60 research outputs found
Anomalous triple gauge couplings from -meson and kaon observables
We consider the three CP-conserving dimension-6 operators that encode the
leading new-physics effects in the triple gauge couplings. The contributions to
the standard-model electromagnetic dipole and semi-leptonic vector and
axial-vector interactions that arise from the insertions of these operators are
calculated. We show that radiative and rare -meson decays provide, under
certain assumptions, constraints on two out of the three anomalous couplings
that are competitive with the restrictions obtained from LEP II, Tevatron and
LHC data. The constraints arising from the electroweak pseudo
observables, and are also
studied.Comment: 17 pages, 4 figures, v2: journal version, extended comments and added
reference
Strong size-dependent photoacoustic effect on gold nanoparticles: A sensitive tool for aggregation-based colorimetric protein detection
Based on measuring the change of the photoacoustic (PA) signal generated by laser-induced nanobubbles, a new way to detect gold nanoparticles (GNPs) aggregation is demonstrated and applied to selective protein detection.Fil: Liu, Xiangjiang. Technische Universitat München; AlemaniaFil: González, Martín Germán. Technische Universitat München; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Niessner, Reinhard. Technische Universitat München; AlemaniaFil: Haisch, Christoph. Technische Universitat München; Alemani
Quantification of formaldehyde production during alkaline methanol electrooxidation
The alkaline methanol electrooxidation reaction (MOR) in alkaline direct methanol fuel cells is still very little understood with regard to its electrochemical behavior. Theoretically, when using a rotating disk (RDE) as working electrode, the limiting current from an electrochemical reaction increases with the rotation rate as described by Levich. Contrary to this principle, the current resulting from the alkaline MOR does not increase, but decreases with rotation rate. In this work, we investigate the reason for this phenomenon using the method described by Nash and modified by Belman to quantify formaldehyde, a reaction intermediate of the alkaline methanol electrooxidation. The amount of formaldehyde is in direct relation to the rotation rate, proving that the current density loss can originate from an intensified removal of formaldehyde into the bulk solution. We analyse the influence of the electrolyte and methanol concentration on the formation of formaldehyde in order to investigate which conditions support the complete oxidation pathway and suppress the incomplete oxidation to formaldehyde. The concentration ratio as well as the absolute concentrations are of great importance for the pathways taking place. A low electrolyte concentration leads to an increase of the formaldehyde but decreasing the methanol concentration results in an absence of formaldehyde in the bulk solution
Assessing Lanthanide‐Dependent Methanol Dehydrogenase Activity: The Assay Matters
Artificial dye-coupled assays have been widely adopted as a rapid and convenient method to assess the activity of methanol dehydrogenases (MDH). Lanthanide(Ln)-dependent XoxF-MDHs are able to incorporate different lanthanides (Lns) in their active site. Dye-coupled assays showed that the earlier Lns exhibit a higher enzyme activity than the late Lns. Despite widespread use, there are limitations: oftentimes a pH of 9 and activators are required for the assay. Moreover, Ln-MDH variants are not obtained by isolation from the cells grown with the respective Ln, but by incubation of an apo-MDH with the Ln. Herein, we report the cultivation of Ln-dependent methanotroph Methylacidiphilum fumariolicum SolV with nine different Lns, the isolation of the respective MDHs and the assessment of the enzyme activity using the dye-coupled assay. We compare these results with a protein-coupled assay using its physiological electron acceptor cytochrome cGJ (cyt cGJ). Depending on the assay, two distinct trends are observed among the Ln series. The specific enzyme activity of La-, Ce- and Pr-MDH, as measured by the protein-coupled assay, exceeds that measured by the dye-coupled assay. This suggests that early Lns also have a positive effect on the interaction between XoxF-MDH and its cyt cGJ thereby increasing functional efficiency
Metal–Organic Framework Nanoparticles Induce Pyroptosis in Cells Controlled by the Extracellular pH
