bluuebunny/crossref_metadata_2025 huggingface dataset:
Joint distributions of successes, failures and patterns in enumeration problems
Authors: Chadjiconstantinidis S , Antzoulakos D. L. , Koutras M. V.
Published: February 2003

Let ε be a (single or composite) pattern defined over a sequence of Bernoulli trials. This article presents a unified approach for the study of the joint distribution of the number Sn of successes (and Fn of failures) and the number Xn of occurrences of ε in a fixed number of trials as well as the joint distribution of the waiting time Tr till the rth occurrence of the pattern and the number STr of successes (and FTr of failures) observed at that time. General formulae are developed for the joint probability mass functions and generating functions of (Xn,Sn), (Tr,STr) (and (Xn,Sn,Fn),(Tr,STr,FTr)) when Xn belongs to the family of Markov chain imbeddable variables of binomial type. Specializing to certain success runs, scans and pattern problems several well-known results are delivered as special cases of the general theory along with some new results that have not appeared in the statistical literature before.
Probabilities of ruin when the safety loading tends to zero
Authors: Malinovskii Vsevolod K.
Published: February 2003

When the premium rate is a positive absolute constant throughout the time period of observation and the safety loading of the insurance business is positive, a classical result of collective risk theory claims that probabilities of ultimate ruin ψ(u) and of ruin within finite time ψ(t,u) decrease as eϰu with a constant ϰ>0, as the initial risk reserve u increases. This paper establishes uniform approximations to ψ(t,u) with slower rates of decrease when the premium rate depends on u in such a way that the safety loading decreases to zero as
u→∞.
Limit laws for the diameter of a random point set
Authors: Appel Martin J. B. , Najim Christopher A. , Russo Ralph P.
Published: February 2003

Let U1,U2,… be a sequence of i.i.d. random vectors distributed uniformly in a compact plane region A of unit area. Sufficient conditions on the geometry of A are provided under which the Euclidean diameter Dn of the first n of the points converges weakly upon suitable rescaling.
The set covariance of a dead leaves model
Authors: Gille Wilfried
Published: February 2003

The set covariance of a dead leaves model, constructed from hard spheres of constant diameter, is calculated analytically. The calculation is based on the covariance of a single sphere and on the pair correlation function of the centres of the spheres. There exist applications in the field of random sequential adsorption and in the interpretation of small-angle scattering experiments.
Generalized contact distributions of inhomogeneous Boolean models
Authors: Hug Daniel , Last Günter , Weil Wolfgang
Published: February 2003

The main purpose of this work is to study and apply generalized contact distributions of (inhomogeneous) Boolean modelsZwith values in the extended convex ring. Given a convex bodyL⊂ ℝdand a gauge bodyB⊂ ℝd, such a generalized contact distribution is the conditional distribution of the random vector (dB(L,Z),uB(L,Z),pB(L,Z),lB(L,Z)) given thatZ∩L= ∅, whereZis a Boolean model,dB(L,Z) is the distance ofLfromZwith respect toB,pB(L,Z) is the boundary point inLrealizing this distance (if it exists uniquely),uB(L,Z) is the corresponding boundary point ofB(if it exists uniquely) andlB(L,·) may be taken from a large class of locally defined functionals. In particular, we pursue the question of the extent to which the spatial density and the grain distribution underlying an inhomogeneous Boolean modelZare determined by the generalized contact distributions ofZ.
Critical intensities of Boolean models with different underlying convex shapes
Authors: Roy Rahul , Tanemura Hideki
Published: February 2003

We consider the Poisson Boolean model of percolation where the percolating shapes are convex regions. By an enhancement argument we strengthen a result of Jonasson (2000) to show that the critical intensity of percolation in two dimensions is minimized among the class of convex shapes of unit area when the percolating shapes are triangles, and, for any other shape, the critical intensity is strictly larger than this minimum value. We also obtain a partial generalization to higher dimensions. In particular, for three dimensions, the critical intensity of percolation is minimized among the class of regular polytopes of unit volume when the percolating shapes are tetrahedrons. Moreover, for any other regular polytope, the critical intensity is strictly larger than this minimum value.
Markov random field models of multicasting in tree networks
Authors: Ramanan Kavita , Sengupta Anirvan , Ziedins Ilze , Mitra Partha
Published: February 2003

In this paper, we analyse a model of a regular tree loss network that supports two types of calls: unicast calls that require unit capacity on a single link, and multicast calls that require unit capacity on every link emanating from a node. We study the behaviour of the distribution of calls in the core of a large network that has uniform unicast and multicast arrival rates. At sufficiently high multicast call arrival rates the network exhibits a ‘phase transition’, leading to unfairness due to spatial variation in the multicast blocking probabilities. We study the dependence of the phase transition on unicast arrival rates, the coordination number of the network, and the parity of the capacity of edges in the network. Numerical results suggest that the nature of phase transitions is qualitatively different when there are odd and even capacities on the links. These phenomena are seen to persist even with the introduction of nonuniform arrival rates and multihop multicast calls into the network. Finally, we also show the inadequacy of approximations such as the Erlang fixed-point approximations when multicasting is present.
A Markovian analysis of additive-increase multiplicative-decrease algorithms
Authors: Dumas Vincent , Guillemin Fabrice , Robert Philippe
Published: February 2003

The additive-increase multiplicative-decrease (AIMD) schemes designed to control congestion in communication networks are investigated from a probabilistic point of view. Functional limit theorems for a general class of Markov processes that describe these algorithms are obtained. The asymptotic behaviour of the corresponding invariant measures is described in terms of the limiting Markov processes. For some special important cases, including TCP congestion avoidance, an important autoregressive property is proved. As a consequence, the explicit expression of the related invariant probabilities is derived. The transient behaviour of these algorithms is also analysed.
Stability classification of a Ricker model with two random parameters
Authors: Fagerholm Henrik , Högnäs Göran
Published: February 2003

We consider a stochastic version of the Ricker model describing the density of an unstructured isolated population. In particular, we investigate the effects of independently varying the per capita growth rate and the parameter governing density dependent feedback. We derive conditions on the distributions sufficient to guarantee different forms of stochastic stability such as null recurrence or positive recurrence. We find, for example, that null recurrence appears in two widely different scenarios: when there is a mean-zero growth rate or via a growth-catastrophe behaviour.
Stationary stochastic control for Itô processes
Authors: Weerasinghe Ananda P. N.
Published: February 2003

Consider a real-valued Itô process X(t) = x + ∫0tμ(s)ds + ∫0tσ(s)dW(s) + A(t) driven by a Brownian motion {W(t) : t > 0}. The controller chooses the real-valued progressively measurable processes μ, σ and A subject to constraints |μ(t)| ≤ μ0(X(t-)) and |σ(t)| ≥ σ0(X(t-)), where the functions μ0 and σ0 are given. The process A is a bounded variation process and |A|(t) represents its total variation on [0,t]. The objective is to minimize the long-term average cost lim supT→∞(1/T)E[|A|(T) + ∫0Th(X(s))ds], where h is a given nonnegative continuous function. An optimal process X* is determined. It turned out that X* is a reflecting diffusion process whose state space is a finite interval [a*, b*]. The optimal drift and diffusion controls are explicitly derived and the optimal bounded variation process A* is determined in terms of local-time processes of X* at the points a* and b*.
Optimal stopping with random intervention times
Authors: Dupuis Paul , Wang Hui
Published: February 2003

We consider a class of optimal stopping problems where the ability to stop depends on an exogenous Poisson signal process - we can only stop at the Poisson jump times. Even though the time variable in these problems has a discrete aspect, a variational inequality can be obtained by considering an underlying continuous-time structure. Depending on whether stopping is allowed att= 0, the value function exhibits different properties across the optimal exercise boundary. Indeed, the value function is only𝒞0across the optimal boundary when stopping is allowed att= 0 and𝒞2otherwise, both contradicting the usual𝒞1smoothness that is necessary and sufficient for the application of the principle of smooth fit. Also discussed is an equivalent stochastic control formulation for these stopping problems. Finally, we derive the asymptotic behaviour of the value functions and optimal exercise boundaries as the intensity of the Poisson process goes to infinity or, roughly speaking, as the problems converge to the classical continuous-time optimal stopping problems.
Conditional limit theorems for spectrally positive Lévy processes
Authors: Konstantopoulos Takis , Richardson Gregory S.
Published: February 2003

We consider spectrally positive Lévy processes with regularly varying Lévy measure and study conditional limit theorems that describe the way that various rare events occur. Specifically, we are interested in the asymptotic behaviour of the distribution of the path of the Lévy process (appropriately scaled) up to some fixed time, conditionally on the event that the process exceeds a (large) positive value at that time. Another rare event we study is the occurrence of a large maximum value up to a fixed time, and the corresponding asymptotic behaviour of the (scaled) Lévy process path. We study these distributional limit theorems both for a centred Lévy process and for one with negative drift. In the latter case, we also look at the reflected process, which is of importance in applications. Our techniques are based on the explicit representation of the Lévy process in terms of a two-dimensional Poisson random measure and merely use the Poissonian properties and regular variation estimates. We also provide a proof for the asymptotic behaviour of the tail of the stationary distribution for the reflected process. The work is motivated by earlier results for discrete-time random walks (e.g. Durrett (1980) and Asmussen (1996)) and also by their applications in risk and queueing theory.
Extremal behavior of heavy-tailed ON-periods in a superposition of ON/OFF processes
Authors: Stegeman Alwin
Published: February 2003

Empirical studies of data traffic in high-speed networks suggest that network traffic exhibits self-similarity and long-range dependence. Cumulative network traffic has been modeled using the so-called ON/OFF model. It was shown that cumulative network traffic can be approximated by either fractional Brownian motion or stable Lévy motion, depending on how many sources are active in the model. In this paper we consider exceedances of a high threshold by the sequence of lengths of ON-periods. If the cumulative network traffic converges to stable Lévy motion, the number of exceedances converges to a Poisson limit. The same holds in the fractional Brownian motion case, provided a very high threshold is used. Finally, we show that the number of exceedances obeys the central limit theorem.
Power spectra of general shot noises and Hawkes point processes with a random excitation
Authors: Brémaud P. , Massoulié L.
Published: February 2003

