Nerodia valida

Number of Pages: 3Integrative BiologyGeological Science

Numerical modelling of the compression-after-impact behaviour of composite sandwich panels

Sandwich panels using fibre-reinforced composite skins and low-density cores are being increasingly used in the aerospace industry due to their superior specific strength and stiffness, and increased design flexibility over traditional metallic and composite structures. However, it is well-known that sandwich panels are highly vulnerable to the effects of impact damage, with even low-energy impacts potentially causing very severe reductions in the in-plane compressive strength of these structures. The objective of this project was to produce a faithful and reliable numerical model for the simulation of the compression-after-impact strength of composite sandwich panels. An in-depth literature review revealed that delamination within the skins of a sandwich panel is a damage mechanism that has gone almost entirely neglected in previous efforts at modelling this problem, despite the proven significance of this mechanism in the failure of impact damaged sandwich panels in compression. Consequently, the use of the cohesive zone model for delamination initiation and propagation is the key unique feature of this model, with Hashin s criteria being used for intra-laminar damage formation, and a simple plasticity response capturing core crushing. An experimental study is performed to produce a thorough dataset for model validation, featuring differing levels of damage induced via quasi-static indentation, and novel asymmetric panels with skins of unequal thickness (the thinner skin being on the unimpacted side). The experimental study revealed that the use of a thinner distal (undamaged) skin could improve the strength of mildly damaged sandwich panels over undamaged sandwich panels using the same asymmetric configuration. It is believed that this effect is due to the movement of the neutral plane of the sandwich panel caused by the reduction in the stability of the damaged skin through stiffness reduction and geometric imperfections. This removes the eccentricity of the compressive loading that exists in the undamaged asymmetric panels, which has mismatched axial stiffness between the indented skin and the thinner distal skin, and thus a noticeably lower ultimate strength than the undamaged symmetric panels. The sandwich model is developed using pre-existing experimental and material data, and trialled for a variety of different skin lay-ups, core thicknesses and indenter sizes. The numerical model generally agreed well with the ultimate stress found in the experiments for these different configurations, but is quite poor at estimating the magnitude of the damage induced by the indentation. When used to model the experimental study, the model gave generally good, conservative estimates for the residual compressive strength of both the symmetric and asymmetric panels. The tendency of the asymmetric panels to become stronger with mild damage was not captured by the model per se, with the numerical results instead showing an insensitivity to damage in the asymmetric panels, which was not shared by the symmetric panels. However, the numerical model did exhibit erroneous strain-stress responses for both panel configurations, particularly for the undamaged and mildly damaged cases. Investigations revealed that this erroneous behaviour was caused by inconsistency in the material data, which had been collected partially via experimentation and partly from literature sources. Overall, the model developed here represents a promising advancement over previous efforts, but further development is required to provide accurate damage states

Providing True Opportunity for Opportunity Youth: Promising Practices and Principles for Helping Youth Facing Barriers to Employment

Many "opportunity youth" -- youth who are not working or in school -- would benefit substantially from gaining work experience but need help overcoming barriers to employment and accessing the labor market.Those opportunity youth facing the most significant challenges, such as extreme poverty, homelessness, and justice system involvement, often need even more intensive assistance in entering and keeping employment, and are at risk of being left behind even by employment programs that are specifically designed to serve opportunity youth.This paper builds on the research literature with extensive interviews with employment program providers who have had success in helping the most vulnerable opportunity youth succeed in the workforce. Six principles for effectively serving these youth are identified

Classification and analysis of emission-line galaxies using mean field independent component analysis

We present an analysis of the optical spectra of narrow emission-line galaxies, based on mean field independent component analysis (MFICA). Samples of galaxies were drawn from the Sloan Digital Sky Survey (SDSS) and used to generate compact sets of `continuum' and `emission-line' component spectra. These components can be linearly combined to reconstruct the observed spectra of a wider sample of galaxies. Only 10 components - five continuum and five emission line - are required to produce accurate reconstructions of essentially all narrow emission-line galaxies; the median absolute deviations of the reconstructed emission-line fluxes, given the signal-to-noise ratio (S/N) of the observed spectra, are 1.2-1.8 sigma for the strong lines. After applying the MFICA components to a large sample of SDSS galaxies we identify the regions of parameter space that correspond to pure star formation and pure active galactic nucleus (AGN) emission-line spectra, and produce high S/N reconstructions of these spectra. The physical properties of the pure star formation and pure AGN spectra are investigated by means of a series of photoionization models, exploiting the faint emission lines that can be measured in the reconstructions. We are able to recreate the emission line strengths of the most extreme AGN case by assuming the central engine illuminates a large number of individual clouds with radial distance and density distributions, f(r) ~ r^gamma and g(n) ~ n^beta, respectively. The best fit is obtained with gamma = -0.75 and beta = -1.4. From the reconstructed star formation spectra we are able to estimate the starburst ages. These preliminary investigations serve to demonstrate the success of the MFICA-based technique in identifying distinct emission sources, and its potential as a tool for the detailed analysis of the physical properties of galaxies in large-scale surveys.Comment: MNRAS accepted. 29 pages, 24 figures, 3 table

