Chopra A.,Drexel University |
Chopra A.,University of Pennsylvania |
Murray M.E.,University of Pennsylvania |
Byfield F.J.,University of Pennsylvania |
And 15 more authors.
Biomaterials | Year: 2014
Changes in tissue and organ stiffness occur during development and are frequently symptoms of disease. Many cell types respond to the stiffness of substrates and neighboring cells invitro and most cell types increase adherent area on stiffer substrates that are coated with ligands for integrins or cadherins. Invivo cells engage their extracellular matrix (ECM) by multiple mechanosensitive adhesion complexes and other surface receptors that potentially modify the mechanical signals transduced at the cell/ECM interface. Here we show that hyaluronic acid (also called hyaluronan or HA), a soft polymeric glycosaminoglycan matrix component prominent in embryonic tissue and upregulated during multiple pathologic states, augments or overrides mechanical signaling by some classes of integrins to produce a cellular phenotype otherwise observed only on very rigid substrates. The spread morphology of cells on soft HA-fibronectin coated substrates, characterized by formation of large actin bundles resembling stress fibers and large focal adhesions resembles that of cells on rigid substrates, but is activated by different signals and does not require or cause activation of the transcriptional regulator YAP. The fact that HA production is tightly regulated during development and injury and frequently upregulated in cancers characterized by uncontrolled growth and cell movement suggests that the interaction of signaling between HA receptors and specific integrins might be an important element in mechanical control of development and homeostasis. © 2013 Elsevier Ltd.
Abstract: Iron oxides occur in nature in many forms, often significantly different from each other in terms of structure and physical properties. However, a new variety of iron oxide, recently created and tested by scientists in Cracow, surprised both physicists and engineers, as it revealed features previously unobserved in any other material. The new form of iron oxide (FeO) is a metallic crystal with virtually no defects, a unique conglomerate of electrical and magnetic characteristics, and atoms that vibrate as if the number of dimensions has been reduced. This remarkable material has been prepared, modelled and tested by physicists at the Leading National Research Centre (KNOW) in Cracow, Poland, which includes, among others, the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN), the Institute of Catalysis and Surface Chemistry of the PAS (IKiFP PAN) and the Faculty of Physics and Applied Computer Science of the University of Science and Technology (WFiIS AGH). A group at IFJ PAN was responsible for computer simulations of material. The team from IKiFP PAN and WFiIS AGH, who initiated the research, carried out experiments determining the formation of new iron oxide layers and its properties. Physicists at the European Synchrotron Radiation Facility (ESRF) in Grenoble, the University of the Sorbonne in Paris, and the Pedagogical University of Cracow also participated in the work. "We've been working with modelling materials, including varieties of iron oxide, for years. Our models, constructed on the basis of the fundamental principles of quantum mechanics and statistical physics, have allowed us to determine the positions of atoms in the crystal lattice and to predict the electric, magnetic and thermodynamic properties of materials," explains Dr. Przemyslaw Piekarz, head of Computational Materials Science at IFJ PAN. The theorists in Cracow specialize in studying lattice dynamics, allowing them to determine how atoms in a crystal of a material vibrate. One of the basic tools they use is the PHONON program, created and developed by Prof. Krzysztof Parlinski (IFJ PAN). The VASP (Vienna Ab-initio Simulation Package) software was used to optimize the model. "Our model contains a layer of oxygen and iron with the thickness of a single atom deposited on a substrate made of platinum. The atoms in the monolayer are arranged in a hexagonal structure, like a honeycomb, a construction similar to the famous hexagonal two-dimensional graphene layers," describes Dr. Piekarz. He stresses that graphene creates a perfectly flat surface, entirely composed of carbon atoms. The modeled iron oxide layer, however turns out to be crimped: each iron atom was here surrounded by three oxygen atoms, located a little further from the substrate than the iron was. Calculations carried out for a single monolayer have established what types of vibrations are performed by atoms in the crystal lattice at different energies. The theoretical predictions were verified against the measurements thanks to a group headed by Prof. Jozef Korecki (IKiFP PAN and AGH). Not only have they developed a procedure for the preparation of samples with multiple monolayers of iron oxide on a platinum substrate, but over the past few years they have also been carrying out a series of measurements of their properties using the ESRF synchrotron in Grenoble. "In our laboratory the key to stabilizing materials of unnatural origin