bluuebunny/crossref_metadata_2025 huggingface dataset:
The Longitudinal Interplay of Maternal Warmth and Adolescents' Self‐Disclosure in Predicting Maternal Knowledge
Authors: Blodgett Salafia Elizabeth H. , Gondoli Dawn M. , Grundy Amber M.
Published: November 2009

This study examined the longitudinal associations among maternal warmth, adolescents' self‐disclosure, and maternal knowledge during the transition to adolescence. Three years of self‐report data were collected from 131 married mothers and their adolescents. Results from longitudinal analysis using adolescent reports indicated that greater maternal warmth in sixth grade predicted higher levels of adolescents' self‐disclosure in seventh grade, which in turn led to higher levels of maternal knowledge in eighth grade. Thus, adolescents' self‐disclosure served as an indirect link between higher maternal warmth and greater knowledge over time. An alternative model with prior self‐disclosure predicting subsequent maternal warmth and knowledge was not supported. Overall, this study demonstrated a time‐ordered process by which maternal warmth and adolescents' self‐disclosure predict maternal knowledge. Understanding such processes that affect parental knowledge may be beneficial for future prevention and intervention efforts during the transition to adolescence.
Losing Sleep Over It: Daily Variation in Sleep Quantity and Quality in Canadian Students' First Semester of University
Authors: Galambos Nancy L. , Dalton Andrea L. , Maggs Jennifer L.
Published: November 2009

Daily covariation of sleep quantity and quality with affective, stressful, academic, and social experiences were observed in a sample of Canadian 17–19‐year‐olds in their first year of university. Participants (N=191) completed web‐based checklists for 14 consecutive days during their first semester. Multilevel models predicting sleep quantity and quality from daily experiences indicated that more time on schoolwork, expecting a test, and alcohol use predicted less sleep whereas socializing predicted more sleep. More positive affect and no alcohol use predicted better sleep quality. Models predicting daily experiences from sleep the night before indicated that less sleep preceded increases in negative affect, decreases in schoolwork time, and a higher likelihood of socializing. Better sleep quality preceded increased positive affect, decreased negative affect and stress, and less time on schoolwork. These data are informative for understanding relations between sleep and daily experiences as they occur naturally in first‐year university students.
Physical activity and quality of life in schoolchildren aged 11–13 years of Cuenca, Spain
Authors: Sánchez‐López M. , Salcedo‐Aguilar F. , Solera‐Martínez M. , Moya‐Martínez P. , Notario‐Pacheco B. , Martínez–Vizcaíno V.
Published: November 2009

This study examined the differences in quality of life (QoL) between active and sedentary schoolchildren and analyzed these differences by gender and weight status. A total of 1409 children, aged 11–13 years, from 20 schools located in 20 municipalities of the province of Cuenca were invited to participate in a cross‐sectional study; 1073 children agreed (76.15% response rate), of which 536 (49.9%) were boys. QoL was measured with Child Health and Illness Profile–Child Edition (CHIP‐CE), an instrument measuring children's perception of their own health using a Likert‐type scale with five dimensions: satisfaction, comfort, resilience, risk avoidance, and achievement. Multivariate analysis of variance using the scores of the different CHIP‐CE dimensions as dependent variables, physical activity, gender, and body mass index (BMI) category as fixed factors, and age as co‐variate showed the following: (1) the scores of active children were significantly better than the scores of sedentary children for every dimension except risk avoidance; (2) there were no significant differences in QoL by BMI category; and (3) girls had better mean scores than boys for resilience, risk avoidance, and achievement, and worse scores for comfort. These results suggest that active children have a better QoL and that gender differences favoring boys diminish or even reverse to favor active girls.
Higher skeletal muscular metabolic reserve capacity in COPD patients than healthy subjects
Authors: Rud B. , Christensen C. C. , Ryg M. , Edvardsen A. , Skumlien S. , Hallén J.
Published: November 2009

We investigated the interaction between skeletal muscle exercise capacity and central restrictions using exercise modalities, which recruit differing levels of muscle mass in eight patients chronic obstructive lung disease (COPD) (FEV1% of predicted; 35 [SE 4%]) and eight healthy controls. Subjects performed conventional bicycling, two‐leg knee extensor (2‐KE) and single‐leg knee extensor (1‐KE) exercises. Maximal values for pulmonary V̇O2 (VO2max), power output, blood lactate, heart rate, blood pressure, and arterial oxygen saturation of hemoglobin were registered. VO2max in controls was 2453 (210), 1468 (124), and 976 (76) mL/min during bicycling, 2‐KE and 1‐KE, respectively. The COPD patients achieved 48% (P<0.05), 62% (P<0.05), and 81% (P=0.10) of the control values. The mass‐specific VO2max (VO2max/exercising muscle mass) during 1‐KE was 345 (25) and 263 (30) mL/kg/min (P<0.05) in controls and COPD patients, respectively. During 2‐KE the controls and COPD patients achieved 85% (4%) and 67% (5%) (P=0.06) of the mass‐specific V̇O2 during 1‐KE, while during bicycling they achieved 31% (2%) and 17% (1%) (P<0.05), respectively. The COPD patients have central restrictions when exercising with a relatively small muscle mass (2‐KE) and have a higher muscular metabolic reserve capacity than controls during whole body exercise.
Prevalence of injuries among young adults in sport centers: relation to the type and pattern of activity
Authors: Lubetzky‐Vilnai A. , Carmeli E. , Katz‐Leurer M.
Published: November 2009

