Exact analysis of asymmetric random polling systems with single buffers and correlated input process

We introduce a simple approach for modeling and analyzing asymmetric random polling systems with single buffers and correlated input process. We consider two variations of single buffers system: the conventional system and the buffer relaxation system. In the conventional system, at most one customer may be resided in any queue at any time. In the buffer relaxation system, a buffer becomes available to new customers as soon as the current customer is being served. Previous studies concentrate on conventional single buffer system with independent Poisson process input process. It has been shown that the asymmetric system requires the solution ofm 2 ^m –1) linear equations; and the symmetric system requires the solution of 2 ^m–1–1 linear equations, wherem is the number of stations in the system. For both the conventional system and the buffer relaxation system, we give the exact solution to the more general case and show that our analysis requires the solution of 2 ^m –1 linear equations. For the symmetric case, we obtain explicit expressions for several performance measures of the system. These performance measures include the mean and second moment of the cycle time, loss probability, throughput, and the expected delay observed by a customer.     

Novel microchip for in situ TEM imaging of living organisms and bio-reactions in aqueous conditions

A novel and disposable microchip (K-kit) with SiO(2) nano-membranes was developed and used as a specimen kit for in situ imaging of living organisms in an aqueous condition using transmission electron microscopy (TEM) without equipment modification. This K-kit enabled the successful TEM observation of living Escherichia coli cells and the tellurite reduction process in Klebsiella pneumoniae. The K. pneumoniae and Saccharomyces cerevisiae can stay alive in K-kit after continuous TEM imaging for up to 14 s and 42 s, respectively. Besides, different tellurite reduction profiles in cells grown in aerobic and anaerobic environments can be clearly revealed. These results demonstrate that the K-kit developed in this paper can be useful for observing living organisms and monitoring biological processes in situ.     

Novel polymer composite to eliminate background matrix ions in matrix assisted laser desorption/ionization-mass spectrometry

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is rarely used for the analysis of small molecules (< 700 Da) because the low m/z signal is overwhelmed by a high background of matrix ions. We have developed a solution to this problem that employs a novel polymer composite which is formed by covalently cross-linking alpha-cyano-4-hydroxycinnamic acid (HCCA) to SU-8 photoresist via cationic photo-polymerization. Since the HCCA molecules are immobilized, background noise resulting from the matrix ions is significantly reduced or eliminated. Moreover, owing to the hydrophobic surface of the polymer film, the sample spots shrink during solvent evaporation and thus the analytes can be concentrated. As a result, this polymer composite improves detection sensitivity and extends the analyzable species to the low-mass region. The covalent incorporation of HCCA with SU-8 was validated with reflectance FTIR spectroscopy, and the polymer surface was characterized with scanning electron microscopy (SEM). Using MRFA, a small peptide as a standard, 8 mg of HCCA per mL of SU-8 photoresist was found to yield the highest sensitivity and the lowest background noise. Analytes such as peptides or small organic molecules were further examined on this composite surface and no analyte degradation was observed. In a trial of peptide mass fingerprinting of cytochrome c on the composite substrate, the inclusion of low m/z tryptic peptides in the database search dramatically improved the protein identification probability score.     

Controlled synthesis of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by chemical reducing method in ethylene glycol

Antimony trioxide (Sb₂O₃) nanoparticles with particle size range from 2 to 12 nm were successfully synthesized by chemical reducing method. Antimony trichloride was reduced by hydrazine with the presence of sodium hydroxide (NaOH) as catalyst in ethylene glycol at 120 °C for 1 h. Effects of hydrazine concentration ([N₂H₅OH]/[Sb³⁺] = 0.75, 5, 10, 20, and 30, when concentration of NaOH was fixed [NaOH]/[Sb³⁺] = 3) and NaOH concentration ([NaOH]/[Sb³⁺] = 0, 1, 3, and 5, when concentration of hydrazine was fixed [N₂H₅OH]/[Sb³⁺] = 10) on the particle size and shape of the Sb₂O₃ nanoparticles were investigated. Transmission electron microscope, selected area electron diffraction pattern, and high resolution electron microscope were employed to study the morphology and crystallinity of the nanoparticles. It was observed that the particle size decreased and remained constant when [N₂H₅OH]/[Sb³⁺]) ≥ 10 and [NaOH]/[Sb³⁺] = 3. Further study on the crystallinity and phase of the nanoparticles was assisted by X-ray diffractometer (XRD). XRD revealed a cubic phase of Sb₂O₃ (ICDD file no. 00-043-1071) with preferred plane of (622) and lattice spacing of 1.68 Å. Correlation between UV–visible absorption wavelengths of the nanoparticles and their sizes was established.     

upper bond 1 start]PdCl[PPh(2)CH(2)CH(2)C[upper bond 1 end]HCH(2)CH(2)PPh(2)] as a precursor to homo- and hetero-metallic species directed by ESMS (electrospray ionisation mass spectrometry)

The cyclometallated Pd compound [upper bond 1 start]PdCl[PPh(2)CH(2)CH(2)C[upper bond 1 end]HCH(2)CH(2)PPh(2)], obtained from PdCl(2)(Ph(2)P(CH(2))(5)PPh(2)) in refluxing DMF (N,N-dimethylformamide), was characterized by NMR and X-ray single-crystal diffraction analysis. The cyclometallation of MCl(2)(Ph(2)P(CH(2))(5)PPh(2))(M = Pd, Pt) to give and its Pt(ii) analogue was probed using electrospray ionisation mass spectrometry (ESMS). The reactivity of towards neutral ligands such as phosphines and pyridines as well as basic metal complexes such as pyridine-thiolate compounds of Au(i), Hg(ii) and Pt(ii) in solution was also investigated. The results showed that the chloride trans to the Pd-C bond is susceptible to ligand replacement. A number of entry metalloligands was examined in an attempt to establish a route to cyclometallated aggregates and clusters.     

