Diamond-based electron emission:Structure,properties and mechanisms

Diamond has an ultrawide bandgap with excellent physical properties,such as high critical electric field,excellent thermal conductivity,high carrier mobility,etc.Diamond with a hydrogen-terminated(H-terminated)surface has a negative electron affinity(NEA)and can easily produce surface electrons from valence or trapped electrons via optical absorption,thermal heating energy or carrier transport in a PN junction.The NEA of the H-terminated surface enables surface electrons to emit with high efficiency into the vacuum without encountering additional barriers and promotes further development and application of diamond-based emitting devices.This article reviews the electron emission properties of H-terminated diamond surfaces exhibiting NEA characteristics.The electron emission is induced by different physical mechanisms.Recent advancements in electron-emitting devices based on diamond are also summarized.Finally,the current challenges and future development opportunities are discussed to further develop the relevant applications of diamond-based electronemitting devices.

Kuicolong-yu enema decoction retains traditional Chinese medicine enema attenuates inflammatory response ulcerative colitis through TLR4/NF-κB signaling pathway

BACKGROUND Ulcer colitis(UC)is a chronic,nonspecific,and noninfectious inflammatory bowel disease.Recently,Toll-like receptors(TLRs)have been found to be closely associated with clinical inflammatory diseases.Achieving complete remission in patients with intermittent periods of activity followed by dormancy is challenging.Moreover,no study has explored the mechanism by which Kuicolong-yu enema decoction retains traditional Chinese medicine enemas to attenuate the inflammatory response in UC.AIM To explore the mechanism by which Kuicolong-yu enema decoction retains traditional Chinese medicine enemas to attenuate the inflammatory response in UC.METHODS This prospective clinical study included patients who met the exclusion criteria in 2020 and 2021.The patients with UC were divided into two groups(control and experimental).The peripheral blood of the experimental and control groups were collected under aseptic conditions.The expression of TLR4 protein,NF-κB,IL-6,and IL-17 was detected in the peripheral blood of patients in the experimental group and control group before and 1 month after taking the drug.Linear co rrelation analysis was used to analyze the relationship between the expression level of TLR4 protein and the expression levels of downstream signal NF-κB and inflammatory factors IL-6 and IL-17,and P<0.05 was considered statistically significant.RESULTS There were no significant differences in the patient characteristics between the control and experimental groups.The results showed that the expression levels of TLR4 and NF-κB in the experimental group were significantly lower than those in the control group(P<0.05).The levels of IL-6 and IL-17 in the experimental group were significantly lower than those in the control group(P<0.05).The TLR4 protein expression in the experimental group was positively correlated with the expression level of downstream signal NF-κB and was positively correlated with the levels of downstream inflammatory cytokines IL-6 and IL-17(r=0.823,P<0.05).CONCLUSION Kuicolong-yu enema decoction retains traditional Chinese medicine enema attenuates the inflammatory response of UC through the TLR4/NF-κB signaling pathway.

Reform of Teaching Practice of Modern Instrumental Analysis in Biotechnology Programs

Through the online and offline practical reform of the Modern Instrumental Analysis course of biotechnology majors from teaching content,teaching method,teaching demonstration to teaching effect,the traditional single offline lecture is transformed into diversified and interactive modern teaching.The practical reform enriches and optimizes the course content,perfects and improves the course assessment system,and improves the teaching quality.It achieves the student-centered and application-oriented teaching goal,and also provides reference for further cultivating high-quality applied talents.

The Chemical Mechanism of Pestilences or Coronavirus Disease 2019 (COVID-19)

In this paper, the chemical mechanism of the coronavirus disease 2019 (COVID-19) has been explored and clearly revealed.

