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Search Results: 1 - 10 of 800 matches for " Giuliano Silvi "
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Tensor Networks: a quantum-information perspective on numerical renormalization groups
Pietro Silvi
Physics , 2012,
Abstract: Exact many-body quantum problems are known to be computationally hard due to the exponential scaling of the numerical resources required. Since the advent of the Density Matrix Renormalization Group, it became clear that a successful strategy to work around this obstacle was to develop numerical methods based on the well-known theoretical renormalization group. In recent years, it was realized that quantum states engineered via numerical renormalization allow a variational representation in terms of a tensor network picture. The discovery provided a further boost to the effectiveness of these techniques, not only due to the increased flexibility and manipulability, but also because tensor network states embed a direct interface to the entanglement they carry, so that one can directly address many-body quantum correlations within these variational ansatz states. This lead to the application of several numerical tools, originally developed in the field of quantum-information, to approach condensed matter problems.
General Introduction to the Role of the Library for University Education
Sirje Virkus,Silvi Metsar
Liber Quarterly : The Journal of European Research Libraries , 2004,
Abstract: Our society is undergoing a process of rapid change, moving toward what is called the information society, the knowledge society, the network society or the informational mode of development (Castells, 1996; Inglis et al, 2002: 17) refer to the following features of the current period: dynamic and continuous change and transformation; the failure of great theories such as Marxism to locate and predict directions of change; the discontinuous and erratic rather than evolutionary nature of social change; the juxtaposition of various images of social, economic and political life and the transformation of images like Disney world, TV sports and Web pages into the realities with which we deal. It is believed that information and knowledge are distinguishing features of this modern society and the main driver of this change is the growing use of information and communication technologies (ICT).
Relationship between plasma adipokines, inflammation, insulin resistance and subclinical atherosclerosis in newly diagnosed type 2 diabetes  [PDF]
Razvan Vasilescu, Silvi Ifrim, Constantin Ionescu-Tirgoviste
Journal of Diabetes Mellitus (JDM) , 2011, DOI: 10.4236/jdm.2011.12004
Abstract: Background: The aim of this study was to investigate the occurrence of subclinical atherosclerosis, evaluated by carotid artery intima-media thickness (CIMT) in subjects with newly diagnosed type 2 diabetes. Methods: A total of 167 subjects, 50 newly diagnosed type 2 diabetic subjects and 117 non-diabetic subjects were included in the study. Obese and overweight newly diagnosed type 2 diabetic patients were matched for age and BMI with obese and overweight non-diabetic subjects. Only postmenopausal women were selected. The following biomarkers were analyzed: fasting glucose, HbA1c, fasting insulin, fasting proinsulin, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, adiponectin, leptin, hs-CRP, urine albumin/creatinine ratio. 75 g oral glucose tolerance test was performed in all subjects. Ultrasound imaging was used to evaluate IMT of the common carotid artery. Results: CIMT was greater in newly diagnosed type 2 patients compared to non-diabetic subjects. When analyzed by BMI, the difference regarding CIMT between diabetic and non-diabetic subjects was significant only in overweight subjects, in both sexes. In univariate analysis in men with newly diagnosed type 2 diabetes, CIMT was positively correlated with age, SBP, triglycerides, leptin and negatively correlated with HDL-cholesterol and in women CIMT was positively correlated with SBP and leptin. Independent determinants of CIMT in patients with newly diagnosed type 2 diabetes were in men age (β = 0.556, p = 0.0028) and log leptin (β = 0.393, p = 0.049) and in women systolic blood pressure (β = 0.48, p = 0.026). Conclusions: Subclinical atherosclerosis is present in newly diagnosed type 2 diabetic subjects. Body fat accumulation in men and hypertension in postmenopausal women have a primary role in increase carotid intima-media thickness.
