High Pressure Theoretical Studies of Actinide Dioxides

Actinide dioxides (ThO 2 , UO 2 , Pu 2 etc.) compounds have the CaF 2 -type structure at ambient pressure and temperature. Under high pressure, they exist in the PbCl 2 -type structure, belonging to space group Pnma [1]. We have studied crystal structures under high pressure in actinide dioxides by means of first-principles self-consistent total-energy calculations with the non-local Perdew, Burke and Ernzerhof (PBE) exchange correlation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. The atomic equilibrium volume, bulk modulus and transition pressure for actinide dioxides were calculated, covering the full pressure range for which the mentioned experiments have been done [2].     

Microwave Heating of Metal Power Clusters

The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies.     

Theory of Thermal Fatigue Caused by RF Pulsed Heating

The normal conducting electron-positron Linear Collider projects imply that accelerating structures and other RF components will undergo an action of extremely high RF fields. Except for the RF breakdown threat, there is an effect of the copper surface being damage due to multi-pulse mechanical stress caused by Ohmic losses in the skin layer. In this paper we would like to introduce a new “grain” model of the processes responsible for the fatigue of the metal surface. This model is based on the quasi-elastic interaction between neighboring grains in the metal due to the thermal expansion of the skin layer. This mechanism of fatigue is compared with another, where stresses are generated by the temperature gradient towards the bulk of the material. With the proposed formalism one can estimate the total number of the RF pulses required to fracture the surface depending on the temperature rise, pulse length and steady state temperature. The parameters necessary to finalize the proposed approach were found through the comparison of experimental data obtained at 11.424 GHz.     

平面刻槽离子阱的热噪声引起的离子加热研究

研究了和平面刻槽离子阱中的电压热涨落噪声引起的离子加热和离子加热的直接计算模型,给出了离子加热的加热尺度,并利用有限元分析方法计算了当刻槽宽度和射频电极宽度比例α发生变化时加热尺度的变化。同时,还利用涨落耗散原理计算了控制电极的阻抗热涨落对离子产生的加热效应,并给出了x和y方向电场涨落的谱密度表达式,通过计算给出了较好的α值。     

Heating of Powders in the Fire Ball of an Induction Plasma

A theoretical model has been developed for the calculation of the trajectories and temperature histories of particles injected in the fire-ball of an inductively coupled plasma. Calculations were made for alumina particles of different diameters ranging between 10 and 250 ?m. The particles were injected through a water cooled probe upstream of the fire-ball. The results shows that the internal plasma recirculation in the coil region is responsable for the bouncing of the particles on the fire-ball. Particles of the order of 10 ?m and smaler are entrained in the fire-ball by the inward radial flow caused by the electromagnetic pumping, and are subsequently completely evaporated. Larger particles, depending on their initial position and velocity of injection, could by-pass the plasma fire-ball, and in some cases, end up deposited on the wall of the plasma confining tube. Particles with diameters larger than 100 ?m were found to pass straight through the fire-ball when injected close to the center line of the torch.     

Flash Sintering of Oxide Ceramics under Microwave Heating

We report on the results of the analysis of the effect of flash sintering, which is observed upon heating compacted powder materials by high-intensity microwave radiation. Ceramic samples of Y₂O₃, MgAl₂O₄, and Yb: (LaO)₂O₃ were sintered to a density exceeding 98–99% of the theoretical value during 0.5–5 min without isothermal hold. The specific microwave power absorbed volumetrically in the samples was 20–400 W/cm³. Based on the analysis of the experimental data (microwave radiation power and heating and cooling rates) and of the microstructure of the obtained materials, we propose a mechanism of flash sintering based on the evolution of the thermal instability and softening (melting) of the grain boundaries. The proposed mechanism also explains the flash sintering effect observed when a dc or a low-frequency ac voltage is applied to the samples. The microwave heating makes it possible to implement flash sintering without using electrodes for supplying energy to the articles being sintered.     

Reduction of the Polarization-Dependent Loss of Long-Period Fiber Gratings by Thermal Heating

The polarization-dependent loss of UV-written long-period fiber gratings was significantly reduced by increasing the pulse repetition rate of the writing UV beam. The effect is closely related with the enhanced photosensitivity induced by thermal heating.     

