bluuebunny/crossref_metadata_2025 huggingface dataset:
The NRAMP6 metal transporter contributes to cadmium toxicity
Authors: Cailliatte Rémy , Lapeyre Bruno , Briat Jean-François , Mari Stéphane , Curie Catherine
Published: June 2009

NRAMP (natural resistance-associated macrophage protein) homologues are evolutionarily conserved bivalent metal transporters. In Arabidopsis, AtNRAMP3 and AtNRAMP4 play a key role in iron nutrition of the germinating plantlet by remobilizing vacuolar iron stores. In the present paper we describe the molecular and physiological characterization of AtNRAMP6. AtNRAMP6 is predominantly expressed in the dry seed embryo and to a lesser extent in aerial parts. Its promoter activity is found diffusely distributed in cotyledons and hypocotyl, as well as in the vascular tissue region of leaf and flower. We show that the AtNRAMP6 transcript coexists with a partially spliced isoform in all shoot cell types tested. When expressed in yeast, AtNRAMP6, but not its misspliced derivative, increased sensitivity to cadmium without affecting cadmium content in the cell. Likewise, Arabidopsis transgenic plants overexpressing AtNRAMP6 were hypersensitive to cadmium, although plant cadmium content remained unchanged. Consistently, a null allele of AtNRAMP6, named nramp6-1, was more tolerant to cadmium toxicity, a phenotype that was reverted by expressing AtNRAMP6 in the mutant background. We used an AtNRAMP6::HA (where HA is haemagglutinin) fusion, shown to be functional in yeast, to demonstrate through immunoblot analysis of membrane fractions and immunofluorescence localization that, in yeast cells, AtNRAMP6 is targeted to a vesicular-shaped endomembrane compartment distinct from the vacuole or mitochondria. We therefore propose that AtNRAMP6 functions as an intracellular metal transporter, whose presence, when modified, is likely to affect distribution/availability of cadmium within the cell.
Sodium nitrite therapy attenuates the hypertensive effects of HBOC-201 via nitrite reduction
Authors: Rodriguez Cilina , Vitturi Dario A. , He Jin , Vandromme Marianne , Brandon Angela , Hutchings Anne , Rue Loring W. , Kerby Jeffrey D. , Patel Rakesh P.
Published: June 2009

Hypertension secondary to scavenging of NO remains a limitation in the use of HBOCs (haemoglobin-based oxygen carriers). Recent studies suggest that nitrite reduction to NO by deoxyhaemoglobin supports NO signalling. In the present study we tested whether nitrite would attenuate HBOC-mediated hypertension using HBOC-201 (Biopure), a bovine cross-linked, low-oxygen-affinity haemoglobin. In a similar way to unmodified haemoglobin, deoxygenated HBOC-201 reduced nitrite to NO with rates directly proportional to the extent of deoxygenation. The functional importance of HBOC-201-dependent nitrite reduction was demonstrated using isolated aortic rings and a murine model of trauma, haemorrhage and resuscitation. In the former, HBOC-201 inhibited NO-donor and nitrite-dependent vasodilation when oxygenated. However, deoxygenated HBOC-201 failed to affect nitrite-dependent vasodilation but still inhibited NO-donor dependent vasodilation, consistent with a model in which nitrite-reduction by deoxyHBOC-201 counters NO scavenging. Finally, resuscitation using HBOC-201, after trauma and haemorrhage, resulted in mild hypertension (~5–10 mmHg). Administration of a single bolus nitrite (30–100 nmol) at the onset of HBOC-201 resuscitation prevented hypertension. Nitrite had no effect on mean arterial pressure during resuscitation with LR (lactated Ringer's solution), suggesting a role for nitrite–HBOC reactions in attenuating HBOC-mediated hypertension. Taken together these data support the concept that nitrite can be used as an adjunct therapy to prevent HBOC-dependent hypertension.
Functional conservation of tRNase ZL among Saccharomyces cerevisiae, Schizosaccharomyces pombe and humans
Authors: Zhao Zhen , Su Wenchen , Yuan Sheng , Huang Ying
Published: June 2009

Although tRNase Z from various organisms was shown to process nuclear tRNA 3′ ends in vitro, only a very limited number of studies have reported its in vivo biological functions. tRNase Z is present in a short form, tRNase ZS, and a long form, tRNase ZL. Unlike Saccharomyces cerevisiae, which contains one tRNase ZL gene (scTRZ1) and humans, which contain one tRNase ZL encoded by the prostate-cancer susceptibility gene ELAC2 and one tRNase ZS, Schizosaccharomyces pombe contains two tRNase ZL genes, designated sptrz1+ and sptrz2+. We report that both sptrz1+ and sptrz2+ are essential for growth. Moreover, sptrz1+ is required for cell viability in the absence of Sla1p, which is thought to be required for endonuclease-mediated maturation of pre-tRNA 3′ ends in yeast. Both scTRZ1 and ELAC2 can complement a temperature-sensitive allele of sptrz1+, sptrz1–1, but not the sptrz1 null mutant, indicating that despite exhibiting species specificity, tRNase ZLs are functionally conserved among S. cerevisiae, S. pombe and humans. Overexpression of sptrz1+, scTRZ1 and ELAC2 can increase suppression of the UGA nonsense mutation ade6–704 through facilitating 3′ end processing of the defective suppressor tRNA that mediates suppression. Our findings reveal that 3′ end processing is a limiting step for defective tRNA maturation and demonstrate that overexpression of sptrz1+, scTRZ1 and ELAC2 can promote defective tRNA 3′ processing in vivo. Our results also support the notion that yeast tRNase ZL is absolutely required for 3′ end processing of at least a few pre-tRNAs even in the absence of Sla1p.
Recombinant production of eight human cytosolic aminotransferases and assessment of their potential involvement in glyoxylate metabolism
Authors: Donini Stefano , Ferrari Manuela , Fedeli Chiara , Faini Marco , Lamberto Ilaria , Marletta Ada Serena , Mellini Lara , Panini Michela , Percudani Riccardo , Pollegioni Loredano , Caldinelli Laura , Petrucco Stefania , Peracchi Alessio
Published: June 2009

