11,648 research outputs found
Disentanglement and decoherence in two-spin and three-spin systems under dephasing
We compare disentanglement and decoherence rates within two-spin and
three-spin entangled systems subjected to all possible combinations of local
and collective pure dephasing noise combinations. In all cases, the bipartite
entanglement decay rate is found to be greater than or equal to the
dephasing-decoherence rates and often significantly greater. This sharpens
previous results for two-spin systems [T. Yu and J. H. Eberly Phys. Rev. B 68,
165322 (2003)] and extends them to the three-spin context.Comment: 17 page
Coherent State Quantum Key Distribution with Entanglement Witnessing
An entanglement witness approach to quantum coherent state key distribution
and a system for its practical implementation are described. In this approach,
eavesdropping can be detected by a change in sign of either of two witness
functions, an entanglement witness S or an eavesdropping witness W. The effects
of loss and eavesdropping on system operation are evaluated as a function of
distance. Although the eavesdropping witness W does not directly witness
entanglement for the system, its behavior remains related to that of the true
entanglement witness S. Furthermore, W is easier to implement experimentally
than S. W crosses the axis at a finite distance, in a manner reminiscent of
entanglement sudden death. The distance at which this occurs changes measurably
when an eavesdropper is present. The distance dependance of the two witnesses
due to amplitude reduction and due to increased variance resulting from both
ordinary propagation losses and possible eavesdropping activity is provided.
Finally, the information content and secure key rate of a continuous variable
protocol using this witness approach are given
Thermal convection in mono-disperse and bi-disperse granular gases: A simulation study
We present results of a simulation study of inelastic hard-disks vibrated in
a vertical container. An Event-Driven Molecular Dynamics method is developed
for studying the onset of convection. Varying the relevant parameters
(inelasticity, number of layers at rest, intensity of the gravity) we are able
to obtain a qualitative agreement of our results with recent hydrodynamical
predictions. Increasing the inelasticity, a first continuous transition from
the absence of convection to one convective roll is observed, followed by a
discontinuous transition to two convective rolls, with hysteretic behavior. At
fixed inelasticity and increasing gravity, a transition from no convection to
one roll can be evidenced. If the gravity is further increased, the roll is
eventually suppressed. Increasing the number of monolayers the system
eventually localizes mostly at the bottom of the box: in this case multiple
convective rolls as well as surface waves appear. We analyze the density and
temperature fields and study the existence of symmetry breaking in these fields
in the direction perpendicular to the injection of energy. We also study a
binary mixture of grains with different properties (inelasticity or diameters).
The effect of changing the properties of one of the components is analyzed,
together with density, temperature and temperature ratio fields.
Finally, the presence of a low-fraction of quasi-elastic impurities is shown
to determine a sharp transition between convective and non-convective steady
states.Comment: 11 pages, 12 figures, accepted for publication on Physical Review
Intruders in the Dust: Air-Driven Granular Size Separation
Using MRI and high-speed video we investigate the motion of a large intruder
particle inside a vertically shaken bed of smaller particles. We find a
pronounced, non-monotonic density dependence, with both light and heavy
intruders moving faster than those whose density is approximately that of the
granular bed. For light intruders, we furthermore observe either rising or
sinking behavior, depending on intruder starting height, boundary condition and
interstitial gas pressure. We map out the phase boundary delineating the rising
and sinking regimes. A simple model can account for much of the observed
behavior and show how the two regimes are connected by considering pressure
gradients across the granular bed during a shaking cycle.Comment: 5 pages, 4 figure
Addressing Mental Health with the Somali Population in the Twin Cities Area
Minnesota is home to one of the highest populations of Somali heritage in North America. Mental illness is reported to be prevalent in this population and there is an underutilization of available mental health services. The purpose of this study was to see how health providers can better identify and discuss mental illness with the Somali community to improve utilization rates of mental health clinics in the Twin Cities area. To do this, six qualitative interviews were conducted with participants who at the time were currently working with Somalis, in a hospital, clinic, or health care agency setting. Content Analysis was used as a method of analysis to identify and interpret themes found from the recorded interviews. The main themes that emerged were: 1) prevalence and recognizing mental illness; 2) the stigma of mental illness; 3) impact of interpreters; and, 4) dialoging about mental health. Findings confirm previous research studies in that there is little uniformity between health professionals on what treatments to recommend to improve utilization. However, findings showed that being culturally aware, building rapport, and discussing mental illness in terms of physical symptoms, all improve utilization rates of Mental Health Services. Somali Americans access medical health through hospitals, clinics, and health care agencies. Because of this, it is important for health care professionals to be culturally aware of Somalis and how to mutually discuss mental illness due to their access to this population
Addressing Mental Health with the Somali Population in the Twin Cities Area
Minnesota is home to one of the highest populations of Somali heritage in North America. Mental illness is reported to be prevalent in this population and there is an underutilization of available mental health services. The purpose of this study was to see how health providers can better identify and discuss mental illness with the Somali community to improve utilization rates of mental health clinics in the Twin Cities area. To do this, six qualitative interviews were conducted with participants who at the time were currently working with Somalis, in a hospital, clinic, or health care agency setting. Content Analysis was used as a method of analysis to identify and interpret themes found from the recorded interviews. The main themes that emerged were: 1) prevalence and recognizing mental illness; 2) the stigma of mental illness; 3) impact of interpreters; and, 4) dialoging about mental health. Findings confirm previous research studies in that there is little uniformity between health professionals on what treatments to recommend to improve utilization. However, findings showed that being culturally aware, building rapport, and discussing mental illness in terms of physical symptoms, all improve utilization rates of Mental Health Services. Somali Americans access medical health through hospitals, clinics, and health care agencies. Because of this, it is important for health care professionals to be culturally aware of Somalis and how to mutually discuss mental illness due to their access to this population
A new algorithm for recognizing the unknot
The topological underpinnings are presented for a new algorithm which answers
the question: `Is a given knot the unknot?' The algorithm uses the braid
foliation technology of Bennequin and of Birman and Menasco. The approach is to
consider the knot as a closed braid, and to use the fact that a knot is
unknotted if and only if it is the boundary of a disc with a combinatorial
foliation. The main problems which are solved in this paper are: how to
systematically enumerate combinatorial braid foliations of a disc; how to
verify whether a combinatorial foliation can be realized by an embedded disc;
how to find a word in the the braid group whose conjugacy class represents the
boundary of the embedded disc; how to check whether the given knot is isotopic
to one of the enumerated examples; and finally, how to know when we can stop
checking and be sure that our example is not the unknot.Comment: 46 pages. Published copy, also available at
http://www.maths.warwick.ac.uk/gt/GTVol2/paper9.abs.htm
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