bluuebunny/crossref_metadata_2025 huggingface dataset:
Vesicle size and transmitter release at the frog neuromuscular junction when quantal acetylcholine content is increased or decreased
Authors: Van, der Kloot William , Molgó Jordi , Cameron Roger , Colasante Cesare
Published: July 2002

We investigated whether the synaptic vesicles at the neuromuscular junction change size when their acetylcholine (ACh) content is altered. The size of the miniature endplate potential (MEPP) increased 3‐ or 4‐fold in preparations pre‐treated in a hypertonic solution in which the anion was gluconate. We measured the dimensions of synaptic vesicles in such preparations and in controls. The size of the vesicles and size distribution were indistinguishable. Quanta contained about half of the usual amount of ACh in preparations stimulated in the presence of hemicholinium‐3, an inhibitor of choline uptake, or in NH4+, which diminishes the proton gradient for ACh uptake into the vesicles. Neither treatment changed the size of the synaptic vesicles. ACh content and vesicle size were both decreased in preparations stimulated in (‐)‐vesamicol, an inhibitor of ACh uptake in vesicles. Since the other inhibitors decreased ACh content by a similar amount without altering vesicle size, (‐)‐vesamicol may decrease vesicle size by acting on another target. We also found that a hypertonic solution in which the anion was aspartate increased quantal size similar to gluconate. Both anions have high hydration energy and a large volume. When these treatments increased quantal size the mean 20‐80 % rise time of MEPPs recorded with an extracellular electrode was 170 μs. In the controls it was 97 μs. Perhaps some of the added ACh is bound within the vesicles, which slows the rise. Our major conclusion is that ACh content can change notably without any change in the size of the synaptic vesicles.
Renomedullary and intestinal hyaluronan content during body water excess: a study in rats and gerbils
Authors: Göransson Viktoria , Johnsson Cecilia , Nylander Olof , Hansell Peter
Published: July 2002

Our previous studies in rats have suggested a role for renomedullary hyaluronan (HA) in water homeostasis. The gerbil is known for its unique ability to conserve water. In the present study renal papillary and intestinal HA were compared between groups of anaesthetized gerbils and rats before and after up to 6 h of i.v. water loading. Baseline papillary HA in gerbils was only 37 % of that in the rat. Water loading in rats increased the papillary HA content. Elevation was maximal (+27 %, P < 0.05) after 2 h of water loading and then declined to control levels after 6 h of water loading (+3 %, n.s.). In contrast, the gerbil responded with a decreased papillary HA content during water loading. The depression was maximal after 2 h (‐49 %, P < 0.05) and was still 41 % below the control values after 6 h (P < 0.05). The urine flow rate increased rapidly in the rat and its maximum, 21 times above the control level (P < 0.05), occurred at the HA peak, i.e. after 2 h of water loading while in the gerbil, the urine flow rate increased slowly and slightly and was only six times above control values after 6 h of water loading (P < 0.05). The HA content along the intestine was similar in the two species: lowest in the duodenum and jejunum and highest in the distal colon. To conclude, in the rat, the elevation of papillary interstitial HA during acute water loading would counteract water reabsorption by changing the physico‐chemical characteristics of the interstitial matrix favouring rapid water diuresis. This would work as a complement to the powerful regulation by ADH. The gerbil has a diametrically different regulation of papillary HA turnover during water loading. The decreased papillary HA level during water loading and the slow and small diuretic response may represent a genetic difference in adaptation to enhance the ability to conserve water in an arid environment.
Enhancement of calcium signalling dynamics and stability by delayed modulation of the plasma‐membrane calcium‐ATPase in human T cells
Authors: Bautista Diana M. , Hoth Markus , Lewis Richard S.
Published: July 2002

In addition to its homeostatic role of maintaining low resting levels of intracellular calcium ([Ca2+]i), the plasma‐membrane calcium‐ATPase (PMCA) may actively contribute to the generation of complex Ca2+ signals. We have investigated the role of the PMCA in shaping Ca2+ signals in Jurkat human leukaemic T cells using single‐cell voltage‐clamp and calcium‐imaging techniques. Crosslinking the T‐cell receptor with the monoclonal antibody OKT3 induces a biphasic elevation in [Ca2+]i consisting of a rapid overshoot to a level > 1 μM, followed by a slow decay to a plateau of ≈0.5 μM. A similar overshoot was triggered by a constant level of Ca2+ influx through calcium‐release‐activated Ca2+ (CRAC) channels in thapsigargin‐treated cells, due to a delayed increase in the rate of Ca2+ clearance by the PMCA. Following a rise in [Ca2+]i, PMCA activity increased in two phases: a rapid increase followed by a further calcium‐dependent increase of up to approximately fivefold over 10‐60 s, termed modulation. After the return of [Ca2+]i to baseline levels, the PMCA recovered slowly from modulation (τ≈4 min), effectively retaining a ‘memory’ of the previous [Ca2+]i elevation. Using a Michaelis‐Menten model with appropriate corrections for cytoplasmic Ca2+ buffering, we found that modulation extended the dynamic range of PMCA activity by increasing both the maximal pump rate and Ca2+ sensitivity (reduction of KM). A simple flux model shows how pump modulation and its reversal produce the initial overshoot of the biphasic [Ca2+]i response. The modulation of PMCA activity enhanced the stability of Ca2+ signalling by adjusting the efflux rate to match influx through CRAC channels, even at high [Ca2+]i levels that saturate the transport sites and would otherwise render the cell defenceless against additional Ca2+ influx. At the same time, the delay in modulation enables small Ca2+ fluxes to transiently elevate [Ca2+]i, thus enhancing Ca2+ signalling dynamics.
Neurotrophin modulation of voltage‐gated potassium channels in rat through TrkB receptors is time and sensory experience dependent
Authors: Tucker K. , Fadool D. A.
Published: July 2002

