The phase behavior of a solution containing a mixture of large and small, cross-bridging (''two-sided sticker'') particles is studied using a lattice model analyzed with the aid of mean-field calculations and Monte Carlo simulations. Neither the large nor the small particles interact with each other (except for excluded volume effects). However, the small particles can adsorb onto the surface of one or two large particles, in the latter case providing a cross-bridge, i.e., an adhesive bond, between the large particles. The formulation of the model is motivated by experimental studies involving aqueous solutions of vesicles (the large particles) and biotin-avidin-biotin cross-bridges. This system exhibits a first-order phase transition from a dilute to a condensed phase of vesicles once the average number of stickers per vesicle exceeds a certain threshold value. The statistical thermodynamic description of the system becomes particularly simple upon (Legendre) transformation from the two-component canonical ensemble to a ``mixed'' ensemble involving a constant chemical potential of the cross-bridge particles. The phase separation behavior of the system is calculated for two sets of molecular parametrs, revealing good qualitative agreement with relevant experiments.
An approach based on He scattering is used to develop an atomic-level structural model for an epitaxially grown disordered submonolayer of Ag on Pt(111) at 38 K. Quantum scattering calculations are used to fit structural models to the measured angular intensity distribution of He atoms scattered from this system. The structure obtained corresponds to narrowly size-dispersed compact clusters with a modest translational disorder, and not to fractals, which might be expected due to the low surface temperature. The clusters are up to two layers in height, the lower one having only a few defects. The relations between specific features of the angular scattering distribution, and properties such as the cluster sizes and shapes, the inter-cluster distance distribution, etc, are discussed. The results demonstrate the usefulness of He scattering as a tool for unraveling new complex surface phases. (C) 1998 Elsevier Science B.V. All rights reserved.
We develop a statistical thermodynamic model for the phase evolution of DNA-cationic lipid complexes in aqueous solution, as a function of the ratios of charged to neutral lipid and charged lipid to DNA. The complexes consist of parallel strands of DNA intercalated in the water layers of lamellar stacks of mixed lipid bilayers, as determined by recent synchrotron x-ray measurements Elastic deformations of the DNA and the lipid bilayers are neglected, but DNA-induced spatial inhomogeneities in the bilayer charge densities are included. The relevant nonlinear Poisson-Boltzmann equation is solved numerically, including self-consistent treatment of the boundary conditions at the polarized membrane surfaces. For a wide range of lipid compositions, the phase evolution is characterized by three regions of lipid to DNA charge ratio, rho: 1) for low rho, the complexes coexist with excess DNA, and the DNA-DNA spacing in the complex, d, is constant; 2) for intermediate rho, including the isoelectric point rho = 1, all of the lipid and DNA in solution is incorporated into the complex, whose inter-DNA distance d increases linearly with rho; and 3) for high rho, the complexes coexist with excess liposomes (whose lipid composition is different from that in the complex), and their spacing d is nearly, but not completely, independent of rho. These results can be understood in terms of a simple charging model that reflects the competition between counterion entropy and inter-DNA (rho < 1) and interbilayer (rho > 1) repulsions. Finally, our approach and conclusions are compared with theoretical work by others, and with relevant experiments.
Disclosed are stabilized total nutrient admixt. (TNA) compns. useful for parenteral delivery of pharmacol. acceptable lipids or fats as well as methods for the prepn. thereof. In particular, the pharmacol. acceptable lipid or fat is contained within a protein-walled shell. In a particular embodiment of the invention, a TNA compn. using human serum albumin (HSA) as a stabilizer has been prepd. as a convenient three-in-one formulation (i.e., contg. a fat emulsion, dextrose, and amino acids plus electrolytes). This "three-in-one" formulation can be prepd. in liq. form or in dry form (comprising submicron-sized nanoparticles). The dried material is stable, even under long-term storage, and is easily reconstituted immediately before use by simply adding sterile water (with or without vitamin supplementation). This serves to rehydrate the powder into a TNA suitable for injection. The long-shelf life, ease of reconstitution, and single-component injectability of invention compns. provide significant cost savings, as such compns. can be reconstituted and administered safely, even in the home. In addn., HSA, the stabilizing agent of choice for use in the practice of the present invention, has been shown to improve survival and wellness when given as a supplement to patients receiving conventional forms of total nutrient admixts. Thus, 15 mL of 10 % amino acid soln. (FreAmine III), 4.3 mL of 70 % dextrose soln., 0.5 mL phosphate buffer, 0.4 mL KCl (2 M), NaCl (4 M), 0.5 mL MgSO4 (0.406 M), 0.5 mL Na citrate (10 %), 0.5 mL Ca gluconate (0.46 M) were mixed with 0.25 g of HSA until a clear soln. was obtained. The soln. was filtered and 2.5 mL soybean oil was added to the aq. soln. and the mixt. was homogenized (condition was detailed). The emulsion was stored under N in a polypropylene test tube for 1 wk at 4°, followed by one day at room temp.; the droplet size was not changed and there were no signs of oil sepn. or creaming. [on SciFinder(R)]
A strong phonological theory of reading is proposed and discussed. The first claim of this article is that current debates on word recognition are often based on different axioms regarding the cognitive structures of the mental lexicon rather than conflicting empirical evidence. These axioms lead to different interpretations of the same data. It is argued that once the implicit axioms of competing theories in visual word recognition are explicated, a strong phonological model presents a viable and coherent approach. The assumptions underlying a strong phonological theory of reading are outlined, and 4 theoretical questions are examined: Is phonological recoding a mandatory phase of print processing? Is phonology necessary for lexical access? Is phonology necessary for accessing meaning? How can phonology be derived from orthographic structure? These issues are integrated into a general theory that is constrained by all of the findings.
