SU Uma stars: Rebrightenings after superoutburst

SU Uma stars after their long superoutbursts often show single or multiple rebrightenings. We show how this phenomenon can be understood as repeated reflections of transition waves which mediate changes between the hot and the cool state of the accretion disk and travel back and forth in the outer disk region, leaving an inner part permanently hot. This points to a temporarily increased viscosity, possibly related to the formation of large-scale and longer persisting magnetic fields by the dynamo operation during the long superoutburst. The 'mini-rebrightenings' in the early post-outburst light curve of V585 Lyr discovered by Kato and Osaki in Kepler observations seem to be understandable as a small limit cycle of low luminosity changes originating from a wiggle-feature in the thermal equilibrium curve of the cool optically thick disk.Comment: 9 pages, 6 figures, accepted for publication in PAS

A disk in the Galactic Center in the past ?

We raise the question whether in the past a disk could have existed in our Galactic Center which has disappeared now. Our model for the interaction of a cool disk and a hot corona above (Liu et al. 2004) allows to estimate an upper limit for the mass that might have been present in a putative accretion disk after a last star forming event, but would now have evaporated by coronal action.Comment: 2 pages, Contribution to Conference Proc. "Growing Black Holes", Garching, 2004, Eds. A. Merloni, S. Nayakshin, R. Sunyaev, Springer series "ESO Astrophysics Symposia", in prin

An O(n^{2.75}) algorithm for online topological ordering

We present a simple algorithm which maintains the topological order of a directed acyclic graph with n nodes under an online edge insertion sequence in O(n^{2.75}) time, independent of the number of edges m inserted. For dense DAGs, this is an improvement over the previous best result of O(min(m^{3/2} log(n), m^{3/2} + n^2 log(n)) by Katriel and Bodlaender. We also provide an empirical comparison of our algorithm with other algorithms for online topological sorting. Our implementation outperforms them on certain hard instances while it is still competitive on random edge insertion sequences leading to complete DAGs.Comment: 20 pages, long version of SWAT'06 pape

A self-regulating braking mechanism in black hole X-ray binaries

The outbursts of black hole X-ray transients can be understood as caused by a limit cycle instability in the accretion disk, similar to dwarf nova outbursts. For adequately low mass overflow rates from the companion star long outburst recurrence times are expected. But the fact that we find predominantly long recurrence times or that only one X-ray nova outburst was detected at all poses a problem. The question arises whether any braking mechanism could act in a way that long recurrence times are favored. We suggest that a circumbinary disk exists and brakes the orbital motion of the binary stars by tidal interaction. The irradiation during an outburst leads to mass loss by winds from the circumbinary disk, releaving the braking force until the removed matter is refilled by diffusion from outer parts. We show that this reduction of braking will self-adjust the mass transfer to the marginal rate that gives long recurrence times.Comment: 10 pages, 3 figures; in: Conference Proceedings "Evolution of Binary and Multiple Star Systems", Bormio 2000, ASP Conference Series, Vol. 229, 2001, in pres

Efficiently Generating Geometric Inhomogeneous and Hyperbolic Random Graphs

Hyperbolic random graphs (HRG) and geometric inhomogeneous random graphs (GIRG) are two similar generative network models that were designed to resemble complex real world networks. In particular, they have a power-law degree distribution with controllable exponent beta, and high clustering that can be controlled via the temperature T. We present the first implementation of an efficient GIRG generator running in expected linear time. Besides varying temperatures, it also supports underlying geometries of higher dimensions. It is capable of generating graphs with ten million edges in under a second on commodity hardware. The algorithm can be adapted to HRGs. Our resulting implementation is the fastest sequential HRG generator, despite the fact that we support non-zero temperatures. Though non-zero temperatures are crucial for many applications, most existing generators are restricted to T = 0. We also support parallelization, although this is not the focus of this paper. Moreover, we note that our generators draw from the correct probability distribution, i.e., they involve no approximation. Besides the generators themselves, we also provide an efficient algorithm to determine the non-trivial dependency between the average degree of the resulting graph and the input parameters of the GIRG model. This makes it possible to specify the desired expected average degree as input. Moreover, we investigate the differences between HRGs and GIRGs, shedding new light on the nature of the relation between the two models. Although HRGs represent, in a certain sense, a special case of the GIRG model, we find that a straight-forward inclusion does not hold in practice. However, the difference is negligible for most use cases

The physiology of coral reef calcifiers under local and global stressors

Anthropogenic activities have caused coral reefs worldwide to face extreme changes in their environment at both global and local scales. This thesis covers the effects of ocean acidification (OA) and eutrophication through increased dissolved organic carbon (DOC) availability on coral reef calcifiers. In this thesis the individual and combined effects of OA as increased dissolved inorganic carbon (DIC) and high availability of DOC on the physiology of reef building corals from the Great Barrier Reef and calcifying green algae from the Indo-Pacific and the Caribbean are investigated. More specifically, calcification processes, photosynthesis and nitrogen fixation of the coral holobiont and calcifying green algae were investigated. This thesis revealed that the physiology of the calcifiers investigated is negatively affected by both high DIC and DOC concentrations. These findings will be crucial to be able to investigate future reef changes under high DIC and increased DOC concentrations. Our findings on calcification rates and calcification structures can be used as indicators of environmental change and as future predictors

