Moderate Bending Research Articles

Shear and Flexural Buckling Modes of a Spherical Sandwich Shell in a Centrosymmetric Temperature Field Inhomogeneous across the Thickness

Problems on buckling modes (BMs) are considered for a spherical sandwich shell with thin isotropic external layers and a transversely soft core of arbitrary thickness in a centrosymmetric temperature field inhomogeneous across the shell thickness. For their statement, the two-dimensional equations of the theory of moderate bending of thin Kirchhoff–Love shells are used for the external layers, with regard for their interaction with the core; for the core, maximum simplified geometrically nonlinear equations of thermoelasticity theory, in which a minimum number of nonlinear summands is retained to correctly describe its pure shear BM, are utilized. An exact analytical solution to the problem on initial centrosymmetric deformation of the shell is found, assuming that the temperature increments in the external layers are constant across their thickness. It is shown that the three-dimensional equations for the core, linearized in the neighborhood of the solution, can be integrated along the radial coordinate and reduced to two two-dimensional differential equations, which supplement the six equations that describe the neutral equilibrium of the external layers. It is established that the system of eight differential equations of stability, upon introduction of new unknowns in the form of scalar and vortical potentials, splits into two uncoupled sets of equations. The first of them has two kinds of solutions, by which the pure shear BM is described at an identical value of the parameter of critical temperature. The second system describes a mixed flexural BM, whose realization, at definite combinations of determining parameters of the shell and over wide ranges of their variation, is possible for critical parameters of temperature by orders of magnitude exceeding the similar parameter of shear BM.

Inducing and modulating anisotropic DNA bends by pseudocomplementary peptide nucleic acids.

DNA bending is significant for various DNA functions in the cell. Here, we demonstrate that pseudocomplementary peptide nucleic acids (pcPNAs) represent a class of versatile, sequence-specific DNA-bending agents. The occurrence of anisotropic DNA bends induced by pcPNAs is shown by gel electrophoretic phasing analysis. The magnitude of DNA bending is determined by circular permutation assay and by electron microscopy, with good agreement of calculated mean values between both methods. Binding of a pair of 10-meric pcPNAs to its target DNA sequence results in moderate DNA bending with a mean value of 40-45 degrees, while binding of one self-pc 8-mer PNA to target DNA yields a somewhat larger average value of the induced DNA bend. Both bends are found to be in phase when the pcPNA target sites are separated by distances of half-integer numbers of helical turns of regular duplex DNA, resulting in an enhanced DNA bend with an average value in the range of 80-90 degrees. The occurrence of such a sharp bend within the DNA double helix is confirmed and exploited through efficient formation of 170-bp-long DNA minicircles by means of dimerization of two bent DNA fragments. The pcPNAs offer two main advantages over previously designed classes of nonnatural DNA-bending agents: they have very mild sequence limitations while targeting duplex DNA and they can easily be designed for a chosen target sequence, because their binding obeys the principle of complementarity. We conclude that pcPNAs are promising tools for inducing bends in DNA at virtually any chosen site.

Mechanism of bending with kinking of a single-walled carbon nanotube

This paper explores the mechanism of bending with kinking of a long single-walled carbon nanotube under pure bending with moderate bending angles. The prebuckling response was modeled using the existing continuum mechanics theory accounting for the ovalization of the cross section. The post-buckling behavior was characterized by the development of an elastic kink mechanism, considering the van der Waals force. It was found that the post-buckling strain energy increases almost linearly with the bending angle. The van der Waals force facilitates the kink development and its effect becomes more pronounced at large bending angles.

A LuxR-type regulator from Agrobacterium tumefaciens elevates Ti plasmid copy number by activating transcription of plasmid replication genes.

TraR, a LuxR-type quorum-sensing transcription factor in Agrobacterium tumefaciens, activates genes required for conjugal transfer of the Ti plasmid and also enhances the copy number of a nopaline-type Ti plasmid. Here, we show that TraR increases the copy number of an octopine-type Ti plasmid up to eightfold and that TraR activates transcription of the repABC operon up to 25-fold. The ability of TraR to increase copy number was strictly dependent on several TraR-activated promoters of this operon, indicating that TraR affects copy number solely at the level of transcription. Promoter resections and mRNA transcript analysis revealed the presence of three TraR-dependent promoters. Two TraR-dependent transcription start sites are located 45.5 and 65.5 nucleotides downstream of a site called tra box II, whereas the third start site lies 42.5 nucleotides downstream of a site called tra box III. Purified TraR bound to both tra boxes with comparable affinities, causing moderate DNA bending. TraR bound and bent these two sites independently rather than synergistically. Alteration of tra box III to match the consensus sequence dramatically increased TraR-dependent expression of repABC and plasmid copy number. TraR-dependent elevation of Ti plasmid copy number caused a three- to fourfold increase in plant tumorigenesis.

A comparative study on vehicle aluminum and steel hood assemblies

A vehicle hood experiences several loading conditions during its lifetime. It may vary from the application of moderate torsion and bending moments during hood opening and closing to a severe dynamic crumpling in vehicle frontal crash. Hence, hood assembly should be capable to fulfill various structural requirements. The present study aims at comparing two alternative designs (steel and aluminum) from static strength, pedestrian protection, and crashworthy points of view. Torsion and bending strengths, head injury criterion (HIC) values, energy absorption capacities, and hinge forces are the main results which the comparison is made on. In spite of a forty percent reduction in hood assembly weight, the aluminum hood shows an acceptable level of behavior in most cases.

Bond angle versus torsional deformation in an overcrowded alkene: 9-(2,2,2-triphenylethylidene)fluorene.

Competition between bond angle and torsional strain in sterically crowded alkenes generally causes twisting in tetrasubstituted alkenes, while most structurally characterized trisubstituted alkenes are planar. To investigate structural effects of steric repulsion between a planar aromatic ring and a vicinal triphenylmethyl (trityl) group, 9-(2,2,2-triphenylethylidene)fluorene (1 a) was synthesized by reaction of 9-bromomethylenefluorene with triphenylmethyllithium. For comparison with a less strained analogue, 9-ethylidenefluorene (1 b) was prepared by reaction of fluorenone with ethylmagnesium bromide. The X-ray crystal structures show that the difference between bond angles at the 9-fluorenyl carbon atom is much larger for 1 a (12.9 degrees) than 1 b (2.6 degrees). Bond angle and torsional deformations were compared theoretically (HF/6-31+G*) with the tert-butyl analogue (1 c), 1,2,2-tri-tert-butylethene (7), and 2,4,4-trimethyl-2-pentene (8) and crystallographically with six known 1,1-diaryl-2-tert-alkylethenes (2). The trisubstituted alkenes formed three groups with 1) large angle distortion with moderate twisting (1 a, 1 b, and 7), 2) moderate bending with a large range of torsional angles (2), and 3) little bending or twisting (1 b and 8). For the entire series, there appears to be a delicate balance between angle and torsional deformation, but twisting appears to produce smaller relief from steric strain than angle bending. In the crystallographically characterized trisubstituted alkenes, the choice between the two is mainly determined by more subtle packing forces.

Compression wood has little impact on the water relations of Douglas-fir (Pseudotsuga menziesii) seedlings despite a large effect on shoot hydraulic properties.

• Compression wood has been shown to reduce stem permeability, but it is not known to what extent it affects leaf-level processes. Here, we report whole-plant hydraulic properties of Douglas-fir (Pseudotsuga menziesii) seedlings induced to form varying amounts of compression wood. • Seedlings were grown under three bending treatments to assess the impact of compression wood on hydraulic properties, including stomatal conductance (gs ), above-ground shoot conductance (Kl(abg) ), and both specific and leaf area-specific conductivity (ks and kl , respectively). • Kl(abg) was significantly lower (50% reduction) in severely bent seedlings than in controls. Similarly, both ks and kl of the main axis were significantly reduced (by 52% and 46%, respectively) in severely bent seedlings relative to controls. Seedlings in the moderate bending treatments had ks and kl that were intermediate between controls and severe bending. • Despite clear differences in above-ground shoot hydraulic properties, severely bent seedlings maintained the same water potentials as controls and had similar diurnal patterns of gs . This suggests that when the entire soil-plant-atmosphere continuum is considered, even a severe reduction in stem ks caused by compression wood has little impact on leaf-level processes.

