Influence of hydrodynamics on the growth kinetics of glass-adhering Pseudomonas putida cells through a parallel plate flow chamber     

S. Mbaye  P. Séchet  F. Pignon  J. M. F. Martins 《Biomicrofluidics》2013,7(5)

The objective of this work was to investigate the influence of hydrodynamics on the growth kinetics of surface-adhering Pseudomonas putida cells. The results showed in particular that under non substrate-limiting conditions, the early step of bacterial apparent growth rate is lower than those measured with suspended cells. Contrary to previously cited authors which explain this behavior to the different adhesive properties of the “daughter”-cells (which makes more probable the detachment of these daughter-cells), in our experimental conditions, that explanation does not hold and we show a clear dependence of growth kinetics with flow conditions, due to the formation of boundary layer concentration at low Reynolds number. These results revealed that using Monod law in the modeling of biofilm growth in fixed-biomass processes should be performed with care.  相似文献   

A hybrid microfluidic platform for cell-based assays via diffusive and convective trans-membrane perfusion     

Elizaveta Vereshchagina  Declan Mc Glade  Macdara Glynn  Jens Ducrée 《Biomicrofluidics》2013,7(3)

We present a novel 3D hybrid assembly of a polymer microfluidic chip with polycarbonate track-etched membrane (PCTEM) enabling membrane-supported cell culture. Two chip designs have been developed to establish either diffusive or convective reagent delivery using the integrated PCTEM. While it is well suited to a range of cell-based assays, we specifically employ this platform for the screening of a common antitumor chemotoxic agent (mitomycin C – MMC) on the HL60 myeloid leukemia cell line. The toxic activity of MMC is based on the generation of severe DNA damage in the cells. Using either mode of operation, the HL60 cells were cultured on-chip before, during, and after exposure to MMC at concentrations ranging from 0 to 50 μM. Cell viability was analysed off-chip by the trypan blue dye exclusion assay. The results of the on-chip viability assay were found to be consistent with those obtained off-chip and indicated ca. 40% cell survival at MMC concentration of 50 μM. The catalogue of capabilities of the here described cell assay platform comprises of (i) the culturing of cells either under shear-free conditions or under induced through-membrane flows, (ii) the tight time control of the reagent exposure, (iii) the straightforward assembly of devices, (iv) the flexibility on the choice of the membrane, and, prospectively, (v) the amenability for large-scale parallelization.  相似文献   

An effective splitting-and-recombination micromixer with self-rotated contact surface for wide Reynolds number range applications     

Xiangsong Feng  Yukun Ren  Hongyuan Jiang 《Biomicrofluidics》2013,7(5)

It is difficult to mix two liquids on a microfluidic chip because the small dimensions and velocities effectively prevent the turbulence. This paper describes two 2-layer PDMS passive micromixers based on the concept of splitting and recombining the flow that exploits a self-rotated contact surface to increase the concentration gradients to obtain fast and efficient mixing. The designed micromixers were simulated and the mixing performance was assessed. The mixers have shown excellent mixing efficiency over a wide range of Reynolds number. The mixers were reasonably fabricated by multilayer soft lithography, and the experimental measurements were performed to qualify the mixing performance of the realized mixer. The results show that the mixing efficiency for one realized mixer is from 91.8% to 87.7% when the Reynolds number increases from 0.3 to 60, while the corresponding value for another mixer is from 89.4% to 72.9%. It is rather interesting that the main mechanism for the rapid mixing is from diffusion to chaotic advection when the flow rate increases, but the mixing efficiency has not obvious decline. The smart geometry of the mixers with total length of 10.25 mm makes it possible to be integrated with many microfluidic devices for various applications in μ-TAS and Lab-on-a-chip systems.  相似文献   

The dynamic impact characteristics of tennis balls with tennis rackets     

S.J. Haake  M.J. Carré  S.R. Goodwill 《Journal of sports sciences》2013,31(10):839-850

