Tunable Quantum Chaos in the Sachdev-Ye-Kitaev Model Coupled to a Thermal Bath

The Sachdev-Ye-Kitaev (SYK) model describes Majorana fermions with random interaction, which displays many interesting properties such as non-Fermi liquid behavior, quantum chaos, emergent conformal symmetry and holographic duality. Here we consider a SYK model or a chain of SYK models with $N$ Majorana fermion modes coupled to another SYK model with $N^2$ Majorana fermion modes, in which the latter has many more degrees of freedom and plays the role as a thermal bath. For a single SYK model coupled to the thermal bath, we show that although the Lyapunov exponent is still proportional to temperature, it monotonically decreases from $2\pi/\beta$ ($\beta=1/(k_BT)$, $T$ is temperature) to zero as the coupling strength to the thermal bath increases. For a chain of SYK models, when they are uniformly coupled to the thermal bath, we show that the butterfly velocity displays a crossover from a $\sqrt{T}$-dependence at relatively high temperature to a linear $T$-dependence at low temperature, with the crossover temperature also controlled by the coupling strength to the thermal bath. If only the end of the SYK chain is coupled to the thermal bath, the model can introduce a spatial dependence of both the Lyapunov exponent and the butterfly velocity. Our models provide canonical examples for the study of thermalization within chaotic models.Comment: 28 pages, 9 figures. References adde

Low Power Adaptive Circuits: An Adaptive Log Domain Filter and A Low Power Temperature Insensitive Oscillator Applied in Smart Dust Radio

This dissertation focuses on exploring two low power adaptive circuits. One is an adaptive filter at audio frequency for system identification. The other is a temperature insensitive oscillator for low power radio frequency communication. The adaptive filter is presented with integrated learning rules for model reference estimation. The system is a first order low pass filter with two parameters: gain and cut-off frequency. It is implemented using multiple input floating gate transistors to realize online learning of system parameters. Adaptive dynamical system theory is used to derive robust control laws in a system identification task. Simulation results show that convergence is slower using simplified control laws but still occurs within milliseconds. Experimental results confirm that the estimated gain and cut-off frequency track the corresponding parameters of the reference filter. During operation, deterministic errors are introduced by mismatch within the analog circuit implementation. An analysis is presented which attributes the errors to current mirror mismatch. The harmonic distortion of the filter operating in different inversion is analyzed using EKV model numerically. The temperature insensitive oscillator is designed for a low power wireless network. The system is based on a current starved ring oscillator implemented using CMOS transistors instead of LC tank for less chip area and power consumption. The frequency variance with temperature is compensated by the temperature adaptive circuits. Experimental results show that the frequency stability from 5°C to 65°C has been improved 10 times with automatic compensation and at least 1 order less power is consumed than published competitors. This oscillator is applied in a 2.2GHz OOK transmitter and a 2.2GHz phase locked loop based FM receiver. With the increasing needs of compact antenna, possible high data rate and wide unused frequency range of short distance communication, a higher frequency phase locked loop used for BFSK receiver is explored using an LC oscillator for its capability at 20GHz. The success of frequency demodulation is demonstrated in the simulation results that the PLL can lock in 0.5μs with 35MHz lock-in range and 2MHz detection resolution. The model of a phase locked loop used for BFSK receiver is analyzed using Matlab

Adaptive Log Domain Filters Using Floating Gate Transistors

In this thesis, an adaptive first order lowpass log domain filter and an adaptive second order log domain filter are presented with integrated learning rules for model reference estimation. Both systems are implemented using multiple input floating gate transistors to realize on-line learning of system parameters. Adaptive dynamical system theory is used to derive robust control laws in a system identification task for the parameters of both a first order lowpass filter and a second order tunable filter. The log domain filters adapt to estimate the parameters of the reference filters accurately and efficiently as the parameters are changed. Simulation results for both the first order and the second order adaptive filters are presented which demonstrate that adaptation occurs within milliseconds. Experimental results and mismatch analysis are described for the first order lowpass filter which demonstrates the success of our adaptive system design using this model-based learning method

Investigation of mechanical stress-induced failure in transfer-bonded vertically aligned carbon nanotube arrays

