Network Physics

Mountain View, CA, United States

Network Physics

Mountain View, CA, United States
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Ngo H.-T.,Network Physics | Bechtold T.,Network Physics
Journal of Applied Polymer Science | Year: 2017

Regeneration of silk fibroin from calcium chloride/ethanol/water solution is of high interest to shape biomaterial based products for medical and technical application. In this study a continuous process for surface modification of cellulose or polyamide fibers by regenerated fibroin deposits has been investigated. The decomposition of the fibroin-calcium complex was initiated by addition of K2CO3 followed by a methanol rinse. Reactive Blue 19 labeled fibroin was used to monitor the deposition of fibroin on the substrates by colour measurement. The fibroin deposits on the fabric were characterised by microscopy, N-content, calcium, and protein content. Stiffness and surface resistivity of modified fabrics were determined as representative physical parameters. The reduced mobility of fibers increased fabric stiffness. Surface resistivity of treated samples was reduced by a factor of 10 to 100, which gives an example for the potential of the technique as coating for man-made fiber textiles. © 2017 Wiley Periodicals, Inc.

Johansson J.,Institute of Cosmology and Gravitation | Johansson J.,Max Planck Institute for Astrophysics | Thomas D.,Institute of Cosmology and Gravitation | Thomas D.,Network Physics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We discuss chemical enrichments of ∼4000 Sloan Digital Sky Survey early-type galaxies using as tracers a large variety of element abundance ratios, namely [C/Fe], [N/Fe], [O/Fe], [Mg/Fe], [Ca/Fe] and [Ti/Fe]. We utilize the stellar population models of absorption line indices from Thomas, Maraston and Johansson which are based on the MILES stellar library. We confirm previous results of increasing age, [Z/H] and [O/Fe] ratios (most often represented by [α/Fe] in the literature) with velocity dispersion. We further derive identical correlations with velocity dispersion for the abundance ratios [O/Fe], [Mg/Fe] and [C/Fe], implying that C/Mg and C/O are close to solar values. This sets a lower limit on the formation time-scales and starburst components of early-type galaxies to ∼0.4Gyr, which is the lifetime of a 3M ⊙ star, since the full C enrichment must be reached. [N/Fe] correlates with velocity dispersion, but offset to lower values and with a steeper slope compared to the other element ratios. We do not find any environmental dependencies for the abundances of C and N, contrary to previous reports in the literature. [Fe/H] does not correlate with velocity dispersion over the entire parameter range covered, but for fixed age we find a steep trend for the [Fe/H]-σ relation. This trend is weaker than the analogous for total metallicity (which also shows steeper trends at fixed age) owing to the lower Fe contribution from Type Ia supernova (SNIa) for more massive early-type galaxies. We find [Ca/Fe] ratios that are close to solar values over the entire velocity dispersion range covered. Tentative, due to large scatter, the results for [Ti/Fe] indicate that Ti follows the trends of Ca. This implies a significant contribution from SNIa to the enrichment of heavy α-elements and puts strong constraints on supernova nucleosynthesis and models of galactic chemical evolution. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Bolmatov D.,Queen Mary, University of London | Trachenko K.,Queen Mary, University of London | Trachenko K.,Network Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Calculating liquid energy and heat capacity in general form is an open problem in condensed matter physics. We develop a recent approach to liquids from the solid state by accounting for the contribution of anharmonicity and thermal expansion to liquid energy and heat capacity. We subsequently compare theoretical predictions to the experiments results of five commonly discussed liquids, and find a good agreement with no free fitting parameters. We discuss and compare the proposed theory to previous approaches. © 2011 American Physical Society.

Bolmatov D.,Queen Mary, University of London | Brazhkin V.V.,Russian Academy of Sciences | Trachenko K.,Queen Mary, University of London | Trachenko K.,Network Physics
Nature Communications | Year: 2013

Since their discovery in 1822, supercritical fluids have been of enduring interest and have started to be deployed in many important applications. Theoretical understanding of the supercritical state is lacking and is seen to limit further industrial deployment. Here we study thermodynamic properties of the supercritical state and discover that specific heat shows a crossover between two different regimes, an unexpected result in view of currently perceived homogeneity of supercritical state in terms of physical properties. We subsequently formulate a theory of system thermodynamics above the crossover, and find good agreement between calculated and experimental specific heat with no free-fitting parameters. In this theory, energy and heat capacity are governed by the minimal length of the longitudinal mode in the system only, and do not explicitly depend on system-specific structure and interactions. We derive a power law and analyse supercritical scaling exponents in the system above the Frenkel line. © 2013 Macmillan Publishers Limited. All rights reserved.

