Natural language processing (NLP) has recently gained much attention for representing and analyzing human language computationally. It has spread its applications in various fields such as machine translation, email spam detection, information extraction, summarization, medical, and question answering etc. In this paper, we first distinguish four phases by discussing different levels of NLP and components of N atural L anguage G eneration followed by presenting the history and evolution of NLP. We then discuss in detail the state of the art presenting the various applications of NLP, current trends, and challenges. Finally, we present a discussion on some available datasets, models, and evaluation metrics in NLP.

Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C–C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.

No abstract

In this paper, we consider the problem of estimating unknown parameters of an inverse Weibull distribution when it is known that samples are progressive type-I interval censored. We propose an EM algorithm to obtain maximum likelihood estimates and mid point estimates. For comparison purpose Bayes estimates are also obtained under the square error loss function. A simulation study is conducted to access the performance of the proposed estimators and recommendations are made on the basis of simulation results. A real data set is also analyzed in detail for an illustration purpose. Finally, by making use of expected Fisher information matrix various inspection times and optimal censoring schemes are obtained.

Structurally simple, ferrocene-pyrene imine dyad 1 has been developed as a 'turn-on' chemodosimeter for Cr(3+). The sensing event is based upon the hydrolysis of the imine functionality. Further, 1, which is also non-cytotoxic (100% cell viability), detects intracellular Cr(3+) in the human breast cancer (MCF-7) cells.

The distant functionalization of ω-ene cyclopropanols is induced by a Pd-catalyzed Heck reaction triggering a "metal-walk" and selective ring-opening of the three-membered ring. This approach provides a new class of acyclic aldehydes possessing concomitantly a stereodefined double bond and a quaternary carbon stereocenter α to the carbonyl group.

Several approaches using organozirconocene species for the remote cleavage of strained three-membered ring carbocycles are described. ω-Ene polysubstituted cyclopropanes, alkylidenecyclopropanes, ω-ene spiro[2.2]pentanes, and ω-ene cyclopropyl methyl ethers were successfully transformed into stereodefined organometallic intermediates, allowing an easy access to highly stereoenriched acyclic scaffolds in good yields and, in most cases, excellent selectivities. DFT calculations and isotopic labeling experiments were performed to delineate the origin of the obtained chemo- and stereoselectivities, demonstrating the importance of microreversibility.

No abstract