A new signal processing technique for ISAR ranging: the Vernierranging method

A new technique for inversed synthetic aperture radar (ISAR) ranging, which resembles the principle of the Vernier measuring system, is presented. In this technique, the transmitted ISAR pulse comprises a train of chirp subpulses with uniformly stepped up center frequencies. The return ISAR echo is first processed, using hardware, to determine a coarse estimate of the target range. Further refinements of the range estimate are achieved through software processing, consisting of two stages of discrete Fourier transform operation. The ranging accuracy can be increased without the need for increased bandwidth, but at the expense of a slight increase in computational complexity. Numerical evaluation shows that a noiseless system is capable of achieving high-ranging accuracy, of the order of millimeters, even in the presence of dispersion and target motion. From computer simulations, the proposed system is also found to be robust against additive system noise and frequency jitter under practical conditions     

Total Domination in Graphs with Given Girth

A set S of vertices in a graph G without isolated vertices is a total dominating set of G if every vertex of G is adjacent to some vertex in S. The minimum cardinality of a total dominating set of G is the total domination number γ _t (G) of G. In this paper, we establish an upper bound on the total domination number of a graph with minimum degree at least two in terms of its order and girth. We prove that if G is a graph of order n with minimum degree at least two and girth g, then γ _t (G) ≤ n/2 + n/g, and this bound is sharp. Our proof is an interplay between graph theory and transversals in hypergraphs. Michael A. Henning: Research supported in part by the South African National Research Foundation and the University of KwaZulu-Natal.     

The Re(I) coordination chemistry of a series of pyrido[2,3-b]pyrazine-derived ligands: Syntheses,characterisation and crystal structures

Reaction of 2,3-diaminopyridine with one equivalent of a functionalised vicinal diketone, in ethanol, yields a series of ligands based upon the pyrido[2,3-b]pyrazine core. The ligands were characterised by ¹H, ¹³C–{¹H} NMR, MS and UV–Vis spectroscopy. Reaction of the ligands with one equivalent of {ReBr(CO)₅} gave a series of Re-Lⁿ complexes based upon the general formula fac-{ReBr(CO)₃(L)} (where L = pyrido[2,3-b]pyrazine-derived ligands, L¹–L⁶). Solution IR studies confirmed the retention of the facially capped, tri-carbonyl coordination geometry at rhenium, and ¹H NMR studies confirmed coordination of the ligand to Re(I). EI HR MS data were obtained for each complex confirming the proposed formulation and stoichiometry. Single crystal X-ray structures were obtained for three of the complexes (Re-L¹, Re-L², Re-L⁶), with each demonstrating that the ligands coordinate to Re(I) in a bidentate manner, via a four-membered chelate ring, which was unsymmetrical in the former two cases. The electronic absorption spectra of the complexes showed absorption into the visible region ca. 375–500 nm, (the complexes are orange-red in appearance). Following irradiation at 350–450 nm, the complexes display a solid-state broad emission peaking between 600–700 nm. The complexes were not sufficiently luminescent in solution to allow further investigation into the origin of this emission band, although with reference to related 1,8-naphthyridine complexes of Re(I) it is likely to incorporate significant ³MLCT character.     

Dynamic Transmission Scheduling for Streaming Applications via P2P Overlay

In current Peer-to-Peer streaming applications, a lot of research attempts to provide timely stream services to the end users. Most of them focus on how to organize the peer connections into an efficient overlay network. Due to the variation in the network, a lot of overhead is generated when the overlay structure adapts to the changes. In order to minimize the impact of network fluctuation, we proposed a scheduling algorithm which helps to distribute stream data efficiently through the fluctuating networks. It needs only partial information about overlay structure and provides the services to satisfy most number of users. The global latency experienced by peers in the system is thus minimized. To alleviate the problem of packet loss along the overlay, we introduce retransmission requests into our scheduling algorithm. Requests for much needed data are treated with higher priority. Parent peers which receive the request will re-send the missing data to minimize the loss impact. The missing data which are needed by more peers will have a larger cumulative impact through the tree overlay and these are thus scheduled and sent earlier. Simulation results showed that our prioritization and scheduling algorithm minimizes the negative impact of fluctuation and data loss in a dynamic network environment.     

