Separation,optimization, and quantification of cytokinins by a recently developed amide-embedded stationary phase

In this study, some plant growth regulators known as cytokinins [kinetin (K), zeatin (Z), thidiazuron (TDZ), benzylaminopurine (BAP), and dimethylallylaminopurine (AAP)] were separated by HPLC using an amide-embedded mixed-mode stationary phase which was synthesized by Aral et al. in recent years. The effect of mobile phase content, mobile phase pH, buffer concentration, and temperature on separation process was studied. In addition, a quantitative determination of cytokinins from Salvia limbata extract was studied, and some validation parameters such as limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation (RSD) were calculated as a range of 0.03–0.1, 0.1–0.26?mg/L, and 0.03–0.08, respectively.     

Dynamic Scheduling of a Multiclass Fluid Model with Transient Overload

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.     

Novel and highly efficient bifunctional calixarene thiourea derivatives as organocatalysts for enantioselective Michael reaction of nitroolefins with diketones

New bifunctional calixarene thiourea organocatalysts were synthesized and applied in catalytic asymmetric Michael addition of acetylacetone to various nitroolefins at room temperature. The corresponding adducts were obtained in good to excellent yields with excellent enantioselectivities (up to 92% ee). The present research demonstrates the advantages of incorporating two stereocontrolling structures into a single catalyst. Notably, it offers a simple and convenient doubly stereocontrolled approach for the catalytic asymmetric synthesis of a chiral organic molecule.     

Expansions for Joint Laplace Transform of Stationary Waiting Times in (max,+)-linear Systems with Poisson Input

We give a Taylor series expansion for the joint Laplace transform of stationary waiting times in open (max,+)-linear stochastic systems with Poisson input. Probabilistic expressions are derived for coefficients of all orders. Even though the computation of these coefficients can be hard for certain systems, it is sufficient to compute only a few coefficients to obtain good approximations (especially under the assumption of light traffic). Combining this new result with the earlier expansion formula for the mean stationary waiting times, we also provide a Taylor series expansion for the covariance of stationary waiting times in such systems.It is well known that (max,+)-linear systems can be used to represent stochastic Petri nets belonging to the class of event graphs. This class contains various instances of queueing networks like acyclic or cyclic fork-and-join queueing networks, finite or infinite capacity tandem queueing networks with various types of blocking, synchronized queueing networks and so on. It also contains some basic manufacturing models such as kanban networks, assembly systems and so forth. The applicability of this expansion technique is discussed for several systems of this type.     

HPLC Separation of Different Groups of Small Polar Compounds on a Novel Amide-Embedded Stationary Phase

Retention behaviors of an amide-embedded silica base stationary phase, which was recently developed by our group, were studied by using six different groups of small polar compounds including phenolic compounds, substituted anilines, chlorinated herbicides, Sudan dyes and some nucleotides and nucleosides in HPLC. The chromatographic behaviors of the prepared stationary phase for these analytes were compared with those of a commercially available reversed-phase column ACE C18 under same conditions. Among the six groups of analytes studied, the amide-silica stationary phase showed enhanced selectivity towards phenolic compounds, substituted anilines, Sudan dyes and herbicides under reversed-phase conditions and satisfactory selectivity towards nucleosides and nucleotides which could not be separated with ACE C18 column under HILIC conditions. Experimental data provided some evidence that functional groups on the stationary phases might have certain degrees of influence on selectivity possibly through secondary interactions with the model compounds. The retentions of the moderately polar compounds such as phenolic acids, anilines and herbicides on the stationary phase are higher than highly polar compounds such as nucleotides and nucleosides due to both the hydrophobic and hydrophilic interactions between the stationary phase and analytes. The quantitative determination of Sudan dyes (I, II, III, and IV) in red chilli peppers was performed. Many red chilli peppers were screened and three of them contained Sudans dyes.     