The whole‐cell configuration of the patch‐clamp technique, immunoprecipitation experiments and unilateral naris occlusions were used to investigate whether the voltage‐gated potassium channel Kv1.3 was a substrate for neurotrophin‐induced tyrosine phosphorylation and subsequent functional modulation of current properties in cultured rat olfactory bulb (OB) neurons. Membrane proteins of the OB included all three Trk receptor kinases, but the truncated form of the receptor, lacking an intact kinase domain, was the predominant form of the protein for TrkA and TrkC, while TrkB was predominantly found as the full‐length receptor. Acute (15 min) stimulation of OB neurons with bath application of 50 ng ml−1 brain‐derived neurotrophic factor (BDNF), which is a selective ligand for TrkB, caused suppression of the whole‐cell outward current and no changes in the kinetics of inactivation or deactivation. Acute stimulation with either nerve growth factor or neurotrophin‐3 failed to evoke any changes in Kv1.3 function in the OB neurons. Chronic exposure to BDNF (days) caused an increase in the magnitude of Kv1.3 current and speeding of the inactivation and deactivation of the channel. Acute BDNF‐induced activation of TrkB receptors significantly increased tyrosine phosphorylation of Kv1.3 in the OB, as shown using a combined immunoprecipitation and Western blot analysis. With unilateral naris occlusion, the acute BDNF‐induced tyrosine phosphorylation of Kv1.3 was increased in neurons lacking odour sensory experience. In summary, the duration of neurotrophin exposure and the sensory‐dependent state of a neuron can influence the degree of phosphorylation of a voltage‐gated ion channel and its concomitant functional modulation by neurotrophins.
Independence of extracellular tortuosity and volume fraction during osmotic challenge in rat neocortex
Authors: Kume‐Kick June , Mazel Tomáš , Voříšek Ivan , Hrabětová Sabina , Tao Lian , Nicholson Charles
Published: July 2002

The structural properties of brain extracellular space (ECS) are summarised by the tortuosity (λ) and the volume fraction (α). To determine if these two parameters were independent, we varied the size of the ECS by changing the NaCl content to alter osmolality of bathing media for rat cortical slices. Values of λ and α were extracted from diffusion measurements using the real‐time ionophoretic method with tetramethylammonium (TMA+). In normal medium (305 mosmol kg−1), the average value of λ was 1.69 and of α was 0.24. Reducing osmolality to 150 mosmol kg−1, increased λ to 1.86 and decreased α to 0.12. Increasing osmolality to 350 mosmol kg−1, reduced λ to about 1.67 where it remained unchanged even when osmolality increased further to 500 mosmol kg−1. In contrast, α increased steadily to 0.42 as osmolality increased. Comparison with previously published experiments employing 3000 Mr dextran to measure λ, showed the same behaviour as for TMA+, including the same constant λ in hypertonic media but with a steeper slope in the hypotonic solutions. These data show that λ and α behave differently as the ECS geometry varies. When α decreases, λ increases but when α increases, λ rapidly attains a constant value. A previous model allowing cellular shape to alter during osmotic challenge can account qualitatively for the plateau behaviour of λ.
Reduction of high‐frequency network oscillations (ripples) and pathological network discharges in hippocampal slices from connexin 36‐deficient mice
Authors: Maier Nikolaus , Güldenagel Martin , Söhl Goran , Siegmund Herbert , Willecke Klaus , Draguhn Andreas
Published: July 2002

Recent evidence suggests that electrotonic coupling is an important mechanism for neuronal synchronisation in the mammalian cortex and hippocampus. Various types of network oscillations have been shown to depend on, or be sharpened by, gap junctions between inhibitory interneurones or excitatory projection cells. Here we made use of a targeted disruption of the gene coding for Cx36, a recently discovered neuronal gap junction subunit, to analyse its role in hippocampal network behaviour. Mice lacking Cx36 are viable and lack obvious morphological or behavioural abnormalities. Stimulation of afferent and efferent fibre pathways in hippocampal slices revealed a largely normal function of the synaptic circuitry, including tetanically evoked network oscillations. Spontaneous sharp waves and ripple (∼200 Hz) oscillations, however, occurred less frequently in slices from Cx36 ‐/‐ mice, and ripples were slightly slower than in littermate controls. Moreover, epileptiform discharges elicited by 4‐aminopyridine were attenuated in slices from Cx36 ‐/‐ mice. Our findings indicate that Cx36 plays a role in the generation of certain forms of network synchronisation in the hippocampus, namely sharp wave‐ripple complexes and hypersynchronous epileptiform discharges.
New light shed on fluid formation in the seminiferous tubules of the rat
Authors: Fisher David
Published: July 2002