系统教学法的构建及其应用

随着教育理念的不断进步,系统教学法逐渐受到教育界的广泛关注。系统教学法的基本理念在于将教学视为一个完整的系统,通过逐步对系统进行剖析,最终实现对要素个体的深入理解。而《公司战略与风险管理》是一门拓宽视野、丰富思维、实践性较强的管理类课程,着重分析讨论企业具体经营策略与发展战略问题。将系统教学法应用其中,不仅可以有效提升教学效果,还能增强学生的实践能力。对此,本文通过阐述现存不足,重构教学思想,进而探究系统教学法的内容及实施,以期帮助学生全面、系统地掌握知识和技能。

Homogenous charge distribution by free-standing porous structure for dendrite-free Li metal anode

Lithium metal has a high theoretical capacity of 3860 mAh g^-1 and a low electrochemical potential(-3.04 V vs.H2/H^+).Hence,using a lithium anode significantly improves the energy density of a secondary battery.However,the lithium dendrites generated on the lithium anode during the platingdissolution process significantly reduce its cycling life and safety.Here,we provide a simple method for lithium anode protection,by applying a free-standing porous carbon film with a high specific surface area to reduce the local current density and obtain a homogenous ion distribution.The protected lithium anode has a long cycle life over 1000 h when cycled at 3 mA cm^-2 with a lithium capacity of 2.5 mAh cm^-2.Moreover,the deposited lithium has a smoother surface than Li anode without carbon protection.This study will promote the wide application of Li-metal-based batteries with high safety levels.

Material Removal Characteristics of Single-Crystal 4H-SiC Based on Varied-Load Nanoscratch Tests

Single-crystal silicon carbide(SiC)has been widely applied in the military and civil fields because of its excellent physical and chemical properties.However,as is typical in hard-to-machine materials,the good mechanical properties result in surface defects and subsurface damage during precision or ultraprecision machining.In this study,single-and double-varied-load nanoscratch tests were systematically performed on single-crystal 4H-SiC using a nanoindenter system with a Berkovich indenter.The material removal characteristics and cracks under different planes,indenter directions,normal loading rates,and scratch intervals were analyzed using SEM,FIB,and a 3D profilometer,and the mechanisms of material removal and crack propagation were studied.The results showed that the Si-plane of the single-crystal 4H-SiC and edge forward indenter direction are most suitable for material removal and machining.The normal loading rate had little effect on the scratch depth,but a lower loading rate increased the ductile region and critical depth of transition.Additionally,the crack interaction and fluctuation of the depth-distance curves of the second scratch weakened with an increase in the scratch interval,the status of scratches and chips changed,and the comprehensive effects of the propagation and interaction of the three cracks resulted in material fractures and chip accumulation.The calculated and experimental values of the median crack depth also showed good consistency and relativity.Therefore,this study provides an important reference for the high-efficiency and precision machining of single-crystal SiC to ensure high accuracy and a long service life.

Significant suppression of residual nitrogen incorporation in diamond film with a novel susceptor geometry employed in MPCVD

This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition(MPCVD)reaction chamber,that is,to introduce a small hole in the center of the susceptor to study its suppression effect on the incorporation of residual nitrogen in the MPCVD diamond film.By using COMSOL multiphysics software simulation,the plasma characteristics and the concentration of chemical reactants in the cylindrical cavity of MPCVD system were studied,including electric field intensity,electron number density,electron temperature,the concentrations of atomic hydrogen,methyl,and nitrogenous substances,etc.After introducing a small hole in the center of the molybdenum support susceptor,we found that no significant changes were found in the center area of the plasma,but the electron state in the plasma changed greatly on the surface above the susceptor.The electron number density was reduced by about 40%,while the electron temperature was reduced by about 0.02 eV,and the concentration of atomic nitrogen was decreased by about an order of magnitude.Moreover,we found that if a specific lower microwave input power is used,and a susceptor structure without the small hole is introduced,the change results similar to those in the surface area of the susceptor will be obtained,but the spatial distribution of electromagnetic field and reactant concentration will be changed.

Effects of Nickel Chloride on Histopathological Lesions and Oxidative Damage in the Thymus

The purpose of this study was to observe the histopathological lesions and oxidative damage induced by dietary nickel chloride (NiCl2) in the thymus. A total of 280 one-day-old avian broilers were divided into four groups and fed on a corn-soybean basal diet as the control diet or the same basal diet supplemented with 300, 600, and 900 mg/kg of NiCl2 for 42 days. In the NiCl2-treated groups, the broiler weight and thymic relative weight were significantly (P P < 0.01) decreased. Histopathologically, thymic corpuscles were increased and enlarged;the reticular cells were degenerate and necrotic, and lymphocytes were slightly decreased and loosely arranged in the medulla of thymus in the 600 mg/kg and 900 mg/kg groups. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), and the ability to inhibit hydroxy radical and glutathione (GSH) content were significantly (P P < 0.01) lower in the NiCl2-treated groups than those in the control group, while MDA content was higher. The above-mentioned results demonstrated that dietary NiCl2 in excess of 300 mg/kg could reduce the broiler weight and thymic relative weight, and cause histopathological lesions and oxidative damage in the thymus, which finally impaired the thymic function.

Prediction of Grinding Force by an Electroplated Grinding Wheel with Orderly-Micro-Grooves

The ability to predict a grinding force is important to control,monitor,and optimize the grinding process.Few theoretical models were developed to predict grinding forces when a structured wheel was used in a grinding process.This paper aimed to establish a single-grit cutting force model to predict the ploughing,friction and cutting forces in a grinding process.It took into the consideration of actual topography of the grinding wheel,and a theoretical grinding force model for grinding hardened AISI 52100 by the wheel with orderly-micro-grooves was proposed.The model was innovative in the sense that it represented the random thickness of undeformed chips by a probabilistic expression,and it reflected the microstructure characteristics of the structured wheel explicitly.Note that the microstructure depended on the randomness of the protruding heights and distribution density of the grits over the wheel.The proposed force prediction model was validated by surface grinding experiments,and the results showed(1)a good agreement of the predicted and measured forces and(2)a good agreement of the changes of the grinding forces along with the changes of grinding parameters in the prediction model and experiments.This research proposed a theoretical grinding force model of an electroplated grinding wheel with orderly-micro-grooves which is accurate,reliable and effective in predicting grinding forces.

Suppression and compensation effect of oxygen on the behavior of heavily boron-doped diamond films

This work investigates the suppression and compensation effect of oxygen on the behaviors and characteristics of heavily boron-doped microwave plasma chemical vapor deposition(MPCVD)diamond films.The suppression effect of oxygen on boron incorporation is observed by an improvement in crystal quality when oxygen is added during the diamond doping process.A relatively low hole concentration is expected and verified by Hall effect measurements due to the compensation effect of oxygen as a deep donor in diamond.A low acceptor concentration,high compensation donor concentration and relatively larger acceptor ionization energy are then induced by the incorporation of oxygen;however,a heavily boron-doped diamond film with high crystal quality can also be expected.The formation of an oxygen–boron complex structure instead of oxygen substitution,as indicated by the results of x-ray photoelectron spectroscopy,is suggested to be more responsible for the observed enhanced compensation effect due to its predicted low formation energy.Meanwhile,density functional theory calculations show that the boron–oxygen complex structure is easily formed in diamond with a formation energy of-0.83 eV.This work provides a comprehensive understanding of oxygen compensation in heavily boron-doped diamond.

Effects of oxygen/nitrogen co-incorporation on regulation of growth and properties of boron-doped diamond films

Regulation with nitrogen and oxygen co-doping on growth and properties of boron doped diamond films is studied by using laughing gas as dopant. As the concentration of laughing gas(N2O/C) increases from 0 to 10%, the growth rate of diamond film decreases gradually, and the nitrogen-vacancy(NV) center luminescence intensity increases first and then weakens. The results show that oxygen in laughing gas has a strong inhibitory effect on formation of NV centers, and the inhibitory effect would be stronger as the concentration of laughing gas increases. As a result, the film growth rate and nitrogen-related compensation donor decrease, beneficial to increase the acceptor concentration(~3.2×10^(19)cm^(-3)) in the film. Moreover, it is found that the optimal regulation with the quality and electrical properties of boron doped diamond films could be realized by adding appropriate laughing gas, especially the hole mobility(~700cm^(2)/V·s), which is beneficial to the realization of high-quality boron doped diamond films and high-level optoelectronic device applications in the future.

