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1.
True zero-field critical current density J
c
of a well-characterized BPSCCO/Ag tape has been determined by means of high-resolution ac susceptibility in the temperature range 77–110 K. The resultant values (30,000 A/cm 2 at 77 K) agree well with the transport J
c
of the same tape. Because of a very thin BPSCCO, the core J
c
determined from the imaginary part of the ac susceptibility is nearly the same as the zero field one. All J
c
's follow the same (1- T/T
c
) n with n=1.45 dependence. J
c
shows an approximate H
–0.5 field dependence over the explored temperature range. Accordingly, the variations of J
c
with T and H seem to be determined by the flux creep. 相似文献
2.
An approximation method for the energy spectrum of a stationary stochastic dynamical system is presented, which allows approximate functional rational factorization.This paper is in three parts. The first deals with a theoretical problem of approximation in Hardy Spaces, whose main result is the following:Let S(in), S be positive functions belonging to L1( Rgw), such that log S(n) and log S belong to L1( Rω, dω/1 + ω 2).Let h(n), h be the outer functions of the Hardy Space H2(Π +) such that S(g) = | h(n)| 2 and S = | h| 2 on iR.If S(n) n→∝ S in L1( Rω), and log S(n) n→∝ log S in L1( Rω, dω/1 + ω 2), then: h(n) n→∝ h in H2(Π +).The second part describes an effective algorithm, using random search methods, and gives an almost sure convergence result for it.The third part treats numerically two examples, permitting comparison of this algorithm with others (whenever there are…): the first example is a problem of approximation for a nonrational process (turbulence) that was considered in Ref. 22: the second example is a problem of model reduction (automatic) considered in Ref. 4. 相似文献
3.
Objective: The suitability of the rabbit as an animal model for the primary screening and selection of the pilot scale batches during the early stages of the formulation development was studied. Materials and methods: Three modified-release formulations of aminophylline consisted of Carbopol® 971P/HPMC K4M (F-I), and HPMC K100M (F-II) or HPMC K4M (F-III) were used. Commercial products were Aminofilin retard 350?mg tablets, Srbolek, Serbia (R-I) and Phyllocontin ® 350, tablets Purdue Frederic, Canada (R-II). Results: Calculated release rate constants and the ?2 values between R-I/F-I (84.1) and R-II/F-III (83.4) indicated similar in vitro release while the coefficient n showed presence of different mechanisms of release from Anomalous transport, Fickian diffusion to Case-II transport. Higher Tmax, was found in the rabbits, dosed with F-II (12.00?h), F-III (10.50?h), and R-II (15.00?h) formulation. The highest Cmax (9.22?mg/L) was obtained with F-II, similar lower values was seen for F-I and F-III, while commercial products showed the lowest values R-I (5.58?mg/L) and R-II (4.18?mg/L). Higher AUC values were detected for all three formulations (from 115.90 to 204.06 mgh/L) in relation to commercial products (105.33 and 113.25 mgh/L). Discussion and conclusion: The results demonstrated a good correlation of Level A ( r2 = 0.97) for the two formulations (F-I, F-III) and commercial product (R-I) indicates that there is a reasonable assumption that the rabbit might be use as a model for the preliminary comparison of scale up formulations in the early stages of the product development. 相似文献
4.
The ac susceptibility data was employed to extract the temperature dependence of the critical current density, J
c( T), as well as the variation of flux-creep exponent n( T, H
ac) with temperature and ac field amplitude in bulk samples of polycrystalline magnetic superconductor RuSr 2GdCu 2O 8 (Ru-1212). The critical state models and the collective flux-creep approximation model were successfully accounted to describe
such behavior below the transition temperature. The calculated values of n( T, H) are well fitted to a power law of the following form: n( T, H)= n
0( H) T
−s(H), where s is field dependent exponent whose values varied from −2.4, −1.01 for field amplitudes ranging from 0.5 G and 3.8 G. The power
law describing the frequency dependence of χ′ is found to be consistent with the results of the current-dependent effective activation energy of the form U( J)= U
0ln ( J
c/ J).
Additionally, the dependence of the current density is found to scale according as: J
c( T)= J
c0(1− T/ T
c)
n
, where the exponent n values varied from 1.05 to 1.25. Such dependence is an indication of intergrain coupling that could be ascribed in terms
of superconductor–insulator–superconductor junctions. The derived temperature dependence of J
c( T) is in good agreement with the data obtained from the measurements using the traditional “loss-maximum” approach. Furthermore,
the flux-creep effect increased with increasing both ac fields and temperatures except at about 15–25 K below the onset of
T
c, where a slowing down of the flux creep was observed. 相似文献
5.
