Numerical investigation of the effect of the Prandtl number on the temperature recovery and the Reynolds analogy factors in the boundary layer on a plate

We performed a numerical study of the boundary layer on a wall in a supersonic gas flow using a differential turbulence model. The dependences of the recovery factor and the Reynolds analogy factor on the main flow parameters, such as the Reynolds, Mach, and Prandtl numbers, are obtained for a series of the temperature factor values. The results of calculations are approximated by the dependences of the recovery factor and the Reynolds analogy factor on the Prandtl number.     

Reconfiguration of spectral absorption features using a frequency-chirped laser pulse

A technique is proposed to manipulate atomic population in an inhomogeneously broadened medium, which can set an arbitrary absorption spectrum to a uniform transparency (erasure) or to a nearly complete inversion. These reconfigurations of atomic spectral distribution are achieved through excitation of electronic transitions using a laser pulse with chirped frequency, which precisely affects selected spectral regions while leaving the rest of the spectrum unperturbed. An erasure operation sets the final atomic population inversion to zero and the inversion operation flips the population between the ground and the excited states, regardless of the previously existing population distribution. This technique finds important applications both in optical signal processing, where fast, recursive processing and high dynamic range are desirable and in quantum memory and quantum computing, which both require high efficiency and high fidelity in quantum state preparation of atomic ensembles. Proof-of-concept demonstrations were performed in a rare-earth doped crystal.     

Quasi-balanced two-wave mixing interferometer for remote ultrasound detection

We present an improved detection scheme for a two-wave mixing interferometer with a Bi₁₂SiO₂₀ crystal. The proposed detection scheme allows quasi-balanced detection of ultrasonic signals whereby electrical disturbances are suppressed. Quasi-balancing is achieved by changing the polarity of the high voltage at the photorefractive crystal, leading to an inversion of the optical interference signal, in combination with inversion of the detector signal using a signal inverter before the data acquisition device. The polarity of the high voltage is changed by utilizing an H-bridge consisting of five high-voltage relays. Microcontrollers are used to synchronize the reversion of the high voltage at the photorefractive crystal and the inversion of the measured signals. We demonstrate remote measurement of ultrasonic waves and shown that electrical disturbances are suppressed using the quasi-balanced mode.     

Measurement of atomic concentrations in reacting flows through the use of stimulated gain or loss

Apump laser at 226 nm was used to generate a population inversion between the 3p (3)P(2) and 3s (3)S(1) states of the oxygen atom in the postflame gases of a 7-torr H(2)/O(2) flame by means of resonant two-photon absorption from the ground state. The inversion produced an amplified spontaneous emission (ASE) signal at 845 nm. A probe laser tuned to this transition was crossed at a small angle with the pump beam. The probe beam experienced gain at the expense of theASE signal. By analyzing the gain on the probe beam and the loss on the ASE signal, we have determined the density of oxygen atoms in the flame environment.     

Standoff determination of the particle size and concentration of small optical depth clouds based on double-scattering measurements: validation with calibrated target plates and limitations for daytime and nighttime measurements

Diffractive target plates are used to emulate aerosols of known size and concentration. These target plates are used to validate and determine the sensitivity of a multiple-field-of-view lidar signal inversion technique based on double-scattering measurement to retrieve the particle size and the concentration of small optical depth clouds. We estimate that nighttime and daytime quantification (size and concentration) is possible for optical depths as low as 0.005 and 0.016, respectively. The recovery technique limiting factors are the shot noise, the laser features, the optical lens quality, the background illumination level, the background aerosol fluctuations, and the noise introduced by the lidar detector, a gated intensified camera (camera G-ICCD).     

Discrete Fourier Transform for Short Samples in the Presence of Noise

We consider the dependences of the error of a discrete Fourier transform on the length of the realization of the considered signal. The introduction of a procedure of making a preliminary determination of the period makes it possible to consider signals in short samples and this significantly reduces the computing and apparatus costs.     

Inversion of elastic characteristics of beryllium condensate under the action of weak magnetic field

We have studied the effect of a weak magnetic field (∼10⁻³–10⁻² T) on the elastic and inelastic characteristics of a diamagnetic beryllium condensate. It is established that the field effect is most pronounced in a magnetic aftereffect, which leads to inversion of the amplitude and temperature dependences of the effective shear modulus at an almost unchanged level of the elastic energy absorption.     

