bluuebunny/crossref_metadata_2025 huggingface dataset:
A Power Efficient Electronic Implant for a Visual Cortical Neuroprosthesis
Authors: Coulombe Jonathan , Carniguian Sylvain , Sawan Mohamad
Published: February 2005

Abstract:  An integrated microstimulator designed for a cortical visual prosthesis is presented, along with a pixel reordering algorithm, together minimizing the peak total current and voltage required for stimulation of large numbers of electrodes at a high rate. In order to maximize the available voltage for stimulation at a given supply voltage for generating biphasic pulses, the device uses monopolar stimulation, where the return electrode voltage is dynamically varied. Thus, the voltage available for stimulation is maximized, as opposed to the conventional fixed return voltage monopolar approach, and impedance is significantly lower than can be achieved using bipolar stimulation with microelectrodes. This enables the use of a low voltage power supply, minimizing power consumption of the device. An important constraint resulting from this stimulation strategy, however, is that current generation needs to be simultaneous and in‐phase for all active parallel channels, imposing heavy stress on the wireless power recovery and regulation circuitry in large electrode count systems such as a visual prosthesis. An ordering algorithm to be implemented in the external controller of the prosthesis is then proposed. Based on the data for each frame of the video signal to be transmitted to the implant, the algorithm minimizes the total generated current standard deviation between time multiplexed stimulations by determining the most appropriate combination of parallel stimulation channels to be activated simultaneously. A stimulator prototype has been implemented in CMOS technology and successfully tested. Execution of the external controller reordering algorithm on an application specific hardware architecture has been verified using a System‐On‐Chip development platform. A near 75% decrease in the total stimulation current standard deviation was observed with a one‐pass algorithm, whereas a recursive variation of the algorithm resulted in a greater than 95% decrease of the same variable.
Electrical Stimulation to Induce Propulsive Contractions in the Porcine Descending Colon
Authors: Sevcencu Cristian , Rijkhoff Nico J.M. , Gregersen Hans , Sinkjær Thomas
Published: February 2005

Abstract:  Electrical stimulation of the colon can improve transit in slow‐transit constipation, or enable controlled emptying in colostomy patients. Preliminary studies showed that sequential stimulation of consecutive colon segments induced serial contractions resulting in colonic propulsion. This study was performed to optimize the stimulation parameters. The electrodes were inserted under the serosa of the descending colon of pigs. Charge‐balanced rectangular pulses at 10 Hz were delivered in consecutive sessions. Electrically evoked contractions (ECs) were monitored using impedance planimetry and manometry. The luminal pressure and cross‐sectional area (CSA), the latency and velocity of CSA decrease, and the wall tension were compared for ECs induced using 3 ms pulses of 9, 12, 15, and 30 mA. When using 15 mA, ECs induced by 0.03, 0.3, and 3 ms long pulses were compared. A current increase from 9 to 30 mA induced a significant increase in the pressure generated by contraction. The increase in pulse duration from 0.03 to 3 ms resulted in shorter latency, faster contraction, higher pressure, and higher wall tension. It is concluded that, at a frequency of 10 Hz, the best combination of current and pulse duration to elicit propulsive contractions in the descending colon of pigs is 15 mA and 3 ms.
Switch from Bicarbonate Hemodialysis to Hemodiafiltration with Online Regeneration of the Ultrafiltrate (HFR): Effects on Nutritional Status, Microinflammation, and β2‐Microglobulin
Authors: Bossola Maurizio , Muscaritoli Maurizio , Tazza Luigi , Giungi Stefania , Panocchia Nicola , Fanelli Filippo Rossi , Luciani Giovanna
Published: February 2005

Abstract:  Background. Hemodiafiltration (HFR) with on‐line regeneration of the ultrafiltrate, a technique of hemodiafiltration in which the ultrafiltrate passes through a cartridge containing uncoated charcoal, has been shown to be safe, simple, and well tolerated and has been claimed to improve nutritional status or to prevent its deterioration while decreasing the inflammatory response via a reduced production of proinflammatory cytokines. The purpose of the present prospective study was to ascertain whether HRF improves the nutritional status, reduces microinflammation, and decreases serum β2‐microglobulin levels in patients with end‐stage renal disease (ESRD). Methods. Eight patients, four males and four females, with a mean age of 49.4 ± 16.8 years, stable on hemodialysis over a period of 8.7 ± 6.1 years and on standard 4–4.5 h three‐times‐a‐week bicarbonate hemodialysis, were switched to three‐times‐a‐week, 4‐h HFR. At baseline and every two months for 12 months at mid‐week, serum levels of urea, creatinine, albumin, total cholesterol, C‐reactive protein, fibrinogen, complement, ferritin, β2‐microglobulin, intact parathyroid hormone (PTH), hemoglobin concentrations, and hematocrit and the EPO weekly dose were determined. At baseline and at the end of the study, the Malnutrition Inflammatory Score (MIS) was calculated. Results. Nutritional and inflammatory parameters remained constant during the 12‐month period of the study. After 12 months of HFR, the MIS trended to be lower, but the difference was not statistically significant. Serum β2‐microglobulin and PTH levels remained constant during all time intervals. Neither hematocrit nor hemoglobin changed over the course of the study as well as the weekly EPO dose. Conclusion. The change from bicarbonate hemodialysis to HFR was safe and well tolerated but was not associated with an improvement of nutritional and inflammatory parameters or a reduction of serum β2‐microglobulin levels.
The SlideReactor—A Simple Hollow Fiber Based Bioreactor Suitable for Light Microscopy
Authors: Sauer Igor M. , Schwartlander Ruth , Schmid Jochen , Efimova Ekaterina , Vondran Florian W.R. , Kehr Daniel , Pless Gesine , Spinelli Antonio , Brandenburg Börries , Hildt Eberhardt , Neuhaus Peter
Published: February 2005

