Swimming Efficiency of Bacterium Escherichia Coli

We use in vivo measurements of swimming bacteria in an optical trap to determine fundamental properties of bacterial propulsion. In particular, we determine the propulsion matrix, which relates the angular velocity of the flagellum to the torques and forces propelling the bacterium. From the propulsion matrix dynamical properties such as forces, torques, swimming speed and power can be obtained from measurements of the angular velocity of the motor. We find significant heterogeneities among different individuals even though all bacteria started from a single colony. The propulsive efficiency, defined as the ratio of the propulsive power output to the rotary power input provided by the motors, is found to be 0.2%.Comment: 6 page

The role of body rotation in bacterial flagellar bundling

In bacterial chemotaxis, E. coli cells drift up chemical gradients by a series of runs and tumbles. Runs are periods of directed swimming, and tumbles are abrupt changes in swimming direction. Near the beginning of each run, the rotating helical flagellar filaments which propel the cell form a bundle. Using resistive-force theory, we show that the counter-rotation of the cell body necessary for torque balance is sufficient to wrap the filaments into a bundle, even in the absence of the swirling flows produced by each individual filament

Film support and the challenge of ‘sustainability’: on wing design, wax and feathers, and bolts from the blue

In recognition of the importance of film in generating both economic and cultural value, the UK Labour government set up a new agency – the United Kingdom Film Council (UKFC) – in 2000 with a remit to build a sustainable film industry. But, reflecting a plethora of differing expectations in relation to the purposes behind public support for film, the UKFC's agenda shifted and broadened over the organisation's lifetime (2000–11). Apparently unconvinced by the UKFC's achievements, the Coalition government which came to power in May 2010 announced the Council's abolition and reassigned its responsibilities as part of a general cost-cutting strategy. Based on original empirical research, this article examines how the UKFC's sense of strategic direction was determined, how and why the balance of objectives it pursued changed over time and what these shifts tell us about the nature of film policy and the challenges facing bodies that are charged with enacting it in the twenty-first century

Predictors of recurrence and reoperation for prosthetic valve endocarditis after valve replacement surgery for native valve endocarditis

ObjectiveSurgical treatment of native valve endocarditis remains challenging, especially in cases with paravalvular destruction. Basic principles include complete debridement and reconstruction. This study is designed to evaluate the outcomes of surgical reconstruction of complex annular endocarditis using standard techniques and materials, including autologous and bovine pericardium.MethodsFrom 1975 to 2000, 358 cases (357 patients, mean age 49 ± 16 years, range 18–88 years) of native valve endocarditis were surgically managed. Bioprosthetic valves were implanted in 189 cases, and mechanical prostheses were implanted in 169 cases. A total of 78 cases of paravalvular destruction were identified: 62 annular abscesses, 8 fistulas, and 8 combined abscesses/fistulas. These were managed with 46 pericardial patches and 32 isolated suture reconstructions after radical debridement and prosthetic valve replacement.ResultsThe overall early mortality was 8.4% (n = 30). The mortality with paravalvular destruction was 17.9%, and the mortality with simple leaflet infection was 5.7% (P = .001). The unadjusted survival at 20 years was 26.4% ± 4.9% for bioprosthetic valves and 56.5% ± 8.1% for mechanical prostheses (P = .007). The freedom from recurrent prosthetic valve endocarditis was 78.9% ± 4.4% at 15 years. The freedom from reoperation for recurrent prosthetic valve endocarditis was 85.8% ± 4.2% at 15 years. The freedom from reoperation after reconstruction for paravalvular destruction was 88.2% ± 6.9% at 15 years. The freedom from mortality for recurrent prosthetic valve endocarditis was 92.7% ± 3.4% at 15 years. The independent predictors of reoperation were age (hazard ratio 0.930, P = .005) and intravenous drug use/human immunodeficiency virus plus surgical technique (hazard ratio 12.8, P = .003 for patch reconstruction plus valve and hazard ratio 3.6, P = .038 for valve replacement only). Prosthesis type was not predictive when separated from intravenous drug use/human immunodeficiency virus (hazard ratio 3.268, P = .088).ConclusionParavalvular destruction is associated with a higher operative mortality. Native valve endocarditis can be managed with reasonable long-term survival and low rates of reinfection with radical debridement and pericardial reconstruction with bioprostheses and mechanical prostheses. The type of prosthesis implanted does not influence long-term outcome. Patients with a history of intravenous drug use and human immunodeficiency virus are at increased risk for recurrent infection and reoperation

