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Technology And The Global Economy, Jonathan Eaton, Samuel Kortum
Technology And The Global Economy, Jonathan Eaton, Samuel Kortum
Cowles Foundation Discussion Papers
Interpreting individual heterogeneity in terms of probability theory has proved powerful in connecting behaviour at the individual and aggregate levels. Returning to Ricardo's focus on comparative efficiency as a basis for international trade, much recent quantitative equilibrium modeling of the global economy builds on particular probabilistic assumptions about technology. We review these assumptions and how they deliver a unified framework underlying a wide range of static and dynamic equilibrium models.
Can Random Friends Seed More Buzz And Adoption? Leveraging The Friendship Paradox, Vineet Kumar, K. Sudhir
Can Random Friends Seed More Buzz And Adoption? Leveraging The Friendship Paradox, Vineet Kumar, K. Sudhir
Cowles Foundation Discussion Papers
A critical element of word of mouth (WOM) or buzz marketing is to identify seeds, often central actors with high degree in the social network. Seed identification typically requires data on the full network structure, which is often unavailable. We therefore examine the impact of WOM seeding strategies motivated by the friendship paradox to obtain more central nodes without knowing network structure on adoption. Higher-degree nodes may be less effective as seeds if these nodes communicate less with neighbors or are less persuasive when they communicate; therefore whether friendship paradox motivated seeding strategies increase or reduce WOM and adoption remains …
Can Friends Seed More Buzz And Adoption?, Vineet Kumar, K. Sudhir
Can Friends Seed More Buzz And Adoption?, Vineet Kumar, K. Sudhir
Cowles Foundation Discussion Papers
A critical element of word of mouth (WOM) or buzz marketing is to identify seeds, often central actors with high degree in the social network. Seed identification typically requires data on the full network structure, which is often unavailable. We therefore examine the impact of WOM seeding strategies motivated by the friendship paradox to obtain more central nodes without knowing network structure. But higher-degree nodes may communicate less with neighbors; therefore whether friendship paradox motivated seeding strategies increase or reduce WOM and adoption remains an empirical question. We develop and estimate a model of WOM and adoption using data on …
Understanding Temporal Aggregation Effects On Kurtosis In Financial Indices, Offer Lieberman, Peter C.B. Phillips
Understanding Temporal Aggregation Effects On Kurtosis In Financial Indices, Offer Lieberman, Peter C.B. Phillips
Cowles Foundation Discussion Papers
Indices of financial returns typically display sample kurtosis that declines towards the Gaussian value 3 as the sampling interval increases. This paper uses stochastic unit root (STUR) and continuous time analysis to explain the phenomenon. Limit theory for the sample kurtosis reveals that STUR specifications provide two sources of excess kurtosis, both of which decline with the sampling interval. Limiting kurtosis is shown to be random and is a functional of the limiting price process. Using a continuous time version of the model under no-drift, local drift, and drift inclusions, we suggest a new continuous time kurtosis measure for financial …
When And Why Does Bioturbation Lead To Diffusive Mixing?, Filip J. R. Meysman, Bernard P. Boudreau, Jack J. Middelburg
When And Why Does Bioturbation Lead To Diffusive Mixing?, Filip J. R. Meysman, Bernard P. Boudreau, Jack J. Middelburg
Journal of Marine Research
Bioturbation in aquatic sediments results from many different biological activities, inducing particle displacement over a variety of length and time scales. Despite this inherent complexity, empirical tracer studies show that bioturbational mixing is often well described by a simple diffusive model. To resolve this apparent contradiction between biological complexity and modeling simplicity, we present an investigation into the diffusive nature of bioturbation. To this end, we examine a stochastic description of bioturbation, where particle mixing is described as a sequence of random bioturbation events. Particle movement is governed by three basic variables: the direction of jumping, the jumping distance, and …
An Estimate Of Lagrangian Eddy Statistics And Diffusion In The Mixed Layer Of The Southern Ocean, J. B. Sallée, Kevin Speer, R. Morrow, R. Lumpkin
