Global water scarcity is an enormous and yet imminent challenge for our time. Industries such as machinery manufacturing, metallurgy, etc., generate increasing volumes of wastewaters containing heavy metals. These wastewaters are often directly or indirectly discharged into the environment. Heavy metals are not biodegradable; therefore, they can accumulate in the body, creating severe health problems such as cancer, nausea, or even death. It is necessary to remove heavy metals from wastewaters before their discharge to the environment. There are different methods to do that. Among them, membrane separation technology is a promising method for wastewater treatment. In particular, nanofiltration (NF) membranes, due to their rejection mechanism (size exclusion and charge repulsion), are most suitable to remove s heavy metals from wastewater. A new class of high-performance semipermeable membranes for reverse osmosis (RO), nanofiltration (NF), and forward osmosis (FO) applications are thin-film nanocomposite (TFN) membranes. In this work, novel NF TFN membranes were fabricated by incorporating the functionalized halloysite nanotubes (HNTs) with the first generation of poly(amidoamine) (PAMAM) dendrimers (G1). Also, the same membranes were used for the removal of heavy metals in FO separation. The combination of FO and NF processes represents the novel two-stage FO-NF hybrid process for heavy metal removal. The membranes showed high rejections of Na2SO4 (97%-98%) and MgCl2 (82%-90%) in NF tests. Although lower than Na2SO4, the rejections of MgCl2 are much greater than those reported in the literature. The remarkable rejections of MgCl2 are attributed to positively charged HNTs-G1 nanoparticles incorporated in the selective polyamide (PA) layer of TFN membranes. The FO experiments using MgCl2 as a draw solution revealed excellent rejections of Cu2+ and Pb2+ by TFN membranes ranging from 95% to 98%. The presence of heavy metal in the feed solution enhanced the FO performance of the membranes. In particular, the reverse flux of draw solute (MgCl2) decreased by at least 2.5 times compared to the experiments with pure water as a feed. Simultaneously, the water flux also increased. The improved FO performance in the presence of heavy metals is attributed to their adsorption by the membranes.

In this study, two different strategies were carried out to modify the polyvinylidene fluoride (PVDF) distillation membrane for desalination. The first strategy was the addition of TiO2 nanoparticles into the target membranes and a synergistic effect of hydrophilic and hydrophobic nanoparticles was found for the first time in this work. And the other strategy was the introduction of another polymer material, polytetrafluoroethylene (PTFE), to the PVDF membranes to fabricate a flat sheet PVDF-PTFE composite membrane and this is the first attempt that such a membrane to be made. Two types of membranes were characterized by scanning electron microscopy (SEM) detection, porosity measurement, energy dispersive X-ray spectroscopy (EDX), Attenuated total reflectance (ATR)-Fourier transformed infrared spectroscopy (FTIR), contact angle (CA) measurement, atomic force spectroscopy (AFM) detection and liquid entry pressure of water (LEPw) measurement. Their performance was evaluated by vacuum membrane distillation (VMD) experiments. And the best VMD pure water permeate flux of the membranes fabricated under these two modify strategies could achieve 4.26 kg/m2h (M-L5-B2) and 5.61 kg/m2h (M-40), respectively, when that of pure PVDF membrane is only 0.71 kg/m2h. The salt rejection of the prepared composite membranes are all stably higher than 99.5% which demonstrate their capacity for desalination.

The current "diffusion-retention" model for protein trafficking to the inner nuclear membrane (INM) proposes that INM proteins diffuse laterally from the membrane of the endoplasmic reticulum into the INM and are then retained in the INM by binding to nuclear proteins or DNA. Because some data indicate that the sorting of baculovirus envelope proteins to the INM is protein-mediated, we have examined the early stages of INM protein integration and sorting using photocrosslinking. Both viral and host INM-directed proteins were integrated cotranslationally through the endoplasmic reticulum translocon, and their nonrandom photocrosslinking to two translocon proteins, Sec61± and translocating chain-associated membrane protein (TRAM), revealed that the first transmembrane sequence (TMS) of each viral and host INM-directed protein occupied a very similar location within the translocon. Because few TMSs of non-INM-directed membrane proteins photocrosslink to TRAM, it seems that the INM-directed TMSs occupy different sites within the translocon than do non-INM-directed TMSs. The distinct proximities of translocon components to INM-directed TMSs strongly suggest that such TMSs are recognized and initially sorted within the translocon. Previous work with the envelope protein ODV-E66 (E66) showed that E66 trafficking to the INM is mediated via an INM sorting signal (Sorting Motif or SM). In this study, using a site-specific crosslinking approach we demonstrate that following ER membrane integration, the SM is adjacent to two viral proteins: FP25K & BV/ODV-E26 (E26). Deletion of FP25K from the viral genome results in the accumulation of E66 at the ONM, suggesting that FP25K may facilitate protein movement at the nuclear pore. While the role of the E66-E26 interaction remains to be determined, these data suggest that E66 trafficking to the INM is a protein-facilitated process. Crosslinking experiments using E66 integration intermediates revealed that during co-translational integration at the ER, the SM is adjacent to two cellular proteins of ~10kDa and ~25kDa, referred to as SMAP 10 (SM associated protein of 10kDa) & SMAP25 respectively. Thus, contrary to the widely accepted "diffusion-retention" model for protein trafficking to the INM, our data indicate that protein sorting to the INM is a multistep process initiated upon membrane integration in which the INM sorting signal sequentially associates with various sorting factors.

