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PubMed2003

Experimental searches for galactic halo axions.

A very light axion would be copiously produced during the Big Bang as a zero-temperature Bose gas, and it would possess vanishingly small couplings to matter and radiation. It thus represents an ideal cold dark matter candidate. Galactic halo axions may be detected by their resonant conversion to microwave photons in a high-Q cavity permeated by a strong magnetic field. A large-scale search for the axion is ongoing in the US with sufficient sensitivity to see axions of plausible model couplings. Dramatic breakthroughs in the development of near-quantum limited superconducting quantum interference device amplifiers promise to improve the sensitivity of the experiment by a factor of 30 in the near future. In Japan, a group has been developing a Rydberg atom single-quantum detector as an alternative to linear amplifiers for a microwave-cavity axion experiment. Should the axion be discovered, the predicted fine structure in the axion signal would be rich in information about the history of galactic formation.

Journal Article↗

PubMedDate not supplied

Cytochrome P-450 spin state: inorganic biochemistry of haem iron ligation and functional significance.

Haem ligation in cytochrome P-450 has been reviewed and the nature of the fifth and sixth ligands of the haemoprotein in the ferric low-spin, ferric high-spin, ferrous and ferrous-carbon-monoxy states have been discussed. Factors controlling the cytochrome P-450 spin equilibrium have been described, including substrate and functional components of the mixed-function oxidase system. In addition, a thermodynamic model describing the interaction of substrate with ferric cytochrome P-450 has been developed in terms of the micro-equilibrium constants governing substrate binding. The functional significance of the cytochrome P-450 spin state with particular reference to control of the first electron reduction of the haemoprotein has been summarized, and a subsequent validation of the spin-redox coupling model of cytochrome P-450-dependent catalysis has been presented.

Animals↗

PubMed2005

EEG analysis with nonlinear excitable media.

The detection of patterns embedded within a complex, nonstationary, and noisy background activity is a crucial and important task in EEG analysis. The authors present a biologically inspired, analog approach to EEG analysis that is conceptually different from a variety of statistical approaches currently used. A nonlinear, excitable, spatially extended medium that is composed of diffusively coupled model neurons is considered. When EEG recordings are applied as local perturbations to such an excitable neural tissue, the induced transient changes in the dynamics of the perturbed system can be regarded as an instantaneous characterization of transient processes in the brain reflected by the EEG, e.g., in the form of a sequence of correlated dynamical events (patterns). Nonlinear excitable media can be implemented in form of an array of locally coupled integrated analog nonlinear electrical circuits called cellular neural networks, which represent a next evolutionary step in the parallel analog computer architecture. Using cellular neural networks, the authors show that the concept of signal-induced pattern generation allows an almost instantaneous and unsupervised detection of seizure onsets in EEG recordings. In addition, they show that a cellular neural network can be trained in a supervised way to approximate the degree of synchronization in EEG recordings. The resulting pattern-recognition device may be suitable for the prediction of epileptic seizures.

Animals↗

PubMed2005

Primary and secondary relaxations in bis-5-hydroxypentylphthalate revisited.

The molecular structure of bis-5-hydroxypentylphthalate (BHPP) is like dihexyl phthalate but having appended to it two hydroxyl end groups, which contribute additional dipole moments and capacity for hydrogen-bond formation. In a previously published dielectric study of the primary and secondary relaxations of BHPP, it was found that all the dynamic properties are normal except for the anomalously large width of the primary relaxation loss peak. There are two secondary relaxations, the relaxation time of the slower one increases with increasing pressure, whereas that of the faster one is practically insensitive to pressure. Hence, the slower secondary relaxation is the "universal" Johari-Goldstein (JG) [J. Chem. Phys. 53, 2372 (1970); 55, 4245 (1971)] relaxation in BHPP. All is well except if the observed large width of the primary relaxation were an indication of a corresponding large coupling parameter n=0.45 in the coupling model. Then the predicted relations between the primary relaxation time tau(alpha) and the JG relaxation time tau(JG) found previously to hold in many glass formers would be violated. It was recognized that this singular behavior of BHPP is likely due to broadening of the primary loss peak by the overlapping contributions of two independent dipole moments present in BHPP, and the actual coupling parameter is smaller. However, at the time of publication of the previous work there were not enough data to support this explanation. By making broadband dielectric measurements of dibutyl phthalate (DBP) and dioctyl phthalate (DOP) that have chemical structures closely related to BHPP but with only one dipole moment, we show that all their dynamic properties are almost the same as BHPP but the widths of their primary relaxation loss peaks are significantly narrower corresponding to a smaller coupling parameter n=0.34. The new data presented here indicate that the coupling parameter of BHPP is about the same as DBP and DOP, and the predicted relations between tau(alpha) and tau(JG) of BHPP are brought back in agreement with the experimental data.

