共查询到20条相似文献,搜索用时 46 毫秒
1.
A. I. Shames R. Nucci S. D’Auria F. Febbraio C. Vaccaro E. Lozinsky M. Rossi G. I. Likhtenshtein 《Applied magnetic resonance》2000,18(4):515-526
The conformational transitions of thermophilic β-glycosidase fromSulfolobus solfataricus and the mechanism of its thermal and chemical activation were studied by electron paramagnetic resonance (EPR) of nitroxide
spin labels immobilized on the protein matrix. For this purpose, β-glycosidase was covalently modified by maleimide nitroxide
spin label (MAR⋅) and iodoacetamide nitroxide spin label (IAR⋅), both specific for -SH groups. The degree of modification was found to be independent of the temperature as well as of the
presence of two enzyme activators, sodium dodecyl sulphate (SDS) and butanol. In addition, a dansyl-piperidine nitroxide radical
probe (DR⋅), which has an affinity to the hydrophobic surfaces of proteins, was used in this study. The noncovalent binding of DR⋅ results in immediate formation of a probe-enzyme complex. At room temperature, the rotation frequency of the immobilized
labels decreases in order of IAR⋅ > MAR⋅ ≥ DR⋅. The temperature measurements of rotation correlation frequencies (v
c
) display values ranging from 6·107 to 2·108 s−1 and indicate a discontinuity with the inflection point at temperatureT
in in a range from 312 to 313 K. The observed enthalpies (ΔH
≠) and entropies (ΔS
≠) of the activation of spin label rotation were derived from the Arrhenius plots. The activation parameters were found to
be typical for rigid model systems. The addition of SDS and butanol produced a slight shift of the inflection point and changes
of spin-label mobility. A correlation between conformational transitions and enzyme thermal activation was discussed. 相似文献
2.
V. M. Astashynski A. M. Kuzmitski A. A. Mishchuk 《Journal of Applied Spectroscopy》2011,78(3):377-382
Spectroscopic studies of compression plasma flows generated by a miniature magnetoplasma compressor and of the shock compressed
plasma layer formed near a target surface exposed to these flows are reported. The peak electron temperature and density are
found to be 3 eV and 1.2⋅1016 cm−3, respectively, in the compressor flow and 4.5 eV and 6.7⋅1016 cm−3 in the shock compressed layer. 相似文献
3.
Lithium ion conductors of the overall composition LixLa2/3Ti1−xPxO3+x (hereafter referred to as LTP) based on La2/3TiO3 were prepared by solid state reaction at high temperature (1300 °C). AC impedance measurements indicate that the total conductivities
are of the order of 10−4 S·cm−1 when x=0.28 − 0.35 at room temperature and have an activation energy of 18 kJ·mol−1 in the temperature range from room temperature to 400 °C. X-ray powder diffraction patterns showed that the LTP system has
a complex composition, which contains the solid solution perovskite Li3xLa2/3−xTiO3 and LaPO4. 相似文献
4.
A nanoparticle TiO2 solid-state photoelectrochemical cell utilizing as a solid electrolyte of poly(acrylonitrile)–propylene–carbonate–lithium
perchlorate (PAN–PC–LiClO4) has been fabricated. The performance of the device has been tested in the dark and under illumination of 100-mW cm−2 light. A nanoparticle TiO2 film was deposited onto indium tin oxide-covered glass substrate by controlled hydrolysis technique assisted with spin-coating
technique. The average grain size for the TiO2 film is 76 nm. LiClO4 salt was used as a redox couple. The room temperature conductivity of the electrolyte is 4.2 × 10−4 S cm−1. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows the rectification
property in the dark and shows the photovoltaic effect under illumination. The best J
sc and V
oc of the device were 2.82 μA cm−2 and V
oc of 0.58 V, respectively, obtained at the conductivity of 4.2 × 10−4 S cm−1 and intensity of 100 mW cm−2. The J
sc was improved by about three times by introducing nanoparticle TiO2 and by using a solid electrolyte of PAN–PC–LiClO4 replacing PVC–PC–LiClO4 in the device. The current transport mechanism of the cell is also presented in this paper. 相似文献
5.
Dillip K. Pradhan B. K. Samantaray R. N. P. Choudhary N. K. Karan Reji Thomas R. S. Katiyar 《Ionics》2011,17(2):127-134
The solid polymer electrolyte films based on polyethylene oxide, NaClO4 with dodecyl amine modified montmorillonite as filler, and polyethylene glycol as plasticizer were prepared by a tape casting
method. The effect of plasticization on structural, microstructural, and electrical properties of the materials has been investigated.
