Дисертації з теми "Oxygen supply and demand"

Because of the aerobic nature of cellular metabolism in mammalian organisms, a continuous supply of oxygen is necessary to maintain normal physiological function. As organisms age, their metabolic rates generally decline and there are accompanying alterations in the structure and function of the microcirculation, as this part of the cardiovascular system is especially important for oxygen exchange. The overall Oxygen Transport System can be considered as being composed of two complementary components: one for Oxygen Demand and one for Oxygen Supply. The purpose of the current work is to describe the age-dependent changes in both oxygen demand and oxygen supply at the level of the microcirculation, using intravital microscopic observations of the rat spinotrapezius muscle, along with optical techniques to delineate the structural, hemodynamic and oxygenation variables needed to characterize the Oxygen Transport System in this tissue. A summary of the findings is that basal oxygen consumption gradually declined with age (from 2 to 12 months) and there were corresponding decreases in tissue blood flow, blood hemoglobin concentration and capillary surface area for oxygen exchange, so that oxygen supply and demand were generally well-matched.

Skeletal muscle dysfunction in chronic obstructive pulmonary disease (COPD) is a condition in which peripheral skeletal muscle undergoes myopathic changes which impair muscle function, limit physical performance, and can lead to significant disability. While the etiology of the dysfunction is unknown, this study was conducted to test the hypothesis that chronic hypoxemia leads to alterations in oxygen transport and muscle function. A primary objective was to validate elastase-induced emphysema in rats as an animal model of skeletal muscle dysfunction in COPD.Arterial blood gases were used to determine the severity of hypoxemia and sodium dodecyl sulfate- polyacrylamide gel electrophoresis was used to determine the proportions of myosin heavy chain isoforms I, IIa, IIx, and IIb. Measures of microvascular oxygenation and blood flow in the spinotrapezius muscle allowed for determination of both convective and diffusive oxygen supply to the muscle, as well as calculation of muscle oxygen consumption at rest and during electrically stimulated three-minute muscle contractions. Muscle performance measures included peak force, force-time integral, and fatigue index. Due to a presumed rat respiratory virus, which likely resulted in the control group being nearly as hypoxemic as the elastase-induced emphysema group, this study was not able to definitively test the hypothesis that chronic hypoxemia leads to both a diminished supply and demand of oxygen in skeletal muscle. Although many of the results of the present study were not statistically significant, they exhibited consistent trends over time and are likely of physiological significance. All measures of muscle performance were lower in the emphysema group. In addition, spinotrapezius muscle oxygen consumption and blood flow were lower in the emphysema group. The addition of supplemental oxygen during isolated, small-muscle mass exercise did increase the force-time integral by ~18% in both groups, suggesting that muscle work in these hypoxemic animals may be limited by oxygen supply. Thus, the data on muscle fiber type, oxygen consumption and muscle performance suggest that elastase-induced emphysema in rats leads to a similar skeletal muscle dysfunction that is observed in humans with COPD, and indicates that it is a valid animal model of skeletal muscle dysfunction in COPD.

Approximately 30% of people admitted to ICU in the UK have co-existing cardiovascular disease (CVD), and this may rise as life-expectancy increases. Patients with CVD have impaired compensatory mechanisms to enable maximum oxygen delivery to the tissues in the event of critical illness, which itself increases global oxygen demand, further stressing the heart. This is exacerbated by tachycardia and hypotension, which may relatively reduce blood flow to the coronary arteries, and catecholamines which increase myocardial oxygen demand. The myocardium extracts 75% of the oxygen supplied by the coronary arteries at rest, and atheroma-related flow limitation further compromises myocardial oxygen delivery. However, the diagnosis of acute coronary syndrome in critical illness is not straightforward, due to patient inability to communicate symptoms, non-specific ECG changes, and poorly understood cardiac biomarker troponin elevation. My overall hypothesis is that patients with CVD benefit from increased oxygen delivery to the myocardium during critical illness. A focus is the importance of anaemia. The aims of the studies presented in this thesis are (i) to systematically review the literature regarding blood transfusion thresholds specifically in patients with CVD; (ii) to explore the association between Troponin I (TnI) within 24 hours of ICU admission and hospital mortality (iii) to describe and quantify the dynamics of TnI in patients with CVD during the first ten days after ICU admission; and (iv) to define myocardial infarction in the context of critical illness. I have performed a systematic review and meta-analysis of randomised controlled trials comparing a restrictive with liberal transfusion threshold and that included patients with CVD. In total, 11 trials enrolling patients with CVD (n=3033) were included for meta-analysis (restrictive n=1514, liberal=1519). The pooled risk ratio for the association between a restrictive transfusion threshold and 30 day mortality was 1.15 (95% CI 0.88 to 1.50, p=0.50, I2=14%). The risk of acute coronary syndrome in patients managed with restrictive compared with liberal transfusion was increased (nine trials, risk ratio 1.78, 95% CI 1.18 to 2.70, p=0.0, I2=0%). In contrast to broader literature supporting restrictive thresholds, our systematic review shows that a restrictive transfusion threshold of less than 80g/l may not be safe in patients with co-existing CVD, and highlights the variability in diagnostic definitions of ACS and the potential for ascertainment bias in transfusion trials. I undertook a retrospective cohort study in two independently collected cohorts of general ICU patients who had TnI measured within 24 hours of ICU admission. Importantly, the majority of TnI samples were collected routinely rather than for clinical indications. We used the Abbott ARCHITECT Stat assay (limit of detection 0.01mcg/l. We performed multivariable regression, adjusting for components of the APACHE II model. We derived the risk prediction score from the multivariable model with TnI. TnI was associated with all cause hospital mortality (OR per doubling TnI 1.16, 95% CI 1.13 to 1.20, p < 0.001) which persisted after adjustment for APACHE II model components (OR TnI 1.05, 95% CI 1.01 to 1.09, p=0.003). TnI correlated highly with the Acute Physiological Score component of APACHE II (r=0.39), suggesting that TnI release may be largely explained by acute physiological stress. Addition of TnI to the APACHE II model did not improve the performance of the risk prediction model and we would not advocate the adoption of a routine single troponin sample at admission. I designed, set up, and recruited 279 patients to a prospective cohort study TROPonin I in Cardiovascular patients in CriticAL care (TROPICCAL, UKCRN 19253) in 11 UK centres. The aims were to (i) determine the incidence of Myocardial Injury and Infarction, defined by the Third Universal Definition of Myocardial Infarction; (ii) explore factors associated with Injury and Infarction from multivariable analyses; and (iii) explore the relationship between Injury/Infarction and outcome in unadjusted and adjusted analyses. We recorded baseline characteristics, and took daily hs-TnI for ten days after ICU admission, severity of illness measures and ECGs for 5 days. There was a wide range of peak TnI (med 114ng/l (min 3, Q1 27, Q3 412, max 58820ng/l)) and a high prevalence of myocardial injury on systematic screening: 71% of patients had peak TnI greater than the sex-specific diagnostic threshold ('Injury'), and 24% had peak TnI greater than the sex-specific diagnostic threshold and dynamic changes on ECG consistent with ischaemia ('Infarction'). TnI consistently showed a rise-and-fall pattern consistent with an acute myocardial 'hit' rather than persisting injury, which peaked early during ICU stay. Importantly, only 12 (4.4%) patients were diagnosed with MI by the clinicians looking after the patients. Independent predictors of peak TnI in the preceding 24 hours were SOFA score, dynamic ECG ischaemia, lactate, haemoglobin, and age. The lack of association with CRP (representing systemic inflammation), with stronger association with lactate (representing inadequate perfusion/oxygen supply), Hb and ECG ischaemia support the conjecture that injury results in part from an acute ischaemic hit in this population. Patients with Infarction had similar baseline demographics to patients with Injury, but had higher peak TnI concentrations, and higher hospital and six month mortality (Figure 2). This supports the importance of including systematic assessment of dynamic ECG changes in the myocardial injury 'construct' in ICU. My work has shown an increased risk of ACS in patients with CVD randomised to restrictive transfusion thresholds. TnI elevation is prevalent in general ICU patients, and is independently associated with hospital mortality. A systematic approach to the detection of myocardial injury in critically ill patients with co-existing CVD who are unable to communicate symptoms, can identify a high risk population who have poorer survival than patients with no injury. Markers of ischaemia are more associated with TnI rise than markers of inflammation, supporting the hypothesis that myocardial injury in this population is at least in part due to oxygen supply-demand imbalance 'myocardial infarction'. From this work, I would recommend (i) a more liberal transfusion threshold of at least 80g/l in patients with coexisting CVD; (ii) systematic use of sequential ECGs in ICU to screen for myocardial injury in 'at risk' patients; and (iii) manipulation of physiological parameters such as anaemia, hypotension and tachycardia should be considered for patients with dynamic ECG changes plus troponin increase consistent with Infarction. Future research should include 'precision medicine' trials in the substantial cohort of ICU patients with co-existing CVD to explore whether interventions that increase myocardial oxygen supply and/or treat infarction alter outcomes.

