Stochastic resonance for spectrum sensing of multi-carrier modulated waveforms

Spectrum sensing has received abundant attention from the research community. However, with sensing scenarios becoming increasingly complex, existing spectrum sensing schemes can hardly meet the demand for fast, accurate spectrum sensing, particularly in the very low signal-to-noise ratio (SNR) range, without dramatically increasing system complexity and the need for precise information about signal and noise. Furthermore, the widespread adoption of multicarrier modulation in various existing and evolving standards is driving efforts to develop a robust and practical solution for multicarrier signal spectrum sensing. The main challenges identified in lieu of changing spectrum scenarios are detection in low SNR, high accuracy, low computational and sample complexity, and possible operation without the knowledge of the primary user (PU) signal and channel. Stochastic Resonance (SR) is a phenomenon in which a signal too weak to cross the detection threshold becomes detectable in a nonlinear system with the addition of noise. This research considers the application of SR to sense multi-frequency/multi-carrier signals. The effect of the SR receiver has never been verified for multi-carrier signals, which is a popular modulation system in various existing and evolving standards. The thesis provides an understanding of how and why the SR effect for multi-frequency signals differs from the SR effect for single frequency signals. Special features such as ghost resonance, multi-resonance and doubly SR are demonstrated with simulations. A novel method to identify ghost resonance is proposed and the relationship of noise intensity and frequencies of the driving signal is derived. SR for multi-frequency signals is quantified in terms of the SNR. In the presented research, SR is used as a pre-processing technique to enhance SNR prior to the detector, which significantly improves spectrum sensing performance. The two main contributions in this part of the research are (i) A novel algorithm for dynamic determination of SR system parameters and noise intensity, which results in maximum SNR; (ii) An SR-based sensing method particularly tailored to give near-optimal performance for multi-carrier signals by using the multi-taper spectral estimate (MTSE) method. A simple Fourier transform-based method is also evaluated as a computationally light alternative to MTSE. The FFT-based method combined with (i) provides near-optimal performance for single-carrier modulated schemes. The performance is evaluated in low SNR, flat/frequency selective fading, iii shadowing, interference and time/frequency offset. The results show that by using SR pre-processing, the performance of energy-based detection (ED) can be significantly improved. The proposed method is also evaluated in cooperative sensing scenarios. The results show that the proposed SR-ED with a basic cooperative mechanism can match the performance of ED-based cooperative sensing with optimal fusion. The proposed method has several distinctive features including low latency, high accuracy, reasonable computational complexity, robustness to low SNR, robustness to flat/frequency selective fading, robustness to noise/channel uncertainty. It also requires no prior knowledge of the PU signal

How to extend the chart of nuclides?

In the past 85 years the number of known nuclides increased by more than a factor of ten, resulting in 4000 presently known isotopes of 118 elements. This considerable progress we owe to the discovery of new reaction types along with the development of powerful accelerators and experimental techniques for separation and identification of reaction products. Model predictions indicate that still about 4000 further nuclides are waiting for their discovery. The vastest unexplored territory is located on the neutron-rich side in the upper half of the chart of nuclides and hides the answers to some of the most fundamental questions of nuclear physics like the limits of nuclear stability, element synthesis in the universe or stellar evolution. The access to these nuclei is presently limited by available beam intensities and/or the lack of appropriate methods for their production and identification. The latter concerns particularly new neutron-rich isotopes of transuranium and superheavy elements. To extend this area, the hope is presently based on multinucleon transfer reactions and on the application of fusion reactions with radioactive ion beams. But how promising are these approaches? Based on a survey of present-day knowledge, we will treat the questions where we currently are on our journey towards new territory on the chart of nuclides, how the chances are to gain new territory in the future and which challenges we will have to face

Development of novel semiconductor based photodetector devices

This thesis investigates novel range semiconductor materials and structures for use in optoelectronic devices operating from UV to mid-IR. These devices have an abundant variety of applications, including optical communications and imaging. The studies primarily focus on the electronic band structure of the materials and how this impacts device performance. Dilute bismide III-V alloys are a material of great interest for IR applications, especially with the band structure engineering that can be carried out to fulfil the condition where the spin-orbit splitting energy,

