Standard Measurement Procedures Research Articles

Residential exposure from extremely low frequency electromagnetic field (ELF EMF) radiation

ELF EMF radiation have received considerable attention as a potential threat to the safety and health of people living in the vicinity of high voltage transmission lines, electric distribution substations, power stations and even in close proximity to electronics and electrical household appliances. The paper highlights the study on the ELF EMF safety assessment performed at residences comprising of an owner-occupied house, a completed vacant house and an under construction condominium. The objectives of this study were to determine the ELF EMF radiation exposure level from the high voltage transmission line, electric distribution substation, power station and electrical household appliances in the residences, and to assess the potential exposure received by the occupants at the assessed locations. The results were logged in the electric and magnetic field strength with the units of volt per meter (V/m) and miliGauss (mG) respectively. The instrument setup and measurement protocols during the assessment were adopted from standard measurement method and procedures stipulated under the Institute of Electrical and Electronics Engineers (IEEE) Standard. The results were compared with the standards recommended in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines.

Reference range and variability of Laser-Doppler-Fluxmetry.

The Laser Doppler technique (Laser-Doppler-Fluxmetry, LDF), a noninvasive method to estimate skin blood flow (LDF), is frequently used in research and clinical routine [1]. Here, the measurements were carried out with a new Laser Doppler system, the DOP-system, which allows to measure frequency spectra in four different frequency windows according to the velocities in venules (low velocity), capillaries (low to medium velocities), and in arteries (with high and very high velocities). However, the diagnostic reliability or the effectiveness of the LDF has not yet been evaluated sufficiently, which is indispensable, where medical diagnostics and therapy controls are concerned. For a valid interpretation of LDF values of individual patients, the knowledge of the reference range and the variability of the measured parameters is required.In four successive studies the reference range (62 apparently healthy subjects), the circadian variability (8 subjects), the variability from day-to-day (6 subjects) and over one year with monthly measurements (6 subjects) were evaluated.With the knowledge of the reference range, microcirculatory disorders can now be diagnosed using the DOP method. Following a standard measurement procedure there was no dependence of the measured data on the day or season of measurement.

Validity and Intra-Rater Reliability of Laser Goniometer Versus Electro-Goniometer in Measuring Shoulder Range of Motion

Background: Providing new objective valid and reliable methods of assessment of a range of motion is always a persistent need for clinical practitioners and researchers in physical therapy for obtaining precised and realistic diagnostic and treatment decisions. So this study was carried out to test the validity and intra-rater reliability of the laser goniometer via comparing repeated measures of laser and electro-goniometers in measuring a range of motion of shoulder movements considering the electro-goniometer as the reference standard.Methods: one hundred healthy males with ages ranging between 20-30 years shared in this study. Three consecutive measures of bilateral shoulder flexion, abduction, internal and external rotation range of motion were performed by the same examiner on each subject by each of the laser and electro-goniometer, with standardized measurement procedures, subjects’ positions, and stabilizations.Results: Pearson (r), paired T-test, and intra-class (ICC) correlation coefficients were used to test the validity and intra-rater reliability of the laser goniometer in comparison to the electro-goniometer. And the results of the validity testing showed a very strong relationship between readings by both devices (r=0.84 to 0.93) and also no significant differences between means of readings of both devices with the p-value ranging between 0.13 and 0.97. Also, ICC revealed high intra-rater reliability of laser goniometer on repeated measures of shoulder range of motions (ICC=0.98-0.99).Conclusion: laser goniometer can be used as a new valid, reliable digital objective method of measurement of shoulder range of motion.