Journal Article↗

PubMed2006

Computer simulation of native epidermal enzyme structures in the presence and absence of hydrogen peroxide (H2O2): potential and pitfalls.

The human epidermis is especially vulnerable to oxidative stress, which in turn leads to oxidation of important antioxidant enzymes, other proteins, and peptides. Molecular dynamic computer modelling is a new powerful tool to predict or confirm oxidative stress-mediated structural changes consequently altering the function of enzymes/proteins/peptides. Here we used examples of important epidermal antioxidant enzymes before and after hydrogen peroxide (H(2)O(2))-mediated oxidation of susceptible amino-acid residues (i.e. tryptophan, methionine, cysteine, and selenocysteine), which can affect enzyme active sites, cofactor binding, or dimerization/tetramerization domains. Computer modelling predicts that enzyme active sites are altered by H(2)O(2)-mediated oxidation in thioredoxin reductase (TR) and acetylcholinesterase (AchE), whereas cofactor nicotinamide adenine dinucleotide phosphate (reduced form) binding is affected in both catalase and TR but not in glutathione peroxidase. Dimerization is prevented in catalase. These structural changes lead to impaired functionality. Fourier transform-Raman- and Fluorescence spectroscopy together with enzyme kinetics support the results. There are limitations of modelling as demonstrated on the AchE substrate-binding domain, where the computer predicted deactivation, which could not be confirmed by enzyme kinetics. Computer modelling coupled with classical biochemical techniques offers a new powerful tool in cutaneous biology to explore oxidative stress-mediated metabolic changes in the skin.

Computer Simulation↗

PubMedDate not supplied

Cost-effectiveness of harm reduction in preventing hepatitis C among injection drug users.

OBJECTIVES: Hepatitis C (HCV) has emerged as a major epidemic among injection drug users (IDUs), with observed prevalence exceeding 70% in many American and European cities. This article explores the potential of syringe exchange programs (SEPs) to reduce HCV incidence and prevalence. DESIGN: A random-mixing epidemiological model is used to examine the potential impact of harm reduction interventions. METHODS: Steady-state analysis is used to scrutinize the impact of SEP on HCV incidence and prevalence and to examine the accuracy of short-term incidence analysis in predicting long-run program effects. RESULTS: SEP is predicted to have little impact on HCV incidence and prevalence within realistic populations of IDUs. CONCLUSIONS: Short-term incidence analysis substantially overstates SEP effectiveness and cost-effectiveness in preventing HCV. More comprehensive harm reduction models, coupled with referral of active IDUs to treatment, must complement syringe exchange to successfully contain highly infectious blood-borne diseases.

Blood-Borne Pathogens↗

PubMed2005

Modelled atmospheric temperatures and global sea levels over the past million years.

Marine records of sediment oxygen isotope compositions show that the Earth's climate has gone through a succession of glacial and interglacial periods during the past million years. But the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep-water temperature affect the recorded isotopic composition. Separating these two effects would require long records of either sea level or deep-ocean temperature, which are currently not available. Here we use a coupled model of the Northern Hemisphere ice sheets and ocean temperatures, forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores, to quantify both contributions simultaneously. We find that the ice-sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima, suggesting that strong ocean cooling preceded slow ice-sheet build-up. The model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 degrees N, ice volume and global sea level. We find that during extreme glacial stages, air temperatures were 17 +/- 1.8 degrees C lower than present, with a 120 +/- 10 m sea level equivalent of continental ice present.

Animals↗

PubMedDate not supplied

Comparative life-cycle assessments for biomass-to-ethanol production from different regional feedstocks.