Abstract:  Most bioartificial liver support systems are based on hollow fiber capillaries within modified dialysis cartridges or more sophisticated bioreactor constructions. Due to their design microscopic follow‐up of reorganization and growth of tissue between the hollow fibers is not possible. The SlideReactor is a simple hollow fiber based bioreactor construction suitable for light microscopy and time‐lapse video observation. The SlideReactor offers a cell compartment separated from a medium inflow and outflow compartment. Cell compartment access ports enable easy filling of the cell compartment with cell suspension, as well as fixation of the tissue. For more complex procedures or full access to all the cells, the bioreactor can be opened easily by cutting the silicone seal with a scalpel. Due to its simple design and the utilization of standard materials, it could serve as a suitable, cost‐efficient tool to evaluate the behavior of cells cultured between hollow fiber capillaries. The paper describes the production process: similar to open source projects in software engineering, we would like to propose the concept as an open platform to anyone interested in hollow fiber based cell culture.
Melatonin enhances the hypoxic response of rat carotid body chemoreceptor
Authors: Chen Yueping , Tjong Yung‐Wui , Ip Shing‐Fat , Tipoe George L. , Fung Man‐Lung
Published: February 2005

Abstract:  Melatonin attenuates carotid chemoreceptor response to hypercapnic acidosis and may contribute to the effect of circadian rhythms on the chemoreflex. The purpose of this study was to test the hypothesis that melatonin modulates rat carotid chemoreceptor response to hypoxia. To examine the effect of melatonin on the hypoxic response of the chemosensitive cells, cytosolic calcium ([Ca2+]i) was measured by spectrofluorometry in fura‐2‐loaded type‐I (glomus) cells dissociated from rat carotid bodies. Melatonin (0.01–10 nm) did not change the resting [Ca2+]i level of the glomus cells but it concentration‐dependently increased peak [Ca2+]i response to cyanide or deoxygenated buffer. An agonist of melatonin receptors, iodomelatonin also enhanced the [Ca2+]i response to hypoxia. The melatonin‐induced enhancement of the [Ca2+]i response was abolished by pretreatment with nonselective mt1/MT2 antagonist, luzindole, and by MT2 antagonists, 4‐phenyl‐2‐propionamidotetraline or DH97. These findings suggest that melatonin receptors in the glomus cells mediate the effect of melatonin on the chemoreceptor response to hypoxia. In addition, melatonin increased the carotid afferent response to hypoxia in unitary activities recorded from the sinus nerve in isolated carotid bodies superfused with bicarbonate‐buffer saline. Furthermore, plethysmographic measurement of ventilatory activities in unanesthetized rats revealed that melatonin (1 mg/kg, i.p.) increased the ventilatory response to hypoxia. Hence, the circadian rhythm of melatonin in arterial blood can modulate the carotid chemoreceptor response to hypoxia. This modulation may be a physiological mechanism involved in the day‐light differences in ventilatory activities.
Melatonin‐induced modulation of glucose metabolism in primary cultures of rabbit kidney‐cortex tubules
Authors: Derlacz Rafal A. , Poplawski Piotr , Napierala Malgorzata , Jagielski Adam K. , Bryla Jadwiga
Published: February 2005

Abstract:  The effect of melatonin on glucose metabolism in the presence and absence of insulin has been investigated in the primary cultures of renal tubules grown in a defined medium. In the absence of glucose in the medium containing 5 μg/mL of insulin and 2 mm alanine + 5 mm glycerol + 0.5 mm octanoate, 100 nm melatonin stimulated both glucose and lactate synthesis, while in the medium devoid of insulin melatonin action was negligible. Melatonin‐induced increase in glucose and lactate synthesis was accompanied by an enhancement of alanine and glycerol consumption. In view of measurements of [U‐14C]l‐alanine and [U‐14C]l‐glycerol incorporation into glucose, it is likely that melatonin increased alanine utilization for glucose production, while accelerated lactate synthesis was because of an enhanced glycerol consumption. As (i) 10 nm luzindole attenuated the stimulatory action of melatonin on glucose formation and (ii) the indole induced a decrease in intracellular cAMP level, it seems likely that in renal tubules melatonin binds to ML1 membrane receptor subtype. In view of a decline of intracellular fructose‐1,6‐bisphosphate content accompanied by a significant rise in hexose‐6‐phosphate and glucose levels, melatonin might result in an acceleration of flux through fructose‐1,6‐bisphosphatase probably because of an increase in the active, dephosphorylated form of this enzyme. Thus, the administration of melatonin in combination with insulin might be beneficial for diabetic therapy because of protection against hypoglycemia.
Dopamine receptor activation in bovine pinealocyte via a cAMP‐dependent transcription pathway
Authors: Santanavanich Chorthip , Ebadi Manuchair , Govitrapong Piyarat
Published: February 2005

