waveguide

We obtain an approximating formula for the low-energy impedance of a two-layer cylindrical waveguide, which allows constructing explicit expressions for the space-time functions that characterize the radiation of a charged particle in a waveguide. The general laws of the evolution of impedance and wake potentials with increasing particle energy and with the change of geometric and electrodynamical parameters of the waveguide are obtained. The settings of waveguides convenient for experimental research and having resonance properties at energies of about 20 MeV are revealed.

Evaluation of Densitometric and Geometric Parameters of the Femur in 14-Month-Old Ostriches Depending on Sex with the Use of Computed Tomography

Abstract The aim of the study was to analyse densitometric and geometric parameters of the compact bone and the trabecular diaphysis of the femur of ostriches with the use of computed tomography. The method has been applied in ostriches for the first time. The study was conducted on the femur of 14-month-old ostriches of both sexes. The obtained results were analysed statistically using one-way ANOVA, with Bonferroni correction for multiple-group comparisons. It was stated that the mineral content (BMC) in the middle of the diaphysis of the femur was significantly higher in males (465.52 mg/mm) than in females (417.67 mg/mm). Similar tendencies were observed for the total bone area (TOT_ A), trabecular area (TRAB_ A), cortical area (CRT_ A), and strength strain index (SSI). The average area of the CRT_A for both sexes was 568.62 mm2 and was lower than the TRAB_A - 884 mm2, at P≤0.05. Moreover, it was found that strength strain index (SSI) of the diaphysis depended on the TOT_A and the TRAB_A. Both features positively correlated with SSI. Pearson’s correlation coefficient for both features was r = 0.97, at P≤0.01. Further research concerning the dynamics of changes of densitometric and geometric parameters occurring with age and involving both sexes is recommended, as there are many locomotion problems in ostriches, especially older ones, used intensively on farms for many years.

Mechanism of the Humicola insolens Cel7B E197S mutant catalyzed flavonoid glycosides synthesis: a QM/MM metadynamics simulation study

The reaction path of Humicola insolens Cel7B E197S catalyzed glycosylation of luteolin by α-lactosyl fluoride was investigated using QM/MM metadynamics simulations. The catalysis proceeds via a sequential mechanism. Firstly, a proton transfers from the glycosyl acceptor, luteolin, to the catalytic acid/base residue, E202. Secondly, the C1–F covalent bond of the glycosyl donor, α-lactosyl fluoride, is cleaved with the assistance of the hydroxyl group of S197, and the F anion captures the carboxylic proton of D199, while the conformation of the glycosyl ring at −1 subsite changes from a chair to a half-chair. Thirdly, a new glycosidic bond is formed between C1 of the lactosyl cation and O4′ of the luteolin anion during which a 1,4B boat conformation comes into being for the subsite −1 glycosyl ring. The rate-limiting step is the C1–F bond cleavage with a barrier of ~25.9 kcal/mol. The change of geometric parameters and hydrogen bonds in the active site along the reaction is analyzed, revealing the important role of residues S197, D199, and E202.

Vitamin D Deficiency Is Not Associated with Changes in Retinal Geometric Parameters in Young People with Type 1 Diabetes

Changes in retinal geometric parameters predict risk and progression of diabetic retinopathy (DR). We have shown that vitamin D deficiency (VDD) is associated with DR. We hypothesized that VDD mediates changes in retinal geometric parameters. Retinal vascular geometric parameters were assessed using a semiautomated computer program in photographs from young people with type 1 diabetes (T1D) (n = 481) and summarized as central retinal arteriolar and venular equivalents (CRAE, CRVE), fractal dimension, length-diameter ratio, branching angle and curvature tortuosity. Parameters were compared between those with and without DR and VDD (25-hydroxyvitamin D concentration ≤ 50 nmol/L). Retinal vascular geometric parameters were also compared across quartiles of vitamin D levels. Median CRVE was higher in patients with DR compared with those without (median (IQR) CRVE 247.3 μm (31.3) versus 238.8 μm (23.5), P = 0.01). Fractal dimension was marginally greater in patients without VDD (1.49 (0.06) versus 1.47 (0.07) P = 0.03). There was no difference in CRAE, CRVE, length-diameter ratio, branching angle, and curvature tortuosity between those with and without VDD and across quartiles of 25OHD. In conclusion, DR is associated with higher CRVE in young people with T1D; however, VDD is not associated with changes in retinal vascular geometric measures, suggesting an earlier role in the time course of DR pathogenesis.

