A new modular structural system for tall buildings based on tetrahedral configuration

Inspired by the high mechanical performance of diagrid structures, the minimization of material consumption on braced tubes and the expressive potency of tensegrity modular structures, this work proposes an innovative three-dimensional system for tall buildings. A new modular structural system generated from the assembly of tetrahedral units is investigated. The paper integrates insights on the architectural implications and mechanical performance of the reticular system arranged in repetitive triangular-based modules. The impact of different geometric configurations of the structural members on the economic design is also discussed and recommendations for the optimal topology are made. Guidelines for the design and analytical formula for accessing preliminary member sizes are proposed on the basis of stiffness requirements

YAP scintillators for resonant detection of epithermal neutrons at pulsed neutron sources

Recent studies indicate the resonance detector (RD) technique as an interesting approach for neutron spectroscopy in the electron volt energy region. This work summarizes the results of a series of experiments where RD consisting of YAlO3 (YAP) scintillators were used to detect scattered neutrons with energy in the range 1-200 eV. The response of YAP scintillators to radiative capture gamma emission from a U-238 analyzer foil was characterized in a series of experiments performed on the VESUVIO spectrometer at the ISIS pulsed neutron source. In these experiments a biparametric data acquisition allowed the simultaneous measurements of both neutron time-of-flight and gamma pulse height (energy) spectra. The analysis of the gamma pulse height and neutron time of flight spectra permitted to identify and distinguish the signal and background components. These measurements showed that a significant improvement in the signal-to-background ratio can be achieved by setting a lower level discrimination on the pulse height at about 600 keV equivalent photon energy. Present results strongly indicate YAP scintillators as the ideal candidate for neutron scattering studies with epithermal neutrons at both very low (<5degrees) and intermediate scattering angles. (C) 2004 American Institute of Physics

Study of archaeological samples via neutron techniques

The discovery of ancient artefacts and artworks usually raises a variety of questions such as the correct determination of their historical and cultural timeframe, the place and method of production, the choice of treatments and conditions for restoration and preservation. In the field of archaeometry, new perspectives are opened up by the use of neutron techniques. Results on a selection of archaeological samples, Etruscan bronzes coming from the Museo Nazionale di Villa Giulia and Roman marbles from Villa Adriana (Tivoli, Rome), are presented. ANCIENT CHARM project aims to develop a quantitative 3D imaging technique. This work presents some of results on a series of experimental investigation performed on test samples called “Black Boxes”. Elements’ and compounds’ identification on the internal features of the boxes are obtained by the combined use of different neutron analysis methods. The presented studies successfully showed the high potential of neutron techniques in the study of ancient archaeological artefacts

The very low angle detector for high-energy inelastic neutron scattering on the VESUVIO spectrometer

The Very Low Angle Detector (VLAD) bank has been installed on the VESUVIO spectrometer at the ISIS spallation neutron source. The new device allows for high-energy inelastic neutron scattering measurements, at energies above 1 eV, maintaining the wave vector transfer lower than 10 A^- 1. This opens a still unexplored region of the kinematical (q,w) space, enabling new and challenging experimental investigations in condensed matter. This paper describes the main instrumental features of the VLAD device, including instrument design, detector response, and calibration procedure

Texture and structure studies on marbles from Villa Adriana via neutron diffraction technique

The primary objective of this work is the characterisation of ancient roman marble fragments through neutron diffraction, a non-destructive experimental method. The neutron diffractometer ROTAX, operating at the pulsed neutron source ISIS, in the UK has been used to determine composition down to a 0.5 wt% level and to obtain information on preferred orientations of grains in the marble tiles

Minority and mode conversion heating in (3He)-H JET plasma

Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (He-3)-H plasmas at full field, with fundamental cyclotron heating of He-3 as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the He-3 concentration were observed and mode conversion (MC) heating proved to be as efficient as He-3 minority heating. The unwanted presence of both He-4 and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the He-3 concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[He-3]: (i) a regime at low concentration (X[He-3] < 1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8 < X[He-3] < 5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at He-3 concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[He-3] < 4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low He-3 concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8 < X[He-3] < 5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in He-3-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics

The investigation of YAlO3-NdAlO3 system, synthesis and characterization

The binary phase diagram of the YAlO3 (YAP) - NdAlO3 (NAP) system was determined by differential thermal analysis (DTA) and X-ray powder diffraction (XRD) measurements. High purity nanocrystalline powders and small single crystals of Y_{1-x}Nd_{x}AlO_3 (0 \leq x \leq 1) have been produced successfully by modified sol-gel (Pechini) and micro-pulling-down methods, respectively. Both end members show high mutual solubility >25% in the solid phase, with a miscibility gap for intermediate compositions. A solid solution with x \approx 0.2 melts azeotropic ca. 20 degrees below pure YAP. Such crystals can be grown from the melt without segregation. The narrow solid/liquid region near the azeotrope point could be measured with a "cycling" DTA measurement technique.Comment: 12 pages, 8 figures, submitted to J. Alloys. Comp