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1.
The acoustic emission from collapsing cavitation bubbles generated using ultrasound of 20 kHz and 515 kHz frequencies in water has been measured and correlated with sonoluminescence and hydroxyl radical production to yield further information on the frequency dependence of sonochemical reactions. A reasonable correlation was found, and the results suggest differences in the predominant types of cavitation observed under laboratory conditions.  相似文献   

2.
In this study, the current–voltage (IV) characteristics of Au/Poly(4-vinyl phenol)/p-Si structures have been measured over a wide temperature range (100–300 K). These structures have been analyzed according to thermionic emission (TE) theory, as a result of which an abnormal decrease occurred in the zero-bias barrier height (fb0 \phi_{b0} ) and an increase in the ideality factor (n) was observed with temperature decrease and nonlinearity in the activation energy plot. By assuming a Gaussian distribution (GD) of barrier heights of the Au/Poly(4-vinyl phenol)/p-Si structures, barrier inhomogeneities are believed to responsible for this behavior. Evidence is given for the existence of a double GD with mean barrier heights ([`(f)]b0 \bar{\phi }_{b0} ) of 1.042 and 0.623 eV, standard deviations of 0.138 and 0.081 V, and ideality factors 2.76 and 7.26, which remain effective in the temperature ranges of 180–300 and 100–160 K, respectively. As a result, without using the temperature coefficient of the barrier height, the modified ln(I o /T 2) − q 2 σ o 2/2(kT)2 vs. q/kT plot gives [`(f)]b0 \bar{\phi }_{b0} values and Richardson constants (A * ) as 1.036 and 0.623 eV, and 36.20 and 19.99 A/cm2 K2, respectively. The effective Richardson constant value of 36.20 A/cm2 K2 is very similar to the theoretical value of 32 A/cm2K2 for p-Si. Consequently, the temperature dependence of the forward bias IV characteristics of Au/Poly(4-vinyl phenol)//p-Si (MIS) structure could be attributed to the thermionic emission (TE) mechanism with double GD of the barrier heights.  相似文献   

3.
The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high‐intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au3+ to Au0 by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size‐ and shape‐controlled metal nanoparticles.  相似文献   

4.
The title complexes (NH4)3[YIII(Nta)2] (I) (H3Nta = nitrilotriacetic acid) and {K[YIII(Egta)] · 4H2O} n (II) (H4Egta = ethyleneglycol-bis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) were prepared, and their molecular and crystal structures were determined by single-crystal X-ray diffraction techniques. Complex I crystallizes in the rhombohedral crystal system with R $ \bar 3 $ \bar 3 c space group. The central Y3+ ion is eight-coordinated by two nitrogen and six oxygen atoms, which come from two tetradentate Nta ligands. The crystal data are as follows: a = 7.9340(14) ?, c = 54.611(15) ?, V = 2977.1(11) ?3, Z = 6, ρcalcd = 1.738 mg/cm3, μ = 3.011 mm−1, F(000) = 1596, R = 0.0234 and wR = 0.0641 for 686 observed reflections with I ≥ 2σ(I). The {K[YIII(Egta)] · 4H2O} n is nine-coordinated by two nitrogen and seven oxygen atoms and produces a 1D unlimited zigzag-type chain through a bridging carboxylic group. {K[YIII(Egta)] · 4H2O} n crystallizes in the monoclinic crystal system with C2/c space group. The crystal data are as follows: a = 37.588(5) ?, b = 13.7101(19) ?, c = 8.6070(12) ?, β = 99.929(2)°, V = 4369.0(11) ?3, Z = 8, ρcalcd = 1.753 mg/cm3, μ = 2.934 mm−1, F(000) = 2368, R = 0.0385 and wR = 0.0800 for 4082 observed reflections with I ≥ 2σ(I).  相似文献   

