scholarly journals Фракто- и фотолюминесценция кварца при разрушении

2021 ◽  
Vol 63 (8) ◽  
pp. 1120
Author(s):  
В.И. Веттегрень ◽  
А.Г. Кадомцев ◽  
И.П. Щербаков ◽  
Р.И. Мамалимов
Keyword(s):  
Rate Constants ◽  
Time Interval ◽  
Quartz Surface ◽  
Micro Cutting ◽  
Pl Spectra ◽  
Order Of Magnitude ◽  
Average Size

The fractoluminescence (FL) spectra at the destruction of the quartz surface by "micro-cutting" of diamond micro crystals and impact on its surface with a steel striker and photoluminescence (PL) spectra after "micro-cutting" are obtained. Band of 2.12 eV in the FL spectra was attributed to excited Si-O● radicals. FL consist from a set of signals whose duration was ≈ 50 ns, and their intensity varies by an order of magnitude. The time interval between the signals varies from ≈ 0.1 to several µs. Signals generated at impact contain five, and at "micro-cutting" contain four superimposed maxima. It is assumed that the FL signals appear when the barriers that prevent the movement of dislocations along the sliding planes breaks, and the smallest "primary" cracks are formatted. The rate constants of growth the cracks and fading of FL after the cracks stops are determined. The average size of the "primary" cracks surfaces after impact is ≈ 5 nm2, and after "micro-cutting" is ≈ 25 nm2. In the PL spectra after the fracture, a band of 2.4 eV was observed, which is attributed to non excited ≡Si-O- radicals on the cracks surface after their stop.

Influence of the Dispersion of the Size of the Si Nanocrystals on their Emission Spectra

1994 ◽  
Vol 358 ◽  
Author(s):  
J. B. Khurgin ◽  
E. W. Forsythe ◽  
S. I. Kim ◽  
B. S. Sywe ◽  
B. A. Khan ◽  
...  
Keyword(s):  
Systematic Study ◽  
Quantum Confinement ◽  
Emission Spectra ◽  
Emission Peak ◽  
Nanocrystal Size ◽  
Pl Spectra ◽  
Si Nanocrystals ◽  
Average Size ◽  
Size Dispersion ◽  
Confinement Model

ABSTRACTA systematic study of the PL spectra of Si quantum nanocrystals in the SiO2 matrix has been performed. The results have been fitted to a quantum-confinement model that includes the nanocrystal size dispersion rather than a specific size of the nanocrystal. This serves as a strong confirmation of the confinement-induced nature of the PL. It has been shown that if the dispersion is taken into account, the position of the emission peak as well as the PL width can always be correlated with the average size of the nanocrystal.

Deacylation of Fluorine-substituted trans-Cinnamoyl-α-chymotrypsins

1975 ◽  
Vol 53 (4) ◽  
pp. 513-518 ◽  
Author(s):  
J. T. Gerig ◽  
R. S. McLeod
Keyword(s):  
Rate Constants ◽  
Rate Effect ◽  
Ionization State ◽  
Hydrolysis Rates ◽  
Order Of Magnitude ◽  
Model Reactions

Deacylation of unsubstituted and of o-F-, m-F, p-F, α-F, pentafluoro-, p-methyl-, and p-trifluoromethyl-substituted trans-cinnamoyl- α-chymotrypsins has been studied from pH 4 to 8. The deacylation rate constants were found to depend upon the ionization state of a group on the enzyme with an apparent pK in the range 6.3–7.3. The hydrolysis rates of the correspondingly substituted p-nitrophenylcinnamate esters were determined at pH 10.6. Correlation of the data for these model reactions with the corresponding rates of enzyme deacylation suggests that the p-methyl-substituted acylenzyme is about an order of magnitude more reactive than expected while p-trifluoromethyl substitution results in deacylation at a rate 10 times slower than expected. The remaining substituents exert about the anticipated rate effect on deacylation.

scholarly journals COMPARISON BETWEEN THE RESULTS OF LITTORAL-DRIFT COMPUTATIONS AND CUBATURE OF DEPOSITS IN A DREDGED CHANNEL

