5,236 research outputs found
Creation and Growth of Components in a Random Hypergraph Process
Denote by an -component a connected -uniform hypergraph with
edges and vertices. We prove that the expected number of
creations of -component during a random hypergraph process tends to 1 as
and tend to with the total number of vertices such that
. Under the same conditions, we also show that
the expected number of vertices that ever belong to an -component is
approximately . As an immediate
consequence, it follows that with high probability the largest -component
during the process is of size . Our results
give insight about the size of giant components inside the phase transition of
random hypergraphs.Comment: R\'{e}sum\'{e} \'{e}tend
Spatially resolved spectroscopy of the exoplanet HR 8799 c
HR 8799 is a multi-planet system detected in direct imaging, with three
companions known so far. Here, we present spatially resolved VLT/NACO
3.88--4.10 micron spectroscopy of the middle planet, HR 8799 c, which has an
estimated mass of ~10 Mjup, temperature of ~1100 K and projected separation of
38 AU. The spectrum shows some differences in the continuum from existing
theoretical models, particularly longwards of 4 microns, implying that detailed
cloud structure or non-equilibrium conditions may play an important role in the
physics of young exoplanetary atmospheres.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter
Large quantum fluctuations in the strongly coupled spin-1/2 chains of green dioptase: a hidden message from birds and trees
The green mineral dioptase Cu6Si6O18(H2O)6 has been known since centuries and
plays an important role in esoteric doctrines. In particular, the green
dioptase is supposed to grant the skill to speak with trees and to understand
the language of birds. Armed with natural samples of dioptase, we were able to
unravel the magnetic nature of the mineral (presumably with hidden support from
birds and trees) and show that strong quantum fluctuations can be realized in
an essentially framework-type spin lattice of coupled chains, thus neither
frustration nor low-dimensionality are prerequisites. We present a microscopic
magnetic model for the green dioptase. Based on full-potential DFT
calculations, we find two relevant couplings in this system: an
antiferromagnetic coupling J_c, forming spiral chains along the hexagonal c
axis, and an inter-chain ferromagnetic coupling J_d within structural Cu2O6
dimers. To refine the J_c and J_d values and to confirm the proposed spin
model, we perform quantum Monte-Carlo simulations for the dioptase spin
lattice. The derived magnetic susceptibility, the magnetic ground state, and
the sublattice magnetization are in remarkably good agreement with the
experimental data. The refined model parameters are J_c = 78 K and J_d = -37 K
with J_d/J_c ~ -0.5. Despite the apparent three-dimensional features of the
spin lattice and the lack of frustration, strong quantum fluctuations in the
system are evidenced by a broad maximum in the magnetic susceptibility, a
reduced value of the Neel temperature T_N ~ 15 K >> J_c, and a low value of the
sublattice magnetization m = 0.55 Bohr magneton. All these features should be
ascribed to the low coordination number of 3 that outbalances the
three-dimensional nature of the spin lattice.Comment: Dedicated to Stefan-Ludwig Drechsler on the occasion of his 60th
birthday (9 pages, 6 figures
Moulding the democratic citizen of the future: On the discourses and practices of film education in Sweden
The aim of this article is to convey the history, practices and central discourses of film education in Sweden. The first part takes the pioneering efforts, dating back to 1908, as a starting point for describing the development of nationwide school cinema, financed by public funding and coordinated by the Swedish Film Institute. As I will argue, film education in Sweden is primarily used as a tool for fostering democratic citizens. The second part of the article discusses the main discourses of this film education model – that is, what constitutes this democratic citizen – and how these are conveyed. An analysis of film study guides produced by the Swedish Film Institute between 1988 and 2018 demonstrates that the main aim of what could be referred to as the Swedish model is to foster the basic principles of human rights as defined by the United Nations, and that this is achieved in a very convincing manner
Marriage and Divorce in Survivors of Childhood Cancer: A Report from the Childhood Cancer Survivor Study
In this report from the Childhood Cancer Survivor Study (CCSS), we described marriage and divorce rates in survivors of childhood cancer, as compared to a sibling control group and the general U.S. population. We also sought to identify patient and treatment characteristics that were associated with survivor marital status. This study included 8,930 five-year survivors of childhood malignancy and 2,855 sibling controls participating in the CCSS. Data on marital status, sociodemographic factors, and current health status were obtained from questionnaires; detailed disease and treatment histories were available from medical records. Marital status of the U.S. population was obtained from the 2002 Current Population Survey of the U.S. Census. We found that survivors were more likely to have never married than both sibling (odds ratio [OR] = 1.79; 95 % CI = 1.65-1.94; p \u3c 0.0001) and population controls (OR = 2.29; 95 % CI = 2.19-2.38; p \u3c 0.0001), with persistence of trends across age and gender strata. Once married, survivors divorced at rates equivalent to controls. In adjusted analysis, we found that several survivor characteristics predicted never-married status, including treatment involving cranial radiation (OR = 2.41; p \u3c 0.0001), CNS tumor diagnosis (OR = 2.05; p \u3c 0.0001), history of growth hormone deficiency (OR = 2.02; p \u3c 0.0001), and unemployment secondary to disability (OR = 1.78; p = 0.0001). Survivor characteristics predictive of divorce included unemployment (OR = 1.91; p \u3c 0.0001, for unemployed or disabled), lower educational achievement (OR = 1.74; p \u3c 0.0001, for non-college graduates), and psychological distress (OR = 1.60; p \u3c 0.0001). This study confirms prior reports of lower marriage rates in survivors of childhood cancer, providing further evidence that this population struggles with psychosocial adjustment to adult life
