Air Absorption Error in Room Acoustical Modeling

Most statistical and ray-tracing computer models take into account the absorption of sound by air to estimate the reverberation time. Extensive research by many scientists lead to the standardized calculation model for pure tone air absorption. The phenomenon was discovered from a room acoustical point of view by Sabine, while the further development of the calculation model took place in the fields of physics and environmental noise. As a result, several parameters and units are used for the same phenomenon. However, air absorption is calculated for pure tones, while room acoustics calculations are performed in frequency bands. Most computer models use the centre-frequency of the normalised frequency bands to calculate the air absorption by the pure tone method. Reverberation measurements in frequency bands under laboratory and practical conditions show that errors larger than the Just Noticeable Difference result in calculating the air absorption by this ‘centre-frequency method’. No literature was found that provides an accurate air absorption calculation for frequency bands in relation to the reverberation time without the use of iteration. An existing rule of thumb is validated for application to room acoustics

Air Absorption Error in Room Acoustical Modeling

Most statistical and ray-tracing computer models take into account the absorption of sound by air to estimate the reverberation time. Extensive research by many scientists lead to the standardized calculation model for pure tone air absorption. The phenomenon was discovered from a room acoustical point of view by Sabine, while the further development of the calculation model took place in the fields of physics and environmental noise. As a result, several parameters and units are used for the same phenomenon. However, air absorption is calculated for pure tones, while room acoustics calculations are performed in frequency bands. Most computer models use the centre-frequency of the normalised frequency bands to calculate the air absorption by the pure tone method. Reverberation measurements in frequency bands under laboratory and practical conditions show that errors larger than the Just Noticeable Difference result in calculating the air absorption by this ‘centre-frequency method’. No literature was found that provides an accurate air absorption calculation for frequency bands in relation to the reverberation time without the use of iteration. An existing rule of thumb is validated for application to room acoustics

Solar Magnetic Carpet I: Simulation of Synthetic Magnetograms

This paper describes a new 2D model for the photospheric evolution of the magnetic carpet. It is the first in a series of papers working towards constructing a realistic 3D non-potential model for the interaction of small-scale solar magnetic fields. In the model, the basic evolution of the magnetic elements is governed by a supergranular flow profile. In addition, magnetic elements may evolve through the processes of emergence, cancellation, coalescence and fragmentation. Model parameters for the emergence of bipoles are based upon the results of observational studies. Using this model, several simulations are considered, where the range of flux with which bipoles may emerge is varied. In all cases the model quickly reaches a steady state where the rates of emergence and cancellation balance. Analysis of the resulting magnetic field shows that we reproduce observed quantities such as the flux distribution, mean field, cancellation rates, photospheric recycle time and a magnetic network. As expected, the simulation matches observations more closely when a larger, and consequently more realistic, range of emerging flux values is allowed (4e16 - 1e19 Mx). The model best reproduces the current observed properties of the magnetic carpet when we take the minimum absolute flux for emerging bipoles to be 4e16 Mx. In future, this 2D model will be used as an evolving photospheric boundary condition for 3D non-potential modeling.Comment: 33 pages, 16 figures, 5 gif movies included: movies may be viewed at http://www-solar.mcs.st-and.ac.uk/~karen/movies_paper1

New species of Entomobrya from Germany (Collembola, Entomobryini)

The systematic study of specimens of Entomobrya from various European museums, private collections and other samplings, allows us to describe several species new of the genus. Specimens from Germany, deposited at the Senckenberg Museum of Natural History Görlitz (SMNG), identified as new species as result of this study, are described: Entomobrya dungeri n. sp., Entomobrya germanica n. sp., Entomobrya saxoniensis n. sp., Entomobrya schulzi Jordana & Baquero n. sp. and Entomobrya dorsolineata n. sp

Transport current dependence of the hysterisis loss in silver sheathed BSCCO-2212 conductors

A technique is described to study the critical current density and penetration fieldassociated with the transport current in a silver sheathed BSCCO conductor. A transport current flowing in a conductor in a varying magnetic field will only influence magnetisation currents that are in competition with the transport current, i.e. currents that use the same path. By measuring the transport current dependence of the magnetisation loss information can be obtained on the related critical current and penetration field. The combination of these two quantities contains information about the geometry of the current distribution and can be used to test different models for the current distribution in BSCCO conductors

Silicon Drift Detector Readout Electronics for a Compton Camera

A prototype detector for Compton camera imaging is under development. A monolithic array of 19 channel Silicon drift detector with on-chip electronics is going to be used as a scatter detector for the prototype system. Custom designed analog and digital readout electronics for this detector was first tested by using a single cell Silicon drift detector. This paper describes the readout architecture and presents the results of the measurement.Comment: 10 pages, 9 figures, submitted to Nucl. Instr. Meth.

Fictitious fluxes in doped antiferromagnets

In a tight binding model of charged spin-1/2 electrons on a square lattice, a fully polarized ferromagnetic spin configuration generates an apparent U(1) flux given by $2\pi$ times the skyrmion charge density of the ferromagnetic order parameter. We show here that for an antiferromagnet, there are two ``fictitious'' magnetic fields, one staggered and one unstaggered. The staggered topological flux per unit cell can be varied between $-\pi\le\Phi\le\pi$ with a negligible change in the value of the effective nearest neighbor coupling constant whereas the magnitude of the unstaggered flux is strongly coupled to the magnitude of the second neighbor effective coupling.Comment: RevTeX, 5 pages including 4 figure