Fluoroalkyl aryl ethers are valuable structural motifs in pharmaceuticals because compounds with these motifs are more metabolically stable and more lipophilic than their nonfluorinated analogues. ...However, hexafluoroisopropyl aryl ethers have not been extensively studied, presumably because of the lack of efficient synthetic methods. Herein, we describe a rhodium‐catalyzed nucleophilic aromatic substitution of aryl chlorides or bromides, which act as the limiting reagents, with weakly nucleophilic hexafluoro‐2‐propanol under mild reaction conditions. This method provides diverse hexafluoroisopropyl aryl ethers. We demonstrated the generality of this method by carrying out reactions of a large array of unactivated aryl halides, and we found that the success of the reactions relied on arene activation by means of η6‐coordination.
A rhodium catalyzed SNAr hexafluoroisopropoxylation of unactivated aryl chlorides and bromides was demonstrated. The catalyst activates the aromatic ring via η6‐coordination, dramatically facilitating the attack by weakly nucleophilic hexafluoro‐2‐propanol. Given that fluoroalkyl aryl ethers are valuable structural motifs in bioactive molecules, this method might find utility in medicinal and agricultural chemistry.
The focus of this research is evolutionary low-carbon supply chain enterprise behavior and the strategic issues associated with government low-carbon policies and the emerging low-carbon market. A ...two-level supply chain consisting of a retailer and a manufacturer is established. A Stackelberg game approach employed to solve four retailer and manufacturer low-carbon strategy combinations, after which these strategies are further analyzed using an evolutionary theoretical game approach, from which an evolutionary stability strategy (ESS) is determined. The ESS indicated that: 1) in the low-carbon technology development stage, only one player (the manufacturer or the retailer) should employ low-carbon behavior; and 2) in the advanced low-carbon technology stage, only the retailer should employ low-carbon behavior. These positive results achieved economic, environmental and social Pareto improvements that complied with the government low-carbon requirements, catered to the low-carbon consumer demand, and improved supply chain economic and environmental performances. Finally, the impact of the changes from the government low-carbon policies, consumer sensitivities, and retailer carbon financing interest/subsidy rates on the ESS were analyzed, from which it was found: 1) the government could encourage enterprises to reduce carbon emissions by controlling carbon prices rather than imposing a carbon cap; 2) the enterprises need to focus on consumer sensitivities as the increase of these will reduce the long-term operational carbon emissions; and 3) retailers could stabilize the evolutionary supply chain system by lowering the carbon financing interest rate.
•Low-carbon strategies are analyzed by evolutionary game theory.•Four low-carbon strategy combination models for supply chain enterprises are built.•Low-carbon policy and low-carbon market are considered.•The influence of external and internal factors on evolution is analyzed.•Managerial insights about improving supply chain performance are presented.
Nucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited ...to electron‐deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron‐rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise‐like energy profile. Notably, we isolated a rhodium η5‐cyclohexadienyl complex intermediate with an sp3‐hybridized carbon bearing both a nucleophile and a leaving group.
A rhodium‐catalyzed hydroxylation of aryl fluorides via η6‐coordination was achieved. This method was also applicable in the alkoxylation. A Meisenheimer‐type intermediate was successfully isolated and well characterized. Density functional theory calculations and mechanistic studies suggested a stepwise or stepwise‐like energy profile for the SNAr reaction.
Mimicking the active site and the substrate binding cavity of the enzyme to achieve specificity in catalytic reactions is an essential challenge. Herein, porous coordination cages (PCCs) with ...intrinsic cavities and tunable metal centers have proved the regulation of reactive oxygen species (ROS) generating pathways as evidenced by multiple photo‐induced oxidations. Remarkably, in the presence of the Zn4‐μ4‐O center, PCC converted dioxygen molecules from triplet to singlet excitons, whereas the Ni4‐μ4‐O center promoted the efficient dissociation of electrons and holes to conduct electron transfer towards substrates. Accordingly, the distinct ROS generation behavior of PCC‐6‐Zn and PCC‐6‐Ni enables the conversion of O2 to 1O2 and O2⋅−, respectively. In contrast, the Co4‐μ4‐O center combined the 1O2 and O2⋅− together to generate carbonyl radicals, which in turn reacted with the oxygen molecules. Harnessing the three oxygen activation pathways, PCC‐6‐M (M=Zn/Ni/Co) display specific catalytic activities in thioanisole oxidation (PCC‐6‐Zn), benzylamine coupling (PCC‐6‐Ni), and aldehyde autoxidation (PCC‐6‐Co). This work not only provides fundamental insights into the regulation of ROS generation by a supramolecular catalyst but also demonstrates a rare example of achieving reaction specificity through mimicking natural enzymes by PCCs.
Porous coordination cages with Zn‐, Ni‐ and Co‐metal clusters exhibited different electronic structures which dictated the reactive oxygen species evolution. Three photoreactions were achieved by the three cages, respectively, because of the distinct charge transfer and energy transfer pathways. This work demonstrated a rare case that a supramolecular photocatalyst exhibited reaction specificity.
Deep Convolution Neural Networks (CNNs) have shown impressive performance in various vision tasks such as image classification, object detection and semantic segmentation. For object detection, ...particularly in still images, the performance has been significantly increased last year thanks to powerful deep networks (e.g. GoogleNet) and detection frameworks (e.g. Regions with CNN features (RCNN)). The lately introduced ImageNet 6 task on object detection from video (VID) brings the object detection task into the video domain, in which objects' locations at each frame are required to be annotated with bounding boxes. In this work, we introduce a complete framework for the VID task based on still-image object detection and general object tracking. Their relations and contributions in the VID task are thoroughly studied and evaluated. In addition, a temporal convolution network is proposed to incorporate temporal information to regularize the detection results and shows its effectiveness for the task. Code is available at https://github.com/ myfavouritekk/vdetlib.