1974 ◽  
Vol 1 (14) ◽  
pp. 42
Author(s):  
V.F. Motta ◽  
J.V. Bandeira
Keyword(s):  
Time Interval ◽  
Littoral Drift ◽  
Monthly Basis ◽  
Wave Characteristics ◽  
Order Of Magnitude ◽  
Annual Volume ◽  
Offshore Oil ◽  
Remarkable Agreement

The total annual volume of littoral drift on either side of the mouth of Sergipe estuary, in the Northeast of Brazil, has been de_ termined by applying Caldwell's, Castanho's and Bijker's methods to the wave characteristics that had been recorded at a twenty-metre depth of water, over a whole year, for the design of an offshore oil terminal. The three computation methods yielded the same order of maj> nitude which was found to amount to about 80000Om^/year. The dominant drift is s outhwes tward, and its predicted amount is 660000m-*/year. It was also found that although the three methods lead to total re suits of the same order of magnitude, they do not agree as to the vari^ ation of littoral drift over the year for the s ame waves. An eight-metre deep shipping channe 1 has been dredgedaccross the bar. The channel was surveyed in December 1971, August and Decem ber 1972, and a cubature of the deposits was made after the littoraldrift computations had been carried out. As the latter had been per formed on a monthly basis, a comparison became possible between pre dieted and actual volumes of deposits for the same lengths of time. The predicted volumes for the whole year were found to be from 34 to 46% greater than the actual results. However, for the time interval August-December 1972 a remarkable agreement was found be^ tween predicted and actual results.

scholarly journals KINETICS OF PALM OIL TRANSESTERIFICATION IN METHANOL WITH POTASSIUM HYDROXIDE AS A CATALYST

2010 ◽  
Vol 8 (2) ◽  
pp. 219-225
Author(s):  
Yoeswono Yoeswono ◽  
Triyono Triyono ◽  
Iqmal Tahir
Keyword(s):  
Activation Energy ◽  
Palm Oil ◽  
Rate Constants ◽  
Potassium Hydroxide ◽  
Catalyst Concentration ◽  
Time Interval ◽  
Pseudo First Order Reaction ◽  
Exponential Factor ◽  
Potassium Methoxide ◽  
First Order

A study on palm oil transesterification to evaluate the effect of some parameters in the reaction on the reaction kinetics has been carried out. Transesterification was started by preparing potassium methoxide from potassium hydroxide and methanol and then mixed it with the palm oil. An aliquot was taken at certain time interval during transesterification and poured into test tube filled with distilled water to stop the reaction immediately. The oil phase that separated from the glycerol phase by centrifugation was analyzed by 1H-NMR spectrometer to determine the percentage of methyl ester conversion. Temperature and catalyst concentration were varied in order to determine the reaction rate constants, activation energies, pre-exponential factors, and effective collisions. The results showed that palm oil transesterification in methanol with 0.5 and 1 % w/w KOH/palm oil catalyst concentration appeared to follow pseudo-first order reaction. The rate constants increase with temperature. After 13 min of reaction, More methyl esters were formed using KOH 1 % than using 0.5 % w/w KOH/palm oil catalyst concentration. The activation energy (Ea) and pre-exponential factor (A) for reaction using 1 % w/w KOH was lower than those using 0.5 % w/w KOH.   Keywords: palm oil, transesterification, catalyst, first order kinetics, activation energy, pre-exponential factor

scholarly journals 100 nm-Gap Fingers Dielectrophoresis Functionalized MOX Gas Sensor Array for Low Temperature VOCs Detection

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 1027
Author(s):  
Luca Francioso ◽  
Pasquale Creti ◽  
Maria Concetta Martucci ◽  
Simonetta Capone ◽  
Antonietta Taurino ◽  
...  
Keyword(s):  
Low Temperature ◽  
Gas Sensor ◽  
Sensor Array ◽  
Gas Sensing ◽  
Enhanced Sensitivity ◽  
Sno2 Nanocrystals ◽  
Gas Sensor Array ◽  
Order Of Magnitude ◽  
Nanogap Electrodes ◽  
Average Size