The rate of injuries resulting from physical exercise in sport centers as well as related factors has not yet been described. The aims of this study were to describe the prevalence of self‐reported activity‐specific injuries, to identify the relations between injury profile and different types and patterns of physical activity and to assess whether gender is a modifying variable in that connection. Four hundred and fifty‐seven men and women aged 20–35 years participated in this cross‐sectional study. A questionnaire was used to evaluate the types and patterns of physical activity performed in the 12 months preceding the study and sports injuries sustained during that time. One hundred and ninety of the 457 subjects reported an injury as a result of exercising (41.6%). A relationship was found between weight training and injuries of the upper extremity (UE) for men and between spinning classes and knee injuries for women. Among those who participated in weight‐training exercises, more frequent and longer duration exercise was associated with UE injury, and among those who participated in spinning classes more frequent exercise was associated with knee injury. Future injury prevention programs in sport centers should pay special attention to men who participate in weight training and to women who participate in spinning classes.
Physical performance and muscular characteristics in different stages of COPD
Authors: Eliason G. , Abdel‐Halim S. , Arvidsson B. , Kadi F. , Piehl‐Aulin K.
Published: November 2009

This study has examined exercise capacity and muscle morphology in patients with different severities of chronic obstructive pulmonary disease (COPD). Twenty‐three patients and 12 healthy matched controls were recruited. Based on the severity of airflow obstruction, patients were divided into two subgroups. Exercise capacity was determined using a 6‐min walk test. Muscle fiber composition, fiber area and number of satellite cells/muscle fiber were determined in muscle biopsies using immunohistochemistry. A progressive decline in exercise capacity was noted with ascending disease severity. Furthermore, a correlation between reduction in exercise capacity and changes in muscle fiber composition was observed in COPD. The group with severe and very severe COPD had a lower proportion of type I and a higher proportion of type IIa fibers compared with the other groups. In severe and very severe COPD, a reduction in fiber area of type IIa fibers was also seen. The number of satellite cells/muscle fiber did not differ between the groups. In conclusion, a decline in exercise capacity occurs already in mild and moderate COPD, indicating that the 6‐min walk test is a reliable indicator of disease severity. Furthermore, changes in skeletal muscle morphology are associated with disease severity while muscle regenerative capacity is not altered.
Structural analysis of rat patellar tendon in response to resistance and endurance training
Authors: Barone R. , Bellafiore M. , Leonardi V. , Zummo G.
Published: November 2009

Little is known about tendon adaptations induced by mechanical loading. Our goal was to evaluate the effects of two different exercise training protocols on adult rat patellar tendon. Ninety‐six male Wistar rats were divided into a sedentary group (control), a resistance‐trained group and an endurance‐trained group. The examinations were performed after 15, 30 and 45 days of training and after 2 weeks of rest since training was stopped. The content of collagen fibers and the cell nuclei number were quantified on tendon cross sections. In order to assess the training effectiveness, we evaluated the heart/body weight ratio, which was higher in 45 day‐trained rats than their controls (P<0.01), showing the presence of cardiac hypertrophy. An increase in the content of collagen fibers was observed in the 45 day‐trained groups and after 2 weeks of rest in the endurance group. Moreover, both trained groups showed a decrease in cell nuclei number after 30 and 45 days of training and 2 weeks of rest (P<0.05). Endurance and resistance training induces a tendon tissue remodeling that depends on the length and intensity of workload rather than the training type. Further studies are necessary to evaluate whether these structural modifications are associated with an increase in the mechanical strength of tendon.
Transcriptional profiling: a potential anti‐doping strategy
Authors: Rupert J. L.
Published: November 2009

Evolving challenges require evolving responses. The use of illicit performance enhancing drugs by athletes permeates the reality and the perception of elite sports. New drugs with ergogenic or masking potential are quickly adopted, driven by a desire to win and the necessity of avoiding detection. To counter this trend, anti‐doping authorities are continually refining existing assays and developing new testing strategies. In the post‐genome era, genetic‐ and molecular‐based tests are being evaluated as potential approaches to detect new and sophisticated forms of doping. Transcriptome analysis, in which a tissue's complement of mRNA transcripts is characterized, is one such method. The quantity and composition of a tissue's transcriptome is highly reflective of milieu and metabolic activity. There is much interest in transcriptional profiling in medical diagnostics and, as transcriptional information can be obtained from a variety of easily accessed tissues, similar approaches could be used in doping control. This article briefly reviews current understanding of the transcriptome, common methods of global analysis of gene expression and non‐invasive sample sources. While the focus of this article is on anti‐doping, the principles and methodology described could be applied to any research in which non‐invasive, yet biologically informative sampling is desired.
Some Bioelectrical Properties of Amoeba proteus
Authors: Josefsson J.‐O.
Published: November 2009

The membrane potential, resistance and capacitance of Amoeba proteus was measured with intracellular microelectrodes. Specific membrane resistance was 3 700 ohmcm2 and membrane ca pacitance 1.9 μ/cm2. Resting membrane potential during culture conditions was 65 pL 1.3 mV inside negative. Potassium and sodium ions decreased the membrane potential 40 and 35 mV per tenfold increase of external concentration. Substitution of chloride for ethanesulphonate did not affect the membrane potential. A transient biphasic shift of membrane potential and decrease of membrane resistance simultaneous with the spontaneous emptying of the contractile vacuole was recorded. The hyperpolarizing component of this potential was evaluated in the light of a positive potential recorded during the impalement of the vacuolar membrane and the subsequent emptying of the vacuole. All agents with ability to induce pinocytosis which were tested caused a transient “burst” of depolarizing potentials before a steady depolarized state was established. Anionic compounds did not depolarize the membrane. It is suggested that the permeability of the cell membrane is largely governed by negatively charged groups of the mucopolysaccharide layer of the membrane.
Storage and in vitro Release Rate of Catecholamines from Granules Isolated from Preaortal Paraganglia and Adrenals of Newborn Rabbits
Authors: Brundin Tomas
Published: November 2009

Catecholamine containing granules from paraganglia and adrenals were isolated by homogenization and high speed centrifugation. On incubation at 37d̀ C in potassium phosphate buffer, pH 7.4, the rate of spontaneous release from paraganglionic granules was similar to that of adrenomedullary granules with a half‐time of 30 min. These similarities between granules from the two organs are discussed in view of the different hormone contents in paraganglia (noradrenaline) and adrenals (adrenaline).
Histidine Induced Secretion in the Pyloric Ligated Rat Stomach
Authors: Räsänen Toimi
Published: November 2009

The amount and the pH of the gastric juice in the 1 hr pyloric ligated rat stomach were measured. The amount and the hydrogen ion concentration of the gastric juice were greater when the rats were injected with histidine than with histamine. The pretreatment with 5 times 1 mg of dexamethasone at 12‐hr intervals degranulated the mast cells of the gastric mucosa and increased the pH in the gastric juice. The difference of the secretory activity in histidine or histamine injected rats disappeared after the dexamethasone treatment. The results suggest that the gastric parenchyma is stimulated immediately with histamine formed from histidine and stored in the gastric mucosal mast cell organ.
Firing with Multiple‐Spike Discharges in the Slowly Adapting Stretch Receptor Neuron of the Lobster
Authors: Gramp Wolfgang
Published: November 2009

The phenomenon of firing with multiple‐spike discharges in the slowly adapting nerve cell of the isolated abdominal stretch receptor organ of the lobster (Homarus gammarus) was studied. All cells investigated fired with single action potentials at temperatures below, but with multiple‐spike discharges at temperatures above a critical value which being different for different cells usually occurred above 20d̀ C. In all cells the number of the impulses making up the multiple‐spike discharges increased with rising, and decreased with falling temperature. In most cases at any constant temperature the spike number of the discharges could be increased by relaxing, and decreased by stretching the receptor muscle; in a few cells the contrary was the case. The initiation of the extra spikes took place during the course of three different types of after‐depolarizations which succeeded the first and, sometimes, a number of the subsequent impulses of the multiple‐spike discharges. From its reproducibility and reversibility it is concluded that the phenomenon of firing with multiple‐spike discharges reflects a (reversible) modification of the cell's excitatory state due to changes of the conditions of the external milieu.
Geochemistry of K‐feldspar and Muscovite in Rare‐element Pegmatites and Granites from the Totoral Pegmatite Field, San Luis, Argentina
Authors: Oyarzábal Julio , Galliski Miguel Ángel , Perino Ernesto
Published: November 2009

The geochemistry of K‐feldspar for K, P, Sr, Ba, Rb, Cs, Ga, and of muscovite for the same elements plus Nb and Ta, was used for proving the parental relationships of S‐type granites and LCT (Li, Cs, Ta) rare‐element pegmatites in the southernmost pegmatitic field of the Pampean pegmatite province in Argentina. The variation of K/Rb‐Cs, K/Cs‐Rb, K/Rb‐Rb/Sr, K/Rb‐Ba in K‐feldspar from the granites and pegmatites show that they form an association with the evolutional sequence: granites → barren‐ to transitional pegmatites → beryl type, beryl‐columbite‐phosphate pegmatites → complex type of spodumene subtype pegmatites → albite‐spodumene type → albite type pegmatites. This sequence reflects the regional distribution of the different magmatic units. The Ta‐Cs diagram for muscovite reveals that none of the studied pegmatites exceed the threshold established in previous studies for being considered with important tantalum oxide mineralization. The granites and pegmatites constitute a rare‐element pegmatitic field in which different magmatic units form a continuous fractionation trend, extended from the less evolved granitic facies to the most geochemically specialized pegmatites
Samarium–Neodymium and Rubidium–Strontium Isotopic Dating of Veined REE Mineralization for the Bayan Obo REE‐Nb‐Fe Deposit, Northern China
Authors: Hu Fang‐Fang , Fan Hong‐Rui , Liu Shuang , Yang Kui‐Feng , Chen Fukun
Published: November 2009

