Hexagonal Section Research Articles

Numerical simulation on flow field in circumferential overlap trisection helical baffle heat exchanger

A novel helical heat exchanger structure consisting of circumferential-overlap trisection helical baffle shell-and-tube heat exchangers (cothSTHXs) is proposed as a means of overcoming the limitations imposed by non-uniformity of the quadrant baffle sectors with natural intervals used in helical baffle heat exchangers with equilateral triangle tube layouts. The cothSTHXs also exhibit anti-shortcut protection by using one row of tubes in each gap between adjacent circumferential overlap baffles to damp the shortcut leakage. A numerical model was used to determine the flow field in a cothSTHX of the same geometric size as the test exchanger. A figure showing the pressure nephogram with superimposed velocity vectors is presented. The Dean vortex secondary flow field, which is one of the key mechanisms of enhancing heat transfer in heat exchangers, is clearly depicted. The unfolded concentric hexagonal section charts demonstrate that the shortcut leakage flow is restricted and that the flow pattern in the cothSTHX is very nearly “plug flow”.

Characterization of size-controlled ZnO nanorods produced by electrochemical deposition technique

ZnO nanorods have been grown onto indium thin oxide (ITO) coated glass substrates by electrochemical deposition technique using oxygenated zinc chloride solutions at the bath temperature of 80°C and pH value of 5.8. The effect of the galvonostatic pretreatment process according to the size of the ZnO nanorods has been examined. The pretreatment consists of the formation of ZnO seed layers at different currents of −1.0mA and −2.0mA by the galvonostatic process and then the subsequent ZnO nanorods had been produced using the potentiostatic mode at the potential of −1.0V. ZnO nanorods produced on the seed layers exhibited different morphological, structural, and optical properties. X-ray diffraction results showed that ZnO nanorods are highly crystalline and wurtzite hexagonal phase with preferred orientation along (002) direction. The energy band gaps were found to be 3.50eV, 3.52eV and 3.60eV without and with the seed layer of −1.0mA and −2.0mA respectively. Atomic Force Microscopy (AFM) images revealed that the ZnO nanorods deposited on the ITO-coated substrates without and with the seed layer are composed of rod-shaped grains with a cross hexagonal section perpendicular to the substrate. The average diameters of the ZnO nanorods were found to be 560±16.78nm, 450±32.12nm and 370±18.46nm without and with the seed layer of −1.0mA and −2.0mA respectively. The SEM images have shown that the lengths of the ZnO nanorods varied between 1.0μm and 2.0μm.

Termite coprolites (Insecta: Isoptera) from the Cretaceous of western France: A palaeoecological insight

This paper presents fossil faecal pellets – also named coprolites or frass – attributed to termites, which were found in amber and lignitic clay from the Wealden (Hauterivian-Barremian?), Late Albian and Early Cenomanian of south-western France. These coprolites have a characteristic subcylindrical shape and hexagonal transverse section and are assignable to Microcarpolithes hexagonalis Vangerow. The termite families that possibly produced these coprolites are discussed. The noticeable lack of termite attacks on the fossil wood associated with amber and lignitic clay is taphonomically analyzed in relation with the palaeoflora and palaeoclimate of these amber forests. The different medium where coprolites were found (amber, wood, sediments) suggests that primitive Cretaceous termites had already developed various biologies, such as wood or cryptic foraging, but probably not yet soil-feeding.

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

AbstractThe electrochemical deposition of ZnO nanowires (NW) was optimized by growing onto a previously deposited seed layer. The ZnO seed layer was prepared by a sol–gel process from different precursor solutions and deposited onto FTO/glass by spin coating. Afterwards, NW were electrochemically grown onto those seed layers. The electrolyte was an aqueous solution of the Zn+2 precursor (1 mM zinc acetate) and a supporting electrolyte (0.1 M sodium acetate), saturated with bubbling oxygen. The films were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmittance. The XRD measurements show typical diffraction pattern of ZnO wurtzite structure. The SEM micrographs show the presence of smooth NW with hexagonal sections with diameters ranging from 40 to 250 nm. The optical transmittance reveals the presence of ZnO with bandgap energy between 3.23 and 3.29 eV. These spectra show a monotonically increasing transmittance from the UV into the red part of the spectrum. This feature may be originated in the dispersion of light at the NW and can be used to enhance below‐gap absorption.magnified image

