Re-identification of c. 15 700 cal yr BP tephra bed at Kaipo Bog, eastern North Island: implications for dispersal of Rotorua and Puketarata tephra beds.

A 10 mm thick, c. 15 700 calendar yr BP (c. 13 100 14C yr BP) rhyolitic tephra bed in the well-studied montane Kaipo Bog sequence of eastern North Island was previously correlated with Maroa-derived Puketarata Tephra. We revise this correlation to Okataina-derived Rotorua Tephra based on new compositional data from biotite phenocrysts and glass. The new correlation limits the known dispersal of Puketarata Tephra (sensu stricto, c. 16 800 cal yr BP) and eliminates requirements to either reassess its age or to invoke dual Puketarata eruptive events. Our data show that Rotorua Tephra comprises two glass-shard types: an early-erupted low-K2O type that was dispersed mostly to the northwest, and a high-K2O type dispersed mostly to the south and southeast, contemporary with late-stage lava extrusion. Late-stage Rotorua eruptives contain biotite that is enriched in FeO compared with biotite from Puketarata pyroclastics. The occurrence of Rotorua Tephra in Kaipo Bog (100 km from the source) substantially extends its known distribution to the southeast. Our analyses demonstrate that unrecognised syn-eruption compositional and dispersal changes can cause errors in fingerprinting tephra deposits. However, the compositional complexity, once recognised, provides additional fingerprinting criteria, and also documents magmatic and dispersal processes

Probabilistic Search for Object Segmentation and Recognition

The problem of searching for a model-based scene interpretation is analyzed within a probabilistic framework. Object models are formulated as generative models for range data of the scene. A new statistical criterion, the truncated object probability, is introduced to infer an optimal sequence of object hypotheses to be evaluated for their match to the data. The truncated probability is partly determined by prior knowledge of the objects and partly learned from data. Some experiments on sequence quality and object segmentation and recognition from stereo data are presented. The article recovers classic concepts from object recognition (grouping, geometric hashing, alignment) from the probabilistic perspective and adds insight into the optimal ordering of object hypotheses for evaluation. Moreover, it introduces point-relation densities, a key component of the truncated probability, as statistical models of local surface shape.Comment: 18 pages, 5 figure

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)

Plant disease - early blight or target spot of potatoes

Early blight or target spot caused by the fungus Alternaria solani is a widespread disease of potatoes which in Western Australia is most prevalent in crops dug in autumn and early summer. The disease may attack both foliage and tubers, but the tuber rot phase of the disease has hitherto caused most concern to local growers because it causes obvious losses in storage. The less obvious but more serious effects of the foliage blight have generally been overlooked, chiefly because the disease usually develops late in the season when the crops are approaching maturity. However recent spray trials with new fungicides have clearly demonstrated that the destructiveness of the foliage attack has been greatly underestimated, for it may cause considerable reduction in yield

Further experiements on the control of early blight or target spot of potatoes

The effective control of Potato Early Blight or Target Spot by the use of Zineb fungicide (used in the proprietary form Dithane Z.78) has previously been reported in this Journal. It was shown in preliminary spray trials that the foliage blight caused by this disease is very destructive, and by the application of four Dithane sprays yields were increased in the order of 30 per cent., equivalent to approximately four tons per acre. Further experiments have now been conducted and the results indicate that even two applications of Dithane spray may, under conditions of severe blight attack, promote worthwhile higher yields

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

AdS/CFT and the Information Paradox

The information paradox in the quantum evolution of black holes is studied within the framework of the AdS/CFT correspondence. The unitarity of the CFT strongly suggests that all information about an initial state that forms a black hole is returned in the Hawking radiation. The CFT dynamics implies an information retention time of order the black hole lifetime. This fact determines many qualitative properties of the non-local effects that must show up in a semi-classical effective theory in the bulk. We argue that no violations of causality are apparent to local observers, but the semi-classical theory in the bulk duplicates degrees of freedom inside and outside the event horizon. Non-local quantum effects are required to eliminate this redundancy. This leads to a breakdown of the usual classical-quantum correspondence principle in Lorentzian black hole spacetimes.Comment: 16 pages, harvmac, reference added, minor correction

Quantum Coherence in Two Dimensions

The formation and evaporation of two dimensional black holes are discussed. It is shown that if the radiation in minimal scalars has positive energy, there must be a global event horizon or a naked singularity. The former would imply loss of quantum coherence while the latter would lead to an even worse breakdown of predictability. CPT invariance would suggest that there ought to be past horizons as well. A way in which this could happen with wormholes is described.Comment: 11 pages, DAMTP-R93/15, CALT-68-1861, Tex, 3 appended uuencoded figure

Semiclassical Approach to Black Hole Evaporation

Black hole evaporation may lead to massive or massless remnants, or naked singularities. This paper investigates this process in the context of two quite different two dimensional black hole models. The first is the original CGHS model, the second is another two dimensional dilaton-gravity model, but with properties much closer to physics in the real, four dimensional, world. Numerical simulations are performed of the formation and subsequent evaporation of black holes and the results are found to agree qualitatively with the exactly solved modified CGHS models, namely that the semiclassical approximation breaks down just before a naked singularity appears.Comment: 15 pages, PUPT-1340, harvmac, 11 figures available on reques