Determining the Minimum Waiting Times in a Hybrid Flow Shop Using Simulation-Optimization Approach

Planning the order and size of batches is an extremely complex task especially if these tasks are related to production companies in a real environment. This research deals with the problem of determining the entry order and size of product batches in order to optimize inter-operational waits, in the form of waiting in queues for processing and waiting due to the setting-up of the workplace. In real environment, these waits represent a large share of the time spent in the production of a unit of product in a hybrid flow shop. This problem is almost impossible to be solved with analytical models because they may require many simplifying assumptions. Therefore, a simulation-optimization approach is used to solve this problem. Discrete event simulation allows greater flexibility in the representation of the real production system, while the integrated optimization tool, a genetic algorithm, serves to find the optimal solution relatively quickly. To ensure simpler production management, batch size is defined as a fixed value with the exception of a different first or last batch which represents the difference to the required production volume. Therefore, two optimization cases are presented in the paper. Although both cases show improvements, the case when a different batch is the first batch shows better results. In that case, the share of setup time in the total production time of the product unit was reduced from 4% to 3%, and the share of waiting time in the queue for processing was reduced from 76% to 32%

Characterisation of polyamide (PA)12 nanocomposites with montmorillonite (MMT) filler clay used for the incremental forming of sheets

In this paper, the preparation and characterisation of polymer materials suitable for single point incremental forming (SPIF) technology were performed. Three different kinds of mixtures were selected: a mixture of neat polyamide 12 (PA12), a nanocomposite with PA12 matrix and 1% clay (Cloisite 93A), and a nanocomposite with PA12 matrix and 3% clay (Cloisite 93A). Materials were produced using a melt intercalation method followed by compression moulding. According to the needs of SPIF technology, morphological and mechanical properties were investigated in the obtained mixtures. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize morphological properties. It was determined that the most desired obtained exfoliated structure of clay in the polymer matrix was achieved. Static tensile testing and dynamic mechanical analysis as well as the determination of glass transition temperature and crystallinity of all analysed materials were used to obtain mechanical and thermal properties of the mixtures. The results obtained for each mixture were compared with respect to the content of clay. The content of clay (Cloisite 93A) showed a strong influence on the properties of the obtained materials. The presence of clay (Cloisite 93A) affected the increase of tensile strength and Young's modulus, while its influence on the attained elongation was not unique.Ministry of Education, Youth and Sports of the Czech Republic (Program NPU I) [LO1504]; Slovenian Research AgencySlovenian Research Agency - Slovenia [P2-0248]; University of Rijeka [Uniri-tehnic-18-100-589]; Tomas Bata University in Zlin RVO

Ground stone artefacts from Aria Babi

The Early Neolithic settlement at the site of Aria Babi (the Danube Gorges or Iron Gates area, northeastern Serbia) is chronologically contemporaneous with the Starčevo horizon at Lepenski Vir, and it is located in its immediate vicinity. Our analysis of the stone tools ncompassed the material from trench 1–2/2005, investigated in 2005 and 2006. Judging on the basis of the ground stone assemblage from this site, and with the same conclusion reached based on the ceramic analysis, a rural household was identified in this place, in a small settlement with ispersed dug-in features, typical of the Starčevo culture. In this household, the every-day life of the community was probably focused on farming. There were items found which were used for food preparation – aside from pottery, such as stone querns – but there were also tools and household items produced from materials softer than stone, such as wood and bone, which were not preserved. Various fragments of raw material, not so numerous in this assemblage, indirectly point to a small-scale ground stone tool production at this place. The secondary use of fragmented abrasive tools bears witness to, in most cases, expedient tools used by the inhabitants of this household. It is probable that in the mountainous hinterland of the Early Neolithic sites discovered along the Danube’s banks in this region existed smaller villages which provided both agricultural and perhaps also some artisanal products

Stable population structure in Europe since the Iron Age, despite high mobility

Ancient DNA research in the past decade has revealed that European population structure changed dramatically in the prehistoric period (14,000–3000 years before present, YBP), reflecting the widespread introduction of Neolithic farmer and Bronze Age Steppe ancestries. However, little is known about how population structure changed from the historical period onward (3000 YBP - present). To address this, we collected whole genomes from 204 individuals from Europe and the Mediterranean, many of which are the first historical period genomes from their region (e.g. Armenia and France). We found that most regions show remarkable inter-individual heterogeneity. At least 7% of historical individuals carry ancestry uncommon in the region where they were sampled, some indicating cross-Mediterranean contacts. Despite this high level of mobility, overall population structure across western Eurasia is relatively stable through the historical period up to the present, mirroring geography. We show that, under standard population genetics models with local panmixia, the observed level of dispersal would lead to a collapse of population structure. Persistent population structure thus suggests a lower effective migration rate than indicated by the observed dispersal. We hypothesize that this phenomenon can be explained by extensive transient dispersal arising from drastically improved transportation networks and the Roman Empire’s mobilization of people for trade, labor, and military. This work highlights the utility of ancient DNA in elucidating finer scale human population dynamics in recent history

