One-way Coupled Hydroelastic Analysis of Aluminum Wedge Under Slamming

The concept of using aluminum as the primary construction material for high speed ships and the hydroelastic behavior of the structure is widely gaining importance as a significant research topic in naval architecture. Aluminum is lighter than steel and hence can be predominantly used in high speed crafts which experiences significant slamming. This thesis work is focused on wedge shaped models. Free fall wedge impact is studied and a FORTRAN 90 computer program is developed to estimate the structural response of the wedge experiencing slamming by the use of matrix methods, finite element techniques and Newmark-Beta numerical time integration methods. The numerical solution is validated by comparison with the static solution. The theoretical hydrodynamic pressures which are used as input for this work was originally developed by using a flat cylinder theory [26]. The wedge drop at 0.6096 m (24 inch) drop height with an impact veloc- ity of v=3.05 m/s is based as the premise and the experimental pressure distributions measured by the pressure-transducers and the theoretical pressure predictions are used as inputs and the structural response is derived. Additionally, the response is compared for three different plate thicknesses and the results are compared against each other. The maximum deflection is comparable to the deflection evaluated from the experiment and tends to attain convergence as well. As the plate thickness reduces there tends to be a significant rise in the deflection values for the wedge plate, in the manner that when the plate thickness is halved there is a deviation of more than 75% in the deflection values as such

Polyolefin/layered silicate nanocomposites via surface initiated ring opening metathesis polymerization

This thesis reports about the synthesis of thermoplastic elastomers via polyolefin/layered silicate nanocomposites and fabrication of porous membranes using a triblock Poly(styrene-b-isoprene-b-dimethylsiloxane) (SID) block copolymer. The first project work started as second phase of a NSF CAREER grant to study the properties of nanocomposites synthesized using polyolefins like norbornenes, alkyl substituted norbornenes and cyclopentene to engineer high performance nanocomposites. The polymers will be surface initiated from clay using ring opening metathesis polymerization and subsequent hydrogenation forms thermoplastic elastomeric nanocomposites with synergistic properties from mechanical reinforcement offered by layered silicates, enhanced thermal properties due to changed chain conformations and effects of block copolymers to combine different polymeric properties. First published article on this work reported the successful synthesis of diblock copolymer/layered silicate nanocomposite via surface initiated ring opening metathesis polymerization (SI-ROMP) of norbornene and cyclopentene from montmorillonite clay (MMT) surface. The surface of MMT clay was organo modified using norbornene-terminated alkyl ammonium surfactant and block copolymer brushes were polymerized from the clay surface and disordering and dispersing the clay platelets in polymer matrix. Non-clay counterparts were obtained via reverse ion exchange methods and characterized in parallel with corresponding nanocomposite. Thermal, mechanical and morphological characterization showed the property enhancement due to addition of clay and showed good exfoliation of MMT. After successful demonstration of exfoliated nanocomposites using surface initiated polymerization technique, we focused on development of nanocomposites with ethylidene norbornene as first block and cyclopentene as second block; subsequent hydrogenation of first block results in a soft and elastomeric poly(ethyl norbornene) block and second block results in a perfectly linear semi crystalline poly(ethylene) block. We followed the same experimental procedure used in the first article with necessary changes accommodating the needs of new monomer to synthesize exfoliated nanocomposites. We were successful in synthesizing surface initiated hydrogenated nanocomposites with clay exfoliation, however subsequent property evaluation in conjunction with the non-clay analogs showed that addition of clay negatively effects the thermal properties of hydrogenated poly(ethylidene norbornene) block. This observation was contrary to our hypothesis that clay confines the polymer chain movement and results in enhancement of thermal properties. The second project in my thesis work focused on the study of porous membranes fabricated from a class of triblock copolymers for carrying out separations. This project exploits the microstructures formed due to self-assembly of block copolymers to form percolating network of pores in membranes fabricated using block copolymer material. A Poly(styrene-b-isoprene-b-dimethylsiloxane) (SID) block copolymer was studied as a potential system. A SID triblock copolymer resulting in gyroid phase was synthesized, characterized and fabricated as a thin porous membrane after chemical etching of D block and forming a network of pores with I block as pore lining and S block as membrane backbone. This membrane was tested via flow through experiments to establish successful separation based on size

Synthesis of Polyolefin/Layered Silicate Nanocomposites via Surface-Initiated Ring-Opening Metathesis Polymerization

