Markov Chain Random Fields for Estimation of Categorical Variables

Multi-dimensional Markov chain conditional simulation (or interpolation) models have potential for predicting and simulating categorical variables more accurately from sample data because they can incorporate interclass relationships. This paper introduces a Markov chain random field (MCRF) theory for building one to multi-dimensional Markov chain models for conditional simulation (or interpolation). A MCRF is defined as a single spatial Markov chain that moves (or jumps) in a space, with its conditional probability distribution at each location entirely depending on its nearest known neighbors in different directions. A general solution for conditional probability distribution of a random variable in a MCRF is derived explicitly based on the Bayes’ theorem and conditional independence assumption. One to multi-dimensional Markov chain models for prediction and conditional simulation of categorical variables can be drawn from the general solution and MCRF-based multi-dimensional Markov chain models are nonlinear.     

一种改进的基于非高斯性最大化的预测反褶积算法

The predictive deconvolution algorithm （PD）, which is based on second-order statistics, assumes that the primaries and the multiples are implicitly orthogonal. However, the seismic data usually do not satisfy this assumption in practice. Since the seismic data （primaries and multiples） have a non-Gaussian distribution, in this paper we present an improved predictive deconvolution algorithm （IPD） by maximizing the non-Gaussianity of the recovered primaries. Applications of the IPD method on synthetic and real seismic datasets show that the proposed method obtains promising results.     

Turbulent kinetic energy budget in a gravel-bed channel flow

The present experimental investigation focuses on the characteristics of near bed turbulence in a fully rough, uniform open-channel flow over a gravel-type bed. Due to bed topography small scale heterogeneity, the flow is not uniform locally in the near bed region and a double averaging methodology is applied over a length scale much larger than the gravel size. The double-averaged Turbulent Kinetic Energy (TKE) budget derived in the context of the present flow over a gravel bed differs from the TKE budget written for flow over a vegetation canopy. The non-constant shape of the roughness function measured in our gravel bed leads to an additional bed-induced production term which is null for vertical roughness elements, such as simplified vegetation elements. The experimental estimation of the terms of the TKE budget reveals that the maximum turbulent activity takes place away from the reference plane, near the roughness crests. However, within the interface sublayer the work of the bed induced velocity fluctuations against the Reynolds stress is of the same magnitude as the main turbulence production term. Consequently, the characteristics of the TKE budget have similarities with uniform flows over canopies and strongly differ from uniform flows over smooth and transitionally rough flows over sedimentlike beds.     

The last 40 ka tephrostratigraphic record of Lake Ohrid,Albania and Macedonia: a very distal archive for ash dispersal from Italian volcanoes

A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896–897 cm and 1070–1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310–315 cm. Major element analyses on glass shards of the tephra layers at 896–897 cm and 1070–1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310–315 cm has a mugearitic–benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five ¹⁴C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core.     

Source depletion and extent of melting in the Tongan sub-arc mantle

The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab.     

Validity of the Bouchet’s complementary relationship at 102 observatories across China

Bouchet in 1963 hypothesized that for large homogeneous land surface with minimum advection of heat and moisture, there exists a 1:1 complementary relationship of potential and actual evaporation coupled through land-atmosphere feedbacks. The complementary relationship has been widely used to estimate regional actual evaporation and explain the pan evaporation paradox. We examine the standardized potential evaporation (potential evaporation divided by wet environment evaporation) at 102 observatories at different elevations across China. Generally, the relationship is appropriate at the low elevations (<1000 m). With the increase of elevation, vapor transfer power becomes much less than radiation energy budget because of lower vapor pressure deficit and stronger global solar radiation. As a result, at the high elevations (over 1000 m), the excess energy resulted by limited moisture availability is not enough to be converted into drying power of the air. This result suggests that the complementary relationship is asymmetric at the high elevations. Supported by the Presidential Special Award Foundation, the Chinese Academy of Sciences (Grant No. O7R70020SD) and the National Key Technology R & D Program (Grant No. 2006BAC08B0408)     

The prospects for modernizing very broadband seismometers

This paper considers the possibilities for modernizing the KSESh broadband seismic station developed earlier at the IPE AS USSR. The goal of the modernization was to extend the frequency and dynamic ranges and to decrease nonlinear distortions. The ways and concrete methods for improving the mechanical construction and electronic components of the station are shown and the intermediate results are described. As preliminary estimates show, there is an opportunity to build devices with the velocimeter response up to 520–540 s periods on the basis of this pendulum.