is the deposition of monocrystalline layers on the substrate - in this case it was properly oriented single-crystal platinum - which enforces the structure of the growing medium layer. In the laboratories scientists managed to produce a structure of stoichiometric FeO numbering no more than two monolayers of the oxide. Upon adding successive layers, the whole automatically transformed into magnetite Fe3O4. We were able to choose the parameters of the process so that the structure of FeO remained stable for a thickness of several atomic layers," says Prof. Korecki. Experiments at the synchrotron in Grenoble revealed that measurement data concerning vibrations of atoms in the crystal lattice of the new form of iron oxide perfectly agree with the theoretical model. Analysis of the results for samples with varying numbers of layers did more than just confirm the accuracy of the theoretical description. Iron oxide usually forms crystal lattices in which atoms are arranged at the corners of a cube (this is the structure of wustite, and among other substances, table salt). It was expected that after applying successive layers of FeO such a cubic structure would emerge automatically. But analysis of vibrations of atoms in the crystal lattice of the samples showed that the systems that count up to around a dozen monolayers still retain the hexagonal structure. This means that the researchers from Cracow were able to produce a new variety of iron oxide, different from the existing crystal structures. Subsequent measurements showed that for the monolayers number from six to ten, the iron atoms in the crystal have a long-range magnetic order. This is an unusual feature since a basic version of iron oxide is an antiferromagnet, wherein the magnetic moments of iron atoms at different locations are oriented in opposite directions, and therefore the substance as a whole is not magnetized. Meanwhile, the magnetic properties of a new phase of FeO are visible even at room temperature. "Spintronic materials for construction equipment have been sought after for many years. These instruments make use not only of the electrical current, but also the conduction of electron spin, which is responsible for its magnetic properties," relates Dr. Piekarz. "Our new material is not an insulator, like most oxides, but metal. So this combination of electrical and magnetic properties, rare for oxides, may be interesting for spintronics, as well as in the construction of various types of sensors and detectors." Of particular interest, however, was the analysis of the vibration of atoms depending on the number of layers of FeO on the platinum substrate. For one or two layers the movement of atoms is of a two-dimensional nature. When the number of layers reaches six or more, atoms vibrate as in a typical three-dimensional crystal. In the materials studied to date the nature of the vibration was closely associated with the dimensionality of the system. Meanwhile, a new variant of iron oxide at three, four and five layers of atoms proved to vibrate in an intermediate manner, corresponding to the fractional numbers of dimensions. "We're dealing with the first material in which the nature of vibration of atoms gradually passes from two-dimensional to three-dimensional. A similar effect, although expected in theory, has never before been observed in any other substance," claims Dr. Piekarz. Research on a new form of iron oxide, funded by grants from the Polish National Science Centre, are described in the renowned journal Physical Review Letters. About The Henryk Niewodniczanski Institute of Nuclear Physics The Henryk Niewodniczanski Institute of Nuclear Physics (IFJ PAN) is currently the largest research institute of the Polish Academy of Sciences. The broad range of studies and activities of IFJ PAN includes basic and applied research, ranging from particle physics and astrophysics, through hadron physics, high-, medium-, and low-energy nuclear physics, condensed matter physics (including materials engineering), to various applications of methods of nuclear physics in interdisciplinary research, covering medical physics, dosimetry, radiation and environmental biology, environmental protection, and other related disciplines. The average yearly yield of the IFJ PAN encompasses more than 450 scientific papers in the Journal Citation Reports published by the Thomson Reuters. The part of the Institute is the Cyclotron Centre Bronowice (CCB) which is an infrastructure, unique in Central Europe, to serve as a clinical and research centre in the area of medical and nuclear physics. IFJ PAN is a member of the Marian Smoluchowski Krakow Research Consortium: "Matter-Energy-Future" which possesses the status of a Leading National Research Centre (KNOW) in physics for the years 2012-2017. The Institute is of A+ Category (leading level in Poland) in the field of sciences and engineering. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Matisoff G.,Case Western Reserve University |
Ketterer M.E.,Northern Arizona University |
Rosen K.,Swedish University of Agricultural Sciences |
Mietelski J.W.,The Henryk Niewodniczanski Institute of Nuclear Physics |
And 3 more authors.
