63 research outputs found
Random Matrices and Chaos in Nuclear Physics
The authors review the evidence for the applicability of random--matrix
theory to nuclear spectra. In analogy to systems with few degrees of freedom,
one speaks of chaos (more accurately: quantum chaos) in nuclei whenever
random--matrix predictions are fulfilled. An introduction into the basic
concepts of random--matrix theory is followed by a survey over the extant
experimental information on spectral fluctuations, including a discussion of
the violation of a symmetry or invariance property. Chaos in nuclear models is
discussed for the spherical shell model, for the deformed shell model, and for
the interacting boson model. Evidence for chaos also comes from random--matrix
ensembles patterned after the shell model such as the embedded two--body
ensemble, the two--body random ensemble, and the constrained ensembles. All
this evidence points to the fact that chaos is a generic property of nuclear
spectra, except for the ground--state regions of strongly deformed nuclei.Comment: 54 pages, 28 figure
Reduced Bloch mode expansion for periodic media band structure calculations
Reduced Bloch mode expansion is presented for fast periodic media band
structure calculations. The expansion employs a natural basis composed of a
selected reduced set of Bloch eigenfunctions. The reduced basis is selected
within the irreducible Brillouin zone at high symmetry points determined by the
medium's crystal structure and group theory (and possibly at additional related
points). At each of the reciprocal lattice selection points, a number of Bloch
eigenfunctions are selected up to the frequency range of interest for the band
structure calculations. Since it is common to initially discretize the periodic
unit cell and solution field using some choice of basis, reduced Bloch mode
expansion is practically a secondary expansion that uses a selected set of
Bloch eigenvectors. Such expansion therefore keeps, and builds on, any
favorable attributes a primary expansion approach might exhibit. Being in line
with the well known concept of modal analysis, the proposed approach maintains
accuracy while reducing the computation time by up to two orders of magnitudes
or more depending on the size and extent of the calculations. Results are
presented for phononic, photonic and electronic band structures.Comment: 15 pages of text, 8 figures, submitted for journal publication, minor
edits and correction of typo
Operative versus non-operative treatment for 2-part proximal humerus fracture: A multicenter randomized controlled trial
Background Although increasingly used, the benefit of surgical treatment of displaced 2-part proximal humerus fractures has not been proven. This trial evaluates the clinical effectiveness of surgery with locking plate compared with non-operative treatment for these fractures. Methods and findings The NITEP group conducted a superiority, assessor-blinded, multicenter randomized trial in 6 hospitals in Finland, Estonia, Sweden, and Denmark. Eighty-eight patients aged 60 years or older with displaced (more than 1 cm or 45 degrees) 2-part surgical or anatomical neck proximal humerus fracture were randomly assigned in a 1:1 ratio to undergo either operative treatment with a locking plate or non-operative treatment. The mean age of patients was 72 years in the non-operative group and 73 years in the operative group, with a female sex distribution of 95% and 87%, respectively. Patients were recruited between February 2011 and April 2016. The primary outcome measure was Disabilities of Arm, Shoulder, and Hand (DASH) score at 2-year follow-up. Secondary outcomes included ConstantâMurley score, the visual analogue scale for pain, the quality of life questionnaire 15D, EuroQol Groupâs 5- dimension self-reported questionnaire EQ-5D, the Oxford Shoulder Score, and complications. The mean DASH score (0 best, 100 worst) at 2 years was 18.5 points for the operative treatment group and 17.4 points for the non-operative group (mean difference 1.1 [95% CI â7.8 to 9.4], p = 0.81). At 2 years, there were no statistically or clinically significant between-group differences in any of the outcome measures. All 3 complications resulting in secondary surgery occurred in the operative group. The lack of blinding in patient-reported outcome assessment is a limitation of the study. Our assessor physiotherapists were, however, blinded. Conclusions This trial found no significant difference in clinical outcomes at 2 years between surgery and non-operative treatment in patients 60 years of age or older with displaced 2-part fractures of the proximal humerus. These results suggest that the current practice of performing surgery on the majority of displaced proximal 2-part fractures of the humerus in older adults may not be beneficial. Trial registration ClinicalTrials.gov NCT01246167.Peer reviewe
Registered Replication Report: Rand, Greene, and Nowak (2012)