Measurement of intensity of the second optical harmonic in heteroepitaxial cadmium-mercury telluride structures

Features of the generation of the second optical harmonic in the heterostructures HgCdTe/GaAs and CdTe/HgCdTe/GaAs manufactured by means of molecular-beam epitaxy are experimentally investigated for the first time. The dependences of the intensity of a nonlinearly optical signal on the direction of the pumping radiation polarization and the position of the laser beam on the study surfaces are measured for a pure monocrystalline substrate and for a sample with a deposited functional polycrystalline CdTe layer. Substantial differences between these dependences are discovered.     

Measurement of Small Lateral Vibrations of Speckle Patterns Using a Non-steady-state Photo-EMF in GaAs: Cr

Abstract

We report the observation of a non-steady-state photo-EMF generated in a semi-insulating GaAs: Cr crystal by vibrating speckle patterns. The experimentally observed basic dependences of the output signal on the vibration frequency and amplitude as well as on the light intensity are in reasonable agreement with those observed earlier for vibrating sinusoidal light patterns. Using this novel technique, lateral vibrations of diffusely scattering objects can be easily detected over a wide range of frequencies and amplitudes.     

Removal of Probe Liftoff Effects on Crack Detection and Sizing in Metals by the AC Field Measurement Technique

In the alternative current field measurement (ACFM) technique, the nonzero value of liftoff distance for the magnetic sensor acts as a low-pass filter on surface crack signals, causing errors in crack detection and sizing. We present a blind deconvolution algorithm for liftoff evaluation and surface crack signal restoration. The algorithm employs the available closed-form expressions for the distribution of electromagnetic fields at the metal surface in the vicinity of a crack. To examine the accuracy of the algorithm, we use the original and the restored signals for crack sizing by a wavelet network inversion method. We present simulated and experimental results to demonstrate the role of the proposed algorithm in improving the inversion process.      

Quantum Optics with One Atom in an Optical Cavity

Abstract

The quantum mechanical master equation for a single two-level atom in a single-mode optical cavity is numerically solved in both the quantum and the semiclassical limits. The quantum limit of few cavity photons shows semiclassically forbidden behaviour such as steady state two-level population inversion. Qualitatively new fluorescent spectra, having sidebands broadened by the cavity interaction, also occur. The quantum theory of the single-atom laser with injected signal is presented. At the interface between its quantum and semiclassical dynamics we elucidate the signature of semiclassical limit cycles.     

Collapse-revival Phenomenon in the Jaynes-Cummings Model Interacting with the Multiphoton Holstein-Primakoff SU(2) Coherent State

Abstract

We have analysed the behaviour of the atomic population inversion of the two-level atom interacting with a single-mode field initially prepared in the multiphoton Holstein-Primakoff SU(2) coherent state. It is shown that the behaviour of the atomic inversion depends on the parameters characterizing the initial state of the field. In particular, the atomic inversion can exhibit periodical oscillations as well as the collapse-revival phenomenon.     

The evolution of a cavitation zone in a focused ultrasonic field

We have experimentally studied the generation of sonoluminescence (SL) and cavitation noise in the field of a focusing ultrasonic radiator during a gradual smooth increase in the applied voltage. In addition to the SL signal, we have recorded the output signal of a hydrophone situated behind the focal region of the radiator and measured the cavitation-noise spectrum. Four stages in the development of a cavitation zone have been distinguished as manifested by the specific character of dependences of the measured parameters on the voltage applied to the radiator. Spectral signs of the cavitation-noise characteristic of each stage of development of the cavitation zone.     

On the Variation of Ortho-hydrogen and?Para-hydrogen Ratio with Magnetic Field Strength at?Low Temperature

We report inversion of population between the ortho and para states of hydrogen at very low temperature with homogeneous external magnetic field. At low temperature, one needs to apply very high magnetic fields to get this population inversion when ortho states will be more populated than the para one. A?numerical study of the change of bond length with magnetic field has been employed to find the precise field strengths at crossover points.     

Population trapping in the Jaynes-Cummings model with a Kerr nonlinearity in the cavity

Abstract

An electromagnetic field state is found which maintains the population inversion of the atom stationary during the interaction with the field through a Jaynes-Cummings model (JCM) with a Kerr type nonlinearity in the cavity. The condition of stationarity of the population inversion includes the phase coupling of atomic dipole with the field. We have shown that the Kerr nonlinearity in the cavity field significantly modifies the photon statistics of the trapped field state through an intensity dependent detuning in the field compared to the normal JCM trapping state. We have also demonstrated the novel features of sub-Poissonian character and the squeezing of the trapped field state. The dynamics of the initial trapped field is studied in terms of squeezing and the Q-function.     

