Provenance and recycling of Sahara Desert sand

We here present the first comprehensive provenance study of the Sahara Desert using a combination of multiple provenance proxies and state-of-the-art statistical analysis. Our dataset comprises 44 aeolian-dune samples, collected across the region from 12°N (Nigeria) to 34°N (Tunisia) and from 33°E (Egypt) to 16°W (Mauritania) and characterized by bulk-petrography, heavy-mineral, and detrital-zircon Usingle bondPb geochronology analyses. A set of statistical tools including Multidimensional Scaling, Correspondence Analysis, Individual Difference Scaling, and General Procrustes Analysis was applied to discriminate among sample groups with the purpose to reveal meaningful compositional patterns and infer sediment transport pathways on a geological scale. The overall homogenity across sand samples, however, precluded a detailed narrative. Saharan dune fields are, with a few local exceptions, composed of pure quartzose sand with very poor heavy-mineral suites dominated by durable zircon, tourmaline, and rutile. Some feldspars, amphibole, epidote, garnet, or staurolite occur closer to basement exposures, and carbonate grains, clinopyroxene and olivine near a basaltic field in Libya. Relatively varied compositions also characterize sand along the Nile Valley and the southern front of the Anti-Atlas fold belt in Morocco. Otherwise, from the Sahel to the Mediterranean Sea and from the Nile River to the Atlantic Ocean, sand consists nearly exclusively of quartz and durable minerals. These have been concentrated through multiple cycles of erosion, deposition, and diagenesis of Phanerozoic siliciclastic rocks during the long period of relative tectonic quiescence that followed the Neoproterozoic Pan-African orogeny, the last episode of major crustal growth in the region. The principal ultimate source of recycled sand is held to be represented by the thick blanket of quartz-rich sandstones that were deposited in the Cambro-Ordovician from the newly formed Arabian-Nubian Shield in the east to Mauritania in the west. Durability of zircon grains and their likelihood to be recycled from older sedimentary rocks argues against the assumption, too often implicitly taken for granted in provenance studies based on detrital-zircon ages, that their age distribution reflects transport pathways existing at the time of deposition rather than inheritance from multiple and remote landscapes of the past

Representations of the Canonical group, (the semi-direct product of the Unitary and Weyl-Heisenberg groups), acting as a dynamical group on noncommuting extended phase space

The unitary irreducible representations of the covering group of the Poincare group P define the framework for much of particle physics on the physical Minkowski space P/L, where L is the Lorentz group. While extraordinarily successful, it does not provide a large enough group of symmetries to encompass observed particles with a SU(3) classification. Born proposed the reciprocity principle that states physics must be invariant under the reciprocity transform that is heuristically {t,e,q,p}->{t,e,p,-q} where {t,e,q,p} are the time, energy, position, and momentum degrees of freedom. This implies that there is reciprocally conjugate relativity principle such that the rates of change of momentum must be bounded by b, where b is a universal constant. The appropriate group of dynamical symmetries that embodies this is the Canonical group C(1,3) = U(1,3) *s H(1,3) and in this theory the non-commuting space Q= C(1,3)/ SU(1,3) is the physical quantum space endowed with a metric that is the second Casimir invariant of the Canonical group, T^2 + E^2 - Q^2/c^2-P^2/b^2 +(2h I/bc)(Y/bc -2) where {T,E,Q,P,I,Y} are the generators of the algebra of Os(1,3). The idea is to study the representations of the Canonical dynamical group using Mackey's theory to determine whether the representations can encompass the spectrum of particle states. The unitary irreducible representations of the Canonical group contain a direct product term that is a representation of U(1,3) that Kalman has studied as a dynamical group for hadrons. The U(1,3) representations contain discrete series that may be decomposed into infinite ladders where the rungs are representations of U(3) (finite dimensional) or C(2) (with degenerate U(1)* SU(2) finite dimensional representations) corresponding to the rest or null frames.Comment: 25 pages; V2.3, PDF (Mathematica 4.1 source removed due to technical problems); Submitted to J.Phys.

Targeting the choroid plexus-CSF-brain nexus using peptides identified by phage display.

Drug delivery to the central nervous system requires the use of specific portals to enable drug entry into the brain and, as such, there is a growing need to identify processes that can enable drug transfer across both blood-brain and blood-cerebrospinal fluid barriers. Phage display is a powerful combinatorial technique that identifies specific peptides that can confer new activities to inactive particles. Identification of these peptides is directly dependent on the specific screening strategies used for their selection and retrieval. This chapter describes three selection strategies, which can be used to identify peptides that target the choroid plexus (CP) directly or for drug translocation across the CP and into cerebrospinal fluid

Static solitons with non-zero Hopf number

We investigate a generalized non-linear O(3) $\sigma$-model in three space dimensions where the fields are maps $S^3 \mapsto S^2$. Such maps are classified by a homotopy invariant called the Hopf number which takes integer values. The model exhibits soliton solutions of closed vortex type which have a lower topological bound on their energies. We explicitly compute the fields for topological charge 1 and 2 and discuss their shapes and binding energies. The effect of an additional potential term is considered and an approximation is given for the spectrum of slowly rotating solitons.Comment: 13 pages, RevTeX, 7 Postscript figures, minor changes have been made, a reference has been corrected and a figure replace

Targeting choroid plexus epithelia and ventricular ependyma for drug delivery to the central nervous system

Background: Because the choroid plexus (CP) is uniquely suited to control the composition of cerebrospinal fluid (CSF), there may be therapeutic benefits to increasing the levels of biologically active proteins in CSF to modulate central nervous system (CNS) functions. To this end, we sought to identify peptides capable of ligand-mediated targeting to CP epithelial cells reasoning that they could be exploited to deliver drugs, biotherapeutics and genes to the CNS.Methods: A peptide library displayed on M13 bacteriophage was screened for ligands capable of internalizing into CP epithelial cells by incubating phage with CP explants for 2 hours at 37C and recovering particles with targeting capacity.Results: Three peptides, identified after four rounds of screening, were analyzed for specific and dose dependant binding and internalization. Binding was deemed specific because internalization was prevented by co-incubation with cognate synthetic peptides. Furthermore, after i.c.v. injection into rat brains, each peptide was found to target phage to epithelial cells in CP and to ependyma lining the ventricles.Conclusion: These data demonstrate that ligand-mediated targeting can be used as a strategy for drug delivery to the central nervous system and opens the possibility of using the choroid plexus as a portal of entry into the brain