We give (i) the Cramér power spectral measure of the general shot noise process with random excitation and non-Poisson stationary driving point processes and (ii) the Bartlett power spectral measure of the self-exciting Hawkes point process with random excitation, also called the Hawkes branching point process with random fertility rate. The latter is obtained via the isometry formula for integrals with respect to the canonical martingale measure associated with a marked point process.
Compound Poisson approximation for the distribution of extremes
Authors: Barbour A. D. , Novak S. Y. , Xia A.
Published: February 2003

Empirical point processes of exceedances play an important role in extreme value theory, and their limiting behaviour has been extensively studied. Here, we provide explicit bounds on the accuracy of approximating an exceedance process by a compound Poisson or Poisson cluster process, in terms of a Wasserstein metric that is generally more suitable for the purpose than the total variation metric. The bounds only involve properties of the finite, empirical sequence that is under consideration, and not of any limiting process. The argument uses Bernstein blocks and Lindeberg's method of compositions.
On ageing properties of first-passage times of increasing Markov processes
Authors: Belzunce Félix , Ortega Eva-María , Ruiz José M.
Published: February 2003

The purpose of this paper is to study ageing properties of first-passage times of increasing Markov chains. We extend the literature to some new ageing classes, such as the IFR(2), NBU(2), DRLLt
and NBULt classes. We also give sufficient conditions in the finite case, that are more efficient computationally, just in terms of the transition matrix K, in the discrete case, or the generator matrix Q, in the continuous case. For the uniformizable, continuous-time Markov processes, we derive conditions in terms of the discrete uniformized Markov chain for the NBU(2) and the NBULt
classes. In the last section, a review of the main results in this direction in the literature is given, and we compare some of the conditions stated in this paper with others given in the literature about some other ageing classes. Some examples where these results are applied are given.
Predicting the metabolic energy costs of bipedalism using evolutionary robotics
Authors: Sellers W. I. , Dennis L. A. , Crompton R. H.
Published: February 2003

To understand the evolution of bipedalism among the hominoids in an ecological context we need to be able to estimate the energetic cost of locomotion in fossil forms. Ideally such an estimate would be based entirely on morphology since, except for the rare instances where footprints are preserved, this is the only primary source of evidence available. In this paper we use evolutionary robotics techniques (genetic algorithms, pattern generators and mechanical modeling) to produce a biomimetic simulation of bipedalism based on human body dimensions. The mechanical simulation is a seven-segment, two-dimensional model with motive force provided by tension generators representing the major muscle groups acting around the lower-limb joints. Metabolic energy costs are calculated from the muscle model, and bipedal gait is generated using a finite-state pattern generator whose parameters are produced using a genetic algorithm with locomotor economy(maximum distance for a fixed energy cost) as the fitness criterion. The model is validated by comparing the values it generates with those for modern humans. The result (maximum efficiency of 200 J m–1) is within 15% of the experimentally derived value, which is very encouraging and suggests that this is a useful analytic technique for investigating the locomotor behaviour of fossil forms. Initial work suggests that in the future this technique could be used to estimate other locomotor parameters such as top speed. In addition, the animations produced by this technique are qualitatively very convincing, which suggests that this may also be a useful technique for visualizing bipedal locomotion.
Steady swimming muscle dynamics in the leopard sharkTriakis semifasciata
Authors: Donley Jeanine M. , Shadwick Robert E.
Published: February 2003

Patterns of red muscle strain and activation were examined at three positions along the body (0.42, 0.61 and 0.72 L, where L is total body length) and correlated with simultaneous measurements of midline kinematics during steady swimming (approx. 1.0 Ls–1) in the leopard shark Triakis semifasciata. Analysis of lateral displacement along the body indicates that the leopard shark is a subcarangiform swimmer. Longitudinal variation in red muscle strain was observed with strain amplitudes ranging from ±3.9% in the anterior,±6.6% in the mid, to ±4.8% in the posterior body position. Strain was in-phase with local midline curvature. In addition, strain amplitude calculated from a bending beam model closely matched strain measured using sonomicrometry at all three body positions. There is a high degree of similarity in red muscle activation patterns along the body between the leopard shark and many fish species, in that the onset of activation occurs during muscle lengthening while offset occurs during muscle shortening. However, we found no significant longitudinal variation in the EMG/strain phase relationship and duty cycles, with onset of muscle activation occurring at 51.4–61.8° and offset at 159.7–165.2° (90° is peak length). This consistent pattern of activation suggests that red muscle along the entire length of the body contributes to positive power production. Thus,sharks such as Triakis may have no regional specialization in red muscle function like that seen in many teleosts, which may indicate that the evolution of differential muscle function along the body occurred after the divergence of cartilaginous and bony fishes.
The toxic and lethal effects of the trehalase inhibitor trehazolin in locusts are caused by hypoglycaemia
Authors: Wegener Gerhard , Tschiedel Volker , Schlöder Paul , Ando Osamu
Published: February 2003

