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Optimal Level (optimal + level)
Selected AbstractsHerbivore-Mediated Competition between Defended and Undefended Plant Species: A Model to Investigate Consequences of Climate ChangePLANT BIOLOGY, Issue 5 2002C. F. Dormann Abstract: Optimal levels of anti-herbivore defence are determined not only by grazing pressure on the target plant, but also by the efficiency of the defence and by competitive interactions with neighbours. In the high Arctic on Svalbard, grazing by reindeer is a process that can be modelled without plant-to-herbivore feedback, as reindeer population sizes are not correlated with plant growth. However, growing conditions are extreme: a short season and low temperatures inhibit optimal growth. Therefore, it is possible to model anti-herbivore defence in competition in this system, assess how its optimum depends on grazing intensity and defence efficiency, and, finally, how global climate change will effect plant-plant interactions. This model, based on a Lotka-Volterra type competition and temperature-dependent growth, indicates that competition is of considerable importance even in extreme environments. Herbivory mediates displacement of the defended plant by releasing it from competition. This process is more pronounced under high grazing pressure than under low pressure. In other words, competition potentially magnifies the effect of herbivory. Elevated temperatures and a longer growing season have no qualitative impact on these processes, as the dominant defended plant profits most. [source] Competition and Cost Accounting: Adapting to Changing Markets,CONTEMPORARY ACCOUNTING RESEARCH, Issue 2 2002Ranjani Krishnan Abstract The relation of competition and cost accounting has been the subject of conflicting prescriptions, theories, and empirical evidence. Practitioner literature and textbooks argue that higher competition generally requires more accurate product costing. Theoretical economic analysis, in contrast, predicts that the optimal level of product-costing accuracy is sometimes higher at lower levels of competition. Results of survey research are inconsistent, suggesting a need for further identification of conditions under which higher competition leads to more accurate product costing. This study shows experimentally that individuals' choices of the level of product-costing accuracy depend not only on the current level of competition but also on the previous level of competition , that is, on an interaction between market structure (monopoly, duopoly, and four-firm competition) and market history (increasing versus decreasing competition). In the experiment, subjects decide on the quantity of data to collect at a pre-set price per datum to support more accurate product-cost estimates. Subjects collect the most cost data (i.e., choose the most accurate product costing) in monopoly, collect the least in duopoly, and an intermediate amount in the four-firm market, consistent with the pattern of optimal cost-data collection in Hansen's 1998 model. The process of convergence to the optimum differs significantly across market types and market histories, however. Subjects who begin in four-firm competition adapt more successfully to change than those who begin in monopoly. The lowest levels of decision performance occur when ex-monopolists face their first competitor: they overreact to this first encounter with competition and overspend on cost data. [source] Optimal Board Monitoring in Family-owned Companies: Evidence from AsiaCORPORATE GOVERNANCE, Issue 1 2010En-Te Chen ABSTRACT Manuscript Type: Empirical Research Question/Issue: We propose that high levels of monitoring are not always in the best interests of minority shareholders. In family-owned companies the optimal level of board monitoring required by minority shareholders is expected to be lower than that of other companies. This is because the relative benefits and costs of monitoring are different in family-owned companies. Research Findings/Insights: At moderate levels of board monitoring, we find concave relationships between board monitoring variables and firm performance for family-owned companies but not for other companies. The optimal level of board monitoring for our sample of Asian family-owned companies equates to board independence of 38 per cent, separation of the chairman and CEO positions, and establishment of audit and remuneration committees. Additional testing shows that the optimal level of board monitoring is sensitive to the magnitude of the agency conflict between the family group and minority shareholders and the presence of substitute monitoring. Theoretical/Academic Implications: This study shows that the effect of additional monitoring on agency costs and firm performance differs across firms with different ownership structures. Practitioner/Policy Implications: For policymakers, the results show that more monitoring is not always in the best interests of minority shareholders. Therefore, it may be inappropriate for regulators to advise all companies to follow the same set of corporate governance guidelines. However, our results also indicate that the board governance practices of family-owned companies are still well below the identified optimal levels. [source] Channel Strategies