Bounds on Information Propagation in Disordered Quantum Spin Chains

We investigate the propagation of information through the disordered XY model. We find, with a probability that increases with the size of the system, that all correlations, both classical and quantum, are suppressed outside of an effective lightcone whose radius grows at most polylogarithmically with |t|.Comment: 4 pages, pdflatex, 1 pdf figure. Corrected the bound for the localised propagator and quantified the probability it bound occur

Controlling hole spin dynamics in two‐dimensional hole systems at low temperatures

With the recent discovery of very long hole spin decoherence times in GaAs/AlGaAs heterostructures of more than 70 ns in two-dimensional hole systems, using the hole spin as a viable alternative to electron spins in spintronic applications seems possible. Furthermore, as the hyperfine interaction with the nuclear spins is likely to be the limiting factor for electron spin lifetimes in zero dimensions, holes with their suppressed Fermi contact hyperfine interaction due to their p-like nature should be able to show even longer lifetimes than electrons. For spintronic applications, electric-field control of hole spin dynamics is desirable. Here, we report on time-resolved Kerr rotation and resonant spin amplification measurements on a two-dimensional hole system in a p-doped GaAs/AlGaAs heterostructure. Via a semitransparent gate, we tune the charge density within the sample. We are able to observe a change in the hole g factor, as well as in the hole spin dephasing time at high magnetic fields

Resonant spin amplification of hole spin dynamics in two‐dimensional hole systems: experiment and simulation

Spins in semiconductor structures may allow for the realization of scalable quantum bit arrays, an essential component for quantum computation schemes. Specifically, hole spins may be more suited for this purpose than electron spins, due to their strongly reduced interaction with lattice nuclei, which limits spin coherence for electrons in quantum dots. Here, we present resonant spin amplification (RSA) measurements, performed on a p-modulation doped GaAs-based quantum well at temperatures below 500 mK. The RSA traces have a peculiar, butterfly-like shape, which stems from the initialization of a resident hole spin polarization by optical orientation. The combined dynamics of the optically oriented electron and hole spins are well-described by a rate equation model, and by comparison of experiment and model, hole spin dephasing times of more than 70 ns are extracted from the measured data

Taking the Perfect Selfie: Investigating the Impact of Perspective on the Perception of Higher Cognitive Variables

Taking selfies is now becoming a standard human habit. However, as a social phenomenon, research is still in the fledgling stage and the scientific framework is sparse. Selfies allow us to share social information with others in a compact format. Furthermore, we are able to control important photographic and compositional aspects, such as perspective, which have a strong impact on the assessment of a face (e.g., demonstrated by the height-weight illusion, effects of gaze direction, faceism-index). In Study 1, we focused on the impact of perspective (left/right hemiface, above/below vs. frontal presentation) on higher cognitive variables and let 172 participants rate the perceived attractiveness, helpfulness, sympathy, dominance, distinctiveness, and intelligence, plus important information on health issues (e.g., body weight), on the basis of 14 3D faces. We could show that lateral snapshots yielded higher ratings for attractiveness compared to the classical frontal view. However, this effect was more pronounced for left hemifaces and especially female faces. Compared to the frontal condition, 30° right hemifaces were rated as more helpful, but only for female faces while faces viewed from above were perceived as significant less helpful. Direct comparison between left vs. right hemifaces revealed no effect. Relating to sympathy, we only found a significant effect for 30° right male hemifaces, but only in comparison to the frontal condition. Furthermore, female 30° right hemifaces were perceived as more intelligent. Relating to body weight, we replicated the so-called “height-weight illusion.” Other variables remained unaffected. In Study 2, we investigated the impact of a typical selfie-style condition by presenting the respective faces from a lateral (left/right) and tilted (lower/higher) vantage point. Most importantly, depending on what persons wish to express with a selfie, a systematic change of perspective can strongly optimize their message; e.g., increasing their attractiveness by shooting from above left, and in contrast, decreasing their expressed helpfulness by shooting from below. We could further extent past findings relating to the height-weight illusion and showed that an additional rotation of the camera positively affected the perception of body weight (lower body weight). We discuss potential explanations for perspective-related effects, especially gender-related ones

