Quantified Uncertainty in Thermodynamic Modeling for Materials Design

Phase fractions, compositions and energies of the stable phases as a function of macroscopic composition, temperature, and pressure (X-T-P) are the principle correlations needed for the design of new materials and improvement of existing materials. They are the outcomes of thermodynamic modeling based on the CALculation of PHAse Diagrams (CALPHAD) approach. The accuracy of CALPHAD predictions vary widely in X-T-P space due to experimental error, model inadequacy and unequal data coverage. In response, researchers have developed frameworks to quantify the uncertainty of thermodynamic property model parameters and propagate it to phase diagram predictions. In previous studies, uncertainty was represented as intervals on phase boundaries (with respect to composition) or invariant reactions (with respect to temperature) and was unable to represent the uncertainty in eutectoid reactions or in the stability of phase regions. In this work, we propose a suite of tools that leverages samples from the multivariate model parameter distribution to represent uncertainty in forms that surpass previous limitations and are well suited to materials design. These representations include the distribution of phase diagrams and their features, as well as the dependence of phase stability and the distributions of phase fraction, composition activity and Gibbs energy on X-T-P location - irrespective of the total number of components. Most critically, the new methodology allows the material designer to interrogate a certain composition and temperature domain and get in return the probability of different phases to be stable, which can positively impact materials design

Historical patterns of phytoplankton productivity in Lake Mead

Lake Mead was impounded in 1935 by the construction of Hoover Dam. The Colorado River was unregulated prior to then and therefore was subjected to extreme variations in flows and suspended sediment loads. Hoover Dam stabilized flows and reduced suspended sediment loads downstream, but Lake Mead still received silt-laden inflows from the upper Colorado River Basin. The Colorado River contributed 97% of the suspended sediment inputs to Lake Mead, and up to 140 x 1O6 metric tons (t) entered the reservoir in years of high runoff. Most of the sediments were deposited in the river channel and formed an extensive delta in upper Lake Mead. However, sediments were also transported into the Virgin Basin and Overton Arm by the overflow that occurred during spring runoff. The limnology of Lake Mead is thought to have been strongly influenced by this turbid overflow until Glen Canyon Dam was constructed 450 km upstream in 1963. The construction of Glen Canyon Dam and formation of Lake Powell drastically altered the characteristics of the Colorado River inflow to Lake Mead. The operation of Glen Canyon Dam stabilized flows, reduced river temperatures and cut the suspended sediment loads by 70-80%. Nitrate loads decreased initially during 1963 and 1964, then increased through 1970, but have since decreased again to a lower steady state. Phosphorus loads were decreased due to reductions in suspended sediment inputs. Lake Powell now retains 70% of the dissolved phosphorus and 96% of the total phosphorus inputs that once flowed into Lake Mead. The Colorado River still provides 85% of the inorganic nitrogen to Lake Mead, but Las Vegas Wash now contributes 60% of the phosphorus inputs. Wastewater discharges from Las Vegas Wash into Las Vegas Bay increased steadily during the post-Lake Powell period. The morphometry and hydrodynamics of Lake Mead are such that the Las Vegas Wash inflow is confined to the Lower Basin where historically it has elevated phytoplankton productivity. However, high phosphorus loading and productivity have resulted in decreases in nitrate concentrations, and the Las Vegas Bay and parts of Boulder Basin have become nitrogen limited since 1972. A unique situation has therefore developed in Lake Mead in that the Upper Basin has become more phosphorus limited and the Lower Basin more nitrogen limited since the formation of Lake Powell. Paulson and Baker theorized that these changes in nutrient loading and limitation must also have been accompanied by decreases in reservoir-wide productivity. There is some evidence for this hypothesis in apparent improvements in water quality of Las Vegas Bay since 1968. Chlorophyll-a concentrations in the inner Las Vegas Bay have decreased considerably since the first measurements were made in 1968 and during the period of the Lake Mead Monitoring Program. Improvements in water quality of the bay have confounded efforts to establish water quality standards on effluent discharges and are contrary to predictions made in the early 1970s that water quality would continue to degrade with increased phosphorus loading. The decline in the largemouth bass fishery documented by the Nevada Department of Wildlife could also be a symptom of lower productivity in Lake Mead. In this paper, the hypothesis that algal productivity has declined in Lake Mead as a result of impoundment of Lake Powell is evaluated. The chemical status of six stations in the Upper and Lower Basins of Lake Mead is analyzed and current and past rates of organic carbon and phosphorus sedimentation are calculated. The relationship between algal productivity and accretion of organic carbon in sediment is determined, and this is used to construct a historical record of algal productivity for Lake Mead

