Gravitational lensing by black holes

We review the theoretical aspects of gravitational lensing by black holes, and discuss the perspectives for realistic observations. We will first treat lensing by spherically symmetric black holes, in which the formation of infinite sequences of higher order images emerges in the clearest way. We will then consider the effects of the spin of the black hole, with the formation of giant higher order caustics and multiple images. Finally, we will consider the perspectives for observations of black hole lensing, from the detection of secondary images of stellar sources and spots on the accretion disk to the interpretation of iron K-lines and direct imaging of the shadow of the black hole.     

Stable Sulfur Isotope Effects Related to Local Intense Sulfate Reduction in a Tidal Sandflat (Southern North Sea): Results from Loading Experiments

Abstract

Anoxic sediment surfaces coloured black by iron monosulfides (“black spots”) evolve in tidal sandflats of the Wadden Sea (southern North Sea) as a result of the degradation of buried organic matter. To follow the short- and long-term effects of organic matter burial on pore water and sediment isotopic biogeochemistry, formation of artificial black spots was initiated on the Groninger Plate (site RP63) in the backbarrier tidal flats of Spiekeroog island. Changes in concentrations (DOC, TA, TOC, sulfate, sulfide, TRS, Fe) and isotopic compositions (sulfate, sulfide, TRS, pyrite, TOC) were followed for up to 12 months and compared to reference areas. 13°C ratios of TOC clearly mirror the early diagenetic degradation of organic matter. At least temporarily closed system sulfate reduction is inferred for the artificial black spot from the variation of sulfate concentrations and stable sulfur isotope partitioning, In the interstitial waters of the black spot, 34S/32S values of coexisting dissolved sulfate and sulfide yield fractionation degrees between ?5 and ?25%. On the reference area, 34S/32S are fractionated by ?32 to ?42% as calculated from the isotope composition of solid phase reduced sulfur and pore water sulfate. Sulfur isotope fractionation seems to increase with decreasing sulfate reduction rate. Limiting factor seems to be the availability of DOC. Between the pyrite pool and the dissolved sulfide in the black spot, no significant isotope exchange is observed within 12 months.     

基于旋滤波法的干涉条纹预处理技术

 提出了一种新的基于旋滤波法的干涉条纹预处理方法。该方法根据条纹图灰度值梯度分布规律，只在干涉条纹切线方向进行中值滤波，它能有效地处理各种相干噪声而不会使条纹变模糊。实验证明该方法能有效地去除随机噪声、椒盐噪声以及由于光照不均匀引起的较大面积的亮斑或暗斑等噪声。对于亮斑或暗斑，其滤波效果要明显优于Gerchberg外插迭代算法。以WYKO相移干涉仪5次测量的面形平均值作为被测面形的参考值，则经过预处理后，抑制了噪声引起的局部误差，傅里叶变换法计算得到PV值的误差从未预处理的14.4%(全口径)、131%(95%口径)分别减小到3.4%(全口径)、1.5%(95%口径)；RMS误差从28.7%(全口径)、23.3%(95%口径)分别减小到5.0%(全口径)、2.3%(95%口径)。     

Evolution of the vortex structures and turbulent spots at the late-stage of transitional boundary layers

The nonlinear evolution process of new vortex structures at the late-stage of the transition, including the 3-D spatial structure of barrel-shaped vortex and dark spots structure observed by experiment research, has been confirmed by our computational results. The formation mechanisms of these structures have been explored. It is revealed that the new vortex structures, the ring-like vortex chain and induced disturbance velocities play a dominant role in the generation of turbulent spots.     

Visualization of turbulent spots and unsteady wake-induced boundary-layer transition with thermochromic liquid crystals

A method of using thermochromic liquid crystals has been developed to visualize the thermal footprints of turbulent spots convecting downstream in an otherwise laminar boundary layer over a heated surface. This technique has been employed to visualize the development of turbulent spots under the influence of adverse pressure gradients. It has also been used to visualize the transitional events that occur during unsteady wake-induced boundary layer transition typically of those occurring in multi-stage turbomachines. The results show that liquid crystal is not only capable of providing quantitative information about the growth and development of individual spots but also allows a detailed study of formation of turbulent spots occurring naturally during a complicated transition process.     

