Electrostatic interactions between rotor and stator in the bacterial flagellar motor

Bacterial flagellar motors rotate, obtaining power from the membrane gradient of protons or, in some species, sodium ions. Torque generation in the flagellar motor must involve interactions between components of the rotor and components of the stator. Sites of interaction between the rotor and stator have not been identified. Mutational studies of the rotor protein FliG and the stator protein MotA showed that both proteins contain charged residues essential for motor rotation. This suggests that functionally important electrostatic interactions might occur between the rotor and stator. To test this proposal, we examined double mutants with charged-residue substitutions in both the rotor protein FliG and the stator protein MotA. Several combinations of FliG mutations with MotA mutations exhibited strong synergism, whereas others showed strong suppression, in a pattern that indicates that the functionally important charged residues of FliG interact with those of MotA. These results identify a functionally important site of interaction between the rotor and stator and suggest a hypothesis for electrostatic interactions at the rotor–stator interface.

Molecular dynamics of a grid-mounted molecular dipolar rotor in a rotating electric field

Classical molecular dynamics is applied to the rotation of a dipolar molecular rotor mounted on a square grid and driven by rotating electric field E(ν) at T ≃ 150 K. The rotor is a complex of Re with two substituted o-phenanthrolines, one positively and one negatively charged, attached to an axial position of Rh\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{4+}}}\end{equation*}\end{document} in a [2]staffanedicarboxylate grid through 2-(3-cyanobicyclo[1.1.1]pent-1-yl)malonic dialdehyde. Four regimes are characterized by a, the average lag per turn: (i) synchronous (a < 1/e) at E(ν) = |E(ν)| > Ec(ν) [Ec(ν) is the critical field strength], (ii) asynchronous (1/e < a < 1) at Ec(ν) > E(ν) > Ebo(ν) > kT/μ, [Ebo(ν) is the break-off field strength], (iii) random driven (a ≃ 1) at Ebo(ν) > E(ν) > kT/μ, and (iv) random thermal (a ≃ 1) at kT/μ > E(ν). A fifth regime, (v) strongly hindered, W > kT, Eμ, (W is the rotational barrier), has not been examined. We find Ebo(ν)/kVcm−1 ≃ (kT/μ)/kVcm−1 + 0.13(ν/GHz)1.9 and Ec(ν)/kVcm−1 ≃ (2.3kT/μ)/kVcm−1 + 0.87(ν/GHz)1.6. For ν > 40 GHz, the rotor behaves as a macroscopic body with a friction constant proportional to frequency, η/eVps ≃ 1.14 ν/THz, and for ν < 20 GHz, it exhibits a uniquely molecular behavior.

Intrasarcomere [Ca2+] gradients in ventricular myocytes revealed by high speed digital imaging microscopy.

Cardiac muscle contraction is triggered by a small and brief Ca2+ entry across the t-tubular membranes, which is believed to be locally amplified by release of Ca2+ from the adjacent junctional sarcoplasmic reticulum (SR). As Ca2+ diffusion is thought to be markedly attenuated in cells, it has been predicted that significant intrasarcomeric [Ca2+] gradients should exist during activation. To directly test for this, we measured [Ca2+] distribution in single cardiac myocytes using fluorescent [Ca2+] indicators and high speed, three-dimensional digital imaging microscopy and image deconvolution techniques. Steep cytosolic [Ca2+] gradients from the t-tubule region to the center of the sarcomere developed during the first 15 ms of systole. The steepness of these [Ca2+] gradients varied with treatments that altered Ca2+ release from internal stores. Electron probe microanalysis revealed a loss of Ca2+ from the junctional SR and an accumulation, principally in the A-band during activation. We propose that the prolonged existence of [Ca2+] gradients within the sarcomere reflects the relatively long period of Ca2+ release from the SR, the localization of Ca2+ binding sites and Ca2+ sinks remote from sites of release, and diffusion limitations within the sarcomere. The large [Ca2+] transient near the t-tubular/ junctional SR membranes is postulated to explain numerous features of excitation-contraction coupling in cardiac muscle.

Transcribing of Escherichia coli genes with mutant T7 RNA polymerases: stability of lacZ mRNA inversely correlates with polymerase speed.

