4D printed tunable mechanical metamaterials with shape memory operations

The aim of this paper is to introduce tunable continuous-stable metamaterials with reversible thermomechanical memory operations by four-dimensional (4D) printing technology. They are developed based on an understanding on glassy-rubbery behaviors of shape memory polymers and hot/cold programming derived from experiments and theory. Fused decomposition modeling as a well-known 3D printing technology is implemented to fabricate mechanical metamaterials. They are experimentally tested revealing elastic-plastic and hyper-elastic behaviors in low and high temperatures at a large deformation range. A computational design tool is developed by implementing a 3D phenomenological constitutive model coupled with a geometrically non-linear finite element method. Governing equations are then solved by an elastic-predictor plastic-corrector return map procedure along with the Newton-Raphson and Riks techniques to trace non-linear equilibrium path. A tunable reversible mechanical metamaterial unit with bistable memory operations is printed and tested experimentally and numerically. By a combination of cold and hot programming, the unit shows potential applications in mimicking electronic memory devices like tactile displays and designing surface adaptive structures. Another design of the unit shows potentials to serve in designing self-deployable bio-medical stents. Experiments are also conducted to demonstrate potential applications of cold programming for introducing recoverable rolling-up chiral metamaterials and load-resistance supportive auxetics

Use of Antipsychotic Medications and Cholinesterase Inhibitors and the Risk of Falls and Fractures: self-controlled case series

Objective: To evaluate the association between the use of antipsychotic medications and cholinesterase inhibitors, and the risk of falls and fractures in elderly patients with major neurocognitive disorders. / Design: Self-controlled case series / Setting: Taiwan’s National Health Insurance Database / Participants: 15,278 patients who were aged 65 or older, were newly prescribed antipsychotic medications and cholinesterase inhibitors, and suffered an incident fall or fracture between 2006 and 2017. Prescription records of cholinesterase inhibitors were used to confirm the diagnosis of major neurocognitive disorders since all use of cholinesterase inhibitors was subject to review by experts based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition and patients’ scores of Mini-Mental State Examination. We excluded those with schizophrenia and bipolar disorder before the first prescription of cholinesterase inhibitors to ensure that antipsychotic medications were used for neuropsychiatric symptoms of major neurocognitive disorders. / Main outcome measures: We used conditional Poisson regression to derive the incidence rate ratio and the 95% confidence interval for evaluating the association between the risk of falls and fractures and different exposure periods, including cholinesterase inhibitors alone, antipsychotic medications alone, and combination, as compared with the non-exposure period for the same individual. Moreover, we defined a 14-day pre-exposure period before study drug initiation over concerns about confounding by indication. / Results: Compared with the non-exposure period (incidence rate per 100 person-years; 95% confidence interval: 8.30; 8.14 to 8.46), the highest risk of falls and fractures occurred during the pre-exposure period (52.35; 48.46 to 56.47), followed by combination (10.55; 9.98 to 11.14), antipsychotic medications alone (10.34; 9.80 to 10.89), and cholinesterase inhibitors alone (9.41; 8.98 to 9.86). Conclusions: The incidence of falls and fractures was especially high in the pre-exposure period, suggesting that factors other than the study medications, such as underlying diseases, should be taken into consideration when evaluating the association between the risk of falls and fractures, and the use of cholinesterase inhibitors and antipsychotic medications. The exposure periods were also associated with a higher risk of falls and fractures, compared with the non-exposure period, although the magnitude was much lower than during the pre-exposure period. Prevention strategies and close monitoring of the risk of falls are still necessary until there is evidence that patients have regained a steady status

