Ultralow-jitter, 1550-nm mode-locked semiconductor laser synchronized to a visible optical frequency standard

Using high-bandwidth feedback, we have synchronized the pulse train from a mode-locked semiconductor laser to an external optical atomic clock signal and achieved what is to our knowledge the lowest timing jitter to date (22 fs, integrated from 1 Hz to 100 MHz) for such devices. The performance is limited by the intrinsic noise of the phase detector used for timing-jitter measurement. We expect such a highly stable device to play an important role in fiber-network-based precise time/frequency distribution.     

The prospects for high resolution optical brain imaging: the magnetic resonance perspective

Various analogs of NMR and MRI are now technically possible in optics; specifically, high-resolution laser-pulse shaping and complex pulse sequence generation with well-defined phase shifts has been demonstrated. Here we summarize this technology and discuss the potential for these methods to enhance optical functional imaging, competing with (and surpassing?) what is possible by functional MRI.     

Imaging the internal electronic structure of a surface adsorbate with low energy ions

Time-of-flight spectra were collected for 2.5 keV 7Li+ backscattered from Fe surfaces covered with submonolayers of iodine. Li singly scattered from the adatoms has a consistently larger neutral fraction than for scattering from the substrate, implying a region of positive charge atop the iodine. The neutral fraction decreases for off-normal exit angles, indicating a nonuniform charge distribution around the polarizable adsorbates. This demonstrates that ion scattering can image the internal electronic structure of an adatom and provides an explanation for anomalous work function changes.     

Quantum phase transition in quasi-one-dimensional BaRu6O12

We report the first systematic study of the electrical transport and magnetic properties of BaRu6O12, which has a quasi-one-dimensional (quasi-1D) hollandite structure. We show that BaRu6O12 is quasi-1D electronically as well. Its physical properties were found to be extremely sensitive to disorder. Furthermore, a transition from being metallic with a resistance drop around 2 K to being weakly insulating as the applied magnetic field was increased was also found. We propose that these two features are related to the possible presence of a quantum phase transition in this material system.     

PNA for one-base differentiating protection of DNA from nuclease and its use for SNPs detection

By the combination of peptide nucleic acid (PNA) with single-stranded DNA specific nucleases, alteration of a single base to another in DNA has been detected with high accuracy. Only the DNAs in DNA/PNA duplexes involving a mismatch are efficiently hydrolyzed by these enzymes, whereas fully matching sequences are kept intact. This difference is visually scored by adding 3,3'-diethylthiadicarbocyanine, which changes its color from blue to purple upon binding to DNA/PNA duplexes. These findings are applied to the convenient and straightforward detection of single nucleotide polymorphisms (SNPs). When the target site in the sample DNA is completely complementary with the PNA, a notable amount of DNA/PNA duplex remains and thus the solution exhibits purple color. In the presence of even one mismatch between PNA and DNA, however, the DNA is completely digested by the enzyme and therefore the dye shows its intrinsic blue color. The SNPs in the apolipoprotein E gene of human DNA have been successfully genotyped by this method.     

The solid-phase synthesis and use of N-monosubstituted piperazines in chemical library synthesis

An efficient solid-phase synthesis of mono-N-substituted piperazines is presented. The key transformation involves a selective borane amide bond reduction in the presence of a carbamate resin linkage. This synthetic route takes advantage of the large diverse pool of commercially available carboxylic acids, acid chlorides, and sulfonyl chlorides. The solid-phase approach facilitates parallel processing by eliminating the need for column chromatography after each synthetic step. The N-monosubstituted piperazines were shown to react with polymeric activated tetrafluorophenol (TFP) reagents to generate arrays of amides and sulfonamides in good purity for biological testing.     

Simultaneous determination and pharmacokinetic studies on (3,4-Dihydroxyphenyl)-lactic acid and protocatechuic aldehyde in rat serum after oral administration of Radix Salviae miltiorrhizae extract

A simple and sensitive high-performance liquid chromatography method is developed for the simultaneous determination of (3,4-dihydroxyphenyl)-lactic acid (Dhpl) and protocatechuic aldehyde (Pal) in rat serum after oral administration of Radix Salviae miltiorrhizae extract. Serum samples are acidified with hydrochloric acid and extracted with ethyl acetate. Analysis of the extract is performed on a reversed-phase column and a mobile phase of 0.02% phosphoric acid-acetonitrile (91:9, v/v) with UV detection at 280 nm. Standard curves are linear in the range of 1.47-456.96 microg/mL for Dhpl and 0.124-7.936 microg/mL for Pal. For both regression coefficients, r(2) is greater than 0.993. Mean recovery is determined to be 75.23% and 84.06%, respectively, by analyzing serum standard containing 7.14, 57.12, and 228.48 microg/mL of Dhpl and 0.124, 0.992, and 3.968 microg/mL of Pal. The intraday precision (relative standard deviation) ranges from 3.91% to 12.03% at concentrations of 1.43, 57.12, and 228.48 microg/mL for Dhpl and 3.79% to 8.12% at concentrations of 0.124, 0.992, and 3.968 microg/mL for Pal. The interday precision (relative standard deviation) ranges from 5.06% to 9.93% for Dhpl and 3.05% to 10.00% for Pal, respectively, at the same three concentrations. This validated assay is applied to the determination of Dhpl and Pal concentrations and used to take a limited view of the pharmacokinetic profile in rat serum after oral administration of Radix Salviae miltiorrhizae extract.     

Precise rate in the law of iterated logarithm for <Emphasis Type="Italic">ρ</Emphasis>-mixing sequence

Let {X, X _n;n≥1} be a strictly stationary sequence of ρ-mixing random variables with mean zero and finite variance. Set . Suppose lim _n→∞ and , where d=2, if −1<b<0 and d>2(b+1), if b≥0. It is proved that, for any b>−1,

QUALITATIVE THEORY OF THE KUKLES SYSTEMS:(Ⅰ) NUMBER OF CRITICAL POINTS

The special cubic system (a natural and simPlest generaIization of thequadratic system of C1ass (l) to cubic system)f.'x = yl y = --x 6y a,x' a2xy a,y' a#x' a,x'y a.xy' a,y' (1)was first studied by the Russian Mathematician I.S.KukIes [ll on the Ilecessaryand sufficient conditions fot O(0,0) to be a ccnter of (1). After [ll, the sameproblem and also the order of O as a fine fOcus were also studied iIl [2--l0] and[13-19], so (l) is now called as a "Kukles system". In l988-…     

Correlation of substituent effects and energy levels of the two lowest excited states of the azulenic chromophore

[structure: see text] Experimental and calculated data show that the relative energy levels of the two lowest excited states of azulene are sensitive to the nature and position of substituents on the nonalternant hydrocarbon. Extending such investigations led to a rational explanation for some of the baffling data on azulenic bacteriorhodopsin analogues in the literature.