bluuebunny/crossref_metadata_2025 huggingface dataset:
ATP and heat production in human skeletal muscle during dynamic exercise: higher efficiency of anaerobic than aerobic ATP resynthesis
Authors: Krustrup Peter , Ferguson Richard A. , Kjær Michael , Bangsbo Jens
Published: May 2003

The aim of the present study was to simultaneously examine skeletal muscle heat production and ATP turnover in humans during dynamic exercise with marked differences in aerobic metabolism. This was done to test the hypothesis that efficiency is higher in anaerobic than aerobic ATP resynthesis. Six healthy male subjects performed 90 s of low intensity knee‐extensor exercise with (OCC) and without thigh occlusion (CON‐LI) as well as 90 s of high intensity exercise (CON‐HI) that continued from the CON‐LI bout. Muscle heat production was determined by continuous measurements of muscle heat accumulation and heat release to the blood. Muscle ATP production was quantified by repeated measurements of thigh oxygen uptake as well as blood and muscle metabolite changes. All temperatures of the thigh were equalized to ≈37 °C prior to exercise by a water‐perfused heating cuff. Oxygen uptake accounted for 80 ± 2 and 59 ± 4 %, respectively, of the total ATP resynthesis in CON‐LI and CON‐HI, whereas it was negligible in OCC. The rise in muscle temperature was lower (P < 0.05) in OCC than CON‐LI (0.32 ± 0.04 vs. 0.37 ± 0.03 °C). The mean rate of heat production was also lower (P < 0.05) in OCC than CON‐LI (36 ± 4 vs. 57 ± 4 J s−1). Mechanical efficiency was 52 ± 4 % after 15 s of OCC and remained constant, whereas it decreased (P < 0.05) from 56 ± 5 to 32 ± 3 % during CON‐LI. During CON‐HI, mechanical efficiency transiently increased (P < 0.05) to 47 ± 4 %, after which it decreased (P < 0.05) to 36 ± 3 % at the end of CON‐HI. Assuming a fully coupled mitochondrial respiration, the ATP turnover per unit of work was calculated to be unaltered during OCC (≈20 mmol ATP kJ−1), whereas it increased (P < 0.05) from 21 ± 4 to 29 ± 3 mmol ATP kJ−1 during CON‐LI and further (P < 0.05) to 37 ± 3 mmol ATP kJ−1 during CON‐HI. The present data confirm the hypothesis that heat loss is lower in anaerobic ATP resynthesis than in oxidative phosphorylation and can in part explain the finding that efficiency declines markedly during dynamic exercise. In addition, the rate of ATP turnover apparently increases during constant load low intensity exercise. Alternatively, mitochondrial efficiency is lowered as exercise progresses, since ATP turnover was unaltered during the ischaemic exercise bout.
Organization of the central control of muscles of facial expression in man
Authors: Root A. A. , Stephens J. A.
Published: May 2003

Surface EMGs were recorded simultaneously from ipsilateral pairs of facial muscles while subjects made three different common facial expressions: the smile, a sad expression and an expression of horror, and three contrived facial expressions. Central peaks were found in the cross‐correlograms of EMG activity recorded from the orbicularis oculi and zygomaticus major during smiling, the corrugator and depressor anguli oris during the sad look and the frontalis and mentalis during the horror look. The size of the central peak was significantly greater between the orbicularis oculi and zygomaticus major during smiling. It is concluded that co‐contraction of facial muscles during some facial expressions are accompanied by the presence of common synaptic drive to the motoneurones supplying the muscles involved. Central peaks were found in the cross‐correlograms of EMG activity recorded from the frontalis and depressor anguli oris during a contrived expression. However, no central peaks were found in the cross‐correlograms of EMG activity recorded from the frontalis and orbicularis oculi or from the frontalis and zygomaticus major during the other two contrived expressions. It is concluded that a common synaptic drive is not present between all possible facial muscle pairs and suggests a functional role for the synergy. The origin of the common drive is discussed. It is concluded that activity in branches of common stem last‐order presynaptic input fibres to motoneurones innervating the different facial muscles and presynaptic synchronization of input activity to the different motoneurone pools is involved. The former probably contributes more to the drive to the orbicularis oculi and zygomaticus major during smiling, while the latter is probably more prevalent in the corrugator and depressor anguli oris during the sad look, the frontalis and mentalis during the horror look and the frontalis and depressor anguli oris during one of the contrived expressions. The strength of common synaptic drive is inversely related to the degree of separate control that can be exhibited by the facial muscles involved.
Cardiovascular and endocrine responses to acute hypoxaemia during and following dexamethasone infusion in the ovine fetus
Authors: Fletcher Andrew J. W. , Gardner David S. , Edwards C. Mark B. , Fowden Abigail L. , Giussani Dino A.
Published: May 2003

