Permissible Time Research Articles

Integrated deteriorating inventory model when order quantity is linked to freight rate and credit period

In this paper, a collaborative inventory model is developed when units in an inventory are subject to deterioration at a constant rate. The demand is price sensitive and production rate varies with respect to demand rate. The buyer is offered permissible delay in payments against the purchases which is dependent on the quantity ordered. It is assumed that the buyer pays the freight charge according to a weight loaded. The optimum policy is discussed to maximise the joint total profit when the permissible delay payment time and freight rate are both linked to the order quantity. The optimal retail price of the buyer, order quantity and number of shipments are decision variables. In this article, the solutions are derived for the buyer and the vendor to make decision jointly on purchase quantity, floor management, transportation logistics, shipments and payment schedule. It is observed that there is significant profit increase for the supply chain of the single-vendor and single-buyer when order quantity is linked to both permissible delay payment time and freight rate. An algorithm is developed to determine the optimal solution. In addition, numerical examples and sensitivity analysis are given to analyse the theoretical results.

Ant colony optimisation based heuristic for one-sided time constraint vehicle routing problem

In this paper, an approach based on Ant Colony Optimisation (ACO) is described for one-sided time constraint Vehicle Routing Problem (VRP), where the delivery of products from the depot to distribution centres has to take place within the maximum permissible time. The problem is described with the aim to achieve maximum customer satisfaction and to develop a solution strategy based on ACO. Here, ACO-based approach is compared with heuristic based on shortest path approach. With the help of computational experiments, it is found that ACO-based approach is more effective approach than the heuristic approach for VRP with one-sided time constraint.

Personal noise exposures of operators of agricultural tractors

Approximately one million agricultural tractors are used in Turkey for crop production and about one-third of the population lives in rural areas. The objectives of this study were to determine sound pressure levels, A-weighted sound pressure levels, and the permissible exposure time for tractors without cabins, field-installed cabins, and original cabins at ear level of agricultural tractor operators for following machines: plows, cultivators, top soil cultivators, rotary tillers, tool combinations (harrow + roller), mechanical drills, pneumatic drills, chemical applicators, fertilizer applicators, drum mowers, balers, and forage harvesters. Variance analyses showed that type of operation, type of cabins, and operation × cabin interactions were statistically significant ( P < 0.01) both for sound pressure levels and equivalent (A-weighted) sound pressure levels. The use of original cabins had a greater effect in decreasing average sound pressures and resulted in more efficient noise insulation, especially at higher center frequencies compared to field-installed cabins whereas field-installed cabins proved to be more favorable compared to tractors without cabins. Sound pressure levels at 4000 Hz center frequency was reduced 2–13 dB and 4–18 dB by using a field-installed cabin and an original cabin, respectively. The measured A-weighted equivalent sound pressure levels were compared to the threshold limit level, and was concluded that depending on the cabin types used, the operators could usually work from 4 to 6 h a day without suffering from noise induced inconveniences while 2–3 h is permissible for plowing and forage harvesting on tractors without cabins. Due to timeliness considerations in agricultural machine operations, a farmer would not be willing to interrupt the operation based on permissible exposure time set by the standards. Based on the findings of this study, particularly an original cabin is recommended to reduce machine-induced noise below the danger limit during agricultural machine operations. Personal protection devices should be used when tractors are operated without cabins, which could reduce A-weighted equivalent sound pressure levels by 10–45 dB(A).

Implicit Element Clustering for Tetrahedral Transmission-Line Modeling (TLM)

Time-domain electromagnetic simulations employing unstructured tetrahedral meshes can be sensitive to local mesh characteristics. In particular, the maximum permissible time step for stable operation can be unacceptably small. In this paper, a cell clustering technique is described for the transmission line modeling algorithm that reduces the sensitivity to local mesh characteristics and permits substantial increases in time step to be made without compromising accuracy or stability.

The effect of diaphragm opening time on the feasibility of tuned operation in free piston shock tunnels

The effect of diaphragm opening time on the feasibility of tuned operation is analyzed by parametric calculations. The effect on the duration of pressure holding is also investigated. Characteristic parameters are defined to show the effects of dimensions, operation conditions and diaphragm opening time. It is shown that diaphragm opening time needs to be less than a certain limit to achieve tuned operation. The limit depends on pressure at diaphragm rupture and the ratio of diameters between a downstream shock tube and a compression tube. The permissible diaphragm opening time is also proportional to the length of the compression tube. The existence of the limit required for tuned operation is shown to be caused by the increase of pressure in the driver gas during the diaphragm opening. Moreover, the effect of diaphragm opening time on the duration of the pressure holding is shown to be weak once tuned operation becomes feasible.

