Tuning the electronic transport properties of graphene through functionalisation with fluorine

Engineering the electronic properties of graphene has triggered great interest for potential applications in electronics and opto-electronics. Here we demonstrate the possibility to tune the electronic transport properties of graphene monolayers and multilayers by functionalisation with fluorine. We show that by adjusting the fluorine content different electronic transport regimes can be accessed. For monolayer samples, with increasing the fluorine content, we observe a transition from electronic transport through Mott variable range hopping in two dimensions to Efros - Shklovskii variable range hopping. Multilayer fluorinated graphene with high concentration of fluorine show two-dimensional Mott variable range hopping transport, whereas CF0.28 multilayer flakes have a band gap of 0.25eV and exhibit thermally activated transport. Our experimental findings demonstrate that the ability to control the degree of functionalisation of graphene is instrumental to engineer different electronic properties in graphene materials.Comment: 6 pages, 5 figure

Properties of Phase transitions of a Higher Order

The following is a thermodynamic analysis of a III order (and some aspects of a IV order) phase transition. Such a transition can occur in a superconductor if the normal state is a diamagnet. The equation for a phase boundary in an H-T (H is the magnetic field, T, the temperature) plane is derived. by considering two possible forms of the gradient energy, it is possible to construct a field theory which describes a III or a IV order transition and permits a study of thermal fluctuations and inhomogeneous order parameters.Comment: 13 pages, revtex, no figure

Higher Spin BRS Cohomology of Supersymmetric Chiral Matter in D=4

We examine the BRS cohomology of chiral matter in $N=1$, $D=4$ supersymmetry to determine a general form of composite superfield operators which can suffer from supersymmetry anomalies. Composite superfield operators \Y_{(a,b)} are products of the elementary chiral superfields $S$ and \ov S and the derivative operators D_\a, \ov D_{\dot \b} and \pa_{\a \dot \b}. Such superfields \Y_{(a,b)} can be chosen to have `$a$' symmetrized undotted indices \a_i and `$b$' symmetrized dotted indices \dot \b_j. The result derived here is that each composite superfield \Y_{(a,b)} is subject to potential supersymmetry anomalies if $a-b$ is an odd number, which means that \Y_{(a,b)} is a fermionic superfield.Comment: 15 pages, CPT-TAMU-20/9

Transition to turbulence via spatiotemporal intermittency in one-dimensional Rayleigh-Bénard convection

International audienceRayleigh-Benard convection is studied in quasi-one-dimensional geometries. Fixed and periodic boundary conditions are imposed using a rectangular and an annular cell, respectively. The destabilization process of the homogeneous convective pattern is studied for increasing Rayleigh number A. The first time-dependent behaviors are given by the appearance of coupled oscillators. At larger A values, the spatial breakdown appears through the propagation of spatial defects, which appear to be solitary waves. This spatiotemporal destabilization is followed at higher % by a spatiotem-poral intermittent regime, which corresponds to a dramatic decrease of the spatial coherence and to a mixing of turbulent patches within laminar domains. This last regime is studied within the frame of phase transitions. The statistical analysis evidences a second-order phase transition at least in the rectangular geometry (fixed boundary conditions), while this transition looks imperfect in the annu-lar geometry (periodic boundary conditions). Nevertheless, the essential qualitative features shown by theoretical and numerical models are observed in both geometries. Comparison with a simple model of directed percolation shows that the imperfect nature of the transition in the annulus could be the consequence of some mechanism of self-generation of the turbulent domains. This mechanism is, however, unknown but is probably related to the influence of the boundaries

Relationship between clustering and algorithmic phase transitions in the random k-XORSAT model and its NP-complete extensions

We study the performances of stochastic heuristic search algorithms on Uniquely Extendible Constraint Satisfaction Problems with random inputs. We show that, for any heuristic preserving the Poissonian nature of the underlying instance, the (heuristic-dependent) largest ratio $\alpha_a$ of constraints per variables for which a search algorithm is likely to find solutions is smaller than the critical ratio $\alpha_d$ above which solutions are clustered and highly correlated. In addition we show that the clustering ratio can be reached when the number k of variables per constraints goes to infinity by the so-called Generalized Unit Clause heuristic.Comment: 15 pages, 4 figures, Proceedings of the International Workshop on Statistical-Mechanical Informatics, September 16-19, 2007, Kyoto, Japan; some imprecisions in the previous version have been correcte

Minorities, immigrants and HIV/AIDS epidemiology: Concerns about the use and quality of data

A European Community concerted action charged with assessing AIDS prevention for migrants and/or ethnic minorities raised the problem of the quality and possibility for misuse of existing HIV and AIDS data. Basing statistics on the number of foreigners in a country is problematical as numbers are affected by variations in definitions and policies concerning immigration. Categorizing by ethnic origin raises serious definitional problems. For the numerator, epidemiology must be based on AIDS case data since systematic HIV testing of migrants is excluded on both practical and human rights grounds, but there are reasons for both over- and under-reporting of AIDS in migrant groups. Underlying issues of stigmatization and of racism are discussed. While there Is need for improvement in the epidemiological data collected, both planning and evaluation of HIV/AIDS prevention programmes should more reasonably be based on proxy indicators, essentially those of knowledge, attitudes and behaviours, as well as on good ethnographie

Fatal anaphylactic sting reaction in a patient with mastocytosis

We report on a 33-year-old female patient with indolent systemic mastocytosis and urticaria pigmentosa who died of an anaphylactic reaction after a yellow jacket sting. As she had no history of previous anaphylactic sting reaction, there was no testing performed in order to detect hymenoptera venom sensitization. But even if a sensitization had been diagnosed, no venom immunotherapy (VIT) would have been recommended. It is almost certain that VIT would have saved her life and it is most likely that VIT is indicated in some patients with mastocytosis with no history of anaphylactic sting reaction. However, no criteria have been established in order to allow a selection of mastocytosis patients eligible for such a `prophylactic' VIT. Copyright (C) 2008 S. Karger AG, Basel

Fuzzy Surfaces of Genus Zero

A fuzzy version of the ordinary round 2-sphere has been constructed with an invariant curvature. We here consider linear connections on arbitrary fuzzy surfaces of genus zero. We shall find as before that they are more or less rigidly dependent on the differential calculus used but that a large number of the latter can be constructed which are not covariant under the action of the rotation group. For technical reasons we have been forced to limit our considerations to fuzzy surfaces which are small perturbations of the fuzzy sphere.Comment: 11 pages, Late