Hydrodynamics of Micro-swimmers in Films

One of the principal mechanisms by which surfaces and interfaces affect microbial life is by perturbing the hydrodynamic flows generated by swimming. By summing a recursive series of image systems we derive a numerically tractable approximation to the three-dimensional flow fields of a Stokeslet (point force) within a viscous film between a parallel no-slip surface and no-shear interface and, from this Green's function, we compute the flows produced by a force- and torque-free micro-swimmer. We also extend the exact solution of Liron & Mochon (1976) to the film geometry, which demonstrates that the image series gives a satisfactory approximation to the swimmer flow fields if the film is sufficiently thick compared to the swimmer size, and we derive the swimmer flows in the thin-film limit. Concentrating on the thick film case, we find that the dipole moment induces a bias towards swimmer accumulation at the no-slip wall rather than the water-air interface, but that higher-order multipole moments can oppose this. Based on the analytic predictions we propose an experimental method to find the multipole coefficient that induces circular swimming trajectories, allowing one to analytically determine the swimmer's three-dimensional position under a microscope.Comment: 35 pages, 11 figures, 5 table

Upstream Swimming in Microbiological Flows

Interactions between microorganisms and their complex flowing environments are essential in many biological systems. We develop a model for microswimmer dynamics in non-Newtonian Poiseuille flows. We predict that swimmers in shear-thickening (-thinning) fluids migrate upstream more (less) quickly than in Newtonian fluids and demonstrate that viscoelastic normal stress differences reorient swimmers causing them to migrate upstream at the centreline, in contrast to well-known boundary accumulation in quiescent Newtonian fluids. Based on these observations, we suggest a sorting mechanism to select microbes by swimming speed

Covariant derivative expansion of Yang-Mills effective action at high temperatures

Integrating out fast varying quantum fluctuations about Yang--Mills fields A_i and A_4, we arrive at the effective action for those fields at high temperatures. Assuming that the fields A_i and A_4 are slowly varying but that the amplitude of A_4 is arbitrary, we find a non-trivial effective gauge invariant action both in the electric and magnetic sectors. Our results can be used for studying correlation functions at high temperatures beyond the dimensional reduction approximation, as well as for estimating quantum weights of classical static configurations such as dyons.Comment: Minor changes. References added. Paper accepted for publication in Phys.Rev.

Hotspots of boundary accumulation: dynamics and statistics of micro-swimmers in flowing films

Biological flows over surfaces and interfaces can result in accumulation hotspots or depleted voids of microorganisms in natural environments. Apprehending the mechanisms that lead to such distributions is essential for understanding biofilm initiation. Using a systematic framework we resolve the dynamics and statistics of swimming microbes within flowing films, considering the impact of confinement through steric and hydrodynamic interactions, flow, and motility, along with Brownian and run-tumble fluctuations. Micro-swimmers can be peeled o↵ the solid wall above a critical flow strength. However, the interplay of flow and fluctuations causes organisms to migrate back towards the wall above a secondary critical value. Hence, faster flows may not always be the most e"cacious strategy to discourage biofilm initiation. Moreover, we find run-tumble dynamics commonly used by flagellated microbes to be an intrinsically more successful strategy to escape from boundaries than equivalent levels of enhanced Brownian noise in ciliated organisms

Covariant derivative expansion of fermionic effective action at high temperatures

We derive the fermionic contribution to the 1-loop effective action for A_4 and A_i fields at high temperatures, assuming that gluon fields are slowly varying but allowing for an arbitrary amplitude of A_4.Comment: RevTex 4, 11 pages, 3 figures. Version 2: Typos corrected; magnetic fields restricted to parallel sector. Version accepted for publication in PR

A Multi-Level View of the Antecedents and Consequences of Trust in Virtual Leaders

Although trust is widely acknowledged as critical to virtual teams, little is known regarding the causes and consequences of trust in leaders of virtual teams. This paper examines the antecedents and consequences of trust in virtual team leaders. Using survey and archival data from a massively multiplayer online game (MMOG), this study’s findings show that trust in the leader is affected by team members’ use of synchronous communication and breadth of communication with leaders as well as team members’ distance from each other. Furthermore, reasoning that team size and culture create a shared context qualifying team members’ experiences, we found that team size and collectivistic values diminished the benefits of synchronous communication and breadth of communication, respectively. The findings also revealed that trust in leaders had a positive relationship to team performance. Detailed discussion of the findings is provided in the conclusion of the paper

MMOGs as Emerging Opportunities for Research on Virtual Organizations and Teams

Massively Multiplayer Online Games (MMOG) offer new promising opportunities to research virtual organizations and teams. The characteristics of MMOGs allow researchers to obtain objective data from a large and multi-national population. Lasting over months or even years, MMOGs facilitate longitudinal studies and ensure a high involvement of participants. Moreover, collecting data from online surveys and game servers keeps the costs of MMOG studies low. In this paper, we illustrate how research in MMOGs can utilize these opportunities to overcome some limitations of traditional research environments. Further we discuss the diverse information and communication technology (ICT) usage in MMOGs and therefore argue that research in MMOGs can provide a glimpse into the future application of ICT in real life organizations

