bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polynomial biasing importance sampling for markov fluid models
Authors: D'Acquisto Giuseppe , Naldi Maurizio 
Published: September 2008

AbstractImportance Sampling is an established technique for the simulation of rare events in Markov fluid systems, a widely used model in the context of high‐speed multiservice networks. The main issue with Importance Sampling is the definition of the biasing procedure which strongly affects the effectiveness of the simulation technique. In this paper a biasing procedure is proposed which couples the simplicity of application with a performance close to the optimal procedure. The new procedure, named Polynomial Biasing, relies on a single biasing parameter which is used to alter all the elements of the transition rate matrix of the Markov chain with a polynomial sequence. A one‐dimensional minimization algorithm is employed to arrive at the best value of the biasing parameter. Polynomial Biasing provides results identical to the optimal biasing for any superposition of two‐state sources. For the general case of multi‐state sources its performance, analysed through the comparison with the overflow probability obtained through optimal biasing and the evaluation of the optimality indicator in some numerical examples, results close to the optimal one.
An importance sampling algorithm for the simulation of a GPS scheduler
Authors: Giordano Stefano , Pagano Michele , Tartarelli Sandra 
Published: September 2008

AbstractA key requirement of modern telecommunications networks is the capability of providing a variety of Quality of Service (QoS) guarantees to different classes of users. In this scenario scheduling systems play a major role, thanks to their ability of offering different levels of service, while preventing some “greedy users” from degrading the QoS of other classes. A primary QoS parameter is the Cell Loss Probability (CLP), whose typical values are very small and therefore difficult to estimate through standard Monte Carlo (MC) simulation, since long run times are required to achieve accurate results. Under proper conditions, Importance Sampling (IS) techniques can speed up simulations involving rare events. In this paper we propose an application of IS to the simulation of a Generalized Processor Sharing (GPS) scheduler, fed by Markov Arrival Processes (MAP). The algorithms we propose are based on large deviations principles, which provide asymptotic results on the decay rate of per‐session queue length tail distributions in an idealized GPS discipline. In particular, we first present a scheme for the simulation of a two‐buffer system, then we extend the technique to the general case of a multi‐buffer scheduler. We subsequently employ our algorithms to simulate a packetized realistic system, namely the Packet‐by‐packet Generalized Processor Sharing.
Capacity optimisation in MC‐CDMA systems
Authors: Costa Elena , Haas Harald , Schulz Egon , Filippi Alessio 
Published: September 2008

AbstractA novel efficient algorithm is proposed for the optimisation of capacity assignment in a MC‐CDMA system with an additional frequency division multiplexing component. Based on an estimate of the frequency‐selective channel, the algorithm optimises the assignment of the sub‐bands to the users with respect to the overall system capacity. Moreover, in the optimisation process the algorithm can efficiently cope with a given prioritisation among classes of user‐services, i.e. user‐groups, identified on the basis of a certain demand, such as throughput, tolerable delay and/or error rate etc. From an initial random solution, the algorithm proceeds progressively towards the optimisation of the target function, yielding, in general, a local optimum. By trying a few different initial solutions a very good approximation of the global optimum can be obtained. Futhermore, the algorithm complexity grows only as the square of the number of carriers. Simulation results show that its application provides a very significant gain in the downlink performance of the overall system or of the prioritised user‐groups.
Joint direction of arrival and delay channel characteristics estimation using circular array antenna for optimal frequency‐space diversity in MC/CDMA receivers
Authors: Fujii Masahiro , Suzuki Shinnosuke , Itami Makoto , Itoh Kohji 
Published: September 2008