Abstract:  D1‐ and D2‐dopamine receptors in the bovine pineal gland were previously identified and characterized. The data indicate that the density of D1‐dopamine receptors far exceeded that of D2‐dopamine receptors. In our previous study, the mRNA for both the D1‐ and D2‐dopamine receptors which elucidated the status of dopamine and its possible involvement in the pineal function was identified. A selective D1‐agonist enhanced N‐acetyltransferase (NAT) activity and increased the melatonin level, whereas, a selective D2‐agonist inhibited NAT activity and decreased the melatonin level. An attempt has been made in the present study to clarify the mechanism of dopamine in controlling melatonin production in bovine pineal. The level of intracellular cyclic 3′,5′‐adenosine monophosphate (cAMP) was determined after a 2‐hr incubation of bovine pinealocytes with selected combinations of drugs. SKF 38393, a selective D1‐agonist, enhanced intracellular level of cAMP, and its effect was blocked by SCH 23390, a D1‐selective antagonist. In contrast quinpirole, a selective D2‐agonist, inhibited forskolin‐stimulated intracellular level of cAMP while its effect was blocked by a D2‐selective antagonist, spiperone. In addition, the dopamine‐dependent phosphorylation of the transcription factors, cAMP responsive element‐binding protein (CREB) was investigated. Immunoblots showed that SKF 38393 enhanced CREB phosphorylation and the stimulatory effect was abolished by SCH 23390 whereas quinpirole inhibited forskolin‐stimulated phosphorylated CREB production and the inhibitory effect was prevented by spiperone. Taken together with our previous data, the results indicate that activation of D1‐dopamine receptor in bovine pinealocyte stimulates NAT activity and enhances melatonin level whereas activation of D2‐dopamine receptor leads to an inhibitory effect and these stimulatory and inhibitory effects act, in part, via a cAMP‐dependent transcription mechanism.
Effects of temperature on 2‐[125I]‐iodomelatonin binding to melatonin receptors in the neural retina of the frog Rana perezi
Authors: Isorna Esther , Guijarro Ana , López‐Patiño Marcos A. , Delgado María Jesús , Alonso‐Bedate Mercedes , Alonso‐Gómez Angel L.
Published: February 2005

Abstract:  The present study analyzes the effect of temperature‐dependent modifications on the binding of the analog 2‐[125I]‐melatonin to melatonin receptors in isolated neural retina membranes from the greenfrog Rana perezi. Association and dissociation rate constants (K+1, K−1) were exponentially increased by the assay temperature. At 15°C, association and dissociation required several hours; meanwhile, at 35°C, rate constants were 100‐ and 34‐fold faster, respectively. However, the Kd constant calculated as K−1/K+1 was unmodified by the assay temperature. When frogs were acclimated at either 5 or 22°C for 1 month, K+1, and K−1 constants determined at 15 and 25°C were identical in both cold‐ and warm‐acclimated groups. Thus, the binding kinetics of melatonin receptors in frog retinas did not shown any thermal compensation. Results from saturation curves and pharmacological profiles of melatonin binding sites support a lack of effect of assay temperature on the affinity of melatonin receptors in the frog retina. The inhibition of [125I]Mel binding by GTPγS showed clearly that the coupling of melatonin receptors to G proteins is temperature‐dependent. Higher concentrations of the GTP analog were needed to inhibit specific binding when temperature decreased. The temperature effect on binding kinetics and on the G protein coupling to melatonin receptors suggests that the melatonin signal could be transduced distinctly depending on the temperature. Thus, temperature plays a major role, not only on melatonin synthesis, but also in the transduction of melatonin signal in ectotherms.
Corticosterone modulates noradrenaline‐induced melatonin synthesis through inhibition of nuclear factor kappa B
Authors: Ferreira Zulma S. , Fernandes Pedro A. C. M. , Duma Danielle , Assreuy Jamil , Avellar Maria C. W. , Markus Regina P.
Published: February 2005

Abstract:  In chronically inflamed animals, adrenal hormones exert a positive control on the secretion of melatonin by the pineal gland. In this paper, the mechanism of corticosterone as a modulator of melatonin and N‐acetylserotonin (NAS) was determined. Rat pineal glands in culture, stimulated for 5 hr with noradrenaline (10 nm), were previously incubated with corticosterone (1.0 nm–1.0 μm) for 48 hr in the presence or absence of the glucocorticoid receptor (GR) antagonist, mifepristone (1.0 μm), the proteasome inhibitor, N‐acetyl‐leucinyl‐leucinyl‐norleucinal‐H (ALLN, 12.5 μm) or the antagonist of the nuclear factor kappa B (NFκB), pyrrolidinedithiocarbamate (PDTC, 12.5 μm). Corticosterone potentiated noradrenaline‐induced melatonin and NAS production in a bell‐shaped manner. The increase in NAS (12.9 ± 2.7, n = 6 versus 34.3 ± 8.3 ng per pineal) and melatonin (16.3 ± 2.0, n = 6 versus 44.3 ± 12.9 ng per pineal) content induced by 1 μm corticosterone was blocked by mifepristone, and mimicked by ALLN and PDTC. The presence of GRs was shown by [3H]‐dexamethasone binding (0.30 ± 0.09 pmol/mg protein) and corticosterone inhibition of NFκB nuclear translocation was demonstrated by electromobility shift assay. Therefore, corticosterone potentiates noradrenaline‐induced melatonin and NAS production through GR inhibition of NFκB nuclear translocation. To the best of our knowledge, this is the first time that this relevant pathway for passive and acquired immune response is shown to modulate melatonin production in pineal gland.
Environmental control and adrenergic regulation of pineal activity in the diurnal tropical rodent, Arvicanthis ansorgei
Authors: Garidou‐Boof Marie‐Laure , Sicard Bruno , Bothorel Béatrice , Pitrosky Bruno , Ribelayga Christophe , Simonneaux Valérie , Pévet Paul , Vivien‐Roels Berthe
Published: February 2005

