A new substrate for sampling deep river macroinvertebrates

We compared macroinvertebrate communities colonising multiplate samplers constructed from perspex or tempered hardboard (wood) with an alternative artificial substrate constructed from folded coconut fibre matting (coir) enclosed in nylon netting. Substrates were incubated for 62 days over January to March 2007 at six sites over 240 km along the Waikato River. The three substrates supported similar numbers of invertebrate taxa (27 - 29 taxa), but coir samples contained 71% of total invertebrate numbers from all substrates combined, compared with <17% for each type of multiplate sampler. Coir faunas were heavily dominated by the hydrobiid snail Potamopyrgus (84 % of numbers), and this taxon along with the amphipod Paracalliope comprised 58 - 66 % of invertebrates on both types of multiplate samplers. Analysis of a Bray-Curtis matrix suggested statistically significant differences in percent community composition between coir samplers and each type of multiplate sampler over the late summer study period. Densities per cm3 of Oligochaeta, Mollusca, and "other worms" (Platyhelminthes, Rhabdocoela, Nemertea and Hirudinea combined) were significantly higher in coir samples than one or both of the multiplate samplers. Results suggest coir samplers may provide a useful supplement to multiplate samplers for deep river invertebrate studies by collecting a different range of taxa, including those favouring cover and characteristic of depositional environments

Aerosol seeding systems for the NSWC wind tunnels

Four types of laskin nozzles which are used to generate the primary aerosol mist are illustrated. This mist may be used directly as laser doppler velocimeters (LDV) particles. However, in general, a wide range of particle size exists at this stage and requires the use of some type of mono-dispersion refinement technique. These nozzles rely on the shearing action of high speed air near a column of seeding liquid. Typically, olive oil or dioctyl phthalate (DOP) is used, but within the past year solid polystyrene particles in an alcohol suspension have been used with great success. Air, at a typical pressure of five psig, is supplied to the top of the nozzle which is merely a hollow tube. This air issues radially from one or more small jets located near the collar close to the bottom of the tube. When the collar is submerged in the seeding liquid, the hollow columns located in the collar become filled with liquid. The air from the jet shears the liquid into the fine mist

TriCheck: Memory Model Verification at the Trisection of Software, Hardware, and ISA

Memory consistency models (MCMs) which govern inter-module interactions in a shared memory system, are a significant, yet often under-appreciated, aspect of system design. MCMs are defined at the various layers of the hardware-software stack, requiring thoroughly verified specifications, compilers, and implementations at the interfaces between layers. Current verification techniques evaluate segments of the system stack in isolation, such as proving compiler mappings from a high-level language (HLL) to an ISA or proving validity of a microarchitectural implementation of an ISA. This paper makes a case for full-stack MCM verification and provides a toolflow, TriCheck, capable of verifying that the HLL, compiler, ISA, and implementation collectively uphold MCM requirements. The work showcases TriCheck's ability to evaluate a proposed ISA MCM in order to ensure that each layer and each mapping is correct and complete. Specifically, we apply TriCheck to the open source RISC-V ISA, seeking to verify accurate, efficient, and legal compilations from C11. We uncover under-specifications and potential inefficiencies in the current RISC-V ISA documentation and identify possible solutions for each. As an example, we find that a RISC-V-compliant microarchitecture allows 144 outcomes forbidden by C11 to be observed out of 1,701 litmus tests examined. Overall, this paper demonstrates the necessity of full-stack verification for detecting MCM-related bugs in the hardware-software stack.Comment: Proceedings of the Twenty-Second International Conference on Architectural Support for Programming Languages and Operating System

Bistable molecular conductors with a field-switchable dipole group

A class of bistable "stator-rotor" molecules is proposed, where a stationary bridge (stator) connects the two electrodes and facilitates electron transport between them. The rotor part, which has a large dipole moment, is attached to an atom of the stator via a single sigma bond. Hydrogen bonds formed between the rotor and stator make the symmetric orientation of the dipole unstable. The rotor has two potential minima with equal energy for rotation about the sigma bond. The dipole orientation, which determines the conduction state of the molecule, can be switched by an external electric field that changes the relative energy of the two potential minima. Both orientation of the rotor correspond to asymmetric current-voltage characteristics that are the reverse of each other, so they are distinguishable electrically. Such bistable stator-rotor molecules could potentially be used as parts of molecular electronic devices.Comment: 8 pages, 7 figure

Folding of a donor–acceptor polyrotaxane by using noncovalent bonding interactions

