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1.
本文在Thomas-Fermi势能基础上,导出了全射程R的解析解:R=2/a[E 1/2-A 1(arctg(2E 1/2-f)/△ 1/2+arctg f/△ 1/2)+B 1ln((E 1/2-f) 2)/(E-fE 1/2+d) ·d/f 2],其中A 1,B 1,f,d和△均为与离子及靶的质量、原子序数有关的常数。结合导出的η=R/(R p)(R p指投影射程)比值的双曲线函数关系 η=F(μ)[A 2(μ)+(B 2(μ))/(ε 1/2+C)],和ω=R p/△R p(△R p指投影射程的标准偏差)比值的线性关系ω=A 3(μ)ε 1/21/2+B 3(μ),可简便而又准确地计算R,△R p,R p.这里F(μ),A 2(μ),B 2(μ), B 3(μ)和A 3(μ)为μ的代数函数,μ为离子与靶的质量比,C是经验常数.并对η等关系式的物理意义作了讨论。上述公式的计算结果与Gibbons的数值解结果及有关实验结果作了比较,表明可用于元素半导体如Si、二元化合物如GaAs以及三元化合物如SiO 2等;既对较轻离子适用,也对重离子适用,具有一定的普适范围。 相似文献
2.
The mean-square radius of gyration of poly(methyl methacrylate) (PMMA) with Bemoullian statistics was theoretically investigated utilizing the method of periodic condition. The dependent curve of the characteristic ratio of mean-square end-to-end distance on periodic microstructure length increases monotonously with the length and goes gradually to its asymptotic value for atactic PMMA chains ( P m = 0.5). Conformational energies E α ~1.3 kcal mol ?1 and E β ~-0.6 kcal mol ?1 of the two-state scheme are acceptable, from which the derived meansquare end-to-end distance and mean-square radius of gyration conform to the experimental data. The ratio ?S 2? /χ of atactic PMMA ( P m = 0.2) as a function of the degree of polymerization χ first increases with increasing chain length, then passes through a maximum at χ = 30, and finally decreases to its asymptotic value, which is in reasonable agreement with the experimental measurements reported elsewhere. The ratio ?S 2? /χ as a function of stereochemical composition indicates that theoretical and experimental data are in accord for isotactic and atactic PMMA, but small-angle neutron scattering (SANS) measurements are higher than the calculated values for syndiotactic PMMA. 相似文献
3.
The (Bi 1/9Na 2/3)(Mn 1/3Nb 2/3)O 3 ceramics with perovskite structure were sintered. The XRD test proved that the samples are cubic ( a?=?3.920?±?0.001?Å). Microstructure and atomic composition were determined with a SEM (JSM-5410) equipped with energy dispersion X-ray analyser (ISIS-300). The fluctuation in the chemical composition was found indicating on local disorder. Broadband dielectric spectroscopy in the range 10 ?1–3?·?10 7?Hz was applied within the range of 100–650?K. The real, ?′( f,? T), and imaginary, ?″( f,? T), parts of complex dielectric permitivity characteristics, both in the temperature and frequency domain, show relaxation processes partially covered by electric conductivity. At high temperatures the electric conductivity exhibits a thermally activated behaviour σ( f,? T)?∝?exp(? E a/ kT) but the variable range hopping (VRH) dependence σ?∝?exp[?( T 0/ T) 1/4] is manifested at low temperatures. The derivatives technique in the frequency (??log??/??log?ω) and temperature (??log??/? T) domain enabled various relaxation processes to be distinguished. The data converted to electric modulus representation, M*( f,? T)?=?1/?*, exhibited clearly resolved relaxation peaks. The relaxation times obtained from the peaks position show a slightly non-Arrhenius temperature behaviour with the activation energy varying in 0.4–0.6?eV range and characteristic time of the electric conductivity relaxation of the order of 10 ?12?s. The relaxation times can be fitted at better accuracy with the VRH dependence where T 0 are of the order of 10 8?K. It is shown that the low frequency ac-conductivity converges to dc-conductivity and the relation σ(0)?~?ω m?~?τ m ?1 typical for the disordered solids applies. The conduction current relaxation relationship behaves in accord with the VRH system: σ dc?∝?( T/ T 0) q ( e 2/ kT) ω c, where ω c?=?ν ph exp[?( T 0/ T) 1/4] is valid for the locally disordered (Bi 1/9Na 2/3)(Mn 1/3Nb 2/3)O 3 compound. 相似文献
4.
Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T carb ranging from 600 to 1600°C have been studied. The dependences E( T carb) and δ( T carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, Δ E ~ AΔ T carb and Δδ ~ BΔ T carb, with A ≈ 13.4 MPa/K and B ≈ ?2.2 × 10 ?6 K ?1 for T carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ ?3.0 × 10 ?7 K ?1 for T carb > 1000°C. The transition observed in the behavior of E( T carb) and δ( T carb) at T carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature. 相似文献
5.
Novel polyurethane (PU) adhesive was prepared and coated on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/fullerene (PMMA/Full-C 60) composite. Dip-coating technique was employed as facile and cost-effective procedure to coat polyurethane on film substrate. The properties of PU/PMMA and PU/PMMA/Full-C 60 composite were studied using Fourier transform infrared spectroscopy, Field Emission Scanning Electron Microscopy, tensile, adhesion, thermal and flammability measurement. Testing polyurethane-coated PMMA exhibited crumpled surface while fullerene addition formed unique pattern of dispersed spherical structures. Fullerene nanofiller loading improved the adhesion and mechanical properties of composite films due to polymer–carbon interaction. In PU/PMMA/Full-C 60 0.5 composite with 0.5 wt.% nanofiller, tensile strength (71.4 MPa) was increased by 18.6% while tensile modulus was increased by 143.85% compared with PU/PMMA. In PU/PMMA/Full-C 60 0.5, T0 of 473 °C and Tmax of 655 °C were observed. Increasing the fullerene content up to 0.5 wt.% decreased the peak heat release rate to 131 kW/m 2. Novel polyurethane-coated PMMA/Full-C 60 composite have potential applications as adhesive coatings in electronic and automotive appliances. 相似文献
6.
Although PVDF/PMMA blends have been studied extensively, the phase behavior as a function of melt quenching conditions has not been examined in detail in the past. In this paper we report our results on the isotropic blends of PVDF/PMMA quenched into ice water as well as on a casting roll set at 30°C in all composition ranges. The results confirm the miscibility of this blend for all composition ranges, although at high PVDF (~85%) concentration micro heterogeneities were evidenced through thermal analysis. Though pure PVDF is observed to be mostly in the α crystalline form, the addition of PMMA favors the β crystal structure in composition range 85/15–60/40. Ice water quenching yields amorphous blends containing more than 40% PMMA and these films are deemed good candidates for rubbery state processes (between T g and T cc), including tenter frame biaxial stretching, where they can be oriented significantly at these low temperatures while undergoing strain induced crystallization. 相似文献
7.
Extending our earlier findings for [3.3]paracyclophane, NMR line shape studies of the conformational dynamics in [3.2] and [4.3]paracyclophanes are reported, of which the former is conformationally homogeneous and the latter occurs in two enantiomeric forms. For [3.2]paracyclophane, the Arrhenius activation energy Ea = 11.6 ± 0.1 kcal/mol and preexponential factor log ( A/s ?1) = 12.92 ± 0.07 were found. In [4.3]paracyclophane, the conformational dynamics are quite complicated because, apart from interconversions of each enantiomer into itself proceeding via inversion of the propano bridge with rate constant k1, the enantiomers mutually rearrange with rate constant k2 due to inversion of the butano bridge. The determination of Arrhenius parameters from dynamic 1H spectra of the aromatic protons for these two conformational processes ( Ea = 11.2 ± 0.5 kcal/mol and log ( A/s ?1) = 13.6 ± 0.5 for the former, and Ea = 9.7 ± 0.4 kcal/mol and log ( A/s ?1) = 13.2 ± 0.4 for the latter) is the highlight of this work. In the investigated temperature range, in [4.3]paracyclophane, the occurrence of other conformational processes beyond those mentioned above can be excluded, because they would produce different line shape patterns than those actually observed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
The prompt gamma-ray/X-ray emission of gamma-ray burst (GRB) 060218 was simultaneously observed by the Burst Alert Telescope (BAT) and X-ray Telescope (XRT) onboard Swift. Its peak energy of the joint vf
v
spectrum (E
p) clearly evolves with time from tens of keV to ∼1 keV, crossing both the BAT and XRT bands. The best fit yields log E
p=(4.61±0.23)+(−1.29±0.08) log t, with a correlation coefficient of 0.98 and a chance probability of p<10−4. We derive its bolometric flux (F) in the 0.01–104 keV band, and find that its F-E
p relation, with a power-law index of 0.37, is much shallower than that observed in typical GRB pulses. Discussion of this shallowness is presented. 相似文献
9.
