Analysis of SPDEs Arising in Path Sampling Part I: The Gaussian Case

In many applications it is important to be able to sample paths of SDEs conditional on observations of various kinds. This paper studies SPDEs which solve such sampling problems. The SPDE may be viewed as an infinite dimensional analogue of the Langevin SDE used in finite dimensional sampling. Here the theory is developed for conditioned Gaussian processes for which the resulting SPDE is linear. Applications include the Kalman-Bucy filter/smoother. A companion paper studies the nonlinear case, building on the linear analysis provided here

Key Dimension 4: Environmental Waste Security

Asia and the Pacific shows a positive trend in strengthening water security with the number of water insecure countries dropping to 29 from 38 in 2013, according to this latest edition of the Asian Water Development Outlook (AWDO). Despite this progress, enormous challenges in water security remain. Asia is home to half of the world’s poorest people. Water for agriculture continues to consume 80% of water resources. A staggering 1.7 billion people lack access to basic sanitation. With a predicted population of 5.2 billion by 2050 and 22 megacities by 2030, the region’s finite water resources will be under enormous pressure—especially with increasing climate variability. Recent estimates indicate up to 3.4 billion people could be living in water-stressed areas of Asia by 2050. With a Sustainable Development Goal dedicated to water and sanitation for all, AWDO 2016 is a tool to help assess the region’s progress in meeting this ambitious target

Hydrogen bonding in infinite hydrogen fluoride and hydrogen chloride chains

Hydrogen bonding in infinite HF and HCl bent (zigzag) chains is studied using the ab initio coupled-cluster singles and doubles (CCSD) correlation method. The correlation contribution to the binding energy is decomposed in terms of nonadditive many-body interactions between the monomers in the chains, the so-called energy increments. Van der Waals constants for the two-body dispersion interaction between distant monomers in the infinite chains are extracted from this decomposition. They allow a partitioning of the correlation contribution to the binding energy into short- and long-range terms. This finding affords a significant reduction in the computational effort of ab initio calculations for solids as only the short-range part requires a sophisticated treatment whereas the long-range part can be summed immediately to infinite distances.Comment: 9 pages, 4 figures, 3 tables, RevTeX4, corrected typo

Accuracy assessment of ISI-MIP modelled flows in the Hidukush-Karakoram-Himalayan basins

Large Asian rivers heading in the Hindukush-Karakoram-Himalayan mountains, and whose streamflow includes significant snow-melt and glacier-melt components, may be highly susceptible to climate warming and pattern changes. Millions of people depend on these streamflows for agriculture and power generation. Reliable predictions of future water availability are therefore needed for planning under a changing climate, and depend on the quality of hydro-climatic modelling. ISI-MIP provides global hydrological modelling results, and need validation at regional scale. This study evaluates the accuracy of modelled flows from the hydrological models used in ISI-MIP, in various sub-basins of the Upper Indus Basin (UIB) and for the reference period 1985-1998. The modelled flows are based on six hydrological models, which are: i) H08, ii) VIC, iii) WaterGAP, iv) WBM, v) MPI-HM, vi) PCR-GLOBWB. Of these models, H08 and VIC are energy-based hydrological models, while the others are temperature-based hydrological models. WBM and MPI are not suitable for the UIB, due to significant under-estimation (by 70-90%) of measured flows by their modelled flows. The remaining four models provide consistent, but still significantly under-estimated flows (up to 60% of measured flows) in all sub-basins, except the Kharmong basin. Monthly differences between modelled and measured flows vary between sub-basins, but with noticeable over-estimation in winter-spring months and under-estimation during summer months. Accuracy of the bias-corrected precipitation data sets (based on five GCMs) used in the ISI-MIP hydrological models has been assessed, using a basin-wide water balance assessment method. This method shows that all precipitation data sets significantly under-estimate precipitation in the UIB, particularly in the Karakoram sub-basins. The selected ISI-MIP hydrological models have used precipitation data which are under-estimates, which may be a main reason for under-estimated flows. ISI-MIP hydrological modelling needs to use the best available precipitation data for the UIB, but other input data and calibration parameters also need revision. An important message from this study is that caution must be exercised in selecting precipitation data sets and hydrological models in alpine regions such as the Hindukush-Karakoram-Himalayas

Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf

Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 27 (2007): 375-399, doi:10.1016/j.csr.2005.07.008.A mooring and tripod array was deployed from the fall of 2002 through the spring of 2003 on the Po prodelta to measure sediment transport processes associated with sediment delivered from the Po River. Observations on the prodelta revealed wave-supported gravity flows of high concentration mud suspensions that are dynamically and kinematically similar to those observed on the Eel shelf (Traykovski et al., 2000). Due to the dynamic similarity between the two sites, a simple one-dimensional across-shelf model with the appropriate bottom boundary condition was used to examine fluxes associated with this transport mechanism at both locations. To calculate the sediment concentrations associated with the wave-dominated and wave-current resuspension, a bottom boundary condition using a reference concentration was combined with an “active layer” formulation to limit the amount of sediment in suspension. Whereas the wave-supported gravity flow mechanism dominates the transport on the Eel shelf, on the Po prodelta flux due to this mechanism is equal in magnitude to transport due to wave resuspension and wind-forced mean currents in cross-shore direction. Southward transport due to wave resuspension and wind forced mean currents move an order of magnitude more sediment along-shore than the downslope flux associated wave-supported gravity flows.This work funded by the U.S. Office of Naval Research under grant number #N00014-02-10378, under the direction of program manager, Tom Drake

