569 research outputs found
Mutual optical injection in coupled DBR laser pairs
We report an experimental study of nonlinear effects, characteristic of mutual optical coupling, in an ultra-short coupling regime observed in a distributed Bragg reflector laser pair fabricated on the same chip. Optical feedback is amplified via a double pass through a common onchip optical amplifier, which introduces further nonlinear phenomena. Optical coupling has been introduced via back reflection from a cleaveended fibre. The coupling may be varied in strength by varying the distance of the fibre from the output of the chip, without significantly affecting the coupling time. © 2008 Optical. Society of America
A New Simulated Annealing Algorithm for the Multiple Sequence Alignment Problem: The approach of Polymers in a Random Media
We proposed a probabilistic algorithm to solve the Multiple Sequence
Alignment problem. The algorithm is a Simulated Annealing (SA) that exploits
the representation of the Multiple Alignment between sequences as a
directed polymer in dimensions. Within this representation we can easily
track the evolution in the configuration space of the alignment through local
moves of low computational cost. At variance with other probabilistic
algorithms proposed to solve this problem, our approach allows for the creation
and deletion of gaps without extra computational cost. The algorithm was tested
aligning proteins from the kinases family. When D=3 the results are consistent
with those obtained using a complete algorithm. For where the complete
algorithm fails, we show that our algorithm still converges to reasonable
alignments. Moreover, we study the space of solutions obtained and show that
depending on the number of sequences aligned the solutions are organized in
different ways, suggesting a possible source of errors for progressive
algorithms.Comment: 7 pages and 11 figure
Incorporating Ambipolar and Ohmic Diffusion in the AMR MHD code RAMSES
We have implemented non-ideal Magneto-Hydrodynamics (MHD) effects in the
Adaptive Mesh Refinement (AMR) code RAMSES, namely ambipolar diffusion and
Ohmic dissipation, as additional source terms in the ideal MHD equations. We
describe in details how we have discretized these terms using the adaptive
Cartesian mesh, and how the time step is diminished with respect to the ideal
case, in order to perform a stable time integration. We have performed a large
suite of test runs, featuring the Barenblatt diffusion test, the Ohmic
diffusion test, the C-shock test and the Alfven wave test. For the latter, we
have performed a careful truncation error analysis to estimate the magnitude of
the numerical diffusion induced by our Godunov scheme, allowing us to estimate
the spatial resolution that is required to address non-ideal MHD effects
reliably. We show that our scheme is second-order accurate, and is therefore
ideally suited to study non-ideal MHD effects in the context of star formation
and molecular cloud dynamics
Against Chaos in Temperature in Mean-Field Spin-Glass Models
We study the problem of chaos in temperature in some mean-field spin-glass
models by means of a replica computation over a model of coupled systems. We
propose a set of solutions of the saddle point equations which are
intrinsically non-chaotic and solve a general problem regarding the consistency
of their structure. These solutions are relevant in the case of uncoupled
systems too, therefore they imply a non-trivial overlap distribution
between systems at different temperatures. The existence of such
solutions is checked to fifth order in an expansion near the critical
temperature through highly non-trivial cancellations, while it is proved that a
dangerous set of such cancellations holds exactly at all orders in the
Sherrington-Kirkpatrick (SK) model. The SK model with soft-spin distribution is
also considered obtaining analogous results. Previous analytical results are
discussed.Comment: 20 pages, submitted to J.Phys.
Stabilization of apple peel by drying. Influence of temperature and ultrasound application on drying kinetics and product quality
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Drying Technology on 2019, available online at: http://www.tandfonline.com/10.1080/07373937.2018.1474476[EN] Increasing the value of the waste generated by food processing is a must from an environmental and economic point of view. This paper addresses the influence of drying temperature and ultrasound application on the drying kinetics and quality of apple peel (Royal Gala var.). Samples were dried at -10, 30, 50 and 70 ºC without and with (50 W) ultrasound application. Color, antioxidant capacity, total phenolic and ascorbic acid content were measured. Ultrasound application and drying temperature significantly shortened the drying time and affected the quality parameters. The drying carried out at 30 ºC with ultrasound application was a fast process that provided samples with good color and antioxidant attributes.The authors acknowledge the financial support of INIA-ERDF throughout the project RTA2015-00060-C04-02.Martins, MP.; Cortés, EJ.; Eim, V.; Mulet Pons, A.; Carcel, JA. (2019). Stabilization of apple peel by drying. Influence of temperature and ultrasound application on drying kinetics and product quality. Drying Technology. 37(5):559-568. https://doi.org/10.1080/07373937.2018.1474476S55956837
Near-field heat transfer in a scanning thermal microscope
We present measurements of the near-field heat transfer between the tip of a
thermal profiler and planar material surfaces under ultrahigh vacuum
conditions. For tip-sample distances below 10-8 m our results differ markedly
from the prediction of fluctuating electrodynamics. We argue that these
differences are due to the existence of a material-dependent small length scale
below which the macroscopic description of the dielectric properties fails, and
discuss a corresponding model which yields fair agreement with the available
data. These results are of importance for the quantitative interpretation of
signals obtained by scanning thermal microscopes capable of detecting local
temperature variations on surfaces
Polynomial iterative algorithms for coloring and analyzing random graphs
We study the graph coloring problem over random graphs of finite average
connectivity . Given a number of available colors, we find that graphs
with low connectivity admit almost always a proper coloring whereas graphs with
high connectivity are uncolorable. Depending on , we find the precise value
of the critical average connectivity . Moreover, we show that below
there exist a clustering phase in which ground states
spontaneously divide into an exponential number of clusters. Furthermore, we
extended our considerations to the case of single instances showing consistent
results. This lead us to propose a new algorithm able to color in polynomial
time random graphs in the hard but colorable region, i.e when .Comment: 23 pages, 10 eps figure
Transport on percolation clusters with power-law distributed bond strengths: when do blobs matter?