Effect of oxygen on regulation of properties of moderately boron-doped diamond films

Regulation of oxygen on properties of moderately boron-doped diamond films is fully investigated.Results show that,with adding a small amount of oxygen(oxygen-to-carbon ratio<5.0%),the crystal quality of diamond is improved,and a suppression effect of residual nitrogen is observed.With increasing ratio of O/C from 2.5%to 20.0%,the hole concentration is firstly increased then reduced.This change of hole concentration is also explained.Moreover,the results of Hall effect measurement with temperatures from 300 K to 825 K show that,with adding a small amount of oxygen,boron and oxygen complex structures(especially B_(3)O and B_(4)O)are formed and exhibit as shallow donor in diamond,which results in increase of donor concentration.With further increase of ratio of O/C,the inhibitory behaviors of oxygen on boron leads to decrease of acceptor concentration(the optical emission spectroscopy has shown that it is decreased with ratio of O/C more than 10.0%).This work demonstrates that oxygen-doping induced increasement of the crystalline and surface quality could be restored by the co-doping with oxygen.The technique could achieve boron-doped diamond films with both high quality and acceptable hole concentration,which is applicable to electronic level of usage.

Origin,characteristics,and suppression of residual nitrogen in MPCVD diamond growth reactor

Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition(MPCVD)-grown samples.No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity.By a comprehensive investigation including the analysis of the plasma composition,we found that a minor leakage of the system could be significantly magnified by the thermal effect,resulting in a considerable residual nitrogen in the diamond material.Moreover,the doping mechanism of leaked air is different to pure nitrogen doping.The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond,while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen.The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen.As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application,we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry.This study indicates that even if a normal base pressure can be reached,the nitrogen residing in the chamber can be“activated”by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor.

The Preparation Technology Research and Composition Analysis of Anti-fatigue Yikangshu Granules

[Objectives]To optimize the preparation technology of Yikangshu granule,an anti-fatigue health food.[Methods]The process was studied from three aspects(raw material extraction,excipient selection and forming process),and then it was verified in pilot production,and the content of the three components of the product was determined.[Results]The optimum production process of the formula granules was as follows:raw materials were extracted(adding 1∶9 water,extracting twice,2.5 h each time);vacuum concentration;adding excipients and mixing after vacuum drying,crushing and sieving;granulation of 75%ethanol sifted by a 20-mesh sieve;drying at 60℃,sifting through 14-mesh,and packaging.The average content of products obtained was as follows:crude polysaccharides(3204 mg/100 g),total saponins(2295 mg/100 g),astragaloside A(21 mg/100 g).[Conclusions]The optimized preparation technology is stable and feasible,and has a quality that can be controlled,which can provide a reference for the development of health food in food industry.

Determination of the Content of Astragaloside IV in Yikangshu Granules by High Performance Liquid Chromatography

[Objectives]The research aimed to establish a high performance liquid chromatography method for the content determination of astragaloside IV in Yikangshu Granules.[Methods]Kromasil 5μm C18(2),100 A,250 mm×4.6 mm was used;the mobile phase was acetonitrile-water(32∶68);flow velocity was 1.0 mL/min;the temperature of evaporator and sprayer was 80 and 30℃;the column temperature was set at 30℃,and injection volume was 20μL.[Results]Astragaloside IV showed a good linear relationship in the range of 1.01-10.14μg with the peak area,and regression equation was lgY=1.7728lgX+1.597(r=0.9999).The limit of detection for astragaloside IV was 1.96 ng,and the average recovery rate was 95.31%.[Conclusions]This method is sensitive,accurate and reproducible,with good linearity,and it is suitable for the content determination of astragaloside IV in health food Yikangshu Granules.