The optical second-harmonic response of a finite hexagonal lattice is computed as a function of the inter particle separation. In agreement with experiments on Langmuir monolayers of silver quantum dots, the computed response exhibits a peak due to a transition from localized electronic states to a band-like structure. The localization is due to the fluctuations in the particle size and position. For a perfect lattice the variation of the nonlinear response with the inter particle separation is qualitatively different. The role of the symmetry breaking is demonstrated at the tight binding level of electronic structure computations. (C) 1998 Elsevier Science B.V. All rights reserved.
We have discovered a new class of smart-gels, poly(4-vinylpyridine) (PVPy) swollen with pyridine (Py), that following photoexcitation (395, 455, 557 nm) emits three independent colors: blue, green, and red (477, 527, 585 nm, respectively). These excitation wavelengths also induced large reversible changes in pH and electrical conductivity. The primary photoexcitation paths within this photo-active gel are singlet-excitons. The origin of this phenomenon is attributed to the combined properties of weak coupling via hydrogen-bonding and high polarizability. Our preliminary model suggests, that C—H ⃛N based Py associates are formed during the gelation process. Photoexcitation leads to proton transfer within three different kinds of assemblies and to a solid-state-like electronic behavior of the gel. This system, i. e. a photoconducting transparent organic gel with multiple color emission, is very attractive for a wide range of promising applications in the field of optoelectronic devices such as organic LED's and 3D holography.
Control over the surface chemistry and physics of electronic and optical materials is essential for constructing devices and fine-tuning their performance. In the past few years we have started to explore the use of organic molecules for systematic modification of semiconductor surface electronic properties. In this paper, manipulation of silicon surfaces by self-assembly of various quinolinium-based chromophores is reported. The progress of the assembly process is monitored by XPS, UV-Vis, and FTIR spectroscopies as well as with surface wettability. The effect of the monolayer's dipole-moment on the Si surface potential and the interaction with surface states is monitored by CPD measurements. A pronounced effect of a sub-nanometer coupling-agent layer alone on the electron affinity and band-bending of Si was observed. We also show a way to modulate the Si work-function by tuning the dipole strength of the chromophore-containing organic, self-assembled monolayer and of its orientation with respect to the silicon surface.
HL Selzle, EW Schlag, F Remacle, and RD LEVINE. 1998. “Two classes of ZEKE spectroscopy.” COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 63, Pp. 1143-1151. Abstract
A classification of ZEKE spectra into two classes based on operational criteria is useful for discussion. The proposal is that some of the different and seemingly conflicting effects reported for different molecular (or the same molecule for different excitations), such as the role of an external field, are due to these two distinct classes of states which can be optically accessed. Class A is the direct, ``front door'' entry where the states excited are those which are detected by the delayed ionization. Class B is a very prevalent but indirect ``backdoor'' route where it is only the interaction of the Rydberg electron with the core, possibly aided by external perturbations, that allows a signal to be detected upon ionization. The operational criteria for distinguishing between or even exploiting the features of the two classes are discussed. Such attention might be useful as new techniques for class B spectra are developed.
A two-dimensional conducting polyaniline (PAN) monolayer has been formed on an elec. insulating monolayer. The approach is based on the electrochem. polymn. of surface-confined anilinium ions that were electrostatically attached to a neg. charged self-assembled monolayer of ω-mercaptodecanesulfonate (MDS), HS(CH2)10SO3-, on a gold surface. The formation and characterization of the two-dimensional film and the MDS monolayer have been examd. by cyclic voltammetry, Fourier transform IR spectroscopy, XPS, wettability, and scanning electrochem. microscope. The formation of a capacitor-like assembly, in which electron transfer was blocked between PAN and the gold surface, was accomplished by electrochem. incorporating hexadecanethiol (C16) into the MDS monolayer. The PAN monolayer exhibits properties similar to those of a thin polymer film. [on SciFinder(R)]
{{A semiempirical model is developed, based on ab initio calculations, to provide an analytic representation of excited-state potential energy surfaces for (H2O)(n)
Anonymus. 1998. “Unit 10: The Anusim.” In Jews and Christians in Western Europe: Encounter between cultures in the Middle Ages and the Renaissance, Pp. 183-297. Tel Aviv: The Open University.
