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From Aspiration to Attainment: African American Community College Transfer Student Experiences Through Baccalaureate Degree Attainment
The purpose of this dissertation was to explore African American community college transfer student experiences through baccalaureate degree completion. The current study used qualitative methods to examine the experiences and perceptions of eighteen African American community college transfer students who recently graduated or were within 30 credit hours of graduating from a four-year university in Texas. Ten female and eight male students, ranging in age from 21 to 56 years old, with an average age of 28, composed the sample. Data were collected through semi-structured interviews which were transcribed and analyzed based on an integrated conceptual model of Padilla’s (1999) Model of Minority Student Success and Yosso’s (2005) Community Cultural Wealth Model. Findings suggest that African American community college transfer student experiences are very similar to transfer student experiences revealed in current literature. However, findings indicate students perceive their experiences differ from student of other races/ethnicities when dealing with negative stereotypes, lack of role models, and racial bias. Findings also suggest African American community college transfer student persist by employing transfer student capital, familial, aspirational, and resistant capital to learn how the traverse transfer, transition, and persistence through baccalaureate degree attainment.
Date:
December 2013
Creator:
Wilson, Dawna
System:
The UNT Digital Library
Functional Characterization of Mtnip/latd’s Biochemical and Biological Function
Symbiotic nitrogen fixation occurs in plants harboring nitrogen-fixing bacteria within the plant tissue. The most widely studied association is between the legumes and rhizobia. In this relationship the plant (legumes) provides the bacteria (rhizobia) with reduced carbon derived from photosynthesis in exchange for reduced atmospheric nitrogen. This allows the plant to survive in soil, which is low in available of nitrogen. Rhizobia infect and enter plant root and reside in organs known as nodules. In the nodules the bacteria fix atmospheric nitrogen. The association between the legume, Medicago truncatula and the bacteria Sinorhizobium meliloti, has been studied in detail. Medicago mutants that have defects in nodulation help us understand the process of nitrogen fixation better. One such mutant is the Mtnip-1. Mtnip-1 plants respond to S. meliloti by producing abnormal nodules in which numerous aberrant infection threads are produced, with very rare rhizobial release into host plant cells. The mutant plant Mtnip-1 has an abnormal defense-like response in root nodules as well as defects in lateral root development. Three alleles of the Mtnip/latd mutants, Mtnip-1, Mtlatd and Mtnip-3 show different degrees of severity in their phenotype. Phylogenetic analysis showed that MtNIP/LATD encodes a protein belonging to the NRT1(PTR) family of …
Date:
December 2013
Creator:
Bagchi, Rammyani
System:
The UNT Digital Library
Funds of Knowledge in a Hispanic Household: a Case Study of Family Experiences, Values, and Connections to Education
Traditionally, the field of education has often adopted a negative perspective in their views of minority families’ contributions to the educational progress of their children. However, research embodying the theoretical framework of ‘funds of knowledge’ attempts to counter that model through its assertion that all families possess extensive bodies of knowledge that have developed through social, historical, and cultural contexts. Teachers carry out studies of familial funds of knowledge in order to understand how family experiences shape the knowledge that a child brings to the classroom. There is then, the potential to use that body of knowledge to create meaningful learning experiences that connect prior understanding and experiences to classroom practice. This research served as a case study of the funds of knowledge existing in the home of a Hispanic family and the connections that existed between that knowledge and literacy. The results indicated that the family possessed extensive funds of knowledge that developed through their historical, cultural, and social experiences. They often used family networks, as well as formal and informal literacy experiences to share this knowledge with their children. A key component of the literacy value system that they communicated resulted from a desire to maintain aspects of …
Date:
December 2013
Creator:
Feild, Kelly A.
