Recovering the state sequence of hidden Markov models using mean-field approximations

Inferring the sequence of states from observations is one of the most fundamental problems in Hidden Markov Models. In statistical physics language, this problem is equivalent to computing the marginals of a one-dimensional model with a random external field. While this task can be accomplished through transfer matrix methods, it becomes quickly intractable when the underlying state space is large. This paper develops several low-complexity approximate algorithms to address this inference problem when the state space becomes large. The new algorithms are based on various mean-field approximations of the transfer matrix. Their performances are studied in detail on a simple realistic model for DNA pyrosequencing.Comment: 43 pages, 41 figure

28. STRUCTURAL IMPLICATIONS OF GRAVITY ANOMALIES, RESOLUTION AND HEEZEN GUYOTS, MID-PACIFIC MOUNTAINS 1

ABSTRACT Drilling showed that carbonate rocks make up most of Resolution Guyot, located in the western Mid-Pacific Mountains. Density data from Hole 866A, in the top of the guyot, were used to calculate a forward model of the gravity anomaly caused by the guyot's topography. After this anomaly was subtracted from the observed free-air anomaly, a significant positive residual, 35 mGal in amplitude, remained. The same densities were used for nearby Heezen Guyot, which yielded a similar, 45 mGal residual. Inverse models of the Resolution Guyot residual indicate that most of the mass excess can be attributed to the contrast between surrounding sediments and the dolomites at the bottom of the guyot's limestone section and the basalt pedestal beneath the guyot. Nevertheless, models with a central mass concentration fit the residual significantly better than those without, suggesting that there may be either a buried, conical, seamount remanent in the center of the guyot or a central conduit with dense intrusive rocks. The latter seems more plausible because seismic reflection profiles show no evidence of a buried conical structure. In addition, models with bottoms below the predicted top of the underlying basaltic plateau give more plausible density contrasts, suggesting that either a dense zone exists within the plateau beneath the guyot or that the extrapolated depth to the plateau top is incorrect by 500 m to 1000 m. The Resolution Guyot models imply that the carbonate bank buried a small seamount or igneous pedestal and retained nearly the same shape and width. Although the Heezen Guyot residual anomaly was not explicitly modeled, it is similar to that of Resolution Guyot and implies an analogous subsurface structure. In contrast, the Heezen Guyot residual is located to the west side of that edifice and does not have the same elongated shape as the guyot. Thus, it appears that the carbonate bank of Heezen Guyot expanded eastward from its pedestal

24. GEOMAGNETIC-FIELD VARIATIONS RECORDED WITHIN DRILL PIPE AT SITE 865: IMPLICATIONS FOR PALEOMAGNETIC STUDIES 1

ABSTRACT In this study, we measured the magnetic field within the drill string with a wireline magnetometer log and estimated the effect that this magnetic-field might have on paleomagnetic core samples. Sharp decreases in the vertical magnetic-field component and sharp increases in the horizontal component were observed at approximately 10-m intervals, corresponding to the pipe joints. Induced magnetization by the greater thicknesses of iron at these connection points apparently causes the magnetic-field variations. The bottom-hole assembly of the drill string was dominated by induced magnetization and possibly was affected by permanent magnetization. In general, the magnetic-field throughout most of the drill pipe and bottom-hole assembly is only two to five times greater than the Earth's magnetic field at Site 865 and so is not likely to affect paleomagnetic samples. However, the magnetometers vertical sensor became saturated in a downward direction between 344 and 356 m below the rig floor at Site 865, suggesting negative inclination of a strong permanent magnetization of two pipes within this zone. Such a strong magnetic field is a likely cause of remagnetization of core samples

China Energy Databook. Revision 4

The Energy Analysis Program at LBL first became involved in Chinese energy issues through a joint China-US symposium on markets and energy demand held in Nanjing Nov. 1988. EAP began to collaborate on projects with the Energy Research Institute of China`s State Planning Commission. It was decided to compile, assess, and organize Chinese energy data. Primary interest was to use the data to help understand the historical evolution and likely future of the Chinese energy system; thus the primary criterion was to relate the data to the structure of energy supply and demand in the past and to indicate probable developments (eg, as indicated by patterns of investment). Caveats are included in forewords to both the 1992 and 1996 editions. A chapter on energy prices is included in the 1996 edition. 1993 energy consumption data are not included since there was a major disruption in energy statistical collection in China that year

China Energy Databook. Revision 4

The Energy Analysis Program at LBL first became involved in Chinese energy issues through a joint China-US symposium on markets and energy demand held in Nanjing Nov. 1988. EAP began to collaborate on projects with the Energy Research Institute of China`s State Planning Commission. It was decided to compile, assess, and organize Chinese energy data. Primary interest was to use the data to help understand the historical evolution and likely future of the Chinese energy system; thus the primary criterion was to relate the data to the structure of energy supply and demand in the past and to indicate probable developments (eg, as indicated by patterns of investment). Caveats are included in forewords to both the 1992 and 1996 editions. A chapter on energy prices is included in the 1996 edition. 1993 energy consumption data are not included since there was a major disruption in energy statistical collection in China that year

Effects of variable magma supply on mid-ocean ridge eruptions : constraints from mapped lava flow fields along the Galápagos Spreading Center

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q08014, doi:10.1029/2012GC004163.Mapping and sampling of 18 eruptive units in two study areas along the Galápagos Spreading Center (GSC) provide insight into how magma supply affects mid-ocean ridge (MOR) volcanic eruptions. The two study areas have similar spreading rates (53 versus 55 mm/yr), but differ by 30% in the time-averaged rate of magma supply (0.3 × 106 versus 0.4 × 106 m3/yr/km). Detailed geologic maps of each study area incorporate observations of flow contacts and sediment thickness, in addition to sample petrology, geomagnetic paleointensity, and inferences from high-resolution bathymetry data. At the lower-magma-supply study area, eruptions typically produce irregularly shaped clusters of pillow mounds with total eruptive volumes ranging from 0.09 to 1.3 km3. At the higher-magma-supply study area, lava morphologies characteristic of higher effusion rates are more common, eruptions typically occur along elongated fissures, and eruptive volumes are an order of magnitude smaller (0.002–0.13 km3). At this site, glass MgO contents (2.7–8.4 wt. %) and corresponding liquidus temperatures are lower on average, and more variable, than those at the lower-magma-supply study area (6.2–9.1 wt. % MgO). The differences in eruptive volume, lava temperature, morphology, and inferred eruption rates observed between the two areas along the GSC are similar to those that have previously been related to variable spreading rates on the global MOR system. Importantly, the documentation of multiple sequences of eruptions at each study area, representing hundreds to thousands of years, provides constraints on the variability in eruptive style at a given magma supply and spreading rate.This work was supported by the National Science Foundation grants OCE08–49813, OCE08–50052, and OCE08– 49711.2013-02-2

Microfluidic systems for the analysis of the viscoelastic fluid flow phenomena in porous media

In this study, two microfluidic devices are proposed as simplified 1-D microfluidic analogues of a porous medium. The objectives are twofold: firstly to assess the usefulness of the microchannels to mimic the porous medium in a controlled and simplified manner, and secondly to obtain a better insight about the flow characteristics of viscoelastic fluids flowing through a packed bed. For these purposes, flow visualizations and pressure drop measurements are conducted with Newtonian and viscoelastic fluids. The 1-D microfluidic analogues of porous medium consisted of microchannels with a sequence of contractions/ expansions disposed in symmetric and asymmetric arrangements. The real porous medium is in reality, a complex combination of the two arrangements of particles simulated with the microchannels, which can be considered as limiting ideal configurations. The results show that both configurations are able to mimic well the pressure drop variation with flow rate for Newtonian fluids. However, due to the intrinsic differences in the deformation rate profiles associated with each microgeometry, the symmetric configuration is more suitable for studying the flow of viscoelastic fluids at low De values, while the asymmetric configuration provides better results at high De values. In this way, both microgeometries seem to be complementary and could be interesting tools to obtain a better insight about the flow of viscoelastic fluids through a porous medium. Such model systems could be very interesting to use in polymer-flood processes for enhanced oil recovery, for instance, as a tool for selecting the most suitable viscoelastic fluid to be used in a specific formation. The selection of the fluid properties of a detergent for cleaning oil contaminated soil, sand, and in general, any porous material, is another possible application