Effect of bending load on the creep failure behaviour of a pressurised thick walled CrMoV pipe weldment

This paper describes the results of a finite element investigation into the effects of bending on the creep failure behaviour of an internally pressurised thick walled pipe weld. The material properties used were those for a service-exposed 1/2Cr1/2Mo1/4V:2 1/4Cr1Mo weldment at 640 °C. The peak rupture stresses in each material zone, which were obtained from steady-state analyses, were used to predict failure lives for a range of bending load levels. The rupture stresses showed very little variation across the heat-affected zone, in the dominant stress regions, for low and moderate bending loads. However, the variation is more significant when the bending load is high but still within the allowable limits of design codes. The results obtained indicate that, in addition to the pressure, there is a higher probability of type IV cracking occurring, when an external (system) bending load is present. The results obtained were compared with those obtained for the uniform end load cases.

Solution structure of a DNA duplex with a chiral alkyl phosphonate moiety.

The solution structures of two DNA decamers of sequence d(CCACCpxGGAAC).(GTTCCGGTGG) with a chiral alkyl phosphonate moiety (px) have been determined using NMR and restrained molecular dynamics simulations and compared with the solution structure of the unmodified duplex. The (1)H NMR spectra of two samples with pure stereochemistry in the modified phosphate have been assigned. The structures of both diastereoisomers, as well as the unmodified control duplex, have been determined from NMR-derived distance and torsion angle constraints. Accurate distance constraints were obtained from a complete relaxation matrix analysis of the NOE intensities. The structures have been refined with state of the art molecular dynamics methods, including explicit solvent and applying the particle mesh Ewald method to properly evaluate the long-range electrostatic interactions. In both cases, the calculations converge to well-defined structures, with RMSDs of approximately 1 A. The resulting structures belong to the general B family of DNA structures, even though the presence of the alkyl phosphonate moiety induces some slight displacement to the A-form in the neighborhood of the modified phosphate. Partial neutralization of this phosphate and the steric effect of the alkyl moiety provoke moderate bending in the DNA. This effect is more pronounced in the S diastereoisomer, where the alkyl group points inwards to the double helix.

A population of variants of a viroid closely related to citrus viroid-I in citrus plants.

Sequencing analyses showed a population of variants consisting of 325-330 nucleotides (nt) of a viroid closely related to citrus viroid (CVd)-I in citrus plants. These variants, for which we propose the tentative acronym CVd-I-LSS (low sequence similarity), have only 82-85% sequence similarities to CVd-I variants. A phylogenetic tree showed that the CVd-I-LSS variants formed an individual cluster that was distinct from that of the CVd-I variants, but no intermediate variants were found which could continuously connect the population of CVd-I-LSS variants with that of CVd-I variants. Citrons (Citrus medica L.) inoculated with the CVd-I-LSS seemed to show not only moderate leaf bending like citrons infected with CVd-I but also slightly more severe epinasty than citrons with CVd-I. Other biological properties of CVd-I-LSS, such as the host range, will need to be determined in order to clarify whether CVd-I-LSS is a new viroid species or a distinct strain of CVd-I. Most of the nucleotide changes between the CVd-I-LSS and CVd-I variants were found at complementary positions of the upper and lower strands within the putative pathogenic, variable, and right terminal domains, as well as in the region surrounding the central conserved region of the predicted secondary structure of CVd-I-LSS.

NMR structure of tissue inhibitor of metalloproteinases-1 implicates localized induced fit in recognition of matrix metalloproteinases

A high quality solution structure of the matrix metalloproteinase inhibitory N-terminal domain of recombinant human tissue inhibitor of metalloproteinases-1 (N-TIMP-1) has been determined. For the rigidly packed residues, the average RMSD to the mean structure is 0.57 Å for the backbone atoms and 1.00 Å for all heavy atoms. Comparison of the solution structure of free N-TIMP-1 with the crystal structure of TIMP-1 bound to the catalytic domain of MMP-3 (Gomis-Rüth et al., 1997) shows that the structural core of the β barrel flanked by helices is nearly unchanged by the association with MMP-3, evident from a backbone RMSD of 1.15 Å. However, clear differences in the conformation of the MMP-binding ridge of free and MMP-bound TIMP-1 suggest induced fit throughout the ridge. The MMP-dependent conformational changes in the ridge include a dramatic bending of AB loop residues Glu28 through Leu34, moderate hinge bending of the CD-loop about residues Ala65 and Cys70, and modest bending of the Cys1 through Pro6 segment. A large number of interresidue Nuclear Overhauser enhancements (NOEs) augmented by stereospecific assignments, torsion restraints, and dipolar couplings (an average of 18 non-trivial restraints per residue) engender confidence in these structural inferences. A tight cluster of three lysine residues and one arginine residue atop β-strands A and B, and identical among TIMP sequences, form the heart of a highly conserved electropositive patch that may interact with anionic components of the extracellular matrix.

