Used item replacement policy

1969 ◽  
Vol 6 (2) ◽  
pp. 309-318 ◽  
Author(s):  
B.R. Bhat
Keyword(s):  
Life Time ◽  
Replacement Policy ◽  
Exponential Distributions ◽  
The Difference ◽  
Negative Exponential

The block replacement policy, wherein items are replaced at regular intervals of time and on failure, is rather wasteful because sometimes almost new items are also removed. As an alternative a policy of replacement by new items at regular intervals of time and by used items on failure, is suggested. The consequences of this policy, called used item replacement policy, are studied for Erlangian and sub-exponential life-time distributions. The latter distribution which is the difference of two negative exponential distributions, does not seem to have received much attention in the literature so far.

Used item replacement policy

1969 ◽  
Vol 6 (02) ◽  
pp. 309-318 ◽  
Author(s):  
B.R. Bhat
Keyword(s):  
Life Time ◽  
Replacement Policy ◽  
Exponential Distributions ◽  
The Difference ◽  
Negative Exponential

The block replacement policy, wherein items are replaced at regular intervals of time and on failure, is rather wasteful because sometimes almost new items are also removed. As an alternative a policy of replacement by new items at regular intervals of time and by used items on failure, is suggested. The consequences of this policy, called used item replacement policy, are studied for Erlangian and sub-exponential life-time distributions. The latter distribution which is the difference of two negative exponential distributions, does not seem to have received much attention in the literature so far.

A semi-Markov storage model

1973 ◽  
Vol 5 (02) ◽  
pp. 362-378 ◽  
Author(s):  
Jerome Senturia ◽  
Prem S. Puri
Keyword(s):  
Asymptotic Behavior ◽  
Markov Process ◽  
Laplace Transforms ◽  
Exact Distribution ◽  
Exponential Distributions ◽  
Random Inputs ◽  
Storage Model ◽  
Semi Markov Process ◽  
Negative Exponential ◽  
Independent Identically Distributed

In this paper a storage model is described in which fluctuations in the content are governed by a sequence of independent identically distributed (i.i.d.) random inputs and i.i.d. random releases. This sequence proceeds according to an underlying semi-Markov process. Laplace transforms of the exact distribution of the content are given for the case of negative exponential distributions for both inputs and releases. Exact expressions for limiting (in time) content distributions are found. In the general case, the asymptotic behavior of the content is described for critical and supercritical limiting conditions.

Perspectives on the age and distribution of large wood in riparian carbon pools

2002 ◽  
Vol 59 (3) ◽  
pp. 578-585 ◽  
Author(s):  
Richard P Guyette ◽  
William G Cole ◽  
Daniel C Dey ◽  
Rose-Marie Muzika
Keyword(s):  
Woody Debris ◽  
Age Distribution ◽  
Terrestrial Ecosystems ◽  
Large Wood ◽  
Riparian Ecosystems ◽  
Riparian Areas ◽  
Exponential Distributions ◽  
Drainage Patterns ◽  
Order Of Magnitude ◽  
Negative Exponential

Most knowledge of carbon budgets is derived from the productivity and sequestration of carbon in terrestrial and marine ecosystems. Less is known of carbon stored in riparian areas associated with lakes and rivers. Case studies of the age distribution of carbon in aquatic large wood (Clw) from two different landscapes with different drainage patterns were established using tree-ring and 14C dating. Cumulative negative exponential distributions of the age of Clw ranged over periods from 1000 to 9485 years. Large woody debris had mean residence times of 261 years in small oligotrophic lakes and 350–800 years in a stream reach. Large wood can reside for an order of magnitude longer in freshwater–riparian ecosystems than in comparable above-ground terrestrial ecosystems. Although riparian areas make up only a small fraction of most landscapes, they may account for a relatively larger proportion of aged Clw than is stored above ground in terrestrial ecosystems.

