Re-entrant Mode Research Articles

Numerical investigation on the formation of the re-entrant flow and the transformation of varying shedding modes in cloud cavitation

The objective of this paper is to investigate two types of cloud shedding processes around the NACA66 (mod) hydrofoil with emphasis on the formation of the re-entrant flows and the transformation of varying shedding modes. The LES method combines the Schnerr-Sauer cavitation model in OpenFOAM to capture the detailed flow structures. Combining the experimental observation, the cloud shedding process can be divided into main re-entrant flow mode, transition mode, and side re-entrant flow mode. The re-entrant flow is primed from the middle of the attached cavity closure for the main re-entrant flow pattern. The velocity is more stable as it develops in a fan shape towards the leading edge of the hydrofoil. For the side re-entrant flow mode, the rotation and local collapse of cloud cavity in the previous cycle resulted in the incipient of the side re-entrant flow. Compared with the main re-entrant flow, the velocity of the side re-entrant flow fluctuates more significantly. The transition between the side re-entrant flow mode and the main re-entrant flow mode can be characterized by the normalized cavity length (lmax/c) and the cavity shedding frequency (St number).

Microwave breakdown of sub-atmospheric argon gas in the vicinity of a microgap

The microwave electric field at breakdown for argon gas in a microgap (generally, gap size <1 mm) over a wide range of pressures and gap sizes was found to exhibit two behavioral pressure regimes. A high microwave electric field was established in the gap of a re-entrant mode resonator. By slowly raising the microwave electric field level, a breakdown level is reached where impact ionization induces low pressure argon gas to breakdown preferentially outside of the gap. At high pressure, breakdown is found to occur preferentially inside the gap, but only after the pressure is high enough for impact ionization to produce breakdown there. Impact ionization has a lower threshold electric field than the boundary-controlled processes, such as secondary electron emission, that would eventually produce breakdown inside the microgap if impact ionization did not occur first. Thus, the lower pressure regime is characterized by breakdown outside of the gap, while in the high-pressure regime, breakdown occurs inside the gap, in both cases by impact ionization. The transition pressure PT between these two pressure regimes depends on the gap size dgap, roughly as PT ∝ dgap−2. Consistent with the model developed here, this corresponds to the full-amplitude of electron oscillation in the gap field being commensurate with the gap size.

Application of dynamic display technology to identify gaps after pulmonary vein isolation in catheter ablation of atrial fibrillation

BackgroundThe identification of post pulmonary vein isolation (PVI) gaps by activation and voltage maps is time-consuming. This study aimed to investigate the characteristics, efficiency and accuracy of LiveView dynamic display module (EnSite™ Dynamic Display; Abbott, Abbott Park, IL, USA) in unmasking post PVI gaps and conduction block line. MethodTwenty four patients with paroxysmal atrial fibrillation (PAF) who failed to achieve first-pass PVI or with recurrent PAF were enrolled. Ninety-six pulmonary veins (PVs) were evaluated, and gaps were identified in 25 (26.0%) PVs. The gap location was confirmed by activation and propagation maps; 110 frames on gaps and 118 frames on block lines were analyzed by using LiveView module. We defined isochronal crowding in the local activation time (LAT) mode as three colors between two adjacent electrodes. Each frame was classified as with or without isochronal crowding in LAT mode and one/continuous color or isochronal discontinuity in reentrant mode. The gray color inside the PVs was considered to represent conduction block. ResultThe isochronal crowding could be found on both gap and block line in LAT mode, whereas isochronal discontinuity only presented on the block line in reentrant mode. The sensitivity and specificity of isochronal discontinuity or gray color in reentrant mode to identify block line were 61.0% and 100%, respectively. The sensitivity and specificity of isochronal crowding or gray color in LAT mode to identify block line were 71.2% and 71.8%, respectively. ConclusionReentrant mode in LiveView module is very specific in identifying block lines. We proposed an efficient, practical algorithm to differentiate the block line from PV gaps.

