Modeling and mitigation of supply-demand mismatches

In this thesis, I develop analytical models to price the value of supply chain investments under demand uncer¬tainty. This thesis includes three self-contained papers. In the first paper, we investigate the value of lead-time reduction under the risk of sudden and abnormal changes in demand forecasts. We first consider the risk of a complete and permanent loss of demand. We then provide a more general jump-diffusion model, where we add a compound Poisson process to a constant-volatility demand process to explore the impact of sudden changes in demand forecasts on the value of lead-time reduction. We use an Edgeworth series expansion to divide the lead-time cost into that arising from constant instantaneous volatility, and that arising from the risk of jumps. We show that the value of lead-time reduction increases substantially in the intensity and/or the magnitude of jumps. In the second paper, we analyze the value of quantity flexibility in the presence of supply-chain dis- intermediation problems. We use the multiplicative martingale model and the "contracts as reference points" theory to capture both positive and negative effects of quantity flexibility for the downstream level in a supply chain. We show that lead-time reduction reduces both supply-chain disintermediation problems and supply- demand mismatches. We furthermore analyze the impact of the supplier's cost structure on the profitability of quantity-flexibility contracts. When the supplier's initial investment cost is relatively low, supply-chain disin¬termediation risk becomes less important, and hence the contract becomes more profitable for the retailer. We also find that the supply-chain efficiency increases substantially with the supplier's ability to disintermediate the chain when the initial investment cost is relatively high. In the third paper, we investigate the value of dual sourcing for the products with heavy-tailed demand distributions. We apply extreme-value theory and analyze the effects of tail heaviness of demand distribution on the optimal dual-sourcing strategy. We find that the effects of tail heaviness depend on the characteristics of demand and profit parameters. When both the profit margin of the product and the cost differential between the suppliers are relatively high, it is optimal to buffer the mismatch risk by increasing both the inventory level and the responsive capacity as demand uncertainty increases. In that case, however, both the optimal inventory level and the optimal responsive capacity decrease as the tail of demand becomes heavier. When the profit margin of the product is relatively high, and the cost differential between the suppliers is relatively low, it is optimal to buffer the mismatch risk by increasing the responsive capacity and reducing the inventory level as the demand uncertainty increases. In that case, how¬ever, it is optimal to buffer with more inventory and less capacity as the tail of demand becomes heavier. We also show that the optimal responsive capacity is higher for the products with heavier tails when the fill rate is extremely high.

Quality of Learners' Time and Learning Performance Beyond Quantitative Time-on-Task

Peer-reviewed

¿Es eficaz especializar la actividad de tutoria? Análisis de una experiencia online

En un entorno online la actividad de tutoría de los estudiantes juega un papel fundamental. Su eje central es el acompañamiento del estudiante a lo largo del programa académico que curse, desde el momento en que muestra su interés en matricularse hasta que se titula. La literatura disponible sobre cómo organizar la actividad tutorial en entornos virtuales es escasa. En esta comunicación, basada en la experiencia de la Universitat Oberta de Catalunya (UOC), se analizan dos niveles de especialización de la acción tutorial online. En un primer nivel organizativo, se presenta y evalúa una especialización de la coordinación de la tutoría en función del tipo de conocimiento necesario para ejercerla, académico o administrativo. Esto genera una estructura organizativa de tipo matricial que aporta flexibilidad y conocimiento especializado a la actividad tutorial, y que es valorada muy positivamente por las partes implicadas. En un segundo nivel, se analiza la separación de dos tipos de tutoría especializadas, una de inicio y otra de seguimiento, en función de la antigüedad del estudiante tutorizado. Los resultados de los análisis cualitativos y cuantitativos realizados no permiten concluir que esta segunda forma de especialización contribuya claramente a la mejora de los objetivos de la función tutorial.

Non-viral ocular gene therapy: potential ocular therapeutic avenues.

