Electrical & Computer Engineering Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1658
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Item Code and Data for "Sparse high-dimensional decomposition of non-primary auditory cortical receptive fields"(2024) Mukherjee, Shoutik; Babadi, Behtash; Shamma, Shihab A.Characterizing neuronal responses to natural stimuli remains a central goal in sensory neuroscience. In auditory cortical neurons, the stimulus selectivity of elicited spiking activity is summarized by a spectrotemporal receptive field (STRF) that relates neuronal responses to the stimulus spectrogram. Though effective in characterizing primary auditory cortical responses, STRFs of non-primary auditory neurons can be quite intricate, reflecting their mixed selectivity. The complexity of non-primary STRFs hence impedes understanding how acoustic stimulus representations are transformed along the auditory pathway. Here, we focus on the relationship between ferret primary auditory cortex (A1) and a secondary region, dorsal posterior ectosylvian gyrus (PEG). We propose estimating receptive fields in PEG with respect to a well-established high-dimensional computational model of primary-cortical stimulus representations. These ``cortical receptive fields'' (CortRF) are estimated greedily to identify the salient primary-cortical features modulating spiking responses and in turn related to corresponding spectrotemporal features. Hence, they provide biologically plausible hierarchical decompositions of STRFs in PEG. Such CortRF analysis was applied to PEG neuronal responses to speech and temporally orthogonal ripple combination (TORC) stimuli and, for comparison, to A1 neuronal responses. CortRFs of PEG neurons captured their selectivity to more complex spectrotemporal features than A1 neurons; moreover, CortRF models were more predictive of PEG (but not A1) responses to speech. Our results thus suggest that secondary-cortical stimulus representations can be computed as sparse combinations of primary-cortical features that facilitate encoding natural stimuli. Thus, by adding the primary-cortical representation, we can account for PEG single-unit responses to natural sounds better than bypassing it and considering as input the auditory spectrogram. These results confirm with explicit details the presumed hierarchical organization of the auditory cortex.Item Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H2S in the Gastrointestinal Tract(Wiley, 2023-11-20) Stine, Justin M.; Ruland, Katie L.; Beardslee, Luke A.; Levy, Joshua A.; Abianeh, Hossein; Botasini, Santiago; Pasricha, Pankaj J.; Ghodssi, RezaHydrogen sulfide (H2S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H2S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H2S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H2S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H2S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H2S concentration ranging from 0.21 to 4.5 ppm (R2 = 0.954) with a normalized sensitivity of 12.4% ppm−1 when evaluated in a benchtop setting. The sensor proves highly selective toward H2S in the presence of known interferent gases, such as hydrogen (H2), with a selectivity ratio of H2S:H2 = 1340, as well as toward methane (CH4) and carbon dioxide (CO2). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H2S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H2S.Item Spintronic Quantum Phase Transition in aGraphene/Pb0.24 Sn 0.76 Te Heterostructure with Giant RashbaSpin-Orbit Coupling(Wiley, 2023-12-07) DeMell, Jennifer E.; Naumov, Ivan; Stephen, Gregory M.; Blumenschein, Nicholas A.; Leo Sun, Y.-J.; Fedorko, Adrian; Robinson, Jeremy T.; Campbell, Paul M.; Taylor, Patrick J.; Heiman, Don; Dev, Pratibha; Hanbicki, Aubrey T.; Friedman, Adam L.Mechanical stacking of two dissimilar materials often has surprising consequences for heterostructure behavior. In particular, a 2D electron gas (2DEG) is formed in the heterostructure of the topological crystalline insulator Pb0.24Sn0.76Te and graphene due to contact of a polar with a nonpolar surface and the resulting changes in electronic structure needed to avoid polar catastrophe. The spintronic properties of this heterostructure with non-local spin valve devices are studied. This study observes spin-momentum locking at lower temperatures that transitions to regular spin channel transport only at ≈40 K. Hanle spin precession measurements show a spin relaxation time as high as 2.18 ns. Density functional theory calculations confirm that the spin-momentum locking is due to a giant Rashba effect in the material and that the phase transition is a Lifshitz transition. The theoretically predicted Lifshitz transition is further evident in the phase transition-like behavior in the Landé g-factor and spin relaxation time.Item Changes in Cortical Directional Connectivity during Difficult Listening in Younger and Older Adults(Wiley, 2023-05) Soleimani, Behrad; Dushyanthi Karunathilake, I. M.; Das, Proloy; Kuchinsky, Stephanie E.; Babadi, Behtash; Simon, Jonathan E.One way to investigate the mechanisms that underlie speech comprehension under difficult listening conditions is via cortical connectivity. The innovative Network Localized Granger Causality (NLGC) framework was applied to magnetoencephalography (MEG) data, obtained from older and younger subjects performing a speech listening task in noisy conditions, in delta and theta frequency bands. Directional connectivity between frontal, temporal, and parietal lobes was analyzed. Both aging- and condition-related changes were found, particularly in theta. In younger adults, as background noise increased, there was a transition from predominantly temporal-to-frontal (bottom-up) connections, to