The novel metalloligand [Fe(bppd)3] (bppd = 1,3-bis(4-pyridyl)-1,3-propanedionate) for the crystal engineering of heterometallic coordination networks with different silver salts. Anionic control of the structures

The crystal engineering of heterometallic coordination networks based on the novel tris-chelate metalloligand [FeIII(bppd)3] (bppd = 1,3-bis(4-pyridyl)-1,3-propanedionate) is reported here. The building block [Fe(bppd)3] crystallizes with a balanced packing of the Δ and Λ forms and exhibits distorted octahedral chiral structure with six exo-oriented pyridyl donor groups suitable for networking via interactions with external metal ions. It was reacted with many silver salts AgX (X = BF4−, ClO4−, PF6−, AsF6−, SbF6−, NO3−, CF3SO3−, tosylate) giving polymeric products with structures depending on the nature of the counter-anions X−. With pseudo-spherical anions (such as BF4−, ClO4−, PF6−, AsF6− and SbF6−) 2D polymeric species [Fe(bppd)3Ag](X) are obtained showing sql topology, because the metalloligands use only four, out of the six pyridyl donors, to bind silver ions. The reaction with Ag(CF3SO3) affords a quite different type of [Fe(bppd)3Ag]+ 2D polymeric frame, with the metalloligands that again employ only four pyridyl groups for networking, i.e. a double layered species comprised of two superimposed honeycomb sheets, exhibiting a (43.63) topology. By using AgNO3 a 3D framework, [Fe2(bppd)6Ag3](NO3)3, is obtained that, interestingly, consists of double layers like those of the previous species connected viaAg bridges on both sides to produce a binodal 5,4-connected 2-fold interpenetrated network. The reaction with silver p-toluenesulfonate produces the complex 3D nanoporous network [Fe3(bppd)9Ag5](tosylate)5 with 6-connected metalloligands and 3- and 4-connected silver ions. An interesting rationalization of this network is that it is comprised of 1D parallel nanotubular motifs of hexagonal section with square-meshed walls; these nanotubes are laterally interconnected by Ag triple-bridging atoms to generate the whole 3D array. We observe that in these species the metalloligands use a variable number of pyridyl donors for networking, i.e. four, five and six, leading to frames of increased complexity and dimensionality that are strongly dependent on the anionic shape and nature. The reactions of the analogous metalloligand [AlIII(bppd)3] with the same AgX salts under similar conditions produce polycrystalline materials that in the cases of silver triflate and tosylate are isostructural with the corresponding iron containing species, as evidenced by their X-ray powder diffraction spectra.

Controlled Growth and Field-Emission Properties of NbSe2 Micro/Nanostructured Films

Single-crystalline NbSe2 nanobelt, nanorod (containing nanotube), and microplate films were grown on Nb substrates by a surface-assisted chemical-vapor-transport (CVT), respectively. The nanobelts have a rectangular section of 50 x 250 to 300 x 4500 nm2, and a length up to 330 microm. The nanorods have a hexagonal section with a diameter of about 0.1-0.5 microm, and a length up to 15 microm. The nanotubes have rectangular, pentagonal or round sections with a diameter of about 0.4-0.5 microm, a tube-wall thickness of about 45 nm, and a length up to several microns. The microplates have a hexagonal section with a diameter of about 0.05-10 microm and a thickness of about 100 to 600 nm. Field-emission experiments using the films as cold electron cathodes showed that they had notable emission currents and low turn-on fields, suggesting their potential applications in field emission devices.

Research of Simplified B Pillar Model for Roof Crashworthiness

The B pillar structure, which affects automotive roof crashworthiness, must have a perfect surrogate model to satisfy the early design demands. This work aims to explore the proper approach of simplified model construction. To create the simplified B pillar, the collapse theories of thin-walled hexagonal and channel beams under bending collapse are reviewed and applied to simulate the deforming behavior. Meanwhile, the simplified model is constructed from parallel connection of curved hexagonal and channel section beams. After distributing different rotational nonlinear springs, the same crashworthiness analyses are performed on both simplified and initial FE models to verify the simplified effects. The results demonstrate the potential of the approach and process proposed in developing the simplified model for the concept design of autobody.

