Exosome is involved in liver graft protection after remote ischemia reperfusion conditioning

Background:Remote ischemic perconditioning(RIPerC)has been demonstrated to protect grafts from hepatic ischemia-reperfusion injury(IRI).This study investigated the role of exosomes in RIPerC of liver grafts in rats.Methods:Twenty-five rats(including 10 donors)were randomly divided into five groups(n=5 each group):five rats were used as sham-operated controls(Sham),ten rats were for orthotopic liver transplantation(OLT,5 donors and 5 recipients)and ten rats were for OLT+RIPerC(5 donors and 5 recipients).Liver architecture and function were evaluated.Results:Compared to the OLT group,the OLT+RIPerC group exhibited significantly improved liver graft histopathology and liver function(P<0.05).Furthermore,the number of exosomes and the level of P-Akt were increased in the OLT+RIPerC group.Conclusions:RIPerC effectively improves graft architecture and function,and this protective effect may be related to the increased number of exosomes.The upregulation of P-Akt may be involved in underlying mechanisms.

Nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in aerospace community:a comparative analysis

The aerospace community widely uses difficult-to-cut materials,such as titanium alloys,high-temperature alloys,metal/ceramic/polymer matrix composites,hard and brittle materials,and geometrically complex components,such as thin-walled structures,microchannels,and complex surfaces.Mechanical machining is the main material removal process for the vast majority of aerospace components.However,many problems exist,including severe and rapid tool wear,low machining efficiency,and poor surface integrity.Nontraditional energy-assisted mechanical machining is a hybrid process that uses nontraditional energies(vibration,laser,electricity,etc)to improve the machinability of local materials and decrease the burden of mechanical machining.This provides a feasible and promising method to improve the material removal rate and surface quality,reduce process forces,and prolong tool life.However,systematic reviews of this technology are lacking with respect to the current research status and development direction.This paper reviews the recent progress in the nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in the aerospace community.In addition,this paper focuses on the processing principles,material responses under nontraditional energy,resultant forces and temperatures,material removal mechanisms,and applications of these processes,including vibration-,laser-,electric-,magnetic-,chemical-,advanced coolant-,and hybrid nontraditional energy-assisted mechanical machining.Finally,a comprehensive summary of the principles,advantages,and limitations of each hybrid process is provided,and future perspectives on forward design,device development,and sustainability of nontraditional energy-assisted mechanical machining processes are discussed.

Remote ischemic perconditioning prevents liver transplantation-induced ischemia/reperfusion injury in rats: Role of ROS/RNS and e NOS

AIM To investigate the underlying mechanisms of the protective role of remote ischemic perconditioning(RIPerC) in rat liver transplantation. METHODS Sprague-Dawley rats were subjected to sham, orthotopic liver transplantation(OLT), ischemic postconditioning(IPostC) or RIPerC. After 3 h reperfusion, blood samples were taken for measurement of alanine aminotransferase, aspartate aminotransferase, creatinine(Cr) and creatinine kinase-myocardial band(CK-MB). The liver lobes were harvested for the following measurements: reactive oxygen species(ROS), H2O2, mitochondrial membrane potential(ΔΨm) and total nitric oxide(NO). These measurements were determined using an ROS/H2O2, JC1 and Total NOx Assay Kit, respectively. Endothelial NO synthase(e NOS) was analyzed by reverse transcription-polymerase chain reaction(RTPCR) and western blotting, and peroxynitrite was semiquantified by western blotting of 3-nitrotyrosine. RESULTS Compared with the OLT group, the grafts subjected to RIPerC showed significantly improved liver and remote organ functions(P < 0.05). ROS(P < 0.001) including H2O2(P < 0.05) were largely elevated in the OLT group as compared with the sham group, and RIPerC(P < 0.05) reversed this trend. The collapse of ΔΨm induced by OLT ischemia/reperfusion(I/R) injury was significantly attenuated in the RIPerC group(P < 0.001). A marked increase of NO content and phosphoserine eN OS, both in protein and mR NA levels, was observed in liver graft of the RIPer C group as compared with the OLT group(P < 0.05). I/R-induced 3-nitrotyrosine content was significantly reduced in the RIPerC group as compared with the OLT group(P < 0.05). There were no significant differences between the RIPerC and IPostC groups for all the results except Cr. The Cr level was lower in the RIPerC group than in the IPostC group(P < 0.01).CONCLUSION Liver graft protection by RIPerC is similar to or better than that of IPostC, and involves inhibition of oxidative stress and up-regulation of the PI3K/Akt/e NOS/NO pathway.

