Empirical Modification Research Articles

Stress analysis in a screw conveyor axis under a specific fault condition

This work presents an analytical and numerical methodology that allows determining stress distribution during the functioning of a screw conveyor utilized for conveying granular material. Different operating conditions were studied analytically and numerically. Initially, the reactions generated when the mechanism was fully braced with four supports along the longitudinal axis of the shaft were estimated. In addition, the system was analyzed with a typical fault in one of the central supports. The faults studied occur primarily due to the empirical modifications that companies make to these kinds of mechanisms and to the continuous operation of the conveyor system. Finally, a comparative analysis is presented between the analytical and the numerical results in order to validate the proposed methodology.

Spatial and temporal variation in chlorophyll a concentration in the Eastern China Seas based on a locally modified satellite dataset

Satellite chlorophyll a (Chl) is an essential parameter for large-scale studies on changes in the marine ecosystem and biogeochemistry. However, in the eastern China seas (ECSs), the coexistence and interaction of turbid and clear water pose challenges to the application of standard satellite Chl products to studies on phytoplankton dynamics. Based on the empirical modification of the OC-CCI (Ocean Colour Climate Change Initiative) standard products, we herein provide a locally modified chlorophyll a (LMC) dataset and compare the large-scale Chl distributions with satellite and in-situ Chl datasets. Compared with standard Chl, LMC has a higher correlation with in-situ data (R2 = 0.58) and lower Bias (0.08) and is more consistent with the ship-measured Chl distributions. Using the LMC dataset, we analyzed the climatological Chl distributions in the ECSs and classified the Chl annual cycles into four types. Our results suggest that high Chl patterns not only rely on nutrient supply, but also relate to light conditions controlled by vertical mixing and suspended matter. The different Chl annual cycles are mainly caused by differences in the duration and range of nutrients and light limitation, and thus their distributions tend to vary with water depth. We believe that this work presents a more accurate dataset in the ECSs and can improve the understanding of local biogeochemical cycles.

Calculation of plastic viscosity of concrete mixture using the modified empirical formula

Nowadays various types of viscometers are being designed to measure the rheological properties of cement paste and fresh concrete. Most of them are very expensive and require specific knowledge about their usage. Then in practice usually the empirical formulas are used to calculate the main rheological properties – yield stress (Pa) and plastic viscosity (Pa·s). Therefore, in the literature, there are some formulas which can’t be used to calculate analytically plastic viscosity of concrete mixture, e.g. it cannot estimate the influence of different chemical admixture on plastic viscosity of concrete. The paper focuses on the modification of the empirical formula to calculate the plastic viscosity of fresh concrete mixture. In this paper the way of viscosity formula modification was described. For an empirical formula modification, the coefficients which describe the influence of different chemical admixture on plastic viscosity of concrete mixture were used. Coefficients Kcalc. were calculated as a ratio between different viscosity values of cement pastes obtained without and with certain chemical admixtures. Viscosity of cement paste was obtained by using rotational viscometer Rheotest RN4. Coefficients describe the change in cement pastes viscosity when adding different type (superplasticizer, viscosity modifying agent, air-entraining agent and air voids removing agent) and amount of chemical admixture.

ВЛАГОСОДЕРЖАНИЕ ПРИРОДНОГО ГАЗА В ПРИЗАБОЙНОЙ ЗОНЕ ПЛАСТА

Для модельной задачи отбора реального газа из скважины в центре кругового пласта с непроницаемыми кровлей и подошвой выполнен анализ влияния начальных пластовых условий на динамику распределения его влагосодержания. Использовалась математическая модель неизотермической фильтрации, в которой теплопроводность считалась пренебрежимо малой по сравнению с конвективным переносом. Для ее замыкания использовалась эмпирическая зависимость коэффициента несовершенства газа от давления и температуры, апробированная в предыдущих публикациях авторов. Связь между влагосодержанием, давлением и температурой газа описывалась эмпирическими зависимостями, основанными на формуле Бюкачека. Вычислительный эксперимент выполнялся следующим образом. Вначале из численного решения осесимметричной задачи неизотермической фильтрации реального газа определись давление и температура газа при заданном давлении на забое скважины. При этом условия на внешней границе пласта имитировали водонапорный режим отбора газа. Затем эти найденные функции времени и координат использовались для вычисления аналогичной зависимости для влагосодержания. Результаты эксперимента показали, что если пластовая температура существенно превышает равновесную температуру гидратообразования, то распределение влагосодержания в призабойной зоне будет практически идентично распределению температуры. В противном случае газ будет содержать пары воды только вблизи забоя скважины, а далее его влагосодержание будет практически равно нулю. Роль давления и в том и в другом случаях проявляется через интенсивность отбора газа, от которого, в свою очередь, зависят и интенсивность конвективного переноса тепла, и степень охлаждения газа за счет дросселирования.

