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1.
We investigate the possibility of phantom crossing in the dark energy sector and the solution for the Hubble tension between early and late universe observations. We use robust combinations of different cosmological observations, namely the Cosmic Microwave Background (CMB), local measurement of Hubble constant (), Baryon Acoustic Oscillation (BAO) and SnIa for this purpose. For a combination of CMB+BAO data that is related to early universe physics, phantom crossing in the dark energy sector was confirmed at a 95% confidence level and we obtained the constraint km/s/Mpc at a 68% confidence level, which is in perfect agreement with the local measurement by Riess et al. We show that constraints from different combinations of data are consistent with each other and all of them are consistent with phantom crossing in the dark energy sector. For the combination of all data considered, we obtained the constraint km/s/Mpc at a 68% confidence level and the phantom crossing happening at the scale factor at a 68% confidence level. 相似文献
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Phenol and its derivatives are extremely useful compounds in organic synthesis, medicinal chemistry and material sciences. The synthesis of phenols involving selective construction of the C?O bond at a C?H bond of arenes using transition‐metal catalysis represents the most appealing strategy. Indeed, active research is currently going on for the synthesis of valuable phenolic compounds using a transition‐metal‐catalyzed C?H functionalization strategy. This short review summarizes recent advances on palladium‐catalyzed C?O bond forming reactions that enable direct access to phenolic compounds. These catalytic reactions proceed either via C?H esterification with trifluoroacetic acid/trifluoroacetic anhydride followed by in situ hydrolysis of the ester or via direct C?H hydroxylation. A brief analysis of substrate scope and limitation, reaction mechanism as well as synthetic utility of these reactions has been included. 相似文献
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Siddhartha Biswas 《Waves in Random and Complex Media》2020,30(4):759-775
ABSTRACT The article deals with the study of plane wave propagation in the thermoelastic medium in the presence of voids. The problem is considered in the context of three-phase-lag model of generalized thermoelasticity. There exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode) and volume fraction (V-mode) in addition to transverse waves which get decoupled from the rest of motion and not affected by thermal and volume fraction fields. The fundamental solution of the system of differential equations in case of steady oscillations in terms of the elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically. 相似文献
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A new HfIV‐based metal‐organic framework with UiO‐66 topology was synthesized via a one‐step solvothermal method by using 3‐methyl‐4‐phenylthieno[2,3‐b]thiophene‐2,5‐dicarboxylic acid (H2MPTDC) as a ligand. The MOF material showed a high stability in a broad pH range (from pH 2 to pH 12) in an aqueous medium. The presence of hydrophobic methyl and phenyl substituents in the carboxylic acid ligand and strong Hf?O bond play crucial roles in its stability. The new MOF material was systematically characterized by various techniques such as XRPD, N2 sorption, thermogravimetric analyses and FT‐IR spectroscopy. The photophysical properties of the MOF material were also examined by steady‐state and time‐resolved fluorescence studies. It was observed that the blue fluorescence of the MOF material was selectively quenched in the presence of Fe3+ ion in pure aqueous medium. A mechanistic study disclosed that quenching occurs via a strong inner filter effect (IFE) arising from Fe3+ ion in aqueous medium. Interestingly, the fluorescence of the MOF material can be recovered by elimination of the IFE of Fe3+ ion via reduction of Fe3+ ion by ascorbic acid (AA). Based on the fluorescence recovery by AA, a MOF based on‐off‐on probe was developed for the sensing of Fe3+ ion and AA in aqueous medium. Inspired by this reversible sensing event, we demonstrate basic (NOT, OR, YES, INHIBIT and IMP) and higher integrated logic operations utilizing this fluorescent MOF. This MOF‐based logic systems could be potentially used for next‐generation logic‐gate based analytical applications as well as for the detection and discrimination of targeted molecules in various complex domains. 相似文献
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Raghida Bou Zerdan Zhishuai Geng Benjaporn Narupai Yvonne J. Diaz Morgan W. Bates David S. Laitar Biswas Souvagya Antony K. Van Dyk Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2020,58(14):1989-1997
The utility of pentafluorophenyl esters for the selective introduction of functional units and branch points in well-defined poly(acrylic acid) (PAA) derivatives is demonstrated using a combination of controlled radical polymerization and postpolymerization modification. Reversible addition-fragmentation chain transfer enables the synthesis of well-defined copolymers—poly(pentafluorophenyl acrylate-co-tert-butyl acrylate)—with the active ester repeat units serving as attachment points for reaction with primary amines, specifically tris(2-(t-butoxycarbonyl)ethyl)methyl amine (Behera's amine). Deprotection using trifluoroacetic acid removes both the backbone and side chain t-butyl esters to give a series of branched PAA derivatives containing novel tricarboxylic acid side chains that are well suited to complexation and multidentate interactions. Surprisingly, the active ester homopolymer is shown to have the highest reactivity with Behera's amine when compared to copolymers with lower incorporation of pentafluorophenyl esters, suggesting an intriguing interplay of neighboring group effects and steric interactions. The ability to tune the efficiency of postpolymerization modification gives a library of PAA derivatives. 相似文献
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Nonlinear Dynamics - Phase-shift controlling can attenuate the interactions between solitons and gives practical advantage in optical communication systems. For the variable-coefficient nonlinear... 相似文献
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A new exactly solvable ()-dimensional complex nonlinear wave equation exhibiting rich analytic properties has been introduced. A rogue wave (RW), localized in space–time like Peregrine RW solution, though richer due to the presence of free parameters is discovered. This freedom allows to regulate amplitude and width of the RW as needed. The proposed equation allows also an intriguing topology changing accelerated dark soliton solution in spite of constant coefficients in the equation. 相似文献