Direct Numerical Simulation (DNS) data obtained earlier from two statistically stationary, 1D, planar, weakly turbulent premixed flames are analyzed in order to examine the influence of ...combustion-induced thermal expansion on the flow structure within the mean flame brushes and upstream of them. The two flames are associated with the flamelet combustion regime and are characterized by significantly different density ratios, i.e.
σ
=
7.53
and 2.5. The Helmholtz–Hodge decomposition is applied to the DNS data in order to extract rotational and potential velocity fields. Comparison of the two fields shows that combustion-induced thermal expansion can significantly change the local structure of the incoming constant-density turbulent flow of unburned reactants by significantly increasing the relative magnitude of the potential velocity fluctuations when compared to the rotational velocity fluctuations in the flow. Such effects are documented not only within the mean flame brush, but also well upstream of it. The effect magnitude is increased by the density ratio
σ
, with the effects being well (weakly) pronounced at
σ
=
7.53
(2.5, respectively). Moreover, the potential and rotational velocity fields can cause opposite variations of the local area of an iso-scalar surface
c
x
,
t
=
const
within flamelets by generating the local strain rates of opposite signs.
When a premixed flame propagates in a turbulent flow, not only does turbulence affect the burning rate (e.g., by wrinkling the flame and increasing its surface area), but also the heat release in the ...flame perturbs the pressure field, and these pressure perturbations affect the turbulent flow and scalar transport. For instance, the latter effects manifest themselves in the so-called countergradient turbulent scalar flux, which has been documented in various flames and has challenged the combustion community for approximately 35 years. Over the past decade, substantial progress has been made in investigating (
a
) the influence of thermal expansion in a premixed flame on the turbulent flow and turbulent scalar transport within the flame brush, as well as (
b
) the feedback influence of countergradient scalar transport on the turbulent burning rate. The present article reviews recent developments in this field and outlines issues to be solved in future research.
Liver cirrhosis and hepatocellular carcinoma are the most common outcomes of chronic hepatitis B. Hepatitis B virus (HBV) induces transformation and cell death in chronic hepatitis B (CHB). DNA ...double strand breaks (DSBs) represent the most dangerous type of genome damage. It was shown previously that generation of phosphorylated histone H2AX foci is a reliable marker of DSBs. The aim of this study was to analyse generation of yH2AX foci in HBV and hepatitis D virus (HDV) infection in vitro and in liver biopsies of patients with CHB and CHB with delta-agent (CHD). Human hepatoma cell line HepG2-1.1merHBV with activated HBV life cycle was used to perform real-time PCR for analysis of pregenomic RNA, HBV DNA, HBV cccDNA and for immunocytochemical analysis of yH2AX. Liver biopsies from CHB and CHD patients were analyzed to confirm the results. HBV induces multiple discrete yH2AX foci in HepG2-1.1merHBV cells in vitro and in biopsies of CHB and CHB+D patients. The ratio of hepatocytes w/o yH2AX foci is significantly lower (49,9+/-12,3% vs. 85,5+/-0,9%, p
Introduction.
Glycans play an important role in the pathogenesis of malignant neoplasms, including stomach cancer. In recent years, the attention of many researchers has been drawn to mannose (Man) – ...hexose, which is an indispensable component of all N-chains of glycoproteins involved in both normal physiological and pathological processes.
Aim.
To investigate the role of innate immunity factors and ways to influence them through mannose and mannose-containing glycans in gastric cancer patients.
Materials and methods.
Data on the role of mannose – one of the key monosaccharides in the formation of glycoprotein N-chains – and its binding receptors (mannose receptor, mannose-binding lectin, antibodies) in gastric cancer since 2006 are presented. Levels of anti-glycan antibodies in blood serum samples of 235 gastric cancer patients and 76 healthy donors were evaluated using a glycochip.
Results.
It has been shown that the level of IgM-class antibodies to Manβ – the core part of N-glycans – in gastric cancer patients is significantly lower compared to the donor group, regardless of age (p = 0.0001). To assess the effect of age on the levels of antiglycan antibodies, patients were divided into two subgroups – before and after 45 years. In the group under 45 years of age, significant differences in the levels of antiglycan antibodies to Manβ persisted, while significant differences in the levels of antiglycan antibodies to Manβ1-4GlcNAcβ were not observed. when comparing groups of patients and donors older than 45 years, the levels of antibodies to Manβ and Manβ1-4GlcNAcβ were significantly higher only in donors.
Conclusion.
Deficiency of humoral immunity may be one of the key factors in the initiation and progression of carcinogenesis in humans. In our work, in patients with stomach cancer, we revealed a deficiency of antiglycan antibodies to Manβ and to Manβ1-4GlcNAcβ – core fragments of N-chains of glycoproteins, and the deficiency increased with age. The results of the study are a promising platform for further research aimed not only at studying the role of anti-mannose antibodies, but also at developing approaches to adoptive immunoprophylaxis.