The Bayan Obo REE‐Nb‐Fe deposit in Inner Mongolia, China, consists of later REE‐mineralizing fluorocarbonate veins cutting the earlier banded and massive ores in the deposit. Samarium–neodymium dating using the minerals including huanghoite and rubidium–strontium dating using single‐grain biotites both from the later veins show concordant isochrons corresponding to 442 ± 42 Ma (2σ uncertainty) and 459 ± 41 Ma, respectively. The isochron ages suggest that the later REE vein mineralization took place during the middle Paleozoic at Bayan Obo, consistent with geological observations and age data previously reported.
Environmental factors associated with reproductive barrier breakdown in sympatric trout populations on Vancouver Island
Authors: Heath Daniel , Bettles Cory M. , Roff Derek
Published: November 2009

The incidence of hybridization between coastal cutthroat (Oncorhynchus clarki clarki) and rainbow trout (Oncorhynchus mykiss) varies widely among populations. The breakdown of reproductive isolation is of concern to managers, and raises the question: how have the two species retained their genetic and morphological divergence? Using a combination of mitochondrial DNA and nuclear DNA markers coupled with watershed attribute and disturbance data, we determined the distribution and frequency of trout hybridization on Vancouver Island, BC and the environmental factors associated with the hybridization. We found 284 hybrids (among 1004 fish) in 29 of 36 sampled populations. High variation in levels of hybridization was observed among populations, and no single environmental factor was found to dominate in determining hybridization levels. However, logging activity, urban infrastructure development, and stocking of hatchery rainbow trout played significant roles in determining hybridization levels, and populations in small watersheds are more at risk of reproductive barrier breakdown. This study illustrates that cutthroat–rainbow trout reproductive barrier breakdown is widespread on Vancouver Island and that anthropogenic disturbance plays a role in the process. As similar environmental disturbance is common in much of coastal trout habitat, large‐scale hybridization may be occurring elsewhere and thus may represent a critical management issue for Pacific trout species.
‘Lord God! Jesus! What a House!’: Describing and Visiting Strawberry Hill
Authors: CLARKE STEPHEN
Published: November 2009

This paper analyses the transmission of the text of Horace Walpole's Description of Strawberry Hill from the printing of its first component in 1760 to its last appendix in 1791 and beyond. It uses Walpole's copious manuscript amendments in a number of copies to consider the purpose of the book in the context both of the steady stream of visitors to Walpole's collection at Strawberry Hill and of Walpole's passionate engagement in recording that ever‐expanding collection. It also discusses a number of unrecorded examples of printing from Walpole's Strawberry Hill Press, which the research for the paper has revealed.
Friction, Wear, and Temperature in Sliding Contact
Authors: Al-Rubeye Hamid S.
Published: November 2009

The temperature criterion plays a significant part in the attempt to interpret the scoring phenomenon of lubricated load-carrying machine members. Investigations were carried out to examine the correlation of the scoring bulk body temperatures, which have been measured on point and line contact machines using a modified Four-Ball and Spur Gear Tester. The simulation of the thermal model of both systems proved to be the only criterion for the correlation of the desired temperatures. A systematical investigation on the Four-Ball machine using a new temperature measuring method provided the basis to study the heating process of the sliding elements. The results show the influence of the loading and sliding velocity on both the bulk body temperature and the surface temperature.
An Analytical Solution for Thermal Behavior of the Step Thrust Bearing
Authors: Tichy J. A. , Smith R. N.
Published: November 2009

An analytical solution to the energy equation is presented for the one-dimensional step thrust bearing. Constant lubricant properties are assumed which decouples the momentum and energy equations resulting in a known velocity distribution according to the usual lubrication theory. The energy equation is then linear and yields to a separation of variables solution which results in Sturm-Liouville problems for both domains of the step, which are married at the discontinuity. Conduction, convection and dissipation are all considered and convenient non-dimensional parameters are developed for their relative magnitudes. Expressions for temperature distribution, (along and across the film) heat transfer, and dissipation rates are developed. Results are presented for the Rayleigh step geometry although any other step configuration is easily handled. A wide range of thermal behavior is obtained (rising or falling temperatures, higher temperatures before or after the step, etc.) depending on the dimensionless parameters. The solution presented cannot substitute for the more detailed numerical studies but does offer advantages. The effects of various thermal modes of operation are easily studied and the method is relatively simple to use requiring only a small computer program to evaluate the eigenvalues and eigenfunctions. In addition, general conclusions drawn here can probably be applied with caution to more complex bearing geometries.
Pressurized Oil Squeeze Film Dampers
Authors: Stiffler A. Kent
Published: November 2009