This study compares life-cycle (cradle-to-gate) energy consumption and environmental impacts for producing ethanol via fermentation-based processes starting with two lignocellulosic feedstocks: virgin timber resources or recycled newsprint from an urban area. The life-cycle assessment in this study employed a novel combination of computer-aided tools. These tools include fermentation process simulation coupled with an impact assessment software tool for the manufacturing process life-cycle stage impacts. The process simulation file was provided by the National Renewable Energy Laboratory (NREL) and was modified slightly to accommodate these different feedstocks. For the premanufacturing process life-cycle stage impacts, such as the fuels and process chemicals used, transportation, and some preparatory steps (wood chipping, etc.), a life-cycle inventory database (the Boustead Model) coupled with an impact assessment software tool were used (the Environmental Fate and Risk Assessment Tool). The Newsprint process has a slightly lower overall composite environmental index (created from eight impact categories) compared to the Timber process. However, the Timber process consumes less electricity, produces fewer emissions in total, and has less of a human health impact. The amount of life-cycle fossil energy required to produce ethanol is 14% of the energy content of the product, making the overall efficiency 86%. Process improvement strategies were evaluated for both feedstock processes, including recycle of reactor vent air and heat integration. Heat integration has the greatest potential to reduce fossil-derived energy consumption, to an extent that fossil-derived energy over the life cycle is actually saved per unit of ethanol produced. These energy efficiency values are superior to those observed in conventional fossil-based transportation fuels.

Biotechnology↗

PubMed2006

Identifying perinatal risk factors for infant maltreatment: an ecological approach.

BACKGROUND: Child maltreatment and its consequences are a persistent problem throughout the world. Public health workers, human services officials, and others are interested in new and efficient ways to determine which geographic areas to target for intervention programs and resources. To improve assessment efforts, selected perinatal factors were examined, both individually and in various combinations, to determine if they are associated with increased risk of infant maltreatment. State of Georgia birth records and abuse and neglect data were analyzed using an area-based, ecological approach with the census tract as a surrogate for the community. Cartographic visualization suggested some correlation exists between risk factors and child maltreatment, so bivariate and multivariate regression were performed. The presence of spatial autocorrelation precluded the use of traditional ordinary least squares regression, therefore a spatial regression model coupled with maximum likelihood estimation was employed. RESULTS: Results indicate that all individual factors or their combinations are significantly associated with increased risk of infant maltreatment. The set of perinatal risk factors that best predicts infant maltreatment rates are: mother smoked during pregnancy, families with three or more siblings, maternal age less than 20 years, births to unmarried mothers, Medicaid beneficiaries, and inadequate prenatal care. CONCLUSION: This model enables public health to take a proactive stance, to reasonably predict areas where poor outcomes are likely to occur, and to therefore more efficiently allocate resources. U.S. states that routinely collect the variables the National Center for Health Statistics (NCHS) defines for birth certificates can easily identify areas that are at high risk for infant maltreatment. The authors recommend that agencies charged with reducing child maltreatment target communities that demonstrate the perinatal risks identified in this study.

Child Abuse↗

PubMed2001

Impaired inhibitory G-protein function contributes to increased calcium currents in rats with diabetic neuropathy.

There is a growing body of evidence that sensory neuropathy in diabetes is associated with abnormal calcium signaling in dorsal root ganglion (DRG) neurons. Enhanced influx of calcium via multiple high-threshold calcium currents is present in sensory neurons of several models of diabetes mellitus, including the spontaneously diabetic BioBred/Worchester (BB/W) rat and the chemical streptozotocin (STZ)-induced rat. We believe that abnormal calcium signaling in diabetes has pathologic significance as elevation of calcium influx and cytosolic calcium release has been implicated in other neurodegenerative conditions characterized by neuronal dysfunction and death. Using electrophysiologic and pharmacologic techniques, the present study provides evidence that significant impairment of G-protein-coupled modulation of calcium channel function may underlie the enhanced calcium entry in diabetes. N- and P-type voltage-activated, high-threshold calcium channels in DRGs are coupled to mu opiate receptors via inhibitory G(o)-type G proteins. The responsiveness of this receptor coupled model was tested in dorsal root ganglion (DRG) neurons from spontaneously-diabetic BB/W rats, and streptozotocin-induced (STZ) diabetic rats. Intracellular dialysis with GTPgammaS decreased calcium current amplitude in diabetic BB/W DRG neurons compared with those of age-matched, nondiabetic controls, suggesting that inhibitory G-protein activity was diminished in diabetes, resulting in larger calcium currents. Facilitation of calcium current density (I(DCa)) by large-amplitude depolarizing prepulses (proposed to transiently inactivate G proteins), was significantly less effective in neurons from BB/W and STZ-induced diabetic DRGs. Facilitation was enhanced by intracellular dialysis with GTPgammaS, decreased by pertussis toxin, and abolished by GDPbetaS within 5 min. Direct measurement of GTPase activity using opiate-mediated GTPgamma[(35)S] binding, confirmed that G-protein activity was significantly diminished in STZ-induced diabetic neurons compared with age-matched nondiabetic controls. Diabetes did not alter the level of expression of mu opiate receptors and G-protein alpha subunits. These studies indicate that impaired regulation of calcium channels by G proteins is an important mechanism contributing to enhanced calcium influx in diabetes.

