EMPIRE: A robust empirical reconstruction of solar irradiance variability

We present a new empirical model of total and spectral solar irradiance (TSI and SSI) variability entitled EMPirical Irradiance REconstruction (EMPIRE). As with existing empirical models, TSI and SSI variability is given by the linear combination of solar activity indices. In empirical models, UV SSI variability is usually determined by fitting the rotational variability in activity indices to that in measurements. Such models have to date relied on ordinary least squares regression, which ignores the uncertainty in the activity indices. In an advance from earlier efforts, the uncertainty in the activity indices is accounted for in EMPIRE by the application of an error-in-variables regression scheme, making the resultant UV SSI variability more robust. The result is consistent with observations and unprecedentedly, with that from other modelling approaches, resolving the long-standing controversy between existing empirical models and other types of models. We demonstrate that earlier empirical models, by neglecting the uncertainty in activity indices, underestimate UV SSI variability. The reconstruction of TSI and visible and IR SSI from EMPIRE is also shown to be consistent with observations. The EMPIRE reconstruction is of utility to climate studies as a more robust alternative to earlier empirical reconstructions.Comment: J. Geophys. Res. (2017

Solar cycle variation in solar irradiance

The correlation between solar irradiance and the 11-year solar activity cycle is evident in the body of measurements made from space, which extend over the past four decades. Models relating variation in solar irradiance to photospheric magnetism have made significant progress in explaining most of the apparent trends in these observations. There are, however, persistent discrepancies between different measurements and models in terms of the absolute radiometry, secular variation and the spectral dependence of the solar cycle variability. We present an overview of solar irradiance measurements and models, and discuss the key challenges in reconciling the divergence between the two

Quantum nonlocality of four-qubit entangled states

Quantum nonlocality of several four-qubit states is investigated by constructing a new Bell inequality. These include the Greenberger-Zeilinger-Horne (GHZ) state, W state, cluster state, and the state $|\chi>$ that has been recently proposed in [PRL, {\bf 96}, 060502 (2006)]. The Bell inequality is optimally violated by $|\chi>$ but not violated by the GHZ state. The cluster state also violates the Bell inequality though not optimally. The state $|\chi>$ can thus be discriminated from the cluster state by using the inequality. Different aspects of four-partite entanglement are also studied by considering the usefulness of a family of four-qubit mixed states as resources for two-qubit teleportation. Our results generalize those in [PRL, {\bf 72}, 797 (1994)].Comment: 13 pages, 1 figur

Analysis and modeling of solar irradiance variations

A prominent manifestation of the solar dynamo is the 11-year activity cycle, evident in indicators of solar activity, including solar irradiance. Although a relationship between solar activity and the brightness of the Sun had long been suspected, it was only directly observed after regular satellite measurements became available with the launch of Nimbus-7 in 1978. The measurement of solar irradiance from space is accompanied by the development of models aimed at describing the apparent variability by the intensity excess/deficit effected by magnetic structures in the photosphere. The more sophisticated models, termed semi-empirical, rely on the intensity spectra of photospheric magnetic structures generated with radiative transfer codes from semi-empirical model atmospheres. An established example of such models is SATIRE-S (Spectral And Total Irradiance REconstruction for the Satellite era). One key limitation of current semi-empirical models is the fact that the radiant properties of network and faculae are not adequately represented due to the use of plane-parallel model atmospheres (as opposed to three-dimensional model atmospheres). This thesis is the compilation of four publications, detailing the results of investigations aimed at setting the groundwork necessary for the eventual introduction of three-dimensional atmospheres into SATIRE-S and a review of the current state of the measurement and modelling of solar irradiance. Also presented is an update of the SATIRE-S model. We generated a daily reconstruction of total and spectral solar irradiance, covering 1974 to the present, that is more reliable and, in most cases, extended than similar reconstructions from contemporary models.Comment: Doctoral thesis, ISBN 978-3-944072-07-

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature

Detailed studies of mid-ocean ridge volcanism at the Mid-Atlantic Ridge (45°N) and elsewhere

This thesis provides a comprehensive study of the Axial Volcanic Ridge (AVR) at 45˚30 N on the Mid-Atlantic Ridge. A number of datasets were collected over the area, including: EM120 ship based bathymetry, TOBI sidescan sonar, Isis high-resolution bathymetry, Isis video and sampling dives and crustal magnetisation surveys. In this thesis I seek to explore the questions of the volcanic building blocks of AVRs and their spatial and temporal evolution in a number of ways. Very detailed volcanological mapping of the seafloor is used to provide semi-quantitative estimates of the relative proportions of different lava morphologies on and off the AVR and within the upper oceanic crust. I find that the AVR is characterised by predominantly pillow lavas while the flatter areas of seafloor around the AVR are covered by higher effusion rate lava morphologies. These observations are combined with the bathymetry and sidescan sonar datasets to elucidate the detailed nature of the building blocks of AVRs, which I find to be volcanic hummocks, composed predominantly of pillow lavas. These hummocks are morphologically the same as pillow mounds described at intermediate-spreading rate ridges. From these observations we identify common collapse scarps and associated talus deposits, which if buried may contribute significantly to increased porosity and lower seismic velocity in seismic layer 2A. Sediment cover is used as a proxy for seafloor age, and suggests that both the AVR and the flat seafloor around it are a similar age. Statistical analysis of the distribution and size of volcanic hummocks on the AVR finds their numbers to have been vastly underestimated in previous studies. I also show that hummock density is very variable across the AVR, possibly corresponding to many discrete melt sources. Evidence from 45˚N does not support either a uniform, long period life cycle model as has been proposed, or a steady state AVR. Instead I suggest that the AVR is the surface representation of robust magma supply, and irregular nature of this melt supply will control the surface appearance of the AV