提高大反射负载牵引测量准确度研究

针对大反射负载牵引测量过程中,由于矢网系统误差导致的负载牵引测量误差较大问题,提出可行的解决方案。首先,以矢网8项系统误差模型为基础,推导出大反射负载牵引功率增益测量模型。以直通线功率的增益误差和为目标函数,通过优化阻抗点分布、重新构建优化权重函数,实现大反射负载牵引测量准确度的进一步提高。经优化比较,在8 mm频段(负载反射系数模值0.9),系统测量直通线功率增益的最大误差由±1 dB优化到±0.2 dB以内(国内文献报道±0.3 dB),进一步提高在片大反射负载牵引系统测量准确度。此外,通过比较分析,明确反射跟踪误差是影响大反射负载牵引测量准确度的主要系统误差项。

弹性波模拟中局部透射边界的反射特征及参数优化

研究一种新型局部透射边界对弹性波的反射特征,以提高模拟复杂波动问题时的边界精度。此时存在P-P、P-S和S-P、S-S两组(4种)反射,反射系数基于P波和S波势函数定义。将势函数表示的波场转化为u和w分量形式,再代入边界公式,推导出反射系数R_(pp),R_(ps),R_(sp),R_(ss)的表达式。理论分析与数值试验相结合,得出如下研究结果:新型边界的多种计算波速配置能够很好地实现对P,S两种物理波速波动能量的同步吸收;弹性介质自身特性给反射系数带来了附加零反射角度,这对边界精度有利;S-P反射有时会出现异常大值,这会严重破坏边界精度,不过,当大部分(如1/1,2/2,2/3,3/4,3/5,…)人工波速参数被严格设定为S波波速时就不会出现这个问题。

冲击载荷下弹簧质量系统瞬态响应的近似求法

提出了一种冲击载荷下,弹簧质量系统瞬态响应的近似算法,简化了弹簧质量系统的强度分析过程,有 利于对其进一步进行优化设计和可靠性设计.并对机械系统的静强度可靠性设计有一事实上的参考价值.

Numerical analysis of reflective cracking and fatigue lives of semi-rigid pavement structures using ABAQUS and FE-SAFE

In order to compare the impact of thickness of different layers on fatigue lives of different semi-rigid asphalt pavement structures, the mechanical results from finite element models in ABAQUS are incorporated with the fatigue results from fatigue models in FE-SAFE to calculate the mechanical response and fatigue lives of semi-rigid pavement structures under heavy traffic loads. Then the influences on fatigue lives caused by the changes in the thickness of layers in pavement structures are also evaluated. The numerical simulation results show that the aggregated base and the large stone porous mixture （LSPM） base have better anti-cracking performance than the conventional semi-rigid base. The appropriate thickness range for the aggregated layer in the aggregated base is 15 to 18 cm. The thickness of the LSPM layer in the LSPM base is recommended to be less than 15 cm.

Detection of Acid Rain Stress Effect on Plant Using Hyperspectral Data in Three Gorges Region,China

This paper aims to use hyperspectral data to detect the spectral change caused by acid stress to a native forest type in the Three Gorges region of China. For this purpose, a ground-based hyperspectral experiment was conducted at the Three Gorges region to detect acid deposition that caused Masson pine (Pinus massoniana) forest degra-dation. Continuum removal method was used to isolate wavebands more responsive to stress in wavelengths 450-750nm. The differences in chlorophyll concentrations and needle thickness caused by acidic stress are found to be explicable to the different spectral reflectance patterns in the visible and near-infrared wavelengths. Two new chlorotic indices were utilized to explain the stress-caused leaf chlorosis. The comparison of simulated vegetation indices and principal component analysis (PCA) results suggests that it would be possible to monitor acid rain stress effect on forest ecosystem from some wider spectral regions.

Reaction thrust characteristics of high-pressure submerged water jet of cylinder nozzles

The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. The simulation of the flow field characteristics was conducted via the FLUENT computational fluid dynamics package. Effects of the inlet conditions and the nozzle dimensions on the reaction thrust of a water jet were addressed particularly. The reaction thrust experiments were performed on a custom-designed test apparatus. The experimental results reveal that a） the nozzle diameter and the inlet conditions exert great influence on the water jet reaction thrust; and b） for L≤4d0, where the nozzle is treated as a thin plate-orifice, the reaction thrust is independent of nozzle length; for L〉4d0, where the nozzle is treated as a long orifice, the reaction thrust can reach maximum under the condition of a certain flow rate. These findings lay a theoretical foundation for the design of nozzles and have significant value, especially for the future development of high-oressure water-let orooulsion technology.