Analysis of technological parameters and deformation of polymer nanocomposites sheets during single point incremental forming process. : Doctoral dissertation

Proteklih godina, nekoliko inovativnih postupka oblikovanja deformiranjem je razvijeno s ciljem proizvodnje visoko individualiziranih proizvoda s razumnim troškovima proizvodnje. Inkrementalno oblikovanje ploča (engl. Incremental Sheet Forming – ISF) predstavlja jednu od tih novih tehnologija koja je postala fokusom interesa mnogih znanstvenika i znanstvenih institucija. Inkrementalno oblikovanje u jednoj točki (engl. Single Point Incremental Forming – SPIF) je jedan od postupaka inkrementalnog oblikovanja ploča. Navedeni postupak se u početku primjenjivao prilikom oblikovanja limova, a zadnjih nekoliko godina i na polimernim pločama. U ovoj doktorskoj disertaciji postupak inkrementalnog oblikovanja u jednoj točki po prvi puta je uspješno primijenjen na polimernim nanokompozitnim pločama s matricom od poliamida 12 (PA12) koja je ojačana punilom od nanogline. Planiranje eksperimenta je izvršeno prema Taguchijevu planu pokusa. Izvedeno je ispitivanje temperatura, sila i deformacija tijekom SPIF procesa oblikovanja. Primjenom ANOVA metode analizirani su dobiveni rezultati te su utvrđeni utjecajni tehnološki parametri procesa. Provedena je optimizacija tehnoloških parametara obzirom na oblikovljivost s ciljem povećanja stabilnosti i upravljivosti procesa oblikovanja. Kao referentna vrijednost prilikom analize i optimizacije ključnih parametara procesa inkrementalnog oblikovanja u jednoj točki, temperature, sile i deformacije, polimernih nanokompozitnih ploča poslužio je istoimeni polimer bez nanoojačala. Provedena su mehanička ispitivanja polimernih ploča te njihova morfološka i strukturna karakterizacija. Ovaj rad daje značajan znanstveni doprinos istraživanju nekonvencionalnih postupka oblikovanja, odnosno inkrementalnom oblikovanju u području polimernih nanokompozitnih ploča.In the last years, several innovative forming processes have been developed to produce highly individualized products at reasonable cost of production. Incremental Sheet Forming (ISF) represents one of these modern technologies that has become the focus of interest of many scientists and scientific institutions. Single Point Incremental Forming (SPIF) is one of the methods of Incremental Sheet Forming. The above procedure was initially used in forming sheet metal, and in the last few years it has been applied to polymer sheets. In this doctoral thesis, the single point incremental forming has been successfully applied for the first time on polymer nanocomposite sheets with polyamide 12 (PA12) matrix and nanoclay filler. Design of experiment was done according to the Taguchi experimental design. Temperature, force, and deformation tests were performed during the SPIF forming process. Using the ANOVA method, the results were analysed, and influential technological parameters of the process were determined. Optimization of technological parameters with respect to formability was carried out with the aim of increasing the stability and controllability of the forming process. As a reference value in the analysis and optimization of key parameters of the process of single point incremental forming, temperature, force, and deformation of polymer nanocomposite sheets, the homonymous polymer without nano reinforcement was used. Mechanical tests of polymer sheets and their morphological and structural characterization were carried out. This dissertation provides a significant scientific contribution to the research of unconventional forming process or incremental forming of polymeric nanocomposite sheets

Characterisation of Polyamide (PA)12 Nanocomposites with Montmorillonite (MMT) Filler Clay Used for the Incremental Forming of Sheets

