169 research outputs found
Broadband mm-wave signal generation and amplification in CMOS using synthetic impedance
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 75-76).This thesis explores the concept of synthesizing tunable impedances by establishing the appropriate phase relationship between the drain voltage and drain current of a MOS transistor. A high frequency, wide tuning range 105-121GHz oscillator and a small-footprint 20-40GHz oscillator using synthetic resonance are presented. The concept of impedance synthesis is also used to generate a novel frequency-adaptive loss compensation scheme for distributed amplifiers which is shown to improve the bandwidth by 30%. The performance of these circuits was analyzed and simulated on a TSMC 65nm bulk CMOS process.by Pranav R Kaundinya.M. Eng
Homogeneous catalyst mediated glucose mutarotation studies using vibrational spectroscopy
No full textThe pitfalls of overdependence on fossil fuels are well documented. Current research aims to focus on biomass obtained from renewable cellulose for the production of fuels and chemicals. In that regard, with cellulose as source, 5-hydroxymethylfurfural (HMF) is a versatile platform chemical for the production of chemicals like levulinic acid. The isomerization of glucose to fructose is one of the steps in the synthesis of HMF from cellulose. Glucose exists in several anomeric forms and it has been shown that the isomerization reaction is anomer specific. This work focuses on the study of mutarotation in glucose in the presence of homogeneous Lewis acid catalysts. A combination of spectroscopic tools: ATR-IR and Raman spectroscopy are used to study the vibrational modes of glucose in aqueous solution. At room temperature, changes in vibrational modes can be attributed to the mutarotation reaction. This work compares the rate of mutarotation in different concentrations of AlCl3, CrCl3 and SnCl4. The influence of metal salts in solution, pH and ionic strength were also probed by comparing with the rates obtained in Brönsted acids. The mutarotation in Lewis acid is faster than that in water. It is fastest in SnCl4 and increases with increase in concentration of SnCl4. Results also indicate a lack of glucose-Lewis acid interactions. However, rates vary depending on the nature of metal salts in solution indicating that the mutarotation is influenced by the nature of Lewis acid-water interactions.M.S.Includes bibliographical referencesby Pranav Rames
Do share pledges by insiders influence firm performance and value?
No full textThe first chapter demonstrates the prevalence and importance of pledging of shares by insiders in the U.S. I create the first comprehensive database of share pledges by insiders in the U.S. to reveal the prevalence of this practice and its role in encouraging earnings management. I find that, during the fiscal years 2006 to 2014, insiders at one of every three S&P1500 firms pledged their ownership in the firm as collateral to obtain loans at least once. I exploit a 2012 market-wide advisory against share pledges by Institutional Shareholder Services, the largest proxy advisory firm, as a quasi-natural experiment. A difference-in-differences estimation reveals that, after the shock, insiders curtailed share pledge activity by approximately 40% and firms with share pledges reduced earnings manipulation by an average 15% of their reported profits. The results suggest that share pledges distort the incentives of insiders and motivate them to inflate earnings.
The second chapter segregates the two types of share pledges and shows that they have divergent effects on firm performance and value. Insiders pledge their ownership in the firm to offer collateral for not only their personal loans but also the loans to the firm. Pledging of shares modifies their payoff structure without altering their control rights. This modification in the payoff structure can influence the incentives of controlling shareholders and have real effects on the firm's value and performance. Using hand-collected data from India,I find that share pledges for personal loans reduce the effective ownership of controlling shareholders and destroy firm value. In contrast, share pledges for firm's loans mitigate borrowing constraints for the firm and add value to firms with limited access to debt finance or high growth opportunities.
