arXiv subjects

Linda Li

Publications and source records attributed to Linda Li.

8 recordsLinked to original sources

arXiv2026

Social bots weaken activist cohesion

Social bots now make up a substantial share of online political communication, where they are studied mainly as producers of misinformation and amplified content. Far less is known about whether their presence reshapes the human relationships that hold movements together. We ask whether exposure to bots during a protest peak is followed by the erosion of cohesion in human networks. Tracking retweet networks of core participants in the 2020 Black Lives Matter (BLM) protests before, during, and after the peak, we measure change in cohesion at two scales: triadic closure in individual ego networks and edge density within detected communities. Greater bot exposure during the peak predicts steeper subsequent declines in human cohesion at both scales, and the loss concentrates among supporters of the movement. Bots may weaken activism less by changing what people believe than by dissolving the ties through which collective action is sustained.

cs.SI↗

arXiv2026

Grid2Matrix: Revealing Digital Agnosia in Vision-Language Models

Vision-Language Models (VLMs) excel on many multimodal reasoning benchmarks, but these evaluations often do not require an exhaustive readout of the image and can therefore obscure failures in faithfully capturing all visual details. We introduce Grid2Matrix (G2M), a controlled benchmark in which a model is shown a color grid and a color-to-number mapping, and must output the corresponding matrix. By varying grid size and the number of colors, G2M provides a simple way to increase visual complexity while minimizing semantic confounds. We find that VLMs exhibit a sharp early collapse in zero-shot end-to-end evaluation, failing on surprisingly small grids rather than degrading gradually as the task becomes denser. We probe the visual encoders of VLMs from two representative families and find that they preserve substantially more of the grid information than the corresponding end-to-end outputs. This suggests that the failure is not explained by visual encoding alone, but also reflects a gap between what remains recoverable from visual features and what is ultimately expressed in language. We term this gap \textit{Digital Agnosia}. Further analyses show that these errors are highly structured and depend strongly on how grid cells overlap with visual patch boundaries. We also find that common strategies such as model scaling and multimodal alignment do not fully eliminate this failure mode. We expect G2M to serve as a useful testbed for understanding where and how VLMs lose fine visual details, and for evaluating tasks where missing even small visual details can matter, such as tables, charts, forms, and GUIs.

cs.CV↗

arXiv2024

Social bots sour activist sentiment without eroding engagement

Social media platforms have witnessed a substantial increase in social bot activity, significantly affecting online discourse. Our study explores the dynamic nature of bot engagement related to Extinction Rebellion climate change protests from 18 November 2019 to 10 December 2019. We find that bots exert a greater influence on human behavior than vice versa during heated online periods. To assess the causal impact of human-bot communication, we compared communication histories between human users who directly interacted with bots and matched human users who did not. Our findings demonstrate a consistent negative impact of bot interactions on subsequent human sentiment, with exposed users displaying significantly more negative sentiment than their counterparts. Furthermore, the nature of bot interaction influences human tweeting activity and the sentiment towards protests. Political astroturfing bots increase activity, whereas other bots decrease it. Sentiment changes towards protests depend on the user's original support level, indicating targeted manipulation. However, bot interactions do not change activists' engagement towards protests. Despite the seemingly minor impact of individual bot encounters, the cumulative effect is profound due to the large volume of bot communication. Our findings underscore the importance of unrestricted access to social media data for studying the prevalence and influence of social bots, as with new technological advancements distinguishing between bots and humans becomes nearly impossible.

cs.CY↗

arXiv2022

Time-resolved vibrational-pump visible-probe spectroscopy for thermal conductivity measurement of metal-halide perovskites

Understanding thermal transport at the micro- to nanoscale is crucially important for a wide range of technologies ranging from device thermal management and protection systems to thermal-energy regulation and harvesting. In the past decades, non-contact optical methods such as time-domain and frequency-domain thermoreflectance (TDTR and FDTR) have emerged as extremely powerful and versatile thermal metrological techniques for the measurement of material thermal conductivities. Here, we report the measurement of thermal conductivity of thin films of CH3NH3PbI3 (MAPbI3), a prototypical metal-halide perovskite, by developing a time-resolved optical technique called vibrational-pump visible-probe (VPVP) spectroscopy. The VPVP technique relies on the direct thermal excitation of MAPbI3 by femtosecond (fs) mid-infrared (MIR) optical pump pulses that are wavelength-tuned to a vibrational mode of the material, after which the time dependent optical transmittance across the visible range is probed in the ns to the us time window using a broadband pulsed laser. Using the VPVP method, we determine the thermal conductivities of MAPbI3 thin films deposited on different substrates. The transducer-free VPVP method reported here is expected to permit spectrally resolving and spatiotemporally imaging the dynamic lattice temperature variations in organic, polymeric, and hybrid organic-inorganic semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

On the Equity-Efficiency Trade-off in Food-Bank Network Operations

In this paper, we present a novel modelling perspective to the food-bank donation allocation problem under equity and efficiency performance measures. Using a penalty factor in the objective function, our model explicitly accounts for both efficiency and equity, simultaneously. We give the tightest lower and upper bounds of the penalty factor, which can conveniently characterize closed-form optimal solutions for the perfect efficiency and perfect equity cases. Testing our model on the full spectrum of our penalty factor, using real data from Feeding America, we demonstrate that the solutions from our model dominate those of a benchmark from the literature in terms of equity, efficiency, and utilization equity (utiloquity). Our sensitivity analysis demonstrates that the society should put its priority on helping eliminate poverty before investing on capacity expansions in charity organizations like food-banks. This will ensure that adding more capacity to the network will always lead to a decrease in the price of equity for the food-banks. On the other hand, we observed that encouraging the society towards charitability is always beneficial for the food-banks, albeit with diminishing returns. Finally, our experiments demonstrate that reducing poverty, as the most important element in achieving higher equity, is dependent on reducing demand variability, as opposed to the average level of demand.

math.OC↗

arXiv2021

An Integrated Vaccination Site Selection and Dose Allocation Problem with Fairness Concerns

Fairness in vaccination is not only important from a social justice point of view, but experience has shown that a fair distribution of vaccine proves more effective in public immunization by preventing highly-concentrated infected areas to form among the population. In this paper, we address fairness from two simultaneous points of view: equity and accessibility. Equity in our setting means that as far as possible, each demand zone should receive a fair-share of the total doses available. On the other hand, accessibility means that as far as possible, each demand zone should have equal travel distance to access their assigned vaccination site.

math.OC↗

arXiv2021

Dynamics of Equity, Efficiency, and Efficacy in Home Health Care with Patient and Caregiver Preferences

There are three main entities in an HHC setting: the firm, the caregivers, and the patients. Often times the interests of each group of entities conflict with the other two. Whether a non-profit or a for-profit HHC, the firm generally seeks efficiency in terms of maximum utilization of the resources and highest level of care provided to the patients. Caregivers, seek a fair utilization across the network in order to increase job satisfaction. Finally, the patients seek maximum satisfaction level and a fair share of the care provided by the firm. Therefore, looking at HHCs from either one of these lenses by themselves leads to decisions that may neglect the interests of the others. The goal of this paper is to integrate the objectives of these three groups into one place and study their dynamics.

math.OC↗

arXiv2020

Fake News Detection with Different Models

This is a paper for exploring various different models aiming at developing fake news detection models and we had used certain machine learning algorithms and we had used pretrained algorithms such as TFIDF and CV and W2V as features for processing textual data.

cs.CL↗