Improved Bounds for Quaternary Linear Codes of Dimension 6

In this paper, twenty new codes of dimension 6 are presented which give improved bounds on the maximum possible minimum distance of quaternary linear codes. These codes belong to the class of quasi-twisted (QT) codes, and have been constructed using a stochastic optimization algorithm, tabu search. A table of upper and lower bounds for d ⁴(n,6) is presented for n≤ 200. Received: 20 December 1996 / Accepted: 13 May 1997     

Effect of additives on the melt rheology and thermal degradation of poly[(R)‐3‐hydroxybutyric acid]

Thermal degradation of poly[(R)−3‐hydroxybutyric acid] (PHB) during melt mixing results in random chain scission that produces shorter polymer chains containing crotonic and carboxyl end groups. One way of preventing this serious reduction of molar mass is to add agents that react with at least two of the newly generated end groups. Different types of commercially available additives known to react with carboxyl group, namely bis(3,4‐epoxycyclohexylmethyl) adipate (BECMA), 2,2'‐bis(2‐oxazoline) (BOX), trimethylolpropane tris(2‐methyl‐1‐aziridinepropionate) (PETAP), triphenyl phosphate (TPP), tris(nonylphenyl) phosphate (TNPP), polycarbodiimide (PCDI), and poly(methyl metharylate‐co‐glycidyl methacrylate) (GMA.MMA) were mixed with PHB by cocasting from solution in chloroform. Dynamic rheology as well as measurements of molar masses before and after dynamic analysis was used to evaluate the effect of the additives on the melt stability of PHB. Measurements of the dynamic shear modulus and the molar mass of molten PHB with the additives PCDI and GMA.MMA showed a minor improvement on the thermal stability. Furthermore, TPP and TNPP did not affect the thermal stability of PHB, whereas the presence of BECMA, BOX, and PETAP gave a strong decrease of the dynamic modulus compared with neat PHB. © 2014 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41836.     

Fast 3D imaging of giant unilamellar vesicles using reflected light-sheet microscopy with single molecule sensitivity

Observation of highly dynamic processes inside living cells at the single molecule level is key for a better understanding of biological systems. However, imaging of single molecules in living cells is usually limited by the spatial and temporal resolution, photobleaching and the signal-to-background ratio. To overcome these limitations, light-sheet microscopes with thin selective plane illumination, for example, in a reflected geometry with a high numerical aperture imaging objective, have been developed. Here, we developed a reflected light-sheet microscope with active optics for fast, high contrast, two-colour acquisition of -stacks. We demonstrate fast volume scanning by imaging a two-colour giant unilamellar vesicle (GUV) hemisphere. In addition, the high contrast enabled the imaging and tracking of single lipids in the GUV cap. The enhanced reflected scanning light-sheet microscope enables fast 3D scanning of artificial membrane systems and potentially live cells with single-molecule sensitivity and thereby could provide quantitative and molecular insight into the operation of cells.     

Poly(arylene piperidinium) Hydroxide Ion Exchange Membranes: Synthesis,Alkaline Stability,and Conductivity

A series of poly(arylene piperidinium)s (PAPipQs) devoid of any alkali‐sensitive aryl ether bonds or benzylic sites are prepared and studied as anion exchange membranes (AEMs) for alkaline fuel cells. First, the excellent alkaline stability of the model compound 4,4‐diarylpiperidinium is confirmed. Medium molecular weight poly(arylene piperidine)s are then synthesized in polycondensations of N‐methyl‐4‐piperidone and either bi‐ or terphenyl via superelectrophilic activation in triflic acid. Film‐forming PAPipQs are subsequently prepared in Menshutkin reactions with methyl, butyl, hexyl, and octyl halides, respectively. AEMs based on poly(terphenyl dimethylpiperidinium) show the best performance with no structural degradation detectable by ¹H NMR spectroscopy after storage in 2 m aq. NaOH at 60 °C after 15 d, and a mere 5% ionic loss at 90 °C. In the fully hydrated state these AEMs reach an OH^? conductivity of 89 mS cm^?1 at 80 °C. The presence of longer pendant N‐alkyl chains (butyl to octyl) is found to significantly promote Hofmann ring‐opening elimination reactions and the degradation rate increases with increasing alkyl chain length. The results of the present study demonstrate that PAPipQs are efficiently prepared from readily available monomers and show excellent alkaline stability and OH^? conductivity when devoid of pendant N‐alkyl chains.     

On optimal binary codes with unbalanced coordinates

A coordinate of a binary code of size M is said to be balanced if the number of zero and ones in the coordinate is either $\lfloor M/2\rfloor $ ? M / 2 ? or $\lceil M/2 \rceil $ ? M / 2 ? (that is, exactly $M/2$ M / 2 for even M). Since good codes (of various types) tend to be balanced in all coordinates, various conjectures have been made regarding the existence of such codes. It is here shown that there are parameters for which there are no optimal binary error-correcting codes with a balanced coordinate. This is proved by the code attaining $A(17,8) = 36$ A ( 17 , 8 ) = 36 , which is shown to be unique here; $A(n,d)$ A ( n , d ) denotes the maximum size of a binary code of length n and minimum distance d. It is further shown that $A(18,8) \le 68$ A ( 18 , 8 ) ≤ 68 .     

Observation of shear band formation in nanocrystalline Pd–Au alloy during in situ SEM compression testing

Understanding the deformation behavior of nanocrystalline (nc) materials is important because of their possible application as structural materials. The investigation of macroscopic nc samples during in situ mechanical tests can shed light on operating deformation mechanisms. For example, observations during a compression test in a scanning electron microscope (SEM) or results obtained by more localized methods like transmission electron microscopy can extend our knowledge on this subject. In this study, we present the results of in situ SEM compression tests on nc Pd–10 at.% Au alloy with a mean grain size of 23 nm produced using the combination of inert gas condensation with subsequent high-pressure torsion. We show that plastic flow in this material is very inhomogeneous on both the macro and the mesoscale as it is localized in one area of the compression sample and within shear bands. The formation of shear bands is accompanied by strain softening. We propose that such behavior can be explained by the activation of grain boundary mediated deformation mechanisms instead of dislocation-based plasticity. This conclusion was supported by in situ synchrotron XRD measurements which revealed that no preferential grain orientation is forming during the compression of identically prepared samples of the same material.     

Polymeric vesicles: from drug carriers to nanoreactors and artificial organelles

One strategy in modern medicine is the development of new platforms that combine multifunctional compounds with stable, safe carriers in patient-oriented therapeutic strategies. The simultaneous detection and treatment of pathological events through interactions manipulated at the molecular level offer treatment strategies that can decrease side effects resulting from conventional therapeutic approaches. Several types of nanocarriers have been proposed for biomedical purposes, including inorganic nanoparticles, lipid aggregates, including liposomes, and synthetic polymeric systems, such as vesicles, micelles, or nanotubes. Polymeric vesicles--structures similar to lipid vesicles but created using synthetic block copolymers--represent an excellent candidate for new nanocarriers for medical applications. These structures are more stable than liposomes but retain their low immunogenicity. Significant efforts have been made to improve the size, membrane flexibility, and permeability of polymeric vesicles and to enhance their target specificity. The optimization of these properties will allow researchers to design smart compartments that can co-encapsulate sensitive molecules, such as RNA, enzymes, and proteins, and their membranes allow insertion of membrane proteins rather than simply serving as passive carriers. In this Account, we illustrate the advances that are shifting these molecular systems from simple polymeric carriers to smart-complex protein-polymer assemblies, such as nanoreactors or synthetic organelles. Polymeric vesicles generated by the self-assembly of amphiphilic copolymers (polymersomes) offer the advantage of simultaneous encapsulation of hydrophilic compounds in their aqueous cavities and the insertion of fragile, hydrophobic compounds in their membranes. This strategy has permitted us and others to design and develop new systems such as nanoreactors and artificial organelles in which active compounds are simultaneously protected and allowed to act in situ. In recent years, we have created a variety of multifunctional, proteinpolymersomes combinations for biomedical applications. The insertion of membrane proteins or biopores into the polymer membrane supported the activity of co-encapsulated enzymes that act in tandem inside the cavity or of combinations of drugs and imaging agents. Surface functionalization of these nanocarriers permitted specific targeting of the desired biological compartments. Polymeric vesicles alone are relatively easy to prepare and functionalize. Those features, along with their stability and multifunctionality, promote their use in the development of new theranostic strategies. The combination of polymer vesicles and biological entities will serve as tools to improve the observation and treatment of pathological events and the overall condition of the patient.     

Block copolymers combining semi-fluorinated poly(arylene ether) and sulfonated poly(arylene ether sulfone) segments for proton exchange membranes

A series of aromatic multiblock copolymers based on alternating segments of hydrophilic sulfonated polysulfone (PSU) and hydrophobic polyfluoroether (PFE) were prepared and characterized as proton exchange membranes. PSU precursor blocks were synthesized by polycondensation of dichlorodiphenylsulfone and resorcinol, and PFE precursor blocks were prepared by combining decafluorobiphenyl and isopropylidenediphenol. After preparation of the multiblock copolymers via a mild coupling reaction of the precursor blocks, the resorcinol units of the PSU blocks were selectively and almost completely sulfonated under mild reaction conditions using trimethylsilylchlorosulfonate. Transparent and robust membranes with different PSU-PFE copolymer compositions and ion-exchange capacities were cast from solution. Atomic force microscopy of the membranes revealed a distinct nanophase separated morphology. At 80 °C, the proton conductivity reached 10 mS cm⁻¹ under 65% relative humidity and 100 mS cm⁻¹ under fully hydrated conditions.