800 research outputs found
Formation of Kuiper Belt Binaries
The discovery that a substantial fraction of Kuiper Belt objects (KBOs)
exists in binaries with wide separations and roughly equal masses, has
motivated a variety of new theories explaining their formation. Goldreich et
al. (2002) proposed two formation scenarios: In the first, a transient binary
is formed, which becomes bound with the aid of dynamical friction from the sea
of small bodies (L^2s mechanism); in the second, a binary is formed by three
body gravitational deflection (L^3 mechanism). Here, we accurately calculate
the L^2s and L^3 formation rates for sub-Hill velocities. While the L^2s
formation rate is close to previous order of magnitude estimates, the L^3
formation rate is about a factor of 4 smaller. For sub-Hill KBO velocities (v
<< v_H) the ratio of the L^3 to the L^2s formation rate is 0.05 (v/v_H)
independent of the small bodies' velocity dispersion, their surface density or
their mutual collisions. For Super-Hill velocities (v >> v_H) the L^3 mechanism
dominates over the L^2s mechanism. Binary formation via the L^3 mechanism
competes with binary destruction by passing bodies. Given sufficient time, a
statistical equilibrium abundance of binaries forms. We show that the frequency
of long-lived transient binaries drops exponentially with the system's lifetime
and that such transient binaries are not important for binary formation via the
L^3 mechanism, contrary to Lee et al. (2007). For the L^2s mechanism we find
that the typical time, transient binaries must last, to form Kuiper Belt
binaries (KBBs) for a given strength of dynamical friction, D, increases only
logarithmically with D. Longevity of transient binaries only becomes important
for very weak dynamical friction (i.e. D \lesssim 0.002) and is most likely not
crucial for KBB formation.Comment: 20 pages, 3 figures, Accepted for publication in ApJ, correction of
minor typo
Microwave absorption/reflection and magneto-transport experiments on high-mobility electron gas
We have performed simultaneous measurements of microwave
absorption/reflection and magneto-transport characteristics of a high mobility
two-dimensional electrons in GaAs/AlGaAs heterostructure in regime of
Microwave-Induced Resistance Oscillations (MIROs). It is shown that the
electrodynamic aspect of the problem is important in these experiments. In the
absorption experiments a broad cyclotron resonance line was observed due to a
large reflection from the highly conductive electron gas. There were no
additional features observed related to absorption at harmonics of the
cyclotron resonance. In near-field reflection experiments a very different
oscillation pattern was revealed when compared to MIROs. The oscillation
pattern observed in the reflection experiments is probably due to plasma
effects occurring in a finite-size sample. The whole microscopic picture of
MIROs is more complicated than simply a resonant absorption at harmonics of the
cyclotron resonance. Nevertheless, the experimental observations are in good
agreement with the model by Ryzhii et al. involving the photo-assisted
scattering in the presence of a crossed magnetic field and dc bias. The
observed damping factor of MIROs may be attributed to a change in the electron
mobility as a function of temperature.Comment: to be published in IEEE Transactions On Nanotechnolog
Влияние фотосенсибилизаторов на ультраструктурные элементы брюшины в эксперименте
БРЮШИНАПЕРИТОНИТФОТОХИМИОТЕРАПИ
Probing the Electrostatics of Integer Quantum Hall Edges with Momentum-Resolved Tunnel Spectroscopy
We present measurements of momentum-resolved magneto-tunneling from a
perpendicular two-dimensional (2D) contact into integer quantum Hall (QH) edges
at a sharp edge potential created by cleaved edge overgrowth. Resonances in the
tunnel conductance correspond to coincidences of electronic states of the QH
edge and the 2D contact in energy-momentum space. With this dispersion relation
reflecting the potential distribution at the edge we can directly measure the
band bending at our cleaved edge under the influence of an external voltage
bias. At finite bias we observe significant deviations from the flat-band
condition in agreement with self-consistent calculations of the edge potential
The Ratio of Retrograde to Prograde Orbits: A Test for Kuiper Belt Binary Formation Theories
With the discovery of Kuiper Belt binaries that have wide separations and
roughly equal masses new theories were proposed to explain their formation. Two
formation scenarios were suggested by Goldreich and collaborators: In the
first, dynamical friction that is generated by a sea of small bodies enables a
transient binary to become bound ( mechanism); in the second, a transient
binary gets bound by an encounter with a third body ( mechanism).
