Adaptation kinetics in bacterial chemotaxis

Cells of Escherichia coli, tethered to glass by a single flagellum, were subjected to constant flow of a medium containing the attractant alpha-methyl-DL-aspartate. The concentration of this chemical was varied with a programmable mixing apparatus over a range spanning the dissociation constant of the chemoreceptor at rates comparable to those experienced by cells swimming in spatial gradients. When an exponentially increasing ramp was turned on (a ramp that increases the chemoreceptor occupancy linearly), the rotational bias of the cells (the fraction of time spent spinning counterclockwise) changed rapidly to a higher stable level, which persisted for the duration of the ramp. The change in bias increased with ramp rate, i.e., with the time rate of change of chemoreceptor occupancy. This behavior can be accounted for by a model for adaptation involving proportional control, in which the flagellar motors respond to an error signal proportional to the difference between the current occupancy and the occupancy averaged over the recent past. Distributions of clockwise and counterclockwise rotation intervals were found to be exponential. This result cannot be explained by a response regular model in which transitions between rotational states are generated by threshold crossings of a regular subject to statistical fluctuation; this mechanism generates distributions with far too many long events. However, the data can be fit by a model in which transitions between rotational states are governed by first-order rate constants. The error signal acts as a bias regulator, controlling the values of these constants

Incentives for Residential Water Conservation: Water Price, Revenue, and Consumer Equity in Florida

Economic theory suggests that price incentives can be used to encourage water conservation in residential consumers. Conservation water rates are designed to send price signals that encourage households to reduce discretionary water use in the long term. However, it is not always clear that conservation rates effectively provide meaningful incentives. Utilities themselves may also not have strong incentives to implement conservation rates. If conservation rates have a negative impact on revenue, or if they lead to increased revenue variability, utilities may have a disincentive to use them. In addition, block pricing structures (where unit water rate increases with water usage) may be inequitable, in the sense that the “revenue burden” is borne disproportionately by some customer groups. This may make some rate structures unpopular with consumers and politically unfeasible. Because there is no consensus about what defines conservation rates, they take many forms. In Florida, the two most common are: uniform rates- where customers pay a set fee for each unit of water used, and inclining block rates- where the price per unit becomes progressively higher. Empirical evidence about the incentives provided by various structures is limited. This research has three main objectives. The first is to analyze whether or not the number of price blocks affects the conservation incentives faced by residential consumers. The second is to test for statistical evidence that rate structure effects revenue variability. And, the third is to analyze the impact of different rate structures on consumer equity. Secondary data from sixteen Florida utilities are used to meet the objectives of the study. The sample was originally chosen by Dr. John Whitcomb as a part of his study Florida Water Rates Evaluation of Single-Family Homes (2005). Whitcomb (2005) includes rate information, customer survey results, and empirical data on actual water use for 7,200 households from 1998 to 2003. For the first objective, a descriptive analysis of rate structures is used. Household reductions in water use are compared to corresponding reductions in water bills for all rate structure periods. Larger reductions in corresponding bills indicate stronger conservation price signals. Distribution of utility revenues between volumetric and fixed water and wastewater charges is also examined, and larger share of volumetric charges is linked to a stronger conservation price signal. The second part of the study uses graphical analysis and a simple OLS model to examine rate structure and revenue variability. For the third objective, Gini coefficients and Lorenz curves were used, following Morgan (1987). Households are divided into income groups and usage groups. Gini Coefficients are calculated based on these groups. Lower coefficients indicate a more equitable rate structure. The results indicate that the conservation price signals are strongest for inclining block structures with more than three price blocks. Block structures with three or less price blocks do not send stronger price signals than uniform rate structures. In some cases, the price incentive to reduce water consumption by 40% was stronger for uniform structures than for inclining block structures with three blocks. Within the sample, the price incentive is strongest for inclining block structures with more than three price blocks. Alternatively, the utility revenue distribution results suggest that the number of price blocks is not necessarily a good indicator of how conservation oriented a rate structure is. In several cases, the percentage of revenue from volumetric sources was higher for uniform structures than for block structures. Analysis for objectives two and three will be completed in October 2009. Preliminary results for objective two provide evidence that revenue variability could be a significant disincentive for utilities to adopt conservation rates. While there was no statistical evidence that overall revenue is affected by changes in rate structure, there is some evidence that utility revenue streams are more variable for block structures than for uniform structures. Preliminary objective three results suggest that customer equity is not adversely affected by conservation rates. When divided into income groups, the estimated Gini coefficients for uniform and inclining block rate structures were similar and close to zero, indicating equitable pricing.Conservation, water, price, revenue, equity, Community/Rural/Urban Development, Consumer/Household Economics, Demand and Price Analysis, Environmental Economics and Policy,

Coordination of flagella on filamentous cells of Escherichia coli

Video techniques were used to study the coordination of different flagella on single filamentous cells of Escherichia coli. Filamentous, nonseptate cells were produced by introducing a cell division mutation into a strain that was polyhook but otherwise wild type for chemotaxis. Markers for its flagellar motors (ordinary polyhook cells that had been fixed with glutaraldehyde) were attached with antihook antibodies. The markers were driven alternately clockwise and counterclockwise, at angular velocities comparable to those observed when wild-type cells are tethered to glass. The directions of rotation of different markers on the same cell were not correlated; reversals of the flagellar motors occurred asynchronously. The bias of the motors (the fraction of time spent spinning counterclockwise) changed with time. Variations in bias were correlated, provided that the motors were within a few micrometers of one another. Thus, although the directions of rotation of flagellar motors are not controlled by a common intracellular signal, their biases are. This signal appears to have a limited range

