Low-temperature formation of polycyclic aromatic hydrocarbons in Titan’s atmosphere

The detection of benzene in Titan’s atmosphere led to the emergence of polycyclic aromatic hydrocarbons (PAHs) as potential nucleation agents triggering the growth of Titan’s orange-brownish haze layers. However, the fundamental mechanisms leading to the formation of PAHs in Titan’s low-temperature atmosphere have remained elusive. We provide persuasive evidence through laboratory experiments and computations that prototype PAHs like anthracene and phenanthrene (C14H10) are synthesized via barrierless reactions involving naphthyl radicals (C10H7•) with vinylacetylene (CH2=CH–C≡CH) in low-temperature environments. These elementary reactions are rapid, have no entrance barriers, and synthesize anthracene and phenanthrene via van der Waals complexes and submerged barriers. This facile route to anthracene and phenanthrene—potential building blocks to complex PAHs and aerosols in Titan—signifies a critical shift in the perception that PAHs can only be formed under high-temperature conditions, providing a detailed understanding of the chemistry of Titan’s atmosphere by untangling elementary reactions on the most fundamental level

Hemodynamic changes in progressive cerebral infarction: An observational study based on blood pressure monitoring.

Progressive cerebral infarction (PCI) is a common complication in patients with ischemic stroke that leads to poor prognosis. Blood pressure (BP) can indicate post-stroke hemodynamic changes which play a key role in the development of PCI. The authors aim to investigate the association between BP-derived hemodynamic parameters and PCI. Clinical data and BP recordings were collected from 80 patients with cerebral infarction, including 40 patients with PCI and 40 patients with non-progressive cerebral infarction (NPCI). Hemodynamic parameters were calculated from the BP recordings of the first 7 days after admission, including systolic and diastolic BP, mean arterial pressure, and pulse pressure (PP), with the mean values of each group calculated and compared between daytime and nighttime, and between different days. Hemodynamic parameters and circadian BP rhythm patterns were compared between PCI and NPCI groups using t-test or non-parametric equivalent for continuous variables, Chi-squared test or Fisher's exact test for categorical variables, Cox proportional hazards regression analysis and binary logistic regression analysis for potential risk factors. In PCI and NPCI groups, significant decrease of daytime systolic BP appeared on the second and sixth days, respectively. Systolic BP and fibrinogen at admission, daytime systolic BP of the first day, nighttime systolic BP of the third day, PP, and the ratio of abnormal BP circadian rhythms were all higher in the PCI group. PCI and NPCI groups were significantly different in BP circadian rhythm pattern. PCI is associated with higher systolic BP, PP and more abnormal circadian rhythms of BP

Static and Dynamic Properties of Semi-Crystalline Polyethylene.

Properties of extruded polymers are strongly affected by molecular structure. For two different semi-crystalline polymers, low-density polyethylene (LDPE) and ultra-high molecular weight polyethylene (UHMWPE), this investigation measures the elastic modulus, plastic flow stress and strain-rate dependence of yield stress. Also, it examines the effect of molecular structure on post-necking tensile fracture. The static and dynamic material tests reveal that extruded UHMWPE has a somewhat larger yield stress and much larger strain to failure than LDPE. For both types of polyethylene, the strain at tensile failure decreases with increasing strain-rate. For strain-rates 0.001⁻3400 s-1, the yield stress variation is accurately represented by the Cowper⁻Symonds equation. These results indicate that, at high strain rates, UHMWPE is more energy absorbent than LDPE as a result of its long chain molecular structure with few branches.This work was partially sponsored by Foundation of State Key Laboratory of Explosion Science and Technology of China under Grant No.KFJJ13-1Z, No. YBKT15-02 and Natural Science Foundation of China under Grant No.11102023. The authors would like to thank Chunmei Liu of the First Research Institute of the China Ministry of Public Security for assistance with the static tensile tests.This is the final version of the article. It first appeared from the Multidisciplinary Digital Publishing Institute via http://dx.doi.org/10.3390/polym804007

Over-expression of NAD kinase in Corynebacterium crenatum and its Impact on L-Arginine Biosynthesis