When in Escherichia coli the host RNA polymerase is replaced by the 8-fold faster bacteriophage T7 enzyme for transcription of the lacZ gene, the beta-galactosidase yield per transcript drops as a result of transcript destabilization. We have measured the beta-galactosidase yield per transcript from T7 RNA polymerase mutants that exhibit a reduced elongation speed in vitro. Aside from very slow mutants that were not sufficiently processive to transcribe the lacZ gene, the lower the polymerase speed, the higher the beta-galactosidase yield per transcript. In particular, a mutant which was 2.7-fold slower than the wild-type enzyme yielded 3.4- to 4.6-fold more beta-galactosidase per transcript. These differences in yield vanished in the presence of the rne-50 mutation and therefore reflect the unequal sensitivity of the transcripts to RNase E. We propose that the instability of the T7 RNA polymerase transcripts stems from the unmasking of an RNase E-sensitive site(s) between the polymerase and the leading ribosome: the faster the polymerase, the longer the lag between the synthesis of this site(s) and its shielding by ribosomes, and the lower the transcript stability.

Increase of skeletal muscle relaxation speed by direct injection of parvalbumin cDNA.

Parvalbumin (PV) is a high affinity Ca(2+)-binding protein found at high concentration in fast-contracting/relaxing skeletal muscle fibers of vertebrates. It has been proposed that PV acts in the process of muscle relaxation by facilitating Ca2+ transport from the myofibrils to the sarcoplasmic reticulum. However, on the basis of metal-binding kinetics of PV in vitro, this hypothesis has been challenged. To investigate the function of PV in skeletal muscle fibers, direct gene transfer was applied in normal and regenerating rat soleus muscles which do not synthesize detectable amounts of PV. Two weeks after in vivo transfection with PV cDNA, considerable levels of PV mRNA and protein were detected in normal muscle, and even higher amounts were detected in regenerating muscle. Twitch half-relaxation time was significantly shortened in a dose-dependent way in transfected muscles, while contraction time remained unaltered. The observed shortening of half-relaxation time is due to PV and its ability to bind Ca2+, because a mutant protein lacking Ca(2+)-binding capacity did not promote any change in physiology. These results directly demonstrate the physiological function of PV as a relaxing factor in mammalian skeletal muscle.

High-speed polynomial basis multipliers over GF(2(m)) for special pentanomial.

Efficient hardware implementations of arithmetic operations in the Galois field are highly desirable for several applications, such as coding theory, computer algebra and cryptography. Among these operations, multiplication is of special interest because it is considered the most important building block. Therefore, high-speed algorithms and hardware architectures for computing multiplication are highly required. In this paper, bit-parallel polynomial basis multipliers over the binary field GF(2(m)) generated using type II irreducible pentanomials are considered. The multiplier here presented has the lowest time complexity known to date for similar multipliers based on this type of irreducible pentanomials.

Medidas de dispersão de gás em células mecânicas industriais e seus condicionantes.

A qualidade da dispersão de gás em células de flotação é comumente caracterizada através de parâmetros como velocidade superficial do gás (Jg), hold-up do gás (?g), distribuição de tamanho de bolha (db ou D3,2) e fluxo de superfície de bolha (Sb). Sendo um processo de separação de minerais que é dependente da interação (colisão + adesão) entre partículas hidrofóbicas e bolhas de ar, a flotação tem seu desempenho dependente de uma dispersão de gás apropriada na polpa de minério. Desta forma, este trabalho objetivou caracterizar o estado da dispersão de gás de duas células em um banco composto por quatro células Wemco de 42,5 m³ (subaeradas), operando em série na usina da Vale Fertilizantes (Cajati-SP). Realizaram-se três campanhas de medidas que foram conduzidas sob diferentes condições operacionais: a) Diâmetro do rotor (D) de 1,09 m e rotação (N) entre 145 RPM e 175 RPM; b) D = 0,99 m e N entre 110 RPM e 190 RPM; c) D = 0,99 m e N de 120 RPM e de 130 RPM. Observaram-se os seguintes valores de dispersão de gás: 0,7 <= Jg <= 5,4 cm/s, 7 <= ?g <= 15%, 1,6 <= D3,2 <= 2,4 mm e Sb na faixa de 24 a 162 s-1. A magnitude de Jg medida na 1ª e 2ª campanhas mostrou-se acima dos valores reportados pela literatura, indicando necessidade de modificação de condições operacionais dos equipamentos, assim como cuidadosa manutenção. Posteriormente, a 3ª campanha indicou maior conformidade dos parâmetros de dispersão de gás em relação à literatura, constatando-se uma considerável melhora de desempenho do processo de flotação.

