Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.

The modification of conventional longitudinal recording media by ion-beam irradiation is of both scientific and technological interest. In particular, patterning by irradiation through a stencil mask at the 50 nm length scale may fulfill the promise of a commercially viable patterned media architecture. In this context, the magnetic properties and microstructural evolution of high-coercivity longitudinal thin film media were investigated after ion-beam irradiation. TRIM simulations were used to calculate the depth profiles and damage distributions as a function of energy and dose for carbon, nitrogen, and chromium ions and three different media (C, Cr, no capping layer). Corresponding implantations were carried out and hysteresis curves were measured using a vibrating sample magnetometer (VSM). Using chromium ion implantation at 20 keV, both remanence and coercivity were reduced to zero, i.e., rendering the ferromagnetic thin film paramagnetic, at doses as low as 1×1016 cm−2. For C+ implantation at 20 keV, remanence and coercivity were also reduced to varying extent up to doses of 5×1016 cm−2 after which further irradiation had no effect. Slight decreases in remanence and coercivity were observed for 20 keV N2+ irradiation. XRD measurements indicate that the hexagonal cobalt alloy phase remains intact after irradiation. The physical and magnetic domain structures at the surface were assessed by atomic force and magnetic force microscopy. Combined with the development of a suitable stencil mask, such chromium ion implantation can be used to develop a viable patterned media with nanoscale dimensions, consisting of locally defined ferromagnetic and paramagnetic regions. This work is in progress.

Nasopharyngeal carcinoma (NPC) is one of the most difficult diseases to diagnose at an early stage. The clinical presentation of 122 patients with confirmed NPC is described and the findings analysed. The common modes of presentation and cases where detailed nasopharyngeal examination need to be performed are highlighted. We emphasize the importance of health education and training for primary care physicians for early detection of these cases.

Rapid thermal chemical vapor deposition (RTCVD) is a processing technique that results from the combination of radiant heating lamps and a CVD chamber. It is the ultimate cold-wall CVD reactor and allows one to clean wafers in-situ and immediately thereafter deposit epitaxial layers. Very thin layers (<100 Å) can be deposited by either gas or lamp power switching. We report here the growth of high quality Si and Si-Ge layers, both intrinsic and in-situ doped, and the in-situ growth of a heterojunction bipolar transistor. These HJBT's show gains as high as 350 and are promising as microwave transistors. RTCVD processing is a production-worthy technology that will play an important role in the manufacture of future heterostructural devices.

We study a stochastic differential equation model of prey-predator evolution. To keep in line with a known deterministic model we include the social and interaction terms with the drift in our model, and the randomness arises as fluctuations in the ecosystem. The notion of equilibrium population level and special types of fluctuations force us to work with degenerate elliptic operators. We consider the propagation of the population system in a sufficiently large but bounded domain. This enables us to look at not only the population extinction, but also the explosion beyond a certain level. Both extinction and explosion are possible; and, when they are not, we show that the population asymptotically reaches the equilibrium level. We show that the extinction, explosion and saturation probabilities satisfy, as functions of the initial population size, an integral equation arising out of a Dirichlet problem for a non-degenerate elliptic equation; and these probabilities are also smooth solutions of the Dirichlet problems. They are also used to express the solution of another Dirichlet problem for a degenerate elliptic equation.