Effective Length K-Factors For Flexural Buckling Strengths Of Web Members In Open Web Steel Joists

Open web steel joists are designed in the United States following the governing specification published by the Steel Joist Institute. For compression members in joists, this specification employs an effective length factor, or K-factor, in confirming their adequacy. In most cases, these K-factors have been conservatively assumed equal to 1.0 for compression web members, regardless of the fact that intuition and limited experimental work indicate that smaller values could be justified. Given that smaller K-factors could result in more economical designs without a loss in safety, the research presented in this thesis aims to suggest procedures for obtaining more rational values. Three different methods for computing in-plane and out-of-plane K-factors are investigated, including (1) a hand calculation method based on the use of alignment charts, (2) computational critical load (eigenvalue) analyses using uniformly distributed loads, and (3) computational analyses using a compressive strain approach. The latter method is novel and allows for computing the individual buckling load of a specific member within a system, such as a joist. Four different joist configurations are investigated, including an 18K3, 28K10, and two variations of a 32LH06. Based on these methods and the very limited number of joists studied, it appears promising that in-plane and out-of-plane K-factors of 0.75 and 0.85, respectively, could be used in computing the flexural buckling strength of web members in routine steel joist design. Recommendations for future work, which include systematically investigating a wider range of joist configurations and connection restraint, are provided.

Comparative study of anchorage strengths of epoxy coated hooked bars

Hooked reinforcing bars (rebar) are used frequently to carry the tension forces developed in beams and transferred to columns. Research into epoxy coated hooked bars has only been minimally performed and no research has been carried out incorporating the coating process found in ASTM A934. This research program compares hooked rebar that are uncoated, coated by ASTM A775, and coated by ASTM A934. In total, forty-two full size beam-column specimens were created, instrumented and tested to failure. The program was carried out in three phases. The first phase was used to refine the test setup and procedures. Phase two explored the spacing of column ties within the joint region. Phase three explored the three coating types found above. Each specimen included two hooked rebar which were loaded and measured independently for relative rebar slip. The load and displacement of the hooked rebar were analyzed, focusing on behavior at the levels of 30 ksi, 42 ksi and 60 ksi of rebar stress. Statistical and general comparisons were made using the coating types, tie spacing, and rebar stress level. Many of the parameters composing the rebar and concrete were also tested to characterize the components and specimens. All rebar tested met ASTM standards for tensile strength, but the newer ASTM A934 method seemed to produce slightly lower yield strengths. The A934 method also produced coating thicknesses that were very inconsistent and were higher than ASTM maximum limits in many locations. Continuity of coating surfaces was found to be less than 100% for both A775 and A934 rebar, but for different reasons. The many comparisons made did not always produce clear conclusions. The data suggests that the ACI Code (318-05) parameter of 1.2 for including epoxy coating on hooked rebar may need to be raised, possibly to 2.5, but more testing needs to be performed before such a large value change is set forth. This is particularly important as variables were identified which may have a larger influence on rebar capacity than the Development Length, of which the current 1.2 factor modifies. Many suggestions for future work are included throughout the thesis to help guide other researchers in carrying out successful and productive programs which will further the highly understudied topic of hooked rebar.

Fluidic oscillator design for water removal enhancement in a PEM fuel cell

This research initiative was triggered by the problems of water management of Polymer Electrolyte Membrane Fuel Cell (PEMFC). In low temperature fuel cells such as PEMFC, some of the water produced after the chemical reaction remains in its liquid state. Excess water produced by the fuel cell must be removed from the system to avoid flooding of the gas diffusion layers (GDL). The GDL is responsible for the transport of reactant gas to the active sites and remove the water produced from the sites. If the GDL is flooded, the supply gas will not be able to reach the reactive sites and the fuel cell fails. The choice of water removal method in this research is to exert a variable asymmetrical force on a liquid droplet. As the drop of liquid is subjected to an external vibrational force in the form of periodic wave, it will begin to oscillate. A fluidic oscillator is capable to produce a pulsating flow using simple balance of momentum fluxes between three impinging jets. By connecting the outputs of the oscillator to the gas channels of a fuel cell, a flow pulsation can be imposed on a water droplet formed within the gas channel during fuel cell operation. The lowest frequency produced by this design is approximately 202 Hz when a 20 inches feed-back port length was used and a supply pressure of 5 psig was introduced. This information was found by setting up a fluidic network with appropriate data acquisition. The components include a fluidic amplifier, valves and fittings, flow meters, a pressure gage, NI-DAQ system, Siglab®, Matlab software and four PCB microphones. The operating environment of the water droplet was reviewed, speed of the sound pressure which travels down the square channel was precisely estimated, and measurement devices were carefully selected. Applicable alternative measurement devices and its application to pressure wave measurement was considered. Methods for experimental setup and possible approaches were recommended, with some discussion of potential problems with implementation of this technique. Some computational fluid dynamic was also performed as an approach to oscillator design.