In this study the effects of perfusing isolated seminiferous tubules of the testes are reported for the first time. Initial perfusion studies (fast rate perfusion) resulted in gross morphological damage to the seminiferous tubules. The recorded transepithelial potential (Vt) was close to 0 mV. Slow perfusion rates eliminated morphological damage to the perfused tubules. These tubules exhibited a Vt of −5.4 ± 1.8 mV which was significantly different (P < 0.0001) from tubules that were perfused at a fast rate. Additional non‐perfusion electrophysiological experiments (oil‐gap and agar probe techniques) provided the confirmation that tubules not morphologically compromised produced a higher Vt which was not statistically different (P < 0.0001) from slowly perfused tubules. A revised hypothesis on fluid secretion is postulated. In brief, that the seminiferous tubule is solely responsible for the production of its luminal fluid. This hypothesis is contrary to the long standing ‘Tuck’ hypothesis which suggested that the source of luminal fluid in the seminiferous tubule originated from secretions of Sertoli cells as well as from distal testicular structures, e.g. the rete testis.
Intramuscular triacylglycerol, glycogen and acetyl group metabolism during 4 h of moderate exercise in man
Authors: Watt Matthew J. , Heigenhauser George J. F. , Dyck David J. , Spriet Lawrence L.
Published: July 2002

This study investigated intramuscular triacylglycerol (IMTG) and glycogen utilisation, pyruvate dehydrogenase activation (PDHa) and acetyl group accumulation during prolonged moderate intensity exercise. Seven endurance‐trained men cycled for 240 min at 57 % maximal oxygen consumption (V̇O2,max) and duplicate muscle samples were obtained at rest and at 10, 120 and 240 min of exercise. We hypothesised that IMTG utilisation would be augmented during 2‐4 h of exercise, while PDHa would be decreased secondary to reduced glycogen metabolism. IMTG was measured on both muscle samples at each time point and the coefficient of variation was 12.3 ± 9.4 %. Whole body respiratory exchange ratio (RER) decreased from 0.89 ± 0.01 at 30 min to 0.83 ± 0.01 at 150 min and remained low throughout exercise. Plasma glycerol and free fatty acids (FFAs) had increased compared with rest at 90 min and progressively increased until exercise cessation. Although plasma glucose tended to decrease with exercise, this was not significant. IMTG was reduced at 120 min compared with rest (0 min, 15.6 ± 0.8 mmol kg−1 d.m.; 120 min, 12.8 ± 0.7 mmol kg−1 d.m.) but no further reduction in IMTG was observed at 240 min. Muscle glycogen was 468 ± 49 mmol kg−1 d.m. at rest and decreased at 120 min and again at 240 min (217 ± 48 and 144 + 47 mmol kg−1 d.m.). PDHa increased above rest at 10 and 120 min, but decreased at 240 min, which coincided with reduced whole body carbohydrate oxidation. Muscle pyruvate and ATP were unchanged with exercise. Acetyl CoA increased at 10 min and remained elevated throughout exercise. Acetylcarnitine increased at exercise onset but returned to resting values by 240 min. Contrary to our first hypothesis, significant utilisation of IMTG occurred during the first 2 h of moderate exercise but not during hours 2‐4. The reduced utilisation of intramuscular fuels during the last 120 min was offset by greater FFA delivery and oxidation. Consistent with the second hypothesis, PDHa decreased late in moderate exercise and closely matched the estimates of lower carbohydrate flux. Although the factor underlying the PDHa decrease was not apparent, reduced pyruvate provision secondary to diminished glycolytic flux is the most likely mechanism.
Lactate dehydrogenase is not a mitochondrial enzyme in human and mouse vastus lateralis muscle
Authors: Rasmussen Hans N. , van Hall Gerrit , Rasmussen Ulla F.
Published: July 2002

The presence of lactate dehydrogenase in skeletal muscle mitochondria was investigated to clarify whether lactate is a possible substrate for mitochondrial respiration. Mitochondria were prepared from 100 mg samples of human and mouse vastus lateralis muscle. All fractions from the preparation procedure were assayed for marker enzymes and lactate dehydrogenase (LDH). The mitochondrial fraction contained no LDH activity (detection limit ∼0.05 % of the tissue activity) and the distribution of LDH activity among the fractions paralleled that of pyruvate kinase, i.e. LDH was fractionated as a cytoplasmic enzyme. Respiratory experiments with the mitochondrial fraction also indicated the absence of LDH. Lactate did not cause respiration, nor did it affect the respiration of pyruvate + malate. The major part of the native cytochrome c was retained in the isolated mitochondria, which, furthermore, showed high specific rates of state 3 respiration. This excluded artificial loss from the mitochondria of all activity of a possible LDH. It was concluded that skeletal muscle mitochondria are devoid of LDH and unable to metabolize lactate.
Ionic currents in isolated and in situ squid Schwann cells
Authors: Inoue Isao , Tsutsui Izuo , Joan Abbott N. , Brown Euan R.
Published: July 2002

