Strategies for a centralized single product multiclass M/G/1 make-to-stock queue

Make-to-stock queues are typically investigated in the M/M/1 settings. For centralized single-item systems with backlogs, the multilevel rationing (MR) policy is established as optimal and the strict priority (SP) policy is a practical compromise, balancing cost and ease of implementation. However, the optimal policy is unknown when service time is general, i.e., for M/G/1 queues. Dynamic programming, the tool commonly used to investigate the MR policy in make-to-stock queues, is less practical when service time is general. In this paper we focus on customer composition: the proportion of customers of each class to the total number of customers in the queue. We do so because the number of customers in M/G/1 queues is invariant for any nonidling and nonanticipating policy. To characterize customer composition, we consider a series of two-priority M/G/1 queues where the first service time in each busy period is different from standard service times, i.e., this first service time is exceptional. We characterize the required exceptional first service times and the exact solution of such queues. From our results, we derive the optimal cost and control for the MR and SP policies for M/G/1 make-to-stock queues

The relationship between religiosity with stress, anxiety, and depression among the students in Kurdistan University of Medical Sciences, Iran, 2017

BACKGROUND: Religion affects all aspects of the life. One of the most important aspects of human health is its mental health, and how it gets affected by stress, anxiety, and depression. The purpose of this study was to evaluate whether there was any relationship between religiosity with stress, anxiety, and depression among the students of Kurdistan University of Medical Sciences, Iran.METHODS: This cross-sectional study was conducted at Kurdistan University of Medical Sciences in 2017. The total number of 282 students were selected using a two-stage stratified sampling method to fulfill univariate religiosity questionnaire and Depression, Anxiety and Stress Scale-21 (DASS-21). All statistical analysis was performed using SPSS software.RESULTS: The mean age of participants was 22.34 ± 3.05 years. 70.9% of participants were women, and 92.2% were single. Out of four dimensions of religiosity, only ritual dimension was found to have a significant correlation with stress (P = 0.030). The correlation between other dimensions of religiosity (belief, emotional, and consequential (and aspects of mental health found to be not statistically significant (P > 0.050).CONCLUSION: Based on the findings of this study, religious activities can reduce the stress of individuals. Designing non-syllabus interventions is recommended in order to increase religious activities in order to improve students’ mental health

Uniform fractional part: a simple fast method for generating continuous random variates

A known theorem in probability is adopted and through a probabilistic approach, it is generalized to develop a method for generating random deviates from the distribution of any continuous random variable. This method, which may be considered as an approximate version of the Inverse Transform algorithm, takes two random numbers to generate a random deviate, while maintaining all the other advantages of the Inverse Transform method, such as the possibility of generating ordered as well as correlated deviates and being applicable to all density functions, regardless of their parameter value

Removal Efficiency of Electrochemical Process by Iron Oxide Nanoparticles Impregnated on Rod Carbon for Arsenite Anions in a High Ionic Strength Solution

The entry of heavy metals (e.g., arsenite anions) into water sources due to industrial and mining activities is considered a serious problem for the environment. Therefore, arsenite removal from polluted water has attracted the attention of researchers due to its toxic effects on human health. In the present study, the efficiency of the electrochemical (EC) purification of arsenite anions in a high ionic strength solution was investigated using a carbon electrode impregnated with iron oxide nanoparticles (NPs). These NPs were synthesized by the co-precipitation method and immediately impregnated on the carbon rod. Experiments were performed by two electrodes (carbon and carbon impregnated with NP electrode) in a 50 mL EC reactor. The effect of different parameters such as electrical current (0.1, 0.3, 0.5, 0.7, & 0.9 A), EC time (2, 5, 10, 15, and 20 minutes), pH (3, 5, 7, 9, & 11), and the initial concentrations of arsenite anion (2, 5, 10, 15 and 20 mg/L) was investigated on the removal efficiency to achieve the highest removal of arsenite anions. Arsenite anions (10 mg/L) were completely removed from the aqueous solution with an ionic strength of 0.141 M at an electrical current of 0.7 A, a pH of 8, and an EC time of 20 minutes. In addition, pH was the most effective parameter in removing arsenite anions from aqueous solution in the EC method. According to the results, EC treatment using an electrode impregnated with iron oxide NPs is highly efficient in removing arsenite anions from the contaminated water

Toksikopatološke promjene izazvane kombiniranom izloženosti buci i toluenu u novozelandskih bijelih kunića

