WIMP event rates in directional experiments: The diurnal variation signature

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Modern particle theories provide viable cold dark matter candidates with masses in the GeV-TeV region. All such candidates will be called WIMPs (Weakly Interacting Massive Particles). The nature of dark matter can only be unraveled by its direct detection in the laboratory. In this work we present some theoretical elements relevant to the direct dark matter detection experiments, paying particular attention to directional experiments, i.e. experiments in which not only the energy but the direction of the recoiling nucleus is observed. Since the direction of observation is fixed with respect to the Earth, while the Earth is rotating around its axis, in a directional experiment the angle between the direction of observation and the Sun’s direction of motion will change during the day. So, since the event rates sensitively depend on this angle, the observed signal in such experiments will exhibit very interesting and characteristic periodic diurnal variation.     

Organization of matter into one-dimensional units on designed media

The organization of magnetic materials into one-dimensional micro- and nanowires on designed media is discussed, exemplified by two experiments on the microscale and nanoscale, with regard to particles as basic building blocks for the growth and development of matter.     

Improved and isotropic resolution in tomographic diffractive microscopy combining sample and illumination rotation

Tomographic Diffractive Microscopy is a technique, which permits to image transparent living specimens in three dimensions without staining. It is commonly implemented in two configurations, by either rotating the sample illumination keeping the specimen fixed, or by rotating the sample using a fixed illumination. Under the first-order Born approximation, the volume of the frequency domain that can be mapped with the rotating illumination method has the shape of a “doughnut”, which exhibits a so-called “missing cone” of non-captured frequencies, responsible for the strong resolution anisotropy characteristic of transmission microscopes. When rotating the sample, the resolution is almost isotropic, but the set of captured frequencies still exhibits a missing part, the shape of which resembles that of an apple core. Furthermore, its maximal extension is reduced compared to tomography with rotating illumination. We propose various configurations for tomographic diffractive microscopy, which combine both approaches, and aim at obtaining a high and isotropic resolution. We illustrate with simulations the expected imaging performances of these configurations.     

Abrasive resistance of arc sprayed carbonitride alloying self-shielded coatings

Wear-resistant coatings were prepared on the surface of the Q235 low-carbon steel plate by HVAS with the carbonitride alloying self-shielded flux-cored wire. Detection and analysis on the microstructure and properties of the coatings were carried out by using scanning electron microscope, microhardness tester and wear tester. The forming, the wear resistance and its mechanism of the coatings were studied. The results show that the coatings have good forming, homogeneous microstructure and compact structure. The coatings have good hardness, the average microhardness value reaches 520 HV_0.1, and the highest value is up to about 560 HV_0.1. As a result, the coatings have good abrasive wear performance and adhesion strength.     

Quark-diagram estimates ofCP violation in two-body baryonicB_d^0 - \bar B_d^0 decays

CP violation in partial-decay-rate asymmetries are examined for some two-body baryonic decays of \(B_d^0 - \bar B_d^0 \) system. We discuss two feasible experimental circumstances: the symmetrice ⁺ e ^? collisions (i) on theZ ⁰ resonance to produce incoherent \(B_d^0 \bar B_d^0 \) states, and (ii) just above the ?(4S) resonance to produceC=even \(B_d^0 \bar B_d^0 \) states. Using the quark-diagram scheme, we estimate the branching ratios of those decays, and the numbers ofb \(\bar b\) pairs needed for testing theCP-violating effects for 3σ signature. We find that the promising channels may beB _d ⁰ , \(\bar B_d^0 \to p\bar p\) , \(\Delta ^ + \bar \Delta ^ - \) , \(p\bar \Delta ^ - \) , \(\Delta ^ + \bar p\) , \(n\bar n\) , \(\Delta ^0 \bar \Delta ^0 \) , \(n\bar \Delta ^0 \) , \(\Delta ^0 \bar n\) , \(\Sigma _c^ + \bar \Sigma _c^ - \) , \(\Lambda _c^ + \bar \Lambda _c^ - \) , \(\Sigma _c^ + \bar \Lambda _c^ - \) , \(\Lambda _c^ + \bar \Sigma _c^ - \) , \(\Sigma _c^0 \bar \Sigma _c^0 \) , \(\Xi _c^0 \bar \Xi _c^0 \) , which should be interesting for experimental observation.     

