438 research outputs found
Localizations at infinity and essential spectrum of quantum Hamiltonians: I. General theory
We isolate a large class of self-adjoint operators H whose essential spectrum
is determined by their behavior at large x and we give a canonical
representation of their essential spectrum in terms of spectra of limits at
infinity of translations of H. The configuration space is an arbitrary abelian
locally compact not compact group.Comment: 63 pages. This is the published version with several correction
The quantum structure of spacetime at the Planck scale and quantum fields
We propose uncertainty relations for the different coordinates of spacetime
events, motivated by Heisenberg's principle and by Einstein's theory of
classical gravity. A model of Quantum Spacetime is then discussed where the
commutation relations exactly implement our uncertainty relations.
We outline the definition of free fields and interactions over QST and take
the first steps to adapting the usual perturbation theory. The quantum nature
of the underlying spacetime replaces a local interaction by a specific nonlocal
effective interaction in the ordinary Minkowski space. A detailed study of
interacting QFT and of the smoothing of ultraviolet divergences is deferred to
a subsequent paper.
In the classical limit where the Planck length goes to zero, our Quantum
Spacetime reduces to the ordinary Minkowski space times a two component space
whose components are homeomorphic to the tangent bundle TS^2 of the 2-sphere.
The relations with Connes' theory of the standard model will be studied
elsewhere.Comment: TeX, 37 pages. Since recent and forthcoming articles (hep-th/0105251,
hep-th/0201222, hep-th/0301100) are based on this paper, we thought it would
be convenient for the readers to have it available on the we
Quantum Transport in Nonuniform Magnetic Fields: Aharonov-Bohm Ring as a Spin Switch
We study the spin-dependent magneto conductance in mesoscopic rings subject
to an inhomogeneous in-plane magnetic field. We show that the polarization
direction of transmitted spin-polarized electrons can be controlled via an
additional magnetic flux such that spin flips are induced at half a flux
quantum. This quantum interference effect is independent of the strength of the
nonuniform field applied. We give an analytical explanation for one-dimensional
rings and numerical results for corresponding ballistic microstructures.Comment: 5 pages, 3 figures. To be published in Physical Review Letter
Fish Oil-Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring
Š 2016 Massachusetts Medical Society. Bisgaard, H., Stokholm, J., Chawes, B. L., Vissing, N. H., BjarnadĂłttir, E., Schoos, A.-M. M., ⌠Bønnelykke, K. (2016). Fish OilâDerived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring. New England Journal of Medicine, 375(26), 2530â2539. https://doi.org/10.1056/NEJMoa1503734BACKGROUND Reduced intake of n-3 long-chain polyunsaturated fatty acids (LCPUFAs) may be a contributing factor to the increasing prevalence of wheezing disorders. We assessed the effect of supplementation with n-3 LCPUFAs in pregnant women on the risk of persistent wheeze and asthma in their offspring. METHODS We randomly assigned 736 pregnant women at 24 weeks of gestation to receive 2.4 g of n-3 LCPUFA (fish oil) or placebo (olive oil) per day. Their children formed the Copenhagen Prospective Studies on Asthma in Childhood 2010 (COPSAC 2010) cohort and were followed prospectively with extensive clinical phenotyping. Neither the investigators nor the participants were aware of group assignments during follow-up for the first 3 years of the children's lives, after which there was a 2-year follow-up period during which only the investigators were unaware of group assignments. The primary end point was persistent wheeze or asthma, and the secondary end points included lower respiratory tract infections, asthma exacerbations, eczema, and allergic sensitization. RESULTS A total of 695 children were included in the trial, and 95.5% completed the 3-year, double-blind follow-up period. The risk of persistent wheeze or asthma in the treatment group was 16.9%, versus 23.7% in the control group (hazard ratio, 0.69; 95% confidence interval [CI], 0.49 to 0.97; P=0.035), corresponding to a relative reduction of 30.7%. Prespecified subgroup analyses suggested that the effect was strongest in the children of women whose blood levels of eicosapentaenoic acid and docosahexaenoic acid were in the lowest third of the trial population at randomization: 17.5% versus 34.1% (hazard ratio, 0.46; 95% CI, 0.25 to 0.83; P=0.011). Analyses of secondary end points showed that supplementation with n-3 LCPUFA was associated with a reduced risk of infections of the lower respiratory tract (31.7% vs. 39.1%; hazard ratio, 0.75; 95% CI, 0.58 to 0.98; P=0.033), but there was no statistically significant association between supplementation and asthma exacerbations, eczema, or allergic sensitization. CONCLUSIONS Supplementation with n-3 LCPUFA in the third trimester of pregnancy reduced the absolute risk of persistent wheeze or asthma and infections of the lower respiratory tract in offspring by approximately 7 percentage points, or one third. (Funded by the Lund-beck Foundation and others; ClinicalTrials.gov number, NCT00798226.)Lundbeck Foundatio
MR-proADM as a Prognostic Marker in Patients With ST-Segment-Elevation Myocardial Infarction - DANAMI-3 (a Danish Study of Optimal Acute Treatment of Patients With STEMI) Substudy
Background
Midregional proadrenomedullin (
MR
âpro
ADM
) has demonstrated prognostic potential after myocardial infarction (
MI
). Yet, the prognostic value of
MR
âpro
ADM
at admission has not been examined in patients with STâsegmentâelevation
MI
(
STEMI
).