predominantly frontal-to-temporal (top-down). In contrast, older adults showed bidirectional information flow between frontal and temporal cortices even for speech in quiet, not changing substantially with increased noise. Additionally, younger listeners did not show changes in the nature of their cortical links for different listening conditions, whereas older listeners exhibited a switch from predominantly facilitative links to predominantly sharpening, when noise increased.Item Oscillating Cosmological Force Modifies Newtonian Dynamics(MDPI, 2020-05-22) Smolyaninov, Igor I.In the Newtonian limit of general relativity a force acting on a test mass in a central gravitational field is conventionally defined by the attractive Newtonian gravity (inverse square) term plus a small repulsive cosmological force, which is proportional to the slow acceleration of the universe expansion. In this paper we considered the cosmological-force correction due to fast quantum oscillations of the universe scale factor as a potential solution of the cosmological constant problem. These fast fluctuations of the cosmological scale factor violate Lorentz invariance at the Planck scale, and they induce strong changes to the current sign and magnitude of the average cosmological force, thus making it one of the potential probable causes for the modification of Newtonian dynamics in galaxy-scale systems. The modified cosmological force may be responsible for the recently discovered “cosmic-clock” behavior of disk galaxies in the low-redshift universe. The obtained results have strong implications for astroparticle physics since they demonstrate that typical galaxy rotation curves may be obtained without (or almost without) dark-matter particles.Item Development of Broadband Underwater Radio Communication for Application in Unmanned Underwater Vehicles(MDPI, 2020-05-23) Smolyaninov, Igor I.; Balzano, Quirino; Young, DendyThis paper presents several novel designs of small form factor underwater radio antennas operating in the 2 MHz, 50 MHz and 2.4 GHz bands. These antennas efficiently excite surface electromagnetic waves (SEW) which propagate along the surface of seawater. The antenna operation is made possible due to implementation of an impedance matching enclosure, which is filled with de-ionized water. Enhanced coupling to surface electromagnetic waves is enabled by the enhancement of the electromagnetic field at the antenna apex. These features allow us to make antenna dimensions considerably smaller compared to typical free space designs. They also considerably improve coupling of electromagnetic energy to the surrounding seawater. Since SEW propagation length is considerably larger than the skin depth in seawater, this technique is useful for underwater broadband wireless communication. We conclude that the developed broadband underwater radio communication technique will be useful in networking of unmanned underwater vehicles.Item Automation: A New Open-Access Journal with a Broad Scope and an Exciting Mission(MDPI, 2020-10-29) Abed, Eyad H.Item Effect of Fast Scale Factor Fluctuations on Cosmological Evolution(MDPI, 2021-05-27) Smolyaninov, Igor I.In this paper, we study the corrections to the Friedmann equations due to fast fluctuations in the universe scale factor. Such fast quantum fluctuations were recently proposed as a potential solution to the cosmological constant problem. They also induce strong changes to the current sign and magnitude of the average cosmological force, thus making them one of the potential probable causes of the modification of Newtonian dynamics in galaxy-scale systems. It appears that quantum fluctuations in the scale factor also modify the Friedmann equations, leading to a considerable modification of cosmological evolution. In particular, they give rise to the late-time accelerated expansion of the universe, and they may also considerably modify the effective universe potential.Item Scheduling to Minimize Age of Incorrect Information with Imperfect Channel State Information(MDPI, 2021-11-25) Chen, Yutao; Ephremides, AnthonyIn this paper, we study a slotted-time system where a base station needs to update multiple users at the same time. Due to the limited resources, only part of the users can be updated in each time slot. We consider the problem of minimizing the Age of Incorrect Information (AoII) when imperfect Channel State Information (CSI) is available. Leveraging the notion of the Markov Decision Process (MDP), we obtain the structural properties of the optimal policy. By introducing a relaxed version of the original problem, we develop the Whittle’s index policy under a simple condition. However, indexability is required to ensure the existence of Whittle’s index. To avoid indexability, we develop Indexed priority policy based on the optimal policy for the relaxed problem. Finally, numerical results are laid out to showcase the application of the derived structural properties and highlight the performance of the developed scheduling policies.Item Novel Approach and Methods for Optimizing Highly Sensitive Low Noise Amplifier CMOS IC Design for Congested RF Environments(MDPI, 2022-03-22) Chung, Jooik; Illiadis, Agis A.This work details the optimization and evaluation of a CMOS low-noise amplifier by developing a new algorithm for the 𝑔𝑚/𝐼𝐷 approach and combining with a modified figure of merit index method. The amplifier includes on-chip matching elements (such as IC inductors) for resonance at the targeted frequencies. The simulation results of the optimized LNA model showed scattering parameter 𝑆21 = 19.91 dB, noise figure NF = 3.54 dB and excellent linearity for third-order intermodulation parameter IIP3 = 5.89 dBm for the targeted frequency of 𝑓0 = 2.4 GHz.