The role of traction in membrane curvature generation.

Curvature of biological membranes can be generated by a variety of molecular mechanisms including protein scaffolding, compositional heterogeneity, and cytoskeletal forces. These mechanisms have the net effect of generating tractions (force per unit length) on the bilayer that are translated into distinct shapes of the membrane. Here, we demonstrate how the local shape of the membrane can be used to infer the traction acting locally on the membrane. We show that buds and tubes, two common membrane deformations studied in trafficking processes, have different traction distributions along the membrane and that these tractions are specific to the molecular mechanism used to generate these shapes. Furthermore, we show that the magnitude of an axial force applied to the membrane as well as that of an effective line tension can be calculated from these tractions. Finally, we consider the sensitivity of these quantities with respect to uncertainties in material properties and follow with a discussion on sources of uncertainty in membrane shape

Non-integrability of density perturbations in the FRW universe

We investigate the evolution equation of linear density perturbations in the Friedmann-Robertson-Walker universe with matter, radiation and the cosmological constant. The concept of solvability by quadratures is defined and used to prove that there are no "closed form" solutions except for the known Chernin, Heath, Meszaros and simple degenerate ones. The analysis is performed applying Kovacic's algorithm. The possibility of the existence of other, more general solutions involving special functions is also investigated.Comment: 13 pages. The latest version with added references, and a relevant new paragraph in section I

Many-body aspects of positron annihilation in the electron gas

We investigate positron annihilation in electron liquid as a case study for many-body theory, in particular the optimized Fermi Hypernetted Chain (FHNC-EL) method. We examine several approximation schemes and show that one has to go up to the most sophisticated implementation of the theory available at the moment in order to get annihilation rates that agree reasonably well with experimental data. Even though there is basically just one number to look at, the electron-positron pair distribution function at zero distance, it is exactly this number that dictates how the full pair distribution behaves: In most cases, it falls off monotonously towards unity as the distance increases. Cases where the electron-positron pair distribution exhibits a dip are precursors to the formation of bound electron--positron pairs. The formation of electron-positron pairs is indicated by a divergence of the FHNC-EL equations, from this we can estimate the density regime where positrons must be localized. This occurs in our calculations in the range 9.4 <= r_s <=10, where r_s is the dimensionless density parameter of the electron liquid.Comment: To appear in Phys. Rev. B (2003

Placing the university: thinking in and beyond globalization

In some respects, the impact of globalization on universities is well rehearsed (competition for international students; the drive for status in global rankings; the opening of overseas campuses; the dream of massive open online courses and other forms of digital education), but the relationship between universities as place-based institutions and globalization is less well understood. It is on that this chapter focuses. Drawing on work undertaken as part of an Economic and Social Research Council project (“Higher Education and Regional Social Transformation”) the author sets the arguments in a wider context. He explores the extent to which and ways in which universities have become key players in the reimagination of their city regions in a (neoliberal) global context. As well as reflecting on the wider public (and local) role of universities, he also considers how universities use the tools available to them to position themselves effectively as successful businesses within the new world in which they find themselves

Rendezvous of Distance-aware Mobile Agents in Unknown Graphs

We study the problem of rendezvous of two mobile agents starting at distinct locations in an unknown graph. The agents have distinct labels and walk in synchronous steps. However the graph is unlabelled and the agents have no means of marking the nodes of the graph and cannot communicate with or see each other until they meet at a node. When the graph is very large we want the time to rendezvous to be independent of the graph size and to depend only on the initial distance between the agents and some local parameters such as the degree of the vertices, and the size of the agent's label. It is well known that even for simple graphs of degree $\Delta$, the rendezvous time can be exponential in $\Delta$ in the worst case. In this paper, we introduce a new version of the rendezvous problem where the agents are equipped with a device that measures its distance to the other agent after every step. We show that these \emph{distance-aware} agents are able to rendezvous in any unknown graph, in time polynomial in all the local parameters such the degree of the nodes, the initial distance $D$ and the size of the smaller of the two agent labels $l = \min(l_1, l_2)$. Our algorithm has a time complexity of $O(\Delta(D+\log{l}))$ and we show an almost matching lower bound of $\Omega(\Delta(D+\log{l}/\log{\Delta}))$ on the time complexity of any rendezvous algorithm in our scenario. Further, this lower bound extends existing lower bounds for the general rendezvous problem without distance awareness

