587 research outputs found
Short-lived brominated hydrocarbons – observations in the source regions and the tropical tropopause layer
We conducted measurements of the five important short-lived organic bromine species in the marine boundary layer (MBL). Measurements were made in the Northern Hemisphere mid-latitudes (Sylt Island, North Sea) in June 2009 and in the tropical Western Pacific during the TransBrom ship campaign in October 2009. For the one-week time series on Sylt Island, mean mixing ratios of CHBr3, CH2Br2, CHBr2Cl and CH2BrCl were 2.0, 1.1, 0.2, 0.1 ppt, respectively. We found maxima of 5.8 and 1.6 ppt for the two main components CHBr3 and CH2Br2. Along the cruise track in the Western Pacific (between 41° N and 13° S) we measured mean mixing ratios of 0.9, 0.9, 0.2, 0.1 and 0.1 ppt for CHBr3, CH2Br2, CHBrCl2, CHBr2Cl and CH2BrCl. Air samples with coastal influence showed considerably higher mixing ratios than the samples with open ocean origin. Correlation analyses of the two data sets yielded strong linear relationships between the mixing ratios of four of the five species (except for CH2BrCl). Using a combined data set from the two campaigns and a comparison with the results from two former studies, rough estimates of the molar emission ratios between the correlated substances were: 9/1/0.35/0.35 for CHBr3/CH2Br2/CHBrCl2/CHBr2Cl. Additional measurements were made in the tropical tropopause layer (TTL) above Teresina (Brazil, 5° S) in June 2008, using balloon-borne cryogenic whole air sampling technique. Near the level of zero clear-sky net radiative heating (LZRH) at 14.8 km about 2.25 ppt organic bromine was bound to the five short-lived species, making up 13% of total organic bromine (17.82 ppt). CH2Br2 (1.45 ppt) and CHBr3 (0.56 ppt) accounted for 90% of the budget of short-lived compounds in that region. Near the tropopause (at 17.5 km) organic bromine from these substances was reduced to 1.35 ppt, with 1.07 and 0.12 ppt attributed to CH2Br2 and CHBr3, respectively
Deformation and phase transformation in polycrystalline cementite (FeC) during single- and multi-pass sliding wear
Cementite (FeC) plays a major role in the tribological performance of rail and bearing steels. Nonetheless, the current understanding of its deformation behavior during wear is limited because it is conventionally embedded in a matrix. Here, we investigate the deformation and chemical evolution of bulk polycrystalline cementite during single-pass sliding at a contact pressure of 31 GPa and reciprocating multi-pass sliding at 3.3 GPa. The deformation behavior of cementite was studied by electron backscatter diffraction for slip trace analysis and transmission electron microscopy. Our results demonstrate activation of several deformation mechanisms below the contact surface: dislocation slip, shear band formation, fragmentation, grain boundary sliding, and grain rotation. During sliding wear, cementite ductility is enhanced due to the confined volume, shear/compression domination, and potentially frictional heating. The microstructural alterations during multi-pass wear increase the subsurface nanoindentation hardness by up to 2.7 GPa. In addition, we report Hägg carbide (FeC) formation in the uppermost deformed regions after both sliding experiments. Based on the results of electron and X-ray diffraction, as well as atom probe tomography, we propose potential sources of excess carbon and mechanisms that promote the phase transformation
N\'eel transition, spin fluctuations, and pseudogap in underdoped cuprates by a Lorentz invariant four-fermion model in 2+1 dimensions
We show that the N\'eel transition and spin fluctuations near the N\'eel
transition in planar cuprates can be described by an SU(2) invariant
relativistic four-fermion model in 2+1 dimensions. Features of the pseudogap
phenomenon are naturally described by the appearance of an anomalous dimension
for the spinon propagator.Comment: 5 pages, 2 figures (revtex4). Final revised and corrected versio
Predicting a Gapless Spin-1 Neutral Collective Mode branch for Graphite
Using the standard tight binding model of 2d graphite with short range
electron repulsion, we find a gapless spin-1, neutral collective mode branch
{\em below the particle-hole continuum} with energy vanishing linearly with
momenta at the and points in the BZ. This spin-1 mode has a wide
energy dispersion, 0 to and is not Landau damped. The `Dirac cone
spectrum' of electrons at the chemical potential of graphite generates our
collective mode; so we call this `spin-1 zero sound' of the `Dirac sea'.
Epithermal neutron scattering experiments, where graphite single crystals are
often used as analyzers (an opportunity for `self-analysis'!), and spin
polarized electron energy loss spectroscopy (SPEELS) can be used to confirm and
study our collective mode.Comment: 4 pages of LaTex file, 3 eps figure file
Increased fibrosis in a mouse model of anti-laminin 332 mucous membrane pemphigoid remains unaltered by inhibition of aldehyde dehydrogenase
Mucous membrane pemphigoid (MMP) is an autoimmune blistering disease characterized by autoantibodies against the basal membrane zone of skin and surface-close epithelia and predominant mucosal lesions. The oral cavity and conjunctivae are most frequently affected, albeit clinical manifestations can also occur on the skin. MMP-associated lesions outside the oral cavity typically lead to scarring. Mechanisms underlying scarring are largely unknown in MMP and effective treatment options are limited. Herein, we assessed the collagen architecture in tissue samples of an antibody-transfer mouse model of anti-laminin-332 MMP. In MMP mice, increased collagen fibril density was observed in skin and conjunctival lesions compared to mice injected with normal rabbit IgG. The extracellular matrix of MMP skin samples also showed altered post-translational collagen cross-linking with increased levels of both lysine- and hydroxylysine-derived collagen crosslinks supporting the fibrotic phenotype in experimental MMP compared to control animals. In addition, we evaluated a potential anti-fibrotic therapy in experimental anti-laminin-332 MMP using disulfiram, an inhibitor of the aldehyde dehydrogenase (ALDH), which has been implicated in immune-mediated mucosal scarring. In addition, disulfiram also acts as a copper chelator that was shown to block lysyl oxidase activity, an enzyme involved in formation of collagen crosslinks. Topical use of disulfiram (300 μM in 2 [w/v] methocel) did not improve ocular lesions in experimental MMP over the 12-day treatment period in disulfiram-treated mice compared to vehicle-treated mice (n=8/group). Furthermore, C57BL6/J mice (n=8/group) were treated prophylactically with 200 mg/kg p.o. disulfiram or the solvent once daily over a period of 12 days. Systemic treatment did not show any reduction in the severity of oral and ocular lesions in MMP mice, albeit some improvement in skin lesions was observed in disulfiram- vs. vehicle-treated mice (p=0.052). No reduction in fibrosis was seen, as assessed by immunohistochemistry. Whilst blocking of ALDH failed to significantly ameliorate disease activity, our data provide new insight into fibrotic processes highlighting changes in the collagenous matrix and cross-linking patterns in IgG-mediated MMP
Exploring Entrepreneurial Skills and Competencies in Farm Tourism
Diversification to farm tourism is increasingly seen as a viable development strategy to promote a more diverse and sustainable rural economy and to counter declining farm incomes. However, our understanding of the dynamics of the modern farm tourism business and the entrepreneurial and competitive skills farmers require in making the transition from agriculture to a diversified - and service based - enterprise remains limited. Hence, the aim of this paper is to explore the range of skills and competencies that farmers in the North West of England identify as important when adopting a diversification strategy to farm tourism. With the findings indicating that that whilst a range of managerial skills are valued by farmers, they lack many of the additional business and entrepreneurial competencies required for success. Moreover, this paper acknowledges the need to generate consensus on the requisite skill-set that farm tourism operators require, along with a need for a currently fragmented rural tourism literature to acknowledge the significance of rural entrepreneurship and the characteristics of successful farmers and farm tourism ventures
Interlayer pair tunneling and gap anisotropy in YBaCuO
Recent ARPES measurement observed a large -axis gap anisotropy,
, in clean YBaCuO. This
indicates that some sub-dominant component may exist in the -wave
dominant gap. We propose that the interlayer pairing tunneling contribution can
be determined through the investigation of the order parameter anisotropy.
Their potentially observable features in transport and spin dynamics are also
studied.Comment: 4 pages, 3 figure
The magnetic neutron scattering resonance of high-T_c superconductors in external magnetic fields: an SO(5) study
The magnetic resonance at 41 meV observed in neutron scattering studies of Y
Ba_2 Cu_3 O_7 holds a key position in the understanding of high-T_c
superconductivity. Within the SO(5) model for superconductivity and
antiferromagnetism, we have calculated the effect of an applied magnetic field
on the neutron scattering cross-section of the magnetic resonance. In the
presence of vortices, the neutron scattering cross-section shows clear
signatures of not only the fluctuations in the superconducting order parameter
\psi, but also the modulation of the phase of \psi due to vortices. In
reciprocal space we find that i) the scattering amplitude is zero at
(pi/a,pi/a), ii) the resonance peak is split into a ring with radius pi/d
centered at (pi/a,pi/a), d being the vortex lattice constant, and consequently,
iii) the splitting pi/d scales with the magnetic field as sqrt{B}.Comment: 4 pages including 3 eps-figures - minor changes and one reference
added. Accepted for publication in Phys. Rev.
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