Blank Collapse: Compressing CTC emission for the faster decoding

Connectionist Temporal Classification (CTC) model is a very efficient method for modeling sequences, especially for speech data. In order to use CTC model as an Automatic Speech Recognition (ASR) task, the beam search decoding with an external language model like n-gram LM is necessary to obtain reasonable results. In this paper we analyze the blank label in CTC beam search deeply and propose a very simple method to reduce the amount of calculation resulting in faster beam search decoding speed. With this method, we can get up to 78% faster decoding speed than ordinary beam search decoding with a very small loss of accuracy in LibriSpeech datasets. We prove this method is effective not only practically by experiments but also theoretically by mathematical reasoning. We also observe that this reduction is more obvious if the accuracy of the model is higher.Comment: Accepted in Interspeech 202

Fluid-like Surface Layer and Its Flow Characteristics in Glassy Nanotubes

We observed strongly size-dependent viscoelasticity in amorphous SiO2 and Si nanotubes with shell thickness down to ~8 nm. A core-shell model shows that a ~1 nm thick fluid-like surface layer has a significant effect on the mechanical behavior of nanotubes and matches well with our experimental results. Surprising, the surface layer exhibits a room temperature viscosity equivalent to that of bulk glass above 1000 C. Additionally, a low activation energy extracted from temperature dependent creep tests indicates that the viscous flow in the surface layer is due to bond motion/switching, instead of bond breaking. These findings unambiguously show the presence of a fluid-like surface layer and elucidate its role on dynamic mechanical behavior in nanoscale inorganic glass.Comment: 18 pages, 4 figure

Encoder-decoder multimodal speaker change detection

The task of speaker change detection (SCD), which detects points where speakers change in an input, is essential for several applications. Several studies solved the SCD task using audio inputs only and have shown limited performance. Recently, multimodal SCD (MMSCD) models, which utilise text modality in addition to audio, have shown improved performance. In this study, the proposed model are built upon two main proposals, a novel mechanism for modality fusion and the adoption of a encoder-decoder architecture. Different to previous MMSCD works that extract speaker embeddings from extremely short audio segments, aligned to a single word, we use a speaker embedding extracted from 1.5s. A transformer decoder layer further improves the performance of an encoder-only MMSCD model. The proposed model achieves state-of-the-art results among studies that report SCD performance and is also on par with recent work that combines SCD with automatic speech recognition via human transcription.Comment: 5 pages, accepted for presentation at INTERSPEECH 202

High-Performance Screen-Printed Thermoelectric Films on Fabrics.

Printing techniques could offer a scalable approach to fabricate thermoelectric (TE) devices on flexible substrates for power generation used in wearable devices and personalized thermo-regulation. However, typical printing processes need a large concentration of binder additives, which often render a detrimental effect on electrical transport of the printed TE layers. Here, we report scalable screen-printing of TE layers on flexible fiber glass fabrics, by rationally optimizing the printing inks consisting of TE particles (p-type Bi0.5Sb1.5Te3 or n-type Bi2Te2.7Se0.3), binders, and organic solvents. We identified a suitable binder additive, methyl cellulose, which offers suitable viscosity for printability at a very small concentration (0.45-0.60 wt.%), thus minimizing its negative impact on electrical transport. Following printing, the binders were subsequently burnt off via sintering and hot pressing. We found that the nanoscale defects left behind after the binder burnt off became effective phonon scattering centers, leading to low lattice thermal conductivity in the printed n-type material. With the high electrical conductivity and low thermal conductivity, the screen-printed TE layers showed high room-temperature ZT values of 0.65 and 0.81 for p-type and n-type, respectively

Ge and Si based nanowires/nanotubes synthesis and their applications in wearable device, biochemical sensor, and thermoelectronics

Si and Ge nanowires and their heterostructure have been received widespread attention in various research fields because of the inherent advantages and the major historical roles played by these materials in contemporary microelectronics. From decades of research on two materials, integrated in-depth knowledge on the nature of material properties and manufacture process provide useful guidelines to design nanostructures and related devices with increased structural and functional complexity. In this dissertation, synthesis and applications of Ge and Si based nanowires and nanotubes in electronics, photonics, biochemical sensor, and thermoelectrics are discussed. In chapter 2, self-organizing characteristics of misfit- guided Ge quantum dots growth on Si core nanowires are systematically demonstrated. Unique Ge quantum dots growth mode caused by strain supperlattice along the Si nanowire backbone can be controlled by the choice of core diameter. Such strain-guided growth opens up a new avenue towards growth of self-organized nanoscale heterostructures. In chapter 3, fundamental study of crystalline Si nanotubes properties as a platform for electrically and biochemically functional devices is demonstrated. Four- probe current-voltage characterization of precisely probe the inherent electrical properties of crystalline Si nanotubes. Selective functionalization and loading of fluorescence dye and biomolecule inside the core of nanotubes are demonstrated lighting the potential as in- vivo drug carrier. In chapter 4, characterization of thermal transport behavior of crystalline and amorphous Si nanotubes are presented. Ultra-low thermal conductivity of crystalline nanotube below the amorphous counterpart is observed. Study on elastic properties of those nanotubes reveals new possible control mechanism of phonon transport behavior. In chapter 5, fabrication of optical polarizer by printing Ge or Ge/Si core/shell nanowires into highly compacted and ordered fashion is presented. Transmission measurement under various mechanically stressed circumstances reveals potential of nanowire polarizer as high flexible and stretchable optical filte

