温度对长焦距测量精度的影响

 基于Ronchi光栅的泰伯效应,在理论上分析了温度场的波动对长焦距测量系统稳定性的影响。通过大量实验研究验证了在长焦距测量系统中内部和外部温度场的波动引起空气折射率的随机变化,进而影响到测量系统焦距测量值的稳定性。在对测量系统He-Ne激光源采取水循环降温、切断系统外部冷热源、对测量系统中光栅对采取隔热封装等有效措施后,使长焦距测量系统的重复性测量精度提高了5～8倍,标准差达到了0.1‰左右,测量数据波动范围在5 mm左右,其测量精度及其稳定性均达到了实际测量的要求。     

Ictal imaging using functional magnetic resonance

Magnetic resonance imaging (MRI) can now provide maps of human brain function with high spatial and temporal resolution. This noninvasive technique can also map the coritical activation that occurs during focal seizures, as demonstrated here by the results obtained using a conventional 1.5 T clinical MRI system for the investigation of a 4-year-old boy suffering from frequent partial motor seizures of his right side. FLASH images (TE = 60 ms) were acquired every 10 s over a period of 25 min, and activation images derived by subtracting baseline images from images obtained during clinical seizures. Functional MRI revealed sequential activation associated with specific gyri within the left hemisphere with each of five consecutive clinical seizures, and also during a period that was not associated with a detectable clinical seizure. The activated regions included gyri that were structurally abnormal. These results demonstrate (a) that functional MRI can potentially provide new insights into the dynamic events that occur in the epileptic brain and their relationship to brain structure; and (b) that there is the possibility of obtaining similar information in the absence of clinical seizures, suggesting the potential for studies in patients with interictal electrical disturbances.     

Algebraic and geometric interpretations of adsorption excess quantities

The algebraic methods of Hansen and Goodrich and the geometric methods of Motomura, Good and Everett were applied to define and investigate adsorption excess quantities at a solid/binary liquid interface. Both single-plane and two-plane geometric constructions were found to be consistent with the algebraic method. Relations between the relative, molar reduced and volumetric reduced areal excess concentrations and the amounts of components actually present in the interfacial layer are discussed.     

The smooth solutions of a class of coupled KdV equations.

This paper is devoted to the study of the periodic initial boundary value problem and Cauchy problem for the coupled KdV equations. By the Galerkin method and sequential approximation, we get a seies of priori estimates and establish the existence of classical local solution to the periodic problem for the system. Then we obtain the existence and uniqueness of global smooth solution when the coefficients of the system satisfy certain conditions by energy menthod, conserved quantities and nonconservative quatity I(u,v).     

Preliminary observations on magnetic resonance imaging in refractory epilepsy

We are studying the use of magnetic resonance (MR) imaging in localization of epileptogenic foci in patients with medically refractory partial epilepsy. Imaging is performed using a prototype resistive unit operating at 0.15 T. All studies include 7 mm axial sections obtained with a partial saturation sequence (TR = 200 msec) in which signals are recovered with a spin echo (TE = 11 msec) and images reconstructed using a modified 2D Fourier transform technique. Since the temporal lobe and limbic system are the commonest site of seizure foci in this group of patients, examinations were performed with the plane of section parallel to the temporal horns of the lateral ventricles.

Consensus interpretations by a radiologist, neurologist and neurosurgeon have recognized findings considered possibly abnormal in six of 11 epilepsy patients and none of six normal volunteers.

These preliminary results indicate that further study is warranted in this group of patients. Critical evaluation of such findings must be carried out in a larger group including normals and patients with a variety of neurologic disorders.     

关于有心力的几点注记

分别讨论了三种类型的有心力：Ｆ＝Ｆ（ｒ）ｅｒ、Ｆ＝Ｆ（ｒ）ｅｒ及Ｆ＝（α／ｒ２）ｅｒ的对称性与守恒量；并指出偏心率矢量或Ｒｕｎｇｅ－Ｌｅｎｚ矢量ε＝［αｅｒ＋Ｖ×Ｌ］／｜α｜的重要性．     

高功率超短脉冲激光的远场描述方法

 以随机统计和数值模拟为研究手段，对高功率超短脉冲激光的远场描述方法进行了分析研究。结果表明：对理想超高斯光束，半高全宽内包含的能量百分数最大不超过70%，且随着阶数增大而逐渐降低。在光束质量较好时，远场焦斑的半高全宽基本保持不变。由焦斑的半高全宽计算得到的聚焦功率密度，与半高全宽之间没有明确的关系，但与Strehl比以及半高全宽内包含的能量之间具有明确的线性增长关系。对追求高的功率密度的激光脉冲，单纯用半高全宽或者几倍的衍射极限来描述远场是远远不够的，用Strehl比或者半高全宽内包含的能量百分数来表征功率密度更为恰当。     

THALES long wave QWIP thermal imagers

THALES have developed for volume manufacture high performance low cost thermal imaging cameras based on the THALES Research Technology (TRT) third generation gallium arsenide long wave QWIP array. Catherine XP provides 768 × 575 CCIR video resolution and Catherine MP provides 1280 × 1024 SXGA video resolution. These compact and rugged cameras provide 24 h passive observation, detection, recognition, identification (DRI) in the 8–12 μm range, providing resistance to battlefield obscurants and solar dazzle, and are fully self contained with standard power and communication interfaces. The cameras have expansion capabilities to extend functionality (for example, automatic target detection) and have network battlefield capability. Both cameras benefit from the high quantum efficiency and freedom from low frequency noise of the TRT QWIP, allowing operation at 75 K, low integration times and non interruptive non uniformity correction. The cameras have successfully reached technology readiness level 6/7 and have commenced environmental qualification testing in order to complete the development programmes. These latest additions to the THALES Catherine family provide high performance thermal imaging at an affordable cost.     

Towards dualband megapixel QWIP focal plane arrays

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024 × 1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95 K operating temperature with f/2.5 optics at 300 K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70 K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90 K and 70 K operating temperatures respectively, with similar optical and background conditions. In addition, we have demonstrated MWIR and LWIR pixel co-registered simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024 × 1024 pixel arrays and the progress of dualband QWIP focal plane array development work.     

Focal shift of apodized truncated hyperbolic-cosine-Gaussian beam

Focal shift of hyperbolic-cosine-Gaussian beams induced by pure phase apodizer was investigated theoretically. The pure phase apodizer consists of three concentric zones: center circle zone, inner annular zone and outer annular zone. And the phase variance of the inner annular zone is adjustable. Results show that intensity peak moves far from optical aperture and then shrinks sharply for certain radii of zones with increasing phase variance of the inner annular zone. Simultaneously, one new intensity peak occurs near optical aperture, moves far from the optical aperture, and then becomes intensity maximum peak, and repeats the evolution process of the former intensity peak. Tunable focal shift occurs with focal switch. Decreasing the phase variance can change the move direction of the intensity peaks. In addition, the maximum distance between the two intensity peaks can be altered by beam parameters of cosh parts, and the distance value increases and then decreases with increasing beam parameters of cosh parts for certain radii of zones. Tunable focal shift is also discussed to construct optical tweezers.