We investigate the unique mechanical properties of reentrant 3D origami structures based on the Tachi-Miura polyhedron (TMP). We explore the potential usage as mechanical metamaterials that exhibit ...tunable negative Poisson's ratio and structural bistability simultaneously. We show analytically and experimentally that the Poisson's ratio changes from positive to negative and vice versa during its folding motion. In addition, we verify the bistable mechanism of the reentrant 3D TMP under rigid origami configurations without relying on the buckling motions of planar origami surfaces. This study forms a foundation in designing and constructing TMP-based metamaterials in the form of bellowslike structures for engineering applications.
The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, ...were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400°C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism.
A novel design of an elastic metamaterial with anisotropic mass density is proposed to manipulate flexural waves at a subwavelength scale. The three-dimensional metamaterial is inspired by kirigami, ...which can be easily manufactured by cutting and folding a thin metallic plate. By attaching the resonant kirigami structures periodically on the top of a host plate, a metamaterial plate can be constructed without any perforation that degrades the strength of the pristine plate. An analytical model is developed to understand the working mechanism of the proposed elastic metamaterial and the dispersion curves are calculated by using an extended plane wave expansion method. As a result, we verify an anisotropic effective mass density stemming from the coupling between the local resonance of the kirigami cells and the global flexural wave propagations in the host plate. Finally, numerical simulations on the directional flexural wave propagation in a two-dimensional array of kirigami metamaterial as well as super-resolution imaging through an elastic hyperlens are conducted to demonstrate the subwavelength-scale flexural wave control abilities. The proposed kirigami-based metamaterial has the advantages of no-perforation design and subwavelength flexural wave manipulation capability, which can be highly useful for engineering applications including non-destructive evaluations and structural health monitoring.
The growth mechanisms of primary Cu6Sn5 are studied in Sn-Cu alloys and solder joints by combining EBSD, FIB-tomography and synchrotron radiography. With increasing cooling rate and Cu content, ...Cu6Sn5 crystals developed from faceted hexagonal rods to grooved rods, in-plane branched faceted crystals and, finally, to nonfaceted dendrites. This range of growth morphologies has been rationalised into a kinetic microstructure map. Cu6Sn5 hexagonal rods grew along 0001 bounded by {101¯0} facets and Cu6Sn5 dendrites branched along in the {101¯0} planes. The faceted to nonfaceted transition indicates a kinetic interface roughening transition and a gradual change in mechanism from lateral growth governed by anisotropic attachment kinetics to continuous growth governed by diffusion and curvature. Finally, it is shown that the full range of Cu6Sn5 morphologies that grew for different composition and cooling rate combinations in bulk alloys can be engineered to grow in solder joints made with a single composition (Sn-0.7 wt%Cu/Cu) by altering the peak temperature and the cooling rate.
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Eutectic Ag
3
Sn can grow with a variety of morphologies depending on the solidification conditions and plays an important role in the performance of Pb-free solders. Here, we study morphology ...transitions in the
β
-Sn + Ag
3
Sn eutectic at increasing growth velocity using a combination of real-time X-ray imaging and analytical electron microscopy. Orthorhombic Ag
3
Sn grew as faceted plates or rods with 010 growth direction and (001) as the largest facet in all three eutectic growth morphologies: Irregular plate, broken-lamellar, and rod. Reproducible
β
-Sn + Ag
3
Sn orientation relationships formed for the latter two morphologies. The mechanisms of spacing adjustment and the reversible transition from plate to rod growth are studied for transient solidification after velocity changes. The transition from fully eutectic growth to
β
-Sn dendrites plus eutectic is reasonably reproduced using a competitive growth criterion. At the highest velocities, Ag
3
Sn rods developed perturbations whose break down into particles is discussed in terms of unsteady growth and pinch-off mechanisms.
Large Ag3Sn plates in solder joints can affect the reliability of electronics, however, the factors affecting their nucleation and morphology are not well understood. Here, the faceted solidification ...of Ag3Sn was studied as a function of melt undercooling, revealing transitions from single crystal {001} plates to cyclic twinned plates and then to highly branched structures created by twin mediated branching. Real-time X-ray imaging proved that Ag3Sn cyclic twins come from a common point, indicating they initiate in the process of nucleation or in the very early stages of growth in the undercooled melt. Soldering to copper substrates significantly catalysed Ag3Sn nucleation. This is shown to be due to constitutional supercooling generated by Ag solute rejection into the liquid ahead of the Cu6Sn5 reaction layer, with additional contributions from geometrical catalysis in the grooves between Cu6Sn5 scallops and heterogeneous nucleation of Ag3Sn on Cu6Sn5. The relative ease of Ag3Sn nucleation on the Cu6Sn5 reaction layer is responsible for the large plates often reported in electronic solder joints.
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Summary
This study revealed the change in the paravertebral muscles in patients with osteoporotic vertebral fracture. Increased pain is likely to be the driver for reduced activity, reduced ...activities of daily living, and consequent increase in fat infiltration of the paravertebral muscles, assumed to be secondary to reduced activity level or, conversely, partial immobilization.
