Wave Configuration Research Articles

Influence of the adiabatic index on switching between different types of shock wave reflection in a steady supersonic gas flow

A comprehensive pattern of different types of shock wave reflection in a steady supersonic gas flow is analytically constructed with regard to a new wave configuration found by the authors-negative-angle irregular reflection. A double Mach reflection with a negative reflection angle in a steady supersonic gas flow is numerically obtained for the first time.

Spin Wave Excitation and Propagation Properties in a Permalloy Film

Spin wave excitation and propagation properties in a permalloy were investigated using a vector network analyzer for the magnetostatic surface wave (MSSW) and magnetostatic backward volume wave (MSBVW) configurations. In the MSSW configuration, the excitation and transmission spectra show many peaks. They originate at the distance of antenna lines of the coplanar waveguide, and the waveguide design is important for selecting the excitation and transmission wave vectors of the spin wave. The attenuation length of the MSSW was estimated to be 7.1 µm, and the group velocity of the MSSW with a wave number of 0.26 µm-1 was estimated to be about 8.6 µm/ns for an external magnetic field of 20 mT. In the MSBVW configuration, however, the excitation spin wave spectrum shows a single peak, since many quantized peaks overlap. A transmission signal with a single peak was also detected, but this could be an artifact such as an induced current.

High-efficiency cross-phase modulation in a gas-filled waveguide

Strong cross-Kerr non-linearities have been long sought after for quantum information applications. Recent work has shown that they are intrinsically unreliable in travelling wave configurations: cavity configurations avoid this, but require knowledge of both the non-linearity and the loss. Here we present a detailed systematic study of cross-phase modulation, and absorption, in a rubidium vapour confined within a hollow-core photonic crystal fibre. Using a two-photon transition, we observe phase modulations of up to $\pi$rad with a signal power of 25$\mu$W, corresponding to a non-linear Kerr coefficient, $n_2$, of $0.8 \times 10^{-6}$ cm$^2$/W, or $1.3 \times 10^{-6}$ rad per photon.

Nonlinear dynamics of magnetohydrodynamic shallow water flows over an arbitrary surface

The magnetohydrodynamic equations system for a heavy fluid over an arbitrary surface in shallow water approximation is studied. All self-similar discontinuous and continuous solutions are found. The exact explicit solutions of the initial discontinuity decay problem over a flat plane and a slope are found. It is shown that the initial discontinuity decay solution is represented by one of five possible wave configurations. For each configuration the necessary and sufficient conditions for its realization are found. The changes in dependent and independent variables transforming the initial equations over a slope into those over a flat plane are found.

Nonlinear theory of the compressible gas flows over a nonuniform boundary in the gravitational field in the shallow-water approximation

A set of equations is derived for the motion of a compressible ideal gas over a nonuniform boundary in the gravitational field in the shallow-water approximation. Classical simple waves are shown not to be the solutions to this set of equations. Generalized simple waves are found to exist only in the case of a linear underlying-surface profile. All continuous and discontinuous solutions are obtained in an explicit form for the case of the boundary in the form of an inclined plane, and an analytical solution is found for the problem of the decay of an arbitrary discontinuity. This solution consists of four wave configurations. Necessary and sufficient conditions are determined for the existence of each configuration.

Additive Runge-Kutta methods for H2/O2/Ar detonation with a detailed elementary chemical reaction model

We report here the additive Runge-Kutta methods for computing reactive Euler equations with a stiff source term, and in particular, their applications in gaseous detonation simulations. The source term in gaseous detonation is stiff due to the presence of wide range of time scales during thermal-chemical non-equilibrium reactive processes and some of these time scales are much smaller than that of hydrodynamic flow. The high order, L-stable, additive Runge-Kutta methods proposed in this paper resolved the stiff source term into the stiff part and non-stiff part, in which the stiff part was solved implicitly while the non-stiff part was handled explicitly. The proposed method was successfully applied to simulating the gaseous detonation in a stoichiometric H2/O2/Ar mixture based on a detailed elementary chemical reaction model comprised of 9 species and 19 elementary reactions. The results showed that the stiffly accurate additive Runge-Kutta methods can capture the discontinuity well, and describe the detonation complex wave configurations accurately such as the triple wave structure and cellular pattern.

