Health benefits of the use of portable air purifiers that reduce exposure to PM2.5 in residences: The case of childhood asthma in London

Home air purifiers (HAPs), utilizing HEPA filtration as the primary mechanism of air cleaning aim to reduce particulate matter (PM) concentrations that are known to be harmful to health. In the work described here, PM2.5 concentrations were continuously monitored for 6 months inside and at the ground floor exterior of 18 flats in London. Median bedroom PM2.5 concentration of all flats was measured at 14 µg m-3 in the bedroom at the start of HAP operation. In the bedrooms where the HAP was in use, a clear decay curve was seen resulting in a 45% reduction of PM2.5 over 90 minutes of run time. Based upon these findings, and the published positive association between PM2.5 and asthma (OR = 1.28 per 3.2µg/m3 ), an estimated 1,361 additional QALYs per 10,000 children were achieved using HAPs in health impact models

Quantum Relaxation of Magnetisation in Magnetic Particles

At temperatures below the magnetic anisotropy energy, monodomain magnetic systems (small particles, nanomagnetic devices, etc.) must relax quantum mechanically. This quantum relaxation must be mediated by the coupling to both nuclear spins and phonons (and electrons if either particle or substrate is conducting. We analyze the effect of each of these couplings, and then combine them. Conducting systems can be modelled by a "giant Kondo" Hamiltonian, with nuclear spins added in as well. At low temperatures, even microscopic particles on a conducting substrate (containing only $10-50$ spins) will have their magnetisation frozen over millenia by a combination of electronic dissipation and the "degeneracy blocking" caused by nuclear spins. Raising the temperature leads to a sudden unblocking of the spin dynamics at a well defined temperature. Insulating systems are quite different. The relaxation is strongly enhanced by the coupling to nuclear spins. At short times the magnetisation of an ensemble of particles relaxes logarithmically in time, after an initial very fast decay; this relaxation proceeds entirely via the nuclear spins. At longer times phonons take over, but the decay rate is still governed by the temperature-dependent nuclear bias field acting on the particles - decay may be exponential or power-law depending on the temperature. The most surprising feature of the results is the pivotal role played by the nuclear spins. The results are relevant to any experiments on magnetic particles in which interparticle dipolar interactions are unimportant. They are also relevant to future magnetic device technology.Comment: 30 pages, RevTex, e:mail , Submitted to J.Low Temp.Phys. on 1 Nov. 199

Macroscopic Quantum Tunneling of a Domain Wall in a Ferromagnetic Metal

The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic metal is studied based on the Hubbard model. It is found that the ohmic dissipation is present even at zero temperature due to the gapless Stoner excitation, which is the crucial difference from the case of the insulating magnet. The dissipative effect is calculated as a function of width of the wall and is shown to be effective in a thin wall and in a weak ferromagnet. The results are discussed in the light of recent experiments on ferromagnets with strong anisotropy. PACS numbers:75.60.Ch, 03.65.Sq, 75.10.LpComment: 13page

Use of portable air purifiers in homes: Operating behaviour, effect on indoor PM2.5 and perceived indoor air quality

In much of the world, people spend on average 65% of their time indoors at home. It is, therefore, important to understand the quality of air in homes, and how best to improve it. Negative health impacts associated with exposure to particulate matter are well documented, and account for significant morbidity and mortality worldwide. Technologies are rapidly being developed and adopted to mitigate indoor air pollution, and portable home air purifiers (HAPs) are one of the most effective technologies available to clean the surrounding air of harmful pollutants of both indoor and outdoor origin. The aims of the research presented here were to explore the impact of a commercially available air purifier used in actual bedrooms on indoor PM2.5 concentrations and perceived indoor air quality, as well as to understand and describe how portable air purifiers are used by occupants. Results from the present study showed that PM2.5 concentrations in bedrooms were reduced by a mean of 45% over 90 min with HAP use. Participants’ subjective assessment of the indoor air when the HAP was on was positive. However, the predominant motivation and indicator of HAP use was thermal comfort, and not perceived air quality. If used properly, portable air purifiers used at home could be effective at reducing exposure to PM2.5 indoors

Sharp transition for single polarons in the one-dimensional Su-Schrieffer-Heeger model

We study a single polaron in the Su-Schrieffer-Heeger (SSH) model using four different techniques (three numerical and one analytical). Polarons show a smooth crossover from weak to strong coupling, as a function of the electron-phonon coupling strength $\lambda$, in all models where this coupling depends only on phonon momentum $q$. In the SSH model the coupling also depends on the electron momentum $k$; we find it has a sharp transition, at a critical coupling strength $\lambda_c$, between states with zero and nonzero momentum of the ground state. All other properties of the polaron are also singular at $\lambda = \lambda_c$, except the average number of phonons in the polaronic cloud. This result is representative of all polarons with coupling depending on $k$ and $q$, and will have important experimental consequences (eg., in ARPES and conductivity experiments)

Cross-sectoral assessment of the performance gap using calibrated building energy performance simulation

The energy performance gap in buildings is a well-known phenomenon. However, its actual definition and extent is dependent on the baseline used for defining the gap. In this paper a calibration-based methodology is used to identify and validate the root causes of the performance gap. Following analysis of the performance of four case studies in the UK, from different building sectors, cross sectoral learnings that are applicable in the wider industry context are uncovered. Through the model calibration process and in the overall performance assessment, Indoor Environmental Quality (IEQ) parameters have been used to improve the robustness of validation of the calibrated models and to highlight the interrelationship of energy and IEQ. The study shows the importance of contractual accountability to minimise performance issues, building a case for having IEQ in energy performance contracts to manage the trade-offs of IEQ against energy performance that leads to unintended health consequences for the occupants

What do we know about indoor air quality of nurseries? A review of the literature

Considering the alarming rise in the rate of asthma and respiratory diseases among school children, it is of great importance to investigate all probable causes. Outside of the home, children spend most of their time in school. Many studies have researched the indoor environmental quality of primary and secondary school buildings to determine the exposure of school children to indoor air pollution. However, studies of very young children in nurseries are scarce. Unlike at elementary schools or universities, children in nurseries are more vulnerable due to their physiology, inability to articulate discomfort and to adapt their behaviour to avoid exposures. This article reviews current studies on the indoor environment in nurseries. It summarizes air pollution levels and related environmental and behavioural factors in nurseries that have been reported in the literature. Additionally, exposure to indoor air pollution and related potential health outcomes are examined. This review concludes that indoor air pollution in nurseries often exceeds current guidelines, and designers and policymakers should be made aware of the impact on the health and wellbeing of children in nurseries. Proper interventions and guidelines should be considered to create a healthy indoor environment for nursery children. Practical application : Previous IAQ assessments have mainly focused on indoor temperatures and CO levels. Data on comprehensive monitoring (including PMs, NO , O and other pollutants) of indoor air quality of nurseries are scarce. Particularly in the UK, studies about indoor air quality in nurseries have not been founded. This paper categorized relevant articles according to the focus of the study, to provide evidence to a better understanding of current indoor air quality in nursery environments. 2 2

Quantum Thermoactivation of Nanoscale Magnets

The integral relaxation time describing the thermoactivated escape of a uniaxial quantum spin system interacting with a boson bath is calculated analytically in the whole temperature range. For temperatures T much less than the barrier height \Delta U, the level quantization near the top of the barrier and the strong frequency dependence of the one-boson transition probability can lead to the regularly spaced deep minima of the thermoactivation rate as a function of the magnetic field applied along the z axis.Comment: 4 pages, no figures, rejected from Phys. Rev. Let