Mitofusin-2 mediated mitochondrial Ca2+ uptake 1/2 induced liver injury in rat remote ischemic perconditioning liver transplantation and alpha mouse liver-12 hypoxia cell line models

AIM To investigate the protective mechanism of mitofusin-2(Mfn2) in rat remote ischemic perconditioning(RIC) models and revalidate it in alpha mouse liver-12(AML-12) hypoxia cell lines.METHODS Sprague-Dawley rats were divided into three groups(n = 6 each): sham, orthotopic liver transplantation and RIC. After operation, blood samples were collected to test alanine aminotransferase and aspartate aminotransferase. The liver lobes were harvested for histopathological examination, western blotting(WB) and quantitative real-time(q RT)-PCR. AML-12 cell lines were then subjected to normal culture, anoxic incubator tank culture(hypoxia) and anoxic incubator tank culture with Mfn2 knockdown(hypoxia + Si), and data of q RT-PCR, WB, mitochondrial membrane potential(ΔΨm), apoptosis, endoplasmic reticulum Ca2+ concentrations and mitochondrial Ca2+ concentrations were collected.RESULTS Both sham and normal culture groups showed no injury during the experiment. The RIC group showed amelioration of liver function compared with the orthotopic liver transplantation group(P < 0.05). q RTPCR and WB confirmed that Mfn2-mitochondrial Ca2+ uptake 1/2(MICUs) axis was changed(P < 0.005). In AML-12 cell lines, compared with the hypoxia group, the hypoxia + Si group attenuated the collapse of ΔΨm and apoptosis(P < 0.005). The endoplasmic reticulum Ca2+ decrease and mitochondrial Ca2+ overloading observed in the hypoxia group were also attenuated in the hypoxia + Si group(P < 0.005). Finally, q RT-PCR and WB confirmed the Mfn2-MICUs axis change in all the groups(P < 0.005).CONCLUSION Mfn2 participates in liver injury in rat RIC models and AML-12 hypoxia cell lines by regulating the MICUs pathway.

New insights into the biological roles of immune cells in neural stem cells in post-traumatic injury of the central nervous system

Traumatic injuries in the central nervous system,such as traumatic brain injury and spinal cord injury,are associated with tissue inflammation and the infiltration of immune cells,which simultaneously affect the self-renewal and differentiation of neural stem cells.Howeve r,the tissue repair process instigated by endogenous neural stem cells is incapable of restoring central nervous system injuries without external intervention.Recently,resident/peripheral immune cells have been demonstrated to exert significant effects on neural stem cells.Thus,the resto ration of traumatic injuries in the central nervous system by the immune intervention in neural stem cells represents a potential therapeutic method.In this review,we discuss the roles and possible mechanisms of immune cells on the selfrenewal and differentiation of neural stem cells along with the prognosis of central nervous system injuries based on immune intervention.Finally,we discuss remaining research challenges that need to be considered in the future.Further elucidation of these challenges will fa cilitate the successful application of neural stem cells in central nervous system injuries.

