800 research outputs found
Introducing Quantum Ricci Curvature
Motivated by the search for geometric observables in nonperturbative quantum
gravity, we define a notion of coarse-grained Ricci curvature. It is based on a
particular way of extracting the local Ricci curvature of a smooth Riemannian
manifold by comparing the distance between pairs of spheres with that of their
centres. The quantum Ricci curvature is designed for use on non-smooth and
discrete metric spaces, and to satisfy the key criteria of scalability and
computability. We test the prescription on a variety of regular and random
piecewise flat spaces, mostly in two dimensions. This enables us to quantify
its behaviour for short lattices distances and compare its large-scale
behaviour with that of constantly curved model spaces. On the triangulated
spaces considered, the quantum Ricci curvature has good averaging properties
and reproduces classical characteristics on scales large compared to the
discretization scale.Comment: 43 pages, 27 figure
How round is the quantum de Sitter universe?
We investigate the quantum Ricci curvature, which was introduced in earlier
work, in full, four-dimensional quantum gravity, formulated nonperturbatively
in terms of Causal Dynamical Triangulations (CDT). A key finding of the CDT
approach is the emergence of a universe of de Sitter-type, as evidenced by the
successful matching of Monte Carlo measurements of the quantum dynamics of the
global scale factor with a semiclassical minisuperspace model. An important
question is whether the quantum universe exhibits semiclassicality also with
regard to its more local geometric properties. Using the new quantum curvature
observable, we examine whether the (quasi-)local properties of the quantum
geometry resemble those of a constantly curved space. We find evidence that on
sufficiently large scales the curvature behaviour is compatible with that of a
four-sphere, thus strengthening the interpretation of the dynamically generated
quantum universe in terms of a de Sitter space.Comment: 24 pages, 8 figure
Geometric flux formula for the gravitational Wilson loop
Finding diffeomorphism-invariant observables to characterize the properties
of gravity and spacetime at the Planck scale is essential for making progress
in quantum gravity. The holonomy and Wilson loop of the Levi-Civita connection
are potentially interesting ingredients in the construction of quantum
curvature observables. Motivated by recent developments in nonperturbative
quantum gravity, we establish new relations in three and four dimensions
between the holonomy of a finite loop and certain curvature integrals over the
surface spanned by the loop. They are much simpler than a gravitational version
of the nonabelian Stokes' theorem, but require the presence of totally geodesic
surfaces in the manifold, which follows from the existence of suitable Killing
vectors. We show that the relations are invariant under smooth surface
deformations, due to the presence of a conserved geometric flux.Comment: 36 pages, 5 figures; minor text changes, clarifying the role of
diffeomorphism invariance; agrees with published versio
Exploring corruption in fisheries
This paper explores corruption in global fisheries. While reducing corruption is critical for the effective management of the fisheries sector and the fulfilment of the UNâs sustainable development goals (SDGs, and SDGs14 and 16 in particular), to do so, it is necessary to first have a systematic and comprehensive understanding of what corruption is and how it is manifested in the sector. There is literature on illegal, unregulated and unreported (IUU) fishing, but not much on corruption. The paper proposes an analytical framework and applies it with six revelatory cases to improve the conceptual clarity of corruption in fisheries. Specific corruption problems found in licensing, negotiating access agreements, lax enforcement, extortion, political corruption, money laundering and tax manipulation, human trafficking etc. can therefore be better identified through this analysis, which lays a base for systematic responses to tackling corruption in fisheries and accordingly furthering the sustainable development of the sector
Computers, Coders, and Voters: Comparing Automated Methods for Estimating Party Positions
Assigning political actors positions in ideological space is a task of key importance to political scientists. In this paper we compare estimates obtained using the automated Wordscores and Wordfish techniques, along with estimates from voters and the Comparative Manifesto Project (CMP), against expert placements. We estimate the positions of 254 manifestos across 33 elections in Germany and Denmark, two cases with very different textual data available. We find that Wordscores approximately replicates the CMP, voter, and expert assessments of party positions in both cases, whereas Wordfish replicates the positions in the German manifestos only. The results demonstrate that automated methods can produce valid estimates of party positions, but also that the appropriateness of each method hinges on the quality of the textual data. Additional analyses suggest that Wordfish requires both longer texts and a more ideologically charged vocabulary in order to produce estimates comparable to Wordscores. The paper contributes to the literature on automated content analysis by providing a comprehensive test of convergent validation, in terms of both number of cases analyzed and number of validation measures