5.
The temperature dependence of the heat capacity C p o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C p o(T), H o(T)-H o(0), S o(T)-S o(0), and G o(T)-H o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δc H o, and the thermodynamic characteristics of formation Δf H o, Δf S o, and Δf G o at 298.15 K and p = 0.1 MPa.  相似文献   

6.
The dependence of the intensity (I i ) of X-ray fluorescence on the size (D) of finely ground particles was studied for saturated and unsaturated samples. It was found that even at the wet grinding (addition of ethanol) of powders with D < 10 μm, the aggregation and covering of larger grains (α) with smaller grains of different compositions occur, which changes the character of the dependence I i = f(D), particularly, if fluorescence is emitted by the grains α. The nature of the observed effects is proved by the results of granulometric analysis and by electron probe X-ray analysis. In the transition from saturated to unsaturated samples, the discussed effects are enhanced.  相似文献   

7.
In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between 6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C p 0 (T), H 0(T)-H 0(0), S 0(T)-S0(0), G 0(T)-H 0(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH comb 0 and thermodynamic parameters of formation-enthalpies ΔH f 0, entropies ΔH f 0, Gibbs functions ΔG f 0 - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH f 0S f 0, ΔG f 0) of phenylated polyphenylene synthesis in the range from 0 to 340 K. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The luminescence excitation spectra and the luminescence spectra of the I2 + Rg (Rg = He, Ar, Xe; p Rg = 2–20 Torr) mixtures measured at room temperature by the method of double optical resonance in the spectral range corresponding to the population of the I2(f0 g +, v f = 8.9) levels and in its vicinity are analyzed in this work. The experimental data and their interpretation, according to which these spectra can be explained by the energy transfer in the intermediate I2(B0 u +) and final I2(f0 g +) states of the free iodine molecule rather than by the optical population, luminescence, and predissociation of the ion-pair RgI2(IP) complexes, are discussed. It is shown that these data can be explained only with account taken of the optical population of the RgI2(IP) complexes. Original Russian Text ? M.E. Akopyan, S.S. Lukashov, S.A. Poretsky, A.M. Pravilov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 1, pp. 132–141.  相似文献   

9.
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n0.42(1−α)0.56.  相似文献   

10.
刘岩  张志强 《无机化学学报》2007,23(11):1979-1982
采用气液传质的双膜理论建立了开放体系中声化学反应的动力学模型,同时用声源频率为500 kHz,声强为3 W·cm-2的超声波在开放式声化学反应器内引发被空气饱和溶解的KI纯水溶液中的声化学反应,并检测反应过程中溶液的电导率,pH值改变及KI溶液中I2的析出量,结果表明,它们与超声辐照时间之间呈线性关系,与理论模型吻合。  相似文献   

11.
The analyses of the composition of a binary mixture composed of two kinds of industrial complicated materials have great importance for formulation in practice. The present paper provides a quantitative size exclusion chromatography (SEC) method based on the principle of absolute quantification of SEC to solve the problem. The conventional data treatment procedure for the differential refractive index (DRI) signal of SEC H(V) is improved first by dividing it with the injected sample weight and leads to a novel defined weight normalized distribution H w(V) and its integral I w(V). These two distributions reflect the response constant of the sample in addition to the conventional normalized distribution F(V). The difference of the average response constants of the composing components provides a sensitive method to compute the composition of their mixture from its H w(V) or I w(V). The method was applied to mixtures of a kind of industrial asphalt and paraffin diluents as an example, and successful results are obtained. __________ Translated from Acta Polymerica Sinica, 2007, 8: 689–692 [译自:高分子学报]  相似文献   

12.
To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τp=3 × 10−13 s, fp = 0.5 Hz, Ep = 1.1 × 10−3J cm−2, Iav = 5.5 × 10−4 W cm−2, Ip = 109 W cm−2) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm−2). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 103 lower for pulsed radiation than for CW radiation (3.3 × 10−1 and 7.8 × 102 J cm−2 respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.  相似文献   

