Modeling of noise and distortion associated with ultra‐high‐speed modulation of VCSEL with slow‐light feedback

This paper presents numerical modeling on the noise properties and signal distortion associated with millimeter‐frequency modulation of vertical‐cavity surface‐emitting laser (VCSEL) under with a transverse‐coupled cavity. The study is based on a time‐delay rate equation model that takes into account the multiple round trips in the feedback cavity and the optical loss and phase delay in each round trip. Strong slow‐light feedback is found to boost the modulation bandwidth to frequencies approaching 70 GHz and induce resonance modulation due to photon–photon resonance (PPR) over passbands centered on frequencies reaching 90 GHz. We show that the relative intensity noise of the VCSEL with resonance modulation is enhanced when the noise frequency approaches the corresponding PPR frequency VCSEL. The same effect applies for the VCSEL with extended carrier‐photon resonance (CPR) at the CPR frequency. The low‐frequency part is characterized by flat (white) noise of level nearly equal to −140 dB/Hz. The second‐harmonic distortion (2HD) values are smaller than −10 dB under small‐signal modulation and increase to lower than −5 dB when the modulation index becomes 0.3. Copyright © 2015 John Wiley & Sons, Ltd.     

Fatty Acid Conjugates of Water‐Soluble (±)‐trans‐Selenolane‐3,4‐diol: Effects of Alkyl Chain Length on the Antioxidant Capacity

Fatty acid monoesters of the title compound (DHS^red), of variable carbon chain length (propionate, laurate, myristate, palmitate, and stearate), were synthesized, and their antioxidant capacities were evaluated by means of a lipid peroxidation assay with lecithin/cholesterol liposomes. The selenides with long alkyl chains exhibited significant antioxidant activity (IC₅₀=9–34 μM ) against accumulation of lipid hydroperoxide. Incorporation of the myristate into the liposome was ≈50 % by EPMA analysis. Intermediacy of the selenoxide was examined by NMR. In addition, enhancement of interfacial redox catalytic activity was observed for the myristate, but not for PhSeSePh and edaravone, in a PhCl/H₂O biphasic peroxidation assay. These results suggested that a combination of a hydrophilic selenide moiety as a redox center with a long alkyl chain is an effective approach to selenium antioxidants with interfacial glutathione‐peroxidase‐like (GPx‐like) activity. The activity can be controlled by the alkyl chain length.     

High-purity hydrogen gas production by catalytic thermal decomposition using mechanochemical treatment

The objectives of this work, were to produce high-purity hydrogen gas from rice husk by two-step process and to study the effect of nickel hydroxide/nickel acetate/sodium acetate and calcium hydroxide on the concentration of gaseous products. The samples were characterized by X-ray diffraction (XRD) and thermogravimetry-mass spectroscopy (TG/MS). The gaseous products were analyzed by gas chromatography (GC). The results indicated that hydrogen gas was produced from the milled samples by heating at 400–600 °C with the low concentrations of methane, carbon monoxide and carbon dioxide. The highest concentration of hydrogen gas from milled samples with the catalyst, was approximately 95–97 %mol. Furthermore, the milled samples with the carbon dioxide capture agent gave the carbon dioxide concentration, was below 2 %mol.     

Ageing Effects on the Yielding Characteristics of Cement-Mixed Granular Materials

Ageing effects on the elasto-viscoplastic property of compacted moist cement-mixed granular material (GM) were evaluated by performing a series of non-standard drained triaxial compression (TC) tests. Two types of GM, crushed gravelly soil from a quarry and crushed concrete aggregate (i.e., a recycled material), were used. The specimens were produced by moist-compaction and then cured at constant water content under unstressed conditions for seven days. They were re-cured basically for two days under different stress states during otherwise drained TC loading at a constant strain rate. Yielding characteristics upon the restart of drained monotonic loading (ML) at a constant strain rate toward ultimate failure at the same or increased or decreased confining pressure were evaluated. The stress-strain behaviour before the stress state reaches the current yield locus is very stiff and highly reversible. Unlike elasto-plastic materials exhibiting no ageing effects, the yield locus expands during sustained loading at a fixed effective stress state due to not only yielding associated with creep deformation, controlled basically by the viscous property, but also ageing, controlled basically by time-elapsing. The shape and location of current yield locus depends on the location of the current stress state relative to the current ultimate failure envelope. The observed yield characteristics were analyzed based on a newly introduced interactive double-yield concept while in the framework of the non-linear three-component elasto-viscoplastic model that takes into account ageing effects as well as an interaction between ageing and inviscid yielding (and its potential decay by irreversible straining). The trends of stress-strain-time behaviour observed with the two types of cement-mixed GMs are essentially the same.     

