bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of protein models obtained by small-angle X-ray scattering and crystallography
Authors: Durchschlag Helmut , Zipper Peter , Krebs Angelika
Published: November 2007

The technique of small-angle scattering can be used advantageously for deriving the shape of proteins in solution. Presently, advancedab initioapproaches allow the reliable automated reconstruction of particle shapes. In particular, the procedures based on simulated annealing such asDAMMINin combination with tight constraints turn out to be highly qualified for establishing realistic models. The appearance of the models, the comparison of experimental and calculated scattering profiles, and the agreement of both structural and hydrodynamic parameters can be used as evaluation criteria. In addition, the comparison of the SAXS-based low-resolution models with high-resolution crystal structures allows the models under analysis to be checked. Superimposing the SAXS models and the crystallographic structures yields evidence for the validity of the SAXS-derived models and far-reaching agreement of the protein structure in the crystal and in solution, both in the case of small molecules and giant multisubunit proteins, and for proteins of quite different shape. Modelling of molecules requires application of a variety of sophisticated approaches and consideration of several precautions. These include the use of substitutes for amino-acid residues missing in the crystallographic databases, application of special aligning, superimposing, filtering and averaging procedures, drastic reduction of the enormous number of beads to be used for modelling large molecules from crystal data, and the application of hydration contributions. Reconstructions of low-resolution SAXS-based shapes and comparisons with high-resolution X-ray structures were performed with glycogen phosphorylase, citrate synthase and an annelid haemoglobin. In the latter case, both the dodecameric subunit and the giant 3.5 MDa complex were studied, together with reconstructions of hypothetical complexes from building blocks.
Least-squares thermal expansion tensor of vanadate and arsenate triclinic apatites derived from laboratory X-ray powder diffraction cell data
Authors: Whitfield Pamela S. , Le Page Yvon , Mercier Patrick H. J. , Kim Jean Y.
Published: November 2007

Cell data for triclinic end-member Ca10(VO4)6F2and Ca10(AsO4)6F2apatites were measured in the temperature range from 303 to 773 K. Reversible phase transitions at, respectively, 453 and 583 K are shown and attributed to mobility of contact surfaces for triclinic twins within a mosaic block at about the transition temperature. The simple method developed here is based on 12 separate linear regressions. The first six regressions are on observations for individual lattice parametersa,b,c, α, β or γ. The last six are on linear data sets, each involving a single expansion coefficient α11, α22, α33, α12, α13or α23. Singular-value decomposition of the least-squares thermal expansion tensors obtained below the transition temperatures shows that both materials actually contract considerably along [2\bar14] upon heating. Expansion in the plane perpendicular to this direction differs somewhat for the two materials. In contrast, the expansion above the transition temperature is barely anisotropic in both materials. The ability to measure thermal expansion tensors for triclinic materials with decent accuracy from routine powder data is demonstrated. This possibility extends the applications of the powder method because some samples may not be readily available in single-crystal form.
Microstrain-like diffraction-line broadening as exhibited by incommensurate phases in powder diffraction patterns
Authors: Leineweber Andreas , Petricek Vaclav
Published: November 2007

Variations of lattice and modulation parameters of an incommensurately modulated phase as well as the resulting line broadening arising in powder diffraction patterns were theoretically analysed. The resulting line broadening is in principle microstrain-like. For the case that only the modulation parameters vary, only the satellite reflections are broadened, and for constant-order satellite reflections, the line broadening can then be regarded as size-like.
Temperature dependence of the crystal structure of α-AgSCN by powder neutron diffraction
Authors: Williams Darrick J. , Daemen L. L. , Vogel S. C. , Proffen Th.
Published: November 2007

A structural study of α-AgSCN was carried out using the neutron powder diffractometer HIPPO (high-pressure preferred orientation powder) at ten different temperatures between 25 and 275 K. The structure of α-AgSCN was refined using the Rietveld method and the symmetry elements for the material were found to be: space group No. 15,C2/c,a= 8.7210 (8) Å,b= 7.9318 (8) Å,c= 12.3329 (5) Å, β = 138.750 (3)°, volume = 562.497 (9) Å3andZ= 8. The Ag+cation has tetrahedral coordination and is surrounded by three –SCN thiocyanate ligands and one isothiocyanate –NCS ligand down to 25 K, with no structural changes. The bond lengths at 275 K are Ag—S1 = 2.749 (10), Ag—S2 = 2.995 (11), Ag—S3 = 2.411 (11), Ag—N = 2.150 (5), S—C = 1.783 (11) and C—N = 1.1447 (35) Å. The bond lengths at 25 K are Ag—S1 = 2.782 (5), Ag—S2 = 2.941 (5), Ag—S3 = 2.431 (5), Ag—N = 2.1526 (26), S—C = 1.749 (5) and C—N = 1.140 (2) Å.
Characterization of polycapillary X-ray lens for application in confocal three-dimensional energy-dispersive micro X-ray diffraction experiments
Authors: Sun Tianxi , Zhang Meirong , Ding Xunliang , Liu Zhiguo , Lin Xiaoyan , Liu Hui
Published: November 2007

