1,204 research outputs found
A study of long range order in certain two-dimensional frustrated lattices
We have studied the Heisenberg antiferromagnets on two-dimensional frustrated
lattices, triangular and kagome lattices using linear spin-wave theory. A
collinear ground state ordering is possible if one of the three bonds in each
triangular plaquette of the lattice becomes weaker or frustrated. We study
spiral order in the Heisenberg model along with Dzyaloshinskii-Moriya (DM)
interaction and in the presence of a magnetic field. The quantum corrections to
the ground state energy and sublattice magnetization are calculated
analytically in the case of triangular lattice with nearesr-neighbour
interaction. The corrections depend on the DM interaction strength and the
magnetic field. We find that the DM interaction stabilizes the long-range
order, reducing the effect of quantum fluctuations. Similar conclusions are
reached for the kagome lattice. We work out the linear spin-wave theory at
first with only nearest-neighbour (nn) terms for the kagome lattice. We find
that the nn interaction is not sufficient to remove the effects of low energy
fluctuations. The flat branch in the excitation spectrum becomes dispersive on
addition of furthet neighbour interactions. The ground state energy and the
excitation spectrum have been obtained for various cases.Comment: 18 pages, 9 figure
Theoretical Analysis of the Reduction of Neel Temperature in La(CuZn(or Mg)O
Using Tyablikov's decoupling approximation, we calculate the initial
suppression rate of the Neel temperature, , in a quasi two-dimensional diluted Heisenberg antiferromagnet with
nonmagnetic impurities of concentration . In order to explain an
experimental fact that of the Zn-substitution is different
from of the Mg-substitution, we propose a model in which
impurity substitution reduces the intra-plane exchange couplings surrounding
impurities, as well as dilution of spin systems. The decrease of 12% in
exchange coupling constants by Zn substitution and decrease of 6% by Mg
substitution explain those two experimental results, when an appropriate value
of the interplane coupling is used.Comment: 2 pages, 3 figure
Surface spin dynamics of antiferromagnetically coupled frustrated triangular films
Results are presented for spin-wave dispersions in geometrically frustrated
stacked triangular antiferromagnets with a thin film or semi-infinite geometry
having either zero, easy-plane, or easy-axis anisotropy. Surface effects on the
equilibrium spin configurations and excitation spectrum are investigated for
the case of antiferromagnetically coupled films, serving to extend previous
results on ferromagnetically coupled layers [E. Meloche et al., Phys. Rev. B
74, 094424 (2006)]. An operator equation of motion formalism is applied to
systems which are quasi-one and quasi-two dimensional in character. In contrast
to the case of ferromagnetically coupled films the new results show surface
modes that are well separated in frequency from bulk excitations. Magnetic
excitations in thin films with an even or an odd number of layers show
qualitatively different behavior. These results are relevant for a wide variety
of stacked triangular antiferromagnetics materials.Comment: 24 pages, 9 figure
Long distance synchronization of mobile robots
This paper considers the long distance master-slave and mutual synchronization of unicycle-type mobile robots. The issues that arise when the elements of a robotic network are placed in different locations are addressed, specifically the time-delay induced by the communication channel linking the robots. Experiments between wirelessly controlled mobile robots located in Eindhoven, The Netherlands and Tokyo, Japan demonstrate the applicability of the proposed approach
Consumer perspectives on product lifetimes: a national study of lifetime satisfaction and purchasing factors
The extension of product lifetimes of consumer goods has the potential to encourage sustainable consumption, reduce carbon emissions and facilitate a transition to a circular economy. However, current understandings of consumer perspectives on product lifetimes are limited. This paper presents the findings of the first national study of consumer satisfaction with product lifetimes across an exhaustive range of consumer durables. The research was undertaken in the United Kingdom where consumer satisfaction and purchasing factors were studied across eighteen product categories. These product categories were devised from academic and market research undertaken at Nottingham Trent University. In total, 2,207 participants completed the survey and the sample profile was similar to the United Kingdom's population with respect to age and gender. The results indicate that consumers appear generally satisfied with the lifetimes of their products and suggest that efforts to extend product lifetimes should focus on developing business and policy options. However, participants also emphasised that longevity, reliability and guarantee length were important factors in their purchasing decisions. Consumer interest in these factors could indicate that lifetime labelling and the promotion of longer guarantees by manufacturers and retailers may offer pathways to reduce energy and material consumption associated with short-lived products, facilitating movement towards a low carbon circular economy
Consumer expectations of product lifetimes around the world: a review of global research findings and methods
This paper presents the findings of research to identify and evaluate current studies into consumer expectations of product lifetimes across durable goods. Following a literature review, studies were classified using a product categorisation scheme formulated at Nottingham Trent University and a product lifetime expectations typology adapted from Oguchi et al. (2016a) was developed. The results would appear to suggest that consumer expectations of product lifetimes are in decline, and that those in the United Kingdom appear to be lower than those in other parts of the world. However, identifying differences in consumer expectations of product lifetimes is hindered by the different methods employed in studies, as face-to-face interviews, and online, telephone and postal studies all have the potential to produce different results. Three key challenges to furthering research into consumer expectations of product lifetimes were identified: Product coverage, definitions of consumer expectations and sampling strategies. Only if these challenges can be addressed will researchers be able to draw meaningful conclusions on both personal and cultural trends in expected product lifetimes and make a positive contribution to addressing both material and social aspects of the circular economy
Magnetism and superconductivity in TaSC (M = Fe, Co, Ni, and Cu)
Magnetic properties of TaSC ( = Fe, Co, Ni, Cu) have
been studied using SQUID DC and AC magnetic susceptibility. In these systems
magnetic ions are intercalated into van der Waals gaps between
adjacent S layers of host superconductor TaSC.
FeTaSC is a quasi 2D -like antiferromagnet on the
triangular lattice. It undergoes an antiferromagnetic phase transition at
(= 117 K). The irreversible effect of magnetization occurs below
, reflecting the frustrated nature of the system. The AF phase coexists
with two superconducting phases with the transition temperatures
K and K. CoTaSC is a quasi 2D Ising-like
antiferromagnet on the triangular lattice. The antiferromagnetic phase below
K coexists with a superconducting phase below K.
Both NiTaSC and CuTaSC are
superconductors with ( K for Ni and 6.4 K for Cu) and
(= 4.6 K common to TaSC). Very small effective magnetic
moments suggest that Ni and Cu spins are partially delocalized.Comment: 15 pages, 17 figures, and 3 table
Microscopic Evidence for Evolution of Superconductivity by Effective Carrier Doping in Boron-doped Diamond:11B-NMR study
We have investigated the superconductivity discovered in boron (B)-doped
diamonds by means of 11B-NMR on heteroepitaxially grown (111) and (100) films.
11B-NMR spectra for all of the films are identified to arise from the
substitutional B(1) site as single occupation and lower symmetric B(2) site
substituted as boron+hydrogen(B+H) complex, respectively. A clear evidence is
presented that the effective carriers introduced by B(1) substitution are
responsible for the superconductivity, whereas the charge neutral B(2) sites
does not offer the carriers effectively. The result is also corroborated by the
density of states deduced by 1/T1T measurement, indicating that the evolution
of superconductivity is driven by the effective carrier introduced by
substitution at B(1) site.Comment: 4 pages, 6 figures, to be published in Phys. Rev. B (Brief report
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