基于环境一号卫星的霾监测应用

随着我国城市的发展,霾已经成为大气污染的重要形式。从霾的物理性质出发,利用米理论和RT3计算了霾的光学性质和反射特性,表明环境一号(HJ-1)卫星CCD相机的第一和第二波段最适宜霾的反演。然后,利用深蓝算法,基于MODIS地表反射率产品建立地表反射率库,实现霾的反演。最后,以北京为试验区进行了2009年全年的反演试验,结合地面观测结果的验证表明,HJ-1监测结果与地面结果有着较好的相关性(相关系数大于0.9),但整体大于地面监测结果。讨论表明,地表反射率库的误差对区分霾影响较小(带来的霾光学厚度误差小于0.1),HJ-1的CCD传感器的辐射分辨率尚不能完全满足霾监测需求。     

Affirming nonlinear optical coefficient constancy from z-scan measurement

Goodness of fit is demonstrated for theoretical calculation of z-scan data based on beams propagating in the nonlinear medium and the Fresnel–Kirchhoff diffraction integral in experiments with high nonlinear refraction and absorption. The constancy of nonlinear optical parameters is achieved regardless of sample thickness and laser intensity, which clarifies the physical significance of optical parameters. We have obtained γ = 2.0 × 10-19 m2/W and β = 5.0 × 10-13 m/W for carbon disulfide excited by a pulsed laser at 800 nm with pulse duration of 35 fs,which are independent of sample thickness and laser intensity. Affirming constancy of the extracted parameters to the incident light intensity may become a practice to verify the goodness of the z-scan experiment.     

Periodic composites: quasi-uniform heat conduction,Janus thermal illusion,and illusion thermal diodes

Manipulating thermal conductivities at will plays a crucial role in controlling heat flow. By developing an effective medium theory including periodicity, here we experimentally show that nonuniform media can exhibit quasi-uniform heat conduction. This provides capabilities in proposing Janus thermal illusion and illusion thermal rectification. For the former, we study, via experiment and theory, a big periodic composite containing a small periodic composite with circular or elliptic particles. As a result, we reveal the Janus thermal illusion that describes the whole periodic system with both invisibility illusion along one direction and visibility illusion along the perpendicular direction, which is fundamentally different from the existing thermal illusions for misleading thermal detection. Further, the Janus illusion helps to design two different periodic systems that both work as thermal diodes but with nearly the same temperature distribution, heat fluxes and rectification ratios, thus being called illusion thermal diodes. Such thermal diodes differ from those extensively studied in the literature, and are useful for the areas that require both thermal rectification and thermal camouflage. This work not only opens a door for designing novel periodic composites in thermal camouflage and heat rectification, but also holds for achieving similar composites in other disciplines like electrostatics, magnetostatics, and particle dynamics.     

Ear and pitch segregation in Deutsch's octave illusion persist following switch from stimulus alternation to repetition

Deutsch's octave illusion occurs when two tones that are spaced an octave apart are repeatedly presented in alternation; the sequence is presented to both ears simultaneously but offset by one tone, so that two dichotic chords are repeatedly presented in alternation. The most common illusory percept consists of an intermittent high tone in one ear alternating with an intermittent low tone in the other ear. The aim of this study was to investigate whether, once the illusory percept has emerged, the illusion will persist when the original sequence is followed by another sequence consisting of the repeated presentation of one of the two dichotic chords. Forty nai?ve subjects were tested with stimuli consisting first of a priming sequence containing dichotic octaves alternating between ears followed immediately by a test sequence consisting of a single dichotic octave presented repeatedly. The durations of the priming and test sequences were manipulated. The findings showed that the illusory percept is maintained after the switch from alternation to repetition and that the relative length of the priming and test sequences has a negligible influence on the persistence of the illusory percept.     

Lightness Change as Perceived in Relation to the Size of Recognized Visual Space of Illumination

According to the concept of the recognized visual space of illumination (RVSI) the lightness of an object surface is perceived in relation to its conceptualized size. To prove this proposition the lightness of gray test patches was judged when they were located at various positions inside an illuminated space composed of two rooms in the depth direction from a subject. No retinal image arrangement was changed in the test patch and its immediate surroundings, but the front room had walls, floors and furniture lower in lightness by the amount of N1.5 than the back room to make the RVSI of the former smaller despite the illuminance in the entire space being the same. The results showed that the apparent lightness of the patches was perceived higher by amount of about 13 in L units for the N4 test patch and about 20 for N6 when the patches were located in the front room, in accordance with the prediction. It was stressed that the experiment of lightness judgment should be conducted in a three dimensional space rather than two dimensional plane as done by several investigators.     

