Propagation of hydrodynamic interactions in colloidal suspensions

We describe direct measurements of the dynamics of two colloidal spheres before hydrodynamic interactions have had time to fully develop. We find that the dynamics of the two spheres are coupled at times significantly shorter than tau(nu), the time required for vorticity to diffuse between the two spheres. From the distance dependence of the measured coupling, we infer that hydrodynamic interactions develop in a sonic time scale.

Nurse-led ear care: training needs and the latest techniques

Patients requiring ear care have reported higher levels of satisfaction when this was provided by nurses. The wisdom of ear syringing, the traditional method of cleaning the ear, is now being questioned for many patients, and the aural toilet should be used as an alternative when appropriate. Nurses should remember that good communications skills are vital.

Direct measurements of colloidal friction coefficients

The time-independent hydrodynamic forces operating between two hard spheres were studied as a function of the interparticle separation r. Two colloids were positioned a distance r apart using a dual-beam optical tweezer similar to that described by Meiners and Quake [Phys. Rev. Lett. 82, 2211 (1999)]. Brownian fluctuations in the positions of the two spheres were followed by recording the intensity of forward scattered laser light. The two particles move cooperatively as a result of hydrodynamic forces. The strength of the correlation increased strongly with decreasing separation r. We show that the temporal and spatial correlations in the particle displacements are determined by the distance dependence of the pair friction tensor xi. The distance and geometry dependence of the measured friction tensor is found to be in excellent agreement with the predictions of low-Reynolds number calculations.

Treatment of dentin with polyacrylic acid--a retrospective observational study of the effect upon the durability of glass ionomer restorations

This paper reports on the results of a material specific, retrospective observational study. It sought to determine the consequence of pretreatment of cavity margins with the conventional glass polyalkenoate Chemfil II prior to restoration with Tooth Cleanser on restoration durability. All restorations were placed and varnished by senior dental students under the supervision of a staff member. Manufacturer recommendations were followed. Data on each restoration was collected and entered into a relational computer database. Data included details of cavity morphology and the use or non-use of Tooth Cleanser. Six years following the study start a manual search of all records was carried out to determine, for those patients continuing to attend the Dental Hospital, the number of failed and surviving restorations. This yielded a dataset of 149 restorations, of which 41 had been placed with the aid of Tooth Cleanser and 108 without. The number of failed restorations was 20 and 62, respectively. Survival analysis by the Kaplan-Meier method revealed median survival times of 2,094 days, when Tooth Cleanser was used and 1,748 days when not. Although 80% survival times of 1111.0 (SE = 6.3) (With Tooth Cleanser) and 285.0 (SE = 3.8) (Without Tooth Cleanser) days were observed, together with a Hazard Ratio of 1.49 (95% Confidence Intervals 0.92 & 2.31), a Logrank test revealed no statistically significant difference between the survival curves (p = 0.12). It was concluded that although there was a trend for the application of Tooth Cleanser to improve the chances of obtaining a dependable restoration, this effect was not statistically significant.

Legal madness in the nineteenth century

Legal sources remain under-exploited in the history of madness, and the legal character of some documents is sometimes unrecognized. This article examines the inter-relations between legal and medical histories of madness, and discusses use and availability of nineteenth-century legal source material relating to criminal insanity, mental incapacity, and the confinement of the insane.

Superlattice formation in mixtures of hard-sphere colloids

We report a detailed experimental study of the superlattice structures formed in dense binary mixtures of hard-sphere colloids. The phase diagrams observed depend sensitively on the ratio alpha=R(S)/R(L) of the radii of the small (S) and large (L) components. Mixtures of size ratio alpha=0.72, 0.52, 0.42, and 0.39 are studied. The structures of the colloidal phases formed were identified using a combination of light-scattering techniques and confocal fluorescent microscopy. At alpha=0.39, ordered binary crystals are formed in suspensions containing an equal number of large and small spheres which microscopy shows have a three-dimensional structure similar to either NaCl or NiAs. At the larger size ratio, alpha=0.52, we observe LS2 and LS13 superlattices, isostructural to the molecular compounds AlB2 and NaZn13, while at alpha=0.72 the two components are immiscible in the solid state and no superlattice structures are found. These experimental observations are compared with the predictions of Monte Carlo simulations and cell model theories.

Radiologic versus surgical placement of vena cava filters: a comparative study of cost, time and complications

OBJECTIVE

To compare the cost- and time-effectiveness of 2 methods of placement of vena cava filters for the prevention of pulmonary embolism: the radiologic percutaneous placement of the Vena Tech LGM filter and the surgical cutdown placement of the 24 Fr Greenfield filter.

METHODS

Retrospective review of radiologic and clinical records for 15 consecutive patients who had the Vena Tech LGM filter placed radiologically and 15 consecutive patients who had the Greenfield filter placed surgically. Factors studied were cost, procedure time, waiting time and rates of immediate and delayed complications. The follow-up period ranged from 1 to 26 months (mean 7 months).

RESULTS

The procedure cost for the radiologic method was $702 less than for the surgical method. The procedure time for the radiologic method was 30 minutes shorter, and the waiting time for placement was also shorter. There was no difference in the complication rates following each procedure. The higher cost of the Greenfield filter accounted for 80% of the total cost difference.