In this paper, the preparation and characterisation of polymer materials suitable for single point incremental forming (SPIF) technology were performed. Three different kinds of mixtures were selected: a mixture of neat polyamide 12 (PA12), a nanocomposite with PA12 matrix and 1% clay (Cloisite 93A), and a nanocomposite with PA12 matrix and 3% clay (Cloisite 93A). Materials were produced using a melt intercalation method followed by compression moulding. According to the needs of SPIF technology, morphological and mechanical properties were investigated in the obtained mixtures. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize morphological properties. It was determined that the most desired obtained exfoliated structure of clay in the polymer matrix was achieved. Static tensile testing and dynamic mechanical analysis as well as the determination of glass transition temperature and crystallinity of all analysed materials were used to obtain mechanical and thermal properties of the mixtures. The results obtained for each mixture were compared with respect to the content of clay. The content of clay (Cloisite 93A) showed a strong influence on the properties of the obtained materials. The presence of clay (Cloisite 93A) affected the increase of tensile strength and Young’s modulus, while its influence on the attained elongation was not unique

Analysis of technological parameters and deformation of polymer nanocomposites sheets during single point incremental forming process. : Doctoral dissertation

Proteklih godina, nekoliko inovativnih postupka oblikovanja deformiranjem je razvijeno s ciljem proizvodnje visoko individualiziranih proizvoda s razumnim troškovima proizvodnje. Inkrementalno oblikovanje ploča (engl. Incremental Sheet Forming – ISF) predstavlja jednu od tih novih tehnologija koja je postala fokusom interesa mnogih znanstvenika i znanstvenih institucija. Inkrementalno oblikovanje u jednoj točki (engl. Single Point Incremental Forming – SPIF) je jedan od postupaka inkrementalnog oblikovanja ploča. Navedeni postupak se u početku primjenjivao prilikom oblikovanja limova, a zadnjih nekoliko godina i na polimernim pločama. U ovoj doktorskoj disertaciji postupak inkrementalnog oblikovanja u jednoj točki po prvi puta je uspješno primijenjen na polimernim nanokompozitnim pločama s matricom od poliamida 12 (PA12) koja je ojačana punilom od nanogline. Planiranje eksperimenta je izvršeno prema Taguchijevu planu pokusa. Izvedeno je ispitivanje temperatura, sila i deformacija tijekom SPIF procesa oblikovanja. Primjenom ANOVA metode analizirani su dobiveni rezultati te su utvrđeni utjecajni tehnološki parametri procesa. Provedena je optimizacija tehnoloških parametara obzirom na oblikovljivost s ciljem povećanja stabilnosti i upravljivosti procesa oblikovanja. Kao referentna vrijednost prilikom analize i optimizacije ključnih parametara procesa inkrementalnog oblikovanja u jednoj točki, temperature, sile i deformacije, polimernih nanokompozitnih ploča poslužio je istoimeni polimer bez nanoojačala. Provedena su mehanička ispitivanja polimernih ploča te njihova morfološka i strukturna karakterizacija. Ovaj rad daje značajan znanstveni doprinos istraživanju nekonvencionalnih postupka oblikovanja, odnosno inkrementalnom oblikovanju u području polimernih nanokompozitnih ploča.In the last years, several innovative forming processes have been developed to produce highly individualized products at reasonable cost of production. Incremental Sheet Forming (ISF) represents one of these modern technologies that has become the focus of interest of many scientists and scientific institutions. Single Point Incremental Forming (SPIF) is one of the methods of Incremental Sheet Forming. The above procedure was initially used in forming sheet metal, and in the last few years it has been applied to polymer sheets. In this doctoral thesis, the single point incremental forming has been successfully applied for the first time on polymer nanocomposite sheets with polyamide 12 (PA12) matrix and nanoclay filler. Design of experiment was done according to the Taguchi experimental design. Temperature, force, and deformation tests were performed during the SPIF forming process. Using the ANOVA method, the results were analysed, and influential technological parameters of the process were determined. Optimization of technological parameters with respect to formability was carried out with the aim of increasing the stability and controllability of the forming process. As a reference value in the analysis and optimization of key parameters of the process of single point incremental forming, temperature, force, and deformation of polymer nanocomposite sheets, the homonymous polymer without nano reinforcement was used. Mechanical tests of polymer sheets and their morphological and structural characterization were carried out. This dissertation provides a significant scientific contribution to the research of unconventional forming process or incremental forming of polymeric nanocomposite sheets

Analysis of technological parameters and deformation of polymer nanocomposites sheets during single point incremental forming process. : Doctoral dissertation

