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1.
Jinxiu Cao Sui Boon Liaw Yu Long Yun Yu Hongwei Wu 《Proceedings of the Combustion Institute》2021,38(3):4301-4308
This study aims to understand the fundamental reaction mechanisms during fast pyrolysis of the acid-impregnated cellulose in a wire-mesh reactor at 40–450 °C and 20 °C/s, via quantifying key compounds in the reaction intermediates and primary volatiles. Acid impregnation reduces the onset reaction temperature of cellulose pyrolysis. During acid-catalysed cellulose pyrolysis, 1,6-anhydro-β-d-glucofuranose (AGF), levoglucosenone (LGO) and 5-hydroxymethylfurfural (5-HMF) are identified as major products in the primary volatiles, and the formation of levoglucosan is greatly suppressed. At temperatures < 100 °C, acid catalyses hydrolysis reactions to produce glucose, which is further dehydrated to AGF at 120 °C. At temperatures > 160 °C, acid enhances the dehydration of glucose, levoglucosan and AGF to produce 5-HMF and LGO as major primary products. Once produced, those products can be easily released into the vapour phase, as either aerosols via thermal ejection or vapours via evaporation. As the pyrolysis temperature increases to 240 °C, aromatic compounds can be identified in the primary volatiles, indicating condensation reactions also play important roles during acid-catalysed cellulose pyrolysis under the conditions. As a result, char formation becomes the favoured pathway during acid-catalysed cellulose pyrolysis at temperatures > 300 °C. 相似文献
2.
650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD)
have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes
can be as low as 350 A/cm2. Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are
(22–40) mA and (0.2–0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15
mW has been obtained. Their operation temperature can be up to 90°C under power of 5 mW. After operating under 90°C and 5
mW for 72 hrs, the average increments for the threshold currents of the lasers at 25°C and the operation currents at 5 mW
(at 25°C) are (2–3) mA and (3–5) mA, respectively. Reliability tests showed that no obvious degradation was observed after
1400 hours of CW operation under 50°C and 2.5 mW.
Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17,
1998. 相似文献
3.
We optimize the preparation of BZY20 and BCY10 by a wet chemistry route (the polyacrylamide gel process) and mixed oxide route,
respectively. For both materials, the purity of powders drastically depends on the annealing conditions of the raw materials.
Pure BZY20 powder can be prepared at 1250 °C while, for pure BCY10, completion of the reaction is achieved if the raw powder
is pressed. After polishing the surface and crushing the bulk of the pellet annealed at 1425 °C, pure powder of BCY10 is obtained.
Water uptake measurement is leading to values corresponding to an almost complete filling of the oxygen vacancies. Furthermore,
we check the sample degradation during sintering of pellets from pure BCY10 and BZY20 powder. Dense ceramic of pure material
can be prepared after sintering at 1500 °C for 10 h. Above this temperature, a degradation of the pellets both in the surface
and the bulk occurs.
This paper points out the difficulties in preparing pure BayM1−xYx O3–δ (M=Zr, Ce) for use in electrical characterization or functional for fuel cell technology studies. 相似文献
4.
In this paper, we report a new method to determine the effective atomic number, Z
eff, of composite materials for Compton effect in the γ-ray region 280–1115 keV based on the theoretically obtained Klein–Nishina scattering cross-sections in the angular range
50°–100° as well as a method to experimentally measure differential incoherent (Compton) scattering cross-sections in this
angular range. The method was employed to evaluate Z
eff for different inorganic compounds containing elements in the range Z = 1–56, at three scattering angles 60°, 80° and 100° at three incident gamma energies 279.1 keV, 661.6 keV and 1115.5 keV
and we have verified this method to be an appropriate method. Interestingly, the Z
eff values so obtained for the inorganic compounds were found to be equal to the total number of electrons present in the sample
as given by the atomic number of the elements constituting the sample in accordance with the chemical formula of the sample.
This was the case at all the three energies. 相似文献
5.
Anomalous behavior of the interlayer resistance of a BSCCO-2212 crystal in a parallel magnetic field
V. N. Zavaritskii 《JETP Letters》1996,63(2):139-145
The electrical resistance across the Cu-O layers of a BSCCO-2212 single crystal is investigated in the range of angles 0°⩽φ⩽90°
between the magnetic field H⩽15 T and the ab plane. It is found that the temperature dependence R(T) at the transition into the mixed state is much sharper for φ≃0° than for 1°≲φ≲90°, where R is determined by the perpendicular component of the magnetic field and is described by the Arrhenius law R∼exp(−U/T). For H∥ ab hysteretic jumps in R(T, H), which vanish as the current increases, are observed at fields in the range 5.5⩽H⩽11 T. This effect can be attributed to
a commensurate phase transition in a lattice of Josephson vortices.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 123–128 (25 January 1996) 相似文献
6.
