Exciton localization and interface roughness in growth-interrupted GaAs/AlAs quantum wells

We have used photoluminescence spectroscopy to investigate the influence of interface roughness in GaAs/AlAs quantum wells on their optical properties over a wide continuous range of well thicknesses. In order to compare different correlation lengths of the in-plane disorder potential, the wells were fabricated with growth interruption at both, one, or neither of the interfaces. Growth-interruption increases the correlation length of the monolayer-island structure on the surface, which gives rise to a long-range interface roughness after overgrowth. The relation between the correlation lengths of the in-plane disorder potential and the exciton localization length determines the spectral shape of the exciton luminescence. When the correlation length of the in-plane disorder potential is larger than the exciton localization length, the excitonic spectrum splits up into discrete peaks, stemming from regions differing in effective thickness by an integral number of monolayers. The energies of monolayers peaks, taking into account the in-plane localization energy, are found to be reproducible in wafers grown under similar conditions. We conclude that atomically smooth growth islands are formed on both AlAs and GaAs surfaces after growth interruption. During overgrowth, surface segregation leads to the generation of an atomic-scale disorder in the first overgrown monolayers. This results in an additional in-plane disorder potential with a much shorter correlation length than the original surface. It also modifies the shape of the well potential in the growth direction, as we have modelled by growth simulations, blueshifting the excitonic transition energies with respect to a square-well model

A Pooled Data Analysis from Three Research Labs

Paired associative stimulation (PAS) is a widely used transcranial magnetic stimulation (TMS) paradigm to non-invasively induce synaptic plasticity in the human brain in vivo. Altered PAS-induced plasticity has been demonstrated for several diseases. However, researchers are faced with a high inter- and intra- subject variability of the PAS response. Here, we pooled original data from nine PAS studies from three centers and analyzed the combined dataset of 190 healthy subjects with regard to age dependency, the role of stimulation parameters and the effect of different statistical methods. We observed no main effect of the PAS intervention over all studies (F(2;362) = 0.44; p = 0.644). The rate of subjects showing the expected increase of motor evoked potential (MEP) amplitudes was 53%. The PAS effect differed significantly between studies as shown by a significant interaction effect (F(16;362) = 1.77; p = 0.034) but post-hoc testing did not reveal significant effects after correction for multiple tests. There was a trend toward increased variability of the PAS effect in older subjects. Acquisition parameters differed across studies but without systematically influencing changes in MEP-size. The use of post/baseline quotients systematically indicated stronger PAS effects than post/baseline difference or the logarithm of the post/baseline quotient. The non-significant PAS effects across studies and a wide range of responder rates between studies indicate a high variability of this method. We were thus not able to replicate findings from a previous meta-analysis showing robust effects of PAS. No pattern emerged regarding acquisition parameters that at this point could guide future studies to reduce variability and help increase response rate. For future studies, we propose to report the responder rate and recommend the use of the logarithmized post/baseline quotient for further analyses to better address the possibility that results are driven by few extreme cases

Immune regulation of a chronic bacteria infection and consequences for pathogen transmission

<p>Abstract</p> <p>Background</p> <p>The role of host immunity has been recognized as not only playing a fundamental role in the interaction between the host and pathogen but also in influencing host infectiousness and the ability to shed pathogens. Despite the interest in this area of study, and the development of theoretical work on the immuno-epidemiology of infections, little is known about the immunological processes that influence pathogen shedding patterns.</p> <p>Results</p> <p>We used the respiratory bacterium <it>Bordetella bronchiseptica </it>and its common natural host, the rabbit, to examine the intensity and duration of oro-nasal bacteria shedding in relation to changes in the level of serum antibodies, blood cells, cytokine expression and number of bacteria colonies in the respiratory tract. Findings show that infected rabbits shed <it>B. bronchiseptica </it>by contact up to 4.5 months post infection. Shedding was positively affected by number of bacteria in the nasal cavity (CFU/g) but negatively influenced by serum IgG, which also contributed to the initial reduction of bacteria in the nasal cavity. Three main patterns of shedding were identified: i- bacteria were shed intermittently (46% of individuals), ii- bacteria shedding fell with the progression of the infection (31%) and iii- individuals never shed bacteria despite being infected (23%). Differences in the initial number of bacteria shed between the first two groups were associated with differences in the level of serum antibodies and white blood cells. These results suggest that the immunological conditions at the early stage of the infection may play a role in modulating the long term dynamics of <it>B. bronchiseptica </it>shedding.</p> <p>Conclusions</p> <p>We propose that IgG influences the threshold of bacteria in the oro-nasal cavity which then affects the intensity and duration of individual shedding. In addition, we suggest that a threshold level of infection is required for shedding, below this value individuals never shed bacteria despite being infected. The mechanisms regulating these interactions are still obscure and more studies are needed to understand the persistence of bacteria in the upper respiratory tract and the processes controlling the intensity and duration of shedding.</p