Here we report the synthesis and characterization of block copolymer/layered silicate (BCPLS) nanocomposites via the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene and cyclopentene from montmorillonite clay (MMT). The MMT particle surfaces were functionalized with a norbornene-terminated alkylammonium surfactant through ion exchange. Block copolymer brushes of norbornene and cyclopentene were polymerized directly from the surface of these functionalized clay platelets, yielding highly exfoliated nanocomposites. A fraction of the polymer brushes were removed from their substrate by reverse ion exchange and characterized in parallel with their corresponding nanocomposite analogues. The thermal, mechanical, and morphological characteristics of the BCPLSs and their neat analogues were then compared directly. This enabled us to assess the role of the MMT filler in the thermal properties, solid/melt state rheology, and morphology

Selectively strong coupling MoS2_2 excitons to a metamaterial at room temperature

Light emitters in vicinity of a hyperbolic metamaterial (HMM) show a range of quantum optical phenomena from spontaneous decay rate enhancement to strong coupling. In this study, we integrate monolayer Molybdenum disulfide (MoS$_2$) emitter in near field region of HMM. The MoS$_2$ monolayer has A and B excitons, which emit in the red region of visible spectrum. We find that the B excitons couple to HMM differently compared to A excitons. The fabricated HMM transforms to a hyperbolic dispersive medium at 2.13 eV, from an elliptical dispersive medium. The selective coupling of B Excitons to the HMM modes is attributed to the inbuilt field gradient of the transition. The B exciton energy lies close to the transition point of the HMM, relative to A Exciton. So, the HMM modes couple more to the B excitons and the metamaterial functions as selective coupler. The coupling strength calculations show that coupling is 2.5 times stronger for B excitons relative to A excitons. High near field of HMM, large magnitude and the in-plane transition dipole moment of MoS$_2$ Excitons, result in strong coupling of B excitons and formation of hybrid light-matter states. The measured differential Reflection and Photoluminescence spectra indicate the presence of hybrid light-matter states i.e. Exciton-Polaritons. Rabi splitting of at least 129 meV at room temperature is observed. The low temperature Photoluminescence measurement shows mode anticrossing, which is characteristic feature of hybrid states. Our results show that the HMM works as a energy selective coupler for multi-excitonic systems as MoS$_2$

“I am the father and head of the household, but I can’t just give commands”: Father’s involvement, roles, and support practices in care, feeding, and ART adherence for HIV exposed uninfected infants in Zambia

Background: HIV exposed infants who are uninfected may be at risk for poorer health outcomes and often face challenges such as living in poverty. Infant care and feeding practices are especially important for these infants as they are more likely to experience stressors putting them at a higher risk for poor health and development. While prevention of mother-to-child transmission (PMTCT) programs have had success in reducing rates of transmission and increasing antiretroviral therapy (ART) adherence, they are often focused solely on mothers. Family-centered approaches have the potential to be more effective than engaging mothers solely since fathers can influence whether the mother is following optimal care and feeding practices and may either support or hinder ART adherence. Objectives: This study aimed to explore fathers' involvement in infant care and feeding, examine fathers’ views of their roles in infant care and feeding and the roles of other family members, and to assess the types of support practices fathers engage in to help with infant care, feeding, and ART adherence. Methods: Eight interviews with fathers from a larger qualitative, formative research study in Lusaka, Zambia were analyzed using thematic analysis. Results: Fathers in this study are involved in infant feeding by providing food or drink to the baby and by encouraging and supporting both breastfeeding and responsive feeding. Fathers consider play as both a way to show love to the baby and as a form of learning. Fathers engaged in a variety of care and stimulation activities. Fathers generally believe that both parents are responsible for care and feeding and fulfill a variety of roles, the most common being a provider for the family followed by encouraging or reminding mothers to breastfeed. The main types of support practices that fathers offer fall under financial or practical help and encouragement of breastfeeding and/or ART adherence. Conclusions: Fathers are involved and interested in infant care and feeding and can potentially have a positive influence on breastfeeding, responsive feeding, as well as child development. Fathers' perception of their roles aligned closely with the actual support practices they engage in to encourage or facilitate breastfeeding, stimulation activities, and ART adherence. Findings support the need for PMTCT programs that are more family-centered and utilize the promising potential of father support in improving rates of optimal care and feeding practices as well as increasing ART adherence.Bachelor of Science in Public Healt

Determination of the ensemble transition dipole moments of self-assembled quantum dot films by time and angle resolved emission spectroscopy measurements

