bluuebunny/crossref_metadata_2025 huggingface dataset:
New Phenylethanoid Glycosides and Sugar Esters from Ku‐Ding‐Cha, a Herbal Tea Produced from Ligustrum purpurascens
Authors: She G.‐M. , Wang D. , Zeng S.‐F. , Yang C.‐R. , Zhang Y.‐J.
Published: July 2008

ABSTRACT:  Ku‐Ding‐Cha is a kind of herbal tea used commonly in China for its effects on hypertension, fatness, inflammation, and diuresis. The chlorophyll removal fraction from 60% aqueous acetone extract of Ku‐Ding‐Cha produced from the leaves of Ligustrum purpurascens (Oleaceae) exhibited observable antioxidant activity on 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging assay (SC50= 45 μg/mL). Further detailed phytochemical investigation on this fraction led to the isolation of 2 new phenylethanoid glycosides, ligupurpurosides C‐D (1 and 2), and 2 new sugar esters, ligupurpurosides E‐F (3 and 4), together with 15 known compounds (5 to 19). All of them, except for 7, 8, 9, 11, and 12, were isolated from Ku‐Ding‐Cha and its original plants for the first time. The chemical structures were elucidated based on the analysis of spectroscopic data, including 1D, 2D NMR, and FABMS. In addition, the isolated compounds were evaluated for their antioxidant activities by DPPH assay.
Effect of Hot Water Treatments on Quality of Highbush Blueberries
Authors: Fan L. , Forney C.F. , Song J. , Doucette C. , Jordan M.A. , McRae K.B. , Walker B.A.
Published: July 2008

ABSTRACT:  Highbush blueberries, cv ‘Burlington’, were treated with 22, 45, 50, or 60 °C water for 15 or 30 s along with an untreated control. Fruit were then stored for 0, 1, 2, or 4 wk at 0 °C and 2 or 9 d at 20 °C prior to evaluation of microbial population and fruit quality. After 4 wk of storage, the hot water treatment at 60 °C resulted in 92% marketable berries, followed by 90% at 50 °C, 88% at 45 °C, and 83% at 22 °C compared with 76% in untreated controls. Decay incidence was reduced to 0.6%, 1.2%, 1.4%, or 2.8% with 60, 50, 45, or 22 °C water treatments, respectively, compared with 5.1% in controls following 4 wk at 0 °C and 2 d at 20 °C. After an additional 7 d at 20 °C, decay in fruit treated at 60 °C for 15 or 30 s remained at 1.8% and 0.4%, respectively, compared to 37.4% in controls. Weight loss of berries treated with hot water was 0.4% against 3.8% in controls, and shriveled and split berries were also reduced compared to controls (P < 0.001). Aerobic plate count and yeast and mold count were reduced by 0.45 to 0.7 log at 60 °C for 30 s. Botrytis cinerea and Colletotrichum sp. were the dominant fungal pathogens causing decay of Burlington blueberries during storage. Hot water treatments also immediately induced an increase in ethanol and reduced fruit titratable acidity and soluble solids content, but had no significant effect on fruit firmness, pH, or most flavor volatile concentrations.
Purification and Characteristics of Feruloyl Esterase from Aspergillus awamori G‐2 Strain
Authors: Kanauchi M. , Watanabe S. , Tsukada T. , Atta K. , Kakuta T. , Koizumi T.
Published: July 2008

ABSTRACT:  For food industry production processes and other uses, a mold that produces high levels of feruloyl esterase was obtained from laboratory mold collections and other sources. It was Aspergillus awamori G‐2 that produces high levels of feruloyl esterase. The feruloyl esterase was purified using ion‐exchange chromatography, size‐exclusion chromatography, and HPLC chromatography. The enzyme was identified as a monomer protein using size‐exclusion chromatography. Its optimum temperature and pH were, respectively, 40 °C and pH 5. Its activity was stable at pH 3 to 5. The enzyme was combined with xylan and starch, but it was absorbed by cellulose. The km of the feruloyl esterase was 0.0019% (0.01 mM). The enzyme showed stable activity at pH 3 and 50 °C, making this enzyme useful for food production.
In vitro Inhibition of Food Spoilage and Foodborne Pathogenic Bacteria by Essential Oil and Leaf Extracts of Magnolia liliflora Desr.
Authors: Bajpai V.K. , Rahman A. , Dung N.T. , Huh M.K. , Kang S.C.
Published: July 2008