(NH 4) 2S
x
Surface treatment was found to increase the barrier height ( Bn) for Au/In 0.53Ga 0.47As Schottky junctions from 0.26 eV to 0.58 eV at 300 K as determined from Richardson plots. The ideality factor n thus decreased from 2.7 to 1.6 and the reverse saturation current density J
0 from 9.4 Acm –2 to 3.4×10 –5A cm –2. The values of the effective Richardson constant were also evaluated. The chemical state of In 0.53Ga 0.47As surfaces before and after (NH 4) 2S
x
modification, examined by X-ray photoelectron spectroscopy (XPS), indicated bond formation of S with In, Ga and As. 相似文献
6.
Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density
versus voltage ( J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region
space charge limited conduction (SCLC) is observed. Number of states in the valence band ( Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density ( Nt) and activation energy are determined. The values of Nv and Nt are in the order 10 23 m −3 and 10 27 m −3 respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10 −7 cm 2 V −1 S −1. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable
for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕ b), diode ideality factor ( n) and saturation current density ( J0) are determined. The value of n increases and ϕ b decreases on annealing. 相似文献
7.
Rotational-state resolved measurements of H 2O−H 2 and H 2O−CH 3Cl intermolecular interactions were performed. Using light-induced drift as a tool, we measured changes in transport collision
rate v upon rovibrational ( J, r)-excitation of H 2O. We studied P- and R-branch excitation with J ranging from O through 9 for H 2O excited in the fundamental asymmetric stretch mode. Combination of P and R data yields the dependencies of v upon rotational ( J) and vibrational ( r) quantum numbers separately. For H 2O−CH 3Cl it is found that v decreases by 25% as J increases from 0 to 9. For H 2O−H 2 the decrease is only 1.0%. These data seem to exemplify a fundamental aspect of dipole-dipole interaction: the familiar 1 r
3 interaction term is highly J-dependent. This is attributed to the increasing averaging-out of the dipolar potential as the rotational quantum number increases.
Paper dedicated to Professor Edward A. Mason. 相似文献
8.
The variation of elastic moduli, M, of sintered powder compacts with porosity, p, has been analysed in terms of an equation M = M
0 (1– p)
n
, where M
0 is the elastic modulus of non-porous material and n is a constant. The variation of ultrasonic velocities has also been described in terms of a similar equation derived from the relations given by physical acoustics theory. It has been shown that the parameter n is related to a stress concentration factor around pores in the material and is dependent on pore geometry and its orientation in the material. The observed variation in moduli and velocities with porosity has been compared with the theoretically predicted values based on self-consistent oblate spheroidal theory. 相似文献
9.
The dependence of viscoelastic properties on the molecular weight of fractionated and and blended petroleum pitches was examined in relation to the creep and glass transition behaviour. The steady-state viscosity, , as a measure of energy dissipation, and the steady-state creep compliance, J
e
0
, as a measure of elastic stored energy, were empirically related to the glass transition point, T
g. The values of showed a steep dependence on the number average molecular weight, ¯M
n ( f
¯M
n
42
). It was proved that the molecular weight dependence of and J
e
0
manifest through the dependence of T
g on ¯M
n ( T
gf 1/ ¯M
n). Discussion of the blending laws to elucidate the effect of molecular weight distribution has revealed that In , J
e
0
, and T
g are expressed additively by using the mole fraction of each pitch component with different molecular weights. 相似文献
10.
AbstractBackground: In the present age of polypharmacy, limited sampling strategy becomes important to verify if drug levels are within the prescribed threshold limits from efficacy and safety considerations. The need to establish reliable single time concentration dependent models to predict exposure becomes important from cost and time perspectives. Methods: A simple unweighted linear regression model was developed to describe the relationship between Cmax versus AUC for fexofenadine, losartan, EXP3174, itraconazole and hydroxyitraconazole. The fold difference, defined as the quotient of the observed and predicted AUC values, were evaluated along with statistical comparison of the predicted versus observed values. Results: The correlation between Cmax versus AUC was well established for all the five drugs with a correlation coefficient ( r) ranging from 0.9130 to 0.9997. Majority of the predicted values for all the five drugs (77%) were contained within a narrow boundary of 0.75- to 1.5-fold difference. The r values for observed versus predicted AUC were 0.9653 ( n?=?145), 0.8342 ( n?=?76), 0.9524 ( n?=?88), 0.9339 ( n?=?89) and 0.9452 ( n?=?66) for fexofenadine, losartan, EXP3174, itraconazole and hydroxyitraconazole, respectively. Conclusions: Cmax versus AUC relationships were established for all drugs and were amenable for limited sampling strategy for AUC prediction. However, fexofenadine, EXP3174 and hydroxyitraconazole may be most relevant for AUC prediction by a single time concentration as judged by the various criteria applied in this study. 相似文献
11.