Interpreting the Ionization Sequence in AGN Emission-Line Spectra

We investigate the physical cause of the great range in the ionization level seen in the spectra of narrow lined active galactic nuclei (AGN). Mean field independent component analysis identifies examples of individual SDSS galaxies whose spectra are not dominated by emission due to star formation (SF), which we designate as AGN. We assembled high S/N ratio composite spectra of a sequence of these AGN defined by the ionization level of their narrow-line regions (NLR), extending down to very low-ionization cases. We used a local optimally emitting cloud (LOC) model to fit emission-line ratios in this AGN sequence. These included the weak lines that can be measured only in the co-added spectra, providing consistency checks on strong line diagnostics. After integrating over a wide range of radii and densities our models indicate that the radial extent of the NLR is the major parameter in determining the position of high to moderate ionization AGN along our sequence, providing a physical interpretation for their systematic variation. Higher ionization AGN contain optimally emitting clouds that are more concentrated towards the central continuum source than in lower ionization AGN. Our LOC models indicate that for the objects that lie on our AGN sequence, the ionizing luminosity is anticorrelated with the NLR ionization level, and hence anticorrelated with the radial concentration and physical extent of the NLR. A possible interpretation that deserves further exploration is that the ionization sequence might be an age sequence where low ionization objects are older and have systematically cleared out their central regions by radiation pressure. We consider that our AGN sequence instead represents a mixing curve of SF and AGN spectra, but argue that while many galaxies do have this type of composite spectra, our AGN sequence appears to be a special set of objects with negligible SF excitation.Comment: 57 pages; 18 figures, accepted by MNRA

Organizational Effectiveness Measures and Their Relationship to Donor Contributions

The purpose of this study was to examine the relationship between organizational effectiveness measures and donor contributions for National Collegiate Athletic Association Division I athletic departments. For this study, donor contributions were used as a proxy for donors’ perception of organizational effectiveness for these athletic departments. Using a combination of the goals attainment model (Price, 1972) and the strategic constituencies model (Connolly, Conlon, & Deutsch, 1980) the effectiveness measures used were athletic performance, student athlete welfare, and student athlete academic success. The whole of Division I, as well as the three subdivisions, were examined for the five-year period from 2013 to 2017. The results of hierarchical multiple linear regressions suggested that a significant proportion of the variance in donor contributions was predicted by a combination of athletic performance, student athlete welfare, and student athlete academic success. This was true for all of Division I, but varied by subdivision. Approximately 60% of variance was predicted by the combination of effectiveness measures for the Football Bowl Subdivision, 12% for the Football Championship Subdivision (FCS), and 20% for Division I without football. Student athlete academic success proved to only be a significant predictor on its own for the FCS

Millipeds (Arthropoda: Diplopoda) of the Ark-La-Tex. I. New Distributional and State Records for Seven Counties of the West Gulf Coastal Plain of Arkansas

Unlike the Diplopoda of the Ozark Mountains region of north Arkansas, the millipeds of the West Gulf Coastal Plain of the state are poorly known. During the winter months of 2001-2002, we collected millipeds in four counties (Hempstead, Lafayette, Little River, and Miller) of southwest Arkansas and three counties (Columbia, Nevada, and Ouachita) of south Arkansas. We found the following species/subspecies Eurymerodesmus dubuis and Pseudopolydesmus pinetorum from Hempstead County; E. birdi birdi, E. mundus, Oxidus gracilis, and Pseudopolydesmus ? minor from Lafayette County; Aniulus (Hakiulus) diversifrons diversifrons, P. pinetorum, and a possible new species of Tiganogona in Little River County; Abacion ? texense, E. Mundus, 0. gracilis, P. pinetorum, Thrinaxoria lampra, and a new species of Aniulus (Hakiulus) from Miller County; Auturus louisianus louisianus, E. dubuis, Cambala minor, O. gracilis, P. pinetorum, and a female xystodesmid of the tribe Pachydesmini from Columbia County; Virgoiulus minutus, C. minor, P. pinetorum, and A. l. louisianus from Nevada County; and P. pinetorum, Eurymerodesmus sp., Narceus americanus, and C. minor from Ouachita County. A new state record is documented for T. lampra from Miller County, and the finding of V. minutus in Miller and Nevada counties represents the southwesternmost distributional records for the genus and species. To our knowledge, all millipeds reported herein for Little River County are the first ever documented for that county, including a potentially new species of Tiganogona, a genus known previously from Carroll, Clay, Sebastian, and Washington counties, Arkansas, Lincoln Parish, Louisiana, and more distant locales in Missouri and Indiana