As society increasingly embraces the digital world, technological progress is inevitable. With the proliferation of technology, the demand for advanced electronic devices that are both high-performing and portable is rising. This presents a challenge in terms of protecting these devices from electromagnetic interference using conventional methods. Carbon nanotubes have been identified as a potential alternative material for electromagnetic shielding. However, directly synthesizing carbon nanotubes onto microelectronic devices is not practical due to the high temperature required. As a result, a new transfer technique for carbon nanotubes is being investigated. This project focuses on the characterisation and optimisation of a novel carbon nanotube transfer technique based on of mechanical stress-induced failure analyses. Scanning Electron Microscopy is utilized for characterization. Multiple process parameters such as growth duration, etch durations, thickness of gold, spacer height and spacer material choices are examined throughout this project. In conclusion, the results of conductivity and bonding strength are analyzed and discussed.Bachelor of Engineering (Electrical and Electronic Engineering

An exploration of drivers and inhibitors of digital transformation in professional service firms : A multiple case study in management consulting industry

Background: Professional services have not been digitally disrupted in more than decades. Different emerging technologies are changing the business environment today. The rapidly increasing amount of different available technologies are affecting organisations and their industries and require them to conduct digital transformation (DT). Yet little attention has been paid to professional service firms. This gap in the literature, together with the relevance of the topic guided the authors to research further what the specific influencing factors in the adoption of digital transformation in professional service firms (PSFs) are.  Purpose: The purpose of this study is to explore the underlying factors influencing and affecting DT in PSFs, one type of PSFs in particular - management consulting firms (MCFs). The aim is to find the most influential factors and better understand their effects on the adoption process. By exploring these factors, this study can contribute significantly to the existing literature and increase the understanding of the phenomenon.     Method: This is an exploratory qualitative multiple case study with four pilot interviews to create a broader and in-depth knowledge on the phenomenon, and 6 case companies to collect rich and insightful data. The qualitative approach of interviews created primary data for empirical findings which were further coded and analysed together with secondary data.     Conclusion: From the findings and analysis, the authors extended the TOE framework to fit the topic of DT in PSFs. This was created based on the empirical findings and analysis to answer the research question. Altogether, 15 factors were classified within the super-themes of technology, organisation, and environment with driving or inhibiting effects. The findings indicate that most factors found are organisational. However, some interesting contradictions were noted between the empirical findings from both primary data as well as the secondary data. The research demonstrates the similarities and the different perceptions of the phenomenon and therefore it provides insights and understandings of the topic in its specified context. What is more, it leaves room and suggestions for future research regarding DT in PSFs.

The impact of COVID-19 on ischemic stroke

BACKGROUND: The outbreak of a novel coronavirus since December 2019, became an emergency of major international concern. As of June 21, 2020, the SARS-CoV-2 pandemic has caused 8,769,844 confirmed infections with 463,745 fatal cases worldwide. The SARS-CoV-2 outbreak is a major challenge for clinicians. In our clinic, we found a rare case that a COVID-19 patient combined with ischemic stroke. CASE PRESENTATION: A 79-year-old man was admitted to the Hubei Provincial Hospital of Traditional Chinese Medicine due to right limb weakness for 1 day and slight cough for 1 week. At presentation, his oxygen saturation was 94.2% on room air and body temperature was 37.3 °C (99.0 °F) with some moist rales. Neurological examination showed right limb weakness, and the limb muscle strength was grade 4. The left leg and arms were unaffected. In addition, runs of speech were not fluent enough with tongue deviation. Laboratory studies showed lymphopenia and eosinophilic granulocytopenia. Chest CT revealed bilateral pulmonary parenchymal ground-glass and consolidative pulmonary opacities, with a peripheral lung distribution. Real-time polymerase chain reaction (RT-PCR) from throat swab sample was positive for SARS-CoV-2 nucleic acid. This patient was treated with antiviral drugs and anti-inflammatory drugs with supportive care until his discharge. Clopidogrel (75 mg) and atorvastatin (20 mg) were administered orally to treat acute ischemic stroke. After 12 days of treatment, he can walk normally and communicate with near fluent language. CONCLUSION: We report an even more unusual case, a patient who was hospitalized for right limb weakness and was later diagnosed with COVID-19. Here, SARS-CoV-2 infection caused hypoxemia and excessive secretion of inflammatory cytokines, which contribute to the occurrence and development of ischemic stroke. Once COVID-19 patients show acute ischemic stroke, neurologists should cooperate with infectious disease doctors to help patients