4,373 research outputs found
Ontology-Based Quality Evaluation of Value Generalization Hierarchies for Data Anonymization
In privacy-preserving data publishing, approaches using Value Generalization
Hierarchies (VGHs) form an important class of anonymization algorithms. VGHs
play a key role in the utility of published datasets as they dictate how the
anonymization of the data occurs. For categorical attributes, it is imperative
to preserve the semantics of the original data in order to achieve a higher
utility. Despite this, semantics have not being formally considered in the
specification of VGHs. Moreover, there are no methods that allow the users to
assess the quality of their VGH. In this paper, we propose a measurement
scheme, based on ontologies, to quantitatively evaluate the quality of VGHs, in
terms of semantic consistency and taxonomic organization, with the aim of
producing higher-quality anonymizations. We demonstrate, through a case study,
how our evaluation scheme can be used to compare the quality of multiple VGHs
and can help to identify faulty VGHs.Comment: 18 pages, 7 figures, presented in the Privacy in Statistical
Databases Conference 2014 (Ibiza, Spain
Synthetic Data Generation using Benerator Tool
Datasets of different characteristics are needed by the research community
for experimental purposes. However, real data may be difficult to obtain due to
privacy concerns. Moreover, real data may not meet specific characteristics
which are needed to verify new approaches under certain conditions. Given these
limitations, the use of synthetic data is a viable alternative to complement
the real data. In this report, we describe the process followed to generate
synthetic data using Benerator, a publicly available tool. The results show
that the synthetic data preserves a high level of accuracy compared to the
original data. The generated datasets correspond to microdata containing
records with social, economic and demographic data which mimics the
distribution of aggregated statistics from the 2011 Irish Census data.Comment: 12 pages, 5 figures, 10 reference
Raman and XPS analyses of pristine and annealed N-doped double-walled carbon nanotubes
N-doped single/multi-walled carbon nanotubes (CNTs) were studied for long
time from synthesis to properties. However, the stability of N in the CNT
lattice still needs further developments. In this work, to obtain more stable
N-doped CNTs, concentric double-walled (DW) CNTs with more N were synthesized
using benzylamine as C and N source. In order to test the stability of N-doped
DWCNTs, high-temperature annealing in vacuum was performed. By XPS and Raman
spectroscopic measurements, we found that the N-doped DWCNTs are still stable
under 1500 \,^{\circ}\mathrm{C}: the graphitic N does not change at all, the
molecular N is partly removed, and the pyridinic N ratio greatly increases by
more than two times. The reason could be that the N atoms from the surrounded
N-contained materials combine into the CNT lattice during the annealing.
Compared with the undoped DWCNTs, no Raman frequency shift was observed for the
RBM, the G-band, and the G'-band of the N-doped DWCNTs.Comment: 6 pages, 5 figure
Electronic band gaps of confined linear carbon chains ranging from polyyne to carbyne
Ultra long linear carbon chains of more than 6000 carbon atoms have recently
been synthesized within double-walled carbon nanotubes, and they show a
promising new route to one--atom--wide semiconductors with a direct band gap.
Theoretical studies predicted that this band gap can be tuned by the length of
the chains, the end groups, and their interactions with the environment.
However, different density functionals lead to very different values of the
band gap of infinitely long carbyne. In this work, we applied resonant Raman
excitation spectroscopy with more than 50 laser wavelengths to determine for
the first time the band gap of long carbon chains encapsulated inside DWCNTs.
The experimentally determined band gaps ranging from 2.253 to 1.848 eV follow a
linear relation with Raman frequency. This lower bound is the smallest band gap
of linear carbon chains observed so far. The comparison with experimental data
obtained for short chains in gas phase or in solution demonstrates the effect
of the DWCNT encapsulation, leading to an essential downshift of the band gap.
This is explained by the interaction between the carbon chain and the host
tube, which greatly modifies the chain's bond length alternation.Comment: 7 pages, 5 figure
Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes
The orbital and spin magnetic properties of iron inside transforming metallic
and semiconducting 1D carbon nanotube hybrids are studied by means of local
x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum
interference device (SQUID) measurements. Nanotube hybrids are initially
ferrocene filled single-walled carbon nanotubes (SWCNT) of different
metallicities. After a high temperature nanochemical reaction ferrocene
molecules react with each other to form iron nano clusters. We show that the
ferrocenes molecular orbitals interact differently with the SWCNT of different
metallicities without significant XMCD response. This XMCD at various
temperatures and magnetic fields reveals that the orbital and/or spin magnetic
moments of the encapsulated iron are altered drastically as the transformation
to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are
both found to be larger in filled semiconducting nanotubes than in the metallic
sample. This could mean that the magnetic polarizations of the encapsulated
material is dependent on the metallicity of the tubes. From a comparison
between the iron 3d magnetic moments and the bulk magnetism measured by SQUID,
we conclude that the delocalized magnetisms dictate the magnetic properties of
these 1D hybrid nanostructures
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