3,618 research outputs found
Dynamical renormalization group approach to relaxation in quantum field theory
The real time evolution and relaxation of expectation values of quantum
fields and of quantum states are computed as initial value problems by
implementing the dynamical renormalization group (DRG).Linear response is
invoked to set up the renormalized initial value problem to study the dynamics
of the expectation value of quantum fields. The perturbative solution of the
equations of motion for the field expectation values of quantum fields as well
as the evolution of quantum states features secular terms, namely terms that
grow in time and invalidate the perturbative expansion for late times. The DRG
provides a consistent framework to resum these secular terms and yields a
uniform asymptotic expansion at long times. Several relevant cases are studied
in detail, including those of threshold infrared divergences which appear in
gauge theories at finite temperature and lead to anomalous relaxation. In these
cases the DRG is shown to provide a resummation akin to Bloch-Nordsieck but
directly in real time and that goes beyond the scope of Bloch-Nordsieck and
Dyson resummations. The nature of the resummation program is discussed in
several examples. The DRG provides a framework that is consistent, systematic
and easy to implement to study the non-equilibrium relaxational dynamics
directly in real time that does not rely on the concept of quasiparticle
widths.Comment: LaTex, 27 pages, 2 .ps figure
Potential for non-destructive astrochemistry using the ExoMars PanCam
We investigate the utility of adding a 365 nm ultraviolet (UV) light source to the ExoMars panoramic camera (PanCam) scheduled for launch in 2013. The modification makes it feasible to monitor rover drill cuttings for aromatic organic molecules and provide constraints on polycyclic aromatic hydrocarbons (PAH) as a function of depth to the 2-meter limit of the ExoMars drill. This non-destructive triage allows prioritized deployment of organic detection experiments requiring sample destruction and/or expenditure of non-replaceable resources. Utilizing the Beagle 2 PanCam backup filter wheel fitted with original blue (440 nm), green ( 530 nm), and red ( 670 nm) filters we captured fluorescent images following 365 nm excitation of 3-, 4- and 5-ring PAH species doped on Mars analog peridotite grains. We demonstrate a detection limit for pyrene of 1.5 mu g in granular peridotite doped at pyrene levels of 50 +/- 5 ppm for camera-to-target distance of 1 meter
Theorems on existence and global dynamics for the Einstein equations
This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local-in-time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity that offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure or late-time asymptotics are given. A
conjectural picture of the asymptotic behaviour of general cosmological
solutions of the Einstein equations is built up. Some miscellaneous topics
connected with the main theme are collected in a separate section.Comment: Submitted to Living Reviews in Relativity, major update of Living
Rev. Rel. 5 (2002)
Constitutional patriotism
Constitutional patriotism is a political theory that seeks to provide an explanation for the sense of ownership that most individuals have towards their national constitutional system. Specifically, constitutional patriotism assumes that free-thinking individuals involved in a discussion over the common good will reach an agreement that is perceived, at least by those involved in the debate, as having normative value. The awareness that such a deliberative process has historically been a part of the constitutional system also induces a sense of ownership of past historical accommodations of constitutional principles. The shared perception of being part of historically grounded institutions within a deliberative democracy is sometimes called the ânormative surplus effectâ or ânormative spill-over effectâ of the deliberative process. The theory, in its current form, was proposed by JĂŒrgen Habermas and Jean-Werner MĂŒller.
Debates over the common good might take place informally or within the stateâs institutions. Pell-mell informal debates, with few exceptions, have a limited effect on amending constitutional norms. Yet, the prerogative to openly discuss laws and policies legitimised by constitutional norms is normally sufficient to develop an inner sense of belonging to a constitutional system. Deliberative debates within public institutions (e.g. parliaments and courts) are more likely to change the functioning of a constitutional system, but they are, by way of comparison to informal political discussions, normally constrained by the system of rules that regulate representative democracy and the administration of justice. Thus, the theory of constitutional patriotism provides an explanatory model for the historical development of a democratic constitutional system.
As one of the most persuasive explanatory theories of modern pluralist democracy, constitutional patriotism has attracted a series of well-articulated critiques. It has been suggested, for instance, that constitutional patriotism might not provide a plausible model of social integration for international organisations such as the European Union (EU). In this essay, I will provide an overview of the theory and a selection of its critiques
Segond's fracture: a biomechanical cadaveric study using navigation
Background Segondâs fracture is a well-recognised radiological
sign of an anterior cruciate ligament (ACL) tear.
While previous studies evaluated the role of the anterolateral
ligament (ALL) and complex injuries on rotational
stability of the knee, there are no studies on the biomechanical
effect of Segondâs fracture in an ACL deficient
knee. The aim of this study was to evaluate the effect of a
Segondâs fracture on knee rotation stability as evaluated by
a navigation system in an ACL deficient knee.