A method to estimate wood surface moisture content during drying

A method to estimate the surface moisture content below the fibre saturation point that is a function of the surface temperature, wet- and dry bulb temperatures, equilibrium moisture content, and fibre saturation point was evaluated. The method is based on the premise that the surface temperature is solely influenced by the surface moisture content and the climate that the surface is exposed to. The prediction model contends that the surface moisture content is equal to the fibre saturation point when the surface temperature is equal to the wet bulb temperature, and equal to the equilibrium moisture content when the surface temperature is equal to the dry bulb temperature, with a linear interpolation between those two points. The model thus predicts that the average moisture content of a thin piece of veneer can be predicted with fairly good accuracy. Also, when drying boards in a fast changing climate, e.g. fan reversals in industrial kilns, the surface temperature and surface moisture content should change as abruptly as the climate does. Additionally, the surface moisture content should correlate to the known drying phases, with a consistently high surface moisture content during the capillary phase when the wet line is close to the surface, and a quickly decreasing surface moisture content when the wet line moves into the wood during the transition to the diffusion phase. The prediction model was tested in these three scenarios and the results suggest that the basic premise is reasonable, and that the method is useful for surface moisture content estimation

Perfluoroalkyl acids (PFAAs) in children’s serum and contribution from PFAA-contaminated drinking water

We investigated associations between serum perfluoroalkyl acid (PFAA) concentrations in children aged 4, 8, and 12 years (sampled in 2008–2015; n = 57, 55, and 119, respectively) and exposure via placental transfer, breastfeeding, and ingestion of PFAA-contaminated drinking water. Sampling took place in Uppsala County, Sweden, where the drinking water has been historically contaminated with perfluorobutanesulfonate (PFBS), perfluorohexanesulfonate (PFHxS), perfluorooctanesulfonate (PFOS), perfluoroheptanoate (PFHpA), and perfluorooctanoate (PFOA). PFOS showed the highest median concentrations in serum (3.8–5.3 ng g–1 serum), followed by PFHxS (1.6–5.0 ng g–1 serum), PFOA (2.0–2.5 ng g–1 serum), and perfluorononanoate (PFNA) (0.59–0.69 ng g–1 serum) in children. Including all children, serum PFOA, PFHxS, and PFOS concentrations in children increased 10, 10, and 1.3% (adjusted mean), respectively, per unit (ng g–1 serum) of increase in the maternal serum level (at delivery), the associations being strongest for 4 year-old children. PFHxS and PFOS significantly increased 3.9 and 3.8%, respectively, per month of nursing, with the highest increase for 4 year-olds. PFOA, PFBS, PFHxS, and PFOS increased 1.2, 207, 7.4, and 0.93%, respectively, per month of cumulative drinking water exposure. Early life exposure to PFOA, PFHxS, and PFOS is an important determinant of serum concentrations in children, with the strongest influence on younger ages. Drinking water with low to moderate PFBS, PFHxS, PFOS, and PFOA contamination is an important source of exposure for children with background exposure from other sources

Dynamical models for sand ripples beneath surface waves

We introduce order parameter models for describing the dynamics of sand ripple patterns under oscillatory flow. A crucial ingredient of these models is the mass transport between adjacent ripples, which we obtain from detailed numerical simulations for a range of ripple sizes. Using this mass transport function, our models predict the existence of a stable band of wavenumbers limited by secondary instabilities. Small ripples coarsen in our models and this process leads to a sharply selected final wavenumber, in agreement with experimental observations.Comment: 9 pages. Shortened version of previous submissio

Wave-formed sediment ripples: Transient analysis of ripple spectral development

A new method has been developed that models the changes a wave-formed rippled sediment bed undergoes as it is actively evolving between two given equilibrium states due to a change in surface wave conditions. The transient analysis of rippled beds has received very little attention within the literature. Dynamic changes within ripple parameters have implications for the estimation of flow dissipation and sediment transport by changing the bottom roughness height. The method uses the spectral density function of the rippled bed and is based on a series of ripple growth and ripple transition experimental tests. The ripple evolution model was developed from the well-known Logistic Growth Law. Fitting the general solution of the logistic nonlinear differential equation to the experimental data enabled the evolution rate of the bed to be determined for each experimental test. It was concluded that there was no difference between the evolution rate determined from the ripple growth tests and the ripple transition tests. This indicated that the two types of growth are special cases of the same evolution processes, which is adequately modeled by the logistic growth equation. A functional dependence was established between the ripple evolution rate and the Shields parameter. This allows the evolution rate to be estimated from flow and sediment properties. The estimation of the rate at which rippled sediment beds evolve under a variable sea state has the potential to lead to significant improvements to the way ripple transition and hence bottom roughness is approximated in coastal wave models.Joseph P. Davis, David J. Walker, Murray Townsend, Ian R. Youn