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11.
Isothermal adsorption of Ar on single walled carbon nanotubes (SWNTs) has been studied at 77 and 87 K. The SWNTs have been grown by laser vaporization of a graphite pellet containing 0.6% (atomic) Ni/Co catalyst. The nanotubes have been prepared for argon adsorption measurements by prolonged outgassing of as-grown material in a vacuum at room temperature (295 K), at elevated temperatures of up to 475 K, and by oxidization for 2 h in dry air at 470 K. Formation of two condensed phases of Ar in the interior of SWNTs has been observed at 77 K. The low-density phase is formed at 155(5) microTorr, while the high-density phase, at 120(5) microTorr. At 87 K, only a single phase has been observed at 185(5) microTorr. Condensation at both 77 and 87 K appears to be the first-order phase transition. Onset of the quasi-one-dimensional linear (one-channel) phase and the quasi-two-dimensional monolayer (six-channel) phase formation on the external surface of bundles has been observed at 77 K near 0.0017 and 0.8 Torr, respectively, and at 87 K near 0.018 and 5 Torr, respectively. Isosteric heats of adsorption for the one-channel phase, the first external layer, and the second external layer have been determined to be equal to 137, 107, and 70 meV, respectively. 相似文献
12.
Summary A new sensitive, spectrophotometric determination of gallium, based on the ternary gallium-Eriochrome Cyanine R-cetyltrimethylammonium system has been developed. At
max=588 nm the molar absorptivity is 1.20×105l·mole–1·cm–1. The maximum absorbance is attained in 5 min in the presence of a 10-fold molar ratio of Eriochrome Cyanine R and an approx. 50-fold ratio of cetyltrimethylammonium bromide (to Ga). Citrate, EDTA and to a lesser extent tartrate, interfere. Interference by metals can be eliminated by a preliminary extraction of gallium with di-isopropyl ether from 7 M hydrochloric acid in the presence of ascorbic acid as reductant. The results for gallium (at a concentration level of 1×10–4%) in aluminium metal and chloride indicate good precision and accuracy.
Empfindliche spektrophotometrische Bestimmung von Gallium mit Eriochromcyanin-R- und Cetyltrimethylammonium-Ionen
Zusammenfassung Ein neues, empfindliches spektrophotometrisches Verfahren zur Galliumbestimmung wurde ausgearbeitet. Es beruht auf der Verwendung des ternären Systems Gallium — EriochromcyaninR — Cetyltrimethylammonium. Bei max=588 nm beträgt die molare Extinktion 1,20·105 1·Mol–1·cm–1. Die maximale Absorption wird innerhalb von 5 min bei Gegenwart der 10fachen molaren Menge EriochromcyaninR und der etwa 50fachen Menge Cetyltrimethylammoniumbromid erreicht. Citrat, ÄDTA und in geringerem Maß Tartrat stören. Störende Wirkung durch Metalle kann durch vorhergehende Extraktion des Galliums mit Diisopropyläther aus 7 M Salzsäure in Gegenwart von Askorbinsäure als Reduktionsmittel vermieden werden. Die Ergebnisse (im Konzentrationsbereich von 10–4% Ga) in metallischem Aluminium und AICI3 sind genau.相似文献
13.
The synthesis of 8-aza-2′-deoxyadenosine ( = 7-amino-3H-1,2,3 triazolo[4,5-d]pyrimidine N3-(2′-deoxy-β-D-ribofuranoside); 1 ) as well as the N2- and N1-(2′-deoxy-β-D-ribofuranosides) 2 and 3 is described. Glycosylation of the anion of 7-amino-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 6 ) in DMF yielded three regioisomeric protected 2′-deoxy-β-D-ribofuranosides, i.e. the N3-, N2-, and N4-glycosylated isomers 7 (14%), 9 (11%), and 11 (3%), respectively, together with nearly equal amounts of their α-D-anomers 8 (13%), 10 (12%), and 12 (4%; Scheme 1). The reaction became Stereoselective for the β-D-nucleosides if the anion of 7-methoxy-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 13 ) was glycosylated in MeCN: only the N3-, N2, and N1-(2′-deoxy-β-D-nucleosides) 14 (29%), 15 (32%), and 16 (23%), respectively, were formed (Scheme 2). NH3 Treatment of the methoxynucleosides 14–16 afforded the aminonucleosides 1–3 . The anomeric configuration as well as the position of glycosylation were determined by combination of 13 C-NMR , 1 H-NMR , and 1D-NOE difference spectroscopy. Compound 1 proved to be a substrate for adenosine deaminase, whereas the regioisomers 2 and 3 were not deaminated. 相似文献
14.
