Detection and generation of first sound in4He by vibrating superleak transducers

Measurement is made of the first-sound generation and detection efficiencies of vibrating superleak transducers (VSTs) operated in superfluid⁴He. This is accomplished by using an ordinary pressure transducer to generate first sound with a VST as the detector, and by using a pressure transducer to detect the sound generated by a VST. The results are in reasonably good agreement with the current theory of VST operation.     

Multihop Ad Hoc Networking: The Reality

In this article we show that, although pure general-purpose MANET (mobile ad hoc networks) does not yet exist in the real world, the multihop ad hoc networking paradigm was successfully applied in several classes of networks that are penetrating the mass market. We present as examples mesh, opportunistic, vehicular, and sensor networks, where the multi-hop ad hoc paradigm is applied in a pragmatic way to extend the Internet and/or to support well-defined application requirements. We contrast these successful areas of ad hoc networking to the lack of impact of pure general-purpose MANET, demonstrating how a more pragmatic approach is a winner     

Estimation of token bucket parameters for aggregated VoIP sources

The paper presents an analytical study aimed to establish a dimensioning procedure for the token bucket algorithm, used as a meter in a Differentiated Services network architecture, when a stochastic model for the multiplexed traffic is available. In the work, we propose an equivalent queueing system method to ‘on line’ estimate the linear bounded arrival processes (LBAP) parameters when a non‐zero probability of non‐conforming packets is accepted. Then, we validate our approach considering an aggregation of fluidic On‐Off processes with exponentially distributed sojourn time in each state, used to model telephone sources with voice activity detection (VAD). To test the goodness of our analytical results, we employ discrete event simulations, which have highlighted the accuracy of the proposed dimensioning procedure in a voice over IP (VoIP) scenario. Moreover, we investigate the multiplexing gain and the effect of different parameters on the LBAP characterization of the VoIP traffic, taking into account a non‐zero probability of non‐conforming packets. Copyright © 2002 John Wiley & Sons, Ltd.     

Anatomical,Morphological, and Phytochemical Effects of Inoculation with Plant Growth- Promoting Rhizobacteria on Peppermint (<Emphasis Type="Italic">Mentha piperita</Emphasis>)

Plant growth-promoting rhizobacteria (PGPR) generally exert their effects through enhancement of plant nutrient status and/or phytohormone production. The effects of PGPR on aromatic plant species are poorly known. We measured plant growth parameters, chlorophyll content, trichome density, stomatal density, and levels of secondary metabolites in peppermint (Mentha piperita) seedlings inoculated with PGPR strains Bacillus subtilis GB03, Pseudomonas fluorescens WCS417r, P. putida SJ04, or a combination of WCS417r?+?SJ04. The treated plants, in comparison with controls, showed increases in shoot biomass, root biomass, leaf area, node number, trichome density, and stomatal density, and marked qualitative and quantitative changes in monoterpene content. Improved knowledge of the factors that control or affect biosynthesis of secondary metabolites and monoterpene accumulation will lead to strategies for improved cultivation and productivity of aromatic plants and other agricultural crops without the use of chemical fertilizers or pesticides.     

Palladium‐Catalyzed [2+1] Cycloadditions Affording Vinylidenecyclopropanes as Precursors of 7‐Membered Carbocycles

Palladium(II) acetate in association with secondary phosphine oxides provides an efficient catalytic system for [2+1] cycloadditions starting from oxanorbornene derivatives and tertiary propargyl esters giving rise to vinylidenecyclopropanes. This reaction is specific to bidentate phosphinito–phosphinous acid ligands generated from secondary phosphine oxides. The [2+1] cycloaddition was found broad in scope with a high tolerance to various functional groups. Moreover, vinylidenecyclopropanes were straightforwardly converted into oxabicyclo[3.2.1]oct‐2‐ene derivatives through a palladium‐catalyzed ring‐expansion. Finally, the oxa bridge cleavage of oxatricyclic compounds yields functionalized 7‐membered carbocycles.

     

Effects of grain refinement on the microstructure,mechanical properties and reliability of AlSi7Cu3Mg gravity die cast cylinder heads

The effects of grain refinement on the microstructure and mechanical properties of a secondary AlSi7-Cu3Mg gravity die cast cylinder head are reported. Metallographic and image analysis techniques have been used to quantitatively examine the macro- and microstructural changes occurring with the addition of grain-refining agent. The results indicate that the AlTi5B1 addition produces a fine and uniform grain structure throughout the casting; this effect is more pronounced in the slowly solidified regions. The initial contents of Ti and B, which are present as impurity elements in the supplied secondary alloy ingots, are not sufficient to produce effective grain refinement. Under the present casting conditions, the combined addition of AlTi5B1 and Sr does not produce any reciprocal interaction or effect on primary α-Al and eutectic solidification. Grain refinement improves the mechanical properties of the as-cast AlSi7Cu3Mg alloy and produces higher Weibull moduli, thus increasing the reliability of the casting. For automotive structural components, this could be considered an increase in safety.     

