Refractive index of a transparent liquid measured with a concave mirror

This paper describes the spherical concave mirror method for measuring the index of refraction of transparent liquids. We derived the refractive index equation using Snell's law and the small-angle approximation. We also verified the validity of this method using the traditional spherical mirror and thin-lens Gaussian equations.Comment: IOPart, 8 pages, 4 figure

Comunicación corta. Rhizoctonia solani, agente causal de la muerte de plántulas de acelga en España

During September 2011, post-emergence damping off of Swiss chard (Beta vulgaris subsp. cicla L.) was observed in a greenhouse in Villa del Prado (Spain). About 20% of the seedlings showed damping off symptoms. Lesions were initially water soaked, dark brown necrosis of crown tissue, irregular in shape and sunken in appearance on large plants, causing the infected seedlings to collapse and eventually die. Rhizoctonia solani was isolated consistently from symptomatic plants. After morphological and molecular identification of the isolates, pathogenicity was tested by placing agar plugs of four isolates adjacent to the stem at the three or four true leaf stage. In inoculated plants, brown crown and stem necrosis occurred while control plants did not show disease symptoms. Pathogenicity using non-germinated seeds was also tested. All four isolates produced extensive damping off when inoculated on non-germinated seeds. To our knowledge, this is the first report of damping off of Swiss chard caused by R. solani in Europe.En el mes de septiembre de 2011, se observó muerte de plántulas en acelgas cultivadas en un invernadero en Villa del Prado (España). Cerca del 20% de los semilleros mostraban síntomas de caída de plántulas. Las lesiones iniciales tenían un aspecto húmedo y consistían en una necrosis del tejido de la corona de color marrón oscuro, de bordes irregulares y deprimidos en las plantas adultas, produciendo el colapso de las plántulas y, ocasionalmente, la muerte de las mismas. Rhizoctonia solani se aisló de manera consistente de las plantas sintomáticas. Tras una identificación morfológica y molecular, la patogenicidad de los aislados se probó colocando discos de agar adyacentes al tallo de la planta en estados de tres o cuatro hojas verdaderas. En las plantas inoculadas se observó un oscurecimiento de la corona y la necrosis del tallo en todos los casos, síntomas que no mostraron las plantas control. Por otro lado, se comprobó la patogenicidad de los aislados en semillas no germinadas. Los cuatro aislados produjeron muerte de plántulas cuando se inocularon en semillas no germinadas. Hasta donde hemos podido comprobar, este trabajo parece ser la primera cita de muerte de plántulas de acelga causada por R. solani en Europa

Adaptive multi-stage integration schemes for Hamiltonian Monte Carlo

Hamiltonian Monte Carlo (HMC) is a powerful tool for Bayesian statistical inference due to its potential to rapidly explore high dimensional state space, avoiding the random walk behavior typical of many Markov Chain Monte Carlo samplers. The proper choice of the integrator of the Hamiltonian dynamics is key to the efficiency of HMC. It is becoming increasingly clear that multi-stage splitting integrators are a good alternative to the Verlet method, traditionally used in HMC. Here we propose a principled way of finding optimal, problem-specific integration schemes (in terms of the best conservation of energy for harmonic forces/Gaussian targets) within the families of 2- and 3-stage splitting integrators. The method, which we call Adaptive Integration Approach for statistics, or s-AIA, uses a multivariate Gaussian model and simulation data obtained at the HMC burn-in stage to identify a system-specific dimensional stability interval and assigns the most appropriate 2-/3-stage integrator for any user-chosen simulation step size within that interval. s-AIA has been implemented in the in-house software package HaiCS without introducing computational overheads in the simulations. The efficiency of the s-AIA integrators and their impact on the HMC accuracy, sampling performance and convergence are discussed in comparison with known fixed-parameter multi-stage splitting integrators (including Verlet). Numerical experiments on well-known statistical models show that the adaptive schemes reach the best possible performance within the family of 2-, 3-stage splitting schemes.PID2019-104927GB-C21 MCIN/AEI/10.13039/501100011033 ERDF (“A way of making Europe”) KK-2022/00006 KK-2021/00022 KK-2021/00064 LCF/BQ/DI20/1178002

Structural basis of complement membrane attack complex formation

In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a ‘multi-hit’ mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a ‘split-washer’ configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration