3,959 research outputs found
Synchronization of a WDM Packet-Switched Slotted Ring
In this paper, we present two different strategies of
slot synchronization in wavelength-division-multiplexing (WDM)
packet-switched slotted-ring networks. Emphasis is given to the
architecture behind the WDM Optical Network Demonstrator
over Rings (WONDER) project, which is based on tunable
transmitters and fixed receivers. The WONDER experimental
prototype is currently being developed at the laboratories
of Politecnico di Torino. In the former strategy, a slotsynchronization
signal is transmitted by the master station on a
dedicated control wavelength; in the latter, slave nodes achieve
slot synchronization aligning on data packets that are received
from the master. The performance of both synchronization strategies,
particularly in terms of packet-collision probability, was
evaluated by simulation. The technique based on transmitting a
timing signal on a dedicated control wavelength achieves better
performance, although it is more expensive due to the need for an
additional wavelength. However, the technique based on aligning
data packets that are received from the master, despite attaining
lower timing stability, still deserves further study, particularly
if limiting the number of wavelengths and receivers is a major
requirement. Some experimental results, which were measured on
the WONDER prototype, are also shown. Measurement results,
together with theoretical findings, demonstrate the good synchronization
performance of the prototype
Tomographic approach to the violation of Bell's inequalities for quantum states of two qutrits
The tomographic method is employed to investigate the presence of quantum
correlations in two classes of parameter-dependent states of two qutrits. The
violation of some Bell's inequalities in a wide domain of the parameter space
is shown. A comparison between the tomographic approach and a recent method
elaborated by Wu, Poulsen and Molmer shows the better adequacy of the former
method with respect to the latter one.Comment: 9 pages, 4 figure
Field localization on a brane intersection in anti-de Sitter spacetime
We discuss the localization of scalar, fermion, and gauge field zero modes on
a brane that resides at the intersection of two branes in
six-dimensional anti-de Sitter space. This set-up has been introduced in the
context of brane world models and, higher-dimensional versions of it, in string
theory. In both six- and ten-dimensional cases, it has been shown that
four-dimensional gravity can be reproduced at the intersection, due to the
existence of a massless, localized graviton zero-mode. However, realistic
scenarios require also the Standard Model to be localized on the brane. In
this paper, we discuss under which conditions a higher-dimensional field
theory, propagating on the above geometry, can have a zero-mode sector
localized at the intersection and find that zero modes can be localized only if
masses and couplings to the background curvature satisfy certain relations. We
also consider the case when other 4-branes cut the bulk at some distance from
the intersection and argue that, in the probe brane approximation, there is no
significant effect on the localization properties at the brane. The case of
bulk fermions is particularly interesting, since the properties of the geometry
allow localization of chiral modes independently.Comment: 13 pages, 3 figures, the version to be published in PR
Branes and Black holes in Collision
We study the collision of a brane with a black hole. Our aim is to explore
the topology changing process of perforation of a brane. The brane is described
as a field theoretical domain wall in the context of an axion-like model
consisting of a complex scalar effective field theory with approximate U(1)
symmetry. We simulate numerically the dynamics of the collision and illustrate
the transition from the configuration without a hole to the pierced one with
the aid of a phase diagram. The process of perforation is found to depend on
the collisional velocity, and, contrary to our expectation, we observe that
above a critical value of the velocity, the black hole has no chance to
perforate the wall. That is: high energy collisions do not assist piercing. We
also show that, only when the model parameters are fine-tuned so that the
energy scale of the string is very close to that of the domain wall, the
collision of the wall with the black hole has a possibility to provide a
mechanism to erase domain walls, if the hole expands. However, in such cases,
domain walls will form with many holes edged by a string and therefore
disappear eventually. Therefore this mechanism is unlikely to be a solution to
the cosmological domain wall problem, although it may cause some minor effects
on the evolution of a domain wall network.Comment: 14 pages; 9 figure
On the generation of multipartite entangled states in Josephson architectures
We propose and analyze a scheme for the generation of multipartite entangled
states in a system of inductively coupled Josephson flux qubits. The qubits
have fixed eigenfrequencies during the whole process in order to minimize
decoherence effects and their inductive coupling can be turned on and off at
