574 research outputs found
Strong disorder renormalization group on fractal lattices: Heisenberg models and magnetoresistive effects in tight binding models
We use a numerical implementation of the strong disorder renormalization
group (RG) method to study the low-energy fixed points of random Heisenberg and
tight-binding models on different types of fractal lattices. For the Heisenberg
model new types of infinite disorder and strong disorder fixed points are
found. For the tight-binding model we add an orbital magnetic field and use
both diagonal and off-diagonal disorder. For this model besides the gap spectra
we study also the fraction of frozen sites, the correlation function, the
persistent current and the two-terminal current. The lattices with an even
number of sites around each elementary plaquette show a dominant
periodicity. The lattices with an odd number of sites around each elementary
plaquette show a dominant periodicity at vanishing diagonal
disorder, with a positive weak localization-like magnetoconductance at infinite
disorder fixed points. The magnetoconductance with both diagonal and
off-diagonal disorder depends on the symmetry of the distribution of on-site
energies.Comment: 19 pages, 20 figure
Clear-cuts are temporary habitats, not matrix, for endangered grassland burnet moths (Zygaena spp.)
Burnet moths (Zygaena spp.) are day-flying Lepidoptera considered indicative of species-rich grasslands. In the present study, our aim was to clarify whether clear-cuts are habitat, supporting habitat or matrix for three species of Zygaena. We did so by sampling these species with sex pheromones on 48 clear-cuts, varying in amount of host and nectar plants, in southern Sweden. To compare the efficiency of such sampling, we also conducted transect walks on these clearcuts. Overall, host-plants on clear-cuts best explained the abundance of Zygaena spp. recorded, better than nectar-plants or connectivity with nearby grasslands. These results indicate that clear-cuts with an abundance of host plants are used as a fully functional habitat, and not a supporting habitat in the sense of only providing nectar. There is no support in these results for considering clear-cuts as an inert matrix. With about half the work-effort, pheromone traps recorded 100 times more Zygaena spp. as transect walks. The poor correspondence between observations during transects walks and pheromone trap catches suggest Zygaena spp. being difficult to monitor by transect walks. In contrast to grasslands, clear-cuts are short-term in nature requiring repeated recolonization, indicating the importance of permanent grasslands. However, clear-cuts are important temporary insect habitats due to their great acreage, and suitable management can increase the time they remain a habitat
Multiplicity of Gamma-Ray Transitions Observed in Lithium-Induced Reactions
This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit
Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets
It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and
main text. Final accepted versio
Colorectal cancer screening with fecal immunochemical testing or primary colonoscopy:An analysis of health equity based on a randomised trial
Background: We have addressed health equity attained by fecal immunochemical testing (FIT) and primary colonoscopy (PCOL), respectively, in the randomised controlled screening trial SCREESCO conducted in Sweden. Methods: We analysed data on the individuals recruited between March 2014, and March 2020, within the study registered with ClinicalTrials.gov, NCT02078804. Swedish population registry data on educational level, household income, country of birth, and marital status were linked to each 60-year-old man and woman who had been randomised to two rounds of FIT 2 years apart (n = 60,123) or once-only PCOL (n = 30,390). Furthermore, we geo-coded each study individual to his/her residential area and assessed neighbourhood-level data on deprivation, proportion of non-Western immigrants, population density, and average distance to healthcare center for colonoscopy. We estimated adjusted associations of each covariate with the colonoscopy attendance proportion out of all invited to respective arms; ie, the preferred outcome for addressing health equity. In the FIT arm, the test uptake and the colonoscopy uptake among the test positives were considered as the secondary outcomes. Findings: We found a marked socioeconomic gradient in the colonoscopy attendance proportion in the PCOL arm (adjusted odds ratio [95% credibility interval] between the groups categorised in the highest vs. lowest national quartile for household income: 2.20 [2.01-2.42]) in parallel with the gradient in the test uptake of the FIT x 2 screening (2.08 [1.96-2.20]). The corresponding gradient in the colonoscopy attendance proportion out of all invited to FIT was less pronounced (1.29 [1.16-1.42]), due to higher proportions of FIT positives in socioeconomically disadvantaged groups. Interpretation: The unintended risk of exacerbating inequalities in health by organised colorectal cancer screening may be higher with a PCOL strategy than a FIT strategy, despite parallel socioeconomic gradients in uptake
Blackbody emission from light interacting with an effective moving dispersive medium
Intense laser pulses excite a nonlinear polarisation response that may create
an effective flowing medium and, under appropriate conditions, a blocking
horizon for light. Here we analyse in detail the interaction of light with such
laser-induced flowing media, fully accounting for the medium dispersion
properties. An analytical model based on a first Born-approximation is found to
be in excellent agreement with numerical simulations based on Maxwell's
equations and shows that when a blocking horizon is formed, the stimulated
medium scatters light with a blackbody emission spectrum. Based on these
results, diamond is proposed as a promising candidate medium for future studies
of Hawking emission from artificial, dispersive horizons
Numerical renormalization-group study of spin correlations in one-dimensional random spin chains
We calculate the ground-state two-spin correlation functions of spin-1/2
quantum Heisenberg chains with random exchange couplings using the real-space
renormalization group scheme. We extend the conventional scheme to take account
of the contribution of local higher multiplet excitations in each decimation
step. This extended scheme can provide highly accurate numerical data for large
systems. The random average of staggered spin correlations of the chains with
random antiferromagnetic (AF) couplings shows algebraic decay like ,
which verifies the Fisher's analytic results. For chains with random
ferromagnetic (FM) and AF couplings, the random average of generalized
staggered correlations is found to decay more slowly than a power-law, in the
form close to . The difference between the distribution functions of
the spin correlations of the random AF chains and of the random FM-AF chains is
also discussed.Comment: 14 pages including 8 figures, REVTeX, submitted to Physical Review
The Low-Energy Fixed Points of Random Quantum Spin Chains
The one-dimensional isotropic quantum Heisenberg spin systems with random
couplings and random spin sizes are investigated using a real-space
renormalization group scheme. It is demonstrated that these systems belong to a
universality class of disordered spin systems, characterized by weakly coupled
large effective spins. In this large-spin phase the uniform magnetic
susceptibility diverges as 1/T with a non-universal Curie constant at low
temperatures T, while the specific heat vanishes as T^delta |ln T| for T->0.
For broad range of initial distributions of couplings and spin sizes the
distribution functions approach a single fixed-point form, where delta \approx
0.44. For some singular initial distributions, however, fixed-point
distributions have non-universal values of delta, suggesting that there is a
line of fixed points.Comment: 19 pages, REVTeX, 13 figure
Inhomogeneous magnetism in single crystalline SrCuIrO: Implications to phase-separation concepts
The single crystalline form of an insulator, SrCuIrO, is
shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K)
with spin-glass-like magnetic susceptibility behaviour. On the basis of this
finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we
propose that the idea of "phase- separation" described for manganites [1] is
more widespread in different ways. The observed experimental features enable us
to make a comparison with the predictions of a recent toy model [2] on {\it
magnetic} phase separation in an insulating environment.Comment: 4 pages, 4 figure
Real Space Renormalization Group Study of the S=1/2 XXZ Chains with Fibonacci Exchange Modulation
Ground state properties of the S=1/2 antiferromagnetic XXZ chain with
Fibonacci exchange modulation are studied using the real space renormalization
group method for strong modulation. The quantum dynamical critical behavior
with a new universality class is predicted in the isotropic case. Combining our
results with the weak coupling renormalization group results by Vidal et al.,
the ground state phase diagram is obtained.Comment: 9 pages, 9 figure
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