Fracture toughness of silicon nitride balls via thermal shock

A new method for fracture toughness determination of ceramic balls is presented. The starter crack is introduced into the surface of the ball by a Knoop indentation followed by grinding off the deformed zone. The loading through surface tensile stresses is realized by water quenching, i.e. dropping the heated ball into water. The temperature difference is stepwise increased to find the critical temperature difference for the initiation of crack growth. The geometric factor is calculated in a parametric finite element study, whereas the temperature distribution in the ball was previously determined by using the Biot concept. Combining experimentally measured critical temperature differences for different cracksizes and ball diameters with numerical results of the geometric factor, the fracture toughness of the silicon nitride balls is evaluated. For the evaluation, the knowledge of several material properties (e.g. the CTE) and other parameters is necessary, which have influence on the precision of the measurement. The overall measurement uncertainty is estimated to be about ±10 %, what roughly corresponds to the value determined with standard measurement procedures. There is an excellent agreement with published fracture toughness results of these balls determined by the modified Surface Crack in Flexure procedure.

Characterization of Phosphorus Fractions in the Soil of Water-Level-Fluctuation Zone and Unflooded Bankside in Pengxi River, Three Gorges Reservoir

The concentrations of phosphorus fractions in the soils of the water-level-fluctuating zone (WLFZ) of Pengxi River in the Three Gorges Reservoir were analyzed. The total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) were studied using the standard measurement and test (SMT) procedure. The average TP concentration was 575.29 mg·kg-1 and the average OP concentration was 91.23 mg·kg-1 in the soils of WLFZ. The fractions of phosphorus were analyzed by the Hedley method. In the soils of WLFZ, the relative abundance of WA-Pi (weakly adsorbed inorganic phosphorus), PA-Pi(potential active inorganic phosphorus), and Fe/Al-Pi(Fe/Al-bound inorganic phosphorus) accounted for 11.61% of the extractable Pi, lower than that in the unflooded bankside soils. The relative abundance of WA-Po (weakly adsorbed organic phosphorus) and PA-Po (potential active organic phosphorus) accounted for 22.28% of the extractable Po and the Fe/Al-Po (Fe/Al-bound organic phosphorus) accounted for 66.30%. In addition, the Po content of the soils of WLFZ was lower than that of the unflooded bankside soils and the difference in the Fe/Al-Po content in both soil types was the highest. WA-Pt and PA-Pt were significantly correlated with TP in the soils of WLFZ, which indicated that the active phosphorus content was mainly affected by TP. There was no statistical correlation between different fractions of phosphorus, suggesting different sources of phosphorus fractions. The Fe/Al-Pt content was significantly correlated with OM, implying that the OM content may affect the Fe/Al-Pt content. Therefore, under flood conditions, the potential impacts of phosphorus in the soils of WLFZ on overlying water should not be neglected.

PP.06.05] IS OFFICE BLOOD PRESSURE MEASUREMENT RELIABLE FOR INDIVIDUAL DECISION MAKING – RESULTS OF THE IPARR TRIAL

Objective: Standard operating procedures (SOP) for office blood pressure measurement (OBPM) vary highly between different guidelines. Similarly, outcome studies have used different methods to measure office blood pressure. Until today OBPM is used for clinical decision making. We aimed to compare an OBPM procedure based on the one used in the SPRINT study, but attended by an operator, to a single OBPM as used in early outcome studies and many clinical settings. Design and method: In this cross-sectional, single-center trial, 1000 adult subjects were recruited until February 2016. Seven sequential blood pressure measurements were performed after five minutes of rest in a quiet room and in sitting position in the presence of an operator. The initial measurement was taken using a standard device (Omron HBP-1300 professional blood pressure monitor, appropriate cuff size), alternating with a tested smartphone app. Over all, 4 standard and 3 smartphone measurements were taken, however, only the standard measurements were used for this study. The standard OBPM were spaced 2 min apart. Additional information about cardiovascular risk factors, concomitant disease, and medication were collected. We compared the first measurement out of 4 to the mean of last three measurements. Results: Complete measurements were available in 802 subjects. The first measurement had a median of 129 mmHg (IQR 116–140) in comparison to the mean of the last 3 measurements of 123 mmHg (IQR 113–134), which were significantly different (p-value < 0.0005). The Bland-Altman plot showed a high variability between the measurement methods (Figure 1). 662 subjects (82.5%) showed a difference of >2 mmHg, 441 (55.0%) a difference of >5 mmHg and 208 (25.9%) of >10 mmHg between the methods. Both a decrease and increase of the values were observed and could not be predicted clinically.Conclusions: There are significant differences in the results of two different SOP leading to a discrepancy of more than 5 mmHg in more than half of the patients in one measurement session. This difference could not be predicted by clinical parameters obtained in the trial. Therefore OBPM seems to be unreliable for individual clinical decision making until there are proper SOP.