AbstractThis paper derives the Maximum Likelihood (ML) algorithm for jointly estimating Direction Of Arrival (DOA) and delay path characteristics of multipath propagation by using array antennas whose elements are placed on a circular circumference. The algorithm is especially made of in a quasi‐synchronous Multi‐Carrier (MC) / Code Division Multiple Access (CDMA) systems in order to achieve the optimal diversity effect. The estimated channel characteristics may be used in Multiple Access Interference (MAI) cancellation or suppression, which remains as the subject of future study. Assuming in the acquisition period, e. g. the preamble period of packet transmission, mutually orthogonal codes are assigned to the set of multiple carrier channels of the CDMA users and the assignments are cyclically shifted from one symbol period to another. Each of the received carrier channel signals at each of the antenna elements is correlated on the time axis with the orthogonal code assigned to each user and in this way the data characterizing the radio wave propagation from each of the users can be separately supplied to the algorithm to follow. The algorithm performs a 2‐dimensional Discrete Fourier Transform (DFT) on the signal sequence thus supplied from the antenna elements and the carrier channels, giving a sufficient statistic by which the DOA and delay path characteristics can be estimated for each of the multiple paths from each of the users. Use of the estimation is demonstrated to obtain the optimal weights for frequency‐space diversity and significant improvement in Bit Error Rate (BER) performance was observed over the conventional way of obtaining the weights.
Array antenna assisted doppler spread compensator for OFDM
Authors: Okada Minoru , Takayanagi Hideaki , Yamamoto Heiichi 
Published: September 2008

AbstractThis paper proposes a novel array‐antenna‐assisted Doppler spread compensator for orthogonal frequency division multiplexing (OFDM), which is sensitive to fast time‐variation of the radio propagation channel. In the proposed compensator, a linear array antenna is installed on top of the vehicle. The compensator estimates the received signal at a certain point on the linear array antenna by using space domain interpolation. Because the relative position of the estimated receiving point with respect to the ground does not change during the effective symbol duration of an OFDM signal, the time variation due to the movement of the vehicle can be compensated for. Computer simulation shows that the compensator can compensate for the bit error rate performance degradation due to time‐variation of the channel when the velocity of the vehicle is up to 180km/h and a two‐element array antenna is used at the carrier frequency of 600 MHz. The bit error rate performance can be further improved by using a four‐element array antenna.
Implementation of a sic based MC‐CDMA base station receiver
Authors: McCormick Andrew C. , Thompson John S. , Grant Peter M. , Arslan Tughrul , Erdogan Ahmet T. 
Published: September 2008

AbstractThe implementation of a multi carrier‐code division multiple access (MC‐CDMA) base station receiver incorporating decision statistic ordered successive interference cancellation multi‐user detection in low power CMOS hardware is investigated. Serial and parallel cancellation architectures are compared and it is shown that the parallel one operates in far fewer clock cycles than its serial counterpart. A detailed description of architecture is given including the parallel algoridim used to implement the multi‐user detection. Results show the power consumption and fixed point performance of the circuit.
A comparison of an OFDM system and a single carrier system using frequency domain equalization
Authors: Witschnig Haralo , Koppler Alois , Springer Andreas , Weigel Robert , Huemer Mario 
Published: September 2008

AbstractIn this work we compare an OFDM (Orthogonal Frequency Division Multiplexing) system and a SC/FDE (Single Carrier System with Frequency Domain Equalization) system in terms of their BER performance, channel estimation techniques, bandwidth‐efficiency and other design parameters. In both systems an estimation of the channel transfer function is needed for equalization purposes. Different frequency domain based channel estimation techniques for both systems are presented and compared. BER‐simulations have been performed for channel‐coded data in typical indoor multipath environments. The parameters of both systems are adapted to the Hiperlan/2 and IEEE 802.1 la standards. It will be pointed out that OFDM shows slight advantages when taking the BER performance into account, while the SC/FDE system exhibits advantages in terms of signal processing complexity. Finally a combination of OFDM and SC/FDE is described that exhibits significant advantages.
Transmit/Receive‐antenna diversity techniques for OFDM systems
Authors: Dammann Armin , Kaiser Stefan 
Published: September 2008

