4,080 research outputs found
Linear Tabulated Resolution Based on Prolog Control Strategy
Infinite loops and redundant computations are long recognized open problems
in Prolog. Two ways have been explored to resolve these problems: loop checking
and tabling. Loop checking can cut infinite loops, but it cannot be both sound
and complete even for function-free logic programs. Tabling seems to be an
effective way to resolve infinite loops and redundant computations. However,
existing tabulated resolutions, such as OLDT-resolution, SLG- resolution, and
Tabulated SLS-resolution, are non-linear because they rely on the
solution-lookup mode in formulating tabling. The principal disadvantage of
non-linear resolutions is that they cannot be implemented using a simple
stack-based memory structure like that in Prolog. Moreover, some strictly
sequential operators such as cuts may not be handled as easily as in Prolog.
In this paper, we propose a hybrid method to resolve infinite loops and
redundant computations. We combine the ideas of loop checking and tabling to
establish a linear tabulated resolution called TP-resolution. TP-resolution has
two distinctive features: (1) It makes linear tabulated derivations in the same
way as Prolog except that infinite loops are broken and redundant computations
are reduced. It handles cuts as effectively as Prolog. (2) It is sound and
complete for positive logic programs with the bounded-term-size property. The
underlying algorithm can be implemented by an extension to any existing Prolog
abstract machines such as WAM or ATOAM.Comment: To appear as the first accepted paper in Theory and Practice of Logic
Programming (http://www.cwi.nl/projects/alp/TPLP
Mechanism of Polarization Fatigue in BiFeO3: the Role of Schottky Barrier
By using piezoelectric force microscopy and scanning Kelvin probe microscopy,
we have investigated the domain evolution and space charge distribution in
planar BiFeO3 capacitors with different electrodes. It is observed that charge
injection at the film/electrode interface leads to domain pinning and
polarization fatigue in BiFeO3. Furthermore, the Schottky barrier at the
interface is crucial for the charge injection process. Lowering the Schottky
barrier by using low work function metals as the electrodes can also improve
the fatigue property of the device, similar to what oxide electrodes can
achieve
Effects of Neuropeptide y on Stem Cells and Their Potential Applications in Disease Therapy
Neuropeptide Y (NPY), a 36-amino acid peptide, is widely distributed in the central and peripheral nervous systems and other peripheral tissues. It takes part in regulating various biological processes including food intake, circadian rhythm, energy metabolism, and neuroendocrine secretion. Increasing evidence indicates that NPY exerts multiple regulatory effects on stem cells. As a kind of primitive and undifferentiated cells, stem cells have the therapeutic potential to replace damaged cells, secret paracrine molecules, promote angiogenesis, and modulate immunity. Stem cell-based therapy has been demonstrated effective and considered as one of the most promising treatments for specific diseases. However, several limitations still hamper its application, such as poor survival and low differentiation and integration rates of transplanted stem cells. The regulatory effects of NPY on stem cell survival, proliferation, and differentiation may be helpful to overcome these limitations and facilitate the application of stem cell-based therapy. In this review, we summarized the regulatory effects of NPY on stem cells and discussed their potential applications in disease therapy
The unique rapid variabilities of the iron K line profiles in NGC 4151
We present a detailed analysis of the iron K line variabilities in
NGC 4151 by using long ASCA observation data obtained in May 1995. Despite the
relatively small amplitude variations in the continuum flux, the iron K
line flux and profile show dramatic variations. Particularly, the line profile
changes from single peak to seeming double peaks and back in time scales of a
few 10 sec. The seemingly double-peaked profiles can be well interpreted as
line emission from a Keplerian ring around a massive black hole. An absorption
line at around 5.9 keV is also marginnaly detected. We discussed current Fe K
line models, but none of them can well explain the observed line and continuum
variations.Comment: 18 pages, latex, 3 figures, ApJ accepte
High-quality multi-wavelength quantum light sources on silicon nitride micro-ring chip
Multi-wavelength quantum light sources, especially at telecom band, are
extremely desired in quantum information technology. Despite recent impressive
advances, such a quantum light source with high quality remains challenging.
Here we demonstrate a multi-wavelength quantum light source using a silicon
nitride micro-ring with a free spectral range of 200 GHz. The generation of
eight pairs of correlated photons is ensured in a wavelength range of 25.6 nm.
With device optimization and noise-rejecting filters, our source enables the
generation of heralded single-photons - at a rate of 62 kHz with
, and the generation of energy-time entangled
photons - with a visibility of in the Franson interferometer.
These results, at room temperature and telecom wavelength, in a CMOS compatible
platform, represent an important step towards integrated quantum light devices
for the quantum networks.Comment: 7 pages, 4 figure
- âŠ