Rationale: Lead-exposure during developmental periods may alter reinforcing patterns of drugs of abuse in adulthood. Anxiety related mechanisms may also influence drug intake. Interactions between the two altering factors may exist. Objectives: The present study examined the effects of perinatal lead-exposure on cocaine self-administration after a GABAA antagonist pre-treatment. Methods: Female rats were exposed to a regimen of 16 mg lead daily for 30 days prior to breeding with un-exposed males. This continued throughout gestation and lactation until postnatal day (PND) 21. On PND 63, animals were implanted with indwelling jugular catheters. After a 7 day recovery period, animals were trained to self-administer 0.50 mg/kg cocaine intravenously [IV]. After stable responding had been established, testing procedures began using combinations of 0.03 and 0.06 mg/kg cocaine [IV] and 0.00, 0.50, 1.00 and 2.00 mg/kg bicuculline (a GABAA antagonist) intraperitoneal [IP]. Results: Bicuculline pre-treatment caused directionally opposite effects in both treatment groups (Group 0-Lead and Group 16-Lead) at the 0.06 mg/kg cocaine dose. Group 0-Lead animals showed an increase in self-administration, while Group 16-Lead animals showed a decrease in responding on the active (cocaine) lever. Results at the 0.03 mg/kg cocaine dose showed no discernable pattern. Group 0-Lead animals decreased in active lever responding at the 2.00 mg/kg bicuculline dose. Group 16-Lead animals showed no differences in responding at any dose of bicuculline. Conclusions: These data further suggest the influential role of GABA in mediating cocaine reward and the ability of developmental lead-exposure to alter mechanisms mediating drug responsiveness even after exposure has terminated.

Lead screw drives are used in various motion delivery systems ranging from manufacturing to high precision medical devices. Lead screws come in many different shapes and sizes; they may be big enough to move a 140 tons theatre stage or small enough to be used in a 10ml liquid dispensing micro-pump. Disproportionate to the popularity of lead screws and their wide range of applications, very little attention has been paid to their dynamical behavior. Only a few works can be found in the literature that touch on the subject of lead screw dynamics and the instabilities caused by friction. The current work aims to fill this gap by presenting a comprehensive study of lead screw dynamics focusing on the friction-induced instability in such systems. In this thesis, a number of mathematical models are developed for lead screw drive systems. Starting from the basic kinematic model of lead screw and nut, dynamic models are developed with varying number of degrees of freedom to reflect different components of a real lead screw drive from the rotary driver (motor) to the translating payload. In these models, velocity-dependent friction between meshing lead screw and nut threads constitute the main source nonlinearity. A practical case study is presented where friction-induced vibration in a lead screw drive is the cause of excessive audible noise. Using a complete dynamical model of this drive, a two-stage system parameter identification and fine-tuning method is developed to estimate parameters of the velocity-dependent coefficient of friction. In this approach the coupling stiffness and damping in the lead screw supports are also estimated. The numerical simulation results using the identified parameters show the applicability of the developed method in reproducing the actual systems behavior when compared with the measurements. The verified mathematical model is then used to study the role of various system parameters on the stability of the system and the amplitude of vibrations. These studies lead to possible design modifications that solve the system’s excessive noise problem. Friction can cause instability in a dynamical system through different mechanisms. In this work, the three mechanisms relevant to the lead screw systems are considered. These mechanisms are: 1. negative damping; 2. kinematic constraint, and; 3. mode coupling. The negative damping instability, which is caused by the negative gradient of friction with respect to sliding velocity, is studied thorough linear eigenvalue analysis of a 1-DOF lead screw drive model. The first order averaging method is applied to this model to gain deeper insight into the role of velocity-dependent coefficient of friction and to analyze the stability of possible periodic solutions. This analysis also is extended to a 2-DOF model. It is also shown that higher order averaging methods can be used to predict the amplitude of vibrations with improved accuracy. Unlike the negative damping instability mechanism, kinematic constraint and mode coupling instability mechanisms can affect a system even when the coefficient of friction is constant. Parametric conditions for these instability mechanisms are found through linear eigenvalue analysis. It is shown that kinematic constraint and mode coupling instability mechanisms can only occur in self-locking lead screws. The experimental case study presented in this work demonstrates the need for active vibration control when eliminating vibration by design fails or when it is not feasible. Using the sliding mode control method, two speed regulators are developed for 1-DOF and 2-DOF lead screw drive system models where torque generated by the motor is the controlled input. In these robust controllers, no knowledge of the actual value of any of the system parameters is required and only the upper and lower bounds of parameters are assumed to be available. Simulation results show the applicability and performance of these controllers. The current work provides a detailed treatment of the dynamics of lead screw drives and the topic of friction-induced vibration in such systems. The reported findings regarding the three instability mechanisms and the friction parameters identification approach can improve the design process of lead screw drives. Furthermore, the developed robust vibration controllers can be used to extend the applicability of lead screws to cases where persistent vibrations caused by negative damping cannot be eliminated by design modifications due to constraints.

