Line-dependent veiling in very active T Tauri Stars

The T Tauri stars with active accretion disks show veiled photospheric spectra. This is supposedly due to non-photospheric continuum radiated by hot spots beneath the accretion shocks at stellar surface and/or chromospheric emission lines radiated by the post-shocked gas. The amount of veiling is often considered as a measure of the mass-accretion rate. We analysed high-resolution photospheric spectra of accreting T Tauri stars LkHa 321, V1331 Cyg, and AS 353 A with the aim of clarifying the nature of the line-dependent veiling. Each of these objects shows a highly veiled, strong emission line spectrum and powerful wind features indicating high rates of accretion and mass loss. Equivalent widths of hundreds of weak photospheric lines were measured in the observed spectra and compared with those in synthetic spectra with the same spectral type. We found that the veiling is strongly line-dependent: larger in stronger photospheric lines and weak or absent in the weakest ones. No dependence of veiling on excitation potential within 0 to 5 eV was found. Different physical processes responsible for these unusual veiling effects are discussed in the framework of the magnetospheric accretion model. The observed veiling has two origins: 1) an abnormal structure of stellar atmosphere heated up by the accreting matter, and 2) a non-photospheric continuum radiated by a hot spot with temperature lower than 10000 K. The true level of the veiling continuum can be derived by measuring the weakest photospheric lines with equivalent widths down to $\approx$10 m\AA. A limited spectral resolution and/or low signal-to-noise ratio results in overestimation of the veiling continuum. In the three very active stars, the veiling continuum is a minor contributor to the observed veiling, while the major contribution comes from the line-dependent veiling.Comment: 10 pages, 10 figures. Accepted for publication in Astronomy and Astrophysic

Simulation-based evaluation of spectrum opportunities in UMTS cellular networks

A scenario based on an UMTS TDD opportunistic cellular system that operates over UMTS FDD licensed cellular networks is considered. Therefore we develop a simulation tool that addresses the goal of analysis and assessment of UMTS TDD opportunistic radio system in a coexistence environment with UMTS FDD primary cellular networks. The communication presents the scenario considered, the main features of the tool, discusses and proposes metrics to evaluate the communication opportunities in UMTS FDD primary cellular networks, and presents numerical simulation results. These show that a moderate number of UMTS TDD available frequencies and a reasonable UMTS TDD opportunistic radio transmission power will allow the deployment of UMTS TDD opportunistic radio networks in a coexistence environment with existing licensed systems

Direct time-domain channel impulse response estimation for OFDM-based systems

A method to estimate the channel impulse response using the received serial data in time-domain, without using DFT operations, is investigated. The processing required by the proposed method is substantially reduced when compared with LS-DFT channel estimation method, with no performance degradation. Furthermore, this method can incorporate the results of other published works that are DFT-based, at little or no added complexity, to improve the estimate of channel impulse response

Vectorial channel estimation for uplink MC-CDMA in beyond 3G wireless systems

In beyond 3G wireless systems the bandwidth efficiency can be increased with the use of adaptive antenna arrays. This paper focus on a key issue for adaptive antenna arrays, that is, channel parameters estimation including Direction-Of-Arrival (DOA). In order to estimate DOA. the channel frequency responses for the links between the mobile users and each of base station array elements are estimated by pilot-aided minimum mean square error (MMSE) algorithm. This estimator is not sensitive to the channel statistics. Based on frequency response estimatives DOA's of impinging multipath components to the base station are estimated by a low complex Wlauimuni Likelihood (ML) approach. Furthermore an uplink burst structure with specifically designed midamble field for multiuser channel estimation in MC-CDMA is proposed. The performance is assessed in terms of channel estimation errors for a MC-CDMA TDD system over fast and slow fading mobile channels

Application of game theory in ad- hoc opportunistic radios

The application of mathematical analysis to the study of wireless ad hoc networks has met with limited success due to the complexity of mobility, traffic models and the dynamic topology. A scenario based UMTS TDD opportunistic cellular system with an ad hoc behaviour that operates over UMTS FDD licensed cellular network is considered. In this paper, we describe how ad hoc opportunistic radio can be modeled as a game and how we apply game theory based Power Control in ad-hoc opportunistic radio

