1,721,132 research outputs found
Nanocharacterization of nanowires, nanomagnets and laser diodes for sensors, optoelectronics and data storage
No full textProgetto Bilaterale di Grande Rilevanza Italia-Giappone (finanziato dal Ministero degli Esteri)
Dispositivi ad alta mobilita' elettronica ad eterostruttura (HEMT, High Electron Mobility Transistors) a base di Nitruro di Gallio (GaN)
No full textProgetto Bilaterale di Grande Rilevanza Italia-Giappone (finanziato dal Ministero degli Affari Esteri).
Scopi del progetto:
- il progresso delle conoscenze scientifiche di interesse applicativo, riguardanti (i) l'identificazione e distinzione dei meccanismi di degrado microscopici e nanoscopici, (ii) lo studio della correlazione tra metodologie di crescita e proprietà strutturali ed ottiche di singoli nanowire a base di semiconduttori, (iii) l'ottimizzazione delle proprietà magnetiche in film sottili e nanostrutture per la registrazione magnetica ad altissima densità;
- il progresso della ricerca e sviluppo a livello industriale in collaborazione con la Matsushita Electric Industrial Ltd
Indium phosphide high mobility heterostructure devices (HEMT, High Electron Mobility Transistors) for integrated circuits and microwave with very wide band
No full textL'obiettivo del progetto riguarda lo studio dei dispositivi ad alta mobilita' basati su eterostrutture cresciute su fosfuro di indio (InP) e relativi composti (InGaAs, InAlAs). Gli High Electron Mobility Transistor (HEMT) su InP sono attualmente i dispositivi elettronici piu' veloci (con frequenze di taglio superiori a 300 GHz) e rappresentano quindi i componenti di riferimento per circuiti di comunicazione su fibra ottica operanti sopra i 40 Gbps, per reti locali wireless e per sistemi di comunicazione satellitare a larghissima banda, per i ricevitori a bassissimo rumore per radioastronomia. La rete di ricercatori si propone di studiare le caratteristiche, le prestazioni e l'affidabilita' di HEMT con gate submicrometrico fabbricati da NTT (Japan), e di correlare queste con le proprieta' dei materiali e con i processi di fabbricazione
Effects of age on sarcoplasmic reticulum properties and histochemical composition of fast- and slo-twitch rat muscles
No full textCalcium release activity of sarcoplasmic reticulum and enzyme-histochemical properties were investigated in extensor digitorum longus (e.d.l.) and soleus muscles in young (4 months and old (24 months) male rats. With age, the caffeine threshold concentration for calcium release from the sarcoplasmic reticulum of soleus skinned muscle fibres showed only minor modifications. On the other hand, in e.d.l. skinned muscle fibres, the caffeine threshold concentration decreased significantly (P < 0.05). The histochemical fibre type composition changed with age both in soleus and in e.d.l. muscles, showing a common transformation toward a more oxidative histochemical profile. In fact, in aged soleus, a significant (P < 0.05) increase was observed of type 1 fibres to represent almost the totality of the muscle fibres (more than 98%), while types 2C and 2A were reduced in proportion. In aged e.d.l. the percentage of type 1 (P < 0.05), 2A and 2X (a recently identified fourth component of the fast-twitch muscle types) fibres increased, with a reduction of type 2B (P < 0.01) fibres. The present results suggest that the changes in contractile properties of aged muscles may be related to the changes not only in fibre composition but also in the mechanism of calcium release from sarcoplasmic reticulum
Doxorubicin induces calcium release from terminal cisternae of skeletal muscle. A study on isolated sarcoplasmic reticulum and chemically skinned fibers
No full textIn this study, we investigated the effect of the anticancer drug doxorubicin on Ca2+ fluxes of isolated highly purified sarcoplasmic reticulum fractions (longitudinal tubules and terminal cisternae (Saito, A., Seiler, S., Chu, A., and Fleischer, S. (1984) J. Cell Biol. 99, 875-885] and of chemically skinned skeletal muscle fibers of the rabbit. In terminal cisternae, doxorubicin inhibits Ca2+ uptake (IC50 at 0.5 microM) and increases 2.6-fold Ca2+-dependent ATPase rate (half-maximal activation at 3 microM) and unidirectional Ca2+ efflux (8-fold stimulation at 25 microM). On the contrary, doxorubicin is without effect on longitudinal tubules. In skinned muscle fibers, doxorubicin induces rapid and transient Ca2+ release, as measured by tension development (half-maximal stimulation at 6 microM), which is completely and reversibly inhibited by ruthenium red, a known inhibitor of Ca2+ release from isolated terminal cisternae. Doxorubicin has no effect on the sarcoplasmic reticulum Ca2+ pump and on the contractile apparatus of skinned muscle fibers. It is concluded that doxorubicin activates Ca2+ release from sarcoplasmic reticulum and opens a Ca2+ efflux pathway (Ca2+ channel) selectively localized in terminal cisternae. Doxorubicin might interact with Ca2+ channels involved in physiological Ca2+ releas
Solid solutions and phase transitions in (Ca,M2+)M2+Si2O6 pyroxenes (M2+ = Co, Fe, Mg).
