Proximate Causes of Alternative Reproductive Tactics in Blue Ridge Two-Lined Salamanders (Eurycea cf. wilderae)

Alternative reproductive tactics (ARTs) refer to discrete variation in reproductive behavior between members of a sex and within a species. ARTs are present in Blue Ridge two-lined salamanders (Eurcyea cf. wilderae) in the form of male polymorphism. Two male morphs exist: “searching” males and “guarding” males. Each phenotype has a unique reproductive ecology and associated discrete morphological differences. Another trait that shows discrete variation in E. cf. wilderae is the larval period, which may be one or two years in length. This thesis explores the proximate causes of ARTs in a population of E. cf. wilderae from the Blue Ridge of North Carolina. The first chapter of this thesis surveys for a genetic cause for these ARTs. In this chapter, I use genomic data to evaluate population structure, identify sex-linked and ART-linked genetic markers, and estimate effective population size and kinship. The results suggest that E. cf. wilderae follow an XY sex determination system wherein alternative haplotypes of the Y chromosome determine male ARTs. The effective population size was found to be consistent with estimates from other studies on closely related taxa and the kinship coefficients within the sample were found to be low. The second chapter of this thesis assesses the relationship between ARTs and the length of the larval period, another axis of discrete life history variation in E. cf. wilderae. In this chapter, I use the ART-specific genetic markers identified in the first chapter to identify the reproductive phenotypes of 200 larvae belonging to two age classes and calculate the relative frequencies of phenotypes within the population. The results suggest no relationship between ARTs and larval period. However, I found an even sex ratio and that searching males are almost twice as abundant as guarding males in the population. Overall, this thesis not only contributes to the body of knowledge on genetically determined ARTs and the evolutionary ecology of E. cf. wilderae by: 1) identifying an XY sex determination system; 2) identifying that ARTs are linked to alternative Y chromosome haplotypes; and 3) demonstrating that larval period is not associated with ARTs; but also addresses broader topics such as: 1) the causes of alternative phenotypes with discrete life history differences; 2) the genomic bases of polymorphism and sex determination in species; and 3) the relationship between genotype, phenotype, and environmental factors

Risk Disclosure in SEC Corporate Filings

Beginning in 2005, the SEC required firms to include qualitative disclosures of risk factors in item 1A in their annual 10-K forms. In this paper, we examine the textual content of this section and determine whether it reflects the firm’s performance. We first categorized each risk disclosure that a firm presented into one of 29 categories and then examined these categorizations. Our investigation yields three main results. First, we find that several risk factor categories, such as government and competitive risks, are common across our sample of firms. Second, we find that a firm’s industry classification (as given by its SIC code) is not a differentiating factor in the disclosures that a firm makes. Third, we find that risk factor disclosures are generally not predictive of a firm’s financial performance in the form of leverage, capital structure, cash, and acquisitions. Our analysis expands on previous work by considering the content of the disclosures in more detail rather than focusing on more quantitative characteristics of disclosures

Numerical simulation of fluid flow, proppant transport and fracture propagation in hydraulic fractures for unconventional reservoirs.

The distribution of proppant injected in hydraulic fractures significantly affects fracture-conductivity and well-performance. The proppant transport and suspension in thin fracturing fluid used in unconventional reservoirs are considerably different from those of fracturing fluids in conventional reservoirs, due to the very low viscosity of fracturing fluids used in the unconventional reservoirs, poor ability to suspend proppants and hence quick deposition of the proppants. This research presents the development of a three-dimensional computational fluid dynamics (CFD) modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures for unconventional reservoirs. The Eulerian-Lagrangian multiphase modelling approach has been applied to model the fluid flow and proppant transport, and the kinetic theory of granular flow is used to model the inter-proppant, fluid-proppant and proppantwall interactions. The existing proppant transport models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture roughness. Thus, at the interface between the fracture and surrounding porous medium, the mass flow rate from the fracture to porous rock is calculated based on the permeability and porosity of the rock. The leakage mass flow rate is then used to define the mass and momentum source term at the fracture wall as a user-defined function, to investigate the proppant transport in hydraulic fractures with fluid leak-off effect. Furthermore, the hydrodynamic and mechanical behaviour of proppant transport on fracture roughness was studied in detail using different rough fracture profiles, and a relationship between the fracture roughness and proppant transport velocity is proposed. Lastly, an integrated model is developed, which simulates the proppant transport in dynamically propagating hydraulic fractures. The existing models either model the proppant transport physics in static predefined fracture geometry or account for the analytical models for defining the fracture propagation using linear elastic fracture mechanics. This limits the fracture propagation model to brittle rocks and neglect plastic deformations. Thus, in the present study, the fracture propagation was modelled using the extended finite element method (XFEM) and cohesive zone model (CZM), which can model the plastic deformations in the ductile rock. The fracture propagation was coupled with the CFD based proppant transport model, to model the fluid flow and proppant transport. The parametric study was then performed to investigate the effect of variation in proppant properties, fracturing fluid properties and geomechanical properties on the proppant transport. This study has enhanced the understanding of the flow and interaction phenomenon between proppant and fracturing fluid, and provides a technique with potential application in fracturing design for increasing well-productivity. The model can accurately simulate the proppant transport dynamics in hydraulic fracture and the present study proposes a solution to a frequent fracture tip screen out challenge faced in the petroleum industry. Thus, the developed modelling techniques provide petroleum engineers with a more suitable option for designing hydraulic fracturing operations, simultaneously modelling fracture propagation and fluid flow with proppant transport, and improves confidence by accurately tracking the distribution of proppants inside the fracture