B-PO05-096 USING REENTRANT MODE IN A REAL-TIME DYNAMIC SOFTWARE (LIVEVIEW) IN IDENTIFYING PV GAPS AND CONDUCTION BLOCKS DURING PV ISOLATION

The identification of post pulmonary vein isolation (PVI) gap by traditional activation and voltage maps are time-consuming. To investigate the characteristics, efficiency and accuracy of LiveView, a novel dynamic software, in identifying the post PVI gaps and block lines. Patients with PAF who failed to achieve first-pass PVI and with recurrent PAF were enrolled. The gap location was confirmed by activation and propagation maps. Of 25 PVs with gaps, 110 frames on gaps and 124 frames on conduction block lines were analyzed by using LiveView (EnSiteTM Dynamic Display). We defined isochronal crowding in the LAT mode as 3 colors between 2 adjacent electrodes. Each frame was classified as with or without isochronal crowding in LAT mode and one color or continuous color or isochronal discontinuity in reentrant mode. The gray color seen inside the pulmonary veins was considered to represent conduction block. Presentations of gap and block line in LiveView are shown in table 1. LAT mode demonstrated isochronal crowding on both the gap and block line, but reentrant mode showed isochronal discontinuity only on the block line (figure 1A). The sensitivity and specificity of isochronal discontinuity or gray color in reentrant mode to identify block line were 56.45% and 100%, respectively. The sensitivity and specificity of isochronal crowding or gray color in LAT mode to identify block line were 50.8% and 64.5%, respectively. Reentrant mode in LiveView is more accurate than LAT mode in identifying block lines at PV. We proposed an efficient, practical algorithm to differentiate the block line from PV gaps during AF ablation procedure (Figure 1B).

Numerical investigation of supercavity geometry and gas leakage behavior for the ventilated supercavities with the twin-vortex and the re-entrant jet modes

To investigate the supercavity geometry and gas flow structure for the supercavities with two closure types under the different flow conditions, an inhomogeneous multiphase model with the SST turbulence model was established, and validated by experimental results. The results show that two distinct regions exist inside the supercavity, which include the downstream flow region along the gas-water interface and the reverse flow region. For the twin-vortex supercavity, the internal gas leaks from the supercavity boundary by two paths: the supercavity surface and the two-vortex tubes. Increasing Froude number leads to more internal gas stripped from the supercavity surface. Two types of gas loss exist for the re-entrant jet supercavity with high Froude number, one type is the steady process of gas loss, and the major gas-leaking path is the supercavity surface rather than supercavity closure region. The other type is the unsteady periodic ejection, and the gas cluster of periodic ejection is merely a small part of the gas stored inside the supercavity.

Analytical Study of Quasi-One-Dimensional Flat Band Networks and Slow Light Analogue

Exact method of analytical solution of flat, non-dispersive eigenstates in a class of quasi-one dimensional structures is reported within the tight-binding framework. The states are localized over certain sublattice sites. One such finite size cluster of atomic sites is decoupled from the rest of the system by the special non-permissible vertex having zero amplitude. This immediately leads to the self-trapping of the incoming excitation. We work out an analytical scheme to discern the localizing character of the diffraction free dispersionless modes using real space renormalization group technique. Supportive numerical calculations of spectral profile and transport are demonstrated to substantiate the essence of compact localized states. Possible experimental scope regarding the photonic analogue of the tight-binding electronic case is also discussed elaborately. This eventually unfolds the concepts of slow light and the related re-entrant mode switching from the study of optical dispersion.

Competition and coexistence of polar and non-polar states in Sr1−xCaxTiO3: an investigation using pressure dependent Raman spectroscopy

The competition and cooperation between ferroelectric and anti-ferro-distortion (AFD) instabilities are studied using pressure dependent Raman spectroscopy on polycrystalline powder samples of Sr1−xCaxTiO3(x = 0.0, 0.06, 0.25, 0.35). For x = 0.0 composition, a broad polar mode is detected in the Raman spectra above 6 GPa, while for x = 0.06 composition, the polar modes appear well above 9 GPa where the AFD modes showed strong suppression. In x = 0.25 and 0.35 composition, the application of small pressure resulted in the appearance of strong AFD modes suppressing the polar modes. At elevated pressures, re-entrant polar modes are observed along with the broad AFD modes and some new peaks are also observed, signifying the lowering of local symmetry. The reappearance of polar modes is found to be related to pressure induced symmetry disorder at local level, suggesting its electronic origin. The re-entrant polar modes observed at higher pressure values are found to be significantly broad and asymmetric in nature, signifying the development of ferroelectric micro regions/nano domains coexisting with AFD. The lower symmetry at local length scale provides a conducive atmosphere for coexisting AFD and FE instabilities.