Ion homeostasis is essential for cellular survival, and elevated concentrations of specific ions are used to start distinct forms of programmed cell death. However, investigating the influence of certain ions on cells in a controlled way has been hampered due to the tight regulation of ion import by cells. Here, it is shown that lipid‐coated iron‐based metal–organic framework nanoparticles are able to deliver and release high amounts of iron ions into cells. While high concentrations of iron often trigger ferroptosis, here, the released iron induces pyroptosis, a form of cell death involving the immune system. The iron release occurs only in slightly acidic extracellular environments restricting cell death to cells in acidic microenvironments and allowing for external control. The release mechanism is based on endocytosis facilitated by the lipid‐coating followed by degradation of the nanoparticle in the lysosome via cysteine‐mediated reduction, which is enhanced in slightly acidic extracellular environment. Thus, a new functionality of hybrid nanoparticles is demonstrated, which uses their nanoarchitecture to facilitate controlled ion delivery into cells. Based on the selectivity for acidic microenvironments, the described nanoparticles may also be used for immunotherapy: the nanoparticles may directly affect the primary tumor and the induced pyroptosis activates the immune system
From dust to planetesimals: an improved model for collisional growth in protoplanetary disks
Planet formation occurs within the gas and dust rich environments of
protoplanetary disks. Observations of these objects show that the growth of
primordial sub micron sized particles into larger aggregates occurs at the
earliest stages of the disks. However, theoretical models of particle growth
that use the Smoluchowski equation to describe collisional coagulation and
fragmentation have so far failed to produce large particles while maintaining a
significant populations of small grains. This has been generally attributed to
the existence of two barriers impeding growth due to bouncing and fragmentation
of colliding particles. In this paper, we demonstrate that the importance of
these barriers has been artificially inflated through the use of simplified
models that do not take into account the stochastic nature of the particle
motions within the gas disk. We present a new approach in which the relative
velocities between two particles is described by a probability distribution
function that models both deterministic motion and stochastic motion. Taking
both into account can give quite different results to what has been considered
recently in other studies. We demonstrate the vital effect of two "ingredients"
for particle growth: the proper implementation of a velocity distribution
function that overcomes the bouncing barrier and, in combination with mass
transfer in high-mass-ratio collisions, boosts the growth of larger particles
beyond the fragmentation barrier. A robust result of our simulations is the
emergence of two particle populations (small and large), potentially explaining
simultaneously a number of long-standing problems in protoplanetary disks,
including planetesimal formation close to the central star, the presence of mm
to cm size particles far out in the disk, and the persistence of micron-size
grains for millions of years.Comment: Accepted for publication in ApJ. Additional appendix included. Minor
changes from previous versions. 46 pages, 10 figure
Complete next-to-leading order gluino contributions to b--> s gamma and b--> s g
We present the first complete order alpha_s corrections to the Wilson
coefficients (at the high scale) of the various versions of magnetic and
chromomagnetic operators which are induced by a squark-gluino exchange. For
this matching calculation, we work out the on-shell amplitudes b--> s gamma and
b --> s g, both in the full and in the effective theory up to order alpha_s^2.
The most difficult part of the calculation is the evaluation of the two-loop
diagrams in the full theory; these can be split into two classes: a) diagrams
with one gluino and a virtual gluon; b) diagrams with two gluinos or with one
gluino and a four-squark vertex. Accordingly, the Wilson coefficients can be
split into a part a) and a part b). While part b) of the Wilson coefficients is
presented in this paper for the first time, part a) was given in (Bobeth et
al.). We checked their results for the coefficients of the magnetic operators
and found perfect agreement. Moreover, we work out the renormalization
procedure in great detail. Our results for the complete next-to-leading order
Wilson coefficients are fully analytic, but far too long to be printed. We
therefore publish them in the form of a C++ program. They constitute a crucial
building block for the phenomenological next-to-leading logarithmic analysis of
the branching ratio Bbar --> X_s gamma in a supersymmetric model beyond minimal
flavor violation.Comment: 38 pages, including c++ cod
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