Regulation of cargo transfer between ESCRT-0 and ESCRT-I complexes by flotillin-1 during endosomal sorting of ubiquitinated cargo

Ubiquitin-dependent sorting of membrane proteins in endosomes directs them to lysosomal degradation. In the case of receptors such as the epidermal growth factor receptor (EGFR), lysosomal degradation is important for the regulation of downstream signalling. Ubiquitinated proteins are recognised in endosomes by the endosomal sorting complexes required for transport (ESCRT) complexes, which sequentially interact with the ubiquitinated cargo. Although the role of each ESCRT complex in sorting is well established, it is not clear how the cargo is passed on from one ESCRT to the next. We here show that flotillin-1 is required for EGFR degradation, and that it interacts with the subunits of ESCRT-0 and -I complexes (hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and Tsg101). Flotillin-1 is required for cargo recognition and sorting by ESCRT-0/Hrs and for its interaction with Tsg101. In addition, flotillin-1 is also required for the sorting of human immunodeficiency virus 1 Gag polyprotein, which mimics ESCRT-0 complex during viral assembly. We propose that flotillin-1 functions in cargo transfer between ESCRT-0 and -I complexes

Fault Models for Quantum Mechanical Switching Networks

The difference between faults and errors is that, unlike faults, errors can be corrected using control codes. In classical test and verification one develops a test set separating a correct circuit from a circuit containing any considered fault. Classical faults are modelled at the logical level by fault models that act on classical states. The stuck fault model, thought of as a lead connected to a power rail or to a ground, is most typically considered. A classical test set complete for the stuck fault model propagates both binary basis states, 0 and 1, through all nodes in a network and is known to detect many physical faults. A classical test set complete for the stuck fault model allows all circuit nodes to be completely tested and verifies the function of many gates. It is natural to ask if one may adapt any of the known classical methods to test quantum circuits. Of course, classical fault models do not capture all the logical failures found in quantum circuits. The first obstacle faced when using methods from classical test is developing a set of realistic quantum-logical fault models. Developing fault models to abstract the test problem away from the device level motivated our study. Several results are established. First, we describe typical modes of failure present in the physical design of quantum circuits. From this we develop fault models for quantum binary circuits that enable testing at the logical level. The application of these fault models is shown by adapting the classical test set generation technique known as constructing a fault table to generate quantum test sets. A test set developed using this method is shown to detect each of the considered faults.Comment: (almost) Forgotten rewrite from 200

The Effect of Third Party Investigation on Pay-Per-Click Advertising

Click fraud is a critical problem in pay-per-click advertising. While both service providers (SPs) and advertisers employ technologies to identify fraudulent clicks, prior work shows that they cannot be induced to make further improvements to their respective technologies. We consider the use of third-party investigation to address this problem and examine whether the responsibility of investigation payments helps induce both parties to work towards improving their technologies unilaterally. Using a principal-agent setting, we show that the advertiser always has incentives to improve his verification technology and the SP will improve his detection technology only when the detection cost is not too large. Given that the cost of detection technology is likely to be small due to the use of inexpensive online filters, our result suggests that third-party investigation helps induce further enhancements to the technologies and is a good mechanism to address the incentive problems in the click fraud setting

Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal

The accurate characterization of eigenmodes and eigenfrequencies of two-dimensional ion crystals provides the foundation for the use of such structures for quantum simulation purposes. We present a combined experimental and theoretical study of two-dimensional ion crystals. We demonstrate that standard pseudopotential theory accurately predicts the positions of the ions and the location of structural transitions between different crystal configurations. However, pseudopotential theory is insufficient to determine eigenfrequencies of the two-dimensional ion crystals accurately but shows significant deviations from the experimental data obtained from resolved sideband spectroscopy. Agreement at the level of 2.5 x 10^(-3) is found with the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and the effect is understood from the dynamics of two-dimensional ion crystals in the Paul trap. The results represent initial steps towards an exploitation of these structures for quantum simulation schemes.Comment: 5 pages, 4 figures, supplemental material (mathematica and matlab files) available upon reques

