The Quest for a Microscopic Nuclear Mass Formula

After stressing how well the purely macroscopic 1935 mass formula of von Weizsäcker works, we discuss the general problem of deriving nuclear masses from basic nucleonic interactions. We then describe the very recent Skyrme-Hartree-Fock-BCS mass formula of Goriely et al., the first and only to be entirely microscopic. We conclude by stressing how much more work has to be done before reliable extrapolations can be made from the mass data out to the highly neutron-rich part of the nuclear chart where the r-process of nucleosynthesis takes place.     

Reynolds Number Dependence of Velocity Structure Functions in a Turbulent Pipe Flow

Low-order moments of the increments δu andδv where u and v are the axial and radial velocity fluctuations respectively, have been obtained using single and X-hot wires mainly on the axis of a fully developed pipe flow for different values of the Taylor microscale Reynolds numberR _λ. The mean energy dissipation rate〉ε〈 was inferred from the uspectrum after the latter was corrected for the spatial resolution of the hot-wire probes. The corrected Kolmogorov-normalized second-order structure functions show a continuous evolution withR _λ. In particular, the scaling exponentζ _v , corresponding to the v structure function, continues to increase with R _λ in contrast to the nearly unchanged value of ζ _u . The Kolmogorov constant for δu shows a smaller rate of increase with R _λ than that forδv. The level of agreement with local isotropy is examined in the context of the competing influences ofR _λ and the mean shear. There is close but not perfect agreement between the present results on the pipe axis and those on the centreline of a fully developed channel flow. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of a method for high LET irradiation of liquid systems

A variety of processes, from material sterilization and cancer treatment to used nuclear fuel recycling, benefit from quantifying the sensitivity of the system to radiation. Determining the effects of alpha irradiation on a system may be of complementary interest to the effects of gamma irradiation, as alpha radiation has higher linear energy transfer (LET) and will likely result in different chemical damage effects. This becomes important in advanced nuclear fuel cycle processes where the radioactive materials to be handled in solutions contain significant amounts of alpha emitters. Here we describe a method for studying high LET radiation in a liquid system using a TRIGA^® reactor and the ¹⁰B(n,α)⁷Li reaction. By fitting a model based on neutron diffusion and absorption to experimentally obtained Fricke dosimetry data, the high LET dose to a sample was predictable over the full range of reactor power available and varying ¹⁰B concentration. This method may be applied to study the effects of high LET radiation on any liquid system as long as a suitable molecule containing boron is used and appropriate neutron diffusion coefficients are known. A wide range of high LET dose rates from <10 Gy/h to >1,000 kGy/h may be obtained with this method.     

Synthesis of platinum complexes of fluorenyl-substituted porphyrins used as phosphorescent dyes for solution-processed organic light-emitting devices

Platinum(II) complexes of symmetrical meso-substituted A₄-porphyrins bearing four fluorene donor moieties 5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin, referred to as TOFP, or eight fluorene arms, 5,10,15,20-octa(3,5-(2 methyloxyfluorenyl)phenyl)porphyrin, OOFP, were synthesised and characterised. The photophysical properties of the new compounds are reported and compared to those of PtTPP and PtTFP {TPP=tetraphenylporphyrin and TFP=tetra(2-fluorenyl)porphyrin}. The luminescence quantum yields of PtTOFP and PtOOFP are 11% and 4.2%, respectively, compared to 4.6% for the reference PtTPP and only 2.0% for the previously studied compound PtTFP. The electronic and optoelectronic behaviour of solution-processed organic light-emitting devices (OLEDs) are reported that incorporate these platinum porphyrins as phosphorescent dyes doped into different layers of a polyvinylcarbazole (PVK) host.     

Drag reduction and thrust generation by tangential surface motion in flow past a cylinder

Sensitivity of drag to tangential surface motion is calculated in flow past a circular cylinder in both two- and three-dimensional conditions at Reynolds number \(\textit{Re} \le 1000\). The magnitude of the sensitivity maximises in the region slightly upstream of the separation points where the contour lines of spanwise vorticity are normal to the cylinder surface. A control to reduce drag can be obtained by (negatively) scaling the sensitivity. The high correlation of sensitivities of controlled and uncontrolled flow indicates that the scaled sensitivity is a good approximation of the nonlinear optimal control. It is validated through direct numerical simulations that the linear range of the steady control is much higher than the unsteady control, which synchronises the vortex shedding and induces lock-in effects. The steady control injects angular momentum into the separating boundary layer, stabilises the flow and increases the base pressure significantly. At \(\textit{Re}=100\), when the maximum tangential motion reaches 50% of the free-stream velocity, the vortex shedding, boundary-layer separation and recirculation bubbles are eliminated and 32% of the drag is reduced. When the maximum tangential motion reaches 2.5 times of the free-stream velocity, thrust is generated and the power savings ratio, defined as the ratio of the reduced drag power to the control input power, reaches 19.6. The mechanism of drag reduction is attributed to the change of the radial gradient of spanwise vorticity (\(\partial _{r} \hat{\zeta }\)) and the subsequent accelerated pressure recovery from the uncontrolled separation points to the rear stagnation point.     

Experimental and Computational Investigation of Low-Impact Velocity and Quasi-Static Failure of PMMA

An investigation of the low velocity impact and quasi-static failure of polymethylmethacrylate (PMMA) based on global and local post-impact strain measurements was conducted. Local strains were obtained from surface mounted Fiber Bragg Grating (FBG) sensors, and they were combined with global measurements from quasi-static indentation and low-velocity impact experiments, and finite-element analyses to obtain detailed maps of how failure spatially initiates and evolves. For both loading regimes, the interactions between the host PMMA specimens and the sensors played a crucial role in the evolution of residual strains. A mapping of the strains clearly shows that strains decrease radially, from high values near the point of impact to far-field values. Sensors located in critical locations, which are near the impact region, had the highest residual strains prior to PMMA fracture. Furthermore, it was determined that strain transfer to the sensor is strongly influenced by the bonding conditions at the specimen’s surface. Due to the debonding of the sensor and the frictional effects associated with the bonding agent, compressive residual strains occurred on the rear-surface. Hence, a detailed understanding of how strain evolves due to sensor-host interactions and catastrophic fracture can be obtained, which can potentially be used to mitigate damage in PMMA for a range of strain-rates.     

Colored Noise Induced Nonequilibrium Transition in a New Chemical Oscillator

The effects of colored noise on a new chemical oscillator in CSTR are studied by computer simulation. Colored noise induced nonequilibrium transitions from one limit-cycle to two and more than two limit-cycles when the correlation time and the intensity of noise are varied. Chemical chaos is also observed.