Impact of hydraulic tortuosity on microporous and nanoporous media flow.

Using two-dimensional porous structures made up of homogeneously arranged solid obstacles, we examine the effects of rarefaction on the hydraulic tortuosity in the slip and early transition flow regimes via extended lattice Boltzmann method. We observed that modification in either the obstacle's arrangement or the porosity led to a power-law relation between the porosity-tortuosity. Along with this, we also found that in the slip-flow regime, the exponent of this relation contains the effect of finite Knudsen number (Kn). In addition, we observed that on properly scaling Kn with porosity and hydraulic tortuosity, a generalized correlation can be obtained for apparent permeability.

Two-fluid kinetic theory for dilute polymer solutions.

We provide a Boltzmann-type kinetic description for dilute polymer solutions based on two-fluid theory. This Boltzmann-type description uses a quasiequilibrium based relaxation mechanism to model collisions between a polymer dumbbell and a solvent molecule. The model reproduces the desired macroscopic equations for the polymer-solvent mixture. The proposed kinetic scheme leads to a numerical algorithm which is along the lines of the lattice Boltzmann method. Finally, the algorithm is applied to describe the evolution of a perturbed Kolmogorov flow profile, whereby we recover the major elastic effect exhibited by a polymer solution, specifically, the suppression of the original inertial instability.

Impact of the kinetic boundary condition on porous media flow in the lattice Boltzmann formulation.

To emphasize the importance of the kinetic boundary condition for micro- to nanoscale flow, we present an ad hoc kinetic boundary condition suitable for torturous geological porous media. We found that the kinetic boundary condition is one of the essential features which should be supplemented to the standard lattice Boltzmann scheme in order to obtain accurate continuum observables. The claim is validated using a channel flow setup by showing the agreement of mass flux with analytical value. Further, using a homogeneous porous structure, the importance of the kinetic boundary condition is shown by comparing the permeability correction factor with the analytical value. Finally, the proposed alternate to the kinetic boundary condition is validated by showing its capability to capture the basic feature of the kinetic boundary condition.

Lattice Fokker Planck for dilute polymer dynamics.

We show that the actual diffusive dynamics, governing the momentum relaxation of a polymer molecule, and described by a Fokker-Planck equation, may be replaced by a BGK-type relaxation dynamics without affecting the slow (Smoluchowski) dynamics in configuration space. Based on the BGK-type description, we present a lattice-Boltzmann (LB) based direct discretization approach for the phase-space description of inertial polymer dynamics. We benchmark this formulation by determining the bulk rheological properties for both steady and time-dependent shear and extensional flows at moderate to large Weissenberg numbers. Finally, we compare the usefulness of the different discrete velocity models, typically used in the LB framework, for solving diffusive dynamics based on the Fokker-Planck equation.

A lattice Boltzmann method for dilute polymer solutions.

We present a lattice Boltzmann approach for the simulation of non-Newtonian fluids. The method is illustrated for the specific case of dilute polymer solutions. With the appropriate local equilibrium distribution, phase-space dynamics on a lattice, driven by a Bhatnagar-Gross-Krook (BGK) relaxation term, leads to a solution of the Fokker-Planck equation governing the probability density of polymer configurations. Results for the bulk rheological characteristics for steady and start-up shear flow are presented, and compare favourably with those obtained using Brownian dynamics simulations. The new method is less expensive than stochastic simulation techniques, particularly in the range of small to moderate Weissenberg numbers (Wi).

HCV-genotypes: a review on their origin, global status, assay system, pathogenecity and response to treatment.

The present report is a review article on various aspects of Hepatitis C virus (HCV) genotypes and their subtypes. HCV has six genotypes and several subtypes showing important epidemiological and clinical implications. The information based on previous studies and presented through this article highlight the origin, classification and causes of genetic diversity, global status, detection assays, pathogenicity and response to treatment of HCV-genotypes. The six genotypes differ in 30-35% of nucleotide sites over the complete genome. The difference in genomic composition of sub-types of genotype is usually found to be 20-25%. The variability remains more frequent in structural genes as compared to non-structural or untranslated genes. Both genotypes and their sub-types show a varied prevalence globally and raise several issues related to their transmission and treatment of HCV-infection. All this information has a great significance while planning future strategies for eradication and therapeutic management of HCV. In addition, these reports produce a further scope for more studies to unravel the mystery behind HCV-genotypes and formulate guidelines to resolve this public health problem noted worldwide.

Torque teno virus infection in hemodialysis patients in North India.

This study describes the prevalence and association of Torque teno virus (TTV) infection with blood-transmitted viral hepatitis including hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in patients with chronic renal failure (CRF) on maintenance hemodialysis (HD). TTV infection was diagnosed by detection of TTV-DNA in serum, using the polymerase chain reaction (PCR) technique. TTV-DNA was estimated in a total number of one hundred patients with CRF and in 100 voluntary blood donors as controls. The markers of HBV and HCV were also tested in sera samples of these patients. TTV-DNA was detected in 39 of 100 patients (39%) with CRF and in 27 of 100 (27%) healthy controls. The analysis of the results demonstrated HBsAg, IgM anti-HBc, anti-HCV, and HCV core antigen in 5.0, 3.0, 6.0, and 4.0% of patients, respectively. This study could not show any association of TTV with HBV and HCV infections for the transmission pattern or any impact on severity of diseases caused by these viruses in CRF patients. TTV also could not show any association with demographic characteristics of patients, duration of dialysis, number of blood transfusions and renal/liver function of the patients. As such, this study concludes that TTV appears as a benign pathogen, showing no sign of renal/liver damage or any change in the severity of diseases caused by blood-borne hepatitis viruses.

