Mathematical and numerical approach for a crashworthy problem

Vehicle crashworthiness has been improving in recent years with attention mainly directed towards reducing the impact of the crash on the passengers. An optimal way to achieve this target is by exclusive use of specific impact attenuators, such as strategically placed tubular elements. Many of the mechanical devices are designed to absorb impact energy under axial crushing, bending and/or combined loading. An important requirement is that these structural members must be able to dissipate large amount of energy by controlled collapse in the event of a collision. Generally, the total energy dissipated depends on the governing deformation phenomena of all or part of the structural components of simple geometry, such as thin-walled tubes, cones, frames and sections. The energy absorbing capacity differs from one component to the next in a manner which depends on the mode of deformation involved and the material used. During the last decades the attention given to crash energy management has been centred on composite structures. The use of fibre-reinforced plastic composite materials in automotive structures may result in many potential economic and functional benefits due to their improved properties respect to metal ones, ranging from weight reduction to increased strength and durability features. Although significant experimental work on the collapse of fibre-reinforced composite shells has been carried out, studies on the theoretical modelling of the crushing process are quite limited since the complex and brittle fracture mechanisms of composite materials. Most of the studies have been directed towards the axial crush analysis, because it represents more or less the most efficient design. In the present paper, a mathematical approach on the failure mechanisms, pertaining to the stable mode of collapse (Mode I) of thin-walled composite circular tubes subjected to axial loading, was investigated. The analysis was conducted from an energetic point of view; it is therefore necessary to identify the main energy contributions and then equate the total internal energy to the work done by the external load. The average crush load can be obtained minimizing the force contribution, function of several variables, on a domain using a numerical approach. Comparison between theory and experiments concerning crushing loads and total displacements was analysed, showing how the proposed analytical model is efficient for predicting the energy absorption capability of axially collapsing composite shells

Miniaturised wearable UHF-RFID tag with tuning capability

By carving a 'square-smile'slot profile over a folded patch, a miniaturised UHF-RFID tag is obtained, having a convenient two-step tuning mechanism (coarse and fine). This is useful to adapt the same tag to European and US frequencies and to make on-site corrections. The antenna is half the size of a credit card and can be read up to 5m when attached onto the body. The flexible and lightweight EPDM foam substrate makes the tag suited to be integrated in badges, wallets, pockets, plasters, wristbands and various garments

On the Evidence for Axion-like Particles from Active Galactic Nuclei

Burrage, Davis, and Shaw recently suggested exploiting the correlations between high and low energy luminosities of astrophysical objects to probe possible mixing between photons and axion-like particles (ALP) in magnetic field regions. They also presented evidence for the existence of ALP's by analyzing the optical/UV and X-ray monochromatic luminosities of AGNs. We extend their work by using the monochromatic luminosities of 320 unobscured Active Galactic Nuclei from the Sloan Digital Sky Survey/Xmm-Newton Quasar Survey (Young et al., 2009), which allows the exploration of 18 different combinations of optical/UV and X-ray monochromatic luminosities. However, we do not find compelling evidence for the existence of ALPs. Moreover, it appears that the signal reported by Burrage et al. is more likely due to X-ray absorption rather than to photon-ALP oscillation.Comment: 16 pages, 12 figures. Updated to reflect the minor changes introduced in the published versio

Ruthenium(II) Arene Complexes Bearing Tris(pyrazolyl)methanesulfonate Capping Ligands.Electrochemistry, Spectroscopic, and X-ray Structural Characterization

