Quantifying Fluid Shear Stress in a Rocking Culture Dish

Fluid shear stress (FSS) is an important stimulus for cell functions. Compared with the well established parallel-plate and cone-and-plate systems, a rocking “see-saw” system offers some advantages such as easy operation, low cost, and high throughput. However, the FSS spatiotemporal pattern in the system has not been quantified. In the present study, we developed a lubrication-based model to analyze the FSS distributions in a rocking rectangular culture dish. We identified an important parameter (the critical flip angle) that dictates the overall FSS behaviors and suggested the right conditions to achieving temporally oscillating and spatially relatively uniform FSS. If the maximal rocking angle is kept smaller than the critical flip angle, which is defined as the angle when the fluid free surface intersects the outer edge of the dish bottom, the dish bottom remains covered with a thin layer of culture medium. The spatial variations of the peak FSS within the central 84% and 50% dish bottom are limited to 41% and 17%, respectively. The magnitude of FSS was found to be proportional to the fluid viscosity and the maximal rocking angle, and inversely proportional to the square of the fluid depth-to-length ratio and the rocking period. For a commercial rectangular dish (length of 37.6 mm) filled with ∼2 mL culture medium, the FSS at the center of the dish bottom is expected to be on the order of 0.9 dyn/cm2 when the dish is rocked +5° at 1 cycle/s. Our analysis suggests that a rocking “see-saw” system, if controlled well, can be used as an alternative method to provide low-magnitude, dynamic FSS to cultured cells

Research on the Relationship Between IT Employee’s Work Pressure, Control Points and Turnover Intention

The increasingly fierce competition, IT enterprise employees will feel more and more pressure of work. And in recent years, due to the rapid development of the Internet industry, the IT industry develops fast in the digital revolution, many of the factors make IT enterprise employees turnover rate increased year by year. Based on the IT enterprise employees as investigation object, this article using hierarchical regression method to verify the control points between work pressure and turnover intention has a regulatory role. IT companies in the recruitment and staff training should put employees control points included in the examination scope which can alleviate the pressure on employees to a certain extent and reduce employee turnover rate

Analysis of particle trajectories in a quick-contact cyclone reactor using discrete phase model (DPM)

A quick-contact cyclone reactor has been designed for residue fluid catalytic cracking instead of riser reactor. It mainly consists of a mixing-reaction chamber and a separation chamber. So the cracking reactions and the separations between the products and catalysts could occur respectively and simultaneously. In order to reveal the mechanism of the mixing and separation of gas-solid in the quick-contact cyclone reactor, the particle trajectories in the reactor were investigated using discrete phase model (DPM). The results show that the particle trajectories in the quick-contact cyclone reactor could be described as three types: escaped, trapped and ring. And the pre-vortex flow was observed in the mixing-reaction chamber. However, the solid-gas following property in it was inferior to that in the separation chamber. In addition, the particle grade efficiencies of the cyclone were obtained by counting the numbers of escaping and capturing particles. It was shown that the particles which have a size larger than 10 μm were separated completely from the reactor. Moreover, the Rossin-Rammler equation was found to the size distribution curve fitting. The separation efficiency in simulated method was higher than 98%. And the error between the simulated and experimental results was no more than 1.31%, which indicates that the simulated results are reliable and accurate. Please click Additional Files below to see the full abstract

Effect of Low-magnitude, High-frequency Vibration on Osteocytes in the Regulation of Osteoclasts

Osteocytes are well evidenced to be the major mechanosensor in bone, responsible for sending signals to the effector cells (osteoblasts and osteoclasts) that carry out bone formation and resorption. Consistent with this hypothesis, it has been shown that osteocytes release various soluble factors (e.g. transforming growth factor-β, nitric oxide, and prostaglandins) that influence osteoblastic and osteoclastic activities when subjected to a variety of mechanical stimuli, including fluid flow, hydrostatic pressure, and mechanical stretching. Recently, low-magnitude, high-frequency (LMHF) vibration (e.g., acceleration less than \u3c 1 × g, where g = 9.81 m/s2, at 20–90 Hz) has gained much interest as studies have shown that such mechanical stimulation can positively influence skeletal homeostasis in animals and humans. Although the anabolic and anti-resorptive potential of LMHF vibration is becoming apparent, the signaling pathways that mediate bone adaptation to LMHF vibration are unknown. We hypothesize that osteocytes are the mechanosensor responsible for detecting the vibration stimulation and producing soluble factors that modulate the activity of effector cells. Hence, we applied low-magnitude (0.3 × g) vibrations to osteocyte-like MLO-Y4 cells at various frequencies (30, 60, 90 Hz) for 1 h. We found that osteocytes were sensitive to this vibration stimulus at the transcriptional level: COX-2 maximally increased by 344% at 90 Hz, while RANKL decreased most significantly (−55%, p \u3c 0.01) at 60 Hz. Conditioned medium collected from the vibrated MLO-Y4 cells attenuated the formation of large osteoclasts (≥ 10 nuclei) by 36% (p \u3c 0.05) and the amount of osteoclastic resorption by 20% (p = 0.07). The amount of soluble RANKL (sRANKL) in the conditioned medium was found to be 53% lower in the vibrated group (p \u3c 0.01), while PGE2 release was also significantly decreased (−61%, p \u3c 0.01). We conclude that osteocytes are able to sense LMHF vibration and respond by producing soluble factors that inhibit osteoclast formation

