1,096 research outputs found
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
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 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
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
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
Inferring Long-term Dynamics of Ecological Communities Using Combinatorics
In an increasingly changing world, predicting the fate of species across the
globe has become a major concern. Understanding how the population dynamics of
various species and communities will unfold requires predictive tools that
experimental data alone can not capture. Here, we introduce our combinatorial
framework, Widespread Ecological Networks and their Dynamical Signatures
(WENDyS) which, using data on the relative strengths of interactions and growth
rates within a community of species predicts all possible long-term outcomes of
the community. To this end, WENDyS partitions the multidimensional parameter
space (formed by the strengths of interactions and growth rates) into a finite
number of regions, each corresponding to a unique set of coarse population
dynamics. Thus, WENDyS ultimately creates a library of all possible outcomes
for the community. On the one hand, our framework avoids the typical
``parameter sweeps'' that have become ubiquitous across other forms of
mathematical modeling, which can be computationally expensive for ecologically
realistic models and examples. On the other hand, WENDyS opens the opportunity
for interdisciplinary teams to use standard experimental data (i.e., strengths
of interactions and growth rates) to filter down the possible end states of a
community. To demonstrate the latter, here we present a case study from the
Indonesian Coral Reef. We analyze how different interactions between anemone
and anemonefish species lead to alternative stable states for the coral reef
community, and how competition can increase the chance of exclusion for one or
more species. WENDyS, thus, can be used to anticipate ecological outcomes and
test the effectiveness of management (e.g., conservation) strategies.Comment: 25 pages, 9 figure
The PML-RAR alpha transcript in long-term follow-up of acute promyelocytic leukemia patients
Background and Objectives. Detection of PML-RAR alpha transcripts by RT-PCR is now established as a rapid and sensitive method for diagnosis of acute promyelocytic leukemia (APL), Although the majority of patients in longterm clinical remission are negative by consecutive reverse transcription polymerase chain reaction (RT-PCR) assays, negative tests are still observed in patients who ultimately relapse. Conversion from negative to positive PCR has been observed after consolidation and found to be a much stronger predictor of relapse. This study reports on 47 APL patients to determine the correlation between minimal residual disease (MRD) status and clinical outcome in our cohort of patients. Design and Methods. The presence of PML-RAR alpha t transcripts was investigated in 47 APL patients (37 adults and 10 children) using a semi-nested reverse transcriptase-polymerase chain reaction to evaluate the prognostic value of RT-PCR tests. Results. All patients achieved complete clinical remission (CCR) following induction treatment with all-trans retinoic acid (ATRA) and chemotherapy (CHT) or ATRA alone. Patients were followed up between 2 and 117.6 months (median: 37 months). Relapses occurred in 11 patients (9 adults and 2 children) between 11.4 and 19 months after diagnosis (median: 15.1 months) while 36 patients (28 adults and 8 children) remained in CCR, Seventy-five percent of patients carried the PML-RARa long isoform (bcr 1/2) which also predominated among the relapsed cases (9 of 11) but did not associate with any adverse outcome (p = 0.37), For the purpose of this analysis, minimal residual disease tests were clustered into four time-intervals: 0-2 months, 3-5 months, 5-9 months and 10-24 months. Interpretation and Conclusions. Children showed persisting disease for longer than adults during the first 2 months of treatment, At 2 months, 10 (50%) of 20 patients who remained in CCR and 4 (80%) of 5 patients who subsequently relapsed were positive. Patients who remained in CCR had repeatedly negative results beyond 5.5 months from diagnosis. A positive MRD test preceded relapse in 3 of 4 tested patients. The ability of a negative test to predict CCR (predictive negative value, PNV) was greater after 6 months (> 83%), while the ability of a positive test to predict relapse (predictive positive value, PPV) was most valuable only beyond 10 months (100%). This study (i) highlights the prognostic value of RT-PCR monitoring after treatment of APL patients but only from the end of treatment, (ii) shows an association between conversion to a positive test and relapse and (iii) suggests that PCR assessments should be carried out at 3-month intervals to provide a more accurate prediction of hematologic relapses but only after the end of treatment, (C) 2001, Ferrata Storti Foundatio
Combined distributed turbo coding and space frequency block coding techniques
The distributed space-time (frequency) coding and distributed channel turbo coding used independently represent two cooperative techniques that can provide increased throughput and spectral efficiency at an imposed maximum Bit Error Rate (BER) and delay required from the new generation of cellular networks. This paper proposes two cooperative algorithms that employ jointly the two types of techniques, analyzes their BER and spectral efficiency performances versus the qualities of the channels involved, and presents some conclusions regarding the adaptive employment of these algorithms. © 2010 V. Bota et al.FP7/ICT/2007/21547
The indirect effect of contextual factors on the emotional distress of infertile couples
Few studies were dedicated to study the role of contextual factors, such as the socioeconomic status and urban rural residence in emotional distress of infertile couples. This study aimed to explore the impact of contextual factors on emotional distress, either directly or by affecting the importance of parenthood in one’s life which in turn affects emotional distress. In this cross-sectional study, 70 couples recruited during hormonal stimulation phase prior to IVF completed clinical and sociodemographic forms and self-report questionnaires assessing representations about the importance of parenthood and emotional distress. Path analysis using structural equation modelling was used to examine direct and indirect effects among variables. Results indicated that social economic status and Urban-Rural residence had an impact in emotional distress by affecting the representations about the importance of parenthood in one’s life. Gender differences were found regarding model paths, suggesting that the social context may contribute more to women’s emotional distress than to their partners’ distress. When delineating psychological interventions, health care providers should consider that cultural values about children and parenthood contribute to shape the infertility experienc
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