Kinds Of Junctions Research Articles

Nonohmic behavior of SnO2-MnO polycrystalline ceramics. I. Correlations between microstructural morphology and nonohmic features

This report discusses important microstructural features of SnO2.MnO-based polycrystalline ceramics. The influence of the sintering time and the concentration of donor Nb2O5 on the microstructure of these ceramics are investigated, and the correlation between the microstructural features and nonohmic behavior are also discussed. High resolution analytical electron microscopy was used for a detailed characterization of the microstructure and grain boundary chemistry of the compositions, revealing that SnO2-MnO dense ceramics consist of two phases, SnO2 grains and Mn2SnO4, precipitated mainly at triple grain points. In addition, two types of SnO2-SnO2 grain boundary were identified: type I, Mn-rich and thin, and type II, Mn-poor and thick. Changes in Mn concentrations at the grain boundaries are ascribed to both grain misorientation and Mn diffusivity along the grain boundary. The identification of two kinds of junctions in SnO2-MnO has significant implications in the material’s nonohmic behavior, as will be discussed in detail here and in Part II, and is important in understanding the sintering mechanism and microstructural formation of SnO2 ceramics.

Carbon nanotube structures: Y-junctions and nanorings

The possibility of coupling two Y-junctions of carbon nanotubes, forming a type of nanotube ring is addressed here. Recent experimental evidences of growing carbon nanotube structures forming basically Y-kind junctions give support to this theoretical proposition. A single-band tight-binding Hamiltonian is considered and local electronic properties are investigated via the Green function formalism following renormalization techniques. Modulation on the transport properties of those nanostructured systems may be induced by considering different kind of junctions and different symmetries. Quantum interference phenomena are proven to reduce partial or completely the conductance of such nanoring structures.

Investigation on the flanking transmission of impact sound insulation of floor

Impact sound pressure level of floors depends, as general rule, on direct sound radiated by the floor excited by a standard tapping machine and on flanking transmission of lateral walls. Depending on the kind of junction between the floor and walls of the receiving room, flanking paths can be more or less important. Requirements of laboratory test specimens are not well specified in EN ISO 140 standards, particularly for junctions of the test floor and lateral walls. In this paper measurements performed at DIENCA laboratory are presented in order to evaluate the influence of flanking transmission on impact sound pressure levels of a standard floor and on impact sound reduction level of standard floor with a resilient layer. Measurements are performed on a 14-cm-thick concrete floor in two different conditions: first connected on two sides of the receiving room and then on all four sides. Impact sound pressure levels and vibration levels are analyzed in order to evaluate the contribution of different transmission paths. As the measurements were carried on in the new facility for measurement of the contribution of the flanking transmission, this facility will be exhaustively presented in the paper.

Point-contact tunneling involving low-dimensional spin-triplet superconductors.

We modify and extend previous microscopic calculations of tunneling in superconducting junctions based on a nonequilibrium Green function formalism to include the case of spin-triplet pairing. We show that distinctive features are present in the I-V characteristics of different kinds of junctions, in particular, when the effects of magnetic fields are taken into account, that permit to identify the type of pairing. We discuss the relevance of these results in the context of quasi-one-dimensional organic superconductors such as (TMTSF)2PF6 and layered compounds like Sr2RuO(4).

Junctions formed in Y Ba2Cu3O7−δ nanowires

We report the fabrication and characterization ofY Ba2Cu3O7−δ nanowires with various kinds of junctions, including Dayem bridges, crossed junctions andS–I–S junction arrays. Ideal flux pinning centres were introduced into these nanowires andthe ceramic nanowires were found to have potential plasticities favourable for nanoscaleprocessing. Prospective physical properties and superconducting nanoelectronicapplications of these nanowires are expected.

Fabrication of NbN tunnel junctions with a magnetic barrier

NbN tunnel junctions with a magnetic barrier, NiO x , were fabricated using dc and rf sputtering deposition. It is found that the Josephson current is severely suppressed without applying external magnetic field. Three kinds of junctions were fabricated with the structure, NbN/NiO x /NbN and NbN/NiO x /AlN/NbN. In the former type junctions, the magnetic barrier, NiO x , was formed by thermal oxidation or was deposited by sputtering a NiO target. The junctions show a nonlinear I– V characteristics and a low junction resistance. It can work as a moderately good mixer near 1 THz. They will be promising junctions in constructing a submillimeter imaging mixer array.

Measurement and simulation of brick wall sound reduction index

This paper presents the procedures and results of an experimental, numerical simulation and analytical model of sound reduction index of solid brick wall. The solid brick used has the following dimensions: 22×10×5 cm and density of 1850 kg/m3. The physic-mechanical characteristics: density, resistance, and elasticity modulus were measured using a set of small walls (0.60×0.63 m). One wall of 4.10×3.20×0.10 m (length/height/thickness) was built between two reverberant rooms, with 60 and 63 cubic meters in volume, respectively. Two kinds of junctions were used between the wall and the concrete walls of the reverberant rooms: elastic junction (with a thin layer of rubber, sealed with silicon rubber on both sides and the top of the wall) and rigid junction (using the normal mortar). The sound reduction index was measured according to ISO 140-3 using airborne transmission. The brick characteristics were used as input data for the statistical energy analysis (SEA) model. The results from SEA, analytical, and measured models are compared.

