A regional perspective on the palynofloral response to K-T boundary event(s) with emphasis on variations imposed by the effects of sedimentary facies and latitude

Palynological studies deal with fossil reproductive bodies that were produced by fully functioning plants, whereas most faunal studies are based on death assemblages. Therefore, changes in pollen and spore assemblages cannot be used directly as evidence of catastrophic mass killings but only to indicate changes in ecological conditions. The impact of the Cretaceous-Tertiary boundary event on terrestrial plant communities is illustrated by the degree, rate and selectivity of change. As in most classical palynological studies, the degree of change is expressed in terms of relative abundance and changes in species diversity. It is recognized that sampling interval and continuity of the rock record within individual sections can affect the percieved rate of change. Even taking these factors into account, a gradual change in relative abundance and multiple levels of apparent extinctions, associated with the interval bounding the K-T boundary, can be demonstrated. Climatic change, which locally exceeds the tolerance of individual species, and the possible loss of a group of pollinating agents are examined as possible explanations for the selectivity of apparent extinctions and/or locally truncated occurrences. The aspects of change are demonstrated with data from four different K-T boundary localities in Western Canada between paleolatitudes 60 and 75 deg north. Together, the four localities discussed allow changes imposed by latitude and differences in the depositional environment be isolated from the boundary event itself which is reflected by the truncated ranges of several species throughout the region of study. What must be recognized is that variations in the response of vegetation to the K-T boundary event(s) occurred throughout the Western Interior basin

On the exceptional damage-tolerance of gradient metallic materials

An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse macro-scale to nano-scale (CG → NG) and vice versa (NG → CG), with the measured crack-resistance R-curves compared to the corresponding behavior in uniform nano-grained (NG) and coarse-grained (CG) materials. It is found that the gradient structures display a much-improved combination of high strength and toughness compared to uniform grain-sized materials. However, based on J-integral measurements in the gradient materials, the crack-initiation toughness is far higher for cracks grown in the direction of the coarse-to-nano grained gradient than vice versa, a result which we ascribe primarily to excessive crack-tip blunting in the coarse-grained microstructure. Both gradient structures, however, display marked rising R-curve behavior with exceptional crack-growth toughnesses exceeding 200 MPa.m½

Database Search Strategies for Proteomic Data Sets Generated by Electron Capture Dissociation Mass Spectrometry

Large data sets of electron capture dissociation (ECD) mass spectra from proteomic experiments are rich in information; however, extracting that information in an optimal manner is not straightforward. Protein database search engines currently available are designed for low resolution CID data, from which Fourier transform ion cyclotron resonance (FT-ICR) ECD data differs significantly. ECD mass spectra contain both z-prime and z-dot fragment ions (and c-prime and c-dot); ECD mass spectra contain abundant peaks derived from neutral losses from charge-reduced precursor ions; FT-ICR ECD spectra are acquired with a larger precursor m/z isolation window than their low-resolution CID counterparts. Here, we consider three distinct stages of postacquisition analysis: (1) processing of ECD mass spectra prior to the database search; (2) the database search step itself and (3) postsearch processing of results. We demonstrate that each of these steps has an effect on the number of peptides identified, with the postsearch processing of results having the largest effect. We compare two commonly used search engines: Mascot and OMSSA. Using an ECD data set of modest size (3341 mass spectra) from a complex sample (mouse whole cell lysate), we demonstrate that search results can be improved from 630 identifications (19% identification success rate) to 1643 identifications (49% identification success rate). We focus in particular on improving identification rates for doubly charged precursors, which are typically low for ECD fragmentation. We compare our presearch processing algorithm with a similar algorithm recently developed for electron transfer dissociation (ETD) data

Self-Regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition

I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly-reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nano-flares), evaporation episodes, and long periods of slow magnetic stress build-up and radiative cooling of the coronal plasma.Comment: 4 pages; Phys. Rev. Lett., in pres