ABSTRACT:  The aim of this study was to examine the chemical composition of the essential oil isolated from the floral parts of Magnolia liliflora Desr. by hydrodistillation, and to test the efficacy of essential oil and various leaf extracts against a diverse range of microorganisms comprising food spoilage and foodborne pathogenic bacteria. The chemical composition of essential oil was analyzed by GC‐MS. It was determined that 52 compounds, which represented 78.07% of total oil, were present in the oil. The oil contained mainly levoxine (15.59%), methylcyclopropane (24.26%), 2‐β‐pinene (5.3%), caryophyllene oxide (4.01%), and β‐caryophyllene (1.7%). The oil (1000 ppm/disc) and leaf extracts (1500 ppm/disc) exhibited promising antibacterial effects against the tested pathogens as a diameter of zones of inhibition (9 to 18 and 7 to 12 mm) and MIC values (125 to 1000 and 500 to 3000 μg/mL), respectively. Also, the oil had a potent detrimental effect on the viable count of the tested bacteria. The results obtained in this study support the role of essential oil and the leaf extracts derived from M. liliflora as a remarkable approach to inhibit the growth of food spoilage and foodborne pathogens.
OUR CAUSE1
Authors: Astor James
Published: July 2008

abstract  Starting from the knowledge that the Freudocentric view of the relationship of Freud and Jung, how the heir became the apostate, has been shown to be false, I examine the many features of this correspondence which reveal differences and similarities between their approach to the psyche, the political, the personal and the theoretical in this historic oedipal drama.
ABDICATION OF A FATHER: SOME REFLECTIONS ON THE FREUD–JUNG CORRESPONDENCE1
Authors: Fisher James V.
Published: July 2008

abstract  This paper explores one dimension of the complex relationship linking Freud and Jung as revealed in their correspondence between 1906 and 1912. It focuses on Freud's adoption of Jung as his heir, particularly in terms of his repeated proposal to Jung ‘to continue and complete my work by applying to psychoses what I have begun with neuroses’. The paper tracks the fate of this proposal in the words of these two men and suggests that the ambivalence of both can be seen as an expression of an unconscious dynamic portrayed in Shakespeare's King Lear, a dynamic characterized by the author as the developmental task of ‘heriting’. Emma Jung captured the heart of the dilemma of ‘heriting’ in her question to Freud: ‘Doesn't one often give much because one wants to keep much?’ Although the trajectory of the heritage Freud sought for his ‘adopted eldest son’, ‘crown prince’ and ‘successor’ was not the same as that of the tragedy of Lear, it was no less poignant in its tensions and disappointments – even for a time in its reversal of the ‘heriting’– and finally in the disintegration of the relationship.
Release of ATP and glutamate in the nucleus tractus solitarii mediate pulmonary stretch receptor (Breuer–Hering) reflex pathway
Authors: Gourine Alexander V. , Dale Nicholas , Korsak Alla , Llaudet Enrique , Tian Faming , Huckstepp Robert , Spyer K. Michael
Published: July 2008

The Breuer–Hering inflation reflex is initiated by activation of the slowly adapting pulmonary stretch receptor afferents (SARs), which monosynaptically activate second‐order relay neurones in the dorsal medullary nucleus of the solitary tract (NTS). Here we demonstrate that during lung inflation SARs release both ATP and glutamate from their central terminals to activate these NTS neurones. In anaesthetized and artificially ventilated rats, ATP‐ and glutamate‐selective microelectrode biosensors placed in the NTS detected rhythmic release of both transmitters phase‐locked to lung inflation. This release of ATP and glutamate was independent of the centrally generated respiratory rhythm and could be reversibly abolished during the blockade of the afferent transmission in the vagus nerve by topical application of local anaesthetic. Microionophoretic application of ATP increased the activity of all tested NTS second‐order relay neurones which receive monosynaptic inputs from the SARs. Unilateral microinjection of ATP into the NTS site where pulmonary stretch receptor afferents terminate produced central apnoea, mimicking the effect of lung inflation. Application of P2 and glutamate receptor antagonists (pyridoxal‐5′‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid, suramin and kynurenic acid) significantly decreased baseline lung inflation‐induced firing of the second‐order relay neurones. These data demonstrate that ATP and glutamate are released in the NTS from the central terminals of the lung stretch receptor afferents, activate the second‐order relay neurones and hence mediate the key respiratory reflex – the Breuer–Hering inflation reflex.
Phosphate metabolite concentrations and ATP hydrolysis potential in normal and ischaemic hearts
Authors: Wu Fan , Zhang Eric Y. , Zhang Jianyi , Bache Robert J. , Beard Daniel A.
Published: July 2008

