禁带区域内负的群速度

研究超声波经过两个烧结样品的行为.两个烧结样品为有序的面心立方结构,它们的结构几乎相同.研究表明:在两个有序的准均匀的介质中分别有一个禁带区域.就禁带区域而言,在两个样品中产生禁带的区域非常接近.同时在禁带出现的区域群速度为负值.我们的结果表明群速度的负值的确存在于有序介质中的禁带区域内.     

Self-assembly of nanoscale cuboctahedra by coordination chemistry

Self-assembled polyhedral structures are common in biology. The coats of many viruses, for example, have a structure based on icosahedral symmetry. The preparation of synthetic polyhedral molecular assemblies represents a challenging problem, but supramolecular chemistry has now advanced to the point where the task may be addressed. Macromolecular and supramolecular entities of predefined geometric shape and with well-defined internal environments are potentially important for inclusion phenomena, molecular recognition and catalysis. Here we report the use of self-assembly of molecular units driven by coordination to transition-metal ions to prepare a cuboctahedron from 20 tridentate and bidentate subunits in a single step. The cuboctahedron is an archimedean semiregular polyhedron that combines square and triangular faces. Our self-assembled polyhedral capsules, characterized by NMR and electrospray mass spectrometry, are around 5 nanometres in diameter.     

Mutations in kelch-like 3 and cullin 3 cause hypertension and electrolyte abnormalities

Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. Pseudohypoaldosteronism type II (PHAII), a rare Mendelian syndrome featuring hypertension, hyperkalaemia and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption and K(+) and H(+) excretion. Here we used exome sequencing to identify mutations in kelch-like 3 (KLHL3) or cullin 3 (CUL3) in PHAII patients from 41 unrelated families. KLHL3 mutations are either recessive or dominant, whereas CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-domain-containing kelch proteins such as KLHL3 are components of cullin-RING E3 ligase complexes that ubiquitinate substrates bound to kelch propeller domains. Dominant KLHL3 mutations are clustered in short segments within the kelch propeller and BTB domains implicated in substrate and cullin binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3 and CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite the combined complexities of locus heterogeneity, mixed models of transmission and frequent de novo mutation, and establish a fundamental role for KLHL3 and CUL3 in blood pressure, K(+) and pH homeostasis.     

传统农业生态系统的保护

世界的生物多样性很大程度上受到传统农业耕作方式的保护。这些生态上复杂的农业系统与作物遗传多样性中心相联系,有传统的栽培品种或“地方品种”,作为世界作物遗传资源的重要组成,还有野生的植物和动物种群,作为生物资源服务于人类。