Observations of Aerosol Optical Properties in the Beijing Urban Area in Summer

To investigate aerosol optical properties in the Beijing metropolitan area, aerosol absorption coefficient （Ab）, scattering coefficient （So）, and fine particulate matter （PM2.5） were measured in the Beijing urban area from 20 May to 30 August 2009. The average Ab, So, single scat- tering albedo （SSA）, and PM2.5 concentration were 58.0±39.5 M m^-1, 343.5±353.7 M m 1, 0.80±0.10 and 63.6＋50.0 μg m^-3, respectively, during the observation period. Ab, Sc, and SSA all showed single peak diurnal variations, with their maximum values being measured at 0500, 1000, and 1300 local time, respectively. Ab and Sc had a strong positive correlation with PM2.5, and Ab, Sc, and PM25 all had positive correlations with relative humidity and negative correlations with wind speed.

Effects of the coupling process on shortwave radiative feedback during ENSO in FGOALS-g

Satisfactory simulation of negative shortwave（SW） radiative feedback during ENSO in the equatorial Pacific remains a challenging issue for climate models. Previous studies have focused on specific physical processes in the atmospheric and/or oceanic model, but the coupling process in coupled models has not received much attention. To investigate the coupling effect on SW feedback, two versions of an AGCM and their corresponding coupled models are analyzed. Results indicate that the effects of the coupling process in the two versions lead to weakening and enhancement of the negative feedback in the earlier and new versions, respectively, mainly due to their different changes in cloud fraction feedback and dynamical feedback. Further examination of the nonlinearity of the feedback reveals that the opposite coupling effects in the two versions originate from their different responses to El Nio and to La Nia.

Impact of Different Aerosols on the Evolution of the Atmospheric Boundary Layer

The present work analyzes the effect of aerosols on the evolution of the atmospheric boundary layer (ABL) over Shangdianzi in Beijing.A one-dimensional ABL model and a radiative transfer scheme are incorporated to develop the structure of the ABL.The diurnal variation of the atmospheric radiative budget,atmospheric heating rate,sensible and latent heat fluxes,surface and the 2 m air temperatures as well as the ABL height,and its perturbations due to the aerosols with different single-scattering albedo (SSA) are studied by comparing the aerosol-laden atmosphere to the clean atmosphere.The results show that the absorbing aerosols cause less reduction in surface evaporation relative to that by scatting aerosols,and both surface temperature and 2 m temperature decrease from the clean atmosphere to the aerosol-laden atmosphere.The greater the aerosol absorption,the more stable the surface layer.After 12:00 am,the 2 m temperature increases for strong absorption aerosols.In the meantime,there is a slight decrease in the 2 m temperature for purely scattering aerosols due to radiative cooling.The purely scattering aerosols decrease the ABL temperature and enhance the capping inversion,further reducing the ABL height.

Seismic volcanostratigraphy of large, extrusive complexes in continental rift basins of Northeast China：Analysis of general bedding patterns in volcanostratigraphy and their seismic reflection configurations

The aim of this work is to establish volcanic seismic reflection configuration models in the rift basins of Northeast China from a new perspective,the volcanostratigraphic structure.Accordingly,the volcanostratigraphic structure of an outcrop near the Hailaier Rift Basin was analyzed to understand the characteristics and causal factors of physical boundaries.Further,3D seismic reflection data and analysis of deep boreholes in the Songliao Rift Basin were used to establish the relationship between volcanic seismic reflection configurations and volcanostratigraphic structures.These studies suggested that in volcanic successions,physical boundaries coincide with volcanic boundaries,and their distributions are controlled by the stacking patterns of volcanic units.Therefore,volcanic seismic reflection configurations can be interpreted in terms of the stacking patterns of volcanic units.These are also referred to as general bedding patterns in volcanostratigraphy.Furthermore,four typical seismic reflection configurations were identified,namely,the chaotic,the parallel continuous,the hummocky,the multi-mound superimposed and the composite.The corresponding interpretation models comprised single massive unit,vertical,intersectional,lateral multi-mound,and composite stacking patterns.The hummocky and composite reflection configurations with intersectional and composite stacking patterns are the most favorable for the exploration of volcanic reservoirs in rift basins.