To understand how cardiac ATP and CrP remain stable with changes in work rate – a phenomenon that has eluded mechanistic explanation for decades – data from 31phosphate‐magnetic resonance spectroscopy (31P‐MRS) are analysed to estimate cytoplasmic and mitochondrial phosphate metabolite concentrations in the normal state, during high cardiac workstates, during acute ischaemia and reactive hyperaemic recovery. Analysis is based on simulating distributed heterogeneous oxygen transport in the myocardium integrated with a detailed model of cardiac energy metabolism. The model predicts that baseline myocardial free inorganic phosphate (Pi) concentration in the canine myocyte cytoplasm – a variable not accessible to direct non‐invasive measurement – is approximately 0.29 mm and increases to 2.3 mm near maximal cardiac oxygen consumption. During acute ischaemia (from ligation of the left anterior descending artery) Pi increases to approximately 3.1 mm and ATP consumption in the ischaemic tissue is reduced quickly to less than half its baseline value before the creatine phosphate (CrP) pool is 18% depleted. It is determined from these experiments that the maximal rate of oxygen consumption of the heart is an emergent property and is limited not simply by the maximal rate of ATP synthesis, but by the maximal rate at which ATP can be synthesized at a potential at which it can be utilized. The critical free energy of ATP hydrolysis for cardiac contraction that is consistent with these findings is approximately −63.5 kJ mol−1. Based on theoretical findings, we hypothesize that inorganic phosphate is both the primary feedback signal for stimulating oxidative phosphorylation in vivo and also the most significant product of ATP hydrolysis in limiting the capacity of the heart to hydrolyse ATP in vivo. Due to the lack of precise quantification of Piin vivo, these hypotheses and associated model predictions remain to be carefully tested experimentally.
An Imaging Study of Compression Ignition Phenomena of Iso-Octane, Indolene, and Gasoline Fuels in a Single-Cylinder Research Engine
Authors: Zigler Bradley T. , Walton Stephen M. , Assanis Dimitris , Perez Elizabeth , Wooldridge Margaret S. , Wooldridge Steven T.
Published: July 2008

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from ϕ=0.69 to 0.27. The time-resolved imaging and pressure data show that high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.
Effects of Temperature and Particle Size on Deposition in Land Based Turbines
Authors: Crosby Jared M. , Lewis Scott , Bons Jeffrey P. , Ai Weiguo , Fletcher Thomas H.
Published: July 2008

Four series of tests were performed in an accelerated deposition test facility to study the independent effects of particle size, gas temperature, and metal temperature on ash deposits from two candidate power turbine synfuels (coal and petcoke). The facility matches the gas temperature and velocity of modern first stage high pressure turbine vanes while accelerating the deposition process. Particle size was found to have a significant effect on capture efficiency with larger particles causing significant thermal barrier coating (TBC) spallation during a 4 h accelerated test. In the second series of tests, particle deposition rate was found to decrease with decreasing gas temperature. The threshold gas temperature for deposition was approximately 960°C. In the third and fourth test series, impingement cooling was applied to the back side of the target coupon to simulate internal vane cooling. Capture efficiency was reduced with increasing mass flow of coolant air; however, at low levels of cooling, the deposits attached more tenaciously to the TBC layer. Postexposure analyses of the third test series (scanning electron microscopy and X-ray spectroscopy) show decreasing TBC damage with increased cooling levels.
Roentgen Stereophotogrammetric Analysis Methods for Determining Ten Causes of Lengthening of a Soft-Tissue Anterior Cruciate Ligament Graft Construct
Authors: Smith Conrad , Hull M. L. , Howell S. M.
Published: July 2008

There are many causes of lengthening of an anterior cruciate ligament soft-tissue graft construct (i.e., graft+fixationdevices+bone), which can lead to an increase in anterior laxity. These causes can be due to plastic deformation and∕or an increase in elastic deformation. The purposes of this in vitro study were (1) to develop the methods to quantify eight causes (four elastic and four plastic) associated with the tibial and femoral fixations using Roentgen stereophotogrammetric analysis (RSA) and to demonstrate the usefulness of these methods, (2) to assess how well an empirical relationship between an increase in length of the graft construct and an increase in anterior laxity predicts two causes (one elastic and one plastic) associated with the graft midsubstance, and (3) to determine the increase in anterior tare laxity (i.e., laxity under the application of a 30N anterior tare force) before the graft force reaches zero. Markers were injected into the tibia, femur, and graft in six cadaveric legs whose knees were reconstructed with single-loop tibialis grafts. To satisfy the first objective, legs were subjected to 1500cycles at 14Hz of 150N anterior force transmitted at the knee. Based on marker 3D coordinates, equations were developed for determining eight causes associated with the fixations. After 1500 load cycles, plastic deformation between the graft and WasherLoc tibial fixation was the greatest cause with an average of 0.8±0.5mm followed by plastic deformation between the graft and cross-pin-type femoral fixation with an average of 0.5±0.1mm. The elastic deformations between the graft and tibial fixation and between the graft and femoral fixation decreased averages of 0.3±0.3mm and 0.2±0.1mm, respectively. The remaining four causes associated with the fixations were close to 0. To satisfy the remaining two objectives, after cyclic loading, the graft was lengthened incrementally while the 30N anterior tare laxity, 150N anterior laxity, and graft tension were measured. The one plastic cause and one elastic cause associated with the graft midsubstance were predicted by the empirical relationships with random errors (i.e., precision) of 0.9mm and 0.5mm, respectively. The minimum increase in 30N anterior tare laxity before the graft force reached zero was 5mm. Hence, each of the eight causes of an increase in the 150N anterior laxity associated with the fixations can be determined with RSA as long as the overall increase in the 30N anterior tare laxity does not exceed 5mm. However, predicting the two causes associated with the graft using empirical relationships is prone to large errors.
Static and Dynamic Characteristics for a Pressure-Dam Bearing
Authors: Al-Jughaiman Bader , Childs Dara
Published: July 2008

