1,881 research outputs found
Macro- and micro-strain in GaN nanowires on Si(111)
We analyze the strain state of GaN nanowire ensembles by x-ray diffraction.
The nanowires are grown by molecular beam epitaxy on a Si(111) substrate in a
self-organized manner. On a macroscopic scale, the nanowires are found to be
free of strain. However, coalescence of the nanowires results in micro-strain
with a magnitude from +-0.015% to +-0.03%.This micro-strain contributes to the
linewidth observed in low-temperature photoluminescence spectra
Heisenberg Uncertainty Principle as Probe of Entanglement Entropy: Application to Superradiant Quantum Phase Transitions
Quantum phase transitions are often embodied by the critical behavior of
purely quantum quantities such as entanglement or quantum fluctuations. In
critical regions, we underline a general scaling relation between the
entanglement entropy and one of the most fundamental and simplest measure of
the quantum fluctuations, the Heisenberg uncertainty principle. Then, we show
that the latter represents a sensitive probe of superradiant quantum phase
transitions in standard models of photons such as the Dicke Hamiltonian, which
embodies an ensemble of two-level systems interacting with one quadrature of a
single and uniform bosonic field. We derive exact results in the thermodynamic
limit and for a finite number N of two-level systems: as a reminiscence of the
entanglement properties between light and the two-level systems, the product
diverges at the quantum critical point as . We
generalize our results to the double quadrature Dicke model where the two
quadratures of the bosonic field are now coupled to two independent sets of two
level systems. Our findings, which show that the entanglement properties
between light and matter can be accessed through the Heisenberg uncertainty
principle, can be tested using Bose-Einstein condensates in optical cavities
and circuit quantum electrodynamicsComment: 7 pages, 3 figures. Published Versio
Recommended from our members
Microstructure and High Temperature Oxidation Behavior of Cr-W Alloys
Cr alloys containing 0-30%W by weight were investigated for use in elevated temperature applications. The alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was characterized using x-ray diffraction, scanning electron microscopy, and light microscopy. A pseudocyclic oxidation test was employed to study scale formation at 1000ºC in dry air. The scale was predominantly chromia and spalled upon cooling. Alloying with aluminum up to 8 weight percent reduced the spalling drastically. Furthermore, aluminizing the surface of the Cr-W alloys completely stopped the spalling
Operation of carbon nanotube thin-film transistors at elevated temperatures
[No abstract available
Discovery of Delta Scuti variables in eclipsing binary systems II.Southern TESS field search
The presence of pulsating stars in eclipsing binary systems (EBs) makes these
objects significant since they allow us to investigate the stellar interior
structure and evolution. Different types of pulsating stars could be found in
EBs such as Delta Scuti variables. Delta Scuti stars in EBs have been known for
decades and the increasing number of such systems is important for
understanding pulsational structure. Hence, in this study, a research was
carried out on the southern TESS field to discover new Delta Scuti stars in
EBs. We produced an algorithm to search for detached and semi-detached EBs
considering three steps; the orbital period (P)'s harmonics in the
Fourier spectrum, skewness of the light curves, and classification of
\textsc{UPSILON} program. If two of these steps classify a system as an EB, the
algorithm also identifies it as an EB. The TESS pixel files of targets were
also analyzed to see whether the fluxes are contaminated by other systems. No
contamination was found. We researched the existence of pulsation through EBs
with a visual inspection. To confirm Delta Scuti-type oscillations, the binary
variation was removed from the light curve, and residuals were analyzed.
Consequently, we identified 42 Delta Scuti candidates in EBs. The P,
, and M of systems were calculated. Their positions on the H-R diagram
and the known orbital-pulsation period relationship were analyzed. We also
examined our targets to find if any of them show frequency modulation with the
orbital period and discovered one candidate of tidally tilted pulsators.Comment: Published in MNRA
Properties of 42 Solar-type Kepler Targets from the Asteroseismic Modeling Portal
Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved
into individual mode frequencies has increased dramatically. While only a few such data sets were available
for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds
of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis
and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use
previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type
Kepler targets from the Asteroseismic Modeling Portal (AMP). We find that fitting the individual frequencies
typically doubles the precision of the asteroseismic radius, mass and age compared to grid-based modeling of
the global oscillation properties, and improves the precision of the radius and mass by about a factor of three
over empirical scaling relations. We demonstrate the utility of the derived properties with several applications
- …