bluuebunny/crossref_metadata_2025 huggingface dataset:
The Developmental Course of Personal Authority in the Family System
Authors: Lawson David M. , Brossart Daniel F.
Published: August 2004

The present study examined the differences in participants' intergenerational family relationships across the following three age/stage groups based onWilliamson's (1991)theory of Personal Authority in the Family System (PAFS) and adult developmental theory (Levinson, 1986): ages 18–23, 24–29, and 30–45. The most noteworthy variables were intergenerational intimacy and intimidation with mothers and fathers, with significant but less contribution by intergenerational triangulation with fathers. Results indicated that each successively older group reported significantly less intimacy and less intimidation with each parent, and less triangulation with fathers than the previous younger group. Small gender differences were also present, but without an interaction with age/stage groups. Females reported slightly healthier intergenerational relationships with parents than did males. Finally, implications for clinical practice are presented.
Recapture after exocytosis causes differential retention of protein in granules of bovine chromaffin cells
Authors: Perrais David , Kleppe Ingo C. , Taraska Justin W. , Almers Wolfhard
Published: August 2004

After exocytosis, chromaffin granules release essentially all their catecholamines in small fractions of a second, but it is unknown how fast they release stored peptides and proteins. Here we compare the exocytic release of fluorescently labelled neuropeptide Y (NPY) and tissue plasminogen activator from single granules. Exocytosis was tracked by measuring the membrane capacitance, and single granules in live cells were imaged by evanescent field microscopy. Neuropeptide Y left most granules in small fractions of a second, while tissue plasminogen activator remained in open granules for minutes. Taking advantage of the dependence on pH of the fluorescence of green fluorescent protein, we used rhythmic external acidification to determine whether and when granules re‐sealed. One‐third of them re‐sealed within 100 s and retained significant levels of tissue plasminogen activator. Re‐sealing accounts for only a fraction of the endocytosis monitored in capacitance measurements. When external [Ca2+] was raised, even neuropeptide Y remained in open granules until they re‐sealed. It is concluded that a significant fraction of chromaffin granules re‐seal after exocytosis, and retain those proteins that leave granules slowly. We suggest that granules vary the stoichiometry of release by varying both granule re‐sealing and the association of proteins with the granule matrix.
External Ca2+‐dependent excitation–contraction coupling in a population of ageing mouse skeletal muscle fibres
Authors: Payne Anthony Michael , Zheng Zhenlin , González Estela , Wang Zhong‐Min , Messi María Laura , Delbono Osvaldo
Published: August 2004

In the present work, we investigate whether changes in excitation–contraction (EC) coupling mode occur in skeletal muscles from ageing mammals by examining the dependence of EC coupling on extracellular Ca2+. Single intact muscle fibres from flexor digitorum brevis muscles from young (2–6 months) and old (23–30 months) mice were subjected to tetanic contractile protocols in the presence and absence of external Ca2+. Contractile experiments in the absence of external Ca2+ show that about half of muscle fibres from old mice are dependent upon external Ca2+ for maintaining maximal tetanic force output, while young fibres are not. Decreased force in the absence of external Ca2+ was not due to changes in charge movement as revealed by whole‐cell patch‐clamp experiments. Ca2+ transients, measured by fluo‐4 fluorescence, declined in voltage‐clamped fibres from old mice in the absence of external Ca2+. Similarly, Ca2+ transients declined in parallel with tetanic contractile force in single intact fibres. Examination of inward Ca2+ current and of mRNA and protein assays suggest that these changes in EC coupling mode are not due to shifts in dihydropyridine receptor (DHPR) and/or ryanodine receptor (RyR) isoforms. These results indicate that a change in EC coupling mode occurs in a population of fibres in ageing skeletal muscle, and is responsible for the age‐related dependence on extracellular Ca2+.
Tetanic depression is overcome by tonic adenosine A2A receptor facilitation of L‐type Ca2+ influx into rat motor nerve terminals
Authors: Oliveira Laura , Timóteo M. Alexandrina , Correia‐de‐Sá Paulo
Published: August 2004

