Browsing by Subject "Plasticity"
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Item A finite element complementary energy formulation for plane elastoplastic stress analysis(Texas Tech University, 1979-05) Azene, MulunehThe m.ethod of analysis presented herein parallels that of Ref (8) with two added major distingushing features. First, the present model consists of an eighteen degree of freedom self-equilibrating finite element model wherein the stress function is expressed by means of a complete set of quintic Hermitian polynomials. The function used, while allowing for selfequilibrating stresses that are continuous within the element, also enables the admission of all the second derivatives of the function as nodal parameters, thereby permitting the determination of nodal stress values directly without the need of additional computation. Second, the present work introduces an additional force parameter that is essential to satisfy complete static equilibrium of external forces constistent with the assumed stress function.Item A study of the development of plastic hinges in beam-column connections for the application of limit design methods to reinforced concrete frames(Texas Tech University, 1964-05) Scoggin, Harry LynnNot availableItem Burst timing-dependent plasticity of NMDA receptor-mediated transmission in midbrain dopamine neurons : a putative cellular substrate for reward learning(2009-08) Harnett, Mark Thomas; Morikawa, HitoshiThe neurotransmitter dopamine (DA) represents a neural substrate for positive motivation as its spatiotemporal distribution across the brain is responsible for goaldirected behavior and learning reward associations. The critical determinant of DA release throughout the brain is the firing pattern of DA-producing neurons. Synchronized bursts of spikes can be triggered by sensory stimuli in these neurons, evoking phasic release of DA in target brain areas to drive reward-based reinforcement learning and behavior. These bursts are generated by NMDA-type glutamate receptors (NMDARs). This dissertation reports a novel form of long-term potentiation (LTP) of NMDARmediated excitatory transmission at DA neurons as a putative cellular substrate for changes in DA neuron firing during reward learning. Patch-clamp electrophysiological recording from DA neurons in acute brain slices from young adult rats demonstrated that synaptic NMDARs exhibit LTP in an associative manner, requiring coordinated pre- and postsynaptic burst firing. Ca2+ signals produced by postsynaptic burst firing needed to be amplified by preceding metabotropic neurotransmitter inputs to effectively drive plasticity. Activation of NMDARs themselves was also necessary. These two coincidence detectors governed the timingdependence of NMDAR plasticity in a manner analogous to the timing rule for cuereward learning paradigms in behaving animals. Further mechanistic study revealed that PKA, but not PKC, activity gated LTP induction by regulating the magnitude of Ca2+ signal amplification via the inositol 1,4,5-triphospate (IP3) receptor and release of Ca2+ from intracellular stores. Plasticity of NMDARs was input specific and appeared to be expressed postsynaptically, but was not associated with a change in NMDAR subunit stoichiometry. LTP of NDMARs was DA-independent, and was specific for NMDARs: the same induction protocol produced long-term depression of AMPA receptors. NMDARs that had undergone LTP could be depotentiated in a spike-conditional manner, consistent with active unlearning. Finally, repeated, in vivo amphetamine experience dramatically increased facilitation of spike-evoked Ca2+ signals, which in turn drove enhanced plasticity. NMDAR plasticity thus represents a potential neural substrate for conditioned DA neuron burst responses to environmental stimuli acquired during reward-based learning as well a novel therapeutic target for intervention-based therapy of addictive disorders.Item Domain decomposition methods in geomechanics(2012-08) Florez Guzman, Horacio Antonio; Wheeler, Mary F. (Mary Fanett); Delshad, Mojdeh; Mear, Mark; Landis, Chad; Rodriguez, AdolfoHydrocarbon production or injection of fluids in the reservoir can produce changes in the rock stresses and in-situ geomechanics, potentially leading to compaction and subsidence with harmful effects in wells, cap-rock, faults, and the surrounding environment as well. In order to tackle these changes and their impact, accurate simulations are essential. The Mortar Finite Element Method (MFEM) has been demonstrated to be a powerful technique in order to formulate a weak continuity condition at the interface of sub-domains in which different meshes, i.e. non-conforming or hybrid, and / or variational approximations are used. This is particularly suitable when coupling different physics on different domains, such as elasticity and poroelasticity, in the context of coupled flow and geomechanics. In this dissertation, popular Domain Decomposition Methods (DDM) are implemented in order to carry large simulations by taking full advantage of current parallel computer architectures. Different solution schemes can be defined depending upon the way information is exchanged between sub-domain interfaces. Three different schemes, i.e. Dirichlet-Neumann (DN), Neumann-Neumann (NN) and MFEM, are tested and the advantages and disadvantages of each of them are identified. As a first contribution, the MFEM is extended to deal with curve interfaces represented by Non-Uniform Rational B-Splines (NURBS) curves and surfaces. The goal is to have a more robust geometrical representation for mortar spaces, which allows gluing non-conforming interfaces on realistic geometries. The resulting mortar saddle-point problem will be decoupled by means of the DN- and NN-DDM. Additionally, a reservoir geometry reconstruction procedure based on NURBS surfaces is presented as well. The technique builds a robust piecewise continuous geometrical representation that can be exploited by MFEM in order to tackle realistic problems, which is a second contribution. Tensor product meshes are usually propagated from the reservoir in a conforming way into its surroundings, which makes non-matching interfaces highly attractive in this case. In the context of reservoir compaction and subsidence estimation, it is common to deal with serial legacy codes for flow. Indeed, major reservoir simulators such as compositional codes lack parallelism. Another issue is the fact that, generally speaking, flow and mechanics domains are different. To overcome this limitation, a serial-parallel approach is proposed in order to couple serial flow codes with our parallel mechanics code by means of iterative coupling. Concrete results in loosely coupling are presented as a third contribution. As a final contribution, the DN-DDM is applied to couple elasticity and plasticity, which seems very promising in order to speed up computations involving poroplasticity. Several examples of coupling of elasticity, poroelasticity, and plasticity ranging from near-wellbore applications to field level subsidence computations help to show that the proposed methodology can handle problems of practical interest. In order to facilitate the implementation of complex workflows, an advanced Python wrapper interface that allows programming capabilities have been implemented. The proposed serial-parallel approach seems to be appropriate to handle geomechanical problems involving different meshes for flow and mechanics as well as coupling parallel mechanistic codes with legacy flow simulators.Item Mating evolution in Gambusia (Poeciliidae) : an integration of behavior, molecules and morphology(2014-05) Wang, Silu; Cummings, Molly E.; Hofmann, Hans A; Ryan, Michael JFemale mate choice and male courtship display are critical behaviors for the understanding of character evolution driven by sexual selection. This thesis is designated to understand the evolutionary mechanism of these two behaviors with mosquito fish (Gambusia). In the first chapter, collaborated with Dr. Mark Kirkpatrick, we demonstrated positive coevolution of courtship display and morphological signatures of male coercion and male advantage in sexually antagonistic adaptation across 10 Gambusia species. This finding suggested that male display may have caused the evolution of morphologies involved in SAC, or conversely it may have evolved as a palliative byproduct of the morphologies. This unexpected observation raised new interpretation about evolutionary cause and consequence of displays across different mating systems. The second chapter examined whether neuromolecular underpinning of G. affinis female mate choice is canalized or plastic in mating systems that show variable extant of mate choice. With Dr. Mary Ramsey, we should positive correlations between gene expression and female preference strength during exposure to courting heterospecific males, but a reversed pattern following exposure to coercive heterospecific males. This suggested that the neuromolecular entities associated with female preference are plastic and responsive to different male phenotypes (courting or coercive) rather than a canalized response