Home About us Contact
|
Home About us Contact | ||
|
|
||
X-ray Tomography (x-ray + tomography)
Selected AbstractsAnalytical Modelling of the Radiative Properties of Metallic Foams: Contribution of X-Ray TomographyADVANCED ENGINEERING MATERIALS, Issue 4 2008M. Loretz Two metallic foams exhibiting a similar porosity but different cell sizes have been characterized using X-ray tomography. The images have been processed and analysed to retrieve the morphological properties required for the calculation of the radiative properties such as the extinction coefficient. The multiple possibilities of using the X-ray tomography method rather than conventional optical methods like SEM have been quantified. The extinction coefficient has then been determined from two approaches. First, the resulting morphological properties have been used as the input data of the conventional independent scattering theory. A special emphasis is put on the determination of morphological properties and their influence on the results. In the second approach, an original method is also proposed in order to determine the extinction coefficient of highly porous open cell metal foams, from the tomographic images and without any calculation or hypothesis. Results show a good agreement with the extinction coefficient obtained from experimental measurements. Our novel method enables to reduce uncertainties considerably. [source] Al and Zn Foams Blown by an Intrinsic Gas SourceADVANCED ENGINEERING MATERIALS, Issue 6 2010M. Mukherjee A method was developed to produce Al- and Zn-based foams with a uniform distribution of small cells. Pre-alloyed AlMg50 powder containing hydrogen was used as a replacement for the usual blowing agent TiH2. AlMg50 powder released gas uniformly in the entire sample, caused the nucleation of a large number of cells and led to simultaneous growth that finally resulted in a uniform cell structure. The expansion behavior of these foams was studied by means of in situ X-ray radioscopy. The macrostructure of the solidified foams was then analyzed through optical microscopy and X-ray tomography and proved to be very uniform. The high strength of the foams was demonstrated by uni-axial compression tests. [source] Analytical Modelling of the Radiative Properties of Metallic Foams: Contribution of X-Ray TomographyADVANCED ENGINEERING MATERIALS, Issue 4 2008M. Loretz Two metallic foams exhibiting a similar porosity but different cell sizes have been characterized using X-ray tomography. The images have been processed and analysed to retrieve the morphological properties required for the calculation of the radiative properties such as the extinction coefficient. The multiple possibilities of using the X-ray tomography method rather than conventional optical methods like SEM have been quantified. The extinction coefficient has then been determined from two approaches. First, the resulting morphological properties have been used as the input data of the conventional independent scattering theory. A special emphasis is put on the determination of morphological properties and their influence on the results. In the second approach, an original method is also proposed in order to determine the extinction coefficient of highly porous open cell metal foams, from the tomographic images and without any calculation or hypothesis. Results show a good agreement with the extinction coefficient obtained from experimental measurements. Our novel method enables to reduce uncertainties considerably. [source] Fatigue of Metal Hollow Spheres Structures,ADVANCED ENGINEERING MATERIALS, Issue 3 2008O. Caty Fatigue properties of three kinds of hollow metal spheres structures were determined in compression/compression. These results were completed with a fatigue damage process study by ex-situ X-ray tomography and a finite element simulation using tomographic 3D images. All these data permitted to understand the chronology of damage in the structure. The difference in behaviour of the three kinds of materials is mainly explained by the process root used (brazing and sintering) and by the nature of the constitutive material. [source] Landweber scheme for compact operator equation in Hilbert space and its applicationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2009Gangrong Qu Abstract We study the Landweber scheme for linear compact operator equation in infinite Hilbert spaces. Using the singular value decomposition for compact operators, we obtain a formula for the Landweber scheme after n iterations and iterative truncated error and consequently establish its convergence conditions. Our results extend known results on convergence conditions. As applications, we apply the Landweber scheme to the X-ray tomography and extrapolation of band-limited functions, and establish accelerated strategies for each application. Copyright © 2008 John Wiley & Sons, Ltd. [source] Compaction of pharmaceutical tablets with different polymer matrices studied by FTIR imaging and X-ray microtomographyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2008Patrick Wray Abstract Water soluble polymers are often used in tablet compaction for their desirable compaction and dissolution properties. ATR-FTIR spectroscopic imaging has been used to analyze in situ the spatial distribution of different components in tablets with different compositions. Caffeine tablets made of three different polymer matrices, microcrystalline cellulose, hydroxypropyl methylcellulose (HPMC) and lactose, were investigated. It was found that the distribution of caffeine is strongly affected by the composition of polymer matrix used in the tablet. X-ray tomography was used to analyze the caffeine distribution as a complementary technique. The results obtained were compared to the ATR-FTIR spectroscopic images. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4269,4277, 2008 [source] Deterministic and statistical methods for reconstructing multidimensional NMR spectra,MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2006Ji Won Yoon Abstract Reconstruction of an image from a set of projections is a well-established science, successfully exploited in X-ray tomography and magnetic resonance imaging. This principle has been adapted to generate multidimensional NMR spectra, with the key difference that, instead of continuous density functions, high-resolution NMR spectra comprise discrete features, relatively sparsely distributed in space. For this reason, a reliable reconstruction can be made from a small number of projections. This speeds the measurements by orders of magnitude compared to the traditional methodology, which explores all evolution space on a Cartesian grid, one step at a time. Speed is of crucial importance for structural investigations of biomolecules such as proteins and for the investigation of time-dependent phenomena. Whereas the recording of a suitable set of projections is a straightforward process, the reconstruction stage can be more problematic. Several practical reconstruction schemes are explored. The deterministic methods,additive back-projection and the lowest-value algorithm,derive the multidimensional spectrum directly from the experimental projections. The statistical search methods include iterative least-squares fitting, maximum entropy, and model-fitting schemes based on Bayesian analysis, particularly the reversible-jump Markov chain Monte Carlo procedure. These competing reconstruction schemes are tested on a set of six projections derived from the three-dimensional 700-MHz HNCO spectrum of a 187-residue protein (HasA) and compared in terms of reliability, absence of artifacts, sensitivity to noise, and speed of computation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Bulk mineralogy and three-dimensional structures of individual Stardust particles deduced from synchrotron X-ray diffraction and microtomography analysisMETEORITICS & PLANETARY SCIENCE, Issue 1-2 2008Tomoki Nakamura The analyses were performed at synchrotron facilities, KEK and SPring-8 in Japan. Twenty-eight particles from 5 to 25 ,m in size, including 25 particles from Track 35 and 3 particles from Track 44, were first analyzed by X-ray diffraction and then 4 out of 28 particles were analyzed by X-ray tomography. All particles are classified into two groups based on silicate crystallinity: crystalline type and amorphous-rich type. The abundance of the former is approximately 10% of the particles investigated. Crystalline type shows very sharp reflections of olivine and low-Ca pyroxene, while amorphous-rich type shows no or very weak silicate reflections, suggesting that silicates are mostly amorphous. Broad reflections of Fe sulfides and Fe silicides are detected from most of amorphous-rich type particles. Subsequent tomography analysis revealed that the crystalline type is non-porous material consisting of coarse silicate crystals larger than 1 ,m in size, while the amorphous-rich type is very porous aggregates with amorphous silicates and small Fe sulfide and Fe metallic grains. All characteristics of amorphous-rich type particles indicate that most of them are melted and rapidly solidified during capture in the silica aerogel. On the other hand, the crystalline type is indigenous cometary particle formed through high-temperature heating episodes that have taken place prior to formation of comet Wild 2. One of the crystalline-type particles (C2054,0,35,6,0) consists of Mg-rich olivine, pyroxene, and kamacite and exhibits porphyritic or poikilitic texture very similar to chondrules. [source] Cross-calibration of X-ray µCT and MRX for tissue analysisPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009H. Rahn Ferrofluids are being considered as an aid for local cancer treatments, such as Magnetic Drug Targeting (MDT) and Magnetic Hyperthermia (MHT). Both methods make use of the strong influence of a magnetic field on the nanoparticles, with the aim of treating the cancer locally while reducing, or even eliminating, the side effects that usually occur during conventional cancer treatments. Microcomputed tomography analysis has been performed on tumour tissue after MDT and MHT in order to examine the distribution of the magnetic nanoparticles within the tissue. The majority of the measurements has been performed in a laboratory based on a polychromatic X-ray source. The strong energy dependence of the attenuation coefficient and the occurrence of the so called beam hardening artefacts make the quantitative evaluation of data acquired with polychromatic tomography equipment very difficult. In this paper we present a cross-calibration method for magnetorelaxometry and polychromatic X-ray tomography for biological tissue samples enriched with magnetic nanoparticles. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Can implants be correctly angulated based on surgical templates used for osseointegrated dental implants?CLINICAL ORAL IMPLANTS RESEARCH, Issue 5 2000Munetaka Naitoh When placing osseointegrated dental implants, the site, angulation and depth of implants can be designed using a computed tomography (CT) or conventional X-ray tomography. To correctly identify placement pre-surgically, various kinds of surgical templates have been proposed. Although it is thought to be important to use templates, no material has been published on their accuracy. The purpose of this study was to propose a method for evaluating the placement accuracy using a specific surgical template. Twenty-one implants were evaluated in 6 patients with mean age of 50.7 years. All implants were implanted by two step surgery in the posterior mandible. A surgical template based on the CT images and the abutment replica on the working models were used for the evaluation of the accuracy of implant placement. The difference between the proposed and actual directions was measured by a milling machine. The difference in the angles between the proposed direction and actual direction were from 0.5 degrees to 14.5 degrees. The average was 5.0 degrees, and there were 12 implants (57%) within 5.0 degrees. This study demonstrated the accuracy of the template described in this article. [source] Glucocorticoid-induced bone loss in mice can be reversed by the actions of parathyroid hormone and risedronate on different pathways for bone formation and mineralizationARTHRITIS & RHEUMATISM, Issue 11 2008Wei Yao Objective Glucocorticoid excess decreases bone mineralization and microarchitecture and leads to reduced bone strength. Both anabolic (parathyroid hormone [PTH]) and antiresorptive agents are used to prevent and treat glucocorticoid-induced bone loss, yet these bone-active agents alter bone turnover by very different mechanisms. This study was undertaken to determine how PTH and risedronate alter bone quality following glucocorticoid excess. Methods Five-month-old male Swiss-Webster mice were treated with the glucocorticoid prednisolone (5 mg/kg in a 60-day slow-release pellet) or placebo. From day 28 to day 56, 2 groups of glucocorticoid-treated animals received either PTH (5 ,g/kg) or risedronate (5 ,g/kg) 5 times per week. Bone quality and quantity were measured using x-ray tomography for the degree of bone mineralization, microfocal computed tomography for bone microarchitecture, compression testing for trabecular bone strength, and biochemistry and histomorphometry for bone turnover. In addition, real-time polymerase chain reaction (PCR) and immunohistochemistry were performed to monitor the expression of several key genes regulating Wnt signaling (bone formation) and mineralization. Results Compared with placebo, glucocorticoid treatment decreased trabecular bone volume (bone volume/total volume [BV/TV]) and serum osteocalcin, but increased serum CTX and osteoclast surface, with a peak at day 28. Glucocorticoids plus PTH increased BV/TV, and glucocorticoids plus risedronate restored BV/TV to placebo levels after 28 days. The average degree of bone mineralization was decreased after glucocorticoid treatment (,27%), but was restored to placebo levels after treatment with glucocorticoids plus risedronate or glucocorticoids plus PTH. On day 56, RT-PCR revealed that expression of genes that inhibit bone mineralization (Dmp1 and Phex) was increased by continuous exposure to glucocorticoids and glucocorticoids plus PTH and decreased by glucocorticoids plus risedronate, compared with placebo. Wnt signaling antagonists Dkk-1, Sost, and Wif1 were up-regulated by glucocorticoid treatment but down-regulated after glucocorticoid plus PTH treatment. Immunohistochemistry of bone sections showed that glucocorticoids increased N-terminal Dmp-1 staining while PTH treatment increased both N- and C-terminal Dmp-1 staining around osteocytes. Conclusion Our findings indicate that both PTH and risedronate improve bone mass, degree of bone mineralization, and bone strength in glucocorticoid-treated mice, and that PTH increases bone formation while risedronate reverses the deterioration of bone mineralization. [source] | ||||||||||||||||