11,884 research outputs found
Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.
We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene)
Modifying the Einstein Equations off the Constraint Hypersuface
A new technique is presented for modifying the Einstein evolution equations
off the constraint hypersurface. With this approach the evolution equations for
the constraints can be specified freely. The equations of motion for the
gravitational field variables are modified by the addition of terms that are
linear and nonlocal in the constraints. These terms are obtained from solutions
of the linearized Einstein constraints.Comment: 4 pages, 1 figure, uses REVTe
Macrofossils and pollen representing forests of the pre-Taupo volcanic eruption (c. 1850 yr BP) era at Pureora and Benneydale, central North Island, New Zealand.
Micro- and macrofossil data from the remains of forests overwhelmed and buried at Pureora and Benneydale during the Taupo eruption (c. 1850 conventional radiocarbon yr BP) were compared. Classification of relative abundance data separated the techniques, rather than the locations, because the two primary clusters comprised pollen and litter/wood. This indicates that the pollen:litter/wood within-site comparisons (Pureora and Benneydale are 20 km apart) are not reliable. Plant macrofossils represented mainly local vegetation, while pollen assemblages represented a combination of local and regional vegetation. However, using ranked abundance and presence/absence data, both macrofossils and pollen at Pureora and Benneydale indicated conifer/broadleaved forest, of similar forest type and species composition at each site. This suggests that the forests destroyed by the eruption were typical of mid-altitude west Taupo forests, and that either data set (pollen or macrofossils) would have been adequate for regional forest interpretation.
The representation of c. 1850 yr BP pollen from the known buried forest taxa was generally consistent with trends determined by modern comparisons between pollen and their source vegetation, but with a few exceptions.
A pollen profile from between the Mamaku Tephra (c. 7250 yr BP) and the Taupo Ignimbrite indicated that the Benneydale forest had been markedly different in species dominance compared with the forest that was destroyed during the Taupo eruption. These differences probably reflect changes in drainage, and improvements in climate and/or soil fertility over the middle Holocene
Hidden and Generalized Conformal Symmetry of Kerr-Sen Spacetimes
It is recently conjectured that generic non-extremal Kerr black hole could be
holographically dual to a hidden conformal field theory in two dimensions.
Moreover, it is known that there are two CFT duals (pictures) to describe the
charged rotating black holes which correspond to angular momentum and
electric charge of the black hole. Furthermore these two pictures can be
incorporated by the CFT duals (general picture) that are generated by
modular group. The general conformal structure can be
revealed by looking at charged scalar wave equation in some appropriate values
of frequency and charge. In this regard, we consider the wave equation of a
charged massless scalar field in background of Kerr-Sen black hole and show in
the "near region", the wave equation can be reproduced by the Casimir operator
of a local hidden conformal
symmetry. We can find the exact agreement between macroscopic and microscopic
physical quantities like entropy and absorption cross section of scalars for
Kerr-Sen black hole. We then find an extension of vector fields that in turn
yields an extended local family of hidden conformal symmetries, parameterized by one
parameter. For some special values of the parameter, we find a copy of
hidden conformal algebra for the charged
Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole in the strong deflection
limit.Comment: 16 pages, new material and results added, extensive improvements in
interpretation of results, references adde
Quantum Theory of Black Holes
A solvable 2-dimensional conformally invariant midi-superspace model for
black holes is obtained by imposing spherical symmetry in 4-dimensional
conformally invariant Einstein gravity. The Wheeler-DeWitt equation for the
theory is solved exactly to obtain the unique quantum wave functional for an
isolated black hole with fixed mass. By suitably relaxing the boundary
conditions, a non-perturbative ansatz is obtained for the wave functional of a
black hole interacting with its surroundings.Comment: Plain-TeX, 13 pages, no figures, WIN-92-9, UNB Tech. Rep. 92-0
User Intent Prediction in Information-seeking Conversations
Conversational assistants are being progressively adopted by the general
population. However, they are not capable of handling complicated
information-seeking tasks that involve multiple turns of information exchange.
Due to the limited communication bandwidth in conversational search, it is
important for conversational assistants to accurately detect and predict user
intent in information-seeking conversations. In this paper, we investigate two
aspects of user intent prediction in an information-seeking setting. First, we
extract features based on the content, structural, and sentiment
characteristics of a given utterance, and use classic machine learning methods
to perform user intent prediction. We then conduct an in-depth feature
importance analysis to identify key features in this prediction task. We find
that structural features contribute most to the prediction performance. Given
this finding, we construct neural classifiers to incorporate context
information and achieve better performance without feature engineering. Our
findings can provide insights into the important factors and effective methods
of user intent prediction in information-seeking conversations.Comment: Accepted to CHIIR 201
Non-singular four-dimensional black holes and the Jackiw-Teitelboim theory
A four-dimensional dilaton-gravity action whose spherical reduction to two
dimensions leads to the Jackiw-Teitelboim theory is presented. A nonsingular
black hole solution of the theory is obtained and its physical interpretation
is discussed. The classical and semiclassical properties of the solution and of
its 2d counterpart are analysed. The 2d theory is also used to model the
evaporation process of the near-extremal 4d black hole. We describe in detail
the peculiarities of the black hole solutions, in particular the purely
topological nature of the Hawking radiation, in the context of the
Jackiw-Teitelboim theory.Comment: 24 pages, 6 figures available upon request, Plain Tex,
INFN-CA-TH-94-2
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