Abstract:  Like nocturnal rodents, the diurnal tropical rodent Arvicanthis ansorgei shows a daily rhythm in pineal melatonin content. Seasonal and photoperiodic variations in the biosynthetic activity of the pineal gland: arylalkylamine‐N‐acetyltransferase (AA‐NAT), hydroxyindole‐O‐methyltransferase (HIOMT) activities and melatonin content were measured in male and female A. ansorgei captured near Samaya, Mali, and kept either under artificial laboratory photoperiods [light‐dark (LD) cycles: LD 14:10, LD 12:12 or LD 10:14 or caught in the field in Mali and killed at four different times of the year (January, April, June and November). Under artificial photoperiod, the duration of the nocturnal peak of AA‐NAT activity and melatonin content increased with the duration of the dark period while the amplitude did not significantly change. In the field, annual variations in the amplitude of the nocturnal melatonin peak were observed with a maximum in April (highest temperature, low humidity and no grass availability, only seeds) and a minimum in November (high humidity, maximum green grass availability). The variations in the amplitude of the melatonin peak were not correlated with changes in AA‐NAT HIOMT activities, suggesting that seasonal variations in the amplitude of the melatonin peak are not driven by these enzymes. Daytime injections of the β‐adrenergic agonist, isoproterenol, stimulated melatonin synthesis in January, April and June, but not in November. The annual differences in the amplitude of the melatonin peak as well as the seasonal differences in the response to an adrenergic stimulation suggest that environmental factors other than photoperiod, such as temperature, humidity and consequent food availability, could be important in the regulation of the annual variations in the pineal biosynthetic activity in this species.
Attenuation in the evolution of experimental spinal cord trauma by treatment with melatonin
Authors: Genovese Tiziana , Mazzon Emanuela , Muià Carmelo , Bramanti Placido , Sarro Angelina De , Cuzzocrea Salvatore
Published: February 2005

Abstract:   Melatonin is the principal secretory product of the pineal gland and its role as an immumo‐modulator is well established. Recent evidence shows that melatonin is a scavenger of oxyradicals and peroxynitrite and exerts protective effects in septic shock, hemorrhagic shock and inflammation. In the present study, we evaluated the effect of melatonin treatment, in a model of spinal cord injury (SCI). SCI was induced by the application of vascular clips (force of 50 g) to the dura via a four‐level T5‐T8 laminectomy. SCI in rats resulted in severe trauma characterized by edema, neutrophil infiltration and apoptosis (measured by terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end‐labeling staining). Infiltration of spinal cord tissue with neutrophils (measured as increase in myeloperoxidase activity) was associated with enhanced lipid peroxidation (increased tissue levels of malondialdehyde). Immunohistochemical examination demonstrated a marked increase in immunoreactivity for nitrotyrosine and Poly(ADP‐ribose) (PAR) in the spinal cord tissue. In contrast, the degree of (a) spinal cord inflammation and tissue injury (histological score), (b) nitrotyrosine and PAR formation, (c) neutrophils infiltration and (d) apoptosis was markedly reduced in spinal cord tissue obtained from rats treated with melatonin (50 mg/kg i.p., 30 min before SCI, 30 min, 6 hr, 12 hr and 24 hr after SCI). In a separate set of experiment we have clearly demonstrated that melatonin treatment significantly ameliorated the recovery of limb function (evaluated by motor recovery score). Taken together, our results demonstrate that treatment with melatonin reduces the development of inflammation and tissue injury events associated with spinal cord trauma.
Characterization of Fatigue Damage Modes in Nicalon/Calcium Aluminosilicate Composites
Authors: Kim Jeongguk , Liaw Peter K.
Published: February 2005

High-cycle fatigue behavior of Nicalon™ fiber-reinforced calcium aluminosilicate (CAS) glass–ceramic matrix composites (Nicalon™/CAS) was investigated with the aid of a nondestructive evaluation (NDE) technique. Infrared (IR) thermography was employed to study two different types of Nicalon™/CAS composites: crossply and unidirectional specimens. During fatigue testing, an IR camera was used for in-situ monitoring of temperature evolution of Nicalon™/CAS samples. Stress versus cycles to failure curves were generated for predicting the lifetime of Nicalon™/CAS composites, and the IR camera measured the temperature changes during high-cycle fatigue testing. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture modes and failure mechanisms of Nicalon™/CAS samples. In this study, the NDE technique and SEM characterization were used to facilitate a better understanding of damage evolution and progress of Nicalon™/CAS composites during high-cycle fatigue.
A Cyclic Microbend Study on LIGA Ni Microelectromechanical Systems Thin Films
Authors: Lou J. , Shrotriya P. , Soboyejo W. O.
Published: February 2005

This paper presents the results of recent studies of cyclic microbend experiments and their consequences for plasticity length-scale phenomena in LIGA Ni microelectromechanical systems (MEMS) thin films. The strain–life fatigue behavior of LIGA Ni thin films is studied by performing fully reversed cyclic microbend experiments that provide insights into cyclic stress/strain evolution and cyclic failure phenomena. The effects of cyclic deformation on the plasticity length-scale parameters are also considered within the context of strain gradient plasticity theories. The implications of the results are then discussed for the analysis of plasticity and cyclic deformation in MEMS structures and other microscale systems.
Effects of Local Grain Orientation on Fatigue Crack Growth in Multicrystalline fcc Metallic Materials
Authors: Peralta P. , Dickerson R. , Dellan N. , Komandur K. , Jameel M. A.
Published: February 2005

