2,600 research outputs found
Third Level Trigger for the Fluorescence Telescopes of the Pierre Auger Observatory
The trigger system for the Auger fluorescence telescopes is implemented in
hard- and software for an efficient selection of fluorescence light tracks
induced by high-energy extensive air showers. The algorithm of the third stage
uses the multiplicity signal of the hardware for fast rejection of lightning
events with above 99% efficiency. In a second step direct muon hits in the
camera and random triggers are rejected by analyzing the space-time correlation
of the pixels. The trigger algorithm was tested with measured and simulated
showers and implemented in the electronics of the fluorescence telescopes. A
comparison to a prototype trigger without multiplicity shows the superiority of
this approach, e.g. the false rejection rate is a factor 10 lower.Comment: 8 pages, 7 figures, to be published in NIM A; 1 typo correcte
Nuclear Resonance Vibrational Spectroscopy of Iron Sulfur Proteins
Nuclear inelastic scattering in conjunction with density functional theory
(DFT) calculations has been applied for the identification of vibrational modes
of the high-spin ferric and the high-spin ferrous iron-sulfur center of a
rubredoxin-type protein from the thermophylic bacterium Pyrococcus abysii
Fourth order gravity: equations, history, and applications to cosmology
The field equations following from a Lagrangian L(R) will be deduced and
solved for special cases. If L is a non-linear function of the curvature
scalar, then these equations are of fourth order in the metric. In the
introduction we present the history of these equations beginning with the paper
of H. Weyl from 1918, who first discussed them as alternative to Einstein's
theory. In the third part, we give details about the cosmic no hair theorem,
i.e., the details how within fourth order gravity with L= R + R^2 the
inflationary phase of cosmic evolution turns out to be a transient attractor.
Finally, the Bicknell theorem, i.e. the conformal relation from fourth order
gravity to scalar-tensor theory, will be shortly presented.Comment: 51 pages, LaTeX, no figure, lecture for 42nd Karpacz Winter School
6.-11.2.06, references 99-109 and related comments are adde
Re-visiting the Protamine-2 locus: deletion, but not haploinsufficiency, renders male mice infertile
Protamines are arginine-rich DNA-binding proteins that replace histones in elongating spermatids. This leads to hypercondensation of chromatin and ensures physiological sperm morphology, thereby protecting DNA integrity. In mice and humans, two protamines, protamine-1 (Prm1) and protamine-2 (Prm2) are expressed in a species-specific ratio. In humans, alterations of this PRM1/PRM2 ratio is associated with subfertility. By applying CRISPR/Cas9 mediated gene-editing in oocytes, we established Prm2-deficient mice. Surprisingly, heterozygous males remained fertile with sperm displaying normal head morphology and motility. In Prm2-deficient sperm, however, DNA-hypercondensation and acrosome formation was severely impaired. Further, the sperm displayed severe membrane defects resulting in immotility. Thus, lack of Prm2 leads not only to impaired histone to protamine exchange and disturbed DNA-hypercondensation, but also to severe membrane defects resulting in immotility. Interestingly, previous attempts using a regular gene-targeting approach failed to establish Prm2-deficient mice. This was due to the fact that already chimeric animals generated with Prm2+/− ES cells were sterile. However, the Prm2-deficient mouse lines established here clearly demonstrate that mice tolerate loss of one Prm2 allele. As such they present an ideal model for further studies on protamine function and chromatin organization in murine sperm
Bianchi Cosmological Models and Gauge Symmetries
We analyze carefully the problem of gauge symmetries for Bianchi models, from
both the geometrical and dynamical points of view. Some of the geometrical
definitions of gauge symmetries (=``homogeneity preserving diffeomorphisms'')
given in the literature do not incorporate the crucial feature that local gauge
transformations should be independent at each point of the manifold of the
independent variables ( = time for Bianchi models), i.e, should be arbitrarily
localizable ( in time). We give a geometrical definition of homogeneity
preserving diffeomorphisms that does not possess this shortcoming. The proposed
definition has the futher advantage of coinciding with the dynamical definition
based on the invariance of the action ( in Lagrangian or Hamiltonian form). We
explicitly verify the equivalence of the Lagrangian covariant phase space with
the Hamiltonian reduced phase space. Remarks on the use of the Ashtekar
variables in Bianchi models are also given.Comment: 16 pages, Latex file, ULB-PMIF-92/1
Role of Nanoscale Inhomogeneities in Co<sub>2</sub>FeO<sub>4</sub> Catalysts during the Oxygen Evolution Reaction
Spinel-type catalysts are promising anode materials for the alkaline oxygen evolution reaction (OER), exhibiting low overpotentials and providing long-term stability. In this study, we compared two structurally equal Co2FeO4 spinels with nominally identical stoichiometry and substantially different OER activities. In particular, one of the samples, characterized by a metastable precatalyst state, was found to quickly achieve its steady-state optimum operation, while the other, which was initially closer to the ideal crystallographic spinel structure, never reached such a state and required 168 mV higher potential to achieve 1 mA/cm2. In addition, the enhanced OER activity was accompanied by a larger resistance to corrosion. More specifically, using various ex situ, quasi in situ, and operando methods, we could identify a correlation between the catalytic activity and compositional inhomogeneities resulting in an X-ray amorphous Co2+-rich minority phase linking the crystalline spinel domains in the as-prepared state. Operando X-ray absorption spectroscopy revealed that these Co-rich domains transform during OER to structurally different Co3+-rich domains. These domains appear to be crucial for enhancing OER kinetics while exhibiting distinctly different redox properties. Our work emphasizes the necessity of the operando methodology to gain fundamental insight into the activity-determining properties of OER catalysts and presents a promising catalyst concept in which a stable, crystalline structure hosts the disordered and active catalyst phase
Dark-State Polaritons in Electromagnetically Induced Transparency
We identify form-stable coupled excitations of light and matter (``dark-state
polaritons'') associated with the propagation of quantum fields in
Electromagnetically Induced Transparency. The properties of the dark-state
polaritons such as the group velocity are determined by the mixing angle
between light and matter components and can be controlled by an external
coherent field as the pulse propagates. In particular, light pulses can be
decelerated and ``trapped'' in which case their shape and quantum state are
mapped onto metastable collective states of matter. Possible applications of
this reversible coherent-control technique are discussed.Comment: 4 pages, 2 figure
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