394 research outputs found
Privacy in times of COVID-19: a pilot study in the Republic of Ireland
Contact tracing apps used in tracing and mitigating the spread of COVID-19 have sparked discussions and controversies worldwide with major concerns around privacy. COVID Tracker app used in the Republic of Ireland was praised in general for the way it addressed privacy and was used as baseline for other contact tracing apps worldwide. The success of the app is dependent on the general public uptake, hence their voice and attitude is the one that really matters. This paper focuses on developing a survey and the methods aiming to examine the attitudes toward privacy during COVID-19 of the general public in the Republic of Ireland and their impact on the uptake of the COVID tracker app. Various privacy models are used and health belief model as well in this purpose. A pilot study with 286 participants show a change in attitude towards privacy during COVID-19 pandemic, with more people willing to share their data in the interest of saving lives. However, privacy attitudes are shown to have impacted the adoption of the app in Ireland
Pumping Metallic Nanoparticles with Spatial Precision within Magnetic Mesoporous Platforms: 3D Characterization and Catalytic Application
The present work shows an efficient strategy to assemble two types of functional nanoparticles onto mesoporous MCM-41 silica nanospheres with a high degree of spatial precision. In a first stage, magnetite nanoparticles are synthesized with a size larger than the support pores and grafted covalently through a peptide-like bonding onto their external surface. This endowed the silica nanoparticles with a strong superparamagnetic response, while preserving the highly ordered interior space for the encapsulation of other functional guest species. Second, we report the finely controlled pumping of preformed Pt nanoparticles (1.5 nm) within the channels of the magnetic MCM-41 nanospheres to confer an additional catalytic functionality to the multiassembled nanoplatform. The penetration depth of the metallic nanoparticles can be explained as a result of the interplay between the particle-wall electrostatic attraction and the repulsive forces between neighboring Pt nanoparticles. A detailed transmission electron microscopy and a 3D high-resolution high-angle annular dark-field detector electron tomography study were carried out to characterize the material and to explain the assembly mechanism. Finally, the performance of these multifunctional nanohybrids as magnetically recoverable catalysts has been evaluated in the selective hydrogenation of p-nitrophenol, a well-known pollutant and intermediate in multiple industrial processes
SU(5) D-brane realizations, Yukawa couplings and proton stability
We discuss SU(5) Grand Unified Theories in the context of orientifold
compactifications. Specifically, we investigate two and three D-brane stack
realizations of the Georgi-Glashow and the flipped SU(5) model and analyze them
with respect to their Yukawa couplings. As pointed out in arXiv:0909.0271 the
most economical Georgi-Glashow realization based on two stacks generically
suffers from a disastrous large proton decay rate. We show that allowing for an
additional U(1) D-brane stack this as well as other phenomenological problems
can be resolved. We exemplify with globally consistent Georgi-Glashow models
based on RCFT that these D-brane quivers can be indeed embedded in a global
setting. These globally consistent realizations admit rigid O(1) instantons
inducing the perturbatively missing coupling 10105^H. Finally we show that
flipped SU(5) D-brane realizations even with multiple U(1) D-brane stacks are
plagued by severe phenomenological drawbacks which generically cannot be
overcome.Comment: 34 pages v2 minor correction
Non-Perturbative Effects on a Fractional D3-Brane
In this note we study the N=1 abelian gauge theory on the world volume of a
single fractional D3-brane. In the limit where gravitational interactions are
not completely decoupled we find that a superpotential and a fermionic bilinear
condensate are generated by a D-brane instanton effect. A related situation
arises for an isolated cycle invariant under an orientifold projection, even in
the absence of any gauge theory brane. Moreover, in presence of supersymmetry
breaking background fluxes, such instanton configurations induce new couplings
in the 4-dimensional effective action, including non-perturbative contributions
to the cosmological constant and non-supersymmetric mass terms.Comment: 18 pages, v3: refs adde
Instanton Induced Neutrino Majorana Masses in CFT Orientifolds with MSSM-like spectra
Recently it has been shown that string instanton effects may give rise to
neutrino Majorana masses in certain classes of semi-realistic string
compactifications. In this paper we make a systematic search for supersymmetric
MSSM-like Type II Gepner orientifold constructions admitting boundary states
associated with instantons giving rise to neutrino Majorana masses and other L-
and/or B-violating operators. We analyze the zero mode structure of D-brane
instantons on general type II orientifold compactifications, and show that only
instantons with O(1) symmetry can have just the two zero modes required to