PH1 (primary hyperoxaluria type 1) is a severe inborn disorder of glyoxylate metabolism caused by a functional deficiency of the peroxisomal enzyme AGXT (alanine-glyoxylate aminotransferase), which converts glyoxylate into glycine using L-alanine as the amino-group donor. Even though pre-genomic studies indicate that other human transaminases can convert glyoxylate into glycine, in PH1 patients these enzymes are apparently unable to compensate for the lack of AGXT, perhaps due to their limited levels of expression, their localization in an inappropriate cell compartment or the scarcity of the required amino-group donor. In the present paper, we describe the cloning of eight human cytosolic aminotransferases, their recombinant expression as His6-tagged proteins and a comparative study on their ability to transaminate glyoxylate, using any standard amino acid as an amino-group donor. To selectively quantify the glycine formed, we have developed and validated an assay based on bacterial GO (glycine oxidase); this assay allows the detection of enzymes that produce glycine by transamination in the presence of mixtures of potential amino-group donors and without separation of the product from the substrates. We show that among the eight enzymes tested, only GPT (alanine transaminase) and PSAT1 (phosphoserine aminotransferase 1) can transaminate glyoxylate with good efficiency, using L-glutamate (and, for GPT, also L-alanine) as the best amino-group donor. These findings confirm that glyoxylate transamination can occur in the cytosol, in direct competition with the conversion of glyoxylate into oxalate. The potential implications for the treatment of primary hyperoxaluria are discussed.
Gain-of-function mutations identify amino acids within transmembrane domains of the yeast vacuolar transporter Zrc1 that determine metal specificity
Authors: Lin Huilan , Burton Damali , Li Liangtao , Warner David E. , Phillips John D. , McVey Ward Diane , KAPLAN Jerry
Published: June 2009

Cation diffusion facilitator transporters are found in all three Kingdoms of life and are involved in transporting transition metals out of the cytosol. The metals they transport include Zn2+, Co2+, Fe2+, Cd2+, Ni2+ and Mn2+; however, no single transporter transports all metals. Previously we showed that a single amino acid mutation in the yeast vacuolar zinc transporter Zrc1 changed its substrate specificity from Zn2+ to Fe2+ and Mn2+ [Lin, Kumanovics, Nelson, Warner, Ward and Kaplan (2008) J. Biol. Chem. 283, 33865–33873]. Mutant Zrc1 that gained iron transport activity could protect cells with a deletion in the vacuolar iron transporter (CCC1) from high iron toxicity. Utilizing suppression of high iron toxicity and PCR mutagenesis of ZRC1, we identified other amino acid substitutions within ZRC1 that changed its metal specificity. All Zrc1 mutants that transported Fe2+ could also transport Mn2+. Some Zrc1 mutants lost the ability to transport Zn2+, but others retained the ability to transport Zn2+. All of the amino acid substitutions that resulted in a gain in Fe2+ transport activity were found in transmembrane domains. In addition to alteration of residues adjacent to the putative metal- binding site in two transmembrane domains, alteration of residues distant from the binding site affected substrate specificity. These results suggest that substrate selection involves co-operativity between transmembrane domains.
Methylation status of oestrogen receptor α-A: a predictor of prognosis in leukaemias
Authors: Yao Jie , Zhang Xiao-Bing , Zhang Xiao-li , Fu Wei-Ling
Published: June 2009

Many studies have shown that epigenetic regulation of ERs (oestrogen receptors) plays a key role in the pathogenesis of leukaemia. In the present study, it was found that the methylated status of ERα-A might serve as an epigenetic biomarker of leukaemias. In this study, the protein expression and cell apoptosis, cycle, proliferation and viability with and without 5-aza-dC (5-aza-2′-deoxycytidine) were evaluated with Western blotting, 3H-TdR (3H-thymidine) incorporation, propidium iodide staining and Trypan Blue staining respectively. The protein expression of ERα was significantly enhanced in all leukaemic cell lines using treatment with the DNA demethylation reagent 5-aza-dC. However, no obvious change in the protein expression of ERβ takes place with 5-aza-dC. And with 5-aza-dC, cell apoptosis, cell cycle, cell proliferation and viability were all inhibited significantly. We also tracked 40 cases of leukaemias with ERα-A methylation (95%; 38 of 40) to observe the prognosis 1 year after chemotherapy treatment. The patients with ERα-A methylation have no obvious symptomatic relief; however, two patients without ERα-A methylation have obtained effective relief. This result suggested that ERα plays a significant role in leukaemogenesis, and the methylated status of ERα-A not only might serve as an epigenetic biomarker of leukaemias for diagnosis, but also has the potential to serve as a predictor of prognosis in leukaemias.
Identification and functional characterization of legumain in amphioxus Branchiostoma belcheri
Authors: Teng Lei , Wada Hiroshi , Zhang Shicui
Published: June 2009

