Bell-shaped Model Research Articles

Influence of population density, temperature, and absolute humidity on spread and decay durations of COVID-19: A comparative study of scenarios in China, England, Germany, and Japan

In this study, we analyzed the spread and decay durations of the COVID-19 pandemic in several cities of China, England, Germany, and Japan, where the first wave has undergone decay. Differences in medical and health insurance systems, as well as in regional policies incommoded the comparison of the spread and decay in different cities and countries. The spread and decay durations in the cities of the four studied countries were reordered and calculated based on an asymmetric bell-shaped model. We acquired the values of the ambient temperature, absolute humidity, and population density to perform multivariable analysis. We found a significant correlation (p < 0.05) of the spread and decay durations with population density in the four analyzed countries. Specifically, spread duration showed a high correlation with population density and absolute humidity (p < 0.05), whereas decay duration demonstrated the highest correlation with population density, absolute humidity, and maximum temperature (p < 0.05). The effect of population density was almost nonexistent in China because of the implemented strict lockdown. Our findings will be useful in policy setting and governmental actions in the next pandemic, as well as in the next waves of COVID-19.

Methane Production Potential of Azolla Under Different Ratios of C/N, Chemical and Thermal Pre-Treatment

Abstract Azolla algae currently represent a major threat to the environment and rice cultivation fields. Various studies have shown that one of the practical solutions is to turn this threat into an opportunity for biomass energy production. This research investigates the production potential of methane in Azolla. Test was conducted in a completely randomized design (CRD) with Mini Tap software. Three different C/N ratios, 30, 34 and 38, two levels of thermal pre-treatment (raw and steamed Azolla) and two levels of chemical pre-treatment (NaOH 0% and 9%) were used and effects of each case on the methane production rate was studied. The highest amount of methane (247.7 ml·g−1 vs) was produced at C/N ratio of 30 with application of NaOH (9%) and no thermal pre-treatment (raw Azolla). ANOVA analysis showed that interactions of the effective variables were significant, but the trend was not incremental or decreasing; therefore, ANFIS and stepwise regression modelling were used. The results showed that the ANFIS model provides more accurate mapping between the empirical and predicted values than the regression model. Furthermore, among examined models (triangular; trapezoidal; Gaussian; bell-shaped models), the best model for methane production prediction was Gaussian linear membership function (R 2 = 0.997 and ε (%) = 0.32). According to the regression model, the thermal-chemical factor is the most efficient in prediction of the model (b = 35.6).

Heat and mass transfer characteristics of three-dimensional bell-shaped polysilicon chemical vapor deposition reactor

Polysilicon, the crucial material of photovoltaic field, is commonly produced in a Siemens chemical vapor deposition (CVD) reactor with a complex physical and chemical phenomenon included inside as well as complicated geometry structure. In order to study the performance of silicon CVD reactor, a three-dimensional bell-shaped reactor model with 24 rods is constructed and verified to investigate the heat and mass transfer performance inside. The distributions of velocity, temperature, complex concentrations of six main components, silicon deposition rate, and energy of the reduction furnace at high and low inlet velocities are analyzed in detail. Results show that high inlet velocity is more conductive to obtain uniform distributions of velocity, temperature, complex concentration, and silicon deposition rate, leading to better silicon CVD performance. The inner rods are easier to collapse than the outer rods. In addition, radiation loss is the main energy consumption in the silicon reduction furnace and accounts for more than 60% of the total energy consumption. The convective heat transfer, chemical reaction heat, proportion of convective heat, and the proportion of chemical reaction heat increase with the rise in inlet velocity due to a fully developed flow field.

Analytical Solution of the Complex Polymer Equation Systems via the Homogeneous Balance Method

In this article, we solve analytically the nonlinear Doubly Dispersive Equation (DDE) in (1+1)-D by the homogeneous balance method, introduced to investigate the strain waves propagating in a cylindrical rod in complex polymer systems. The linear dispersion relation plays important role in connecting the frequency of the emitted nonlinear waves with the wave number of the ablating laser beam affecting the polymers with their characteristic parameters. In accordance with the normal dispersion conditions, the resulting solitary wave solutions show the compression characters in the nonlinearly elastic materials namely Polystyrene (PS) and PolyMethylMethAcrylate (PMMA). The ratio between the estimated potential and kinetic energies shows good agreement with the physical situation, and as well in making comparisons with the bell-shaped model conducted in the literature.