Veridicality of self-concept of strengths in male adolescents

Changes in physical self-concept and veridicality (i.e., the appropriateness of one’s self-perceptions to reality) during childhood and adolescence are related to performance in physical fi tness, exercise, and global self-esteem, particularly in male adolescents. This cross-sectional study examined the relation between the self-concept of strength and actual strength in groups of male adolescents ages 12 to 15 years. For this purpose, 889 male adolescents (M age = 13.2 yr., SD = 1.0) were questioned about their self-concept of strength, after which a test of strength was carried out. The results showed that the correlation between self- concept of strength and actual strength was higher in older (14- and 15-year-old) than younger (12- and 13-year-old) adolescents. There was a statistically signifi cant association between age group and veridicality, indicating that realistic self-concept is underrepresented among younger, but overrepresented among older adolescents. No association was found between the adolescents’ physical activity and veridicality. The consequences for further research on the development of veridicality in the physical domain are discussed.

Immediate shear bond strengths of a composite, a compomer and a glass ionomer to a ceramic substrate.

PURPOSE To determine the best-performing combination of three core buildup materials and three bonding materials based on their bond strength to ceramic blocks in vitro. MATERIALS AND METHODS The materials used for core buildup were a composite (Tetric EvoCeram), a compomer (Compoglass F), and a glass-ionomer cement (Ketac Fil Plus), and for bonding, a three-step etch-and-rinse adhesive (Syntac), a two-step etch-and-rinse adhesive (ExciTE), and a single-step system (RelyX Unicem). Bond strength to ceramic blocks was determined by shear bond strength testing. Fracture behavior was evaluated by scanning electron microscopy. RESULTS The highest adhesive values between buildup and ceramic were obtained using the materials Compoglass F and Syntac, followed by Compoglass F and ExciTE. Among the two other core buildups, Tetric EvoCeram performed better than Ketac Fil Plus, which was independent of the bonding materials. Adhesive fractures were characteristically observed with Syntac and ExciTE, and cohesive fractures were characteristically observed with RelyX Unicem. CONCLUSION These data show that compomers bonded with a multistep adhesive system achieved statistically significantly higher shear bond strength than composites and glass-ionomer cements. Within the limitations inherent to this in vitro study, the use of compomers for core buildup can be recommended.

Harmonic Oscillator in a 1D or 2D Cavity with General Perfectly Reflecting Walls

We investigate the simple harmonic oscillator in a 1-d box, and the 2-d isotropic harmonic oscillator problem in a circular cavity with perfectly reflecting boundary conditions. The energy spectrum has been calculated as a function of the self-adjoint extension parameter. For sufficiently negative values of the self-adjoint extension parameter, there are bound states localized at the wall of the box or the cavity that resonate with the standard bound states of the simple harmonic oscillator or the isotropic oscillator. A free particle in a circular cavity has been studied for the sake of comparison. This work represents an application of the recent generalization of the Heisenberg uncertainty relation related to the theory of self-adjoint extensions in a finite volume.

A reduced model clarifies the role of feedback loops and time delays in the Drosophila circadian oscillator.

