Direct and indirect measurement of magnetocaloric effect in NiCoMnGa alloys

The Co-substitution for Ni in the Mn-rich NiMnGa Heusler alloys changes substantially their structural and magnetic ordering. The results will be discussed within the basic thermodynamic relations

Pressure dependence of magnetism and martensitic properties in Co-doped NiMnGa alloys

NiMnGa alloys display several "giant" effects due to the interplay between magnetic and structural degrees of freedom. A large magnetization difference, between martensitic phases and austenitic phases iso f great importance to obtain higher performances due to the improbe possibilit? of driving structural trasformations by magnetic fields. A deltaM enhancement was recently achieved by adding Co to Mn-rich NiMnGa alloy

Автоматический выпуск конструкторской документации в PDM-системе

BaFe12O19 powders were prepared by coprecipitation and by glass crystallization. Electron microscopic investigations revealed that the particles of the glass crystallized powder exhibit excellent uniform shapes and narrow size distribution in comparison to the coprecipitated one consisting of irregularly shaped, polycrystalline particles with a broad and inhomogeneous size distribution. The crystallites of the coprecipitated powder particles, however, are smaller (mean diameter D = 0.11 μm) and the size distribution is narrower than that of the particles of the glass crystallized powder with a mean diameter of D = 0.42 μm. The lattice perfection of the particles and the crystallites of both ensembles is quite good. In order to determine the magnetic properties - above all the effective anisotropy field - we used six different methods: transverse susceptibility χt, singular point detection (SPD), ferromagnetic resonance (FMR), torsion pendulum (TP), rotational hysteresis losses (RHL), remanence curves (RC). It has been found that differences in coercivity values HcJ are not dramatic (about ±3%). Effective anisotropy fields Ha measured with “switching” methods (RHL, RC) are smaller than those measured with “stiffness” ones (FMR, TP, SPD, χt), by about 1700 Oe for the coprecipitated powder and about 2500 Oe for the glass crystallized one. The glass crystallized particle assemblies used for the present investigations do not exhibit pure Stoner-Wohlfarth behaviour, because of their relatively large particle diameters. The ratio HcJ/Ha ≈ 0.39 of the coprecipitated powder is relatively near the ideal value of 0.48, although the particles are considerably mechanically aggregated. © 1992

Protective Effects of Aryl Hydrocarbon Receptor Signaling in Celiac Disease Mucosa and in Poly I:C-Induced Small Intestinal Atrophy Mouse Model

Aryl hydrocarbon receptor (AhR), a transcription factor activated by a large number of natural and synthetic agents, modulates the activity of immune cells in the gut and represents an important link between the environment and immune-mediated pathologies. In this study, we investigated the role of AhR in celiac disease (CD), a gluten-driven enteropathy. AhR expression was evaluated in intestinal biopsies taken from patients with CD and controls by real-time polymerase chain reaction (PCR), immunohistochemistry and flow cytometry. AhR was also analyzed in ex vivo organ cultures of duodenal biopsies taken from inactive CD patients incubated in presence or absence of peptic-tryptic digest of gliadin. IFN-γ, TNF-α, granzyme B, and perforin expression was evaluated in anti-CD3/CD28-activated intestinal lamina propria mononuclear cells (LPMC) and intestinal intra-epithelial cells (IEL) of active CD patients cultured in the presence or absence of the AhR agonist 6-formylindolo(3, 2-b)carbazole (Ficz). Finally, the protective role of AhR was evaluated in a mouse model of poly I:C-driven small intestine damage. AhR RNA transcripts were reduced in active CD samples as compared to inactive CD and normal controls. Flow cytometry confirmed such results and showed a reduction of AhR in both IEL and LPMC of active CD patients. The addition of a peptic-tryptic digest of gliadin to ex vivo organ cultures of duodenal biopsies taken from inactive CD patients reduced AhR expression. Treatment of CD IEL and LPMC with Ficz reduced the levels of inflammatory cytokines, granzyme B and perforin. Mice injected with Ficz were protected against poly I:C-induced intestinal lesions. Our findings suggest that defective AhR-driven signals could contribute to amplify pathogenic responses in the gut of CD patients

Morphologically and immunohistochemically undifferentiated gastric neoplasia in a patient with multiple metastatic malignant melanomas: a case report

Introduction: Malignant melanoma is a neoplasia which frequently involves the gastrointestinal tract (GIT). GIT metastases are difficult to diagnose because they often recur many years after treatment of the primary cutaneous lesion and also manifest clinically at an advanced stage of the neoplasia. Furthermore, GIT metastases can appear in various morphological forms, and therefore immunohistochemistry is often useful in distinguishing between a malignant melanoma and other malignancies. Case presentation: We report the case of a 60-year-old man with a multiple metastatic melanoma who underwent an upper endoscopy to clarify the possible involvement of the gastric wall with a mass localized in the upper abdomen involving the pancreas and various lymph nodes, which was previously described with computed tomography. Clinically, the patient reported a progressive loss of appetite, nausea and vomiting. The upper endoscopy and histological examination revealed a gastric location of an undifferentiated neoplasm with an absence of immunohistochemical characteristics referable to the skin malignant melanoma that was removed previously. Conclusion: The present case report shows the difficulty in diagnosing a metastatic melanoma in the GIT and therefore, it seems worthwhile to consider metastatic malignant melanoma in the differential diagnosis of undifferentiated neoplasia. © 2008 Alghisi et al; licensee BioMed Central Ltd

A nuclear magnetic resonance and magnetic susceptibility study of the Ca-Al metallic glass system and related crystalline compounds

