Quantum interference in atomic-sized point contacts

The conductance of atomic-sized metallic point contacts is shown to be strongly voltage dependent due to quantum interference with impurities even in samples with low impurity concentrations. Transmission through these small contacts depends not only on the local atomic structure at the contact but also on the distribution of impurities or defects within a coherence length of the contact. In contrast with other mesoscopic systems we show that transport through atomic contacts is coherent even at room temperature. The use of a scanning tunneling microscope (STM) makes it possible to fabricate one atom contacts of gold whose transmission can be controlled by manipulation of the contact allowing inelastic spectroscopy in such small contacts.

Convergence analysis and validation of low cost distance metrics for computational cost reduction of the Iterative Closest Point algorithm

The Iterative Closest Point algorithm (ICP) is commonly used in engineering applications to solve the rigid registration problem of partially overlapped point sets which are pre-aligned with a coarse estimate of their relative positions. This iterative algorithm is applied in many areas such as the medicine for volumetric reconstruction of tomography data, in robotics to reconstruct surfaces or scenes using range sensor information, in industrial systems for quality control of manufactured objects or even in biology to study the structure and folding of proteins. One of the algorithm’s main problems is its high computational complexity (quadratic in the number of points with the non-optimized original variant) in a context where high density point sets, acquired by high resolution scanners, are processed. Many variants have been proposed in the literature whose goal is the performance improvement either by reducing the number of points or the required iterations or even enhancing the complexity of the most expensive phase: the closest neighbor search. In spite of decreasing its complexity, some of the variants tend to have a negative impact on the final registration precision or the convergence domain thus limiting the possible application scenarios. The goal of this work is the improvement of the algorithm’s computational cost so that a wider range of computationally demanding problems from among the ones described before can be addressed. For that purpose, an experimental and mathematical convergence analysis and validation of point-to-point distance metrics has been performed taking into account those distances with lower computational cost than the Euclidean one, which is used as the de facto standard for the algorithm’s implementations in the literature. In that analysis, the functioning of the algorithm in diverse topological spaces, characterized by different metrics, has been studied to check the convergence, efficacy and cost of the method in order to determine the one which offers the best results. Given that the distance calculation represents a significant part of the whole set of computations performed by the algorithm, it is expected that any reduction of that operation affects significantly and positively the overall performance of the method. As a result, a performance improvement has been achieved by the application of those reduced cost metrics whose quality in terms of convergence and error has been analyzed and validated experimentally as comparable with respect to the Euclidean distance using a heterogeneous set of objects, scenarios and initial situations.

Germany on Russia. Yes to links, no to rapprochement. OSW Point of View Number 39, March 2014

The German media have been correctly describing the atmosphere between the Chancellor's Office and the Kremlin as the chilliest in years. Various factors have laid bare the fact that the strategic partnership between Germany and Russia is at best currently undergoing a 'technical pause’: the underwhelming outcomes of the German-Russian intergovernmental consultations in the autumn of 2012 and of Chancellor Merkel's meeting with President Putin during the Hanover fair in the spring of 2013, as well as the way in which the EU dealt with the Cyprus debt issue and, finally, the support that Germany has extended to the anti-presidential protests in Ukraine. Meanwhile, the priorities of Germany's foreign and economic policy have changed considerably, not only as a result of the eurozone crisis, but also, even more importantly, because the attention of German business and politics has been shifting to the so-called neue Gestaltungsmächte, or new regional powers. German politicians increasingly believe that Russia should not be offered new methods or mechanisms of co-operation. Firstly, because the existing ones have not been fully utilised, and secondly, because Germany at this stage seems to have no idea of what the long-term strategy of co-operation with Putin's Russia should be.

Unity stronger than divisions. Ukraine's internal diversity. OSW Point of View Number 40, March 2014

Ukraine is deeply divided internally, although as a result of the changes that have taken place since its independence, the country’s internal divisions now have less and less to do with territorial divides, and the split into historical ‘sub-Ukraines’ has become less pronounced, especially for the younger generation. Ukraine is not a country of two competing regional identities, one in the west, the other in the east. The western identity, in which the unity of Ukraine is a key value, coexists with the multiple and diverse local patriotisms of the different regions in the east and the south of the country. The present protest movement has consolidated the country’s sense of unity. Its opponents have also been championing the indivisibility of Ukraine, even while they demanded a thorough decentralisation of the country, which was often mistaken for separatism. Russia has been stirring up separatist tendencies in Ukraine, but with little success. Crimea is an exception here, because in most respects it has remained unaffected by the dynamics of the social processes transforming mainland Ukraine – separatist tendencies are indeed deeply rooted in the peninsula.

