Measuring T₂ and T₁, and imaging T₂ without spin echoes

During adiabatic excitation, the nuclear magnetization in the transverse plane is subject to T(2) (spin-spin) relaxation, depending on the pulse length τ. Here, this property is exploited in a method of measuring T(2) using the ratio of NMR signals acquired with short and long-duration self-refocusing adiabatic pulses, without spin-echoes. This Dual-τ method is implemented with B(1)-insensitive rotation (BIR-4) pulses. It is validated theoretically with Bloch equation simulations independent of flip-angle, and experimentally in phantoms. Dual-τT(2) measurements are most accurate at short T(2) where results agree with standard spin-echo measures to within 10% for T(2) ≤ 100 ms. Dual-τ MRI performed with a long 0° BIR-4 pre-pulse provides quantitative T(2) imaging of phantoms and the human foot while preserving desired contrast and functional properties of the rest of the MRI sequence. A single 0° BIR-4 pre-pulse can provide T(2) contrast-weighted MRI and serve as a "T(2)-prep" sequence with a lower B(1) requirement than prior approaches. Finally, a Tri-τ experiment is introduced in which both τ and flip-angle are varied, enabling measurement of T(2), T(1) and signal intensity in just three acquisitions if flip-angles are well-characterized. These new methods can potentially save time and simplify relaxation measurements and/or contrast-weighted NMR and MRI.     

T–T Neutron Spectrum from Inertial Confinement Implosions

A new technique that uses inertial confinement implosions for measuring low-energy nuclear reactions important to nuclear astrophysics is described. Simultaneous measurements of n–D and n–T elastic scattering at 14.1 MeV using deuterium–tritium gas-filled capsules provide a proof of principle for this technique. Measurements have been made of D(d,p)T (dd) and T(t,2n)⁴He (tt) reaction yields relative to the D(t,n)⁴He (dt) reaction yield for deuterium–tritium mixtures with f _T /f _D between 0.62 and 0.75 and for a wide range of ion temperatures to test our understanding of the implosion processes. Measurements of the shape of the neutron spectrum from the T(t,2n)⁴He reaction have been made for each of these target configurations.     

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介绍了一种强磁场高温超导螺线管磁体电磁性能的优化方法。通过编写Matlab数据处理程序优化了一个中心磁感应强度为8T、内径为20cm的磁体。利用有限元分析法分析已优化磁体的磁场分布,得到磁体在垂直方向的最大磁感应强度值与Matlab数据处理程序计算的结果基本吻合。     

核磁共振T1、T2加权成像

探讨核磁共振T1、T2加权成像的图像特点。     

T1系超导体中T1含量的控制

Ｔ１－２２２３和Ｔ１－２２１２相超导样品经Ｔｌ２Ｏ３蒸气处理超导转变温度发生明显的变化，Ｔｃ的变化来源于样品中Ｔ１含量的变化，Ｔｌ２Ｏ３蒸气能有效地阻止Ｔ１基超导体中Ｔ１的损失，随着Ｔｌ２Ｏ３蒸气压的增加Ｔ１损失明显减少，这是一种控制Ｔ１浓度的有效方法。     

T ∞-Fuzzy observables

Observables are defined as homomorphisms from the Borel-algebra into a family of fuzzy sets considered with respect to the Giles connectives. Algebraic operations with observables are introduced and their relation to the corresponding operations with fuzzy random variables is explained.     

Determination of T1ρ values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T₁ρ relaxation times for normal tissues were determined. Furthermore, T₁ρ was compared to T₁ and T₂ relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T₁ρ values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T₁ρ relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T₁ρ demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T₁ρ values measured at locking field strength (B1L) of 35 μT were close to T₂ values, the only exception being fat tissue, which showed T₁ρ values much longer than T₂ values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.     

New pulse sequences for T1− and T1/T2−contrast enhancing in NMR imaging

Improved pulse sequences DIFN (abbreviation of the words: DIFferentiation by N pulses), 90° − τ₁ − 180° − τ₁ − … 180° − τ_n, with optimised time intervals τ₁ for T₁ measurement and contrast enhancing in NMR imaging are presented. The pulse sequences DIFN have a better sensitivity to T₁ than the well-known pulse sequence SR. In contrast to the IR pulse sequence, the information given by the DIFN pulse sequence is more reliable, because the NMR signal does not change its sign. For a given time interval τ₀ ≤ (0.1 − 0.3) T₁′ the DIFN pulse sequences serve as T₁-filters. They pass the signal components with relatively short T₁ < T₁′ and suppress the components with relatively long T₁ < T₁′. The effects of the radiofrequency field inhomogeneity and inaccurate adjusting of pulse lengths are also considered. It is also proposed in this work to use the joint T₁T₂-contrast in NMR imaging obtained as a result of applying the DIFN pulse sequences in combination with the well-known Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The region of interest, where the contrast should be especially enhanced, is specified by the two times at which measurements are performed, which allow the amplitudes of pixels to reach some defined levels by spin-lattice and spin-spin relaxation.     

