On the universality of nonthermal electron acceleration due to quasi-turbulent wakefields

Nonthermal acceleration of relativistic electrons in a wakefield induced by large amplitude light waves is discussed. It is considered that large amplitude light waves are excited as the precursor waves in the upstream of relativistic perpendicular shocks in the universe, and that the wakefield is excited by the light ponderomotive force. Thus, the wakefield acceleration is possible in the astrophysical circumstances. We model such shock environments in a laboratory plasma by substituting an intense laser pulse for the large amplitude light waves. By performing 2-D particle-in-cell simulations, we discuss the properties of the wakefield acceleration in various laser and plasma conditions. With the relativistic intensities of the laser pulses, the electrons are nonthermally accelerated by the wakefield. When the pulse length and the spot size are comparable to the electron inertial scale, the energy distribution functions of the electrons can be monoenergetic. On the other hand, when the pulse spatial scales are much larger than the electron inertial scale, which occurs in the case of the shock precursor light waves, the distribution functions are universally represented by power law spectra with an index of 2, independent of the laser intensity, the plasma density, and the laser pulse size.     

Phase transitions of 6-(4-n-alkoxybenzoyloxy)-flavones and 3-cyano-7-(4-n-alkoxybenzoyloxy)-coumarins

Phase transitions of 6-(4-n-alkoxybenzoyloxy)-flavones (ABF) and 3-cyano-7-(4-n-alkoxybenzoyloxy)-coumarins (CABC) were studied using D.S.C. and polarized microscopy. ABF series showed a nematic phase which has an excellent thermal stability, whereas CABC series exhibited a smectic A phase in the longer 4-n-alkoxybenzoyloxy ones than 4-n-hexyloxybenzoyloxy. This difference in the mesogenicity was discussed from the structure and polarity of flavone and coumarin skeletons which may be associated with an intermolecular interaction in the mesophase.     

Synthesis and solution properties of poly(methacrylate)s with semipolar structures on the side chains

Poly{2‐(N,N‐dimethylamino)ethyl methacrylate [poly(DMMA)]}, which was prepared by radical polymerization initiated with dimethyl 2,2‐azobis(2‐methylpropionate), was reacted with hydrogen peroxide, diethyl sulfate, and chloroacetic acid to yield poly[N,N‐dimethyl‐N‐(2‐methacryloyloxyethyl)amine N‐oxide] [poly(DMANO)], poly[N‐ethyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxyethyl)ammonium ethyl sulfate] [poly(EDMES)], and poly[N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonioacetate] [poly(DMEAA)] as ion‐containing water‐soluble polymers, respectively. The solution properties of these charged polymers were compared via the reduced viscosities of these three charged polymers in aqueous solutions as a function of the concentration. Poly(EDMES) showed typical polyelectrolyte behavior, and the other two polymers [poly(DMANO) and poly(DMEAA)] exhibited antipolyelectrolyte behavior. Furthermore, the antipolyelectrolyte behavior was different for poly(DMANO) and poly(DMEAA); that is, poly(DMANO) was less dependent on small electrolytes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 129–141, 2005     

Oxygen‐Tolerant Electrodes with Platinum‐Loaded Covalent Triazine Frameworks for the Hydrogen Oxidation Reaction

Reducing the use of platinum (Pt) on polymer electrolyte fuel cell anodes is critical for the widespread dissemination of these energy conversion systems. Although Pt usage can be minimized by the even dispersion of isolated Pt atoms, no atomically dispersed Pt catalysts that promote hydrogen oxidation at a rate required for practical fuel cells have been reported to date. Covalent triazine frameworks with atomically dispersed Pt atoms (0.29 wt %) are described and it is demonstrated that the material has a high electrocatalytic hydrogen oxidation activity without an overpotential. Importantly, when the loading amount was increased to 2.8 wt %, the electrocatalytic hydrogen oxidation activity of the resulting electrode was comparable to that of commercial carbon supported 20 wt % Pt catalysts, and the catalytic activity for oxygen reduction was markedly reduced. Thus, Pt‐modified covalent triazine frameworks selectively catalyze hydrogen oxidation, even in the presence of dissolved oxygen, which is critical for limiting cathode degradation during the start–stop cycles of fuel cells.     

Polymerization of an optically active phenylacetylene derivative bearing an azide residue by click reaction and reaction with a rhodium catalyst

A facile method for synthesizing diverse optically active polymers with different backbone structures was developed by the polymerization of an optically active aromatic azide bearing an acetylene unit with a rhodium catalyst followed by the click reaction of the pendant azides or by the click polymerization of the monomer.     

Synthesis of chromogenic crown ethers and liquid—liquid extraction of alkaline earth metal ions

New crown ether dyes carrying two pendent anionic side-arms were synthesized for the extraction-spectrophotometry of alkaline earth metal ions. In the extraction of alkaline earth metal ions by these dianionic reagents, size recognition by the crown ether ring was more remarkable than in the case of alkali metal ion extraction by a similar type of monoanionic reagents. Dramatic changes in metal selectivity were observed when the nature of the anionic side-arm was changed while the crown ether skeleton was kept the same. The structure/selectivity relationship is discussed in terms of “chelate” and “intramolecular ion-pair” formation. Typically, when the basicity of the pendent anions was relatively high and a six-membered chelate was structurally possible for the pendent anions and the crown-bound metal, the extraction of calcium was favored by up to a factor of 3000 in the ratio of the Ca/Ba extraction constants for reagents of the diaza-18-crown-6 type. In contrast, the reagents which had pendent anions with only poor coordination ability for metal ions seemed to form complexes of the ion-pair type, and calcium ion was 10⁵ times less extractable than barium ion for the same diaza-18-crown-6-skeleton. Strontium ion seemed to be extracted most effectively when the extracted complex assumed properties intermediate between the chelate and intramolecular ion-pair.     

Radiation curing of intelligent coating for controlled release and permeation

Intelligent membranes for pH and temperature-responsive drug releases were developed by coating and curing of polymer-drug composite film with electrolyte or N-isopropyl acrylamide curable mixture. It was proved that those intelligent membranes showed the stimule-sensitive and responsive release functions and could be produced efficiently by radiation curing prosessing with a conveyer system.     

Reverse enantioselectivity in the lipase-catalyzed desymmetrization of prochiral 2-carbamoylmethyl-1,3-propanediol derivatives

Enantioselective acetylation of 2-carbamoylmethyl-1,3-propanediol derivatives was catalyzed effectively by lipase PS to give monoacetates with high enantioselectivity: The enantioselectivity depended on the 2-carbamoylmethyl groups. The reaction of N-monoalkylcarbamoylmethyl-1,3-propanediol afforded the monoacetate with the (S)-configuration, whereas N,N-dialkylcarbamoylmethyl-1,3-propanediol gave the monoacetate with the (R)-configuration.     

Interaction of high Mach-number shocks in laser-produced plasmas

We report the laboratory experiment for high Mach-number collisionless shock formation and for studying the interaction of them. These shocks are formed in high-velocity counterstreaming plasmas produced by ablating a double-foil plastic target with a high-power laser. The laser-produced plasmas are diagnosed with space and time-resolved optical pyrometry and shadowgraphy. Multiple shocks are formed and interact with each other, resulting in the increase of plasma temperature and density.