心率恢复性在活动平板试验诊断冠心病中的临床意义

目的探讨心率恢复性(HRR)活动平板试验(TET)中诊断冠心病(CHD)的临床意义。方法选取拟诊冠心病者110例行TET在检查,并于检查后2周内行冠状动脉造影(CAG),以是否植入支架分为支架植入(A组)66例与非支架植入(B组)44例,比较2组TET参数:包括ST段、最大ST/HR斜率(ST/HR)、HRR、收缩压恢复比(rSBP)等。结果A组ST段、ST/RR和rSBP指标均高于B组,差异有统计学意义(P<0.05,P<0.01),而HRR明显低于B组,差异有统计学意义(P<0.01)。比较TET各种指标的诊断价值,ST段指标敏感度最高为93.9%,rSBP敏感度次之为90.9%,最大ST/HR斜率的敏感度为89.4%,HRR敏感度最低为87.9%;HRR特异度为90.9%、正确指数为78.0%。HRR指标与ST指标、最大ST/HR斜率、rSBP结合,敏感度分别为90.1%、86.2%、85.4%,特异度分别为72.3%、77.4%、87.0%。结论HRR有较高的特异度,与其他指标结合可用于冠心病的诊断。

人工分子伴侣系统辅助鸡IL-18重组蛋白复性过程中研究的影响因素

将重组原核表达质粒pGEX-mChIL-18转化宿主细胞大肠杆菌BL21(DE3),并用IPTG于37℃诱导培养获得表达。表达的包涵体经超声波破碎、洗涤后以6 mol/L的盐酸胍溶解,使蛋白彻底变性。然后按照试验设计,考察不同浓度组成的人工分子伴侣体系对不同浓度鸡IL-18重组蛋白复性率的影响。试验结果表明,利用人工分子伴侣系统辅助鸡IL-18重组蛋白的复性存在最佳的条件,优化该条件能够提高该融合蛋白的复性率,且产物都具有良好的生物学活性,为鸡IL-18重组蛋白的进一步应用研究奠定了基础。

油田生产用超分子除垢剂效果评价及机理研究

油田开发过程中产生的无机垢会影响生产开发,导致油田效益下降。针对海上C油田地层条件,通过室内实验与模拟相结合明确无机垢的组成及井下形成位置。之后采用γ-聚谷氨酸等制备中性超分子除垢剂,使用Materials Studio 2020软件分析并明确超分子体系的自组装过程,并对比评价其与传统酸性除垢剂的除垢效果及体系适用范围。最后,通过密度泛函理论(DFT)进行分子模拟,并结合室内实验结果研究分析超分子体系对无机垢的去除机理。结果表明,区块典型井主要在水平井井底生成碳酸钙/镁和碳酸亚铁垢,自制超分子除垢剂对碳酸钙垢、硫酸钙垢和模拟垢的除垢率分别为74.2%、45.1%和65.8%,均明显高于常规除垢剂,且体系可将岩心注入压力恢复12%。超分子除垢剂最佳使用温度为40~90℃,作用时间为12 h。动力学模拟分析认为,虽然空间位阻一定程度影响了超分子体系对离子的吸附,但由于分子间相互作用力更大,超分子体系更容易螯合结垢离子。机理研究表明,体系是通过超分子配位除垢作用、超分子聚集作用和渗透作用的协同进行除垢,具有良好的应用前景。

Microstructure and properties of Cu matrix composites reinforced with surface-modified Kovar particles

The thermal conductivity of Cu/Kovar composites was improved by suppressing element diffusion at the interfaces through the formation of FeWO_(4)coating on the Kovar particles via vacuum deposition.Cu matrix composites reinforced with unmodified(Cu/Kovar)and modified Kovar(Cu/Kovar@)particles were prepared by hot pressing.The results demonstrate that the interfaces of Cu/FeWO_(4)and FeWO_(4)/Kovar in the Cu/Kovar@composites exhibit strong bonding,and no secondary phase is generated.The presence of FeWO_(4)impedes interfacial diffusion within the composite,resulting in an increase in grain size and a decrease in dislocation density.After surface modification of the Kovar particle,the thermal conductivity of Cu/Kovar@composite is increased by 110%from 40.6 to 85.6 W·m^(-1)·K^(-1).Moreover,the thermal expansion coefficient of the Cu/Kovar@composite is 9.8×10^(-6)K^(-1),meeting the electronic packaging requirements.

