Sensitivity of the plasma electric potential to the transport barriers formation

Heavy Ion Beam Probe diagnostics was used to study plasma potential and density in the regimes with improvement in confinement on the T-10 tokamak. Time-spatial potential distribution was analyzed during the formation of transport barriers. The time evolution of the potential profile shows simultaneous formation of the internal negative potential well and external layer with strong Er, during the simultaneous formation of the internal and external transport barriers. The time history of the plasma potential in the inner region (0.6<ρ<1) shows its clear correlation with theD _α intensity. Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000. This work was supported by Russian Basic Research Foundation, Grant No. 99-02-18457.     

Exponentially growing tearing modes in Rijnhuizen Tokamak Project plasmas

The local measurement of the island width w, around the resonant surface, allowed a direct test of the extended Rutherford model [P. H. Rutherford, PPPL Report-2277 (1985)], describing the evolution of radiation-induced tearing modes prior to disruptions of tokamak plasmas. It is found that this model accounts very well for the observed exponential growth and supports radiation losses as being the main driving mechanism. The model implies that the effective perpendicular electron heat conductivity in the island is smaller than the global one. Comparison of the local measurements of w with the magnetic perturbed field B showed that w proportional to B1/2 was valid for widths up to 18% of the minor radius.     

An Approach for Extracting Small-Signal Equivalent Circuit of Double Heterojunction δ-Doped PHEMTs for Millimeter Wave Applications

Pseudomorphic high electron mobility transistors (PHEMTs) are very important in millimeterwave application. A simple and accurate method for extracting small-signal equivalent curcuit for Double Heterojunction -doped PHEMT valid up to 40GHz is presented. First, the parasitic parameters of the equivalent circuit are determined using pinch off PHEMT except for PAD capacitances. The initial intrinsic elements are then determined by conventional analytical method. Advanced Design System is then used to optimize the whole model parameters with very small dispersion of initial values. Good agreement is obtained between simulation results and measured results for a 0.25um DH PHEMT.     

Photopolymerization of methyl methaerylate initiated by benzil in non-aqueous media

Summary Kinetics of polymerization of methyl methacrylate initiated by photolysis of benzil with 420 nm radiation, have been investigated at 35 °C. The rate of monomer disappearance has been followed gravimetrically and the chain-length of the polymer formed, measured by viscometry. The dependence of the rate of polymerization and quantum yield of monomer conversion on the concentrations of the monomer and the initiator, absorbed light-intensity etc. has been studied in detail. A kinetic scheme has been proposed in the light of experimental results, involving i) a primary photochemical act of excitation of the sensitizer producing free radicals by hydrogen abstraction, ii) initiation of polymerization by free radicals generated and iii) termination of the active chain by mutual combination involving either coupling or disproportionation.With 3 figures and 2 tables     

Axially chiral biaryl diols catalyze highly enantioselective hetero-Diels-Alder reactions through hydrogen bonding

Axially chiral 1,1'-biaryl-2,2'-dimethanol (3, BAMOL) family of diols are highly effective catalysts for enantioselective hetero-Diels-Alder reactions between aminosiloxydiene 1 and a wide variety of unactivated aldehydes. The reactions proceed in useful yields and excellent enantioselectivities. The diols function in the same capacity as Lewis acids, by activating the aldehyde carbonyl group through hydrogen bonding.     

Porous GaN as a template to produce surface-enhanced Raman scattering-active surfaces

Surface-enhanced Raman spectroscopy (SERS) substrates have been prepared by depositing Au or Ag on porous GaN (PGaN). The PGaN used as the template for the metal deposition in these studies was generated by a Pt-assisted electroless etching technique. PGaN was chosen as a potential SERS template due to its nanostructured surface and high surface area, two characteristics that are important for SERS substrates. Metal films were deposited either by solution-based electroless deposition or by thermal vacuum evaporation. SERS spectra were recorded at lambda = 752.5 nm for Au films and at lambda = 514.5 nm for Ag films deposited on PGaN. The SERS signal strength across the metal coated PGaN substrates was uniform and was not plagued by "hot" or "cold" spots on the surface, a common problem with other SERS surfaces. The Ag film deposited by electroless deposition had the highest overall SERS response, with an enhancement factor (EF) relative to normal Raman spectroscopy of 10(8). A portion of the increase in EF relative to typical SERS-active substrates can be assigned to the large surface area characteristic of the PGaN-Ag structures, but some of the enhancement is intrinsic and is likely related to the specific morphology of the metal-nanopore composite structure.     

Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers

Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden–Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)₂(MA)_n−1Pb_nI_3n+1 (RA = IBA, IAA; MA = methylammonium n = 1–4). Surprisingly, the IAA n = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb–I–Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA''s small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for n = 2, in which the modulated structure has a lower bandgap because of its larger Pb–I–Pb angles. Photo-response was tested for the n = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two n = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.

Using branched spacer cations results in a modulated rippled 2D perovskite structure and materials for solar cells.     

Metal complexes of 1-hydroxy-2,3-dimethyl-4-(3′-methyl-4′-amino-5′-mercapto-1′, 2′, 4′-triazole)-1,4-diaza-1, 3-butadiene with manganese(II), cobalt(II), nickel(II) and copper(II)

Summary Binuclear metal complexes of the type [M(HDDB)-(H₂O)₂]₂: where HDDB=1-hydroxy-2,3-dimethyl-4-(3-methyl-4-amino-5-mercapto-1, 2, 4-triazole)-1,4-diaza-1, 3-butadiene and M=manganese(II), cobalt(II), nickel(II) and copper(II), have been prepared and characterised by elemental and thermal analyses, magnetic measurements, electronic and i.r. spectra. Octahedral geometry around the metal(II) ions is proposed and the crystal field parameters of the cobalt(II) and nickel(II) complexes are also calculated. Fungicidal screening of the complexes has been made aginstHelminthosporium oryzae andFusarium oxysporium.     

Investigating the potential of tetrahydropyridinyl chalcones as useful agents against breast carcinoma: An in vitro and in vivo study

N-Benzyltetrahydropyridinyl-4,6-dimethoxy phenyl-substituted 2′-hydroxychalcones SJC1–15 were synthesized using Claisen–Schmidt condensation, their structures confirmed by spectral analysis, and their anticancer activity evaluated. To support their biological activity, physicochemical parameters such as lipophilicity and oxidation potential were determined. To assess their relative cytotoxicity, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed using MCF-7, T-47D, MDA MB-231, HepG₂, and Vero cell lines. The cytotoxicity of the chalcones was found to vary with the nature of the ring B substituents. The lipophilicity of the cytotoxic compounds expressed in terms of distribution coefficient was found to lie in the range of 2.4–4.2. Further evaluation of their antioxidant potential revealed antioxidant activity by 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging assay and irreversible electrochemical reaction with oxidation potential in the range of 0.879–1.048 V. Of the 15 chalcones, SJC4, 5, 9 were selected for further in vitro studies using MCF-7. The compounds exhibited significant apoptotic effect and caused cell cycle arrest at G0/G1 and G2/M phase. Among them, two of the O-alkylated chalcones (SJC5, 9) showing promising activity against hormone-responsive breast cancer cells were evaluated for their in vivo anticancer activity using 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumor model. Three-week treatment with the test compounds at oral dosage of 100 mg kg^?1 per day significantly improved elevated tumor parameters compared with tumor control. Treatment with chalcone SJC5 (a 2,4,5-trimethoxy derivative) exhibited anticancer effects similar to those of doxorubicin (2 mg kg^?1 per week, i.p.) and was free from toxic effects observed with doxorubicin treatment.     

Three dimensional quantum dynamics of (H-, H2) and its isotopic variants

We present the results of a time-dependent quantum mechanical investigation using centrifugal sudden approximation in the form of reaction probability as a function of collision energy (E(trans)) in the range 0.3-3.0 eV for a range of total angular momentum (J) values and the excitation function sigma(E(trans)) for the exchange reaction H(-) + H(2) (v = 0, j = 0) --> H(2) + H(-) and its isotopic variants in three dimensions on an accurate ab initio potential energy surface published recently (J. Chem. Phys. 2004, 121, 9343). The excitation function results are shown to be in excellent agreement with those obtained from crossed beam measurements by Zimmer and Linder for H(-) + D(2) collisions for energies below the threshold for electron detachment channel and somewhat larger than the most recent results of Haufler et al. for (H(-), D(2)) and (D(-), H(2)) collisions.