Magnetic properties of iron nitride-alumina nanocomposite materials prepared by high-energy ball milling

in European Physical Journal D -- Atoms, Molecules, Clusters & Optical Physics (2003), 24(1-3), 93-96

The structural and magnetic properties of the granular iron nitride-alumina composite materials: (FexN)(0.2)(Al2O3)(0.8) and (FexN)(0.6)(Al2O3)(0.4), fabricated using high-energy ball milling have been ... [more ▼]

The structural and magnetic properties of the granular iron nitride-alumina composite materials: (FexN)(0.2)(Al2O3)(0.8) and (FexN)(0.6)(Al2O3)(0.4), fabricated using high-energy ball milling have been determined by using X-ray diffraction, Mossbauer spectroscopy, and magnetization measurements. The Mossbauer spectra, fit with a distribution of hyperfine fields between zero and 40 T. indicate that the weighted average field decreases with increasing milling time. The isomer shift increases with milling time because of a reduced iron 4s-electron density at the grain boundaries. Coercive fields as high as 325 and 110 Oe are obtained for (FexN)(0.2)(Al2O3)(0.8) at 5 and 300 K, respectively; the increase in the coercive field upon cooling indicates the presence of superparamagnetic particles. The coercive field increases with milling time because of the reduced particle size. The decrease in the magnetization results from the increase in both the superparamagnetic fraction and the concentration of surface defects with increased milling time. [less ▲]

Magnetic properties of melt-textured DyBCO single domains

in Materials Research Society Symposium Proceedings (2001), 659

This communication aims at reporting the superconducting properties of several bulk melt-processed DyBa2Cu3O7-x samples determined by using various measuring techniques. The original single domain ... [more ▼]

This communication aims at reporting the superconducting properties of several bulk melt-processed DyBa2Cu3O7-x samples determined by using various measuring techniques. The original single domain material was first cut into 9 similar cubic samples which have been characterized by AC susceptibility, flux profiles and DC magnetization. The results indicate good quality melt-processed (RE)BCO materials with Tc = 89 K. Next, the effect of post oxygen annealing treatments on these samples was studied. The influence of the non-uniformity of the oxygen content on the magnetic property anisotropy is discussed. Finally, additional magnetic measurements were carried out by using a couple of parallel pick-up coils wound on the same sample. From the results we conclude that geometric effects have to be taken into account in order to extract the critical current density from the magnetic properties. [less ▲]

Magnetic properties of Np2T2Sn compounds

in Physica B: Condensed Matter (1995), 206 & 207

The magnetic properties of the Np2T2Sn series investigated by 237Np Mössbauer spectroscopy are reported. Magnetic ordering is shown to occur for T --- Ni, Pd, Pt, whereas the Np ions do not carry a local ... [more ▼]

The magnetic properties of the Np2T2Sn series investigated by 237Np Mössbauer spectroscopy are reported. Magnetic ordering is shown to occur for T --- Ni, Pd, Pt, whereas the Np ions do not carry a local moment when T --- Co, Ru, Rh. Comparisons are made with the corresponding Np2T2In and U2T2Sn compounds. [less ▲]

Magnetic resonance arthrography of cubital joint in dogs affected with fragmented medial coronoid process

in American Journal of Veterinary Research (1999), 20

Objective-To evaluate efficacy of intra-articular injection of gadolinium tetra- azacyclododecane tetraacetic acid (gadolinium-DOTA) for delineating fragmented medial coronoid processes (FMCP) and lesions ... [more ▼]

Objective-To evaluate efficacy of intra-articular injection of gadolinium tetra- azacyclododecane tetraacetic acid (gadolinium-DOTA) for delineating fragmented medial coronoid processes (FMCP) and lesions on the medial aspect of the humeral condyle (MAHC). Sample Population-14 cubital joints in 9 dogs. Procedure-Magnetic resonance imaging (MRI) was performed with and without intra-articular injection of a solution of 2 mmol of gadolinium-DOTA/L. Arthrographic images obtained after injection of contrast medium were compared with those obtained without contrast medium. Evidence of contrast medium around or in the medial coronoid process and infiltration of contrast medium in subchondral bone lesions was recorded, Twenty-four hours after imaging, arthroscopy was performed, and lesions detected were correlated with results of MRI. Results-An abnormal coronoid process was diagnosed in 13 of 14 joints. A fragmented process (free) was seen in 7 of 14 joints; nondisplaced mineralized medial tin situ) coronoid processes were evident in 4 joints; and nondisplaced unmineralized medial coronoid processes were evident in 2 joints. Lesions on the MAHC were diagnosed in 4 of 12 joints. In 5 joints, a hyperintense signal resulted from contrast medium that infiltrated between the fragmented process and ulna. In 2 joints, contrast medium did not infiltrate completely around the process and was stopped by an isointense structure tie, abnormal cartilage). Subchondral bone lesions were enhanced by use of contrast medium. Conclusion and Clinical Relevance-Use of arthrography enabled us to identify FMCP easily, but did not provide important additional information about changes on the medial coronoid process, compared with MRI performed without contrast medium. [less ▲]

