7,214 research outputs found
Surfactant effects in monodisperse magnetite nanoparticles of controlled size
Monodisperse magnetite Fe3O4 nanoparticles of controlled size within 6 and 20
nm in diameter were synthesized by thermal decomposition of an iron organic
precursor in an organic medium. Particles were coated with oleic acid. For all
samples studied, saturation magnetization Ms reaches the expected value for
bulk magnetite, in contrast to results in small particle systems for which Ms
is usually much smaller due to surface spin disorder. The coercive field for
the 6 nm particles is also similar to that of bulk magnetite. Both results
suggest that the oleic acid molecules covalently bonded to the nanoparticle
surface yield a strong reduction in the surface spin disorder. However,
although the saturated state may be similar, the approach to saturation is
different and, in particular, the high-field differential susceptibility is one
order of magnitude larger than in bulk materials. The relevance of these
results in biomedical applications is discussed.Comment: 3 pages, 3 figures. Presented at JEMS 2006 (San Sebastian, Spain).
Submitted to JMM
Study of a Dynamic Cooperative Trading Queue Routing Control Scheme for Freeways and Facilities with Parallel Queues
This article explores the coalitional stability of a new cooperative control
policy for freeways and parallel queuing facilities with multiple servers.
Based on predicted future delays per queue or lane, a VOT-heterogeneous
population of agents can agree to switch lanes or queues and transfer payments
to each other in order to minimize the total cost of the incoming platoon. The
strategic interaction is captured by an n-level Stackelberg model with
coalitions, while the cooperative structure is formulated as a partition
function game (PFG). The stability concept explored is the strong-core for PFGs
which we found appropiate given the nature of the problem. This concept ensures
that the efficient allocation is individually rational and coalitionally
stable. We analyze this control mechanism for two settings: a static vertical
queue and a dynamic horizontal queue. For the former, we first characterize the
properties of the underlying cooperative game. Our simulation results suggest
that the setting is always strong-core stable. For the latter, we propose a new
relaxation program for the strong-core concept. Our simulation results on a
freeway bottleneck with constant outflow using Newell's car-following model
show the imputations to be generally strong-core stable and the coalitional
instabilities to remain small with regard to users' costs.Comment: 3 figures. Presented at Annual Meeting Transportation Research Board
2018, Washington DC. Proof of conjecture 1 pendin
Regulation of BCL6: p38 MAPK signalling and CTCF transcriptional regulation converge at exon 1
BCL6 is a zinc finger transcriptional repressor, which is highly expressed in
germinal centre B-cells, and is essential for germinal centre formation and T-dependent
antibody responses. Deregulated BCL6 expression is associated with certain non-
Hodgkin’s lymphomas. High expression is observed in breast cancer. Tight lineage and
temporal regulation of BCL6 is, therefore, required for normal immunity and abnormal
regulation occurs in cancer. Regulatory mechanisms have been analysed in two
settings. Firstly, BCL6 is strongly induced by the tyrosine kinase inhibitor, Imatinib, in
chronic myeloid leukaemia lymphoid blast crisis cell lines, and this effect was used in
order to study the effects of phospho-protein signalling on BCL6 expression and a major
finding is that p38 MAPK induced BCL6. Also, p38 is, at least in part, responsible for
BCL6 expression in basal conditions in the germinal centre representative Burkitt’s
lymphoma cell lines and that qualitatively different CD40 stimuli can either induce or
repress BCL6 expression. Luciferase assays showed that p38 acts at a 300bp sequence
immediately 5’ of exon 1, and probably also at more distal sequences. Overall it appears
that the balance between positive and negative regulatory controls BCL6 expression
with inhibitory signalling pathways being predominant in most circumstances. Focusing
on BCL6 exon 1, a binding site for the multifunctional regulator CTCF was identified.
CTCF interacts in vitro and in vivo with this sequence. Reduced expression of CTCF in
germinal centre cells caused a moderate reduction of BCL6 expression. Finally,
although no clear differences were observed in the methylation status of the CTCF
binding site on exon 1, a significant enrichment of active histone modifications at this
site was observed in BCL6 expressing cells, suggesting that CTCF may have a role in
the epigenetic regulation of BCL6
Canonical Realization of (2+1)-dimensional Bondi-Metzner-Sachs symmetry
We construct canonical realizations of the algebra as
symmetry algebras of a free Klein-Gordon (KG) field in dimensions, for
both the massive and massless case. We consider two types of realizations, one
on-shell, written in terms of the Fourier modes of the scalar field, and the
other one off-shell with non-local transformations written in terms of the KG
field and its momenta. These realizations contain both supertranslations and
superrotations, for which we construct the corresponding Noether charges.Comment: Version accepted for publication in PRD. Expanded title and expanded
discussion about superrotations in the massive cas
Modelling exchange bias in core/shell nanoparticles
We present an atomistic model of a single nanoparticle with core/shell
structure that takes into account its lattice strucutre and spherical geometry,
and in which the values of microscopic parameters such as anisotropy and
exchange constants can be tuned in the core, shell and interfacial regions. By
means of Monte Carlo simulations of the hysteresis loops based on this model,
we have determined the range of microscopic parameters for which loop shifts
after field cooling can be observed. The study of the magnetic order of the
interfacial spins for different particles sizes and values of the interfacial
exchange coupling have allowed us to correlate the appearance of loop
asymmetries and vertical displacements to the existence of a fraction of
uncompensated spins at the shell interface that remain pinned during field
cycling, offering new insight on the microscopic origin of the experimental
phenomenology.Comment: 7 pages, 3 figures. Contribution presented at HMM 2007 held at Napoli
4-6 June 2007. To be published in J. Phys. Condens. Matte
Extended Galilean symmetries of non-relativistic strings
We consider two non-relativistic strings and their Galilean symmetries. These strings are obtained as the two possible non-relativistic (NR) limits of a relativistic string. One of them is non-vibrating and represents a continuum of non-relativistic massless particles, and the other one is a non-relativistic vibrating string. For both cases we write the generator of the most general point transformation and impose the condition of Noether symmetry. As a result we obtain two sets of non-relativistic Killing equations for the vector fields that generate the symmetry transformations. Solving these equations shows that NR strings exhibit two extended, infinite dimensional space-time symmetries which contain, as a subset, the Galilean symmetries. For each case, we compute the associated conserved charges and discuss the existence of non-central extensions.Postprint (author's final draft
Dynamical sectors for a spinning particle in AdS_3
We consider the dynamics of the motion of a particle of mass M and spin J in
AdS_3. The study reveals the presence of different dynamical sectors depending
on the relative values of M, J and the AdS_3 radius R. For the subcritical M^2
R^2-J^2 >0 and supercritical M^2 R^2-J^2<0 cases, it is seen that the equations
of motion give the geodesics of AdS_3. For the critical case M^2R^2=J^2 there
exist extra gauge transformations which further reduce the physical degrees of
freedom, and the motion corresponds to the geodesics of AdS_2. This result
should be useful in the holographic interpretation of the entanglement entropy
for 2d conformal field theories with gravitational anomalies.Comment: 12 pages, 1 figure, Some comments, references and formulas are adde
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