On Depth and Depth+ of Boolean Algebras

We show that the Depth⁺ of an ultraproduct of Boolean Algebras cannot jump over the Depth⁺ of every component by more than one cardinal. Consequently we have similar results for the Depth invariant. Research supported by the United States-Israel Binational Science Foundation. Publication 878 of the second author.     

Reactions of α-chloronitrones with unsaturated ethers

The Ag⁺ induced reaction of α-chloronitrones with unsaturated ethers goes in two parallel competitive directions. On the one hand cycloadducts like 3 are formed and on the other hand oxonium ions like 4. Formation of analogous oxonium compounds occurs also when α-alkoxynitrones are treated with Et₃O⁺BF₄^? in 1,2-dichloroethane. Formation of oxonium compounds with the enol-ethers is practically irreversible and leads to enol-ether fragmentation. With the saturated ethers compounds like 25 were formed and were used as a potential source of N-alkyl-N-vinyl-nitrosonium ions.     

Shot-noise limited single-molecule FRET histograms: comparison between theory and experiments

We describe a simple approach and present a straightforward numerical algorithm to compute the best fit shot-noise limited proximity ratio histogram (PRH) in single-molecule fluorescence resonant energy transfer diffusion experiments. The key ingredient is the use of the experimental burst size distribution, as obtained after burst search through the photon data streams. We show how the use of an alternated laser excitation scheme and a correspondingly optimized burst search algorithm eliminates several potential artifacts affecting the calculation of the best fit shot-noise limited PRH. This algorithm is tested extensively on simulations and simple experimental systems. We find that dsDNA data exhibit a wider PRH than expected from shot noise only and hypothetically account for it by assuming a small Gaussian distribution of distances with an average standard deviation of 1.6 A. Finally, we briefly mention the results of a future publication and illustrate them with a simple two-state model system (DNA hairpin), for which the kinetic transition rates between the open and closed conformations are extracted.     

Electronic perturbation in a molecular nanowire of [IrCl5(NO)]- units

The nitrosyl in [IrCl5(NO)]- is probably the most electrophilic known to date. This fact is reflected by its extremely high IR frequency in the solid state, electrochemical behavior, and remarkable reactivity in solution. PPh4[IrCl5(NO)] forms a crystal in which the [IrCl5(NO)]- anions are in a curious wire-like linear arrangement, in which the distance between the N--O moiety of one anion and the trans chloride of the upper one nearby is only 2.8 A. For the same complex [IrCl5(NO)]- but with a different counterion, Na[IrCl5(NO)], the anions are stacked one over the other in a side-by-side arrangement. In this case the electronic distribution can be depicted as the closed-shell electronic structure Ir III-NO+, as expected for any d(6) third-row transition metal complex. However, in PPh4[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NO*-Cl- acceptor-donor interactions among a large number of [IrCl5(NO)]- units, favoring a different electronic distribution, namely the open-shell electronic structure Ir IV-NO*. This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidation state for iridium in PPh4[IrCl5(NO)] is +4, as compared with +3 in K[IrCl5(NO)]. In agreement, solid-state DFT calculations show that the ground state for [IrCl5(NO)]- in the PPh4+ salt comprises an open-shell singlet with an electronic structure which encompasses half of the spin density mainly localized on a metal-centered orbital, and the other half on an NO-based orbital. The electronic perturbation could be seen as an electron promotion from a metal-chloride to a metal-NO orbital, due to the small HOMO-LUMO gap in PPh4[IrCl5(NO)]. This is probably induced by electrostatic interactions acting as a result of the closeness and wire-like spatial arrangement of the Ir metal centers, imposed by lattice forces due to pi-pi stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4[IrCl5(NO)] the Ir-N-O moiety is partially bent and tilted.     