No full textThe effect of the substitution of Ca with Co, on the phase transition and on the extension of the miscibility gap, was studied to model the general mechanism of phase transitions and solid solutions in (Ca,M2+)M2+Si2O6 pyroxenes. Eleven pyroxenes with composition Ca1-xCo1+xSi2O6, (0 ≤ x ≤ 1) were therefore synthesized by piston cylinder at P = 3 GPa, and T between 1100 and 1350 °C. The samples were characterized by SEM-EDS, XRD powder diffraction, and TEM. The results were compared with those of Ca-Fe and Ca-Mg pyroxenes. The phase diagram of Ca-Co pyroxenes is similar to that of Ca-Fe and Ca-Mg ones, with a wide asymmetric miscibility gap, and higher solubility in the Ca-rich side of the gap. The solubility on the Ca-rich side of the gap is related to the radius of the cation substituting.
The cell parameters of the Ca-Co pyroxenes undergo a sudden change at the composition of about 0.4 Ca apfu, due to the C2/c-P21/c phase transition. The change in volume with composition follows an ideal trend, in the C2/c phase, dictated by the ionic size of the substituting cation. Deviation from the C2/c behavior are instead observed in the P21/c field and ascribed to volume strain. The same turnover was found in Ca-Mg, Ca-Fe, and Ca-Mn pyroxenes. The C2/c-P21/c transition occurs with decreasing the M2 average cation radius, down to a critical value between 0.85 and 0.88 Å, depending on the series. A stabilization of the C2/c phase related to crystal field in Ca-Fe and Ca-Co pyroxenes is suggested by the analysis of the volume strain in the P21/c field. A key finding is that a miscibility gap may develop either by lattice strain related to cation substitution, within a series where all endmembers have the same structure, or for the combined effect of lattice strain and a phase transition, as is the case for pyroxene
Selective ion-channeling study of misfit dislocation grids in semiconductor heterostructures: theory and experiments
No full textPlanar dechanneling by networks of misfit dislocations was measured in a series of InxGa1-xAs/GaAs samples (001) grown by molecular-beam epitaxy. At the beginning of the strain-relaxation process the dechanneling probability exhibits different values for nominally equivalent (110) planes. At larger strain relaxation, the dechanneling probability saturates at a value around 1/2 as the beam-energy increases. In order to explain these results a new model for planar dechanneling by dislocations is proposed. This model is based on the harmonic approximation of the continuum potential but anharmonicity effects are taken into account. The perturbation to the harmonic oscillations caused by the lattice plane curvature around a dislocation is written in terms of a distortion function that depends only on the geometrical configuration of the channeling direction and of the dislocation line. This function is explicitly calculated for geometrical configurations relevant to the present samples allowing us then to solve the equation of motion. The results show that the dechanneling a probability saturates at a level sensibly lower than 100% due to the quasiplanar distribution of dislocations. Without any adjustable parameter, the comparison between computed and measured dechanneling probabilities supplies dislocation density values in excellent agreement with those measured by transmission electron microscopy and in good agreement with results deduced from previous strain-relaxation data
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