A confocal technology based on polycapillary X-ray optics is proposed to perform three-dimensional energy-dispersive micro X-ray diffraction. A three-dimensional energy-dispersive micro X-ray diffractometer based on a polycapillary focusing X-ray lens (PFXRL) in the excitation channel and a polycapillary parallel X-ray lens (PPXRL) in the detection channel has been designed. At 2\theta = 90^ \circ, the lateral resolution l_X \times l_Y of this diffractometer is 49.7 \times 49.9 \rm \micro m at 7.5 keV, and its depth resolution d_Z is 48.1 \rm \micro m at 8.0 keV. The total resolution of this diffractometer in \Delta d/d is 6.5% at 6.4 keV and 2\theta = 140.2^ \circ.
TRY, a new computer program for crystal structure analysis from diffraction data based on internal coordinates and on a molecular modelling procedure free of redundant coordinates
Authors: Immirzi Attilio
Published: November 2007

A procedure is described which allows structure modelling using a number of internal coordinates that does not exceed the number of degrees of freedom of the problem. The modelling then becomes a strictly analytical procedure and structural refinement from diffraction data can be carried out avoiding the use of singular matrices. A practical `symbolic language' with a simple syntax allows easy molecular building even in intricate cases. Based on this procedure, a new computer program for the study of crystal structures (TRY), particularly suited for fibrous polymers, has been created. The program is available at http://www.theochem.unisa.it/try.html.
Structural investigation of the cubic perovskite-type doped lanthanum cobaltite La0.6Sr0.4CoO3−δat 1531 K: possible diffusion path of oxygen ions in an electrode material
Authors: Yashima Masatomo , Tsuji Takayuki
Published: November 2007

The crystal structure of a cubic Pm\overline 3 m perovskite-type doped lanthanum cobaltite, La0.6Sr0.4CoO3−δ, has been studied usingin situneutron powder diffraction data measured at 1531 K. The refined occupancy 0.886 (6) of O atoms at the 3d1/2, 0, 0 site indicated an oxygen deficiency of δ = 0.34 (2) and an average valence of +2.7 for Co cations in La0.6Sr0.4CoO3−δat 1531 K. Refined anisotropic atomic displacement parameters and nuclear density mapping reveal that the oxygen ions in La0.6Sr0.4CoO3−δexhibit a large thermal motion perpendicular to the Co—O bond. A curved path for oxygen-ion migration between adjacent anion sites in La0.6Sr0.4CoO3−δis proposed, although it was not observed as a connected density in the experimental mapping.
GenOVa: a computer program to generate orientational variants
Authors: Cayron Cyril
Published: November 2007

A computer program calledGenOVa, written in Python, calculates the orientational variants, the operators (special types of misorientations between variants) and the composition table associated with a groupoid structure. The variants can be represented by three-dimensional shapes or by pole figures.
ARPGE: a computer program to automatically reconstruct the parent grains from electron backscatter diffraction data
Authors: Cayron Cyril
Published: November 2007

A computer program calledARPGEwritten in Python uses the theoretical results generated by the computer programGenOVato automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase. The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established. Some examples with martensitic transformations in iron and titanium alloys were treated. Variant selection phenomena were revealed.
Long‐term effects of anal sphincter rupture during vaginal delivery: faecal incontinence and sexual complaints
Authors: Mous M , Muller SA , De Leeuw JW
Published: November 2007

Objective  To determine the long‐term effects of obstetric anal sphincter rupture on the frequency of faecal incontinence and sexual complaints.

Design  Retrospective case–control study.

Setting  Department of Gynaecology and Obstetrics, Ikazia Hospital, The Netherlands.

Population  All 171 women operated for anal sphincter rupture between 1971 and 1990 and 171 controls matched for parity and date of delivery.

Methods  Postal questionnaires regarding faecal incontinence were sent in 1996 and 2005 to all cases and controls with questions regarding sexual complaints added to the questionnaire in 2005.

Main outcome measures  Anorectal complaints defined as any form of faecal incontinence including faecal urgency and faecal soiling. Sexual complaints defined as dyspareunia or faecal incontinence during intercourse.

Results  Sixty‐one percent of the women responded to both questionnaires. Anorectal complaints were reported by 38% of case versus 16% of controls in 1996 (risk difference: 0.22, 95% CI 0.10–0.34) and by 61% of cases versus 22% of controls in 2005 (risk difference: 0.41, 95% CI 0.29–0.53). In contrast to the control group, the increase of anorectal complaints in the case group between 1996 and 2005 was highly significant (P < 0.0001). Postmenopausal state was not associated with an increased risk for faecal incontinence. Dyspareunia was reported by 29% of cases versus 13% of controls (P = 0.01). Faecal incontinence during intercourse was reported by 13% of cases versus 1% of controls (P = 0.005).

Conclusions  Obstetric anal sphincter rupture is an important risk factor for sexual complaints and for faecal incontinence increasing with age irrespective of menopausal state.
Managing back pain in pregnancy using a support garment: a randomised trial
Authors: Kalus SM , Kornman LH , Quinlivan JA
Published: November 2007

Objective  Large population studies have shown that low back pain affects about 50% of pregnant women. The aim of this study was to determine whether the use of the BellyBra® in pregnant women with back pain is associated with changes in assessments of pain severity, physical activity and satisfaction with life after 3 weeks of intervention compared with tubigrip, a more generic form of support.

