3,502 research outputs found
RKKY interaction and intervalley processes in p-doped transition metal dichalcogenides
We study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in p-doped
transition metal dichalcogenides such as MoS and WS. We consider
magnetic impurities hybridized to the Mo d-orbitals characteristic of the
valence bands. Using the Matsubara Green's function formalism, we obtain the
two-impurity interaction vs their separation and chemical potential of the
system, accounting for the important angular dependence which reflects the
underlying triangular lattice symmetry. The inclusion of the valence band
valley at the point results in a strong enhancement of the
interaction. Electron scattering processes transferring momentum between
valleys at different symmetry points give rise to complex spatial oscillation
patterns. Variable doping would allow the exploration of rather interesting
behavior in the interaction of magnetic impurities on the surfaces of these
materials, including the control of the interaction symmetry, which can be
directly probed in STM experiments.Comment: Includes supplemental materia
Kondo screening suppression by spin-orbit interaction in quantum dots
We study the transport properties of a quantum dot embedded in an
Aharonov-Bohm ring in the presence of spin-orbit interactions. Using a
numerical renormalization group analysis of the system in the Kondo regime, we
find that the competition of Aharonov-Bohm and spin-orbit dynamical phases
induces a strong suppression of the Kondo state singlet, somewhat akin to an
effective intrinsic magnetic field in the system. This effective field breaks
the spin degeneracy of the localized state and produces a finite magnetic
moment in the dot. By introducing an {\em in-plane} Zeeman field we show that
the Kondo resonance can be fully restored, reestablishing the spin singlet and
a desired spin filtering behavior in the Kondo regime, which may result in full
spin polarization of the current through the ring.Comment: 4 pages, 4 figure
Currents and pseudomagnetic fields in strained graphene rings
We study the effects of strain on the electronic properties and persistent
current characteristics of a graphene ring using the Dirac representation. For
a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic
(gauge) fields that may effectively reduce or enhance locally the applied
magnetic flux through the ring. Flux-induced persistent currents in a flat ring
have full rotational symmetry throughout the structure; in contrast, we show
that currents in the presence of a circularly symmetric deformation are
strongly inhomogeneous, due to the underlying symmetries of graphene. This
result illustrates the inherent competition between the `real' magnetic field
and the `pseudo' field arising from strains, and suggest an alternative way to
probe the strength and symmetries of pseudomagnetic fields on graphene systems
Graphene zigzag ribbons, square lattice models and quantum spin chains
We present an extended study of finite-width zigzag graphene ribbons (ZGRs)
based on a tight-binding model with hard-wall boundary conditions. We provide
an exact analytic solution that clarifies the origin of the predicted width
dependence on the conductance through junctions of ribbons with different
widths. An analysis of the obtained solutions suggests a new description of
ZGRs in terms of coupled chains. We pursue these ideas further by introducing a
mapping between the ZGR model and the Hamiltonian for N-coupled quantum chains
as described in terms of 2N Majorana fermions. The proposed mapping preserves
the dependence of ribbon properties on its width thus rendering metallic
ribbons for N odd and zero-gap semiconductor ribbons for N even. Furthermore,
it reveals a close connection between the low-energy properties of the ZGR
model and a continuous family of square lattice model Hamiltonians with similar
width-dependent properties that includes the flux and the trivial square
lattice models. As a further extension, we show that this new description makes
it possible to identify various aspects of the physics of graphene ribbons with
those predicted by models of quantum spin chains (QSCs)
Relay- and double-crop production systems for wheat
"May 2014."Thesis supervisor: Dr. Kelly Nelson.Cover crops are important to provide organic matter to soils, diversify cropping systems, and provide economic benefits if the correct cropping systems are utilized. Relay-intercrop production involves overlapping growth cycles of two or more crops. This production system is common with legumes seeded into small grains; however, the companion crops may compete for water, nutrients, and sunlight, which may slow development of either crop. Relay-intercropped soybean [Glycine max (L.) Merr.] production involves seeding wheat in the fall and an intercrop seeding of soybeans into standing wheat (Triticum aestivum L.). This cropping system has been proposed to reduce risk associated with double-crop soybean production, move double-crop production farther north, and increase farm profitability. Diversifying crops used in these cropping systems may allow farmers more crop production choices. Double-cropping may also be an alternative to avoid competition for resources among intercrops. Field research was needed to determine what alternative crops would be successful in various cropping systems. The objectives of this research were to 1) determine the feasibility of intercropping alternative crops into standing wheat, 2) observe the effect of wheat row spacing on wheat and alternative crop yields, 3) evaluate the effects of intercropping and double-crop planting dates on alternative crops, and 4) evaluate double-crop planting dates of oil seed radishes on winter annual weed suppression and corn yields.Includes bibliographical references
The effect of different forms of heparin on point-of-care blood gas analysis
Background. Point-of-care blood gas analysis plays an integral role in the management of critically ill and injured patients presenting to the emergency department (ED). While the use of specially manufactured syringes containing electrolyte-balanced dried heparin is recommended when processing these specimens, alternatives including manually self-prepared syringes washed with liquid heparin or heparin vacutainers are still often used.Objectives. To assess the effect of two concentrations of liquid heparin and the use of heparin vacutainers on the reliability of blood gas analysis results compared with the recommended standard of dried heparin syringes in the ED setting.Methods. Blood samples were drawn from 54 patients attending a tertiary-level hospital ED. Individual samples were distributed equally among each of four different collection devices: a dried heparin syringe, self-prepared syringes washed separately with 1 000 IU/mL and 5 000 IU/mL liquid heparin, and a heparin vacutainer. Results obtained from the standard dried heparin syringes were compared with those from the other three methods.Results. For both the liquid heparin cohorts, partial pressure of carbon dioxide (pCO2), potassium (K+), sodium (Na+), ionised calcium (iCa2+) and haemoglobin had >20% of results falling beyond the total allowable error. iCa2+ and K+ results were most affected in the 5 000 IU/mL cohort and iCa2+ and Na+ in the 1 000 IU/ml cohort. pCO2, pH and iCa2+ were the most significantly affected in the heparin vacutainer cohort.Conclusions. Use of liquid heparin can result in significant negative bias in the majority of blood gas analytes, especially electrolytes. Heparin vacutainer use can result in unacceptable variations in the respiratory analytes. While standard dried heparin syringes may not always be available, it is of vital importance that practitioners be aware of these biases and limitations when using substitutes
Real-time image-based investigation of spheronization and drying phenomena using different pellet formulations
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