AbstractIn this paper, we investigate different antenna diversity concepts, which can be easily applied to orthogonal frequency division multiplexing (OFDM) systems. The focus is on standard compatibility, i.e. these schemes can be implemented to already existing OFDM systems without changing the standards. The introduced diversity techniques are applied exemplarily to the DVB‐T system. Bit error performance investigations were done by simulation for different DVB‐T and diversity parameter sets.
Generalized window advertising for TCP congestion control
Authors: Gerla Mario , Cigno Renato Lo , Mascolo Saverio , Weng Wenjie 
Published: September 2008

AbstractCongestion in the Internet is a major cause of network performance degradation. The Generalized Window Advertising (GWA) scheme proposed in this paper is a new approach for enhancing the congestion control properties of TCP. GWA requires only minor modifications to the existing protocol stack and is completely backward compatible, allowing GWA‐hosts to interact with non‐GWA hosts without modifications. GWA exploits the notion of end‐host‐network cooperation, with the congestion level notified from the network to end hosts. It is based on solid control theory results mat guarantee performance and stable network operation. GWA is able to avoid window oscillations and the related fluctuations in offered load and network performance. This makes it more robust to sustained network overload due to a large number of connections competing for the same bottleneck, a situation where traditional TCP implementations fail to provide satisfactory performance. GWA‐TCP is compared with traditional TCP, TCP with RED and also ECN using the ns‐2 simulator. Results show that in most cases GWA‐TCP outperforms the traditional schemes. In particular, when compared with ECN, it provides smoother network operation and increased fairness.
Performance evaluation of combined spatial processing and multiple access interference equalization for DS‐CDMA systems
Authors: Cavalcanti Francisco R. P. , Romano Joāo M. T. 
Published: September 2008

AbstractAdaptive detection in code division multiple access (CDMA) systems aims the reduction of interference in order to allow capacity increase. Spatial processing and multiple access interference (MAI) equalization are two important techniques that have been used separately in adaptive detection for CDMA. The first contribution of this paper is die proposal and performance assessment of a detector that operates simultaneously as a spatial processor and MAI equalizer. Its minimum mean square error performance in a multiple cell CDMA system is addressed and compared with die two existing techniques. A blind adaptive implementation of a similar concept is a second proposition of the paper. Its performance is assessed in terms of wrong capture probability and compared with two other existing techniques, based on constant modulus (CM) or decision‐directed (DD) algorithms. Simulation results show that the first combined scheme performs better than the separated existing techniques, while the proposed blind approach also overcomes limitations of CM and DD‐based solutions.
A new broadband uniform accuracy doa estimator
Authors: Ghavami Mohammad , Kohno Ryuji 
Published: September 2008

AbstractConventional estimators of the bearing angle suffer from different accuracies for different angles. In the method discussed in this letter, a set of two‐dimensional digital filters are employed for beamforming. Each filter is called a fan filter and performs broadband characteristics. It will be shown analytically that the accuracy of the bearing estimation is strongly dependent to the angle of arrival in such a way that it is maximum in the broadside and minimum in the endfire of the antenna. We will derive a simple expression for calculating the number of coefficients necessary for beamforming with uniform accuracy. A set of filters is then designed according to this criteria. It will be demonstrated by computer simulations that in the presence of noisy broadband incoming signals, the estimation of different arriving angles is accomplished with almost the same accuracy and hence using this method a complex and separately sectored antenna wilt not be required.
Notes on cost functions and estimators for ‘Bussgang’ adaptive blind equalization
Authors: Fiori Simone 
Published: September 2008

AbstractThe aim of this paper is to present some remarks on the cost functions for blind channel equalization by ‘Bussgang’ algorithms recently discussed in the literature; also, some possible associated non‐Bayesian estimators are considered with details, and the effects of the choice of such estimators in relation to ‘Bussgang’ filtering are investigated.
Infant health production functions: what a difference the data make
Authors: Reichman Nancy E. , Corman Hope , Noonan Kelly , Dave Dhaval 
Published: September 2008

