Dependence of Pressure,Combustion and Frequency Characteristics on Valved Pulsejet Combustor Geometries

An experimental analysis of valved pulsejets based on the Curtis-Dyna design and the concomitant results are discussed in the current paper. By altering the combustor length, the tail pipe length and by adding a flare at the aft-end, twelve different pulsejet configurations are tested. An axially-distributed array of piezoelectric pressure sensors and ion probes reveal the pressure and combustion dynamics inside these devices. Evidence is attained to support the claim that valved Curtis-Dyna pulsejets of the tested configurations behave like a Helmholtz resonator. Each cycle of a pulsejet is composed of temporally and spatially restrained combustion events. Altering the geometry induces an amplitude modulated low frequency instability inside the pulsejet that is characterized by sinusoidally-varying peak cycle pressures. The operating frequency, peak pressures and combustion activity of the pulsejets are characterized to reveal that reliable pulsejet operation requires proper amount of coupling — defined by low time lags — between the pressure peaks and combustion events.     

Adsorption of lipid liquid crystalline nanoparticles: effects of particle composition, internal structure, and phase behavior

Controlling the interfacial behavior and properties of lipid liquid crystalline nanoparticles (LCNPs) at surfaces is essential for their application for preparing functional surface coatings as well as understanding some aspects of their properties as drug delivery vehicles. Here we have studied a LCNP system formed by mixing soy phosphatidylcholine (SPC), forming liquid crystalline lamellar structures in excess water, and glycerol dioleate (GDO), forming reversed structures, dispersed into nanoparticle with the surfactant polysorbate 80 (P80) as stabilizer. LCNP particle properties were controlled by using different ratios of the lipid building blocks as well as different concentrations of the surfactant P80. The LCNP size, internal structure, morphology, and charge were characterized by dynamic light scattering (DLS), synchrotron small-ange X-ray scattering (SAXS), cryo-transmission electron microscopy (cryo-TEM), and zeta potential measurements, respectively. With increasing SPC to GDO ratio in the interval from 35:65 to 60:40, the bulk lipid phase structure goes from reversed cubic micellar phase with Fd3m space group to reversed hexagonal phase. Adding P80 results in a successive shift toward more disorganized lamellar type of structures. This is also seen from cryo-TEM images for the LCNPs, where higher P80 ratios results in more extended lamellar layers surrounding the inner, more dense, lipid-rich particle core with nonlamellar structure. When put in contact with a solid silica surface, the LCNPs adsorb to form multilayer structures with a surface excess and thickness values that increase strongly with the content of P80 and decreases with increasing SPC:GDO ratio. This is reflected in both the adsorption rate and steady-state values, indicating that the driving force for adsorption is largely governed by attractive interactions between poly(ethylene oxide) (PEO) units of the P80 stabilizer and the silica surface. On cationic surface, i.e., silica modified with 3-aminopropltriethoxysilane (APTES), the slightly negatively charged LCNPs give rise to a very significant adsorption, which is relatively independent of LCNP composition. Finally, the dynamic thickness measurements indicate that direct adsorption of intact particles occurred on the cationic surface, while a slow buildup of the layer thickness with time is seen for the weakly interacting systems.     

Horse heart cytochrome c entrapped into the hydrated liquid-crystalline phases of phytantriol: X-ray diffraction and Raman spectroscopic characterization

Small angle X-ray diffraction (SAXD), resonance Raman (RR) spectroscopy with 413 nm excitation, and non-resonance Raman technique with 785 nm excitation were used to probe the influence of entrapped cytochrome c (Cyt c) on the structure of hydrated phytantriol (Phyt) liquid-crystalline phases as well as conformational changes of heme group and secondary structure of the protein. SAXD measurements indicated that incorporation of Cyt c affects both nanostructure dimensions and type of liquid-crystalline phases of hydrated Phyt. The unit cell dimensions decrease with increasing Cyt c concentration for all phases. In addition, protein perturbs the nanostructure of Q(230) and Q(224) liquid-crystalline phases of hydrated Phyt to such an extent that they transform into the Q(229) phase with the Im3m space group. RR data revealed that entrapment of oxidized Cyt c into the Q(230) phase at 1 wt.% content results in near complete reduction of central iron ion of the heme group, while its low-spin state and six-ligand coordination configuration are preserved. Based on the analysis of heme out-of-plane folding vibration near 568 cm(-1) (γ(21)) and ν(48) mode at 633 cm(-1), it was demonstrated that the protein matrix tension on the heme group is relaxed upon incorporation of protein into Q(230) phase. Non-resonant Raman bands of difference spectra showed the preservation of α-helix secondary structure of Cyt c in the liquid-crystalline phase at relatively high (5 wt.%) content. The Cyt c induced spectroscopic changes of Phyt bands were found to be similar as decrease in temperature.     

Upper bounds for discrete moments of the derivatives of the riemann zeta-function on the critical line*

Assuming the Riemann hypothesis, we establish upper bounds for discrete moments of the Riemann zeta-function and its derivatives on the critical line. Moreover, we express continuous moments of the Riemann zeta-function and its derivatives in terms of these discrete moments. This allows us to give conditional upper bounds for $ {\int_0^T {\left| {{\zeta^{(l)}}\left( {{{1} \left/ {2} \right.} + {\text{i}}t} \right)} \right|}^{2k}}{\text{d}}t $ , where l and k are nonnegative integers.     

