Topology optimization of manufacturable photonic crystals with complete bandgaps

Periodic structures consisting of dielectric material, i.e. photonic crystals, are capable of prohibiting the transmission of electromagnetic waves within frequency ranges referred to as bandgaps. This principle was first demonstrated with alternating slabs of material and later demonstrated with three-dimensional (3D) structures capable of reflecting waves from any incident angle. A number of potential applications for photonic bandgap structures exist, including waveguides, integrated circuits, fiber optics, and photonic cavities. Additionally, many other optical devices could benefit from the perfect-mirror behavior of photonic crystals. The design of photonic crystals for complete bandgap has challenged researchers for the past three decades. Bandgap structures are often quite complicated and therefore difficult to design heuristically. Thus, the application of automated design tools, such as topology or shape optimization, is very attractive. Unfortunately, bandgap analysis is very computationally intensive, and it is difficult to employ effective low-dimensional design parameterizations capable of generating bandgap structures. Until recently, computational power was insufficient to design 3D structures with complete bandgaps. The development of computing clusters has reduced this burden significantly, although computational cost remains a challenge. A major obstacle when numerically designing for bandgap, or any other design metric derived from eigenvalues, is the presence of degenerate eigenmodes. Optimal bandgap structures often possess many planes of symmetry; this is helpful to reduce the overall cost of the required dispersion analysis, but it often leads to wave frequencies that have multiple propagation directions, the physical result of degenerate eigenmodes. Herein lies the challenge; we would like to use gradient-based optimization algorithms to design bandgap structures, but the presence of degenerate eigenmodes renders our design metric non-smooth. Solving this conundrum by leveraging symmetric polynomials was a major contribution of this work. Further, an efficient sensitivity analysis and a successive mesh refinement strategy were developed to augment the design framework. Finally, it was observed that bandgap structures often exhibit poor stiffness properties, sometimes even making the structures unable to be physically realized. A series of physics-based, nonlinear constraints were developed to ensure the algorithmically-generated structures are manufacturable. These constraints were demonstrated by designing a series of photonic crystals that were fully self-supporting without the presence of enclosed void space. Additionally, the trade-off between bandgap and bulk stiffness was investigated. The proposed design framework is the first of its kind; a technique able to leverage traditional, gradient-based nonlinear programming solvers to generate 3D bandgap structures with manufacturing constraints

Measurement of residual stresses and solving the inverse problem to infer dislocation distributions

Residual stresses are present in the absence of external loads. All manufactured parts exhibit some degree of residual stress, which can drastically impact fatigue life. The simulation of these stresses has become exceedingly difficult as manufacturing processes have become more complex, and especially important as the desire to reduce over-designing to save on material costs has grown. As an alternative to computer simulations, a technique for measuring strains and then inferring an optimal dislocation distribution to generate the residual stress state is presented here. A continuum dislocation formulation is described in detail and optimization results are compared with a simpler discrete dislocation formulation. The ability of the optimization problem to match the full strain field is explored as regions of measurements and components of strain are withheld. The aim is to develop a technique to reduce the number of residual strain measurements necessary to fully characterize the residual stress in a manufactured part

Wake structure and kinematics in two insectivorous bats

We compare kinematics and wake structure over a range of flight speeds (4.0–8.2 m s(−1)) for two bats that pursue insect prey aerially, Tadarida brasiliensis and Myotis velifer. Body mass and wingspan are similar in these species, but M. velifer has broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body–wingtip distance and sweep angle. The distinct body vortex seen at low speed in T. brasiliensis and other bats studied to date is considerably weaker or absent in M. velifer. We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, in M. velifer, there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’

Development and Validation of a Simple Method for the Detection of Fascaplysin in Plasma

Fascaplysin is a cytotoxic natural product isolated from a variety of Indo-Pacific marine organisms, primarily Fascaplysinopsis sponges and Didemnum tunicates. Positive xenograft studies involving this alkaloid structural class have indicated that fascaplysin may serve as an important lead compound for preclinical development. This study was undertaken as a prelude to a full pharmacokinetics and therapeutic assessment of fascaplysin. We describe here a simple plasma preparation and a rapid HPLC method for the detection of fascaplysin in mice. The method was validated by parameters including good linear correlation, a limit of quantification of 107.1 μg/ mL, and a good precision with a coefficient of variation of 0.92% for 10 μg/mL. This method provides excellent sensitivity and visualization of fascaplysin as a single peak allowing for rapid analysis of plasma samples involving absorption, distribution, and metabolism studies. A preliminary pharmacokinetics study in C57Bl/6 mice using 20.6 mg/kg fascaplysin yielded a biphasic curve with T½α=16.7 min, T½β=11.7 h, and C0 of 17.1 μg/mL

