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"Critical speed"

Alex H Williams, Cian O'Donnell, Terrence J Sejnowski, Timothy O'Leary
Nervous system function requires intracellular transport of channels, receptors, mRNAs, and other cargo throughout complex neuronal morphologies. Local signals such as synaptic input can regulate cargo trafficking, motivating the leading conceptual model of neuron-wide transport, sometimes called the 'sushi-belt model' (Doyle and Kiebler, 2011). Current theories and experiments are based on this model, yet its predictions are not rigorously understood. We formalized the sushi belt model mathematically, and show that it can achieve arbitrarily complex spatial distributions of cargo in reconstructed morphologies...
December 30, 2016: ELife
J Timothy Baldwin, Iki Adachi, John Teal, Christopher A Almond, Robert D Jaquiss, M Patricia Massicotte, Kurt Dasse, Flora S Siami, Victor Zak, Jonathan R Kaltman, William T Mahle, Robert Jarvik
The Infant Jarvik ventricular assist device (VAD; Jarvik Heart, Inc., New York, NY) has been developed to support the circulation of infants and children with advanced heart failure. The first version of the device was determined to have elevated hemolysis under certain conditions. The objective of this work was to determine appropriate modifications to the Infant Jarvik VAD that would result in acceptably low hemolysis levels. In vitro hemolysis testing revealed that hemolysis was related to the shape of the pump blade tips and a critical speed over which hemolysis would occur...
January 2017: Seminars in Thoracic and Cardiovascular Surgery. Pediatric Cardiac Surgery Annual
Artur H de F Avelar, Jean A Canestri, Camila Bim, Maíra G M Silva, Rudolf Huebner, Marcos Pinotti
The use of porcine or bovine pericardium biological cardiac valves has as its main disadvantage a relatively short lifespan, with failures due to calcification and fatigue. Increasing these valves' durability constitutes a great challenge. An understudied phenomenon is the effect of flutter, an oscillation of the leaflets that can cause regurgitation and accelerate calcification and fatigue. As a starting point to study how to reduce or prevent these oscillations, a method was developed to quantify the flutter frequencies occurring at the point of the valve's full opening...
December 7, 2016: Artificial Organs
Ann I Larsson, Lena M Granhag, Per R Jonsson
Water flow affects settlement of marine larvae on several scales. At the smallest scale local flow regime may control the probability of adhesion to the substrate. Our aim was to mechanistically understand the transition from suspended to attached larvae in turbulent flow. Recently it was proposed that opportunities for larval settlement in turbulent boundary layers depend on time windows with suitable instantaneous flow properties. In flume flow we characterized the proportion of suitable time windows in a series of flow velocities with focus on the near-bed flow...
2016: PloS One
Badrane Zinoubi, Henry Vandewalle, Tarak Driss
The concepts of power law and critical speed (SCrit) have been applied to the analysis of individual running performances. We have analysed the results of two exceptional runners (Nurmi and Gebrselassie) and 11 physical education students (PES) who performed three exhausting running exercises. Power laws can accurately describe the relationships between exhaustion time (tlim) and distance (Dlim) or speed (S) [Dlim = ktlim and S = ktlim ] in elite runners and PES. However, the validity of the application of power laws must be verified for higher values of tlim in non-elite runners...
July 15, 2016: Journal of Strength and Conditioning Research
Argyris G Toubekis, Nikolaos Beidaris, Petros G Botonis, Maria Koskolou
The purpose of this study was to examine the metabolic responses during submaximal swimming with self-selected normal breathing (N) and prolonged expiration along with reduced frequency breathing (RB). Ten male swimmers (age: 23.1 ± 2.2 years; VO2max: 47.3 ± 7.2 ml · kg(-1) · min(-1)) performed 75-, 100-, 175-, 200-, 275-, 300-, 375- and 400-m trials with N and RB at intensity corresponding to 90% of the critical speed. In RB condition, all trials longer than 75 m were interspersed with 25 m of self-selected N in regular intervals...
