Hyperuniformity in amorphous speckle patterns

Hyperuniform structures possess the ability to confine and drive light, although their fabrication is extremely challenging. Here we demonstrate that speckle patters obtained by a superposition of randomly arranged sources of Bessel beams can be used to generate hyperunifrom scalar fields. By exploiting laser light tailored with a spatial filter, we experimentally produce (without requiring any computational power) a speckle pattern possessing maxima at locations corresponding to a hyperuniform distribution. By properly filtering out intensity fluctuation from the same speckle pattern, it is possible to retrieve an intensity profile satisfying the hyperuniformity requirements. Our findings are supported by extensive numerical simulations.Comment: 13 pages, 7 figure

Mining Twitter: Graph Analysis of Interactions among Users

Starting from early 2000s, social network websites became very popular; these social media allow users to interact and share content using social links. Users of these platforms often have the possibility to establish hundreds or thousands of social links with other users. While initial studies have focused on social networks topology, a natural and important aspect of networks has been neglected: the focus on user interactions. These links can be monitored to generate knowledge on said users as well as their relationships with others. There has been, lately, an increasing interest on examining the activity network - network able to provide, once traversed, the actual user interactions rather than friendships links - to filter and mine patterns or communities. The goal of this work is to exploit the Twitter traffic in order to analyze the users interactions. In order to do so, our work models tweets posted by users as activities list in a graph called activity network. Then, we traverse it looking for Direct (e.g. mentions by user, retweets, direct replies etc.) and indirect (list of users mentioned in a tweet, users retwitting the same tweet produced by another user, etc.) relationships among users in order to create the users interactions graph. We provide a weight schema by which assign a value to interactions found. The obtained graph shows the connections among users and, thanks to their weighted links, those users who have stronger links, such as Verified Accounts or "propaganda users" or cliques of users, clusters of users interacting with each other. Those entities may be interesting to investigate in several fields like Open Source Intelligence or Business Intelligence. This work has been developed on a distributed infrastructure able to perform these tasks efficiently. The network analysis leads to some considerations: firstly, it is necessary to identify all meaningful interactions among users, which typically depend from the social network and the activities performed. Secondly, many nodes (profiles) with high indegree are associated to mass media and famous people, and thus a filtering phase is a crucial step. Finally, it is remarkable to see that experiments carried out at different moments could lead to very different results since many similar topics may not involve the same users in different moments. This work will describe the state-of-the-art of the network analysis, and will introduce the architectural design of the system, as well as the analysis performed with the challenges encountered. Results collected by our analysis lead us to the conclusion that, despite being in its preliminary stages, focusing on social interactions is important because it may reveal connection of particular users willing to perform actual activities which may gain interest in intellingence organizations

Phase-Retrieved Tomography enables imaging of a Tumor Spheroid in Mesoscopy Regime

Optical tomographic imaging of biological specimen bases its reliability on the combination of both accurate experimental measures and advanced computational techniques. In general, due to high scattering and absorption in most of the tissues, multi view geometries are required to reduce diffuse halo and blurring in the reconstructions. Scanning processes are used to acquire the data but they inevitably introduces perturbation, negating the assumption of aligned measures. Here we propose an innovative, registration free, imaging protocol implemented to image a human tumor spheroid at mesoscopic regime. The technique relies on the calculation of autocorrelation sinogram and object autocorrelation, finalizing the tomographic reconstruction via a three dimensional Gerchberg Saxton algorithm that retrieves the missing phase information. Our method is conceptually simple and focuses on single image acquisition, regardless of the specimen position in the camera plane. We demonstrate increased deep resolution abilities, not achievable with the current approaches, rendering the data alignment process obsolete.Comment: 21 pages, 5 figure