Chechnya: Between a Caucasian Jihad and ‘hidden’ separatism. OSW Point of View, January 2007

1. Even though Chechnya remains the most unstable republic in the Russian North Caucasus, the open armed conflict known as the Second Chechen War, which broke out in the autumn of 1999, is gradually dying down. 2. Several years ago, the conflict in Chechnya could have been characterised as a war between Chechen separatists and the government of the Russian Federation. However, the nature of the conflict has changed significantly over the last four or five years. 3. Even though the intensity of fighting in Chechnya has abated in recent years, the conflict has spilt over to the other Caucasus republics such as Ingushetia, Dagestan and Kabardino-Balkaria. As a result, this is presently not so much a Chechen conflict as a regional clash between the authorities and the Caucasian (including Chechen) Islamists. 4. The Chechen militants are weaker now, and the conflict has changed from a struggle for national liberation into a fight for the Islamic cause; but this does not mean that Russia has ultimately solved the problem of Chechen separatism.

The Paradoxes of Moldovan Sports. An insight into the nature of the Transnistrian conflict. OSW Point of View, November 2011

Mutual relations in the area of sports, which in contemporary international contacts often not only reflect the true nature of political relations but sometimes even affect them, can be a valuable contribution to the analysis of this conflict’s nature. Why did the Transnistrian government, despite the use of anti-Moldovan rhetoric, agree to Transnistrian athletes representing Moldova during the Olympics and in other international competitions? Why does it accept the presence of sports teams from both banks of the Dniester playing in the same leagues? Why does Transnistria, despite being much smaller, predominate in many sports? How is it that Sheriff Tiraspol, the flagship football club of the business and political circles controlling Transnistria, managed to win the Moldovan championship ten times in a row and is the main source of players for Moldova’s national team? Does sport really ‘know no borders’ or perhaps the border on the Dniester is different than seems at first sight?

In Putin’s Shadow: Dmitry Medvedev’s presidency. OSW Point of View, November 2011

Dmitry Medvedev’s presidency was an experiment carried out by the Russian ruling elite. Even though the new president has been a loyal member of the ruling camp, this decision involved certain risk that the extensive constitutional powers could eventually encourage the new president to seek emancipation, which could provoke internal conflicts and splits in the elite. This paper analyses Medvedev’s presidency and tries to answer the question why this scenario did not take place and why Medvedev failed to overcome the restrictions imposed on him at the start of his presidential term. The paper also presents the activation of certain social groups during Medvedev’s presidency and their calls for a new social contract with the government.

'The power gained, we will never surrender': Russian ruling elite versus the succession and economic crisis. OSW Point of View (Policy Brief), October 2009

Even though the economic crisis proved harmful to the Russian economy and people's living standards, it has nonetheless failed to make the elite revise its policy. Despite some problems, the government has managed to sustain economic and political stability, thanks to the reserves it amassed in the times of prosperity, and to the propaganda campaign that protected it, above all Vladimir Putin. The crisis failed to force the elite to implement deeper structural and political reforms. Moreover, it has actually reinforced existing tendencies, such as state control over the economy and its oil-oriented character, the elite's economic expansion at the expense of private businesses, and the preservation of political power. Thus, the crisis has so far failed to dismantle Putinism, indeed quite the reverse - it has in fact contributed to its becoming 'set in stone'.

Ukraine, Another point of view. OSW Point of View (Unspecified), February 2003

Ukraine is a difficult partner for the West, and recently, it has been perceived as an enfant terrible because of the Kolchuga affair. Western and Polish press describe Ukraine as an authoritarian regime plagued by an internal crisis or even threatened by destabilisation. This picture is certainly one-sided and oversimplified, and it fails to accurately present the reality of Ukraine. Apart from experiencing definitely adverse political developments, Ukraine has also been successful in some ways in terms of its internal and foreign policies and the economy. At the same time, certain processes take place among the Ukrainian elites, that might be difficult to capture in social surveys, but may become the starting point for the future modernisation and democratisation of the country. To realise that there are some favourable aspects to the changes occurring in Ukraine is not to recognise Ukraine as a country heading to democratisation and a market economy in the Western sense. Still, it is worthwhile to understand that the positive developments, even if isolated, do occur in Ukraine and that they could be strengthened by adequate policies of the Ukrainian authorities and the Western states.