Optimal box-covering algorithm for fractal dimension of complex networks

The self-similarity of complex networks is typically investigated through computational algorithms the primary task of which is to cover the structure with a minimal number of boxes. Here we introduce a box-covering algorithm that not only outperforms previous ones, but also finds optimal solutions. For the two benchmark cases tested, namely, the E. Coli and the WWW networks, our results show that the improvement can be rather substantial, reaching up to 15% in the case of the WWW network.Comment: 5 pages, 6 figure

Temporally Resolved Intensity Contouring (TRIC) for characterization of the absolute spatio-temporal intensity distribution of a relativistic, femtosecond laser pulse

Today's high-power laser systems are capable of reaching photon intensities up to $10^{22}$ W/cm^2, generating plasmas when interacting with material. The high intensity and ultrashort laser pulse duration (fs) make direct observation of plasma dynamics a challenging task. In the field of laser-plasma physics and especially for the acceleration of ions, the spatio-temporal intensity distribution is one of the most critical aspects. We describe a novel method based on a single-shot (i.e. single laser pulse) chirped probing scheme, taking nine sequential frames at framerates up to THz. This technique, to which we refer as temporally resolved intensity contouring (TRIC) enables single-shot measurement of laser-plasma dynamics. Using TRIC, we demonstrate the reconstruction of the complete spatio-temporal intensity distribution of a high-power laser pulse in the focal plane at full pulse energy with sub picosecond resolution.Comment: Daniel Haffa, Jianhui Bin and Martin Speicher are corresponding author

Estimating tourism statistics with Wikipedia page views

Decision makers depend on socio-economic indicators to shape the world we inhabit. Reports of these indicators are often delayed due to the effort involved in gathering and aggregating the underlying data. Our increasing interactions with large scale technological systems are generating vast datasets on global human behaviour which are immediately accessible. Here we analyse whether data on how often people view Wikipedia articles might help us to improve estimates of the current number of tourists leaving the UK. Our analyses suggest that in the absence of sufficient history, Wikipedia page views provide an advantage. We conclude that when using adaptive models, Wikipedia usage opens up the possibility to improve estimates of tourism demand

Influence of static electric fields on an optical ion trap

We recently reported on a proof-of-principle experiment demonstrating optical trapping of an ion in a single-beam dipole trap superimposed by a static electric potential [Nat. Photonics 4, 772--775 (2010)]. Here, we first discuss the experimental procedures focussing on the influence and consequences of the static electric potential. These potentials can easily prevent successful optical trapping, if their configuration is not chosen carefully. Afterwards, we analyse the dipole trap experiments with different analytic models, in which different approximations are applied. According to these models the experimental results agree with recoil heating as the relevant heating effect. In addition, a Monte-Carlo simulation has been developed to refine the analysis. It reveals a large impact of the static electric potential on the dipole trap experiments in general. While it supports the results of the analytic models for the parameters used in the experiments, the analytic models cease their validity for significantly different parameters. Finally, we propose technical improvements for future realizations of experiments with optically trapped ions.Comment: 16 pages, 16 figure

Prostate Cancer Nodal Staging: Using Deep Learning to Predict 68Ga-PSMA-Positivity from CT Imaging Alone

Lymphatic spread determines treatment decisions in prostate cancer (PCa) patients. 68Ga-PSMA-PET/CT can be performed, although cost remains high and availability is limited. Therefore, computed tomography (CT) continues to be the most used modality for PCa staging. We assessed if convolutional neural networks (CNNs) can be trained to determine 68Ga-PSMA-PET/CT-lymph node status from CT alone. In 549 patients with 68Ga-PSMA PET/CT imaging, 2616 lymph nodes were segmented. Using PET as a reference standard, three CNNs were trained. Training sets balanced for infiltration status, lymph node location and additionally, masked images, were used for training. CNNs were evaluated using a separate test set and performance was compared to radiologists' assessments and random forest classifiers. Heatmaps maps were used to identify the performance determining image regions. The CNNs performed with an Area-Under-the-Curve of 0.95 (status balanced) and 0.86 (location balanced, masked), compared to an AUC of 0.81 of experienced radiologists. Interestingly, CNNs used anatomical surroundings to increase their performance, "learning" the infiltration probabilities of anatomical locations. In conclusion, CNNs have the potential to build a well performing CT-based biomarker for lymph node metastases in PCa, with different types of class balancing strongly affecting CNN performance