Ionic currents from Schwann cells isolated enzymatically from the giant axons of the squids Loligo forbesi, Loligo vulgaris and Loligo bleekeri were compared with those obtained in situ. Macroscopic and single channel ionic currents were recorded using whole‐cell voltage and patch clamp. In the whole‐cell configuration, depolarisation from negative holding potentials evoked two voltage‐dependent currents, an inward current and a delayed outward current. The outward current resembled an outwardly rectifying K+ current and was activated at −40 mV after a latent period of 5‐20 ms following a step depolarisation. The current was reduced by externally applied nifedipine, Co2+ or quinine, was not blocked by addition of apamin or charibdotoxin and was insensitive to externally applied l‐glutamate or acetylcholine. The voltage‐gated inward current was activated at −40 mV and was identified as an L‐type calcium current sensitive to externally applied nifedipine. Schwann cells were impaled in situ in split‐open axons and voltage clamped using discontinuous single electrode voltage clamp. Voltage dependent outward currents were recorded that were kinetically identical to those seen in isolated cells and that had similar current‐voltage relations. Single channel currents were recorded from excised inside‐out patches. A single channel type was observed with a reversal potential close to the equilibrium potential for K+ (EK) and was therefore identified as a K+ channel. The channel conductance was 43.6 pS when both internal and external solutions contained 150 mm K+. Activity was weakly dependent on membrane voltage but sensitive to the internal Ca2+ concentration. Activity was insensitive to externally or internally applied l‐glutamate or acetylcholine. The results suggest that calcium channels and calcium‐activated K+ channels play an important role in the generation of the squid Schwann cell membrane potential, which may be controlled by the resting intracellular Ca2+ level.
Finger movement is associated with attenuated cutaneous reflexes recorded from human first dorsal interosseous muscle
Authors: Turner L. C. , Harrison L. M. , Stephens J. A.
Published: July 2002

Cutaneomuscular reflexes (CMR) have been recorded from the first dorsal interosseous muscle (1DI) of the preferred hand, somatosensory evoked potentials (SEP) were recorded from the contralateral sensory cortex and the sensory nerve action potential (SNAP) was recorded from the median nerve of 15 adult subjects whilst electrically stimulating the digital nerves of the index finger. Subjects performed the following tasks (a) a sustained abduction of the index finger against resistance at 10–20 % maximum voluntary contraction (MVC), and (b) abduction of the index finger as in (a) whilst performing self paced low amplitude tapping of the (i) index finger, (ii) thumb, (iii) middle finger, (iv) little finger and (v) ipsilateral foot. The E2 component of the CMR and the N20/P25 components of the SEP were significantly reduced during finger tapping (P < 0.05). This reduction was independent of which finger was tapping (P > 0.05). There was a significant (qualitative) relationship between the decrease in the size of the E2 component of the CMR and the N20/P25 components of the SEP (χ2 test; P < 0.05). There were no significant changes in E1 and I1 (P > 0.05). The size of the SNAP was independent of task (P > 0.05). The size of the E1, I1, E2 components of the CMR, and the N20/P25 components of the SEP were unaltered during foot tapping (P > 0.05, n= 4). We conclude that the decrease in size of the E2 component associated with finger tapping results from gating of the digital nerve input.
Kalaeloa: Combined Cycle Power Station Burning Low Sulfur Fuel Oil in Its Ninth Successful Year
Authors: Khalaf Z. R. , Basler B.
Published: July 2002

This paper presents the O&M experience at the Kalaeloa Cogeneration Plant. Performance issues and other problems related to firing heavy oil in a combustion turbine are presented together with their long-term solutions leading to the current successful operation of the IPP power station in Hawaii, USA.
Nonlinear Time-Dependent Thermoelastic Response in a Multilayered Anisotropic Medium
Authors: Chen T.-C. , Hwang S.-J. , Chen C.-Q.
Published: July 2002

A time-dependent nonlinear thermoelastic problem of a multilayered anisotropic medium with a certain specific form of temperature-dependent material properties in generalized plane deformation is analyzed by flexibility/stiffness matrix technique in the article. The closed-form general solutions of temperature, displacements, and stresses can then be obtained in the Fourier and the Laplace transform domains by using the technique of Kirchhoff transformation. The effects of temperature-dependent material properties on the distributions of temperature and thermal stresses are also calculated and discussed.
A Converging Slot-Hole Film-Cooling Geometry—Part 2: Transonic Nozzle Guide Vane Heat Transfer and Loss
Authors: Sargison J. E. , Guo S. M. , Oldfield M. L. G. , Lock G. D. , Rawlinson A. J.
Published: July 2002

This paper presents the first experimental measurements on an engine representative nozzle guide vane, of a new film-cooling hole geometry, a con¯vergings¯lot-hole¯ or console. The patented console geometry is designed to improve the heat transfer and aerodynamic performance of turbine vane and rotor blade cooling systems. These experiments follow the successful validation of the console design in low-speed flat-plate tests described in Part 1 of this paper. Stereolithography was used to manufacture a resin model of a transonic, engine representative nozzle guide vane in which seven rows of previously tested fan-shaped film-cooling holes were replaced by four rows of consoles. This vane was mounted in the annular vane ring of the Oxford cold heat transfer tunnel for testing at engine Reynolds numbers, Mach numbers and coolant to mainstream momentum flux ratios using a heavy gas to simulate the correct coolant to mainstream density ratio. Heat transfer data were measured using wide-band thermochromic liquid crystals and a modified analysis technique. Both surface heat transfer coefficient and the adiabatic cooling effectiveness were derived from computer-video records of hue changes during the transient tunnel run. The cooling performance, quantified by the heat flux at engine temperature levels, of the console vane compares favourably with that of the previously tested vane with fan-shaped holes. The new console film-cooling hole geometry offers advantages to the engine designer due to a superior aerodynamic efficiency over the fan-shaped hole geometry. These efficiency measurements are demonstrated by results from midspan traverses of a four-hole pyramid probe downstream of the nozzle guide vane.
An Embedded Friction Sensor Based on a Strain-Gauged Diaphragm
Authors: Dellah A. , Wild P. M. , Moore T. N. , Shalaby M. , Jeswiet J.
Published: July 2002

