Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 16 de 16
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Org Lett ; 23(12): 4823-4827, 2021 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-34080868

RESUMO

The first asymmetric synthesis of 3-methyleneindolines from alkynyl imines has been developed via a rhodium-catalyzed tandem process: regioselective alkynylation of the internal alkynes and subsequent intramolecular addition to the imines. The reaction proceeded with unconventional chemoselectivity and provided 3-methyleneindolines with good yields (up to 82% yield) and high enantioselectivities (up to 97% ee). Moreover, this transformation also features mild reaction conditions, perfect atom economy, and a broad substrate scope.

2.
ACS Appl Mater Interfaces ; 13(14): 16987-16996, 2021 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-33787205

RESUMO

Recent advances in high-entropy alloys have spurred many breakthroughs in the fields of high-temperature materials and optical materials and they provide incredible application potentialities for photothermal conversion systems. Solar-selective absorbers (SSAs), as key components, play a vital role in photothermal conversion efficiency and service life. The most pressing problem with SSAs is their inconsistent optical performance, an instability constraint induced by thermal stress. A feasible method of improving performance stability is the introduction of high-entropy materials, such as high-entropy alloy nitrides. In this study, enabled by an intrinsic MoTaTiCrN absorption layer, the solar configuration achieves greatly enhanced, exceptional thermotolerance and optical properties, leading to the formation of a scalable, highly efficient, and cost-effective structure. Computational and experimental approaches are employed to achieve optimum preparation parameters for thicknesses and constituents. The crystal structure of high-entropy ceramic MoTaTiCrN is fully investigated, including thickness-dependent crystal nucleation. High-temperature and long-term thermal stability tests demonstrate that our proposed SSA is mechanically robust and chemically stable. Moreover, a low thermal emittance (15.86%) at 500 °C promotes the photothermal conversion efficiency. In addition, due to the exceptional spectral selectivity (α/ε = 92.3/6.5%), thermal robustness (550 °C for 168 h), and photothermal conversion efficiency (86.9% at 550 °C under 100 sun), it is possible for our proposed SSA to enhance the practical realization of large-area photothermal conversion applications, especially for concentrated solar power systems.

3.
Nat Commun ; 11(1): 4293, 2020 08 27.
Artigo em Inglês | MEDLINE | ID: mdl-32855405

RESUMO

Among about 150 identified allenic natural products, the exocyclic allenes constitute a major subclass. Substantial efforts are devoted to the construction of axially chiral allenes, however, the strategies to prepare chiral exocyclic allenes are still rare. Herein, we show an efficient strategy for the asymmetric synthesis of chiral exocyclic allenes with the simultaneous control of axial and central chirality through copper(I)-catalyzed asymmetric intramolecular reductive coupling of 1,3-enynes to cyclohexadienones. This tandem reaction exhibits good functional group compatibility and the corresponding optically pure exocyclic allenes bearing cis-hydrobenzofuran, cis-hydroindole, and cis-hydroindene frameworks, are obtained with high yields (up to 99% yield), excellent diastereoselectivities (generally >20:1 dr) and enantioselectivities (mostly >99% ee). Furthermore, a gram-scale experiment and several synthetic transformations of the chiral exocyclic allenes are also presented.

4.
Sci Total Environ ; 734: 139394, 2020 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-32485462

RESUMO

Freshwater consumption and wastewater discharge of economic activities have caused water scarcity problem in many regions. This study aims to develop a multi-dimensional diagnosis model (MDDM) to provide new insights for the sustainable development of regions which face water scarcity problem. In detail, the sectorial blue water, grey water and total water consumptions are assessed to reveal the direct effects of economic activities on water quantity and water quality. Then, hypothetical extraction method is integrated into input-output model and ecological network analysis to quantify the system-based effects of sectors in three dimensions: economy, water and metabolism. A case study of Guangdong province, China is conducted to illustrate the availability of the developed model. We found that the multi-dimensional performances of Guangdong's socioeconomic system are dominated by a few sectors. Wastewater, especially that discharged from the primary industry, is the main reason for the local water scarcity. Specifically, the unique role that every sector plays in the socioeconomic system is quantitatively revealed by MDDM, which could guide the relevant policy development at sectorial level.

