505 research outputs found
Fresh-Register Automata
What is a basic automata-theoretic model of computation with names and fresh-name generation? We introduce Fresh-Register Automata (FRA), a new class of automata which operate on an infinite alphabet of names and use a finite number of registers to store fresh names, and to compare incoming names with previously stored ones. These finite machines extend Kaminski and Francezâs Finite-Memory Automata by being able to recognise globally fresh inputs, that is, names fresh in the whole current run. We exam-ine the expressivity of FRAâs both from the aspect of accepted languages and of bisimulation equivalence. We establish primary properties and connections between automata of this kind, and an-swer key decidability questions. As a demonstrating example, we express the theory of the pi-calculus in FRAâs and characterise bisimulation equivalence by an appropriate, and decidable in the finitary case, notion in these automata
The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias
Dark matter halo clustering depends not only on halo mass, but also on other
properties such as concentration and shape. This phenomenon is known broadly as
assembly bias. We explore the dependence of assembly bias on halo definition,
parametrized by spherical overdensity parameter, . We summarize the
strength of concentration-, shape-, and spin-dependent halo clustering as a
function of halo mass and halo definition. Concentration-dependent clustering
depends strongly on mass at all . For conventional halo definitions
(), concentration-dependent clustering
at low mass is driven by a population of haloes that is altered through
interactions with neighbouring haloes. Concentration-dependent clustering can
be greatly reduced through a mass-dependent halo definition with for haloes with . Smaller implies larger radii and
mitigates assembly bias at low mass by subsuming altered, so-called backsplash
haloes into now larger host haloes. At higher masses () larger overdensities, , are necessary. Shape- and spin-dependent clustering are
significant for all halo definitions that we explore and exhibit a relatively
weaker mass dependence. Generally, both the strength and the sense of assembly
bias depend on halo definition, varying significantly even among common
definitions. We identify no halo definition that mitigates all manifestations
of assembly bias. A halo definition that mitigates assembly bias based on one
halo property (e.g., concentration) must be mass dependent. The halo
definitions that best mitigate concentration-dependent halo clustering do not
coincide with the expected average splashback radii at fixed halo mass.Comment: 19 pages, 13 figures. Updated to published version. Main result
summarized in Figure 1
Injection Matching Studies using Turn by Turn Beam Profile Measurements in the CERN PS
The very small emittance beam needed for the LHC requires that the emittance blow-up in its injector machines must be kept to a minimum. Mismatch upon the beam transfer from one machine to the next is a potential source of such blow-up. The CERN PS ring is equipped with 3 Secondary Emission Grids (SEM-Grids) which are used for emittance measurement at injection. One of these has been converted to a multi-turn mode, in which several tens of consecutive beam passages can be observed. This allows the study of mismatch between the PS-Booster and the PS. This paper describes the instrument and experimental results obtained during the last year
Statics and dynamics of weakly coupled antiferromagnetic spin-1/2 ladders in a magnetic field
We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work
is motivated by recent experiments on the compound (C5H12N)2CuBr4 (BPCB). We
use a combination of numerical and analytical methods, in particular the
density matrix renormalization group (DMRG) technique, to explore the phase
diagram and the excitation spectra of such a system. We give detailed results
on the temperature dependence of the magnetization and the specific heat, and
the magnetic field dependence of the nuclear magnetic resonance (NMR)
relaxation rate of single ladders. For coupled ladders, treating the weak
interladder coupling within a mean-field or quantum Monte Carlo approach, we
compute the transition temperature of triplet condensation and its
corresponding antiferromagnetic order parameter. Existing experimental
measurements are discussed and compared to our theoretical results. Furthermore
we compute, using time dependent DMRG, the dynamical correlations of a single
spin ladder. Our results allow to directly describe the inelastic neutron
scattering cross section up to high energies. We focus on the evolution of the
spectra with the magnetic field and compare their behavior for different
couplings. The characteristic features of the spectra are interpreted using
different analytical approaches such as the mapping onto a spin chain, a
Luttinger liquid (LL) or onto a t-J model. For values of parameters for which
such measurements exist, we compare our results to inelastic neutron scattering
experiments on the compound BPCB and find excellent agreement. We make
additional predictions for the high energy part of the spectrum that are
potentially testable in future experiments.Comment: 35 pages, 26 figure
Trapdoor Memory-Hard Functions
Memory-hard functions (MHF) are functions whose evaluation provably requires a lot of memory. While MHFs are an unkeyed primitive, it is natural to consider the notion of trapdoor MHFs (TMHFs). A TMHF is like an MHF, but when sampling the public parameters one also samples a trapdoor which allows evaluating the function much cheaper.