Introduction
To reveal the time courses and impact of the paravertebral muscles (PVMs) on the healing process of osteoporotic vertebral fractures and risk factors for PVM decrease.
Methods
Consecutive patients with symptomatic osteoporotic vertebral fractures were enrolled in 11 hospitals. At enrollment and 3- and 6-month follow-up, PVMs, including the multifidus and erector spinae, were examined using magnetic resonance imaging (MRI). The PVM cross-sectional area (CSA) and fat signal fraction (FSF) were measured at L3. Low back pain (LBP), activities of daily living (ADLs), and risk factors for PVM decrease at the 6-month follow-up were investigated. PVM decrease was defined as > 1 standard deviation decrease of the CSA or > 1 standard deviation increase of the FSF.
Results
Among 153 patients who completed the 6-month follow-up, 117 (92 women, 79%) had MRI of L3 at enrollment and 3- and 6-month follow-up (mean age at enrollment, 78.5 years). The CSA did not change 6 months from onset (
p
for trend = 0.634), whereas the FSF significantly increased (
p
for trend = 0.033). PVM decrease was observed in 30 patients (26%). LBP was more severe, and delayed union was more frequent in patients with PVM decrease (
p
= 0.021 mixed-effect model and
p
= 0.029 chi-square test, respectively). The risk factors for PVM decrease were ADL decline at the 3-month follow-up (adjusted odds ratio = 5.35,
p
= 0.026).
Conclusion
PVM decrease was significantly related to LBP and delayed union after osteoporotic vertebral fracture onset. ADL decline at the 3-month follow-up was a risk factor for PVM decrease. Therefore, restoring ADLs within 3 months after onset is important.
The most effective skin antiseptic solution to reduce the incidence of catheter-related bloodstream infections (CRBSI) remains unknown.
To compare solutions with different chlorhexidine (CHG)-based ...concentrations and povidone-iodine (PVI) in adults with a central venous catheter (CVC) or arterial catheter, and identify an association with the incidence of CRBSI.
This study evaluated randomized controlled trials comparing CHG and PVI antiseptic agents in patients aged ≥18 years with an underlying illness and a CVC or arterial catheter. The primary outcome was CRBSI rate. Network meta-analysis was performed by a frequentist-based approach with multi-variate random effects meta-analysis, and the effect size was expressed as relative risk (RR) with 95% confidence interval (CI).
The search yielded 1511 records, of which five studies (2815 catheters) were included in the network meta-analysis. The risk of CRBSI was significantly lower with 1% CHG-alcohol than with 0.5% CHG-alcohol (RR 0.40, 95% CI 0.16–0.98; high certainty) or 10% PVI-aqueous (RR 0.31, 95% CI 0.15–0.63; high certainty). There was no significant difference in the risk of CRBSI between 1% CHG-alcohol and 2% CHG-aqueous (RR 0.35, 95% CI 0.12–1.04; moderate certainty) or other antiseptic solutions. The hierarchy of efficacy in reducing CRBSI was 1% CHG-alcohol, 0.5% CHG-alcohol, 2% CHG-aqueous and 10% PVI-aqueous.
Antiseptic agents containing 1% CHG-alcohol were more strongly associated with reduced risk for CRBSI compared with agents containing 0.5% CHG-alcohol or 10% PVI-aqueous.
Urinary exosomes containing apical membrane and intracellular fluid are normally secreted into the urine from all nephron segments, and may carry protein markers of renal dysfunction and structural ...injury. We studied methods for collection, storage, and preservation of urinary exosomal proteins. We collected urine from healthy volunteers, added protease inhibitors, and stored urine samples at 4, -20, and -80°C for 1 week or 7 months. Samples were thawed with and without extensive vortexing, and three fractions were isolated: urinary sediment, supernatant, and exosome fraction. Protein concentration, electrophoresis patterns, and abundance of seven exosome-associated proteins were measured. Exosome-associated proteins were not detected in sediment or supernatant fractions. Protease inhibitors prevented degradation of exosome-associated proteins. Freezing at -20°C caused a major loss in exosomes compared to fresh urine. In contrast, recovery after freezing at -80°C was almost complete. Extensive vortexing after thawing markedly increased exosome recovery in urine frozen at -20 or -80°C, even if frozen for 7 months. The recovery from first and second morning urine was similar. The abundance of cytosolic exosome-associated proteins did not decrease during long-term storage. We concluded: (1) protease inhibitors are essential for preservation; (2) storage at -80°C with extensive vortexing after thawing maximizes the recovery of urinary exosomes; (3) the difference between first and second morning urine exosome-associated protein was small, suggesting minimal protein degradation in the urinary tract/bladder; (4) urinary exosomes remain intact during long-term storage. These urine collection, storage, and processing conditions may be useful for future biomarker discovery efforts.
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