1,688 research outputs found
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models
The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.Comment: 7 pages, 1 figur
A strong-coupling expansion for the Hubbard model
We reconsider the strong-coupling expansion for the Hubbard model recently
introduced by Sarker and Pairault {\it et al.} By introducing slave particles
that act as projection operators onto the empty, singly occupied and doubly
occupied atomic states, the perturbation theory around the atomic limit
distinguishes between processes that do conserve or do not conserve the total
number of doubly occupied sites. This allows for a systematic expansion
that does not break down at low temperature ( being the intersite hopping
amplitude and the local Coulomb repulsion). The fermionic field becomes a
two-component field, which reflects the presence of the two Hubbard bands. The
single-particle propagator is naturally expressed as a function of a matrix self-energy. Furthermore, by introducing a time- and
space-fluctuating spin-quantization axis in the functional integral, we can
expand around a ``non-degenerate'' ground-state where each singly occupied site
has a well defined spin direction (which may fluctuate in time). This formalism
is used to derive the effective action of charge carriers in the lower Hubbard
band to first order in . We recover the action of the t-J model in the
spin-hole coherent-state path integral. We also compare our results with those
previously obtained by studying fluctuations around the large- Hartree-Fock
saddle point.Comment: 20 pages RevTex, 3 figure
Temperature dependence of the resistivity in the double-exchange model
The resistivity around the ferromagnetic transition temperature in the double
exchange model is studied by the Schwinger boson approach. The spatial spin
correlation responsible for scattering of conduction electrons are taken into
account by adopting the memory function formalism. Although the correlation
shows a peak lower than the transition temperature, the resistivity in the
ferromagnetic state monotonically increases with increasing temperature due to
a variation of the electronic state of the conduction electron. In the
paramagnetic state, the resistivity is dominated by the short range correlation
of scattering and is almost independent of the temperature. It is attributed to
a cancellation between the nearest-neighbor spin correlation, the fermion
bandwidth, and the fermion kinetic energy. This result implies the importance
of the temperature dependence of the electronic states of the conduction
electron as well as the localized spin states in both ferromagnetic and
paramagnetic phases.Comment: RevTex, 4 pages, 4 PostScript figures, To appear in Phys. Rev.
Whole-Genome Sequence of a Beak and Feather Disease Virus Isolate from a Fledgling Red-Capped Parrot (Purpureicephalus spurius)
The complete genome sequence of beak and feather disease virus (BFDV) from a fledgling red-capped parrot (Purpureicephalus spurius) was assembled and characterized. The genome consists of 1,995 nucleotides and encodes two major proteins in opposing directions. This is the first evidence of BFDV infectivity and a complete genome sequence for this novel host
Conservation tillage and residue management improve soil health and crop productivity-Evidence from a rice-maize cropping system in Bangladesh.
The rice-maize (R-M) system is rapidly expanding in Bangladesh due to its greater suitability for diverse soil types and environments. The present conventional method of cultivating puddled transplanted rice and maize is input-intensive, decreases soil health through intense ploughing, and ultimately reduces farm profitability. There is a need to investigate alternatives. Accordingly, we conducted a replicated 2-year (2020–2021) field study to investigate the effects of conservation agriculture (CA) based tillage and crop establishment (TCE) techniques and residue management practices on the physical, chemical, and biological properties of soil along with crop productivity and the profitability of rice-maize systems in the sandy loam soil of Northwest Bangladesh. Two TCE techniques Puddled transplanted rice (PTR) followed by Conventional tillage maize (CTM) and strip tillage direct-seeded rice (STDSR) followed by strip-tilled maize (STM) were assigned to the main plots and different percentages of crop residue retention (0, 25, and 50% by height) were allocated to the subplots. Results showed that a reduction in bulk density (BD), soil penetration resistance (SPR), and increased soil porosity were associated with STDSR/STM-based scenarios (strip tillage coupled with 25 and 50% residue retention). The soil organic carbon (SOC) fractions, such as dissolved organic C (DOC), light and heavy particulate organic matter C (POM-C), MAOM, and microbial biomass C (MBC) levels in the 0–10 cm layer under ST based treatments were 95, 8, 6, 2 and 45% greater, respectively, compared to CT with no residue treatment. When compared to the CT treatment, the DOC, light POM-C, heavy POM-C, and MAOM in the 10–20 cm layer with ST treatment were 8, 34, 25, 4 and 37% higher, respectively. Residue retention in ST increased average rice, maize, and system yields by 9.2, 14.0, and 14.12%, respectively, when compared to CT. The system gross margin and benefit-cost ratio (BCR) were 1,696 ha−1 and 2.15 under strip-tillage practices. Thus, our study suggests that CA could be an appropriate practice for sustaining soil fertility and crop yield under R-M systems in light-textured soils or other similar soils in Banglades
Selection of cemented carbide turning tools using EMF and optimization criteria
Tool life and quality of surface finish of the workpiece influence production rate and production cost. Cemented carbide tools have found wide application in the production arena of Bangladesh. In the absence of any testing facility in the country for the selection of cost-effective tools, poor quality carbide tools are frequently imported. A testing method and a selection criteria were developed for testing carbide tools of different shapes and sizes and for selecting the most cost-effective tool. For each tool cutting tests were performed to generate tool life data under different cutting conditions. Mild steel served as the work material. The relationship between tool life and cutting speed was developed using a curve-fitting software on a PC. From these relationships the values of the constants of the Taylor’s equation were determined. The cost equation was then derived for each tool for a given
amount of work in a cutting speed range. Finally, the most cost-effective tool was selected on the basis of the relative location of the cost curves of the tools tested
Validating a consumer-based service brand equity (CBSBE) model in the airline industry
Over time, scholars have argued that consumer-based brand equity (CBBE) models are less suitable for servicedominant
brands, mainly because the role of customer experience with services is often disregarded. Also, the
absence of two essential components, brand consistency and perceived value, signals a lack of depth in creating
service brand equity. To address these gaps, we examine service-branding theory by conceptualizing and validating
a consumer-based service brand equity (CBSBE) model in Sarker et al. (2019) in the context of airlines.
Airline service direct experience and brand consistency are highly important aspects for strengthening brand
equity components of services. Subsequently, maximizing perceived value, followed by creating favorable brand
meaning are the nucleus of branding services. Using the most advanced PLS-SEM techniques, our CBSBE model is
highly robust in explaining the theoretical notion of creating service brand equity. Thus, achieving a pleasant and
desirable experience and maintaining consistency across direct service touchpoints would be an effective strategy
for service organizations
Considerations on the quantum double-exchange Hamiltonian
Schwinger bosons allow for an advantageous representation of quantum
double-exchange. We review this subject, comment on previous results, and
address the transition to the semiclassical limit. We derive an effective
fermionic Hamiltonian for the spin-dependent hopping of holes interacting with
a background of local spins, which is used in a related publication within a
two-phase description of colossal magnetoresistant manganites.Comment: 7 pages, 3 figure
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