178 research outputs found
High-fidelity, broadband stimulated-Brillouin-scattering-based slow light using fast noise modulation
We demonstrate a 5-GHz-broadband tunable slow-light device based on
stimulated Brillouin scattering in a standard highly-nonlinear optical fiber
pumped by a noise-current-modulated laser beam. The noise modulation waveform
uses an optimized pseudo-random distribution of the laser drive voltage to
obtain an optimal flat-topped gain profile, which minimizes the pulse
distortion and maximizes pulse delay for a given pump power. Eye-diagram and
signal-to-noise ratio (SNR) analysis show that this new broadband slow-light
technique significantly increases the fidelity of a delayed data sequence,
while maintaining the delay performance. A fractional delay of 0.81 with a SNR
of 5.2 is achieved at the pump power of 350 mW using a 2-km-long highly
nonlinear fiber with the fast noise-modulation method, demonstrating a 50%
increase in eye-opening and a 36% increase in SNR compared to a previous
slow-modulation method
Don't Thrash: How to Cache Your Hash on Flash
This paper presents new alternatives to the well-known Bloom filter data
structure. The Bloom filter, a compact data structure supporting set insertion
and membership queries, has found wide application in databases, storage
systems, and networks. Because the Bloom filter performs frequent random reads
and writes, it is used almost exclusively in RAM, limiting the size of the sets
it can represent. This paper first describes the quotient filter, which
supports the basic operations of the Bloom filter, achieving roughly comparable
performance in terms of space and time, but with better data locality.
Operations on the quotient filter require only a small number of contiguous
accesses. The quotient filter has other advantages over the Bloom filter: it
supports deletions, it can be dynamically resized, and two quotient filters can
be efficiently merged. The paper then gives two data structures, the buffered
quotient filter and the cascade filter, which exploit the quotient filter
advantages and thus serve as SSD-optimized alternatives to the Bloom filter.
The cascade filter has better asymptotic I/O performance than the buffered
quotient filter, but the buffered quotient filter outperforms the cascade
filter on small to medium data sets. Both data structures significantly
outperform recently-proposed SSD-optimized Bloom filter variants, such as the
elevator Bloom filter, buffered Bloom filter, and forest-structured Bloom
filter. In experiments, the cascade filter and buffered quotient filter
performed insertions 8.6-11 times faster than the fastest Bloom filter variant
and performed lookups 0.94-2.56 times faster.Comment: VLDB201
Hybrid Electrically Pumped Evanescent Si/InGaAsP Lasers
Hybrid Si/InGaAsP Fabry-Perot evanescent lasers are fabricated via wafer bonding. Compared with previous similar devices, the current threshold density, turn-on voltage, output power and slope efficiency are all improved. Images show modal confinement to Silicon
Trapping polarization of light in nonlinear optical fibers: An ideal Raman polarizer
The main subject of this contribution is the all-optical control over the
state of polarization (SOP) of light, understood as the control over the SOP of
a signal beam by the SOP of a pump beam. We will show how the possibility of
such control arises naturally from a vectorial study of pump-probe Raman
interactions in optical fibers. Most studies on the Raman effect in optical
fibers assume a scalar model, which is only valid for high-PMD fibers (here,
PMD stands for the polarization-mode dispersion). Modern technology enables
manufacturing of low-PMD fibers, the description of which requires a full
vectorial model. Within this model we gain full control over the SOP of the
signal beam. In particular we show how the signal SOP is pulled towards and
trapped by the pump SOP. The isotropic symmetry of the fiber is broken by the
presence of the polarized pump. This trapping effect is used in experiments for
the design of new nonlinear optical devices named Raman polarizers. Along with
the property of improved signal amplification, these devices transform an
arbitrary input SOP of the signal beam into one and the same SOP towards the
output end. This output SOP is fully controlled by the SOP of the pump beam. We
overview the sate-of-the-art of the subject and introduce the notion of an
"ideal Raman polarizer"
A rare case of Takotsubo syndrome in a patient 5 months after heart transplantation
Takotsubo syndrome is an acute heart failure syndrome with a pathogenesis that is attributed to sympathetic stimulation. This case report describes a unique case of a 5 month heart‐transplanted female patient who developed apical ballooning on an echocardiography exam performed following an emotional stress event. Detailed clinical investigations and imaging techniques confirmed the diagnosis of Takatsubo syndrome. Our case indicates that Takatsubo's cardiomyopathy should be included in the differential diagnosis of heart‐transplanted patients presenting with sudden graft dysfunction mimicking acute graft rejection or acute coronary syndrome
Secret key exchange in ultra-long lasers by radio-frequency spectrum coding
We propose a new approach to the generation of an alphabet for secret key exchange relying on small variations in the cavity length of an ultra-long fiber laser. This new concept is supported by experimental results showing how the radio-frequency spectrum of the laser can be exploited as a carrier to exchange information. The test bench for our proof of principle is a 50 km-long fiber laser linking two users, Alice and Bob, where each user can randomly add an extra 1 km-long segment of fiber. The choice of laser length is driven by two independent random binary values, which makes such length become itself a random variable. The security of key exchange is ensured whenever the two independent random choices lead to the same laser length and, hence, to the same free spectral range
Hybrid Electrically Pumped Evanescent Si/InGaAsP Lasers
Hybrid Si/InGaAsP Fabry-Perot evanescent lasers are fabricated via wafer bonding. Compared with previous similar devices, the current threshold density, turn-on voltage, output power and slope efficiency are all improved. Images show modal confinement to Silicon
Estimating Level of Engagement from Ocular Landmarks
E-learning offers many advantages like being economical, flexible and customizable, but also has challenging aspects such as lack of – social-interaction, which results in contemplation and sense of remoteness. To overcome these and sustain learners’ motivation, various stimuli can be incorporated. Nevertheless, such adjustments initially require an assessment of engagement level. In this respect, we propose estimating engagement level from facial landmarks exploiting the facts that (i) perceptual decoupling is promoted by blinking during mentally demanding tasks; (ii) eye strain increases blinking rate, which also scales with task disengagement; (iii) eye aspect ratio is in close connection with attentional state and (iv) users’ head position is correlated with their level of involvement. Building empirical models of these actions, we devise a probabilistic estimation framework. Our results indicate that high and low levels of engagement are identified with considerable accuracy, whereas medium levels are inherently more challenging, which is also confirmed by inter-rater agreement of expert coders
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