Recently, the Urmia Lake located in northwestern Iran which is the second largest hyper saline in the world suffers from the significant fluctuations of water level and surface area. The current study tries to investigate the spatiotemporal trends of mean (Tmean), maximum (Tmax) and minimum (Tmin) temperatures of monthly, seasonal and annual time-series. To do so, the data of 15 temperature gauge stations within the Urmia Lake basin, for the period 1972–2011 was employed. The pre-whitening approach was applied to remove the effects of serial correlation in the air temperature series based on the Mann-Kendall (MK) test. The results of Ljung-Box test showed positive serial correlation in the Tmean and Tmax series for all of the stations at the 0.05 significance level. In the monthly series, the significant warming trends in the Tmean series were more perceptible than the same ones in Tmax series; however, Tmax trend was found more than Tmin series. The Mann–Whitney (MW) test detected a significance upward shift changes in the annual Tmean, Tmax and Tmin series of about 86, 73 and 80 % of the stations, respectively. The average magnitude of significant warming trends in annual Tmean, Tmax and Tmin series were (+) 0.58 °C, (+) 0.52 °C and (+) 0.69 °C per decade, respectively. Furthermore, the interpolation maps showed that warming trends in the east and west of Urmia Lake were more than southern area. Therefore, the results showed that the basin has suffered from increasing trends in the Tmean, Tmax and Tmin over the recent decades. Finally, significant changes were found in 1980s and 1990s based on the Mann-Kendall ranks and change point tests. In this study, it is interesting that the period of significant changes in warming trends were close to the beginning of decreasing water level of the Lake. 相似文献
An eXtended Finite Element Method (XFEM) is presented that can accurately predict the stress intensity factors (SIFs) for
thermoelastic cracks. The method uses higher order terms of the thermoelastic asymptotic crack tip fields to enrich the approximation
space of the temperature and displacement fields in the vicinity of crack tips—away from the crack tip the step function is
used. It is shown that improved accuracy is obtained by using the higher order crack tip enrichments and that the benefit
of including such terms is greater for thermoelastic problems than for either purely elastic or steady state heat transfer
problems. The computation of SIFs directly from the XFEM degrees of freedom and using the interaction integral is studied.
Directly computed SIFs are shown to be significantly less accurate than those computed using the interaction integral. Furthermore,
the numerical examples suggest that the directly computed SIFs do not converge to the exact SIFs values, but converge roughly to values near the exact result. Numerical simulations of straight
cracks show that with the higher order enrichment scheme, the energy norm converges monotonically with increasing number of
asymptotic enrichment terms and with decreasing element size. For curved crack there is no further increase in accuracy when
more than four asymptotic enrichment terms are used and the numerical simulations indicate that the SIFs obtained directly
from the XFEM degrees of freedom are inaccurate, while those obtained using the interaction integral remain accurate for small
integration domains. It is recommended in general that at least four higher order terms of the asymptotic solution be used
to enrich the temperature and displacement fields near the crack tips and that the J- or interaction integral should always be used to compute the SIFs. 相似文献
We propose a uniform method to encode various types of trees succinctly. These families include ordered (ordinal), k-ary (cardinal), and unordered (free) trees. We will show the approach is intrinsically suitable for obtaining entropy-based encodings of trees (such as the degree-distribution entropy). Previously-existing succinct encodings of trees use ad hoc techniques to encode each particular family of trees. Additionally, the succinct encodings obtained using the uniform approach improve upon the existing succinct encodings of each family of trees; in the case of ordered trees, it simplifies the encoding while supporting the full set of navigational operations. It also simplifies the implementation of many supported operations. The approach applied to k-ary trees yields a succinct encoding that supports both cardinal-type operations (e.g. determining the child label i) as well as the full set of ordinal-type operations (e.g. reporting the number of siblings to the left of a node). Previous work on succinct encodings of k-ary trees does not support both types of operations simultaneously (Benoit et al. in Algorithmica 43(4):275–292, 2005; Raman et al. in ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 233–242, 2002). For