Purpose: To improve the biosynthesis of L-arginine by overexpressing homologous NAD kinase (ppnk) in Corynebacterium crenatum SYPA5-5 and to study its impact in presence of high (HOS) and low oxygen supply (LOS).Methods: A recombinant plasmid (pJC1-tac-ppnK) harboring homologous NAD kinase (ppnk) was constructed in a shuttle vector pJC1 and transferred in L-arginine producing strain Corynebacterium crenatum SYPA5-5. Furthermore, fermentation was performed by shake flask method with consecutive determination of cell growth and glucose concentration. NAD+ kinase activity was studied by stop method and NADP(H) concentrations were determined by spectrophotometric enzymatic cycling method. To check the biosynthesis of amino acids, HPLC method was used to determine extracellular amino acid concentrations.Results: In HOS condition, NAD+ kinase activity increased by 116 %, while intracellular concentrations of NADP+ and NADPH increased by 7.3 and 36.8 %, respectively. Whereas, in LOS condition , NAD+ kinase activity increased 49 % , with intracellular 14.67 and 15 % increases in NADP+ and NADPHrespectively. More importantly, recombinant strain could produce 26.47 and 11.36 g/L L-arginine in HOS and LOS respectively, which is higher than control strain value of 24.29 and 7.58 g/L respectively.Conclusion: These results suggest that altering the concentration of co-enzymes by NAD kinase in Corynebacterium crenatum is an effective way to increase NADP+ with concurrent production of NADPH for further enhanced L-arginine biosynthesis in Corynebacterium crenatum in both conditions of high and low oxygen supply.Keywords: NAD kinase, PpnK, L-arginine, Corynebacterium crenatu

Perforation resistance of aluminum/polyethylene sandwich structure

© 2016 Elsevier Ltd. Ballistic tests were performed on two types of polyethylene core sandwich structures (AA6082/LDPE/AA6082 and AA6082/UHMWPE/AA6082) to investigate their perforation resistance. Bulging and dishing deformation of layered plates were compared under low-velocity impact by hemispherical-nosed projectiles. Different impact failure mechanisms leading to perforation were revealed for laminates composed of a pair of aluminum alloy face sheets separated by a polyethylene interlayer. Using the finite element code Abaqus/Explicit, the perforation behavior and distribution of energy dissipation of each layer during penetration were simulated and analysed. The deformation resistance and anti-penetration properties of polyethylene core sandwich structures were compared with those of monolithic AA6082-T6 plates that had the same areal density. Although the polyethylene interlayer enlarged the plastic deformation zone of the back face, the polyethylene core sandwich structure was a little less effective than the monolithic Al alloy target at resisting hemispherical-nosed projectile impact.The authors gratefully acknowledge the Foundation of State Key Laboratory of Explosion Science and Technology of China under Grant No. KFJJ13-1Z, and Natural Science Foundation of China under Grant No. 11102023, 11172071

Thyroid hormone affects both endothelial and vascular smooth muscle cells in rat arteries

Hypothyroidism impairs endothelium-dependent dilatations, while hyperthyroidism augments the production of endothelial nitric oxide. Thus, experiments were designed to determine if thyroid hormone causes endothelium-dependent responses, or alleviates diabetic endothelial dysfunction. Isometric tension was measured in rings with or without endothelium of arteries from normal and diabetic Sprague-Dawley rats. Release of 6-keto prostaglandin F1α and thromboxane B2 were measured by enzyme linked immunosorbent assay and protein levels [endothelial nitric oxide synthase (eNOS), cyclooxygenases (COX)] by immunoblotting. Triiodothyronine (T3) caused concentration-dependent (3×10−6–3×10−5 M) relaxations in mesenteric (pEC50, 4.96±0.19) and femoral (pEC50, 4.57±0.35) arteries without endothelium. In femoral arteries of rats with diabetes, 5-methylamino-2-[[(2S,3R,5R,8S,9S)-3,5,9-trimethyl-2-(1-oxo-(1H-pyrrol-2- -yl)propan-2-yl)-1,7-dioxaspiro-(5,5)undecan-8-yl]methyl]benzooxazole-4-carboxylic acid (A23187, 3×10−7 to 10−6 M) caused partly endothelium-dependent contractions. After chronic T3-treatment with (10 μg/kg/day; four weeks), the contractions to A23187 of preparations with and without endothelium were comparable, the thromboxane B2-release was reduced (by 38.1±9.2%). The pEC50 of 9, 11-dideoxy-11α, 9α-epoxymethanoprostaglandin F2α (U46619, TP-receptor agonist) was increased in T3-treated diabetic rats compared with controls (8.53±0.06 vs 7.94±0.09). The protein expression of eNOS increased (by 228%) but that of COX-1 decreased (by 35%) after chronic T3 treatment. In human umbilical vein endothelial cells incubated for one week with T3 (10−10–10−7 M) in the presence but not in the absence of interleukin-1β (1 ng/ml), the expression of eNOS was increased compared to control. In conclusion, thyroid hormone acutely relaxes mesenteric and femoral vascular smooth muscle, but given chronically reduces the release of endothelium-derived vasoconstrictor prostanoids while enhancing the responsiveness of TP receptors of vascular smooth muscle.postprin

