共查询到20条相似文献,搜索用时 218 毫秒
1.
M. Merzlyakov A. Wurm M. Zorzut C. Schick 《Journal of Macromolecular Science: Physics》2013,52(5-6):1045-1054
Amplitude and frequency dependence of reversible melting of polycaprolactone (PCL) and an ethylene octene copolymer (EOM) were studied using temperature-modulated differential scanning calorimetry (TMDSC) (2?10?1 Hz <f < 0.05 Hz) and shear spectroscopy (dynamic mechanical analysis, DMA) (5?10?4 Hz < f < 100 Hz). It was found that the excess heat capacity of PCL is constant for temperature amplitudes in the range 5 mK < AT < 2 K. The excess heat capacity decreases with frequency of temperature perturbation and tends to zero at about 0.1 Hz and 100 Hz for PCL and EOM, respectively. The constant excess heat capacity and the frequency dependence support the idea that reversible melting is related to a relaxation process on the surface of the polymer crystals. The occurrence of such a relaxation process was shown by shear modulus measurements in the same frequency and temperature region. The relaxation process is, in the melting region, much slower than main relaxation (glass transition). At low temperatures, a crossover can be seen, indicating the independence of both processes because of spatial separation. The main relaxation is related to the melt, while the other is related to the crystal surface. 相似文献
2.
The dielectric parameters in the frequency range 50 Hz to 1 MHz have been measured in a SmC* liquid crystal mixture in planar alignment. The relaxation frequency (fr), distribution parameter (α) and dielectric strength (δε) have been evaluated and their corresponding values were found to be 206.62 Hz, 0.06 and 114.6 respectively. The Goldstone mode, domain mode, soft mode and a new relaxation mode have been observed. 相似文献
3.
Different thermal treatments were used in order to follow the structural relaxation of m-toluidine by thermally stimulated depolarization currents (TSDC) in the sub-T g temperature region. In some of these thermal treatments, the ageing time, t a, and the probing (or polarization) time, t P, are varied independently in order to allow a clear understanding of the exploration of the energy landscape which occurs as a consequence of the structural relaxation. The TSDC results show that ageing induces a shift to higher temperatures of the TSDC peaks, in a way similar to that observed in the calorimetric heat capacity overshoot. More importantly, TSDC results show that ageing induces a decrease of the activation energies with regard to the window defined by the probing time and a sharpening of the energy distribution of the modes of motion that are present in the glass, in the studied sub-T g temperature region. 相似文献
4.
Nuclear magnetic double resonance experiments were performed on the strongly coupled two-proton system (AB) in 2-chloroacrylontirile to study the spin relaxation processes. The single resonance parameters of the AB spectrum are (operating frequency 100 MHz): |vA - vB|=9.85±0.1 Hz and J AB=2.8±0.1 Hz. Frequency-sweep double resonance spectra were obtained by irradiating each of the four transitions at different strengths of irradiation in the range 0.015 Hz to 2.35 Hz. These spectra were analysed by using the ‘Bloch approximation’ in the rotating frame for the ‘high’ irradiation strengths and the ‘simple line’ approximation for the ‘low’ irradiation strengths. The analysis showed that the proton relaxation in this molecule can be described by interaction with isotropic random fields of nearly equal strengths at the two nuclei with no appreciable correlation between them. Internal dipole-dipole interaction is not a significant mechanism (at room temperature). It is shown that for analysing ‘low’ irradiation spectra the choice of certain functions of intensity changes would lead to a marked distinction between the different relaxation mechanisms. 相似文献
5.
Summary The effects of heat treatments in vacuum on magnetic permeability, Young's modulus and magnetoelastic wave amplitude were
investigated in the amorphous ferromagnetic alloys Fe73.5Cu1Ta3Si15.5B7 and Fe73.5Cu1W3Si15.5B7 where tantalum or tungsten replaces niobium, which was generally used with the same atomic fractions of the other elements.
The stress sensitivity coefficient was also theoretically deduced in its developmentvs. the applied magnetic bias field. Structural relaxation and crystallization consequences are evidenced. Moreover an already
predicted relation between the maximum of magnetoelastic wave amplitude and the minimum of stress sensitivity coefficient
was confirmed. 相似文献
6.