Effect of non-stoichiometry on oxidation processes in n-type PbTe thin films

The dependences of the galvanomagnetic and thermoelectric properties on the thicknesses d (5-200 nm) of PbTe thin films prepared by the thermal evaporation of non-stoichiometric PbTe with 2 at.% excess lead were studied, with measurements conducted in air at room temperature on freshly grown films. It was established that with decreasing film thicknesses, an inversion of the dominant charge carrier sign from n to p takes place at d∼40 nm. A comparison of the results obtained in this work with those for PbTe films prepared from stoichiometric PbTe showed that the increase in n-type charge carrier concentration results in a shift of the inversion point to smaller d values. The observed effect is attributed to oxidation processes taking place in PbTe thin films at room temperature in air, and the effect is interpreted in terms of compensating acceptor states created by oxygen on the film surface.     

Nonlinear forward scattering in cesium vapor: experiment with simultaneous scanning of laser frequency and B-field

We present the results of an experimental study of nonlinear magneto-optical rotation in a buffer-gas-free uncoated Cs cell on hyperfine transitions F(g) = 3 --> F(e) = 2, 3, 4 of the D(2) line at high laser irradiance (up to 40 mW/cm(2)). The measurements were done in a forward scattering configuration, with simultaneous linear scanning of laser frequency and magnetic field at different temporal rates. The latter revealed, in a single measurement, the dependences of maximum nonlinear Faraday signal and the corresponding B-field on the laser frequency within the Doppler profile.     

Motion artifacts of pulse inversion-based tissue harmonic imaging

Motion artifacts of the pulse inversion technique were studied for finite amplitude distortion-based harmonic imaging. Motion in both the axial and the lateral directions was considered. Two performance issues were investigated. One is the harmonic signal intensity relative to the fundamental intensity and the other is the potential image quality degradation resulting from spectral leakage. A one-dimensional (1-D) correlation-based correction scheme also was used to compensate for motion artifacts. Results indicated that the tissue harmonic signal is significantly affected by tissue motion. For axial motion, the tissue harmonic intensity decreases much more rapidly than with lateral motion. The fundamental signal increases for both axial and lateral motion. Thus, filtering is still required to remove the fundamental signal, even if the pulse inversion technique is applied. The motion also potentially decreases contrast resolution because of the uncancelled spectral leakage. Also, it was indicated that 1-D motion correction is not adequate if nonaxial motion is present.     

Electromagnetic NDE signal inversion by function-approximation neural networks

In the magnetic flux leakage (MFL) method of nondestructive testing commonly used to inspect ferromagnetic materials, a crucial problem is signal inversion, wherein the defect profiles must be recovered from measured signals. This paper proposes a neural-network-based inversion algorithm to solve the problem. Neural networks (radial-basis function and wavelet-basis function) are first trained to approximate the mapping from the signal to the defect space. The trained networks are then used iteratively in the algorithm to estimate the profile, given the measurement signal. The paper presents the results of applying the algorithm to simulated MFL data.     

Deriving Analytical Expressions for the Ideal Curves and Using the Curves to Obtain the Temperature Dependence of Equation-of-State Parameters

Different equations of state (EOSs) have been used to obtain analytical expressions for the ideal curves, namely, the Joule–Thomson inversion curve (JTIC), Boyle curve (BC), and Joule inversion curve (JIC). The selected EOSs are the Redlich–Kwong (RK), Soave–Redlich–Kwong (SRK), Deiters, linear isotherm regularity (LIR), modified LIR (MLIR), dense system equation of state (DSEOS), and van der Waals (vdW). Analytical expressions have been obtained for the JTIC and BC only by using the LIR, MLIR, and vdW equations of state. The expression obtained using the LIR is the simplest. The experimental data for the JTIC and the calculated points from the empirical EOSs for the BC are well fitted into the derived expression from the LIR, in such a way that the fitting on this expression is better than those on the empirical expressions given by Gunn et al. and Miller. No experimental data have been reported for the BC and JIC; therefore, the calculated curves from different EOSs have been compared with those calculated from the empirical equations. On the basis of the JTIC, an approach is given for obtaining the temperature dependence of an EOS parameter(s). Such an approach has been used to determine the temperature dependences of A ₂ of the LIR, a and b parameters of the vdW, and the cohesion function of the RK. Such temperature dependences, obtained on the basis of the JTIC, have been found to be appropriate for other ideal curves as well.