Impact of aging on spreading depolarizations induced by focal brain ischemia in rats

Spreading depolarization (SD) contributes to the ischemic damage of the penumbra. Although age is the largest predictor of stroke, no studies have examined age dependence of SD appearance. We characterized the electrophysiological and hemodynamic changes in young (6 weeks old, n = 7), middle-aged (9 months old, n = 6), and old (2 years old, n = 7) male Wistar rats during 30 minutes of middle cerebral artery occlusion (MCAO), utilizing multimodal imaging through a closed cranial window over the ischemic cortex: membrane potential changes (with a voltage-sensitive dye), cerebral blood volume (green light reflectance), and cerebral blood flow (CBF, laser-speckle imaging) were observed. The initial CBF drop was similar in all groups, with a significant further reduction during ischemia in old rats (p < 0.01). Age reduced the total number of SDs (p < 0.05) but increased the size of ischemic area displaying prolonged SD (p < 0.01). The growth of area undergoing prolonged SDs positively correlated with the growth of ischemic core area (p < 0.01) during MCAO. Prolonged SDs and associated hypoperfusion likely compromise cortical tissue exposed to even a short focal ischemia in aged rats.     

Precise Modeling of Thermal and Strain Rate Effect on the Hardening Behavior of SiC/Al Composite

Temperature and strain rate have significant effects on the mechanical behavior of SiC/Al 2009 composites. This research aimed to precisely model the thermal and strain rate effect on the strain hardening behavior of SiC/Al composite using the artificial neural network (ANN). The mechanical behavior of SiC/Al 2009 composites in the temperature range of 298–623 K under the strain rate of 0.001–0.1 s⁻¹ was investigated by a uniaxial tension experiment. Four conventional models were adopted to characterize the plastic flow behavior in relation to temperature, strain rate, and strain. The ANN model was also applied to characterize the flow behavior of the composite at different strain rates and temperatures. Experimental results showed that the plastic deformation behavior of SiC/Al 2009 composite possesses a coupling effect of strain, strain rate, and temperature. Comparing the prediction error of these models, all four conventional models could not provide satisfactory modeling of flow curves at different strain rates and temperatures. Compared to the four conventional models, the suggested ANN structure dramatically improved the prediction accuracy of the flow curves at different strain rates and temperatures by reducing the prediction error to a maximum of 4.0%. Therefore, the ANN model is recommended for precise modeling of the thermal and strain rate effect on the flow curves of SiC/Al composites.     

一种无线闭环迷走神经刺激器及系统

为了治疗药物难治性癫痫,提出一种无线闭环迷走神经刺激器及系统,包括头戴式头皮脑电记录器、迷走神经刺激器、电磁耦合能量发射器和控制应用App,设计一种可以分离局部场电位和动作电位的生物信号前置放大器,一种刺激脉冲参数可调的迷走神经刺激器,一种电磁耦合能量发射器以及一个控制应用App。使用海岸线参数检测算法判定癫痫脑电信号的产生。测试结果表明,生物信号前置放大器对局部场电位和动作电位的放大增益分别为40和60 dB。迷走神经刺激器接收到来自控制应用App的刺激参数后,可以产生对应参数的双极性刺激脉冲。当发射器发射功率为30 dBm,发射线圈和接收线圈距离2 cm时,电磁耦合能量传输效率最大为15.4%。海岸线参数算法的正检率为88%。     

Broadband Perfect Absorber in the Visible Range Based on Metasurface Composite Structures

The broadband perfect absorption of visible light is of great significance for solar cells and photodetectors. The realization of a two-dimensional broadband perfect absorber in the visible range poses a formidable challenge with regard to improving the integration of optical systems. In this paper, we numerically demonstrate a broadband perfect absorber in the visible range from 400 nm to 700 nm based on metasurface composite structures. Simulation results show that the average absorptance is ~95.7% due to the combination of the intrinsic absorption of the lossy metallic material (Au) and the coupling resonances of the multi-sized resonators. The proposed perfect absorber may find potential applications in photovoltaics and photodetection.     