Mechanochromic and Thermochromic Sensors Based on Graphene Infused Polymer Opals

High quality opal-like photonic crystals containing graphene are fabricated using evaporation-driven self-assembly of soft polymer colloids. A miniscule amount of pristine graphene within a colloidal crystal lattice results in the formation of colloidal crystals with a strong angle-dependent structural color and a stop band that can be reversibly shifted across the visible spectrum. The crystals can be mechanically deformed or can reversibly change color as a function of their temperature, hence their sensitive mechanochromic and thermochromic response make them attractive candidates for a wide range of visual sensing applications. In particular, we show that the crystals are excellent candidates for visual strain sensors or integrated time-temperature indicators which act over large temperature windows. Given the versatility of these crystals, this method represents a simple, inexpensive and scalable approach to produce multifunctional graphene infused synthetic opals and opens up exciting applications for novel solution-processable nanomaterial based photonics

Exploiting Deep Learning in Limited-Fronthaul Cell-Free Massive MIMO Uplink

A cell-free massive multiple-input multiple-output (MIMO) uplink is considered, where quantize-and-forward (QF) refers to the case where both the channel estimates and the received signals are quantized at the access points (APs) and forwarded to a central processing unit (CPU) whereas in combinequantize- and-forward (CQF), the APs send the quantized version of the combined signal to the CPU. To solve the non-convex sum rate maximization problem, a heuristic sub-optimal scheme is exploited to convert the power allocation problem into a standard geometric programme (GP). We exploit the knowledge of the channel statistics to design the power elements. Employing largescale-fading (LSF) with a deep convolutional neural network (DCNN) enables us to determine a mapping from the LSF coefficients and the optimal power through solving the sum rate maximization problem using the quantized channel. Four possible power control schemes are studied, which we refer to as i) small-scale fading (SSF)-based QF; ii) LSF-based CQF; iii) LSF use-and-then-forget (UatF)-based QF; and iv) LSF deep learning (DL)-based QF, according to where channel estimation is performed and exploited and how the optimization problem is solved. Numerical results show that for the same fronthaul rate, the throughput significantly increases thanks to the mapping obtained using DCNN

Voice-hearers’ understanding and experience of help: an interpretative phenomenological analysis.

Objectives: The literature on voice-hearers’ experience of help is relatively scant and the forms of help studied tend to be defined by researchers. The present study aims to contribute to the extant literature by exploring what help means to voice-hearers and how they experience it in the context of their lives. Method: Six participants who identified as voice-hearers and who had experiences of help took part in semi-structured interviews. The interviews were transcribed verbatim and analysed using Interpretative Phenomenological Analysis (IPA). Results: The analysis produced four superordinate themes representing different facets of voice-hearers’ lived experience of help. These were: 1. Treat me like a human being; 2. The darker side of help; 3. Like moving to a new country; and 4. Becoming agents of change. Conclusions: Voice-hearers are very aware of and sensitive to the interpersonal nature of help and this can have a profound influence on whether their experiences of help are positive or negative. Importantly, voice-hearers’ relationship with their voices can be a source of help as well as distress. It is possible that voice-hearers do not need help for voices but rather for the underlying trauma of which voices may be a manifestation. Finally, help can be experienced as a journey and this conceptualisation may usefully inform clinical practice

Suppression of Parathyroid Hormone as a Proxy for Optimal Vitamin D Status: Further Analysis of Two Parallel Studies in Opposite Latitudes

