Interaction of strangelets with ordinary nuclei

Strangelets (hypothetical stable lumps of strange quarkmatter) of astrophysical origin may be ultimately detected in specific cosmic ray experiments. The initial mass distribution resulting from the possible astrophysical production sites would be subject to reprocessing in the interstellar medium and in the earth`s atmosphere. In order to get a better understanding of the claims for the detection of this still hypothetic state of hadronic matter, we present a study of strangelet-nucleus interactions including several physical processes of interest (abrasion, fusion, fission, excitation and de-excitation of the strangelets), to address the fate of the baryon number along the strangelet path. It is shown that, although fusion may be important for low-energy strangelets in the interstellar medium (thus increasing the initial baryon number A), in the earth`s atmosphere the loss of the baryon number should be the dominant process. The consequences of these findings are briefly addressed.

Role of alpha 7 Nicotinic Acetylcholine Receptor in Calcium Signaling Induced by Prion Protein Interaction with Stress-inducible Protein 1

The prion protein (PrP(C)) is a conserved glycosylphosphatidyl-inositol-anchored cell surface protein expressed by neurons and other cells. Stress-inducible protein 1 (STI1) binds PrP(C) extracellularly, and this activated signaling complex promotes neuronal differentiation and neuroprotection via the extracellular signal-regulated kinase 1 and 2 (ERK1/2) and cAMP-dependent protein kinase 1 (PKA) pathways. However, the mechanism by which the PrPC-STI1 interaction transduces extracellular signals to the intracellular environment is unknown. We found that in hippocampal neurons, STI1-PrP(C) engagement induces an increase in intracellular Ca(2+) levels. This effect was not detected in PrP(C)-null neurons or wild-type neurons treated with an STI1 mutant unable to bind PrP(C). Using a best candidate approach to test for potential channels involved in Ca(2+) influx evoked by STI1-PrP(C), we found that alpha-bungarotoxin, a specific inhibitor for alpha 7 nicotinic acetylcholine receptor (alpha 7nAChR), was able to block PrP(C)-STI1-mediated signaling, neuroprotection, and neuritogenesis. Importantly, when alpha 7nAChR was transfected into HEK 293 cells, it formed a functional complex with PrP(C) and allowed reconstitution of signaling by PrP(C)-STI1 interaction. These results indicate that STI1 can interact with the PrP(C).alpha 7nAChR complex to promote signaling and provide a novel potential target for modulation of the effects of prion protein in neurodegenerative diseases.

Formulation of the standard model in terms of spinor fields

We propose an alternative formulation of the Standard Model which reduces the number of free parameters. In our framework, fermionic fields are assigned to fundamental representations of the Lorentz and the internal symmetry groups, whereas bosonic field variables transform as direct products of fundamental representations of all symmetry groups. This allows us to reduce the number of fundamental symmetries. We formulate the Standard Model by considering the SU(3) and SU(2) symmetry groups as the underlying symmetries of the fundamental interactions. This allows us to suggest a model, for the description of the interactions of the intermediate bosons among themselves and interactions of fermions, that makes use of just two parameters. One parameter characterizes the symmetric phase, whereas the other parameter (the asymmetry parameter) gives the breakdown strength of the symmetries. All coupling strengths of the Standard Model are then derived in terms of these two parameters. In particular, we show that all fermionic electric charges result from symmetry breakdown.

A model for the stabilization of atomic hydrogen centers in borate glasses

A previously proposed model describing the trapping site of the interstitial atomic hydrogen in borate glasses is analyzed. In this model the atomic hydrogen is stabilized at the centers of oxygen polygons belonging to B-O ring structures in the glass network by van der Waals forces. The previously reported atomic hydrogen isothermal decay experimental data are discussed in the light of this microscopic model. A coupled differential equation system of the observed decay kinetics was solved numerically using the Runge Kutta method. The experimental untrapping activation energy of 0.7 x 10(-19) J is in good agreement with the calculated results of dispersion interaction between the stabilized atomic hydrogen and the neighboring oxygen atoms at the vertices of hexagonal ring structures. (C) 2009 Elsevier B.V. All rights reserved.

On the interaction of the anthraquinone barbaloin with negatively charged DMPG bilayers

Barbaloin is a bioactive glycosilated 1,8-dihydroxyanthraquinone present in several exudates from plants, Such as Aloe vera, which are used for cosmetic or food purposes. It has been shown that barbaloin interacts with DMPG (dimyristoylphosphatidylglycerol) model membranes, altering the bilayer structure (Alves, D. S.; Perez-Fons, L.; Estepa, A.; Micol, V. Biochem. Pharm. 2004, 68, 549). Considering that ESR (electron spin resonance) of spin labels is one of the best techniques to monitor structural properties at the molecular level, the alterations caused by the anthraquinone barbaloin on phospholipid bilayers will be discussed here via the ESR signal of phospholipid spin probes intercalated into the membranes. In DMPG at high ionic strength (10 mM Hepes pH 7.4 + 100 mM NaCl), a system that presents a gel-fluid transition around 23 degrees C, 20 mol % barbaloin turns the gel phase more rigid, does not alter much the fluid phase packing, but makes the lipid thermal transition less sharp. However, in a low-salt DMPG dispersion (10 mM Hepes pH 7.4 + 2 mM NaCl), which presents a rather complex gel-fluid thermal transition (Lamy-Freund, M. T.; Riske, K. A. Chem. Phys. Lipids 2003, 122, 19), barbaloin strongly affects bilayer structural properties, both in the gel and fluid phases, extending the transition region to much higher temperature values. The position of barbaloin in DMPG bilayers will be discussed on the basis of ESR results, in parallel with data from sample viscosity, DSC (differential scanning calorimetry), and SAXS (small-angle X-ray scattering).

