Application of terahertz spectroscopy to the characterization of biological samples using birefringence silicon grating

We present a device and method for performing vector transmission spectroscopy on biological specimens at terahertz (THz) frequencies. The device consists of artificial dielectric birefringence obtained from silicon microfluidic grating structures. The device can measure the complex dielectric function of a liquid, across a wide THz band of 2 to 5.5 THz, using a Fourier transform infrared spectrometer. Measurement data from a range of liquid specimens, including sucrose, salmon deoxyribonucleic acid (DNA), herring DNA, and bovine serum albumin protein solution in water are presented. The specimen handling is simple, using a microfluidic channel. The transmission through the device is improved significantly and thus the measurement accuracy and bandwidth are increase

Analysis of heat transfer and entropy generation of TiO2-water nanofluid flow in a pipe under transition

Single and multi-phase numerical simulations are carried out to investigate the heat transfer and entropy generation behaviour of transitional flow of TiO2H2O nanofluid in a circular pipe. Results reveal that the small diameter of nanoparticles has the highest heat transfer rate for χ = 6% and the TiO2-water nanofluid shows higher heat transfer rate using multi-phase model compared to that of the single phase model. Also no optimal Reynolds has been observed which could minimise the total entropy generation. New correlations are proposed to calculate the average Nusselt number using a nonlinear regression analysis with a standard deviation of error of less than 0.5%

Discrete phase approach for nanofluids flow in pipe

Nanofluid is known as a new generation of fluid and it has been introduced almost several decades ago. But its effectiveness in practical thermal engineering applications has started to diminish with time due to the several factors such as physical instability, complex procedure for production of nanofluids and its cost, instability of suspension of nanoparticles into a base fluid, choice of thermophysical properties and reliability of nanofluids. To overcome these problems, two different phases such as a base fluid (water) and nanoparticles can be considered instead of a typical nanofluid which actually acts like a fluid-solid mixture. However, the interaction between the fluid and particles needs to be investigated to assess its performance. In the present work, Eulerian- Lagrangian discrete phase model has been used with temperature dependent thermophysical properties of the base fluid (water) and nanoparticles to study the thermal performance behaviour of Al2O3 and TiO2 nanoparticles inside a horizontal pipe within the transition to turbulent flow regimes. SST and Realizable models are considered for the modelling of transition and turbulent flow fields respectively with an enhanced near wall treatment. Results reveal that the different phases for water and nanoparticles can be used instead of a nanofluid and no thermophysical properties of nanofluid are needed to explain such behaviour. Also, it is found that the enhancement of heat transfer rate is feasible and such enhancement is fully dependent of the thermal conductivity of nanoparticles as well as nanoparticles size diameters and volume concentrations

Nonlinear Spinor Fields and its role in Cosmology

Different characteristic of matter influencing the evolution of the Universe has been simulated by means of a nonlinear spinor field. Exploiting the spinor description of perfect fluid and dark energy evolution of the Universe given by an anisotropic Bianchi type-VI, VI$_0$, V, III, I or isotropic Friedmann-Robertson-Walker (FRW) one has been studied. It is shown that due to some restrictions on metric functions, initial anisotropy in the models Bianchi type-VI, VI$_0$, V and III does not die away, while the anisotropic Bianchi type-I models evolves into the isotropic one.Comment: 22 pages, 12 Figure

LES modelling of nitric oxide (NO) formation in a propane-air turbulent reacting flame

Large Eddy Simulation (LES) technique is applied to investigate the nitric oxide (NO) formation in the propane-air flame inside a cylindrical combustor. In LES a spatial filtering is applied to the governing equations to separate the flow field into large scale eddies and small scale eddies. The large scale eddies which carry most of the turbulent energy are resolved explicitly while the unresolved small scale eddies are modelled. A Smagorinsky model with model constant Cs = 0.1 as well as a dynamic model has been employed for modelling of the sub-grid scale eddies, while the nonpremixed combustion process is modelled through the conserved scalar approach with laminar flamelet model. In NO formation model, the extended Zeldovich (thermal) reaction mechanism is taken into account through a transport equation for NO mass fraction. The computational results are compared with those of the experimental results investigated by Nishida and Mukohara [1] in co-flowing turbulent flame

Global lopsided instability in a purely stellar galactic disc

It is shown that pure exponential discs in spiral galaxies are capable of supporting slowly varying discrete global lopsided modes, which can explain the observed features of lopsidedness in the stellar discs. Using linearized fluid dynamical equations with the softened self-gravity and pressure of the perturbation as the collective effect, we derive self-consistently a quadratic eigenvalue equation for the lopsided perturbation in the galactic disc. On solving this, we find that the ground-state mode shows the observed characteristics of the lopsidedness in a galactic disc, namely the fractional Fourier amplitude A$_1$ increases smoothly with the radius. These lopsided patterns precess in the disc with a very slow pattern speed with no preferred sense of precession. We show that the lopsided modes in the stellar disc are long-lived because of a substantial reduction ($\sim$ a factor of 10 compared to the local free precession rate) in the differential precession. The numerical solution of the equations shows that the ground-state lopsided modes are either very slowly precessing stationary normal mode oscillations of the disc or growing modes with a slow growth rate depending on the relative importance of the collective effect of the self-gravity. N-body simulations are performed to test the spontaneous growth of lopsidedness in a pure stellar disc. Both approaches are then compared and interpreted in terms of long-lived global $m=1$ instabilities, with almost zero pattern speed.Comment: 15 pages, 23 figures, accepted in MNRA