174 research outputs found
Microcanonical distributions for quantum systems
The standard assumption for the equilibrium microcanonical state in quantum mechanics, that the system must be in one of the energy eigenstates, is weakened so as to allow superpositions of states. The weakened form of the microcanonical postulate thus asserts that all quantum states giving rise to the same energy expectation value must be realised with equal probability. The consequences that follow from this assertion are investigated. In particular, a closed-form expression for the density of states associated with any system having a nondegenerate energy spectrum is obtained. The result is applied to a variety of examples, for which the behaviour of the state density, as well as the relation between energy and temperature, are determined. Numerical studies indicate that the density of states converges to a distribution when the number of energy levels approaches infinity
Behavior of eigenvalues in a region of broken PT symmetry
PT-symmetric quantum mechanics began with a study of the Hamiltonian H=p2+x2(ix)ɛ. When ɛ≥0, the eigenvalues of this non-Hermitian Hamiltonian are discrete, real, and positive. This portion of parameter space is known as the region of unbroken PT symmetry. In the region of broken PT symmetry, ɛ<0, only a finite number of eigenvalues are real and the remaining eigenvalues appear as complex-conjugate pairs. The region of unbroken PT symmetry has been studied but the region of broken PT symmetry has thus far been unexplored. This paper presents a detailed numerical and analytical examination of the behavior of the eigenvalues for −4<ɛ<0. In particular, it reports the discovery of an infinite-order exceptional point at ɛ=−1, a transition from a discrete spectrum to a partially continuous spectrum at ɛ=−2, a transition at the Coulomb value ɛ=−3, and the behavior of the eigenvalues as ɛ approaches the conformal limit ɛ=−4
Assessment of possible impact of a health promotion program in Korea from health risk trends in a longitudinally observed cohort
BACKGROUND: Longitudinally observed cohort data can be utilized to assess the potential for health promotion and healthcare planning by comparing the estimated risk factor trends of non-intervened with that of intervened. The paper seeks (1) to estimate a natural transition (patterns of movement between states) of health risk state from a Korean cohort data using a Markov model, (2) to derive an effective and necessary health promotion strategy for the population, and (3) to project a possible impact of an intervention program on health status. METHODS: The observed transition of health risk states in a Korean employee cohort was utilized to estimate the natural flow of aggregated health risk states from eight health risk measures using Markov chain models. In addition, a reinforced transition was simulated, given that a health promotion program was implemented for the cohort, to project a possible impact on improvement of health status. An intervened risk transition was obtained based on age, gender, and baseline risk state, adjusted to match with the Korean cohort, from a simulated random sample of a US employee population, where a health intervention was in place. RESULTS: The estimated natural flow (non-intervened), following Markov chain order 2, showed a decrease in low risk state by 3.1 percentage points in the Korean population while the simulated reinforced transition (intervened) projected an increase in low risk state by 7.5 percentage points. Estimated transitions of risk states demonstrated the necessity of not only the risk reduction but also low risk maintenance. CONCLUSIONS: The frame work of Markov chain efficiently estimated the trend, and captured the tendency in the natural flow. Given only a minimally intense health promotion program, potential risk reduction and low risk maintenance was projected
Nonlinear Localization in Metamaterials
Metamaterials, i.e., artificially structured ("synthetic") media comprising
weakly coupled discrete elements, exhibit extraordinary properties and they
hold a great promise for novel applications including super-resolution imaging,
cloaking, hyperlensing, and optical transformation. Nonlinearity adds a new
degree of freedom for metamaterial design that allows for tuneability and
multistability, properties that may offer altogether new functionalities and
electromagnetic characteristics. The combination of discreteness and
nonlinearity may lead to intrinsic localization of the type of discrete
breather in metallic, SQUID-based, and symmetric metamaterials. We
review recent results demonstrating the generic appearance of breather
excitations in these systems resulting from power-balance between intrinsic
losses and input power, either by proper initialization or by purely dynamical
procedures. Breather properties peculiar to each particular system are
identified and discussed. Recent progress in the fabrication of low-loss,
active and superconducting metamaterials, makes the experimental observation of
breathers in principle possible with the proposed dynamical procedures.Comment: 19 pages, 14 figures, Invited (Review) Chapte
A Structure-Based Approach for Detection of Thiol Oxidoreductases and Their Catalytic Redox-Active Cysteine Residues
Cysteine (Cys) residues often play critical roles in proteins, for example, in
the formation of structural disulfide bonds, metal binding, targeting proteins
to the membranes, and various catalytic functions. However, the structural
determinants for various Cys functions are not clear. Thiol oxidoreductases,
which are enzymes containing catalytic redox-active Cys residues, have been
extensively studied, but even for these proteins there is little understanding
of what distinguishes their catalytic redox Cys from other Cys functions.
Herein, we characterized thiol oxidoreductases at a structural level and
developed an algorithm that can recognize these enzymes by (i) analyzing amino
acid and secondary structure composition of the active site and its similarity
to known active sites containing redox Cys and (ii) calculating accessibility,
active site location, and reactivity of Cys. For proteins with known or modeled
structures, this method can identify proteins with catalytic Cys residues and
distinguish thiol oxidoreductases from the enzymes containing other catalytic
Cys types. Furthermore, by applying this procedure to Saccharomyces
cerevisiae proteins containing conserved Cys, we could identify the
majority of known yeast thiol oxidoreductases. This study provides insights into
the structural properties of catalytic redox-active Cys and should further help
to recognize thiol oxidoreductases in protein sequence and structure
databases
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