Moisture Migration in Wood Under Heating Measured by Thermal Neutron Radiography

The article addresses the transport of moisture due to high-temperature gradients resulting from heating by means of thermal neutron radiography. Moisture migration due to heating is quantified along the orthotropic directions of two wood species, spruce and beech, with high spatial and moisture content resolution. As the heat wave is propagating into the wood, the moisture content in the heated zone rapidly decreases, and moisture is transported due to the high-temperature gradient ahead of the heated zone, resulting in a zone with higher moisture content. Both the drying and the moisture accumulation areas evolve non-uniformly, depending on wood microstructure and orientation.     

Synthesis of Ultrafine Silicon Carbide Powders in Thermal Arc Plasmas

Ultrafine ?-SiC powders are synthesized in thermal plasmas by a reaction between methane and silicon monoxide. The reaction is carried out in an unconfined plasma jet (22.5 kW) operating at atmospheric Ar pressure. High temperatures (> 10 000 K) combined with ultrarapid quench rates (? 106 K/s) of the plasma lead to a high degree of supersaturation of the chemical vapor, resulting in homogeneous nucleation of ultrafine particles. Product characterizations are pursued with X-ray diffraction analysis, X-ray photoelectron spectroscopy (XPS), scanning, and transmission electron microscopy. The maximum SiC yield determined by thermogravimetric analysis (TGA) is 97.3 percent. Particle size analyses show a bimodal distribution with the majority of the particles falling in a size range from 2 to 40 nm. Triangular and hexagonal SiC particles are observed throughout this work and the nucleation and growth of these particles are discussed.     

橡胶微波加热的数值模拟研究

本文运用ANSYS有限元软件对橡胶的微波加热过程进行了数值模拟研究,分别获得了传统加热方式下和微波功率为5 kW,6 kW,7 kW,8 kW,9 kW,10 kW时橡胶的升温效应,结果表明,微波加热的时间短,效率高。经微波加热后橡胶内部的焦耳热密度分布和温度分布不均匀,但橡胶的温度分布规律与焦耳热密度分布规律相同,胶料中间部位升温最高,并且胶料的温度随微波功率的升高而升高。     

Volume Heating of a Vertical Air Column by Microwave Radiation in the Atmospheric Absorption Line

Radiophysics and Quantum Electronics - We propose a method of volume heating of a vertical air column by the vertically directed microwave radiation at the frequency of the spectral...     

用手机检测微波炉的屏蔽效果

微波炉能屏蔽手机信号吗?还用问吗!当然能,不然它怎么屏蔽微波信号呢!如果你是这种观点,那么请你试试.很简单,将一部手机放人微波炉,用另一部手机拨打看能否拨通?听到了铃声吗?结果你会发现,不但能拨通还能听到铃声.     

High Sensitivity Transmission-Type SPR Sensor by Using Metallic--Dielectric Mixed Gratings

We theoretically investigate transmission-type SPR sensors with novel metallic-dielectric mixed gratings by rig- orous coupled-wave analysis （RCWA）, compared to the conventional dielectric gratings based structure. It is found that the transmittance efficiency and the full width at half-maximum （FWHM） of the transmission curve can be modulated by increasing or decreasing the metallic part. Therefore, appropriate proportion of metal part will induce enhancement factor of sensor merit. Furthermore, this novel structure will also bring enhancement of resonant angle shift, which can be explained by plasmonie interpretation based on a surface limited increase of interaction area and excitation of localized surface plasmons （LSPs）. The proposed configuration has a wide range of potential applications not only as sensor but also other optical devices.     

Study of Microwave Multiphoton Transition of Rydberg Potassium Atom by Using B-Spline

Abstract The B-spline expansion technique and time-dependent two-level approach are applied to study the interaction between the microwave field and potassium atoms in a static electric field. We obtain theoretical multiphoton resonance spectra that can be compared with the experimental data. We also obtain the time evolution of the final state in different microwave fields.     

Study of Microwave Multiphoton Transition of Rydberg Potassium Atom by Using B-Spline

The B-spline expansion technique and time-dependent two-level approach are applied to study the interaction between the microwave field and potassium atoms in a static electric field. We obtain theoretical multiphoton resonance spectra that can be compared with the experimental data. We also obtain the time evolution of the final state in different microwave fields.     