Novel [Ru(L)(Tpms)]Cl and [Ru(L)(Tpms(Ph))]Cl complexes (L = p-cymene, benzene, or hexamethylbenzene, Tpms = tris(pyrazolyl)-methanesulfonate, Tpms(Ph) = tris(3-phenylpyrazoly)methanesulfonate) have been prepared by reaction of [Ru(L)(mu-Cl)(2)](2) with Li[Tpms] and Li[Tpms(Ph)], respectively. [Ru(p-cymene)(Tpms)]BF4 has been synthesized through a metathetic reaction of [Ru(p-cymene)(Tpms)]Cl with AgBF4. [RuCl(cod)(Tpms)] (cod = 1,5-cyclooctadiene) and [RuCl(cod)(Tpms(Ph))] are also reported, being obtained by reaction of [RuCl2(cod)(MeCN)(2)] with Li[Tpms] and Li[Tpms(Ph)], respectively. The structures of the complexes and the coordination modes of the ligands have been established by IR, NMR, and single-crystal X-ray diffraction (for [RuL(Tpms)]X (L = p-cymene or HMB, X = Cl; L = p-cymene, X = BF4)) studies. Electrochemical studies showed that each complex undergoes a single-electron R-II -> R-III oxidation at a potential measured by cyclic voltammetry, allowing to compare the electron-donor characters of the tris(pyrazolyl)methanesulfonate and arene ligands, and to estimate, for the first time, the values of the Lever E-L ligand parameter for Tmps(Ph), HMB, and cod

Evidence of an association between poly(3-hydroxybutyrate) accumulation and phosphotransbutyrylase expression in Bacillus megaterium

Molecular analysis of a genomic region of Bacillus megaterium, a polyhydroxybutyrate (PHB)- producing microorganism, revealed the presence of a gene coding for the enzyme phosphotransbutyrylase (Ptb). Enzyme activity was measured throughout the different growth phases of B. megaterium and was found to correlate with PHB accumulation during the late-exponential growth phase. Ptb expression was repressed by glucose and activated by the branched amino acids isoleucine and valine. Overexpression of ActBm, a σ 54 regulator from B. megaterium whose gene is located upstream from ptb, caused an increase in Ptb activity and PHB accumulation in B. megaterium

Statistical optimization of a culture medium for biomass and poly(3-hydroxybutyrate) production by a recombinant Escherichia coli strain using agroindustrial byproducts

A statistically based Plackett-Burman screening design identified milk whey and corn steep liquor concentrations as well as ionic strength (based on phosphate buffer concentration) as the three main independent components of the culture medium that significantly (p < 0.05) influenced biomass and poly(3-hydroxybutyrate) (PHB) production in recombinant cells of Escherichia coli. This strain carries a plasmid encoding phb genes from a natural isolate of Azotobacte sp. Response surface methodology, using a central composite rotatable design, demonstrated that the optimal concentrations of the three components, defined as those yielding maximal biomass and PHB production in shaken flasks, were 37.96 g deproteinated milk whey powder/l, 29.39 g corn steep liquor/l, and 23.76 g phosphates/l (r2 = 0.957). The model was validated by culturing the recombinant cells in medium containing these optimal concentrations, which yielded 9.41 g biomass/l and 6.12 g PHB/l in the culture broth. Similar amounts of PHB were obtained following batch fermentations in a bioreactor. These results show that PHB can be produced efficiently by culturing the recombinant strain in medium containing cheap carbon and nitrogen sources. [Int Microbiol 2005; 8(4):243-250

Synthesis and Structures of Two Triorganotin(IV) Polymers R3Sn{O2CC6H4[N=C(H)}{C(CH3)CH(CH3)-3-OH]-p}n (R = Me and Ph) Containing a 4-[(2Z)-(3-Hydroxy-1-methyl-2-butenylidene)amino] benzoic Acid Framework

Two new polymeric triorganotin(IV) complexes R3Sn{O2CC6H4[N=C(H)}{C(CH3)CH(CH3)-3-OH]-p}n ([Me3Sn(LH)]n: 1) and([Ph3Sn(LH)]n: 2) containing a 4-[(2Z)-(3-hydroxy-1-methyl-2-butenylidene)amino]benzoate (LH) framework were prepared.Both compounds have been characterized by 1H, 13C, 119Sn NMR, IR and 119Sn Mossbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of complexes 1 and 2 reveal that they exist as polymeric zig-zag chains in which the LH-bridged Sn-atoms adopt a trans-R3SnO2 trigonal bipyramidal configuration with R groups in the equatorial positions and the axial sites occupied by an oxygen atom from the carboxylate ligand and the alcoholic oxygen atom of the next carboxylate ligand in the chain. The carboxylate ligands coordinate in the zwitterionic form with the alcoholic proton moved to the nearby nitrogen atom