Chemical and biological structure of Lake Mead sediments

Lake Mead has undergone a serious decline since Glen Canyon Dam was constructed 450 km upstream in 1963. State fisheries management agencies are concerned that the decline was caused by water level fluctuations and more severe drawdowns during the bass spawning season, when the operation of Hoover Dam was altered during the post-Lake Powell period. The construction of Glen Canyon Dam and formation of Lake Powell in 1963 drastically altered the natural discharge and temperature cycles and decreased suspended sediment and nutrient loading in the Colorado River inflow to Lake Mead. Recent studies indicate that these changes in nutrient loading have caused a decrease in the fertility and productivity of Lake Mead, and this, in turn, could have contributed to the decline in the largemouth bass fishery. The Water and Power Resources Service initiated a detailed investigation of the chemical and biological properties of Lake Mead sediments in order to: (i) resolve questions regarding historical changes in fertility and productivity of the reservoir, (ii) better assess the cause(s) for the decline in the largemouth bass fishery and (iii) predict future impacts associated with the proposed power modifications to Hoover Dam and operation of pump-storage hydroelectric units. Sediment cores were collected with a Vibra-corer by a commercial, oceanographic drilling firm in non-delta areas of the inner Las Vegas Bay, middle Las Vegas Bay, Boulder Basin, Virgin Basin, Bonelli Bay and the Overton Arm. Sediments were dated by 137Cs assays and analyzed for organic content, organic carbon, total nitrogen, total phosphorus, organic phosphorus, NaOH -extractable phosphorus, calcium carbonate, bulk density and water of hydration. Individual-basin (Lower and Upper Basins) and reservoir-wide sedimentation rates were estimated for autochthonous and allochthonous organic carbon and calcium carbonate, nitrogen and phosphorus and dry weight during three periods (\u3c1954, 1955-1962, \u3c1963) of Lake Mead history. Autochthonous organic carbon sedimentation in the post-Lake Powell period was used with recent measurements of phytoplankton productivity to develop a regression model for predicting historic rates of productivity. Reservoir-wide sedimentation rates and productivity in Lake Mead were relatively low during the period prior to 1954. Increased nutrient loading in years of high runoff during the 1955-1962 period caused a sharp increase in reservoir-wide sedimentation and productivity. The Upper Basin was especially productive during this period due to large inputs of suspended sediments and phosphorus. Phosphorus loading in the Colorado River decreased by over 90% in the post-Lake Powell period and caused a severe reduction in productivity in the Upper Basin. Increased phosphorus loading from the discharges of secondary-treated sewage effluents into Las Vegas Bay, combined with relatively high nitrogen loading from the Colorado River, elevated productivity in the Lower Basin. However, this was not sufficient to offset reductions that occurred in the Upper Basin, and reservoir-wide productivity decreased by 77% during the post-Lake Powell period and was equivalent to productivity in the period prior to 1954. This decline in productivity was accompanied by a decrease in abundance of zooplankton, which comprise the principal food source for largemouth bass fry. Survival of bass fry appears to have decreased in the face of low zooplankton abundance, and this may be the cause for the historic decline of the largemouth bass fishery. The fertility and productivity of Lake Mead could be improved to benefit the bass fishery if: (i) Hoover Dam were operated from a surface, rather than deep, discharge, (ii) pump-storage hydroelectric units were operated to recirculate nutrients in the reservoir, (iii) nutrient loading from Las Vegas Wash were maintained at current levels or allowed to increase with some type of diffuser system to minimize the point source problem in the inner Las Vegas Bay