A magnetic resonance imaging approach for the diagnosis of a triplet cornual pregnancy.

in Fertility and Sterility (1995), 64(5), 1029-31

Objectives: To describe a rare case of triplet cornual pregnancy after IVF-ET and to assess the role of magnetic resonance imaging (MRI) for early diagnosis. DESIGN: Case report. SETTING: Infertility and ... [more ▼]

Objectives: To describe a rare case of triplet cornual pregnancy after IVF-ET and to assess the role of magnetic resonance imaging (MRI) for early diagnosis. DESIGN: Case report. SETTING: Infertility and IVF Unit, in an university medical center. PATIENT: A 31-year-old healthy patient with a 3-year history of primary male infertility. INTERVENTION: Standard IVF-ET treatment cycle, using a GnRH-agonist (long protocol) and hMG for ovarian stimulation. RESULTS: A cornual triplet pregnancy is described with the approach for the diagnosis. Magnetic resonance imaging was complementary to endovaginal sonography for early diagnosis and permitted a timed conservative management. CONCLUSIONS: When transvaginal ultrasound findings did not provide an accurate location of the pregnancy, MRI was indicated to confirm the diagnosis. [less ▲]

Magnetic resonance imaging findings in the equine deep digital flexor tendon and distal sesamoid bone in advanced navicular disease--an ex vivo study.

in Veterinary Radiology & Ultrasound (2005), 46(4), 279-86

We describe the abnormal magnetic resonance (MR) imaging findings in the deep digital flexor tendon (DDFT) and distal sesamoid bone in horses with radiographic changes compatible with navicular syndrome ... [more ▼]

We describe the abnormal magnetic resonance (MR) imaging findings in the deep digital flexor tendon (DDFT) and distal sesamoid bone in horses with radiographic changes compatible with navicular syndrome. Thirteen postmortem specimens were examined using a 1.5-T magnetic field, with spin echo (SE) T1-weighted, turbo SE (TSE) proton density-weighted (with and without fat saturation), and fat saturation TSE T2-weighted sequences. The limbs were then dissected to compare the MR findings with the gross assessment and histologic examination of the DDFT and distal sesamoid bones. Tendonous abnormalities were detected by MR imaging in 12 DDFTs and confirmed at necropsy. Most tendon lesions were located at the level of the distal sesamoid bone and the proximal recess of the podotrochlear bursa. Tendon lesions were classified based on their MR imaging features as core lesions, dorsal lesions, dorsal abrasions, and parasagittal splits. Areas of increased MR signal in the DDFTs were characterized by tendon fiber disturbance and lack of continuity of the collagen fibers, foci of edema, hemorrhages, and formation of lakes containing eosinophilic plasma-like material or amphophilic material of low density. Bone marrow signal alterations in the distal sesamoid bone were seen in all digits. Two main phenomena were responsible for the abnormal signal, respectively, in T1-weighted (decreased signal) and in T2-weighted fat-suppressed images (increased signal): a decrease in the fat marrow content in the trabecular spaces and an increase in the fluid content. Histologic examination revealed foci of bone marrow edema, hemorrhage, necrosis, and fibrosis. Cyst formation and trabecular abnormalities (disorganization, thinning, remodelling) were also observed in areas of abnormal signal intensity. Increased bone density because of trabecular thickening induced a decrease in signal in all sequences. [less ▲]

Magnetic resonance imaging of the palmar aspect of the equine podotrochlear apparatus: Normal appearance

in Veterinary Radiology & Ultrasound (2004), 45(3), 198-204

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of ... [more ▼]

