1,092 research outputs found
Dynamics and pattern formation in invasive tumor growth
In this work, we study the in-vitro dynamics of the most malignant form of
the primary brain tumor: Glioblastoma Multiforme. Typically, the growing tumor
consists of the inner dense proliferating zone and the outer less dense
invasive region. Experiments with different types of cells show qualitatively
different behavior. Wild-type cells invade a spherically symmetric manner, but
mutant cells are organized in tenuous branches. We formulate a model for this
sort of growth using two coupled reaction-diffusion equations for the cell and
nutrient concentrations. When the ratio of the nutrient and cell diffusion
coefficients exceeds some critical value, the plane propagating front becomes
unstable with respect to transversal perturbations. The instability threshold
and the full phase-plane diagram in the parameter space are determined. The
results are in a good agreement with experimental findings for the two types of
cells.Comment: 4 pages, 4 figure
Low molecular weight cellulose ethers as aerosols for the the consolidation of cohesively weak paint layers
Due to Edvard Munch’s (1863-1944) unconventional painting technique, choice of materials, and the unstable climate conditions of his studios, where the paintings were stored during his lifetime, many of his paintings, now housed at MUNCH, have cohesively weak and loose paint layers. As a result, consolidation and re-adhesion of these fragile paint layers are the most frequently performed conservation treatments on his paintings. A selection of low molecular weight (lmw) hydroxypropyl methylcellulose ethers (HPMC), new to the field of conservation, have been evaluated in comparison to methylcellulose (MC) A4C and sturgeon glue regarding their suitability for the consolidation of cohesively weak paint layers. The mock-ups used for these investigations were of a similar composition (pigment, binding medium and pigment-binding medium ratio) and porosity to a paint sample from the painting “Beach Landscape with Trees and Boats” from 1905-06 by Edvard Munch.
Viscosity and surface tension of aqueous solutions of the consolidants and their influence on the imbibition time and depth into porous paint layers were investigated. Fluorescence labelling was used to visualize the imbibition depth of an aqueous solution of the lmw HPMC E3 and MC A4C, applied as an aerosol. With this method it could be shown that the applied amount and the application method of the consolidant (with or without intermediate drying steps) can play a crucial role in the imbibition depth. To evaluate the consolidation effect of the tested polymers, the aerosols of their aqueous solutions were applied on the paint mock-ups in a reproducible and standardized way, using an automated two-axis-table. A customised abrasion test was developed to evaluate the comparative increase of the paint layer cohesion after consolidation. These preliminary investigations show lmw HPMC as promising alternatives to established consolidants. They allow for an ultrasonic nebulisation in higher concentrations and thus for the paint layer’s consolidation in a lower number of applications
Singular Modes of the Electromagnetic Field
We show that the mode corresponding to the point of essential spectrum of the
electromagnetic scattering operator is a vector-valued distribution
representing the square root of the three-dimensional Dirac's delta function.
An explicit expression for this singular mode in terms of the Weyl sequence is
provided and analyzed. An essential resonance thus leads to a perfect
localization (confinement) of the electromagnetic field, which in practice,
however, may result in complete absorption.Comment: 14 pages, no figure
Lieb-Thirring Bound for Schr\"odinger Operators with Bernstein Functions of the Laplacian
A Lieb-Thirring bound for Schr\"odinger operators with Bernstein functions of
the Laplacian is shown by functional integration techniques. Several specific
cases are discussed in detail.Comment: We revised the first versio
Schroedinger operators with singular interactions: a model of tunneling resonances
We discuss a generalized Schr\"odinger operator in , with an attractive singular interaction supported by a
-dimensional hyperplane and a finite family of points. It can be
regarded as a model of a leaky quantum wire and a family of quantum dots if
, or surface waves in presence of a finite number of impurities if .
