45 research outputs found
Formation and control of electron molecules in artificial atoms: Impurity and magnetic-field effects
Interelectron interactions and correlations in quantum dots can lead to
spontaneous symmetry breaking of the self-consistent mean field resulting in
formation of Wigner molecules. With the use of spin-and-space unrestricted
Hartree-Fock (sS-UHF) calculations, such symmetry breaking is discussed for
field-free conditions, as well as under the influence of an external magnetic
field. Using as paradigms impurity-doped (as well as the limiting case of
clean) two-electron quantum dots (which are analogs to helium-like atoms), it
is shown that the interplay between the interelectron repulsion and the
electronic zero-point kinetic energy leads, for a broad range of impurity
parameters, to formation of a singlet ground-state electron molecule,
reminiscent of the molecular picture of doubly-excited helium. Comparative
analysis of the conditional probability distributions for the sS-UHF and the
exact solutions for the ground state of two interacting electrons in a clean
parabolic quantum dot reveals that both of them describe formation of an
electron molecule with similar characteristics. The self-consistent field
associated with the triplet excited state of the two-electron quantum dot
(clean as well as impurity-doped) exhibits symmetry breaking of the Jahn-Teller
type, similar to that underlying formation of nonspherical open-shell nuclei
and metal clusters. Furthermore, impurity and/or magnetic-field effects can be
used to achieve controlled manipulation of the formation and pinning of the
discrete orientations of the Wigner molecules. Impurity effects are futher
illustrated for the case of a quantum dot with more than two electrons.Comment: Latex/Revtex, 10 pages with 4 gif figures. Small changes to explain
the difference between Wigner and Jahn-Teller electron molecules. A complete
version of the paper with high quality figures inside the text is available
at http://shale.physics.gatech.edu/~costas/qdhelium.html For related papers,
see http://www.prism.gatech.edu/~ph274c
Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study
Objective: To examine whether the association of
inadequate or unclear allocation concealment and lack of
blinding with biased estimates of intervention effects
varies with the nature of the intervention or outcome.
Design: Combined analysis of data from three metaepidemiological
studies based on collections of metaanalyses.
Data sources 146 meta-analyses including 1346 trials
examining a wide range of interventions and outcomes.
Main outcome measures Ratios of odds ratios quantifying
the degree of bias associated with inadequate or unclear
allocation concealment, and lack of blinding, for trials
with different types of intervention and outcome. A ratio of
odds ratios <1 implies that inadequately concealed or nonblinded
trials exaggerate intervention effect estimates.
Results: In trials with subjective outcomes effect estimates
were exaggerated when there was inadequate or unclear
allocation concealment (ratio of odds ratios 0.69 (95% CI
0.59 to 0.82)) or lack of blinding (0.75 (0.61 to 0.93)). In
contrast, there was little evidence of bias in trials with
objective outcomes: ratios of odds ratios 0.91 (0.80 to
1.03) for inadequate or unclear allocation concealment
and 1.01 (0.92 to 1.10) for lack of blinding. There was little
evidence for a difference between trials of drug and nondrug
interventions. Except for trials with all cause mortality
as the outcome, the magnitude of bias varied between
meta-analyses.