Shear strength criteria for design of RC beam–column joints in building codes

The paper presents a comprehensive review on shear strength provisions of RC beam–column joint in various national codes viz. ACI 318-2014, NZS 3101-1:2006, EN 1998-1:2004, CSA A23.3:2004, AIJ:2010, and IS 13920:2016. The shear strength equation given in these codes are generic and simple in application, which is based on the contribution of only a few governing parameters. However, the effects of governing parameters in different codes are considered in different ways. As a result, the code prediction varies significantly among themselves as well as with experimental studies. Considering these differences, the influence of various governing parameters on the joint shear strength are evaluated. A database is compiled from 492 experimental results of beam–column joints from literature. To find the cause of variation between code prediction and experimental observations, different type of failure modes of beam–column joints is studied. Consequently, two parameters namely, aspect ratio of joint and area ratio of column to beam cross-section is observed to be affecting the code predictions considerably. The influence of these two parameters on the joint shear strength is validated with the compiled experimental results. Therefore, to ameliorate the code prediction, two approaches i.e. aspect ratio approach and area ratio approach are proposed. The first approach is based on the effect of variation of strut angle on joint shear strength, whereas, the second approach proposes various empirical modification factors based on area ratio of column to beam cross-section. By using these two approaches, it is observed that the difference between the code predictions and experimental results can be minimized considerably. These approaches make the code prediction suitable for design purpose.

Impact of a prolonged interatrial conduction time for predicting the recurrence of atrial fibrillation after circumferential pulmonary vein isolation of persistent atrial fibrillation.

There are some cases that are difficult to cure with only circumferential pulmonary vein isolation (CPVI) of persistent atrial fibrillation (PerAF). Recently, prolonged interatrial conduction times (IACTs), which seem to be associated with progressive remodeled atria, have been reported as a predictor of new-onset AF. This study aimed to investigate the prognostic value of a prolonged IACT for predicting AF recurrences after CPVI of PerAF. One hundred thirteen patients who underwent CPVI without an empirical substrate modification of PerAF were retrospectively analyzed. The IACT was defined as the interval from the earliest P-wave onset on the ECG to the latest activation in the coronary sinus and was measured after achieving the CPVI and conversion to sinus rhythm. During a mean 22.7-month follow-up after the initial procedure, 56 patients (50%) had AF recurrences. Patients with AF recurrence had a longer IACT than those without AF recurrence (p < 0.001). The best discriminative cut-off value for the IACT was 123ms (sensitivity 53%, specificity 85%). In a Cox multivariate analysis, a prolonged IACT of ≥ 123ms was the only independent predictor (hazard ratio: 2.38; 95% confidence interval: 1.36-4.16, p = 0.002) of being associated with the incidence of an AF recurrence. Even after multiple CPVI procedures, patients with an IACT ≥ 123ms had a higher AF recurrence rate than those with an IACT < 123ms (p = 0.002). In conclusion, a prolonged IACT of ≥ 123ms may be a useful marker for predicting AF recurrences after both initial and multiple CPVI procedures for PerAF.

Semiclassical transition state theory based on fourth order vibrational perturbation theory: Model system studies beyond symmetric Eckart barrier.