Design  Randomised controlled trial.

Setting  A tertiary referral hospital in Australia.

Population  Women between 20 and 36 weeks of pregnancy with lumbar back or posterior pelvic pain.

Methods  Participants were randomised to the BellyBra® (the study device) or to tubigrip (the control) by means of computer‐generated numbered, sealed, opaque envelopes.

Main outcome measures  The primary outcomes were pain severity and physical activity, and the secondary outcome was satisfaction with life.

Results  One hundred and fifteen women consented to participate in the trial. Mean visual analogue scale scores of pain severity decreased from 6.1 to 4.5 in the study device group (P= 0.001) and from 6.0 to 4.7 in the control group (P= 0.003). There was no significant difference between the groups in this outcome (P= 0.61). However, the study device group demonstrated a significantly greater reduction in Likert scale assessments of the impact of back pain on sleeping (P= 0.007), getting up from a sitting position (P= 0.02) and walking (P= 0.001) than the control group. There was also a significant reduction in the use of analgesic medication in the study group (P= 0.01).

Conclusion  The BellyBra® and tubigrip were both associated with a reduction in the severity of pregnancy‐related low back pain. The BellyBra® was more effective than tubigrip, however, in alleviating the impact of pain on a number of physical activities that constitute daily life.
Antiepileptic drug use, folic acid supplementation, and congenital abnormalities: a population‐based case–control study
Authors: Kjær D , Horvath‐Puhó E , Christensen J , Vestergaard M , Czeizel AE , Sørensen HT , Olsen J
Published: November 2007

Objective  To investigate whether folic acid supplementation in early pregnancy modifies the association between the prevalence of congenital abnormalities in the offspring and maternal use of carbamazepine (CBZ), phenobarbital (PB), phenytoin (PHT), and primidone (PRI).

Design  A population‐based case–control study.

Setting  The Hungarian Case–Control Surveillance of Congenital Abnormalities (HCCSCA) (1980–1996) and its information on children from the Hungarian Congenital Abnormality Registry and the Hungarian National Birth Registry.

Population  Children with congenital abnormalities (cases; n= 20 792, of whom 148 had been exposed to antiepileptic drugs [AEDs]) and unaffected children (controls; n= 38 151, of whom 184 had been exposed to AEDs).

Methods  Information on drug exposure and background variables for the mothers were collected from antenatal logbooks, discharge summaries, and structured questionnaires completed by the mothers at the time of HCCSCA registration.

Main outcome measures  Congenital abnormalities detected at termination of pregnancy, at birth or until 3 months of age according to CBZ, PB, PHT, or PRI exposure at 5–12 weeks from first day of the last menstrual period (LMP), stratified by folic acid supplementation.

Results  Compared with children unexposed to AEDs and folic acid, the odds ratio of congenital abnormalities was 1.47 (95% CI 1.13–1.90) in children exposed to AEDs without folic acid supplementation and 1.27 (95% CI 0.85–1.89) for children exposed to AEDs with folic acid supplementation.

Conclusion  The results indicate that the risk of congenital abnormalities in children exposed in utero to CBZ, PB, PHT, and PRI is reduced but not eliminated by folic acid supplementation at 5–12 weeks from LMP. The statistical precision in our study is limited due to rarity of the exposures, and further studies are needed.
Mediolateral episiotomy reduces the risk for anal sphincter injury during operative vaginal delivery
Authors: De Leeuw JW , De Wit C , Kuijken JPJA , Bruinse HW
Published: November 2007

Objective  To determine the risk factors for anal sphincter injuries during operative vaginal delivery.

Setting and design  A population‐based observational study.

Population  All 21 254 women delivered with vacuum extraction and 7478 women delivered with forceps, derived from the previously validated Dutch National Obstetric Database from the years 1994 to 1995.

Methods  Anal sphincter injury was defined as any injury, partial or complete, of the anal sphincters. Risk factors were determined with multivariate logistic regression analysis.

Main outcome measures  Individual obstetric factors, e.g. fetal birthweights, duration of second stage, etc.

Results  Anal sphincter injury occurred in 3.0% of vacuum extractions and in 4.7% of forceps deliveries. Primiparity, occipitoposterior position and fetal birthweight were associated with an increased risk for anal sphincter injury in both types of operative vaginal delivery, whereas duration of second stage was associated with an increased risk only in vacuum extractions. Mediolateral episiotomy protected significantly for anal sphincter damage in both vacuum extraction (OR 0.11, 95% CI 0.09–0.13) and forceps delivery (OR 0.08, 95% CI 0.07–0.11). The number of mediolateral episiotomies needed to prevent one sphincter injury in vacuum extractions was 12, whereas 5 mediolateral episiotomies could prevent one sphincter injury in forceps deliveries.