Lead screw drives are used in various motion delivery systems ranging from manufacturing to high precision medical devices. Lead screws come in many different shapes and sizes; they may be big enough to move a 140 tons theatre stage or small enough to be used in a 10ml liquid dispensing micro-pump. Disproportionate to the popularity of lead screws and their wide range of applications, very little attention has been paid to their dynamical behavior. Only a few works can be found in the literature that touch on the subject of lead screw dynamics and the instabilities caused by friction. The current work aims to fill this gap by presenting a comprehensive study of lead screw dynamics focusing on the friction-induced instability in such systems. In this thesis, a number of mathematical models are developed for lead screw drive systems. Starting from the basic kinematic model of lead screw and nut, dynamic models are developed with varying number of degrees of freedom to reflect different components of a real lead screw drive from the rotary driver (motor) to the translating payload. In these models, velocity-dependent friction between meshing lead screw and nut threads constitute the main source nonlinearity. A practical case study is presented where friction-induced vibration in a lead screw drive is the cause of excessive audible noise. Using a complete dynamical model of this drive, a two-stage system parameter identification and fine-tuning method is developed to estimate parameters of the velocity-dependent coefficient of friction. In this approach the coupling stiffness and damping in the lead screw supports are also estimated. The numerical simulation results using the identified parameters show the applicability of the developed method in reproducing the actual systems behavior when compared with the measurements. The verified mathematical model is then used to study the role of various system parameters on the stability of the system and the amplitude of vibrations. These studies lead to possible design modifications that solve the system’s excessive noise problem. Friction can cause instability in a dynamical system through different mechanisms. In this work, the three mechanisms relevant to the lead screw systems are considered. These mechanisms are: 1. negative damping; 2. kinematic constraint, and; 3. mode coupling. The negative damping instability, which is caused by the negative gradient of friction with respect to sliding velocity, is studied thorough linear eigenvalue analysis of a 1-DOF lead screw drive model. The first order averaging method is applied to this model to gain deeper insight into the role of velocity-dependent coefficient of friction and to analyze the stability of possible periodic solutions. This analysis also is extended to a 2-DOF model. It is also shown that higher order averaging methods can be used to predict the amplitude of vibrations with improved accuracy. Unlike the negative damping instability mechanism, kinematic constraint and mode coupling instability mechanisms can affect a system even when the coefficient of friction is constant. Parametric conditions for these instability mechanisms are found through linear eigenvalue analysis. It is shown that kinematic constraint and mode coupling instability mechanisms can only occur in self-locking lead screws. The experimental case study presented in this work demonstrates the need for active vibration control when eliminating vibration by design fails or when it is not feasible. Using the sliding mode control method, two speed regulators are developed for 1-DOF and 2-DOF lead screw drive system models where torque generated by the motor is the controlled input. In these robust controllers, no knowledge of the actual value of any of the system parameters is required and only the upper and lower bounds of parameters are assumed to be available. Simulation results show the applicability and performance of these controllers. The current work provides a detailed treatment of the dynamics of lead screw drives and the topic of friction-induced vibration in such systems. The reported findings regarding the three instability mechanisms and the friction parameters identification approach can improve the design process of lead screw drives. Furthermore, the developed robust vibration controllers can be used to extend the applicability of lead screws to cases where persistent vibrations caused by negative damping cannot be eliminated by design modifications due to constraints.

The composition dependent variation of ferroelectric domain structure in lead zirconate titanate (Pb(Zr0.52Ti0.48)O3) ceramics have been investigated within the morphotropic phase boundary (MPB). Tetragonal phase in sintered samples were identified via X-ray diffractometry (XRD). Representative microstructures of ferroelectric domains were examined using scanning electron microscopy (SEM). £\-boundaries, £_- boundaries, and £k-boundaries were analyzed from the contrast of extreme fringe patterns by transmission electron microscopy (TEM). Twin planes for 90o domains lie in {011) and for 180o domains lie in {100) and {220) were determined by selected area diffraction patterns (SADP). Traditional contrast analysis was adopted for determining displacement vectors (R). 90o domains with R = £`[011] and 180o domains with R = n[001]. Convergent beam electron diffraction (CBED) was performed to identify crystalline phases of different domain configurations. By examined the symmetry along the Z = [100], [110], and [111] zone axis, both £_-boundaries and £k-boundaries are tetragonal phase.

1.Sn/Ag4.0/Cu0.5 solder with better performance by the improved reflow profile. 2.The Sn/Ag2.6/Cu0.6¡BSn/Ag4.0/Cu0.5 with similar reliability test performance.