This study investigated the effects of fetal treatment with dexamethasone on ovine fetal cardiovascular defence responses to acute hypoxaemia, occurring either during or 48 h following the period of glucocorticoid exposure. To address the mechanisms underlying these responses, chemoreflex function and plasma concentrations of catecholamines, neuropeptide Y (NPY) and vasopressin were measured. Under general halothane anaesthesia, 26 Welsh Mountain sheep fetuses were surgically prepared for long‐term recording at between 117 and 120 days of gestation (dGA; term is ∼145 days) with vascular catheters and a Transonic flow probe around a femoral artery. Following at least 5 days of recovery, fetuses were randomly assigned to one of two experimental groups. After 48 h of baseline recording, at 125 ± 1 dGA, half of the fetuses (n= 13) were continuously infused i.v. with dexamethasone for 48 h at a rate of 2.06 ± 0.13 μg kg−1 h−1. The remaining 13 fetuses were infused with heparinized saline at the same rate (controls). At 127 ± 1 dGA, 2 days from the onset of infusions, seven fetuses from each group were subjected to 1 h of acute hypoxaemia. At 129 ± 1 dGA, 2 days after the end of infusions, six fetuses from each group were subjected to 1 h of acute hypoxaemia. Similar reductions in fetal partial pressure of arterial oxygen occurred in control and dexamethasone‐treated fetuses during the acute hypoxaemia protocols. In control fetuses, acute hypoxaemia led to transient bradycardia, femoral vasoconstriction and significant increases in plasma concentrations of catecholamines, vasopressin and NPY. In fetuses subjected to acute hypoxaemia during dexamethasone treatment, the increase in plasma NPY was enhanced, the bradycardic response was prolonged, and the plasma catecholamine and vasopressin responses were diminished. In fetuses subjected to acute hypoxaemia 48 h following dexamethasone treatment, femoral vasoconstriction and plasma catecholamine and vasopressin responses were enhanced, whilst the prolonged bradycardia and augmented plasma NPY responses persisted. These data show that fetal treatment with dexamethasone modifies the pattern and magnitude of fetal cardiovascular responses to acute oxygen deprivation. Modifications to different mechanisms mediating the fetal defence responses to acute hypoxaemia that occur during dexamethasone treatment may reverse, persist or even become enhanced by 48 h following the treatment period.
Highly H+‐sensitive neurons in the caudal ventrolateral medulla of the rat
Authors: Ribas‐Salgueiro J. L. , Gaytán S. P. , Crego R. , Pásaro R. , Ribas J.
Published: May 2003

The ventral surface of the caudal ventrolateral medulla (cVLM) has been shown to generate intense respiratory responses after surface acid‐base stimulation. With respect to their chemosensitive characteristics, cVLM neurons have been less studied than other rostral‐most regions of the brainstem. The purpose of these experiments was to determine the bioelectric responses of cVLM neurons to acidic stimuli and to determine their chemosensitive properties. Using extracellular and microiontophoretic techniques, we recorded electrical activities from 117 neurons in an area close to the ventral surface of the cVLM in anaesthetised rats. All neurons were tested for their sensitivity to H+. The fluorescent probe BCECF was used to measure extracellular pH changes produced by the microiontophoretic injection of H+ in brainstem slices. This procedure provided an estimation of the local changes in pH produced by microiontophoretic H+ application in the anaesthetised rat. Neurons coupled to the respiratory cycle, R (n= 51), were not responsive to direct stimulation with H+. Sixty‐six neurons that did respond to H+ stimulation were uncoupled from respiration, and identified as NR neurons. These neurons presented distinct ranges of H+ sensitivity. The neuronal sensitivity to H+ was mainly assessed by the slope of the stimulus‐response curve, where the steeper the slope, the higher the H+ sensitivity. On this basis, NR neurons were classed as being either weakly or highly sensitive to H+. NR neurons with a high H+ sensitivity (n= 12) showed an average value of 34.17 ± 7.44 spikes s−1 (100 nC)−1 (mean ±s.d.) for maximal slope and an EC50 of 126.76 ± 33 nC. Suprathreshold H+ stimulation of highly sensitive NR neurons elicited bursting pattern responses coupled to the respiratory cycle. The bursting responses, which were synchronised with the inspiratory phase and the early expiratory phase of the respiratory cycle, lasted for several seconds before returning to the steady state firing pattern characteristic of the pre‐stimulus condition. These NR neurons, which possess the capacity to detect distinct H+ concentrations in the extracellular microenvironment, are excellent candidates to serve in a chemoreceptor capacity in the caudal medulla.
A‐, T‐, and H‐type Currents Shape Intrinsic Firing of Developing Rat Abducens Motoneurons
Authors: Russier Michaël , Carlier Edmond , Ankri Norbert , Fronzaroli Laure , Debanne Dominique
Published: May 2003

During postnatal development, profound changes take place in the excitability of nerve cells, including modification in the distribution and properties of receptor‐operated channels and changes in the density and nature of voltage‐gated channels. We studied here the firing properties of abducens motoneurons (aMns) in transverse brainstem slices from postnatal day (P) 1–13 rats. Recordings were made from aMNs in the whole‐cell configuration of the patch‐clamp technique. Two main types of aMn could be distinguished according to their firing profile during prolonged depolarizations. Both types were identified as aMns by their fluorescence following retrograde labelling with the lipophilic carbocyanine DiI in the rectus lateralis muscle. The first type (BaMns) exhibited a burst of action potentials (APs) followed by an adaptation of discharge and were encountered in ∼70 % of aMns. Their discharge profile resembled that of adult aMns and was encountered in all aMns after P9. BaMns exhibited a hyperpolarization‐induced rebound potential that was blocked by low concentrations of Ni2+ or by Ca2+‐free external solution. This current had the properties of the T‐type current. Action potentials of BaMns showed a complex afterhyperpolarization (AHP). An inward rectification was evidenced following hyperpolarization and was blocked by external application of caesium or ZD7288, indicating the presence of the hyperpolarization‐activated cationic current (IH). Blocking the IH current almost doubled the input resistance of BaMns. The second class of aMns (DaMns) displayed a delayed excitation that was mediated by A‐type K+ currents and was observed only between P4 and P9. DaMns exhibited immature characteristics: an action potential with a simple AHP, a linear current‐voltage relation and a large input resistance. The number of aMns remained unchanged when both types were present (P5–P6) and later in development when only BaMns were encountered (P19), suggesting that DaMns mature into BaMns during postnatal development. We conclude that aMns display profound reorganization in their intrinsic excitability during postnatal development.
Temperature dependence of the force‐generating process in single fibres from frog skeletal muscle
Authors: Piazzesi G. , Reconditi M. , Koubassova N. , Decostre V. , Linari M. , Lucii L. , Lombardi V.
Published: May 2003

