Management system for the SND experiments

A new management system for the SND detector experiments (at VEPP-2000 collider in Novosibirsk) is developed. We describe here the interaction between a user and the SND databases. These databases contain experiment configuration, conditions and metadata. The new system is designed in client-server architecture. It has several logical layers corresponding to the users roles. A new template engine is created. A web application is implemented using Node.js framework. At the time the application provides: showing and editing configuration; showing experiment metadata and experiment conditions data index; showing SND log (prototype).Comment: 6 pages, 3 figures; INSTR17 conferenc

Optical Absorption and Raman Spectroscopy Study of the Fluorinated Double-Wall Carbon Nanotubes

Double-wall carbon nanotube (DWNT) samples have been fluorinated at room temperature with varied concentration of a fluorinating agent BrF3. Content of the products estimated from X-ray photoelectron data was equal to CF0.20 and CF0.29 in the case of deficit and excess of BrF3. Raman spectroscopy showed considerable decrease of carbon nanotube amount in the fluorinated samples. Analysis of optical absorption spectra measured for pristine and fluorinated DWNT samples revealed a selectivity of carbon nanotube fluorination. Nanotubes with large chiral angle are more inert to the fluorinating agent used

Low-frequency Raman spectra in LiNbO3 : Within and beyond the standard paradigm of ferroelectric dynamics

Low-frequency Raman spectra of stoichiometric LiNbO3 crystals are investigated in the frequency range down to ∼1 cm−1 and in the temperature range of 300–1423 K . The central peak (quasielastic light scattering) is found and described for all temperatures studied and in both scattering geometries explored, zz - and xy -configurations. The central peak features follow the standard paradigm, predicting the critical narrowing of the width, only at T≳1300 K in the zz -configuration. At lower temperatures the inverse relaxation time increases with the temperature increase, in contradiction to the standard theoretical predictions. This experimental result was interpreted as the importance of local fluctuations of the order parameter. The ferroelectric dynamics of LiNbO3 is described by the soft mode coupled to a relaxation, sharing both displacement and order-disorder features

Algorithm and performance of a clinical IMRT beam-angle optimization system

This paper describes the algorithm and examines the performance of an IMRT beam-angle optimization (BAO) system. In this algorithm successive sets of beam angles are selected from a set of predefined directions using a fast simulated annealing (FSA) algorithm. An IMRT beam-profile optimization is performed on each generated set of beams. The IMRT optimization is accelerated by using a fast dose calculation method that utilizes a precomputed dose kernel. A compact kernel is constructed for each of the predefined beams prior to starting the FSA algorithm. The IMRT optimizations during the BAO are then performed using these kernels in a fast dose calculation engine. This technique allows the IMRT optimization to be performed more than two orders of magnitude faster than a similar optimization that uses a convolution dose calculation engine.Comment: Final version that appeared in Phys. Med. Biol. 48 (2003) 3191-3212. Original EPS figures have been converted to PNG files due to size limi

Broken Local Symmetry in Paraelectric BaTiO3 Proved by Second Harmonic Generation

Precursor dynamics of a cubic to tetragonal ferroelectric phase transition in BaTiO3 is studied by the accurate measurement of the second harmonic generation (SHG) integral intensities. A finite signal holds for the SHG integrated intensity above the ferroelectric Curie temperature Tc=403  K. Above the Burn’s temperature Td≈580  K, the power law with the exponent γ=1 shows normal SHG nature originating from the hyper-Raman scattering by dynamical polar excitations, while, below Td, a SHG signal from polar nanoregions becomes dominant with the larger exponent γ=2. Such a crossover of the power law exponent near Td is discussed on the basis of the effective Hamiltonian method and Monte Carlo simulation

IMRT beam angle optimization using electromagnetism-like algorithm

The selection of appropriate beam irradiation directions in radiotherapy – beam angle optimization (BAO) problem – is very impor- tant for the quality of the treatment, both for improving tumor irradia- tion and for better organs sparing. However, the BAO problem is still not solved satisfactorily and, most of the time, beam directions continue to be manually selected in clinical practice which requires many trial and error iterations between selecting beam angles and computing fluence patterns until a suitable treatment is achieved. The objective of this pa- per is to introduce a new approach for the resolution of the BAO problem, using an hybrid electromagnetism-like algorithm with descent search to tackle this highly non-convex optimization problem. Electromagnetism- like algorithms are derivative-free optimization methods with the ability to avoid local entrapment. Moreover, the hybrid electromagnetism-like algorithm with descent search has a high ability of producing descent directions. A set of retrospective treated cases of head-and-neck tumors at the Portuguese Institute of Oncology of Coimbra is used to discuss the benefits of the proposed algorithm for the optimization of the BAO problem.Fundação para a Ciência e a Tecnologia (FCT