5.
Org Lett ; 22(9): 3661-3666, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32275152

RESUMO

The rhodium(III)-catalyzed kinetic resolution of racemic nonactivated terminal alkene-tethered cyclohexadienones (1,6-dienes) has been developed with high to excellent selectivities (s up to 458) via asymmetric borylative cyclization, providing recovered cyclohexadienones and cis-hydrobenzofuranones with good to excellent yields and enantioselectivities (up to 99% ee). This reaction shows broad functional group tolerance and allows the further conversions of these two-type products to many optically active derivatives bearing multiple functionalities via Rh, Cu, Pd, and Ag catalysis.

6.
Chem Commun (Camb) ; 56(11): 1693-1696, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-31939945

RESUMO

Asymmetric conjugate addition of PhMe2SiBPin to a wide range of N-heteroaryl alkenes proceeded in the presence of a copper catalyst coordinated with an easily accessible chiral phosphoramidite ligand to afford useful ß-silyl N-heteroarenes in high yields (up to 96%) and excellent enantioselectivities (up to 97% ee).

7.
Sci Total Environ ; 705: 135857, 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-31841923

RESUMO

Energy usage and CO2 emission have intimate and inseparable linkages. The growth of energy usage causes an increase in CO2 emissions, which will in turn constrain the related energy policies and challenge the energy-system stability. It is essential to quantify China's CO2 emission inventories embodied in production-driven, demand-driven and supply-driven chains considering different energy types. A Three-Perspective Energy-Carbon Nexus model is developed to facilitate comprehensive CO2 emission-reduction analysis in China. The model incorporates environmental input-output analysis and ecological network analysis within a general framework to clarify the relationships among provinces in terms of the production-based, consumption-based and income-based accountings. A new indicator, indirect emission dominant factor, is for the first time examined to evaluate the dominant capabilities of indirect emissions. It is discovered that the emissions triggered by the demand-side are not sensitive to energy types. Furthermore, the changes of integral flow control intensity in each province are insignificant from consumption-based and income-based perspectives. Final demand contributes 80% of consumption-based emissions and gross value-added creation leads to a total of 82% income-based CO2 emissions in China in 2012. When controlling emissions from multiple perspectives, traditional methods may not be effective since they do not consider the forms of emissions; some methods (e.g., product allocation) are not suitable for suppressing indirect emissions. Moreover, the prosperity of developed regions (e.g. Guangdong) highly rely on support from underdeveloped regions (e.g. Inner Mongolia). Some underdeveloped provinces are receptors of CO2, while the developed ones are emitting CO2 to the system without assuming their emission-reduction responsibilities. In addition, secondary energy consumptions in developed regions are conducive in increasing their emission contributions to the system. In this research, an innovative perspective is initiated to disclose the energy-carbon interconnections across Chinese provinces. The obtained findings could help support the formulation of China's CO2 emission-reduction policies.

8.
J Contin Educ Nurs ; 50(3): 121-126, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30835322

RESUMO

BACKGROUND: This multicenter cross-sectional study sought to determine the knowledge, attitudes, and practices regarding the use of physical restraints by Chinese nurses in intensive care units (ICUs) of tertiary hospitals. METHOD: A scale technique was used to measure the knowledge, attitudes, and practices of 383 RNs from eight tertiary hospitals in Chongqing, China. RESULTS: A total of 383 valid questionnaires were returned, for a response rate of 89.49%. Approximately 8.1% of the nurses were male, 67.1% had a bachelor's degree or above, and 55.09% were ICU specialists. The average age was 28.62 years (SD = 4.56). The mean scores were 74.33 of 111 (SD = 9.552), 24.41 of 40 (SD = 4.872), and 65.66 of 130 (SD = 20.880) regarding knowledge, attitudes, and nursing practices, respectively. For the attitude scale, the scores of nurses who were certified ICU specialists and had extensive working experience were higher than those with less experience; the difference was statistically significant (p < .05). CONCLUSION: Results indicated that nurses employed in the ICUs of tertiary hospitals in Chongqing, China, have relatively insufficient knowledge, comparatively incorrect attitudes, and unreasonable means of practicing physical restraint. Continuing education should focus strongly on the relationship between physical restraint and unplanned extubation, and guidelines on physical restraint urgently need to be developed. [J Contin Educ Nurs. 2019;50(3):121-126.].