Noise and toluene can have significant adverse effects on different systems in the human body, but little is known about their combination. The aim of this study was to see how their combined action reflects on serum levels of inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β), body weight, and pathological changes in the heart, lung, stomach, and spleen tissues. To do that we exposed New Zealand rabbits to 1000 mg/L toluene and 100 dB of white noise in a chamber specifically designed for the purpose over two consecutive weeks. Serum levels of TNF-α and IL-1β were measured with the enzyme-linked immunosorbent assay (ELISA), whereas Bax and Bcl-2 expressions in tissues were determined with real-time polymerase chain reaction (PCR). Noise and toluene changed TNF-α and IL-1β serum levels on different days following the end of exposure and significantly increased the Bax/Bcl-2 ratio in the lung and spleen. In addition, they induced different pathological changes in the heart, lung, spleen, and stomach tissues. This study has confirmed that exposure to noise and toluene can induce a range of toxicopathological changes, probably by inducing inflammatory pathways and apoptosis, but their combined effects look weaker than those of its components, although histopathological findings suggest the opposite.Buka i toluen mogu prouzročiti značajne štetne posljedice u različitim organskim sustavima u ljudi, ali je malo poznato kako djeluju zajedno. Stoga je cilj ovog istraživanja bio utvrditi kako izloženost njihovoj kombinaciji utječe na razine upalnih citokina u serumu [tumorskoga nekrotskog čimbenika alfa (TNF-α) i interleukina 1 beta (IL-1β)], na tjelesnu masu te na apoptotske i histopatološke promjene na srčanom, plućnom, želudčanom i slezenskom tkivu. U tu smo svrhu novozelandske kuniće izložili buci (100 dB) i/ili toluenu (1000 mg/L) u posebnoj komori u neprekidnom trajanju od dva tjedna. Razine TNF-α i IL-1β izmjerene su u 14 dana nakon svršetka izloženosti pomoću imunoenzimske metode ELISA, a ekspresije proteina Bax i Bcl-2 povezanih s apoptozom pomoću kvantitativne polimerazne lančane reakcije (engl. real-time polymerase chain reaction, PCR). Buka i toluen, zasebno i u kombinaciji, doveli su do različitih promjena razina TNF-α i IL-1β u serumu te značajno povećali omjer proteina Bax/Bcl-2 u plućima i slezeni. Usto su prouzročili različite patološke promjene u srčanom, plućnom, slezenskom i želučanom tkivu. Istraživanje je potvrdilo da izloženost buci i toluenu dovodi do cijelog niza toksikopatoloških promjena, vjerojatno tako što pokreće upalne putove i mehanizme apoptoze. Također se doima da kombinirana izloženost ima slabije djelovanje od djelovanja svake sastavnice zasebno, premda histopatološki nalazi upućuju na suprotno

Managing Inventory, Transportation and Location in a Supply Chain

We consider three problems on inventory, transportation and location in a supply chain. In Chapter 2, we study Multilevel Rationing (MR) and Strict Priority (SP) stock allocation policies for a centralized single product multi-class M/G/1 make-to-stock queueing systems. To obtain the total cost of the system under these policies, we introduce a new method called “customer composition”. Using this method, we focus on the proportion of customers of each class out of the total number of customers in the queue since the number of customers in M/G/1 queues is invariant for any non-idling and non-anticipating policy. We consider a series of two-priority M/G/1 queues with an exceptional service time in each busy period to characterize the customer composition. We derive closed form expressions for the costs of SP and MR policies using these results. In Chapter 3, we consider a two-echelon inventory system with a congested centralized production facility and several Distribution Centers (DCs). We assume that the production and transportation times are stochastic that are generally distributed, and customers arrive to each DC according to an independent Poisson process. Inventory at DCs is managed using the one-for-one replenishment policy. We use the customer composition approach to characterize the total inventory carrying and backlog costs of the system under the FCFS, SP and MR allocation policies at the warehouse. For the special case of exponentially distributed production and transportation times, we use the unit-flow method and derive closed form expressions for the optimal cost and base-stock level of the DCs. We numerically demonstrate that prioritization using either the SP or the MR policy could be very beneficial in comparison with the FCFS policy. In Chapter 4, we study a two-echelon supply chain with a set of suppliers, a set of retailers and a set of capacitated cross-docks which are to be established. The demand of the retailers could be satisfied from the suppliers through the cross-docks. The objective is to determine the number and location of cross-docks, the assignment of retailers to suppliers so that the total cost of pipeline and retailers’ inventory, transportation, and facility location is minimized. We formulate the problem as a non-linear mixed integer programming and derive several structural results for special cases of the problem. To solve the general problem, we show that it can be written as a cutting stock problem and develop a column generation algorithm to solve it. We investigate the efficiency of the proposed algorithm numerically.Ph