Wilkistar Otieno

Integrated location-inventory modelling under forward and reverse product flows in the used merchandise retail sector: A multi-echelon formulation

This study presents a joint three-echelon location inventory model for a donation-demand driven industry in which the main warehouse (MW), distribution centers (DC), retail stores (RS) and donation-only centers (ADCs) exist. This unique inventory-location problem involves demand and supply uncertainties, coverage radius limitations, service level requirements, and multiple products consideration. Each retailer has two classes of products flowing from the assigned DC due to demands minus donations occurring in that retailer. The proposed model simultaneously determines the number of DCs to open, DC locations, and assignments of retailers to the open DCs for particular product types. The objective is to minimize the total annual cost including: facility location costs, transportation costs, inventory costs, and the lost sale costs. Due to the complexity of the problem, the proposed model structure allows for relaxing complicating constraints through recourse to Lagrangian relaxation. The use of robust branch-cut and price heuristics solves the mixed integer nonlinear problem to obtain a lower bound and a distance-based heuristic to get an upper bound. We formulate essential features of this novel problem, solve several numerical example problems and evaluate solution performance. We believe this is a novel problem environment, and that this initial study extends integrated location-inventory modeling to a new context.

System availability under redundancy sharing of standby components

Conventional approaches to system availability assurance usually revolve around reliability-redundancy allocation and spare parts provisioning. This paper proposes a new scheme called redundancy sharing to enhance the availability of k-out-of-n:G systems. Under the new scheme, hot standby components in one system can be transferred to other systems for which the number of functional components drops below k. Although redundancy sharing is frequently practiced in private and defense industries, the underlying theory is rarely investigated in literature. This paper makes an early attempt to estimate the system availability considering redundancy sharing, and further discuss its potential benefits to the overall fleet availability. We strive to achieve two objectives: 1) estimating system availability by jointly considering redundancy sharing, redundancy allocation, and spare parts inventory; and 2) demonstrating the effectiveness and benefit of redundancy sharing in a variety of operating conditions. Continuous-time Markov model and multi-echelon inventory theory are employed to characterize the operation and maintenance of small and large fleets, respectively.

Assessing the impact of different auction-based CO 2 allowance allocation mechanisms

Auction based CO2 allowance allocation is a fundamental element of all cap-and-trade programs that are being discussed around the world. Multi-unit auctions usually follow a uniform or discriminatory pricing mechanism. Each of the auction mechanisms result in different strategic behavior by bidders. In this paper, we develop a game-theoretic model to assess the impact of these auction mechanisms on cap-and-trade and electricity markets. The game-theoretic model is solved using a nested two-stage diagonalization algorithm. The methodology is demonstrated on power network data from northern Illinois electricity market and results are discussed.

Impact of lightweight and conventional jackhammers on the operator

Jackhammer manufacturers have recently developed lightweight (45-60 lbs) jackhammers intended to reduce the required lifting and pushing forces during operation. However, the vibration characteristics of the lightweight jackhammers and their effect on muscle activity are currently unknown. The objective of this study was to compare the measured vibration and muscle activity between: (i) conventional (90 lb) and light weight (60 lb) jackhammers, (ii) different pavement type/thickness combinations, and (iii) pneumatic and hydraulic jackhammers. Five jackhammers were tested on 4 and 6 inch thick asphalt and concrete pavements by four experienced operators. Analysis of the results revealed that both weight classes averaged 9.7 m/s(2) at the 20 Hz weighted 1/3 octave band frequency, and the TLV of daily exposure for either weight class of jackhammer was less than 1.5 hours/per day. There was an approximately 33% difference in vibration measured on the hand of the operators due to pavement thickness, 30% due pavement type, and no difference due to power source. Conventional jackhammers overall produced higher muscle activity than lightweight jackhammers. Although selection of the correct jackhammer for the job involves many factors including pavement type and thickness, the results of this research can be used to assist in selecting the appropriate jackhammer.

