1,273 research outputs found
Relativistic Ring-Diagram Nuclear Matter Calculations
A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon
request), UI-NTH-92-0
Gauge fields, ripples and wrinkles in graphene layers
We analyze elastic deformations of graphene sheets which lead to effective
gauge fields acting on the charge carriers. Corrugations in the substrate
induce stresses, which, in turn, can give rise to mechanical instabilities and
the formation of wrinkles. Similar effects may take place in suspended graphene
samples under tension.Comment: contribution to the special issue of Solid State Communications on
graphen
Sorption direct air capture with CO2 utilization
Direct air capture (DAC) is gathering momentum since it has vast potential and high flexibility to collect CO2 from discrete sources as “synthetic tree” when compared with current CO2 capture technologies, e.g., amine based post-combustion capture. It is considered as one of the emerging carbon capture technologies in recent decades and remains in a prototype investigation stage with many technical challenges to be overcome. The objective of this paper is to comprehensively discuss the state-of-the-art of DAC and CO2 utilization, note unresolved technology bottlenecks, and give investigation perspectives for commercial large-scale applications. Firstly, characteristics of physical and chemical sorbents are evaluated. Then, the representative capture processes, e.g., pressure swing adsorption, temperature swing adsorption and other ongoing absorption chemical loops, are described and compared. Methods of CO2 conversion including synthesis of fuels and chemicals as well as biological utilization are reviewed. Finally, techno-economic analysis and life cycle assessment for DAC application are summarized. Based on research achievements, future challenges of DAC and CO2 conversion are presented, which include providing synthesis guidelines for obtaining sorbents with the desired characteristics, uncovering the mechanisms for different working processes and establishing evaluation criteria in terms of technical and economic aspects
Dirac Hartree-Fock for Finite Nuclei Employing realistic Forces
We discuss two different approximation schemes for the self-consistent
solution of the {\it relativistic} Brueckner-Hartree-Fock equation for finite
nuclei. In the first scheme, the Dirac effects are deduced from corresponding
nuclear matter calculations, whereas in the second approach the local-density
approximation is used to account for the effects of correlations. The results
obtained by the two methods are very similar. Employing a realistic
one-boson-exchange potential (Bonn~A), the predictions for energies and radii
of O and Ca come out in substantially better agreement with
experiment as compared to non-relativistic approaches. As a by-product of our
study, it turns out that the Fock exchange-terms, ignored in a previous
investigation, are not negligible.Comment:
Absence of First-order Transition and Tri-critical Point in the Dynamic Phase Diagram of a Spatially Extended Bistable System in an Oscillating Field
It has been well established that spatially extended, bistable systems that
are driven by an oscillating field exhibit a nonequilibrium dynamic phase
transition (DPT). The DPT occurs when the field frequency is on the order of
the inverse of an intrinsic lifetime associated with the transitions between
the two stable states in a static field of the same magnitude as the amplitude
of the oscillating field. The DPT is continuous and belongs to the same
universality class as the equilibrium phase transition of the Ising model in
zero field [G. Korniss et al., Phys. Rev. E 63, 016120 (2001); H. Fujisaka et
al., Phys. Rev. E 63, 036109 (2001)]. However, it has previously been claimed
that the DPT becomes discontinuous at temperatures below a tricritical point
[M. Acharyya, Phys. Rev. E 59, 218 (1999)]. This claim was based on
observations in dynamic Monte Carlo simulations of a multipeaked probability
density for the dynamic order parameter and negative values of the fourth-order
cumulant ratio. Both phenomena can be characteristic of discontinuous phase
transitions. Here we use classical nucleation theory for the decay of
metastable phases, together with data from large-scale dynamic Monte Carlo
simulations of a two-dimensional kinetic Ising ferromagnet, to show that these
observations in this case are merely finite-size effects. For sufficiently
small systems and low temperatures, the continuous DPT is replaced, not by a
discontinuous phase transition, but by a crossover to stochastic resonance. In
the infinite-system limit the stochastic-resonance regime vanishes, and the
continuous DPT should persist for all nonzero temperatures
Hodge Theory on Metric Spaces
Hodge theory is a beautiful synthesis of geometry, topology, and analysis,
which has been developed in the setting of Riemannian manifolds. On the other
hand, spaces of images, which are important in the mathematical foundations of
vision and pattern recognition, do not fit this framework. This motivates us to
develop a version of Hodge theory on metric spaces with a probability measure.
