Three-dimensional Binary Superlattices of Oppositely-charged Colloids

We report the equilibrium self-assembly of binary crystals of oppositely-charged colloidal microspheres at high density. By varying the magnitude of the charge on near equal-sized spheres we show that the structure of the binary crystal may be switched between face-centered cubic, cesium chloride and sodium chloride. We interpret these transformations in terms of a competition between entropic and Coulombic forces

Lattice distortion in hcp rare gas solids

The lattice distortion parameter $\delta \equiv c/a-\sqrt{8/3}$ has been calculated as a function of molar volume for the hcp phases of He, Ar, Kr and Xe. Results from both semi-empirical potentials and density functional theory are presented. Our study shows that $\delta$ is negative for helium in the entire pressure range. For Ar, Kr and Xe, however, $\delta$ changes sign from negative to positive as the pressure increases, growing rapidly in magnitude at higher pressures.Comment: Submitted to Low. Temp. Phys., 14 pages, 5 figure

Paediatric biobanking: Dutch experts reflecting on appropriate legal standards for practice

Large sets of data and human specimens, such as blood, tumour tissue and DNA, are deposited in biobanks for research purposes, preferably for long periods of time and with broadly defined research aims. Our research focuses on the retention of data and biological materials obtained from children. However important such paediatric biobanks may be, the privacy interests of the children involved and the related risks may not be ignored. The privacy issues arising from paediatric biobanks are the central focus of this article. We first review the international regulations that apply to biobanks and then summarise viewpoints expressed by experts in a round-table discussion. We confine ourselves here to two normative questions: (1) How much control should children's parents or legal representatives, and later the children themselves, have over the stored materials and data? (2) What should be done if research findings emerge that have serious implications for a child's health? On the basis of international legal standards and the views of experts, involved in paediatric biobanking, we argue that biological material of children may only be stored in a biobank for scientific purposes if parents provide their explicit consent, the child is re-contacted at 16 or 18 years of age to reconsider storage and use of its material, and the biobank maintains a limited policy in disclosure of individual research findings to the child's parents. What is Known: • Increasingly, biological material of children is stored in biobanks for research purposes. • Clear standards on the conditions under which children's cells or tissues may be stored and used are lacking. What is New: • According to experts, storage and use of children's materials should only be allowed if performed in accordance with appropriate consent procedures and feedback policie

Bloeiende Clusters in de Betuwse Bloem, Integratienotitie, Thema’s, schaalniveaus en businesscases

De Betuwe kent een sterke tuinbouwsector dat opgesplitst kan worden in vier tuinbouwsectoren: glastuinbouw (555 ha, Bommelerwaard en Arnhem-Nijmegen), paddenstoelenteelt (15 ha Maasdriel), fruitteelt (5.200 ha, regio Buren/Geldermalsen) en laanboomteelt (1.300 ha, regio Opheusden). Door meer samenwerking, onderling en binnen de tuinbouwketen, willen de clusters hun gezamenlijke economische positie verder versterken. De ambitie is om de tuinbouw in het Rivierengebied op de (inter)nationale kaart zetten. Doorvoor is in 2006 door de provincie Gelderland en de ondernemers uit de verschillende sectoren gezamenlijk het initiatief genomen om samen te werken onder de noemer Greenport Betuwse Bloem. Samen met kennisinstellingen en maatschappelijke organisaties zien zij mogelijkheden om de logistieke kansen, de energiestromen, het hoogwaardige landschap en het kennisnetwerk in het gebied veel beter te benutten dan nu gebeurt. Deze samenwerking moet de winstgevendheid van de tuinbouw versterken en tegelijkertijd een bijdrage leveren aan het behoud van het typerende landschap. Deze notitie geeft handvatten om te komen tot duurzame agroclusters in de Betuwe

The S0_0(0) structure in highly compressed hydrogen and the orientational transition

A calculation of the rotational S$_0$(0) frequencies in high pressure solid para-hydrogen is performed. Convergence of the perturbative series at high density is demonstrated by the calculation of second and third order terms. The results of the theory are compared with the available experimental data to derive the density behaviour of structural parameters. In particular, a strong increase of the value of the lattice constant ratio $c/a$ and of the internuclear distance is determined. Also a decrease of the anisotropic intermolecular potential is observed which is attributed to charge transfer effects. The structural parameters determined at the phase transition may be used to calculate quantum properties of the rotationally ordered phase.Comment: accepted Europhysics Letter