Liquid crystalline phases and their dispersions in aqueous mixtures of glycerol monooleate and glyceryl monooleyl ether

The aqueous phase behavior of mixtures of 1-glycerol monooleate (GMO) and its ether analogue, 1-glyceryl monooleyl ether (GME) has been investigated by a combination of polarized microscopy, X-ray diffraction, and NMR techniques. Three phase diagrams of the ternary GMO/GME/water system have been constructed at 25, 40, and 55 degrees C. The results demonstrate that the increasing amount of GME favors the formation of the reversed phases, evidenced by the transformation of the lamellar and bicontinuous cubic liquid crystalline phases of the binary GMO/water system into reversed micellar or reversed hexagonal phases. For a particular liquid crystalline phase, increasing the GME content has no effect on the structural characteristics and hydration properties, thus suggesting ideal mixing with GMO. Investigations of dispersed nanoparticle samples using shear and a polymeric stabilizer, Pluronic F127, show the possibility of forming two different kinds of bicontinuous cubic phase nanoparticles by simply changing the GMO/GME ratio. Also NMR self-diffusion measurements confirm that the block copolymer, Pluronic F127, used to facilitate dispersion formation, is associated with nanoparticles and provides steric stabilization.     

Aqueous phase behavior and dispersed nanoparticles of diglycerol monooleate/glycerol dioleate mixtures

The first part of this study concerns the aqueous phase behavior of mixtures of diglycerol monooleate (DGMO) and glycerol dioleate (GDO) examined by X-ray diffraction (XRD). The ternary phase diagram displays a multitude of liquid crystalline phases (polymorphism). With increasing GDO content the following phase sequence was observed: lamellar (L(alpha)); two reversed bicontinuous cubic phases (Q(230) and Q(224)); reversed hexagonal (H(II)); the reversed micellar (L(2)) phase. The second part deals with the preparation and characterization of aqueous dispersions of the reversed hexagonal phase in the presence of the nonionic triblock copolymer Pluronic F127. Submicrometer-sized monocrystalline H(II) phase particles were obtained, as evidenced by cryo-transmission electron microscopy (cryo-TEM), laser diffraction, and XRD, by use of a simple and reproducible preparation method including a heat-treatment step. Moreover, the particle size distributions of the H(II) phase nanoparticle dispersions were narrow as determined by laser diffraction measurements. Using XRD, we show that the polymeric stabilizer is depleted from the core of the hexagonal particles and preferentially located at the surface. It is concluded that the preferential distribution of stabilizing agents at particle surfaces is a prerequisite for the formation of structurally well-defined and kinetically stable H(II) phase particles (Hexosome).     

Trainable structure–activity relationship model for virtual screening of CYP3A4 inhibition

A new structure–activity relationship model predicting the probability for a compound to inhibit human cytochrome P450 3A4 has been developed using data for >800 compounds from various literature sources and tested on PubChem screening data. Novel GALAS (Global, Adjusted Locally According to Similarity) modeling methodology has been used, which is a combination of baseline global QSAR model and local similarity based corrections. GALAS modeling method allows forecasting the reliability of prediction thus defining the model applicability domain. For compounds within this domain the statistical results of the final model approach the data consistency between experimental data from literature and PubChem datasets with the overall accuracy of 89%. However, the original model is applicable only for less than a half of PubChem database. Since the similarity correction procedure of GALAS modeling method allows straightforward model training, the possibility to expand the applicability domain has been investigated. Experimental data from PubChem dataset served as an example of in-house high-throughput screening data. The model successfully adapted itself to both data classified using the same and different IC₅₀ threshold compared with the training set. In addition, adjustment of the CYP3A4 inhibition model to compounds with a novel chemical scaffold has been demonstrated. The reported GALAS model is proposed as a useful tool for virtual screening of compounds for possible drug-drug interactions even prior to the actual synthesis.     

"Sponge" nanoparticle dispersions in aqueous mixtures of diglycerol monooleate, glycerol dioleate, and polysorbate 80

Lipid nanoparticles of nonlamellar lyotropic phases have a wide solubilizing and encapsulating spectrum for a range of substances thanks to their nanostructured interior featuring both lipophilic and hydrophilic domains. As a consequence, these systems have emerged as promising drug delivery systems in various pharmaceutical and diagnostic applications. Here we present the phase behavior and dispersion properties of a novel three-component lipid system composed of diglycerol monooleate (DGMO), glycerol dioleate (GDO), and polysorbate 80 (P80) which shows several advantageous features relating to drug delivery applications including: spontaneous dispersion formation with a narrow size distribution and tunable particle phase-structure. The obtained phase diagram shows the presence of lamellar (L(alpha)), hexagonal (H(2)), and reverse bicontinuous cubic (V(2)) liquid crystalline phases and an inverse micellar (L(2)) solution. A particularly interesting observation is the presence of a phase region where two liquid phases coexist, most likely the L(2) and L(3) ("sponge phase"). These two phase structures appear also to coexist in the submicron particles formed in the dilute water region, where the L(3) element appears to stabilize nanoparticles with inner L(2) structure. Increasing the fraction of the dispersing P80 component results in the growth of the more water rich L(3) "surface phase" at the expense of the size of the inner L(2) core.