Delivery Lag Research Articles

Parametric Probabilistic Routing in Sensor Networks

Motivated by realistic sensor network scenarios that have mis-informed nodes and variable network topologies, we propose an approach to routing that combines the best features of limited-flooding and information-sensitive path-finding protocols into a reliable, low-power method that can make delivery guarantees independent of parameter values or information noise levels. We introduce Parametric Probabilistic Sensor Network Routing Protocols, a family of light-weight and robust multi-path routing protocols for sensor networks in which an intermediate sensor decides to forward a message with a probability that depends on various parameters, such as the distance of the sensor to the destination, the distance of the source sensor to the destination, or the number of hops a packet has already traveled. We propose two protocol variants of this family and compare the new methods to other probabilistic and deterministic protocols, namely constant-probability gossiping, uncontrolled flooding, random wandering, shortest path routing (and a variation), and a load-spreading shortest-path protocol inspired by (Servetto and Barrenechea, 2002). We consider sensor networks where a sensor's knowledge of the local or global information is uncertain (parametrically noised) due to sensor mobility, and investigate the trade-off between robustness of the protocol as measured by quality of service (in particular, successful delivery rate and delivery lag) and use of resources (total network load). Our results for networks with randomly placed nodes and realistic urban networks with varying density show that the multi-path protocols are less sensitive to misinformation, and suggest that in the presence of noisy data, a limited flooding strategy will actually perform better and use fewer resources than an attempted single-path routing strategy, with the Parametric Probabilistic Sensor Network Routing Protocols outperforming other protocols. Our results also suggest that protocols using network information perform better than protocols that do not, even in the presence of strong noise.

PCBs and OCPs in Sediment Cores from the Lower St. Lawrence Estuary, Canada: Evidence of Fluvial Inputs and Time Lag in Delivery to Coring Sites

Three sediment cores were collected along the longitudinal axis of the Laurentian Trough in the Lower St. Lawrence Estuary (LSLE) and an additional one at the junction of the Estuary and the Gulf of St. Lawrence. After core-slicing, each sediment layer was analyzed for polychlorinated biphenyls (PCBs) and some organochlorine pesticides (OCPs) including p,p'-dichlorodiphenyltrichloroethane (DDT) and its metabolites, hexachlorobenzene (HCB) and Mirex. 210Pb activity was also measured in these sediments, which allowed us to confirm that these cores were too much affected by the overall impact of surface mixing to be dated. Nevertheless, POP sedimentary profiles in cores from the LSLE upstream stations showed well-defined subsurface peak concentrations. Apparently, the peak inputs of POPs to these sediment cores had occurred after the years of maximum sales and production of these chemicals in North America, suggesting a time lag in the delivery of POPs to the LSLE sediments. Concentrations of POPs in the LSLE surface sediments as well as POP inventories in sediment cores decreased in the seaward direction, confirming that the head of the LSLE acts as a sink for sediments and associated constituents. Surface concentrations of sigmaPCBs, sigmaDDTs, and HCB in the most upstream core were on average similar to those reported in two fluvial lakes of the St. Lawrence River but were between 12 and 39 times lower than those from Lake Ontario. For Mirex, the surface concentration in that core was 5 and 130 times lower than the average values found in the fluvial lakes and Lake Ontario, respectively. Differences between Lake Ontario sediment cores and the most upstream core from the LSLE were much smaller on the basis of POP inventories than surface concentrations of POPs, but were still important. The total burdens of POPs in LSLE sediments below the 200 m isobath were 8704 kg for sigmaPCBs, 1825 kg for sigmaDDTs, 319 kg for HCB, and 27.5 kg for Mirex. These values represent between 1% and 10% of the total burdens of these POPs in Lake Ontario sediments. The estimated contribution of POPs by direct atmospheric deposition into the water column area of the LSLE represented at most 30% of the total sediment burdens of POPs in the LSLE, illustrating the importance of fluvial inputs.

Equilibrium Forward Contracts on Nonstorable Commodities in the Presence of Market Power

Bilateral supply contracts are widely used despite the presence of spot markets. In this paper we provide a potential explanation for this prevalence of supply contracts even when spot markets are liquid and without delivery lag. Specifically, we consider the determination of an equilibrium forward contract on a nonstorable commodity between two firms that have mean-variance preferences over their risky profits and negotiate the forward contract through a Nash bargaining process. We derive the unique equilibrium forward in closed form and provide an extensive analysis of the equilibrium contract. We show that it is the risk hedging benefit from a forward that justifies its prevalence in spite of liquid spot markets. In addition, while a forward does not affect production decisions due to the presence of spot markets, it does affect inventory decisions of the storable input factor due to its hedging effect against the inventory risk. We also show that price volatilities and correlations are important determinants of the equilibrium contract. In particular, the equilibrium forward price can be nonmonotonic in the spot price volatility and can decrease as the initial spot price increases.