蛋白质的氧化重折叠

经过近几十年来广泛而深入的研究 ,蛋白质氧化重折叠的机制已得到相当详细的阐明。 1 在已研究过的蛋白质中 ,大多数蛋白质都是沿着多途径而非单一、特定的途径进行氧化重折叠 ,这与折叠能量景观学说是一致的。 2 正是氨基酸残基间的天然相互作用而不是非天然的相互作用控制蛋白质的折叠过程。这一结论与含非天然二硫键的折叠中间体在牛胰蛋白酶抑制剂 (BPTI)折叠中所起的重要作用并非相互排斥 ,因为后者仅仅是进行链内二硫键重排的化学反应所必需 ,与控制肽链折叠无直接关系。 3 根据对BPTI的研究 ,二硫键曾被认为仅仅具有稳定蛋白质天然结构的作用 ,既不决定折叠途径也不决定其三维构象。这一观点不适用于其它蛋白质。对凝乳酶原的研究表明 ,天然二硫键的形成是恢复天然构象的前提。天然二硫键的形成与肽键的正确折叠相辅相成 ,更具有普遍意义。 4 在氧化重折叠的早期 ,二硫键的形成基本上是一个随机过程 ,随着肽链的折叠二硫键的形成越来越受折叠中间体构象的限制。提高重组蛋白质的复性产率是生物技术领域中的一个巨大的挑战。除了分子聚集外 ,在折叠过程中所形成的二硫键错配分子是导致低复性率的另一个主要原因。氧化重折叠机制的阐明为解决此问题提供了有益的启示。如上所述 ,在折叠的后期 。

HIGH STRAIN RATE SU PERPLASTICITY IN SiCp REINFORCED AZ31 MAGNESIUM MATRIX COMPOSITE

Superplasticity of AZ 31 magnesium matrix composites reinforced with 10 vol% SiC（2 μm） particulate i s investigated at temperature range from 365℃ to 565℃ and strain rate from 2.0 8×10-3 to 5.21×10-1 s-1. The maximum total elongation of 228 % is obtained at a strain rate of 2.08×10-1 s-1. The strain rate se nsitivity exponent （m） higher than 0.3, is observed when the strain rate is high er than 10-1 s-1 at 525℃. Increasing the test temperature to 540℃, the maximum total elongation exceeding 195% is achieved at a higher strain rate of 5.21×10-1 s-1 than that at 525℃. SiC in AZ31/SiCp composite ca n fine the matrix grain size. Filament is observed on the fracture surface of th e specimens showing superplasticity.

Polynomial rooting based frequency offset estimation for MIMO OFDM systems

Based on the frequency domain training sequences, the polynomial-based carrier frequency offset （CFO） estimation in multiple-input multiple-output （ MIMO ） orthogonal frequency division multiplexing （ OFDM ） systems is extensively investigated. By designing the training sequences to meet certain conditions and exploiting the Hermitian and real symmetric properties of the corresponding matrices, it is found that the roots of the polynomials corresponding to the cost functions are pairwise and that both meger CFO and fractional CFO can be estimated by the direct polynomial rooting approach. By analyzing the polynomials corresponding to the cost functions and their derivatives, it is shown that they have a common polynomial factor and the former can be expressed in a quadratic form of the common polynomial factor. Analytical results further reveal that the derivative polynomial rooting approach is equivalent to the direct one in estimation at the same signal-to-noise ratio（SNR） value and that the latter is superior to the former in complexity. Simulation results agree well with analytical results.

Compressive behavior of high particle content B_4C/Al composite at elevated temperature

The compressive properties of the aluminum matrix composite reinforced with 55% B4C （volume fraction） particles were characterized using Gleeble 3500 thermal-mechanical testing machine. The compressive stress--strain curves were obtained at the temperature ranging from 298 to 773 K and strain rate ranging from 1×10^（-3） to 5 s ^（-1）. The results showed that the dynamic compressive strength decreased more slowly than the quasi-static compressive strength at elevated temperatures, which was attributed to the different failure modes of the composite under dynamic and quasi-static load. The strain rate sensitivity increased from 0.02 to 0.13 when the temperature increased from room temperature to 773 K, suggesting that the strain rate sensitivity of this type of composite is a function of temperature.

Modification on epoxy-based adhesive

This research adopted four methods to toughen epoxy adhesives. They were liquid hydroxyl group terminated polybutadiene (HTPB) rubber modification, silicon rubber modification, polyacrylate multiplicity elastomer particulates emulsion modification and chemical grafting modification. After modification, the shearing strength and the rupture elongation were tested. The interface and the chemical reaction between the modifiers and the epoxy were analyzed by scanning electron microscope (SEM) and infrared optical spectrum. The results show that the elastomer particulates modification and the chemical grafting modification can reach the better toughening effects.

Approximate Iteration Detection and Precoding in Massive MIMO

Massive multiple-input multiple-output provides improved energy efficiency and spectral efficiency in 5 G. However it requires large-scale matrix computation with tremendous complexity, especially for data detection and precoding. Recently, many detection and precoding methods were proposed using approximate iteration methods, which meet the demand of precision with low complexity. In this paper, we compare these approximate iteration methods in precision and complexity, and then improve these methods with iteration refinement at the cost of little complexity and no extra hardware resource. By derivation, our proposal is a combination of three approximate iteration methods in essence and provides remarkable precision improvement on desired vectors. The results show that our proposal provides 27%-83% normalized mean-squared error improvement of the detection symbol vector and precoding symbol vector. Moreover, we find the bit-error rate is mainly controlled by soft-input soft-output Viterbi decoding when using approximate iteration methods. Further, only considering the effect on soft-input soft-output Viterbi decoding, the simulation results show that using a rough estimation for the filter matrix of minimum mean square error detection to calculating log-likelihood ratio could provideenough good bit-error rate performance, especially when the ratio of base station antennas number and the users number is not too large.

Dielectric characteristics and nonlinear properties of ZnO-polypyrrole composites

The nonlinear properties and frequency characteristics of ZnO-polypyrrole composites were investigated at 200 Hz-5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 ℃. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 k Hz. These parameters fall off by increasing frequency up to 1 k Hz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1 k Hz is related to the Maxwell-Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.

FREQUENCY ESTIMATION OF SINUSIODE FROM WIDEBAND USING SUB-NYQUIST SAMPLING

A novel frequency estimation algorithm for wideband signal with sub-Nyquist sampling is proposed in this paper. With the aid of information provided by the auxiliary delayed sampling channel and the aliased frequency estimation for wideband signal with sub-Nyquist sampling, the frequency aliasing due to sub-Nyquist sampling can be solved. This method can reduce the complexity of the overall hardware at the cost of an auxiliary sampling channel. Furthermore, in order to alleviate the computation burden for its practicability, a more simplified algorithm is put forward and its validity is proved by our numerical simulation results. The Cramer-Rao Lower Bound (CRLB) of the frequency estimation is also derived at the end of this paper.

Generation of low jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates

A novel and simple method to generate low timing jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates is demonstrated in this paper.Two multiple quantum wells distributed feedback laser diodes,were used as the external seeding sources to inject the external photons into a gain-switched Fabry-Perot laser diode.The output wavelengths can be tuned discretely to coincide with any two lasing modes in the gain spectra range of the Fabry-Perot Laser diode,and the output side mode suppression ratio was better than 25 dB.Moreover,the timing jitter of optical pulses was reduced from 1.89 ps to 0.83 ps.It was empirically found that the lowest timing jitter operation occurred when the injected light wavelength is 0.2-0.3 nm shorter than the locked mode of the Fabry-Perot laser diode.To our knowledge,this is the first report of using two DFB laser diodes as a seeding source to reduce pulses jitter and select lasing dual-wavelength simultaneously.

Uncertainty of Slope Length Derived from Digital Elevation Models of the Loess Plateau, China

Although many studies have investigated slope gradient uncertainty derived from Digital Elevation Models(DEMs), the research concerning slope length uncertainty is far from mature. This discrepancy affects the availability and accuracy of soil erosion as well as hydrological modeling. This study investigates the formation and distribution of existing errors and uncertainties in slope length derivation based on 5-m resolution DEMs of the Loess Plateau in the middle of China. The slope length accuracy in three different landform areas is examined to analyse algorithm effects. The experiments indicate that the accuracy of the flat test area is lower than that of the rougher areas. The value from the specific contributing area(SCA) method is greater than the cumulative slope length(CSL), and the differences between these two methods arise from the shape of the upslope area. The variation of mean slope length derived from various DEM resolutions and landforms. The slope length accuracy decreases with increasing grid size and terrain complexity at the six test sites. A regression model is built to express the relationship of mean slope length with DEM resolution less than 85 m and terrain complexity represented by gully density. The results support the understanding of the slope length accuracy, thereby aiding in the effective evaluation of the modeling effect of surface process.