Spin and mass of the nearest supermassive black hole

Quasi-periodic oscillations (QPOs) of the hot plasma spots or clumps orbiting an accreting black hole contain information on the black hole mass and spin. The promising observational signatures for the measurement of black hole mass and spin are the latitudinal oscillation frequency of the bright spots in the accretion flow and the frequency of black hole event horizon rotation. Both of these frequencies are independent of the accretion model and defined completely by the properties of the black hole gravitational field. Interpretation of the known QPO data by dint of a signal modulation from the hot spots in the accreting plasma reveals the Kerr metric rotation parameter, \(a=0.65\pm 0.05\) , and mass, \(M=(4.2\pm 0.2)10^6M_\odot \) , of the supermassive black hole in the Galactic center. At the same time, the observed 11.5 min QPO period is identified with a period of the black hole event horizon rotation, and, respectively, the 19 min period is identified with a latitudinal oscillation period of hot spots in the accretion flow. The described approach is applicable to black holes with a low accretion rate, when accreting plasma is transparent up to the event horizon region.     

Surface fission tracks in diamond

Scanning Probe Microscope (SPM) images reveal important fingerprint features of latent tracks induced in diamond by fission fragments from a californium source. Collimated fission fragments with a binary distribution of the predominant energies of 79.4 and 103.8 MeV, are assumed. Cavities, reticular formations around these cavities, and black spots of graphite were found. A brief discussion on the possible track formation mechanism is given on the basis of the explosion spike theory; an attempt to determine latent track core and halo parameters is included.     

Halo-based black point detection method of microchannel plate北大核心CSCD

根据微通道板黑点检测原理与黑点光晕特征设计了一种检测方法,该方法利用圆提取技术实现荧光屏图像的半径和圆心提取,通过高斯拉普拉斯算子实现目标黑点粗检测。基于黑点在不同电压下外围呈现光晕的特征,利用对比度受限的直方图均衡化并结合阈值分割的光晕检测法实现黑点光晕的提取。测试结果表明,该方法可以将荧光屏划痕、灰尘与微通道板黑点有效区分,从而实现黑点的自动提取。     

采用热处理方法提高MEH-PPV单层聚合物有机发光二极管发光性能的研究

对以MEH－PPV为发光层的单层聚合物有机发光二极管（OLED）器件在最佳条件下进行真空热处理，并用金相显微镜观察施加电压后器件的阴极表面形貌。发现处理后的器件阴极表面的气泡及黑斑明显减少。器件的发光性能显著提高。与未经处理的器件相比，最大相对发光强度提高了一个数量级、启亮电压降低了2．0V，半寿命提高了12．7倍。初步分析表明热处理方法提高器件发光性能的主要原因在于有效地减少了器件在工作过程中由于焦耳热产生的某些气体，从而减少阴极表面气泡及黑斑的出现，另一方面，热处理方法也增强了有机发光层与阴极接触界面的结合力，提高电子注入水平。     

Small-Scale Anode Activity in Vacuum Arcs

Coordinated high-speed movies, streak photographs, and voltage/current oscillograms have been taken for vacuum arcs on copper-based electrodes at peak currents up to 70 kA in half-cycle pulses. These results show that small-scale transient luminous anode-spot activity is associated with the strong voltage noise that precedes the establishment of the conventional large anode spots. The characteristic dimensions of the small-scale spots go below a millimeter, and may be less than 100 ?m. Unlike cathode spots of that size, these small anode spots always move in the I × B direction. This small-scale activity is especially pronounced in experimental systems initially containing surface films of volatile matter. Good correlations have been established between bursts of anode light and corresponding bursts of arc voltage noise, both of which appear to be associated with variations in the small luminous structures. The practical importance of the small transient luminous anode activity reported here is in its clear tendency to advance the formation of electrode jets, particularly under experimental conditions favoring the evolution of gas or vapor from anode surfaces. It has theoretical significance as a precursor to the formation of the usual large anode spots and jets, and as a possible source of structure within large anode spots.     

