6,065 research outputs found
Correlated charge polarization in a chain of coupled quantum dots
Coherent charge transfer in a linear array of tunnel-coupled quantum dots,
electrostatically coupled to external gates, is investigated using the Bethe
ansatz for a symmetrically biased Hubbard chain. Charge polarization in this
correlated system is shown to proceed via two distinct processes: formation of
bound states in the metallic phase, and charge transfer processes corresponding
to a superposition of antibound states at opposite ends of the chain in the
Mott-insulating phase. The polarizability in the insulating phase of the chain
exhibits a universal scaling behavior, while the polarization charge in the
metallic phase of the model is shown to be quantized in units of .Comment: 9 pages, 3 figures, 1 tabl
Universality of Decay out of Superdeformed Bands in the 190 Mass Region
Superdeformed nuclei in the 190 mass region exhibit a striking universality
in their decay-out profiles. We show that this universality can be explained in
the two-level model of superdeformed decay as related to a strong separation of
energy scales: a higher scale related to the nuclear interactions, and a lower
scale caused by electromagnetic decay. Furthermore, we present the results of
the two-level model for all decays for which sufficient data are known,
including statistical extraction of the matrix element for tunneling through
the potential barrier.Comment: 7 pages, 3 figures. v2: some minor clarifications, minor correction
to Fig.
Simple model for decay of superdeformed nuclei
Recent theoretical investigations of the decay mechanism out of a
superdeformed nuclear band have yielded qualitatively different results,
depending on the relative values of the relevant decay widths. We present a
simple two-level model for the dynamics of the tunneling between the
superdeformed and normal-deformed bands, which treats decay and tunneling
processes on an equal footing. The previous theoretical results are shown to
correspond to coherent and incoherent limits of the full tunneling dynamics.
Our model accounts for experimental data in both the A~150 mass region, where
the tunneling dynamics is coherent, and in the A~190 mass region, where the
tunneling dynamics is incoherent.Comment: 4 page
Constraining the extra heating of the Diffuse Ionized Gas in the Milky Way
The detailed observations of the diffuse ionized gas through the emission
lines H, [NII], and [SII] in the Perseus Arm of our Galaxy by the
Wisconsin H Mapper (WHAM)--survey challenge photoionization models.
They have to explain the observed rise in the line ratios [NII]/H and
[SII]/H. The models described here consider for the first time the
detailed observational geometry toward the Perseus Arm. The models address the
vertical variation of the line ratios up to height of 2 kpc above the midplane.
The rising trends of the line ratios are matched. The increase in the line
ratios is reflected in a rise of the temperature of the gas layer. This is due
to the progressive hardening of the radiation going through the gas. However an
extra heating above photoionization is needed to explain the absolute values.
Two different extra heating rates are investigated which are proportional to
and . The models show that a combination of both are best to explain
the data, where the extra heating independent of density is dominant for z
0.8 kpc.Comment: accepted for publication in Ap
How to measure the spreading width for decay of superdeformed nuclei
A new expression for the branching ratio for the decay via the E1 process in
the normal-deformed band of superdeformed nuclei is given within a simple
two-level model. Using this expression, the spreading or tunneling width
Gamma^downarrow for superdeformed decay can be expressed entirely in terms of
experimentally known quantities. We show how to determine the tunneling matrix
element V from the measured value of Gamma^downarrow and a statistical model of
the energy levels. The accuracy of the two-level approximation is verified by
considering the effects of the other normal-deformed states.Comment: 4 pages, 4 figure
Neighbourhood social environment and depressive symptoms in mid-life and beyond
This prospective study examines the relationship between aspects of the neighbourhood social environment and subsequent depressive symptoms in over 7,500 participants of the English Longitudinal Study of Ageing (ELSA). Neighbourhood social environment at baseline was operationalised using four items capturing social cohesion and three items capturing perceived safety and associations with the Center for Epidemiologic Studies Depression Scale (CES-D) at two-year follow-up were assessed. Friendship quality and personal sense of control were tested as mediators of this relationship using structural equation modelling. Neighbourhood social cohesion was found to be associated with reporting fewer depressive symptoms independent of demographic and socioeconomic factors and baseline depressive symptoms. Friendship quality and sense of control mediated this association. The study highlights that greater personal sense of control, higher quality friendships and fewer depressive symptoms are found in neighbourhoods seen to be characterised by higher social cohesion
Coherent Resonant Tunneling Through an Artificial Molecule
Coherent resonant tunneling through an artificial molecule of quantum dots in
an inhomogeneous magnetic field is investigated using an extended Hubbard
model. Both the multiterminal conductance of an array of quantum dots and the
persistent current of a quantum dot molecule embedded in an Aharanov-Bohm ring
are calculated. The conductance and persistent current are calculated
analytically for the case of a double quantum dot and numerically for larger
arrays using a multi-terminal Breit-Wigner type formula, which allows for the
explicit inclusion of inelastic processes. Cotunneling corrections to the
persistent current are also investigated, and it is shown that the sign of the
persistent current on resonance may be used to determine the spin quantum
numbers of the ground state and low-lying excited states of an artificial
molecule. An inhomogeneous magnetic field is found to strongly suppress
transport due to pinning of the spin-density-wave ground state of the system,
and giant magnetoresistance is predicted to result from the ferromagnetic
transition induced by a uniform external magnetic field.Comment: 23 pages, 12 figure
To blame? The effects of moralized feedback on implicit racial bias
Implicit bias training (IBT) is now frequently provided by employers, in order to raise awareness of the problems related to implicit biases, and of how to safeguard against discrimination that may result. However, as Atewologun et al (2018) have noted, there is very little systematicity in IBT, and there are many unknowns about what constitutes good IBT. One important issue concerns the tone of information provided regarding implicit bias. This paper engages this question, focusing in particular on the observation that much bias training is delivered in exculpatory tone, emphasising that individuals are not to blame for possessing implicit biases. Normative guidance around IBT exhorts
practitioners to adopt this strategy (Moss-Racusin et al 2014). However, existing evidence about the effects of moralized feedback about implicit bias is equivocal (Legault et al 2011; Czopp et al 2006). Through a series of studies, culminating in an experiment with a pre-registered analysis plan, we develop a paradigm for evaluating the impact of moralized feedback on participants’ implicit racial bias scores. We also conducted exploratory analyses of the impact on their moods, and behavioural intentions. Our results indicated that an exculpatory tone, rather than a blaming or neutral tone, did not make participants less resistant to changing their attitudes and behaviours. In fact, participants in the blame condition had significantly stronger explicit intentions to change future behaviour than those in the ‘no feedback’ condition (see experiment 3). These results indicate that considerations of
efficacy do not support the need for implicit bias feedback to be exculpatory. We tease out the implications of these findings, and directions for future research
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