Conclusions  Primiparity and occipitoposterior presentation are strong risk factors for the occurrence of anal sphincter injury during operative vaginal delivery. The highly significant protective effect of mediolateral episiotomies in both types of operative vaginal delivery warrants the conclusions that this type of episiotomy should be used routinely during these interventions to protect the anal sphincters.
Increased perinatal mortality and morbidity in monochorionic versus dichorionic twin pregnancies: clinical implications of a large Dutch cohort study
Authors: Hack KEA , Derks JB , Elias SG , Franx A , Roos EJ , Voerman SK , Bode CL , Koopman‐Esseboom C , Visser GHA
Published: November 2007

Objective  To evaluate mortality and morbidity in a large cohort of twin pregnancies according to chorionicity. We aimed to estimate the optimal time of delivery.

Design  Historical cohort design.

Setting  Two teaching hospitals.

Population  Twin pregnancies delivered in the University Medical Centre, Utrecht, and the St Elisabeth Hospital, Tilburg (1995–2004), The Netherlands (n = 1407).

Methods  Pregnancy outcomes were documented according to chorionicity. Mortality ≥32 weeks was reviewed carefully with special attention to antenatal fetal monitoring, autopsy and placental histopathology to find an explanation for adverse outcome.

Main outcome measures  Perinatal mortality and morbidity in monochorionic (MC) and dichorionic (DC) twins.

Results  Perinatal mortality was 11.6% in MC twin pregnancies and 5.0% in DC twin pregnancies. After 32 weeks, the risk of intrauterine death (IUD) was significantly higher in MC twins than in DC twins (hazard ratio 8.8, 95% CI 2.7–28.9). In most of these cases of IUD, no antenatal signs of impaired fetal condition had been present. Median gestational age was 1 week longer in DC twins than in MC twins, and the mean birthweight was 221 g higher. Severe birthweight discordancy (>20%) occurred more often in MC twins than in DC twins (OR 1.23, 95% CI 0.97–1.55). The incidence of necrotising enterocolitis (NEC) was higher in MC twins, after adjustment for age and weight at birth (OR 4.05, 95% CI 1.97–8.35). There was a trend towards higher neuromorbidity in MC twins.

Conclusions  This is the largest cohort study of twin pregnancies evaluating outcome according to chorionicity thus far. MC twins are at increased risk for fetal death (even at term), NEC and neuromorbidity. Current antenatal care is insufficient to predict and prevent this excess perinatal mortality and morbidity. Planned delivery at or even before 37 weeks of gestation seems to be justified for MC twins.
Right Ventricular Perforation with an ICD Defibrillation Lead Managed by Surgical Revision and Epicardial Leads—Case Reports
Authors: KŘIVAN LUBOMÍR , KOZÁK MILAN , VLAŠÍNOVÁ JITKA , SEPŠI MILAN
Published: November 2007

The authors present two cases of patients with perforation of the right ventricular wall by the implantable cardioverter defibrillator (ICD) lead. The complication was resolved by cardiosurgical revision and epicardial leads stitched onto the diaphragmatic wall of the heart. The perforation was identified by electrical parameter changes of the leads, echocardiography, and computed tomography. Both patients had satisfactory values of electrical parameters and ICD function with epicardial leads. The importance of regular follow‐up and a check of the lead parameters are emphasized.
Asymptomatic Anterior Perforation of an ICD Lead into Subcutaneous Tissues
Authors: FISHER JOHN D. , FOX MARSHAL , KIM SOO G. , GOLDSTEIN DANIEL , HARAMATI LINDA B.
Published: November 2007

A 71‐year‐old woman underwent routine impantable cardioverter defibrillator implantation. On a predischarge check the next day, electrical signals and thresholds were excellent and similar to those at implant. The chest X‐ray was unremarkable and showed good lead position at the right ventricular apex (RVA). At a routine one‐month postimplant visit, electrograms were found to be miniscule, and pacing could not be achieved. Chest X‐ray and fluoroscopy suggested perforation, then this was confirmed by computed tomography scan. The tip of the lead was estimated to be within 7 mm of the surface of the skin. The system was removed surgically, and the patient continued to do well.
Delayed Defibrillator Lead Perforation: An Increasing Phenomenon
Authors: SATPATHY RUBY , HEE TOM , ESTERBROOKS DENNIS , MOHIUDDIN SYED
Published: November 2007

Delayed intracardiac lead perforation has been defined as migration and perforation after one month of implantation. It is a rare complication; pathophysiology and optimal management are currently unclear. Recognition of these cases becomes important with increasing use of these devices. We describe such a case of delayed lead perforation.
Experiment and Theory on the Nonlinear Vibration of a Shallow Arch Under Harmonic Excitation at the End
Authors: Chen Jen-San , Yang Cheng-Han
Published: November 2007

In this paper we study, both theoretically and experimentally, the nonlinear vibration of a shallow arch with one end attached to an electro-mechanical shaker. In the experiment we generate harmonic magnetic force on the central core of the shaker by controlling the electric current flowing into the shaker. The end motion of the arch is in general not harmonic, especially when the amplitude of lateral vibration is large. In the case when the excitation frequency is close to the nth natural frequency of the arch, we found that geometrical imperfection is the key for the nth mode to be excited. Analytical formula relating the amplitude of the steady state response and the geometrical imperfection can be derived via a multiple scale analysis. In the case when the excitation frequency is close to two times of the nth natural frequency two stable steady state responses can exist simultaneously. As a consequence jump phenomenon is observed when the excitation frequency sweeps upward. The effect of geometrical imperfection on the steady state response is minimal in this case. The multiple scale analysis not only predicts the amplitudes and phases of both the stable and unstable solutions, but also predicts analytically the frequency at which jump phenomenon occurs.
Localized Magnetoelastic Bending Vibration of an Electroconductive Elastic Plate
Authors: Belubekyan M. , Ghazaryan K. , Marzocca P. , Cormier C.
Published: November 2007

