Absorption-based hyperspectral thermal ranging: performance analyses, optimization, and simulations.

The wavelength dependence of atmospheric absorption creates range cues in hyperspectral measurements that can be exploited for passive ranging using only thermal emissions. In this work, we present fundamental limits on absorption-based ranging under a model of known air temperature and wavelength-dependent attenuation coefficient, with object temperature and emissivity unknown; reflected solar and environmental radiance is omitted from our analysis. Fisher information computations illustrate how performance limits depend on atmospheric conditions such as air temperature and humidity; temperature contrast in the scene; spectral resolution of measurement; and distance. These results should prove valuable in sensor system design.

Experimentally generated randomness certified by the impossibility of superluminal signals.

From dice to modern electronic circuits, there have been many attempts to build better devices to generate random numbers. Randomness is fundamental to security and cryptographic systems and to safeguarding privacy. A key challenge with random-number generators is that it is hard to ensure that their outputs are unpredictable1-3. For a random-number generator based on a physical process, such as a noisy classical system or an elementary quantum measurement, a detailed model that describes the underlying physics is necessary to assert unpredictability. Imperfections in the model compromise the integrity of the device. However, it is possible to exploit the phenomenon of quantum non-locality with a loophole-free Bell test to build a random-number generator that can produce output that is unpredictable to any adversary that is limited only by general physical principles, such as special relativity1-11. With recent technological developments, it is now possible to carry out such a loophole-free Bell test12-14,22. Here we present certified randomness obtained from a photonic Bell experiment and extract 1,024 random bits that are uniformly distributed to within 10-12. These random bits could not have been predicted according to any physical theory that prohibits faster-than-light (superluminal) signalling and that allows independent measurement choices. To certify and quantify the randomness, we describe a protocol that is optimized for devices that are characterized by a low per-trial violation of Bell inequalities. Future random-number generators based on loophole-free Bell tests may have a role in increasing the security and trust of our cryptographic systems and infrastructure.

Recent UK retirees' views about the work-related factors which influenced their decision to retire: a qualitative study within the Health and Employment After Fifty (HEAF) cohort.

BACKGROUND: Lower birth rates and increasing longevity have resulted in ageing populations in European countries. These demographic changes place challenges on pension provision as numbers of those who are economically inactive and retired increase relative to those in paid work. Therefore, governments need workers to postpone retirement and work to older ages. Whilst health and wealth are important in retirement decision-making, considerably less is known about the effects of workplace factors. The aim of this study was to explore the views of recent UK retirees about the role that work-related factors played in their decision to retire. METHODS: This qualitative study was nested within the Health and Employment After Fifty (HEAF) cohort. People who had retired 3-6 years previously (not for health reasons) were purposively sampled to obtain the views of men and women from a range of socio-economic backgrounds and jobs. Semi-structured interviews were carried out by telephone using a pre-defined topic guide. Interviews were audio-recorded, transcribed and analysed thematically. RESULTS: Seventeen interviews were conducted. Thematic analysis showed that retirement decisions were complex and multi-factorial but that work-related factors contributed to decision-making in two main ways. First, some work factors pushed participants towards retirement. These were perceptions that: workplace change had affected the way they were valued or increased pressure on them; work demands, including commuting, had intruded excessively on personal time, effects that were exacerbated by modern technology; work was draining, isolating or under-appreciated; and /or that work was causing physical strain or discomfort relative to their perception of their capacity. In contrast, work factors could also cause participants to pull back towards work, particularly: autonomy; supportive work colleagues; a sense of being appreciated; and perceived job flexibility. CONCLUSIONS: Recent retirees explained that their decision to retire was multi-factorial but work-related factors contributed importantly. Potentially, employers could: review workers' perceptions about their work; their capacity in relation to job demands; increase flexibility; and facilitate a supportive work community to encourage longer working lives.

Experimental Low-Latency Device-Independent Quantum Randomness.

Applications of randomness such as private key generation and public randomness beacons require small blocks of certified random bits on demand. Device-independent quantum random number generators can produce such random bits, but existing quantum-proof protocols and loophole-free implementations suffer from high latency, requiring many hours to produce any random bits. We demonstrate device-independent quantum randomness generation from a loophole-free Bell test with a more efficient quantum-proof protocol, obtaining multiple blocks of 512 random bits with an average experiment time of less than 5 min per block and with a certified error bounded by 2^{-64}≈5.42×10^{-20}.

Mid-infrared Laser-Induced Fluorescence with Nanosecond Time Resolution Using a Superconducting Nanowire Single-Photon Detector: New Technology for Molecular Science.

