High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars

The kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of either sub-Keplerian or super-Keplerian accretion flow depending on the relative fastness of the neutron spin as compared to the Keplerian frequency at the inner disk radius. Within the magnetosphere-disk interaction model, the frequency difference between the two kHz QPOs observed in a given source can be estimated to be slightly higher than or nearly around the neutron star spin frequency if the neutron star is a slow rotator and less than the stellar spin frequency if the neutron star is a fast rotator.Comment: 4 pages, 2 figures, already published in AIP Conference Proceedings, Astrophysics of Neutron Stars 2010: A Conference in Honor of M. Ali Alpa

Auctions with Anticipated Regret

This paper demonstrates theoretically and experimentally that in first price auctions, overbidding with respect to risk neutral Nash equilibrium might be driven from anticipated loser regret (felt when bidders lose at an affordable price). Different information structures are created to elicit regret: bidders know they will learn the winning bid if they lose (loser regret condition); or the second highest bid if they win (winner regret condition); or no information regarding the other bids. Bidders only in loser regret condition anticipated regret and significantly overbid; in the other conditions bidders did not anticipate regret and hence did not overbid.overbidding, first price auction, anticipated regret

Spatio-Temporal Saliency Networks for Dynamic Saliency Prediction

Computational saliency models for still images have gained significant popularity in recent years. Saliency prediction from videos, on the other hand, has received relatively little interest from the community. Motivated by this, in this work, we study the use of deep learning for dynamic saliency prediction and propose the so-called spatio-temporal saliency networks. The key to our models is the architecture of two-stream networks where we investigate different fusion mechanisms to integrate spatial and temporal information. We evaluate our models on the DIEM and UCF-Sports datasets and present highly competitive results against the existing state-of-the-art models. We also carry out some experiments on a number of still images from the MIT300 dataset by exploiting the optical flow maps predicted from these images. Our results show that considering inherent motion information in this way can be helpful for static saliency estimation

Parallel tracks as quasi-steady states for the magnetic boundary layers in neutron-star low-mass X-ray binaries

The neutron stars in low-mass X-ray binaries (LMXBs) are usually thought to be weakly magnetized objects accreting matter from their low-mass companions in the form of a disk. Albeit weak as compared to those in young neutron-star systems, the neutron-star magnetospheres in LMXBs can play an important role in determining the correlations between spectral and temporal properties. Parallel tracks appearing in the plane of kilohertz (kHz) quasi-periodic oscillation (QPO) frequency versus X-ray flux can be used as a tool to study the magnetosphere-disk interaction in neutron-star LMXBs. For dynamically important weak fields, the formation of a non-Keplerian magnetic boundary layer at the innermost disk truncated near the surface of the neutron star is highly likely. Such a boundary region may harbor oscillatory modes of frequencies in the kHz range. We generate parallel tracks using the boundary region model of kHz QPOs. We also present the direct application of our model to the reproduction of the observed parallel tracks of individual sources such as 4U 1608--52, 4U 1636--53, and Aql X-1. We reveal how the radial width of the boundary layer must vary in the long-term flux evolution of each source to regenerate the parallel tracks. The run of the radial width looks similar for different sources and can be fitted by a generic model function describing the average steady behavior of the boundary region in the long term. The parallel tracks then correspond to the possible quasi-steady states the source can occupy around the average trend.Comment: 16 pages, 15 figures, accepted for publication in Ap

Ultra-luminous X-ray sources as super-critical propellers

We study the evolution of newborn neutron stars in high-mass X-ray binaries interacting with a wind-fed super-Eddington disk. The inner disk is regularized to a radiation-dominated quasi-spherical configuration for which we calculate the inner radius of the disk, the total luminosity of the system and the torque acting on the neutron star accordingly, following the evolution of the system through the ejector and early propeller stages. We find that the systems with $B \gtrsim 10^{13}$ G pass through a short ($\sim 20\,{\rm yr}$) ejector stage appearing as supernova impostors followed by a propeller stage lasting $\sim 10^3\,{\rm yr}$. In the super-critical propeller stage the system is still bright ($L\sim 10^{40}\,{\rm erg\, s^{-1}}$) due to the spindown power and therefore appears as an ultra-luminous X-ray source (ULX). The system evolves into pulsating ULX (PULX) when the neutron star spins down to a period ($P\sim 1$ s) allowing for accretion onto its surface to commence. Systems with lower magnetic fields, $B \sim 10^{11}$ G, pass through a long ($10^5\,{\rm yr}$) super-critical propeller stage with luminosities similar to those of the ultra-luminous super-soft sources (ULS), $L \lesssim 10^{40}\,{\rm erg\, s^{-1}}$. The equilibrium periods of these systems in the accretion stage is about $10\,{\rm ms}$, which is much smaller than the typical period range of PULX observed to date. Such systems could have a larger population, but their pulsations would be elusive due to the smaller size of the magnetosphere. Our results suggest that the ULS and some nonpulsating ULX are rapidly spinning and highly magnetized young neutron stars at the super-critical propeller stage.Comment: ApJ in press. 9 pages, 4 figure