The third and last chapter documents that share pledges by insiders create moral hazards by motivating them to alter the risk-taking ability of firms and encouraging them to avoid reporting small losses. During the years 2009 to 2015, firms in India displayed a higher tendency to avoid reporting small losses by converting them to small profits when their controlling shareholders pledged shares. Share pledges for personal loans and firm's loans have contrasting effects on the aggregate risk-taking ability of firms. Share pledges for personal loans predict a decline in the risk-taking ability of firms over the subsequent year. On the contrary, share pledges for firm's loans may lead to excessive risk-taking.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-05-01The student, Pranav Singh, accepted the attached license on 2019-04-07 at 18:54.The student, Pranav Singh, submitted this Dissertation for approval on 2019-04-07 at 19:05.This Dissertation was approved for publication on 2019-04-12 at 07:42.DSpace SAF Submission Ingestion Package generated from Vireo submission #13508 on 2019-08-22 at 16:20:51Made available in DSpace on 2019-08-23T20:44:39Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-04-12Embargo set by: Seth Robbins for item 112285
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ANALYZING COMMUNICATIVE CHOICES TO UNDERSTAND THEIR MOTIVATIONS, CONTEXT-BASED VARIATION, AND SOCIAL CONSEQUENCES
No full textIn many settings, communicating in a language requires making choices among different possibilities — the issues to focus on, the aspects to highlight within any issue, the narratives to include, and more. These choices, deliberate or not, aresocially structured. The ever-increasing availability of unstructured large-scale textual data, in part due to the bulk of communication and information dissemination happening in online or digital spaces, makes natural language processing (NLP) techniques a natural fit for helping understand socially-situated communicative choices using that textual data. Within NLP methods, unsupervised NLP methods are often needed since digital large-scale textual data in the wild is often available without accompanying labels, and any existing labels or categorization might not be appropriate for answering specific research questions.
This dissertation seeks to address the following question: how can we use unsupervised NLP methods to study texts authored by specific people or institutions in order to effectively explicate the communicative choices being made, as well as to investigate their potential motivations, context-based variation, and consequences?
Our first set of contributions centers on methodological innovation. We focus on topic modeling: a class of generally unsupervised NLP methods that can automatically discover authors’ communicative choices in the form of topics or categorical themes present in a collection of documents. We introduce a new neural topic model (NTM) that effectively incorporates contextualizing sequential knowledge. Next, we find critical gaps in the near-universal automated evaluation paradigm that compares different models in the topic modeling methods literature, which calls into question much of the recent work in NTM development claiming “state-of-the-art” and emphasizes the importance of validating the outputs of unsupervised NLP methods.
In order to use unsupervised NLP methods to investigate potential motivations, context-based variation, and consequences of communicative choices, we link textual data with information about the authors, social contexts, and media involved in their production — these connected information sources help us conduct empirical research in social sciences.
In our second set of contributions, we analyze a previously unexplored connection between a politician’s donors and their communicative choices in their floor speeches to show how donations influence issue-attention in US Congress, enabling a new look at money in politics and providing an example of studying motivations behind communicative choices.
Our third set of contributions uses text-based ideal points to better understand the role of institutional constraints and audience considerations in the varying expression and ideological positioning of politicians. The application of this tool for expanding knowledge of legislative politics is enabled by comprehensive annotations for modeling outputs provided by domain experts in order to establish the tool’s validity and reliability.
In our fourth set of contributions, we demonstrate the potential of both unsupervised NLP techniques and social network data and methods in better understanding the downstream consequences of communicative choices. We focus on misinformation narratives in mainstream media, viewing and highlighting misinformation as something that goes beyond just false claims published by certain bad actors or stories published by certain ‘fake news’ outlets. Our findings suggest a strategic repurposing of mainstream news by conveyors of misinformation as a way to enhance the reach and persuasiveness of misleading narratives
Misinformation is more than "fake news": Using co-sharing to identify use of mainstream news for promoting misinformation narratives (Code-only V1)
No full text<p>Code to help reproduce the main results for a paper under review. NOTE that data files are not available in this version, due to certain data access restrictions. Aggregated data files will be added later to help reproduce results; current version is for instructional code view only. </p>
Code and Data for: Creating the Main File to Study Legislators' Ideological Expression across Audiences
No full textLegislator Information and Text-based Ideal Point Values - Result Files, Replication Code, and Data for Creating the Main File used for all Analyses in our Work in Express Yourself (Ideologically): Legislators' Ideal Points Across Audiences
Data for Contrasting action and posture coding with hierarchical deep neural network models of proprioception
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Contrasting action and posture coding with hierarchical deep neural network models of proprioception, eLife 2023
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Authors: Kai J Sandbrink, Pranav Mamidanna, Claudio Michaelis, Matthias Bethge, Mackenzie W Mathis and Alexander Mathis
Affiliation: Brain Mind Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Switzerland, The Rowland Institute at Harvard, Harvard University, United States; Tübingen AI Center, Eberhard Karls Universität Tübingen & Institute for Theoretical Physics, Germany
Date of upload: December, 2024
Earlier the data was available via dropbox (see github).