System:
The UNT Digital Library
The Glass Is Neither Half Full Nor Empty, It Is Shattered: a Prospective Study of Shattered Assumptions Theory and Psychological Flexibility
Shattered assumptions theory posits that each individual has a core set of assumptions about the world and the self, often termed the assumptive world which includes: the world is a benevolent place, the world is meaningful, and the self is worthy. Experiencing a traumatic event is believed to lead individuals to question these assumptions in light of the new contradictory information that causes the assumptive world to shatter, leaving the individual to rebuild a more negative perception of the world and themselves. This rebuilding of a fragile new set of core beliefs is believed to be a cause of posttraumatic stress disorder (PTSD) symptoms. Although shattered assumptions theory has been widely accepted in the field of trauma psychology, the shattering of the assumptive world has not been empirically supported due to measurement issues and poor research designs. The current study implemented a prospective design to assess a new measure of the individual’s assumptive world when there is an intervening trauma. In a college sample (N = 336), individuals who experienced a traumatic event over the course of the semester (n = 40) evidenced decreases in optimism in their assumptive worlds, in comparison to individuals who did not experience a traumatic …
Date:
December 2013
Creator:
Schuler, Eric Robert
System:
The UNT Digital Library
Grace After Fire: an Analysis of Table Talk: Color Me Camo-realities of Female Veterans
Beginning May of 2013 and ending in September, I worked with Grace After Fire (Grace), a virtual nonprofit organization that focuses on issues related to female veterans. Grace’s mission is to provide female veterans with the means to gain knowledge, insight and self-renewal. Grace’s mission is accomplished through peer support and resource referral. The aim of my thesis project was to conduct an analysis of Grace’s peer support system, Table Talk: Color Me Camo (Table Talk). Because Table Talk is a fairly new program for Grace, just over a year old, the outreach coordinators were eager to learn: 1) if they were indeed meeting their mission of empowering female veterans, and 2) the point-of-view of the peer facilitators who conduct Table Talk. To help Grace gain perspective, I interviewed women who had previously attended Table Talk, as well as peer facilitators responsible for coordinating the peer support system-all of whom are female veterans. The following is their story.
Date:
December 2013
Creator:
Phillips, Jessica Laureano
System:
The UNT Digital Library
Hermanos De Raza: Alonso S Perales and the Creation of the Lulac Spirit
There were two great ambitions in the life of Alonso S. Perales: the first was to help his people, the Mexican-Americans; the second was to help all of mankind. To pursue this first ambition, Perales became very active as a major political leader who supported civil rights and the abolishment of racial discrimination. Many viewed him as a defender of la raza (the Mexican-American race) and one of the most influential Mexican-Americans of his time. As such, Perales devoted most of his work to defending Mexican-Americans and battling charges that Mexicans were an inferior people and a social problem. He participated in various Civil Rights organizations and was one of the founders of the League of United Latin American Citizens (LULAC). This author argues that without Perales’ involvement, LULAC would have never existed. This work solely focuses on Perales’ life from the late 1920s to the early 1930s. It begins by examining Perales’ roots and his first involvement with Mexican-American civil rights. It then covers his role in the origin of LULAC, specifically its predecessor organization, the League of Latin American Citizens. Furthermore, this work explores Perales’ involvement in the defeat of the 1930 Box Bill and his role in …
Date:
December 2013
Creator:
Mila, Brandon H.
