292 research outputs found
Hug-like island growth of Ge on strained vicinal Si(111) surfaces
We examine the structure and the evolution of Ge islands epitaxially grown on
vicinal Si(111) surfaces by scanning tunneling microscopy. Contrary to what is
observed on the singular surface, three-dimensional Ge nanoislands form
directly through the elastic relaxation of step-edge protrusions during the
unstable step-flow growth. As the substrate misorientation is increased, the
islands undergo a shape transformation which is driven by surface energy
minimization and controlled by the miscut angle. Using finite element
simulations, we show that the dynamics of islanding observed in the experiment
results from the anisotropy of the strain relaxation.Comment: 4 figure
Correlated Nanoscopic Josephson Junctions
We discuss correlated lattice models with a time-dependent potential across a
barrier and show how to implement a Josephson-junction-like behavior. The
pairing occurs by a correlation effect enhanced by the symmetry of the system.
In order to produce the effect we need a mild distortion which causes avoided
crossings in the many-body spectrum. The Josephson-like response involves a
quasi-adiabatic evolution in the time-dependent field. Besides, we observe an
inverse-Josephson (Shapiro) current by applying an AC bias; a supercurrent in
the absence of electromotive force can also be excited. The qualitative
arguments are supported by explicit exact solutions in prototype 5-atom
clusters with on-site repulsion. These basic units are then combined in
ring-shaped systems, where one of the units sits at a higher potential and
works as a barrier. In this case the solution is found by mapping the
low-energy Hamiltonian into an effective anisotropic Heisenberg chain. Once
again, we present evidence for a superconducting flux quantization, i.e. a
Josephson-junction-like behavior suggesting the build-up of an effective order
parameter already in few-electron systems. Some general implications for the
quantum theory of transport are also briefly discussed, stressing the
nontrivial occurrence of asymptotic current oscillations for long times in the
presence of bound states.Comment: 12 pages, 2 figures, to appear in J. Phys. - Cond. Ma
HyBIS: Windows Guest Protection through Advanced Memory Introspection
Effectively protecting the Windows OS is a challenging task, since most
implementation details are not publicly known. Windows has always been the main
target of malwares that have exploited numerous bugs and vulnerabilities.
Recent trusted boot and additional integrity checks have rendered the Windows
OS less vulnerable to kernel-level rootkits. Nevertheless, guest Windows
Virtual Machines are becoming an increasingly interesting attack target. In
this work we introduce and analyze a novel Hypervisor-Based Introspection
System (HyBIS) we developed for protecting Windows OSes from malware and
rootkits. The HyBIS architecture is motivated and detailed, while targeted
experimental results show its effectiveness. Comparison with related work
highlights main HyBIS advantages such as: effective semantic introspection,
support for 64-bit architectures and for latest Windows (8.x and 10), advanced
malware disabling capabilities. We believe the research effort reported here
will pave the way to further advances in the security of Windows OSes
Urban Voids After the Pandemic. A New Chance for Greenway
Our proposal deals with the meaning of urban voids in the post-COVID-19 period to suggest new understandings of how urban green corridors can positively affect design for healthier and more sustainable cities. According to Secchi (1986), planning through the void involves a profound revision of the way we think about the city, reversing the points of interest, proposing as polarities the spaces that do not usually emerge. The void thus becomes an opportunity, a chance to improve the structure of our urban landscape (Lopez-Pineiro, 2020). A city is a powerful place, always in motion and transformation. It has an artificial spirit full of surprises and vague limits. It is the scene of remarkable transformations that in their wildness are partially ungovernable by the designers themselves. The desire to control them leaves a series of abandoned and unfinished spaces, “holes” that live from their discontinuity with the surroundings (Labriola, 2021).
During a period of crisis, like the one that we are still living with COVID-19 (Fabris et al, 2020), it is common to re-think our cities to create better places for the community. After the long period of forced distance that we lived, an evolution of public space is recommended.