Pyroelectric detection of a CO 2 laser beam has been investigated by using organic copolymers such as VDF/TrFE- and VDCN/VAc copolymers, and compared with that of PVDF polymer. The voltage responsitivies R
v are 40 mV/W for VDF/TrFE and 2 mV/W for VDCN/VAc at room temperature and at a chopping frequency of 200 Hz. (For comparison, the value of PVDF is 20 mV/W.) From the frequency dependence of the detected output, the electric time constant E is evaluated to be about 6.4 ms and 2.6 ms for the former and latter copolymers with the detection area 3×3 mm 2, respectively. Some theoretical discussion is also given of the responsivity, frequency dependence and temperature dependence obtained. 相似文献
10.
Crystals of KZnF 3 and KMgF 3 doped with Mn 2+ and Ni 2+ were used to study the spectroscopic properties of Mn 2+-F --Ni 2+ pairs. Pair transitions to the doubly excited states 4 Eg a , 4 A 1g (Mn) 3 T 1g a (Ni) and 4 Eg b (Mn) 3 T 1g a (Ni) were observed. The participation of the spin-allowed 3 A 2g → 3 T 1g a excitation on Ni 2+ in the pair transition is explained by spin-orbit mixing between 3 T 1g a and 1 Eg . The prominent electronic origins are assigned to the double spin-flip transitions 6 A 1g (Mn) 3 A 2g (Ni) → 4 Egu(Mn) 3 T 1g a (Γ 3) v(Ni) and 4 A 1g (Mn) 3 T 1g a (Γ 3) v(Ni). The former lie at lower energy and are more intense than the corresponding 6 A 1g (Mn) 3 A 2g (Ni) → 4 Egv(Mn) 3 T 1g a (Γ 3) u(Ni) transitions involving two orbital jumps. The well-resolved vibronic structure is composed of three basic vibrations of ~ 150 cm -1, ~ 294 cm -1 and ~ 508 cm -1 in the KZnF 3 host. 相似文献
11.
The threshold temperature T
t at which thermally generated vacancies produce measurable positron trapping is a linear function of the energy of self-diffusion Q. Since Q is also linearly related to the vacancy formation energy E
1v
f
, a measurement of T
t leads directly to a determination of the latter. It is possible to make a precise determination of E
1v
f
without approaching the melting point—a major advantage in dealing with refractories or with metals having a high vapour
pressure in the solid state. 相似文献
12.
Abstract Radiation defects created by γ-irradiation of Co 60 and fast neutrons in high purity p-Si ( p = 5×10 3 to 4 × 10 4 Ω.cm) and n-Si ( p = 4 × 10 2 to 5 × 10 3 Ω.cm) are investigated by measurements of Hall effect, resistivity and minority carrier lifetime. The oxygen concentration in the crystals is in the range of 5 × 10 14 to 5 × 10 15 cm ?3. It is shown that stable γ-defects at 300 °K are divacancies and complexes of vacancies with donor or acceptor impurities. Divacancies introduced by γ-irradiation are the secondary defects. They become predominant after ‘exhaustion’ of the dopant. When divacancies become the predominant defects the Fermi level occupies its boundary position Ev +0.39 eV in the gap. At low doses (Φ<10 16 photons/cm 2) vacancy-impurity complexes and at heavy doses (Φ>10 17 photons/cm 2) divacancies play the main role in the recombination process. In neutron irradiation disordered regions are introduced and the level at Ev +0.35 eV is observed. The Fermi level in both n- and p-Si shifts to the middle of the gap. At the annealing of disordered regions in the interval 200 to 250 °C the level at Ev +0.27 eV appears and Fermi level occupies its boundary position at Ev +0.39 eV. This indicates that divacancies become the predominant defects which can be formed as secondary defects at the destruction of the disordered regions. 相似文献
13.