System:
The UNT Digital Library
Historical and Theological Backgrounds of the Whore of Babylon in Revelation 17 & 18 in a Jewish Context
I argue that some ancient Jewish sects, specifically the community at Qumran and the early Christians, did in fact write against, speak out against, and interpret ancient tests as being against their fellow Jews, the Temple, Jerusalem or all three. Given the time in which these occurred, I argue that those sects believed that the Roman Empire would be means in which their god would punish/destroy Jews that did not believe as they did, the Temple that did not represent what they thought it should, and Jerusalem as they believed it had become a sinful city. I examine the writings and persons of the Greek Bible. I examine specifics such as the Parable of the Tenants and demonstrate that this was delivered against Jewish leadership and the Olivet Discourse that, like the book of Jubilees, presents a series of tribulations that will fall on a wicked generation, specifically the one living in Jerusalem during the first century C.E. I also demonstrate how the motif of these writings affected the book of Revelation. I examine the prophetic books of the Hebrew Bible and show how the author used them as allusions in regards to the Whore of Babylon that appear in …
Date:
December 2013
Creator:
Wheatley, Warren
System:
The UNT Digital Library
Immunohistochemistry of the Gills of the Channel Catfish Ictalurus Punctatus: Cells and Neurochemicals That May Be Involved in the Control of Cardioventilatory Reflexes
In teleost fishes the neurochemicals involved in sensing and responding to hypoxia are unresolved. Serotonergic branchial neuroepithelial cells (NECs) are putative O2 chemoreceptors believed to be homologous to the neural crest (NC) derived APUD (amine-precursor uptake and decarboxylation) pulmonary NECs and carotid body type-1 glomus cells. Branchial NECs contain serotonin (5-HT), thought to be central to the induction of the hypoxic cardioventilatory reflexes. However, application of 5-HT in vivo does not elicit cardioventilatory reflexes similar to those elicited by hypoxia. But previous in vitro neural recordings from glossopharyngeal (IX) afferents innervating O2 chemoreceptors in the trout gill show the same discharge response to hypoxic conditions as does that of acetylcholine (ACh) application. This evidence strongly supports the cholinergic hypothesis of chemoreceptor impulse origin rather than a serotonergic-induced impulse origin model. We therefore hypothesized that NECs contain ACh among other neurochemicals in cells belonging to the APUD series. Although serotonergic branchial NECs did not colocalize with ACh using immunohistochemical methods, several populations of ACh and/or tyrosine hydroxylase (TH) (catecholaminergic) positive, dopamine (DA) negative, cells were found throughout the second gill arch of the channel catfish Ictalurus punctatus. In addition, the NC derivation marker zn-12 labelled the HNK-1-like epitope (Human natural killer) …
Date:
December 2013
Creator:
Oden, David S.
System:
The UNT Digital Library
In-store Event Needs and Technology Use Among Half Price Books Customers
Half Price Books, Records, Magazines, Inc. (HPB), fills a unique niche by selling a variety of new, used and rare merchandise primarily in their chain of 116 stores in sixteen states and online. The company has noticed increased mobile device use among customers in their stores while sales have declined in recent years. To remain viable HPB is attempting to adapt to market forces in a timely manner while remaining continually interested in growth and innovation. A major part of adapting, growing, and innovating is the adoption and astute utilization of technology in-store and a more complete understanding of their customers’ activities and preferences. The goal is to make Half Price Books a more technologically savvy destination for shopping, community events, and entertainment. One purpose of this study is to give the company a better idea of how customers use technology in searching for merchandise including information searches generated in-store from mobile devices and how customers use the internet to find merchandise prior to and following their experiences in HPB’s stores. Another important purpose is to also determine what kinds of events such as book signings, poetry readings and other special events customers would like to see at Half Price …
Date:
December 2013
Creator:
Wilson, Steven K.
System:
The UNT Digital Library
In Vitro Cortical Networks for Disease Modeling and Drug Evaluation
In translational research, disease models in preclinical studies are used as media for discovery of drugs or novel therapeutics. Development of in vitro models for various neurological diseases that enable efficient pharmacological or toxicological screening has been ongoing but challenging. Recognizing the potential benefit of in vitro disease models, dysfunctions in the cortical neuronal networks were induced to mimic the functional pathology of neurological symptoms using microelectrode arrays. Two different disease states – tinnitusand excitotoxicity – were investigated and discussed. In this model, pentylenetetrazol-induced increase in spontaneous firing rate and synchrony in the auditory cortical networks was used as correlate of tinnitus. Potential tinnitus treatment drugs from several different classes – including the novel class of potassium channel openers – were screened and quantified. The potentialtherapeutic values of these drugs were also discussed as the basis for drug repurposing. Functional excitotoxicity was induced by cisplatin (a cancer drug that causes neurological sideeffects) and glutamate (the major excitatory neurotransmitter). As proof-of-principle that the model may contribute to expediting the development of therapeutics, cisplatin excitotoxicity wasprevented by the antioxidant D-methionine, while glutamate excitotoxicity was prevented by ceftriaxone (a modulator of a glutamate reuptake transporter). In the latter part of the study, with …
Date:
December 2013
Creator:
Wu, Calvin
System:
The UNT Digital Library
Infinite Hallways: “Parabola Heretica” and Other Journeys
This creative thesis collects five fictional stories, as well as a critical preface entitled “Fractals and the Gestalt: the Hybridization of Genre.” The critical preface discusses genre as a literary element and explores techniques for effective genre hybridization. The stories range from psychological fiction to science fiction and fantasy fiction. Each story also employs elements from other genres as well. These stories collectively explore the concept of the other and themes of connection and ostracization.
