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A decision support system to improve service quality in multimodal rapid rail systems: A bayesian perspective
Copyright @ 2011 International Conference on Computers and Industrial EngineeringIn this study, the accessibility of the rail transit stations in a multimodal network formed by a trunk line and its feeder lines are defined. Connectivity between lines and the accessibility of the nodes identify the overall spatial structure of the network. The factors influencing the access choices of rail transit stations and satisfaction of transit travelers in rapid rail transit systems are investigated in order to gain insights into the factors and their interrelationships. The quantitative indications of the relationships are produced and the complexity of evaluating the performance of transit services is exhibited. As the interrelationships are mainly stochastic, the problem on hand is treated as a Bayesian Belief Network (BBN). A BBN approach that presents a learning mechanism is employed and is used as an alternative decision making tool to analyze the rapid rail transit services and identify policies to improve the traveler’s level of service
Influence of mixing the low-valent transition metal atoms (Y,Y=Cr,Mn,Fe) on the properties of the quaternary Co[YY]Z (Z=Al,Ga,Si,Ge,Sn) Heusler compounds
We complement our study on the doping and disorder in CoMnZ compounds [I.
Galanakis \textit{et al.}, Appl. Phys. Lett. \textbf{89}, 042502 (2006) and K.
\"Ozdo\~gan \textit{et al.}, Phys. Rev. B \textbf{74}, (2006)] to cover also
the quaterarny Co[YY]Z compounds with the lower-valent
transition metals Y,Y being Cr, Mn or Fe and the sp atom Z being one of Al,
Ga, Si, Ge, Sn. This study gives a global overview of the magnetic and
electronic properties of these compounds since we vary both Y and Z elements.
Our results suggest that for realistic applications the most appropriate
compounds are the ones belonging to the families Co[MnCr]Z with
irrespectively of the nature of the atoms since they combine high
values of majority DOS at the Fermi level due to the presence of Cr, and
half-metallicity with large band-gaps. On the other hand the presence of Fe
lowers considerably the majority density of states at the Fermi level and when
combined with an element belonging to the Si-column, it even can destroy
half-metallicity
Effect of doping and disorder on the half-metallicity of full Heusler alloy
Heusler alloys containing Co and Mn are amongst the most heavily studied
half-metallic ferromagnets for future applications in spintronics. Using
state-of-the-art electronic structure calculations, we investigate the effect
of doping and disorder on their electronic and magnetic properties. Small
degrees of doping by substituting Fe or Cr for Mn scarcely affect the
half-metallicity. A similar effect is also achieved by mixing the sublattices
occupied by the Mn and sp atoms. Thus the half-metallicity is a robust property
of these alloys
Doping and disorder in the CoMnAl and CoMnGa half-metallic Heusler alloys
We expand our study on the full-Heusler compounds [I. Galanakis \textit{et
al.}, Appl. Phys. Lett. \textbf{89}, 042502 (2006)] to cover also the case of
doping and disorder in the case of CoMnAl and CoMnGa half-metallic
Heusler alloys. These alloys present a region of very small minority density of
states instead of a real gap. Electronic structure calculations reveal that
doping with Fe and Cr in the case of CoMnAl retains the half-metallicity
contrary to the CoMnGa compound. Cr impurities present an unusual behavior
and the spin moment of the Cr impurity scales almost linearly with the
concentration of Cr atoms contrary to the CoMnZ (Z= Si, Ge, Sn) where it
was almost constant. Half-metallicity is no more preserved for both CoMnAl
and CoMnGa alloys when disorder occurs and there is either excess of Mn or
atoms
Ab-initio design of half-metallic fully-compensated ferrimagnets: the case of CrMnZ (Z= P, As, Sb, Bi) compounds
Electronic structure calculations from first-principles are employed to
design some new half-metallic fully-compensated ferrimagnets (or as they are
widely known half-metallic antiferromagnets) susceptible of finding
applications in spintronics. CrMnZ (Z= P, As, Sb, Bi) compounds have 24
valence electrons per unit cell and calculations show that their total spin
moment is approximately zero for a wide range of lattice constants in agreement
with the Slater-Pauling behavior for ideal half-metals. Simultaneously, the
spin magnetic moments of Cr and Mn atoms are antiparallel and the compounds are
ferrimagnets. Mean-field approximation is employed to estimate their Curie
temperature, which exceeds room temperature for the alloy with Sb. Our findings
suggest that CrMnSb is the compound of choice for further experimental
investigations. Contrary to the alloys mentioned above half-metallic
antiferromagnetism is unstable in the case of the CrFeZ (Z= Si, Ge, Sn)
alloys
Defects in CrAs and related compounds: a route to half-metallic ferrimagnetism
Half-metallic ferrimagnetism is crucial for spintronic applications with
respect to ferromagnets due to the lower stray fields created by these
materials. Studying the effect of defects in CrAs and related transition-metal
chalcogenides and pnictides crystallizing in the zinc-blende structure, we
reveal that the excess of the transition-metal atoms leads to half-metallic
ferrimagnetism. The surplus of these atoms are antiferromagnetically coupled to
the transition-metal atoms sitting at the perfect lattice sites. The needed
condition to achieve half-metallic ferrimagnetism is to prevent the migration
of the atoms to other sites and the atomic swaps
Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys
Half-metallic Heusler alloys are among the most promising materials for
future applications in spintronic devices. Although most Heusler alloys are
ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated
ferrimagnetic) alloys would be more desirable for applications due to the lower
external fields. Ferrimagnetism can be either found in perfect Heusler
compounds or achieved through the creation of defects in ferromagnetic Heusler
alloys.Comment: To be considered for the proceedings of the International Conference
on Nanoscale Magnetism (ICNM 07
Defects-driven appearance of half-metallic ferrimagnetism in Co-Mn--based Heusler alloys
Half-metallic ferromagnetic full-Heusler alloys containing Co and Mn, having
the formula CoMnZ where Z a sp element, are among the most studied Heusler
alloys due to their stable ferromagnetism and the high Curie temperatures which
they present. Using state-of-the-art electronic structure calculations we show
that when Mn atoms migrate to sites occupied in the perfect alloys by Co, these
Mn atoms have spin moments antiparallel to the other transition metal atoms.
The ferrimagnetic compounds, which result from this procedure, keep the
half-metallic character of the parent compounds and the large
exchange-splitting of the Mn impurities atoms only marginally affects the width
of the gap in the minority-spin band. The case of [CoMn]MnSi is
of particular interest since MnSi is known to crystallize in the Heusler
lattice structure of CoMnZ compounds. Robust half-metallic
ferrimagnets are highly desirable for realistic applications since they lead to
smaller energy losses due to the lower external magnetic fields created with
respect to their ferromagnetic counterparts
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