Grain boundaries in boron-doped CVD diamond films

In this investigation, grain boundaries have been studied in high-quality polycrystalline B-doped CVD diamond films by transmission electron microscopy (TEM). The samples were predominantly grown in 〈110〉 or 〈211〉 growth directions and the boron doping range was approximately 1018 cm−3. Selected-area diffraction (SAD) was taken for each grain in a cluster in order to find the relative misorientations. Σ3, Σ9 and Σ27 coincident site lattice (CSL) grain boundaries were found and they combined to form symmetrical and asymmetrical tri-junctions, quadri- and penta-junctions. Three different types of symmetrical tri-junctions were identified, one of them (obtuse tri-junction) having a very high defect density that is apparently previously unreported. Another (Σ3, Σ9 and Σ27 tri-junction) commonly occurs in the dissociation of higher junctions (four- and five-fold junction). The two different growth directions led to different kinds of junctions.

Pseudo-hysteretic behavior in semiconductor-superconductor junction

A recent work by Th. Schäpers et alli [1] showed the coupling to a superconductor of the two-dimensional electron gas in a doped semiconductor heterostructure. The presented I–V characteristic exhibits a hysteresis at the low-voltage range, similarly to I–V curves of other works for analogous structures. In this work we simulate that kind of junction using the Pereira-Nicolsky simplified model for superconductor-normal metal-superconductor systems applied to the dimensional parameters of that junction and the appropriate Andreev density of states calculated for that doped semiconductor. We show that, at sub-gap voltages, pseudo-hysteresis is probably due to the kind of experimental set-up used in the measurements and actually it hides a negative-differential-resistance behavior. The negative derivative in the I–V characteristic is a direct consequence of the multiple Andreev reflection (AR) mechanisms at the superconductor-semiconductor interfaces because the semiconductor is heavily doped and exhibits a density of states within its energy gap. The negative derivative follows from the competition between the increasing voltage and the decreasing of the allowed AR. Finally, we suggest the kind of experiment should be done for avoiding that pseudo-hysteresis in those junctions.

Observation of Intergranular Films in BaB2O4-added BaTiO3 Ceramics

Distribution characteristics of boundary phase in BaB2O4 added BaTiO3 ceramics were investigated with a focus on the curvature difference of solid–liquid interfaces at two-grain and triple junctions. High-resolution transmission electron microscopy revealed that the triple junction of solid grains showed the positive curvature of solid–liquid interface and consisted of the mixture of liquid phase and crystallized BaB2O4 phase. On the other hand, flat amorphous thin film of 2.5-nm thickness was observed at the two-grain junction. This kind of boundary phase distribution characteristic was explained by the solubility difference between two kinds of junctions of solid grains that had different curvature of solid–liquid interfaces.

Nb-based SNS junctions with Al and TaO/sub x/ barriers for a programmable Josephson voltage standard

We report results achieved in the fabrication of two different Nb-based SNS devices which can be used for the development of a programmable Josephson voltage standard. Junctions with an Al metal barrier, 5 to 100 nm thick, have been fabricated obtaining devices with I/sub C/R/sub N//spl ap/0.5 mV. A second kind of junction has been fabricated using 10 nm thick non-stabilized TaO/sub x/ as a barrier, deposited by bias sputtering. For these devices, using the bias voltage as the main process parameter, I/sub C/R/sub N//spl ap/0.1 mV was obtained. Measurements of the electrical properties of the Nb/Al/Nb and the Nb/TaO/sub x//Nb junctions are reported.

Conductance Peak at Zero-Bias in Ag-SiO-Bi2Sr2CaCu2O8-xPlanar Tunnel Junctions

Two kinds of junctions were fabricated on a single crystal and a polycrystal of Bi 2 Sr 2 CaCu 2 O 8- x . The tunneling conductance characteristics, G ( V ) were measured for the former junction at temperatures from 4.2 K to 100 K, and for the latter one at temperatures from 8.7 K to 90 K. It was found that the conductance peak (CP) at zero-bias is observed for tunneling direction perpendicular to a c -axis, but is not observed for tunneling direction parallel to a c -axis. Kashiwaya et al . theoretically predicted that the junction fabricated on a d -wave superconductor can give various G ( V ) characteristics scattering from a s -wave like spectrum to a d -wave like one, and has CP under certain boundary condition. In the present investigation, the measured G ( V ) characteristics in the high T c Bi-system superconductor were found to qualitatively agree with the theoretical prediction by Kashiwaya et al .

Conductance of nano-tube junctions and its scaling law

The conductance is calculated by Landauer’s formula with a simple tight binding model for junctions connecting two different metallic carbon nanotubes. These junctions are formed by a pair of disclinations, a 5-membered ring and a 7-membered ring, without dangling bonds. Conductances of about eight hundred kinds of junctions are obtained. The conductance is determined only by the ratio i/R where i is the distance between the two disclinations and R is the circumference of the thinner tube. When i/R ≫ 1, the conductance is found to be almost proportional to (i/R)-3. Even when the Fermi energy is shifted by doping, an extended scaling law holds, so far as the channel number is kept two.