Swimming in circles: Motion of bacteria near solid boundaries

Near a solid boundary, E. coli swims in clockwise circular motion. We provide a hydrodynamic model for this behavior. We show that circular trajectories are natural consequences of force-free and torque-free swimming, and the hydrodynamic interactions with the boundary, which also leads to a hydrodynamic trapping of the cells close to the surface. We compare the results of the model with experimental data and obtain reasonable agreement. In particular, we show that the radius of curvature of the trajectory increases with the length of the bacterium body.Comment: Also available at http://people.deas.harvard.edu/~lauga

Adaptation Kinetics in Bacterial Chemotaxis

Cells of Escherichia coli, tethered to glass by a single flagellum, were subjected to constant flow of a medium containing the attractant alpha-methyl-DL-aspartate. The concentration of this chemical was varied with a programmable mixing apparatus over a range spanning the dissociation constant of the chemoreceptor at rates comparable to those experienced by cells swimming in spatial gradients. When an exponentially increasing ramp was turned on (a ramp that increases the chemoreceptor occupancy linearly), the rotational bias of the cells (the fraction of time spent spinning counterclockwise) changed rapidly to a higher stable level, which persisted for the duration of the ramp. The change in bias increased with ramp rate, i.e., with the time rate of change of chemoreceptor occupancy. This behavior can be accounted for by a model for adaptation involving proportional control, in which the flagellar motors respond to an error signal proportional to the difference between the current occupancy and the occupancy averaged over the recent past. Distributions of clockwise and counterclockwise rotation intervals were found to be exponential. This result cannot be explained by a response regular model in which transitions between rotational states are generated by threshold crossings of a regular subject to statistical fluctuation; this mechanism generates distributions with far too many long events. However, the data can be fit by a model in which transitions between rotational states are governed by first-order rate constants. The error signal acts as a bias regulator, controlling the values of these constants.Molecular and Cellular Biolog

Coordination of Flagella on Filamentous Cells of Escherichia Coli

Video techniques were used to study the coordination of different flagella on single filamentous cells of Escherichia coli. Filamentous, nonseptate cells were produced by introducing a cell division mutation into a strain that was polyhook but otherwise wild type for chemotaxis. Markers for its flagellar motors (ordinary polyhook cells that had been fixed with glutaraldehyde) were attached with antihook antibodies. The markers were driven alternately clockwise and counterclockwise, at angular velocities comparable to those observed when wild-type cells are tethered to glass. The directions of rotation of different markers on the same cell were not correlated; reversals of the flagellar motors occurred asynchronously. The bias of the motors (the fraction of time spent spinning counterclockwise) changed with time. Variations in bias were correlated, provided that the motors were within a few micrometers of one another. Thus, although the directions of rotation of flagellar motors are not controlled by a common intracellular signal, their biases are. This signal appears to have a limited range.Molecular and Cellular Biolog

What are Inclusive Pedagogies ? What must faculty do differently to teach inclusively?

At the 2016 All Campus Forum President Hinton called for us to create an ecosystem of inclusion at CSB/SJU. Faculty members\u27 work with students is central to creating such an ecosystem, but what, after all, do we mean by inclusion? In this presentation, FYS and Humanities Mellon cohort members provide an overview of our evolving understanding of inclusive pedagogy, the research that supports it, as well as examples of such pedagogies that we are implementing in our fall 2016 courses

Difference in Brain Densities Between Chronic Alcoholic and Normal Control Patients.

The densities of the brains of 11 chronic alcoholics were compared with those of 11 age-matched normal control subjects. Densities were determined from the density numbers generated by computerized tomography at three levels of the brain-the highest level of the lateral ventricles and the next two higher levels-with adjustments made to control for possible artifacts in the data. The advantage of the dominant hemisphere over the nondominant hemisphere was lessened in alcoholic

Balance Assessment Using a Smartwatch Inertial Measurement Unit with Principal Component Analysis for Anatomical Calibration

Balance assessment, or posturography, tracks and prevents health complications for a variety of groups with balance impairment, including the elderly population and patients with traumatic brain injury. Wearables can revolutionize state-of-the-art posturography methods, which have recently shifted focus to clinical validation of strictly positioned inertial measurement units (IMUs) as replacements for force-plate systems. Yet, modern anatomical calibration (i.e., sensor-to-segment alignment) methods have not been utilized in inertial-based posturography studies. Functional calibration methods can replace the need for strict placement of inertial measurement units, which may be tedious or confusing for certain users. In this study, balance-related metrics from a smartwatch IMU were tested against a strictly placed IMU after using a functional calibration method. The smartwatch and strictly placed IMUs were strongly correlated in clinically relevant posturography scores (r = 0.861–0.970, p \u3c 0.001). Additionally, the smartwatch was able to detect significant variance (p \u3c 0.001) between pose-type scores from the mediolateral (ML) acceleration data and anterior-posterior (AP) rotation data. With this calibration method, a large problem with inertial-based posturography has been addressed, and wearable, “at-home” balance-assessment technology is within possibility