Materials and methods Three different conditions were
tested on seven knee specimens: intact knee, ACL deficient
knee and ACL deficient knee with Segondâs fracture. Static
and dynamic measurements of anterior tibial translation
(ATT) and axial tibial rotation (ATR) were recorded by the
navigation system (2.2 OrthoPilot ACL navigation system
B. Braun Aesculap, Tuttlingen, Germany).
Results Static measurements at 30 showed that the mean
ATT at 30 of knee flexion was 5.1 ± 2.7 mm in the ACL
intact condition, 14.3 ± 3.1 mm after ACL cut
(P = 0.005), and 15.2 ± 3.6 mm after Segondâs fracture
(P = 0.08). The mean ATR at 30 of knee flexion was
20.7 ± 4.8 in the ACL intact condition, 26.9 ± 4.1 in
the ACL deficient knee (P[0.05) and 30.9 ± 3.8 after
Segondâs fracture (P = 0.005). Dynamic measurements
during the pivot-shift showed that the mean ATT was
7.2 ± 2.7 mm in the intact knee, 9.1 ± 3.3 mm in the
ACL deficient knee(P = 0.04) and 9.7 ± 4.3 mm in the
ACL deficient knee with Segondâs fracture (P = 0.07).
The mean ATR was 9.6 ± 1.8 in the intact knee,
12.3 ± 2.3 in the ACL deficient knee (P[0.05) and
19.1 ± 3.1 in the ACL deficient knee with Segondâs
lesion (P = 0.016).
Conclusion An isolated lesion of the ACL only affects
ATT during static and dynamic measurements, while the
addition of Segondâs fracture has a significant effect on
ATR in both static and dynamic execution of the pivot-shift
test, as evaluated with the aid of navigation
The state of kidney replacement therapy in Eastern Cape Province, South Africa: A call to action
Background. South Africa (SA) is one of the most financially unequal countries in the world. This situation is highlighted by disparate
access to healthcare, particularly provision of kidney replacement therapy (KRT). Unlike the private sector, public sector access to KRT is highly rationed, and patient selection is based on suitability for transplantation and capacity.
Objectives. To investigate the state of the KRT service in Eastern Cape Province, SA, by analysing access to and provision of KRT in the
province for individuals with end-stage kidney disease, as well as disparities between the private and public healthcare systems.
Methods. This was a retrospective descriptive study to examine KRT provision and temporal trends in the Eastern Cape. Data were obtained from the South African Renal Registry and the National Transplant Waiting List. KRT provision was compared between the three main referral centres, in Gqeberha (formerly Port Elizabeth), East London and Mthatha, and between the private and public healthcare systems.
Results. There were 978 patients receiving KRT in the Eastern Cape, with an overall treatment rate of 146 per million population (pmp).
The treatment rate for the private sector was 1 435 pmp, compared with 49 pmp in the public sector. Patients treated in the private sector were older at initiation of KRT (52 v. 34 years), and more likely to be male, to be HIV positive, and to receive haemodialysis as their KRT modality. Peritoneal dialysis was more commonly used in Gqeberha and East London as the first and subsequent KRT modality, compared with Mthatha. There were no patients from Mthatha on the transplant waiting list. There were no waitlisted HIV-positive patients in the public sector in East London, compared with 16% of the public sector patients in Gqeberha. The kidney transplant prevalence rate was 58 pmp in the private sector and 19 pmp in the public sector, with a combined prevalence of 22 pmp, constituting 14.9% of all patients on KRT. We estimated the shortfall of KRT provision in the public sector to be ~8 606 patients.
Conclusion. Patients in the private sector were 29 times more likely to access KRT than their public sector counterparts, who were on
average 18 years younger at initiation of KRT, probably reflecting selection bias in an overburdened public health system. Transplantation rates were low in both sectors, and lowest in Mthatha. A large public sector KRT provision gap exists in the Eastern Cape and needs to be addressed urgently
Phase transitions in the early and the present Universe
The evolution of the Universe is the ultimate laboratory to study fundamental
physics across energy scales that span about 25 orders of magnitude: from the
grand unification scale through particle and nuclear physics scales down to the
scale of atomic physics. The standard models of cosmology and particle physics
provide the basic understanding of the early and present Universe and predict a
series of phase transitions that occurred in succession during the expansion
and cooling history of the Universe. We survey these phase transitions,
highlighting the equilibrium and non-equilibrium effects as well as their
observational and cosmological consequences. We discuss the current theoretical
and experimental programs to study phase transitions in QCD and nuclear matter
in accelerators along with the new results on novel states of matter as well as
on multi- fragmentation in nuclear matter. A critical assessment of
similarities and differences between the conditions in the early universe and
those in ultra- relativistic heavy ion collisions is presented. Cosmological
observations and accelerator experiments are converging towards an
unprecedented understanding of the early and present Universe.Comment: 41 pages, 16 figures, to appear in Ann. Rev. Nucl. Part. Sci 2006.
Presentation improved, references adde
Isometry of medial collateral ligament reconstruction
The purpose of this study was to determine the femoral and tibial fixation sites that would result in the most isometric MCL reconstruction technique. Seven cadaveric knees were used in this study. A navigation system was utilized to determine graft isometry continuously from 0Âș to 90Âș. Five points on the medial side of the femur and four on the tibia were tested. A graft positioned in the center of the MCL femoral attachment (FC) and attached in the center of the superficial MCL attachment on the tibia led to the best isometry (2.7 ± 1.1 mm). Movement of the origin superiorly only 4 mm (FS) led to graft excursion of greater than 10 mm (P < 0.01). MCL reconstruction performed with the origin of the MCL within the femoral footprint and the insertion in tibial footprint of the superficial MCL results in the least graft excursion when the knee is cycled between 0Âș and 90Âș. Although the MCL often heals without surgical intervention, surgical reconstruction is occasionally in Grade III MCL and combined ligamentous injuries to the knee. This study demonstrates the optimal position of the MCL reconstruction to reproduce the kinematics of the native knee
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