Correlated geophysical, geochemical, and volcanological manifestations of plume-ridge interaction along the Galápagos Spreading Center

As the Galápagos hot spot is approached from the west along the Galápagos Spreading Center there are systematic increases in crustal thickness and in the K/Ti, Nb/Zr, ³He/⁴He, H₂O, and Na₂O content of lavas recovered from the spreading axis. These increases correlate with progressive transitions from rift valley to axial high morphology along with decreases in average swell depth, residual mantle Bouguer gravity anomaly, magma chamber depth, average lava Mg #, Ca/Al ratio, and the frequency of point-fed versus fissure-fed volcanism. Magma chamber depth and axial morphology display a “threshold” effect in which small changes in magma supply result in large changes in these variables. These correlated variations in geophysical, geochemical, and volcanological manifestations of plume-ridge interaction along the western Galápagos Spreading Center reflect the combined effects of changes in mantle temperature and source composition on melt generation processes, and the consequences of these variations on magma supply, axial thermal structure, basalt chemistry, and styles of volcanism.Keywords: hotspots, mid-ocean ridges, Mantle plume

Lower crustal crystallization and melt evolution at mid-ocean ridges

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 5 (2012): 651–655, doi:10.1038/ngeo1552.Mid-ocean ridge magma is produced when Earth’s mantle rises beneath the ridge axis and melts as a result of the decrease in pressure. This magma subsequently undergoes cooling and crystallization to form the oceanic crust. However, there is no consensus on where within the crust or upper mantle crystallization occurs1-5. Here we provide direct geochemical evidence for the depths of crystallization beneath ridge axes of two spreading centres located in the Pacific Ocean: the fast-spreading-rate East Pacific Rise and intermediate-spreading-rate Juan de Fuca Ridge. Specifically, we measure volatile concentrations in olivine-hosted melt inclusions to derive vapour-saturation pressures and to calculate crystallisation depth. We also analyse the melt inclusions for major and trace element concentrations, allowing us to compare the distributions of crystallisation and to track the evolution of the melt during ascent through the oceanic crust. We find that most crystallisation occurs within a seismically-imaged melt lens located in the shallow crust at both ridges, but over 25% of the melt inclusions have crystallisation pressures consistent with formation in the lower oceanic crust. Furthermore, our results suggest that melts formed beneath the ridge axis can be efficiently mixed and undergo olivine crystallisation in the mantle, prior to ascent into the ocean crust.This research was supported by the National Science Foundation (EAR-0646694) and the WHOI Deep Ocean Exploration Institute/Ocean Ridge Initiative.2013-02-1

Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 460 (2009): 89-93, doi:10.1038/nature08095.The oceanic crust extends over two thirds of the Earth’s solid surface and is generated along mid-ocean ridges from melts derived from the upwelling mantle. The upper and mid crust are constructed by dyking and seafloor eruptions originating from magma accumulated in mid-crustal lenses at the spreading axis, but the style of accretion of the lower oceanic crust is actively debated. Models based on geological and petrological data from ophiolites propose that the lower oceanic crust is accreted from melt sills intruded at multiple levels between the Moho transition zone (MTZ) and the mid-crustal lens, consistent with geophysical studies that suggest the presence of melt within the lower crust. However, seismic images of molten sills within the lower crust have been elusive. To date only seismic reflections from mid-crustal melt lenses and sills within the MTZ have been described, suggesting that melt is efficiently transported through the lower crust. Here we report deep crustal seismic reflections off the southern Juan de Fuca Ridge that we interpret as originating from a molten sill presently accreting the lower oceanic crust. The sill sits 5-6 km beneath the seafloor and 850-900 m above the MTZ, and it is located 1.4-3.2 km off thespreading axis. Our results provide evidence for the existence of low permeability barriers to melt migration within the lower section of modern oceanic crust forming at intermediate-to-fast spreading rates, as inferred from ophiolite studies.This research was supported by grants form the US NSF