645 research outputs found
In silico before in vivo: How to predict the heating efficiency of magnetic nanoparticles within the intracellular space
This work aims to demonstrate the need for in silico design via numerical simulation to produce optimal Fe 3 O 4 -based magnetic nanoparticles (MNPs) for magnetic hyperthermia by minimizing the impact of intracellular environments on heating efficiency. By including the relevant magnetic parameters, such as magnetic anisotropy and dipolar interactions, into a numerical model, the heating efficiency of as prepared colloids was preserved in the intracellular environment, providing the largest in vitro specific power absorption (SPA) values yet reported. Dipolar interactions due to intracellular agglomeration, which are included in the simulated SPA, were found to be the main cause of changes in the magnetic relaxation dynamics of MNPs under in vitro conditions. These results pave the way for the magnetism-based design of MNPs that can retain their heating efficiency in vivo, thereby improving the outcome of clinical hyperthermia experiments
Low-Dimensional Assemblies of Magnetic MnFe2O4 Nanoparticles and Direct In Vitro Measurements of Enhanced Heating Driven by Dipolar Interactions: Implications for Magnetic Hyperthermia
Magnetic fluid hyperthermia (MFH), the procedure of raising the temperature of tumor cells using magnetic nanoparticles (MNPs) as heating agents, has proven successful in treating some types of cancer. However, the low heating power generated under physiological conditions makes it necessary a high local concentration of MNPs at tumor sites. Here, we report how the in vitro heating power of magnetically soft MnFe2O4 nanoparticles can be enhanced by intracellular low-dimensional clusters through a strategy that includes: (a) the design of the MNPs to retain Neel magnetic relaxation in high-viscosity media, and (b) culturing MNP-loaded cells under magnetic fields to produce elongated intracellular agglomerates. Our direct in vitro measurements demonstrated that the specific loss power (SLP) of elongated agglomerates (SLP = 576 +/- 33 W/g) induced by culturing BV2 cells in situ under a dc magnetic field was increased by a factor of 2 compared to the SLP = 305 +/- 25 W/g measured in aggregates freely formed within cells. A numerical mean-field model that included dipolar interactions quantitatively reproduced the SLPs of these clusters both in phantoms and in vitro, suggesting that it captures the relevant mechanisms behind power losses under high-viscosity conditions. These results indicate that in situ assembling of MNPs into low-dimensional structures is a sound possible way to improve the heating performance in MFH
Carotid artery disease: Novel pathophysiological mechanisms identified by gene-expression profiling of peripheral blood
AbstractObjectThe pathogenesis of carotid artery stenosis (CAS) as well as the mechanisms underlying the different localisation of the atherosclerotic lesions remains poorly understood. We used microarray technology to identify novel systemic mediators that could contribute to CAS pathogenesis.Moreover, we compared gene-expression profile of CAS with that of patients affected by abdominal aortic aneurysm (AAA), previously published by our group.Methods and resultsBy global gene-expression profiling in a pool of 10 CAS patients and 10 matched controls, we found 82 genes differentially expressed. Validation study in pools used for profiling and replication study in larger numbers of CAS patients (n = 40) and controls (n = 40) of 14 genes by real-time polymerase chain reaction (RT-PCR) confirmed microarray results. Fourteen out of 82 genes were similarly expressed in AAA patients. Gene ontology analysis identified a statistically significant enrichment in CAS of differentially expressed transcripts involved in immune response and oxygen transport. Whereas alteration of oxygen transport is a common tract of the two localisations, alteration of immune response in CAS and of lipid metabolic process in AAA represents distinctive tracts of the two atherosclerotic diseases.ConclusionsWe describe the systemic gene-expression profile of CAS, which provides an extensive list of potential molecular markers
Diagnostic work-up of arrhythmogenic right ventricular cardiomyopathy by cardiovascular magnetic resonance
Cardiovascular magnetic resonance (CMR) has become a widespread diagnostic tool. Since its introduction, CMR has been used to image patients with a known or suspected arrhythmogenic right ventricular cardiomyopathy (ARVC). Several abnormalities have been found and described by CMR and at present this diagnostic tool is considered very important for the diagnosis. However, the diagnosis of ARVC relies upon the fulfillment of both clinical and functional criteria and CMR can provide several but not all the information useful for the diagnosis. Furthermore, some findings such as evidence of right ventricular epicardial fat, once considered a peculiar marker of ARVC, have been shown to possess a low specificity. This document was prepared by representatives of the three Italian official Organizations involved in CMR. Its main scope is to highlight the problems encountered when studying patients with suspected ARVC at CMR, to indicate the basic technical equipment needed, to recommend a proper imaging protocol and to offer a consensus on the main features relevant for the diagnosis
Linking and causality in globally hyperbolic spacetimes
The linking number is defined if link components are zero homologous.