Joseph R. Lakowicz Ignacy Gryczynski Henryk Cherek Gabor Laczko Nanda Joshi 《Trends in analytical chemistry : TRAC》1986,5(10):257-263
The fluorescence emission from complex chemical and biological samples can be resolved by measuring the frequency-response of the emission, which is now possible from 1 to 2000 MHz. The frequency-response allows determination of the components in a mixture, construction of time-resolved emission spectra, and measurement of the dynamic and hydrodynamic properties of biological macromolecules. The instrumentation is relatively simple, and data acquisition times can be short. At present, this method may be superior to direct measurements of time-resolved fluorescence emission. 相似文献
15.
16.
Pulsed lasers are used mainly in lidar systems as sources of short and highly energetic light pulses. In data transmission
systems continuous wave lasers are typically applied, however it is also possible to use pulsed lasers in such systems. Such
approach seems to be especially reasonable for devices where a pulsed laser is applied anyway and executes another function
(rangefinding). The article discusses a data transmission concept based on a pulsed laser technology. Advantages and limits
of such a transmission method are described. Influence of individual transmission elements on the effective data transmission
speed is analysed. 相似文献
17.
Edward Gleich Zygmunt Warnke 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):211-222
Abstract A study of the reaction of the elemental sulfur with 2-picoline is reported. The process was carried out at the boiling point of the 2-picoline under argon. After removing unreacted solids, the reaction products were identified by means of LC. GC and GC-MS. The following products have been identified by mass spectrometry: 1,2-di/2-pyridyl/-ethane. 1,2-di/2-pyridyl/-ethene. 2-methyl-x-[/2-pyridyl/methyl]pyridines, 2-mercapto-methyl-[x/2-pyridyl/methyl]-pyridines, l-mercapto-1,2-di/2-pyridyl/-ethane, 5,6-di/2-pyridyl/-5H-cyclopenta-[b]pyridine, 5,6-di/2-pyridyl/-7H-cyclopenta[b]pyridine, 1,2,3-tri/2-pyridyl/-propane. 1,2-di/2-pyridyl/-1-[x-/2-methyl/-pyridyl]-ethane, 5,6-di/2-pyridyl/-7-[/2-pyridyl/methyl]-7H-cyclopenta[b]pyridine, 5,6-di/2-pyridyl/-5-[/2-pyridyl/-methyl]-5H-cyclopenta-[b]pyridine. Di{7-[5,6-di/2-pyridyl/-7H-cyclopenta[b]pyridyl]} sulfide and di(7-[5,6-di/2-pyridyl/-7H-cyclopentalblpyridyl]} disulfide. 相似文献
18.
Ryan M. Rich Dorota L. Stankowska Badri P. Maliwal Thomas Just Sørensen Bo W. Laursen Raghu R. Krishnamoorthy Zygmunt Gryczynski Julian Borejdo Ignacy Gryczynski Rafal Fudala 《Analytical and bioanalytical chemistry》2013,405(6):2065-2075
Sample autofluorescence (fluorescence of inherent components of tissue and fixative-induced fluorescence) is a significant problem in direct imaging of molecular processes in biological samples. A large variety of naturally occurring fluorescent components in tissue results in broad emission that overlaps the emission of typical fluorescent dyes used for tissue labeling. In addition, autofluorescence is characterized by complex fluorescence intensity decay composed of multiple components whose lifetimes range from sub-nanoseconds to a few nanoseconds. For these reasons, the real fluorescence signal of the probe is difficult to separate from the unwanted autofluorescence. Here we present a method for reducing the autofluorescence problem by utilizing an azadioxatriangulenium (ADOTA) dye with a fluorescence lifetime of approximately 15 ns, much longer than those of most of the components of autofluorescence. A probe with such a long lifetime enables us to use time-gated intensity imaging to separate the signal of the targeting dye from the autofluorescence. We have shown experimentally that by discarding photons detected within the first 20 ns of the excitation pulse, the signal-to-background ratio is improved fivefold. This time-gating eliminates over 96 % of autofluorescence. Analysis using a variable time-gate may enable quantitative determination of the bound probe without the contributions from the background. 相似文献
19.
The resistivity, thermoelectric power and Hall constant in the temperature range of 78–830 K were determined for polycrystalline Th3As4 samples obtained by annealing thin thorium slabs in arsenic vapour. The samples examined were n-type semiconductors with a carrier concentration ranging from 1.0 × 1018cm?3 to 2.8 × 1018 cm?3 for which the effective mass was found to be equal to 0.55–0.76m0. The Hall mobility, about 450cm2V?1s?1 at room temperature, obeys a law at high temperatures. On the basis of the electrical measurements the forbidden gap of Th3As4 was found to be equal to 0.43 eV. 相似文献
20.
Zygmunt Szymański 《Journal of Quantitative Spectroscopy & Radiative Transfer》1979,22(6):577-583
Population densities of excited levels of mercury atoms were measured in a supersonic plasma flow. Existence of partial LTE permitted determination of the electron temperature from the slope of the Boltzmann plot. 相似文献