Legumain has been reported from diverse sources such as plants, parasites (animals) and mammals, but little is known in the lower chordates. The present study reports the first characterization of legumain cDNA from the protochordate Branchiostoma belcheri. The deduced 435-amino-acid-long protein is structurally characterized by the presence of a putative N-terminal signal peptide, a peptidase_C13 superfamily domain with the conserved Lys123-Gly124-Asp125 motif and catalytic dyad His153 and Cys195 and two potential Asn-glycosylation sites at Asn85 and Asn270. Phylogenetic analysis demonstrates that B. belcheri legumain forms an independent cluster together with ascidian legumain, and is positioned at the base of vertebrate legumains, suggesting that B. belcheri legumain gene may represent the archetype of vertebrate legumain genes. Both recombinant legumain expressed in yeast and endogenous legumain are able to be converted into active protein of ~37 kDa via a C-terminal autocleavage at acid pH values. The recombinant legumain efficiently degrades the legumain-specific substrate Z-Ala-Ala-Asn-MCA (benzyloxycarbonyl-L-alanyl-L-alanyl-L-asparagine-4-methylcoumaryl-7-amide) at optimum pH 5.5; and the enzymatic activity is inhibited potently by iodoacetamide and N-ethylmaleimide, partially by hen's-egg white cystatin, but not by E-64 [trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane], PMSF and pepstatin A. In addition, legumain is expressed in vivo in a tissue-specific manner, with main expression in the hepatic caecum and hind-gut of B. belcheri. Altogether, these results suggest that B. belcheri legumain plays a role in the degradation of macromolecules in food.
Comparison of Acoustic and Kinematic Approaches to Measuring Utterance-Level Speech Variability
Authors: Howell Peter , Anderson Andrew J. , Bartrip Jon , Bailey Eleanor
Published: June 2009

Purpose

The spatiotemporal index (STI) is one measure of variability. As currently implemented, kinematic data are used, requiring equipment that cannot be used with some patient groups or in scanners. An experiment is reported that addressed whether STI can be extended to an audio measure of sound pressure of the speech envelope over time that did not need specialized equipment.

Method

STI indices of variability were obtained from lip track (L-STI) and amplitude envelope (E-STI) signals. These measures were made concurrent while either fluent speakers or speakers who stutter repeated “Buy Bobby a puppy” 20 times.

Results

L-STI and E-STI correlated significantly. STI decreased with age for both L-STI and E-STI. E-STI scores and L-STI scores discriminated successfully between fluent speakers and speakers who stutter.

Conclusion

The amplitude-envelope-over-time signal can be used to obtain an STI score. This STI score can be used in situations where lip movement STI scores are precluded.
Development and Perceptual Evaluation of Amplitude-Based F0 Control in Electrolarynx Speech
Authors: Saikachi Yoko , Stevens Kenneth N. , Hillman Robert E.
Published: June 2009

Purpose

Current electrolarynx (EL) devices produce a mechanical speech quality that has been largely attributed to the lack of natural fundamental frequency (F0) variation. In order to improve the quality of EL speech, in the present study the authors aimed to develop and evaluate an automatic F0 control scheme, in which F0 was modulated based on variations in the root-mean-square (RMS) amplitude of the EL speech signal.

Method

Recordings of declarative sentences produced by 2 male participants before and after total laryngectomy were used to develop procedures for calculating F0 contours for EL speech. Specifically, the positive linear relationship between F0 and RMS amplitude observed in pre-laryngectomy speech was used as the basis for generating an F0 contour based on the amplitude variation of EL speech. An analysis-by-synthesis approach was used to modify the F0 contour, and a perceptual experiment was conducted to examine its impact on the quality of the EL speech.

Results

The results of perceptual experiments showed that modulating the F0 of EL speech using a linear relationship between amplitude and frequency made it significantly more natural sounding than EL speech with constant F0.

Conclusions

The current study provides preliminary support for amplitude-based control of F0 in EL speech.
Directional Effects on Infants and Young Children in Real Life: Implications for Amplification
Authors: Ching Teresa Y. C. , O’Brien Anna , Dillon Harvey , Chalupper Josef , Hartley Lisa , Hartley David , Raicevich George , Hain Jens
Published: June 2009

Purpose

This study examined the head orientation of young children in naturalistic settings and the acoustics of their everyday environments for quantifying the potential effects of directionality.

Method

Twenty-seven children (11 with normal hearing, 16 with impaired hearing) between 11 and 78 months of age were video recorded in naturalistic settings for analyses of head orientation. Reports on daily activities were obtained from caregivers. The effect of directionality in different environments was quantified by measuring the Speech Transmission Index (STI; H. J. M. Steeneken & T. Houtgast, 1980).

