Schlieren Imaging of a Supersonic Wind Tunnel

This project exemplifies Schlieren Imaging on a Supersonic Wind Tunnel. Schlieren Imaging allows one to visualize fluid flow by refracting light through a fluid. The Schlieren Imaging system denoted in this paper is used to visualize the shock waves of air onto a test section within a supersonic wind tunnel. This is done by directing a beam of light through a test section and then focusing the light onto a blade edge. This blade edge then breaks up the light beam so that the refractions, created by the pressure differences, are blocked by the knife edge which allows the pressure differences in the fluid to be visualized. The image provided by this system may be used for an instructional lab or for general experimentation. The main design components in this design project include the fixturing techniques for a set of parabolic mirrors and the correct placement of components to achieve a Schlieren Image

Global axisymmetric Magnetorotational Instability with density gradients

We examine global incompressible axisymmetric perturbations of a differentially rotating MHD plasma with radial density gradients. It is shown that the standard magnetorotational instability, (MRI) criterion drawn from the local dispersion relation is often misleading. If the equilibrium magnetic field is either purely axial or purely toroidal, the problem reduces to finding the global radial eigenvalues of an effective potential. The standard Keplerian profile including the origin is mathematically ill-posed, and thus any solution will depend strongly on the inner boundary. We find a class of unstable modes localized by the form of the rotation and density profiles, with reduced dependence on boundary conditions.Comment: 22 pages, 5 figure

Dissipative Taylor-Couette flows under the influence of helical magnetic fields

The linear stability of MHD Taylor-Couette flows in axially unbounded cylinders is considered, for magnetic Prandtl number unity. Magnetic fields varying from purely axial to purely azimuthal are imposed, with a general helical field parameterized by \beta=B_\phi/B_z. We map out the transition from the standard MRI for \beta=0 to the nonaxisymmetric Azimuthal MagnetoRotational Instability (AMRI) for \beta\to \infty. For finite \beta, positive and negative wave numbers m, corresponding to right and left spirals, are no longer identical. The transition from \beta=0 to \beta\to\infty includes all the possible forms of MRI with axisymmetric and nonaxisymmetric modes. For the nonaxisymmetric modes, the most unstable mode spirals in the opposite direction to the background field. The standard (\beta=0) MRI is axisymmetric for weak fields (including the instability with the lowest Reynolds number) but is nonaxisymmetric for stronger fields. If the azimuthal field is due in part to an axial current flowing through the fluid itself (and not just along the central axis), then it is also unstable to the nonaxisymmetric Tayler instability, which is most effective without rotation. For large \beta this instability has wavenumber m=1, whereas for \beta\simeq 1 m=2 is most unstable. The most unstable mode spirals in the same direction as the background field.Comment: 9 pages, 11 figure

The Origin of Solar Activity in the Tachocline

Solar active regions, produced by the emergence of tubes of strong magnetic field in the photosphere, are restricted to within 35 degrees of the solar equator. The nature of the dynamo processes that create and renew these fields, and are therefore responsible for solar magnetic phenomena, are not well understood. We analyze the magneto-rotational stability of the solar tachocline for general field geometry. This thin region of strong radial and latitudinal differential rotation, between the radiative and convective zones, is unstable at latitudes above 37 degrees, yet is stable closer to the equator. We propose that small-scale magneto-rotational turbulence prevents coherent magnetic dynamo action in the tachocline except in the vicinity of the equator, thus explaining the latitudinal restriction of active regions. Tying the magnetic dynamo to the tachocline elucidates the physical conditions and processes relevant to solar magnetism.Comment: 10 pages, 1 figure, accepted for publication in ApJ

Stimulus Response in Liquid Crystalline Elastomers: Fundamental Characterization To Functional Design