Although several detailed models of molecular processes essential for circadian oscillations have been developed, their complexity makes intuitive understanding of the oscillation mechanism difficult. The goal of the present study was to reduce a previously developed, detailed model to a minimal representation of the transcriptional regulation essential for circadian rhythmicity in Drosophila. The reduced model contains only two differential equations, each with time delays. A negative feedback loop is included, in which PER protein represses per transcription by binding the dCLOCK transcription factor. A positive feedback loop is also included, in which dCLOCK indirectly enhances its own formation. The model simulated circadian oscillations, light entrainment, and a phase-response curve with qualitative similarities to experiment. Time delays were found to be essential for simulation of circadian oscillations with this model. To examine the robustness of the simplified model to fluctuations in molecule numbers, a stochastic variant was constructed. Robust circadian oscillations and entrainment to light pulses were simulated with fewer than 80 molecules of each gene product present on average. Circadian oscillations persisted when the positive feedback loop was removed. Moreover, elimination of positive feedback did not decrease the robustness of oscillations to stochastic fluctuations or to variations in parameter values. Such reduced models can aid understanding of the oscillation mechanisms in Drosophila and in other organisms in which feedback regulation of transcription may play an important role.

Human Trafficking Victims and Their Children: Assessing Needs, Vulnerabilities, Strengths, and Survivorship

Given the increased awareness and attention to human trafficking, including the establishment of federal laws and policies, federally funded task forces that provide law enforcement responses, and specialized victim services, it is important to assess the impact of these procedures and services on survivors/victims of international human trafficking and their immigrant children. By federal definition, certified victims of international human trafficking are eligible for all services provided to refugees in this country, including reunification with their minor children. This research is based on a qualitative study conducted in Austin and Houston, Texas with human trafficking victims/survivors. The project’s goal was to gain an understanding of the needs of human trafficking survivors after their rescue, their overall integration into American life, and the subsequent needs of their immigrant children after reunification. The project objectives examined the factors that either promote or hinder self-sufficiency, the determination of social service needs, and policy and practice recommendations to strengthen survivors, their children and their families living both locally and abroad. For this project, nine (n = 9) in-depth interviews were conducted with adult foreign-born victims of human trafficking. Researchers gathered data using a semi-structured questionnaire that queried about factors that promote or hinder victims’ services and needs. Interviews were conducted in participants’ homes using bilingual research staff and/or trained interpreters, were digitally-recorded, and subsequently transcribed. Participation in this study was completely voluntary. Specific steps were taken to ensure that the participants’ identities were protected. Open coding of data was utilized and the data were subsequently organized or grouped into properties and later developed into contextual themes around the research questions. The findings are grounded with the use of direct quotes from participants. As a result of progressive U.S. policy, many victims of human trafficking are being reunited with their minor children. Immigrant children are one of the largest and fastest growing populations in the U.S. and for a variety of reasons are vulnerable to exploitation. Research also indicates that victims of trafficking are identified by traffickers because of their perceived “vulnerabilities” or lack of opportunities (Clark, 2003). Therefore, it is important that practices and policies are developed to address the unique needs of these families with an eye toward positive outcomes for parent and child safety and well-being. Social service providers are provided a toolkit that may be utilized before and during the reunification period.

Commentary: “Human Trafficking Victims and Their Children: Assessing Needs, Vulnerabilities, Strengths, and Survivorship"

A commentary on Busch-Armendariz, Nsonwu, and Heffron’s article, “Human Trafficking Victims and Their Children: Assessing Needs, Vulnerabilities, Strengths, and Survivorship,” noting key findings and calling for further research.

Practitioners' Views of Family Strengths: A Delphi Study

Reported is a research study to assess the opinions of family practitioners on the status of families in Oklahoma. Researchers employed the Delphi method to achieve consensus among key informants in the family practice field about the strengths and weaknesses of Oklahoma families, threats facing families in the state, and means to strengthening family life in Oklahoma. The study yielded qualitative data from the key informants, which the researchers then condensed into response categories to feed back to informants to rate. Family practitioners identified resilience, spirituality, and access to support systems as the greatest strengths, and listed substance abuse, poverty, and generational cycles of dysfunction as the greatest weaknesses of Oklahoma families. Recommendations by these practitioners are given for improvements in addressing family needs.

Commentary on "Practitioners’ Views of Family Strengths: A Delphi Study"

Commentary on "Practitioners’ Views of Family Strengths: A Delphi Study"