and Stocking Policies in Uncapacitated and Capacitated Supply Chains,DECISION SCIENCES, Issue 2 2002Jayashree Mahajan ABSTRACT A supply chain consisting of a single supplier distributing two independent products through multiple retailers is analyzed in this paper. The supplier needs to incentivize its retailers to adopt stocking policies that are mutually advantageous and that result in the optimal level of market coverage. The focus is on determining the optimal stocking policies for retailers and the resulting distribution strategy given that the supplier has either unlimited or limited capacity. The results provide insights on the optimal distribution strategy and stocking policies for the supply chain. In general, the paper shows that it is optimal for the supplier to use an intensive distribution strategy (i.e., the products are stocked by all retailers). Selective or exclusive strategies are optimal only when retailers are risk averse, stocking synergies exist, and there are differences in demand or supply uncertainties across products. The analysis also shows that retailers hold larger stocks of a product which generates higher supplier margins but only when the supplier has unlimited capacity. If the supplier has limited capacity, then their margins have no effect on retailers' stocking decisions. Contrary to conventional wisdom, retailers hold larger stocks of a product that has less demand uncertainty as compared to one that has more demand uncertainty. [source] THE EFFECTS OF UNCERTAINTY ON THE LEVERAGE OF NONFINANCIAL FIRMSECONOMIC INQUIRY, Issue 2 2009CHRISTOPHER F. BAUM This paper investigates the link between the optimal level of nonfinancial firms' short-term leverage and macroeconomic and idiosyncratic sources of uncertainty. We develop a structural model of a firm's value maximization problem that predicts a negative relationship between uncertainty and optimal levels of borrowing. This proposition is tested using a panel of nonfinancial U.S. firms drawn from the COMPUSTAT quarterly database covering the period 1993,2003. The estimates confirm that as either form of uncertainty increases, firms decrease their levels of short-term leverage. This effect is stronger for macroeconomic uncertainty than for idiosyncratic uncertainty. (JEL C23, D8, D92, G32) [source] Do patents over-compensate innovators?ECONOMIC POLICY, Issue 52 2007Vincenzo Denicolò SUMMARY Do patents over-compensate innovators? Is the current level of patent protection too high or too low? To address this issue, this paper reformulates the theoretical analysis of the optimal level of patent protection to take into account the empirical findings of the innovation production function literature. This literature finds a strong relationship between R&D spending and inventions and estimates an elasticity of the supply of inventions of 0.5 or more. The paper then assesses the current level of patent protection, exploiting estimates of the private and social returns to R&D taken from the empirical literature and other available sources. Although more research is needed for a more precise assessment, the evidence available suggests that patents do not over-compensate innovators. ,Vincenzo Denicolò [source] Oral vitamin E supplementation on oxidative stress, vitamin and antioxidant status in intensely exercised horsesEQUINE VETERINARY JOURNAL, Issue S36 2006C. A. WILLIAMS Summary Reasons for performing study: Vitamin E is the most commonly supplemented antioxidant in horses; however, previous research is not conclusive as to the recommended level for exercising horses. Objective: To evaluate the effects of 3 levels of vitamin E supplementation on oxidative stress and vitamin/antioxidant status in intensely exercised horses to determine the optimal level of vitamin E supplementation. Methods: Twelve unfit Standardbreds were divided into 3 groups, supplemented orally with 0 (CON), 5000 (MOD), or 10,000 (HI) iu/day of DL-,-tocopheryl acetate. The 3 times 3 Latin square design consisted of three 4 week supplementation periods with 4 week wash out periods between. After each period, horses underwent a treadmill interval exercise test. Blood samples were collected and heart rate (HR) measured before, during and after exercise. Data were analysed using ANOVA with repeated measures in SAS. Results: The CON group had lower HR throughout the test compared to the MOD and HI groups (P<0.05). There was an increase in plasma retinol (RET), ,-carotene (BC), red blood cell total glutathione and glutathione peroxidase with exercise (P<0.05), but all groups returned to baseline after 24 h. Plasma ,-tocopherol (TOC) increased from baseline with exercise (P<0.0001) in all groups; treatment differences were observed at 24 h (P<0.05). The HI and CON groups had lower BC compared to the MOD group (P = 0.05). Conclusions: Horses supplemented with vitamin E, at nearly 10-times the 1989 NRC recommended level, did not experience lower oxidative stress compared to control horses. Additionally, lower plasma BC levels observed in the HI group, which may indicate that vitamin E has an inhibitory effect on BC metabolism. Potential relevance: Supplementation above control levels is not more beneficial to oxidative stress and antioxidant status in intensely exercising horses; indeed, levels 10 times