Quantifying the auditory saltation illusion: an objective psychophysical methodology

Under conditions of rapid presentation, brief acoustic stimuli repeatedly delivered first at one location, then at another, are systematically mislocalized, with stimuli perceived as traveling smoothly between the two locations. This robust illusory motion percept is termed "auditory saltation." Currently, the characteristics and mechanisms of auditory saltation are not well understood. The lack of objective methods capable of quantifying the illusion on an individual basis seems a limiting factor for this area of research. In this study, we outline an objective psychophysical task that estimates the interstimulus interval at which the saltation illusion is reliably distinguishable from simulated motion. Experiment 1 examined the psychophysical function relating task performance to ISI and addressed the suitability of the task for use with adaptive psychophysical procedures. Experiment 2 directly compared performance on the task with that of another quantification method. The results suggested that this objective approach to the study of auditory saltation overcomes difficulties associated with more subjective methods, and provides a reliable paradigm within which to quantify the temporal parameters of saltation on an individual basis.     

Conductivity enhancement in carbonate-based composite electrolytes: an ongoing illusion

The recently claimed conductivity enhancement in alkali carbonate-based composite electrolytes and the conductivity enhancement ascribed to heterogeneous-phase mixtures of solid alkali carbonates are unreasonable and violate established knowledge.     

Interior radiances in optically deep absorbing media—III. Scattering from haze L

The interior radiances are calculated within an optically deep absorbing medium scattering according to the Haze L phase function. The dependence on the solar zenith angle, the single scattering albedo, and the optical depth within the medium is calculated by the matrix operator method. The development of the asymptotic angular distribution of the radiance in the diffusion region is illustrated through a number of examples; it depends only on the single scattering albedo and on the phase function for single scattering. The exact values of the radiance in the diffusion region are compared with values calculated from the approximate equations proposed by Van de Hulst. The variation of the radiance near the lower boundary of an optically thick medium is illustrated with examples. The attenuation length is calculated for various single scattering albedos and compared with the corresponding values for Rayleigh scattering. The ratio of the upward to the downward flux is found to be remarkably constant within the medium. The heating rate is calculated and found to have a maximum value at an optical depth of two within a Haze L layer when the sun is at the zenith. The location of this maximum moves toward the top of the haze layer as the solar zenith angle increases and also as the single scattering albedo decreases. When the single scattering albedo is less than 0·8, the downward flux is so small within the diffusion region that experimental measurements are probably not possible.     

Nitrate removal from groundwater using Amberlite IRN-78: Modelling the system

A laboratory study was conducted to investigate the ability of Amberlite IRN-78 ion-exchange resin for the removal of nitrate from different waters. Aim of the present study is to propose a simple model that simulates the equilibrium data for this ion-exchange system.Tests were performed using two synthetic waters and two groundwaters. In the case of synthetic water, experimental data are reported for the ion-exchange equilibria determination in the absence or presence of chloride. For both groundwater types, “Salvatierra city” and “Miajadas city”, an ion-exchange Langmuir-type model is proposed, taking into account the presence of other competitive anions in solution, specifically chloride, sulphate and bicarbonate. Although the model is very simple, it is consistent with the experimental results. Finally, a general Langmuir-type expression is proposed for all water types, synthetic or natural. This equation considers the presence of other anions in solution by means of the parameter C_0T.     

Sonochemical removal of trihalomethanes from aqueous solutions

In this research, ultrasound irradiation was employed to degrade the trihalomethanes, THMs: CHCl₃, CHBrCl₂, CHBr₂Cl, CHBr₃, and CHI₃. The kinetics reaction rates and removal efficiencies of the THMs compounds, as a sole component in the aqueous solutions, were studied. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and acoustic intensity of 3.75 W/cm². The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of CHCl₃ > CHBrCl₂ > CHBr₂Cl > CHBr₃ > CHI₃. Up to 100% of the CHCl₃ was removed, while only 60% of the CHI₃ was sonodegraded, after 180 min sonication. The THMs vapor pressure was found to be the most important parameter affecting the sonodegradation kinetics and efficiency, while the bond dissociation energy and hydrophilic/hydrophobic characteristics of the THMs compounds were found to be of secondary importance.     