Recent advances in minimally invasive colorectal cancer surgery

Laparoscopy has improved surgical treatment of various diseases due to its limited surgical trauma and has developed as an interesting therapeutic alternative for the resection of colorectal cancer. Despite numerous clinical advantages (faster recovery, less pain, fewer wound and systemic complications, faster return to work) the laparoscopic approach to colorectal cancer therapy has also resulted in unusual complications, i.e. ureteral and bladder injury which are rarely observed with open laparotomy. Moreover, pneumothorax, cardiac arrhythmia, impaired venous return, venous thrombosis as well as peripheral nerve injury have been associated with the increased intraabdominal pressure as well as patient's positioning during surgery. Furthermore, undetected small bowel injury caused by the grasping or cauterizing instruments may occur with laparoscopic surgery. In contrast to procedures performed for nonmalignant conditions, the benefits of laparoscopic resection of colorectal cancer must be weighed against the potential for poorer long-term outcomes of cancer patients that still has not been completely ruled out. In laparoscopic colorectal cancer surgery, several important cancer control issues still are being evaluated, i.e. the extent of lymph node dissection, tumor implantation at port sites, adequacy of intraperitoneal staging as well as the distance between tumor site and resection margins. For the time being it can be assumed that there is no significant difference in lymph node harvest between laparoscopic and open colorectal cancer surgery if oncological principles of resection are followed. As far as the issue of port site recurrence is concerned, it appears to be less prevalent than first thought (range 0-2.5%), and the incidence apparently corresponds with wound recurrence rates observed after open procedures. Short-term (3-5 years) survival rates have been published by a number of investigators, and survival rates after laparoscopic surgery appears to compare well with data collected after conventional surgery for colorectal cancer. However, long-term results of prospective randomized trials are not available. The data published so far indicate that the oncological results of laparoscopic surgery compare well with the results of the conventional open approach. Nonetheless, the limited information available from prospective studies leads us to propose that minimally invasive surgery for colorectal cancer surgery should only be performed within prospective trials

Seed-produced anti-globulin VHH-Fc antibodies retrieve globulin precursors in the insoluble fraction and modulate the Arabidopsis thaliana seed subcellular morphology

Key message Nanobody-heavy chain (VHH-Fc) antibody formats have the potential to immunomodulate even highly accumulating proteins and provide a valuable tool to experimentally modulate the subcellular distribution of seed storage proteins. Recombinant antibodies often obtain high accumulation levels in plants, and thus, besides being the actual end-product, antibodies targeting endogenous host proteins can be used to interfere with the localization and functioning of their corresponding antigens. Here, we compared the effect of a seed-expressed nanobody-heavy chain (VHH-Fc) antibody against the highly abundant Arabidopsis thaliana globulin seed storage protein cruciferin with that of a VHH-Fc antibody without endogenous target. Both antibodies reached high accumulation levels of around 10% of total soluble protein, but strikingly, another significant part was present in the insoluble protein fraction and was recovered only after extraction under denaturing conditions. In seeds containing the anti-cruciferin antibodies but not the antibody without endogenous target, the amount of soluble, processed globulin subunits was severely reduced and a major part of the cruciferin molecules was found as precursor in the insoluble fraction. Moreover, in these seeds, aberrant vacuolar phenotypes were observed that were different from the effects caused by the depletion of globulins in knock-out seeds. Remarkably, the seeds with strongly reduced globulin amounts are fully viable and germinate with frequencies similar to wild type, illustrating how flexible seeds can retrieve amino acids from the stored proteins to start germination

Interobserver agreement of Thyroid Imaging Reporting and Data System (TIRADS) and strain elastography for the assessment of thyroid nodules

Background: Thyroid Imaging Reporting and Data System (TIRADS) was developed to improve patient management and cost-effectiveness by avoiding unnecessary fine needle aspiration biopsy (FNAB) in patients with thyroid nodules. However, its clinical use is still very limited. Strain elastography (SE) enables the determination of tissue elasticity and has shown promising results for the differentiation of thyroid nodules. Methods: The aim of the present study was to evaluate the interobserver agreement (IA) of TIRADS developed by Horvath et al. and SE. Three blinded observers independently scored stored images of TIRADS and SE in 114 thyroid nodules (114 patients). Cytology and/or histology was available for all benign (n = 99) and histology for all malignant nodules (n = 15). Results: The IA between the 3 observers was only fair for TIRADS categories 2–5 (Coheńs kappa = 0.27,p = 0.000001) and TIRADS categories 2/3 versus 4/5 (ck = 0.25,p = 0.0020). The IA was substantial for SE scores 1–4 (ck = 0.66,p<0.000001) and very good for SE scores 1/2 versus 3/4 (ck = 0.81,p<0.000001). 92–100% of patients with TIRADS-2 had benign lesions, while 28–42% with TIRADS-5 had malignant cytology/histology. The negative-predictive-value (NPV) was 92–100% for TIRADS using TIRADS-categories 4&5 and 96–98% for SE using score ES-3&4 for the diagnosis of malignancy, respectively. However, only 11–42% of nodules were in TIRADS-categories 2&3, as compared to 58–60% with ES-1&2. Conclusions: IA of TIRADS developed by Horvath et al. is only fair. TIRADS and SE have high NPV for excluding malignancy in the diagnostic work-up of thyroid nodules