Spectrum-, pulsewidth-, and wavelengthswitchable all-fiber mode-locked Yb laser with fiber based birefringent filter

We examined methods of controlling the pulse duration, spectral width and wavelength of the output from an all-fiber Yb laser mode-locked by carbon nanotubes. It is shown that a segment of polarization maintaining (PM) fiber inserted into a standard single mode fiber based laser cavity can function as a spectral selective filter. Adjustment of the length of the PM fiber from 1 to 2 m led to a corresponding variation in the pulse duration from 2 to 3.8 ps, the spectral bandwidth of the laser output changes from 0.15 to 1.26 nm. Laser output wavelength detuning within up to 5 nm was demonstrated with a fixed length of the PM fiber by adjustment of the polarization controller. © 2012 Optical Society of America.

Exact solution for the energy spectrum of Kelvin-wave turbulence in superfluids

We study the statistical and dynamical behavior of turbulent Kelvin waves propagating on quantized vortices in superfluids and address the controversy concerning the energy spectrum that is associated with these excitations. Finding the correct energy spectrum is important because Kelvin waves play a major role in the dissipation of energy in superfluid turbulence at near-zero temperatures. In this paper, we show analytically that the solution proposed by [L’vov and Nazarenko, JETP Lett. 91, 428 (2010)] enjoys existence, uniqueness, and regularity of the prefactor. Furthermore, we present numerical results of the dynamical equation that describes to leading order the nonlocal regime of the Kelvin-wave dynamics. We compare our findings with the analytical results from the proposed local and nonlocal theories for Kelvin-wave dynamics and show an agreement with the nonlocal predictions. Accordingly, the spectrum proposed by L’vov and Nazarenko should be used in future theories of quantum turbulence. Finally, for weaker wave forcing we observe an intermittent behavior of the wave spectrum with a fluctuating dissipative scale, which we interpreted as a finite-size effect characteristic of mesoscopic wave turbulence.

Direct sequence spread spectrum based PWM strategy for harmonic reduction and communication

Switched mode power supplies (SMPSs) are essential components in many applications, and electromagnetic interference is an important consideration in the SMPS design. Spread spectrum based PWM strategies have been used in SMPS designs to reduce the switching harmonics. This paper proposes a novel method to integrate a communication function into spread spectrum based PWM strategy without extra hardware costs. Direct sequence spread spectrum (DSSS) and phase shift keying (PSK) data modulation are employed to the PWM of the SMPS, so that it has reduced switching harmonics and the input and output power line voltage ripples contain data. A data demodulation algorithm has been developed for receivers, and code division multiple access (CDMA) concept is employed as communication method for a system with multiple SMPSs. The proposed method has been implemented in both Buck and Boost converters. The experimental results validated the proposed DSSS based PWM strategy for both harmonic reduction and communication.

The Use of Video Self-Modeling as an Intervention to Teach Rules and Procedures to Students with Autism Spectrum Disorder

The Use of Video Self-Modeling as an Intervention to Teach Rules and Procedures to Students with Autism Spectrum Disorder.

Evaluating the Effectiveness of Discrete Trial Procedures for Teaching Receptive Discrimination to Children with Autism Spectrum Disorders

Research has found that children with autism spectrum disorders (ASD) show significant deficits in receptive language skills (Wiesmer, Lord, & Esler, 2010). One of the primary goals of applied behavior analytic intervention is to improve the communication skills of children with autism by teaching receptive discriminations. Both receptive discriminations and receptive language entail matching spoken words with corresponding objects, symbols (e.g., pictures or words), actions, people, and so on (Green, 2001). In order to develop receptive language skills, children with autism often undergo discrimination training within the context of discrete trial training. This training entails teaching the learner how to respond differentially to different stimuli (Green, 2001). It is through discrimination training that individuals with autism learn and develop language (Lovaas, 2003). The present study compares three procedures for teaching receptive discriminations: (1) simple/conditional (Procedure A), (2) conditional only (Procedure B), and (3) conditional discrimination of two target cards (Procedure C). Six children, ranging in age from 2-years-old to 5-years-old, with an autism diagnosis were taught how to receptively discriminate nine sets of stimuli. Results suggest that the extra training steps included in the simple/conditional and conditional only procedures may not be necessary to teach children with autism how to receptively discriminate. For all participants, Procedure C appeared to be the most efficient and effective procedure for teaching young children with autism receptive discriminations. Response maintenance and generalization probes conducted one-month following the end of training indicate that even though Procedure C resulted in less training sessions overall, no one procedure resulted in better maintenance and generalization than the others. In other words, more training sessions, as evident with the simple/conditional and conditional only procedures, did not facilitate participants’ ability to accurately respond or generalize one-month following training. The present study contributes to the literature on what is the most efficient and effective way to teach receptive discrimination during discrete trial training to children with ASD. These findings are critical as research shows that receptive language skills are predictive of better outcomes and adaptive behaviors in the future.

