2,048 research outputs found
Level attraction in a microwave optomechanical circuit
Level repulsion - the opening of a gap between two degenerate modes due to
coupling - is ubiquitous anywhere from solid state theory to quantum chemistry.
In contrast, if one mode has negative energy, the mode frequencies attract
instead. They converge and develop imaginary components, leading to an
instability; an exceptional point marks the transition. This, however, only
occurs if the dissipation rates of the two modes are comparable. Here we expose
a theoretical framework for the general phenomenon and realize it
experimentally through engineered dissipation in a multimode superconducting
microwave optomechanical circuit. Level attraction is observed for a mechanical
oscillator and a superconducting microwave cavity, while an auxiliary cavity is
used for sideband cooling. Two exceptional points are demonstrated that could
be exploited for their topological properties.Comment: 5 pages, 4 figures; includes Supplementary informatio
Searching for electromagnetic counterpart of LIGO gravitational waves in the Fermi GBM data with ADWO
The Fermi collaboration identified a possible electromagnetic counterpart of
the gravitational wave event of September 14, 2015. Our goal is to provide an
unsupervised data analysis algorithm to identify similar events in Fermi's
Gamma-ray Burst Monitor CTTE data stream. We are looking for signals that are
typically weak. Therefore, they can only be found by a careful analysis of
count rates of all detectors and energy channels simultaneously. Our
Automatized Detector Weight Optimization (ADWO) method consists of a search for
the signal, and a test of its significance. We developed ADWO, a virtual
detector analysis tool for multi-channel multi-detector signals, and performed
successful searches for short transients in the data-streams. We have
identified GRB150522B, as well as possible electromagnetic candidates of the
transients GW150914 and LVT151012. ADWO is an independently developed,
unsupervised data analysis tool that only relies on the raw data of the Fermi
satellite. It can therefore provide a strong, independent test to any
electromagnetic signal accompanying future gravitational wave observations.Comment: 4 pages and 4 figures, A&A Letters accepte
The Flip Diameter of Rectangulations and Convex Subdivisions
We study the configuration space of rectangulations and convex subdivisions
of points in the plane. It is shown that a sequence of
elementary flip and rotate operations can transform any rectangulation to any
other rectangulation on the same set of points. This bound is the best
possible for some point sets, while operations are sufficient and
necessary for others. Some of our bounds generalize to convex subdivisions of
points in the plane.Comment: 17 pages, 12 figures, an extended abstract has been presented at
LATIN 201
On the asymmetry of the forward and reverse martensitic transformations in shape memory alloys
Differential Scanning Calorimetric, DSC, runs taken during martensitic phase
transformations in shape memory alloys, often look differently during cooling
and heating. Similar asymmetry is observed e.g. for the numbers of hits or the
critical exponents of energy and amplitude distributions (\epsilon and \alpha,
respectively) in acoustic emission measurements. It is illustrated that, in
accordance with empirical correlations, the above asymmetry of acoustic noises
can be classified into two groups: the relative changes of the exponents during
cooling and heating (\gamma \epsilon=(\epsilon h-\epsilon c)/\epsilon c as well
as \gamma \alpha=(\alpha h-\alpha c)/\alpha c)) are either positive or
negative. For positive \gamma values the number of hits and the total energy of
acoustic emission are larger for cooling, and the situation is just the reverse
for negative asymmetry. Our interpretation is based on the different ways of
relaxation of the elastic strain energy during cooling as well as heating. It
is illustrated that if the relaxed fraction of the total elastic strain energy
(which would be stored without relaxations) during cooling is larger than the
corresponding relaxed fraction during heating, then the asymmetry is positive.
Magnetic emission noises, accompanied with martensitic phase transformations in
ferromagnetic alloys, show similar asymmetry than those observed for thermal
(DSC) and acoustic noises and depends on the constant external magnetic field
too
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