MPS solidification model. Analysis and calculation of macrosegregation in a casting ingot

Work performed on several existing solidification models for which computer codes and documentation were developed is presented. The models describe the solidification of alloys in which there is a time varying zone of coexisting solid and liquid phases; i.e., the S/L zone. The primary purpose of the models is to calculate macrosegregation in a casting or ingot which results from flow of interdendritic liquid in this S/L zone during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, is modeled as flow through a porous medium. In Model 1, the steady state model, the heat flow characteristics are those of steady state solidification; i.e., the S/L zone is of constant width and it moves at a constant velocity relative to the mold. In Model 2, the unsteady state model, the width and rate of movement of the S/L zone are allowed to vary with time as it moves through the ingot. Each of these models exists in two versions. Models 1 and 2 are applicable to binary alloys; models 1M and 2M are applicable to multicomponent alloys

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 1: Formulation and analysis

The physical and numerical formulation of a model for the horizontal solidification of a binary alloy is described. It can be applied in an ingot. The major purpose of the model is to calculate macrosegregation in a casting ingot which results from flow of interdendritic liquid during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, was modeled as flow through a porous medium. The symbols used are defined. The physical formulation of the problem leading to a set of equations which can be used to obtain: (1) the pressure field; (2) the velocity field: (3) mass flow and (4) solute flow in the solid plus liquid zone during solidification is presented. With these established, the model calculates macrosegregation after solidification is complete. The numerical techniques used to obtain solution on a computational grid are presented. Results, evaluation of the results, and recommendations for future development of the model are given. The macrosegregation and flow field predictions for tin-lead, aluminum-copper, and tin-bismuth alloys are included as well as comparisons of some of the predictions with published predictions or with empirical data

Redefinition of the Upper Pennsylvanian Virgilian Series in Kansas

The Virgilian Series was defined nearly 60 years ago to include those rocks lying between the Missourian Series and the base of the Permian System. In the type area in east-central Kansas, the Virgilian Series comprised the Douglas, Shawnee, and Wabaunsee Groups. In Kansas, the upper boundary of the Virgilian (Pennsylvanian-Permian boundary) was placed at the top of the Brownville Limestone Member on the basis of what was then believed to be a regional disconformity rather than on paleontological criteria. Recent advances in fusulinid and conodont biostratigraphy provide tentative criteria upon which to effect a change in the placement of the Virgilian-Permian boundary. It is now generally agreed that the base of the Permian System is approximated by the first occurrence of Pseudoschwagerina, an inflated schwagerinid. Furthermore, the Subcommission on Permian Stratigraphy has informally agreed that the base of the Permian should coincide with the first occurrence of the conodont species Streptognathodus barskovi. Inflated schwagerinids (Paraschwagerina kansasensis) first occur along with evolutionary changes in the Conodonta in the Neva Limestone of the Council Grove Group. Consequently, the Virgilian Series is herein redefined to include rocks present between the top of the Missourian Series and the base of the Neva Limestone. To increase compatibility between chronostratigraphic and lithostratigraphic nomenclature, the following changes are made: I) the Admire Group is redefined to include rocks between the base of the Onaga Shale and the base of the Neva Limestone; 2) the Admire is reassigned to the upper Virgilian Series; 3) the Neva Limestone is elevated to formational status; 4) the Grenola Limestone is redefined to include strata between the top of the Roca Shale and the base of the Neva Limestone; 5) the overlying Council Grove Group is redefined to include strata lying between the base of the Neva Limestone and the base of the Chase Group; and 6) regionally the base of the emended Council Grove Group marks the base of the Permian System. The emended Council Grove Group is lower Wolfcampian in age and is time equivalent with the Neal Ranch Formation of the west Texas type Wolfcampian