Exploration of the resolving power for a magnetic lens using Glaser field distribution

Resolution estimation for magnetic lenses have been investigated using Glaser Bell-Shaped model. The adopted model used to approximates the magnetic field distribution for the proposed lens. Indeed, the field distribution is formulated in terms of three optimization parameters namely the half width, field beak value and lens length. Four values for each of these parameters selected to check the resolution behavior, where the other two parameter maintained fixed. Results reveals that the resolution get better enhancement whenever the field excitation increases. This behavior attained whenever the variation in the optimization variable leads to increases the field refracting power. Besides, the slope of the approximated model correspondingly influence the resolution behavior. In addition, results shows that resolution always becomes better for long and strong magnetic lenses.

Probability of carcinogenesis due to involved field and involved site radiation therapy techniques for supra- and infradiaphragmatic Hodgkin’s disease

PurposeTo estimate the second cancer risk associated with Hodgkin Lymphoma (HL) radiotherapy at supradiaphragmatic or infradiaphragmatic region, using the involved field (IFRT) and the involved site radiotherapy (ISRT). Materials and methodsIFRT and ISRT treatment plans were created for twenty HL patients. Three dimensional plans (3DRT) were employed for all patients. The organ equivalent dose (OED) and lifetime attributable risk (LAR) for organs at risk were estimated with mechanistic, plateau and bell-shaped model. Estimated risk values were compared with nominal risk of unexposed population. ResultsFor supradiaphragmatic radiotherapy, the mean OED range was 0.63–8.53 Gy and 0.63–7.26 Gy for IFRT and ISRT, respectively. The corresponding range for infradiaphragmatic radiotherapy was 0.18–7.64 Gy and 0.80–4.95 Gy. The LAR for cancer induction in the partially in field organs at risk after IFRT was 0.5%–8.0% and 0.2%–9.3% at supradiaphragmatic and infradiaphragmatic regions, respectively. The corresponding risk after ISRT method was 0.5%–5.2% and 0.9%–6.0%. Estimated cancer risk for breast, lung, thyroid, colon and rectal with ISRT was found significantly reduced compared to IFRT. The risk of secondary malignancies for lung, mouth, pharynx, rectum and colon was assessed more than 1.2 times higher than nominal risk for IFRT. The respective risk using ISRT was above nominal only for pharyngeal cancer. ConclusionISRT compared with IFRT, results in decreased second cancer risk in most organs considered. Second cancer probability with IFRT was higher than the nominal risk for certain organs, while for ISRT remains higher only for pharyngeal cancer.

A Review of Hydrogen Sulfide Synthesis, Metabolism, and Measurement: Is Modulation of Hydrogen Sulfide a Novel Therapeutic for Cancer?

Significance: Hydrogen sulfide (H2S) has been recognized as the third gaseous transmitter alongside nitric oxide and carbon monoxide. In the past decade, numerous studies have demonstrated an active role of H2S in the context of cancer biology. Recent Advances: The three H2S-producing enzymes, namely cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3MST), have been found to be highly expressed in numerous types of cancer. Moreover, inhibition of CBS has shown anti-tumor activity, particularly in colon cancer, ovarian cancer, and breast cancer, whereas the consequence of CSE or 3MST inhibition remains largely unexplored in cancer cells. Intriguingly, H2S donation at high amounts or a long time duration has also been observed to induce cancer cell apoptosis in vitro and in vivo while sparing noncancerous fibroblast cells. Therefore, a bell-shaped model has been proposed to explain the role of H2S in cancer development. Specifically, endogenous H2S or a relatively low level of exogenous H2S may exhibit a pro-cancer effect, whereas exposure to H2S at a higher amount or for a long period may lead to cancer cell death. This indicates that inhibition of H2S biosynthesis and H2S supplementation serve as two distinct ways for cancer treatment. This paradoxical role of H2S has stimulated the enthusiasm for the development of novel CBS inhibitors, H2S donors, and H2S-releasing hybrids. Critical Issues: A clear relationship between H2S level and cancer progression remains lacking. The possibility that the altered levels of these byproducts have influenced the cell viability of cancer cells has not been excluded in previous studies when modulating H2S producing enzymes. Future Directions: The consequence of CSE or 3MST inhibition in cancer cells need to be examined in the future. Better portrayal of the crosstalk among these gaseous transmitters may not only lead to an in-depth understanding of cancer progression but also shed light on novel strategies for cancer therapy.

