111 research outputs found
Clay mineralogy of tephras and associated paleosols and soils, and hydrothermal deposits, North Island [New Zealand]
Tour themes and itinerary
The tour centres on the occurrence and genesis of clay minerals, especially allophane, halloysite, and ferrihydrite, associated with both Quaternary rhyolitic airfall tephra (volcanic ash) deposits and volcanogenic alluvium, and on mineralisation and thermal activity in hydrothermal fields. After a brief overview of the basaltic volcanoes of Auckland City, our route essentially traverses the Central Volcanic Region by way of a large loop with overnight stops at Rotorua (2 nights), Tokaanu, and Auckland (Fig. 0.1). We have around five stops planned for each day (including lunch), three of these being scientific stops except on Day 4 when we have only one scientific stop because of the need to travel greater distances.
Our route takes us progressively towards the locus of the most recently active volcanic centres of the Central Volcanic Region, and so the surficial tephra deposits and buried paleosols become successively younger and generally less weathered: tephras at the Mangawara section (Day 1) span c. 1 Ma; at Tapapa (Day 2), c. 140 ka; at Te Ngae (Day 2), c. 20 ka; and at De Bretts, c. 10 ka, and Wairakei, c. 2 ka (Day 3). Interspersed with these tephra-paleosol sections are stops to examine an allophane-halloysite soil drainage (leaching) sequence on volcanogenic alluvium (Day 1), hydrothermal activity and mineral deposits at Whakarewarewa (Day 2) and Waiotapu (Day 3), and pure ferrihydrite seepage deposits in Hamilton (Day 4). Following introductory and detailed background review material, the tour guide has been arranged on a day-by-day basis and includes an outline of the route and stops, and several pages describing the stratigraphy, mineralogy, chemistry, and pedology of the deposits or features at each of the main stops. We will attempt to point out and describe geological and other features as appropriate during travel periods.
Other activities
Examples of New Zealand's distinctive fauna and flora, including kiwis and tuataras, will be seen at close quarters at Rainbow Springs (Day 2), where we will also enjoy an agricultural farm show. In Rotorua we will partake in a Maori hangi (steam-cooked feast) and concert including traditional dance forms (hakas) and songs (Day 2). In Tokaanu, hot pools will be available to relax in near the slopes of Mt Tongariro (Day 3). At Waitomo, we will visit the Waitomo Cave and in Hamilton spend a short time at the Waikato Museum of Art and History (Day 4). Finally, the tour will conclude with a farewell dinner in Auckland
Wavelet multiscale analysis for hedge funds: scaling and strategies
The wide acceptance of Hedge Funds by Institutional Investors and Pension Funds has led to an explosive growth in assets under management. These investors are drawn to Hedge Funds due to the seemingly low correlation with traditional investments and the attractive returns.
The correlations and market risk (the Beta in the Capital Asset Pricing Model) of Hedge Funds are generally calculated using monthly returns data, which may produce misleading results as Hedge Funds often hold illiquid exchange-traded securities or difficult to price over-the-
counter securities. In this paper, the Maximum Overlap Discrete Wavelet Transform (MODWT) is applied to measure the scaling properties of Hedge Fund correlation and market risk with respect to the S&P 500. It is found that the level of correlation and market risk varies greatly
according to the strategy studied and the time scale examined. Finally, the effects of scaling properties on the risk profile of a portfolio made up of Hedge Funds is studied using correlation matrices calculated over different time horizons
Seizure characterisation using frequency-dependent multivariate dynamics
The characterisation of epileptic seizures assists in the design of targeted pharmaceutical seizure prevention techniques
and pre-surgical evaluations. In this paper, we expand on recent use of multivariate techniques to study the crosscorrelation
dynamics between electroencephalographic (EEG) channels. The Maximum Overlap Discrete Wavelet
Transform (MODWT) is applied in order to separate the EEG channels into their underlying frequencies. The
dynamics of the cross-correlation matrix between channels, at each frequency, are then analysed in terms of the
eigenspectrum. By examination of the eigenspectrum, we show that it is possible to identify frequency dependent
changes in the correlation structure between channels which may be indicative of seizure activity.
The technique is applied to EEG epileptiform data and the results indicate that the correlation dynamics vary over
time and frequency, with larger correlations between channels at high frequencies. Additionally, a redistribution of wavelet energy is found, with increased fractional energy demonstrating the relative importance of high frequencies
during seizures. Dynamical changes also occur in both correlation and energy at lower frequencies during seizures,
suggesting that monitoring frequency dependent correlation structure can characterise changes in EEG signals during
these. Future work will involve the study of other large eigenvalues and inter-frequency correlations to determine
additional seizure characteristics
Continuous Quantum Measurement and the Quantum to Classical Transition
While ultimately they are described by quantum mechanics, macroscopic
mechanical systems are nevertheless observed to follow the trajectories
predicted by classical mechanics. Hence, in the regime defining macroscopic
physics, the trajectories of the correct classical motion must emerge from
quantum mechanics, a process referred to as the quantum to classical
transition. Extending previous work [Bhattacharya, Habib, and Jacobs, Phys.