Proteklih godina, nekoliko inovativnih postupka oblikovanja deformiranjem je razvijeno s ciljem proizvodnje visoko individualiziranih proizvoda s razumnim troškovima proizvodnje. Inkrementalno oblikovanje ploča (engl. Incremental Sheet Forming – ISF) predstavlja jednu od tih novih tehnologija koja je postala fokusom interesa mnogih znanstvenika i znanstvenih institucija. Inkrementalno oblikovanje u jednoj točki (engl. Single Point Incremental Forming – SPIF) je jedan od postupaka inkrementalnog oblikovanja ploča. Navedeni postupak se u početku primjenjivao prilikom oblikovanja limova, a zadnjih nekoliko godina i na polimernim pločama. U ovoj doktorskoj disertaciji postupak inkrementalnog oblikovanja u jednoj točki po prvi puta je uspješno primijenjen na polimernim nanokompozitnim pločama s matricom od poliamida 12 (PA12) koja je ojačana punilom od nanogline. Planiranje eksperimenta je izvršeno prema Taguchijevu planu pokusa. Izvedeno je ispitivanje temperatura, sila i deformacija tijekom SPIF procesa oblikovanja. Primjenom ANOVA metode analizirani su dobiveni rezultati te su utvrđeni utjecajni tehnološki parametri procesa. Provedena je optimizacija tehnoloških parametara obzirom na oblikovljivost s ciljem povećanja stabilnosti i upravljivosti procesa oblikovanja. Kao referentna vrijednost prilikom analize i optimizacije ključnih parametara procesa inkrementalnog oblikovanja u jednoj točki, temperature, sile i deformacije, polimernih nanokompozitnih ploča poslužio je istoimeni polimer bez nanoojačala. Provedena su mehanička ispitivanja polimernih ploča te njihova morfološka i strukturna karakterizacija. Ovaj rad daje značajan znanstveni doprinos istraživanju nekonvencionalnih postupka oblikovanja, odnosno inkrementalnom oblikovanju u području polimernih nanokompozitnih ploča.In the last years, several innovative forming processes have been developed to produce highly individualized products at reasonable cost of production. Incremental Sheet Forming (ISF) represents one of these modern technologies that has become the focus of interest of many scientists and scientific institutions. Single Point Incremental Forming (SPIF) is one of the methods of Incremental Sheet Forming. The above procedure was initially used in forming sheet metal, and in the last few years it has been applied to polymer sheets. In this doctoral thesis, the single point incremental forming has been successfully applied for the first time on polymer nanocomposite sheets with polyamide 12 (PA12) matrix and nanoclay filler. Design of experiment was done according to the Taguchi experimental design. Temperature, force, and deformation tests were performed during the SPIF forming process. Using the ANOVA method, the results were analysed, and influential technological parameters of the process were determined. Optimization of technological parameters with respect to formability was carried out with the aim of increasing the stability and controllability of the forming process. As a reference value in the analysis and optimization of key parameters of the process of single point incremental forming, temperature, force, and deformation of polymer nanocomposite sheets, the homonymous polymer without nano reinforcement was used. Mechanical tests of polymer sheets and their morphological and structural characterization were carried out. This dissertation provides a significant scientific contribution to the research of unconventional forming process or incremental forming of polymeric nanocomposite sheets

The Effect of Intra-articular Injection of Autologous Microfragmented Fat Tissue on Proteoglycan Synthesis in Patients with Knee Osteoarthritis

Osteoarthritis (OA) is one of the leading musculoskeletal disorders in the adult population. It is associated with cartilage damage triggered by the deterioration of the extracellular matrix tissue. The present study explores the effect of intra-articular injection of autologous microfragmented adipose tissue to host chondrocytes and cartilage proteoglycans in patients with knee OA. A prospective, non-randomized, interventional, single-center, open-label clinical trial was conducted from January 2016 to April 2017. A total of 17 patients were enrolled in the study, and 32 knees with osteoarthritis were assessed. Surgical intervention (lipoaspiration) followed by tissue processing and intra-articular injection of the final microfragmented adipose tissue product into the affected knee(s) was performed in all patients. Patients were assessed for visual analogue scale (VAS), delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) and immunoglobulin G (IgG) glycans at the baseline, three, six and 12 months after the treatment. Magnetic resonance sequence in dGEMRIC due to infiltration of the anionic, negatively charged contrast gadopentetate dimeglumine (Gd-DTPA2−) into the cartilage indicated that the contents of cartilage glycosaminoglycans significantly increased in specific areas of the treated knee joint. In addition, dGEMRIC consequently reflected subsequent changes in the mechanical axis of the lower extremities. The results of our study indicate that the use of autologous and microfragmented adipose tissue in patients with knee OA (measured by dGEMRIC MRI) increased glycosaminoglycan (GAG) content in hyaline cartilage, which is in line with observed VAS and clinical results