A pressurized oil squeeze film damper supporting a rigid rotor mounted in antifriction bearings is investigated. Orifice and inherent feed inlets are examined, and it is shown that the clearance determines the inlet resistance for a groove or slot. The film stiffness and damping forces are determined as a function of the restrictor coefficient, rotor unbalance speed and the supply pressure using the short bearing approximation. These forces are related to the system transmissibility. A design methodology for low transmissibilities is presented.
Thermally Induced Whirl of a Rigid Rotor on Hydrodynamic Journal Bearings
Authors: Maki E. R. , Ezzat H. A.
Published: November 2009

An experimental study was conducted on rigid rotors supported on 360° circumferentially grooved journal bearings. The effect of bearing clearance, lubricant inlet temperature, and supply pressure on whirl instability was examined. The experimental results indicate that self-excited whirl exists whenever the lubricant inlet temperature is higher than that of the bearing surface. On the other hand, when the bearing temperature is higher than the lubricant inlet temperature, whirl does not occur even at rotor speeds considerably higher than the instability threshold predicted by isothermal hydrodynamic theory. This thermally-induced whirl phenomenon has not been reported elsewhere and is documented in this paper. While the conditions giving rise to this phenomenon are unlikely to occur in the steady-state operation of high-speed bearings, they can exist under transient conditions. The findings of this study also provide strong evidence of the importance of thermohydrodynamic effects in considerations of stability of journal bearings.
Squeeze Effects in Radial Face Seals
Authors: Etsion I.
Published: November 2009

Squeeze effects in a liquid lubricated radial face seal are analyzed. The analysis considers face misalignment with both axial and angular vibrations of the primary seal ring. Translational, rotational, and cross-coupled damping coefficients of the fluid film are derived analytically from a solution of the Reynolds equation utilizing the narrow seal approximation. Results are given for a wide range of practical radius ratios. At each radius ratio, the complete range of angular misalignment—from parallel faces to touch down—is covered. It is shown that squeeze effects in face seals are usually larger than the more familiar hydrodynamic effects. These effects play an important role in the seal’s mechanism of operation and therefore have to be considered in any realistic seal model.
Development of a Laser Fluorescence Technique For Measuring Piston Ring Oil Film Thickness
Authors: Ting L. L.
Published: November 2009

A single cylinder engine equipped with a transparent cylinder sleeve has been used to develop a technique to make visual investigations of piston ring lubrication behavior and engine oil loss mechanism. This paper describes this apparatus and the development of a laser excited oil fluorescence technique for measuring the oil film thickness change between the piston rings and the transparent cylinder sleeve wall. The amount of oil accumulated in the piston-cylinder clearance spaces above and below the ring pack, and those in the inter-ring spaces, can also be observed. Preliminary results showing oil fluorescence light intensity traces indicate that this technique works very well. Quantitative oil film thickness data should be readily obtainable from these traces once the fluorescent light intensity is calibrated.
Stick-Slip Induced Noise Generation in Water-Lubricated Compliant Rubber Bearings
Authors: Bhushan Bharat
Published: November 2009

The basic tenet of the research reported here has been to develop a fundamental understanding of the mechanism of noise generation in water-lubricated compliant rubber bearings. An experimental model study employed a transparent glass slider rubber against a Buna-N rubber section in order to permit direct measurement of the different aspects of the vibration phenomena, and to be able to observe the type of rubber motion that occurs at the sliding interface. This study has clearly demonstrated that the basic phenomenon is a stick-slip motion of the rubber surface, at times coupled with mechanical resonances of the bearing parts. Shaft torsional resonance does not appear to be involved. The design, geometrical and material conditions that encourage the phenomenon have been established. The direction for improvement is clear, and the paper contains both conclusions and recommendations for corrective means which would lead toward silent operation.
A Finite Length Bearing Correction Factor for Short Bearing Theory
Authors: Barrett L. E. , Allaire P. E. , Gunter E. J.
Published: November 2009

A rapid method for calculating the general nonlinear response of finite-length plain journal and squeeze film damper bearings is presented. The method incorporates a finite-length correction factor which modifies the nonlinear forces obtained from short bearing theory. The steady-state rotational, precessive squeeze, and radial squeeze forces obtained with the correction factor compare extremely well with the forces obtained from an analytic solution of Reynolds equation using a variational approach up to L/D of 1.25 and hence covers the most commonly encountered L/D ratios. The method is no more time consuming than the short bearing analysis and is especially suited to nonlinear transient analysis of flexible rotors.
Spherical Bearings: Static and Dynamic Analysis Via the Finite Element Method
Authors: Goenka P. K. , Booker J. F.
Published: November 2009