A new design of friction sensor, intended for use in industrial process applications, such as metal forming, has been developed. The sensor consists of a diaphragm whose outer surface is flush with the surface of the tool and whose inner surface is instrumented with strain gauges. Relative to previous sensor designs, this sensor offers reduced disturbance of the frictional interaction between the tool and the workpiece. A proof-of-concept prototype has been constructed and tested in a laboratory test apparatus. The results of testing validate the anticipated performance, based on finite element modeling. The sensor is able to measure both shear and normal forces and, of greater significance, is able to simultaneously differentiate between the two types of loading.
The SKN Approximation for Solving Radiative Transfer Problems in Absorbing, Emitting, and Linearly Anisotropically Scattering Plane-Parallel Medium: Part 2
Authors: Altac¸ Zekeriya
Published: July 2002

The SKN (Synthetic Kernel) approximation is proposed for solving radiative transfer problems in linearly anisotropically scattering homogeneous and inhomogeneous participating plane-parallel medium. The radiative integral equations for the incident energy and the radiative heat flux using synthetic kernels are reduced to a set of coupled second-order differential equations for which proper boundary conditions are established. Performance of the three quadrature sets proposed for isotropic scattering medium are further tested for linearly anisotropically scattering medium. The method and its convergence with respect to the proposed quadrature sets are explored by comparing the results of benchmark problems using the exact, P11, and S128 solutions. The SKN method yields excellent results even for low orders using appropriate quadrature set.
Development of a Computer-Aided Manufacturing System for Profiled Edge Lamination Tooling
Authors: Im Yong-Tai , Walczyk Daniel F.
Published: July 2002

Profiled Edge Lamination (PEL) tooling is a promising Rapid Tooling (RT) method involving the assembly of an array of laminations whose top edges are simultaneously profiled and beveled based on a CAD model of the intended tool surface. To facilitate adoption of this RT method by industry, a comprehensive PEL Tooling Development System has been proposed. The two main parts of this system are (1) iterative tool design based on thermal and structural models and (2) fabrication of the tool using a Computer-aided Manufacturing (CAM) software and Abrasive Water Jet (AWJ) cutting. CAM software has been developed to take lamination slice data (profiles) from any proprietary RP software in the form of polylines and create smooth, kinematically desirable cutting trajectories for each tool lamination. Two cutting trajectory algorithms, called Identical Equidistant Profile Segmentation (IEPS) and Adaptively Vectored Profiles Projection (AVPP), were created for this purpose. By comparing the performance of both algorithms with a benchmark part shape, the AVPP algorithm provided better cutting trajectories for complicated tool geometries. A 15-layer aluminum PEL tool was successfully fabricated using a 5-axis CNC AWJ cutter and NC code generated by the CAM software.
Subspace-Based System Identification for an Acoustic Enclosure
Authors: McKelvey Tomas , Fleming Andrew , Moheimani S. O. Reza
Published: July 2002

This paper is aimed at identifying a dynamical model for an acoustic enclosure, a duct with rectangular cross section, closed ends, and side-mounted speaker enclosures. Acoustic enclosures are known to be resonant systems of high order. In order to design a high performance feedback controller for an acoustic enclosure, one needs to have an accurate model of the system. Subspace-based system identification techniques have proven to be an efficient means of identifying dynamics of high order highly resonant systems. In this paper a frequency domain subspace-based method together with a second iterative optimization step minimizing a frequency domain least-squares criterion is successfully employed to identify a dynamical model for an acoustic enclosure.
Generic Simulation Approach for Multi-Axis Machining, Part 1: Modeling Methodology
Authors: Bailey T. , Elbestawi M. A. , El-Wardany T. I. , Fitzpatrick P.
Published: July 2002

This paper presents a new methodology for analytically simulating multi-axis machining of complex sculptured surfaces. A generalized approach is developed for representing an arbitrary cutting edge design, and the local surface topology of a complex sculptured surface. A NURBS curve is used to represent the cutting edge profile. This approach offers the advantages of representing any arbitrary cutting edge design in a generic way, as well as providing standardized techniques for manipulating the location and orientation of the cutting edge. The local surface topology of the part is defined as those surfaces generated by previous tool paths in the vicinity of the current tool position. The local surface topology of the part is represented without using a computationally expensive CAD system. A systematic prediction technique is then developed to determine the instantaneous tool/part interaction during machining. The methodology employed here determines cutting edge in-cut segments by determining the intersection between the NURBS curve representation of the cutting edge and the defined local surface topology. These in-cut segments are then utilized for predicting instantaneous chip load, static and dynamic cutting forces, and tool deflection. Part 1 of this paper details the modeling methodology and demonstrates the capabilities of the simulation for machining a complex surface. Part 2 details both the model calibration procedure and discusses a case study of process optimization through feed rate scheduling.
On Extension of “Heatline” and “Massline” Concepts to Reacting Flows Through Use of Conserved Scalars
Authors: Mukhopadhyay Achintya , Qin Xiao , Aggarwal Suresh K. , Puri Ishwar K.
Published: July 2002

A new formulation for extending the concept of heatlines and masslines to reacting flows through use of conserved scalars has been proposed. The formulation takes into account the distinct diffusion coefficients of different species. Results have been obtained for a number of two-dimensional nonreacting and reacting free shear flows under normal and zero gravity. For nonreacting flows, total enthalpy and elemental mass fractions have been used as the transported conserved scalars. For reacting flows, mixture fractions, defined as normalized elemental mass fractions and enthalpy, have been employed. The results show this concept to be a useful tool for obtaining better insights into the global qualitative picture of scalar transport for both nonreacting and reacting flows.
Development of the Cylindrical Wire Electrical Discharge Machining Process, Part 1: Concept, Design, and Material Removal Rate
Authors: Qu Jun , Shih Albert J. , Scattergood Ronald O.
Published: July 2002

Results of applying the wire Electrical Discharge Machining (EDM) process to generate precise cylindrical forms on hard, difficult-to-machine materials are presented. The design of a precise, flexible, and corrosion-resistant underwater rotary spindle is first introduced. A detailed spindle error analysis identifies the major sources of error at different frequency spectrum. The spindle has been added to a conventional two-axis wire EDM machine to enable the generation of free-form cylindrical geometries. The mathematical model for material removal rate of the free-form cylindrical wire EDM process is derived. Experiments were conducted to explore the maximum material removal rate for cylindrical and 2D wire EDM of carbide and brass work-materials. Compared to the conventional 2D wire EDM of the same work-material, higher maximum material removal rates may be achieved in the cylindrical wire EDM, possibly due to better debris flushing condition.
Buoyancy-Driven Flow Transitions in Deep Cavities Heated From Below
Authors: Xia Chunmei , Murthy Jayathi Y.
Published: July 2002

A numerical investigation has been conducted of flow transitions in deep three-dimensional cavities heated from below. The first critical Rayleigh number, RaI, below which the flow is at rest, and the second critical Rayleigh number, RaII, for transition from steady state to oscillatory flow, have been found for cavities of aspect ratios Ar in the range 1–5. Transition to chaos has also been examined for these cases. The results show that RaI=3583,2.545×104 and 5.5×105 and RaII=4.07×105,1.65×106 and 1.30×107 for aspect ratios of 1, 2, and 5 respectively. The route to chaos is PPeriodic→QP2(Quasi-periodic with two incommensurate frequencies)→QP3(Quasi-periodic with three incommensurate frequencies)→NChaotic for Ar=1 with the Rayleigh number varying from 4.07×105 to 4.89×105. The route is PPeriodic→P2(Periodic doubling)→I(Intermittent)→P(Periodic)→N(Chaotic) for Ar=2 over a Ra range of 1.65×106 to 1.83×106. The interval between periodic and chaotic flow is very short for Ar=5.
Near-Wall Modeling of Turbulent Convective Heat Transport in Film Cooling of Turbine Blades With the Aid of Direct Numerical Simulation Data
Authors: Lakehal Djamel
Published: July 2002

The paper presents novel developments in the DNS-based, turbulence modeling strategy of Lakehal et al. developed for calculating jets in crossflow. The particular features of the model include: 1) dynamic coupling of the high-Re k−ε with a one-equation model resolving the near-wall viscosity-affected layer; 2) inclusion of the anisotropy of turbulent transport coefficients for all transport equations; 3) near-wall variation of the turbulent Prandtl number as a function of the local Reynolds number. Most of the important aspects of the proposed model are based on known DNS statistics of channel and boundary layer flows. The model is validated against experiments for the case of film cooling of a flat plate, where coolant air is injected from a row of streamwise inclined jets. Excellent results were obtained for this configuration as compared to earlier numerical investigations reported in the open literature. The model is then extended to calculate film cooling of a symmetrical turbine blade by a row of laterally injected jets for various blowing rates. Comparison of the calculated and measured wall-temperature distributions show that only with this anisotropy eddy-viscosity/diffusivity model can the spanwise spreading of the temperature field be well predicted and the strength of the secondary vortices reduced. Furthermore, results of additional calculations show that combining the anisotropy eddy viscosity model with the DNS-based relation for turbulent Prandtl number promotes the eddy diffusivity of heat vis-a`-vis that of momentum further, leading to an enhanced spanwise spreading of the jet. The performance of this new approach improves with increasing blowing rate.
Effects of argon addition on a-CNx film deposition by hot carbon filament chemical vapor deposition
Authors: Watanabe Yoshihisa , Aono Masami , Yamazaki Ayumi , Kitazawa Nobuaki , Nakamura Yoshikazu
Published: July 2002

Using a carbon filament which supplies carbon and heat, amorphous carbon nitride (a-CNx) films were prepared on Si (100) substrates by hot filament chemical vapor deposition. Deposition was performed in a low-pressure atmosphere of pure nitrogen and a gas mixture of nitrogen and argon. Effects of argon additions to the nitrogen atmosphere on the film microstructure and interface composition between the film and substrate were studied by field-emission scanning electron microscopy (FESEM) and x-ray photoelectron spectroscopy (XPS). FESEM observations reveal that the film prepared in a pure nitrogen atmosphere has uniform nucleation and a densely packed columnar pieces structure. The film prepared in the nitrogen and argon gas mixture exhibits preferential nucleation and a tapered structure with macroscopic voids. Depth analyses using XPS reveal that the film prepared in pure nitrogen possesses a broad interface, which includes silicon carbide as well as a-CNx, whereas a sharp interface is discerned in the film prepared in the mixed nitrogen and argon gas. We observed that silicon carbide formation is suppressed by an argon addition to the nitrogen atmosphere during deposition.
Reduction of metallic oxides by late Ar–H2–N2 postdischarges. I. Application to copper oxides
Authors: Belmonte T. , Thiébaut J. M. , Michel H. , Cardoso R. P. , Maliska A.
Published: July 2002