In contrast to UV photomultiplier tubes that are widely used in physical chemistry, mid-infrared detectors are notorious for poor sensitivity and slow time response. This helps explain why, despite the importance of infrared spectroscopy in molecular science, mid-infrared fluorescence is not more widely used. In recent years, several new technologies have been developed that open new experimental possibilities for research in the mid-infrared. In this Account, we present one of the more promising technologies, superconducting nanowire single photon detectors (SNSPDs) by sharing our experience with its use in a typical experiment carried out by physical chemists (laser-induced fluorescence) and comparing the SNSPD to a detector commonly used by physical chemists (InSb at LN Temperature). SNSPDs are fabricated from a thin film of superconducting metal, patterned into a meandering nanowire. The nanowire is cooled below its superconducting temperature, Tc, and held in a constant current circuit below the critical current necessary to destroy superconductivity, Ic. Upon absorption of a photon, the resulting heat is sufficient to destroy superconductivity across the entire width of the nanowire, an event that can be detected as a voltage pulse. In contrast to semiconductor-based detectors, which have a long wavelength cutoff determined by the band gap, the SNSPD exhibits single-photon sensitivity across the entire mid-IR spectrum. As these devices have not been used extensively outside the field of light detection technology research, one important goal of this Account is to provide practical details for the implementation of these devices in a physical chemistry laboratory. We provide extensive Supporting Information describing what is needed. This includes information on a liquid nitrogen cooled monochromator, the optical collection system including mid-infrared fibers, as well as a closed-cycle cryogenic cooler that reaches 0.3 K. We demonstrate the advantages of these detectors in a time-resolved laser-induced infrared fluorescence experiment on the energy pooling in crystalline CO overlayers formed on a NaCl(100) surface. We present dispersed fluorescence spectra recorded from 1.9 to 7.0 µm obtained by single-photon counting. We also estimate the sensitivity of this WSi-based detection system at 3 µm; the system's noise equivalent power (NEP) value is ∼10-3 of a conventional InSb photovoltaic device. Straightforward modifications are expected to provide another 100 000-fold improvement. We demonstrate that the temporal resolution of the experiment is limited only by the pulse duration of the laser used in this work (fwhm = 3.7 ns). The use of SNSPDs enables dramatically improved observations of energy pooling in cryogenic molecular crystals.

Ultra-sensitive mid-infrared emission spectrometer with sub-ns temporal resolution.

We evaluate the performance of a mid-infrared emission spectrometer operating at wavelengths between 1.5 and 6 µm based on an amorphous tungsten silicide (a-WSi) superconducting nanowire single-photon detector (SNSPD). We performed laser induced fluorescence spectroscopy of surface adsorbates with sub-monolayer sensitivity and sub-nanosecond temporal resolution. We discuss possible future improvements of the SNSPD-based infrared emission spectrometer and its potential applications in molecular science.

Strong Loophole-Free Test of Local Realism.

We present a loophole-free violation of local realism using entangled photon pairs. We ensure that all relevant events in our Bell test are spacelike separated by placing the parties far enough apart and by using fast random number generators and high-speed polarization measurements. A high-quality polarization-entangled source of photons, combined with high-efficiency, low-noise, single-photon detectors, allows us to make measurements without requiring any fair-sampling assumptions. Using a hypothesis test, we compute p values as small as 5.9×10^{-9} for our Bell violation while maintaining the spacelike separation of our events. We estimate the degree to which a local realistic system could predict our measurement choices. Accounting for this predictability, our smallest adjusted p value is 2.3×10^{-7}. We therefore reject the hypothesis that local realism governs our experiment.

Cardiac autonomic neuropathy predicts renal function decline in patients with type 2 diabetes: a cohort study.

AIMS/HYPOTHESIS: The aim of this work was to assess the impact of cardiac autonomic neuropathy (CAN) on the development and progression of chronic kidney disease (CKD) in patients with type 2 diabetes. METHODS: We conducted a cohort study in adults with type 2 diabetes. Patients with end-stage renal disease were excluded. CKD was defined as the presence of albuminuria (albumin/creatinine ratio GFR > 3.4 mg/mmol) or an estimated (eGFR) < 60 ml min(-1) 1.73 m(-2). CKD progression was based on repeated eGFR measurements and/or the development of albuminuria. CAN was assessed using heart rate variability. RESULTS: Two hundred and four patients were included in the analysis. At baseline, the prevalence of CKD and CAN was 40% and 42%, respectively. Patients with CAN had lower eGFR and higher prevalence of albuminuria and CKD. Spectral analysis variables were independently associated with eGFR, albuminuria and CKD at baseline. After a follow-up of 2.5 years, eGFR declined to a greater extent in patients with CAN than in those without CAN (-9.0 ± 17.8% vs -3.3 ± 10.3%, p = 0.009). After adjustment for baseline eGFR and baseline differences, CAN remained an independent predictor of eGFR decline over the follow-up period (ß = -3.5, p = 0.03). Spectral analysis variables were also independent predictors of eGFR decline. CONCLUSIONS/INTERPRETATION: CAN was independently associated with CKD, albuminuria and eGFR in patients with type 2 diabetes. In addition, CAN was an independent predictor of the decline in eGFR over the follow-up period. CAN could be used to identify patients with type 2 diabetes who are at increased risk of rapid decline in eGFR, so that preventative therapies might be intensified.

