3,899 research outputs found
Scattering and Sequestering of Blow-Up Moduli in Local String Models
We study the scattering and sequestering of blow-up fields - either local to
or distant from a visible matter sector - through a CFT computation of the
dependence of physical Yukawa couplings on the blow-up moduli. For a visible
sector of D3-branes on orbifold singularities we compute the disk correlator <
\tau_s^{(1)} \tau_s^{(2)} ... \tau_s^{(n)} \psi \psi \phi > between orbifold
blow-up moduli and matter Yukawa couplings. For n = 1 we determine the full
quantum and classical correlator. This result has the correct factorisation
onto lower 3-point functions and also passes numerous other consistency checks.
For n > 1 we show that the structure of picture-changing applied to the twist
operators establishes the sequestering of distant blow-up moduli at disk level
to all orders in \alpha'. We explain how these results are relevant to
suppressing soft terms to scales parametrically below the gravitino mass. By
giving vevs to the blow-up fields we can move into the smooth limit and thereby
derive CFT results for the smooth Swiss-cheese Calabi-Yaus that appear in the
Large Volume Scenario.Comment: 51 pages, 7 figures; v2: references adde
M\"obius molecules and fragile Mott insulators
Motivated by the concept of M\"obius aromatics in organic chemistry, we
extend the recently introduced concept of fragile Mott insulators (FMI) to
ring-shaped molecules with repulsive Hubbard interactions threaded by a
half-quantum of magnetic flux (). In this context, a FMI is the
insulating ground state of a finite-size molecule that cannot be adiabatically
connected to a single Slater determinant, i.e., to a band insulator, provided
that time-reversal and lattice translation symmetries are preserved. Based on
exact numerical diagonalization for finite Hubbard interaction strength and
existing Bethe-ansatz studies of the one-dimensional Hubbard model in the
large- limit, we establish a duality between Hubbard molecules with and
sites, with integer. A molecule with sites is an FMI in the
absence of flux but becomes a band insulator in the presence of a half-quantum
of flux, while a molecule with sites is a band insulator in the absence
of flux but becomes an FMI in the presence of a half-quantum of flux. Including
next-nearest-neighbor-hoppings gives rise to new FMI states that belong to
multidimensional irreducible representations of the molecular point group,
giving rise to a rich phase diagram
Local DRLs and automated risk estimation in paediatric interventional cardiology
Introduction : Cardiac catheterization procedures result in high radiation doses and often multiple procedures are necessary for congenital heart disease patients. However, diagnostic reference levels (DRL) remain scarce. Our first goal was finding the optimal DRL parameter and determining appropriate DRLs. The second goal was to calculate organ doses (OD), effective doses (ED) and lifetime attributable risks (LAR) per procedure and to provide conversion factors based on dose area product (DAP).
Materials and methods : DRLs are calculated for each procedure type, as the 75th percentile of the cumulative value per procedure from the corresponding parameter. All irradiation events in the DICOM Structured Reports were automatically processed and simulated using PCXMC, resulting in OD, ED and LAR. Using a Kruskal Wallis H test and subsequent pairwise comparisons, differences in median values of the DRL parameter between procedure types were assessed.
Results : Linear regression showed a strong correlation and narrow confidence interval between DAP and product of body weight and fluoroscopy time (BWxFT), even when all procedures (diagnostic and interventional) are combined. Only 15% of the pairwise comparisons were statistically significant for DAP normalized to BWxFT (DAP(BWxFT)). The latter pairs contained less frequent procedure types with significant outliers. For DAP normalized to BW (DAP(BW)), 38% of the pairwise comparisons showed statistically significant differences. Conversion factors from DAP(BW) to OD and ED were reported for various weight groups, due to the higher correlation between DAP(BW) and both OD and ED than between DAP and both OD and ED.