Acoustic emission during thermoelastic martensitic transformations in titanium nickelide is investigated. Phase transitions
are initiated by loading the specimen to 200 MPa under isothermal conditions. It is found out that deformation buildup and
acoustic emission in the loading-unloading cycles are observed in the first cycle only, during further cycles the acoustic
emission is comparable to the background, while the deformation buildup and recovery are not associated with martensitic transformations.
It is shown that recovery of the deformation built up during loading occurs due to heating to 600 °C, with the major part
of accumulated deformation undergoing recovery already at 250 °C and recovery of its minor part observed at 400 °C. This behavior
of acoustic emission and accumulation and recovery of deformation provide evidence of martensitic phase stabilization during
cycling of martensitic transformations under conditions of thermo-mechanical cycling.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 89–94, February, 2008. 相似文献
7.
In this work, the use of ultrasound energy for the production of furanic platforms from cellulose was investigated and the synthesis of furfural was demonstrated. Several systems were evaluated, as ultrasound bath, cup horn and probe, in order to investigate microcrystalline cellulose conversion using simply a diluted acid solution and ultrasound. Several acid mixtures were evaluated for hydrolysis, as diluted solutions of HNO3, H2SO4, HCl and H2C2O4. The influence of the following parameters in the ultrasound-assisted acid hydrolysis (UAAH) were studied: sonication temperature (30 to 70 °C) and ultrasound amplitude (30 to 70% for a cup horn system) for 4 to 8 mol L−1 HNO3 solutions. For each evaluated condition, the products were identified by ultra-performance liquid chromatography with high-resolution time-of-flight mass spectrometry (UPLC-ToF-MS), which provide accurate information regarding the products obtained from biomass conversion. The furfural structure was confirmed by nuclear magnetic resonance (1H and 13C NMR) spectroscopy. In addition, cellulosic residues from hydrolysis reaction were characterized using scanning electron microscopy (SEM), which contributed for a better understanding of physical-chemical effects caused by ultrasound. After process optimization, a 4 mol L−1 HNO3 solution, sonicated for 60 min at 30 °C in a cup horn system at 50% of amplitude, lead to 78% of conversion to furfural. This mild temperature condition combined to the use of a diluted acid solution represents an important contribution for the selective production of chemical building blocks using ultrasound energy. 相似文献
8.
Seung Kwon Hong Hye Young Koo You Na Ko Jung Hyun Kim Jang Heui Yi Yun Chan Kang 《Applied Physics A: Materials Science & Processing》2010,98(3):671-677
Eu-doped B2O3–ZnO–PbO glass phosphor powders with spherical shape and fine size were directly prepared by spray pyrolysis. The glass phosphor
powders prepared at a temperature of 1100°C had broad XRD peak at around 28°. One glass phosphor powder was formed from one
droplet at the preparation temperature range from 900 to 1100°C. The mean size of the glass phosphor powders was 0.75 μm.
The glass transition temperature (T
g
) of the glass phosphor powders prepared by spray pyrolysis was 378.5°C. The excitation spectrum of the glass phosphor powders
prepared at the optimum preparation temperature of 1100°C had bands at 362, 381, 392, 463, 525, and 532 nm. The glass phosphor
powders had emission spectra with bands at 579, 614, and 653 nm. The glass phosphor powders with doping concentration of Eu
of 7 wt% had the maximum photoluminescence intensity. The glass phosphor layer formed from the glass phosphor powders had
high transparencies above 90%. 相似文献
9.
Silver-doped calcium phosphate nanopowders were successfully prepared by the cost-effective electrostatic spray-pyrolysis
process. The properties of the silver-doped nanopowder annealed at 500°C for 30 min were investigated through X-ray diffraction
analysis, field emission scanning electron microscope, and Fourier transform infrared spectroscopy. The silver-doped nanopowders
with 70–90 nm particle size showed an antibacterial performance against Escherichia coli. 相似文献
10.
G. V. Danilyan J. Klenke V. A. Krakhotin Yu. N. Kopach V. V. Novitsky V. S. Pavlov P. B. Shatalov 《Physics of Atomic Nuclei》2011,74(5):671-674
Study of the T-odd three-vector correlation in the emission of prompt neutrons from 235U fission by polarized cold neutrons has been continued at the facility MEPHISTO of the FRM II reactor (Technical University
of Munich). The sought correlation was not found within experimental error of 2.3 × 10−5. The upper limit for the asymmetry coefficient has been set to |D
n
| < 6 × 10−5 at 99% confidence level, whereas for ternary fission correlation coefficient D
α
= (170±20) × 10−5. This limit casts doubt on a model that explains the three-vector correlation in ternary fission by the Coriolis mechanism.