Determination of the Content of Gastrodin in Jingtianshenma Tablets by High Performance Liquid Chromatography

[Objectives]The research aimed to establish a high performance liquid chromatography method for the content determination of gastrodin in Jingtianshenma Tablets.[Methods]A phenomenex Luna C18(250 mm×4.6 mm,5μm)column was used;the mobile phase was acetonitrile-0.05%phosphoric acid solution(3∶97);the detection wavelength was 220 nm,and the column temperature was set at 25℃.[Results]Gastrodin showed a good linear relationship in the range of 0.0984-0.5904μg with the peak area,and regression equation was Y=2000000X-51999(r=0.9999).The limits of detection and quantification for gastrodin were 2.50 and 4.20 ng respectively,and the average recovery rate was 95.95%.[Conclusions]This method is sensitive,accurate and reproducible,with good linearity,and it is suitable for the content determination of gastrodin in health food Jingtianshenma Tablets.

Disciplinary development of global health academic degree programs in China

This study aims to provide a brief overview of the history and development of global health education(GHE)as academic degree programs worldwide,and to identify GHE’s development opportunities and obstacles in China.This is a state-of-the-art review of published and unpublished information that described and evaluated disciplinary development of global health degree programs worldwide,written in English,and published or shared between 1990 and 2020.Data were derived from official websites of leading global health institutions,like“Google Scholar”,“PubMed”,and unpublished information such as presentation files and unpublished manuscripts collected from knowledgeable leaders in the field.We retrieved and reviewed a total of 35 articles and a large amount of unpublished information or sources on the internet.Global Health emerged as a new discipline around the end of the last millennium and proliferated in the last two decades in developed nations,especially the United States and the United Kingdom.The development of China’s GHE programs was built on China’s increasing engagement in global health affairs and research.In 2012,Wuhan University established the first official global health department in China.Several universities such as Peking University and Duke Kunshan University subsequently set up departments or programs to offer undergraduate and postgraduate majors and degrees.The first school-level global health unit was established in Shanghai in 2019.The Consortium of Chinese Universities for Global Health(CCUGH)grew from 10 founding members in 2013 to 25 in 2020.Major desirable attributes“unique”to students majoring in global health include global-mindedness,health interests,compassion,intercultural sensitivity,and adventurous spirit.Graduates from GHE programs have a diverse set of career choices spanning research,government,not-for-profit,and private sector occupations.We identified a number of strengths,weaknesses,opportunities,and threats to the future development of GHE in China.To ensure sustainable future growth,we advocate addressing the following key aspects:(1)clearer disciplinary distinctions;(2)multidisciplinary collaborations;(3)public-sector investments;and(4)non-public sectors participation.Amidst China’s increasing engagement in health affairs globally and the proliferation of GHE programs in developed nations,China has experienced fast growth in GHE degree programs since 2012 while a number of challenges remain for its future development.

Development Countermeasures of County-level Edible Fungi Industry in Hebei Province from the Perspective of Rural Revitalization

In recent years,the edible fungi industry in Hebei Province has developed rapidly,with gradually increased cultivation scale and production output,and has become the pillar industry of the province,playing a certain role in promoting the development of rural economy and rural revitalization.Based on the in-depth analysis of the development status,future development direction and current constraints of the edible fungi industry in each typical county of Hebei Province in recent years,the paper puts forward corresponding development countermeasures,which has certain reference value for the county-level edible fungi industry of Hebei Province to promote rural revitalization.

Enones from aldehydes and alkenes by carbene-catalyzed dehydrogenative couplings

Enones are widely explored in synthetic chemistry as fundamental building blocks for a wide range of reactions and exhibit intriguing biological activities that are pivotal for drug discovery.The development of synthetic strategies for highly efficient preparation of enones thereby receives intense attention,in particular through the transition metal-catalyzed coupling reactions.Here,we describe a carbene-catalyzed cross dehydrogenative coupling(CDC)reaction that enables effective assembly of simple aldehydes and alkenes to afford a diverse set of enone derivatives.Mechanistically,the in situ generated aryl radical is pivotal to“activate”the alkene by forming an allyl radical through intermolecular hydrogen atom transfer(HAT)pathway and thus forging the carbon-carbon bond formation with aldehyde as the acyl synthon.Notably,our method represents the first example on the enone synthesis through coupling of“non-functionalized”aldehydes and alkenes as coupling partners,and offers a distinct organocatalytic pathway to the transition metal-catalyzed coupling transformations.