Regional Integration in the Black Sea Region: the Case of Two Sisters, Istanbul and Odessa

The political change in the 1980’es and 1990’es in the Black Sea Region has introduced many questions regarding its future as the region faces massive problems like conflicts on territory, drop of production levels in the 1990’es and related poverty, and last but not the least, environmental problems. The size of the region also blurs the picture. However, briefly there are three major influences that mark the future development of the region: globalization, regionalization and Euro-Asian integration. We propose that under these three influences, a new global integration zone, consisting of multiple networks between cities of the Black Sea Region is emerging. Our proposition that a new global integration zone is emerging within the Black Sea Region depends on three assumptions: Our first assumption is that neo-liberal globalization and regionalization (and particularly Euro-Asian integration) lead to development of similar political changes in the region. Our second assumption is that neo-liberal globalization and regionalization lead to development of similar spatial socio-economic developments within the Black Sea Region which brings some cities to the fore to gain power in the national and global organization of production. Our third assumption is that there is increasing trans-national integration between subject cities. Emergence of such a zone is perhaps most important for policy makers at the local level who have to face either positive or negative on-site effects of globalization and regionalization. Increasing socio-economic inequalities, excessive agglomeration of economic activities and population, diversification of population and increasing complexity of problems cripple traditional city management and planning practices in these countries which have a strong central planning and administration background. Due to practical reasons, we limit our study to integration of two sub-national regions, the province of Istanbul, and the province of Odessa which are also sister cities. Province of Istanbul may be recalled as Greater Istanbul, or Istanbul Metropolitan City since at 2004 due to change in the administrative legislation. Province of Odessa includes the city of Odessa as well as other cities within the province. We may conclude that there is progressive convergence in the political grounds between Turkey-Ukraine and Istanbul-Odessa, mainly in the framework of the global structures that are predominantly part of the Euro-Atlantic supra-structure. Though there is not much evidence of similarity in spatial development of Istanbul and Odessa, particularly due to political inclarity and problems of administrative decentralization in Ukraine, there is evidence of economic and social integration, between Turkey-Ukraine and Istanbul-Odessa, which experiences slow development, and negative side effects like informal activities. As a conclusion we may argue that integration of two regions might heavily depend on the Ukrainian foreign and domestic policies, and the decisions of supra-national structures like the World Trade Organization and EU. We may expect a progress in economic integration by the removal of trade barriers, where Istanbul and Odessa would be direct beneficiaries as both production and transfer centres. Further administrative decentralization in Ukraine might lead to a re-population in Odessa Region, as happened in Istanbul after the 1980 period.

EU Integration and the Change of Spatial Organization in Turkey

After 1980, economic agenda changed and international trade and integration to global and regional systems gained more importance in Turkey, like in many countries. As a candidate of the EU Turkey as well has experienced a change in the spatial organization. It has been shown by many other studies that integration process leads to a change in the industrial structure and spatial organization. The effect of the removal or lowering of trade barriers and its effects on the industrial location has been widely investigated in the New Economic Geography literature. These effects are of great importance for some essential grounds of European Integration, such as a balanced regional development and decreasing inequalities among regions to increase overall competitiveness, since they may cause an increase in the regional disparities and conflict with main targets of integration. This paper analyses the change of spatial organization in Turkey through the integration process to the EU by using location quotient, dissimilarity index and some other indicators and tries to show whether if spatial organization changed in favour of existing centres or if new centres have emerged.

Discrete Clock Auctions: An Experimental Study

We analyze the implications of different pricing rules in discrete clock auctions. The two most common pricing rules are highest-rejected bid (HRB) and lowest-accepted bid (LAB). Under HRB, the winners pay the lowest price that clears the market; under LAB, the winners pay the highest price that clears the market. Both the HRB and LAB auctions maximize revenues and are fully efficient in our setting. Our experimental results indicate that the LAB auction achieves higher revenues. This also is the case in a version of the clock auction with provisional winners. This revenue result may explain the frequent use of LAB pricing. On the other hand, HRB is successful in eliciting true values of the bidders both theoretically and experimentally.Auctions, clock auctions, spectrum auctions, experimental economics, behavioral economics, market design