Martinez-Sansigre A.,University of Portsmouth | Martinez-Sansigre A.,University of Oxford | Martinez-Sansigre A.,Network Physics | Rawlings S.,University of Oxford
Monthly Notices of the Royal Astronomical Society | Year: 2011

We use recent progress in simulating the production of magnetohydrodynamic jets around black holes to derive the cosmic spin history of the most massive black holes. Our work focuses on black holes with masses ≳ 108M⊙. Under the assumption that the efficiency of jet production is a function of spin, as given by the simulations, we can approximately reproduce the observed 'radio loudness' of quasars and the local radio luminosity function. Using the X-ray luminosity function and the local mass function of supermassive black holes (SMBHs), we can reproduce the individual radio luminosity functions of radio sources showing high- and low-excitation narrow emission lines. We find that the data favour spin distributions that are bimodal, with one component around spin zero and the other close to maximal spin. The 'typical' spin is therefore really the expectation value, lying between the two peaks. In the low-excitation galaxies, the two components have similar amplitudes, meaning approximately half of the sources have very high spins, and the other have very low spins. For the high-excitation galaxies, the amplitude of the high-spin peak is typically much smaller than that of the low-spin peak, so that most of the sources have low spins. However, a small population of nearly maximally spinning high accretion rate objects is inferred. A bimodality should be seen in the radio loudness of quasars, although there are a variety of physical and selection effects that may obfuscate this feature. We predict that the low-excitation galaxies are dominated by SMBHs with masses ≳108M⊙, down to radio luminosity densities ~1021 W Hz-1sr-1 at 1.4 GHz. Under reasonable assumptions, our model is also able to predict the radio luminosity function at z= 1, and predicts it to be dominated by radio sources with high-excitation narrow emission lines above luminosity densities ≳ 1026 W Hz-1sr-1 at 1.4 GHz, and this is in full agreement with the observations. From our parametrization of the spin distributions of the high and low accretion rate SMBHs, we derive an estimate of the spin history of SMBHs, which shows a weak evolution between z= 1 and 0. A larger fraction of low-redshift SMBHs has high spins compared to high-redshift SMBHs. Using the best-fitting jet efficiencies there is marginal evidence for evolution in spin: the mean spin increases slightly from at z= 1 to at z= 0, and the fraction of SMBHs with increases from 0.16 ± 0.03 at z= 1 to 0.24 ± 0.09 at z= 0. Our inferred spin history of SMBHs is in excellent agreement with constraints from the mean radiative efficiency of quasars, as well as the results from recent simulations of growing SMBHs. We discuss the implications in terms of accretion and SMBH mergers. We also discuss other work related to the spin of SMBHs as well as work discussing the spin of galactic black holes and their jet powers. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Thomas D.,University of Portsmouth | Thomas D.,Network Physics | Maraston C.,University of Portsmouth | Maraston C.,Network Physics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present new stellar population models of Lick absorption-line indices with variable element abundance ratios. The models are based on our new calibrations of absorption-line indices with stellar parameters derived from the MILES stellar library. The key novelty compared to our previous models is that they are now available at the higher spectral resolution of MILES (2.5Å full width at half-maximum) and flux calibrated, hence not tied anymore to the Lick/IDS system. This is essential for the interpretation of galaxy spectra where calibration stars are not available, such as large galaxy redshift surveys or other high-redshift observations. We note that the MILES resolution appears to be comparable to Sloan Digital Sky Survey (SDSS) resolution, so that our models can be applied to SDSS data without any corrections for instrumental spectral resolution. For the first time we provide random errors for the model predictions based on the uncertainties in the calibration functions and the underlying stellar parameter estimates. We show that random errors are small except at the edges of the parameter space (high/low metallicities and young ages ≲1Gyr) where the stellar library is undersampled. We calibrate the base model for the parameters age, metallicity and α/Fe ratio with galactic globular cluster and galaxy gradient data. We discuss two model flavours with different input stellar evolutionary tracks from the Frascati and Padova groups. The new model release now includes abundance variations of the elements C, N, Mg, Na, Si, Ca, Ti, Cr and Fe. The individual elements that are best accessible with these models and the standard set of Lick absorption features are C, N, Mg, Ca, Ti and Fe. The model data are available at ∼thomasd. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Moore L.S.,Network Physics | Stolovicki E.,Network Physics | Braun E.,Network Physics
PLoS ONE | Year: 2013