At the same time, five-vector correlation in the emission of prompt fission neutrons has been measured, which describes the
rotation of the fissioning nucleus at the moment it breaks (ROT effect). At the angle 22.5° to the fission axis, the correlation
coefficient was found to be (1.57 ± 0.20) × 10−4, while at the angle of 67.5° it is zero within the experimental uncertainty. The existence of ROT effect in the emission
of prompt fission neutrons can be explained by the anisotropy of neutron emission in the rest frame of the fragment (fission
fragments are aligned with respect to the axis of deformation of the fissioning nucleus), similar to the mechanism of ROT
effect in the emission of prompt γ-rays. 相似文献
11.
The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A
P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data
(SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum
solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot
numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of
disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing
a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH
α
, X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e.,
SF during the period 1978-93.H
α
, X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH
α
, X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S,
the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number
of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares,
type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated
with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and
maximum activity lies between 58 and 118 h causing GMSs at the Earth. 相似文献
12.
The electrophysical properties and structure of the nonstoichiometric high-temperature superconductor YBa2Cu3O
y
restored at T = 930–950°C after low-temperature decomposition (T = 200°C) into phases different in the oxygen content have been studied. It has been shown that, unlike heat treatments at
T ≤ 900°C, the superconducting properties are almost completely restored for 3–5 h during grain recrystallization, which is
impossible at lower temperatures. After short-term annealing at T = 930–950°C (for 1–2 h), the ceramic material still contains a significant number of structural defects, most likely, in
cation sublattices. These defects can contribute to the pinning of magnetic vortices, which substantially increases the critical
current density in magnetic fields up to 2 T as compared to ceramic materials produced by the conventional technology. 相似文献
13.
We present the results of experimental studies of the spectra of the stimulated electromagnetic emission excited in the ionosphere
by powerful radio waves during the pump wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron cyclotron frequency nf
ce. The frequency sweep was carried out for long (continuous) pumping in vertical and inclined directions (at 14° and 18° south
of the zenith), as well as for the pulse diagnostic wave both with and without additional pumping far from the gyroharmonics.
The dependences of the spectral features of the stimulated electromagnetic emission on the ratio between the pump-wave frequency
f
0 (or on the diagnostic-wave frequency fDW) and nf
ce were analyzed. It is found that near the multiple gyroresonance, different spectral features of the stimulated emission are
quenched at the same frequency for different pump-wave frequencies. For a sufficiently large inclination of the pump wave
beam from the vertical direction, the intensity of the stimulated electromagnetic emission is notably decreased for f
0 ≲ nf
ce as compared with f
0 > nf
ce.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 461–476, June 2008. 相似文献
14.
The study reported in this paper contributes to better understanding the thermal oxidation effect on structural and optical
properties of polycrystalline silicon heavily in situ P-LPCVD films. The deposits, doped at levels 3×1019 and 1.6×1020 cm−3, have been elaborated from silane decomposition (400 mTorrs, 605°C) on monosilicon substrate oriented 〈111〉. The thermal
oxidation was performed at temperatures: 850°C during 1 hour, 1000, 1050, and 1100°C during 15 minutes. The XRD spectra analysis
pointed out significant 〈111〉 texture evolution, while in the case of 〈220〉 and 〈311〉 textures, the intensities are practically
invariant (variations fall in the uncertainty intervals). The optical characterizations showed that refractive index and absorption
coefficient are very sensitive to the oxidation treatment, mainly when the doping level is not very high. We think that atomic
oxygen acts as defects passivating agent leading to carriers’ concentration increasing. Besides, the optical behavior is modeled
in visible and near infrared, by a seven-term polynomial function n
2=f(λ
2), with alternate signs, instead of theoretically unlimited terms number from Drude’s model. It has been shown that fitting
parameters fall on Gaussian curves like they do in the theoretical model. 相似文献
15.
dos Santos AM 《Journal of fluorescence》2012,22(1):151-154
The emission behaviour of Aequorea green fluorescent protein (A-GFP) chromophore, in both neutral (N) and anionic (A) form, was studied in the temperature range
from 20 °C to 75 °C and at pH = 7. Excitation wavelengths of 399 nm and 476 nm were applied to probe the N and A forms environment,
respectively. Both forms exhibit distinct fluorescence patterns at high temperature values. The emission quenching rate, following
a temperature increase, is higher for the chromophore N form as a result of the hydrogen bond network weakening. The chromophore
anionic form emission maximum is red shifted, upon temperature increase, due to a charge transfer process occurring after
A form excitation. 相似文献
16.