Frequency Effect of Formulaic Sequences on CAF in Academic Writing:Examples from L2 Master’s Theses

This study was conducted to explore the individual uses of formulaic sequence(FS)frequency and their effects on complexity,accuracy,and fluency(CAF)in academic writing.Data was collected from the conclusion sections of a self-compiled corpus of 30 L2 master’s theses.Statistical analysis revealed several notable conclusions.1)Student writers tend to make repetitive use of particular FSs in single texts.2)FS use has a significant frequency effect on fluency,and the high-frequency group slightly outperforms the low-frequency group.3)FS use has a certain frequency effect on accuracy,and the high-frequency group demonstrates the strongest correlation between FS frequency and accuracy.4)FS use has a significant frequency effect on lexical complexity,and the low-frequency group slightly outperforms the high-frequency group.In the low-frequency group,FS use has a significant frequency effect on syntactic complexity as well.Finally,5)The results support Skehan’s trade-off effect,a competition between CAF,which,to a certain degree,is affected by individual uses of FS frequency.The low-frequency group displays a greater trade-off effect than the high-frequency group.

Frame complexity optimized selection for H.264/AVC video coding

To improve the coding performance of H.264/AVC, this paper proposes a rate control scheme composed of a novel flame complexity optimized selection and a quantization parameter （QP） value computation approach. First, it extracts the frame coding complexity from two rate distortion models, and then introduces five statistic modes to estimate the frame coding complexity. An optimal mode is selected according to the coding efficiency. Finally the paper presents a novel QP calculation method for the H.264/AVC rate control. Experimental results show that the proposed algorithra outperforms the algorithm integrated in the 3M model in obtaining precise frame coding complexity, achieving robust buffer control and improving coding quality. And the improving visual quality is high up to 0.90dB for CIF sequences.

Matrix metalloproteinases in the restorative proctocolectomy pouch of pediatric ulcerative colitis

AIM:To investigate matrix metalloproteinases(MMPs) and their tissue inhibitors(TIMPs) in pouch mucosa of pediatric onset ulcerative colitis(UC).METHODS:In this cross-sectional study,28 patients with pediatric onset UC underwent ileal pouch biopsy 13 years(median) after proctocolectomy.Expression of MMPs-3,-7,-8,-9,-12 and-26 and TIMPs-1,-2 and-3 in samples was examined using immunohistochemichal methods,and another biopsy was used to evaluate the grade of histological inflammation.Two investigators independently graded the immunohistochemical specimens in a semiquantitative fashion,using a scale marking staining intensity as follows:0 = less than 20 positive cells;1 = 20-50 positive cells;2 = 50-200 positive cells;3 = over 20 positive cells.Fecal calprotectin and blood inflammatory markers [serum C-reactive protein(CRP) and erythrocyte sedimentation rate] were determined during a follow-up visit to examine correlations between these markers and the expression of MMPs and TIMPs.RESULTS:Of the 28 patients with pediatric onset UC,nine had not experienced pouchitis,whereas thirteen reported a single episode,and six had recurrent pouchitis(≥ 4 episodes).At the time of the study,six patients required metronidazole.In all of the others,the most recent episode of pouchitis had occurred over one month earlier,and none were on antibiotics.Only four samples depicted no sign of inflammation,and these were all from patients who had not had pouchitis.Two samples were too small to determine the grade of inflammation,but both had suffered pouchitis,the other recurrent.No sample depicted signs of colonic metaplasia.Most pouch samples showed expression of epithelial(e) and stromal(s) MMP-3(e,n = 22;s,n = 20),MMP-7(e,n = 28;s,n = 27),MMP-12(e,n = 20;s,n =24),TIMP-2(e,n = 23;s,n = 23) and MMP-3(e,n = 23;s,n = 28) but MMP-8(e,n = 0;s,n = 1),MMP-9(e,n = 0;s,n = 9) and MMP-26(e,n = 0;s,n = 3) and TIMP-1(n = 0,both) were lacking.In samples with low grade of inflammatory activity,the epithelial MMP-3 and MMP-7 expression was increased(r =-0.614 and r =-0.472,respectively,P < 0.05 in both).MMPs and TIMPs did not correlate with the markers of inflammation,fecal calprotectin,erythrocyte sedimentation rate,or CRP,with the exception of patients with low fecal calprotectin(< 100 μg/g) in whom a higher expression of epithelial MMP-7 was found no differences in MMPor TIMP-profiles were seen in patients with a history of pouchitis compared to ones with no such episodes.Anastomosis with either straight ileoanal anastomosis or ileoanal anastomosis with J-pouch did depict differences in MMP-or TIMP-expression.CONCLUSION:The expression of MMPs pediatric UC pouch in the long-term shares characteristics with inflammatory bowel disease,but inflammation cannot be classified as a reactivation of the disease.