Redefinition of the Upper Pennsylvanian Virgilian Series in Kansas

The Virgilian Series was defined nearly 60 years ago to include those rocks lying between the Missourian Series and the base of the Permian System. In the type area in east-central Kansas, the Virgilian Series comprised the Douglas, Shawnee, and Wabaunsee Groups. In Kansas, the upper boundary of the Virgilian (Pennsylvanian-Permian boundary) was placed at the top of the Brownville Limestone Member on the basis of what was then believed to be a regional disconformity rather than on paleontological criteria. Recent advances in fusulinid and conodont biostratigraphy provide tentative criteria upon which to effect a change in the placement of the Virgilian-Permian boundary. It is now generally agreed that the base of the Permian System is approximated by the first occurrence of Pseudoschwagerina, an inflated schwagerinid. Furthermore, the Subcommission on Permian Stratigraphy has informally agreed that the base of the Permian should coincide with the first occurrence of the conodont species Streptognathodus barskovi. Inflated schwagerinids (Paraschwagerina kansasensis) first occur along with evolutionary changes in the Conodonta in the Neva Limestone of the Council Grove Group. Consequently, the Virgilian Series is herein redefined to include rocks present between the top of the Missourian Series and the base of the Neva Limestone. To increase compatibility between chronostratigraphic and lithostratigraphic nomenclature, the following changes are made: I) the Admire Group is redefined to include rocks between the base of the Onaga Shale and the base of the Neva Limestone; 2) the Admire is reassigned to the upper Virgilian Series; 3) the Neva Limestone is elevated to formational status; 4) the Grenola Limestone is redefined to include strata between the top of the Roca Shale and the base of the Neva Limestone; 5) the overlying Council Grove Group is redefined to include strata lying between the base of the Neva Limestone and the base of the Chase Group; and 6) regionally the base of the emended Council Grove Group marks the base of the Permian System. The emended Council Grove Group is lower Wolfcampian in age and is time equivalent with the Neal Ranch Formation of the west Texas type Wolfcampian

Proposed Repositioning of the Pennsylvanian-Permian Boundary in Kansas

The Pennsylvanian-Permian boundary in North America has not corresponded with the Carboniferous-Permian boundary in Europe for decades. To facilitate global correlations, an attempt is here made to suggest a possible solution to the dilemma by making the best possible correlation of the Kansas stratigraphic section with the recently proposed boundary location in the Russian type section. The Virgilian Stage (Upper Pennsylvanian) was defined nearly 60 years ago to include those rocks lying between the Missourian Stage and the base of the Permian System. In the type area in east-central Kansas, the Virgilian Stage comprised the Douglas, Shawnee, and Wabaunsee Groups. In Kansas, the Pennsylvanian-Permian boundary was placed eventually at the top of the Brownville Limestone Member on the basis of what was then believed to be a regional disconformity rather than on paleontological criteria. Recent advances in fusulinid and conodont biostratigraphy provide tentative criteria upon which to suggest a change in the placement of the Virgilian-Permian boundary. A Russian delegation formally proposed at the International Congress on the Permian System of the World held in Perm, U.S.S.R. (Russia) in August 1991 that the base of the Permian System be established at the base of the Asselian Stage at the approximate stratigraphic position of the first inflated fusulinids (Sphaeroschwagerina vulgaris-S. fusiformis). Inflated schwagerinids (Paraschwagerina kansasensis) first occur, along with evolutionary changes in conodonts, in the Neva Limestone Member of the Grenola Limestone (Council Grove Group). Thus, if we assume that inflated schwagerinids arose globally at about the same time, the Neva Limestone Member is the oldest definitive Permian in the United States midcontinent, as related to the newly proposed boundary in Russia and Kazakhstan. Consequently, we propose that the Virgilian Stage in Kansas include rocks between the top of the Missourian Stage and the base of the Neva Limestone Member

Proposed Repositioning of the Pennsylvanian-Permian Boundary in Kansas

The Pennsylvanian-Permian boundary in North America has not corresponded with the Carboniferous-Permian boundary in Europe for decades. To facilitate global correlations, an attempt is here made to suggest a possible solution to the dilemma by making the best possible correlation of the Kansas stratigraphic section with the recently proposed boundary location in the Russian type section. The Virgilian Stage (Upper Pennsylvanian) was defined nearly 60 years ago to include those rocks lying between the Missourian Stage and the base of the Permian System. In the type area in east-central Kansas, the Virgilian Stage comprised the Douglas, Shawnee, and Wabaunsee Groups. In Kansas, the Pennsylvanian-Permian boundary was placed eventually at the top of the Brownville Limestone Member on the basis of what was then believed to be a regional disconformity rather than on paleontological criteria. Recent advances in fusulinid and conodont biostratigraphy provide tentative criteria upon which to suggest a change in the placement of the Virgilian-Permian boundary. A Russian delegation formally proposed at the International Congress on the Permian System of the World held in Perm, U.S.S.R. (Russia) in August 1991 that the base of the Permian System be established at the base of the Asselian Stage at the approximate stratigraphic position of the first inflated fusulinids (Sphaeroschwagerina vulgaris-S. fusiformis). Inflated schwagerinids (Paraschwagerina kansasensis) first occur, along with evolutionary changes in conodonts, in the Neva Limestone Member of the Grenola Limestone (Council Grove Group). Thus, if we assume that inflated schwagerinids arose globally at about the same time, the Neva Limestone Member is the oldest definitive Permian in the United States midcontinent, as related to the newly proposed boundary in Russia and Kazakhstan. Consequently, we propose that the Virgilian Stage in Kansas include rocks between the top of the Missourian Stage and the base of the Neva Limestone Member

