54 research outputs found
Attractors, Bifurcations and Curvature in Multi-field Inflation
Recent years have seen the introduction of various multi-field inflationary
scenarios in which the curvature and geodesics of the scalar manifold play a
crucial role. We outline a simple description that unifies these different
proposals and discuss their stability criteria. We demonstrate how the
underlying dynamics is governed by an effective potential, whose critical
points and bifurcations determine the late-time behaviour of the system, thus
unifying hyperinflation, angular, orbital and side-tracked inflation.
Interestingly, we show that hyperinflation is a special case of side-tracked
inflation, relying on the enhanced isometries of the hyperbolic manifold. We
provide the explicit coordinate transformation that maps the two models into
each other. Finally, we relax the assumption of a field-space isometry along
the inflationary direction that has been considered a prerequisite in the
literature so far. We explicitly construct inflationary solutions that do not
proceed along a field-space isometry or geodesic and use them to discuss
stability criteria.Comment: 22 pages and 5 figures. Manifestly covariant form of the attractor
solution added, small changes to match JCAP versio
Scaling attractors in multi-field inflation
Multi-field inflation with a curved scalar geometry has been found to support
background trajectories that violate the slow-roll, slow-turn conditions and
thus have the potential to evade the swampland constraints. In order to
understand how generic this novel behaviour is and what conditions lead to it,
we perform a classification of dynamical attractors of two-field inflation that
are of the scaling type. Scaling solutions form a one-parameter generalization
of De Sitter solutions with a constant value of the first Hubble flow parameter
and, as we argue and demonstrate, form a natural starting point for
the study of non-slow-roll slow-turn behaviour.
All scaling solutions can be classified as critical points of a specific
dynamical system. We recover known multi-field inflationary attractors as
approximate scaling solutions and classify their stability using dynamical
system techniques. In particular, we discover that dynamical bifurcations play
an integral role in the transition between geodesic and non-geodesic motion and
discuss the ability of scaling solutions to describe realistic multi-field
models. We revisit the criteria for background stability and show cases where
the usual criteria found in the literature do not capture the background
evolution of the system.Comment: 41 pages, 10 figure
Is it possible to test directly General Relativity in the gravitational field of the Moon?
In this paper the possibility of measuring some general relativistic effects
in the gravitational field of the Moon via selenodetic missions, with
particular emphasis to the future Japanese SELENE mission, is investigated. For
a typical selenodetic orbital configuration the post-Newtonian Lense-Thirring
gravitomagnetic and the Einstein's gravitoelectric effects on the satellites
orbits are calculated and compared to the present-day orbit accuracy of lunar
missions. It turns out that for SELENE's Main Orbiter, at present, the
gravitoelectric periselenium shift, which is the largest general relativistic
effect, is 1 or 2 orders of magnitude smaller than the experimental
sensitivity. The systematic error induced by the mismodelled classical
periselenium precession due to the first even zonal harmonic J2 of the Moon's
non-spherical gravitational potential is 3 orders of magnitude larger than the
general relativistic gravitoelectric precession. The estimates of this work
could be used for future lunar missions having as their goals relativistic
measurements as well.Comment: Latex2e, 7 pages, no figures, ets2000.cls and art12.sty used. Major
rewriting in introduction. References adde
On the Possibility of Measuring the Gravitomagnetic Clock Effect in an Earth Space-Based Experiment
In this paper the effect of the post-Newtonian gravitomagnetic force on the
mean longitudes of a pair of counter-rotating Earth artificial satellites
following almost identical circular equatorial orbits is investigated. The
possibility of measuring it is examined. The observable is the difference of
the times required to in passing from 0 to 2 for both senses of
motion. Such gravitomagnetic time shift, which is independent of the orbital
parameters of the satellites, amounts to 5 s for Earth; it is
cumulative and should be measured after a sufficiently high number of
revolutions. The major limiting factors are the unavoidable imperfect
cancellation of the Keplerian periods, which yields a constraint of 10
cm in knowing the difference between the semimajor axes of the satellites,
and the difference of the inclinations of the orbital planes which, for
, should be less than . A pair of spacecrafts
endowed with a sophisticated intersatellite tracking apparatus and drag-free
control down to 10 cm s Hz level might allow to meet
the stringent requirements posed by such a mission.Comment: LaTex2e, 22 pages, no tables, 1 figure, 38 references. Final version
accepted for publication in Classical and Quantum Gravit
Influence of Lung Reconstruction Algorithms on Interstitial Lung Pattern Recognition on CT.