The following one-dimensional model potential barriers are studied to compute the tunneling probabilities using semiclassical transition state theory (SCTST) based on fourth order vibrational perturbation theory (VPT4): (i) Morse barrier, (ii) asymmetric Eckart barrier, (iii) adjacent well barrier, and (iv) first order approximation to the symmetric Eckart barrier. The current investigation extends a previous study performed for the symmetric Eckart barrier. The performance of VPT4-SCTST is investigated for a broad range of energies, including the very deep tunneling regime (approximately 1% of the barrier height), and the results are compared to the exact quantum mechanical treatment, as well as to the popular second order vibrational perturbation theory (VPT2)-SCTST approach. While the VPT4-SCTST results are in excellent agreement with their quantum mechanical counterparts for a wide range of energies above and below the barrier, it is found for systems (ii) and (iv) that higher order terms (in ) in energy expansion are important for similarly excellent agreement in the deep tunneling regime. For the asymmetric Eckart barrier, the convergence properties of SCTST are analyzed in terms of its analytically known Siegert eigenvalues. A simple empirical modification of VPT2-SCTST advocated in the aforementioned previous work for the symmetric Eckart barrier is also tested here for the new model systems, and it is shown not to provide a uniformly systematic improvement.

Modeling Eruption Source Parameters by Integrating Field, Ground‐Based, and Satellite‐Based Measurements: The Case of the 23 February 2013 Etna Paroxysm

AbstractVolcanic plumes from Etna volcano (Italy) are governed by easterly winds driving ash over the Ionian Sea. The limited land tephra deposit makes total grain‐size distribution (TGSD) assessment and its fine ash fraction highly uncertain. On 23 February 2013, a lava fountain produced a ~9‐km‐high column above sea level (a.s.l.). The atypical north‐easterly wind direction dispersed the tephra from Etna to the Puglia region (southern Italy) allowing sampling up to very distal areas. This study uses field measurements to estimate the field‐based TGSD. Very fine ash distribution (particle matter below 10 μm—PM10) is explored parameterizing the field‐TGSD through a bi‐lognormal and bi‐Weibull distribution. However, none of the two latter TGSDs allow simulating any far‐traveling airborne ash up to distal areas. Accounting for the airborne ash retrieved from satellite (Spinning Enhanced Visible and Infrared Imager), we proposed an empirical modification of the field‐based TGSD including very fine ash through a power law decay of the distribution. The input source parameters are inverted by comparing simulations against measurements. Results suggest a column height of ~8.7 km a.s.l., a total erupted mass of ~4.9 × 109 kg, a PM10 content between 0.4 and 1.3 wt%, and an aggregate fraction of ~2 wt% of the fine ash. Aerosol optical depth measurements from the AErosol RObotic NETwork are also used to corroborate the results at ~1,700 km from the source. Integrating numerical models with field, ground‐based, and satellite‐based data aims at providing a better TGSD estimation including very fine ash, crucial for air traffic safety.

Is the choice of a standard zeroth-order hamiltonian in CASPT2 ansatz optimal in calculations of excitation energies in protonated and unprotonated schiff bases of retinal?

To account for systematic error of CASPT2 method empirical modification of the zeroth-order Hamiltonian with Ionization Potential-Electron Affinity (IPEA) shift was introduced. The optimized IPEA value (0.25 a.u.), called standard IPEA (S-IPEA), was recommended but due to its unsatisfactory performance in multiple metallic and organic compounds it has been questioned lately as a general parameter working properly for all molecules under CASPT2 study. As we are interested in Schiff bases of retinal, an important question emerging from this conflict of choice, to use or not to use S-IPEA, is whether the introduction of the modified zeroth-order Hamiltonian into CASPT2 ansatz does really improve their energetics. To achieve this goal, we assessed an impact of the IPEA shift value, in a range of 0-0.35 a.u., on vertical excitation energies to low-lying singlet states of two protonated (RPSBs) and two unprotonated (RSBs) Schiff bases of retinal for which experimental data in gas phase are available. In addition, an effect of geometry, basis set, and active space on computed VEEs is also reported. We find, that for these systems, the choice of S-IPEA significantly overestimates both S0 →S1 and S0 →S2 energies and the best theoretical estimate, in reference to the experimental data, is provided with either unmodified zeroth-order Hamiltonian or small value of the IPEA shift in a range of 0.05-0.15 a.u., depending on active space and basis set size, equilibrium geometry, and character of the excited state. © 2018 Wiley Periodicals, Inc.