Factors associated with underweight among lactating women in Womberma woreda, Northwest Ethiopia; a cross-sectional study

BackgroundEnsuring nutritional status of women is important because the malignant effects of malnutrition are procreated to the next generation through women and their off-springs. Malnutrition causes 3.5 million death of women and children each year and almost 11% of the disease burden in the world. Therefore, this study was conducted to assess nutritional status and factors associated with underweight among lactating women in Womberma woreda, Northwest Ethiopia, 2016.MethodsA Community-based cross-sectional study was carried out in Womberma woreda, Northwest Ethiopia. A total of 668 lactating women who have 6–24 months of child were included in the study. Study participants were selected using a multistage sampling technique. Data were collected using interview-administered questionnaire. Body mass index (BMI) was used to measure the nutritional status of lactating women. Women’s body weight and height were measured using the standard anthropometric measurement procedures. Data were entered using EpiData software and analysis was done using SPSS software. Descriptive, bivariate and multivariable logistics regression analysis were used to present the findings. Variables with a p-value less than 0.05 on multiple variable logistic regression were taken as significant variables.ResultsLactating women with normal nutritional status (BMI = 18.5–24.99 kg/m2) were 498 (74.5%), and underweight women (BMI < 88.5 kg/m2) were 170(25.4%). Respondents with less than five family size (AOR: 0.46, 95% CI: 0.26, 0.81, p-value = 0.007), women whose age of first pregnancy was less than 18 years old (AOR: 3.72, 95% CI: 2.33, 6.49 at p-value = 0.0001), home delivery for the recent child birth (AOR: 2.36, 95% CI: 1.50, 3.72 at p-value = 0.0001), and the absence of nutritional education programs in the community (AOR: 5.5, 95% CI: 1.8, 16.79 at p-value = 0.003) were the significant variables with underweight of lactating women.ConclusionsNutritional status of lactating women in the study area was poor. One fourth of lactating women was underweight. Factors associated with underweight of lactating women include; respondents with less than five family size, women whose age of first pregnancy was less than 18 years old, home delivery for the recent childbirth, and the absence of nutritional education programs in the community. Early childbearing and short birth intervals between births should be discouraged. Programs which encourage institutional delivery and community-based nutritional education are important to improve women nutritional status.

Building Tianjin driving cycle based on linear discriminant analysis

Driving cycles are standardized measurement procedure for the certification of vehicles’ economy and emission, and could help evaluate driving distance and new vehicular technologies. Thus driving cycle is always a hot research topic in vehicle industry. Linear discriminant analysis is a typical multivariate statistical method which has been used in many fields such as geology and economics in recent years, but its application to driving cycles is scarce. In this paper, Tianjin driving cycle is developed by using linear discriminant analysis. The effectiveness of the developed driving cycle is confirmed by comparing the parameter of the driving cycle and real-world driving data and evaluating the economy of electric vehicle. The uniqueness of this methodology is also discussed compared with traditional methodology in cycle development. This research could offer a new methodology for building driving cycles and has reference value to related researches.

