Extrinsic Fabry-Perot interferometer for measuring the stiffness of ciliary bundles on hair cells

We have developed an extrinsic Fabry-Perot interferometer (EFPI) to measure displacements of microscopic, living organelles in the inner ear. The EFPI is an optical phase-shifted instrument that can be used to measure nanometer displacements. The instrument transmits a coherent light signal to the end of a single glass optical fiber where the measurement is made. As the coherent light reaches the end of the fiber, part of this incident signal is reflected off the internal face of the fiber end (reference reflection) and part is transmitted through the end of the fiber. This transmitted light travels a short distance and is reflected off the surface whose displacement is to be measured (the target). This sensing reflection then reenters the fiber where it interferes with the reference reflection. The resulting interference signal then travels up the same optical fiber to a detector, where it is converted into a voltage that can be read from an oscilloscope. When the target moves, the phase relation between reference and sensing reflections changes, and the detector receives a modulated signal proportional to the target movement. Reflections of as little as 1% at both the sensor tip and target surfaces produce good results with this system. We use the EFPI in conjunction with fine glass whiskers to measure the stiffness (force per unit deflection) of stereociliary bundles on hair cells of the inner ear. The forces generated are in the tenths of picoNewton range and the displacements are tens of nanometers. Here we describe the EFPI and its development as a method for measuring displacements of microscopic organelles in a fluid medium. We also report experiments to validate the accuracy of the EFPI output and preliminary measurements of ciliary bundle stiffness in the posterior semicircular canal.     

Resource scheduling with variable requirements over time

The problem of scheduling resources for tasks with variable requirements over time can be stated as follows. We are given two sequences of vectors A=A ₁,…,A _n and R=R ₁,…,R _m . Sequence A represents resource availability during n time intervals, where each vector A _i has q elements. Sequence R represents resource requirements of a task during m intervals, where each vector R _i has q elements. We wish to find the earliest time interval i, termed latency, such that for 1≤k≤m, 1≤j≤q: A _i+k−1 ^j ≥R _k ^j , where A _i+k−1 ^j and R _k ^j are the jth elements of vectors A _i+k−1 and R _k , respectively. One application of this problem is I/O scheduling for multimedia presentations. The fastest known algorithm to compute the optimal solution of this problem has computation time (Amir and Farach, in Proceedings of the ACM-SIAM symposium on discrete algorithms (SODA), San Francisco, CA, pp. 212–223, 1991; Inf. Comput. 118(1):1–11, 1995). We propose a technique that approximates the optimal solution in linear time: . We evaluated the performance of our algorithm when used for multimedia I/O scheduling. Our results show that 95% of the time, our solution is within 5% of the optimal.     

Risk factors contributing to microbiological contamination of shallow groundwater in Kampala,Uganda

A study of water quality variation in shallow protected springs in Kampala was undertaken over a 12-month period to assess the causes of microbiological contamination. The microbiological quality of water was assessed using thermotolerant coliforms and faecal streptococci. Sanitary inspections and hazard assessments were undertaken to identify faecal sources (hazards), contaminant pathways and contributory factors. Data were collected on rainfall and population as additional factors potentially exerting an influence on microbiological quality. Initial analysis of the data showed a significant relationship between median level of contamination and rainfall, in particular to short-term rainfall events. Total sanitary risk score showed a significant relationship with median level of contamination, but population density may be a confounding factor. The raw microbiological data were transformed into five water quality targets: <1 and < or =10 cfu 100ml(-1) for faecal streptococci; and <1, < or =10 and < or=50 cfu 100 ml(-1) for thermotolerant coliforms. The presence of individual risk factors as well as variables for rainfall and population density were analysed with respect to failure to meet these water quality targets using contingency tables. Logistic regression models were developed for each of the five water quality targets. The analysis strongly suggested that there is rapid recharge of the springs after rainfall and this leads to microbiological contamination. On-site sanitation was less important than other sources of faecal matter, which was consistent with a low sanitation coverage in the study area. The study suggested that improving sanitary completion and local environmental hygiene was more important than controlling on-site sanitation in improving the quality of these springs.     