A genotype-to-phenotype map of in vitro selected RNA-cleaving DNAzymes: implications for accessing the target phenotype

Herein, we describe a case study into the population dynamics of in vitro selection, using RNA-cleaving DNAzymes as a model system. We sought to understand how the composition of the population can change over time in response to different levels of selection pressure, and how well these changes are correlated with selection of the target phenotype. The model population is composed of 857 DNAzyme clones representing 215 discrete sequence classes, which had previously been identified from two parallel selection experiments, conducted under an increasingly stringent, or permissive and constant selection time pressure. In this report, we determined the principal phenotypic properties (i.e. kobs, maximum cleavage yield and PCR efficiency) from a sample of 58 clones representing 46 different major and minor sequence classes from various rounds of each selection experiment. Interestingly, a positive correlation between the catalytic rate constant and the corresponding frequency and temporal position of a given DNAzyme was not consistently observed; however, the strength of the correlation was qualitatively higher under conditions of more stringent selection time pressure. These results suggest that the selective sampling paradigm on which in vitro selection is based, may underestimate the true functional capacity of any given random-sequence library.

In vitro efficacy and risk for adverse effects of light-assisted tooth bleaching

The use of optical radiation in the so-called light-assisted tooth bleaching procedures has been suggested to enhance the oxidizing effect of the bleaching agent, hydrogen peroxide. Documentation is scarce on the potential adverse effects of bleaching products and on optical exposure risks to eyes and skin. The efficacy of seven bleaching products with or without simultaneous use of seven different bleaching lamps was investigated using extracted human teeth. The bleaching effect was determined immediately after treatment and one week later. Tooth surfaces were examined for adverse alterations after bleaching using a scanning electron microscope. Source characteristics of eight lamps intended for tooth bleaching were determined. International guidelines on optical radiation were used to assess eye and skin exposure hazards due to UV and visible light emission from the lamps. Inspection of teeth one week after bleaching showed no difference in efficacy between teeth bleached with or without irradiation for any of the products. Scratches, probably from the cleaning procedure were frequently seen on bleached enamel irrespective of irradiation. Maximum permissible exposure time (t(max)) and threshold limit values were exceeded for about half the bleaching lamps investigated. One lamp exceeded t(max) even for reflected blue light within the treatment time. This lamp also exceeded t(max) values for UV exposure. The lamps were classified as "low risk" and as borderline to "moderate risk" according to a relevant lamp standard.

A $Q$– $f$ Droop Curve for Facilitating Islanding Detection of Inverter-Based Distributed Generation

This paper presents a new method for islanding detection of distributed generation (DG) inverter that relies on analyzing the reactive power versus frequency (Q-f) characteristic of the DG and the islanded load. The proposed method is based on equipping the DG interface with a Q-f droop curve that forces the DG to lose its stable operation once an islanding condition occurs. A simple passive islanding detection scheme that relies on frequency relays can then be used to detect the moment of islanding. The performance of the proposed method is evaluated under the IEEE 1547 and UL 1741 antiislanding test configuration. The studies reported in this paper are based on time-domain simulations in the power systems computer-aided design (PSCAD)/EMTDC environment. The results show that the proposed technique has negligible nondetection zone and is capable of accurately detecting islanding within the standard permissible detection times. In addition, the technique proves to be robust under multiple-DG operation.

Quasi-synchronous Coherent Time-spreading Optical CDMA System using LA Sequence

We propose a novel quasi-synchronous coherent time-spreading optical CDMA (TS-OCDMA) system, where the synchronization among users can be controlled within permissible time delay. Relationship between the system performance and code parameters is analyzed. In quasi-synchronous coherent TS-OCDMA system, beat noise (BN) and multiple-access interference (MAI) are depend- ent on the mean intensity of aperiodic cross-correlation within permissible time delay. LA sequence is employed in this network, and code performance is analyzed. Within permissible time delay, the mean intensity of aperiodic cross-correlation equals zero, and hence the BN and MAI can be eliminated in quasi-synchronous coherent TS- OCDMA system. When the time delay is out of zero correlation zone, crosstalk value of LA sequence is less than that of Gold sequence. Therefore, quasi-synchronous coherent TS-OCDMA using LA sequence is beneficial in a low-user-load OCDMA network.