The spontaneous emission of light in semiconductors is due to the excitonic relaxation process. The emission of light requires a change in the transition dipole matrix of the system. This is captured in terms of the physical quantity called transition dipole moment. The transition dipole moment (TDM) characterizes the line strength of the emission process. TDM is of fundamental importance in emitter-cavity interaction as its magnitude decides the interaction strength of emitters and cavities. In all light emitting devices, the orientation of the transition dipole moments is directly related to the optical power output of the devices. In this manuscript, the basic framework of spontaneous emission and Einstein coefficients is discussed for two level systems. Semiconducting alloyed quantum dots (AQDs) are synthesized in hydrophobic phase. AQDs are used as the experimental two level system. The AQDs are then self-assembled into monolayers by the Langmuir-Schaefer method. The ensemble averaged TDM magnitude and orientation of AQDs are extracted from the time resolved and the angle resolved emission spectroscopy measurements respectively. The procedure for finding out the TDM, described in this manuscript is generalized. The mentioned procedure can be extended to any emitters in hydrophobic phase

Inhibited spontaneous emission of quantum dots weakly coupled to off resonant silver nanoplatelets and silver nanowires

Spontaneous emission (SE) rate of any light emitters directly scales with the locally available modes for photons. The emission rate can be modified, by changing the dielectric environment of light emitters. Generally cavities with modes in resonance to light emission frequency, are used to amplify the light emission rate. The Fermi golden rule predicts that if the cavity modes are offresonant to the emission frequency, then the SE rate is suppressed. In this study, we demonstrate that the SE of colloidal alloyed quantum dots is inhibited by coupling them to chemically synthesized Silver nanowires and Silver nanoplatelet systems. The silver nanoplatelet and silver nanowire plasmonic resonance modes are in ultraviolet and infrared regions of the electromagnetic spectrum. The quantum dots emit in visible region of light. This off-resonant weak coupling of emitters and cavities results in emission rate suppression and is quantified by time resolved photoluminescence (TRPL) measurements. TRPL decay profiles show that the emission rate can be suppressed by coupling self assembled quantum dot monolayers to a single silver nanoplatelet and a single silver nanowire respectively

Selektivna i osjetljiva metoda određivanja metoprolola u humanoj plazmi tekućinskom kromatografijom spregnutom s masenom spektrometrijom

A high-performance liquid chromatography-tandem mass spectrometric method was developed and validated for the determination of metoprolol in human plasma. The analyte and internal standard, nevirapine,were extracted from plasma matrix by liquid–liquid extraction with ethyl acetate. Cromatographic separation was achieved on a C-18 analytical column with an isocratic mobile phase of 15:85 (V/V) 10 m mol L–1 ammonium acetate (pH 5.0)/acetonitrile. The atmospheric pressure chemical ionization technique was used for sample ionization in positive ion mode and enhanced selectivity was achieved by tandem mass spectrometric analysis via two multiple reaction monitoring (MRM) transitions, 268.2 → 116.2 for metoprolol and 267.1 → 226.2 for nevirapine, respectively. The assay was validated for human plasma over a concentration range of 1200 ng mL–1 with the precision and accuracy ranging from 0.9 to 8.8 % and 89.9 to 105.8 %, respectively.U radu je opisano određivanje metoprolola u humanoj plazmi tekućinskom kromatografijom visoke učinkovitosti spregnutom s masenom spektrometrijom. Analit i interni standard, nevirapin, ekstrahirani su iz plazme etil-acetatom. Kromatografsko odjeljivanje provedeno je na C-18 koloni uz mobilnu fazu sljedećeg sastava: 10 mmol L–1 amonijev acetat (pH 5,0)/acetonitril 15:85 (V/V). Ionizacija uzoraka provedena je pri atmosferskom tlaku. Povećanje selektivnosti postignuto je spregnutom masenom spektrometrijskom analizom praćenjem dvaju prijelaza (MRM) – 268,2 → 116,2 za metoprolol, odnosno 267,1 → 226,2 za nevirapin. Metoda je validirana za koncentracijsko područje 1200 ng mL–1 uz preciznost i točnost od 0,9 do 8,8 %, odnosno 89,9 do 105,8 %

Aseptic meningitis rare complication of mumps in an adult

Mumps is endemic worldwide, with epidemics every 3-5 years in unvaccinated populations. After the introduction of the mumps vaccine in the national immunization schedule, the number of reported cases declined by >97% in 1989 until an outbreak of 6584 cases was reported in 2006 even in populations with high-level vaccination coverage and all the patients had a history of vaccination. Here we present a case of mumps with aseptic meningitis in a 42-year-old female. Although historically mumps was a disease of childhood, with most cases occurring in children 5-9 years of age, mumps now most frequently occur in older age groups. This shift in age distribution and the occurrence of mumps in the vaccinated population suggest a waning of vaccine immunity