BACKGROUND
âDespite current recommendations, there is no recent scientific study comparing the influence of CT reconstruction kernels on lung pattern recognition in interstitial lung disease (ILD).
PURPOSE
âTo evaluate the sensitivity of lung (i70) and soft (i30) CT kernel algorithms for the diagnosis of ILD patterns.
MATERIALS AND METHODS
âWe retrospectively extracted between 15-25 pattern annotations per case (1 annotationâ=â15 slices of 1âmm) from 23 subjects resulting in 408 annotation stacks per lung kernel and soft kernel reconstructions. Two subspecialized chest radiologists defined the ground truth in consensus. 4 residents, 2 fellows, and 2 general consultants in radiology with 3 to 13 years of experience in chest imaging performed a blinded readout. In order to account for data clustering, a generalized linear mixed model (GLMM) with random intercept for reader and nested for patient and image and a kernel/experience interaction term was used to analyze the results.
RESULTS
âThe results of the GLMM indicated, that the odds of correct pattern recognition is 12â% lower with lung kernel compared to soft kernel; however, this was not statistically significant (OR 0.88; 95%-CI, 0.73-1.06; pâ=â0.187). Furthermore, the consultants' odds of correct pattern recognition was 78â% higher than the residents' odds, although this finding did not reach statistical significance either (OR 1.78; 95%-CI, 0.62-5.06; pâ=â0.283). There was no significant interaction between the two fixed terms kernel and experience. Intra-rater agreement between lung and soft kernel was substantial (Îșâ=â0.63â±â0.19). The mean inter-rater agreement for lung/soft kernel was Îșâ=â0.37â±â0.17/Îșâ=â0.38â±â0.17.
CONCLUSION
âThere is no significant difference between lung and soft kernel reconstructed CT images for the correct pattern recognition in ILD. There are non-significant trends indicating that the use of soft kernels and a higher level of experience lead to a higher probability of correct pattern identification.
KEY POINTS
â · There is no significant difference between lung and soft kernel reconstructed CT images for the correct pattern recognition in interstitial lung disease.. · There are even non-significant tendencies that the use of soft kernels lead to a higher probability of correct pattern identification.. · These results challenge the current recommendations and the routinely performed separate lung kernel reconstructions for lung parenchyma analysis..
CITATION FORMAT
· Klaus JB, Christodoulidis S, Peters AA etâal. Influence of Lung Reconstruction Algorithms on Interstitial Lung Pattern Recognition on CT. Fortschr Röntgenstr 2022; DOI: 10.1055/a-1901-7814
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
Within the heart's darkness:The role of emotions in Arendt's political thought
Interest in the political relevance of the emotions is growing rapidly. In light of this, Hannah Arendtâs claim that the emotions are apolitical has come under renewed fire. But many critics have misunderstood her views on the relationship between individuals, emotions and the political. This paper addresses this issue by reconstructing the conceptual framework through which Arendt understands the emotions. Arendt often describes the heart â where the emotions reside â as a place of darkness. I begin by tracing this metaphor through her work to demonstrate that it is meant to convey the inherently uncertain nature of emotions rather than a devaluation of them. I proceed to challenge the notion that Arendt adopts the Enlightenment dichotomy between reason and emotion. In fact, she rejects both as a basis for politics. However, she does identify some constructive roles for the emotions. I argue that fear is intrinsically connected to courage â the principal political virtue â in Arendtâs philosophy. In light of my discussion, I then reinterpret the role of compassion and pity in On Revolution, concluding that Arendtâs insights can help us avoid the potential pitfalls of the contemporary project to recuperate the emotions in politics
Evidence of functional deficits at the single muscle fiber level in experimentally-induced renal insufficiency
Chronic kidney disease patients present with metabolic and functional muscle
abnormalities, called uremic myopathy, whose mechanisms have not yet been fully
elucidated. We investigated whether chronic renal insufficiency (CRI) affects skeletal
muscle contractile properties at the cellular level. CRI was induced surgically in New
Zealand rabbits (UREM), with sham-operation for controls (CON), and samples were
collected at 3 months post-surgery, following euthanasia. All protocols had University
Ethics approval following national and European guidelines. Sample treatments and
evaluations were blinded. Maximal isometric force was assessed in 382 permeabilized
psoas fibers (CON, n=142, UREM, n=240) initially at pH7, 10oC (âstandardâ
conditions), in subsets of fibers in acidic conditions (pH6.2, 10oC) but also at near
physiological temperature (pH7, 30oC and pH6.2, 30oC). CRI resulted in significant
smaller average CSA (~11%) for UREM muscle fibers (vs CON, P<0.01). At
standard conditions, UREM fibers produced lower absolute and specific forces (i.e.
