5,673 research outputs found
Classifying the Arithmetical Complexity of Teaching Models
This paper classifies the complexity of various teaching models by their
position in the arithmetical hierarchy. In particular, we determine the
arithmetical complexity of the index sets of the following classes: (1) the
class of uniformly r.e. families with finite teaching dimension, and (2) the
class of uniformly r.e. families with finite positive recursive teaching
dimension witnessed by a uniformly r.e. teaching sequence. We also derive the
arithmetical complexity of several other decision problems in teaching, such as
the problem of deciding, given an effective coding of all uniformly r.e. families, any such that
, any and , whether or not the
teaching dimension of with respect to is upper bounded
by .Comment: 15 pages in International Conference on Algorithmic Learning Theory,
201
Vortex deformation and breaking in superconductors: A microscopic description
Vortex breaking has been traditionally studied for nonuniform critical
current densities, although it may also appear due to nonuniform pinning force
distributions. In this article we study the case of a
high-pinning/low-pinning/high-pinning layered structure. We have developed an
elastic model for describing the deformation of a vortex in these systems in
the presence of a uniform transport current density for any arbitrary
orientation of the transport current and the magnetic field. If is above a
certain critical value, , the vortex breaks and a finite effective
resistance appears. Our model can be applied to some experimental
configurations where vortex breaking naturally exists. This is the case for
YBaCuO (YBCO) low angle grain boundaries and films on vicinal
substrates, where the breaking is experienced by Abrikosov-Josephson vortices
(AJV) and Josephson string vortices (SV), respectively. With our model, we have
experimentally extracted some intrinsic parameters of the AJV and SV, such as
the line tension and compared it to existing predictions based on
the vortex structure.Comment: 11 figures in 13 files; minor changes after printing proof
Optimal Investment in the Development of Oil and Gas Field
Let an oil and gas field consists of clusters in each of which an investor
can launch at most one project. During the implementation of a particular
project, all characteristics are known, including annual production volumes,
necessary investment volumes, and profit. The total amount of investments that
the investor spends on developing the field during the entire planning period
we know. It is required to determine which projects to implement in each
cluster so that, within the total amount of investments, the profit for the
entire planning period is maximum.
The problem under consideration is NP-hard. However, it is solved by dynamic
programming with pseudopolynomial time complexity. Nevertheless, in practice,
there are additional constraints that do not allow solving the problem with
acceptable accuracy at a reasonable time. Such restrictions, in particular, are
annual production volumes. In this paper, we considered only the upper
constraints that are dictated by the pipeline capacity. For the investment
optimization problem with such additional restrictions, we obtain qualitative
results, propose an approximate algorithm, and investigate its properties.
Based on the results of a numerical experiment, we conclude that the developed
algorithm builds a solution close (in terms of the objective function) to the
optimal one
The Lambek calculus with iteration: two variants
Formulae of the Lambek calculus are constructed using three binary
connectives, multiplication and two divisions. We extend it using a unary
connective, positive Kleene iteration. For this new operation, following its
natural interpretation, we present two lines of calculi. The first one is a
fragment of infinitary action logic and includes an omega-rule for introducing
iteration to the antecedent. We also consider a version with infinite (but
finitely branching) derivations and prove equivalence of these two versions. In
Kleene algebras, this line of calculi corresponds to the *-continuous case. For
the second line, we restrict our infinite derivations to cyclic (regular) ones.