Generation of force and shortening in striated muscle is due to the cyclic interactions of the globular portion (the head) of the myosin molecule, extending from the thick filament, with the actin filament. The work produced in each interaction is due to a conformational change (the working stroke) driven by the hydrolysis of ATP on the catalytic site of the myosin head. However, the precise mechanism and the size of the force and length step generated in one interaction are still under question. Here we reinvestigate the endothermic nature of the force‐generating process by precisely determining, in tetanised intact frog muscle fibres under sarcomere length control, the effect of temperature on both isometric force and force response to length changes. We show that raising the temperature: (1) increases the force and the strain of the myosin heads attached in the isometric contraction by the same amount (∼70 %, from 2 to 17 °C); (2) increases the rate of quick force recovery following small length steps (range between −3 and 2 nm (half‐sarcomere)−1) with a Q10 (between 2 and 12 °C) of 1.9 (releases) and 2.3 (stretches); (3) does not affect the maximum extent of filament sliding accounted for by the working stroke in the attached heads (10 nm (half‐sarcomere)−1). These results indicate that in isometric conditions the structural change leading to force generation in the attached myosin heads can be modulated by temperature at the expense of the structural change responsible for the working stroke that drives filament sliding. The energy stored in the elasticity of the attached myosin heads at the plateau of the isometric tetanus increases with temperature, but even at high temperature this energy is only a fraction of the mechanical energy released by attached heads during filament sliding.
Impaired vasomodulation is associated with reduced neuronal nitric oxide synthase in skeletal muscle of ovariectomized rats
Authors: Fadel Paul J. , Zhao Weiying , Thomas Gail D.
Published: May 2003

In exercising skeletal muscle, vasoconstrictor responses to α‐adrenoceptor activation are attenuated in part by nitric oxide (NO) produced by the neuronal isoform of NO synthase (nNOS), which is expressed constitutively in skeletal muscle cells. In skeletal muscle of pregnant animals, nNOS mRNA is upregulated, suggesting that muscle nNOS expression is modulated by the steroid hormone oestrogen. Whether oestrogen‐induced changes in nNOS expression have measurable effects on vasoregulation in skeletal muscle is unknown. In this study, we hypothesized that oestrogen deficiency would reduce muscle nNOS expression, resulting in impaired modulation of sympathetic vasoconstriction in exercising skeletal muscle. Compared to gonadally intact rats, we found that ovariectomized (OVX) rats were characterized by greater sympathetic vasoconstriction in contracting hindlimb and reduced nNOS, but not eNOS, in skeletal muscle. In addition, NOS inhibition resulted in a greater enhancement of sympathetic vasoconstriction in contracting hindlimbs of intact compared to OVX rats. These effects of oestrogen deficiency were prevented by chronic treatment of OVX rats with 17β‐oestradiol, but not with chronic progesterone or acute oestradiol. Further analysis revealed that skeletal muscle nNOS correlated directly with plasma 17β‐oestradiol and inversely with the magnitude of sympathetic vasoconstrictor responses in contracting hindlimbs. These data indicate that NO‐dependent attenuation of sympathetic vasoconstriction in contracting skeletal muscle is impaired in oestrogen‐deficient female rats, and suggest that this impairment may be mediated by reduced skeletal muscle nNOS expression.
Acute regulation of the SLC26A3 congenital chloride diarrhoea anion exchanger (DRA) expressed in Xenopus oocytes
Authors: Chernova Marina N. , Jiang Lianwei , Shmukler Boris E. , Schweinfest Clifford W. , Blanco Paola , Freedman Steven D. , Stewart Andrew K. , Alper Seth L.
Published: May 2003

