636 research outputs found
Model-Based Speech Enhancement
Abstract
A method of speech enhancement is developed that reconstructs clean speech from
a set of acoustic features using a harmonic plus noise model of speech. This is a significant
departure from traditional filtering-based methods of speech enhancement.
A major challenge with this approach is to estimate accurately the acoustic features
(voicing, fundamental frequency, spectral envelope and phase) from noisy speech.
This is achieved using maximum a-posteriori (MAP) estimation methods that operate
on the noisy speech. In each case a prior model of the relationship between the
noisy speech features and the estimated acoustic feature is required. These models
are approximated using speaker-independent GMMs of the clean speech features
that are adapted to speaker-dependent models using MAP adaptation and for noise
using the Unscented Transform.
Objective results are presented to optimise the proposed system and a set of subjective
tests compare the approach with traditional enhancement methods. Threeway
listening tests examining signal quality, background noise intrusiveness and
overall quality show the proposed system to be highly robust to noise, performing
significantly better than conventional methods of enhancement in terms of background
noise intrusiveness. However, the proposed method is shown to reduce signal
quality, with overall quality measured to be roughly equivalent to that of the Wiener
filter
Photonic crystals modified by optically resonant systems
We investigate light propagation in periodic nanoscale structures known as photonic crystals. The goal is to gain insight into how the propagation of light can be modified and exploited for uses in telecommunication, regenerative energy, quantum information processing and optical computing. To this end, we dope photonic crystals with optically resonant systems: systems which strongly modify light propagation
Prosthechea mejia
Platystele colombiana is most similar to P. caudatisepala, P. posadarum and P. baqueroi but can be easily distinguished by the completely glandular-hirsute tepals and the very narrowly linear to acuminate petals that are about a third the width of the sepals, but similar in length.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Agroalimentarias::Jardín Botánico Lankester (JBL
Dynamical ultrafast all-optical switching of planar GaAs/AlAs photonic microcavities
The authors study the ultrafast switching-on and -off of planar GaAs/AlAs
microcavities. Up to 0.8% refractive index changes are achieved by optically
exciting free carriers at 1720 nm and a pulse energy of 1.8 micro Joules. The
cavity resonance is dynamically tracked by measuring reflectivity versus time
delay with tunable laser pulses, and is found to shift by as much as 3.3
linewidths within a few picoseconds. The switching-off occurs with a decay time
of around 50 ps. The authors derive the dynamic behavior of the carrier density
and of the complex refractive index. They propose that the inferred 10 GHz
switching rate may be tenfold improved by optimized sample growth.Comment: 1.) Replaced figure 1 (linear reflectivity) with a more recent and
improved measurement 2.) Included a Figure of Merit for switching and
compared to other recent contributions 3.) Explained more precisely the
effect of embedded Quantum Dots (namely no effect on measurement) 4.) Changed
wording in a few place
Observation of a stronger-than-adiabatic change of light trapped in an ultrafast switched GaAs-AlAs microcavity
We study the time-resolved reflectivity spectrum of a switched planar
GaAs-AlAs microcavity. Between 5 and 40 ps after the switching (pump) pulse we
observe a strong excess probe reflectivity and a change of the frequency of
light trapped in the cavity up to 5 linewidths away from the cavity resonance.