Correction of low-Reynolds number turbulence model to hydrocarbon fuel at supercritical pressure

At supercritical pressure, due to the drastic change of thermophysical property near the pseudo-critical temperature, the density fluctuation and density variation, along with buoyancy, play an important role in supercritical turbulence modelling. Based on the original LS (Launder–Sharma) low-Reynolds number turbulence model, the buoyancy modification, the density fluctuation modification, the density variation modification and the empirical coefficients modification are considered and the corresponding correction terms are derived and applied in the governing equations. Numerical simulation of heat transfer to hydrocarbon fuel flowing through the uniformly heated round pipe at supercritical pressure has been performed by the modified LS turbulence model incorporated into the in-house numerical code. Inlet temperature varied from 373 K to 473 K, with heat flux varying from 241 kW/m2 to 470 kW/m2. Inlet mass flux was 736 kg/(m2⋅s) and operating pressure was 4 MPa. The flow directions included upflow and downflow. Compared with the original LS turbulence model, the modified LS turbulence model leads to the better agreement with the experimental results, with 41.16% improvement in computation accuracy in the current study. The consideration of density fluctuation and density variation effects makes the turbulence model more suitable for thermophysical property variation at supercritical pressure.

Scatter I: The Politics of Politics in Foucault, Heidegger, and Derrida

Scatter I: The Politics of Politics in Foucault, Heidegger, and Derrida

Prescribing patterns for FOLFIRINOX in the real world.

463 Background: FOLFIRINOX therapy is associated with improved outcome in patients with gastrointestinal cancers. The regimen can be associated with significant toxicity and empiric dose modifications are often used. We analyzed 1) real-world prescribing patterns of FOLFIRINOX and 2) toxicity of therapy. Methods: Patients undergoing FOLFIRINOX chemotherapy at an academic, NCI-Designated Comprehensive Cancer Center were identified and electronic medical records reviewed. Patients who received at least one dose of FOLFIRINOX were included. Chemotherapy dose, growth factor use and toxicity data was abstracted for the first 8 weeks. ‘Standard FOLFIRNOX’ was defined as the regimen utilized by Conroy et al (NEJM 2011). Any empiric reduction/withholding of drug dose for cycle 1 was classified as ‘modified FOLFIRINOX’. Bivariate analysis was performed on the data. Results: There were 111 patients seen between 5/2011-3/2017 and 94% had pancreatic cancer. Age range was 29-87 years and 52% were female. 59% received ‘modified FOLFIRINOX’ and 20% received empiric growth factors. Line of therapy for standard vs modified respectively was 71.1% vs 45.5% for 1st, 17.8% vs 36.4% for 2nd, and 11.1% vs 18.2% for beyond 2nd (p = 0.03). Patients with ‘modified FOLFIRINOX’ were more likely to have metastatic disease (p = 0.01), have received second line or beyond, and higher ECOG score (p = 0.03). Patients with ‘modified FOLFIRINOX’ had a trend toward fewer treatment-related ED visits or hospitalization vs ‘standard FOLFIRINOX’ (27.2% vs 42.2% p = 0.10) and fewer treatment delays (25.8% vs 42.2% p = 0.07). Conclusions: In the real world setting, a majority of patients on FOLFIRINOX receive empiric dose modifications. Although modified dose did not translate to a significant difference in ED visits, hospitalizations or treatment delays, there was a trend toward fewer events.

Trends in erythemal doses at the Polish Polar Station, Hornsund, Svalbard based on the homogenized measurements (1996–2016) and reconstructed data (1983–1995)

