Controlled DNA compaction within chromatin: the tail-bridging effect

We study the mechanism underlying the attraction between nucleosomes, the fundamental packaging units of DNA inside the chromatin complex. We introduce a simple model of the nucleosome, the eight-tail colloid, consisting of a charged sphere with eight oppositely charged, flexible, grafted chains that represent the terminal histone tails. We demonstrate that our complexes are attracted via the formation of chain bridges and that this attraction can be tuned by changing the fraction of charged monomers on the tails. This suggests a physical mechanism of chromatin compaction where the degree of DNA condensation can be controlled via biochemical means, namely the acetylation and deacetylation of lysines in the histone tails.Comment: 4 pages, 5 figures, submitte

Glass-Like Heat Conduction in High-Mobility Crystalline Semiconductors

The thermal conductivity of polycrystalline semiconductors with type-I clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr and/or Eu) exhibit lattice thermal conductivities typical of amorphous materials. Remarkably, this behavior occurs in spite of the well-defined crystalline structure and relatively high electron mobility ($\sim 100 cm^2/Vs$). The dynamics of dopant ions and their interaction with the polyhedral cages of the structure are a likely source of the strong phonon scattering.Comment: 4 pages, 3 postscript figures, to be published, Phys. Rev. Let

Impact of boundaries on fully connected random geometric networks

Many complex networks exhibit a percolation transition involving a macroscopic connected component, with universal features largely independent of the microscopic model and the macroscopic domain geometry. In contrast, we show that the transition to full connectivity is strongly influenced by details of the boundary, but observe an alternative form of universality. Our approach correctly distinguishes connectivity properties of networks in domains with equal bulk contributions. It also facilitates system design to promote or avoid full connectivity for diverse geometries in arbitrary dimension.Comment: 6 pages, 3 figure

Wireless communication with chaos

Peer reviewedPublisher PD

Winter Counts as Transformative Inquiry: The Role of Creative Imagery as an Expression of Adaptive Change

Pre-service teachers face a complex educational context and Transformative Inquiry is a useful approach for negotiating this terrain. We interpret the movement of students via the adaptive cycle put forth in panarchy theory as they engage in the inquiry process through ‘winter counts’, a Plains First Nation tradition, as expressions of their understanding. These image-based expressions demonstrate the emotional, mental, spiritual and physical movement students have made within their inquiry. Panarchy theory moves beyond interpreting systems using simplistic equilibrium models and acknowledging the more complex and dynamic set of equilibria that describes transformation in ecological, social, and economic systems and considers the multiple complexities of systems thinking while providing insight into how change occurs as a constantly adaptive cycle process. Used sparingly within social sciences until recently, we argue it as particularly relevant for seeing Transformative Inquiry through Indigenist and interconnected lenses

Path integral Monte Carlo simulations of silicates

We investigate the thermal expansion of crystalline SiO$_2$ in the $\beta$-- cristobalite and the $\beta$-quartz structure with path integral Monte Carlo (PIMC) techniques. This simulation method allows to treat low-temperature quantum effects properly. At temperatures below the Debye temperature, thermal properties obtained with PIMC agree better with experimental results than those obtained with classical Monte Carlo methods.Comment: 27 pages, 10 figures, Phys. Rev. B (in press

Shrinking Point Bifurcations of Resonance Tongues for Piecewise-Smooth, Continuous Maps

Resonance tongues are mode-locking regions of parameter space in which stable periodic solutions occur; they commonly occur, for example, near Neimark-Sacker bifurcations. For piecewise-smooth, continuous maps these tongues typically have a distinctive lens-chain (or sausage) shape in two-parameter bifurcation diagrams. We give a symbolic description of a class of "rotational" periodic solutions that display lens-chain structures for a general $N$-dimensional map. We then unfold the codimension-two, shrinking point bifurcation, where the tongues have zero width. A number of codimension-one bifurcation curves emanate from shrinking points and we determine those that form tongue boundaries.Comment: 27 pages, 6 figure

Composite CDMA - A statistical mechanics analysis

Code Division Multiple Access (CDMA) in which the spreading code assignment to users contains a random element has recently become a cornerstone of CDMA research. The random element in the construction is particular attractive as it provides robustness and flexibility in utilising multi-access channels, whilst not making significant sacrifices in terms of transmission power. Random codes are generated from some ensemble, here we consider the possibility of combining two standard paradigms, sparsely and densely spread codes, in a single composite code ensemble. The composite code analysis includes a replica symmetric calculation of performance in the large system limit, and investigation of finite systems through a composite belief propagation algorithm. A variety of codes are examined with a focus on the high multi-access interference regime. In both the large size limit and finite systems we demonstrate scenarios in which the composite code has typical performance exceeding sparse and dense codes at equivalent signal to noise ratio.Comment: 23 pages, 11 figures, Sigma Phi 2008 conference submission - submitted to J.Stat.Mec

Veni Vidi Dixi: Reliable Wireless Communication with Depth Images

The upcoming industrial revolution requires deployment of critical wireless sensor networks for automation and monitoring purposes. However, the reliability of the wireless communication is rendered unpredictable by mobile elements in the communication environment such as humans or mobile robots which lead to dynamically changing radio environments. Changes in the wireless channel can be monitored with frequent pilot transmission. However, that would stress the battery life of sensors. In this work a new wireless channel estimation technique, Veni Vidi Dixi, VVD, is proposed. VVD leverages the redundant information in depth images obtained from the surveillance cameras in the communication environment and utilizes Convolutional Neural Networks CNNs to map the depth images of the communication environment to complex wireless channel estimations. VVD increases the wireless communication reliability without the need for frequent pilot transmission and with no additional complexity on the receiver. The proposed method is tested by conducting measurements in an indoor environment with a single mobile human. Up to authors best knowledge our work is the first to obtain complex wireless channel estimation from only depth images without any pilot transmission. The collected wireless trace, depth images and codes are publicly available.Comment: Accepted for publication in CoNext 2019 with reproducibility badges. The measurements and the processing codes are available at https://gitlab.lrz.de/lkn_measurements/vvd_measurements for your evaluatio

Theory of Light Emission in Sonoluminescence as Thermal Radiation

Based on the model proposed by Hilgenfeldt {\it at al.} [Nature {\bf 398}, 401 (1999)], we present here a comprehensive theory of thermal radiation in single-bubble sonoluminescence (SBSL). We first invoke the generalized Kirchhoff's law to obtain the thermal emissivity from the absorption cross-section of a multilayered sphere (MLS). A sonoluminescing bubble, whose internal structure is determined from hydrodynamic simulations, is then modelled as a MLS and in turn the thermal radiation is evaluated. Numerical results obtained from simulations for argon bubbles show that our theory successfully captures the major features observed in SBSL experiments.Comment: 17 pages, 20 figure