Biryukov and Perrin (Asiacrypt\u2717) were the first to consider TMHFs and put forth a candidate TMHF construction called Diodon that is based on the Scrypt MHF (Percival, BSDCan\u2709). To allow for a trapdoor, Scrypt\u27s initial hash chain is replaced by a sequence of squares in a group of unknown order where the order of the group is the trapdoor. For a length sequence of squares and a group of order , Diodon\u27s cumulative memory complexity (CMC) is without the trapdoor and with knowledge of it.
While Scrypt is proven to be optimally memory-hard in the random oracle model (Alwen et al., Eurocrypt\u2717), Diodon\u27s memory-hardness has not been proven so far. In this work, we fill this gap by rigorously analyzing a specific instantiation of Diodon. We show that its CMC is lower bounded by which almost matches the upper bound. Our proof is based Alwen et al.\u27s lower bound on Scrypt\u27s CMC but requires non-trivial modifications due to the algebraic structure of Diodon. Most importantly, our analysis involves a more elaborate compression argument and a solvability criterion for certain systems of Diophantine equations
Big data simulations for capacity improvement in a general ophthalmology clinic
PURPOSE Long total waiting times (TWT) experienced by patients during a clinic visit have a significant adverse effect on patient's satisfaction. Our aim was to use big data simulations of a patient scheduling calendar and its effect on TWT in a general ophthalmology clinic. Based on the simulation, we implemented changes to the calendar and verified their effect on TWT in clinical practice.
DESIGN AND METHODS For this retrospective simulation study, we generated a discrete event simulation (DES) model based on clinical timepoints of 4.401 visits to our clinic. All data points were exported from our clinical warehouse for further processing. If not available from the electronic health record, manual time measurements of the process were used. Various patient scheduling models were simulated and evaluated based on their reduction of TWT. The most promising model was implemented into clinical practice in 2017.
RESULTS During validation of our simulation model, we achieved a high agreement of mean TWT between the real data (229 ± 100 min) and the corresponding simulated data (225 ± 112 min). This indicates a high quality of the simulation model. Following the simulations, a patient scheduling calendar was introduced, which, compared with the old calendar, provided block intervals and extended time windows for patients. The simulated TWT of this model was 153 min. After implementation in clinical practice, TWT per patient in our general ophthalmology clinic has been reduced from 229 ± 100 to 183 ± 89 min.
CONCLUSION By implementing a big data simulation model, we have achieved a cost-neutral reduction of the mean TWT by 21%. Big data simulation enables users to evaluate variations to an existing system before implementation into clinical practice. Various models for improving patient flow or reducing capacity loads can be evaluated cost-effectively
Response of neovascular central serous chorioretinopathy to an extended upload of anti-VEGF agents
Purpose
To determine the anatomical and functional outcomes of an extended 6-month intravitreal anti-vascular endothelial growth factor (anti-VEGF) upload in choroidal neovascularization (CNV) secondary to chronic central serous chorioretinopathy (CSCR).
Methods
A retrospective database analysis was performed applying the following inclusion criteria: (1) diagnosis of CSCR, (2) diagnosis of secondary CNV, and (3) treatment of at least six consecutive injections of anti-VEGF. Outcome measures included the change of central retinal subfield thickness, remodeling of the pigment epithelium detachments, and change in visual function.
Results
Twenty-one eyes of 21 patients were included. Mean patient age was 65â±â8.3 years, and 35% of the patients (nâ=â8) were female. Mean disease duration before diagnosis of CNV was 48â±â25.3 months. Mean central retinal thickness decreased from 346â±â61 to 257â±â57 ÎŒm (pâ<â0.01) after the sixth injection while mean visual acuity improved from 0.65â±â0.35 to 0.49â±â0.29 (logMAR; pâ<â0.01). Of note, an extended upload of six as opposed to three injections yielded an additional mean central retinal thickness reduction (280â±â46 ÎŒm vs. 257â±â57 ÎŒm, pâ=â0.038). Significant CNV remodeling was observed as a decrease in pigment epithelium detachment (PED) vertical (pâ=â0.021) and horizontal diameter (pâ=â0.024) as well as PED height (pâ<â0.01).