Electrochemistry of Layered Graphitic Carbon Nitride Synthesised from Various Precursors: Searching for Catalytic Effects

Graphitic carbon nitride (g‐C₃N₄), synthesised by pyrolysis of different precursors (dicyandiamide, melamine and urea) under varying reaction conditions (air and nitrogen gas) is subjected to electrochemical studies for the elucidation of the inherent catalytic efficiency of the pristine material. Contrary to popular belief, pristine g‐C₃N₄ shows negligible, if any, enhancement in its electrochemical behaviour in this comprehensive study. Voltammetric analysis reveals g‐C₃N₄ to display similar catalytic efficiency to the unmodified glassy carbon electrode surface on which the bulk material was deposited. This highlights the non‐catalytic nature of the pristine material and challenges the feasibility of using g‐C₃N₄ as a heterogeneous catalyst to deliver numerous promised applications.     

Water absorption and enzymatic degradation of poly(lactic acid)/rice starch composites

Poly(lactic acid) (PLA) composites consisting of PLA, rice starch (RS) (0–50 wt%) and epoxidised natural rubber (ENR50) were compounded by a twin-screw extruder and compression moulded into dumbbell specimens. Tensile tests were performed to characterize the mechanical properties of the PLA/RS composites. Morphological studies were done on the tensile fractured surface of the specimens by using scanning electron microscopy (SEM). Twenty weight percent of RS achieved a good balance of strength and stiffness. Beyond 20 wt% loading of RS, the tensile strength and elongation at break of PLA decreased drastically. This may be attributed to the agglomeration of RS, which could then act as stress concentrator. The incorporation of ENR50 increased the tensile strength and elongation at break of the PLA/RS composites remarkably, owing to the elastomeric behaviour and compatibilisation effects of ENR50. Interestingly, the morphology of PLA/RS composites transformed to a more ductile one with the addition of ENR. The kinetics of water absorption of the PLA/RS composites conforms to Fick's law. The M_m and D values are dependent on the RS and ENR concentrations. The tensile properties of the PLA/RS composites deteriorated after water absorption. The retention-ability and recoverability of the PLA/RS composites are relatively low, attributed to the hydrolysis of PLA, degradation of the PLA–RS interface and leaching of the RS particles. In addition, the tensile properties of PLA/RS composites decreased drastically upon exposure to enzymatic degradation. Extensive pinhole and surface erosion on the PLA/RS composites indicate high degree of hydrolysis. Whilst the addition of ENR leads to some improvements in tensile properties, nevertheless, it enhanced the biodegradability of the PLA/RS composites when exposed to water and -amylase enzymatic treatments.     

Synthesis of Poly(2,5‐benzimidazole) for Use as a Fuel‐Cell Membrane

Summary: Poly(2,5‐benzimidazole) (ABPBI) was synthesized in a novel polymerization medium containing CH₃SO₃H and P₂O₅. 3,4‐Diaminobenzoic acid, a monomer for ABPBI, is soluble in the medium and the polymerization was therefore performed in a homogeneous state. It produced polymer fibers, thus simplifying the work‐up process. The membrane was cast directly from the polymerization mixture. Proton conductivities of the ABPBI membranes ranged from 0.02 to 0.06 S · cm⁻¹ above 100 °C, without humidification, and the tensile strength of the membrane was approximately 100 MPa.

Synthesis of ABPBI in a medium containing methanesulfonic acid and P₂O₅.     

Tune-out and magic wavelengths for hydrogenlike and screened-hydrogenlike atoms

The tune-out and magic wavelengths (TMWs) for the hydrogenlike and screened-hydrogenlike atoms (Z = 1-8) are calculated using a variational method. The first three tune-out wavelengths for each of the nS (n = 1, 2, 3) states and the first three magic wavelengths for each of the 1S-nS (n = 2, 3) transitions of the hydrogenlike atoms in terms of nuclear charge Z, and the first TMWs for the above mentioned states or transitions of the screened-hydrogenlike atoms in terms of the screening parameter μ and Z are presented. All the results for the TMWs are reported for the first time in the literature except the magic wavelengths for the hydrogen atom. The magic wavelengths for hydrogen atom are in agreement with the available data. The precise estimation of the TMWs would be helpful for the design of the ion-trapping experiment of the hydrogenic systems. Our study is expected to be useful for the measurements of the hydrogenic 1S-2S and 1S-3S transitions spectroscopy for the improved accuracy.