Second cancer risk assessments after involved-site radiotherapy for mediastinal Hodgkin lymphoma.

This study was conducted to provide second cancer risk assessments attributable to involved-site radiotherapy (ISRT) of mediastinal Hodgkin lymphoma (HL) and to compare these risks with those from the conventional involved-field radiation therapy (IFRT). Both ISRT and IFRT plans were made for 11 patients (six females, five males) with HL in the region of mediastinum. All three-dimensional plans involved 6 MV photon beams and delivered 30 Gy to the target site. Differential dose-volume histograms were defined for the lung, female breast, and esophagus which were partly included within the planned treatment fields. The patient-specific organ equivalent dose (OED) and the relevant lifetime attributable risk (LAR) of developing malignancies in each of the above critical organs were determined with the aid of a mechanistic, plateau and bell-shaped models. The LAR estimates were compared with the baseline risks for unexposed people. The OED range of lung, breast, and esophagus calculated by the ISRT plans was 176.1-360.2, 19.5-124.1, and 42.6-157.7 cGy, respectively. The resultant LARs of developing lung and breast cancer as estimated by the three different models were at least 1.8 and 5.3 times lower than the baseline risks, respectively. The probability for the appearance of radiation-induced esophageal malignancies from ISRT in males was also up to 3.8 times smaller than the nominal incidence cancer rates. The corresponding probability in irradiated females exceeded the baseline risks. The estimated lifetime risks for lung and breast cancer induction due to ISRT were systematically and significantly lower than those from the IFRT irrespective of the model used for analysis (P < 0.05). No significant difference was found between the LARs for esophageal cancer development estimated by the ISRT and IFRT plans (P = 0.63). The presented second cancer risk data may be of value in the selection of the optimal radiotherapy technique for the management of mediastinal HL and in the subsequent follow-up of irradiated patients.

Performance and kinetics of ANAMMOX granular sludge with pH shock in a sequencing batch reactor.

As an efficient and cost-effective nitrogen removal process, anaerobic ammonium oxidation (ANAMMOX) could be well operated at suitable pH condition. However, pH shock occurred in different kinds of wastewater and affected ANANNOX process greatly. The present research aimed at studying the performance and kinetics of ANAMMOX granular sludge with pH shock. When influent pH was below 7.5, effluent [Formula: see text]-N and [Formula: see text]-N increased with decreasing pH. At Ph 6.0, effluent [Formula: see text]-N approached 100mg/L, and the ratios of [Formula: see text] approached 2.2 and 1.3, respectively. Both greatly deviated from theoretical values. When influent pH was above 7.5, effluent [Formula: see text]-N and [Formula: see text]-N increased with increasing pH. At pH 9.0, ammonium removal rate (ARR) and nitrite removal rate (NRR) decreased to 0.011±0.004 and 0.035±0.004kg/(m3·d), respectively. Besides, [Formula: see text]-N:[Formula: see text]-N deviated from theoretical value. Longer recovery time from pH 9.0 than from pH 6.0 indicated that alkaline surroundings inhibited anaerobic ammonium oxidizing bacteria (AAOB) greater. The sludge settling velocity was 2.15cm/s at pH 7.5. However, it decreased to 2.02cm/s when pH was 9.0. Acidic pH had little effect on sludge size, but disintegration of ANAMMOX granule was achieved with pH of 9.0. The Bell-shaped (A) model and the Ratkowsky model were more applicable to simulate the effect resulting from pH shock on ANAMMOX activity (R2>0.95), and both could describe ANAMMOX activity well with pH shock. They indicated that qmax was 0.37 kg [Formula: see text]-N/(kgMLSS·d) at the optimum pH value (7.47) in present study. The minimum pH during which ANAMMOX occurred was 5.68 while the maximum pH for ANAMMOX reaction was 9.26. Based on nitrogen removal performance with different pH, strongly acidic (pH≤6.5) or alkaline (pH≥8.5) inhibited ANAMMOX process. Besides, ANAMMOX appeared to be more susceptible to alkaline wastewater. Compared to extremely acidic condition (low pH), extremely alkaline condition (high pH) affected ANAMMOX granules much more.