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of MR imaging studies of 16 cadaver limbs. The articular aspect of the distal sesamoid bone was not evaluated in this study. Equine digits were imaged with a human knee radiofrequency coil in a 1.5 T magnetic field, using spin echo (SE) T1-weighted, turbo spin echo proton density (TSE PD)-weighted with and without fat saturation (FS), and FS TSE T2-weighted sequences. The limbs were dissected after imaging to validate the absence of gross abnormalities of the flexor aspect of the distal sesamoid bone, of the deep digital flexor tendon, and the distal impar sesamoidean ligament. Seven deep digital flexor tendons were subjected to histologic examination to exclude any microscopic tendon pathology. The anatomic structures of the podotrochlear apparatus were easily identified on MR images. Compact bone of the flexor cortex of the distal sesamoid bone had low intensity signal on all sequences. In 11 digits an increased signal was seen within the thickness of the sagittal eminence of the flexor cortex in SE T1-weighted images and in TSE PD-weighted images without FS. Trabecular bone had a granular appearance and high signal in SE T1-weighted sequences and TSE images without FS. The deep digital flexor tendon had low signal on FS T2-weighted images, while on short echo time sequences (T1- and PD-weighted sequences), the tendon signal varied depending on the relative orientation between its fibers and the static magnetic field. Seven tendons had stippled appearance due to small intratendonous foci of slightly increased signal on transverse T1-weighted images. MR imaging provides a thorough evaluation of the anatomical structure of the podotrochlear apparatus: A good knowledge of the MR imaging appearance and anatomy and an awareness of potential pitfalls will improve diagnostic specificity for the detection of pathologic changes. [less ▲]

Magnetic resonance spectroscopy and diffusion tensor imaging in coma survivors: promises and pitfalls.

in Progress in Brain Research (2009), 177

The status of comatose patient is currently established on the basis of the patient-exhibited behaviors. Clinical assessment is subjective and, in 40% of patients, fails to distinguish vegetative state ... [more ▼]

The status of comatose patient is currently established on the basis of the patient-exhibited behaviors. Clinical assessment is subjective and, in 40% of patients, fails to distinguish vegetative state (VS) from minimally conscious states (MCS). The technologic advances of magnetic resonance imaging (MRI) have dramatically improved our understanding of these altered states of consciousness. The role of neuroimaging in coma survivors has increased beyond the simple evaluation of morphological abnormalities. The development of 1H-MR spectroscopy (MRS) and diffusion tensor imaging (DTI) provide opportunity to evaluate processes that cannot be approached by current morphologic MRI sequences. They offer potentially unique insights into the histopathology of VS and MCS. The MRS is a powerful noninvasive imaging technique that enables the in vivo quantification of certain chemical compound or metabolites as N-acetylaspartate (NAA), Choline (Cho), and Creatine (Cr). These biomarkers explore neuronal integrity (NAA), cell membrane turnover (Cho), and cell energetic function (Cr). DTI is an effective and proved quantitative method for evaluating tissue integrity at microscopic level. It provides information about the microstructure and the architecture of tissues, especially the white matter. Various physical parameters can be extracted from this sequence: the fractional anisotropy (FA), a marker of white matter integrity; mean diffusivity (MD); and the apparent diffusion coefficient (ADC) which can differentiate cytotoxic and vasogenic edema. The most prominent findings with MRS and DTI performed in traumatic brain-injured (TBI) patients in subacute phase are the reduction of the NAA/Cr ratio in posterior pons and the decrease of mean infratentorial and supratentorial FA except in posterior pons that enables to predict unfavorable outcome at 1 year from TBI with up to 86% sensitivity and 97% specificity. This review will focus on the interest of comatose patients MRI multimodal assessment with MRS and DTI. It will emphasize the advantages and pitfalls of these techniques in particular in predicting the coma survivors' outcome. [less ▲]

Magnetic shielding properties of high- Tc superconducting hollow cylinders: model combining experimental data for axial and transverse magnetic field configurations

in Superconductor Science and Technology (2009), 22(10), 10500210

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The ... [more ▼]

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77 K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10 uT s[?]1 and 10 mT s[?]1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n', is found between Blim and dBapp/dt. The values of n' are nearly the same for both configurations. We show that the main features of the curves Bin(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)[?]1). In particular, a linear relationship between the measured n'-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields. [less ▲]

Magnetic Shielding with Bulk High Temperature Superconductors: Factors Influencing the Magnetic Field Penetration in Hollow Cylinders

in Muralidhar, Miryala (Ed.) Superconductivity: Recent Developments and New Production Technologies (2012)