The great leap. Turkey under Erdogan. OSW Point of View 51, 27 May 2015

Since the AKP took power in 2002, Turkey has seen a replacement of the state’s elites, a real change of the political system and a redefinition of the state identity. All this has been accompanied by economic development and rapid social transformation. The pro-democratic reforms and improved prosperity in the first decade of the AKP’s rule created the opportunity for Turkey to become part of the West in terms of legal and political standards, while maintaining its cultural distinctness. However, from the point of view of Recep Tayyip Erdogan, the leader of a new Turkey, the political reforms turned out not to be a goal per se but a means to the end of achieving a monopoly on power. Once this goal was achieved, Erdogan began leading Turkey towards the status of an autocratic state focused on the Middle East and resentful towards the West. This trend is unlikely to be reversed under Erdogan’s rule. However, even if the government were to change, there would be no return to the Turkey from before the AKP era. In turn, the Turkish public will have to answer the questions regarding its civilisational identity and the vision of the political and social order.

Ramzanistan. Russia's Chechen Problem. OSW POINT OF VIEW Number 54, 2015-08-25

The political activity and growing independence of Chechnya’s leader Ramzan Kadyrov raises questions about his loyalty and the possibility of his openly renouncing his servitude to Moscow. Such a scenario seems unlikely because of the dependence of Kadyrov’s regime on Russia. He is burdened by his republic’s financial dependence, the stain of collaboration and the crimes committed on his own people, and so his regime cannot exist without Moscow’s support. However, Kadyrov’s dependence on Moscow and the apparent stability of the situation in Chechnya do not mean that a lasting peace has been established there. The current plan for governing the republic and the relationship between Moscow and Grozny is a temporary solution, based not on durable solutions, but on the situational convergence of the Kremlin and Kadyrov’s interests. A change of government in the Kremlin, or to an even greater degree a domestic crisis in Russia which weakens its position in the Caucasus, would mean the fall of Kadyrov’s regime, and the reactivation of pro-independence rhetoric in Chechnya.

Late Putin. The end of growth, the end of stability. OSW POINT OF VIEW #55, 2015-10-05

Since Vladimir Putin returned to the Kremlin as President in May 2012, the Russian system of power has become increasingly authoritarian, and has evolved towards a model of extremely personalised rule that derives its legitimacy from aggressive decisions in internal and foreign policy, escalates the use of force, and interferes increasingly assertively in the spheres of politics, history, ideology or even public morals. Putin’s power now rests on charismatic legitimacy to a much greater extent than it did during his first two presidential terms; currently the President is presented not only as an effective leader, but also as the sole guarantor of Russia’s stability and integrity. After 15 years of Putin’s rule, Russia’s economic model based on revenue from energy resources has exhausted its potential, and the country has no new model that could ensure continued growth for the economy. The Putinist system of power is starting to show symptoms of agony – it has been unable to generate new development projects, and has been compensating for its ongoing degradation by escalating repression and the use of force. However, this is not equivalent to its imminent collapse.

Sun and sky:does human vision assume a mixture of point and diffuse illumination when interpreting shape-from-shading?

People readily perceive smooth luminance variations as being due to the shading produced by undulations of a 3-D surface (shape-from-shading). In doing so, the visual system must simultaneously estimate the shape of the surface and the nature of the illumination. Remarkably, shape-from-shading operates even when both these properties are unknown and neither can be estimated directly from the image. In such circumstances humans are thought to adopt a default illumination model. A widely held view is that the default illuminant is a point source located above the observer's head. However, some have argued instead that the default illuminant is a diffuse source. We now present evidence that humans may adopt a flexible illumination model that includes both diffuse and point source elements. Our model estimates a direction for the point source and then weights the contribution of this source according to a bias function. For most people the preferred illuminant direction is overhead with a strong diffuse component.

Enclosing the behavior of a hybrid system up to and beyond a Zeno point

Even simple hybrid systems like the classic bouncing ball can exhibit Zeno behaviors. The existence of this type of behavior has so far forced simulators to either ignore some events or risk looping indefinitely. This in turn forces modelers to either insert ad hoc restrictions to circumvent Zeno behavior or to abandon hybrid modeling. To address this problem, we take a fresh look at event detection and localization. A key insight that emerges from this investigation is that an enclosure for a given time interval can be valid independently of the occurrence of a given event. Such an event can then even occur an unbounded number of times, thus making it possible to handle certain types of Zeno behavior.

The Point of Continuity Property: Descriptive Complexity and Ordinal Index

∗ Supported by D.G.I.C.Y.T. Project No. PB93-1142