Analytical solutions are not available for spherical bearing problems except for very specialized cases. However, the finite element method presented here can be used to analyze virtually any such bearing having an incompressible lubricant between surfaces which are smooth, rigid, and impermeable. The method can be easily extended to account for permeable surfaces and lubricants with variable viscosity and density. Triangular finite elements with linear interpolation functions are used to model the lubricant film. For complete films an elimination method solves the resulting system of equations; for incomplete films an iteration scheme incorporates Reynolds boundary conditions. The method is extended from “direct” (explicit) problems of specified planar motion to “indirect” (implicit) problems with specified planar loads and can be further extended to solve these problems with general spatial motion and loads. The results for spherical bearings are similar in trend to those for cylindrical journal bearings and suggest the former as possible alternatives, especially if axial as well as radial forces are present.
An Improved Short Bearing Analysis for the Submerged Operation of Plain Journal Bearings and Squeeze-Film Dampers
Authors: Pan C. H. T.
Published: November 2009

By allowing the film pressure to assume some subambient value and by allowing natural boundaries of the film to form in the unloaded region, the short-bearing theory of Ocvirk and Dubois is extended to include a detailed description of the cavitation zone. Two alternative cavitation configurations are shown to be possible, rendering different eccentricity (orbit size), attitude angle (phase), for the same load and minimum film pressure. The first configuration features an enclosed cavity maintained at a subambient level and is called “0” cavitation, which is crudely emulated by the conventional “half-film” approximation. The second configuration features ambient level side cavities, the boundaries of which are drawn inside the bearing ends by a sub-cavity film pressure, and is called “I” cavitation. The “I” cavitation, which is initiated by the aggregation of entrained bubbles in the ambient fluid, can present itself in the form of multiple striations causing substantial loss of load capacity.
An Evaluation of the Average Flow Model [1] for Surface Roughness Effects in Lubrication
Authors: Teale J. L. , Lebeck A. O.
Published: November 2009

The average flow model presented by Patir and Cheng [1] is evaluated. First, it is shown that the choice of grid used in the average flow model influences the results. The results presented are different from those given by Patir and Cheng. Second, it is shown that the introduction of two-dimensional flow greatly reduces the effect of roughness on flow. Results based on one-dimensional flow cannot be relied upon for two-dimensional problems. Finally, some average flow factors are given for truncated rough surfaces. These can be applied to partially worn surfaces. The most important conclusion reached is that an even closer examination of the average flow concept is needed before the results can be applied with confidence to lubrication problems.
Micropitting in Hertzian Contacts
Authors: Berthe D. , Flamand L. , Foucher D. , Godet M.
Published: November 2009

This paper shows that both micropits and spalls occur near pure rolling conditions. The first are initiated at the surface and are related to asperity interaction. The second are well described in the literature and will not be discussed here. A model capable of predicting the mechanical conditions under which micropits are generated is presented. In this model the pressures on asperities are analyzed for given separations of the surfaces; elastic, elasto-plastic, or plastic deformations are deduced. Master curves can be obtained if a pressure index is used, the model requires a comprehensive description of the surface as it calls for the distributions of both profiles height and asperity tip radii of curvature. A new approach was proposed to define the peaks which carries the load in the contact. In this model a peak is defined with respect to the separation of the surfaces. Good correlation between theory and experiment was obtained for materials as different as mild and case hardened steels and with ground and “as received” treated specimen surfaces. The rate of micropit formation which depends necessarily on running-in cannot be predicted at this time. Results however clearly show that when running-in takes place, i.e. when the pressure on asperity tips decreases to a value compatible with elastic deformation, the rate of formation of micropits with time tends to zero and of course fatigue life is increased.
Friction and Wear of Semicrystalline Polymers Sliding Against Steel Under Water Lubrication
Authors: Tanaka Kyuichiro
Published: November 2009

Two types of experiments were carried out in this work. In one experiment, the smooth steel sphere was slid on polymer plates at a very low speed. Water reduced to some extent or very much the friction of polymers. In another experiment, the polymer pins were rubbed against the stainless steel disk at various speeds. In the sliding of polymers on the disk without the transferred polymer, a slight reduction of friction generally occurred under boundary lubrication; however, it occurred clearly in some cases on the disk with the transferred polymer. In these experiments, surface roughness plays an important role in boundary lubrication with water. The wear of polymers increases generally under lubrication. The amount of polymer transferred under lubrication is similar to that transferred in the dry condition. However, the features of worn surfaces of polymers under lubrication are different from those in a dry condition. The mechanism of polymer wear under lubrication is discussed on the basis of these findings.
The Optimization of Hydrodynamic Journal Bearings for Aerodynamically Excited Flexible Rotor-Bearing Systems
Authors: Barrett L. E.
Published: November 2009

This paper is concerned with the design of hydrodynamic journal bearings to stabilize a large generic class of turbomachinery subjected to aerodynamic excitation. A modal representation of the rotor is used together with a generalized representation of the bearings. This produces a rather simple set of algebraic equations which may be used to determine optimum bearing designs to maximize the level of aerodynamic excitation for stable operation. This approach has proved useful to quickly select bearing designs which warrant more detailed further investigation. A comparison of results obtained from more elaborate and time consuming analysis methods is made. Also an example bearing optimization is given which illustrates one way in which the present analysis method may be used in the design process.
Optimum Design of Flexible Mechanisms
Authors: Zhang Ce , Grandin H. T.
Published: November 2009