The main blood sugar of locusts is trehalose, which is hydrolysed to two glucose units by trehalase. Homogenates of locust flight muscles are rich in trehalase activity, which is bound to membranes. A minor fraction of trehalase is in an overt form while the remainder is latent, i.e. active only after impairing membrane integrity. Trehazolin, an antibiotic pseudosaccharide,inhibits locust flight muscle trehalase with apparent Ki-and EC50 values of 10–8 mol l–1and 10–7 mol l–1, respectively. Trehazolin is insecticidal: 50 μg injected into locusts completely and selectively blocked the overt form of muscle trehalase (with little effect on latent activity) and killed 50% of the insects within 24 h. Here, it is demonstrated for the first time that trehazolin causes dramatic hypoglycaemia. Injection of 10 μg trehazolin caused glucose levels to fall by over 90% in 24 h, from 2.8 mmol l–1 to 0.23 mmol l–1, while trehalose increased from 61 mmol l–1 to 111 mmol l–1. Feeding glucose to the locusts fully neutralized the effects of a potentially lethal dose of trehazolin. This indicates that hypertrehalosaemia is not acutely toxic, whereas lack of glucose causes organ failure (presumably of the nervous system), and that sufficient haemolymph glucose can only be generated from trehalose by trehalase. The results also suggest that overt flight muscle trehalase is located in the plasma membrane with the active site accessible to the haemolymph. Trehalase inhibitors are valuable tools for studying the molecular physiology of trehalase function and sugar metabolism in insects.
Photolysis of caged calcium in cilia induces ciliary reversal inParamecium caudatum
Authors: Iwadate Yoshiaki
Published: February 2003

Intracellular Ca2+ concentration controls both the pattern and frequency of ciliary and flagellar beating in eukaryotes. In Paramecium, it is widely accepted that the reversal of the direction of ciliary beating (ciliary reversal) is induced by an increase in intra-ciliary Ca2+ levels. Despite this, the Ca2+-sensitive region of the cilium that initiates ciliary reversal has not been clearly identified.

We injected caged calcium into living P. caudatum cells and applied ultraviolet (UV) light to portions of the injected cells to raise artificially the intracellular Ca2+ level([Ca2+]i). UV application to the upper ciliary region above the basal body induced ciliary reversal in injected cells. Furthermore,UV application to the tips of cilia induced weak ciliary reversal. Larger areas of photolysis in the cilium gave rise to greater angles of ciliary reversal. These results strongly suggest that the Ca2+-sensitive region for ciliary reversal is distributed all over the cilium, above the basal body.
Mitogen-activated protein kinases: new signaling pathways functioning in cellular responses to environmental stress
Authors: Cowan Kyra J. , Storey Kenneth B.
Published: February 2003

The mitogen-activated protein kinase (MAPK) superfamily consists of three main protein kinase families: the extracellular signal-regulated protein kinases (ERKs), the c-Jun N-terminal kinases (JNKs) and the p38 family of kinases. Each is proving to have major roles in the regulation of intracellular metabolism and gene expression and integral actions in many areas including growth and development, disease, apoptosis and cellular responses to external stresses. To date, this cellular signal transduction network has received relatively little attention from comparative biochemists,despite the high probability that MAPKs have critical roles in the adaptive responses to thermal, osmotic and oxygen stresses. The present article reviews the current understanding of the roles and regulation of ERKs, JNKs and p38,summarizes what is known to date about MAPK roles in animal models of anoxia tolerance, freeze tolerance and osmoregulation, and highlights the potential that studies of MAPK pathways have for advancing our understanding of the mechanisms of biochemical adaptation.
Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?
Authors: MacArthur Robert A. , Weseen Gillian L. , Campbell Kevin L.
Published: February 2003

We tested the hypothesis that the body oxygen stores, aerobic dive limit(ADL) and dive performance of muskrats can be enhanced by dive-conditioning in a laboratory setting. We compared several key variables in 12 muskrats trained to swim a 16 m underwater course to a feeding station (`divers') with those of 12 animals precluded from diving but required to travel identical distances in water to feed (`surface swimmers'). Acclimated muskrats assigned to each group were trained concurrently over a 9–11 week period. We observed significant gains in the haematocrit (P=0.0005) and blood haemoglobin concentration (P=0.015) of `divers', but not `surface swimmers'. The post-training blood O2 store calculated for `divers' (22.9 ml O2 kg–1) was nearly 26% higher than that (18.2 ml O2 kg–1) derived for `surface swimmers'(P=0.03). Dive-conditioning had no apparent effect on lung volume,whole blood and plasma volumes, nor on the glycogen level and buffering capacity of skeletal muscles. Cardiac and skeletal muscle myoglobin levels were also similar in both test groups following training. The mean total body oxygen store of `divers' (37.8ml O2 STPD kg–1) was 13.5% higher (P=0.037) than for `surface swimmers' (33.3 ml O2 STPD kg–1), an increase attributed entirely to the gain in blood O2 storage capacity of the former group. However,owing to a slightly higher estimate of diving metabolic rate in dive-conditioned animals, the calculated ADL for this group (61.3 s) was indistinguishable from that of `surface swimmers' (61.8 s). Few differences were observed in the post-training dive behaviour of `surface swimmers' and`divers', a finding consistent with the strong similarity in their calculated aerobic dive capacities.
The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodileCrocodylus porosus
Authors: Franklin Craig E. , Seebacher Frank
Published: February 2003

The effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions;(2) heated via radiant energy while half-submerged in flowing water at 23°C and (3) heated via convective transfer by increasing water temperature from 23°C to 35°C. Cooling was achieved in all treatments by removing the heat source and with C. porosushalf-submerged in flowing water at 23°C. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate (`rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (<0.5°C) resulted in Q10 values greater than 4000, calling into question the usefulness of this measure on heart rate during the initial stages of heating and cooling. In the later phases of heating and cooling, heart rate changed with body temperature, with Q10 values of 2–3. The magnitude of the heart rate response differed between treatments, with radiant heating during submergence eliciting the smallest response. The heart rate of C. porosus outside of the`rapid response' periods was found to be a function of the heat load experienced at the animal surface, as well as on the mode of heat transfer. Heart rate increased or decreased rapidly when C. porosus experienced large positive (above 25 W) or negative (below –15 W) heat loads,respectively, in all treatments. For heat loads between –15 W and 20 W,the increase in heart rate was smaller for the `unnatural' heating by convection in water compared with either treatment using radiant heating. Our data indicate that changes in heart rate constitute a thermoregulatory mechanism that is modulated in response to the thermal environment occupied by the animal, but that heart rate during heating and cooling is, in part,controlled independently of body temperature.
Seasonal acclimatisation of muscle metabolic enzymes in a reptile(Alligator mississippiensis)
Authors: Seebacher Frank , Guderley Helga , Elsey Ruth M. , Trosclair Phillip L.
Published: February 2003

Reptiles living in heterogeneous thermal environments are often thought to show behavioural thermoregulation or to become inactive when environmental conditions prevent the achievement of preferred body temperatures. By contrast, thermally homogeneous environments preclude behavioural thermoregulation, and ectotherms inhabiting these environments (particularly fish in which branchial respiration requires body temperature to follow water temperature) modify their biochemical capacities in response to long-term seasonal temperature fluctuations. Reptiles may also be active at seasonally varying body temperatures and could, therefore, gain selective advantages from regulating biochemical capacities. Hence, we tested the hypothesis that a reptile (the American alligator Alligator mississippiensis) that experiences pronounced seasonal fluctuations in body temperature will show seasonal acclimatisation in the activity of its metabolic enzymes. We measured body temperatures of alligators in the wild in winter and summer (N=7 alligators in each season), and we collected muscle samples from wild alligators (N=31 in each season) for analysis of metabolic enzyme activity (lactate dehydrogenase, citrate synthase and cytochrome coxidase). There were significant differences in mean daily body temperatures between winter (15.66±0.43°C; mean ± S.E.M.) and summer(29.34±0.21°C), and daily body temperatures fluctuated significantly more in winter compared with summer. Alligators compensated for lower winter temperatures by increasing enzyme activities, and the activities of cytochrome c oxidase and lactate dehydrogenase were significantly greater in winter compared with summer at all assay temperatures. The activity of citrate synthase was significantly greater in the winter samples at the winter body temperature (15°C) but not at the summer body temperature(30°C). The thermal sensitivity (Q10) of mitochondrial enzymes decreased significantly in winter compared with in summer. The activity of mitochondrial enzymes was significantly greater in males than in females, but there were no differences between sexes for lactate dehydrogenase activity. The differences between sexes could be the result of the sex-specific seasonal demands for locomotor performance. Our data indicate that biochemical acclimatisation is important in thermoregulation of reptiles and that it is not sufficient to base conclusions about their thermoregulatory ability entirely on behavioural patterns.
N-methyl-D-aspartate receptors mediate chemoreflexes in the shorthorn sculpinMyoxocephalus scorpius
Authors: Turesson J. , Sundin L.
Published: February 2003

Glutamate microinjected into the vagal sensory area in the medulla produces cardiorespiratory responses mimicking oxygen chemoreflexes in fish. Here we directly investigate whether these reflexes are dependent on the ionotropic N-methyl-D-aspartate (NMDA) glutamate receptor.

Fish were equipped with opercular, branchial and snout cannulae for measurements of cardiorespiratory parameters and drug injections. Oxygen chemoreceptor reflexes were evoked by rapid hypoxia, NaCN added into the blood(internal, 0.3 ml, 50 μgml–1) and the mouth (external, 0.5 ml, 1 mg ml–1), before and after systemic administration of the NMDA receptor antagonist MK801 (3 mg kg–1).