Third-order antibunching from an imperfect single-photon source.

We measure second- and third-order temporal coherences, g((2))(τ) and g((3))(τ1,τ2), of an optically excited single-photon source: an InGaAs quantum dot in a microcavity pedestal. Increasing the optical excitation power leads to an increase in the measured count rate, and also an increase in multi-photon emission probability. We show that standard measurements of g((2)) provide limited information about this multi-photon probability, and that more information can be gained by simultaneously measuring g((3)). Experimental results are compared with a simple theoretical model to show that the observed antibunchings are consistent with an incoherent addition of two sources: 1) an ideal single-photon source that never emits multiple photons and 2) a background cavity emission having Poissonian photon number statistics. Spectrally resolved cross-correlation measurements between quantum-dot and cavity modes show that photons from these two sources are largely uncorrelated, further supporting the model. We also analyze the Hanbury Brown-Twiss interferometer implemented with two or three "click" detectors, and explore the conditions under which it can be used to accurately measure g((2))(τ) and g((3))(τ1,τ2).

Musculoskeletal pain affects the age of retirement and the risk of work cessation among older people.

OBJECTIVES: Many people with chronic pain cannot work, while working despite chronic pain is linked to absenteeism and presenteeism and a host of other deleterious effects. This disproportionately affects older adults, who are closer to retirement, while the exact relationship between pain and work cessation as well as retirement among older adults is not known. We explore longitudinally the relationship between chronic pain and the risk of ceasing work and entering retirement. METHODS: Data from 1156 individuals 50 years or older living in England taking part in the English Longitudinal Study of Ageing were used in this study. Cox proportional hazards regression analyses were used to examine the nature of the relationship between musculoskeletal pain and work cessation as well as retirement longitudinally over the course of fourteen years. RESULTS: Suffering from frequent musculoskeletal pain was associated with an increased risk of ceasing work and retiring at an earlier age, as did work dissatisfaction, higher perceived social status, female gender, and not receiving the recognition they felt they deserved in their job. Severity of depressive symptoms, psychosocial job demands, decision authority, and social support did not influence the age at which participants reported work cessation or retirement. CONCLUSIONS: Frequent musculoskeletal pain may increase the risk of earlier work exit and earlier retirement. Further research should establish the mechanisms and decision making involved in leaving the workforce in people with frequent musculoskeletal pain.

Do current methods of measuring the impact of chronic pain on work reflect the experience of working-age adults? An integrated mixed-methods systematic narrative review.

ABSTRACT: Chronic pain affects individuals' work participation. The impact of chronic pain on work has historically been measured through sickness absence, though it is now appreciated that the impacts on work are far wider. This mixed-methods review aimed to identify the full range of impacts of pain on work in addition to impacts that are currently measured quantitatively to inform the development of a new questionnaire assessing the wider impacts of chronic pain on work. MEDLINE, Embase, PsychINFO, and CINAHL were searched for studies that included quantitative measures of the impact of chronic pain on work and for qualitative studies where individuals described impacts of their chronic pain on work. Quantitative measures, and text from qualitative studies, were analysed thematically. A thematic framework was developed for establishing the types of impacts measured or described in the literature. Forty-four quantitative and 16 qualitative papers were identified. The literature described impacts within 5 areas: changes at work and to working status; aspects of the workplace and work relationships; pain and related symptoms at work; psychological factors; and factors and impacts outside the work environment related to work. Quantitative measures mainly assessed impacts related to the quantity and quality of work (29 of 42 measures). Seventeen aspects were only discussed within the qualitative literature. This study identifies a discrepancy between the impacts that have been the focus of quantitative measures and the range that individuals working with chronic pain experience and highlights the need for a new measure assessing a wider range of issues.

Obstructive sleep apnoea and diabetes: an update.