Characterization of the M.S structure by the surface photoelectrical voltage method

Photovoltages (surface photovoltage plus Dember voltage) were calculated, taking into consideration the influence of charge exchange between a continuum of surface states and the semiconductor, the barrier lowering as a result of the Schottky effect, the applied voltage drop and transmission coefficient across the interfacial layer. For moderate band bending, the photovoltage depends on several parameters which renders their reliable determination very difficult. For extreme band bending, however, only doping factor, mobility ratio and relative excess concentration enter into given formulas. The obtained analytical expression includes saturation effects at the surface, so that the photovoltage (SPV) does not exceed the thermodynamic band bending. The bulk effect of the Dember voltage is then added to obtain the relationship between the light generated current and open circuit voltage at the terminals. Results were applied to Schottky barrier diodes Au/InP(n). The InP substrate is restructured by some monolayers of InSb thin film [L. Bideux, B. Gruzza, A. Porte, H. Robert, Surface and Interface Analysis 20 (1993) 803]. Good agreement between parameters determined in this way and otherwise indicates the validity of the model and the approximations used in this work.

Investigations of trans-Rh(PY 3) 2(CO)X (X = NCO, NCS; Y = H, Me, Ph) complexes using density functional theory

In our computational study of trans-Rh(PH 3) 2(CO)X (X = NCO, NCS), we employed the Becke hybrid three-parameter DFT method using the Lee, Yang and Parr correlation functional (B3LYP) and the double-ζ plus polarization basis set (DZP). Our optimized complexes have a slightly distorted square-planar structure with moderate bending of the phosphine ligands towards the uninegative ligand X −. The predicted structures compare favorably with experimental data for trans-Rh(PPh 3) 2(CO)NCO. Computationally predicted vibrational frequencies ν(CO) and ν(CN) for trans-Rh(PPh 3) 2(CO)NCO compare well with solution-phase FTIR data. Based upon trends in computed and experimental frequency shifts, we predict solution-phase ν(CO) frequencies for trans-Rh(PY 3) 2(CO)NCS (Y = Me, Ph). Performance of B3LYP and BLYP functionals is also discussed and compared to results obtained using the Hartree-Fock (HF) method.

Geometrically nonlinear bending of thin-walled shells and plates under creep-damage conditions

A phenomenological constitutive model for characterization of creep and damage processes in metals is applied to the simulation of mechanical behaviour of thin-walled shells and plates. Basic equations of the shell theory are formulated with geometrical nonlinearities at finite time-dependent deflections of shells and plates in moderate bending. Numerical solutions of initial/boundary-value problems have been obtained for rectangular thin plates (two-dimensional case) and axisymmetrically loaded shells of revolution (one-dimensional case). Based on the numerical examples for the two problems, the influence of geometrical nonlinearities on the creep deformation and damage evolution in shells and plates is discussed.

Creep bending of thin-walled shells and plates by consideration of finite deflections

A phenomenological constitutive model for the characterization of creep-damage processes of metals is applied to the numerical analysis of thin-walled shells and plates. The governing equations of the theory of shallow shells are used taking into account geometrical nonlinearities connected with finite time-dependent deflections by moderate bending. The solutions of the initial-boundary value problem are obtained for thin rectangular plates in order to show the influence of geometrical nonlinearity on results of time-dependent deformation and stress redistribution as well as on estimations of the failure time.

Structural Investigations of trans-Rh(PY3)2(CO)X (X = F, Cl, NCO; Y = H, Me, Ph) Using Density Functional Theory and X-ray Analysis

A study of trans-Rh(PY3)2(CO)X (X = F, Cl; Y = H, Me) and trans-Rh(PH3)2(CO)NCO using density functional theory is presented together with the results of new high-resolution, low-temperature x-ray data analysis of trans-Rh(PPh3)2(CO)X (X = F, NCO). In our calculations, we employed the Becke-exchange functional with the Lee, Yang, and Parr correlation functional (B-LYP) and the double-ζ plus polarization basis set (DZP). Our optimized complexes have a slightly distorted square-planar structure with moderate bending of the phosphine ligands toward the uninegative ligand X-. The predicted structures compare favorably with experimental data for trans-Rh(PPh3)2(CO)X (X = F, Cl, NCO). New X-ray data for trans-Rh(PPh3)2(CO)X (X = F, NCO) clearly indicate a nonlinear configuration of P−Rh−P atoms, in agreement with our calculations. The apparent linear configuration of P−Rh−P atoms recently reported for the structure of the orthorhombic form of trans-Rh(PPh3)2(CO)Cl is most likely an artifact resulting from the d...