Motor nerve terminals possess multiple voltage‐sensitive calcium channels operating acetylcholine (ACh) release. In this study, we investigated whether facilitation of neuromuscular transmission by adenosine generated during neuronal firing was operated by Ca2+ influx via ‘prevalent’ P‐type or via the recruitment of ‘silent’ L‐type channels. The release of [3H]ACh from rat phrenic nerve endings decreased upon increasing the stimulation frequency of the trains (750 pulses) from 5 Hz (83 ± 4 × 103 disintegrations per minute per gram (d.p.m. g−1); n= 11) to 50 Hz (30 ± 3 × 103 d.p.m. g−1; n= 5). The P‐type Ca2+ channel blocker, ω‐agatoxin IVA (100 nm) reduced (by 40 ± 10%; n= 6) the release of [3H]ACh evoked by 50‐Hz trains, while nifedipine (1 μm, an L‐type blocker) was inactive. Tetanic depression was overcome (88 ± 6 × 103 d.p.m. g−1; n= 12) by stimulating the phrenic nerve with 50‐Hz bursts (five bursts of 150 pulses, 20 s interburst interval). In these conditions, ω‐agatoxin IVA (100 nm) failed to affect transmitter release, but nifedipine (1 μm) decreased [3H]ACh release by 21 ± 7% (n= 4). Inactivation of endogenous adenosine with adenosine deaminase (ADA, 0.5 U ml−1) reduced (by 54 ± 8%, n= 5) the release of [3H]ACh evoked with 50‐Hz bursts. This effect was opposite to the excitatory actions of adenosine (0.5 mm), S‐(p‐nitrobenzyl)‐6‐thioinosine (5 μm, an adenosine uptake blocker) and CGS 21680C (3 nm, a selective A2A receptor agonist); as the A1 receptor agonist R‐N6‐phenylisopropyl adenosine (R‐PIA, 300 nm) failed to affect the release of [3H]ACh, the results indicate that adenosine generated during 50‐Hz bursts exerts an A2A‐receptor‐mediated tonus. The effects of ADA (0.5 U ml−1) and CGS 21680C (3 nm) were prevented by nifedipine (1 μm). Blocking tonic A2A receptor activation, with ADA (0.5 U ml−1) or 3,7‐dimethyl‐1‐propargyl xanthine (10 μm, an A2A antagonist), recovered ω‐agatoxin IVA (100 nm) inhibition and caused the loss of function of nifedipine (1 μm). Data indicate that, in addition to the predominant P‐type Ca2+ current triggering ACh release during brief tetanic trains, motoneurones possess L‐type channels that may be recruited to facilitate transmitter release during high‐frequency bursts. The fine‐tuning control of Ca2+ influx through P‐ or L‐type channels is likely to be mediated by endogenous adenosine. Therefore, tonic activation of presynaptic A2A receptors operating Ca2+ influx via L‐type channels may contribute to overcome tetanic depression during neuronal firing.
Albumin transcytosis across the epithelium of the lactating mouse mammary gland
Authors: Monks Jenifer , Neville Margaret C.
Published: August 2004

Murine milk contains 18 mg ml−1 serum albumin, a concentration equal to that in the serum of the lactating mouse. We examined cellular transport using in vivo methods in the mouse. At steady state the specific activity of 125I‐albumin injected into the blood stream was equal in plasma and whey, confirming that milk albumin is extra‐mammary in origin. Fluorescent albumin crossed the gland from basolateral surface to lumen via cytoplasmic vesicles, but was not transported in the apical to basal direction. Albumin was segregated from transferrin at the basal surface of the epithelial cells and did not colocalize with either caveolin‐1 or ‐2. Vesicular transport was not disrupted by filipin providing additional evidence that, unlike the vascular endothelium, caveoli are not involved. Cytoplasmic albumin was localized to vesicles containing IgA and transport was disrupted by agents that interfere with clathrin‐mediated endocytosis. Together, these findings provide evidence that albumin is transported across the mammary epithelium by the same pathway as immunoglobulin. The possibility that the massive transfer of albumin into mouse milk is mediated by fluid phase transport is considered.
Electrophysiological mapping of the nociceptive inputs to the substantia gelatinosa in rat horizontal spinal cord slices
Authors: Kato Go , Furue Hidemasa , Katafuchi Toshihiko , Yasaka Toshiharu , Iwamoto Yukihide , Yoshimura Megumu
Published: August 2004

To study the functional projection patterns of the primary afferents in the spinal cord, the postsynaptic responses of substantia gelatinosa (SG) neurones evoked by L5 dorsal root stimulation (DRS) were examined from the neurones located at L2 to S1 in horizontal slices of the adult rat spinal cord using a blind whole‐cell patch‐clamp technique. In the voltage‐clamp mode, the L5 DRS evoked the Aδ‐ and C‐afferent‐mediated excitatory postsynaptic currents (EPSCs) in more than 70% of the neurones tested at the L5 level. Both Aδ‐ and C‐afferent EPSCs were also recorded in more than 50% of the neurones at L4. At L3 and L6, the number of neurones receiving the C‐afferent EPSCs (> 40%) was significantly greater than that of Aδ‐afferent EPSCs (< 20%). On the other hand, the Aδ‐ and C‐afferent‐mediated inhibitory postsynaptic currents (IPSCs) elicited by L5 DRS were almost equally observed from L2 to S1. In the current‐clamp mode, L5 DRS evoked Aδ‐ and C‐afferent‐mediated EPSPs, some of which initiated action potentials (APs). Most of the Aδ‐afferent‐mediated APs were limited at the L5 level, while C‐afferent‐mediated APs were observed at L5 and L4. As the L2 DRS‐evoked APs in the L2 SG neurones were suppressed by L5 DRS, the widespread distribution of the inhibitory inputs was considered to be functional. These findings suggest that the excitatory projection of the C afferents to the SG neurones was thus spread more rostrocaudally than that of the Aδ afferents, thereby contributing to more diffuse pain transmission. In addition, the widespread distribution of the inhibitory inputs may thus play a role as a lateral inhibitory network and thereby prevent the expansion of the excitatory inputs of noxious stimuli.
Persistent abnormalities of membrane excitability in regenerated mature motor axons in cat
Authors: Moldovan Mihai , Krarup Christian
Published: August 2004