Isolating Triggered Star Formation

Galaxy pairs provide a potentially powerful means of studying triggered star formation from galaxy interactions. We use a large cosmological N-body simulation coupled with a well-tested semi-analytic substructure model to demonstrate that the majority of galaxies in close pairs reside within cluster or group-size halos and therefore represent a biased population, poorly suited for direct comparison to ``field'' galaxies. Thus, the frequent observation that some types of galaxies in pairs have redder colors than ``field'' galaxies is primarily a selection effect. We select galaxy pairs that are isolated in their dark matter halos with respect to other massive subhalos (N=2 halos) and a control sample of isolated galaxies (N=1 halos) for comparison. We then apply these selection criteria to a volume-limited subset of the 2dF Galaxy Redshift Survey with M_Bj <= -19 and obtain the first clean measure of the typical fraction of galaxies affected by triggered star formation and the average elevation in the star formation rate. We find that 24% (30.5%) of these L^\star and sub-L^{\star} galaxies in isolated 50 (30) kpc/h pairs exhibit star formation that is boosted by a factor of >~ 5 above their average past value, while only 10% of isolated galaxies in the control sample show this level of enhancement. Thus, 14% (20 %) of the galaxies in these close pairs show clear triggered star formation. The isolation criteria we develop provide a means to constrain star formation and feedback prescriptions in hydrodynamic simulations and a very general method of understanding the importance of triggered star formation in a cosmological context. (Abridged.)Comment: 12 pages, 10 figures, emulateapj format, accepted by Ap

The bound on viscosity and the generalized second law of thermodynamics

We describe a new paradox for ideal fluids. It arises in the accretion of an \textit{ideal} fluid onto a black hole, where, under suitable boundary conditions, the flow can violate the generalized second law of thermodynamics. The paradox indicates that there is in fact a lower bound to the correlation length of any \textit{real} fluid, the value of which is determined by the thermodynamic properties of that fluid. We observe that the universal bound on entropy, itself suggested by the generalized second law, puts a lower bound on the correlation length of any fluid in terms of its specific entropy. With the help of a new, efficient estimate for the viscosity of liquids, we argue that this also means that viscosity is bounded from below in a way reminiscent of the conjectured Kovtun-Son-Starinets lower bound on the ratio of viscosity to entropy density. We conclude that much light may be shed on the Kovtun-Son-Starinets bound by suitable arguments based on the generalized second law.Comment: 11 pages, 1 figure, published versio

Distribution and Abundance of Zooplankton in Anthropogenic-Impacted Stream, Nsit-Ibom, Nigeria

This study aimed to investigate the distribution and abundance of zooplankton in Mbiokporo stream Nsit-Ibom Local Government Area, Akwa Ibom State, Nigeria. Samples were collected and analyzed using standard methods. The result revealed that there were 9 zooplankton taxonomic groups (namely: Arachnida, Bdelloidae, Branchiopoda, Chromadorae, Euglenoidea, Hexanauplia, Insecta, Polychaeta, Tubulinea), comprising 12 species and 91 individuals. The most abundant zooplankton species was Temora longicornis with the highest number of species across all the stations 24 > 19 > 7 for station 1, station 2, and station 3 respectively. Branchiopoda had the highest number of species (4) and highest species composition (33.33%), while Hexanauplia recorded the highest individual abundance (54.95%). The relative abundance of zooplankton phyla was as follows: (Hexanauplia, 54.95 %) > (Branchiopoda, 13.19 %) > (Bdelloidae, 8.79) % > (Chromadorae, 7.69 %) > (Polychaeta and Arachnida, 5.49 % each) > (Insecta, 2.20 %) > (Tubulinea, 1.10 %) respectively. Indices of species dominance were as follows: station 1 > station 2 > station 3, with the following values 0.4349 > 0.4235 > 0.2397 each. Meanwhile, the highest species evenness was in station 3 (0.7887), followed by station 2 (0.5495), while the lowest was in station 1 (0.486). Margalef’s species diversity was slightly higher in station 1 (1.649) than in station 3 (1.618) while the lowest was in station 2 (1.456). The equitability index among stations was as follows: 3 (0.8675) > station 2 (0.6659) > station 1 (0.6292). However, this result revealed that ongoing anthropogenic activities along the stream may resulted in the deterioration of the stream thereby leading low species composition of zooplankton as observed in this study