Non-viral vectors for potential gene replacement and therapy have been developed in order to overcome the drawbacks of viral vectors. The diversity of non-viral vectors allows for a wide range of various products, flexibility of application, ease of use, low-cost of production and enhanced "genomic" safety. Using non-viral strategies, oligonucleotides (ODNs) can be delivered naked (less efficient) or entrapped in cationic lipids, polymers or peptides forming slow release delivery systems, which can be adapted according to the organ targeted and the therapy purposes. Tissue and cell internalization can be further enhanced by changing by physical or chemical means. Moreover, a specific vector can be selected according to disease course and intensity of manifestations fulfilling specific requirements such as the duration of drug release and its level along with cells and tissues specific targeting. From accumulating knowledge and experience, it appears that combination of several non-viral techniques may increase the efficacy and ensure the safety of these evolving and interesting gene therapy strategies.

The CerdàPlan for the Extension of Barcelona: A Constructivist Analysis of a Town-planning Controversy

Peer-reviewed

Securing dynamic itineraries for mobile agent applications

In this paper we present a novel mechanism for the protection of dynamic itineraries for mobile agent applications. Itineraries that are decided as the agent goes are essential in complex applications based on mobile agents, but no approach has been presented until now to protect them. We have conceived a cryptographic scheme for shielding dynamic itineraries from tampering, impersonation and disclosure. By using trust strategically, our scheme provides a balanced trade-off between flexibility and security. Our protection scheme has been thought always bearing in mind a feasible implementation, and thus facilitates the development of applications that make use of it. An example application based on a real healthcare scenario is also presented to show its operation.

Using MILP to plan holidays and working hours under an annualised hours agreement

Annualising work hours (AH) is a means of achievement flexibility in the use of human resources to face the seasonal nature of demand. In Corominas et al. (1) two MILP models are used to solve the problem of planning staff working hours with annual horizon. The costs due to overtime and to the employment of temporary workers are minimised, and the distribution of working time over the course of the year for each worker and the distribution of working time provided by temporary workers are regularised.In the aforementioned paper, the following is assumed: (i) the holiday weeks are fixed a priori and (ii) the workers are from different categories who are able to perform specific type of task have se same efficiency; moreover, the values of the binary variables (and others) in the second model are fixed to those in the first model (thus, in the second model these will intervene as constants and not as variables, resulting in an LP model).In the present paper, these assumptions are relaxed and a more general problem is solved. The computational experiment leads to the conclusion that MILP is a technique suited to dealing with the problem.

Linear and nonlinear terrain deformation maps from a reduced set of interferometric SAR images

In this paper, an advanced technique for the generation of deformation maps using synthetic aperture radar (SAR) data is presented. The algorithm estimates the linear and nonlinear components of the displacement, the error of the digital elevation model (DEM) used to cancel the topographic terms, and the atmospheric artifacts from a reduced set of low spatial resolution interferograms. The pixel candidates are selected from those presenting a good coherence level in the whole set of interferograms and the resulting nonuniform mesh tessellated with the Delauney triangulation to establish connections among them. The linear component of movement and DEM error are estimated adjusting a linear model to the data only on the connections. Later on, this information, once unwrapped to retrieve the absolute values, is used to calculate the nonlinear component of movement and atmospheric artifacts with alternate filtering techniques in both the temporal and spatial domains. The method presents high flexibility with respect to the required number of images and the baselines length. However, better results are obtained with large datasets of short baseline interferograms. The technique has been tested with European Remote Sensing SAR data from an area of Catalonia (Spain) and validated with on-field precise leveling measurements.

