Local Defect Resonance (LDR): A Route to Highly Efficient Thermosonic and Nonlinear Ultrasonic NDT

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A local defect resonance for linear and nonlinear ultrasonic thermography

An efficient wave-defect interaction is the key to a high thermal response of flaws in ultrasonic thermography. To selectively enhance defect vibrations a concept of local defect resonance is developed and applied to ultrasonic activation of defects. The frequency match between the defect resonance frequency and the probing ultrasonic wave results in a substantial rise of a local defect temperature. The defect resonance is accompanied by depletion of the excitation frequency vibration due to nonlinear frequency conversion to higher harmonics. The local generation of higher frequency components provides a high thermal defect response in such an acoustically nonlinear thermography mode

Invisible Quarkonium Decays as a Sensitive Probe of Dark Matter

We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model - dark matter interaction, it can mediate invisible decays of quarkonium states such as the $\Upsilon$, $J/\Psi$, and $\eta$. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric $\mu$ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing B-factories running at the $\Upsilon(4S)$ can produce lower $\Upsilon$ resonances by emitting an Initial State Radiation (ISR) photon. Using a combination of ISR and radiative decays, the initial state of an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to the spin and CP-nature of the particle that mediates standard model-dark matter interactions. These measurements can discover or place strong constraints on dark matter scenarios where the dark matter is approximately lighter than the $b$-quark. For the decay chains $\Upsilon(nS) \to \pi^+ \pi^- \Upsilon(1S)$ (n=2,3) we analyze the dominant backgrounds and determine that with $400 fb^{-1}$ collected at the $\Upsilon(4S)$, the B-factories can limit BR(\Upsilon(1S) \to invisible) \lsim 0.1%.Comment: 20 pages, 1 figure, accepted for publication in PR

Highly-Sensitive Defect-Selective Imaging and NDT via Resonant Nonlinearity of Defects

AbstractIn this paper, it is proposed to use a combination of mechanical resonance and nonlinearity of defects to enhance substantially the efficiency of input-output frequency conversion in nonlinear NDT. The concept of a defect as a nonlinear oscillator brings about new dynamic and frequency scenarios characteristic of nonlinear and parametric oscillations. The experiments confirm transition to resonant modes of nonlinear vibrations in simulated and realistic defects. All resonant nonlinear modes are strongly localised in the defect area that provides a background for high-contrast highly-sensitive defect- and frequency-selective imaging

Descent methods with linesearch in the presence of perturbations

AbstractWe consider the class of descent algorithms for unconstrained optimization with an Armijo-type stepsize rule in the case when the gradient of the objective function is computed inexactly. An important novel feature in our theoretical analysis is that perturbations associated with the gradient are not assumed to be relatively small or to tend to zero in the limit (as a practical matter, we expect them to be reasonably small, so that a meaningful approximate solution can be obtained). This feature makes our analysis applicable to various difficult problems encounted in practice. We propose a modified Armijo-type rule for computing the stepsize which guarantees that the algorithm obtains a reasonable approximate solution. Furthermore, if perturbations are small relative to the size of the gradient, then our algorithm retains all the standard convergence properties of descent methods

He-broadening and shift coefficients of water vapor lines in infrared spectral region

The water vapor line broadening and shift coefficients in the ν1+ν2, ν2+ν3, ν1+ν3, 2ν3, 2ν1, 2ν2+ν3, and ν1+2ν2 vibrational bands induced by helium pressure were measured using a Bruker IFS 125HR spectrometer. The vibrational bands 2ν3 and ν1+2ν2 were investigated for the first time. The interaction potential used in the calculations of broadening and shift coefficients was chosen as the sum of pair potentials, which were modeled by the Lennard-Jones (6-12) potentials. The vibrational and rotational contributions to this potential were obtained by use of the intermolecular potential parameters and intramolecular parameters of H2O molecule. The calculated values of the broadening and shift coefficients were compared with the experimental data. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only