987 research outputs found
Random projection to preserve patient privacy
With the availability of accessible and widely used cloud services, it is natural that large components of healthcare systems migrate to them; for example, patient databases can be stored and processed in the cloud. Such cloud services provide enhanced flexibility and additional gains, such as availability, ease of data share, and so on. This trend poses serious threats regarding the privacy of the patients and the trust that an individual must put into the healthcare system itself. Thus, there is a strong need of privacy preservation, achieved through a variety of different approaches. In this paper, we study the application of a random projection-based approach to patient data as a means to achieve two goals: (1) provably mask the identity of users under some adversarial-attack settings, (2) preserve enough information to allow for aggregate data analysis and application of machine-learning techniques. As far as we know, such approaches have not been applied and tested on medical data. We analyze the tradeoff between the loss of accuracy on the outcome of machine-learning algorithms and the resilience against an adversary. We show that random projections proved to be strong against known input/output attacks while offering high quality data, as long as the projected space is smaller than the original space, and as long as the amount of leaked data available to the adversary is limited
Crossing the c=1 barrier in 2d Lorentzian quantum gravity
In an extension of earlier work we investigate the behaviour of
two-dimensional Lorentzian quantum gravity under coupling to a conformal field
theory with c>1. This is done by analyzing numerically a system of eight Ising
models (corresponding to c=4) coupled to dynamically triangulated Lorentzian
geometries. It is known that a single Ising model couples weakly to Lorentzian
quantum gravity, in the sense that the Hausdorff dimension of the ensemble of
two-geometries is two (as in pure Lorentzian quantum gravity) and the matter
behaviour is governed by the Onsager exponents. By increasing the amount of
matter to 8 Ising models, we find that the geometry of the combined system has
undergone a phase transition. The new phase is characterized by an anomalous
scaling of spatial length relative to proper time at large distances, and as a
consequence the Hausdorff dimension is now three. In spite of this qualitative
change in the geometric sector, and a very strong interaction between matter
and geometry, the critical exponents of the Ising model retain their Onsager
values. This provides evidence for the conjecture that the KPZ values of the
critical exponents in 2d Euclidean quantum gravity are entirely due to the
presence of baby universes. Lastly, we summarize the lessons learned so far
from 2d Lorentzian quantum gravity.Comment: 21 pages, 18 figures (postscript), uses JHEP.cls, see
http://www.nbi.dk/~ambjorn/lqg2 for related animated simulation
The QCD sign problem and dynamical simulations of random matrices
At nonzero quark chemical potential dynamical lattice simulations of QCD are
hindered by the sign problem caused by the complex fermion determinant. The
severity of the sign problem can be assessed by the average phase of the
fermion determinant. In an earlier paper we derived a formula for the
microscopic limit of the average phase for general topology using chiral random
matrix theory. In the current paper we present an alternative derivation of the
same quantity, leading to a simpler expression which is also calculable for
finite-sized matrices, away from the microscopic limit. We explicitly prove the
equivalence of the old and new results in the microscopic limit. The results
for finite-sized matrices illustrate the convergence towards the microscopic
limit. We compare the analytical results with dynamical random matrix
simulations, where various reweighting methods are used to circumvent the sign
problem. We discuss the pros and cons of these reweighting methods.Comment: 34 pages, 3 figures, references added, as published in JHE
A new perspective on matter coupling in 2d quantum gravity
We provide compelling evidence that a previously introduced model of
non-perturbative 2d Lorentzian quantum gravity exhibits (two-dimensional)
flat-space behaviour when coupled to Ising spins. The evidence comes from both
a high-temperature expansion and from Monte Carlo simulations of the combined
gravity-matter system. This weak-coupling behaviour lends further support to
the conclusion that the Lorentzian model is a genuine alternative to Liouville
quantum gravity in two dimensions, with a different, and much `smoother'
critical behaviour.Comment: 24 pages, 7 figures (postscript
Higher myocardial strain rates duringisovolumic relaxation phase than duringejection characterize acutely ischemic myocardium
AbstractObjectivesThe aim of this study was to define an index that can differentiate normal from ischemic myocardial segments that exhibit postsystolic shortening (PSS).BackgroundIdentification of ischemia based on the reduction of regional systolic function is sometimes challenging because other factors such as normal nonuniformity in contraction between segments, tethering effect, pharmacologic agents, or alterations in loading conditions can also cause reduction in regional systolic deformation. The PSS (contraction after the end of systole) is a sensitive marker of ischemia; however, inconsistent patterns have also been observed in presumed normal myocardium.MethodsTwenty-eight open-chest pigs underwent echocardiographic study before and during acute myocardial ischemia induced by coronary artery occlusion. Ultrasound-derived myocardial longitudinal strain rates were calculated during systole (SSR), isovolumic relaxation (IVRSR), and rapid filling (ESR) phases in both ischemic and normal myocardium. Systolic strain (ϵsys) and postsystolic strain (ϵps) were calculated by integrating systolic and postsystolic strain rates, respectively.ResultsDuring ischemia, SSR, ESR, and ϵsys in ischemic segments were significantly lower (in magnitude) than in nonischemic segments or at baseline. However, some overlap occurred between ischemic and normal values for all three parameters. At baseline, 18 of 28 animals had negative IVRSR (i.e., PSS) in at least one segment. During coronary artery occlusion, IVRSR became negative and larger in magnitude than SSR in all ischemic segments. The IVRSR/SSR and ϵps best differentiated ischemic from nonischemic segments.ConclusionsIn the presence of reduced regional systolic deformation, a higher rate of PSS than systolic shortening identifies acutely ischemic myocardium
Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms
The transitions in pionic nitrogen and muonic oxygen were measured
simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to
the precise knowledge of the muon mass the muonic line provides the energy
calibration for the pionic transition. A value of
(139.57077\,\,0.00018)\,MeV/c (\,1.3ppm) is derived for the
mass of the negatively charged pion, which is 4.2ppm larger than the present
world average
Line shape of the muH(3p - 1s) hyperfine transitions
The (3p - 1s) X-ray transition to the muonic hydrogen ground state was
measured with a high resolution crystal spectrometer. A Doppler effect
broadening of the X-ray line was established which could be attributed to
different Coulomb de-excitation steps preceding the measured transition. The
assumption of a statistical population of the hyperfine levels of the muonic
hydrogen ground state was directly confirmed by the experiment and measured
values for the hyperfine splitting can be reported. The results allow a
decisive test of advanced cascade model calculations and establish a method to
extract fundamental strong-interaction parameters from pionic hydrogen
experiments.Comment: Submitted to Physical Review Letter
Relativistic calculations of pionic and kaonic atoms hyperfine structure
We present the relativistic calculation of the hyperfine structure in pionic
and kaonic atoms. A perturbation method has been applied to the Klein-Gordon
equation to take into account the relativistic corrections. The perturbation
operator has been obtained \textit{via} a multipole expansion of the nuclear
electromagnetic potential. The hyperfine structure of pionic and kaonic atoms
provide an additional term in the quantum electrodynamics calculation of the
energy transition of these systems. Such a correction is required for a recent
measurement of the pion mass
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