MX100, a new Escherichia coli tester strain for use in genotoxicity studies

The development of a new Escherichia coli tester strain for use in metabolic and mechanistic studies of genotoxins, strain MR2101/pKR11, has recently been reported. This strain, a derivative of the E.coli K12 laboratory strain AB1157, has sensitivity towards the detection of base-substitution mutagenesis, monitored by the reversion of arginine auxotrophy [argE3, (ochre)]. Besides arginine, MR2101/pKR11 is auxotrophic for histidine (hisG4), leucine (leuB6), proline (ΔproA) and threonine (thr-1). MX100 was developed to overcome the auxotrophy for four amino acids of MR2101/pKR11 which are non-essential for the mutagenic responsiveness of the strain. We restored the biosynthesis for these four amino acids in MR2101/pKR11, resulting in strain MX100. This strain showed an almost 2-fold increase in mutagenic activity relative to MR2101/pKR11 with a set of diagnostic mutagens (aflatoxin B1, benzo[α]pyrene, 4-nitroquinoline-1-oxide, 2,7-dimethyl-benz[a]anthracene and others) and was further characterized with other types of mutagens in which it showed sensitivity towards the detection of oxidative (H2O2, t-butyl-hydroperoxide, cumene-hydroperoxide, KO2) and carbonyl mutagens (methylglyoxal, malondialdehyde). As MX100 seems to have the right characteristics of a versatile genotoxicity tester strain and due to the extensive genetic and physiological knowledge of E.coli K12 in general and AB1157 in particular, we propose that MX100 could serve as mother strain for the development of specialized tester strains, of interest in studies of metabolism and/or mechanism of action of genotoxic carcinogens.publishersversionpublishe

Spontaneous Magnetization of the O(3) Ferromagnet at Low Temperatures

We investigate the low-temperature behavior of ferromagnets with a spontaneously broken symmetry O(3) $\to$ O(2). The analysis is performed within the perspective of nonrelativistic effective Lagrangians, where the dynamics of the system is formulated in terms of Goldstone bosons. Unlike in a Lorentz-invariant framework (chiral perturbation theory), where loop graphs are suppressed by two powers of momentum, loops involving ferromagnetic spin waves are suppressed by three momentum powers. The leading coefficients of the low-temperature expansion for the partition function are calculated up to order $p^{10}$. In agreement with Dyson's pioneering microscopic analysis of the cubic ferromagnet, we find that, in the spontaneous magnetization, the magnon-magnon interaction starts manifesting itself only at order $T^4$. The striking difference with respect to the low-temperature properties of the O(3) antiferromagnet is discussed from a unified point of view, relying on the effective Lagrangian technique.Comment: 23 pages, 4 figure

Nanostratification of optical excitation in self-interacting 1D arrays

The major assumption of the Lorentz-Lorenz theory about uniformity of local fields and atomic polarization in dense material does not hold in finite groups of atoms, as we reported earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev. Lett., v. 101, 133902 (2008)]. The uniformity is broken at sub-wavelength scale, where the system may exhibit strong stratification of local field and dipole polarization, with the strata period being much shorter than the incident wavelength. In this paper, we further develop and advance that theory for the most fundamental case of one-dimensional arrays, and study nanoscale excitation of so called "locsitons" and their standing waves (strata) that result in size-related resonances and related large field enhancement in finite arrays of atoms. The locsitons may have a whole spectrum of spatial frequencies, ranging from long waves, to an extent reminiscent of ferromagnetic domains, -- to super-short waves, with neighboring atoms alternating their polarizations, which are reminiscent of antiferromagnetic spin patterns. Of great interest is the new kind of "hybrid" modes of excitation, greatly departing from any magnetic analogies. We also study differences between Ising-like near-neighbor approximation and the case where each atom interacts with all other atoms in the array. We find an infinite number of "exponential eigenmodes" in the lossless system in the latter case. At certain "magic" numbers of atoms in the array, the system may exhibit self-induced (but linear in the field) cancellation of resonant local-field suppression. We also studied nonlinear modes of locsitons and found optical bistability and hysteresis in an infinite array for the simplest modes.Comment: 39 pages, 5 figures; v2: Added the Conclusions section, corrected a typo in Eq. (5.3), corrected minor stylistic and grammatical imperfection

Role of Protein-Protein Interactions in Metabolism: Genetics, Structure, Function

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Equilibrium phase behavior of polydisperse hard spheres

We calculate the phase behavior of hard spheres with size polydispersity, using accurate free energy expressions for the fluid and solid phases. Cloud and shadow curves, which determine the onset of phase coexistence, are found exactly by the moment free energy method, but we also compute the complete phase diagram, taking full account of fractionation effects. In contrast to earlier, simplified treatments we find no point of equal concentration between fluid and solid or re-entrant melting at higher densities. Rather, the fluid cloud curve continues to the largest polydispersity that we study (14%); from the equilibrium phase behavior a terminal polydispersity can thus only be defined for the solid, where we find it to be around 7%. At sufficiently large polydispersity, fractionation into several solid phases can occur, consistent with previous approximate calculations; we find in addition that coexistence of several solids with a fluid phase is also possible