Correction Factors In Order Research Articles

Calculation of the transport properties of a dilute gas consisting of Lennard-Jones chains

The transport properties in the dilute gas limit have been calculated by the classical-trajectory method for a gas consisting of chain-like molecules. The molecules were modelled as rigid chains consisting of spherical segments that interact through a combination of site-site Lennard-Jones 12-6 potentials. Results are reported for shear viscosity, self-diffusion, and thermal conductivity for chains consisting of 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, and 16 segments in the reduced temperature range of 0.3-50. The results indicate that the transport properties increase with temperature and decrease with chain length. At high temperatures the dependence of the transport properties is governed effectively by the repulsive part of the potential. No simple scaling with chain length has been observed. The higher order correction factors are larger than observed for real molecules so far, reaching asymptotic values of 1.019-1.033 and 1.060-1.072 for viscosity and thermal conductivity, respectively. The dominant contribution comes from the angular momentum coupling. The agreement with molecular dynamics calculations for viscosity is within the estimated accuracy of the two methods for shorter chains. However, for longer chains differences of up to 7% are observed.

Fold-change correction values for testicular somatic transcripts in gene expression studies of human spermatogenesis

What are the reference values for delineating altered somatic cell gene expression from transcript enrichment/dilution in gene expression studies of human spermatogenesis? We have designed a crosstable and rule-of-thumb values for different stages of spermatogenic impairment that define the reference cut-off values for altered gene expression in Sertoli and Leydig cells in the context of impaired spermatogenesis. Morphometrical studies have shown that on the cellular level, impaired spermatogenesis results in a relative enrichment of somatic cell types. However, until now it is not known how this affects transcript levels in gene expression studies. In this study, 31 testis biopsies from men with different stages of spermatogenic impairment (full spermatogenesis, hypospermatogenesis, meiotic arrest, spermatogonial presence, Sertoli cell-only syndrome, complete tubular atrophy) were used to define reference ratios of somatic transcript enrichment/dilution. The reference ratios were validated on an independent test set of 28 samples and on gene expression data from men with Y-chromosomal microdeletions. High-quality microarray data were filtered with respect to Sertoli- and Leydig-cell-specific genes. General reference enrichment/dilution factors for these two cell types for all combinations of spermatogenic impairment were calculated using robust permutation statistics. To validate the specificity of the filtered transcripts, we calculated ratios for an independent test set of spermatogenic impairment and for transcriptional data from men with Y-chromosomal microdeletions, and checked the functional enrichment (gene ontology) and cellular localization of the corresponding proteins in a histological database and assessed their correlation with testicular size. Filtering of Sertoli- and Leydig-cell-specific genes resulted in a set of 54 and 332 transcripts, respectively. These were used in defining robust reference dilution/enrichment factors of somatic transcripts for all spermatogenic levels and were compiled in a reference crosstable. Validation on an independent test set showed ratios within 0.5 units of our reference crosstable. Analysis of the resulting transcripts with respect to functional enrichment for Sertoli- and Leydig-cell-specific functions and protein expression, as obtained from an immunohistochemical database, indicated filtering of data sets highly enriched for Sertoli and Leydig cell function. The dilution/enrichment ratios differed significantly when transcripts were interrogated in samples with Y-chromosomal microdeletions, pointing to an overall decreased expression of somatic markers in a genetically altered background. The defined reference ratios might apply with some restrictions in samples that display very heterogeneous histology (e.g. Sertoli cell only with a significant proportion of spermatogenic foci) or when spermatogenic impairment is a consequence of an altered genetic background. The reference dilution/enrichment values for somatic testicular transcripts as defined in this study are to be seen as cut-off values for discriminating between simple transcript dilution/enrichment as a consequence of an altered germ cell composition and actual transcriptional regulation. Future studies dealing with transcriptional changes in testicular somatic cells in a background of altered germ cell quantities should consider these correction factors in order to avoid the description of transcriptional changes that are based simply on shifts in somatic cellular quantities. Financial support was from grant Sp721/1-3 of the German Research Foundation. There are no competing interests to be declared.

Regional variation of seasonal correction factors for indoor radon levels

Abstract Radon levels measured for any duration less than one year are subject to seasonal variation. Such radon measurements must therefore be adjusted using an appropriate seasonal correction factor in order to estimate an annual average radon level. Radon mapping has shown that radon concentrations vary between regions within a country but there has been little work examining regional variation in the seasonality of radon levels. This paper investigates this regional variation in indoor radon seasonality in Ireland. Mean regional seasonal correction factors are estimated through Fourier decomposition and we find that there is significant regional variation in the computed seasonal correction factors. We conclude that the use of one national set of mean seasonal correction factors may not be appropriate in all countries.

