762 research outputs found
Relativistic Lagrangian displacement field and tensor perturbations
We investigate the purely spatial Lagrangian coordinate transformation from
the Lagrangian to the basic Eulerian frame. We demonstrate three techniques for
extracting the relativistic displacement field from a given solution in the
Lagrangian frame. These techniques are (a) from defining a local set of
Eulerian coordinates embedded into the Lagrangian frame; (b) from performing a
specific gauge transformation; and (c) from a fully non-perturbative approach
based on the ADM split. The latter approach shows that this decomposition is
not tied to a specific perturbative formulation for the solution of the
Einstein equations. Rather, it can be defined at the level of the
non-perturbative coordinate change from the Lagrangian to the Eulerian
description. Studying such different techniques is useful because it allows us
to compare and develop further the various approximation techniques available
in the Lagrangian formulation. We find that one has to solve the gravitational
wave equation in the relativistic analysis, otherwise the corresponding
Newtonian limit will necessarily contain spurious non-propagating tensor
artefacts at second order in the Eulerian frame. We also derive the magnetic
part of the Weyl tensor in the Lagrangian frame, and find that it is not only
excited by gravitational waves but also by tensor perturbations which are
induced through the non-linear frame-dragging. We apply our findings to
calculate for the first time the relativistic displacement field, up to second
order, for a CDM Universe in the presence of a local primordial
non-Gaussian component. Finally, we also comment on recent claims about whether
mass conservation in the Lagrangian frame is violated.Comment: 19 pages, two figures, improved discussion, matches published versio
Living Tangent
A living tangent is how I am known by many and how I have lived my life for some time. I think in tangents and my life and art seem to evolve through them. Everything I make is connected by multiple thoughts or tangent lines that run from something as simple as the color red, to the idea that I believe communism has invaded my family’s homeland. This then leads to the recollection of childhood games, taught to me by my family in Venezuela and the importance these games played in my psychological development and in my presence as an individual in society. These tangent understandings are the first few stones thrown onto the path that has become my life as an artist and politically conscious individual. In my thesis work, I am exploring the connection of random thoughts in the construction of reality and art. As one idea flows into many different tangents, these elements are linked in the chain of events that connect them together, helping to create a more unified world. My art is an attempt to unify my world.
Living Tangent is about exploring the connections in my psyche and in the real world (that have become strained over the years) through the reimagining of childhood games, new games, and the political problems in Venezuela. Games are played in cycles, and as children, we play them over and over each time hoping to beat the person we lost to last time or hoping to stay on top. The rules to these games almost never change, and while there may be variations to the rules, they can be played over and over with one thing never changing; there will always be a winner and a loser. This cycle repeats and everyone has a chance of winning, but when the cycle is disrupted the continuity is broken, leaving the only one that can win being the one that caused the disruption in the first place. This is represented in the way the political parties in Venezuela have rigged elections, killed or captured their rivals, and basically changed the rules of the game. Consequently, I have decided to change the way the games are played and the way they are set up and able to be played
Unusual weak magnetic exchange in two different structure types: YbPtSn and YbPtIn
We present the structural, magnetic, thermodynamic, and transport properties
of the two new compounds YbPtSn and YbPtIn. X-ray powder diffraction
shows that they crystallize in different structure types, the hexagonal
ZrPtAl and the cubic Heusler type, respectively. Despite quite different
lattice types, both compounds present very similar magnetic properties: a
stable trivalent Yb, no evidence for a sizeable Kondo interaction, and
very weak exchange interactions with a strength below 1K as deduced from
specific heat . Broad anomalies in suggest short range magnetic
ordering at about 250mK and 180mK for YbPtSn and YbPtIn, respectively.
