1,505 research outputs found
Recommended from our members
Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers
The results of an experimental study into the oxidative degradation of proxies for atmospheric aerosol are presented. We demonstrate that the laser Raman tweezers method can be used successfully to obtain uptake coeffcients for gaseous oxidants on individual aqueous and organic droplets, whilst the size and composition of the droplets is simultaneously followed. A laser tweezers system was used to trap individual droplets containing an unsaturated organic compound in either an aqueous or organic ( alkane) solvent. The droplet was exposed to gas- phase ozone and the reaction kinetics and products followed using Raman spectroscopy. The reactions of three different organic compounds with ozone were studied: fumarate anions, benzoate anions and alpha pinene. The fumarate and benzoate anions in aqueous solution were used to represent components of humic- like substances, HULIS; a alpha- pinene in an alkane solvent was studied as a proxy for biogenic aerosol. The kinetic analysis shows that for these systems the diffusive transport and mass accommodation of ozone is relatively fast, and that liquid- phase di. ffusion and reaction are the rate determining steps. Uptake coe. ffcients, g, were found to be ( 1.1 +/- 0.7) x 10(-5), ( 1.5 +/- 0.7) x 10 (-5) and ( 3.0 - 7.5) x 10 (-3) for the reactions of ozone with the fumarate, benzoate and a- pinene containing droplets, respectively. Liquid- phase bimolecular rate coe. cients for reactions of dissolved ozone molecules with fumarate, benzoate and a- pinene were also obtained: k(fumarate) = ( 2.7 +/- 2) x 10 (5), k(benzoate) = ( 3.5 +/- 3) x 10 (5) and k(alpha-pinene) = ( 1-3) x 10(7) dm(3) mol (-1) s (- 1). The droplet size was found to remain stable over the course of the oxidation process for the HULIS- proxies and for the oxidation of a- pinene in pentadecane. The study of the alpha- pinene/ ozone system is the first using organic seed particles to show that the hygroscopicity of the particle does not increase dramatically over the course of the oxidation. No products were detected by Raman spectroscopy for the reaction of benzoate ions with ozone. One product peak, consistent with aqueous carbonate anions, was observed when following the oxidation of fumarate ions by ozone. Product peaks observed in the reaction of ozone with alpha- pinene suggest the formation of new species containing carbonyl groups
A survey of spinning test particle orbits in Kerr spacetime
We investigate the dynamics of the Papapetrou equations in Kerr spacetime.
These equations provide a model for the motion of a relativistic spinning test
particle orbiting a rotating (Kerr) black hole. We perform a thorough parameter
space search for signs of chaotic dynamics by calculating the Lyapunov
exponents for a large variety of initial conditions. We find that the
Papapetrou equations admit many chaotic solutions, with the strongest chaos
occurring in the case of eccentric orbits with pericenters close to the limit
of stability against plunge into a maximally spinning Kerr black hole. Despite
the presence of these chaotic solutions, we show that physically realistic
solutions to the Papapetrou equations are not chaotic; in all cases, the
chaotic solutions either do not correspond to realistic astrophysical systems,
or involve a breakdown of the test-particle approximation leading to the
Papapetrou equations (or both). As a result, the gravitational radiation from
bodies spiraling into much more massive black holes (as detectable, for
example, by LISA, the Laser Interferometer Space Antenna) should not exhibit
any signs of chaos.Comment: Submitted to Phys. Rev. D. Follow-up to gr-qc/0210042. Figures are
low-resolution in order to satisfy archive size constraints; a
high-resolution version is available at http://www.michaelhartl.com/papers
An analysis of the FIR/RADIO Continuum Correlation in the Small Magellanic Cloud
The local correlation between far-infrared (FIR) emission and radio-continuum
(RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales
from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ~15 pc.