Results

Averaged across 4 scenarios, children looked in the direction of a talker for 40% of the time when speech was present. Head orientation was not affected by age or hearing status. The STI measurements revealed a directional advantage of 3 dB when a child looked at a talker but a deficit of 2.8 dB when the talker was sideways or behind the child. The overall directional effect in real life was between −0.4 and 0.2 dB.

Conclusions

The findings suggest that directional microphones in personal hearing devices for young children are not detrimental and have much potential for benefits in real life. The benefits may be enhanced by fitting directionality early and by counseling caregivers on ways to maximize benefits in everyday situations.
‘Built to last‘ or ‘new and improved’? Trajectories of industrial evolution in the European motorcycle industry, 1885–1993
Authors: Wezel Filippo Carlo , Lomi Alessandro
Published: June 2009

Abstract Technological innovation is widely considered as one of the major determinants of industrial evolution and corporate change. The distinction between competence enhancing and competence destroying innovation provides a suggestive theoretical link between technological change and the dynamics of organizational populations and industries. Yet, empirical evidence in support of this theoretical distinction is relatively weak, and agreement is still lacking about the long‐term consequences of technological innovation for the demography of corporations and industries. In this paper we use data collected on the evolution of the motorcycle manufacturing industries in Great Britain, Germany, France and Italy during the period 1895 and 1993 to analyze the relationship between innovation and demographic rotation in organizational populations. The findings that we report corroborate selected aspects of the theoretical distinction between competence‐enhancing and competence‐destroying innovation. While we find the survival experience of organizations in different countries to be roughly similar, we also discover relevant elements of differentiation across them with respect to radical technological innovation, and to the competitive experience of incumbent companies.
Social knowledge and SMEs' innovative gains from internationalization
Authors: Zahra Shaker A. , Ucbasaran Deniz , Newey Lance R.
Published: June 2009

Abstract Faced with rising competition in their domestic markets and attracted to opportunities in foreign markets, smaller and medium‐sized enterprises (SMEs) are increasingly looking towards internationalization as a means of creating and sustaining competitive advantage. This has heightened researchers' interest in examining the benefits of internationalization beyond just financial outcomes. Internationalization can promote learning and the accumulation of the knowledge, skills and capabilities that SMEs need to survive and prosper. Learning and knowledge accumulation can also improve SMEs' product innovations. Using data from 384 US‐based SMEs, we find that having a wider international market scope exposes SMEs to a rich network of information that encourages and enhances future product innovation. Similar results are observed when SMEs use high control or high involvement modes of entry in foreign markets. Our analyses also show that social knowledge magnifies and strengthens the effects of international market scope and mode of entry (high control as well as high involvement) on SMEs' product innovation.
Adaptive strategy making: The effects of emergent and intended strategy modes
Authors: Andersen Torben Juul , Nielsen Bo Bernhard
Published: June 2009

Abstract It is generally recognized that strategies can evolve from both intended and emergent actions and this understanding gradually permeates the strategy literature. Yet, the two phenomena are rarely analyzed as complementary processes and, if so, the analyses are usually conducted around case‐based studies. To circumvent this, this paper develops an adaptive strategy‐making model and incorporates measures of emergent and intended strategy modes to underpin quantitative analysis. Structural equation modeling applied on data from 185 business entities then shows that emergence fostered by autonomous and participatory strategy‐making facilitates adaptive behavior, which in turn leads to higher performance outcomes. However, performance is enhanced further when the adaptive initiatives are integrated through strategic planning. These findings indicate that emergence is an essential driver of performance but is more effective if mediated by planning activities. This result has important implications for strategy research and strategic management practice.
Systematic comparison between line integrated densities measured with interferometry and polarimetry at JET
Authors: Brombin M. , Boboc A. , Murari A. , Zilli E. , Giudicotti L. ,   JET-EFDA Contributors
Published: June 2009

A systematic comparison between the line integrated electron density derived from interferometry and polarimetry at JET has been carried out. For the first time the reliability of the measurements of the Cotton–Mouton effect has been analyzed for a wide range of main plasma parameters and the possibility to evaluate the electron density directly from polarimetric data has been studied. The purpose of this work is to recover the interferometric data with the density derived from the measured Cotton–Mouton effect, when the fringe jump phenomena occur. The results show that the difference between the line integrated electron density from interferometry and polarimetry is with one fringe (1.143×1019 m−2) for more than 90% of the cases. It is possible to consider polarimetry as a satisfactory alternative method to interferometry to measure the electron density and it could be used to recover interferometric signal when a fringe jumps occurs, preventing difficulties for the real-time control of many experiments at the JET machine.
Lateral stability of the spring-mass hopper suggests a two-step control strategy for running
Authors: Carver Sean G. , Cowan Noah J. , Guckenheimer John M.
Published: June 2009