Diffusion and transport in the human interphase cell nucleus - FCS experiments compared to simulations.

Despite the succesful linear sequencing of the human genome the three-dimensional arrangement of chromatin, functional, and structural components is still largely unknown. Molecular transport and diffusion are important for processes like gene regulation, replication, or repair and are vitally influenced by the structure. With a comparison between fluorescence correlation spectroscopy (FCS) experiments and simulations we show here an interdisciplinary approach for the understanding of transport and diffusion properties in the human interphase cell nucleus. For a long time the interphase nucleus has been viewed as a 'spaghetti soup' of DNA without much internal structure, except during cell division. Only recently has it become apparent that chromosomes occupy distinct 'territories' also in interphase. Two models for the detailed folding of the 30 nm chromatin fibre within these territories are under debate: In the Random-Walk/Giant-Loop-model big loops of 3 to 5 Mbp are attached to a non-DNA backbone. In the Multi-Loop-Subcompartment (MLS) model loops of around 120 kbp are forming rosettes which are also interconnected by the chromatin fibre. Here we show with a comparison between simulations and experiments an interdisciplinary approach leading to a determination of the three-dimensional organization of the human genome: For the predictions of experiments various models of human interphase chromosomes and the whole cell nucleus were simulated with Monte Carlo and Brownian Dynamics methods. Only the MLS-model leads to the formation of non-overlapping chromosome territories and distinct functional and dynamic subcompartments in agreement with experiments. Fluorescence in situ hybridization is used for the specific marking of chromosome arms and pairs of small chromosomal DNA regions. The labelling is visualized with confocal laser scanning microscopy followed by image reconstruction procedures. Chromosome arms show only small overlap and globular substructures as predicted by the MLS-model. The spatial distances between pairs of genomic markers as function of their genomic separation result in a MLS-model with loop and linker sizes around 126 kbp. With the development of GFP-fusion-proteins it is possible to study the chromatin distribution and dynamics resulting from cell cycle, treatment by chemicals or radiation in vivo. The chromatin distributions are similar to those found in the simulation of whole cell nuclei of the MLS-model. Fractal analysis is especially suited to quantify the unordered and non-euclidean chromatin distribution of the nucleus. The dynamic behaviour of the chromatin structure and the diffusion of particles in the nucleus are also closely connected to the fractal dimension. Fractal analysis of the simulations reveal the multi-fractality of chromosomes. First fractal analysis of chromatin distributions in vivo result in significant differences for different morphologies and might favour a MLS-model-like chromatin distribution. Simulations of fragment distributions based on double strand breakage after carbon-ion irradiation differ in different models. Here again a comparison with experiments favours a MLS-model. FCS in combination with a scanning device is a suitable tool to study the diffusion characteristics of fluorescent proteins in living cell nuclei with high spatial resolution. Computer simulations of the three-dimensional organization of the human interphase nucleus allows a detailed test of theoretical models in comparison to experiments. Diffusion and transport in the nucleus are most appropriately described with the concept of obstructed diffusion. A large volume fraction of the nucleus seems to contain a cytosol-like liquid with an apparent viscosity 5 times higher than in water. The geometry of particles and structure as well as their interactions influence the mobilities in terms of speed and spatial coverage. A considerable amount of genomic sites is accessible for not too large particles. FCS experiments and simulations based on the polymer model are in a good agreement. Using recently developed in vivo chromatin markers, a detailed study of mobility vs. structure is subject of current work