Signal-processing machines at the postsynaptic density

Dendrites of individual neurons in the vertebrate central nervous system are contacted by thousands of synaptic terminals relaying information about the environment. The postsynaptic membrane at each synaptic terminal is the first place where information is processed as it converges on the dendrite. At the postsynaptic membrane of excitatory synapses, neurotransmitter receptors are attached to large protein "signaling machines" that delicately regulate the strength of synaptic transmission. These machines are visible in the electron microscope and are called the postsynaptic density. By changing synaptic strength in response to neural activity, the postsynaptic density contributes to information processing and the formation of memories.     

Sediments at the top of Earth's core

Unusual physical properties at the core-mantle boundary have been inferred from seismic and geodetic observations in recent years. We show how both types of observations can be explained by a layer of silicate sediments, which accumulate at the top of the core as Earth cools. Compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material, which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes. Extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo.     

Amalthea's density is less than that of water

Radio Doppler data from the Galileo spacecraft's encounter with Amalthea, one of Jupiter's small inner moons, on 5 November 2002 yield a mass of (2.08 +/- 0.15) x 10(18) kilograms. Images of Amalthea from two Voyager spacecraft in 1979 and Galileo imaging between November 1996 and June 1997 yield a volume of (2.43 +/- 0.22) x 10(6) cubic kilometers. The satellite thus has a density of 857 +/- 99 kilograms per cubic meter. We suggest that Amalthea is porous and composed of water ice, as well as rocky material, and thus formed in a cold region of the solar system, possibly not at its present location near Jupiter.     

Proteolytic self-cleavage of hepatitis B virus core protein may generate serum e antigen

A model is proposed to explain the presence of the e antigen (HBeAg) of hepatitis B virus (HBV) in the serum of individuals infected with this virus. The e antigen, which has only recently been characterized, is a fragment of the virus core, or nucleocapsid, protein. Serum HBeAg is a valuable clinical marker for active HBV infection because its appearance correlates both with virus replication in the liver and with the presence of circulating virions. In this study a protease-like amino acid sequence was identified at the amino terminus of the core protein sequence. Experimental evidence indicates that HBeAg may be produced by proteolytic self-cleavage of the core protein.     

Identification of a specialized adenylyl cyclase that may mediate odorant detection

The mammalian olfactory system may transduce odorant information via a G protein-mediated adenosine 3',5'-monophosphate (cAMP) cascade. A newly discovered adenylyl cyclase, termed type III, has been cloned, and its expression was localized to olfactory neurons. The type III protein resides in the sensory neuronal cilia, which project into the nasal lumen and are accessible to airborne odorants. The enzymatic activity of the type III adenylyl cyclase appears to differ from nonsensory cyclases. The large difference seen between basal and stimulated activity for the type III enzyme could allow considerable modulation of the intracellular cAMP concentration. This property may represent one mechanism of achieving sensitivity in odorant perception.     

Physics of iron at Earth's core conditions

The bulk properties of iron at the pressure and temperature conditions of Earth's core were determined by a method that combines first-principles and classical molecular dynamic simulations. The theory indicates that (i) the iron melting temperature at inner-core boundary (ICB) pressure (330 gigapascals) is 5400 (+/-400) kelvin; (ii) liquid iron at ICB conditions is about 6% denser than Earth's outer core; and (iii) the shear modulus of solid iron close to its melting line is 140 gigapascals, consistent with the seismic value for the inner core. These results reconcile melting temperature estimates based on sound velocity shock wave data with those based on diamond anvil cell experiments.     

Equatorially dominated magnetic field change at the surface of Earth's core

Slow temporal variations in Earth's magnetic field originate in the liquid outer core. We analyzed the evolution of nonaxisymmetric magnetic flux at the core surface over the past 400 years. We found that the most robust feature is westward motion at 17 kilometers per year, in a belt concentrated around the equator beneath the Atlantic hemisphere. Surprisingly, this motion is dominated by a single wavenumber and persists throughout the observation period. This phenomenon could be produced by an equatorial jet of core fluid, by hydromagnetic wave propagation, or by a combination of both. Discrimination between these mechanisms would provide useful constraints on the dynamics of Earth's core.     

Percolation of core melts at lower mantle conditions

Experiments at high pressure and temperature to determine the dihedral angle of core melts in lower mantle phases yielded a value of approximately 71 degrees for perovskite-dominated matrices. This angle, although greater than the 60 degrees required for completely efficient percolation, is considerably less than the angles observed in mineral matrices at upper mantle pressure-temperature conditions in experiments. In other words, molten iron alloy can flow much more easily in lower mantle mineralogies than in upper mantle mineralogies. Accordingly, although segregation of core material by melt percolation is probably not feasible in the upper mantle, core formation by percolation may be possible in the lower mantle.     

不同养鸭密度对水稻病虫草害影响试验初报

该文阐述了不同养鸭密度对水稻病虫草害影响,试验表明：稻鸭共育能有效防治二化螟、稻飞虱、纹枯病、稻田主要杂草危害,且在水稻全生育期内少用农药2～3次,保护了稻田生态环境,提高水稻的品质。     

海黍子有性生殖相关形态建成因子分析

为了评估海黍子Sargassum muticum有性繁殖生殖力情况,利用统计学方法对海黍子有性生殖相关的形态建成因子进行了初步研究,通过分析藻体长度与侧枝数、侧枝长度与生殖托数、生殖托长度与生殖托挂卵数之间的数量相关性,利用回归方程估算了海黍子的个体生殖力。结果表明:海黍子成熟藻体平均长度为(164.5±59.9)cm,侧枝平均长度为(10.4±5.3)cm,生殖托平均长度为(9.3±1.5)mm,单个生殖托平均挂卵数量为(378±121)粒,各因子间存在线性正相关性(P0.05)。研究表明,单株海黍子成熟藻体能够产生(21~400)万粒受精卵,可基本满足1 m~2的采苗生产需要。