linked to mating system. Further, I proposed that female behavioral plasticity may involve learning because female association patterns shifted with experience/age. Compared to younger females, I find that more experienced females spend less time near coercive males but associate more with males in the presence of courters. We thus suggested a conserved learning-based neuromolecular process underlying the diversity of female mate preference across the mate choice and coercion-driven mating systems.Item Max Weber at work 1910-1912 : 'primitive' experiments beyond the known dimensions(2015-08) Plunger, Brady James; Henderson, Linda Dalrymple, 1948-; Rather, SusanThis thesis seeks to build on earlier interpretations of Weber's writings and paintings in the years between 1910 and 1912 by illustrating how the contemporary discourses of primitivism inflected Weber's assimilation of these and other areas of knowledge into his understanding of the intellectual, affective, and sensorial processes involved in the making and viewing of art. Of particular interest here are the intersections that Weber created in his two 1910 essays, "The Fourth Dimension from a Plastic Point of View" and "Chinese Dolls and Modern Colorists," between certain key primitivist tropes, his interest in "plastic" formal values and aspects of popular science and mathematics, and the wider cultural fascination with the spiritual. This thesis explores this web of associations to reveal that Weber's transformative engagement with primitivism alongside these other key concerns that governed his theorizing on the function and value of works of art. Central to this thesis are Weber's two 1910 texts along with his paintings of 1910-1912, including his "Crystal Figures," which stand as Weber's most substantive theoretical and aesthetic statements at this early moment of his career. These various productions are analyzed simultaneously to illustrate the ways in which Weber's writings and visual experimenting complement each other and reveal the novel ways in which he integrated diverse areas of knowledge into his arguments for the importance of art in the new world of the twentieth century.Item Men, masculinity, and heterosexual exclusivity : a study of the perception and construction of human sexual orientation(2013-08) Gordon, Aqualus Mondrell; Ainslie, Ricardo C.In this dissertation I investigate how individuals group others into sexual orientation (SO) categories based on a target's known sexual behaviors and romantic interests. I hypothesize that individuals known to have any non-heterosexual sexual or romantic interests are more likely to be perceived as "gay" (and not "straight") even when there is clear evidence of heterosexual interests and behaviors as well. This phenomenon has been termed "heterosexual exclusivity" in this work. In the process, I examine relevant writings and research on SO, including works related to SO in history, the conceptualization and measurement of SO, determinants of and influences on SO, the essentialism and social constructionism debate with regard to SO, innate bisexuality, and bisexual erasure. Additionally, I give specific focus to how and why men are affected by, as well as perpetuate heterosexual exclusivity. In doing so, I examine writings and research on the role and construction of masculinity as well as homophobia and the overlap of the two. I hypothesize that adherence to traditional masculinity and increased homophobia are predictive of increased heterosexual exclusivity in men. I also hypothesize that men are more likely to be the primary agents and targets of heterosexual [exclusivity]. The results supported most of these hypotheses.Item Molecular mechanisms of phenotypic plasticity in Astatotilapia burtoni(2011-12) Huffman, Lin Su; Hofmann, Hans A.; Crews, David; Gore, Andrea; Ryan, Michael; Zakon, HaroldThe ability of an animal to respond and adapt to stimuli is necessary for its survival and involves plasticity and coordination of multiple levels of biological organization, including behavior, tissue organization, hormones, and gene expression. Each of these levels of response is complex, and none of them responds to stimuli in isolation. Thus, to understand how each system responds, it is necessary to consider its role in the context of the entire organism. Here, I have used the African cichlid fish Astatotilapia burtoni and its extraordinary phenotypic plasticity to investigate how animals respond to a change in social status from subordinate to dominant and attempted to integrate these multiple levels of biological response, as well as the roles of several candidate neuromodulators,. First, I have described how male A. burtoni become more aggressive and reproductive during their transition to dominance as well as increasing circulating levels of testosterone and estradiol and the histological organization of their testes. I then mapped the distribution of expression of two behaviorally relevant neuropeptides, arginine vasotocin and isotocin, and their respective receptors, throughout the A. burtoni brain, and found that they were highly expressed in several brain areas important for social behavior and decision-making. I then investigated the role of arginine vasotocin in social status and behavior via pharmacological manipulation and qPCR, showing the importance of arginine vasotocin in controlling the transition to dominance. Lastly, I investigated the role of aromatase, testosterone, and estradiol in male A. burtoni, both in stable dominant males and in males as they transition to dominance, using pharmacological manipulation and quantitative radioactive in situ hybridization, illustrating that estradiol synthesis during dominance is dependent on aromatase activity and necessary for aggressive behavior.Item Multiscale Computational Modeling of Multiphase Composites with Damage(2013-11-01) Cheng, FeifeiA multiscale computational framework for multiphase composites considering damage is developed in this research. In micro-scale, micromechanics based homogenization methods are used to estimate effective elastic moduli of graded Ti_(2)AlC/Al composites (GCMeCs) considering existence of damage (micro-voids). Then, in macro-scale, these properties are implemented in finite element model by using user material subroutine (UMAT) in Abaqus for numerical analysis of plate. In meso-scale, detailed 3D RVEs are created based on the microstructure of composites. Effective thermal and elastic properties are obtained from the corresponding FE models of 3D RVEs and compared with experimental results and micromechanics based homogenization methods. Two constitutive models are used to model plastic-damage behavior of two IPCs regarding their different material properties of constituent phases: (1) Due to the ductile properties of constituent phases for stainless-steel/bronze IPCs, a widely used porous plasticity constitutive model, Gurson-Tvergaard-Needleman (GTN) model, is adopted to investigate elastoplastic-damage behavior of stainless-steel/bronze IPCs. (2) For porous Ti_(2)AlC, a continuum damage mechanics (CDM) based plastic-damage coupled constitutive model is used to study damage evolution in porous Ti_(2)AlC, which can take distinct tensile and compressive inelastic behaviors of Ti_(2)AlC into consideration. From the simulation results of FE models of 3D RVEs, it is found that: Porosity and interfacial layer with low effective thermal conductivity lowers the overall heat flux flowing through NiTi/Ti_(3)SiC_(2) IPC. The existence of thermal residual stress within stainless-steel/bronze IPCs leads to plastic deformation, especially in bronze phase, which further results in reduction of apparent moduli subjected to uniaxial tension. Nucleation of the new voids, which occurs at the second-phase particles by decohesion of the particle-matrix interface, has the main contribution to the overall damage. For porous Ti_(2)AlC with aligned ellipsoid-like pores, tensile stress plays a very important role in local damage of porous Ti_(2)AlC due to the relatively low tensile strength and brittle-like tensile behavior of dense Ti_(2)AlC. Different than typical porous ceramic, porous Ti_(2)AlC fails in a quasi-brittle manner even with 30-40 vol. % porosity. The transversely isotropic material system has higher compressive strength in transverse direction than that in longitudinal direction.Item Plasticity in the startle-escape response of the African cichlid fish, Astatotilapia burtoni(2011-12) Whitaker, Keith William; Hofmann, Hans A.; Preuss, Thomas; Ryan, Michael; Morgan, Jennifer; Zakon, HaroldEcological context, sensory inputs, and the internal physiological state are integrated for an animal to make appropriate behavioral decisions. However, these factors have rarely been studied in the same system. In the African cichlid fish Astatotilapia burtoni, males alternate between four phenotypes. Two are determined by social status and two are identified by the principle body coloration (yellow or blue). When socially dominant (DOM), fish display bright body coloration and a wealth of aggressive and reproductive behaviors. Subordinate (SUB) males decrease predation risk by adopting cryptic coloration and schooling behavior. Yellow males are more conspicuous than blue males, and DOMs and more conspicuous than SUBs, which means that yellow DOMs are most likely to be seen by predators. We therefore hypothesized that DOMs, yellow DOMs in particular, would show enhanced startle-escape responsiveness to compensate for their increased predation risk. Indeed, behavioral responses to sound clicks of various intensities showed a significantly higher mean startle rate in DOMs than SUBs. When testing the same males after social change, yellow DOMs respond at a higher rate than yellow SUBs but blue males do not show plasticity. Electrophysiological recordings from the Mauthner cells (Mcells), the neurons triggering startle, were performed in anesthetized animals and showed larger synaptic responses to sound clicks in DOMs, consistent with the behavioral results. In addition, the inhibitory drive mediated by interneurons presynaptic to the M-cell was significantly reduced in DOMs. Using behavioral tests, intracellular recordings, and single-cell molecular analysis, immunohistochemistry and in-situ hybridization, I show here that serotonin modulates this socially regulated plasticity via the 5-HT receptor subtype 2 (HTR2A). Specifically, SUBs display increased sensitivity to pharmacological blockade of HTR2A compared with DOMs in both startle-escape behavior and electrophysiological properties of the M-cell. These receptors, however, are not expressed in the Mauthner neurons, but in the inhibitory interneurons that regulate the Mcell’s membrane properties. I show a role for 5-HT in modulating startle plasticity and increase our understanding of the neural basis of behavioral plasticity. More broadly, this study provides an integrative explanation of an ecological and social trade-off at the level of an identifiable decision-making neural circuit.Item Social isolation enhances calcium signaling and synaptic plasticity in dopamine neurons of the ventral tegmental area(2012-08) Ramsey, Leslie Anne; Morikawa, Hitoshi; Mauk, Michael; Jones, Theresa; Harris, Adron; Johnston, DanielEnvironmental experiences play a critical role in an individualʼs risk of becoming addicted. Positive experiences may mitigate addiction vulnerability, whereas adverse experiences, particularly during adolescence, have been shown to increase addiction risk. Social isolation in rodents is a model system used to study the effects of such experiences, yet its impact on the learning and memory processes that underlie addiction remains elusive. Although social isolation is known to alter the functioning of the dopaminergic system, as well as reward processing and learning, its effect on dopamine (DA) neurons of the ventral tegmental area (VTA) is unknown. The data presented in this dissertation demonstrate that social isolation of rats during a critical period in adolescence (postnatal days 21-42) enhances long-term potentiation (LTP) of N-methyl D-aspartate receptor (NMDAR)-mediated glutamatergic transmission in the VTA. Activation of NMDARs is critical to the generation of DA neuron bursts that encode rewards and reward-predictive cues, and NMDARs are necessary for associative reward learning. The isolation-induced enhancement of NMDAR LTP results from augmentation of metabotropic glutamate receptor (mGluR)-dependent calcium (Ca²⁺) signaling via an increase in inositol 1,4,5-trisphosphate(IP3) sensitivity. Isolation-mediated effects on Ca²⁺ signaling and NMDAR plasticity were not reversed by a subsequent period of resocialization. Furthermore, social isolation during this critical period occludes the effect of repeated amphetamine exposure on mGluR/IP₃-mediated Ca²⁺ signaling and synaptic plasticity. Although corticotropin releasing factor (CRF) further facilitates mGluR/IP3-mediated Ca²⁺ signaling in DA neurons, alterations in CRF receptors are not responsible for the effects of isolation on Ca²⁺ signaling and synaptic plasticity. In addition, the learning of associations between environmental stimuli and drug rewards is acquired more quickly and is more resistant to extinction in isolated animals. Data presented in this dissertation lend support to the theory that enhanced mGluR/IP₃-mediated Ca²⁺ signaling and NMDAR plasticity facilitate the learning and memory of drug-associated stimuli. This dissertation provides the first demonstration of a cellular basis for the critical time window of social isolation during adolescence. NMDAR plasticity in the VTA may thus represent a neural substrate by which early life experiences regulate addiction