Equilibrium Forward Contracts on Nonstorable Commodities in the Presence of Market Power

Bilateral supply contracts are widely used despite the presence of spot markets. In this paper, we provide a potential explanation for this prevalence of supply contracts even when spot markets are liquid and without delivery lag. Specifically, we consider the determination of an equilibrium forward contract on a nonstorable commodity between two firms that have mean-variance preferences over their risky profits and negotiate the forward contract through a Nash bargaining process. We derive the unique equilibrium forward contract in closed form and provide an extensive analysis. We show that it is the risk-hedging benefit from a forward that justifies its prevalence in spite of liquid spot markets. In addition, while a forward does not affect production decisions due to the presence of spot markets, it does affect inventory decisions of the storable input factor due to its hedging effect against the inventory risk. We also show that price volatilities and correlations are important determinants of the equilibrium contract. In particular, the equilibrium forward price can be nonmonotonic in the spot price volatility and can decrease as the initial spot price increases.

Bilateral J-curve between India and her trading partners

India, a land of over one billion people and one of the newly emerging industrial powers in the world, is going through a slow but steady metamorphism. For centuries, India has played a major role in the international trade. It was not uncommon to see her ships carrying silk and spices across the Arabian seas and bringing back machine-made textile. Invasions of India first by Mughals and latter by the British through the East India Company were all trade oriented. India’s presence in the world trade is relatively small at this time but is gaining momentum. After independence in 1947, India for a brief period experimented with socialism. The Five Year plans were mainly focused towards building infrastructure and development of small-scale agriculture based industries. The industrial development even though extremely important for growth, played a secondary role. The foreign investment was encouraged but only in the selected sectors of the economy. However, threat of nationalization, a large bureaucracy, corruption, lack of understanding of the Indian business practices and the requirement that a major share holder must be an Indian national, discouraged foreign capital investment in India. During 1991-1992, India adopted a policy of trade liberalization. To attract foreign capital and to encourage Non-resident Indians to invest in their home country, Government of India established a separate unit within the Home Ministry whose main function was to expedite processing of applications. India also relaxed the requirement that a major partner be an Indian national. India provided export subsidies to the exporters in terms of cash as well as foreign exchange so that they could import machines and raw materials. Exports responded to the trade liberalization and increased from 44 041 crores of rupees in 1991–1992 to 141 603 crores in 1998–1999 where one crore is equivalent to ten million. In US dollar terms at a current exchange rate of 42.48 rupees per dollar, this translates to an increase from $10.37 billion to $33.34 billion over eight years. India also anticipates that through a major increase in the information technology, mainly software industry, her exports will increase to 90 billion by 2005. The trade liberalization has been accompanied by changes in the monetary policies. The inflation rate has been reduced from about 12% to 9% per year, the interest rates have declined from 14% to 10% and the exchange rate has been allowed to respond to market forces. As a result from 1991–1992 to 1998–1999, the rupee has declined from 19.62 rupees per dollar to 42.48 rupees per dollar. By December 2000 rupee had further devalued to 46.25 per dollar with a hope that it will further boost India’s exports and improve her trade balance. However, the impact of currency depreciation on the trade balance is not instantaneous. Indeed, there is ample evidence in the literature that after currency depreciation, the trade balance worsens in the short-run before improving in the long-run. Since this pattern of movement of the trade balance over time resembles the letter J, Magee (1973) labelled it the J-curve phenomenon. Magee argued that after devaluation, contracts that are in transit at old exchange rates dominate the short-run response of the trade balance. Over time, new contracts at new prices begin to exert their favourable impact. At this stage, elasticities may increase leading to an eventual improvement in the trade balance. Of course, the delayed response could also be due to lags in the process of increasing the production of exportables. Junz and Rhomberg (1973) have identified five lags, namely, recognition lags, decision lags, delivery lags, replacement lags and production lags. Only after the realization of these lags, the trade balance could improve. Early studies that tried to investigate the impact of currency depreciation on the trade balance relied upon estimating the Marshall-Lerner condition. The condition

Low intensity exercise in humans accelerates mitochondrial ATP production and pulmonary oxygen kinetics during subsequent more intense exercise.

