On the classification of the low energy excitations in the doped antiferromagnet

A long-wavelength, low energy hamiltonian is derived to describe the dynamic of a single hole in a quantum antiferromagnet in two or higher spatial dimensions. In thisexactly solvable limit anew kind of symmetry is important to classify the elementary spin excitations of a single hole in the t — J model. This symmetry is hidden at finite size or at short wavelength. The resulting classification has important consequences for understanding the physics of doped antiferromagnets. Fermi liquid like s = 1/2 and charge one excitations are still well defined in a quantum antiferromagnet, but are not a complete set to describe the low energy physics.     

Daily Dialysis: Toward a New Standard in Well‐Being

Daily hemodialysis (DHD) is a promising option; however, logistic obstacles and clinical perplexities limit its dissemination. Understanding the mechanisms of, and the time until, the onset of improved well‐being may help to quantify clinical advantages and to define the minimum length of a “trial” of daily dialysis. By following 30 patients treated in 4 centers, this study aimed to determine how long a period of time is needed until a patient experiences subjective improvement. From November 1998 to November 2000, 30 patients tried at least 2 weeks of short daily dialysis in four Northern Italian centers of Piemonte and Valle d'Aosta. The DHD (2 – 3 hours; blood flow 270 – 350 mL/min; individual HCO₃, Na, K) was performed at home or in a center. Motivations to try DHD, fears and concerns regarding DHD, and changes in perceived well‐being were assessed by semi‐structured interview. The main clinical indications for a trial of DHD were poor tolerance of conventional treatment, cardiovascular disease, and hypertension or hypotension; only 6 patients had no comorbidity at start. The patients' main reasons for choosing DHD were related to job problems and the search for a better treatment. Most of the patients continued DHD because of improved well‐being; logistic reasons accounted for the drop‐outs (5 patients). The main fears were related to logistic aspects, vascular access problems, and excessive involvement of the partner on home dialysis. Improved well‐being was reported by 28 of 30 patients; 2 patients reported no difference. Subjective improvement was perceived within 2 weeks in 22 of 30 patients, and within 1 month in 28 of 30 patients. An offer of a 2 – 4 week trial of DHD may help patients and caregivers to determine whether subjective and objective benefits outweigh logistic problems and whether a permanent transfer to DHD is worthwhile.     

A Fast Algorithm to Estimate the Distance Spectrum of Turbo Codes and Tail-Biting Turbo Codes

The computational complexity required by the complete calculation of the distance spectrum of turbo codes, even limited to low weight input sequences, makes it too slow for practical purposes such as interleaver optimization or effective bit error rate bounding. In this paper, a fast algorithm for distance spectrum estimation purposes is presented. A comparison with complete computed spectra, theoretically derived spectra and results from previous works will be presented for both deterministic and uniform interleavers.     

Gray-box monitoring of hyperproperties with an application to privacy

Formal Methods in System Design - Runtime verification is a complementary approach to testing, model checking and other static verification techniques to verify software properties. Monitorability...     

Communication constraints in the average consensus problem

The interrelationship between control and communication theory is becoming of fundamental importance in many distributed control systems, such as the coordination of a team of autonomous agents. In such a problem, communication constraints impose limits on the achievable control performance. We consider as instance of coordination the consensus problem. The aim of the paper is to characterize the relationship between the amount of information exchanged by the agents and the rate of convergence to the consensus. We show that time-invariant communication networks with circulant symmetries yield slow convergence if the amount of information exchanged by the agents does not scale well with their number. On the other hand, we show that randomly time-varying communication networks allow very fast convergence rates. We also show that by adding logarithmic quantized data links to time-invariant networks with symmetries, control performance significantly improves with little growth of the required communication effort.     

