1,553 research outputs found
Guided Unfoldings for Finding Loops in Standard Term Rewriting
In this paper, we reconsider the unfolding-based technique that we have
introduced previously for detecting loops in standard term rewriting. We
improve it by guiding the unfolding process, using distinguished positions in
the rewrite rules. This results in a depth-first computation of the unfoldings,
whereas the original technique was breadth-first. We have implemented this new
approach in our tool NTI and compared it to the previous one on a bunch of
rewrite systems. The results we get are promising (better times, more
successful proofs).Comment: Pre-proceedings paper presented at the 28th International Symposium
on Logic-Based Program Synthesis and Transformation (LOPSTR 2018), Frankfurt
am Main, Germany, 4-6 September 2018 (arXiv:1808.03326
Dirac's hole theory versus quantum field theory
Dirac's hole theory and quantum field theory are usually considered
equivalent to each other. For models of a certain type, however, the
equivalence may not hold as we discuss in this Letter. This problem is closely
related to the validity of the Pauli principle in intermediate states of
perturbation theory.Comment: No figure
The Dirac Oscillator. A relativistic version of the Jaynes--Cummings model
The dynamics of wave packets in a relativistic Dirac oscillator is compared
to that of the Jaynes-Cummings model. The strong spin-orbit coupling of the
Dirac oscillator produces the entanglement of the spin with the orbital motion
similar to what is observed in the model of quantum optics. The collapses and
revivals of the spin which result extend to a relativistic theory our previous
findings on nonrelativistic oscillator where they were known under the name of
`spin-orbit pendulum'. There are important relativistic effects (lack of
periodicity, zitterbewegung, negative energy states). Many of them disappear
after a Foldy-Wouthuysen transformation.Comment: LaTeX2e, uses IOP style files (included), 14 pages, 9 separate
postscript figure
Relativistic confinement of neutral fermions with a trigonometric tangent potential
The problem of neutral fermions subject to a pseudoscalar potential is
investigated. Apart from the solutions for , the problem is
mapped into the Sturm-Liouville equation. The case of a singular trigonometric
tangent potential () is exactly solved and the
complete set of solutions is discussed in some detail. It is revealed that this
intrinsically relativistic and true confining potential is able to localize
fermions into a region of space arbitrarily small without the menace of
particle-antiparticle production.Comment: 12 page
Identification of targets of tumor suppressor microRNA-34a using a reporter library system
miRNAs play critical roles in various biological processes by targeting specific mRNAs. Current approaches to identifying miRNA targets are insufficient for elucidation of a miRNA regulatory network. Here, we created a cell-based screening system using a luciferase reporter library composed of 4,891 full-length cDNAs, each of which was integrated into the 3′ UTR of a luciferase gene. Using this reporter library system, we conducted a screening for targets of miR-34a, a tumor-suppressor miRNA. We identified both previously characterized and previously uncharacterized targets. miR-34a overexpression in MDA-MB-231 breast cancer cells repressed the expression of these previously unrecognized targets. Among these targets, GFRA3 is crucial for MDA-MB-231 cell growth, and its expression correlated with the overall survival of patients with breast cancer. Furthermore, GFRA3 was found to be directly regulated by miR-34a via its coding region. These data show that this system is useful for elucidating miRNA functions and networks
Controlling a resonant transmission across the -potential: the inverse problem
Recently, the non-zero transmission of a quantum particle through the
one-dimensional singular potential given in the form of the derivative of
Dirac's delta function, , with , being a
potential strength constant, has been discussed by several authors. The
transmission occurs at certain discrete values of forming a resonance
set . For
this potential has been shown to be a perfectly reflecting wall. However, this
resonant transmission takes place only in the case when the regularization of
the distribution is constructed in a specific way. Otherwise, the
-potential is fully non-transparent. Moreover, when the transmission
is non-zero, the structure of a resonant set depends on a regularizing sequence
that tends to in the sense of
distributions as . Therefore, from a practical point of
view, it would be interesting to have an inverse solution, i.e. for a given
to construct such a regularizing sequence
that the -potential at this value is
transparent. If such a procedure is possible, then this value
has to belong to a corresponding resonance set. The present paper is devoted to
solving this problem and, as a result, the family of regularizing sequences is
constructed by tuning adjustable parameters in the equations that provide a
resonance transmission across the -potential.Comment: 21 pages, 4 figures. Corrections to the published version added;
http://iopscience.iop.org/1751-8121/44/37/37530
Magnetoresistivity in a Tilted Magnetic Field in p-Si/SiGe/Si Heterostructures with an Anisotropic g-Factor: Part II
The magnetoresistance components and were measured in
two p-Si/SiGe/Si quantum wells that have an anisotropic g-factor in a tilted
magnetic field as a function of temperature, field and tilt angle. Activation
energy measurements demonstrate the existence of a ferromagnetic-paramagnetic
(F-P) transition for a sample with a hole density of
=2\,cm. This transition is due to crossing of the
0 and 1 Landau levels. However, in another sample, with
=7.2\,cm, the 0 and 1 Landau
levels coincide for angles =0-70. Only for >
70 do the levels start to diverge which, in turn, results in the
energy gap opening.Comment: 5 pages, 6 figure
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