We undertook this study to determine whether low intensity exercise (55 % (O2,max) would significantly alter the metabolic and ventilatory responses observed during 10 min of subsequent moderate intensity exercise (75 % (O2,max). By executing this work, we hoped to further our understanding of the mechanisms that limit mitochondrial ATP production at the onset of exercise. Seven healthy human subjects performed 10 min of moderate intensity exercise in the presence and absence of 10 min of low intensity exercise, which preceded the moderate intensity exercise by 3 min. Muscle biopsy samples were obtained from the vastus lateralis at pre-determined time points and oxygen consumption kinetics were determined at rest and during low and moderate intensity exercise. Following low intensity exercise and 3 min of passive recovery, muscle lactate and acetylcarnitine concentrations were elevated above basal levels, but (O2) had returned to the resting rate. When moderate intensity exercise was preceded by low intensity exercise, there was a significant sparing of phosphocreatine (PCr, approximately 25 %, P < 0.05) and reductions in glucose 6-phosphate (G-6-P, approximately 50 %, P < 0.05) and lactate (approximately 50 %, P < 0.05) accumulation during the first minute of moderate intensity exercise. No differences were observed after 10 min of moderate intensity exercise. The (O2) on-kinetic response over the first minute of moderate intensity exercise was accelerated when preceded by low intensity exercise. Collectively, our results suggest the lag in the oxidative ATP delivery at the onset of moderate intensity exercise can be overcome by prior low intensity exercise. Furthermore, our findings support the view that this lag is at least in part attributable to a limitation in acetyl group delivery/availability at the onset of exercise, rather than delayed oxygen supply.

The impact of delivery lags on irreversible investment under uncertainty

We consider the valuation and rational exercise of irreversible investment opportunities in the presence of revenue uncertainty and delivery lags. In order to capture supply side market imperfections in the markets for investment goods, we assume that the lag depends on the revenue process faced by the investor. We show that such imperfections have a pronounced decelerating impact on rational investment demand as they may increase the value of waiting in excess of the exercise payoff even for projects which otherwise would be perceived as highly remunerative. We also consider the comparative static properties of the optimal investment policy and its value, and demonstrate that typically increased uncertainty decreases the investment incentives by increasing the value of waiting.

The volatility of the socially optimal level of investment

In this paper, an annual series for the socially optimal level of investment from 1960–1961 to 1993–1994 for Australia is derived from a vintage production function and compared to the actual series for investment over the same period. The vintage production function can be expected to yield a smoother socially optimal investment series than that derived from a nonvintage, homogenous capital production function. Even so, the resulting series for socially optimal investment is much more volatile than the series for actual investment. Several alternative assumptions are tried in an attempt to further smooth the socially optimal investment series. These include smoothing the assumed values of the exogenous variables, modelling adjustment costs and delivery lags, and changing the form of the production function. While these approaches do succeed in smoothing the investment series, in order for the socially optimal investment series to be as smooth as the actual series the assumed values of the parameters must be quite unrealistic. In the conclusion, we suggest that, in the future research on the socially optimal level of investment, the role of liquidity constraints and of irreversible investment should be investigated.

A multi-item continuous review inventory system with compound Poisson demands

In this paper, we consider a multi-item continuous review inventory system with compound Poisson demands under a general cost structure. Excess demand is backlogged and a fixed delivery lag is assumed. A new algorithm for computing an exact optimal policy is derived based upon the policy iteration method (PIM) using properties of the optimal policy. This algorithm reduces substantially computation times in both the policy evaluation and the policy improvement routines of the PIM. In fact, numerical examples show that the computation times of the new algorithm are less than three percent of those of the PIM. Moreover, three joint ordering policies – the (s, c, S), the (R, T) and the (Q, S) policies – are compared with the optimal ordering policy computed by the new algorithm. It is shown that the (Q, S) policy is almost best among the three joint ordering policy and gives more than ten percent higher expected cost rate than the optimal ordering policy.

Size of IgG-Opsonized Particles Determines Macrophage Response during Internalization