Laser removal of mold growth from paper

Femtosecond laser nano-processing by enhanced light scattered from nanospheres has received much attention. Enhanced scattered near field enables us to ablate nanoholes at nanometer scales below the diffraction limit. In addition, the interference between the scattered far field and the irradiated laser enables us to fabricate spatially controlled periodic surface structures. In this paper, we simulated the time evolution of scattered near field and far field during the free electron excitation in silicon (Si) by femtosecond laser irradiation. The optical property of Si changes from dielectric to metal-like Si due to the increase of the free electron number density excited by femtosecond laser pulse. It is elucidated that the scattered field of Si shifts from Mie scattering to plasmonic scattering during laser irradiation. We achieved the optimal free electron density and laser intensity for precisely controlled periodic surface structures fabrication. We explained the temporal behavior of the scattering near field and far field from the standpoint of dielectric function of the materials.     

Ultrashort light pulses generated from modulation instability: background removal and soliton content

Modulation instability can be used to convert a continuous light wave into a train of pulses on a constant background. It is a longstanding discussion whether these pulses can be converted into solitons. We clarify the situation by using a more general mathematical context, invoking the Akhmediev breather, Peregrine soliton and Kuznetsov-Ma soliton solutions of the wave equation, and suggest the use of a Mach–Zehnder interferometer to remove the background. Expressions for the pulse widths and peak powers thus obtained are presented, and their soliton content is determined. It turns out that more than 95 % of each pulse’s energy can be converted to a soliton.     

Random removal of edges from scale free graphs

It has been discovered that many naturally occurring networks (the internet, the power grid of the western US, various biological networks, etc.) satisfy a power-law degree distribution. Such scale-free networks have many interesting properties, one of which is robustness to random damage. This problem has been analyzed from the point of view of node deletion and connectedness. Recently, it has also been considered from the point of view of node deletion and scale preservation. In this paper we consider the problem from the point of view of edge deletion and scale preservation. In agreement with the work on node deletion and scale preservation, we show that a scale-free graph should not be expected to remain scale free when edges are removed at random.     

Effect of ultrasound on oil removal from soils

The soil-flushing method enhanced by ultrasonic waves is a new technique that potentially can become an effective method for in situ remediation of the ground contaminated by NAPL hydrocarbons. This study investigated the effectiveness of ultrasound enhancement in the soil-flushing method for a range of conditions involving soil type, soil density, flushing rate, and sonication power. The study was conducted in the laboratory using specially designed and fabricated equipment. The test results indicated that the rate of contaminant extraction increased considerably with increasing sonication power up to the level where cavitation occurred. The effectiveness of sonication-enhanced soil-flushing can be expressed as a function of (D(10))(2)*i, in which D(10) is the effective grain size, and i is the hydraulic gradient.     

Few-neutron removal from238U at relativistic energies

As part of a comprehensive study of uranium fragmentation at relativistic energies at the GSI projectile fragment separator, FRS, inclusive neutron-removal cross sections have been measured for severalxn channels at projectile energies of 600 and 950A MeV using targets of Al, Cu and Pb. The variation of the experimental cross sections with target nuclear charge is used to disentangle nuclear and electromagnetic contributions. The electromagnetic cross sections agree surprisingly well with a simple harmonic oscillator calculation of giant dipole resonances based on measured photonuclear cross sections and do not require an extra enhancement of the two-phonon giant dipole excitation as concluded from similar measurements with¹⁹⁷Au.     

Using high haze (> 90%) light-trapping film to enhance the efficiency of a-Si:H solar cells

The high haze light-trapping (LT) film offers enhanced scattering of light and is applied to a-Si:H solar cells. UV glue was spin coated on glass, and then the LT pattern was imprinted. Finally, a UV lamp was used to cure the UV glue on the glass. The LT film effectively increased the Haze ratio of glass and decreased the reflectance of a-Si:H solar cells. Therefore, the photon path length was increased to obtain maximum absorption by the absorber layer. High Haze LT film is able to enhance short circuit current density and efficiency of the device, as partial composite film generates broader scattering light, thereby causing shorter wave length light to be absorbed by the P layer so that the short circuit current density decreases. In case of lab-made a-Si:H thin film solar cells with v-shaped LT films, superior optoelectronic performances have been found (V_oc = 0.74 V, J_sc = 15.62 mA/cm², F.F. = 70%, and η = 8.09%). We observed ~ 35% enhancement of the short-circuit current density and ~ 31% enhancement of the conversion efficiency.     

From finite to infinite volumes: removal of boundaries in diffuse wave imaging

In this Letter, we present a method that removes the contribution of the boundaries on the measurements from highly scattering media, transforming the signals captured from a bounded medium to measurements that would have been obtained if no boundary were present. This approach opens new possibilities in tomographic imaging in diffuse media as it eliminates the need for explicitly modeling boundaries and significantly simplifies reconstruction requirements.     

On removal of impurities from water by acoustic pulses

Water degassing and removal of salts by high-power acoustic pulses are analyzed. A model explaining the mechanisms of these processes is proposed.