Maximum Sustainable Rate Research Articles

Maximizing Personal Surplus: Liability-Driven Investment for Individuals

To date, the financial literature has focused on very simple algorithms designed to improve the solution to the two-part challenge of determining the optimal portfolio asset allocation strategy and determining the maximum sustainable withdrawal rate for retirees. Most research, for example the well-known of Cooley, Hubbard, and Walz, pursues the asset-allocation problem by maximizing long-run asset growth subject to a withdrawal rule and a given acceptable probability of remorse (a.k.a. shortfall). However, the Liability-Driven Investing (LDI) thought process improves the approach by seeking instead to maximize return for a given level of volatility of the portfolio surplus, rather than optimizing on the basis of the volatility the assets themselves; by more closely matching assets and liabilities, the sensitivity of the strategy to unexpected returns, risks, and correlations is greatly decreased. I update the Trinity Study to incorporate inflation-indexed bonds and then illustrate how the LDI thought process may be applied to individual investors.

Malthus Gets Fat: The Beginnings of Income Growth in Britain and Beyond

The first part of this paper develops a simple dynamic model to examine the takeoff, or breakout, from a Malthusian economy to a modern growth regime. It finds that several factors, most notably the rate of technological progress and the economic structure, determine the fastest rate at which the population can grow without declining living standards; this is termed maximum sustainable population growth. It is only when this maximum sustainable rate exceeds the peak rate at which a society expands that takeoff can occur. I also investigate the effects of trade and international income transfers on the ability to sustain takeoff, and find that the results are not what might be expected. In particular, it is shown that present income growth is not necessarily indicative of the ability to sustain takeoff and that factors which increase current income growth may actually inhibit takeoff, and vice versa.The second part of this paper applies the sustainable population growth framework to Britain during the Industrial Revolution. The model shows a dramatic increase in sustainable population growth at the time of the Industrial Revolution, well before the beginning of modern levels of income growth. The main contributions to the British breakout were technological improvements and structural change away from agricultural production. At least until the middle of the 19th Century, coal, capital and trade played a minor role.

Deficit Round Robin with Fragmentation Scheduling to Achieve Generalized Weighted Fairness for Resource Allocation in IEEE 802.16e Mobile WiMAX Networks

Deficit Round Robin (DRR) is a fair packet-based scheduling discipline commonly used in wired networks where link capacities do not change with time. However, in wireless networks, especially wireless broadband networks, i.e., IEEE 802.16e Mobile WiMAX, there are two main considerations violate the packet-based service concept for DRR. First, the resources are allocated per Mobile WiMAX frame. To achieve full frame utilization, Mobile WiMAX allows packets to be fragmented. Second, due to a high variation in wireless channel conditions, the link/channel capacity can change over time and location. Therefore, we introduce a Deficit Round Robin with Fragmentation (DRRF) to allocate resources per Mobile WiMAX frame in a fair manner by allowing for varying link capacity and for transmitting fragmented packets. Similar to DRR and Generalized Processor Sharing (GPS), DRRF achieves perfect fairness. DRRF results in a higher throughput than DRR (80% improvement) while causing less overhead than GPS (8 times less than GPS). In addition, in Mobile WiMAX, the quality of service (QoS) offered by service providers is associated with the price paid. This is similar to a cellular phone system; the users may be required to pay air-time charges. Hence, we have also formalized a Generalized Weighted Fairness (GWF) criterion which equalizes a weighted sum of service time units or slots, called temporal fairness, and transmitted bytes, called throughput fairness, for customers who are located in a poor channel condition or at a further distance versus for those who are near the base stations, or have a good channel condition. We use DRRF to demonstrate the application of GWF. These fairness criteria are used to satisfy basic requirements for resource allocation, especially for non real-time traffic. Therefore, we also extend DRRF to support other QoS requirements, such as minimum reserved traffic rate, maximum sustained traffic rate, and traffic priority. For real-time traffic, i.e., video traffic, we compare the performance of DRRF with deadline enforcement to that of Earliest Deadline First (EDF). The results show that DRRF outperforms EDF (higher achievable throughput under the promised delay latency) and maintains fairness under an overload scenario.

