13,671 research outputs found
In Silico Generation of Chromium-Based MOFs with Abundant Active Sites for N2/CH4 Separation
No full textSelective nitrogen capture from natural gas using the adsorption properties of porous materials is promising due to its environmental benefits. However, N-2 removal from N-2/CH4 mixtures has been quite challenging because of their similar physical properties. Targeting the Cr-trimer-based cluster with an open metal site, known for selective nitrogen capture through the pi-back-bonding mechanism, we screened nearly one hundred thousand chromium trimer-based metal-organic frameworks (MOFs), both experimentally synthesized and computationally constructed. Using criteria such as Cr-density, polymorphism, resistance to activation, and separation performance, we identified a promising in silico MOF. This hypothetical MOF showed a simulated nitrogen uptake of 2.13 mmol/g and a selectivity of 10.2 at 1 bar, surpassing the performance of the previously known best-performing MOF, Cr-MIL-100.
Pore site partition by Size-Matching Ligand Insertion of Metal-Organic Frameworks for CO2 Capture in the Presence of Water
No full textRing-opening functionalizations of unstrained cyclic amines enabled by difluorocarbene transfer
No full textChemical synthesis based on the skeletal variation has been prolifically utilized as an attractive approach for modification of molecular properties. Given the ubiquity of unstrained cyclic amines, the ability to directly alter such motifs would grant an efficient platform to access unique chemical space. Here, we report a highly efficient and practical strategy that enables the selective ring-opening functionalization of unstrained cyclic amines. The use of difluorocarbene leads to a wide variety of multifaceted acyclic architectures, which can be further diversified to a range of distinctive homologative cyclic scaffolds. The virtue of this deconstructive strategy is demonstrated by successful modification of several natural products and pharmaceutical analogues. Cyclic amines are commonly present in natural products and synthetic compounds, but methods for their skeletal diversification are limited. Here, the authors report a strategy for selective ring-opening functionalization of unstrained cyclic amines to pluripotent products that can be further diversified.11sciescopu
Conflict order-based view refreshment scheme for transaction management in data warehouse environment
No full textOnline analytical processing transactions (OLAP for short) are executed in integrated a data warehouse (DWH for short). DWH should be refreshed by recent value of data in source databases in order to prevent OLAP transactions from reading excessively stale data. This refreshing process is referred to as view maintenance. There have been many researches on ways to guarantee data consistency during the process of view maintenance. The most commonly used approach among them is to execute updated transactions in the nighttime while OLAP transactions are executed only in daytime. It is, however, meaningless to argue about absolute nighttime for a specific corporation. which is globalized. We proposed so called COB algorithm for view maintenance in DWH environment. COB can improve data freshness by supporting concurrent execution of one or more update transactions. COB can, moreover, reduce the cost of space management by maintaining only one additional version during the process of view maintenance
An efficient tree-based group key agreement using bilinear map
No full textSecure and reliable group communication is an increasingly active research area by growing popularity in group-oriented and collaborative application. One of the important challenges is to design secure and efficient group key management. While centralized management is often appropriate for key distribution in large multicast-style groups, many collaborative group settings require distributed key agreement. The communication and computation cost is one of important factors in the group key management for Dynamic Peer Group. In this paper, we extend TGDH (Tree-based Group Diffie-Hellman) protocol to improve the computational efficiency by utilizing pairing-based cryptography. The resulting protocol reduces computational cost of TGDH protocol without degrading the communication complexity
Parametric study on the flight envelope of a radio-frequency ion thruster based atmosphere-breathing electric propulsion system
No full textThe atmosphere-breathing electric propulsion (ABEP) system utilizes atmospheric species as propellants to generate thrust for drag compensation of a satellite in very-low-Earth-orbit (VLEO). A parametric approach is used to assess the impact of different parameters on the flight envelope of a sample VLEO satellite with an ABEP system based on a radio-frequency ion thruster (RIT). The considered parameters include capture efficiency, maximum input power, solar activity, and atomic oxygen recombination factor. The NRLMSIS 2.0 atmosphere model is used to determine the flow conditions at VLEO, at a target altitude of 150–300 km with high, moderate, and low solar activity levels. DSMC method is employed to calculate the drag of the sample satellite with the ABEP system. The 0-D model of the RIT discharge chamber is used to predict the thrust of the RIT-based ABEP system. The flight envelope of a sample RIT-based ABEP system shows that drag can be compensated at altitudes between 196 km and 248 km. Increasing capture efficiency and maximum input power expands the feasible range for drag compensation to higher and lower altitudes, respectively. Also, the flight envelope shifts to higher altitudes with increasing solar activity levels. However, the atomic oxygen recombination factor of the intake device has minimal effects on the flight envelope.
Author Correction: Evaluation of skin cancer resection guide using hyper‑realistic in‑vitro phantom fabricated by 3D printing
No full textThe original version of this Article contained an error in the spelling of the author Taehun Kim which was incorrectly given as Teahun Kim. The original Article has been corrected
Endo-Selective Intramolecular Alkyne Hydroamidation Enabled by NiH Catalysis Incorporating Alkenylnickel Isomerization
No full text© Intramolecular alkyne hydroamidation represents a straightforward approach for the access to synthetically valuable cyclic enamides. Despite some advances made in this realm, the ability to attain a precise regiocontrol still remains challenging, especially for endo cyclization that leads to six-membered and larger azacyclic rings. Herein, we report a NiH-catalyzed intramolecular hydroamidation of alkynyl dioxazolones that allows for an excellent endo selectivity, thus affording a range of six- to eight-membered endocyclic enamides with a broad scope. Mechanistic investigations revealed that Ni(I) catalysis is operative in the current system, proceeding via regioselective syn-hydronickelation, alkenylnickel E/Z isomerization, and Ni-centered inner-sphere nitrenoid transfer. In particular, the key alkenylnickel isomerization step, which previously lacked mechanistic understandings, was found to take place through the η2-vinyl transition state. The synthetic value of this protocol was demonstrated by diastereoselective modifications of the obtained endocyclic enamides to highly functionalized δ-lactam scaffolds.11Nsciescopu
ThickPad
No full textWe explored the use of a hover tracking touchpad in a laptop environment. In order to study the new experience, we implemented a prototype touchpad consisting of infrared LEDs and photo-transistors, which can track fingers as far as 10mm over the surface. We demonstrate here three major interaction techniques that would become possible when a hovertracking touchpad meets a laptop
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