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61.
A variety of rings including those that are Morita equivalent to local perfect rings, two by two upper triangular matrix rings over a division ring or certain rings arising in the framework of rings described by various test modules for injectivity satisfy a common property: there is a nonzero homomorphism between any two non-injective modules. In this paper, after settling a special case inspired by a concept due to Enochs as the first step, we provide a complete characterization of the rings of the title. 相似文献
62.
Probabilistically constrained problems, in which the random variables are finitely distributed, are non-convex in general and hard to solve. The p-efficiency concept has been widely used to develop efficient methods to solve such problems. Those methods require the generation of p-efficient points (pLEPs) and use an enumeration scheme to identify pLEPs. In this paper, we consider a random vector characterized by a finite set of scenarios and generate pLEPs by solving a mixed-integer programming (MIP) problem. We solve this computationally challenging MIP problem with a new mathematical programming framework. It involves solving a series of increasingly tighter outer approximations and employs, as algorithmic techniques, a bundle preprocessing method, strengthening valid inequalities, and a fixing strategy. The method is exact (resp., heuristic) and ensures the generation of pLEPs (resp., quasi pLEPs) if the fixing strategy is not (resp., is) employed, and it can be used to generate multiple pLEPs. To the best of our knowledge, generating a set of pLEPs using an optimization-based approach and developing effective methods for the application of the p-efficiency concept to the random variables described by a finite set of scenarios are novel. We present extensive numerical results that highlight the computational efficiency and effectiveness of the overall framework and of each of the specific algorithmic techniques. 相似文献
63.
High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders.
In this work, NdCo5 nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to
prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo5 flakes have a thickness below 150 nm and an aspect ratio as high as 102–103; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low
temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large
surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy
of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin
reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures,
T
SR1 = 276 and T
SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk. 相似文献
64.
Nilay Noyan 《Annals of Operations Research》2010,181(1):559-589
The stochastic nature of emergency service requests and the unavailability of emergency vehicles when requested to serve demands
are critical issues in constructing valid models representing real life emergency medical service (EMS) systems. We consider
an EMS system design problem with stochastic demand and locate the emergency response facilities and vehicles in order to
ensure target levels of coverage, which are quantified using risk measures on random unmet demand. The target service levels
for each demand site and also for the entire service area are specified. In order to increase the possibility of representing
a wider range of risk preferences we develop two types of stochastic optimization models involving alternate risk measures.
The first type of the model includes integrated chance constraints (ICCs ), whereas the second type incorporates ICCs and
a stochastic dominance constraint. We develop solution methods for the proposed single-stage stochastic optimization problems
and present extensive numerical results demonstrating their computational effectiveness. 相似文献
65.
Shuman NS Miller TM Hazari N Luzik ED Viggiano AA 《The Journal of chemical physics》2010,133(23):234304
Rate constants for several processes including electron attachment to SF(2), SF(3), and SF(5) and individual product channels of ion-ion mutual neutralization between SF(6)(-), SF(5)(-), and SF(4)(-) with Ar(+) were determined by variable electron and neutral density attachment mass spectrometry. The experiments were conducted with a series of related neutral precursors (SF(6), SF(4), SF(5)Cl, SF(5)C(6)H(5), and SF(3)C(6)F(5)) over a temperature range of 300-500 K. Mutual neutralization rate constants for SF(6)(-), SF(5)(-), and SF(4)(-) with Ar(+) are reported with uncertainties of 10-25% and show temperature dependencies in agreement with the theoretical value of T(-0.5). Product branching in the mutual neutralizations is temperature independent and dependent on the electron binding energy of the anion. A larger fraction of product neutrals from the SF(6)(-) mutual neutralization (0.9 ± 0.1) are dissociated than in the SF(5)(-) mutual neutralization (0.65 ± 0.2), with the SF(4)(-) (0.7 ± 0.3) likely lying in between. Electron attachment to SF(5) (k = 2.0 × 10(-8) ±(1)(2) cm(3) s(-1) at 300 K) and SF(3) (4 ± 3 × 10(-9) cm(3) s(-1) at 300 K) show little temperature dependence. Rate constants of electron attachment to closed-shell SF(n) species decrease as the complexity of the neutral decreases. 相似文献
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69.
Microwave irradiation of ketosemicarbazones with wet antimony trichloride under solvent-free condition provides a fast, efficient and simple method for the regeneration of ketones in good yields. 相似文献
70.
İsmet Kaya Ali Bilici Ruhiye Nilay Tezel Kevser Temizkan Fatih Doğan 《高分子科学杂志,A辑:纯化学与应用化学》2017,54(4):243-248
A new florescent oligo(aminopyrene) (OAP) was successfully synthesized by enzymatic approach. For this, H2O2 and Horse Radish peroxidase (HRP) were used as catalyst and oxidant, respectively. The structures of monomer and oxidation product were confirmed by NMR, FT-IR and UV-Vis measurements. The oxidation product was characterized by gel permeation chromatography (GPC), thermogravimetry (TG), differential scanning calorimetry (DSC), cyclic voltammetry (CV), photoluminescence (PL) and scanning electron microscopy (SEM) analyses. OAP was soluble in a wide range of organic solvents. UV-Vis spectrum of the OAP showed a dramatic red shift compared to that of the monomer. The optical and electrochemical band gaps of OAP were found to be 1.65 and 1.56 eV, respectively. OAP emitted turquoise color in THF and green color in toluene. SEM observations indicated the presence of a heterogeneous cauliflower like morphology. 相似文献