Semi-theoretical prediction of volumetric mass transfer coefficients in bubble columns with organic liquids at ambient and elevated temperatures

A semi-theoretical approach for predicting k L a values (referred to liquid volume) in 18 organic liquids [acetone, aniline, 1-butanol, benzene, cyclohexane, decalin, 1,2-dichloroethane, 1,4-dioxane, ethanol (96%), ethylacetate, ethylbenzene, ligroin, methanol, nitrobenzene, 2-propanol, tetralin, toluene, and xylene] at various operating conditions (including elevated temperatures and pressures) was developed. It was found that the approach is applicable regardless of the hydrodynamic regime (at u G ≤ 0.1 m/s). Temperatures up to 353 K and pressures up to 0.5 MPa were tested. Two different distributors (multiple-hole and single-hole type) were employed. The liquid-phase mass transfer coefficient k L was calculated theoretically from the penetration theory on the basis of original definition of gas-liquid contact time. The interfacial area a was defined with respect to the liquid volume. It was found that their product k L a must be multiplied by some correction factor in order to take account of the non-spherical (ellipsoidal) shape of the bubbles. When the correction term is correlated to both the Eotvos number (Eo) and the dimensionless temperature ratio, 198 experimental k L a values can be fitted reasonably well (average relative error 9.3%).

Morphologic Evaluation of Spermatozoa in Different Laboratories

The principles of morphologic evaluation of human spermatozoa may vary from time to time and between different laboratories. These principles are reflected in the mean and standard deviation of the results obtained from analysis of samples delivered by all new patients. These figures and distribution diagrams based on the same data were collected from eight different scandinavian fertility laboratories. It is suggested that such data should be used to define the investigational profile of the laboratory in question and to check that inadvertent changes in the principles of evaluation do not develop. The data may also be used to calculate correction factors in order to facilitate the comparison of results when the patient has delivered samples to more than one laboratory.

SU-GG-T-233: Development of Glass Dosimeter Postal Dose Intercomparison for High-Energy Photon Beam

Purpose: The purpose of this study is to evaluate whether the glass dosimeter would be suitable for external dosimetric audit in the radiotherapy. We investigate the methodology of the absorbed dose determination with the glass dosimeter, which requires various correction factors in order to achieve the dosimetric accuracy. Method and Materials: The model GD-301 glass dosimeter and FGD-1000 automatic readout system were used. In order to assure dose measurement accuracy, the calibration coefficient and correction factors (non-linearity dose response, fading, energy dependence and angular dependence) of the glass dosimeter should be determined. We also performed the feasibility test of the glass dosimeter postal dose intercomparison for 8 beams output checks of high photon energy involving 4 centers in Korea. The glass dosimeter results were compared to the measurement obtained with a LiFTLD. Results: The feasibility results can be observed that, the relative deviations of the glass dosimeter were 3.5% smaller than the corresponding TLD values for all photon beams. It is possible that the agreement between the doses obtained with the glass dosimeter and stated doses by participants for following two main reasons: (1) the same dosimetry protocol is used at all participating centers to determine the dose given to the glass dosimeter: (2) the participating centers where the physicists have already experienced from a previous TLD audit program and have sufficient knowledge of the glass dosimeter system. Conclusion: This feasibility study has shown that the new glass dosimeter system has considerable potential to be used for a postal dose audit program. The next step in the glass dosimeter postal program will be the expansion of participating centers. We will investigate the other factors, such as the glass dosimeter holder correction used in this study which might influence the accuracy of determination of absorbed dose from glass dosimeter response.

Computation of Octanol−Water Partition Coefficients by Guiding an Additive Model with Knowledge

We have developed a new method, i.e., XLOGP3, for logP computation. XLOGP3 predicts the logP value of a query compound by using the known logP value of a reference compound as a starting point. The difference in the logP values of the query compound and the reference compound is then estimated by an additive model. The additive model implemented in XLOGP3 uses a total of 87 atom/group types and two correction factors as descriptors. It is calibrated on a training set of 8199 organic compounds with reliable logP data through a multivariate linear regression analysis. For a given query compound, the compound showing the highest structural similarity in the training set will be selected as the reference compound. Structural similarity is quantified based on topological torsion descriptors. XLOGP3 has been tested along with its predecessor, i.e., XLOGP2, as well as several popular logP methods on two independent test sets: one contains 406 small-molecule drugs approved by the FDA and the other contains 219 oligopeptides. On both test sets, XLOGP3 produces more accurate predictions than most of the other methods with average unsigned errors of 0.24-0.51 units. Compared to conventional additive methods, XLOGP3 does not rely on an extensive classification of fragments and correction factors in order to improve accuracy. It is also able to utilize the ever-increasing experimentally measured logP data more effectively.