Genomic characterization of peritoneal lavage cytology-positive gastric cancer

Objective: Positive peritoneal lavege cytology(CY1) gastric cancer is featured by dismal prognosis, with high risks of peritoneal metastasis. However, there is a lack of evidence on pathogenic mechanism and signature of CY1and there is a continuous debate on CY1 therapy. Therefore, exploring the mechanism of CY1 is crucial for treatment strategies and targets for CY1 gastric cancer.Methods: In order to figure out specific driver genes and marker genes of CY1 gastric cancer, and ultimately offer clues for potential marker and risk assessment of CY1, 17 cytology-positive gastric cancer patients and 31matched cytology-negative gastric cancer patients were enrolled in this study. The enrollment criteria were based on the results of diagnostic laparoscopy staging and cytology inspection of exfoliated cells. Whole exome sequencing was then performed on tumor samples to evaluate genomic characterization of cytology-positive gastric cancer.Results: Least absolute shrinkage and selection operator(LASSO) algorithm identified 43 cytology-positive marker genes, while Mut Sig CV identified 42 cytology-positive specific driver genes. CD3G and CDKL2 were both driver and marker genes of CY1. Regarding mutational signatures, driver gene mutation and tumor subclone architecture, no significant differences were observed between CY1 and negative peritoneal lavege cytology(CY0).Conclusions: There might not be distinct differences between CY1 and CY0, and CY1 might represent the progression of CY0 gastric cancer rather than constituting an independent subtype. This genomic analysis will thus provide key molecular insights into CY1, which may have a direct effect on treatment recommendations for CY1and CY0 patients, and provides opportunities for genome-guided clinical trials and drug development.

Abnormal splenic artery diameter/hepatic artery diameter ratio in cirrhosis-induced portal hypertension

AIM:To determine an optimal cutoff value for abnormal splenic artery diameter/proper hepatic artery diameter(S/P) ratio in cirrhosis-induced portal hypertension.METHODS:Patients with cirrhosis and portal hypertension(n = 770) and healthy volunteers(n = 31) underwent volumetric computed tomography threedimensional vascular reconstruction to measure the internal diameters of the splenic artery and proper hepatic artery to calculate the S/P ratio.The cutoff value for abnormal S/P ratio was determined using receiver operating characteristic curve analysis,and the prevalence of abnormal S/P ratio and associations between abnormal S/P ratio and major complications of portal hypertension were studied using logistic regression.RESULTS:The receiver operating characteristic analysis showed that the cutoff points for abnormal splenic artery internal diameter and S/P ratio were > 5.19 mm and > 1.40,respectively.The sensitivity,specificity,positive predictive value,and negative predictive value were 74.2%,45.2%,97.1%,and 6.6%,respectively.The prevalence of an abnormal S/P ratio in the patients with cirrhosis and portal hypertension was 83.4%.Patients with a higher S/P ratio had a lower risk of developing ascites [odds ratio(OR) = 0.708,95%CI:0.508-0.986,P = 0.041] and a higher risk of developing esophageal and gastric varices(OR = 1.483,95%CI:1.010-2.175,P = 0.044) and forming collateral circulation(OR = 1.518,95%CI:1.033-2.230,P = 0.034).After splenectomy,the portal venous pressure and maximum and mean portal venous flow velocities were reduced,while the flow rate and maximum and minimum flow velocities of the hepatic artery were increased(P < 0.05).CONCLUSION:The prevalence of an abnormal S/P ratio is high in patients with cirrhosis and portal hypertension,and it can be used as an important marker of splanchnic hemodynamic disturbances.

