Dimensional Accuracy in X-Ray Computed Tomography Imaging

X-ray computed tomography (CT) has become an important non-destructive evaluation technique. CT contributes to a wide range of nondestructive evaluation (NDE) applications [1]. These include typical NDE applications (e.g., defect detection and quality control), more advanced NDE applications (e.g., process development and model verification), and the more recent application of CT-based metrology (e.g., geometric inspection and reverse engineering). In the traditional applications of CT, the user is concerned with defect sensitivity, which is a combination of spatial resolution, contrast sensitivity and slice thickness [2]. For CT-based metrology, the term “defect sensitivity” has little meaning; dimensional accuracy of the system becomes paramount

Reversed halo sign on CT as a presentation of lymphocytic interstitial pneumonia.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.A 52 year-old African American female with a past medical history of symptomatic uterine fibroids and increasing abdominal circumference underwent abdominal computed tomography (CT) as part of her workup. Because of an abnormality in the left lower lobe, CT of the chest was subsequently performed and showed a focal region of discontinuous crescentic consolidation with central ground glass opacification in the right lower lobe, suggestive of the reversed halo sign. The patient underwent percutaneous CT-guided core biopsy of the lesion, which demonstrated lymphocytic interstitial pneumonia, a benign lymphoproliferative disease characterized histologically by small lymphocytes and plasma cells. This case report describes the first histologically confirmed presentation of lymphocytic interstitial pneumonia with the reversed halo sign on CT

Exploring 'unstructured proteins'

In the post genomic era, as more and more genome sequences are becoming known and hectic efforts are underway to decode the information content in them, it is becoming increasingly evident that flexibility in proteins plays a crucial role in many of the biological functions. Many proteins have intrinsic disorder, either wholly or in specific regions. It appears that this disorder may be important for regulatory functions of the proteins, on the one hand, or, may help in directing the folding process to reach the compact native state, on the other. Nuclear Magnetic Resonane (NMR) has over the last two decades emerged as the sole, most powerful technique to help characterize these disordered protein systems. In this review, we first discuss the significance of disorder in proteins and then survey the NMR methods available for their characterization. A brief description of the results obtained on several disordered proteins is presented at the end

Observation of magnetization reversal and negative magnetization in a double perovskite compound Sr2YbRuO6

Detailed magnetic properties of the compound Sr2YbRuO6 are presented here. The compound belongs to the family of double perovskites forming a monoclinic structure. Magnetization meas-urements reveal clear evidence for two components of magnetic ordering aligned opposite to each other, leading to a magnetization reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at low temperatures and low magnetic fields. Heat capacity measurements corroborate the presence of two components in the magnetic ordering and a noticeable third anomaly at low temperatures (~15 K) which cannot be attributed the Schottky effect. The calcu-lated magnetic entropy is substantially lower than that expected for the ground states of the or-dered moments of Ru5+ and Yb3+, indicating the presence of large crystal field effects and/ or in-complete magnetic ordering and/or magnetic frustrations well above the magnetic ordering. An attempt is made to explain the magnetization reversal within the frameworks of available models.Comment: 15 pages text, 6 figures Journal-ref: J.Phys.:Condens.Matter 20(2008)23520

Finite size effects with variable range exchange coupling in thin-film Pd/Fe/Pd trilayers

The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded ~1.5 A-thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd have been investigated. The thickness of the ferromagnetic trilayer is controlled by varying the thickness of the top Pd layer over a range from 8 A to 56 A. As the thickness of the top Pd layer decreases, or equivalently as the embedded Fe layer moves closer to the top surface, the saturated magnetization normalized to area and the Curie temperature decrease whereas the coercivity increases. These thickness-dependent observations for proximity-polarized thin-film Pd are qualitatively consistent with finite size effects that are well known for regular thin-film ferromagnets. The critical exponent $\beta$ of the order parameter (magnetization) is found to approach the mean field value of 0.5 as the thickness of the top Pd layer increases. The functional forms for the thickness dependences, which are strongly modified by the nonuniform exchange interaction in the polarized Pd, provide important new insights to understanding nanomagnetism in two-dimensions.Comment: 14 pages, 5 figures, submitted to JMM

Z2_2 topology and superconductivity from symmetry lowering of a 3D Dirac Metal Au2_2Pb

3D Dirac semi-metals (DSMs) are materials that have massless Dirac electrons and exhibit exotic physical properties It has been suggested that structurally distorting a DSM can create a Topological Insulator (TI), but this has not yet been experimentally verified. Furthermore, quasiparticle excitations known as Majorana Fermions have been theoretically proposed to exist in materials that exhibit superconductivity and topological surface states. Here we show that the cubic Laves phase Au$_2$Pb has a bulk Dirac cone above 100 K that gaps out upon cooling at a structural phase transition to create a topologically non trivial phase that superconducts below 1.2 K. The nontrivial Z$_2$ = -1 invariant in the low temperature phase indicates that Au$_2$Pb in its superconducting state must have topological surface states. These characteristics make Au$_2$Pb a unique platform for studying the transition between bulk Dirac electrons and topological surface states as well as studying the interaction of superconductivity with topological surface states

Towards the theory of ferrimagnetism

Two-sublattice ferrimagnet, with spin-$s_1$ operators $\bf{S_{1i}}$ at the sublattice $A$ site and spin-$s_2$ operators $\bf{S_{2i}}$ at the sublattice $B$ site, is considered. The magnon of the system, the transversal fluctuation of the total magnetization, is a complicate mixture of the transversal fluctuations of the sublattice $A$ and $B$ spins. As a result, the magnons' fluctuations suppress in a different way the magnetic orders of the $A$ and $B$ sublattices and one obtains two phases. At low temperature $(0,T^*)$ the magnetic orders of the $A$ and $B$ spins contribute to the magnetization of the system, while at the high temperature $(T^*,T_N)$, the magnetic order of the spins with a weaker intra-sublattice exchange is suppressed by magnon fluctuations, and only the spins with stronger intra-sublattice exchange has non-zero spontaneous magnetization. The $T^*$ transition is a transition between two spin-ordered phases in contrast to the transition from spin-ordered state to disordered state ($T_N$-transition). There is no additional symmetry breaking, and the Goldstone boson has a ferromagnetic dispersion in both phases. A modified spin-wave theory is developed to describe the two phases. All known Neel's anomalous $M(T)$ curves are reproduced, in particular that with "compensation point". The theoretical curves are compared with experimental ones for sulpho-spinel $MnCr2S_{4-x}Se_{x}$ and rare earth iron garnets.Comment: 9 pages, 8 figure