Generation of low-frequency radiation by a nonequilibrium plasma of an RF discharge in a linear mirror magnetic confinement system

The generation of ion-cyclotron radiation in a plasma resonator formed by an RF discharge in a linear mirror magnetic confinement system is revealed and investigated. It is shown that the experimental setup makes it possible to study the composition of a multicomponent discharge plasma and to detect multiply charged ions. Collisional losses in such a resonator are estimated, and the pressure range within which the growth rate of the ion-cyclotron instability substantially exceeds the collisional damping rate is determined.     

人工同龄纯林冠层辐射场模拟模型 II.应用与验证

应用建立的人工同龄林辐射场模型对杉木 (Cunninghamialanceolata)人工林冠层辐射场进行了模拟 ,以实测的冠层辐射数据对模型进行了验证 ,对模型的不确定性以及叶面积密度和叶片散射的影响进行了计算和分析。结果表明 ,模拟和实测辐射场及日总量无显著差异 ,所建模型适于对杉木人工林冠层辐射的模拟。模型可能的误差来源包括树冠形状的不规则性、树冠大小和高低的不一致性、叶片在小范围内的簇生性等。考虑二维叶面积密度 (LAD)分布的模拟结果优于平均LAD。叶片的散射辐射约占总辐射的 3%～ 11%,且越靠近树冠里层和下部 ,散射作用越大。     

Measurements of the electron energy spectrum by using small-angle Thomson scattering

A novel diagnostic method is developed for studying the high-energy plasma electron component in the GOL-3 facility by using small-angle Thomson scattering. The method is based on the enhancement of the spectral density of scattered radiation as compared to the conventional large-angle scattering technique.     

Interaction of microwave radiation undergoing stochastic phase jumps with plasmas or gases

New types of beam-plasma devices generating intense stochastic microwave radiation in the interaction of electron beams with hybrid plasma waveguides were developed and put into operation at the National Science Center Kharkov Institute of Physics and Technology (Ukraine). The objective of the paper is to discuss the results of theoretical and experimental studies and numerical simulations of the normal and oblique incidence of linearly polarized electromagnetic waves on an interface between a vacuum and an overcritical plasma. The main results of the reported investigations are as follows: (i) for the parameter values under analysis, the transmission coefficient for microwaves with a stochastically jumping phase is one order of magnitude greater than that for a broadband regular electromagnetic wave with the same spectral density; (ii) the electrons are heated most efficiently by obliquely incident waves with a stochastically jumping phase and, in addition, the electron distribution function has a high-energy tail; and (iii) necessary conditions for gas breakdown and for the initiation of a microwave discharge in stochastic fields in a light source are determined. The anomalously large transmission coefficient for microwaves, the anomalous character of the breakdown conditions, the anomalous behavior of microwave gas discharges, and the anomalous nature of collisionless electron heating, are attributed to stochastic jumps in the phase of microwave radiation.     

Effect of microwave radiation on a dusty plasma

The effect of microwave radiation on a complex plasma produced by an external ionizer is studied using numerical simulations. It is shown that, as the radiation intensity increases, the scattering of the incident radiation by charged metal grains is enhanced and radiation at the second harmonic of the incident radiation appears in the scattered spectrum. This effect is associated with the grain charge oscillations caused by the nonlinear action of the microwave field. It is found that, under the action of strong microwave radiation, the grain charge can increase by one order of magnitude. It is shown that, when the microwave intensity is high enough, the distribution of the electric field near a dust grain is shown to change so radically that the field component normal to the grain surface can even change its sign.     

Scattering of an ultrashort electromagnetic pulse in a plasma

An analytic approach is developed to describing how ultrashort electromagnetic pulses with a duration of one period or less at the carrier frequency are scattered in a plasma. Formulas are derived to calculate and analyze the angular and spectral probabilities of radiation scattering via two possible mechanisms-Compton and transition radiation channels-throughout the entire pulse. Numerical simulations were carried out for a Gaussian pulse. The effect of the phase of the carrier frequency relative to the pulse envelope on the scattering parameters is investigated.     

Recovery of the characteristics of plasma turbulence from the radial correlation backscattering diagnostics

Signals of the backscattering radial correlation Doppler diagnostics of plasma density fluctuations in the presence of the cutoff of the probing wave are analyzed theoretically with allowance for the curvature of magnetic surfaces. The scattering of the probing electromagnetic wave is considered in the linear (Born) approximation with respect to the amplitude of fluctuations. Using the Wentzel?Kramers?Brillouin approach, analytical expressions for the scattered signal and the correlation function of two scattered signals corresponding to oblique probing at different frequencies are derived. A criterion is obtained for the tilt angle of the antenna pattern at which the two-point turbulence correlation function can be measured directly. A method is proposed to recover the spectrum of plasma density fluctuations from the data on the radial wavenumbers even if this criterion is violated.     

