Letteratura scientifica selezionata sul tema "Nonoptical astronomy"

In this paper, we study some optimal inequalities of the Riccati type and of the Bihari type. We also consider nonoptimal inequalities of the Wendorf type. At the same time, we get a partial answer to Problems 5 and 9, formulated by I. A. Rus. This paper is also motivated by the fact that, in many inequalities, the upper bound is not an optimal one.

In recent years, several methods of noise cleaning have been devised, of which projective methods have been particularly effective. In our paper, we explain in detail why orthogonal projections are nonoptimal and how the nonorthogonal projections suggested by Grassberger et al., naturally emerge from the SVD method. We show that this approach when combined with a dynamic neighborhood selection yields optimal results of noise cleaning.

Wireless technologies based on electromagnetic wave are crucial in the modern industry but nonoptimal in electromagnetic-restricted conditions such as underwater applications, where acoustic wave has been proposed as an indispensable approach. However, most of the current acoustic wireless methods could support single wireless function and control single device. A converged wireless infrastructure that simultaneously supports the mainstream wireless functions remains inaccessible for acoustics. The difficulty lies in constructing the dynamic control network consisting of multiple nodes with acoustic method. Here, we develop the converged wireless infrastructure based on the acoustic holographic array, which serves as the central hub of the system. The holographic array allows for simultaneous control of multiple targets and integrates multiple mainstream wireless functions. We experimentally present the acoustic version of the converged wireless system that realizes a series of functions, including (i) selective wireless power transfer, (ii) stable remote monitoring, (iii) dynamic programmable logic control, and (iv) wireless acoustic communication. The wireless system is capable of powering and controlling free-moving devices. The unique immunity against electromagnetic and biological interferences is further demonstrated. The acoustic-based wireless infrastructure provides a route to wireless technologies, especially for those in electromagnetic-restricted conditions.

In this paper, we will study the key enumeration problem, which is connected to the key recovery problem posed in the cold boot attack setting. In this setting, an attacker with physical access to a computer may obtain noisy data of a cryptographic secret key of a cryptographic scheme from main memory via this data remanence attack. Therefore, the attacker would need a key-recovery algorithm to reconstruct the secret key from its noisy version. We will first describe this attack setting and then pose the problem of key recovery in a general way and establish a connection between the key recovery problem and the key enumeration problem. The latter problem has already been studied in the side-channel attack literature, where, for example, the attacker might procure scoring information for each byte of an Advanced Encryption Standard (AES) key from a side-channel attack and then want to efficiently enumerate and test a large number of complete 16-byte candidates until the correct key is found. After establishing such a connection between the key recovery problem and the key enumeration problem, we will present a comprehensive review of the most outstanding key enumeration algorithms to tackle the latter problem, for example, an optimal key enumeration algorithm (OKEA) and several nonoptimal key enumeration algorithms. Also, we will propose variants to some of them and make a comparison of them, highlighting their strengths and weaknesses.

The experiments at the Large Hadron Collider (LHC) rely upon a complex distributed computing infrastructure (WLCG) consisting of hundreds of individual sites worldwide at universities and national laboratories, providing about half a billion computing job slots and an exabyte of storage interconnected through high speed networks. Wide Area Networking (WAN) is one of the three pillars (together with computational resources and storage) of LHC computing. More than 5 PB/day are transferred between WLCG sites. Monitoring is one of the crucial components of WAN and experiments operations. In the past years all experiments have invested significant effort to improve monitoring and integrate networking information with data management and workload management systems. All WLCG sites are equipped with perfSONAR servers to collect a wide range of network metrics. We will present the latest development to provide the 3D force directed graph visualization for data collected by perfSONAR. The visualization package allows site admins, network engineers, scientists and network researchers to better understand the topology of our Research and Education networks and it provides the ability to identify nonreliable or/and nonoptimal network paths, such as those with routing loops or rapidly changing routes.

Context. The most massive galaxies (Mstellar ≥ 1011 M⊙) in the local Universe are characterized by a bulge-dominated morphology and old stellar populations, in addition to being confined to a tight mass-size relation. Identifying their main components can provide insights into their formation mechanisms and subsequent mass assembly. Aims. Taking advantage of Hubble Space Telescope (HST) CANDELS data, we analyze the lowest redshift (z < 0.5) massive galaxies in the H and I band in order to disentangle their structural constituents and study possible faint non-axisymmetric features. Methods. Our final sample consists of 17 massive galaxies. Due to the excellent HST spatial resolution for intermediate redshift objects, they are hard to model by purely automatic parametric fitting algorithms. We performed careful single and double (bulge-disk decompositions) Sérsic fits to their galaxy surface brightness profiles. We compare the model color profiles with the observed ones and also derive multi-component global effective radii attempting to obtain a better interpretation of the mass-size relation. Additionally, we test the robustness of our measured structural parameters via simulations. Results. We find that the Sérsic index does not offer a good proxy for the visual morphological type for our sample of massive galaxies. Our derived multi-component effective radii give a better description of the size of our sample galaxies than those inferred from single Sérsic models with GALFIT. Our galaxy population lies on the scatter of the local mass-size relation, indicating that these massive galaxies have not experienced a significant growth in size since z ∼ 0.5. Interestingly, the few outliers are late-type galaxies, indicating that spheroids must reach the local mass-size relation earlier. For most of our sample galaxies, both single- and multi-component Sérsic models with GALFIT show substantial systematic deviations from the observed surface brightness profiles in the outskirts. These residuals may be partly due to several factors, namely a nonoptimal data reduction for low surface brightness features or the existence of prominent stellar haloes for massive galaxies, or they could also arise from conceptual shortcomings of parametric 2D image decomposition tools. They consequently propagate into galaxy color profiles. This is a significant obstacle to the exploration of the structural evolution of galaxies, which calls for a critical assessment and refinement of existing surface photometry techniques.

The horn plays an elemental role in the make up of a radio-telescope. The focus of this research is on one particular type of horn – the diagonal horn. An analysis of the diagonal horn is made using the Fourier method. The analysis begins from Maxwell’s equations, as the basic building block, and describes the steps involved in developing the radiation pattern. Based on the theory, a program was written that produces the theoretical graphs referred to throughout the thesis. A diagonal horn was manufactured and the radiation patterns were measured. A comparison of these measured patterns is made against the theoretically generated patterns. Further research was carried out to demonstrate the effects on the radiation patterns when the horn is fitted with a dielectric plug. This practice may enhance the directivity of the horn at the cost of introducing new losses
Master of Engineering (Hons)

The horn plays an elemental role in the make up of a radio-telescope. The focus of this research is on one particular type of horn – the diagonal horn. An analysis of the diagonal horn is made using the Fourier method. The analysis begins from Maxwell’s equations, as the basic building block, and describes the steps involved in developing the radiation pattern. Based on the theory, a program was written that produces the theoretical graphs referred to throughout the thesis. A diagonal horn was manufactured and the radiation patterns were measured. A comparison of these measured patterns is made against the theoretically generated patterns. Further research was carried out to demonstrate the effects on the radiation patterns when the horn is fitted with a dielectric plug. This practice may enhance the directivity of the horn at the cost of introducing new losses