Uplink Cross-Layer Scheduling with Differential QoS Requirements in OFDMA Systems

Fair and efficient scheduling is a key issue in cross-layer design for wireless communication systems, such as 3GPP LTE and WiMAX. However, few works have considered the multiaccess of the traffic with differential QoS requirements in wireless systems. In this paper, we will consider an OFDMA-based wireless system with four types of traffic associated with differential QoS requirements, namely, minimum reserved rate, maximum sustainable rate, maximum latency, and tolerant jitter. Given these QoS requirements, the traffic scheduling will be formulated into a cross-layer optimization problem, which is convex fortunately. By separating the power allocation through the waterfilling algorithm in each user, this problem will further reduce to a kind of continuous quadratic knapsack problem in the base station which yields low complexity. It is then demonstrated that the proposed cross-layer method cannot only guarantee the application layer QoS requirements, but also minimizes the integrated residual workload in the MAC layer. To further enhance the ability of QoS assurance in heavily loaded scenario, a call admission control scheme will also be proposed. The simulation results show that the QoS requirements for the four types of traffic are guaranteed effectively by the proposed algorithms.

Peak energy turnover in lactating European hares: a test of the heat dissipation limitation hypothesis

It has been suggested that maximum sustained metabolic rate (SusMR) in mammals as reached, for instance, during lactation, is due to a limited capacity for heat dissipation. Here, we experimentally tested whether heat dissipation limitation (HDL) also constrains energy turnover in lactating European hares. Experimentally, we made use of the fact that hares nurse their young only once per day, which allowed us to keep females and young either at the same or at different ambient temperatures. During the last lactation week (week 4) females kept at thermoneutrality (22 degrees C), irrespective of the cold load of their young, had significantly lower rates of metabolisable energy intake (MEI) than cold-exposed mothers (5 degrees C), as predicted by the HDL hypothesis. However, in week 2 of lactation females at thermoneutrality rearing cold-exposed young were able to increase MEI to levels indistinguishable from those of cold-exposed females. Thus, even at thermoneutral temperature females reached maximum rates of energy turnover, which was inconsistent with the HDL hypothesis. We conclude that SusMR in lactating European hares typically results not from physiological constraints but from an active restriction of their energy turnover in order to maximise lifetime reproductive success.

Maximum rates of sustained metabolic rate in cold-exposed Djungarian hamsters (Phodopus sungorus): the second wind

Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (T(a)s) down to -70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at T(a)s as high as ≥-2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation and temporal patterns of T(a) changes experienced by the animals, as average T(a) declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously determined and were able to maintain positive energy balances down to T(a) -9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by T(a)s cycling between +3°C and as low as -25°C, at hourly intervals. At mean T (a)s between +3 and -3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body mass at lower T (a)s (-5 to -9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake.

Evaluation of biogas production from seaweed in batch tests and in UASB reactors combined with the removal of heavy metals

Seaweed can be anaerobically digested for the production of energy-rich methane. However, the use of seaweed digestate as a fertilizer may be restricted because of the high heavy metal content especially cadmium. Reducing the concentration of heavy metals in the digestate will enable its use as a fertilizer. In this laboratory-scale study, the potential of seaweed and its leachate in the production of methane were evaluated in batch tests. The effect of removing the heavy metals from seaweed leachate was evaluated in both batch test and treatment in an upflow anaerobic sludge blanket (UASB) reactor. The heavy metals were removed from seaweed leachate using an imminodiacetic acid (IDA) polyacrylamide cryogel carrier. The methane yield obtained in the anaerobic digestion of seaweed was 0.12 N l CH 4/g VS added. The same methane yield was obtained when the seaweed leachate was used for methane production. The IDA-cryogel carrier was efficient in removing Cd 2+, Cu 2+, Ni 2+ and Zn 2+ ions from seaweed leachate. The removal of heavy metals in the seaweed leachate led to a decrease in the methane yield. The maximum sustainable organic loading rate (OLR) attained in the UASB reactor was 20.6 g tCOD/l/day corresponding to a hydraulic retention time (HRT) of 12 h and with a total COD removal efficiency of about 81%. Hydrolysis and treatment with IDA cryogel reduced the heavy metals content in the seaweed leachate before methane production. This study also demonstrated the suitability of the treatment of seaweed leachate in a UASB reactor.