Liquid crystalline elastomers (LCEs) are functional materials capable of undergoing large deformations. The distinctive deformation of these materials is founded upon the ordered packing of mesogenic moieties and subsequent order disruption by stimuli such as heat or light. Numerous approaches have been explored to locally dictate (program) the stimuli-response of LCEs to realize 3-D shape transformation. Motivated by potential for use in applications ranging from soft robotics to biology, this thesis details fundamental structure-property relationships relating to material composition, processing, and programming.&nbsp; The stimuli-response of LCEs was found to be strongly correlated to fundamental properties spanning the molecular to macromolecular level. First, LCEs were prepared with a liquid crystalline monomer exhibiting reduced intermolecular interactions. These LCEs had faster, higher magnitude photomechanical response as a function of reducing energy required for order disruption. Further, preparation of LCEs via radical-mediated thiol-acrylate photopolymerization was studied, elucidating network structures that retain unreacted pendant thiols. Next, thermomechanical actuation properties were characterized for LCEs prepared using two-step polymerizations. Differences were attributed to discrepancies during aza- or thiol-Michael oligomerization before photopolymerization of acrylate-capped oligomers. Additionally, theoretical predictions based on the state of order during crosslinking inspired study of stimuliresponse of LCEs prepared with common alignment methods. Results demonstrated the contribution of alignment method on the thermomechanical response of LCE.&nbsp; These fundamental studies inspired functionally-motivated examinations. In one instance, LCEs prepared with variation in modulus were laminated to create mechanical elements with a through-thickness modulus gradient and a +1 topological defect director pattern. The LCE element leapt from the surface when heated. In another demonstration, crosslink density was patterned spatially across an LCE with a uniform director. This LCE exhibited thermomechanical deformations with Gaussian curvature.&nbsp; LCEs were also prepared with dynamic covalent bonds to realize shape permanence and reprogrammability. One composition incorporated a thermally stable photochrome and thermally active dynamic bonds to allow photoinduced deformation and shape retention via thermal bond rearrangement. Further, photo-active dynamic bonds were incorporated in LCEs via a thiolMichael reaction amenable to surface enforced alignment. This LCE exhibited complex deformations upon heating by combining the directed self-assembly and material reprogrammability via dynamic bond exchange.</p

Relativistic stars with purely toroidal magnetic fields

We investigate the effects of the purely toroidal magnetic field on the equilibrium structures of the relativistic stars. The master equations for obtaining equilibrium solutions of relativistic rotating stars containing purely toroidal magnetic fields are derived for the first time. To solve these master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for calculating relativistic rotating stars containing no magnetic field to incorporate the effects of the purely toroidal magnetic fields. By using the numerical scheme, we then calculate a large number of the equilibrium configurations for a particular distribution of the magnetic field in order to explore the equilibrium properties. We also construct the equilibrium sequences of the constant baryon mass and/or the constant magnetic flux, which model the evolution of an isolated neutron star as it loses angular momentum via the gravitational waves. Important properties of the equilibrium configurations of the magnetized stars obtained in this study are summarized as follows ; (1) For the non-rotating stars, the matter distribution of the stars is prolately distorted due to the toroidal magnetic fields. (2) For the rapidly rotating stars, the shape of the stellar surface becomes oblate because of the centrifugal force. But, the matter distribution deep inside the star is sufficiently prolate for the mean matter distribution of the star to be prolate. (3) The stronger toroidal magnetic fields lead to the mass-shedding of the stars at the lower angular velocity. (4) For some equilibrium sequences of the constant baryon mass and magnetic flux, the stars can spin up as they lose angular momentum.Comment: 13 figures, 7 tables, submitted to PR

Investigation of the field-induced ferromagnetic phase transition in spin polarized neutron matter: a lowest order constrained variational approach

In this paper, the lowest order constrained variational (LOCV) method has been used to investigate the magnetic properties of spin polarized neutron matter in the presence of strong magnetic field at zero temperature employing $AV_{18}$ potential. Our results indicate that a ferromagnetic phase transition is induced by a strong magnetic field with strength greater than $10^{18}\ G$, leading to a partial spin polarization of the neutron matter. It is also shown that the equation of state of neutron matter in the presence of magnetic field is stiffer than the case in absence of magnetic field.Comment: 23 pages, 9 figures Phys. Rev. C (2011) in pres

Sexual violence in post-conflict Liberia: survivors and their care.