in excess may be detrimental to BC and should be avoided. [source] The Underinvestment and Overinvestment Hypotheses: an Analysis Using Panel DataEUROPEAN FINANCIAL MANAGEMENT, Issue 2 2003Artur Morgado G31 We study the relationship between firm value and investment to test the underinvestment and overinvestment hypotheses. The results obtained, using panel data methodology as the estimation method, indicate that the abovementioned relation is quadratic, which implies that there exists an optimal level of investment. As a consequence, firms that invest less than the optimal level suffer from an underinvestment problem, while those investing more than the optimum suffer from overinvestment. The quadratic relation is maintained when firms are classified depending on their investment opportunities, the optimum being in accordance with the quality of investment opportunities. [source] Effects of dopamine-related gene,gene interactions on working memory component processesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2009Christine Stelzel Abstract Dopamine modulates complex cognitive functions like working memory and cognitive control. It is widely accepted that an optimal level of prefrontal dopamine supports working memory performance. In the present study we used a molecular genetic approach to test whether the optimal activity of the dopamine system for different component processes of working memory is additionally related to the availability of dopamine D2 receptors. We sought evidence for this assumption by investigating the interaction effect (epistasis) of variations in two dopaminergic candidate genes: the catechol- O -methyltransferase (COMT) Val158Met polymorphism, which has been shown to influence prefrontal dopamine concentration, and the DRD2/ANKK1-Taq-Ia polymorphism, which has been related to the density of D2 receptors. Our results show that COMT effects on working memory performance are modulated by the DRD2/ANKK1-TAQ-Ia polymorphism and the specific working memory component process under investigation. Val, participants , supposedly characterized by increased prefrontal dopamine concentrations , outperformed Val+ participants in the manipulation of working memory contents, but only when D2 receptor density could be considered to be high. No such effect was present for passive maintenance of working memory contents or for maintenance in the face of distracting information. This beneficial effect of a balance between prefrontal dopamine availability and D2 receptor density reveals the importance of considering epistasis effects and different working memory subprocesses in genetic association studies. [source] Female zebra finches compromise clutch temperature in energetically demanding incubation conditionsFUNCTIONAL ECOLOGY, Issue 5 2010Andreas Nord Summary 1.,Avian embryos depend on the incubating parent to provide a thermal environment suitable for embryogenesis, but as the maintenance of optimal incubation temperatures is energetically costly, an incubating bird often must trade off embryonic investment against self-maintenance. 2.,We manipulated the energetic cost of incubation in female zebra finches (Taeniopygia guttata Vieillot) by varying ambient temperature and clutch size during nocturnal incubation and recorded the corresponding effects on incubation metabolic rate and clutch temperature. 3.,Females increased their night-time incubation metabolic rate more than twofold when incubating at 10 °C compared to when incubating close to thermoneutrality (28 °C). Furthermore, clutch enlargement caused females to elevate their metabolic rate with 2·8% per additional egg added to the clutch. 4.,However, despite spending more energy, females did not fully cover the increased costs of incubation, because clutch temperature decreased with decreasing ambient temperature and increasing clutch size. 5.,These findings suggest that parental investment in incubation can be energetically constrained and sometimes result in clutch temperatures below the optimal level for embryonic development, at least during nocturnal incubation. [source] Optimal treatment of hypertension in the elderly: A Korean perspectiveGERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 1 2008Kwang-Il Kim With the progression of the aging population, common diseases of the elderly have become the center of attention in most developed countries. Hypertension is one of the most common morbid conditions in the elderly and has a great impact on their health status because it is the main risk factor of cardiovascular and cerebrovascular diseases. However, a considerable amount of uncertainty remains regarding hypertension in the elderly, such as the benefits of hypertension control in oldest-old populations, the optimal level of blood pressure control, and the efficacy of antihypertensive drugs for the prevention of cognitive dysfunction. While there are many controversial issues concerning the optimal management of hypertension in the elderly, the number of elderly hypertensive patients that require treatment is expected to increase due to the aging population. As a result, knowledge regarding the mechanisms of hypertension in the elderly and specific consideration in managing hypertensive elderly patients are needed to improve the clinical