contribute to the 4d superpotential. We however discuss how the addition of
fluxes and/or possible non-perturbative extensions of the orientifold
compactifications would allow also instantons with and U(1) symmetries
to generate such superpotentials. In the context of Gepner orientifolds with
MSSM-like spectra, we find no models with O(1) instantons with just the
required zero modes to generate a neutrino mass superpotential. On the other
hand we find a number of models in one particular orientifold of the Gepner
model with instantons with a few extra uncharged
non-chiral zero modes which could be easily lifted by the mentioned effects. A
few more orientifold examples are also found under less stringent constraints
on the zero modes. This class of instantons have the interesting
property that R-parity conservation is automatic and the flavour structure of
the neutrino Majorana mass matrices has a simple factorized form.Comment: 68 pages, 2 figures; v2. typos corrected, refs adde
A 3D insight on the catalytic nanostructuration of few-layer graphene
The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting
FCNC Processes from D-brane Instantons
Low string scale models might be tested at the LHC directly by their Regge
resonances. For such models it is important to investigate the constraints of
Standard Model precision measurements on the string scale. It is shown that
highly suppressed FCNC processes like K0- bar K^0 oscillations or leptonic
decays of the D0-meson provide non-negligible lower bounds on both the
perturbatively and surprisingly also non-perturbatively induced string theory
couplings. We present both the D-brane instanton formalism to compute such
amplitudes and discuss various possible scenarios and their constraints on the
string scale for (softly broken) supersymmetric intersecting D-brane models.Comment: 28 pages, 13 figures, reference added, 1 typo corrected, style file
adde
Non-perturbative effective interactions from fluxes
Motivated by possible implications on the problem of moduli stabilization and
other phenomenological aspects, we study D-brane instanton effects in flux
compactifications. We focus on a local model and compute non-perturbative
interactions generated by gauge and stringy instantons in a N = 1 quiver theory
with gauge group U(N_0) x U(N_1) and matter in the bifundamentals. This model
is engineered with fractional D3-branes at a C^3/(Z_2 x Z_2) singularity, and
its non-perturbative sectors are described by introducing fractional
D-instantons. We find a rich variety of instanton-generated F- and D-term
interactions, ranging from superpotentials and Beasley-Witten like
multi-fermion terms to non-supersymmetric flux-induced instanton interactions.Comment: 37 pages, 7 figures. Final version published on JHEP. Section 4
modified in several points regarding string corrections in absence of fluxes;
in particular, section 4.3 is removed. Some other minor changes and two
references adde
Phenomenological analysis of D-brane Pati-Salam vacua
In the present work we perform a phenomenological analysis of the effective
low energy models with Pati-Salam (PS) gauge symmetry derived in the context of
D-branes. A main issue in these models arises from the fact that the
right-handed fermions and the PS-symmetry breaking Higgs field transform
identically under the PS symmetry, causing unnatural matter-Higgs mixing
effects. We argue that this problem could be solved in particular D-brane
setups where these fields arise in different intersections. We further observe
that whenever a large Higgs mass term is generated in a particular class of
mass spectra, a splitting mechanism -reminiscent of the doublet triplet
splitting- may protect the neutral Higgs components from a heavy mass term. We
analyze the implications of each individual representation which in principle
is available in these models in order to specify the minimal spectrum required
to build up a consistent PS model which reconciles the low energy data. A short
discussion is devoted on the effects of stringy instanton corrections,
particularly those generating missing Yukawa couplings and contributing to the
fermion mass textures. We discuss the correlations of the intersecting D-brane
spectra with those obtained from Gepner constructions and analyze the
superpotential, the resulting mass textures and the low energy implications of
some examples of the latter along the lines proposed above.Comment: 50 pages, 3 figures (v2 - Minor corrections
Black String Entropy and Fourier-Mukai Transform
We propose a microscopic description of black strings in F-theory based on
string duality and Fourier-Mukai transform. These strings admit several
different microscopic descriptions involving D-brane as well as M2 or M5-brane
configurations on elliptically fibered Calabi-Yau threefolds. In particular our
results can also be interpreted as an asymptotic microstate count for D6-D2-D0
configurations in the limit of large D2-charge on the elliptic fiber. The
leading behavior of the microstate degeneracy in this limit is shown to agree
with the macroscopic entropy formula derived from the black string supergravity
solution.Comment: 22 pages, latex; v2: substantial revision of the macroscopic
description of the system; results essentially unchange
- …