Spermatocytic Seminoma: Clinical Case and Review

Introdução: O seminoma espermatocítico é um diagnóstico incomum de tumores do testículo, frequentemente exuberantes na sua dimensão, mas com bom prognóstico. Apesar da designação errónea, trata-se de tumores de células germinativas do tipo não-seminoma. Caso Clínico: Descreve-se o caso clínico de um homem de 49 anos de idade, com exuberante aumento de volume escrotal de agravamento recente, à custa de massa indolor do testículo direito. Foi feita ecografia escrotal que mostrou hidrocelo e imagem sugestiva de massa atípica do epidídimo direito. TC torácica, abdominal e pélvica não mostrou adenomegalias retroperitoneais ou outra alteração; os valores de LDH, αFP e βHCG eram normais. Foi feita orquidectomia por via escrotal à direita, com excisão de uma ampla área do escroto. Identificou-se na peça operatória, com 1375g, seminoma espermatocítico com invasão vascular da túnica albugínea (pT2). O doente iniciou quimioterapia com BEP (dois ciclos). Discussão: O seminoma espermatocítico é raro, com cerca de 2% de incidência, o diagnóstico faz-se habitualmente na 6ª década de vida, e tem localização exclusivamente testicular. A orquidectomia é frequentemente curativa. Apesar de estarem descritos tumores de maior volume do que o seminoma clássico, destaca-se neste caso a exuberância clínica incomum pela dimensão do testículo, bem como do hidrocelo que o acompanhava

Facing the wind of the pre-FUor V1331 Cyg

The mass outflows in T Tauri stars (TTS) are thought to be an effective mechanism to remove angular momentum during the pre-main-sequence contraction of a low-mass star. The most powerful winds are observed at the FUor stage of stellar evolution. V1331 Cyg has been considered as a TTS at the pre-FUor stage. We analyse high-resolution spectra of V1331 Cyg collected in 1998-2007 and 20-d series of spectra taken in 2012. For the first time the photospheric spectrum of the star is detected and stellar parameters are derived: spectral type G7-K0 IV, mass 2.8 Msun, radius 5 Rsun, vsini < 6 km/s. The photospheric spectrum is highly veiled, but the amount of veiling is not the same in different spectral lines, being lower in weak transitions and much higher in strong transitions. The Fe II 5018, Mg I 5183, K I 7699 and some other lines of metals are accompanied by a `shell' absorption at radial velocity of about -240 km/s. We show that these absorptions form in the post-shock gas in the jet, i.e. the star is seen though its jet. The P Cyg profiles of H-alpha and H-beta indicate the terminal wind velocity of about 500 km/s, which vary on time-scales from several days to years. A model of the stellar wind is developed to interpret the observations. The model is based on calculation of hydrogen spectral lines using the radiative transfer code TORUS. The observed H-alpha and H-beta line profiles and their variability can be well reproduced with a stellar wind model, where the mass-loss rate and collimation (opening angle) of the wind are variable. The changes of the opening angle may be induced by small variability in magetization of the inner disc wind. The mass-loss rate is found to vary within (6-11)x10^{-8} Msun/yr, with the accretion rate of 2.0x10^{-6} Msun/yr.Comment: 11 pages, 12 figures; accepted for publication in MNRAS. Typographical errors have been corrected after the proof stag

Capacity and Fairness of Distributed Antenna Systems in Multi-Cell Environments with User Scheduling, Power Control and Imperfect CSI

Distributed antenna systems (DASs) have attractedlots of attention as a method to improve the performance of futurewireless networks. Capacity analysis and optimum power allocationfor the physical layer of DASs have been extensively exploredin the literature. However, the study of cross-layer issues, suchas channel-aware scheduling and fairness evaluation, is relativelyscarce. This paper partially fills this gap by addressing the downlinkcapacity and fairness analysis of a DAS assisted by jointuser scheduling and transmit power control. The algorithm isevaluated in a multi-cell environment assuming imperfect channelstate information. The algorithm exploits the spatial diversityprovided by the distributed antennas in order to schedule over thesame frequency band a different user attached to each one of thedistributed nodes. The objective is to optimize the power levelsto control the interference created between the transmissionsof the selected users, thereby multiplexing as many of them aspossible while maximizing capacity. To achieve this goal, a sumratecapacity optimization with respect to the power levels ishere proposed by using a gradient descent iterative technique.The result is the set of optimum user-antenna pairs to bescheduled and their optimum power levels. Inter-cell interferenceis calculated by reusing the results of previous simulation runsin the transmission parameters of outer-cells, thereby efficientlyreplicating system-level behavior. The algorithm is also evaluatedin terms of fairness by using the spatial distribution of the usercapacity. Capacity and fairness of the algorithm considerablyoutperform previous solutions, particularly in scenarios withgood line-of-sight and optimum node location

Coder and Decoder of Block mBnB Principally the 1B2B or Manchester

This work presents the coder and decoder of block mBnB of the type 1B2B or Manchester. In the coder 1B2B each block/word of 1 input bit is coded in the block / word of 2 output bits. In the decoder 1B2B happen the inverse, each block of 2 input bits is newly converted in the original block of 1 output bit. The coder injects in the transmission line a number of 1’s exactly equal to the number of 0’s, what guarantees a DC constant component and maximizes the transitions number.&nbsp; The objective is&nbsp; to implement the pair coder and decoder 1B2B so that it improves the transmission quality and increases the information security. Keywords: Block codes, Digital systems, Transmission line