Effect of micro-patterning on bacterial adhesion on polyethylene terephthalate surface.

Bacterial adhesion on surfaces commonly used in medicine and food industry could lead to infections and illnesses. Topographically patterned surfaces recently have shown to be a promising alternative to chemical antibacterial methods, which might release cytotoxin and promote antibiotic resistance. In this study, we fabricated micro-patterned polyethylene terephthalate surfaces, and quantitatively explored the amount and localization of Escherichia coli MG1655 cells attached on a series of defined topographies. The adhesion was conducted in static conditions and under a weak flow, in both physiological buffer and nutritious solutions. The results showed that in the presence of weak shear force, live bacteria could still maintain sensing ability in nutritious culture, but not in buffer solution. The finely textured surface, which could inhibit bacterial adhesion in the early stage of attachment, reversed its effect to enhance the adhesion after 24 h incubation, indicating that microbial cells seemed to be able to sense the disadvantageous condition and eventually overcome it. In terms of adhesion localization, bacteria exhibited preferential adhesion onto the edges of topographic features. The patterned substrates that have the most even (homogeneous) bacterial localization on topographic features retained the least attachment after 24 h exposure.Financial support from China Scholarship Council and Unilever Corporate Research is acknowledged.This is the accepted manuscript. The final version is available from Sage at http://jba.sagepub.com/content/early/2014/12/16/0885328214563998.refs

Generalize Hilbert operator acting on Dirichlet spaces

Let $\mu$ be a positive Borel measure on the interval $[0,1)$. For $\gamma>0$, the Hankel matrix $\mathcal{H}_{\mu,\gamma}=(\mu_{n,k})_{n,k\geq0}$ with entries $\mu_{n,k}=\mu_{n+k}$, where $\mu_{n+k}=\int_{0}^{\infty}t^{n+k}d\mu(t)$. formally induces the operator $$\mathcal{H}_{\mu,\gamma}=\sum_{n=0}^{\infty}\left(\sum_{k=0}^{\infty}\mu_{n,k}a_k\right)\frac{\Gamma(n+\gamma)}{n!\Gamma(\gamma)}z^n,$$ on the space of all analytic functions $f(z)=\sum_{k=0}^{\infty}{a_k}{z^k}$ in the unit disc $\mathbb{D}$. Following ideas from \cite{author3} and \cite{author4}, in this paper, for $0\leq\alpha<2$, $2\leq\beta<4$, $\gamma\geq1$. we characterize the measure $\mu$ for which $\mathcal{H}_{\mu,\gamma}$ is bounded(resp.,compact)from $\mathcal{D}_{\alpha}$ into $\mathcal{D}_{\beta}$.Comment: 7 page

Staphylococcal Infection and Infertility

Staphylococcus sp. is not only a commensal bacterium but also a major human pathogen that causes a wide range of clinical infections, such as skin and soft tissue infection, pleuropulmonary and osteoarticular infection, and endocarditis as well as life-threatening systemic infections. More evidence is currently emerging to show that Staphylococcus, particularly Staphylococcus aureus, can colonize the reproductive systems and affect their structure and function. Staphylococcal infection has become one of the most common causes of infertility in both males and females. This chapter focuses on the epidemiology, pathophysiology, clinical manifestations, and treatment of staphylococcal infection and infertility

Estudi contrastiu de l’estructura sil·làbica del català i del xinès estàndards i de les implicacions segmentals més rellevants per als aprenents sinòfons