Dynamic mechanical analysis (DMA) is used to investigate the effect of alkyl side chain length on the relaxation behavior of poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) above the glass transition temperature (T g). Master curves and shift factors (log a T) were obtained using the time–temperature superposition (TTS) principle. The log a T curves of PnAA and PnAMA exhibit a dynamic crossover from one Vogel–Fulcher–Tammann–Hesse (VFTH) equation to another above T g. The corresponding temperature was designated as the dynamic crossover temperature (T c). It is found that T c/T g and the apparent activation energy (E g) increases, e whereas the fragility index (m) decreases with increasing alkyl side chain length. Further analysis shows that m ∝ T g, E g∝ , and E g∝ m 2 for both PnAA and PnAMA. 相似文献
14.
本文从描述光激射器工作的基本方程出发,讨论了光激射器光束线宽的“短期”(short-time)部分。通常都以下式描写这部分线宽:△v s=(8πhv(△v′) 2)/P,(1)其中△v′是谐振腔电磁模的半宽度;v为光束频率;P为输出功率。我们的主要结论可以归结为以下三点:(1)线宽主要是由与电磁模耦合的耗散体系引起的,与分子耦合的耗散体系的贡献是可以忽略的;(2)在单模近似下,只要分子的线宽比电磁模的线宽大得多,则(1)式是正确的;(3)如果多模谐振腔中激发模与其他模之间的相互作用是强的,则式(1)将被推广为 △v s=(8πhv(△v′) 2)/P+(4hv(△v′))/P somefromn=(λ′≠λ)(r λλ′2/(rλ′),(2) 其中r λλ′是相关弛豫系数;r λ′是模λ′的线宽。在某些情况下,式(2)中第二项可以比其第一项还大。所以,这可能是目前关于线宽的实验结果与由式(1)计算结果不相符合的原因之一。 相似文献
15.
In a dc glow discharge in oxygen, the concentrations of minor components of O 2( a1Δ g), O 2( b1 Σ g), O 3, O( 1D), as well as nagative ions and electrons have been measured. Balance equations have been derived which describe satisfactorily the stationary concentrations of these components as functions of gas pressure and discharge current. For the first time, the rate constants of important aeronomical reactions (a) O ? + O 2(a 1Δ g) → O 3 + e, (b) O 2? + O 2(a 1Δ g) → 2O 2 + e and (c) e + O 3 → O 2? +O have been measured as functions of gas temperature T and mean energies of ions Ei and electron E6: K a = (2.5 ± 0.5) · 10 ?9 · ( T/300) 4 ± 0.4· (E i/0.04) ?2.6 ± 0.4 cm 3/s for T = 385?605 K and Ei = 0.10 ? 0.66 eV; Kb = (1.0 ± 0.3) · 10 ?10 · ( T/300) ?2 ± 0.5 · ( Ei/0.04) 0.23 ± 0.05 cm 3/s for T = 330?605 K and Ei = 0.09 + 1.5 eV; Kc for Ee = 0.8÷5 eV. 相似文献
16.
Abstract Generation of microcellular poly(methy1 methacrylate) (PMMA) was studied in CO 2 and N 2O at pressures from 2 to 15MPa at three temperatures, 293.2K, 308.2K, and 323.2 K. The average diameter d and average number density N of voids generated by a rapid expansion of compressed gases in PMMA were measured by use of an optical microscope. Effects of gases, temperature, and pressure on the d and N values were examined. Even at pressure below glass transition pressure of PMMA with both gases, voids of diameter being as small as those found at high pressure, 15MPa, were obtained at each temperature. However, the void density of PMMA at lower pressure by both gases was not so good as those obtained at high pressures. 相似文献
17.