Effect of Temporary Overvoltages on Transmission Network Equipment

During abnormal conditions of under-frequency load shedding in the Powerlink Queensland high voltage network, it is possible that a temporary overvoltage (TOV) condition of from 1.15 p.u. up to 1.25 p.u. of the nominal voltage of275 kV could occur. Because this overvoltage exceeds the maximum continuous operating voltage of the network (300 kV), it raises concern about the withstand capability of the power transmission equipment. This paper describes the problem and the network conditions under which the TOV could occur. The paper also discusses the effect of this on transmission equipment and the time necessary to re-establish the voltage to normal levels. An investigation into the maximum permissible time that the high voltage equipment can withstand the TOV has been carried out. The withstand capability of high voltage equipment differs with the design characteristics and functions of the apparatus. Therefore a classification of sensitivity to TOVs for each type of equipment (transformers, switchgear, capacitor banks, etc.) can be made. Finally, possible solutions by which to mitigate the risk and consequences of TOVs in the network are discussed.

Utilizing Intraluminal Pressure Gradients to Predict Esophageal Clearance: A Validation Study

Esophageal bolus clearance requires a preferential esophagogastric pressure gradient sustained for a sufficient period. We aimed to validate a high-resolution manometry (HRM) paradigm for predicting bolus clearance. Twenty volunteers and 30 patients were studied with HRM during barium swallows with concurrent fluoroscopy. Simultaneous bolus domain pressure and esophagogastric junction (EGJ) obstruction pressure were plotted and flow permissive time was tallied during which the bolus domain pressure exceeded the EGJ obstruction pressure. Distal peristaltic integrity was assessed at incrementally increasing pressure isobaric contour thresholds from 15-40 mmHg. ROC analysis was performed to assess the sensitivity and specificity of cutoff values for flow permissive time and peristaltic amplitude for predicting incomplete clearance as verified fluoroscopically. Flow permissive time < or =2.5 s had a sensitivity of 86% and specificity of 92% for predicting incomplete clearance. In contrast, a 30-mmHg peristaltic amplitude had a sensitivity of only 48% and specificity of 88%. Incomplete clearance was variably attributable to functional EGJ obstruction, hiatus hernia, or impaired peristalsis. A detailed analysis of intraluminal pressure gradients in the distal esophagus and across the EGJ in the postdeglutitive period predicts esophageal bolus clearance with far greater accuracy than any threshold value of peristaltic amplitude.

A Nonlinear Distortion Compensation Method with Adaptive Predistorter and Negative Feed-Back for a Narrow-Band Signal

The adaptive predistorter and the negative feedback system are known as methods to compensate for the nonlinear distortion of a power amplifier. Although the feedback method is a simple technique, its instability impedes the capability of high-feedback gain to achieve a high-compensation effect. On the other hand, the predistorter requires a long time for convergence of the adaptive predistorters. In this paper, we propose a nonlinear distortion compensation method for a narrow-band signal. In this method, an adaptive predistorter and negative feedback are combined. In addition, to shorten the convergence time to minimize nonlinear distortion, a variable step-size (VS) method is also applied to the algorithm to determine the parameters of the adaptive predistorter. Using computer simulations, we show that the proposed scheme achieves both five times faster convergence speed than that of the predistorter and three times higher permissible delay time in the feedback amplifier than that of a negative feedback only amplifier.

Implicit Higher-Order Accuracy Method for Numerical Integration in Dynamic Analysis

New implicit higher-order accuracy (IHOA) time integration, which uses constant time step, is presented for dynamic analysis. By defining weighted factors, current displacement and velocity are assumed to be functions of the accelerations in the several previous time steps. Then, the optimum weighted factors are determined so that displacement and velocity errors in the Taylor series are minimized. The IHOA is conditionally stable and by using the Routh–Hurwitz criterion, permissible time step is obtained. For numerical verification of the proposed technique, some linear and nonlinear dynamic systems from finite element and finite difference will be analyzed and the results are compared with common implicit methods such as Newmark- β and Wilson- θ approach. Further, the dynamic relaxation method is applied to solve equivalent static systems, obtained in implicit algorithms. Results show that the proposed time integration is stable for common time steps and exhibits improved accuracy. The highly accurate, ...