Angular optimization for cancer identification with circularly polarized light

Depolarization of circularly polarized light scattered from biological tissues depends on structural changes in cell nuclei, which can provide valuable information for differentiating cancer tissues concealed in healthy tissues. In this study, we experimentally verified the possibility of cancer identification using scattering of circularly polarized light. We investigated the polarization of light scattered from a sliced biological tissue with various optical configurations. A significant difference between circular polarizations of light scattered from cancerous and healthy tissues is observed, which is sufficient to distinguish a cancerous region. The line-scanning experiments along a region incorporating healthy and cancerous parts indicate step-like behaviors in the degree of circular polarization corresponding to the state of tissues, whether cancerous or normal. An oblique and perpendicular incidence induces different resolutions for identifying cancerous tissues, which indicates that the optical arrangement can be selected according to the priority of resolution.     

Fluorescence lifetime spectroscopy of a pH-sensitive dye encapsulated in hydrogel beads

A pH-sensing dye, carboxy seminaphthofluorescein-1 (C-SNAFL-1), was immobilized in poly(ethylene glycol) (PEG) microparticles via ester-amine reaction. Following photopolymerization, the hydrogel particles were then immersed in buffered pH solutions of varying pH with added polystyrene. Measurements of phase shift and amplitude attenuation of the generated and multiply scattered fluorescent light were attained as a function of modulation frequency of the incident excitation light. Upon regressing the measured data to the coupled optical diffusion equations, the average lifetimes of protonated and deprotonated forms of C-SNAFL-1 were obtained and compared to the values acquired from conventional fluorescence lifetime spectroscopy in nonscattering media. The results demonstrate the ability to perform analyte sensing with fluorescence lifetime without the confounding effect of fluorophore loading or the use of a "reference" measurement within multiply scattering systems. When extended to the immobilized fluorophore-enzymatic systems, fluorescence lifetime spectroscopy with multiply scattered light may provide a new ultrasensitive approach for analyte or toxin screening.     

南京地区太阳辐射资源量子年总量的理论计算

为了从量子角度探讨南京地区的太阳辐射资源,在理想大气条件下对2008年南京地区的光合有效辐射波段的量子辐射进行了计算.在2008年的366天中每隔20分钟计算一次量子照度,然后通过累积计算得到太阳直接辐射年总量.应用相关公式,计算出了散射辐射年总量,总辐射年总量和光合有效辐射年总量.经过与一些相关资料的对比分析,认为计算结果正确合理.     

The fertilization effect of global dimming on crop yields is not attributed to an improved light interception

Global dimming, a decadal decrease in incident global radiation, is often accompanied with an increase in the diffuse radiation fraction, and, therefore, the impact of global dimming on crop production is hard to predict. A popular approach to quantify this impact is the statistical analysis of historical climate and crop data, or use of dynamic crop simulation modelling approach. Here, we show that statistical analysis of historical data did not provide plausible values for the effect of diffuse radiation versus direct radiation on rice or wheat yield. In contrast, our field experimental study of 3 years demonstrated a fertilization effect of increased diffuse radiation fraction, which partly offset yield losses caused by decreased global radiation, in both crops. The fertilization effect was not attributed to any improved canopy light interception but mainly to the increased radiation use efficiency (RUE). The increased RUE was explained not only by the saturating shape of photosynthetic light response curves but also by plant acclimation to dimming that gradually increased leaf nitrogen concentration. Crop harvest index slightly decreased under dimming, thereby discounting the fertilization effect on crop yields. These results challenge existing modelling paradigms, which assume that the fertilization effect on crop yields is mainly attributed to an improved light interception. Further studies on the physiological mechanism of plant acclimation are required to better quantify the global dimming impact on agroecosystem productivity under future climate change.     

An artifact in measurements of in vivo light-induced absorbance changes

The effects of scattered actinic radiation on photomultipliers (Hamamatsu R-562) were investigated. Using cotton-wool to model dense biological preparations, it was found that the scattered actinic radiation received by the photomultiplier gives rise to phytochrome-like signals. This demonstrated the necessity to shield the photomultiplier from scattered actinic light for sensitive measurements with light-scattering preparations.     