Rev. Lett. {\bf 85}, 4852 (2000)], here we elucidate this transition in some
detail, showing that once the measurement processes which affect all
macroscopic systems are taken into account, quantum mechanics indeed predicts
the emergence of classical motion. We derive inequalities that describe the
parameter regime in which classical motion is obtained, and provide numerical
examples. We also demonstrate two further important properties of the classical
limit. First, that multiple observers all agree on the motion of an object, and
second, that classical statistical inference may be used to correctly track the
classical motion.Comment: 12 pages, 4 figures, Revtex
Cosmological constraints from galaxy clustering
In this manuscript I review the mathematics and physics that underpins recent
work using the clustering of galaxies to derive cosmological model constraints.
I start by describing the basic concepts, and gradually move on to some of the
complexities involved in analysing galaxy redshift surveys, focusing on the 2dF
Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky survey (SDSS).
Difficulties within such an analysis, particularly dealing with redshift space
distortions and galaxy bias are highlighted. I then describe current
observations of the CMB fluctuation power spectrum, and consider the importance
of measurements of the clustering of galaxies in light of recent experiments.
Finally, I provide an example joint analysis of the latest CMB and large-scale
structure data, leading to a set of parameter constraints.Comment: 30 pages, 13 figures. Lecture given at Third Aegean Summer School,
The invisible universe: Dark matter and Dark energ
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
-Strands
A -strand is a map for a Lie
group that follows from Hamilton's principle for a certain class of
-invariant Lagrangians. The SO(3)-strand is the -strand version of the
rigid body equation and it may be regarded physically as a continuous spin
chain. Here, -strand dynamics for ellipsoidal rotations is derived as
an Euler-Poincar\'e system for a certain class of variations and recast as a
Lie-Poisson system for coadjoint flow with the same Hamiltonian structure as
for a perfect complex fluid. For a special Hamiltonian, the -strand is
mapped into a completely integrable generalization of the classical chiral
model for the SO(3)-strand. Analogous results are obtained for the
-strand. The -strand is the -strand version of the
Bloch-Iserles ordinary differential equation, whose solutions exhibit dynamical
sorting. Numerical solutions show nonlinear interactions of coherent wave-like
solutions in both cases. -strand equations on the
diffeomorphism group are also introduced and shown
to admit solutions with singular support (e.g., peakons).Comment: 35 pages, 5 figures, 3rd version. To appear in J Nonlin Sc
Classical approach in quantum physics
The application of a classical approach to various quantum problems - the
secular perturbation approach to quantization of a hydrogen atom in external
fields and a helium atom, the adiabatic switching method for calculation of a
semiclassical spectrum of hydrogen atom in crossed electric and magnetic
fields, a spontaneous decay of excited states of a hydrogen atom, Gutzwiller's
approach to Stark problem, long-lived excited states of a helium atom recently
discovered with the help of Poincar section, inelastic
transitions in slow and fast electron-atom and ion-atom collisions - is
reviewed. Further, a classical representation in quantum theory is discussed.
In this representation the quantum states are treating as an ensemble of
classical states. This approach opens the way to an accurate description of the
initial and final states in classical trajectory Monte Carlo (CTMC) method and
a purely classical explanation of tunneling phenomenon. The general aspects of
the structure of the semiclassical series such as renormgroup symmetry,
criterion of accuracy and so on are reviewed as well. In conclusion, the
relation between quantum theory, classical physics and measurement is
discussed.Comment: This review paper was rejected from J.Phys.A with referee's comment
"The author has made many worthwhile contributions to semiclassical physics,
but this article does not meet the standard for a topical review"
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Clustering of dark matter tracers: generalizing bias for the coming era of precision LSS
On very large scales, density fluctuations in the Universe are small,
suggesting a perturbative model for large-scale clustering of galaxies (or
other dark matter tracers), in which the galaxy density is written as a Taylor
series in the local mass density, delta, with the unknown coefficients in the
series treated as free "bias" parameters. We extend this model to include
dependence of the galaxy density on the local values of nabla_i nabla_j phi and
nabla_i v_j, where phi is the potential and v is the peculiar velocity. We show
that only two new free parameters are needed to model the power spectrum and
bispectrum up to 4th order in the initial density perturbations, once symmetry
considerations and equivalences between possible terms are accounted for. One
of the new parameters is a bias multiplying s_ij s_ji, where s_ij=[nabla_i
nabla_j \nabla^-2 - 1/3 delta^K_ij] delta. The other multiplies s_ij t_ji,
where t_ij=[nabla_i nabla_j nabla^-2 - 1/3 delta^K_ij](theta-delta), with
theta=-(a H dlnD/dlna)^-1 nabla_i v_i. (There are other, observationally
equivalent, ways to write the two terms, e.g., using theta-delta instead of
s_ij s_ji.) We show how short-range (non-gravitational) non-locality can be
included through a controlled series of higher derivative terms, starting with
R^2 nabla^2 delta, where R is the scale of non-locality (this term will be a
small correction as long as k^2 R^2 is small, where k is the observed
wavenumber). We suggest that there will be much more information in future huge
redshift surveys in the range of scales where beyond-linear perturbation theory
is both necessary and sufficient than in the fully linear regime.Comment: 24 pg., 5 fi
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