1,499 research outputs found
Quantum engineering of atomic phase-shifts in optical clocks
Quantum engineering of time-separated Raman laser pulses in three-level
systems is presented to produce an ultra-narrow optical transition in bosonic
alkali-earth clocks free from light shifts and with a significantly reduced
sensitivity to laser parameter fluctuations. Based on a quantum artificial
complex-wave-function analytical model, and supported by a full density matrix
simulation including a possible residual effect of spontaneous emission from
the intermediate state, atomic phase-shifts associated to Ramsey and
Hyper-Ramsey two-photon spectroscopy in optical clocks are derived. Various
common-mode Raman frequency detunings are found where the frequency shifts from
off-resonant states are canceled, while strongly reducing their uncertainties
at the 10 level of accuracy.Comment: accepted for publication in PR
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
The Mass Profile and Accretion History of Cold Dark Matter Halos
We use the Millennium Simulation series to study the relation between the
accretion history (MAH) and mass profile of cold dark matter halos. We find
that the mean density within the scale radius, r_{-2} (where the halo density
profile has isothermal slope), is directly proportional to the critical density
of the Universe at the time when the main progenitor's virial mass equals the
mass enclosed within r_{-2}. Scaled to these characteristic values of mass and
density, the mean MAH, expressed in terms of the critical density of the
Universe, M(\rho_{crit}(z)), resembles that of the enclosed density profile,
M(), at z=0. Both follow closely the NFW profile, suggesting that the
similarity of halo mass profiles originates from the mass-independence of halo
MAHs. Support for this interpretation is provided by outlier halos whose
accretion histories deviate from the NFW shape; their mass profiles show
correlated deviations from NFW and are better approximated by Einasto profiles.
Fitting both M() and M(\rho_{crit}) with either NFW or Einasto profiles
yield concentration and shape parameters that are correlated, confirming and
extending earlier work linking the concentration of a halo with its accretion
history. These correlations also confirm that halo structure is insensitive to
initial conditions: only halos whose accretion histories differ greatly from
the NFW shape show noticeable deviations from NFW in their mass profiles. As a
result, the NFW profile provides acceptable fits to hot dark matter halos,
which do not form hierarchically, and for fluctuation power spectra other than
CDM. Our findings, however, predict a subtle but systematic dependence of mass
profile shape on accretion history which, if confirmed, would provide strong
support for the link between accretion history and halo structure we propose
here.Comment: 12 pages, 8 figures, MNRAS 432 1103L (2013
Earth-mass haloes and the emergence of NFW density profiles
We simulate neutralino dark matter (χDM) haloes from their initial collapse, at ∼ earth mass, up to a few percent solar. Our results confirm that the density profiles of the first haloes are described by a ∼r−1.5 power law. As haloes grow in mass, their density profiles evolve significantly. In the central regions, they become shallower and reach on average ∼r−1, the asymptotic form of an NFW profile. Using non-cosmological controlled simulations, we observe that temporal variations in the gravitational potential caused by major mergers lead to a shallowing of the inner profile. This transformation is more significant for shallower initial profiles and for a higher number of merging systems. Depending on the merger details, the resulting profiles can be shallower or steeper than NFW in their inner regions. Interestingly, mergers have a much weaker effect when the profile is given by a broken power law with an inner slope of −1 (such as NFW or Hernquist profiles). This offers an explanation for the emergence of NFW-like profiles: after their initial collapse, r−1.5 χDM haloes suffer copious major mergers, which progressively shallows the profile. Once an NFW-like profile is established, subsequent merging does not change the profile anymore. This suggests that halo profiles are not universal but rather a combination of (1) the physics of the formation of the microhaloes and (2) their early merger history – both set by the properties of the dark matter particle – as well as (3) the resilience of NFW-like profiles to perturbations
Narrow Line Cooling: Finite Photon Recoil Dynamics
We present an extensive study of the unique thermal and mechanical dynamics
for narrow-line cooling on the 1S0 - 3P1 88Sr transition. For negative
detuning, trap dynamics reveal a transition from the semiclassical regime to
the photon-recoil-dominated quantum regime, yielding an absolute minima in the
equilibrium temperature below the single-photon recoil limit. For positive
detuning, the cloud divides into discrete momentum packets whose alignment
mimics lattice points on a face-centered-cubic crystal. This novel behavior
arises from velocity selection and "positive feedback" acceleration due to a
finite number of photon recoils. Cooling is achieved with blue-detuned light
around a velocity where gravity balances the radiative force.Comment: 4 pages, 3 figures, Phys. Rev. Lett., in pres
An Investigation of Behavioural and Self-Reported Cognitive Empathy Deficits in Adolescents With Autism Spectrum Disorders and Adolescents With Behavioural Difficulties
© 2021 Vilas, Reniers and Ludlow. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). https://creativecommons.org/licenses/by/4.0/Deficits in empathy have been considered hallmarks in individuals with autism spectrum disorders (ASD) but are also considered to underlie antisocial behaviour associated with individuals with callous unemotional traits (CU). Research has suggested that individuals with autism spectrum disorders show more difficulties with cognitive empathy, and that individuals diagnosed with behaviours difficulties, characterised by CU traits and antisocial behaviour, demonstrate low affective empathy. In the current manuscript we present findings of two studies. The first study describes the validation of a new stimulus set developed for the empathic accuracy task, focused on its cognitive component. The second study compares the performance of 27 adolescents with ASD, 27 age matched typically developing adolescents and 17 adolescents with behavioural difficulties on the empathic accuracy task and a self-report measure of empathy. While, no differences were observed between the three groups across the empathy accuracy task, the adolescents with ASD and CD showed deficits in their cognitive empathy across the self-report measure. Adolescents with ASD showed lower scores in particularly their perspective taking abilities, whereas the adolescences with behavioural difficulties showed more difficulties with their online simulation. No differences in self-reported affective empathy across the three groups were observed. Clinical implications of the findings are discussed.Peer reviewedFinal Published versio
Development and preliminary testing of the psychosocial adjustment to hereditary diseases scale
Background: The presence of Lynch syndrome (LS) can bring a lifetime of uncertainty to an entire family as
members adjust to living with a high lifetime cancer risk. The research base on how individuals and families adjust
to genetic-linked diseases following predictive genetic testing has increased our understanding of short-term
impacts but gaps continue to exist in knowledge of important factors that facilitate or impede long-term
adjustment. The failure of existing scales to detect psychosocial adjustment challenges in this population has led researchers to question the adequate sensitivity of these instruments. Furthermore, we have limited insight into the role of the family in promoting adjustment.
Methods: The purpose of this study was to develop and initially validate the Psychosocial Adjustment to Hereditary
Diseases (PAHD) scale. This scale consists of two subscales, the Burden of Knowing (BK) and Family Connectedness (FC). Items for the two subscales were generated from a qualitative data base and tested in a sample of 243 participants from families with LS.
Results: The Multitrait/Multi-Item Analysis Program-Revised (MAP-R) was used to evaluate the psychometric
properties of the PAHD. The findings support the convergent and discriminant validity of the subscales. Construct
validity was confirmed by factor analysis and Cronbach’s alpha supported a strong internal consistency for BK (0.83)
and FC (0.84).
Conclusion: Preliminary testing suggests that the PAHD is a
psychometrically sound scale capable of assessing
psychosocial adjustment. We conclude that the PAHD may be a valuable monitoring tool to identify individuals and
families who may require therapeutic interventions
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