370 research outputs found
Complexified coherent states and quantum evolution with non-Hermitian Hamiltonians
The complex geometry underlying the Schr\"odinger dynamics of coherent states
for non-Hermitian Hamiltonians is investigated. In particular two seemingly
contradictory approaches are compared: (i) a complex WKB formalism, for which
the centres of coherent states naturally evolve along complex trajectories,
which leads to a class of complexified coherent states; (ii) the investigation
of the dynamical equations for the real expectation values of position and
momentum, for which an Ehrenfest theorem has been derived in a previous paper,
yielding real but non-Hamiltonian classical dynamics on phase space for the
real centres of coherent states. Both approaches become exact for quadratic
Hamiltonians. The apparent contradiction is resolved building on an observation
by Huber, Heller and Littlejohn, that complexified coherent states are
equivalent if their centres lie on a specific complex Lagrangian manifold. A
rich underlying complex symplectic geometry is unravelled. In particular a
natural complex structure is identified that defines a projection from complex
to real phase space, mapping complexified coherent states to their real
equivalents.Comment: 18 pages, small improvements made, similar to published versio
Propagation of Gaussian beams in the presence of gain and loss
We consider the propagation of Gaussian beams in a waveguide with gain and
loss in the paraxial approximation governed by the Schr\"odinger equation. We
derive equations of motion for the beam in the semiclassical limit that are
valid when the waveguide profile is locally well approximated by quadratic
functions. For Hermitian systems, without any loss or gain, these dynamics are
given by Hamilton's equations for the center of the beam and its conjugate
momentum. Adding gain and/or loss to the waveguide introduces a non-Hermitian
component, causing the width of the Gaussian beam to play an important role in
its propagation. Here we show how the width affects the motion of the beam and
how this may be used to filter Gaussian beams located at the same initial
position based on their width
Classical and quantum dynamics in the (non-Hermitian) Swanson oscillator
The non-Hermitian quadratic oscillator studied by Swanson is one of the
popular -symmetric model systems. Here a full classical description of its
dynamics is derived using recently developed metriplectic flow equations, which
combine the classical symplectic flow for Hermitian systems with a dissipative
metric flow for the anti-Hermitian part. Closed form expressions for the metric
and phase-space trajectories are presented which are found to be periodic in
time. Since the Hamiltonian is only quadratic the classical dynamics exactly
describes the quantum dynamics of Gaussian wave packets. It is shown that the
classical metric and trajectories as well as the quantum wave functions can
diverge in finite time even though the -symmetry is unbroken, i.e., the
eigenvalues are purely real.Comment: extended version, accepted for publication in J. Phys.
TERAHERTZ RESONATOR
A tunable terahertz resonator includes a semiconductor Substrate and a metal layer contacting a surface of the semiconductor substrate. A depletion layer is formed in the semiconductor substrate near an interface between the metal layer and the semiconductor Substrate. A chiral nanostructure is coupled to the substrate or the metal layer, the chiral nanostructure including a conducting or semiconducting material and having an inductance. A bias circuit applies a bias Voltage across the metal layer and the semiconductor Substrate to control a capacitance of a tunable capacitor that includes the depletion layer. The chiral nanostructure and the tunable capacitor form a tunable resonant circuit. The tunable terahertz resonator can be used in a terahertz radiation emitter or receiver
Tunable plasmonic resonances in highly porous nano-bamboo Si-Au superlattice-type thin films
We report on fabrication of spatially-coherent columnar plasmonic
nanostructure superlattice-type thin films with high porosity and strong
optical anisotropy using glancing angle deposition. Subsequent and repeated
depositions of silicon and gold lead to nanometer-dimension subcolumns with
controlled lengths. The superlattice-type columns resemble bamboo structures
where smaller column sections of gold form junctions sandwiched between larger
silicon column sections ("nano-bamboo"). We perform generalized spectroscopic
ellipsometry measurements and finite element method computations to elucidate
the strongly anisotropic optical properties of the highly-porous nano-bamboo
structures. The occurrence of a strongly localized plasmonic mode with
displacement pattern reminiscent of a dark quadrupole mode is observed in the
vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like
mode frequency within the near-infrared spectral range by varying the geometry
of the nano-bamboo structure. In addition, coupled-plasmon-like and inter-band
transition-like modes occur in the visible and ultra-violet spectral regions,
respectively. We elucidate an example for the potential use of the nano-bamboo
structures as a highly porous plasmonic sensor with optical read out