Date:
December 2013
Creator:
Garay, Christopher
System:
The UNT Digital Library
An Instructional Approach to Introducing Twentieth-century Piano Music to Piano Students From Beginning to Advanced Levels: a Graded Repertoire for Mastering the Challenges Posed by Logan Skelton’s Civil War Variations
Beginning and intermediate piano students typically study the repertoire of the eighteenth and nineteenth centuries. This pedagogical approach leaves them underprepared to approach compositions written since the latter part of the twentieth-century which are significantly different in terms of harmony, rhythm, meter, and compositional procedure. Therefore, a step-by-step method is necessary to prepare a student for the challenges of learning twentieth and twenty-first century piano music. Civil War Variations (1988), by Logan Skelton, is an excellent example of a piece that presents a number of challenges characteristically found in late twentieth-century piano music. The twenty-five variations that comprise the work incorporate a series of twentieth-century musical techniques, namely complex rhythms, extreme dissonance, frequent metric changes, dissonant counterpoint, the inclusion of blues scales and rhythms, and new notations. The purpose of this study is to identify the technical, musical, structural and notational challenges posed by a work such as Logan Skelton’s Civil War Variations; examination of this piece will lead to suggestions regarding repertoire that a teacher may assign to beginning, intermediate, and advanced students in order to prepare them logically and in a step-by-step fashion to cope with and meet the challenges posed by this and other compositions having similar …
Date:
December 2013
Creator:
Kim, Dajeong
System:
The UNT Digital Library
Integrated Computational and Experimental Approach to Control Physical Texture During Laser Machining of Structural Ceramics
The high energy lasers are emerging as an innovative material processing tool to effectively fabricate complex shapes on the hard and brittle structural ceramics, which previously had been near impossible to be machined effectively using various conventional machining techniques. In addition, the in-situ measurement of the thermo-physical properties in the severe laser machining conditions (high temperature, short time duration, and small interaction volume) is an extremely difficult task. As a consequence, it is extremely challenging to investigate the evolution of surface topography through experimental analyses. To address this issue, an integrated experimental and computational (multistep and multiphysics based finite-element modeling) approach was employed to understand the influence of laser processing parameters to effectively control the various thermo-physical effects (recoil pressure, Marangoni convection, and surface tension) during transient physical processes (melting, vaporization) for controlled surface topography (surface finish). The results indicated that the material lost due to evaporation causes an increase in crater depth of machined cavity, whereas liquid expulsion created by the recoil pressure increases the material pileup height around the lip of machined cavity, the major attributes of surface topography (roughness). Also, it was found that the surface roughness increased with increase in laser energy density and pulse rate …
Date:
December 2013
Creator:
Vora, Hitesh D.