Present work reports the fabrication process and functional gas sensing tests of a 100 nm-gap fingers DiElectroPhoresis (DEP) functionalized MOX (Metal OXide) gas sensor array for VOCs detection at low temperature. The Internet of Things (IoT) scenario applications of the chemical sensing-enabled mobiles or connected devices are many ranging from indoor air quality to novel breath analyser for personal healthcare monitoring. However, the commercial MOX gas sensors operate at moderate temperatures (200–400 °C) [1], and this limits the mobile and wearable gadgets market penetration. Nanogap devices may represent the alternative devices with enhanced sensitivity even at low or room temperature. A nanogap electrodes MOX gas sensor array functionalized with 5 nm average size SnO2 nanocrystals with positive dielectrophoresis technique is presented. The single sensor active area is 4 × 4 µm2. The devices exhibited about 1 order of magnitude response at 100 °C to 150 ppm of acetone.

Comparison of Novel Conductive Open- and Closed-Porous PPy-PLA Composites

2009 ◽  
Author(s):  
Christine Chan ◽  
Ellen Chan ◽  
Weijia Zhang ◽  
Hani E. Naguib
Keyword(s):  
Relative Density ◽  
In Situ Polymerization ◽  
Compression Molding ◽  
Salt Leaching ◽  
Conductive Composites ◽  
Order Of Magnitude ◽  
Density Values ◽  
Average Size ◽  
Porous Composites

This study compared the fabrication techniques and characterization of novel open- and closed-porous structures in PPy-PLA conductive composites. For the open-porous composites, PLA samples were fabricated using compression molding and salt leaching with varying salt-to-polymer mass ratios, which were subsequently coated with PPy by in situ polymerization of pyrrole and iron (III) chloride. For the closed-porous composites, a patterned structure of PPy within PLA was created using compression molding of PPy-coated PLA pellets, followed by gas saturation and foaming techniques in order to create the closed pores. Characterization of both porous composites included their physical, mechanical, and electrical properties. Results showed that the modulus increased with increasing relative density and decreasing open porosity. The open-porous composites had lower relative density values but higher open porosities compared to the closed-porous composites. The average size of the closed pores was approximately an order of magnitude larger than the open pores. Lastly, the open-porous composites had higher conductivity values than the closed-porous composites due to the greater surface area of the continuous conductive pathway. The comparisons between open- and closed-porous composites established their characteristic properties for their future development in applications.

Arrhenius Parameters for Reaction of tert-Butylperoxy Radicals with some Hindered Phenols and Aromatic Amines

1973 ◽  
Vol 51 (22) ◽  
pp. 3738-3745 ◽  
Author(s):  
James Anthony Howard ◽  
Edward Furimsky
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Aromatic Amines ◽  
Activation Parameters ◽  
Peroxy Radical ◽  
Hydrogen Atom Transfer ◽  
Tert Butyl ◽  
Radical Decay ◽  
Order Of Magnitude ◽  
Hindered Phenols

The reaction of tert-butylperoxy radicals with some 2,6-di-tert-butyl-4-substituted phenols, α-naphthol, α-naphthylamine, and N-phenyl-α-naphthylamine has been studied by following the change in radical concentration with time using an e.p.r. spectrometer. Rates of radical decay were first-order in both reactants and were not influenced by the presence of tert-butyl hydroperoxideAbsolute values of the second-order rate constants were measured from −35 to −100° and the preexponential factors and activation energies fell in the range 104–105 M−1 s−1 and 0.5–1.0 kcal mol−1. Rate constants for deuterated phenols (OD) and aromatic amines (ND) were an order of magnitude lower than for the corresponding light compoundsThere was no evidence for quantum mechanical tunneling in these hydrogen atom transfer reactions and it would appear that the activation parameters are low because reaction initially involves the formation of a hydrogen bonded peroxy radical – phenol (or aromatic amine) complex, followed by the transfer of a hydrogen atom within the complex

The Monte Carlo Independent Column Approximation’s Conditional Random Noise: Impact on Simulated Climate

2005 ◽  
Vol 18 (22) ◽  
pp. 4715-4730 ◽  
Author(s):  
P. Räisänen ◽  
H. W. Barker ◽  
J. N. S. Cole
Keyword(s):  
Monte Carlo ◽  
Global Climate ◽  
Random Noise ◽  
Radiative Heating ◽  
Time Interval ◽  
Additional Time ◽  
Time Step ◽  
Order Of Magnitude ◽  
Independent Column ◽  
The Impact