We have reviewed the methods of extracting current density dependence of the effective activation energy Ueff( J) from experimental data, including transport measurements and magnetic relaxations. Then we applied the method proposed by Maley etc. on our single-phase HgBaCaCuO-1223 sample to obtain the effective activation energy. The effective activation energy Ueff( J, H = 1~ T) is extracted from the magnetization relaxation data. On the other hand, Ueff( J) can be theoretically estimated for the model of a sinusoidal washboard potential in superconductors. By comparing the two results we believe that the single curve obtained in the former way can be seen as real current density dependence of effective activation energy Ueff( J). In addition, we have analyzed the reasons why the magnetic decay data at various temperatures can be scaled onto a single curve. The pinning mechanism in the measured temperature range does not change, and the activation energy depends separately on the three variables: T, B, and J are thought as two important factors for this. In the temperature close to zero and near Tc, thermally assisted flux motion would no longer valid since other processes predominate. 相似文献
12.
We report on the magnetic properties, magnetocaloric effect (MCE) and critical exponents in amorphous Co 100?xEr x ( x = 55 and 65), prepared by liquid quenching technique. The transition temperature from ferromagnetic to paramagnetic state has been evaluated according to M( T) measurements, and it is found to be 26 and 15 K for Co 45Er 55 and Co 35Er 65, respectively. The magnetization dependence M( H, T) on the temperature T and magnetic field H was measured carefully in the critical region. Magnetic entropy change (– Δ S M ) allowing estimation of the MCE was determined based on thermodynamic Maxwell’s relation. The magnetocaloric study exposes a quite large value of the magnetic entropy change, which decreases when increasing Er concentration. For an applied magnetic field of 5 T,the values of (– Δ S Max) peak are about 10.8 and 9.8 J kg ?1 K ?1 for Co 45Er 55 and Co 35Er 65, respectively. From the field dependence of the magnetic entropy Δ S M (Δ S M α H n ) and the relative cooling power (RCP) (RCP α H 1+1/δ), it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method. 相似文献
13.
Magnetic relaxation, with magnetic fields applied parallel to the c axis, was measured in a high-quality melt-textured YBa 2Cu 3O x bar. Zero-field-cooled magnetization-versus-time data were obtained within a regime of field and temperatures dominated by single vortex pinning. The activation pinning energy U = U
M
was calculated from experimental data and compared to U = U
0
ln( J
c
/ J), where U, is a constant, J
c
is the critical current density, and J the current density. This expression for U obtains within the individual pinning regime. A logarithmic dependence of U
M
on J was found, and the data indicated that a scaling function of U
M
, g( T/ T
c
) = (1– T/ T
c
) 1/2, was appropriate for describing the single-vortex pinning regime. 相似文献
14.
CdGa 2Se 4 thin films were prepared by vapour deposition onto either room temperature or preheated quartz and glass substrates ( T
S) or they were deposited at room temperature and then annealed at about ( T
A) 623 K. The films thus prepared were crystalline with a thiogallate tetragonal structure. The optical constants (the refractive index n and the absorption index, k) were determined for CdGa 2Se 4 films deposited onto quartz substrates held at either room temperature or at T
S = 573 K. These constants were also determined for preannealed films ( T
A = 623 K). Plots of ( hv) 2 = f(hv) and ( hv) 1/2 = g(hv) were linear, indicating the existence of both direct and indirect optical transitions. It was found that the values of E
g
d and E
g
ind for as-deposited CdGa 2Se 4 films were 2.46 and 1.91 eV, respectively. The corresponding values for the annealed films and the films deposited at T
S = 573 K were 2.56 and 2.06 eV, respectively. 相似文献
15.
We investigate a spin 1/2 Heisenberg antiferromagnet (AFM) H = J 1
i
N
=1 s 0s
i
+ J 2H Rs
i
describing a central spin which interacts with a surrounding medium h r. We present general relations for the eigen values, the eigen states and the spin correlation function and study the model in more detail for H r being either a linear chain or a Lieb-Mattis AFM. Additional to the ground state properties we calculate the full thermodynamics in the case of H r being a Lieb-Mattis AFM. 相似文献
16.