Measured rotordynamic force coefficients (stiffness, damping, and added mass) and static characteristics (eccentricity and attitude angle) of a pressure-dam bearing are presented and compared to predictions from a Reynolds-equation model, using an isothermal and isoviscous laminar analysis. The bearing’s groove dimensions are close to the optimum predictions of Nicholas and Allaire (1980, “Analysis of Step Journal Bearings-Infinite Length and Stability,” ASLE Trans., 22, pp. 197–207) and are consistent with current field applications. Test conditions include four shaft speeds (4000rpm, 6000rpm, 8000rpm, and 10000rpm) and bearing unit loads from 0kPato1034kPa(150psi). Laminar flow was produced for all test conditions. A finite-element algorithm was used to generate solutions to the Reynolds-equation model. Excellent agreement was found between predictions and measurements for the eccentricity ratio and attitude angles. Predictions of stiffness and damping coefficients are in reasonable agreement with measurements. However, experimental results show that the bearing has significant added mass of about 60kg at no-load conditions, versus zero mass for predictions from the Reynolds-equation model and 40kg using Reinhardt and Lund’s (1975, “The Influence of Fluid Inertia on the Dynamic Properties of Journal Bearings,” ASME J. Lubr. Technol., 97, pp. 159–167) extended Reynolds-equation model for a plain journal bearing. The added mass quickly drops to zero as the load increases. Measured results also show a whirl frequency ratio near 0.36 at no-load conditions; however, a zero whirl frequency ratio was obtained at all loaded conditions, indicating an inherently stable bearing from a rotordynamics viewpoint.
Modeling Cyclic Variability in Spark-Assisted HCCI
Authors: Daw C. Stuart , Edwards K. Dean , Wagner Robert M. , Green Johney B.
Published: July 2008

Spark assist appears to offer considerable potential for increasing the speed and load range over which homogeneous charge compression ignition (HCCI) is possible in gasoline engines. Numerous experimental studies of the transition between conventional spark-ignited (SI) propagating-flame combustion and HCCI combustion in gasoline engines with spark assist have demonstrated a high degree of deterministic coupling between successive combustion events. Analysis of this coupling suggests that the transition between SI and HCCI can be described as a sequence of bifurcations in a low-dimensional dynamic map. In this paper, we describe methods for utilizing the deterministic relationship between cycles to extract global kinetic rate parameters that can be used to discriminate multiple distinct combustion states and develop a more quantitative understanding of the SI-HCCI transition. We demonstrate the application of these methods for indolene-containing fuels and point out an apparent HCCI mode switching not previously reported. Our results have specific implications for developing dynamic combustion models and feedback control strategies that utilize spark assist to expand the operating range of HCCI combustion.
Experimental Examination of Prechamber Heat Release in a Large Bore Natural Gas Engine
Authors: Olsen Daniel B. , Kirkpatrick Allan T.
Published: July 2008

A common solution in reducing NOx emissions to meet new emission regulations has been lean burn combustion. However, with very lean air∕fuel (A∕F) ratios, both carbon monoxide and hydrocarbon emissions become unacceptably high due to the spark misfiring and combustion instabilities. In order to mitigate this, a prechamber ignition system is often used to stabilize combustion at very lean A∕F ratios. In this paper, the heat release in a retrofit prechamber system installed on a large bore natural gas engine is examined. The heat release analysis is based on dynamic pressure measurements both in the main chamber and prechamber. The Woschni correlation is utilized to model heat transfer. Based on heat release modeling and test data analysis, the following observations are made. Main chamber heat release rates are much more rapid for prechamber ignition compared to spark ignition. During combustion in the prechamber, much of the fuel flows into the main chamber unreacted. About 52% of the mass in the prechamber, at ignition, flows into the main chamber during prechamber combustion. Prechamber total heat release, pressure rise, and maximum jet velocity all increase with increasing prechamber equivalence ratio. Prechamber combustion duration and coefficient of variation of peak pressure are minimized at a prechamber equivalence ratio of about 1.09.
Characteristics of Particulate Emissions of Compression Ignition Engine Fueled With Biodiesel Derived From Soybean
Authors: Kim Myung Yoon , Yoon Seung Hyun , Hwang Jin Woo , Lee Chang Sik
Published: July 2008