An anthropometric study of the normal auricle of Cross River State indigenes of Nigeria

IntroductionTo analyse and document anthropometric parameters of the normal human auricle among Nigerians of Cross River State origin as well as to evaluate sexual dimorphism and auricular growth variation among the age groups of this population. MethodsThe present study was carried out on 217 adult volunteers made up of 117 females and 100 males, within the age range of 21–60 years; with no evidence of congenital ear anomalies or previous ear surgeries. All subjects were indigenes of Cross River State and were randomly selected across the three senatorial districts of the State. Standard measurement procedures were followed to obtain the following Auricular parameters: Auricular Length (AL), Auricular Width (AW), Lobular Length (LL), Lobular Width (LW), Protrusion at Supra-Aurale (PS) Protrusion at Tragus (PT), Auricular and Lobular Indices. ResultsThis study revealed that the mean Lobular length and Protrusion at Supra-aurale values are sexually dimorphic at age group of 21–30 while the Auricular length where sexually dimorphic at 21–30 and 31–40 years age groups with higher values noted in males than in females. Other parameters measured were not sexually dimorphic. DiscussionStandard anthropometric methods where employed in carrying out this study, hence this result is recommended to Plastic Surgeons who may need to rectify any auricular abnormalities involving patients from this ethnic group.

Assessment of Bifacial Photovoltaic Module Power Rating Methodologies—Inside and Out

One-sun power ratings for bifacial modules are currently undefined. This is partly because there is no standard definition of rear irradiance given 1000 Wcm−2 on the front. Using field measurements and simulations, we evaluate multiple deployment scenarios for bifacial modules and provide details on the amount of irradiance that could be expected. A simplified case that represents a single module deployed under conditions consistent with existing one-sun irradiance standards lead to a bifacial reference condition of 1000 Wcm −2 G front and 130–140 Wcm−2 G rear. For fielded systems of bifacial modules, G rear magnitude and spatial uniformity will be affected by self-shade from adjacent modules, varied ground cover, and ground-clearance height. A standard measurement procedure for bifacial modules is also currently undefined. A proposed international standard is under development, which provides the motivation for this paper. Here, we compare field measurements of bifacial modules under natural illumination with proposed indoor test methods, where irradiance is only applied to one side at a time. The indoor method has multiple advantages, including controlled and repeatable irradiance and thermal environment, along with allowing the use of conventional single-sided flash test equipment. The comparison results are promising, showing that indoor and outdoor methods agree within 1%–2% for multiple rear-irradiance conditions and bifacial module construction. A comparison with single-diode theory also shows good agreement to indoor measurements, within 1%–2% for power and other current–voltage curve parameters.

Optimized mixed-domain signal synthesis for broadband impedance spectroscopy measurements on lithium ion cells for automotive applications

Abstract. A new impedance spectroscopy measurement procedure for automotive battery cells is presented, which is based on waveform shaping. The method is optimized towards a short measurement duration, high excitation power and increased frequency resolution and overcomes limitations of established methods. For a given spectral magnitude profile, a corresponding time domain waveform is derived from the inverse discrete Fourier transform. Applying an identical initial phase angle for each frequency component, the resulting signal exhibits a high peak-to-peak amplitude at relatively low total excitation power. This limits the maximum allowed power for quasi-linear excitation. Altering the phase angles randomly spreads the excitation power across the complete measurement duration. Thereby, linearity is preserved at higher excitation power. A large set of phase patterns is evaluated statistically in order to obtain a phase pattern with a significant peak-to-peak amplitude decrease. By means of numerical optimization, even further peak-to-peak amplitude reduction is achieved. Including window functions in the synthesis concept minimizes spectral leakage without compromising the spectral signal magnitude in the frequency range of interest. A time domain waveform optimized for impedance spectroscopy on lithium ion cells is synthesized based on the proposed approach and evaluated on real automotive cells. The resulting impedance data show good concordance with established standard measurement procedures at significantly reduced measurement duration and charge throughput. Additionally, increased frequency resolution is achieved, enhancing the level of detail of the obtained impedance data. The method is used for improved localization of aging effects in the cells, without further stress of the cells by the measurement procedure.

Vitamin B1 in critically ill patients: needs and challenges.