It is generally assumed that particles >1 μm elicit a phagocytic response. To determine whether this is the case, we examined the uptake and transport of IgG-opsonized polystyrene beads of defined size, ranging from 0.2 to 3 μm, by mouse bone marrow-derived macrophages. The kinetics of opsonized bead internalization were comparable for each of the different beads examined. We used rhodamine phalloidin to examine particle-induced assembly of F-actin phagocytic cups by fluorescence microscopy. Phagocytic cup formation was size dependent in a nonlinear fashion. Less than 30% of 0.2- to 0.75-μm particles and greater than 80% of 2- and 3-μm particles were associated with F-actin. Cells treated with 0.25 μm cytochalasin D showed decreased phagocytic cup formation and a linear decrease in bead uptake as a function of particle surface area. In contrast, potassium depletion, which preferentially inhibits clathrin-mediated endocytosis, was more effective at inhibiting the uptake of smaller beads. Thus, with increasing particle size, IgG-opsonized particle uptake became less clathrin dependent and more actin dependent. The kinetics of ligand delivery to lysosomes was measured using an immunoprecipitation assay based on the intermixing of internalized anti-dinitrophenol (DNP) IgG with DNP-derivitized β-glucuronidase (DNP–β-glu) incorporated into lysosomes. Soluble mannosylated anti-DNP IgG was delivered to lysosomes after an 8-min lag period. The kinetics of anti-DNP IgG-opsonized beads showed a size-dependent response, where beads sized 0.2, 0.5, and 0.75 μm showed a lag period prior to delivery to lysosomes. In contrast, beads 1.0 μm or larger showed no lag in delivery to lysosomes. Since beads that had no lag in delivery to lysosomes also showed high levels of phagocytic cup formation, this suggests that phagocytic cups may be important in the rapid delivery of internalized particles to lysosomes.

Buffer stock analysis for a single source-single location inventory model with delivery lag

This paper treats a buffer stock inventory system with a single source of supply and a single location of demand. It extends the work of Salameh (1997) by assuming a non-zero lead time and a finite rather than instantaneous delivery. Two cases of deterministic demand are treated: (1) the constant consumption rate case; and (2) the fluctuating demand case. The optimum inventory policy is to determine the buffer stock level that minimizes the sum of the expected holding and inventory stockout costs. Numerical examples are provided to illustrate the solution procedures for the mathematical models developed.

Pyruvate dehydrogenase complex activation status and acetyl group availability as a site of interchange between anaerobic and oxidative metabolism during intense exercise.

During high intensity muscular contraction ATP is supplied at near maximal rates by PCr degradation and glycolysis. However, as exercise duration increases, the contribution of anaerobic ATP turnover to energy delivery declines due to the depletion of PCr stores and a reduction in the rate of glycogenolysis, which together may be responsible for the parallel reduction in muscle force production and power output. The importance of oxidative phosphorylation to total ATP production during intense muscle contraction has been underestimated to date. Recent studies have, however, demonstrated that the reduction in work production during repeated bouts of maximal exercise is less than the reduction observed in anaerobic energy provision. This observation has been suggested to reflect an increased contribution from oxidative phosphorylation to total energy production; but the mechanism responsible for this increased contribution is poorly understood. Recent evidence has pointed to the activation status of the pyruvate dehydrogenase complex and/or acetyl group availability as being focal in dictating temporal changes in ADP flux at the onset of intense exercise and, hence, the relative contribution made by anaerobic and oxidative ATP regenerating pathways under these conditions. As might be expected, therefore, maximising the contribution from oxidative ATP regeneration at the onset of exercise (by pharmacologically activating the pyruvate dehydrogenase complex prior to exercise) has been shown to have substantial functional benefits during high intensity contraction. This body of work has also illustrated that, contrary to popular theory, a large proportion of muscle lactate accumulation at the onset of exercise is associated with a lag in the activation of oxidative ATP production rather than with a lag in oxygen delivery.

Investment gestation lags: the difference between time-to-build and delivery lags

The timing of investment and capital stock accumulation can differ as a result of time-to-build and/or delivery lags. In this paper simple (calibration) methods are used to illustrate the differences in these sources of gestation lags.

Explicit Solution of Inventory Problems with Delivery Lags

We consider a continuous-time inventory system with fixed delivery lag, subject to a demand modelled as a diffusion process with drift. Excess demand is backlogged. We prove that the optimal ordering policy is a function of the sum of the stock on hand and the stock ordered but not yet delivered. Moreover, we state a relation linking the value function when orders are pending with the value function when no order is pending. As a consequence, the (a priori) infinite dimensional Quasi-Variational inequality (QVI) satisfied by the value function reduces to a finite dimensional one. The one-product inventory problem is then solved explicitly in the case of linear holding and shortage costs with fixed and proportional ordering cost. The optimal policy is determined; it is an (s, S) policy applied to the sum of stock on hand and orders pending, which means that when this sum decays below a critical level s, an order to level S is placed.