Interpreting the Ionization Sequence in Star-Forming Galaxy Emission-Line Spectra

High ionization star forming (SF) galaxies are easily identified with strong emission line techniques such as the BPT diagram, and form an obvious ionization sequence on such diagrams. We use a locally optimally emitting cloud model to fit emission line ratios that constrain the excitation mechanism, spectral energy distribution, abundances and physical conditions along the star-formation ionization sequence. Our analysis takes advantage of the identification of a sample of pure star-forming galaxies, to define the ionization sequence, via mean field independent component analysis. Previous work has suggested that the major parameter controlling the ionization level in SF galaxies is the metallicity. Here we show that the observed SF- sequence could alternatively be interpreted primarily as a sequence in the distribution of the ionizing flux incident on gas spread throughout a galaxy. Metallicity variations remain necessary to model the SF-sequence, however, our best models indicate that galaxies with the highest and lowest observed ionization levels (outside the range -0.37 < log [O III]/H\b{eta} < -0.09) require the variation of an additional physical parameter other than metallicity, which we determine to be the distribution of ionizing flux in the galaxy.Comment: 41 pages, 17 figures, 9 tables, accepted to MNRA

Millipeds (Arthropoda: Diplopoda) of the Ark-La-Tex. II. Distributional Records for Some Species of Western and Central Arkansas and Easter and Southeastern Oklahoma

We collected millipeds between November 2001 and March 2002 at several sites in the Ouachita Provinces of western (Garland, Hot Spring, Pike, and Polk counties) and central Arkansas (Pulaski County) and the Ouachita and Kiamichi Provinces of southeastern Oklahoma (LeFlore and McCurtain counties). The following millipeds were found: Eurymerodesmus dubius, Auturus louisianus louisianus, Pseudopolydesmus pinetorum, and Cambala minor in Garland County; Eurymerodesmus sp., A. I. louisianus, P. pinetorum, and juveniles of the family Parajulidae (tribe Aniulini) from Hot Spring County; E. dubius, A. I. louisianus, and juveniles of the family Cleidogonidae from Pike County; Brachycybe lecontei, A. I. louisianus, Abacion tesselatum, and P. pinetorum in Polk County; Eurymerodesmus pulaski, P. pinetorum, Auturus evides, C. minor, B. lecontei, and a possible new species of Cleidogona in Pulaski County; A. I. louisianus, Apheloria virginiensis ?reducta, P. pinetorum, Narceus americanus, and E. dubius in McCurtain County; and B. lecontei, A.l. louisianus, Eurymerodesmus b. birdi, A. Ptesselatum, and juveniles of the family Parajulidae (tribe Aniulini) in LeFlore County. Two new state records are documented for Oklahoma: B. lecontei (Platydesmida: Andrognathidae), a record not only for the genus and species but also for the family and order; and E. dubius, the westernmost locality ever reported for the species

Geographic Distribution Records for Scolopendromorph Centipedes (Arthropoda: Chilopoda) from Arkansas, Oklahoma, and Texas

During 2001-2003, we collected eight species of scolopendromorph centipedes from 17 counties of Arkansas (AR), seven counties of Oklahoma (OK), and 17 counties of Texas (TX). The following taxa were collected: Cryptops leucopodus (Rafinesque) from Bowie and Cass counties, TX, and Pulaski County, AR; Hemiscolopendra marginata (Say) from Columbia, Garland, Hempstead, Little River, Pike, Polk, and Yell counties, AR, and Cass, Cherokee, Coryell, Houston, Johnson, Kimble, Marion, Nacogdoches, Smith, and Tom Green counties, TX; Scolopocryptops rubiginosus L. Koch from Bowie and Dallas counties, TX; Scolopocryptops sexspinosus (Say) from Clark, Columbia, Conway, Faulkner, Hot Spring, Garland, Miller, Montgomery, Polk, Pope, and Pulaski counties, AR, LeFlore and McCurtain counties, OK, and Marion, Red River, and Rusk counties, TX; Scolopendra hews Girard from Atoka, Major, and McCurtain counties, OK; Scolopendra polymorpha Wood from Woodward County, OK; Theatops posticus (Say) from Montgomery County, AR, Choctaw, Marshall, and McCurtain counties, OK, and Cass, Dallas, Freestone, Hopkins, Houston, Red River, and Titus counties, TX; and Theatops spinicaudus (Wood) from Garland, Hot Spring, Little River, Pike, and Scott counties, AR, and Atoka, Choctaw, and McCurtain counties, OK. Most significantly, our records of S. rubiginosus are well outside its distributional range as depicted in Shelley (2002). A total of 43 new county records is documented, including 14 in Arkansas, nine in Oklahoma, and 20 in Texas