Oocyte donation to women of advanced reproductive age: pregnancy results and obstetrical outcomes in patients 45 years and older

We analysed the results of oocyte donation to women of advanced reproductive age (≥45 years old) and followed their pregnancies through to delivery in order to assess obstetrical outcomes. Patients (n = 162) aged 45–59 years (mean ± SD; 47.3 ± 3.4 years) underwent 218 consecutive attempts to achieve pregnancy. Oocytes (16.2 ± 7.2 per retrieval) were provided by donors ≤35 years old. Cleaving embryos (8.2 ± 4.8 zygotes/couple) were transferred trans-cervically (4.5 ± 1.1 per embryo transfer) to recipients prescribed oral micronized oestradiol and intramuscular progesterone. Following oocyte aspiration there were six instances of non-fertilization (2.8%) and 212 embryo transfers. A total of 103 pregnancies was established for an overall pregnancy rate (PR) of 48.6%, which included 17 preclinical pregnancies, 12 spontaneous abortions, and 74 delivered pregnancies (clinical PR 40.6%; delivered PR 34.9%). Multiple gestations were frequent (n = 29; 39.2% of pregnancies) and included 20 twins, seven triplets, and two quadruplets. Two of the triplet and both of the quadruplet pregnancies underwent selective reduction to twins. Antenatal complications occurred in 28 women (37.8% of deliveries) and included preterm labour (n = 9), gestational hypertension (n = 8), gestational diabetes (n = 6), carpel tunnel syndrome (n = 2), pre-eclampsia (n = 2), HELLP syndrome (n = 2), and fetal growth retardation (n = 2). 48 (64.8%) deliveries were by Caesa-rean section. The gestational age at delivery for singletons was 383 ± 1.3 weeks (range 35–41 weeks), with birth weight 3218 ± 513 g (range 1870–4775 g); twins 35.9 ± 2.0 weeks (range 32–39 weeks), birth weight 2558 ± 497 g (range 1700-3450 g); and triplets 33.5 ± 0.7 weeks (range 32-34 weeks), birth weight 1775 ± 190 g (range 1550-2100 g). Neonatal complications (4.6% of babies born) included growth retardation (n = 2), trisomy 21 (n = 1), ventricular septal defect (n = 1), and small bowel obstruction (n = 1). There were no maternal or neonatal deaths. We conclude that oocyte donation to women of advanced reproductive age is highly successful in establishing pregnancy. However, despite careful antenatal screening, obstetrical complications are common, often secondary to multiple gestation

Efficacy of oocytes donated by older women in an oocyte donation programme

Population and insemination studies indicate that women experience declining fertility with ageing. The question therefore arises whether older women are suitable oocyte donors. This study addresses this issue by examining the relationship between oocyte donor age and clinical outcome in a large oocyte donation programme. We retrospectively reviewed data from 458 consecutive oocyte donation cycles completed by 164 different designated oocyte donors. Data were divided into two groups: group A, cycles with donors aged 21–30 years at the time of follicular aspiration (193 cycles, 88 donors); and group B, cycles with donors aged 31–40 years at the time of follicular aspiration (265 cycles, 86 donors). Five donors, because of ageing during repetitive donations, contributed data to groups A and B. In a given cycle, all oocytes for a recipient came from only one designated donor. Comparing the two donor groups, there was no difference in the amount of gonadotrophin used to achieve optimal stimulation; however, more oocytes were obtained from group A than group B donors (16.8 ± 6.9 and 15.1 ± 8.1 respectively, P < 0.05). Similar percentages of oocytes were fertilized in each group, resulting in the transfer of comparable numbers of embryos (4.5 ± 1.1 and 4.4 ± 13 respectively). Comparable clinical pregnancy rates were achieved (group A, 36%; group B, 37%). The spontaneous abortion rates were also similar (group A, 20%; group B, 12%), resulting in comparable ongoing and delivered pregnancy rates per cycle (group A, 29%; group B, 32%) and per embryo transferred (group A, 6.4%; group B, 7.3%). In conclusion, women of proven fertility should not be excluded from donating oocytes simply because of their age. There exists a cohort of fertile women who resist the decreasing fecundity and increasing spontaneous abortion rates associated with ageing. With careful screening, many women of proven fertility can donate oocytes until the age of 40 years with an efficacy equal to that of younger women. Given the relative shortage of suitable oocyte donors, and increasing requests from recipients with previous donor oocyte babies to obtain oocytes from the same, now older, donor, the findings of this study are of practical clinical importance