A systematic change in the structural and microstructural properties of plasticized polymer nanocomposite electrolytes (PPNCEs)
on addition of plasticizer was observed in our X-ray diffraction pattern and scanning electron microscopy micrographs. Complex
impedance analysis technique was used to calculate the electrical properties of the nanocomposites. Addition of plasticizer
has resulted in the lowering of the glass transition temperature, effective dissociation of the salt, and enhancement in the
electrical conductivity. The maximum value of conductivity obtained was ∼4.4 × 10−6 S cm−1 (on addition of ∼20% plasticizer), which is an order of magnitude higher than that of pure polymer nanocomposite electrolyte
films (2.82 × 10−7 S cm−1). The enhancement in conductivity on plasticization was well correlated with the change in other physical properties. 相似文献
6.
In the present study, a kind of solid polymer electrolyte (SPE) based on poly(vinylidene difluoride-co-hexafluoropropylene)/poly(methyl methacrylate) blends was prepared by a casting method to solve the safety problem of lithium
secondary batteries. Owing to being plasticized with a room temperature ionic liquid, N-butyl-N′-methyl-imidiazolium hexafluorophosphate, the obtained SPE shows a thermal decomposition temperature over 300°C and an ionic
conductivity close to 10−3 S cm−1. The SPE-3 sample, in which the weight of two polymers is equivalent, possesses an ionic conductivity of 0.45 × 10−3 S cm−1 at 25°C and presents an electrochemical window of 4.43 V. The ionic conductivity of the SPE-3 is as high as 1.73 × 10−3 S cm−1 at 75°C approaching to that of liquid electrolyte. The electrochemical performances of the Li/LiFePO4 cells confirmed its feasibility in lithium secondary batteries. 相似文献
7.
S. Vatnik M. C. Pujol J. J. Carvajal X. Mateos M. Aguiló F. Díaz V. Petrov 《Applied physics. B, Lasers and optics》2009,95(4):653-656
The three thermo-optic coefficients of the biaxial laser host KLu(WO4)2 are measured at 633 nm by a deflection method. Their values at 300 K amount to ∂
n
g
/∂
T=−7.4×10−6 K−1; ∂
n
m
/∂
T=−1.6×10−6 K−1 and ∂
n
p
/∂
T=−10.8×10−6 K−1. Nearly athermal propagation directions are found for polarizations along the N
m
and N
p
dielectric axes. 相似文献
8.
Grafted natural rubber-based polymer electrolytes: ATR-FTIR and conductivity studies 总被引:2,自引:0,他引:2
Attenuated total reflectance–Fourier transformed infrared spectroscopy measurement is employed to study the interactions between
the components of 30% methyl-grafted natural rubber (MG30), lithium trifluromethanesulfonate (LiCF3SO3 or LiTF), and propylene carbonate (PC). Vibrational spectra data of LiTF reveals that the νs(SO3) at 1,045 cm−1, δs(CF3) at 777 cm−1, and C=O stretching mode at 1,728 cm−1 for MG30 have shifted to lower wave numbers in MG30–LiTF complexes indicating that complexation has occurred between MG30
and LiTF. The solvation of lithium ion is manifested in Li+ ← O=C interaction as shown by the downshifting and upshifting of C=O mode at 1,788 to 1,775 cm−1 and νas(SO3) at 1,250 to 1258 cm−1, respectively, in LiTF–PC electrolytes. There is no experimental evidence of the interaction between MG30 and PC. Competition
between MG30 and PC on associating with lithium ion is studied, and the studies show that the interaction between MG30–LiTF
is stronger than that of the PC–LiTF in plasticized polymer–salt complexes. The effect of PC on the ionic conductivity of
the MG30–LiTF system is explained in terms of the polymer, plasticizer, and salt interactions. The temperature dependence
of conductivity of the polymer films obeys the Vogel–Tamman–Fulcher relation. Values of conductivity and activation energy
of the MG30-based polymer electrolyte systems are presented and discussed. 相似文献
9.
We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO4 single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio
of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian
corresponding to axial symmetry with the parameters g
∥1=1.9305, g
⊥1=1.9565, A
∥1=−168.2×10−4cm−1, and A
⊥1=−54.3×10−4cm−1 for V1 centers and g
∥2=1.9340, g
⊥2=1.9523, A
∥2=−169.0×10−4cm−1, and A
⊥2=−55.2×10−4cm−1 for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally
distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO2+ ion forms when α-RbTiOPO4 crystals and crystals of the KTP group (KTiOPO4, NaTiOPO4, α-and β-LiTiOPO4), studied earlier, are doped with vanadium is discussed.
Fiz. Tverd. Tela (St. Petersburg) 40, 534–536 (March 1998) 相似文献
10.