An Estimate Of Lagrangian Eddy Statistics And Diffusion In The Mixed Layer Of The Southern Ocean, J. B. Sallée, Kevin Speer, R. Morrow, R. Lumpkin
Journal of Marine Research
A statistical analysis of surface drifter observations is used to compute eddy length and time scales and eddy diffusion in the Southern Ocean. Eddy diffusion values of the order of 104 m2 s–1 are found in the energetic western boundary currents north of the Antarctic Circumpolar Current (ACC) and secondary peaks occur where the ACC negotiates topography. The diffusivity shows an increase from the Antarctic continent to the core of the ACC, then a slight decrease or a stable plateau within the ACC. North of the ACC, diffusivity generally decreases into the interior of ocean basins, except …
Diffusively-Driven Overturning Of A Stable Density Gradient, Andrew F. Thompson, George Veronis
Diffusively-Driven Overturning Of A Stable Density Gradient, Andrew F. Thompson, George Veronis
Journal of Marine Research
We present the results of an experimental study on the formation and propagation of thermohaline intrusions from an initial state that is stably stratified in two diffusing components. The intrusions form in a layer that contains compensating horizontal gradients of the two components and that lies above a denser reservoir layer that is homogeneous. In the initial state, a vertical barrier separates the upper layer into two half layers each with a different concentration but with the same density. Differential diffusion of solute from the reservoir into the upper layer initiates intrusions that are separated by an interface and that …
Diffusion Of Organic And Inorganic Solutes Through Macrofaunal Mucus Secretions And Tube Linings In Marine Sediments, Angelos K. Hannides, Shannon M. Dunn, Robert C. Aller
Diffusion Of Organic And Inorganic Solutes Through Macrofaunal Mucus Secretions And Tube Linings In Marine Sediments, Angelos K. Hannides, Shannon M. Dunn, Robert C. Aller
Journal of Marine Research
Transport models in sediments commonly assume that diffusion occurs through water saturated pore space and that diffusive properties are largely homogeneous and isotropic. The bioturbated zone of marine sediments is characterized by sediment pores filled with mucus gel and criss-crossed by organic membranes that line macrofaunal tubes and burrows. Diffusion experiments utilizing pedal mucus from the naticid snails, Neverita (=Polinices) duplicata and Euspira (=Lunatia) heros, and organic tube linings from the polychaetes Onuphis jenneri, Diopatra cupria, and Chaetopterus variopedatus, demonstrated that the diffusion of both organic and inorganic solutes is inhibited by …
The Influence Of Macrofaunal Burrow Spacing And Diffusive Scaling On Sedimentary Nitrification And Denitrification: An Experimental Simulation And Model Approach, Franck Gilbert, Robert C. Aller, Stefan Hulth
The Influence Of Macrofaunal Burrow Spacing And Diffusive Scaling On Sedimentary Nitrification And Denitrification: An Experimental Simulation And Model Approach, Franck Gilbert, Robert C. Aller, Stefan Hulth
Journal of Marine Research
The influence of burrow spacing on sedimentary nitrification and denitrification was simulated experimentally using sediment plugs of different thicknesses immersed in aerated seawater reservoirs. Different plug thicknesses mimic different distances between oxygenated burrow centers and produce similar changes in aerobic-anaerobic reaction balances as a function of diffusive transport scaling. The thicknesses used were roughly equivalent to transport scales (interburrow spacing) that could be produced by burrow abundances of ~400 to 50,000 m-2, depending on burrow lumen radii (e.g., 0.05-1 cm). Following the exposure of anoxic sediment plugs to aerated water, an efficient aerobic nitrification zone was established within …
Diffusion In A Lattice-Automaton Model Of Bioturbation By Small Deposit Feeders, Bernard P. Boudreau, Jae Choi, Filip Meysman, Fréderique François-Carcaillet
Diffusion In A Lattice-Automaton Model Of Bioturbation By Small Deposit Feeders, Bernard P. Boudreau, Jae Choi, Filip Meysman, Fréderique François-Carcaillet
Journal of Marine Research