Comparison of static and dynamic closed chambers for measurement of soil respiration under field conditions

1992 ◽  
Vol 72 (4) ◽  
pp. 605-609 ◽  
Author(s):  
P. Rochette ◽  
E. G. Gregorich ◽  
R. L. Desjardins
Keyword(s):  
Soil Respiration ◽  
Sandy Loam ◽  
Flux Measurement ◽  
Organic Soil ◽  
Exponential Model ◽  
Field Conditions ◽  
Parameter Estimates ◽  
Static Chamber ◽  
The Difference ◽  
Negative Exponential

The objective of this study was to compare the dynamic closed and static chamber techniques for the measurement of soil respiration under field conditions. The static chamber method consistently produced lower soil respiration values than did the dynamic closed system and the difference was larger at higher CO2 fluxes. A negative exponential model describes the relation between CO2 fluxes measured by both techniques. A good fit was obtained for measurements on a sandy loam soil (R2 = 0.61) and an organic soil (R2 = 0.74) but parameter estimates were different for each soil. Key words: Carbon dioxide, enclosure, gas flux measurement

Regenerative stochastic processes

1955 ◽  
Vol 232 (1188) ◽  
pp. 6-31 ◽  
Keyword(s):  
Central Limit Theorem ◽  
Limit Theorem ◽  
Probability Distribution ◽  
Stochastic Processes ◽  
Wide Class ◽  
Initial Conditions ◽  
Limiting Distribution ◽  
Regenerative Processes ◽  
Exponential Distributions ◽  
Negative Exponential

A wide class of stochastic processes, called regenerative, is defined, and it is shown that under general conditions the instantaneous probability distribution of such a process tends with time to a unique limiting distribution, whatever the initial conditions. The general results are then applied to 'S.M.-processes’, a generalization of Markov chains, and it is shown that the limiting distribution of the process may always be obtained by assuming negative exponential distributions for the ‘waits’ in the different ‘states’. Lastly, the behaviour of integrals of regenerative processes is considered and, amongst other results, an ergodic and a multi-dimensional central limit theorem are proved.

Modelling DCD effect on nitrate leaching under controlled conditions

Soil Research ◽  
2007 ◽  
Vol 45 (4) ◽  
pp. 310 ◽  
Author(s):  
Iris Vogeler ◽  
Adeline Blard ◽  
Nanthi Bolan
Keyword(s):  
Nitrate Leaching ◽  
Nitrification Inhibitor ◽  
Life Time ◽  
Potential Effect ◽  
Nitrification Rate ◽  
Nitrogen Transformations ◽  
Column Leaching ◽  
Loam Soil ◽  
Leaching Experiments ◽  
The Difference

Effects of nitrogen losses through nitrate leaching are one of the major environmental issues worldwide. To determine the potential effect of dicyandiamide (DCD), a nitrification inhibitor, on the transformation of urea nitrogen and subsequent nitrate leaching, incubation and column leaching experiments were performed. Tokomaru silt loam soil was treated with urea, DCD, or urea plus DCD. A control was also used. In the laboratory incubation experiment, the conversion of urea to ammonium (i.e. ammonification process or urea hydrolysis) occurred within a day, thereby increasing the soil pH from 5.8 to 6.9. DCD did not affect the ammonification process. However, DCD did slow down the subsequent oxidation of ammonium to nitrate (i.e. nitrification process). The half-life time of ammonium in this soil was increased from 9 days for the urea treatment to 31 days for the urea + DCD treatment. The production of nitrate was 5 times slower when DCD was added. In the leaching experiments, half the columns were leached after 1 day of incubation (Day 1), the other half 7 days later (Day 7). For Day 1, no significant differences in nitrate leaching could be seen between the treatments, as the nitrification had not yet taken place. For Day 7, DCD decreased nitrate leaching by 71% with a corresponding decrease in nitrate-induced cation leaching, including ammonium. Thus, DCD seems to be effective in decreasing both ammonium and nitrate leaching, but its high solubility and thus mobility could be a limitation to its use. The convection–dispersion equation, including source–sink terms for nitrogen transformations, ammonification, and nitrification rate constants, and a factor for nitrification inhibition by DCD, accounting for degradation and efficiency of DCD, could be used reasonably well to simulate nitrate leaching from the column leaching experiments. However, model parameter values for nitrification rate, and efficiency and decay rate for DCD, were different from those obtained from the incubation experiments, which was probably because of the difference in water content of soil between the incubation and leaching experiments.

scholarly journals Application of the Exponentiated Log-Logistic Weibull Distribution to Censored Data

2019 ◽  
pp. 12-19
Author(s):  
Adeniyi F. Fagbamigbe ◽  
Gomolemo K. Basele ◽  
Boikanyo Makubate ◽  
Broderick O. Oluyede
Keyword(s):  
Survival Analysis ◽  
Censored Data ◽  
Life Time ◽  
Parametric Model ◽  
Exponential Distributions ◽  
Wide Range ◽  
Competitive Model ◽  
Income Data ◽  
Censored Observations ◽  
Better Than