A metacognitive-based instruction for Primary Four students to approach non-routine mathematical word problems

Many Primary Four students (fourth graders) in Singapore have difficulties initiating or persevering in the problem-solving process even though the curriculum has focused on problem solving since 1992. This study served to examine the role of metacognition in self-regulated problem solving. The study, a quasi-experimental pretest–posttest design involving a convenience sample of 63 students from two intact mixed-ability Primary Four classes, examined the impact of using a metacognitive scheme that focuses on the understanding and planning stages of Pòlya’s four-stage approach on students’ mathematical problem-solving behavior, performance and attitudes. The findings revealed that the metacognitive-based scheme had a positive impact on students’ understanding of the problem posed, solution planning, confidence in and personal control of problem-solving behavior and emotions. It had also helped them to initiate and persevere in the problem-solving process to achieve a higher level of problem-solving success. Limitations and instructional implications are discussed.     

Distinguishing-Transversal in Hypergraphs and Identifying Open Codes in Cubic Graphs

The open neighborhood N(v) of a vertex v in a graph G is the set of vertices adjacent to v in G. A graph is twin-free (or open identifiable) if every two distinct vertices have distinct open neighborhoods. A separating open code in G is a set C of vertices such that \({N(u) \cap C \neq N(v) \cap C}\) for all distinct vertices u and v in G. An open dominating set, or total dominating set, in G is a set C of vertices such that \({N(u) \cap C \ne N(v) \cap C}\) for all vertices v in G. An identifying open code of G is a set C that is both a separating open code and an open dominating set. A graph has an identifying open code if and only if it is twin-free. If G is twin-free, we denote by \({\gamma^{\rm IOC}(G)}\) the minimum cardinality of an identifying open code in G. A hypergraph H is identifiable if every two edges in H are distinct. A distinguishing-transversal T in an identifiable hypergraph H is a subset T of vertices in H that has a nonempty intersection with every edge of H (that is, T is a transversal in H) such that T distinguishes the edges, that is, \({e \cap T \neq f \cap T}\) for every two distinct edges e and f in H. The distinguishing-transversal number \({\tau_D(H)}\) of H is the minimum size of a distinguishing-transversal in H. We show that if H is a 3-uniform identifiable hypergraph of order n and size m with maximum degree at most 3, then \({20\tau_D(H) \leq 12n + 3m}\) . Using this result, we then show that if G is a twin-free cubic graph on n vertices, then \({\gamma^{\rm IOC}(G) \leq 3n/4}\) . This bound is achieved, for example, by the hypercube.     

Rapid detection of Mycobacterium tuberculosis cells by using microtip-based immunoassay

This paper describes a microtip-based approach of concentrating target analytes for a highly sensitive bioassay. As an example, rapid screening of bacterial whole cells is presented to detect Mycobacterium tuberculosis (MTB), a pathogenic bacterium for human tuberculosis (TB). The concentration and detection is performed with three sequential steps of (1) attracting bacterial whole cells in the vicinity of a microtip by alternating current electroosmotic flow; (2) capturing the cells onto the microtip by capillary action; (3) binding fluorophore-labeled polyclonal antibodies to the cells followed by fluorescence measurement (immunofluorescence). Through this mechanism, MTB cells have been detected to the concentration of 8,000 cells/mL within 10 min. This sensitivity is comparable to that of Ziehl–Neelsen smear microscopy, a common culture-free screening method for diagnosis of TB. For comparison, Escherichia coli O157:H7 cells have also been detected to the concentration of 30,000 cells/mL in the same way.     

Trisneopentylgallium as a precursor for atomic layer epitaxy of GaAs

We report the use of a new precursor, trisneopentylgallium (NPG) for the growth of GaAs by atomic layer epitaxy (ALE). In contrast to most other alkyl gallium precursors such as triethylgallium, which decompose via a β-hydride elimination mechanism, this compound undergoes homolysis similar to that of trimethylgallium (TMGa), the normal choice as an ALE precursor. Clear self-limiting growth behavior similar to that of TMGa was observed over a reasonably wide range of growth conditions (430–500°C). Carbon incorporation was not significantly reduced compared with TMGa suggesting that the adsorbed neopentyl radicals undergo decomposition to result in a methyl terminated surface identical to that obtained for growth with TMGa.