13.
The temperature dependence of heat capacity of C70 fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic characteristics were determined. From the experimental data obtained, the thermodynamic functionsH o (T)-H o(0),S o(T),G o(T)-H o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δf S o, Δf G o, and logK f o for the formation of C70 from graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998.  相似文献   

14.
Magnetic exchange couplings in bis(ketimide) binuclear UIV/UIV complexes [Cp′2UCl]2(μ-ketimide) diuranium(IV) and [(C5H5)2(Cl)An]2(μ-ketimide) (Cp′ = C5Me4Et; ketimide = N=CMe-(C6H4)-MeC=N) have been investigated computationally using relativistic density functional theory (DFT) combined with the broken symmetry (BS) approach. Using the B3LYP hybrid functional, the BS ground state of these UIV/UIV 5f 2–5f 2 complexes has been found of lower energy than the high spin (HS) quintet state, indicating an antiferromagnetic character (estimated coupling constant |J| < 5 cm−1) which has not yet been evidenced unambiguously experimentally. On the contrary, the BP86 GGA functional overestimates greatly the antiferromagnetic character of the complexes (|J| > 100 cm−1). As recently reported for para-bis(imido) [(C5H5)3U]2(μ-imido) uranium(V) complex, spin polarization is mainly responsible for the antiferromagnetic coupling through the π-network orbital pathway within the bis(ketimide) bridge. Furthermore, spin polarization is exalted by the combined roles of the 5f metal orbitals and of the π-conjugated ketimide bridging ligand which permit electronic communication between the two uranium atoms albeit separated by a distance of the order of 10 ?. The MO analysis clarifies which MOs contribute to the antiferromagnetic coupling in the binuclear complexes under consideration and brings to light the 5f orbitals driving contribution.  相似文献   

15.
Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La0.8Sr0.2)0.9MnO3 (LSM)–Gd0.2Ce0.8O1.9(GDC) composite powder (LSM ~70 wt%, GDC ~30 wt%) was prepared through modification of LSM powder by Gd0.2Ce0.8(NO3) x solution impregnation, followed by calcination. The electrode polarization resistance of the LSM–GDC cathode prepared from the composite powder was ~0.60 Ω cm2 at 750 °C, which is ~13 times lower than that of pure LSM cathode (~8.19 Ω cm2 at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSM–GDC composite cathode at 700 °C under 500 mA/cm2 was ~0.42 Ω cm2, which is close to that of pure LSM cathode at 850 °C. Gd0.2Ce0.8(NO3) x solution impregnation modification not only inhibits the growth of LSM grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O2-δ, leading to the significant reduction of electrode polarization resistance of LSM cathode.  相似文献   

16.
The temperature dependence of the heat capacity C p o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86 K. Standard thermodynamic functions C p o(T), H o(T) — H o(0), S o(T), and G o(T) — H o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium oxide are recommended: S o(298.15) = 39.58 ± 0.15 J/(K mol), Δf H o(298.15) = −112.69 ± 0.32 kJ/mol, Δf G o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)2 (amorph.) with respect to PdO(cr.) was estimated.  相似文献   

17.
It is shown that the cross product t I J (R x )≡g I J (R x h I J (R x ), where g τ I J (R)=(c I (R x )−c J (c I (R x )+c J (R x )), h τ I J (R)=c I (R x ) c J (R x ), τ is an internal nuclear coordinate, the c I (R) satisfy [H(R)−E I (R)]c I (R)=0 and H(R) is the electronic Hamiltonian matrix, is a unique property of a conical intersection at R x . t I J (R x )=0 when R x is located at the intersection of two (or more) seams of conical intersection. This criterion for an intersection of two seams of conical intersection has important implications for algorithms that seek to locate such points. Here it␣is␣used to analyze the trifurcation of a generic C2v 2S+1 A2S+1 B seam of conical intersection, analogous to those recently found in AlH2 and CH2. Received: 31 July 1997 / Accepted: 27 August 1997  相似文献   

