Continuous-wave room-temperature diamond maser

The maser, older sibling of the laser, has been confined to relative obscurity due to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this it has found application in deep-space communications and radio astronomy due to its unparalleled performance as a low-noise amplifier and oscillator. The recent demonstration of a room-temperature solid- state maser exploiting photo-excited triplet states in organic pentacene molecules paves the way for a new class of maser that could find applications in medicine, security and sensing, taking advantage of its sensitivity and low noise. However, to date, only pulsed operation has been observed in this system. Furthermore, organic maser molecules have poor thermal and mechanical properties, and their triplet sub-level decay rates make continuous emission challenging: alternative materials are therefore required. Therefore, inorganic materials containing spin-defects such as diamond and silicon carbide have been proposed. Here we report a continuous-wave (CW) room-temperature maser oscillator using optically pumped charged nitrogen-vacancy (NV) defect centres in diamond. This demonstration unlocks the potential of room-temperature solid-state masers for use in a new generation of microwave devices.Comment: 7 pages, 4 figure

Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3

Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed

Measurements of permittivity, dieletric loss tangent, and resistivity of float-zone silicon at microwave frequencies

Published versio

The neutral silicon-vacancy center in diamond: spin polarization and lifetimes

We demonstrate optical spin polarization of the neutrally-charged silicon-vacancy defect in diamond ($\mathrm{SiV^{0}}$), an $S=1$ defect which emits with a zero-phonon line at 946 nm. The spin polarization is found to be most efficient under resonant excitation, but non-zero at below-resonant energies. We measure an ensemble spin coherence time $T_2>100~\mathrm{\mu s}$ at low-temperature, and a spin relaxation limit of $T_1>25~\mathrm{s}$. Optical spin state initialization around 946 nm allows independent initialization of $\mathrm{SiV^{0}}$ and $\mathrm{NV^{-}}$ within the same optically-addressed volume, and $\mathrm{SiV^{0}}$ emits within the telecoms downconversion band to 1550 nm: when combined with its high Debye-Waller factor, our initial results suggest that $\mathrm{SiV^{0}}$ is a promising candidate for a long-range quantum communication technology

All-Inorganic Spin-Cast Nanoparticle Solar Cells with Non-Selective Electrodes

Spin-cast all-inorganic nanoparticle solutions have been used to make a CdTe/CdSe solar cell with an efficiency of up to 2.8% without alumina or calcium buffer layers. The type of junction and non-selective nature of the contacts made to these devices is explored

Reconstructing palaeoclimate and hydrological fluctuations in the Fezzan Basin (southern Libya) since 130 ka: a catchment-based approach

We propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the problems caused by the discontinuous nature of palaeoenvironmental data found in deserts. The technique involves processing satellite imagery and DEM’s to map past rivers, catchments and evaluate the areas and volumes of palaeolakes. This information is used to determine the new Lake Evaluation Index (LEI) that allows a qualitative estimate of the amount of sediment received by lakes and how long-lived those lakes are. Lakes with considerable longevity and large sediment stores are selected for study. Validation is performed using image interpretation of remote sensing data, UltraGPR surveys and fieldwork. These techniques are also used to identify and study spring deposits and fluvial landforms that provide valuable palaeoclimate information. The method is applied to the Fezzan Basin in southern Libya focusing on the Wadi ash Shati and Wadi el-Agial catchments. Results indicate that the palaeohydrology is accurately mapped except within dune fields. We analysed the sedimentology of the key deposits identified by this methodology, developing a chronology using optically stimulated luminescence (OSL) and radiocarbon dating. We find evidence for relatively humid conditions during MIS 5c/d and e, as well as during the early to middle Holocene. Larger lakes and more extensive river systems were present during MIS 5 than are found during the Holocene, suggestive of greater humidity. The Holocene humid period started at ~11 ka and continued until ~5 ka being interrupted by abrupt periods of aridity at ~8.2 ka and ~6 ka that coincide with North Atlantic cooling. After each of these arid events the climate was less humid than previously, suggesting that they were superimposed upon an overall drying trend. The termination of the Holocene humid period in the Sahara has received much scrutiny in recent years, and sediments of Palaeolake Shati provide a continuous record of this. We do not find evidence to support the hypothesis of either sudden or gradual aridification of the Sahara at ~5 ka, instead we find that that aridity started to develop at ~6.5 ka, whereupon the lake levels oscillated until finally drying-up by 5.3 ka. Most of the other lakes in the Fezzan also dried up at ~ 5ka. We suggest that thousands of years of aridification prior to 5 ka shrunk these lakes so that additional aridity at this time led to their final desiccation. Because lakes are prodigious dust sources this mechanism potentially explains the rapid rise in dust flux to the Atlantic at 5 ka, with this final drying being the culmination of longer term aridity, albeit overprinted with considerable climate variability

SPHR Diabetes Prevention Model: Detailed Description of Model Background, Methods, Assumptions and Parameters

Type-2 diabetes is a complex disease with multiple risk factors and health consequences whose prevention is a major public health priority. We have developed a microsimulation model written in the R programming language that can evaluate the effectiveness and cost-effectiveness of a comprehensive range of different diabetes prevention interventions, either in the general population or in subgroups at high risk of diabetes. Within the model individual patients with different risk factors for diabetes follow metabolic trajectories (for body mass index, cholesterol, systolic blood pressure and glycaemia), develop diabetes, complications of diabetes and related disorders including cardiovascular disease and cancer, and eventually die. Lifetime costs and quality-adjusted life-years are collected for each patient. The model allows assessment of the wider social impact on employment and the equity impact of different interventions. Interventions may be population-based, community-based or individually targeted, and administered singly or layered together. The model is fully enabled for probabilistic sensitivity analysis (PSA) to provide an estimate of decision uncertainty. This discussion paper provides a detailed description of the model background, methods and assumptions, together with details of all parameters used in the model, their sources and distributions for PSA

Impact of Type 2 diabetes prevention programmes based on risk identification and lifestyle intervention intensity strategies: a cost-effectiveness analysis

Aim To develop a cost-effectiveness model to compare Type 2 diabetes prevention programmes that target different at-risk population subgroups through lifestyle interventions of varying intensity. Methods An individual patient simulation model simulated the development of diabetes in a representative sample of adults without diabetes from the UK population. The model incorporates trajectories for HbA1c, 2-h glucose, fasting plasma glucose, BMI, systolic blood pressure, total cholesterol and HDL cholesterol. In the model, patients can be diagnosed with diabetes, cardiovascular disease, microvascular complications of diabetes, cancer, osteoarthritis and depression, or can die. The model collects costs and utilities over a lifetime horizon. The perspective is the UK National Health Service and Personal Social Services. We used the model to evaluate the population-wide impact of targeting a lifestyle intervention of varying intensity to six population subgroups defined as at high risk for diabetes. Results The intervention produces 0.0020 to 0.0026 incremental quality-adjusted life-years and saves £15 to £23 per person in the general population, depending on the subgroup targeted. Cost-effectiveness increases with intervention intensity. The most cost-effective options were to target South-Asian people and those with HbA1c levels > 42 mmol/mol (6%). Conclusion The model indicates that diabetes prevention interventions are likely to be cost-saving. The criteria for selecting at-risk individuals differentially has an impact on diabetes and cardiovascular disease outcomes, and on the timing of costs and benefits. The model is not currently able to account for potential differential uptake or efficacy between subgroups. These findings have implications for deciding who should be targeted for diabetes prevention interventions.NIH