A REVIEW OF THE EFFECTS OF SEWER LEAKAGE ON GROUNDWATER QUALITY

Exfiltration (of sewage into the ground from faults in ageing sewerage networks) has been recognised for many years but has never been quantified. It was considered that this leakage did not pose a groundwater-contamination threat because it was assumed that pathogens in sewage would either die off or be attenuated before reaching the groundwater level.
This paper identifies why sewers have faults that could allow sewage exfiltration where the sewer is above a groundwater resource. Because of a lack of UK data on sewage exfiltration, research work in Germany is discussed and analogies are made between the sewerage networks of the two countries.
Until recently, it has not been possible to positively identify sewage contamination of groundwater because of other pollutants and potential sources within an urban environment. The development of sewage-fingerprinting techniques has overcome these difficulties and provides conclusive evidence of sewage contamination of shallow and deep groundwater resources in researched areas. Studies of groundwater recharge and total solute loadings allow quantification of sewage exfiltration reaching the groundwater within the Midlands conurbation. The paper concludes that urban aquifers are potentially more vulnerable to microbiological contamination from leaking sewers than has previously been assumed.     

Effects of a Permeable Friction Course on Highway Runoff

This project documents the impact of a porous asphalt overlay on the quality and quantity of highway storm-water runoff. A permeable friction course, also known as open graded friction course, is a layer of porous asphalt approximately 50?mm thick, which is often applied on top of conventional asphalt or concrete highways to enhance safety and reduce noise. Storm-water runoff from a four-lane divided highway in the Austin, Texas area was monitored at two sites before and after the installation of a PFC. Observed concentrations of total suspended solids and pollutants associated with particulate material were much lower in the runoff from the PFC than that derived from the conventional asphalt surface. Concentration reductions were observed for total suspended solids, total lead, total copper, and total zinc at both monitoring locations. In addition to the above-mentioned constituents, concentrations of chemical oxygen demand and total Kjeldahl nitrogen were also lower in the runoff from the PFC at a site collecting paired samples from both pavement types. Concentrations of dissolved constituents were not significantly different and concentrations of polycyclic aromatic hydrocarbons were below the detection limit for both pavement types. The runoff coefficient for the PFC appears to be higher than for conventional pavements.     

Peptide-conjugated quantum dots activate neuronal receptors and initiate downstream signaling of neurite growth

Quantum dots (QDs) could serve as fluorescent scaffolds for effecting specific physiological and pharmacological responses in cells. Here, we conjugate the peptide ligand betaNGF to QD surfaces, and confirm surface modification and single QD nanostructure using AFM. We show that betaNGF-QDs retain bioactivity, activate TrkA receptors, and initiate neuronal differentiation in PC12 cells. Receptor-evoked activity of QD-immobilized ligands has wide-ranging implications for the development of molecular tools and therapeutics targeted at understanding and regulating cell function.     

Dielectrophoretic manipulation of particles and cells using insulating ridges in faceted prism microchannels

This paper presents a novel device for the dielectrophoretic manipulation of particles and cells. A two-level isotropic etch of a glass substrate was used to create three-dimensional ridge-like structures in micrometer-sized channels. Due to the insulating properties of glass, locally patterned regions of nonuniform electric field form near the ridges when a dc field is applied along the channel. The ridges are designed using the method of faceted prisms, such that substantially uniform fields are produced on each side of the faceted interfaces that form each ridge. The dielectrophoretic force that results from the electric field gradient near the ridges is used to affect particle motion parallel to the ridges in the absence of a bulk pressure-driven flow. Trapping and deflection of particles and continuous concentration and separation of Bacillus subtilis from a two-component sample mixture are demonstrated. The flow of B. subtilis is restricted to a selected channel of a planar, multichannel device as a result of negative dielectrophoresis arising from the presence of the insulating ridges when the applied electric field exceeds a threshold of 30 V/mm. Dielectrophoresis has a negligible impact on 200-nm-diameter polystyrene particles under the same conditions.