An experimental investigation was performed on the effect of engine speed, exhaust gas recirculation (EGR), and boosting intake pressure on the particulate size distribution and exhaust gas emissions in a compression ignition engine fueled with biodiesel derived from soybean. The results obtained by biodiesel fuel were compared to those obtained by petroleum diesel fuel with a sulfur content of 16.3ppm. A scanning mobility particulate sizer was used for size distribution analysis, and it measured mobility equivalent particulate diameter in the range of 10.4–392.4nm. In addition to the size distribution of the particulates, exhaust emissions, such as oxides of nitrogen (NOx), hydrocarbon, and carbon monoxide emissions, and combustion characteristics under different engine operating parameters were investigated. The engine operating parameters in terms of engine speed, EGR, and intake pressure were varied to investigate their individual impacts on the combustion and exhaust emission characteristics. As the engine speed was increased for both fuels, the larger size particulates, which dominantly contribute particulate mass, were increased; however, total numbers of particulate were reduced. Compared to diesel fuel, the combustion of biodiesel fuel reduced particulate concentration of relatively larger size where most of the particulate mass is found. Moreover, dramatically lower hydrocarbon and carbon monoxide emissions were found in the biodiesel-fueled engine. However, the NOx emission of the biodiesel-fueled diesel engine shows slightly higher concentration compared to diesel fuel at the same injection timing. EGR significantly increased the larger size particulates, which have diameter near the maximum measurable range of the instrument; however, the total number of particulates was found not to significantly increase with increasing EGR rate for both fuels. Boosting intake pressure shifted the particulate size distribution to smaller particulate diameter and effective reduction of larger size particulate was found for richer operating conditions.
Can Markers Injected Into a Single-Loop Anterior Cruciate Ligament Graft Define the Axes of the Tibial and Femoral Tunnels? A Cadaveric Study Using Roentgen Stereophotogrammetric Analysis
Authors: Smith Conrad , Hull M. L. , Howell S. M.
Published: July 2008

Lengthening of a soft-tissue anterior cruciate ligament (ACL) graft construct over time, which leads to an increase in anterior laxity following ACL reconstruction, can result from relative motions between the graft and fixation devices and between the fixation devices and bone. To determine these relative motions using Roentgen stereophotogrammetry (RSA), it is first necessary to identify the axes of the tibial and femoral tunnels. The purpose of this in vitro study was to determine the error in using markers injected into the portions of a soft-tissue tendon graft enclosed within the tibial and femoral tunnels to define the axes of these tunnels. Markers were injected into the tibia, femur, and graft in six cadaveric legs the knees of which were reconstructed with single-loop tibialis grafts. The axes of the tunnels were defined by marker pairs that were injected into the bones on lines parallel to the walls of the tibial and femoral tunnels (i.e., standard). By using marker pairs injected into the portions of the graft enclosed within the tibial and femoral tunnels and the marker pairs aligned with the tunnel axes, the directions of vectors were determined by using RSA, while a 150N anterior force was transmitted at the knee. The average and standard deviations of the angle between the two vectors were 5.5±3.3deg. This angle translates into an average error and standard deviation of the error in lengthening quantities (i.e., relative motions along the tunnel axes) at the sites of fixation of (0.6±0.8)%. Identifying the axes of the tunnels by using marker pairs in the graft rather than marker pairs in the walls of the tunnels will shorten the surgical procedure by eliminating the specialized tools and time required to insert marker pairs in the tunnel walls and will simplify the data analysis in in vivo studies.
Effect of Stiff Coatings on EHL Film Thickness in Point Contacts
Authors: Liu Yuchuan , Wang Q. Jane , Zhu Dong
Published: July 2008

Coatings are widely used for interface performance enhancement and component life improvement, as well as for corrosion prevention and surface decoration. More and more mechanical components, especially those working under severe conditions, are coated with stiff (hard) thin coatings. However, the effects of coatings on lubrication characteristics, such as film thickness and friction, have not been well understood, and designing coating for optimal tribological performance is a grand challenge. In this paper, the influences of coating material properties and coating thickness on lubricant film thickness are investigated based on a point-contact isothermal elastohydrodynamic lubrication (EHL) model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Curve fitting of numerical results indicates that the maximum increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2max, can be expressed in the following forms: Imax=0.769M0.0238R20.0297L0.1376exp(−0.0243ln2L) and H2max=0.049M0.4557R2−0.1722L0.7611exp(−0.0504ln2M−0.0921ln2L). These formulas can be used to estimate the effect of coatings on film thickness for EHL applications.
Numerical Model of a Tandem Reciprocating Hydraulic Rod Seal
Authors: Yang Bo , Salant Richard F.
Published: July 2008

A numerical model of a tandem reciprocating hydraulic rod seal, consisting of two elastomeric U cup seals, has been constructed. It is applicable to cases in which the stroke length is significantly larger than the seal width. The model consists of coupled steady state fluid mechanics, deformation mechanics, and contact mechanics analyses, with an iterative computational procedure. The behaviors of the two seals are coupled through the pressure∕density in the interseal region and through flow continuity. Results for a typical tandem seal are compared to those of a single seal and a double lip seal.
A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition
Authors: Cohen D. , Kligerman Y. , Etsion I.
Published: July 2008