Mode Coupling at around M-Point in PZT

The question of the microscopic origin of the M-superstructure and additional satellite peaks in the Zr-rich lead zirconate-titanate is discussed for nearly 50 years. Clear contradiction between the selection rules of the critical scattering and the superstructure was found preventing unambiguous attributing of the observed superstructure either to the rotation of the oxygen octahedra or to the antiparallel displacements of the lead cations. Detailed analysis of the satellite pattern explained it as the result of the incommensurate phase transition rather than antiphase domains. Critical dynamics is the key point for the formulated problems. Recently, the oxygen tilt soft mode in the PbZr0.976Ti0.024O3 (PZT2.4) was found. But this does not resolve the extinction rules contradiction. The results of the inelastic X-ray scattering study of the phonon spectra of PZT2.4 around M-point are reported. Strong coupling between the lead and oxygen modes resulting in mode anticrossing and creation of the wide flat part in the lowest phonon dispersion curves is identified. This flat part corresponds to the mixture of the displacements of the lead and oxygen ions and can be an explanation of the extinction rules contradiction. Moreover, a flat dispersion surface is a typical prerequisite for the incommensurate phase transition.     

Direct measurement of the viscoelectric effect in water

The viscoelectric effect concerns the increase in viscosity of a polar liquid in an electric field due to its interaction with the dipolar molecules and was first determined for polar organic liquids more than 80 y ago. For the case of water, however, the most common polar liquid, direct measurement of the viscoelectric effect is challenging and has not to date been carried out, despite its importance in a wide range of electrokinetic and flow effects. In consequence, estimates of its magnitude for water vary by more than three orders of magnitude. Here, we measure the viscoelectric effect in water directly using a surface force balance by measuring the dynamic approach of two molecularly smooth surfaces with a controlled, uniform electric field between them across highly purified water. As the water is squeezed out of the gap between the approaching surfaces, viscous damping dominates the approach dynamics; this is modulated by the viscoelectric effect under the uniform transverse electric field across the water, enabling its magnitude to be directly determined as a function of the field. We measured a value for this magnitude, which differs by one and by two orders of magnitude, respectively, from its highest and lowest previously estimated values.