Applied Geochemistry | Year: 2011
Vertical profiles of 137Cs and 239,240Pu were measured in soils collected from two sites in southern Sweden and three sites in southern Poland and were modeled using both a solute transport model and a bioturbation model to better understand their downward migration. A time series of measured 137Cs profiles indicates that 137Cs from Chernobyl was found at the soil surface in 1986 but it has migrated progressively downward into the soil 4.5-25.5cm since. However, because of dispersion during the migration and mixing following Chernobyl deposition and the much higher activities of 137Cs from Chernobyl, stratospheric fallout of 137Cs from the 1960s cannot be identified as a second 137Cs activity maximum lower in the soil column at any of the sites. Conversely, the 240Pu/239Pu ratio indicates that no Chernobyl-derived Pu is present in any of the cores with the exception of one sample in Sweden. This difference may be attributed to the nature of the release from Chernobyl. Cesium volatilized at the reactor temperature during the accident, and was released as a vapor whereas Pu was not volatile and was only released in the form of minute fuel particles that traveled regionally. Both the solute diffusion and the bioturbation models accurately simulate the downward migration of the radionuclides at some sites but poorly describe the distributions at other sites. The distribution coefficients required by the solute transport model are about 100 times lower than reported values from the literature indicating that even though the solute transport model can simulate the profile shapes, transport as a solute is not the primary mechanism governing the downward migration of either Cs or Pu. The bioturbation model uses reported values from the literature of the distribution coefficients and can simulate the downward migration because that model buries the fallout by placing soil from depth on top and mixing it slightly throughout the mixing zone (0.6-2% per year of mixing). However, mixing in that model predicts concentrations in the top parts of the soil profiles which are too high in many cases. Future progress at understanding the downward migration of radionuclides and other tracers will require a more comprehensive approach, combining solute transport with bioturbation and including other important soil processes. © 2010 Elsevier Ltd.
Lokas E.,The Henryk Niewodniczanski Institute of Nuclear Physics |
Mietelski J.W.,The Henryk Niewodniczanski Institute of Nuclear Physics |
Ketterer M.E.,Northern Arizona University |
Kleszcz K.,The Henryk Niewodniczanski Institute of Nuclear Physics |
And 4 more authors.
Applied Geochemistry | Year: 2013
This paper presents a detailed survey of the activities of selected man-made radionuclides in peat deposits located in SW Spitsbergen. Peat cores from the High Arctic (SW Spitsbergen) were analyzed by gamma spectrometry (137Cs), alpha spectrometry (238Pu, 239,240Pu, 241Am activities) and by ICPMS (240Pu/239Pu atom ratios). Maximum activities evident in the peats correspond to the 1963/1964 global maximum fallout from atmospheric testing of nuclear weapons; some of the activity profiles have been altered post-deposition by water infiltration. Activity ratios of 238Pu/239+240Pu, 241Am/239+240Pu, 239+240Pu/137Cs and 240Pu/239Pu atom ratios indicate mixing between global (stratospheric) and regional (tropospheric) sources of these radionuclides in the Svalbard area. The 238Pu/239+240Pu activity ratios varied from 0.02±0.01 to 0.09±0.03, suggesting global fallout as the dominant source of Pu. The 239+240Pu/137Cs activity ratios varied from 0.01±0.01 to 0.42±0.11, which apparently arises from the post-depositional mobility of 137Cs. The 241Am/239+240Pu activity ratios ranged between 0.10±0.02 and 1.5±0.3 and exceed the published global fallout ratio for Svalbard of 0.37 due to the relatively higher geochemical mobility of Pu vs. Am and/or ingrowth of Am from the decay of 241Pu. The atom ratio 240Pu/239Pu ranged from 0.142±0.006 to 0.241±0.027; however, the vast majority of peat samples exhibited 240Pu/239Pu atom ratios similar to the stratospheric fallout (∼0.18). © 2012 Elsevier Ltd.
Dworak D.,The Henryk Niewodniczanski Institute of Nuclear Physics |
Woznicka U.,The Henryk Niewodniczanski Institute of Nuclear Physics |
Zorski T.,AGH University of Science and Technology |
Wicek U.,The Henryk Niewodniczanski Institute of Nuclear Physics
Applied Radiation and Isotopes | Year: 2011
A signal of a spectrometric gamma-gamma density tool in specific borehole conditions has been numerically calculated. Transport of gamma rays, from a point 137Cs gamma source situated in a borehole tool, through rock media to detectors, has been simulated using a Monte Carlo code. The influence of heterogeneity of the rock medium surrounding the borehole on the signal of the detectors has been examined. This heterogeneity results from the presence of an interface between two different geological layers, parallel to the borehole wall. The above conditions may occur in horizontal logging, when the borehole is drilled along the boundary of geological layers. It is possible to assess the distance from the boundary on the basis of the responses of the gamma-gamma density tool, using the classic interpretation "spine & ribs" procedure. The effect of different densities of the bordered layers on the tool response has been analyzed. The presented calculations show the wide possibilities of numerical modeling of the complex borehole geometry and solving difficult interpretation problems in nuclear well logging. © 2010 Elsevier Ltd.