The purpose of our study was to assess by threshold tracking internodal and nodal membrane excitability during the maturation process after tibial nerve crush in cat. Various excitability indices (EI) were computed non‐invasively by comparing the threshold of a submaximal compound motor potential at different stimulation durations (strength–duration relationship), after a conditioning nerve impulse (recovery of excitability), or during the application of a polarizing current (threshold electrotonus). Four months after the lesion, regenerated nerves showed a higher rheobase, shorter chronaxie, shorter refractory period and higher than normal threshold variations during threshold electrotonus (TE). A partial recovery was observed during the first 2 years of maturation. The recovery to depolarizing TE seemed complete but all other EI remained abnormal even after 5 years of regeneration, the most pronounced being the 157 ± 8% (mean ±S.E.M.) increase in threshold during hyperpolarizing TE compared with 94 ± 4% in controls. These EI abnormalities are consistent with increased input impedance. Nevertheless, the time course of maturation and incomplete recovery of EI could only be partially explained by changes in fibre morphology. The highly abnormal response to hyperpolarizing but not to depolarizing TE suggests that voltage‐dependent membrane function also remained abnormal, possibly due to membrane hyperpolarization.
Differential effect of bicycling exercise intensity on activity and phosphorylation of atypical protein kinase C and extracellular signal‐regulated protein kinase in skeletal muscle
Authors: Richter Erik A. , Vistisen Bodil , Maarbjerg Stine J. , Sajan Mini , Farese Robert V. , Kiens Bente
Published: August 2004

Atypical protein kinase C (aPKC) and extracellular signal‐regulated kinase (ERK) are emerging as important signalling molecules in the regulation of metabolism and gene expression in skeletal muscle. Exercise is known to increase activity of aPKC and ERK in skeletal muscle but the effect of exercise intensity hereon has not been studied. Furthermore, the relationship between activity and phosphorylation of the two enzymes during exercise is unknown. Nine healthy young men exercised for 30 min on a bicycle ergometer on two occasions. One occasion consisted of three consecutive 10 min bouts of 35, 60 and 85% of peak pulmonary oxygen uptake and the second of one 30 min bout at 35% of . Both trials also included 30 min recovery. Muscle biopsies were obtained from the vastus lateralis muscle before and after each exercise bout. Exercise increased muscle aPKC activity at 35%, whereupon no further increase was observed at higher exercise intensities. Activation of aPKC was not accompanied by increased phosphorylation of aPKC Thr410/403. ERK1/2 activity increased in a similar pattern to aPKC, reaching maximal activity at 35%, whereas ERK1 Thr202/Tyr204 and ERK2 Thr183/Tyr185 phosphorylation increased with increasing exercise intensity. Thus, aPKC and ERK1/2 activity in muscle during exercise did not correspond to phosphorylation of sites on aPKC or ERK1/2, respectively, which are considered important for their activation. It is concluded that assessment of aPKC and ERK1/2 activity in muscle using phosphospecific antibodies did not reflect direct activity measurements on immunoprecipitated enzyme in vitro. Thus, estimation of enzyme activity during exercise by use of phosphospecific antibodies should not be performed uncritically. In addition, increase in muscle activity of aPKC or ERK1/2 during exercise is not closely related to energy demands of the muscle but may serve other regulatory or permissive functions in muscle.
Spontaneous, synchronous electrical activity in neonatal mouse cortical neurones
Authors: Corlew Rebekah , Bosma Martha M. , Moody William J.
Published: August 2004

Spontaneous [Ca2+]i transients were measured in the mouse neocortex from embryonic day 16 (E16) to postnatal day 6 (P6). On the day of birth (P0), cortical neurones generated widespread, highly synchronous [Ca2+]i transients over large areas. On average, 52% of neurones participated in these transients, and in 20% of slices, an average of 80% participated. These transients were blocked by TTX and nifedipine, indicating that they resulted from Ca2+ influx during electrical activity, and occurred at a mean frequency of 0.91 min−1. The occurrence of this activity was highly centred at P0: at E16 and P2 an average of only 15% and 24% of neurones, respectively, participated in synchronous transients, and they occurred at much lower frequencies at both E16 and P2 than at P0. The overall frequency of [Ca2+]i transients in individual cells did not change between E16 and P2, just the degree of their synchronicity. The onset of this spontaneous, synchronous activity correlated with a large increase in Na+ current density that occurred just before P0, and its cessation with a large decrease in resting resistance that occurred just after P2. This widespread, synchronous activity may serve a variety of functions in the neonatal nervous system.
Inhibitory regulation of constitutive transient receptor potential‐like cation channels in rabbit ear artery myocytes
Authors: Albert A. P. , Large W. A.
Published: August 2004

