Extremely slow Drude relaxation of correlated electrons

The electrical conduction of metals is governed by how freely mobile electrons can move throughout the material. This movement is hampered by scattering with other electrons, as well as with impurities or thermal excitations (phonons). Experimentally, the scattering processes of single electrons are not observed, but rather the overall response of all mobile charge carriers within a sample. The ensemble dynamics can be described by the relaxation rates, which express how fast the system approaches equilibrium after an external perturbation. Here we measure the frequency-dependent microwave conductivity of the heavy-fermion metal UPd2Al3 (ref. 4), finding that it is accurately described by the prediction for a single relaxation rate (the so-called Drude response). This is notable, as UPd2Al3 has strong interactions among the electrons that might be expected to lead to more complex behaviour. Furthermore, the relaxation rate of just a few gigahertz is extremely low--this is several orders of magnitude below those of conventional metals (which are typically around 10 THz), and at least one order of magnitude lower than previous estimates for comparable metals. These observations are directly related to the high effective mass of the charge carriers in this material and reveal the dynamics of interacting electrons.     

Über die Speicherung von Lipiden durch Knallgasbakterien

Summary The ability to accumulate lipids was investigated in two strains of hydrogen oxidizing bacteria (Hydrogenomonas H 16 and strain 11/x). Along with the deposition of poly--hydroxybutyrate the amount of other lipids is shown to increase 1.8 times in strain H 16. It is suggested that the increase of the latter lipids is due to the formation of membrane lipids that are needed for the formation of membranes around the intracellular globules of poly--hydroxybutyrate. In strain 11/x the amount of lipids increases 7 times along with the storage of carbohydrates. In this case, the majority of lipids consists of triglycerides. It is suggested that there is a true storage of neutral fat in strain 11/x.     

Structure of recombinant human rheumatoid arthritic synovial fluid phospholipase A2 at 2.2 A resolution

Phospholipases A2 (PLA2s) may be grouped into distinct families of proteins that catalyse the hydrolysis of the 2-acyl bond of phospholipids and perform a variety of biological functions. The best characterized are the small (relative molecular mass approximately 14,000) calcium-dependent, secretory enzymes of diverse origin, such as pancreatic and venom PLA2s. The structures and functions of several PLA2s are known. Recently, high-resolution crystal structures of complexes of secretory PLA2s with phosphonate phospholipid analogues have provided information about the detailed stereochemistry of transition-state binding, confirming the proposed catalytic mechanism of esterolysis. By contrast, studies on mammalian nonpancreatic secretory PLA2s (s-PLA2s) have only recently begun; s-PLA2s are scarce in normal cells and tissues but large amounts are found in association with local and systemic inflammatory processes and tissue injury in animals and man. Such s-PLAs have been purified from rabbit and rat inflammatory exudate, from synovial fluid from patients with rheumatoid arthritis and from human platelets. Cloning and sequencing shows that the primary structure of the human s-PLA2 has about 37% homology with that of bovine pancreatic PLA2 and 44% homology with that of Crotalus atrox PLA2. The human s-PLA2 is an unusually basic protein, yet contains most of the highly conserved amino-acid residues and sequences characteristic of the PLA2s sequenced so far. Here we report the refined, three-dimensional crystal structure at 2.2 A resolution of recombinant human rheumatoid arthritic synovial fluid PLA2. This may aid the development of potent and specific inhibitors of this enzyme using structure-based design.     

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales.     

Apoptosis induced by titanium dioxide nanoparticles in cultured murine microglia N9 cells

Owing to the rapidly increasing output of nano-scale titanium dioxide （TiO2） particles, their potential risk for central nerve system （CNS） has elicited much concern recently. Microglia is the resident macrophage in CNS and essential for the homeostasis of the CNS microenvironment. They are supposed to response to nanoparticles depositing in the brain tissues. Therefore, we investigated the cytotoxic effects of TiO2 NPs on microglia N9 cells in vitro. Results of propidium iodide/fluorescein diacetate （PI/FDA） double staining and MTT test clearly showed that TiO2 NPs more efficiently affected the viability of microglia N9 cells. Further Hoechst 33258 staining and flow cytometric analysis proved that nano-scale but not normal scale TiO2 induced apoptosis in vitro, These data suggest that TiO2 NPs can elicit apoptosis of N9 cells in vitro and thus present a potential risk for CNS.     

