24,073 research outputs found
Prospect of detecting single-photon-force effects in cavity optomechanics
No full textCavity optomechanical systems are approaching a strong-coupling regime where the coherent dynamics of nanomechanical resonators can be manipulated and controlled by optical fields at the single-photon level. Here we propose an interferometric scheme able to detect optomechanical coherent interaction at the single-photon level which is experimentally feasible with state-of-the-art devices
Effects Of A Logging Tool On The Stoneley Wave Propagation In Elastic And Porous Formations
No full textA detailed study is carried out to investigate the effects of an acoustic logging tool on
the propagation characteristics of Stoneley waves in both elastic and porous formations.
In an elastic formation, the presence of the tool in the borehole reduces the Stoneley
velocity and enhances the Stoneley wave excitation. When intrinsic attenuation due to
formation and bore fluid anelasticity is present, the tool reduces Stoneley attenuation
due to fluid and increases the attenuation due to formation. For a permeable porous
formation, the simplified Biot-Rosenbaum model of Tang et al. (1990) is modified to
incorporate the effects of the tool on the Stoneley propagation. The presence of the tool
increases the sensitivity of the Stoneley waves to the formation flow properties. Specifically, the dispersion of Stoneley velocity due to formation permeability is increased and the attenuation of the Stoneley waves is more pronounced, compared with the results without the tool. Consequently, in the determination of formation flow properties using Stoneley wave measurements, the effects of permeability may be better estimated using a tool with large diameter.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636
Consensus of multi-agent systems via fully distributed event-triggered control
No full textThis article studies consensus of linear multi-agent systems (MASs) on undirected graphs. An adaptive event-triggering protocol is constructed for consensus control by using relative information between agents. Sufficient conditions are established for consensus of linear MASs without and with external disturbances, respectively. Zeno behavior is proved to be excluded. Moreover, a self-triggered realization based on sampled information is formulated for the protocol. Since the proposed protocol incorporates both adaptive control and event-triggered control, it can be implemented in a fully distributed way and only makes use of the sampled relative information between neighboring agents. Two numerical examples are finally provided for demonstrating the effectiveness and advantages of the theoretical results
Surveying silk fibre degradation by crystallinity determination: a study on the Tang-Dynasty silk treasure from Famen Temple, China
No full textWhen Chinese archaeologists opened an unknown vault under the collapsed pagoda of Famen Temple near Xian (Shaanxi Province, NW China) in 1987, they found a vast amount of valuable silk textiles. The degraded textiles were part of a treasure comprising hundreds of artifacts deposited by Tang dynasty (ad 618–907) emperors as a gift to the temple. Run as a bilateral German-Chinese project, the Roemisch-Germanisches Zentralmuseum Mainz established a textile conservation laboratory in Shaanxi´s provincial capital Xian in 2001, joining numerous other laboratories that have existed there since the early 1990s.This preliminary study represents part of an ongoing investigation programme that accompanies the conservation work. The Tang dynasty silk is generally in a very poor state of preservation as a result of its long burial period. Large sections have only survived as an amorphous brown mass of fibre debris. Some parts are better preserved, however, offering the unique opportunity to study the whole range of degradation stages on ancient silks.This preliminary scientific investigation focuses on the determination of the silk fibres’ crystallinity and its relation to the ageing process. As we know from modern material, silk is mainly crystalline, albeit in a somewhat amorphous state. The methods of investigation used were X-ray diffraction (XRD) using synchrotron radiation, which is a new way to determine crystallinity of ancient silk fibres; and polarized Fourier transform infrared spectroscopy (FTIR) for the determination of crystallite orientation. Both methods were specifically devised to gain information on small single fibres