Abstract

The dynamic properties of six types of tennis balls were measured using a force platform and high-speed digital video images of ball impacts on rigidly clamped tennis rackets. It was found that the coefficient of restitution reduced with velocity for impacts on a rigid surface or with a rigidly clamped tennis racket. Pressurized balls had the highest coefficient of restitution, which decreased by 20% when punctured. Pressureless balls had a coefficient of restitution approaching that of a punctured ball at high speeds. The dynamic stiffness of the ball or the ball-racket system increased with velocity and pressurized balls had the highest stiffness, which decreased by 35% when punctured. The characteristics of pressureless balls were shown to be similar to those of punctured balls at high velocity and it was found that lowering the string tension produced a smaller range of stiffness or coefficient of restitution. It was hypothesized that players might consider high ball stiffness to imply a high coefficient of restitution. Plots of coefficient of restitution versus stiffness confirmed the relationship and it was found that, generally, pressurized balls had a higher coefficient of restitution and stiffness than pressureless balls. The players might perceive these parameters through a combination of sound, vibration and perception of ball speed off the racket.  相似文献   

Training of elite cyclists: effects on mood state and selected hormonal responses     

Edith Filaire  Bruno Legrand  Gérard Lac  Jean-Marie Pequignot 《Journal of sports sciences》2013,31(11-12):1025-1033

The psychobiological status of cyclists over a period of 8 months of training was assessed by measuring the sympatho-adrenal level, the central noradrenergic activity, and the cortisol?-?testosterone ratio status non-invasively. Alteration of these indices after a large increase in training load lasting 4 days (?+?187%) was also examined. Urinary excretion of methoxyamines (metanephrine, normetanephrine) and 3-methoxy-4-hydroxyphenylglycol sulphate (MHPG-S), and salivary concentrations of cortisol and testosterone, were measured in 12 national cyclists after a non-specific training period and 48 h before 4 days of increased training (T₁), after these 4 days (T₂) and at the end of 4 months of specific training (T₃). Urinary and salivary samples were also collected during a rest period (T₀). At each of these times, mood states and ratings of perceived muscle soreness were assessed, and a questionnaire of early clinical symptoms of the overtraining syndrome (Profile of Mood States) was administered. A significant increase in normetanephrine (P <?0.05) and a decrease in the testosterone?-?cortisol ratio (P <?0.05) were observed at T₂, while MHPG-S excretion remained unchanged. Over the same periods, increased training loads did not induce mood disturbances. Eight months of training were associated with significant alterations in metanephrine (P?<?0.05) and MHPG-S (P?<?0.05). These results suggest a dissociation between the neural and endocrine catecholaminergic components systems. Opposite responses between MHPG-S and Profile of Mood States scores show that further investigations are needed to understand the relationship between central noradrenergic function, which is recognized as a regulatory factor of mood, and psychological tests measuring mood.  相似文献   

Activity profile of top-class association football referees in relation to performance in selected physical tests     

Javier Mallo  José-María García-Aranda  Bart Gilis  Werner Helsen 《Journal of sports sciences》2013,31(7):805-813

Abstract

The aims of the present study were (1) to analyse the physical demands of top-class referees and (2) to compare their official FIFA fitness test results with physical performance during a match. The work rate profiles of 11 international referees were assessed during 12 competitive matches at the 2003 FIFA Under-17 World Cup and then analysed using a bi-dimensional photogrammetric video analysis system based on direct lineal transformation (DLT) algorithms. In the first 15 min of matches, the referees were more active, performing more high-intensity exercise (P < 0.01) than in the first 15 min of the second half. During the second half of matches, the referees covered a shorter distance (P < 0.01), spent more time standing still (P < 0.05), and covered less ground cruising (P < 0.05), sprinting (P < 0.05), and moving backwards (P < 0.001) than in the first half. Also in the second 45 min, the distance of referees from infringements increased (P < 0.05) in the left attacking zone of the filed. There was also a decrease (P < 0.05) in performance in the period following the most high-intensity activity, compared with the mean for the 90 min. Time spent performing high-intensity activities during a match was not related to performance in the 12-min run (r ² = 0.30; P < 0.05), the 200-m sprint (r ² = 0.05; P < 0.05), or the 50-m sprint (r ² = 0.001; P < 0.05). The results of this study show that: (1) top-class referees experienced fatigue at different stages of the match, and (2) the typical field tests used by FIFA (two 50-m and 200-m sprints, followed by a 12-min run) are not correlated with match activities.  相似文献   