In the present study we have investigated an inhibitory pathway regulating a constitutively active Ca2+‐permeable non‐selective cation conductance (Icat) in rabbit ear artery smooth muscle cells. Constitutive single channel activity of Icat was recorded in cell‐attached and inside‐out patches with similar unitary conductance values. In inside‐out patches with relatively high constitutive activity the G‐protein activator GTPγS inhibited channel activity which was reversed by the protein kinase C (PKC) inhibitor chelerythrine indicating a G‐protein pathway inhibits channel activity via PKC. Spontaneous channel activity was also suppressed by the G‐protein inhibitor GDPβS suggesting a G‐protein is also involved in initiation of constitutive channel activity. Bath application of antibodies to Gαq/Gα11 enhanced channel activity whereas anti‐Gα1−3/Gαo antibodies decreased basal channel activity which suggests that Gαq/Gα11 and Gαι/Gαo proteins initiate, respectively, the inhibitory and excitatory cascades. The phospholipase C (PLC) inhibitor U73122 increased spontaneous activity which implies a role for PLC in the inhibitory pathway. Bath application of the diacylycerol (DAG) analogue 1‐oeoyl‐2‐acetyl‐sn‐glycerol (OAG) decreased the probability of channel opening (NPo) and this was reversed by chelerythrine. Application of the PKC activator phorbol 12, 13‐dibutyrate (PDBu) and chelerythrine, respectively, decreased and increased NPo. These data indicate that spontaneously active cation channels are inhibited by a tonic inhibitory pathway involving Gαq/Gα11‐mediated stimulation of PLC to generate DAG which activates PKC to inhibit channel opening. There were some patches with relatively low NPo and it was evident that the inhibitory pathway was particularly marked in these cases. Moreover in the latter patches GTPγS and OAG caused marked increases in NPo. Together with inhibitory effects of GDPβS and anti‐Gα1−3/Gαo antibodies the results suggest that there is constitutive Gαi/Gαo protein activity leading to channel opening via a DAG‐mediated but PKC‐independent mechanism. Finally, with whole‐cell recording it is shown that noradrenaline increases Icat and the noradrenaline‐evoked response is markedly potentiated by PKC inhibition. This latter observation shows that PKC also limits agonist‐evoked Icat in these arterial myocytes.
Integrating Inertial Sensors With Global Positioning System (GPS) for Vehicle Dynamics Control
Authors: Ryu Jihan , Gerdes J. Christian
Published: August 2004

This paper demonstrates a method of estimating several key vehicle states—sideslip angle, longitudinal velocity, roll and grade—by combining automotive grade inertial sensors with a Global Positioning System (GPS) receiver. Kinematic Kalman filters that are independent of uncertain vehicle parameters integrate the inertial sensors with GPS to provide high update estimates of the vehicle states and the sensor biases. Using a two-antenna GPS system, the effects of pitch and roll on the measurements can be quantified and are demonstrated to be quite significant in sideslip angle estimation. Employing the same GPS system as an input to the estimator, this paper develops a method that compensates for roll and pitch effects to improve the accuracy of the vehicle state and sensor bias estimates. In addition, calibration procedures for the sensitivity and cross-coupling of inertial sensors are provided to further reduce measurement error. The resulting state estimates compare well to the results from calibrated models and Kalman filter predictions and are clean enough to use in vehicle dynamics control systems without additional filtering.
Global Positioning System (GPS): A Low-Cost Velocity Sensor for Correcting Inertial Sensor Errors on Ground Vehicles
Authors: Bevly David M.
Published: August 2004

This paper demonstrates the ability of a standard low-cost Global Positioning System (GPS) receiver to reduce errors inherent in low-cost accelerometers and rate gyroscopes used on ground vehicles. Specifically GPS velocity is used to obtain vehicle course, velocity, and road grade, as well as to correct inertial sensors errors, providing accurate longitudinal and lateral acceleration, and pitch, roll, and yaw angular velocities. Additionally, it is shown that transient changes in sideslip (or lateral velocity), roll, and pitch angles can be measured. The method utilizes GPS velocity measurements to determine the inertial sensor errors using a kinematic Kalman Filter estimator. Simple models of the inertial sensors, which take into account the sensor noise and bias drift properties, are developed and used to design the estimator. Based on the characteristics of low-cost GPS receivers and IMU sensors, this paper presents the achievable performance of the combined system using the covariance analysis from the Kalman filter. Subsequent simulations and experiments validate both the error analysis and the methodology for utilizing GPS as a velocity sensor for correcting low-cost inertial sensor errors and providing critical vehicle state measurements.
Friction Estimation on Highway Vehicles Using Longitudinal Measurements
Authors: Wang Junmin , Alexander Lee , Rajamani Rajesh
Published: August 2004

This paper develops a real-time tire-road friction coefficient measurement system that can reliably distinguish between different road surface friction levels and quickly detect abrupt changes in friction coefficient. The measurement system relies on the use of differential GPS and utilizes a nonlinear longitudinal tire force model. Compared to previously published results in literature, the advantage of the system developed in this paper is that it is applicable during both vehicle acceleration and braking and works reliably for a wide range of slip ratios, including high slip conditions. The system can be utilized on front/rear-wheel drive as well as all-wheel drive vehicles. Extensive results are presented from experimental results conducted on various surfaces with a winter maintenance vehicle called the “SAFEPLOW.” The experimental results show that the system performs reliably and quickly in estimating friction coefficient on different road surfaces during various vehicle maneuvers. The developed friction measurement system has many applications in vehicle safety systems such as ABS, skid control and collision avoidance systems and is also useful for winter maintenance vehicles in which knowledge of the friction coefficient can be used to determine the amount and type of deicing chemicals to be applied to a winter roadway.
Utilizing Sensor Arrays to Attain High-Operating Bandwidth
Authors: Suranthiran Sugathevan , Jayasuriya Suhada
Published: August 2004

Proposed in this paper is a methodology for the design of a sensor array of small bandwidth passband sensors (sensors with small bandwidth but different bandwidths) to attain a high operating bandwidth. In certain control applications, it is necessary that a high bandwidth sensor be used for feedback efficiency. The design of a single sensor with the desired high bandwidth may not be easy and economically feasible. A new approach, which recommends the use of an array of small bandwidth pass-band sensors in place of a single sensor of high bandwidth is proposed. It is shown that the idea of sensor arrays can be utilized to obtain a cost effective and efficient solution to the problem posed. The proposed sensor array that consists of multiple sensors with possible overlapping operating regions as defined by their pass-bands requires that an effective fusion technique be used to unite multi-sensor data. A multi-sensor data fusion scheme using Frequency Response Methods is developed to facilitate the possible implementation of proposed sensor arrays.
A Capacitive Microcantilever: Modelling, Validation, and Estimation Using Current Measurements
Authors: Napoli Mariateresa , Bamieh Bassam , Turner Kimberly
Published: August 2004

