Učinak temperature i dodatka indija na mehanička svojstva legure Al–0.21wt%Au

Tensile characteristics of both Al–0.21wt%Au and Al–0.21wt%Au–0.21wt%In alloys were investigated in the temperature range 493 K to 553 K. The coefficient of work hardening, χ = ∂σ2/∂², yield stress, σy, and fracture stress, σf , decreased with increasing deformation temperature (T) and exhibited abrupt increase at about 523 K. On the other hand, the fracture strain, ²f , and dislocation slip distance, L, increased with increasing deformation temperature and exhibited minima at about 523 K. The activation energy was determined in the range around 523 K to clarify the observed change in the behaviour of the hardening characteristics of the investigated samples.Istraživali smo istezna svojstva legura Al–0.21wt%Au i Al–0.21wt%Au–0.21wt%In na temperaturama 493 K do 553 K. Koeficijent mehaničkog očvršćivanja, χ = ∂σ2/∂², granica elastičnosti, σy, i granica loma, σf , smanjuju se pri povišenim temperaturama istezanja (T) te pokazuju nagao porast na oko 523 K. Nasuprot tome, lomno istezanje, ²f , i prosječna duljina klizanja dislokacija, L, povećali su se s povišenom temperaturom istezanja, a pokazuju i minimum na oko 523 K. Radi objašnjenja opaženih promjena u procesu očvršćivanja ispitivanih uzoraka odredili smo aktivacijsku energiju na temperaturama oko 523 K

Central limit theorem for signal-to-interference ratio of reduced rank linear receiver

Let $\mathbf{s}_k=\frac{1}{\sqrt{N}}(v_{1k},...,v_{Nk})^T,$ with $\{v_{ik},i,k=1,...\}$ independent and identically distributed complex random variables. Write $\mathbf{S}_k=(\mathbf{s}_1,...,\mathbf {s}_{k-1},\mathbf{s}_{k+1},... ,\mathbf{s}_K),$ $\mathbf{P}_k=\operatorname {diag}(p_1,...,p_{k-1},p_{k+1},...,p_K)$, $\mathbf{R}_k=(\mathbf{S}_k\mathbf{P}_k\mathbf{S}_k^*+\sigma ^2\mathbf{I})$ and $\mathbf{A}_{km}=[\mathbf{s}_k,\mathbf{R}_k\mathbf{s}_k,... ,\mathbf{R}_k^{m-1}\mathbf{s}_k]$. Define $\beta_{km}=p_k\mathbf{s}_k^*\mathbf{A}_{km}(\mathbf {A}_{km}^*\times\ mathbf{R}_k\mathbf{A}_{km})^{-1}\mathbf{A}_{km}^*\mathbf{s}_k$, referred to as the signal-to-interference ratio (SIR) of user$k$under the multistage Wiener (MSW) receiver in a wireless communication system. It is proved that the output SIR under the MSW and the mutual information statistic under the matched filter (MF) are both asymptotic Gaussian when$N/K\to c>0$. Moreover, we provide a central limit theorem for linear spectral statistics of eigenvalues and eigenvectors of sample covariance matrices, which is a supplement of Theorem 2 in Bai, Miao and Pan [Ann. Probab. 35 (2007) 1532--1572]. And we also improve Theorem 1.1 in Bai and Silverstein [Ann. Probab. 32 (2004) 553--605].Comment: Published in at http://dx.doi.org/10.1214/07-AAP477 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

The kinetics of the methanol synthesis on a copper catalyst: An experimental study

The kinetics of the low pressure of methanol from feed gases containing solely CO and H2 were studied in an internally recycled gradientless reactor. As experimental accuracy impeded the application of high CO contents, the experimental range of mole fraction of CO was limited to 0.04 to 0.22. The total pressure was varied from 3 to 7 MPa and the temperature from 503 to 553 K. Residence time distribution experiments confirmed the assumption of perfect mixing on a macroscale. A maximum likelihood approach was used to fit possible kinetic equations. Although more accurate results and better fits—compared to previous experiments in a simple integral reactor—were obtained, no single rate expression could be selected as the most appropriate one. This was mainly attributed to the effects of small amounts of CO2 and H2O formed in the reactor. Three different reaction rate equations fit the experiments equally well. Arguments are given that we never can expect to elucidate the reaction mechanisms on the basis of kinetic experiments