System:
The UNT Digital Library
Investigation of the Pharmacokinetics of Diazepam in Juvenile Channel Catfish (Ictalurus Punctatus)
The presence of pharmaceuticals in the environment is becoming an increasing regulatory and scientific concern. Thus, the metabolic profile and bioconcentration potential of diazepam, a model benzodiazepine, were examined, as well as effects on the endocrine system in channel catfish. Through the use of specific and non-specific cytochrome P450 (CYP450) inhibitors, it was determined that CYP3A-like enzymes may play a role in the biotransformation of diazepam into temazepam; however, the isoform(s) required for the formation of other metabolites is still unknown. Overall, only around 7-8% of diazepam is biotransformed into two known metabolites. Due to the lack of inherent metabolism of diazepam in channel catfish, further analysis was conducted to determine the tissue-specific bioconcentration potential of diazepam in catfish. Various tissues were analyzed for the presence of diazepam as well as metabolites and bioconcentration factors (BCF) were calculated, which were all well below regulatory threshold values (> 2000). Additionally, modulation of the endocrine system by diazepam was examined by measuring steroid hormone concentrations and analyzing mRNA expression of selected steroidogenic enzymes and receptors. Two steroidogenic enzymes were modulated following diazepam exposure, indicating potential endocrine disrupting properties of diazepam. Together, these data suggest that diazepam exhibits low metabolic transformation rates in …
Date:
December 2013
Creator:
Overturf, Carmen L.
System:
The UNT Digital Library
Josephus’ Jewish War and the Causes of the Jewish Revolt: Re-examining Inevitability
The Jewish revolt against the Romans in 66 CE can be seen as the culmination of years of oppression at the hands of their Roman overlords. The first-century historian Josephus narrates the developments of the war and the events prior. A member of the priestly class and a general in the war, Josephus provides us a detailed account that has long troubled historians. This book was an attempt by Josephus to explain the nature of the war to his primary audience of predominantly angry and grieving Jews. The causes of the war are explained in different terms, ranging from Roman provincial administration, Jewish apocalypticism, and Jewish internal struggles. The Jews eventually reached a tipping point and engaged the Romans in open revolt. Josephus was adamant that the origin of the revolt remained with a few, youthful individuals who were able to persuade the country to rebel. This thesis emphasizes the causes of the war as Josephus saw them and how they are reflected both within The Jewish War and the later work Jewish Antiquities. By observing the Roman provincial administration spanning 6-66 CE, I argue that Judaea had low moments sprinkled throughout the time but in 66 there was something …
Date:
December 2013
Creator:
Lopez, Javier
System:
The UNT Digital Library
Laser Surface Modification on Az31b Mg Alloy for Bio-wettability
Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle with 3 different standard liquid (D.I water, Formamide, and 1-Bromonaphthalen). The bio-wettability of the laser surface modification samples can be conducted by simulated body fluid contact angle measurement. The results of SEM, 3D morphology, XRD, and contact angle measurement show that the grain size and roughness play role for wetting behavior of …
Date:
December 2013
Creator:
Ho, YeeHsien
System:
The UNT Digital Library
Light, Bright, and Out of Sight: Hollywood’s Representation of the Tragic Mulatto
The purpose of this research is to examine the longevity of the stereotype of the tragic mulatto in American film history. Specifically, my research focuses on the portrayals and perceptions of biracial actresses. Media informs, entertains, and influences how we, and especially youth, self-identify and interact with others. This research focuses on the portrayal of biracial actresses throughout film history. It is also important in its investigation of the perpetuation of the one-drop rule. In this research, I will examine if historical stereotypes of tragic mulatto are apparent in contemporary Hollywood film. The methodologies used in this research include a content analysis of films with biracial actresses and an online survey of respondents’ perceptions of four actresses. Statistical techniques used for analysis include ordinary least square regression and multinomial logistic regression. Findings suggest that the tragic mulatto stereotype is not blatant in contemporary Hollywood film, but issues of colorism may be apparent.
