Lyophilisation of lentiviral pseudotypes for the development and distribution of virus neutralisation assay kits for rabies, Marburg and influenza viruses

Purpose: Some conventional serological assays can accurately quantify neutralising antibody responses raised against epitopes on virus glycoproteins, enabling mass vaccine evaluation and serosurveillance studies to take place. However, these assays often necessitate the handling of wild-type virus in expensive high biosafety laboratories, which restricts the scope of their application, particularly in resource-deprived areas. A solution to this issue is the use of lentiviral pseudotype viruses (PVs)—chimeric, replication-deficient virions that imitate the binding and entry mechanisms of their wild-type equivalents. Pseudotype virus neutralisation assays (PVNAs) bypass high biosafety requirements and yield comparable results to established assays. This study explores the potential for using lyophilisation of pseudotypes as a cost-effective, alternative means for production, distribution and storage of a PVNAbased diagnostic kit. Methods & Materials: Rabies, Marburg and H5 subtype Influenza virus pseudotypes were each suspended in cryoprotectant solutions of various molarities and subjected to freeze-drying before incubation at a variety of temperatures, humidities and time periods. Samples were then employed in antibody neutralisation assays using specific sera. Results: High levels of PV titre were retained post-lyophilisation, with acceptable levels of virus activity maintained even after medium-term storage in tropical conditions. Also, the performance of PVs in neutralisation assays was not affected by the lyophilisation process. Conclusion: These results confirm the viability of a freeze-dried PVNA-based diagnostic kit, which could considerably facilitate in-field serology for a number of clinically important viruses

On the number of prime order subgroups of finite groups

Let G be a finite group and let ?(G) be the number of prime order subgroups of G. We determine the groups G with the property ?(G)??G?/2?1, extending earlier work of C. T. C. Wall, and we use our classification to obtain new results on the generation of near-rings by units of prime order

Efficient Production of Large 39K Bose-Einstein Condensates

We describe an experimental setup and the cooling procedure for producing 39K Bose-Einstein condensates of over 4x10^5 atoms. Condensation is achieved via a combination of sympathetic cooling with 87Rb in a quadrupole-Ioffe-configuration (QUIC) magnetic trap, and direct evaporation in a large volume crossed optical dipole trap, where we exploit the broad Feshbach resonance at 402 G to tune the 39K interactions from weak and attractive to strong and repulsive. In the same apparatus we create quasi-pure 87Rb condensates of over 8x10^5 atoms.Comment: 7 pages, 5 figures; figure font compatibility improve

Redshifted 21cm Signatures Around the Highest Redshift Quasars

The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm radiation in excess of the Cosmic Microwave Background, and enable future radio telescopes to measure the transverse extent of these HII regions. At early times, the HII regions expand with a relativistic speed. Consequently, their measured sizes along the line-of-sight (via Ly-alpha absorption) and transverse to it (via 21 cm emission) should have different observed values due to relativistic time-delay. We show that the combined measurement of these sizes would directly constrain the neutral fraction of the surrounding intergalactic medium (IGM) as well as the quasar lifetime. Based on current number counts of luminous quasars at z>6, an instrument like LOFAR should detect >2 redshifted 21cm shells per field (with a radius of 11 degrees) around active quasars as bright as those already discovered by SDSS, and >200 relic shells of inactive quasars per field. We show that Ly-alpha photons from the quasar are unable to heat the IGM or to couple the spin and kinetic temperatures of atomic hydrogen beyond the edge of the HII region. The detection of the IGM in 21cm emission around high redshift quasars would therefore gauge the presence of a cosmic Ly-alpha background during the reionization epoch.Comment: 11 pages, 6 figures. Submitted to Ap

Stability of Filters for the Navier-Stokes Equation

Data assimilation methodologies are designed to incorporate noisy observations of a physical system into an underlying model in order to infer the properties of the state of the system. Filters refer to a class of data assimilation algorithms designed to update the estimation of the state in a on-line fashion, as data is acquired sequentially. For linear problems subject to Gaussian noise filtering can be performed exactly using the Kalman filter. For nonlinear systems it can be approximated in a systematic way by particle filters. However in high dimensions these particle filtering methods can break down. Hence, for the large nonlinear systems arising in applications such as weather forecasting, various ad hoc filters are used, mostly based on making Gaussian approximations. The purpose of this work is to study the properties of these ad hoc filters, working in the context of the 2D incompressible Navier-Stokes equation. By working in this infinite dimensional setting we provide an analysis which is useful for understanding high dimensional filtering, and is robust to mesh-refinement. We describe theoretical results showing that, in the small observational noise limit, the filters can be tuned to accurately track the signal itself (filter stability), provided the system is observed in a sufficiently large low dimensional space; roughly speaking this space should be large enough to contain the unstable modes of the linearized dynamics. Numerical results are given which illustrate the theory. In a simplified scenario we also derive, and study numerically, a stochastic PDE which determines filter stability in the limit of frequent observations, subject to large observational noise. The positive results herein concerning filter stability complement recent numerical studies which demonstrate that the ad hoc filters perform poorly in reproducing statistical variation about the true signal

U.S. Agricultural Policy Effectiveness: An Analysis of Income and Capital Gain Returns Impacts

This paper examines the effects of agricultural policy upon the first three moments (mean, variance, and skewness) of aggregate farm income distributions. For the income variables examined, the program period distributions were positively skewed relative to the nonprogram period. However, it appears that the significant impact of the programs on risk reduction encourages the asset and product markets to shift the distribution of total returns toward asset appreciation rather than income enhancement

Can a Bose gas be saturated?

Bose-Einstein condensation is unique among phase transitions between different states of matter in the sense that it occurs even in the absence of interactions between particles. In Einstein's textbook picture of an ideal gas, purely statistical arguments set an upper bound on the number of particles occupying the excited states of the system, and condensation is driven by this saturation of the quantum vapour. Dilute ultracold atomic gases are celebrated as a realisation of Bose-Einstein condensation in close to its purely statistical form. Here we scrutinise this point of view using an ultracold gas of potassium (39K) atoms, in which the strength of interactions can be tuned via a Feshbach scattering resonance. We first show that under typical experi-mental conditions a partially condensed atomic gas strongly deviates from the textbook concept of a saturated vapour. We then use measurements at a range of interaction strengths and temperatures to extrapolate to the non-interacting limit, and prove that in this limit the behaviour of a Bose gas is consistent with the saturation picture. Finally, we provide evidence for the universality of our observations through additional measurements with a different atomic species, 87Rb. Our results suggest a new way of characterising condensation phenomena in different physical systems.Comment: 6 pages, 5 figure