Hypolimnetic oxygen diffusers increase sediment oxygen demand (SOD) and, if not accounted for in design, can further exacerbate anoxic conditions. A study using extracted sediment cores, that included both field and laboratory experiments, was performed to investigate SOD kinetics in Carvinâ s Cove Reservoir, a eutrophic water supply reservoir for Roanoke, Virginia. A bubble-plume diffuser is used in Carvinâ s Cove to replenish oxygen consumed while the reservoir is thermally stratified. The applicability of zero-order, first-order, and Monod kinetics to describe transient and steady state SOD was modeled using analytical and numerical techniques. Field and laboratory experiments suggested that first-order kinetics characterize Carvinâ s Cove SOD. SOD calculated from field experiments reflected diffuser flow changes. Laboratory experiments using mini-diffusers to vary dissolved oxygen concentration and turbulence were conducted at 4°C and 20°C. Similar to field observations, the laboratory results followed changes in mini-diffuser flow. Kinetic-temperature relationships were also observed in the laboratory experiments. A definitive conclusion could not be made on the broad applicability of first-order kinetics to Carvinâ s Cove SOD due to variability within field experiments. However, in situ experiments are underway that should assist in the overall understanding of the reservoirâ s SOD kinetics.
Master of Science

Purpose: This research aims to enhance the current understanding and knowledge of the demand-supply chain management (DSCM) concept by determining its elements, benefits, and requirements, as well as by analyzing key elements of the concept. Methodology: This research has utilized the case study strategy and the survey strategy, however, the case study strategy dominates. The case study research has involved five companies originating from Sweden and the collection of empirical data mainly from in-depth interviews with key persons representing senior and middle management. The survey research targeted the largest firms in Sweden and Finland and empirical data was collected through an online questionnaire. Findings: This research has established that the main elements of DSCM include market orientation, coordination of the demand and supply processes, viewing the demand and supply processes as being equally important, as well as value creation, differentiation, innovativeness, responsiveness, and cost-efficiency in the demand and supply processes. It has also been revealed that the main benefits of DSCM include enhanced competiveness, enhanced demand chain performance, as well as enhanced supply chain performance, while the main requirements of DSCM include organizational competences, company established principles, demand-supply chain collaboration, and information technology support. A key element of DSCM further investigated is differentiation focused supply chain design. It has been shown that these efforts can be organized into a process of five stages. In addition, it is important that this process is addressed in parallel with the new product development (NPD) process, that information is exchanged between them, and that they are directed on the basis of the same segmentation model. Another key element of DSCM further investigated is coordination between NPD and SCM. This research has identified several significant linkages between these management directions, which motivate the use of an integrative NPD process where the NPD functions are aligned with the main supply functions in the company and other sales-related functions supporting the commercialization. A final key element of DSCM further investigated is the significance of regarding the demand processes and the supply processes as being equally important. This research has revealed that logistics outsourcing can be risky, if it results in the supply processes being considered less important. Nevertheless, if senior management regards the outsourced processes as equally important as the in-house processes, the effect of logistics outsourcing on company strategies and direction in SCM could be reduced and logistics outsourcing could instead provide an opportunity to improve the design and differentiation of the supply chain. Research limitations/implications: This research has proposed, described, and further analyzed a demand-supply oriented management approach. Such a management approach stresses that the demand processes and the supply processes have to be coordinated and directed at an overlying level, in order to gain and sustain a competitive advantage in competitive and fragmented markets. This research is mainly explorative in nature, and more empirical data, from similar and other research settings, is needed to further validate the findings. Another limitation of the research is that it is essentially limited to Swedish companies (even if some Finnish companies are involved in the survey), however, many of the case companies have a large international presence and are among the top three in their industries, facts which provide some grounds for generalization. Practical implications: This research provides researchers and practitioners with insights into how to develop a demand-supply oriented business. It shows that companies should organize themselves around understanding how customer value is created and delivered, as well as how these processes and management directions can be coordinated. In order for this to occur, the demand and supply processes must be considered as being equally important and the firm needs to be managed jointly and in a coordinated manner by the demand- and supply-side of the company. It is also important that value creation is considered in both the demand and supply processes. Originality/value: Despite strong arguments from both researchers and practitioners for a demand-supply oriented management approach only a minority of companies appear to have effectively coordinated the demand and supply processes. This might be influenced by the lack of research examining how the demand and supply processes can be coordinated, what benefits can be gained by coordinating them, and what requirements are necessary to succeed. This research contributes by investigating these types of aspects further.

Cephalopods are an important component of many marine ecosystems and support large fisheries. Their active lifestyles and complex behaviors are thought to be driven in large part by competition with fishes. Although cephalopods appear to compete successfully with fishes, a number of their important physiological traits are arguably inferior, such as an inefficient mode of locomotion via jet propulsion and a phylogenetically limited means of blood-borne gas transport. In active shallow-water cephalopods, these traits result in an interesting combination of very high oxygen demand and limited oxygen supply. The ability to maintain active lifestyles despite these metabolic constraints makes cephalopods a fascinating subject for metabolic physiology. This dissertation focuses on the physiological adaptations that allow coleoid cephalopods to maintain a balance of oxygen supply and demand in a variety of environmental conditions. A critical component of understanding oxygen supply in any animal is knowing the means of oxygen delivery from the environment to the mitochondria. Squids are thought to obtain a fairly large portion of their oxygen via simple diffusion across the skin in addition to uptake at the gills. Although this hypothesis has support from indirect evidence and is widely accepted, no empirical examinations have been conducted to assess the validity of this hypothesis. In Chapter 2, I examined cutaneous respiration in two squid species, Doryteuthis pealeii and Lolliguncula brevis, by using a divided chamber to physically separate the mantle cavity and gills from the outer mantle surface. I measured the oxygen consumption rate in the two compartments and found that, at rest, squids only obtain enough oxygen cutaneously to meet demand of the skin tissue locally (12% of total). The majority of oxygen is obtained via the traditional branchial pathway. In light of these findings, I re-examine and discuss the indirect evidence that has supported the cutaneous respiration hypothesis. Ocean acidification is believed to limit the performance of squids due to their exceptional oxygen demand and pH-sensitivity of blood-oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), defined as the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In Chapter 3, I assessed the effects of CO2 (40 to 140 Pa) on the metabolic rate and Pcrit of two squid species: Dosidicus gigas and Doryteuthis pealeii. Carbon dioxide had no effect on metabolic rate or hypoxia tolerance in either species. Furthermore, considering oxygen transport parameters (e.g. Bohr coefficient, blood P50) and blood PCO2 values from the literature, I estimated an increase in seawater PCO2 to 100 Pa (≈1000 μatm/ppmv) would result in a maximum drop in hemocyanin-O2 saturation by 6% at normoxia and a Pcrit increase of ≈1 kPa (≈5% air saturation) in the absence of active extracellular pH compensation. Such changes are unlikely given the capacity for acid-base regulation in many cephalopods. Moreover, this estimated change is within the 95% confidence intervals of the Pcrit measurements reported here. Squid blood-O2 binding is more sensitive to pH than most other marine animals measured to date. Therefore, the lack of effect in squids suggests that ocean acidification is unlikely to have a limiting effect on blood-O2 supply in most marine animals. The pelagic octopod, Japetella diaphana, is known to inhabit meso- and bathypelagic depths worldwide. Across its range, individuals encounter oxygen levels ranging from nearly air-saturated to nearly anoxic. In Chapter 4, we assessed the physiological adaptations of individuals from the eastern tropical Pacific (ETP) where oxygen is extremely low. Ship-board measurements of metabolic rate and hypoxia tolerance were conducted and a metabolic index was constructed to model suitable habitat for aerobic metabolism. I found that animals from the ETP had a higher metabolic rate than animals from more oxygen-rich habitats. Despite their higher oxygen demand, they maintained better hypoxia tolerance than conspecifics from oxygen-rich Hawaiian waters. Furthermore, I found that hypoxia tolerance in Japetella has a reverse temperature dependence from most marine ectotherms, a characteristic that uniquely suits the physical characteristics of its oxygen-poor environment. Even with their high tolerance to hypoxia, the OMZ core likely has insufficient oxygen supply to meet the basal oxygen demand of Japetella. Despite the limited aerobic habitat in this region, species abundance was comparable to more oxygenated ocean regions, suggesting that physiological or behavioral plasticity such as altered hypoxia tolerance or hypoxic avoidance in this globally-distributed species is sufficient to maintain species fitness in this extreme environment. These findings contribute towards our understanding of the impacts of climate change on cephalopod physiology and biogeography. The study of environmental physiology provides a mechanistic basis for the understanding and prediction of ecological responses to climate change.