A thin film of cobalt selenide is deposited on the fluorescence tin oxide-coated glass surface material using a simple chemical growth technique. In this article, we report on the study of photoelectrochemical characteristics (PEC), including current–voltage, capacitance–voltage characteristics, photovoltaic power output, and spectral response in dark and light conditions. For the above parameter study, we prepared using cobalt selenide and carbon electrode (using polysulfide as electrolyte), the battery configuration is expressed as n-CoSe/NaOH (1 M)?+?Na2S (1 M)?+?S (1 M)/C (graphite). The performance of the cobalt selenide thin film material the resulted values of respective series (RS) and shunt (RSh) resistance 2.280 kΩ and 1.224 Ω, respectively. The efficiency and fill factor of these PEC cells were found to be 0.899 and 28.72%. The junction ideality value are found to be (nD) is 0.69 in the dark and 2.72 in the light (nL). The M–S plots are constructed using C?2 against applied bias voltage (with respect to SCE) for CoSe PEC cell. The positive slope of the M–S plot confirms n-type conductivity of the CoSe films. The carrier density values of the samples obtained from the M–S plots varied from 3.48?×?1014 cm?3. 相似文献
17.
The magnetic properties of evaporated Co/Pt multilayers have been studied by magnetic measurements and ferromagnetic resonance
(FMR). The spin-wave resonances were observed in some multilayers in FMR experiments, which implied that spin waves were sustained
by the whole and propagated through Pt layers. The relation of the resonance field H
res with the mode number n obeys the so-called n
2 law and the interlayer coupling strength J
I
has been determined. The temperature dependence of the spontaneous magnetization can be well described by Bloch’s law, in
all multilayers. The increase of the spin-wave parameter B with decreasing cobalt thickness has been discussed. A spin-wave
theory has been used to explain the temperature dependence of the magnetization and the approximate values for the bulk exchange
interaction J
b
and surface exchange interaction J
S
for various Co/Pt multilayers have been obtained. 相似文献
18.
AbstractWe synthesize ScCoO 3 perovskite and its solid solutions, ScCo 1?xFe xO 3 and ScCo 1?xCr xO 3, under high pressure (6 GPa) and high temperature (1570 K) conditions. We find noticeable shifts from the stoichiometric compositions, expressed as (Sc 1?xMx) MO 3 with x = 0.05–0.11 and M = Co, (Co, Fe) and (Co, Cr). The crystal structure of (Sc 0.95Co 0.05)CoO 3 is refined using synchrotron x-ray powder diffraction data: space group Pnma (No. 62), Z = 4 and lattice parameters a = 5.26766(1) Å, b = 7.14027(2) Å and c = 4.92231(1) Å. (Sc 0.95Co 0.05)CoO 3 crystallizes in the GdFeO 3-type structure similar to other members of the perovskite cobaltite family, ACoO 3 ( A3+ = Y and Pr-Lu). There is evidence that (Sc 0.95Co 0.05)CoO 3 has non-magnetic low-spin Co 3+ ions at the B site and paramagnetic high-spin Co 3+ ions at the A site. In the iron-doped samples (Sc 1?xMx) MO 3 with M = (Co, Fe), Fe 3+ ions have a strong preference to occupy the A site of such perovskites at small doping levels. 相似文献
19.
ZnO:M
n+(M
n+ = Cd 2+, Co 2+, Ni 2+, Sc 3+, In 3+, Ga 3+, Fe 3+, Te 4+, V 5+) single crystals have been grown under hydrothermal conditions in ZnO-M
x
O
y
-KOH-LiOH-H 2O systems, and their Raman spectra have been measured under visible (514.5 nm) and near-IR (1064 nm) excitation. The anomalous
band between 500 and 600 cm −1 in the Raman spectra of ZnO:Mn 2+ has A
1 symmetry and is due to vibrations involving Mn 2+. 相似文献
20.
The insulating and metallic behavior of the grain-boundary weak links has been studied in thallium rich and the samples with
small amount of thallium in the charge reservoir layer of Cu 1−x
Tl
x
Ba 2Ca 3Cu 4O 12−δ
superconductor thin films. The influence of the nature of grain boundaries on the inter-granular critical current density
( J
c) has also been investigated. From the power law dependence of H
ac∼(1− T
p/ T
c)
n
, it was observed that n=1 gives a best fit for the J
c of thallium rich samples and n=2 provides a best fit for the J
c of the samples with small amount of thallium. The polycrystalline thin film samples showing the power law dependence of J
c as n=1 make superconductor-insulator-superconductor (SIS) type while the samples with n=2 follow superconductor-normal metal-superconductor (SNS) types of Josephson junctions. The insulating grain boundaries decrease
the inter-granular Josephson coupling and hence the transport properties are suppressed.
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