June 2017: Journal of Sports Sciences
Alfred Nimmerichter, Nina Novak, Christoph Triska, Bernhard Prinz, Brynmor C Breese
Nimmerichter, A, Novak, N, Triska, C, Prinz, B, and Breese, BC. Validity of treadmill-derived critical speed on predicting 5,000-meter track-running performance. J Strength Cond Res 31(3): 706-714, 2017-To evaluate 3 models of critical speed (CS) for the prediction of 5,000-m running performance, 16 trained athletes completed an incremental test on a treadmill to determine maximal aerobic speed (MAS) and 3 randomly ordered runs to exhaustion at the [INCREMENT]70% intensity, at 110% and 98% of MAS. Critical speed and the distance covered above CS (D') were calculated using the hyperbolic speed-time (HYP), the linear distance-time (LIN), and the linear speed inverse-time model (INV)...
March 2017: Journal of Strength and Conditioning Research
Parisa Saen, Mohammad Atai, Azizollah Nodehi, Laleh Solhi
OBJECTIVE: The aim of this study was to evaluate the mechanical properties of dental resins and dental nanocomposites by means of 3-point bending, 4-point bending and piston-on-three ball biaxial static tests and also to investigate their dynamic mechanical properties. The obtained results from the static 3-point bending test also were compared with the corresponding mode in DMTA. METHODS: The hydrophilic surface of the inorganic OX-50 particles was treated with γ-MPS and the resulting silanized OX-50 was characterized using FTIR and TGA...
August 2016: Dental Materials: Official Publication of the Academy of Dental Materials
Robert W Pettitt
The use of personal records (PRs) for running different distances may be used to derive critical speed (CS) and the finite capacity for running speeds exceeding CS (D'). Using CS and D', individualized speed-time and distance-time relationships can be modeled (ie, time limits associated with running at a given speed or a given distance can be derived via linear regression with a high degree of accuracy). The running 3-min all-out exercise test (3 MT) has emerged as a method for estimating CS and D' on a large group of athletes in a single visit...
October 2016: International Journal of Sports Physiology and Performance
Marta Bianciardi, Nicola Toschi, Jonathan R Polimeni, Karleyton C Evans, Himanshu Bhat, Boris Keil, Bruce R Rosen, David A Boas, Lawrence L Wald
The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain-heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes...
May 13, 2016: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Ming-Chang Tsai, Scott G Thomas
PURPOSE: To validate the 3-minute all-out exercise test (3MT) protocol against the traditional critical-speed (CS) model (CSM) in front-crawl swimming. METHODS: Ten healthy swimmers or triathletes (mean ± SD age 35.2 ± 10.5 y, height 176.5 ± 5.4 cm, body mass 69.6 ± 8.2 kg) completed 5 tests (3MT, 100m, 200m, 400m, 800m) over 2 wk on separate days. Traditional CS and anaerobic distance capacity (D') were determined for each of the 3 traditional CSMs (linear distance-time, LIN; linear speed/time, INV; nonlinear time-speed, NLIN) from the 4 set-distance time trials...
January 2017: International Journal of Sports Physiology and Performance
Paulo C do Nascimento Salvador, Juliano Dal Pupo, Ricardo D De Lucas, Rafael A de Aguiar, Francimara B Arins, Luiz G A Guglielmo
do Nascimento Salvador, PC, Dal Pupo, J, De Lucas, RD, de Aguiar, RA, Arins, FB, and Guglielmo, LGA. The V[Combining Dot Above]O2 kinetics of maximal and supramaximal running exercises in sprinters and middle-distance runners. J Strength Cond Res 30(10): 2857-2863, 2016-The aim of this study was to compare the V[Combining Dot Above]O2 kinetics parameters during maximal and supramaximal running exercises in sprinters (SPR) and middle-distance runners (MDR). Twelve SPR (age 20.6 ± 3.4 years; and body mass 74...
October 2016: Journal of Strength and Conditioning Research
Biplab Bhattacherjee, Shradha Mishra, S S Manna
We have studied a flocking model with binary interactions (binary flock), where the velocity of an agent depends on the velocity of only another agent and its own velocity, topped by the angular noise. The other agent is selected as the nth topological neighbor; the specific value of n being a fixed parameter of the problem. On the basis of extensive numerical simulation results, we argue that for n = 1, the phase transition from the ordered to the disordered phase of the flock is a special kind of discontinuous transition...