Link to the eLife article:
https://elifesciences.org/articles/81499
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Here we provide the data and code for this project:
We share the proprioceptive character recognition dataset (contained in 'pcr_data.zip') it has approximately ~29GB when uncompressed.
We share the weights of all the trained networks (contained in 'network-weights.zip'): about ~3.5GB
The compressed code is also available here ('DeepDrawCode.zip').
The activations are shared in a separate Zenodo project (due to the size). Check out the repository below to find the link.
The up to date code is at: https://github.com/amathislab/DeepDraw
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The datasets, weights, activations and predictions are released with Creative Commons Attribution 4.0 license.
If you find this useful, please cite:
@article{sandbrink2023contrasting, title={Contrasting action and posture coding with hierarchical deep neural network models of proprioception}, author={Sandbrink, Kai J and Mamidanna, Pranav and Michaelis, Claudio and Bethge, Matthias and Mathis, Mackenzie Weygandt and Mathis, Alexander}, journal={Elife}, volume={12}, pages={e81499}, year={2023}, publisher={eLife Sciences Publications Limited}}UPAMATHISUPMWMATHI
Sensory-Motor Mechanisms Underlying Postural Control
No full textPosture control is one of the most fundamental motor tasks; however, the underlying mechanisms are still under debate. No systematic research has been conducted to identify the link between levels of postural instability and involvement of different sensorimotor cortical regions. Also, it is not known whether the supplementary motor area (SMA) - one of the “higher” motor areas in humans play a crucial role in posture control. Thus, this dissertation involved two distinct but conceptually related experiments. The primary focus of the first experiment was to use MRI-guided noninvasive transcranial magnetic stimulation (TMS) to determine a causal link between postural response and SMA when unexpectedly altering the somatosensory information during continuous regulation of balance. The primary focus of the second experiment was to assess the effect of different biomechanical parameters in modulating cortical activity (N1) and balance responses while subjects underwent unpredictable translations of the support surface in forward or backward direction and of varying speed and amplitude. Cortical activity, ground reaction forces, joint kinematics and head acceleration, were recorded.
Twenty healthy young adults participated in this study and were randomly assigned to one of intervention or control groups. Subjects in the intervention group received MRI-guided inhibitory TMS over the left SMA to create a temporary virtual lesion while subjects in the control group received sham TMS before the performance of all posture tasks with closed eyes.
The results of this dissertation suggest that 1) During performance of a continuous balance task, the involvement of SMA is critical for the reprogramming of postural responses and this can potentially be linked to SMA’s role in internal model. Also, center of pressure velocity was found to be key behavioral variable that leads to the involvement of cortical regions, 2) During performance of a standing task in an unpredictable environment, speed but not direction was found to modulate the N1 response. However, the onset of balance response was modulated by the direction. These results provide novel insights regarding cortical mechanisms underlying posture control and have potential to contribute to future studies to design effective rehabilitation paradigms for clinical population with increased fall risk.Health and Human Performance, Department o
Regulation of Acetate Kinase Isozymes and Its Importance for Mixed-Acid Fermentation in Lactococcus lactis
No full textAcetate kinase (ACK) converts acetyl phosphate to acetate along with the generation of ATP in the pathway for mixed-acid fermentation in Lactococcus lactis. The reverse reaction yields acetyl phosphate for assimilation purposes. Remarkably, L. lactis has two ACK isozymes, and the corresponding genes are present in an operon. We purified both enzymes (AckA1 and AckA2) from L. lactis MG1363 and determined their oligomeric state, specific activities, and allosteric regulation. Both proteins form homodimeric complexes, as shown by size exclusion chromatography and static light-scattering measurements. The turnover number of AckA1 is about an order of magnitude higher than that of AckA2 for the reaction in either direction. The Km values for acetyl phosphate, ATP, and ADP are similar for both enzymes. However, AckA2 has a higher affinity for acetate than does AckA1, suggesting an important role under acetate-limiting conditions despite the lower activity. Fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate, and phospho-enol-pyruvate inhibit the activities of AckA1 and AckA2 to different extents. The allosteric regulation of AckA1 and AckA2 and the pool sizes of the glycolytic intermediates are consistent with a switch from homolactic to mixed-acid fermentation upon slowing of the growth rate.BiotechnologyApplied Science
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