A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.
Mechanical Model of the Tubulin Dimer Based on Molecular Dynamics Simulations
Authors: Enemark Søren , Deriu Marco A. , Soncini Monica , Redaelli Alberto
Published: July 2008

The basic unit in microtubules is αβ-tubulin, a heterodimer consisting of an α- and a β-tubulin monomer. The mechanical characteristics of the dimer as well as of the individual monomers may be used to obtain new insight into the microtubule tensile properties. In the present work, we evaluate the elastic constants of each monomer and the interaction force between them by means of molecular dynamics simulations. Molecular models of α-, β-, and αβ-tubulins were developed starting from the 1TUB.pdb structure from the RCSB database. Simulations were carried out in a solvated environment by using explicit water molecules. In order to measure the monomers’ elastic constants, simulations were performed by mimicking experiments carried out with atomic force microscopy. A different approach was used to determine the interaction force between the α- and β-monomers by using 16 different monomer configurations based on different intermonomer distances. The obtained results show an elastic constant value for α-tubulin of 3.8–3.9N∕m, while for the β-tubulin, the elastic constant was measured to be 3.3–3.6N∕m. The maximum interaction force between the monomers was estimated to be 11.9nN. A mechanical model of the tubulin dimer was then constructed and, using the results from MD simulations, Young’s modulus was estimated to be 0.6GPa. A fine agreement with Young’s modulus values from literature (0.1–2.5GPa) is found, thus validating this approach for obtaining molecular scale mechanical characteristics. In perspective, these outcomes will allow exchanging atomic level description with key mechanical features enabling microtubule characterization by continuum mechanics approach.
Gender Differences in Capitate Kinematics are Eliminated After Accounting for Variation in Carpal Size
Authors: Rainbow Michael J. , Crisco Joseph J. , Moore Douglas C. , Wolfe Scott W.
Published: July 2008

Previous studies have found gender differences in carpal kinematics, and there are discrepancies in the literature on the location of the flexion∕extension and radio-ulnar deviation rotation axes of the wrist. It has been postulated that these differences are due to carpal bone size differences rather than gender and that they may be resolved by normalizing the kinematics by carpal size. The purpose of this study was to determine if differences in radio-capitate kinematics are a function of size or gender. We also sought to determine if a best-fit pivot point (PvP) describes the radio-capitate joint as a ball-and-socket articulation. By using an in vivo markerless bone registration technique applied to computed tomography scans of 26 male and 28 female wrists, we applied scaling derived from capitate length to radio-capitate kinematics, characterized by a best-fit PvP. We determined if radio-capitate kinematics behave as a ball-and-socket articulation by examining the error in the best-fit PvP. Scaling PvP location completely removed gender differences (P=0.3). This verifies that differences in radio-capitate kinematics are due to size and not gender. The radio-capitate joint did not behave as a perfect ball and socket because helical axes representing anatomical motions such as flexion-extension, radio-ulnar deviation, dart throwers, and antidart throwers, were located at distances up to 4.5mm from the PvP. Although the best-fit PvP did not yield a single center of rotation, it was still consistently found within the proximal pole of the capitate, and rms errors of the best-fit PvP calculation were on the order of 2mm. Therefore, the ball-and-socket model of the wrist joint center using the best-fit PvP is appropriate when considering gross motion of the hand with respect to the forearm such as in optical motion capture models. However, the ball-and-socket model of the wrist is an insufficient description of the complex motion of the capitate with respect to the radius. These findings may aid in the design of wrist external fixation and orthotics.
Fully Coupled Frictional Contact Using Elastic Halfspace Theory
Authors: Willner K.
Published: July 2008

The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts.
Thermal Study of the Dry Sliding Contact With Third Body Presence
Authors: Richard David , Iordanoff Ivan , Renouf Mathieu , Berthier Yves
Published: July 2008

When the thermal aspect of sliding contacts is investigated, few models take into account the presence of a third body at the contact interface. Moreover, when the presence of the third body is considered, its rheology is neglected. For this reason, the thermal study of such contact configuration is not fully understood and relies on strong hypothesis or even important simplifications. To fill this lack of knowledge, a thermal model has been developed embedded in a discrete element scheme. Such investigations highlight the key role played by both thermal and mechanical properties of the contact elements. If the third body rheology can affect the localization of the heat generation leading to important thermal asymmetries, the diffusive nature of the first bodies can also strongly control the phenomenon and accentuate or diminish the initial differences of surfaces temperature for the contacting volumes. The goal of this paper is to bring information or complete existing theories (Blok, H. A., 1937, “Theoretical Study of Temperature Rise at Surface at Actual Contact Under Oilness Lubricating Conditions,” I. Mech. E. Conf. Publ., 2, pp. 222–235;Ryhming, I. L., 1979, “On Temperature and Heat Source Distributions in Sliding Contact Problems,” Acta Mech., 32, pp. 261–274;Dragon-Louiset, M., and Stolz, C., 1999, “Approche Thermodynamique des Phénomenès liés à l’Usure de Contact,” Acad. Sci. Paris, C. R., 327, pp. 1275–1280) but also to bring a new point of view on the differences observed in the past between the numerical predictions and experimental measurements.
A Continuum Description of Dense Granular Lubrication Flow
Authors: Tichy John , Berthier Yves , Iordanoff Ivan
Published: July 2008

