699 research outputs found
Determination of ferroelectric compositional phase transition using novel virtual crystal approach
We employ a new method for studying compositionally disordered ferroelectric
oxides. This method is based on the virtual crystal approximation (VCA), in
which two or more component potentials are averaged into a composite atomic
potential. In our method, we construct a virtual atom with the correctly
averaged atomic size and atomic eigenvalues. We have used our new method to
study the composition dependent phase transition in Pb(Zr_{1-x}Ti_x)O_3 lying
between x=0.5 and x=0.4. We correctly predict the experimentally determined
phase transition from the tetragonal phase to a low-temperature rhombohedral
phase between these two compositions.Comment: 7 pages, 2 figures, Proceedings for Fundamental Physics of
Ferroelectrics, Aspen, CO February 13-20, 200
Accurate construction of transition metal pseudopotentials
We generate a series of pseudopotentials to examine the relationship between
pseudoatomic properties and solid-state results. We find that lattice constants
and bulk moduli are quite sensitive to eigenvalue, total-energy difference and
tail norm errors, and clear correlations emerge. These trends motivate our
identification of two criteria for accurate transition metal pseudopotentials.
We find that both the preservation of all-electron derivative of tail norm with
respect to occupation and the preservation of all-electron derivative of
eigenvalue with respect to occupation {[Phys. Rev. B {\bf 48}, 5031 (1993)]}
are necessary to give accurate bulk metal lattice constants and bulk moduli. We
also show how the fairly wide range of lattice constant and bulk modulus
results found in the literature can be easily explained by pseudopotential
effects.Comment: submitted to Phys. Rev
The Scripture of Helices
This thesis comprises poems written during my two years of study for the Master of Arts Degree in English with a creative writing emphasis. The majority of the poems are written in either a received or contemporary form, although a substantial minority are written in free verse. Many of the poems deal with extreme circumstances such as combat and imprisonment. Others address family stresses due to birth, death, remarriage, and clashes of values. Some poems have a religious emphasis while others are firmly rooted in the natural world. All, however, are explorations of human nature
Virtual-crystal approximation that works: Locating a composition phase boundary in Pb(Zr_{1-x}Ti_3)O_3
We present a new method for modeling disordered solid solutions, based on the
virtual crystal approximation (VCA). The VCA is a tractable way of studying
configurationally disordered systems; traditionally, the potentials which
represent atoms of two or more elements are averaged into a composite atomic
potential. We have overcome significant shortcomings of the standard VCA by
developing a potential which yields averaged atomic properties. We perform the
VCA on a ferroelectric oxide, determining the energy differences between the
high-temperature rhombohedral, low-temperature rhombohedral and tetragonal
phases of Pb(Zr_{1-x}Ti_x)O_3 at x=0.5 and comparing these results to
superlattice calculations and experiment. We then use our new method to
determine the preferred structural phase at x=0.4. We find that the
low-temperature rhombohedral phase becomes the ground state at x=0.4, in
agreement with experimental findings.Comment: 5 pages, no figure
Micro- and nanoparticulates for DNA vaccine delivery
DNA vaccination has emerged as a promising alternative to traditional protein-based vaccines for the induction of protective immune responses. DNA vaccines offer several advantages over traditional vaccines, including increased stability, rapid and inexpensive production, and flexibility to produce vaccines for a wide variety of infectious diseases. However, the immunogenicity of DNA vaccines delivered as naked plasmid DNA is often weak due to degradation of the DNA by nucleases and inefficient delivery to immune cells. Therefore, biomaterial-based delivery systems based on micro- and nanoparticles that encapsulate plasmid DNA represent the most promising strategy for DNA vaccine delivery. Microparticulate delivery systems allow for passive targeting to antigen presenting cells through size exclusion and can allow for sustained presentation of DNA to cells through degradation and release of encapsulated vaccines. In contrast, nanoparticle encapsulation leads to increased internalization, overall greater transfection efficiency, and the ability to increase uptake across mucosal surfaces. Moreover, selection of the appropriate biomaterial can lead to increased immune stimulation and activation through triggering innate immune response receptors and target DNA to professional antigen presenting cells. Finally, the selection of materials with the appropriate properties to achieve efficient delivery through administration routes conducive to high patient compliance and capable of generating systemic and local (i.e. mucosal) immunity can lead to more effective humoral and cellular protective immune responses. In this review, we discuss the development of novel biomaterial- based delivery systems to enhance the delivery of DNA vaccines through various routes of administration and their implications for generating immune responses
Micro- and nanoparticulates for DNA vaccine delivery