We show that this system is equivalent to a variant of action logic that
corresponds to general residuated Kleene algebras, not necessarily
*-continuous. Finally, we show that, in contrast with the case without division
operations (considered by Kozen), the first system is strictly stronger than
the second one. To prove this, we use a complexity argument. Namely, we show,
using methods of Buszkowski and Palka, that the first system is -hard,
and therefore is not recursively enumerable and cannot be described by a
calculus with finite derivations
Spontaneous intracranial arterial dissection in the young: diagnosis by CT angiography
BACKGROUND: Spontaneous carotid artery dissections have been rarely reported in children. Diagnosis has traditionally been confirmed by catheter arteriography. More recently diagnosis has been made by magnetic resonance imaging and magnetic resonance angiography; however the sensitivity of these techniques has yet to be determined. The authors are unaware of reports of carotid dissection confirmed by dynamic computed tomography (computerized tomographic arteriography) in the young. CASE PRESENTATION: We recently evaluated a fourteen year-old male following the development of transient neurologic symptoms. There was no antecedent illness or trauma. Dynamic computed tomography revealed an intracranial dissection involving the supraclinoid segment of the left internal carotid artery (confirmed by catheter arteriography). Studies for vasculitis, pro-thrombotic states, and defects of collagen were negative. CONCLUSION: Spontaneous carotid artery dissection is a potential cause of transient neurological symptoms and ischemic stroke in the pediatric population. Dynamic computed tomography appears to be a reliable diagnostic tool which can lead to early diagnosis
Ages for exoplanet host stars
Age is an important characteristic of a planetary system, but also one that
is difficult to determine. Assuming that the host star and the planets are
formed at the same time, the challenge is to determine the stellar age.
Asteroseismology provides precise age determination, but in many cases the
required detailed pulsation observations are not available. Here we concentrate
on other techniques, which may have broader applicability but also serious
limitations. Further development of this area requires improvements in our
understanding of the evolution of stars and their age-dependent
characteristics, combined with observations that allow reliable calibration of
the various techniques.Comment: To appear in "Handbook of Exoplanets", eds. Deeg, H.J. & Belmonte,
J.A, Springer (2018
High prevalence of syphilis among demobilized child soldiers in Eastern Congo: a cross-sectional study
<p>Abstract</p> <p>Background</p> <p>Syphilis, a known major public health issue for soldiers during periods of conflict, is exacerbated in the Democratic Republic of Congo due to widespread sexual violence. However, there has been no previous study to determine the extent of this problem. Therefore, we determined the prevalence of syphilis among young demobilized soldiers.</p> <p>Methods</p> <p>Screening of syphilis using the rapid plasma reagin test and the <it>Treponema pallidum </it>hemagglutination assay was conducted in three transit sites of soldier reintegration in 2005. The Fisher Exact probability test was used to compare results.</p> <p>Results</p> <p>The prevalence of syphilis was found to be 3.4%, with almost equal distribution in respect to sex, location.</p> <p>Conclusion</p> <p>Syphilis continues to be highly prevalent in demobilized child soldiers in Eastern Congo. Syphilis screening tests are recommended.</p
Multiscale methods for the solution of the Helmholtz and Laplace equations
This paper presents some numerical results about applications of multiscale techniques to boundary integral equations. The numerical schemes developed here are to some extent based on the results of the papers [6]—[10]. Section 2 deals with a short description of the theory of generalized Petrov-Galerkin methods for elliptic periodic pseudodifferential equations in covering classical Galerkin schemes, collocation, and other methods. A general setting of multiresolution analysis generated by periodized scaling functions as well as a general stability and convergence theory for such a framework is outlined. The key to the stability analysis is a local principle due to one of the authors. Its applicability relies here on a sufficiently general version of a so-called discrete commutator property of wavelet bases (see [6]). These results establish important prerequisites for developing and analysing methods for the fast solution of the resulting linear systems (Section 2.4). The crucial fact which is exploited by these methods is that the stiffness matrices relative to an appropriate wavelet basis can be approximated well by a sparse matrix while the solution to the perturbed problem still exhibits the same asymptotic accuracy as the solution to the full discrete problem. It can be shown (see [7]) that the amount of the overall computational work which is needed to realize a required accuracy is of the order , where is the number of unknowns and is some real number
Angiography suite concept for an interdisciplinary centre for cardiovascular interventions
A permanently mounted angiography suite in an operating room (OR) is considered to be a hybrid OR. However, regular use for angiographic interventions is restricted with this setup. We introduce an alternative use of space for the efficient utilisation of an angiographic suite outside the surgical unit. This concept includes three scenarios that describe a modification of the catheter suite according to the specific clinical demands by adapting the workflow
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