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2006.
Includes bibliographical references (leaves 73-75).
Globalization increases product variety and shortens product life cycles. These lead to an increase in demand uncertainty and variability. Outsourcing to low-cost countries increases supply lead-time and supply uncertainty and variability. Coupled with the increase of mergers and acquisitions, which increase supply chain complexity, and the unforgiving nature of having too little or too much inventory, these factors have accelerated the importance and adoption of the Sales and Operations Planning (S&OP) process. S&OP is driven by a cross functional team, with the purpose of balancing supply and demand with the objective of maximizing a company's goals. It manages the supply and demand uncertainties, balances the different internal and external stakeholders' interests, and aligns the operations towards its strategy and vision. In support of the Supply Chain 2020 Project at MIT, this thesis focuses on analyzing the S&OP function across industries. Using the Phase I SC 2020 theses, literature, white papers, and interviews with industry experts, this thesis compares and contrasts the S&OP practices across nine industries.
(cont.) It examines their best practices and underlying principles, as well as the macro factors that have shaped the practices for the last ten to fifteen years, as well as what is expected in the future. Companies with the "best" S&OP processes collaborate internally to balance sales and operations, and align all internal stakeholders' interests. Furthermore, they collaborate externally with suppliers and customers to reduce supply and demand uncertainties. They also understand and manage demand and supply uncertainties, and align their effort towards their goals. These companies synchronize operations and are agile to changing environments.
by Peng Kuan Tan.
M.Eng.in Logistics

The aim of this thesis is to extend the empirical research which has been undertaken using the GNP function approach to measuring export supply and import demand responsiveness. Exports and imports are divided into several components and detailed sets of elasticities produced. In the second part o£ the thesis imperfect adjustment is allowed for in the GNP function model. The GNP function framework treats imports as an input to the domestic technology while exports are an output. The aggregate technology can then be represented by a restricted profit function facilitating the derivation of net output supply elasticities. In this study the aggregate net outputs are exports, imports, labour and domestic sales supply. Capital is treated as a fixed input. Time-series of input-output data for Canada are used covering the period 1961 to 1980. In the first model estimated, four export and four import components are included by the use of aggregator functions and a two-stage estimation process. The recently developed Symmetric Generalised McFadden functional form which permits imposition of the correct curvature conditions while retaining flexibility is used at both the aggregator and GNP function levels. The aggregate export own-price supply elasticity was found to be 1.67 in 1970 while the aggregate import own-price demand elasticity was -1.62. Increases in the prices of both imports and labour were found to decrease the supply of exports while exports were found to be complementary to the output of domestic sales supply. The demand for labour was found to be more elastic than in earlier studies and a general trend towards increasing price responsiveness in the Canadian economy was observed. The own-price elasticities for the four export and four import components were stable and of reasonable magnitude. All the export and import components were found to be complementary. To remove the assumption of separability, modelling was extended to two larger disaggregated Generalised McFadden GNP function models containing four export (import) components, aggregate imports (exports), labour and domestic sales as net outputs. Using this procedure more substitution between the export and import components was found. A planning price model whereby the producers' notional price adjusts gradually to actual price changes indicated that imperfect adjustment is particularly important in the traded goods sector. Exports fully adjusted to price changes only over an extended period. Finally, an adjustment costs model was estimated which indicated that the main effect of allowing for imperfect adjustment was on input use. Differences between long-run and short-run export supply and import demand responsiveness were relatively small. Considerable substitutability between labour and capital in the long-run was observed and since labour was also variable in the short-run this produced overshooting of labour demand. An increase in export prices thus caused a large short-run increase in labour demand but in the long-run the capital stock was increased and substituted for much of the short-run labour increase.
Arts, Faculty of
Vancouver School of Economics
Graduate

Thesis: S.M. in Real Estate Development, Massachusetts Institute of Technology, Program in Real Estate Development in conjunction with the Center for Real Estate, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 66-69).
This thesis documents new methods for gauging supply and demand of data center capacity and addresses issues surrounding potential threats to data center demand. This document is divided between a primer on the composition and engineering of a current data center, discussion of issues surrounding data center demand, Moore's Law and cloud computing, and then transitions to presentation of research on data center demand and supply.
by Laird Bennion.
S.M. in Real Estate Development