During the pandemic, the emptiness of our cities permitted Nature to re-appropriate its spaces. Following this trend and thinking about a new kind of public space where Nature and its inside processes are the protagonists, it is possible to intervene in our cities. The porosity of the urban fabric in towns without humans, blocked at home by the never-ending lockdowns, became a new green corridor that revealed the presence of wildlife (both fauna and flora) as part of a forgotten urban layer that turned visible again. The preservation of this new asset should be possible. The spaces to allow this change can be the abandoned and empty areas present in the contemporary city’s sick body that we can finally heal. The so-called wastelands, voids, or terrain vague, have a significant value independent from the environment in which they are inserted, showing a relationship with the contemporary city extraneous to its rhythms. For this reason, they are the perfect place for experimentation in terms of greenways, a possible starting point to re-think how green can be part of the urban texture and how to conceive public and open spaces after the nowadays crisis. The paper considers the Metropolitan City of Milan as a remarkable case study to understand the pivotal role played by urban voids in the formation of greenways and their capacity of reshaping the environmental, aesthetic and healthy dimensions of urban landscapes
Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag
Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100%
and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively
From Majorana theory of atomic autoionization to Feshbach resonances in high temperature superconductors
The Ettore Majorana paper - Theory of incomplete P triplets- published in
1931, focuses on the role of selection rules for the non-radiative decay of two
electron excitations in atomic spectra, involving the configuration interaction
between discrete and continuum channels. This work is a key step for
understanding the 1935 work of Ugo Fano on the asymmetric lineshape of two
electron excitations and the 1958 Herman Feshbach paper on the shape resonances
in nuclear scattering arising from configuration interaction between many
different scattering channels. The Feshbach resonances are today of high
scientific interest in many different fields and in particular for ultracold
gases and high Tc superconductivity.Comment: 13 pages, 7 figures. Journal of Superconductivity and Novel Magnetism
to be publishe
Structural Learning of Attack Vectors for Generating Mutated XSS Attacks
Web applications suffer from cross-site scripting (XSS) attacks that
resulting from incomplete or incorrect input sanitization. Learning the
structure of attack vectors could enrich the variety of manifestations in
generated XSS attacks. In this study, we focus on generating more threatening
XSS attacks for the state-of-the-art detection approaches that can find
potential XSS vulnerabilities in Web applications, and propose a mechanism for
structural learning of attack vectors with the aim of generating mutated XSS
attacks in a fully automatic way. Mutated XSS attack generation depends on the
analysis of attack vectors and the structural learning mechanism. For the
kernel of the learning mechanism, we use a Hidden Markov model (HMM) as the
structure of the attack vector model to capture the implicit manner of the
attack vector, and this manner is benefited from the syntax meanings that are
labeled by the proposed tokenizing mechanism. Bayes theorem is used to
determine the number of hidden states in the model for generalizing the
structure model. The paper has the contributions as following: (1)
automatically learn the structure of attack vectors from practical data
analysis to modeling a structure model of attack vectors, (2) mimic the manners
and the elements of attack vectors to extend the ability of testing tool for
identifying XSS vulnerabilities, (3) be helpful to verify the flaws of
blacklist sanitization procedures of Web applications. We evaluated the
proposed mechanism by Burp Intruder with a dataset collected from public XSS
archives. The results show that mutated XSS attack generation can identify
potential vulnerabilities.Comment: In Proceedings TAV-WEB 2010, arXiv:1009.330
High real-space resolution measurement of the local structure of Ga_1-xIn_xAs using x-ray diffraction
High real-space resolution atomic pair distribution functions (PDF)s from the
alloy series Ga_1-xIn_xAs have been obtained using high-energy x-ray
diffraction. The first peak in the PDF is resolved as a doublet due to the
presence of two nearest neighbor bond lengths, Ga-As and In-As, as previously
observed using XAFS. The widths of nearest, and higher, neighbor pairs are
analyzed by separating the strain broadening from the thermal motion. The
strain broadening is five times larger for distant atomic neighbors as compared
to nearest neighbors. The results are in agreement with model calculations.Comment: 4 pages, 5 figure
Local structure study of In_xGa_(1-x)As semiconductor alloys using High Energy Synchrotron X-ray Diffraction
Nearest and higher neighbor distances as well as bond length distributions
(static and thermal) of the In_xGa_(1-x)As (0<x<1) semiconductor alloys have
been obtained from high real-space resolution atomic pair distribution
functions (PDFs). Using this structural information, we modeled the local
atomic displacements in In_xGa_(1-x)As alloys. From a supercell model based on
the Kirkwood potential, we obtained 3-D As and (In,Ga) ensemble averaged
probability distributions. This clearly shows that As atom displacements are
highly directional and can be represented as a combination of and
displacements. Examination of the Kirkwood model indicates that the standard
deviation (sigma) of the static disorder on the (In,Ga) sublattice is around
60% of the value on the As sublattice and the (In,Ga) atomic displacements are
much more isotropic than those on the As sublattice. The single crystal diffuse
scattering calculated from the Kirkwood model shows that atomic displacements
are most strongly correlated along directions.Comment: 10 pages, 12 figure
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