515 research outputs found
Jamming, relaxation, and memory in a structureless glass former
Real structural glasses form through various out-of-equilibrium processes,
including temperature quenches, rapid compression, shear, and aging. Each of
these processes should be formally understandable within the recently
formulated dynamical mean-field theory of glasses, but many of the numerical
tools needed to solve the relevant equations for sufficiently long timescales
do not yet exist. Numerical simulations of structureless (and therefore
mean-field-like) model glass formers can nevertheless aid searching for and
understanding such solutions, thanks to their ability to disentangle structural
from dimensional effects. We here study the infinite-range Mari-Kurchan model
under simple non-equilibrium processes and compare the results with those from
the random Lorentz gas [J. Phys. A: Math. Theor. 55 334001, (2022)], which are
both mean-field-like and become formally equivalent in the limit of infinite
spatial dimensions. Of particular interest are jamming from crunching and under
instantaneous temperature quenches. The study allows for an algorithmic
understanding of the jamming density and of its approach to the
infinite-dimensional limit. The results provide important insight into the
eventual solution of the dynamical mean-field theory, including onsets and
anomalous relaxation, as well as into the various algorithmic schemes for
jamming.Comment: 13 pages, 6 figure
Local stability of spheres via the convex hull and the radical Voronoi diagram
Jamming is an emergent phenomenon wherein the local stability of individual
particles percolates to form a globally rigid structure. However, the onset of
rigidity does not imply that every particle becomes rigid, and indeed some
remain locally unstable. These particles, if they become unmoored from their
neighbors, are called \textit{rattlers}, and their identification is critical
to understanding the rigid backbone of a packing, as these particles cannot
bear stress. The accurate identification of rattlers, however, can be a
time-consuming process, and the currently accepted method lacks a simple
geometric interpretation. In this manuscript, we propose two simpler
classifications of rattlers based on the convex hull of contacting neighbors
and the maximum inscribed sphere of the radical Voronoi cell, each of which
provides geometric insight into the source of their instability. Furthermore,
the convex hull formulation can be generalized to explore stability in
hyperstatic soft sphere packings, spring networks, non-spherical packings, and
mean-field non-central-force potentials.Comment: 9 pages, 9 figure
Generating large disordered stealthy hyperuniform systems with ultra-high accuracy to determine their physical properties
Hyperuniform many-particle systems are characterized by a structure factor
that is precisely zero as ; and
stealthy hyperuniform systems have for the finite range , called the "exclusion region." Through a process of
collective-coordinate optimization, energy-minimizing disordered stealthy
hyperuniform systems of moderate size have been made to high accuracy, and
their novel physical properties have shown great promise. However, minimizing
in the exclusion region is computationally intensive as the
system size becomes large. In this Letter, we present an improved methodology
to generate such states using double-double precision calculations on GPUs that
reduces the deviations from zero within the exclusion region by a factor of
approximately for systems sizes more than an order of magnitude
larger. We further show that this ultra-high accuracy is required to draw
conclusions about their corresponding characteristics, such as the nature of
the associated energy landscape and the presence or absence of Anderson
localization, which might be masked, even when deviations are relatively small.Comment: 7 pages, 3 figure
Blooms of Dinoflagellate Mixotrophs in a Lower Chesapeake Bay Tributary: Carbon and Nitrogen Uptake over Diurnal, Seasonal, and Interannual Timescales
A multi-year study was conducted in the eutrophic Lafayette River, a sub-tributary of the lower Chesapeake Bay during which uptake of inorganic and organic nitrogen (N) and C compounds was measured during multiple seasons and years when different dinoflagellate species were dominant. Seasonal dinoflagellate blooms included a variety of mixotrophic dinoflagellates including Heterocapsa triquetra in the late winter, Prorocentrum minimum in the spring, Akashiwo sanguinea in the early summer, and Scrippsiella trochoidea and Cochlodinium polykrikoides in late summer and fall. Results showed that no single N source fueled algal growth, rather rates of N and C uptake varied on seasonal and diurnal timescales, and within blooms as they initiated and developed. Rates of photosynthetic C uptake were low yielding low assimilation numbers during much of the study period and the ability to assimilate dissolved organic carbon augmented photosynthetic C uptake during bloom and non-bloom periods. The ability to use dissolved organic C during the day and night may allow mixotrophic bloom organisms a competitive advantage over co-occurring phytoplankton that are restricted to photoautotrophic growth, obtaining N and C during the day and in well-lit surface waters
SNP data reveals the complex and diverse evolutionary history of the blue-ringed octopus genus (Octopodidae: Hapalochlaena) in the Asia-Pacific
The blue-ringed octopus species complex (Hapalochlaena spp.), known to occur from Southern Australia to Japan, currently contains four formally described species (Hapalochlaena maculosa, Hapalochlaena fasciata, Hapalochlaena lunulata and Hapalochlaena nierstraszi). These species are distinguished based on morphological characters (iridescent blue rings and/or lines) along with reproductive strategies. However, the observation of greater morphological diversity than previously captured by the current taxonomic framework indicates that a revision is required. To examine species boundaries within the genus we used mitochondrial (12S rRNA, 16S rRNA, cytochrome c oxidase subunit 1 [COI], cytochrome c oxidase subunit 3 [COIII] and cytochrome b [Cytb]) and genome-wide SNP data (DaRT seq) from specimens collected across its geographic range including variations in depth from 3 m to >100 m. This investigation indicates substantially greater species diversity present within the genus Hapalochlaena than is currently described. We identified 10,346 SNPs across all locations, which when analysed support a minimum of 11 distinct clades. Bayesian phylogenetic analysis of the mitochondrial COI gene on a more limited sample set dates the diversification of the genus to ∼30 mya and corroborates eight of the lineages indicated by the SNP analyses. Furthermore, we demonstrate that the diagnostic lined patterning of H. fasciata found in North Pacific waters and NSW, Australia is polyphyletic and therefore likely the result of convergent evolution. Several “deep water” (>100 m) lineages were also identified in this study with genetic convergence likely to be driven by external selective pressures. Examination of morphological traits, currently being undertaken in a parallel morphological study, is required to describe additional species within the complex
Angular distribution studies on the two-photon ionization of hydrogen-like ions: Relativistic description
The angular distribution of the emitted electrons, following the two-photon
ionization of the hydrogen-like ions, is studied within the framework of second
order perturbation theory and the Dirac equation. Using a density matrix
approach, we have investigated the effects which arise from the polarization of
the incoming light as well as from the higher multipoles in the expansion of
the electron--photon interaction. For medium- and high-Z ions, in particular,
the non-dipole contributions give rise to a significant change in the angular
distribution of the emitted electrons, if compared with the electric-dipole
approximation. This includes a strong forward emission while, in dipole
approxmation, the electron emission always occurs symmetric with respect to the
plane which is perpendicular to the photon beam. Detailed computations for the
dependence of the photoelectron angular distributions on the polarization of
the incident light are carried out for the ionization of H, Xe, and
U (hydrogen-like) ions.Comment: 16 pages, 4 figures, published in J Phys
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