The study of the magnetoelastic vibrations of a flat plate immersed in a uniform applied external magnetic field is presented. Kirchhoff’s plate theory and the model of a perfect conductive medium are used. The conditions for the existence of localized bending vibrations in the vicinity of the free edge of the plate are established. It is shown that the localized vibrations can be detected and eventually can be eliminated by means of an applied magnetic field.
Vibration Characteristics of Multiwalled Carbon Nanotubes Embedded in Elastic Media by a Nonlocal Elastic Shell Model
Authors: Li Renfu , Kardomateas George A.
Published: November 2007

In this paper, the vibrational behavior of the multiwalled carbon nanotubes (MWCNTs) embedded in elastic media is investigated by a nonlocal shell model. The nonlocal shell model is formulated by considering the small length scales effects, the interaction of van der Waals forces between two adjacent tubes and the reaction from the surrounding media, and a set of governing equations of motion for the MWCNTs are accordingly derived. In contrast to the beam models in the literature, which would only predict the resonant frequencies of bending vibrational modes by taking the MWCNT as a whole beam, the current shell model can find the resonant frequencies of three modes being classified as radial, axial, and circumferential for each nanotube of a MWCNT. Big influences from the small length scales and the van der Waals’ forces are observed. Among these, noteworthy is the reduction in the radial frequencies due to the van der Waals’ force interaction between two adjacent nanotubes. The numerical results also show that when the spring constant k0 of the surrounding elastic medium reaches a certain value, the lowest resonant frequency of the double walled carbon nanotube drops dramatically.
Saint-Venant’s Problem for Homogeneous Piezoelectric Beams
Authors: Rovenski Vladimir , Harash Eugene , Abramovich Haim
Published: November 2007

This paper is devoted to the linear analysis of a slender homogeneous piezoelectric beam that undergoes tip loading. The solution of the Saint-Venant’s problem presented in this paper generalizes the known solution for a homogeneous elastic beam. The analytical approach in this study is based on the Saint-Venant’s semi-inverse method generalized to electroelasticity, where the stress, strain, and (electrical) displacement components are presented as a set of initially assumed expressions that contain tip parameters, six unknown coefficients, and three pairs of auxiliary (torsion/bending) functions in two variables. These pairs of functions satisfy the so-called coupled Neumann problem (CNP) in the cross-sectional domain. In the limit “elastic” case the CNP transforms to the Neumann problem, for a beam made of a poled piezoceramics the CNP is decomposed into two Neumann problems. The paper develops concepts of the torsion/bending functions, the torsional rigidity and shear center, the tip coupling matrix for a piezoelectric beam. Examples of exact and numerical solutions for elliptical and rectangular beams are presented.
A Novel
Finite-Element– Numerical-Integration Model for Composite Laminates Supported on Opposite
Edges
Authors: Kant Tarun , Pendhari Sandeep
S. , Desai Yogesh
M.
Published: November 2007

An attempt is made here to devise a new methodology for an integrated stress analysis of laminated composite plates wherein both in-plane and transverse stresses are evaluated simultaneously. The method is based on the governing three-dimensional (3D) partial differential equations (PDEs) of elasticity. A systematic procedure is developed for a case when one of the two in-plane dimensions of the laminate is considered infinitely long (y direction) with no changes in loading and boundary conditions in that direction. The laminate could then be considered in a two-dimensional (2D) state of plane strain in x-z plane. It is here that the governing 2D PDEs are transformed into a coupled system of first-order ordinary differential equations (ODEs) in transverse z direction by introducing partial discretization in the finite inplane direction x. The mathematical model thus reduces to solution of a boundary value problem (BVP) in the transverse z direction in ODEs. This BVP is then transformed into a set of initial value problems (IVPs) so as to use the available efficient and effective numerical integrators for them. Through thickness displacement and stress fields at the finite element discrete nodes are observed to be in excellent agreement with the elasticity solution. A few new results for cross-ply laminates under clamped support conditions are also presented for future reference and also to show the generality of the formulation.
Fatigue Modeling for
Elastic Materials With Statistically Distributed
Defects
Authors: Kudish Ilya
I.
Published: November 2007

