Omega Particles Research Articles

Total Absorption of Electromagnetic Waves in Ultimately Thin Layers

We consider single-layer arrays of electrically small lossy bi-anisotropic particles that completely absorb electromagnetic waves at normal incidence. Required conditions for electromagnetic properties of bi-anisotropic particles have been identified in the most general case of uniaxial reciprocal and nonreciprocal particles. We consider the design possibilities offered by the particles of all four fundamental classes of bianisotropic inclusions: reciprocal chiral and omega particles and nonreciprocal Tellegen and moving particles. We also study the reflection/transmission properties of asymmetric structures with different properties when illuminated from the opposite sides of the sheet. It has been found that it is possible to realize single-layer grids which exhibit the total absorption property when illuminated from one side but are totally transparent when illuminated from the other side (an ultimately thin isolator). Other possible properties are co-polarized or twist polarized reflection from the side opposite to the absorbing one. Finally, we discuss possible approaches to practical realization of particles with the properties required for single-layer perfect absorbers and other proposed devices.

Balanced and optimal bianisotropic particles: maximizing power extracted from electromagnetic fields

Here we introduce the concept of ‘optimal particles’ for strong interactions with electromagnetic fields. We assume that a particle occupies a given electrically small volume in space and study the required optimal relations between the particle polarizabilities. In these optimal particles, the inclusion shape and material are chosen so that the particles extract the maximum possible power from given incident fields. It appears that for different excitation scenarios the optimal particles are bianisotropic chiral, omega, moving and Tellegen particles. The optimal dimensions of resonant canonical chiral and omega particles are found analytically. Such optimal particles have extreme properties in scattering (e.g., zero backscattering or invisibility). Planar arrays of optimal particles possess extreme properties in reflection and transmission (e.g. total absorption or magnetic-wall response), and volumetric composites of optimal particles realize, for example, such extreme materials as the chiral nihility medium.

Omega phase in as-cast high-Nb-containing TiAl alloy

The omega phase in as-cast high-Nb-containing TiAl alloy exhibits particles with sizes on the nano- or microscale within the B2 matrix. Omega particles are transformed from the B2 phase by heterogeneous nucleation on the B2/γ boundaries or homogeneous nucleation within the B2 phase. After annealing at 900 °C, the omega particles disappear and transform into B2 phase. The transformation is rapidly initiated, but is difficult to complete.

Heaviest bound baryons production at the Large Hadron Collider

We calculate the hadronic production of three heaviest bound baryons Omega(bbb), Omega*(bbc), and Omega(bbc) at hadron colliders at tree level. We present the integrated cross section and differential cross section distributions in this paper.

Production of K∗(892)0 and ϕ(1020) in pp collisions at $\sqrt{s}=7\ \mathrm{TeV}$

The production of K$^{*}$(892)$^{0}$ and $\phi$(1020) in pp collisions at $\sqrt{s}=7$ TeV was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d$^{2}$N/d$y$d$p_{\rm T}$ at midrapidity $|y|<0.5$ in the range $0<p_{\rm T}<6$ GeV/$c$ for K$^{*}$(892)$^{0}$ and $0.4<p_{\rm T}<6$ GeV/$c$ for $\phi$(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Omega baryons measured previously by ALICE at $\sqrt{s}=7$ TeV, the ratios K$^{*}$/K$^{-}$, $\phi$/K$^{*}$, $\phi$/K$^{-}$, $\phi/\pi^{-}$, and ($\Omega$ + $\overline{\Omega}$)/$\phi$ are presented. The values of the K$^{*}$/K$^{-}$, $\phi$/K$^{*}$ and $\phi$/K$^{-}$ ratios are similar to those found at lower centre-of-mass energies. In contrast, the $\phi/\pi^{-}$ ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The ($\Omega$ + $\overline{\Omega}$)/$\phi$ ratio in the $p_{\rm T}$ range $1$-$5$ GeV/$c$ is found to be in good agreement with the prediction of the HIJING/BB v2.0 model with a strong colour field.

Production ofΛ0,Λ¯0,Ξ±, andΩ±hyperons inpp¯collisions ats=1.96 TeV

We report a set of measurements of inclusive invariant transverse momentum differential cross sections of lambda, cascade and omega hyperons reconstructed in the central region with pseudorapidity within 1 and transverse momentum up to 10 GeV/c Events are collected with a minimum-bias trigger in ppbar collisions at a center-of-mass energy of 1.96 TeV using the CDF II detector at the Tevatron Collider. As transverse momentum increases, the slopes of the differential cross sections are similar not only to each other but also to those of mesons, which could indicate a universality of the particle production in transverse momentum The invariant differential cross sections are also presented for different charged-particle multiplicity intervals.

Phase Velocities Equalization of Coupled Microstrip Lines Using $\Omega$-Shaped Particles and Suppression of the Second Harmonic

This paper represents a new technique for equalization of phase velocities in coupled microstrip lines using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\Omega$</tex> </formula> -shaped particles. In the first step, the initial idea is investigated by considering a homogenized model for the substrates, and the structure is analyzed using a developed numerical code. This analysis provides an overview in finding the proper orientation of the particles as well as examining the pseudochirality effect. It is demonstrated that placing the omega particles in a specific orientation inside the substrate leads to a remarkable increase in the phase velocity of odd modes and can provide the phase velocities equalization. In the second step, the proposed structure is simulated with few numbers of particles. The results confirm the considered effective medium for the substrate and the presented physical explanations. The dispersive characteristics of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\Omega$</tex></formula> particles found to be valuable in proposing a simple and yet efficient method for designing coupled line filters. This procedure is based on finding the dimensions of a conventional filter with a narrower bandwidth than the desired one. In order to validate the effectiveness of the proposed method, a third order Chebychev filter is designed on FR4 substrate and a suppression level higher than 60 dB is achieved. Finally, the proposed structure is fabricated and it is observed that the experimental results are in good agreement with the simulated data.

Delta and Omega masses in a three-quark covariant Faddeev approach

We present the solution of the Poincare-covariant Faddeev equation for the Delta(1232) and Omega(1672) baryons. The covariant structure of the corresponding baryon amplitudes and their decomposition in terms of internal spin and orbital angular momentum is explicitly derived. The interaction kernel is truncated to a rainbow-ladder dressed-gluon exchange such that chiral symmetry and its dynamical breaking are correctly implemented. The resulting physical masses agree reasonably with experiment and their evolution with the pion mass compares favorably with lattice calculations. Evidence for the non-sphericity of the Delta-resonance is discussed as well.

The static-light baryon spectrum from twisted mass lattice QCD

We compute the static-light baryon spectrum by means of Wilson twisted mass lattice QCD using N_f = 2 flavors of sea quarks. As light u/d valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in the range 340 MeV < m_PS < 525 MeV, as well as partially quenched s quarks, which have a mass around the physical value. We consider all possible combinations of two light valence quarks, i.e. Lambda, Sigma, Xi and Omega baryons corresponding to isospin I = 0, 1/2, 1 and strangeness S = 0, -1, -2 as well as angular momentum of the light degrees of freedom j = 0, 1 and parity P = +, -. We extrapolate in the light u/d and in the heavy b quark mass to the physical point and compare with available experimental results. Besides experimentally known positive parity states we are also able to predict a number of negative parity states, which have neither been measured in experiments nor previously been computed by lattice methods.

Production of strange secondaries in high-energy Σ− A collisions

We describe the WA89 Collaboration experimental data on Lambda, Sigma(-), Sigma(+), Xi(-), and Omega(-) baryons, and bar(Lambda) and bar(Xi(+)) antibaryons production in Sigma(-) collisions with C and Cu targets at 345 GeV/c (sqrt(s_(Sigma N)) ~ 25.5 GeV) in the frame of the Quark-Gluon String Model. How the theoretical results compare to the experimental data is discussed. Finally, some relations among the values of the model parameters obtained with the help of quark combinatorics are presented.

DUAL-BAND MONOPOLE ANTENNA WITH OMEGA PARTICLES FOR WIRELESS APPLICATIONS

A new design of dual-band antenna for DCS/PCS/UMTS/ WLAN/WiMAX applications is proposed. Using two metamaterials omega-shaped structures, a good impedance matching the dual-band mode is obtained. The proposed prototype antenna is fabricated on a 1.5mm thick FR4 epoxy substrate with a relative dielectric permittivity r = 4:4 and a loss tangent tanae = 0:02. Good monopole- like radiation patterns and antenna gains over the operating bands have also been observed. Efiects of each omega particle on the antenna performance and their coupling are all examined and discussed.

Delta and omega electromagnetic form factors in a Dyson-Schwinger/Bethe-Salpeter approach

We investigate the electromagnetic form factors of the Delta and the Omega baryons within the Poincare-covariant framework of Dyson-Schwinger and Bethe-Salpeter equations. The three-quark core contributions of the form factors are evaluated by employing a quark-diquark approximation. We use a consistent setup for the quark-gluon dressing, the quark-quark bound-state kernel and the quark-photon interaction. Our predictions for the multipole form factors are compatible with available experimental data and quark-model estimates. The current-quark mass evolution of the static electromagnetic properties agrees with results provided by lattice calculations.

Electromagnetic form factors of theΩ−in lattice QCD

We present results on the Omega baryon electromagnetic form factors using $N_f=2+1$ domain-wall fermion configurations for three pion masses in the range of about 350 to 300 MeV. We compare results obtained using domain wall fermions with those of a mixed-action (hybrid) approach, which combine domain wall valence quarks on staggered sea quarks, for a pion mass of about 350 MeV. We pay particular attention in the evaluation of the subdominant electric quadrupole form factor to sufficient accuracy to exclude a zero value, by constructing a sequential source that isolates it from the dominant form factors. The $\Omega^-$ magnetic moment, $\mu_{\Omega^{-}}$, the electric charge and magnetic radius, $\langle r^{2}_{E0/M1} \rangle$, are extracted for these pion masses. The electric quadrupole moment is determined for the first time using dynamical quarks.

Hyperons in two-flavor chiral perturbation theory

We use two-flavor chiral perturbation theory to describe hyperons. We focus on the strangeness conserving sector, and, as an example, calculate hyperon masses. Convergence of this two-flavor chiral expansion for observables is improved over the three-flavor theory. The cost, however, is a larger number of low-energy constants that must be ultimately determined from lattice QCD data. A formula for the mass of the omega baryon is derived to sixth order in this expansion, and will aid lattice practitioners in scale setting or tuning the strange quark mass.

Thermal stability of the omega phase in Zr-containing TiAl alloys

The thermal stability of omega phase in TiAl alloys has been investigated using scanning and transmission electron microscopy and it has been found that Zr has a strong effect in stabilising the omega phase. In Ti–44Al–4Nb–4Zr–0.2Si–1B the omega solvus was determined as just over 900 °C. Increasing additions of Zr to Ti–44Al–4Nb–2Mo resulted in an increase in the volume fraction of omega phase at 700 °C and the omega particle distribution was changed from localised to uniformly distributed omega. In the alloy with 2 at% Zr, omega particles were found uniformly throughout the B2 matrix at 700 °C.

ΞandΩbaryons in the Skyrme model

The mass spectrum and magnetic moments of \Xi and \Omega baryon resonances are investigated in the bound state approach of the Skyrme model. The empirical hyperon spectrum shows that several hyperon resonances share a pattern of (approximately) equal mass spacings between the states of same spin but of opposite parity. It is found that this pattern can be explained mostly by the energy difference between the P-wave and S-wave kaons bound to the soliton. Although one cannot exclude the possibility that these states can be described as pion-hyperon resonances, the present approach predicts that \Xi(1620) and \Xi(1690) have J^P = 12^-, while \Xi(1950) has J^P = 12^+. The differences with the quark model predictions for the \Xi and \Omega baryon spectrum are pointed out. Several relations for the masses and magnetic moments of those resonances are also obtained.

Growth Kinetic Model for Isothermal Omega Phase Particles in Low-Cost Beta Titanium Ti&amp;ndash;6.8Mo&amp;ndash;4.5Fe&amp;ndash;1.5Al Alloy

The growth kinetics of the isothermal omega phase in Ti–6.8Mo–4.5Fe–1.5Al can be monitored by the continuous measurement of the electrical resistivity as shown in our previous publication in this Journal. The rate law for the growth of these isothermal omega particles radius riso is obtained assuming the resistivity to be proportional to the surface of the interface between the beta matrix and the quasi spherical isothermal omega particles. The rate law r3iso∝t is observed at the beginning of the growth process, that is before the interaction of the outward diffusion fields from the particles. A mathematical model based on a diffusional transfer of the beta stabilizers from the ωiso particles through the interface between the ωiso particles into the beta matrix is developed. The growth rate slows down when the outward diffusional fields from the particles interact. Ostwald ripening is not observed.

Toward creating isotropic microwave composites with negative refraction

The properties of artificial isotropic microwave composites which would possess simultaneously negative permittivity and permeability are studied theoretically. Four kinds of composites are considered. Two of them concern media with split‐ring resonator particles with different particle arrangements. The other two are realized with Omega particles. An analytical antenna model of the electromagnetic behavior of a split‐ring resonator (SRR) is suggested and verified by numerical simulations. Next, material parameters of composite media made with SRR or Omega particles are calculated. Both mixtures can create negative index media, but Omega composites are more prospective for obtaining negative real values of permittivity and permeability than the split‐ring resonators.

Rate equation network for baryon production in high energy nuclear collisions

We develop and solve a network of rate equations for the production of baryons and anti-baryons in high energy nuclear collisions. We include all members of the baryon octet and decuplet and allow for transformations among them. This network is solved during a relativistic 2+1 hydrodynamical expansion of the of the hot matter created in the collision. As an application we compare to the number of protons, lambdas, negative cascades, and omega baryons measured at mid-rapidity in central collisions of gold nuclei at 65 GeV per nucleon at the Relativistic Heavy Ion Collider (RHIC).

Plane-wave reflection from double arrays of small magnetoelectric scatterers

An analytical model of reflection and transmission of plane waves in double regular arrays of bianisotropic particles is developed. A method to correct approximate values of the particle polarizabilities so that the energy conservation requirements are exactly satisfied is proposed. Double arrays of planar omega particles are studied in detail, and it is shown that very sharp Bragg resonances exist in such arrays. The theory is verified by comparison with numerical simulations based on the method of moments.