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Supply-demand analysis (SDA) is a tool that allows for the control, regulation and behaviour of metabolic pathways to be understood. In this framework, reactions are grouped into reaction blocks that represent the supply and demand of a metabolic product. The elasticities of these supply and demand blocks can be used to determine the degree of control either block has over the flux in the pathway and the degree of homoeostasis of the metabolic product that links the blocks. Rate characteristic plots, on which the rates of supply and demand blocks are plotted as functions of the concentration of the linking metabolite, represent a powerful visual tool in this framework. Generalised supply-demand analysis (GSDA) allows for the analysis of metabolic models of arbitrary size and complexity without prior knowledge of the regulatory structure of the pathway. This is achieved by performing SDA on each variable metabolite in a pathway instead of choosing a single linking metabolite. GSDA also provides other benefits over SDA as it allows for potential sites of regulation and regulatory metabolites to be identified. Additionally it allows for the identification and quantification of the relative contribution of di erent routes of regulation from an intermediate to a reaction block. Moiety-conserved cycles present a challenge in performing in silico SDA or GSDA, as the total concentration of a moiety must remain constant, thereby limiting the range of possible concentrations of the metabolites between which it cycles. The first goal of this thesis was to develop methods to perform GSDA on two-membered and interlinked moiety-conserved cycles. We showed that by expressing the members of a moiety-conserved cycle as a ratio, rather than individual metabolite concentrations, we can freely vary the ratio without breaking moiety conservation in a GSDA. Furthermore, we showed that by linking the concentrations of the members of two interlinked two-membered moiety-conserved cycles to a “linking metabolite”, we could vary the concentration of this metabolite, within constraints, without breaking moiety conservation. The Python Simulator for Cellular Systems (PySCeS) is a software package developed within our group that provides a variety of tools for the analysis of cellular systems. The RateChar module for PySCeS was previously developed as a tool to perform GSDA on kinetic models of metabolic pathways by automatically generating rate characteristic plots for each variable metabolite in a pathway. The plots generated by RateChar, however, were at times unclear when the models analysed were too complex. Additionally, invalid results where steady-states could not be reached were not filtered out, and therefore appeared together with valid results on the rate characteristic plots generated by RateChar. We therefore set out to improve upon RateChar by building plotting interface that produces clear and error-free rate characteristics. The resulting RCFigure class allows users to interactively change the composition of a rate characteristic plot and it includes automatic error checking. It also provides clearer rate characteristics with e ective use of colour. Using these tools two case studies were undertaken. In the first, GSDA was used to investigate the regulation of aspartate-derived amino acid synthesis in Arabidopsis thaliana. A central result was that the direct interaction of aspartate-semialdehyde (ASA), a metabolite at a branch point in the pathway, with the enzyme that produces it only accounts for 7% of the total response in the flux of supply. Instead, 89% of the observed flux response was due to ASA interacting with of the downstream enzymes for which it is a substrate. This result was unexpected as the ASA producing enzyme had a high elasticity towards ASA. In a second case study moiety-conserved cycles in a model of the pyruvate branches in lactic acid bacteria were linearised using the above mentioned method. This served to illustrate how multiple reaction blocks are connected by these conserved moieties. By performing GSDA on this model, we demonstrated that the interactions of these conserved moieties with the various reaction blocks in the pathway, led to non-monotonic behaviour of the rate characteristics of the supply and demand for the moiety ratios. An example of this is that flux would increase in response to an increase in product for certain ranges. This thesis illustrates the power of GSDA as an entry point in studying metabolic pathways, as it can potentially reveal properties of the regulation and behaviour of metabolic pathways that were not previously known, even if these pathways were subjected to previous analysis and a kinetic model is available. In general it also demonstrates how e ective analysis tools and metabolic models are vital for the study of metabolism.
AFRIKAANSE OPSOMMING: Vraag-en-aanbod analise (VAA) is ’n analisemetode wat mens in staat stel om die beheer, regulering en gedrag van metaboliese paaie beter te verstaan. In hierdie raamwerk word reaksies gegroepeer as reaksieblokke wat die aanbod (produksiestappe) en die aanvraag (verbruik-stappe) van ’n metaboliese produk verteenwoordig. Vanaf die elastisiteite van hierdie aanbod- en aanvraag-blokke kan die graad van beheer van elkeen van die blokke oor die fluksie, asook die graad van homeostase van die metaboliese koppelingsintermediaat, bereken word. Snelheidskenmerk-grafieke, waarop die snelhede van die vraag- en aanbod-blokke as funksies van die konsentrasie van die koppelingsmetaboliet uiteengesit word, verteenwoordig ’n kragtige visuele hulpmiddel in hierdie raamwerk. Veralgemeende vraag-aanbod analise (VVAA), die veralgemeende vorm van VAA, maak dit moontlikommetaboliese modelle van arbitrêre grootte en kompleksiteit te analiseer sonder enige vooraf-kennis van die regulatoriese struktuur van die paaie. Die prosedure is om VAA op elk van die veranderlike metaboliete in die pad uit te voer, eerder as om ’n enkele koppelingsmetaboliet te kies. VVAA het ook ander voordele bo VAA aangesien dit potensiële setels van regulering en regulatoriese metaboliete kan identifiseer. Daarbenewens kan dit die relatiewe bydrae van verskillende regulerings-roetes van vanaf ’n intermediaat na ’n reaksieblok identifiseer en hulle kwantifiseer. Groep-gekonserveerde siklusse bied ’n uitdaging vir in silico VAA of VVAA, aangesien die totale konsentrasie van die gekonserveerde groep konstant moet bly. Dit beperk die waardes van moontlike konsentrasies van die metaboliete wat die siklus uitmaak. Die eerste doelstelling van hierdie tesis was dus om metodes te ontwikkel waarmee VVAA op tweeledige en saamgebonde groep-gekonserveerde siklusse uitgevoer kan word. Deur die lede van groep-gekonserveerde siklusse eerder as verhoudings uit te druk in plaas van as individuele metabolietkonsentrasies, het ons gewys dat ons hierdie verhouding vrylik kan varieer sonder om die groep-konservering te breek in ’n VVAA. Ons het ook gewys dat die konsentrasies van die lede van ’n saamgebonde groep-gekonserveerde siklus gekoppel kan word aan ’n “koppelingsmetaboliet”, waarvan die konsentrasie dan binne perke gevarieer kan word sonder om die groep-konservering te breek. Die “Python Simulator for Cellular Systems” (PySCeS) is ’n programmatuur-pakket wat binne ons navorsingsgroep ontwikkel is met die doel om sellulêre sisteme numeries te analiseer. Die RateChar module vir PySCeS was reeds voor die aanvang van hierdie projek ontwikkel om VVAAop kinetiese modelle van metaboliese paaie uit te voer deur outomaties snelheidskenmerke vir elke veranderlikke metaboliet te genereer. Die grafieke wat deur RateChar gegenereer is, was egter soms onduidelik wanneer die modelle te groot of kompleks geraak het. Daarbenewens is ongeldige resultate, waar ’n bestendige toestand nie bereik kon word nie, nie uitgefiltreer nie, en het dus saam met geldige resultate op die snelheidskenmerke verskyn. Een van die doelstellings was dus om RateChar te verbeter deur ’n koppelvlak vir grafieke te ontwikkel wat duidelike en foutlose snelheidskenmerke kon produseer. Dit het gelei tot die RCFigure klas wat outomatiese foutopsporing uitvoer en gebruikers in staat stel om op ’n interaktiewe wyse die samestelling van ’n snelheidskenmerkgrafiek te verander. Dit bied ook duideliker snelheidskenmerke deur e ektief van kleur gebruik te maak. Met hierdie ontwikkelde gereedskap is twee gevallestudies onderneem. In die eerste is VVAA gebruik om die regulering van aspartaat-afgeleide aminosuursintese in Arabidopsis thaliana te bestudeer. Die belangrikste resultaat was dat die direkte interaksie van aspartaat-semialdehied (ASA), ’n metaboliet by ’n vertakkingspunt in die pad, met die ensiem wat dit produseer, slegs vir 7% van die totale respons in die aanbod-fluksie verantwoordelik was. Daarteen was 89% van die waargenome fluksierespons die gevolg van die interaksie van ASA met drie van die stroomafensieme, waarvoor dit ’n substraat is. Hierdie resultaat was onverwag aangesien die ensiem wat ASA produseer ’n hoë elastisiteit teenoor ASA toon. In ’n tweede gevallestudie is die groep-gekonserveerde siklusse in ’n model van die pirovaat-takke in melksuurbakterie-metabolisme gelineariseer deur gebruik te maak van die bo beskrewe metode. Dit illustreer hoe verskeie reaksieblokke verbind word deur hierdie gekonserveerde groepe. M.b.v. ’n VVAA van hierdie model het ons gedemonstreer dat die interaksies van die gekonserveerde groepe met die verskeie reaksieblokke in die pad kan lei tot nie-monotoniese gedrag van die snelheidskenmerke van die vraag- en aanbod-reaksies vir die verhouding van die gekonserveerde groep-komponente. ’n Voorbeeld hiervan is die onverwagte waarneming dat die fluksie toeneem met toenemende produk-konsentrasie oor sekere gebiede. Hierdie tesis illustreer die krag van VVAA as ’n beginpunt vir die studie van metaboliese paaie, aangesien dit onbekende regulatoriese eienskappe en gedragspatrone kan ontbloot, selfs al is die paaie vantevore m.b.v. kinetiese modelle geanaliseer. Oor die algemeen demonstreer dit die noodsaaklikheid van e ektiewe analisegereedskap en metaboliese modelle vir die bestudering van metabolisme.
National Research Foundation