Kinetic Inductance Detectors for the OLIMPO experiment: design and pre-flight characterization

We designed, fabricated, and characterized four arrays of horn--coupled, lumped element kinetic inductance detectors (LEKIDs), optimized to work in the spectral bands of the balloon-borne OLIMPO experiment. OLIMPO is a 2.6 m aperture telescope, aimed at spectroscopic measurements of the Sunyaev-Zel'dovich (SZ) effect. OLIMPO will also validate the LEKID technology in a representative space environment. The corrected focal plane is filled with diffraction limited horn-coupled KID arrays, with 19, 37, 23, 41 active pixels respectively at 150, 250, 350, and 460$\:$GHz. Here we report on the full electrical and optical characterization performed on these detector arrays before the flight. In a dark laboratory cryostat, we measured the resonator electrical parameters, such as the quality factors and the electrical responsivities, at a base temperature of 300$\:$mK. The measured average resonator $Q$s are 1.7$\times{10^4}$, 7.0$\times{10^4}$, 1.0$\times{10^4}$, and 1.0$\times{10^4}$ for the 150, 250, 350, and 460$\:$GHz arrays, respectively. The average electrical phase responsivities on resonance are 1.4$\:$rad/pW, 1.5$\:$rad/pW, 2.1$\:$rad/pW, and 2.1$\:$rad/pW; the electrical noise equivalent powers are 45$\:\rm{aW/\sqrt{Hz}}$, 160$\:\rm{aW/\sqrt{Hz}}$, 80$\:\rm{aW/\sqrt{Hz}}$, and 140$\:\rm{aW/\sqrt{Hz}}$, at 12 Hz. In the OLIMPO cryostat, we measured the optical properties, such as the noise equivalent temperatures (NET) and the spectral responses. The measured NET$_{\rm RJ}$s are $200\:\mu\rm{K\sqrt{s}}$, $240\:\mu\rm{K\sqrt{s}}$, $240\:\mu\rm{K\sqrt{s}}$, and $\:340\mu\rm{K\sqrt{s}}$, at 12 Hz; under 78, 88, 92, and 90 mK Rayleigh-Jeans blackbody load changes respectively for the 150, 250, 350, and 460 GHz arrays. The spectral responses were characterized with the OLIMPO differential Fourier transform spectrometer (DFTS) up to THz frequencies, with a resolution of 1.8 GHz.Comment: Published on JCA

Raman scattering reveals strong LO-phonon-hole-plasmon coupling in nominally undoped GaAsBi: optical determination of carrier concentration

We report room-temperature Raman scattering studies of nominally undoped (100) GaAs1−xBix epitaxial layers exhibiting Biinduced (p-type) longitudinal-optical-plasmon coupled (LOPC) modes for 0.018≤x≤0.048. Redshifts in the GaAs-like optical modes due to alloying are evaluated and are paralleled by strong damping of the LOPC. The relative integrated Raman intensities of LO(Γ) and LOPC ALO/ALOPC are characteristic of heavily doped p-GaAs, with a remarkable near total screening of the LO(Γ) phonon (ALO/ALOPC →0) for larger Bi concentrations. A method of spectral analysis is set out which yields estimates of hole concentrations in excess of 5 × 1017 cm−3 and correlates with the Bi molar fraction. These findings are in general agreement with recent electrical transport measurements performed on the alloy, and while the absolute size of the hole concentrations differ, likely origins for the discrepancy are discussed. We conclude that the damped LO-phonon-hole-plasmon coupling phenomena plays a dominant role in Raman scattering from unpassivated nominally undoped GaAsBi