Interfacial micellar structures from novel amphiphilic star polymers

An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface.     

Commensurate-incommensurate magnetic phase transition in magnetoelectric single crystal LiNiPO(4)

Neutron scattering studies of single crystal LiNiPO4 reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short- and long-range incommensurate phases are intermediate between the high temperature paramagnetic and the low temperature antiferromagnetic phases. The modulated structure has a predominant antiferromagnetic component, giving rise to satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg reflection, and a ferromagnetic component, giving rise to peaks at small momentum transfers around the origin at (0,+/-Q,0). The wavelength of the modulated magnetic structure varies continuously with temperature. It is argued that the incommensurate short- and long-range phases are due to spin-dimensionality crossover from a continuous to the discrete Ising state.     

Evolution of the mean instantaneous intensity in fibers affected by polarization mode dispersion

It is shown that the mean instantaneous intensity (MII) of a pulse propagating in an optical fiber affected by polarization mode dispersion is related to the frequency autocorrelation of the fiber's Jones matrix through a Fourier transform. A simple derivation of the diffusion equation satisfied by the MII and the autocorrelation function of a Jones matrix is described.     

Determinants in Triangulated Categories

For a small triangulated category , Bass's K ₁ group is described, and the theorem of the heart is proved. We define the determinant map from to Neeman's , and we compute this map when is the derived category of an Abelian category .     

Polymeric actuators for biological applications.

To shed light on the role of cell rheology and mechanotransduction in various physiological and disease states, different techniques of force application, such as optical tweezers and deformable substrates, are employed. In this present paper we describe a new approach for the deformation of cells based on the temperature-sensitive polymer poly(N-isopropylacrylamide), PNIPAM. In response to temperature changes, PNIPAM gels undergo extensive and reversible changes in volume that allow them to be used as actuators for stretching and compressing cells and tissues. Herein we focus mainly on our experience with the deformation of red blood cells as proof of principle, and demonstrate the wealth of possibilities such stimuli-responsive materials may offer as actuators.     

Soft X-ray resonant scattering study of single-crystal LaSr<Subscript>2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Soft X-ray resonant scattering studies at the Mn L_{II, III}- and the La M_{IV, V}- edges of single-crystal LaSr₂Mn₂O₇ are reported. At low temperatures, below T_N ≈ 160 K, energy scans with a fixed momentum transfer at the A-type antiferromagnetic (0 0 1) reflection around the Mn L_{II, III}-edges with incident linear σ and π polarizations show strong resonant enhancements. The splitting of the energy spectra around the Mn L_{II, III}-edges may indicate the presence of a mixed valence state, e.g., Mn³⁺/Mn⁴⁺. The relative intensities of the resonance and the clear shoulder-feature as well as the strong incident σ and π polarization dependences strongly indicate its complex electronic origin. Unexpected enhancement of the charge Bragg (0 0 2) reflection at the La M_{IV, V}-edges with σ polarization has been observed up to 300 K, with an anomaly appearing around the orbital-ordering transition temperature, T_OO ≈ 220 K, suggesting a strong coupling (competition) between them.     

In situ characterization of functional purple membrane monolayers at the air-water interface

The purple membrane (PM) of Halobacterium salinarum contains a single type of protein, bacterio-rhodopsin (bR), which is a member of the seven alpha-helices transmembrane protein family. This protein is a photoactive proton pump, translocating one proton from the cytoplasmic to the extracellular side of the PM per photon absorbed. bR is found in trimers in PM, where they are assembled in a two-dimensional hexagonal lattice. We show herein that stable and functional films can be built in monolayers at the air-water interface by spreading aqueous suspensions of purified and native PM patches. In situ spectroscopic measurements at the air-water interface indicate that bR remains photoactive in this environment. Physical parameters of these PM films, such as protein molecular area, irreversible in-plane aggregation, z-axis orientation, film thickness, and surface roughness, were determined from surface pressure and surface potential-area isotherms, fluorescence spectroscopy, and X-ray reflectivity at the air-water interface. We find that PM do form organized monolayers of membranes, with an optimal packing density at a surface pressure of approximately 20 mN/m, although no preferential vectorial alignment, with respect to the plane normal to the membrane, can be detected from fluorescence quenching experiments.     

The asymptotic core,nucleolus and Shapley value of smooth market games with symmetric large players

We examine the asymptotic nucleolus of a smooth and symmetric oligopoly with an atomless sector in a transferable utility (TU) market game. We provide sufficient conditions for the asymptotic core and the nucleolus to coincide with the unique TU competitive payoff distribution. This equivalence results from nucleolus of a finite TU market game belonging to its core, the core equivalence in a symmetric oligopoly with identical atoms and single-valuedness of the core in the limiting smooth game. In some cases (but not always), the asymptotic Shapley value is more favourable for the large traders than the nucleolus, in contrast to the monopoly case (Einy et al. in J Econ Theory 89(2):186–206, 1999), where the nucleolus allocation is larger than the Shapley value for the atom.     

Nanoscale memory provided by thermoreversible stochastically structured polymer aggregates on mica

Stimuli-responsive polymers are used in a large variety of applications due to the controlled manner in which their physical properties can be reversibly altered. In this study, we demonstrate the thermoreversible structuring of poly(N-isopropylacrylamide)-based polymer. By temperature-controlled atomic force microscopy, we demonstrate that polymer aggregates form on mica above the polymer lower critical solution temperature and disperse below it, and in so doing, display positional "memory" in that the nanodomains are retained in the same positions and with the same shapes during repeated cooling/heating cycles. Such positional "memory" may be useful for multiple applications in nano-microscale devices.