The implementation of nature conservation as a land use form is characterized by persistent conflicts and low acceptance by landowners and other users of the considered land area. The thesis applies an economic approach that is understood as the consideration of opportunities and problems of social interaction that aims at mutual benefits (Homann 2002: 63; Homann & Suchanek 2005: 4). Nature conservation is treated as a normal economic good that is demanded and supplied. Human action and human choices regarding the good "nature conservation" can be explained and predicted when including the structure of the exchange and transfer of property rights for nature conservation. The property rights perspective on nature conservation demonstrates an unambiguous understanding of the rights individuals are willing to abandon for demanding and supplying nature conservation. The successful implementation of different aims and strategies of nature conservation requires different property rights. The loss of the right to choose other alternatives implies subjective costs (Knight 1924: 592f.; Buchanan 1981: 14) that cannot be reduced to pecuniary units and landowners. This approach broadens the understanding of the term "costs" related to nature conservation. Different organizational and institutional arrangements can be found in practical nature conservation. Both, the demand for and the supply of nature conservation is organized either individually or collectively. Property rights for the good “nature conservation” are either exchanged voluntarily or involuntarily by applying takings and eminent domain. The application of the methodological individualism, the homo economicus and microeconomic theory, allows to elaborate a simple model of individual demand and supply of one property right that is allocated to nature conservation. This model excludes transaction costs, considers only one normal economic good - “nature conservation”. The analysis demonstrates the outcomes, which can be expected when aggregating these individual demand and supply curves within two different organizations. A vertical aggregation represents the process of choice-making within politics in a direct democracy. A horizontal aggregation illustrates the determination of choices within a market. The analysis includes all possible institutional and organizational arrangements. The results reveal the quantity and quality of implemented nature conservation and the expected relation between available and required budgets. It is highlighted, how susceptible collective outcomes are to changing expenditure and revenue sharing systems and voting rules. When making collective choices, only one revenue and expenditure sharing system exists that allows a unanimously chosen quantity of nature conservation. These specific sharing systems are different when considering different collectives. Only voluntary exchanges ensure mutual benefits and a balanced budget. I can show that the institution of takings increases conflicts and reduce the acceptance for implementing nature conservation. A preference order of the considered institutional arrangements is revealed. The majority of the analyzed arrangements allows unambiguous expectations on the quantity and quality of the implemented nature conservation. The discussion justifies the chosen economic approach for examining problems of social interaction within nature conservation. Furthermore, the application of the elaborated model to representative democratic systems is discussed. The thesis closes with examples of the current and expected future development of practical nature conservation. These cases are discussed in the light of the elaborated model and the analysis' results. The present thesis offers an explanation of past and present processes and outcomes in nature conservation and a support for making expectations on the constellation of actors and their acceptance regarding future strategies in practical nature conservation
Die Umsetzung von Naturschutz als Landnutzungsform ist durch beständige Konflikte und niedrige Akzeptanz durch Landeigentümer und andere Landnutzer gekennzeichnet. Die Arbeit verwendet einen ökonomischen Ansatz. Sie betrachtet Möglichkeiten und Probleme sozialer Interaktion, die auf gegenseitigen Nutzen abzielt (Homann 2002: 63; Homann & Suchanek 2005: 4). Naturschutz wird als normales ökonomisches Gut betrachtet. Dieses wird durch interagierende Individuen angeboten und nachgefragt. Das individuelle Handeln und Entscheiden in Bezug auf "Naturschutz" kann durch das Einbeziehen von Verfügungsrechten, welche bei dem Tausch ausgetauscht und übertragen werden, beschrieben und vorhergesagt werden. Die verfügungsrechtliche Betrachtung von Naturschutz ermöglicht ein eindeutiges Verständnis auf jene Rechte, auf die Individuen verzichten würden, um Naturschutz nachzufragen und anzubieten. Die erfolgreiche Umsetzung der unterschiedlichen Naturschutzziele und –strategien erfordert ein Eigentum an unterschiedlichen Verfügungsrechten. Der Verlust des Rechtes, eine Alternative zu wählen, verursacht subjektive Kosten (Knight 1924: 592f.; Buchanan 1981: 14), welche nicht auf Geldeinheiten und nicht auf Landeigentümer begrenzt werden können. Dieser Ansatz erweitert das Verständnis von Kosten in Bezug auf Naturschutz. Unterschiedliche organisatorische und institutionelle Arrangements sind im praktischen Naturschutz zu finden. Nachfrage und Angebot können jeweils individuell oder kollektiv organisiert sein. Verfügungsrechte für das Gut „Naturschutz“ werden entweder freiwillig oder erzwungen - durch Konfiskation und Enteignung getauscht. Die Anwendung des methodologischen Individualismus, des Konzeptes des Homo Economicus und mikroökonomischer Theorie, erlaubt die Entwicklung eines simplen Modells des individuellen Angebots und der individuellen Nachfrage nach Verfügungsrechten für Naturschutz. Dieses Modell schließt Transaktionskosten aus und betrachtet ausschließlich ein normales ökonomisches Gut – Naturschutz. Die Analyse zeigt die zu erwartenden Ergebnisse auf, wenn die individuelle Nachfrage und das individuelle Angebot durch zwei unterschiedliche Organisationen aggregiert werden. Eine vertikale Aggregation verdeutlicht eine politische Wahlhandlung innerhalb einer direkten Demokratie. Eine horizontale Aggregation repräsentiert die Wahl innerhalb eines Marktes. Die Analyse beinhaltet alle Kombinationen der unterschiedlichen institutionellen und organisatorischen Arrangements für die Bereitstellung des Gutes "Naturschutz". Die Ergebnisse dieser Analyse zeigen (1) die zu erwartende Quantität und Qualität des durchgeführten Naturschutzes und (2) das zu erwartende Verhältnis zwischen dem verfügbaren und dem notwendigen Budget auf. Zusätzlich wird die Empfindlichkeit kollektiver Entscheidungsergebnisse gegenüber sich verändernden Abstimmungsregeln und Teilungsregeln von Ausgaben und Einnahmen herausgearbeitet. Bei kollektiven Wahlhandlungen existiert nur jeweils eine Ausgaben- und Einnahmenteilung, die eine einstimmige Wahl einer Menge von Naturschutz ermöglicht. Diese Teilungsregel variiert zwischen unterschiedlichen Kollektiven. Ausschließlich ein freiwilliger Tausch sichert gegenseitige Vorteile und ein ausgeglichenes Budget. Weiterhin zeige ich auf, dass die Institution Konfiskation die Konflikte mit Landnutzern erhöht und deren Akzeptanz für die Umsetzung von Naturschutz reduziert. Eine Präferenzordnung für die verschiedenen Institutionen wird erarbeitet. Der Großteil der analysierten institutionellen und organisatorischen Arrangements erlaubt eindeutige Aussagen über die Quantität und Qualität des praktizierten Naturschutzes. Die Diskussion begründet die gewählte ökonomische Methode zur Untersuchung von Interaktionsproblemen des Naturschutzes. Weiterhin wird die Anwendbarkeit des erarbeiteten Modells für repräsentative Demokratien erörtert. Die Arbeit schließt mit Beispielen der aktuellen und künftig zu erwartenden praktischen Naturschutzarbeit. Diese Beispiele werden anhand des Modells und der Analyseergebnisse diskutiert. Die vorliegende Arbeit bietet ein Erklärungsmodell für vergangene und gegenwärtige Entwicklungen und Ergebnisse im praktischen Naturschutz. Sie stellt eine Unterstützung für die realistische Einschätzung von Akteurskonstellationen und deren Akzeptanz von zukünftigen Implementierungsansätzen von Naturschutz dar

The market mechanism is the mechanism of interrelation and interaction of the basic elements of the market – demand, supply, prices, competition, and the basic economic laws of the market. Supply and demand are interdependent elements of the mechanism. The former is determined by the solvent demand of consumers and offer a set of goods proposed by sellers. The ratio between them is formed in an inverse relationship, determining the corresponding changes in the level of prices for goods.