T=+0及T=-0状态的涨落特性

本文指出，当 Ｔ→±０时，热力学量的涨落并非都趋于零．特别象温度、能量和熵这样一些重要热力学量的相对涨落，随着Ｔ→±０而迅速地增大．它是由于体系能级的分立性所造成的．这表明了在足够低或足够高的温度下，唯象热力学将失去意义．这个结论具有原则性的意义，尽管目前低温或负温技术还远不能达到这样的温度领域．此外，Ｔ＝±０状态还可能存在非热运动所引起的涨落，如量子力学的描述本身所固有的不确定性等现象．     

Geodesic Deviation Equation in ΛCDM f(T,T) Gravity

The geodesic deviation equation has been investigated in the framework of \(f(T,\mathcal {T})\) gravity, where T denotes the torsion and \(\mathcal {T}\) is the trace of the energy-momentum tensor, respectively. The FRW metric is assumed and the geodesic deviation equation has been established following the General Relativity approach in the first hand and secondly, by a direct method using the modified Friedmann equations. Via fundamental observers and null vector fields with FRW background, we have generalized the Raychaudhuri equation and the Mattig relation in \(f(T,\mathcal {T})\) gravity. Furthermore, we have numerically solved the geodesic deviation equation for null vector fields by considering a particular form of \(f(T,\mathcal {T})\) which induces interesting results susceptible to be tested with observational data.     

双T网络相量图

本文从分析双T网络虚地输出端着手，借助串／并联等效变换，给出双T网络的电压／电流相量图和阻抗图；引入对称化处理概念；界定了双T网络的实际输入阻抗；建立了完备的阻抗方程组，并做了按指定输入阻抗设计电路的示范。     

管形装药T型发动机实验

本文给出了利用管形装药T型发动机实验的一些结果,说明了在装药几何的某一界限内,响应函数与推进剂燃烧面积无关. 一、实验条件与管形装药的特点 实验用燃烧室内径为5cm,内长为50cm.由于装药燃烧面积的改变带来的压力变化可通过掉换不同喉部直径的燃烧室喷管使其控制在要求的范围内.测量稳态压力的BYY-3传感器和测量振荡压力的BPR-3传感器分别安装在燃烧室两端.管形装药一端     

T2铜的低温比热

在1.4—27K的温区内测量了纯度为99.9％的国产T_2铜的比热,得出了T_2铜的电子比热系数γ为0.68mJ·mol_(-1)·K_(-2),德拜温度θ_D为339.7K。与国外的比热数据比较,显然在纯度相同的条件下,比热数据是一致的,且可以互换。     

解析T矩阵的变化性质

用Ｓｃｈｗｉｎｇｅｔ变分原理分析二体相互作用Ｔ矩阵解析式，在选定的势函数和参量条件下，Ｔ矩阵元具有理想的收敛性质。     

拉格朗日函数中的T与V

拉氏函数Ｌ＝Ｔ－Ｖ中的Ｔ与Ｖ必须是运动系统在惯性系中的动能与势能．当取非惯性系坐标作为广义坐标时，拉氏方程将直接给出运动系统在非惯性系中的相对运动微分方程．本文就单质点运动给出了直接证明．     

Mazatrol Fusion640T数控系统特点

本文主要通过作者对Mazatrol Fusion640T数控系统的使用，介绍了系统与其它控制系统不同的功能特点，包括强大的数据处理功能、PC与CNC融合技术、智能化对话式编程功能。同时，还举例说明了对话式编程与G功能代码和M功能代码编程的区别，以及对话式编程与其它编程方式相比，具有方便、快捷的优势。     

Generation of human thalamus atlases from 7 T data and application to intrathalamic nuclei segmentation in clinical 3 T T1-weighted images

The thalamus serves as the central relay station for the brain. It processes and relays sensory and motor signals between different subcortical regions and the cerebral cortex and it can be divided into several neuronal clusters referred to as nuclei. Each of these can possibly be subdivided into sub-nuclei. Accurate and reliable identification of thalamic nuclei is important for surgical interventions and neuroanatomical studies. This is however a challenging task because the small size of the nuclei and the lack of contrast over the thalamus region in clinically acquired images does not permit the visualization of their boundaries. A number of methods have been developed for thalamus parcellation but the vast majority of these relies on diffusion imaging or functional imaging. The low resolution of these images only permit localizing the largest nuclei. In this work we propose a method to segment smaller nuclei. We first present a protocol to build histological-like atlases from a series of high-field (7 Tesla) MR images acquired with different pulse sequences that each permits to visualize the boundaries of a subset of the nuclei. We use this protocol to scan 9 subjects and we manually delineate 23 thalamic nuclei following the Morel atlas naming convention for each of these subjects. Manual contours for the nuclei are subsequently utilized to create statistical shape models. With these data, we compare four methods for the segmentation of thalamic nuclei in 3 T images we have also acquired for the 9 subjects included in the study: (1) single atlas, (2) multi atlas, (3) statistical shape, and (4) hierarchical statistical shape in which thalamic nuclei are hierarchically fitted to the images, starting from the largest ones. Results of a leave-one-out validation study conducted on the nine image sets we have acquired show that the multi atlas approach improves upon the single atlas approach for most nuclei. Segmentations obtained with the hierarchical statistical shape model yield the highest accuracy, with dice coefficients ranging from 0.53 to 0.90, mean surface errors from 0.27 mm to 0.64 mm, and maximum surface errors from 1.31 mm to 2.52 mm for all nuclei averaged across test cases. This suggests the feasibility of using such approach for localizing thalamic substructures in clinically acquired MR volumes. It may have a direct impact on surgeries such as Deep Brain Stimulation procedures that require the implantation of stimulating electrodes in specific thalamic nuclei.