We present a mathematical model for the dynamics of an electrostatically actuated micro-cantilever. For the common case of cantilevers excited by a periodic voltage, we show that the underlying linearized dynamics are those of a periodic system described by a Mathieu equation. We present experimental results that confirm the validity of the model, and in particular, illustrate that parametric resonance phenomena occur in capacitively actuated micro-cantilevers. We propose a system where the current measured is used as the sensing signal of the cantilever state and position through a dynamical observer. By investigating how the best achievable performance of an optimal observer depends on the excitation frequency, we show that the best such frequency is not necessarily the resonant frequency of the cantilever.
Synthesis of Nominal Motion of the Multi-Arm Cooperating Robots With Elastic Interconnections at the Contacts
Authors: Zˇivanovic´ Milovan , Vukobratovic´ Miomir
Published: August 2004

A procedure for determining the cooperative system nominal motion whereby the system’s desired motion belongs to a set of nominal motions, is proposed. The procedure originates from the solution of the elastic structure cooperative motion taking into account all specific properties of the cooperative manipulation. The starting basis of the procedure is determined by some essential properties of the mathematical model of the dynamics of the cooperative manipulation of the object by the nonredundant manipulators with 6 degrees of freedom (DOFs), whereby the problem of the force indefiniteness is solved by introducing elastic properties for a part of the cooperative system.
A Lyapunov-Based Piezoelectric Controller for Flexible Cartesian Robot Manipulators
Authors: Dadfarnia Mohsen , Jalili Nader , Xian Bin , Dawson Darren M.
Published: August 2004

A Lyapunov-based control strategy is proposed for the regulation of a Cartesian robot manipulator, which is modeled as a flexible cantilever beam with a translational base support. The beam (arm) cross-sectional area is assumed to be uniform and Euler-Bernoulli beam theory assumptions are considered. Moreover, two types of damping mechanisms; namely viscous and structural dampings, are considered for the arm material properties. The arm base motion is controlled utilizing a linear actuator, while a piezoelectric (PZT) patch actuator is bonded on the surface of the flexible beam for suppressing residual beam vibrations. The equations of motion for the system are obtained using Hamilton’s principle, which are based on the original infinite dimensional distributed system. Utilizing the Lyapunov method, the control force acting on the linear actuator and control voltage for the PZT actuator are designed such that the base is regulated to a desired set-point and the exponential stability of the system is attained. Depending on the composition of the controller, some favorable features appear such as elimination of control spillovers, controller convergence at finite time, suppression of residual oscillations and simplicity of the control implementation. The feasibility of the controller is validated through both numerical simulations and experimental testing.
A New Motion-Planning Scheme for Overhead Cranes With High-Speed Hoisting
Authors: Lee Ho-Hoon
Published: August 2004

This paper proposes a motion-planning method for a high-performance anti-swing control of overhead cranes, where the motion-planning problem is solved as a kinematic problem. First, an anti-swing regulating control law is proposed based on the Lyapunov stability theorem, where the proposed anti-swing control drives trolley velocity regulating error asymptotically to zero while suppressing load swing rapidly to zero for given arbitrary high-speed hoisting motions. Then a motion-planning scheme is designed based on the concept of minimumtime control, the proposed anti-swing control law, and typical anti-swing crane-operation practices. The motion-planning scheme is free from the usual mathematical constraints in anti-swing control such as small swing angle, small hoisting speed, and small hoisting distance. The effectiveness of the proposed motion planning is shown by generating high-performance anti-swing trajectories with high hoisting speed and hoisting ratio.
On the Modeling of Flexible-Link Planar Mechanisms: Experimental Validation of an Accurate Dynamic Model
Authors: Gasparetto Alessandro
Published: August 2004

The experimental validation of an accurate dynamic model of flexible multi-body planar mechanisms is presented in this paper. The proposed mathematical model, which is valid for whatever planar mechanism with any number of flexible links, accounts for the geometric and inertial nonlinearities of the mechanism, and considers coupling effects among rigid-body and elastic motion as well. In order to experimentally validate the dynamic model, a flexible five-bar planar linkage actuated by two electric motors is employed as a test case. The experimentally measured deformations and accelerations of the flexible links are compared with the numerical results obtained by simulating the system dynamic behavior through the mathematical model. It turns out that the experimental results are in good agreement with the numerical ones, thus proving that the dynamical model proposed is very effective in the difficult task of accurately representing the dynamic behavior of flexible mechanisms.
Servo Pneumatic Position Control Using Fuzzy PID Gain Scheduling
Authors: Situm Z. , Pavkovic D. , Novakovic B.
Published: August 2004

In this paper, a design procedure and experimental implementation of a PID controller is presented. The PID controller is tuned according to damping optimum in order to achieve precise position control of a pneumatic servo drive. It is extended by a friction compensation and stabilization algorithm in order to deal with friction effects. In a case of supply pressure variations, more robust control system is needed. It is implemented by extending the proposed PID controller with friction compensator with the gain scheduling algorithm, which is provided by means of fuzzy logic. The effectiveness of proposed control algorithms is experimentally verified on an industrial cylindrical rodless actuator controlled by a proportional valve.
The Dynamics of Lead-Screw Drives: Low-Order Modeling and Experiments
Authors: Varanasi Kripa K. , Nayfeh Samir A.
Published: August 2004

