Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor (DMS) single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field are varied. An interesting beat pattern in the TMR and spin polarization is found for different NMS/DMS double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are splitted by the s-d exchange interaction.Comment: 4 pages, 6 figures, submitted to Phys. Rev.

Speciation, Luminescence, and Alkaline Fluorescence Quenching of 4-(2-methylbutyl)aminodipicolinic acid (H2MEBADPA)

4-(2-Methylbutyl)aminodipicolinic acid (H2MEBADPA) has been synthesized and fully characterized in terms of aqueous phase protonation constants (pKa\u27s) and photophysical measurements. The pKa\u27s were determined by spectrophotometric titrations, utilizing a fully sealed titration system. Photophysical measurements consisted of room temperature fluorescence and frozen solution phosphorescence as well as quantum yield determinations at various pH, which showed that only fully deprotonated MEBADPA2– is appreciably emissive. The fluorescence of MEBADPA2– has been determined to be quenched by hydroxide and methoxide anions, most likely through base-catalyzed excited-state tautomerism or proton transfer. This quenching phenomenon has been quantitatively explored through steady-state and time-resolved fluorescence measurements. Utilizing the determined pKas and quenching constants, the fluorescent intensity of MEBADPA2– has been successfully modeled as a function of pH

Scaling the state: Egypt in the third millennium BC

Discussions of the early Egyptian state suffer from a weak consideration of scale. Egyptian archaeologists derive their arguments primarily from evidence of court cemeteries, elite tombs, and monuments of royal display. The material informs the analysis of kingship, early writing, and administration but it remains obscure how the core of the early Pharaonic state was embedded in the territory it claimed to administer. This paper suggests that the relationship between centre and hinterland is key for scaling the Egyptian state of the Old Kingdom (ca. 2,700-2,200 BC). Initially, central administration imagines Egypt using models at variance with provincial practice. The end of the Old Kingdom demarcates not the collapse, but the beginning of a large-scale state characterized by the coalescence of central and local models

Settlement of vertical piles exposed to waves

In recent years, several authors have conducted experimental studies on the scour around piles fixed in the wave flume. In addition, the settlement of structures has been studied for the case of pipelines, due either to steady currents [International Journal of Offshore and Polar Engineering 4 (1) (1994) 30] or to wave forcing [Coastal Engineering 42(2001)313]. However, the settlement of a pile due to scour in waves has so far not been investigated.http://www.sciencedirect.com/science/article/B6VCX-47CBC4H-1/1/c6265960eb72f4b12ce7cfc5503873a

7‑Hydroxyquinoline-8-carbaldehydes. 1. Ground- and Excited-State Long-Range Prototropic Tautomerization

Ground- and excited-state long-range prototropic tautomerization were studied for a series of 7-hydroxyquinoline-8-carbaldehydes (<b>7-HQCs</b>) by ¹H and ¹³C NMR spectroscopy, photostationary and time-resolved UV–vis spectroscopic methods, and quantum chemical computations. These molecules represent trifunctional proton-donating/accepting systems that have been proposed to serve as models of a reversible optically driven molecular switch composed of two moieties: a molecular “frame” (7-hydroquinolines, <b>7-HQs</b>) and a proton “crane” (carbaldehyde group). The NMR and electronic absorption spectra indicate a solvent-dependent equilibrium between two tautomeric forms, <b>OH</b> (7-quinolinol)) and <b>NH</b> (7­(1<i>H</i>)-quinolinone), already in the ground state of all the compounds under study (7-hydroxy-2-methoxy-4-methylquinoline-8-carbaldehyde, <b>HMMQC</b>, shows only a trace of the <b>NH</b> form in highly polar and/or protic media). Electronic absorption and fluorescence of <b>7-HQCs</b> are rationalized in terms of the ground- and excited-state hydrogen atom transfer (HAT). This process was identified by comparing the UV–vis spectroscopic properties of <b>7-HQCs</b> with those of <b>7-HQs</b>, synthetic precursors of the former, as well as with the characteristics of corresponding protonated cations and deprotonated anions (part 2). The experimental results are corroborated by the density functional theory (DFT) and ab initio computations, which shed some light on the differences in photophysics between variously substituted <b>7-HQCs</b>