The viscoelectric effect concerns the change in the viscosity of polar liquids in the presence of an electric field (1–3). It arises from the interaction of the field with the dipolar molecules, and while its molecular origins are still not well understood (4–6), it has considerable relevance in areas ranging from surface potential measurements (7–9) and boundary lubrication (10) to nanofluidics and its applications (11–13). Knowing the magnitude of the viscoelectric effect is thus of clear importance. It was first measured by Andrade and Dodd (1–3) for a range of polar organic liquids, by monitoring their flow in a narrow channel between metal electrodes across which a known electric field E was applied, and quantified via a viscoelectric coefficient f using an empirical relation based on their results:η(E)= η0(1 + f∣E∣2),[1]a simplified analysis leading to such a relation is given in Ref. (8). Here, η₀ is the unperturbed bulk liquid viscosity (i.e., in the absence of any field). For the case of water, however, the most ubiquitous and important polar liquid, measurement of its viscosity in the presence of a strong, uniform field presents a strong challenge (as discussed later in this section), and to our knowledge no such direct measurements have been reported. Over the past six decades, therefore, the magnitude of the viscoelectric effect in water has been only indirectly estimated by extrapolation from its values for organic liquids (8), from estimates of its effect on electrokinetic phenomena (11, 14–19), or by other approaches (7, 12, 20, 21). These estimated values, as expressed in the viscoelectric coefficient f, vary over more than three orders of magnitude, ranging from f ∼10⁻¹⁷–2.5 × 10⁻¹⁴ (V/m)² (SI Appendix, Section 7). For completeness, we note that results contradictory to the viscoelectric model have also been reported (22) (i.e., suggesting a decreased water viscosity in an electric field). The reasons for the large span of these estimated f values were attributed to various factors such as solid/liquid coupling, varying ionic sizes, and varying water permittivity (12, 19); however, while these factors may play some role, there is no evidence that they could lead to such large discrepancies.We believe, rather, that the origin of the large variance in the estimated magnitude of the viscoelectric effect arises because none of the experimental studies on water to date in which the f values were estimated was direct, in the sense of probing how the water viscosity varied with field in a uniform electric field. In all cases, viscosity changes were assumed to occur only in the nonuniform, rapidly decaying electrostatic potential near charged surfaces immersed in water. Changes in electrophoretic mobility, electro-osmosis, or hydrodynamic dissipation or water mobility between similarly charged solid surfaces were then attributed to some mean viscosity increase in these thin surface-adjacent layers (7, 11, 12, 14–21). In practice, however, the effect on these electrokinetic phenomena of viscosity or water mobility changes in the thin layers where such nonuniform, rapidly decaying fields are present is not easy to quantify reliably, especially in the presence of salt ions (12). At the same time, measuring the viscosity of water in a uniform electric field between two surfaces at different potentials, as was done for the polar organic solvents (2, 3) and which would provide a direct determination of its viscoelectric effect, presents a considerable difficulty. This is due to two main factors and arises because, in contrast to organic solvents, water may self-dissociate. Firstly, the potential difference that may be applied between the surfaces across water is limited, if electrolysis is to be avoided (23, 24), and secondly, electrostatic screening implies that the field decays strongly (within a Debye screening length) away from the surfaces (25–27). Even in purified water with no added salt (as in the present study), the potential decays rapidly away from a charged surface (see, e.g., Fig. 1C), so that to measure viscosity in a uniform field between two surfaces, one would require flow channels of width of order some tens of nanometers or less, presenting a major challenge.Open in a separate windowFig. 1.Numerical solution to the nonlinearized PB equation with σ_mica = −8.1 mC/m², ψ_gold = 0.07 V, and ion concentration c_b = 8 × 10⁻⁵ M, corresponding to the conditions of Fig. 4A. (A) Surface potential on the mica surface and surface charge on the gold surface as a function of separation D. (B) Average electric field approximated as (|ψ_gold − ψ_mica|/D). (C) Local potential ψ as a function of distance d from the mica surface for different separations D. Dashed line in larger-scale inset is an eye guide of a linear approximation.In the present study, we overcome this by directly probing the viscosity of purified water across which a uniform electric field acts while it is confined between two surfaces in a surface force balance (SFB). In our experiments, a molecularly smooth gold surface at a controlled (positive) surface potential approaches an atomically smooth mica surface at constant surface (negative) charge density, so that a known electric field acts across the water-filled gap of width D between them; moreover, this field is very close to uniform at the most relevant surface separations (D ≲ 30 nm, Fig. 1C). The dynamics of approach is strongly modulated by the viscous damping due to squeeze-out of the water as D decreases, and hence by its viscosity in the uniform electric field; by monitoring the approach rate of the surfaces at high temporal (millisecond) and spatial (approximately angstrom) resolutions, we are able therefore to directly evaluate the magnitude of the viscoelectric effect (the value of f).     

From the Cover: A genetic switch for male UV iridescence in an incipient species pair of sulphur butterflies

Mating cues evolve rapidly and can contribute to species formation and maintenance. However, little is known about how sexual signals diverge and how this variation integrates with other barrier loci to shape the genomic landscape of reproductive isolation. Here, we elucidate the genetic basis of ultraviolet (UV) iridescence, a courtship signal that differentiates the males of Colias eurytheme butterflies from a sister species, allowing females to avoid costly heterospecific matings. Anthropogenic range expansion of the two incipient species established a large zone of secondary contact across the eastern United States with strong signatures of genomic admixtures spanning all autosomes. In contrast, Z chromosomes are highly differentiated between the two species, supporting a disproportionate role of sex chromosomes in speciation known as the large-X (or large-Z) effect. Within this chromosome-wide reproductive barrier, linkage mapping indicates that cis-regulatory variation of bric a brac (bab) underlies the male UV-iridescence polymorphism between the two species. Bab is expressed in all non-UV scales, and butterflies of either species or sex acquire widespread ectopic iridescence following its CRISPR knockout, demonstrating that Bab functions as a suppressor of UV-scale differentiation that potentiates mating cue divergence. These results highlight how a genetic switch can regulate a premating signal and integrate with other reproductive barriers during intermediate phases of speciation.