This paper investigates the control of running gaits in the context of a spring loaded inverted pendulum model in three dimensions. Specifically, it determines the minimal number of steps required for an animal to recover from a perturbation to a specified gait. The model has four control inputs per step: two touchdown angles (azimuth and elevation) and two spring constants (compression and decompression). By representing the locomotor movement as a discrete-time return map and using the implicit function theorem we show that the number of recovery steps needed following a perturbation depends upon the goals of the control mechanism. When the goal is to follow a straight line, two steps are necessary and sufficient for small lateral perturbations. Multistep control laws have a larger number of control inputs than outputs, so solutions of the control problem are not unique. Additional constraints, referred to here as synergies, are imposed to determine unique control inputs for perturbations. For some choices of synergies, two-step control can be expressed as two iterations of its first step policy and designed so that recovery occurs in just one step for all perturbations for which one-step recovery is possible.
Delayed and lasting effects of deep brain stimulation on locomotion in Parkinson's disease
Authors: Beuter Anne , Modolo Julien
Published: June 2009

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a variety of motor signs affecting gait, postural stability, and tremor. These symptoms can be improved when electrodes are implanted in deep brain structures and electrical stimulation is delivered chronically at high frequency (>100 Hz). Deep brain stimulation (DBS) onset or cessation affects PD signs with different latencies, and the long-term improvements of symptoms affecting the body axis and those affecting the limbs vary in duration. Interestingly, these effects have not been systematically analyzed and modeled. We compare these timing phenomena in relation to one axial (i.e., locomotion) and one distal (i.e., tremor) signs. We suggest that during DBS, these symptoms are improved by different network mechanisms operating at multiple time scales. Locomotion improvement may involve a delayed plastic reorganization, which takes hours to develop, whereas rest tremor is probably alleviated by an almost instantaneous desynchronization of neural activity in subcortical structures. Even if all PD patients develop both distal and axial symptoms sooner or later, current computational models of locomotion and rest tremor are separate. Furthermore, a few computational models of locomotion focus on PD and none exploring the effect of DBS was found in the literature. We, therefore, discuss a model of a neuronal network during DBS, general enough to explore the subcircuits controlling locomotion and rest tremor simultaneously. This model accounts for synchronization and plasticity, two mechanisms that are believed to underlie the two types of symptoms analyzed. We suggest that a hysteretic effect caused by DBS-induced plasticity and synchronization modulation contributes to the different therapeutic latencies observed. Such a comprehensive, generic computational model of DBS effects, incorporating these timing phenomena, should assist in developing a more efficient, faster, durable treatment of distal and axial signs in PD.
Carbon nanotube photovoltaic device with asymmetrical contacts
Authors: Chen Changxin , Zhang Wei , Kong Eric Siu-Wai , Zhang Yafei
Published: June 2009

A photovoltaic (PV) device based on “high-work-function metal/single-walled carbon nanotube/low-work-function metal” hybrid junction has been studied theoretically by the self-consistent nonequilibrium Green’s function approach. The PV effect and power conversion efficiency (η) of the device under light illumination are simulated, with a monochromatic η of higher than 40% for incident photon energies near the nanotube band-gap energy predicted. It is shown that the gate voltage and gate oxide thickness have an important influence on the device η.
Neuromechanical models for insect locomotion: Stability, maneuverability, and proprioceptive feedback
Authors: Kukillaya R. , Proctor J. , Holmes P.
Published: June 2009

We describe a hierarchy of models for legged locomotion, emphasizing relationships among feedforward (preflexive) stability, maneuverability, and reflexive feedback. We focus on a hexapedal geometry representative of insect locomotion in the ground plane that includes a neural central pattern generator circuit, nonlinear muscles, and a representative proprioceptive sensory pathway. Although these components of the model are rather complex, neglect of leg mass yields a neuromechanical system with only three degrees of freedom, and numerical simulations coupled with a Poincaré map analysis shows that the feedforward dynamics is strongly stable, apart from one relatively slow mode and a neutral mode in body yaw angle. These modes moderate high frequency perturbations, producing slow heading changes that can be corrected by a stride-to-stride steering strategy. We show that the model’s response to a lateral impulsive perturbation closely matches that of a cockroach subject to a similar impulse. We also describe preliminary studies of proprioceptive leg force feedback, showing how a reflexive pathway can reinforce the preflexive stability inherent in the system.
Optimal speeds for walking and running, and walking on a moving walkway
Authors: Srinivasan Manoj
Published: June 2009

Many aspects of steady human locomotion are thought to be constrained by a tendency to minimize the expenditure of metabolic cost. This paper has three parts related to the theme of energetic optimality: (1) a brief review of energetic optimality in legged locomotion, (2) an examination of the notion of optimal locomotion speed, and (3) an analysis of walking on moving walkways, such as those found in some airports. First, I describe two possible connotations of the term “optimal locomotion speed:” that which minimizes the total metabolic cost per unit distance and that which minimizes the net cost per unit distance (total minus resting cost). Minimizing the total cost per distance gives the maximum range speed and is a much better predictor of the speeds at which people and horses prefer to walk naturally. Minimizing the net cost per distance is equivalent to minimizing the total daily energy intake given an idealized modern lifestyle that requires one to walk a given distance every day—but it is not a good predictor of animals’ walking speeds. Next, I critique the notion that there is no energy-optimal speed for running, making use of some recent experiments and a review of past literature. Finally, I consider the problem of predicting the speeds at which people walk on moving walkways—such as those found in some airports. I present two substantially different theories to make predictions. The first theory, minimizing total energy per distance, predicts that for a range of low walkway speeds, the optimal absolute speed of travel will be greater—but the speed relative to the walkway smaller—than the optimal walking speed on stationary ground. At higher walkway speeds, this theory predicts that the person will stand still. The second theory is based on the assumption that the human optimally reconciles the sensory conflict between the forward speed that the eye sees and the walking speed that the legs feel and tries to equate the best estimate of the forward speed to the naturally preferred speed. This sensory conflict theory also predicts that people would walk slower than usual relative to the walkway yet move faster than usual relative to the ground. These predictions agree qualitatively with available experimental observations, but there are quantitative differences.
Maneuvers during legged locomotion
Authors: Jindrich Devin L. , Qiao Mu
Published: June 2009

