210 research outputs found
An Infra-marginal Analysis of the Ricardian Model
This paper applies the infra-marginal analysis, which is a combination of marginal and total cost-benefit analysis, to the Ricardian model. It demonstrates that the rule of marginal cost pricing does not always hold. It shows that in a 2x2 Ricardian model, there is a unique general equilibrium and that the comparative statics of the equilibrium involve discontinuous jumps -- as transaction efficiency improves, the general equilibrium structure jumps from autarky to partial division of labor and then to complete division of labor. The paper also discusses the effects of tariff in a model where trade regimes are endogenously chosen. It finds that (1) if partial division of labor occurs in equilibrium, the country that produces both goods chooses unilateral protection tariff, and the country producing a single good chooses unilateral laissez faire policy; (2) if complete division of labor occurs in equilibrium, the governments in both countries would prefer a tariff negotiation to a tariff war. Finally, the paper shows that in a model with three countries the country which does not have a comparative advantage relative to the other two countries and/or which has low transaction efficiency may be excluded from trade.Ricardo model, trade policy, division of labor
Multi-objective optimization design for a battery pack of electric vehicle with surrogate models
In this investigation, a systematic surrogate-based optimization design framework for a battery pack is presented. An air-cooling battery pack equipped on electric vehicles is first designed. Finite element analysis (FEA) results of the baseline design show that global maximum stresses under x-axis and y-axis transient acceleration shock condition are both above the tensile limit of material. Selecting the panel and beam thickness of battery pack as design variables, with global maximum stress constraints in shock cases, a multi-objective optimization problem is implemented using metamodel technique and multi-objective particle-swarm-optimization (MOPSO) algorithm to simultaneously minimize the total mass and maximize the restrained basic frequency. It is found that 2nd order polynomial response surface (PRS), 3rd order PRS and radial basis function (RBF) are the most accurate and appropriate metamodels for restrained basic frequency, global maximum stresses under x-axis and y-axis shock conditions respectively. Results demonstrate that all the optimal solutions in Pareto Frontier have heavier weight and lower frequency compared with baseline design due to the restriction of global maximum stress response. Finally, two optimal schemes, “Knee Point” and “lightest weight”, satisfied both of the stress constraint conditions, show great consistency with FEA results and can be selected as alternative improved schemes
Robust Topology Optimization Based on Stochastic Collocation Methods under Loading Uncertainties
A robust topology optimization (RTO) approach with consideration of loading uncertainties is developed in this paper. The stochastic collocation method combined with full tensor product grid and Smolyak sparse grid transforms the robust formulation into a weighted multiple loading deterministic problem at the collocation points. The proposed approach is amenable to implementation in existing commercial topology optimization software package and thus feasible to practical engineering problems. Numerical examples of two- and three-dimensional topology optimization problems are provided to demonstrate the proposed RTO approach and its applications. The optimal topologies obtained from deterministic and robust topology optimization designs under tensor product grid and sparse grid with different levels are compared with one another to investigate the pros and cons of optimization algorithm on final topologies, and an extensive Monte Carlo simulation is also performed to verify the proposed approach
Tree based Progressive Regression Model for Watch-Time Prediction in Short-video Recommendation
An accurate prediction of watch time has been of vital importance to enhance
user engagement in video recommender systems. To achieve this, there are four
properties that a watch time prediction framework should satisfy: first,
despite its continuous value, watch time is also an ordinal variable and the
relative ordering between its values reflects the differences in user
preferences. Therefore the ordinal relations should be reflected in watch time
predictions. Second, the conditional dependence between the video-watching
behaviors should be captured in the model. For instance, one has to watch half
of the video before he/she finishes watching the whole video. Third, modeling
watch time with a point estimation ignores the fact that models might give
results with high uncertainty and this could cause bad cases in recommender
systems. Therefore the framework should be aware of prediction uncertainty.
Forth, the real-life recommender systems suffer from severe bias amplifications
thus an estimation without bias amplification is expected. Therefore we propose
TPM for watch time prediction. Specifically, the ordinal ranks of watch time
are introduced into TPM and the problem is decomposed into a series of
conditional dependent classification tasks which are organized into a tree
structure. The expectation of watch time can be generated by traversing the
tree and the variance of watch time predictions is explicitly introduced into
the objective function as a measurement for uncertainty. Moreover, we
illustrate that backdoor adjustment can be seamlessly incorporated into TPM,
which alleviates bias amplifications. Extensive offline evaluations have been
conducted in public datasets and TPM have been deployed in a real-world video
app Kuaishou with over 300 million DAUs. The results indicate that TPM
outperforms state-of-the-art approaches and indeed improves video consumption
significantly
Discrete Conditional Diffusion for Reranking in Recommendation
Reranking plays a crucial role in modern multi-stage recommender systems by
rearranging the initial ranking list to model interplay between items.
Considering the inherent challenges of reranking such as combinatorial
searching space, some previous studies have adopted the evaluator-generator
paradigm, with a generator producing feasible sequences and a evaluator
selecting the best one based on estimated listwise utility. Inspired by the
remarkable success of diffusion generative models, this paper explores the
potential of diffusion models for generating high-quality sequences in
reranking. However, we argue that it is nontrivial to take diffusion models as
the generator in the context of recommendation. Firstly, diffusion models
primarily operate in continuous data space, differing from the discrete data
space of item permutations. Secondly, the recommendation task is different from
conventional generation tasks as the purpose of recommender systems is to
fulfill user interests. Lastly, real-life recommender systems require
efficiency, posing challenges for the inference of diffusion models. To
overcome these challenges, we propose a novel Discrete Conditional Diffusion
Reranking (DCDR) framework for recommendation. DCDR extends traditional
diffusion models by introducing a discrete forward process with tractable
posteriors, which adds noise to item sequences through step-wise discrete
operations (e.g., swapping). Additionally, DCDR incorporates a conditional
reverse process that generates item sequences conditioned on expected user
responses. Extensive offline experiments conducted on public datasets
demonstrate that DCDR outperforms state-of-the-art reranking methods.
Furthermore, DCDR has been deployed in a real-world video app with over 300
million daily active users, significantly enhancing online recommendation
quality
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