Carrying Capacity of Horizontal Cylindrical Shells on Saddle Supports

The article is devoted to the influence of carrying capacity on the stability of laterally loaded cylindrical shells. The influence of initial imperfections on the stability of the laterally loaded shell is also taken into consideration. The investigated structure is a simplified variant of the case of cylindrical shell (road tank – for example Pascenko, 2009; Pascenko, Stejskal, 2008) located on two saddle supports. The initial shape imperfections are created by pushing the saddle support into the shell. The new deformed shape is used as an imperfect shell in the following nonlinear analysis of stability. The main objective of the analysis is to find the reduction factor α depending on the change of geometric parameters of the numerical model (embracing angle 2θ, wall thickness t). The shell deformation around the saddle support is also monitored. Numerical analysis is carried out by means of a computer program COSMOS/M based on the finite element method (FEM).

Effects of eccentric training on mechanical properties of the plantar flexor muscle-tendon complex

Eccentric training is a mechanical loading classically used in clinical environment to rehabilitate patients with tendinopathies. In this context, eccentric training is supposed to alter tendon mechanical properties but interaction with the other components of the muscle-tendon complex remains unclear. The aim of this study was to determine the specific effects of 14 wk of eccentric training on muscle and tendon mechanical properties assessed in active and passive conditions in vivo. Twenty-four subjects were randomly divided into a trained group (n = 11) and a control group (n = 13). Stiffness of the active and passive parts of the series elastic component of plantar flexors were determined using a fast stretch during submaximal isometric contraction, Achilles tendon stiffness and dissipative properties were assessed during isometric plantar flexion, and passive stiffness of gastrocnemii muscles and Achilles tendon were determined using ultrasonography while ankle joint was passively moved. A significant decrease in the active part of the series elastic component stiffness was found (P < 0.05). In contrast, a significant increase in Achilles tendon stiffness determined under passive conditions was observed (P < 0.05). No significant change in triceps surae muscles and Achilles tendon geometrical parameters was shown (P > 0.05). Specific changes in muscle and tendon involved in plantar flexion are mainly due to changes in intrinsic mechanical properties of muscle and tendon tissues. Specific assessment of both Achilles tendon and plantar flexor muscles allowed a better understanding of the functional behavior of the muscle-tendon complex and its adaptation to eccentric training.

Research on Secondary Stress for Steel-Pipe Truss under the Influence of Geometric Parameters

Based on FEA software ANSYS, 26 steel-pipe truss models with hinge joints or rigid joints are presented, the distributions of total structure secondary stress are analysed under the influences of the mechenical behavior of total structure. The results indicate that the secondary stresses on several links have reached the certain value, and changed regularly following the change of geometric parameters. These changes should be considered in engineering design.

Diametral compression test with composite disk for dentin bond strength measurement – Finite element analysis

ObjectiveA novel technique using a composite disk under diametral compression was presented in a previous study for measuring the bond strength between intracanal posts and dentin. This study deals with the stress distribution within the composite disk to allow the bond strength to be calculated accurately. The effects of changing geometrical and material parameters on the post–dentin interfacial stress are also evaluated. MethodsThe finite element method with 3D models is used to analyze the stress distribution and to carry out the sensitivity analysis. Progressive post–dentin interfacial debonding is also simulated to better understand the failure process observed in experiments. ResultsMaterial mismatch causes stress concentrations at the interfaces. The results are presented as correction factors to be used in conjunction with the analytical solution for a homogeneous disk. Comparison between the stresses at the post–dentin interface and those in dentin confirms that interfacial debonding will take place prior to fracture in the dentin. SignificanceThe numerical solutions presented here will facilitate the adoption of the composite disk in diametral compression for bond strength measurement.

