Preparation of modified polyesters containing triphosphorous and their applications to PU flame-retardant coatings

Three phosphorous functional groups were introduced in one structural unit of polymer backbone to enhance the flame retardancy of PU coatings. In the first step, we synthesized tetramethylene bis(orthophosphate) (TBOP) that contained two phosphorus functional groups in one structural unit. In the next step, we synthesized modified polyesters (ATBTP-10,-20,-30) that contained triphosphorous groups by condensing polymerization of TBOP, 1,4-butanediol, trimethylolpropane, adipic acid, and phenylphosphonic acid (PPA). The amount of PPA in the ATBTPs was 10, 20, and 30 wt%. Then, flame-retardant PU coatings (AHFC−10,−20,−30) were prepared by curing ATBTPs with hexamethylene diisocyanate-biuret (curing agent) at room temperature. From the TGA analysis of diphosphorus-modified polyester (ATBT) and ATBTPs, the residues of ATBT, ATBTP-10, ATBTP-20, and ATBTP-30 were 24.6, 27.5, 29.2, and 31.9%, respectively. From this result, it was found that the residue increased in relation to the amount of PPA. Physical properties of the films of flame-retardant coatings were deteriorated with the addition of PPA (flame retarding component), however, all the films of flame-retardant coatings, except AHFC-30, met the required physical properties standard for coatings. Char lengths of the AHFCs measured by the 45° Meckel burner method were 2.9∼4.8 cm, and LOI values were 28∼31%, which indicates that the prepared AHFCs showed good flame retardancy.     

Isolation and characterization of a novel analyte from Bacillus subtilis SC-8 antagonistic to Bacillus cereus

In this study, an effective substance was isolated from Bacillus subtilis SC-8, which was obtained from traditionally fermented soybean paste, cheonggukjang. The substance was purified by HPLC, and its properties were analyzed. It had an adequate antagonistic effect on Bacilluscereus, and its spectrum of activity was narrow. When tested on several gram-negative and gram-positive foodborne pathogenic bacteria such as Salmonella enterica, Salmonella enteritidis, Staphylococcus aureus, and Listeria monocytogenes, no antagonistic effect was observed. Applying the derivative from B. subtilis SC-8 within the same genus did not inhibit the growth of major soybean-fermenting bacteria such as Bacillus subtilis, Bacillus licheniformis, and Bacillus amyloquefaciens. The range of pH stability of the purified antagonistic substance was wide (from 4.0 to >10.0), and the substance was thermally stable up to 60 °C. In the various enzyme treatments, the antagonistic activity of the purified substance was reduced with proteinase K, protease, and lipase; its activity was partially destroyed with esterase. Spores of B. cereus did not grow at all in the presence of 5 μg/mL of the purified antagonistic substance. The isolated antagonistic substance was thought to be an antibiotic-like lipopeptidal compound and was tentatively named BSAP-254 because it absorbed to UV radiation at 254 nm.     

In situ synthesis of thermochemically reduced graphene oxide conducting nanocomposites

Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42,000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 10(4) times higher conductivity (~1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ~3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems.     

Hybrid multiferroic nanostructure with magnetic-dielectric coupling

The development of methods to economically synthesize single wire structured multiferroic systems with room temperature spin-charge coupling is expected to be important for building next-generation multifunctional devices with ultralow power consumption. We demonstrate the fabrication of a single nanowire multiferroic system, a new geometry, exhibiting room temperature magnetodielectric coupling. A coaxial nanotube/nanowire heterostructure of barium titanate (BaTiO(3), BTO) and cobalt (Co) has been synthesized using a template-assisted method. Room temperature ferromagnetism and ferroelectricity were exhibited by this coaxial system, indicating the coexistence of more than one ferroic interaction in this composite system.     

A normally off GaN n-MOSFET with Schottky-barrier source and drain on a Si-auto-doped p-GaN/Si

We have fabricated an enhancement-mode n-channel Schottky-barrier-MOSFET (SB-MOSFET) for the first time on a high mobility p-type GaN film grown on silicon substrate. The metal contacts were formed by depositing Al for source/drain contact and Au for gate contact, respectively. Fabricated SB-MOSFET exhibited a threshold voltage of 1.65 V, and a maximum transconductance(g/sub m/) of 1.6 mS/mm at V/sub DS/=5V, which belongs to one of the highest value in GaN MOSFET. The maximum drain current was higher than 3 mA/mm and the off-state drain current was as low as 3 nA/mm.     

Novel Rewritable,Non‐volatile Memory Devices Based on Thermally and Dimensionally Stable Polyimide Thin Films

Novel digital memory devices were fabricated with a thermally and dimensionally stable polyimide containing carbazole moieties in its side groups by using a simple and conventional solution coating process. The devices exhibit excellent unipolar ON and OFF switching behavior. With very low power consumption, the devices can be repeatedly written, read, and erased in air. The ON/OFF current ratio of the devices is high up to 10¹¹. The high ON/OFF switching ratio and stability of the devices, as well as their repeatable writing, reading, and erasing capability with low power consumption, open up the possibility of the mass production of high performance non‐volatile memory devices at low cost.     

Minimizing Cost and Delay in Shared Multicast Trees

Existing tree construction mechanisms are classified into source‐based trees and center‐based trees. The source‐based trees produce a source‐rooted tree with a low delay. However, for the applications with multiple senders, the management overheads for routing tables and resource reservations are too high. The center‐based trees are easy to implement and manage, but a priori configuration of candidate center nodes is required, and the optimization nature such as tree cost and delay is not considered. In this paper, we propose a new multicast tree building algorithm. The proposed algorithm basically builds a non‐center based shared tree. In particular, any center node is not pre‐configured. In the proposed algorithm, a multicast node among current tree nodes is suitably assigned to each incoming user. Such a node is selected in a fashion that tree cost and the maximum end‐to‐end delay on the tree are jointly minimized. The existing and proposed algorithms are compared by experiments. In the simulation results, it is shown that the proposed algorithm approximately provides the cost saving of 30 % and the delay saving of 10 %, compared to the existing approaches. In conclusion, we see that the cost and delay aspects for multicast trees can be improved at the cost of additional computations.     

Performance enhancement of GaN SB-MOSFET on Si substrate using two-step growth method

We have grown high quality GaN layers on (1 1 1)-oriented silicon substrate using a two-step growth method and fabricated high-performance normally-off n-channel GaN Schottky-barrier MOSFET (SB-MOSFET). Indium-tin-oxide (ITO) was used as Schottky-barrier contact for source and drain (S/D) because the work function of ITO is close to the electron affinity of GaN. Due to enhanced crystalline quality and reduced surface roughness of GaN layer grown by two-step process, the fabricated device exhibited much improved performances: sufficiently high threshold voltage of 3.75 V, subthreshold slope of 171 mV/dec, low specific on-resistance of 9.98 mΩ cm², and very high field-effect mobility of 271 cm²/V s. This is the highest mobility value among the GaN MOSFETs ever reported so far.