Abstract The Monte Carlo Independent Column Approximation (McICA) method for computing domain-average radiative fluxes is unbiased with respect to the full ICA, but its flux estimates contain conditional random noise. Results for five experiments are used to assess the impact of McICA-related noise on simulations of global climate made by the NCAR Community Atmosphere Model (CAM). The experiment with the least noise (an order of magnitude below that of basic McICA) is taken as the reference. Two additional experiments help demonstrate how the impact of noise depends on the time interval between calls to the radiation code. Each experiment is an ensemble of seven 15-month simulations. Experiments with very high noise levels feature significant reductions to cloudiness in the lowermost model layer over tropical oceans as well as changes in highly related quantities. This bias appears immediately, stabilizes after a couple of model days, and appears to stem from nonlinear interactions between clouds and radiative heating. Outside the Tropics, insignificant differences prevail. When McICA sampling is confined to cloudy subcolumns and when, on average, 50% more samples, relative to basic McICA, are drawn for selected spectral intervals, McICA noise is much reduced and the results of the simulation are almost statistically indistinguishable from the reference. This is true both for mean fields and for the nature of fluctuations on scales ranging from 1 day to at least 30 days. While calling the radiation code once every 3 h instead of every hour allows the CAM additional time to incorporate McICA-related noise, the impact of noise is enhanced only slightly. In contrast, changing the radiative time step by itself produces effects that generally exceed the impact of McICA’s noise.

scholarly journals Образование нанокристаллов кремния при трении

2020 ◽  
Vol 62 (7) ◽  
pp. 1070
Author(s):  
В.И. Веттегрень ◽  
Р.И. Мамалимов ◽  
И.П. Щербаков ◽  
В.Б. Кулик
Keyword(s):  
Raman Spectroscopy ◽  
Single Crystal ◽  
Time Dependence ◽  
Silicon Nanocrystals ◽  
Time Interval ◽  
Pl Spectra ◽  
Linear Dimensions ◽  
Superimposed Signals ◽  
Twofold Decrease

Abstract It is found using triboluminescence (TL) that nanocrystals of silicon (ncSi) with linear dimensions of about 4 nm are formed from a single crystal of silicon (Si) under friction. The time dependence of the intensity of TL signals is investigated. It consists of many superimposed signals. An analysis of their dynamics shows that nanocrystals are located on the microcrack faces formed during fracture. At the same time, a powder flies out of the friction region. Using the photoluminescence (PL) and Raman spectroscopy methods, the size of silicon nanocrystals in the powder was determined. It is about 2.2 nm. Probably, microcracks grow further in the time interval between friction and recording the Raman and PL spectra (several hours), which leads to an approximately twofold decrease in the size of nanocrystals.

scholarly journals Nanocracks upon Fracture of Oligoclase

2021 ◽  
Vol 57 (6) ◽  
pp. 894-899
Author(s):  
V. I. Vettegren ◽  
A. V. Ponomarev ◽  
R. I. Mamalimov ◽  
I. P. Shcherbakov
Keyword(s):  
Free Radicals ◽  
Power Law ◽  
Time Interval ◽  
Electron Traps ◽  
Surface Areas ◽  
Electronically Excited ◽  
Order Of Magnitude ◽  
20 Nm

Abstract—The spectrum of fractoluminescence (FL) upon fracture of the surface of oligoclase is obtained. The analysis of the spectrum has shown that fracture of crystals leads to the formation of electronically excited free radicals ≡Si−O• and Fe3• ions as well as electron traps. FL consisted of a set of the signals with the intensities varying by an order of magnitude. The duration of the signals was ~50 ns and the time interval between them varied from ~0.1 to 1 μs. Each signal contained four maxima associated with the destruction of barriers preventing the motion of dislocations along the sliding planes. These breakthroughs cause the formation of the smallest (“primary”) cracks. All other, larger cracks are formed by the coalescence of the “primary” cracks. The sizes of “primary” cracks range from ~10 to 20 nm and the time of their formation is 16 ns. The distribution of cracks by size (surface areas of crack walls) is power law with the exponent –1.9.

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