The anomalous behavior of microstructurally “short” cracks that can control fatigue life at very high cycles can be attributed to the local conditions around these cracks, since the length scale involved requires the consideration of anisotropic material behavior and the effect of changes in grain orientation as the crack grows. The effect of local crystallography was studied in multicrystalline Compact-Tension (CT) specimens of pure nickel and a cast Ni-based superalloy. Orientation Imaging Microscopy (OIM) was used to map the crystallography of the grains ahead of the notch. A standard fatigue crack growth test was then carried out to characterize the crack path in relation to the grain orientations. Two extreme cases were identified: at one end cracks grew with small deviations through all the grains ahead of it, whereas at the other end large deflections from a path perpendicular to the applied load were observed. Intergranular cracks were found to prefer high angle boundaries, whereas transgranular cracks had a tendency to nucleate and display stage I growth along slip traces of systems with high Schmid factors, as determined by the uniaxial conditions expected at the notch tips. In addition, crack path tortuosity was more pronounced in grains with loading axes close to 〈111〉. Finally, the influence of changes on slip geometry as cracks moved across grain boundaries is also discussed.
Fatigue of As-Fabricated Open Cell Aluminum Foams
Authors: Zhou J. , Gao Z. , Cuitino A. M. , Soboyejo W. O.
Published: February 2005

This paper presents the results of the combined experimental investigation and digital image correlation (DIC) analysis of the fatigue failure of open cell aluminum foams. Compression–compression cyclic loads were applied to foam specimens under the as-fabricated condition. Following characterization of the S-N curve behavior, the macroscale deformation of the tested foam under fatigue was recorded using an in-situ digital camera. The deformation sequence was then analyzed using DIC technique. It was found that foams failed with an abrupt strain jump when shear bands were formed, and serious deformation up to more than 30% was developed in the center of the shear band. The ex-situ scanning electron microscopy analysis indicated that the abrupt strain jump was due to the microscale damage accumulation in struts where surface cracks were formed and propagated.
An Investigation of the Effects of Microstructure on Fatigue Crack Growth in Ti-6242
Authors: McBagonluri F. , Akpan E. , Mercer C. , Shen W. , Soboyejo W. O.
Published: February 2005

Surface and subsurface crack nucleation and growth mechanisms are elucidated for equiaxed (microstructure 1), elongated (microstructure 2), and colony (microstructure 3) microstructures of Ti6242. Prominent cleavage facets, indicative of a Stroh-type dislocation-pile phenomenon characterize the nucleation sites. Beachmarking and scanning electron microscopy (SEM) techniques are used to study fatigue crack growth rates and crack shape evolution in the short and long crack regimes. The studies reveal that surface crack growth rate data are generally comparable to the through-crack growth rate data in the long crack growth regime. However, the depth crack growth rates are somewhat slower than the through-crack growth rates. Surface crack evolution profiles are shown to exhibit a tendency towards “Preferred Propagation Paths” (PPPs). However, the magnitudes of the aspect ratios along the PPPs are different from those reported for square or rectangular cross sections subjected to cyclic tension or bending loads. Finally, the measured crack lengths and aspect ratios are compared with predictions obtained from a fracture mechanics model.
Goodman Diagram Via Vibration-Based Fatigue Testing
Authors: George Tommy J. , Shen M.-H. Herman , Scott-Emuakpor Onome , Nicholas Theodore , Cross Charles J. , Calcaterra Jeffrey
Published: February 2005

A new vibration-based fatigue testing methodology for assessing high-cycle turbine engine material fatigue strength at various stress ratios is presented. The idea is to accumulate fatigue energy on a base-excited plate specimen at high frequency resonant modes and to complete a fatigue test in a much more efficient way at very low cost. The methodology consists of (1) a geometrical design procedure, incorporating a finite-element model to characterize the shape of the specimen for ensuring the required stress state/pattern; (2) a vibration feedback empirical procedure for achieving the high-cycle fatigue experiments with variable-amplitude loading; and finally (3) a pre-strain procedure for achieving various uniaxial stress ratios. The performance of the methodology is demonstrated with experimental results for mild steel, 6061-T6 aluminum, and Ti-6Al-4V plate specimens subjected to a fully reversed bending, uniaxial stress state.
Microstructural Characterization of Ultrasonically Welded Aluminum
Authors: Allameh S. M. , Mercer C. , Popoola D. , Soboyejo W. O.
Published: February 2005

The microstructure and mechanical properties of ultrasonically welded AA6111-T4 specimens are discussed. The effects of welding time on the mechanical properties of welded joints are investigated. A longer welding time results in a more continuous welded interface and higher yield and fracture strengths. Accordingly, fatigue properties of the welded specimens with longer welding times are improved. The results of electron microscopy on the cross section of ultrasonically welded joints show three distinct zones: weld zone, weld affected zone and compression zone each with a distinct microstructure. TEM results show nanocrystalline grains along with second phase particles in the range of 15–25 nm in the weld zone. Flow patterns consistent with the geometry of weld–tip were observed at the weld interface.
Stress Analyses and Geometry Effects During Cyclic Loading Using Thermography
Authors: Yang B. , Liaw P. K. , Huang J. Y. , Kuo R. C. , Huang J. G. , Fielden D. E.
Published: February 2005