实名SNS社交网络与微博的特征分析——以人人网与新浪微博为例     

任蔷  丁振国 《现代情报》2013,33(7):94-98

以人人网和新浪微博为例,通过SPSS统计软件分析比较实名SNS社交网络与微博的功能特征与用户行为特点。研究认为人人网用户活跃度与用户本身隐私保护意识有一定联系;新浪微博用户活跃度与用户的学历存在一定联系。人人网与新浪微博同时存在用户被动接收推送广告信息问题,影响了用户的体验度。探讨了人人网与新浪微博的商业化运营趋势,为实名社交网站和微博的完善与差别化发展提供了理论依据。  相似文献   

针对WMSN图像传输能耗优化方法的技术研究     

任燕 《科技通报》2013,29(3)

建立了井下安全监控系统,采用无线多媒体传感器网络(WMSN)来构建.针对WMSN图像传输能耗大的问题,提出了利用节点协同的方式进行图像传输,并且在图像压缩编码上采用了改进型JPEG2000算法.仿真结果表明,减小量子化层级即可降低图像压缩能量的损耗;节点协同方式下的图像传输能耗最小,网络运行周期最长.在环境监控、危险预警等方面具有广阔的应用前景.  相似文献   

大蒜花苞的生物反应器扩繁     

王菁菁  贾明良  张本厚  刘刃  陈集双 《科技通报》2013,29(3)

利用间歇浸没式生物反应器对大蒜花苞进行培养,研究了不同外植体类型对大蒜种苗生长的影响,并与传统固体培养方式进行了比较,随后对得到的微型鳞茎进行驯化栽培研究.结果表明:(1)不同生长阶段的大蒜外植体进行60 d的培养,反应器中Ⅱ型(固体培养基培养20 d的花苞)每个容器鳞茎数(942.40个)和增殖系数(23.56)均是I型(新鲜花苞)的1.15倍;Ⅱ型每个容器生物量(8.82 g)和平均鲜重(0.22 g)均是I型的1.1倍.因此,Ⅱ型比I型花苞更适合作为间歇浸没式生物反应器培养的外植体.(2)生物反应器培养的外植体每个容器生物量(8.48 g)是固体培养基培养的70.67倍,平均鲜重(0.26 g)是后者的4.33倍,增殖系数(21.22)是后者的4.21倍,每个容器鳞茎数(848.80个)是后者的84.37倍.因此,间歇浸没式生物反应器培养方式优于固体培养基培养方式.(3)将生物反应器培养得到的微型鳞茎按照直径大小分为①型,4.0～6.0 mm;②型,3.0～4.0 mm;③型,＜3.0 mm.直径大小为3.0～4.0 mm的鳞茎,即②型发芽率最高,为68.11％,生根率和存活率分别为57.83％和85.73％,是水培鳞茎的适宜类型.利用育苗盘进行栽培,同样得到直径大小为3.0～4.0 mm的鳞茎表现最佳,其发芽率最高,为60.43％,生根率和存活率分别为58.43％和89.33％,鳞茎苗生长状态最好,是鳞茎栽培的适宜类型.  相似文献   

双离合式自动变速器换挡控制方法的研究     

夏伟强  蔡锦波  任华林  滕伯印 《科技通报》2013,(1):106-109

双离合式自动变速器换挡能够实现平稳快速的动力性换挡,提高乘坐的舒适性。由双离合器式自动变速器换挡过程的分析可知,当上一档位的离合器分离,下一档位的离合器滑摩的时候,由于两个档位变速比的差别,为了使换挡过程中车速平稳变化,没有明显的冲击,必须在这过程中,对发动机转速进行有效控制以匹配下一档位的输入轴转速。本文研究双离合式自动变速器换挡控制方法,编写相应的换挡控制程序,对发动机和离合器同时进行有效的控制。实验结果表明,本文采用的控制方法实现了汽车平稳变速。  相似文献