In this paper the optimality criterion technique transplanted by Khan and his coworkers into mechanism design and the kinematical refinement technique proposed by the authors are combined into a novel procedure of optimum design of flexible mechanisms. Cross-sectional parameters are taken as the first group of design variables; a fully-stressed mechanism is obtained by using previous researchers’ recursion formulas which contain some improvements introduced by the authors. Geometrical parameters are used as the second group of design variables; a mechanism with improved criterion of kinematic performance is obtained by means of the kinematic refinement technique. The method presented is effective and steady. An example problem in the design of a four-bar path-generating mechanism is given to illustrate the procedure.
Complete Balancing of Space Mechanisms—Shaking Force Balancing
Authors: Bagci C.
Published: November 2009

Complete balancing of shaking forces and shaking moments in space mechanisms is the subject of this article. Using real vectors, it presents methods of balancing shaking forces completely in space mechanisms. Force balancing of a mechanism is achieved by attaining a stationary center of the total mass of the mechanism. Design equations for force balancing of the RSSR, RSSP slider-crank and RSRC, CSC, and RCRC screw generators are developed. These mechanisms, their pair inversion mechanisms are force balanced thus establishing general guidelines for force balancing of space mechanisms. It is shown that SC and SRC dyads in space mechanisms also introduce force transmission irregularity in addition to the CRC, CCC, CRP, PRP, PSP, PSC dyads that introduce force transmission irregularity. Space mechanisms with force transmission irregularities are balanced by attaching a force balancing RRR dyad or a linearly moving conterbalancer driven by gear-rack drive, a belt, chain, or rolomite mechanism.
Analysis of Angular Velocities and Accelerations in Plane Linkages by Means of Numerical Procedure
Authors: Di Benedetto A. , Pennestri´ E.
Published: November 2009

Briefly recalling some of the latest procedures of kinematic analysis that technical literature records, a numerical method is proposed for approximate calculus of angular velocities and accelerations in plane mechanisms. The algorithm is obtained by mathematical induction through Newton’s formulae for repeating integrations and it consists of a four points formula of numerical differentiation which is also easily programmable on automatic computers. A numerical example illustrated below shows the degree of reliability of the method proposed.
Structural Kinematics of In-Parallel-Actuated Robot-Arms
Authors: Hunt K. H.
Published: November 2009

An alternative is here put forward to counterbalance the present-day preoccupation with series-actuated robot-arms. A systematic study of robots and manipulators, now concentrating on “in-parallel” actuator-arrangements, reveals many geometries applicable either to entire robot-arms or to parts of otherwise series-actuated arms. No survey of this kind is possible without drawing heavily on the theory of screw systems. Having established a means of enumerating possible geometries, screw theory is again invoked to highlight, in broad terms, the patterns considered to be most promising. Criteria for avoiding undesirable robot-arm-configurations are touched upon, and certain aspects of the performance of in-parallel-actuated robot-arms are compared and contrasted with those of series-actuated arms. Within the bounds here set (thought to be realistic) the survey on its own is intended to be exhaustive, but many details remain to be investigated. This paper aims to do no more than edge open the door a little further towards in-parallel actuation in robot-arms; others may then consider that further study could be productive.
Analytical Reconstruction of the Running Surfaces of Gear Teeth Using Standard Profile and Lead Measurements
Authors: Mark W. D.
Published: November 2009

A method is developed for analytically reconstructing the geometric deviations of the running surface of a gear tooth from a perfect involute surface. The method uses standard profile and lead deviation measurements and is applicable to both helical and spur gears. The reconstruction is carried out by using normalized Legendre polynomials. For this class of functions, it is shown that the optimum locations of the profile and lead deviation measurements are the locations of the zeros of the Legendre polynomial of degree equal to the number of profile or lead deviation measurements taken–after appropriate normalization of the tooth width or depth, as appropriate. A least squares fit procedure for establishing a common origin of ordinates for sets of profile and lead deviation measurements is formulated, and its solution is carried out in closed form. Account is taken of the noninsignificant errors that typically arise in profile and lead deviation measurements so that the final analytically reconstructed tooth surface is free of inconsistencies.
Dynamic Analysis of a Multi-Rigid-Body Open-Chain System
Authors: Pennock G. R. , Yang A. T.
Published: November 2009

In this paper we present an analytical technique, based on Newtonian mechanics with screw calculus and dual-number matrices, to derive the dynamic equations of a multi-rigid-body open-chain system. Next, we outline a systematic procedure to derive closed-form expressions for the joint forces and torques and the reaction forces and moments exerted on each member in the system. Finally, we illustrate the procedure with two examples of robot manipulators. It is hoped that the analytical technique presented here will provide a meaningful alternative, or serve as a complement to existing methods, in our common effort to advance the design of robot manipulators.
Gear-Tooth Interference
Authors: Colbourne J. R.
Published: November 2009

