共查询到20条相似文献,搜索用时 15 毫秒
1.
Calculations are performed together with the summarization of published data on the measurement of positron annihilation rates in a number of simple substances. The information potential of different methods underlying positron annihilation spectroscopy is analyzed as applied to the study of condensed matter. The features of the mechanism of positron annihilation in metals are discussed. The possibility of investigating the electronic and defect structures of metals and alloys using the method of the time distribution of annihilation photons is considered. 相似文献
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A. D. Rychkov V. E. Zarko V. D. Liseikin A. V. Kofanov 《Thermophysics and Aeromechanics》2010,17(4):587-594
Thermal interaction of a thermocouple embedded into a solid substance pyrolyzed by an external heat source with the thermal
wave propagating inward the substance from the pyrolysis surface is considered. Numerical simulations show that a heat sink
through thermocouple wires inward the substance occurs because of a significant difference in thermal conductivities of the
solid substance and thermocouple material, which leads to substantial changes in thermojunction, thus, distorting thermocouple
data. 相似文献
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An equation is derived on semi-theoretical grounds which expresses the solid-vapour surface free energy as a function of the liquid surface tension and the solid-liquid interfacial free energy. A means of calculating reliable values for the solid-liquid energy is presented, which then allows an accurate estimate of solid surface energy at the melting temperature, Tm, to be made for the large number of elements for which dependable liquid surface tension data exist. A method of estimating surface entropy is presented, and has been used to calculate the energies typical of “average”, high-index surfaces at temperatures ranging from 0 K to Tm. It is felt that this paper describes the most accurate method presently available for the calculation of the surface energy of solids in the absence of direct experimental measurement. 相似文献
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How to concentrate non-maximally entangled states for quantum communication is a fundamental problem in quantum information. In this paper, we will apply generalized measurements to entanglement concentration of known non-maximally entangled pure states in arbitrary dimensional system. How to design the generalized measurements for the unambiguous discrimination of linearly independent non-orthogonal states is crucial for the concentration of the known non-maximally entangled states. The result shows that, any known non-maximally entangled pure state (for arbitrary dimensional system) can be transformed to the maximally entangled state only by introducing a qubit as ancilla and a joint unitary transformation operation on one of the entangled particles and the ancilla. In addition, because the less entangled state of each fail round will be re-concentrated too, the entanglement waste during the concentration process will be greatly reduced. 相似文献
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Physics of Atomic Nuclei - A method for measuring the volume distribution of hydrogen in various objects by means of tagged neutron probing is proposed. The existing probing methods, which permit... 相似文献
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Cottrell’s binding energy between a dislocation and vacancy and concentration of vacancies has been calculated using ultrasonic
attenuation measurements in single crystals of pure tin at 300K for frequencies varying from 3 to 50 MHz and at different
dislocation densities. 相似文献
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We report measurements of the pressure and (?P/?T)V in samples of solid hydrogen of orthohydrogen concentrations of 40–55% and 150 mK ? T ? 1 K. No evidence of a first or second order phase transition is seen at temperatures associated with the formation of a quadrupolar glass. 相似文献
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A one-laser-shot measurement technique, which can characterize the nonlinear optical properties of the film prepared on the opaque substrates conveniently and exactly, is presented. This method is based on the reflection 4f coherent imaging system with phase objects. The proposed technique is examined in the case of a novel ultrathin film [CuPc(COONa)4]/PDDA coated on an opaque silicon substrate with 532 nm picosecond laser pulses. By measuring the reflected intensity, but not the transmitted one, we verify both nonlinear absorption and refraction of the coated thin film. This progress obviously ensures that nonlinearities caused by reflection of opaque surfaces are measurable. 相似文献
10.
Stefan A. Maier 《Optical and Quantum Electronics》2006,38(1-3):257-267
The controlled squeezing of electromagnetic energy into nanometric volumes via surface plasmon-polariton excitations in plasmonic nanoresonators is analyzed using the concept of an effective electromagnetic mode volume V eff, while taking careful account of the plasmon-polariton dispersion and the electromagnetic energy stored in the metal. Together with the quality factor Q of the cavity resonance, this enables a comparison with dielectric optical cavities, where V eff is limited by diffraction. For a Fabry–Perot type planar metallic cavity, a one-dimensional analytic model as well as a three-dimensional finite-difference time-domain simulation reveal that V eff is not bounded by diffraction, and that Q/V eff increases for decreasing cavity size. In this picture, matter–plasmon interactions can be quantified in terms of Q and V eff, and a resonant cavity model for the enhancement of spontaneous Raman scattering is presented. 相似文献
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We consider the dynamics of small closed submanifolds (‘bubbles’) under the volume preserving mean curvature flow. We construct a map from (\(\text {n}+1\))-dimensional Euclidean space into a given (\(\text {n}+1\))-dimensional Riemannian manifold which characterizes the existence, stability and dynamics of constant mean curvature submanifolds. This is done in terms of a reduced area function on the Euclidean space, which is given constructively and can be computed perturbatively. This allows us to derive adiabatic and effective dynamics of the bubbles. The results can be mapped by rescaling to the dynamics of fixed size bubbles in almost Euclidean Riemannian manifolds. 相似文献
13.
D. Brüggemann 《Il Nuovo Cimento D》1992,14(10):1075-1084
Summary Different strategies are discussed to use CARS spectroscopy for measuring mole fractions of combustion species. The influence
of various physical parameters on both shape and total intensity of spectral bands is studied. Two variants for concentration
measurements are compared based either on spectralshape analysis or frequency-integrated intensity ratios. The analysis leads
to the conclusion that concentrations from a spectral-shape fit are more sensitive to inaccuracies of input parameters than
band intensities.
Paper presented at the ?XI European CARS Workshop?, Florence, Italy, 23–25 March, 1992. 相似文献
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采用激光测量了蔗糖溶液的旋光率及其浓度,利用计算机实时采集数据并输出图形,使实验具有直观、准确度高、操作简便等特点. 相似文献
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The velocities of ultrasonic waves have been measured in solidified argon in the pressure range up to 6 kb (600 MPa). Shear wave velocities could be measured to temperatures very close to the melting point, such that both liquid and solid phases coexisted, . The measurements show that neither the shear velocity tends to zero nor its derivative with temperature tends to -8 as T→Tm. 相似文献
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We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique capable of high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the ν1+ν3 water vapor combination band near ˜ν=7181.156 cm-1, we compare spectroscopic and thermodynamic determinations of trace water vapor in N2, and find systematic differences attributable to water vapor background effects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, the frequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1.2×10-10 cm-1 Hz-1/2, which further corresponds to a minimum detectable water vapor mole fraction equal to 0.7×10-9 for an absorption spectrum of 10 minutes duration. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi 相似文献
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C. Gericke R. Ghose G. J nsson K. Freyer H. -C. Treutler W. Enge 《Radiation measurements》1999,31(1-6):363-366
An experimental calibration of indoor room and outdoor soil detector devices which are based on LR 115 as sensitive element has taken place at the Swedish Radiation Protection Institute in Stockholm (Sweden) in 1994 and 1996, at the Physikalisch-Technischen Bundesanstalt in Braunschweig (Germany) in 1997 and at the Umweltforschungszentrum Leipzig-Halle (Germany) in 1997. Special properties of the used solid state nuclear track detector (SSNTD) material LR 115* have been measured to define the application of the experimental calibration. 相似文献
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In a preceding study a new technique to non-invasively measure the bladder volume on the basis of non-linear wave propagation was validated. It was shown that the harmonic level generated at the posterior bladder wall increases for larger bladder volumes. A dedicated transducer is needed to further verify and implement this approach. This transducer must be capable of both transmission of high-pressure waves at fundamental frequency and reception of up to the third harmonic. For this purpose, a multi-layer transducer was constructed using a single element PZT transducer for transmission and a PVDF top-layer for reception. To determine feasibility of the multi-layer concept for bladder volume measurements, and to ensure optimal performance, an equivalent mathematical model on the basis of KLM-circuit modeling was generated. This model was obtained in two subsequent steps. Firstly, the PZT transducer was modeled without PVDF-layer attached by means of matching the model with the measured electrical input impedance. It was validated using pulse-echo measurements. Secondly, the model was extended with the PVDF-layer. The total model was validated by considering the PVDF-layer as a hydrophone on the PZT transducer surface and comparing the measured and simulated PVDF responses on a wave transmitted by the PZT transducer. The obtained results indicated that a valid model for the multi-layer transducer was constructed. The model showed feasibility of the multi-layer concept for bladder volume measurements. It also allowed for further optimization with respect to electrical matching and transmit waveform. Additionally, the model demonstrated the effect of mechanical loading of the PVDF-layer on the PZT transducer. 相似文献