Perovskite-type lithium fast ion conductors of Li3xLa0.67−xScyTi1−2yNbyO3 system were prepared by solid state reaction. X-Ray powder diffraction shows that perovskite solid solution form in the ranges
of x=0.10, y≤0.10. AC impedance measurements indicate that the bulk conductivities and the total conductivities are of the
order of 10−4 S·cm−1 and 10−5 S·cm−1 at 25 °C respectively. The compositions have low bulk activation energies of about 17 kJ/mol in the temperature ranges of
298 – 523 K and total activation energies of about 37 kJ/mol in the temperature ranges of 298 – 523 K. 相似文献
11.
To investigate the influence of cation mobility variation due to the mixed glass former effect, 0.45Li2O-(0.55 − x) P2O5−x B2O3 glasses (0 ≤; x ≤ 0.55) are studied keeping the molar ratio of Li2O/(P2O5 + B2O3) constant. Addition of B2O3 into lithium phosphate glasses increases the glass transition temperature (T
g) and number density, decreases the molar volume, and generally renders the glasses more fragile. The glass system has been
characterised experimentally by XRD, XPS and impedance studies and studied computationally by constant volume molecular dynamics
(MD) simulations and bond valence (BV) method to identify the structural variation with increasing the B2O3 content, its consequence for Li+ ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms. These studies indicate the increase
of P-O-B bonds (up to Y = [B2O3]/([B2O3] + [P2O5]) ≈ 0.5 and B-O-B bonds, as well as the decrease of P-O-P bonds and non-bridging oxygens (NBOs) with rising B2O3 content. The system with Y ≈ 0.5 exhibits maximum ionic conductivity, 1.0 × 10−7 S cm−1, with activation energy 0.63 V. Findings are rationalised by a model of structure evolution with varying B2O3 content Y and an empirical model quantifying the effect of the various structural building blocks on the ionic conductivity in this
mixed glass former system. 相似文献
12.
Kinetic regularities and mechanism of polymerization of perfluoromethylvinyl ether at high pressures
A. A. Zharov O. K. Nikolaeva 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(5):839-845
The kinetics of the thermal polymerization of perfluoromethylvinyl ether (PFMVE) is studied at pressures of 3–13 kbar (300–1300
MPa) and temperatures of 80–260°C. The activation energy (E
act = (76 ± 3) kJ/mol) and activation volume (ΔV0⪼ = −(27 ± 2) cm3/mol) for the overall polymerization rate are determined. The inhibition method is used to estimate the activation energy
of thermal initiation (E
in = (79.9 ± 3) kJ/mol). The quantity E
p
− (1/2)E
t
was calculated to be 36.6 ± 3 kJ/mol. The limiting polymerization temperature was evaluated: T
lim = (180 ± 3)°C. A mechanism of PFMVE polymerization is proposed on the assumption that the reaction is bimolecular. 相似文献
13.
Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)0.7 and sodium iodide (NaI)0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural
properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric
acid disrupt the semi-crystalline nature of (PVA)0.7(NaI)0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing
sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)0.7(NaI)0.3 matrix at room temperature was 10−5 S cm−1 and this increased to 10−3 S cm−1 with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out.
The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration
Na/SPE/MnO2. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ. 相似文献
14.
A. L. Stepanov V. F. Valeev Yu. N. Osin V. I. Nuzhdin I. A. Faizrakhmanov 《Technical Physics》2009,54(7):997-1001
A new method is proposed for synthesizing metallic nanoparticles in a polymer matrix. These nanoparticles are synthesized
during thermal vacuum evaporation of a metal (4.8 × 10−6 g/cm2) onto the surface of viscousfluid epoxy resin (at a viscosity of 20–120 Pa s) having room temperature, which is well below
the glass transition temperature of the polymer. As a result, epoxy resin layers containing silver nanoparticles in their
volume form; these nanoparticles are studied by transmission electron microscopy and optical absorption spectroscopy. Various
types of disperse structures formed by metallic nanoparticles in the polymer are detected. The morphology of the composite
material is found to be controlled by the polymer viscosity and the metal deposition time. 相似文献
15.
Thin films of ZnSe and PEO–chitosan blend polymer doped with NH4I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited
on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer
blend was complexed with ammonium iodide (NH4I), and some iodine crystals were added to the polymer–NH4I solution to provide the I−/I3−redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10−6 S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO
photovoltaic cell. The open circuit voltage (V
oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA. 相似文献
16.
New Na+ ion conducting composite polymer electrolytes comprising of polyethylene oxide (PEO)-NaClO4 and PEO-NaI complexes dispersed with SnO2 are reported. The results of the studies based on optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry
(DSC), Fourier transform infra-red (FTIR) spectroscopy, impedance analysis and mechanical testing are presented and discussed.