Influence of Jackhammer Weight on Grip Pressure, Muscle Activity, and Hand–Arm Vibration of the Operator

OCCUPATIONAL APPLICATIONS The conventional (41 kg) jackhammer is most commonly used in construction, and it is widely believed that a lighter jackhammer would be less effective or unable to perform certain tasks. We compared the performance of two hammers (conventional and 35% lighter) at breaking a 15 cm reinforced concrete slab, and found that some trade-offs exist between the two. Benefits of using a 35% lighter tool were mainly in reduction of muscle activity, shorter lifts, and some reduction in grip pressure. However, the lighter tool resulted in an elevated vibration dose, mainly due to an increase in task time though there were no major changes in vibration magnitude measured on the hand. Based on these results, a lightweight jackhammer may be suitable for breaking a concrete slab, and could provide a two-fold reduction in low-back injury risk due to lifting, as well as allow a population with a larger range of strength and stature to perform this task. TECHNICAL ABSTRACT Background: Construction and utility workers traditionally use 40 kg jackhammers to break pavement, and this task involves exposures to several injury risk factors. Lighter jackhammers are not commonly utilized, as it is commonly believed that they would not be able to perform the task. While some preliminary research by our team has determined that lightweight jackhammers can perform the wide range of tasks required for breaking pavement, the benefits/limitations of using a lightweight jackhammer have not been fully explored. Purpose: To perform a biomechanical evaluation of and quantify the difference between operating a conventional and a lightweight jackhammer during the lifting and operating phases. Methods: Twelve volunteer jackhammer operators were instructed to break a 0.9 m × 0.9 m section of 15 cm thick reinforced concrete along pre-painted diagonal lines. Two pneumatic jackhammers were used: a lightweight jackhammer (27 kg) and conventional jackhammer (41 kg). Throughout each task, upper-body muscle activity, task time, grip pressure, and vibration magnitude and frequency were measured. Results: Using the lightweight jackhammer resulted in a 58% increase in task time and consequently resulted in increasing the partial vibration dose value by 36%. Nevertheless, 40% less muscle activity was required to lift the lighter jackhammer and 25% less upper-body muscle activity was used during the operational phase. Surprisingly, an inverse relationship was found between grip pressure and hand–arm vibration for both jackhammer weights. Conclusions: A reduction in jackhammer weight offers some potential biomechanical benefits to the operator, specifically reducing the overall muscular effort during task performance and up to two-fold reduction in muscular demands due to lifting, as well as a reduction in grip pressure. Potential adverse effects of the lightweight jackhammer are an increased task time and duration-adjusted vibration dose.

A Sensitivity Based Approach to Determining Non-Cooperative Solutions in Nash and Stackelberg Games

A sensitivity based approach is presented to determine Nash solution(s) in multiobjective problems modeled as a non-cooperative game. The proposed approach provides an approximation to the rational reaction set (RRS) for each player. An intersection of these sets yields the Nash solution for the game. An alternate approach for generating the RRS based on design of experiments (DOE) combined with response surface methodology (RSM) is also explored. The two approaches for generating RRS are compared on three example problems to find Nash and Stackelberg solutions. It is seen that the proposed sensitivity based approach (i) requires less computational effort than a RSM-DOE approach, (ii) is less prone to numerical errors than the RSM-DOE approach, (iii) is able to find all Nash solutions when the Nash solution is not a singleton, (iv) is able to approximate non linear RRS, and (v) is able to find better a Nash solution on an example problem than the one reported in the literature.Copyright

Environmental Analysis of Self-Lubricating Composites: A Review

Human activities have affected the balance in the eco-system and put the habitant surrounding us in a catastrophic danger. Most of these wrecking effects which had been strengthened or emerged recently would also last for a long period of time. Taking immediate thoughtful actions are necessary to prevent high risk human activities. Based on the data collected for global surface mean temperature and CO2 emission, it has been shown that a huge discrepancy in climate is already occurring. There are various reasons which are causing climate change, specifically global warming, which most of those would be discussed in this study. The negative effects of different materials on the eco-system have one of the biggest shares in environmental concerns. Emerging Eco-tribology science helped design products and processes for the environment. The design of products has been significantly modified to be more environmental friendly and sustainable. A brief review of tribology and different definitions, which had been changed during the time, will be discussed in this study. Furthermore, eco-tribology has a positive effect in reducing energy consumption and increasing the lifetime of the products. Lubricant is an example of the materials which produce environment destructive waste. In the recent decades, researchers improved the lubricant materials to be less destructive for the environment. Self-lubricant composites, for instance, significantly reduced the drawbacks of lubricant materials. The advantage is not only improving wear resistance and reduced COF, but also the elimination of the need for external lubricants. Aluminum/graphite (Al/Gr) composites have been used as self-lubricating materials due to the superior lubricating effect of graphite during sliding process. This study reviews the environmental concerns and advances of eco-tribological, lubricant and self-lubricant composites.