Renal perfusion with venous blood extends the permissible suprarenal clamp time in abdominal aortic surgery

Suprarenal clamping in abdominal aortic surgery is associated with a significant risk of postoperative renal failure, general morbidity, and mortality. Arterial access for temporary shunting in these patients is difficult, and arterial perfusion techniques are typically complex. This study evaluated if renal perfusion with venous blood using a minimal pump setup and intermediate-level heparinization prevents a decline in postoperative renal function in patients requiring suprarenal clamping for aortic reconstructive surgery. Renal perfusion was achieved using a roller pump supplied with venous blood from a central venous catheter under medium-level heparinization to feed two perfusion balloon catheters. The calculated glomerular filtration rate was observed for 10 postoperative days and compared with the rate in patients with suprarenal clamping without renal perfusion. From 2001 to 2007, 158 patients underwent surgical reconstruction involving the pararenal aorta through a midline abdominal incision. Renal perfusion was started in 2006 and was always attempted if suprarenal clamping was anticipated preoperatively. Twenty-six patients received renal perfusion, and 132 also requiring suprarenal clamping did not. Of the latter, 109 were included in the control group. Five patients died <or=30 days (3.7%), one in the perfusion group. On average, there was a postoperative loss of renal performance in both groups. Dialysis was required postoperatively in 13 patients without renal perfusion, 4 of them long term (3.7%), but not in patients with renal perfusion. The reduction in glomerular filtration rate at 10 days in the nonperfused group was significantly higher than in the perfused group (7.24 vs 0.89 mL/min) despite a significantly longer suprarenal clamp time in the latter (25.5 vs 45.5 minutes). Multivariate analysis showed a significant reduction in the loss of glomerular filtration rate with perfusion (P = .007) if clamp time and preoperative renal function were taken into account. Patients with preoperative renal impairment showed the greatest benefit from the perfusion. The setup for renal perfusion with venous blood during suprarenal clamping was simple and safe. Perfusion significantly reduced the reduction of renal function in the immediate postoperative period, suggesting that clamp time may thus be safely be extended to allow for complex reconstruction of the pararenal aortic segment. The benefit was most marked for patients with preoperative renal impairment.

VAZÕES ESPECÍFICAS MÍNIMAS PARA SECAGEM DO MILHO COM AR NATURAL EM BOTUCATU-SP

Minimum airflow rates are recommended to ambient air grain drying to reduce fan power requirements and grain overdrying. Historical weather records from 1971 were selected to determine airflow rates for drying corn with ambient air in Botucatu, Sao Paulo State. 1971 was the poorest drying year in the 10-year period from 1971 through 1975 and l977 through 1981. In the simulation of ambient air corn drying initial moisture contents, wet basis used were 22%, 20% and 18% within allowable storage periods of 7, 11 and 29 days, respectively, for monthly average dry bulb temperature of 23.40C, the upmost in the 10-year period. The average dry bulb temperature and relative humidity were calculated from the hourly data recorded at the Faculdade de Ciencias Agronomicas, Botucatu county, Sao Paulo State, weather station. Due to impracticable continuous drying occurrence, only selective ambient air drying was considered, within daily periods from 9 a. m. to 5 p.m., 9 a. am. to 6 p.m. and 8 a.m. to 6 p.m. The simulation results showed that the minimum airflow rates decrease rapidly with decreasing grain equilibrium moisture content a few percentage points. Furthermore, the reduction in daily fan operation a few hours requires significant increases in minimum airflow rates to accomplish ambient air corn drying within the permissible storage time.

Utilizing intraluminal pressure differences to predict esophageal bolus flow dynamics

Successful esophageal emptying depends on the generation of a sustained intrabolus pressure (IBP) sufficient to overcome esophagogastric junction (EGJ) obstruction. Our aim was to develop a manometric analysis paradigm that describes the bolus driving pressure difference and the flow permissive time for esophageal bolus transit. Twenty normal subjects were studied with a 36-channel manometry assembly (1-cm spacing) during two 5- and one 10-ml barium swallows and concurrent fluoroscopy. Bolus domain pressure plots were generated by plotting bolus domain pressure (BDP) and EGJ relaxation pressure. BDP was defined as the pressure midway between the peristaltic ramp-up and the proximal margin of the EGJ. The flow permissive time was defined as the period where the BDP was > or = EGJ relaxation pressure. The mean BDP was 11.7 +/- 1.0 mmHg (SE), and the mean flow permissive time was 3.9 +/- 0.4 s for 5-ml swallows in normal controls. The mean BDP difference during flow was 4.0 +/- 1.0 mmHg. There was no significant difference in the fluoroscopic transit time and the flow permissive time calculated from the BDP plots (5 ml: fluoroscopy 3.4 +/- 0.2 s; BDP 3.9 +/- 0.4 s, P > 0.05). BDP plots provide a reliable measurement of IBP and its relationship with EGJ relaxation. The time available for flow can be readily delineated from this analysis, and the driving pressure responsible for flow can be accurately described and quantified. This may help predict abnormal bolus transit and the underlying mechanical properties of the EGJ.