Triple shape memory polymers by 4D printing

This article aims at introducing triple shape memory polymers (SMPs) by four-dimensional (4D) printing technology and shaping adaptive structures for mechanical/bio-medical devices. The main approach is based on arranging hot–cold programming of SMPs with fused decomposition modeling technology to engineer adaptive structures with triple shape memory effect (SME). Experiments are conducted to characterize elasto-plastic and hyper-elastic thermo-mechanical material properties of SMPs in low and high temperatures at large deformation regime. The feasibility of the dual and triple SMPs with self-bending features is demonstrated experimentally. It is advantageous in situations either where it is desired to perform mechanical manipulations on the 4D printed objects for specific purposes or when they experience cold programming inevitably before activation. A phenomenological 3D constitutive model is developed for quantitative understanding of dual/triple SME of SMPs fabricated by 4D printing in the large deformation range. Governing equations of equilibrium are established for adaptive structures on the basis of the nonlinear Green–Lagrange strains. They are then solved by developing a finite element approach along with an elastic-predictor plastic-corrector return map procedure accomplished by the Newton–Raphson method. The computational tool is applied to simulate dual/triple SMP structures enabled by 4D printing and explore hot–cold programming mechanisms behind material tailoring. It is shown that the 4D printed dual/triple SMPs have great potential in mechanical/bio-medical applications such as self-bending gripers/stents and self-shrinking/tightening staples

Dynamics of one-dimensional tight-binding models with arbitrary time-dependent external homogeneous fields

The exact propagators of two one-dimensional systems with time-dependent external fields are presented by following the path-integral method. It is shown that the Bloch acceleration theorem can be generalized to the impulse-momentum theorem in quantum version. We demonstrate that an evolved Gaussian wave packet always keeps its shape in an arbitrary time-dependent homogeneous driven field. Moreover, that stopping and accelerating of a wave packet can be achieved by the pulsed field in a diabatic way.Comment: 8 pages, 6 figure

Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment

LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4×10-48 cm2 for a 40 GeV/c2 mass WIMP. Additionally, a 5σ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3×10-43 cm2 (7.1×10-42 cm2) for a 40 GeV/c2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020

Simulations of events for the LUX-ZEPLIN (LZ) dark matter experiment

The LUX-ZEPLIN dark matter search aims to achieve a sensitivity to the WIMP-nucleon spin-independent cross-section down to (1–2)×10−12 pb at a WIMP mass of 40 GeV/c2. This paper describes the simulations framework that, along with radioactivity measurements, was used to support this projection, and also to provide mock data for validating reconstruction and analysis software. Of particular note are the event generators, which allow us to model the background radiation, and the detector response physics used in the production of raw signals, which can be converted into digitized waveforms similar to data from the operational detector. Inclusion of the detector response allows us to process simulated data using the same analysis routines as developed to process the experimental data

Projected sensitivity of the LUX-ZEPLIN experiment to the 0νββ decay of Xe 136

The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double β decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to Xe136 neutrinoless double β decay, taking advantage of the significant (>600 kg) Xe136 mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of Xe136 is projected to be 1.06×1026 years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with Xe136 at 1.06×1027 years

The five dimensions of B cell tolerance

B cell tolerance has been generally understood to be an acquired property of the immune system that governs antibody specificity in ways that avoid auto‐toxicity. As useful as this understanding has proved, it fails to fully explain the existence of auto‐reactive specificities in healthy individuals and contribution these may have to health. Mechanisms underlying B cell tolerance are considered to select a clonal repertoire that generates a collection of antibodies that do not bind self, ie tolerance operates more or less in three dimensions that largely spare autologous cells and antigens. Yet, most B lymphocytes in humans and probably in other vertebrates are auto‐reactive and absence of these auto‐reactive B cells is associated with disease. We suggest that auto‐reactivity can be embodied by extending the concept of tolerance by two further dimensions, one of time and circumstance and one that allows healthy cells to actively resist injury. In this novel concept, macromolecular recognition by the B cell receptor leading to deletion, anergy, receptor editing or B cell activation is extended by taking account of the time of development of normal immune responses (4th dimension) and the accommodation (or tolerance) of normal cells to bound antibody, activation of complement, and interaction with inflammatory cells (fifth dimension). We discuss how these dimensions contribute to understanding B cell biology in health or disease.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153034/1/imr12813.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153034/2/imr12813_am.pd