Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

关于K个复相关矩阵相等的检验

§ 1.Ｉｎｔｒｏｄｕｃｔｉｏｎ　ＷｅａｒｅｇｉｖｅｎｋｉｎｄｅｐｅｎｄｅｎｔＷｉｓｈａｒｔｄｅｎｓｉｔｉｅｓｏｆｔｈｅ (ｐ +ｑ)× (ｐ +ｑ)ｒａｎｄｏｍｓｙｍｍｅｔｒｉｃｐｏｓｉｔｉｖｅｄｅｆｉｎｉｔｅｍａｔｒｉｃｅｓＧ1,… ,Ｇｋｔｏｂｅｇ(Ｇｉ) =Ｋｅｘｐ -12 ｔｒＲ- 1ｉ Ｇｉ Ｇｉ12 (ｎｉ- ｑ-ｐ- 1) ,(1 )ｗｈｅｒｅｉ=1 ,… ,ｋ,ａｎｄＲｉｄｅｎｏｔｅｓｔｈｅｐｏｐｕｌａｔｉｏｎｃｏｒｒｅｌａｔｉｏｎｍａｔｒｉｘｏｆｔｈｅｉ ｔｈｐｏｐｕｌａｔｉｏｎａｎｄＫａｓａｇｅｎｅｒｉｃｌｅｔｔｅｒｄｅｎｏｔｅ…     

Rab5 in the regulation of cell motility and invasion

Cellular invasion requires careful regulation of the cell migration and apoptotic signaling cascades, allowing cell movement and survival of the emigrating populations. Components of the endosomal machinery are involved in these processes, and in particular the role of small GTPases of the Rab family has become appreciated. Rab5 is best known for its role in regulating the trafficking of early endosomes, however, it has recently been appreciated to associate with and regulate the routing of complexes containing integrins, the primary cellular receptors for the extracellular matrix. The association regulates the spatio temporal activation of signals of downstream growth factors and integrins. Rab proteins have also been linked to apoptosis mediated by cell surface death receptors, which elicit the activation of the death cascade via activation of caspase 8. Recently, the link between trafficking, apoptosis and cell migration was strengthened, as Rab5 was determined to work in conjunction with caspase 8 in promoting tumor cell motility and metastasis by regulating β1 integrin traffic. The capacity to connect and regulate these pathways identifies Rab5 as a key player in future studies of cell migration and tumor dissemination.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).