This frequency change does not adiabatically follow the fast-changing cavity
resonance. The frequency change is attributed to an accumulated phase change
due to the time-dependent refractive index. An analytical model predicts
dynamics in qualitative agreement with the experiments, and points to crucial
parameters that control future applications.Comment: Discussed effect of probe bandwidth. Included functional forms of
n(z) and R(z
Multilingualism in London: LUCIDE city report
This report is produced for LUCIDE (Languages in Urban Contexts: Integration and Diversity in Europe) project and network, funded by the EU Lifelong learning programme 2010- 2014, based on the collected primary and secondary data. It includes a brief historic overview of London’s demolinguistic features and a range of evidence relevant to current manifestations of multilingualism and plurilingualism in this global city. Considering the size, population and complexity of London our specific focus is on one local authority (out of an existing 33): the City of Westminster, geographically the heart of this metropolis. Westminster is in many ways representative of London language trends. It shows some of the most prominent features of multilingualism in London: an extraordinary linguistic variety with a wide distribution of languages, where no one language is dominant. Nevertheless, we also make reference to examples of multilingualism from outside Westminster, when we have considered it to be pertinent
High-Rate Data-Capture for an Airborne Lidar System
A high-rate data system was required to capture the data for an airborne lidar system. A data system was developed that achieved up to 22 million (64-bit) events per second sustained data rate (1408 million bits per second), as well as short bursts (less than 4 s) at higher rates. All hardware used for the system was off the shelf, but carefully selected to achieve these rates. The system was used to capture laser fire, single-photon detection, and GPS data for the Slope Imaging Multi-polarization Photo-counting Lidar (SIMPL). However, the system has applications for other laser altimeter systems (waveform-recording), mass spectroscopy, xray radiometry imaging, high-background- rate ranging lidar, and other similar areas where very high-speed data capture is needed. The data capture software was used for the SIMPL instrument that employs a micropulse, single-photon ranging measurement approach and has 16 data channels. The detected single photons are from two sources those reflected from the target and solar background photons. The instrument is non-gated, so background photons are acquired for a range window of 13 km and can comprise many times the number of target photons. The highest background rate occurs when the atmosphere is clear, the Sun is high, and the target is a highly reflective surface such as snow. Under these conditions, the total data rate for the 16 channels combined is expected to be approximately 22 million events per second. For each photon detection event, the data capture software reads the relative time of receipt, with respect to a one-per-second absolute time pulse from a GPS receiver, from an event timer card with 0.1-ns precision, and records that information to a RAID (Redundant Array of Independent Disks) storage device. The relative time of laser pulse firings must also be read and recorded with the same precision. Each of the four event timer cards handles the throughput from four of the channels. For each detection event, a flag is recorded that indicates the source channel. To accommodate the expected maximum count rate and also handle the other extreme of very low rates occurring during nighttime operations, the software requests a set amount of data from each of the event timer cards and buffers the data. The software notes if any of the cards did not return all the data requested and then accommodates that lower rate. The data is buffered to minimize the I/O overhead of writing the data to storage. Care was taken to optimize the reads from the cards, the speed of the I/O bus, and RAID configuration
Broadband sensitive pump-probe setup for ultrafast optical switching of photonic nanostructures and semiconductors
We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at
studying the switching of nanophotonic structures. Both fs pump and probe
pulses can be independently tuned over broad frequency range between 3850 and
21050 cm. A broad pump scan range allows a large optical penetration
depth, while a broad probe scan range is crucial to study strongly photonic
crystals. A new data acquisition method allows for sensitive pump-probe
measurements, and corrects for fluctuations in probe intensity and pump stray
light. We observe a tenfold improvement of the precision of the setup compared
to laser fluctuations, allowing a measurement accuracy of better than
R= 0.07% in a 1 s measurement time. Demonstrations of the improved
technique are presented for a bulk Si wafer, a 3D Si inverse opal photonic
bandgap crystal, and z-scan measurements of the two-photon absorption
coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in
the infrared wavelength range.Comment: 31 pages, 15 figure
Laser Transmitter Design and Performance for the Slope Imaging Multi-Polarization Photon-Counting Lidar (SIMPL) Instrument
The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) instrument is a polarimetric, two-color, multibeam push broom laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program and has been flown successfully on multiple airborne platforms since 2008. In this talk we will discuss the laser transmitter performance and present recent science data collected over the Greenland ice sheet and sea ice in support of the NASA Ice Cloud and land Elevation Satellite 2 (ICESat-2) mission to be launched in 2017
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