The weak exchange and the low ordering temperature result in a large
magnetocaloric effect as deduced from the magnetic field dependence of ,
making these compounds interesting candidates for magnetic cooling. In addition
we found in YbPtIn evidences for a charge density wave transition at about
290K. The occurrence of such transitions within several RETX compound
series (RE = rare earth, T = noble metal, X = In, Sn) is analyzed.Comment: 16 pages, 7 figure
Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging
<p>Abstract</p> <p>Background</p> <p>Traditional comparative morphological analyses and subsequent three-dimensional reconstructions suffer from a number of drawbacks. This is particularly evident in the case of soft tissue studies that are technically demanding, time-consuming, and often prone to produce artefacts. These problems can partly be overcome by employing non-invasive, destruction-free imaging techniques, in particular micro-computed tomography or magnetic resonance imaging.</p> <p>Results</p> <p>Here, we employed high-field magnetic resonance imaging techniques to gather numerous data from members of a major marine invertebrate taxon, the sea urchins (Echinoidea). For this model study, 13 of the 14 currently recognized high-ranking subtaxa (orders) of this group of animals were analyzed. Based on the acquired datasets, interactive three-dimensional models were assembled. Our analyses reveal that selected soft tissue characters can even be used for phylogenetic inferences in sea urchins, as exemplified by differences in the size and shape of the gastric caecum found in the Irregularia.</p> <p>Conclusion</p> <p>The main focus of our investigation was to explore the possibility to systematically visualize the internal anatomy of echinoids obtained from various museum collections. We show that, in contrast to classical preparative procedures, magnetic resonance imaging can give rapid, destruction-free access to morphological data from numerous specimens, thus extending the range of techniques available for comparative studies of invertebrate morphology.</p
Effectiveness of agricultural interventions that aim to improve nutritional status of children: systematic review
Objective To assess the effectiveness of agricultural interventions in improving the nutritional status of children in developing countries
A new approach to cosmological structure formation with massive neutrinos
We show how Newtonian cosmological simulations can be employed to investigate
the non-linear evolution of two particle species in a relativistic context. We
discuss the application for massive neutrinos and other multi-species systems
such as Cold Dark Matter (CDM) plus baryons or Warm Dark Matter (WDM). We
propose a method that allows us to perform simulations including massive
neutrinos and general relativistic effects at almost the same computational
cost as ordinary CDM only N-body simulations, employing tailor-made initial
conditions and a dictionary for the interpretation of the simulation output.Comment: 28 pages, 9 figure
Simultaneous optimization of gait and design parameters for bipedal robots
A walking bipedal robot’s energy efficiency depends on its gait as well as its design, whereas design changes affect the optimal gaits. We propose a method to take these interdependencies into account via simultaneous optimization of gait as well as design parameters. The method is applied to a planar robot with hybrid zero dynamics control and a torsion spring between its thighs. Periodic gaits are simulated by means of the hybrid zero dynamics. The implementation of the simultaneous optimization of gait parameters and spring stiffness via sequential quadratic programming is presented. Subsequently, an error analysis is performed to gain good convergence and short computation times of the optimization. The evaluation of gradients is identified as crucial for the algorithm’s convergence and therefore performed via complex step derivative approximations. The resulting implementation exhibits good convergence behavior and is provided as supplement to this paper. At 2.3 m/s, the simultaneous optimization results in savings in energy expenditure of up to 55%. A consecutive optimization of first gait and then stiffness yields only 11%, demonstrating the advantage of the presented method
Emergence of superconductivity in the canonical heavy-electron metal YbRh2Si2
We report magnetic and calorimetric measurements down to T = 1 mK on the
canonical heavy-electron metal YbRh2Si2. The data reveal the development of
nuclear antiferromagnetic order slightly above 2 mK. The latter weakens the
primary electronic antiferromagnetism, thereby paving the way for
heavy-electron superconductivity below Tc = 2 mK. Our results demonstrate that
superconductivity driven by quantum criticality is a general phenomenon.Comment: 39 pages including Supplementary Materials. Version before
copy-edited by the journa
REDUCED SENSITIVITY OF GENOTYPE 3 HEPATITIS C VIRUS TO DIRECT ACTING ANTIVIRALS
PhDSofosbuvir is a uridine based nucleotide inhibitor of the hepatitis C viral (HCV)
polymerase that is the backbone of many treatment regimens. In combination with
drugs targeting other viral enzymes (including the poorly potent guanosine analogue
ribavirin or highly potent inhibitors of viral NS5A or protease) most patients clear virus
and resistance to sofosbuvir is rare, allowing effective retreatment with sofosbuvir.
Patients with Genotype 3 HCV respond less well than other genotypes and response
is reduced in those previously exposed to interferon. Here we show that patientderived
virus from patients with Genotype 3 HCV who relapse to sofosbuvir-based
therapies have a reduced sensitivity to SOF in an in-vitro phenotyping assay. Analysis
of viral sequencing data revealed two distinct polymorphisms (A150V and K206E) in
the HCV polymerase that are associated with treatment failure and in-vitro; they
reduce sofosbuvir sensitivity against genotype 3 hepatitis C virions. However both
polymorphisms modify the cellular response to type I interferon and in cells lacking
response to interferon the impact on sofosbuvir sensitivity is minimal. The A150V
polymorphism reduces the response to interferon 70 fold whereas the K206E
substitution has minimal effects on interferon in isolation but in combination with
A150V reduces the response 100 fold. Preliminary data indicates that the A150V
polymorphism interferes with the late response to type I interferons enabling the virus
to overcome the induction of interferon-stimulated genes. These data indicate a
complex interaction between direct acting antiviral drugs and the innate antiviral
response
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