388 research outputs found
Multi-wavelength observations of planet forming disks: Constraints on planet formation processes
Our understanding of protoplanetary disks has greatly improved over the last
decade due to a wealth of data from new facilities. Unbiased dust surveys with
Spitzer leave us with good constraints on the dust dispersal timescale of small
grains in the terrestrial planet forming region. In the ALMA era, this can be
confronted for the first time also with evolutionary timescales of mm grains in
the outer disk. Gas surveys in the context of the existing multi-wavelength
dust surveys will be a key in large statistical studies of disk gas evolution.
Unbiased gas surveys are limited to ALMA CO submm surveys, where the
quantitative interpretation is still debated. Herschel gas surveys have been
largely biased, but [OI] 63 mic surveys and also accretion tracers agree
qualitatively with the evolutionary timescale of small grains in the inner
disk. Recent advances achieved by means of consistent multi-wavelength studies
of gas AND dust in planet forming disks reveal the subtleties of the
quantitative interpretation of gas surveys. Observational methods to determine
disk masses e.g. from CO submm lines require the knowledge of the dust
properties in the disk. Understanding not only the gas evolution, but also its
chemical composition will provide crucial input for planet formation models.
Kinetic chemical results give profoundly different answers than thermodynamic
equilibrium in terms of the C/O ratios as well as the water ice/rock ratios.
Again, dust has a key impact on the chemical evolution and composition of the
gas. Grain growth for example affects freeze-out processes and strongly
increases the cosmic ray induced UV field.Comment: appears in the proceedings of the conference "The Cosmic Wheel and
the Legacy of the AKARI archive: from galaxies and stars to planets and
life", October 17-20, 2017, Tokyo, Japa
The Nicastrin ectodomain adopts a highly thermostable structure
Nicastrin is a type I transmembrane glycoprotein, which is part of the high molecular weight gamma-secretase complex. gamma-Secretase is one of the key players associated with the generation of Alzheimer's disease pathology, since it liberates the neurotoxic amyloid beta-peptide. Four proteins Nicastrin, anterior pharynx-defective-1 (Aph-1), presenilin enhancer-2 (Pen-2) and Presenilin are essential to form the active gamma-secretase complex. Recently it has been shown, that Nicastrin has a key function in stabilizing the mature gamma-secretase complex and may also be involved in substrate recognition. So far no structural data for the Nicastrin ectodomain or any other gamma-secretase component are available. We therefore used Circular Dichroism (CD) spectroscopy to demonstrate that Nicastrin, similar to its homologues, the Streptomyces griseus aminopeptidase (SGAP) and the transferrin receptor (TfR), adopts a thermostable secondary structure. Furthermore, the Nicastrin ectodomain has an exceptionally high propensity to refold after thermal denaturation. These findings provide evidence to further support the hypothesis that Nicastrin may share evolutionary conserved properties with the aminopeptidase and the transferrin receptor family
Nonlinear spectroscopy of exciton-polaritons in a GaAs-based microcavity
We present a systematic investigation of two-photon excitation processes in a
GaAs-based microcavity in the strong-coupling regime. We observe second
harmonic generation resonant to the upper and lower polariton level, which
exhibits a strong dependence on the photonic fraction of the corresponding
polariton. In addition we have performed two-photon excitation spectroscopy to
identify exciton states which are crucial for the operation as a terahertz
lasing device, which was suggested recently [A. V. Kavokin et al., Phys. Rev.
Lett. \textbf{108}, 197401 (2012)]. However, no distinct signatures of a
exciton state could be identified, which indicates a low two-photon pumping
efficiency
Zero Dimensional Polariton Laser in a Sub-Wavelength Grating Based Vertical Microcavity
Semiconductor exciton-polaritons in planar microcavities form coherent
two-dimensional condensates in non-equilibrium. However, coupling of multiple
lower-dimensional polariton quantum systems, critically needed for polaritonic
quantum device applications and novel cavity-lattice physics, has been limited
due to the conventional cavity structures. Here we demonstrate full confinement
of the polaritons non-destructively using a hybrid cavity made of a
single-layer sub-wavelength grating mirror and a distributed Bragg reflector.
Single-mode polariton lasing was observed at a chosen polarization.
