320 research outputs found
Cyclic Orbit Codes
In network coding a constant dimension code consists of a set of
k-dimensional subspaces of F_q^n. Orbit codes are constant dimension codes
which are defined as orbits of a subgroup of the general linear group, acting
on the set of all subspaces of F_q^n. If the acting group is cyclic, the
corresponding orbit codes are called cyclic orbit codes. In this paper we give
a classification of cyclic orbit codes and propose a decoding procedure for a
particular subclass of cyclic orbit codes.Comment: submitted to IEEE Transactions on Information Theor
The role of Coulomb anti-blockade in the photoassociation of long-range Rydberg molecules
We present a new mechanism contributing to the detection of photoassociated
long-range Rydberg molecules via pulsed-field ionization: ionic products,
created by the decay of a long-range Rydberg molecule, modify the excitation
spectrum of surrounding ground-state atoms and facilitate the excitation of
further atoms into Rydberg states by the photoassociation light. Such an
ion-mediated excitation mechanism has been previously called "Coulomb
anti-blockade". Pulsed-field ionisation typically doesn't discriminate between
the ionization of a long-range Rydberg molecule and an isolated Rydberg atom,
and thus the number of atomic ions detected by this mechanism is not
proportional to the number of long-range Rydberg molecules present in the probe
volume. By combining high-resolution UV and RF spectroscopy of a dense,
ultracold gas of cesium atoms, theoretical modeling of the molecular level
structures of long-range Rydberg molecules bound below nP_3/2 Rydberg states of
cesium, and a rate model of the photoassociation and decay processes, we
unambiguously identify the signatures of this detection mechanism in the
photoassociation of long-range Rydberg molecules bound below atomic asymptotes
with negative Stark shifts.Comment: 8 pages, 7 figure
XMCD studies of thin Co films on BaTiO
Different layer thicknesses of Cobalt ranging from 2.6 {\AA} (1.5 ML) up to
55 {\AA} (30.5 ML) deposited on ferroelectric BaTiO have been studied
regarding their magnetic behavior. The layers have been characterized using
XMCD spectroscopy at remanent magnetization. After careful data analysis the
magnetic moments of the Cobalt could be determined using the sum rule
formalism. There is a sudden and abrupt onset in magnetism starting at
thicknesses of 9 {\AA} (5 ML) of Cobalt for measurements at 120 K and of 10
{\AA} (5.5 ML) if measured at room temperature. Initial island growth and
subsequent coalescence of Co on BaTiO is suggested to explain the sudden
onset. In that context, no magnetically dead layers are observed.Comment: 9 pages, 5 figures, submitted to J. Phys. Condens. Matte
Evaluierung des Projekts zur partizipativen Haushaltsplanaufstellung, -entscheidung, und -kontrolle im Bezirk Marzahn-Hellersdorf (BĂĽrgerhaushalt)
EVALUIERUNG DES PROJEKTS ZUR PARTIZIPATIVEN HAUSHALTSPLANAUFSTELLUNG, -ENTSCHEIDUNG, UND -KONTROLLE IM BEZIRK MARZAHN-HELLERSDORF (BĂśRGERHAUSHALT)
Evaluierung des Projekts zur partizipativen Haushaltsplanaufstellung, -entscheidung, und -kontrolle im Bezirk Marzahn-Hellersdorf (BĂĽrgerhaushalt) / Jung, Stefan (Rights reserved) ( -
Peeking beyond peaks:Challenges and research potentials of continuous multimodal multi-objective optimization
Multi-objective (MO) optimization, i.e., the simultaneous optimization of multiple conflicting objectives, is gaining more and more attention in various research areas, such as evolutionary computation, machine learning (e.g., (hyper-)parameter optimization), or logistics (e.g., vehicle routing). Many works in this domain mention the structural problem property of multimodality as a challenge from two classical perspectives: (1) finding all globally optimal solution sets, and (2) avoiding to get trapped in local optima. Interestingly, these streams seem to transfer many traditional concepts of single-objective (SO) optimization into claims, assumptions, or even terminology regarding the MO domain, but mostly neglect the understanding of the structural properties as well as the algorithmic search behavior on a problem's landscape. However, some recent works counteract this trend, by investigating the fundamentals and characteristics of MO problems using new visualization techniques and gaining surprising insights. Using these visual insights, this work proposes a step towards a unified terminology to capture multimodality and locality in a broader way than it is usually done. This enables us to investigate current research activities in multimodal continuous MO optimization and to highlight new implications and promising research directions for the design of benchmark suites, the discovery of MO landscape features, the development of new MO (or even SO) optimization algorithms, and performance indicators. For all these topics, we provide a review of ideas and methods but also an outlook on future challenges, research potential and perspectives that result from recent developments.</p
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Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles
The solar optical properties of Saharan mineral dust observed during the Saharan Mineral Dust Experiment (SAMUM) were explored based on measured size-number distributions and chemical composition. The size-resolved complex refractive index of the dust was derived with real parts of 1.51–1.55 and imaginary parts of 0.0008–0.006 at 550 nm wavelength. At this spectral range a single scattering albedo ωo and an asymmetry parameter g of about 0.8 were derived. These values were largely determined by the presence of coarse particles. Backscatter coefficients and lidar ratios calculated with Mie theory (spherical particles) were not found to be in agreement with independently measured lidar data. Obviously the measured Saharan mineral dust particles were of non-spherical shape. With the help of these lidar and sun photometer measurements the particle shape as well as the spherical equivalence were estimated. It turned out that volume equivalent oblate spheroids with an effective axis ratio of 1:1.6 matched these data best. This aspect ratio was also confirmed by independent single particle analyses using a scanning electron microscope. In order to perform the non-spherical computations, a database of single particle optical properties was assembled for oblate and prolate spheroidal particles. These data were also the basis for simulating the non-sphericity effects on the dust optical properties: ωo is influenced by up to a magnitude of only 1% and g is diminished by up to 4% assuming volume equivalent oblate spheroids with an axis ratio of 1:1.6 instead of spheres. Changes in the extinction optical depth are within 3.5%. Non-spherical particles affect the downwelling radiative transfer close to the bottom of the atmosphere, however, they significantly enhance the backscattering towards the top of the atmosphere: Compared to Mie theory the particle non-sphericity leads to forced cooling of the Earth-atmosphere system in the solar spectral range for both dust over ocean and desert
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