Status of the MAX IV Laboratory

On the day of the 2016 summer solstice, June 21, MAX IV, the new synchrotron radiation facility in Lund, Sweden, will be inaugurated. MAX IV is setting a new standard in terms of emittance, thereby providing beamlines with the best possible brilliance and coherence. At the same time, MAX IV continues a more than three-decades-long successful history of Swedish synchrotron-radiation-based research. The activities at the present MAX-lab, which officially started when the MAX I storage ring opened for users in 1986, have been concluded with a “last beamdump” ceremony for the MAX II and MAX III storage rings on December 13, 2015, Saint Lucy's Day. In Sweden, the winter solstice is celebrated with a festival of light.     

EquatorialE region electric fields — longitudinal differences in diurnal reversal times

The times of reversal of east-west electrostatic field in the ionosphere near the equator in the Indian zone have been estimated from the measurements of ionospheric drift at Thumba. The reversal of electric field in the morning from westward to eastward is delayed with respect to the sunrise at 100 km by 1.5 hr during winter and by about 3 hr during summer months. The reversal in the evening from eastward to westward occurs around 2100 hrs,i.e., well after sunset during winter months and around 16–17 hrs,i.e., well before sunset during summer months. The electric field in the American zone is known to reverse 1–2 hr after the sunrise and sunset at 100 km; the duration of daytime eastward electric field varies with season between 12 and 16 hr. In the Indian zone, duration of the eastward field during the J months is only 8 hr. These longitudinal differences in the reversal times of electrostatic field are suggested to be the cause of longitudinal differences in the equatorial ionosphere,viz., high incidence of blanketing sporadicE layer in the Indian zone and the longitudinal differences in the occurrence of spreadF.     

西藏地区近地晴天大气电场气象效应和时间变化研究

基于西藏羊八井宇宙线观测站在2006年3月至2011年6月期间记录的近地大气电场数据, 分析研究了该地区近地晴天大气电场气象效应和时间变化特征. 气象效应分析结果显示, 该地区近地晴天大气电场与三个气象参量(大气压强、温度和相对湿度)的长时间变化趋势基本一致, 并有明显的季节效应. 冬春季, 大气电场强度整体水平相对较低, 约为0.14 kV/m; 夏秋季, 电场强度水平相对较高, 为0.18 kV/m左右. 近地晴天大气电场强度与大气温度间的线性相关性最强, 拟合相关系数达到0.89; 与大气压强和相对湿度间的线性相关性相对较弱, 拟合相关系数依次为0.43和0.53. 傅里叶分析结果表明: 晴天大气电场时间变化受太阳日周期、半太阳日周期及其三、四次谐波分量调制作用, 调制强度依次减弱. 西藏地区近地晴天大气电场日变化特征呈大陆简单型, 即双峰双谷. 主、次峰谷分别出现在白天和夜间, 主峰谷出现的早晚因季节不同略有差异, 次峰谷出现的早晚因季节不同差异相对较大.     

电磁脉冲与窄缝腔体耦合共振特性分析

 应用时域有限差分法模拟计算了电磁脉冲对窄缝和窄缝腔体的线性耦合过程。通过定义能量耦合传输系数，分析耦合能量随窄缝宽度和厚度及时间的变化关系，得出在正弦波调制的高斯脉冲源激励下，窄缝和窄缝腔体的耦合共振特性。     

微波脉冲与孔阵矩形腔体耦合的数值模拟研究

利用时域有限差分(FDTD)方法对微波脉冲与孔阵矩形腔体的耦合过程进行了数值模拟研究. 当孔缝阵中的孔缝长边垂直于入射电场方向时, 详细分析了微波脉冲与孔缝阵矩形腔体的耦合过程中孔阵面上各个孔缝中心点的电场分布情况. 结果表明, 在平行于入射电场方向上排列的孔缝中, 处在中心的孔缝场增强效应最弱, 孔缝场增强效应由中心向两侧依次对称的增强; 在垂直于入射电场方向上排列的孔缝中, 处在中心的孔缝场增强效应最强, 孔缝场增强效应由中心向两边依次对称的减弱. 同时, 讨论了孔缝孔阵中孔缝个数、间隔等因素对各孔缝中心点的场增强效应和腔体内的耦合场分布的影响.     

