680 research outputs found
Incommensurate nodes in the energy spectrum of weakly coupled antiferromagnetic Heisenberg ladders
Heisenberg ladders are investigated using the bond-mean-field theory
[M.Azzouz, Phys. Rev. B 48, 6136 (1993)]. The zero inter-ladder coupling energy
gap, the uniform spin susceptibility and the nuclear magnetic resonance
spin-relaxation rate are calculated as a function of temperature and magnetic
field. For weakly coupled ladders, the energy spectrum vanishes at
incommensurate wavevectors giving rise to nodes. As a consequence, the spin
susceptibility becomes linear at low temperature. Our results for the single
ladder successfully compare to experiments on SrCu_2O_3 and (VO)_2P_2O_7
materials and new predictions concerning the coupling to the magnetic field are
made.Comment: 4 revtex pages, 3 figures available upon reques
Spectrum of p-adic linear differential equations
This paper generalizes our works in [Azz20] and [Azz21], which concern the
determination of the spectrum in the sense of Berkovich of ultrametric linear
differential equations, in the special cases with constant coefficients or over
a field of formal power series. In this paper, we determine the spectrum of any
p-adic differential equation. This permits to establish a strong link between
the spectrum and all the radii of convergence of a differential equation.
Moreover, the spectrum provides a finer decomposition than Robba's
decomposition by spectral radii [Rob75].Comment: 45 pages. The comments are welcom
Quantum and classical criticalities in the frustrated two-leg Heisenberg ladder
This talk was about the frustration-induced criticality in the
antiferromagnetic Heisenberg model on the two-leg ladder with exchange
interactions along the chains, rungs, and diagonals, and also about the effect
of thermal fluctuations on this criticlity. The method used is the bond
mean-field theory, which is based on the Jordan-Wigner transformation in
dimensions higher than one. In this paper, we will summarize the main results
presented in this talk, and report on new results about the couplings and
temperature dependences of the spin susceptibility.Comment: 6 pages, 4 figures, talk presented at the Theory Canada 3 conference
in 2007, submitted to the Canadian Journal of Physic
Boundary spanning and knowledge brokering for digital innovation
The adoption of digital innovations in construction is a topic with growing importance,
as organisations restructure to adopt and sustain innovations. Building Information
Modelling (BIM) is currently at the forefront of this digital shift in Architecture,
Engineering, and Construction (AEC) industry. The relation between knowledge
sharing and sustained innovation adoption in organisations has been previously
acknowledged by management scholars. There is further room to adopt a
structurational view of knowledge and focus on how agency contributes to knowledge
sharing for increasing digital innovation adoption in firms. This paper uses the
theoretical lens of boundaries and boundary brokers to guide the data selection and
interpret a rich dataset about boundary brokers of digital innovation. The research aim
is to explore how these boundary brokers, referred to as digital innovation champions,
facilitate knowledge of digital innovations and BIM to support digital transformation
in firms. A single case study of a large international multi-disciplinary consultancy was
used as a research setting. Data were collected through interviews with the digital
champions as well as with additional data collected from the internal online platform
for data triangulation and research validation. Key findings include the multi-faceted
levels of boundaries crossed by the digital champions to share knowledge about digital
innovation: hierarchical, professional and organisational boundaries. Namely, the
digital champions were found to hold multiple memberships in groups, holding both
technical and inter-personal competences as well as engaging in conflict resolution.
The study concludes with implications for practice and suggests courses of actions to
increase knowledge sharing in firms for innovation adoption by developing and
incentivising individuals
Boundary-spanning for managing digital innovation in the AEC sector
Managing projects in Architecture, Engineering, Construction (AEC) undergoes a digital transformation as novel technologies emerge. Digital technologies, such as Building Information Modelling (BIM), push this transformation. Innovation happens in firms and project-based organisations where agents shape how digital technologies are adopted and implemented. This study offers insights into agents of digital innovation, by conducting engaged scholarship within the case study of one large international multi-disciplinary consultancy. The study first builds upon qualitative data collected by interviewing digital agents. Additional data, for triangulation and research validation, were collected from an internal online platform. The analysis revealed a disconnect between digital agents’ technical background, skills and their managerial routines. These individuals crossed professional, hierarchical and organisational boundaries, showed multi-membership and held fluid identities. This has implications for the interfaces between organisational behaviour and projects. The study concludes with suggestions for AEC organisations to reap the benefits of digitalisation
Viral delivery of antioxidant genes as a therapeutic strategy in experimental models of amyotrophic lateral sclerosis.