Influence of perfusate on liver viability during hypothermic machine perfusion

AIM: To optimize the perfusates used for hypothermicmachine perfusion(HMP).METHODS: Sprague-Dawley rats were assigned randomly to three groups(n = 12 per group) that received either saline, University of Wisconsin coldstorage solution(UW) or histidine-tryptophan-ketoglutarate solution(HTK) as the perfusate. Each group was divided into two subgroups: static cold storage(SCS) and HMP(n = 6 per subgroup). The liver graft was retrieved according to the method described by Kamada. For the SCS group, the graft was directly placed into cold perfusate(0-4?℃) for 6 h after liver isolation while the portal vein of the graft was connected to the perfusion machine for the HMP group. Then the perfusates were collected at different time points for analysis of aspartate aminotransferase(AST), alanine transaminase(ALT) and lactate dehydrogenase(LDH) levels. Liver tissues were obtained for evaluation of histology, dry/wet weight(D/W) ratio, and malondialdehyde(MDA) and adenosine-triphosphate(ATP) levels. The portal vein pressure and velocity were monitored in real time in all HMP subgroups.RESULTS: Comparison of HMP and SCS: Regardless of the perfusate, HMP improved the architecture of donor graft in reducing the congestion around sinusoids and central vein and maintaining sinusoid lining in morphology; HMP improved liver function in terms of ALT, AST and LDH, especially during the 3-6 h period(SCS vs HMP using saline: ALT3, 225.00 ± 105.62 vs 49.50 ± 18.50, P = 0.047; LDH3, 1362.17 ± 563.30 vs 325.75 ± 147.43, P = 0.041; UW: LDH6, 2880.14 ± 948.46 vs 2135.00 ± 174.27, P = 0.049; HTK, AST6, 307.50 ± 52.95 vs 185.20 ± 20.46, P = 0.041); HMP decreased MDA level(saline, 2.79 ± 0.30 vs 1.09 ± 0.09, P = 0.008; UW, 3.01 ± 0.77 vs 1.23 ± 0.68, P = 0.005; HTK, 3.30 ± 0.52 vs 1.56 ± 0.22, P = 0.006). Comparison among HMP subgroups: HTK showed less portal vein resistance than UW and saline(vs saline, 3.41 ± 0.49 vs 5.00 ± 0.38, P < 0.001; vs UW, 3.41 ± 0.49 vs 4.52 ± 0.63, P = 0.007); UW reduced edema most efficiently(vs saline, 0.68 ± 0.02 vs 0.79 ± 0.05, P = 0.013), while HTK maintained ATP levels best(vs saline, 622.60 ± 29.11 vs 327.43 ± 44.66, P < 0.001; vs UW, 622.60 ± 29.11 vs 301.80 ± 37.68, P < 0.001).CONCLUSION: HMP is superior to SCS in maintaining both architecture and function of liver grafts. Further, HTK was found to be the optimal perfusate for HMP.

Pt supported on Zn modified silicalite-1 zeolite as a catalyst for n-hexane aromatization

Platinum(Pt)supported on Zinc(Zn)modified silicalite-1(S-1)zeolite(denoted as Pt-Zn/S-1)was prepared by using a wetness-impregnation method and applied in the n-hexane aromatization reaction for the first time.Both Lewis and Bronsted acid sites were detected in Pt-Zn/S-1 catalyst by means of FT-IR adsorption of NH3 experiment,which were identified as mostly weak and medium ones.Besides,Pt and Zn species showed strong interaction,as revealed by the TPR(Temperature-programmed reduction)and XPS(X-ray photoelectron spectroscopy)experiments.Pt-Zn/S-1 catalyst exhibited excellent aromatization function rather than isomerization and cracking side reactions in the conversion of n-hexane.Pulse experimental study showed that 75.6%of n-hexane conversion and 76.8%of benzene selectivity were obtained over Pt0.1-Zn60/S-l catalyst at 550℃ and under atmospheric pressure.By spectroscopy tests and pulse experimental results,it was concluded that the n-hexane aromatization over Pt-Zn/S-1 catalyst follows a metal-acid bifunctional mechanism.Furthermore,with the assistance of Zn,the electron-deficient Pt species in Pt-Zn/S-1 showed good sulfur tolerance performance.