The mixing of 210Pb and tagged particles is examined in a lattice-automaton model for bioturbation containing small deposit feeders. The values of the biodiffusion coefficient, DB, calculated using typical biological parameter values, i.e., size, abundance, feeding and locomotion rates, are similar to those expected from marine sediments of a given sedimentation rate. Most biological parameters appear to exert primarily linear effects on DB values, while most nonlinearities seem to be model artifacts or failures of the assumptions in the basic DB model. The model highlights the importance of ingestion-egestion, over simple particle displacement, as an …
On The Eddy Transfer Of Tracers: Advective Or Diffusive?, Mei-Man Lee, David P. Marshall, Richard G. Williams
On The Eddy Transfer Of Tracers: Advective Or Diffusive?, Mei-Man Lee, David P. Marshall, Richard G. Williams
Journal of Marine Research
Geostrophic eddies have traditionally been viewed within oceanography as diffusing water masses and tracers in a down-gradient manner. However, eddies also have an advective role that may lead to an up-gradient transfer of tracers, as has been recognized in atmospheric tracer studies and recent eddy parameterizations developed for the ocean. Eddies provide an advective transfer or “bolus” velocity through the secondary circulation formed by the slumping of density surfaces in baroclinic instability. Here we use an eddy-resolving isopycnal ocean model to investigate the meridional transfer across a zonal jet. The jet undergoes baroclinic instability, forming a vibrant eddy field and …
New Similarity Solutions Of The Thermocline Equations With Vertical Variations Of Diffusion, Simon Hood
New Similarity Solutions Of The Thermocline Equations With Vertical Variations Of Diffusion, Simon Hood
Journal of Marine Research
Three new classes of exact solution of the thermocline equations are obtained through use of an ansatz based method (Clarkson and Kruskal, 1989), which is related to the older Classical Lie Group Method used by Salmon and Hollerbach (1991) to obtain exact solutions. The newer method has not previously been applied to oceanographic problems. Our results are more general than those of Salmon and Hollerbach in two distinct ways: we obtain new classes of solution not obtainable by the older method and, in addition, we determine solutions in which the vertical temperature diffusion profile is an arbitrary function of depth. …
Oxygen, Sulfide And Diffusion: Why Thiobiotic Meiofauna Must Be Sulfide-Insensitive First-Order Respirers, Eric Powell
Oxygen, Sulfide And Diffusion: Why Thiobiotic Meiofauna Must Be Sulfide-Insensitive First-Order Respirers, Eric Powell
Journal of Marine Research
Thiobios (sulfide-dependent) meiofauna have an aerobic metabolism, are sulfide-insensitive and rarely contain symbiotic sulfur-oxidizing bacteria. Adaptations so far observed in thiobios are consistent with the overriding need to maximize the diffusive flux of oxygen and sulfide to optimize energy yield. Both accrue from the requirement that oxygen and sulfide uptake and metabolism be controlled by diffusion and first-order rate reactions. These adaptations include variation in shape, mitochondrial distribution and respiratory capacity. Meiofauna can substantially supplement a more inefficient anaerobic metabolism with aerobic metabolism at oxygen concentrations as low as 0.1 μM. Hence, an aerobic capacity is useful even in …
Dissipation And Diffusion By Internal Wave Breaking, Ann E. Gargett, Greg Holloway
Dissipation And Diffusion By Internal Wave Breaking, Ann E. Gargett, Greg Holloway
Journal of Marine Research
Recent direct observations of the rate of kinetic energy dissipation, ε, tend to vary systematically with buoyancy frequency, N. This note presents arguments leading to an expected relationship between these two parameters. We first suggest that the classical separation of velocity field into “turbulent” and “mean” (including internal waves) is inappropriate for a stratified system such as the ocean, in which nonlinear forces and buoyant restoring forces act over a wide range of space-time scales. Reconsidering the steady-state kinetic energy equation without this separation, we obtain ε ∝ N1.0 or ε ∝ N1.5, where the ambiguity …
Estuarine Circulation Induced By Diffusion, Donald V. Hansen, Maurice Rattray Jr.
Estuarine Circulation Induced By Diffusion, Donald V. Hansen, Maurice Rattray Jr.
Journal of Marine Research
Similarity solutions of the equations for estuarine circulation and salt balance are presented for a circulation generated by diffusive modification of stratification maintained at the entrance to an inlet by external dynamics rather than by fresh water discharged directly into the inlet....