Neo-Darwinian evolution has presented a paradigm for population dynamics built on random mutations and selection with a clear separation of time-scales between single-cell mutation rates and the rate of reproduction. Laboratory experiments on evolving populations until now have concentrated on the fixation of beneficial mutations. Following the Darwinian paradigm, these experiments probed populations at low temporal resolution dictated by the rate of rare mutations, ignoring the intermediate evolving phenotypes. Selection however, works on phenotypes rather than genotypes. Research in recent years has uncovered the complexity of genotype-to-phenotype transformation and a wealth of intracellular processes including epigenetic inheritance, which operate on a wide range of time-scales. Here, by studying the adaptation dynamics of genetically rewired yeast cells, we show a novel type of population dynamics in which the intracellular processes intervene in shaping the population structure. Under constant environmental conditions, we measure a wide distribution of growth rates that coexist in the population for very long durations (>100 generations). Remarkably, the fastest growing cells do not take over the population on the time-scale dictated by the width of the growth-rate distributions and simple selection. Additionally, we measure significant fluctuations in the population distribution of various phenotypes: the fraction of exponentially-growing cells, the distributions of single-cell growth-rates and protein content. The observed fluctuations relax on time-scales of many generations and thus do not reflect noisy processes. Rather, our data show that the phenotypic state of the cells, including the growth-rate, for large populations in a constant environment is metastable and varies on time-scales that reflect the importance of long-term intracellular processes in shaping the population structure. This lack of time-scale separation between the intracellular and population processes calls for a new framework for population dynamics which is likely to be significant in a wide range of biological contexts, from evolution to cancer. Copyright: © 2013 Moore et al.

Braun E.,Network Physics
Reports on Progress in Physics | Year: 2015

Biological cells present a paradox, in that they show simultaneous stability and flexibility, allowing them to adapt to new environments and to evolve over time. The emergence of stable cell states depends on genotype-to-phenotype associations, which essentially reflect the organization of gene regulatory modes. The view taken here is that cell-state organization is a dynamical process in which the molecular disorder manifests itself in a macroscopic order. The genome does not determine the ordered cell state; rather, it participates in this process by providing a set of constraints on the spectrum of regulatory modes, analogous to boundary conditions in physical dynamical systems. We have developed an experimental framework, in which cell populations are exposed to unforeseen challenges; novel perturbations they had not encountered before along their evolutionary history. This approach allows an unbiased view of cell dynamics, uncovering the potential of cells to evolve and develop adapted stable states. In the last decade, our experiments have revealed a coherent set of observations within this framework, painting a picture of the living cell that in many ways is not aligned with the conventional one. Of particular importance here, is our finding that adaptation of cell-state organization is essentially an efficient exploratory dynamical process rather than one founded on random mutations. Based on our framework, a set of concepts underlying cell-state organization - exploration evolving by global, non-specific, dynamics of gene activity - is presented here. These concepts have significant consequences for our understanding of the emergence and stabilization of a cell phenotype in diverse biological contexts. Their implications are discussed for three major areas of biological inquiry: evolution, cell differentiation and cancer. There is currently no unified theoretical framework encompassing the emergence of order, a stable state, in the living cell. Hopefully, the integrated picture described here will provide a modest contribution towards a physics theory of the cell. © 2015 IOP Publishing Ltd.

Green F.,Network Physics
Physics Education | Year: 2012

The cloud chambers described here are large, made from readily available parts, simple to set up and always work. With no source in the chamber, background radiation can be observed. A large chamber means that a long rod containing a weakly radioactive material can be introduced, increasing the chance of seeing decays. Details of equipment and construction are given. © 2012 IOP Publishing Ltd.

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