Feedforward correction of nonlinearities in piezoelectric scanner constructions and its experimental verification

Piezoelectrical actuators widely used in scanning devices for highly resolved displacement generation exhibit a number of known nonlinear effects as hysteresis and creep. This article describes an attempt to minimize those nonlinearities by recognizing the relation between scan range and voltage magnitude in a scanner specific function. In addition, by utilizing a strain gauge sensor system, a forward displacement correction is realized. The mathematical procedure behind the hysteresis correction is described in detail. The dependence of the higher order correction factors on parameters such as scan speed, scan range, or center position is studied carefully to extract their influence on the result. Finally, integral nonlinearities of about 1% are proven in experiments with an atomic force microscope.

Health Impact Assessment of Long-Term Exposure to Particulate Air Pollution: Sensitivity of Results to the Correction of PM10 Levels Measured with Teom

P-034 Introduction: Health Impact Assessments (HIA) of long-term exposure to PM10 conducted in 9 French cities as part of the APHEIS European project (APHEIS, Air pollution and health, a European information system, June 2005 www.apheis.net) were based on exposure-response functions obtained using gravimetric measurements of PM10 levels (Pope CA 3rdet al. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. JAMA. 2002 6;287(9):1132–41). In France, PM10 levels are routinely monitored using Tapered Element Oscillating Microbalances (TEOM) and APHEIS recommended the use of correction factors in order to compensate for losses of volatile compounds. Nevertheless, there is no consensus regarding the method that should eventually be used for correction. The objective of this study was therefore to assess the sensitivity of HIA results to the use of various correction methods. Methods: Data on mortality and annual mean concentrations of PM10 for year 2001 were collected in 9 French cities. Long-term HIAs for a reduction of PM10 annual mean level to 20μg/m3 were conducted using both non-corrected and corrected PM10 levels. Three correction methods were used: the default European correction factor (http://europa.eu.int/comm/environment/air/pdf/finalwgreporten.pdf) (1.3); local seasonal conversion factors; and local polynomial regressions derived from parallel gravimetric and TEOM measurements (Jean-Luc Houdret, François Mathe. Programme pilote national de surveillance des particules PM10 et PM2,5). Results: Among the nine cities, local correction factors ranged from 1 to 1.18 during winter, and from 1.13 to 1.37 during summer. Annual mean levels of PM10 measured with TEOM ranged from 21 to 29 μg/m3. Corrected annual mean levels ranged respectively from 27 to 38 μg/m3, 23 to 31 μg/m3 and 22 to 33 μg/m3 when European, local seasonal and local polynomial corrections were used. When compared to the HIA results obtained using PM10 levels corrected with local seasonal correction factors, the direct use of levels measured with TEOM induced an underestimation varying from 17 to 82%, depending on the city. The total number of attributable cases over the nine cities was estimated to 1034 (95%CI [628; 1460]) when TEOM measures were used directly, whereas it was estimated to 3286 [1986; 4665], 2268 [1374; 3211] and 2501 [1514; 3543] when European, local seasonal or local polynomial corrections were used, respectively. Discussion and conclusion: The use of a correction has a non-negligible impact on HIA results. Non-specific correction factors do not seem appropriate, as the proportion of volatile matter varies according to localization-dependent factors. Local correction methods derived from parallel measurements seem more appropriate, but are not systematically available. For the future, the improvement of automatic methods of measurement minimizing losses of volatile compounds seems promising.

