Nonlinear signatures of entangled polymer solutions in active microbead rheology.

We present experimental data and numerical modeling of a nonlinear phenomenon in active magnetic microbead rheology that appears to be common to entangled polymer solutions (EPS). Dynamic experiments in a modest range of magnetic forces show: 1. a short-lived high viscosity plateau, followed by 2. a bead acceleration phase with a sharp drop in apparent viscosity, and 3. a terminal steady state that we show resides on the shear-thinning slope of the steady-state flow curve from cone and plate data. This latter feature implies a new protocol to access the nonlinear steady-state flow curve for many biological EPS only available in microliter-scale volumes. We solve the moment-closure form of the Rolie-Poly kinetic model for EPS hydrodynamics, together with a decoupling approximation that obviates the need for a full 3D flow solver, and show that the model qualitatively reproduces the dynamic experimental sequence above. In this way, we explain the phenomenon in terms of entangled polymer physics, and show how the nonlinear event (acceleration and termination on the shear-thinning response curve) is tunable by the interplay between molecular-scale mechanisms (relaxation via reptation and chain retraction) and magnetic force controls. The experimental conditions mimic movement of cilia tips, bacteria, and sperm in mucus barriers, implying a physiological relevance of the phenomenon, and compelling further development of the fully coupled, 3D flow-microstructure model to achieve quantitative accuracy.

Thin-foil magnetic force system for high-numerical-aperture microscopy.

Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 mum paramagnetic particle and 13 nN on a 4.5 mum paramagnetic particle, forces over the full 4pi sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 mum xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function.

A bacteriological study of the effect on the environment of using a one- or two-trolley system in theatre.

In a survey of 53 hospitals, 62% still had a transfer zone in theatre, involving the use of two trolleys. Reluctance to use one trolley without patient transfer was probably because of concerns about excessive bacterial contamination of the theatre. In an attempt to see if these concerns were justified, air in the operating theatre was sampled for bacterial content, as were the surfaces and wheels of trolleys and the floor in the theatre, anaesthetic room and at the 'red line' in the transfer zone. Samples were taken during the first and second cases on the list of each session in one plenum-ventilated theatre over a four-week period, alternating each week between a one- and two-trolley system. Using one trolley did not significantly influence the bacterial counts in the theatre and anaesthetic room. There were significant differences between counts from the trolley wheels and from the floor of the transfer zone, with counts being higher for one trolley than two. These differences were greatly diminished after the trolleys were washed half way through the study. We conclude that there is no deleterious effect on the environment of the operating theatre, the most sensitive area, if only one trolley is used. If it is considered desirable to decrease the contamination of less important areas when using a one-trolley system, trolleys should be washed regularly, particularly the wheels.

The origin of acquired immune deficiency syndrome: Can science afford to ignore it?

There is a crisis of public faith in science and scientists. Recent research shows concern over scientific ethics, transparency and who benefits from research and development, exemplified in the genetically modified organism debate. Scientific discussion of the polio vaccine hypothesis for the origin of acquired immune deficiency syndrome (AIDS) has been systematically suppressed for more than 12 years. The author calls for an international multidisciplinary inquiry into the origin of AIDS, arguing it is essential to human health, prevention of new pandemics, and to protect the integrity of science in the eyes of the public.

Hand-held computers.

Changes in healthcare delivery, such as patient-focused, point-of-service care, demand that data be entered and accessed at the site where the patient is located (bedside, ER, home, ambulance). But this is not possible without some type of portable information system. The first step to bring information to the patient's side was through the use of bedside computers, but this delivery method has received limited acceptance. At present, some hospitals have begun to use hand-held computers that follow the healthcare clinician, not the patient. Why? Fewer terminals are needed. Handhelds have become easier to use with intuitive graphical user interfaces. As the size of computers has decreased, so has the cost. Personal-sized assistants come in many formats, using proprietary or off the shelf software, or bar code attachments, and with various ports for card or cable access. Most people are becoming computer literate, adapting to downloading, recharging, inserting, and pen/keystroking.

The incidence and epidemiology of beta-lactam resistance in Haemophilus influenzae.

Consecutive isolates of Haemophilus influenzae were collected by the Public Health Laboratory, Bath between 1 June 1992 and 31 May 1993. Of 379 apparently distinct isolates, 216 originated from the respiratory tract, 102 from eyes and 61 from other sites. The minimum inhibitory concentrations of amoxycillin, amoxycillin/clavulanate, cefaclor, cefuroxime, cefotaxime and cefpodoxime were determined for each isolate. Forty strains (10.6%) were beta-lactamase producers. MIC50 and MIC90 values and the range of MICs were determined for all isolates. The overall resistance rates were: amoxycillin (MIC > 1.0 mg/L), 22.7%; amoxycillin/clavulanate (MIC > 1.0 mg/L), 14.8%; cefuroxime (MIC > 1.0 mg/L), 18.5%, (MIC > 4.0 mg/L), 5.5%; cefaclor (MIC > 8 mg/L), 15.6%; cefpodoxime (MIC > 1.0 mg/L), 0.3%; cefotaxime (MIC > 1.0 mg/L), 0%. Twenty non-beta-lactamase producing but beta-lactam resistant strains (cefuroxime MIC > 4.0 mg/L) were matched with 20 susceptible strains on the basis of patient age, sex, and specimen type. The strains were characterised by outer-membrane protein (OMP), random amplified polymorphic DNA (RAPD) and ribotyping patterns. Eleven of the 20 resistant strains were indistinguishable by the methods used, suggesting spread of a single beta-lactam resistant, non-beta-lactamase producing clone. The distribution of resistant strains within the local community was plotted geographically.