normalized force per fiber CSA) (vs CON, P<0.01); force increased in 30oC for both
groups (P<0.01), but the disparity between UREM and CON remained significant.
Acidosis significantly reduced force (vs pH7, 10oC P<0.01), similarly in both groups
(in UREM by -48% and in CON by -43%, P>0.05). For the first time, we give
evidence that CRI can induce significant impairments in single psoas muscle fibers
force generation, only partially explained by fiber atrophy, thus affecting muscle
mechanics at the cellular level
Evidence of blood and muscle redox status imbalance in experimentally induced renal insufficiency in a rabbit model
Chronic kidney disease (CKD) is accompanied by a disturbed redox homeostasis, especially in end-stage patients, which is associated with pathological complications such as anemia, atherosclerosis, and muscle atrophy. However, limited evidence exists about redox disturbances before the end stage of CKD. Moreover, the available redox literature has not yet provided clear associations between circulating and tissue-specific (muscle) oxidative stress levels. The aim of the study was to evaluate commonly used redox status indices in the blood and in two different types of skeletal muscle (psoas, soleus) in the predialysis stages of CKD, using an animal model of renal insufficiency, and to investigate whether blood redox status indices could be reflecting the skeletal muscle redox status. Indices evaluated included reduced glutathione (GSH), oxidized glutathione (GSSG), glutathione reductase (GR), catalase (CAT), total antioxidant capacity (TAC), protein carbonyls (PC), and thiobarbituric acid reactive substances (TBARS). Results showed that blood GSH was higher in the uremic group compared to the control (17.50 ± 1.73 vs. 12.43 ± 1.01, p = 0.033). In both muscle types, PC levels were higher in the uremic group compared to the control (psoas: 1.086 ± 0.294 vs. 0.596 ± 0.372, soleus: 2.52 ± 0.29 vs. 0.929 ± 0.41, p < 0.05). The soleus had higher levels of TBARS, PC, GSH, CAT, and GR and lower TAC compared to the psoas in both groups. No significant correlations in redox status indices between the blood and skeletal muscles were found. However, in the uremic group, significant correlations between the psoas and soleus muscles in PC, GSSG, and CAT levels emerged, not present in the control. Even in the early stages of CKD, a disturbance in redox homeostasis was observed, which seemed to be muscle type-specific, while blood levels of redox indices did not seem to reflect the intramuscular condition. The above results highlight the need for further research in order to identify the key mechanisms driving the onset and progression of oxidative stress and its detrimental effects on CKD patients.This work was supported by the European Union (European Social Fund, ESF) and Greek national funds through the Operational Program âEducational and Lifelong Learningâ of the National Strategic Reference Framework (NSRF), Research Funding Program: Thales (MuscleFun Project-MIS 377260) Investing in Knowledge Society through the European Social Fund, and the European Union Horizon 2020 Research and Innovation Programme âH2020 MSCAS-RISE-Muscle Stress Reliefâ under grant agreement no. 645648.Published versio
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