A high-speed and high-sensitivity thermographic-infrared (IR) imaging system has been used to investigate the temperature evolutions of SA533B1 steel specimens during high-cycle fatigue experiments. Both thermodynamics and heat-transfer theories are applied to quantify the relationship between the observed temperature variations and stress–strain states during fatigue. The thermoelastic effect has been utilized to calculate the maximum stress level during fatigue testing. The predicted results matched the experimental data quite well. Different temperature and strain behaviors have been observed between cylindrical and flat specimens during high-cycle fatigue experiments. Explanations have been provided, based on Lu¨ders band evolutions in flat specimens during fatigue, which have been observed in detail by thermography. Numerical methods have been provided to convert the temperature map (thermograph) into heat-dissipation-rate (HDR) map, which illustrates the kinetics of the Lu¨ders-band evolution. Thus, the thermography technology can provide an effective means to “watch” and “quantify” the heat-evolution processes, such as the mechanical-damage behaviors, which can open up new opportunities for in- situ studying mechanical and phase-transformation behaviors in detail.
A New Failure Criterion for Woven-Roving Fibrous Composites Subjected to Tension-Compression Local Plane Stresses With Different Stress Ratios
Authors: Nasr M. , Abouelwafa M. N. , Gomaa A. , Hamdy A. , Morsi E.
Published: February 2005

Thin-walled tubular specimens, made from woven-roving glass fiber-reinforced polyester (GFRP) with two fiber orientations, [±45°]2s and [0,90°]2s, were tested under torsional fatigue tests at negative stress ratios R,R=−1,−0.75,−0.5,−0.25, 0. The mean-amplitude diagram of the [0,90°]2s specimens was found to be divided into two regions; region (1) in which the mean stress is ineffective and region (2) in which the mean stress has a detrimental effect on the amplitude component. All examined failure criteria were found to be valid for the [0,90°]2s specimens, without any modifications; using the amplitude component and the corresponding fatigue strength in region (1), and the equivalent static stress with the corresponding static strength in region (2). For the [±45]2s specimens, having the mean stress being effective in the whole mean-amplitude diagram, the equivalent static stress was used with the corresponding static strength in different failure criteria. None of the available criteria succeeded in predicting failure for the studied case; consequently, was introduced, which a new modifying term SWT2/F1sF1f was introduced, which made Norris-Distortional, Tsai-Hahn, and Tsai-Hill criteria suitable for this case.
A Cobalt Diffusion Based Model for Predicting Crater Wear of Carbide Tools in Machining Titanium Alloys
Authors: Hua Jiang , Shivpuri Rajiv
Published: February 2005

In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant wear mechanism influencing tool life and productivity. An analytical wear model that relates crater wear rate to thermally driven cobalt diffusion from cutting tool into the titanium chip is proposed in this paper. This cobalt diffusion is a function of cobalt mole fraction, diffusion coeficient, interface temperature and chip velocity. The wear analysis includes theoretical modeling of the transport-diffusion process, and obtaining tool–chip interface conditions by a nonisothermal visco-plastic finite element method (FEM) model of the cutting process. Comparison of predicted crater wear rate with experimental results from published literature and from high speed turning with WC/Co inserts shows good agreement for different cutting speeds and feed rate. It is seen that wear rates are independent of cutting time.
A New Approach for Single Crystal Materials Analysis: Theory and Application to Initial Yielding
Authors: Bande G. , Nemes J. A.
Published: February 2005

A new approach used for single crystal (SC) materials analysis is described. Its principle is based on the extension of predictive models for isotropic material behavior to anisotropic materials such as SC nickel base superalloys. A viscoplastic model describes the material in the macroscopic level while a factor, based on the crystallographic approach, accounts for the global state of micro slip on the crystal. The combination of both elements defines the so-called “combined approach” (CA). This paper presents the development of the theory and its applications to the determination of initial yielding and tension–compression asymmetry.
The Effect of Tool–Sheet Interaction on Damage Evolution in Electromagnetic Forming of Aluminum Alloy Sheet
Authors: Imbert J. M. , Winkler S. L. , Worswick M. J. , Oliveira D. A. , Golovashchenko S.
Published: February 2005

A study of the effect of tool–sheet interaction on damage evolution in electromagnetic forming is presented. Free form and conical die experiments were carried out on 1 mm AA5754 sheet. Safe strains beyond the conventional forming limit diagram (FLD) were observed in a narrow region in the free form experiments, and over a significant region of the part in the conical die experiments. A parametric numerical study was undertaken, that showed that tool–sheet interaction had a significant effect on damage evolution. Metallographic analysis was carried out to quantify damage in the parts and to confirm the numerical results.
Determining Brinell Hardness From Analysis of Indentation Load-Depth Curve Without Optical Measurement
Authors: Kim Sung-Hoon , Jeon Eun-chae , Kwon Dongil
Published: February 2005

Hardness tests are performed to determine not only hardness but also other properties such as strength, wear resistance, and deformation resistance. They are also performed to predict residual lifetime through analysis of the hardness reduction or hardness ratio. However, hardness tests require observation of the residual indentation, and for that reason are not widely used in industrial fields. This study thus examines obtaining Brinell hardness values without optical observation, using instead quantitative formulas and analyzing the relationship between the indentation depths from the indentation load-depth curve and mechanical properties such as the work-hardening exponent, yield strength, and elastic modulus on the basis of finite-element analysis.
Modeling of Anisotropic Deformation in Superplastic Sheet Metal Stretching
Authors: Abu-Farha Fadi K. , Khraisheh Marwan K.
Published: February 2005