DNA vaccination has emerged as a promising alternative to traditional protein-based vaccines for the induction of protective immune responses. DNA vaccines offer several advantages over traditional vaccines, including increased stability, rapid and inexpensive production, and flexibility to produce vaccines for a wide variety of infectious diseases. However, the immunogenicity of DNA vaccines delivered as naked plasmid DNA is often weak due to degradation of the DNA by nucleases and inefficient delivery to immune cells. Therefore, biomaterial-based delivery systems based on micro- and nanoparticles that encapsulate plasmid DNA represent the most promising strategy for DNA vaccine delivery. Microparticulate delivery systems allow for passive targeting to antigen presenting cells through size exclusion and can allow for sustained presentation of DNA to cells through degradation and release of encapsulated vaccines. In contrast, nanoparticle encapsulation leads to increased internalization, overall greater transfection efficiency, and the ability to increase uptake across mucosal surfaces. Moreover, selection of the appropriate biomaterial can lead to increased immune stimulation and activation through triggering innate immune response receptors and target DNA to professional antigen presenting cells. Finally, the selection of materials with the appropriate properties to achieve efficient delivery through administration routes conducive to high patient compliance and capable of generating systemic and local (i.e. mucosal) immunity can lead to more effective humoral and cellular protective immune responses. In this review, we discuss the development of novel biomaterial- based delivery systems to enhance the delivery of DNA vaccines through various routes of administration and their implications for generating immune responses
Spinning, breathing, and flapping: Periodicities in Saturnâs middle magnetosphere
In Saturnâs magnetosphere, ubiquitous fluctuations with a period of ~10.7âh have been observed in Saturn kilometric radiation (SKR), auroral emissions, the magnetic field, the electron density, and energetic particle fluxes. Here we characterize previously unstudied periodicities in plasma properties inside of 15âRS near the equatorial plane. Although periodically varying magnetic perturbations rotate relatively smoothly (spinning), plasma properties do not. The phase of the peak value of plasma density or pressure perturbations can change substantially across a few hours of local time or RS. As a means of interpreting observations, we use a magnetohydrodynamic simulation that generates fieldâaligned currents centered at 70° invariant latitude in Saturnâs southern ionosphere and rotating at the SKR period. The simulation reproduces many periodic features of the data including not only spinning perturbations but also globalâscale compression and expansion (breathing). Simulated plasma properties are also modulated by periodic largeâscale northâsouth motion (flapping) in regions beyond ~15 Saturn radii (RS), which we do not analyze here. Inside of 15âRS, plasma responds to a superposition of spinning and breathing at the spin period, developing perturbations that peak at different phases depending on what is measured and where. Strong compressional effects act impulsively over a limited range of rotation phase. Superposition of local and globalâscale variations produces phase jumps across short distances and can introduce multiple peaks in the variation of plasma properties within one rotation period, accounting for anomalies in the phase dependence of periodic fluctuations identified in the sparse data available.Key PointsEquatorial plasma and field moments in the core region are modulated at the SKR periodThe peak phase of observed plasma properties depends on the location of measurementPeriodic changes in the magnetosphere can be described as spinning, breathing, and flappingPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136320/1/jgra53132-sup-0001-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136320/2/jgra53132_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136320/3/jgra53132-sup-0003-Figure_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136320/4/jgra53132.pd
Amphiphilic Polyanhydride Nanoparticles Stabilize \u3ci\u3eBacillus anthracis\u3c/i\u3e Protective Antigen
Advancements towards an improved vaccine against Bacillus anthracis, the causative agent of anthrax, have focused on formulations composed of the protective antigen (PA) adsorbed to aluminum hydroxide. However, due to the labile nature of PA, antigen stability is a primary concern for vaccine development. Thus, there is a need for a delivery system capable of preserving the immunogenicity of PA through all the steps of vaccine fabrication, storage, and administration. In this work, we demonstrate that biodegradable amphiphilic polyanhydride nanoparticles, which have previously been shown to provide controlled antigen delivery, antigen stability, immune modulation, and protection in a single dose against a pathogenic challenge, can stabilize and release functional PA. These nanoparticles demonstrated polymer hydrophobicity-dependent preservation of the biological function of PA upon encapsulation, storage (over extended times and elevated temperatures), and release. Specifically, fabrication of amphiphilic polyanhydride nanoparticles composed of 1,6-bis(p-carboxyphenoxy)hexane and 1,8-bis(p-carboxyphenoxy)-3,6- dioxaoctane best preserved PA functionality. These studies demonstrate the versatility and superiority of amphiphilic nanoparticles as vaccine delivery vehicles suitable for long-term storage
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