A 54.4-90 GHz Low-Noise Amplifier in 65-nm CMOS Yu, Yiming; Liu, Huihua; Wu, Yunqiu ...
IEEE journal of solid-state circuits,
2017-Nov., 2017-11-00, Letnik:
52, Številka:
11
Journal Article
Recenzirano
This paper proposes a transformer-based broadband low-noise amplifier (LNA) for millimeter-wave application. The proposed LNA has four common-source stages. Three transformers are used to connect the ...drains of the former transistors and the sources of the following transistors to boost the transconductances of the following transistors. Thus, the gain of the circuit is effectively increased. In addition, the noise figure (NF) is decreased because the noise contributions of the following stages are further suppressed by the application of the transformers. To enhance the gain bandwidth, the gate inductor in each inter-stage matching network is independently adjusted to separate the main poles of the four stages. The LNA is demonstrated using a commercial 65-nm CMOS process. According to the measurement results, a maximum gain of 17.7 GHz at 67 GHz and a 3-dB gain bandwidth of 35.6 GHz are achieved. The measured NF is 5.4-7.4 dB at 54-67 GHz. The tested input 1-dB gain compression point (IP1dB) ranges from -15.4 to -11.7 dBm in the entire 3-dB gain bandwidth. With 1-V power supply, the LNA consumes 19-mA dc current. The chip size is only 0.37 mm 2 with all pads.
Preparing valuable olefins from cheap and abundant alkane resources has long been a challenging task in organic synthesis, which mainly suffers from harsh reaction conditions and narrow scopes. ...Homogeneous transition metals catalyzed dehydrogenation of alkanes has attracted much attention for its excellent catalytic activities under relatively milder conditions. Among them, base metal catalyzed oxidative alkane dehydrogenation has emerged as a viable strategy for olefin synthesis for its usage of cheap catalysts, compatibility with various functional groups, and low reaction temperature. In this review, we discuss recent development of base metal catalyzed alkane dehydrogenation under oxidative conditions and their application in constructing complex molecules.
Despite improved retention and reduced complication rates paving the way for the current expansion of applications and surge in prevalence for the Boston type I Keratoprosthesis (KPro), the most ...frequent indication for its implantation today remains prior graft failure. The purpose of this study is to evaluate the long-term outcomes of primary KPro and compare to secondary implantation in a matched cohort study. This study included patients who underwent KPro implantation in a single center by two surgeons between July 2008 and October 2014. All eyes with KPro implantation as the primary procedure with a minimum follow up of 12 months were matched with eyes with same preoperative diagnoses that underwent secondary KPro implantation. Main outcomes included visual acuity and device retention. A total of 56 eyes were included with 28 eyes in each group. Mean follow up was 5.0 years for both groups. Twenty-nine percent (8) of the eyes in the primary group had a diagnosis of chemical or thermal injuries, 25% (7) aniridia, 18% (5) autoimmune disease, 4% (1) infectious keratitis/neurotrophic cornea, 7% (2) gelatinous corneal dystrophy, 7% (2) ectrodactyly ectodermal dysplasia/limbal stem cell deficiency, and 11% (3) uveitis/hypotony. Sixty-one percent (17) of the eyes in the primary group and 39% (11) in the secondary group maintained a final best-corrected visual acuity of 20/200 or better at a mean follow up of 5.0 years; the probability of maintaining best-corrected vision is 0.83 and 0.49 for primary and secondary groups at 5.0 years (p = 0.02). There is no statistically significant difference between groups in device retention (p = 0.22) or postoperative complication rates (p >0.05). This study demonstrates that Boston KPro implantation may be successful as a primary procedure in patients at high risk of failure with traditional penetrating keratoplasty. The device has a good long-term retention rate and visual outcomes are promising however a larger study is needed for more definitive results.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper investigates the characteristic length scale in an analytical correlation of critical ventilation velocity. The critical ventilation velocity is defined as the minimum airflow velocity to ...prevent smoke backlayering and is often used for smoke control in tunnels. Using a one-dimensional assumption of uniform mixing, the correlation of critical ventilation velocity was derived from the Froude number, which considered tunnel height as the characteristic length scale. Using numerical modelling, this study examines the effects of enclosure blockage ratio and tunnel width or aspect ratio on critical ventilation velocity. In particular, the results suggest that the correlation with tunnel hydraulic diameter may provide a better characterization of critical ventilation velocity. This is supported from the experimental data reported by others on the effect of tunnel width. The practical implications of using hydraulic diameter in determining critical ventilation velocity are discussed.
Face detection and recognition plays an important role in many occasions. This study explored the application of convolutional neural network in face detection and recognition. Firstly, convolutional ...neural network was briefly analyzed, and then a face detection model including three convolution layers, four pooling layers, introduction layers and three fully connected layers was designed. In face recognition, the self-learning convolutional neural network (CNN) model for global and local extended learning and Spatial Pyramid Pooling (SPP)-NET model were established. LFW data sets were used as model test samples. The results showed that the face detection model had an accuracy rate of 99%. In face recognition, the self-learning CNN model had an accuracy rate of 94.9% accuracy, and the SPP-Net model had an accuracy rate of 92.85%. It suggests that the face detection and recognition model based on convolutional neural network has good accuracy, and the face recognition efficiency of self-learning CNN model was better, which deserves further research and promotion.
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