Maneuverability is essential for locomotion. For animals in the environment, maneuverability is directly related to survival. For humans, maneuvers such as turning are associated with increased risk for injury, either directly through tissue loading or indirectly through destabilization. Consequently, understanding the mechanics and motor control of maneuverability is a critical part of locomotion research. We briefly review the literature on maneuvering during locomotion with a focus on turning in bipeds. Walking turns can use one of several different strategies. Anticipation can be important to adjust kinematics and dynamics for smooth and stable maneuvers. During running, turns may be substantially constrained by the requirement for body orientation to match movement direction at the end of a turn. A simple mathematical model based on the requirement for rotation to match direction can describe leg forces used by bipeds (humans and ostriches). During running turns, both humans and ostriches control body rotation by generating fore-aft forces. However, whereas humans must generate large braking forces to prevent body over-rotation, ostriches do not. For ostriches, generating the lateral forces necessary to change movement direction results in appropriate body rotation. Although ostriches required smaller braking forces due in part to increased rotational inertia relative to body mass, other movement parameters also played a role. Turning performance resulted from the coordinated behavior of an integrated biomechanical system. Results from preliminary experiments on horizontal-plane stabilization support the hypothesis that controlling body rotation is an important aspect of stable maneuvers. In humans, body orientation relative to movement direction is rapidly stabilized during running turns within the minimum of two steps theoretically required to complete analogous maneuvers. During straight running and cutting turns, humans exhibit spring-mass behavior in the horizontal plane. Changes in the horizontal projection of leg length were linearly related to changes in horizontal-plane leg forces. Consequently, the passive dynamic stabilization associated with spring-mass behavior may contribute to stability during maneuvers in bipeds. Understanding the mechanics of maneuverability will be important for understanding the motor control of maneuvers and also potentially be useful for understanding stability.
Understanding the complexity of human gait dynamics
Authors: Scafetta Nicola , Marchi Damiano , West Bruce J.
Published: June 2009

Time series of human gait stride intervals exhibit fractal and multifractal properties under several conditions. Records from subjects walking at normal, slow, and fast pace speed are analyzed to determine changes in the fractal scalings as a function of the stress condition of the system. Records from subjects with different age from children to elderly and patients suffering from neurodegenerative disease are analyzed to determine changes in the fractal scalings as a function of the physical maturation or degeneration of the system. A supercentral pattern generator model is presented to simulate the above two properties that are typically found in dynamical network performance: that is, how a dynamical network responds to stress and to evolution.
Gait dynamics in Parkinson’s disease: Common and distinct behavior among stride length, gait variability, and fractal-like scaling
Authors: Hausdorff Jeffrey M.
Published: June 2009

Parkinson’s disease (PD) is a common, debilitating neurodegenerative disease. Gait disturbances are a frequent cause of disability and impairment for patients with PD. This article provides a brief introduction to PD and describes the gait changes typically seen in patients with this disease. A major focus of this report is an update on the study of the fractal properties of gait in PD, the relationship between this feature of gait and stride length and gait variability, and the effects of different experimental conditions on these three gait properties. Implications of these findings are also briefly described. This update highlights the idea that while stride length, gait variability, and fractal scaling of gait are all impaired in PD, distinct mechanisms likely contribute to and are responsible for the regulation of these disparate gait properties.
Entanglement network in nanoparticle reinforced polymers
Authors: Riggleman Robert A. , Toepperwein Gregory , Papakonstantopoulos George J. , Barrat Jean-Louis , de Pablo Juan J.
Published: June 2009

Polymer nanocomposites have been widely studied in efforts to engineer materials with mechanical properties superior to those of the pure polymer, but the molecular origins of the sought-after improved properties have remained elusive. An ideal polymer nanocomposite model has been conceived in which the nanoparticles are dispersed throughout the polymeric matrix. A detailed examination of topological constraints (or entanglements) in a nanocomposite glass provides new insights into the molecular origin of the improved properties in polymer nanocomposites by revealing that the nanoparticles impart significant enhancements to the entanglement network. Nanoparticles are found to serve as entanglement attractors, particularly at large deformations, altering the topological constraint network that arises in the composite material.
Well-aligned and suspended single-walled carbon nanotube film: Directed self-assembly, patterning, and characterization
Authors: Lu Miao , Jang Min-Woo , Haugstad Greg , Campbell Stephen A. , Cui Tianhong
Published: June 2009

