Narrow Results

This study aims to investigate the magnetoconvection of an electrically conducting fluid within a rectangular enclosure through a comprehensive three-dimensional computational analysis. The enclosure has a hemispherical block for bottom heating and incorporates two elliptical sources with differing temperatures along its vertical sidewalls. The primary focus is to optimize heat transfer and fluid flow characteristics within this thermal system by analyzing various control parameters. The simulations were carried out with the relevant parameters of the problem, including the Rayleigh number $(10^3\le \mathrm{\text{Ra}}\le 10^6)$, Hartmann number $(0\le \mathrm{\text{Ha}}\le 100)$, the inclination of the magnetic field $(0^{\circ }\le \chi \le 90^{\circ })$, and the radius of the hemispherical block $(0.2\le \mathrm{\text{HR}}\le 0.5)$. Three distinct scenarios represent different positions for the localized heat sources. Among these configurations, the Middle–Middle (MM) arrangement is the most favorable, with the specific value for the radius $\mathrm{\text{HR}}$ yet to be determined. The findings highlight the effective control of heat transfer rate and irreversibility effects by manipulating the parameters $\mathrm{\text{Ha}}$, $\mathrm{\text{HR}}$ and $\chi$. It is demonstrated that selecting $\mathrm{\text{HR}}$ and $\mathrm{\text{Ha}}$ values of $0.4$ and 15 allows for optimal thermal system configuration. A correlation with two variables $(\mathrm{\text{Ha}},\mathrm{\text{HR}})$ expressing the rate of heat transfer through the cavity was established and verified. The analysis of the helicity confirms the predicted optimal case.

Here we illustrate how Jones’ polynomials are derived from the kinetic helicity of vortical flows, and how they can be used to measure the topological complexity of fluid knots by numerical values. Relying on this new findings, we show how to use our adapted Jones polynomial in a new framework by introducing a knot polynomial space whose discrete points are the adapted Jones polynomials of fluid knots, interpreting the topological simplification associated with the natural decay of reconnecting fluid knots as geodesic flows on this space.

Creation of novel $\pi$-conjugated molecules is an important research topic. I describe in this account an approach to this aim that is based on the use of the distorted conformation of porphyrins. Planarization of distorted molecules enables the synthesis of heteroatom-containing porphyrin derivatives. Furthermore, dearomatization reaction proves effective to construct distorted conformations from planar $\pi$-conjugated molecules under mild reaction conditions. According to this protocol, we have succeeded in the synthesis of heteroatom-containing curved-$\pi$ conjugated molecules that had never been achieved by conventional protocols. In particular, a nitrogen-embedded buckybowl is the first example of a buckybowl having a heteroatom in its central position, which exhibits unique properties due to the incorporation of the heteroatom in its curved $\pi$-surface.

In this paper, we discuss fundamental aspects related to the helicity and dynamics of the spin-1/2 fermions encompassed within the very well-known Lounesto’s classification. More specifically, we investigate how the bi-spinorial structures behave under discrete symmetries, as well as analyze some consequences on the spinors dynamics. In addition, we find an interesting relation between the spinor helicity and the Lounesto spinor classification.

For a massive spin 1/2 field, we present the reduced spin and helicity density matrix, respectively, for the same pure one particle state. Their relation has also been developed. Furthermore, we calculate and compare the corresponding entanglement entropy for spin and helicity within the same inertial reference frame. Due to the distinct dependence on momentum degree of freedom between spin and helicity states, the resultant helicity entropy is different from that of spin in general. In particular, we find that both helicity entanglement for a spin eigenstate and spin entanglement for a right handed or left handed helicity state do not vanish, and their Von Neumann entropy has no dependence on the specific form of momentum distribution, as long as it is isotropic.

Arnold showed that the Euler equations of an ideal fluid describe geodesics in the Lie algebra of incompressible vector fields. We will show that helicity induces a splitting of the Lie algebra into two isotropic subspaces, forming a Manin triple. Viewed another way, this shows that there is an infinitesimal quantum group (a.k.a. Lie bi-algebra) underlying classical fluid mechanics.

In this paper, we study CP violation in and decays, where B, P and V denote a light spin-½ baryon, pseudoscalar and a vector meson respectively. In these processes the T odd CP violating triple-product (TP) correlations are examined. The genuine CP violating observables which are composed of the helicity amplitudes occurring in the angular distribution are constructed. Experimentally, by performing a full angular analysis it is shown how one may extract the helicity amplitudes and then obtain the TP asymmetries. We estimate the TP asymmetries in decays to be negligible in the Standard Model making these processes an excellent place to look for new physics. Taking a two-Higgs doublet model, as an example of new physics, we show that large TP asymmetries are possible in these decays. Finally, we discuss how BES-III and super τ-charm experiments will be sensitive to these CP violating signals in decays.

Single-walled carbon nanotubes (SWNTs) synthesized by catalytic decomposition of an alcohol were purified by extraction. The purified SWNTs were characterized on the basis of visible-near infrared (vis-NIR) absorption, photoluminescence and Raman spectroscopic analyses, scanning electron microscopy (SEM) observation, and thermal analysis. Selective extraction of metallic nanotubes was also achieved by the extraction condition.

The extension of the statistical parton distributions to include their transverse momentum dependence (TMD) is revisited by considering that the proton target has a finite longitudinal momentum. The TMD will be generated by means of a transverse energy sum rule. The new results are mainly relevant for electron–proton inelastic collisions in the low Q² region. We take into account the effects of the Melosh–Wigner rotation for the helicity distributions.

We introduce topological helicity, an invariant for oriented framed links. Topological helicity provides an elementary means of computing helicity for a magnetic flux rope by measuring its knotting, linking, and twisting. We present an equivalence relation, reconnection-equivalence, for framed links and prove that topological helicity is a complete invariant for the resulting equivalence classes. We conclude by showing that one can use magnetic reconnection to transform one collection of linked flux ropes into another collection if and only if they have the same helicity.

As the complex transmission coefficient for a Fabry–Perot dielectric plate is well-known, the density of states (DOS) approach by J. Bendickson et al. [Phys. Rev. E53, 4107 (1996)] was applied to the plate and a formula was found for the spectrum of its threshold gain for lasing from the dye-doped plate. Next, the dispersion relation and the spectrum of the threshold gain was discussed for the infinite helical cholesteric liquid crystal (CLC). Then the DOS approach was applied to the non-absorbing CLC layers having finite, different thickness. The threshold gain spectra were calculated and dependences were found of the minimum threshold gain on the layer thickness and the optical anisotropy of the material. Finally, the results of the DOS analytical technique were compared with numerical calculations based on the precise solutions of the Maxwell equations and, in such a way, the DOS technique has been proven. The contribution of the dye absorption was discussed separately. The experimental data presented in the paper are in good agreement with the threshold gain calculations.

The present study numerically simulated the physiological pulsatile flow in helical grafts to increase understanding of its flow mechanism which may contribute to the design of better grafts. The wall-indices like time-averaged wall shear stress (WSS) and oscillatory shear index (OSI), joint with a quantitative index for helical flow by means of Lagrangian approach, were introduced as effective instruments to classify the hemodynamic performance of helical grafts. The simulation suggests that the helical geometry created amplified WSS magnitudes as well as elevated velocities near the wall. The calculated oscillatory shear index (OSI) values were never exceeded to 0.07 which is not considered physiologically significant. In addition, the strong secondary flow in helical graft helped the flow mixing between low-momentum fluid closer to the surface and high-momentum fluid at the center which brought the high-momentum fluid to the surface. Furthermore, Helicity analysis revealed that most of the fluid particles experienced counter-clockwise rotation during the whole cardiac cycle which helps to protect the graft wall from damage by reducing the laterally directed forces and keep flow stability. It concluded that a helical graft provides guaranties for the graft wall surface to get smooth and even washing by the blood and eliminates mechanical trauma to blood cells so that atherosclerotic plaques can hardly form in the graft wall.

Electroproduction of a ρ⁰ vector meson in the process γ* + N → V + N^′ is measured with a 27.6 GeV longitudinally polarized electron/positron beam in the HERMES experiment. Kinematical dependences of real and imaginary parts of the ratio of the helicity amplitudes are extracted from the data.

Intimal hyperplasia developed at the end-to-side anastomosis of artery bypass is closely related to unphysiological hemodynamics. The helical flow as a normal physiological phenomenon in arteries is beneficial to endothelial damage repair. To deeply understand the physiological flow properties in a S-type bypass (StB) graft, four end-to-side bypass models including 30°, 45°, 60° conventional bypasses and a 45° StB were compared numerically under physiological pulsatile flow. The results showed that strong helical flow was observed at the distal anastomosis of StB. The distribution of hemodynamic parameters such as helicity, average wall shear stress and oscillating shear index, etc. were significantly improved at the S-type anastomosis as compared with those of three conventional models. The area-averaged normalized helicity in StB reached maxima at the moments of maximum flow rate and systolic deceleration. The hemodynamic performance in a 45° StB was improved as compared with a 30° conventional model. It is concluded that large StB anastomosis angle can be taken to achieve good hemodynamic performance while much smaller anastomosis angle has to be adopted for conventional bypass. As such, a S-type anastomosis should be a feasible choice of clinical artery bypass grafting due to its significant improvement in hemodynamic performance.

Recently Nieto has proposed a link between oriented matroid theory and the Schild type action of p-branes. This particular matroid theory satisfies the local condition, i.e., the degenerate form must be closed. This allows us to explain the dynamics of p-branes in terms of Nambu–Poisson structure. In this paper using an infinitesimal canonical transformation of Nambu brackets we show that the helicity is conserved in the dynamics of p-branes. Applying Filippov algebra (or quantum Nambu bracket) we define a generalized Yang–Mills action in 4k space. We show that this action is equivalent to Dolan–Tchrakian type action.

We comment on a previous calculation¹ for the scattering amplitude for the Dirac field in an external Coulomb potential in the expanding de Sitter space. The result implies that for initial and final fermion states with identical momenta |p_i|=|p_f| the helicity of the particle is conserved. We make a classical analysis of the scattering problem in the small scattering angle approximation using the Bargmann–Michel–Telegdi equation and show that helicity conservation also manifests in the classical case. We also show that in Minkowski space there is a complete agreement between the classical and quantum polarization angle of the scattered particle.

This review paper stresses the possible connection between time-reversal violation and new physics processes beyond the standard model. In particular, this violation is proposed as an alternative to CP violation in the search for such unkown processes. Emphasis is put on the weak decays of heavy hadrons, especially beauty ones. Specific methods for extracting useful parameters from experimental data are elaborated in order to test TR symmetry. These methods could be used successfully in the analysis of the LHC data.

Competitive ability of helical and two-dimensional models of generation of large-scale atmospheric hazardous events is discussed, and the conclusion is made that the helical model deserves more attention than it currently has in the world literature. A number of mechanisms of nonlinear stabilization of helical vortex instability are considered which are possible under different conditions. Intermittent nature of large-scale velocity field generated by such instability, and possibility of development of helical wave-turbulent instability are analyzed. The example of application of helical vortex instability for explanation of some phenomena observed after collision of Shoemaker-Levy 9 comet fragments with Jupiter in July 1994 is presented.

Columnar vortices aligned with the rotation axis frequently dominate the large scales in rapidly-rotating turbulence, both in laboratory experiments and in numerical simulations. We argue that, often, these columnar vortices are simply low-frequency inertial wave packets propagating away from a localised disturbance (a turbulent eddy or buoyant blob). An important feature of these low-frequency wave packets is that they transport negative helicity upward and positive helicity downward (relative to the rotation vector). This generation and subsequent spatial segregation of positive and negative helicity is potentially important for planetary dynamos.

Recent numerical simulations suggest that magnetic field generation in planets occurs predominantly within columnar vortices located outside the tangent cylinder, and these dynamos may be classified (at least approximately) as α². The simulations, which operate in a regime very far from that of the planets, also suggest that the helicity outside the tangent cylinder is predominantly negative in the north and positive in the south. In the more viscous and weakly forced simulations this helicity is often attributed to Ekman pumping at the mantle. However, Ekman pumping is less evident in the less viscous and more strongly driven simulations, and almost certainly plays no significant dynamical role in planetary interiors. We argue that, in the absence of Ekman pumping, the observed helicity distribution is a consequence of low-frequency helical wave packets initiated near the equatorial plane by buoyant plumes floating out towards the mantle. This provides a mechanism for maintaining a dynamo in the Earth, as well as in the gas giants.

Subgrid-scale (SGS) turbulence models for large eddy simulations (LES) are quantitatively assessed for the strongly-stratified helical transition-to-turbulence, Arnold-Beltrami-Childress (ABC) problem through comparisons to in-house direct numerical simulations (DNS). LES predictions using the classical non-dynamic and dynamic Smagorinsky models (SSM and DSM, respectively) are compared to a modified Smagorinsky model (MSM) designed specifically for natural convection. DSM predicts the best results when compared to DNS, although none of the SGS models are able to predict the peak of nonlinearities.