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91.
We demonstrate experimentally and numerically that, by spectrally filtering the delayed optical feedback into a semiconductor laser, one can elicit novel dynamics in the frequency of the laser output light on a time scale that is set by the delay time of the feedback. In particular, we show that through a judicious choice of the filter bandwidth, and its frequency relative to that of the laser, one can produce controlled oscillations in the frequency of light from the laser. 相似文献
92.
Carter EB Culver SL Fox PA Goode RD Ntai I Tickell MD Traylor RK Hoffman NW Davis JH 《Chemical communications (Cambridge, England)》2004,(6):630-631
The anions of the sweeteners saccharin and acesulfame form ionic liquids when paired with a variety of organic cations. 相似文献
93.
The efficient syntheses of the ABCD ring system of the originally proposed structure of azaspiracid-1 and the ABCDE ring system of the revised structure of azaspiracid-1 containing the correct stereochemistry at C(6), C(10), C(13), C(14), C(16), C(17), C(19), C(21), C(22), C(24) and C(25) have been achieved. 相似文献
94.
Novel chemical methods have been developed to allow for the determination of the components of silica fume produced by zircon desilication. Hitherto, no methods have been described for the analysis of this material. The amorphous silica is first removed by treatment with sodium hydroxide. The residue from the hydroxide treatment may then be subjected to a suite of reagents to determine the zircon, the total zirconia, the monoclinic zirconia and the tetragonal zirconia content of the fume. The zircon content of the fume is determined by treatment of the hydroxide residue with concentrated hydrofluoric acid (HF). The total zirconia content of the fume is determined by digestion of the hydroxide residue with fuming sulphuric acid (oleum), while the relative amounts of monoclinic and tetragonal zirconia may be found by treatment of the hydroxide residue with 10%w/v HF, which attacks the less stable tetragonal phase. Both X-ray diffraction and particle size analysis were used to validate the steps in the analytical procedure. An explanation of the presence of tetragonal zirconia in the fume is proposed. A greater understanding of the composition of the fume led to the installation of a separator in the company's production line to remove the zircon. Australian Fused Materials (AFM) now produces a vastly superior grade of fume marketed under the code SF-98. 相似文献
95.
Stereoselectivity of nitrile oxide cycloadditions to chiral allylic fluorides: experiment and theory
Prakesch M Grée D Grée R Carter J Washington I Houk KN 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(22):5664-5672
The cycloadditions of nitrile oxides with new and previously studied allylic fluorides were examined. The 1,3-dipolar cycloaddition reactions were also investigated theoretically with density functional theory (B3LYP) based transition-state modelling. The predictions provided reasonable agreement with experiment, indicating that both steric and electronic effects have important influences on the stereoselectivities of these reactions. 相似文献
96.
Nucleobase radicals (e.g., 1) are the major family of reactive intermediates formed when DNA is exposed to gamma-radiolysis. Independent generation of 1 in chemically synthesized oligonucleotides reveals that formation of this nucleobase radical under aerobic conditions results in the formation of tandem lesions approximately 65% of the time. The distribution of lesions formed with the 5'- and 3'-adjacent nucleotides is dependent upon the secondary structure of duplex DNA. Tandem lesions, which are defined as two contiguously, damaged nucleotides in a single DNA strand, are of significant biological interest. The yield of tandem lesions from 1 is much greater than was previously believed. The observations presented could have significant ramifications on how scientists interpret the effects of gamma-radiolysis on DNA. 相似文献
97.
White JD Carter RG Sundermann KF Wartmann M 《Journal of the American Chemical Society》2001,123(23):5407-5413
The phosphonium salt 35, representing one of the two principal subunits of the epothilones, was prepared from propargyl alcohol via heptenone 22. A Wittig reaction of the phosphorane from 35 with aldehyde 33, obtained from aldol condensation of ketone 27 with aldehyde 28, afforded 37. Seco acid 42 derived from 37 underwent lactonization to give cis-9,10-dehydroepothilone D (43) which was selectively reduced with diimide to yield epothilone D (4) and, after epoxidation, epothilone B (2). An alternative route to epothilone D employed alkyne 39, obtained from 33, in a Castro-Stephens reaction with allylic bromide 34 to furnish enyne 40. The latter was semi-hydrogenated to provide 37. Alkyne 46, prepared from alcohol 45, was converted to trans-vinylstannane 47 which, in a Stille coupling with allylic chloride 50, gave 51. Seco acid 52 derived from 51 underwent lactonization to give trans-9,10-dehydroepothilone D (54). Bioassay data comparing the antiproliferative activity and tubulin polymerization of 43 and 54 with epothilone B (2), epothilone D (4), and paclitaxel (7) showed that the synthetic analogues were less potent than their natural counterparts, although both retain full antiproliferative activity against a paclitaxel-resistant cell line. No significant difference in potency was noted between cis analogue 43 and its trans isomer 54. 相似文献
98.
99.
de La Figuera J Pohl K de La Fuente OR Schmid AK Bartelt NC Carter CB Hwang RQ 《Physical review letters》2001,86(17):3819-3822
Using scanning tunneling microscopy we have observed thermally induced dislocation glide in monolayer Cu films on Ru(0001) at room temperature. The motion is governed by a Peierls barrier that depends on the detailed structure of the dislocations, in particular upon whether the threading dislocations that terminate them are dissociated or not. Calculations based on the Frenkel-Kontorova model reproduce the threading dislocation structure and provide estimates of the Peierls barrier and dislocation stiffness which are consistent with experiment. 相似文献
100.
Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Copty NK Cremaldi LM Darling C Denisenko K Devmal S Fernandez A Fox GF Gagnon P Gobel C Gounder K Halling AM Herrera G Hurvits G James C Kasper PA Kwan S Langs DC Leslie J Lundberg B Magnin J Massafferri A MayTal-Beck S Meadows B de Mello Neto JR Mihalcea D Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV 《Physical review letters》2001,86(5):770-774
From a sample of 1172 +/- 61 D(+)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)-->pi(-)pi(+)pi(+))/gamma(D(+)-->K-pi(+)pi(+)) = 0.0311 +/- 0.0018(+0.0016)(-0.0026). Using a coherent amplitude analysis to fit the Dalitz plot of these decays, we find strong evidence that a scalar resonance of mass 478(+24)(-23) +/- 17 MeV/c(2) and width 324(+42)(-40) +/- 21 MeV/c(2) accounts for approximately half of all decays. 相似文献