Thermostat for non-equilibrium multiparticle collision dynamics simulations

Multiparticle collision dynamics (MPC), a particle-based mesoscale simulation technique for com- plex fluid, is widely employed in non-equilibrium simulations of soft matter systems. To maintain a defined thermodynamic state, thermalization of the fluid is often required for certain MPC variants. We investigate the influence of three thermostats on the non-equilibrium properties of a MPC fluid under shear or in Poiseuille flow. In all cases, the local velocities are scaled by a factor, which is either determined via a local simple scaling approach (LSS), a Monte Carlo-like procedure (MCS), or by the Maxwell-Boltzmann distribution of kinetic energy (MBS). We find that the various scal- ing schemes leave the flow profile unchanged and maintain the local temperature well. The fluid viscosities extracted from the various simulations are in close agreement. Moreover, the numerically determined viscosities are in remarkably good agreement with the respective theoretically predicted values. At equilibrium, the calculation of the dynamic structure factor reveals that the MBS method closely resembles an isothermal ensemble, whereas the MCS procedure exhibits signatures of an adi- abatic system at larger collision-time steps. Since the velocity distribution of the LSS approach is non-Gaussian, we recommend to apply the MBS thermostat, which has been shown to produce the correct velocity distribution even under non-equilibrium conditions.Comment: 12 pages, 5 figures in Phys. Rev. E, 201

Quantification of spatial intensity correlations and photodetector intensity fluctuations of coherent light reflected from turbid particle suspensions

We present a model for predicting the spatial intensity correlation function of dynamic speckle patterns formed by light backscattered from turbid suspensions, and an experimental validation of these predictions. The spatial correlation varies remarkably with multiple scattering. The provided computational scheme is a step towards correctly interpreting signals obtained from instruments based on the measurement of dynamic speckle patterns in the far field

Hydrodynamic correlations in shear flow: A Multiparticle--Collision--Dynamics simulation study

The nonequilibrium hydrodynamic correlations of a Multiparticle-Collision-Dynamics (MPC) fluid in shear flow are studied by analytical calculations and simulations. The Navier-Stokes equations for a MPC fluid are linearized about the shear flow and the hydrodynamic modes are evaluated as an expansion in the momentum vector. The shear-rate dependence and anisotropy of the transverse and longitudinal velocity correlations are analyzed. We demonstrate that hydrodynamic correlations in shear flow are anisotropic, specifically, the two transverse modes are no longer identical. In addition, our simulations reveal the directional dependence of the frequency and attenuation of the longitudinal velocity correlation function. Furthermore, the velocity autocorrelation functions of a tagged fluid particle in shear flow are determined. The simulations results for various hydrodynamic correlations agree very well with the theoretical predictions.Comment: 8 pages, 5 figure

Measurement of particle flux in a static matrix with suppressed influence of optical properties, using low coherence interferometry

Perfusion measurements using conventional laser Doppler techniques are affected by the variations in tissue optical properties. Differences in absorption and scattering will induce different path lengths and consequently will alter the probability that a Doppler shift will occur. In this study, the fraction of Doppler shifted photons and the Doppler broadening of a dynamic medium, are measured with a phase modulated low coherence Mach-Zehnder interferometer. Path length-resolved dynamic light scattering measurements are performed in various media having a constant concentration of dynamic particles inside a static matrix with different scattering properties and the results are compared with a conventional laser Doppler technique, with a simple model and with Monte Carlo simulations. We demonstrate that, for larger optical path lengths, the scattering coefficient of the static matrix in which the moving particles are embedded have a small to minimal effect on the measured fraction of Doppler shifted photons and on the measured average Doppler frequency of the Doppler shifted light. This approach has potential applications in measuring perfusion independent of the influence of optical properties in the static tissue matrix

Evolution of electromagnetic and Dirac perturbations around a black hole in Horava gravity

The evolution of electromagnetic and Dirac perturbations in the spacetime geometry of Kehagias-Sfetsos(KS) black hole in the deformed Horava-Lifshitz(HL) gravity is investigated and the associated quasinormal modes are evaluated using time domain integration and WKB methods. We find a considerable deviation in the nature of field evolution in HL theory from that in the Schwarzschild spacetime and QNMs region extends over a longer time in HL theory before the power-law tail decay begins. The dependence of the field evolution on the HL parameter $\alpha$ are studied. In the time domain picture we find that the length of QNM region increases with $\alpha$. But the late time decay of field follows the same power-law tail behavior as in the case of Schwarzschild black hole.Comment: The article was fully rewritten, references added, to appear in MPL

Discrete Morse Theory and Extended L2 Homology

AbstractA brief overview of Forman's discrete Morse theory is presented, from which analogues of the main results of classical Morse theory can be derived for discrete Morse functions, these being functions mapping the set of cells of a CW complex to the real numbers satisfying some combinatorial relations. The discrete analogue of the strong Morse inequality was proved by Forman for finite CW complexes using a Witten deformation technique. This deformation argument is adapted to provide strong Morse inequalities for infinite CW complexes which have a finite cellular domain under the free cellular action of a discrete group. The inequalities derived are analogous to the L2 Morse inequalities of Novikov and Shubin and the asymptotic L2 Morse inequalities of an inexact Morse 1-form as derived by Mathai and Shubin. We also obtain quantitative lower bounds for the Morse numbers whenever the spectrum of the Laplacian contains zero, using the extended category of Farber

Evaluation of a multimode fiber optic low coherence interferometer for path length resolved Doppler measurements of diffuse light \ud

The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian and translational motion. The path length resolution of this instrument is compared with a system using single mode fibers for illumination and detection. The optical path lengths are determined from the zero order moment of the phase modulation peak in the power spectrum. The weighted first moment, which is equal to the average Doppler shift, shows a linear response for different mean flow velocities within the physiological rang

Identification of Escherichia coli from potable water sources of Durg-Bhilai, Chhattisgarh (India), using 16S rRNA gene sequence Analysis

Potable water sources mainly municipal water and ground water (from tube wells) were studied for the presence of multidrug resistant pathogenic Escherichia coli. A total of 11 isolates were obtained, eight from municipal water and three from tube well water. Antibiotic resistance analysis (ARA) showed that only two strains named EcPH2 and EcPul2 isolated from municipal tap waters were multidrug resistant (MDR). The strains were characterized using 16S ribosomal RNA gene sequencing. Phylogenetic analysis and similarity search showed isolate EcPH2 had 98% similarity and EcPul2 had 94% similarity to E. coli. The 16S rRNA sequences were submitted to Genbank with accession no. KC254645, KC254646 for isolate EcPH2 and isolate EcPul2 respectively

Studies on antibiotic resistance profiles of thermotolerant Escherichia coli and multiple antibiotic resistance index of different water sources

The rationale behind this study was that no clear data from Durg District is available on the antibiotic resistance profiles of E. coli, the most common pathogen of both humans and animals. Water being one of the most prevalent routes of transmission of E. coli, the present study aimed at isolation and characterization of the same from widely used water sources of Durg-Bhilai region. Thermotolerant E. coli (n=50) were isolated from municipal water, ground water, lake (Talpuri Talab), and river Shivnath. Multiple antibiotic resistance (MAR) indexing was performed using antibiotics viz. amoxicillin, chloramphenicol, co-trimoxazole, ceftriaxone, ciprofloxacin, cephotaxime, nalidixic acid, gentamycin and tetracycline. 85.4% of isolates showed resistance to 2 or more antibiotics. Resistance to three or more antibiotics (multidrug resistance) was shown by 24.4% of isolates. Plasmid bands ranging in size from 0.5 kb – 35 kb were present in 35 out of 50 isolates. Multiple plasmids were shown in 6 isolates. MAR index of isolates ranged from 0.11 to 0.55. 61% of isolates in this study had an index of 0.22, 14.63% had 0.44, 7.23% had 0.33 and 2.44% had 0.55. A high index of 0.79 was shown by River Shivnath followed by 0.2 by Talpuri Talab. The MAR index >0.2 is considered to originate from high risk source of contamination. High MAR indices of individual isolates and sampling sites in Durg-Bhilai region showed that water sources are contaminated with antibiotic resistant E. coli arising from high risk sources of contamination