We analyze the discrete spectrum, and furthermore, we show that the resonance
problem in this setting can be explicitly solved; by Birman-Schwinger method it
is cast into a form similar to the Friedrichs model.Comment: LaTeX2e, 34 page
Gender score development in the Berlin Aging Study II: A retrospective approach
In addition to biological sex, gender, defined as the sociocultural dimension of being a woman or a man, plays a central role in health. However, there are so far few approaches to quantify gender in a retrospective manner in existing study datasets. We therefore aimed to develop a methodology that can be retrospectively applied to assess gender in existing cohorts. We used baseline data from the Berlin Aging Study II (BASE-II), obtained in 2009-2014 from 1869 participants aged 60 years and older. We identified 13 gender-related variables and used them to construct a gender score by using primary component and logistic regression analyses. Of these, nine variables contributed to a gender score: chronic stress, marital status, risk-taking behaviour, personality attributes: agreeableness, neuroticism, extraversion, loneliness, conscientiousness, and level of education. Females and males differed significantly in the distribution of the gender score, but a significant overlap was also found. Thus, we were able to develop a gender score in a retrospective manner from already collected data that characterized participants in addition to biological sex. This approach will allow researchers to introduce the notion of gender retrospectively into a large number of studies
Multilingual assessment of early child development: Analyses from repeated observations of children in Kenya.
In many low- and middle-income countries, young children learn a mother tongue or indigenous language at home before entering the formal education system where they will need to understand and speak a countrys official language(s). Thus, assessments of children before school age, conducted in a nations official language, may not fully reflect a childs development, underscoring the importance of test translation and adaptation. To examine differences in vocabulary development by language of assessment, we adapted and validated instruments to measure developmental outcomes, including expressive and receptive vocabulary. We assessed 505 2-to-6-year-old children in rural communities in Western Kenya with comparable vocabulary tests in three languages: Luo (the local language or mother tongue), Swahili, and English (official languages) at two time points, 5-6 weeks apart, between September 2015 and October 2016. Younger children responded to the expressive vocabulary measure exclusively in Luo (44%-59% of 2-to-4-year-olds) much more frequently than did older children (20%-21% of 5-to-6-year-olds). Baseline receptive vocabulary scores in Luo (β = 0.26, SE = 0.05, p < 0.001) and Swahili (β = 0.10, SE = 0.05, p = 0.032) were strongly associated with receptive vocabulary in English at follow-up, even after controlling for English vocabulary at baseline. Parental Luo literacy at baseline (β = 0.11, SE = 0.05, p = 0.045) was associated with child English vocabulary at follow-up, while parental English literacy at baseline was not. Our findings suggest that multilingual testing is essential to understanding the developmental environment and cognitive growth of multilingual children
Quantum light transport in phase-separated Anderson localization fiber
Anderson localization, a strong localization effect that prevents wave diffusion, is fundamentally important in manipulating wave propagation in a disordered medium. This work uses a phase separated glass Anderson localization optical fiber and demonstrates quantum light transport, which shows the potential for transmission of high dimensional quantum information, thereby enabling quantum imaging and quantum communication applications.Propagation of light by Anderson localization has been demonstrated in micro-nano-structured fibers. In this work, we introduce a phase separated glass Anderson localization optical fiber for quantum applications. By using a spontaneous parametric down-conversion source, multi-photon detection with a single-photon avalanche diode array camera, and signal post-processing techniques, we demonstrate quantum light transport, where spatial correlations between photon pairs are preserved after propagation. In order to better understand and improve light transport, we study light localization, observing a dependence on wavelength. Our results indicate that the proposed phase separated fiber may become an effective platform for quantum imaging and communication
Transformation Pathways of Silica under High Pressure
Concurrent molecular dynamics simulations and ab initio calculations show
that densification of silica under pressure follows a ubiquitous two-stage
mechanism. First, anions form a close-packed sub-lattice, governed by the
strong repulsion between them. Next, cations redistribute onto the interstices.
In cristobalite silica, the first stage is manifest by the formation of a
metastable phase, which was observed experimentally a decade ago, but never
indexed due to ambiguous diffraction patterns. Our simulations conclusively
reveal its structure and its role in the densification of silica.Comment: 14 pages, 4 figure
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