Volumetric Breast Ultrasound as a Screening Modality in Mammographically Dense Breasts
Vincenzo Giuliano,Concetta Giuliano
ISRN Radiology , 2013, DOI: 10.5402/2013/235270
Abstract: This investigation is part of an ongoing large scale study using volumetric breast ultrasound (VBUS) as a screening modality in mammographically dense breasts, offering a substantial benefit to MR imaging of the breast in terms of cost and efficiency. The addition of VBUS to mammography in women with greater than 50% breast density resulted in the detection of 12.3 per 1,000 breast cancers, compared to 4.6 per 1,000 by mammography alone with an overall attributable risk of breast cancer of 19.92 (95% confidence level, 16.75–23.61) in our screened population. These preliminary results may justify the cost benefit of implementing the judicious use of VBUS as an alternative to MR imaging of the breast in conjunction with mammography in the dense breast screening population. 1. Introduction Mammographic density as an independent risk factor for developing breast cancer has been documented since the 1970s [1]. The appearance of breast tissue is variable among women. The appearance of density on mammography is the result of the relative proportion of breast stroma, which is less radiolucent compared to fat, accounting for increased breast density. Wolfe classified breast density as an independent risk factor for breast cancer in women [2, 3]. Approximately 70 to 80% of breast cancers occur in women with no major predictors [4–6]. Population-based screening for early detection of breast cancer is therefore the primary strategy for reducing breast cancer mortality. Mammography has been used as the standard imaging method for breast cancer screening, with reduction in breast cancer mortality [7]. Computer-aided detection (CAD) technology with full-field digital mammography (FFDM) has been shown to have several advantages over screen-film mammography, including higher contrast resolution, better dynamic range, and lower noise [8, 9]. Previous studies have shown that CAD performance is similar for the detection of cancer in fatty breasts and dense breasts with screen-film mammography (90% versus 88%, resp.; ) [10] and with FFDM (95% versus 98%; ) [11]. Sensitivity in extremely dense breasts was only 60% [12]. There are numerous studies showing that CAD performance is limited by background parenchymal breast density, where the sensitivity of the detection of breast masses sensitivity is significantly higher for fatty breasts than for dense breasts [11, 13–15]. Breast density significantly reduces the ability to visualize cancers on mammography. All false-negative lesions detected with CAD manifested as masses [16]. The number of missed cancers is substantially
A simple representation of quantum process tomography
Giuliano Benenti,Giuliano Strini
Physics , 2009, DOI: 10.1103/PhysRevA.80.022318
Abstract: We show that the Fano representation leads to a particularly simple and appealing form of the quantum process tomography matrix $\chi_{_F}$, in that the matrix $\chi_{_F}$ is real, the number of matrix elements is exactly equal to the number of free parameters required for the complete characterization of a quantum operation, and these matrix elements are directly related to evolution of the expectation values of the system's polarization measurements. These facts are illustrated in the examples of one- and two-qubit quantum noise channels.
Computing the distance between quantum channels: Usefulness of the Fano representation
Giuliano Benenti,Giuliano Strini
Physics , 2010, DOI: 10.1088/0953-4075/43/21/215508
Abstract: The diamond norm measures the distance between two quantum channels. From an operational vewpoint, this norm measures how well we can distinguish between two channels by applying them to input states of arbitrarily large dimensions. In this paper, we show that the diamond norm can be conveniently and in a physically transparent way computed by means of a Monte-Carlo algorithm based on the Fano representation of quantum states and quantum operations. The effectiveness of this algorithm is illustrated for several single-qubit quantum channels.
Optimal purification of a generic n-qudit state
Giuliano Benenti,Giuliano Strini
Physics , 2008, DOI: 10.1103/PhysRevA.79.052301
Abstract: We propose a quantum algorithm for the purification of a generic mixed state $\rho$ of a $n$-qudit system by using an ancillary $n$-qudit system. The algorithm is optimal in that (i) the number of ancillary qudits cannot be reduced, (ii) the number of parameters which determine the purification state $|\Psi>$ exactly equals the number of degrees of freedom of $\rho$, and (iii) $|\Psi>$ is easily determined from the density matrix $\rho$. Moreover, we introduce a quantum circuit in which the quantum gates are unitary transformations acting on a $2n$-qudit system. These transformations are determined by parameters that can be tuned to generate, once the ancillary qudits are disregarded, any given mixed $n$-qudit state.
Gaussian wave packets in phase space: The Fermi g_F function
Giuliano Benenti,Giuliano Strini
Physics , 2008, DOI: 10.1119/1.3083268
Abstract: Any pure quantum state can be equivalently represented by means of its wave function psi(q) or of the Fermi function g_F(q,p), with q and p coordinates and conjugate momenta of the system under investigation.We show that a Gaussian wave packet can be conveniently visualized in phase space by means of the curve g_F(q,p)=0. The evolution in time of the g_F=0 curve is then computed for a Gaussian packet evolving freely or under a constant or a harmonic force. As a result, the spreading or shrinking of the packet is easily interpreted in phase space. Finally, we discuss a gedanken prism microscope experiment for measuring the position-momentum correlation. This gedanken experiment, together with the well-known Heisenberg microscope and von Neumann velocimeter, is sufficient to fully determine the state of a Gaussian packet.
Quantum simulation of the single-particle Schrodinger equation
Giuliano Benenti,Giuliano Strini
Physics , 2007, DOI: 10.1119/1.2894532
Abstract: The working of a quantum computer is described in the concrete example of a quantum simulator of the single-particle Schrodinger equation. We show that a register of 6-10 qubits is sufficient to realize a useful quantum simulator capable of solving in an efficient way standard quantum mechanical problems.
A bird's eye view of quantum computers
Giuliano Benenti,Giuliano Strini
Physics , 2007,
Abstract: Quantum computers are discussed in the general framework of computation, the laws of physics and the foundations of quantum mechanics.
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