Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Ozonolysis of dipterocarpol and its derivatives

Oxidation of dipterocarpol and its derivatives with ozone gave compounds containing lactone, lactol, alkoxytetrahydrofuran, aldehyde, and methyl ketone fragments in the side chain, as well as 1,2,4-trioxolane fragment in the A ring. The molecular and crystalline structures of dipterocarpol were determined by X-ray analysis.     

Inducing anisotropy in bulk Nd-Fe-Co-Al-B nanocrystalline alloys by quenching in magnetic field

We have observed magnetic anisotropy in bulk Nd_55−xCo_xFe₃₀Al₁₀B₅ (x=10, 15 and 20) alloys prepared by copper mold suction casting method with a presence of external magnetic field (quenching field) μ₀H=0.25 T. By changing direction of the measuring field from perpendicular to parallel one in comparison with that of the quenching field, coercive force of the alloys slightly decreases while remanent magnetization and squareness of hysteresis loop increase more clearly. It is also found that the higher Co-concentration in the alloys the larger magnetic anisotropy is induced. The structure analyses manifest nanocrystalline particles embedded in residual amorphous matrix of the alloys. The size of the particles is in range of 10-30 nm and their crystalline phases consist of Nd₂(Fe,Co)₁₄B, Nd₃Co, Nd₃Al, NdAl₂ and Nd.     

Stages of melting of graphene model in two-dimensional space

Spontaneous melting of a perfect crystalline graphene model in 2D space is studied via molecular dynamics simulation. Model containing 10⁴ atoms interacted via long-range bond-order potential (LCBOP) is heated up from 50 to 8,450 K in order to see evolution of various thermodynamic quantities, structural characteristics and occurrence of various structural defects. We find that spontaneous melting of our graphene model in 2D space exhibits a first-order behaviour of the transition from solid 2D graphene sheet into a ring-like structure 2D liquid. Occurrence and clustering of Stone–Wales defects are the first step of melting process followed by breaking of C–C bonds, occurrence/growth of various types of vacancies and multi-membered rings. Unlike that found for melting of a 2D crystal with an isotropic bonding, these defects do not occur homogeneously throughout the system, they have a tendency to aggregate into a region and liquid phase initiates/grows from this region via tearing-like or crack-propagation-like mechanism. Spontaneous melting point of our graphene model occurs at T_m = 7,750 K. The validity of classical nucleation theory and Berezinsky–Kosterlitz–Thouless–Nelson–Halperin–Young (BKTNHY) one for the spontaneous melting of our graphene model in strictly 2D space is discussed.     

Facile synthesis of SnO2–ZnO core–shell nanowires for enhanced ethanol-sensing performance

The design of core–shell heteronanostructures is powerful tool to control both the gas selectivity and the sensitivity due to their hybrid properties. In this work, the SnO₂–ZnO core–shell nanowires (NWs) were fabricated via two-step process comprising the thermal evaporation of the single crystalline SnO₂ NWs core and the spray-coating of the grainy polycrystalline ZnO shell for enhanced ethanol sensing performance. The as-obtained products were investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The ethanol gas-sensing properties of pristine SnO₂ and ZnO–SnO₂ core–shell NW sensors were studied and compared. The gas response to 500 ppm ethanol of the core–shell NW sensor increased to 33.84, which was 12.5-fold higher than that of the pristine SnO₂ NW sensor. The selectivity of the core–shell NW sensor also improved. The response to 100 ppm ethanol was about 14.1, whereas the response to 100 ppm liquefied petroleum gas, NH₃, H₂, and CO was smaller, and ranged from 2.5 to 5.3. This indicates that the core–shell heterostructures have great potential for use as gas sensing materials.     

The optical properties and energy transition process in nanocomposite of polyvinyl-pyrrolidone polymer and Mn-doped ZnS

This study has been carried out on the optical properties of polyvinyl-pyrrolidone (PVP), the energy transition process in nanocomposite of PVP capped ZnS:Mn nanocrystalline and the influence of the PVP concentration on the optical properties of the PVP capped ZnS:Mn nanocrystalline thin films synthesized by the wet chemical method. The microstructures of the samples were investigated by X-ray diffraction, the atomic absorption spectroscopy, and transmission electron microscopy. The results showed that the prepared samples belonged to the sphalerite structure with the average particle size of about 2–3 nm. The optical properties of samples are studied by measuring absorption, photoluminescence (PL) spectra and time-resolved PL spectra in the wavelength range from 200 to 700 nm at 300 K. From data of the absorption spectra, the absorption edge of PVP polymer was found about of 230 nm. The absorption edge of PVP capped ZnS:Mn nanoparticles shifted from 322 to 305 nm when the PVP concentration increases. The luminescence spectra of PVP showed a blue emission with peak maximum at 394 nm. The luminescence spectra of ZnS:Mn–PVP exhibits a blue emission with peak maximum at 437 nm and an orange–yellow emission of ion Mn²⁺ with peak maximum at 600 nm. While the PVP coating did not affect the microstructure of ZnS:Mn nanomaterial, the PL spectra of the PVP capped ZnS:Mn samples were found to be affected strongly by the PVP concentration.     

New Deformation of Para-Bose Statistics

We propose commutation relations for a single mode -deformed para-Bose oscillator. In this new deformation of para-Bose statistics the distribution function has the same form as in the para-Bose statistics. Furthermore, we show analogies between the coherent states of -deformed and q-deformed para-Bose statistics.     

Tuning of fiber lasers by use of a single-mode biconic fiber taper

We report a novel scheme to build a compact, tunable fiber laser. The tuning mechanism is based on the transmission property of a single-mode biconic fiber taper. While pulling the taper, we observe oscillations in the transmitted optical power that are due primarily to interference between a pair of excited modes within the tapered region, which are eventually coupled into the unstretched single-mode fiber at the end of the taper. A similar mechanism causes the modulation of the transmitted optical spectrum after the taper has been pulled and stabilized. It is this spectral modulation by the taper that is exploited here to control the wavelength of a fiber laser. The modulation can be adjusted by stretching the taper, thus enabling the tuning of the laser wavelength. We have built a 32 mW Er-doped tunable ring fiber laser with a continuous tuning range of over 20 nm and a signal-to-noise ratio of better than 45 dB over the entire tuning range; our output power is limited only by the available pump power.     

Determination of microelement distribution in different components of soil-plant systems

The leaves, stem, and roots of two types of shrubs (tea (Camellia sinensis) and sweet leaf (Sauropus androgynus)) and two types of herbs (vetiver grass (Vetiveria zizanioides L. Nash) and maize (Zea mays L)) and the Thucuc soil where the plants were growing were collected to be studied. The contents of 22 elements in the samples were determined by three methods: X-Ray fluorescence analysis (XRFA), gamma activation analysis (GAA), and the tracking method to study the distribution of these elements in plants and the soil-plant relationship. This study was carried out at the Flerov Laboratory of Nuclear Reactions (FLNR), Joint Institute for Nuclear Research (JINR), Dubna, Russia. The distribution of the elements in the soil-plant system was studied.