Flexural behavior of reinforced concrete beams with high performance fiber reinforced cementitious composites

This article presents an experimental study on the flexural performance of reinforced concrete(RC)beams with fiber reinforced cementitious composites(FRCC)and hybrid fiber reinforced cementitious composites(HFRCC)in the hinge portion.Beam specimens with moderate confinement were used in the study and tested under monotonic loading.Seven diverse types of FRCC including hybrid composites using fibers in different profiles and in different volumes are employed in this study.Companion specimens such as cylindrical specimens and prism specimens are also used to study the physical properties of composites employed.The moment?curvature,stiffness behavior,ductility,crack pattern and modified flexural damage ratio are the main factors considered in this study to observe the efficacy of the employed hybrid composites.The experimental outputs demonstrate the improved post yield behavior with less rate of stiffness degradation and better damage tolerance capacity than conventional technique.

Effect of WS_2 particle size on mechanical properties and tribological behaviors of Cu-WS_2 composites sintered by SPS

The mechanical properties and tribological behaviors of Cu-WS2 composites fabricated by spark plasma sintering（SPS） using two different WS2 particle sizes of 0.6 and 5.0 μm and Cu powders as raw materials were investigated. The results indicate that the bending strength and tribological behavior of Cu-WS2 composites are greatly affected by the size of WS2 particles. The bending strength of Cu-WS2 composites with the WS2 particle size of 5.0 μm is 292.2 MPa. As the size of WS2 particle decreases to 0.6 μm, the bending strength also decreases to 181.5 MPa. Moreover, as the WS2 particle size decreases from 5.0 to 0.6 μm, the wear rate of Cu-WS2 composite sharply increases from 2.99×10^-14 to 6.13×10^-14 m^3/（N·m） and its friction coefficient increases from 0.158 to 0.172. The size of WS2 particle（5.0 μm） plays an important role in forming transfer film formed on the counter-face. The sample with 5.0 μm WS2 particle forms smoother and more continuous transfer film, which results in a low wear rate and friction coefficient of the Cu-WS2 composites.

Thermal decomposition and mechanical properties of hydroxyapatite ceramic

Pure hydroxyapatite（HAP）ceramic and HAP composite ceramic with B2O3 were prepared by isostatic press forming and pressureless sintering.The relationships between thermal decomposition ratio and mechanical properties for pure HAP ceramic and the composite ceramic were investigated by means of FTIR,X-ray diffraction and three-point bending method.The results indicate that the decomposition ratio of pure HAP ceramic increases with ascending the sintering temperature and nearly reaches 80%at 1 350？殆or the HAP composite ceramic,the thermal decomposition is inhibited obviously due to the addition of B2O3.The added B atoms incorporate into the crystal lattice of HAP to form solid solution,resulting in an enlargement in the crystal spacing and an improvement in the binding strength of HAP crystal cell.Thermal decomposition ratio of HAP decreases but bending strength and fracture toughness are enhanced for HAP composite ceramics.However,when the added B2O3 is more than 5%（mass fraction）,HAP decomposition is promoted and a steady？-TCP is formed due to the fact that when B atoms with higher negative electricity are combined with O,sp2 and a full-air p are formed,and those voids have a strong trend to intake of the outer electrons.So,it is very possible to occupy the place where HAP loses OH - or PO4 3- .