WiFi and LTE Coexistence in the Unlicensed Spectrum

Today, smart-phones have revolutionized wireless communication industry towards an era of mobile data. To cater for the ever increasing data traffic demand, it is of utmost importance to have more spectrum resources whereby sharing under-utilized spectrum bands is an effective solution. In particular, the 4G broadband Long Term Evolution (LTE) technology and its foreseen 5G successor will benefit immensely if their operation can be extended to the under-utilized unlicensed spectrum. In this thesis, first we analyze WiFi 802.11n and LTE coexistence performance in the unlicensed spectrum considering multi-layer cell layouts through system level simulations. We consider a time division duplexing (TDD)-LTE system with an FTP traffic model for performance evaluation. Simulation results show that WiFi performance is more vulnerable to LTE interference, while LTE performance is degraded only slightly. Based on the initial findings, we propose a Q-Learning based dynamic duty cycle selection technique for configuring LTE transmission gaps, so that a satisfactory throughput is maintained both for LTE and WiFi systems. Simulation results show that the proposed approach can enhance the overall capacity performance by 19% and WiFi capacity performance by 77%, hence enabling effective coexistence of LTE and WiFi systems in the unlicensed band.

Mand – to Tact Training Transfer Acquisition Rates in Children Diagnosed with Autism Spectrum Disorder with Limited Verbal Skills

Autism Spectrum Disorder () is defined as “the presence of severe and pervasive impairments in reciprocal social interaction and in verbal and nonverbal communication skills” (Diagnostic & Statistical Manual, 2000). It is estimated that 1 in 68 children across the United States are diagnosed with ASD. One of the most common delays that children diagnosed with ASD experience are language delays. Children with ASD that have a language delay will often develop maladaptive behaviors as a result of poor communication skills (Carr & Durand, 1985). The failure to develop mand acquisition in typical fashion results in behaviors ranging from social withdrawal to self-injurious behaviors (Cooper et. al, 2007). A lack of a strong tact repertoire can further impede and complicate the learning of other necessary components of language due to the inability to successfully label items and events in the physical environment of the child. The purpose of this study is to replicate with a reversal in verbal operant training of the procedures described in Wallace et al. (2006) in which two children with ASD underwent tact training to facilitate the formation of mands; essentially this study aims to accomplish mand training first to establish as tact. It is hypothesized that mand training will result in a greater repertoire of tacts due to strength of the relationship between mands and the control over the social environment (Cooper et al., 2007). The two children in the study will be taught to mand items that will be ranked in order of preference via stimulus preference assessment. This study is of great importance due to the indispensable value of effective social communication skills. Data gathered on improving communication skills is of great value to the ASD community as the implications for functional skills result in better communication with family and greater control of individual functioning.

Mand – to Tact Training Transfer Acquisition Rates in Children Diagnosed with Autism Spectrum Disorder with Limited Verbal Skills

Autism Spectrum Disorder () is defined as “the presence of severe and pervasive impairments in reciprocal social interaction and in verbal and nonverbal communication skills” (Diagnostic & Statistical Manual, 2000). It is estimated that 1 in 68 children across the United States are diagnosed with ASD. One of the most common delays that children diagnosed with ASD experience are language delays. Children with ASD that have a language delay will often develop maladaptive behaviors as a result of poor communication skills (Carr & Durand, 1985). The failure to develop mand acquisition in typical fashion results in behaviors ranging from social withdrawal to self-injurious behaviors (Cooper et. al, 2007). A lack of a strong tact repertoire can further impede and complicate the learning of other necessary components of language due to the inability to successfully label items and events in the physical environment of the child. The purpose of this study is to replicate with a reversal in verbal operant training of the procedures described in Wallace et al. (2006) in which two children with ASD underwent tact training to facilitate the formation of mands; essentially this study aims to accomplish mand training first to establish as tact. It is hypothesized that mand training will result in a greater repertoire of tacts due to strength of the relationship between mands and the control over the social environment (Cooper et al., 2007). The two children in the study will be taught to mand items that will be ranked in order of preference via stimulus preference assessment. This study is of great importance due to the indispensable value of effective social communication skills. Data gathered on improving communication skills is of great value to the ASD community as the implications for functional skills result in better communication with family and greater control of individual functioning.