In a recent paper, a new model called the Exponentiated Log-Logistic Weibull (ELLoGW) distribution with applications to reliability, survival analysis and income data was proposed. In this study, we applied the recently developed ELLoGW model to a wide range of censored data. We found that the ELLoGW distribution is a very competitive model for describing censored observations in life-time reliability problems such as survival analysis. This work shows that in certain cases, the ELLoGW distribution performs better than other parametric model such as the Log-Logistic Weibull, Exponentiated Log-Logistic Exponential, Log-Logistic Exponential distributions and the non-nested Gamma-Dagum (GD).

scholarly journals ANALISIS KETAHANAN ABRASI MATERIAL OUTSOLE POLYURETHANE (PU) & NITRILE BUTADINE RUBBER (NBR) PADA SAFETY SHOES CHEETAH DI PT. X

2019 ◽  
Vol 13 (1) ◽  
pp. 26
Author(s):  
Suherna Suherna ◽  
Patunru P ◽  
Maspah Maspah
Keyword(s):  
Abrasion Resistance ◽  
Resistance Index ◽  
Life Time ◽  
Butadiene Rubber ◽  
Tolerance Limits ◽  
Operational Procedure ◽  
Nitrile Butadiene Rubber ◽  
Process Use ◽  
Maintenance Factors ◽  
The Difference

Improved quality, strength and life time in terms of abrasion resistance on safety shoes outsole Cheetah material where the process use of some material has decreased in quality, besides due to usage factors, maintenance factors, and some of these materials also experience problems during use. This study is done to determine the abrasion resistance of each Outsole Polyurethane (PU) material and Nitrile Butadiene Rubber (NBR). Abrasion resistance test on the material method used the DIN Abrasion tester. Retrieval of data on outsole material was carried out on the outsole material with new conditions and that has been used in the field for a period of 1 year with a method of measuring abrasion resistance index and density of material. Calculation of average abrasion resistance for new Polyurethane (PU) type was 37 , 11 mm3 / year, while the average abrasion resistance for Polyurethane (PU) type that has been used for 1 year was 33.19 mm3 / year so that the difference is 3.92 mm3 / year or about 11% quality decrease of abrasion resistance. The average abrasion resistance with the new Nitrile Butadiene Rubber (NBR) type was 108.26 mm3 / year, the average abrasion resistance for Nitrile Butadiene Rubber (NBR) type with conditions already used in 1 year period was 107.44 mm3 / year so that the difference is 0.82 mm3 / year or about 1% decrease in quality decrease of abrasion resistance. Abrasion tolerance limits that have been set according to the SOP (Standard Operational Procedure) against abrasion resistance if SG ≥ 0.9 then the Abrasive Max is 150 and if SG ≤ 0.9 Then the Abrasive Max is 250.

scholarly journals A New Mathematical Approach for the Estimation of epidemic Model Parameters with Demonstration on COVID-19 Pandemic in Libya

2020 ◽  
Author(s):  
Mohamed E Saleh ◽  
Zeinab Elmehdi Saleh
Keyword(s):  
Exponential Function ◽  
Epidemic Model ◽  
Model Parameters ◽  
Cumulative Number ◽  
Epidemic Spread ◽  
Exponential Distributions ◽  
Negative Exponential Function ◽  
Seir Model ◽  
Start Date ◽  
Negative Exponential

Background: The SEIR model or a variation of it is commonly used to study epidemic spread and make predictions on how it evolves. It is used to guide officials in their response to an epidemic. This research demonstrates an effective and simple approach that estimates the parameters of any variations of the SEIR model. This new technique will be demonstrated on the spread of COVID-19 in Libya. Methods: A five compartmental epidemic model is used to model the COVID-19 pandemic in Libya. Two sets of data are needed to evaluate the model parameters, the cumulative number of symptomatic cases and the total number of active cases. This data along with the assumption that the cumulative number of symptomatic cases grows exponentially, to determine most of the model parameters. Results: Libya epidemic start-date was estimated as t_o=-18.5 days, corresponding to May 5th. We mathematically demonstrated that the number of active cases follows two competing exponential distributions: a positive exponential function, measuring how many new cases are added, and a negative exponential function, measuring how many cases recovered. From this distribution we showed that the average recovery time is 48 days, and the incubation period is 15.2 days. Finally, the productive number was estimated as R0 = 7.6. Conclusions: With only the cumulative number of cases and the total number of active cases of COVID19, several important SEIR model parameters can be measured effectively. This approach can be applied for any infectious disease epidemic anywhere in the world.

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