Signature of the interaction between dark energy and dark matter in galaxy clusters

We investigate the influence of ail interaction between dark energy and dark matter upon the dynamics of galaxy clusters. We obtain file general Layser-Irvine equation in the presence of interactions, and find how, in that case. the virial theorem stands corrected. Using optical, X-ray and weak lensing data from 33 relaxed galaxy clusters, we put constraints on the strength of the coupling between the dark sectors. Available data Suggests that this coupling is small but positive, indicating that dark energy might be decaying into dark matter. Systematic effects between the several mass estimates, however, should be better known, before definitive conclusions oil the magnitude and significance of this coupling could be established. (C) 2009 Published by Elsevier B.V.

On S-matrix factorization of the Landau-Lifshitz model

We consider the three-particle scattering S-matrix for the Landau-Lifshitz model by directly computing the set of the Feynman diagrams up to the second order. We show, following the analogous computations for the non-linear Schrdinger model [1, 2], that the three-particle S-matrix is factorizable in the first non-trivial order.

Effects of confinement on the electron-phonon interaction in Al(0.18)Ga(0.82)As/GaAs quantum wells

Photoluminescence measurements at different temperatures have been performed to investigate the effects of confinement on the electron-phonon interaction in GaAs/AlGaAs quantum wells (QWs). A series of samples with different well widths in the range from 150 up to 750 A was analyzed. Using a fitting procedure based on the Passler-p model to describe the temperature dependence of the exciton recombination energy, we determined a fit parameter which is related to the strength of the electron-phonon interaction. On the basis of the behavior of this fit parameter as a function of the well width thickness of the samples investigated, we verified that effects of confinement on the exciton recombination energy are still present in QWs with well widths as large as 450 angstrom. Our findings also show that the electron-phonon interaction is three times stronger in GaAs bulk material than in Al(0.18)Ga(0.82)As/GaAs QWs.

Observational constraints on holographic tachyonic dark energy in interaction with dark matter

We discuss an interacting tachyonic dark energy model in the context of the holographic principle. The potential of the holographic tachyon field in interaction with dark matter is constructed. The model results are compared with CMB shift parameter, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. The coupling constant of the model is compatible with zero, but dark energy is not given by a cosmological constant.

The interaction of an antiparasitic peptide active against African Sleeping Sickness with cell membrane models

Zwitterionic peptides with trypanocidal activity are promising lead compounds for the treatment of African Sleeping Sickness, and have motivated research into the design of compounds capable of disrupting the protozoan membrane. In this study, we use the Langmuir monolayer technique to investigate the surface properties of an antiparasitic peptide, namely S-(2,4-dinitrophenyl)glutathione di-2-propyl ester, and its interaction with a model membrane comprising a phospholipid monolayer. The drug formed stable Langmuir monolayers. whose main feature was a phase transition accompanied by a negative surface elasticity. This was attributed to aggregation upon compression due to intermolecular bond associations of the molecules, inferred from surface pressure and surface potential isotherms. Brewster angle microscopy (BAM) images, infrared spectroscopy and dynamic elasticity measurements. When co-spread with dipalmitoyl phosphatidyl choline (DPPC). the drug affected both the surface pressure and the monolayer morphology, even at high surface pressures and with low amounts of the drug. The results were interpreted by assuming a repulsive, cooperative interaction between the drug and DPPC molecules. Such repulsive interaction and the large changes in fluidity arising from drug aggregation may be related to the disruption of the membrane, which is key for the parasite killing property. (C) 2009 Elsevier B.V. All rights reserved.

The lipid composition of a cell membrane modulates the interaction of an antiparasitic peptide at the air-water interface

The antiparasitic property of peptides is believed to be associated with their interactions with the protozoan membrane, which calls for research on the identification of membrane sites capable of peptide binding. In this study we investigated the interaction of a lipophilicglutathioine peptide known to be effective against the African Sleeping Sickness (ASS - African Trypanosomiasis) and cell membrane models represented by Langmuir monolayers. It is shown that even small amounts of the peptide affect the monolayers of some phospholipids and other lipids, which points to a significant interaction. The latter did not depend on the electrical charge of the monolayer-forming molecules but the peptide action was particularly distinctive for cholesterol + sphingomyelin monolayers that roughly resemble rafts on a cell membrane. Using in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we found that the orientation of the peptide is affected by the phospholipids and dioctadecyldimethylammonium bromide (DODAB), but not in monolayers comprising cholesterol + sphingomyelin. In this mixed monolayer resembling rafts, the peptide still interacts and has some induced order, probably because the peptide molecules are fitted together into a compact monolayer. Therefore, the lipid composition of the monolayer modulates the interaction with the lipophilic glutathioine peptide, and this may have important implications in understanding how the peptide acts on specific sites of the protozoan membrane. (C) 2011 Elsevier B.V. All rights reserved.