Stabilization of higher-order structure of poly(phenyleneethynylene)s by metathesis polymerization at the side chains

Novel poly(m-phenyleneethynlene-p-phenyleneethynylene)s bearing polymerizable diene or norbornene groups were synthesized by the Sonogashira–Hagihara coupling polymerization of the corresponding d-hydroxyphenylglycine-derived diiodo monomers with p-diethynylbenzene. These polymers exhibited strong Cotton effects derived from a predominantly one-handed helical conformation in CHCl₃ and tetrahydrofuran, but exhibited weak or no Cotton effects in N,N-dimethylformamide. The metathesis polymerization of the diene and norbornene moieties was performed at the side chains of the polymers under diluted conditions in the presence of a chain-transfer agent, if necessary. The reaction took place intramolecularly, which was confirmed by size exclusion chromatography (SEC) measurements. The polymers exhibited stronger Cotton effects even in polar media after the intramolecular crosslinking, which indicated stabilization of the predominantly one-handed helical structures.     

Effects of electric field and poling on the fatigue of cracked piezoelectric ceramics in cyclic three-point bending

This paper deals with the fatigue behavior of cracked piezoelectric ceramics in cyclic bending under electric fields both numerically and experimentally. Fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created normal to the poling direction. Number of cycles to failure was measured under different electric fields. A plane strain finite element analysis was also performed, and the effect of polarization switching on the energy release rate was discussed under a high negative electric field. In addition, possible mechanisms for crack growth were discussed by scanning electron microscope examination of the fracture surface of the piezoelectric ceramics.     

Improvement of Processability of PCL and PBS Blend by Irradiation and its Biodegradability

Poly(ε‐caprolactone) (PCL) was blended with poly(butylene succinate) (PBS), (PCL/PBS = 30/70) to improve the heat stability of PCL. The processability of the blended samples (PHB02) was improved due to enhancing of melt strength by γ‐rays irradiation in the dose range between 10 and 50 kGy. High speed production of a thin film and production of foam have been achieved by this process. The soil degradation test showed that PHB02 film buried in the soil was almost degraded (97%) after two months and completely degraded after two and a half months. On the contrary, the sample on the surface degraded to only 3.5% after four months. From these findings it was confirmed that microorganisms contribute to degradation in the soil. In the case of PHB02 foam samples, 65% degradation was achieved after four months. The PHB02 sample used as garbage bags was well degraded (almost 50%) after a two months burial test. The enzymatic degradation test showed that after treatment for 24 h, the weight loss of PHB02 irradiated with 30 kGy and unirradiated samples were 80% and 90%, respectively. Enzymatic degradation for PHB02 films led to the suggestion that the biodegradation process proceeds from the surface to the inside of the sample by erosion.     

Surface modification processing of synthetic rubbers by ultraviolet irradiation and sputter ion etching treatment

The mechanism by which surface modification of two kinds of synthetic rubbers (ethylene-propylene and chloroprene) was brought about by ultraviolet (UV) irradiation and sputter ion etching treatments was studied from a physicochemical point of view. The most remarkable effect of this irradiation treatment was the rapid increase in adhesion properties and the simultaneous decrease in self-stickiness. This nonsticking effect was particularly important for the rapid production of articles from thin rubber sheets. The surface modification mechanism was studied by use of SEM, ESCA, FTIR, and related interfacial analytical procedures. It was shown that surface roughening with a quite thin layer of surface oxidation (∼0.5 μm in depth) is a key factor for the development of nonsticking properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1625–1633, 1997     

Evaluation of polybutene electrofusion joint performance

This paper describes methods of evaluating polybutene electrofusion joints and results of mechanical strength measurements for an electrofusion joint. Suitable fusion conditions were determined qualitatively through measurement of fusion interface temperatures and observation of the fusion zone. A method of determining standard fusion conditions, based on the relation between heating time and tensile strength, is also indicated. Differences in thermal properties between polybutene and polyethylene resins are discussed. It was found that polybutene required less supplied power per unit fusion area for suitable fusion. It was also confirmed that an electrofusion joint required a cold zone.