Enantioselective synthesis of m-carboranylalanine, a boron-rich analogue of phenylalanine

The enantiomers of the highly lipophilic α-amino acid m-carboranyl-alanine [3-(1,7-dicarba-closo-dodecaborane(12)-1-yl)-2-aminopropanoic acid], a carborane containing analogue of phenylalanine, have been synthesised via hydroxyamination of the N-acyl derivative formed from 3-(m-carboranyl)propionic acid [3-(1,7-dicarba-closo-dodeca-borane(12)-1-yl)-2-propanoic acid] and Oppolzer's camphor sultam. The enantiomeric excess of both enantiomers of the amino acid was >98%. (S)-Configuration was assigned to the (+)-enantiomer (CH₃OH, 589 nm).     

同轴电缆自感系数问题的两种新解法

本文对圆柱型同轴电缆自感系数问题进行了深入的讨论．文中把同轴电缆看成是由大量的“子回路”并联构成“单匝回路”，从子回路间的磁耦合角度出发提出了两种全新的同轴电缆自感系数的求解方法。     

Detection of mycotic pseudoaneurysm of the ascending aorta using MRI

Mycotic pseudoaneurysms of the ascending aorta are rare cardiovascular lesions that carry the risk of potentially disastrous complications such as aortic rupture or widespread sepsis. Regardless of its location in the arterial system, this lesion carries a high mortality rate. Early diagnosis of mycotic pseudoaneurysm is paramount for optimizing the chances of surgical therapy. While imaging strategies of this lesion have included aortography, echocardiography, and computed tomography, the information gained from each of these individual studies may be acquired in a single MR imaging session. MRI offers the fundamental advantages of noninvasiveness, nonionization, and multiplanar imaging capabilities. Additionally, MRI provides excellent soft tissue contrast, a wide field of view, qualitative and quantitative flow analysis, and an independence of operator expertise or patient body habitus.     

Application of spectroscopic imaging in epilepsy

Functional and anatomical neuroimaging has had a dramatic effect on the evaluation of patients for seizure surgery. The demonstration by PET that the epileptogenic focus has interictal metabolic abnormalities has allowed a greater number of patients to come to seizure surgery, with fewer of these patients requiring intracranial electrode evaluations. Metabolic changes have also been demonstrated utilizing single voxel and whole brain ¹H and ³¹P MRS imaging techniques with the interictal focus characterized by increased Pi, pH, and decreased PME and NAA. These findings can be used to accurately lateralize temporal lobe as well as frontal lobe epilepsy. Furthermore, there is evidence that these findings can be used to localize the seizure focus with the changes specific for the epileptogenic region; although, more diffuse changes both ipsilaterally and contralaterally have been seen. In patients with anterior hippocampal seizure foci the pH is significantly alkaline only in the ipsilateral hippocampus, whereas the increased Pi and decreased PME can be seen throughout the ipsilateral temporal lobe. When compared to controls the contralateral hemisphere is acidotic. Decreased NAA concentrations as well as NAA/Cr ratios have been demonstrated in the epileptogenic region in temporal and frontal lobe epilepsy. The decreased NAA has been correlated with the severity of cell loss, and may be a more sensitive measure than qualitative or quantitative measures of the hippocampal atrophy; however, the NAA decrease is more widespread than just the epileptogenic focus but may be maximal at the site of seizure initiation. In preliminary work, NAA maps of deviation from normality have suggested the maximal change to coincide with the epileptogenic region. These results suggest that in focal epilepsy there is abnormal metabolic activity throughout the brain detectable by MRS, with patterns of metabolic asymmetry that are useful for seizure localization.     

