2,318 research outputs found
Quantum walks based on an interferometric analogy
There are presently two models for quantum walks on graphs. The "coined" walk
uses discrete time steps, and contains, besides the particle making the walk, a
second quantum system, the coin, that determines the direction in which the
particle will move. The continuous walk operates with continuous time. Here a
third model for a quantum walk is proposed, which is based on an analogy to
optical interferometers. It is a discrete-time model, and the unitary operator
that advances the walk one step depends only on the local structure of the
graph on which the walk is taking place. No quantum coin is introduced. This
type of walk allows us to introduce elements, such as phase shifters, that have
no counterpart in classical random walks. Walks on the line and cycle are
discussed in some detail, and a probability current for these walks is
introduced. The relation to the coined quantum walk is also discussed. The
paper concludes by showing how to define these walks for a general graph.Comment: Latex,18 pages, 5 figure
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From Children's Arithmetic To Medical Problem Solving An Extension of the Kintch-Greeno Model
It has been found that expert physicians use forward reasoning in diagnostic explanations of clinical cases. This paper shows that the Kintsch-Greeno model for solving arithmetic word problems, which assumes a forward chaining process, can be extended to explain this phenomena. The basic approach is to modify the lexicon and the schema structure of the existing simulation program while retaining the basic control structure. The principle modifications are in the structure of the schemata which make use of three slots: indicator,abnormality and consequence. As with the Kintsch-Greeno theory,the model proceeds by using these schemata to build super-schemata from the propositional representation of the problem text
Vesicular-arbuscular mycorrhizae in two tropical monodominant trees
Journal ArticleMycorrhizae, symbioses between plant roots and fungi, are in virtually all terrestrial plant ecosystems. Substantial evidence indicates that mycorrhizal associations are beneficial to both partners. In most systems, the fungus benefits the host plant by effectively scavenging nutrients and in return, utilizes carbohydrates produced by the plant (Allen 1991, Harley & Smith 1983)
Dynamics in a Respiratory Control Model With Two Delays
In this paper we study ventilation patterns in a set of parameter dependent nonlinear delay equations with two transport delays modeling the human respiratory control system with peripheral and central control loops. We present a convergent numerical scheme suitable to perform simulations when all disturbances and system parameters are known, then we consider the numerical identifiability of various system parameters based on ventilation data. We are especially interested in the identification of the transport delays in the control loops because these parameters are not measurable directly, but they have a strong influence on system stability/instability
Scattering in an environment
The cross section of elastic electron-proton scattering taking place in an
electron gas is calculated within the Closed Time Path method. It is found to
be the sum of two terms, one being the expression in the vacuum except that it
involves dressing due to the electron gas. The other term is due to the
scattering particles-electron gas entanglement. This term dominates the usual
one when the exchange energy is in the vicinity of the Fermi energy.
Furthermore it makes the trajectories of the colliding particles more
consistent and the collision more irreversible, rendering the scattering more
classical in this regime.Comment: final version to appear in Phys. Rev.
Phase Transition Study of Superconducting Microstructures
The presented results are part of a feasibility study of superheated
superconducting microstructure detectors. The microstructures (dots) were
fabricated using thin film patterning techniques with diameters ranging from
m up to m and thickness of m. We used arrays and single
dots to study the dynamics of the superheating and supercooling phase
transitions in a magnetic field parallel to the dot surface. The phase transi-
tions were produced by either varying the applied magnetic field strength at a
constant temperature or changing the bath temperature at a constant field.
Preliminary results on the dynamics of the phase transitions of arrays and
single indium dots will be reported.Comment: 7pages in LaTex format, five figures available upon request by
[email protected], preprint Bu-He 93/
Modeling broadband X-ray absorption of massive star winds
We present a method for computing the net transmission of X-rays emitted by
shock-heated plasma distributed throughout a partially optically thick stellar
wind from a massive star. We find the transmission by an exact integration of
the formal solution, assuming that the emitting plasma and absorbing plasma are
mixed at a constant mass ratio above some minimum radius, below which there is
assumed to be no emission. This model is more realistic than either the slab
absorption associated with a corona at the base of the wind or the exospheric
approximation that assumes that all observed X-rays are emitted without
attenuation from above the radius of optical depth unity. Our model is
implemented in XSPEC as a pre-calculated table that can be coupled to a
user-defined table of the wavelength dependent wind opacity. We provide a
default wind opacity model that is more representative of real wind opacities
than the commonly used neutral interstellar medium (ISM) tabulation.
Preliminary modeling of \textit{Chandra} grating data indicates that the X-ray
hardness trend of OB stars with spectral subtype can largely be understood as a
wind absorption effect.Comment: 9 pages, 9 figures. Includes minor corrections made in proof
Molecular diversity of arbuscular mycorrhizal fungi and patterns of host association over time and space in a tropical forest
We have used molecular techniques to investigate the diversity and distribution of the arbuscular mycorrhizal (AM) fungi colonizing tree seedling roots in the tropical forest on Barro Colorado Island (BCI), Republic of Panama. In the first year, we sampled newly emergent seedlings of the understory treelet Faramea occidentalis and the canopy emergent Tetragastris panamensis, from mixed seedling carpets at each of two sites. The following year we sampled surviving seedlings from these cohorts. The roots of 48 plants were analysed using AM fungal-specific primers to amplify and clone partial small subunit (SSU) ribosomal RNA gene sequences. Over 1300 clones were screened for random fragment length polymorphism (RFLP) variation and 7% of these were sequenced. Compared with AM fungal communities sampled from temperate habitats using the same method, the overall diversity was high, with a total of 30 AM fungal types identified. Seventeen of these types have not been recorded previously, with the remainder being similar to types reported from temperate habitats. The tropical mycorrhizal population showed significant spatial heterogeneity and nonrandom associations with the different hosts. Moreover there was a strong shift in the mycorrhizal communities over time. AM fungal types that were dominant in the newly germinated seedlings were almost entirely replaced by previously rare types in the surviving seedlings the following year. The high diversity and huge variation detected across time points, sites and hosts, implies that the AM fungal types are ecologically distinct and thus may have the potential to influence recruitment and host composition in tropical forests
Supplementary data for the article: Meszaros, J. P.; Poljarević, J.; Gal, T. G.; May, N. V.; Spengler, G.; Enyedy, E. A. Comparative Solution and Structural Studies of Half-Sandwich Rhodium and Ruthenium Complexes Bearing Curcumin and Acetylacetone. Journal of Inorganic Biochemistry 2019, 195, 91–100. https://doi.org/10.1016/j.jinorgbio.2019.02.015
Supplementary material for: [https://doi.org/10.1016/j.jinorgbio.2019.02.015]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2873
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