EMQ: Evolving Training-free Proxies for Automated Mixed Precision Quantization

Mixed-Precision Quantization~(MQ) can achieve a competitive accuracy-complexity trade-off for models. Conventional training-based search methods require time-consuming candidate training to search optimized per-layer bit-width configurations in MQ. Recently, some training-free approaches have presented various MQ proxies and significantly improve search efficiency. However, the correlation between these proxies and quantization accuracy is poorly understood. To address the gap, we first build the MQ-Bench-101, which involves different bit configurations and quantization results. Then, we observe that the existing training-free proxies perform weak correlations on the MQ-Bench-101. To efficiently seek superior proxies, we develop an automatic search of proxies framework for MQ via evolving algorithms. In particular, we devise an elaborate search space involving the existing proxies and perform an evolution search to discover the best correlated MQ proxy. We proposed a diversity-prompting selection strategy and compatibility screening protocol to avoid premature convergence and improve search efficiency. In this way, our Evolving proxies for Mixed-precision Quantization~(EMQ) framework allows the auto-generation of proxies without heavy tuning and expert knowledge. Extensive experiments on ImageNet with various ResNet and MobileNet families demonstrate that our EMQ obtains superior performance than state-of-the-art mixed-precision methods at a significantly reduced cost. The code will be released.Comment: Accepted by ICCV202

Aspects of Modeling and Verifying Secure Procedures

Security protocols are specifications for exchanging messages on a possibly insecure network. They aim at achieving some security goals (eg authenticating the parties involved in a communication, or preserving confidentiality of certain messages) preventing some malicious party to achieve advantages for its own. Goals of security protocols are generally achieved through the use of cryptography, the art of writing in secret characters, not comprehensible to anyone but the sender and the intended recipient. There is however a branch, in the computer science community, that, among its wide field of activities, aims at studying possible attacks on secure procedures without breaking cryptography, eg by manipulating some of the exchanged messages. This is the formal methods community, with an eye for security. This thesis mainly investigates the formal modeling and analysis of security protocols, both with finite and non finite behaviour, both within a process-algebraic and an automata framework. Real life protocols for signing and protecting digital contents and for giving assurance about authentic correspondences will be specified by means of the above cited formalisms, and some of their properties will be verified by means of formal proofs and automated tools. The original contributions of this thesis are the following. Within the framework of a formal modeling and verification of security protocols, we have applied an automated tool to better understand some secure mechanisms for the delivery of electronic documents. This has given us a deep insight on revealing the effects of omitted (or even erroneously implemented) security checks. Furthermore, a formal framework for modeling and analysing secure multicast and wireless communication protocols has been proposed. The analysis is mostly based on some new compositional principles giving sufficient conditions for safely composing an arbitrary number of components within a unique system. Also, steps towards providing the Team Automata formalism (TA) with a framework for security analysis have been taken. Within the framework, we model and analyse integrity and privacy properties, contributing to testify the expressive power and modelling capabilities of TA

Towards simultaneous electroencephalography and functional near-infrared spectroscopy for improving diagnostic accuracy in prolonged disorders of consciousness: a healthy cohort study

Qualitative clinical assessments of the recovery of awareness after severe brain injury require an assessor to differentiate purposeful behaviour from spontaneous behaviour. As many such behaviours are minimal and inconsistent, behavioural assessments are susceptible to diagnostic errors. Advanced neuroimaging tools such as functional magnetic resonance imaging and electroencephalography (EEG) can bypass behavioural responsiveness and reveal evidence of covert awareness and cognition within the brains of some patients, thus providing a means for more accurate diagnoses, more accurate prognoses, and, in some instances, facilitated communication. As each individual neuroimaging method has its own advantages and disadvantages (e.g., signal resolution, accessibility, etc.), this thesis studies on healthy individuals a burgeoning technique of non-invasive electrical and optical neuroimaging—simultaneous EEG and functional near-infrared spectroscopy (fNIRS)—that can be applied at the bedside. Measuring reliable covert behaviours is correlated with participant engagement, instrumental sensitivity and the accurate localisation of responses, aspects which are further addressed over three studies. Experiment 1 quantifies the typical EEG changes in response to covert commands in the absence and presence of an object. This is investigated to determine whether a goal-directed task can yield greater EEG control accuracy over simple monotonous imagined single-joint actions. Experiment 2 characterises frequency domain NIRS changes in response to overt and covert hand movements. A method for reconstructing haemodynamics using the less frequently investigated phase parameter is outlined and the impact of noise contaminated NIRS measurements are discussed. Furthermore, classification performances between frequency-domain and continuous-wave-like signals are compared. Experiment 3 lastly applies these techniques to determine the potential of simultaneous EEG-fNIRS classification. Here a sparse channel montage that would ultimately favour clinical utility is used to demonstrate whether such a hybrid method containing rich spatial and temporal information can improve the classification of covert responses in comparison to unimodal classification of signals. The findings and discussions presented within this thesis identify a direction for future research in order to more accurately translate the brain state of patients with a prolonged disorder of consciousness

The impact of patient-specific vascular structure on localized cooling in the human heart

Acute Myocardial Infarction (AMI) is the leading cause of worldwide death and disability, and approximately 720,000 Americans will experience an AMI in 2018. Studies have shown that rapid hypothermia therapy (\u3c35°C) before reperfusion in patients with AMI can reduce infarct size by 37%. Localized therapeutic hypothermia has proven the potential to cool heart tissue rapidly following AMI, 3°C in 5 minutes. Using Materialise Mimics digital imaging software and the finite volume method we analyzed temperature distributions in six patient-specific left main coronary artery (LMCA) models. A mock circulatory loop was used to determine the exiting temperatures of a standard 7 Fr catheter to feed into our model with flow rates ranging from 29.2 ml/min to 68.85 ml/min. Our work showed that therapeutic hypothermia (TH) temperatures were evident at the outlets of three out of all six heart models, which varied in each left anterior descending (LAD) and left circumflex (LCX) artery depending on flowrate. Results of this study indicate that biovariability in patient-specific vascular structures significantly impacts therapeutic hypothermia (TH) treatment methods. These results indicate that further research is needed to examine more accurate physiological effects, such as pulsatile flow and vessel wall thickness. Future models will be used to provide insight to guide more efficient TH device designs and operation parameters to optimize patient outcomes following AMI

Long-Term Paired Associative Stimulation for Restoration of Motor Function after Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition and consequent loss of motor control remains one of the main causes of disability. Motor recovery after SCI depends on the amount of spared and restored neural connections in the spinal cord. Most SCIs are incomplete and even neurologically complete injuries possess some spared neural connections. Damaged motor pathways can be reactivated by external stimulation. However, current treatment approaches are mainly palliative, such as assisting adaptation to impairments. Thus, there is a need for novel therapies to induce neuroplasticity in the spinal cord and strengthen weak and disrupted neural connections. In this thesis, paired associative stimulation (PAS) was applied as a long-term treatment for chronic incomplete SCI of traumatic origin. PAS is a non-invasive neuromodulation paradigm where descending volleys induced by transcranial magnetic stimulation (TMS) of the motor cortex are timed to coincide with antidromic volleys elicited by peripheral nerve electrical stimulation (PNS). The stimulation protocol was designed to coincide TMS- and PNS-induced volleys at the cortico-motoneuronal synapses in the spinal cord. Continuous pairing of TMS and PNS stimuli can change synaptic efficacy and produce long-term potentiation (LTP)-like plasticity in the corticospinal tract. Augmentation of synaptic strength at the spinal level has clear therapeutic value for SCI, as it can enhance motor control over paralyzed muscles. The aim of the thesis was to investigate the possible therapeutic effects of long-term PAS on hand and leg motor function in individuals with chronic incomplete SCI of traumatic origin. Study I explored long-term PAS therapeutic potential by providing long-term PAS until full recovery of hand muscle strength or until improvements ceased. The PAS protocol was designed to coincide TMS- and PNS-induced volleys in the cervical spinal cord, which is both the location of the stimulated lower motor neuron cell bodies and the site of the injury. Improvements up to normal values of hand muscle strength (Manual Muscle Test [MMT]) and increased amplitude of motor evoked potentials (MEPs) were obtained after more than 1-year stimulation in a participant with SCI. The participant regained almost complete self-care of the upper body. This was the first demonstration of restoring normal strength and range of movement of individual hand muscles by means of long-term PAS. The effect persisted over 6 months of follow up. Study II probed the effects of long-term PAS on leg muscle strength and walking in a group of five people with SCI. The PAS protocol was designed to coincide TMS- and PNS-induced volleys in the lumbar spinal cord but the site of the injury was in the cervical spinal cord. Long-term PAS delivered for 2 months significantly increased the total lower limb MMT score. This effect was stable over a 1-month follow up. Walking speed increased after 2 months of PAS in all participants. This study was the first demonstration that long-term PAS may significantly increase leg muscle strength and affect walking. The MMT score prior to the intervention was a good predictor of changes in walking speed. Study III developed a novel technique that enables probing neural excitability at the cervical spinal level by utilizing focal magnetic coil and anatomy-specific models for re-positioning of the coil. The technique enabled recording of highly reproducible MEPs and was suitable for accurate maintenance and retrieval of the focal coil position at the cervical level. In summary, this thesis contributes to the understanding of therapeutic efficacy of long-term PAS for restoration of motor control over hand and leg muscles after chronic SCI. This work challenges the view that chronic SCI is an irreversible pathologic condition and demonstrates the possibility of restoring neurological function many years postinjury when spontaneous recovery is extremely rare. The increased amplitude of MEPs, sustainable motor improvements, and the effects observed regardless of injury location indicate that PAS induces stable changes in the corticospinal pathways.Selkäydinvamma on ihmiseen kokonaisvaltaisesti vaikuttava tila, ja motorinen heikkous on yksi tärkeimmistä tekijöistä, jotka aiheuttavat rajoituksia päivittäiseen elämään. - Nykyiset hoitomenetelmät pääasiassa lievittävät oireita. Ne helpottavat kivun ja spastisuuden hallintaa ja sopeutumista vammaan sekä estävät sekundaarisia komplikaatioita. Keskushermosto voi kuitenkin järjestyä uudelleen sopeutuakseen heikentyneeseen toimintaan, ja tätä muovautuvuutta voidaan käyttää terapeuttisena mahdollisuutena. Vaurioituneet hermoradat voidaan aktivoida uudelleen ulkoisella stimulaatiolla. Toipuminen selkäydinvamman jälkeen riippuu niistä selkäytimen hermoyhteyksistä, jotka ovat säästyneet ja jotka on onnistuttu palauttamaan. Usein selkäydinvammat ovat osittaisia, ja neurologisesti täydellisissäkin vammoissa on joitakin säästyneitä hermoyhteyksiä. Uusilla hoitomenetelmillä voidaan aktivoida selkäytimen neuroplastisuutta ja vahvistaa heikkoja ja katkenneita hermoyhteyksiä. Tässä väitöskirjassa kaksoisstimulaatiota (PAS) käytettiin pitkäaikaisena hoitona potilailla, joilla oli krooninen, traumaattinen osittainen selkäydinvamma. PAS on neuromodulaatiomenetelmä, jossa aivokuoren transkraniaalinen magneettistimulaatio (TMS) synkronoidaan perifeeristen hermojen sähköstimulaatioon (PNS). Stimulaatioprotokolla suunniteltiin niin että TMS: n ja PNS: n synnyttämät aktivaatiot kohtaavat selkäytimen synapseissa. Jatkuva TMS:n ja PNS:n aikaansaamien ärsykkeiden kohtaaminen selkäydintasolla voi voimistaa synapsien tehokkuutta ja tuottaa pitkäaikaisen synaptisen potentiaation (long-term potentiation, LTP) selkäytimessä. Synaptisen tehokkuuden kasvu selkäytimessä todennäköisesti parantaa lihasten tahdonalaista hallintaa. Väitöskirjan päätavoitteena on ollut tutkia pitkäaikaisen kaksoisstimulaation (PAS) mahdollisia terapeuttisia vaikutuksia käden ja jalkojen tahdonalaiseen lihasaktiivisuuteen henkilöillä, joilla on traumaattinen krooninen osittainen selkäydinvamma. Tutkimuksessa I selvitin pitkäaikaista PASin terapeuttista potentiaalia antamalla PAS-hoitoa niin kauan kunnes käden lihasten voima palautui kokonaan, tai voimassa ei tapahtunut enää kasvua. Yli vuoden kestäneen stimulaation jälkeen käsien lihasvoimat kohenivat normaaliarvoihin (Manuaalinen lihastesti, MMT) osallistujalla, jolla oli krooninen osittainen neliraajahalvaus. Sen lisäksi herätevastet (motor-evoked potentials) kasvoivat. Koehenkilön ylävartalon lihashallinta palautui lähes täydellisesti. Tämä on ensimmäinen osoitus yksittäisten käsilihasten normaalin voiman ja liikeratojen palautumisesta pitkäaikaisen PAS:n avulla selkäydinvammapotilaalla. Vaikutus säilyi 6 kuukauden seurannassa. Tutkimuksessa II tutkittiin pitkäaikaisen PAS: n vaikutuksia alaraajalihasten voimaan ja kävelyyn viidellä henkilöllä, joilla on krooninen tetraplegia. Kahden kuukauden ajan annettu pitkäaikainen PAS lisäsi merkittävästi alaraajojen MMT-pistemäärää keskimäärin yhdellä pisteellä lihasta kohden. Tämä tulos säilyi kuukauden seurannassa. Kaikkien osallistujien kävelynopeus kasvoi PAS-hoitojakson jälkeen. Tutkimus on ensimmäinen osoitus siitä, että pitkäaikainen PAS voi lisätä merkittävästi alaraajojen lihasvoimaa. MMT-pistemäärä ennen interventiota ennusti hyvin kävelynopeuden muutoksia. Tutkimuksessa III kehitettiin uusi tekniikka, joka mahdollistaa magneettistimulaation selkäydinalueella käyttäen fokaalista magneettikelaa ja pään anatomisia malleja magneettikelan toistettuun kohdentamiseen. Menetelmä mahdollisti toistettavien MEP-signaalien mittaamisen sekä kelan sijainnin tarkan, toistettavan paikannuksen ja kohdentamisen niskan alueella. Yhteenvetona voidaan todeta, että väitöskirja lisää ymmärrystä pitkäaikaisen PAS: n terapeuttisesta tehosta ylä- ja alaraajalihasten hallinnan palauttamisessa ja omatoimisuuden lisäämisessä kroonisen selkäydinvamman jälkeen. Väitöskirja haastaa käsityksen kroonisen selkäydinvamman aiheuttamien toimintahäiriöiden pysyvästä luonteesta. Sen lisäksi väitöskirja osoittaa mahdollisuuden palauttaa lihasaktiivisuutta nimenomaan kroonisessa selkäydinvammassa, jossa spontaani koheneminen on erittäin harvinaista. Voimistuneet lihasvasteet ja pysyvä lihashallinnan parannus vamman sijainnista riippumatta osoittavat, että PAS oikein käytettynä muokkaa liikejärjestelmää hyödyllisellä tavalla

Silicon-Based Tandem Solar Cells with Silicon Heterojunction Bottom Cells

abstract: Silicon photovoltaics (PV) is approaching its theoretical efficiency limit as a single-junction technology. To break this limit and further lower the PV-generated levelized cost of electricity, it is necessary to engineer a silicon-based “tandem” technology in which a solar cell of another material is stacked on top of silicon to make more efficient use of the full solar spectrum. This dissertation understands and develops four aspects of silicon-based tandem PV technology. First, a new “spectral efficiency” concept is proposed to understand how tandem cells should be designed and to identify the best tandem partners for silicon cells. Using spectral efficiency, a top-cell-design guide is constructed for silicon-based tandems that sets efficiency targets for top cells with various bandgaps to achieve targeted tandem efficiencies. Second, silicon heterojunction solar cells are tuned to the near-infrared spectrum to enable world-record perovskite/silicon tandems both in two- and four-terminal configurations. In particular, for the 23.6%-efficient two-terminal tandem, a single-side textured silicon bottom cell is fabricated with a low-refractive-index silicon nanoparticle layer as a rear reflector. This design boosts the current density to 18.5 mA/cm2; this value exceeds that of any other silicon bottom cell and matches that of the top cell. Third, “PVMirrors” are proposed as a novel tandem architecture to integrate silicon cells with various top cells. A strength of the design is that the PVMirror collects diffuse light as a concentrating technology. With this concept, a gallium-arsenide/silicon PVMirror tandem is demonstrated with an outdoor efficiency of 29.6%, with respect to the global irradiance. Finally, a simple and versatile analytical model is constructed to evaluate the cost competitiveness of an arbitrary tandem against its sub-cell alternatives. It indicates that tandems will become increasingly attractive in the market, as the ratio of sub-cell module cost to area-related balance-of-system cost—the key metric that will determine the market success or failure of tandems—is decreasing. As an evolution of silicon technology, silicon-based tandems are the future of PV. They will allow more people to have access to clean energy at ultra-low cost. This thesis defines both the technological and economic landscape of silicon-based tandems, and makes important contributions to this tandem future.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201