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为优化表面波放电的狭缝天线阵设计,给表面波放电装置的设计提供理论依据,对狭缝天线布局进行了理论和仿真计算分析。结果表明,宽缝辐射的电磁场比纵缝强,同相激励天线辐射的电磁场比异相激励强,更容易击穿空气产生等离子体。基于磁场强度同相分布规律对已经采用的纵缝天线阵进行改进,纵缝按照两侧交互并间隔半个波导波长布置,各个纵缝均为同相,产生等离子体效果更好。     

高功率微波缝隙耦合效应的试验研究

 利用高功率微波源对预设的11种不同尺寸的缝隙做了耦合效应试验，得到了这11种缝隙对试验波段的一般耦合特性。试验结果表明：窄缝的耦合效应有较强的极化特性；从波长与缝隙的长度相对关系对耦合效应的影响来看，波长与缝隙的长度相当时耦合效应最强；在UWB，L，S，X几个波段内，缝隙的宽度越窄，耦合效应越弱；缝隙的深度能明显影响其耦合效应，随缝深的增加，耦合效应逐渐减弱；辐射波脉宽变化对耦合效应基本没有影响。     

Runaway reaction due to gas-dynamic choking in solid explosive containing a single crack

This work predicts the critical conditions required for the onset of reaction runaway in a narrow high-explosive slot intended to simulate a crack. A model is developed where slot pressurization is attributed to gas-dynamic choking at the slot exit. The combination of the choking and a pressure-dependent reaction rate is shown to be capable of predicting runaway reaction for a range of slot dimensions and pressures, even when the explosive regression is considered. This model agrees with experimental pressure measurements of reaction runaway in slots and provides a mechanism for the erratic burning observed with some explosives under high pressure.     

超宽带电磁脉冲对腔体孔缝耦合效应的数值模拟

 为了解孔缝耦合对超宽带电磁脉冲干扰和毁伤电子设备的影响,应用时域有限差分法对长方腔体上不同形状的孔缝耦合效应进行了数值研究。选取mm量级的微小孔缝为研究对象,分析不同入射角度、不同脉宽的激励源对耦合效应的影响,得到了孔腔共振效应、孔缝增强效应和腔体内场强的分布规律。研究表明：长方孔在孔缝附近存在明显的增强效应,超宽带脉冲对正三角孔和方阵的耦合系数最小,脉宽短的入射脉冲耦合效应明显强于脉宽长的脉冲,耦合效应基本随入射角的减小而缓慢减小。     

Enhanced coupling of subterahertz radiation with semiconductor periodic slot arrays

In this work, a theoretical study of the coupling of TM polarized subterahertz (THz) radiation with periodic semiconductor rectangular slot arrays was conducted, using InSb as an example. Simulation results showed that the structure with 4-12 microm thickness provides over a 20-30-fold increase in the electric field at slot edges in a nanosize region ( approximately 500 nm). The enhancement of the THz electromagnetic field extends across the slots and reaches peak values at the edges due to discontinuity effects. Because of the strong local electromagnetic field enhancement, the structure can potentially be used for the development of novel biophotonic sensors, leading to improved detection sensitivity.     

放气槽布局形式及开槽角度对二元高超声速进气道性能的影响

通过对典型二元高超声速进气道进行数值仿真,研究了放气槽的布局形式以及放气槽的开槽角度θ对进气道总体性能的影响规律。研究结果表明:在放气总有效流通面积不变的前提下,多个放气槽的布局形式能够以更少的流量损失换取总压恢复系数的显著提升,且槽的数量越多,单个槽的有效流通面积越小,σ提升得越多,但当单个槽的有效流通面积d小于0.4H_th（按喉道高度无量纲化）时,这种变化趋势趋于平缓。当开槽角θ介于30°~120°时,放气量流量比随角度的增加而降低;当120°≤θ≤150°时,放气流量比随θ的增加而增加;30°≤θ≤150°时,喉道总压恢复系数σ随θ的增加而降低,而喉道压比Π随θ的增加而单调增加。因此采用多个0.2H_th~0.4H_th有效流通面积的放气槽为较理想的放气布局形式,而开槽角度可根据实际需要来选取。      

高功率微波行波阵列纵向宽角扫描特性

利用机械调节波导宽边尺寸可变化波导波长,从而实现变频波束扫描相同的效果,针对窄边辐射波导行波阵的波束扫描特性进行了分析,以实现宽角波束扫描为目标,着重分析了不同辐射缝隙间距下变化宽边所能得到的最大波束扫描范围。设计了通过变化宽边尺寸实现宽角扫描的X波段窄边辐射波导缝隙阵,设计波束扫描范围指向波导馈入端,避开阵列法向辐射(此方向辐射效率较低),实现了29°的连续波束扫描范围,在波束扫描范畴内增益下降小于3 dB,辐射效率大于62%;设计缝隙宽度3 mm, 波导长度约1 m(缝隙数40),单根波导缝隙天线可实现高功率微波功率容量70 MW。     

不同形状孔缝微波耦合的实验研究

 探讨了椭圆、圆环、方环、十字交叉形、圆形、正方形、正三角形及双矩形孔缝在2～18GHz频率范围内的耦合系数，并与矩形孔缝的耦合特性进行了比较。结果表明: 各种不同形状孔缝微波耦合的共振特性与其纵横比有关, 纵横比较大的孔缝耦合共振现象比较明显，纵横比较小的孔缝耦合特性趋于高通；各种孔缝的共振频率与孔缝长度有密切关系。     

Diffraction of monochromatic waves on a metallic cylinder with longitudinal slots

The projection matching method is applied to the calculation of a circular cylindrical slot line with one and two slots. The diffraction problem is studied at near-resonance frequencies.     