Preparation of a Novel Oriented Structure in Carbon Black Filled Isotactic Polypropylene Composites by Microwave Selective Heating

Microwave heating technology has numerous advantages compared with the traditional heating methods and has been widely used to process materials. However, most thermoplastics do not possess a sufficiently high dielectric property to be heated by microwaves. In this study, carbon black (CB) was utilized as the microwave absorber to improve the microwave heatability of isotactic polypropylene (iPP). Effects of CB contents on the microwave heatability of iPP/CB composites were studied. The temperature of iPP/CB composites with relatively low CB content (5% and 10%) increased slowly and tended to remain unchanged after 120 s of microwave exposure. In contrast, iPP/CB composites with relatively high CB content (15% and 20%) presented a much faster heating rate and the temperature of the sample kept increasing with the prolongation of exposure time. On the basis of the fact that iPP/CB composites with different CB contents have different microwave heatability, a novel oriented structure, in which the core layer has relatively high orientation and the surface layer has relatively low orientation, was prepared by selective microwave heating. Two-dimensional wide angle X-ray diffraction (2D-WAXD) analysis indicates that the orientation parameter calculated by the (040) plane of the surface layer (0.45) was lower than that of the core layer (0.83). The novel oriented structure is different from the common skin-core structure formed in the samples of semicrystalline polymers by traditional polymer processing methods, in which orientation of the skin layer is higher than that of the core layer. The novel oriented structure has not been reported before to our knowledge and its formation mechanism is also discussed in this paper.     

Thermal Effects of Microwave Energy in Agricultural Soil Radiation

The thermal treatment by millimeter waves for the soil disinfection can be one possible alternative to chemical treatments. This physical method is based on incrementing the soil temperature and its pathogens irradiating with high frequency electromagnetic waves. So the previous knowledge of the temperature distribution in the irradiated soil is essential for achieving an effective bad microorganism and weed seeds elimination. This report analyse the heating kinetic and spatial distribution of the maximum temperatures reached by the soil. It is presented a mathematic model about how are distributed the reached temperatures in the depth of the irradiated soil. This model concludes that when an orchard soil is irradiated superficially by microwaves, the microwaves have a big attenuation due to the soil dielectric properties and the water located in the pores of the most superficial layer. This fact causes a shield effect blocking the waves penetration in few centimetres. The heating by radiation is reduced to the superficial layer. The heating propagation in the depth is occurred by conduction following the Fourier equations.     

Luminescent Microthermometry of Laser Heating Using Semiconductor Nanoplatelets

Optics and Spectroscopy - The effect of temperature on luminescence of semiconductor nanocrystals is used for monitoring local heating of specimens studied at laser scanning microscope. The...     

绝对辐射计预测辐射电补偿的快速测量方法

绝对辐射计测量光辐射需要接收辐射和电定标两个阶段,这两个阶段都要使辐射计的接收腔达到热平衡才能比较它们的腔温响应．电定标其辐射量值。根据绝对辐射计接收腔在光入射(或电加热)时腔温升响应的指数变化规律,研究出在辐射入射腔之初就动态预测其功率．电加热补偿,使腔的温度住接收辐射和电定标阶段维持恒定的状态下．快速达到平衡进行测量的新方法。为世界辐射中心(PMOD／WRC)研制的两台太阳辐照绝对辐射计SIAR-2a和SIAR-2b采用了这种快速测量的厅法。斤在世界辐射中心进行一年半10000多次同世界标准(辐射计)组(WSG)一起同时观测太阳辐照度的比刘实验．结果表明其绝对辐射精度达到了0．08％．既保持了原有测量方法(慢速热平衡、测量时间长)的精度．又缩短了秒测量时间。     

Distributed Entangled State Production by Using Quantum Repeater Protocol

We consider entangled state production utilizing a full optomechanical arrangement, based on which we create entanglement between two far three-level V-type atoms using a quantum repeater protocol. At first, we consider eight identical atoms (1,2,? ,8), while adjacent pairs (i,i +?1) with i =?1,3,5,7 have been prepared in entangled states and the atoms 1, 8 are the two target atoms. The three-level atoms (1,2,3,4) and (5,6,7,8) distinctly become entangled with the system including optical and mechanical modes by performing the interaction in optomechanical cavities between atoms (2,3) and (6,7), respectively. Then, by operating appropriate measurements, instead of Bell state measurement which is a hard task in practical works, the entangled states of atoms (1,4) and (5,8) are achieved. Next, via interacting atoms (4,5) of the pairs (1,4) and (5,8) and operating proper measurement, the entangled state of target atoms (1,8) is obtained. In the continuation, entropy and success probability of the produced entangled state are then evaluated. It is observed that the time period of entropy is increased by increasing the mechanical frequency (ω_M) and by decreasing optomechanical coupling strength to the field modes (G). Also, in most cases, the maximum of success probability is increased by decreasing G and via decreasing ω_M.