Carbon nanotube-guided thermopower waves

Thermopower waves are a new concept for the direct conversion of chemical to electrical energy. A nanowire with large axial thermal diffusivity can accelerate a self-propagating reaction wave using a fuel coated along its length. The reaction wave drives electrical carriers in a thermopower wave, creating a high-power pulse of as much as 7 kW/kg in experiments using carbon nanotubes. We review nanomaterials designed to overcome limitations of thermoelectricity and explore the emerging scientific and practical outlook for devices using thermopower waves

Understanding Distributed Representations of Concepts in Deep Neural Networks without Supervision

Understanding intermediate representations of the concepts learned by deep learning classifiers is indispensable for interpreting general model behaviors. Existing approaches to reveal learned concepts often rely on human supervision, such as pre-defined concept sets or segmentation processes. In this paper, we propose a novel unsupervised method for discovering distributed representations of concepts by selecting a principal subset of neurons. Our empirical findings demonstrate that instances with similar neuron activation states tend to share coherent concepts. Based on the observations, the proposed method selects principal neurons that construct an interpretable region, namely a Relaxed Decision Region (RDR), encompassing instances with coherent concepts in the feature space. It can be utilized to identify unlabeled subclasses within data and to detect the causes of misclassifications. Furthermore, the applicability of our method across various layers discloses distinct distributed representations over the layers, which provides deeper insights into the internal mechanisms of the deep learning model.Comment: Published in AAAI2024. First two authors contributed equally. The code is available at https://github.com/daheekwon/RD

New concepts in energy and mass transport within carbon nanotubes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 164-177).The unique structure of carbon nanotubes (CNTs) contributes to their distinguished properties, making them useful in nanotechnology. CNTs have been explored for energy transport in next-generation, such as light-emitting diodes, field-effect transistors, and phonon wave guides due to their high axial electrical and thermal conductivity. Also, their subnanometer scale with atomically smooth surfaces is promising for selective mass transport in nanoscale, such as molecular transport, selective gas permeation, and nanofluidics. The first part of this thesis considers CNTs as substrates for guided chemical reactivity and thermal waves for energy generation. Coupling an exothermic chemical reaction with a nanowire possessing a high axial thermal conductivity creates a self-propagating reactive wave. Such waves are realized using a 7-nm cyclotrimethylene-trinitramine (TNA) annular shell around a CNT and are amplified by 104 times the bulk TNA value, propagating more than 2 m/s, with an effective thermal conductivity of 1.28 ± 0.2 kW/m/K at 2860 K. Thermally excited carriers in the direction of the propagating reaction produces a concomitant electrical pulse of high specific power, as large as 7 kW/kg, that we identify as a thermopower wave. The specific power increases with a decreasing system size, resulting in usually efficient sub-micron and nano-sized pulse power sources. In the second portion, we develop a nanopore platform using the interior of a single walled carbon nanotube (SWNT) for study of single ion transport. Such pores can undergo a resonance in ion transport such that coherent waveforms are generated (CR). The asymmetric electrostatic barriers at their ends show that above the threshold bias, traversing the nanopore end is not rate limiting and that the pore blocking behavior of two parallel nanotubes follows an idealized Markov process. We report two channels undergoing this CR simultaneously, the dynamics of ion transport for different cations (Li+, Na+, K+, Cs+) and the effect of varying the applied voltage on transport across the SWNT channel. Finally, the diameter and temperature dependence (1-2 nm) of ion transport shows the distinct trend in dwell time and blockade current that study its transfer mechanism by proton 'hop' and 'turn', and single ion transport.by Wonjoon Choi.Ph.D

The Nordic Culture Fund Going Global: Nordic Added Value and Regionalist Logic after 2000

This study examines the concept of Nordic added value in Nordic cultural cooperation through the case study of the Nordic Culture Fund. This study aims to understand how the Nordic culture fund implemented the concept and to identify regionalist logic utilised during this process. By doing so, this work aims to contribute to the scholarship on the Nordic added value, exploring its practical application within the cultural sector of Nordic cooperation. To achieve this goal, non-negative matrix factorisation topic modeling was used to analyse a collection of policy documents and web pages of the Nordic culture fund published between 2002 to 2023. This study found a shift in how the concept is operationalized, alongside its regionalist logic. Initially, the Fund emphasised internal Nordic collaboration, based on heritage identity to foster the sense of Nordic community and legitimise Nordic cultural cooperation. However, since the late 2010s, the focus shifted towards the global context, integrating neoliberal values to promote Nordic culture on the global stage. This extension of scale from the regional to global level illustrates a relational characteristic of Nordic added value. By mapping the aforementioned shifts of the concept, this study contributes to the holistic understanding of the Nordic added value

Incremental placement for timing optimization

An incremental timing driven placement algorithm is presented. We introduce a fast path-based analytical approach for timing improvement. Our method achieves timing optimization by reducing the enclosing bounding boxes of selected nets on critical paths. Furthermore, this technique tries to minimize modifications to the initial placement while improving the delay of the circuit incrementally. Two contributions of this work are 1) efficient conversion of a path-based timing minimization problem to a geometric net-constraint problem and 2) minimal modification of a placement to improve timing. Our technique can take an initial placement from any algorithm and improve timing iteratively. The experiments show that the proposed approach is very efficient. 1

Understanding Distributed Representations of Concepts in Deep Neural Networks without Supervision

Understanding intermediate representations of the concepts learned by deep learning classifiers is indispensable for interpreting general model behaviors. Existing approaches to reveal learned concepts often rely on human supervision, such as pre-defined concept sets or segmentation processes. In this paper, we propose a novel unsupervised method for discovering distributed representations of concepts by selecting a principal subset of neurons. Our empirical findings demonstrate that instances with similar neuron activation states tend to share coherent concepts. Based on the observations, the proposed method selects principal neurons that construct an interpretable region, namely a Relaxed Decision Region (RDR), encompassing instances with coherent concepts in the feature space. It can be utilized to identify unlabeled subclasses within data and to detect the causes of misclassifications. Furthermore, the applicability of our method across various layers discloses distinct distributed representations over the layers, which provides deeper insights into the internal mechanisms of the deep learning model

Fish Forensics: Exposing Discrepancies in Contemporary Species of Sculpin

The McCloud River is an aquatic sanctuary in Northern California, whose roaring waterfalls, luscious fish and scenic views attract hordes of recreationists. A lesser known fact is that the McCloud holds a scientific significance which rivals its capabilities as an entertainer: it contains the endemic native species known as McCloud River Redband Trout. This suggests that other endemic species may thrive in the McCloud. Our attention was brought to three species of fish from family Cottidae, namely the Pit, Riffle and Prickly Sculpin. Individuals from said groups were sampled from select rivers in Central/Northern California including the McCloud, and their genomic information was used in a statistical procedure known as a principal component analysis (PCA). This analysis compiles and rearranges data points in a way that accentuates variation between and within loci. The first PCA affirmed that Prickly sculpin were far different from Pit and Riffle Sculpin and those samples collected at the mouth of the McCloud River grouped with Prickly Sculpin. It also suggested that an extra group existed in the McCloud River and Hot Springs Creek which had genetic characteristics intermediate between known Pit and Riffle Sculpin. A second PCA was conducted to investigate this newly emerged group, and the results showed that this new group was significantly different from both Pit and Riffle sculpin. Additionally within it were two distinct groups of fish, one in the McCloud and one in Hot Springs Creek. This indicates that either there was secondary contact between the Pit and Riffle sculpin which led to a now-independent hybrid species, or this new group diverged from the same ancestor as Riffle and Pit Sculpin. Either way, our results differentiate McCloud River Sculpin from currently known species and suggest a full investigation is needed to unearth additional endemic species in the McCloud

Fish Forensics: Exposing Discrepancies in Contemporary Species of Sculpin

The McCloud River is an aquatic sanctuary in Northern California, whose roaring waterfalls, luscious fish and scenic views attract hordes of recreationists. A lesser known fact is that the McCloud holds a scientific significance which rivals its capabilities as an entertainer: it contains the endemic native species known as McCloud River Redband Trout. This suggests that other endemic species may thrive in the McCloud. Our attention was brought to three species of fish from family Cottidae, namely the Pit, Riffle and Prickly Sculpin. Individuals from said groups were sampled from select rivers in Central/Northern California including the McCloud, and their genomic information was used in a statistical procedure known as a principal component analysis (PCA). This analysis compiles and rearranges data points in a way that accentuates variation between and within loci. The first PCA affirmed that Prickly sculpin were far different from Pit and Riffle Sculpin and those samples collected at the mouth of the McCloud River grouped with Prickly Sculpin. It also suggested that an extra group existed in the McCloud River and Hot Springs Creek which had genetic characteristics intermediate between known Pit and Riffle Sculpin. A second PCA was conducted to investigate this newly emerged group, and the results showed that this new group was significantly different from both Pit and Riffle sculpin. Additionally within it were two distinct groups of fish, one in the McCloud and one in Hot Springs Creek. This indicates that either there was secondary contact between the Pit and Riffle sculpin which led to a now-independent hybrid species, or this new group diverged from the same ancestor as Riffle and Pit Sculpin. Either way, our results differentiate McCloud River Sculpin from currently known species and suggest a full investigation is needed to unearth additional endemic species in the McCloud

Rapid Electromechanical Transduction on a Single-Walled Carbon Nanotube Film: Sensing Fast Mechanical Loading via Detection of Electrical Signal Change

Carbon nanotubes (CNTs) have been widely explored as next generation embedded-strain-pressure sensors. However, most investigations of CNT sensors did not consider the response time as a critical factor, although the ultrafast sensing of mechanical deformation is very important for the detection of dynamic loading or impact, such as in reactive armor systems. Owing to the low capacitance that shortens the response time of the electrical resistance changes induced by mechanical deformation, CNTs are expected to detect rapid electromechanical transduction without delay. Herein, we fabricate single-walled carbon nanotube (SWNT) films on diverse substrates, and evaluate their applications as sensors to detect rapid electromechanical transduction on a macroscopic scale. Under repetitive, high-speed mechanical loading, the SWNT films generate consistent electrical signal changes, which are accurately synchronized with their strain and the beginning of the deformation