Date:
December 2013
Creator:
Brunson, Alicia
System:
The UNT Digital Library
Long Distance International Caregiving to Elderly Parents Left Behind: a Case of Nigerian Adult Children Immigrants in Usa
The intent of this qualitative, grounded theory study was to understand why the Nigerian (Igbo) adult immigrants in the United States provide long distance international caregiving to their elderly parents left behind in Nigeria, the challenges they encounter, and their views on long-term service care. This study was grounded in semi-structured interviews of 20 Igbo adult immigrants residing in the Dallas/Fort Worth Metropolis. Analysis of the literature demonstrates a lack of existent topic on long distance international caregiving to elderly parents left behind in Nigeria. Findings show that reasons for Igbo adult children immigrants providing care to their elderly parents left behind stem from filial obligation, immigrant’s position in the family, perceived vulnerability of parents, and lack of government support. Also because of cultural expectations, the participants felt obligated to reciprocate to the care their elderly parents gave to them when they were growing up. While providing long distance international care, the participants encountered some challenges like adjusting to their new country, distance, financial constraints, being available for family procreation, issues with means of communication, and legal papers and parental adjustment to life in the U.S. This study also revealed that the participants would support the Nigerian government and private …
Date:
December 2013
Creator:
Okoro, Onyekachi
System:
The UNT Digital Library
Maximum Likelihood Estimation of Logistic Sinusoidal Regression Models
We consider the problem of maximum likelihood estimation of logistic sinusoidal regression models and develop some asymptotic theory including the consistency and joint rates of convergence for the maximum likelihood estimators. The key techniques build upon a synthesis of the results of Walker and Song and Li for the widely studied sinusoidal regression model and on making a connection to a result of Radchenko. Monte Carlo simulations are also presented to demonstrate the finite-sample performance of the estimators
Date:
December 2013
Creator:
Weng, Yu
System:
The UNT Digital Library
The Measurement of the Third-order Elastic Constants for La3ga5sio14 (Lgs) and La3ga55ta05o14 (Lgt) Single Crystal
Recently, the development of electronic technology towards higher frequencies and larger band widths has led to interest in finding new piezoelectric materials, which could be used to make filters with larger pass band widths and oscillators with better frequency stability. Langasite (La3Ga5SiO14, LGS) and its isomorphs have enticed considerable attention of researchers as a potential substrate material for piezoelectric device applications because of its high frequency stability and fairly good electromechanical coupling factors for acoustic wave devices. Nonlinear effect including drive level dependence, mode coupling, force-frequency effect and electroelasic effect are critical for the design of these devices. Third-order elastic constants (TOEC) play an important role in a quantitative analysis of these nonlinear effects. In particular these elastic constants are of great importance when the BAW (Bulk Acoustic Wave) and SAW (Surface Acoustic Wave) sensors of force, acceleration and so on are designed. Until now Langasite (LGS) and Langatate (LGT) crystal resonators have been qualified in terms of quality factor, temperature effect, isochronism defect and material quality. One of the most important advantages of those crystals is that they will not undergo phase transitions up to its melting temperature of 1450°. Presently there is no data on TOEC of LGT …
Date:
December 2013
Creator:
Karim, Md Afzalul
System:
The UNT Digital Library
Mexican Mothers’ Experiences with Depression, Intimate Partner Violence, and Immigration: a Mixed Methods Study of Maternal Self-efficacy
This study investigated the relation between maternal self-efficacy, depression, and intimate partner violence among Mexican immigrant and Mexican mothers. The research was conducted using a parallel mixed methods approach including both qualitative and quantitative methods. A total of 136 mothers living in the United States and Mexico completed surveys, and 10 mothers participated in semi-structured interviews. In a regression on maternal depression, living in Mexico as opposed to the U.S., psychological violence, and maternal self-efficacy were significant predictors of maternal depression. In the qualitative data analysis, we found five main themes: perceptions, cultural influence, involvement, resources, and barriers. In this stage of the study, Mexican and Mexican immigrant mothers described in detail their experiences of being a mother, their perceptions of maternal self-efficacy, and the influence of intimate partner violence and depression on their effectiveness as mothers. Overall, Mexican immigrant families appeared to have healthier relationships and greater well-being than Mexican families.
