Phase behavior of a phospholipid/fatty acid/water mixture studied in atomic detail

Molecular dynamics simulations have been used to study the phase behavior of a dipalmitoylphosphatidylcholine (DPPC)/palmitic acid (PA)/water 1:2:20 mixture in atomic detail. Starting from a random solution of DPPC and PA in water, the system adopts either a gel phase at temperatures below similar to 330 K or an inverted hexagonal phase above similar to 330 K in good agreement with experiment. It has also been possible to observe the direct transformation from a gel to an inverted hexagonal phase at elevated temperature (similar to 390 K). During this transformation, a metastable fluid lamellar intermediate is observed. Interlamellar connections or stalks form spontaneously on a nanosecond time scale and subsequently elongate, leading to the formation of an inverted hexagonal phase. This work opens the possibility of studying in detail how the formation of nonlamellar phases is affected by lipid composition and (fusion) peptides and, thus, is an important step toward understanding related biological processes, such as membrane fusion.

DOSY NMR studies of chemical exchange behavior of poly(2-hydroxyethyl methacrylate)

PFG-NMR was used to study the chemical exchange of linear PHEMA having a range of molecular weights with water in DMSO containing varying quantities of water. The aim was to investigate the use of PFG-NMR to study chemical exchange between a polymer with exchangeable protons and a small fast diffusing molecule to provide insight into the conformation adopted by a polymer in solution. The experimental data were simulated closely for the two-site exchange case using the Bloch equations modified for chemical exchange and diffusion. The exchange rate could be used to detect changes in polymer conformation resulting from changes in the solvent. PHEMA of MW 10 000 showed significant time-dependent changes in exchange rate, resulting from preferential solvation of the OH sites by water, and subsequent conformational changes which altered accessibility of the OH sites to water. This behavior was not observed for larger MW PHEMA, which adopted a stable conformation immediately. Large changes in the exchange rate were not reflected in changes to the hydrodynamic radius, suggesting that a minimal overall change in the chain dimensions occurred. DMSO was found to be a poor solvent for PHEMA, which adopts a compact conformation in DMSO. This work has demonstrated that PFG-NMR is a sensitive method for detecting subtle changes in polymer conformation in polymers with exchangeable protons.

Typical behavior of relays in communication channels

The typical behavior of the relay-without-delay channel under low-density parity-check coding and its multiple-unit generalization, termed the relay array, is studied using methods of statistical mechanics. A demodulate-and- forward strategy is analytically solved using the replica symmetric ansatz which is exact in the system studied at Nishimori's temperature. In particular, the typical level of improvement in communication performance by relaying messages is shown in the case of a small and a large number of relay units. © 2007 The American Physical Society.

Do social capital building strategies influence the financing behavior of Chinese private small and medium-sized enterprises?

Using data from 65,485 Chinese private small and medium-sized enterprises over the period 2000-2006, we examine the extent to which firms can improve access to debt by adopting strategies aimed at building social capital, namely entertaining and gift giving to others in their social network, and obtaining political affiliation. We find that although entertainment and gift-giving expenditure leads to higher levels of total and short-term debt, it does not enable firms to obtain greater long-term debt. In contrast, we demonstrate that obtaining political affiliation allows firms greater access to long-term debt.

Enclosing the behavior of a hybrid system up to and beyond a Zeno point

Even simple hybrid systems like the classic bouncing ball can exhibit Zeno behaviors. The existence of this type of behavior has so far forced simulators to either ignore some events or risk looping indefinitely. This in turn forces modelers to either insert ad hoc restrictions to circumvent Zeno behavior or to abandon hybrid modeling. To address this problem, we take a fresh look at event detection and localization. A key insight that emerges from this investigation is that an enclosure for a given time interval can be valid independently of the occurrence of a given event. Such an event can then even occur an unbounded number of times, thus making it possible to handle certain types of Zeno behavior.

A comparison of compacting and caking behavior of carbonate-based washing powders

Two types of sodium carbonate powder produced by spray drying (SD) and dry neutralization (DN) were studied for their compaction properties using a uniaxial compression tester. A comparison was also made with Persil washing powder. Dry neutralized sodium carbonate showed greater resistance to compression and also produced a weaker compact when compressed to 100 kPa. Spray-dried sodium carbonate had an absence of fine particles but compacted easily. Differential scanning calorimetry (DSC) showed that both types of powder were predominantly amorphous in nature. Moisture sorption measurements showed that both powders behaved in a similar way below 50% relative humidity (RH). However, dry neutralized sodium carbonate had a high moisture affinity above this RH. Particle structures were also examined using scanning electron microscopy, showing the heterogeneous interior of the spray-dried particles. © 2013 Copyright Taylor and Francis Group, LLC.

Thermal decomposition behavior of 1,2-bis-(2,4,6-tribromophenoxy)ethane

The thermal decomposition behavior of 1,2-bis-(2,4,6-tribromophenoxy)ethane (BTBPE) widely used as flame retardant plastics additive was studied by HRTG and differential scanning calorimetries. It was pyrolysed in inert atmosphere at 240 and 340 °C in isothermal conditions, the decomposition products were collected and investigated by means of IR and GC-MS, most of them are identified. It was found that BTBPE mostly evaporates at 240 °C. The decomposition products at 340°C depend on rate of their removal from the hot reaction zone. Main primary decomposition products found in case of rapid removal are tribromophenol and vinyl tribromophenyl ether. Whereas, prolonged contact with heating zone also produces hydrogen bromide, ethylene bromide, polybrominated vinyl phenyl ethers and diphenyl ethers, and dibenzodioxins. The nature of the identified compounds are in accordance with a molecular and radical pyrolysis reaction pathway. © 2002 Elsevier Science B.V. All rights reserved.