The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is
shown to be greatest in the most active star forming regions with a power law
slope of ~1.14 indicating that the RC emission increases faster than the FIR
emission. The slope of the other regions and the SMC are much flatter and in
the range of 0.63-0.85. The slopes tend to follow the thermal fractions of the
regions which range from 0.5 to 0.95. The thermal fraction of the RC emission
alone can provide the expected FIR/RC correlation. The results are consistent
with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray
electrons (CRe-s) diffusing away from the star forming regions. Since the CRe-s
appear to escape the SMC so readily, the results here may not provide support
for coupling between the local gas density and the magnetic field intensity.Comment: 19 pages, 7 Figure
Configurations of Entrepreneurial Orientation, Knowledge Management, and Positional Advantage: A Comparative Analysis between Native and Immigrant Entrepreneurial Firms (abstract only)
Entrepreneurial firms survive and ultimately succeed when they are able to marshal their resources
into productive advantages. The entrepreneurial orientation (EO) and knowledge management
(KM) process are broadly seen as antecedents to such an outcome. However, the interplay between
EO and KM elements through a configurational approach is still unaccounted for. Moreover, the
existing literature is replete with single solutions for entrepreneurs and managers. But,
advancements in configuration theory suggest that EO may combine with elements of KM in
different ways to create separate but equifinal pathways to performance. In addition, the
contingency theory suggests that these configurational paths are contextually dependent.
Moreover, contingency theory also proffers that these configurational pathways may differ for
native versus immigrant entrepreneurial firms. To address these research gaps, we perform a fuzzyset qualitative comparative analysis (fsQCA) on data collected from service-oriented firms owned
by native and immigrant entrepreneurs in Malaysia. Our results identify that configurational paths
vary based on the types of firms. Four causal pathways are identified for immigrant entrepreneurial
firms and five pathways for native firms. Although EO is critical for both types of firms, different
configurational paths of KM elements are identified, which are further complemented by positional
advantages in achieving performance success. We opine that knowledge acquisition and
application ensure intelligent conversion of EO behaviour. Secondly, EO itself can create valuable
knowledge; thereby, the acquisition and application are bypassed, and knowledge conversion and
protection becoming critical for holistic success
Solar Flares and Coronal Mass Ejections: A Statistically Determined Flare Flux-CME Mass Correlation
In an effort to examine the relationship between flare flux and corresponding
CME mass, we temporally and spatially correlate all X-ray flares and CMEs in
the LASCO and GOES archives from 1996 to 2006. We cross-reference 6,733 CMEs
having well-measured masses against 12,050 X-ray flares having position
information as determined from their optical counterparts. For a given flare,
we search in time for CMEs which occur 10-80 minutes afterward, and we further
require the flare and CME to occur within +/-45 degrees in position angle on
the solar disk. There are 826 CME/flare pairs which fit these criteria.
Comparing the flare fluxes with CME masses of these paired events, we find CME
mass increases with flare flux, following an approximately log-linear, broken
relationship: in the limit of lower flare fluxes, log(CME mass)~0.68*log(flare
flux), and in the limit of higher flare fluxes, log(CME mass)~0.33*log(flare
flux). We show that this broken power-law, and in particular the flatter slope
at higher flare fluxes, may be due to an observational bias against CMEs
associated with the most energetic flares: halo CMEs. Correcting for this bias
yields a single power-law relationship of the form log(CME mass)~0.70*log(flare
flux). This function describes the relationship between CME mass and flare flux
over at least 3 dex in flare flux, from ~10^-7 to 10^-4 W m^-2.Comment: 28 pages, 16 figures, accepted to Solar Physic
On the application of radio frequency voltages to ion traps via helical resonators
Ions confined using a Paul trap require a stable, high voltage and low noise
radio frequency (RF) potential. We present a guide for the design and
construction of a helical coil resonator for a desired frequency that maximises
the quality factor for a set of experimental constraints. We provide an
in-depth analysis of the system formed from a shielded helical coil and an ion