The Effect of Internal Temperature Gradients on Regenerator Matrix Performance

Background. One-dimensional regenerator models treat the solid material as a lumped capacitance with negligible temperature gradients. Advanced regenerator geometries operating at low temperatures or active magnetic regenerators which use a liquid heat transfer fluid may have temperature gradients in the solid regenerator that significantly affect performance. It is advantageous to utilize a one-dimensional, or lumped, model of the regenerator that is coupled with a correction factor in order to account for the impact of the internal temperature gradients. Previous work relative to developing such a correction factor is shown here to be inadequate or only valid over a limited range of dimensionless conditions. Method of Approach. This paper describes a numerical model of a sphere subjected to a time varying fluid temperature (representing a passive process) or time varying internal heat generation induced by a magnetic field (representing an active magnetic process). The governing equations are nondimensionalized and the efficiency of the sphere is presented as a function of the Fourier number and Biot number. Results. An approximate correction (or degradation) factor is obtained based on these results that is valid over a wide range of dimensionless conditions and therefore useful to regenerator designers. The degradation factor correlation was developed for a sinusoidal variation in the fluid temperature, however, the same results can be applied to different functional forms of the time variation using the concept of an effective cycle time that is weighted by the magnitude of the driving temperature difference. Conclusions. The heat transfer degradation factor presented here can be applied to one-dimensional regenerator models in order to accurately account for the transient performance of a matrix with finite thermal conductivity. This degradation factor allows regenerator models to approximately account for internal temperature gradients without explicitly modeling them and therefore remain computationally efficient while improving the range of applicability and accuracy.

Fatigue behaviour analysis of mechanical components subject to random bimodal stress process: frequency domain approach

A frequency domain approach to fatigue life evaluation is an important task in the design of mechanical components subject to random loads. The greatest advantages of this method are the computational efficiency and the capability to give a synthetic representation of a random process. The importance of this method is clear, especially when it is used in the postprocessing phase of a numerical analysis, for example Finite Element (FEA) or Multibody (MBS) simulation. The weak step in this procedure is the direct evaluation of the probability density function (pdf) of the cycles amplitude from stress power spectral density (PSD). In fact, the translation to frequency domain of the Rainflow cycle counting is a serious problem but there is a body of important literature concerning this. After reviewing the most important literature from this research field, a new original index to compare the reliability of the frequency domain methods is proposed. This index efficiently achieves this purpose, and a future objective could be to use such index to define a correction factor in order to exactly evaluate the fatigue damage. A very important class of random processes was considered: the bimodal power spectral density (PSD) random processes. The aim of this paper is to identify independent parameters in these processes and through them evaluate the cycles probability density function (pdf) amplitude.

Precision Lamb-shift polarimeter for polarized atomic and ion beams

The Lamb-shift polarimeter described here enables the polarization of a beam of hydrogen (deuterium) atoms, or of a slow proton (deuteron) beam, to be measured with an absolute precision better than 1% within a few seconds. The polarimeter measures the intensity ratios of Lyman-α transitions after Stark quenching of metastable hyperfine substates that were selected in a spin filter. For that purpose the hydrogen (deuterium) atoms are ionized in a Glavish-type ionizer. By charge exchange of the protons (deuterons) in cesium vapor, atoms in the metastable 2S state are produced. For a hydrogen beam of 3×1016 atoms/s, ∼3×106 photons/s are registered in a photomultiplier, i.e., the polarimeter efficiency is about 10−10. The signal-to-background ratio in the Lyman-α spectrum is excellent, thus beam intensities of one to two orders of magnitude less would still be sufficient to carry out a precise measurement. The different components of the polarimeter affect the measured polarization in several ways. It was, therefore, crucial to determine precisely the associated correction factors in order to derive the nuclear polarization from the measured Lyman-α spectra.

ADME evaluation in drug discovery. 2. Prediction of partition coefficient by atom-additive approach based on atom-weighted solvent accessible surface areas.

A novel method for the calculations of 1-octanol/water partition coefficient (log P) of organic molecules has been presented here. The method, SLOGP v1.0, estimates the log P values by summing the contribution of atom-weighted solvent accessible surface areas (SASA) and correction factors. Altogether 100 atom/group types were used to classify atoms with different chemical environments, and two correlation factors were used to consider the intermolecular hydrophobic interactions and intramolecular hydrogen bonds. Coefficient values for 100 atom/group and two correction factors have been derived from a training set of 1850 compounds. The parametrization procedure for different kinds of atoms was performed as follows: first, the atoms in a molecule were defined to different atom/group types based on SMARTS language, and the correction factors were determined by substructure searching; then, SASA for each atom/group type was calculated and added; finally, multivariate linear regression analysis was applied to optimize the hydrophobic parameters for different atom/group types and correction factors in order to reproduce the experimental log P. The correlation based on the training set gives a model with the correlation coefficient (r) of 0.988, the standard deviation (SD) of 0.368 log units, and the absolute unsigned mean error of 0.261. Comparison of various procedures of log P calculations for the external test set of 138 organic compounds demonstrates that our method bears very good accuracy and is comparable or even better than the fragment-based approaches. Moreover, the atom-additive approach based on SASA was compared with the simple atom-additive approach based on the number of atoms. The calculated results show that the atom-additive approach based on SASA gives better predictions than the simple atom-additive one. Due to the connection between the molecular conformation and the molecular surface areas, the atom-additive model based on SASA may be a more universal model for log P estimation especially for large molecules.