Aim. To define the role of DNA-methyltransferases of type 1 and type 3A in hepatitis B viral cycle. Materials and methods. Human hepatoma cells HepG2 with stable expression of 1.1-mer HBV genome were ...transfected with vectors encoding DNA-methyltransferase 1 (DNMT1), DNA-methyltransferase 3A (DNMT3A) or were co-transfected with these vectors. Total HBV DNA copy number, relative expression of pregenomic RNA (pgRNA), S-protein-encoding RNA (S-RNA) and cccDNA were analyzed by quantitative and semi-quantitative real-time PCR-analysis with TaqMan probes for assessment of DNMTs-mediated effects on HBV. Results. DNMT1 and DNMT3A suppress HBV transcription and replication, though to different magnitude. cccDNA pool is enlarged statistically significantly ≈2-fold (P
A recent analysis (Lipatnikov et al., 2020) of complex-chemistry direct numerical simulation (DNS) data obtained from lean hydrogen-air flames associated with corrugated-flame (case A), ...thin-reaction-zone (case B), and broken-reaction-zone (case C) regimes of turbulent burning has shown that the flamelet concept (i) can predict mean concentrations of various species in those flames if the probability density function (PDF) for the fuel-based combustion progress variable c is extracted from the DNS data, but (ii) poorly performs for the mean rate W¯c of product creation. These results suggest applying the concept to evaluation of mean species concentration (but not the mean rate) in combination with another closure relation for W¯c whose predictive capabilities are better. This proposal is developed in the present paper whose focus is placed on studying a new flamelet-based presumed PDF P(c) for predictions of mean concentration of radicals in engineering computational fluid dynamics (CFD) applications. Analysis of the DNS data shows that (i) the flamelet PDF performs well at intermediate values of c in cases A and B, but should be truncated at small and large c, (ii) modeling P(c) in the radical recombination zone (i.e., at large c) is of importance for predicting mean concentrations of H,O, and OH. Accordingly, the flamelet PDF is truncated and combined with a uniform P(c) at large c. Moreover, the mean rate W¯c extracted from the DNS data is used to calibrate the PDF (the rate is considered to be given by another model). Assessment of the approach against the DNS data shows that it well predicts mean density, temperature, and concentrations of reactants, product, and the aforementioned radicals in cases A and B. In case C, the approach performs worse for OandOH at large c¯ and moderately underestimates the mean concentration of H in the entire flame brush.
Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean, complex-chemistry, hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent ...burning are analyzed (by adapting five alternative definitions of combustion progress variable c) in order to examine three different models that (i) are based on the flamelet paradigm and (ii) aim at evaluating mean concentrations of various species in applied CFD research into turbulent combustion. Mean mole fractions of all considered species and mean density are predicted if the laminar-flame profiles of species mole fractions and density, respectively, are directly averaged using a Probability Density Function (PDF) P(c). The best predictions are obtained by extracting P(c) from the DNS data and defining c based on hydrogen mass fraction. These predictions suggest that mean mole fractions of various species in a premixed turbulent flame can be evaluated at a post-processing stage of a CFD study by adopting P(c), obtained at the major stage of the simulations, to average a flamelet library. When applied in such a way, the flamelet paradigm is useful even for lean hydrogen-air flames and even at Karlovitz number as large as 13. If the same PDF is applied to average reaction rates from the same flamelet library, the mean rates of production/consumption of species n are poorly predicted, e.g. for radicals H, O, OH, HO2, and H2O2 if c is defined using hydrogen mass fraction. A hypothesis that conditioned rates 〈Wn|c〉 can be predicted using conditioned mole fractions 〈Xn|c〉, temperature 〈T|c〉, and density 〈ρ|c〉 is not supported either, e.g. for radicals O and OH. These differences between predictive capabilities of the first approach (directly averaging concentration profiles) and two other approaches (averaging reaction rates) are attributed to weakly (highly) non-linear dependencies of the concentrations (rates, respectively) on c.
•Newly introduced approach to modeling mean heat-release rate in flames is validated.•The approach works in flamelet and thin-reaction-zone regimes of turbulent burning.•The approach predicts ...significant oscillations of burning velocity found in DNS.
Recently, a transport equation for the mean rate of product creation in a premixed turbulent flame was derived and a joint closure relation for dominant terms in that equation was developed and validated against Direct Numerical Simulation (DNS) data obtained from weakly turbulent flames. Present communication reports results of further DNS tests of this newly introduced approach, performed using recent data computed under substantially different turbulent conditions. In particular, the ability of the approach to predict significant oscillations of the turbulent burning velocity with time is shown under conditions associated with not only the flamelet but also the thin-reaction-zone regimes of premixed turbulent burning. While such oscillations are documented in the present and other DNS studies, capabilities of other models of premixed turbulent combustion to reproduce this challenging phenomenon have not yet been demonstrated in the literature.
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