An efficient analytical model for the dimensioning of WiMAX networks supporting multi-profile best effort traffic

This paper tackles the challenging task of developing a simple and accurate analytical model for performance evaluation of WiMAX networks. The need for accurate and fast-computing tools is of primary importance to face complex and exhaustive dimensioning issues for this promising access technology. In this paper, we present a generic Markovian model developed for three usual scheduling policies (slot sharing fairness, throughput fairness and opportunistic scheduling) that provides closed-form expressions for all the required performance parameters instantaneously. We also present and evaluate the performance of a fourth policy, called throttling policy, that limits the maximum user throughput and makes use of the Maximum Sustained Traffic Rate (MSTR) parameter foreseen by the standard. At last, we extend these studies to multi-profile traffic patterns. The proposed models are compared in depth with realistic simulations that show their accuracy and robustness regarding the different modeling assumptions. Finally, the speed of our analytical tools allows us to carry on dimensioning studies that require several thousands of evaluations, which would not be tractable with any simulation tool.

Estimating thresholds to optimal harvest rate for long-lived, low-fecundity sharks accounting for selectivity and density dependence in recruitment

Deepwater dogsharks (Order Squaliformes) are thought to be particularly vulnerable to overfishing due to life history strategies that place them at the lower end of the shark productivity spectrum. Sharks frequently have relatively low value in multispecies fisheries, where management is usually aimed at maintaining harvest of more valuable and productive teleosts. This results in low priority being given to data collection for sharks and hampers identification of appropriate harvest strategies. Here an age-structured model with maximum sustainable harvest rate (UMSY) as leading productivity parameter is systematically applied to show that for certain growth and reproductive schedules that apply to some sharks, the range of possible values that can be taken by UMSYcan become very small. The model was applied to 12 Australian dogshark species and was used to show that UMSYis highly constrained under some selectivity schedules. Results were consistent with estimates of the intrinsic rate of growth obtained using a demographic model, suggesting that there may be more certainty about UMSYthan expected for many shark species, given uncertainty in recruitment parameters. The approach could be used to inform policy for some sharks and may be useful in the development of informative Bayesian priors for assessment models.

A better budget rule

AbstractDebt limits, interest coverage ratios, one‐off balanced budget requirements, pay‐as‐you‐go rules, and tax and expenditure limits are among the most important fiscal rules for constraining intertemporal transfers. There is considerable evidence that the least costly and most effective of such rules are those that focus directly on the rate of spending growth, even with their seemingly ad hoc nature and possibilities for circumvention. In this paper, we use optimal control theory and martingale methods to justify a transparent, nonarbitrary rule governing maximum sustainable rate of spending growth, treating the revenue structure of a jurisdiction as a given continuous‐time stochastic process. Our results can be used to determine whether a proposed rate of spending growth is sustainable or not. © 2009 by the Association for Public Policy Analysis and Management

Population structure of bottlenose dolphins (Tursiops aduncus) impacted by bycatch along the east coast of South Africa

Shark nets placed along the coast of KwaZulu-Natal to protect bathers from shark attacks result in an incidental by-catch of bottlenose dolphins (Tursiops aduncus) at twice the level suggested by the IWC as the maximum sustainable capture rate for a cetacean population. Observational data reported the presence of at least two putative populations, one a seasonal migratory population moving into the KwaZulu-Natal area following the movement of sardines, and the other a coastal, apparently resident population. Some observations indicated possible further subdivision of the coastal population. We analysed nine microsatellite loci and 599 bps of the mitochondrial control region and found small but significant differentiation within the putative coastal population (FST = 0.022) separated north and south of Ifafa. There was weaker evidence for differentiation between the southern coastal and migratory populations (FST = 0.012). Genetic diversity was low for both types of markers in all populations, and the pattern of mtDNA variation was consistent with a founder event. Considering the high capture rate, the low level of genetic diversity, and the evidence of possible population differentiation along the coast, we suggest that particular care should be taken in managing the take from shark nets especially in the north coastal area of KZN where the population showed the higher degree of differentiation.