Mutations in the human SLC26A3 gene, also known as down‐regulated in adenoma (hDRA), cause autosomal recessive congenital chloride‐losing diarrhoea (CLD). hDRA expressed in Xenopus oocytes mediated bidirectional Cl−‐Cl− and Cl−‐HCO3− exchange. In contrast, transport of oxalate was low, and transport of sulfate and of butyrate was undetectable. Two CLD missense disease mutants of hDRA were nonfunctional in oocytes. Truncation of up to 44 C‐terminal amino acids from the putatively cytoplasmic C‐terminal hydrophilic domain left transport function unimpaired, but deletion of the adjacent STAS (sulfate transporter anti‐sigma factor antagonist) domain abolished function. hDRA‐mediated Cl− transport was insensitive to changing extracellular pH, but was inhibited by intracellular acidification and activated by NH4+ at acidifying concentrations. These regulatory responses did not require the presence of either hDRA's N‐terminal cytoplasmic tail or its 44 C‐terminal amino acids, but they did require more proximate residues of the C‐terminal cytoplasmic domain. Although only weakly sensitive to inhibition by stilbenes, hDRA was inhibited with two orders of magnitude greater potency by the anti‐inflammatory drugs niflumate and tenidap. cAMP‐insensitive Cl−‐HCO3− exchange mediated by hDRA gained modest cAMP sensitivity when co‐expressed with cystic fibrosis transmembrane conductance regulator (CFTR). Despite the absence of hDRA transcripts in human cell lines derived from CFTR patients, DRA mRNA was present at wild‐type levels in proximal colon and nearly so in the distal ileum of CFTR(‐/‐) mice. Thus, pharmacological modulation of DRA might be a useful adjunct treatment of cystic fibrosis.
Effect of the KCNQ potassium channel opener retigabine on single KCNQ2/3 channels expressed in CHO cells
Authors: Tatulian L. , Brown D. A.
Published: May 2003

KCNQ2/3 potassium channel subunits were co‐expressed in Chinese hamster ovary (CHO) cells and currents through single channels recorded using cell‐attached patches. Channels had a similar slope conductance in the presence (8.04 ± 0.02 pS) and absence (7.6 ± 0.01 pS) of 10 μm retigabine. The mean maximal open probability (Po) for single KCNQ2/3 channels was 0.13 ± 0.02, with a half‐maximal Po potential (Vo) of −28.7 ± 1.4 mV for control recordings. Retigabine increased mean maximal Po to 0.38 ± 0.04 and produced a hyperpolarising shift of Vo to −40.1 ± 3.4 mV. Single KCNQ2/3 channels have multiple voltage‐dependent kinetic components in their activity (CL‐OS‐CM‐OL‐CS; C = closed, O = open, L = long, S = short, M = medium), giving short, medium and long closed times (τCS, τCM, τCL) and short and long open times (τOS and τOL). In the presence of retigabine at 0 mV the combined duration and contributions of the longest closed time τCL decreased tenfold, while the short and long open times increased fourfold and twofold, respectively. Thus, steady‐state kinetics were modified to favour the open channel configuration.
Connections between respiratory neurones in the neonatal rat transverse medullary slice studied with cross‐correlation
Authors: Li Yan Mei , Shen Linlin , Peever John H. , Duffin James
Published: May 2003

In the transverse medullary slice prepared from neonatal rats the hypoglossal nerve rootlets exhibit a bursting ‘respiratory’ rhythm as do neurones in the pre‐Bötzinger complex (PBC). We used cross‐correlation analysis of the rhythmic multiunit discharges recorded from hypoglossal nerve rootlets, hypoglossal nucleus neurones and PBC neurones to investigate the connections between these groups. All cross‐correlograms computed between left and right hypoglossal nerves, and between hypoglossal neurones and contralateral hypoglossal nerves, displayed central peaks with broad half‐amplitude widths (mean ±s.d. of 29.6 ± 10.4 and 37.3 ± 6.0 ms, respectively), which we interpreted as evidence for activation from a common source. Five of the 18 cross‐correlograms computed between left and right PBC neurones displayed peaks either side of time zero with narrower half‐amplitude widths (mean ±s.d. of 9.3 ± 1.9 ms) superimposed on broader central peaks, which we interpreted as evidence for mutual excitation and common activation, respectively. Cross‐correlograms computed between PBC neurones and contralateral hypoglossal neurones or nerves did not display consistent features, but some of those computed between PBC and ipsilateral hypoglossal neurones (two of eight) or nerves (two of five) displayed peaks with broad half‐amplitude widths (mean ±s.d. of 36.8 ± 6.9 ms), offset from time zero by 6 ms (except for one at 18 ms), which we interpreted as evidence for excitation of hypoglossal neurones and motoneurones by PBC neurones. We concluded that rhythm is synchronised between left and right sides by mutual excitatory connections between left and right PBC neurones. The rhythm is transmitted to ipsilateral hypoglossal neurones by a paucisynaptic pathway. Both hypoglossal neurones and PBC neurones receive a common activation from as yet unidentified sources.
Development of nociceptive synaptic inputs to the neonatal rat dorsal horn: glutamate release by capsaicin and menthol
Authors: Baccei Mark L. , Bardoni Rita , Fitzgerald Maria
Published: May 2003

To study the postnatal development of nociceptive synaptic inputs in the superficial dorsal horn of the neonatal rat spinal cord, we examined the effect of capsaicin and menthol on glutamatergic mEPSCs in postnatal day (P) 0–1, P5–6 and P9–11 slices of spinal cord. Capsaicin (100 nm to 2 μm) increased the mEPSC frequency in a concentration‐dependent manner at all ages tested, with a significant enhancement of the effect between P5 and P10. This effect was sensitive to vanilloid receptor (VR) antagonists. The elevation in mEPSC frequency occurred at concentrations of capsaicin (100 nm) that did not alter the distribution of mEPSC amplitudes and was abolished by a dorsal rhizotomy, demonstrating that capsaicin acts via presynaptic VR1 receptors localized on primary afferents. Menthol significantly increased the mEPSC frequency with a similar developmental pattern to capsaicin without consistently affecting mEPSC amplitude. The increase in mEPSC frequency following capsaicin did not depend on transmembrane calcium influx since it persisted in zero [Ca2+]o. The facilitation of spontaneous glutamate release by capsaicin was sufficient to evoke action potentials in neonatal dorsal horn neurons but was accompanied by a block of EPSCs evoked by electrical stimulation of the dorsal root. These results indicate that VR1‐expressing nociceptive primary afferents form functional synaptic connections in the superficial dorsal horn from birth and that activation of the VR1 receptor increases spontaneous glutamate release via an undetermined mechanism. In addition, the data suggest that immature primary afferents express functional menthol receptors that are capable of modulating transmitter release. These results have important functional implications for infant pain processing.
Characteristics of 24 h Telemetered Blood Pressure in eNOS‐Knockout and C57Bl/6J Control Mice
Authors: Van Vliet Bruce N. , Chafe Linda L. , Montani Jean‐Pierre
Published: May 2003

