Cryopreparation of Tissue for Electron Microscopy

An apparatus able to remove amorphous phase tissue water without recrystallization or rehydration has been produced. Application of this technique to biological samples achieves both the preservation of ultrastructure and the retention of cellular macromolecules and solute without redistribution or modification. Small pieces of fresh tissue were cryofixed by the method of bounce free metal-mirror freezing on polished copper bars at liquid nitrogen temperature. Tissue samples were then placed under liquid nitrogen in a copper sample holder equipped with a thermocouple and feedback controlled heating circuit. Under liquid nitrogen the sample block was placed in a stainless steel sample chamber which was then evacuated to a hydrocarbon-free ultrahigh vacuum (1x10-8mbar). Equilibrium temperature prior to the onset of the drying cycle was -192°C. Tissue was dried by increasing the temperature of the specimen block 1.33°C each hour while monitoring the rate of water removal with a partial pressure analyzer. Results indicate that drying is complete below the devitrification temperature of amorphous phase tissue water. After drying, tissue was fixed with osmium tetroxide vapour, vacuum embedded in low viscosity epoxy resin, sectioned, stained and viewed with the electron microscope. Tissue processed in this manner exhibits excellent morphological preservation with out the need for prefixation or cryoprotective agents. In addition, by avoiding prefixation and solvent contact during resin embedding, this method provides the basis for combining ultrastructural preservation with optimum material for immunocytochemical staining and elecron microprobe analysis

The importance of the aggregation of ticks on small mammal hosts for the establishment and persistence of tick-borne pathogens : an investigation using the R0 model

Aggregation of parasites amongst hosts is important for the epidemiology of vector-borne diseases because hosts that support the majority of the vector population are responsible for the majority of pathogen transmission. Ixodes ricinus ticks transmit numerous pathogens of medical importance including Borrelia burgdorferi s.l. and tick-borne encephalitis virus. One transmission route involved is ‘co-feeding transmission’, where larvae become infected via feeding alongside infected nymphs. The aggregation of ticks on hosts leads to an increase in the number of larvae feeding alongside nymphs, increasing the transmission potential via this route. The basic reproduction number, R0, can be used to identify whether a pathogen will become established if introduced. In the current study we use previously published tick, and pathogen, specific data to parameterize an R0 model to investigate how the degree of aggregation of ticks on hosts affects pathogen persistence. The coincident aggregated distribution permitted the establishment of tick-borne encephalitis virus but did not influence whether B. burgdorferi s.l. became established. The relationship between the k-exponent of the negative binomial distribution and R0 was also defined. Therefore, the degree of aggregation of ticks on small mammal hosts has important implications for the risk to human health in a given area.A University of Pretoria Postdoctoral Fellowship awarded to A. Harrison and the DSTNRF South African Research Chair of Behavioural Ecology and Physiology awarded to N.C. Bennett.http://journals.cambridge.org/action/displayJournal?jid=parab201

Low Cost and Compact Quantum Cryptography

We present the design of a novel free-space quantum cryptography system, complete with purpose-built software, that can operate in daylight conditions. The transmitter and receiver modules are built using inexpensive off-the-shelf components. Both modules are compact allowing the generation of renewed shared secrets on demand over a short range of a few metres. An analysis of the software is shown as well as results of error rates and therefore shared secret yields at varying background light levels. As the system is designed to eventually work in short-range consumer applications, we also present a use scenario where the consumer can regularly 'top up' a store of secrets for use in a variety of one-time-pad and authentication protocols.Comment: 18 pages, 9 figures, to be published in New Journal of Physic

First results of the BATSE/COMPTEL/NMSU rapid burst response campaign

The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gamma‐ray bursts which occur inside the instrument’s ∼1 sr field‐of‐view. COMPTEL images bursts in the 0.75–30 MeV energy range with a typical location accuracy of 1–3 degrees, depending on burst strength, position, duration, and spectrum. COMPTEL’s imaging capability has been exploited in order to search for fading gamma‐ray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near real‐time identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a world‐wide network of observers to search COMPTEL error boxes as quickly as possible. Timely, deep searches for lingering counterpart emission of several bursts per year are the realized goal of this campaign. During its first year of operation, the rapid response program has been successfully applied to two strong bursts: GRB 930131 and GRB 930309. These bursts were imaged in record time only hours after their occurrence. Subsequently, several observations were made at radio and optical observatories world‐wide

Mortality in Levodopa-Treated Parkinson\u27s Disease

Parkinson’s disease (PD) is associated with increased mortality despite many advances in treatment. Following the introduction of levodopa in the late 1960’s, many studies reported improved or normalized mortality rates in PD. Despite the remarkable symptomatic benefits provided by levodopa, multiple recent studies have demonstrated that PD patients continue to die at a rate in excess of their peers. We undertook this retrospective study of 211 deceased PD patients to determine the factors associated with mortality in levodopa-treated PD. Our findings confirm that PD is associated with increased mortality in both men and women. Unlike the majority of other mortality studies, we found that women have a greater reduction in lifespan compared to men. We also found that patients with early onset PD (onset at the age of 50 or before) have reduced survival relative to PD patients with later ages of onset. A final important finding is that survival is equal in PD patients treated with levodopa early (within 2 years or less of PD onset) versus later

Dynamics of monatomic liquids

We present a theory of the dynamics of monatomic liquids built on two basic ideas: (1) The potential surface of the liquid contains three classes of intersecting nearly-harmonic valleys, one of which (the ``random'' class) vastly outnumbers the others and all whose members have the same depth and normal mode spectrum; and (2) the motion of particles in the liquid can be decomposed into oscillations in a single many-body valley, and nearly instantaneous inter-valley transitions called transits. We review the thermodynamic data which led to the theory, and we discuss the results of molecular dynamics (MD) simulations of sodium and Lennard-Jones argon which support the theory in more detail. Then we apply the theory to problems in equilibrium and nonequilibrium statistical mechanics, and we compare the results to experimental data and MD simulations. We also discuss our work in comparison with the QNM and INM research programs and suggest directions for future research.Comment: 53 pages, 16 figures. Differs from published version in using American English spelling and grammar (published version uses British English

Modulation of UK lightning by heliospheric magnetic field polarity

Observational studies have reported solar magnetic modulation of terrestrial lightning on a range of time scales, from days to decades. The proposed mechanism is two-step: lightning rates vary with galactic cosmic ray (GCR) flux incident on Earth, either via changes in atmospheric conductivity and/or direct triggering of lightning. GCR flux is, in turn, primarily controlled by the heliospheric magnetic field (HMF) intensity. Consequently, global changes in lightning rates are expected. This study instead considers HMF polarity, which doesnʼt greatly affect total GCR flux. Opposing HMF polarities are, however, associated with a 40–60% difference in observed UK lightning and thunder rates. As HMF polarity skews the terrestrial magnetosphere from its nominal position, this perturbs local ionospheric potential at high latitudes and local exposure to energetic charged particles from the magnetosphere. We speculate as to the mechanism(s) by which this may, in turn, redistribute the global location and/or intensity of thunderstorm activity