Our affine linking invariant generalizes to the case of linked
submanifolds with arbitrary homology classes. We apply to the study of
causality in Lorentz manifolds. Let be a spacelike Cauchy surface in a
globally hyperbolic spacetime . The spherical cotangent bundle
is identified with the space of all null geodesics in
Hence the set of null geodesics passing through a point gives an
embedded -sphere in called the sky of Low observed
that if the link is nontrivial, then are causally
related. This motivated the problem (communicated by Penrose) on the Arnold's
1998 problem list to apply link theory to the study of causality. The spheres
are isotopic to fibers of They are nonzero
homologous and is undefined when is closed, while is well defined. Moreover, if is not an
odd-dimensional rational homology sphere. We give a formula for the increment
of \alk under passages through Arnold dangerous tangencies. If is
such that takes values in and is conformal to having all
the timelike sectional curvatures nonnegative, then are causally
related if and only if . We show that in
nonrefocussing are causally unrelated iff can be deformed
to a pair of -fibers of by an isotopy through skies. Low
showed that if (\ss, g) is refocussing, then is compact. We show that the
universal cover of is also compact.Comment: We added: Theorem 11.5 saying that a Cauchy surface in a refocussing
space time has finite pi_1; changed Theorem 7.5 to be in terms of conformal
classes of Lorentz metrics and did a few more changes. 45 pages, 3 figures. A
part of the paper (several results of sections 4,5,6,9,10) is an extension
and development of our work math.GT/0207219 in the context of Lorentzian
geometry. The results of sections 7,8,11,12 and Appendix B are ne
Technical Note: The air quality modeling system Polyphemus
International audiencePolyphemus is an air quality modeling platform which aims at covering the scope and the abilities of modern air quality systems. It deals with applications from local scale to continental scale, using two Gaussian models and two Eulerian models. It manages passive tracers, radioactive decay, photochemistry and aerosol dynamics. The structure of the system includes four independent levels with data management, physical parameterizations, numerical solvers and high-level methods such as data assimilation. This enables sensitivity and uncertainty analysis, primarily through multimodel approaches. On top of the models, drivers implement advanced methods such as model coupling or data assimilation
On the computation of zone and double zone diagrams
Classical objects in computational geometry are defined by explicit
relations. Several years ago the pioneering works of T. Asano, J. Matousek and
T. Tokuyama introduced "implicit computational geometry", in which the
geometric objects are defined by implicit relations involving sets. An
important member in this family is called "a zone diagram". The implicit nature
of zone diagrams implies, as already observed in the original works, that their
computation is a challenging task. In a continuous setting this task has been
addressed (briefly) only by these authors in the Euclidean plane with point
sites. We discuss the possibility to compute zone diagrams in a wide class of
spaces and also shed new light on their computation in the original setting.
The class of spaces, which is introduced here, includes, in particular,
Euclidean spheres and finite dimensional strictly convex normed spaces. Sites
of a general form are allowed and it is shown that a generalization of the
iterative method suggested by Asano, Matousek and Tokuyama converges to a
double zone diagram, another implicit geometric object whose existence is known
in general. Occasionally a zone diagram can be obtained from this procedure.
The actual (approximate) computation of the iterations is based on a simple
algorithm which enables the approximate computation of Voronoi diagrams in a
general setting. Our analysis also yields a few byproducts of independent
interest, such as certain topological properties of Voronoi cells (e.g., that
in the considered setting their boundaries cannot be "fat").Comment: Very slight improvements (mainly correction of a few typos); add DOI;
Ref [51] points to a freely available computer application which implements
the algorithms; to appear in Discrete & Computational Geometry (available
online
Magnetoresistance in FeGa thin films presenting striped magnetic pattern: the role of closure domains and domain walls
In this work we show the existence of closure domains in FeGa
thin films featuring a striped magnetic pattern and study the effect of the
magnetic domain arrangement on the magnetotransport properties. By means of
X-ray resonant magnetic scattering, we experimentally demonstrate the presence
of such closure domains and estimate their sizes and relative contribution to
surface magnetization. Magnetotransport experiments show that the behavior of
the magnetoresistance depends on the measurement geometry as well as on the
temperature. When the electric current ows perpendicular to the stripe
direction, the resistivity decreases when a magnetic field is applied along the
stripe direction (negative magnetoresistance) in all the studied temperature
range, and the calculations indicate that the main source is the anisotropic
magnetoresistance. In the case of current flowing parallel to the stripe
domains, the magnetoresistance changes sign, being positive at room temperature
and negative at 100 K. To explain this behavior, the contribution to
magnetoresistance from the domain walls must be considered besides the
anisotropic one.Comment: 8 pages, 5 figure
Phenolic compounds in young developing kiwifruit in relation to light exposure: Implications for fruit calcium accumulation
The interaction between light availability and the biosynthesis of phenolic compounds in fruit of kiwifruit (Actinidia deliciosa var. deliciosa, C.F. Liang et A. R. Ferguson) was investigated. Fruits were exposed either to natural light or were artificially shaded while growing on mature vines and were analysed weekly during the first 11 weeks of development. Phenols were identified and quantified by using High Performance Liquid Chromatography (HPLC). Results showed that the predominant phenolic compounds were hydroxycinnamic acids (HCAs), flavonols and the flavan 3-ol epicatechin. Calcium (Ca2+), the main mineral nutrient involved in fruit quality was also determined. Light significantly increased the accumulation of both phenols and Ca2+ into the fruit. This work expands the list of known phenolics in kiwifruit and provides a possible explanation for the seasonal pattern of Ca2+ import into the fruit. Results on light–phenol interaction being apparently beneficial for fruit Ca2+ accumulation, suggest that accurate canopy management could enhance fruit quality
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