ATM-based switching for the integrated broadband network

Telecommunications networks based on synchronous 64 kbit/s channels are too restrictive for the future realisation of integrated broadband networks. New switching and transmission techniques, particularly those based on asynchronous transfer modes (ATM), are required. Roke Manor Research Ltd. and Plessey Research Caswell Ltd. are actively developing these new techniques at a system and technology level under the auspices of the European Commission's RACE programme. The authors introduce the issues pertinent to ATM, highlighting the system and technology aspects of the work being carried out within a RACE project entitled `Broadband Local Network Technology' (BLNT) and also describes previous ATM work relevant to the current research activities     

Note on calculating energy values of rotationally hindered linear molecules

The variational principle based on an integral equation equivalent to the Schrödinger equation is employed to calculate energy levels ofDevonshire's model.     

XeCl laser generated infra-red SRS in barium vapour

Radiation at 2.36 μm is produced by stimulated electronic Raman scattering in barium vapour. The pump radiation is provided by a XeCl excimer laser. Photon conversion efficiencies of up to 1% are observed. The variations of the infra-red Stokes output with barium number density and with pump intensity are described.     

Kinetic determination of cysteine and thiosulphate by inhibition of Hg(II) catalyzed ligand substitution reaction

The sulphur containing inhibitors (I), cysteine (Cys) and sodium thiosulphate (THS), have been found to inhibit Hg(II) catalyzed exchange of cyanide in hexacyanoferrate(II) by nitroso-R-salt (NRS). The inhibitory effect of both the ligands are attributed to their binding tendencies with Hg(II) leading to the formation of catalyst-inhibitor (C-I) complex. The reactions have been followed spectrophotometrically in aqueous medium at 720 nm by noting the increase in absorbance of the green colour product, [Fe(CN)₅NRS]³⁻ at pH 6.50 ± 0.02, temp 25.0 ± 0.1 °C and ionic strength (μ) 0.1 M (KNO₃). A most plausible mechanistic scheme involving the role of analytes (inhibitors) has been proposed. The values of equilibrium constants for complex formation between catalyst-inhibitor (K_CI), catalyst-substrate (K_S) and Mechaelis-Menton constant (K_m) have been computed from the kinetic data. The linear calibration curves have been established between absorbance and inhibitor concentrations under specified conditions. Cys and THS have been determined in the range 1-5 × 10^− 7 M and 4.9-16.9 × 10^− 7 M respectively. The detection limits have been computed to be 1 × 10^− 7 M and 4.9 × 10^− 7 M for Cys and THS, respectively.     

Quantitation of methylated hemoglobin adducts in a signature peptide from rat blood by liquid chromatography/negative electrospray ionization tandem mass spectrometry

Hemoglobin adducts are often used as biomarkers for exposure to reactive chemicals in toxicology studies. Therefore, fast, sensitive, accurate, and reproducible methods for quantifying these protein adducts are key to evaluate test material dosimetry. A methodology has been developed for the quantitation of methylated hemoglobin adducts isolated from rats exposed to the model alkylating agent: methyl methane sulfonate (MMS). After 4 days of MMS exposure by oral gavage, hemoglobin was isolated from rat blood and digested with trypsin. The tryptic digestion solution was used for the adducted hemoglobin signature peptide quantitation via liquid chromatography/negative tandem mass spectrometry (LC/ESI-MS/MS). The limit of quantitation (LOQ) for the methylated hemoglobin beta chain N-terminal signature peptide (MeVHLTDAEK) was 1.95 ng/mL (5.9 pmol/mg globin). The calibration curves were linear over a concentration range of 1.95 to 625 ng/mL, with a correlation coefficient R2 >0.998, accuracy of 85.8 to 119.3%, and precision of 0.9 to 19.4%.     

Selective one-electron oxidation of duplex DNA oligomers: reaction at thymines

The one-electron oxidation of duplex DNA generates a nucleobase radical cation (electron "hole") that migrates long distances by a hopping mechanism. The radical cation reacts irreversibly with H2O or O2 to form oxidation products (damaged bases). In normal DNA (containing the four common DNA bases), reaction occurs most frequently at guanine. However, in DNA duplexes that do not contain guanine (i.e., those comprised exclusively of A/T base pairs), we discovered that reaction occurs primarily at thymine and gives products resulting from oxidation of the T-C5 methyl group and from addition to its C5-C6 double bond. This surprising result shows that it is the relative reactivity, not the stability, of a nucleobase radical cation that determines the nature of the products formed from oxidation of DNA. A mechanism for reaction is proposed whereby a thymine radical cation may either lose a proton from its methyl group or H2O/O2 may add across its double bond. In the latter case, addition may initiate a tandem reaction that converts both thymines of a TT step to oxidation products.     