Theoretical and numerical study of hydraulic characteristics of orifice energy dissipator

Different factors affecting the efficiency of the orifice energy dissipator were investigated based on a series of theoretical analyses and numerical simulations. The main factors investigated by dimension analysis were identified, including the Reynolds number （Re）, the ratio of the orifice diameter to the inner diameter of the pipe （ did ）, and the ratio of distances between orifices to the inner diameter of the pipe （ LID ）. Then, numerical simulations were conducted with a k-ε two-equation turbulence model. The calculation results show the following： Hydraulic characteristics change dramatically as flow passes through the orifice, with abruptly increasing velocity and turbulent energy, and decreasing pressure. The turbulent energy appears to be low in the middle and high near the pipe wall. For the energy dissipation setup with only one orifice, when Re is smaller than 105, the orifice energy dissipation coefficient K increases rapidly with the increase of Re. When Re is larger than l05, K gradually stabilizes. As diD increases, K and the length of the recirculation region L1 show similar variation patterns, which inversely vary with diD. The function curves can be approximated as straight lines. For the energy dissipation model with two orifices, because of different incoming flows at different orifices, the energy dissipation coefficient of the second orifice （K2） is smaller than that of the first. If LID is less than 5, the K value of the LID model, depending on the variation of/（2, increases with the spacing between two orifices L, and an orifice cannot fulfill its energy dissipation function. If LID is greater than 5, K2 tends to be steady; thus, the K value of the LID model gradually stabilizes. Then, the flow fully develops, and L has almost no impact on the value of K.

In situ synthesis of a spherical covalent organic framework as a stationary phase for capillary electrochromatography

Covalent organic frameworks(COFs)are a novel type of crystalline porous organic polymer materials recently developed.It has several advantages in chromatographic separation field,such as high thermal stability,porosity,structural regularity,and large specific surface area.Here,a novel spherical COF 1,3,5-tris(4-aminophenyl)benzene(TAPB)and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde(BPTA)was developed as an electrochromatographic stationary phase for capillary electrochromatography separation.The COF TAPB-BPTA modified capillary column was fabricated via a facile in situ growth method at room temperature.The characterization results of scanning electron microscopy(SEM),Fourier transform infrared(FT-IR)spectroscopy,and X-ray diffraction(XRD)confirmed that COF TAPB-BPTA were successfully modified onto the capillary inner surface.The electrochromatography separation performance of the COF TAPB-BPTA modified capillary was investigated.The prepared column demonstrated outstanding separation performance toward alkylbenzenes,phenols,and chlorobenzenes compounds.Furthermore,the baseline separations of non-steroidal anti-inflammatory drugs(NSAIDs)and parabens with good efficiency and high resolution were achieved.Also,the prepared column possessed satisfactory precision of the intra-day runs(n=5),inter-day runs(n=3),and parallel columns(n=3),and the relative standard deviations(RSDs)of the retention times of tested alkylbenzenes were all less than 2.58%.Thus,this new COF-based stationary phase shows tremendous application potential in chromatographic separation field.

A Novel Tuning Method for Predictive Control of VAV Air Conditioning System Based on Machine Learning and Improved PSO

The variable air volume(VAV)air conditioning system is with strong coupling and large time delay,for which model predictive control(MPC)is normally used to pursue performance improvement.Aiming at the difficulty of the parameter selection of VAV MPC controller which is difficult to make the system have a desired response,a novel tuning method based on machine learning and improved particle swarm optimization(PSO)is proposed.In this method,the relationship between MPC controller parameters and time domain performance indices is established via machine learning.Then the PSO is used to optimize MPC controller parameters to get better performance in terms of time domain indices.In addition,the PSO algorithm is further modified under the principle of population attenuation and event triggering to tune parameters of MPC and reduce the computation time of tuning method.Finally,the effectiveness of the proposed method is validated via a hardware-in-the-loop VAV system.