Design of fiber-optic collector for spectrometer based on curved mirror

To enlarge the detection range of traditional fiber-optic spectrometer,two rotating parabolic mirrors were first used in the design of fiber-optic collector for spectrometer,which can extend the detection range of spectrometer from centimeter-scale to50m,as a super-low altitude remote sensing detector under passive lighting conditions.According to the performance requirements of fiber-spectrometer for optical collector,this study deduced the calculation formulae of design size of parabolic optical collector applied to different sensitivity spectrometers,different detection targets,different detection ranges and different weathers.Based on the calculation results,the model of fiber-optic collector with a diameter of16mm and a height of7.8mm was designed by ZEMAX.And then,TracePro,a light simulation software,was applied to ray tracing.The simulation results of optical radiation magnification agrees well with theoretical value,and the relative error is less than0.78%.This optical collector can effectively extend the detection range of spectrometer and expand its application fields and scopes.Compared with traditional refractive optical collector,it has several advantages of compact structure,low weight and low cost.

Chemical Composition of Summertime PM_(2.5) and Its Relationship to Aerosol Optical Properties in Guangzhou,China

Urban aerosols have a large effect on the deterioration of air quality and the degradation of atmospheric visibility.Characterization of the chemical composition of PM 2.5 and in situ measurements of the optical properties of aerosols were conducted in July 2008 at an urban site in Guangzhou,Southern China.The mean PM 2.5 concentration for the entire period was 53.7±23.2 μg m 3.The mean PM 2.5 concentration (82.7±25.4 μg m 3) on hazy days was roughly two times higher than that on clear days (38.8±8.7 μg m 3).The total water-soluble ion species and the total average carbon accounted for 47.9%±4.3% and 35.2%±4.5%,respectively,of the major components of PM 2.5.The increase of secondary and carbonaceous aerosols,in particular ammonium sulfate,played an important role in the formation of haze pollution.The mean absorption and scattering coefficients and the single scattering albedo over the whole period were 53±20 M m 1,226±111 M m 1,and 0.80±0.04,respectively.PM 2.5 had a high linear correlation with the aerosol extinction coefficient,elemental carbon (EC) was correlated with aerosol absorption,and organic carbon (OC) and SO 4 2 were tightly linked to aerosol scattering.

10-Gb/s Transmission in WDM PON Employing Reflective Semiconductor Optical Amplifier and Fibre Bragg Grating Equaliser

We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.

Nitric oxide inhibits excitatory vagal afferent input to nucleus tractus solitarius neurons in anaesthetized rats

Objective Endogenous nitric oxide （NO） has been implicated in the regulation of neuronal activity which mediates cardiovascular reflexes. However, there is controversy concerning the role of NO in the nucleus tractus solitarius （NTS）. The present study aims to elucidate the possible physiological role of endogenous NO in modulating the excitatory vagal afferent input to NTS neurons. Methods All the experiments in the rat were conducted under anaesthetic conditions. Ionophoresis method was used for the application of NO donor or nitric oxide synthase （NOS） inhibitor, and single unit recording method was employed to detect the effects of these applications on vagal afferentor cardio-pulmonary C-fibre reflex-evoked neuronal excitation in NTS. Results Ionophoresis applications of L-arginine （L-Arg）, a substrate of NOS, and sodium nitroprusside （SNP）, a NO donor, both attenuated the vagal afferent-evoked discharge by （51.5±7.6）% （n = 17） and （68.3±7.1）% （n = 9）, respectively. In contrast, application of D-Arg at the same current exerted no overall effect on this input. Also, both L-Arg and SNP inhibited spontaneous firing of most of the recorded neurons. In contrast, ionophoresis application of NG-nitro-Larginine methyl ester （L-NAME） enhanced vagal afferent-evoked excitation by （66.3±11.4）% （n = 7）. In addition, ionophoresis application of L-Arg and SNP significantly attenuated cardio-pulmonary C-fibre reflex-induced excitation in the tested NTS neurons. Conclusion Activation of local NO pathway in the NTS could suppress vagal afferent-evoked excitation, suggesting that NO is an important neuromodulator of visceral sensory input in the NTS.