On the mechanics of a detaching retina

A mechanics-based mathematical model for retinal detachment is developed, incorporating an energy-based criterion for propagation. Retinas with and without central tears are considered and contraction of the vitreous and extension of its fibrils, along with a pressure difference across the retina, are taken as the stimuli for detachment propagation. In addition to the equations of motion, boundary and matching conditions, the variational formulation yields the self-consistent energy release rate that governs detachment, and formulae for critical stress and critical deflections that provide a rational basis for measuring critical parameters. Exact analytical solutions are established for axisymmetric detachment of retinas with and without tears, and numerical simulations are performed based on these solutions. The results yield characteristic behaviour, including threshold levels and stability of detachment, 'dimpling' of the detaching retina, the effects of changes in material and geometric parameters, and the influence of the presence and size of the retinal tear on detachment propagation. The model predicts that once detachment ensues it does so in an unstable manner and is extensive in scope. This is in agreement with clinical observation. Results also suggest that, under appropriate conditions, the presence and size of a retinal tear or hole can have a 'stabilizing' effect with regard to detachment propagation.

Theoretical study on ion-pair recognition of M+X- (M = Li, Na, K and X = F, Cl, Br) by formylaminocalix[4]arene derivatives

DFT calculations were reported for calix[4]arene derivatives [i.e., formylaminocalix[4]arene (1) and formylaminocalix[4]bis-crown-3 (2)] binding cations M(+) (Li(+), Na(+), and K(+)) and anions X(-) (F(-), Cl(-), and Br(-)) simultaneously. The B3LYP function together with the LANL2DZp basis set was used in order to obtain insights into the factors determining the nature of the interactions of these compounds with X(-) and M(+). Based on the molecular electrostatic potential (MEP) analysis, the result complexes M(+)X(-)/H (H = 1, 2) were investigated. For all the complex structures, the most pronounced changes in geometric parameters upon interaction were observed in the host segment compared with the free receptors. Two main types of driving force, N-H∙∙∙X(-) hydrogen bonds and electrostatic interactions between M(+) and oxygen atoms, were confirmed. The recognition trends for 1 and 2 toward M(+)X(-) followed the same order: M(+)F(-) > M(+)Cl(-) > M(+)Br(-) (M(+) is same to each other) and Li(+)X(-) > Na(+)X(-) > K(+)X(-) (X(-) is same to each other). The binding energy, enthalpy change, Gibbs free energy change, and entropy change of complexation formation have been studied by the calculated thermodynamic data. In all cases, the inclusion energy changes with 2 were more negative than those with 1, correlating with the flexible space available by the two crown ether moieties in 2. The calculated results of the model system have been reported and should be useful to the experimental research in this field.

Skew ray tracing and sensitivity analysis of hyperboloid optical boundary surfaces

One of the most popular mathematical tools in fields of robotics, mechanisms and computer graphics is the 4×4 homogeneous transformation matrix. Our group's previous application of the homogeneous transformation matrix to flat and spherical optical boundaries has been extended to hyperboloid surfaces for: (1) skew ray tracing to determine the paths of reflected/refracted skew rays; (2) sensitivity analysis for direct mathematical expression of differential changes of incident points and reflected/refracted vectors with respect to changes in incident light sources and boundary geometric parameters; (3) a sensitivity analysis-based merit function derived directly from mathematical expression of catadioptric imaging system components. The presented methodology is highly suited to digital implementation and offers direct and rapid analytical statement of ray path, chief ray, marginal rays and merit functions of optical systems.