Date:
December 2013
Creator:
Orozco Vargas, Arturo Enrique
System:
The UNT Digital Library
Miniature Mass Spectrometry: Theory, Development and Applications
As mass analyzer technology has continued to improve over the last fifty years, the prospect of field-portable mass spectrometers has garnered interest from many research groups and organizations. Designing a field portable instrument entails more than the scaling down of current commercial systems. Additional considerations such as power consumption, vacuum requirements and ruggedization also play key roles. In this research, two avenues were pursued in the initial development of a portable system. First, micrometer-scale mass analyzers and other electrostatic components were fabricated using silicon on insulator-deep reactive ion etching, and tested. Second, the dimensions of an ion trap were scaled to the millimeter level and fabricated from common metals and commercially available vacuum plastics. This instrument was tested for use in ion isolation and collision induced dissociation for secondary mass spectrometry and confirmatory analyses of unknowns. In addition to portable instrumentation, miniature mass spectrometers show potential for usage in process and reaction monitoring. To this end, a commercial residual gas analyzer was used to monitor plasma deposition and cleaning inside of a chamber designed for laser ablation and soft landing-ion mobility to generate metal-main group clusters. This chamber was also equipped for multiple types of spectral analysis in order to …
Date:
December 2013
Creator:
Fox, James D.
System:
The UNT Digital Library
Modeling the Effects of Chronic Toxicity of Pharmaceutical Chemicals on the Life History Strategies of Ceriodaphnia Dubia: a Multigenerational Study
Trace quantities of pharmaceuticals (including carbamazepine and sertraline) are continuously discharged into the environment, which causes concern among scientists and regulators regarding their potential long-term impacts on aquatic ecosystems. These compounds and their metabolites are continuously interacting with the orgranisms in various life stages, and may differentially influence development of embryo, larvae, juvenile, and adult stages. To fully understand the potential ecological risks of two candidate pharmaceutical chemicals (carbamazepine (CBZ) and sertraline (SERT)) exposure on survival, growth and reproduction of Ceriodaphnia dubia in three sucessive generations under static renewal toxicity test, a multigenerational approach was taken. Results indicate that SERT exposure showed higher sensitivity to chronic exposure to C. dubia growth and reproduction than CBZ exposure. The lowest concentration to affect fecundity and growth was at 50 µg L-1 SERT in the first two generations. These parameters become more sensitive during the third generation where the LOEC was 4.8 µg L-1. The effective concentrations (EC50) for the number of offspring per female, offspring body size, and dry weight were 17.2, 21.2, and 26.2 µg SERT L-1, respectively. Endpoints measured in this study demonstrate that chronic exposure of C. dubia to SERT leads to effects that occur at concentrations an order …
Date:
December 2013
Creator:
Lamichhane, Kiran
System:
The UNT Digital Library
Molecular and Functional Characterization of Medicago Truncatula Npf17 Gene
Legumes are unique among plants for their ability to fix atmospheric nitrogen with the help of soil bacteria rhizobia. Medicago truncatula is used as a model legume to study different aspects of symbiotic nitrogen fixation. M. truncatula, in association with its symbiotic partner Sinorhizobium meliloti, fix atmospheric nitrogen into ammonia, which the plant uses for amino acid biosynthesis and the bacteria get reduced photosynthate in return. M. truncatula NPF1.7 previously called MtNIP/LATD is required for symbiotic nitrogen fixing root nodule development and for normal root architecture. Mutations in MtNPF1.7 have defects in these processes. MtNPF1.7 encodes a member of the NPF family of transporters. Experimental results showing that MtNPF1.7 functioning as a high-affinity nitrate transporter are its expression restoring chlorate susceptibility to the Arabidopsis chl1-5 mutant and high nitrate transport in Xenopus laevis oocyte system. However, the weakest Mtnip-3 mutant allele also displays high-affinity nitrate transport in X. laevis oocytes and chlorate susceptibility to the Atchl1-5 mutant, suggesting that MtNPF1.7 might have another biochemical function. Experimental evidence shows that MtNPF1.7 also functions in hormone signaling. Constitutive expression of MtNPF1.7 in several species including M. truncatula results in plants with a robust growth phenotype. Using a synthetic auxin reporter, the presence …
Date:
December 2013
Creator:
Salehin, Mohammad
System:
The UNT Digital Library