Generation of EMIC Waves and Effects on Particle Precipitation During a Solar Wind Pressure Intensification With Bz>0.

During geomagnetic storms, some fraction of the solar wind energy is coupled via reconnection at the dayside magnetopause, a process that requires a southward interplanetary magnetic field Bz. Through a complex sequence of events, some of this energy ultimately drives the generation of electromagnetic ion cyclotron (EMIC) waves, which can then scatter energetic electrons and ions from the radiation belts. In the event described in this paper, the interplanetary magnetic field remained northward throughout the event, a condition unfavorable for solar wind energy coupling through low‐latitude reconnection. While this resulted in SYM/H remaining positive throughout the event (so this may not be considered a storm, in spite of the very high solar wind densities), pressure fluctuations were directly transferred into and then propagated throughout the magnetosphere, generating EMIC waves on global scales. The generation mechanism presumably involved the development of temperature anisotropies via perpendicular pressure perturbations, as evidenced by strong correlations between the pressure variations and the intensifications of the waves globally. Electron precipitation was recorded by the Balloon Array for RBSP Relativistic Electron Losses balloons, although it did not have the same widespread signatures as the waves and, in fact, appears to have been quite patchy in character. Observations from Van Allen Probe A satellite (at postmidnight local time) showed clear butterfly distributions, and it may be possible that the EMIC waves contributed to the development of these distribution functions. Ion precipitation was also recorded by the Polar‐orbiting Operational Environmental Satellite satellites, though tended to be confined to the dawn‐dusk meridians

Application of a nested-grid ocean circulation model to a shallow coastal embayment: Verification against observations

A nested-grid ocean circulation modeling system is used to study the response of Lunenburg Bay in Nova Scotia, Canada, to local wind-forcing, tides, remotely generated waves, and buoyancy forcing in the summer and fall of 2003. Quantitative comparisons between observations and model results demonstrate that the modeling system reproduces reasonably well the observed sea level, temperature, salinity, and currents in the bay. Numerical results reveal that the spatial and temporal variability of temperature and salinity in the bay during the study period is mainly forced by the local wind stress and surface heat/freshwater fluxes, with some contribution from tidal circulation. In particular, the local heat balance on the monthly timescale is dominated by cooling due to vertical advection and warming due to horizontal advection and net surface heat flux, while high-frequency variations (timescales of 1–30 days) are mainly associated with vertical advection, i.e., wind-induced upwelling and downwelling. There is also a strong baroclinic throughflow over the deep water region outside Lunenburg Bay that is strongly influenced by wind-forcing. The vertically integrated momentum balance analysis indicates a modified geostrophic balance on the monthly timescale and longer, and is dominated by the pressure term and wind minus bottom stress in the high-frequency band

Lake Mead prefertilization study: Preliminary nutrient enhancement studies in Lake Mead