Assuntos
Grupo com Ancestrais do Continente Asiático/psicologia , Atitude do Pessoal de Saúde , Enfermagem de Cuidados Críticos/métodos , Conhecimentos, Atitudes e Prática em Saúde , Recursos Humanos de Enfermagem no Hospital/psicologia , Restrição Física/psicologia , Adulto , China , Estudos Transversais , Feminino , Humanos , Unidades de Terapia Intensiva/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Inquéritos e Questionários , Centros de Atenção Terciária
9.
Kardiol Pol ; 77(2): 207-216, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30740643

RESUMO

BACKGROUND: Due to the myopathic adverse events of statins, safer alternatives are being studied. Bempedoic acid (ETC-1002) is a novel low-density lipoprotein cholesterol (LDL-C)-lowering agent, currently under trial in hypercholesterolaemic patients. AIM: To investigate the tolerability and efficacy of ETC-1002 in hypercholesterolaemic patients through a systematic review of published randomised controlled trials (RCTs). METHODS: Five databases were searched for RCTs that investigated the safety and efficacy of ETC-1002 in hypercholesterol-aemic patients. The retrieved search results were screened, and then data were extracted and analysed (as mean difference [MD] or odds ratio [OR]) using the RevMan software. RESULTS: Five RCTs (625 hypercholesterolaemic patients) were identified. ETC-1002 was superior to placebo in terms of percent-age changes from baseline in serum levels of LDL-C (MD -26.58, 95% confidence interval [CI] -35.50 to -17.66, p < 0.0001), non-high-density lipoprotein cholesterol (MD -21.54, 95% CI -28.48 to -14.6, p < 0.00001), and apolipoprotein-B (MD -15.97, 95% CI -19.36 to -12.57, p < 0.0001). When compared to ezetimibe, ETC-1002 was superior in reducing LDL-C (-30.1 ± 1.3 vs. -21.1 ± 1.3). Regarding safety, ETC-1002 did not increase the risk of all adverse events (OR 0.58, 95% CI 0.37-0.91, p = 0.02) and arthralgia (OR 0.32, 95% CI 0.13-0.81, p = 0.02) compared to placebo. All other adverse events including myalgia, headache, and urinary tract infections were similar between ETC-1002 and placebo groups. The evidence certainty in the assessed outcomes was moderate to high except for lipoprotein(a), free fatty acids, and very low-density lipoprotein particle number (very low certainty). CONCLUSIONS: ETC-1002 is a safe and effective lipid-lowering agent and may be a suitable alternative in statin-intolerant pa-tients. Well-designed studies are needed to explore the long-term safety and efficacy of ETC-1002 in these patients.


Assuntos
Ácidos Dicarboxílicos/uso terapêutico , Ácidos Graxos/uso terapêutico , Hipercolesterolemia/tratamento farmacológico , Hipolipemiantes/uso terapêutico , Idoso , LDL-Colesterol/sangue , Ácidos Dicarboxílicos/efeitos adversos , Ezetimiba/efeitos adversos , Ezetimiba/uso terapêutico , Ácidos Graxos/efeitos adversos , Feminino , Humanos , Hipercolesterolemia/sangue , Hipolipemiantes/efeitos adversos , Masculino , Pessoa de Meia-Idade , Segurança do Paciente , Ensaios Clínicos Controlados Aleatórios como Assunto , Resultado do Tratamento
10.
Lipids Health Dis ; 17(1): 131, 2018 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-29859112