In this first part of a study dealing with the reduction of metallic oxides by Ar–N2–H2 postdischarges, copper oxide (CuO) is studied. The influence of the composition of both the gas mixture and the temperature on the reduction kinetics was measured, respectively, between 473 and 673 K. Measurements of the activation energies of the reduction reactions, together with optical emission spectroscopy in discharge and postdischarge, suggest that the reduction mechanisms of CuO is limited by the diffusion of hydrogen in copper below 573 K and by the dissociation of molecular hydrogen above. Atomic nitrogen can also react, but the reduction kinetics of metallic oxides by this specie is much slower than by H.
Anomalous growth of Ba on Ag(111)
Authors: Teodoro O. M. N. D. , Los J. , Moutinho A. M. C.
Published: July 2002

Electropositive elements are often adsorbed on metals to produce a well-known decrease in the surface work function. During deposition, the work function drops steeply and reaches a minimum at coverage lower than one monolayer. Then, it increases slightly and the work function converges to the value of the deposited element. In this work, we report anomalous behavior found during the deposition of barium on a Ag(111) surface. After a minimum of about 2.4 eV the work function did not increase up to 2.7 eV, the bulk barium work function, no matter what amount of barium was deposited. Auger electron spectroscopy corroborated these results in which we measured a permanent and constant intensity of the Ag MNN peak for high barium coverage. To explain this anomalous growth of barium on Ag(111) we propose an explanation based on the diffusion of silver atoms into the barium film. Further experiments showed that coadsorption of oxygen before a second deposition of barium blocked the diffusion thus allowing the work function to reach 2.7 eV.
Surface phase transitions of Pt(110) studied by desorption dynamics of product CO2 in steady-state CO oxidation
Authors: Rzeznicka I. , Morales de la Garza L. , Matsushima T.
Published: July 2002

The transformation of (1×2) into (1×1) on a Pt(110) surface in the course of CO oxidation was studied through the analysis of both angular and velocity distributions of desorbing product CO2 and low-energy electron diffraction (LEED) intensity. The intensity of half-order LEED spots decreased quickly, showing the beginning of the transformation of (1×2)→(1×1) just below the kinetic transition, where the rate-determining step switched from CO adsorption to O2 dissociation. On the other hand, the angular distribution of desorbing CO2 sharply changed at a CO pressure far above the kinetic transition, where (1×2) domains disappeared. Below this approximate CO pressure, CO2 was mostly formed on (1×2) domains regardless of its reduced area.
Copper Pthalocyanine by XPS
Authors: Adolphi Barbara , Berger Olena , Fischer Wolf-Joachim
Published: July 2002

Copper pthalocyanine (CuPc) is an important technological material, being used for both dyes and chemical sensors. Our interest is focused on the sensors. The thin films were deposited by a sublimation technique on polycrystalline SiO2 layers (1.65 μm) on a silicon wafer from a commercial CuPc powder. Films were deposited at a substrate temperature of 293 K and with a deposition rate of 0.3 nm/s forming an α-form with a preferential orientation in the [200] direction. After deposition the thin films were heated to investigate the α→β phase transformation in a separate chamber. X-ray diffraction analysis indicated that annealing at 300 °C for 3 h in nitrogen resulted in a complete α→β transformation. The crystals of β phase forming the film have preferential growth orientation in the [100] and [011] direction to the surface of the SiO2 layer. Surface analysis by XPS was used in order to clarify the molecular structure and chemical compositions of the thin films. The measurements from the core level peaks, as well as the valence bands, showed systematic changes resulting from the annealing procedure.
Zinc Diisopropyl Dithiophosphate by XPS
Authors: Eglin Michael , Rossi Antonella , Piras Federica M. , Spencer Nicholas D.
Published: July 2002

X-ray photoelectron spectroscopy was used to characterize zinc diisopropyl dithiophosphate (ZnDTP). This compound belongs to the family of zinc dialkyldithiophosphates, which have been used since 1940 as extreme-pressure, high-temperature additives for lubricant formulations. A full XPS characterization of this compound is presented here for the first time. Zinc diisopropyl dithiophosphate is a white powder. NMR and FT-IR spectroscopies, as well as chemical analysis, have been performed and the results are in agreement with the expected chemical structure of the molecule. The substance is sensitive to x-ray irradiation. The sample was cooled by liquid nitrogen (to approximately 100 K) during the analysis and the conditions chosen such that no degradation of the substance could be observed. Quantitative XPS spectroscopy yielded a composition that coincides with the expected chemical formula.
Fast cross‐projection algorithm for reconstruction of seeds in prostate brachytherapy
Authors: Narayanan Sreeram , Cho Paul S. , Marks Robert J.
Published: July 2002

