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1.
Summary The experimental temperature dependence of the heat capacityC p(T) of solid tin (Sn) in its premelting region 402.07–502.22 K was investigated and two regions with different temperature dependences ofC p(T) were found. In the far (from the melting temperatureT m) region 402.07–485.88 K the experimentalC p(T) of Sn is described by the standard vacancy model. In the close region 485.88–502.22 K it is described by the formation of complicated volumetric defects in the crystalline lattice of solid Sn near itsT m.  相似文献   

2.
The evidence of the change of the complex refractive index function E(m) of carbon and iron nanoparticles as a function of their size was found from two-color time-resolved laser-induced incandescence (TiRe-LII) measurements. Growing carbon particles were observed from acetylene pyrolysis behind a shock wave and iron particles were synthesized by pulse Kr–F excimer laser photo-dissociation of Fe(CO)5. The magnitudes of refractive index function were found through the fitting of two independently measured values of particle heat up temperature, determined by two-color pyrometry and from the known energy of the laser pulse and the E(m) variation. Small carbon particles of about 1–14 nm in diameter had a low value of E(m)∼0.05–0.07, which tends to increase up to a value of 0.2–0.25 during particle growth up to 20 nm. Similar behavior for iron particles resulted in E(m) rise from ∼0.1 for particles 1–3 nm in diameter up to ∼0.2 for particles >12 nm in diameter.  相似文献   

3.
The ferrihydrite mineral core of ferritin is a semi-conductor capable of catalyzing oxidation/reduction reactions. This report shows that ferritin can photoreduce AuCl4 to form gold nanoparticles (AuNPs). An important goal was to identify innocent reaction conditions that prevented formation of AuNPs unless the sample was illuminated in the presence of ferritin. TRIS buffer satisfied this requirement and produced AuNPs with spherical morphology with diameters of 5.7 ± 1.6 nm and a surface plasmon resonance (SPR) peak at 530 nm. Size-exclusion chromatography of the AuNP–ferritin reaction mixture produced two fractions containing both ferritin and AuNPs. TEM analysis of the fraction close to where native ferritin normally elutes showed that AuNPs form inside ferritin. The other peak eluted at a volume indicating a particle size much larger than ferritin. TEM analysis revealed AuNPs adjacent to ferritin molecules suggesting that a dimeric ferritin–AuNP species forms. We propose that the ferritin protein shell acts as a nucleation site for AuNP formation leading to the AuNP-ferritin dimeric species. Ferrihydrite nanoparticles (~10 nm diameter) were unable to produce soluble AuNPs under identical conditions unless apo ferritin was present indicating that the ferritin protein shell was essential for stabilizing AuNPs in aqueous solution.  相似文献   

4.
The magnetocaloric properties of cobalt ferrite nanoparticles were investigated to evaluate the potential of these materials as magnetic refrigerants. Nanosized cobalt ferrites were synthesized by the method of sol–gel combustion. The nanoparticles were found to be spherical with an average crystallite size of 14 nm. The magnetic entropy change (ΔS m) calculated indirectly from magnetization isotherms in the temperature region 170–320 K was found to be negative, signifying an inverse magnetocaloric effect in the nanoparticles. The magnitudes of the ΔS m values were found to be larger when compared to the reported values in the literature for the corresponding ferrite materials in the nanoregime.  相似文献   

5.
Conjugated polyamides containing porphyrin and [60]fullerene (C60) in the main chain were prepared by a direct polycondensation of the 3′H,3″H-dicyclopropa[1, 9:16, 17] [5, 6]fullerene-C60-I h -3′,3″-dicarboxylic acid and 5,15-bis(4-aminophenyl)-10,20-bis(3,5-dialkoxyphenyl)porphyrin in the presence of triphenyl phosphite and pyridine. Gel permeation chromatography (GPC) analysis of the polyamides showed the weight-average molecular weight was about 23,626–23,736, and the temperature at 5% weight loss determined by thermogravimetric analysis (TGA) was above 216 °C. The transmission electron microscopy (TEM) images displayed the regular one-dimensional linear arrays of the polyamides with lengths exceeded 200 nm. The photoinduced electron transfer from porphyrin to C60 in the polyamides was observed in nanosecond laser-flash photolysis experiments at ambient temperature, which produced a charge-separated state (porphyrin radical cation–C60 radical anion pair) with a lifetime as long as 40 μs. The calculated ratio of k CS/k CR was found to be 2.1 × 104. They could have potential applications for photoelectronic devices, organic solar cells and so on.  相似文献   

