Twisted scroll waves organize Dictyostelium mucoroides slugs

Cellular slime moulds (Dictyosteloids) are characterised by at least two different modes of slug migration. Most species, e.g. Dictyostelium mucoroides, produce a stalk continuously during slug migration, while a few species, e.g. Dictyostelium discoideum are characterised by stalk-less slug migration and only produce a stalk upon culmination. Experiments on D. discoideum and theoretical model calculations have shown that D. discoideum slugs are organized by a cAMP scroll wave in the tip which produces planar waves in the back. These waves guide cell movement in slugs: spiralling in the tip and forward movement parallel to the slug axis in the back. Simple changes in model parameters can lead to the formation of a twisted scroll wave which extends throughout the slug. In order to investigate whether such twisted scroll waves occur naturally we have analysed the movement of fluorescently labelled single cells in migrating D. mucoroides slugs. The results show that cells in the prespore zone of D. mucoroides slugs move in a spiral path. Although the velocity of single cells in D. mucoroides is faster than in D. discoideum, the net forward component of their movement is less due to their spiral trajectories. As a result D. mucoroides slugs move more slowly than D. discoideum slugs. The entire D. mucoroides slug also describes a spiralling path leaving corkscrew shaped stalks behind. Based on these observations we propose that cell movement in D. mucoroides slugs is controlled by a propagating twisted scroll wave of cAMP which extends throughout the length of the slug

Talking with pictures: Exploring the possibilities of iconic communication

As multimedia computing becomes the order of the day, so there is a greater need to understand and to come to terms with the problems of visual presentation. This paper deals with iconic languages as a means of communicating ideas and concepts without words. Two example systems, developed respectively at the universities of Exeter and Brighton, are described. Both embody basic principles of the iconic communication which,, though not unique to learning technology, is forming an increasingly important part of user‐interfaces, including those in the area computer‐assisted learning

Surface anisotropy in nanomagnets: transverse or N\'eel ?

Through the hysteresis loop and magnetization spatial distribution we study and compare two models for surface anisotropy in nanomagnets: a model with transverse anisotropy axes and N\'eel's model. While surface anisotropy in the transverse model induces several jumps in the hysteresis loop because of the cluster-wise switching of spins, in the N\'eel model the jumps correspond to successive {\it coherent partial rotations} of the whole bunch of spins. These calculations together with experimental results suggest that N\'eel's model for surface anisotropy is more appropriate.Comment: 12 pages, 6 eps figure

Magnetization of nanomagnet assemblies: Effects of anisotropy and dipolar interactions

We investigate the effect of anisotropy and weak dipolar interactions on the magnetization of an assembly of nanoparticles with distributed magnetic moments, i.e., assembly of magnetic nanoparticles in the one-spin approximation, with textured or random anisotropy. The magnetization of a free particle is obtained either by a numerical calculation of the partition function or analytically in the low and high field regimes, using perturbation theory and the steepest-descent approximation, respectively. The magnetization of an interacting assembly is computed analytically in the range of low and high field, and numerically using the Monte Carlo technique. Approximate analytical expressions for the assembly magnetization are provided which take account of the dipolar interactions, temperature, magnetic field, and anisotropy. The effect of anisotropy and dipolar interactions are discussed and the deviations from the Langevin law they entail are investigated, and illustrated for realistic assemblies with the lognormal moment distribution.Comment: 21 pages, 5 eps figure

Synthetic Studies on Small Molecule Src Homology 2 Domain Containing Inositol 5’Phosphatase (SHIP) Modulators and Studies towards the Design and Synthesis of a SHIP PROTAC

The PI3K pathway is a biological pathway of great importance to the biomedical community. PI3K and mutations associated with it have often associated as the cause for various disease states due to its role in signaling other enzymes such as AKT. Targeting PI3K is one way to help regulate the PI3K pathway but there are other enzymes such as SHIP that also contribute to the delicate balance of the cell. It has been proposed that the modulation of SHIP could also provide some therapeutic benefit as its behavior opposes that of PI3K. Detailed in this work is the design and synthesis of aminosteroid inhibitors as well as agonist studies involving the optimization of an AQX-1125 analog synthetic route. These inhibitors and agonists may be used further to help analyze the role SHIP plays in certain disease states such as Alzheimer’s Disease. Proteolysis Targeting Chimeras or PROTACs have become a topic of discussion in the biomedical community in recent years. They provide an alternate route of modulating proteins by lowering protein levels in cells as opposed to inhibitor-based strategies. The potential for this strategy to be of therapeutic relevance is immense as it allows for the targeting of proteins and receptors, even ones that do not have enzymatic roles. A proper PROTAC can also incorporate a weak binding inhibitor and still be a potent and selective therapeutic which expands the library of possibilities for protein targets. With these studies, two proposed SHIP based PROTACs were synthesized and made. If proven to degrade SHIP, these molecules could provide valuable knowledge towards the role SHIP plays in disease. These molecules would also be useful in probing the scaffolding role of SHIP which has not been investigated in human disease

Effect of exchange interaction on superparamagnetic relaxation

We use Langer's approach to calculate the reaction rate of a system of two (classical) spins interacting via the exchange coupling $J$ in a magnetic field $H$, with uniaxial anisotropy of constant $K$. We find a particular value of the exchange coupling, that is $j\equiv J/K = j_c\equiv 1-h^2$, where $h\equiv H/2K$, which separates two regimes corresponding to a two-stage and one-stage switching. For $j\gg j_c$ the N\'eel-Brown result for the one-spin problem is recovered.Comment: 7 pages, 2 eps figures, fig.1 of better quality can be provided upon reques