EMF risk for operators mounting, adjusting and maintaining base stations

In the recent years concerns whether exposure to electromagnetic fields (EMF) from base station antennae can cause adverse health effects are grown. Great attention is paid on risk of EMF exposure to people living in a close proximity of base stations. In this issue, a point of interest is the personnel mounting, adjusting and maintaining base stations. Their working tasks require stay in high EMF levels’ conditions. There are only few studies concerning this specific occupational group. The results from our previous investigation (COST 281—Graz, 2006) show that in many cases on performing some specific tasks operators are overexposed according to our national legislation, and ICNIRP guidelines. Here, we present an extended study covering more base stations and more precise scenario for performed tasks and working positions. Results of exposure assessment are presented. They include energetic load calculations on the basis of Bulgarian national legislation, and the corresponding SAR values. Data are used to determine permissible time duration for each particular work operation and served as a base for limiting the exposure and proposal for protective measures for the personnel.

Needs of communications with general public about the potential risk of electromagnetic fields and methods for achieving this goal

In the recent years concerns whether exposure to electromagnetic fields (EMF) from base station antennae can cause adverse health effects are grown. Great attention is paid on risk of EMF exposure to people living in a close proximity of base stations. In this issue, a point of interest is the personnel mounting, adjusting and maintaining base stations. Their working tasks require stay in high EMF levels’ conditions. There are only few studies concerning this specific occupational group. The results from our previous investigation (Zaryabova and Israel 2006) show that in␣many cases on performing some specific tasks operators are overexposed according to our national legislation, and ICNIRP guidelines. Here, we present an extended study covering more base stations and more precise scenario for performed tasks and working positions. Results of exposure assessment are presented. They include energetic load calculations on the basis of Bulgarian national legislation, and the corresponding SAR values. Data are used to determine permissible time duration for each particular work operation and served as a base for limiting the exposure and proposal for protective measures for the personnel.

Accelerating the molecular time steps for nanomechanical simulations: Hybrid Monte Carlo method

A majority of computational mechanical analyses of nanocrystalline materials or nanowires have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at a time scale of the order of microseconds in a reasonable computing time. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed during experiments. In this investigation, a modified hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain-rate-dependent) atomistic mechanical deformation of nanostructures at higher time scales than currently possible using MD is established for a Cu nanowire and for a nanocrystalline Ni sample. In this method, there is no restriction on the size of MD time step except that it must ensure a reasonable acceptance rate between consecutive Monte Carlo (MC) steps. In order to establish the method, HMC analyses of a Cu nanowire deformation at two different strain rates, viz., 108 and 109 s−1, and of a nanocrystalline Ni sample deformation at a strain rate of 109 s−1 with three different time steps, viz., 2, 4, and 8 fs, are compared with the analyses based on MD simulations at the same strain rates and with a MD time step of 2 fs. MD simulations of the Cu nanowire as well as nanocrystalline Ni deformations reproduce the defect nucleation and propagation results as well as strength values reported in the literature. Defect formation and stress-strain responses of the Cu nanowire, as well as of the nanocrystalline Ni sample during HMC simulations with a time step of 8 fs, are similar to that observed in the case of MD simulations with the maximum permissible time step of 2 fs (for the interatomic potential used, 2 fs is the highest MD time step). Simulation time analyses show that by using HMC approximately 4 times saving in computational time can be achieved bringing the atomistic analyses closer to the continuum time scales.

UVR MEASUREMENT OF A UV GERMICIDAL LAMP

Ultraviolet radiation (UVR) exposure is known to cause serious effects such as conjunctivitis and keratitis in eyes and erythema in skin. The exposure assessment of UVR has not been well established and developed in workplaces due to the lack of suitable UV detecting instruments. Therefore, UV monitoring and measuring procedures were investigated and developed with commercial spectroradiometry devices described in this paper. The UVR irradiance integrated with a biological effective parameter (S lambda) represents the impacts on human skin and eyes as UV effective irradiance. The spectral weighting function derived from the American Conference of Governmental Industrial Hygienists was applied and evaluated to indicate the degree of harmfulness of UVR as a function of wavelength. A portable UV germicidal lamp with short and long wavelengths (254 nm and 365 nm) served as the UVR emission source. The UVR photon count similar to the perceived brightness of a source, irradiance, and effective irradiance (E eff) of the germicidal lamp were measured and analyzed, then the permissible exposure times (T max) were derived for UVR exposure assessment. This monitoring provided a comprehensive approach to detecting UVR magnitude, evaluated the performance of the approach, and quantified the effective exposure based on measured data. From this study, the methodology of UV measurement was established and could be applied to further UVR exposure assessment in the workplace.