will by tuning an external control flux. Within this framework, we will show
that a W state in a system of three or more qubits can be generated by
exploiting the sequential one by one coupling of the qubits with one of them
playing the role of an entanglement mediator.Comment: 10 pages, 3 figure
Usefulness of image guidance in the surgical treatment of petrous apex cholesterol granuloma
The petrous apex is a pyramid-shaped structure, located medial to the inner ear and the intrapetrous segment of the internal carotid artery. Lesions of the petrous apex can be surgically treated through different surgical routes. Because of the important neurovascular structures located inside the temporal bone, anatomical 3D knowledge is paramount. For this reason, image-guided surgery could represent a useful tool. We report the case of a young woman who came to our observation for a trigeminal neuralgia due to a petrous apex cholesterol granuloma. The lesion was treated through the placement of a drainage tube via an infracochlear approach, with the aid of neuronavigation and intraoperative MRI. Preoperative CT scan images and intraoperative MRI images were fused for surgical planning. The accuracy of the neuronavigation system has proved to be good, and the safety of the procedure was enhanced. Therefore, neuronavigation and intraoperative MRI, though not available in all neurootological centres, should be considered useful tools in these challenging procedures
INFERRING GENE NETWORKS FROM MICROARRAY WITH GRAPHICAL MODELS
ABSTRACT. Microarray technology allows to collect a large amount of genetic data, such as gene expression data. The activity of the genes are coordinate by a complex network that regulates their expressions controlling common functions, such as the formation of a transcriptional complex or the availability of a signalling pathway. Understanding this organization is crucial to explain normal cell physiology as well as to analyse complex pathological phenotypes. Graphical models are a class of statistical models that can be used to infer gene regulatory networks. In this paper, we examine a class of graphical models: the strongly decomposable graphical models for mixed variables. Among oth- ers properties, explicit expressions of maximum likelihood estimators are available for decomposable graphical models. This property makes the use of decomposable model suitable for high-dimensional data. We apply decomposable graphical models to a real dataset example
Supergravity and Superstring Signatures of the One-Parameter Model at LHC
Many string constructions have a classical no-scale structure, resulting in a
one-parameter model (OPM) for the supersymmetry breaking soft terms. As a
highly constrained subset of mSUGRA, the OPM has the potential to be
predictive. Conversely, if the observed superpartner spectrum at LHC is a
subset of the OPM parameter space, then this may provide a clue to the
underlying theory at high energies. We investigate the allowed supersymmetry
parameter space for a generic one-parameter model taking into account the most
recent experimental constraints. We find that in the strict moduli scenario,
there are no regions of the parameter space which may satisfy all constraints.
However, for the dilaton scenario, there are small regions of the parameter
space where all constraints may be satisfied and for which the observed dark
matter density may be generated. We also survey the possible signatures which
may be observable at the Large Hadron Collider (LHC). Finally, we compare
collider signatures of OPM to those from a model with non-universal soft terms,
in particular those of an intersecting D6-brane model. We find that it may be
possible to distinguish between these diverse scenarios at LHC.Comment: 25 pages, 10 figures, accepted for publication in PR
Differential Dynamics at Glycosidic Linkages of an Oligosaccharide as Revealed by 13C NMR Spin Relaxation and Stochastic Modeling
Among biomolecules, carbohydrates are unique in that not only can linkages be formed through different positions but the structures may also be branched. The trisaccharide \uf062-D-Glcp-(1\uf0ae3)[\uf062-D-Glcp-(1\uf0ae2)]-\uf061-D-Manp-OMe represents a model of a branched vicinally disubstituted structure. A 13C site-specific isotopologue with labeling in each of the two terminal glucosyl residues enabled acquisition of high-quality 13C NMR relaxation parameters T1, T2 and heteronuclear NOE, with standard deviations of \uf0a3 0.5%. For interpretation of the experimental NMR data a diffusive chain model was used in which the dynamics of the glycosidic linkages is coupled to the global reorientation motion of the trisaccharide. Brownian dynamics simulations relying on the potential of mean force at the glycosidic linkages were employed to evaluate spectral densities of the spin probes. Calculated NMR relaxation parameters showed very good agreement with experimental data, deviating < 3%. The resulting dynamics is described by correlation times of 196 ps and 174 ps for the \uf062-(1\uf0ae2)- and \uf062-(1\uf0ae3)-linked glucosyl residues, respectively, i.e., different and linkage dependent. Notably, the devised computational protocol was performed without any fitting of parameters
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