298 research outputs found
Introduction to \u3cem\u3eGerman Ecocriticism in the Anthropocene\u3c/em\u3e
How do we approach, read, discuss, and teach German literature in light of the transnational and global environmental problems and crises caused by human activities? In what way does the current geological era of the Anthropocene marked by traceable human impact across the globe lead us to reflect on the role and interconnectedness of human and non-human forces? Since human activities and human cultures have caused so many of the current ecological problems, how can scholars address broad-scale interdisciplinary problems with attention to both cultural and scientific knowledge? What is the role of the humanities in this inextricably nature-culture mix of problems? Many recent works in American and Anglophone literature attempt to answer such questions, yet there is still much to be done in other language and cultural traditions, especially when considering such broad-scale and shared challenges. We were motivated by such a need to gather together a collection of current work reflecting environmental attention in both canonical and non-canonical German-language texts and films
Human and Non-Human Agencies in the Anthropocene
The era of human impact throughout the Earth’s biosphere since the Industrial Revolution that has recently been named the Anthropocene poses many challenges to the humanities, particularly in terms of human and non-human agency. Using diverse examples from literature, travel reflections, and science that document a wide range of agencies beyond the human including landscape, ice, weather, volcanic energy or gastropods, and insects, this essay seeks to formulate a broader sense of agency. All of our examples probe new kinds of relationships between humans and nature. By configuring a close interconnection and interdependence between these entities, the Anthropocene discourse defines such relationships anew. On the one hand, our examples highlight the negative effects of anthropocentric control and supremacy over nature, but on the other, they depict ambivalent positions ranging from surrender and ecstasy to menace and demise that go hand in hand with the acknowledgment of non-human agencies.
La era del impacto humano en la biosfera de la Tierra desde la Revolución Industrial y que ha sido recientemente nombrada Antropoceno plantea mucho retos a las humanidades, especialmente en términos de agencia humana y no-humana. Usando varios ejemplos de la literatura, reflexiones de viajes y ciencia que documentan una gran variedad de agencias más allá de la humana incluyendo el paisaje, el hielo, el clima, la energÃa volcánica o los gasterópodos e insectos, este ensayo busca formular un sentido más amplio de agencia. Todos nuestros ejemplos investigan nuevos tipos de relaciones entre ser humano y naturaleza. Al configurar una interconexión e interdependencia cercanas entre estas entidades, el discurso del Antropoceno define tales relaciones de forma diferente. Por un lado, nuestros ejemplos destacan los efectos negativos del control antropocéntrico y de la supremacÃa sobre la naturaleza; pero, por otro lado, representan posiciones ambivalentes que van desde la rendición y el éxtasis a la amenaza y la desaparición que van codo con codo con el reconocimiento de las agencias no-humanas
The bend stiffness of S-DNA
We formulate and solve a two-state model for the elasticity of nicked,
double-stranded DNA that borrows features from both the Worm Like Chain and the
Bragg--Zimm model. Our model is computationally simple, and gives an excellent
fit to recent experimental data through the entire overstretching transition.
The fit gives the first value for the bending stiffness of the overstretched
state as about 10 nm*kbt, a value quite different from either B-form or
single-stranded DNA.Comment: 7 pages, 1 figur
Unzipping Kinetics of Double-Stranded DNA in a Nanopore
We studied the unzipping kinetics of single molecules of double-stranded DNA
by pulling one of their two strands through a narrow protein pore. PCR analysis
yielded the first direct proof of DNA unzipping in such a system. The time to
unzip each molecule was inferred from the ionic current signature of DNA
traversal. The distribution of times to unzip under various experimental
conditions fit a simple kinetic model. Using this model, we estimated the
enthalpy barriers to unzipping and the effective charge of a nucleotide in the
pore, which was considerably smaller than previously assumed.Comment: 10 pages, 5 figures, Accepted: Physics Review Letter
Theory of High-Force DNA Stretching and Overstretching
Single molecule experiments on single- and double stranded DNA have sparked a
renewed interest in the force-extension of polymers. The extensible Freely
Jointed Chain (FJC) model is frequently invoked to explain the observed
behavior of single-stranded DNA. We demonstrate that this model does not
satisfactorily describe recent high-force stretching data. We instead propose a
model (the Discrete Persistent Chain, or ``DPC'') that borrows features from
both the FJC and the Wormlike Chain, and show that it resembles the data more
closely. We find that most of the high-force behavior previously attributed to
stretch elasticity is really a feature of the corrected entropic elasticity;
the true stretch compliance of single-stranded DNA is several times smaller
than that found by previous authors. Next we elaborate our model to allow
coexistence of two conformational states of DNA, each with its own stretch and
bend elastic constants. Our model is computationally simple, and gives an
excellent fit through the entire overstretching transition of nicked,
double-stranded DNA. The fit gives the first values for the elastic constants
of the stretched state. In particular we find the effective bend stiffness for
DNA in this state to be about 10 nm*kbt, a value quite different from either
B-form or single-stranded DNAComment: 33 pages, 11 figures. High-quality figures available upon reques
Guided Electromagnetic Discharge Pulses Driven by Short Intense Laser Pulses: Characterisation and Modelling
Strong electromagnetic pulses (EMP) are generated from intense laser
interactions with solid-density targets, and can be guided by the target
geometry, specifically through conductive connections to the ground. We present
an experimental characterization, by time- and spatial-resolved proton
deflectometry, of guided electromagnetic discharge pulses along wires including
a coil, driven by 0.5 ps, 50 J, 1e19 W/cm2 laser pulses. Proton-deflectometry
data allows to time-resolve first the EMP due to the laser-driven target
charging and then the return EMP from the ground through the conductive target
stalk. Both EMPs have a typical duration of tens of ps and correspond to
currents in the kA-range with electric-field amplitudes of multiple GV/m. The
sub-mm coil in the target rod creates lensing effects on probing protons, due
to both magnetic- and electric-field contributions. This way, protons of 10
MeV-energy range are focused over cm-scale distances. Experimental results are
supported by analytical modelling and high-resolution numerical
particle-in-cell simulations, unraveling the likely presence of a surface
plasma, which parameters define the discharge pulse dispersion in the
non-linear propagation regime
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Single Molecule Statistics and the Polynucleotide Unzipping Transition
We present an extensive theoretical investigation of the mechanical unzipping
of double-stranded DNA under the influence of an applied force. In the limit of
long polymers, there is a thermodynamic unzipping transition at a critical
force value of order 10 pN, with different critical behavior for homopolymers
and for random heteropolymers. We extend results on the disorder-averaged
behavior of DNA's with random sequences to the more experimentally accessible
problem of unzipping a single DNA molecule. As the applied force approaches the
critical value, the double-stranded DNA unravels in a series of discrete,
sequence-dependent steps that allow it to reach successively deeper energy
minima. Plots of extension versus force thus take the striking form of a series
of plateaus separated by sharp jumps. Similar qualitative features should
reappear in micromanipulation experiments on proteins and on folded RNA
molecules. Despite their unusual form, the extension versus force curves for
single molecules still reveal remnants of the disorder-averaged critical
behavior. Above the transition, the dynamics of the unzipping fork is related
to that of a particle diffusing in a random force field; anomalous,
disorder-dominated behavior is expected until the applied force exceeds the
critical value for unzipping by roughly 5 pN.Comment: 40 pages, 18 figure
High intensity neutrino oscillation facilities in Europe
The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fréjus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of μ+ and μ− beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He6 and Ne18, also stored in a ring. The far detector is also the MEMPHYS detector in the Fréjus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive
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