Dimensioning and Power Management of Hybrid Energy Storage Systems for Electric Vehicles with Multiple Optimization Criteria
No full textHybrid energy storage systems (HESS) that combine lithium-ion batteries and supercapacitors are considered as an attractive solution to overcome the drawbacks of battery-only energy storage systems, such as high cost, low power density, and short cycle life, which hinder the popularity of electric vehicles. A properly sized HESS and an implementable real-time power management system are of great importance to achieve satisfactory driving mileage and battery cycle life. However, dimensioning and power management problems are quite complicated and challenging in practice. To address these challenges, this article proposes a bilevel multiobjective design and control framework with the nondominated sorting genetic algorithm NSGA-II and fuzzy logic control (FLC) as key components, to obtain an optimal sized HESS and the corresponding optimal real-time power management system based on FLC simultaneously. In particular, a vectorized fuzzy inference system is devised, which allows large-scale fuzzy logic controllers to run in parallel, thereby improving optimization efficiency. Pareto optimal results of different HESSs incorporating both optimal design and control parameters are obtained efficiently thanks to the vectorization. An example solution chosen from the Pareto front shows that the proposed method can achieve a competitive number of covered laps while improving the battery cycle life significantly
The use of a multi-set-up, reduced-scale accelerated trafficking simulator for evaluating roadway systems and products
No full textThis paper describes the use of an accelerated trafficking device, the one-third scale model mobile load simulator (MMLS3), for evaluating roadway systems and products. While the majority of accelerated load testers have focused on investigating rutting behaviours and moisture damage susceptibility of bituminous materials, this paper sheds light on broader applications using the MMLS3, including accelerated tests on field sections, scaled pavement structures, roadway reflective markings, roadway slip-resistant plates, in addition to performance evaluation tests on hot-mix asphalt mixtures. Results of experiments for the various applications indicate that the MMLS3, when equipped with ancillary instrumentation and devices, is a valuable tool for investigating the structural responses of a roadway system and for evaluating the effectiveness and durability of roadway pavement products. This study shows that the results of accelerated trafficking tests using the MMLS3 are comparable with field full-scale accelerated tests due to the nature of similitude in the MMLS3 design. Using the MMLS3 for accelerated traffic testing for practical and research purposes in the area of pavement engineering is a reliable and economical alternative to full-scale accelerated testing, given the savings in the required time and resources. © 2012 Copyright Taylor and Francis Group, LLC.Aktan F, 2004, TRANSPORT RES REC, P38; Al-Qadi L., 2007, TRB 2007 ANN M; Anderson D., 1984, 4 CYCLE PAVEMENT RES, V1; [Anonymous], 2007, ANN BOOK ASTM STAND; [Anonymous], 2007, ANN BOOK ASTM STAND; Barksdale R. D., 1989, 315 NCHRP TRANSP BOA; Bhattacharjee S., 2005, THESIS WORCESTER POL; Chehab G.R., 2007, FHWAPA2007009050110; Cooley Jr L. A., 2000, EC016 TRB NAT RES CO; Donnell ET, 2009, TRANSP RES RECORD, P76, DOI 10.3141-2107-08; Epps A. L., 2003, J TRANSPORTATION ENG, V129, P451, DOI 10.1061-(ASCE)0733-947X(2003)129:4(451); Epps A. L., 2001, 21341 TEX A M U TEX; Hufenus R, 2006, GEOTEXT GEOMEMBRANES, V24, P21, DOI 10.1016-j.geotexmem.2005.06.002; Hugo F. H., 2006, NCHRP SYNTHESIS HIGH; Kim S-M., 1995, 29141F U TEX CTR TRA; Lee S., 2003, THESIS N CAROLINA ST; Metcalf J. B., 1996, NCHRP SYNTHESIS HIGH; MLS Test Systems, 2003, MMLS3 OP MAN; Palacios C, 2008, PAVEMENT CRACKING: MECHANISMS, MODELING, DETECTION, TESTING AND CASE HISTORIES, P721; Pennsylvania Department of Transportation (PennDOT, 1995, PENNS DEP TRANSP PUB; Perkins S. S., 1999, FHWAMT990018138 US D; Smit A., 2004, P 2 INT APT C US SEA; Smit A., 1999, FHWATX00018142 U TEX; Smit A., 2003, TRB 82 ANN M; Tang X., 2008, GEOTECHNICAL SPECIAL, P1049; Tang X., 2008, GEOTECHNICAL SPECIAL, P1089; Xiaochao Tang, 2008, INT J PAVEMENT ENG, V9, P413, DOI 10.1080-102984308022798270
