Phase behavior of grafted chain molecules: Influence of head size and chain length

Constant pressure Monte Carlo simulations of a coarse grained off-lattice model for monolayers of amphiphilic molecules at the air/water interface are presented. Our study focusses on phase transitions within a monolayer rather than on self aggregation. We thus model the molecules as stiff chains of Lennard-Jones spheres with one slightly larger repulsive end bead (head) grafted to a planar surface. Depending on the size of the head, the temperature and the pressure, we find a variety of phases, which differ in tilt order (including tilt direction), and in positional order. In particular, we observe a modulated phase with a striped superstructure. The modulation results from the competition between two length scales, the head size and the tail diameter. As this mechanism is fairly general, it may conceivably also be relevant in experimental monolayers. We argue that the superstructure would be very difficult to detect in a scattering experiment, which perhaps accounts for the fact that it has not been reported so far. Finally the effect of varying the chain length on the phase diagram is discussed. Except at high pressures and temperatures, the phase boundaries in systems with longer chains are shifted to higher temperatures.Comment: To appear in J. Chem. Phy

Nutritional determinants in the developmental programming of autoimmune diseases - facts and hypotheses

Autoimmune disorders (AID) are a group of debilitating non-communicable chronic diseases (NCDs) affecting the immune system’s capacity to differentiate between foreign and autoantigens. This set of pathologies has experienced a fast-tracked increase in incidence over the last decades. Other types of NCDs, especially the metabolic syndrome, cardiovascular diseases and diabetes have been shown to have their origins in early life, early life nutrition being a key predictor of their occurrence. This observation has opened an entirely new field of research which, today, is known as Developmental Origins of Health and Disease (DOHaD). Literature on AID in adulthood is abundant, however, aside from type 1 diabetes (T1D), research on AID in the context of DOHaD remains relatively scarce. Due to the prevalence of AID in modern society and the public health challenge it represents in numerous countries, this review will 1) present the state of the literature to explore mechanisms that link perinatal nutrition to the development of autoimmunity in later life, and 2) build hypotheses for the purpose of future research in the domain of nutritional programming of AID. Its purpose is to provide an oversight primarily for an audience of early-career researchers and practitioners who have an interest in the subject and who might find it useful to develop and test hypotheses of their own. It should also be clarified that this review does not test the cited hypotheses. Rather, the purpose of this review is to attempt to answer the following question: Given the state of the literature on the development of the immune system, as well as on pre-and post-natal nutrition, what can be said to be the nutritional determinants in the developmental programming of autoimmune disorders (AID)

Discretely exact derivatives for hyperbolic PDE-constrained optimization problems discretized by the discontinuous Galerkin method

This paper discusses the computation of derivatives for optimization problems governed by linear hyperbolic systems of partial differential equations (PDEs) that are discretized by the discontinuous Galerkin (dG) method. An efficient and accurate computation of these derivatives is important, for instance, in inverse problems and optimal control problems. This computation is usually based on an adjoint PDE system, and the question addressed in this paper is how the discretization of this adjoint system should relate to the dG discretization of the hyperbolic state equation. Adjoint-based derivatives can either be computed before or after discretization; these two options are often referred to as the optimize-then-discretize and discretize-then-optimize approaches. We discuss the relation between these two options for dG discretizations in space and Runge-Kutta time integration. Discretely exact discretizations for several hyperbolic optimization problems are derived, including the advection equation, Maxwell's equations and the coupled elastic-acoustic wave equation. We find that the discrete adjoint equation inherits a natural dG discretization from the discretization of the state equation and that the expressions for the discretely exact gradient often have to take into account contributions from element faces. For the coupled elastic-acoustic wave equation, the correctness and accuracy of our derivative expressions are illustrated by comparisons with finite difference gradients. The results show that a straightforward discretization of the continuous gradient differs from the discretely exact gradient, and thus is not consistent with the discretized objective. This inconsistency may cause difficulties in the convergence of gradient based algorithms for solving optimization problems

Protection of personal information Act No. 4 of 2013: Implications for biobanks

The Protection of Personal Information Act (POPIA) No. 4 of 2013 is the first comprehensive data-protection regulation to be passed in South Africa (SA). Its objectives include giving effect to the constitutional right to privacy by regulating the way in which personal information must be processed, balancing the right to privacy against other rights, and establishing an Information Regulator to ensure that the rights protected by POPIA are respected. POPIA will have an impact on health research, including biobanks. As sharing of samples and data is a central feature of biobanks, POPIA could change the way in which data are obtained, shared and exported. In particular, the provisions regarding data minimisation, requirements pertaining to the transfer of data abroad, consent provisions and identification of the 'responsible person' will impact the operation of biobanks in SA. With POPIA soon to come into force, it is now time to consider its implications for biobanks in SA

Integrated Vertical Bloch Line (VBL) memory

Vertical Bloch Line (VBL) Memory is a recently conceived, integrated, solid state, block access, VLSI memory which offers the potential of 1 Gbit/sq cm areal storage density, data rates of hundreds of megabits/sec, and submillisecond average access time simultaneously at relatively low mass, volume, and power values when compared to alternative technologies. VBLs are micromagnetic structures within magnetic domain walls which can be manipulated using magnetic fields from integrated conductors. The presence or absence of BVL pairs are used to store binary information. At present, efforts are being directed at developing a single chip memory using 25 Mbit/sq cm technology in magnetic garnet material which integrates, at a single operating point, the writing, storage, reading, and amplification functions needed in a memory. The current design architecture, functional elements, and supercomputer simulation results are described which are used to assist the design process

Axisymmetric Dynamic Response of Spherical and Cylindrical Shells

Axisymmetric dynamic response of spherical and cylindrical shell

Non-volatile, high density, high speed, Micromagnet-Hall effect Random Access Memory (MHRAM)

The micromagnetic Hall effect random access memory (MHRAM) has the potential of replacing ROMs, EPROMs, EEPROMs, and SRAMs because of its ability to achieve non-volatility, radiation hardness, high density, and fast access times, simultaneously. Information is stored magnetically in small magnetic elements (micromagnets), allowing unlimited data retention time, unlimited numbers of rewrite cycles, and inherent radiation hardness and SEU immunity, making the MHRAM suitable for ground based as well as spaceflight applications. The MHRAM device design is not affected by areal property fluctuations in the micromagnet, so high operating margins and high yield can be achieved in large scale integrated circuit (IC) fabrication. The MHRAM has short access times (less than 100 nsec). Write access time is short because on-chip transistors are used to gate current quickly, and magnetization reversal in the micromagnet can occur in a matter of a few nanoseconds. Read access time is short because the high electron mobility sensor (InAs or InSb) produces a large signal voltage in response to the fringing magnetic field from the micromagnet. High storage density is achieved since a unit cell consists only of two transistors and one micromagnet Hall effect element. By comparison, a DRAM unit cell has one transistor and one capacitor, and a SRAM unit cell has six transistors