Scheduling policies for a repair shop problem

In this paper, we analyze a repair shop serving several fleets of machines that fail from time to time. To reduce downtime costs, a continuous-review spare machine inventory is kept for each fleet. A spare machine, if available on stock, is installed instantaneously in place of a broken machine. When a repaired machine is returned from the repair shop, it is placed in inventory for future use if the fleet has the required number of machines operating. Since the repair shop is shared by different fleets, choosing which type of broken machine to repair is crucial to minimize downtime and holding costs. The optimal policy of this problem is difficult to characterize, and, therefore, is only formulated as a Markov Decision Process to numerically compute the optimal cost and base-stock level for each spare machine inventory. As an alternative, we propose the dynamic Myopic(R) policy, which is easy to implement, yielding costs very close to the optimal. Most of the time it outperforms the static first-come-first-served, and preemptive-resume priority policies. Additionally, via our numerical study, we demonstrate that repair shop pooling is better than reserving a repair shop for each fleet.     

A Simple Product Formula for Certain Kazhdan-Lusztig R-Polynomials

We give a new characterization of the analytic spread of ideals in local rings with infinite residue fields. This new characterization answers a question of Huneke and can simplify Huneke's constructions in [1]     

Investigation of free and conjugated seleno‐amino acids in wheat bran by hydrophilic interaction liquid chromatography with tandem mass spectrometry

An analytical method for determining seleno‐methionine, methyl‐seleno‐cysteine, and seleno‐cystine in wheat bran was developed and validated. Four different extraction procedures were evaluated to simultaneously extract endogenous free and conjugated seleno‐amino acids in wheat bran in order to select the best extraction protocol in terms of seleno amino acid quantitation. The extracted samples were subjected to a clean‐up by a reversed phase/strong cation exchange solid‐phase extraction and analyzed by chiral hydrophilic interaction liquid chromatography‐tandem mass spectrometry. The optimized extraction protocol was employed to validate the methodology. Process efficiency ranged from 58 to 112% and trueness from 73 to 98%. Limit of detection and limit of quantification were lower than 1 ng/g. Four wheat bran samples were analyzed for both total Se and single seleno‐amino acids determination. The results showed that Se‐ seleno‐methyl‐l selenocysteine was the major seleno‐amino acid in wheat bran while seleno‐methionine and seleno‐cysteine were both minor species.     

Chemically and Biologically Harmless versus Harmful Ferritin/Copper–Metallothionein Couples

The simultaneous measurement of the decrease of available Fe^II ions and the increase of available Fe^III ions allowed the analysis of the ferroxidase activity of two distinct apoferritins. Although recombinant human apoferritin (HuFtH) rapidly oxidizes Fe^II to Fe^III, this iron is not properly stored in the ferritin cavity, as otherwise occurs in horse‐spleen H/L‐apoferritin (HsFt; H=heavy subunit, L=light subunit). Iron storage in these apoferritins was also studied in the presence of two copper‐loaded mammalian metallothioneins (MT2 and MT3), a scenario that occurs in different brain‐cell types. For HuFtH, unstored Fe^III ions trigger the oxidation of Cu–MT2 with concomitant Cu^I release. In contrast, there is no reaction with Cu–MT2 in the case of HsFt. Similarly, Cu–MT3 does not react during either HuFtH or HsFt iron reconstitution. Significantly, the combination of ferritin and metallothionein isoforms reported in glia and neuronal cells are precisely those combinations that avoid a harmful release of Fe^II and Cu^I ions.     

Regularity results for a class of obstacle problems under nonstandard growth conditions

We prove regularity results for minimizers of functionals in the class , where is a fixed function and f is quasiconvex and fulfills a growth condition of the type

L⁻¹|z|^p(x)?f(x,ξ,z)?L(1+|z|^p(x)),     

(−)-Quinic acid: a versatile precursor for the synthesis of analogues of 2-crotonyloxymethyl-(4R,5R,6R)-4,5,6-trihydroxycyclohex-2-enone (COTC) which possess anti-tumour properties

Syntheses of three novel analogues of the Streptomyces metabolite COTC are described, using the versatile chiral pool starting material, (−)-quinic acid. The results of bioassays of the target compounds against two lung cancer cell lines, A549 and H460, are presented.     

Evidence for Multiple Binding Modes in the Initial Contact Between SARS-CoV-2 Spike S1 Protein and Cell Surface Glycans**

Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required.     

Hydrolytic and photoinduced degradation of tribenuron methyl studied by HPLC-DAD-MS/MS

The paper studies, with the help of HPLC-DAD-MS/MS technique, the hydrolytic and photoinduced degradation processes that take place in aqueous solutions of tribenuron methyl, both when preserved in the dark and when undergoing solar box irradiation under conditions that simulate sun light. The results indicate that the degradation products formed by hydrolysis alone and by photoirradiation are the same, but kinetics of the hydrolysis reaction is much slower. The degradation products are identified as 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (P1), methyl 2-aminosulfonylbenzoate (P2), and saccharin (P3) and quantified. Ecotoxicological biotests performed on 0.1 microg L(-1) photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization.