Large Relative Distances Research Articles

He8 and Li9 cluster structures in light nuclei

The possibility of the $^8$He and $^{9}$Li clusters in atomic nuclei is discussed. Until now most of the clusters in the conventional models have been limited to the closures of the three-dimensional harmonic oscillators, such as $^4$He, $^{16}$O, and $^{40}$Ca. In the neutron-rich nuclei, however, the neutron to proton ratio is not unity, and it is worthwhile to think about more neutron-rich objects with $N>Z$ as the building blocks of cluster structures. Here the nuclei with the neutron number six, which is the subclosure of the $p_{3/2}$ subshell of the $jj$-coupling shell model, are assumed to be clusters, and thus we study the $^8$He and $^9$Li cluster structures in $^{16}$Be ($^8$He+$^8$He), $^{17}$B ($^8$He+$^9$Li), $^{18}$C ($^9$Li+$^9$Li), and $^{24}$C ($^8$He+$^8$He+$^8$He). Recent progress of the antisymmetrized quasi cluster model (AQCM) enables us to utilize $jj$-coupling shell model wave functions as the clusters rather easily. It is shown that the $^8$He+$^9$Li and $^9$Li+$^9$Li cluster configurations cover the lowest shell-model states of $^{17}$B and $^{18}$C, respectively. To predict the cluster states with large relative distances, we increase the expectation value of the principal quantum numbers by adding the nodes to the lowest states under the condition that the total angular momentum is unchanged (equal to $J^\pi =0$). As a result, developed cluster states are obtained around the corresponding threshold energies. The rotational band structure of $^{24}$C, which reflect the symmetry of equilateral triangular configuration ($D_{3h}$ symmetry) of three $^8$He clusters, also appears around the threshold energy.

Search for coincident air showers over large scale distances with the EEE network

The existence of time correlations in detectors separated by distances much larger than the size of the highest energy extensive air showers (EAS) has been long discussed over the years. Several mechanisms have been proposed to justify the existence of such events and, in the last decade, some experiments have also tried to search for correlations on a large scale distance, beyond one hundred kilometers. The approaches were based on the construction of clusters of detectors placed at large relative distances, with the capability of selecting extensive air showers.Within this context, the Extreme Energy Events (EEE) experiment can provide new inputs in the search for long distance correlations, thanks to its sparse array of muon telescopes spanning all the Italian territory.The EEE telescopes are taking data since more than 10 years and enough statistics has been already accumulated to be able to search for such events, whose observation is intrinsically difficult due to the very low rates expected, many order of magnitudes smaller than the overall cosmic ray flux. In order to reduce the accidental correlations, different analysis approaches have been investigated for the selection of EAS events with the EEE telescopes. In this paper we will present preliminary results obtained by analyzing a large fraction of the statistics currently available.

Propagation of Optical Coherence Vortex Lattices in Turbulent Atmosphere

Propagation properties in the turbulence atmosphere of the optical coherence vortex lattices (OCVLs) are explored by the recently developed convolution approach. The evolution of spectral density distribution, the normalized M 2 -factor, and the beam wander of the OCVLs propagating through the atmospheric turbulence with Tatarskii spectrum are illustrated numerically. Our results show that the OCVLs display interesting propagation properties, e.g., the initial Gaussian beam distribution will evolve into hollow array distribution on propagation and finally becomes a Gaussian beam spot again in the far field in turbulent atmosphere. Furthermore, the OCVLs with large topological charge, large beam array order, large relative distance, and small coherence length are less affected by the negative effects of turbulence. Our results are expected to be used in the complex system optical communications.

Morphological support for a clade comprising two vermiform mite lineages: Eriophyoidea (Acariformes) and Nematalycidae (Acariformes)

A morphology-based parsimony analysis (50 taxa; 110 characters) focused on relationships among basal acariform mites places Eriophyoidea (formerly in Trombidiformes) within Nematalycidae (Sarcoptiformes). Although both taxa have worm-like bodies, this grouping is unexpected because it combines obligate plant inhabitants (Eriophyoidea) with obligate inhabitants of deep-soil or mineral regolith (Nematalycidae sensu stricto). The Eriophyoidea + Nematalycidae clade, which is strongly supported (Bremer =5; bootstrap =85%), retains moderately good support (Bremer=3; bootstrap=66%) when three ratio-based characters pertaining to body shape are excluded. A total of eleven unambiguous synapomorphies unite all or some of Nematalycidae with Eriophyoidea. These include an annulated opisthosoma, an unpaired vi seta on the prodorsum, fusion of the palp trochanter with the palp femur, and a large relative distance between the anus and the genitalia. Three of the four Triassic genera of eriophyoid-like mites were also included in our analysis. Although all four genera have been tentatively placed within a new superfamily, we found no support for the monophyly of this group. One other interesting result of the analysis is the placement of a “living fossil”, Proterorhagia oztotloica (Proterorhagiidae), as sister to the rest of Acariformes. However, support for this relationship is weak.

Nonlinear Control of Formation Flying with State Constraints

Nonlinear Control of Formation Flying with State Constraints

A Time-Efficient Method for Anomaly Detection in Hyperspectral Images

We propose a computationally efficient method for determining anomalies in hyperspectral data. In the first stage of the algorithm, the background classes, which are the dominant classes in the image, are found. The method consists of robust clustering of a randomly chosen small percentage of the image pixels. The clusters are the representatives of the background classes. By using a subset of the pixels instead of the whole image, the computation is sped up, and the probability of including outliers in the background model is reduced. Anomalous pixels are the pixels with spectra that have large relative distances from the cluster centers. Several clustering techniques are investigated, and experimental results using realistic hyperspectral data are presented. A self-organizing map clustered using the local minima of the U-matrix (unified distance matrix) is identified as the most reliable method for background class extraction. The proposed algorithm for anomaly detection is evaluated using realistic hyperspectral data, is compared with a state-of-the-art anomaly detection algorithm, and is shown to perform significantly better.

Asymptotic Expansions of the Dirac Density Matrix

Asymptotic expansions are derived for the density operator ρN(x′, x)= ∑ n=1Nψn(x′)ψn(x)for small and large values of the relative distance x′ − x with a WKB expansion for bound-state wavefunctions in a plane, one-dimensional potential. In addition to some previously obtained corrections, the particle-density expansion includes a number of steady and oscillating correction terms to the zero-order Thomas-Fermi density which are related to the more recently derived corrections of Payne and of Kohn and Sham. A convenient and accurate approximation to the density operator for all arguments is also obtained from the first two terms of the expansion for large relative distances. The expansions become inadequate in the vicinity of the classical turning point of the highest energy state, as illustrated by numerical comparisons with the exact-density operator for the quadratic potential. A novel method is described for summing a finite series of oscillating terms such as occur in the density operator.