PURPOSE OF REVIEW: The relationship between obstructive sleep apnoea (OSA) and dysglycaemia is well established. However, uncertainty remains as to the extent that obesity mediates this relationship. The impact of OSA treatment on glucose metabolism and the consequences of having OSA in patients with diabetes is unclear. This review aims to summarize the latest evidence regarding the links between OSA and dysglycaemia. RECENT FINDINGS: OSA is associated with insulin resistance in lean individuals and predicts insulin resistance worsening longitudinally. Continuous positive airway pressure (CPAP) lowers insulin resistance in CPAP-compliant patients. OSA is associated with impaired ß-cell function. In patients with type 2 diabetes (T2D), the association between OSA and glycosylated haemoglobin (HbA1c) is related to nocturnal hypoxaemia. Apnoea hypopnoea index (AHI) during rapid eye movement (REM) (not non-REM) sleep is associated with HbA1c. In-laboratory, supervised CPAP improves glycaemia. OSA is associated with and predicts the progression of some diabetic vascular complications. Intensive lifestyle intervention in patients with T2D improves OSA independent of weight loss. SUMMARY: OSA is associated with insulin resistance and ß-cell dysfunction independent of obesity. OSA is associated with HbA1c and vascular complications in patients with T2D. CPAP might improve insulin resistance and glycaemic measures. Lifestyle intervention has a significant impact on AHI in patients with T2D.

Obstructive sleep apnea and diabetic neuropathy: a novel association in patients with type 2 diabetes.

RATIONALE: Diabetic peripheral neuropathy is common and causes significant morbidity. Obstructive sleep apnea (OSA) is also common in patients with type 2 diabetes. Because OSA is associated with inflammation and oxidative stress, we hypothesized that OSA is associated with peripheral neuropathy in type 2 diabetes. OBJECTIVES: To assess the relationship between OSA and peripheral neuropathy in patients with type 2 diabetes. METHODS: A cross-sectional study of adults with type 2 diabetes recruited randomly from the diabetes clinic of two UK hospitals. MEASUREMENTS AND MAIN RESULTS: Peripheral neuropathy was diagnosed using the Michigan Neuropathy Screening Instrument. OSA (apnea-hypopnea index ≥ 5 events/h) was assessed using home-based, multichannel respiratory monitoring. Serum nitrotyrosine was measured by ELISA, lipid peroxide by spectrophotometer, and microvascular function by laser speckle contrast imaging. Two hundred thirty-four patients (mean [SD] age, 57 [12] yr) were analyzed. OSA prevalence was 65% (median apnea-hypopnea index, 7.2; range, 0-93), 40% of which were moderate to severe. Neuropathy prevalence was higher in patients with OSA than those without (60% vs. 27%, P < 0.001). After adjustment for possible confounders, OSA remained independently associated with diabetic neuropathy (odds ratio, 2.82; 95% confidence interval, 1.44-5.52; P = 0.0034). Nitrotyrosine and lipid peroxide levels (n = 102, 74 with OSA) were higher in OSA and correlated with hypoxemia severity. Cutaneous microvascular function (n = 71, 47 with OSA) was impaired in OSA. CONCLUSIONS: We describe a novel independent association between diabetic peripheral neuropathy and OSA. We identified increased nitrosative/oxidative stress and impaired microvascular regulation as potential mechanisms. Prospective and interventional studies are needed to assess the impact of OSA and its treatment on peripheral neuropathy development and progression in patients with type 2 diabetes.

Occupational demands associated with rotator cuff disease surgery in the UK Biobank.

OBJECTIVES: Physically-demanding occupations may increase rotator cuff disease (RCD) risk and need for surgery. We linked a job-exposure matrix (JEM) to the UK Biobank cohort study to measure physical occupational exposures and estimate associations with RCD surgery. METHODS: Jobs and UK Standard Occupational Classification (SOC) codes were recorded during the UK Biobank verbal interview. Lifetime job histories were captured through a web-based survey. UK SOC codes were linked to a JEM based on the US O*NET database. O*NET-based scores [static strength, dynamic strength, general physical activities, handling/moving objects (range=1-7), time spent using hands, whole body vibration, and cramped/awkward positions (range=1-5)] were assigned to jobs. RCD surgeries were identified through linked national hospital inpatient records. Multivariable Cox regression was used to calculate hazard ratios (HR) as estimates of associations with RCD surgery. Among those with lifetime job histories, associations were estimated for duration of time with greatest exposure (top quartile of exposure). RESULTS: Of 277 808 people reporting jobs, 1997 (0.7%) had an inpatient RCD surgery. After adjusting for age, sex, race, education, area deprivation, and body mass index, all O*NET variables considered were associated with RCD surgery (HR per point increase range=1.10-1.45, all P<0.005). A total of 100 929 people reported lifetime job histories, in which greater exposures were significantly associated with RCD surgery after >10 years of work (eg, HR for 11-20 versus 0 years with static strength score ≥4 = 2.06, 95% confidence interval 1.39-3.04). CONCLUSIONS: Workplace physical demands are an important risk factor for RCD surgery, particularly for workers with more than a decade of exposure.