The anode space of short-time high-intensity electric discharges

The influence of electrode evaporation on the forming of an anode region of short-time discharges has so far been neglected. A comparison of the amount of vapours produced in spots and the magnitude of the thermal flow to the electrodes for anodes of different materials shows the important connection between the formation of spots on electrodes and the flow of vapours and permits the characteristic effects (high current density in spots, splitting of spots, two forms of contraction) of the anode region of the given type of discharge to be explained.In conclusion the author thanks J. Chudoba and B. Grycz for valuable remarks.     

Modeling soot formation in flames and reactors: Recent progress and current challenges

The study of soot has long been motivated by its adverse impacts on health and the environment. However, this combustion knowledge is also relevant to the production of carbon black and hydrogen via methane pyrolysis which are important commodities. Over the last decade, steady progress has been made in the development of detailed continuum models of soot formation in flames and reactors. Developing more comprehensive models has often been motivated by the need for predicting soot formation over a wider range of conditions (e.g., temperature, pressure, fuels). Measurements with novel experimental techniques have given us new insights into the chemistry, particle dynamics and optical properties of soot particles and even molecules and radicals forming them. Also, multi-scale modeling has enabled us to translate the detailed mechanisms of soot processes based on first principles into computationally efficient but accurate continuum models of soot formation in flames and reactors. However, important questions remain including (1) what is the mechanism of soot inception and surface growth, (2) which gas-phase species are involved in soot inception and surface growth (3) how surface growth and oxidation are affected by soot surface properties. Proposed models need to be evaluated against experimental data over a wide range of conditions to determine their predictive strength. These questions are critical for the accurate prediction of soot formation in flames and its emissions from engines. However, this knowledge can also be used to develop predictive process design and optimization tools for carbon black and other nanocarbon formation in reactors.     

Anode spot plasma deposition of insulating layers on aluminum

The deposition of an insulating layer upon an aluminum plate in an argon plasma is described. The process is effected in a low-power DC discharge to which a small amount of sulfur hexafluoride (SF₆) has been added, causing the formation of anode spots at sharp metallic surfaces. The insulator is deposited in the region beneath the spot     

On the Nature and the Motion of Arc Cathode Spots in UHV

Cathode spot types and spot motion of arcs in ultra high vacuum have been investigated with large area cathodes that consisted of two adjacent pieces of Mo and Cu. Arc currents were 20–60 A dc and 8–20 kA pulse (duration about 1 ms). Two spot types occured with different velocities and surface erosion: Type 1 spots are typical for surfaces covered by oxides or thick adsorption layers, whereas clean surfaces show only type 2 spots. During arc-conditioning both types exist simultaneously in a complex mutual dependence. Type 1 spots react weakly on the cathode material, while type 2 spots burn preferentially on Cu and at the boundary line between Mo and Cu. The motion of type 1 spots is determined by the expanding spot plasma, whereas type 2 spots show a step-by step motion, determined by explosions in the arc craters. Generally a spontaneous formation of type 2 spots beneath the arc plasma takes place only with contaminated surfaces (probably by a transition from type 1 to type 2 spots). Thus a breakdown between plasma and cathode surface requires the presence of contaminations. The observed effects occur in low current dc-arcs as well as in high current pulse arcs. They are discussed for different spot models.     

A new strategy to assemble CdSe/ZnS quantum dots with multi-walled carbon nanotubes for potential application in imaging and photosensitization

With objective to enhance luminescence intensities of carbon nanotubes (CNTs), we hereby report the attachment of CdSe/ZnS quantum dots (QDs) on to the surface of shortened Multi Walled Carbon Nanotubes (sMWCNTs). The resultant QDs-sMWCNTs nanohybrid complex have been characterized by Fourier transform infrared (FT-IR) spectroscopy, optical microscopy (OM), ultraviolet (UV) light, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) diffraction spectroscopy and thermogravimetric analysis (TGA). Based on IR peaks characteristics of organic functional groups, optical brightness of sMWCNTs under polarized and UV light, the roughness of the sMWCNTs surface as observed in SEM images and black spots observed on the surface of sMWCNTs in TEM images, it is reasonable to conclude that CdSe/ZnS quantum dots (QDs) were attached on to the surface of sMWCNTs. Additionally, signals of Zn, S, Cd and Se along with carbon on the surface of sMWCNTs in EDX data and onset of thermal degradation of QDs-sMWCNTs nanohybrid complex at much lower temperature than that of sMWCNTs under TGA analysis further confirms the formation of QDs-sMWCNTs nanohybrid complex.     