Mechanically interlocked compounds, such as bistable catenanes and bistable rotaxanes, have been used to bring about actuation in nanoelectromechanical systems (NEMS) and molecular electronic devices (MEDs). The elaboration of the structural features of such rotaxanes into macromolecular materials might allow the utilization of molecular motion to impact their bulk properties. We report here the synthesis and characterization of polymers that contain π electron-donating 1,5-dioxynaphthalene (DNP) units encircled by cyclobis(paraquat-p-phenylene) (CBPQT4+), a π electron-accepting tetracationic cyclophane, synthesized by using the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The polyrotaxanes adopt a well defined “folded” secondary structure by virtue of the judicious design of two DNP-containing monomers with different binding affinities for CBPQT4+. This efficient approach to the preparation of polyrotaxanes, taken alongside the initial investigations of their chemical properties, sets the stage for the preparation of a previously undescribed class of macromolecular architectures

Exposing errors related to weak memory in GPU applications

© 2016 ACM.We present the systematic design of a testing environment that uses stressing and fuzzing to reveal errors in GPU applications that arise due to weak memory effects. We evaluate our approach on seven GPUS spanning three NVIDIA architectures, across ten CUDA applications that use fine-grained concurrency. Our results show that applications that rarely or never exhibit errors related to weak memory when executed natively can readily exhibit these errors when executed in our testing environment. Our testing environment also provides a means to help identify the root causes of such errors, and automatically suggests how to insert fences that harden an application against weak memory bugs. To understand the cost of GPU fences, we benchmark applications with fences provided by the hardening strategy as well as a more conservative, sound fencing strategy

Mapping the Evolution of Optically-Generated Rotational Wavepackets in a Room Temperature Ensemble of D2_2

A coherent superposition of rotational states in D$_2$ has been excited by nonresonant ultrafast (12 femtosecond) intense (2 $\times$ 10$^{14}$ Wcm$^{-2}$) 800 nm laser pulses leading to impulsive dynamic alignment. Field-free evolution of this rotational wavepacket has been mapped to high temporal resolution by a time-delayed pulse, initiating rapid double ionization, which is highly sensitive to the angle of orientation of the molecular axis with respect to the polarization direction, $\theta$. The detailed fractional revivals of the neutral D$_2$ wavepacket as a function of $\theta$ and evolution time have been observed and modelled theoretically.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. A. Full reference to follow.

Is Alpha-Synuclein Loss-of-Function a Contributor to Parkinsonian Pathology? Evidence from Non-human Primates

Accumulation of alpha-synuclein (α-syn) in Lewy bodies and neurites of midbrain dopamine neurons is diagnostic for Parkinson’s disease (PD), leading to the proposal that PD is a toxic gain-of-function synucleinopathy. Here we discuss the alternative viewpoint that α-syn displacement from synapses by misfolding and aggregation results in a toxic loss-of-function. In support of this hypothesis we provide evidence from our pilot study demonstrating that knockdown of endogenous α-syn in dopamine neurons of nonhuman primates reproduces the pattern of nigrostriatal degeneration characteristic of PD

The first magnetic maps of a pre-main sequence binary star system - HD 155555

We present the first maps of the surface magnetic fields of a pre-main sequence binary system. Spectropolarimetric observations of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) system were obtained at the Anglo-Australian Telescope in 2004 and 2007. Both datasets are analysed using a new binary Zeeman Doppler imaging (ZDI) code. This allows us to simultaneously model the contribution of each component to the observed circularly polarised spectra. Stellar brightness maps are also produced for HD 155555 and compared to previous Doppler images. Our radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes. We find rings of azimuthal field on both stars, most of which are found to be non-axisymmetric with the stellar rotational axis. We also examine the field strength and the relative fraction of magnetic energy stored in the radial and azimuthal field components at both epochs. A marked weakening of the field strength of the secondary star is observed between the 2004 and 2007 epochs. This is accompanied by an apparent shift in the location of magnetic energy from the azimuthal to radial field. We suggest that this could be indicative of a magnetic activity cycle. We use the radial magnetic maps to extrapolate the coronal field (by assuming a potential field) for each star individually - at present ignoring any possible interaction. The secondary star is found to exhibit an extreme tilt (~75 deg) of its large scale magnetic field to that of its rotation axis for both epochs. The field complexity that is apparent in the surface maps persists out to a significant fraction of the binary separation. Any interaction between the fields of the two stars is therefore likely to be complex also. Modelling this would require a full binary field extrapolation.Comment: 17 pages, 12 figures, accepted for publication in MNRA