Non-thermal plasma observations using EISCAT: Aspect angle dependence

Recent observations with the EISCAT incoherent scatter radar have shown large rises in dayside, auroral plasma velocities (>2 km s^{−1}) over a wide range of latitudes and lasting about an hour. These are larger than the neutral thermal speed, and allow, for the first time, observations of a non-thermal plasma over a range of observing angles, revealing a clear angular dependence. The observed ion temperature anisotropy, deduced by assuming a Maxwellian line-of-sight ion velocity distribution, is at least 1.75, which exceeds the theoretical value for a bi-Maxwellian based on a realistic ion-neutral collision model. The aspect angle dependence of the signal spectra also indicates non-Maxwellian plasma

Observations of nonthermal plasmas at different aspect angles

Data are presented from the EISCAT (European Incoherent Scatter (Facility)) CP-3-E experiment which show large increases in the auroral zone convection velocities (>2 km s−1) over a wide range of latitudes. These are larger than the estimated neutral thermal speed and allow a study of the plasma in a nonthermal state over a range of observing angles. Spectra are presented which show a well-defined central peak, consistent with an ion velocity distribution function which significantly departs from a Maxwellian form. As the aspect angle decreases, the central peak becomes less obvious. Simulated spectra, derived using theoretical expressions for the O+ ion velocity distribution function based on the generalized relaxation collision model, are compared with the observations and show good first-order, qualitative agreement. It is shown that ion temperatures derived from the observations, with the assumption of a Maxwellian distribution function, are an overestimate of the true ion temperature at large aspect angles and an underestimate at low aspect angles. The theoretical distribution functions have been included in the “standard” incoherent scatter radar analysis procedure, and attempts have been made to derive realistic ionospheric parameters from nonthermal plasma observations. If the expressions for the distribution function are extended to include mixed ion composition, a significant improvement is found in fitting some of the observed spectra, and estimates of the ion composition can be made. The non-Maxwellian analysis of the data revealed that the spectral shape distortion parameter, D*, was significantly higher in this case for molecular ions than for atomic ions in a thin height slab roughly 40 km thick. This would seem unlikely if the main molecular ions present were NO+. We therefore suggest that N2+ formed a significant proportion of the molecular ions present during these observations

Synthesis of Au, Ag, Curcumin Au/Ag, and Au-Ag Nanoparticles and Their Nonlinear Refractive Index Properties

Nanoparticles of gold and silver were prepared by a reduction method and by employing green chemistry principles such as using curcumin as a reducing and a stabilizing agent. The formation of nanoparticles was confirmed by UV-Vis absorption spectra and TEM. Mie theory was used to determine the particle sizes. The nonlinear refraction and absorption properties of the particles were measured using the z-scan technique. A large value of third-order nonlinearities was obtained using the nanoparticles produced

Tai Chi for balance and falls incidence in neurological disorders : a systematic review and meta-analysis

ACRM 94th Annual Conference, 23–28 October 2017, Atlanta202106 bcrcAuthor’s OriginalOthersStart-up fund (1-ZE8G) provided for early-career academics by the Hong Kong Polytechnic UniversityPublishe

Does Tai Chi improve balance and reduce falls incidence in neurological disorders? A systematic review and meta-analysis

2017-2018 > Academic research: refereed > Publication in refereed journal201806 bcrcAccepted ManuscriptOthersP0000477Publishe

Synthesis of Au, Ag, Curcumin Au/Ag, and Au-Ag Nanoparticles and Their Nonlinear Refractive Index Properties

Nanoparticles of gold and silver were prepared by a reduction method and by employing green chemistry principles such as using curcumin as a reducing and a stabilizing agent. The formation of nanoparticles was confirmed by UV-Vis absorption spectra and TEM. Mie theory was used to determine the particle sizes. The nonlinear refraction and absorption properties of the particles were measured using the z-scan technique. A large value of third-order nonlinearities was obtained using the nanoparticles produced

A sociology of caravans

Why do caravans matter? Australians, like others, holiday in them, travel in them, cook, eat, drink, play, sleep and have sex in them. They also live in them, often involuntarily. Caravans have a longer history than this, however caravan life has almost no presence in existing historical or cultural sociology scholarship. Our immediate interest is in caravans in Australia, modernity and mobility. Some broader interest is apparent. Theoretical arguments about mobility on a global scale have been developed by Bauman and Urry. Sociologists like Jasper have connected mobility, masculinity and automobility in Restless Nation. The sociologist and writer Marina Lewycka has used caravans as the locus of everyday life study in her novel Two Caravans. In this paper we background some of these broader issues, and offer a case study of postwar caravan manufacturing. This paper anticipates a larger possible research project in these fields. We anticipate this project raising themes like freedom, mobility, escape, utopia; images of domesticity on wheels, décor and design, materials, technology, DIY production and Fordism; caravan parks as homes and as itinerant and long-term accommodation. These themes and images are also necessarily interwoven with class, gender, sex and age. We are interested in the possibilities of using the caravan as a carrier for making sense of postwar Australia

Incoherent scatter radar observations of non-Maxwellian ion velocity distributions in the auroral F-region

Observations by the EISCAT experiments “POLAR” and Common Programme CP-3 reveal non-Maxwellian ion velocity distributions in the auroral F-region ionosphere. Analysis of data from three periods is presented. During the first period, convection velocities are large (≈2 km s-1) and constant over part of a CP-3 latitude scan; the second period is one of POLAR data containing a short-lived (1.5 km s-1) flow. We concentrate on these two periods as they allow the study of a great many features of the ion-neutral interactions which drive the plasma non-thermal and provide the best available experimental test for models of the 3-dimensional ion velocity distribution function. The third period is included to illustrate the fact that non-thermal plasma frequently exists in the auroral ionosphere: the data, also from the POLAR experiment, cover a three-hour period of typical auroral zone flow and analysis reveals that the ion distribution varies from Maxwellian to the threshold of a toroidal form