排序方式: 共有23条查询结果,搜索用时 296 毫秒
1.
2.
N. K. Paschos D. G. Aggelis N.-M. Barkoula A. Paipetis D. Gartzonikas T. E. Matikas A. D. Georgoulis 《Experimental Mechanics》2013,53(5):767-774
The analysis of the acoustic signals produced during anterior cruciate ligament (ACL) failure could be useful in understanding its behavior. The purpose of the present study was to evaluate the role of coupling conditions of the sensors and to determine the value of newly introduced acoustic emission (AE) parameters. Seven femur-ACL-tibia complex (FATC) specimens were fixed in a universal tensile testing machine and load was applied. Different coupling conditions were applied in two groups of specimens. The load-time curve was monitored, with the simultaneous recording of the acoustic signals and the failure mode. During ACL tear, detectable changes in the load-time curve occurred linked to changes in the macroscopic sequence of events and the measured AE parameters irrespective the coupling conditions. AE provides information on the determination of the moment (or load) when crucial irreversible damage occurs. Furthermore, specific AE indices exhibit changes throughout the testing, and imply shift of the failure mechanisms. 相似文献
3.
Results from an experimental study concerning wave propagation in cementitious materials are presented in this paper. Narrow band pulses at several frequencies were introduced into specimens of cement paste, mortar and concrete allowing direct measurement of longitudinal wave velocities and amplitude for each frequency. It is shown that aggregate content play an important role in wave propagation increasing considerably the wave velocity, while the aggregate size seems to control the attenuation observed. Slight velocity variations observed with frequency are discussed in relation to the degree of inhomogeneity of the materials. 相似文献
4.
Aggelis DG Paschos NK Barkoula NM Paipetis AS Matikas TE Georgoulis AD 《The Journal of the Acoustical Society of America》2011,129(6):EL217-EL222
The scope of this study is to relate the acoustic emission (AE) during rupture of human soft tissue (anterior cruciate ligament, ACL) to the mechanisms leading to its failure. The cumulative AE activity highlights the onset of serious damage, while other parameters, show repeatable tendencies, being well correlated with the tissue's mechanical behavior. The frequency content of AE signals increases throughout the experiment, while other indices characterize between different modes of failure. Results of this preliminary study show that AE can shed light into the failure process of this tissue, and provide useful data on the ACL reconstruction. 相似文献
5.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
6.
§ 1.Introduction WearegivenkindependentWishartdensitiesofthe (p +q)× (p +q)randomsymmetricpositivedefinitematricesG1,… ,Gktobeg(Gi) =Kexp -12 trR- 1i Gi Gi12 (ni- q-p- 1) ,(1 )wherei=1 ,… ,k,andRidenotesthepopulationcorrelationmatrixofthei thpopulationandKasagenericletterdenote… 相似文献
7.
The study occupies with acoustic emission monitoring of several types of concrete during bending. The signals emitted at the different fracturing stages exhibit distinct signatures. Specifically, frequency and shape parameters of the acquired waveforms shift during the experiment, closely following the sequence of fracture mechanisms from tensile micro-cracking to brittle macro-cracking and fiber pull out. A number of AE indices are proposed, the use of which will enable classification of the cracks according to their mode. The study sheds light to the fracture process of cementitious materials, and enables a warning against the final failure. The simplicity of the scheme renders it applicable in situ. 相似文献
8.
D.G. Aggelis D. Polyzos T.P. Philippidis 《Journal of the mechanics and physics of solids》2005,53(4):857-883
In the present paper, the dispersive and attenuative behavior of fresh cementitious material is examined through a series of ultrasonic, through-transmission measurements. The sand size and content dominate attenuation behavior, while the effect of entrapped air bubbles is mostly obvious at lower frequencies elevating phase velocity to values much higher than that of water. Theoretical investigation seems to explain the observed dispersion and attenuation mainly through two scattering interactions: sand embedded in paste and air bubbles in mortar. The predictions made by scattering theory follow closely the experimental data. The possibility of material characterization is discussed. 相似文献
9.
Bellou S Moustogianni A Makri A Aggelis G 《Applied biochemistry and biotechnology》2012,166(1):146-158
Several strains of Zygomycetes cultivated on glycerol produced mycelia rich in lipids containing higher amounts of neutral
lipids (NL) than glycolipids plus sphingolipids and phospholipids (P), while biosynthesis of P in Mortierella ramanniana, Mucor sp., and Cunninghamella echinulata occurred though NL accumulation process was in progress. Polyunsaturated fatty acids (PUFA) concentration gradually decreased
in all lipid fractions of M. ramanniana during growth. In contrast, in C. echinulata concentration of both linoleic and γ-linolenic acids increased with time, especially in P. Taking for granted that the main
function of PUFA is associated to their participation in mycelial membranes, we could suppose that biosynthesis of these fatty
acids is associated to mycelial growth. However, this is accurate only for some Zygomycetes, e.g., M. ramanniana. On the contrary, PUFA biosynthesis in C. echinulata persists after growth cessation, suggesting that in this species biosynthetic ability is not a strictly growth-associated
process. Phosphatidyl-inositol and phosphatidyl-choline were the major P classes in C. echinulata and M. ramanniana, respectively. In M. ramanniana, a decrease of PUFA concentration was noticed even when mycelia were incubated in low temperature (conditions that normally
favor PUFA biosynthesis), indicating that PUFA biosynthesis in this fungus is associated to primary metabolism. 相似文献
10.
Panagiota Diamantopoulou Seraphim Papanikolaou Eleni Katsarou Michael Komaitis George Aggelis Antonios Philippoussis 《Applied biochemistry and biotechnology》2012,167(7):1890-1906
Volvariella volvacea strains were studied in relation with their ability to produce biomass, lipids and polysaccharides. Firstly, screening of four strains (AMLR 188, 190, 191 and 192) was performed in agar cultures, where the mycelial growth rate of the strains was measured, and in static liquid cultures, where the production of biomass, the biosynthesis of total cellular lipids and the consumption of glucose were monitored. For all strains, biomass production was significant (13?C15?g?l?1) and total lipid in dry weight (%, w/w) ranged from 3 to 12?%. Afterwards, a detailed kinetic analysis of mycelial biomass, extra- and intra- cellular polysaccharides (EPS, IPS, respectively) as well as lipid production by a V. volvacea selected strain was conducted in submerged static and agitated cultures. Maximum values of 15?g?l?1 biomass, ??1.0?g?l?1 EPS and 5.5?g?l?1 IPS were recorded. Agitation did not have severe impact on biomass, EPS and IPS production, but it increased total lipid in dry weight quantities. EPS, IPS and lipid in dry weight values decreased with time. Glucose was the major cellular carbohydrate detected. Total fatty acid analysis of cellular lipids was performed for all V. volvacea strains and linoleic acid ??9,12C18:2 was predominant. Neutral lipids constituted the major fraction of cellular lipids, but their quantity decreased as fermentation proceeded. Phospholipids were the most saturated lipid fraction. 相似文献