Edge servers, which are small servers located close to mobile users, have the potential to greatly reduce delay and backhaul traffic of mobile Internet applications by moving cloud services to the ...edge of the network. Due to limited capacity of edge servers and dynamic request arrival, proper service caching at the edge is essential to guarantee good performance. This paper proposes a tractable online algorithm called retrospective download with least-requested deletion that caches services dynamically without any assumptions on the arrival patterns of mobile applications. We evaluate the competitive ratio of our policy, which quantifies the worst case performance in comparison to an optimal offline policy. We prove that the competitive ratio of our policy is linear with the capacity of the edge server. We also show that no deterministic online policy can achieve a competitive ratio that is asymptotically better than ours. Moreover, we prove that our policy is scalable, in the sense that it only needs doubled capacity to achieve a constant competitive ratio. The utility of our online policy is further evaluated on real-world traces. These trace-based simulations demonstrate that our policy has better, or similar, performance compared with many intelligent offline policies.
Polarization‐sensitive photodetectors are gaining numerous attention since polarization detection is important in geological remote sensing, atmospheric monitoring, military recon, and medical ...examination. Among various reported photoactive materials for photodetectors, metal halide perovskites have outstanding advantages such as tunable band gaps, excellent optoelectronic properties, and easy fabrication. Moreover, the characteristics of crystal structure anisotropy and controllable growth orientation of perovskite crystals endow the perovskite photodetector with the ability to identify light polarization states. This review outlines the recent research progress of perovskite photodetectors on polarization‐sensitive detection. Firstly, key device parameters of polarization‐sensitive detection are introduced. Then, the recent progress of polarization‐sensitive perovskite detectors in the field of linear and circular polarization is reviewed according to the different principles of polarization response. Finally, the challenges of polarization‐sensitive perovskite photodetector are discussed.
Polarization‐sensitive photodetectors are important in geological remote sensing, atmospheric monitoring, military recon, and medical examination. The review addresses the recent research progress of perovskite photodetectors on polarization‐sensitive detection in terms of key device parameters, linear and circular polarization via different principles of polarization response.
1,4‐Dicarbonyl compounds are intriguing motifs and versatile precursors in numerous pharmaceutical molecules and bioactive natural compounds. Direct incorporation of two carbonyl groups into a double ...bond at both ends is straightforward, but also challenging. Represented herein is the first example of 1,2‐dicarbonylation of alkenes by photocatalysis. Key to success is that N(n‐Bu)4+ not only associates with the alkyl anion to avoid protonation, but also activates the α‐keto acid to undergo electrophilic addition. The α‐keto acid is employed both for acyl generation and electrophilic addition. By tuning the reductive and electrophilic ability of the acyl precursor, unsymmetric 1,4‐dicarbonylation is achieved for the first time. This metal‐free, redox‐neutral and regioselective 1,2‐dicarbonylation of alkenes is executed by a photocatalyst for versatile substrates under extremely mild conditions and shows great potential in biomolecular and drug molecular derivatization.
Direct incorporation of two carbonyl groups into a double bond by diacylation is achieved for the first time via visible‐light catalysis. Key to success is that N(n‐Bu)4+ not only associates with the alkyl anion to avoid protonation, but also activates the α‐keto acid to undergo electrophilic addition. The metal‐free, redox‐neutral and regioselective symmetric and unsymmetric 1,2‐dicarbonylation of alkenes has the potential for many applications.
Background
The impacts of chronic airway diseases on coronavirus disease 2019 (COVID‐19) are far from understood.
Objective
To explore the influence of asthma and chronic obstructive pulmonary ...disease (COPD) comorbidity on disease expression and outcomes, and the potential underlying mechanisms in COVID‐19 patients.
Methods
A total of 961 hospitalized COVID‐19 patients with a definite clinical outcome (death or discharge) were retrospectively enrolled. Demographic and clinical information were extracted from the medical records. Lung tissue sections from patients suffering from lung cancer were used for immunohistochemistry study of angiotensin‐converting enzyme II (ACE2) expression. BEAS‐2B cell line was stimulated with various cytokines.
Results
In this cohort, 21 subjects (2.2%) had COPD and 22 (2.3%) had asthma. After adjusting for confounding factors, COPD patients had higher risk of developing severe illness (OR: 23.433; 95% CI 1.525‐360.135; P < .01) and acute respiratory distress syndrome (OR: 19.762; 95% CI 1.461‐267.369; P = .025) than asthmatics. COPD patients, particularly those with severe COVID‐19, had lower counts of CD4+ T and CD8+ T cells and B cells and higher levels of TNF‐α, IL‐2 receptor, IL‐10, IL‐8, and IL‐6 than asthmatics. COPD patients had increased, whereas asthmatics had decreased ACE2 protein expression in lower airways, compared with that in control subjects without asthma and COPD. IL‐4 and IL‐13 downregulated, but TNF‐α, IL‐12, and IL‐17A upregulated ACE2 expression in BEAS‐2B cells.