Disappeared persons and homicide in El Salvador

During 2012–2013, the homicide rate in El Salvador came down from 69.9 to 42.2 per 100,000 population following a government brokered truce between the leaders of the two major gangs, Mara Salvatrucha and Barrio 18. But despite the apparent successes of the truce, it was speculated that the drop in murders could have been due to the killers simply hid the bodies of their victims. This paper aims at determining whether gangs effectively disappeared their victims to cut down the official counts of murders, or they committed these crimes for other reasons. The results from this study suggest that Salvadoran gangs had been using disappearance as a method to gain sustained social control among residents of already gang-dominated areas, that together with homicide, disappearance is part of a process of territorial spread and strategic strengthening by which these groups are enhancing their capabilities to interfere in the alliances of Mexican drug trafficking organizations with Central American criminal organizations specializing in the trans-shipment of drugs and in providing access to local markets to distribute and sell drugs. Our findings show that the risk for disappearance has been large even before the truce was in place and that actually, it continues as such and going through a process of geographic expansion

Risk of pregnancy-related hypertension within 5 years of exposure to drinking water contaminated with Escherichia coli O157:H7

The authors evaluated the risk for pregnancy-related hypertension among previously healthy women who conceived within 5 years of exposure to drinking water contaminated with Escherichia coli O157.H7 in Walkerton, Canada (2000). Chronic hypertension was defined as systolic/diastolic blood pressure ≥140/90 mm Hg before 20 weeks gestation; gestational hypertension was defined as new onset systolic/diastolic blood pressure ≥140/90 mm Hg ≥20 weeks gestation. The incidence of hypertension was compared between women who were asymptomatic during the outbreak to those who experienced acute gastroenteritis. Blood pressure data were available for 135 of 148 eligible pregnancies. The adjusted relative risks for chronic and gestational hypertension were 1.5 (95% confidence interval [CI]: 0.3-7.7) and 1.0 (95% CI: 0.4-2.5), respectively. Mean arterial pressure before 20 weeks gestation was 2.7 mm Hg higher in women who had acute gastroenteritis (95% CI: 0.05-5.4). A trend toward higher chronic hypertension and mean arterial pressure in early pregnancy was observed among women who experienced gastroenteritis after exposure to bacterially-contaminated drinking water. © 2010 Wiley Periodicals, Inc

Twirling and Whirling: Viscous Dynamics of Rotating Elastica

Motivated by diverse phenomena in cellular biophysics, including bacterial flagellar motion and DNA transcription and replication, we study the overdamped nonlinear dynamics of a rotationally forced filament with twist and bend elasticity. Competition between twist injection, twist diffusion, and writhing instabilities is described by a novel pair of coupled PDEs for twist and bend evolution. Analytical and numerical methods elucidate the twist/bend coupling and reveal two dynamical regimes separated by a Hopf bifurcation: (i) diffusion-dominated axial rotation, or twirling, and (ii) steady-state crankshafting motion, or whirling. The consequences of these phenomena for self-propulsion are investigated, and experimental tests proposed.Comment: To be published in Physical Review Letter

Optimal relative timing of stance push-off and swing leg retraction

Abstract-Swing leg retraction, the backward rotation of the swing leg prior to heel-strike, is known to have several advantages in legged locomotion. To achieve this motion, a hip torque is required at the end of the swing phase to brake the forward rotation of the leg and/or accelerate its backward motion. In walking, pre-emptive push-off of the stance leg also occurs at the end of the swing, so its relative timing with late-swing retracting torque influences gait energetics. To find the best relative timing between the stance leg's pushoff force and the swing leg retraction torque, we calculate their work-based energetics in a simple bipedal model using impulsive approximations and with the aid of the so-called overlap parameter that quantifies the relative order and the percentage overlap of the push-off and retraction impulses. By minimizing the energetic cost of the gait, we found that it is energetically favorable to start with the push-off force, and postpone braking the leg swing until completely after the push-off (impulsive force/torque). The implication for the more realistic non-impulsive cases is to apply the retraction torque at the very end of the push-off before heel-strike. We show that the results are valid for many other bipedal models, for both periodic and aperiodic gaits, and regardless of the actuator efficiencies for positive and negative work

Protecting Wild Land from Wind Farms in a Post-EU Scotland

Scotland is one of the places in Europe to have experienced significant wind farm development over recent years. Concern about impacts on wild land has resulted in legal challenges based on European Union (EU) law. This article analyses whether wild land can be protected from wind farms and the differences that the United Kingdom (UK) departure from the EU will make. It considers the concept of 'wild land' compared with 'wilderness', analyses the legal basis (if any) for wild land protection, and examines potential impacts from wind farms. It highlights the significance of EU environmental law, particularly nature conservation and environmental assessment law, and analyses recent Scottish jurisprudence that has applied this. The role of the European Commission and Court of Justice of the EU (CJEU) is emphasised as a key part of EU environmental law. The article asks whether relevant global and regional environmental agreements can effectively replace the content of the substantive law and context of the Commission and CJEU. Four environmental agreements and two related compliance procedures are briefly evaluated. The conclusion is that while EU law does not directly provide protection for wild land, it is considerably stronger than the international environmental agreements that may replace it