7.
Dielectric spectroscopy investigations in the frequency range 50?Hz to 1?MHz have been carried out on a new ferroelectric liquid-crystalline material (S-(-)-4-(2-n-hexylpropionyloxy)biphenyl-4′-(3-methyl-4-decyloxy)benzoate) possessing a relatively large spontaneous polarization (P s?~?240?nC?cm?2) and containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit. The effect of temperature on the dielectric relaxation modes has been investigated in the SmC* and N* phases. From dielectric dispersion data, relaxation frequency and dielectric strength of all detected relaxation modes have been evaluated and discussed. A new surface-like mode of relaxation frequency ~11?kHz and dielectric strength 3.8, is seen to appear in the SmC* phase. 相似文献
8.
The relaxation processes of α-form nylon 1212 from 50°C up to 160°C were studied by dielectric relaxation spectroscopy (DRS) in a wide frequency range of 63 Hz to 5 MHz. The α relaxation, the electrode relaxation, and the conductivity relaxation of nylon 1212 were observed and analyzed in detail using permittivity and modulus formalism. Electrode polarization and dc conductivity were the origin of high dielectric permittivity values at low frequencies and high temperatures. The strength of the imaginary part of the electric modulus of conductivity relaxation M″ max was nearly independent of temperature. The distribution of local conductivity and relaxation time became broader with decreasing temperature. 相似文献
9.
M. Schlott B. Elschner M. Herrmann W. Assmus 《Zeitschrift für Physik B Condensed Matter》1988,72(3):385-389
The heavy fermion systems CeCu2Si2 and CeAl3 are characterized by a huge quasiparticle density of states responsible for the large electronic specific heat. The observation of a Gd3+ electron spin resonance (ESR) in single crystals CeCu2Si2 and in polycrystalline CeAl3 clearly demonstrates the local character of these quasiparticles. Nevertheless, the Gd-spin relaxation shows remarkable anomalies with respect to the isostructural compounds LaCu2Si2 and LaAl3: Probably via RKKY coupling, Ce 4f-spin fluctuations give rise to an enhanced Gd-spin relaxation resulting in an unusual non-linear thermal broadening around the Kondo temperature. From this we obtain information about the temperature dependence of the Ce 4f-spin correlation time. 相似文献
10.
K. Fürderer K.-P Döring M. Gladisch N. Haas D. Herlach J. Major H. -J. Mundinger J. Rosenkranz W. Schäfer L. Schimmele M. Schmolz W. Schwarz A. Seeger 《Hyperfine Interactions》1986,31(1-4):81-86
Muon spin precession frequencies and transverse relaxation rates have been measured on demagnetized iron, cobalt, and FeCo
alloys (3 at%–50 at% Co) between room temperature and the Curie temperatureT
c. The increase of the relaxation rate in iron between 930 K and 1010 K could be quantitatively attributed to the trapping
of positive muons by vacancies in thermal equilibrium, resulting in an enthalpy of monovacancy formation ofH
1V
F
=(1.7±0.1) eV. the smallest vacancy concentrations detected are = 10−8. 相似文献
11.
Abstract In antiferroelectric lead zirconate crystal with one phase transition a nearly monodispersive dipolar relaxation has been found in the paraelectric phase and temperature range 20 K below T c in the frequency region 20—3 ′ 105 Hz. This relaxation has a dominating influence on the temperature dependence of dielectric susceptibility. Relaxation time obeys the Arrhenius law increasing up to 1.5 ′ 10?2s (11 Hz) at T c and then exhibiting a distinct jump. 相似文献
12.
Alternating-current electrical resistance measurements between 17 Hz and 100 kHz were made on high purity Fe, Co, and Ni wires in the vicinity of their Curie temperatures (T c). The electrical resistance was independent of frequency for temperatures (T) aboveT c. As the temperature was lowered, however, there was an abrupt jump in the electrical resistance atT c followed by a gradual decrease toward its dc value. The magnitude of the electrical resistance jump atT c increased as the square root of the frequency. The enhancement of the electrical resistance forT≦T c is produced by an abrupt decrease of the skin depth atT c which, in turn, is due to the sudden increase in the initial magnetic permeability atT c. Measurements of the ac electrical resistance in the vicinity of the Curie temperature of certain ferromagnetic metals can be utilized to 1) accurately determine the Curie temperature using frequencies as low as 17 Hz, and 2) quantitatively determine the initial magnetic permeability as a function of temperature and heat treatment. 相似文献
13.
