Electrical & Computer Engineering Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1658
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Item Metamaterial Model of Tachyonic Dark Energy(MDPI, 2014-02-17) Smolyaninov, Igor I.Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic) matter. Here, we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2 + 1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.Item Fractional Effective Charges and Misner-Wheeler Charge without Charge Effect in Metamaterials(MDPI, 2016-07-08) Smolyaninov, IgorTransformation optics enables engineering of the effective topology and dimensionality of the optical space in metamaterials. Nonlinear optics of such metamaterials may mimic Kaluza-Klein theories having one or more kinds of effective charges. As a result, novel photon blockade devices may be realized. Here we demonstrate that an electromagnetic wormhole may be designed, which connects two points of such an optical space and changes its effective topological connectivity. Electromagnetic field configurations, which exhibit fractional effective charges, appear as a result of such topology change. Moreover, such effects as Misner-Wheeler “charge without charge” may be replicated.Item Thermally Induced Effective Spacetimes in Self-Assembled Hyperbolic Metamaterials(MDPI, 2017-03-08) Smolyaninov, Igor I.Recent developments in gravitation theory indicate that the classic general relativity is an effective macroscopic theory which will be eventually replaced with a more fundamental theory based on thermodynamics of yet unknown microscopic degrees of freedom. Here we consider thermodynamics of an effective spacetime which may be formed under the influence of an external magnetic field in a cobalt ferrofluid. It appears that the extraordinary photons propagating inside the ferrofluid perceive thermal gradients in the ferrofluid as an effective gravitational field, which obeys the Newton law. Moreover, the effective de Sitter spacetime behaviour near the metric signature transition may mimic various cosmological inflation scenarios, which may be visualized directly using an optical microscope. Thus, some features of the hypothetic microscopic theory of gravity are illustrated in the ferrofluid-based analogue models of inflation.Item Extra-Dimensional “Metamaterials”: A Model of Inflation Due to a Metric Signature Transition(MDPI, 2017-09-20) Smolyaninov, Igor I.Lattices of topological defects, such as Abrikosov lattices and domain wall lattices, often arise as metastable ground states in higher-dimensional field theoretical models. We demonstrate that such lattice states may be described as extra-dimensional “metamaterials” via higher-dimensional effective medium theory. A 4 + 1 dimensional extension of Maxwell electrodynamics with a compactified time-like dimension is considered as an example. It is demonstrated that from the point of view of macroscopic electrodynamics an Abrikosov lattice state in such a 4 + 1 dimensional spacetime may be described as a uniaxial hyperbolic medium. Extraordinary photons perceive this medium as a 3 + 1 dimensional Minkowski spacetime in which one of the original spatial dimensions plays the role of a new time-like coordinate. Since the metric signature of this effective spacetime depends on the Abrikosov lattice periodicity, the described model may be useful in studying metric signature transitions.Item Secure Degrees of Freedom in Networks with User Misbehavior(MDPI, 2019-09-26) Banawan, Karim; Ulukus, SennurWe investigate the secure degrees of freedom (s.d.o.f.) of three new channel models: broadcast channel with combating helpers, interference channel with selfish users, and multiple access wiretap channel with deviating users. The goal of introducing these channel models is to investigate various malicious interactions that arise in networks, including active adversaries. That is in contrast with the common assumption in the literature that the users follow a certain protocol altruistically and transmit both message-carrying and cooperative jamming signals in an optimum manner. In the first model, over a classical broadcast channel with confidential messages (BCCM), there are two helpers, each associated with one of the receivers. In the second model, over a classical interference channel with confidential messages (ICCM), there is a helper and users are selfish. By casting each problem as an extensive-form game and applying recursive real interference alignment, we show that, for the first model, the combating intentions of the helpers are neutralized and the full s.d.o.f. is retained; for the second model, selfishness precludes secure communication and no s.d.o.f. is achieved. In the third model, we consider the multiple access wiretap channel (MAC-WTC), where multiple legitimate users wish to have secure communication with a legitimate receiver in the presence of an eavesdropper. We consider the case when a subset of users deviate from the optimum protocol that attains the exact s.d.o.f. of this channel. We consider two kinds of deviation: when some of the users stop transmitting cooperative jamming signals, and when a user starts sending intentional jamming signals. For the first scenario, we investigate possible responses of the remaining users to counteract such deviation. For the second scenario, we use an extensive-form game formulation for the interactions of the deviating and well-behaving users. We prove that a deviating user can drive the s.d.o.f. to zero; however, the remaining users can exploit its intentional jamming signals as cooperative jamming signals against the eavesdropper and achieve an optimum s.d.o.f.Item The Capacity of Private Information Retrieval from Decentralized Uncoded Caching Databases(MDPI, 2019-11-28) Wei, Yi-Peng; Arasli, Batuhan; Banawan, Karim; Ulukus, SennurWe consider the private information retrieval (PIR) problem from decentralized uncoded caching databases. There are two phases in our problem setting, a caching phase, and a retrieval phase. In the caching phase, a data center containing all the K files, where each file is of size L bits, and several databases with storage size constraint 𝜇𝐾𝐿 bits exist in the system. Each database independently chooses 𝜇𝐾𝐿 bits out of the total 𝐾𝐿 bits from the data center to cache through the same