Fabrication of a freestanding GaN layer by direct growth on a ZnO template using hydride vapor phase epitaxy

A new hydride vapor phase epitaxy (HVPE)-based approach for the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters were optimized: the polarity of ZnO, the growth temperature, and the V/III ratio. The FS-GaN layer was achieved by gas etching in an HVPE reactor. A fingerprint of Zn out-diffusion was detected in the photoluminescence measurements, especially for the thin (80 μm) FS-GaN film; however, a thicker film (400 μm) was effectively reduced by optimization of GaN growth.     

Characterization of the chloranilate(*3-) pi radical as a strong spin-coupling bridging ligand

Dinuclear [(TPA)Co(II)(CA2-)Co(II)(TPA)](BF4)2.2MeOH (1) [TPA = tris(2-pyridylmethyl)amine] and [(TPA)CoII(CA*3-)CoII(TPA)](BF4).2Et2O (2) with a bridging chloranilate radical ligand formed by reduction of 1 are crystallographically and magnetically characterized. 1 has shown a weak antiferromagnetic coupling within the Co(II) dimer [J/kB = -0.65 K (-0.45 cm(-1))], while 2 has a 2 orders of magnitude stronger antiferromagnetic interaction between the Co(II) ion and a radical [J/kB = -75 K (52 cm(-1))].     

Synthesis, characterization, and spectroscopic analysis of antiaromatic benzofused metalloporphyrins

A two-electron oxidation of the Cu(II) (9) and Zn(II) (12) complexes of tetraphenyltetrabenzoporphyrin (TPTBP) results in the formation of stable antiaromatic [(TPTBP)Cu(II)(H(2)O)](2+)?2?[SbF(6)](-) (10) and [(TPTBP)Zn(II)(H(2)O)(2)](2+)?2?[SbF(6)](-) (13) with 16π electrons on the inner ligand perimeter. X-ray structures of the parent TPTBP complexes, the dications, and singly oxidized species [(TPTBP)Cu(II)](?+)[SbF(6)](-) (11) reveal that the use of TPTBP rather than a porphyrin ligand reduces the degree of nonplanarity in the 16π-electron species relative to the parent 18π complex. Significant high-field shifts of the (1)H?NMR signals of the outer ring protons and large positive values in calculations of nucleus-independent chemical shifts on the central cavity of the porphyrin ring provide unambiguous evidence for the antiaromatic character of the 16π Zn(II) species. A combination of magnetic circular dichroism spectroscopic studies and TD-DFT calculations on both the Zn(II) and Cu(II) species demonstrates that the main electronic bands of the dicationic species can be readily assigned by using Michl's 4N perimeter model. Femtosecond transient absorption studies clearly demonstrated that the number of π electrons on the inner ligand perimeter and the configuration of the central metal ion play a critical role in the excited-state relaxation dynamics. Redox potentials for conversion between the 16π, 17π, and 18π systems were measured by cyclic voltammetry in dichloromethane and benzonitrile, and UV/Vis spectra of each oxidation/reduction product were monitored by thin-layer spectroelectrochemistry.     

Discretization of nonlinear input-driven dynamical systems using the Adomian Decomposition Method

A numerical decomposition method proposed by Adomian provides solutions to nonlinear, or stochastic, continuous time systems without the usual restrictive restraints. It is applicable to differential, delay differential, integro-differential, and partial differential equations without the need for linearization or other restrictions. It also works through both uncoupled boundary conditions as well as delay systems. In the following paper, a new time discretization method for the development of a sample-data representation of a nonlinear continuous-time input-driven dynamical system is proposed. The proposed method is based on both the zero-order hold (ZOH) assumption as well as the Adomian Decomposition Method which exhibit unique algorithmic and computational advantages. To take advantage of this method, the following steps must be followed. First, the method is applied to a linear input-driven dynamical system to explicitly derive an exact sample-data representation, producing proper results. Second, the method is then applied to a nonlinear input-driven dynamical system, which thereby derives exact and approximate sample-data representations, the latter being most suited for practical applications. To evaluate the performance, the proposed discretization procedure was tested using simulations in a case study which involved an illustrative two-degree-of-freedom mechanical system that exhibited nonlinear behavior considering various control and input variable profiles. In conclusion, the suggested algorithm, in comparison to the results of a Taylor-Lie series expansion method, demonstrated increased performance and efficiency.     