[cat] La tesi Estudi contrastiu de l’estructura sil·làbica del català i del xinès estàndards i de les implicacions segmentals més rellevants per als aprenents sinòfons estudia la pronunciació del català pel que fa als aspectes segmentals i als suprasegmentals relatius a l’estructura sil·làbica per part dels estudiants xinesos que parlen el xinès estàndard (mandarí/putonghuà) com a llengua materna (L1). És el primer treball que no només aborda de manera global els problemes de pronunciació del català que presenten els aprenents sinòfons sinó que també ofereix solucions per millorar l’aprenentatge de la llengua oral catalana. L’interès per l’estudi ha estat suscitat, d’una banda, per l’augment d’alumnes xinesos que venen a estudiar a les universitats catalanes, els quals presenten accents estrangers molt notables, i, de l’altra, per les grans diferències que existeixen entre ambdues llengües, tant a nivell fonètic com a nivell fonològic. L’estudi es basa en l’anàlisi contrastiva, per la qual cosa es comparen tots els sons del xinès i del català estàndards, les estructures sil·làbiques i la configuració dels diftongs i els triftongs de les dues llengües, així com les regles fonològiques que afecten el català. La comparació global i contrastiva ha permès localitzar les dificultats de pronunciació que normalment afronten els estudiants sinòfons. També s’han tingut en compte els trets de l’anglès i l’espanyol, perquè són les dues llengües que els estudiants xinesos normalment han après abans del català i, per tant, poden interferir, tant positivament com negativament, en les pronunciacions del català. La investigació s’ha realitzat a partir d’un corpus de 248 paraules respost per 19 informants d’entre 18 i 33 anys que estudien a Barcelona i parlen el xinès estàndard com a L1, l’anglès i l’espanyol com a L2 i L3, i el català i altres llengües com a L4/L5/etc., repartits en tres nivells de coneixement del català: nivell inicial-bàsic, nivell mitjà i nivell avançat. Les dades obtingudes han permès detectar els errors i les imprecisions que presenten a cada nivell, i agrupar-los en aspectes de prioritat alta (desviacions bàsiques per a la intel·ligibilitat), de prioritat baixa (imprecisions que no afecten la intel·ligibilitat) i d’atenció esporàdica (problemes que indiquen accents estrangers però que no causen problemes d’intel·ligibilitat). Finalment, els resultats han servit per proposar solucions pràctiques per facilitar el procés d’adquisició i de perfeccionament de la pronunciació de la llengua catalana.[eng] The thesis Contrastive study of the syllabic structure of Standard Catalan and Standard Chinese and the most important segmental implications for Chinese-speaking students is a study of Catalan pronunciation by Chinese students who speak Standard Chinese (Mandarin/Putonghua) as their mother tongue (L1). We have focused on segments difficult to master and suprasegmental aspects related to syllable structure. It is the first work that deals with the problems of Catalan pronunciation faced by Chinese-speaking students and offers suggestions to improve the acquisition of oral Catalan. The interest in this study has been motivated, on the one hand, by the increasing number of Chinese students who come to study in Catalan universities and the remarkable foreign accents that they display, and, on the other, by the great phonetic and phonological differences between Catalan and Chinese. The study, based on the Contrastive Analysis theory, compares all the sounds of Standard Chinese and Catalan, their syllabic structures and vowel glide configuration of both languages, as well as the phonological rules that affect Catalan. The global and contrastive comparison serves to locate the pronouncing difficulties that the Chinese-speaking students normally face when speak Catalan. We have also considered the phonetic features of English and Spanish because they are the two languages Chinese students have normally learned before they start studying Catalan and, therefore, they can interfere, both positively and negatively, in their pronunciation of Catalan. The research has been based on a corpus of 248 words pronounced by 19 informants aged between 18 and 33 who study in Barcelona and speak Standard Chinese as L1, English and Spanish as L2 and L3, and Catalan and other languages as L4/L5/etc. They are divided into three groups according to their Catalan levels: initial-basic, middle, and advanced levels. The data obtained has allowed to detect the errors and inaccuracies that they have presented in each level, and classify them as high priority (great deviations that affect intelligibility), low priority (inaccuracies that do not affect intelligibility) and sporadic attention (foreign accents that do not affect intelligibility). Finally, the results have helped us to propose practical solutions to facilitate the acquisition and improvement of Catalan pronunciation

Image Analyses of Two Crustacean Exoskeletons and Implications of the Exoskeletal Microstructure on the Mechanical Behavior

The microstructures of exoskeletons from Homarus americanus (American lobster) and Callinectes sapidus (Atlantic blue crab) were investigated to elucidate the mechanical behavior of such biological composites. Image analyses of the cross-sectioned exoskeletons showed that the two species each have three well-defined regions across the cuticle thickness where the two innermost regions (exocuticle and endocuticle) are load bearing. These regions consist of mineralized chitin fibers aligned in layers, where a gradual rotation of the fiber orientation of the layers results in repeating stacks. The exocuticle and endocuticle of the two species have similar morphology, but different thicknesses, number of layers, and number of stacks. Mechanics-based analyses showed that the morphology of the layered structure corresponds to a nearly isotropic structure. The cuticles are inter-stitched with pore canal fibers, running transversely to the layered structure. Mechanics-based analyses suggested that the pore canal fibers increase the interlaminar strength of the exoskeleton