6.
The phase transitions Pm3mP4mm and domain-structure formation in 5–500 μm isometric PbTiO3 crystals were investigated. The phase transition is characterized by a high rate and by the formation of a single flat interphase boundary {023}. A size effect was observed: In crystals smaller than a critical size (about 20 μm), formation of 90° domains stops and, in agreement with a phenomenological theory, the temperature hysteresis of the phase transition doubles. Fiz. Tverd. Tela (St. Petersburg) 40, 1546–1547 (August 1998)  相似文献   

7.
The mass spectra of secondary cluster ions Bi n + (n = 1–9) from bismuth sputtered by (6–21) keV Au m (m = 1–9) and Bi m (m = 1–5) cluster ions have been investigated. New features of manifestation of dense nonlinear cascades and thermal spikes have been revealed. It is concluded that the thermal spike regime makes a significant contribution to the mechanism of formation of small cluster ions, containing up to seven atoms for a bismuth target.  相似文献   

8.
The effect of easy-plane anisotropy on the damping of the nonlinear magnetization oscillations that accompany 90° pulsed magnetization of magnetic films and plates is analyzed numerically. It is shown that the magnetization time can be decreased to ∼0.5 ns at an effective anisotropy field H K p ≥ 6 kOe and that magnetization oscillations are fully damped at H K p ≥ 20–40 kOe. The magnetization time can be ∼0.15–0.20 ns at a magnetizing pulse amplitude H m ∼ 20–40 Oe.  相似文献   

9.
Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with controlled particle size were synthesized with simple variation of concentration of gelatin by reducing in situ tetrachloroauric acid with sodium citrate. The nanoparticles showed excellent colloidal stability. Transmission electron microscopy (TEM) revealed the formation of well-dispersed gold nanoparticles (AuNPs) with different sizes. The methodology produces particles 10–15 nm in size depending on the concentration of gelatin used. The measured AuNPs are 10, 11, 12, 13, 14, and 15 nm for AuNPs-gelatin 1, 0.5, 0.25, 0.1 and 0.05%, and pure AuNPs, respectively. The AuNPs-gelatin exhibit size-dependent localized surface plasmon resonance behavior as measured by UV–visible spectroscopy. UV–vis spectroscopy and TEM results suggest that higher concentration of gelatin favor smaller particle size and vice versa. FTIR spectroscopy analysis of AuNPs-gelatin revealed the amino bands and carboxyl peak of gelatin. The crystalline nature of AuNPs was investigated by X-ray diffraction.  相似文献   

10.
The canonical statistical model analysis of strange and multistrange hadron production in central AA relative to pp/pA collisions is presented over the energy range from GeV up to GeV. It is shown that the relative enhancement of strange particle yields from pp/pA to AA collisions substantially increases with decreasing collision energy. It is largest at GeV, where the enhancement of and is of the order of 100, 20 and 3, respectively. In terms of the model these results are due to the canonical suppression of particle thermal phase space at lower energies, which increases with the strangeness content of the particle and with decreasing size of the collision fireball. The comparison of the model with existing data on the energy dependence of the kaon/pion ratio is also discussed. Received: 25 October 2001 / Published online: 5 July 2002  相似文献   

11.
The process of new-phase nucleation in the YBa2Cu3O7−x system deposited by magnetron sputtering has been studied. The first experimental observation of the phenomenon of temporal self-organization in the course of new-phase formation, which was predicted theoretically,1–3 is reported. Auto-oscillations in the number of nuclei of various chemical compounds 20–60 nm in size were observed to occur within the 15 to 300-s time interval, the total number of nuclei varying aperiodically from 1013 m−2 to less than 1011 m−2. Fiz. Tverd. Tela (St. Petersburg) 39, 216–218 (February 1997)  相似文献   

