Persistent narrowing of nuclear-spin fluctuations in InAs quantum dots using laser excitation

We demonstrate the suppression of nuclear-spin fluctuations in an InAs quantum dot and measure the timescales of the spin narrowing effect. By initializing for tens of milliseconds with two continuous wave diode lasers, fluctuations of the nuclear spins are suppressed via the hole-assisted dynamic nuclear polarization feedback mechanism. The fluctuation narrowed state persists in the dark (absent light illumination) for well over 1 s even in the presence of a varying electron charge and spin polarization. Enhancement of the electron spin coherence time (T2*) is directly measured using coherent dark state spectroscopy. By separating the calming of the nuclear spins in time from the spin qubit operations, this method is much simpler than the spin echo coherence recovery or dynamic decoupling schemes.     

Synthesis and Antiinflammatoryand Anticancer Activity Evaluation of Some Condensed Pyrimidines

Summary.  Upon condensation with 4-isothiocyanato-4-methyl-2-pentanone, 2,3-diaminonaphthalene and N-aminoethyladenosine gave in good yields substituted pyrimidonaphthoimidazole and imidazopyrimidine thione. Refluxing pyrimidobenzthiazole with methanol H₂SO₄ at pH∼1 resulted in S-methyl pyrimidobenzthiazole in moderate yield. Pyrimidobenzimidazole derivatives could be reacted to S-alkylated and N-acylated derivatives by refluxing with ethyl bromoacetate in the presence of anhydrous potassium carbonate in THF and by heating in an acetic acid/acetic anhydride mixture. Heating of pyrimidobenzimidazole with 75% aqueous H₂SO₄ on a water bath ended up in a rearranged product. All compounds gave correct ¹H NMR, IR, and HR mass spectra. Results of antiinflammatory, analgesic, and anticancer activity screening of the new compounds are described. Received October 29, 1999. Accepted (revised) January 13, 2000     

A New Butyrolactone Charlesolide and Other Constituents from Roots of Geranium charlesii

Chemistry of Natural Compounds - A new butyrolactone that was called charlesolide and the known phenolic compounds gallic acid (3,4,5-trihydroxybenzoic acid) and its methyl gallate and ethyl...     

Valence band mixing in GaAs-(AlGa)As heterostructures

In optical emission from electrons confined in quantum wells, the component with polarization normal to the planes was observed to be unexpectedly strong. This suggests a breakdown of the point group symmetry of the highest valence state beyond the reduction from cubic to laminar symmetry. Effective mass theories that include excitonic interactions and conventional symmetry-breaking mechanisms do not account for this phenomenon.     

Core level binding energy shifts of K and Cs adlayers on Ru(001)

Using synchrotron radiation from the VUV ring at NSLS and vacuum ultraviolet radiation from a HeI resonance lamp, we have recorded high resolution photoemission spectra of K and Cs overlayers on Ru(001). It is found that for “thin” multilayer coverages ( 3 ML) the K3p and Cs5p core levels exhibit three sets of core levels which can be assigned to interface, “bulkrd and surface emission in increasing binding energy. The results are discussed in terms of the nature of electronic interaction and a thermodynamic model. The K3p core level spin-orbit splitting is also resolved in these measurements for K in the condensed phase, for the first time with photoemission spectroscopy.     

High-throughput determination of seven trace elements in food samples by inductively coupled plasma-mass spectrometry

A method was developed for high-throughput determinations of 7 elements in food samples, namely antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and tin (Sn). The samples were digested by closed-vessel microwave-assisted digestion using concentrated nitric acid (HNO3) as the medium, followed by microwave- assisted evaporation to concentrate the sample solutions before dilution to the desired volume. The microwave-assisted evaporation procedure effectively reduced the final acid concentration to around 8% before analysis by inductively coupled plasma-mass spectrometry (ICP-MS). This reduction allows determination by ICP-MS to proceed without further sample dilution, which would affect the detection limit. The method was validated, and method recoveries for As, Cd, Cr, Pb, and Hg were within the certified ranges of the chosen certified reference materials. Recoveries of the 7 elements from spiked samples ranged from 93.1 to 103.6%. The standard uncertainties of precision for the 7 elements were between 3.1 and 4.3%. Interlaboratory comparison studies for As, Cd, and Pb gave z-scores ranging from -0.2 to 0.3.