ПОВЕДЕНИЕ КАТОДНЫХ П ЯТЕН В СИЛЬНОТОЧНОМ ЭЛЕКТРИЧЕСКОМ РАЗРЯ ДЕ

A magnetooptical rapid-action shutter was used to study the formation of cathode spots on the electrodes of a short-time high-intensity electric discharge. It was found that there exist two types of cathode spots. Spots of the first type are transported with a high velocity to the cathode surface not yet reached by the discharge. Spots of the second type, on the other hand, move in the neighbourhood of the centre of evaporation. On metals which evaporate with difficulty (Ni, Cu, Al) only spots of the first type may exist. On metals which easily evaporate (Cd, Sn, Zn) spots of both types exist simultaneously. The formation of cathode spots is explained by means of the cold emission of electrons from the cathode.     

Cathode processes in free burning and stabilized by axial magneticfield vacuum arcs

Collective behavior of the cathode spots (CS) has been investigated in free burning and stabilized by axial magnetic field (AMF) vacuum arcs. Experiments carried out proved previously discovered phenomenon of CS group formation in free burning arc to be a general phenomenon for a short high-current vacuum arc. The dependency of CS group size in the developed are on arc current for different contact materials has been analyzed. Application of AMF with even relatively low intensity strongly affects on cathode processes. In short arcs, it hinders formation of the CS group and consequently reduces thermal stress applied to the electrodes. It has been revealed that high current vacuum arc under the action of AMF can exist only at current densities exceeding certain minimal value that depends on AMF intensity, contact gap, and does not depend on current itself. The dependency of this minimal (or normal) current density on AMF intensity has been studied for short and long vacuum arcs. A qualitative model of the cathode spot dynamics has also been proposed     

Microscopic high speed investigations of vacuum arc cathode spots

The main parameters and dimensions of cathode spots have been under discussion for years. To solve these current questions, a new system was specially designed. The image converting high speed framing camera (HSFC) combines a micrometer lateral resolution with a nanosecond time resolution and a very high optical sensitivity. This camera was used to study the microscopic behavior of vacuum arc cathode spots in a pulsed high current arc discharge on copper. The direct observation of these spots with high resolution revealed that one single cathode spot, as normally observed by optical means, consists of a number of simultaneously existing microscopic subspots, each with a diameter of about 10 μm and a mean distance of 30-50 μm between them. The mean existence time of these subspots on copper was found to be about 3 μs, where the position of a subspot remains unchanged (with an upper limit of about 5 μm) during its existence time. The lower limit of the current density in the cathode spots was estimated to be on the order of 10¹⁰-10¹¹ A/m². An upper limit of the crater surface temperature was estimated by a comparison between the brightnesses of a cathode spot and of a black body radiation lamp to about 3000 K     

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si_xO_yF_z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF_x⁺ (x ≤ 5) and F⁺ ions etching effect, Si_xO_yF_z passivation and ion bombardment.     

Droplet spot as a new object in physics of vacuum discharge

It is established experimentally that the burning of a low-current (several and tens of amperes) pulsed (microseconds) vacuum discharge is accompanied by the formation of plasma microbunches around some of the droplets leaving the cathode spot. The parameters of these bunches (electron concentration n _e～10²⁶ m^?3 and equilibrium temperature T _e～1 eV) are close to the parameters of cathode-spot plasma. The data obtained suggest that the initial temperature of droplets and the thermionic emission from them play a key role in the formation of such plasma microbunches. By analogy with the well-known cathode and anode spots in vacuum discharges, these droplet plasma formations are classified as “droplet spots.” This work reports the first results on studying the formation dynamics and the characteristics of the droplet spots. It is noted that the concept of droplet spots will require a certain refinement of the plasma formation mechanism in vacuum discharges.