Interaction of polysaccharide-protein complex from Agaricus blazei with Langmuir and Langmuir-Blodgett films of phospholipids

The use of natural substances in health applications may be hampered by the difficulties in establishing the mechanisms of action, especially at molecular-level. The protein-polysaccharide complex extracted from the mushroom Agaricus blazei Murill, referred to as CAb, has been considered for treating various diseases with probable interaction with cell membranes. In this study, we investigate the interaction between CAb and a cell membrane model represented by a Langmuir monolayer of dimyristoyl phosphatidic acid (DMPA). CAb affects the structural properties of DMPA monolayers causing expansion and increasing compressibility. In addition, interaction with DMPA polar heads led to neutralization of the electrical double layer, yielding a zero surface potential at large areas per molecule. CAb remained at the interface even at high surface pressures, which allowed transfer of Langmuir-Blodgett (LB) films onto solid supports with the CAb-DMPA mixture. The mass transferred, according to quartz crystal microbalance (QCM) measurements, increased linearly with the number of deposited layers. With UV-vis absorption, fluorescence and FTIR spectroscopies, we confirmed that the LB films contain polysaccharides, proteins and DMPA. Therefore, the CAb biological action must be attributed not only to polysaccharides but also to proteins in the complex. (C) 2008 Elsevier Inc. All rights reserved.

Exact vortex solutions in a CP(N) Skyrme-Faddeev type model

We consider a four dimensional field theory with target space being CP(N) which constitutes a generalization of the usual Skyrme-Faddeev model defined on CP(1). We show that it possesses an integrable sector presenting an infinite number of local conservation laws, which are associated to the hidden symmetries of the zero curvature representation of the theory in loop space. We construct an infinite class of exact solutions for that integrable submodel where the fields are meromorphic functions of the combinations (x(1) + i x(2)) and (x(3) + x(0)) of the Cartesian coordinates of four dimensional Minkowski space-time. Among those solutions we have static vortices and also vortices with waves traveling along them with the speed of light. The energy per unity of length of the vortices show an interesting and intricate interaction among the vortices and waves.

Interaction of oligonucleotide-based amphiphilic block copolymers with cell membrane models

Oligonucleotides have unique molecular recognition properties, being involved in biological mechanisms such as cell-surface receptor recognition or gene silencing. For their use in human therapy for drug or gene delivery, the cell membrane remains a barrier, but this can be obviated by grafting a hydrophobic tail to the oligonucleotide. Here we demonstrate that two oligonucleotides, one consisting of 12 guanosine units (G(12)), and the other one consisting of five adenosine and seven guanosine (A(5)G(7)) units, when functionalized with poly(butadiene), namely PB-G(12) and PB-A(5)G(7), can be inserted into Langmuir monolayers of dipalmitoyl phosphatidyl choline (DPPC), which served as a cell membrane model. PB-G(12) and PB-A(5)G(7) were found to affect the DPPC monolayer even at high surface pressures. The effects from PB-G(12) were consistently stronger, particularly in reducing the elasticity of the DPPC monolayers, which may have important biological implications. Multilayers of DPPC and nucleotide-based copolymers could be adsorbed onto solid supports, in the form of Y-type LB films, in which the molecular-level interaction led to lower energies in the vibrational spectra of the nucleotide-based copolymers. This successful deposition of solid films opens the way for devices to be produced which exploit the molecular recognition properties of the nucleotides. (C) 2010 Elsevier Inc. All rights reserved.

The double Caldeira-Leggett model: Derivation and solutions of the master equations, reservoir-induced interactions and decoherence

In this paper we analyze the double Caldeira-Leggett model: the path integral approach to two interacting dissipative harmonic oscillators. Assuming a general form of the interaction between the oscillators, we consider two different situations: (i) when each oscillator is coupled to its own reservoir, and (ii) when both oscillators are coupled to a common reservoir. After deriving and solving the master equation for each case, we analyze the decoherence process of particular entanglements in the positional space of both oscillators. To analyze the decoherence mechanism we have derived a general decay function, for the off-diagonal peaks of the density matrix, which applies both to common and separate reservoirs. We have also identified the expected interaction between the two dissipative oscillators induced by their common reservoir. Such a reservoir-induced interaction, which gives rise to interesting collective damping effects, such as the emergence of relaxation- and decoherence-free subspaces, is shown to be blurred by the high-temperature regime considered in this study. However, we find that different interactions between the dissipative oscillators, described by rotating or counter-rotating terms, result in different decay rates for the interference terms of the density matrix. (C) 2010 Elsevier B.V. All rights reserved.