Computers, Coders, and Voters: Comparing Automated Methods for Estimating Party Positions
Assigning political actors positions in ideological space is a task of key importance to political scientists. In this paper we compare estimates obtained using the automated Wordscores and Wordfish techniques, along with estimates from voters and the Comparative Manifesto Project (CMP), against expert placements. We estimate the positions of 254 manifestos across 33 elections in Germany and Denmark, two cases with very different textual data available. We find that Wordscores approximately replicates the CMP, voter, and expert assessments of party positions in both cases, whereas Wordfish replicates the positions in the German manifestos only. The results demonstrate that automated methods can produce valid estimates of party positions, but also that the appropriateness of each method hinges on the quality of the textual data. Additional analyses suggest that Wordfish requires both longer texts and a more ideologically charged vocabulary in order to produce estimates comparable to Wordscores. The paper contributes to the literature on automated content analysis by providing a comprehensive test of convergent validation, in terms of both number of cases analyzed and number of validation measures
Exercise conditioning in old mice improves skeletal muscle regeneration
Skeletal muscle possesses the ability to regenerate after injury, but this ability is impaired or delayed with aging. Regardless of age, muscle retains the ability to positively respond to stimuli, such as exercise. We examined whether exercise is able to improve regenerative response in skeletal muscle of aged mice. Twentyâtwoâmonthâold male C57Bl/6J mice (n = 20) underwent an 8âwk progressive exercise training protocol [old exercised (OâEx) group]. An old sedentary (OâSed) and a sedentary young control (YâCtl) group were included. Animals were subjected to injections of cardiotoxin into the tibialis anterior muscle. The tibialis anterior were harvested before [OâEx/OâSed/ YâCtl control (CTL); n = 6], 10 d (OâEx/OâSed/YâCtl d 10; n = 8), and 28 d (OâEx/OâSed/YâCtl d 28; n = 6) postinjection. Average fiber crossâsectional area was reduced in all groups at d 10 (CTL: OâEx: 2499 ± 140; OâSed: 2320 ± 165; YâCtl: 2474 ± 269; d 10: OâEx: 1191 ± 100; OâSed: 1125 ± 99; YâCtl: 1481 ± 167 ÎŒm2; P 0.05). Satellite cell content was greater at CTL in OâEx (2.6 ± 0.4 satellite cells/100 fibers) compared with OâSed (1.0 ± 0.1% satellite cells/100 fibers; P < 0.05). Exercise conditioning appears to improve ability of skeletal muscle to regenerate after injury in aged mice.âJoanisse, S., Nederveen, J. P., Baker, J. M., Snijders, T., Iacono, C., Parise, G. Exercise conditioning in old mice improves skeletal muscle regeneration. FASEB J. 30, 3256â3268 (2016)
Picking a loser? A social choice perspective on the Danish government formation of 1975
Structure-Activity Study of an All-d Antimicrobial Octapeptide D2D
The increasing emergence of multi-drug resistant bacteria is a serious threat to public health worldwide. Antimicrobial peptides have attracted attention as potential antibiotics since they are present in all multicellular organisms and act as a first line of defence against invading pathogens. We have previously identified a small all-d antimicrobial octapeptide amide kk(1-nal)fk(1-nal)k(nle)-NH2 (D2D) with promising antimicrobial activity. In this work, we have performed a structure-activity relationship study of D2D based on 36 analogues aimed at discovering which elements are important for antimicrobial activity and toxicity. These modifications include an alanine scan, probing variation of hydrophobicity at lys5 and lys7, manipulation of amphipathicity, N-and C-termini deletions and lys-arg substitutions. We found that the hydrophobic residues in position 3 (1-nal), 4 (phe), 6 (1-nal) and 8 (nle) are important for antimicrobial activity and to a lesser extent cationic lysine residues in position 1, 2, 5 and 7. Our best analogue 5, showed MICs of 4 µg/mL against A. baumannii, E. coli, P. aeruginosa and S. aureus with a hemolytic activity of 47% against red blood cells. Furthermore, compound 5 kills bacteria in a concentration-dependent manner as shown by time-kill kinetics. Circular dichroism (CD) spectra of D2D and compounds 1–8 showed that they likely fold into α-helical secondary structure. Small angle x-ray scattering (SAXS) experiments showed that a random unstructured polymer-like chains model could explain D2D and compounds 1, 3, 4, 6 and 8. Solution structure of compound 5 can be described with a nanotube structure model, compound 7 can be described with a filament-like structure model, while compound 2 can be described with both models. Lipid interaction probed by small angle X-ray scattering (SAXS) showed that a higher amount of compound 5 (~50–60%) inserts into the bilayer compared to D2D (~30–50%). D2D still remains the lead compound, however compound 5 is an interesting antimicrobial peptide for further investigations due to its nanotube structure and minor improvement to antimicrobial activity compared to D2D
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