Evaluation of Lead Time in Production/Inventory Systems with Non-stationary Stochastic Demand

For the past decade, new techniques for production management–such as kanban (pull-through) systems, internal set-ups, zero inventory, etc–have gained tremendous interest. However, research indicates that the production environment is more important than specific techniques. One aspect of this environment is the production lead time. This paper examines the impact of lead time, in conjunction with the characteristics of the demand process, on costs through the use of a periodic-review production/inventory model with a non-stationary stochastic demand process. Our results indicate that costs are affected by a combination of production lead time and demand variances. While the demand means have no effect on costs, both the shapes of the demand distributions and the relative magnitude of the penalty costs do have an effect.     

First results of a quantitative study of DNA adducts of melphalan in the rat by isotope dilution mass spectrometry using capillary liquid chromatography coupled to electrospray tandem mass spectrometry

Rats were intravenously injected with a single high dose (10 mg/kg) of the alkylating agent melphalan in order to study DNA-adduct formation. Quantitation of a dGuo-melphalan adduct was done by isotope dilution mass spectrometry using capillary liquid chromatography/mass spectrometry (LC/MS) and [15N5]-labeled dGuo-melphalan as internal standard. DNA-adduct levels were studied in bone marrow, liver and kidney. The instrumental detection limit of the method was determined to be 900 fg (S/N 3, pure standard). These first results clearly show a 10 times higher adduct level in bone marrow compared to kidney and a 6 times higher level compared to liver. More experiments will be necessary to gather more information on the pharmacokinetics of melphalan-DNA adducts under in vivo conditions.     

Intriguing Mass Spectrometric Behavior of Guanosine Under Low Energy Collision-Induced Dissociation: H<Subscript>2</Subscript>O Adduct Formation and Gas-Phase Reactions in the Collision Cell

An in-depth study of the fragmentation pathway of guanosine was conducted by using an in-source collision-induced dissociation high-mass accuracy tandem mass spectrometry experiment. The equivalent of MS4 data, a level of information normally achieved on ion trap instruments, was obtained on a Q-TOF mass spectrometer. The combination of the features of high-resolution, accuracy, and in-source CID permitted the unambiguous elucidation of the different fragmentation pathways. Furthermore the elemental compositions of the product ions generated were assigned and their mutual genealogical relationships established. Formerly proposed dissociation pathways of guanosine were revisited and elaborated on more deeply. Furthermore, the presence of H2O in the collision cell of several tandem MS instruments was demonstrated and its effect on the product ion spectra investigated. The neutral gain of H2O by particular fragments of guanosine was experimentally proven by using argon, saturated with H2(18)O, as the collision gas. Data indicating the occurrence of more complex reactions in the collision cell as a result of the presence of H2O were produced, specifically relating to neutral gain/neutral loss sequences. In silico calculations supported the experimental observation of neutral gain by guanosine fragments and predicted a similar behavior for adenosine. The latter was subsequently experimentally confirmed.     

A Thermodynamic Analysis of Nonequilibrium Argon Plasma Torches

The nonequilibrium process of argon plasma torches is analyzed theoretically. Thermodynamic diagrams of different degrees of ionization are developed to aid in understanding and analyzing the transition from chemical equilibrium to frozen flow in dc plasma torch operations. A thermodynamic model is developed to describe the nonequilibrium processes in a dc argon plasma torch. In the model the ionization process is approximated as a constant-pressure heating process, with little deviation from the equilibrium state upon completion of heating. If the plasma flow is frozen shortly after heating, the entropy increase is small during the transition from equilibrium to frozen flow. In this case the frozen flow will have nearly the same composition and entropy as the flow at the heating section exit. For singly ionized argon plasmas in the entropy range relevant to dc torch operation, the frozen flow solutions on the affinity–pressure diagram are found to be insensitive to entropy change. Therefore the present model predicts that argon plasmas generated at different power levels will have almost identical affinity at the torch exit for the same operating pressure. This prediction agrees with experimental observations except for very low torch power levels.     

Synthesis of 1-substituted-6-methyluracils

A series of 6-methyl-1H-pyrimidin-2,4-diones bearing different substituents in the 1-position of the uracil ring were prepared starting from substituted ureas and diketene.     

Pore morphology of porous polymer particles probed by NMR relaxometry and NMR cryoporometry

The pore size distribution (PSD) and pore connectivity (PC) within porous polymer particles are probed by combining NMR cryoporometry and NMR relaxometry (spin-spin relaxation). With water as a probe molecule, the constant K in the so-called Gibbs-Thompson equation and the surface relaxivity (rho2) were determined to be K = (420 +/- 50) KA and rho2 = (0.44 +/- 0.01) x 10(-6) ms(-1), respectively. Also, the thickness of the interface layer was estimated to be of the order of one monolayer of water molecules. A detailed analysis of the complete set of NMR data enabled the morphology or pore structure to be probed, and is thoroughly discussed in the text.     

1,5-dimethyl-6H-pyridazino[4,5-b]carbazole,a 3-aza bioisoster of the antitumor alkaloid olivacine

A series of b-fused carbazoles structurally related to pyrido[4,3-b]carbazole-type alkaloids was prepared, utilizing the Diels-Alder reaction of 1-methylpyrano[3,4-b]indol-3(9H)-one with electron-deficient acetylenic dienophiles as the key step. The title compound (14) thus obtained in only four steps represents a new 3-aza analog of the antitumor natural product, olivacine.     

Separation of living and dead polymers in synthetic polypeptide mixtures by nonaqueous capillary electrophoresis using differences in ionization states

The complexity in the mechanisms of polymerization of N-carboxyanhydrides requires the development of new analytical techniques able to separate mixtures of synthetic polypeptides. This work focuses on the separation of poly(N(epsilon)-trifluoroacetyl-L-lysine) (PTLL) mixtures by nonaqueous capillary electrophoresis (CE). The main goal of this work was to find electrophoretic conditions that permit the separation and the quantification of the dead polymer families that were previously identified in the samples. The influence of the pH of the electrolyte on the selectivity of the separation was carefully investigated. The mechanisms of separation of the PTTLs are discussed as a function of their ionization state. The separations obtained on a noncovalently coated capillary were compared with those obtained on a fused-silica capillary. Finally, using two different electrolytes, it is possible to quantify the three families of PTLLs, namely, the living PTLLs, the dead PTLLs with N-formyl end group and the dead PTLLs with a carboxylic end group. These results confirm the importance of CE for the separation of synthetic organic polymers in nonaqueous electrolytes.