Designing perturbative metamaterials from discrete models

Identifying material geometries that lead to metamaterials with desired functionalities presents a challenge for the field. Discrete, or reduced-order, models provide a concise description of complex phenomena, such as negative refraction, or topological surface states; therefore, the combination of geometric building blocks to replicate discrete models presenting the desired features represents a promising approach. However, there is no reliable way to solve such an inverse problem. Here, we introduce ‘perturbative metamaterials’, a class of metamaterials consisting of weakly interacting unit cells. The weak interaction allows us to associate each element of the discrete model with individual geometric features of the metamaterial, thereby enabling a systematic design process. We demonstrate our approach by designing two-dimensional elastic metamaterials that realize Veselago lenses, zero-dispersion bands and topological surface phonons. While our selected examples are within the mechanical domain, the same design principle can be applied to acoustic, thermal and photonic metamaterials composed of weakly interacting unit cells

Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects

Insect steroid hormones (ecdysteroids) are important for female reproduction in many insect species and are required for the initiation and coordination of vital developmental processes. Ecdysteroids are also important for adult male physiology and behavior, but their exact function and site of synthesis remains unclear, although previous studies suggest that the reproductive system may be their source. We have examined expression profiles of the ecdysteroidogenic Halloween genes, during development and in adults of the flour beetle Tribolium castaneum. Genes required for the biosynthesis of ecdysone (E), the precursor of the molting hormone 20-hydroxyecdysone (20E), are expressed in the tubular accessory glands (TAGs) of adult males. In contrast, expression of the gene encoding the enzyme mediating 20E synthesis was detected in the ovaries of females. Further, Spookiest (Spot), an enzyme presumably required for endowing tissues with competence to produce ecdysteroids, is male specific and predominantly expressed in the TAGs. We also show that prothoracicotropic hormone (PTTH), a regulator of E synthesis during larval development, regulates ecdysteroid levels in the adult stage in Drosophila melanogaster and the gene for its receptor Torso seems to be expressed specifically in the accessory glands of males. The composite results suggest strongly that the accessory glands of adult male insects are the main source of E, but not 20E. The finding of a possible male-specific source of E raises the possibility that E and 20E have sex-specific roles analogous to the vertebrate sex steroids, where males produce primarily testosterone, the precursor of estradiol. Furthermore this study provides the first evidence that PTTH regulates ecdysteroid synthesis in the adult stage and could explain the original finding that some adult insects are a rich source of PTTH

Effects of discontinuing oral bisphosphonate treatments for postmenopausal osteoporosis on bone turnover markers and bone density

The antiresorptive potency varies between different bisphosphonates. We investigated the effect of stopping oral bisphosphonate treatment for postmenopausal osteoporosis (ibandronate, alendronate, risedronate) on BTMs and BMD. After stopping treatment, all three groups showed an increase in BTMs and a decrease in hip BMD; however, none returned to pre-treatment baseline values. INTRODUCTION: Bisphosphonates (BPs) continue to suppress bone turnover markers (BTMs) after treatment has stopped, leading to the suggestion that a pause in treatment could be considered for low-risk patients. Indirect comparisons suggest that after cessation of treatment, the effects on bone may differ between drugs. We investigated the effects of stopping oral BP treatments for postmenopausal osteoporosis on BTMs and bone mineral density (BMD). METHODS: We studied postmenopausal osteoporotic women who had previously taken part in a 2-year randomised study of three oral BPs (ibandronate, alendronate, or risedronate). At the end of the study, women with hip BMD T-score > - 2.5 and considered clinically appropriate to discontinue treatment were invited to participate in a further 2-year observational study. Biochemical response was assessed using BTMs, and BMD was measured by dual-energy X-ray absorptiometry. RESULTS: All BTMs increased after treatment withdrawal but remained below the pre-treatment baseline with less suppression of BTMs for the risedronate group compared to alendronate and ibandronate up to 48 weeks. There was no difference between the BP groups 96 weeks after stopping treatment. The change in BMD during the 96 weeks after stopping treatment was - 1.6% (95% CI - 1.9 to - 1.2, P < 0.001) for the total hip and - 0.6% (95% CI - 1.1 to - 0.2, P = 0.17) at the lumbar spine with no difference between the three BP groups (P = 0.85 and P = 0.48, respectively). CONCLUSION: For all treatment groups, there was an increase in BTMs and a decrease in hip BMD after stopping BPs for 2 years; however, none returned to pre-treatment baseline values