Hot-Band Absorption Can Mimic Entangled Two-Photon Absorption.

It has been proposed that entangled two-photon absorption (E2PA) can be observed with up to 1010 lower photon flux than its classical counterpart, therefore enabling ultralow-power two-photon fluorescence microscopy. However, there is a significant controversy regarding the magnitude of this quantum enhancement in excitation efficiency. We investigated the fluorescence signals from Rhodamine 6G and LDS798 excited with a CW laser or an entangled photon pair source at ∼1060 nm. We observed a signal that originates from hot-band absorption (HBA), which is one-photon absorption from thermally populated vibrational levels of the ground electronic state. This mechanism, which has not been previously discussed in the context of E2PA, produces a signal with a linear power dependence, as would be expected for E2PA. For the typical conditions under which E2PA measurements are performed, contributions from the HBA process could lead to a several orders of magnitude overestimate of the quantum advantage.

Temporal correlation of photons following frequency up-conversion.

We demonstrate an approach to measure temporal correlations of photons in the near infrared range using frequency up-conversion. In this approach, the near infrared signal photons are converted into the visible range, in which highly efficient silicon avalanche photodiodes are used to perform the temporal correlation measurements. A coherent light source and a pseudo-thermal light source were used in the experiment. The results are in agreement with theoretical values and those obtained from measurements directly made using superconducting nanowire single photon detectors. We conclude that the temporal correlation (up to 4th order) of photons was preserved in the frequency up-conversion process. We further theoretically and experimentally studied the influence of the dark counts on the measurement. The setup uses commercially available components and achieves high total detection efficiency (~26%).

Photon antibunching from a single lithographically defined InGaAs/GaAs quantum dot.

We demonstrate photon antibunching from a single lithographically defined quantum dot fabricated by electron beam lithography, wet chemical etching, and overgrowth of the barrier layers by metalorganic chemical vapor deposition. Measurement of the second-order autocorrelation function indicates g(2)(0)=0.395±0.030, below the 0.5 limit necessary for classification as a single photon source.

Generation of degenerate, factorizable, pulsed squeezed light at telecom wavelengths.

We characterize a periodically poled KTP crystal that produces an entangled, two-mode, squeezed state with orthogonal polarizations, nearly identical, factorizable frequency modes, and few photons in unwanted frequency modes. We focus the pump beam to create a nearly circular joint spectral probability distribution between the two modes. After disentangling the two modes, we observe Hong-Ou-Mandel interference with a raw (background corrected) visibility of 86% (95%) when an 8.6 nm bandwidth spectral filter is applied. We measure second order photon correlations of the entangled and disentangled squeezed states with both superconducting nanowire single-photon detectors and photon-number-resolving transition-edge sensors. Both methods agree and verify that the detected modes contain the desired photon number distributions.

Witnessing the survival of time-energy entanglement through biological tissue and scattering media.

We demonstrate the preservation of the time-energy entanglement of near-IR photons through thick biological media (≤1.55 mm) and tissue (≤ 235 µm) at room temperature. Using a Franson-type interferometer, we demonstrate interferometric contrast of over 0.9 in skim milk, 2% milk, and chicken tissue. This work supports the many proposed opportunities for nonclassical light in biological imaging and analyses from sub-shot noise measurements to entanglement-enhanced fluorescence imaging, clearly indicating that the entanglement characteristics of photons can be maintained even after propagation through thick, turbid biological samples.

Observation of transparency of Erbium-doped silicon nitride in photonic crystal nanobeam cavities.

One dimensional nanobeam photonic crystal cavities are fabricated in an Er-doped amorphous silicon nitride layer. Photoluminescence from the cavities around 1.54 microm is studied at cryogenic and room temperatures at different optical pump powers. The resonators demonstrate Purcell enhanced absorption and emission rates, also confirmed by time resolved measurements. Resonances exhibit linewidth narrowing with pump power, signifying absorption bleaching and the onset of stimulated emission in the material at both 5.5 K and room temperature. We estimate from the cavity linewidths that Er has been pumped to transparency at the cavity resonance wavelength.