Thiamine has a crucial role in energy production, and consequently thiamine deficiency (TD) has been associated with cardiac failure, neurological disorders, oxidative stress (lactic acidosis and sepsis) and refeeding syndrome (RFS). This review aims to explore analytical methodologies of thiamine compound quantification and highlight similarities, variances and limitations of current techniques and how they may be relevant to patients. An electronic search of Medline, PubMed and Embase databases for original articles published in peer-reviewed journals was conducted. MethodsNow was used to search for published analytical methods of thiamine compounds. Keywords for all databases included "thiamine and its phosphate esters", "thiamine methodology" and terms related to critical illness. Enquiries were also made to six external quality assurance (EQA) programme organisations for the inclusion of thiamine measurement. A total of 777 published articles were identified; 122 were included in this review. The most common published method is HPLC with florescence detection. Two of the six EQA organisations include a thiamine measurement programme, both measuring only whole-blood thiamine pyrophosphate (TPP). No standard measurement procedure for thiamine compound quantification was identified. Overall, there is an absence of standardisation in measurement methodologies for thiamine in clinical care. Consequently, multiple variations in method practises are prohibiting the comparison of study results as they are not traceable to any higher order reference. Traceability of certified reference materials and reference measurement procedures is needed to provide an anchor to create the link between studies and help bring consensus on the clinical importance of thiamine.

Consistency of the national realization of dew-point temperature using NIS standard humidity generators

A comparison of two standard humidity generators (two-temperature (2-T) and one-temperature (1-T) generators) that are developed by the National Institute for Standards (NIS) has been performed using a transfer standard chilled-mirror hygrometer and measurement procedures to realize dew-point temperature Td in the range from −50 °C to 0 °C. The main objective of this comparison was to compare the realizations of dew-point temperature and to establish the level of consistency between the two generators. For a level of consistency between two measurements, it is expressed by the difference between the measured values, m1 − m2, and the expanded pair uncertainty of this difference Up [1]. The comparison measurements revealed dew-point temperature differences of 0.02 °C and 0.07 °C with expanded pair uncertainties of ±0.09 °C and ±0.15 °C.

All Sky Camera for CTA Site characterization

The All Sky Camera (ASC) for CTA Site characterization is an automated optical instrument providing optical observation of the night sky conditions above the future Cherenkov Telescope Array observatory. It provides the basic sky condition analysis like cloud coverage, cloud position, nightsky background in visible light wave range and basic raw photometry. The result will serve for further Monte Carlo design studies and calculations. The ASC and additional auxiliary instruments (e.g. Ceilometer) will provide input data for smart scheduler during the standard measurement procedure of the CTA observatory.

Investigation of the thermal properties of spacer fabrics with bio-ceramic additives using the finite element model and experiment

The heat resistance of fabric enhanced by bio-ceramic additives (BCAs) is investigated theoretically and experimentally in order to determine the influence of modification of the infrared (IR) absorption property of the fabric. The enhanced IR sensitivity of textiles improves the thermoregulatory processes when worn in cold environments. The finite element model has been developed by taking into account the coupled phenomena of heat conduction, surface convection and the interaction of the fabric with IR power flux by employing heat transfer differential equations and the Stefan–Boltzmann law. Evaluations of IR absorptivity, reflectivity and transmissivity, the temperature transients during the hot plate chamber test and heat retaining properties of the fabric heated by an IR lamp have been obtained experimentally and simulated by means of the developed finite element model. The values of model parameters have been found, which provided a satisfactory match between the computation and the experiment in all considered cases. Simultaneously, the obtained values were reasonably close to rough theoretical estimations. Efforts have been made to distinguish from each other the influence of diffusive and radiative components of heat transfer, which affect the results of thermal resistance tests. The comparative analysis of contributions of different heat exchange mechanisms allows a better understanding of the peculiarities of standard heat resistance measurement procedures applied to BCA-enhanced fabrics and facilitates the validation of the computational models.