Studies conducted by the University of Nevada-Las Vegas (UNLV), the Nevada Department of Wildlife (NDOW), the Arizona Game and Fish Department (AGFD), The Nevada Division of Environmental Protection (NDEP), and the United States Bureau of Reclamation (USBR) have identified decreased algal production as a major factor involved in the decline of the Lake Mead sport fishery. Phosphorus-laden silt particles in the Colorado River have been sedimenting out in Lake Powell since the completion of Glen Canyon Dam 286 miles upstream in 1963. This sharp decrease in phosphorus loading to Lake Mead (\u3e5000 tons per year) has resulted in decreased biomass and growth at all levels of the food chain. Phosphorus loading to the lower basin (Boulder Basin) has decreased even further since 1981 when Clark County and the City of Las Vegas began removing phosphorus from wastewaters discharged into Las Vegas Bay. Most of Lake Mead is now oligotrophic according to almost all of the trophic status indices which have been developed. Only the inner and middle regions of Las Vegas Bay (treated wastewater influent), the Overton Arm upstream of Fish Island (Muddy and Virgin River discharges), and the Iceberg Canyon/Grand Wash area (Colorado River influence) have been found to have phosphorus levels sufficient to sustain relatively higher productivity. Phytoplankton production becomes tightly regulated by the supply of phosphorus during most of the growing season. Zooplankton graze on planktonic algae, and threadfin shad feed primarily on these zooplankton and phytoplankton. Since game fish feed primarily on either zooplankton or shad at different stages of their life cycle, it is clear how a nutrient limitation of phytoplankton growth can cascade up the food chain. The declines in the sport fisheries, particularly largemouth bass, striped bass and trout, began in the early 1960\u27s and have become much more dramatic since the mid to late 1970\u27s as evidenced by declines in total yields of largemouth bass and trout, and striped bass condition factors, and increased angler effort. It is likely that as fish were increasingly stressed by food shortages, conditions were worsened by indirect factors such as lack of suitable cover for littoral populations and by fish predation. The only way to restore the previous fertility of the lake water is to add nutrients. Large-scale fertilization programs in British Columbia and Alaska have been very successful at stimulating the productivity of all levels of the food chain, ultimately producing more salmon. Nevada and Arizona completed an intensive study of the black bass (largemouth bass) fishery in Lake Mead in 1982 which was funded by the U.S. Bureau of Reclamation (USBR). A major recommendation was that pilot fertilizations be conducted as a demonstration project for future large-scale nutrient enrichment. UNLV subsequently submitted a proposal to the Bureau of Reclamation in November 1984 to artificially fertilize about 30,000 acres in the Overton Arm and about 11,000 acres in Gregg Basin. Since that time a technical advisory panel (the Lake Mead Nutrient Enhancement Technical Committee) comprised of representatives from UNLV, NDOW, AGFD, USBR, NDEP, the National Park Service (NPS), and the U.S. Fish and Wildlife Service (USFWS), was formed to review the original proposal and develop a feasible plan for implementing an experimental program of large-scale fertilization. Subsequently, the USBR funded the present study for 16 months (May 1986-August 1987) to conduct laboratory and pilot-scale field experiments designed to evaluate the potential for successfully stimulating algal growth on a large scale in Lake Mead using artificial fertilization

Quantified Uncertainty in Thermodynamic Modeling for Materials Design

Phase fractions, compositions and energies of the stable phases as a function of macroscopic composition, temperature, and pressure (X-T-P) are the principle correlations needed for the design of new materials and improvement of existing materials. They are the outcomes of thermodynamic modeling based on the CALculation of PHAse Diagrams (CALPHAD) approach. The accuracy of CALPHAD predictions vary widely in X-T-P space due to experimental error, model inadequacy and unequal data coverage. In response, researchers have developed frameworks to quantify the uncertainty of thermodynamic property model parameters and propagate it to phase diagram predictions. In most previous studies, uncertainty was represented as intervals on phase boundaries (with respect to composition or temperature) and was unable to represent the uncertainty in invariant reactions or in the stability of phase regions. In this work, we propose a suite of tools that leverages samples from the multivariate model parameter distribution to represent uncertainty in forms that surpass previous limitations and are well suited to materials design. These representations include the distribution of phase diagrams and their features, as well as the dependence of phase stability and the distributions of phase fraction, composition, activity and Gibbs energy on X-T-P location - irrespective of the total number of components. Most critically, the new methodology allows the material designer to interrogate a certain composition and temperature domain and get in return the probability of different phases to be stable, which can positively impact materials design