AbstractWe examine the extent to which infant health production functions are sensitive to model specification and measurement error. We focus on the importance of typically unobserved but theoretically important variables (typically unobserved variables, TUVs), other non‐standard covariates (NSCs), input reporting, and characterization of infant health. The TUVs represent wantedness, taste for risky behavior, and maternal health endowment. The NSCs include father characteristics. We estimate the effects of prenatal drug use, prenatal cigarette smoking, and first trimester prenatal care on birth weight, low birth weight, and a measure of abnormal infant health conditions. We compare estimates using self‐reported inputs versus input measures that combine information from medical records and self‐reports. We find that TUVs and NSCs are significantly associated with both inputs and outcomes, but that excluding them from infant health production functions does not appreciably affect the input estimates. However, using self‐reported inputs leads to overestimated effects of inputs, particularly prenatal care, on outcomes, and using a direct measure of infant health does not always yield input estimates similar to those when using birth weight outcomes. The findings have implications for research, data collection, and public health policy. Copyright © 2008 John Wiley & Sons, Ltd.
Prognosis of Primary Hepatocellular Carcinoma
Authors: Okuda Kunio , Obata Hiroshi , Nakajima Yukio , Ohtsuki Toshio , Okazaki Nobuo , Ohnishi Kunihiko 
Published: September 2008

Prognosis of 600 consecutive patients with hepatocellular carcinoma was analyzed in relation to treatment. They were divided into three stages based on four parameters of advanced disease: ascites, tumor greater than 50% of the two-dimensional size of the liver, serum albumin below 3 gm per dl, and serum bilirubin above 3 mg per dl. Stage I had none of these signs; Stage II one or two signs, and Stage III three or all signs. Of 600 patients, 98 had resection, 333 had nonsurgical treatment (158 treated by intraarterial chemotherapy, 94 systemic chemotherapy, 77 transcatheter embolization, and 4 others) and 169 no treatment.
The median survival of untreated patients was only 1.6 months from diagnosis, and no untreated Stage III patient lived more than 3 months; there was a median survival of 0.7 month. Surgically treated patients lived significantly longer than nonsurgical patients of comparable stages; median survival was 19.6 months in the former and 2.8 months in the latter. Whereas Stage I patients did fairly well without treatment, chemotherapy significantly prolonged survival of patients of Stages II and III. These results suggest that early diagnosis and hepatic resection improve prognosis in patients with hepatocellular carcinoma in the areas where this cancer frequently emerges unicentrically. In view of the generally poor prognosis, liver transplantation is recommended when resection is not possible or indicated, and before extrahepatic metastasis occurs.
Liver Procurement for Orthotopic Transplantation: An Analysis of the Pittsburgh Experience
Authors: Van Thiel David H. , Schade Robert R. , Hakala Thomas R. , Starzl Thomas E. , Denny Donald 
Published: September 2008

The incidence of prospective organ donors in the United States and the techniques which are to used to guarantee their optimal use after identification are analyzed. Attitudes of the public and health professionals toward organ donation are discussed.
The organization of the Pittsburgh Organ Procurement Agency and its relationship to other such agencies is described.
Finally, the presently used techniques of liver salvaging and preservation are outlined.
The Etiology of Pigment Gallstones
Authors: Ostrow Donald J. 
Published: September 2008