Currently available models describing superplastic deformation are mostly based on uniaxial tensile test data and assume isotropic behavior, thus leading to limited predictive capabilities of material deformation and failure. In this work we present a multi-axial microstructure-based constitutive model that describes the anisotropic superplastic deformation within the continuum theory of viscoplasticity with internal variables. The model accounts for microstructural evolution and employs a generalized anisotropic dynamic yield function. The anisotropic yield function can describe the evolution of the initial state of anisotropy through the evolution of unit vectors defining the direction of anisotropy during deformation. The generalized model is then reduced to the plane stress condition to simulate sheet metal stretching in superplastic blow forming using pressurized gas. Different ratios of biaxial stretching were investigated, including the case simulating the uniaxial loading condition, where the model successfully captured the uniaxial experimental data. The model is also used to develop a new forming pressure profile that accounts for anisotropy and microstructural evolution.
Micromechanical Modeling of the Static Loading of an Al 359-SiC MMC
Authors: Bruzzi M. S. , McHugh P. E.
Published: February 2005

The objective of this work was to use micromechanical finite element models to simulate the static mechanical behavior of a metal matrix composite: a cast Al 359 alloy reinforced with 20% SiC particles, at two different temperatures: room temperature and 150°C. In the simulations, periodic unit cell models incorporating the explicit representation of the matrix, reinforcing particles and precipitated primary silicon crystals in both 2D and 3D were used. Micromechanical models with both idealized and realistic reinforcing particle geometries and distributions were generated. The realistic particle geometries and distributions were inferred from experimental SEM micrographs. The pattern and intensity of the plastic deformation within the matrix was studied and the macroscale behavior of the composite was inferred from average stress and strain values. In order to include the effects of residual stresses due to the processing of the material, a quenching simulation was performed, prior to mechanical loading, and its effects on the macroscopic and microscopic behavior of the MMC was assessed. The effects of introducing the damage mechanisms of ductile void growth and brittle failure of the reinforcing particles was also investigated. The results of the simulations were compared with experimental results for the MMC in terms of macroscopic tensile stress–strain curves and conclusions were drawn.
BOSON SEA VERSUS DIRAC SEA: GENERAL FORMULATION OF THE BOSON SEA THROUGH SUPERSYMMETRY
Authors: HABARA YOSHINOBU , NIELSEN HOLGER B. , NINOMIYA MASAO
Published: February 2005

We consider the long standing problem in field theories of bosons that the boson vacuum does not consist of a "sea," unlike the fermion vacuum. We show with the help of supersymmetry considerations that the boson vacuum indeed does also consist of a sea in which the negative energy states are all "filled," analogous to the Dirac sea of the fermion vacuum, and that a hole produced by the annihilation of one negative energy boson is an antiparticle. Here, we must admit that it is only possible if we allow — as occurs in the usual formalism anyway — that the "Hilbert space" for the single particle bosons is not positive definite. This might be formally coped with by introducing the notion of a double harmonic oscillator, which is obtained by extending the condition imposed on the wave function. This double harmonic oscillator includes not only positive energy states but also negative energy states. We utilize this method to construct a general formalism for a boson sea analogous to the Dirac sea, irrespective of the existence of supersymmetry. The physical result is consistent with that of the ordinary second quantization formalism. We finally suggest applications of our method to the string theories.
CURVATURE EXCITATION THROUGH QUANTUM WILSON LOOPS IN FOUR-DERIVATIVE GRAVITY
Authors: SHAO D. , SHAO L. , SHAO C. G. , NODA H.
Published: February 2005

In the n-dimensional Minkowski space–time, the graviton propagators of the (R+R2+Rμv Rμv+Rμvλτ Rμvλτ)-gravity are shown in arbitrary and harmonic coordinates systems by using the perturbative expansion of the metric density. We calculated expressions for the leading terms of the quantum Wilson loop using these propagators and showed that they do not vanish. This implies the existence of the possible curvature excitation through the quantum Wilson loop in the gravity. We also discussed relations of the possible curvature excitations among (R+R2+Rμv Rμv+Rμvλτ Rμvλτ)-gravity, (R+R2+Rμv Rμv)-gravity, (R+F2)-gravity and R-gravity.
THE ENERGY–MOMENTUM TENSOR IN NONCOMMUTATIVE GAUGE FIELD MODELS
Authors: GRIMSTRUP J. M. , KLOIBÖCK B. , POPP L. , SCHWEDA M. , WICKENHAUSER M. , PUTZ V.
Published: February 2005

We discuss the different possibilities of constructing the various energy–momentum tensors for noncommutative gauge field models. We use Jackiw's method in order to get symmetric and gauge invariant stress tensors — at least for commutative gauge field theories. The noncommutative counterparts are analyzed with the same methods. The issues for the noncommutative cases are worked out.
CLOSED STRING TACHYONS ON C/ZN
Authors: SARKAR S. , SATHIAPALAN B.
Published: February 2005

We analyze the condensation of closed string tachyons on the C/ZN orbifold. We construct the potential for the tachyons up to the quartic interaction term in the large N limit. In this limit there are near marginal tachyons. The quartic coupling for these tachyons is calculated by subtracting from the string theory amplitude for the tachyons, the contributions from the massless exchanges, computed from the effective field theory. We argue that higher point interaction terms are also of the same order in 1/N as the quartic term and are necessary for existence of the minimum of the tachyon potential that is consistent with earlier analysis.
SELF-DUALITY AND VACUUM SELECTION
Authors: FARAGGI ALON E.
Published: February 2005