trap by treating the system as a lumped element model. This allows us to
predict the resonant frequency and quality factor in terms of the physical
parameters of the resonator and the properties of the ion trap. We also compare
theoretical predictions with experimental data for different resonators, and
predict the voltage applied to the ion trap as a function of the Q-factor,
input power and the properties of the resonant circuit
Perspectives on the future of manufacturing within the Industry 4.0 era
The technological choices facing the manufacturing industry are vast and complex as the industry contemplates the increasing levels of digitization and automation in readiness for the modern competitive age. These changes broadly categorized as Industry 4.0, offer significant transformation challenges and opportunities, impacting a multitude of operational aspects of manufacturing organizations. As manufacturers seek to deliver increased levels of productivity and adaptation by innovating many aspects of their business and operational processes, significant challenges and barriers remain. The roadmap toward Industry 4.0 is complex and multifaceted, as manufacturers seek to transition toward new and emerging technologies, whilst retaining operational effectiveness and a sustainability focus. This study approaches many of these significant themes by presenting a critical evaluation of the core topics impacting the next generation of manufacturers, challenges and key barriers to implementation. These factors are further evaluated via the presentation of a new Industry 4.0 framework and alignment of I4.0 themes with the UN Sustainability Goals
Diffusion-limited reactions and mortal random walkers in confined geometries
Motivated by the diffusion-reaction kinetics on interstellar dust grains, we
study a first-passage problem of mortal random walkers in a confined
two-dimensional geometry. We provide an exact expression for the encounter
probability of two walkers, which is evaluated in limiting cases and checked
against extensive kinetic Monte Carlo simulations. We analyze the continuum
limit which is approached very slowly, with corrections that vanish
logarithmically with the lattice size. We then examine the influence of the
shape of the lattice on the first-passage probability, where we focus on the
aspect ratio dependence: Distorting the lattice always reduces the encounter
probability of two walkers and can exhibit a crossover to the behavior of a
genuinely one-dimensional random walk. The nature of this transition is also
explained qualitatively.Comment: 18 pages, 16 figure
Quantum cryptography using balanced homodyne detection
We report an experimental quantum key distribution that utilizes balanced
homodyne detection, instead of photon counting, to detect weak pulses of
coherent light. Although our scheme inherently has a finite error rate, it
allows high-efficiency detection and quantum state measurement of the
transmitted light using only conventional devices at room temperature. When the
average photon number was 0.1, an error rate of 0.08 and "effective" quantum
efficiency of 0.76 were obtained.Comment: Errors in the sentence citing ref.[20] are correcte
In vitro neuroprotective activities of two distinct probiotic consortia
Neurodegeneration has been linked to changes in the gut microbiota and this study compares the neuroprotective capability of two bacterial consortia, known as Lab4 and Lab4b, using the established SH-SY5Y neuronal cell model. Firstly, varying total antioxidant capacities (TAC) were identified in the intact cells from each consortia and their secreted metabolites, referred to as conditioned media (CM). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Crystal Violet (CV) assays of cell viability revealed that Lab4 CM and Lab4b CM could induce similar levels of proliferation in SH-SY5Y cells and, despite divergent TAC, possessed a comparable ability to protect undifferentiated and retinoic acid-differentiated cells from the cytotoxic actions of rotenone and undifferentiated cells from the cytotoxic actions of 1-methyl-4-phenylpyridinium iodide (MPP+). Lab4 CM and Lab4b CM also had the ability to attenuate rotenone-induced apoptosis and necrosis with Lab4b inducing the greater effect. Both consortia showed an analogous ability to attenuate intracellular reactive oxygen species accumulation in SH-SY5Y cells although the differential upregulation of genes encoding glutathione reductase and superoxide dismutase by Lab4 CM and Lab4b CM, respectively, implicates the involvement of consortia-specific antioxidative mechanisms of action. This study implicates Lab4 and Lab4b as potential neuroprotective agents and justifies their inclusion in further in vivo studies
- …