Sub-amorphous Thermal Conductivity in Ultrathin Crystalline Silicon Nanotubes

Thermal transport behavior in nanostructures has become increasingly important for understanding and designing next generation electronic and energy devices. This has fueled vibrant research targeting both the causes and ability to induce extraordinary reductions of thermal conductivity in crystalline materials, which has predominantly been achieved by understanding that the phonon mean free path (MFP) is limited by the characteristic size of crystalline nanostructures, known as the boundary scattering or Casimir limit. Herein, by using a highly sensitive measurement system, we show that crystalline Si (c-Si) nanotubes (NTs) with shell thickness as thin as ∼5 nm exhibit a low thermal conductivity of ∼1.1 W m^–1 K^–1. Importantly, this value is lower than the apparent boundary scattering limit and is even about 30% lower than the measured value for amorphous Si (a-Si) NTs with similar geometries. This finding diverges from the prevailing general notion that amorphous materials represent the lower limit of thermal transport but can be explained by the strong elastic softening effect observed in the c-Si NTs, measured as a 6-fold reduction in Young’s modulus compared to bulk Si and nearly half that of the a-Si NTs. These results illustrate the potent prospect of employing the elastic softening effect to engineer lower than amorphous, or subamorphous, thermal conductivity in ultrathin crystalline nanostructures

Misfit-Guided Self-Organization of Anticorrelated Ge Quantum Dot Arrays on Si Nanowires

Misfit-strain guided growth of periodic quantum dot (QD) arrays in planar thin film epitaxy has been a popular nanostructure fabrication method. Engineering misfit-guided QD growth on a nanoscale substrate such as the small curvature surface of a nanowire represents a new approach to self-organized nanostructure preparation. Perhaps more profoundly, the periodic stress underlying each QD and the resulting modulation of electro-optical properties inside the nanowire backbone promise to provide a new platform for novel mechano-electronic, thermoelectronic, and optoelectronic devices. Herein, we report a first experimental demonstration of self-organized and self-limited growth of coherent, periodic Ge QDs on a one-dimensional Si nanowire substrate. Systematic characterizations reveal several distinctively different modes of Ge QD ordering on the Si nanowire substrate depending on the core diameter. In particular, Ge QD arrays on Si nanowires of around 20 nm diameter predominantly exhibit an anticorrelated pattern whose wavelength agrees with theoretical predictions. The correlated pattern can be attributed to propagation and correlation of misfit strain across the diameter of the thin nanowire substrate. The QD array growth is self-limited as the wavelength of the QDs remains unchanged even after prolonged Ge deposition. Furthermore, we demonstrate a direct kinetic transformation from a uniform Ge shell layer to discrete QD arrays by a postgrowth annealing process

Three-Terminal Nanoelectromechanical Field Effect Transistor with Abrupt Subthreshold Slope

We report the first experimental demonstration of a three-terminal nanoelectromechanical field effect transistor (NEMFET) with measurable subthreshold slope as small as 6 mV/dec at room temperature and a switching voltage window of under 2 V. The device operates by modulating drain current through a suspended nanowire channel via an insulated gate electrode, thus eliminating the need for a conducting moving electrode, and yields devices that reliably switch on/off for up to 130 cycles. Radio-frequency measurements have confirmed operation at 125 MHz. Our measurements and simulations suggest that the NEMFET design is scalable toward sub-1 V ultrahigh-frequency operation for future low-power computing systems

High-Performance Screen-Printed Thermoelectric Films on Fabrics.

Printing techniques could offer a scalable approach to fabricate thermoelectric (TE) devices on flexible substrates for power generation used in wearable devices and personalized thermo-regulation. However, typical printing processes need a large concentration of binder additives, which often render a detrimental effect on electrical transport of the printed TE layers. Here, we report scalable screen-printing of TE layers on flexible fiber glass fabrics, by rationally optimizing the printing inks consisting of TE particles (p-type Bi0.5Sb1.5Te3 or n-type Bi2Te2.7Se0.3), binders, and organic solvents. We identified a suitable binder additive, methyl cellulose, which offers suitable viscosity for printability at a very small concentration (0.45-0.60 wt.%), thus minimizing its negative impact on electrical transport. Following printing, the binders were subsequently burnt off via sintering and hot pressing. We found that the nanoscale defects left behind after the binder burnt off became effective phonon scattering centers, leading to low lattice thermal conductivity in the printed n-type material. With the high electrical conductivity and low thermal conductivity, the screen-printed TE layers showed high room-temperature ZT values of 0.65 and 0.81 for p-type and n-type, respectively