5,598 research outputs found
Learning to integrate reactivity and deliberation in uncertain planning and scheduling problems
This paper describes an approach to planning and scheduling in uncertain domains. In this approach, a system divides a task on a goal by goal basis into reactive and deliberative components. Initially, a task is handled entirely reactively. When failures occur, the system changes the reactive/deliverative goal division by moving goals into the deliberative component. Because our approach attempts to minimize the number of deliberative goals, we call our approach Minimal Deliberation (MD). Because MD allows goals to be treated reactively, it gains some of the advantages of reactive systems: computational efficiency, the ability to deal with noise and non-deterministic effects, and the ability to take advantage of unforseen opportunities. However, because MD can fall back upon deliberation, it can also provide some of the guarantees of classical planning, such as the ability to deal with complex goal interactions. This paper describes the Minimal Deliberation approach to integrating reactivity and deliberation and describe an ongoing application of the approach to an uncertain planning and scheduling domain
Anisotropic magnetoresistance of spin-orbit coupled carriers scattered from polarized magnetic impurities
Anisotropic magnetoresistance (AMR) is a relativistic magnetotransport
phenomenon arising from combined effects of spin-orbit coupling and broken
symmetry of a ferromagnetically ordered state of the system. In this work we
focus on one realization of the AMR in which spin-orbit coupling enters via
specific spin-textures on the carrier Fermi surfaces and ferromagnetism via
elastic scattering of carriers from polarized magnetic impurities. We report
detailed heuristic examination, using model spin-orbit coupled systems, of the
emergence of positive AMR (maximum resistivity for magnetization along
current), negative AMR (minimum resistivity for magnetization along current),
and of the crystalline AMR (resistivity depends on the absolute orientation of
the magnetization and current vectors with respect to the crystal axes)
components. We emphasize potential qualitative differences between pure
magnetic and combined electro-magnetic impurity potentials, between short-range
and long-range impurities, and between spin-1/2 and higher spin-state carriers.
Conclusions based on our heuristic analysis are supported by exact solutions to
the integral form of the Boltzmann transport equation in archetypical
two-dimensional electron systems with Rashba and Dresselhaus spin-orbit
interactions and in the three-dimensional spherical Kohn-Littinger model. We
include comments on the relation of our microscopic calculations to standard
phenomenology of the full angular dependence of the AMR, and on the relevance
of our study to realistic, two-dimensional conduction-band carrier systems and
to anisotropic transport in the valence band of diluted magnetic
semiconductors.Comment: 15 pages, Kohn-Littinger model adde
Proximity effects and triplet correlations in Ferromagnet/Ferromagnet/Superconductor nanostructures
We report the results of a study of superconducting proximity effects in
clean Ferromagnet/Ferromagnet/Superconductor ()
heterostructures, where the pairing state in S is a conventional singlet
s-wave. We numerically find the self-consistent solutions of the Bogoliubov-de
Gennes (BdG) equations and use these solutions to calculate the relevant
physical quantities. By linearizing the BdG equations, we obtain the
superconducting transition temperatures as a function of the angle
between the exchange fields in and . We find that
the results for in systems are clearly different
from those in systems, where monotonically increases
with and is highest for antiparallel magnetizations. Here,
is in general a non-monotonic function, and often has a minimum
near . For certain values of the exchange field and
layer thicknesses, the system exhibits reentrant superconductivity with
: it transitions from superconducting to normal, and then returns to a
superconducting state again with increasing . This phenomenon is
substantiated by a calculation of the condensation energy. We compute, in
addition to the ordinary singlet pair amplitude, the induced odd triplet
pairing amplitudes. The results indicate a connection between equal-spin
triplet pairing and the singlet pairing state that characterizes . We find
also that the induced triplet amplitudes can be very long-ranged in both the S
and F sides and characterize their range. We discuss the average density of
states for both the magnetic and the S regions, and its relation to the pairing
amplitudes and . The local magnetization vector, which exhibits reverse
proximity effects, is also investigated.Comment: 14 pages including 11 figure
Multi-Lepton Collider Signatures of Heavy Dirac and Majorana Neutrinos
We discuss the possibility of observing multi-lepton signals at the Large
Hadron Collider (LHC) from the production and decay of heavy Standard Model
(SM) singlet neutrinos added in extensions of SM to explain the observed light
neutrino masses by seesaw mechanism. In particular, we analyze two `smoking
gun' signals depending on the Dirac or Majorana nature of the heavy neutrino:
(i) for Majorana case, the same-sign di-lepton signal which can be used as a
probe of lepton-number violation, and (ii) for Dirac case, the tri-lepton
signal which conserves lepton number but may violate lepton flavor. Within a
minimal Left-Right symmetric framework in which these additional neutrino
states arise naturally, we find that in both cases, the signals can be
identified with virtually no background beyond a TeV, and the heavy gauge boson
W_R can be discovered in this process. This analysis also provides a direct way
to probe the nature of seesaw physics involving the SM singlets at TeV scale,
and in particular, to distinguish type-I seesaw with purely Majorana heavy
neutrinos from inverse seesaw with pseudo-Dirac counterparts.Comment: 19 pages, 7 figures; typo in eq. 5 fixed; matches published versio
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
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Zero reverse recovery in SiC and GaN Schottky diodes: A comparison
Similarly to the unipolar SiC Schottky diodes, AlGaN/GaN Schottky devices have been suggested to have a negligible reverse recovery current during turn-off and can therefore be switched at very high frequencies with low power losses [1-2]. This study aims to investigate this claim by comparing the reverse recovery characteristic of an AlGaN/GaN diode with that of a SiC diode and a fast recovery Si P-N diode for the same current (4 A) and voltage rating (700 V). TCAD models of a SiC Schottky diode and an AlGaN/GaN diode have been developed and calibrated against fabricated devices for a better physical understanding of the experimentally observed results. The analysis is based on the trade-off between on-state and reverse recovery parameters at both room and high temperatures. Experimental and TCAD results show that while the AlGaN/GaN heterostructure Schottky diode is expected to provide a significant improvement in switching performance when compared to the conventional bipolar Si P-N diodes, the SiC diode offers a more favourable trade-off between on-state and reverse recovery
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PacBio assembly of a Plasmodium knowlesi genome sequence with Hi-C correction and manual annotation of the SICAvar gene family.
Plasmodium knowlesi has risen in importance as a zoonotic parasite that has been causing regular episodes of malaria throughout South East Asia. The P. knowlesi genome sequence generated in 2008 highlighted and confirmed many similarities and differences in Plasmodium species, including a global view of several multigene families, such as the large SICAvar multigene family encoding the variant antigens known as the schizont-infected cell agglutination proteins. However, repetitive DNA sequences are the bane of any genome project, and this and other Plasmodium genome projects have not been immune to the gaps, rearrangements and other pitfalls created by these genomic features. Today, long-read PacBio and chromatin conformation technologies are overcoming such obstacles. Here, based on the use of these technologies, we present a highly refined de novo P. knowlesi genome sequence of the Pk1(A+) clone. This sequence and annotation, referred to as the 'MaHPIC Pk genome sequence', includes manual annotation of the SICAvar gene family with 136 full-length members categorized as type I or II. This sequence provides a framework that will permit a better understanding of the SICAvar repertoire, selective pressures acting on this gene family and mechanisms of antigenic variation in this species and other pathogens
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