Retrieval of aerosol optical depth over bright targets in the urban areas of North China during winter

Two factors that affect satellite retrieval of Aerosol Optical Depth(AOD) are aerosol model assumptions and the separation of surface reflectance.NASA/MODIS Dense Dark Vegetation(DDV) algorithm has been proven valuable in deriving aerosol distribution and properties over land;however,it cannot be applied to bright targets.As a supplement to the DDV algorithm,an algorithm to retrieve AOD over urban areas in North China in winter is developed using MODIS data,including(1) the generation and analysis of adjacent clear-days surface reflectance using MOD09 product from 2007 to 2008,and(2) seasonal aerosol models derived from AERONET data in Beijing and Xianghe sites.Ground-based measurements using sun photometers were used to validate the retrieved AOD,and the correlation coefficient(r) is up to 0.931.Especially for high AOD values(AOD>0.4),more retrievals meet the inversion accuracy.The temporal variations of retrieval errors over urban,rural and mountain regions were examined,and the results indicated that the variation of blue-band surface reflectance is less than 0.02 in a short period except for unusual weather conditions,the retrieval bias is under 0.08,and the relative error decreases as the AOD increases.

The crustal structures of the central Longmenshan along and its margins as related to the seismotectonics of the 2008 Wenchuan Earthquake

In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008,which occurred in the central part of the Longmenshan.The profile also passes through the northwestern Sichuan Plateau,along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded.Seismic wave phase records that reflect the structural characteristics of different tectonic blocks,especially the complicated phase features associated with the Wenchuan earthquake,were calculated and analyzed in detail.A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined,and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were characterized.Lithological variations within the upper and lower crust in the interior of the plateau,especially a great velocity decrease and plastic rheological properties associated with strong lithologic weakening in lower crust,were detected.From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau,a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part;this is inferred to be related to the fault systems in the central Longmenshan.An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement beneath a central fault system in the Longmenshan.The data,combined with an understanding of the regional tectonic stress field and previous geological results,enable a discussion of basin-and-range coupling,orogenic tectonics,the crustal fault system,and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.

Determining maximum shear stress in confined substrate from elastic wave reflection coefficient

The relationship between the maximum shear stress in a substrate solid and the elastic wave reflection coefficient from the interface between the substrate solid and an overlying solid half-space is investigated. Both substrate and overlying solid media are assumed to be initially isotropic and stress-free. Then as the substrate is subjected to horizontal confined stresses it becomes anisotropic. It is shown that longitudinal and shear wave reflection coefficients are related to the degree of stress induced anisotropy in the substrate medium. From this relation the confined stress level and the maximum shear stress generated on the vertical planes of the substrate are estimated. Authors in their previous investigation computed plane wave reflection coefficient in a biaxially compressed solid substrate immersed in a fluid. This paper reports for the first time how the maximum shear stress in a biaxially compressed substrate medium can be measured from the plane wave reflection coefficients when the overlying medium is also a solid half-space.

Global Solutions of Shock Reflection by Wedges for the Nonlinear Wave Equation

When a plane shock hits a wedge head on, it experiences a reflection-diffraction process and then a self-similar reflected shock moves outward as the original shock moves forward in time. In this paper, shock reflection by large-angle wedges for compressible flow modeled by the nonlinear wave equation is studied and a global theory of existence, stability and regularity is established. Moreover, C^0,1 is the optimal regularity for the solutions across the degenerate sonic boundary.

An Interrogation System Based on Two Semiconductor Optical Amplifiers for Weak Fiber Bragg Gratings

An interrogation system based on two semiconductor optical amplifiers for weak fiber Bragg gratings （FBGs） was proposed. The first semiconductor optical amplifier （SOA） was used to modulate the light, and the second SOA separated the reflected signal from the different FBGs through delayed switching. The proposed system has lower insertion loss and higher spatial resolution, and can interrogate the time- and wavelength-division multiplexed FBG array. Up to 50 FBGs, with a reflectivity of 0.2% and a spatial resolution of 5 m along the optical fiber, were distinguished to demonstrate the interrogation system.