Dielectromagnetics made from organic–inorganic hybrid silica-coated iron powders were characterised by determination of their physical, mechanical and magnetic properties. The influence of three main factors, dielectric composition, addition level and heat treatment conditions were investigated. Results showed that these factors have significant effects on the performance of the dielectromagnetics. Increase in the organic phase content in these dielectric coatings tends to increase both the electrical resistivity and magnetic permeability of dielectromagnetics, although the strength and density are slightly impaired. Increasing the coating thickness leads to improvements in resistivity and thus reduced eddy current losses, but these are offset by reductions in density, strength and particularly magnetic permeability. A hybrid organic–inorganic coating formulation based on 40 mol% MTMS and 60 mol% TEOS precursors was found to be the optimum composition investigated. Addition levels between 0.1% and 0.3% were found to offer a good compromise between maximum permeability (μmax>400) and minimum loss (typically <8 W/kg) for operation at 50 Hz/1 T, and the system can be optimised within this range for the desired performance. 相似文献
14.
S. V. Khonik N. P. Kobelev V. V. Sviridov V. A. Khonik 《Physics of the Solid State》2008,50(10):1812-1818
The structural relaxation of a bulk Pd40Cu30Ni10P20 metallic glass is studied by measuring the electrical resistivity and infralow-frequency (0.05 Hz) internal friction. It is demonstrated that the structural relaxation in thermally aged samples can be restored by quenching them from a supercooled liquid state. It is found that the degree of relaxation after quenching can exceed the initial one by several times. 相似文献
15.
Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu61.13Zn33.94Al4.93 alloys
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The phase transformation activation energy of the Cu61.13Zn33.94Al4.93 alloys, which were treated at 4 GPa and 700℃ for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu61.13Zn33.94Al4.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from (111) to (200) of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β′→β and β→β' transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5-20℃/min. 相似文献
16.
A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells 总被引:1,自引:0,他引:1
N. Castagna G. Bison G. Di Domenico A. Hofer P. Knowles C. Macchione H. Saudan A. Weis 《Applied physics. B, Lasers and optics》2009,96(4):763-772
We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel
atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined
the intrinsic longitudinal, Γ
01, and transverse, Γ
02, relaxation rates. Our best cell shows Γ
01/2π≈0.5 Hz, and Γ
02/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation.
For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic
field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT
. Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon
shot noise limit. 相似文献
17.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
18.
19.
Several experiments using pulse electron spin resonance (ESR) equipment reveal that homogeneous free induction decay (FID) signals are given by electron spins in polypyrrole (PPy). FID signals obtained from PPy are accurately fitted via single-exponential curves, thus indicating that PPy can be used as a standard sample for several experiments with pulse ESR. We particularly pay attention to the nutation phenomena resulting from two-pulse irradiation (θ-t−2θ-t) in the homogeneous systems. The analysis by the vector model suggests that the nutation curves are affected by spin-lattice relaxation. Such a tendency is actually observed for two types of PPy used as examples ofT 1 >T 2 andT 1 ≈T 2. Thus the fitting over the nutation curve can be utilized for estimatingT 1. We particularly point out that such a procedure can be advantageously performed for electron spins with a short spin-lattice relaxation time. 相似文献
20.
Temperature-dependent dielectric characterization of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl (HIEB), which exhibits smectic B and nematic phases, has been carried out over the frequency range of 1 Hz to 10 MHz for homeotropic and planar alignment of sample molecules. This compound shows positive dielectric anisotropy (Δε = ε ∥ ? ε ⊥ > 0) in the nematic (N) phase. One mode of dielectric relaxation showing Arrhenius behaviour has been detected in the hexatic smectic B (SmB) phase. Various electrical parameters, namely, dielectric anisotropy, relaxation frequency and activation energy, have been determined in the N and SmB phases. 相似文献