Browsing by Subject "Machinery"

Now showing 1 - 9 of 9

Open Access
Customer order scheduling on a single machine with family setup times: complexity and algorithms
(Elsevier, 2007) Erel, E.; Ghosh, J. B.
We consider a situation where C customers each order various quantities (possibly zero in some cases) of products from P different families, which can be produced on a continuously available machine in any sequence (requiring a setup whenever production switches from one family to another). We assume that the time needed for a setup depends only on the family to be produced immediately after it, and we follow the item availability model (which implies that all units are ready for dispatch as soon as they are produced). However, an order is shipped only when all units required by a customer are ready. The time from the start (time zero) to the completion of a customer order is called the order lead time. The problem, which restates the original description of the customer order scheduling problem, entails finding a production schedule that will minimize the total order lead time. While this problem has received some attention in the literature, its complexity status has remained vexingly open. In this note, we show for the first time that the problem is strongly NP-hard. We proceed to give dynamic programming based exact solution algorithms for the general problem and a special case (where C is fixed). These algorithms allow us to solve small instances of the problem and understand the problem complexity more fully. In particular, the solution of the special case shows that the problem is solvable in polynomial time when C is fixed.
Open Access
Generating robust and stable schedules in a single machine environment
(IIE, 2004) Gören, Selçuk; Sabuncuoğlu, İhsan
Scheduling is a decision making process that concerns with allocation of limited resources (machines, material handling equipment, operators, tools, etc.) to competing tasks (operations of jobs) over time with the goal of optimizing one or more objectives. The output of this process is time/machine/operation assignments. In the scheduling theory, the objective is generally to optimize one or more regular performance measures such as makespan, flow-time, and tardiness. Recently, two new measures have been also used in scheduling applications: "robustness" and "stability". In this paper, we develop a new surrogate measure to achieve robustness and stability. This measure is embedded in a tabu search algorithm to generate schedules in a single machine environment subject to random machine breakdowns. The results of extensive computational experiments indicate that the proposed method performs better than the average slack method used in the literature.
Open Access
Genetically encoded conductive protein nanofibers secreted by engineered cells
(Royal Society of Chemistry, 2017-06) Kalyoncu, E.; Ahan, R. E.; Olmez, T. T.; Safak Seker, U. O.
Bacterial biofilms are promising tools for functional applications as bionanomaterials. They are synthesized by well-defined machinery, readily form fiber networks covering large areas, and can be engineered for different functionalities. In this work, bacterial biofilms have been engineered for use as conductive biopolymers to interface with electrodes and connect bacterial populations to electronic gadgets. Bacterial biofilms are designed with different conductive peptide motifs, as the aromatic amino acid content of fused peptide motifs has been suggested to contribute to electronic conductivity by influencing monomer stacking behavior. To select the best candidates for constructing conductive peptide motifs, conductivity properties of aromatic amino acids are measured using two different fiber scaffolds, an amyloid-like fiber (ALF) forming peptide, and the amyloidogenic R5T peptide of CsgA protein. Three repeats of aromatic amino acids are added to fiber-forming peptide sequences to produce delocalized π clouds similar to those observed in conductive polymers. Based on the measurements, tyrosine and tryptophan residues provide the highest conductivity. Therefore, the non-conductive E. coli biofilm is switched into a conductive form by genetically inserted conductive peptide motifs containing different combinations of tyrosine and tryptophan. Finally, synthetic biofilm biogenesis is achieved with conductive peptide motifs using controlled biofilm production. Conductive biofilms on living cells are formed for bioelectronics and biosensing applications.
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II. Dünya Savaşı sonrası Türkiye tarımında modernizasyonun ekonomiye ve istihdama etkisi
(Bilkent University, 2023) Tosun, Ahmet Emir; Say, Ege Barış; Özcan, Can; Köse, Ege Eren; Baydar, Yüksel Barkın
Günümüz tarımında birçok farklı modern teknik kullanılmaktadır ve bunlar yapılan tarımın verimliliğini arttırmaktadır. Tarımda yapılan bu makineleşme işlemleri Türkiye’de İkinci Dünya Savaşı’nın ardından gelen ekonomik ve politik sorunların etkisiyle başlamıştır ve her geçen yıl ile birlikte Türkiye ekonomisini ve Türk halkının istihdam durumunu doğrudan etkilemiştir. Bu araştırma sınırları dahilinde, 2. Dünya Savaşı sonrasında Türkiye’de uygulanmaya başlayan tarımda modernizasyonun ülkeye nasıl empoze edildiği incelenecek; bu gelişmelerin sonucu olarak ortaya çıkan tarımda modernizasyonun ülke ekonomisine ve istihdama katkısı değerlendirilecektir. Bu çalışma sonucunda tarımda makineleşmenin Türkiye Cumhuriyeti’ne olan etkilerinin anlaşılabilmesi hedeflenmektedir.
Open Access
An integrated process planning approach for CNC machine tools
(Springer-Verlag, 1996) Aktürk, M. S.; Avcı, S.
In view of the high investment and tooling cost of a CNC machining centre, the cutting and idle times should be optimised by considering the tool consumption and the non-machining time cost components. In this paper, we propose a detailed mathematical model for the operation of a CNC machine tool which includes the system characterisation, the cutting conditions and tool life relationship, and related constraints. This new module will be a part of an overall computer-aided process planning system to improve the system effectiveness and to provide consistent process plans. A hierarchical approach is presented for finding tool-operation assignments, machining conditions, appropriate tool magazine organisation and an operations sequence which results in the minimum production cost. © 1996 Springer-Verlag London Limited.
Open Access
A neural network model for scheduling problems
(Elsevier, 1996) Sabuncuoğlu, İ.; Gurgun, B.
Artificial neural networks (ANNs) have been successfully applied to solve a variety of problems. This paper proposes a new neural network approach to solve the single machine mean tardiness scheduling problem and the minimum makespan job shop scheduling problem. The proposed network combines the characteristics of neural networks and algorithmic approaches. The performance of the network is compared with the existing scheduling algorithms under various experimental conditions. A comprehensive bibliography is also provided in the paper.
Open Access
New insights on the single machine total tardiness problem
(Palgrave Macmillan, 1997) Tansel, B. C.; Sabuncuoğlu, İ.
Virtually all algorithmic studies on the single machine total tardiness problem use Emmons' theorems that establish precedence relations between job pairs. In this paper, we investigate these theorems with a geometric viewpoint. This approach provides a compact way of representing Emmons' theorems and promotes better insights into dominance properties. We use these insights to differentiate between certain classes of easy and hard instances.
Open Access
Scheduling to minimize the coefficient of variation
(Elsevier, 1996) De, P.; Ghosh, J. B.; Wells, C. E.
In this paper, we address the problem of uninterruptedly scheduling a set of independent jobs that are ready at time zero with the objective of minimizing the coefficient of variation (CV) of their completion times. We first show that, for high processing time values of the longest job, a variance (V) minimizing schedule also minimizes CV. Using this equivalence, we next demonstrate the invalidity of an earlier conjecture about the structure of a CV-optimal schedule and proceed to establish the NP-hardness of the CV problem. Finally, drawing from our prior work on the V problem, we provide a pseudo-polynomial dynamic programming algorithm for the solution of the CV problem.
Open Access
Structural analysis of an InGaN/GaN based light emitting diode by X-ray diffraction
(Springer, 2009-04-18) Öztürk, M. K.; Hongbo, Y.; SarIkavak, B.; Korçak, S.; Özçelik, S.; Özbay, Ekmel
The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample.