Quasiabelian landscapes of the traveling salesman problem are elementary

Regarding a permutation as a (multi-traveler) tour of the traveling salesman problem, we show that—regardless of the distance matrix—the landscape based on a quasiabelian Cayley graph belongs to the class of elementary landscapes, where the cost vector is an eigenvector of the Cayley Laplacian, and where local minima are below average.The quasiabelian case has the additional property that, because the cost vector is an eigenvector of the Cayley Laplacian, the landscape can be reduced into independent components under a Fourier transformation. We indicate the way this may result in parallel (and therefore computationally distributed) traversal of the landscape.     

Dissolution and assay of neptunium oxide

A case study for dissolution and assay of neptunium oxide is presented in this paper. A simple analytical method for completely dissolving neptunium oxide is described. Addition of 12 M HNO₃ is sufficient to dissolve neptunium oxide without precipitate formation. Various analytical chemistry methods were evaluated for neptunium assay including controlled potential coulometry, gas proportional counting/alpha spectrometry, gamma spectrometry using a high purity germanium detector, inductively coupled plasma-mass spectrometry, and isotope dilution-inductively coupled plasma-mass spectrometry. The precision and uncertainty of each analytical method is discussed.     

Spinal MR imaging in suspected metastases: correlation with skeletal scintigraphy

Bone scintigraphy (RN) and magnetic resonance imaging (MR) were prospectively and retrospectively correlated in 64 patients with suspected spinal metastatic disease and possible spinal cord compression. Images were retrospectively interpreted and compared with the prospective official RN and MR reports to help decide relative prospective lesion conspicuity. Spinal lesions were confirmed by radiography, computed tomography, myelography or MR and RN follow-up in 56 patients (88%). Prospectively, MR detected 11 lesions not reported on RN while RN detected two lesions not reported on MR. Retrospective review of RN detected six lesions previously not reported. Retrospectively MR showed all lesions. Those lesions seen only in retrospect by RN were rather subtle and would be difficult to detect prospectively. In general, lesions not well seen on RN had relatively more bone marrow abnormality and less cortical bone involvement. In some cases, MR imaging shows spinal marrow lesions not well seen on planar RN.     

Diagnosis of vertebral metastasis, epidural metastasis, and malignant spinal cord compression: are T(1)-weighted sagittal images sufficient?

The objective of this study was to determine whether T(1)-weighted sagittal images alone are adequate in the diagnosis of vertebral metastasis, epidural metastasis, and malignant spinal cord compression. Ninety-four complete magnetic resonance (MR) studies of the spinal column (a complete study consisting of T(1)-weighted sagittal images, T(2)-weighted sagittal images, and T(1)- and/or T(2)-weighted axial images) and 94 T(1)-weighted sagittal images alone (a subset of the complete studies) from 57 consecutive cancer patients over the last 2 years with clinically suspected cord compression were blindly and independently evaluated by four radiologists. The complete MR studies were used as the standard. Overall, the sensitivity of T(1)-weighted sagittal images alone to vertebral metastasis (87%) was statistically greater than cord compression (70%) (p = 0.05), and statistically greater than epidural metastasis (46%) (p 相似文献   

MRI findings in pulmonary sarcoidosis

Postero-anterior radiographs and magnetic resonance imaging (MRI) of the chest were performed in nine biopsy proven cases of sarcoidosis. MRI was more sensitive than a postero-anterior chest roentgenogram in detecting hilar and mediastinal adenopathy but less informative in detecting pleural and parenchymal disease.     

Collective spin states in the electron gas in different dimensions and geometries

We study spin longitudinal and transverse linear response of the 3-dimensional electron gas, metal clusters and quantum dots. When the systems are spin unpolarized in the ground state, a low energy collective state emerges in finite size systems due to the discrete shell structure, whereas it is absent in the bulk due to the Landau damping. In the case of spin polarization of the ground state a collective state is present also in the bulk and a family of new collective states appears in finite size systems. Presented by E. Lipparini at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Demonstration of aortic lesions via cine magnetic resonance imaging

Cine-MRI was used to evaluate eight patients with known thoracic aorta disease. Included in this study were three aortic coarctations, two aortic dissections, an aneurysm, a posttraumatic pseudoaneurysm, and a patent ductus arteriosus. Cine-MRI was found to be valuable in the assessment of the pathologic anatomy and associated flow disturbances in these disorders. In seven cases, the images demonstrated the aortic lesion and aberrant blood flow. Our technique was unable to image the structural lesion in the patient with patent ductus arteriosus, but the abnormal blood flow was shown. Angiographic data were available on three of the cases to confirm the MR findings. The MRI images were obtained in axial, coronal, sagittal, and oblique planes using fast field echo acquisition technique of cine-MRI. We found the additional data or benefits provided by cine-MRI, when compared to cardiac gated spin echo images, to be most advantageous in the cases of aortic coarctation and dissection only.     

The motion artifact suppression technique (MAST) in magnetic resonance imaging: clinical results

The Motion Artifact Suppression Technique (MAST) is a method which uses a series of gradient echos that are computed to cancel velocity, acceleration and pulsatility components of involuntary motion in MR imaging. A total of 916 patient studies were performed over a nine month period using MAST sequences with a TE 40, 60, 80, 100, 120, and 26/112. There was considerable improvement in long TR, long TE images. Cerebrospinal fluid flow artifacts were reduced. Body and spine images had reduced flow and respiratory artifacts. Spin rephasing in blood vessels caused increase intraluminal signal. This might be useful for cardiovascular imaging.     

Oxazoline functionalization of polyethylenes and their blends with polyamides and polyesters

The compatibilization of blends of polyamide‐6 (PA6) with linear low density polyethylene (LLDPE) and of poly(ethylene terephthalate) (PET) with high density polyethylene (HDPE), by functionalization of the polyethylenes with oxazoline groups was investigated. Chemical modification of LLDPE and HDPE was carried out by melt free radical grafting with ricinoloxazoline maleinate. Blends preparation was made either with a two‐steps procedure comprising functionalization and blending, and in a single step in which the chemical modification of polyethylene with the oxazoline monomer was realized in situ, during blending. The characterization of the products was carried out by FTIR spectroscopy and scanning electron microscopy (SEM). The rheological and mechanical properties of the blends were also investigated. The results show that functionalization of the polyethylenes can be achieved by melt blending with ricinoloxazoline maleinate even in the absence of free radical initiators. The compatibilization of the blends enhances the dispersion of the minor phase significantly, increases the melt viscosity, and improves the mechanical properties. The one‐step preparation of the compatibilized blends was also found to be effective, and is thought to be even more promising in view of commercial application.     

Investigation of excitation energies and Hund's rule in open shell quantum dots by diffusion Monte Carlo

We use diffusion Monte Carlo to study the ground state, the low-lying excitation spectrum and the spin densities of circular quantum dots with parabolic radial potentials containing N = 16 and N = 24 electrons, each having four open-shell electrons and compare the results to those obtained from Hartree-Fock (HF) and density functional local spin density approximation (LSDA) calculations. We find that Hund's first rule is obeyed in both cases and that neither HF nor LSDA correctly predict the ordering of the energy levels. Received 20 November 2001 and Received in final form 20 February 2002 Published online 6 June 2002