The (S−1,S) inventory model and its counterparts in queueing theory

We explore the relationship between the ($S?1,S$) inventory model and three well-known queueing models: the Erlang loss system, the machine-repair model and a two-node Jackson network. Exploiting this relationship allows us to obtain key performance measures of the ($S?1,S$) model, like the so-called virtual outdating time, the number of items on the shelf in steady state, the long-run rate of unsatisfied demands and the distribution of the empty shelf period.     

Heavy-Ion Collisions: Experimental Highlights

Lattice QCD predicts a phase transition between hadronic matter and a system of deconfined quarks and gluons (the Quark Gluon Plasma) at high energy densities. Our current understanding of this new state of matter will be discussed with two key results from the Relativistic Heavy Ion Collider (RHIC).     

A conformal mapping approach for investigating the free-boundary seepage from symmetric channels

We present a new method to investigate the two-dimensional free-boundary groundwater seepage from symmetric soil channels into a homogeneous isotropic porous medium. We use Levi–Civitá’s function to construct an integral representation for the conformal mapping of the complex potential domain onto the physical flow domain. A genetic algorithm (GA) is used to calculate the coefficients of the Maclaurin series expansion of Levi–Civitá’s function. The coordinates of the points from the channel contour, calculated by means of the integral representation, must satisfy the analytic equation of the contour. We use this condition to define the objective function of the genetic algorithm. Levi–Civitá’s function is afterwards used to calculate the seepage loss, the free lines, the streamlines, the equipotential lines, the isobars and the velocity field. Some examples illustrate the method.     

Asymmetric formal total synthesis of the stemofoline alkaloids: the evolution,development, and application of a catalytic dipolar cycloaddition cascade

A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-d-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama–Itô cyclization, and a useful modification of the Barton decarboxylation protocol.     

Synthetic studies directed toward the AB decalin common to HMP-Y1 and hibarimicinone

Efforts toward the synthesis of the decalin ring system common to the hibarimicin shunt metabolite HMP-Y1 and parent aglycone hibarimicinone are reported herein. An intramolecular Diels–Alder cyclization rapidly generated the decalin framework. Two approaches toward completion of the AB decalin were vetted. Incorporation of a phenylsulfonyl leaving group β- to both a ketone and a γ-lactone followed by base-induced elimination of sulfinate led to the undesired α,β-unsaturated lactone. Methanolysis of the γ-lactone followed by elimination produced the unexpected bridged cyclic ether by way of an intramolecular oxy-Michael addition of the endo oriented C13 alcohol.     

Total synthesis of lansiumamides A and B and alatamide

The total syntheses of lansiumamide A, lansiumamide B and alatamide have been completed taking advantage of the dihalo-olefination of N-formylimides. The syntheses are convergent, flexible and allow for the generation of analogues not accessible through other routes.     

Miscibility in poly(L-lactide)- b -poly( $ \upvarepsilon$ -caprolactone) double crystalline diblock copolymers

Thermally stimulated depolarization currents, TSDC, wide-angle X-ray scattering, WAXS, differential scanning calorimetry, DSC, and polarized light optical microscopy, PLOM, have been used to examine poly(L-lactide)-b -poly( -caprolactone) diblock copolymers in a wide composition range. Both components are crystallizable and the miscibility in the amorphous phase has been determined from the behavior of the primary relaxations which are the dielectric manifestation of the glass transition, and also from the superstructural morphology revealed by PLOM and the compositional dependence of the melting points as determined by DSC. Distinct segmental mobilities in the amorphous phase which can be well resolved by TSDC are present; the mode of the slower component shifts to lower temperatures as the PCL content increases while the glass transition of neat PCL is present for all compositions. A relaxation times bimodal distribution is apparent for PCL-rich copolymers. The composition dependence of the multiple glass transitions detected in these weakly segregated copolymers are predicted by the self-concentration model for a miscible blend made of components with a large T_g contrast.     

Composition of oxygen precipitates in Czochralski silicon wafers investigated by STEM with EDX/EELS and FTIR spectroscopy

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO₂. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO₂ was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm^–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO₂. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Swift heavy ion induced capacitance and dielectric properties of Ni/n-GaAs Schottky diode

The in-situ capacitance and dielectric properties of 25 MeV C⁴⁺ ion irradiated Ni/n-GaAs Schottky barrier diode (SBD) were studied at 100 kHz in the fluence range 5 × 10¹⁰ – 5 × 10¹³ ions/cm². The investigation shows reduction in capacitance and charge density with increase in ion fluence. Consequent changes were observed in other related parameters like conductance, dielectric constant, dielectric loss, loss tangent and electrical modulus. The results were interpreted in terms of generation of swift heavy ion induced acceptor trap states by electronic energy loss mechanism. Besides, the switch over characteristics of depletion to inversion regions in the CV plot reveals minority carrier recombination centers also. The dispersion and relaxation peaks observed in bias dependent dielectric plots were ascribed to the polarization and relaxation mechanism due to the interfacial trap states. The traps and recombination centers were found to alter the barrier characteristics of the fabricated SBD depending upon the ion fluence.     

医疗保险索赔数据的广义Pareto分布拟合

How to choose an optimal threshold is a key problemin the generalized Pareto distribution (GPD) model.This paper attains the exactthreshold by testing for GPD,and shows that GPD model allows the actuary to easily estimate high quantiles and the probable maximum loss from the medical insurance claims data.