vulnerability. (Note: Behavioral data were acquired by Mickael Degoulet)Item Synaptic encoding of in vivo ethanol experience in the nucleus accumbens(2015-08) Renteria, Rafael III; Morrisett, Richard A.; Gonzales, Rueben A; Harris, Robert A; Golding, Nace L; Morikawa, HitoshiThe nucleus accumbens (NAc) is a critical component of the brain reward system and neuroadaptations in the NAc are thought to underlie the development and persistence of addiction. The NAc is composed of two subregions, the core and shell, in which medium spiny neurons (MSNs) are the primary cell type. There are two distinct subtypes of MSNs in the NAc depending on the dopamine receptor expression: D1 dopamine receptor expressing (D1+) MSNs and D2 dopamine receptor expressing MSNs (D1-). We conducted whole-cell patch clamp recordings using transgenic mice to selectively record from D1+ and D1- MSNs in the NAc and found that chronic intermittent ethanol (CIE) vapor exposure resulted in cell type specific alterations in the intrinsic properties and expression of plasticity. To detect changes in plasticity of AMPA receptor (AMPAR) mediated currents we used a well described form of NMDAR-dependent long-term depression (LTD) that is induced by pairing low frequency stimulation with postsynaptic depolarization. Similar to previous findings from our lab we found that LTD was expressed exclusively in D1+ MSNs of ethanol naïve mice. In slices prepared from CIE treated mice, the induction protocol instead resulted in long-term potentiation (LTP) in D1+ MSNs. The expression of LTP in D1+ MSNs was accompanied by an increase in excitability as well as an increase in the frequency of spontaneous EPSCs. Interestingly, CIE exposure uncovered the expression of LTD in D1- MSNs. To further our understanding as to how these neuroadaptations contribute to maladaptive ethanol drinking behaviors we used CIE vapor exposure to induce an increase in voluntary ethanol consumption. Electrophysiological experiments were conducted in the core and shell to determine if excitatory signaling and plasticity is differentially modulated between the two subregions. CIE induced an increase in ethanol drinking and resulted in the long-lasting disruption of LTD in D1+ MSNs of the NAc shell with no changes in the core. In addition we found that AMPAR conductance was significantly reduced at positive holding potentials suggesting the presence of GluA2-lacking AMPARs. These findings may constitute important neuroadaptations that underlie alcohol dependence and excessive alcohol consumption.Item Towards the predictive modeling of ductile failure(2015-12) Gross, Andrew Jeffrey; Ravi-Chandar, K.; Kovar, Desiderio; Landis, Chad; Liechti, Kenneth; Kyriakides, SteliosThe ability to predict ductile failure is considered by an experimental examination of the failure process, validation exercises to assess predictive ability, and development of a coupled experimental-numerical strategy to enhance model development. In situ loading of a polycrystalline metal inside a scanning electron microscope is performed on Al 6061-T6 that reveals matrix-dominated response for both deformation and failure. Highly localized deformation fields are found to exist within each grain as slip accumulates preferentially on a small fraction of crystallographic planes. No evidence of damage or material softening is found, implying that a strain-to-failure model is adequate for modeling fracture in this and similar material. This modeling insight is validated through blind predictive simulations performed in response to the 2012 and 2014 Sandia Fracture Challenges. Constitutive and failure models are calibrated and then embedded in highly refined finite element simulations to perform blind predictions of the failure behavior of the challenge geometries. Comparison of prediction to experiment shows that a well-calibrated model that captures the essential elastic-plastic constitutive behavior is necessary to capture confidently the response for structures with complex stress states, and is a prerequisite for a precise prediction of material failure. The validation exercises exposed the need to calibrate sophisticated plasticity models without a large experimental effort. To answer this need, a coupled experimental and numerical method is developed for characterizing the elastic-plastic constitutive properties of ductile materials using local deformation field information to enrich calibration data. The method is applied to a tensile test specimen and the material’s constitutive model, whose parameters are unknown a priori, is determined