370 research outputs found
Spatial periodic and homogeneous transverse stress loading on ITER TF Nb3Sn bronze and internal tin strand
The transport properties of the superconducting Nb3Sn layers in the strands
strongly depend on the strain state. Knowledge of the influence of axial
strain, periodic bending and contact stress on the critical current (Ic) of the
used Nb3Sn strands is inevitable to gain sufficient confidence in an economic
design and stable operation of ITER CICCs. In the past years we have measured
the Ic and n-value of various ITER Nb3Sn strands with different layout in the
TARSIS facility, when subjected to spatial periodic contact stress at a
temperature of 4.2 K and in a magnet field of 12 T. Recently we have made the
setup suitable for application of homogeneous load along the length of the wire
(125 mm) in order to evaluate possible differences related to spatial stress
and possible current distribution. We present an overview of the results
obtained so far on an ITER TF bronze and internal tin strand.Comment: to be published in IEEE Trans Appl Supercon
Proper ferroelastic phase transitions in thin epitaxial films with symmetry-conserving and symmetry-breaking misfit strains
We study how the ferroelastic domain structure sets in in an epitaxial film
of a material with second order proper ferroelastic transition. The domain
structures considered are similar to either or
structures in perovskite ferroelectrics. If the "extrinsic" misfit
strain, not associated with the transition, does not break the symmetry of the
high-temperature phase, the phase transition in the film occurs at somewhat
lower temperature compared to the bulk. The loss of stability then occurs with
respect to a sinusoidal strain wave, which evolves into the domain structure
with practically the same geometry and approximately the same period. In the
presence of the symmetry-breaking component of the misfit strain ("extrinsic"
misfit) the character of the phase transition is qualitatively different. In
this case it is a {\em topological} transition between single-domain and
multi-domain states, which starts from a low density of the domain walls.Comment: 7 pages, 2 figures, REVTeX 3.
Induction of apoptosis in human cancer cells by targeting mitochondria with gold nanoparticles
A major challenge in designing cancer therapies is the induction of cancer cell apoptosis, although activation of intrinsic apoptotic pathways by targeting gold nanoparticles to mitochondria is promising. We report an in vitro procedure targeting mitochondria with conjugated gold nanoparticles and investigating effects on apoptosis induction in the human breast cancer cell line Jimt-1. Gold nanoparticles were conjugated to a variant of turbo green fluorescent protein (mitoTGFP) harbouring an amino-terminal mitochondrial localization signal. Au nanoparticle conjugates were further complexed with cationic maltotriose-modified poly(propylene imine) third generation dendrimers. Fluorescence and transmission electron microscopy revealed that Au nanoparticle conjugates were directed to mitochondria upon transfection, causing partial rupture of the outer mitochondrial membrane, triggering cell death. The ability to target Au nanoparticles into mitochondria of breast cancer cells and induce apoptosis reveals an alternative application of Au nanoparticles in photothermal therapy of cancer
Distinguishing autocrine and paracrine signals in hematopoietic stem cell culture using a biofunctional microcavity platform
Homeostasis of hematopoietic stem cells (HSC) in the mammalian bone marrow stem cell niche is regulated by signals of the local microenvironment. Besides juxtacrine, endocrine and metabolic cues,
paracrine and autocrine signals are involved in controlling quiescence, proliferation and differentiation of HSC with strong implications on expansion and differentiation ex vivo as well as in vivo transplantation.
Towards this aim, a cell culture analysis on a polymer microcavity carrier platform was combined with a partial least square analysis of a mechanistic model of cell proliferation. We could demonstrate the discrimination of specific autocrine and paracrine signals from soluble factors as stimulating and inhibitory effectors in hematopoietic stem and progenitor cell culture. From that we hypothesize autocrine signals
to be predominantly involved in maintaining the quiescent state of HSC in single-cell niches and advocate our analysis platform as an unprecedented option for untangling convoluted signaling mechanisms in complex cell systems being it of juxtacrine, paracrine or autocrine origin
Wetting films on chemically heterogeneous substrates
Based on a microscopic density functional theory we investigate the
morphology of thin liquidlike wetting films adsorbed on substrates endowed with
well-defined chemical heterogeneities. As paradigmatic cases we focus on a
single chemical step and on a single stripe. In view of applications in
microfluidics the accuracy of guiding liquids by chemical microchannels is
discussed. Finally we give a general prescription of how to investigate
theoretically the wetting properties of substrates with arbitrary chemical
structures.Comment: 56 pages, RevTeX, 20 Figure
Spatial clustering of childhood leukaemia: summary results from the EUROCLUS project.