Robust Machine Learning for Malware Detection over Time

The presence and persistence of Android malware is an on-going threat that plagues this information era, and machine learning technologies are now extensively used to deploy more effective detectors that can block the majority of these malicious programs. However, these algorithms have not been developed to pursue the natural evolution of malware, and their performances significantly degrade over time because of such concept-drift. Currently, state-of-the-art techniques only focus on detecting the presence of such drift, or they address it by relying on frequent updates of models. Hence, there is a lack of knowledge regarding the cause of the concept drift, and ad-hoc solutions that can counter the passing of time are still underinvestigated. In this work, we commence to address these issues as we propose (i) a drift-analysis framework to identify which characteristics of data are causing the drift, and (ii) SVM-CB, a time-aware classifier that leverages the drift-analysis information to slow down the performance drop. We highlight the efficacy of our contribution by comparing its degradation over time with a state-of-the-art classifier, and we show that SVM-CB better withstand the distribution changes that naturally characterizes the malware domain. We conclude by discussing the limitations of our approach and how our contribution can be taken as a first step towards more time-resistant classifiers that not only tackle, but also understand the concept drift that affect data

Modulated linear dynamics of nanobeams accounting for higher gradient effects

We present some numerical results for the linear dynamics of nanobeams modulated by an axial force, basing on a recent proposal of literature that encompasses both the standard nonlocal elasticity, according to Eringen, and second-order strain elasticity. Three different possibilities for the elastic potential energy provide different responses that highlight the contributions of nonlocality and strain gradient, plus their combination. An axial force affects the linear stationary dynamics of such nanobeams, inducing suitable variation of the natural angular frequencies for benchmark cases, until static buckling occurs when the natural angular frequency vanishes. Effects of the various elastic potentials on this modulation are investigated and thoroughly commented

Il futuro del calcio in Cina. Tra esperimenti sociali, scandali e fallimenti

Since the end of the 1970s, when it was already preparing for the ‘great opening’, China has sought to legitimize itself before the international community through various strategies, including seeking international recognition in sport and attempting to rapidly extend its influence over transnational sporting institutions by using and combining soft power, national status and the internal development of Olympic disciplines and, in particular, football. Already Deng Xiaoping, a passionate lover of the ‘beautiful game’, after the Cultural Revolution had rehabilitated football and tried to rebuild a Chinese football movement. But it was with the election of Xi Jinping as General Secretary of the Communist Party of China in 2012 that a real strategy was launched to develop Chinese football through structural reforms. Investment, participation and media consumption in football have increased since the implementation of this reform plan and the revitalization of football has become a key strategic objective for China. The continuing failures of the men’s senior national team, scandals – however – and, in recent times, the Covid-19 pandemic with the subsequent downturn in the Asian giant’s economic growth, have brought the contradictions of Chinese football to the surface. Our contribution will attempt to highlight the entanglements that link football to the complex and varied Chinese power system

Abnormal temporal coupling of tactile perception and motor action in Parkinson's disease

Evidence shows altered somatosensory temporal discrimination threshold (STDT) in Parkinson's disease in comparison to normal subjects. In healthy subjects, movement execution modulates STDT values through mechanisms of sensory gating. We investigated whether STDT modulation during movement execution in patients with Parkinson's disease differs from that in healthy subjects. In 24 patients with Parkinson's disease and 20 healthy subjects, we tested STDT at baseline and during index finger abductions (at movement onset "0", 100, and 200 ms thereafter). We also recorded kinematic features of index finger abductions. Fifteen out of the 24 patients were also tested ON medication. In healthy subjects, STDT increased significantly at 0, 100, and 200 ms after movement onset, whereas in patients with Parkinson's disease in OFF therapy, it increased significantly at 0 and 100 ms but returned to baseline values at 200 ms. When patients were tested ON therapy, STDT during index finger abductions increased significantly, with a time course similar to that of healthy subjects. Differently from healthy subjects, in patients with Parkinson's disease, the mean velocity of the finger abductions decreased according to the time lapse between movement onset and the delivery of the paired electrical stimuli for testing somatosensory temporal discrimination. In conclusion, patients with Parkinson's disease show abnormalities in the temporal coupling between tactile information and motor outflow. Our study provides first evidence that altered temporal processing of sensory information play a role in the pathophysiology of motor symptoms in Parkinson's disease