2,380 research outputs found
Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors
II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light
elements are investigated as potential dilute magnetic semiconductors (DMS).
Based on our first-principle calculations, nitrogen doped ZnO, carbon doped
ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism
of such DMS materials can be attributed to a p-d exchange-like p-p coupling
interaction which is derived from the similar symmetry and wave function
between the impurity (p-like t_2) and valence (p) states. We also propose a
co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance
the ferromagnetic coupling and to increase the solubility and activity
Effect of styrene–butadiene rubber latex on the properties of modified porous cement-stabilised aggregate
As road base materials, porous cement-stabilised aggregates (PCSA) can reduce the erosion damage caused by the water inside pavement structure. However, due to the reduced deformation resistance and anti-cracking ability associated with the high porosity, the application of PCSA has been held back. A laboratory experiment was conducted in this study to improve the cracking properties of PCSA through the incorporation of the styrene–butadiene rubber (SBR) latex. The effects of the SBR latex usage on permeability, compressive strength, flexural strength and anti-freezing ability (AFA) of PCSA were investigated. In addition, the modification mechanisms of the SBR latex on the PCSA properties were analysed. Test results indicated that the air voids and permeability coefficient decreased with the increase in the SBR latex dosages. The flexural strength and AFA were improved when the SBR latex dosages are between 10% and 15%. 7 d compressive strength has a slight decrease, while the 28 d compressive strength is increased. The significant increase in flexural strength and AFA can be attributed to the interpenetrating matrices formation, stretching effect as well as flexibility enhancement after adding the SBR latex
Exploration of the Gap Problem between Planning and Execution in the Supply Chain', -- A Case of Taiwan IC Industry
[[abstract]]The purpose of this study is to investigate the gap between the planning response goal and the execution outcome in supply chain management. Gaps occur due to the incompetence of supply chain partners in successively responding toward the ever-changing market environment. It is very important to check whether the decision by supply chain partner firms to cut down the level of re-integrated coordination will create an unpredictable risk to the downstream firm. In the real world practice, a firm is apt to take action to reduce the coordination level so as to save the accrued cost. The integrated circuit (IC) manufacturing industry in Taiwan is by no means an exception. Therefore, in this paper we present a case study of Taiwan's IC industry to justify our argument. It is carried out with a comprehensive survey with the top management personnel in the related area to collect the primary data, and the outcome of the factor analysis and an LISREL analysis toward these data indicates that the reduction in the supply chain partners' re-integrated coordination level does allow the occurrence of a gap between the planning goal and the execution outcome. Based on our findings a proposal for improvement is presented
Evolution of spin-wave excitations in ferromagnetic metallic manganites
Neutron scattering results are presented for spin-wave excitations of three
ferromagnetic metallic MnO manganites (where and
are rare- and alkaline-earth ions), which when combined with
previous work elucidate systematics of the interactions as a function of
carrier concentration , on-site disorder, and strength of the lattice
distortion. The long wavelength spin dynamics show only a very weak dependence
across the series. The ratio of fourth to first neighbor exchange ()
that controls the zone boundary magnon softening changes systematically with
, but does not depend on the other parameters. None of the prevailing models
can account for these behaviors.Comment: Submitted to Phys. Rev. Let
Persistent Current From the Competition Between Zeeman Coupling and Spin-Orbit Interaction
Applying the non-adiabatic Aharonov-Anandan phase approach to a mesoscopic
ring with non-interacting many electrons in the presence of the spin-orbit
interaction, Zeeman coupling and magnetic flux, we show that the time-reversal
symmetry breaking due to Zeeman coupling is intrinsically different from that
due to magnetic flux. We find that the direction of the persistent currents
induced by the Zeeman coupling changes periodically with the particle number,
while the magnetic flux determines the direction of the induced currents by its
sign alone.Comment: 5 pages, ReVTeX, including 3 figures on request,Submitted to
Phys.Rev.Let
Spin Precession and Time-Reversal Symmetry Breaking in Quantum Transport of Electrons Through Mesoscopic Rings
We consider the motion of electrons through a mesoscopic ring in the presence
of spin-orbit interaction, Zeeman coupling, and magnetic flux. The coupling
between the spin and the orbital degrees of freedom results in the geometric
and the dynamical phases associated with a cyclic evolution of spin state.
Using a non-adiabatic Aharonov-Anandan phase approach, we obtain the exact
solution of the system and identify the geometric and the dynamical phases for
the energy eigenstates. Spin precession of electrons encircling the ring can
lead to various interference phenomena such as oscillating persistent current
and conductance. We investigate the transport properties of the ring connected
to current leads to explore the roles of the time-reversal symmetry and its
breaking therein with the spin degree of freedom being fully taken into
account. We derive an exact expression for the transmission probability through
the ring. We point out that the time-reversal symmetry breaking due to Zeeman
coupling can totally invalidate the picture that spin precession results in
effective, spin-dependent Aharonov-Bohm flux for interfering electrons.