Modelling second malignancy risks from low dose rate and high dose rate brachytherapy as monotherapy for localised prostate cancer

Background and purposeTo estimate the risks of radiation-induced rectal and bladder cancers following low dose rate (LDR) and high dose rate (HDR) brachytherapy as monotherapy for localised prostate cancer and compare to external beam radiotherapy techniques. Materials and methodsLDR and HDR brachytherapy monotherapy plans were generated for three prostate CT datasets. Second cancer risks were assessed using Schneider’s concept of organ equivalent dose. LDR risks were assessed according to a mechanistic model and a bell-shaped model. HDR risks were assessed according to a bell-shaped model. Relative risks and excess absolute risks were estimated and compared to external beam techniques. ResultsExcess absolute risks of second rectal or bladder cancer were low for both LDR (irrespective of the model used for calculation) and HDR techniques. Average excess absolute risks of rectal cancer for LDR brachytherapy according to the mechanistic model were 0.71 per 10,000 person-years (PY) and 0.84 per 10,000 PY respectively, and according to the bell-shaped model, were 0.47 and 0.78 per 10,000 PY respectively. For HDR, the average excess absolute risks for second rectal and bladder cancers were 0.74 and 1.62 per 10,000 PY respectively. The absolute differences between techniques were very low and clinically irrelevant. Compared to external beam prostate radiotherapy techniques, LDR and HDR brachytherapy resulted in the lowest risks of second rectal and bladder cancer. ConclusionsThis study shows both LDR and HDR brachytherapy monotherapy result in low estimated risks of radiation-induced rectal and bladder cancer. LDR resulted in lower bladder cancer risks than HDR, and lower or similar risks of rectal cancer. In absolute terms these differences between techniques were very small. Compared to external beam techniques, second rectal and bladder cancer risks were lowest for brachytherapy.

Estimated Risk of Radiation Induced Contra Lateral Breast Cancer Following Chest Wall Irradiation by Conformal Wedge Field and Forward Intensity Modulated Radiotherapy Technique for Post-Mastectomy Breast Cancer Patients

Background:Epidemiological studies have indicated an increasing incidence of radiation induced secondary cancer (SC) in breast cancer patients after radiotherapy (RT), most commonly in the contra-lateral breast (CLB). The present study was conducted to estimate the SC risk in the CLB following 3D conformal radiotherapy techniques (3DCRT) including wedge field and forward intensity modulated radiotherapy (fIMRT) based on the organ equivalent dose (OED).Material and Methods:RT plans treating the chest wall with conformal wedge field and fIMRT plans were created for 30 breast cancer patients. The risks of radiation induced cancer were estimated for the CLB using dose-response models: a linear model, a linear-plateau model and a bell-shaped model with full dose response accounting for fractionated RT on the basis of OED.Results:The plans were found to be ranked quite differently according to the choice of model; calculations based on a linear dose response model fIMRT predict statistically significant lower risk compared to the enhanced dynamic wedge (EDW) technique (p-0.0089) and a non-significant difference between fIMRT and physical wedge (PW) techniques (p-0.054). The widely used plateau dose response model based estimation showed significantly lower SC risk associated with fIMRT technique compared to both wedge field techniques (fIMRT vs EDW p-0.013, fIMRT vs PW p-0.04). The full dose response model showed a non-significant difference between all three techniques in the view of second CLB cancer. Finally the bell shaped model predicted interestingly that PW is associated with significantly higher risk compared to both fIMRT and EDW techniques (fIMRT vs PW p-0.0003, EDW vs PW p-0.0032).Conclusion:In conclusion, the SC risk estimations of the CLB revealed that there is a clear relation between risk associated with wedge field and fIMRT technique depending on the choice of model selected for risk comparison.