The interpretation of reports of clusters of childhood leukaemia is difficult, first because little is known about the causes of the disease, and second because there is insufficient information on whether cases show a generalized tendency to cluster geographically. The EUROCLUS project is a European collaborative study whose primary objective is to determine whether the residence locations of cases at diagnosis show a general tendency towards spatial clustering. The second objective is to interpret any patterns observed and, in particular, to see if clustering can be explained in terms of either infectious agents or environmental hazards as aetiological agents. The spatial distribution of 13351 cases of childhood leukaemia diagnosed in 17 countries between 1980 and 1989 has been analysed using the Potthoff-Whittinghill method. The overall results show statistically significant evidence of clustering of total childhood leukaemia within small census areas (P=0.03) but the magnitude of the clustering is small (extra-Poisson component of variance (%) = 1.7 with 90% confidence interval 0.2-3.1). The clustering is most marked in areas that have intermediate population density (150-499 persons km[-2]). It cannot be attributed to any specific age group at diagnosis or cell type and involves spatial aggregation of cases of different ages and cell types. The results indicate that intense clusters are a rare phenomenon that merit careful investigation, although aetiological insights are more likely to come from investigation of large numbers of cases. We present a method for detecting clustering that is simple and readily available to cancer registries and similar groups
Thermodynamic theory of epitaxial ferroelectric thin films with dense domain structures
A Landau-Ginsburg-Devonshire-type nonlinear phenomenological theory is
presented, which enables the thermodynamic description of dense laminar
polydomain states in epitaxial ferroelectric thin films. The theory explicitly
takes into account the mechanical substrate effect on the polarizations and
lattice strains in dissimilar elastic domains (twins). Numerical calculations
are performed for PbTiO3 and BaTiO3 films grown on (001)-oriented cubic
substrates. The "misfit strain-temperature" phase diagrams are developed for
these films, showing stability ranges of various possible polydomain and
single-domain states. Three types of polarization instabilities are revealed
for polydomain epitaxial ferroelectric films, which may lead to the formation
of new polydomain states forbidden in bulk crystals. The total dielectric and
piezoelectric small-signal responses of polydomain films are calculated,
resulting from both the volume and domain-wall contributions. For BaTiO3 films,
strong dielectric anomalies are predicted at room temperature near special
values of the misfit strain.Comment: 19 pages, 8 figure
Fully three-dimensional sound speed-corrected multi-wavelength photoacoustic breast tomography
Photoacoustic tomography is a contrast agent-free imaging technique capable
of visualizing blood vessels and tumor-associated vascularization in breast
tissue. While sophisticated breast imaging systems have been recently
developed, there is yet much to be gained in imaging depth, image quality and
tissue characterization capability before clinical translation is possible. In
response, we have developed a hybrid photoacoustic and ultrasound-transmission
tomographic system PAM3. The photoacoustic component has for the first time
three-dimensional multi-wavelength imaging capability, and implements
substantial technical advancements in critical hardware and software
sub-systems. The ultrasound component enables for the first time, a
three-dimensional sound speed map of the breast to be incorporated in
photoacoustic reconstruction to correct for inhomogeneities, enabling accurate
target recovery. The results demonstrate the deepest photoacoustic breast
imaging to date namely 48 mm, with a more uniform field of view than hitherto,
and an isotropic spatial resolution that rivals that of Magnetic Resonance
Imaging. The in vivo performance achieved, and the diagnostic value of
interrogating angiogenesis-driven optical contrast as well as tumor mass sound
speed contrast, gives confidence in the system's clinical potential.Comment: 33 pages Main Body, 9 pages Supplementary Materia
Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions
Excess contributions to the free energy due to interfaces occur for many
problems encountered in the statistical physics of condensed matter when
coexistence between different phases is possible (e.g. wetting phenomena,
nucleation, crystal growth, etc.). This article reviews two methods to estimate
both interfacial free energies and line tensions by Monte Carlo simulations of
simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid
exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is
based on thermodynamic integration. This method is useful to study flat and
inclined interfaces for Ising lattices, allowing also the estimation of line
tensions of three-phase contact lines, when the interfaces meet walls (where
"surface fields" may act). A generalization to off-lattice systems is described
as well.
The second method is based on the sampling of the order parameter
distribution of the system throughout the two-phase coexistence region of the
model. Both the interface free energies of flat interfaces and of (spherical or
cylindrical) droplets (or bubbles) can be estimated, including also systems
with walls, where sphere-cap shaped wall-attached droplets occur. The
curvature-dependence of the interfacial free energy is discussed, and estimates
for the line tensions are compared to results from the thermodynamic
integration method. Basic limitations of all these methods are critically
discussed, and an outlook on other approaches is given
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