The intrinsic determinants of the critical current in SIS′ and SIS high-T c Josephson junctions

We discuss the influence of a depressed order parameter at the surface of a high-Tc superconductor on the temperature dependence of the Josephson critical current in SIS′ and SIS junctions, where S denotes the high-Tc superconductor, S′ a conventional one, and I the insulating layer. The comparison with experimental data of planar YBCO-based SIS′ and SIS junctions shows that, when the quality of the junction interfaces is particularly good, the fit by using the depressed-gap models can accurately reproduce the experimental Ic(T) curves. As a consequence, the surface depression of the order parameter is the most plausible cause for the intrinsic deviations of the IcRN products from the ideal BCS values in this kind of junctions.

Flux flow characteristics of step-edge junctions made of thin films

Current - voltage characteristics of step-edge junctions made of thin films were studied as a function of magnetic field and temperature within the framework of the Bardeen - Stephen flux flow model. The influence of a locally applied magnetic field was also studied by utilizing two kinds of junction, i.e. a single-layer junction made on a step on an MgO substrate and a multi-layer junction having a control line just below the junctions.

Radiation loss of Y-junctions in rib waveguide

In this paper we analyze the effects of radiation in Y-junctions in rib waveguide by combining the effective dielectric constant method and the concept of local modes of a five-layer slab guide. The evaluation of the fields of the junction is performed together with the analysis of the radiation effects at the end of the transition; various kinds of junctions are examined and discussed, in both LSE and LSM polarizations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low field microwave absorption study of defects in YBa 2Cu 3O 7 crystals and films

We have studied the microwave absorption at low fields of superconducting loops made with YBa 2Cu 3O 7 thin film. Series of well-resolved periodic lines are observed. Angular and microwave dependences of the spectra are discussed. We have measured the microwave power dissipated within the loop. All the results show a quantitative agreement with the model of Silver and Zimmerman describing the microwave absorption of a superconducting loop closed by a junction and give a quantitative evaluation of the critical current of intrinsic junction in the film. The effect of the static field on the spectra allows us to distinguish two kinds of junction.

Differential synthesis of type 1 and type 2 desmocollin mRNAs in human stratified epithelia.

Epithelial cells are tightly connected by various kinds of junctions, of which the desmosomes (maculae adhaerentes) are particularly prominent. The desmosomes are characterized by two subgroups of constitutive transmembrane glycoproteins, the desmogleins and the desmocollins, which have been identified as specific members of the larger multigene family of CAMs of the cadherin category. Following our recent observation in bovine tissues that different desmoglein and desmocollin genes can be expressed in different cell types (Koch, P.J. et al., Proc. Natl. Acad. Sci. USA 89:353-357, 1992), we have now isolated cDNAs encoding human desmocollins type 1 and type 2. The complete sequence of human type 1 desmocollin has been determined and identified by its homology to the corresponding bovine gene product. Using in situ hybridization on sections through frozen human tissues, we show that mRNAs for type 2 desmocollin are synthesized in various stratified epithelia such as epidermis, esophagus and exocervix, whereas type 1 desmocollin was detected in appreciable amounts only in epidermis. In addition, a striking difference has been observed within the epidermis, where type 2 desmocollin mRNA can be detected in several basal layers of living cells but type 1 desmocollin mRNA is restricted to suprabasal layers. The possible functional involvement of desmocollins in the differentiation of stratified tissues is discussed and the potential value of molecular probes for desmosomal cadherins in tumor diagnosis is emphasized.

Rate and Mechanism of Nonhomologous Recombination During a Single Cycle of Retroviral Replication

Oncogenes discovered in retroviruses such as Rous sarcoma virus were generated by transduction of cellular proto-oncogenes into the viral genome. Several different kinds of junctions between the viral and proto-oncogene sequences have been found in different viruses. A system of retrovirus vectors and a protocol that mimicked this transduction during a single cycle of retrovirus replication was developed. The transduction involved the formation of a chimeric viral-cellular RNA, strand switching of the reverse transcription growing point from an infectious retrovirus to the chimeric RNA, and often a subsequent deletion during the rest of viral DNA synthesis. A short region of sequence identity was frequently used for the strand switching. The rate of this process was about 0.1 to 1 percent of the rate of homologous retroviral recombination.

New criterion for determining the character of intrinsic Josephson junctions

Abstract The theories on tunneling and metallic Josephson junctions in equilibrium are reviewed. It is shown that the most commonly used criterion for determining whether an intrinsic junction is of the tunneling or metallic (weak link) type, the temperature dependence of the critical current, is not efficient for this purpose. A new criterion, based on the nonequilibrium current-voltage characteristics (CVC), is proposed. It is shown that, in the sub-gap voltage range, the CVC of each kind of junction is different and there is no ambiguity in the junction-type determination.