Ranosrednjovjekovno koplje s krilcima iz okolice Dugog Sela u svjetlu novih saznanja o ovoj vrsti oružja na motki

U središtu znanstvene analize nalazi se vrijedna akvizicija Arheološkog muzej u Zagrebu – vrlo dobro očuvano ranosrednjovjekovno koplje s krilcima iz okolice Dugog Sela, grada dvadesetak kilometara istočno od Zagreba. Koplje je tipičan ranokarolinški proizvod koji prema starijim tipološko-kronološkim shemama pripada Petersenovu tipu B te bi shodno tomu pripadalo ranokarolinoškom razdoblju i vremenu oko 800. godine. Novija arheološka istraživanja i spoznaje do kojih se došlo u posljednjih dvadesetak godine drukčije promatraju i analiziraju predmete ove vrste pa je i koplje iz okolice Dugog Sela analizirano na temelju tih novih spoznaja (Solberg, Westphal). Analizi su osim toga podvrgnuti i svi dosad poznati primjerci kopalja s krilcima u muzejskim i drugim zbirkama u Hrvatskoj (11+1 kom.) i Bosni i Hercegovini (8 kom.), koji su za ovu prigodu podvrgnuti analizi mjera i proporcija kako bi i oni napokon bili uspoređeni i interpretirani u okviru morfoloških postavki i zaključaka do kojih je svojedobno došao njemački arheorestaurator H. Westphal. Istraživanja su pokazala postojanje nekoliko tipoloških skupina čije su predložene kronološke koordinate drukčije od onih u kojima su se dosad kretala istraživanja i interpretacije kopalja s krilcima u radovima naših arheologa. Mjerni pristup analizi hrvatskih nalaza potvrdio je postojanje primjerka koji pripada najranijoj tradiciji ranokarolinških koplja s krilcima te uputio na još nekoliko kopalja čija morfološka obilježja upućuju na prvu polovinu 8. stoljeća. Preostala koplja pripadaju uglavnom dvjema glavnim tipološkim skupinama, tj. vremenu od druge polovine 8. dou drugu polovinu 9. stoljeća.

English

The extrusion of section from round billet poses a great challenge for theoretical modeling of the process using upper bound method. The greatest difficulty in three-dimensional upper bound method is to determine kinematically admissible velocity field. The SERR (Spatial Elementary Rigid Region) technique is fairly applicable for analyzing extrusion of sections having re-entrant corners. A modified version of SERR technique has been used for extrusion of hexagon sections from round billet through a linearly converging die. The circular cross section of the round billet is approximated by a regular polygon of equal area. The extrusion pressure has been computed for different boundary condition at the die billet interface. The optimum die geometry has been determined. An extrusion test rig is designed and all extrusion is carried out using round billets for extrusion of hexagonal sections using converging dies. The experimental results are validated with SERR analysis.

Optical waveguide and cavity effects on whispering-gallery mode resonances in a ZnO nanonail

Spatially resolved cathodoluminescence (CL) study of a ZnO nanonail, having thin shank, tapered neck, and hexagonal head sections, is reported. Monochromatic imaging and line-scan profiling indicate that the wave guiding and leaking from growth imperfections in addition to the oxygen-deficiency variation determine the spatial contrast of CL emissions. Occurrence of resonance peaks at identical wavelengths regardless of CL-excitation spots is inconsistent with the whispering-gallery mode (WGM) resonances of a two-dimensional cavity in the finite-difference time domain simulation. However, three-dimensioanl cavity simulation produced WGM peaks that are consistent with the experimental spectra, including transverse-electric resonances that are comparable to transverse-magnetic ones.

Simulation of waveguiding and emitting properties of semiconductor nanowires with hexagonal or circular sections

Nanowires as an active medium are promising for getting high brightness light emitting diodes. Semiconductors such as GaN and ZnO grow as nanowires with a hexagonal cross section and their optical properties have been little explored. We study important properties for nanowire LED optimization. In particular we review the modal properties of hexagonal nanowires and compare them with those of circular nanowires. We also study the modal reflectivity of guided modes at nanowire end facets and explore the relevance of a comparison with plane-wave reflectivity. Finally we analyze the distribution of the emitted power in three different cases: a single point emitter and an axial and a radial nanowire heterostructure.