Time-to-Build, Delivery Lags, and the Equilibrium Pricing of Capital Goods

This paper characterizes the behavior of investment expenditures, optimal capital stocks, and real interest rates in the time-to-build model of investment. The paper derives equilibrium pricing relationships involving the prices of new and used capital and uses these relationships to obtain simple tests of the underlying investment technology. The paper also demonstrates that empirical versions of the delivery lag model are misspecified because the term structure of interest rates over the time horizon for which investment yields productive capital are omitted and that the use of stock market data to measure Tobin's q is inappropriate within the time-to-build model. Copyright 1993 by Ohio State University Press.

Import price adjustments with staggered import contracts

In this paper we develop a linear rational expectations equilibrium model of staggered import contracts with incomplete exchange rate indexing to explain the slow and moderate adjustment of import prices and quantities to exchange rate changes. The existence and stability of the equilibrium are proved by establishing equivalence between the solution to the equilibrium problem and the solution of an optimal linear regulator problem. Simulation analysis illustrates that the nature of the adjustment of import prices and quantities to exchange rate changes depends crucially on the length of the contract and the length of the delivery lag. Thus, an alternative to the ‘hysteresis’ explanation of the slow and moderate adjustment of import prices and quantities to exchange rate changes is established. The new explanation, however, has significantly different implications for exchange rate management and trade policies.

Materials management with a bar code reader.

A materials management system capable of inventory control, accounting and the automatic recording of supplies for a clinical department has been developed for the George Washington University Hospital Department of Anesthesia. This system combines a microprocessor-based computer for data storage and a hand-held bar code reader to record the bar code scan of each item in the inventory. A relational software program with easy-to-use menus and help keys was written. Bar code information stored for each item includes item number, quantity, date and time of issue. Accumulated bar code scans are loaded into the computer by use of a serial port and then used to update current inventory in the computer. Comparison between current inventory and reorder levels by the computer will initiate automatic printing of appropriate purchase orders. Reorder levels are adjusted regularly, by comparing previous year or month usage to current needs; items already on order, items on back order and delivery lag time are also taken into account.

Two-stage optimal control problems with an explicit switch point dependence: Optimality criteria and an example of delivery lags and investment

This paper provides necessary conditions for the solution of two-stage optimal control problems where the switch point is a choice variable and where the switch point appears as an argument of the integrands in each integral which comprise the criterion index to be maximized. Problems of this variety have arisen in the exhaustible resource and neoclassical investment literature. Using the conditions necessary for the solution of these problems, we analyze an example of optimal investment in the presence of delivery lags and show how the optimal switch point (delivery lag) responds to shifts in exogenous parameters.

Contracts, delivery lags, and currency risks

This paper presents a competitive model in which exchange rate uncertainty has real effects on how trade contracts are written and executed. In this model, exporting firms have an incentive to delay delivery on trade contracts whenever they can sell their products on the domestic market for a higher price than the domestic currency value of the price specified by the trade contracts. In general, it is costly for a firm to offer a credible commitment to the promised delivery date of a trade contract. We demonstrate that under certain conditions a firm can costlessly commit to a policy of no delivery lags by the appropriate choice of the currency of denomination of trade contracts.

Money Demand and the Effects of Fiscal Policies: Comment

Mankiw and Summers (1986) argue on theoretical and empirical grounds for consumption as the appropriate scale variable in the money demand function. This serves as the primary basis for their provocative result that personal income tax cuts may be contractionary on equilibrium real income in a short-run, IS-LM model. Moreover, they cite evidence on the interest elasticity of investment demand and on the interest and income elasticities of money demand for the U.S. economy that leads them to conclude that tax cuts are, indeed, contractionary in the United States. In this paper, theoretical and empirical arguments are combined in order to show that the tax cut is likely to be expansionary on real income even though consumption is taken as the scale variable in the money demand function. In section 2, a theoretical model of the interaction of taxes and the opportunity cost of holding money is sketched, with the implication that a cut in personal income taxes, ceteris paribus, reduces the excess demand for money, whereas a cut in corporate income tax rates likely has no effect (although it possibly reduces money demand in one case examined). This is shown in section 3 to generalize the Mankiw-Summers elasticity condition determining the sign of the (personal) tax cut multiplier. In section 4, empirical evidence is brought to bear on this elasticity condition. It is seen that a crucial magnitude is the short-run interest elasticity of investment demand (and, hence, the slope of the IS curve); empirical estimates of this elasticity depend on the nature of the frictions that prevent an immediate adjustment to the new desired capital stock following a change in interest rates. Such frictions include delivery lags and the putty-clay nature of certain types of capital. Upon evaluation of the empirical evidence, it is concluded that a cut in income tax rates is, indeed, expansionary on aggregate demand. Finally, in section 5, some previously omitted factors that may affect outcomes in the short run are briefly discussed; these include supply-side and expectational effects.