outcome. Furthermore, new therapeutic interventions that are aimed at attenuating age-related vascular changes should be investigated, because hypertension in the elderly, especially isolated systolic hypertension has specific characteristics of increased arterial stiffness in most cases. [source] Rational Migration Policy Should Tolerate Non-zero Illegal Migration Flows: Lessons from Modelling the Market for Illegal MigrationINTERNATIONAL MIGRATION, Issue 1 2002Horst Entorf The debate on the immigration policies in OECD countries has turned its attention towards illegal migrants. Given that migration flows are determined by immigration laws, the probability of potential detection, penalties for unauthorized migrants and their employers, and income differences between sending and receiving countries, this paper presents a new approach to the problem of illegal migration, grounded on the economic theory of illegal behaviour. The framework considers the interaction of potential migrants, citizens, employers, and the government. After introducing the supply function of illegal migration and its determinants, the trade-off between social costs and benefits of preventing and combating illegal migration is demonstrated. This trade-off results in an optimal level of migration larger than zero. A complete "market model" of illegal migration is offered by presentation of a demand curve of illegal migration, based on the tolerance of the society towards clandestine foreigners. Equilibrium forces predict a non-zero level of illegal migration. The rule of law of our legal systems, according to which any illegal activity has to be reduced to zero, bears the danger of producing inefficient disequilibria. A reasonable policy of wanted and unwanted migration should address the question of how to allocate scarce resources. Ignoring social optima and equilibrium forces means to abandon public resources that could be used for other public assignments, such as schooling or foreign aid, for instance, i.e., measures that could strike the problem of illegal migration at its root. [source] Increasing Dietary Protein Requirements in Elderly People for Optimal Muscle and Bone HealthJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 6 2009Erin Gaffney-Stomberg MS Osteoporosis and sarcopenia are degenerative diseases frequently associated with aging. The loss of bone and muscle results in significant morbidity, so preventing or attenuating osteoporosis and sarcopenia is an important public health goal. Dietary protein is crucial for development of bone and muscle, and recent evidence suggests that increasing dietary protein above the current Recommended Dietary Allowance (RDA) may help maintain bone and muscle mass in older individuals. Several epidemiological and clinical studies point to a salutary effect of protein intakes above the current RDA (0.8 g/kg per day) for adults aged 19 and older. There is evidence that the anabolic response of muscle to dietary protein is attenuated in elderly people, and as a result, the amount of protein needed to achieve anabolism is greater. Dietary protein also increases circulating insulin-like growth factor, which has anabolic effects on muscle and bone. Furthermore, increasing dietary protein increases calcium absorption, which could be anabolic for bone. Available evidence supports a beneficial effect of short-term protein intakes up to 1.6 to 1.8 g/kg per day, although long-term studies are needed to show safety and efficacy. Future studies should employ functional measures indicative of protein adequacy, as well as measures of muscle protein synthesis and maintenance of muscle and bone tissue, to determine the optimal level of dietary protein. Given the available data, increasing the RDA for older individuals to 1.0 to 1.2 g/kg per day would maintain normal calcium metabolism and nitrogen balance without affecting renal function and may represent a compromise while longer-term protein supplement trials are pending. J Am Geriatr Soc 57:1073,1079, 2009. [source] TOWARD A MORE COMPLETE MODEL OF OPTIMAL CAPITAL STRUCTUREJOURNAL OF APPLIED CORPORATE FINANCE, Issue 1 2002Roger Heine Most corporate finance practitioners understand the trade-off involved in making effective use of debt capacity while safeguarding the firm's ability to execute its business strategy without disruption. But quantifying that trade-off to arrive at an optimal level of debt can be a complicated and challenging task. This paper develops a simulation model of capital structure that starts by generating multiple estimates of market rates (LIBOR, currency rates) and corresponding company operating cash flows. To arrive at an optimal capital structure, the model then incorporates the shareholder value effects of alternative financing decisions by directly measuring the costs of financial distress, including the costs of missed investment opportunities and higher working capital requirements. The model generates both a target credit rating and a lower fallback rating that permits a higher level of debt to maintain investments and dividends when operating cash flows are weak. As the model shows, companies with volatile cash flows and significant investment opportunities can add substantial shareholder value by establishing a fallback credit rating that is one or two