A statistical light scattering approach to separating fast and slow dynamics

Light scattering is a powerful technique to study the structural and dynamical properties of biomolecular systems or other soft materials such as polymeric solutions and blends or gels. An important application of this technique is the study of the kinetics of formation of supramolecular structures. However, in such cases, the system under study is rapidly changing, and consequently the integration time for each measurement is limited. In order to overcome this difficulty, a statistical approach has been developed based on the analysis of the scattered light intensity distribution (Manno et al. 2006, 2004). Indeed the intensity distribution depends upon the ratio between the integration time of each measurement and the coherence time of scattered radiation. This method has been applied to protein aggregation (Manno et al. 2006) and to sol-gel transition (Manno et al. 2004), to obtain information on the heterogeneity of morphological and dynamical features during such processes. In the present work, we accurately test the validity of this approach by analyzing the statistical properties of the light scattered by a model system: a solution of polystyrene spherical macromolecules of different sizes. Each molecular size is related to a given diffusion coefficient and to a given coherence time of the scattered intensity. The effect of changing the experimental integration time is systematically investigated. A mixture of particles of two different sizes is also analyzed to test the validity and robustness of the model based on the convolution of a gaussian with an exponential distribution. Proceedings of the XVIII Congress of the Italian Society of Pure and Applied Biophysics (SIBPA), Palermo, Sicily, September 2006.     

The low dose and low dose rate cytogenetic effects induced by gamma-radiation in human blood lymphocytes in vitro. I. the results of physical and dosimetric study

Physical and dosimetric characteristics of the gamma-radiation field which is formed in the room containing the 60Co radiation source were investigated on condition of an unclosed breech mechanism and the presence of the lead layer on the beam pathway. The inverse square law was approximately found for the dependence of the dose rate vs distance on the radiation source both for the unclosed breech mechanism and lead layer (4 and 9 cm wide) in the beam pathway. This finding indicated a non-significant contribution of the radiation scattered from the walls at the point of cytogenetic experiments. The Monte Carlo calculations showed that some changes in the efficient spectrum of gamma-radiation resulted in a decreased average energy of 60Co gamma-rays to 1.03, 1.17 and 1.07 MeV for the unclosed breech mechanism, behind 4 and 9 cm lead layers, respectively.     

Mutability of the liver cells in the progeny of irradiated male rats

The descendants of the first generation of radiation exposed rat males exhibited an increased sensitivity of liver cells to the mutagenic effect of ionizing radiation as was determined by the incidence of chromosome aberrations. It is assumed that the stability of the hereditary apparatus of these animal cells is diminished due to the presence therein of radiation induced injuries of mutation and epigenomic origin at a heterozygous condition.     

长白山阔叶红松林生长季反射率特征

根据长白山阔叶红松林气象观测塔上太阳总辐射和反射辐射资料 ,计算了 2 0 0 1年 5月 2 2日～10月 14日森林下垫面的每日整点反射率 .结果表明 ,森林的反射率与太阳高度角有关 ,在太阳高度角很小的日出和日落附近反射率较高 ,太阳高度角大于 30°时反射率变化不大 ,反射率的日变化曲线为U形 .森林的反射率与天空状况有关 ,晴天条件下低太阳高度时的反射率高值明显 ,U形曲线突出 ,昙天时曲线两端高值相对较低 ,U形曲线也相对平坦 ,阴天的日变化曲线则没有明显的规律 ,在某范围内波动 .生长季反射率的变化特点为 6月上旬较高 ,6月下旬稍有下降 ,7～ 9月较稳定 ,10月上旬则逐渐下降 ,反映了冠层叶片物候变化特征 .     

Interaction of the equipotential surface of a charged object with weak laser radiation

Experiments were carried out on how laser radiation affects both the shape of an escaping plasma jet and the formation of a luminous object after the jet has been ejected from the electrode. It is shown that a 1-mW laser beam with an intensity as low as 0.001 W/cm² can change the shape of the jet and its propagation direction. In applying laser diagnostic methods, it is necessary to take into account possible change in the configuration of such objects when they interact with laser radiation. It is confirmed that the temperature of a luminous object decreases sharply with time.     

Why locusts start to feed: A comparison of causal factors

New statistical methods have allowed a quantitative comparison of a number of causal factors affecting feeding in fifth-instar nymphs of the migratory locust (Locusta migratoria). The methods allow one to measure the way the probability of feeding changes with time since the last meal, and how it is affected by previous meal-size, light, food-stimuli, recent defaecation and a short-term rhythm. Since all these factors are measured on the same scale (the extent to which they multiply the probability of feeding) their relative importance can be assessed. Such measures can then be related to the known physiology that underlies the initiation of feeding. For example, the effect of recent defaecation was unexpectedly large, increasing the probability of feeding seven-fold. It is likely that the size of this effect is due to a sudden change in firing rate of the stretch receptors which monitor the shape and fullness of the hindgut.