The purpose of the present study was to characterize in detail the 24 h blood pressure (BP) phenotype of mice lacking the gene for endothelial nitric oxide synthase (eNOS−/−) and the corresponding control strain (C57Bl/6J). Twenty‐four hour BP recordings were made in conscious 12‐ to 16‐week‐old male mice 10 days following the implantation of a BP telemeter (n= 9 per group). The BP and heart rate of both strains were markedly affected by brief locomotor activity cycles, resulting in bimodal distributions of BP and heart rate within both light and dark periods. Data from active periods were associated with the higher of the two modes, whereas data from inactive periods were associated with the lower of the two modes. In eNOS−/− mice, the 24 h average BP level was significantly elevated (+15 %, 104 ± 2 vs. 119 ± 1 mmHg), as was its daily range (+44 %), its coefficient of variation (+26 %), dark‐light difference (+48 %), and the separation of the two modes of its distribution (+41 %). Pulse pressure was also significantly greater (+23 %) in eNOS−/− mice. The 24 h heart rate level did not differ between control and eNOS−/− mice. Considerable variation was noted among previously published values of BP in eNOS−/− mice, but not in the corresponding control mice. Our results indicate that eNOS−/− mice have mild hypertension that is accompanied by more pronounced increases in BP lability and/or reactivity. Our results also demonstrate a marked effect of locomotor activity on BP in mice, which may confound short‐term measurements of BP.
Applications of the GapSpace Model for Multidimensional Mechanical Assemblies
Authors: Zou Zhihua , Morse Edward P.
Published: May 2003

The most fundamental, and perhaps most important, task in the tolerance analysis of assemblies is to test whether or not the components with tolerances are actually able to fit together (called assembleability). Another important task of tolerance analysis is to check how the tolerances affect the quality or functionality of a product when they are assembled together. This paper presents the way the tolerance analyses are implemented by an assembly model, called the GapSpace model. The model can not only capture the necessary and sufficient conditions for assembleability analysis, but also transfers the functionality into the modeling variables (gaps). The assembleability analyses based on the GapSpace model for nominal components and those with worst case or statistical tolerances are introduced through an example. The problems of testing the quality of assemblies and calculating sensitivities are solved quickly and precisely using the model. The GapSpace model is more suitable for certain GD&T tolerancing methods than for parametric plus/minus tolerancing.
3D Transfer of Tolerances Using a SDT Approach: Application to Turning Process
Authors: Vignat Fre´de´ric , Villeneuve Franc¸ois
Published: May 2003

The following paper aims to apply the concept of the small displacements torsor (SDT) in order to predict the defects of a part resulting in successive machining set-up. The proposition is to enlarge the 1D dispersion method to a 3D analysis of the feasibility of a machined part. This paper follows our previous works on the development of a method using this concept to simulate a manufacturing process. These developments are adapted to the turning process and its particularities. The relevant parameters allowing to describe the manufacturing and positioning defects are determined. These defects are analyzed with regards to the functional specifications of a part.
Computer Aided Tolerancing Using Positioning Features
Authors: Anselmetti Bernard , Mawussi Kwamivi
Published: May 2003

The quality of the interfaces between parts ensures the assembly requirements of a mechanism and the right positioning of functional surfaces. When defining a mechanism, a designer analyzes the failures generated by the geometrical defects of the junction surfaces between the parts. To formalize the design intents clearly, the method proposed, named TLIC, uses positioning tables of the parts to clearly indicate the set up surfaces associated as features and the preponderance order of the features. The requirements of assembly between parts and the tolerancing of the interfaces can then be generated automatically by defining the reference systems.
Reconstruction of Virtual Parts from Unorganized Scanned Data for Automated Dimensional Inspection
Authors: Kuo Chuan-Chu , Yau Hong-Tzong
Published: May 2003

In the framework of Virtual CMM [1], virtual parts are proposed to be constructed as triangulated surface models. This paper presents a novel surface reconstruction method to the creation of virtual parts. It is based on the idea of identification and sculpting of concave regions of a Delaunay triangulation of the sample data. The proposed algorithm is capable of handling the reconstruction of surfaces with or without boundaries from unorganized points. Comparisons with other Delaunay-based algorithms show that it is more efficient in that it can optimally adapt to the geometric complexity of the sampled object. To validate the proposed algorithm, some detailed illustrations are given.
Computer Modeling of Geometric Variations in Mechanical Parts and Assemblies
Authors: Wu, Yanyan , Shah Jami J. , Davidson Joseph K.
Published: May 2003

