Wall-sheared thermal convection: heat transfer enhancement and turbulence relaminarization

We studied the flow organization and heat transfer properties in two-dimensional and three-dimensional Rayleigh-B\'enard cells that are imposed with different types of wall shear. The external wall shear is added with the motivation of manipulating flow mode to control heat transfer efficiency. We imposed three types of wall shear that may facilitate the single-roll, the horizontally stacked double-roll, and the vertically stacked double-roll flow modes, respectively. Direct numerical simulations are performed for fixed Rayleigh number $Ra = 10^{8}$ and fixed Prandtl number $Pr = 5.3$, while the wall-shear Reynolds number ($Re_{w}$) is in the range $60 \le Re_{w} \le 6000$. Generally, we found enhanced heat transfer efficiency and global flow strength with the increase of $Re_{w}$. However, even with the same magnitude of global flow strength, the heat transfer efficiency varies significantly when the cells are under different types of wall shear. An interesting finding is that by increasing the wall-shear strength, the thermal turbulence is relaminarized, and more surprisingly, the heat transfer efficiency in the laminar state is higher than that in the turbulent state. We found that the enhanced heat transfer efficiency at the laminar regime is due to the formation of more stable and stronger convection channels. We propose that the origin of thermal turbulence laminarization is the reduced amount of thermal plumes. Because plumes are mainly responsible for turbulent kinetic energy production, when the detached plumes are swept away by the wall shear, the reduced number of plumes leads to weaker turbulent kinetic energy production. We also quantify the efficiency of facilitating heat transport via external shearing, and find that for larger $Re_{w}$, the enhanced heat transfer efficiency comes at a price of a larger expenditure of mechanical energy.Comment: 27 pages, 16 figure

Pore-scale statistics of temperature and thermal energy dissipation rate in turbulent porous convection

We report pore-scale statistical properties of temperature and thermal energy dissipation rate in a two-dimensional porous Rayleigh-B\'enard (RB) cell. High-resolution direct numerical simulations were carried out for the fixed Rayleigh number ($Ra$) of $10^{9}$ and the Prandtl numbers ($Pr$) of 5.3 and 0.7. We consider sparse porous media where the solid porous matrix is impermeable to both fluid and heat flux. The porosity ($\phi$) range $0.86 \leq \phi \le 0.98$, the corresponding Darcy number ($Da$) range $10^{-4}<Da<10^{-2}$ and the porous Rayleigh number ($Ra^{*}=Ra\cdot Da$) range $10^{5} < Ra^{*} < 10^{7}$. Our results indicate that the plume dynamics in porous RB convection are less coherent when the solid porous matrix is impermeable to heat flux, as compared to the case where it is permeable. The averaged vertical temperature profiles remain almost a constant value in the bulk, whilst the mean square fluctuations of temperature increases with decreasing porosity. Furthermore, the absolute values of skewness and flatness of the temperature are much smaller in the porous RB cell than in the canonical RB cell. We found that intense thermal energy dissipation occurs near the top and bottom walls, as well as in the bulk region of the porous RB cell. In comparison with the canonical RB cell, the small-scale thermal energy dissipation field is more intermittent in the porous cell, although both cells exhibit a non-log-normal distribution of thermal energy dissipation rate. This work highlights the impact of impermeable solid porous matrices on the statistical properties of temperature and thermal energy dissipation rate, and the findings may have practical applications in geophysics, energy and environmental engineering, as well as other fields that involve the transport of heat through porous media.Comment: 30 pages, 16 figure

A chalcone derivative reactivates latent HIV-1 transcription through activating P-TEFb and promoting Tat-SEC interaction on viral promoter.

The principal barrier to the eradication of HIV/AIDS is the existence of latent viral reservoirs. One strategy to overcome this barrier is to use latency-reversing agents (LRAs) to reactivate the latent proviruses, which can then be eliminated by effective anti-retroviral therapy. Although a number of LRAs have been found to reactivate latent HIV, they have not been used clinically due to high toxicity and poor efficacy. In this study, we report the identification of a chalcone analogue called Amt-87 that can significantly reactivate the transcription of latent HIV provirses and act synergistically with known LRAs such as prostratin and JQ1 to reverse latency. Amt-87 works by activating the human transcriptional elongation factor P-TEFb, a CDK9-cyclin T1 heterodimer that is part of the super elongation complex (SEC) used by the viral encoded Tat protein to activate HIV transcription. Amt-87 does so by promoting the phosphorylation of CDK9 at the T-loop, liberating P-TEFb from the inactive 7SK snRNP, and inducing the formation of the Tat-SEC complex at the viral promoter. Together, our data reveal chalcones as a promising category of compounds that should be further explored to identify effective LRAs for targeted reversal of HIV latency

1-Diphenyl­phosphino-1′-(diphenyl­phosphinoyl)cobaltocenium hexa­fluorido­phosphate

The title compound, [Co(C17H14OP)(C17H14P)]PF6, was obtained unintentionally as the product of an attempted synthesis of [1,1′-bis­(oxodiphenyl­phospho­ranyl)cobaltocenium] hexa­fluorido­phosphate. The O atom of the oxo group is disordered over two positions with site occupancies of 0.65:0.35. The crystal structure contains weak inter­molecular C—H⋯F hydrogen bonds, connecting the components of the structure into chains parallel to [010]