Analgesics, Opioid↗

PubMed2004

Proportional odds ratio model for comparison of diagnostic tests in meta-analysis.

BACKGROUND: Consider a meta-analysis where a 'head-to-head' comparison of diagnostic tests for a disease of interest is intended. Assume there are two or more tests available for the disease, where each test has been studied in one or more papers. Some of the papers may have studied more than one test, hence the results are not independent. Also the collection of tests studied may change from one paper to the other, hence incomplete matched groups. METHODS: We propose a model, the proportional odds ratio (POR) model, which makes no assumptions about the shape of ORp, a baseline function capturing the way OR changes across papers. The POR model does not assume homogeneity of ORs, but merely specifies a relationship between the ORs of the two tests. One may expand the domain of the POR model to cover dependent studies, multiple outcomes, multiple thresholds, multi-category or continuous tests, and individual-level data. RESULTS: In the paper we demonstrate how to formulate the model for a few real examples, and how to use widely available or popular statistical software (like SAS, R or S-Plus, and Stata) to fit the models, and estimate the discrimination accuracy of tests. Furthermore, we provide code for converting ORs into other measures of test performance like predictive values, post-test probabilities, and likelihood ratios, under mild conditions. Also we provide code to convert numerical results into graphical ones, like forest plots, heterogeneous ROC curves, and post test probability difference graphs. CONCLUSIONS: The flexibility of POR model, coupled with ease with which it can be estimated in familiar software, suits the daily practice of meta-analysis and improves clinical decision-making.

Data Interpretation, Statistical↗

PubMed2006

Simulation of future stream alkalinity under changing deposition and climate scenarios.

Models of soil and stream water acidification have typically been applied under scenarios of changing acidic deposition, however, climate change is usually ignored. Soil air CO2 concentrations have potential to increase as climate warms and becomes wetter, thus affecting soil and stream water chemistry by initially increasing stream alkalinity at the expense of reducing base saturation levels on soil exchange sites. We simulate this change by applying a series of physically based coupled models capable of predicting soil air CO2 and stream water chemistry. We predict daily stream water alkalinity for a small catchment in the Virginia Blue Ridge for 60 years into the future given stochastically generated daily climate values. This is done for nine different combinations of climate and deposition. The scenarios for both climate and deposition include a static scenario, a scenario of gradual change, and a scenario of abrupt change. We find that stream water alkalinity continues to decline for all scenarios (average decrease of 14.4 microeq L-1) except where climate is gradually warming and becoming more moist (average increase of 13 microeq L-1). In all other scenarios, base cation removal from catchment soils is responsible for limited alkalinity increase resulting from climate change. This has implications given the extent that acidification models are used to establish policy and legislation concerning deposition and emissions.

Acid Rain↗

PubMed1994

Factors influencing organic carbon preservation in marine sediments.

The organic matter that escapes decomposition is buried and preserved in marine sediments, with much debate as to whether the amount depends on bottom-water O2 concentration. One group argues that decomposition is more efficient with O2, and hence, organic carbon will be preferentially oxidized in its presence, and preserved in its absence. Another group argues that the kinetics of organic matter decomposition are similar in the presence and absence of O2, and there should be no influence of O2 on preservation. A compilation of carbon preservation shows that both groups are right, depending on the circumstances of deposition. At high rates of deposition, such as near continental margins, little difference in preservation is found with varying bottom-water O2. It is important that most carbon in these sediments decomposes by anaerobic pathways regardless of bottom-water O2. Hence, little influence of bottom-water O2 on preservation would, in fact, be expected. As sedimentation rate drops, sediments deposited under oxygenated bottom water become progressively more aerobic, while euxinic sediments remain anaerobic. Under these circumstances, the relative efficiencies of aerobic and anaerobic decomposition could affect preservation. Indeed, enhanced preservation is observed in low-O2 and euxinic environments. To explore in detail the factors contributing to this enhanced carbon preservation, aspects of the biochemistries of the aerobic and anaerobic process are reviewed. Other potential influences on preservation are also explored. Finally, a new model for organic carbon decomposition, the "pseudo-G" model, is developed. This model couples the degradation of refractory organic matter to the overall metabolic activity of the sediment, and has consequences for carbon preservation due to the mixing together of labile and refractory organic matter by bioturbation.