Risk of radiation-induced secondary rectal and bladder cancer following radiotherapy of prostate cancer

ABSTRACTBackground. An elevated risk of radiation-induced secondary cancer (SC) has been observed in prostate cancer patients after radiotherapy (RT), rising to as high as one in 70 patients with more than 10 years follow-up. In this study we have estimated SC risks following RT with both previous and contemporary techniques, including proton therapy, using risk models based on different dose-response relationships.Material and methods. RT plans treating the prostate and seminal vesicles with either conformal radiotherapy (CRT), volumetric modulated arc therapy (VMAT) or intensity-modulated proton therapy (IMPT) were created for 10 patients. The risks of radiation-induced cancer were estimated for the bladder and rectum using dose-response models reflecting varying degrees of cell sterilisation: a linear model, a linear-plateau model and a bell-shaped model also accounting for fractionated RT.Results. The choice of risk models was found to rank the plans quite differently, with the CRT plans having the lowest SC risk using the bell-shaped model, while resulting in the highest risk applying the linear model. Considering all dose-response scenarios, median relative risks of VMAT versus IMPT were 1.1–1.7 for the bladder and 0.9–1.8 for the rectum. Risks of radiation-induced bladder and rectal cancers were lower from VMAT if exposed at 80 years versus IMPT if exposed at 50 years.Conclusions. The SC risk estimations for the bladder and rectum revealed no clear relative relationship between the contemporary techniques and CRT, with divergent results depending on choice of model. However, the SC risks for these organs when using IMPT were lower or comparable to VMAT. SC risks could be assessed when considering referral of prostate cancer patients to proton therapy, taking also general patient characteristics, such as age, into account.

MODELING AND VALIDATION OF ELECTRONIC WEDGE BRAKE MECHANISM FOR VEHICLE SAFETY SYSTEM

This paper presents the performance characteristic of an electronic wedge brake (EWB) mechanism for a vehicle braking system. Based on a Gaussian cumulative distribution method, a non-parametric model, using Bell-Shaped curve method has been proposed in this study to characterize the behavior of an actual EWB mechanism. Therefore, a brake test rig has been developed to investigate the performance of the Bell-Shaped curve model. For the purpose of validation of EWB, an electronic control unit (ECU) which consists of microcontroller unit (MCU), H-Bridge driver and opto-coupler is designed to control the EWB’s pinion according to the given rotational input during the experiment. The response measured throughout the experiment is the gapping displacement of the brake piston, clamping force and also brake torque of the EWB mechanism. The responses of the actual EWB mechanism obtained from the experiment are compared with the proposed Bell-Shaped curve. The result of the study shows that the response of the Bell-Shaped curve model closely follows the response of a real EWB actuator in term of clamping force and brake torque with percentage of errors less than 10%.

Non-renewable Recourses Life Cycles Modeling Aspects

Abstract The task of modeling and forecasting non-renewable resources production using bell-shaped curve-fitting models is considered. Identification of model parameters is based on the genetic algorithm. The purpose of this article is to determine the best genetic algorithm configuration for the task of bell-shaped life cycle models parameters identification. We find the initial population optimal size, and find that heuristic function is the best for crossover and adaptive feasible function is the best for mutation. The experience of modeling 235 time series of oil and gas production is summed up. On the basis of it we made the frequency analysis of models using for every kind of task. It allows to select the preferred models for describing oil, gas and shale gas production at the different levels of aggregation: from a country and a region to a single field.