notches below the target rating. The model also optimizes the mix of fixed versus floating debt, the maturity structure, and the currency composition. Another distinctive feature of the model is its ability to estimate the expected cost of alternative liability structures that can provide the liquidity insurance necessary to sustain the firm through periods of severe stress. This cost turns out to be quite small relative to the total market capitalization of the average firm. [source] Migration and welfare: a very simple modelJOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 7 2007Roberto Cellini Abstract The paper presents a very simple model of migration, relying on three widely accepted points: first, labour productivity and wages in a country depend on the present average human capital; second, agents maximise their utility, so that migration decisions depend on the wage gap across economies; third, the larger the personal human capital, the higher the propensity is to migrate (ceteris paribus). The model shows that migration through its external effects always lowers the welfare in the sending country, while the effects on the receiving country can be positive or negative. As a consequence, selfish developed economies could desire a larger migration than the optimal level for a benevolent World Planner. This calls for international coordination concerning the regulation of migration flows. Copyright © 2007 John Wiley & Sons, Ltd. [source] The two faces of knowledge diffusion: the Chilean caseJOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 1 2006Piergiuseppe Morone This paper analyses the dynamics of return to knowledge where knowledge is acquired through the combination of interactive and individual learning. We suggest that in light of this new definition of knowledge, choosing the optimal level of education is no longer an individual exercise of present and future utility maximization as suggested by formal human capital theory. We find that other external (environmental) variables might affect the individual decision of investment. We calculate the effect of individual and interactive learning on determining the wage of Chilean male workers resident in urban areas and aged between 14 and 65. Copyright © 2005 John Wiley & Sons, Ltd. [source] Firm value, managerial confidence, and investments: The case of ChinaJOURNAL OF LEADERSHIP STUDIES, Issue 3 2008Bei Ye The purpose of this article is to test empirically the impact of Chinese managerial confidence on firm value through investment decisions. We use a simultaneous equation model, which treats firm value, investments, and managerial confidence as endogenous to the firm. With a sample of 329 Chinese listed firms and a confidence measure based on management shareholding, the 3SLS regression results show significant interactions among the three variables. Firm value has a positive impact on managerial confidence while the latter's impact on the former turns from positive to negative at a certain point. The results suggest a non-monotonic relationship between managerial self-confidence and firm value and imply an optimal level of managerial confidence. Therefore, while the leader selection process encourages confident talents to become decision-makers, proper measures are required to prevent the confidence transformed into overconfidence. [source] Monetary Policy under Alternative Asset Market Structures: The Case of a Small Open EconomyJOURNAL OF MONEY, CREDIT AND BANKING, Issue 7 2009BIANCA DE PAOLI welfare; optimal monetary policy; asset markets; small open economy Can the structure of asset markets change the way monetary policy should be conducted? Following a linear-quadratic approach, the present paper addresses this question in a New Keynesian small open economy framework. Our results reveal that the configuration of asset markets significantly affects optimal monetary policy and the performance of standard policy rules. In particular, when comparing complete and incomplete markets, the ranking of policy rules is entirely reversed, and so are the policy prescriptions regarding the optimal level of exchange rate volatility. [source] Modernization of Tax Administrations and Optimal Fiscal PoliciesJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 6 2009MARTIN BESFAMILLE Since Sandmo (1981), many articles have analyzed optimal fiscal policies in economies with tax evasion. All share a feature: they assume that the cost of enforcing the tax law is exogenous. However, governments often invest resources to reduce these enforcement costs. In a very simple model, we incorporate such investments in the analysis of an optimal fiscal policy. We characterize their optimal level and we show numerically how they interact with the other dimensions of the optimal fiscal policy. Finally, we highlight the differences between our results and those obtained in a model without investment in the tax administration. [source] Noise and background removal in Raman spectra of ancient pigments using wavelet transformJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2005Pablo Manuel Ramos Abstract The wavelet transform was applied to Raman spectra to remove heteroscedastic noise from ancient pigments such as azurite and ultramarine blue. Wavelets from the Daubechies, Coiflet and Symmlet