We believe that this constitutes a step towards understanding the geometry of
vision.
The appendix by Anthony Baker provides a separable, compact metric space with
infinite dimensional \alpha-scale homology.Comment: appendix by Anthony W. Baker, 48 pages, AMS-LaTeX. v2: final version,
to appear in Foundations of Computational Mathematics. Minor changes and
addition
Low-energy p-d Scattering: High Precision Data, Comparisons with Theory, and Phase-Shift Analyses
Angular distributions of sigma(theta), A_y, iT_11, T_20, T_21, and T_22 have
been measured for d-p scattering at E_c.m.=667 keV. This set of high-precision
data is compared to variational calculations with the nucleon-nucleon potential
alone and also to calculations including a three-nucleon (3N) potential.
Agreement with cross-section and tensor analyzing power data is excellent when
a 3N potential is used. However, a comparison between the vector analyzing
powers reveals differences of approximately 40% in the maxima of the angular
distributions which is larger than reported at higher energies for both p-d and
n-d scattering. Single-energy phase-shift analyses were performed on this data
set and a similar data set at E_c.m.=431.3 keV. The role of the different
phase-shift parameters in fitting these data is discussed.Comment: 18 pages, 6 figure
Electron Rearrangement Dynamics in Dissociating I 2 n Molecules Accessed by Extreme Ultraviolet Pump Probe Experiments
The charge rearrangement in dissociating In 2 molecules is measured as a function of the internuclear distance R using extreme ultraviolet pulses delivered by the free electron laser in Hamburg. Within an extreme ultraviolet pump probe scheme, the first pulse initiates dissociation by multiply ionizing I2, and the delayed probe pulse further ionizes one of the two fragments at a given time, thus triggering charge rearrangement at a well defined R. The electron transfer between the fragments is monitored by analyzing the delay dependent ion kinetic energies and charge states. The experimental results are in very good agreement with predictions of the classical over the barrier model demonstrating its validity in a thus far unexplored quasimolecular regime relevant for free electron laser, plasma, and chemistry application
ADAM12 is a circulating marker for stromal activation in pancreatic cancer and predicts response to chemotherapy
Pancreatic ductal adenocarcinoma (PDAC) is characterized by abundant stroma that harbors tumor-promoting properties. No good biomarkers exist to monitor the effect of stromal targeting therapies or to predict response. We set out to identify such non-invasive markers for PDAC stroma and predict response to therapy. Gene expression datasets, co-culture experiments, xenografts, and patient samples were analyzed. Serum samples were measured from a cohort of 58 resected patients, and 87 metastatic or locally advanced PDAC patients. Baseline and follow-up levels were assessed in 372 additional metastatic PDAC patients who received nab-paclitaxel with gemcitabine (n = 184) or gemcitabine monotherapy (n = 188) in the phase III MPACT trial. Increased levels of ADAM12 were found in PDAC patients compared to healthy controls (p < 0.0001, n = 157 and n = 38). High levels of ADAM12 significantly associated with poor outcome in resected PDAC (HR 2.07, p = 0.04). In the MPACT trial survival was significantly longer for patients who received nab-paclitaxel and had undetectable ADAM12 levels before treatment (OS 12.3 m vs 7.9 m p = 0.0046). Consistently undetectable or decreased ADAM12 levels during treatment significantly associated with longer survival as well (OS 14.4 m and 11.2 m, respectively vs 8.3, p = 0.0054). We conclude that ADAM12 is a blood-borne proxy for stromal activation, the levels of which have prognostic significance and correlate with treatment benefit
Two refreshing views of Fluctuation Theorems through Kinematics Elements and Exponential Martingale
In the context of Markov evolution, we present two original approaches to
obtain Generalized Fluctuation-Dissipation Theorems (GFDT), by using the
language of stochastic derivatives and by using a family of exponential
martingales functionals. We show that GFDT are perturbative versions of
relations verified by these exponential martingales. Along the way, we prove
GFDT and Fluctuation Relations (FR) for general Markov processes, beyond the
usual proof for diffusion and pure jump processes. Finally, we relate the FR to
a family of backward and forward exponential martingales.Comment: 41 pages, 7 figures; version2: 45 pages, 7 figures, minor revisions,
new results in Section
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