Within the past few years, there has been a growing interest in the utilisation of airships for a variety of missions. Studies funded by NASA and the US Navy have shown that modern airships not only could perform certain tasks more economically and silently than other aeronautical vehicles (short-haul passenger and freight transport, and long-duration ocean patrol), but that they could perform unique missions, such as the V/STOL transportation of bulky loads an order of magnitude beyond helicopter capability.

The types of modern airships envisioned fall into two categories: modernised blimps and heavy-load carriers. Blimps are receiving reconsideration for their traditional role of patrol and surveillance because of their fuel efficiency and the development of modern sensing devices which require a quiet, stationary vehicle for deployment.

This paper studies the behavior of second grade viscoelastic fluid past a cavity in a horizontal channel. The effects of Reynolds number, fluid elasticity and the aspect ratio of the cavity on the flow field are simulated numerically. The equations are converted into the vorticity and stream function equations. The solution is obtained by the finite difference method.

The behavior of viscoelastic fluids is quite different from the Newtonian fluid, due to the effects of fluid elasticity. Only one flow pattern appears when the Newtonian fluid past the cavity. However, three kinds of flow patterns appear while the viscoelastic fluids past the cavity by increasing Reynolds number from 20 to 300. The flow field is affected by the fluid elasticity as well as the aspect ratio of the cavity. The transitional flow pattern appears at lower Reynolds number as the higher elasticity fluid past the cavity with larger aspect ratio.

The purpose of the present study is to investigate laminar fully developed flow in a horizontal rectangular channel with a cylinder solutal source adjacent to planar boundary. The boundaries in this experiment include four cases:

(A) Cylinder is cathode and top plate is anode;

(B) Cylinder is anode and top plate is cathode;

(C) Cylinder is cathode and bottom plate is anode;

(D) Cylinder is anode and bottom plate is cathode.

The influences of the mass transfer rate and the boundary types between the sources have also been investigated. An experimental investigation of mixed convection mass transfer between a cylinder and a plate mass source with an electrochemical system is carried in a horizontal rectangular channel. The working fluid here is CuSO4 + H2SO4 + H2O. The shadowgraph technique is used to visualize the flow and to determine the nature and effect of solutal driven secondary flows in a horizontal channel. The ranges of the parameters in the work are Pr = 7, Ar = 1, Sc = 1700 ∼ 2400, Re = 50 ∼ 200 (Red= 12.5 ∼50), Grm = 9.45 × 105, d/H = 0.25, h/d=0, 3.

Three-dimensional conformal radiotherapy (3DCRT) has been introduced to treat nasopharyngeal carcinoma (NPC) in Hong Kong. Three more commonly used techniques, which are labelled as 3-field, 4-field and 6-field techniques, are currently employed as a booster treatment and no standard 3DCRT technique has yet been established. This study is aimed to evaluate and compare the dose distributions for the three common 3DCRT techniques so as to provide basis for the development of a routine protocol in future.

For each 3DCRT technique, eight patients with T3 tumours treated between 1997 to 1998 were recruited. Treatment planning was performed with the patients' CT images loaded into the 3-D treatment planning systems. The planning target volume (PTV) and eight organs at risk were delineated for dose assessment. Treatment plans were produced based on the criteria of the corresponding 3DCRT techniques. Dose volume histograms, 2-D and 3-D dose displays were used for dose evaluation.

All three techniques produced reasonable homogenous dose to the PTV. There was no significant difference in the mean doses of the PTV, spinal cord, lens, eyeball, temporal lobe and pituitary. The 3-field technique was superior in sparing the thyroid and optic nerve. The 6-field technique offered lower brain stem dose, and the 4-field technique was in between the two. The use of a vertex field slightly improved dose homogeneity of PTV and reduced the brain stem dose, but the doses to the optic nerve, thyroid, pituitary and temporal lobe were increased.

Nickel-based superalloys have been coated with magnesium oxide (MgO) using ion-beam-assisted deposition (IBAD). This technique produced a well-oriented bi-axially textured MgO template layer with a Ф scan full width half maximum of 6.4°. The layer architecture for these samples was as follows: polished hastelloy C276/amorphous Si3N4/IBAD MgO/ pulsed laser deposited (PLD) Y2O3–ZrO2/PLD CeO2/PLD YBa2Cu3O7?δ. The subsequent heteroepitaxial PLD of 1.5-mm-thick YBCO showed a nominal critical current density of over 1 MA/cm2 (75 K, self-field) along a microbridge and had an in-plane mosaic spread of 4.8° and an out-of-plane spread of 1.3°. These results compare well with our earlier work using IBAD yttria-stabilized zirconia (YSZ) as a template layer and indicate that IBAD MgO is a suitable substitute. Furthermore, these results suggest that IBAD MgO could be adapted to and increase the feasibility of a continuous process to fabricate longer lengths of coated conductors at speeds 100 times faster than that previously realized with IBAD YSZ.