Conclusion
Patients with asthma and COPD likely have different risk of severe COVID‐19, which may be associated with different ACE2 expression.
After adjusting for confounding factors, COVID‐19 patients with COPD have higher risks of developing severe illness and acute respiratory distress syndrome than COVID‐19 patients with asthma. COPD patients have increased, whereas asthmatics have decreased ACE2 protein expression in lower airways, compared with that in control subjects without asthma and COPD. IL‐17A, TNF‐α, and IL‐12 promote, while IL‐4 and IL‐13 suppress ACE2 expression in airway BEAS‐2B cells. Abbreviations: ACE2, angiotensin‐converting enzyme II; ARDS, acute respiratory distress syndrome; BEAS‐2B, adenovirus‐12 SV40 hybrid virus transformed bronchial epithelial cells; COPD, chronic obstructive pulmonary disease; COVID‐19, coronavirus disease 2019.
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•Large porosity, micropore size, thickness, and low density are beneficial to increase of sound absorption.•Addition of back cavity bring a absorption peak in middle and high ...frequency.•Multilayer regular hole is beneficial to sound absorption.
Different from earlier researches, we study low frequency acoustic characteristics of mesophase pitch based carbon foams by impedance tube, and prove that carbon foams has low frequency absorption characteristics besides the application of thermal insulation and foreign matter adsorption. Three different samples are made of three asphalt raw materials: PNJ, PTZ and PDD. By carbonation and graphitization of the asphalt foam, different samples are prepared and corresponding sound absorption experiments display the porosity, density and micropore size of samples have a strong relationship with sound absorption capacity; increasing thickness of samples could heighten low frequency sound absorption coefficient, but increasement of back cavity would has almost no effects on low frequency. Combined with SEM images, the large porous microstructure with layered distribution is beneficial to absorption coefficient improvement of porosity material. This research shows carbon foams to be as the porous lightweight materials has a potential application in acoustics field, mechanism analysis in this research provides guidelines for design of sound absorption material having a microstructure porosity properties.
Background
The missing asymptomatic COVID‐19 infections have been overlooked because of the imperfect sensitivity of the nucleic acid testing (NAT). Globally understanding the humoral immunity in ...asymptomatic carriers will provide scientific knowledge for developing serological tests, improving early identification, and implementing more rational control strategies against the pandemic.
Measure
Utilizing both NAT and commercial kits for serum IgM and IgG antibodies, we extensively screened 11 766 epidemiologically suspected individuals on enrollment and 63 asymptomatic individuals were detected and recruited. Sixty‐three healthy individuals and 51 mild patients without any preexisting conditions were set as controls. Serum IgM and IgG profiles were further probed using a SARS‐CoV‐2 proteome microarray, and neutralizing antibody was detected by a pseudotyped virus neutralization assay system. The dynamics of antibodies were analyzed with exposure time or symptoms onset.
Results
A combination test of NAT and serological testing for IgM antibody discovered 55.5% of the total of 63 asymptomatic infections, which significantly raises the detection sensitivity when compared with the NAT alone (19%). Serum proteome microarray analysis demonstrated that asymptomatics mainly produced IgM and IgG antibodies against S1 and N proteins out of 20 proteins of SARS‐CoV‐2. Different from strong and persistent N‐specific antibodies, S1‐specific IgM responses, which evolved in asymptomatic individuals as early as the seventh day after exposure, peaked on days from 17 days to 25 days, and then disappeared in two months, might be used as an early diagnostic biomarker. 11.8% (6/51) mild patients and 38.1% (24/63) asymptomatic individuals did not produce neutralizing antibody. In particular, neutralizing antibody in asymptomatics gradually vanished in two months.
Conclusion
Our findings might have important implications for the definition of asymptomatic COVID‐19 infections, diagnosis, serological survey, public health, and immunization strategies.
The combination of NAT and serological testing for IgM antibody significantly improves the detection sensitivity of asymptomatic COVID‐19 infections, compared with NAT alone. S1‐specific IgM antibody response with rapid emergence and disappearance might be helpful to assist NAT for early identification of infectious individuals. A majority of asymptomatics induce very low levels of neutralizing antibody that disappear in two months. Abbreviations: NAT, nucleic acid testing; FI, fluorescence intensity; NT50, half‐maximal neutralizing titer.
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•A water-soluble CS-graft-PVA was synthesized by copolymerized.•The CS-graft-PVA film exhibited a desirable long-term sustained release ability.•The film possessed excellent ability ...to food preservation.