Timing of Capacity Change: Models for Capital Intensive Industry

The suitable timing of capacity investments is a remarkable issue especially in capital intensive industries. Despite its importance, fairly few studies have been published on the topic. In the present study models for the timing of capacity change in capital intensive industry are developed. The study considers mainly the optimal timing of single capacity changes. The review of earlier research describes connections between cost, capacity and timing literature, and empirical examples are used to describe the starting point of the study and to test the developed models. The study includes four models, which describe the timing question from different perspectives. The first model, which minimizes unit costs, has been built for capacity expansion and replacement situations. It is shown that the optimal timing of an investment can be presented with the capacity and cost advantage ratios. After the unit cost minimization model the view is extended to the direction of profit maximization. The second model states that early investments are preferable if the change of fixed costs is small compared to the change of the contribution margin. The third model is a numerical discounted cash flow model, which emphasizes the roles of start-up time, capacity utilization rate and value of waiting as drivers of the profitable timing of a project. The last model expands the view from project level to company level and connects the flexibility of assets and cost structures to the timing problem. The main results of the research are the solutions of the models and analysis or simulations done with the models. The relevance and applicability of the results are verified by evaluating the logic of the models and by numerical cases.

Smart antennas in software radio base stations

The application of adaptive antenna techniques to fixed-architecture base stations has been shown to offer wide-ranging benefits, including interference rejection capabilities or increased coverage and spectral efficiency.Unfortunately, the actual implementation ofthese techniques to mobile communication scenarios has traditionally been set back by two fundamental reasons. On one hand, the lack of flexibility of current transceiver architectures does not allow for the introduction of advanced add-on functionalities. On the other hand, theoften oversimplified models for the spatiotemporal characteristics of the radio communications channel generally give rise toperformance predictions that are, in practice, too optimistic. The advent of software radio architectures represents a big step toward theintroduction of advanced receive/transmitcapabilities. Thanks to their inherent flexibilityand robustness, software radio architecturesare the appropriate enabling technology for theimplementation of array processing techniques.Moreover, given the exponential progression ofcommunication standards in coexistence andtheir constant evolution, software reconfigurabilitywill probably soon become the only costefficientalternative for the transceiverupgrade. This article analyzes the requirementsfor the introduction of software radio techniquesand array processing architectures inmultistandard scenarios. It basically summarizesthe conclusions and results obtained withinthe ACTS project SUNBEAM,1 proposingalgorithms and analyzing the feasibility ofimplementation of innovative and softwarereconfigurablearray processing architectures inmultistandard settings.

Monipolttoainekattilan päästöjen tarkkailu ja raportointi

Suurten polttolaitosten päästöjen tarkkailu- ja raportointivaatimukset ovat uudistuneet viime vuosina paljon. Suurimpia muutosten aiheuttajia ovat Valtioneuvoston asetus 1017/2002 ja standardi EN-14181. Tässä työssä kuvataan uudet vaatimukset täyttävän päästöjen tarkkailu- ja raportointijärjestelmän rakentaminen monipolttoainekattilalle. Aluksi esitellään mitä uusia vaatimuksia päästöjen tarkkailulle ja raportoinnille on tullut viime aikoina. Lisäksi selvitetään vaatimusten mahdolliset ristiriidat ja ristiriitatilanteiden ratkaisutavat. Seuraavaksi esitellään vaatimukset täyttävän järjestelmän määritelmät. Erityisestiselvitetään kattilan erityispiirteiden vaatimia ratkaisuja. Lopuksi esitellään päästöjen tarkkailu- ja raportointijärjestelmän käyttökokemuksia ja parantamismahdollisuuksia. Kaikki tarkastelut tehdään ensisijaisesti toiminnanharjoittajan näkökulmasta. Järjestelmä toteutettiin Stora Enso Oyj:n Heinolan Flutingtehtaan voimalaitoksen pääkattilalle, jossa käytetään laajaa polttoainevalikoimaa. Toteutuspaikan valinta tehtiin sillä perusteella, että uudet päästöjen tarkkailu- ja raportointivaatimukset ovat erityisen haasteellisia monipolttoainekattiloiden tapauksessa. Työssä selvitetään järjestelmän soveltamismahdollisuuksia myös kahdella muulla Stora Enson tehtaalla. Käyttöönottovaiheen johtopäätöksenä todettiin päästöjen tarkkailu- ja raportointijärjestelmän täyttävän sille asetetut vaatimukset. Lisäksi havaittiin, että toiminnanharjoittajan kannattaa panostaa erityisesti järjestelmän joustavuuteen, luotettavuuteen, helppokäyttöisyyteen ja vikasietoisuuteen. Toiminnanharjoittaja pystyy määrittelyvaiheessa vaikuttamaan järjestelmän ominaisuuksiin helpommin ja edullisemmin kuin käyttöönoton jälkeen. Toiminnanharjoittajalta vaadittu työtuntimäärä arvioitiin Heinolan Flutingtehtaan tapauksen perusteella. Lopuksi selvitettiin mahdollisia tulevaisuuden kehityskohteita vastaavissa järjestelmissä.

The Dynamic Analysis of a Human Skeleton Using the Flexile Multibody Simulation Approach

The human motion study, which relies on mathematical and computational models ingeneral, and multibody dynamic biomechanical models in particular, has become asubject of many recent researches. The human body model can be applied to different physical exercises and many important results such as muscle forces, which are difficult to be measured through practical experiments, can be obtained easily. In the work, human skeletal lower limb model consisting of three bodies in build using the flexible multibody dynamics simulation approach. The floating frame of reference formulation is used to account for the flexibility in the bones of the human lower limb model. The main reason of considering the flexibility inthe human bones is to measure the strains in the bone result from different physical exercises. It has been perceived the bone under strain will become stronger in order to cope with the exercise. On the other hand, the bone strength is considered and important factors in reducing the bone fractures. The simulation approach and model developed in this work are used to measure the bone strain results from applying raising the sole of the foot exercise. The simulation results are compared to the results available in literature. The comparison shows goof agreement. This study sheds the light on the importance of using the flexible multibody dynamic simulation approach to build human biomechanical models, which can be used in developing some exercises to achieve the optimalbone strength.

Virtuaalitodellisuuslaboratorion laiteympäristön kehittäminen - ohjaimet ja ohjelmistot

Tämä diplomityö on tehty osana HumanICT-projektia, jonka tavoitteena on kehittää uusi, virtuaalitekniikoita hyödyntävä, työkoneiden käyttäjäliityntöjen suunnittelumenetelmä. Työn tarkoituksena oli kehittää VTT:n Tuotteet ja tuotanto tutkimusyksikköön kuluvan Ihminen-kone-turvallisuus ryhmän nykyistä virtuaalitodellisuuslaboratoriota siten, että sitä voidaan käyttää työkoneiden suunnittelussa sekä monipuolisissa ergonomiatarkasteluissa. Itse ympäristön kehittäminen pitää sisällään uuden ohjainjärjestelmän suunnittelun sekä sen implementoinnin nykyisin käytössä olevaan virtuaaliympäristöön. Perinteisesti ohjaamosimulaattorit ovat olleet sovelluskohteisiin räätälöityjä, joten ne ovat kalliita ja niiden konfiguroinnin muuttaminen on vaikeaa, joskus jopa mahdotonta. Tämän työntarkoituksena oli kehittää PC-tietokoneeseen ja yleiseen käyttöjärjestelmään perustuva ohjainjärjestelmä, joka on nopeasti kytkettävissä erilaisiin virtuaaliympäristön sovelluksiin, kuten ohjaamomalleihin. Työssä tarkasteltiin myös tapoja mallintaa fysikaalisia ilmiöitä reaaliaikasovelluksissa, eli on-line simuloinnissa. Tämän tarkastelun perusteella etsittiin ja valittiin jatkokäsittelyyn ohjelmistoja, joiden reaaliaikaisen dynamiikan simulointialgoritmitolivat kaikkein kehittyneimpiä ja monipuolisia.

