Static magnetic fields affect capillary flow of red blood cells in striated skin muscle

Blood flowing in microvessels is one possible site of action of static magnetic fields (SMFs). We evaluated SMF effects on capillary flow of red blood cells (RBCs) in unanesthetized hamsters, using a skinfold chamber technique for intravital fluorescence microscopy. By this approach, capillary RBC velocities (v(RBC)), capillary diameters (D), arteriolar diameters (D(art)), and functional vessel densities (FVD) were measured in striated skin muscle at different magnetic flux densities. Exposure above a threshold level of about 500 mT resulted in a significant (P < 0.001) reduction of v(RBC) in capillaries as compared to the baseline value. At the maximum field strength of 587 mT, v(RBC) was reduced by more than 40%. Flow reduction was reversible when the field strength was decreased below the threshold level. In contrast, mean values determined at different exposure levels for the parameters D, D(art), and FVD did not vary by more than 5%. Blood flow through capillary networks is affected by strong SMFs directed perpendicular to the vessels. Since the influence of SMFs on blood flow in microvessels directed parallel to the field as well as on collateral blood supply could not be studied, our findings should be carefully interpreted with respect to the setting of safety guidelines.     

Magnetic nanopantograph in the SrCu2(BO3)2 Shastry–Sutherland lattice

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu₂(BO₃)₂ (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu^ superexchange angle that, due to the orthogonal Cu²⁺ dimers acting as pantographs, can shrink significantly (0.44%) with minute (0.01%) variations in the lattice parameters. With this original approach we also find a reduction of ∼10% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.It has long been understood that magnetoelastic coupling can move magnetic materials phase boundaries in temperature and field and even change the order and/or universality class of magnetic transitions (1). Model Hamiltonians with effective exchange interactions are the common theoretical tool to tackle the complex behaviors of quantum magnet systems (2) and, indeed, these effective exchange interactions depend on subtleties of the electronic structure that, in turn, are naturally linked to the structural degrees of freedom of the system. When magnetoelastic effects are present, structural changes can also modify the macroscopic magnetic state via changes in the effective parameters of the model Hamiltonian. Simply posed, it is challenging to interpret experimental results at a point of high interest in a predicted (H,T) phase diagram of a magnetic material under consideration for fundamental studies or applications without knowing the effects that unavoidable lattice changes have in the exchange interactions as we drive our system toward such a point. Hence, it is highly desirable to be able to quantify such lattice effects.SrCu₂(BO₃)₂ (SCBO) is an especially fascinating example of a low-dimension, frustrated quantum antiferromagnetic system. It crystallizes in a tetragonal structure (3) in which layers of [CuBO₃]⁻ (Fig. 1A) are stacked along the c axis and separated by planes of Sr²⁺ ions (Fig. 1B). The magnetically active Cu²⁺ ions form a 2D arrangement of mutually orthogonal dimers (Fig. 1A). The magnetic properties of this compound can be closely described through a 2D Heisenberg Hamiltonian (4):H=J∑nnSi⋅Sj+J′∑nnnSi⋅Sj,[1]where J and J′ are respectively the nearest-neighbor (intradimer) and next-nearest-neighbor (interdimer) exchange integrals in the [CuBO₃]⁻ planes. Although J and J′ are both positive, leading to frustrated antiferromagnetic (AFM) interactions, Shastry and Sutherland (5) have shown the remarkable property that the Hamiltonian (Eq. 1) admits the direct product of dimer singlet states as an exact eigenstate. It has been first shown that this S = 0 wavefunction is the ground state for J′/J ? 0.7, separated from the first excited state by a spin gap (4, 6, 7). More recently, the critical value has been refined to be  ? 0.675 (8–10). The spin gap can be closed [the spin gap never strictly closes, as Dzyaloshinsky–Moriya terms cause mixing of spin-triplet and spin-singlet states (11)], and cascading magnetic states can be induced, by magnetic fields exceeding ≃20 T (12).Open in a separate windowFig. 1.Atomic structure and magnetic orders of SrCu₂(BO₃)₂. (A) Top view of the [CuBO₃]⁻ layer. Sr²⁺ ions are omitted for clarity. Dashed ellipses emphasize structural dimers. (B) Side view of the tetragonal unit cell: Sr in magenta, O in red, B in green, and Cu in blue. The buckling of the [CuBO₃]⁻ layers along the [001] direction is visible. (C–F) Néel-like AFM (C and D) and saturated FM (E and F) orders for DFT. Spin-up Cu ions are represented in light blue and spin-down Cu ions are represented in dark blue.The first indications of a significant lattice involvement in this system were evidenced in the sound velocity measurements by Wolf et al. (13), subsequently studied using X-ray diffraction at low temperature and under high magnetic field by Narumi et al. (14). These were followed by neutron diffraction experiments carried out by Vecchini et al. (15) and Haravifard et al. (16). In the former, structural changes due to the thermal excitation of the magnetic degrees of freedom were directly measured. In the latter the increased lifetime (inelastic linewidths) in a subset of the acoustic phonons has been shown to correlate with the formation of the singlet ground state near 10 K in zero field. In a recent study, Jaime et al. (17) performed magnetostriction experiments to 100 T, showing that the crystallographic c axis is an extraordinarily sensitive witness to the magnetic structure and superstructure. However sensitive, the c-axis results do not allow for a direct examination of the spin-lattice correlations within the Cu-dimer planes (Fig. 1A).     