A model for learning objects adaptation in light of mobile and context-aware computing

The growth usage of mobile technologies and devices such as smartphones and tablets, and the almost ubiquitous wireless communication set the stage for the development of novel kinds of applications. One possibility is exploiting this scenario in the field of education, so creating more intelligent, flexible and customizable systems. Mobile devices can be used to help students to learn, considering their learning styles, surroundings, devices and profiles. In this way, the main goal of this article is to propose EduAdapt, an architectural model for the adaptation of learning objects considering device characteristics, learning style and other student’s context information. To make this adaptation we used inferences and rules in a proposed ontology, named OntoAdapt. We believe that such ontology can help recommending learning objects to students or adapt these objects according to the context (context-aware computing). We evaluate this proposal in two ways. Firstly, we used scenarios and metrics to assess the ontology. Secondly, we developed a prototype of EduAdapt model and submitted to a class of 20 students with the intention of evaluating the usability and adherence to adapted objects, resulting in a 78 % of acceptance. In brief, the evaluation presented encouraging results, indicating that the proposed model would be useful in the learning process.     

Maximal Discrepancy for Support Vector Machines

The Maximal Discrepancy (MD) is a powerful statistical method, which has been proposed for model selection and error estimation in classification problems. This approach is particularly attractive when dealing with small sample problems, since it avoids the use of a separate validation set. Unfortunately, the MD method requires a bounded loss function, which is usually avoided by most learning algorithms, including the Support Vector Machine (SVM), because it gives rise to a non-convex optimization problem. We derive in this work a new approach for rigorously applying the MD technique to the error estimation of the SVM and, at the same time, preserving the original SVM framework.     

Model-based qualitative risk assessment for availability of IT infrastructures

For today’s organisations, having a reliable information system is crucial to safeguard enterprise revenues (think of on-line banking, reservations for e-tickets etc.). Such a system must often offer high guarantees in terms of its availability; in other words, to guarantee business continuity, IT systems can afford very little downtime. Unfortunately, making an assessment of IT availability risks is difficult: incidents affecting the availability of a marginal component of the system may propagate in unexpected ways to other more essential components that functionally depend on them. General-purpose risk assessment (RA) methods do not provide technical solutions to deal with this problem. In this paper we present the qualitative time dependency (QualTD) model and technique, which is meant to be employed together with standard RA methods for the qualitative assessment of availability risks based on the propagation of availability incidents in an IT architecture. The QualTD model is based on our previous quantitative time dependency (TD) model (Zambon et al. in BDIM ’07: Second IEEE/IFIP international workshop on business-driven IT management. IEEE Computer Society Press, pp 75–83, 2007), but provides more flexible modelling capabilities for the target of assessment. Furthermore, the previous model required quantitative data which is often too costly to acquire, whereas QualTD applies only qualitative scales, making it more applicable to industrial practice. We validate our model and technique in a real-world case by performing a risk assessment on the authentication and authorisation system of a large multinational company and by evaluating the results with respect to the goals of the stakeholders of the system. We also perform a review of the most popular standard RA methods and discuss which type of method can be combined with our technique.     

On using alternative perturbation theory methodologies in the evaluation of reactivity effects in ADS cores

Core-average Doppler and coolant void reactivity coefficients, as well as the kinetic parameters (β_eff and Λ), have been determined for sub-critical accelerator-driven systems employing lead–bismuth eutectic (LBE) and helium gas coolants. To determine these parameters use is made of the standard procedure for analyzing critical reactors, which is based on “perturbation-theory” (PT), while in addition two dedicated methodologies for sub-critical systems, i.e. “inhomogeneous perturbation-theory” (IPT) and “heuristically based generalized perturbation-theory” (HGPT), have been employed to compute these parameters in a more rigorous manner.The two methods (PT and IPT/HGPT) are found to give similar results for each application and despite a smaller target k_eff-value, the sensitivity of the method is small in the case of the gas-cooled system, thus confirming the adequacy of the standard procedure. As regards the coolant void reactivity coefficient in the gas-cooled ADS, this finding can mostly be attributed to the fact that the core is always transparent with respect to the source neutrons, irrespective of the specific helium content.The sensitivity of the Doppler coefficient is also rather low in the case of the LBE cooled system. However, the dedicated methods are needed for the correct prediction of the coolant void reactivity coefficient, especially if minor actinides are introduced into the core. More important, in this case, is the fact that the PT-approach does not produce conservative results. Finally the sensitivity of the reactivity and kinetic parameters to the different methods is of the same order as that due to uncertainties in nuclear data and therefore these will need to be included in any overall evaluation of the impact of uncertainties on steady-state and transient ADS performance.