Engineered two-dimensional Ising interactions in a trapped-ion quantum simulator with hundreds of spins

The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N?≈?30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0?≤?a?≤?3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05???a???1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism.     

基于最大和最小选择的两种新的恒虚警检测器

本文提出两种基于有序统计（ＯＳ）和单元平均（ＣＡ）产生局部估计，并分别应用最大选择（ＧＯ）和最小选择（ＳＯ）产生检测单元干扰功率水平估计Ｚ的新的恒虚警检测器（ＯＳＣＡＧＯ）和（ＯＳＣＡＳＯ）。我们推导出了它们在ＳｗｅｒｌｉｎｇⅡ型目标假设下的Ｐ＿（ｆａ），Ｐ＿（ｃｌ）和度量ＡＤＴ的解析表达式。分析了它们在均匀背景和强干扰目标环境之中的检测性能，并把它们与ＯＳ－、ＧＯＳＧＯ－、ＧＯＳＳＯ－ＣＦＡＲ进行了比较。结果表明，ＯＳＣＧＯ在均匀干扰背景和多目标情况下的检测性能与ＯＳ和ＧＯＳＧＯ相比，都有很明显的提高。在干扰目标数为某些值时，ＯＳＣＡＧＯ的ＣＦＡＲ损失比ＧＯＳＧＯ小近３ｂＢ。在均匀背景中，ＯＳＣＡＳＯ的检测性能与ＧＯＳＳＯ相近。但是，在多目标环境中，一定条件下的ＯＳＣＡＳＯ的检测性能甚至超过了ＯＳ和ＧＯＳＧＯ。     

Symbolic Languages and Natural Structures a Mathematician’s Account of Empiricism

The ancient dualism of a sensible and an intelligible world important in Neoplatonic and medieval philosophy, down to Descartes and Kant, would seem to be supplanted today by a scientific view of mind-in-nature. Here, we revive the old dualism in a modified form, and describe mind as a symbolic language, founded in linguistic recursive computation according to the Church-Turing thesis, constituting a world L that serves the human organism as a map of the Universe U. This methodological distinction of L vs. U helps to understand how and why structures of phenomena come to be opposed to their nature in human thought, a central topic in Heideggerian philosophy. U is uncountable according to Georg Cantor’s set theory but Language L, based on the recursive function system, is countable, and anchored in a Gray Area within U of observable phenomena, typically symbols (or tokens), prelinguistic structures, genetic-historical records of their origins. Symbols, the phenomena most familiar to mathematicians, are capable of being addressed in L-processing. The Gray Area is the human Environment E, where we can live comfortably, that we manipulate to create our niche within hostile U, with L offering overall competence of the species to survive. The human being is seen in the light of his or her linguistic recursively computational (finite) mind. Nature U, by contrast, is the unfathomable abyss of being, infinite labyrinth of darkness, impenetrable and hostile to man. The U-man, biological organism, is a stranger in L-man, the mind-controlled rational person, as expounded by Saint Paul. Noumena can now be seen to reside in L, and are not fully supported by phenomena. Kant’s noumenal cause is the mental L-image of only partly phenomenal causation. Mathematics occurs naturally in pre-linguistic phenomena, including natural laws, which give rise to pure mathematical structures in the world of L. Mathematical foundation within philosophy is reversed to where natural mathematics in the Gray Area of pre-linguistic phenomena can be seen to be a prerequisite for intellectual discourse. Lesser, nonverbal versions of L based on images are shared with animals.