Record-breaking earthquake intervals in a global catalogue and an aftershock sequence

For the purposes of this study, an interval is the elapsed time between two earthquakes in a designated region; the minimum magnitude for the earthquakes is prescribed. A record-breaking interval is one that is longer (or shorter) than preceding intervals; a starting time must be specified. We consider global earthquakes with magnitudes greater than 5.5 and show that the record-breaking intervals are well estimated by a Poissonian (random) theory. We also consider the aftershocks of the 2004 Parkfield earthquake and show that the record-breaking intervals are approximated by very different statistics. In both cases, we calculate the number of record-breaking intervals (<i>n</i><sub>rb</sub>) and the record-breaking interval durations Δ<i>t</i><sub>rb</sub> as a function of "natural time", the number of elapsed events. We also calculate the ratio of record-breaking long intervals to record-breaking short intervals as a function of time, <i>r(t)</i>, which is suggested to be sensitive to trends in noisy time series data. Our data indicate a possible precursory signal to large earthquakes that is consistent with accelerated moment release (AMR) theory

Mobile camera-space manipulation

The invention is a method of using computer vision to control systems consisting of a combination of holonomic and nonholonomic degrees of freedom such as a wheeled rover equipped with a robotic arm, a forklift, and earth-moving equipment such as a backhoe or a front-loader. Using vision sensors mounted on the mobile system and the manipulator, the system establishes a relationship between the internal joint configuration of the holonomic degrees of freedom of the manipulator and the appearance of features on the manipulator in the reference frames of the vision sensors. Then, the system, perhaps with the assistance of an operator, identifies the locations of the target object in the reference frames of the vision sensors. Using this target information, along with the relationship described above, the system determines a suitable trajectory for the nonholonomic degrees of freedom of the base to follow towards the target object. The system also determines a suitable pose or series of poses for the holonomic degrees of freedom of the manipulator. With additional visual samples, the system automatically updates the trajectory and final pose of the manipulator so as to allow for greater precision in the overall final position of the system

Taxonomic Work as Information Work: Design for Semantic Refactoring

Taxonomy is the branch of science concerned with classi- fying organisms: drawing the line between cats and dogs, fish and fowl, animals and vegetables. Modern taxonomic work is built on a hundreds-year-old tradition of qualitative research and description. There are aspects of this work that illustrate the pervasiveness and difficulty of a particular kind of qualitative data wrangling, which we call semantic refactoring: the review, normalization, and re-engineering of semantic structures. Because taxonomic work is con- ducted over long time spans, the processes underlying se- mantic refactoring become more visible. An examination of taxonomic data practices may inform our understanding of how (and if) collections of qualitative data scale, particularly when collaboratively created.NSF ABI Grant 1356515.Ope

Topological and subsystem codes on low-degree graphs with flag qubits

In this work we introduce two code families, which we call the heavy hexagon code and heavy square code. Both code families are implemented by assigning physical data and ancilla qubits to both vertices and edges of low degree graphs. Such a layout is particularly suitable for superconducting qubit architectures to minimize frequency collisions and crosstalk. In some cases, frequency collisions can be reduced by several orders of magnitude. The heavy hexagon code is a hybrid surface/Bacon-Shor code mapped onto a (heavy) hexagonal lattice whereas the heavy square code is the surface code mapped onto a (heavy) square lattice. In both cases, the lattice includes all the ancilla qubits required for fault-tolerant error-correction. Naively, the limited qubit connectivity might be thought to limit the error-correcting capability of the code to less than its full distance. Therefore, essential to our construction is the use of flag qubits. We modify minimum weight perfect matching decoding to efficiently and scalably incorporate information from measurements of the flag qubits and correct up to the full code distance while respecting the limited connectivity. Simulations show that high threshold values for both codes can be obtained using our decoding protocol. Further, our decoding scheme can be adapted to other topological code families.Comment: 20 pages, 21 figures, Comments welcome! V2 conforms to journal specification