Optimal vitamin D status has commonly been defined as the level of 25-hydroxyvitamin D (25(OH)D) at which parathyroid hormone (PTH) concentrations would be maximally suppressed, represented by an observed minimum plateau. Previous findings indicate a large variation in this plateau, with values ranging from 75 nmol/L) (p < 0.001). Regression modelling was used to investigate the relationship between serum 25(OH)D and PTH for the sample as a whole and for each group separately. A cubic model was statistically significant for the total sample (p < 0.001), whereas a linear model presented the best fit for Brazilian women living in England (p = 0.04) and there were no statistically significant models fitted for Brazilian women living in Brazil. The cubic model suggests that 25(OH)D concentrations above 70–80 nmol/L are optimal to suppress the parathyroid gland in Brazilian women. These findings contribute to a better understanding of the relationship between 25(OH)D and PTH in populations living in a low latitude location and are of great relevance for discussions regarding the estimation of optimal cut-offs for vitamin D levels in the Brazilian population as well as for other low latitude locations

A novel scaffold based hybrid multicellular model for pancreatic ductal adenocarcinoma – towards a better mimicry of the in vivo tumour microenvironment

With a very low survival rate, pancreatic ductal adenocarcinoma (PDAC) is a deadly disease. This has been primarily attributed to – (i) its late diagnosis and (ii) its high resistance to current treatment methods. The later, specifically requires the development of robust, realistic in vitro models of PDAC, capable of accurately mimicking the in vivo tumour niche. Advancements in the field of Tissue Engineering (TE) have helped the development of such models for PDAC. Herein, we report for the first time a novel hybrid, poly- urethane (PU) scaffold based, long term, multicellular (tri-culture) model of pancreatic cancer involving cancer cells, endothelial cells and stellate cells. Recognising the importance of ECM proteins for optimal growth of different cell types, the model consists of two different zones/compartments: an inner tumour compartment consisting of cancer cells (fibronectin coated) and a surrounding stromal compartment consisting of stellate and endothelial cells (collagen I coated). Our developed novel hybrid, tri-culture model supports the proliferation of all different cell types for 35 days (5 weeks), which is the longest reported time frame in vitro. Furthermore, the hybrid model showed extensive collagen I production by the cells, mimicking desmoplasia, one of PDAC’s hallmark features. Fibril alignment of the stellate cells was observed, which attested for their activated state. All three cell types expressed various cell specific markers within the scaffolds, throughout the culture period and showed cellular migration between the two zones of the hybrid scaffold. Our novel model has great potential as a low cost tool for in vitro studies of PDAC as well as for treatment screening

Novel approaches for assessing circadian rhythmicity in humans A review

Temporal organisation of molecular and physiological processes is driven by environmental and behavioural cycles, as well as by self-sustained molecular circadian oscillators. Quantification of phase, amplitude, period, and disruption of circadian rhythms is essential for understanding their contribution to sleep-wake disorders, social jet-lag, inter-individual differences in entrainment and the development of chrono-therapeutics. Traditionally, assessment of the human circadian system, and the output of the SCN in particular, required collection of long time series of univariate markers such as melatonin or core body temperature. Data were collected in specialised laboratory protocols designed to control for environmental and behavioural influences on rhythmicity. These protocols are time-consuming, expensive, and are not practical for assessing circadian status in patients or in participants in epidemiologic studies. Novel approaches for assessment of circadian parameters of the SCN or peripheral oscillators have been developed. They are based on machine learning or mathematical model-informed analyses of features extracted from one or a few samples of high dimensional data such as transcriptomes, metabolomes, long term simultaneous recording of activity, light exposure, skin temperature, and heart rate, or in vitro approaches. Here, we review whether these approaches successfully quantify parameters of central and peripheral circadian oscillators as indexed by gold standard markers. While several approaches perform well under entrained conditions when sleep occurs at night, the methods either perform worse in other conditions such as shift work, or they have not been assessed under any conditions other than entrainment and thus we do not yet know how robust they are. Novel approaches for the assessment of circadian parameters hold promise for circadian medicine, chrono-therapeutics, and chrono-epidemiology. There remains a need to validate these approaches against gold standard markers, in individuals of all sexes and ages, in patient populations, and, in particular, under conditions in which behavioural cycles are displaced.</p