Methods and Results
The aim of this substudy, DANAMIâ3 (The Danish Study of Optimal Acute Treatment of Patients with
ST
âsegmentâelevation myocardial infarction), was to examine the associations of admission concentrations of
MR
âpro
ADM
with shortâ and longâterm mortality and hospital admission for heart failure in patients with
ST
âsegmentâelevation myocardial infarction. Outcomes were assessed using Cox proportional hazard models and area under the curve using receiver operating characteristics. In total, 1122 patients were included. The median concentration of
MR
âpro
ADM
was 0.64Â nmol/L (25thâ75th percentiles, 0.53â0.79). Within 30Â days 23 patients (2.0%) died and during a 3âyear followâup 80 (7.1%) died and 38 (3.4%) were admitted for heart failure. A doubling of
MR
âpro
ADM
was, in adjusted models, associated with an increased risk of 30âday mortality (hazard ratio, 2.67; 95% confidence interval, 1.01â7.11;
P
=0.049), longâterm mortality (hazard ratio, 3.23; 95% confidence interval, 1.97â5.29;
P
<0.0001), and heart failure (hazard ratio, 2.71; 95% confidence interval, 1.32â5.58;
P
=0.007). For 30âday and 3âyear mortality, the area under the curve for
MR
âpro
ADM
was 0.77 and 0.78, respectively. For 3âyear mortality, area under the curve (0.84) of the adjusted model marginally changed (0.85;
P
=0.02) after addition of
MR
âpro
ADM
.
Conclusions
Elevation of admission
MR
âpro
ADM
was associated with longâterm mortality and heart failure, whereas the association with shortâterm mortality was borderline significant.
MR
âpro
ADM
may be a marker of prognosis after STâsegmentâelevation myocardial infarction but does not seem to add substantial prognostic information to established clinical models.
Clinical Trial Registration
URL
:
http:/www.ClinicalTrials.gov
/. Unique identifiers:
NCT
01435408 and
NCT
01960933.
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Growth of the thoracic aorta in the smoking population: The Danish Lung Cancer Screening Trial
Background: Although the descending aortic diameter is larger in smokers, data about thoracic aortic growth is missing. Our aim is to present the distribution of thoracic aortic growth in smokers and to compare it with literature of the general population. Methods: Current and ex-smokers aged 50â70 years from the longitudinal Danish Lung Cancer Screening Trial, were included. Mean and 95th percentile of annual aortic growth of the ascending aortic (AA) and descending aortic (DA) diameters were calculated with the first and last non-contrast computed tomography scans during follow-up. Determinants of change in aortic diameter over time were investigated with linear mixed models. Results: A total of 1987 participants (56% male, mean age 57.4 Âą 4.8 years) were included. During a median follow-up of 48 months, mean AA and DA growth rates were comparable between males (AA 0.12 Âą 0.31 mm/year and DA 0.10 Âą 0.30 mm/year) and females (AA 0.11 Âą 0.29 mm/year and DA 0.13 Âą 0.27 mm/year). The 95th percentile ranged from 0.42 to 0.47 mm/year, depending on sex and location. Aortic growth was comparable between current and ex-smokers and aortic growth was not associated with pack-years. Our findings are consistent with aortic growth rates of 0.08 to 0.17 mm/years in the general population. Larger aortic growth was associated with lower age, increased height, absence of medication for hypertension or hypercholesterolemia and lower Agatston s
Robustness of genome-wide scanning using archived dried blood spot samples as a DNA source
<p>Abstract</p> <p>Background</p> <p>The search to identify disease-susceptible genes requires access to biological material from numerous well-characterized subjects. Archived residual dried blood spot (DBS) samples, also known as Guthrie cards, from national newborn screening programs may provide a DNA source for entire populations. Combined with clinical information from medical registries, DBS samples could provide a rich source for productive research. However, the amounts of DNA which can be extracted from these precious samples are minute and may be prohibitive for numerous genotypings. Previously, we demonstrated that DBS DNA can be whole-genome amplified and used for reliable genetic analysis on different platforms, including genome-wide scanning arrays. However, it remains unclear whether this approach is workable on a large sample scale. We examined the robustness of using DBS samples for whole-genome amplification following genome-wide scanning, using arrays from Illumina and Affymetrix.</p> <p>Results</p> <p>This study is based on 4,641 DBS samples from the Danish Newborn Screening Biobank, extracted for three separate genome-wide association studies. The amount of amplified DNA was significantly (P < 0.05) affected by the year of storage and storage conditions. Nine (0.2%) DBS samples failed whole-genome amplification. A total of 4,586 (98.8%) samples met our criterion of success of a genetic call-rate above 97%. The three studies used different arrays, with mean genotyping call-rates of 99.385% (Illumina Infinium Human610-Quad), 99.722% (Illumina Infinium HD HumanOmni1-Quad), and 99.206% (Affymetrix Axiom Genome-Wide CEU). We observed a concordance rate of 99.997% in the 38 methodological replications, and 99.999% in the 27 technical replications. Handling variables such as time of storage, storage conditions and type of filter paper were shown too significantly (P < 0.05) affect the genotype call-rates in some of the arrays, although the effect was minimal.</p> <p>Conclusion</p> <p>Our study indicates that archived DBS samples from the Danish Newborn Screening Biobank represent a reliable resource of DNA for whole-genome amplification and subsequent genome-wide association studies. With call-rates equivalent to high quality DNA samples, our results point to new opportunities for using the neonatal biobanks available worldwide in the hunt for genetic components of disease.</p
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