Self-assembly process, patterning, and characterization of well-aligned single-walled carbon nanotube (SWNT) films are presented in this letter. The dc current in an ac dielectrophoresis of an SWNT solution was measured and used to control the self-assembly process to get an oriented, compact SWNT film 15–20 nm thick. The film was further patterned to form submicron beams by focused ion beams, or lithography and oxygen plasma etching. The Young’s modulus of the film ranged from 350 to 830 GPa. The electrical resistivity was about 8.7×10−3 Ω cm. The temperature coefficient of resistance was −1.2%/K.
Computational fluid dynamics analysis of a combined three-bucket Savonius and three-bladed Darrieus rotor at various overlap conditions
Authors: Debnath Biplab Kumar , Biswas Agnimitra , Gupta Rajat
Published: June 2009

In this paper, a computational fluid dynamics analysis using the FLUENT package 6.2 was carried out to predict the performance characteristics such as power coefficient (Cp), torque coefficient (Ct), and tip speed ratio of a combined three-bucket Savonius and three-bladed Darrieus rotor for various overlap conditions, namely, 16.2%, 20%, 25%, 30%, and 35%. In the upper part of the rotor model, there was a three-bucket Savonius rotor of bucket diameter of 8 cm and height of 10 cm, whereas, in the lower part, there was a three-bladed Darrieus rotor of blade diameter of 8 cm and height of 10 cm. A two-dimensional unstructured computational grid was developed for the combined Savonius–Darrieus rotor model. A k-ε turbulence closure model with enhanced wall treatment function was chosen. A first-order upwind discretization scheme was adopted for pressure-velocity coupling of the flow. The values of Cp and Ct obtained computationally were then compared with those of the values of Cp and Ct obtained experimentally for all the overlap conditions. The experimental values of Cp and Ct for different overlap conditions were obtained from the tests conducted previously in an open-circuit subsonic wind tunnel available in the department. The comparison of experimental and computational studies is quite encouraging.
Effects of ultramicroelectrode dimensions on the electropolymerization of polypyrrole
Authors: Fletcher Benjamin L. , Fern Jared T. , Rhodes Kevin , McKnight Timothy E. , Fowlkes Jason D. , Retterer Scott T. , Keffer David J. , Simpson Michael L. , Doktycz Mitchel J.
Published: June 2009

Anode geometry can significantly affect the electrochemical synthesis of conductive polymers. Here, the effects of anode dimensions on the electropolymerization of pyrrole are investigated. Band microelectrodes were prepared with widths ranging from 2 to 500 μm. The anode dimension has a significant effect on the resulting thickness of polymer film. The electropolymerization process deviates significantly from that predicted by simple mass transfer considerations when electrode dimensions are less than ∼20 μm. Polymer film thickness is thinner than expected when electrode dimensions become less than ∼10 μm. A simple mathematical model was derived to explain the observed effects of anode dimensions on the polymerization process. Simulation results confirm that diffusive loss of reaction intermediates accounts for the observed experimental trends. The described simulation facilitates understanding of the electropolymerization processes and approaches to the controlled deposition of polypyrrole, particularly at the submicron scale, for microelectromechanical systems and biomedical applications.
Introduction to Focus Issue: Bipedal Locomotion—From Robots to Humans
Authors: Milton John G.
Published: June 2009

Running and walking, collectively referred to as bipedal locomotion, represent self-organized behaviors generated by a spatially distributed dynamical system operating under the constraint that a person must be able to move without falling down. The organizing principles involve both forces actively regulated by the nervous system and those generated passively by the biomechanical properties of the musculoskeletal system and the environment in which the movements occur. With the development of modern motion capture and electrophysiological techniques it has become possible to explore the dynamical interplay between the passive and active controllers of locomotion in a manner that directly compares observation to predictions made by relevant mathematical and computer models. Consequently, many of the techniques initially developed to study nonlinear dynamical systems, including stability analyses, phase resetting and entrainment properties of limit cycles, and fractal and multifractal analysis, have come to play major roles in guiding progress. This Focus Issue discusses bipedal locomotion from the point of view of dynamical systems theory with the goal of stimulating discussion between the dynamical systems, physics, biomechanics, and neuroscience communities.
Coherent detection of nonlinear nanomechanical motion using a stroboscopic downconversion technique
Authors: Unterreithmeier Quirin P. , Manus Stephan , Kotthaus Jörg P.
Published: June 2009

A method is presented that overcomes bandwidth limitations arising in a fiber-optic setup transducing mechanical motion. The reflected light from a sample incorporating a nanomechanical resonator is analyzed. Modulating the incoming laser intensity at a suitably chosen frequency, the mechanically induced oscillation of the reflected light is coherently downconverted to a frequency within the detection bandwidth. Additionally, based on the mechanical nonlinear response, the optical signal can be quantitatively converted into displacement, yielding a sensitivity of 7 pm/Hz at optical power levels of 20 μW. We detect and image mechanical modes up to the seventh harmonic of the fundamental mode at 7.7 MHz.
Ultrasmall silicon quantum dots
Authors: Zwanenburg F. A. , van Loon A. A. , Steele G. A. , van Rijmenam C. E. W. M. , Balder T. , Fang Y. , Lieber C. M. , Kouwenhoven L. P.
Published: June 2009