利用互补天线原理求解孔缝的共振性能

 利用互补天线原理从理论上推导了真空、介质窄缝的共振频率公式,在理想窄缝长度小于5倍波长、辐射角度偏离垂直方向小于30°的情况下,孔缝的共振频率点仍然可以用半波振子的辐射情况来解释,共振点满足孔缝长度等于入射波的半个波长;介质窄缝等效为半个孔缝深度的微带贴片天线,不同介电常数介质填充时的共振频率理论公式推导值和数值模拟值基本一致,相对误差在5%以内。进一步分析了窄缝阵列的耦合性能,结果表明互补天线原理可以很好地应用于分析和求解孔缝的共振性能。     

宽边可调缝隙波导中缝隙谐振电导的变化规律

通过建立理论模型研究了波导窄边缝隙天线中缝隙随着波导宽边尺寸调节过程中其谐振电导的变化规律,包括缝隙的宽度、缝隙切入宽边的深度、波导壁厚等对谐振电导及谐振长度的影响。得到了较为准确的拟合公式,利用该公式计算得到的缝隙参数能够满足工程设计的需要。此外,还分析了缝隙辐射电场随波导宽边调节的变化情况。     

轴向斜缝机匣处理与转子通道之间耦合流动分析

轴向斜缝机匣处理能够有效地扩大压气机的稳定工作范围,本文对轴向斜缝处理机匣与亚音速压气机转子通道之间的耦合流动进行了时间精确的全三维数值模拟,数值结果所获得的总性能与试验结果符合较好。详细分析了处理机匣与转子通道之间非定常干涉现象以及处理机匣结构引入后转子顶部区域不同的流场结构,数值计算结果表明,对具有高损失高阻塞效应的间隙泄漏流及其间隙泄漏涡的控制是轴向斜缝机匣处理扩大压气机稳定工作裕度的主要原因。     

波导缝隙阵列天线高功率微波应用探索

设计了一种波导窄边缝隙天线阵,其微波传输工作于行波状态,绝大部分能量被缝隙耦合辐射,其余能量被匹配负载吸收。通过等效电路的方法,使得各个缝隙达到均匀辐射,从而具备可拓展组阵能力,此外通过设计移相结构改变相位差,实现方位角方向的波束扫描。该缝隙天线工作在行波状态,避免了电场集中现象的出现,且工作于真空环境,具有较高的功率容量。     

Opportunistic spectrum access for TDMA-based cognitive radio networks

In this paper, opportunistic spectrum access is proposed for TDMA-based cognitive radio networks. In TDMA-based networks, the time is divided into slots with fixed length one by one. If a primary user (PU) needs to transmit data, one or several slots will be used. Otherwise, the slots are idle and can be utilized by secondary users (SUs). When SUs want to use the licensed channel, they should sense the channel at the beginning period of each slot. Then SUs exchange their sensing results and make the same decision about the channel state (idle or used by PUs), which could reduce the probability of false sensing. The aforementioned duration is called spectrum sensing phase. When SUs decide there is an idle channel, they contend to use the channel at the rest time of the slot. The duration is called access phase. In this period, SUs contend the channel with backoff counters. When the remaining time is less than one data transmission duration, SUs cannot transmit data packets. Therefore, the remaining time is wasted. To solve this problem, SUs transmit control packets with small length in the remaining time instead. The SU who exchange control packets successfully reserves the channel and sends a data packet prior to other SUs in access phase of the next idle slot. Obviously, this reserved transmission is without collision. The independent spectrum sensing, channel state decision and control packets reservation influence the performance of SUs. The proposed scheme is formulated with all above factors. Simulations which consist with the numerical results show the proposed access scheme achieve higher throughput than the existed scheme without channel reservation.     

矩形孔缝耦合特性实验研究

 对矩形孔缝在微波频率为2～18GHz范围内的耦合系数进行了实验研究；建立了实验方法和实验装置。实验结果表明：对于矩形孔缝，当入射电场方向垂直于孔缝长边时，在微波波长约等于2倍孔缝长度时，发生共振效应，在该频率附近一定带宽内耦合系数最大，并且在共振频率处存在着场增强效应。