arXiv subjects

Alejandra Martinez

Publications and source records attributed to Alejandra Martinez.

5 recordsLinked to original sources

arXiv2026

Trade relationships during and after a crisis

This paper provides causal evidence that temporary supply disruptions reshape firms' relationship portfolios in international trade. Using exogenous road disruptions during Colombia's 2010-11 La Ni\~na episode, I identify exposure at the buyer-seller relationship level, exploiting variation within importers' supplier portfolios. Exposed relationships are less likely to terminate when importers have alternative non-exposed suppliers. However, firms with broader portfolio exposure gradually reduce their relationship networks and may eventually exit the market. A framework linking relationship surplus to portfolio composition explains these contrasting responses and shows how the same shock generates opposite effects at relationship and firm levels.

econ.GN↗

arXiv2025

Transitivity in International Trade: Evidence from Colombia-U.S. Firm Relationships

A large literature has documented transitivity as a key feature of social networks: individuals are more likely connected with each other if they share common connections with other individuals. We take this idea to trading relationships between firms: firms are more likely to trade with each other if they share common trading partners. Transitivity leads to a clustered pattern of relationship formation and break-up. It is therefore important for understanding how firms meet and how shocks propagate through firm networks. We describe a method for detecting and quantifying transitivity in firm-to-firm transactions, based on systematic deviations from conditional independence across firm-to-firm relationships. We apply the method to Colombia-U.S. exporter-importer data and show in counterfactuals that transitivity is a significant and economically meaningful factor in how firm networks adjust to cost shocks.

econ.GN↗

arXiv2024

Usability of back support, shoulder support and sit-stand passive occupational exoskeletons: A heuristic evaluation of the designs

Occupational exoskeletons promise to alleviate musculoskeletal injuries among industrial workers. Knowledge of the usability of the exoskeleton designs with respect to the user device interaction points, and the problems in design features, functions and parts, evaluated and rated using design principles is still limited. Further, the usability of exoskeletons when assembling, donning, doffing and disassembling them, tasks that can be considered pre and post use tasks are also critical to evaluate, especially from a device design standpoint. We conducted a heuristic evaluation of the usability of three popular exoskeletons, a back support device, a shoulder support device, and a sit stand exoskeleton when assembling, donning, doffing and disassembling them. Seven evaluators used Nielsen and Shneiderman usability heuristics to evaluate the devices. Results indicate that none of the three exoskeletons had any catastrophic usability problems, but all three had major usability problems including accommodating diverse users, the assembly, donning and doffing being a two person operation, poor documentation, a lack of sequence indicators during assembly of the devices, presence of safety hazards while donning and doffing the devices, and manual strength requirements. Further, the assembly task is the most difficult task resulting in the most violations of usability heuristics. The exoskeleton human factors research community should include diverse users in their evaluations and conduct usability, accessibility, and safety evaluations of these devices to provide design feedback to device designers.

cs.HC↗

arXiv2024

Heuristic evaluations of back support, shoulder support, hand grip strength support, and sit-stand support exoskeletons using universal design principles

Occupational exoskeletons promise to reduce the incidence of musculoskeletal injuries; however, we do not know if their designs allow universal use by all workers. We also do not know how easy the tasks of assembling, donning, doffing, and disassembling exoskeletons are. The purpose of our study was to heuristically evaluate a back support, a shoulder support, a handgrip strength support, and a sit-stand exoskeleton for how well they are designed for universal use when assembling, donning, doffing, and disassembling the exoskeleton. Seven evaluators used universal design principles and associated criteria to independently evaluate and rate four exoskeletons when assembling, donning, doffing, and disassembling the devices. The rating scale was a Likert-type scale, where a rating of 1 represented not at all, and a rating of 5 represented an excellent design with respect to the universal design criteria for the task. The results indicate that providing perceptible information to the user, making the design equitable to use for a diverse set of users, making the design simple and intuitive to use with adequate feedback, and designing to prevent user errors, and when errors are made, allowing the user to recover quickly from the errors, were rated poorly. Assembling and donning tasks presented the most challenges.

cs.HC↗

arXiv2015

Marginal integration $M-$estimators for additive models

Additive regression models have a long history in multivariate nonparametric regression. They provide a model in which each regression function depends only on a single explanatory variable allowing to obtain estimators at the optimal univariate rate. Beyond backfitting, marginal integration is a common procedure to estimate each component. In this paper, we propose a robust estimator of the additive components which combines local polynomials on the component to be estimated and marginal integration. The proposed estimators are consistent and asymptotically normally distributed. A simulation study allows to show the advantage of the proposal over the classical one when outliers are present in the responses, leading to estimators with good robustness and efficiency properties.

stat.ME↗