Incorporation of a designable slab mirror into the conventional vertical
cavity, when operating in the strong-coupling regime, enables confinement,
control and coupling of polariton gasses in a scalable fashion. It may open a
door to experimental implementation of polariton-based quantum photonic devices
and coupled cavity quantum electrodynamics systems.Comment: http://www.nature.com/lsa/journal/v3/n1/full/lsa201416a.htm
Experimental verification of the very strong coupling regime in a GaAs quantum well microcavity
When the coupling between light and matter becomes comparable to the energy
gap between different excited states they hybridize, leading to the appearance
of a rich and complex phenomenology which attracted remarkable interest in
recent years. While the mixing between states with different number of
excitations, so-called ultrastrong coupling regime, has been observed in
various implementations, the effect of the hybridization between different
single excitation states, referred to as very strong coupling regime, has
remained elusive. In semiconductor quantum wells such a regime is predicted to
manifest as a photon-mediated electron-hole coupling leading to different
excitonic wavefunctions for the two polaritonic branches when the ratio of the
coupling strength to exciton binding energy approaches unity. Here, we verify
experimentally the existence of this regime in magneto-optical measurements on
a microcavity with 28 GaAs quantum wells, showing that the average
electron-hole separation of the upper polariton is significantly increased
compared to the bare quantum well exciton Bohr radius. This manifests in a
diamagnetic shift around zero detuning that exceeds the shift of the lower
polariton by one order of magnitude and the bare quantum well exciton
diamagnetic shift by a factor of two. The lower polariton exhibits a
diamagnetic shift smaller than expected from the coupling of a rigid exciton to
the cavity mode which suggests more tightly bound electron-hole pairs than in
the bare quantum well
Algebraic order and the Berezinskii-Kosterlitz-Thouless transition in an exciton-polariton gas
We observe quasi-long range coherence in a two-dimensional condensate of
exciton-polaritons. Our measurements are the first to confirm that the spatial
correlation algebraically decays with a slow power-law, whose exponent
quantitatively behaves as predicted by the Berezinskii-Kosterlitz-Thouless
theory. The exciton-polaritons are created by non-resonant optical pumping of a
micro-cavity sample with embedded GaAs quantum-wells at liquid helium
temperature. Michelson interference is used to measure the coherence of the
photons emitted by decaying exciton-polaritons
Servitization and deservitization: Overview, concepts, and definitions
© 2016 Elsevier Inc. The topic of servitization has generated a considerable body of research and many conferences, as well as industry engagement. Yet, despite the extensive literature associated with this now-mature discipline, there is no broad-based consensus on the core concepts and definitions deployed by servitization scholars, and both terminology and usage often seem ambiguous. This paper examines challenges related to service growth strategies, as well as strategies involving deservitization or a retreat from service offerings. Showing that these strategies have been pursued for more than fifty years, clarification is sought here by framing the corresponding processes and proposing definitions for four core terms: servitization, service infusion, deservitization and service dilution. It becomes clear that in focusing on the organizational change entailed by these processes, future research must elucidate “softer” issues such as leadership and business logic
Influence of interactions with non-condensed particles on the coherence of a 1D polariton condensate
One-dimensional polariton condensates (PoCos) in a photonic wire are
generated through non-resonant laser excitation, by which also a reservoir of
background carriers is created. Interaction with this reservoir may affect the
coherence of the PoCo, which is studied here by injecting a condensate locally
and monitoring the coherence along the wire. While the incoherent reservoir is
mostly present within the excitation laser spot, the condensate can propagate
ballistically through the wire. Photon correlation measurements show that far
from the laser spot the second order correlation function approaches unity
value, as expected for the coherent condensed state. When approaching the spot,
however, the correlation function increases up to values of 1.2 showing the
addition of noise to the emission due to interaction with the reservoir. This
finding is substantiated by measuring the first order coherence by a double
slit experiment, which shows a reduced visibility of interference at the
excitation laser spot.Comment: 8 pages, 8 figure
Creation of orbital angular momentum states with chiral polaritonic lenses
Controlled transfer of orbital angular momentum to exciton-polariton
Bose-Einstein condensate spontaneously created under incoherent, off-resonant
excitation conditions is a long-standing challenge in the field of microcavity
polaritonics. We demonstrate, experimentally and theoretically, a simple and
efficient approach to generation of nontrivial orbital angular momentum states
by using optically-induced potentials -- chiral polaritonic lenses.Comment: 5 pages, 5 figure
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