The present paper applies a recent continuum theory due to Aranson and Tsimring (2002, “Continuum Theory of Partially Fluidized Granular Flows,” Phys. Rev. E, 65, p. 061303) for the dense granular flow of particles in sustained contact to lubrication flows. Such third body granular flow may apply to some solid lubrication mechanisms. The continuum theory is unique in that it addresses solidlike behavior and the transition to fully fluidized behavior. The continuum studies are complemented by a discrete particle dynamics model of Iordanoff et al. (2005, “Numerical Study of a Thin Layer of Cohesive Particles Under Plane Shearing,” Powder Technol., 159, pp. 46–54). Three problems are treated: (1) flow due to the gravity of a layer of granular material down an inclined plane, (2) simple shear flow of a layer confined between sliding parallel surfaces, and (3) lubrication flow of a layer confined between a curved surface and a sliding plane. The perspective of this paper is that a continuum model will be more useful than a discrete model in engineering design of solid lubrication systems for the foreseeable future. In the inclined plane problem, the discrete simulations are used to provide material property parameters to the continuum model. In the simple shear problem, for validation, predictions of the continuum model are compared to those of the discrete element computer simulations. Finally, the continuum theory is applied to a more complex lubrication flow.
On the Computation of Stress in Affine Versus Nonaffine Fibril Kinematics Within Planar Collagen Network Models
Authors: Pence Thomas J. , Monroe Ryan J. , Wright Neil T.
Published: July 2008

Some recent analyses modeled the response of collagenous tissues, such as epicardium, using a hypothetical network consisting of interconnected springlike fibers. The fibers in the network were organized such that internal nodes served as the connection point between three such collagen springs. The results for assumed affine and nonaffine deformations are contrasted after a homogeneous deformation at the boundary. Affine deformation provides a stiffer mechanical response than nonaffine deformation. In contrast to nonaffine deformation, affine deformation determines the displacement of internal nodes without imposing detailed force balance, thereby complicating the simplest intuitive notion of stress, one based on free body cuts, at the single node scale. The standard notion of stress may then be recovered via average field theory computations based on large micromesh realizations. An alternative and by all indications complementary viewpoint for the determination of stress in these collagen fiber networks is discussed here, one in which stress is defined using elastic energy storage, a notion which is intuitive at the single node scale. It replaces the average field theory computations by an averaging technique over randomly oriented isolated simple elements. The analytical operations do not require large micromesh realizations, but the tedious nature of the mathematical manipulation is clearly aided by symbolic algebra calculation. For the example case of linear elastic deformation, this results in material stiffnesses that relate the infinitesimal strain and stress. The result that the affine case is stiffer than the nonaffine case is recovered, as would be expected. The energy framework also lends itself to the natural inclusion of changes in mechanical response due to the chemical, electrical, or thermal environment.
Kinematic Analysis and Optimization of a Novel Robot for Surgical Tool Manipulation
Authors: Zhang Xiaoli , Nelson Carl A.
Published: July 2008

The size and limited dexterity of current surgical robotic systems are factors that limit their usefulness. To improve the level of assimilation of surgical robots in minimally invasive surgery (MIS), a compact, lightweight surgical robotic positioning mechanism with four degrees of freedom (DOFs) (three rotational DOFs and one translation DOF) is proposed in this paper. This spatial mechanism based on a bevel-gear wrist is remotely driven with three rotation axes intersecting at a remote rotation center (the MIS entry port). Forward and inverse kinematics are derived, and these are used for optimizing the mechanism structure given workspace requirements. By evaluating different spherical geared configurations with various link angles and pitch angles, an optimal design is achieved, which performs surgical tool positioning throughout the desired kinematic workspace while occupying a small space bounded by a hemisphere of radius 13.7cm. This optimized workspace conservatively accounts for collision avoidance between the patient and robot or internally between the robot links. This resultant mechanism is highly compact and yet has the dexterity to cover the extended workspace typically required in telesurgery. It can also be used for tool tracking and skills assessment. Due to the linear nature of the gearing relationships, it may also be well suited for implementing force feedback for telesurgery.
Modified Reynolds Equation for Aerostatic Porous Radial Bearings With Quadratic Forchheimer Pressure-Flow Assumption
Authors: Nicoletti Rodrigo , Silveira Zilda C. , Purquerio Benedito M.
Published: July 2008