Design of adjustable packaging line

Diplomityön tavoite oli tutkia, mitä toimintoja ja tekniikoita uusi, joustava kartonkipakkauslinja sisältää ja mitkä suuntaukset pakkausteollisuudessa tulevat olemaan tärkeitä tulevaisuudessa. Pakkauslinjan päätoimintoja tarkasteltiin nykyisten jatulevaisuuden tekniikoiden pohjalta. Erityisesti tarkasteltiin laser-sovellusten käytön mahdollisuutta pakkauslinjan eri osatoiminnoissa. Katsaus pakkausteollisuuden tulevaisuuden näkymiin luotiin kirjallisuuden ja aikaisempien tutkimusten pohjalta, minkä perusteella työssä oletetaan, että yksilölliset ja monitoimipakkaukset tulevat lisääntymään tulevaisuudessa. Eri tuotantoerien välillä olevat asetusajat tulee saada minimoitua, mutta millä keinoin joustavuus on saavutettavissa? Yksi ratkaisu pakkausten valmistamisessa on käyttää robottisolua, mikä on mahdollista luultavasti ainakin kuppimuotoisten pakkausten kohdalla. Muutenkin robotiikka on lisääntymässä pakkausteollisuudessa. Digitaalisten painotekniikoiden kehitys on mahdollistanut yksilölliset painatukset. Tulevaisuudessa painatus on mahdollista tehdä pakkauslinjan loppupäässä, jopa vasta täytön ja suljennan jälkeen. Laserleikkaus on jo nyt käytössä, mutta tulevaisuudessa myös saumaus ja perinteinen nuuttaus on mahdollista tehdä lasersovelluksia käyttäen. Kehittynyt, väyläpohjainen ohjausjärjestelmä on tulevaisuudessa välttämätön joustavassa pakkauslinjassa. Internetin välityksellä toimiva etäohjattu virheenkorjausdiagnostiikka tulee myös olemaan itsestäänselvyys tulevaisuudessa. Kustannussäästöjä voidaan saavuttaa käyttämälläpakkauslinjassa modulaarista rakennetta. Standardiosien ja standardiosajärjestelmien käyttäminen pienentää myös käyttö- ja huoltokustannuksia. Tärkeää on kuitenkin muistaa, ettei joustavuutta voida saavuttaa pelkästään yhtä ominaisuutta tai tekniikkaa hyödyntäen vaan monia menetelmiä yhdistäen. Suunniteltavan pakkauslinjan toiminta on myös hyvä varmistaa käyttäen apuna mallinnusta ja simulointia.

Inter-limb coordination and energy cost in swimming.

OBJECTIVES: This study investigated the relationship between inter-arm coordination and the energy cost of locomotion in front crawl and breaststroke and explored swimmers' flexibility in adapting their motor organization away from their preferred movement pattern. DESIGN: Nine front-crawlers performed three 300-m in front crawl and 8 breaststrokers performed three 200-m in breaststroke at constant submaximal intensity and with 5-min rests. Each trial was performed randomly in a different coordination pattern: freely chosen, 'maximal glide' and 'minimal glide'. Two underwater cameras videotaped frontal and side views to analyze speed, stroke rate, stroke length and inter-limb coordination. METHODS: In front crawl, inter-arm coordination was quantified by the index of coordination (IdC) and the leg beat kicks were counted. In breaststroke, four time gaps quantified the arm to leg coordination (i.e., time between leg and arm propulsions; time between beginning, 90° flexion and end of arm and leg recoveries). The energy cost of locomotion was calculated from gas exchanges and blood lactate concentration. RESULTS: In both front crawl and breaststroke, the freely chosen coordination corresponded to glide pattern and showed the lowest energy cost (12.8 and 17.1Jkg(-1)m(-1), respectively). Both front-crawlers and breaststrokers were able to reach 'maximal glide' condition (respectively, +35% and +28%) but not 'minimal glide' condition for front crawl. CONCLUSIONS: The freely chosen pattern appeared more economic because more trained. When coordination was constrained, the swimmers had higher coordination flexibility in breaststroke than in front crawl, suggesting that breaststroke coordination was easier to regulate by changing glide time.