probability distribution in a decentralized manner. In the retrieval phase, a user (retriever) accesses N databases in addition to the data center, and wishes to retrieve a desired file privately. We characterize the optimal normalized download cost to be 𝐷∗=∑𝑁+1𝑛=1(𝑁𝑛−1)𝜇𝑛−1(1−𝜇)𝑁+1−𝑛(1+1𝑛+⋯+1𝑛𝐾−1). We show that uniform and random caching scheme which is originally proposed for decentralized coded caching by Maddah-Ali and Niesen, along with Sun and Jafar retrieval scheme which is originally proposed for PIR from replicated databases surprisingly results in the lowest normalized download cost. This is the decentralized counterpart of the recent result of Attia, Kumar, and Tandon for the centralized case. The converse proof contains several ingredients such as interference lower bound, induction lemma, replacing queries and answering string random variables with the content of distributed databases, the nature of decentralized uncoded caching databases, and bit marginalization of joint caching distributions.Item High Frequency Cortical Processing of Continuous Speech in Younger and Older Listeners - Dataset(2019) Kulasingham, Joshua; Brodbeck, Christian; Presacco, Alessandro; Kuchinsky, Stefanie E.; Anderson, Samira; Simon, Jonathan Z.Neural processing along the ascending auditory pathway is often associated with a progressive reduction in characteristic processing rates. For instance, the well-known frequency-following response (FFR) of the auditory midbrain, as measured with electroencephalography (EEG), is dominated by frequencies from ~100 Hz to several hundred Hz, phase-locking to the stimulus waveform at those frequencies. In contrast, cortical responses, whether measured by EEG or magnetoencephalography (MEG), are typically characterized by frequencies of a few Hz to a few tens of Hz, time-locking to acoustic envelope features. In this study we investigated a crossover, cortically generated responses time-locked to continuous speech features at FFR-like rates. Using MEG, we analyzed high-frequency responses (70-300 Hz) to continuous speech using neural source-localized reverse correlation and its corresponding temporal response functions (TRFs). Continuous speech stimuli were presented to 40 subjects (17 younger, 23 older adults) with clinically normal hearing and their MEG responses were analyzed in the 70-300 Hz band. Consistent with the insensitivity of MEG to many subcortical structures, the spatiotemporal profile of these response components indicated a purely cortical origin with ~40 ms peak latency and a right hemisphere bias. TRF analysis was performed using two separate aspects of the speech stimuli: a) the 70-300 Hz band of the speech waveform itself, and b) the 70-300 Hz temporal modulations in the high frequency envelope (300-4000 Hz) of the speech stimulus. The response was dominantly driven by the high frequency envelope, with a much weaker contribution from the waveform (carrier) itself. Age-related differences were also analyzed to investigate a reversal previously seen along the ascending auditory pathway, whereby older listeners show weaker midbrain FFR responses than younger listeners, but, paradoxically, have stronger cortical low frequency responses. In contrast to both these earlier results, this study does not find clear age-related differences in high frequency cortical responses. Finally, these results suggest that EEG high (FFR-like) frequency responses have distinct and separable contributions from both subcortical and cortical sources. Cortical responses at FFR-like frequencies share some properties with midbrain responses at the same frequencies and with cortical responses at much lower frequencies.Item EEG-MEG(2018) Presacco, Alessandro; Simon, Jonathan; Anderson, Samira; Simon, Jonathan; Anderson, SamiraData collected from normal hearing younger adults (18-30) and from normal hearing and hearing impaired older adults (>= 60) to study age-related deficits in the representation of speech in noise. EEG data were collected with Biosemi system by using the ABR module from one electrode placed in Cz and reference with respect to the left and right ear lobes. The data uploaded are the raw ones in bdf format. BDF files can be opened by using matlab scripts that can be found in toolboxes such as EEGLab or that can be found directly from Biosemi's website. Each mat file contains information about sampling frequency, channels, triggers, etc. Each participants was tested in 9 conditions: Quiet, +3 dB, 0 dB, -3 dB and -6 dB with English (H) and Dutch (L) speakers used as background noise. Files were named based on the SNR and background speaker used. For instance, S01_M3_H, means Subject 01, SNR = -3 dB and English speaker in the background, while S01_P3_L, means Subject 01, SNR = +3 dB and Dutch speaker in the background. The "Q" denomination is used for the condition in quiet. Subjects id# from 1 to 17 are younger adults, subjects with id# from 21 to 35 are normal hearing older adults and subjects named S01_HL.....S17_HL are older adults with hearing loss. MEG data were collected from 157 sensors. Each mat file contains information about the data, such as sampling frequency. A 3D matrix is used to store the 3 repetitions recorded from each conditions. Each participants was tested in 10 conditions: Quiet, +3 dB, 0 dB, -3 dB and -6 dB with English (H) and Dutch (L) speakers used as background noise. Two conditions in quiet were played. Files were named based on the SNR and background speaker used, in the same way as for the EEG data. Auditory stimuli were also uploaded. The stimuli have been pre-processed as described in our publications "Evidence of degraded representation of speech in noise, in the aging midbrain and cortex" and "Effect of informational content of noise on speech representation in the aging midbrain and cortex". The envelope needs to be extracted.Item Data from: Rapid Transformation from Auditory to Linguistic Representations of Continuous Speech(2018) Brodbeck, Christian; Hong, L. Elliot; Simon, Jonathan Z.; Hong, L. Elliot; Simon, Jonathan Z.Magnetoencephalography (MEG) data and predictor variables from the article titled: Transformation from auditory to linguistic representations across auditory cortex is rapid and attention dependent for continuous speech
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