sensitivity to few parts-per-million solvent levels in water
Optical anisotropy of porous polymer film with inverse slanted nanocolumnar structure revealed via generalized spectroscopic ellipsometry
We use generalized spectroscopic ellipsometry to characterize the biaxial optical properties of porous polymer and slanted nanocolumnar template thin films. The porous polymer with inverse columnar structure was prepared via infiltrating polymer into the voids of the slanted nanocolumnar film and selectively removing the column material (cobalt). The anisotropic Bruggeman effective medium approximation was employed to analyze the ellipsometry data of the porous polymer film and nanocolumnar template. The classification and structure of optical anisotropy are found to be identical for both samples. The interchangeable optical behaviors between two complementary structures are attributed to the equivalency in their anisotropic polarizabilities
2. Freiberger Ledertage - Abstractband: 25. und 26. April 2013, Sinsheim: Leder up to date
Der Verein für Gerberei-Chemie und -Technik (VGCT) wurde 1949 zur Förderung wissenschaftlicher und technischer Forschung, zum Zwecke des fachlichen Erfahrungsaustausches sowie zur Förderung des beruflichen Nachwuchses gegründet. Gegenwärtig hat er ca. 300 Mitglieder, welche sowohl einzelne Personen als auch Firmen sind. Im VGCT treffen sich Ledertechniker, Maschinenbauer, Chemiker und andere am „Ledermachen“ interessierte Menschen zum Austausch und zu gemeinsamer Arbeit. Der Verein bietet eine Plattform für den fachlichen Austausch indem er jährliche Fachtagungen und fachliche Kooperationen in firmenübergreifenden Arbeitsgruppen (Kommissionen) organisiert, technische Veröffentlichungen in der Fachpresse mit eigenen Seiten fördert und sich aktiv an Umweltschutz, Arbeitssicherheit sowie Gesundheitsschutz beteiligt.The Association for Chemistry and Technology in Tanning (VGCT) was founded in 1949 in order to facilitate scientifi c and technical research and exchange of professional experience as well as to promote young talents. Currently it has some 300 members – single persons as well as enterprises. In the VGCT, leather technologists, mechanical engineers, chemists and other people interested in “making leather” meet in order to exchange ideas and work together. The association offers a platform for sharing professional experience by organizing annual meetings and professional co-operations in groups from across various companies (commissions), by facilitating technical publications in specialist press with own pages and actively participating in environmental protection, occupational safety and health protection
RFID-Technologie in der MĂĽnchner Stadtbibliothek
Seit Anfang 2006 wird das Bibliothekssystem der Stadt München mit RFID-Selbstverbuchung ausgestattet. Mittlerweile sind außer der Zentralbibliothek weitere 14 Bibliotheken mit unterschiedlich großen Installationen umgestellt. Bis zu 97% der Ausleihen und Rückgaben werden über die Terminals von den Kunden selbst abgewickelt. Besondere Beachtung erfordert die Mediensicherung bei mehrteiligen Medien sowie die Sicherung von umfangreicheren Präsenzbeständen. Im Februar 2008 wurde mit der Einführung eines RFID-Ausweises begonnen, der außer der Benutzeridentifikation weitere Funktionalitäten wie Zutrittskontrolle und Bezahlfunktionen beinhaltet. Auf Initiative der ÖBs von München, Stuttgart und Wien wurde 2006 eine RFID-Anwendergruppe gegründet, der das Kompetenznetzwerk Bibliotheken des DBV eine Seite auf seiner Homepage zur Verfügung stellte, die über die aktuellsten Entwicklungen informiert
Optical, structural, and magnetic properties of cobalt nanostructure thin films
We report on optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85° away from the substrate normal. Comparison is made between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation. Generalized spectroscopic ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the films in the spectral range from 400 to 1000 nm. The magnetic properties are analyzed with a superconducting quantum interference device magnetometer. Both nanostructure thin films show highly anisotropic optical properties such as strong form birefringence and large dichroism. In particular, Co slanted columnar thin films are found to possess monoclinic optical properties. Magnetic measurements at room temperature show hysteresis anisotropy with respect to a magnetic field either parallel or perpendicular to the nanostructures’ long axis. We find extremely large coercive fields of approximately 3 kOe for our achiral columnar nanostructures
Wave packet evolution in non-Hermitian quantum systems
The quantum evolution of the Wigner function for Gaussian wave packets
generated by a non-Hermitian Hamiltonian is investigated. In the semiclassical
limit this yields the non-Hermitian analog of the Ehrenfest
theorem for the dynamics of observable expectation values. The lack of
Hermiticity reveals the importance of the complex structure on the classical
phase space: The resulting equations of motion are coupled to an equation of
motion for the phase space metric---a phenomenon having no analog in Hermitian
theories.Comment: Example added, references updated, 4 pages, 2 figure
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