Site-specific dose-response relationships for cancer induction from the combined Japanese A-bomb and Hodgkin cohorts for doses relevant to radiotherapy

Background and PurposeMost information on the dose-response of radiation-induced cancer is derived from data on the A-bomb survivors. Since, for radiation protection purposes, the dose span of main interest is between zero and one Gy, the analysis of the A-bomb survivors is usually focused on this range. However, estimates of cancer risk for doses larger than one Gy are becoming more important for radiotherapy patients. Therefore in this work, emphasis is placed on doses relevant for radiotherapy with respect to radiation induced solid cancer.Materials and methodsFor various organs and tissues the analysis of cancer induction was extended by an attempted combination of the linear-no-threshold model from the A-bomb survivors in the low dose range and the cancer risk data of patients receiving radiotherapy for Hodgkin's disease in the high dose range. The data were fitted using organ equivalent dose (OED) calculated for a group of different dose-response models including a linear model, a model including fractionation, a bell-shaped model and a plateau-dose-response relationship.ResultsThe quality of the applied fits shows that the linear model fits best colon, cervix and skin. All other organs are best fitted by the model including fractionation indicating that the repopulation/repair ability of tissue is neither 0 nor 100% but somewhere in between. Bone and soft tissue sarcoma were fitted well by all the models. In the low dose range beyond 1 Gy sarcoma risk is negligible. For increasing dose, sarcoma risk increases rapidly and reaches a plateau at around 30 Gy.ConclusionsIn this work OED for various organs was calculated for a linear, a bell-shaped, a plateau and a mixture between a bell-shaped and plateau dose-response relationship for typical treatment plans of Hodgkin's disease patients. The model parameters (α and R) were obtained by a fit of the dose-response relationships to these OED data and to the A-bomb survivors. For any three-dimensional inhomogenous dose distribution, cancer risk can be compared by computing OED using the coefficients obtained in this work.

Feeding Ecology of Cocoi Heron (Ardea Cocoi) in the Flood Valley of the Paraná River

The feeding ecology of Ardea cocoi were analysed based on 29 herons captured on the Carabajal island (Santa Fe, 31°39'S, 60°42'W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, standardisation, circadian rhythm of feeding activity and habitat preference. The trophic spectrum was made up of 17 taxonomic entities, mainly fishes (IRI = 16,000), followed by mammals and amphibians (IRI = 8,000). The highest percentage of prey size was found in the interval 151→200 mm. The amplitude of the trophic niche ranged between 1.98 and 4.21, and the feeding efficiency between 89.9 and 99.9%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded no significant results (rs = 0.078, P&gt;0.001). The rhythm of feeding activity responded to the bell-shaped model. Aquatic vegetation was the unit of vegetation and environment selected more frequently.

Oil and the political economy of energy

The key issues concerning oil exploitation are still open for discussion: there is no agreement about where we presently stand in the world oil extraction curve, what is its exact shape, and how far can oil price grow before it changes irreversibly the world economy and consumer behavior. The paper proposes an alternative scenario to the Hubbert's bell-shaped model of oil exploitation, based on more realistic assumptions regarding political agendas in oil-exporting countries and consumer behavior dynamics in oil-importing countries. Under this scenario, the joint impact of markets and public policy in oil importing countries together with “resource pragmatism” policy in oil-exporting countries allows for a less steep oil supply curve with a much fatter tail compared to the Hubbert's model.

Diet of Cattle Egrets (Bubulcus ibis ibis) in the Flood Valley of the Paraná River, Northern Argentina

We analysed the feeding ecology of Cattle Egrets ( Bubulcus ibis ibis) based on 30 individuals captured on the Carabajal island, Santa Fe, Argentina (31°39′S, 60°42′W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, standardisation, circadian rhythm of feeding activity and habitat preference. The trophic spectrum was made up of 17 taxonomic entities, mainly insects (IRI = 15,000), among which orthopterans were the most numerous followed by spiders and amphibians (IRI = 250). The highest percentage of prey size was found in the interval 21-30 mm. The amplitude of the trophic niche ranged between 1.98 and 3.45, and the feeding efficiency between 89 and 92%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded no significant results (rs = 0.84, P.0:001). The rhythm of feeding activity responded to the bell-shaped model, which meant a peak in its feeding behaviour pattern at the noon hours. The pastures were the units of vegetation and environment selected more frequently.

