10,559 research outputs found
Large-scale instabilities in a STOVL upwash fountain
The fountain flow created by two underexpanded axisymmetric, turbulent jets
impinging on a ground plane was studied through the use of laser-based
experimental techniques. Velocity and turbulence data were acquired in the jet
and fountain flow regions using laser doppler velocimetry and particle image
velocimetry. Profiles of mean and rms velocities along the jet centreline are
presented for nozzle pressure ratios of two, three and four. The unsteady nature
of the fountain flow was examined and the presence of large-scale coherent
structures identified. A spectral analysis of the fountain flow data was
performed using the Welch method. The results have relevance to ongoing studies
of the fountain flow using large eddy simulation techniques
Microfluidics for protein biophysics
Microfluidics has the potential to transform experimental approaches across the life sciences. In this review, we discuss recent advances enabled by the development and application of microfluidic approaches to protein biophysics. We focus on areas where key fundamental features of microfluidics open up new possibilities and present advantages beyond low volumes and short time-scale analysis, conventionally provided by microfluidics. We discuss the two most commonly used forms of microfluidic technology, single-phase laminar flow and multiphase microfluidics. We explore how the understanding and control of the characteristic physical features of the microfluidic regime, the integration of microfluidics with orthogonal systems and the generation of well-defined microenvironments can be used to develop novel devices and methods in protein biophysics for sample manipulation, functional and structural studies, detection and material processing
Probing quasiparticle excitations in a hybrid single electron transistor
We investigate the behavior of quasiparticles in a hybrid electron turnstile
with the aim of improving its performance as a metrological current source. The
device is used to directly probe the density of quasiparticles and monitor
their relaxation into normal metal traps. We compare different trap geometries
and reach quasiparticle densities below 3um^-3 for pumping frequencies of 20
MHz. Our data show that quasiparticles are excited both by the device operation
itself and by the electromagnetic environment of the sample. Our observations
can be modelled on a quantitative level with a sequential tunneling model and a
simple diffusion equation
Measurement of the Michel Parameter xi" in Polarized Muon Decay and Implications on Exotic Couplings of the Leptonic Weak Interaction
The Michel parameter xi" has been determined from a measurement of the
longitudinal polarization of positrons emitted in the decay of polarized and
depolarized muons. The result, xi" = 0.981 +- 0.045stat +- 0.003syst, is
consistent with the Standard Model prediction of unity, and provides an order
of magnitude improvement in the relative precision of this parameter. This
value sets new constraints on exotic couplings beyond the dominant V-A
description of the leptonic weak interaction.Comment: 15 pages, 16 figures, 3 tables; submitted to Phys. Rev.
Nitrogenase activity associated with codium species from New Zealand marine habitats
Nitrogenase activity, measured as acetylene reduction, was recorded at rates up to 1028 nmol.h \g * dry weight for Codium adhaerens (Cabr.) Ag. var. convolutum Dellow and Codium fragile (Sur.) Hariot subsp. tomentosoides (Van Goor) Silva collected from New Zealand habitats. In both species the ability to reduce acetylene is invariably associated with the presence of a heterocystous blue-green alga, Calothrix sp., epiphytic or embedded in the Codium thallus. A highly significant (P < 0.001) correlation between heterocyst frequency and nitrogenase activity was found. Nitrogenase and net photosynthesis of the Codium-Calothrix system have different steady-state responses to light intensity, and the kinetics of the two processes also differ in that nitrogenase is slow to respond to illumination or darkening. Glucose additions to Codium did not significantly increase nitrogenase activity. Nitrogenase is relatively insensitive to oxygen tension over the range 0-1.0 atm (0-1.033 kgf.cnT2) and still occurs at 1.5 atm (1.55 kgf.cm"2); this condition is unique in all nitrogenase systems thus far reported. Collectively these facts suggest that Calothrix is the agent primarily responsible for nitrogenase activity in these Codium species
Solution to the Equations of the Moment Expansions
We develop a formula for matching a Taylor series about the origin and an
asymptotic exponential expansion for large values of the coordinate. We test it
on the expansion of the generating functions for the moments and connected
moments of the Hamiltonian operator. In the former case the formula produces
the energies and overlaps for the Rayleigh-Ritz method in the Krylov space. We
choose the harmonic oscillator and a strongly anharmonic oscillator as
illustrative examples for numerical test. Our results reveal some features of
the connected-moments expansion that were overlooked in earlier studies and
applications of the approach
Nanoscale spatially resolved infrared spectra from single microdroplets
Droplet microfluidics has emerged as a powerful platform allowing a large
number of individual reactions to be carried out in spatially distinct
microcompartments. Due to their small size, however, the spectroscopic
characterisation of species encapsulated in such systems remains challenging.
In this paper, we demonstrate the acquisition of infrared spectra from single
microdroplets containing aggregation-prone proteins. To this effect, droplets
are generated in a microfluidic flow-focussing device and subsequently
deposited in a square array onto a ZnSe prism using a micro stamp. After
drying, the solutes present in the droplets are illuminated locally by an
infrared laser through the prism, and their thermal expansion upon absorption
of infrared radiation is measured with an atomic force microscopy tip, granting
nanoscale resolution. Using this approach, we resolve structural differences in
the amide bands of the spectra of monomeric and aggregated lysozyme from single
microdroplets with picolitre volume.Comment: 5 pages, 3 Figure
Benchmark full configuration-interaction calculations on HF and NH2
Full configuration-interaction (FCI) calculations are performed at selected geometries for the 1-sigma(+) state of HF and the 2-B(1) and 2-A(1) states of NH2 using both DZ and DZP gaussian basis sets. Higher excitations become more important when the bonds are stretched and the self-consistent field (SCF) reference becomes a poorer zeroth-order description of the wave function. The complete active space SCF - multireference configuration-interaction (CASSCF-MRCI) procedure gives excellent agreement with the FCI potentials, especially when corrected with a multi-reference analog of the Davidson correction
- âŠ