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Values Independent (value + independent)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

DRED: a random early detection algorithm for TCP/IP networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2002
James Aweya
Abstract It is now widely accepted that a RED [2] controlled queue certainly performs better than a drop-tail queue. But an inherent weakness of RED is that its equilibrium queue length cannot be maintained at a preset value independent of the number of TCP active connections. In addition, RED's optimal parameter setting is largely correlated with the number of connections, the round-trip time, the buffer space, etc. In light of these observations, we propose DRED, a novel algorithm which uses the basic ideas of feedback control to randomly discard packets with a load-dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The benefits of stabilized queues in a network are high resources utilization, predictable maximum delays, more certain buffer provisioning, and traffic-load-independent network performance in terms of traffic intensity and number of connections. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Convergence study of a Schrödinger-equation algorithm and structure-factor determination from the wavefunction

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2008
Kostas Bethanis
The algorithm [Bethanis, Tzamalis, Hountas & Tsoucaris (2002). Acta Cryst. A58, 265,269] which reformulates the quantum-mechanical problem of solving a Schrödinger (S) equation in a crystallographic context has been upgraded and tested for many aspects of convergence. The upgraded algorithm in reciprocal space aims at determining a wavefunction ,H such that (a) ,H fulfils the S equation within certain precision and (b) ,H minimizes by least squares the differences between the calculated structure factors from the wavefunction and the observed ones. Calculations have been made with three molecules (11, 41 and 110 non-H atoms in the asymmetric unit) for different numbers of initially given phases. Three main questions have been addressed: (I) Does the iterative calculation of the wavefunction converge? (II) Do the calculated wavefunctions converge to a unique set of ,H values independent of the initial random set of ,H? (III) Is the calculated ,H set a good approximation of a wavefunction able to produce within certain errors the correct values of the phases of the structure factors? Concerning questions (I) and (II), our results give a strong hint about fast convergence to a unique wavefunction independent of the arbitrary starting wavefunction. This is an essential prerequisite for practical applications. For question (III) in the case closer to the ab initio situation, the final mean phase error, respectively, for the three structures is 3, 26 and 28°. The combination of (a) and (b) in the upgraded algorithm has been proved crucial especially for the results concerning the larger structures. [source]

Nitrogen balance and ,15N: why you're not what you eat during pregnancy

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2004
Benjamin T. Fuller
Carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios were longitudinally measured in human hair that reflected the period from pre-conception to delivery in 10 pregnant women. There was no significant change in the ,13C results, but all subjects showed a decrease in ,15N values (,0.3 to ,1.1,) during gestation. The mechanisms causing this decrease in hair ,15N have not been fully elucidated. However, since the ,15N values of dietary nitrogen and urea nitrogen are significantly lower compared to maternal tissues, it is hypothesized that the increased utilization of dietary and urea nitrogen for tissue synthesis during pregnancy resulted in a reduction of the steady state diet to a body trophic level effect by approximately 0.5,1,. An inverse correlation (R2,=,0.67) between hair ,15N and weight gain was also found, suggesting that positive nitrogen balance results in a reduction of ,15N values independent of diet. These results indicate that ,15N measurements have the ability to monitor not only dietary inputs, but also the nitrogen balance of an organism. A potential application of this technique is the detection of fertility patterns in modern and ancient species that have tissues that linearly record stable isotope ratios through time. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Magnitude of Error Introduced by Application of Heart Rate Correction Formulas to the Canine QT Interval

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 4 2006
Andrew King B.V.M.S.
Background: Accurate detection of drug-induced QT interval changes is often confounded by concurrent heart rate changes. Application of heart rate correction formulas has been the traditional approach to account for heart rate,induced QT interval changes, and thereby identify the direct effect of the test article on cardiac repolarization. Despite numerous recent studies identifying the imprecision of these formulas they continue to be applied. Methods: Using a chronic atrioventricular dissociated His-paced canine model, heart rate correction methods were evaluated for their ability to generate a corrected QT interval independent of original heart rate. Additionally, His bundle pacing at a heart rate of 60 beats/min allowed calculation of the magnitude of error introduced by application of heart rate correction formulas. Results: Of the fixed parameter heart rate correction formulas, only Van de Water was able to predict corrected QT values independent of the original heart rate. The magnitude of error discovered by application of heart rate correction formulas varied, but in many cases was very large. Bazett's formula was associated with a mean overcorrection of 67.9 ms; Fridericia's 28.7 ms. Van de Water was the best fixed parameter formula with a mean error of 10.8 ms. As expected, group and individual corrections derived from linear regression of the HR-QT data offered improvement over the traditional formulas. Both were able to predict QTc values independent of the heart rate. However, errors of the magnitude of 10 and 6 ms, respectively, were still introduced. Conclusion: Van de Water and linear regression correction methods were superior to others in this study, but all methods generated QTc errors equal to or much greater than the magnitude of interest for drug safety evaluation. [source]