37,396 research outputs found
Ballistic side jump motion of electrons and holes in semiconductor quantum wells
We investigate the ballistic motion of electrons and holes in III-V
semiconductor quantum wells with spin-orbit coupling and a homogeneous in-plane
electric field. As a result of a non-perturbative treatment of both of these
influences, particle wave packets undergo a pronounced side jump perpendicular
to the field direction. For wave packets of sufficient width the amplitude of
this motion can be estimated analytically and increases with decreasing field
strength. We discuss the scaling behavior of the effect and some if its
experimental implicationsComment: 4 pages, 3 figures include
Enhancing the decision-making process of project managers in the built environment: An integrated approach
A study of the project manager’s (PM) function must be to examine: what their role is, their skills, and training needed. The project manager needs wide perspective regarding the classic management functions of control, coordination, communication, and the settling of performance standards. If the PM is a professional, their performance must be of the highest standard, and must be accountable for a high level of productivity. This is the project manager’s Achilles heel.
Another problem is the absence of feedback during the early stages through to completion of the project. During the project’s life the relative importance of their responsibilities may change several times, including the constant changing of the dynamic environment. The PM will aim for a balanced emphasis; they will try to be flexible so they can adapt to new circumstances as they occur. The PM needs tried and tested methods to aid his decision making. This paper posits an integrated development and use of methods such as; scenario planning, effectuation, and reflective thinking to enhance decision making. The paper concludes with potential benefits that this method brings to the PM when fully understood and tested in the application domain
Theoretical study of interacting hole gas in p-doped bulk III-V semiconductors
We study the homogeneous interacting hole gas in -doped bulk III-V
semiconductors. The structure of the valence band is modelled by Luttinger's
Hamiltonian in the spherical approximation, giving rise to heavy and light hole
dispersion branches, and the Coulomb repulsion is taken into account via a
self-consistent Hartree-Fock treatment. As a nontrivial feature of the model,
the self-consistent solutions of the Hartree-Fock equations can be found in an
almost purely analytical fashion, which is not the case for other types of
effective spin-orbit coupling terms. In particular, the Coulomb interaction
renormalizes the Fermi wave numbers for heavy and light holes. As a
consequence, the ground state energy found in the self-consistent Hartree-Fock
approach and the result from lowest-order perturbation theory do not agree. We
discuss the consequences of our observations for ferromagnetic semiconductors,
and for the possible observation of the spin-Hall effect in bulk -doped
semiconductors. Finally, we also investigate elementary properties of the
dielectric function in such systems.Comment: 9 pages, 5 figures, title slightly changed in the course of editorial
process, a few references added, version to appear in Phys. Rev.
Systematic screening of bryophytes for antitumor agents
References are made to cytotoxic and/or antitumor compounds that have been isolated - ansamitocin P-3 from Claopodium crispifolium (Hook.) Ren. & Card. and Anomodon attenuatus Hueb., or an associated actinomycete, and ohioensins and pallidisetums from Polytrichum spp. Several hundred collections, which have been obtained from temperate regions of North America during 1990 and 1991, are currently being screened in new bioassays; active sesquiterpene lactones have been recently isolated from species of Porella. The methodologies of collecting and screening bryophyte samples are discussed with consideration to costs based on expected number of samples that might be collected in a day, the diversity in the collections as related to phytogeography and vegetation types, and the bryophyte cover that is vanishing in many forest regions of the United States. The difficulties in obtaining large collections for isolation of active agents are also discussed by examplerecollection of Claopodium crispifolium
Constructions of biangular tight frames and their relationships with equiangular tight frames
We study several interesting examples of Biangular Tight Frames (BTFs) -
basis-like sets of unit vectors admitting exactly two distinct frame angles
(ie, pairwise absolute inner products) - and examine their relationships with
Equiangular Tight Frames (ETFs) - basis-like systems which admit exactly one
frame angle.
We demonstrate a smooth parametrization BTFs, where the corresponding frame
angles transform smoothly with the parameter, which "passes through" an ETF
answers two questions regarding the rigidity of BTFs. We also develop a general
framework of so-called harmonic BTFs and Steiner BTFs - which includes the
equiangular cases, surprisingly, the development of this framework leads to a
connection with the famous open problem(s) regarding the existence of Mersenne
and Fermat primes. Finally, we construct a (chordally) biangular tight set of
subspaces (ie, a tight fusion frame) which "Pl\"ucker embeds" into an ETF.Comment: 19 page
Spin susceptibilities, spin densities and their connection to spin-currents
We calculate the frequency dependent spin susceptibilities for a
two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit
interaction. The resonances of the susceptibilities depends on the relative
values of the Rashba and Dresselhaus spin-orbit constants, which could be
manipulated by gate voltages. We derive exact continuity equations, with source
terms, for the spin density and use those to connect the spin current to the
spin density. In the free electron model the susceptibilities play a central
role in the spin dynamics since both the spin density and the spin current are
proportional to them.Comment: 6 pages, revtex4 styl
A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)
Recent observations have shown that a growing number of the most massive
Galactic globular clusters contain multiple populations of stars with different
[Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been
recognized as a member of this "iron-complex" cluster class, and we provide
here a chemical and kinematic analysis of > 300 red giant branch (RGB) and
asymptotic giant branch (AGB) member stars using high resolution spectra
obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of
evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that
ranges from about [Fe/H] = -2 to -1 dex, and may include at least three
populations with different [Fe/H] values. The three populations identified here
contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars,
but a Mg-Al anti-correlation may only be present in stars with [Fe/H] > -1.65.
The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process
must have dominated the heavy element enrichment at higher metallicities. A
small group of stars with low [alpha/Fe] is identified and may have been
accreted from a former surrounding field star population. The cluster's large
abundance variations are coupled with a complex, extended, and multimodal blue
horizontal branch (HB). The HB morphology and chemical abundances suggest that
NGC 6273 may have an origin that is similar to omega Cen and M 54.Comment: Accepted for Publication in The Astrophysical Journal; 50 pages; 18
figures; 8 tables; higher resolution figures are available upon request or in
the published journal articl
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