The effective indices of the cladding modes of optical fibers depend on the refractive index of the medium surrounding the fiber. We show experimentally and theoretically that while cladding modes with similar effective indices normally have similar refractometric sensitivities, the addition of a 50 nm thick gold sheath enhances the sensitivity of some EH modes by more than one order of magnitude while nearly completely suppressing the sensitivity of neighbouring HE modes (by three orders of magnitude, down to insignificant levels). A differential sensitivity of ∼1000 nm/(refractive index unit) is experimentally reported between adjacent EH and HE grating resonances.
Silica-based thin-film multilayers are investigated as a means to enhance the effective second-order nonlinearity induced in silica glass structures by corona poling. Structures consisting of phosphorus-doped and undoped silica glass layers exhibit second harmonic generation (SHG) that is higher by an order of magnitude compared to the SHG in bulk silica glass poled under the same conditions. When the poled structure consists of two multilayered stacks separated in space, the stacks exhibit comparable poling-induced nonlinearities. This result suggests that the poling voltage is divided between the two stacks such that simultaneous poling of multiple regions within the sample is realized.
The conformal coating of a 50 nm-thick layer of copper nanoparticles deposited with pulse chemical vapor deposition of a copper (I) guanidinate precursor on the cladding of a single mode optical fiber was monitored by using a tilted fiber Bragg grating (TFBG) photo-inscribed in the fiber core. The pulse-per-pulse growth of the copper nanoparticles is readily obtained from the position and amplitudes of resonances in the reflection spectrum of the grating. In particular, we confirm that the real part of the effective complex permittivity of the deposited nano-structured copper layer is an order of magnitude larger than that of a bulk copper film at an optical wavelength of 1550 nm. We further observe a transition in the growth behavior from granular to continuous film (as determined from the complex material permittivity) after approximately 20 pulses (corresponding to an effective thickness of 25 nm). Finally, despite the remaining granularity of the film, the final copper-coated optical fiber is shown to support plasmon waves suitable for sensing, even after the growth of a thin oxide layer on the copper surface.
We prove that, for every simple polygon P having k ≥ 1 reflex vertices, there exists a point q ε P such that every half-polygon that contains q contains nearly 1/2(k + 1) times the area of P. We also give a family of examples showing that this result is the best possible.
Conventional training simulators commonly use a hexapod configuration to provide motion cues. While widely used, studies have shown that hexapods are incapable of producing the range of motion required to achieve high fidelity simulation required in many applications. A novel alternative is the Atlas motion platform. This paper presents a new generalized kinematic model of the platform which can be applied to any spherical platform actuated by three omnidirectional wheels. In addition, conditions for slip-free and singularity-free motions are identified. Two illustrative examples are given for different omnidirectional wheel configurations.
This paper proposes a pro-active solution to the Frugal Feeding Problem (FFP) in Wireless Sensor Networks. The FFP attempts to find energy-efficient routes for a mobile service entity to rendezvous with each member of a team of mobile robots. Although the complexity of the FFP is similar to the Traveling Salesman Problem (TSP), we propose an efficient solution, completely distributed and localized for the case of a fixed rendezvous location (i.e., service facility with limited number of docking ports) and mobile capable entities (sensors). Our pro-active solution reduces the FFP to finding energy-efficient routes in a dynamic Compass Directed unit Graph (CDG). The proposed CDG incorporates ideas from forward progress routing and the directionality of compass routing in an energy-aware unit sub-graph. Navigating the CDG guarantees that each sensor will reach the rendezvous location in a finite number of steps. The ultimate goal of our solution is to achieve energy equilibrium (i.e., no further sensor losses due to energy starvation) by optimizing the use of the shared resource (recharge station). We also examine the impact of critical parameters such as transmission range, cost of mobility and sensor knowledge in the overall performance.
We motivate, formalize and investigate the notions of data quality assessment and data quality query answering as context dependent activities. Contexts for the assessment and usage of a data source at hand are modeled as collections of external databases, that can be materialized or virtual, and mappings within the collections and with the data source at hand. In this way, the context becomes "the complement" of the data source wrt a data integration system. The proposed model allows for natural extensions, like considering data quality predicates, and even more expressive ontologies for data quality assessment.
Oral narrative skills are assumed to develop through parent-child interactive routines. One such
routine is shared reading. A causal link between shared reading and narrative knowledge,
however, has not been clearly established. The present research tested whether an 8-week
shared-reading intervention enhanced the fictional narrative skills of children entering formal
education. Dialogic reading, a shared reading activity that involves elaborative questioning
techniques, was used to engage children in oral interaction during reading and to emphasize
elements of story knowledge. Forty English-speaking five- and six-year-olds were assigned to
either the dialogic-reading or an alternative-treatment group. ANCOVA results found that the
dialogic-reading children’s post-test narratives were significantly better on structure and context
measures than those for the alternative-treatment children, but results differed for produced or
retold narratives. The dialogic-reading children also showed expressive vocabulary gains.
Overall, this study concretely determined that aspects of fictional narrative construction
knowledge can be learned from interactive book reading.
This paper discusses reverse engineering source code to produce UML sequence diagrams, with the aim to aid program comprehension and other software life cycle activities (e.g.,
verification). As a first step we produce scenario diagrams using the UML sequence diagram notation. We build on previous work, now combining static and dynamic analyses of a Java software, our objective being to obtain a lightweight instrumentation and therefore disturb the software behaviour as little as possible. We extract the control flow graph from the software source code and obtain an execution trace by instrumenting and running the software. Control flow and trace information is represented as models and UML scenario diagram generation becomes a model transformation problem. Our validation shows that we indeed reduce the execution overhead inherent to dynamic analysis, without losing in terms of the quality of the reverse-engineered information, and therefore in terms of the usefulness of the approach (e.g., for program comprehension).
Cough is one of the most common symptoms in all respiratory diseases. It is important to provide the healthcare professionals with useful clinical information such as frequency, severity and nature of cough to have a better diagnosis and hence better treatment. The main objective of this thesis is to analyze cough sounds and extract features that can differentiate dry and wet cough sounds. This thesis proposes two features to achieve this goal. The first feature is the number of peaks of the energy envelope of the cough signal. The second feature is the power ratio of two frequency bands of the second phase of the cough signal. A set of nine highly dry and eight highly wet cough recordings were used in this thesis. Using these two features, a clear separation was observed among the dry and wet cough recordings. Furthermore, a Graphical User Interface (GUI) was designed in this thesis as a tool to analyze the cough signals in both time and frequency domain.