Impact of Polypharmacy on Health-Related Quality of Life in Dialysis Patients

INTRODUCTION: Dialysis patients are often prescribed a large number of medications to improve metabolic control and manage coexisting comorbidities. However, some studies suggest that a large number of medications could also detrimentally affect patients' health-related quality of life (HRQoL). Therefore, this study aims to provide insight in the association between the number of types of medications and HRQoL in dialysis patients. METHODS: A multicentre cohort study was conducted among dialysis patients from Dutch dialysis centres 3 months after initiation of dialysis as part of the ongoing prospective DOMESTICO study. The number of types of medications, defined as the number of concomitantly prescribed types of drugs, was obtained from electronic patient records. Primary outcome was HRQoL measured with the Physical Component Summary (PCS) score and Mental Component Summary (MCS) score (range 0–100) of the Short Form 12. Secondary outcomes were number of symptoms (range 0–30) measured with the Dialysis Symptoms Index and self-rated health (range 0–100) measured with the EuroQol-5D-5L. Data were analysed using linear regression and adjusted for possible confounders, including comorbidity. Analyses for MCS and number of symptoms were performed after categorizing patients in tertiles according to their number of medications because assumptions of linearity were violated for these outcomes. RESULTS: A total of 162 patients were included. Mean age of patients was 58 ± 17 years, 35% were female, and 80% underwent haemodialysis. The mean number of medications was 12.2 ± 4.5. Mean PCS and MCS were 36.6 ± 10.2 and 46.8 ± 10.0, respectively. The mean number of symptoms was 12.3 ± 6.9 and the mean self-rated health 60.1 ± 20.6. In adjusted analyses, PCS was 0.6 point lower for each additional medication (95% confidence interval [95% CI]: −0.9 to −0.2; p = 0.002). MCS was 4.9 point lower (95% CI: −8.8 to −1.0; p = 0.01) and 1.0 point lower (95% CI: −5.1–3.1; p = 0.63) for the highest and middle tertiles of medications, respectively, than for the lowest tertile. Patients in the highest tertile of medications reported 4.1 more symptoms than in the lowest tertile (95% CI: 1.5–6.6; p = 0.002), but no significant difference in the number of symptoms was observed between the middle and lowest tertiles. Self-rated health was 1.5 point lower for each medication (95% CI: −2.2 to −0.7; p < 0.001). DISCUSSION/CONCLUSION: After adjustment for comorbidity and other confounders, a higher number of medications were associated with a lower PCS, MCS, and self-rated health in dialysis patients and with more symptoms

Treatment approach in patients with hyperbilirubinemia secondary to liver metastases in gastrointestinal malignancies: a case series and review of literature

BACKGROUND: Treatment of patients with severe liver dysfunction including hyperbilirubinemia secondary to liver metastases of gastrointestinal (GI) cancer is challenging. Regimen of oxaliplatin and fluoropyrimidine (FP)/folinic acid (FA) ± a monoclonal antibody (moAb), represents a feasible option considering the pharmacokinetics. Clinical data on the respective dosage and tolerability are limited and no recommendations are available. METHODS: Consecutive patients with severe hyperbilirubinemia [>2 × upper limit of the normal range (ULN) and >2.4 mg/dl] due to liver metastases of GI cancer without options for drainage receiving oxaliplatin, FP/FA ± moAb were analyzed. To collect further data a review of the literature was performed. RESULTS: A total of 12 patients were identified between 2011 and 2015. At treatment start, median bilirubin level was 6.1 mg/dl (>5 × ULN, range 2.7-13.6). The majority of patients (n = 11) received dose-reduced regimen with oxaliplatin (60-76%) and FP/FA (0-77%), rapidly escalating to full dose regimen. During treatment, bilirubin levels dropped more than 50% within 8 weeks or normalized within 12 weeks in 6 patients (responders). Median overall survival was 5.75 months (range 1.0-16.0 months) but was significantly prolonged in responders compared to nonresponders [9.7 and 3.0 months, p = 0.026 (two-sided test); 95% confidence interval (CI): 1.10-10.22]. In addition, case reports or series comprising a further 26 patients could be identified. Based on the obtained data a treatment algorithm was developed. CONCLUSION: Treatment with oxaliplatin, FP/FA ± moAb is feasible and may derive relevant benefits in patients with severe liver dysfunction caused by GI cancer liver metastases without further options of drainage

Zebrafish Larvae Exhibit Rheotaxis and Can Escape a Continuous Suction Source Using Their Lateral Line

Zebrafish larvae show a robust behavior called rheotaxis, whereby they use their lateral line system to orient upstream in the presence of a steady current. At 5 days post fertilization, rheotactic larvae can detect and initiate a swimming burst away from a continuous point-source of suction. Burst distance and velocity increase when fish initiate bursts closer to the suction source where flow velocity is higher. We suggest that either the magnitude of the burst reflects the initial flow stimulus, or fish may continually sense flow during the burst to determine where to stop. By removing specific neuromasts of the posterior lateral line along the body, we show how the location and number of flow sensors play a role in detecting a continuous suction source. We show that the burst response critically depends on the presence of neuromasts on the tail. Flow information relayed by neuromasts appears to be involved in the selection of appropriate behavioral responses. We hypothesize that caudally located neuromasts may be preferentially connected to fast swimming spinal motor networks while rostrally located neuromasts are connected to slow swimming motor networks at an early age