Improving the Flexibility of Dynamic Prosody Modification Using Instants of Significant Excitation

Modification of suprasegmental features such as pitch and duration of original speech by fixed scaling factors is referred to as static prosody modification. In dynamic prosody modification, the prosodic scaling factors (time-varying modification factors) are defined for all the pitch cycles present in the original speech. The present work is focused on improving the naturalness of the prosody modified speech by reducing the generation of piecewise constant segments in the modified pitch contour. The prosody modification is performed by anchoring around the accurate instants of significant excitation estimated from the original speech. The division of longer pitch intervals into many equal intervals over long speech segments introduces step-like discontinuities in the form of piecewise constant segments in the modified pitch contours. The effectiveness of proposed dynamic modification method is initially confirmed from the smooth modified pitch contour plot obtained for finer static prosody scaling factors, waveforms, spectrogram plots and comparison subjective evaluations. Also, the average \(F_0\) jitter computed from the pitch segments of each glottal activity region in the modified speech is proposed as an objective measure for the prosody modification. The naturalness of the prosody modified speech using the proposed method is objectively and subjectively compared with that of the existing zero frequency filtered signal-based dynamic prosody modification. Also, the proposed algorithm effectively preserves the dynamics of the prosodic patterns in singing voices where in the \(F_0\) parameters rapidly and continuously fluctuate within a higher \(F_0\) range.     

Social optimum in social groups with give‐and‐take criterion

We consider a ‘Social Group’ of networked nodes, seeking a ‘universe’ of segments. Each node has a subset of the universe and access to an expensive resource for downloading data. Nodes can also acquire the universe by exchanging copies of segments among themselves, at low cost, using inter‐node links. While exchanges over inter‐node links ensure minimum cost, some nodes in the group try to exploit the system. We term such nodes as ‘non‐reciprocating nodes’ and prohibit such behavior by proposing the ‘give‐and‐take’ criterion, where exchange is allowed if each node has segments unavailable with the other. Under this criterion, we consider the problem of maximizing the number of nodes with the universe at the end of local exchanges. First, we present a randomized algorithm that is shown to be optimal in the asymptotic regime. Then, we present greedy links algorithm, which performs well for most of the scenarios and yields an optimal result when the number of nodes is four. The polygon algorithm is proposed, which yields an optimal result when each of the nodes has a unique segment. After presenting some intuitive algorithms (e.g., greedy incremental algorithm and rarest first algorithm), we compare the performances of all proposed algorithms with the optimal. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,characterisation and crystal structures of three trinuclear cadmium(II) complexes with multidentate Schiff base ligands

Three novel Schiff base Cd(II) trimeric complexes, [Cd₃(L¹)₂(SCN)₂(CF₃COO)₂] (1), [Cd₃(L¹)₂(SCN)₂(HCONMe₂)] (2) and [Cd₃(L²)₂{N(CN)₂}₂] (3) have been prepared from two different symmetrical Schiff bases H₂L¹ and H₂L² (where H₂L¹ = N¹,N³-bis(salicylideneimino)diethylenetriamine, a potentially pentadentate Schiff base with a N₃O₂ donor set, and H₂L² = N¹,N³-bis(3-methoxysalicylideneimino)diethylenetriamine, a potentially heptadentate Schiff base with a N₃O₄ donor set). All the complexes have been synthesised under similar synthetic procedures and their crystal structures have been established by single crystal X-ray diffraction methods. The ligands and their metal complexes have been characterised by analytical and spectroscopic techniques. Among the three complexes, 1 and 3 are linear whereas 2 is a cyclic trimer. In 1 and 3, all the doubly phenoxo bridged Cd(II) metal centres are in a distorted octahedral environment. In complex 2, two of the three Cd(II) centres reside in a distorted octahedral environment and the remaining one enjoys a monocapped octahedral geometry. Altogether the variety in the bridging mode of two new salen-type ligands has been established through these complexes.