Concentration-Dependent Effects of Caspofungin on the Metabolic Activity of Aspergillus Species

The minimum effective concentration (MEC) used to assess the in vitro antifungal activity of caspofungin against Aspergillus spp. is a qualitative endpoint requiring microscopic examination of hyphae. We therefore developed a tool for the quantitative assessment of caspofungin activity against Aspergillus spp. at clinically applicable concentrations. Susceptibility to caspofungin (0.008 to 8 microg/ml) was studied for 9 A. fumigatus, 8 A. flavus, and 12 A. terreus isolates based on the Clinical and Laboratory Standards Institute M38-A protocol. After 48 h of incubation, the MEC was defined microscopically, and metabolic activity assessed with a modified XTT assay, using 100 microg of the tetrazolium salt XTT/ml and 6.25 muM menadione. A significant reduction in metabolic activity was demonstrated at the MEC (0.25 to 0.5 microg/ml) for all Aspergillus spp. and was more pronounced for A. flavus (median metabolic activity, 25% of control) compared to A. fumigatus and A. terreus (median metabolism, 42 and 53%, respectively), allowing determination of MEC with the XTT assay (93 to 100% agreement with microscopic MEC). Fungal metabolism tended to reach the lowest levels (median, 17 to 38% of control) one to two dilutions higher than the MEC, at the minimum metabolic activity concentration (MMC). For 5 of 9 A. fumigatus isolates, 6 of 12 A. terreus isolates, and 1 of 8 A. flavus isolates, a paradoxical increase in metabolism was observed at concentrations greater than the MMC. Sigmoid (E(max)) or bell-shaped models described accurately (median R(2) = 0.97) the concentration-dependent metabolic changes in the absence or presence, respectively, of paradoxical response. Assessment of metabolic activity may provide useful quantitative endpoints for in vitro studies of caspofungin against Aspergillus spp.

OPTIMUM TIME LAG DETERMINATION FOR YIELD MONITORING WITH REMOTELY SENSED IMAGERY

The time it takes for the grain to pass through the mechanisms of a harvester before reaching the point ofmeasurement by a yield monitor greatly affects the accuracy of maps generated from yield monitor data. This time lag isgenerally adjusted based on limited field observations. This article presents a method for determining time lag for yieldmonitoring using remotely sensed imagery. This method is based on the assumption that an incorrect time lag will cause areduction in the correlation between yield and remotely sensed imagery of the field. Therefore, a time lag that maximizes thecorrelation can be considered the correct or optimum time lag. To illustrate how this method works, yield monitor data andairborne multispectral imagery collected from a number of grain sorghum fields in 19982000 were used. The yield data wereassociated with their geographic coordinates with time lags ranging from 0 to 25 s at onesecond intervals. The airborneimages were georeferenced to the same coordinate system as the yield data and resampled to 1 m pixel resolution. Both theyield data and the images were then aggregated into grids with a cell size equivalent to the combines effective cutting width.Regression analyses were used to calculate coefficients of determination for equations relating yield to each of three imagebands and four vegetation indices (two band ratios and two normalized differences) and to a combination of the three bandsfor each of the 26 time lags. The plots of coefficients of determination against time lag for each of the seven spectral variablesand the combination of the three bands were bellshaped. The time lags corresponding to the maximum coefficients ofdetermination for all the curves of the spectral variables were essentially the same for a given field in a given year. Moreover,optimum time lags determined from images collected from a given field at different dates during a growing season were almostthe same. For yield monitor data collected with sampling intervals larger than 1 s, a bellshaped model and a quadratic modelwere fitted to the curves to accurately estimate optimum time lags. These results show that optimum time lags can bedetermined from either individual image bands, all the bands combined, or vegetation indices derived from airborne imagerytaken during the growing season.