Fluence correction factors in plastic phantoms for clinical proton beams

In recent codes of practice for reference dosimetry in clinical proton beams using ionization chambers, it is recommended to perform the measurement in a water phantom. However, in situations where the positioning accuracy is very critical, it could be more convenient to perform the measurement in a plastic phantom. In proton beams, a similar approach as in electron beams could be applied by introducing fluence correction factors in order to account for the differences in particle fluence distributions at equivalent depths in plastic and water.In this work, fluence correction factors as a function of depth were determined for proton beams with different energies using the Monte Carlo code PTRAN for PMMA and polystyrene with reference to water. The influence of non-elastic nuclear interaction cross sections was investigated. It was found that differences in proton fluence distributions are almost entirely due to differences in non-elastic nuclear interaction cross sections between the plastic materials and water. For proton beams with energies lower than 100 MeV, for which the contributions from non-elastic interactions become small compared to the total dose, the fluence corrections are smaller than 1%. For beams with energies above 200 MeV, depending on the cross sections dataset for non-elastic nuclear interactions, fluence corrections of 2–5% were found at the largest depths. The results could, with an acceptable accuracy, be represented as a correction per cm penetration of the beam, yielding values between 0.06% and 0.15% per cm for PMMA and 0.06% to 0.20% per cm for polystyrene.Experimental information on these correction factors was obtained from depth dose measurements in PMMA and water. The experiments were performed in 75 MeV and 191 MeV non-modulated and range-modulated proton beams. From the experiments, values ranging from 0.03% to 0.15% per cm were obtained. A decisive answer about which dataset for non-elastic nuclear interactions would result in a better representation of the measurements could not be given.We conclude that below 100 MeV, dosimetry could be performed in plastic phantoms without a dramatic loss of accuracy. On the other hand, in clinical high-energy proton beams, where accurate positioning in water is in general not an issue, substantial correction factors would be required for converting dose measurements in a plastic phantom to absorbed dose to water. It is therefore not advisable to perform absorbed dose measurements nor to measure depth dose distributions in a plastic phantom in high-energy proton beams.

Who is at risk of what?

If you have calculated the sample size required for an employee survey or an observational study of departmental practices but found that the number of observations required is larger than the number of employees, chances are the error is due to use of approximation formulae. Many of us unknowingly were taught to use approximations that fail to include the finite population correction factor. Depending on the objective of a study and the proportion of a population sampled, it may be necessary to consider this correction factor in order to estimate standard error and sample size accurately.

Factors affecting milk production and prolificacy of Alpine goats in Lombardy (Italy)

In order to evaluate the adaptation of a newly introduced breed and of a production system, the effects of herd-year, season of kidding, parity, and, where appropriate, prolificacy on milk yield, lactation length and prolificacy of Alpine goats in the Italian region of Lombardy were investigated. Analysis of two consecutive years, 1298 lactation records, from 34 herds, gave mean values (±SE) of 567±6 kg for milk yield, 231±1 days for lactation length and 1.6±0.01 kids per kidding. Milk yield and lactation length were primarily influenced by the herd-year factor ( p<0.001, partial R 2 0.68 and 0.55, respectively) which mainly reflects differences in herd management. Milk yield was also affected by season of kidding ( p<0.001, partial R 2 0.4), parity ( p<0.001, partial R 2 0.03) and litter size ( p<0.001, partial R 2 0.01). Lactation length was also affected by parity ( p<0.001 R 2 0.16) and season of kidding ( p<0.001 R 2 0.06). Prolificacy was affected by parity and by herd-year factor ( p<0.001, partial R 2 0.09). Kidding early in the year gave higher milk yields, longer lactations and higher prolificacy, but in the choice of the kidding season also the higher prices of kid meat just before Easter have to be considered. Maximum milk yield and prolificacy were attained late (in 4th and 5th lactation), probably due to early age at first kidding. The relevant effect of the herd-year factor indicates that performances of Alpine goats in Lombardy can be successfully improved with an adequate management. Our findings confirm that litter size should not be ignored when establishing correction factors in order to compare milk yields.