families were evaluated. Two different thresholding strategies on the detail coefficients were applied; the first is a one-dimensional variance adaptive thresholding and the second is a block threshold denoising. The block thresholding strategy removes the noise and preserves the band shapes best. Background removal during the denoising process was also investigated and the results were very good when the block thresholding strategy was used to suppress background at the optimal level of the denoising process. Copyright © 2005 John Wiley & Sons, Ltd. [source] Registered nurse-administered propofol sedation for endoscopyALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 2 2004S. C. Chen Summary Propofol has several attractive properties that render it a potential alternative sedative agent for endoscopy. Compared with meperidine and midazolam, it has an ultra-short onset of action, short plasma half-life, short time to achieve sedation, faster time to recovery and discharge, and results in higher patient satisfaction. Shorter times to achieve sedation enhance efficiency in the endoscopy unit. Multiple studies have documented the safe administration of propofol by non-anaesthesiologists. Administration by registered nurses is more cost-effective than administration by anaesthesiologists. However, the administration of propofol by a registered nurse supervised only by the endoscopist is controversial because the drug has the potential to produce sudden and severe respiratory depression. More information is needed on how training nurses and endoscopists should proceed to give propofol, as well as the optimal level of monitoring to ensure the safety of nurse-administered propofol. [source] Behavioral uncertainty and investments in cooperative relationshipsMANAGERIAL AND DECISION ECONOMICS, Issue 1 2004Rudolf Vetschera We study a cooperative relationship between two economic agents, in which one agent can make investments in the relationship to reduce the probability that the other agent defects. The probability of defection is derived from an incomplete information decision model of the transaction partner. We show that the relationship between investment and probability of defection depends on the type of uncertainty considered and analyze the effects of parameter changes on the optimal level of investment. Copyright © 2004 John Wiley & Sons, Ltd. [source] Does asthma control correlate with quality of life related to upper and lower airways?ALLERGY, Issue 6 2009A real life study Background:, The goal of asthma therapy is to achieve an optimal level of disease control, but the relationship between asthma control, impact of comorbid rhinitis and health related quality of life (HRQoL) in real life remains unexplored. Objective:, The aims of this real life study were to evaluate asthma control, the impact of asthma (with and without rhinitis) on HRQoL, the relationship between asthma control and HRQoL, and the role of rhinitis on asthma control and HRQoL. Methods:, 122 asthma patients completed the Asthma Control Test, Rhinitis Symptoms score (T5SS) and RHINASTHMA. Results:, Asthma control was unsatisfactory (44.27% of uncontrolled patients), as well as HRQoL. Controlled patients controlled showed significantly lower scores in all the RHINASTHMA domains compared to uncontrolled. Irrespective of their level of control, patients with rhinitis symptoms showed worse HRQoL in Upper Airways (UA) (P < 0.0001), Lower Airways (LA) (P < 0.001), and Global Summary (GS) (P < 0.0001). In patients with symptomatic rhinitis, RHINASTHMA were lower in controlled asthma patients (UA P = 0.002; LA P < 0.0001; RAI P < 0.01; GS P < 0.0001). Asthma control was associated with lower T5SS score (P = 0.034). Conclusion:, Asthma control in real life is unsatisfactory. Rhinitis and asthma influence each other in terms of control and HRQoL. The control of rhinitis in asthma patients can lead to an optimization of HRQoL related to the upper airways, while this phenomenon is not so evident in asthma. These results suggest to strengthen the ARIA recommendation that asthma patients must be evaluated for rhinitis and vice versa. [source] Translation at higher than an optimal level interferes with coupling at an intercistronic junctionMOLECULAR MICROBIOLOGY, Issue 3 2001Jae-Sung Yu In pairs of adjacent genes co-transcribed on bacterial polycistronic mRNAs, translation of the first coding region frequently functions as a positive factor to couple translation to the distal coding region. Coupling efficiencies vary over a wide range, but synthesis of both gene products at similar levels is common. We report the results of characterizing an unusual gene pair, in which only about 1% of the translational activity from the upstream gene is transmitted to the distal gene. The inefficient coupling was unexpected because the upstream gene is highly translated, the distal initiation site has weak but intrinsic ability to bind ribosomes, and the AUG is only two nucleotides beyond the stop codon for the upstream gene. The genes are those in the filamentous phage IKe genome, which encode the abundant single-stranded DNA binding protein (gene V) and the minor coat protein that caps one tip of the phage (gene VII). Here, we have used chimeras between the related phage IKe and f1 sequences