2,632 research outputs found
Transition to turbulence in slowly divergent pipe flow
The results of a combined experimental and numerical study of the flow in
slowly diverging pipes are presented. Interestingly, an axisymmetric conical
recirculation cell has been observed. The conditions for its existence and the
length of the cell are simulated for a range of diverging angles and expansion
ratios. There is a critical velocity for the appearance of this state. When the
flow rate increases further, a subcritical transition for localized turbulence
arises. The transition and relaminarization experiments described here quantify
the extent of turbulence. The findings suggest that the transition scenario in
slowly diverging pipes is a combination of stages similar to those observed in
sudden expansions and in straight circular pipe flow.Comment: 8 pages, 5 figure
REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture
Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America
Field-Trial of Machine Learning-Assisted Quantum Key Distribution (QKD) Networking with SDN
We demonstrated, for the first time, a machine-learning method to assist the
coexistence between quantum and classical communication channels.
Software-defined networking was used to successfully enable the key generation
and transmission over a city and campus network
Quantum state preparation in semiconductor dots by adiabatic rapid passage
Preparation of a specific quantum state is a required step for a variety of
proposed practical uses of quantum dynamics. We report an experimental
demonstration of optical quantum state preparation in a semiconductor quantum
dot with electrical readout, which contrasts with earlier work based on Rabi
flopping in that the method is robust with respect to variation in the optical
coupling. We use adiabatic rapid passage, which is capable of inverting single
dots to a specified upper level. We demonstrate that when the pulse power
exceeds a threshold for inversion, the final state is independent of power.
This provides a new tool for preparing quantum states in semiconductor dots and
has a wide range of potential uses.Comment: 4 pages, 4 figure
Microcavity quantum-dot systems for non-equilibrium Bose-Einstein condensation
We review the practical conditions required to achieve a non-equilibrium BEC
driven by quantum dynamics in a system comprising a microcavity field mode and
a distribution of localised two-level systems driven to a step-like population
inversion profile. A candidate system based on eight 3.8nm layers of
In(0.23)Ga(0.77)As in GaAs shows promising characteristics with regard to the
total dipole strength which can be coupled to the field mode.Comment: 4 pages, 4 figures, to be published in J. Phys. Conf. Ser. for QD201
Study Physicochemical of the Raw Palm Oils of the Republic of Gabon and Congo
The palm oil exists in several forms: palm oil raw, not refined, of red color because very rich carotenoids, called «red palm oil». In Africa, it is generally sold and consumed rough, i.e. not having undergoes the stages of refining. Taking into account the quantity and relevance of existing work on the palm tree with oil, we limited our study of Elaeis guinensis of Congo Basin to the analysis of the oils taken on the ground of the natural palm plantations and of the plantations of the palm plantation of M'vouna (Gabon) and of the Rural Campus of Loukoko (Congo) the study of our samples reveals the presence of carotenoids between 400 and 480 nm, and the presence of the chlorophyllian pigments with 600 and 670 nm for the great number of analyzed spectra. In the palm oil, the contents of carotenoids extend between 400 and 480 nm. The total content carotenoids varies from 897,1 µg/ml with 1229,3 µg/ml for the samples of the Palm plantation of M'vouna (Franceville, Gabon), whereas for the samples of Loukoko (Congo) that varies from 583,1 µg/ml with 1110,5 µg/ml on average. During precipitation partial of the raw palm oils of Gabon, three cases of figure ariseed (progressive, brutal and null solidification). The content total polyphenols varies from 439 to 2516 µg/ml. Of all the analyzed samples, the sample of Congo contains the maximum of phenolic compounds (2516 µg/ml). Minimum of 439 µg/ml, being obtained on the sample of Gabon. Their high content in carotenoids, fatty-acid unsaturates and the strong content total polyphenols, make our different oils more beneficial as well in the nutritional plan as therapeutic. The objective of work is the physicochemical characterization of the raw palm oils of the Republic of Gabon and Congo. The physicochemical characteristics of these oils are given according to the conventional normalized methods. They are the analyzes such as the spectroscopic evaluation of the color, the content carotene, partial solidification and the content polyphenols
Onset of collective and cohesive motion
We study the onset of collective motion, with and without cohesion, of groups
of noisy self-propelled particles interacting locally. We find that this phase
transition, in two space dimensions, is always discontinuous, including for the
minimal model of Vicsek et al. [Phys. Rev. Lett. {\bf 75},1226 (1995)] for
which a non-trivial critical point was previously advocated. We also show that
cohesion is always lost near onset, as a result of the interplay of density,
velocity, and shape fluctuations.Comment: accepted for publication in Phys. Rev. Let
Integration of Langevin Equations with Multiplicative Noise and Viability of Field Theories for Absorbing Phase Transitions
Efficient and accurate integration of stochastic (partial) differential
equations with multiplicative noise can be obtained through a split-step
scheme, which separates the integration of the deterministic part from that of
the stochastic part, the latter being performed by sampling exactly the
solution of the associated Fokker-Planck equation. We demonstrate the
computational power of this method by applying it to most absorbing phase
transitions for which Langevin equations have been proposed. This provides
precise estimates of the associated scaling exponents, clarifying the
classification of these nonequilibrium problems, and confirms or refutes some
existing theories.Comment: 4 pages. 4 figures. RevTex. Slightly changed versio
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