Mg‐doped Al0.85Ga0.15N layers grown by hot‐wall MOCVD with low resistivity at room temperature

We report on the hot‐wall MOCVD growth of Mg‐doped Al_x Ga_1–xN layers with an Al content as high as x ～ 0.85. After subjecting the layers to post‐growth in‐situ annealing in nitrogen in the growth reactor, a room temperature resistivity of 7 kΩ cm was obtained indicating an enhanced p‐type conductivity compared to published data for Al_x Ga_1–xN layers with a lower Al content of x ～ 0.70 and a room temperature resistivity of about 10 kΩ cm. It is believed that the enhanced p‐type conductivity is a result of reduced compensation by native defects through growth conditions enabled by the distinct hot‐wall MOCVD system. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical symmetries in contemporary nuclear structure applications

In terms of group theory—the language of symmetries, the concept of spontaneous symmetry breaking is represented in terms of chains of group-subgroup structures that define the dynamical symmetry of the system under consideration. This framework enables exact analytic solutions of the associated eigenvalue problems.     

q-analog ofA m−1 ⊕A n−1 ⊂A mn−1

A natural embeddingA _m–1 A _n–1 A _mn–1 for the corresponding quantum algebras is constructed through the appropriate comultiplication on the generators of each of theA _m–1 andA _n–1 algebras. The above embedding is proved in theq-boson realization by means of the isomorphism between theA _q ^– (mn ~ ⁿ A _q ^– (m) ~ ^m A _q ^– (n)algebras.     

Coupling Considerations for Fabrication of Acoustooptic Tunable Filter

Induced acoustic wave to bare fiber through various types of horn are examined. The center wavelength and extinction ratio of the notch filter are dynamically tunable and dependent on the RF signals.     

Low frequency electric polarizability and zeta-potential of Escherichia coli HB101 (K-12) cells during inactivation with ethanol

The electric properties of bacteria determine their non-specific interactions with the environment, in particular their pathogenic activity. The electric polarizability of Escherichia coli HB101 (K-12 strain) was studied while inactivation with ethanol (20–40 vol.%). The current investigation might be regarded as a continuation of previous research on the polarizability of E. coli at lower ethanol concentration (≤ 20 vol.%) and higher frequencies (≥ 20 kHz). The bacteria polarizability at low frequencies (<10⁴ Hz) shows anomalies (unexpected increase in the polarizability at certain ethanol concentrations), while the parameter decreases with an increase in the ethanol concentration at higher frequencies. We investigated for the possible reasons causing the anomalies — in our case reduced to the medium dielectric permittivity, the average cell length and the surface electric charge density distribution, related to bacterial lipopolysaccharides. We suggest a hypothesis for the molecular mechanism of changing the surface charge of E. coli, carried by lipopolysaccharides, induced by the non-ionic ethanol.      

Laser Microspectral Analysts in a Magnetic Field

A series of possibilities are shown of increasing the sensitivity of laser microspectral analytical determinations of impurities in minerals, Steels, and aluminium alloys. When the excitation of the spectrum of the laser beam evaporated substance is transferred to a magnetic field, a considerable increase in the intensity of certain spectral lines of the basic and admixed components and a certain decrease in the intensity of the background, are observed. The intensification factor depends on the regime of the laser and the additional impulse discharge, the intensity of the magnetic field, and the utilized spectral lines.     

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

Effect of the nature of mendiaxon–X interactions (X= Na, Cu, H) and the hydrogen bonding on the ν(C=O) behavior: theoretical and spectroscopic study

Theoretical and spectroscopic (IR and Raman) study of different 7-hydroxy-4-methylcoumarin (mendiaxon) systems (mend⁻, mendNa, mendCu, mendH and mendH · 2H₂O) were performed at B3LYP/6-31G(d) and B3LYP/6-31++G(d,p) levels of theory. The geometric and electronic structures as well as the vibrational behavior of the systems studied were discussed: (1) as to the changes that occurred in the anion coumarin ring upon the mend⁻–X⁺ (X⁺ =Na⁺, Cu⁺, H⁺) interactions and (2) as to the changes that occurred in mendH due to hydrogen bondings in mendH · 2H₂O. The largest bond length changes in the anion coumarin ring were obtained for mendH and the smallest ones for mendNa. The bond length changes were mainly produced from the electrostatic effect of the positive charge of X. The induced polarization of the C=O bond upon the mend⁻–X⁺ interactions was found to be opposite to the basic one and it led to shorter C=O bond lengths (higher ν(C=O) frequencies) in the order: mendNa, mendCu and mendH. Conversely, upon the hydrogen bonding the induced polarization of the C=O bond was found in the same direction as the basic one and it produced elongation to the C=O bond length (lower ν(C=O) frequency). On the basis of the correlations found, the ν(C=O) positions in mendNa, mendCu, mendH and mendH · 2H₂O were explained.     

Immobilization of aminothiols on poly(oxyethylene H‐phosphonate)s and poly(oxyethylene phosphate)s—An approach to polymeric protective agents for radiotherapy of cancer

This study describes the synthesis and characterization of polymer complexes constructed from the radioprotective agent S‐2(3‐aminopropylamino) ethylphosphorothioic acid dihydrate (amifostine or WR‐2721), applied in the radiation cancer treatment, and biodegradable poly(oxyethylene H‐phosphonate), poly(hydroxyoxyethylene phosphate), or poly(methyloxyethylene phosphate). The immobilization of another radioprotector, used in cancer radiotherapy, 1‐(3‐aminopropyl)aminoethanethiol (WR‐1065) on the same polymers is also achieved through a covalent bond (Atherton‐Todd reaction coupling), ionic bond, and physical complexation, respectively. The structure of the complexes formed is elucidated by ¹H‐ ¹³C‐, ³¹P NMR and FTIR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1349–1363, 2007