Using routine data from three clinics offering care to survivors of sexual violence (SV) in Monrovia, Liberia, we describe the characteristics of SV survivors and the pattern of SV and discuss how the current approach could be better adapted to meet survivors' needs. There were 1500 survivors seeking SV care between January 2008 and December 2009. Most survivors were women (98%) and median age was 13 years (Interquartile range: 9-17 years). Sexual aggression occurred during day-to-day activities in 822 (55%) cases and in the survivor's home in 552 (37%) cases. The perpetrator was a known civilian in 1037 (69%) SV events. Only 619 (41%) survivors sought care within 72 h. The current approach could be improved by: effectively addressing the psychosocial needs of child survivors, reaching male survivors, targeting the perpetrators in awareness and advocacy campaigns and reducing delays in seeking care

Design and introduction of a quality of life assessment and practice support system: perspectives from palliative care settings

Background: Quality of life (QOL) assessment instruments, including patient-reported outcome measures (PROMs) and patient-reported experience measures (PREMs), are increasingly promoted as a means of enabling clinicians to enhance person-centered care. However, integration of these instruments into palliative care clinical practice has been inconsistent. This study focused on the design of an electronic Quality of Life and Practice Support System (QPSS) prototype and its initial use in palliative inpatient and home care settings. Our objectives were to ascertain desired features of a QPSS prototype and the experiences of clinicians, patients, and family caregivers in regard to the initial introduction of a QPSS in palliative care, interpreting them in context. Methods: We applied an integrated knowledge translation approach in two stages by engaging a total of 71 clinicians, 18 patients, and 17 family caregivers in palliative inpatient and home care settings. Data for Stage I were collected via 12 focus groups with clinicians to ascertain desirable features of a QPSS. Stage II involved 5 focus groups and 24 interviews with clinicians and 35 interviews with patients or family caregivers during initial implementation of a QPSS. The focus groups and interviews were recorded, transcribed, and analyzed using the qualitative methodology of interpretive description. Results: Desirable features focused on hardware (lightweight, durable, and easy to disinfect), software (simple, user-friendly interface, multi-linguistic, integration with e-health systems), and choice of assessment instruments that would facilitate a holistic assessment. Although patient and family caregiver participants were predominantly enthusiastic, clinicians expressed a mixture of enthusiasm, receptivity, and concern regarding the use of a QPSS. The analyses revealed important contextual considerations, including: (a) logistical, technical, and aesthetic considerations regarding the QPSS as a technology, (b) diversity in knowledge, skills, and attitudes of clinicians, patients, and family caregivers regarding the integration of electronic QOL assessments in care, and (c) the need to understand organizational context and priorities in using QOL assessment data. Conclusion: The process of designing and integrating a QPSS in palliative care for patients with life-limiting conditions and their family caregivers is complex and requires extensive consultation with clinicians, administrators, patients, and family caregivers to inform successful implementation

Lifting, Loading, and Buckling in Conical Shells

Liquid crystal elastomer films that morph into cones are strikingly capable lifters. Thus motivated, we combine theory, numerics, and experiments to reexamine the load-bearing capacity of conical shells. We show that a cone squashed between frictionless surfaces buckles at a smaller load, even in scaling, than the classical Seide/Koiter result. Such buckling begins in a region of greatly amplified azimuthal compression generated in an outer boundary layer with oscillatory bend. Experimentally and numerically, buckling then grows sub-critically over the full cone. We derive a new thin-limit formula for the critical load, $\propto t^{5/2}$, and validate it numerically. We also investigate deep post-buckling, finding further instabilities producing intricate states with multiple Pogorelov-type curved ridges arranged in concentric-circles or Archimedean spirals. Finally, we investigate the forces exerted by such states, which limit lifting performance in active cones.Comment: 7 pages, 4 figures. This version published in PRL, open acces