Shedding light on a potential hazard: Dental light-curing units

BackgroundDental light-curing units (LCUs) are powerful sources of blue light that can cause soft-tissue burns and ocular damage. Although most ophthalmic research on the hazards of blue light pertains to low levels from personal electronic devices, computer monitors, and light-emitting diode light sources, the amount of blue light emitted from dental LCUs is much greater and may pose a “blue light hazard.”MethodsThe authors explain the potential risks of using dental LCUs, identify the agencies that provide guidelines designed to protect all workers from excessive exposure to blue light, discuss the selection of appropriate eye protection, and provide clinical tips to ensure eye safety when using LCUs.ResultsWhile current literature and regulatory standards regarding the safety of blue light is primarily based on animal studies, sufficient evidence exists to suggest that appropriate precautions should be taken when using dental curing lights. The authors found it difficult to find on the U.S. Food and Drug Administration database which curing lights had been cleared for use in the United States or Europe and could find no database that listed which brands of eyewear designed to protect against the blue light has been cleared for use. The authors conclude that more research is needed on the cumulative exposure to blue light in humans. Manufacturers of curing lights, government and regulatory agencies, employers, and dental personnel should collaborate to determine ocular risks from blue light exist in the dental setting, and recommend appropriate eye protection. Guidance on selection and proper use of eye protection should be readily accessible.Conclusions and Practical ImplicationsThe Centers for Disease Control and Prevention Guidelines for Infection Control in the Dental Health-Care Setting–2003 and the Occupational Safety and Health Administration Bloodborne Pathogen Standard do not include safety recommendations or regulations that are directly related to blue light exposure. However, there are additional Occupational Safety and Health Administration regulations that require employers to protect their employees from potentially injurious light radiation. Unfortunately, it is not readily evident that these regulations apply to the excessive exposure to blue light. Consequently employers and dental personnel may be unaware that these Occupational Safety and Health Administration regulations exist.     

低频脉冲电磁场通过IGF-1R/NO信号通路促进大鼠颅骨成骨细胞成熟及矿化

目的观察低频脉冲电磁场（PEMF）是否通过胰岛素样生长因子1受体（IGF-1R）/一氧化氮（NO）信号通路促进大鼠颅骨成骨细胞成熟及矿化。方法体外分离培养乳鼠颅骨成骨细胞，传代后随机分成9组，每天用50 Hz 0.6 mT PEMF处理不同的时间，通过检测成骨细胞中NO含量确定PEMF最佳处理时长。将传代后的成骨细胞随机分成空白对照组、PEMF组、GSK（IGF-1R阻断剂）组、PEMF+GSK组，PEMF处理成骨细胞3 d后，采用蛋白质印迹法检测蛋白激酶（AKT）、诱导型一氧化氮合酶（iNOS）和cGMP依赖性蛋白激酶（PKG）蛋白表达水平；PEMF处理第6天时测定碱性磷酸酶（ALP）活性；PEMF处理第12天时采用茜红素染色法观察钙化结节形成情况。结果经1.5 h电磁场处理后的成骨细胞中NO含量显著提高（ P < 0.01），遂后续采用PEMF处理1.5 h。与空白对照组比较，PEMF组AKT、iNOS、PKG蛋白表达量增加（均 P < 0.01），ALP活性升高（ P < 0.05），且茜红素染色面积增大（ P < 0.01）；GSK组AKT、iNOS、PKG蛋白表达量减少，ALP活性降低（ P < 0.05），茜红素染色面积最小（ P < 0.01）；PEMF+GSK组上述实验结果均高于GSK组但低于PEMF组（ P < 0.05或 P < 0.01）。 结论PEMF可能通过IGF-1R/NO信号通路促进大鼠颅骨成骨细胞成熟与矿化。     

Collective many-body van der Waals interactions in molecular systems

Van der Waals (vdW) interactions are ubiquitous in molecules and condensed matter, and play a crucial role in determining the structure, stability, and function for a wide variety of systems. The accurate prediction of these interactions from first principles is a substantial challenge because they are inherently quantum mechanical phenomena that arise from correlations between many electrons within a given molecular system. We introduce an efficient method that accurately describes the nonadditive many-body vdW energy contributions arising from interactions that cannot be modeled by an effective pairwise approach, and demonstrate that such contributions can significantly exceed the energy of thermal fluctuations-a critical accuracy threshold highly coveted during molecular simulations-in the prediction of several relevant properties. Cases studied include the binding affinity of ellipticine, a DNA-intercalating anticancer agent, the relative energetics between the A- and B-conformations of DNA, and the thermodynamic stability among competing paracetamol molecular crystal polymorphs. Our findings suggest that inclusion of the many-body vdW energy is essential for achieving chemical accuracy and therefore must be accounted for in molecular simulations.     