RESUMO

BACKGROUND: Achilles tendons are the most common sites of tendon xanthomas that are commonly caused by disturbance of lipid metabolism. Achilles tendon thickening is the early characteristic of Achilles tendon xanthomas. The relationship between Achilles tendon thickness (ATT) and LDL-C levels, and risk factors of ATT in patients with hypercholesterolemia, have thus far been poorly documented. METHODS: A total of 205 individuals, aged 18-75 years, were enrolled from March 2014 to March 2015. According to the LDL-C levels and the "Chinese Guidelines on Prevention and Treatment of Dyslipidemia in Adults", all subjects were divided into 3 groups: normal group (LDL-C < 3.37 mmol/L, n = 51); borderline LDL-C group (3.37 mmol/L ≤ LDL-C ≤ 4.12 mmol/L, n = 50); and hypercholesterolemia group (LDL ≥ 4.14 mmol/L, n = 104). ATT was measured using a standardized digital radiography method and the results were compared among the 3 groups. The correlation between ATT and serum LDL-C levels was analyzed by Pearson's correlation, and the risk factors of ATT were determined by the logistic regression model. RESULTS: ATT in borderline LDL-C group was 8.24 ± 1.73 mm, markedly higher than 6.05 ± 0.28 mm of normal group (P < 0.05). ATT in hypercholesterolemia group was 9.42 ± 3.63 mm which was significantly higher than that of normal group (P < 0.005) and that of borderline LDL-C group (P < 0.05). There was a positive correlation between the serum LDL-C levels and ATT (r = 0.346, P < 0.001). The serum LDL-C level was a risk factor (OR = 1.871, 95% CI: 1.067-3.280) while the levels of HDL-C (OR = 0.099, 95% CI: 0.017-0.573) and Apo AI (OR = 0.035, 95% CI: 0.003-0.412) were protective factors of ATT. CONCLUSIONS: ATT might serve as a valuable auxiliary diagnostic index for hypercholesterolemia and used for the assessment and management of cardiovascular disease.


Assuntos
Tendão do Calcâneo/patologia , LDL-Colesterol/sangue , Hipercolesterolemia/patologia , Xantomatose/epidemiologia , Adolescente , Adulto , Idoso , Feminino , Humanos , Hipercolesterolemia/sangue , Masculino , Pessoa de Meia-Idade , Fatores de Risco , Xantomatose/sangue , Adulto Jovem
11.
Adv Mater ; 25(14): 2035-9, 2013 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-23334954

RESUMO

Uniformly cut In2O3 truncated octahedrons are fabricated on a large scale by a simple chemical vapor deposition (CVD) technique. This theoretical analysis predicts that the emergence of {100} facets on the In2O3 truncated octahedrons enhances oxygen evolution significantly in photocatalysis and experimental photoelectrochemical measurements are consistent.

12.
Nano Lett ; 12(3): 1545-8, 2012 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-22385070

RESUMO

Good understanding of the reaction mechanism in the electrochemical reduction of water to hydrogen is crucial to renewable energy technologies. Although previous studies have revealed that the surface properties of materials affect the catalytic reactivity, the effects of a catalytic surface on the hydrogen evolution reaction (HER) on the molecular level are still not well understood. Contrary to general belief, water molecules do not adsorb onto the surfaces of 3C-SiC nanocrystals (NCs), but rather spontaneously dissociate via a surface autocatalytic process forming a complex consisting of -H and -OH fragments. In this study, we show that ultrathin 3C-SiC NCs possess superior electrocatalytic activity in the HER. This arises from the large reduction in the activation barrier on the NC surface enabling efficient dissociation of H(2)O molecules. Furthermore, the ultrathin 3C-SiC NCs show enhanced HER activity in photoelectrochemical cells and are very promising to the water splitting based on the synergistic electrocatalytic and photoelectrochemical actions. This study provides a molecular-level understanding of the HER mechanism and reveals that NCs with surface autocatalytic effects can be used to split water with high efficiency thereby enabling renewable and economical production of hydrogen.