Conclusions: The average bias associated with defects in
the conduct of randomised trials varies with the type of
outcome. Systematic reviewers should routinely assess
the risk of bias in the results of trials, and should report
meta-analyses restricted to trials at low risk of bias either
as the primary analysis or in conjunction with less
restrictive analyses
Non-AIDS defining cancers in the D:A:D Study-time trends and predictors of survival : a cohort study
BACKGROUND:Non-AIDS defining cancers (NADC) are an important cause of morbidity and mortality in HIV-positive individuals. Using data from a large international cohort of HIV-positive individuals, we described the incidence of NADC from 2004-2010, and described subsequent mortality and predictors of these.METHODS:Individuals were followed from 1st January 2004/enrolment in study, until the earliest of a new NADC, 1st February 2010, death or six months after the patient's last visit. Incidence rates were estimated for each year of follow-up, overall and stratified by gender, age and mode of HIV acquisition. Cumulative risk of mortality following NADC diagnosis was summarised using Kaplan-Meier methods, with follow-up for these analyses from the date of NADC diagnosis until the patient's death, 1st February 2010 or 6 months after the patient's last visit. Factors associated with mortality following NADC diagnosis were identified using multivariable Cox proportional hazards regression.RESULTS:Over 176,775 person-years (PY), 880 (2.1%) patients developed a new NADC (incidence: 4.98/1000PY [95% confidence interval 4.65, 5.31]). Over a third of these patients (327, 37.2%) had died by 1st February 2010. Time trends for lung cancer, anal cancer and Hodgkin's lymphoma were broadly consistent. Kaplan-Meier cumulative mortality estimates at 1, 3 and 5 years after NADC diagnosis were 28.2% [95% CI 25.1-31.2], 42.0% [38.2-45.8] and 47.3% [42.4-52.2], respectively. Significant predictors of poorer survival after diagnosis of NADC were lung cancer (compared to other cancer types), male gender, non-white ethnicity, and smoking status. Later year of diagnosis and higher CD4 count at NADC diagnosis were associated with improved survival. The incidence of NADC remained stable over the period 2004-2010 in this large observational cohort.CONCLUSIONS:The prognosis after diagnosis of NADC, in particular lung cancer and disseminated cancer, is poor but has improved somewhat over time. Modifiable risk factors, such as smoking and low CD4 counts, were associated with mortality following a diagnosis of NADC
Obesity paradox' misunderstands the biology of optimal weight throughout the life cycle
10.1038/ijo.2014.59International Journal of Obesity39182-84IJOB
Sleep disturbance as a precursor of severe regression in Kleefstra syndrome suggests a need for firm and rapid pharmacological treatment
Intellectual disability is frequently accompanied by psychiatric symptoms that require pharmacological interventions. Treatment guidelines often provide a general treatment approach for these symptoms in intellectual disability. However, this may not always be the best strategy, as illustrated here in Kleefstra syndrome. We present 3 patients showing severe regression after sleep disturbances. If these are treated with care as usual (eg, behavioral programs and sleep medication) deterioration is likely to follow. It is observed that rapid treatment with relatively high dosages of antipsychotics contributes to restore sleep, halt further regression, and improve daily life functioning
EHMT1 mosaicism in apparently unaffected parents is associated with autism spectrum disorder and neurocognitive dysfunction
Contains fulltext :
182339.pdf (publisher's version ) (Open Access)Genetic mosaicism is only detected occasionally when there are no obvious health or developmental issues. Most cases concern healthy parents in whom mosaicism is identified upon targeted testing of a genetic defect that was initially detected in their children. A germline genetic defect affecting the euchromatin histone methyltransferase 1 (EHMT1) gene causes Kleefstra syndrome, which is associated with the typical triad of distinct facial appearance, (childhood) hypotonia, and intellectual disability. A high degree of psychopathology is associated with this syndrome. A few parents with a mosaic EHMT1 mutation have been detected upon testing after a child was diagnosed with a germline EHMT1 defect. At first glance, carriers of a mosaic EHMT1 mutation appeared to function normally. However, recent studies have shown that de novo, postzygotic mutations in important developmental genes significantly contribute to autism spectrum disorder (ASD). Therefore, we hypothesized that EHMT1 mosaicism could cause neuropsychiatric defects. To investigate this, we performed a detailed investigation of cognitive neuropsychiatric parameters in parents identified with EHMT1 mosaicism.7 p
The context of symptom measures: Interpretation and clinical diagnosis of autism spectrum disorders in intellectual disabilities
Contains fulltext :
173921.pdf (publisher's version ) (Closed access)Last December, Dr. Havdahl et al. highlighted the use of autism spectrum disorder (ASD) symptom measurements in specific groups in their article "Multidimensional Influences on Autism Symptom Measures: Implications for Use in Etiological Research". This is an important and timely topic, because public attention is currently tuned to the increasing prevalence of ASD. Dr. Havdahl et al. carefully mapped which of the tested instruments was most sensitive to detect actual ASD symptoms and to distinguish these from other typical comorbid neurodevelopmental disorders, such as intellectual disability (ID) and attention-deficit/hyperactivity disorder.2 p