12.
A method of calculating the effective deformation-potential constant E 1 for holes and longitudinal acoustic phonons in isotropic polycrystalline silicon is suggested. The deformation-potential constant E 1 is estimated through the deformation potentials a, b, and d of the silicon single crystal. The procedure of averaging of the squared modulus of the hole and acoustic phonon interaction Hamiltonian written in the plane wave basis over the polycrystal ensemble provides the basis for calculation of the constant E 1 . It is demonstrated that for T = 200–600 K, hole concentration p = (5.0–10.0)∙1019 cm–3, and crystallite size d = 300–3000 ?, the deformationpotential constant E 1 is independent of the hole concentration p, temperature T, and crystallite size d.  相似文献   

13.
Motivated by the study of multivortices in the Electroweak Theory of Glashow–Salam–Weinberg [33], we obtain a concentration-compactness principle for the following class of mean field equations: on M, where (M,g) is a compact 2-manifold without boundary, 0 < aK(x)≤b, xM and λ > 0. We take with α i > 0, δ p i the Dirac measure with pole at point p i M, i= 1,…,m and ψ∈L (M) satisfying the necessary integrability condition for the solvability of (1)λ. We provide an accurate analysis for solution sequences of (1)λ, which admit a “blow up” point at a pole p i of the Dirac measure, in the same spirit of the work of Brezis–Merle [11] and Li–Shafrir [35]. As a consequence, we are able to extend the work of Struwe–Tarantello [49] and Ding–Jost–Li–Wang [21] and derive necessary and sufficient conditions for the existence of periodic N-vortices in the Electroweak Theory. Our result is sharp for N= 1, 2, 3, 4 and was motivated by the work of Spruck–Yang [46], who established an analogous sharp result for N= 1, 2. Received: 24 September 2001 / Accepted: 7 December 2001  相似文献   

14.
We developed a new spectrofluorometric method for qualitative and quantitative determination of cyanide in water using the incorporation of naphthoquinone imidazole boronic-based sensors (m -NQB and p -NQB) and a cationic surfactant, certyltrimethyl ammonium bromide (CTAB). This micellar system exhibited great selectivity for cyanide detection with an assistance of the cationic surface of micelle. The interaction of boronic acid of the sensor toward cyanide in CTAB micellar media gave a quantitative measure of cyanide concentration in the micromolar level. Under the optimal condition, fluorescence intensity at 460 nm of m -NQB and p -NQB provided two sets of linear ranges, 0.5–15 μM and 20–40 μM and the limit of cyanide detection of 1.4 μM. Hence, both sensors in CTAB aqueous micellar system offered a considerably promising cyanide detection with 1000–fold enhancement of the detection limit compared to those studied in DMSO: H2O. The proposed sensors could also be used to determine cyanide in water with good analytical characteristics.  相似文献   

15.
The differential cross section of the reaction D(e,pp)eπ is measured in the range of proton momenta 300–720 MeV/c and proton emergence angles 64–83° for invariant masses of the pp system ranging from 2m p to 2220 MeV/c 2. The measured values of the cross section are found to differ substantially from single-particle model calculations. The components of the analyzing power for this reaction are measured. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 730–736 (25 May 1998) Deceased.  相似文献   

16.
The excess 1/f noise in a random lattice with bond resistances r∼exp(−λx), where x is a random variable and λ≪1, is studied theoretically. It is shown that if the correlation function {δr 2}∼r r θ+2, then the relative spectral density of the noise in the system is expressed as C e∼λm exp(−λ(1−p c)), where p c is the percolation threshold and md (ν is the critical exponent of the correlation length and d is the dimensionality of the problem). It is hypothesized that the exponent m possesses a dual universality: It is independent of 1) the geometry of the lattice and 2) the θ-mechanism responsible for the generation of the local noise. Numerical modeling in a three-dimensional lattice gives m=52.3 for θ=1 and θ=0, in agreement with the hypothesis. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 614–618 (25 April 1996)  相似文献   