Conclusions : The P75 of DAP(BWxFT) for all procedures combined serves as an appropriate DRL value. This facilitates local DRL determination in smaller paediatric centres, which often have insufficient data to produce appropriate DRLs for different procedure types. Conversion factors are more reliable starting from DAP(BW) instead of DAP and should be used according to the appropriate BW group
Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background
We show that the soft X-ray excess in the Coma cluster can be explained by a
cosmic background of relativistic axions converting into photons in the cluster
magnetic field. We provide a detailed self-contained review of the cluster soft
X-ray excess, the proposed astrophysical explanations and the problems they
face, and explain how a 0.1-1 keV axion background naturally arises at
reheating in many string theory models of the early universe. We study the
morphology of the soft excess by numerically propagating axions through
stochastic, multi-scale magnetic field models that are consistent with
observations of Faraday rotation measures from Coma. By comparing to ROSAT
observations of the 0.2-0.4 keV soft excess, we find that the overall excess
luminosity is easily reproduced for
GeV. The resulting morphology is highly sensitive to the magnetic field
power spectrum. For Gaussian magnetic field models, the observed soft excess
morphology prefers magnetic field spectra with most power in coherence lengths
on scales over those with most power on scales. Within this scenario, we bound the mean energy of the
axion background to , the axion mass to , and derive a
lower bound on the axion-photon coupling GeV.Comment: 43 pages, 11 figure
Reduced Augmentation Implicit Low-rank (RAIL) integrators for advection-diffusion and Fokker-Planck models
This paper introduces a novel computational approach termed the Reduced
Augmentation Implicit Low-rank (RAIL) method by investigating two predominant
research directions in low-rank solutions to time-dependent partial
differential equations (PDEs): dynamical low-rank (DLR), and step and
truncation (SAT) tensor methods. The RAIL method, along with the development of
the SAT approach, is designed to enhance the efficiency of traditional
full-rank implicit solvers from method-of-lines discretizations of
time-dependent PDEs, while maintaining accuracy and stability. We consider
spectral methods for spatial discretization, and diagonally implicit
Runge-Kutta (DIRK) and implicit-explicit (IMEX) RK methods for time
discretization. The efficiency gain is achieved by investigating low-rank
structures within solutions at each RK stage using a singular value
decomposition (SVD). In particular, we develop a reduced augmentation procedure
to predict the basis functions to construct projection subspaces. This
procedure balances algorithm accuracy and efficiency by incorporating as many
bases as possible from previous RK stages and predictions, and by optimizing
the basis representation through SVD truncation. As such, one can form implicit
schemes for updating basis functions in a dimension-by-dimension manner,
similar in spirit to the K-L step in the DLR framework. We also apply a
globally mass conservative post-processing step at the end of each RK stage. We
validate the RAIL method through numerical simulations of advection-diffusion
problems and a Fokker-Planck model, showcasing its ability to efficiently
handle time-dependent PDEs while maintaining global mass conservation. Our
approach generalizes and bridges the DLR and SAT approaches, offering a
comprehensive framework for efficiently and accurately solving time-dependent
PDEs with implicit treatment
Correspondence between functional scores from deep mutational scans and predicted effects on protein stability
Encountering works by Nyerere and Freire. Exploring the connections between education for liberation and education for self-reliance in contemporary radical popular education
This conceptual paper presents an encounter of a work regarding education on self-reliance by Tanzanian educator Julius K. Nyerere (1922–1999) with a work by Brazilian educator Paolo Freire (1921–1997) on education for liberation to explore their relevance for contemporary radical popular education. To this end, the study aligns with the methodological approaches used in qualitative comparative education research. Entering into a comparative dialogue between both contributions contextualises the respective features of each contribution and allows a systematic dialogue between commonalities and differences and for conclusions to be drawn regarding radical popular education. Solidarity and sustainability serve as guiding categories in this endeavour. They point conclusively to the benefits of further theoretical encounters (with, for example, the philosophy of ubuntu), to the risks of neoliberal reinterpretations and, against this background, to the quest for nurturing contemporary approaches in radical popular education in adult education academia, research and practice under the auspices of social change and transformation. (DIPF/Orig.
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