Abstract. Erythemal daily doses measured at the Polish Polar Station, Hornsund (77°00′ N, 15°33′ E), for the periods 1996–2001 and 2005–2016 are homogenized using yearly calibration constants derived from the comparison of observed doses for cloudless conditions with the corresponding doses calculated by radiative transfer (RT) simulations. Modeled all-sky doses are calculated by the multiplication of cloudless RT doses by the empirical cloud modification factor dependent on the daily sunshine duration. An all-sky model is built using daily erythemal doses measured in the period 2005–2006–2007. The model is verified by comparisons with the 1996–1997–1998 and 2009–2010–2011 measured data. The daily doses since 1983 (beginning of the proxy data) are reconstructed using the all-sky model with the historical data of the column ozone from satellite measurements (SBUV merged ozone data set), the snow depth (for ground albedo estimation), and the observed daily sunshine duration at the site. Trend analyses of the monthly and yearly time series comprised of the reconstructed and observed doses do not reveal a statistically significant trend in the period 1983–2016. The trends based on the observed data only (1996–2001 and 2005–2016) show declining tendency (about −1 % per year) in the monthly mean of daily erythemal doses in May and June, and in the yearly sum of daily erythemal doses. An analysis of sources of the yearly dose variability since 1983 shows that cloud cover changes are a basic driver of the long-term UV changes at the site.

Modeling capillary bridge dynamics and crack healing between surfaces of nanoscale roughness

Capillary bridge formation between adjacent surfaces in humid environments is a ubiquitous phenomenon. It strongly influences tribological performance with respect to adhesion, friction and wear. Only a few studies, however, assess effects due to capillary dynamics. Here we focus on how capillary bridge evolution influences crack healing rates. Experimental results indicated a logarithmic decrease in average crack healing velocity as the energy release rate increases. Our objective is to model that trend. We assume that capillary dynamics involve two mechanisms: capillary bridge growth and subsequently nucleation followed by growth. We show that by incorporating interface roughness details and the presence of an adsorbed water layer, the behavior of capillary force dynamics can be understood quantitatively. We identify three important regimes that control the healing process, namely bridge growth, combined bridge growth and nucleation, and finally bridge nucleation. To fully capture the results, however, the theoretical model for nucleation time required an empirical modification. Our model enables significant insight into capillary bridge dynamics, with a goal of attaining a predictive capability for this important microelectromechanical systems (MEMS) reliability failure mechanism.

Effective equilibrium states in the colored-noise model for active matter I. Pairwise forces in the Fox and unified colored noise approximations

The equations of motion of active systems can be modeled in terms of Ornstein–Uhlenbeck processes (OUPs) with appropriate correlators. For further theoretical studies, these should be approximated to yield a Markovian picture for the dynamics and a simplified steady-state condition. We perform a comparative study of the unified colored noise approximation (UCNA) and the approximation scheme by Fox recently employed within this context. We review the approximations necessary to define effective interaction potentials in the low-density limit and study the conditions for which these represent the behavior observed in two-body simulations for the OUPs model and active Brownian particles. The demonstrated limitations of the theory for potentials with a negative slope or curvature can be qualitatively corrected by a new empirical modification. In general, we find that in the presence of translational white noise the Fox approach is more accurate. Finally, we examine an alternative way to define a force-balance condition in the limit of small activity.

An Empirical Modification of the Force Field Approach to Describe the Modulation of Galactic Cosmic Rays Close to Earth in a Broad Range of Rigidities

AbstractOn their way through the heliosphere, galactic cosmic rays (GCRs) are modulated by various effects before they can be detected at Earth. This process can be described by the Parker equation, which calculates the phase space distribution of GCRs depending on the main modulation processes: convection, drifts, diffusion, and adiabatic energy changes. A first‐order approximation of this equation is the force field approach, reducing it to a one‐parameter dependency, the solar modulation potential ϕ. Utilizing this approach, it is possible to reconstruct ϕ from ground‐based and spacecraft measurements. However, it has been shown previously that ϕ depends not only on the local interstellar spectrum (LIS) but also on the energy range of interest. We have investigated this energy dependence further, using published proton intensity spectra obtained by PAMELA and heavier nuclei measurements from IMP‐8 and ACE/CRIS. Our results show severe limitations at lower energies including a strong dependence on the solar magnetic epoch. Based on these findings, we will outline a new tool to describe GCR proton spectra in the energy range from a few hundred MeV to tens of GeV over the last solar cycles. In order to show the importance of our modification, we calculate the global production rates of the cosmogenic radionuclide 10Be which is a proxy for the solar activity ranging back thousands of years.