Emissione di Bremsstrahlung e applicazioni astrofisiche

Emissione di Bremsstrahlung e applicazioni astrofisiche

Resonance fluorescence spectrum of a \Lambda-type quantum emitter close to a metallic nanoparticle

We theoretically study the resonance fluorescence spectrum of a three-level quantum emitter coupled to a spherical metallic nanoparticle. We consider the case that the quantum emitter is driven by a single laser field along one of the optical transitions. We show that the development of the spectrum depends on the relative orientation of the dipole moments of the optical transitions in relation to the metal nanoparticle. In addition, we demonstrate that the location and width of the peaks in the spectrum are strongly modified by the exciton-plasmon coupling and the laser detuning, allowing to achieve controlled strongly subnatural spectral line. A strong antibunching of the fluorescent photons along the undriven transition is also obtained. Our results may be used for creating a tunable source of photons which could be used for a probabilistic entanglement scheme in the field of quantum information processing.

A Chaotic Spread Spectrum System for Underwater Acoustic Communication

The work is supported in part by NSFC (Grant no. 61172070), IRT of Shaanxi Province (2013KCT-04), EPSRC (Grant no.Ep/1032606/1).

Constructing eigenmode excitation spectrum in synthetic photonic lattices using optical heterodyning

A method based on optical heterodyning is proposed for measuring relative optical phases of pulses circulating in a synthetic photonic lattices. The knowledge of the phases can be further used for qualitative reconstruction of an eigenmode excitation spectrum in the synthetic photonic lattice.

Quality of transmission estimation in WDM and elastic optical networks accounting for space-spectrum dependencies

We develop a framework for estimating the quality of transmission (QoT) of a new lightpath before it is established, as well as for calculating the expected degradation it will cause to existing lightpaths. The framework correlates the QoT metrics of established lightpaths, which are readily available from coherent optical receivers that can be extended to serve as optical performance monitors. Past similar studies used only space (routing) information and thus neglected spectrum, while they focused on oldgeneration noncoherent networks. The proposed framework accounts for correlation in both the space and spectrum domains and can be applied to both fixed-grid wavelength division multiplexing (WDM) and elastic optical networks. It is based on a graph transformation that exposes and models the interference between spectrum-neighboring channels. Our results indicate that our QoT estimates are very close to the actual performance data, that is, to having perfect knowledge of the physical layer. The proposed estimation framework is shown to provide up to 4 × 10-2 lower pre-forward error correction bit error ratio (BER) compared to theworst-case interference scenario,which overestimates the BER. The higher accuracy can be harvested when lightpaths are provisioned with low margins; our results showed up to 47% reduction in required regenerators, a substantial savings in equipment cost.

Brain oscillations and connectivity in autism spectrum disorders (ASD):new approaches to methodology, measurement and modelling

Although atypical social behaviour remains a key characterisation of ASD, the presence ofsensory and perceptual abnormalities has been given a more central role in recentclassification changes. An understanding of the origins of such aberrations could thus prove afruitful focus for ASD research. Early neurocognitive models of ASD suggested that thestudy of high frequency activity in the brain as a measure of cortical connectivity mightprovide the key to understanding the neural correlates of sensory and perceptual deviations inASD. As our review shows, the findings from subsequent research have been inconsistent,with a lack of agreement about the nature of any high frequency disturbances in ASD brains.Based on the application of new techniques using more sophisticated measures of brainsynchronisation, direction of information flow, and invoking the coupling between high andlow frequency bands, we propose a framework which could reconcile apparently conflictingfindings in this area and would be consistent both with emerging neurocognitive models ofautism and with the heterogeneity of the condition.