Quantitative and Qualitative Evaluation of the Lift-assist Device duringJackhammering Task

Background: Jackhammers are commonly used on construction sites, and their general use comes with several injury risks, especially focused on lifting the jackhammer. A Lift-assist (LA) device is available that is aimed at eliminating the risk to the user from lifting. However, to date no scientific study has been conducted to determine if the LA provides any benefits to the user. The goal of this study was to make quantitative comparisons and qualitative assessments of operating a jackhammer with and without a LA. Methods and findings: Eight experienced jackhammer operators broke a 0.9 × 0.9 m section of concrete with two different weights of jackhammers with and without a lift-assist. Muscle activity of the upper body was reduced (approx. 40%) during the lifting portion of the task when using the LA. The reduction of the muscle activity required to lift the jackhammer also enabled the subjects to retain a better posture throughout the lift. Additionally, grip pressure was reduced in the lifting portion of the task. While the LA reduced the time required to lift the jackhammer, no change in overall task completion time was observed due to large variations in the time effect of the lift-assist among subjects and the relatively minor contribution of lifting time to the total task time. A longer study that allowed subjects to better adapt to the LA might be required to assess potential effects on task efficiency. Overall the subjects perceived the LA to provide a benefit to the user during the jackhammer task, and reduced the physiological stress experienced by the operator during the lifting portion of the task. Conclusions: These results indicate that use of the LA can potentially translate to a reduction in lifting related injury risks to the operator.

Survey Based Assessment of Tethered Tool Usage in the Power GenerationIndustry and US Coast Guard

Abstract Background: Struck-by injuries and death caused by dropped objects continue to be a prevalent problem in industries where work is conducted at height. Securing objects from height with tethers, especially hand tools used to conduct work, and an increase in regulatory oversight would reduce these incidences. Currently no research on the multifaceted impact of tethered tool use exists, but they are necessary to maintaining safety while working at heights. Methods and findings: Due to the lack of information on tethered tool usage, it was necessary to develop and distribute a survey to gather data on tethered tool usage patterns, tool carrying methods, drop history and perceived risks while working at height. The survey was administered online for selected Wind Power Generation utilities as well as US Coast Guard employees. The majority (72.5%) of respondents used tethered tools as a general practice, while 27.5% of respondents did not. The frequency of usage was found to be correlated to the employee providing a tethered option for the tool. Other factors associated with increased tethered tool usage were: years of experience, increased perception of injury risk and having a history of dropping tools. Among two dozen tools identified by the users in both industries, the wrench, cordless drill, screwdriver, hammer and pliers were most frequently used and were also recommended for a tethered option while using them at heights. Conclusion: Employers and employees must be trained to understand the safety benefits of using tethered tools, and tool designers must fabricate tools to facilitate comfort and ease of use during work, without causing interference to worker performance. In addition, developing appropriate tether attachment points on commonly worn tool-carrying methods, such as vests, backpacks and tool belts is another consideration in tethered tool design. Ultimately, regulatory development on tethered tool standards should be undertaken to increase usage in the field.

Effects of selected wheel and caster fixture design on the push force: the case of four-wheeled industrial carts

The objective of this study was to determine the significance of the effects of wheel type and caster design on the applied force in pushing an industrial cart. A randomized complete mixed factor experiment was designed and performed, involving two levels of wheel design (split wheels and single wheel), two levels of caster fixture design (swivel-also known as the dual orbital off-set pivot caster and the non-swivel standard caster), two levels of weight (250 lbs. and 750 lbs.) and two wheel positions (all wheels aligned to the direction of travel and rear wheels perpendicular to the direction of travel). The results showed that though caster design did not significantly reduce the push force, the swivel offset-pivot design consistently reduced the push force applied when the rear wheels were perpendicular to the direction of travel. This effect was further impactful when the single wheel type was used. In addition, though the wheel type significantly affected the applied force with the single wheel design outperforming the dual wheel, the mean applied force difference between the two wheel types was not significant enough to warrant an investment into changing the wheel types in four-wheeled industrial carts.