Structural and transport properties of cubic spinel ZnCo2O4 thin films grown by reactive magnetron sputtering

We report on the growth of cubic spinel ZnCo₂O₄ thin films by reactive magnetron sputtering and bipolarity of their conduction type by tuning of oxygen partial pressure ratio in the sputtering gas mixture. Crystal structure of zinc cobalt oxide films sputtered in an oxygen partial pressure ratio of 90% was found to change from wurtzite Zn_1−xCo_xO to spinel ZnCo₂O₄ with an increase of the sputtering power ratio between the Co and Zn metal targets, D_Co/D_Zn, from 0.1 to 2.2. For a fixed D_Co/D_Zn of 2.0 yielding single-phase spinel ZnCo₂O₄ films, the conduction type was found to be dependent on the oxygen partial pressure ratio: n-type and p-type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. The electron and hole concentrations for the ZnCo₂O₄ films at 300 K were as high as 1.37×10²⁰ and 2.81×10²⁰ cm⁻³, respectively, with a mobility of more than 0.2 cm²/V s and a conductivity of more than 1.8 S cm⁻¹.     

Capillary electrophoretic analysis of wild type and mutant Proteus penneri outer membrane proteins

In this study the virulence factors, outer membrane proteins (OMP), lipopolysaccharides (LPS), hemolysin, and the in vivo and in vitro virulence of wild-type Proteus penneri 357 and its two isogenic mutant variants--a transposon and a spontaneous mutant--were examined. The OMPs of these variants were analyzed by a new and fast technique, "dynamic sieving" capillary electrophoresis (CE). The OMP profiles were dominated by two peaks (39 and 43 kDa). In the P. penneri clone examined, both the transposon and the spontaneous mutations induced significant changes in the OMP patterns (in the relative percentage of the dominant proteins). CE was suitable for the comparative analysis of bacterial protein patterns in the genetic variants of this strain, and provided valuable results in connection with the bacteriological virulence. The LPS composition of the genetic variants also showed alterations. The wild type of P. penneri 357 showed a typical ladder pattern, an "S" form, and the mutants possessed "R" LPS patterns (only few bands) in the gels. In the bacteriological virulence tests the wild type of P. penneri 357 was virulent in the in vivo, and toxic in the in vitro assays, while both mutants showed neither toxicity nor pathogenicity.     

Transduction of yeast cytosine deaminase mediated by HIV-1 Tat basic domain into tumor cells induces chemosensitivity to 5-fluorocytosine

Enzyme/prodrug approach is one of the actively developing areas for cancer therapy. In an effort to develop more effective enzyme/prodrug systems, cell-permeable cytosine deaminase was produced by fusing yeast cytosine deaminase (yCD) in frame with RKKRRQRRR domain of HIV-1 Tat which is an efficient delivery peptide of the foreign proteins into cells. The purified Tat-yCD fusion protein expressed in Escherichia coli was readily transduced into mammalian cells in a time- and dose-dependent manner. A significant level of the transduced Tat-yCD protein was recovered in the cell and was stable for 24 h as indicated by both results of the enzymatic assay of 5-fluorocytosine (5-FC) conversion to 5-fluorouracil (5-FU) and Western blot analysis. The cells transduced with Tat-yCD become highly sensitive to the cytotoxicity of 5-FC, while cells treated with yCD are unaffected by 5-FC. In addition, a strong bystander effect was observed with conditioned media from cells transduced with Tat-yCD added to non-transduced cells. Tat-yCD fusion protein demonstrated here for its ability to transduce into cells and convert nontoxic prodrug 5-FC to the toxic antimetabolite 5-FU, may be a useful approach for cancer therapy.