Shelke A.,Indian Institute of Technology Guwahati |
Banerjee S.,University of South Carolina |
Habib A.,Institute for Cell Biology and Neuroscience |
Rahani E.K.,University of Arizona |
And 2 more authors.
Journal of Intelligent Material Systems and Structures | Year: 2014
In this article, we address the effect of regular and irregular distribution of phononic lattices on acoustic wave and investigate wave bending and refraction phenomena for some specific patterns of phononic crystals consisting of a square array of polyvinylchloride cylindrical rods in air matrix using finite element model. Bucay et al. have demonstrated that for a given configuration, the striking acoustic beam angle varying between 20° and 40° at 14.1 kHz central frequency shows positive, negative, and zero angle refraction inside phononic crystal and exhibits beam splitting after exiting the phononic crystal. These results are used as the benchmark in this article to validate the proposed model. Transmission spectrum in the phononic crystal has been studied for complete acoustic band gap as well as for positive and negative dispersion bands at frequencies ranging from 1 to 18 kHz. Using this established theory, in this article, the acoustic beam propagation through irregular phononic crystal structures and waveguides are investigated. It can be seen that small irregularity produces significant change in the acoustic field. It is shown that with a localized defect, resonating cavity waveguide is formed in the proposed acoustic metamaterials. © The Author(s) 2013.
Vafaizadeh V.,Paul Ehrlich Institute |
Klemmt P.A.B.,Institute for Cell Biology and Neuroscience |
Klemmt P.A.B.,Goethe University Frankfurt |
Groner B.,Paul Ehrlich Institute
Frontiers in Bioscience | Year: 2012
The mammary epithelium comprises luminal and basal cells which originate from multipotent mammary stem cells (MaSCs). They form ductal structures embedded in the mammary fat pad in virgin mice and differentiate during pregnancy into alveoli under the control of hormones and growth factors and the activation of specific transcription factors. Genetic manipulations of embryonic stem cells and the derivation of transgenic mice allowed the study of regulatory genes in mammary epithelial cells of particular differentiation states. We describe an alternative approach to investigate stage dependent gene functions in transgenic mammary glands based on ex vivo, genetically manipulated MaSCs and the reconstitution of functional epithelium upon their transplantation into cleared fat pads. Modification of MaSCs with Stat5 suppressing shRNA or a constitutively active variant of Stat5 showed that Stat5 assumes essential roles in alveolar lineage commitment, proliferation, differentiation and survival. Its persistent activation during post-lactational involution causes the formation of non-metastatic adenocarcinomas, resembling the human luminal breast cancer subtype. The tumor cells express estrogen and progesterone receptor (ER+PR+) and activated Stat3 and Stat5. They could become valuable to assess the therapeutic potential of anti-estrogens, aromatase inhibitors and Stat3 and Stat5 inhibition on tumor growth.
Strecker V.,Institute for Cell Biology and Neuroscience |
Mai S.,Institute for Cell Biology and Neuroscience |
Muster B.,Institute for Cell Biology and Neuroscience |
Beneke S.,University of Konstanz |
And 3 more authors.
Mechanisms of Ageing and Development | Year: 2010
Elevated reactive oxygen species (ROS) levels have been observed in mammals during aging, implying an important role of ROS in the aging process. Most bird species are known to live longer and to contain lower ROS levels than mammals of the same body weight. The influence of ROS on the aging process of birds has been investigated using pigeon embryonic fibroblasts (PEF) and chicken embryonic fibroblasts (CEF). ROS levels in young avian cells were much lower than in human cells. When cultivated till replicative senescence, PEF proliferated about one-third longer compared to CEF. However, both senescent avian cell populations showed no increased ROS levels or accumulation of ROS-induced damage on the mtDNA or protein level. The investigation for quality control (QC) mechanisms revealed that the autophagosomal/lysosomal pathway was not downregulated in old avian cells and stable overexpression of the autophagy protein ATG5 improved mitochondrial fitness, enhanced the resistance against oxidative stress and prolonged the life span of CEF. Oxidative stress-mediated apoptosis induced a dose-dependent cell proliferation in CEF as well as in PEF. Taken together, our data indicate that autophagy and compensatory proliferation act as QC mechanisms, while ROS did not influence the aging process in avian cells. © 2009 Elsevier Ireland Ltd. All rights reserved.