Experiments match simulations in a multiple post reentrant cavity.

Microwave reentrant cavities are used for many applications in science and engineering. The potential for both high mechanical tunability and high electric quality factors make them important tools in many areas. They are usually resonant cylindrical cavities with a central post, which makes a small gap spacing with the cavity wall. By adding an arbitrary number of extra posts, they are generalized to a type of multiple post reentrant cavity. This new approach has been theoretically studied but no experimental results have been presented. The main purpose of this work was to compare experimental modes with simulated ones from a reentrant cavity made of forty nine cylindrical posts. Each post could be moved using a screw in order to make tunable gap spacing between the post top and the cavity cover. Eight different gap setups were made making it possible to investigate thirty six different reentrant modes at room temperature. The lowest frequency percentage agreement between experiment and simulation was 91.31%, and the best one was 99.92%. Taking into account all the modes, 94.44% of them agreed above 96%. Thus, we have determined an experimental procedure suitable to investigate the reentrant modes from multiple post cavities. There is a wide range of potential applications for such cavities due to their unique features compared to conventional ones.

Visual Passive Ranging Method Based on Re-entrant Coaxial Optical Path and Experimental Verification**Supported by the National Basic Research Program of China under Grant No 2014CB340102.

To overcome the shortcomings of the traditional passive ranging technology based on image, such as poor ranging accuracy, low reliability and complex system, a new visual passive ranging method based on re-entrant coaxial optical path is presented. The target image is obtained using double cameras with coaxial optical path. Since there is imaging optical path difference between the cameras, the images are different. In comparison of the image differences, the target range could be reversed. The principle of the ranging method and the ranging model are described. The relationship among parameters in the ranging process is analyzed quantitatively. Meanwhile, the system composition and technical realization scheme are also presented. Also, the principle of the method is verified by the equivalent experiment. The experimental results show that the design scheme is correct and feasible with good robustness. Generally, the ranging error is less than 10% with good convergence. The optical path is designed in a re-entrant mode to reduce the volume and weight of the system. Through the coaxial design, the visual passive range of the targets with any posture can be obtained in real time. The system can be widely used in electro-optical countermeasure and concealed photoelectric detection.

Higher order reentrant post modes in cylindrical cavities

Reentrant cavities are microwave resonant devices employed in a number of different areas of physics. They are appealing due to their simple frequency tuning mechanism, which offers large tuning ranges. Reentrant cavities are, in essence, 3D lumped LC circuits consisting of a conducting central post embedded in a resonant cavity. The lowest order reentrant mode (which transforms from the TM010 mode) has been extensively studied in past publications. In this work, we show the existence of higher order reentrant post modes (which transform from the TM01n mode family). We characterize these new modes in terms of their frequency tuning, filling factors, and quality factors, as well as discuss some possible applications of these modes in fundamental physics tests.

Finite Volume, Computational Fluid Dynamics-Based Investigation of Supercavity Pulsations

Computations of pulsating supercavity flows behind axisymmetric disk cavitators are presented. The method of computation is a finite volume discretization of the equations of mixture fluid motion. The gas phase is treated as compressible, the liquid phase as incompressible, and the interface accuracy enhanced using a volume of fluid (VOF) approach. The re-entrant, pulsating, and twin vortex modes of cavity closure are delineated and computationally resolved, including the expected hysteresis. A phase diagram of cavitation number versus ventilation rate at three Froude conditions is computationally constructed. Sample re-entrant, pulsation, and twin vortex snapshots are presented. Pulsation results are compared with stability criterion from the literature as well as examined for their expected character. Computations appear to capture the complete spectrum of cavity closure conditions. A detailed comparison of computational simulation and physical experiment at similar conditions is also included as a means to validate the computational results.

Investigation of Higher Order Reentrant Modes of a Cylindrical Reentrant-Ring Cavity Resonator

Analysis of the properties of resonant modes in a reentrant cavity structure comprising of a post and a ring was undertaken and verified experimentally. In particular we show the existence of higher order reentrant cavity modes in such a structure. Results show that the new cavity has two re-entrant modes, one of which has a better displacement sensitivity than the single post resonator and the other with a reduced sensitivity. The more sensitive mode is better than the single post resonator by a factor of 2 to 1.5 when the gap spacing is below 100 μm. This type of cavity has the potential to operate as a highly sensitive transducer for a variety of precision measurement applications, in particular applications which require coupling to more than one sensitive transducer mode.

Rigorous analysis of highly tunable cylindrical transverse magnetic mode re-entrant cavities

Cylindrical re-entrant cavities are unique three-dimensional structures that resonate with their electric and magnetic fields in separate parts of the cavity. To further understand these devices, we undertake rigorous analysis of the properties of the resonance using "in-house" developed Finite Element Method (FEM) software capable of dealing with small gap structures of extreme aspect ratio. Comparisons between the FEM method and experiments are consistent and we illustrate where predictions using established lumped element models work well and where they are limited. With the aid of the modeling we design a highly tunable cavity that can be tuned from 2 GHz to 22 GHz just by inserting a post into a fixed dimensioned cylindrical cavity. We show this is possible, as the mode structure transforms from a re-entrant mode during the tuning process to a standard cylindrical transverse magnetic mode.

Final report on key comparison CCM.P-K13 in the range 50 MPa to 500 MPa of hydraulic gauge pressure

This report describes a CCM key comparison of hydraulic pressure standards of seven National Metrology Institutes, listed in the chronological order of their measurements, that was carried out in the period from December 2008 to March 2010 in order to determine their degrees of equivalence in the range 50 MPa to 500 MPa of gauge pressure. The pilot laboratory was PTB. The primary pressure standards were pressure balances of different design equipped with piston–cylinder assemblies operated in free-deformation, controlled-clearance or re-entrant operation mode. The transfer standard was a piston–cylinder assembly in a pressure balance. The pressure-dependent effective areas of the transfer standard at specified pressures were reported by the participants and led to the reference values calculated as medians. Results of all participants excepting NIM agree with the reference values and with each other within the expanded uncertainties calculated with a coverage factor 2, most of them even within their standard uncertainties. In addition, the results were analysed in terms of the zero pressure effective area and the pressure distortion coefficient. Also for them agreement within expanded uncertainties (k = 2) is observed. The results of the comparison demonstrate equivalence of the laboratory standards and of the Calibration and Measurement Capabilities currently presented in the BIPM key comparison database.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Zigzag edge modes in aZ2topological insulator: Reentrance and completely flat spectrum

The spectrum and wave function of helical edge modes in Z_2 topological insulator are derived on a square lattice using Bernevig-Hughes-Zhang (BHZ) model. The BHZ model is characterized by a "mass" term M (k) that is parameterized as M (k) = Delta - B k^2. A topological insulator realizes when the parameters Delta and B fall on the regime, either 0 < Delta /B < 4 or 4 < Delta /B < 8. At Delta /B = 4, which separates the cases of positive and negative (quantized) spin Hall conductivities, the edge modes show a corresponding change that depends on the edge geometry. In the (1,0)-edge, the spectrum of edge mode remains the same against change of Delta /B, although the main location of the mode moves from the zone center for Delta /B < 4, to the zone boundary for Delta /B > 4 of the 1D Brillouin zone. In the (1,1)-edge geometry, the group velocity at the zone center changes sign at Delta /B = 4 where the spectrum becomes independent of the momentum, i.e. flat, over the whole 1D Brillouin zone. Furthermore, for Delta/B < 1.354..., the edge mode starting from the zone center vanishes in an intermediate region of the 1D Brillouin zone, but reenters near the zone boundary, where the energy of the edge mode is marginally below the lowest bulk excitations. On the other hand, the behavior of reentrant mode in real space is indistinguishable from an ordinary edge mode.

Final Report on Key Comparison CCM.P-K7 in the range 10 MPa to 100 MPa of hydraulic gauge pressure

This report describes a CCM key comparison of hydraulic pressure standards of nine national metrology institutes that was carried out in the period from November 2002 to June 2004 in order to determine their degrees of equivalence in the range 10 MPa to 100 MPa of the gauge pressure. The pilot laboratory was PTB. The primary pressure standards were pressure balances of different design equipped with piston-cylinder assemblies operated in free-deformation, controlled-clearance or re-entrant operation mode. The transfer standard was a pressure balance equipped with a piston-cylinder assembly and a mass set. The pressure-dependent effective areas of the transfer standard at specified pressures were reported by the participants and led to the reference values calculated as medians. All participants' results agree with the reference values and with each other within the expanded uncertainties calculated with a coverage factor 2, most of them even within their standard uncertainties. In addition, the results were analysed in terms of the zero-pressure effective area and the pressure distortion coefficient. Also for them agreement within expanded uncertainties (k = 2) is observed. The results of the comparison demonstrate equivalence of the laboratory standards and support their measurement capability statements.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the Mutual Recognition Arrangement (MRA).

A spatial scale factor for electrophysiological models of myocardium.

In the United States among males 20-64 years old about 1/3 of deaths are classified as 'sudden cardiac death', and 1/4 had no forewarning, nor did autopsy turn up any visible cause. The heart just switches from its normally periodic pumping to an alternative mode called 'fibrillation' more resembling electrical turbulence. In normal tissue its mechanism is a geometrically re-entrant mode of normal propagation. Everything about this spatial pattern depends upon the magnitude of 'D', the one term with dimension involving space in the pertinent biophysical equations. Explicit or implicit estimates in current literature span orders of magnitude. In this article I argue from a diversity of recent experiments for a narrower range of realistic values. It has an important role in the spatio-temporal evolution of fibrillation and in defibrillation.

Theory of magnetostatic waves for in-plane magnetized anisotropic films

A modified formulation of the Damon-Eshbach theory of magnetostatic waves for in-plane magnetized anisotropic films is presented. New results, relative to the usual backward volume wave, nonreciprocal surface wave, and surface mode critical angle properties for isotropic films, are obtained for films with various anisotropies. These include: (i) Surface mode suppression. (ii) A second critical propagation angle for which the backward volume band of dispersion branches becomes inverted and the dispersion curves change to a forward volume mode character. (iii) Mode conversion and a reentrant mode character for the lowest order dispersion branch; a volume mode character at low wave number which converts to a surface character at high wave number. At the conversion point, this mode corresponds to a propagating plane wave with a uniform mode profile across the film thickness but at nonzero propagation wave number. (iv) A third critical in-plane propagation angle at which the surface mode dispersion branch vanishes and the lowest order branch reverts to a pure volume mode character.

Reflection of electroacoustic waves in piezoelectric solids: Mode conversion into four bulk waves

In the analysis of the reflection of plane electroacoustic waves at the boundary of a piezoelectric half-space, four partial waves are required in the reflection field in order that the mechanical and the electrical boundary conditions can be satisfied. It is usually assumed that at least one of these waves is evanescent. The purpose of this paper is to point out that in strongly piezoelectric solids all four reflected waves may, for certain reflection geometries, be homogeneous bulk waves. This will be the case when the longitudinal sheet of the acoustic slowness surface possesses negatively curved regions, thus permitting a re-entrant longitudinal mode. Calculations are reported on Rochelle salt and Ba2NaNb5O15, which show that for an incident longitudinal wave the reflection coefficient for the fourth bulk wave may be as large as unity, depending on the angle of incidence.

Intercomparison of hydraulic pressure measurements to 28 MPa using a single-piston gauge in the controlled-clearance, reentrant, and simple configurations

The use of controlled-clearance piston gauges as highly accurate primary pressure standards is well established. However, the operation of a controlled-clearance gauge is more complicated than that of the familiar simple or reentrant designs. An investigation has been performed on a modified design of a piston gauge for which the same piston/cylinder can be operated in either the controlled-clearance, simple, or reentrant modes, to determine the degree of degradation in accuracy of measured pressure using the gauge in either the simple or reentrant modes as a standard. How the particular characterization of the standard gauge affects the calibration parameters of a test gauge is also explored. The effective areas of the test gauge are within 4.5 parts per million (ppm) when the standard is used in the simple mode instead of the controlled-clearance mode, up to a pressure of 28 MPa, whereas in the case of the reentrant mode this deviation increases from 2.5 ppm at 7 MPa to 14 ppm at 26 MPa.