Immune induction of human monocyte plasminogen activator. Characteristics of an assay for cell-mediated immunity

We characterized immunologic induction of monocyte plasminogen activator (PA) to determine whether assay for PA induction reliably detected cell-mediated immunity (CMI). Mononuclear leukocytes (MNL) were incubated in teflon-lined culture tubes for 1-4 days in the presence or absence of phytohemagglutinin-P (PHA), concanavalin A (Con A) or Candida antigen. PA activity of the monocytes in those suspensions was then measured using a micro fibrin plate assay.Monocytes in stimulated MNL had more PA activity than monocytes in unstimulated MNL. Maximal differences between stimulated and unstimulated cells were seen after 2 days of culture. Dose-response studies demonstrated that PA induction occurred at submitogenic concentrations of stimuli. Peak induction was seen using suboptimally mitogenic concentrations of PHA, Con A and Candida antigen. PA induction in response to Candida stimulation corresponded with skin test results. More than 90% of healthy adults tested had positive assays to all stimuli. LPS, in picogram concentrations, induced PA activity in the absence of lymphocytes, but such induction was prevented by polymyxin B.Supernates from activated MNL also induced PA in purified monocytes. This indirect assay of PA induction was less sensitive than direct assay of the MNL. A standard indirect assay for leukocyte inhibitory factor (LIF) was also less sensitive than the direct PA induction assay.The direct PA induction assay is sensitive and convenient and requires small volumes of blood. It may prove valuable in in vitro analysis of cell-mediated immunity in health and disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25668/1/0000220.pd

HPLC Plasma Assay of a Novel Anti-MRSA Compound, Kaempferol-3-O-Alpha-L-(2 \u27\u27,3 \u27\u27-di-p-coumaroyl)rhamnoside, from Sycamore Leaves

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious pathogen that is resistant to current antibiotic therapy. Thus, there is an urgent need for novel antimicrobial agents that can effectively combat these new strains of drug-resistant superbugs . Recently, fractionation of an extract from Platanus occidentalis (American sycamore) leaves produced an active kaempferol molecule, 3-O-alpha-L-(2 ,3 -di-p-coumaroyl)rhamnoside (KCR), in four isomeric forms; all four isomers exhibit potent anti-MRSA activity. In order to further the preclinical development of KCR as a new antibiotic class, we developed and validated a simple analytical method for assaying KCR plasma concentration. Because KCR will be developed as a new drug, although comprising four stereoisomers, the analytical method was devised to assay the total amount of all four isomers. In the present work, both a plasma processing procedure and an HPLC method have been developed and validated. Mouse plasma containing KCR was first treated with ethanol and then centrifuged. The supernatant was dried, suspended in ethanol, centrifuged, and the supernatant was injected into an HPLC system comprising a Waters C18, a mobile phase composing methanol, acetonitrile, and trifluoroacetic acid and monitored at 313 nm. The method was validated by parameters including a good linear correlation, a limit of quantification of 0.27 μg/mL, and high accuracy. In summary, this method allows a rapid analysis of KCR in the plasma samples for pharmacokinetics studies

The US National Comorbidity Survey: Overview and future directions

This report presents an overview of the results of the US National Comorbidity Survey (NCS) (Kessler et al., 1994) and future directions based on these results. The NCS is a survey that was mandated by the US Congress to study the comorbidity of substance use disorders and nonsubstance psychiatric disorders in the general population of the US. (...

Kinematic Plasticity during Flight in Fruit Bats: Individual Variability in Response to Loading

All bats experience daily and seasonal fluctuation in body mass. An increase in mass requires changes in flight kinematics to produce the extra lift necessary to compensate for increased weight. How bats modify their kinematics to increase lift, however, is not well understood. In this study, we investigated the effect of a 20% increase in mass on flight kinematics for Cynopterus brachyotis, the lesser dog-faced fruit bat. We reconstructed the 3D wing kinematics and how they changed with the additional mass. Bats showed a marked change in wing kinematics in response to loading, but changes varied among individuals. Each bat adjusted a different combination of kinematic parameters to increase lift, indicating that aerodynamic force generation can be modulated in multiple ways. Two main kinematic strategies were distinguished: bats either changed the motion of the wings by primarily increasing wingbeat frequency, or changed the configuration of the wings by increasing wing area and camber. The complex, individual-dependent response to increased loading in our bats points to an underappreciated aspect of locomotor control, in which the inherent complexity of the biomechanical system allows for kinematic plasticity. The kinematic plasticity and functional redundancy observed in bat flight can have evolutionary consequences, such as an increase potential for morphological and kinematic diversification due to weakened locomotor trade-offs