The paper is devoted to formulation and analysis of a new model of structural fatigue that is a direct extension of the model of contact fatigue developed by Kudish (2000, STLE Tribol. Trans., 43, pp. 711–721). The model is different from other published models of structural fatigue (Collins, J. A., 1993, Failure of Materials and Mechanical Design: Analysis, Prediction, Prevention, 2nd ed., Wiley, New York) in a number of aspects such as statistical approach to material defects, stress analysis, etc. The model is based on fracture mechanics and fatigue crack propagation. The model takes into account local stress distribution, initial statistical distribution of defects versus their size, crack location, and orientation, and material fatigue resistance parameters. The assumptions used for the new model derivation are stated clearly and their validity is discussed. The model considers the kinetics of crack distribution by taking into account the fact that the crack distribution varies with the number of applied loading cycles due to crack growth. A qualitative and quantitative parametric analysis of the model is performed. Some analytical formulas for fatigue life as a function of the initial defect distribution, material fatigue resistance, and stress state are obtained. Examples of application of the model to predicting fatigue of beam bending and torsion and contact fatigue for tapered bearings is presented.
On Some Benchmark Results for the Interaction of a Crack With a Circular Inclusion
Authors: Phan A.-V. , Gray L. J. , Kaplan T.
Published: November 2007

Stress intensity factor calculations for crack-inclusion interaction problems are presented. The problems considered include the benchmark problems first discussed by Helsing and Jonsson (2002, ASME J. Appl. Mech, 69, pp. 88–90), and subsequently by Wang, Mogilevskaya, and Crouch (2003, ASME J. Appl. Mech., 70, pp. 619–621). The numerical results are obtained using the symmetric-Galerkin boundary element method in conjunction with an improved quarter-point element for evaluating the stress intensity factors by means of the displacement correlation technique. The converged results confirm the accuracy of the previous simulations and demonstrate that accurate solutions for these interaction problems can be obtained with numerical methods that are applicable in three dimensions.
Size Effect of Cohesive Delamination Fracture Triggered by Sandwich Skin Wrinkling
Authors: Bažant Zdeněk , Grassl Peter
Published: November 2007

Because the observed size effect follows neither the strength theory nor the linear elastic fracture mechanics, the delamination fracture of laminate-foam sandwiches under uniform bending moment is treated by the cohesive crack model. Both two-dimensional geometrically nonlinear finite element analysis and one-dimensional representation of skin (or facesheet) as a beam on elastic-softening foundation are used. The use of the latter is made possible by realizing that the effective elastic foundation stiffness depends on the ratio of the critical wavelength of periodic skin wrinkles to the foam core thickness, and a simple description of the transition from shortwave to longwave wrinkling is obtained by asymptotic matching. Good agreement between both approaches is achieved. Skin imperfections (considered proportional to the the first eigenmode of wrinkling), are shown to lead to strong size dependence of the nominal strength. For large imperfections, the strength reduction due to size effect can reach 50%. Dents from impact, though not the same as imperfections, might be expected to cause as a similar size effect. Using proper dimensionless variables, numerical simulations of cohesive delamination fracture covering the entire practical range are performed. Their fitting, heeding the shortwave and longwave asymptotics, leads to an approximate imperfection-dependent size effect law of asymptotic matching type. Strong size effect on postpeak energy absorption, important for impact analysis, is also demonstrated. Finally, discrepancies among various existing formulas for critical stress at periodic elastic wrinkling are explained by their applicability to different special cases in the shortwave-longwave transition.
Thermoelastic Interaction Between Singularities and Interfaces in an Anisotropic Trimaterial
Authors: Choi Seung Tae
Published: November 2007

The method of analytic continuation and Schwarz-Neumann’s alternating technique were applied to the thermoelastic interaction problems of singularities and interfaces in an anisotropic “trimaterial,” which denotes an infinite body composed of three dissimilar materials bonded along two parallel interfaces. It was assumed that the linear thermoelastic materials are under general plane deformations in which the plane of deformation is perpendicular to the planes of the two parallel interfaces. The author then showed that by alternately applying the method of analytic continuation across two parallel interfaces the solution for the thermoelastic singularities in an anisotropic trimaterial can be obtained in a series form from a solution for the same singularities in a homogeneous anisotropic medium.
Reynolds-Stress
Modeling of Three-Dimensional Secondary Flows With Emphasis on Turbulent Diffusion
Closure
Authors: Vallet I.
Published: November 2007

The purpose of this paper is to assess the importance of the explicit dependence of turbulent diffusion on the gradients of mean-velocity modeling in second moment closures on three-dimensional (3D) detached and secondary flows prediction. Following recent theoretical work of Younis, Gatski, and Speziale, 2000, [Proc. Royal Society Lon. A, 456, pp. 909–920], we propose a triple-velocity correlation model, including the effects of the spatial gradients of mean velocity. A model for both the slow and rapid parts of the pressure-diffusion term was also developed and added to a wall-normal-free Reynolds-stress model. The present model is validated against 3D detached and secondary flows. Further developments, especially on the echo terms (which should appear in the formulation of pressure-velocity correlation), are discussed.
Minimizing and Restricting Vibrations in High-Speed Cam-Follower
Systems Over a Range of Speeds
Authors: Jiang J. K. , Iwai Y. R. , Su H.
Published: November 2007