ABSTRACT In package, it¡¦s easy to have defects in the solder joint, for the request of environment protection, lead-free solder research is one of the most important topics now. In soldering, the adhesion, diffusion barrier, and wettability of the interface between UBM and a lead-free solder, and the caused IMC structure that are important elements to influence long-term reliability tests. The thesis is aimed to investigate the combination of pure tin/Al-NiV-Cu UBM/STD Au substrate under reliability tests. The samples are bare dies in which the combination is pure tin/ Al-NiV-Cu UBM and packages of is pure tin/Al-NiV-Cu UBM/STD Au substrate. The goals are to realize the mechanical properties under multiple reflows and long term HTST tests with different temperatures and the operational life. We also uses SEM to observe the growth of IMC and the failure modes that help us to realize the connection between failure modes and IMC. The results of experiment can be concluded as follows. In a bare die, 260¢Jmultiple reflows test causes delamination between IMC and die, but doesn¡¦t affect the mechanical properties of it, and HTST test lowers the bump shear strength of it. In package, multiple reflows test and HTST test lower the mechanical properties significantly, the result also means that the adhesion between bump and die will drop significantly as tests go on. In HTOL test with the conditions of 150¢J and 320mA, the average stable service time of the package is 892 hours, and the average ultimate service time of the package is 1,053 hours, most probable failure site is in R1 joint.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains x, 165 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 163-165).

Thesis--Universiteit van Utrecht. / Bibliography: p. 101-104.

Neural stem cells (NSCs) are defined as multipotent stem cells. They are able to self-renew and differentiate into mature cells, such as neurons, oligodendrocytes and astrocytes. Neurotoxicity of lead (Pb2+) has been extensively investigated by many previous studies. These studies proved that lead is a potent toxin that affects nervous system, especially children’s brain. However, most of these studies focused on the negative effects of lead on the differentiated or mature cell types in the brains instead of NSCs. The aim of this study was to reveal the effects of Pb2+ on viability, proliferation and differentiation of NSCs derived from the hippocampus of newborn rats aged 7 days and adult rats aged 90 days in vitro. NSCs harvested from the rat hippocampus were cultured in proliferation medium. After 6-8 days, free-floating neurospheres formed. The neurospheres were dissociated and plated onto poly-L-lysine coated 96-well plate and coverslips. Some dissociated cells were characterized by being stained with anti-nestin to show the presence of NSCs. This project was divided into three parts. In the first part, the Passage 2 (P2) cells plated onto 96-well plate were cultured in the proliferation medium with different concentrations of lead acetate (0-200μM) for 48 hours, followed by 3- (4,5-cimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to detect the effects of Pb2+ on the cell viability. In the second part, P2-NSCs plated onto coverslips in wells were cultured in the proliferation medium with different concentrations of lead acetate (0-200μM). Then, 10 μM bromodeoxyuridine (BrdU) was added into the culture medium for additional 24 hours, followed by immunocytochemistry staining with anti-BrdU. In the last part, the dissociated P2-NSCs plated onto coverslips were allowed to grow in the differentiation medium of neurons, astrocytes or oligodendrocytes with different concentrations of lead acetate (0-200μM). After 6 days, immunocytochemistry staining with anti-microtubule-associated protein 2 (anti-MAP2), anti-glial fibrillary acidic protein (anti-GFAP) or anti-RIP was used to detect the differentiation commitment of affected NSCs. Low level of Pb2+ (1-10μM) had no effect on the viability of adult hippocampal neural stem cells (hNSCs). However, Pb2+ exposure at the concentration of 10μM could lead to significant cell death of newborn hNSCs. High level of Pb2+ (50-200μM) caused significant cell death of both newborn and adult hNSCs. Newborn hNSCs were sensitive to Pb2+ toxicity in proliferation assay. Even a low concentration (1μM) of lead could lead to significant inhibition of cell proliferation. High level of Pb2+ (50-200μM) suppressed proliferation of both newborn and adult hNSCs significantly. Moderate to high levels of Pb2+ exposure (50-200μM) significant decreased the percentage of mature neurons cultured from both newborn and adult hNSCs. Furthermore, 10μM or more Pb2+could significantly inhibited the oligodendrocyte differentiation of both newborn and adult hNSCs. However, Pb2+ could also stimulate the astrocyte differentiation of hNSCs. Lead concentrations higher than 10μM and 50μM could respectively lead to a significant increase in the percentage of mature astrocytes differentiated from newborn and adult hNSCs. The data showed that Pb2+ inhibited not only the viability and proliferation of rat hNSCs but also the neuronal and oligodendrocyte differentiation in vitro; moreover activated astrocyte differentiation of the hNSCs of both newborn and adult rats were observed with high concentration of Pb2+ in vitro. Also, it was revealed that the hNSCs of newborn rats were more sensitive than those from adult rats to Pb2+ cytoxicity. / published_or_final_version / Anatomy / Master / Master of Medical Sciences

published_or_final_version / Chemistry / Master / Master of Philosophy