We have studied the bulk viscosity of strange quark matter in the density dependent quark mass model (DDQM) and compared results with calculations done earlier in the MIT bag model where Ù, masses were neglected and first order interactions were taken into account. We find that at low temperatures and high relative perturbations, the bulk viscosity is higher by 2 to 3 orders of magnitude while at low perturbations the enhancement is by 1-2 order of magnitude as compared to earlier results. Also the damping time is 2-3 orders of magnitude lower implying that the star reaches stability much earlier than in MIT bag model calculations.

The eigenfrequencies of radial pulsations of quark stars are calculated in a general relativistic formalism given by Chandrasekhar in the density-dependent quark mass model in strong magnetic Ðelds. It is found that the squares of the frequencies are always decreasing functions of the central density of the strange star. The maximum mass, the radius, and gravitational redshift of the star are increasing functions of the magnetic Ðeld.

Human interleukin-7 (hIL-7) is a therapeutically important cytokine involved in lymphocyte development and survival. In previous reports, a uniformly poor expression of hIL-7 has been shown in Escherichia coli host with the problem of inclusion body formation. In this study, the role of codon optimization and N-terminus blocking using various solubility enhancer fusion tags was explored to improve its soluble expression. The use of codon optimization strategy improved its expression to 80 ± 5 mg/L at shake flask level. The utilization of pelB leader sequence resulted in an unprocessed protein in the form of cytoplasmic inclusion bodies with lower expression yields. The N-terminus fusion of small ubiquitin-like modifier (SUMO), thioredoxin (Trx), and NusA tags increased the expression in the range of 90-140 mg/L, where >90 % of the fusion protein was obtained in soluble form. The fed-batch fermentation of SUMO-tagged hIL-7 protein was optimized at bioreactor level, where a high volumetric product concentration of 2.65 g/L was achieved by controlling the plasmid segregation instability using high antibiotic concentration. The specific product yield (Y) and volumetric product concentration were 1.38 and 2.55-fold higher compared to batch results, respectively. A preparative scale affinity chromatography resulted in a high recovery yield of 50.6 mg/L with ∼90 % purity. The conformational property of purified recombinant hIL-7 from CD spectroscopy showed a typical helical structure with 31.5 % α-helix and 26.43 % β-sheet. The biological activity of purified protein was tested using IL-7-dependent murine immature B lymphocyte (2E8) cell line by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide salt (MTT) assay, where it showed a similar biological activity as standard control.

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In this paper we study radial oscillations of the rotating strange stars in strong magnetic fields in the Density Dependent Quark Mass (DDQM) model. We see that increase of frequency i.e. difference in frequency of rotating and non-rotating stars is more for higher magnetic fields. The change is small for low mass stars but it increases with the mass of the star. This change of frequency is significant for maximum mass whereas it is marginal for a 1.4M ⊙ star.