This paper reports on part of a project related to the development of a computer model for GD&T (Geometric Dimensioning and Tolerancing) to support tolerance specification, validation and tolerance analysis. The paper examines the basic elements involved in geometric variation and their interrelations. Logical tolerance classes are defined in terms of a target, a datum reference frame, and metric relations. ASME Y14.5 tolerance classes are mapped to these logical classes. The development of a data model for GD&T and its application in supporting design specification, validation, and tolerance analysis are discussed.
A Survey of Mathematical Methods for the Construction of Geometric Tolerance Zones
Authors: Kethara Pasupathy T. M. , Morse Edward P. , Wilhelm Robert G.
Published: May 2003

The physical realization of any part always yields imperfect forms with respect to the ideal geometry specified in the engineering design. To describe and preserve functional requirements of design, the allowable variation is specified using modern geometric tolerances via tolerance zones. Specification using geometric tolerances is intended for unambiguous communication. Mathematically unambiguous specification is required for the application of computing machinery across manufacturing enterprises to lower costs and improve efficiency. Several computer-based tools have been developed to aid in tolerance specification and also in subsequent processing, or applications that utilize tolerance specification information, such as analysis, synthesis, manufacture and measurement. In order to execute these activities, the tolerance zones have to be unambiguously captured by computer programs. The geometric tolerance specification is complex and not completely free of ambiguities. These difficulties pose as challenges in realizing the tolerance zones and limit the applicability of any particular method developed so far. This paper presents a survey of the current computer based methods available to capture tolerance zones of parts. The limitations of the methods are analyzed based on the following criteria: the range of applicability, compatibility with standards, ease in realization and the effects of singularities in shapes that are application specific. Various assembly analysis techniques that utilize the tolerance zone construction and other recent approaches for tolerance design are also reported.
Wave packet construction in two-dimensional quantum billiards: Blueprints for the square, equilateral triangle, and circular cases
Authors: Doncheski M. A. , Heppelmann S. , Robinett R. W. , Tussey D. C.
Published: May 2003

We present quasianalytical and numerical calculations of Gaussian wave packet solutions of the Schrödinger equation for two-dimensional infinite well and quantum billiard problems with equilateral triangle, square, and circular footprints. These cases correspond to N=3, N=4, and N→∞ regular polygonal billiards and infinite wells, respectively. In each case the energy eigenvalues and wave functions are given in terms of familiar special functions. For the first two systems, we obtain closed form expressions for the expansion coefficients for localized Gaussian wave packets in terms of the eigenstates of the particular geometry. For the circular case, we discuss numerical approaches. We use these results to discuss the short-time, quasiclassical evolution in these geometries and the structure of wave packet revivals. We also show how related half-well problems can be easily solved in each of the three cases.
On coupled mechanical harmonic oscillators, transients, and isolated oscillating systems
Authors: McCarthy Lance
Published: May 2003

Experimental results for the transient response of a single oscillator, for two magnetically coupled oscillators, and for oscillations about the center of mass of an isolated system are presented. The apparatus is easy to build. The data for the response and for the forcing term are acquired in a simple way, and allow accurate analysis and comparison with theory.
Measuring Boltzmann’s constant using video microscopy of Brownian motion
Authors: Nakroshis Paul , Amoroso Matthew , Legere Jason , Smith Christian
Published: May 2003

Boltzmann’s constant k was measured by observing the Brownian motion of polystyrene spheres in water. An inexpensive monochrome CCD camera and video card were used to create a video of the spheres’ motion. After preprocessing the images, custom routines were used to examine the video and to identify and track the particles from one frame to the next. From the mean squared displacement of the particles versus time, we extracted the value of k from the slope, assuming that the drag force on an individual sphere is well modeled by Stokes’ law. By averaging over 107 particles, we obtained k=(1.415±0.04)×10−23 J/K.
Mathematics and the science of analogies
Authors: Pask Colin
Published: May 2003

Analogies have been used to great effect in the physical sciences. A brief review is given of the relevant points about the role of mathematics in physics and a simple framework in which analogies are viewed in terms of mechanism and descriptive, usually mathematical, components. The main body of the paper analyzes cases, principally in wave theory and electromagnetism, to emphasize three points: the importance of the mathematical description component in powerful analogies; the possibly destructive aspect of the mechanism component of analogies; and the underlying reasons for the choice of particular analogies.
Almost-periodic wave packets and wave packets of invariant shape
Authors: Mentrup Detlef , Luban Marshall
Published: May 2003

Wave packets of one-dimensional, single-particle quantum systems exhibit a rich diversity of dynamical behavior. We focus on confining potentials where the entire energy spectrum is discrete so that wave packets do not spread indefinitely with time and instead exhibit characteristics of almost-periodic functions. For the harmonic oscillator, for which all wave packets are necessarily strictly periodic, Senitzky has shown that is possible to construct an infinite class of normalized wave packets that maintain a fixed shape while oscillating sinusoidally with time. We present two alternate and instructive methods for deriving this result using coherent states and the displacement operator.
Tracing a planet’s orbit with a straight edge and a compass with the help of the hodograph and the Hamilton vector
Authors: Guillaumı́n-España E. , Salas-Brito A. L. , Núñez-Yépez H. N.
Published: May 2003