through an optimization process that compares these experimental measurements with iterative finite element simulations. The final parameters produce a simulation that tracks the local experimental displacement field to within a couple percent of error. Simultaneously, the percent error in the simulation for the load carried by the specimen throughout the test is less than one percent. The enriched calibration data is found to be sufficient to constrain model parameters describing anisotropy that could not be constrained by the global data alone.Item Upper Bound Analysis of Bearing and Overturning Capacities of Shallow Foundations in Soft Clay(2013-12-03) Hartsfield, Randal JamesThis thesis presents a method to calculate the bearing and overturning capacity of a shallow foundation installed in soft clay using the upper bound method of plasticity. Mudmats are commonly used shallow foundations in offshore projects and are often eccentrically loaded. As economics and project requirements change, mudmats have evolved from simple circles and rectangles to more complex geometries. Computing the bearing and overturning capacities of such complex geometries using existing methods outlined in API procedures becomes difficult, as these procedures have been established for simple shapes. FEM is an alternative and established method for analysis, but these programs can be costly. In this thesis, the procedures for analysis using the upper bound method of plasticity are outlined and used to compute the bearing and overturning interaction for several foundations of varying shapes and undrained shear strength profiles. These results are compared to output of the FEM analysis program ABAQUS for validation. The conclusions of this case study are that the upper bound method of plasticity provides a reasonable prediction of the bearing and overturning capacity of an eccentrically loaded mudmat foundation, though considerations should be made when significant torsion or overturning moments in multiple directions are expected.Item Vesicle-free transition zones, dense core vesicles, and vesicle pool redistribution contribute to synapse growth(2012-05) Bell, Maria Elizabeth; Harris, Kristen M.; Aldrich, Richard; Benson, Deanna; Jones, Theresa; Nishiyama, HiroshiLong-term potentiation (LTP) is a widely studied cellular mechanism of learning and memory. LTP occurs at excitatory synapses on dendritic spines. Two hours after LTP induction in mature rat hippocampal slices, a reduction in spine number that is perfectly balanced by enlargement of the remaining synapses was previously observed. The sequence of events by which mature synapses enlarge is not well understood, but potential pre- and postsynaptic ultrastructural correlates of synapse growth have been identified. Vesicle-free transition zones (VFTZs) are postsynaptic thickenings contiguous with the PSD that have no apposing presynaptic vesicles perpendicular to the presynaptic membrane. VFTZs could be regions where synapses have expanded postsynaptically, but to which presynaptic vesicles have not yet been recruited. Presynaptic 80-nm dense core vesicles (DCVs) transport active zone proteins to the synapse during synaptogenesis, and may perform the same function during synaptic plasticity. 3-D reconstructions from ssTEM were used to investigate changes in VFTZs, DCVs, and presynaptic vesicles following LTP induction. By 30 minutes, VFTZ area and docked vesicle counts decreased, suggesting mobilization of additional vesicles to the synapse and enhanced release or delayed recycling. By two hours, VFTZs enlarged, suggesting VFTZ assembly contributes to synapse enlargement. DCV counts at 2 hours decreased relative to that at 30 minutes in both control and LTP conditions, suggesting DCVs were inserted at existing synapses to enlarge potentiated synapses in the LTP condition and to support ongoing spinogenesis in the control condition. The overall vesicle count in presynaptic boutons decreased at 2 hours following LTP induction, but docked vesicle count did not. Docked vesicle count was elevated at 2 hours relative to 30 minutes, suggesting that the depletion of docked vesicles observed at 30 minutes was followed by a replenishment and enhancement by 2 hours supplied by the non-docked vesicle pool. That the largest spines had more and larger VFTZs and recruited more DCVs and docked vesicles, and that the ratio of the sum of VFTZ area to the sum of PSD area is constant, provide further evidence that dendritic segments serve as functional units that manage resources in a coordinated and homeostatic way.