Hypoxia produced an MK801-sensitive increase in blood pressure and ventilation frequency, whereas the marked bradycardia and the increased ventilation amplitude were NMDA receptor-independent. The fish appeared more responsive to externally applied cyanide, but the injections and MK801 treatment did not distinguish whether external or internal oxygen receptors were differently involved in the hypoxic responses.

In addition, using single-labelling immunohistochemistry on sections from the medulla and ganglion nodosum, the presence of glutamate and NMDA receptors in the vagal oxygen chemoreceptor pathway was established.

In conclusion, these results suggest that NMDA receptors are putative central control mechanisms that process oxygen chemoreceptor information in fish.
Metabolic enzyme activities across an altitudinal gradient: an examination of pikas (genusOchotona)
Authors: Sheafor Brandon A.
Published: February 2003

Changes in metabolic enzyme activities were examined in three species of pikas that occur over a range of altitudes. Because these closely related mammals live in comparable ecosystems and face similar environmental factors regardless of altitude, modifications of metabolic machinery are probably due to differences in oxygen availability. Citrate synthase (CS),β-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH)activities were measured in heart, diaphragm, vastus lateralis, gastrocnemius and soleus muscles. Additionally, the activity levels of both M-LDH (skeletal muscle type) and H-LDH (heart type) isozymes were quantified in tissue samples. Pikas from high altitude had greater CS and HOAD activities in heart and diaphragm when compared with pikas from low altitude, while activity levels did not differ in skeletal muscles. The increase in oxidative enzyme activities in tissues with high metabolic demand is thought to enhance oxygen utilization when oxygen availability is low and may reflect greater metabolic demand on heart and diaphragm tissue. Pikas from high altitude were also found to have greater total LDH activities in all tissues examined. High altitude animals had dramatically higher H-LDH activity (2.3–3.8 times greater)while M-LDH activity was more comparable (1.8 times lower to 1.7 times greater) when compared with low altitude animals. High total LDH activity enables pikas to perform short bouts of anaerobic activity, while high levels of H-LDH isozymes may serve to enhance lactate removal and decrease recovery time in animals living at high altitude.
Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat
Authors: Fuller Andrea , Kamerman Peter R. , Maloney Shane K. , Mitchell Graham , Mitchell Duncan
Published: February 2003

We used implanted miniature data loggers to measure brain (in or near the hypothalamus) and carotid arterial blood temperatures at 5 min intervals in six free-ranging ostriches Struthio camelus in their natural habitat,for a period of up to 14 days. Carotid blood temperature exhibited a large amplitude (3.0–4.6°C) circadian rhythm, and was positively correlated with air temperature. During the day, brain temperature exceeded carotid blood temperature by approx. 0.4°C, but there were episodes when brain temperature was lowered below blood temperature. Selective brain cooling, however, was not present in all ostriches, and was not tightly coupled to the prevailing body temperature. Brain temperature was maintained within narrow daily limits of approx. 2°C, and varied significantly less than blood temperature at short time scales of 5 to 20 min. At night, brain temperature exceeded blood temperature by as much as 3°C. We attribute the elevated brain temperatures to warming of cerebral arterial blood, by reduced heat exchange in the ophthalmic rete or possibly heat gain from cranial structures, before supplying the hypothalamus. Further studies are necessary to elucidate the significance of such variations in brain temperature and the importance of selective brain cooling in free-living birds.
Growth hormone is a weaker candidate than prolactin for the hormone responsible for the development of a larval-type feature in cultured bullfrog skin
Authors: Takada Makoto , Kasai Miyoko
Published: February 2003

Prolactin (PRL) has, for some years, been considered to be the `juvenile hormone' in amphibians. Recently, growth hormone (GH) has been proposed as another candidate, because in the larval stages the expression of the mRNA GH is high but it is downregulated in the climax stages of metamorphosis or following treatment with thyroid hormone. In the present study, we investigated whether GH promotes the development of one particular larval-type feature of bullfrog tadpole skin in vitro. The amiloride-,acetylcholine- and ATP-stimulated short-circuit current (SCC) is a physiological marker of larval-type bullfrog skin. These types of ligand-stimulated SCC (1) developed when EDTA-treated tadpole skin was cultured with corticoids supplemented with PRL or GH and (2) were not significantly different between skin cultured with PRL and intact tadpole skin. However, the amiloride-induced SCC response in skin cultured with GH differed in its kinetics from that of the intact (control) tadpole. On this basis, PRL seems a better candidate than GH for the juvenile hormone, at least with regard to the development of amiloride-stimulated non-selective cation channels.
High mechanical efficiency of the cross-bridge powerstroke in skeletal muscle
Authors: Sugi Haruo , Iwamoto Hiroyuki , Akimoto Tsuyoshi , Kishi Hirohiko
Published: February 2003

