Angiotensin-(1-7): a bioactive fragment of the renin-angiotensin system

Accumulating evidence suggests that angiotensin-(1-7) [Ang-(1-7)] is an important component of the renin-angiotensin system. As the most pleiotropic metabolite of angiotensin I (Ang I) it manifest actions which are most often the opposite of those described for angiotensin II (Ang II). Ang-(1-7) is produced from Ang I bypassing the prerequisite formation of Ang II. The generation of Ang-(1-7) is under the control of at least three enzymes, which include neprilysin, thimet oligopeptidase, and prolyl oligopeptidase depending on the tissue compartment. Both neprilysin and thimet oligopeptidase are also involved in the metabolism of bradykinin and the atrial natriuretic peptide. Moreover, recent studies suggest that in addition to Ang I and bradykinin, Ang-(1-7) is an endogenous substrate for angiotensin converting enzyme. This suggests that there is a complex relationship between the enzymatic pathways forming angiotensin II and other various vasodepressor peptides from either the renin-angiotensin system or other peptide systems. The antihypertensive actions of angiotensin-(1-7) are mediated by an angiotensin receptor that is distinct from the pharmacologically characterized AT1 or AT2 receptor subtypes. Ang-(1-7) mediates it antihypertensive effects by stimulating synthesis and release of vasodilator prostaglandins, and nitric oxide and potentiating the hypotensive effects of bradykinin.     

Intelligent materials—An overview

Development in the area of materials research aims at incorporating intelligence into engineering materials, enabling them to sense the external stimuli and alter their own properties to adapt to the changes in the environment. This paper discusses possible forms of intelligence that may be incorporated in these materials. Three basic mechanisms of intelligent materials, namely, the sensor, processor and actuator functions, are described. Implementation of these in the microstructure of various materials, as well as associated algorithms and techniques are illustrated. Different models, control algorithms and analyses developed by various researchers are reviewed and their potential applications in engineering materials are presented.     

Collector offset voltage of heterojunction bipolar transistorsgrown by molecular beam epitaxy

The collector-emitter offset voltages of InAlAs/InGaAs heterojunction bipolar transistors grown by molecular-beam epitaxy are discussed. Both the difference between emitter and collector areas and electrical asymmetry between emitter and collector junctions in these mesa-isolated transistors account for the offset voltages observed. Devices exhibited offset voltages in the range of 50-300 mV, depending on the structures and device sizes. Several electrical and geometrical factors affecting the offset voltage are discussed in detail     

Superconducting joints for silver-clad BSCCO tapes

The advent of high-T_c superconducting tapes for a variety of applications has resulted in the need for superconducting joints. Although long-length tapes can be custom-made for some applications, interconnections between subcoils of a magnet or shorter-length conductors for coil winding and current leads, make the development of such joints imperative. Additionally, high-quality short-or medium-length conductors, which are easier to make, can be joined for improved performance. Employing a novel chemical etching technique, we have fabricated lap joints between short lengths of silver-clad BSCCO tapes. Each joint was formed by etching the silver away and bringing together the exposed superconductor cores of two tapes together. The joined tapes were then subjected to a series of thermomechanical treatments. Detailed microstructural and electrical characterization within and across the joint was performed. Critical currents of up to 37 A within the joint region and 10 A through the joint region(at 77K) have been achieved.     

Synthesis and single crystal growth of gallium phosphide by the liquid encapsulated vertical Bridgman technique

Gallium phosphide is a typical III–V compound semiconductor and is also an important electronic material. The synthesis and single crystal growth of this compound by melt methods is rendered very difficult because of the large phosphorus vapour pressure. A high pressure vessel with internal heating and a quartz reactor was first developed for the direct synthesis of gallium phosphide. The crystal growth was carried out in a second high pressure chamber rated for 100 bars gas pressure and equipped with the paraphernalia for crystal growth. Single crystals of gallium phosphide were grown from the polycrystalline starting material by the vertical Bridgman method and the vapour pressure problem was overcome by encapsulating the melt in a column of molten boric oxide. Both boron nitride and silica were employed as crucibles, and with the former, single crystal rods of 8–10 mm diameter and 10–15 mm length were obtained.     

Neutron structural study of the Bi-monolayer compound (Bi0.5Cu0.5)Sr2(Y0.8Cu0.2)Cu2O7 + δ—the Role of excess oxygen in superconductivity

Comparative neutron structural investigations are made on nonsuperconducting (slow-cooled) and superconducting (liquid-nitrogen quenched;T _c ^onset=70 K andR=0 at 20 K) samples of (Bi_0.5Cu_0.5)Sr₂(Y_0.8Cu_0.2)Cu₂O_{7 + δ} in order to examine the role of excess oxygen on the superconducting behavior of this “1212”-phase compound. Analysis of refined structural parameters shows that the two main factors which influence the superconductivity in (Bi, Cu)-1212 are: (i) the extent of occupancy of excess oxygen at O(5), the 2(e) site located in between the two CuO₂ pyramidal layers, and (ii) the length of the apical Cu(2)-O(2) bond. The (Bi, Cu)-O monolayer plays the role of the “charge reservoir” quite effectively as reflected by the substantial increase in the length of the apical (bridging) Cu(2)-O(2) bond due to depletion of excess oxygen in this layer. Surprisingly, vacancies at as many as 10% of the O(1) site belonging to the CuO₂ planes do not appear to disrupt the flow of current in the Cu(3d)-O(2p) planar network in the superconducting state. Relevant features of the structure of the (Bi, Cu)-1212 phase, in particular the role of excess oxygen and its occupancy at different sites, are discussed in the light of the available data on the isostructural (Pb, Cu)-1212 phase and the (La, Sr, Ca)₃-Cu₂O_{6 + δ} phase superconductors.     

Localization of the nic site of IncN conjugative plasmid pCU1 through formation of a hybrid oriT

The N-type oriT of plasmid pMUR274 was cloned on a 474-bp RsaI-SspI fragment, and the nucleotide sequence was determined. A comparison of the pMUR274 oriT sequence and the sequence of the oriTs of IncN plasmid pCU1 and IncW plasmid R388 demonstrated 57 and 28% identity, respectively. Intramolecular, site-specific recombination between the pCU1 oriT and the oriT of pMUR274 resulted in the formation of a hybrid oriT containing one half of each parental sequence. The junction point of the hybrid occurred within a 10-bp sequence, GCTATACACC, present in both parental sequences and represents the nic site of each oriT. Mutation of the first A or second T residue within the 10-bp junction sequence reduced transfer less than 20-fold, while mutation of either the second or third A residue reduced transfer over 1,000-fold. Site-specific recombination between a wild-type pCU1 oriT and these four mutant pCU1 oriTs demonstrated that nic lies between the second T and second A residues of the 10-bp junction sequence. Site-specific recombination between wild-type and mutant pCU1 oriTs also demonstrated that point mutations to the right of nic reduced both initiation and termination of transfer while point mutations to the left of nic reduced termination but had little or no effect on initiation. A 28-bp deletion within the AT-rich region 39 bases to the right of nic reduced both initiation and termination, while deletion of a 6-bp inverted repeat sequence at the right-most boundary of the minimal oriT region reduced initiation but not termination.