Parametric investigation of geometric form effects on solar potential of housing units

The paper presents a study of the solar potential of different shapes of two-story single family housing units, located in mid-latitude climate. Seven plan geometries are studied: square, rectangle, trapezoid, L, U, H and T shapes. The study investigates the effect of these shapes on two major response variables - Solar radiation incident on equatorial-facing facades and transmitted by the fenestration of such facades, and electricity production potential of building integrated photovoltaic (BIPV) covering roof surfaces with optimal solar exposure. The parameters, whose effects on the response variables are investigated, include, in addition to the basic shapes and roof design, variations to the geometry of L and U shapes and variations to the roof design. Shape variations include varying values of the relative dimensions of shading and shaded facades and variations to the angle enclosed by the wings of these shapes. Variations of roof design consist of modifications to the tilt and side angles of hip roofs. The results indicate that the number of shading facades in-self shading geometries and their relative dimensions are the major parameters affecting solar incident and transmitted radiation. Manipulation of the orientation of wings in L shape units can result in increased peak electricity generation potential, and in shifting the timing of the peak by up to 2 h either side of solar noon. The shift of peak load may be economically beneficial, facilitating more even distribution of electricity production over an assemblage of buildings. Judicious manipulation of unit shapes and window location can lead to optimization of solar radiation and its utilization for electricity generation and passive solar gain.     

MMSE analysis of certain large isometric random precoded systems

Linear precoding consists in multiplying by an N/spl times/K matrix a K-dimensional vector obtained by serial-to-parallel conversion of a symbol sequence to be transmitted. In this paper, new tools, borrowed from the so-called free probability theory, are introduced for the purpose of analyzing the performance of minimum mean-square error (MMSE) receivers for certain large random isometric precoded systems on fading channels. The isometric condition represents the case of precoding matrices with orthonormal columns. It is shown in this contribution that the signal-to-interference-plus-noise ratio (SINR) at the equalizer output converges almost surely to a deterministic value depending on the probability distribution of the channel coefficients when N/spl rarr/+/spl infin/ and K/N/spl rarr//spl alpha//spl les/1. These asymptotic results are used to analyze the impact of orthogonal spreading as well as to optimally balance the redundancy introduced between linear precoding versus classical convolutional coding, while preserving a simple MMSE equalization scheme at the receiver.     

Monte Carlo simulation of a medical linear accelerator for radiotherapy use

A Monte Carlo code MCNPX (Monte Carlo N-particle) was used to model a 25 MV photon beam from a PRIMUS (KD2-Siemens) medical linear electron accelerator at the Centre Antoine Lacassagne in Nice. The entire geometry including the accelerator head and the water phantom was simulated to calculate the dose profile and the relative depth-dose distribution. The measurements were done using an ionisation chamber in water for different square field ranges. The first results show that the mean electron beam energy is not 19 MeV as mentioned by Siemens. The adjustment between the Monte Carlo calculated and measured data is obtained when the mean electron beam energy is approximately 15 MeV. These encouraging results will permit to check calculation data given by the treatment planning system, especially for small fields in high gradient heterogeneous zones, typical for intensity modulated radiation therapy technique.     

A decomposition approach for the solution of the unit loading problem in hydroplants

This paper presents a decomposition approach for the solution of the dynamic programming formulation of the unit loading problem in hydroplant management. This decomposition approach allows the consideration of network and canal constraints without additional computational effort.     

New order preserving access methods for very large files derivedfrom linear hashing

A class of order-preserving dynamic hashing structures is introduced and analyzed. The access method is referred to as the dynamic random-sequential access method (DRSAM) and is derived from linear hashing. A new logical to physical mapping that is based on sequential bucket allocations in hash order is proposed. With respect to previous methods, this allocation technique has the following characteristics: (1) the structure captures the hashed order in consecutive storage areas so that order preserving (OPH) schemes should result in performance improvements for range queries and sequential processing; and (2) it adapts elastic buckets for the control of file growth. Under specific conditions, this approach outperforms the partial expansion method previously proposed by P.-A. Larson (1982)     

Boundary Layer Development on a Concave Surface： Flow Visualization and Hot Wire Velocity Measurements

Gortler vortices are key issues in the design of gas turbine blades. The present study deals with flow visualization over concave surface for gas turbine applications. The aim is to comprehend qualitatively the flow trends, particularly the Gortler vortices formation and development. Gortler vortices have the shape of mushroom-like vortices regularly spaced at 25 mm. These vortices grow and increase in strength more rapidly along the surface in the case of the same grid of turbulence applied to the measuring section. The curvature radius of the studied blade is 0.5 m and the stream turbulence intensity level is 2.6%. The velocity field is measured by hot wire anemometer in the streamwise direction. The velocity profile is found to be highly distorted by the momentum transfer associated with Gortler vortices. The results are compared to Blasius flow and to literature data for a blade with curvature radius equal to 2 m.     

Combined use of FLUKA and MCNP-4A for the Monte Carlo simulation of the dosimetry of 10B neutron capture enhancement of fast neutron irradiations

Boron neutron capture enhancement (BNCE) of the fast neutron irradiations use thermal neutrons produced in depth of the tissues to generate neutron capture reactions on 10B within tumor cells. The dose enhancement is correlated to the 10B concentration and to thermal neutron flux measured in the depth of the tissues, and in this paper we demonstrate the feasibility of Monte Carlo simulation to study the dosimetry of BNCE. The charged particle FLUKA code has been used to calculate the primary neutron yield from the beryllium target, while MCNP-4A has been used for the transport of these neutrons in the geometry of the Biomedical Cyclotron of Nice. The fast neutron spectrum and dose deposition, the thermal flux and thermal neutron spectrum in depth of a Plexiglas phantom has been calculated. The thermal neutron flux has been compared with experimental results determined with calibrated thermoluminescent dosimeters (TLD-600 and TLD-700, respectively, doped with 6Li or 7Li). The theoretical results were in good agreement with the experimental results: the thermal neutron flux was calculated at 10.3 X 10(6) n/cm2 s1 and measured at 9.42 X 10(6) n/cm2 s1 at 4 cm depth of the phantom and with a 10 cm X 10 cm irradiation field. For fast neutron dose deposition the calculated and experimental curves have the same slope but different shape: only the experimental curve shows a maximum at 2.27 cm depth corresponding to the build-up. The difference is due to the Monte Carlo simulation which does not follow the secondary particles. Finally, a dose enhancement of, respectively, 4.6% and 10.4% are found for 10 cm X 10 cm or 20 cm X 20 cm fields, provided that 100 micrograms/g of 10B is loaded in the tissues. It is anticipated that this calculation method may be used to improve BNCE of fast neutron irradiations through collimation modifications.