We report the realization of extremely small single quantum dots in p-type silicon nanowires, defined by Schottky tunnel barriers with Ni and NiSi contacts. Despite their ultrasmall size the NiSi–Si–NiSi nanowire quantum dots readily allow spectroscopy of at least ten consecutive holes, and additionally they display a pronounced excited-state spectrum. The Si channel lengths are visible in scanning electron microscopy images and match the dimensions predicted by a model based on the Poisson equation. The smallest dots (<12 nm) allow identification of the last charge and thus the creation of a single-charge quantum dot.
Magnetocaloric response of Fe75Nb10B15 powders partially amorphized by ball milling
Authors: Ipus J. J. , Blázquez J. S. , Franco V. , Conde A. , Kiss L. F.
Published: June 2009

The magnetocaloric response of mechanically alloyed Fe75Nb10B15 powders was studied for samples with different amorphous and nanocrystal volume fractions. Thermomagnetic properties scale following a Ω3 law for different milling processes, where Ω is the milling frequency. Curie temperature of the amorphous phase increases as the amorphous fraction increases due to its progressive enrichment in B. The peak magnetic entropy change, |ΔSMpk|, as well as the refrigerant capacity increase with increasing amorphous fraction. The field dependence of |ΔSMpk| can be explained by the multiphase character of the studied samples.
Weak ferromagnetism and spin-glass state with nanosized nickel carbide
Authors: Chen Chinping , He Lin , Leng Yonghua , Li Xingguo
Published: June 2009

Magnetic properties of Ni3C nanoparticles, about 40 nm in diameter, have been investigated. The sample exhibits weak ferromagnetic (FM), spin-glass (SG), and paramagnetic (PM) properties by alternating current susceptibility and direct current magnetization measurements. The freezing temperature of the SG phase at zero applied field is determined as TF0∼11.0 K. At T>TF0, a very weak ferromagnetism has been observed over a strong PM background. The Curie temperature TC is shown to exceed 300 K, and the ferromagnetism at 300 K is determined as about 0.02 emu/g∼6.7×10−4 μB per Ni3C formula unit. An anomalous dip appears in the temperature dependent coercivity HC(T) near the freezing temperature TF0. It reflects the distortedly reduced coercivity in the M(H) hysteresis loop measured at T∼TF0 with the applied sweeping field approaching H=0. This is attributable to the interaction between the SG and the weak FM phases. The possible origin of the magnetic moments that account for the observed FM, SG, and PM properties is discussed.
Vibration energy levels of the PH3, PH2D, and PHD2 molecules calculated from high order potential energy surface
Authors: Nikitin Andrei V. , Holka Filip , Tyuterev Vladimir G. , Fremont Julien
Published: June 2009

Vibrational energy levels of the PH3, PH2D, and PHD2 molecules were calculated from the new extended potential energy surface (PES) determined in this work. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pV5Z was employed in the ab initio calculations of electronic ground state energies. The contribution of relativistic effects to the overall electronic energy surface was computed using quasirelativistic mass-velocity-Darwin approach. These ab initio points were fitted by a parametrized function with one parameter empirically adjusted. The grid of 11 697 geometrical nuclear configurations covers a large domain of the six dimensional internal coordinate space and was designed to provide vibration energy levels of phosphine molecule up to 7000 cm−1 above the zero point vibration energy with reasonable accuracy. The analytical representation of the PES was determined through the expansion in symmetry adapted products of nonlinear internal coordinates for various orders of analytical expansions up to the tenth order. The dependence of calculated vibration energy levels on the analytical representation of PES and on the coordinate choice was studied. Calculated vibration levels are in very good agreement with observations: The root mean squares deviation between theoretically calculated and observed band centers is 1.4 cm−1 for PH3, 0.4 cm−1 for PH2D, and 0.6 cm−1 for PHD2.
Optical polarization anisotropy of a-plane GaN/AlGaN multiple quantum well structures grown on r-plane sapphire substrates
Authors: Badcock T. J. , Dawson P. , Kappers M. J. , McAleese C. , Hollander J. L. , Johnston C. F. , Sridhara Rao D. V. , Sanchez A. M. , Humphreys C. J.
Published: June 2009

A series of nonpolar a-plane GaN/AlGaN multiple quantum well structures of varying quantum well width have been studied by polarization resolved photoluminescence and photoluminescence excitation spectroscopy at low temperature. The photoluminescence spectra from all the structures show two features that are observed to blueshift with reducing well width. The lower energy feature is associated with the recombination of carriers in regions of the wells intersected by basal-plane stacking faults, while the higher energy line is attributed to localized exciton recombination involving only the quantum wells. Using excitation spectroscopy with polarized light, we were able to resolve exciton features associated with both the |Y⟩ and |Z⟩ valence sub-bands. The observed polarization dependence of the transitions is consistent with a modification to the valence band-edge states due to anisotropic biaxial compressive strain in the quantum well. We were also able to determine the exciton binding energies directly from the photoluminescence excitation spectra, which were found to increase from 36 to 76 meV as the quantum well width reduced from 60 to 35 Å.