The closed-loop performance of a lead-screw drive is usually limited by a resonance in which the carriage oscillates in the direction of motion as the screw undergoes longitudinal and torsional deformation. In this paper, we develop a model of lead-screw system dynamics that accounts for the distributed inertia of the screw and the compliance and damping of the thrust bearings, nut, and coupling. The distributed-parameter model of the lead-screw drive system is reduced to a low-order model using a Galerkin procedure and verified by experiments performed on a pair of ball-screw systems. The model is found to accurately predict the presence of a finite right-half plane zero in the transfer function from motor torque to carriage position. A viscoelastic damper incorporated into one of the lead-screw support bearings is shown to give rise to significant, deterministic damping in the system transfer functions.
Control of a Non-Orthogonal Reconfigurable Machine Tool
Authors: Katz Reuven , Yook John , Koren Yoram
Published: August 2004

Computerized control systems for machine tools must generate coordinated movements of the separately driven axes of motion in order to trace accurately a predetermined path of the cutting tool relative to the workpiece. However, since the dynamic properties of the individual machine axes are not exactly equal, undesired contour errors are generated. The contour error is defined as the distance between the predetermined and actual path of the cutting tool. The cross-coupling controller (CCC) strategy was introduced to effectively decrease the contour errors in conventional, orthogonal machine tools. This paper, however, deals with a new class of machines that have non-orthogonal axes of motion and called reconfigurable machine tools (RMTs). These machines may be included in large-scale reconfigurable machining systems (RMSs). When the axes of the machine are non-orthogonal, the movement between the axes is tightly coupled and the importance of coordinated movement among the axes becomes even greater. In the case of a non-orthogonal RMT, in addition to the contour error, another machining error called in-depth error is also generated due to the non-orthogonal nature of the machine. The focus of this study is on the conceptual design of a new type of cross-coupling controller for a non-orthogonal machine tool that decreases both the contour and the in-depth machining errors. Various types of cross-coupling controllers, symmetric and non-symmetric, with and without feedforward, are suggested and studied. The stability of the control system is investigated, and simulation is used to compare the different types of controllers. We show that by using cross-coupling controllers the reduction of machining errors are significantly reduced in comparison with the conventional de-coupled controller. Furthermore, it is shown that the non-symmetric cross-coupling feedforward (NS-CC-FF) controller demonstrates the best results and is the leading concept for non-orthogonal machine tools.
Optimization of Performance Characteristics of Electropneumatic (Two-Stage) Servo Valve
Authors: Krivts Dr. Igor L.
Published: August 2004

Servo valve is the key element in electropneumatic servomechanism. In this study, an electropneumatic two-stage servo valves were investigated in order to improve their static and dynamic characteristics. These servo valves consist of a pilot stage and a power stage. The paper discusses three different pilot stages: the jet pipe pilot stage, the supply (side) flapper nozzle pilot stage and the exhaust (side) flapper nozzle pilot stage. The static and dynamic characteristics of the devices were investigated analytically and by computer simulation. For the three pilot stage types it was found that the optimal value of the static and dynamic characteristics could be obtained if the ratio between the effective areas of the supply channel and exhaust port of the pilot stage has a definite value (depending on the pilot stage type).
The Role of Beam Flexibility and Ground Contact Model in the Clattering of Deformable Beams
Authors: Bao Zhongping , Goyal Suresh , Leu Liang-Jenq , Mukherjee Subrata
Published: August 2004

It has been shown in previous research that, relative to (the usually considered case of) a single impact, multiple impacts (clattering) of rigid casings can greatly enhance the probability of failure of fragile components mounted on or inside them. This paper addresses the important issues of the roles of casing flexibility and contact model in the above situation. A finite element analysis of clattering of a Timoshenko beam is carried out here. Dependence of the maximum change in average velocity due to impact, on the beam stiffness and coefficient of restitution, are studied here.
Evidence for Deep Magma Injection Beneath Lake Tahoe, Nevada-California
Authors: Smith Kenneth D. , von Seggern David , Blewitt Geoffrey , Preston Leiph , Anderson John G. , Wernicke Brian P. , Davis James L.
Published: August 2004

A deep earthquake swarm in late 2003 at Lake Tahoe, California (Richter magnitude < 2.2; depth of 29 to 33 kilometers), was coeval with a transient displacement of 6 millimeters horizontally outward from the swarm and 8 millimeters upward measured at global positioning system station Slide Mountain (SLID) 18 kilometers to the northeast. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters per second up-dip along a 40-square-kilometer structure striking north 30° west and dipping 50° to the northeast. SLID's transient velocity of 20 millimeters per year implies a lower bound of 200 nanostrains per year (parts per billion per year) on local strain rates, an order of magnitude greater than the 1996 to 2003 regional rate. The geodetic displacement is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe.
Src Mediates a Switch from Microtubule- to Actin-Based Motility of Vaccinia Virus
Authors: Newsome Timothy P. , Scaplehorn Niki , Way Michael
Published: August 2004