Actually, such a picture is only valid in the Aharonov-Casher effect induced by
spin-orbit interaction only. Unfortunately, this point has not been realized in
prior works on the transmission probability in the presence of both SO
interaction and Zeeman coupling. We carry out numerical computation to
illustrate the joint effects of spin-orbit interaction, Zeeman coupling and
magnetic flux. By examining the resonant tunneling of electrons in the weak
coupling limit, we establish a connection between the observable time-reversal
symmetry breaking effects manifested by the persistent current and by the
transmission probability. For a ring formed by two-dimensional electron gas, weComment: 20 pages, 5 figure
Aharonov-Anandan Effect Induced by Spin-Orbit Interaction and Charge-Density-Waves in Mesoscopic Rings
We study the spin-dependent geometric phase effect in mesoscopic rings of
charge-density-wave(CDW) materials. When electron spin is explicitly taken into
account, we show that the spin-dependent Aharonov-Casher phase can have a
pronounced frustration effects on such CDW materials with appropriate electron
filling. We show that this frustration has observable consequences for
transport experiment. We identify a phase transition from a Peierls insulator
to metal, which is induced by spin-dependent phase interference effects.
Mesoscopic CDW materials and spin-dependent geometric phase effects, and their
interplay, are becoming attractive opportunities for exploitation with the
rapid development of modern fabrication technology.Comment: 5 pages, 6 figures, to appear in Phys.Rev.B(Aug.15, 1998
Crystal growth of selected II-VI semiconducting alloys by directional solidification
A Hg(0.84)Zn(0.16)Te alloy crystal was back-melted and partially resolidified during the first United States Microgravity Laboratory (USML-1) mission in the Marshall Space Flight Center's Crystal Growth Furnace. The experiment was inadvertently terminated at about 30% of planned completion. Nonetheless, it was successfully demonstrated that HgZnTe alloy ingots partially grown and quenched on the ground can be back-melted and regrown in space under nearly steady state growth conditions. An identical 'ground-truth' experiment was performed following the mission. Preliminary results are presented for both crystals, as well as for a series of other crystals grown prior to the mission for the purposes of optimizing in-flight growth conditions
A Contour Integral Representation for the Dual Five-Point Function and a Symmetry of the Genus Four Surface in R6
The invention of the "dual resonance model" N-point functions BN motivated
the development of current string theory. The simplest of these models, the
four-point function B4, is the classical Euler Beta function. Many standard
methods of complex analysis in a single variable have been applied to elucidate
the properties of the Euler Beta function, leading, for example, to analytic
continuation formulas such as the contour-integral representation obtained by
Pochhammer in 1890. Here we explore the geometry underlying the dual five-point
function B5, the simplest generalization of the Euler Beta function. Analyzing
the B5 integrand leads to a polyhedral structure for the five-crosscap surface,
embedded in RP5, that has 12 pentagonal faces and a symmetry group of order 120
in PGL(6). We find a Pochhammer-like representation for B5 that is a contour
integral along a surface of genus five. The symmetric embedding of the
five-crosscap surface in RP5 is doubly covered by a symmetric embedding of the
surface of genus four in R6 that has a polyhedral structure with 24 pentagonal
faces and a symmetry group of order 240 in O(6). The methods appear
generalizable to all N, and the resulting structures seem to be related to
associahedra in arbitrary dimensions.Comment: 43 pages and 44 figure
Design of a Novel Road Pavement Using Steel and Plastics to Enhance Performance, Durability and Construction Efficiency
Durability is one important problem that pavement engineers need to address in pavement’s long service life. Furthermore, easily recycled pavement materials, and safe and efficient pavement construction are also important areas for development in road engineering. For these reasons, a new asphalt steel plastic (ASP) pavement structure was proposed with an asphalt mixture forming the surface layer, and steel plate and plastic materials functioning as the main load-bearing layers. Based on a comprehensive performance review and cost-benefit analysis, stone mastic asphalt (SMA) is recommended to be used as the surface layer; and A656 steel plate and acrylonitrile butadiene styrene (ABS) plastic materials should be the main load-bearing layer, on top of a foundation layer made with graded crushed stones. A glass fiber reinforced polymer (GFRP) insulation layer is recommended for use between the steel plate and ABS. Mechanical properties of the ASP pavement were analyzed using the finite element method. Laboratory tests were conducted to verify the thermal insulation performance of GFRP, the high-temperature stability and the fatigue resistance of ASP pavement. Results show that some of the mechanical properties of ASP pavement (with a structure of 80 mm SMA asphalt mixture, 8 mm steel plate, 140 mm ABS and 200 mm crushed stones) are comparable with conventional long-life pavement (with 350 mm asphalt layer overlaying 400 mm graded crushed stones). Dynamic stability of the ASP slab specimens can reach 10,000 times/mm, and the fatigue life is about twice that of SMA. Besides, the ASP pavement can be prefabricated and assembled on-site, and thus can greatly improve construction efficiency. From the lifecycle perspective, ASP pavement has many advantages over traditional pavements, such as durability, lower environmental footprint and recyclability, making it is worth further research
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