2MASS J06164006-6407194: The First Outer Halo L Subdwarf

We present the serendipitous discovery of an L subdwarf, 2MASS J06164006-6407194, in a search of the Two Micron All Sky Survey for T dwarfs. Its spectrum exhibits features indicative of both a cool and metal poor atmosphere including a heavily pressured-broadened K I resonant doublet, Cs I and Rb I lines, molecular bands of CaH, TiO, CrH, FeH, and H2O, and enhanced collision induced absorption of H2. We assign 2MASS 0616-6407 a spectral type of sdL5 based on a comparison of its red optical spectrum to that of near solar-metallicity L dwarfs. Its high proper motion (mu =1.405+-0.008 arcsec yr-1), large radial velocity (Vrad = 454+-15 km s-1), estimated uvw velocities (94, -573, 125) km s-1 and Galactic orbit with an apogalacticon at ~29 kpc are indicative of membership in the outer halo making 2MASS 0616-6407 the first ultracool member of this population.Comment: Accepted for publication in Ap

Reuse as heuristic : from transmission to nurture in learning activity design

In recent years a combination of ever more flexible and sophisticated Web technologies and an explosion in the quantity of online content has sparked learning technologists around the world to pursue the promise of the 'reusable learning object' or RLO with the idea that RLOs could be reused in different educational contexts, thereby providing greater overall flexibility and return on investment. In 2002 the ACETS Project undertook a three-year study in the UK to investigate whether RLOs worked in practice and how the pursuit of reuse affected the teacher and their teaching. Teachers working in healthcare-related subjects in Higher and Further Education were asked to create an original learning design or activity from third-party digital resources and to reflect both on the process and its outcomes. The expectation was that teachers would be the ones selecting and reusing third-party materials. This paper describes how one of the ACETS exemplifiers reinterpreted this remit, challenged the anticipated transmissive model of learning, and instead, gave their students an opportunity to create their own original learning designs and learning activities from third-party digital resources. By describing the educational enhancements, the resulting heightened levels of critical thinking, and sensitivity to patient needs, 'reuse' will be shown to be an effective heuristic for student self-direction and professional development

Magnetic Reconnection with Radiative Cooling. I. Optically-Thin Regime

Magnetic reconnection, a fundamental plasma process associated with a rapid dissipation of magnetic energy, is believed to power many disruptive phenomena in laboratory plasma devices, the Earth magnetosphere, and the solar corona. Traditional reconnection research, geared towards these rather tenuous environments, has justifiably ignored the effects of radiation on the reconnection process. However, in many reconnecting systems in high-energy astrophysics (e.g., accretion-disk coronae, relativistic jets, magnetar flares) and, potentially, in powerful laser plasma and z-pinch experiments, the energy density is so high that radiation, in particular radiative cooling, may start to play an important role. This observation motivates the development of a theory of high-energy-density radiative magnetic reconnection. As a first step towards this goal, we present in this paper a simple Sweet--Parker-like theory of non-relativistic resistive-MHD reconnection with strong radiative cooling. First, we show how, in the absence of a guide magnetic field, intense cooling leads to a strong compression of the plasma in the reconnection layer, resulting in a higher reconnection rate. The compression ratio and the layer temperature are determined by the balance between ohmic heating and radiative cooling. The lower temperature in the radiatively-cooled layer leads to a higher Spitzer resistivity and hence to an extra enhancement of the reconnection rate. We then apply our general theory to several specific astrophysically important radiative processes (bremsstrahlung, cyclotron, and inverse-Compton) in the optically thin regime, for both the zero- and strong-guide-field cases. We derive specific expressions for key reconnection parameters, including the reconnection rate. We also discuss the limitations and conditions for applicability of our theory.Comment: 31 pages, 1 figur

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations

What does the arthropathy of alkaptonuria teach us about disease mechanisms in osteoarthritis and ageing of joints? Lessons from a rare disease

AKU Society, the Rosetrees Foundation, the Childwick Trust, the Big Lottery and EUFP

Fast and slow two-fluid magnetic reconnection

We present a two-fluid magnetohydrodynamics (MHD) model of quasi-stationary, two-dimensional magnetic reconnection in an incompressible plasma composed of electrons and ions. We find two distinct regimes of slow and fast reconnection. The presence of these two regimes can provide a possible explanation for the initial slow build up and subsequent rapid release of magnetic energy frequently observed in cosmic and laboratory plasmas.Comment: 16 pages, 2 figures, 1 tabl