The cascade of events that leads to vaccinia-induced actin polymerization requires Src-dependent tyrosine phosphorylation of the viral membrane protein A36R. We found that a localized outside-in signaling cascade induced by the viral membrane protein B5R is required to potently activate Src and induce A36R phosphorylation at the plasma membrane. In addition, Src-mediated phosphorylation of A36R regulated the ability of virus particles to recruit and release conventional kinesin. Thus, Src activity regulates the transition between cytoplasmic microtubule transport and actin-based motility at the plasma membrane.
The Closely Related Species
Candida albicans
and
Candida dubliniensis
Can Mate
Authors: Pujol Claude , Daniels Karla J. , Lockhart Shawn R. , Srikantha Thyagarajan , Radke Joshua B. , Geiger Jeremy , Soll David R.
Published: August 2004

Because
Candida dubliniensis
is closely related to
Candida albicans
, we tested whether it underwent white-opaque switching and mating and whether white-opaque switching depended on
MTL
homozygosity and mating depended on switching, as they do in
C. albicans
. We also tested whether
C. dubliniensis
could mate with
C. albicans
. Sequencing revealed that the
MTL
α locus of
C. dubliniensis
was highly similar to that of
C. albicans
. Hybridization with the
MTL
a
1, MTL
a
2, MTL
α
1
, and
MTL
α
2
open reading frames of
C. albicans
further revealed that, as in
C. albicans
, natural strains of
C. dubliniensis
exist as
a
/α,
a
/
a
, and α/α, but the proportion of
MTL
homozygotes is 33%, 10 times the frequency of natural
C. albicans
strains.
C. dubliniensis
underwent white-opaque switching, and, as in
C. albicans
, the switching was dependent on
MTL
homozygosis.
C. dubliniensis
a
/
a
and α/α cells also mated, and, as in
C. albicans
, mating was dependent on a switch from white to opaque. However, white-opaque switching occurred at unusually high frequencies, opaque cell growth was frequently aberrant, and white-opaque switching in many strains was camouflaged by an additional switching system. Mating of
C. dubliniensis
was far less frequent in suspension cultures, due to the absence of mating-dependent clumping. Mating did occur, however, at higher frequencies on agar or on the skin of newborn mice. The increases in
MTL
homozygosity, the increase in switching frequencies, the decrease in the quality of switching, and the decrease in mating efficiency all reflected a general deterioration in the regulation of developmental processes, very probably due to the very high frequency of recombination and genomic reorganization characteristic of
C. dubliniensis
. Finally, interspecies mating readily occurred between opaque
C. dubliniensis
and
C. albicans
strains of opposite mating type in suspension, on agar, and on mouse skin. Remarkably, the efficiency of interspecies mating was higher than intraspecies
C. dubliniensis
mating, and interspecies karyogamy occurred readily with apparently the same sequence of nuclear migration, fusion, and division steps observed during intraspecies
C. albicans
and
C. dubliniensis
mating and
Saccharomyces cerevisiae
mating.
Disordered Cell Integrity Signaling Caused by Disruption of thekexBGene inAspergillus oryzae
Authors: Mizutani Osamu , Nojima Akira , Yamamoto Morimasa , Furukawa Kentaro , Fujioka Tomonori , Yamagata Youhei , Abe Keietsu , Nakajima Tasuku
Published: August 2004

We isolated thekexBgene, which encodes a subtilisin-like processing enzyme, from a filamentous fungus,Aspergillus oryzae. To examine the physiological role ofkexBinA. oryzae, we constructed akexBdisruptant (ΔkexB), which formed shrunken colonies with poor generation of conidia on Czapek-Dox (CD) agar plates and hyperbranched mycelia in CD liquid medium. The phenotypes of the ΔkexBstrain were restored under high osmolarity in both solid and liquid culture conditions. We found that transcription of thempkAgene, which encodes a putative mitogen-activated protein kinase involved in cell integrity signaling, was significantly higher in ΔkexBcells than in wild-type cells. The ΔkexBcells also contained higher levels of transcripts for cell wall-related genes encoding β-1,3-glucanosyltransferase and chitin synthases, which is presumably attributable to cell integrity signaling through the increased gene expression ofmpkA. As expected, constitutively increased levels of phosphorylated MpkA were observed in ΔkexBcells on the CD plate culture. High osmotic stress greatly downregulated the increased levels of both transcripts ofmpkAand the phosphorylated form of MpkA in ΔkexBcells, concomitantly suppressing the morphological defects. These results suggest that the upregulation of transcription levels ofmpkAand cell wall biogenesis genes in the ΔkexBstrain is autoregulated by phosphorylated MpkA as the active form through cell integrity signaling. We think that KexB is required for precise proteolytic processing of sensor proteins in the cell integrity pathway or of cell wall-related enzymes under transcriptional control by the pathway and that the KexB defect thus induces disordered cell integrity signaling.
The Exchange Factor Cdc24 Is Required for Cell Fusion during Yeast Mating
Authors: Barale Sophie , McCusker Derek , Arkowitz Robert A.
Published: August 2004