The electrical conductivity of ≈5·10−5 S·cm−1 at 40 °C was achieved for the dispersion of ≈10 wt.% of SnO2 in both systems. The composition dependence of the conductivity has been well correlated with the variation in glass transition
temperature and degree of crystallinity. A substantial enhancement in the mechanical properties of the composite films was
observed at the cost of slight decrease in the conductivity at higher concentration of SnO2. The temperature dependence of the conductivity follows apparently the Arrhenius type thermally activated process below and
above the melting temperature of PEO. The conductivity of the materials has been found to be strongly humidity dependent.
The materials are shown to be ionic with tion>0.9. The electrochemical stability of the materials has been observed to be up to ≈3.2 V for (PEO)25NaClO4+x% SnO2 and is limited to ≈1.9 V for (PEO)25NaI+x% SnO2. 相似文献
17.
A. A. Samokhvalov T. I. Arbuzova N. A. Viglin V. V. Osipov N. I. Solin S. V. Naumov V. G. Bamburov N. I. Lobachevskaya O. G. Reznitskikh 《Physics of the Solid State》1999,41(2):262-264
Mg1−x
CuxO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg1−x
CuxO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of
5–550 K. It is shown that χ
−1(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ
eff=1.9 μ
B, close to the 1.73 μ
B of a Cu2+ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10−4 eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg1−x
CuxO at T=300 K is ≈10−11–10−12 Ω−1 cm−1 for x=0 and increases to 10−5–10−6 Ω−1 cm−1 for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg1−x
CuxO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the
structure is discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999) 相似文献
18.
In the paper the dependence of the photorefraction (PhR) in LiNbO3 and LiNbO3−Fe (0.1 wt%, 0.3wt%) crystals on light intensity (within 1016–1023 quanta·cm−2·s−1 at wavelengths 496.5 nm and 600 nm) and temperature (in the region 100–500 K) is studied. For all the crystals the limiting
values of PhR are similar and atT=293 K Δn
sat
lim
≈3·10−3. In LiNbO3 the temperature dependence of PhR in the range 100–500 K requires to take into account at least two trapping centres. 相似文献
19.
The difference of the energies of levels Δ
n
= E
lev(2+0
n
) − E
lev(0+0
n
) at n = 1, 2, and 3 and the multipole-mixture parameter δ for (2+02−2+01) and (2+03−2+01) transitions are contrasted against the structure of the K
π
= 02+ and 03+ rotational bands that was calculated on the basis of the quasiparticle-phonon model. The values of (Δ2 − Δ1), (Δ3 − Δ1), and (Δ2 − Δ3) are found to correlate with the sign of the parameter δ and with the calculated structure of the K
π
= 02+ and 03+ bands.
Original Russian Text ? A.M. Demidov, L.I. Govor, V.A. Kurkin, I.V. Mikhailov, 2009, published in Yadernaya Fizika, 2009,
Vol. 72, No. 2, pp. 236–240. 相似文献
20.
Rault J 《The European physical journal. E, Soft matter》2012,35(4):26
The thermodynamical and mechanical properties of (fragile and strong) glass are modeled based on a generalised activation
energy relationship log
τ
= ΔG
β
/RTn(T′) process of glass-forming liquids. This cooperative process involves 1/n(T′) elementary β motions of activation Gibbs energy ΔG
β
dependent on the equivalent temperature T′, the temperature of the liquid in equilibrium having the volume of the glass, function of temperature and aging conditions.
From this modified VFT law the relaxation of any properties (V , H , stress, creep) can be calculated and approximated by the Kohlrausch function. This model predicts consistency relationships
for: a) the temperature (and aging time) variation of the Kohlrausch exponent; b) the temperature dependence of the stabilisation
time domain of strong and fragile glass; c) the linear relation between the activation parameters (E
* energy, S
* entropy, V
* volume) of the α and β transition. The Lawson and Keyes (LK) relations are recalled and it is shown that these relations (somewhat equivalant to
the compensation law or Meyer-Neldel rule) are observed generally in glass. Morever the (macroscopic) ratios ΔH/ΔV observed during aging or after a temperature jump and the (microscopic) ratio E
*/V
* are found equal to κγ (κ compressibily, γ Grüneisen parameter), in agreement with the LK predictions. From various experiments and in agreement with predictions of
this model we conclude that the Grüneisen parameter γ
B
(pressure derivative of the bulk modulus) and the Mean Square Displacement (MSD) characterising the anharmonicity of solids
(and liquids) are the main parameters which govern the relaxation properties of the glass state. Linear relations between
the parameters γ
B
, the fragility m, and the Kohlrausch exponent n
g
at T
g
are explained. These correlations underscore a strong relationship between the fragilty of glass formers and the extent of
the anharmonicity in the interatomic interactions. 相似文献