Abstract Resonant scattering (RS) of X-ray line emission in supernova remnants (SNRs) may modify the observed line profiles and fluxes and has a potential impact on estimating the physical properties ...of the hot gas and hence on understanding the SNR physics, but has not been theoretically modeled ever. Here we present our Monte Carlo simulation of the RS effect on X-ray resonant-line emission, typified by the O vii He α r line, from SNRs. We employ the physical conditions characterized by the Sedov–Taylor solution and some basic parameters similar to those in Cygnus Loop. We show that the impact of the RS effect is most significant near the edge of the remnant. The line profiles are predicted to be asymmetric because of different temperatures and photon production efficiencies of the expanding gas at different radii. We also predict the surface brightness of the line emission would decrease in the outer projected region but is slightly enhanced in the inner. The G-ratio of the O vii He α triplet can be effectively elevated by RS in the outer region. We show that the RS effect of the O vii He α r line in the southwestern boundary region of Cygnus Loop is nonnegligible. The observed O vii G-ratio of ∼1.8 of the region could be achieved with RS taken into account for properly elevated O abundance from the previous estimates. Additional simulation performed for the SNRs in ejecta-dominated phases like Cas A shows that RS in the shocked ejecta may have some apparent effects on the observational properties of oxygen-resonant lines.
This article analyzes the classification of common embedded databases, including SQLite embedded database, Berkeley embedded database, eXtreme DB embedded database, OpenBASE Lite, etc. By studying ...data replication and backup, embedded database recovery, embedded database backup design, detailed backup design and implementation, the purpose of this article is to improve the security of the database application process and the integrity of the information stored in the database.
The rapid development of big data has brought more problems in network information security and privacy protection. This paper will study the specific network information security and privacy ...protection technologies in this context. The first part of this paper firstly discusses the connotation and characteristics of big data, and then puts forward the information security and privacy protection problems in the era of big data. The last part deeply studies how to solve the solutions corresponding to these problems.
A single-step gold(I)-catalyzed chemoselective protocol to access ortho-substituted diarylsulfones has been established. Acenaphthoimidazolylidene gold complexes are effective catalysts for the ...arylsulfonylation of boronic acids by potassium metabisulfite (K2S2O5) and diaryliodonium salts to access (poly-)ortho-substituted diarylsulfones even in gram scale. Unlike the transition metal-catalyzed two-component coupling systems, the sterically hindered aryl groups in diaryliodonium salts are preferentially transferred over less bulky ones to form synthetically difficult targets, including those of pharmaceutical importance.
An efficient cobalt‐catalyzed redox‐neutral sulfonylative coupling to afford (hetero)aryl alkyl sulfones from boronic acids, ammonium salts and potassium metabisulfite has been realized. Commercially ...available and air‐stable CoCl2, in combination with phenanthroline ligand, is sufficient to achieve rapid and high‐yielding conversion of the reactants into the corresponding sulfones. This practical transformation proceeds smoothly through C−N bond cleavage under redox‐neutral catalytic conditions and shows broad functional‐group tolerance. Other carbon based electrophiles, including diaryliodonium salts, heteroaryl halides, and carbonates were compatible. Further transformation of aryl alkyl sulfones then allows conversion into olefins, alkenyl sulfones and halogenated sulfones, respectively, in a one‐pot process.
Cobalt catalysis: An efficient cobalt‐catalyzed redox‐neutral sulfonylative coupling of boronic acids and ammonium salts to afford (hetero)aryl alkyl sulfones by using potassium metabisulfite has been realized. Various functional sulfones were obtained by using commercially available and air‐stable CoCl2 in combination with phenanthroline ligand. In addition, various carbon based electrophiles, including diaryliodonium salts, heteroaryl halides, and carbonates were compatible. This redox‐neutral catalytic transformation proceeds well without additional base and shows broad functional‐group tolerance.
A large quantity of polysaccharide‐derived conjugate vaccines have been developed to combat various pathogenic infections. Another prominent polysaccharide, heparin, is listed as an essential drug by ...the World Health Organization (WHO) to treat thrombus. One of their common problems is that they all derive from natural polysaccharides. Specifically, capsular polysaccharides are mainly obtained from bacterial fermentation and unfractionated heparin is extracted from animal tissues such as porcine mucosa. The quality of natural polysaccharides is inconsistent and traces of contamination would cause a disaster. By contrast, the use of chemical or chemoenzymatic methods could provide structurally homogeneous and quality‐controlled glycans. To date, large numbers of polysaccharide fragments and their analogues have been synthesized and evaluated. Some of them even showed comparable activities to their corresponding natural polysaccharides. Here, the latest advances in these synthetic glycan analogues ranging from carbohydrate‐based vaccines, heparin‐related therapeutics and glycomimetics of polysaccharides are summarized.