CONCLUSION

The radiologic percutaneous method of filter placement is preferred over the surgical cutdown method because of its benefits in terms of cost and time with no increase in risk. However, when the difference in cost between filters is taken into account, there is little difference in overall costs for the 2 methods. Therefore, radiology and surgery departments can place a filter percutaneously at a similar cost. Other factors such as waiting times, complication rates, venography capabilities and physician interest in performing the procedure will dictate which department places the filter.

Cytokines which signal through the LIF receptor and their actions in the nervous system

A number of different cytokines, each initially characterized on the basis of very different biological activities, all have very similar signalling pathways and share a similar tertiary structure. These cytokines include leukaemia inhibitory factor, ciliary neuronotrophic factor, oncostatin M, growth-promoting activity and cardiotrophin 1. They all have been found to regulate a number of properties of cells of the developing and mature nervous system in vitro and thus are neuroregulatory cytokines. The actions of these cytokines include regulation of neurotransmitter phenotype, differentiation of neuronal precursor cells both in the peripheral nervous system and in the spinal cord, survival of differentiated neurons, and regulation of development of both astrocytes and oligodendrocytes. In addition, studies in animal models show that these factors can rescue sensory and motor neurons from axotomy-induced cell death, which suggests that they can act as trauma factors for injured neurons. Analysis of the expression patterns of the different neuroregulatory cytokines and their receptors reveals that the receptors are expressed throughout nervous system development and following trauma, whereas the cytokines show temporal and spatial specific expression patterns. This is consistent with the idea that specific cytokines have specific roles in neural development and repair, but that their signalling pathways are shared. The phenotypes of the receptor knockouts show clear deficits in nervous system development, indicating a crucial role for LIF receptor signalling. Knockouts of individual cytokines are less dramatic, but LIF and CNTF knockouts do reveal deficits in maintenance of motor neurons or following trauma. Thus, whereas LIF and CNTF have clear roles in maintenance and following trauma, it is unclear which of the cytokines is involved in nervous system development. In clinical terms, these findings add further support to the use of these cytokines in nervous system trauma and disease.

Technique for measuring hippocampal T2 relaxation time

PURPOSE

To implement and validate methods for producing calculated coronal T2 maps with complete coverage of the hippocampus and the rest of the brain.

METHODS

T2 relaxation times were estimated on three occasions for 12 quality assessment test objects with the use of fast spin-echo (FSE) and conventional spin-echo (CSE) sequences. Hippocampal T2 relaxation times were measured in 15 healthy subjects with FSE and CSE sequences. Ten of these subjects were scanned twice with CSE imaging. Twenty-two patients with temporal lobe epilepsy, in whom hippocampal T2 relaxation times were previously estimated by means of a multiecho sequence, were studied with CSE.

RESULTS

CSE data were more reliable than FSE data. Reliability of hippocampal T2 measures on repeated acquisitions was superior for the CSE sequence with echo time 30,120 than for the 30,80 sequence (test-retest reliability, 4.0%; interrater reliability, 4.6%). CSE images were suitable for qualitative reporting, so additional T2-weighted sequences were not required. There was good correlation between these hippocampal T2 data and values obtained on a previously validated multiecho technique, with reliable identification of hippocampal sclerosis.

CONCLUSION

T2 mapping with CSE 30/120 sequences may be readily applied, produces reliable T2 values in contiguous 5-mm sections, and may be useful in the assessment of the hippocampus and other cerebral structures.

Leukemia inhibitory factor and ciliary neurotrophic factor in sensory neuron development

Leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), and related proteins are potentially involved in several aspects of sensory neuron development. There is evidence that LIF promotes the differentiation of sensory neurons from progenitor cells of neural crest origin. Later in development, LIF, CNTF, oncostatin M and interleukin-6 promote the survival of cultured neurons. Some neurons, like those of the nodose ganglion, respond early in their development to these factors, whereas other neurons, like those of the trigeminal ganglion, respond much later. In addition to promoting sensory neuron survival, there is some evidence that LIF is able to influence neurotransmitter and neuropeptide expression in these neurons. These observations suggest that several kinds of sensory neurons may be influenced in various ways by LIF and related factors at different stages of their development.

Role of leukaemia inhibitory factor (LIF) in rat peripheral nerve regeneration

The cytokine leukaemia inhibitory factor (LIF) favours the survival and growth of axons in vitro. The efficacy of this factor in the in vivo model has been the aim of this study. Following nerve transection and immediate entubulation repair in the rat sciatic nerve, this study demonstrated that (1) LIF promotes the growth of a population of axons of greater cross-sectional area after 6 and 12 weeks in comparison to either saline (negative control) or basic fibroblast growth factor (bFGF) (positive control), (2) LIF improves the nerve conduction velocity of regenerating axons, (3) LIF has a positive effect on skeletal muscle mass following nerve repair, (4) the benefits of LIF on skeletal muscle appear to be somewhat independent of reinnervation as similar observations are made where there is no growth of a tissue bridge within the tube, and (5) the effects of LIF seem to be potentiated by the addition of fibronectin.