Pigment gallstones are of two major types, black and earthy brown, each consisting of calcium salts of bilirubin and other anions, along with an unmeasured residue that is largely mucin glycoproteins. Studies in model systems indicate that the small proportion of unconjugated bilirubin in bile is solubilized by bile salts and that the ionized bilirubin is more soluble than the protonated diacid. Solubility is decreased by added lecithin but is unaffected by cholesterol. At the pH of bile, unconjugated bilirubin exists mainly as a monoanion with sufficient solubility in mixed micelles not to precipitate, were it not for the presence of calcium, which forms highly insoluble salts with unconjugated bilirubin anions. Supersaturation of bile with calcium bilirubinates is inhibited by bile salts, which bind calcium, reducing the activity of free calcium ions. When supersaturation occurs, usually due to increased concentrations of bilirubinate anion, nucleation may be initiated by binding of calcium bilirubinate to mucin glycoproteins in bile.
In earthy brown stones, which form mainly in the bile ducts, the pigment is mostly calcium bilirubinate, combined with calcium palmitate. These components form due to hydrolysis, by enzymes in infecting bacteria, of conjugated bilirubin and lecithin, respectively. In black stones, which form mainly in the gallbladder, the pigment is mostly a highly cross-linked network polymer of bilirubin, which is insoluble in all solvents. Concomitant polymerization and oxidation of calcium bilirubinate probably occur in the solid state, after precipitation of the pigment due to hydrolysis of conjugated bilirubin by endogenous β-glucuronidase from the biliary tract and/or liver. This may result from a diet-related decrease in inhibitors of β-glucuronidase in bile. In hemolytic states, increased concentrations of conjugated bilirubin in bile, providing more substrate for hydrolysis, may contribute also to black stone formation. Black stones also contain coprecipitated calcium phosphate and/or carbonate, but the insoluble polymer renders them resistant to physical dissolution therapy.
Survival of pleural malignant mesothelioma in Italy: A population‐based study
Authors: Montanaro Fabio , Rosato Rosalba , Gangemi Manuela , Roberti Sara , Ricceri Fulvio , Merler Enzo , Gennaro Valerio , Romanelli Antonio , Chellini Elisabetta , Pascucci Cristiana , Musti Marina , Nicita Carmela , Barbieri Pietro Gino , Marinaccio Alessandro , Magnani Corrado , Mirabelli Dario 
Published: September 2008

AbstractA median survival time of about 9 months is generally reported among malignant pleural mesothelioma cases. Recently, better results in terms of survival and performance status have been reported in clinical trials that included highly selected patients. We describe the survival of pleural mesothelioma patients and the factors predictive of survival in an unselected, population‐based setting. Pleural mesothelioma cases (4,100) registered from 1990 to 2001 by 9 Italian regional mesothelioma registries contributing to the network of the National Mesothelioma Registry were followed until December 31, 2005. Univariate (Kaplan‐Meier) and multivariate (Cox proportional hazards regression) analyses of survival were carried out according to selected individual characteristics, including limited information on treatment in a subset of 578 cases. The median survival time was 9.8 months (95% confidence interval: 9.4–10.1). In multivariate analysis, younger age at diagnosis and epithelioid histotype were associated with significantly reduced hazard ratios. Positive effects of gender (women) and being diagnosed in a hospital with a thoracic surgery unit were of border‐line statistical significance. No association with calendar period of diagnosis or asbestos exposure was present. Treatment was not associated with a statistically significant improvement in survival. This is the largest population‐based study on survival in patients with pleural mesothelioma to date. Age and morphology were the main prognostic factors. Results regarding the effect of treatment were disappointing but may be useful to assess the future impact, at the population level, of recently introduced therapies. © 2008 Wiley‐Liss, Inc.
Vascular density in carcinoma of the uterine cervix and its predictive value for radiotherapy
Authors: Siracka Eva , Révész L. , Kovač R. , Siracký J. 
Published: September 2008

AbstractThe vascular density (VD) in stage‐III tumors of the uterine cervix was determined by morphometric analysis of histologic, Masson‐trichrome stained sections prepared from biopsies. In a retrospective study, VD was found to be related to results of radiotherapy, larger VD being associated with prolonged survival, in agreement with similar observations made earlier with stage‐IB and ‐IIA tumors of the cervix. In a complementary study the variation of VD within tumors was investigated in relation to the variation between tumors using surgically removed cervical carcinomas in stage IB. Statistically significant F‐ratios were calculated, suggesting a more or less individual pattern of vascularization of the tumors despite a considerable intra‐tumoral heterogeneity of the vas‐culature. It is concluded that VD may reflect oxygenation of neoplastic tissue, and may have a predictive value in regard to the response of tumors to irradiation.