Highly luminescent water-dispersed silicon quantum dots for fluorometric determination of oxytetracycline in milk samples

A fluorescent probe based on silicon quantum dots (SiQDs) was developed for the selective and sensitive detection of oxytetracycline (OTC) via the inner filter effect (IFE). The water-soluble fluorescent SiQD was synthesized based on the reaction of 3-Aminopropyltriethoxysilane (APTES) and sodium citrate as precursors by the one-pot hydrothermal process. The strong fluorescence emission of quantum dots (QDs) was obtained at 440 nm when excited at 350 nm and OTC had a broad absorption band between 200 and 400 nm. The excitation spectrum of SiQDs was completely overlapped with the absorption spectrum of OTC. The light at an excitation wavelength of QDs absorbed by OTC caused a decrease in fluorescence intensity with an increase in the concentration of OTC. Under optimal conditions, the linear concentration range was 0.92–9.2 µg mL1 with a detection limit (LOD; S/N = 3) of 0.19 µg mL ^-1 . The proposed method was applied to the determination of OTC in milk samples and satisfactory recoveries (98.8–100.5%) with low RSD % values (0.93–2.31%) were achieved. This simple, selective, sensitive, rapid, and cheap method can be used as a promising tool for OTC analysis in food safety.     

Efficacy of Low‐Dose Ultraviolet A‐1 Phototherapy for Parapsoriasis/Early‐Stage Mycosis Fungoides

Mycosis fungoides (MF) and parapsoriasis (PP) are major dermatologic conditions for which phototherapy continues to be a successful and valuable treatment option. UVA‐1 phototherapy is effective in the management of cutaneous T‐cell mediated diseases. The aim of the study was to evaluate the efficacy and safety of low‐dose UVA‐1 phototherapy for the management of PP/early‐stage MF. A total of 30 patients, diagnosed with MF (n:19) or PP (n:11) were enrolled to the study. All patients were managed with low‐dose UVA‐1 (20 or 30 J cm^?2). Response was assessed clinically and immunohistochemically. UVA‐1 treatment led to clinical and histological complete remission (CR) in 11 of 19 MF patients (57.9%), partial remission (PR) in three of 19 (15.8%), after a mean cumulative dose of 1665 (range, 860–3120) J cm^?2 and mean number of 73 exposure (range, 43–107) sessions. Five patients with PP (45.5%) showed CR, and PR was observed in six patients with PP (54.5%) after a mean cumulative dose of 1723 (range, 1060–3030) J cm^?2 and mean number of 74 exposure (range, 53–101) sessions. We conclude that low‐dose UVA‐1 therapy seems to be an effective, safe, and well‐tolerated treatment option for patients with PP/early‐stage MF.     

Chiral tetraoxacalix[2]arene[2]triazine-based organocatalysts for Enantioselective Aldol reactions

Novel efficient chiral tetraoxacalix[2]arene[2]triazine-based organocatalysts have been designed and synthesized from the reaction of tetraoxacalix[2]arene[2]triazine with R/S-phenylethylamine or R/S-1-naphthylethylamine for the Aldol reaction of acetone with aromatic aldehydes to furnish the Aldol adducts in 71–92% yields with excellent enantioselectivities (78–99%).     

Sensitivity of optimal prices to system parameters in a steady-state service facility

We consider the problem of maximizing the long-run average reward in a service facility with dynamic pricing. We investigate sensitivity of optimal pricing policies to the parameters of the service facility which is modelled as an M/M/s/K$M/M/s/K$ queueing system. Arrival process to the facility is Poisson with arrival rate a decreasing function of the price currently being charged by the facility. We prove structural results on the optimal pricing policies when the parameters in the facility change. Namely, we show that optimal prices decrease when the capacity of the facility or the number of servers in the facility increase. Under a reasonable assumption, we also show that optimal prices increase as the overall demand for the service provided by the facility increases or when the service rate of the facility decreases. We illustrate how these structural results simplify the required computational effort while finding the optimal policy.     

Profit maximization in flexible serial queueing networks

We analyze the tradeoff between efficiency and service quality in tandem systems with flexible servers and finite buffers. We reward efficiency by assuming that a revenue is earned each time a job is completed, and penalize poor service quality by incorporating positive holding costs. We study the dynamic assignment of servers to tasks with the objective of maximizing the long-run average profit. For systems of arbitrary size, structured service rates, and linear or nonlinear holding costs, we determine the server assignment policy that maximizes the profit. For systems with two stations, two servers with arbitrary service rates, and linear holding costs, we show that the optimal server assignment policy is of threshold type and determine the value of this threshold as a function of the revenue and holding cost. The threshold can be interpreted as the best possible buffer size, and hence our results prove the equivalence of addressing service quality via a holding cost and via limiting the buffer size. Furthermore, we identify the optimal buffer size when each buffer space comes at a cost. We provide numerical results that suggest that the optimal policy also has a threshold structure for nonlinear holding costs. Finally, for larger systems with arbitrary service rates, we propose effective server assignment heuristics.