Aerobiosis↗

PubMed2005

New developments in a strongly coupled cardiac electromechanical model.

AIM: The aim of this study is to develop a coupled three-dimensional computational model of cardiac electromechanics to investigate fibre length transients and the role of electrical heterogeneity in determining left ventricular function. METHODS: A mathematical model of cellular electromechanics was embedded in a simple geometric model of the cardiac left ventricle. Electrical and mechanical boundary conditions were applied based on Purkinje fibre activation times and ventricular volumes through the heart cycle. The mono-domain reaction diffusion equations and finite deformation elasticity equations were solved simultaneously through the full pump cycle. Simulations were run to assess the importance of cellular electrical heterogeneity on myocardial mechanics. RESULTS: Following electrical activation, mechanical contraction moves out through the wall to the circumferentially oriented mid-wall fibres, producing a progressively longitudinal and twisting deformation. This is followed by a more spherical deformation as the inclined epicardial fibres are activated. Mid-way between base and apex peak tensions and fibre shortening of 40 kPa and 5%, respectively, are generated at the endocardial surface with values of 18 kPa and 12% at the epicardial surface. Embedding an electrically homogeneous cell model for the same simulations produced equivalent values of 36.5 kPa, 4% at the endocardium and 14 kPa, 13.5% at the epicardium. CONCLUSION: The substantial redistribution of fibre lengths during the early pre-ejection phase of systole may play a significant role in preparing the mid-wall fibres to contract. The inclusion of transmural heterogeneity of action potential duration has a marked effect on reducing sarcomere length transmural dispersion during repolarization.

Computer Simulation↗

PubMed1996

Heme-Peptide Models for Hemoproteins. 2. N-Acetylmicroperoxidase-8: Study of the pi-pi Dimers Formed at High Ionic Strength Using a Modified Version of Molecular Exciton Theory.

AcMP8 is the Cys-14-acetylated water-soluble heme-octapeptide fragment obtained proteolytically from cytochrome c. Two successive dimerization equilibria are observed with increasing ionic strength in aqueous solution at neutral pH (part 1, preceding article). The electronic spectra of the two pi-pi dimers were extracted from the absorption envelopes at 2.01 and 4.02 M ionic strength and resolved by Gaussian analysis. The principal transitions were assigned using a tailored version of molecular exciton theory based on coupling of the main x- and y-polarized transition dipole moments of the interacting heme groups. The spectra of both pi-pi dimers indicate that the y-polarized exciton states are blue-shifted relative to the excited states of the monomer, while the x-polarized exciton states exhibit a red shift. These shifts were correctly predicted by a simple dipole-dipole coupling model. From an analysis of the resultant transition dipole moments to the exciton states with B(x)()(0,0) and B(y)()(0,0) character and the magnitudes of their red and blue exciton shifts, respectively, we have determined the dipole-dipole interaction geometries for both dimers. The principal difference between the interaction geometry in the first dimer and that in the second is a stronger interaction for the y-polarized transition dipoles and somewhat weakened interaction for the x-polarized transition dipoles. From an analysis of available crystallographic data for porphyrin and metalloporphyrin pi-pi dimers (Scheidt, W. R.; Lee, Y. J. Struct. Bonding 1987, 64, 1) and the results of our exciton model, we conclude that the origin of the coordinate system for the Soret transition dipole moments of AcMP8 is not metal-centered. Furthermore, since the true directions of the x- and y-axes of the low-symmetry heme chromophore in AcMP8 are unknown, we have not been able to determine the structures of the pi-pi dimers from a knowledge of their transition dipole-dipole interaction geometries. This study therefore highlights one of the shortfalls of molecular exciton theory.

Journal Article↗

PubMed2004

The C-neu mammary carcinoma in Oncomice; characterization and monitoring response to treatment with herceptin by magnetic resonance methods.