18.
Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde (GA) in the aqueous phase, where the gelatin concentration was fixed at 5 (w/v) and the GA concentration was varied from 1×10−5 to 1×10−3 (w/v). The dynamic structure factor, S(q,t), was deduced from the measured intensity autocorrelation function, g 2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−D f q 2 t)+Bexp(−tc)β, both in the sol (50 and 60 C) and gel states (25 and 40 C). The fast-mode diffusion coefficient, D f showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, ξ, of the crosslinked network exhibited strong temperature dependence, ξ∼(0.5−χ)1/5exp(−A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched exponential factor exp(−tc)β. β was found to be independent of GA concentration but strongly dependent on the temperature as β=β01 T2 T 2. The slow-mode relaxation time, τc, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found τc(c)=τ01 c2 c 2. Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state. Received: 25 May 1999 /Accepted in revised form: 27 July 1999  相似文献   

19.
The thermal neutron cross-sections and resonance integrals of the 186W (n,γ) 187W and 98Mo (n,γ) 99Mo reactions in the thermal and 1/E regions, respectively, of a thermal reactor neutron spectrum have been experimentally determined by the activation method using 197Au (n,γ) 198Au reaction as a single comparator. The high purity natural W, Mo, and Zr foils; and Au wire diluted in aluminum, were irradiated without Cd shield in two neutron irradiation sites, characterized with different values for the thermal-to-epithermal flux ratios, f at the Second Egyptian Research Reactor (ETRR-2). The induced activities in the samples were measured by high-resolution γ-ray spectrometry with a calibrated germanium detector. Thermal neutron cross-sections for 2200 m/s neutrons and resonance integrals for the 186W (n,γ) 187W and 98Mo (n,γ) 99Mo reactions have been obtained relative to the reference values, σ0 = 98.65 ± 0.09 b and I 0 = 1500 ± 28 b for the 197Au (n,γ) 198Au reaction. The necessary correction factors for thermal neutron and resonance neutron self-shielding effects, and the epithermal flux index (α) were taken into account in the determinations. The results obtained were: σ0 = 38.43 ± 0.4 b and I 0 = 502 ± 65 b for 186W (n,γ) 187W, and σ0 = 0.137 ± 0.014 band I 0 = 6.47 ± 0.8 for 98Mo (n,γ) 99Mo. These results are discussed and compared with previous measurements and evaluated data in literature. The traditional method of determining thermal cross-sections and resonance integrals via neutron irradiation with and without Cd shield in one irradiation position was avoided in this work by neutron irradiation without Cd shield in at least two different neutron irradiation positions. This method provides alternative way for determining thermal cross-sections and resonance integrals simultaneously.  相似文献   

20.
The residual or doped element concentration [E] in GaAs measured by SSMS is only accurate with respect to the relative sensitivity coefficient RSCE. For a trace element concentration, the RSCE = [E]SSMS/[E]TRUE is set to unity, if no reference material or method is available to approximate the concentration to the true value. For boron a relative sensitivity coefficient of RSCB = 0.94 ± 0.08 was obtained using TI-IDMS as a reference method. RSCN = 1 is used for nitrogen determinations. A boron and nitrogen detection limit of 4.4 × 1013 cm–3 is achieved. SSMS was used as reference method to calibrate the FTIR factor fE = [E] / Iα due to the integrated local vibrational mode absorption Iα of atomic boron and nitrogen in GaAs. A factor of fB = (12.0 × 2.7) × 1016 cm–1 (517 cm–1) and fN = (7.4 ± 0.1) × 1015 cm–1 (472 cm–1) was obtained for a boron and nine nitrogen containing GaAs samples at 77 K and 10 K, respectively. Received: 15 December 1998 / Revised: 8 April 1999 / Accepted: 13 April 1999  相似文献   

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