The recently discovered compound LiFeVO4 was prepared by solid-state reaction at 570 °C during a 7-h period. The X-ray diffraction pattern revealed an orthorhombic
crystal structure. Thermogravimetric measurements revealed a reversible mechanism which was attributed to absorption–desorption
of humidity. Impedance spectroscopy measurements were carried out at 25 °C steps in the temperature range from 25 to 500 °C
and equivalent circuits were drawn to fit the impedance measurement results at each temperature level. The elements of the
equivalent circuits were assigned to bulk, grain boundary, and along grain boundary conductivity. All three conduction mechanisms
were found to be humidity sensitive. Arrhenius plots were plotted for the bulk and grain boundary conductivity processes.
The activation energy for the bulk conductivity process was calculated to be 0.25 eV over the temperature range from 175 to
500 °C and the activation energy for the grain boundary conductivity process was calculated to be 0.41 eV from 300 to 500 °C
and 0.20 eV from 175 to 275 °C. An explanation for the existence of these two grain boundary activation energies is attempted.
The dependence of the material conductivity mechanisms on humidity suggests that LiFeVO4 could be used as a humidity sensor. 相似文献
17.
M. Ertuğrul E. Büyükkasap A. Küçükönder A. İ. Kopya H. Erdoğan 《Il Nuovo Cimento D》1995,17(9):993-998
Summary The anisotropy of emission intensity ofL-shell X-rays induced by 59.5 keV photons in Au and Hg was investigated at different angles varying from 45° to 135°. It is
observed thatLl andLα X-rays (originating fromJ=3/2) are anisotropic,Lβ andLγ X-rays (originating fromJ=1/2, commonly) are isotropic. 相似文献
18.
H. L. Bay J. Bohdansky W. O. Hofer J. Roth 《Applied Physics A: Materials Science & Processing》1980,21(4):327-333
Angular differential and total sputtering yields of polycrystalline nickel and tungsten have been measured for 1 and 4 keV
H+ and 4 keV He+ ion bombardment at incidence angles between 0° and 80°. The differential sputtering yields (dY/dΩ) were determined with the aid of the collector technique, whereas the total yieldY was determined from the weight loss of the target during irradiation. Asymmetric angular distributions are observed at oblique
angles of incidence, the emission maximum being shifted in forward direction (with respect to the incident ions). Even more
pronounced than the change in shape of the emission distribution is an increase in the differential yield:dY/dΩ rises with increasing incidence angle over the whole range of ejection angles, the increase being most prominent in the
direction of primary recoil emission. This effect is therefore ascribed to emission of surface atoms in direct projectile-surface
atom collisions.
On short term leave from Institut für Plasmaphysik der Kernforschungsanlage Jülich GmbH, D-5170, Jülich, Fed. Rep. Germany. 相似文献
19.
The pyrolytic decomposition of layered basic zinc acetate (LBZA) nanobelts (NBs) into nanocrystalline ZnO NBs is investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). We also report on the gas sensing response of the resulting ZnO nanomaterial to CO. The LBZA NBs are grown at 65 °C in an aqueous solution of zinc acetate dihydrate. AFM and SEM results show as-grown products possess the characteristic layered structure of the LBZA crystals. XRD and XPS results show that annealing as-grown products at 210 °C in air causes a transformation from zinc acetate to nanocrystalline ZnO NBs via thermal decomposition. The ZnO crystalline domain size increases with temperature from 9.2 nm at 200 °C to 94 nm at 1000 °C, as measured from XRD. SEM shows evidence of sintering at 600 °C. The thickness of the NBs, determined via AFM, ranges from 10 to 50 nm and remains approximately constant with annealing temperature. XPS confirmed the chemical transformation from zinc acetate to ZnO and showed a significant remaining zinc hydroxide component for the ZnO NBs consistent with published results. PL measurements at room temperature show a blue shift in peak emission as the nanobelts change from LBZA to ZnO at 200 °C. Above this transition temperature, the ZnO nanobelts possess strong band edge emission at 390 nm and little broad band emission in the visible region. The AFM and SEM images reveal that the crystallites within the nanobelts orientate in rows along the long axis during annealing. This structure provides a high surface area to volume ratio of aligned nanoparticles which is beneficial for gas sensing applications. Gas sensors fabricated from 400 °C annealed nanobelts showed a response of 1.62 when exposed to 200 ppm of CO in dry air at 400 °C, as defined by the ratio of resistance before and during exposure. This indicates that ZnO nanostructures obtained by thermal decomposition of LBZA NBs could provide a cost effective route to high sensitivity gas sensors. 相似文献
20.
45% semi-crystalline parylene-C (–H2C–C6H3Cl–CH2–)
n
thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass
transition (T
g
=90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency
conductivities from 10−15 to 10−12 S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant
increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS)
polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric
analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting
to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured
at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity
is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps). 相似文献