Over a range of cam speeds, the problems of minimizing and restricting vibrations in high-speed cam-follower systems over a range of speeds are formulated as constrained optimization problems. A universal Hermite cam displacement is suggested. The combination of these methods can form a general design environment. In this environment, the designer can arbitrarily select one to formulate as the objective function from quantifiable cam properties such as the residual vibration, primary vibration, pressure angle, radius of curvature, and contact stress, while the rest of quantifiable cam properties can be formulated as the design constraints.
On the Analytic Solution of Magnetohydrodynamic Flow of a Second
Grade Fluid Over a Shrinking Sheet
Authors: Hayat T. , Abbas Z. , Sajid M.
Published: November 2007

In this study, we derive an analytical solution describing the magnetohydrodynamic boundary layer flow of a second grade fluid over a shrinking sheet. Both exact and series solutions have been determined. For the series solution, the governing nonlinear problem is solved using the homotopy analysis method. The convergence of the obtained solution is analyzed explicitly. Graphical results have been presented and discussed for the pertinent parameters.
Plane Contact of Hot Flat-Ended Punch and Thermoelastic Half-Space Involving Finite Friction
Authors: Pauk Volodymyr
Published: November 2007

Plane normal contact of a rigid flat-ended hot punch and a thermoelastic half-space is considered under the assumption of finite friction between contacting surfaces. The problem is treated with the boundary integral methods. We consider independently normal and tangential contact problems. The rise of slip and stick regions under the punch is studied. The nonlinear equations for the unknown stick region size are obtained and solved numerically.
Rotor Dynamic Analysis of an Eccentric Hydropower Generator With Damper Winding for Reactive Load
Authors: Karlsson Martin , Aidanpää Jan-Olov , Perers Richard , Leijon Mats
Published: November 2007

Asymmetry in the magnetic circuit, around the air gap circumference, in a hydroelectric generator will give rise to a unbalanced magnetic pull. In this paper, a hydropower rotor system is modeled and the influence of electro-mechanical forces due to overexcitation is analyzed. The active power has been kept constant and the rotor excitation has been changed in order to vary the output of reactive power. The electromagnetic field is solved with the finite element method. Two electromagnetic models are compared: one with and one without damper winding. The mechanical model of the generator consists of a four degrees of freedom rigid disk connected to an elastic shaft supported by two bearings with linear properties. It has been found that the unbalanced magnetic pull slightly increases for reactive loads resulting in a decrease of natural frequencies and an increase of unbalance response. When the damper winding is included, the magnetic pull will decrease compared to the model without damper winding, and the pull force has two components: one radial and one tangential. The tangential component can influence the stability of the mechanical system for a range of design parameters.
Stability of the Boiling Two-Phase Flow of a Magnetic Fluid
Authors: Ishimoto Jun
Published: November 2007

Elucidation of magnetic stabilization of boiling two-phase flow by utilizing the magnetization of the fluid is proposed herein. The effect of magnetic field on the stability of the boiling two-phase pipe flow of the magnetic fluid under a nonuniform magnetic field is investigated both theoretically and experimentally. First, governing equations of boiling two-phase flow based on the unsteady thermal nonequilibrium two-fluid model are presented and analytically solved using a linearization method. The analytical results on stabilization are then inspected experimentally using an experimental apparatus composed of a small test loop. Results of the analytical study on the void waves, show that the stabilization of two-phase flow can be obtained by practical use of the magnetic body force acting on the fluid and by applying the appropriate superficial gas-phase velocity. Those results also show that magnetic stabilization is obtained because the two-phase magnetic body force enhances the diffusion effect of the void waves. It is experimentally clarified that the two-phase flow state can be stabilized and homogenized by magnetization of the fluid and that vapor bubbles can be minutely produced by effective use of the magnetic body force. The axial magnetic field is more effective for stabilization and homogenization of the two-phase magnetic fluid flow than the transverse magnetic field.
Measurement of the Total Energy Release Rate for Cracks in PZT Under Combined Mechanical and Electrical Loading
Authors: Jelitto H. , Felten F. , Swain M. V. , Balke H. , Schneider G. A.
Published: November 2007

Four-point-bending V-notched specimens of lead zirconate titanate (PZT) poled parallel to the long axis are fractured under conditions of controlled crack growth in a custom-made device. In addition to the mechanical loading electric fields, up to 500V∕mm are applied parallel and anti-parallel to the poling direction, i.e., perpendicular to the crack surface. To determine the different contributions to the total energy release rate, the mechanical and the piezoelectric compliance, as well as the electrical capacitance of the sample, are recorded continuously using small signal modulation/demodulation techniques. This allows for the calculation of the mechanical, the piezoelectric, and the electrical part of the total energy release rate due to linear processes. The sum of these linear contributions during controlled crack growth is attributed to the intrinsic toughness of the material. The nonlinear part of the total energy release rate is mostly associated to domain switching leading to a switching zone around the crack tip. The measured force-displacement curve, together with the modulation technique, enables us to determine this mechanical nonlinear contribution to the overall toughness of PZT. The intrinsic material toughness is only slightly dependent on the applied electric field (10% effect), which can be explained by screening charges or electrical breakdown in the crack interior. The part of the toughness due to inelastic processes increases from negative to positive electric fields by up to 100%. For the corresponding nonlinear electric energy change during crack growth, only a rough estimate is performed.
Steady-State Dynamic Response of a Kirchhoff’s Slab on Viscoelastic Kelvin’s Foundation to Moving Harmonic Loads
Authors: Sun Lu
Published: November 2007