Conclusion
An extended anti-VEGF upload of six consecutive injections seems to be effective in inducing CNV remodeling and fluid resorption in CNV complicating chronic CSCR
Impact of Sub-Retinal Fluid on the Long-Term Incidence of Macular Atrophy in Neovascular Age-related Macular Degeneration under Treat & Extend Anti-Vascular Endothelial Growth Factor Inhibitors
Sub-retinal fluid (SRF) has been discussed as a protective factor against macular atrophy in eyes with neovascular age-related macular degeneration (nAMD).To gauge the impact of SRF on macular atrophy, a database of 310 nAMD eyes was screened for eyes manifesting an SRF-only phenotype under treat & extend anti-VEGF treatment, defined as nAMD expressing CNV exudation beyond the three monthly anti-VEGF loading doses by SRF only without any signs of exudative intra-retinal fluid (IRF) for >= 3 years. Incidence of macular atrophy and treatment responses were evaluated on multimodal imaging, including optical coherence tomography (OCT), blue autofluorescence (BAF) and near-infrared (NIR) confocal scanning laser ophthalmoscopy and fluorescence and indocyanine green angiography (FAG/ICGA). In total, 27 eyes (8.7%) of 26 patients with a mean follow-up of 4.2 +/- 0.9 (3-5) years met the inclusion criteria. Mean age was 72 +/- 6 (range: 61-86) years. The SRF only phenotype was seen from baseline in 14 eyes (52%), and in 13 eyes (48%) after a mean 1.0 +/- 1.3 (1-3) injections. In years 1 to 5, mean 7.5, 5.9, 6.1, 6.1 and 7.0 anti-VEGF injections were given (p=0.33). Cumulative macular atrophy incidence was 11.5% at year 1, 15.4% throughout years 2 to 4, and 22.4% at year 5. In conclusion, eyes manifesting activity by SRF only in treat & extend anti-VEGF regimen for nAMD seem to exhibit rather low rates of macular atrophy during long-term follow-up. SRF might be an indicator of a more benign form of nAMD
Design of beam optics for the Future Circular Collider e+e- -collider rings
A beam optics scheme has been designed for the Future Circular Collider-e+e-
(FCC-ee). The main characteristics of the design are: beam energy 45 to 175
GeV, 100 km circumference with two interaction points (IPs) per ring,
horizontal crossing angle of 30 mrad at the IP and the crab-waist scheme [1]
with local chromaticity correction. The crab-waist scheme is implemented within
the local chromaticity correction system without additional sextupoles, by
reducing the strength of one of the two sextupoles for vertical chromatic
correction at each side of the IP. So-called "tapering" of the magnets is
applied, which scales all fields of the magnets according to the local beam
energy to compensate for the effect of synchrotron radiation (SR) loss along
the ring. An asymmetric layout near the interaction region reduces the critical
energy of SR photons on the incoming side of the IP to values below 100 keV,
while matching the geometry to the beam line of the FCC proton collider
(FCC-hh) [2] as closely as possible. Sufficient transverse/longitudinal dynamic
aperture (DA) has been obtained, including major dynamical effects, to assure
an adequate beam lifetime in the presence of beamstrahlung and top-up
injection. In particular, a momentum acceptance larger than +/-2% has been
obtained, which is better than the momentum acceptance of typical collider
rings by about a factor of 2. The effects of the detector solenoids including
their compensation elements are taken into account as well as synchrotron
radiation in all magnets. The optics presented in this paper is a step toward a
full conceptual design for the collider. A number of issues have been
identified for further study
The acceleration and storage of radioactive ions for a neutrino factory
The term beta-beam has been coined for the production of a pure beam of
electron neutrinos or their antiparticles through the decay of radioactive ions
circulating in a storage ring. This concept requires radioactive ions to be
accelerated to a Lorentz gamma of 150 for 6He and 60 for 18Ne. The neutrino
source itself consists of a storage ring for this energy range, with long
straight sections in line with the experiment(s). Such a decay ring does not
exist at CERN today, nor does a high-intensity proton source for the production
of the radioactive ions. Nevertheless, the existing CERN accelerator
infrastructure could be used as this would still represent an important saving
for a beta-beam facility. This paper outlines the first study, while some of
the more speculative ideas will need further investigations.Comment: Accepted for publication in proceedings of Nufact02, London, 200
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