Low light level charge coupled devices (L3CCDs) have recently been developed, incorporating on-chip gain. They may be operated to give an effective readout noise much less than one electron by implementing an on-chip gain process allowing the detection of individual photons. However, the gain mechanism is stochastic and so introduces significant extra noise into the system. In this paper we examine how best to process the output signal from an L3CCD so as to minimize the contribution of stochastic noise, while still maintaining photometric accuracy. 
We achieve this by optimising a transfer function which translates the digitised output signal levels from the L3CCD into a value approximating the photon input as closely as possible by applying thresholding techniques. We identify several thresholding strategies and quantify their impact on photon counting accuracy and effective signal-to-noise. 
We find that it is possible to eliminate the noise introduced by the gain process at the lowest light levels. Reduced improvements are achieved as the light level increases up to about twenty photons per pixel and above this there is negligible improvement. Operating L3CCDs at very high speeds will keep the photon flux low, giving the best improvements in signal-to-noise ratio.

https://arxiv.org/pdf/astro-ph/0307305.pdf

Photon counting strategies with low light level CCDs

LET this, from Meredith, be my reply to the electrician in my composite friend Sir Oliver Lodge (NATURE, March 27, p. 453).

What We Know

Cutting-edge biophysical technologies including total internal reflection fluorescence microscopy, single molecule fluorescence, single channel opening events, fluorescence resonance energy transfer, high-speed exposures, two-photon imaging, fluorescence lifetime imaging, and other tools are becoming increasingly important in immunology as they link molecular events to cellular physiology, a key goal of modern immunology. The primary concern in all forms of microscopy is the generation of contrast; for fluorescence microscopy contrast can be thought of as the difference in intensity between the cell and background, the signal-to-noise ratio. High information-content images can be formed by enhancing the signal, suppressing the noise, or both. As improved tools, such as ICCD and EMCCD cameras, become available for fluorescence imaging in molecular and cellular immunology, it is important to optimize other aspects of the imaging system. Numerous practical strategies to enhance fluorescence microscopy experiments are reviewed. The use of instrumentation such as light traps, cameras, objectives, improved fluorescent labels, and image filtration routines applicable to low light level experiments are discussed. New methodologies providing resolution well beyond that given by the Rayleigh criterion are outlined. Ongoing and future developments in fluorescence microscopy instrumentation and technique are reviewed. This review is intended to address situations where the signal is weak, which is important for emerging techniques stressing super-resolution or live cell dynamics, but is less important for conventional applications such as indirect immunofluorescence. This review provides a broad integrative discussion of fluorescence microscopy with selected applications in immunology. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc.

/pdf/fluorescence-microscopy-established-and-emerging-methods-2pj8hqk0zf.pdf

Fluorescence microscopy: established and emerging methods, experimental strategies, and applications in immunology.

Given the continued burden of COVID-19 worldwide, there is a high unmet need for data on the effect of social distancing and face mask use to mitigate the risk of COVID-19. We examined the association of community-level social distancing measures and individual face mask use with risk of predicted COVID-19 in a large prospective U.S. cohort study of 198,077 participants. Individuals living in communities with the greatest social distancing had a 31% lower risk of predicted COVID-19 compared with those living in communities with poor social distancing. Self-reported 'always' use of face mask was associated with a 62% reduced risk of predicted COVID-19 even among individuals living in a community with poor social distancing. These findings provide support for the efficacy of mask-wearing even in settings of poor social distancing in reducing COVID-19 transmission. Despite mass vaccination campaigns in many parts of the world, continued efforts at social distancing and face mask use remain critically important in reducing the spread of COVID-19.

/pdf/association-of-social-distancing-and-face-mask-use-with-risk-2xxezvf7w2.pdf

Association of social distancing and face mask use with risk of COVID-19.

From 2002 to 2019, three deadly human coronaviruses (hCoVs), severe acute respiratory syndrome coronavirus (SARS-CoV), Middle Eastern respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) emerged to produce outbreaks of SARS, MERS and coronavirus disease 2019 (Covid-19), respectively. All three hCoVs are members of the Betacoronavirus genus in the subfamily Orthocoronavirinae and share many similarities in virology and epidemiology. However, the pattern and scale of Covid-19 global spread is similar to 2009 pandemic H1N1 influenza (H1N1pdm09), rather than SARS or MERS. Covid-19 exhibits high viral shedding in the upper respiratory tract at an early stage of infection, and has a high proportion of transmission competent individuals that are pre-symptomatic, asymptomatic and mildly symptomatic, characteristics seen in H1N1pdm09 but not in SARS or MERS. These two traits of Covid-19 and H1N1pdm09 result in reduced efficiency in identification of transmission sources by symptomatic screening and play important roles in their ability to spread unchecked to cause pandemics. To overcome these attributes of Covid-19 in community transmission, identifying the transmission source by testing for virus shedding and interrupting chains of transmission by social distancing and public masking are required.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/rmv.2171

