Search for: All records

Electroosmotic flow is commonly used with other electrokinetic phenomena to manipulate aqueous samples in micro/nanofluidic devices. However, most studies of electroosmosis have been focused upon Newtonian fluids though many chemical and biological samples are complex fluids with shear thinning and viscoelastic characteristics. These rheological properties have been demonstrated to enhance electroosmotic pumping and mixing etc., for which a fundamental understanding of electroosmotic velocity is crucial. We develop here a numerical model to understand and predict the experimentally measured electroosmotic velocity of xanthan gum solutions in a rectangular microchannel from our previous paper (J. Bentor et al., Langmuir 2024, 40, 20113−20119). This model couples interfacial electrokinetics with shear-thinning rheology by considering a polymer depletion layer (PDL) adjacent to each channel wall, which is a Newtonian fluid free of polymer due to the polymer-wall interactions, and a power-law fluid in the bulk. It predicts with good accuracy the experimental electroosmotic velocity in xanthan gum solutions with varying polymer and buffer concentrations across the tested electric fields. The only fitting parameter is the PDL thickness, which decreases with increasing polymer or buffer concentration but is independent of the electric field magnitude. The PDL to electric-double-layer thickness ratio is found to play a critical role in understanding the electric field nonlinearity of electroosmotic velocity. 

In recent decades, considerable research has been devoted to speech enhancement leveraging the short-term Fourier transform (STFT) analysis. As speech processing technology evolves, the significance of phase information in enhancing speech intelligibility becomes more noticeable. Typically, the Hanning window has been widely employed as analysis window in STFT. In this study, we propose the Chebyshev window for phase analysis, and the Hanning window for magnitude analysis. Next, we introduce a novel cepstral domain enhancement approach designed to robustly reinforce the harmonic structure of speech. The performance of our model is evaluated using the DNS challenge test set as well as the naturalistic APOLLO Fearless Steps evaluation set. Experimental results demonstrate that the Chebyshev-based phase solution outperforms the Hanning option for in phase-aware speech enhancement. Furthermore, the incorporation of quefrency emphasis proves effective in enhancing overall speech quality. 

Large language models (LLMs) are notoriously memory-intensive during training, particularly with the popular AdamW optimizer. This memory burden necessitates using more or higher-end GPUs or reducing batch sizes, limiting training scalability and throughput. To address this, various memory-efficient optimizers have been proposed to reduce optimizer memory usage. However, they face critical challenges: (i) reliance on costly SVD operations; (ii) significant performance trade-offs compared to AdamW; and (iii) still substantial optimizer memory overhead to maintain competitive performance. In this work, we identify that AdamW's learning rate adaptation rule can be effectively coarsened as a structured learning rate update. Based on this insight, we propose Approximated Gradient Scaling for Memory-Efficient LLM Optimization (APOLLO), which approximates learning rate scaling using an auxiliary low-rank optimizer state based on pure random projection. This structured learning rate update rule makes APOLLO highly tolerant to further memory reductions while delivering comparable pre-training performance. Even its rank-1 variant, APOLLO-Mini, achieves superior pre-training performance compared to AdamW with SGD-level memory costs. Extensive experiments demonstrate that the APOLLO series performs on-par with or better than AdamW, while achieving greater memory savings by nearly eliminating the optimization states of AdamW. These savings provide significant system-level benefits: (1) Enhanced Throughput: 3x throughput on an 8xA100-80GB setup compared to AdamW by supporting 4x larger batch sizes. (2) Improved Model Scalability: Pre-training LLaMA-13B with naive DDP on A100-80GB GPUs without system-level optimizations. (3) Low-End GPU Friendly Pre-training: Pre-training LLaMA-7B on a single GPU using less than 12 GB of memory with weight quantization. 

With the development of deep neural networks (DNN), many DNN-based speech dereverberation approaches have been proposed to achieve significant improvement over the traditional methods. However, most deep learning-based dereverberation methods solely focus on suppressing time-frequency domain reverberations without utilizing cepstral domain features which are potentially useful for dereverberation. In this paper, we propose a dual-path neural network structure to separately process minimum-phase and all-pass components of single channel speech. First, we decompose speech signal into minimum-phase and all-pass components in cepstral domain, then Conformer embedded U-Net is used to remove reverberations of both components. Finally, we combine these two processed components together to synthesize the enhanced output. The performance of proposed method is tested on REVERB-Challenge evaluation dataset in terms of commonly used objective metrics. Experimental results demonstrate that our method outperforms other compared methods. 

The Fearless Steps Apollo (FS-APOLLO) resource is a collection of 150,000 hours of audio, associated meta-data, and supplemental speech technology infrastructure intended to benefit the (i) speech processing technology, (ii) communication science, team-based psychology, and (iii) education/STEM, history/preservation/archival communities. The FS-APOLLO initiative which started in 2014 has since resulted in the preservation of over 75,000 hours of NASA Apollo Missions audio. Systems created for this audio collection have led to the emergence of several new Speech and Language Technologies (SLT). This paper seeks to provide an overview of the latest advancements in the FS-Apollo effort and explore upcoming strategies in big-data deployment, outreach, and novel avenues of K-12 and STEM education facilitated through this resource.