Age is not just a number: Naive T cells increase their ability to persist in the circulation over time

The processes regulating peripheral naive T-cell numbers and clonal diversity remain poorly understood. Conceptually, homeostatic mechanisms must fall into the broad categories of neutral (simple random birth-death models), competition (regulation of cell numbers through quorum-sensing, perhaps via limiting shared resources), adaptation (involving cell-intrinsic changes in homeostatic fitness, defined as net growth rate over time), or selection (involving the loss or outgrowth of cell populations deriving from intercellular variation in fitness). There may also be stably maintained heterogeneity within the naive T-cell pool. To distinguish between these mechanisms, we confront very general models of these processes with an array of experimental data, both new and published. While reduced competition for homeostatic stimuli may impact cell survival or proliferation in neonates or under moderate to severe lymphopenia, we show that the only mechanism capable of explaining multiple, independent experimental studies of naive CD4+ and CD8+ T-cell homeostasis in mice from young adulthood into old age is one of adaptation, in which cells act independently and accrue a survival or proliferative advantage continuously with their post-thymic age. However, aged naive T cells may also be functionally impaired, and so the accumulation of older cells via 'conditioning through experience' may contribute to reduced immune responsiveness in the elderly

High Speed Photodetectors

High speed photodetectors are important for a number of applications. This work is about accurate design of uni-travelling carrier photodetectors. In particular, integrated devices with antenna for operating frequencies above 100 GHz

Photodiodes for Terahertz Applications

Terahertz generation using high-speed photodiodes has found commercial application in many areas ranging across spectroscopy, imaging and communications. In this paper we discuss the optimization of high-speed photodiodes in terms of bandwidth and output power. We identify some of the main limitations in the generation of high output power in the Terahertz frequency band. We present a modelling tool for the numerical evaluation of antenna coupled uni-travelling carrier photodiodes and experimental evaluation of the fabricated designs. We also present a thermal analysis of the photodiodes alongside pulsed measurements of the output power saturation

Ultra-high-resolution software-defined photonic terahertz spectroscopy

A novel technique for high-resolution 1.5 µm photonics-enabled terahertz (THz) spectroscopy using software control of the illumination spectral line shape (SLS) is presented. The technique enhances the performance of a continuous-wave THz spectrometer to reveal previously inaccessible details of closely spaced spectral peaks. We demonstrate the technique by performing spectroscopy on LiYF4:Ho3+, a material of interest for quantum science and technology, where we discriminate between inhomogeneous Gaussian and homogeneous Lorentzian contributions to absorption lines near 0.2 THz. Ultra-high-resolution (<100 Hz full-width at half maximum) frequency-domain spectroscopy with quality factor Q > 2 × 109 is achieved using an exact frequency spacing comb source in the optical communications band, with a custom uni-traveling-carrier photodiode mixer and coherent down-conversion detection. Software-defined time-domain modulation of one of the comb lines is demonstrated and used to resolve the sample SLS and to obtain a magnetic field-free readout of the electronuclear spectrum for the Ho3+ ions in LiYF4:Ho3+. In particular, homogeneous and inhomogeneous contributions to the spectrum are readily separated. The experiment reveals previously unmeasured information regarding the hyperfine structure of the first excited state in the 5 I8 manifold complementing the results reported in Phys. Rev. B 94, 205132 (2016)

InP Photonic Integrated Circuit for 6.7GHz Spaced Optical Frequency Comb Generator

We have demonstrated a novel approach to photonically integrated optical frequency comb generation on Indium Phosphide (InP) using generic foundry platforms. The optical comb utilized a recirculating loop technique to generate 59 comb lines (within a 20 dB power envelope) which are separated by 6.7 GHz frequency spacing. All comb lines exhibit strong phase coherence as characterized by low phase noise measurements of -105 dBc/Hz at 100 kHz. The choice of InP as an integration platform allowed for an immediate optical amplification of the modulated sideband tones. This approach reduced the requirement for external high-power RF amplifiers and therefore made the entire system more compact and power efficient. The amplified recirculating loop comb occupied 6 x 0.7 mm2 area of InP chip and consisted of electro-optic phase modulator (EOPM) and semiconductor optical amplifier (SOA) components embedded within a short (12 mm long) waveguide loop, such that the round-trip loop frequency corresponding to the loop optical length equated to 6.7 GHz. Modulation frequencies equal to the round-trip loop frequency were used to generate broad comb spans

A Photonics Enabled Millimetre Wave Frequency Domain Spectrometer for Glucose Concentration Sensing

This study reports the experimental demonstration of a free space frequency domain self-heterodyne spectrometer utilising a high-speed Uni- Travelling Carrier photodiode (UTC-PD) as a coherent receiver. The transmission signal through the glucose solution was measured in the V-band (50 - 75 GHz) frequency range with a frequency resolution step of 40 MHz. Variations in glucose concentrations of as small as 1 % weight were resolved

Antenna integrated THz uni-travelling carrier photodiodes (Invited Paper)

High speed photodiodes are a key element of numerous photonic systems. With the development of potential applications in the THz range such as sensing, spectroscopy and wireless transmission, devices with integrated antenna covering the frequency range from 0.1 THz to 3 THz will become essential. In this paper we discuss the development of uni-travelling carrier photodiodes with integrated antennas to address that need. In particular we develop the key elements to present a simple design tool for the efficient integration of the device with an antenna. We also present fabricated device results that show the highest figure of merit to date for photonic THz emitters. When integrated with well-matched antennas the devices have achieved record level of power up to 1 THz compared to other published photomixers

Toward a conceptual framework of the acceptability of tuberculosis treatment in children using a theory generative approach

To describe an early-stage holistic framework towards evaluating factors that impact the overall acceptability of TB treatment along the TB care cascade in children. We developed a conceptual framework utilising a theory generative approach. Domains were developed through review of existing definitions and analysis of existing qualitative data undertaken in acceptability studies of TB treatment in children. Clarity of domain definitions was achieved through iterative refinement among the research team. Three domains, each comprising several dimensions, were identified to holistically evaluate treatment acceptability: (1) usability, which involves the alignment between the requirements of treatment use and caregivers’ and children’s ability to integrate TB treatment into their everyday routines, (2) receptivity, which describes the end-user’s perception and expectations of treatment and its actual use, and (3) integration, which describes the relationship between available health services and caregivers/children’s capacity to make use of those services. Our framework addresses the gaps in current research which do not account for the influence of caregivers’ and children’s contexts on TB treatment uptake and overall acceptability. This approach may support the development of more standard, holistic measures to improve TB treatment delivery and experiences and future research in children