Polymeric biodegradable lipospheres™ as vaccine delivery systems

This study describes the preparation and use of polymeric lipospheres^TM as a potential vehicle for the controlled-release of vaccines. Lipospheres are a new encapsulation technology for parenteral drug delivery that have been also used successfully as carriers of vaccines. A recombinant malaria antigen, R32NS1, derived from the circumsporozoite protein of Plasmodium falciparum, was incorporated in biodegradable polymeric lipospheres in the absence or presence of lipid A as an adjuvant. The immunogenicity of polymeric lipospheres composed of polylactide (PLD) or polycaprolactone (PCL) was tested in rabbits after intramuscular injection of the formulations. High levels of specific IgG antibodies were observed in the sera of the immunized rabbits up to 12 weeks after primary immunization, using a solid phase ELISA assay. PCL lipospheres containing the malaria antigen were able to induce sustained antibody activity after one single injection in the absence of immunomodulators. PCL lipospheres showed superior immunogenicity compared to PLD lipospheres, the difference being attributed to the different biodegradation rates of the polymers. Biodegradable polymeric lipospheres represent a pharmaceutically acceptable vaccine delivery system with immunopotentiating activity for humoral antibody responses. The high permeability to many therapeutic drugs, and a lack of toxicity, has made PCL and its derivatives well suited for controlled drug delivery. The results obtained in this study are very promising, with the expectation that the use of biodegradable polymeric lipospheres might be very useful in the conversion of multiple-dose vaccines to single-dose vaccination, avoiding the need for repeated immunizations.     

A theoretical and experimental study of advanced control methods to suppress vibrations in a small square plate subject to temperature variations

In this paper, we seek to develop an efficient controller for vibration reduction in a small square plate clamped on all edges. The plate mimics a piece of an aircraft's skin. Small plate size results in higher natural frequencies than normally investigated in literature. Such high-frequency systems are more susceptible to time delays. In addition, the control system must be able to operate over a wide range of temperatures, a requirement for in-flight vibration suppression systems. We investigate two methodologies (sliding mode control, and an adaptive H_∞ control) for control over a wide range of temperatures. Theoretical and experimental studies are conducted and produced varying results. The best theoretical and experimental results are obtained with the adaptive H_∞ controller.     

Enhancing the photoluminescence of peptide-coated nanocrystals with shell composition and UV irradiation

The composition and structure of inorganic shells grown over CdSe semiconductor nanocrystal dots and rods were optimized to yield enhanced photoluminescence properties after ligand exchange followed by coating with phytochelatin-related peptides. We show that, in addition to the peptides imparting superior colloidal properties and providing biofunctionality in a single-step reaction, the improved shells and pretreatment with UV irradiation resulted in high quantum yields for the nanocrystals in water. Moreover, peptide coating caused a noticeable red-shift in the absorption and emission spectra for one of the tested shells, suggesting that exciton-molecular orbital (X-MO) coupling might take place in these hybrid inorganic-organic composite materials.     

Radiation of the Plasma of a Transverse Discharge in a Helium–Krypton–Elegas Mixture

We carried out a spectroscopic investigation of the degradation of the active medium of a pulsed-periodic KrF emitter based on a He/Kr/SF₆ mixture (P = 10–150 kPa) with pumping by a transverse volumetric discharge. The plasma radiation spectra in the range 200–620 nm at different stages of degradation of the working mixture and the dynamics of the radiation of inert gases as well as of the products of decomposition of SF₆ molecules in the plasma are studied. It is shown that since the number of discharge pulses is 10⁴, rather effective formation of excited sulfur molecules is observed which decompose with emission in the spectral range 260–550 nm. This can be employed for developing a wideband lamp based on the system of KrF(B–X; D–X), S₂(B–X), and S₂(f–a) bands.     

Osmotic deswelling of weakly charged poly(acrylic acid) solutions and gels

The osmotic pressure of weakly charged aqueous poly(acrylic acid) (PAA) solutions and the swelling pressure PAA gels were studied by osmotic deswelling at different degrees of ionization (α). In solution, the osmotic pressure was found to scale linearly with concentration, whereas the scaling power of the swelling pressure of gels was higher (1.66). The effect of the ionization degree on the osmotic coefficient in PAA solutions was in agreement with the theory of Borue and Erukhimovich [Macromolecules, 21 , 3240 (1988)]. Ionization increases the swelling capacity of the PAA gels until a plateau is reached at about 35% neutralization. The concentration at equilibrium swelling scales as C_e ～ α^?0.6. The contribution of the network to the gel swelling pressure is evaluated by subtracting the osmotic pressure of the polymer solution at the same concentration and degree of ionization. In swollen gels the extended network opposes swelling. As the gel is osmotically deswelled, a state of zero network pressure exists at a certain concentration, below which the network elasticity favors swelling. The crossover concentration shifts to lower values as the degrees of ionization increases. © 1995 John Wiley & Sons, Inc.