to localize the region responsible for inefficient coupling. It mapped upstream from the intercistronic region containing the gene V stop codon and the gene VII initiation site, indicating that low coupling efficiency is associated with gene V. The basis for inefficient coupling emerged when coupling efficiency was found to increase as gene V translation was decreased below the high wild-type level. This was achieved by lowering the rate of elongation and by decreasing the efficiency of suppression at an amber codon within the gene. Increasing the strength of the Shine,Dalgarno interaction with 16S rRNA at the gene VII start also increased coupling efficiency substantially. In this gene pair, upstream translation thus functions in an unprecedented way as a negative factor to limit downstream expression. We interpret the results as evidence that translation in excess of an optimal level in an upstream gene interferes with coupling in the intercistronic junction. [source] Trichome production and spatiotemporal variation in herbivory in the perennial herb Arabidopsis lyrataOIKOS, Issue 1 2007Geir Løe Allocation theory suggests that the optimal level of resistance against herbivores should vary with the risk of herbivory if allocation to resistance is costly. The perennial herb Arabidopsis lyrata has a genetically based polymorphism for trichome production and occurs in a glabrous and a trichome-producing form. Leaf trichomes (hairs) can protect plants against insect herbivores, and may increase tolerance to drought and UV-radiation. To examine the functional significance of trichome production, we documented the frequency of glabrous plants and damage by insect herbivores in 30 A. lyrata populations in Sweden and Norway. The proportion of glabrous plants ranged from 0.10 to 0.71 (median=0.44) in polymorphic populations; 7 of 12 populations in Norway and 14 of 18 populations in Sweden were monomorphic glabrous, i.e. with fewer than 5% trichome-producing plants. The mean proportion of the leaf area removed by herbivores varied substantially among populations and years. With few exceptions, glabrous plants were more damaged than trichome-producing plants in polymorphic populations. The intensity of herbivory quantified as the mean damage to glabrous plants tended to be higher in polymorphic populations than in populations monomorphic for the glabrous morph and was higher in Sweden than in Norway. In Norway, both the magnitude of herbivore damage and the frequency of trichome-producing plants tended to decrease with increasing altitude. The results indicate that leaf trichomes contribute to resistance against herbivorous insects in A. lyrata, and suggest that herbivore-mediated selection contributes to the maintenance of the polymorphism in trichome production. [source] Hedging under counterparty credit uncertaintyTHE JOURNAL OF FUTURES MARKETS, Issue 3 2008Olivier Mahul This study investigates optimal production and hedging decisions for firms facing price risk that can be hedged with vulnerable contracts, i.e., exposed to nonhedgeable endogenous counterparty credit risk. When vulnerable forward contracts are the only hedging instruments available, the firm's optimal level of production is lower than without credit risk. Under plausible conditions on the stochastic dependence between the commodity price and the counterparty's assets, the firm does not sell its entire production on the vulnerable forward market. When options on forward contracts are also available, the optimal hedging strategy requires a long put position. This provides a new rationale for the hedging role of options in the over-the-counter markets exposed to counterparty credit risk. © 2008 Wiley Periodicals, Inc. Jrl Fut Mark 28: 248,263, 2008 [source] A comparison of quality function deployment and conjoint analysis in new product designTHE JOURNAL OF PRODUCT INNOVATION MANAGEMENT, Issue 5 2002Madeleine E. Pullman In this work, we compare two product design approaches, quality function deployment (QFD) and conjoint analysis, by applying each to the design of a new all-purpose climbing harness for the beginning/intermediate ability climber that would complement a leading manufacturer's existing product line. While many of the optimal design features were the same under both approaches, the differences allow us to highlight the strengths of each approach. With conjoint analysis, it was easier to compare the most preferred features (i.e., ones that maximized sales) to profit maximizing features and also to develop designs that optimize product line sales or profits. On the other hand, QFD was able to highlight the fact that certain engineering characteristics or design features had both positive and negative aspects. This tradeoff could point the way to "out of the box" solutions. QFD also highlighted the importance of starting explicitly with customer needs, regardless of which method is used. Rather than competing, we view them as complementary approaches that should be conducted simultaneously; each providing feedback to the other. When the two approaches differed on the optimal level or importance of a feature, it appeared that conjoint analysis better captured customers' current preferences for product features while QFD captured what product developers thought would best