8,372 research outputs found
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
that has been recently proposed in [PRL, {\bf 96}, 060502 (2006)]. The
Bell inequality is optimally violated by but not violated by the GHZ
state. The cluster state also violates the Bell inequality though not
optimally. The state 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
Remembering Dr. Henry W. Gray (1827-1861) and His Timeless Contribution to Modern Medical Education.
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