To characterize spontaneously occurring c-neu/HER2 overexpressing tumours in oncomice and their response to herceptin by non-invasive magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). Oncomice were monitored by localized 31P MRS during unperturbed growth and before and after treatment with 10 mg/kg herceptin (Hoffman La Roche) intraperitoneally for up to 21 days post-treatment. Vascular morphology and function was assessed by quantitation of tumour magnetic resonance (MR) relaxation rates R2* and R2 prior to and either during carbogen (95% O2/5% CO2) breathing or following administration of the blood-pool contrast agent NC100150 (Clariscan, Amersham Health). Immunohistochemistry showed strong membrane staining for HER2 protein overexpression. The 31P MRS showed only a significant (p<0.01) increase of phosphomonoester / total phosphate ratio over 21 days of growth. Herceptin increased the tumour volume doubling time compared to untreated tumours and significantly increased the phosphomonoester / beta-nucleoside triphosphate ratio 2 days after treatment (p=0.01). Tumours showed a highly heterogeneous yet significant (p<0.01) decrease or increase in R2* in response to carbogen or NC100150 respectively. The absence of a decline in tumour bioenergetics with growth, commonly seen in 31P MRS studies of transplanted rodent tumour models, coupled with the heterogeneous blood volume revealed by 1H MRI, suggest a metabolic and vascular phenotype similar to that found in human tumours.

Animals↗

PubMed1979

The induced circular dichroism of proflavine intercalated to DNA. Dye-polymer exciton interactions.

The circular dichroism induced in the visible absorption band of proflavine cation isolatedly intercalated to DNA was investigated in terms of the dye-DNA base pair exciton interaction. The remarkable ionic strength dependence of the induced CD magnitude was in good accord with the CD magnitude calculated on the basis of the dye-polymer Frenkel exciton interaction model and under the extent of helix deformation required for intercalation. In particular the application of the internal and modified intercalation models coupled with the deep trap approximation implied that the preference of the modified intercalation due to electrostatic interaction between the acridine-nitrogen atom and the DNA phosphate group is combined with relatively high ionic strength compared with the internal intercalation.

Acridines↗

PubMed2006

Patterns of mechanical energy change in tetrapod gait: pendula, springs and work.

Kinematic and center of mass (CoM) mechanical variables used to define terrestrial gaits are compared for various tetrapod species. Kinematic variables (limb phase, duty factor) provide important timing information regarding the neural control and limb coordination of various gaits. Whereas, mechanical variables (potential and kinetic energy relative phase, %Recovery, %Congruity) provide insight into the underlying mechanisms that minimize muscle work and the metabolic cost of locomotion, and also influence neural control strategies. Two basic mechanisms identified by Cavagna et al. (1977. Am J Physiol 233:R243-R261) are used broadly by various bipedal and quadrupedal species. During walking, animals exchange CoM potential energy (PE) with kinetic energy (KE) via an inverted pendulum mechanism to reduce muscle work. During the stance period of running (including trotting, hopping and galloping) gaits, animals convert PE and KE into elastic strain energy in spring elements of the limbs and trunk and regain this energy later during limb support. The bouncing motion of the body on the support limb(s) is well represented by a simple mass-spring system. Limb spring compliance allows the storage and return of elastic energy to reduce muscle work. These two distinct patterns of CoM mechanical energy exchange are fairly well correlated with kinematic distinctions of limb movement patterns associated with gait change. However, in some cases such correlations can be misleading. When running (or trotting) at low speeds many animals lack an aerial period and have limb duty factors that exceed 0.5. Rather than interpreting this as a change of gait, the underlying mechanics of the body's CoM motion indicate no fundamental change in limb movement pattern or CoM dynamics has occurred. Nevertheless, the idealized, distinctive patterns of CoM energy fluctuation predicted by an inverted pendulum for walking and a bouncing mass spring for running are often not clear cut, especially for less cursorial species. When the kinematic and mechanical patterns of a broader diversity of quadrupeds and bipeds are compared, more complex patterns emerge, indicating that some animals may combine walking and running mechanics at intermediate speeds or at very large size. These models also ignore energy costs that are likely associated with the opposing action of limbs that have overlapping support times during walking. A recent model of terrestrial gait (Ruina et al., 2005. J Theor Biol, in press) that treats limb contact with the ground in terms of collisional energy loss indicates that considerable CoM energy can be conserved simply by matching the path of CoM motion perpendicular to limb ground force. This model, coupled with the earlier ones of pendular exchange during walking and mass-spring elastic energy savings during running, provides compelling argument for the view that the legged locomotion of quadrupeds and other terrestrial animals has generally evolved to minimize muscle work during steady level movement.

Animals↗