satisfy customer needs. Looking at the problem through these different lenses provides a useful dialogue that should not be missed. QFD's ability to generate creative or novel solutions should be combined with conjoint analysis' ability to forecast market reaction to design changes. © 2002 Elsevier Science Inc. All rights reserved. [source] Dynamics of Capital Structure: The Case of Korean Listed Manufacturing Companies,ASIAN ECONOMIC JOURNAL, Issue 3 2006Hyesung Kim C33; D21; G32 In this paper, we develop a model of dynamic capital structure choice based on a sample of Korean manufacturing firms and estimate the unobservable optimal capital structure using a wide range of observable determinants. Unbalanced panel data of Korean listed firms for the period 1985,2002 is used. In addition to identifying and estimating the effects of the determinants of capital structure, we take into consideration some Korea-specific features, such as the structural break before and after the financial crisis and firms' affiliation to chaebol business groups. Our results indicate that the optimal capital structure has been affected by the financial crisis. Although the results suggest that chaebol-affiliated firms have higher optimal level of leverage and adjust their capital structure faster than non-chaebol firms, firms' leverage might be associated with factors other than chaebol-affiliation, such as size, profitability and growth opportunity. [source] A wheat embryo cell-free protein synthesis system not requiring an exogenous supply of GTPBIOTECHNOLOGY PROGRESS, Issue 5 2009Hirohisa Koga Abstract Most in vitro protein synthesis systems require a supply of GTP for the formation of translation initiation complexes, with two GTP molecules per amino acid needed as an energy source for a peptide elongation reaction. In order to optimize protein synthesis reactions in a continuous-flow wheat embryo cell-free system, we have examined the influence of adding GTP and found that the system does not require any supply of GTP. We report here the preparation of a wheat embryo extract from which endogenous GTP was removed by gel filtration, and the influence of adding GTP to the system on protein synthesis reactions. Using Green Fluorescent Protein (GFP) as a reporter, higher levels of production were observed at lower concentrations of GTP, with the optimal level of production obtained with no supply of GTP. A HPLC-based analysis of the extract and the translation mixture containing only ATP as an energy source revealed that GTP was not detectable in the extract, however, 35 ,M of GTP was found in the translation mixture. This result suggests that GTP could be generated from other compounds, such as GDP and GMP, using ATP. A similar experiment with a C-terminally truncated form of human protein tyrosine phosphatase 1B (hPTP1B1-320) gave almost the same result. The wheat embryo cell-free translation system worked most efficiently without exogenous GTP, producing 3.5 mg/mL of translation mixture over a 48-h period at 26°C. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Determining the optimal concentration of fluoride in drinking water in PakistanCOMMUNITY DENTISTRY AND ORAL EPIDEMIOLOGY, Issue 3 2004Ayyaz Ali Khan Abstract , Objectives:,This study was designed to determine the optimal concentrations of fluoride for drinking water in Pakistan. Clinical dental examination of 1020 school children aged 12 years was carried out in 19 cities of Pakistan. Correlation between concentrations of water fluoride, caries and fluorosis was investigated by analyzing the data on fluoride concentrations in drinking water in the sampled population for which the caries and the fluorosis levels were also measured. Methods:,The optimal level of fluoride in drinking water is universally calculated by applying the equation of Galagan and Vermillion, which permits the calculation of water intake as a function of temperature. The annual mean maximum temperatures (AMMT) recorded during the last 5 years were collected from the meteorological centres of the 28 divisional headquarter stations. The average AMMT of Pakistan is 29°C at which the optimal fluoride in drinking water of Pakistan was calculated to be 0.7 ppm. As drinking habits differ in various parts of the world, determination of optimal concentration of fluoride for drinking water in Pakistan was performed using a modified Galagan and Vermillion equation, which applies a correction factor of 0.56 to the equation. The optimal fluoride in drinking water in Pakistan using this modified equation was determined to be 0.39 ppm. Results:,Observation of the correlation showed that a fluoride concentration of 0.35 ppm in drinking water was associated with maximum reduction in dental caries and a 10% prevalence of fluorosis. Conclusions:,Determining the most appropriate concentrations of fluoride in drinking water is crucial for communities. It is imperative that each country calculates its own optimal level of fluoride in drinking water based on the dose,response relationship of fluoride in drinking water with the levels of caries and fluorosis. Climatic conditions, dietary habits of the population and other possible fluoride exposures need to be considered in formulating these recommendations. [source] | ||||||||||||||||||||||||||||||||||