Nitrogen recycling in coastal waters of southeastern U.S. during summer 1986

Summer-time pelagic nitrogen recycling using an 15NH4+ tracer technique was studied for important biological pathways, sinks, and residence times in the microbial food web of coastal Georgia, U.S.A. Results showed that estimated rates of NH4+ regeneration by a variety of microheterotrophs and microzooplankton balanced rates of NH4+ assimilation by the microbial community, i.e., phytoplankton, bacteria and other microheterotrophs, in surface waters. In bottom water below the 1% light level, NH4+ regeneration exceeded community NH4+ assimilation by 3.5 times. However, over a period of 2 weeks, high NH4+ concentrations rarely occurred in bottom waters, and this was attributed to rapid mixing of the water column by winds and tides. Estimated mixing times from time-dependent numerical models were on the order of NH4+ turnover times of 5 to 10 hours. Overall, rates of community NH4+ assimilation exceeded rate estimates of phytoplankton N demand by 1.8 to 2.7 fold, which were made from rates of 14CO2 incorporation into proteins. In bottom samples where phytoplankton were light limited, rates of NH4+ assimilation exceeded the phytoplankton N demand by 3.6 to 11.1 fold. Calculations concerning the role of dissolved organic nitrogen in N cycling suggest that only 10% is recycled to NH4+ daily. This N could support 12 to 29% of the estimated phytoplankton N demand. Residence times of particulate nitrogen pools, based on rates of NH4+ regeneration, were on the order of 3–10 days. During summer-time hydrographic conditions and despite other losses, particulate nitrogen could recycle as often as 100 times before autumn removal processes occur off southeastern U.S

Enhanced monography in a collaboratively evolved hub for systematic biology

No abstract available

Pinning/depinning of crack fronts in heterogeneous materials

The fatigue fracture surfaces of a metallic alloy, and the stress corrosion fracture surfaces of glass are investigated as a function of crack velocity. It is shown that in both cases, there are two fracture regimes, which have a well defined self-affine signature. At high enough length scales, the universal roughness index 0.78 is recovered. At smaller length scales, the roughness exponent is close to 0.50. The crossover length $\xi_c$ separating these two regimes strongly depends on the material, and exhibits a power-law decrease with the measured crack velocity $\xi_c \propto v^{-\phi}$, with $\phi \simeq 1$. The exponents $\nu$ and $\beta$ characterising the dependence of $\xi_c$ and $v$ upon the pulling force are shown to be close to $\nu \simeq 2$ and $\beta \simeq 2$.Comment: 4 pages, latex, and 4 encapsulated postscript figure

Energy Loss of a High Charge Bunched Electron Beam in Plasma

There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.Comment: Submitted to Physical Review Letter

Soft believers and hard unbelievers in the Xhosa cattle-killing

A substantial minority, perhaps 15 per cent of all Xhosa, refused to obey the prophetess Nongqawuse's orders to kill their cattle and destroy their corn. This divided Xhosaland into two parties, the amathamba (‘soft’ ones, or believers) and the amagogotya (‘hard’ ones, or unbelievers). The affiliation of individuals was partly determined by a number of factors – lungsickness in cattle, political attitude towards the Cape Colony, religious beliefs, kinship, age and gender – but a systematic analysis of each of these factors in turn suggests that none of them was sufficiently important to constitute the basis of either party. The key to understanding the division lies in an analysis of the indigenous Xhosa terms ‘soft’ and ‘hard’. ‘Softness’ in Xhosa denotes the submissiveness of the individual to the common will of the community, whereas ‘hardness’ denotes the determination of the individual to pursue his own ends, even at communal expense. Translated into social terms, the ‘soft’ believers were those who remained committed to the mutual aid ethic of the declining precolonial society, whereas the ‘hard’ unbelievers were those who sought to seize advantage of the new opportunities offered by the colonial presence to increase their wealth and social prominence. The conflict between the social and personal imperatives was well expressed by Chief Smith Mhala, the unbelieving son of a believing father, when he said, ‘They say I am killing my father – so I would kill him before I would kill my cattle.’ Certainly, the division between amathamba and amagogotya ran much deeper than the division between belief and unbelief, and the Xhosa, in conferring these names, seem to have recognized the fact