Micro-buckling of paper during blade metering

Multiphysics models were used to simulate the deformational characteristics experienced by paper under metering blades. Paper is found to slip microscopically at the backing roll interface and subsequently buckle either side of the blade during metering operations. Micro-slippage of the paper at the interface is a linear function of the separation height incurred during buckling. The effects of altering the static coefficient of friction as well as the properties of the backing roll material are studied. Increasing the coefficient of static friction reduces the extent of buckling while a non-linear relationship is found to arise on increasing the elastic modulus of the backing roll material. The mechanisms involved in micro-buckling deformation are explicated herein.     

A pilot-scale fireside deposit study of co-firing Cynara with two coals in a fluidised bed

Costs of biofuel production from energy crops can be reduced by applying the crop residues in heat and power production. Perennial herbaceous crops like Cynara cardunculus L. are challenging fuels because they tend to have high ash and chlorine contents. Coals, however, are often rich in aluminium silicates and sulphur, and co-firing of these biofuels with coal could be expected to reduce operational problems. In addition, CO₂ emissions are lower than during coal firing alone. Blends of Cynara and two coals, South African bituminous and Spanish sub-bituminous coal, were combusted in a 20 kW bubbling bed pilot reactor to ascertain the ability of the coals to reduce operational problems by alkali capture. The Cynara fuel sample contained almost 2 wt% chlorine. The South African coal was rich in kaolinite capable of capturing alkalies from chlorides to produce alkali aluminium silicate and HCl. The Spanish coal was rich in sulphur (mostly present as FeS₂), and produced high concentrations of SO₂ that partially oxidised to SO₃. The SO₃ can capture alkalies from chlorides by sulphation. Up to 30% Cynara, on energy basis, could be co-fired with Spanish coal without operational problems, whereas the same percentage of Cynara with South African coal led to strong Cl deposition. Co-firing of Cynara with both coals resulted in high HCl emissions (up to 1500 mg/Nm³ in 6% O₂). In addition, co-firing of the Spanish coal led to very high SO₂ emissions (up to about 16,000 mg/N m³ in 6% O₂). Thus, a power plant capable of firing such blends must be equipped with flue gas cleaning equipment for effective SO₂ and HCl capture in the flue gas channel after the superheaters, or else the quality of the Cynara must be markedly improved by changing the harvesting technology and fertilisers, which could be major sources of high ash and chlorine content in the fuel.     

Local-field effects in the nonlinear optical response of metamaterials

We investigate optical second-harmonic generation from metamaterials that consist of two-dimensional arrays of lithographically designed T-shaped gold nanodimers, where the horizontal and vertical bars of the T are separated by a nanogap. The response is shown to depend in a nontrivial way on the gap size and to exhibit an unexpected dependence on the polarizations of the fundamental and second-harmonic light. The experimental results are explained by extensive calculations of the polarized local fields at the fundamental and second-harmonic frequencies. Due to the noncentrosymmetry requirement of second-order nonlinear processes, strong local fields in the gap region alone are not sufficient to drive the response efficiently. Instead, polarization properties of the local field and its asymmetric distribution around the dimer perimeters play the key role and enable efficient interaction with the surface nonlinearity of the metal. A small slant in the relative orientations of the vertical and horizontal bars of the dimer gives rise to second-harmonic signals that are forbidden for the ideal dimer with no slant. These signals are also explained by the local-field distributions, now modified by the slant.     

Temperature Dependence of Vortex Nucleation in Gaseous Bose-Einstein Condensates

The formation of quantized vortices in trapped, gaseous Bose-Einstein condensates is considered. The thermodynamic stability of vortex states and the essential role of the surface excitations as a route for vortex penetration into the condensate are discussed. Special focus is on finite-temperature effects of the vortex nucleation process. It is concluded that the critical angular frequencies for exciting surface modes with the relevant multipolarities yield, also at finite temperatures, the appropriate thresholds for the nucleation of vortices in dilute Bose-Einstein condensates, in fair agreement with the recent experiments.     

An open-systems approach to calculating time-dependent spectra

Abstract

A new method to calculate the spectrum using cascaded open systems and a master equation is presented. The method uses two-state analyser atoms which are coupled to the system of interest, whose spectrum of radiation is read from the excitation of these analyser atoms. The ordinary definitions of a spectrum uses two-time averages and Fourier transforms. The present method uses only one-time averages. The method can be used to calculate time-dependent as well as stationary spectra.     

Investigation of air management and energy performance in a data center in Finland: Case study

This is the first research paper on data center from Finland. The objectives of this study are to evaluate air management and energy performance of cooling system and investigate the possibilities of energy saving and reuse in the data center. Field measurements, particularly for long term's IT and facility powers, were conducted. Different performance metrics for the cooling system and power consumption were examined and analysed. Key problem areas and energy saving opportunities were identified. The electrical end use breakdown was estimated. Results show that IT equipment intake conditions were within the recommended or allowable ranges from ASHRAE. The Power Usage Effectiveness (PUE) value for a typical year was about 1.33. Noticeable recirculation of hot air was not observed, but extreme bypass air was found. The air change rate was set much bigger than the recommended ASHRAE's value. There was no heat recovery system. The air management and heat recovery issues therefore need to be addressed. Fan speeds (Computer Room Air-Conditioning Unit) should be reduced and the ventilation rate should be minimized. Further, a simulated heat recovery system was presented demonstrating that the data center could potentially provide yearly space and hot water heating for 30,916 m² non-domestic building.