A numerical procedure is described by which gear pairs can be checked for possible tooth interference. Two commonly used rules for avoiding interference are assessed, and one of them is shown to be unreliable.
A Theory for the Identification of a Single Degree-of-Freedom Machine From its Periodic Operating Characteristics
Authors: Wiederrich J. L.
Published: November 2009

The dynamic properties of a machine are defined by its kinetic energy, potential energy, and dissipation functions. These functions form the basis for the dynamic analysis of a machine. This paper presents a theory whereby these functions may be determined from the observed forced periodic operating response of a single degree of freedom machine. This method may have applications in machinery development and diagnosis.
A Novel Method for Prescribing the Maximum Shaking Force of a Four-Bar Linkage with Flexibility in Counterweight Design
Authors: Tricamo S. J. , Lowen G. G.
Published: November 2009

A new partial force balancing method for four-bar linkages, which allows the prescribing of the maximum shaking force, is presented. This two-counterweight method is based on the controlled reduction of the size of the shaking force hodograph of the unbalanced mechanism. The introduction of what has been called the equipollent circle constraint equation makes it possible to attain the identical reduction in maximum shaking force for a wide theoretical range of counterweight radii and angles. A sample problem, dealing with a 50 percent reduction in the maximum shaking force, shows that the increases in bearing forces, shaking moments, and input moment are minimal over a considerable portion of this design range.
Simultaneous Optimization of Dynamic Reactions of a Four-Bar Linkage With Prescribed Maximum Shaking Force
Authors: Tricamo S. J. , Lowen G. G.
Published: November 2009

A three-counterweight technique for simultaneously minimizing the maximum values of such dynamic reactions as the bearing force, the input moment, and the shaking moment of a constant input speed four-bar linkage, while additionally obtaining a prescribed maximum value of the shaking force, is introduced. The chosen optimization formulation is new to the field of mechanism design; a certain minimization parameter is made the objective function. The maximum values of the individual dynamic reactions are then minimized by inequality constraints which force the differences between these reactions (due to the presence of counterweights) and the maximum value of the same reactions in the unbalanced mechanism to be smaller than the minimization parameter at as many mechanism positions as required. The prescribed maximum shaking force is attained by an equality constraint which has been called the general equipollent circle constraint equation. The method, which employs an augmented Lagrangian penalty function code, produced good results in the optimization of the dynamic reactions of partially and fully force balanced example mechanisms.
On The Dynamics of Intermittent-Motion Mechanisms. Part 1: Dynamic Model and Response
Authors: Lee Ting W. , Wang A. C.
Published: November 2009

This paper deals with a basic problem regarding intermittent-motion mechanisms, namely, how to formulate a predicative model for the study of the dynamics of these mechanisms. A mathematical model is developed in this investigation. The model, which includes clearance, damping, material compliance, and mechanism elasticity, is basic to the determination of the dynamical response such as force amplification and motion characteristics of mechanisms with intermittent motion. A new approach in the modeling of system damping is presented. Instead of using damping ratio, which is difficult to estimate accurately, a new damping function is introduced, which characterizes the speed and load dependent nature of damping. Two types of damping functions are proposed and both of their corresponding damping forces satisfy the expected hysteresis boundary conditions, i.e., zero damping force at zero and maximum relative displacement of contact. A comparative study of the present model with conventional dynamic models is performed. It demonstrates the characteristics and the usefulness of the proposed model for the study of the dynamics of intermittent-motion mechanisms.
Application of Optimal Control Theory to the Synthesis of High-Speed Cam-Follower Systems. Part 2: System Optimization
Authors: Chew M. , Freudenstein F. , Longman R. W.
Published: November 2009

This part is concerned with the determination of optimum values of the design parameters of cam-follower systems according to the criterion developed in Part 1. The nonlinearities associated with the optimization of contact stress, pressure-angle, and friction-dependent forces, which create difficulties in the simpler approaches, can be tolerated in the optimal-control-theory formulation, which is developed in this investigation. The procedure for the optimization of tuned D-R-D and D-R-R-D cams has been described and the results illustrated by means of numerical examples.
Diffractions of Elastic Waves and Stress Concentration Near a Cylindrical Nano-Inclusion Incorporating Surface Effect
Authors: Ru Y. , Wang G. F. , Wang T. J.
Published: November 2009

The diffractions of plane compressional waves (P-wave) and shear waves (SV-wave) by a cylindrical nano-inclusion are investigated in this paper. To account for the surface/interface effect at nanoscale, the surface/interface elasticity theory is adopted in the analysis. Using the displacement potential method, we obtain the solutions for the elastic fields induced by incident P- and SV-waves near a cylindrical nano-inclusion. The results show that surface/interface has a significant effect on the diffractions of elastic waves as the radius of the inclusion shrinks to nanoscale. For incident waves with different frequencies, the effects of interfacial properties on the dynamic stress concentration around the nano-inclusion are discussed in detail.