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.     

Reducing saturation and congestion in VANET networks: Alliance‐based approach and comparisons

A vehicular ad hoc network (VANET) is composed mainly of fixed roadside entities (RSUs) and mobile entities (vehicles). In order to exchange information and data relating to the safety and comfort of road users, these different entities must establish communications between them. In these communications, one of the main problems is related to congestion and saturation of RSUs. In this paper, we first study the main protocols that involve RSUs in their strategy of routing by classifying them according to four levels. Furthermore, to deal with the problem of saturation of RSUs, we present a new approach of cooperation between the RSUs of a VANET in order to reduce its congestion and avoid as much as possible the saturation of these entities. This approach, called “D2A2RS” (defensive alliance–based approach for reducing RSUs saturation), is based on the concept of defensive alliances in graphs that ensures effective collaboration between RSUs. To evaluate the performance of the proposed approach, we conduct a comparative analysis by using both analytical models and simulations. The obtained comparison results have shown the efficiency and the performance of our approach compared with other concurrent approaches in the literature in terms of packet loss/success rate, end‐to‐end transmission delay, and network scalability.     

Resource Allocation for Downlink Cellular OFDMA Systems—Part I: Optimal Allocation

In this pair of papers (Part I and Part II in this issue), we investigate the issue of power control and subcarrier assignment in a sectorized two-cell downlink OFDMA system impaired by multicell interference. As recommended for WiMAX, we assume that the first part of the available bandwidth is likely to be reused by different base stations (and is thus subject to multicell interference) and that the second part of the bandwidth is shared in an orthogonal way between the different base stations (and is thus protected from multicell interference). Although the problem of multicell resource allocation is nonconvex in this scenario, we provide in Part I the general form of the global solution. In particular, the optimal resource allocation turns out to be “binary” in the sense that, except for at most one pivot-user in each cell, any user receives data either in the reused bandwidth or in the protected bandwidth, but not in both. The determination of the optimal resource allocation essentially reduces to the determination of the latter pivot-position.      

MRI in the diagnosis of osteoid osteoma

INTRODUCTION: Osteoid osteoma (OO) is a frequently encountered benign bone tumor, seen in young adults with male predominance. MATERIALS AND METHODS: Nine patients complaining of nonspecific extremity pain underwent MRI examination. The sequences obtained were T1 and T2 weighted spin-echo and T2 weighted gradient echo. A CT scan examination followed in all cases, exploring the region of the abnormal signal seen on MRI. The results of both examinations were compared. RESULTS: In six of the nine patients (66.6%) MRI showed evidence suggestive of osteoid osteoma, comparable that seen on CT scan. In three patients (33.3%), MRI showed a nonspecific and ill-defined bone marrow signal abnormality. CT cuts focused on those areas of signal abnormality showed the nidus. DISCUSSION: MRI is more sensitive than CT scan in detecting soft tissue and bone marrow abnormalities adjacent to an osteoid osteoma. This may produce a misleading aggressive appearance on MR images. CT scanning is more specific than MRI, by showing the nidus. In three patients studied, the nidus was only seen by CT, the other six osteoid osteomas were equally seen by CT and by MRI. In our study, MRI revealed abnormalities in all the cases. It was also highly specific for osteoid osteoma in 66.6%. CONCLUSION: MRI is very sensitive in detecting bone marrow and soft tissue abnormalities, and can suggest the diagnosis of OO in a good number of patients. In the remainder cases MRI guides the CT-scan. CT is more accurate and remains the definite examination for the diagnosis of OO, by showing the nidus.     

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)     

Excited levels in Po and Pb fed by β-decays of Bi (T1/2 = 45.6 min) and Tl (T1/2 = 2.2 min)

The γ-decay of radiochemically separated ²¹³Bi sources (T_1/2 = 45.6 min), in equilibrium with ²⁰⁹Tl (T_1/2 = 2.2 min) and ²¹³Po (T_1/2 = 4.2 μs), has been reinvestigated using coaxial HPGe detectors, a LEPS detector and the γ-γ coincidence method. The energies and intensities of 20 γ-lines were measured, of which 11 are reported for the first time. Of the ten γ-rays attributed to ²¹³Bi β-decay, five are new. All of them were interpreted in a ²¹³Po level scheme using γ-γ coincidence data. New levels at 292.8, 1003.6 and 1119.5 keV are proposed in ²¹³Po. In the ²⁰⁹Tl β-decay, five γ-lines were measured, two of which are new. On the basis of γ-γ coincidence, we suggest that two new levels of 3069.6 and 3388.9 keV are fed into the ²⁰⁹Pb magic nucleus.