Hot-electron photocurrent detection of near-infrared light based on ZnO
No full textWe demonstrate an unconventional near infrared photodetector fabricated from a ZnO chip with a metallic subwavelength grating structure as contact and optical window, which harvests hot electrons generated by plasmonic resonances introduced by incident light. The grating structure has a strong selection of the polarization of incident light, meaning that the detector is naturally polarization-sensitive. In our device, the polarization extinction ratio is as high as 64:1, much higher than that relying on crystal orientations. Since the photoresponse is introduced by plasmonic resonance, a narrow photoresponse spectrum with a linewidth of 32.1 nm at 1.201 µm is obtained. By simply changing the grating period, the spectral position can be tailored freely within the near infrared region, i.e., wavelength-selective. Such a spectral response is not likely to be realized with conventional semiconductor photodetectors, which depend on the band edge absorption. We propose a modified Fowler’s model, which well explains the line shape of photoresponse spectra of such devices
Performance Comparison of a KF-based and a KF+VDFLL Vector Tracking-Loop in Case of GNSS Partial Outage and Low-Dynamic Conditions
No full textNew GNSS tracking architectures are becoming of scientific interest since the last decade. The traditional DLL/PLL
tracking-loops have been progressively substituted by KF/EKF scalar tracking and VDLL/VDFLL vector tracking methods. In this paper we will analyze in depth the performance of a KF
scalar tracking and VDFLL vector in case of signal outage.
Differently from papers on the same topic, we will show how the
performance of a KF, when used within the tracking stage during
a signal’s blockage, are strongly dependent on a proper setting of
the noise covariance matrices Q and P of the system, otherwise
cases of frequency false-lock can occur when the outage condition
lasts for a long time. Conversely, a VDFLL vector tracking
algorithm is able to provide more precise frequency and codephase’s
estimations then the KF scalar in case of signal’s
unavailability, but its performance relies on the navigation
solution. Therefore, the effects of the PVT accuracy on the
estimation of the main tracking parameters are also presented in
this paper
A note on Tang and He’s paper
No full textIn this paper, we establish new Lyapunov-type inequalities for two classes of one-dimensional quasilinear elliptic systems of resonant type, which improve the recent results of Tang and He [X. H. Tang, X. He, Lower bounds for generalized eigenvalues of the quasilinear systems, J. Math. Anal. Appl. 385 (2012) 72-85] when 1 < p(i) < 2 for i = 1,2, ..., n. (C) 2011 Elsevier Inc. All rights reserved
Wave Propagation In A Fluid-Filled Fracture-An Experimental Study
No full textA laboratory experimental study has been carried out to investigate the mode trapping
characteristics of a fluid-filled fracture between two elastic solids. Using a small circular cylindrical receiver of 2.7 mm diameter, we were able to measure the wave motion
directly inside a 2.8 mm thick fracture and to obtain array data for the propagating
waves. The data was processed using Prony's method to give velocity of the wave
modes as a function of frequency. The experimental results agree with the theoretical
predictions quite well. Specifically, in a "hard" (aluminum) fracture where the shear
velocity of the solid is greater than the fluid velocity, four normal modes were detected
in the frequency range up to 2.4 MHz. Whereas in a "soft" (lucite) fracture where the
shear velocity is smaller than the fluid velocity, four leaky-P modes were detected in the same frequency range. In both cases, a fundamental mode analogous to Stoneley waves
in a borehole was detected. In particular, the velocity of this mode approaches zero in
the low frequency limit, as indicated by the theory and confirmed by the experiment
in a low frequency range down to 25 kHz.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ERI3636
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