Neutron self-shielding in irradiation channels of small reactors is isotropic

In order to predict the self-shielding effect in neutron activation of non-spherical samples in reactor neutron spectra, it is important to know whether the neutron field is sufficiently anisotropic to cause significant variations between horizontal and vertical sample orientation or with orientation relative to the direction towards the reactor core. Metal wires with significant neutron self-shielding were irradiated in several channels of the SLOWPOKE reactor at Ecole Polytechnique Montreal and the TRIGA reactor at the Jožef Stefan Institute. In all cases, the amount of thermal or epithermal self-shielding was found to be identical, within the experimental uncertainty, regardless of the orientation of the wire, indicating that the neutron field is essentially isotropic. Models used to predict neutron self-shielding need to be adjusted accordingly. In our Monte Carlo model, the tube-shaped neutron source was moved back into the moderator and reflecting materials near the sample location were included, which produced an isotropic neutron field at the sample location.     

Perceptually based head-related transfer function database optimization

In the context of binaural audio rendering, choosing the best head-related transfer function (HRTF) for an individual from large databases poses several problems. This study proposes a method to reduce the size of a given HRTF database. Participants, 45 in total, were asked to rate the quality of binaural synthesis for 46 HRTFs. The lack of reciprocity in the ratings was noted. Results were used to create a perceptually optimized HRTF subset which satisfied all participants' judgments. The subset was validated using localization tests on a separate group of subjects with results showing reduced errors when subjects were given their best choice, rather than their worst choice HRTF.     

Rapid head-related transfer function adaptation using a virtual auditory environment

The paper reports on the ability of people to rapidly adapt in localizing virtual sound sources in both azimuth and elevation when listening to sounds synthesized using non-individualized head-related transfer functions (HRTFs). Participants were placed within an audio-kinesthetic Virtual Auditory Environment (VAE) platform that allows association of the physical position of a virtual sound source with an alternate set of acoustic spectral cues through the use of a tracked physical ball manipulated by the subject. This set-up offers a natural perception-action coupling, which is not limited to the visual field of view. The experiment consisted of three sessions: an initial localization test to evaluate participants' performance, an adaptation session, and a subsequent localization test. A reference control group was included using individual measured HRTFs. Results show significant improvement in localization performance. Relative to the control group, participants using non-individual HRTFs reduced localization errors in elevation by 10° with three sessions of 12 min. No significant improvement was found for azimuthal errors or for single session adaptation.     

Effectiveness of multilayer viscoelastic insulators to prevent occurrences of brake squeal: A numerical study

The purpose of this publication is to give an overview of the actual role of multi-layered viscoelastic parts, so called “shims”, to prevent squeal noises of automotive brake systems. Since shear stress is usually used to damp thin structures in their bending modes it is commonly believed to be the largest underwent by shims. To check this assumption and considering that stresses underwent by shims cannot be measured experimentally, the authors have computed them with the help of a detailed and realistic finite element model. Contrary to what shims manufacturers say, this study exhibits the fact that shims are almost uniquely solicited in their normal direction in brake systems. Secondly, the study focuses on the added damping and stiffening induced by the viscoelastic materials. In order to take into account these materials, a realistic frequency dependent viscoelastic behavior has been integrated in the simulations. Finally, the study shows certains eigenmodes for which the viscoelastic behavior of the shims reveals instabilities that would not exist without it. It is shown that this is due to coalescence phenomenon.     

Effect of control rod insertion on the TRIGA neutron spectrum and the determination of elemental concentrations with k0-INAA

Journal of Radioanalytical and Nuclear Chemistry - We suspected that changes in the neutron spectrum, caused by varying control rod positions in routine steady state operation of our TRIGA nuclear...     

Some considerations concerning the presentations of universal algebras

The aim of this work is to present some proposals of a general definition of a presentation for universal algebras and some basic conclusions originating from this definition. Next, we formulate Tietze's theorem for varieties of universal algebras in a form which is a generalization of the method used in [4] for groups.The author is greatful to the referee for his helpful suggestions which influenced the version of this paper.Presented by G. Grätzer.     

Crystal and molecular structures of two unsaturated monosaccharides: methyl 6-(N-benzenesulfonylamino)-N,O-isopropylidene-2,3,6,8-tetradeoxy-α-D-erythrooct-2-enopyranos-4-uloside,and 1,1-O,O-ethylidene-3,4-dideoxy-D,L-hex-3-enoz-2-ulopyranos-5-ulose

Methyl 6-(N-benzenesulfonylamino)-N,O-isopropylidene-2,3,6,8-tetradeoxy--d-erythrooct-2-enopyranos-4-uloside, C₁₈H₂₃N₁O₆S₁, (3) crystallizes in the orthorhombic space groupP2₁2₁2₁. The unit cell parameters are:a=7.839(2),b=10.111(2),c=24.217(5) Å. The dihydropyranone ring adopts a deformed sofa conformation with the O5 atom deviating 0.586(2) Å from the least-squares plane and the -face of the carbonyl group shielded by the terminal (C8) methyl group. 1,1-O,O-Ethylidene-3,4-dideoxy-d,l-hex-3-enoz-2-ulopyranos-5-ulose, C₈H₁₀O₅, (6) crystallizes in the monoclinic space groupP2₁/n. The unit cell parameters are:a=6.310(1),b=18.656(3),c=7.604(1) Å, =106.01(1)°. The dihydropyranone ring adopts a deformed sofa conformation with O6 atom deviating 0.482(1) Å from the leastsquares plane and the hydroxy and dioxolanyl substituents are in pseudoaxial and pseudoequatorial positions, respectively. The average planes of six-membered and five-membered rings are approximately coplanar.     

Structure of 4-thioethyl-4-cholesten-3-one,C29H48OS

The crystal structure of 4-thioethyl-4-cholesten-3-one, C₂₉H₄₈OS, has been determined by X-ray methods. The compound is orthorhombic:P2₁2₁2₁,a=7.787(2),b=12.586(4),c=27.960(6) Å,V=2740(3) ų,M _r =444.8,Z=4,D _x =1.08 Mg m^–3, CuK radiation (=1.5418 Å),=11.2 cm^–1,F(000)=984. FinalR=0.073 andR _w =0.057 for 1562 reflections. A comparison with other 4-substituted 4-en-3-ore steroids suggests that theA ring conformation and its relative orientation can be influenced by the thioethyl substituent. The C4 side chain is turned under the steroid skeleton. The cholesterol side chain is fully extended, with atrans, +gauche conformation of the terminal C26 and C27 methyl groups.