ZNF750 is a lineage-specific tumour suppressor in squamous cell carcinoma.

ZNF750 controls epithelial homeostasis by regulating epidermal-differentiation genes, a role underscored by its pathogenic mutations in esophageal squamous cell cancers (SCCs). However, the precise role of ZNF750 in SCC cell biology remains unclear. In this study, we report that ZNF750 is exclusively deleted, mutated and underexpressed in human SCCs, and low ZNF750 expression is associated with poor survival. Restoration of wildtype, but not mutant ZNF750 protein uniquely inhibited the malignant phenotypes of SCC cells both in vitro and in vivo. Notably, ZNF750 promoted the expression of a long non-coding RNA (TINCR), which mediated both cancer-inhibition and differentiation-induction effects of ZNF750. In addition, ZNF750 potently suppressed cell migration by directly inhibiting the transactivation of LAMC2. Together, our findings characterize ZNF750 as a crucial SCC-specific suppressor and uncover its novel anticancer-associated functions

Linear magnetoresistance in commercial n-type silicon due to inhomogeneous doping

Free electron theory tells us that resistivity is independent of magnetic field. In fact, most observations match the semiclassical prediction of a magnetoresistance that is quadratic at low fields before saturating. However, a non-saturating linear magnetoresistance has been observed in exotic semiconductors such as silver chalcogenides, lightly-doped InSb, N-doped InAs, MnAs-GaAs composites, PrFeAsO, and epitaxial graphene. Here we report the observation of a large linear magnetoresistance in the ohmic regime in commonplace commercial n-type silicon wafer. It is well-described by a classical model of spatially fluctuating donor densities, and may be amplified by altering the aspect ratio of the sample to enhance current-jetting: increasing the width tenfold increased the magnetoresistance at 8 T from 445 % to 4707 % at 35 K. This physical picture may well offer insights into the large magnetoresistances recently observed in n-type and p-type Si in the non-ohmic regime.Comment: submitted to Nature Material

Antioxidative potential of Duranta repens (linn.) fruits against H2O2 induced cell death in vitro

The effects of Duranta repens fruits were investigated on H2O2 induced oxidative cell death to evaluate its antioxidative potential in vitro. HEK293T cells were treated with different concentrations [0-1000 ìg/ ml] of ethanol extract (E-Ex) and methanol extract (M-Ex) of D. repens for 24h, and then treated with 100 ìM H2O2 for 24h. Cell viability, antioxidant parameters of cells, and antioxidant constituents of the extracts were determined. Treatment with limited dose of E-Ex or M-Ex increased the survival rate of H2O2–treated HEK293T cells, however the extra-high dose showed growthinhibitory effect. Treatment with E-Ex or M-Ex protected cellular lipid per-oxidation. In vitro analyses showed the 2,2-diphenyl-1-picrylhydrazyl and H2O2 scavenging activities as well as reducing potential of the extracts. We report here that the limited dose of E-Ex and M-Ex possess antioxidative potential, which can protect H2O2-induced oxidative celldamage.Key words: Duranta repens (Linn.), Oxidative cell death, Lipid per-oxidation, Antioxidant, Phytochemical