Robust Chauvenet Outlier Rejection

Sigma clipping is commonly used in astronomy for outlier rejection, but the number of standard deviations beyond which one should clip data from a sample ultimately depends on the size of the sample. Chauvenet rejection is one of the oldest, and simplest, ways to account for this, but, like sigma clipping, depends on the sample's mean and standard deviation, neither of which are robust quantities: Both are easily contaminated by the very outliers they are being used to reject. Many, more robust measures of central tendency, and of sample deviation, exist, but each has a tradeoff with precision. Here, we demonstrate that outlier rejection can be both very robust and very precise if decreasingly robust but increasingly precise techniques are applied in sequence. To this end, we present a variation on Chauvenet rejection that we call "robust" Chauvenet rejection (RCR), which uses three decreasingly robust/increasingly precise measures of central tendency, and four decreasingly robust/increasingly precise measures of sample deviation. We show this sequential approach to be very effective for a wide variety of contaminant types, even when a significant -- even dominant -- fraction of the sample is contaminated, and especially when the contaminants are strong. Furthermore, we have developed a bulk-rejection variant, to significantly decrease computing times, and RCR can be applied both to weighted data, and when fitting parameterized models to data. We present aperture photometry in a contaminated, crowded field as an example. RCR may be used by anyone at https://skynet.unc.edu/rcr, and source code is available there as well.Comment: 62 pages, 48 figures, 7 tables, accepted for publication in ApJ

The fading of Cassiopeia A, and improved models for the absolute spectrum of primary radio calibration sources

Based on five years of observations with the 40-foot telescope at Green Bank Observatory (GBO), Reichart & Stephens (2000) found that the radio source Cassiopeia A had either faded more slowly between the mid-1970s and late 1990s than Baars et al. (1977) had found it to be fading between the late 1940s and mid-1970s, or that it had rebrightened and then resumed fading sometime between the mid-1970s and mid-1990s, in L band (1.4 GHz). Here, we present 15 additional years of observations of Cas A and Cyg A with the 40-foot in L band, and three and a half additional years of observations of Cas A, Cyg A, Tau A, and Vir A with GBO's recently refurbished 20-meter telescope in L and X (9 GHz) bands. We also present a more sophisticated analysis of the 40-foot data, and a reanalysis of the Baars et al. (1977) data, which reveals small, but non-negligible differences. We find that overall, between the late 1950s and late 2010s, Cas A faded at an average rate of $0.670 \pm 0.019$ %/yr in L band, consistent with Reichart & Stephens (2000). However, we also find, at the 6.3$\sigma$ credible level, that it did not fade at a constant rate. Rather, Cas A faded at a faster rate through at least the late 1960s, rebrightened (or at least faded at a much slower rate), and then resumed fading at a similarly fast rate by, at most, the late 1990s. Given these differences from the original Baars et al. (1977) analysis, and given the importance of their fitted spectral and temporal models for flux-density calibration in radio astronomy, we update and improve on these models for all four of these radio sources. In doing so, we additionally find that Tau A is fading at a rate of $0.102^{+0.042}_{-0.043}$ %/yr in L band.Comment: 17 pages, 12 figures, accepted to MNRA

Advanced X-Ray Timing Array Mission: Conceptual Spacecraft Design Study

The Advanced X-Ray Timing Array (AXTAR) is a mission concept for submillisecond timing of bright galactic x-ray sources. The two science instruments are the Large Area Timing Array (LATA) (a collimated instrument with 2-50-keV coverage and over 3 square meters of effective area) and a Sky Monitor (SM), which acts as a trigger for pointed observations of x-ray transients. The spacecraft conceptual design team developed two spacecraft concepts that will enable the AXTAR mission: A minimal configuration to be launched on a Taurus II and a larger configuration to be launched on a Falcon 9 or similar vehicle

Mitochondrial Respiratory Capacity and Content Are Normal in Young Insulin-Resistant Obese Humans

Considerable debate exists about whether alterations in mitochondrial respiratory capacity and/or content play a causal role in the development of insulin resistance during obesity. The current study was undertaken to determine whether such alterations are present during the initial stages of insulin resistance in humans. Young (∼23 years) insulin-sensitive lean and insulin-resistant obese men and women were studied. Insulin resistance was confirmed through an intravenous glucose tolerance test. Measures of mitochondrial respiratory capacity and content as well as H(2)O(2) emitting potential and the cellular redox environment were performed in permeabilized myofibers and primary myotubes prepared from vastus lateralis muscle biopsy specimens. No differences in mitochondrial respiratory function or content were observed between lean and obese subjects, despite elevations in H(2)O(2) emission rates and reductions in cellular glutathione. These findings were apparent in permeabilized myofibers as well as in primary myotubes. The results suggest that reductions in mitochondrial respiratory capacity and content are not required for the initial manifestation of peripheral insulin resistance