In an anonymous 4-person economic game, participants contributed more money to a common project (i.e., cooperated) when required to decide quickly than when forced to delay their decision (Rand, Greene & Nowak, 2012), a pattern consistent with the social heuristics hypothesis proposed by Rand and colleagues. The results of studies using time pressure have been mixed, with some replication attempts observing similar patterns (e.g., Rand et al., 2014) and others observing null effects (e.g., TinghĂśg et al., 2013; Verkoeijen & Bouwmeester, 2014). This Registered Replication Report (RRR) assessed the size and variability of the effect of time pressure on cooperative decisions by combining 21 separate, preregistered replications of the critical conditions from Study 7 of the original article (Rand et al., 2012). The primary planned analysis used data from all participants who were randomly assigned to conditions and who met the protocol inclusion criteria (an intent-to-treat approach that included the 65.9% of participants in the time-pressure condition and 7.5% in the forced-delay condition who did not adhere to the time constraints), and we observed a difference in contributions of â0.37 percentage points compared with an 8.6 percentage point difference calculated from the original data. Analyzing the data as the original article did, including data only for participants who complied with the time constraints, the RRR observed a 10.37 percentage point difference in contributions compared with a 15.31 percentage point difference in the original study. In combination, the results of the intent-to-treat analysis and the compliant-only analysis are consistent with the presence of selection biases and the absence of a causal effect of time pressure on cooperation
Pairing in nuclear systems: from neutron stars to finite nuclei
We discuss several pairing-related phenomena in nuclear systems, ranging from
superfluidity in neutron stars to the gradual breaking of pairs in finite
nuclei. We focus on the links between many-body pairing as it evolves from the
underlying nucleon-nucleon interaction and the eventual experimental and
theoretical manifestations of superfluidity in infinite nuclear matter and of
pairing in finite nuclei. We analyse the nature of pair correlations in nuclei
and their potential impact on nuclear structure experiments. We also describe
recent experimental evidence that points to a relation between pairing and
phase transitions (or transformations) in finite nuclear systems. Finally, we
discuss recent investigations of ground-state properties of random two-body
interactions where pairing plays little role although the interactions yield
interesting nuclear properties such as 0+ ground states in even-even nuclei.Comment: 74 pages, 33 figs, uses revtex4. Submitted to Reviews of Modern
Physic
Registered Replication Report: Rand, Greene & Nowak (2012)
In an anonymous 4-person economic game, participants contributed more money to a common project (i.e., cooperated) when required to decide quickly than when forced to delay their decision (Rand, Greene & Nowak, 2012), a pattern consistent with the âsocial heuristicsâ hypothesis proposed by Rand and colleagues. The results of studies using time pressure have been mixed, with some replication attempts observing similar patterns (e.g., Rand et al., 2014) and others observing null effects (e.g., TinghĂśg et al., 2013, Verkoeijen et al., 2014). This Registered Replication Report (RRR) assessed the size and variability of the effect of time pressure on cooperative decisions by combining 21 separate, pre-registered replications of the critical conditions from Study 7 of the original paper (Rand et al., 2012). The primary planned analysis used data from all participants who were randomly assigned to conditions and who met the protocol inclusion criteria (an intent-to-treat approach that included the 65.9% of participants in the Time Pressure condition and 7.5% in the Forced Delay condition who did not adhere to the time constraints), and observed a difference in contributions of -0.37 percentage points, compared to an 8.6 percentage point difference calculated from the original data. Analyzing the data as the original paper did, including data only for participants who complied with the time constraints, the RRR observed a 10.37 percentage point difference in contributions compared to a 15.31 percentage point difference in the original study. In combination, the results of the intent-to-treat analysis and the compliant-only analysis are consistent with the presence of selection biases and the absence of a causal effect of time pressure on cooperation
Human native lipoprotein-induced de novo DNA methylation is associated with repression of inflammatory genes in THP-1 macrophages
<p>Abstract</p> <p>Background</p> <p>We previously showed that a VLDL- and LDL-rich mix of human native lipoproteins induces a set of repressive epigenetic marks, <it>i.e. de novo </it>DNA methylation, histone 4 hypoacetylation and histone 4 lysine 20 (H4K20) hypermethylation in THP-1 macrophages. Here, we: 1) ask what gene expression changes accompany these epigenetic responses; 2) test the involvement of candidate factors mediating the latter. We exploited genome expression arrays to identify target genes for lipoprotein-induced silencing, in addition to RNAi and expression studies to test the involvement of candidate mediating factors. The study was conducted in human THP-1 macrophages.</p> <p>Results</p> <p>Native lipoprotein-induced <it>de novo </it>DNA methylation was associated with a general repression of various critical genes for macrophage function, including pro-inflammatory genes. Lipoproteins showed differential effects on epigenetic marks, as <it>de novo </it>DNA methylation was induced by VLDL and to a lesser extent by LDL, but not by HDL, and VLDL induced H4K20 hypermethylation, while HDL caused H4 deacetylation. The analysis of candidate factors mediating VLDL-induced DNA hypermethylation revealed that this response was: 1) surprisingly, mediated exclusively by the canonical maintenance DNA methyltransferase DNMT1, and 2) independent of the Dicer/micro-RNA pathway.</p> <p>Conclusions</p> <p>Our work provides novel insights into epigenetic gene regulation by native lipoproteins. Furthermore, we provide an example of DNMT1 acting as a <it>de novo </it>DNA methyltransferase independently of canonical <it>de novo </it>enzymes, and show proof of principle that <it>de novo </it>DNA methylation can occur independently of a functional Dicer/micro-RNA pathway in mammals.</p
- âŚ