Synthesis and characterization of 7-(CH3)3N-4- {2,4-(NO2)2C6H3S}-nido-7-CB10H11 and its Biodistribution in C57B16 Mice Bearing B16 Melanoma

7-(CH₃)₃N-4-{2,4-(NO₂)₂C₆H₃S}-nido-7-CB₁₀H₁₁ has been synthesized through a Friedel-Crafts substitution reaction on 7-(CH₃)3N-nido-7- CB₁₀H₁₂. A biodistribution study in mice with implanted B16 melanoma indicates that the compound locates in neoplastic tissue at concentrations which suggest that its use in ¹⁰B neutron capture therapy may be feasible.     

Entropy production in open volume-preserving systems

We describe a mechanism leading to positive entropy production in volume-preserving systems under nonequilibrium conditions. We consider volume-preserving systems sustaining a diffusion process like the multibaker map or the Lorentz gas. A continuous flux of particles is imposed across the system resulting in a steady gradient of concentration. In the limit where such flux boundary conditions are imposed at arbitrarily separated boundaries for a fixed gradient, the invariant measure becomes singular. For instance, in the multibaker map, the limit invariant measure has a cumulative function given in terms of the nondifferentiable Takagi function. Because of this singularity of the invariant measure, the entropy must be defined as a coarse-grained entropy instead of the fined-grained Gibbs entropy, which would require the existence of a regular measure with a density. The coarse-grained entropy production is then shown to be asymptotically positive and, moreover, given by the entropy production expected from irreversible thermodynamics.     

The multi‐stage centred‐scheme approach applied to a drift‐flux two‐phase flow model

For two‐phase flow models, upwind schemes are most often difficult do derive, and expensive to use. Centred schemes, on the other hand, are simple, but more dissipative. The recently proposed multi‐stage (MUSTA ) method is aimed at coming close to the accuracy of upwind schemes while retaining the simplicity of centred schemes. So far, the MUSTA approach has been shown to work well for the Euler equations of inviscid, compressible single‐phase flow. In this work, we explore the MUSTA scheme for a more complex system of equations: the drift‐flux model, which describes one‐dimensional two‐phase flow where the motions of the phases are strongly coupled. As the number of stages is increased, the results of the MUSTA scheme approach those of the Roe method. The good results of the MUSTA scheme are dependent on the use of a large‐enough local grid. Hence, the main benefit of the MUSTA scheme is its simplicity, rather than CPU ‐time savings. Copyright © 2006 John Wiley & Sons, Ltd.     

Non-Contact Eddy Current Excitation Method for Vibration Testing

When a conductive material is subjected to a time changing magnetic field, eddy currents are induced in that structure. The eddy currents circulate inside the conductor resulting in a magnetic field that interacts with the applied field. The eddy current field is such that it opposes the change in flux resulting in a force between the source and conductor. The time changing magnetic field necessary to induce an electrometric force in the materials can be generated through a variety of different ways. In the present study, a permanent magnet will be mounted to the tip of an electromagnetic shaker such that the motion of the magnet relative to the structure will cause a time changing field and the formation of eddy currents. The actuator will be demonstrated to be beneficial due to its ability to apply actuation forces without contacting the structure. This study will show that the non-contact nature of the system eliminates mass loading and added stiffness which are downfalls of traditional excitation techniques. Additionally, it will be shown that the use of a non-contact device preserves the mode shapes of the structure, whereas a stinger results in distortions due to the added constraint. Using this concept, a model of the actuation system will be developed, allowing the beams response to be simulated. The actuation system will then be used to excite a cantilever beam to obtain the modal parameters without contacting the structure. The novel non-contact actuation system developed in this paper provides a new method performing vibration testing of on lightweight or flexible structures while preserving their dynamics.     

Site selection NMR study on electronic state in and near vortex core of YBa2Cu4O8

We report a site-selective ¹⁷O spin-lattice relaxation rate T₁⁻¹ in the vortex state of YBa₂Cu₄O₈. We found that T₁⁻¹ at the planar sites exhibits an unusual nonmonotonic NMR frequency dependence. Based on T₁⁻¹ in the vortex core region, we establish strong evidence that the local density of states within the vortex core is strongly reduced.