Magnetism of CuX2 frustrated chains (X = F, Cl, Br): the role of covalency
Periodic and cluster density-functional theory (DFT) calculations, including
DFT+U and hybrid functionals, are applied to study magnetostructural
correlations in spin-1/2 frustrated chain compounds CuX2: CuCl2, CuBr2, and a
fictitious chain structure of CuF2. The nearest-neighbor and second-neighbor
exchange integrals, J1 and J2, are evaluated as a function of the Cu-X-Cu
bridging angle, theta, in the physically relevant range 80-110deg. In the ionic
CuF2, J1 is ferromagnetic for theta smaller 100deg. For larger angles, the
antiferromagnetic superexchange contribution becomes dominant, in accord with
the Goodenough-Kanamori-Anderson rules. However, both CuCl2 and CuBr2 feature
ferromagnetic J1 in the whole angular range studied. This surprising behavior
is ascribed to the increased covalency in the Cl and Br compounds, which
amplifies the contribution from Hund's exchange on the ligand atoms and renders
J1 ferromagnetic. At the same time, the larger spatial extent of X orbitals
enhances the antiferromagnetic J2, which is realized via the long-range
Cu-X-X-Cu paths. Both, periodic and cluster approaches supply a consistent
description of the magnetic behavior which is in good agreement with the
experimental data for CuCl2 and CuBr2. Thus, owing to their simplicity, cluster
calculations have excellent potential to study magnetic correlations in more
involved spin lattices and facilitate application of quantum-chemical methods
Microscopic magnetic modeling for the =1/2 alternating chain compounds NaCuSbO and NaCuTeO
The spin-1/2 alternating Heisenberg chain system NaCuSbO features
two relevant exchange couplings: within the structural CuO
dimers and between the dimers. Motivated by the controversially
discussed nature of , we perform extensive density-functional-theory
(DFT) calculations, including DFT+ and hybrid functionals. Fits to the
experimental magnetic susceptibility using high-temperature series expansions
and quantum Monte Carlo simulations yield the optimal parameters =
217 K and = 174 K with the alternation ratio 1.25. For the closely related system
NaCuTeO, DFT yields substantially enhanced , but weaker
. The comparative analysis renders the buckling of the chains as the
key parameter altering the magnetic coupling regime. Numerical simulation of
the dispersion relations of the alternating chain model clarify why both
antiferromagnetic and ferrromagnetic can reproduce the experimental
magnetic susceptibility data.Comment: published version: 11 pages, 8 figures, 5 tables + Supplemental
materia
Terrestrial planets across space and time
The study of cosmology, galaxy formation and exoplanets has now advanced to a
stage where a cosmic inventory of terrestrial planets may be attempted. By
coupling semi-analytic models of galaxy formation to a recipe that relates the
occurrence of planets to the mass and metallicity of their host stars, we trace
the population of terrestrial planets around both solar-mass (FGK type) and
lower-mass (M dwarf) stars throughout all of cosmic history. We find that the
mean age of terrestrial planets in the local Universe is Gyr for FGK
hosts and Gyr for M dwarfs. We estimate that hot Jupiters have
depleted the population of terrestrial planets around FGK stars by no more than
, and that only of the terrestrial planets at the
current epoch are orbiting stars in a metallicity range for which such planets
have yet to be confirmed. The typical terrestrial planet in the local Universe
is located in a spheroid-dominated galaxy with a total stellar mass comparable
to that of the Milky Way. When looking at the inventory of planets throughout
the whole observable Universe, we argue for a total of and terrestrial planets around FGK and M
stars, respectively. Due to light travel time effects, the terrestrial planets
on our past light cone exhibit a mean age of just Gyr. These
results are discussed in the context of cosmic habitability, the Copernican
principle and searches for extraterrestrial intelligence at cosmological
distances.Comment: 11 pages, 8 figures. v.2: Accepted for publication in ApJ. Some
changes in quantitative results compared to v.1, mainly due to differences in
IMF assumption
Crystal water induced switching of magnetically active orbitals in CuCl2
The dehydration of CuCl2*2(H2O) to CuCl2 leads to a dramatic change in
magnetic behavior and ground state. Combining density functional electronic
structure and model calculations with thermodynamical measurements we reveal
the microscopic origin of this unexpected incident -- a crystal water driven
switching of the magnetically active orbitals. This switching results in a
fundamental change of the coupling regime from a three-dimensional
antiferromagnet to a quasi one-dimensional behavior. CuCl2 can be well
described as a frustrated J1-J2 Heisenberg chain with ferromagnetic exchange J1
and J2/J1 ~ -1.5 for which a helical ground state is predicted.Comment: 6 pages, 5 figures, 1 table (PRB, accepted
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