In this paper, fast Fourier transform and complex analysis are used to analyze the dynamic response of slabs on a viscoelastic foundation caused by a moving harmonic load. Critical speed and resonance frequency of the slab to a moving harmonic load are obtained analytically. It is proved that there exists a bifurcation in critical speed. One branch of critical speed increases as load frequency increases, while the other branch of critical speed decreases as load frequency increases. There are two critical speeds when the load frequency is low, but only one critical speed exists when the load frequency is high. A parametric study is also performed to study the effect of load speed, load frequency, material properties of the slab and the damping coefficient on dynamic response. It is found that the damping coefficient has significant influence on dynamic response. For small damping, the maximum response of the slab increases with increased load speed and frequency. However, for large damping, the maximum response of the slab decreases with increased load speed and frequency.
Extension of
Stoney’s Formula to Arbitrary Temperature Distributions in Thin Film/Substrate
Systems
Authors: Huang Y. , Rosakis A.
J.
Published: November 2007

Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. By considering a circular thin film/substrate system subject to nonuniform and nonaxisymmetric temperature distributions, we derive relations between the film stresses and temperature, and between the plate system’s curvatures and the temperature. These relations featured a “local” part that involves a direct dependence of the stress or curvature components on the temperature at the same point, and a “nonlocal” part that reflects the effect of temperature of other points on the location of scrutiny. Most notably, we also derive relations between the polar components of the film stress and those of system curvatures which allow for the experimental inference of such stresses from full-field curvature measurements in the presence of arbitrary nonuniformities. These relations also feature a “nonlocal” dependence on curvatures making full-field measurements of curvature a necessity for the correct inference of stress. Finally, it is shown that the interfacial shear tractions between the film and the substrate are related to the gradients of the first curvature invariant and can also be inferred experimentally.
Optimal Shape of a Rotating Rod With Unsymmetrical Boundary Conditions
Authors: Atanackovic Teodor M.
Published: November 2007

Governing equations of a compressed rotating rod with clamped–elastically clamped (hinged with a torsional spring) boundary conditions is derived. It is shown that the multiplicity of an eigenvalue of this system can be at most equal to two. The optimality conditions, via Pontryagin’s maximum principle, are derived in the case of bimodal optimization. When these conditions are used the problem of determining the optimal cross-sectional area function is reduced to the solution of a nonlinear boundary value problem. The problem treated here generalizes our earlier results presented in Atanackovic, 1997, Stability Theory of Elastic Rods, World Scientific, River Edge, NJ. The optimal shape of a rod is determined by numerical integration for several values of parameters.
The Bridged Crack Model for the Analysis of Brittle Matrix Fibrous Composites Under Repeated Bending Loading
Authors: Carpinteri Alberto , Puzzi Simone
Published: November 2007

In this paper, we present a fracture-mechanics based model, the so-called bridged crack model (Carpinteri, A., 1981, “A Fracture Mechanics Model for Reinforced Concrete Collapse,” Proc. of IABSE Colloquium on Advanced Mechanics of Reinforced Concrete, Delft, I.A.B.S.E., Zürich, pp. 17–30; Carpinteri, A., 1984, “Stability of Fracturing Process in R.C. Beams,” J. Struct. Engng. (A.S.C.E.), 110, pp. 544–558) for the analysis of brittle matrix composites with discontinuous ductile reinforcements under the condition of repeated bending loading. In particular, we address the case of composites with very high number of reinforcements (i.e., fiber-reinforced composites, rather than conventionally reinforced concrete). With this aim, we propose a new iterative procedure and compare it to the algorithm recently proposed by Carpinteri, Spagnoli, and Vantadori (2004, “A Fracture Mechanics Model for a Composite Beam with Multiple Reinforcements Under Cyclic Bending,” Int. J. Solids Struct., 41, pp. 5499–5515), showing the advantages in terms of computational efficiency. Furthermore, we analyze the combined effects of crack length, brittleness number, and fiber number on the cyclic behavior of the composite beam, showing the conditions enhancing the energy dissipation in the composite system. Eventually, we analyze crack propagation and propose, consistently with the model premises, a fracture-mechanics-based crack propagation criterion that allows one to simulate cyclic bending tests under the fixed grip condition.
Exact Solutions for Free-Vibration Analysis of Rectangular Plates Using Bessel Functions
Authors: Wu Jiu Hui , Liu A. Q. , Chen H. L.
Published: November 2007

A novel Bessel function method is proposed to obtain the exact solutions for the free-vibration analysis of rectangular thin plates with three edge conditions: (i) fully simply supported; (ii) fully clamped, and (iii) two opposite edges simply supported and the other two edges clamped. Because Bessel functions satisfy the biharmonic differential equation of solid thin plate, the basic idea of the method is to superpose different Bessel functions to satisfy the edge conditions such that the governing differential equation and the boundary conditions of the thin plate are exactly satisfied. It is shown that the proposed method provides simple, direct, and highly accurate solutions for this family of problems. Examples are demonstrated by calculating the natural frequencies and the vibration modes for a square plate with all edges simply supported and clamped.