Dynamics of Newly Established Elk Populations

Abstract: The dynamics of newly established elk (Cervus elaphus) populations can provide insights about maximum sustainable rates of reproduction, survival, and increase. However, data used to estimate rates of increase typically have been limited to counts and rarely have included complementary estimates of vital rates. Complexities of population dynamics cannot be understood without considering population processes as well as population states. We estimated pregnancy rates, survival rates, age ratios, and sex ratios for reintroduced elk at Theodore Roosevelt National Park, North Dakota, USA; combined vital rates in a population projection model; and compared model projections with observed elk numbers and population ratios. Pregnancy rates in January (early in the second trimester of pregnancy) averaged 54.1% (SE = 5.4%) for subadults and 91.0% (SE = 1.7%) for adults, and 91.6% of pregnancies resulted in recruitment at 8 months. Annual survival rates of adult females averaged 0.96 (95% CI = 0.94‐0.98) with hunting included and 0.99 (95% CI = 0.97‐0.99) with hunting excluded from calculations. Our fitted model explained 99.8% of past variation in population estimates and represents a useful new tool for short‐term management planning. Although we found no evidence of temporal variation in vital rates, variation in population composition caused substantial variation in projected rates of increase (Λ = 1.20‐1.36). Restoring documented hunter harvests and removals of elk by the National Park Service led to a potential rate of Λ = 1.26. Greater rates of increase substantiated elsewhere were within the expected range of chance variation, given our model and estimates of vital rates. Rates of increase realized by small elk populations are too variable to support inferences about habitat quality or density dependence.

QoS Provisioning Method for Downstream VoIP Service Flows in HFC Networks

Conventional researches on QoS provisioning in HFC networks have focused mainly on the upstream channels. However, due to changing network usage patterns, the provisioned capacity for downstream service flows is no longer sufficient. To provide QoS for downstream VoIP service flows in HFC networks, an adaptive committed information rate allocation algorithm is proposed. Given the maximum sustained traffic rate and the minimum reserved rate for each service flow, it allocates service rates to VoIP and best effort connections adaptively for possible cases of network congestion. The proposed algorithm is directly tested in a commercial HFC network, and it is shown to reduce packet losses, jitter, and delay in the HFC network, which results in stable VoIP service quality even in network congestion <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> .

Relationship between fertilization success and the number of milt donors in rainbow smelt Osmerus mordax (Mitchell): implications for population growth rates

A series of artificial fertilizations using rainbow smelt Osmerus mordax were conducted, each designed to assess the fertilization success of a female’s eggs with milt from one to five males. Mean egg fertilization success increased and variance in fertilization success decreased when more males contributed to a constant volume of milt. This may indicate the presence of an Allee effect. The results suggest that potential changes in egg fertilization success due to a decrease in the number of males, in addition to changes in egg production due to a decrease in the number of females, can affect estimates of maximum sustainable harvest rates, and recovery of depleted populations.

The logistic model-generated carrying capacities, maximum sustained off-take rates and optimal stocking rates for Kenya's commercial ranches

This paper deals with the derivation of logistic models for cattle, sheep and goats in a commercial ranching system in Machakos District, Kenya, a savannah ecosystem with average annual rainfall of 589.3 ± 159.3mm and an area of 10 117ha. It involves modelling livestock population dynamics as discrete-time logistic equations with fixed carrying capacities. The fixed carrying capacities are generated endogenously using time-series ranch data, covering a period of 15 years, from 1987 to 2001, in a commercial ranching enterprise. The model incorporates interaction parameters, generated endogenously. The estimation of the logistic models involves estimation of econometric models for each livestock species, followed by the recovery of the logistic models mathematically. Optimisation procedures are employed to determine the optimal stocking levels and the optimal off-take levels. The model-generated carrying capacities are 2 985, 791 and 201 animal units (AUs) for cattle, sheep and goats, respectively. Optimal stocking levels are 1 369, 154 and 69 AUs for cattle, sheep and goats, respectively, while the optimal off-take levels are 857, 88 and 63 for cattle, sheep and goats, respectively. This shows that the logistic models-based system analysis is applicable to the management of mixed-species commercial ranching enterprises.