This study discusses the problem of methanol crossover of a direct methanol fuel cell. By increasing the difficulty in the movement of methanol molecules, and blocking the larger holes in the membrane methanol crossover is reduced. The experimental results were further validated through the MEA performance, and its long term stability, and the carbon dioxide reduction in the cathode. The experimental results show that the most effective way is to soak the membrane in the Nafion solution with ultrasonic vibration applied. Silica, instead of Nafion solution, is able to reduce the methanol crossover the most. However, the MEA thus produced performs poorly because the silica tends to roughen the membrane surface and interfere with the cohesion between the membrane and the electrode. Further studies are needed on this subject.

The current "diffusion-retention" model for protein trafficking to the inner nuclear membrane (INM) proposes that INM proteins diffuse laterally from the membrane of the endoplasmic reticulum into the INM and are then retained in the INM by binding to nuclear proteins or DNA. Because some data indicate that the sorting of baculovirus envelope proteins to the INM is protein-mediated, we have examined the early stages of INM protein integration and sorting using photocrosslinking. Both viral and host INM-directed proteins were integrated cotranslationally through the endoplasmic reticulum translocon, and their nonrandom photocrosslinking to two translocon proteins, Sec61± and translocating chain-associated membrane protein (TRAM), revealed that the first transmembrane sequence (TMS) of each viral and host INM-directed protein occupied a very similar location within the translocon. Because few TMSs of non-INM-directed membrane proteins photocrosslink to TRAM, it seems that the INM-directed TMSs occupy different sites within the translocon than do non-INM-directed TMSs. The distinct proximities of translocon components to INM-directed TMSs strongly suggest that such TMSs are recognized and initially sorted within the translocon. Previous work with the envelope protein ODV-E66 (E66) showed that E66 trafficking to the INM is mediated via an INM sorting signal (Sorting Motif or SM). In this study, using a site-specific crosslinking approach we demonstrate that following ER membrane integration, the SM is adjacent to two viral proteins: FP25K & BV/ODV-E26 (E26). Deletion of FP25K from the viral genome results in the accumulation of E66 at the ONM, suggesting that FP25K may facilitate protein movement at the nuclear pore. While the role of the E66-E26 interaction remains to be determined, these data suggest that E66 trafficking to the INM is a protein-facilitated process. Crosslinking experiments using E66 integration intermediates revealed that during co-translational integration at the ER, the SM is adjacent to two cellular proteins of ~10kDa and ~25kDa, referred to as SMAP 10 (SM associated protein of 10kDa) & SMAP25 respectively. Thus, contrary to the widely accepted "diffusion-retention" model for protein trafficking to the INM, our data indicate that protein sorting to the INM is a multistep process initiated upon membrane integration in which the INM sorting signal sequentially associates with various sorting factors.

No description available.

In this project, nonlinear behavior of biomembrane are modeled as heterogeneous elastic biological systems. In addition to the static behavior of the membranes, their dynamic behavior are modeled to be able to investigate time-dependency of the variables of the systems. Some of the available models are used and some new ones are developed to study static and dynamic analysis of monolayer and bilayer membranes as well as circular axisymmetric biomembranes. The presented models are developed based on the Euler-Bernoulli constitutive law and employed to investigate buckling phenomena in the membranes as one of the most important physical phenomena in biological environment. Static and dynamic behavior of Buckling phenomenon in biological membranes are modeled. The static model results in nonlinear ordinary di erential equation for one-dimensional approximation. In order to extend the model for circular membranes, the criteria of constant length in one-dimensional membranes is changed to constant surface. Moreover, tension-compression and bending springs are added to the model and employed to study buckling of biomembranes. Similar to the procedure of obtaining the equations of static large deformation of the membrane, the equations of motion of the membrane is obtained using free body diagram of an in finitesimal element of the membrane and employing Euler- Bernoulli constitutive law. Hence, nonlinear integro partial di erential equations are obtained t model the dynamic behavior of the membrane. All of the equations, including static and dynamic ones, are changed to the dimensionless forms so that the results can be considered general and can be employed to analyze diff erent systems with diff erent properties. The nondimensional equations of each part of the project are solved using di erent iterative and time-dependent schemes. The schemes are used to obtain the discretized forms of the equations. The discretized equations of all nodes of the domain, with due attention to the considered boundary conditions, are gathered in a matrix and the matrix solved to obtain the solution of the variables at each node and time stage. The solutions obtained for diff erent problems investigated in this project are employed to illustrate variations of diff erent dependent variables of the models with respect to the independent variables and parameters of the problems. As the important step to analyze the problems, diff erent results of the problems investigated in the project are verifi ed using the available information in literature. Membrane pro le are obtained for di erent parameter values and external forces in the stationary condition. In addition, variation of maximum deflection and slope are studied with respect to the variation of diff erent dimensionless parameters of the system. As a verifi cation of the solution, the incompressibility of bilayer membrane is shown as well. Growth of di fferent variables is shown with respect to time employing the solution of dynamic modeling of the membrane. As one of the important parts of this project, e ects of heterogeneity on dynamic behavior of the membrane under buckling is investigated. The heterogeneous region is considered to have di fferent material properties and it position is changed to also study the geometrical e ffects.

Thesis (Ph. D.)--University of Virginia, 1998. / Spine title: SCAMPs 1, 2, & 3. Includes bibliographical references (p. 159-189). Also available online through Digital Dissertations.

Thesis (Ph. D.)--Ohio State University, 2008.

Thesis (PhD)--University of Stellenbosch, 2005. / Bibliography. Also availabe via the Internet.