Pengaruh Strategi Pengulangan terhadap Kemampuan Retensi Belajar Pneumatik Mahasiswa Pendidikan Teknik Mesin UNY

Tujuan penelitian ini adalah untuk mengetahui perbedaan keterampilan merangkai sistem pneumatik pada mahasiswa yang diajar dengan strategi pengulangan dan demonstrasi di Jurusan Diknik Mesin FT UNY. Penelitian ini merupakan penelitian kuasi eksperimen dengan variabel terikat keterampilan merangkai diagram pneumatik, variabel bebasnya adalah perlakuan strategi pembelajaran. Eksperimen menggunakan model classical experimental design. Sebagai populasi adalah 157 dengan sampel mahasiswa yang menjadi sumber data adalah 61 mahasiswa, dimana 31 mahasiswa sebagai kelompok eksperimen dan 30 mahasiswa menjadi kelompok kontrol. Analisis data menggunakan metode analisis deskriptif dan t-test. Hasil dari penelitian menunjukkan sebagian besar respon mahasiswa adalah positip, atau dengan kata lain mahasiswa merasa senang dengan pendekatan pengulangan. Tingkat keterampilan kooperatif mahasiswa dapat dikatakan baik, karena sebagian besar mahasiswa memiliki inisiatif berbagi dan berdiskusi dalam penyelesaian tugas. Keterampilan pneumatik mahasiswa yang diberi perlakuan strategi pembelajaran pengulangan lebih tinggi dari sisi retensi maupun prestasi belajar dibandingkan mahasiswa yang tidak mendapat strategi pembelajaran pengulangan

Cultivating Early Career Teachers’ Purpose: A Mechanism to Sustain Early Career Teachers’ Commitment to the Profession

The attrition rate of early career teachers is high. In fact, the government spends $2 billion annually to replace teachers in the first five years of their tenure (Alliance for Excellent Education, 2005). The purpose of this dissertation is two-fold: 1) to test the relationship between purpose, psychological well-being, and affective commitment to the profession, and 2) to design and examine the impact of a purpose-centered intervention in a sample of early career teachers in their first or second year of teaching, in the northeast. Study 1 examined the relationship between early career teachers’ purpose, psychological well-being, and commitment to the profession through a cross-sectional survey (N = 78) and regression-based analyses of a full mediation model. I hypothesized that early career teachers’ sense of purpose would contribute to their affective commitment to the profession through their feelings of psychological well-being. Results of Study 1 suggested that early career teachers’ purpose was a strong predictor of their psychological well-being and affective commitment to the profession. Building on Study 1, in Study 2 I developed, piloted, and tested a one-hour purpose-centered intervention (called Grounding in Purpose) using two t-tests (independent and dependent samples): 1) comparison of the waiting control group (n = 43) with the intervention group (n = 67) and 2) comparison of pretest and posttest scores of some participants in the intervention group (n = 20). Research findings for Study 2 indicate that a purpose-centered intervention may positively influence early career teachers’ purpose. Theoretically, the findings establish purpose as a key contributor to affective commitment in ECTs. Practically, the results offer educational leaders and professionals who support early career teachers with tangible recommendations to foster early career teachers’ purpose