Cálculo da força contra eletromotriz em máquinas síncronas com ímãs na superfície do rotor

O presente trabalho trata do cálculo da força contra eletromotriz em carga de uma máquina síncrona com ímãs na superfície do rotor (cuja forma de onda de força contra eletromotriz é não senoidal) sendo esta alimentada por correntes de fase cujas forma de onda são quadradas. Para conduzir esta investigação e calcular a força contra eletromotriz da máquina em estudo, faz-se uma revisão sobre o Método da Permeabilidade Fixa, método este que permite a linearização do ponto de operação da máquina. Dessa forma, as simulações são conduzidas por meio do método dos elementos finitos e do Método da Permeabilidade Fixa, levando-se em conta a forma de onda da corrente de alimentação. Atenção especial é dada ao modo que se analisa o fluxo concatenado e a forma de obtenção da força contra eletromotriz uma vez que as formas de onda do fluxo concatenado sofrem variações abruptas a cada 60º elétricos. Além destes parâmetros, analisa-se também cada uma das parcelas do torque eletromagnético, i.e., torque mútuo, torque de relutância e torque de borda, sendo realizado ao final do trabalho, uma comparação entre a soma da estimativa de cada parâmetro com o valor do torque eletromagnético obtido por meio de uma simulação não linear.

High speed imaging and algorithms for non invasive vibrations measurement

Comunicación presentada en EVACES 2011, 4th International Conference on Experimental Vibration Analysis for Civil Engineering Structures, Varenna (Lecco), Italy, October 3-5, 2011.

High speed image techniques for construction safety net monitoring in outdoor conditions

Póster presentado en SPIE Photonics Europe, Brussels, 16-19 April 2012.

Effects of static stretching following a dynamic warm-up on speed, agility and power

Static stretching prior to sport has been shown to decrease force production in comparison to the increasing popularity of dynamic warm-up methods. However some athletes continue to use a bout of static stretching following dynamic methods. The purpose of this study was to investigate the effects on speed, agility and power following a period of additional static stretching following a dynamic warm-up routine. Twenty-five male University students who participated in team sports performed two warm-up protocols concentrating on the lower body one week apart through a randomised cross over design. The dynamic warm-up (DW) protocol used a series of specific progressive exercises lasting 10 minutes over a distance of 20m. The dynamic warm-up plus static stretching (DWS) protocol used the same DW protocol followed by a 5 minute period during which 7 muscle groups were stretched. Following each warm-up the subjects performed a countermovement vertical jump, 20m sprint and Illinois agility test, 1 minute apart. The results demonstrated no significant differences in speed, agility and jump performance following the two protocols DW and DWS. The study concludes that performing static stretching following a dynamic warm-up prior to performance does not significantly affect speed, agility and vertical jump performance.

High-speed video-oculography applied to assess pupil light reflex

Póster presentado en el VII European/ I World Meeting in Visual and Physiological Optics

Water polo throwing speed and body composition: an analysis by playing positions and opposition level

The aim of this study was to develop an anthropometric profile on highly skilled male water polo players by specific playing positions. Also, to identify significant relationships between these features an overhead throwing speed in highly skilled male Water Polo players by specific playing positions. Methods: A total of 94 male water polo players (24.5±5.3 yrs) who were playing in the Spanish King´s cup were studied. Subjects were grouped according to their specific playing positions: 15 goalkeepers, 45 offensive wings, 20 center backs and 14 center forwards. Anthropometric assessment was made following ISAK protocols. Hand grip and throwing speed in several situations were also assessed. A one-way analysis of variance (ANOVA) was used to determine if significant differences existed among the four playing positions. Pearson product-moment correlation coefficients (r) were used to determine the relationships of all anthropometric measures with throwing speed and hand grip. The total player’s somatotype was endomorphic-mesomorphic (2.9–5.8–2.3). Center forwards exhibit important anthropometric differences compared with the other specific playing positions in elite male water polo players, but no differences were found in throwing speed by specific playing positions in each throwing conditions. Moreover, a higher number of relationships between anthropometric and throwing speed were found in wings and also in center backs but no relationships were found in center forwards. The data reflects the importance of muscle mass and upper body in the throwing skill. Coaches can use this information in order to select players for the different specific positions.