The modular tool switching problem

This article analyzes the complexity of the modular tool switching problem arising in flexible manufacturing environments. A single, numerically controlled placement machine is equipped with an online tool magazine consisting of several changeable tool feeder modules. The modules can hold a number of tools necessary for the jobs. In addition to the online modules, there is a set of offline modules which can be changed to the machine during a job change. A number of jobs are processed by the machine, each job requiring a certain set of tools. The sequence of jobs is given as part of the input and fixed. Tools between jobs can be switched individually, or by replacing a whole module containing multiple tools. We consider the complexity of the problem of arranging tools into the modules, so that the work for module and tool loading is minimized. Tools are of uniform size and have unit loading costs. We show that the general problem is NP-hard, and in the case of fixed number of modules and fixed module capacity the problem is solvable in polynomial time.</p

Laaja-alaisen erityisopettajan ja luokanopettajan välinen yhteisopetus inklusiivisessa luokassa

Tiivistelmä. Tässä pro gradu -tutkielmassa on tarkoituksena selvittää laaja-alaisten erityisopettajien ja luokanopettajien kokemuksia heidän välisestä yhteisopetuksesta. Lisäksi tutkielmassa halutaan selvittää, mitkä tekijät opettajien mielestä voivat vaikuttaa toimivan yhteisopetuksen toteutumiseen. Nykyään yhteisopetus on yhä enemmän osana koulujen arkea, joten aihe on hyvin ajankohtainen ja tärkeä. Tutkielman teoreettisen viitekehyksen perustana on yhteisopetuksesta tehdyt tutkimukset sekä aiheesta tehty kirjallisuus. Viitekehyksen teoria pohjautuu tunnettuihin kansainvälisiin ja suomalaisiin teoksiin. Teoriaosassa paneudutaan inkluusioon ja kolmiportaiseen tukeen, jotka ovat osaltaan vaikuttaneet yhteisopetuksen toteutumiseen Suomessa. Lisäksi määritellään yhteisopetus ja sen erilaisia muotoja. Lopuksi tuodaan esille yhteisopetuksen hyötyjä niin opettajien kuin oppilaidenkin näkökulmasta katsoen, sekä haasteita ja edellytyksiä yhteisopetukselle. Tämä tutkielma on laadullinen tutkimus, joka on tehty teemahaastatteluilla. Tutkimuksen kohdejoukkona ovat laaja-alaiset erityisopettajat ja luokanopettajat, joita oli yhteensä kahdeksan. Tutkielmassa käsiteltiin opettajien kokemuksia ja käsityksiä, joten lähestymistapana tutkielmassa on käytetty fenomenologiaa. Tutkielmasta saadut tulokset on analysoitu aineistolähtöisen sisällönanalyysin keinoin. Saaduista tutkimustuloksista nousi esille, että laaja-alaiset erityisopettajat ja luokanopettajat kokivat yhteisopetuksen suurimmaksi osaksi positiivisena. Positiivisena yhteisopetuksesta nähtiin muun muassa opettajien kuormituksen jakaminen ja oppilaan tuen saaminen suoraan hänen omaan luokkaansa. Kuitenkin tuloksista ilmeni myös negatiivisia kokemuksia yhteisopetuksesta. Opettajat kokivat, että yhteisopetus on silloin haastavaa, mikäli opettajat olivat epätasa-arvoisessa roolissa toisiinsa nähden. Tutkimuksen tuloksista nousi esille useita eri tekijöitä, jotka voivat vaikuttaa yhteisopetuksen toteutumiseen. Vaikuttavimmat tekijät olivat resurssit, suunnittelu ja johdon tuki. Tuloksista voidaankin todeta, että yhteisopetuksesta on paljon hyötyjä, mutta tekijöitä sen toimivalle toteutumiselle on monia

Machine configuration and workload balancing of modular placement machines in multi-product PCB assembly

A popular gantry-type placement machine includes several interconnected, autonomously operating component placement modules and the machine was designed so as to able to use different kinds of placement heads and vacuum nozzles in the modules, which can be easily changed. Although this increases the flexibility of the production line, the reconfiguration phases of the modules may be unproductive and one should keep them to a minimum. In addition, the production times can be shortened by balancing the workloads of the machine modules. Here, a two-step optimisation method for the machine reconfiguration and workload balancing in the case of multiple Printed Circuit Borad (PCB) batches of different sizes and PCB types is presented. The objective is to minimise the total production time, and keep the machine configuration the same for all batches. The proposed algorithm is iterative and it applies integer programming for the workload balancing along with an evolutionary algorithm that searches for the best machine configuration. In experiments, for single PCB types the proposed algorithm obtained optimal or near optimal solutions. For multiple PCB types the solutions favour the PCB types that have a bigger production time due to greater batch sizes, but the total production time is still close to optimal.KEYWORDS: Printed circuit board, modular machines, machine configuration, mixed-model workload balancing, integer programing, genetic algorithm</a

Estimating the production time of a PCB assembly job without solving the optimised machine control