Thesis (Ph.D)--Industrial and Systems Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Keskinocak, Pinar; Committee Co-Chair: Vande Vate, John; Committee Member: Ferguson, Mark; Committee Member: Griffin, Paul; Committee Member: Swann, Julie. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Business and Management. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

This investigation studied the physiological means by which myocardium can survive and function properly when oxygen supply is limited and cannot initially match oxygen demand. The effects of isoproterenol (ISO) stimulations during low coronary perfusion pressure or hypoxemia on myocardial oxygen demand, work, and oxygen utilization efficiency were investigated.

This thesis explores Centralised Demand Information Sharing (CDIS) in supply chains. CDIS is an information sharing approach where supply chain members forecast based on the downstream member’s demand. The Bullwhip Effect is a demand variance amplification phenomenon: as the demand moves upstream in supply chains, its variability increases. Many papers in the literature show that, if supply chain members forecast using the less variable downstream member’s demand, this amplification can be reduced leading to a reduction in inventory cost. These papers, using strict model assumptions, discuss three demand information sharing approaches: No Information Sharing (NIS), Downstream Demand Inference (DDI) and Demand Information Sharing (DIS). The mathematical analysis in this stream of research is restricted to the Minimum Mean Squared Error (MMSE) forecasting method. A major motivation for this PhD research is to improve the above approaches, and assess those using less restrictive supply chain assumptions. In this research, apart from using the MMSE forecasting method, we also utilise two non-optimal forecasting methods, Simple Moving Averages (SMA) and Single Exponential Smoothing (SES). The reason for their inclusion is the empirical evidence of their high usage, familiarity and satisfaction in practice. We first fill some gaps in the literature by extending results on upstream demand translation for ARMA (p, q) processes to SMA and SES. Then, by using less restrictive assumptions, we show that the DDI approach is not feasible, while the NIS and DIS approaches can be improved. The two new improved approaches are No Information Sharing – Estimation (NIS-Est) and Centralised Demand Information Sharing (CDIS). It is argued in this thesis that if the supply chain strategy is not to share demand information, NIS-Est results in less inventory cost than NIS for an Order Up To policy. On the other hand, if the strategy is to share demand information, the CDIS approach may be used, resulting in lower inventory cost than DIS. These new approaches are then compared to the traditional approaches on theoretically generated data. NIS-Est improves on NIS, while CDIS improves on the DIS approach in terms of the bullwhip ratio, forecast error (as measured by Mean Squared Error), inventory holding and inventory cost. The results of simulation show that the performance of CDIS is the best among all four approaches in terms of these performance metrics. Finally, the empirical validity of the new approaches is assessed on weekly sales data of a European superstore. Empirical findings and theoretical results are consistent regarding the performance of CDIS. Thus, this research concludes that the inventory cost of an upstream member is reduced when their forecasts are based on a Centralised Demand Information Sharing (CDIS) approach.

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.
"June 2008."
Includes bibliographical references (leaves 68-71).
Sales and operational planning that incorporates unconstrained demand forecasts has been expected to improve long term corporate profitability. Companies are considering such unconstrained demand forecasts in their decisions on investment in supply chain resources. However, demand forecasts are often associated with uncertainty. This research applies Monte Carlo simulation, value at risk and gain curve analysis, and real option analysis to investigate how the uncertainty of demands affects supply chain planning in order to make better supply chain investment decisions. This analytical framework was used to analyze the ocean shipping plans and inland trucking arrangements for Chiquita. Demands for Product A and front haul over a six-year period were simulated based upon forecasted distributions. The net income, revenue and costs as affected by ocean shipping plans were obtained by inputting the simulated demands to ocean shipping models. The major decision for Chiquita is whether to charter one large ship or two ships which provide approximately equivalent capacity. A large ship would save fuel costs. The plans for two smaller ships have the flexibility of using one ship only if future demand or price reactions warrant it. Using the analytical framework, a plan for two smaller ships is superior to that for one large ship because of significant real option value, particularly in the event of increases in fuel costs in the future. Chiquita's current inland trucking model, a mixed arrangement with a dedicated fleet and common carriers, seems to offer a good solution for the future needs. A model provided in this research offers a simple method to optimize the size of the dedicated fleet.
by Yanfeng Anna Huang.
M.Eng.in Logistics

The well-known "law of supply and demand" says that an increase in the price of a commodity leads to a decrease in the aggregate demand for this commodity and an increase in aggregate supply. There is, however, no theoretical foundation for this "law". Empirical evidence, on the other hand, should be interpreted with care. If one estimates the parameters of certain functional forms for demand and supply functions, then the results may simply be consequences of the parametric assumptions made in estimation. The first chapter of the thesis discusses the implications of the assumption of profit and utility maximisation for the properties of demand and supply functions. It explains why economic rationality on the microlevel does not, in general, lead to macroeconomic regularities and suggests replacing the consumption sector of the neoclassical equilibrium model by a large population of individually small consumers. Such a population will be explored in the second chapter. The chapter is a direct outgrowth of a basic contribution by W. Hildenbrand: "On the Law of Demand", Econometrica 1983. In W. Hildenbrand's model the market demand function is defined by integrating an individual demand function with respect to an exogenously given income distribution. We build into the model an individual labour supply function and then compare the matrix of aggregate income effects studied by W. Hildenbrand with that obtained by integrating the individual demand function with respect to a distribution of wage rates. The empirical part of the thesis analyses the labour supply and earnings data in the U.K. Family Expenditure Survey 1970-85. Using non- parametric smoothing methods, the elasticity of labour supply with respect to the wage rate is estimated for several groups of workers. The estimations for full-time workers confirm the famous "downward sloping" labour supply function. The estimated elasticities for the entire population of workers for the years 1970-85 have the mean value 0.2 and the standard deviation 0.02.

Labour market is a system of economic instruments, norms and institutions that establish the link between firms and is influenced by supply and demand price of labor. The most important element of the labor market is the demand for labor, which is determined by the number and structure of employment, volume of means of subsistence, are used to attract the workforce. Labor supply is the need of different groups of the working age population in receipt of employment. Labor demand reflects the need for a certain amount of economy workers on any given time.

Maximal oxygen consumption rates in exercising skeletal muscle are studied using a Krogh-type cylinder model. Effects of the decline in oxygen content of blood flowing along capillaries, intravascular resistance to oxygen diffusion, and myoglobin-facilitated diffusion are included. Parameter values are based on human skeletal muscle. The model is used to predict oxygen consumption rates in exercising skeletal muscle, based on transport processes occurring at the microvascular level. The dependence of maximal oxygen consumption rates on oxygen demand, perfusion, and capillary density (defined as number of capillaries per unit cross-section area of muscle) is examined. When demand is high, model results show that capillary oxygen content declines rapidly with axial distance and radial oxygen transport is limited by diffusion resistance within the capillary and within the tissue. Under these conditions, much of the tissue is hypoxic and consumption is substantially less than demand. Predicted consumption rates are compared with experimentally observed maximal rates of oxygen consumption. Capillary densities in human skeletal muscle are estimated by using the model to determine the minimum number of straight, evenly spaced capillaries required to achieve experimentally observed oxygen consumption rates. Estimated capillary density values are generally higher than values obtained using either histochemical staining techniques or electron microscopy on quadriceps muscle biopsies from healthy subjects. This discrepancy is partly accounted for by the fact that capillary density decreases with muscle contraction, and muscle biopsy samples typically are strongly contracted. These results imply that estimates of maximal oxygen transport rates based on capillary density values obtained from biopsy samples do not fully reflect the oxygen transport capacity of the capillaries in skeletal muscle. The model is also used to predict decreases in oxygen consumption in maximally exercising muscle due to reductions in the inspired partial pressure of oxygen. In general, observed reductions in maximal oxygen consumption rates due to hypoxic breathing conditions are larger than predicted by the model, suggesting that responses to hypoxia not currently included in the model, such as decreases in oxygen demand or in muscle blood flow, may be important in determining maximal oxygen consumption in hypoxic conditions.