Active food packaging materials containing procyanidins (PC) exhibits outstanding antimicrobial activity, but PC is easy to be hydrolyzed by acid. A novel water-soluble chitosan (CS)-based copolymer was prepared to be used as a carrier to provide a pH-stable environment for loading PC. CS was copolymerized with polyvinyl alcohol (PVA) via a coupling reagent-mediated approach. The CS-graft-PVA film exhibited a desirable PC encapsulation efficiency of over 95% and excellent long-term release sustainability, which was better than the conventional CS and CS-blend-PVA films. Moreover, CS-graft-PVA film had satisfactory mechanical properties and barrier properties, as well possessed a desirable antibacterial activity and biofilm inhibition against foodborne pathogenic microbes and spoilage bacteria. The film was also applied in the salmon muscle perseveration and showed a potential ability to prevent microorganism contamination and texture deterioration in 10 days. These results suggested that the CS-graft-PVA film has an excellent promise for future food packaging applications.
Noise pollution has become a significant global problem in recent years. Unfortunately, conventional acoustic materials cannot offer substantial improvements in noise reduction. However, acoustic ...metamaterials are providing new solutions for controlling sound waves, and have huge potential for mitigating noise propagation in particular. Recently, owing to the rapid development of acoustic metamaterials, metamaterials for acoustic noise reduction have drawn the attention of researchers worldwide. These metamaterials are often both light and compact, and are excellent at reducing low‐frequency noise, which is difficult to control with conventional acoustic materials. Recent progress has illustrated that acoustic metamaterials effectively control sound waves, and optimizing their structure can enable functionality based on new physical phenomena. This review introduces the development of acoustic metamaterials, and summarizes the basic classification, underlying physical mechanism, application scenarios, and emerging research trends for both passive and active noise‐reduction metamaterials. Focusing on noise reduction, the shortcomings of current technologies are discussed, and future development trends are predicted. As our knowledge in this area continues to expand, it is expected that acoustic metamaterials will continue to improve and find more practical applications in emerging fields in the future.
This review introduces the development of acoustic metamaterials, the basic classification, the underlying mechanism, application scenario, and emerging trends for both passive and active noise‐reduction metamaterials. Acoustic metamaterials will continue to improve and the authors would likely believe these unusual metamaterials more practical in this emerging field in future.
α‐Acylation of Alkenes by a Single Photocatalyst Cheng, Yuan‐Yuan; Hou, Hong‐Yu; Liu, Yu ...
Angewandte Chemie International Edition,
December 23, 2022, Letnik:
61, Številka:
52
Journal Article
Recenzirano
A direct strategy for the difunctionalization of alkenes, with acylation occurring at the more substituted alkene position, would be attractive for complex ketone synthesis. We report herein a ...reaction driven by a single photocatalyst that enables α‐acylation in this way with the introduction of a fluoromethyl, alkyl, sulfonyl or thioether group at the β‐position of the alkene with high chemo‐ and regioselectivity under extremely mild conditions. Crucial to the success of this method are rate differences in the kinetics of radical generation through single‐electron transfer (SET) between different radical precursors and the excited photocatalyst (PC*). Thus, the β‐position of the alkene is first occupied by the group derived from the radical precursor that can be generated most readily, and α‐keto acids could be used as an electrophilic reagent for the α‐acylation of alkenes.
A reaction for the difunctionalization of terminal alkenes with an acyl group and a fluoromethyl, alkyl, sulfonyl, or thioether group was developed with acylation at the internal position by using a single photocatalyst. Key to success was a kinetic difference in the reactivity of the radical precursors with the excited photocatalyst, whereby the terminal position was first occupied by the more kinetically favorable radical precursor.
Both the uncoordinated Pb2+ and excess PbI2 in perovskite film will create defects and perturb carrier collection, thus leading to the open‐circuit voltage (VOC) loss and inducing rapid performance ...degradation of perovskite solar cells (PSCs). Herein, an additive of 3‐aminothiophene‐2‐carboxamide (3‐AzTca) that contains amide and amino and features a large molecular size is introduced to improve the quality of perovskite film. The interplay of size effect and adequate bonding strength between 3‐AzTca and uncoordinated Pb2+ regulates the mineralization of PbI2 and generates low‐dimensional PbI2 phase, thereby boosting the crystallization of perovskite. The decreased defect states result in suppressed nonradiative recombination and reduced VOC loss. The power conversion efficiency (PCE) of modified PSC is improved to 22.79% with a high VOC of 1.22 V. Moreover, the decomposition of PbI2 and perovskite films is also retarded, yielding enhanced device stability. This study provides an effective method to minimize the concentration of uncoordinated Pb2+ and improve the PCE and stability of PSCs.
The introduction of 3‐AzTca regulates the mineralization of PbI2 and perovskite by strengthening the metallic Pb frame, thereby reducing the defects and improving the environmental stability of PbI2 and perovskite film. The champion perovskite solar cell achieves a low voltage deficit of 0.37 V, an efficiency of 22.79%, and enhanced stability.
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