One common problem of polysaccharide conjugate vaccines and heparin is that natural polysaccharides are structurally heterogeneous and not quality controlled. As an alternative, synthetic glycan conjugates and heparin‐related anticoagulants could provide structurally defined and quality‐consistent molecules. In the future, it may be possible to use synthetic glycans and glycomimetics to replace natural polysaccharides.
The Ag2Mo2O7 and Ag6Mo10O33 ceramics for ultra‐low temperature co‐fired ceramic application were prepared by the solid‐state reaction route. The optimized densification temperatures of Ag2Mo2O7 and ...Ag6Mo10O33 are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag2Mo2O7 ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with εr=13.3, Q×f=25 300 GHz and τf=−142 ppm/°C at 9.25 GHz. The Ag6Mo10O33 ceramic sintered at 500°C/4 h shows the microwave dielectric properties with εr=14.0, Q×f=8500 GHz and τf=−50 ppm/°C at 9.00 GHz. Moreover, when Ag2Mo2O7 samples are sintered at ultra‐low sintering temperatures of 420°C‐490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag2Mo2O7 ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag2Mo2O7 ceramic is a good candidate for ultra‐low temperature co‐fired microwave devices.
An photosensitizer‐ and additive‐free, visible‐light‐induced decarboxylative aminoalkylation/C−O coupling cyclization of enaminones with N‐arylglycine for the synthesis of 3‐aminoalkyl chromones has ...been achieved. This synthetic method features good functional‐group tolerance, mild reaction conditions and no request of photocatalyst or additive, thus making this protocol more practical and sustainable.
Henoch-Schönlein purpura (HSP) is an important cause of chronic kidney disease in children. This meta-analysis identified risk factors associated with renal involvement in childhood HSP.
PubMed, ...Embase, and Web of Science were searched. The quality of all eligible studies was assessed using the Newcastle-Ottawa scale criteria. An analysis of possible risk factors was conducted to report the odds ratio (OR) and weighted mean difference (WMD).
Thirteen studies (2398 children) revealed 20 possible and 13 significant risk factors associated with renal involvement in HSP, with the following meta-analysis estimates of OR and WMD, with 95% confidence intervals: older age (0.90, 0.61-1.19); age > 10 y (3.13, 1.39-7.07); male gender (1.36, 1.07-1.74); abdominal pain (1.94,1.24-3.04); gastrointestinal bleeding (1.86, 1.30-2.65); severe bowel angina (3.38, 1.17-9.80); persistent purpura (4.02, 1.22-13.25); relapse (4.70, 2.42-9.14); WBC > 15 × 109/L (2.42, 1.39-4.22); platelets > 500 × 109/L (2.98, 1.22-7.25); elevated antistreptolysin O (ASO) (2.17, 1.29-3.64); and decreased complement component 3 (C3) (3.13, 1.62-6.05). Factors not significantly associated with renal involvement were: blood pressure; orchitis; elevated C-reactive protein; elevated erythrocyte sedimentation rate (ESR); and elevated serum IgA/IgE or IgG. Arthritis/arthralgia may be a risk factor according to the criteria of the American College of Rheumatology (1.41, 1.01-1.96).
The following are associated with renal involvement in pediatric HSP: male gender; > 10 y old; severe gastrointestinal symptoms (abdominal pain, gastrointestinal bleeding, and severe bowel angina); arthritis/arthralgia; persistent purpura or relapse; WBC > 15 × 109/L; platelets > 500 × 109/L; elevated ASO; and low C3. Relevant clinical interventions for these risk factors may exert positive effects on the prevention of kidney disease during the early stages of HSP. However, the results should be interpreted cautiously due to the limitations of the studies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Allyl sulfones are important sulfur-containing compounds that have widespread applications in organic synthesis, medicinal chemistry and materials science. Herein, nickel-catalysed ...dehydrosulfonylation of unactivated allyl alcohols with aryl sulfonyl hydrazides without additional active agents under mild conditions was developed. A variety of functional allyl sulfones could be efficiently synthesized in the presence of air-stable Ni(acac)
2
as the catalyst and 1,1′-bis(diphenylphosphino)ferrocene (DPPF) as the ligand.
An efficient nickel-catalysed dehydrosulfonylation of unactivated allyl alcohols with sulfonyl hydrazides has been successfully developed for the synthesis of various allyl sulfones without additional acidic active agents under mild conditions.
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