Negative-index metamaterial at visible frequencies based on high order plasmon resonance

A type of negative-index metamaterial composed of periodic arrays of SRRs is proposed and numerically investigated in the visible frequencies. Employing the high order magnetic resonance to induce negative permeability, negative refractive index is obtained between 395 THz and 430 THz with the maximum FOM=4.59. The effective permeability exhibits a rapid convergence with increasing number of metamaterial layers. Different responses from the electric and magnetic resonances to the changing geometric parameters are compared and analyzed in terms of the field distribution. Simulation results show that the high order magnetic resonance can be greatly enhanced at visible frequencies as well as effectively tuned over a wide spectral range without notably altering the coupling between unit cells.

Finite element study on the predicted equivalent stresses in the artificial hip joint

The subsurface fatigue that occurs in the Ultra-High Molecular Weight Polyethylene (UHMWPE) hip joint cup has been identified to be correlated with the contact stress at that cup. This cup stress is known to be affected by the implant design, dimensions and materials. In this study, a 3D finite element modeling has been used to investigate the effects on the cup contact stress when using low stiffness Titanium alloy (Ti) as a femur head. Also, the effects on the cup contact stress due to using different sizes of femur heads, and the presence of metal backing shell with different thicknesses are studied. The finite element results show that the use of low stiffness Ti alloy femur head results in a significant decrease in the cup contact stress compared with Stainless Steel (SS) and Cobalt Chromium (Co Cr Mo) femur heads. The presence of metal backing shell up to 1 mm thickness results in a remarkable decrease in the cup contact stresses especially for small femur heads. Finally, the use of larger femur heads, up to 32 mm diameter, results in significant decrease in the overall predicted hip joint contact. The present results indicate that any changes in design and geometrical parameters of the hip joint have significant consequences in the long term behaviour of the artificial hip joint and should be taken into consideration.

Hydrogen Bonding as a Modulator of Aromaticity and Electronic Structure of Selectedortho-Hydroxybenzaldehyde Derivatives

Properties of hydrogen bonds can induce changes in geometric or electronic structure parameters in the vicinity of the bridge. Here, we focused primarily on the influence of intramolecular H-bonding on the molecular properties in selected ortho-hydroxybenzaldehydes, with additional restricted insight into substituent effects. Static models were obtained in the framework of density functional theory at B3LYP/6-311+G(d,p) level. The electronic structure parameters evolution was analyzed on the basis of Atoms In Molecules (AIM) and Natural Bond Orbitals methods. The aromaticity changes related to the variable proton position and presence of substituents were studied using Harmonic Oscillator Model of Aromaticity (HOMA), Nucleus-Independent Chemical Shift (NICS) and AIM-based parameter of Matta and Hernández-Trujillo. Finally, Car-Parrinello molecular dynamics was applied to study variability of the hydrogen bridge dynamics. The interplay between effects of the substitution and variable position of the bridged proton was discussed. It was found that the hydrogen bond energies are ca. 9-10 kcal/mol, and the bridged proton exhibits some degree of penetration into the acceptor region. The covalent character of the studied hydrogen bond was most observable when the bridged proton reached the middle position between the donor and acceptor regions. The aromaticity indexes showed that the aromaticity of the central phenyl ring is strongly dependent on the bridged proton position. Correlations between these parameters were found and discussed. In the applied time-scale, the analysis of time evolution of geometric parameters showed that the resonance strengthening does not play a crucial role in the studied compounds.

Vibration of functionally graded cylindrical shells with ring support

In this paper, the vibrational behavior of functionally graded cylindrical shells with intermediate ring supports is studied. Theoretical formulation is established based on Sanders’ thin shell theory. The governing equations of motion are derived, using an energy functional and by applying the Ritz method. Using an appropriate set of displacement functions, the energy equations lead to an eigenvalue problem whose roots are the natural frequencies of vibration. Material properties are assumed to be graded in the thickness direction, according to the power-law volume fraction function. A functionally graded cylindrical shell, made up of a mixture of ceramic and metal, is considered. The influence of some commonly used boundary conditions and the effect of changes in shell geometrical parameters and variations in ring support position on vibration characteristics are studied. The results obtained for a number of particular cases show good agreement with those available in the open literature.