Kinetics of the gas-phase reactions of chlorine atoms with CH 2 F 2 , CH 3 CCl 3 , and CF 3 CFH 2 over the temperature range 253–553 K

Relative rate techniques were used to study the title reactions in 930–1200 mbar of N 2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k (Cl + CH 2 F 2 ) = 1.19 × 10 −17 T 2 exp(−1023/T) cm 3 molecule −1 s −1 (253–553 K), k (Cl + CH 3 CCl 3 ) = 2.41 × 10 −12 exp(−1630/T) cm 3 molecule −1 s −1 (253–313 K), and k (Cl + CF 3 CFH 2 ) = 1.27 × 10 −12 exp(−2019/T) cm 3 molecule −1 s −1 (253–313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401–406, 2009Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62132/1/20398_ftp.pd

A contribution of in situ UV/Vis/NIR spectroscopy to characterize molybdenum oxide catalysts

Molybdenum oxide based catalysts are suitable candidates for many selective oxidation reactions [1]. Such catalysts containing only Mo and O have been successfully prepared by controlled adjustment of precursor concentration, temperature or nature of counter cation. The obtained materials, namely orthorhombic and hexagonal MoO3, a supramolecular Mo36 and a trimolybdate compound were thoroughly analysed by XRD, TEM, TG, TPRS and Raman spectroscopy [2]. As such materials undergo electronic changes during catalytic reactions we will present an in situ UV/Vis/NIR study on the different families of molybdenum oxide (MoOx) catalysts. Experimental A commercial UV/Vis/NIR spectrometer (Lambda 9, Perkin Elmer) equipped with a BaSO4 coated integrating sphere was supplemented with a new construction (specially formed light conductor in vertical position) to measure in situ diffuse reflectance spectra of different MoOx from room temperature (RT) to 673 K [3]. The spectra were recorded both from 250 to 2500 nm (scan speed of 240 nmmin-1, slit 1 nm) and 250 to 800 nm (scan speed 60 nmmin-1, slit 0.2 nm) with Spectralon (Labsphere) as a white standard in the reference position. Powder samples (ca. 0.6 g) were charged in the home-made microreactor and fed with a flow of air, pure He or 21 % oxygen in helium. The MoOx samples were prepared using precipitation method (0.28 up to 2 mol/L AHM, Na2MoO4, K2MoO4, Li2MoO4 dissolved in bi-distilled water and 1 mol/L up to 5 mol/L HNO3) from 30oC to 70oC. Results and discussion MoOx spectra show NIR bands with different intensities, distinguishable LMCT bands and band gap energies (Eg) at RT. Based on the exact determination of such spectroscopic characteristics the following LMCT bands (nm) (I) and Eg’s (eV) (II) are attributed to the above mentioned MoOx families: (I) 322 (NH4+), 314 (K+); (II) 3.48 (NH4+), 3.44 (K+) to supramolecular Mo36; (I) 313 (NH4+), 319 (K+), 327 (Na+); (II) 3.35 (NH4+); 3.30 (K+), 3.27 (Na+) to hexagonal MoO3; (I) 296 (Li+); (II) 3.44 (Li+) to orthorhombic MoO3 and (I) 284 (K+); (II) 3.77 (K+) to trimolybdate MoOx. From a blue shift of the LMCT band in the series supramolecular/hexagonal orthorhombic trimolybdate and a decreasing broadening of this band it may be concluded that the cluster size decreases. All MoOx samples evolved NIR bands at 1435, 1940, and 2040 nm. They are assignable to an overtone mode of the OH stretching vibration and a combination mode of the OH stretching and bending vibration, respectively. Other NIR bands, e.g., those detected in MoOx samples prepared from AHM at 1570 and 2150 are caused by ammonia. Initial experiments in dependence on temperature show that the bands at 1440, 1940 and 2030 nm initially decrease at higher temperature and then disappear. In addition, by increasing the temperature the band at 2150 nm begins to disappear at 553 K and the band at 1570 nm dimi- nished around 633 K (not shown). In Vis range a new band at 660/670 nm develops at 553 K which decreases in presence of He and increases in presence of O2 in He with increasing temperature (Fig. 1). This band is assigned to a d-d transition. In He this band suffers a blue shift to about 570 nm at 673 K. The appearance of the new Vis band can be correlate with TG/DSC data. At 553 K ammonia as counter ion de- composes to NOx and reduces the Mo matrix; ammonia is completely removed from the sample at around 693 K