Thermal Quench at Finite t'Hooft Coupling

Using holography we have studied thermal electric field quench for infinite and finite t'Hooft coupling constant. The set-up we consider here is D7-brane embedded in ($\alpha'$ corrected) AdS-black hole background. It is well-known that due to a time-dependent electric field on the probe brane, a time-dependent current will be produced and it will finally relax to its equilibrium value. We have studied the effect of different parameters of the system on equilibration time. As the most important results, we have observed a universal behaviour in the rescaled equilibration time in the very fast quench regime for different values of the temperature and $\alpha'$ correction parameter. It seems that in the slow quench regime the system behaves adiabatically. We have also observed that the equilibration time decreases in finite t'Hooft coupling limit.Comment: 6 pages, 9 figure

Band-edge Bilayer Plasmonic Nanostructure for Surface Enhanced Raman Spectroscopy

Spectroscopic analysis of large biomolecules is critical in a number of applications, including medical diagnostics and label-free biosensing. Recently, it has been shown that Raman spectroscopy of proteins can be used to diagnose some diseases, including a few types of cancer. These experiments have however been performed using traditional Raman spectroscopy and the development of the Surface enhanced Raman spectroscopy (SERS) assays suitable for large biomolecules could lead to a substantial decrease in the amount of specimen necessary for these experiments. We present a new method to achieve high local field enhancement in surface enhanced Raman spectroscopy through the simultaneous adjustment of the lattice plasmons and localized surface plasmon polaritons, in a periodic bilayer nanoantenna array resulting in a high enhancement factor over the sensing area, with relatively high uniformity. The proposed plasmonic nanostructure is comprised of two interacting nanoantenna layers, providing a sharp band-edge lattice plasmon mode and a wide-band localized surface plasmon for the separate enhancement of the pump and emitted Raman signals. We demonstrate the application of the proposed nanostructure for the spectral analysis of large biomolecules by binding a protein (streptavidin) selectively on the hot-spots between the two stacked layers, using a low concentration solution (100 nM) and we successfully acquire its SERS spectrum

Non-linear biases, stochastically-sampled effective Hamiltonians and spectral functions in quantum Monte Carlo methods

In this article we study examples of systematic biases that can occur in quantum Monte Carlo methods due to the accumulation of non-linear expectation values, and approaches by which these errors can be corrected. We begin with a study of the Krylov-projected FCIQMC (KP-FCIQMC) approach, which was recently introduced to allow efficient, stochastic calculation of dynamical properties. This requires the solution of a sampled effective Hamiltonian, resulting in a non-linear operation on these stochastic variables. We investigate the probability distribution of this eigenvalue problem to study both stochastic errors and systematic biases in the approach, and demonstrate that such errors can be significantly corrected by moving to a more appropriate basis. This is lastly expanded to include consideration of the correlation function QMC approach of Ceperley and Bernu, showing how such an approach can be taken in the FCIQMC framework.Comment: 12 pages, 7 figure

Experimental Study of Two-Phase Air–Water Flow in Large-Diameter Vertical Pipes

Recently, due to an increase in production demand in nuclear and oil and gas industries, the requirement to migrate toward larger pipe sizes for future developments has become essential. However, it is interesting to note that almost all the research on two-phase gas–liquid flow in vertical pipe upflow is based on small-diameter pipes (D_100 mm), and the experimental work on the two-phase gas–liquid flow in large-diameter (D>100 mm) vertical pipes is scarce. Under the above circumstances, the application of modelling tools=correlations based on small-diameter pipes in predicting flow behaviour (flow pattern, void fraction, and pressure gradient) poses severe challenges in terms of accuracy. The results presented in this article are motivated by the need to introduce the research work done to the industries where the data pertaining to large-diameter vertical pipes are scarce and there is a lack of understanding of two-phase gas-liquid flow behaviour in large-diameter (D>100 mm) vertical pipes. The unique aspect of the results presented here is that the experimental data have been generated for a 254-mm inner diameter vertical pipe that forms an excellent basis for the assessment of modelling tools=correlations. This article (i) presents the results of a systematic investigation of the flow patterns in large-diameter vertical pipes and identifies the transition between subsequent flow patterns, (ii) compares it directly with the existing large- (150 mm) and small-diameter data (28mm and 32 mm) in the same air–water superficial velocity range, (iii) exemplifies that the existing available empirical correlations=models=codes are significantly in error when applied to large-diameter vertical pipes for predictions, and last (iv) assesses the predictive capability of a well-known commercial multiphase flow simulator

Hydrodynamic Flow Behaviour in Large Diameter Vertical Riser: Experimental and Simulation Studies

An experimental campaign has been performed to investigate the hydrodynamic behaviour in 12m high and 254mm nominal diameter horizontal flowline-vertical riser setup using air-water as working fluid. The data generated from near riser base and flowline pressure variations were used to characterize the stable and unstable flows encountered during the experiments. A model to study the dynamic behaviour of the large diameter horizontal flowline-vertical riser system is developed using OLGA software (v5.1). Experimental results were compared with simulated model. The major objective of undertaking this work is to investigate the performance of the well-known code for flows encountered in large diameter horizontal flowline-vertical riser. Additionally based on the results, also identify the areas of the improvement in the simulator

Performance Assessment of Void Fraction Correlations in Large Diameter Vertical Pipe Up Flow

Recently, due the to increase in the production demand in many industries such as Nuclear, Oil & Gas and process industries, the requirement to migrate toward larger pipe sizes has become essential. However it is interesting to note that almost all of the earlier two phase flow research is based on small diameter pipes (D≤100mm) and experimental work on predicting the two phase flow behaviour in large diameter (D>100mm) pipes is rare. Thus, the application of methodologies/correlations/equations for predicting flow pattern, void fraction, and pressure gradient based on small diameter poses severe challenges in terms of accuracy. Specifically, the prediction of void fraction in two phase flows, as it plays a fundamental role in characterizing the distribution of the phases within the system. With large number of the void fraction correlations available in the different fields of multiphase flows, the choice for the selection of any void fraction correlation existing in the literature is bewildering. This paper presents an assessment of the predictive capabilities of forty (40) void fraction correlations belonging to different multiphase flow industries. The assessment is performed by comparing the independent experimental data obtained from a 254mm diameter and a 12.2m high vertical pipe upflow loop using air-water as working fluid. The final assessment indicated that most of the void fraction correlations are flow regime dependent as none of the correlations successfully predicted all the four regimes (bubbly, agitated bubbly, unstable slug and churn turbulent) encountered in large diameter vertical upflow experiments