The simplest transport problem, namely maxflow, is investigated on critical
percolation clusters in two and three dimensions, using a combination of
extremal statistics arguments and exact numerical computations, for power-law
distributed bond strengths of the type .
Assuming that only cutting bonds determine the flow, the maxflow critical
exponent \ve is found to be \ve(\alpha)=(d-1) \nu + 1/(1-\alpha). This
prediction is confirmed with excellent accuracy using large-scale numerical
simulation in two and three dimensions. However, in the region of anomalous
bond capacity distributions () we demonstrate that, due to
cluster-structure fluctuations, it is not the cutting bonds but the blobs that
set the transport properties of the backbone. This ``blob-dominance'' avoids a
cross-over to a regime where structural details, the distribution of the number
of red or cutting bonds, would set the scaling. The restored scaling exponents
however still follow the simplistic red bond estimate. This is argued to be due
to the existence of a hierarchy of so-called minimum cut-configurations, for
which cutting bonds form the lowest level, and whose transport properties scale
all in the same way. We point out the relevance of our findings to other scalar
transport problems (i.e. conductivity).Comment: 9 pages + Postscript figures. Revtex4+psfig. Submitted to PR
Atmospheric freeze drying assisted by power ultrasound
[EN] Atmospheric freeze drying (AFD) is considered an alternative to vacuum freeze
drying to keep the quality of fresh product. AFD allows continuous drying reducing fix and
operating costs, but presents, as main disadvantage, a long drying time required. The
application of power ultrasound (US) can accelerate AFD process. The main objective of the
present study was to evaluate the application of power ultrasound to improve atmospheric
freeze drying of carrot. For that purpose, AFD experiments were carried out with carrot cubes
(10 mm side) at constant air velocity (2 ms-1), temperature (-10ºC) and relative humidity (10%)
with (20.5 kWm-3, USAFD) and without (AFD) ultrasonic application. A diffusion model was
used in order to quantify the influence of US in drying kinetics. To evaluate the quality of dry
products, rehydration capacity and textural properties were determined. The US application
during AFD of carrot involved the increase of drying rate. The effective moisture diffusivity
identified in USAFD was 73% higher than in AFD experiments. On the other hand, the
rehydration capacity was higher in USAFD than in AFD and the hardness of dried samples did
not show significant (p<0.05) differences. Therefore, US application during AFD significantly
(p<0.05) sped-up the drying process preserving the quality properties of the dry product.Santacatalina Bonet, JV.; Carcel Carrión, JA.; Simal, S.; García Pérez, JV.; Mulet Pons, A. (2012). Atmospheric freeze drying assisted by power ultrasound. IOP Conference Series: Materials Science and Engineering. 42:5-8. doi:10.1088/1757-899X/42/1/012021S5842Stawczyk, J., Li, S., Witrowa-Rajchert, D., & Fabisiak, A. (2006). Kinetics of Atmospheric Freeze-drying of Apple. Transport in Porous Media, 66(1-2), 159-172. doi:10.1007/s11242-006-9012-4Wolff, E., & Gibert, H. (1990). ATMOSPHERIC FREEZE-DRYING PART 1 : DESIGN, EXPERIMENTAL INVESTIGATION AND ENERGY-SAVING ADVANTAGES. Drying Technology, 8(2), 385-404. doi:10.1080/07373939008959890García-Pérez, J. V., Cárcel, J. A., Benedito, J., & Mulet, A. (2007). Power Ultrasound Mass Transfer Enhancement in Food Drying. Food and Bioproducts Processing, 85(3), 247-254. doi:10.1205/fbp07010Gallego-Juárez, J. A., Riera, E., de la Fuente Blanco, S., Rodríguez-Corral, G., Acosta-Aparicio, V. M., & Blanco, A. (2007). Application of High-Power Ultrasound for Dehydration of Vegetables: Processes and Devices. Drying Technology, 25(11), 1893-1901. doi:10.1080/07373930701677371Hassini, L., Azzouz, S., Peczalski, R., & Belghith, A. (2007). Estimation of potato moisture diffusivity from convective drying kinetics with correction for shrinkage. Journal of Food Engineering, 79(1), 47-56. doi:10.1016/j.jfoodeng.2006.01.02
Effect of External Noise Correlation in Optical Coherence Resonance
Coherence resonance occurring in semiconductor lasers with optical feedback
is studied via the Lang-Kobayashi model with external non-white noise in the
pumping current. The temporal correlation and the amplitude of the noise have a
highly relevant influence in the system, leading to an optimal coherent
response for suitable values of both the noise amplitude and correlation time.
This phenomenon is quantitatively characterized by means of several statistical
measures.Comment: RevTeX, 4 pages, 7 figure
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