Hume's Correlationism: On Meillassoux, Necessity and Belief

The article argues that Meillassoux's 'After Finitude' underestimates the nature and profundity of Hume's sceptical challenge; it neglects the fact that Hume's scepticism concerns final causes (and agrees fundamentally with Bacon and Descartes in this respect), and that in Hume even the operations of reason do not furnish entirely a priori knowledge. We contend that Hume himself institutes a form of correlationism (which in part showed Kant the way to counter the sceptical challenge via transcendental idealism), and sought not merely to abolish the 'principle of sufficient reason' but to salvage it in a weak form, in turning his attention to the grounds for our beliefs in necessity. We argue further that the 'mathematizability' of properties is not a sufficient criterion to yield realist, non-correlational knowledge, or to demonstrate the 'irremediable realism' of the 'ancestral' statement. Finally, we contend that Meillassoux himself relies on a certain 'Kantian moment' which exempts the reasoning subject from otherwise 'omnipotent' chaos, and that ultimately the 'speculative materialist' position remains exposed to the original Humean sceptical challenge.

Measuring daylight:a review of dosimetry in daylight photodynamic therapy

Successful daylight photodynamic therapy (DPDT) relies on the interaction of light, photosensitisers and oxygen. Therefore, the ‘dose’ of light that a patient receives during treatment is a clinically relevant quantity, with a minimum dose for effective treatment recommended in the literature. However, there are many different light measurement methods used in the published literature, which may lead to confusion surrounding reliable and traceable dose measurement in DPDT, and what the most appropriate method of light measurement in DPDT might be. Furthermore, for the majority of practitioners who do not carry out any formal dosimetry and for the patients receiving DPDT, building confidence in the evidence supporting this important treatment option is of key importance. This review seeks to clarify the methodology of DPDT and discusses the literature relating to DPDT dosimetry

Potential harm to the skin from unfiltered krypton-chloride “Far-UVC”lamps, even below an occupational exposure limit

Ultraviolet-C (UVC) radiation can effectively inactivate pathogens on surfaces and in the air. Due to the potential for harm to skin and eyes, human exposure to UVC should be limited within the guideline exposure limits produced by the International Commission on Non-Ionising Radiation Protection (ICNIRP) or the American Conference of Governmental Industrial Hygienists (ACGIHs). Both organisations state an effective spectrally weighted limit of 3 mJ cm−2, although the spectral weighting factors of the two organisations diverged following a revision of the ACGIH guidelines in 2022. Using existing published human exposure data, the effective spectrally weighted radiant exposure was calculated for both unfiltered and filtered (to reduce UV emissions above 230 nm) krypton chloride (KrCl*) excimer lamps. The effective radiant exposure of the filtered KrCl* lamp was greater than 3 mJ cm−2 when applying ICNIRP or either of the revised ACGIH spectral weightings. This indicates that both guidelines are appropriately conservative for this specific lamp. However, the effective radiant exposure of the unfiltered KrCl* lamp was as low as 1 mJ cm−2 with the revised ACGIH weighting function that can be applied to the skin if the eyes are protected. Erythema has therefore been directly observed in a clinical study at an exposure within the revised ACGIH guideline limits. Extrapolating this information means that a mild sunburn could be induced in Fitzpatrick skin types I and II if that particular ACGIH weighting function were applied and an individual received an effective exposure of 3 mJ cm−2. Whilst it is improbable that such an effect would be seen in current deployment of KrCl* lamp technology, it does highlight the need for further research into skin sensitivity and irradiance–time reciprocity for UVC wavelengths.Publisher PDFPeer reviewe

A novel light source with tuneable uniformity of light distribution for artificial daylight photodynamic therapy

This project was supported by the University of St. Andrews through the Science and Technology Facilities Council (STFC) Impact Accelerator Award (IAA) and by the Laser Research and Therapy Fund (registered charity SC030850). P O’M is funded by Medi-lase (registered charity SC 037390) and the Alfred Stewart Trust.Objectives: Implementation of daylight photodynamic therapy (dPDT) is somewhat limited by variable weather conditions. Light sources have been employed to provide artificial dPDT indoors, with low irradiances and longer treatment times. Uniform light distribution across the target area is key to ensuring effective treatment, particularly for large areas. A novel light source is developed with tuneable direction of light emission in order to meet this challenge. Methods: Wavelength composition of the novel light source is controlled such that the protoporphyrin-IX (PpIX) weighed spectra of both the light source and daylight match. The uniformity of the light source is characterised on a flat surface, a model head and a model leg. For context, a typical conventional PDT light source is also characterised. Additionally, the wavelength uniformity across the treatment site is characterised. Results: The PpIX-weighted spectrum of the novel light source matches with PpIX-weighted daylight spectrum, with irradiance values within the bounds for effective dPDT. By tuning the direction of light emission, improvements are seen in the uniformity across large anatomical surfaces. Wavelength uniformity is discussed. Conclusions: We have developed a light source that addresses the challenges in uniform, multiwavelength light distribution for large area artificial dPDT across curved anatomical surfaces.PostprintPeer reviewe

Computer Modeling Indicates Dramatically Less DNA Damage from Far-UVC Krypton Chloride Lamps (222 nm) than from Sunlight Exposure

Funding: Dr Paul O’Mahoney is funded by Medi-lase (registered charity SC037390) and the Alfred Stewart Trust. Dr Isla Barnard acknowledges financial support from an UK EPRSC PhD studentship (EP/N509759/1) and Louise Finlayson acknowledges financial support from EPSRC Industrial Doctorate Centre Scheme (2262922) and the Laser Research and Therapy Fund (registered charity SC030850).This study aims to investigate, with computer modeling, the DNA damage (assessed by cyclobutane pyrimidine dimer (CPD) formation) from far-ultraviolet C (far-UVC) in comparison with sunlight exposure in both a temperate (Harwell, England) and Mediterranean (Thessaloniki, Greece) climate. The research utilizes the published results from Barnard et al. [Barnard, I.R.M (2020) Photodermatol. Photoimmunol. Photomed. 36, 476?477] to determine the relative CPD yield of unfiltered and filtered far-UVC and sunlight exposure. Under current American Conference of Governmental Industrial Hygienists (ACGIH) exposure limits, 10 minutes of sunlight at an ultraviolet (UV) Index of 4 ? typical throughout the day in a temperate climate from Spring to Autumn - produces equivalent numbers of CPD as 700 hours of unfiltered far-UVC or more than 30,000 hours of filtered far-UVC at the basal layer. At the top of the epidermis these values are reduced to 30 and 300 hours respectively. In terms of DNA damage induction, as assessed by CPD formation, the risk from sunlight exposure greatly exceeds the risk from far-UVC. However the photochemistry that will occur in the stratum corneum from absorption of the vast majority of the high energy far-UVC photons is unknown, as are the consequences.Publisher PDFPeer reviewe