We show that these different binary formation scenarios leave their own
unique signatures in the relative abundance of prograde to retrograde binary
orbits. This signature is due to stable retrograde orbits that exist much
further out in the Hill sphere than prograde orbits. It provides an excellent
opportunity to distinguish between the different binary formation scenarios
observationally.
We predict that if binary formation proceeded while sub-Hill velocities
prevailed, the vast majority of all comparable mass ratio binaries have
retrograde orbits. This dominance of retrograde binary orbits is a result of
binary formation via the mechanism, or any other mechanism that
dissipates energy in a smooth and gradual manner. For super-Hill velocities
binary formation proceeds via the mechanism which produces a roughly
equal number of prograde and retrograde binaries. These predictions assume that
subsequent orbital evolution due to dynamical friction and dynamical stirring
of the Kuiper belt did not alter the sense of the binary orbit after formation.Comment: 18 pages, 4 figures, minor changes, added section on comparison with
recent observations, accepted for publication in Ap
20 Jahre in die Zukunft: Eine Zeitreise zu Trends und Entwicklungen auf dem Ökomarkt
Die vorgestellte Untersuchung ist ein kleiner Teil des Forschungsprojektes OMIaRD (Organic Marketing Initiatives and Rural Development), das innerhalb des fünften Rahmenprogramms der EU für Forschung und technologische Entwicklung finanziert wird. Teams von Universitäten und Instituten aus Großbritannien, Italien, Frankreich, der Schweiz, Finnland, Dänemark, Österreich und Deutschland bilden die Projektgruppe. Untersucht werden Aspekte der Vermarktung von Öko-Lebensmitteln in Europa. Der Schwerpunkt liegt hierbei auf Entwicklungspotentialen des ländlichen Raumes. OMIaRD verbindet zwei politische Hauptziele der EU: “nachhaltige Landwirtschaft” und “ländliche Entwicklung”. Abgeleitet werden praktische Vorschläge für Marketing- Initiativen und Daten zur Steuerung der Aktivitäten der Öffentlichen Verwaltungen im Bereich der Entwicklung des Ökomarkts als auch der Regionalentwicklung. Die Aufgabe des Teams der HAW Hamburg ist die europaweite Koordination und nationale Durchführung von Gruppendiskussionen zu Trends und Entwicklungen des Verbraucherverhaltens in Bezug auf Öko-Lebensmittel.
Die Teilnehmer prognostizieren der 'Öko-Welt' keinen kühnen Aufbruch zu neuen Ufern, sondern einen mühsamen, steinigen Weg, allerdings mit leichtem Aufwärtstrend. Denn: Öko kann nicht schneller wachsen, als sich Verbraucher ändern
Phase diagram of the integer quantum Hall effect in p-type Germanium
We experimentally study the phase diagram of the integer quantized Hall
effect, as a function of density and magnetic field. We used a two dimensional
hole system confined in a Ge/SiGe quantum well, where all energy levels are
resolved, because the Zeeman splitting is comparable to the cyclotron energy.
At low fields and close to the quantum Hall liquid-to-insulator transition, we
observe the floating up of the lowest energy level, but NO FLOATING of any
higher levels, rather a merging of these levels into the insulating state. For
a given filling factor, only direct transitions between the insulating phase
and higher quantum Hall liquids are observed as a function of density. Finally,
we observe a peak in the critical resistivity around filling factor one.Comment: 4 pages, 4 figures, some changes in the tex
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