Structure of trans-Rh(PH3)2(CO)X (X = F, Cl) Using Hartree-Fock/MBPT(2) and Density Functional Theory

A study of trans-Rh(PH3)2(CO)X (X = F, Cl) using Hartree-FocWmany-body perturbation theory and density functional methods is presented. We report optimized Hartree-Fock and MBPT(2) structures employing effective core potentials with double-g plus polarization basis sets including f-type functions. Optimized structures using density functional methods, including those with gradient-corrected exchange-correlation functionals, are also reported. Both ab initio methods yield complexes which have a slightly distorted squareplanar structure with moderate bending of the phosphine ligands toward the halide. The predicted structure of the chloro complex is compared with experimental data for truns-Rh(PPh3)2(CO)Cl.

Adaptive finite element analysis of geometrically non‐linear plates and shells, especially buckling

AbstractBased on both moderate and finite rotation bending theories of thin elastic shells including shear deformation, adaptive non‐linear static finite element analysis is treated within a displacement approach and h‐adaptivity. The a posteriori error indicator given by Rheinboldt, gained by linearization, is investigated in order to decide whether the deformations influence the indicator explicitely and how parameter dependent problems (like the Reissner–Mindlin model) behave in the process of adaptation. In order to achieve overall consistency, dimensional adaptivity (to 3‐D elasticity) is implemented within disturbed subdomains, especially at supports.Results are that Rheinboldt's error indicator is valid under certain restrictions but not directly at bifurcation points and that robustness is not improved by adaptation.Nested quadrilateral finite elements are used for studying pre‐ and post‐buckling states of plates and shells.

Copper(I)-induced activation of monosubstituted acetylenes. Perturbation of ligand geometry resulting from π-complexation

Three complexes between monosubstituted acetylenes, viz. phenylacetylene, propargyl chloride and propargyl alcohol, and copper(I) chloride have been prepared by direct reaction between copper(I) chloride and the relevant acetylenes. Changes in ligand geometry ensuing from π complexation to copper(I) have been investigated by infrared spectroscopy and crystal structure determinations. In all three compounds copper(I) exhibits trigonal pyramidal coordination geometry with a long apical CuCl bond, the trigonal plane being composed of the midpoint of π-acetylenic linkage and two chloride ligands. The CuC bond lengths are 1.999(4) and 2.066(3) Å in [CuCl(HCCC 6H 5)] ( 1), 2.004(3) and 2.004(4) Å in [CuCl(HCCCH 2Cl)] ( 2) and 2.006(10) and 2.018(9) Å in [CuCl(HCCCH 2OH)] ( 3). The CC bond is lengthened only slightly on coordination, although ν(CC) is lowered by 133, 144 and 154 cm −1 for 1, 2 and 3, respectively, and there is moderate bending back of the HCC and RCC angles, indicating a relatively weak copper (I)alkyne interaction. ν(C sp H) is lowered by 120, 83 and 110 cm −1, relative to the values for the free ligands, in 1–3, respectively. Although this suggests activation of the C sp PH bonds, this is not supported by unusual structural features involving the acetylenic hydrogen atoms.

Mechano-sorptive creep mechanism of wood in compression and bending

A model is introduced which links the mechano-sorptive behaviour of wood subjected to moderate and high compression or bending stresses parallel to grain to the formation of slip planes in the cell wall. Slip plane formation is dependent on the breaking of hydrogen bonds, which process is directly related to the amount of moisture change. The dramatic change of microfibril orientation in slip plane zones cause an increase of the longitudinal shrinkage/swelling and a decrease of the modulus of elasticity. These features of slip plane formation account for both the magnitude and the oscillation of the excessive mechano-sorptive creep associated with compression and bending parallel to grain. A summary is given of the characteristics of the mechano-sorptive effects, and the model is discussed in the light of these effects.