试析大学生校外兼职现象

大学生校外兼职是高校长期存在的一个普遍现象。其动机,或是想减轻家庭经济负担;或是想体验社会角色、积累社会经验;或是想在实践中提高自身的专业素质,以增强就业竞争力,等等。当前,在大学生校外兼职过程中存在着盲目跟风和缺乏自我保护意识等问题。对此,应加强教育引导;同时,健全相关法律法规,规范兼职市场行为。总之,只有为大学生打造一个良好的发展平台,才能促进其快速成长。     

Customer order scheduling to minimize the number of late jobs

In the order scheduling problem, every job (order) consists of several tasks (product items), each of which will be processed on a dedicated machine. The completion time of a job is defined as the time at which all its tasks are finished. Minimizing the number of late jobs was known to be strongly NP-hard. In this note, we show that no FPTAS exists for the two-machine, common due date case, unless P = NP. We design a heuristic algorithm and analyze its performance ratio for the unweighted case. An LP-based approximation algorithm is presented for the general multicover problem. The algorithm can be applied to the weighted version of the order scheduling problem with a common due date.     

Single-machine scheduling with convex resource dependent processing times and deteriorating jobs

In this study, we consider scheduling problems with convex resource dependent processing times and deteriorating jobs, in which the processing time of a job is a function of its starting time and its convex resource allocation. The objective is to find the optimal sequence of jobs and the optimal convex resource allocation separately. This paper focus on the single-machine problems with objectives of minimizing a cost function containing makespan, total completion time, total absolute differences in completion times and total resource cost, and a cost function containing makespan, total waiting time, total absolute differences in waiting times and total resource cost. It shows that the problems remain polynomially solvable under the proposed model.     

Scheduling problems with past-sequence-dependent setup times and general effects of deterioration and learning

In this paper we consider the single-machine setup times scheduling with general effects of deterioration and learning. By the general effects of deterioration and learning, we mean that the actual job processing time is a general function of the processing times of the jobs already processed and its scheduled position. The setup times are proportional to the length of the already processed jobs, i.e., the setup times are past-sequence-dependent (p-s-d). We show that the problems to minimize the makespan, the sum of the δ$\delta$th (δ>0$\delta >0$) power of job completion times, the total lateness are polynomially solvable. We also show that the total weighted completion time minimization problem, the discounted total weighted completion time minimization problem, the maximum lateness (tardiness) minimization problem, the total tardiness minimization problem can be solved in polynomial time under certain conditions.     

A Branch and Bound Algorithm to Minimize the Total Weighed Number of Tardy Jobs and Delivery Costs

This paper addresses the production and delivery scheduling integration problem; a manufacturer receives ₋ orders from one customer while the orders need to be processed on one or two machines and be sent to the customer in batches. Sending several jobs in batches will reduce the transportation cost but it may increase the number of tardy jobs. The objective is to minimize the sum of the total weighted number of tardy jobs and the delivery costs. The structural properties of the problem for a single machine and special cases of the two-machine flow shop problem are investigated and used to set up a new branch and bound algorithm. A heuristic algorithm for upper bound calculation and two approaches for lower bound calculation are also introduced. Results of computational tests show significant improvement over an existing dynamic programming method.     

Single-machine scheduling problems with an actual time-dependent deterioration

In this paper, we consider the single machine scheduling problems with an actual time-dependent deterioration effect. By the actual time-dependent deterioration effect, we mean that the processing time of a job is defined by increasing function of total actual processing time of jobs in front of it in the sequence. We show that even with the introduction of an actual time-dependent deterioration to job processing times, makespan minimization problem, total completion time minimization problem, the total lateness, and the sum of the quadratic job completion times minimization problem remain polynomially solvable, respectively. We also show that the total weighted completion time minimization problem, the discounted total weighted completion time minimization problem, the maximum lateness minimization problem, and the total tardiness minimization problem can be solved in polynomial time under certain conditions.     

Some scheduling problems with time-dependent learning effect and deteriorating jobs

Although machine scheduling problems with learning and deteriorating effects consideration have received increasing attention in the recent years, most studies have seldom considered the two phenomena simultaneously. However, learning and deteriorating effects might co-exist in many realistic scheduling situations. Thus, in this article, a model which takes the effects of time-dependent learning and deterioration simultaneously is proposed and applied into some scheduling problems. Under the proposed model, the processing time of a job is determined by a function of its corresponding starting time and positional sequence in each machine. We show that some single machine and flowshop scheduling problems are polynomially solvable with the certain performance measures such as makespan, total completion time, and weighted completion time.     

组数与组间刚度对成组叶盘振动局部化的影响

组数和组间刚度是影响成组叶盘振动特性的两个重要结构参数。本文基于成组叶盘的集中参数模型,推导了成组叶盘的振动方程,计算得到了不同组数和组间刚度下失谐成组叶盘的振动响应局部化因子,分析了组数和组间刚度对失谐成组叶盘的振动响应局部化的影响规律。结果表明:在叶片总数一定的情况下,随着叶片组数的减少,失谐成组叶盘的局部化程度明显降低;而随着组间刚度的增大,失谐成组叶盘的局部化程度先增大后减小,最终保持在相对稳定状态。研究结果可以为成组叶盘的优化设计提供一定的理论支持。     

高职院校机电专业职业能力强化训练的研究和实践探索

围绕高职院校机电专业学生的职业能力训练展开研究和探索,从能力体系、核心课程和工作岗位这三个方面展开论述,突出职业能力的强化训练培养体系,从而更好地服务于学生的就业需要,增强就业竞争力。     

具有共同松弛时间的恶化型工件排序问题研究

研究工件加工时间具有恶化效应的单机松弛工期排序问题.其中恶化效应指的是工件的实际加工时间是其开工时间的递增函数且所有工件的恶化率相同,工件的松弛工期等于其实际加工时间加上共同的松弛时间.目标是确定工件的一个排序和工件工期的共同松弛时间使得工件的提前时间、延迟时间和工期的共同松弛时间的线性加权和达到最小.用运筹学方法证明了该问题可以转化为两个向量的乘积问题,从而多项式时间可解,并给出了求解的最优算法.