We describe a geometrical method for tracing a planet’s orbit using its velocity hodograph, that is, the path of the planet’s velocity. The method requires only a straight edge, a compass, and the help of the hodograph. We also obtain analytically the hodograph and some of the features of the motion that can be obtained from it.
The effects of an interactive computer-based simulation prior to performing a laboratory inquiry-based experiment on students’ conceptual understanding of physics
Authors: Zacharia Zacharias , Anderson O. Roger
Published: May 2003

We investigate the effects of interactive computer-based simulations which are presented prior to inquiry-based laboratory experiments on students’ conceptual understanding of mechanics, waves/optics, and thermal physics. In principle, the simulations should serve as a cognitive framework for enhancing the subsequent more open-ended inquiry learning in the subject matter domain of the experiments. To test this prediction, the simulations and experiments were integrated into a one semester class for prospective physics teachers who served as students in the study. Semi-structured interviews were used to assess their ability to make correct predictions about the phenomenon in the experiments before using the latter and give correct explanations of the discrepancies between their predictions and their following observations. Conceptual tests were presented to assess conceptual understandings of each topic. Our results indicate that the use of the simulations improved the students’ ability to make acceptable predictions and explanations of the phenomena in the experiments. The use of simulations also fostered a significant conceptual change in the physics content areas that were studied.
A study of the nature of students’ models of microscopic processes in the context of modern physics experiments
Authors: Thacker Beth Ann
Published: May 2003

University students in modern physics classes were interviewed on their understanding of three fundamental experiments to gain information on their development of models of microscopic processes. In addition, interactive demonstrations were used to probe student understanding of modern physics experiments in two high school physics classes. The nature of the students’ models and the type of information that they used to build a model, both before and after instruction, were analyzed.
Slip Partitioning by Elastoplastic Propagation of Oblique Slip at Depth
Authors: Bowman David , King Geoffrey , Tapponnier Paul
Published: May 2003

Oblique motion along tectonic boundaries is commonly partitioned into slip on faults with different senses of motion. The origin of slip partitioning is important to structural geology, tectonophysics, and earthquake mechanics. Partitioning can be explained by the upward elastoplastic propagation of oblique slip from a fault or shear zone at depth. The strain field ahead of the propagating fault separates into zones of predominantly normal, reverse, and strike-slip faulting. The model successfully predicts the distribution of fault types along parts of the San Andreas and Haiyuan faults.
Tumor Response to Radiotherapy Regulated by Endothelial Cell Apoptosis
Authors: Garcia-Barros Monica , Paris Francois , Cordon-Cardo Carlos , Lyden David , Rafii Shahin , Haimovitz-Friedman Adriana , Fuks Zvi , Kolesnick Richard
Published: May 2003

About 50% of cancer patients receive radiation therapy. Here we investigated the hypothesis that tumor response to radiation is determined not only by tumor cell phenotype but also by microvascular sensitivity. MCA/129 fibrosarcomas and B16F1 melanomas grown in apoptosis-resistant
acid sphingomyelinase
(
asmase
)–deficient or
Bax
-deficient mice displayed markedly reduced baseline microvascular endothelial apoptosis and grew 200 to 400% faster than tumors on wild-type microvasculature. Thus, endothelial apoptosis is a homeostatic factor regulating angiogenesis-dependent tumor growth. Moreover, these tumors exhibited reduced endothelial apoptosis upon irradiation and, unlike tumors in wild-type mice, they were resistant to single-dose radiation up to 20 grays (Gy). These studies indicate that microvascular damage regulates tumor cell response to radiation at the clinically relevant dose range.
Giant Magnetic Anisotropy of Single Cobalt Atoms and Nanoparticles
Authors: Gambardella P. , Rusponi S. , Veronese M. , Dhesi S. S. , Grazioli C. , Dallmeyer A. , Cabria I. , Zeller R. , Dederichs P. H. , Kern K. , Carbone C. , Brune H.
Published: May 2003

The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.
Local Selection and Latitudinal Variation in a Marine Predator-Prey Interaction
Authors: Sanford Eric , Roth Melissa S. , Johns Glenn C. , Wares John P. , Somero George N.
Published: May 2003

Although pairs of species often interact over broad geographic ranges, few studies have explored how interactions vary across these large spatial scales. Surveys along 1500 kilometers of the Pacific coast of North America documented marked variation in the frequency of predation by the snail
Nucella canaliculata
on the intertidal mussel
Mytilus californianus
. Laboratory rearing experiments suggest that regional differences in drilling behavior have a genetic basis, and mitochondrial sequence variation confirms that gene flow is low among these snail populations. Marine communities separated by hundreds of kilometers may have intrinsically different dynamics, with interactions shaped by restricted gene flow and spatially varying selection.
Formation of a Black Hole in the Dark
Authors: Mirabel I. Félix , Rodrigues Irapuan
Published: May 2003

We show that the black hole in the x-ray binary Cygnus X-1 was formed in situ and did not receive an energetic trigger from a nearby supernova. The progenitor of the black hole had an initial mass greater than 40solar masses, and during the collapse to form the ∼10–solar mass black hole of Cygnus X-1, the upper limit for the mass that could have been suddenly ejected is ∼1 solar mass, much less than the mass ejected in a supernova. The observations suggest that high-mass stellar black holes may form promptly, when massive stars disappear silently.
Catalysis of Ribosomal Translocation by Sparsomycin
Authors: Fredrick Kurt , Noller Harry F.
Published: May 2003