The ZrO/W(100) Schottky cathode: Morphological modification and its effect on long term operation

An investigation of the change in various geometric and emission parameters over the life cycle of nine ZrO/W(100) Schottky cathodes was performed. The initial shape for all emitters was “Stage 1,” i.e., a large square, low work function (100) facet intersected by four (112) and (110) facets. The ending shape for all emitters was “Stage 0,” i.e., a round central (100) facet with four side (110) planes. Change in geometric parameters such as emitter apex radius r, cone angle α, central (100) facet size f, and neck size L were measured at the beginning and after 10 000 to 18 000 h of cathode operation. For a particular end form (or Stage), f scaled linearly with emitter radius r. In addition, emission parameters such as the axial angular current density I′, total current It, work function ϕ, electric field F, and extraction voltage Ve were monitored continuously. Of the nine sources investigated four experienced collapsing net planes (ring collapse) on the central (100) crystal facet. The emitters with ring collapse events had the largest increase in r and a corresponding reduction in the field factor β = F/Ve. For the most part β, ϕ, and r remained unchanged for those emitters not having ring collapse events. The ending I′ values mostly decreased at a constant Ve, but less so for those emitters with no ring collapse. Experimental results showed that for I′ ≤ 0.3 mA/sr and T = 1800 K ring collapse occurs. In contrast, for I′ ≥ 0.3 mA/sr ring collapse does not occur. For all emitters investigated, the parameters exhibiting the largest increase over the course of the life test were L and It, whereas α was typically unchanged.

Analysis of Mechanical Performance Considering Damage Accumulation of Intersecting Joints in Steel Structures

The mechanical behaviors of intersecting joints considering damage accumulation in steel tube structures is analyzed through the FE-program ABAQUS. The stress characteristic and failure modes of these joints are concluded. Especially, it has been analyzed influence of the change of geometric parameters to mechanical behavior of joints. Finally, the results indicate the joints have a good mechanical performance and good plastic deformation as to excessive local buckling of chord under the loads.

In vitro evaluation of stiffness graded artificial hip joint femur head in terms of joint stresses distributions and dimensions: finite element study

The aim of the present work is to evaluate the artificial hip joint femur head that is made of Stiffness Graded (SG) material in terms of joint stresses distributions and dimensions. In this study, 3D finite element models of femur head that is made of SG material and traditional femur heads made of Stainless Steel (SS), Cobalt Chromium alloy (Co Cr Mo) and Titanium alloy (Ti) have been developed using the ANSYS Code. The effects on the total artificial hip joint system stresses due to using the proposed SG material femur head (with low stiffness at the outer surface and high stiffness at its core) have been investigated. Also, the effects on the polymeric cup contact stresses due to the use of different sizes of femur heads, presence of metal backing shell and presence of radial clearance (gap) between cup and femur head have been investigated. The finite element results showed that using SG femur head resulted in a significant reduction in the cup contact stresses even for small femur heads compared with Ti alloy, SS and Co Cr Mo femur heads. The presence of radial clearance resulted in significant increase in the cup stresses especially for small femur heads. Finally, the presence of SS metal backing shell resulted in slight increase in the hip joint stresses especially for small femur head joints. This work analyzes successfully the usage of proposed SG material as femur head in order to reduce the predicted stresses at the total hip joint replacement due to the redistribution of strain energy in the hip prostheses. Therefore, the present results suggest that minor changes in design and geometrical parameters of the hip joint have significant consequences on the long term use of the joint and should be taken into consideration during the design of the hip joint.