We were interested to estimate the maximum mechanical efficiency with which chemical energy derived from ATP hydrolysis is converted into mechanical work by individual cross-bridges when they perform their powerstroke synchronously. Glycerinated rabbit psoas muscle fibres, containing ATP molecules almost equal in number to the cross-bridges within the fibre, were activated to shorten under various afterloads by laser-flash photolysis of caged Ca2+. In these conditions, almost all the cross-bridges are in the state where the ATP is hydrolyzed but the products have not yet been released from the cross-bridge (M-ADP-Pi) immediately before activation, and can hydrolyze only one ATP molecule during the flash-induced mechanical response. Power output records of the fibres following activation indicated that the cross-bridges actually started their powerstroke almost synchronously. The amount of ATP utilized at 1 s after activation was estimated from the amount of isometric force developed after interruption of fibre shortening, while the amount of work done was calculated by multiplying the amount of afterload by the distance of fibre shortening. A conservative estimation of the maximum mechanical efficiency at a load of 0.5–0.6 Po was 0.7, suggesting that the actual maximum mechanical efficiency of cross-bridge powerstrokes may be close to unity.
Evolution of water conservation mechanisms inDrosophila
Authors: Gibbs Allen G. , Fukuzato Fernando , Matzkin Luciano M.
Published: February 2003

Flies of the genus Drosophila inhabit a wide range of habitats,from the tropics to deserts to boreal forests. The primary physiological mechanism allowing Drosophila and other insects to survive in arid habitats is a reduction in rates of water loss. To understand mechanisms of water retention in greater detail, we investigated the three main routes by which Drosophila lose water: excretion, cuticular transpiration and respiratory loss through the spiracles. Excretory losses comprised <6% of total water flux and did not differ between xeric (cactophilic) and mesic species. No consistent relationship was observed between water-loss rates and the composition, physical properties or amounts of cuticular hydrocarbons,suggesting that cuticular transpiration did not differ among species from different habitats. Metabolic rates and water-loss rates were highly correlated. Cactophilic Drosophila were less active, and female cactophiles had lower metabolic rates than female mesic species of the same size. They were also more likely to exhibit a pattern of cyclic CO2release that may help to conserve water. We conclude that lower overall rates of water loss are achieved primarily by reduction of respiratory losses.
Modulation of foregut synaptic activity controls resorption of molting fluid during larval molts of the mothManduca sexta
Authors: Bestman Jennifer E. , Booker Ronald
Published: February 2003

We examined the role of the foregut in the resorption of molting fluid (MF)from the exuvial space during the last larval–larval molt of the moth Manduca sexta. In intermolt larvae, the activity of the foregut is characterized by robust peristaltic contractions. With the onset of the molt,MF is secreted into the exuvial space where it digests and weakens the old cuticle. The appearance of MF in the exuvial space is accompanied by a dramatic reduction in the amplitude of the foregut contractions. Foregut peristalsis returned about halfway through the molt, followed shortly by the appearance of MF in the gut. These observations suggested that larvae use their foreguts to remove MF from the exuvial space. Animals whose foreguts were surgically inactivated did not resorb their MF and most failed to successfully shed their old cuticles. The reduction in foregut motility at the onset of the molt was correlated with a sharp decline in the amplitude of the excitatory junctional potentials. With the onset of the molt there was also a decline in the number of presynaptic terminals on the foregut that loaded with the activity-dependent dye FM1-43. In the second half of the molt, the appearance of MF in the foregut and the return of foregut motility was correlated with an increase in FM1-43 loading. These data reveal that during a larval–larval molt, vesicle release and/or recycling of the presynaptic endings on the foregut muscles is modulated to assure the proper timing of MF resorption.
Age and aerobic performance in deer mice
Authors: Chappell Mark A. , Rezende Enrico L. , Hammond Kimberly A.
Published: February 2003

Age impacts the phenotype of all multicellular animals, but lifetime changes in physiological traits are poorly understood for all but a few species. Here, we describe a cross-sectional study of age effects on body composition, aerobic performance and ventilation in deer mice Peromyscus maniculatus. This species lives considerably longer in captivity (in excess of 5 years) than most laboratory rodents, and the adaptational biology of its aerobic physiology is well studied. Our deer mice grew throughout life,and, as is typical for mammals, their basal metabolic rate (BMR) and maximal oxygen consumption in exercise(V̇O2max) and thermogenesis(V̇O2sum)increased as power functions of mass. Age did not affect BMR, but we found abrupt decreases in growth rate, V̇O2max and V̇O2sum at approximately 485 days of age, and the mass-adjusted maximal aerobic performance of old mice (5 years of age) was 20%(V̇O2max) to 35%(V̇O2sum) less than that of young animals. Breathing frequency (f) and oxygen extraction (EO2) also declined with age but did not change abruptly. However, there were no consistent age-related changes in tidal volume (VT) or minute volume(V̇min) after accounting for the effects of mass and V̇O2sum. Age influenced several aspects of body composition (lean and fat mass). However,these changes were insufficient to explain the age-related declines in aerobic performance, suggesting that mass-specific oxidative capacity of lean tissue decreased with age. The performance changes we found could engender substantial reductions in the mobility and thermal tolerances of old deer mice. However, very few wild mice are likely to survive to ages where substantial performance decreases occur, so these declines are probably not subjected to strong selection in natural populations.
Tolerance analysis and synthesis using the mean shift model
Authors: Stefano P Di
Published: February 2003