ABSTRACTThe sound velocity properties of single-crystal rhodochrosite (MnCO 3) were determined up to 9.7?GPa at ambient temperature by Brillouin scattering spectroscopy. Six elastic constants were calculated by a genetic algorithm method using the Christoffel's equations at each pressure. The elastic constants increased linearly as a function of pressure and its pressure derivatives ? Cij/? P for C 11, C 33, C 44, C 12, C 13, C 14 were 5.86 (±0.36), 3.82 (±0.44), 2.06 (±0.39), 5.07 (±0.27), 5.34 (±0.44), 1.52 (±0.24), respectively. Based on the derived elastic constants of rhodochrosite, the aggregate adiabatic bulk and shear moduli ( Ks and G) were calculated using the Voigt-Reuss-Hill averages and the linear fitting coefficients (? Ks/? P) T and (? G/? P) T were 5.05(±0.26) and 0.73(±0.05), respectively. The aggregate Vp of rhodochrosite increased clearly as a function of pressure and its pressure derivative ? Vp/? P was 7.99(±0.53)?×?10 ?2?km/(s?GPa), while the aggregate Vs increased slowly and ? Vs/? P was only 1.19(±0.12)?×?10 ?2?km/(s?GPa). The anisotropy factor for As of rhodochrosite increased from ~40% at 0.8?GPa to ~48% at 9.7?GPa, while Ap decreased from ~19% to ~16% at the corresponding pressure. 相似文献
18.
The kinetics of carbamate formation from the reaction of carbon dioxide with α‐amino acids in D 2O was first investigated by means of nuclear magnetic resonance spectroscopy. Potassium carbonate was used as the CO 2 source. For each amino acid, the maximum carbamate yield, the apparent rate constant for the carbamate formation kapp, and the rate constants for the formation k1 and the breakdown k?1 of the carbamate were estimated. Plots of log k1 or log k?1 versus p Ka of amino acids indicated that the formation rate k1 increased with the basicity (p Ka) of amino acid, while the decomposition rate k?1 decreased. A Br?nsted β value of 0.39 was obtained from the former plot, being in good agreement with the previously reported ones (0.26–0.43). The observed negative p Ka dependence of log k?1 (Br?nsted α = 0.34) is reasonable, because the carbamate decomposition is acid‐catalyzed and the steady‐state concentration of H + should be higher for weaker basic amines. The charge (σ) and the lone‐pair energy ( EN) at the nitrogen atom of the amino group were calculated. Although log k1 correlated with σ and EN, log k?1 was unrelated with both of these parameters. Considering that the carbamate formation ( k1) is not only base‐catalyzed but should also be promoted by the nucleophilicity of the amino nitrogen, its correlation with σ and EN in addition to p Ka is rational. The irrelevance of log k?1 to σ and EN is not surprising, because σ and EN are not a direct measure of [H +] of the solution. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
Expressions for power reflection ( R), transmission ( T) and absorption ( A) coefficients for p-polarized wave for a warm, collisional, magnetized and moving plasma slab (with sharp boundaries and thickness d0) are investigated. The effects of plasma slab velocity (β= v/c), electron density (ω p/ω) 2 and plasma temperature ( KBT) on reflection ( R), transmission ( T) and absorption ( A) coefficients are discussed numerically. It is observed that for the value β=?0.6, reflection coefficient ( R) becomes more than unity, whereas absorption coefficient ( A) becomes quite negligible while transmission coefficient ( T) shows oscillatory behaviour. The variation with plasma frequency (ω p/ω) 2 shows that at lower plasma frequency (ω p/ω) 2=0.2 transmission ( T) and absorption ( A) coefficients are minimum while reflection coefficient ( R) is maximum. 相似文献
20.
Fluorescence spectra of crystalline tetracene have been recorded in the temperature range 120 to 300 K under hydrostatic pressure up to 600 MPa. From discontinuities in both emission spectra and spectral intensities it is concluded that two phase transitions occur. The room temperature phase is transformed to a low temperature phase/high pressure phase I at TIt ( p = 0) = 182 K, the temperature coefficient being d TIt/d p = 0.395 K/MPa. The phase transition is induced by a decrease of the specific volume under pressure and/or upon cooling. Lack of a significant shift of the origin of the fluorescence band near TIt at constant pressure is an artifact resulting from the neglect of reabsorption effects. The Stokes shift is 260 cm -1, independent of temperature and crystal modification. In accord with previous Raman data a second phase transition occurs at TIIt ( p) = 143 K, the pressure shift being d TIIt/d p = 0.088 K/MPa.In addition, the shift of the triplet energy as a function of pressure as well as the pressure-dependence of the rate constants governing fission of a singlet exciton into a pair of triplets is discussed utilizing their magnetic field dependences. 相似文献
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