I propose that self-duality in quantum phase-space provides the criteria for the selection of the quantum gravity vacuum. The evidence for this assertion arises from two independent considerations. The first is the phenomenological success of the free fermionic heterotic-string models, which are constructed in the vicinity of the self-dual point under T-duality. The relation between the free fermionic models and the underlying Z2×Z2 toroidal orbifolds is discussed. Recent analysis revealed that the Z2×Z2 free fermionic orbifolds utilize an asymmetric shift in the reduction to three generations, which indicates that the untwisted geometrical moduli are fixed near the self-dual point. The second consideration arises from the recent formulation of quantum mechanics from an equivalence postulate and its relation to phase-space duality. In this context it is demonstrated that the trivial state, with V(q)=E=0, is identified with the self-dual state under phase-space duality. These observations suggest a more general mathematical principle in operation. In physical systems that exhibit a duality structure, the self-dual states under the given duality transformations correspond to critical points.
ABOUT NEUTRAL KAONS AND SIMILAR SYSTEMS: FROM QUANTUM FIELD THEORY TO EFFECTIVE MASS MATRICES
Authors: MACHET B.
Published: February 2005

Systems of neutral interacting mesons are investigated, concerning in particular their description by an effective Hamiltonian, with a special emphasis on discrete symmetries. Several ambiguities are pointed out. First, the connection to quantum field theory, in which the physical masses [Formula: see text] and [Formula: see text] are the poles of the full renormalized propagator, shows that, for mass-split binary systems, two mass matrices rather than a single effective one are at work; they correspond to the two values [Formula: see text] and [Formula: see text] of the momentum squared. Transformation properties of the physical eigenstates by discrete symmetries may not reflect the ones of these two mass matrices (and those of the Lagrangian at any given p2). Then, after showing that a bi-orthogonal basis has to be used to diagonalize the complex mass matrix of such unstable systems, and not a bi-unitary transformation, we turn to the ambiguity linked to the commutation of the fields of the K0and of its charge conjugate [Formula: see text]: any constant effective mass matrix is defined, in the [Formula: see text] basis, up to arbitrary diagonal antisymmetric terms; I use this freedom to deform it in various ways, in both the [Formula: see text] and (KL,KS) basis, and I study the consequences on the spectrum. CPT symmetry is specially concerned. An effective mass matrix can always be cast into a CPT invariant form, and only T violating eigenstates can never be cast into CP eigenstates. The dual formalism of |in> and <out| states and bi-orthogonal basis, suitable for nonnormal matrices, is used. In a subsequent work, the fundamental roles played by the normality of the mass matrix and CPT symmetry in the framework of quantum field theory will be investigated in connection with experimental results.
A FOUR-DIMENSIONAL SUPERSTRING FROM THE BOSONIC STRING WITH SOME APPLICATIONS
Authors: DEO B. B. , MAHARANA L.
Published: February 2005

A string in four dimensions is constructed by supplementing it with 44 Majorana fermions. The later are represented by 11 vectors in the bosonic representation SO (D-1,1). The central charge is 26. The fermions are grouped in such a way that the resulting action is worldsheet supersymmetric. The energy–momentum and current generators satisfy the super-Virasoro algebra. GSO projections are necessary for proving modular invariance. Space–time supersymmetry algebra is deduced and is substantiated for specific modes of zero mass. The symmetry group of the model can descend to the low energy standard model group SU (3)× SU L(2)× U Y(1) through the Pati–Salam group.
SHADOWING CORRECTIONS AND THE PRECISE DETERMINATION OF ELECTROWEAK PARAMETERS IN NEUTRINO-NUCLEON SCATTERING
Authors: MILLER GERALD A. , THOMAS A. W.
Published: February 2005

A systematic error in the extraction of sin 2θW from nuclear deep inelastic scattering of neutrinos and antineutrinos arises from higher-twist effects arising from nuclear shadowing. We explain that these effects cause a correction to the results of the recently reported significant deviation from the Standard Model that is potentially as large as the deviation claimed, and of a sign that cannot be determined without an extremely careful study of the data set used to model the input parton distribution functions.
ON THE JONES POLYNOMIAL OF RIBBON KNOTS
Authors: TANAKA TOSHIFUMI
Published: February 2005

We give the counterexamples for a conjecture of Fiedler concerning the ribbon genus of a link.
EMBEDDINGS OF 2-COMPLEXES INTO 3-MANIFOLDS
Authors: GLOCK JANINA , HOG-ANGELONI CYNTHIA I.
Published: February 2005

Let f: K2→ M3be an embedding of a compact, connected 2-complex into a compact, connected, orientable 3-manifold. We are interested to know, to which extent K2determines (up to homeomorphism) its regular neighborhood N(f(K2)) ⊆ M3. We exhibit a list of four obstructions to uniqueness, and prove that in the absence of these, the regular neighborhoods are uniquely determined: Let f,K2,M3be as above and assume M3is prime and not a Poincaré-counterexample. If N(f(K2)) does not contain essential annuli and has connected boundary, then N is determined by K2.
COMMENSURABILITY CLASSES OF TWIST KNOTS
Authors: HOSTE JIM , SHANAHAN PATRICK D.
Published: February 2005

In this paper we prove that if MK is the complement of a non-fibered twist knot K in [Formula: see text], then MK is not commensurable to a fibered knot complement in a ℤ/2ℤ-homology sphere. To prove this result we derive a recursive description of the character variety of twist knots and then prove that a commensurability criterion developed by Calegari and Dunfield is satisfied for these varieties. In addition, we partially extend our results to a second infinite family of 2-bridge knots.