低频重复经颅磁刺激治疗老年人失眠症的疗效观察

目的 观察低频重复经颅磁刺激（rTMS）对失眠症老年人睡眠和情绪的影响。 方法 选取34例失眠症老年患者,按照随机数字表法将其分为试验组（18例）和对照组（16例）。试验组采用低频rTMS刺激右背外侧前额叶皮质（DLPFC)治疗,对照组给予交变磁场治疗。治疗前及治疗4周后（治疗后）,使用匹兹堡睡眠质量指数(PSQI)、汉密尔顿焦虑量表(HAMA)和汉密尔顿抑郁量表(HAMD)对患者进行评估。为了消除睡眠变化对患者HAMA和HAMD评分的影响,对此两项评分去除睡眠相关项得分后的分值（标记为HAMA-A、HAMD-A）进行评估。 结果 治疗前,2组患者的PSQI、HAMA和HAMD评分比较,差异无统计学意义（P>0.05）。治疗后,试验组与对照组患者的PSQI、HAMA、HAMD评分均明显下降（P<0.05）,且试验组PSQI［(8.44±1.82)分］、HAMA［(10.66±2.59)分］、HAMD［(11.78±3.64)分］较对照组低,差异有统计学意义（P<0.05）。除去HAMA与HAMD的睡眠相关选项得分后,试验组患者治疗后HAMA-A、HAMD-A较组内治疗前低（P<0.05）,对照组患者治疗后HAMA-A、HAMD-A虽较组内治疗前低,但差异无统计学意义（P>0.05）。试验组患者治疗后HAMA-A［(11.11±2.72)分］、HAMD-A［(10.17±3.28)分］较对照组低（P<0.05）。 结论 rTMS治疗老年失眠症的疗效优于交变磁场,能显著改善患者睡眠和情绪。     

Buckling Sensitivity of Tow-Steered Plates Subjected to Multiscale Defects by High-Order Finite Elements and Polynomial Chaos Expansion

It is well known that fabrication processes inevitably lead to defects in the manufactured components. However, thanks to the new capabilities of the manufacturing procedures that have emerged during the last decades, the number of imperfections has diminished while numerical models can describe the ground truth designs. Even so, a variety of defects has not been studied yet, let alone the coupling among them. This paper aims to characterise the buckling response of Variable Stiffness Composite (VSC) plates subjected to spatially varying fibre volume content as well as fibre misalignments, yielding a multiscale sensitivity analysis. On the one hand, VSCs have been modelled by means of the Carrera Unified Formulation (CUF) and a layer-wise (LW) approach, with which independent stochastic fields can be assigned to each composite layer. On the other hand, microscale analysis has been performed by employing CUF-based Mechanics of Structure Genome (MSG), which was used to build surrogate models that relate the fibre volume fraction and the material elastic properties. Then, stochastic buckling analyses were carried out following a multiscale Monte Carlo analysis to characterise the buckling load distributions statistically. Eventually, it was demonstrated that this multiscale sensitivity approach can be accelerated by an adequate usage of sampling techniques and surrogate models such as Polynomial Chaos Expansion (PCE). Finally, it has been shown that sensitivity is greatly affected by nominal fibre orientation and the multiscale uncertainty features.     

磁性附着体模拟静磁场对成骨细胞转化生长因子β1基因表达的影响

目的研究不同强度的磁性附着体模拟静磁场对成骨细胞转化生长因子β1(TGF-β1)基因表达的影响。方法利用细胞静磁场加载装置,对体外培养的SD大鼠成骨细胞分别进行12.5、125和250mT的静磁场加载,连续加载0.5、1、3、5和7d,采用反转录聚合酶链反应(RT-PCR)技术检测成骨细胞的TGF-β1mRNA表达的。结果 12.5mT磁场加载组在加载0.5、1和3d,细胞的TGF-β1mRNA的表达比对照组相应时段明显增强(P<0.05)。125和250mT磁场组加载静磁场0.5、1、3、5和7d后,细胞的TGF-β1mRNA的表达升高更加明显,与对照组和12.5mT磁场加载组细胞相比差异有统计学意义(P<0.05)。静磁场对细胞的TGF-β1mRNA表达的影响有一定的剂量-效应关系。结论在本试验条件下,磁性附着体模拟静磁场可以抑制TGF-β1mRNA基因表达的下降,促进成骨细胞的分化。