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder with no effective treatment to date. Despite its multi-factorial aetiology, oxidative stress is hypothesized to be one of the key pathogenic mechanisms. It is thus proposed that manipulation of the expression of antioxidant genes that are downregulated in the presence of mutant SOD1 may serve as a therapeutic strategy for motor neuronal protection. Lentiviral vectors expressing either PRDX3 or NRF2 genes were tested in the motor neuronal-like NSC34 cell line, and in the ALS tissue culture model, NSC34 cells expressing the human SOD1(G93A) mutation. The NSC34 SOD1(G93A) cells overexpressing either PRDX3 or NRF2 showed a significant decrease in endogenous oxidation stress levels by 40 and 50% respectively compared with controls, whereas cell survival was increased by 30% in both cases. The neuroprotective potential of those two genes was further investigated in vivo in the SOD1(G93A) ALS mouse model, by administering intramuscular injections of adenoassociated virus serotype 6 (AAV6) expressing either of the target genes at a presymptomatic stage. Despite the absence of a significant effect in survival, disease onset or progression, which can be explained by the inefficient viral delivery, the promising in vitro data suggest that a more widespread CNS delivery is needed
Interplay between field-induced and frustration-induced quantum criticalities in the frustrated two-leg Heisenberg ladder
The antiferromagnetic Heisenberg two-leg ladder in the presence of
frustration and an external magnetic field is a system that is characterized by
two sorts of quantum criticalities, not only one. One criticality is the
consequence of intrinsic frustration, and the other one is a result of the
external magnetic field. So the behaviour of each of them in the presence of
the other deserves to be studied. Using the Jordan-Wigner transformation in
dimensions higher than one and bond-mean-field theory we examine the interplay
between the field-induced and frustration-induced quantum criticalities in this
system. The present work could constitute a prototype for those systems showing
multiple, perhaps sometimes competing, quantum criticalities. We calculate
several physical quantities like the magnetization and spin susceptibility as
functions of field and temperature.Comment: 9 pages, 8 figures, submitted to the Canadian Journal of Physic
Levitated droplet dye laser
We present the first observation, to our knowledge, of lasing from a
levitated, dye droplet. The levitated droplets are created by computer
controlled pico-liter dispensing into one of the nodes of a standing ultrasonic
wave (100 kHz), where the droplet is trapped. The free hanging droplet forms a
high quality optical resonator. Our 750 nL lasing droplets consist of Rhodamine
6G dissolved in ethylene glycol, at a concentration of 0.02 M. The droplets are
optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser,
and the dye laser emission is analyzed by a fixed grating spectrometer. With
this setup we have achieved reproducible lasing spectra in the visible
wavelength range from 610 nm to 650 nm. The levitated droplet technique has
previously successfully been applied for a variety of bio-analytical
applications at single cell level. In combination with the lasing droplets, the
capability of this high precision setup has potential applications within
highly sensitive intra-cavity absorbance detection.Comment: 6 pages including 3 figure
Anisotropic two-dimensional Heisenberg model by Schwinger-boson Gutzwiller projected method
Two-dimensional Heisenberg model with anisotropic couplings in the and
directions () is considered. The model is first solved in the
Schwinger-boson mean-field approximation. Then the solution is Gutzwiller
projected to satisfy the local constraint that there is only one boson at each
site. The energy and spin-spin correlation of the obtained wavefunction are
calculated for systems with up to sites by means of the
variational Monte Carlo simulation. It is shown that the antiferromagnetic
long-range order remains down to the one-dimensional limit.Comment: 15 pages RevTex3.0, 4 figures, available upon request, GWRVB8-9
Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg Model on the ladder
The ground state energy and the singlet-triplet energy gap of the
antiferromagnetic Heisenberg model on a ladder is investigated using a mean
field theory and the density matrix renormalization group. Spin wave theory
shows that the corrections to the local magnetization are infinite. This
indicates that no long range order occurs in this system. A flux-phase state is
used to calculate the energy gap as a function of the transverse coupling,
, in the ladder. It is found that the gap is linear in for
and goes to zero for . The mean field theory
agrees well with the numerical results.Comment: 11pages,6 figures (upon request) Revtex 3.0, Report#CRPS-94-0
- …