174 research outputs found
Economic Assessment of the Hydrogenation of CO<sub>2</sub> to Liquid Fuels and Petrochemical Feedstock
To remove high concentrations of CO2 from the off-gas of coal-driven power plants, a new process was proposed. The catalytic hydrogenation of the CO2 leads to the production of C2 – C4 (petrochemical feedstock) and liquid C5+ hydrocarbons (fuel). Thus, environmentally harmful CO2 may be converted sustainably to useful products. On the basis of a process flow sheet, the costs for processing the CO2 are estimated for different plant sizes. The price of hydrogen contributes significantly to the overall production costs. Further price reductions may be achieved by final engineering optimization of the process as a whole and specific unit operations
Spectral singularities in PT-symmetric periodic finite-gap systems
The origin of spectral singularities in finite-gap singly periodic
PT-symmetric quantum systems is investigated. We show that they emerge from a
limit of band-edge states in a doubly periodic finite gap system when the
imaginary period tends to infinity. In this limit, the energy gaps are
contracted and disappear, every pair of band states of the same periodicity at
the edges of a gap coalesces and transforms into a singlet state in the
continuum. As a result, these spectral singularities turn out to be analogous
to those in the non-periodic systems, where they appear as zero-width
resonances. Under the change of topology from a non-compact into a compact one,
spectral singularities in the class of periodic systems we study are
transformed into exceptional points. The specific degeneration related to the
presence of finite number of spectral singularities and exceptional points is
shown to be coherently reflected by a hidden, bosonized nonlinear
supersymmetry.Comment: 16 pages, 3 figures; a difference between spectral singularities and
exceptional points specified, the version to appear in PR
Transient field-resolved reflectometry at 50-100 THz
Transient field-resolved spectroscopy enables studies of ultrafast dynamics in molecules, nanostructures, or solids with sub-cycle resolution, but previous work has so far concentrated on extracting the dielectric response at frequencies below 50 THz. Here, we implemented transient field-resolved reflectometry at 50-100 THz(3-6 mu m) with MHz repetition rate employing 800 nm few-cycle excitation pulses that provide sub-10 fs temporal resolution. The capabilities of the technique are demonstrated in studies of ultrafast photorefractive changes in semiconductors Ge and GaAs, where the high frequency range permits to explore the resonance-free Drude response. The extended frequency range in transient field-resolved spectroscopy can further enable studies with so far inaccessible transitions, including intramolecular vibrations in a large range of systems. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License
Quantum Mechanics of Proca Fields
We construct the most general physically admissible positive-definite inner
product on the space of Proca fields. Up to a trivial scaling this defines a
five-parameter family of Lorentz invariant inner products that we use to
construct a genuine Hilbert space for the quantum mechanics of Proca fields. If
we identify the generator of time-translations with the Hamiltonian, we obtain
a unitary quantum system that describes first-quantized Proca fields and does
not involve the conventional restriction to the positive-frequency fields. We
provide a rather comprehensive analysis of this system. In particular, we
examine the conserved current density responsible for the conservation of the
probabilities, explore the global gauge symmetry underlying the conservation of
the probabilities, obtain a probability current density, construct position,
momentum, helicity, spin, and angular momentum operators, and determine the
localized Proca fields. We also compute the generalized parity (\cP),
generalized time-reversal (\cT), and generalized charge or chirality (\cC)
operators for this system and offer a physical interpretation for its
\cP\cT-, \cC-, and \cC\cP\cT-symmetries.Comment: Published version, typos fixed, a change in symbol, 1 fi
Separable potential model for interactions at low energies
The effective separable meson-baryon potentials are constructed to match the
equivalent chiral amplitudes up to the second order in external meson momenta.
We fit the model parameters (low energy constants) to the threshold and low
energy data. In the process, the -proton bound state problem is
solved exactly in the momentum space and the 1s level characteristics of the
kaonic hydrogen are computed simultaneously with the available low energy
cross sections. The model is also used to describe the
mass spectrum and the energy dependence of the amplitude.Comment: 31 pages, v2 - added corrections to make it compatible with the
published versio
- …