Assessment of additives avoiding the release of problematic species into the gas phase during biomass combustion—development of a fast screening method based on TGA

Particulate matter (PM) emissions formed during combustion of solid biofuels and released with the flue gas into the atmosphere are harmful to humans and the environment. A possibility to reduce such PM emissions is the addition of additives to the solid biofuels avoiding the formation of compounds released as particulate matter emissions. So far, different additives have been identified in the literature assessed by a broad variety of (expensive) chemical analysis techniques. Against this background, the overall objective of this paper is it to show that a thermal gravimetric analysis (TGA) is sufficient to estimate the influence of a specific additive on the particulate matter emissions formed during combustion in the lab scale. This can be realised by comparing mixtures between additives and biomass blends with a TGA standard measurement procedure with a reference sample prepared from the respective biomass blend mixed with SiO2 as an inert additive. To show the applicability of this approach, seven additives (kaolinite, Zn, CaHPO4, MgHPO4, CaO, MgCO3 and MnCO3) are tested with two different wood/straw blends. The results of the presented analytical method demonstrate that especially the additives kaolinite, Zn, CaHPO4 and MnCO3 have a low mass loss (< 10 wt.%) for wood/straw blends with an amount of straw of 10 and 20 wt.% and therefore reduced emission released into the gas phase compared to the reference sample with SiO2. Further analysis in the lab (IC, AAS and XRD) demonstrated that these additives lead to an enrichment of problematic species K, Na, PO43− and SO42−, typically found in PM emissions, in the coarse ashes and thus avoid the transfer of these substances into the gas phase.

Image Quality – Requirements For Clinical and Research Applications

Introduction/ Background The digitalization of slides and subsequent utilization of whole slide images has a highly visible penetration within digital pathology workflows. Not only research applications moving towards daily use, but also clinical pathology applies digital images increasingly. The use of virtual microscopy, with all of their advantages and benefits, requires additional efforts to assure sufficient image quality [1]. This consist of multiple aspects to be fulfilled, such as sharpness, tissue completeness, color fastness primary and additional secondary properties like existence of artifacts, compression, availability of digitalization metadata and others. Aims Scanning devices use multiple different technologies such as brightfield, laser or confocal. Moreover, they partly divide into patch and line scanning concepts. But not only hardware is constantly changing due to upgrades or further developments but also software algorithms, e.g. focus and stitching, are modified. This requires a standardized measurement algorithms and procedures to assure an appropriate quality for relevant aspects, depending on dedicated use cases. Methods Each dedicated requirement towards image quality has to be investigated separately, due to the fact that they differ in their origin. Distortions may be introduced through slide preparation, calibration of scanning device or even scanner software parameter. Therefore, we developed multiple algorithms and software tools to calculate a quality measure for each aspect automatically. Recently we are focusing on image sharpness [2], color fastness [3, 4] and completeness of tissue. Sharpness is measured by a no-reference focus algorithm per slide. Color fastness is calculated based on CIEDE2000 [5] for a reference IT8.7/1 color target mounted onto a glass slide per scanner. Completeness is automatically analyzed based on registration and comparison of whole slide overview image and preview camera data. Secondary quality parameters were not part of this investigation. Results We established a standard operation procedure to automatically apply slide based tests directly after digitalization. This enables scanning personal to execute quality inspection at a glance and schedule insufficient whole slide images for a rescan. Moreover, we made some of these tools available as a web-based service including a based web-frontend with user management. This enables everyone within the digital pathology community to validate their slides, scanning devices and scanning parameter.

Development of a driving cycle to evaluate the energy economy of electric vehicles in urban areas

Understanding real-world driving conditions in the form of driving cycles is instrumental in the design of efficient powertrains and energy storage systems for electric vehicles. In addition, driving cycles serve as a standardised measurement procedure for the certification of a vehicle’s fuel economy and driving range. They also facilitate the evaluation of the economic and lifecycle costs of emerging vehicular technologies. However, discrepancies between existing driving cycles and real-world driving conditions exist due to a number of factors such as insufficient data, inadequate driving cycle development methodologies and methods to assess the representativeness of developed driving cycles. The novel aspect of the work presented here is the use of real-world data from electric vehicles, over a six month period, to derive a driving cycle appropriate for their assessment. A stochastic and statistical methodology is used to develop and assess the representativeness of the driving cycle against a separate set of real world electric vehicle driving data and the developed cycle performs well in that comparison. Although direct comparisons with internal combustion engine driving cycles are not that informative or relevant due to the marked differences between how they and electric vehicles operate, some discussion around how the developed electric vehicle cycle relates to them is also included.

Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time

Abstract The increasing presence of low frequency sources and the lack of acoustic standard measurement procedures make the extension of reverberation time measurements to frequencies below 100 Hz necessary. In typical ordinary rooms with volumes between 30 m 3 and 200 m 3 the sound field is non-diffuse at such low frequencies, entailing inhomogeneities in space and frequency domains. Presence of standing waves is also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays caused by room modes, a new approach based on reverberation time measurements of single resonant frequencies (the modal reverberation time) has been introduced. From background theory, due to the intrinsic relation between modal decays and half bandwidth of resonant frequencies, two measurement methods have been proposed together with proper measurement procedures: a direct method based on interrupted source signal method, and an indirect method based on half bandwidth measurements. With microphones placed at corners of rectangular rooms in order to detect all modes and maximize SNRs, different source signals were tested. Anti-resonant sine waves and sweep signal turned out to be the most suitable for direct and indirect measurement methods respectively. From spatial measurements in an empty rectangular test room, comparison between direct and indirect methods showed good and significant agreements. This is the first experimental validation of the relation between resonant half bandwidth and modal reverberation time. Furthermore, comparisons between means and standard deviations of modal reverberation times and standard reverberation times in third octave bands confirm the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach. Modal reverberation time measurements applied to furnished ordinary rooms confirm previous results in the limit of modal sound field: for highly damped modes due to furniture or acoustic treatment, the indirect method is not applicable due to strong suppression of modes and the consequent deviation of the acoustic field from a non-diffuse condition to a damped modal condition, while standard reverberation times align with direct method values. In the future, further investigations will be necessary in different rooms to improve uncertainty evaluation.

New analytical formulas for prediction of gas–liquid relative permeabilities through fractures – Part I: Incompressible flow

Considering the fact that flow in fractured formations is fracture dominated, relative permeabilities through fractures must be well understood. Contrary to reservoir rocks, there is no standard experimental procedure for measurement of relative permeabilities through fractures. Furthermore, existing techniques are generally inconsistent, time consuming, expensive, complicated, and may fail due to technical difficulties encountered while performing the experiments. Thus, developing an analytical model for accurate prediction of relative permeabilities through fractures is of vital importance for treating one of significant uncertainties associated with characterization and simulation of fractured reservoirs.Historically, the straight-line relative permeability model (X-curve) has been widely used in numerical simulation of fractured reservoirs. However, experimental measurements of gas–liquid relative permeabilities through fractures have revealed high degrees of phase interference which cannot be well represented by the X-model. In this work, idealized flow configurations of stratified and segregated flow are assumed in order to make the analytical derivation tractable without the need of using numerical techniques. Then, basic fluid flow equations are combined to develop simple analytical models for gas–liquid flow in each of the patterns. Combining the models with Darcy's law leads to closed-form analytical expressions for explicit calculation of gas and liquid relative permeabilities through fractures. The relationships simply state that the relative permeabilities depend on several parameters one of which being the saturation, whereas they were considered to be only functions of the saturation in the classic X-model. Afterwards, the formulas are further simplified by adopting a realistic assumption. Eventually, the validity of the derived relative permeability expressions is checked by comparing their predictions with available experimental data. The results show that the ability of the segregated model to accurately predict experimental data is considerably poorer than that of the stratified model. Therefore, the generalized relative permeability expressions proposed for the stratified pattern must be used to describe the dynamics of gas–liquid flow in fractures. It addition to robustness, other advantages of the newly presented formulas such as simplicity, cost effectiveness, and being explicit and analytic make their implementation in numerical simulators straightforward.