Dissolved oxygen (DO) depletion in a water body is governed by two primary mechanisms: biological oxygen demand (BOD) from the water column, and sediment oxygen demand (SOD) from sediments. SOD is the dominant oxygen sink in many water bodies; measurements show as much as 95% of oxygen consumption as attributable to SOD (Truax, Shindala, & Sartain, 1996). Measuring SOD in surface water impoundments is an essential component in evaluating and an important input for modeling the health of a water body. Traditional SOD measurement methods are difficult in deeper waters, such as in reservoirs or lakes, because traditional SOD measurement chambers require direct placement. The goal of this research was to modify an existing SOD chamber design to support deployment and recovery in depths in excess of 5ft, typically from a boat or other floating platform. The design required accurate DO measurements, taken unattended and recorded for several hours to several days, for SOD calculations and other parameters such as cation releases under anaerobic conditions. Using a previously designed chamber, I developed tools and methods to meet these requirements. DO data logger probes were purchased so that DO calculations could be taken without the need of surface support. To mount the chambers inside the previously designed chambers, a new mounting mechanism was designed and installed onto the chamber lids. Deployment and recovery methods and design were developed to ensure the chambers would be recoverable from a boat in deep waters. Previously, the unmodified chambers could not be deployed unattended because of the required power and data link with the surface. Here I present an easily replicated chamber design that allows for remote chamber placement and measurement of SOD in deep waters without the need of SCUBA or other specialized equipment that is traditionally required. The chamber design allows water to circulate through the chambers until they are placed and closed on the sediment bed, at which time the measurements start, ensuring correct initial conditions. During deployment, the data logger will log DO concentrations at predetermined intervals for several hours or days at a time. To recover the chambers, the researcher must only find the buoy attached to the rope and hoist the units back to the surface. Modifications and methods were tested and revised over the course of several months and dozens of tests. Experiments were conducted at various depths, ranging from 12–50ft, which showed the versatility of the chambers. Using this design, other researchers will be able to generate substantial amounts of SOD data at depths that will allow accurate SOD behavior to be included in models of water impoundments.

There have been widespread reports of an impending teacher shortage crisis in the U.S. for more than 30 years. In the U.S., there are claims of a widespread national shortage while research indicates teacher shortages are specific to certain subjects and schools. Part of the reason for the conflicting accounts is how shortage is identified and what information is used to assess it. In this study, I test whether a uniform teacher shortage exists across the state of Arkansas. I hypothesize that, rather than a universal shortage, teacher shortages are more likely to occur in certain regions and subjects. I examine the characteristics of districts with the most favorable teaching supply and those with the greatest teaching need using descriptive and multivariate analysis of data collected from district surveys along with administrative data. In this study, “supply” is defined as the ratio of applications to vacancies and “need” is defined as the ratio of vacancies to full-time equivalent (FTE) certified classroom teachers. This is the third study to use applicants to identify teacher supply, and the first to assess teacher need or shortages in this way. Results indicate teacher supply and need are unequally distributed across the state; there is no uniform teacher shortage statewide. Regarding teacher supply, I find district size, region, and urbanicity appear to drive supply. Teacher supply is most favorable for large districts with student enrollments greater than 3,500, districts in the Northwest, and suburban and city districts. Regarding teacher need, I find urbanicity and region contribute most to need and the need appears greatest for districts in cities, and districts in the Central and Southeast regions. Teacher need does not appear to be significantly influenced by district educational success, teacher salary, or district growth. Looking at the relationship between teacher supply and need, I find three clear relationships. In the Central and Southeast regions, there is lower teacher supply and greater teacher need. In urban districts, there is both greater teacher supply and need. In higher poverty districts, there is significantly less teacher supply and more teacher need.

A presente dissertação tem como principal objetivo a conceituação e apresentação das metodologias básicas de previsão de demanda e, a partir de um estudo de caso, a seleção da metodologia mais adequada e sua respectiva implantação. No primeiro capítulo é apresentada, além da importância do referido tema, a empresa selecionada para aplicação dos conceitos levantados, com a descrição de seus principais processos internos. No segundo capítulo foram abordados os conceitos de previsão de demanda e uma revisão dos principais modelos existentes. No capítulo seguinte, o problema que deverá ser tratado com a metodologia proposta é apresentado. Neste momento a metodologia conceituada é aplicada, através da seleção do método de previsão mais adequado ao caso estudado e respectiva modelagem, buscando melhorias em relação aos métodos de previsão existentes na empresa. Neste processo de modelagem utilizou-se o software Forecast Pro, um dos mais conceituados aplicativos de previsão de demanda no mercado. Por fim, na conclusão, avalia-se o impacto das mudanças propostas nos resultados da empresa, principalmente o aumento da precisão da previsão da demanda e, conseqüentemente, redução dos custos de importação e dos índices de stockout.
The main objective of this dissertation is the presentation of basic forecasting methods and their implementation in a case study in supply chain. The first chapter points out the importance of forecasting in this context and describes the company selected for the case study and some of its internal processes that will be under scrutiny in the case study presented in this dissertation. The second chapter discusses the concepts and models of forecasting and reviews some of the major techniques in the field. In chapter three, standard forecasting techniques are apllied to real data (ten time series) from the company and select the most appropriate model in each case. Model adjustment is performed through the Forecast Pro software, one of the best-known products in the market. Chapter four contains the conclusions and the evaluation of the impacts of the proposed methodology on the company s results, especially the increased accuracy of forecasting and, consequently, the reduction in the import costs and stock out index.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, 2003.
Includes bibliographical references.
Essay One The Impact of Shortages on Push-Pull Production Systems This paper explores the impact of endogenous customer demand on supply chain instability. It investigates how a semiconductor manufacturer's hybrid push-pull production system responds to customer demand, when inventory availability influences demand. While customers' response to variable service level represents an important concern in industry with sizable impacts on company profitability, previous models exploring supply chain instability do not address it. This research incorporates customer response in two important ways. First, a negative feedback loop of lost sales captures the effect that an initial increase (decrease) in demand leads to a decrease (increase) in the manufacturer's service level, causing customer demand to decrease (increase). Second, a positive feedback loop of production push characterizes the manufacturer increase (decrease) in capacity utilization to respond to a surge (drop) in demand, leading to high (low) production volumes and service levels, and a further increase (decrease) in demand. The manufacturer's hybrid push-pull production system is very effective in meeting customer demand. Stockouts at different stages in the supply chain, however, can shift the operation mode of the system to a defacto push system. The shift to a push system decreases the manufacturers' service level and increases demand variability. The analysis suggests that the endogenous customer demand assumption influences the shifts in modes of operation through the lost sales and production push loops, leading to higher supply chain instability than when customer demand is modeled as exogenous.
(cont.) In addition, incorporating the endogenous demand assumption leads to a different inventory and utilization policies than the ones currently adopted. First, this research finds that supply chains can operate in multiple modes, due to demand instability. It also provides policies capable of mitigating the impact from shifts in operation modes. Second, it suggests that models investigating instability in supply chains assuming exogenous demand may underestimate the amplification in demand and the value of inventory buffers. The model analyzed in this paper gives insights into the costs of lean inventory strategies in the context of hybrid production systems. Essay Two Why do Shortages Inflate to Huge Bubbles? When demand exceeds supply, customers often hedge against shortages by placing multiple orders with multiple suppliers. The resulting demand bubble creates instability leading to excess capacity, excess inventory, low capacity utilization, and financial and reputation losses for suppliers and customers. This paper contributes to the understanding of demand bubbles caused by shortages by providing a comprehensive causal map of supplier-customer relationships and a formal mathematical model of a subset of those relationships. It provides closed form solutions for supply chain dynamics when supplier capacity is fixed and simulation analysis when it is flexible. Sensitivity analysis provides a deeper understanding of structures and decision rules that contribute to bubbles and suggests policies for improvement. For instance, the ability to quickly build capacity can reduce bubble size ...
by Paulo M. Gonçalves.
Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; in conjunction with the Leaders for Global Operations Program at MIT, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 80).
This paper attempts to provide a solution to a problem facing many multinational firms: the lack of an accessible and comprehensive database for up-to-date component part forecasts. We consider this problem in the context of ABB BU DMPE. After considering various requirements and constraints regarding the consolidation of forecasting information, we propose a novel combination of standardized process and the use of certain IT tools as a first step. After a test run, we discovered that consolidation of forecasting information increases transparency within the supply chain. As a corollary result of our pilot program, we propose that prior to any attempt at consolidation, enforcement of a standardized form and method of forecasting at the local level.
by Esther Lee.
M.B.A.
S.M.

