104 research outputs found
A realistic quantum capacitance model for quantum Hall edge state based Fabry-P\'{e}rot interferometers
In this work, the classical and the quantum capacitances are calculated for a
Fabry-P\'{e}rot interferometer operating in the integer quantized Hall regime.
We first consider a rotationally symmetric electrostatic confinement potential
and obtain the widths and the spatial distribution of the insulating
(incompressible) circular strips using a charge density profile stemming from
self-consistent calculations. Modelling the electrical circuit of capacitors
composed of metallic gates and incompressible/compressible strips, we
investigate the conditions to observe Aharonov-Bohm (quantum mechanical phase
dependent) and Coulomb Blockade (capacitive coupling dependent) effects
reflected in conductance oscillations. In a last step, we solve the
Schr\"odinger and the Poisson equations self-consistently in a numerical manner
taking into account realistic experimental geometries. We find that, describing
the conductance oscillations either by Aharanov-Bohm or Coulomb Blockade
strongly depends on sample properties also other than size, therefore,
determining the origin of these oscillations requires further experimental and
theoretical investigation
Electrical Properties of Al/p-Si Structures with Colchicine Organic Thin Film
In this study, we have fabricated an Al/Colchicine/p-Si structure and have investigated its current–
voltage (I–V) and capacitance–voltage (C–V) characteristics at room temperature. The barrier height and
ideality factor values of 0.68 eV and 3.22, respectively, have been obtained from the I-V plot. The value of
the barrier height was compared with the barrier height value of 0.50 eV of a conventional Al/p-Si diode.
This was attributed to the Colchicine organic film modifying the effective barrier height by affecting the
space charge region of the inorganic Si semiconductor substrate. By using C – 2-V characteristics the diffusion
potential value has been extracted as 1.32 V.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3514
The current polarization rectification of the integer quantized Hall effect
We report on our theoretical investigation considering the widths of
quantized Hall plateaus (QHPs) depending on the density asymmetry induced by
the large current within the out-of-linear response regime. We solve the
Schrodinger equation within the Hartree type mean field approximation using
Thomas Fermi Poisson nonlinear screening theory. We observe that the two
dimensional electron system splits into compressible and incompressible regions
for certain magnetic field intervals, where the Hall resistance is quantized
and the longitudinal resistance vanishes, if an external current is imposed. We
found that the strong current imposed, induces an asymmetry on the IS width
depending linearly on the current intensity.Comment: 5 pages, 2 figur
Constructing a semantic predication gold standard from the biomedical literature
<p>Abstract</p> <p>Background</p> <p>Semantic relations increasingly underpin biomedical text mining and knowledge discovery applications. The success of such practical applications crucially depends on the quality of extracted relations, which can be assessed against a gold standard reference. Most such references in biomedical text mining focus on narrow subdomains and adopt different semantic representations, rendering them difficult to use for benchmarking independently developed relation extraction systems. In this article, we present a multi-phase gold standard annotation study, in which we annotated 500 sentences randomly selected from MEDLINE abstracts on a wide range of biomedical topics with 1371 semantic predications. The UMLS Metathesaurus served as the main source for conceptual information and the UMLS Semantic Network for relational information. We measured interannotator agreement and analyzed the annotations closely to identify some of the challenges in annotating biomedical text with relations based on an ontology or a terminology.</p> <p>Results</p> <p>We obtain fair to moderate interannotator agreement in the practice phase (0.378-0.475). With improved guidelines and additional semantic equivalence criteria, the agreement increases by 12% (0.415 to 0.536) in the main annotation phase. In addition, we find that agreement increases to 0.688 when the agreement calculation is limited to those predications that are based only on the explicitly provided UMLS concepts and relations.</p> <p>Conclusions</p> <p>While interannotator agreement in the practice phase confirms that conceptual annotation is a challenging task, the increasing agreement in the main annotation phase points out that an acceptable level of agreement can be achieved in multiple iterations, by setting stricter guidelines and establishing semantic equivalence criteria. Mapping text to ontological concepts emerges as the main challenge in conceptual annotation. Annotating predications involving biomolecular entities and processes is particularly challenging. While the resulting gold standard is mainly intended to serve as a test collection for our semantic interpreter, we believe that the lessons learned are applicable generally.</p
Clustering cliques for graph-based summarization of the biomedical research literature
BACKGROUND: Graph-based notions are increasingly used in biomedical data mining and knowledge discovery tasks. In this paper, we present a clique-clustering method to automatically summarize graphs of semantic predications produced from PubMed citations (titles and abstracts). RESULTS: SemRep is used to extract semantic predications from the citations returned by a PubMed search. Cliques were identified from frequently occurring predications with highly connected arguments filtered by degree centrality. Themes contained in the summary were identified with a hierarchical clustering algorithm based on common arguments shared among cliques. The validity of the clusters in the summaries produced was compared to the Silhouette-generated baseline for cohesion, separation and overall validity. The theme labels were also compared to a reference standard produced with major MeSH headings. CONCLUSIONS: For 11 topics in the testing data set, the overall validity of clusters from the system summary was 10% better than the baseline (43% versus 33%). While compared to the reference standard from MeSH headings, the results for recall, precision and F-score were 0.64, 0.65, and 0.65 respectively
Times of Minima of Some Eclipsing Binaries
We present new times of minima in the light curves of some eclipsing binarie
ContextD: an algorithm to identify contextual properties of medical terms in a Dutch clinical corpus
- …