The unique features of SARS-CoV-2 transmission: Comparison with SARS-CoV, MERS-CoV and 2009 H1N1 pandemic influenza virus

Electron Multiplying Charge Coupled Devices (EMCCDs) are CCD cameras with potentially single-photon detection ability. Signal amplification is achieved by way of a unique electron-multiplying structure built into the silicon, and the gain can be varied in order to overcome the read-noise floor, which is the usual limiting factor in reading out a conventional CCD at high frame rates. In combination with its high quantum efficiencies, the EMCCD holds great promise for time-resolved photometry. We report here results from two observing campaigns aimed at assessing the suitability of EMCCD technology for detecting short-timescale, low-amplitude variability in blazars. Data were taken on the 2.2m telescope at Calar Alto using both front-illuminated and back-illuminated EMCCD cameras from Andor Technology’s iXon range. Approximately 410,000 science frames were recorded over 10 nights. The results presented here illustrate the photometric stability achieved with the cameras, under typical observing conditions. In general, photometric precision down to the level of a few millimagnitudes is found to be possible. We argue that reliable photometry is best achieved with high data collection rates (typically 4 frames per second) coupled to ultra-low-noise detectors such as the EMCCD.

EMCCD technology and its impact on rapid low-light photometry

Aim: Face masks are an important addition to our arsenal in the fight against COVID-19. The aim of this study is to present a novel method of measuring mask performance which can simultaneously assess both fabric penetration and leakage due to poor fit. Materials & methods: A synthetic aerosol is introduced into the lung of a medical dummy. A conical laser sheet surrounds the face of the dummy where it illuminates the aerosol emitted during a simulated breath. The system is demonstrated with five mask types. Conclusions: The curved laser sheet highlights both penetration through the mask fabric and leakage around the edges of the mask. A large variation in both material penetration and leakage was observed.

COVID-19: mask efficacy is dependent on both fabric and fit.

Roy D Sleator*,1 , Steven Darby2, Alan Giltinan3 & Niall Smith3 1Department of Biological Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland 2Centre for Advanced Photonics & Process Analysis, Cork Institute of Technology, Bishopstown, Cork, Ireland 3Blackrock Castle Observatory, Cork Institute of Technology, Bishopstown, Cork, Ireland *Author for correspondence: Tel.: +353 214 335 405; roy.sleator@cit.ie

/pdf/covid-19-in-the-absence-of-vaccination-mask-the-nation-5gsr42qvdj.pdf

COVID-19: in the absence of vaccination - 'mask the nation'.

We discuss the advantages and limitations of Electron Multiplying CCD technology in high precision photometry on short timescales, with special emphasis on probing the smallest structures in active galactic jets. Factors external to the EMCCD, rather than the architecture of the EMCCD itself, most often limit the precision of photometry that can be reached with groundbased observations. Although EMCCDs can be used in photon-counting mode, reliable photometry can still only be achieved when careful observing procedures are employed. Observations of a small sample of blazars taken with an EMCCD are briefly discussed. An innovative two-colour photometer, based on simultaneous observations with two EMCCDs is described and the science drivers are discussed. Novel opportunities for the use of EMCCDs in lucky photometry are outlined and it is clear that certain scientific questions cannot be addressed with groundbased observations taken with conventional CCDs.

EMCCD Technology in High Precision Photometry on Short Timescales

We report on a novel data reduction technique that uses the fast, low-noise operation of EMCCD's to provide improvements in ground-based astronomical photometry of up to 48% by removing much of the incoherent wavelength-dependent absorption of the atmosphere. The technique has significant application potential in multicolour photometry where inter-colour short-timescale variability are particularly prone to atmospheric effects. We comment on a two-colour photometer we have developed to take advantage of the technique.

https://iopscience.iop.org/article/10.1088/1742-6596/307/1/012010/pdf

Alan Giltinan

Papers

EMCCD technology and its impact on rapid low-light photometry

COVID-19: mask efficacy is dependent on both fabric and fit.

COVID-19: in the absence of vaccination - 'mask the nation'.

EMCCD Technology in High Precision Photometry on Short Timescales

Using EMCCD's to improve the photometric precision of ground-based astronomical observations