A well-known concept, both in practice and in literature is the logistics market. This market is a place where shippers’ demand for logistics services meets Logistics Service Providers’ (LSPs’) supply of such services. Although this market has been given much attention in previous research, focus has been on shippers, while the LSP perspective has to a large extent been neglected. Several logistics related trends indicate that there is an increasing need for strong relationships between LSPs and supply chains, and one such trend is the “greening” of companies and supply chains. Although it is widely recognised that transports and  logistics are a major cause of greenhouse gas emissions, environmental logistics literature has only focused on the interaction between LSPs and their customers to a very limited extent. This is despite the fact that LSPs could include so-called green categories in their offerings, just as shippers could include green categories in their demands and that this interaction could in turn contribute to a decrease of greenhouse gas emissions. The purpose of this thesis is to describe the extent to which green categories are taken into account in the logistics market and suggest explanations. This includes identifying those green categories that are relevant for the logistics market, as well as a description of matches and mismatches with regard to these green categories. The matches and mismatches are studied from both a general market perspective and a relationship perspective. Initial explanations for the matches and mismatches in the relationship perspective contribute to the final part of the purpose. There are two basic theoretical starting-points in this thesis. Firstly, it is recognised that the logistics market is important to the purpose and different ways to view this market are therefore discussed. Secondly, general environmental logistics literature provides a basis for the research into green categories that can be offered or demanded on the logistics market. In the exploratoryresearch conducted for the thesis, the insights from literature are combined with empirical datafrom a survey, a homepage scan and four case studies of buyer-supplier relationships. One main contribution of this thesis is the large number of green categories that are identified as relevant for LSPs and shippers on the logistics market. These green categories range from environmental management systems, vehicle technologies and CO2 reports, to reviews of sustainability reports, relationship specific green projects and general desires among shippers to decrease CO2 emissions. A comparison of the supply of and demand for the green categories indicates that from a general market perspective, there appear to be clear mismatches between green supply and green demand. The same comparison made from a relationship perspective also indicates severalmismatches between green supply and green demand, but the buyer-supplier relationships studied show matches between green offerings and green demands to a greater extent than the market perspective does. Interestingly, the LSPs seem to include more in their offerings than the shippers appear to include in their demands for almost all mismatches in both the market perspective and the relationship perspective. Seven propositions are made to account for the matches and mismatches between green categories in buyer-supplier relationships. Three of these propositions are related to the characteristics of those green categories that are found in the relationships. It is suggested that the tangibility level of green categories influences the occurrence of matches and mismatches in the relationships and the more tangible a green category is, the higher is the likelihood of a match between supply and demand in that relationship. The opposite is also suggested, as well as the idea that the more relationship specific green categories are, the fewer the mismatches that appear in that relationship. The remaining four propositions relate to the potential connection between the type of relationship between LSPs and shippers and green matches and mismatches in their relationships. It is suggested that the closer a business relationship is, 1) the greater the number of green categories it has 2) the better green categories are communicated 3) the greater the number of matches compared to mismatches of green categories and 4) the higher the level of green category collaboration is.

China has experienced incredible growth in the number of nongovernmental organizations (NGO) that occupy civil society. These organizations came forth at a time of rapid economic and political change. Instead of being given a supportive legal path for their work, NGOs have had to navigate the supply and demand factors in their specific situation in order to flourish. The demand side factors chiefly consist of matters pertaining to the need an NGO is meeting; and supply side factors pertain to an NGO's ability to create infrastructure to support their organization, including both the space in society to function and the processes necessary to fund their operation. By understanding the supply and demand side factors of the third sector, NGOs are able to achieve effectiveness in a variety of different capacities. In the current regulatory framework, many of these capacities are not entirely legal, but NGOs continue to find ways to make these arrangements work. Intermediary NGOs are a special type of NGO that positions itself to benefit both the donor and the beneficiary and help both overcome some of the challenges presented by the difficult regulatory environment. In doing this, intermediary NGOs fulfill a special role in meeting supply and demand in the third sector and can propose many useful solutions for philanthropy in China today.

Thesis: M. Eng. in Supply Chain Management, Massachusetts Institute of Technology, Supply Chain Management Program, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 52-53).
While festivals bring a reason to cheer for everyone, businesses dealing with a spike in demand for perishables may have to live with the misery of lost sales and/or expired items. In the case of the dairy industry that deals with liquid milk, both raw material, and finished goods are perishable, which implies that merely stockpiling inventory of either item, without paying attention to potential inventory losses, cannot be an optimal strategy. In developing countries, the supplier base for perishables like milk, fruits, vegetables, flowers, etc. mostly comprise of small farmers instead of corporate/professional agencies, thus leading to supply variability. During special occasions like festivals, as individuals set aside more of the raw material for their own consumption, we encounter a reduction in supply. Around the same time, we notice a spike in customer demand, leading to a demand-supply mismatch. Companies dealing with perishables need an analytical approach to manage this.
In this thesis, we present a framework to address this problem of intermittent demand-supply mismatch using a 3-stage stochastic optimization model. We decide on the sourcing targets, the production plans based on supply realized, and finally, the dispatch plan based on orders received. As a case study, we analyze the operations and data from a private dairy company in eastern India, to understand the research problem and the applicability of the resulting model. We notice the impact of demand spikes and supply reduction in two areas: we increase supply targets in the periods preceding the demand spike; and we increase supply targets in periods when supply is expected to decrease, while demand is as usual. When there are multiple festival days within the time series, the compounding of impact depends on the sequencing of the events.
Finally, when we introduce the realistic constraint that the supply target needs to be constant throughout the time series, we see a degradation in the profitability, as we need to tradeoff between lost sales and wasted products. While the focus of this case study is the dairy industry, the conclusions from this research are broadly applicable to other industries dealing with perishables.
by Vishwanathan Parameshwaran lyer Nurani.
M. Eng. in Supply Chain Management
M.Eng.inSupplyChainManagement Massachusetts Institute of Technology, Supply Chain Management Program

The Upper Souris River was placed on the Environmental Protection Agencies (EPA) impaired waters list for low dissolved oxygen (DO). A Total Maximum Daily Load (TMDL) study was conducted to determine possible causes of DO depletion. From sampling and site visits it was determined nonpoint sources contributed the majority of organic loadings to the Upper Souris River. Through preliminary testing, it was determined that sediment oxygen demand (SOD) played a key role in depleting DO levels during winter months and required further investigation. River profile surveying, water quality sampling, and laboratory testing of SOD were carried out to determine parameters required for water quality modeling. SOD tests were conducted to determine impacts of sediment organic contents and temperature on SOD rate. Sediment oxygen demand rates ranged from 0.37 to 1.22 g O2/m2/d. The QUAL2K model was calibrated to simulate DO variations along the study reach under ice covered conditions.