Annealing behavior of the novel morphology of poly(butylene succinate) lath‐shaped single crystals

AbstractLamellar single crystals of poly(butylene succinate) (PBS) with novel morphologies were prepared from a chloroform/methanol solution by self‐seeding methods. Crystal structures and morphologies were investigated by means of atomic force microscopy (AFM). Lath‐shaped crystal and hexagonal‐shaped crystals coexist in one PBS single crystal and this has a lamellar thickness of around 5–6 nm as determined by AFM. The thickening of lamellae from 5–6 to 7–9 nm occurred during heating from 41 to 84 °C. In situ temperature‐controlled AFM observations demonstrated that the lath‐shaped crystal sections melted first and then the hexagonal sections while the edge of the single crystals remained regular during annealing. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1492–1496, 2009

Using an Interactive Display to Demonstrate Transportation Planning and Design Issues

An ongoing challenge worldwide has been to attract sufficient numbers of new people into transportation careers. When trying to understand what transportation engineering is about, many people often find that examples of practical applications are particularly useful. In this way, people acquire initial interest in a problem and then realize its real-world application to a career in transportation. Recently, funds donated to the University of Canterbury in New Zealand were used to develop an interactive transportation display board for both existing and prospective students. The display represents a landscape on which a new road route would be determined. The display surface is subdivided into hexagonal sections, each with a “cost” reflecting the relative difficulty of road construction in that location (e.g., due to mountains, rivers, or development). Magnetic road elements (each with a value reflecting the costs to road users) are then placed on the display to create a connection between the chosen endpoints. The intention is that the display's users determine the most optimal road alignment for minimizing construction costs, road user costs, or both. Since its creation, the display has been used at various sites, both on campus and at career expos, and has proven to be immensely popular with visitors. The display's potential as an educational tool for use in math, science, or geography classes has also been identified. This paper outlines the development of the display, its applications to date, and the transportation lessons the display can highlight.

Application of Photogrammetric 3D-PTV Technique to Track Particles in Porous Media

To be able to assess the adequacy of existing theories of flow and transport in porous media, experimental methods must be able to obtain fully three-dimensional descriptions of both the Eulerian velocity field and Lagrangian particle trajectories within the system. Here, we report on matched-refractive porous media experiments that rely upon a three- camera 3D-PTV photogrammetric technique. A hexagonal test section is used for experiments. The goal in the experiment is to image a volume far away from the boundary walls, to design a photogrammetric 3D-PTV system, to lengthen the trajectories through an accurate experimental technique and improve the statistical accuracy of the method. A combination of image and object space based information is employed to establish the spatio-temporal correspondences between particle positions of consecutive time steps. The system calibration features have been examined in detail. The photogrammetric principles used by 3D Particle Tracking Velocimetry are described. First, the fundamental mathematical model of the collinearity condition and its extensions are explained. Then, the epipolar line intersection method built upon multicamera correspondences is discussed. The porous media were constructed of Pyrex and the fluid was glycerol. At the bench scale the porous media were heterogeneous, and various mean flow velocities were applied. The tracer particles were air bubbles which moved passively and were imaged as the glycerol was drained from the system. Particle trajectories, velocity covariance’s, classical dispersion tensors are obtained. Further tests on simulated data were performed to ensure the method’s operability and robustness. The great variety of data sets that were processed during the development of the matching algorithm show its general applicability for a wide range of 3D-PTV measurement tasks.

Dynamic Material Properties of Stainless Steel and Multiphase High Strength Steels

This work presents results of tensile testing of H400 stainless steel, DP600 and TRIP600 at different strain rates. Mechanical properties were determined from tensile test using flat sheet specimens and recurring to different test techniques: servo-hydraulic machine and a tensile-loading Hopkinson bar. The test results were used to compare different mechanical properties of the tested steels and to validate constitutive equations intended to provide a mathematical description of strain rate dependence, namely the Cowper-Symonds equation. Following previous research work in dynamic material proprieties of multiphase and stainless steel grades, the energy absorption in quasi-static crushing of thin walled section made of the tested materials was subsequently investigated. Crush tests were performed in top-hat and hexagonal section tubes manufactured using laser welding. The experimental results were compared in order to assess the efficiency of the different steel grades for energy absorption.