EVOLUTION OF INTRINSIC GROWTH RATE: METABOLIC COSTS DRIVE TRADE-OFFS BETWEEN GROWTH AND SWIMMING PERFORMANCE IN MENIDIA MENIDIA

There is strong evidence that genetic capacity for growth evolves toward an optimum rather than an absolute maximum. This implies that fast growth has a cost and that trade-offs occur between growth and other life-history traits, but the fundamental mechanisms are poorly understood. Previous work on the Atlantic silverside fish Menidia menidia has demonstrated a trade-off between growth and swimming performance. We hypothesize that the trade-off derives from the competing metabolic demands associated with growth and swimming activity. We tested this by measuring standard metabolic rate (M(STD)), maximum sustainable metabolic rate (M(ACT)) and metabolic scope of laboratory-reared silversides originating from two geographically distinct populations with well-documented differences in genetic capacity for growth. The fast-growth genotype had a significantly greater M(STD) than the slow-growth genotype, but a similar MACT when swum to near exhaustion. The scope for activity of the fast-growth genotype was lower than that of the slow-growth genotype. Furthermore, the fast-growth genotype eats larger meals, thereby incurring a greater postprandial oxygen demand. We conclude that a metabolic trade-off occurs between growth and other metabolic demands and that this trade-off provides a general mechanism underlying the evolution of growth rate.

Simulating root responses to grazing of a Mongolian grassland ecosystem

A new Sim-CYCLE grazing model has been obtained by combining a grazing model (Seligman et al. 1992, Ecol. Model. 60: 45–61) with the Sim-CYCLE model (Ito and Oikawa 2002, Ecol. Model. 151: 143–176). The new model has been validated against a set of field data obtained at Kherlen Bayaan-Ulaan (KBU) grassland. On the basis of the model, the root responses to grazing of KBU grassland have been studied under different conditions of stocking rates and precipitation. Model results indicate that both below-ground biomass (BB) and below-ground net primary production (BNPP) generally decrease with increasing stocking rate. However, if stocking rate is not higher than 0.7 sheep ha−1, a sustainable state of the grassland ecosystem can be achieved after about 100 years, which suggests that the maximum sustainable stocking rate at KBU should be 0.7 sheep ha−1. At the sustainable state, the maximum BB in a year is about 11 Mg DM ha−1 under non-grazing condition, 5 Mg DM ha−1 under 0.4 sheep ha−1 stocking rate, and 4 Mg DM ha−1 under 0.7 sheep ha−1 stocking rate; the BNPP is 1.3 Mg DM ha−1 year−1 under non-grazing condition, and 0.6 Mg DM ha−1 year−1 under 0.4 sheep ha−1 stocking rate, and 0.4 Mg DM ha−1 year−1 under 0.7 sheep ha−1 stocking rate. Ratio of non-assimilation organ to assimilation organ (C/F) increases with increasing stocking rate. The C/F ratio is 10.99 under non-grazing conditions, and 12.11 under 0.7 sheep ha−1 stocking rate. Root turnover rate decreases with increasing stocking rate. The rate is 12% each year under non-grazing conditions, and 11% each year under 0.7 sheep ha−1 stocking rate. In addition, the effect of grazing on the grassland ecosystem under different scenarios of precipitation is also analyzed. Both BB and BNPP increase with increased precipitation, and vice versa. When precipitation is set to be 10% higher than the averaged from 1993 to 2002, the maximum sustainable stocking rate is 0.8 sheep ha−1, and when the precipitation is set to be 15% lower than the averaged, the maximum sustainable stocking rate is 0.6 sheep ha−1.