Aerostatic porous bearings are becoming important elements in precision machines due to their inherent characteristics. The mathematical modeling of such bearings depends on the pressure-flow assumptions that are adopted for the flow in the porous medium. In this work, one proposes a nondimensional modified Reynolds equations based on the quadratic Forchheimer assumption. In this quadratic approach, the nondimensional parameter Φ strongly affects the bearing load capacity, by defining the nonlinearity level of the system. For values of Φ>10, the results obtained with the modified Reynolds equation with quadratic Forchheimer assumption tend to those obtained with the linear Darcy model, thus showing that this is a more robust and global approach of the problem, and can be used for both pressure-flow assumptions (linear and quadratic). The threshold between linear and quadratic assumptions is numerically investigated for a bronze sintered porous bearing, and the effects of bearing geometry are discussed. Numerical results show that Φ strongly affects the bearing loading capacity and stiffness coefficients.
Integrating Physicians, Researchers and Engineers—60Years of Medical Device Innovation at Mayo Clinic
Authors: Horne April E. , Bennet Kevin A. , Buntrock Nathan C. , Halovsen Thomas G. , Wehde Mark K.
Published: July 2008

Medical innovation is often delayed by the difficulty in developing cooperation among practicing physicians, academics and medical device developers. In Rochester, Minnesota, the Mayo Clinic Division of Engineering has excelled at integrating these specialties, facilitating medical device innovation for the past 60years. In 1948, Mayo Clinic combined an instrument shop with an engineering design services team and created the Division of Engineering. This enabled a unique partnership between physicians, researchers, and product developers. Early innovations from this team include the Mayo heart-lung machine, cardiac monitoring, advances in aero-medicine, surgical stereotaxy, and early transfusion equipment. Today, the Mayo Division of Engineering consists of mechanical, chemical, electrical, biomedical, and software engineers, machinists, and a scientific glass-blower. The division works in close collaboration with project proponents (primarily physicians) within the clinical environment to analyze problems, propose designs, and deliver a clinical solution. From custom 3-D models for support pre-surgical planning to endoscopic heart valve repair devices, the team identifies opportunities and delivers systems that can be quickly translated into medical practice.
A Detailed Fluid Mechanics Study of Tilting Disk Mechanical Heart Valve Closure and the Implications to Blood Damage
Authors: Manning Keefe B. , Herbertson Luke H. , Fontaine Arnold A. , Deutsch Steven
Published: July 2008

Hemolysis and thrombosis are among the most detrimental effects associated with mechanical heart valves. The strength and structure of the flows generated by the closure of mechanical heart valves can be correlated with the extent of blood damage. In this in vitro study, a tilting disk mechanical heart valve has been modified to measure the flow created within the valve housing during the closing phase. This is the first study to focus on the region just upstream of the mitral valve occluder during this part of the cardiac cycle, where cavitation is known to occur and blood damage is most severe. Closure of the tilting disk valve was studied in a “single shot” chamber driven by a pneumatic pump. Laser Doppler velocimetry was used to measure all three velocity components over a 30ms period encompassing the initial valve impact and rebound. An acrylic window placed in the housing enabled us to make flow measurements as close as 200μm away from the closed occluder. Velocity profiles reveal the development of an atrial vortex on the major orifice side of the valve shed off the tip of the leaflet. The vortex strength makes this region susceptible to cavitation. Mean and maximum axial velocities as high as 7m∕s and 20m∕s were recorded, respectively. At closure, peak wall shear rates of 80,000s−1 were calculated close to the valve tip. The region of the flow examined here has been identified as a likely location of hemolysis and thrombosis in tilting disk valves. The results of this first comprehensive study measuring the flow within the housing of a tilting disk valve may be helpful in minimizing the extent of blood damage through the combined efforts of experimental and computational fluid dynamics to improve mechanical heart valve designs.
Headspace Moisture Analysis in Medical Device Packages
Authors: Lindner Bruce , Curtis Michael , Weissenrieder Jonas , Schwab Mark
Published: July 2008

Moisture levels in medical device packages influence a variety of crucial device properties, e.g. mechanical properties, corrosion and leach rates, drug potency, and ultimately shelf life. This is especially true for drug releasing and biodegradable device materials. It is therefore important to establish a high degree of control and accuracy of the humidity levels at all relevant stages in the production process as well as in the final package. In the current study we demonstrate a newly developed method for accurate headspace moisture trace level analysis in medical device packages using extractive gas phase Fourier transform infrared (FTIR) spectroscopy. Volumetric aliquots were extracted, using a specially designed extraction assembly, from the headspace of medical device relevant packages. The headspace water concentration was analyzed using a validated gas phase FTIR system1. Water bands in the spectral region 1600–2200cm 1 were chosen for the quantitative analysis. Sample spectra were compared, with a least square fit procedure, to water reference spectra at known concentration. Accurate quantification was demonstrated for headspace water vapor concentrations less than 100ppm. This is considerably lower than feasible with conventional package headspace moisture analysis techniques. The results of this study demonstrate the benefits of using extractive gas phase FTIR for low level moisture analysis of small headspace volumes.