Low-temperature thermal conductivity of solid carbon dioxide

Preliminary results of the thermal conductivity measurements performed in the temperature range 1.5-35 K on pure carbon dioxide are presented. The data below 25 K have been obtained for the first time. The thermal conductivity coefficient reaches very high value, of about 700 W/(m×K), unusual for simple molecular crystal. Straightforward analysis applied to the data indicates the case of large-grained sample

The peculiarities of heat transfer in CO₂ and N₂O solids at low temperatures

The thermal conductivities of CO₂ and N₂O solids have been investigated in the low-temperature range 1–40 K. The thermal conductivities of CO₂ and N₂O are large compared with those of simple molecular crystals such as N₂, CO, or O₂ in the whole investigated temperature range. Analysis of the experimental data by the Callaway method shows that relatively large size of crystalline grains, low density of dislocations and weak phonon–phonon interaction might be the reasons for the good thermal conduction in these crystals at temperatures near the maxima. A comparison between calculated values of the intensity of normal phonon scattering processes and experiment gives evidence that in N₂O there is an additional (in comparison with CO₂) giant scattering of phonons. This scattering is described in the frameworks of soft potential model by the resonance phonon scattering on tunnel states and low-energy vibratons

Thermal properties of Ti-doped Cu-Zn soft ferrites used as thermally actuated material for magnetizing superconductors

A great majority of widely used ferrite ceramics exhibit a relatively high temperature of order–disorder phase transition in their magnetic subsystem. For applications related to the magnetization process of superconductors, however, a low value of T c is required. Here we report and analyze in detail the thermal properties of bulk Ti-doped Cu–Zn ferrite ceramics Cu0.3Zn0.7Ti0.04Fe1.96O4 and Mg0.15Cu0.15Zn0.7Ti0.04Fe1.96O4. They are characterized by a Curie temperature in the range 120–170 K and a maximum DC magnetic susceptibility exceeding 20 for the Cu0.3Zn0.7Ti0.04Fe1.96O4 material. The temperature dependence of both the specific heat C p and of the thermal conductivity κ, determined between 2 and 300 K, are found not to exhibit any peculiar feature at the magnetic transition temperature. The low-temperature dependence of both κ and the mean free path of phonons suggests a mesoscopic fractal structure of the grains. From the measured data, the characteristics of thermally actuated waves are estimated. The low magnetic phase transition temperature and suitable thermal parameters make the investigated ferrite ceramics applicable as magnetic wave producers in devices designed for magnetization of high-temperature superconductors.We thank the University of Liège (ULg) and the Ministry of Higher Education of Communauté Française de Belgique for a research grant Action de Recherches Concertées (ARC 11/16-03). We thank Alexander Krivchikov for fruitful discussions and Oksana Mendiuk for taking SEM images. This work is part of a collaboration programme between the FRS-FNRS (Belgium) and the PAS (Polish Academy of Sciences).This is the author accepted manuscript. The final version is available from the Institute of Physics via http://dx.doi.org/10.1088/0022-3727/49/12/12500

The influence of the disordered dipole subsystem on the thermal conductivity of the CO solid at low temperatures

The thermal conductivity of solid CO was investigated in the temperature range 1–20 K. The experimental temperature dependence of thermal conductivity of solid CO was described using the time-relaxation method within the Debye model. The comparison of the experimental temperature dependences of the thermal conductivity of N₂ and CO shows that in the case of CO there is an additional large phonon scattering at temperatures near the maximum. The analysis of the experimental data indicates that this scattering is caused by the frozen disordered dipole subsystem similar to a dipole glass. The scattering is described by the resonant phonon scattering on tunnelling states and on low-energy quasi-harmonic oscillations within the soft potential model