Stimulated secondary emission from semiconductor microcavities

We find strong influence of final-state stimulation on the time-resolved light emission dynamics from semiconductor microcavities after pulsed excitation allowing angle-resonant polariton-polariton scattering on the lower-polariton branch. The polariton dynamics can be controlled by injection of final-state polaritons at densities below a polariton saturation density of 5×108cm−2. A bosonic enhancement factor in the dynamics of up to 700 is evaluated

Subsampling and Knowledge Distillation On Adversarial Examples: New Techniques for Deep Learning Based Side Channel Evaluations

This paper has four main goals. First, we show how we solved the CHES 2018 AES challenge in the contest using essentially a linear classifier combined with a SAT solver and a custom error correction method. This part of the paper has previously appeared in a preprint by the current authors (e-print report 2019/094) and later as a contribution to a preprint write-up of the solutions by the three winning teams (e-print report 2019/860). Second, we develop a novel deep neural network architecture for side-channel analysis that completely breaks the AES challenge, allowing for fairly reliable key recovery with just a single trace on the unknown-device part of the CHES challenge (with an expected success rate of roughly 70 percent if about 100 CPU hours are allowed for the equation solving stage of the attack). This solution significantly improves upon all previously published solutions of the AES challenge, including our baseline linear solution. Third, we consider the question of leakage attribution for both the classifier we used in the challenge and for our deep neural network. Direct inspection of the weight vector of our machine learning model yields a lot of information on the implementation for our linear classifier. For the deep neural network, we test three other strategies (occlusion of traces; inspection of adversarial changes; knowledge distillation) and find that these can yield information on the leakage essentially equivalent to that gained by inspecting the weights of the simpler model. Fourth, we study the properties of adversarially generated side-channel traces for our model. Partly reproducing recent work on useful features in adversarial examples in our application domain, we find that a linear classifier generalizing to an unseen device much better than our linear baseline can be trained using only adversarial examples (fresh random keys, adversarially perturbed traces) for our deep neural network. This gives a new way of extracting human-usable knowledge from a deep side channel model while also yielding insights on adversarial examples in an application domain where relatively few sources of spurious correlations between data and labels exist. The experiments described in this paper can be reproduced using code available at https://github.com/agohr/ches2018

CHES 2018 Side Channel Contest CTF - Solution of the AES Challenges

Alongside CHES 2018 the side channel contest \u27Deep learning vs. classic profiling\u27 was held. Our team won both AES challenges (masked AES implementation), working under the handle AGSJWS. Here we describe and analyse our attack. We can solve the more difficult of the two challenges with $2$ to $5$ power traces, which is much less than was available in the contest. Our attack combines techniques from machine learning with classical techniques. The attack was superior to all classical and deep learning based attacks which we have tried. Moreover, it provides some insights on the implementation

Magnetic fields and extraordinarily bright radio emission in the X-ray faint galaxy group MRC 0116+111

MRC 0116+111 is a nearby ($z=0.132$) poor galaxy group, which was previously known for exhibiting a bright diffuse radio emission with no central point-like source, presumably related to a past activity of the active galactic nucleus (AGN) in its central cD galaxy. Here, we present an X-ray observation ($\sim$30 ks of cleaned XMM-Newton/EPIC exposure) of this system, allowing us for the first time a detailed comparison between the thermal and non-thermal components of its intragroup medium (IGrM). Remarkably, we find that the radio-to-X-ray luminosity ratio is among the highest ever observed for a diffuse extragalactic source so far, while the extent of the observed radio emission is about three times larger than its observed soft X-ray emission. Although powerful AGN activity may have disturbed the dynamics of the thermal IGrM in the form of turbulence, possibly re-energising part of the relativistic electron population, the gas properties lie within the $L_X$-$T$ scaling relation established previously for other groups. The upper limit we find for the non-thermal inverse-Compton X-ray emission translates into a surprisingly high lower limit for the volume-averaged magnetic field of the group ($\ge$4.3 $\mu$G). Finally, we discuss some interesting properties of a distant ($z \simeq 0.525$) galaxy cluster serendipitously discovered in our EPIC field of view.Comment: 12 pages, 6 figures, accepted for publication in MNRA

Entwicklung von Wertschöpfungsketten für Körnererbsen und Ackerbohnen: Fördernde und hemmende Faktoren

Das Demonstrationsnetzwerk DemoNetErBo hat zum Ziel, den Anbau und die Verwertung von Körnererbsen und Ackerbohnen in Deutschland nachhaltig zu steigern und zu verbessern. Dazu werden Wertschöpfungsketten für regional erzeugte Hülsenfrüchte entwickelt und optimiert, wofür die Kenntnis sogenannter kritischer Erfolgsfaktoren, die diesen Prozess von Anbau über Verarbeitung bis hin zur Vermarktung hemmen oder fördern, unerlässlich ist. Beispielhaft wird die unterschiedliche Situation in ökologischen und konventionellen Wertschöpfungsketten betrachtet