Premating signals such as pheromones, calls, and displays often differ between sexes and species and, by helping animals to tell one another apart, they are integral to the formation of reproductive barriers during speciation itself (1, 2). Mating factors can diverge early in the speciation process due to local adaptation or later due to sexual selection that prevents the generation of unfit hybrids (3). While a coupling of premating and postmating isolation mechanisms is thought to be required for the completion of speciation (4), how mating cue variation actually coincides with other barrier loci to split lineages remains elusive in the empirical literature (5–7).Previous work on the genetics of hybridization between the sulphur butterflies Colias eurytheme and Colias philodice highlights their potential for the study of intermediate phases of speciation with gene flow. Initially restricted to the western United States, the range of C. eurytheme expanded following both the spread of agricultural alfalfa and the reduction in forest cover in the past 200 y into regions once limited to C. philodice (8). As a result, the two species occur in secondary sympatry throughout an anthropogenic contact zone that includes the eastern United States and southern Canada. Both pre- and postzygotic reproductive barriers maintain species status in this system. However, heterospecific matings happen at increased frequency in dense populations (9, 10), partly because males can locate newly emerged females incapable of performing mate rejection behaviors [teneral mating (11)]. Hybrid female sterility forms an intrinsic postzygotic barrier that affects one of the two heterospecific crosses: oogenesis fails in female offspring that inherit a C. eurytheme W chromosome and a C. philodice Z chromosome (12, 13). This incompatibility is sex-linked and implies that to produce fully fertile progeny, C. eurytheme females must select males that are homozygous for a conspecific Z chromosome. An iridescent ultraviolet (UV) pattern acts as a visual mating cue in males and accurately displays their Z-chromosome status to females (9, 14) (Fig. 1A and SI Appendix, Fig. S1). UV occurs on the dorsal wing surfaces of C. eurytheme males only. The Mendelian U locus controls this interspecific variation and was previously mapped to the Z chromosome (15): C. eurytheme homozygous recessive males are UV-iridescent (u/u), advertising two compatible Z chromosomes to C. eurytheme females. Incompatible mates such as C. philodice males (U/U) and heterozygous hybrids (U/u) bear the dominant allele and lack UV. Finally, the female preference trait itself is also linked to the Z chromosome (14). This Z-linked inheritance of genetic incompatibility, mating signal, and mating preference supports an “indicator” model of speciation, which was previously theorized as a system where the mating cue can signal species identity and enable selection against hybrids (3, 16). In this study, we examine the genomic footprint of sex-linked reproductive barriers, and fine-map the allelic variation that switches on the male UV signal in C. eurytheme.Open in a separate windowFig. 1.Large-Z architecture of species differentiation includes the U-locus candidate gene bab. (A) UV iridescence differentiates males from two incipient species. (B and B′) PCA (B) and distance-based phylogenetic network (B′) of 22 male whole-genome SNPs from the admixed Maryland population. (C and D) F_ST values for C. philodice vs. C. eurytheme plotted against recombination rate (C), and Manhattan plot (D). Red indicates windows with above-median recombination rate and in the 95^th percentile of F_ST, including on the Z chromosome (asterisk). (E) Quantitative trait locus (QTL) analysis of the presence/absence of UV in 252 male offspring from F₂ and BCs. (F) Genotype plot for the whole Z chromosome with resequencing data from 23 individuals. Each row is an individual, and each column is a color-coded SNP. The red bracket indicates a 2.5-Mb interval with high F_ST and above-median recombination rate. (G) Annotation of the U-locus zero-recombinant interval (box) and surrounding region.