Assuntos
Compostos Inorgânicos de Carbono/química , Carbono/química , Eletroquímica/métodos , Hidrogênio/química , Hidrogênio/isolamento & purificação , Nanoestruturas/química , Compostos de Silício/química , Água/química , Carbono/efeitos da radiação , Compostos Inorgânicos de Carbono/efeitos da radiação , Catálise , Campos Eletromagnéticos , Teste de Materiais , Nanoestruturas/efeitos da radiação , Compostos de Silício/efeitos da radiação
13.
ACS Nano ; 5(2): 1291-6, 2011 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-21284401

RESUMO

AlGaN ternary alloys have unique properties suitable for numerous applications due to their tunable direct band gap from 3.4 to 6.2 eV by changing the composition. Herein we report a convenient chemical vapor deposition growth of the quasi-aligned Al(x)Ga(1-x)N alloy nanocones over the entire composition range. The nanocones were grown on Si substrates in large area by the reactions between GaCl(3), AlCl(3) vapors, and NH(3) gas under moderate temperature around 700 °C. The as-prepared wurtzite Al(x)Ga(1-x)N nanocones have single-crystalline structure preferentially growing along the c-axis, with homogeneous composition distribution, as revealed by the characterizations of electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and selected area electron diffraction. The continuous composition tunability is also demonstrated by the progressive evolutions of the band edge emission in cathodoluminescence and the turn-on and threshold fields in field emission measurements. The successful preparation of Al(x)Ga(1-x)N nanocones provides the new possibility for the further development of advanced nano- and opto-electronic devices.

15.
J Am Chem Soc ; 132(13): 4843-7, 2010 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-20225864

RESUMO

The vapor-liquid-solid (VLS) growth model has been widely used to direct the growth of one-dimensional (1D) nanomaterials, but the origin of the proposed process has not been experimentally confirmed. Here we report the experimental evidence of the origin of VLS growth. Al(69)Ni(31) alloyed particles are used as "catalysts" for growing AlN nanowires by nitridation reaction in N(2)-NH(3) at different temperatures. The nanowire growth occurs following the emergence of the catalyst droplets as revealed by in situ X-ray diffraction and thermal analysis. The physicochemical process involved has been elucidated by quantitative analysis on the evolution of the lattice parameters and relative contents of the nitridation products. These direct experimental results reveal that VLS growth of AlN nanowires is dominated by the phase equilibrium of the Al-Ni alloy catalyst. The in-depth insight into the VLS mechanism indicates the general validity of this growth model and may facilitate the rational design and controllable growth of 1D nanomaterials according to the corresponding phase diagrams.

16.
ACS Appl Mater Interfaces ; 1(9): 1927-30, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20355816

RESUMO

Patterned growth of AlN nanocones on a Ni-coated Si substrate is demonstrated through the reaction between AlCl(3) and NH(3) at 700 degrees C with Mo grid as a mask. The AlN nanocones are selectively deposited in the hollow region of the mask with diameters of approximately 10 nm at the tips and 50-60 nm at the roots. The field-emission (FE) performance is effectively enhanced by the patterned growth mainly because of the decreased screening effect, and both turn-on and threshold fields are dramatically decreased, less than half of the corresponding ones for the unpatterned product with similar sizes. The results indicate that patterned growth is an efficient and reproducible way to enhance the FE performance of AlN nanocones, which could be applied to optimize the FE properties of other nanoscale field emitters.


Assuntos
Compostos de Alumínio/química , Nanotecnologia/métodos , Cloreto de Alumínio , Amônia/química , Cloretos/química , Cristalização/métodos , Eletroquímica/métodos , Teste de Materiais , Microscopia Eletrônica de Varredura , Nanoestruturas/química , Tamanho da Partícula , Propriedades de Superfície , Temperatura , Difração de Raios X
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...