In order to investigate both the atomic and electronic structures, we have carried out steady state and pulsed NMR experiments on the melt spun metallic glass system Ca\sb{\rm 100-x}Al\sb{\rm x} (15 $\le$ x $\le$ 45) and related crystalline compounds. Measurements of the \sp{27}Al NMR Knight shift, spin lattice relaxation time and lineshape have been obtained at 4.2 \sp\circK and room temperature, and for frequencies ranging from 8 to 20 MHz. The experimental results indicate that the Knight shift (k = +0.038% $\pm$ 0.010% at room temperature), spin-lattice relaxation time (T\sb1 = 2.0 $\pm$ 0.2 sec. at 4.2 \sp\circK), and linewidth of the central transition remain constant throughout the entire glassy regime. Furthermore, the small value for the Knight shift and consequently, the long spin-lattice relaxation time, indicate that the local density of s-electron states at the Al sites is small. In addition, spin-echo NMR measurements indicate that the entire \sp{27}Al spectrum is quite broad ($\sim$2 MHz) due to the quadrupole interaction, and also, essentially the same for all compositions. All of the NMR results indicate that certain features of the local environment remain unchanged throughout the entire glassy regime. This has been taken as strong evidence of compositional short-range ordering in these amorphous alloys, contrary to the random packing assumed in the DRPHS model. The symmetry properties of the electric field gradient are compared with those for the related crystalline compounds which include CaAl\sb2 and Ca\sb3Al. This last compound has been found to have two sites for Al. The analysis of the magnetic susceptibility has been carried out by taking into account correlation effects. The magnetic susceptibility results indicate that the amorphous Ca-Al metallic glass system cannot be described simply in terms of a free electron model. This is consistent with the calculated values of the Korringa constant. The difference between the experimental and calculated susceptibilities indicates a small contribution due to the presence of d-like states in the vicinity of the Fermi level.

A nuclear magnetic resonance and magnetic susceptibility study of the Ca-Al metallic glass system and related crystalline compounds

In order to investigate both the atomic and electronic structures, we have carried out steady state and pulsed NMR experiments on the melt spun metallic glass system Ca\sb{\rm 100-x}Al\sb{\rm x} (15 $\le$ x $\le$ 45) and related crystalline compounds. Measurements of the \sp{27}Al NMR Knight shift, spin lattice relaxation time and lineshape have been obtained at 4.2 \sp\circK and room temperature, and for frequencies ranging from 8 to 20 MHz. The experimental results indicate that the Knight shift (k = +0.038% $\pm$ 0.010% at room temperature), spin-lattice relaxation time (T\sb1 = 2.0 $\pm$ 0.2 sec. at 4.2 \sp\circK), and linewidth of the central transition remain constant throughout the entire glassy regime. Furthermore, the small value for the Knight shift and consequently, the long spin-lattice relaxation time, indicate that the local density of s-electron states at the Al sites is small. In addition, spin-echo NMR measurements indicate that the entire \sp{27}Al spectrum is quite broad ($\sim$2 MHz) due to the quadrupole interaction, and also, essentially the same for all compositions. All of the NMR results indicate that certain features of the local environment remain unchanged throughout the entire glassy regime. This has been taken as strong evidence of compositional short-range ordering in these amorphous alloys, contrary to the random packing assumed in the DRPHS model. The symmetry properties of the electric field gradient are compared with those for the related crystalline compounds which include CaAl\sb2 and Ca\sb3Al. This last compound has been found to have two sites for Al. The analysis of the magnetic susceptibility has been carried out by taking into account correlation effects. The magnetic susceptibility results indicate that the amorphous Ca-Al metallic glass system cannot be described simply in terms of a free electron model. This is consistent with the calculated values of the Korringa constant. The difference between the experimental and calculated susceptibilities indicates a small contribution due to the presence of d-like states in the vicinity of the Fermi level.

Crystal Structures of Modulated Martensitic Phases of FSM Heusler Alloys

Multifunctional ferromagnetic shape memory Heusler alloys are frequently characterized by structural modulation in martensitic phases. In particular, modulated martensitic phases, showing the higher magnetic field induced strain (MFIS) performance, are the most promising candidates for technological applications. Depending on the composition, as well as pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along defined crystallographic directions, accompanies the martensitic transformation. Over the years, different Ni-Mn-Ga modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding ideal nM superstructure (where n indicates the number of basic unit cells constituting the superlattices). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure has been fully determined by applying superspace formalism. The results, obtained by structure refinements on powder diffraction data, suggest a unified crystallographic description of the modulated martensitic structures, here presented, where every different “nM” periodicity can be straightforwardly represented

First-order field-induced magnetization processes and magnetostriction in Tb2Co12Fe5

We report the results of magnetization and magnetostriction measurements performed by pulsed-magnetic-field techniques on the intermetallic compound Tb2Co12Fe5. The temperature dependence of the critical field at which the first-order magnetization process takes place was measured by a singular point detection technique on aligned powders. Magnetostriction measurements were performed by a strain-gauge-based technique at different temperatures. The obtained results are compared with observations recently made for the closely related compound Pr2Co 12Fe5, allowing to clarify the crucial role of both the rare-earth and the transition-metal sublattices in the peculiar behaviour of the latter. © 2010 Springer Science+Business Media, LLC.N.M. acknowledges the European Commission for support given in the frame of EuroMagNET (EU Contract No. RII3-CT-2004-506239) and of the program ‘Training and Mobility of Researchers’.Peer Reviewe

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different “nM” periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated