Electro-photo-sensitive memristor for neuromorphic and arithmetic computing

The authors gratefully acknowledge financial support from the European Union [FPVII (2007-2013) under Grant Agreement No. 318287 Landauer], as well as the state of Bavaria.We present optically and electrically tunable conductance modifications of a site-controlled quantum-dot memristor. The conductance of the device is tuned by electron localization on a quantum dot. The control of the conductance with voltage and low-power light pulses enables applications in neuromorphic and arithmetic computing. As in neural networks, applying pre- and postsynaptic voltage pulses to the memristor allows us to increase (potentiation) or decrease (depression) the conductance by tuning the time difference between the electrical pulses. Exploiting state-dependent thresholds for potentiation and depression, we are able to demonstrate a memory-dependent induction of learning. The discharging of the quantum dot can further be induced by low-power light pulses in the nanowatt range. In combination with the state-dependent threshold voltage for discharging, this enables applications as generic building blocks to perform arithmetic operations in bases ranging from binary to decimal with low-power optical excitation. Our findings allow the realization of optoelectronic memristor-based synapses in artificial neural networks with a memory-dependent induction of learning and enhanced functionality by performing arithmetic operations.PostprintPeer reviewe

Calculating with light using a chip-scale all-optical abacus

This is the final version of the article. Available from Springer Nature via the DOI in this record.Machines that simultaneously process and store multistate data at one and the same location can provide a new class of fast, powerful and efficient general-purpose computers. We demonstrate the central element of an all-optical calculator, a photonic abacus, which provides multistate compute-and-store operation by integrating functional phase-change materials with nanophotonic chips. With picosecond optical pulses we perform the fundamental arithmetic operations of addition, subtraction, multiplication, and division, including a carryover into multiple cells. This basic processing unit is embedded into a scalable phase-change photonic network and addressed optically through a two-pulse random access scheme. Our framework provides first steps towards light-based non-von Neumann arithmetic.The authors acknowledge support by Deutsche Forschungsgemeinschaft (DFG) grants PE 1832/2-1 and EPSRC grant EP/J018783/1. M.S. acknowledges support from the Karlsruhe School of Optics and Photonics (KSOP) and the Stiftung der Deutschen Wirtschaft (sdw). C.R. is grateful to JEOL UK and the Clarendon Fund for funding his graduate studies. H.B. acknowledges support from the John Fell Fund and the EPSRC (EP/J00541X/2 and EP/J018694/1). The authors also acknowledge support from the DFG and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN). The authors thank S. Diewald for assistance with device fabrication

In-Memory Computing by Using Nano-ionic Memristive Devices

By reaching to the CMOS scaling limitation based on the Moore’s law and due to the increasing disparity between the processing units and memory performance, the quest is continued to find a suitable alternative to replace the conventional technology. The recently discovered two terminal element, memristor, is believed to be one of the most promising candidates for future very large scale integrated systems. This thesis is comprised of two main parts, (Part I) modeling the memristor devices, and (Part II) memristive computing. The first part is presented in one chapter and the second part of the thesis contains five chapters. The basics and fundamentals regarding the memristor functionality and memristive computing are presented in the introduction chapter. A brief detail of these two main parts is as follows: Part I: Modeling- This part presents an accurate model based on the charge transport mechanisms for nanoionic memristor devices. The main current mechanism in metal/insulator/metal (MIM) structures are assessed, a physic-based model is proposed and a SPICE model is presented and tested for four different fabricated devices. An accuracy comparison is done for various models for Ag/TiO2/ITO fabricated device. Also, the functionality of the model is tested for various input signals. Part II: Memristive computing- Memristive computing is about utilizing memristor to perform computational tasks. This part of the thesis is divided into neuromorphic, analog and digital computing schemes with memristor devices. – Neuromorphic computing- Two chapters of this thesis are about biologicalinspired memristive neural networks using STDP-based learning mechanism. The memristive implementation of two well-known spiking neuron models, Hudgkin-Huxley and Morris-Lecar, are assessed and utilized in the proposed memristive network. The synaptic connections are also memristor devices in this design. Unsupervised pattern classification tasks are done to ensure the right functionality of the system. – Analog computing- Memristor has analog memory property as it can be programmed to different memristance values. A novel memristive analog adder is designed by Continuous Valued Number System (CVNS) scheme and its circuit is comprised of addition and modulo blocks. The proposed analog adder design is explained and its functionality is tested for various numbers. It is shown that the CVNS scheme is compatible with memristive design and the environment resolution can be adjusted by the memristance ratio of the memristor devices. – Digital computing- Two chapters are dedicated for digital computing. In the first one, a development over IMPLY-based logic with memristor is provided to implement a 4:2 compressor circuit. In the second chapter, A novel resistive over a novel mirrored memristive crossbar platform. Different logic gates are designed with the proposed memristive logic method and the simulations are provided with Cadence to prove the functionality of the logic. The logic implementation over a mirrored memristive crossbars is also assessed

On the application of a diffusive memristor compact model to neuromorphic circuits

Memristive devices have found application in both random access memory and neuromorphic circuits. In particular, it is known that their behavior resembles that of neuronal synapses. However, it is not simple to come by samples of memristors and adjusting their parameters to change their response requires a laborious fabrication process. Moreover, sample to sample variability makes experimentation with memristor-based synapses even harder. The usual alternatives are to either simulate or emulate the memristive systems under study. Both methodologies require the use of accurate modeling equations. In this paper, we present a diffusive compact model of memristive behavior that has already been experimentally validated. Furthermore, we implement an emulation architecture that enables us to freely explore the synapse-like characteristics of memristors. The main advantage of emulation over simulation is that the former allows us to work with real-world circuits. Our results can give some insight into the desirable characteristics of the memristors for neuromorphic applications

Indicators of maize (Zea mays L.) seed contamination by aflatoxins

Predmet istraživanja ove doktorske disertacije je praćenje indikatora kvaliteta semena kukuruza (Zea mays L.) kontaminiranog aflatoksinima, u zavisnosti od koncentracije aflatoksina prisutnog u semenu. Kako se kukuruz široko koristi u ljudskoj i životinjskoj ishrani, naučne studije o sadržaju i interakciji mikotoksina u semenima poljoprivrednih kultura su intenzivirana u poslednjoj deceniji. U okviru ove disertacije proučena je veza između nivoa kontaminacije semena kukuruza i marker molekula fenolnog tipa, ukupnog sadržaja i distribucije slobodnih organskih radikala, sadržaja metala, kao i fluorescentnog emisionog profila semena kukuruza. Fokus ovog istraživanja bio je na aflatoksinu B1 (AFB1), jednom od najštetnijih prirodnih kontaminanta koji se mogu naći u semenu kukuruza. Utvrđeno je da aflatoksini dovode do ozbiljnih zdravstvenih problema kod ljudi i životinja, kao i do ogromnih ekonomskih gubitaka, kao posledica smanjenja kvaliteta semena kao stočne hrane i izvozne prehrambene robe. Prvi deo disertacije predstavlja hemijsku karakterizaciju semena kukuruza različitog nivoa kontaminacije aflatoksinom. Ultraefikasnom tečnom hromatografijom sa hibridnim masenim detektorom visoke rezolucije, koji kombinuje linearni trap-kvadrupol i orbitrap maseni analizator (UHPLC–LTQOrbiTrapXL MS), određen je fenolni profil metanolnih ekstrakata i hidrolizata ispitivanih semena. Nadalje, kvalitativna i kvantitativna analiza odabranih fenolnih jedinjenja je urađena pomoću reverzno-fazne visoko-efikasne tečne hromatografije sa ultravioletnim detektorom sa više dioda (DAD) i masenim detektorom sa jednim analizatorom (engl. single quadrupole) i elektrosprej jonizacionim (ESI) izvorom (RP-HPLC–DAD ESI–MS). Rezultati pokazuju da su konjugati poliamina (hidroksicinamični kiseli amidi) i fenolne kiseline (ferulinska i p-kumarinska), redom, dominantna jedinjenja u metanolnim ekstraktima i hidrolizatima ispitivanih uzoraka. Utvrđeno je da sadržaj i odnos specifičnih fenolnih jedinjenja zavisi od koncentracije aflatoksina u semenu. Po prvi put, u ovoj studiji, je ustanovljena dozno-zavisna veza između odnosa zbira konjugata putrescina i spermidina i koncentracije AFB1. Rezultati dobijeni primenom UV-VIS spektrofotometrije potvrđuju postojanje dvofaznog odgovora semena na proučavani toksin. Pri višim nivoima kontaminacije u spoljašnjim frakcijama semena, utvrđen je veći sadržaj lignina, kao i veća količina jedinjenja koja se u literaturi označavaju kao markeri procesa lignifikacije, upućujući na jedan od mehanizama zaštite semena. Primenom indukovano kuplovane plazme sa optičkom emisionom spektrometrijom (ICP–OES) i masenom spektrometrijom (ICP–MS), određen je sadržaj mikro- i makroelemenata. Dobijeni rezultati pokazuju veći sadržaj Zn i Mn u semenima višeg nivoa kontaminacije, u poređenju sa kontrolom i nisko kontaminiranim uzorcima. Na matrice HPLC i ICP podataka, primenjena je analiza glavnih komponenti (engl. Principal component analysis, PCA) u cilju diskriminacije semena različitih nivoa kontaminacije aflatoksinom, kao i za pronalaženje mogućih markera kontaminacije. Elektronska paramagnetna rezonantna (EPR) spektroskopija iskorišćena je za proučavanje sadržaja slobodnih organskih radikala u proučavanim uzorcima. Utvrđene su razlike u koncentraciji ovih radikala između spoljašnje i unutrašnje frakcije, kao i varijacije u pogledu nivoa kontaminacije. Procena redoks statusa u ispitivanim semenima urađena je EPR imidžingom sa spinskim probama. Dobijeni rezultati daju doprinos razumevanju slobodno–radikalskog metabolizma i redoks statusa kontaminiranih semena. Drugi deo doktorske disertacije obuhvatio je primenu naprednih metoda spektralne analize na fluorescentne emisione spektre ispitivanih uzoraka, kao što su multivarijaciona rezolucija krivihnaizmenični najmanji kvadrati (MCR–ALS), analiza glavnih komponenti, linearna diskriminaciona analiza i druge. Ovakav način obrade podataka fluorescentnih spektara analiziranih uzoraka nije bio ranije korišćen. Dobijeni rezultati se mogu uspešno koristiti kao indikator kontaminacije semena kukuruza aflatoksinom. Rezultati predstavljeni u ovoj disertaciji su od velikog praktičnog značaja, pošto osim fundamentalnih saznanja o stanju semena kontaminiranih aflatoksinima, mogu da daju osnovu za razvoj spektroskopsko-statističkih metoda za procenu kontaminacije semena različitih poljoprivrednih kultura.The research topic of this doctoral dissertation is the selection of appropriate indicators for the monitoring of maize (Zea mays L.) seed contamination with aflatoxins and the examination of its dependence on the aflatoxin concentration. As maize (Zea mays L.) is widely used in human and animal nutrition, scientific research on the content and interaction of mycotoxins in agricultural seeds has intensified in the last decade. Overall, the relationship between the degree of maize seeds’ contamination and marker molecules of phenolic type, total content and distribution of free radicals, metal content, as well as the fluorescence emission profile of maize seeds were studied, and the results are presented in this dissertation. The focus of this research is on aflatoxin B1 (AFB1), one of the most hazardous naturally occurring contaminants in maize seeds. As a naturally toxic contaminant, it has led to adverse health effects on humans and animals, as well as to huge economic losses, lowering the value of seeds as feed and as an export food commodity. In the first part of this dissertation, the chemical characterization of maize seeds of different levels of aflatoxin contamination was examined. Phenolic profiles of methanolic extracts and hydrolysates from aflatoxin-containing seeds were evaluated using ultra-high-performance liquid chromatography coupled to a high-resolution hybrid mass spectrometer which consists of a linear ion trap-quadrupole and an Orbitrap mass analyzer (UHPLC-LTQOrbiTrapXL). Furthermore, quality and quantity analysis of selected phenolic compounds was performed by reverse-phase highperformance liquid chromatography with ultraviolet multi-diode detector (DAD) and singlequadrupole mass detector and electrospray ionization (ESI) source (RP-HPLC-DAD ESI-MS). Dominant phenolic compounds which are identified in methanolic extracts and hydrolysates of analysed seeds were conjugates of polyamines (hydroxycinnamic acid amides) and phenolic acids (ferulic acid and p-coumaric), respectively. The obtained results show that the content and ratio between specific phenolic compounds varies depending on the concentration of aflatoxins in the seed. For the first time, in this study, it is showed that level of aflatoxins has an impact on seeds' defense strategy, such as biphasic response regarding the ratio of putrescine and spermidine conjugates. Also, we showed a positive correlation between the lignin content and the AFB1 concentrations in the seeds' outer fraction, which reflects the protective role of lignin during stress conditions. For the first time, in this study, it was found that aflatoxin B1 can induce a dosedependent relationship concerning specific phenolic compounds, mainly on the sum ratio between putrescine and spermidine conjugates in methanolic extracts. The results, obtained using UV-VIS spectrophotometry, confirm the existence of a two-phase seed response to the studied stressor. At higher levels of contamination in the outer seed fractions, higher lignin content was found, as well as a higher amount of those compounds that are listed in the literature as lignification markers, which indicates the structural mechanism of seed protection. The content of individual micro-and macroelements was determined using induced coupled plasma with optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS), respectively. Obtained results show that levels of Zn and Mn were higher in AFB1 high contaminated seeds compared to the control and lowcontaminated samples. Principal component analysis (PCA) was applied to the HPLC as well as ICP results, to distinguish between seeds with different levels of aflatoxin contamination, as well as to find possible markers of seed contamination. Electron paramagnetic resonance (EPR) spectroscopy was used to study the content of free organic radicals in the studied samples. Differences in the concentration of these radicals were determined between the outer and inner fractions of seeds, as well as variations concerning the level of contamination. Estimation of redox status in the examined seeds was done by the technique of EPR imaging with spin probes. These results contribute to the understanding of free radical metabolism, redox status, in seeds containing aflatoxins. In the second part of this dissertation, we used different methods of spectral analysis to fluorescence emission spectra of aflatoxin B1 containing seeds, such as multivariate resolution curves-alternating least squares (MCR-ALS), principal components analysis (PCA), linear discriminant analysis (LDA) and others. This method of processing fluorescencespectral data has not been used before and the obtained parameters can be successfully applied as indicators of maize seeds’contamination with aflatoxin B1 (AFB1). The results presented in this dissertation are of great importance because, in addition to fundamental knowledge about the state of seeds contaminated with aflatoxins, they may be a basis for the development of spectroscopic and statistical methods for seed contamination estimatio