Three-Dimensional Normal Shock-Wave/Boundary-Layer Interaction in a Diffuser

The 3D flow structure induced by a normal shock-wave/boundary-layer interaction in a transonic diffuser is experimentally and computationally investigated. In the diffuser, the shock wave is located in the diverging section. The experiments are done with wall pressure measurements, oil-flow surface visualization, and Mach number measurements with a laser-induced fluorescence (LIF) method. In the computational work, the Reynolds-averaged Navier–Stokes equations are numerically solved with the k-ω two-equation turbulence model. The numerical solution agrees reasonably well with the experiment and clarifies the vortex structure in the interaction zone along with the 3D behavior of the boundary layer downstream of the shock wave. A careful investigation of the calculated flow reveals that the vortices are generated at the foot of the shock wave. It is also found that a complicated wave configuration is formed near the diffuser corner. A flow model is constructed by considering this wave configuration. This model explains the 3D flow characteristics in the transonic diffuser very well.

The configuration of shock wave reflection for the TSD equation

In this paper, we mainly study the nonlinear wave configuration caused by shock wave reflection for the TSD (Transonic Small Disturbance) equation and specify the existence and nonexistence of various nonlinear wave configurations. We give a condition under which the solution of the RR (Regular reflection) for the TSD equation exists. We also prove that there exists no wave configuration of shock wave reflection for the TSD equation which consists of three or four shock waves. In phase space, we prove that the TSD equation has an IR (Irregular reflection) configuration containing a centered simple wave. Furthermore, we also prove the stability of RR configuration and the wave configuration containing a centered simple wave by solving a free boundary value problem of the TSD equation.

Evanescent wave mirror for cold atoms—A quasi-resonant case

The measurements of the inelastic photon scattering in the optical dipole mirror created by a quasi-resonant evanescent wave are presented. The momentum transfer between an evanescent wave and cold atoms accompanying the atom reflection are discussed for a single and double evanescent wave configurations. The latter configuration allows 10-fold reduction of the systematic errors in the measurements. A simple theoretical description is provided to account for any saturation parameter in the interaction of an atom and evanescent field. A large number of photons scattered from a quasi-resonant evanescent wave makes this method a promising tool for investigations of surface related phenomena.

Electrocardiography in conscious releasable andean condors (Vultur gryphus): Reference panel and unusual findings

Electrocardiography is a useful tool when included in healthcare protocols and is increasingly utilized for monitoring wild birds. However, the lack of reference data for many species is limiting the clinical value of this technique. In this study 26 Andean condors (Vultur gryphus) coming from rehabilitation and captive breeding programs were examined to determine electrocardiographic references prior to being released. Standard bipolar (I, II, and III) and augmented unipolar limb (aVR, aVL, and aVF) leads were recorded with birds under physical restraint. Five beats were analyzed on Lead II at 50 mm/sec and 1 cm = 1 mV to determine QRS complex morphology, cardiac rhythm, heart rate, P, PR, R, S, QRS, T, QT, and ST amplitude and/or duration. P and T wave configuration was determined for all leads, and Mean Electrical Axis (MEA) in the frontal plane was determined using leads I and III. Cardiac rhythm corresponded to regular sinus rhythm in 42% of the birds, with a relevant rate of sinus arrhythmia in 58%, and rS as the most common pattern (42%) for QRS complex in lead II. We found an influence of age and heart rate but not of sex on several ECG waves and intervals. Relevant ECG findings for studied Andean condors include a high rate of T(a), R', and U wave detection. Waves T(a) and R' were considered non-pathological, while the significance of U waves remains unclear. Our results provide a useful reference to improve clinical interpretation of full electrocardiographic examination in Andean condors.

Lepton asymmetry growth in the symmetric phase of an electroweak plasma with hypermagnetic fields versus its washing out by sphalerons

We study lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via Higgs decays (inverse decays) entering equilibrium at temperatures below T_RL ~ 10 TeV, T_EW < T < T_RL. We solve appropriate kinetic equations for leptons and Higgs bosons taking into account the lepton number violation due to Abelian anomalies for right and left electrons and neutrinos in the self-consistent hypercharge field obeying Maxwell equations modified by the contribution of the Standard Model of electroweak interactions. The violation of left lepton numbers and the corresponding violation of the baryon number due to sphaleron processes in symmetric phase is taken into account as well. Assuming the Chern-Simons wave configuration of the seed hypercharge field, we get the estimates of baryon and lepton asymmetries evolved from the primordial right electron asymmetry existing alone as partial asymmetry at T > T_RL. One finds a strong dependence of the asymmetries on the Chern-Simons wave number. We predict a nonzero chiral asymmetry \Delta \mu = \mu_e_R - \mu_e_L \neq 0 in this scenario evolved down to the EWPT moment that can be used as an initial value for the Maxwellian field evolution after EWPT.

Thermal analysis of microwave assisted bonding of poly(methyl methacrylate) substrates in microfluidic devices

Electromagnetic heating such as microwave processing has evolved as a promising technique to bond polymer substrates due to its ability to achieve non-contact, selective heating and localized melting. In microwave assisted bonding process, two polymer layers such as PMMA (polymethyl methacrylate) substrates can be bonded by heating a thin layer of dielectric material placed between the polymer layers. To better understand the bonding process of polymer layers, a detailed theoretical analysis has been presented. In this analysis, the bonding process of polymer substrates has been modeled as a multilayered composite slab exposed to microwave radiations. The electric field distribution along each layer is computed from simplified Maxwell’s equation under plane wave configuration, and the Poynting theorem is used to find the volumetric power absorbed by each layer. The absorbed power is then used as the source term in unsteady energy equation which is solved by linear decomposition and separation of variables techniques. Finally, the closed form analytical solution obtained from this analysis is used to study the effect of material properties on temperature distribution of polymer substrate (PMMA) with poly-aniline as intermediate sacrificial layer. The analysis was carried out at household microwave frequency (2.4GHz) with temperature dependent dielectric properties for both poly-aniline and PMMA layers. Our results show that dielectric properties, layer thickness, heat transfer coefficient and processing time have significant influence on the heating pattern. Results also show that the temperature of the PMMA substrate remains below the melting point globally, except at the interface of the poly-aniline layer due to its transparent nature to incident microwave radiation at 2.4GHz.

Variation of friction drag via spanwise transversal surface waves

AbstractIntroducing spanwise velocity components into the near‐wall flow field of a turbulent boundary layer has shown to be an effective mean of influencing the wall shear stress. The underlying physical mechanisms leading to the drag reduction have however not been fully understood. The presented investigation uses sinusoidal transversal travelling surface waves to influence the near‐wall turbulence to achieve drag reduction. Two distinct wave configurations are analysed in detail and compared to an unactuated turbulent flat plate boundary layer flow to gain inside into the drag reducing mechanisms. (© 2012 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Transcranial magnetic stimulation with a half-sine wave pulse elicits direction-specific effects in human motor cortex

BackgroundTranscranial magnetic stimulation (TMS) commonly uses so-called monophasic pulses where the initial rapidly changing current flow is followed by a critically dampened return current. It has been shown that a monophasic TMS pulse preferentially excites different cortical circuits in the human motor hand area (M1-HAND), if the induced tissue current has a posterior-to-anterior (PA) or anterior-to-posterior (AP) direction. Here we tested whether similar direction-specific effects could be elicited in M1-HAND using TMS pulses with a half-sine wave configuration.ResultsIn 10 young participants, we applied half-sine pulses to the right M1-HAND which elicited PA or AP currents with respect to the orientation of the central sulcus.Measurements of the motor evoked potential (MEP) revealed that PA half-sine stimulation resulted in lower resting motor threshold (RMT) than AP stimulation. When stimulus intensity (SI) was gradually increased as percentage of maximal stimulator output, the stimulus–response curve (SRC) of MEP amplitude showed a leftward shift for PA as opposed to AP half-sine stimulation. Further, MEP latencies were approximately 1 ms shorter for PA relative to AP half-sine stimulation across the entire SI range tested. When adjusting SI to the respective RMT of PA and AP stimulation, the direction-specific differences in MEP latencies persisted, while the gain function of MEP amplitudes was comparable for PA and AP stimulation.ConclusionsUsing half-sine pulse configuration, single-pulse TMS elicits consistent direction-specific effects in M1-HAND that are similar to TMS with monophasic pulses. The longer MEP latency for AP half-sine stimulation suggests that PA and AP half-sine stimulation preferentially activates different sets of cortical neurons that are involved in the generation of different corticospinal descending volleys.

TREATMENT OF PAEDIATRIC ATRIAL TACHYCARDIA ORIGINATING FROM ATRIAL APPENDAGES BY RADIOFREQUENCY CATHETER ABLATION UNDER THREE DIMENSIONAL ELECTROANATOMIC MAPPING SYSTEM COMBINED WITH APPENDECTOMY

ObjectivesTo evaluate the electrocardiographic characteristics of atrial tachycardia (AT) originating from atrial appendages in children and to investigate the effects of radiofrequency catheter ablation (RFCA) under guidance of CARTO system...

NUMERICAL SIMULATIONS OF BREAKING SOLITARY WAVES

This paper presents the application of a parallel numerical code to breaking solitary waves impacting a seawall structure. The three-dimensional Navier-Stokes equations are solved in air and water, coupled with a subgrid-scale model to take turbulence into account. We compared three numerical methods for the free-surface description, using the classical VOF-PLIC and VOF-TVD methods, and an original VOF-SM method recently developed in our numerical tool (Vincent et al., 2010). Some experimental data for solitary waves impinging and overtopping coastal structures are available in literature (Hsiao et al., 2010). Solitary waves are often used to model tsunami behaviors because of their hydrodynamic similarities. From a numerical point of view, it allows shorter CPU time simulations, as only one wave breaks. Here we apply the model to simulate three-dimensional solitary waves and compare qualitatively our results with the experimental data. We investigate three configurations of solitary waves impinging and overtopping an impermeable seawall on a 1:20 sloping beach.

Optical transmission through double-layer compound metallic gratings with subwavelength slits

Optical transmission through a double-layer compound metallic grating (DCMG) composed of two identical compound metallic gratings (CMGs) with two subwavelength slits filled with different dielectrics inside each period is investigated by using the finite-difference time-domain method. The results show that the transmission properties of the DCMG are dependent on both the separation G between the two metallic layers and the phase configurations of the electromagnetic waves at the exits of adjacent slits of each layer. When a suitable separation (G ∼ 300 nm) is chosen, for the DCMG a notable transmission peak emerges at a certain wavelength, at which phase resonance appears for the corresponding CMG, while the transmission spectra of the corresponding double-layer simple metallic gratings (DSMGs) with the separation (G ∼ 300 nm) exhibit unexpected transmission suppression in a broad spectral region. When G > 340 nm, the intensity of the transmission around the wavelength for the DCMG gradually decreases down to almost zero as G increases, while the high transmission is nearly maintained for the corresponding DSMGs.

Light with enhanced optical chirality

Tang and Cohen [Phys. Rev. Lett.104, 163901 (2010)] recently demonstrated a scheme to enhance the chiral response of molecules, which relies on the use of circularly polarized light in a standing wave configuration. Here we show a new type of light that possesses orbital angular momentum and enhanced chiral response. In the locations where the beams show enhanced optical chirality, only the longitudinal components of the electric and magnetic fields survive, which has unexpectedly shown what we believe is a new way to yield an enhanced optical chiral response.

Analytical and numerical investigations of the reflection of asymmetric nonstationary shock waves

The reflection of asymmetric nonstationary shock waves is analytically and numerically studied in this paper. An analytical approach, which is a combination of the shock dynamic and shock polar methods, is advanced to predict the reflection wave configurations. The numerical simulations are performed by the finite volume method based on the second-order MUSCL-Hancock scheme and the HLLC approximate Riemann solver, with the self-adaptive unstructured mesh. It is found that the transition between the overall regular reflection and overall Mach reflection in the asymmetric nonstationary reflection agrees with the detachment criterion, which is analogous to the reflection in pseudo-steady flows (i.e. shock reflection over a wedge). Some special reflection wave configurations, which have never been observed in steady or nonstationary shock reflections so far, are found to exist in this asymmetric reflection. Furthermore, the domains and boundaries of various overall reflection wave configurations are analytically predicted, and the effect of mis-synchronization is also discussed.

Numerical investigation of the onset of instability of triple shock configurations in steady supersonic gas flows

Triple configurations of shock waves that arise in a steady supersonic flow of a real gas have been numerically simulated. Previously, we have theoretically predicted that a new triple shock configuration with a negative reflection angle can appear in a gas flow at large Mach numbers and small adiabatic indices. This configuration is now obtained for the first time in numerical experiments. It is shown that the formation of this triple shock configuration leads to instability of the entire flow pattern.