光频支声子对二维Heisenberg铁磁系统磁激发的影响

在二维复式正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型. 利用松原格林函数理论研究了系统的磁激发，计算了布里渊区的主要对称点线上的磁振子色散曲线，比较了光频支声子与声频支声子对系统磁激发的影响以及各项参数的变化对磁振子软化的影响. 发现光频支声子-磁振子耦合对磁振子软化起主要作用，尤其是纵向光频支声子对磁振子软化起更大的作用，并且非磁性离子的光频支声子对磁振子软化的作用比磁性离子的光频支声子对磁振子软化的作用更显著.     

Functional neuroimaging of inner fields-of-view with 2D-selective RF excitations

Echo-planar imaging is widely used in functional neuroimaging but suffers from its pronounced sensitivity to field inhomogeneities that cause geometric distortions and image blurring which both limit the effective in-plane resolution achievable. In this work, it is shown how inner-field-of-view techniques based on 2D-selective RF excitations (2DRF) can be applied to reduce the field-of-view in the phase-encoding direction without aliasing and increase the in-plane resolution accordingly. Free-induction-decay (FID) EPI and echo-train-shifted (T2*-weighted) and standard (T2-weighted) spin-echo (SE) EPI with in-plane resolutions of up to 0.5×1.0 mm² (slice thickness 5 mm) were acquired at 3 T. Unwanted signal contributions of 2DRF side excitations were shifted out of the object (FID-EPI) or of the refocusing plane by tilting the excitation plane (SE-EPI). Brain activation in healthy volunteers was investigated with checkerboard and finger-tapping block-design paradigms. Brain activation could be detected with all sequences and contrasts, most reliably with FID-EPI due to its higher signal amplitude and the longer 2DRF excitation that are more sensitive to magnetic field inhomogeneities. In conclusion, inner-FOV EPI based on 2DRF excitations could help to improve the spatial resolution of fMRI of focal target regions, e.g. for applications in the spinal cord.     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用.     

Excitation of Propagating Plasmons in Semi-Infinite Graphene Layer by Free Space Photons

By investigating the diffraction of plane waves by a semi-infinite solution for propagating surface plasmons in graphene, which can be excited graphene edge. The theoretical results are confirmed by numerical simulations. excite propagating surface plasmons in graphene where the graphene edge plays graphene layer, we present a rigorous by incident plane waves through the Our results reveal a convenient way to an important role.     

Semi-adiabatic Shinnar–Le Roux pulses and their application to diffusion tensor imaging of humans at 7T

The adiabatic Shinnar–Le Roux (SLR) algorithm for radiofrequency (RF) pulse design enables systematic control of pulse parameters such as bandwidth, RF energy distribution and duration. Some applications, such as diffusion-weighted imaging (DWI) at high magnetic fields, would benefit from RF pulses that can provide greater B₁ insensitivity while adhering to echo time and specific absorption rate (SAR) limits. In this study, the adiabatic SLR algorithm was employed to generate 6-ms and 4-ms 180° semi-adiabatic RF pulses which were used to replace the refocusing pulses in a twice-refocused spin echo (TRSE) diffusion-weighted echo planar imaging (DW-EPI) sequence to create two versions of a twice-refocused adiabatic spin echo (TRASE) sequence. The two versions were designed for different trade-offs between adiabaticity and echo time. Since a pair of identical refocusing pulses is applied, the quadratic phase imposed by the first is unwound by the second, preserving the linear phase created by the excitation pulse. In vivo images of the human brain obtained at 7 Testa (7 T) demonstrate that both versions of the TRASE sequence developed in this study achieve more homogeneous signal in the diffusion-weighted images than the conventional TRSE sequence. Semi-adiabatic SLR pulses offer a more B₁-insensitive solution for diffusion preparation at 7 T, while operating within SAR constraints. This method may be coupled with any EPI readout trajectory and parallel imaging scheme to provide more uniform coverage for diffusion tensor imaging at 7 T and 3 T.     

面向传递路径分析方法研究的试验系统设计*

在传递路径分析理论研究中,经典传递路径分析要求在传递函数测量时拆卸激励源,为了减少工作量,设计一套面向传递路径分析方法研究的实验系统。以简化发动机模型作为激励源,真实汽车发动机悬置作为传递路径,简化车身内的响应为目标响应,建立一套完整的传递路径分析模型。在保留主要激励特征情况下简化发动机机体结构,将NI Compact RIO作为控制核心,激振器作为激励施加装置,以缸压信号和机体振动信号为激励信号对机体加载,实现发动机激励特征的模拟。最终验证该实验系统可模拟出发动机的结构噪声,采集信号中阶次成分明显,主要噪声频段基本吻合,可从阶次信号中提取对应转速信息。整个实验系统结构简单,可作为载体用于传递路径分析方法的研究。     

Dynamical properties of the Haldane chain with bond disorder

By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at δ_∆ ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δ_c ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These “spins” can form the weakly coupled longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0.     

Asynchronous sampling for ultrafast experiments with low momentum compaction at the ANKA ring

A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented.     

Crystal Structure and Mass-, Electronic-, Infrared Spectral Studies on Hexaaqua Ni(II) Bis(O-Tolylazo-Citrazinate) Hexahydrate Complex

A new crystalline octahedral hexaaqua Ni(II) bis(o-tolylazo-citrazinate)hexahydrate complex was synthesized. The analytical data proved the formation of 1:2 stoichiometry. An X-ray structure investigation has been carried out. The triclinic space group is p and the unit cell parameters are a = 585.5 pm, b = 993 pm, c = 1139.4 pm, α = 101.6°, β = 97.4°, γ = 102.4°. Evaluation of intensity data revealed the structure with an R-value of 0.03 (2316 observed independent reflections). The compound consists of hexaaqua nickel(2+) ions, univalent anions of the carboxylic acid and six additional water molecules per