Rapid evolution and copy number variation of primate RHOXF2, an X-linked homeobox gene involved in male reproduction and possibly brain function

<p>Abstract</p> <p>Background</p> <p>Homeobox genes are the key regulators during development, and they are in general highly conserved with only a few reported cases of rapid evolution. <it>RHOXF2 </it>is an X-linked homeobox gene in primates. It is highly expressed in the testicle and may play an important role in spermatogenesis. As male reproductive system is often the target of natural and/or sexual selection during evolution, in this study, we aim to dissect the pattern of molecular evolution of <it>RHOXF2 </it>in primates and its potential functional consequence.</p> <p>Results</p> <p>We studied sequences and copy number variation of <it>RHOXF2 </it>in humans and 16 nonhuman primate species as well as the expression patterns in human, chimpanzee, white-browed gibbon and rhesus macaque. The gene copy number analysis showed that there had been parallel gene duplications/losses in multiple primate lineages. Our evidence suggests that 11 nonhuman primate species have one <it>RHOXF2 </it>copy, and two copies are present in humans and four Old World monkey species, and at least 6 copies in chimpanzees. Further analysis indicated that the gene duplications in primates had likely been mediated by endogenous retrovirus (ERV) sequences flanking the gene regions. In striking contrast to non-human primates, humans appear to have homogenized their two <it>RHOXF2 </it>copies by the ERV-mediated non-allelic recombination mechanism. Coding sequence and phylogenetic analysis suggested multi-lineage strong positive selection on <it>RHOXF2 </it>during primate evolution, especially during the origins of humans and chimpanzees. All the 8 coding region polymorphic sites in human populations are non-synonymous, implying on-going selection. Gene expression analysis demonstrated that besides the preferential expression in the reproductive system, <it>RHOXF2 </it>is also expressed in the brain. The quantitative data suggests expression pattern divergence among primate species.</p> <p>Conclusions</p> <p><it>RHOXF2 </it>is a fast-evolving homeobox gene in primates. The rapid evolution and copy number changes of <it>RHOXF2 </it>had been driven by Darwinian positive selection acting on the male reproductive system and possibly also on the central nervous system, which sheds light on understanding the role of homeobox genes in adaptive evolution.</p

Bovine PrPC directly interacts with αB-crystalline

AbstractWe used a bovine brain cDNA library to perform a yeast two-hybrid assay with bovine mature PrPC as bait. The screening result showed that αB-crystalline interacted with PrPC. The interaction was further evaluated both in vivo and in vitro with different methods, such as immunofluorescent colocalization, native polyacrylamide-gel electrophoresis, and IAsys biosensor assays. The results suggested that αB-crystalline may have the ability to refold denatured prion proteins, and provided first evidence that αB-crystalline is directly associated with prion protein

Diagnostic accuracy of serum human epididymis protein 4 in ovarian cancer patients with different ethnic groups and menopausal status: a meta-analysis and systematic evaluation

Objectives: We aimed to analyze and evaluate the diagnostic value of serum human epididymis protein 4 (HE4) in ovarian cancer (OC) of patients with different menopausal status. Material and methods: A comprehensive electronic and manual search of the relevant literature was performed through several databases such as CNKI, Wanfang database, VIP database, Chinese biomedical database, web of science, PubMed, EMBASE, and Cochrane database. We collected Chinese and English articles to assess the diagnostic value of HE4 for ovarian cancer in female with different menopausal status. The quality of the studies included in the systematic review was assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Results: A total of 14 publications were included in this study and we didn’t find publication bias in them. The sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of HE4 for the diagnosis of ovarian cancer in postmenopausal vs. premenopausal female were 0.71 (95% CI, 0.63–0.78) vs 0.78 (95% CI, 0.74–0.81); 0.91 (95% CI, 0.85–0.95) vs 0.90 (95% CI, 0.86–0.93); 11.90 (95% CI, 6.42–22.07) vs 11.03 (95% CI, 6.44–18.89); and 0.30 (95% CI, 0.22–0.39) vs 0.24 (95% CI, 0.20–0.29), respectively. Conclusions: Serum HE4 has greater diagnostic value in detecting ovarian cancer, especially in Asian postmenopausal female

Stavudine exposure results in developmental abnormalities by causing DNA damage, inhibiting cell proliferation and inducing apoptosis in mouse embryos

Stavudine is an anti-AIDS drug widely used to prevent HIV transmission from pregnant mothers to the fetuses in underdeveloped countries for its low price. However, there is still a controversy on whether stavudine affects embryo development. In the current study, embryotoxicity of stavudine was evaluated using cultured mouse embryos with the concentrations: 5, 10, 15 μM and vehicle control. The data indicated that the effect of stavudine was dose-dependent at early neurogenesis. Stavudine exposure reduced somite numbers, yolk sac diameter, crown-rump length, and increased the rate of embryonic degeneration compared with the control. We chose the lowest but clearly toxic concentration: 5 μM to investigate the molecular mechanisms of the damage. At the molecular level, stavudine produced DNA damage, increased the levels of the phospho-CHK1 and cleaved-caspase-3, and decreased the expression level of proliferating cell nuclear antigen. These changes indicated that stavudine caused a coordinated DNA damage response, inhibited cell proliferation, and induced apoptosis in the embryos. Collectively these results suggest that stavudine exposure disturbs the embryonic development, and its use in pregnant mothers should be re-examined