仿长耳鸮翼型的参数化研究

以长耳鸮翼型为仿生原型,采用逆向工程方法提取鸮翼翼型下表面特征点并利用B样条曲线进行拟合建立鸮翼仿生重构模型。通过数值求解耦合Langtry-Menter SST模型的雷诺时均Navier-Stokes方程,研究了仿生翼型的前缘弧线曲率、前缘厚度、前端倾角、翼型中部下表面曲率以及尾部厚度等参数对翼型升阻比的影响,获得了一种能有效抑制大攻角下流动分离发生的仿生翼型。正交试验结果表明:翼型前缘厚度对仿生翼型的升阻比影响最大,随着翼型前缘厚度的减少,翼型升阻比增加;翼型下表面中部曲率和翼型尾部厚度均存在最优值使仿生翼型升阻比最大。     

基于发射光谱诊断的低温等离子体技术转化N2/NO气氛中NO的研究

建立了低温等离子体技术处理N₂/NO气氛中NO的实验系统,利用介质阻挡放电发射光谱诊断法分析了NTP技术处理NO的反应机理,以及研究了NTP系统的运行参数和N₂体积流量对NO转化率的影响规律。研究结果表明,随着V（_P-P）的增加,N₂发射光谱强度相对于NO发射光谱强度的比值增加,N₂第二正带系发射光谱强度增加,表明放电区间的高能电子浓度增大,有利于N₂离解成N原子,从而促使NO还原转化;增加N₂体积流量会使NO转化率降低,NO₂浓度升高。     

2.45 GHz ECR离子源的微波阻抗匹配

ECR离子源的等离子体阻抗对其微波传输与阻抗匹配设计至关重要。在中国科学院近代物理研究所现有的2.45 GHz ECR 质子源上,对等离子体阻抗进行了测量。首先用水吸收负载代替等离子体负载测量得到了所用微波窗阻抗,然后根据质子源测量数据,推算得到了等离子体阻抗。实验结果表明,脊波导输出端阻抗与后续负载不完全匹配,等离子体阻抗随微波功率变化呈非线性。这些结果为ECR离子源过渡匹配和微波窗的设计提供了参考依据。Plasma impedance of an ECR ion source is important for microwave transmission and impedance matching design. Plasma impedance was measured indirectly with the 2.45 GHz ECR proton source at the Institute of Modern Physics, Chinese Academy of Sciences. In the test, we got microwave window mpedance by using water absorption load instead of plasma load, and the source plasma impedance was derived from the test data with the 2.45 GHz ECR proton source and microwave window impedance. The experimental results show that ridge waveguide output impedance and the subsequent load does not exactly match, plasma impedance variation is nonlinear with microwave power. The achievedresult is useful in the design of ridged waveguide and microwave window.     

Ge组分分布对基区杂质非均匀分布的SiGe HBT温度特性的影响

众所周知, 双极型晶体管的设计主要是基区的设计. 一般而言, 基区的杂质分布是非均匀的. 本文首先研究了非均匀的杂质高斯分布对器件温度分布、增益和截止频率的温度特性的影响, 发现增益和截止频率具有正温度系数, 体内温度较高. 随后研究了基区Ge组分分布对这些器件参数的影响. 均匀Ge组分分布和梯形Ge组分分布的SiGe 异质结双极型晶体管增益和截止频率具有负温度系数, 具有较好的体内温度分布. 进一步的研究表明, 具有梯形Ge组分分布的SiGe 异质结双极型晶体管, 由于Ge组分缓变引入了少子加速电场, 不但使它的增益和截止频率具有较高的值, 而且保持了较弱的温度敏感性, 在增益、特征频率大小及其温度敏感性、体内温度分布达到了很好的折中.