17.
The refractive index of soot is an essential parameter for its optical diagnostics. It is necessary for quantitative interpretation of LII (Laser Induced Incandescence) signals, light scattering or extinction measurements as well as for emissivity calculations. The most cited values have been determined by intrusive methods or without taking into account the soot size distribution and its specific morphology. In the present study, soot generated by the combustion of diesel and diesel/rapeseed methyl ester (RME) mixture (70% diesel and 30% RME) are extensively characterized by taking into account the morphology, the aggregate size distribution, the mass fraction and the spectral dispersion of light. The refractive index m for wavelengths λ between 300 and 1000 nm is determined for diesel and diester fuels by both in-situ and ex-situ methods. The ex-situ method is based on the interpretation of extinction spectra by taking into account soot sizes and fractal morphology with the RDG-FA (Rayleigh–Debye–Gans for Fractal Aggregate) theory. The in-situ approach is based on the comparison of the LII signals obtained with two different excitation wavelengths. The absorption function E(m) and the scattering function F(m) are examined. This study reveals similar optical properties of soot particles generated by both studied fuels even at ambient and flame temperatures. The function E(m) is shown to reach a maximum for λ=250 nm and to tend toward a plateau-like behavior close to E(m)=0.3 for higher wavelength (600<λ (nm)<1000). The function F(m) is found to be quite constant for 400<λ (nm)<1000 and equal to 0.31.  相似文献   

18.
The thermo-optic coefficients, dn/dT, were determined for pure and Yb(20 at.%)-doped monoclinic KY(WO4)2 crystals for light polarized along the optical indicatrix axes (N p,N m and N g) in the wavelength range of 0.36–1.06 μm by a laser beam deviation method. The absolute values of thermo-optic coefficients satisfy the relation |dn p/dT|>|dn g/dT|>|dn m/dT| and increase with the wavelength increasing. In the long-wavelength range, all the dn/dT values are negative: dn p/dT=−14.6, dn m/dT=−8.9, dn g/dT=−12.4 [10−6 K−1] for pure KY(WO4)2 at 1.06 μm. The dependency of thermo-optic coefficients on the wavelength was modeled using an approach that takes into account contribution of volumetric thermal expansion and change of electronic bandgap with temperature. Large volumetric expansion of KY(WO4)2 plays a key role in the observed negative dn/dT values. Electronic bandgap and its temperature coefficient were determined for KY(WO4)2 crystals from thermo-optic dispersion curves as E g=4.8–5.0 eV and −dE g/dT=0.7–1.1×10−4 eV/K. Athermal propagation directions were calculated for KY(WO4)2 crystals at the wavelength of 1.06 μm for light polarizations EN m and N p.  相似文献   

19.
The electroplex between (2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole) zinc [Zn(4-TfmBTZ)2] as an electron-acceptor and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) as an electron-donor was characterized by bilayer, blend, and multilayer quantum-well (MQW) device, respectively. The blend composition and quantum-well number are effective parameters for tuning electroluminescence color. White light with high color purity and color rendering index (CRI) was observed from these devices based on Zn(4-TfmBTZ)2/NPB. Moreover, the blend and MQW devices all exhibit high operation stability, hence excellent color stability. For the device with 5 mol% NPB in blend layer, its Commission International Del’Eclairage (CIE) coordinate region is x=0.28–0.31, y=0.33–0.35 and CRI is 83.3–91.2 at 5–9 V. For MQW structure device with NPB of 60 nm thickness, its CIE coordinate region is x=0.29–0.32, y=0.31–0.34 and CRI=87.9–92.5 at 10–15 V. Such high color stability and purity and CRI, being close to ideal white light, are of current important for white OLED.  相似文献   

20.
The microscopic mechanisms controlling the atomic rearrangements during agglomeration of Ni particles 3 to 7 nm in size at temperatures T = 0.6–0.95 T m have been studied by the molecular dynamics method. Pentagonally twinned crystals were obtained as a result of coalescence for the disorientations corresponding to special Σ11 and Σ27 large-angle boundaries.  相似文献   

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