Production planning and control of the printed circuit board (PCB) assembly includes several decisions dealing with, for example, grouping of PCB jobs, allocation of PCB batches to machine lines, sequencing of batches and load balancing of lines. The production time of a PCB job for a given placement machine is a key factor in this context and it must be quickly and accurately estimated, possibly millions of times in a single planning task, to avoid erroneous decisions. The commonly used nominal tact time-based estimators are very rough and the machine simulators too slow. Therefore, the purpose of this study is to give better machine-specific estimators that avoid the construction the actual machine control program. Two new estimators are proposed for gantry machines, one based on the information given by the manufacturer about the operations of the placement head, and the other on the regularised least-squares regression method trained with a set of PCB placement jobs. In practical evaluation with 95 PCB jobs, the mean absolute percentage error of the first and second methods are 3.75% and 6.52%, respectively, while that of the tact time-based approach is more than 17%. This indicates a great potential of the proposed methods as production time estimators.</p

Pripper: prediction of caspase cleavage sites from whole proteomes

Peer reviewe

Childhood risk factors and carotid atherosclerotic plaque in adulthood : The Cardiovascular Risk in Young Finns Study

Background and aims: Carotid plaque is a specific sign of atherosclerosis and adults with carotid plaque are at increased risk for cardiovascular outcomes. Atherosclerosis has roots in childhood and pediatric guidelines provide cut-off values for cardiovascular risk factors. However, it is unknown whether these cut-offs predict adulthood advanced atherosclerosis. Methods: The Cardiovascular Risk in Young Finns Study is a follow-up of children that begun in 1980 when 2653 participants with data for the present analyses were aged 3-18 years. In 2001 and 2007 follow-ups, in addition to adulthood cardiovascular risk factors, carotid ultrasound data was collected. Long-term burden, as the area under the curve, was evaluated for childhood (6-18 years) risk factors. To study the associations of guideline-based cut-offs with carotid plaque, both childhood and adult risk factors were classified according to clinical practice guidelines. Results: Carotid plaque, defined as a focal structure of the arterial wall protruding into lumen > 50% compared to adjacent intima-media thickness, was present in 88 (3.3%) participants. Relative risk for carotid plaque, when adjusted for age and sex, was 3.03 (95% CI, 1.76-5.21) for childhood dyslipidemia, 1.51 (95% CI, 0.99-2.32) for childhood elevated systolic blood pressure, and 1.93 (95% CI, 1.26-2.94) for childhood smoking. Childhood dyslipidemia and smoking remained independent predictors of carotid plaque in models additionally adjusted for adult risk factors and family history of coronary heart disease. Carotid plaque was present in less than 1% of adults with no childhood risk factors. Conclusions: Findings reinforce childhood prevention efforts and demonstrate the utility of guideline-based cutoffs in identifying children at increased risk for adulthood atherosclerosis.Peer reviewe

Influence of early-life body mass index and systolic blood pressure on left ventricle in adulthood - the Cardiovascular Risk in Young Finns Study

BackgroundIncreased left ventricular mass (LVM) predicts cardiovascular events and mortality. The objective of this study was to determine whether early-life exposures to body mass index (BMI) and systolic blood pressure (SPB) affects the left ventricular structure in adulthood.MethodsWe used longitudinal data from a 31-year follow-up to examine the associations between early-life (between ages 6-18) BMI and SPB on LVM in an adult population (N = 1864, aged 34-49). The burden of early-life BMI and SBP was defined as area under the curve.ResultsAfter accounting for contemporary adult determinants of LVM, early-life BMI burden associated significantly with LVM (3.61 g/SD increase in early-life BMI; [1.94 - 5.28], p 25 kg/m2) associated with 4.7% (2.5-6.9%, p 30kg/m2) resulted in a 21% (17.3-32.9%, p ConclusionsHigh BMI in early-life confers a sustained effect on LVM and the risk for eccentric hypertrophy independently of adulthood risk factors.</p

Missing value imputation improves clustering and interpretation of gene expression microarray data

<p>Abstract</p> <p>Background</p> <p>Missing values frequently pose problems in gene expression microarray experiments as they can hinder downstream analysis of the datasets. While several missing value imputation approaches are available to the microarray users and new ones are constantly being developed, there is no general consensus on how to choose between the different methods since their performance seems to vary drastically depending on the dataset being used.</p> <p>Results</p> <p>We show that this discrepancy can mostly be attributed to the way in which imputation methods have traditionally been developed and evaluated. By comparing a number of advanced imputation methods on recent microarray datasets, we show that even when there are marked differences in the measurement-level imputation accuracies across the datasets, these differences become negligible when the methods are evaluated in terms of how well they can reproduce the original gene clusters or their biological interpretations. Regardless of the evaluation approach, however, imputation always gave better results than ignoring missing data points or replacing them with zeros or average values, emphasizing the continued importance of using more advanced imputation methods.</p> <p>Conclusion</p> <p>The results demonstrate that, while missing values are still severely complicating microarray data analysis, their impact on the discovery of biologically meaningful gene groups can – up to a certain degree – be reduced by using readily available and relatively fast imputation methods, such as the Bayesian Principal Components Algorithm (BPCA).</p

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