A benzenesulfonic acid-modified organic polymer monolithic column with reversed-phase/hydrophilic bifunctional selectivity for capillary electrochromatography

Here,a styrene-based polymer monolithic column poly(VBS-co-TAT-co-AHM)with reversed-phase/hydrophilic interaction liquid chromatography(RPLC/HILIC)bifunctional separation mode was success-fully prepared for capillary electrochromatography by the in situ polymerization of sodium p-styrene sulfonate(VBS)with cross-linkers 3-(acryloyloxy)-2-hydroxypropyl methacrylate(AHM)and 1,3,5-triacryloylhexahydro-1,3,5-triazine(TAT).The preparation conditions of the monolith were optimized.The morphology and formation of the poly(VBS-co-TAT-co-AHM)monolith were confirmed by scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FT-IR).The separation perfor-mances of the monolith were evaluated systematically.It should be noted that the incorporation of VBS functional monomer can provideπ-πinteractions,hydrophilic interactions,and ion-exchange in-teractions.Hence,the prepared poly(VBS-co-TAT-co-AHM)monolith can achieve efficient separation of thiourea compounds,benzene series,phenol compounds,aniline compounds and sulfonamides in RPLC or HILIC separation mode.The largest theoretical plate number for N,N0-dimethylthiourea reached 1.7×10^(5)plates/m.In addition,the poly(VBS-co-TAT-co-AHM)monolithic column showed excellent reproducibility and stability.This novel monolithic column has great application value and potential in capillary electrochromatography(CEC).

基于增强相分布均匀性的颗粒增强铝基复合材料的强化机制（英文）

提出一种用于描述颗粒增强铝基复合材料屈服强度的综合强化模型。基于复合材料显微组织及压缩力学性能检测,对铝基复合材料的强化机制进行研究。为了精确地描述增强相分布均匀性和不同位错强化机制间的协同关系对强化效果的影响,在综合强化模型中引入颗粒分布均匀性因子u和协同系数f_c。结果表明,本研究提出的综合强化模型预测结果与实验结果吻合很好,可以精确地描述Al_3Ti/2024 Al复合材料的屈服强度,理论与实验误差小于1.2%,其预测精度远高于现有综合强化模型的预测精度。该模型也可适用于预测具有不同比例增强相的Al_3Ti/2024 Al复合材料的屈服强度。

超声造影在疑似胸壁结核患者穿刺活检术中的应用价值

目的探讨超声造影在疑似胸壁结核患者穿刺活检术中的应用及其临床价值。方法选取2017年4月至2019年6月入住浙江省中西医结合医院的疑似胸壁结核(均局部形成肿块)患者78例,男31例,女47例;年龄18~67岁,平均年龄(33.8±4.7)岁。依据时间对照法,将患者分为两组:A组42例,2017年4月至2018年5月入住我院的疑似胸壁结核患者,依据超声扫描所示行超声引导下组织学穿刺活检术,并对无回声区行穿刺抽液术;B组36例,2018年1月至2019年6月入住我院的疑似胸壁结核患者,先行超声造影,依据超声造影表现在超声选择性引导下行穿刺抽液术或组织学穿刺活检术。对所有患者的超声表现及病理结果进行回顾性分析。两组患者获取的组织标本送病理检查,同时送MTB、普通细菌培养及GeneXpert MTB/RIF检测。结果 A组:42例患者穿刺取出脓液的成功率为77.4%(24/31),获取活检组织标本的成功率为88.1%(37/42)。B组:36例患者穿刺取出脓液的成功率为100.0%(23/23),获取活检组织标本的成功率为100.0%(36/36),较A组均明显提高(χ^2值分别为4.132和2.814,P值分别为0.001和0.003)。A、B两组患者诊断为胸壁结核在内所有疾病的诊断阳性率分别为83.3%(35/42,其中确诊为胸壁结核33例)和100.0%(36/36,其中确诊为胸壁结核34例),B组较A组诊断阳性率明显提高(χ^2=4.713,P=0.001)。结论超声造影在疑似胸壁结核患者穿刺活检术中的临床应用价值突出,对提高诊断阳性率有重要价值。

西部地区上市公司融资租赁影响因素实证分析

融资租赁作为一种融资方式虽然在我国已经又发展几十年之久,但是在具体解决企业融资问题上依然存在较大发展空间。本文首先以关于融资租赁发展比较成熟的三大理论为基础,分析西部地区上市公司釆用融资租赁的影响因素,并提出相应的假设;最后以西部地区上市公司2017年的财务报表数据为依据,进行样本T检验,对理论分析所提出的假设加以验证,根据得出的实证结果提出对策与建议。