During
Saccharomyces cerevisiae
mating, chemotropic growth and cell fusion are critical for zygote formation. Cdc24p, the guanine nucleotide exchange factor for the Cdc42 G protein, is necessary for oriented growth along a pheromone gradient during mating. To understand the functions of this critical Cdc42p activator, we identified additional
cdc24
mating mutants. Two mating-specific mutants, the
cdc24-m5
and
cdc24-m6
mutants, each were isolated with a mutated residue in the conserved catalytic domain. The
cdc24-m6
mutant responds normally to pheromone and orients its growth towards a mating partner yet accumulates prezygotes during mating.
cdc24-m6
prezygotes have two apposed intact cell walls and do not correctly localize proteins required for cell fusion, despite normal exocytosis. Our results indicate that the exchange factor Cdc24p is necessary for maintaining or restricting specific proteins required for cell fusion to the cell contact region during mating.
The Two-Component Signal Transduction Protein Chk1p Regulates Quorum Sensing in
Candida albicans
Authors: Kruppa Michael , Krom Bastiaan P. , Chauhan Neeraj , Bambach Adrienne V. , Cihlar Ronald L. , Calderone Richard A.
Published: August 2004

Regulation of hyphal morphogenesis in
Candida albicans
can occur through quorum sensing (QS). A QS signal, farnesol, is produced during high-density growth and inhibits morphogenesis. However, the signal transduction pathway that regulates QS is unknown. Here, we show that a
C. albicans
mutant lacking Chk1p but not either the Sln1p or the Nik1p histidine kinase is refractory to the inhibitory effect of farnesol both in cell suspension and during the formation of a biofilm. This study is the first to demonstrate a role for a two-component signal transduction protein in QS by a eukaryotic organism.
Genetic Interactions among Regulators of Septin Organization
Authors: Gladfelter Amy S. , Zyla Trevin R. , Lew Daniel J.
Published: August 2004

Septins form a cortical scaffold at the yeast mother-bud neck that restricts the diffusion of cortical proteins between the mother and bud and serves as a signaling center that is important for governing various cell functions. After cell cycle commitment in late G
1
, septins are assembled into a narrow ring at the future bud site, which spreads to form a mature septin hourglass immediately after bud emergence. Although several septin regulators have been identified, it is unclear how they cooperate to assemble the septin scaffold. We have examined septin localization in isogenic strains containing single or multiple mutations in eight septin organization genes (
CDC42
,
RGA1
,
RGA2
,
BEM3
,
CLA4
,
GIN4
,
NAP1
, and
ELM1
). Our results suggest that these regulators act largely in parallel to promote either the initial assembly of the septin ring (
CDC42
,
RGA1
,
RGA2
,
BEM3
, and
CLA4
) or the conversion of the ring to a stable hourglass structure at the neck (
GIN4
,
NAP1
, and
ELM1
). Aberrant septin localization patterns in mutant strains could be divided into apparently discrete categories, but individual strains displayed heterogeneous defects, and there was no clear-cut correspondence between the specific mutations and specific categories of defect. These findings suggest that when they are deprived of their normal regulators, septin scaffolds collapse into a limited repertoire of aberrant states in which the nature of the mutant regulators influences the probability of a given aberrant state.
An Intragenic Guide RNA Location Suggests a Complex Mechanism for Mitochondrial Gene Expression in
Trypanosoma brucei
Authors: Clement Sandra L. , Mingler Melissa K. , Koslowsky Donna J.
Published: August 2004

In
Trypanosoma brucei
, two classes of transcripts are produced from two distinct mitochondrial genome components. Guide RNAs (gRNAs) are usually minicircle encoded and exist as primary transcripts, while the maxicircle-encoded rRNAs and mRNAs are processed from a polycistronic precursor. The genes for the gRNAs gMURF2-II and gCYb(560) each have uncommon kinetoplast DNA (kDNA) locations that are not typically associated with transcription initiation events. We demonstrate that the conserved maxicircle gRNA gMURF2-II has an unusual location within the ND4 gene. This is the first report of a completely intragenic gene in kDNA. In addition, the gMURF2-II and ND4 transcripts are generated by distinctly different events; the ND4 mRNA is processed from a polycistronic precursor, while transcription of the gRNA initiates downstream of the 5′ end of the ND4 gene. The gCYb(560) gene has an atypical minicircle location in that it is not flanked by the inverted repeat sequences that surround the majority of minicircle gRNA genes. Our data indicate that the mature gCYb(560) gRNA is also a primary transcript and that the 5′-end heterogeneity previously observed for this gRNA is a result of multiple transcription initiation sites and not of imprecise 5′-end processing. Together, these data indicate that gRNA genes represent individual transcription units, regardless of their genomic context, and suggest a complex mechanism for mitochondrial gene expression in
T. brucei
.
PF15p Is the
Chlamydomonas
Homologue of the Katanin p80 Subunit and Is Required for Assembly of Flagellar Central Microtubules
Authors: Dymek Erin E. , Lefebvre Paul A. , Smith Elizabeth F.
Published: August 2004

Numerous studies have indicated that the central apparatus plays a significant role in regulating flagellar motility, yet little is known about how the central pair of microtubules or their associated projections assemble. Several
Chlamydomonas
mutants are defective in central apparatus assembly. For example, mutant
pf15
cells have paralyzed flagella that completely lack the central pair of microtubules. We have cloned the wild-type
PF15
gene and confirmed its identity by rescuing the motility and ultrastructural defects in two
pf15
alleles, the original
pf15a
mutant and a mutant generated by insertional mutagenesis. Database searches using the 798-amino-acid polypeptide predicted from the complete coding sequence indicate that the
PF15
gene encodes the
Chlamydomonas
homologue of the katanin p80 subunit. Katanin was originally identified as a heterodimeric protein with a microtubule-severing activity. These results reveal a novel role for the katanin p80 subunit in the assembly and/or stability of the central pair of flagellar microtubules.