Presynchronization with Double-Ovsynch improves fertility at first postpartum artificial insemination in lactating dairy cows

The objective of this study was to compare circulating progesterone (P4) profiles and pregnancies per AI (P/AI) in lactating dairy cows bred by timed artificial insemination (TAI) following Ovsynch-56 after 2 different presynchronization protocols: Double-Ovsynch (DO) or Presynch-Ovsynch (PS). Our main hypothesis was that DO would increase fertility in primiparous cows, but not in multiparous cows. Within each herd (n = 3), lactating dairy cows (n = 1,687; 778 primiparous, 909 multiparous) were randomly assigned to DO [n = 837; GnRH-7d-PGF_2α-3d-GnRH-7d-Ovsynch-56 (GnRH-7d-PGF_2α-56h-GnRH-16hTAI)] or PS (n = 850; PGF_2α-14d-PGF_2α-12d-Ovsynch-56). In 1 herd, concentrations of P4 were determined at the first GnRH (GnRH1) of Ovsynch-56 and at d 11 after TAI (n = 739). In all herds, pregnancy was diagnosed by palpation per rectum at 39 d. In 1 herd, the incidence of late embryo loss was determined at 74 d, and data were available on P/AI at the subsequent second service. Presynchronization with DO reduced the percentage of animals with low P4 concentrations (<0.50 ng/mL) at GnRH1 of Ovsynch-56 (5.4 vs. 25.3%, DO vs. PS). A lesser percentage of both primiparous and multiparous cows treated with DO had low P4 concentrations at GnRH1 of Ovsynch-56 (3.3 vs. 19.7%, DO vs. PS primiparous; and 8.8 vs. 31.9%, DO vs. PS multiparous). Presynchronization with DO improved P/AI at the first postpartum service (46.3 vs. 38.2%, DO vs. PS). Statistically, a fertility improvement could be detected for primiparous cows treated with DO (52.5 vs. 42.3%, DO vs. PS, primiparous), but only a tendency could be detected in multiparous cows (40.3 vs. 34.3%, DO vs. PS, multiparous), consistent with our original hypothesis. Presynchronization treatment had no effect on the incidence of late embryo loss after first service (8.5 vs. 5.5%, DO vs. PS). A lower body condition score increased the percentage of cows with low P4 at GnRH1 of Ovsynch-56 and reduced fertility to the TAI. In addition, P4 concentration at d 11 after TAI was reduced by DO. The method of presynchronization at first service had no effect on P/AI at the subsequent second service (34.7 vs. 36.5%, DO vs. PS). Thus, presynchronization with DO induced cyclicity in most anovular cows and improved fertility compared with PS, suggesting that DO could be a useful reproductive management protocol for synchronizing first service in commercial dairy herds.     

Characterization of solid embeddable reference electrodes for corrosion monitoring in reinforced concrete structures

Metal-metal oxide (MMO), graphite and laboratory-made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarization behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of 2 years. It was found that the MMO pseudo-reference electrode is pH-sensitive, the graphite pseudo-reference electrode is oxygen sensitive and the Ag/AgCl pseudo-reference electrode is chloride sensitive. In spite of the fact that any of them can be used to determine the corrosion rates of rebars because they do not depend on the absolute potential and/or the long-term stability of the reference electrode when using traditional electrochemical techniques, long-term drifts in the electrode potentials may lead to misinterpretations of the rebar state. In this context graphite electrodes are recommended because they provide conservative results regarding the active/passive state of the rebars.     

Zinc‐based compounds as smoke suppressant agents for an aerospace epoxy matrix

Smoke is considered to be the main hazard of fires involving epoxy resins but its production depends on many variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen. The work reported aimed to study the smoke suppressant effect and flammability performance of zinc‐based compounds (FR system) in epoxy matrix composites used in the aerospace and aeronautical industry. The flammability performance of neat and FR‐loaded systems was screened using microcombustion calorimetry, while smoke generation, in terms of carbon monoxide (CO) and carbon dioxide (CO₂) production, was analysed under dynamic conditions using cone calorimetry. Final results indicate that the dispersion of zinc borate and zinc hydroxystannate (ZHS) into epoxy matrices leads to a significant variation in flame retardant properties reducing both total heat release by about 25 and 30%, respectively, and heat release capacity by about 30 and 50%, respectively. The system containing ZHS shows an enhancement in all smoke suppressant properties; both tin compounds (zinc stannate (ZS) and ZHS) give a reduction of CO₂/CO ratio from 41 to 25 for ZS and from 41 to 36 for ZHS compared to neat matrix. Copyright © 2010 Society of Chemical Industry