MULTIPHOTON MICROSCOPIC IMAGING OF MOUSE INTESTINAL MUCOSA BASED ON TWO-PHOTON EXCITED FLUORESCENCE AND SECOND HARMONIC GENERATION

Multiphoton microscopy(MPM),based on two-photon excited fuorescence and second harmonic generation,enables direct noninvasive visualization of tissue architecture and cell morphology in live tissues without the administration of exogenous contrast agents.In this paper,we used MPM to image the microstructures of the mucosa in fresh,unfixed,and unstained intestinal tissue of mouse.The morphology and distribution of the main components in mucosa layer such as columnar cells,goblet cells,intestinal glands,and a little collagen fibers were clearly observed in MPM images,and then compared with standard H&:E images from paired specimens.Our results indicate that MPM combined with endoscopy and miniaturization probes has the potential application in the clinical diagnosis and in vivo monitoring of early intestinal cancer.

An Improved Repetitive Control Strategy for LCL Grid-Connected Inverter

This paper proposes a cascade repetitive control strategy based on odd internal mode,and combines it with proportional-integral(PI)control to establish a compound repetitive control system for improving the quality of grid connected current of LCL grid connected inverter.More specifically,the proposed method could effectively improve the control effect of grid-connected current of LCL inverter,restrain current harmonics and reduce the distortion rate of grid-connected current.Simulation experiment is conducted to verify the proposed repetitive control strategy,and the verification results show that,compared with traditional PI control,the proposed improved compound repetitive control strategy has a higher response speed,and the steady-state and dynamic performance have also been significantly improved.

境外工程进口材料费用的定量计算方法研究分析

随着国家"一带一路"倡议的大力发展,越来越多的国内基建企业实施"走出去"战略并参与国际基建市场竞争。而当今的境外工程市场竞争日益激烈,投标报价的重要性不言而喻,如何更加准确地做好境外工程的投标报价成为了工程造价领域的新难题。由于境外工程所在地很多为不发达地区,材料较为匮乏,也或者因其生产的材料品质较低,产量不足等原因,从许多项目实践来看,除了地材以外,大部分主要材料需要从其他国家进口。文章基于实际调研数据,着眼于境外工程投标报价中占比最大、重要性最高的部分——进口材料费用,通过对比研究境内外工程材料费用的区别、梳理分析境外工程进口材料费用的组成和影响因素,最终总结整理出一套基本合理可行的境外工程进口材料费用定量计算方法。并利用实际工程案例对其合理性和可行性进行验证,为确定境外工程进口材料费用提供较为客观可靠的依据,进而一定幅度地提高境外工程投标报价准确性。

单壁碳纳米管在单金属层状双氢氧化物上的手性选择性生长

制备具有窄手性分布的单壁碳纳米管(single-walled carbon nanotubes,SWNTs)粉体是实现其潜在应用的基础和前提.本文设计并开发了分别含有单金属钴(Co)和镍(Ni)的层状双氢氧化物(layered double hydroxides,LDHs)催化剂前驱体,利用一氧化碳作为碳源,系统研究了碳纳米管在不同温度下的化学气相沉积合成.在反应气氛下,煅烧后的Co/Mg/Al LDHs催化剂在600℃即可活化,进而选择性生长出小直径、富集(6,5)手性的SWNTs产物.而煅烧后的Ni/Mg/Al LDHs催化剂在600℃的低温下无法活化生长出SWNTs.尽管进一步提升反应温度至700℃能够活化催化剂,但是由于还原形成的Ni纳米粒子在较高反应温度下容易团聚,所得到的SWNTs的手性分布相对较宽.这项工作不仅实现了窄手性分布SWNTs在单金属LDHs上的催化生长,同时还有助于加深对催化剂活化及SWNTs生长机制的理解.