Crashworthiness design of multi-corner thin-walled columns

This paper presents a crashworthiness design of regular multi-corner thin-walled columns with different types of cross-sections and different profiles, including straight octagonal columns and curved hexagonal columns. In this paper, the straight octagonal section columns are first optimized, which mainly take axial crash loads during crashes. Next, the curved hexagonal section columns are optimized following the same approach, which are subject to bending moment when impact occurs. During the design optimizations, specific energy absorption ( SEA) is set as the design objective, side length of the cross-sections and wall thickness are selected as design variables, and maximum crushing force ( P m) is set as the design constraint. Both the objective and constraint are formulated using the response surface method (RSM) based on sets of finite element (FE) results obtained from FE analyses (FEA). After obtaining the optimal designs, parametric studies are performed to investigate the influences of the design variables on the crash performance of such multi-corner thin-walled columns.

Face-to-face interactions of metallic oxo-clusters: Synthesis and crystal structure of new isopolyvanadotungstate salts – Co(H 2O) 6K 2V 2W 4O 19 and [Co(H 2O) 6] 2V 2W 4O 19

Crystals of Co(H 2O) 6K 2V 2W 4O 19 ( 1) and [Co(H 2O) 6] 2V 2W 4O 19 ( 2) were obtained from aqueous solution of [V 2W 4O 19] 4− and cobalt(II) nitrate. The structure of [V 2W 4O 19] 4− is that of the Lindqvist anion in which the two vanadium and four tungsten atoms are statistically distributed over the six metallic positions. The [V 2W 4O 19] 4− and the [Co(H 2O) 6] 2+ octahedra are arranged alternately with their faces parallel to each other for maximal interactions (face-to-face interaction). The structure of 1 shows the presence of large mono-directional channels along c-axis with a quasi hexagonal section of 8.52 × 6.35 Å 2 which are filled by cobalt. The structure of 2 can be viewed as a pillar arrangement of [Co(H 2O) 6] 2V 2W 4O 19 units along c-axis.

Theoretical investigation of size and shape effects on the melting temperature of ZnOnanostructures

We report a theoretical investigation concerning the melting temperature,Tm, of ZnO and Zn nanoparticles (NPs), nanowires (NWs) and nanotubes (NTs). The shapesconsidered here for the zinc oxide low dimensional structures include sphericalNPs, NWs with circular, rectangular (nanobelts) and hexagonal sections andNTs with circular and hexagonal sections. A comparison between ZnO and Znnanostructures demonstrates a higher stability of ZnO for most size and shape rangesconsidered. Moreover, the size effect on the melting temperature for ZnO is found to bequite strong: for a spherical ZnO NP with a radius of 5 nm, the size effect onTm correspondsto a decrease of ∼36% relative to the bulk melting temperature, whereas the reductionfor the case of a metallic Zn NP with the same dimension is∼13%. Basedon Tm estimations as a function of size and shape, we predict that certain ZnO nanostructures, such as small(<10 nm) NTs, may not be viable for nanoelectronics or nanophotonic devices, sinceTm is too close to, or in some cases even below, room temperature. Theinfluence of the surface tension uncertainties on the calculated meltingtemperatures is also discussed. Finally, based on the determination ofTm at the nanoscale, the maximal intrinsic residual stress in ahexagonal ZnO NW and in a cylindrical Zn NW is estimated to be∼45 MPaand ∼1.9 GPa, respectively.

Young’s Modulus of In Situ TiB Whiskers in Ti Metal Matrix Composites

The TiB/Ti metal matrix composites (MMCs) with different volume fractions of in situ TiB reinforcements were spark plasma sintered at 1000 °C with a pressure of 20 MPa for 5 minutes in vacuum. The in situ synthesized TiB is whisker shape with a hexagonal transverse section and distributes uniformly and randomly in the Ti matrix. The Young’s modulus of TiB was back-calculated from the elastic properties of the composites using the Halpin-Tsai model. The Young’s moduli of all the composites were found to increase with the increase of TiB volume fraction. The calculated value of TiB Young’s modulus is about 489±83GPa. Values of Young’s moduli of TiB whisker obtained according to different methods were compared and discussed.

Novel Intermetallic Compound UFe5Si3: A New Room‐Temperature Magnet with an Original Atomic Arrangement.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.