December 2015: Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
Melitón Arce
This article describes and discusses issues related to the process of childhood growth and development, with emphasis on the early years, a period in which this process reaches critical speed on major structures and functions of the human economy. We reaffirm that this can contribute to the social availability of a generation of increasingly better adults, which in turn will be able to contribute to building a better world and within it a society that enjoys greater prosperity. In the first chapter, we discuss the general considerations on the favorable evolution of human society based on quality of future adults, meaning the accomplishments that today’s children will gain...
July 2015: Revista Peruana de Medicina Experimental y Salud Pública
Shah H Khan, Peter M Hoffmann
In this study, we present a detailed analysis of the squeeze-out dynamics of nanoconfined water confined between two hydrophilic surfaces measured by small-amplitude dynamic atomic force microscopy. Explicitly considering the instantaneous tip-surface separation during squeeze-out, we confirm the existence of an adsorbed molecular water layer on mica and at least two hydration layers. We also confirm the previous observation of a sharp transition in the viscoelastic response of the nanoconfined water as the compression rate is increased beyond a critical value (previously determined to be about 0...
October 2015: Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
Carl J Ade, Ryan M Broxterman, Jesse C Craig, Susanna J Schlup, Samuel L Wilcox, Thomas J Barstow
BACKGROUND: Missions to terrestrial destinations (i.e., asteroids, the Moon, and Mars) will consist of physically challenging mission-critical tasks. These tasks, coupled with the negative physiological effects of prolonged microgravity exposure, create a plausible situation in which physical requirements may exceed an astronaut's physical capacity. Therefore, the objective of the current study was to evaluate the association of aerobic fitness and muscular strength parameters with performance during two field tests designed to simulate upper-body mission-critical activities...
November 2015: Aerospace Medicine and Human Performance
Jeanne Dekerle, James Paterson
PURPOSE: To examine muscle fatigue of the shoulder internal rotators alongside swimming biomechanics during long-duration submaximal swimming sets performed in 2 different speed domains. METHODS: Eight trained swimmers (mean ± SD 20.5 ± 0.9 y, 173 ± 10 cm, 71.3 ± 10.0 kg) raced over 3 distances (200-, 400-, 800-m races) for determination of critical speed (CS; slope of the distance-time relationship). After a familiarization with muscle isokinetic testing, they subsequently randomly performed 2 constant-speed efforts (6 × 5-min blocks, 2...
July 2016: International Journal of Sports Physiology and Performance
Mustafa Z Yıldız, İpek Toker, Fatma B Özkan, Burak Güçlü
We investigated the gating effect of passive and active movement on the vibrotactile detection thresholds of the Pacinian (P) psychophysical channel and forward masking. Previous work on gating mostly used electrocutaneous stimulation and did not allow focusing on tactile submodalities. Ten healthy adults participated in our study. Passive movement was achieved by swinging a platform, on which the participant's stimulated hand was attached, manually by a trained operator. The root-mean-square value of the movement speed was kept in a narrow range (slow: 10-20 cm/s, fast: 50-60 cm/s)...
2015: Somatosensory & Motor Research
Qin Ye, Zhimin Li, Hui Wu
Gas-liquid contacting is an important unit operation in chemical and biochemical processes, but the gas utilization efficiency is low in conventional gas-liquid contactors especially for sparingly soluble gases. The gas self-inducing impeller is able to recycle gas in the headspace of a reactor to the liquid without utilization of additional equipment such as a gas compressor, and thus, the gas utilization efficiency is significantly enhanced. Gas induction is caused by the low pressure or deep vortex at a sufficiently high impeller speed, and the speed at which gas induction starts is termed the critical speed...
2016: Advances in Biochemical Engineering/biotechnology
Carl J Ade, Ryan M Broxterman, Jesse C Craig, Susanna J Schlup, Samuel L Wilcox, Thomas J Barstow
BACKGROUND: Aerobic exercise capacity provides information regarding cardiorespiratory health and physical capacity. However, in many populations the ability to measure whole-body or leg aerobic exercise capacity is limited due to physical disability or lack of appropriate equipment. Clinically there is a need to evaluate aerobic capacity in individuals who cannot use their legs for locomotion. In astronauts the habitable space for exercise testing in the next generation of space exploration systems may be restricted and may not support the traditional lower body testing...
July 2015: Aerospace Medicine and Human Performance
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