Maximum Sustainable Work Rate for Five Protective Clothing Ensembles with Respect to Moisture Vapor Transmission Rate and Air Permeability

The fabrics associated with protective clothing affect heat stress, which influences productivity and risks of heat-related disorders. This study compared the work limiting effects of five protective coveralls and a semiclothed condition (t-shirt and shorts). Two fabric characteristics determined from bench tests, moisture vapor transmission rate (MVTR), and air permeability were also examined as possible predictors of ensemble performance. A progressive metabolic rate protocol was used where environmentalconditions (Tdb = 32°C; Tpwb = 26°C) were held constant while treadmill speed was slowly increased. The limiting metabolic rate to just maintain thermal equilibrium was the critical point. At this point, critical speed and critical metabolic rate were noted and total evaporative resistance was calculated for each ensemble. Five acclimatized subjects wore each of the six clothing conditions in a random order. Statistically significant differences were found among the five protective garments and a semiclothed ensemble for critical treadmill speed (Scrit ), critical metabolic rate (M crit ), and total evaporative resistance (R e − t ). The semiclothed condition (S crit = 1.77 m/sec; M crit = 580 W; R e−t = 0.0099 kPa m 2 /W) and ensembles made from spunbonded, melt blown, spunbonded polypropylene (SMS) (1.72 m/sec; 560 W; 0.0135 kPa m2/W) and spunbonded polypropylene (1.67 m/sec; 550 W; 0.0126 kPa m2/W) were able to support higher work rates than fabrics made from Tyvek 1422-A (a nonwoven spunbonded olefin) (1.48 m/sec; 470 W; 0.0183 kPa m 2 /W) and a microporous film supported by spunbonded polypropylene (1.34 m/sec; 420 W; 0.0231 kPa m2/W). A tightly woven polyester ensemble (1.59 m/sec; 510 W; 0.0130 kPa m2/W) had intermediate values and was not significantly different from either group. Air permeability was a better predictor of fabric work limiting performance than MVTR. An air permeability on the order of 10,000 L/min cm 2 bar would have little effect on maximum sustainable work.

EVOLUTION OF INTRINSIC GROWTH RATE: METABOLIC COSTS DRIVE TRADE-OFFS BETWEEN GROWTH AND SWIMMING PERFORMANCE IN MENIDIA MENIDIA

There is strong evidence that genetic capacity for growth evolves toward an optimum rather than an absolute maximum. This implies that fast growth has a cost and that trade-offs occur between growth and other life-history traits, but the fundamental mechanisms are poorly understood. Previous work on the Atlantic silverside fish Menidia menidia has demonstrated a trade-off between growth and swimming performance. We hypothesize that the trade-off derives from the competing metabolic demands associated with growth and swimming activity. We tested this by measuring standard metabolic rate (MSTD), maximum sustainable metabolic rate (MACT) and metabolic scope of laboratory-reared silversides originating from two geographically distinct populations with well-documented differences in genetic capacity for growth. The fast-growth genotype had a significantly greater MSTD than the slow-growth genotype, but a similar MACT when swum to near exhaustion. The scope for activity of the fast-growth genotype was lower than that of the slow-growth genotype. Furthermore, the fast-growth genotype eats larger meals, thereby incurring a greater postprandial oxygen demand. We conclude that a metabolic trade-off occurs between growth and other metabolic demands and that this trade-off provides a general mechanism underlying the evolution of growth rate.

Lions in the Kgalagadi Transfrontier Park: modelling the effect of human-caused mortality

An age-structured demographic matrix model is developed to determine the long-term viability of the Southern African Kgalagadi Transfrontier Park lion ( Panthera leo) population that is subjected to persecution along the park boundaries. In doing so, maximum sustainable persecution rates are established, so that efficient conservation measures may be taken, if required, to ensure the continued survival of the species in the park. Sensitivity analyses indicate that adult female survival ability alone is the most important component of the model in terms of long-term population survival. Furthermore, these analyses show that the boundary prides of the park are able to increase their chances of survival and are able to sustain significantly higher human-caused mortality rates by inducing birth-sex ratio biases in favour of females. The model suggests that the persecution rate experienced by the study population over the period 1998–2001 cannot be sustained in the long term, provided that there is no immigration of adult females into the population from the park interior. To ensure the survival of existing park boundary prides, adult lionesses should, as far as possible, be afforded protection from persecution, so that park boundary populations do not merely serve as population sinks for lions from elsewhere, or become extinct.