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71.
We focus on tandem queues with subexponential service time distributions. We assume that number of customers in front of the
first station is infinite and there is infinite room for finished customers after the last station but the size of the buffer
between two consecutive stations is finite. Using (max, +) linear recursions, we investigate the tail asymptotics of transient
response times and waiting times under both communication blocking and manufacturing blocking schemes. We also discuss under
which conditions these results can be generalized to the tail asymptotics of stationary response times and waiting times. 相似文献
72.
Gülgün Ayhan Kilcigil Rahmiye Ertan Süheyla
zbey Engin Kendi 《Journal of heterocyclic chemistry》1998,35(6):1485-1492
In this study, it is aimed to investigate the synthesis and the calcium antagonistic activity of some flavone derivatives which contain the 1,4-dihydropyridine ring system at the A ring of the flavone nucleus. For this purpose we first synthesized 6-formylflavone and then twelve 1,4-dihydropyridine derivatives were synthesized by the reaction of 6-formylflavone with alkylacetoacetates, acetoacetanilide and methyl or ethyl aminocrotonate. Conformational analysis was performed for compound 3a . The calcium antagonistic activity of compound 2a was examined using nifedipine as the reference compound. 相似文献
73.
Salvia ceratophylla L. has yielded four known and two new diterpenoids together with two triterpenic acids, a steroid and a flavone. The structures of the compounds were established by spectroscopic analyses. One of the known compounds candidissiol exhibited a high antibacterial activity against Staphylococcus epidermidis and Proteus mirabilis. 相似文献
74.
We study the optimal dynamic scheduling of different requests of service in a multiclass stochastic fluid model that is motivated by recent and emerging computing paradigms for Internet services and applications. In particular, our focus is on environments with specific performance guarantees for each class under a profit model in which revenues are gained when performance guarantees are satisfied and penalties are incurred otherwise. Within the context of the corresponding fluid model, we investigate the dynamic scheduling of different classes of service under conditions where the workload of certain classes may be overloaded for a transient period of time. Specifically, we consider the case with two fluid classes and a single server whose capacity can be shared arbitrarily among the two classes. We assume that the class 1 arrival rate varies with time and the class 1 fluid can more efficiently reduce the holding cost. Under these assumptions, we characterize the optimal server allocation policy that minimizes the holding cost in the fluid model when the arrival rate function for class 1 is known. Using the insights gained from this deterministic case, we study the stochastic fluid system when the arrival rate function for class 1 is random and develop various policies that are optimal or near optimal under various conditions. In particular, we consider two different types of heavy traffic regimes and prove that our proposed policies are strongly asymptotically optimal. Numerical examples are also provided to demonstrate further that these policies yield good results in terms of minimizing the expected holding cost. 相似文献
75.
在Minkowski空间中,定义了定向曲面上的第二类松弛弹性线,推导了在定向曲面上的第二类松弛弹性线的Euler-Lagrange方程.进一步阐明了,这些曲线是否落在曲率线上,最后给出相关的实例. 相似文献
76.
Emrah Özcan Dr. Burcu Dedeoglu Prof. Dr. Yuri Chumakov Prof. Dr. Ayşe Gül Gürek Prof. Dr. Yunus Zorlu Prof. Dr. Bünyemin Çoşut Dr. Mehmet Menaf Ayhan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(5):1603-1608
The ability to tune the optical features of BODIPY materials in the solid state is essential for their photorelated application and requires efficient control of the crystal packing. In this study, such control of BODIPY supramolecular assemblies was achieved by deliberate design and synthesis of a BODIPY containing a strong halogen-bond (XB) acceptor (−NO2) and donor (I, Br) to mediate XB interactions. The di-halogenated structures formed isostructural mono-coordinate motif B3 , B4 (1D tubular structure) and symmetric bifurcated motif B4-II (1D zigzag chains structure) through N−O⋅⋅⋅I, Br XB interactions. These XB interactions promote singlet-to-triplet intersystem crossing and triplet-to-singlet reverse intersystem crossing due to partial delocalization of oxygen electrons onto Br and I, which leads to unexpected fluorescence enhancement of B4-II . Finally, the indirect optical band gaps of B3 , B4 and B4-II were amenable to tuning in the range of 1.85–2.50 eV by XB-driven crystal packings. 相似文献
77.
78.
Carboxymethyl cellulose (CMC) has been used widely to enhance dry strength of paper and uniformity of sheet in the papermaking
industry. Besides these positive effects, it may affect the fines retention and dewatering processes negatively. These negative
effects are mainly seen when fiber modifications with high CMC dosages are studied in laboratory scale. In this paper, the
effect of fiber modification with CMC on the deposition of precipitated calcium carbonate (PCC) and on the dewatering process
in the presence of cationic polyacrylamide (CPAM)/bentonite microparticle flocculation system is examined. It was determined
that fiber modification with 10 mg g−1 of CMC decreased PCC deposition at the initial addition of CPAM and gave better PCC deposition at 2 mg g−1 of CPAM. It was also observed that PCC deposition on unmodified fibers is higher at lower CPAM concentration. PCC deposition
was found as almost stable after a maximum value obtained at 0.5 mg g−1 of bentonite concentration for fiber modified with 40 mg g−1 of CMC. This indicates that interaction between CPAM and bentonite particles changed due to higher surface charge and CMC
conformation on fibers. Results of the dewatering experiments showed that CMC modification increased the drainage time due
to a denser and more plugged sheet. This negative effect was compensated with higher concentrations of CPAM and bentonite.
On the other hand, dewatering is also affected by the mass ratio of CMC and CPAM, which was not the optimum one in this study
at lower of CPAM. Thus, the increase in the drainage time in the presence of CMC on the fiber surface could be also caused
by incorrect ratios of chemicals because the effect of CMC on the drainage time was not observed at higher concentrations
of CPAM. 相似文献
79.
Ozlem SevenSidika Polat-Cakir Md. Shakhawoat HossainMustafa Emrullahoglu Ayhan S. Demir 《Tetrahedron》2011,67(19):3464-3469
The reactions of organoaluminum reagents (trimethylaluminum, triethylaluminum, etc.) with aryl and alkyl acyl phosphonates, which lead to the formation of α-hydroxy phosphonates in moderate to good yields, are reported. This method provides easy access to secondary and tertiary α-hydroxy phosphonates depending on the reaction conditions. The reactions of triethylaluminum with a series of acyl phosphonates at 0 °C gave the secondary α-hydroxy phosphonates, while at −100 °C they afford the tertiary α-hydroxy phosphonates. 相似文献
80.