During protein synthesis, transfer RNAs (tRNAs) are translocated from the aminoacyl to peptidyl to exit sites of the ribosome, coupled to the movement of messenger RNA (mRNA), in a reaction catalyzed by elongation factor G (EF-G) and guanosine triphosphate (GTP). Here, we show that the peptidyl transferase inhibitor sparsomycin triggers accurate translocation in vitro in the absence of EF-G and GTP. Our results provide evidence that translocation is a function inherent to the ribosome and that the energy to drive this process is stored in the tRNA-mRNA-ribosome complex after peptide-bond formation. These findings directly implicate the peptidyl transferase center of the 50S subunit in the mechanism of translocation, a process involving large-scale movement of tRNA and mRNA in the 30S subunit, some 70 angstroms away.
Sizing Up Democratic Systems
Authors: Orszag Peter R.
Published: May 2003

Rich Democracies
Political Economy, Public Policy, and Performance. Harold L. Wilensky. University of California Press, Berkeley, 2002. 923 pp. $85. ISBN 0-520-23176-7. Paper, $45. ISBN 0-520-23279-8.

Capping some 30 years of comparative research, Wilensky addresses the question of what taxing, spending, and public policies mean for the well-being of people.
Selection of Small-Colony Variants of
Salmonella enterica
Serovar Typhimurium in Nonphagocytic Eucaryotic Cells
Authors: Cano David A. , Pucciarelli M. Graciela , Martínez-Moya Marina , Casadesús Josep , García-del Portillo Francisco
Published: June 2003

Salmonella enterica
strains are enteropathogenic bacteria that survive and proliferate within vacuolar compartments of epithelial and phagocytic cells. Recently, it has been reported that fibroblast cells are capable of restricting
S. enterica
serovar Typhimurium intracellular growth. Here, we show that prolonged residence of bacteria in the intracellular environment of fibroblasts results in the appearance of genetically stable small-colony variants (SCV). A total of 103 SCV isolates, obtained from four independent infections, were subjected to phenotypic analysis. The following phenotypes were observed: (i) δ-aminolevulinic acid auxotrophy; (ii) requirement for acetate or succinate for growth in glucose minimal medium; (iii) auxotrophy for aromatic amino acids; and (iv) reduced growth rate under aerobic conditions not linked to nutrient auxotrophy. The exact mutations responsible for the SCV phenotype in three representative isolates were mapped in the
lpd
,
hemL
, and
aroD
genes, which code for dihydrolipoamide dehydrogenase, glutamate-1-semyaldehyde aminotransferase, and 3-dehydroquinate dehydratase, respectively. The
lpd
,
hemL
, and
aroD
mutants had intracellular persistence rates in fibroblasts that were 3 to 4 logs higher than that of the parental strain and decreased susceptibility to aminoglycoside antibiotics. All three of these SCV isolates were attenuated in the BALB/c murine typhoid model. Complementation with

lpd
+

,

hem
+

, and

aroD
+

genes restored the levels of intracellular persistence and antibiotic susceptibility to levels of the wild-type strain. However, virulence was not exhibited by any of the complemented strains. Altogether, our data demonstrate that similar to what it has been reported for SCV isolates of other pathogens,
S. enterica
SCV display enhanced intracellular persistence in eucaryotic cells and are impaired in the ability to cause overt disease. In addition, they also suggest that
S. enterica
SCV may be favored in vivo.
Variable Lipoprotein Genes of
Mycoplasma agalactiae
Are Activated In Vivo by Promoter Addition via Site-Specific DNA Inversions
Authors: Flitman-Tene Ravenna , Mudahi-Orenstein Sigalit , Levisohn Sharon , Yogev David
Published: June 2003

Mycoplasma agalactiae
, the etiological agent of contagious agalactia of small ruminants, has a family of related genes (
avg
genes) which encode surface lipoprotein antigens that undergo phase variation. A series of 13
M. agalactiae
clonal isolates, obtained from one chronically infected animal over a period of 7 months, were found to undergo major rearrangement events within the
avg
genomic locus. We show that these rearrangements regulate the phase-variable expression of individual
avg
genes. Northern blot analysis and reverse transcription-PCR showed that only one
avg
gene is transcribed, while the other
avg
genes are transcriptionally silent. Sequence analysis and primer extension experiments with two
M. agalactiae
clonal isolates showed that a specific 182-bp
avg
5′ upstream region (
avg
-B
2
) that is present as a single chromosomal copy serves as an active promoter and exhibits a high level of homology with the
vsp
promoter of the bovine pathogen
Mycoplasma bovis
. PCR analysis showed that each
avg
gene is associated with the
avg
-B
2
promoter in a subpopulation of cells that is present in each subclone. Multiple sequence-specific sites for DNA recombination (
vis-
like), which are presumably recognized by site-specific recombinase, were identified within the conserved
avg
5′ upstream regions of all
avg
genes and were found to be identical to the recombination sites of the
M. bovis vsp
locus. In addition, a gene encoding a member of the integrase family of tyrosine site-specific recombinases was identified adjacent to the variable
avg
locus. The molecular genetic basis for
avg
phase-variable expression appears to be mediated by site-specific DNA inversions occurring in vivo that allow activation of a silent
avg
gene by promoter addition. A model for the control of
avg
genes is proposed.