A fast method of seed matching and reconstruction in prostrate brachytherapy is proposed. Previous approaches have required all seeds to be matched with all other seeds in other projections. The fast cross‐projection algorithm for the reconstruction of seeds (Fast‐CARS) allows for matching of a given seed with a subset of seeds in other projections. This subset lies in a proximal region centered about the projection of a line, connecting the seed to its source, onto other projection planes. The proposed technique permits a significant reduction in computational overhead, as measured by the required number of matching tests. The number of multiplications and additions is also vastly reduced at no trade‐off in accuracy. Because of its speed, Fast‐CARS can be used in applications requiring real‐time performance such as intraoperative dosimetry of prostate brachytherapy. Furthermore, the proposed method makes practical the use of a larger number of views as opposed to previous techniques limited to a maximum use of three views.
A systematic method to determine the Lagrangian directly from the equations of motion
Authors: Huang Young-Sea , Lin Chyi-Lung
Published: July 2002

Based on reversing Hamilton’s principle, the Lagrangian can be obtained directly from the equations of motion. The method is illustrated for a relativistic particle moving in an external field, the electromagnetic field, and a damped harmonic oscillator.
Fermat’s principle and the variational analysis of an optical model for light propagation exhibiting a critical radius
Authors: Marklund M. , Anderson D. , Cattani F. , Lisak M. , Lundgren L.
Published: July 2002

Fermat’s principle is used to analyze the trajectories of light propagating in a radially inhomogeneous medium with a singularity in the center. It is found that the light trajectories are similar to those around a black hole, in the sense that there exists a critical radius within which the light cannot escape, but spirals into the singularity.
Breaking the sound barrier: Tunneling of acoustic waves through the forbidden transmission region of a one-dimensional acoustic band gap array
Authors: Robertson W. M. , Ash J. , McGaugh J. M.
Published: July 2002

We demonstrate the tunneling of audio pulses through the forbidden transmission zone of an acoustic band gap array. The acoustic band gap is created in a waveguide with a periodically spaced series of dangling sidebranches. Using an impulse response method, the transmission properties of the array are characterized and the regions of forbidden transmission identified. Tunneling pulses, whose frequency content lies completely with the forbidden transmission region, are used to explore the concepts of tunneling time and group velocity. In an analog of experiments that are well known for electromagnetic waves, we show that the group velocity of the tunneling pulse is considerably larger than the speed of sound. The dynamics of pulse reshaping that lead to this phenomenon are discussed.
Modeling the motion of a toy car traveling on an arbitrarily shaped track
Authors: Wick D. P. , Ramsdell M. W.
Published: July 2002

An analysis is performed on the motion of a Matchbox car racing down an arbitrarily shaped track that resides in a two-dimensional vertical plane. The role of friction, track shape, and air resistance on the car’s performance is investigated. The parameters that describe the car’s effective coefficient of friction and drag constant are experimentally extracted by consideration of its motion on a flat, horizontal track. These parameters are then employed to make predictions of the velocity on an arbitrarily shaped track containing hills and valleys and compared with measured values. A rigidly mounted shield of varying cross-sectional area is used to enhance the effects of drag. This analysis has been successfully incorporated into an advanced group project for an introductory course in classical mechanics and can be customized to accommodate a variety of levels.
Effect of bone cortical thickness on velocity measurements using ultrasonic axial transmission: A 2D simulation study
Authors: Bossy Emmanuel , Talmant Maryline , Laugier Pascal
Published: July 2002

In recent years, quantitative ultrasound (QUS) has played an increasing role in the assessment of bone status. The axial transmission technique allows to investigate skeletal sites such as the cortical layer of long bones (radius, tibia), inadequate to through-transmission techniques. Nevertheless, the type of propagation involved along bone specimens has not been clearly elucidated. Axial transmission is investigated here by means of two-dimensional simulations at 1 MHz. We focus our interest on the apparent speed of sound (SOS) of the first arriving signal (FAS). Its dependence on the thickness of the plate is discussed and compared to previous work. Different time criteria are used to derive the apparent SOS of the FAS as a function of source–receiver distance. Frequency-wave number analysis is performed in order to understand the type of propagation involved. For thick plates (thickness>λbone, longitudinal wavelength in bone), and for a limited range of source–receiver distances, the FAS corresponds to the lateral wave. Its velocity equals the longitudinal bulk velocity of the bone. For plate thickness less than λbone, some plate modes contribute to the FAS, and the apparent SOS decreases with the thickness in a way that depends on both the time criterion and on the source–receiver distance. The FAS corresponds neither to the lateral wave nor to a single plate mode. For very thin plates (thickness<λbone/4), the apparent SOS tends towards the velocity of the lowest order symmetrical vibration mode (S0 Lamb mode).
The effect of channel interactions on speech recognition in cochlear implant subjects: Predictions from an acoustic model
Authors: Throckmorton Chandra S. , Collins Leslie M.
Published: July 2002

Acoustic models that produce speech signals with information content similar to that provided to cochlear implant users provide a mechanism by which to investigate the effect of various implant-specific processing or hardware parameters independent of other complicating factors. This study compares speech recognition of normal-hearing subjects listening through normal and impaired acoustic models of cochlear implant speech processors. The channel interactions that were simulated to impair the model were based on psychophysical data measured from cochlear implant subjects and include pitch reversals, indiscriminable electrodes, and forward masking effects. In general, spectral interactions degraded speech recognition more than temporal interactions. These effects were frequency dependent with spectral interactions that affect lower-frequency information causing the greatest decrease in speech recognition, and interactions that affect higher-frequency information having the least impact. The results of this study indicate that channel interactions, quantified psychophysically, affect speech recognition to different degrees. Investigation of the effects that channel interactions have on speech recognition may guide future research whose goal is compensating for psychophysically measured channel interactions in cochlear implant subjects.