Application of the dissipation theorem to turbulent flow and mass transfer in a pipe

The dissipation theorem is applied to turbulent pipe flow. The eddy-viscosity profiles can be made to agree with some in the literature in the sense that the eddy viscosity starts at zero on the solid pipe wall, rises to a maximum, and declines again toward the center line. A relationship between the volumetric dissipation and the eddy viscosity is derived by means of an energy balance on a core of fluid of radius r. The question of what exponent to use on the radius in another governing equation is clarified, thereby giving better agreement with experimental data than other values tried. Negative values of the eddy viscosity can be obtained in some regions of the flow field, such as near the center line, and it is suggested that these can be eliminated by slight modification of the decay term. Better agreement with the shapes of friction-factor and mass-transfer curves could be achieved by further (empirical) modification of the stress dependence of parameters in the model.

A rheological modelling and microscopic analysis of bigels

Bigels are two-phase systems in which each phase (organic or aqueous) is structured using a specific gelator. Currently, these systems are widely investigated, mainly as matrices for controlled drug delivery, because they possess the advantages of both organogels and hydrogels and are very stable owing to the structuration of the dispersing phase. A deeper knowledge of the relationship between macroscopic properties and microscopic parameters seems necessary to aim at designing materials with specific rheological properties and suitable for specific uses. From a rheological point of view, bigels can be considered as composite materials in which a structured system (organogel or hydrogel, according to the desired use) is dispersed in a gelled continuous phase. In the present paper, a number of rheological models, already proposed in literature for composite systems, were used to relate the bigel complex modulus to the rheological properties of dispersed and continuous phase and to their volumetric ratio. It was observed that these models are not able to describe properly bigel behaviour, probably owing to some theoretical assumptions such as the uniform distribution of spherical particles. An empirical modification of a literature model, proposed to take into account some peculiarities of bigels, yields an improvement of fitting even if further investigations are necessary to better understand the effects of particle size distribution and morphology on observed properties.

Dr Snow killed a bird: The genesis of pharmacokinetics and pharmacodynamics in anaesthesia.

This essay presents a pharmacologist's perspective of what would be now called 'preclinical research' and 'uncontrolled clinical trials' surrounding the first public demonstration by William Thomas Green Morton of painless surgery achieved by the inhalation of ether in a patient at the Massachusetts General Hospital on 16 October 1846. Of the many people who made history in those earliest days of surgical anaesthesia in both the United States and Great Britain, John Snow stands out for his personal research that spanned basic science and clinical medicine. Primarily, Snow used the relationship between the vapour pressure of a volatile liquid and temperature to design a vaporiser. This allowed control of the inspired concentration of the volatile liquid epitomised by diethyl ether, and thus the time-course and depth of anaesthesia. In an era when developments in anaesthesia were almost exclusively based on empirical modifications to apparatus and technique, Snow, and to a lesser extent his contemporary Andrew Buchanan, stood out from all others in advancing the quantitative basis of anaesthesia. Both described the physiological basis of control over gas uptake whereby they related that gas moved across concentration gradients in the body: alveolar to arterial to tissue to venous gas tensions, and Snow devised a progressional semi-quantitative scale of five 'stages' of ether anaesthesia. They thereby introduced the elements of what would be referred to 'pharmacokinetics' and 'pharmacodynamics', a century later. This essay attempts to place them and their scientific insights into context with contemporaneous principal personae and knowledge.

Assessment of thermogravimetric methods for calculating coke combustion-regeneration kinetics of deactivated catalyst

This work compares different methodologies for calculating the kinetic parameters of coke combustion, employed for catalyst regeneration, using thermogravimetric methods. A reference fluid catalytic cracking (FCC) spent catalyst was used as a representative example of the deactivated catalyst for the combustion runs, pre-used in the cracking of a vacuum gas oil at 773K and 3s. Three different types of approaches have been performed in order to obtain kinetic combustion parameters: (i) kinetic model-based, (ii) isoconversional and (iii) modulated methods. Additionally, a series of empirical modifications have been proposed to predict the kinetic behavior at different heating rates for the model-based approach. Using the best conditions and methods, the combustion activation energy of coke, deposited after the reaction mentioned, is in the order of ∼114, ∼156, and ∼162kJmol−1 for the kinetic model-based, isoconversional and modulated methods, respectively. The recommendations for measuring kinetic parameters are reported together with the benefits/disadvantages using the three mentioned approaches.