A note on certain generalizations of the midpoint rule

In this paper we shall be concerned with some interesting generalizations of the so-called midpoint rule to weighted integrals introduced by Jagerman (1966) and Stetter (1968). First, the convergence of the Stetter rule on the class of the Riemann-integrable functions is proved, and numerical experiments are also carried out. Secondly, the introduction of a correction factor in order to accelerate the asymptotic rate of convergence is discussed.

Body composition and body hydration in old age estimated by means of skinfold thickness and deuterium dilution

In this study a group of 30 women and 30 men aged 60-90 years was examined. Body density was predicted from the sum of four skinfold thickness (SFT) as described by Durnin and Womersley (1974). Body composition, expressed as a percentage of total body weight as fat mass (FM) and fat free mass (FFM) was calculated by means of Siri's formula (Siri 1961). Total body water (TBW) was measured from the dilution of an oral deuterium dose and FFM calculated assuming a hydration of 73.2%. The FM% predicted from SFT showed a slight but not significant decreasing age trend from 28.3% to 25.4% in men, and from 40.3% to 37.8% in women. Body hydration (about 50% of body weight in men and 44% in women) remained constant throughout the age range. FFM obtained from TBW assuming a constant hydration of FFM, was found to be unchanged with age. FM% predicted from SFT was correlated with values obtained from TBW on an individual basis (R2 = 0.38; p less than 0.0001 in men and R2 = 0.31; p less than 0.002 in women), but the scatter was large. The Bland and Altman statistical analysis (Bland and Altman 1986) suggests that the discrepancy between the two estimates tends to be significantly more positive with increasing fatness of the subject. The assumption of a constant hydration of FFM between individuals and with advancing age was tested. The hydration of FFM was calculated as the ratio between TBW (from deuterium dilution) and FFM (estimated from SFT). The wide range of values (50% to 90%) suggests large inter-individual differences. The mean values were lower than commonly reported, and differed with age and sex. In men, FFM hydration steadily decreases with age from the 7th decade (70.2 +/- 7.7%) to the 10th decade (65.9 +/- 8.2%). Women showed higher average figures than those of men and a lower age-associated decline (72.5% and 68.5% respectively). Our results suggest that FFM hydration decreases with age, and this indicates the need to develop age-related correction factors in order to derive FFM from TBW in an elderly population.

A new method for the pH calculation of solutions and mixtures of acids, bases and salts

The improved successive approximation method calculates the exact [H +] and pH value of solutions and mixtures of acids, bases and salts, and can be applied to titration data. The procedure consists in the calculation of the concentration of all species present in solution, selection of the appropriate rule of electroneutrality and introduction of suitable correction factors in order to obtain a final quadratic equation which is easily solved. Compared with existing methods of pH calculation, which are based on the Newton-Raphson iteration procedure, the proposed method requires a smaller number of iterations and a shorter calculation time. As there are no limitations on the number of compounds, nor on the number or values of acidity and basicity constants, nor on the concentration range, complex problems can be solved and titration curves plotted in a short time.

Longitudinal mixing in pulmonary airways. analysis of inert gas dispersion in symmetric tube network models

Impulse response data were obtained tor the injection of helium and sulfur hexafluoride into air flowing through symmetric tube networks of uniform branch radii, having branch angles varying from 35 to 70 and branch aspect (length-to-radius) ratios varying from 3.6 to 7.0. These data were reduced in terms of the time variance in order to quantify the extent of longitudinal mixing. Over an inspiratory-like flowrate range of 1 to 400 ml/sec, a change in the branch angle alone did not affect axial mixing, while halving the aspect ratio caused a small increase of the time variance. Moreover, the variances obtained during inspiratory-like flow were found to be quite similar to the corresponding values determined during expiratory-like flow. The results of' these experiments as well as those previously reported by Scherer et al. (1975) were compared to the predictions of a compartmental dispersion analysis. The current data were bounded by two theories which hypothesized that the tracer concentration profile either develops continuously as gas flows along a particular transport path or, alternatively, must redevelop beginning at each branch point that is encountered. In both cases, it was essential to include an ‘unfulfilled dispersion’ correction factor in order to account for the incompletely developed concentration profile. The data of Scherer et al. obtained in a 5-generation network analog of the pulmonary airways, was well fit by assuming a continuously developing concentration profile during inspiratory-like flow and a redeveloping profile during expiratory-like flow. In fact. the linear correlation between the average mixing coefficient and tracheal velocity that was observed by Scherer could be predicted by the theory to an unexpectedly high degree of accuracy.