Tolerance design plays an important role in the modern design process by introducing quality improvements and limiting manufacturing costs. In this paper a method for statistical tolerance analysis and synthesis is presented. This method is implemented using the mean shift model of Chase and Greenwood, providing a systematic approach to evaluate the mean shift factor. This method considers all the principal factors that affect the statistical sum of a certain number of assembly dimensions. In particular, the considered factors include the mean shift ratio, the confidence level, the number of dimension of the assembly and the tolerance assortment between the component dimensions.

An implementation of the mean shift model for tolerances synthesis is described. The tolerances synthesis is performed in an unusual way, taking into account in the optimization process the typical parameters that affect the product variability. For this purpose the method uses four types of condition for the dimensional tolerances: fixed tolerance value, fixed mean shift ratio, fixed mean shift and fixed natural variability. Furthermore, in the optimization process, the service variability is considered under two conditions: fixed and valuable service variability. A case study is presented and the results of some simulations are discussed.
The vibration of ring-stiffened prolate domes under external water pressure
Authors: Ross C T F , Little A P F , Chasapides L , Banks J , Attanasio D
Published: February 2003

The paper presents a theoretical and an experimental investigation into the free vibration of three ring-stiffened prolate domes in air and under external water pressure. The theoretical investigation was via the finite element method where a solid fluid mesh was used to model the water surrounding each dome. Good agreement was found between theory and experiment. Both the theory and the experiment found that, as the external water pressure was increased, the resonant frequencies decreased.
Dynamic absorption in a vibrating beam
Authors: Singh A N , Ram Y M
Published: February 2003

The paper deals with dynamic absorption in a harmonically excited beam. It is shown that the harmonic response of vibration at a desired position can be made to vanish by applying a feedback control at a single point. Two expressions for the control gain are given. One is based on deformation and the other is based on spectral data. The stability of the controlled system is analysed. Numerical examples demonstrate the various results.
Dynamic modelling of the latch needle cam system of weft knitting machines
Authors: Jeong K Y , Kim Y-B
Published: February 2003

Knitted textile fabrics are usually produced on weft knitting machines. The basic mechanism of the machines to convert textile yarn into knitted fabric is called a latch needle cam system. A rigid-body model with five bodies is set up to analyse the motion of the needle of the latch needle cam system. The force element is modelled as a spring damper element between the needle butt and each virtual body on the cam curves. The spring constant is obtained from the cam angle, the friction coefficient and the stiffness of the needle. Numerical examples are given to show the path of the needle butt and the forces between the needle and the cams. For various rotational speeds of the cylinder, the maximum vertical and horizontal forces are obtained.
Closed-form kinematic solution of a non-parallel cable reeving crane system
Authors: Kim D-H , Lee J-W , Park K-T , Oh J-H
Published: February 2003

This paper presents the closed-form kinematic solutions, position and velocity of a non-parallel cable reeving crane system. These solutions are necessary in order to control a container crane that is widely used in cargo terminals. One PSD (position sensitive device) sensor and two IR (infrared) emissive beacons are used to find the angular position and angular velocity information of two reference points of a moving spreader. The sensor and beacons are mounted on trolley and reference points of spreader respectively. By using this information, the exact position and velocity of the spreader are determined analytically. These results can be used in the anti-sway and anti-skew control of a container crane.
The half-wetted bearing. Part 1: Extended Reynolds equation
Authors: Spikes H. A.
Published: February 2003

Recent research has shown that, when a liquid is partially wetting or non-wetting against a very smooth solid surface, the conventional no-slip boundary condition can break down. Under such circumstances, the Reynolds equation is no longer applicable. In the current paper, the Reynolds equation is extended to consider the sliding, hydrodynamic lubrication condition where the lubricant has a no-slip boundary condition against the moving solid surface but can slip at a critical shear stress against the stationary surface. It is shown that such a ‘half-wetted’ bearing is able to combine good load support resulting from fluid entrainment with very low friction due to very low or zero Couette friction.
The half-wetted bearing. Part 2: Potential application in low load contacts
Authors: Spikes H. A.
Published: February 2003

In a companion paper (Part 1) a hydrodynamic lubrication model was developed to describe the flow and pressure in a bearing in which the lubricant has a no-slip boundary condition with one bearing surface but can slip against the other surface at a critical shear stress. This paper examines the current evidence for liquid slip at solid surfaces and outlines the problems inherent in the lubrication of low load contacts. The paper then shows that a bearing design in which one surface is very smooth and oleophobic, thereby allowing lubricant slip to occur, while the other surface is conventionally oleophilic, may provide a very low friction coefficient in low load conditions such as are present in microelectromechanical systems and hard disk drives.