177 research outputs found
Evaporation-triggered segregation of sessile binary droplets
Droplet evaporation of multicomponent droplets is essential for various
physiochemical applications, e.g. in inkjet printing, spray cooling and
microfabrication. In this work, we observe and study phase segregation of an
evaporating sessile binary droplet, consisting of a mixture of water and a
surfactant-like liquid (1,2-hexanediol). The phase segregation (i.e., demixing)
leads to a reduced water evaporation rate of the droplet and eventually the
evaporation process ceases due to shielding of the water by the non-volatile
1,2-hexanediol. Visualizations of the flow field by particle image velocimetry
and numerical simulations reveal that the timescale of water evaporation at the
droplet rim is faster than that of the Marangoni flow, which originates from
the surface tension difference between water and 1,2-hexanediol, eventually
leading to segregation
Nonlinear PI control for variable pitch wind turbine
Wind turbine uses a pitch angle controller to reduce the power captured above the rated wind speed and release the mechanical stress of the drive train. This paper investigates a nonlinear PI (N-PI) based pitch angle controller, by designing an extended-order state and perturbation observer to estimate and compensate unknown time-varying nonlinearities and disturbances. The proposed N-PI does not require the accurate model and uses only one set of PI parameters to provide a global optimal performance under wind speed changes. Simulation verification is based on a simplified two-mass wind turbine model and a detailed aero-elastic wind turbine simulator (FAST), respectively. Simulation results show that the N-PI controller can provide better dynamic performances of power regulation, load stress reduction and actuator usage, comparing with the conventional PI and gain-scheduled PI controller, and better robustness against of model uncertainties than feedback linearization control
Evaporation-Induced Crystallization of Surfactants in Sessile Multicomponent Droplets
Surfactants have been widely studied and used in controlling droplet
evaporation. In this work, we observe and study the crystallization of sodium
dodecyl sulfate (SDS) within an evaporating glycerol-water mixture droplet. The
crystallization is induced by the preferential evaporation of water, which
decreases the solubility of SDS in the mixture. As a consequence, the crystals
shield the droplet surface and cease the evaporation. The universality of the
evaporation characteristics for a range of droplet sizes is revealed by
applying a diffusion model, extended by Raoult's law. To describe the
nucleation and growth of the crystals, we employ the 2-dimensional
crystallization model of Weinberg [J. Non-Cryst. Solids 1991, 134, 116]. The
results of this model compare favorably to our experimental results. Our
findings may inspire the community to reconsider the role of high concentration
of surfactants in a multicomponent evaporation system
An Empathy-Based Sandbox Approach to Bridge Attitudes, Goals, Knowledge, and Behaviors in the Privacy Paradox
The "privacy paradox" describes the discrepancy between users' privacy
attitudes and their actual behaviors. Mitigating this discrepancy requires
solutions that account for both system opaqueness and users' hesitations in
testing different privacy settings due to fears of unintended data exposure. We
introduce an empathy-based approach that allows users to experience how privacy
behaviors may alter system outcomes in a risk-free sandbox environment from the
perspective of artificially generated personas. To generate realistic personas,
we introduce a novel pipeline that augments the outputs of large language
models using few-shot learning, contextualization, and chain of thoughts. Our
empirical studies demonstrated the adequate quality of generated personas and
highlighted the changes in privacy-related applications (e.g., online
advertising) caused by different personas. Furthermore, users demonstrated
cognitive and emotional empathy towards the personas when interacting with our
sandbox. We offered design implications for downstream applications in
improving user privacy literacy and promoting behavior changes
From Awareness to Action: Exploring End-User Empowerment Interventions for Dark Patterns in UX
The study of UX dark patterns, i.e., UI designs that seek to manipulate user
behaviors, often for the benefit of online services, has drawn significant
attention in the CHI and CSCW communities in recent years. To complement
previous studies in addressing dark patterns from (1) the designer's
perspective on education and advocacy for ethical designs; and (2) the
policymaker's perspective on new regulations, we propose an
end-user-empowerment intervention approach that helps users (1) raise the
awareness of dark patterns and understand their underlying design intents; (2)
take actions to counter the effects of dark patterns using a web augmentation
approach. Through a two-phase co-design study, including 5 co-design workshops
(N=12) and a 2-week technology probe study (N=15), we reported findings on the
understanding of users' needs, preferences, and challenges in handling dark
patterns and investigated the feedback and reactions to users' awareness of and
action on dark patterns being empowered in a realistic in-situ setting.Comment: Conditionally Accepted at CSCW 202
Rayleigh-Taylor instability by segregation in an evaporating multi-component microdroplet
The evaporation of multi-component droplets is relevant to various
applications but challenging to study due to the complex physicochemical
dynamics. Recently, Li (2018) reported evaporation-triggered segregation in
1,2-hexanediol-water binary droplets. In this present work, we added 0.5 wt%
silicone oil into the 1,2-hexanediol-water binary solution. This minute
silicone oil concentration dramatically modifies the evaporation process as it
triggers an early extraction of the 1,2-hexanediol from the mixture.
Surprisingly, we observe that the segregation of 1,2-hexanediol forms plumes,
rising up from the rim of the sessile droplet towards the apex during the
droplet evaporation. By orientating the droplet upside down, i.e., by studying
a pendant droplet, the absence of the plumes indicates that the flow structure
is induced by buoyancy, which drives a Rayleigh-Taylor instability (i.e.,
driven by density differences & gravitational acceleration). From micro-PIV
measurement, we further prove that the segregation of the non-volatile
component (1,2-hexanediol) hinders the evaporation near the contact line, which
leads to a suppression of the Marangoni flow in this region. Hence, on long
time scales, gravitational effects play the dominant role in the flow
structure, rather than Marangoni flows. We compare the measurement of the
evaporation rate with the diffusion model of Popov (2005), coupled with
Raoult's law and the activity coefficient. This comparison indeed confirms that
the silicone-oil-triggered segregation of the non-volatile 1,2-hexanediol
significantly delays the evaporation. With an extended diffusion model, in
which the influence of the segregation has been implemented, the evaporation
can be well described
Neuro-Inspired Hierarchical Multimodal Learning
Integrating and processing information from various sources or modalities are
critical for obtaining a comprehensive and accurate perception of the real
world. Drawing inspiration from neuroscience, we develop the
Information-Theoretic Hierarchical Perception (ITHP) model, which utilizes the
concept of information bottleneck. Distinct from most traditional fusion models
that aim to incorporate all modalities as input, our model designates the prime
modality as input, while the remaining modalities act as detectors in the
information pathway. Our proposed perception model focuses on constructing an
effective and compact information flow by achieving a balance between the
minimization of mutual information between the latent state and the input modal
state, and the maximization of mutual information between the latent states and
the remaining modal states. This approach leads to compact latent state
representations that retain relevant information while minimizing redundancy,
thereby substantially enhancing the performance of downstream tasks.
Experimental evaluations on both the MUStARD and CMU-MOSI datasets demonstrate
that our model consistently distills crucial information in multimodal learning
scenarios, outperforming state-of-the-art benchmarks
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