8,559 research outputs found
An Invertible Linearization Map for the Quartic Oscillator
The set of world lines for the non-relativistic quartic oscillator satisfying
Newton's equation of motion for all space and time in 1-1 dimensions with no
constraints other than the "spring" restoring force is shown to be equivalent
(1-1-onto) to the corresponding set for the harmonic oscillator. This is
established via an energy preserving invertible linearization map which
consists of an explicit nonlinear algebraic deformation of coordinates and a
nonlinear deformation of time coordinates involving a quadrature. In the
context stated, the map also explicitly solves Newton's equation for the
quartic oscillator for arbitrary initial data on the real line. This map is
extended to all attractive potentials given by even powers of the space
coordinate. It thus provides classes of new solutions to the initial value
problem for all these potentials
Magnetic Instability in Strongly Correlated Superconductors
Recently a new phenomenological Hamiltonian has been proposed to describe the
superconducting cuprates. This so-called Gossamer Hamiltonian is an apt model
for a superconductor with strong on-site Coulomb repulsion betweenthe
electrons. It is shown that as one approaches half-filling the Gossamer
superconductor, and hence the superconducting state, with strong repulsion is
unstable toward an antiferromagnetic insulator an can undergo a quantum phase
transition to such an insulator if one increases the on-site Coulomb repulsion
FARM LEVEL CONSEQUENCES OF CANADIAN AND U.S. DAIRY POLICIES
Agricultural and Food Policy, Livestock Production/Industries,
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Disparity between General Symptom Relief and Remission Criteria in the Positive and Negative Syndrome Scale (PANSS): A Post-treatment Bifactor Item Response Theory Model.
Objective: Total scale scores derived by summing ratings from the 30-item PANSS are commonly used in clinical trial research to measure overall symptom severity, and percentage reductions in the total scores are sometimes used to document the efficacy of treatment. Acknowledging that some patients may have substantial changes in PANSS total scores but still be sufficiently symptomatic to warrant diagnosis, ratings on a subset of 8 items, referred to here as the "Remission set," are sometimes used to determine if patients' symptoms no longer satisfy diagnostic criteria. An unanswered question remains: is the goal of treatment better conceptualized as reduction in overall symptom severity, or reduction in symptoms below the threshold for diagnosis? We evaluated the psychometric properties of PANSS total scores, to assess whether having low symptom severity post-treatment is equivalent to attaining Remission. Design: We applied a bifactor item response theory (IRT) model to post-treatment PANSS ratings of 3,647 subjects diagnosed with schizophrenia assessed at the termination of 11 clinical trials. The bifactor model specified one general dimension to reflect overall symptom severity, and five domain-specific dimensions. We assessed how PANSS item discrimination and information parameters varied across the range of overall symptom severity (θ), with a special focus on low levels of symptoms (i.e., θ<-1), which we refer to as "Relief" from symptoms. A score of θ=-1 corresponds to an expected PANSS item score of 1.83, a rating between "Absent" and "Minimal" for a PANSS symptom. Results: The application of the bifactor IRT model revealed: (1) 88% of total score variation was attributable to variation in general symptom severity, and only 8% reflected secondary domain factors. This implies that a general factor may provide a good indicator of symptom severity, and that interpretation is not overly complicated by multidimensionality; (2) Post-treatment, 534 individuals (about 15% of the whole sample) scored in the "Relief" range of general symptom severity, but more than twice that number (n = 1351) satisfied Remission criteria (37%). 2 in 3 Remitted patients had scores that were not in a low symptom range (corresponding to Absent or Minimal item scores); (3) PANSS items vary greatly in their ability to measure the general symptom severity dimension; while many items are highly discriminating and relatively "pure" indicators of general symptom severity (delusions, conceptual disorganization), others are better indicators of specific dimensions (blunted affect, depression). The utility of a given PANSS item for assessing a patient depended on the illness level of the patient. Conclusion: Satisfying conventional Remission criteria was not strongly associated with low levels of symptoms. The items providing the most information for patients in the symptom Relief range were Delusions, Preoccupation, Suspiciousness Persecution, Unusual Thought Content, Conceptual Disorganization, Stereotyped Thinking, Active Social Avoidance, and Lack of Judgment and Insight. Lower scores on these items (item scores ≤2) were strongly associated with having a low latent trait θ or experiencing overall symptom relief. The inter-rater agreement between Remission and Relief subjects suggested that these criteria identified different subsets of patients. Alternative subsets of items may offer better indicators of general symptom severity and provide better discrimination (and lower standard errors) for scaling individuals and judging symptom relief, where the "best" subset of items ultimately depends on the illness range and treatment phase being evaluated
Exact Integration of the High Energy Scale in Doped Mott Insulators
We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99},
46404 (2007)) in which we constructed the exact low-energy theory of a doped
Mott insulator by explicitly integrating (rather than projecting) out the
degrees of freedom far away from the chemical potential. The exact low-energy
theory contains degrees of freedom that cannot be obtained from projective
schemes. In particular a new charge bosonic field emerges at low
energies that is not made out of elemental excitations. Such a field accounts
for dynamical spectral weight transfer across the Mott gap. At half-filling, we
show that two such excitations emerge which play a crucial role in preserving
the Luttinger surface along which the single-particle Green function vanishes.
In addition, the interactions with the bosonic fields defeat the artificial
local SU(2) symmetry that is present in the Heisenberg model. We also apply
this method to the Anderson-U impurity and show that in addition to the Kondo
interaction, bosonic degrees of freedom appear as well. Finally, we show that
as a result of the bosonic degree of freedom, the electron at low energies is
in a linear superposition of two excitations--one arising from the standard
projection into the low-energy sector and the other from the binding of a hole
and the boson.Comment: Published veriso
Photoluminescence modification by high-order photonic band with abnormal dispersion in ZnO inverse opal
We measured the angle- and polarization-resolved reflection and
photoluminescence spectra of ZnO inverse opals. Significant enhancement of
spontaneous emission is observed. The enhanced emission not only has good
directionality but also can be linearly polarized. A detailed theoretical
analysis and numerical simulation reveal that such enhancement is caused by the
abnormal dispersion of a high-order photonic band. The frozen mode at a
stationary inflection point of a dispersion curve can strongly modify the
intensity, directionality and polarization of spontaneous emission.Comment: 22 pages, 11 figures, figures modified, references added, more
explanation adde
Collisional Properties of Cold Spin-Polarized Metastable Neon Atoms
We measure the rates of elastic and inelastic two-body collisions of cold
spin-polarized neon atoms in the metastable 3P2 state for 20^Ne and 22^Ne in a
magnetic trap. From particle loss, we determine the loss parameter of inelastic
collisions beta=6.5(18)x10^{-12} cm^3s^{-1} for 20^Ne and
beta=1.2(3)x10^{-11}cm^3{s}^{-1} for 22^Ne. These losses are caused by ionizing
(i.e. Penning) collisions %to more than and occur less frequently than for
unpolarized atoms. This proves the suppression of Penning ionization due to
spin-polarization. From cross-dimensional relaxation measurements, we obtain
elastic scattering lengths of a=-180(40) a_0 for 20^Ne and a=+150(+80/-50) a_0
for 22^Ne, where a_0=0.0529 nm.Comment: 4 pages, 3 figure
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