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

Where is the pi particle?

We discuss the interplay of particle-particle and particle-hole spin-triplet channels in high-T_c superconductors using a quasiparticle dispersion motivated by angle-resolved photoemission. Within a generalized RPA, we find a well defined antibound state of two holes, the pi resonance of Demler and Zhang, as well as a bound state of a particle and a hole, the spin exciton. We show that the energy of the pi resonance always exceeds 2 Delta, twice the maximum d-wave gap, therefore the neutron resonance observed in the cuprates around energy Delta is most likely a spin exciton. At the same time, we speculate that the pi particle can exist at higher energies and might be observed in neutron scattering around 100 meV.Comment: RevTeX, 5 pages, 4 eps figure

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

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 $\Gamma$ and $K$ points in the BZ. This spin-1 mode has a wide energy dispersion, 0 to $\sim 2 eV$ 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

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.

A link between the spin fluctuation and Fermi surface in high T_C cuprates --- A consistent description within the single-band Hubbard model

A link between the spin fluctuation and the "fermiology" is explored for the single-band Hubbard model within the fluctuation exchange (FLEX) approximation. We show that the experimentally observed peak position of the spin structure in the high T_C cuprates can be understood from the model that reproduces the experimentally observed Fermi surface. In particular, both the variation of the incommensurability of the peak in the spin structure and the evolution of the Fermi surface with hole doping in La_{2-x}Sr_xCuO_4 may be understood with a second nearest neighbor hopping decreasing with hole doping.Comment: 5 pages, RevTeX, uses epsf.sty and multicol.st

Resonant Spin Excitation in an Overdoped High Temperature Superconductor

An inelastic neutron scattering study of overdoped Bi_2Sr_2CaCu_2O_{8+\delta} $ (T_c = 83 K) has revealed a resonant spin excitation in the superconducting state. The mode energy is E_res=38 meV, significantly lower than in optimally doped Bi_2Sr_2CaCu_2O_{8+\delta} (T_c = 91 K, E_ res =43 meV). This observation, which indicates a constant ratio E_res /k_B T_c \sim 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high-temperature superconductors.Comment: final version: PRL 86, 1610 (2001

Quantum Impurities and the Neutron Resonance Peak in YBa2Cu3O7{\bf YBa_2 Cu_3 O_7}: Ni versus Zn

The influence of magnetic (S=1) and nonmagnetic (S=0) impurities on the spin dynamics of an optimally doped high temperature superconductor is compared in two samples with almost identical superconducting transition temperatures: YBa$_2$(Cu$_{0.97}$Ni$_{0.03}$)$_3$O$_7$ (T$_c$=80 K) and YBa$_2$(Cu$_{0.99}$Zn$_{0.01}$)$_3$O$_7$ (T$_c$=78 K). In the Ni-substituted system, the magnetic resonance peak (which is observed at E$_r \simeq$40 meV in the pure system) shifts to lower energy with a preserved E$_r$/T$_c$ ratio while the shift is much smaller upon Zn substitution. By contrast Zn, but not Ni, restores significant spin fluctuations around 40 meV in the normal state. These observations are discussed in the light of models proposed for the magnetic resonance peak.Comment: 3 figures, submitted to PR

El estudio de los riesgos con origen hidrológico en el su-reste de la Península Ibérica. Enfoque geográfico y plani-ficación territorial

This paper shows the current studies on hydrological risks in the outh-east Spain, a region specially producing hazard situations. This area is one of the most arid regions of Europe, characterized by extraordinary rains of high hourly intensity causing bulky discharges and overflows, but also by the installation of dense urban nucleus in coastal areas and fertile plains. The scanty one, or in occasions unfortunate, dialog between environment and man has done of this one an area of notable interest for numerous researchers on the risk processes associated with hydrological extreme events. The ephemeral flow regime and the hydraulic effects of the linear infrastructures and drainage works complicate the estimation of the flood discharges, increasing the above mentioned degree of complexity. There are several models, programs and projects focused on these questions, but a major knowledge is still absent on this type of risk processes, particularly in relation with the generation of flood areas. For it is necessary a cartographic information base of more detail and the incorporation of factors till now very little considered as those hydro-morphological or the indicators of vulnerability.El presente artículo muestra el estado de la cuestión en el análisis de los riesgos hidrológicos de una región natural española especialmente productora de situaciones de peligro: el Sureste de la Península Ibérica. Los graves impactos que este tipo de peligros naturales tienen en la economía, la sociedad y el medio ambiente de esta región hacen que el enfoque geográfico revista aquí especial importancia en el estudio de sus riesgos derivados, particularmente en relación con la evaluación y gestión de los mismos, y su indudable implicación en las políticas de planificación territorial. Ésta es una de las regiones más áridas de Europa, caracterizada por lluvias extraordinarias de alta intensidad horaria capaces provocar abultados caudales y desbordamientos de cauces, pero también por la instalación de núcleos densos de poblamiento en sus áreas litorales y de vega. El escaso, o en ocasiones desafortunado, diálogo entre me-dio natural y hombre ha hecho de ésta una zona de notable interés para gran número de investigadores en temas de riesgos asociados a fenómenos hidrológicos extremos. El carácter efímero de las corrientes y los efectos hidráulicos de las infraestructuras lineales y obras de drenaje complican la estimación de los cau-dales de avenida, aumentando dicho grado de complejidad. Aun cuando existen ya varios modelos, pro-gramas y proyectos enfocados a estas cuestiones todavía falta un mayor conocimiento sobre este tipo de procesos de riesgo, particularmente en relación con la generación de áreas inundables, para la que se ne-cesita una información cartográfica base de mayor detalle y la incorporación de factores hasta ahora muy poco considerados como los hidromorfológicos o los indicadores de vulnerabilidad

Renormalized mean-field theory of the neutron scattering in cuprate superconductors

The magnetic excitation spectrum of the t-t'-J-model is studied in mean-field theory and compared to inelastic neutron-scattering (INS) experiments on YBCO and BSCCO superconductors. Within the slave-particle formulation the dynamical spin response is calculated from a renormalized Fermi liquid with an effective interaction ~J in the magnetic particle--hole channel. We obtain the so-called 41meV resonance at wave vector (pi,pi) as a collective spin-1 excitation in the d-wave superconducting state. It appears sharp (undamped), if the underlying Fermi surface is hole-like with a sufficient next-nearest-neighbor hopping t'<0. The double-layer structure of YBCO or BSCCO is not important for the resonance to form. The resonance energy \omega_{res} and spectral weight at optimal doping come out comparable to experiment. The observed qualitative behavior of \omega_{res} with hole filling is reproduced in the underdoped as well as overdoped regime. A second, much broader peak becomes visible in the magnetic excitation spectrum if the 2D wave-vector is integrated over. It is caused by excitations across the maximum gap, and in contrast to the resonance its energy is almost independent of doping. At energies above or below \omega_{res} the commensurate resonance splits into incommensurate peaks, located off (pi,pi). Below \omega_{res} the intensity pattern is of `parallel' type and the dispersion relation of incommensurate peaks has a negative curvature. This is in accordance with recent INS experiments on YBCO.Comment: 17pp including 14 figure