Hepatitis C virus (HCV): a review of immunological aspects.

The present manuscript represents an updated review on different aspects of immunology involved during hepatitis C virus infection in human beings. This includes a brief mention of HCV structure, presentation of viral components to host immune system, and ensuing immune response and immunopathogenesis occurring during HCV infection. The present article also highlights immunodiagnosis of HCV infection and the current status of immunotherapy available for HCV eradication. Its envelope protein, E2, is the primary mediator of virus attachment and cell entry. CD81 molecule on cell surface acts as a major receptor for viral entry into the host cells. Mature dendritic cells play an important role in presenting viral antigen, activate T-cells, and initiate anti-viral immune response. Relative T-cell populations and release of different cytokines from activated T-cells ultimately determine the clearance or persistence of HCV viremia through cellular and humoral immune responses. Natural killer (NK) cells constitute the first line of host defense against invading viruses by recruiting virus-specific T-cells and inducing antiviral immunity in liver. Diagnosis of acute or chronic hepatitis C virus (HCV) infection is established by serological assays for presence of antibodies against different sets of viral proteins during varied periods post infection. An effective immunotherapy and vaccine against HCV is still awaited.

Torque teno virus: its prevalence and isotypes in North India.

AIM: To investigate the prevalence and genotype distribution of Torque teno virus (TTV) in patients with different liver diseases and chronic renal failure treated at a referral hospital in North India. METHODS: Whereas prevalence of TTV was based on amplification of conserved region of ORF2 of TTV genome, the genotyping of TTV was carried out using restriction fragment length polymorphism (RFLP) procedure on the N22 region of ORF1. RESULTS: TTV-DNA was detected in 137 of 513 (26.7%) patients with liver diseases and 38 of 65 (58.5%) patients with chronic renal failure. TTV was also detected in 27% of healthy controls. The sequence analysis of the PCR product from 10 randomly selected cases failed to show a significant sequence divergence when compared with that of the TRM1 isolate of TTV genotype 1. The results of genotyping in 55 randomly selected patients showed the presence of genotype 1 (G1) in 53 (96.4%) and genotype 2 (G2) in 2 cases (3.6%), respectively. Other genotypes were not identified in this patient subgroup, suggesting that G1 is predominant in this area. The results of genotyping by RFLP were also supported by phylogenetic tree analysis, where G1 was found to be the major genotype. CONCLUSION: These results indicate that TTV is moderately present in Indian patients, with G1 to be the major genotype in North India. The pathogenicity and etiological role of TTV in different diseases is still a question mark and warrant further studies.

Comparison of serological and nucleic Acid based assays used to diagnose hepatitis C virus (HCV) infection in acute and chronic liver diseases.

BACKGROUND: This study reports a comparative diagnostic potential of three different assay systems used to detect HCV infection in acute and chronic liver diseases. METHODS: A total number of 364 patients with various types of liver diseases were analyzed for hepatitis C virus (HCV) core antigen using Enzyme Immuno Assay (EIA), HCV-RNA by RT-PCR and anti-HCV antibodies by third generation EIA system. Simultaneously these patients were also tested for markers of other hepatitis viruses, notably, hepatitis A, B, C, D and E. In some cases, even transfusion transmitted virus (TTV) was tested using TTV-DNA as the marker of TTV infection. RESULTS: Analysis of results demonstrated the presence of hepatitis B, C and E in different proportions of patients belonging to these liver diseases. Hepatitis A and D infections could not be detected in these cases TTV infection was prevalent in different liver diseases in different proportions. Though none of control sera demonstrated hepatitis A-E infection, however, TTV infection was noted in control group also. When we analysed all the sera for HCV infection using these different assay systems, we found HCV core, HCV-RNA and anti-HCV antibodies in 18.3%, 18.3% and 5.83% cases of acute viral hepatitis (AVH), 13.3 %, 13.3% and 46.6% cases of chronic viral hepatitis (CVH), 23.8%, 23.8% and 23.8% cases with cirrhosis of liver and 20%, 17.5% and 10% cases respectively, of fulminant hepatic failure (FHF) patients. Whereas HCV core and HCV-RNA assays were comparable and predominantly positive in acute cases (AVH and FHF), anti-HCV antibodies were detected in high proportions in chronic liver diseases. Cirrhosis patients showed all the markers in equal proportions. This pattern of HCV markers remains unaffected by co-infection of HCV with other hepatitis viral infections. CONCLUSION: In conclusion, where HCV core and HCV-RNA are best diagnostic markers in acute liver diseases, anti-HCV diagnoses high proportion of HCV cases in chronic liver diseases. This diagnostic pattern is not changed on co-infection of HCV with other viral infections.