unordered trees, the approach achieves the first succinct encoding. The approach is based on two recursive decompositions of trees into subtrees. Recursive decomposition of a structure into substructures is a common technique in succinct encodings and has even been used to encode (ordered) trees (Geary et al. in ACM Trans. Algorithms 2(4):510–534, 2006; He et al. in ICALP, pp. 509–520, 2007) and dynamic binary trees (Munro et al. in ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 529–536, 2001; Storm in Representing dynamic binary trees succinctly, Master’s thesis, 2000). The main distinction of the approach in this paper is that a tree is decomposed into subtrees in a manner that the subtrees are maximally isolated from each other. This intermediate decomposition result is interesting in its own right and has proved useful in other applications (Farzan et al. in ICALP (1), pp. 451–462, 2009; Farzan and Munro in ICALP (1), pp. 439–450, 2009; Farzan and Kamali in ICALP, 2011). 相似文献
By virtue of the surface plasmon resonance effect, plasmonic nanoparticles (NPs) can localize the light field and significantly enhance the performance of some optoelectronic devices. In this work, NPs are employed for an enhanced generation of terahertz radiation from LT-GaAs-based antennas. Therefore, we have prepared plasmonic TiN NPs by direct ultrasonication (ULS) and pulsed laser ablation (PLA) techniques. The zeta potential, particle size, and absorbance were used to characterize the NPs in their colloidal forms in a comparison to commercial Au NPs. A layer of polydispersed titanium nitride (TiN) NPs prepared by PLA and deposited on the surface of an LT-GaAs device shows a significant improvement of terahertz signal generation from these devices with an enhancement of the peak to peak amplitude of 100%. 相似文献
The viscoelastic and mechanical properties of composites multi walled carbon nanotube (MWNT)/epoxy at different weight fractions (0.1, 0.5, 1 and 2 wt.%) were evaluated by performing tensile and dynamic-mechanical thermal analysis (DMTA) tests. The MWNT/epoxy composite were fabricated by sonication and a cast molding process. The results showed that addition of nanotubes to epoxy had significant effect on the viscoelastic and mechanical properties. However, the use of 0.5 wt.% increased the viscoelastic properties more significantly. Concerning viscoelastic modeling, the COLE–COLE diagram has been plotted by the results of DMTA test. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite. 相似文献
Organic semiconductor to metal Schottky contacts have been widely used in electronic devices and to investigate the properties of organic semiconductors. In designing and characterizing these devices the full depletion approximation is used. The analytical and numerical simulations presented in this paper suggest that this approximation is not generally valid. Simulations of a Schottky contact between regioregular-poly 3 hexylthiophene (rr-P3HT) and aluminum show that this approximation becomes worse as molecular order decreases, with the potential profile increasingly deviating from the expected quadratic function of position. Also the depletion width decreasing well below that predicted using the approximation. In this work the slope of the band tail is used as a measure of disorder. 相似文献
Objective: The objective of this study was to fabricate double-walled poly(lactide-co-glycolide) (PLGA) microspheres to increase encapsulation efficiency and avoid rapid release of hydrophilic drugs such as meglumine antimoniate.
Methods: In this study, double-walled and one-layered microspheres of PLGA were prepared using the emulsion solvent evaporation technique to better control the release of a hydrophilic drug, meglumine antimoniate (Glucantime®), which is the first choice treatment of cutaneous leishmaniasis. The effect of hydrophobic coating on microspheres' size, morphology, encapsulation efficiency and drug release characteristics was evaluated. Furthermore, the presence of antimony in meglumine antimoniate made it possible to observe the drug distribution within the microspheres' cross section by means of energy dispersive X-ray spectroscopy.
Results: Drug distribution images confirmed accumulation of the drug within the inner core of double-walled microspheres. In addition, these microspheres encapsulated the drug more efficiently up to 87% and demonstrated reduced initial burst and prolonged release compared to one-layered microspheres. These superiorities make double-walled microspheres an optimum candidate for sustained delivery of hydrophilic drugs.
Conclusion: Double-walled microspheres provide some advantages over traditional microspheres overcoming most of their limitations. Double-walled microspheres were found to be more efficient than their corresponding one-layered microspheres in terms of encapsulation efficiencies and release characteristics. 相似文献