Newsvendor problem with multiple unreliable suppliers

This paper focuses on supplier-related decisions in a newsvendor setting. We build upon the current literature by analysing the newsvendor problem with multiple unreliable and non-identical suppliers. We also incorporate both fixed ordering costs and capacity limits for supplier selection. We develop an exact algorithm to solve the problem optimally and a heuristic algorithm to solve the problem efficiently. Through structural properties of the optimal solution and a numerical study, we provide useful managerial implications regarding optimal sourcing strategies in complex supply chains. Previous literature concludes that with multiple unreliable (independent) suppliers, cost is the order qualifier and reliability is the order winner. We found that when fixed ordering costs and supply capacities exist, this insight no longer holds. We also examine the sensitivity of the sourcing decisions to supplier capacity levels, demand uncertainty, salvage value and shortage cost. Our results show that high levels of demand uncertainty lead firms to turn to a single-sourcing strategy whereas high salvage values and high shortage cost suggest multi-sourcing strategy.     

Evaluation of membrane fouling and flux decline related with mass transport in nanofiltration of tartrazine solution

BACKGROUND: This work was carried out to investigate and analyze the interrelated dynamics of mass transport, membrane fouling and flux decline during nanofiltration of tartrazine. A combined application including pore diffusion transport model and a material balance approach was used to model an experimental flux data obtained from different values of pH (3, 5, 7 and 10), feed‐dye concentration (25, 100 and 400 mg L^?1), and transmembrane pressure (1200, 1800 and 2400 kPa). RESULTS: Almost 100% dye solution removal and a permeate flux of 135 L m^?2 h^?1 were obtained for 25 mg L^?1 and 1200 kPa at pH 10. At pH 10, lower membrane fouling was obtained due to the increase of electrostatic repulsion between anionic dye molecules and the more negatively charged membrane surface. Flux decline and membrane fouling increased together with transmembrane pressure and dye concentration. Fouling was found to be directly related to proportional‐permeation coefficient (k_O′) of dye which was identified as the solute passing into the permeate with respect to the amount transported into the membrane from the feed. CONCLUSIONS: For a decrease of pH (10 to 3) and transmembrane pressure (2400 to 1200 kPa) or an increase of feed‐dye concentration (25 to 400 mg L^?1), fewer dye molecules passed into the permeate with respect to the amount transported into the membrane from the feed. This situation depended mainly on the combined influences of the gel layer and fouling in the membrane. Copyright © 2010 Society of Chemical Industry     

Texture development in Fe-doped alumina ceramics via templated grain growth and their application to carbon nanotube growth

Fe-doped alumina (Fe-Al₂O₃) materials with a controlled microstructure could be designed for some special uses such as a substrate for carbon nanotube growth. In this study, Fe-doped Al₂O₃ ceramics with varying degrees of texture were prepared via Templated Grain Growth method and utilized for carbon nanotube synthesis by Catalytic Chemical Vapor Deposition in order to investigate how α-Al₂O₃ crystal orientation affects carbon nanotube growth in polycrystalline ceramics. The degree of texture increased with the Fe content in the presence of liquid phase. Three kinds of carbon filaments (few-wall carbon nanotubes bundles, individual multi-wall nanotubes and carbon nanofibres) were observed over Fe-doped Al₂O₃ ceramics with varying degrees of texture depending on the surface roughness, crystallographic orientation and the size of the catalyst nanoparticles. While well-textured substrates with a rough surface led to a small amount of randomly oriented carbon nanotube bundles, perpendicularly oriented individual multi-wall nanotubes were obtained over relatively smooth single crystal α-Al₂O₃ platelet surfaces (basal planes) which remained in the matrix without growing.     

Comparison of restorative materials and surface alterations after prebiotic and probiotic beverages: A nanoindentation and SEM study

The purpose was to investigate the surface characteristics of various resin-based materials by immersing in probiotic beverages. A total of 420 disc-shaped samples (5 mm × 2 mm) were prepared from resin-based composites. Samples were divided into four groups and immersed for 10 min/day for 1 month in either a probiotic sachet, kefir, kombucha, or artificial saliva (control). Surface roughness was measured at baseline and 1 month. One sample of each of the tested materials was examined under nanoindentation to evaluate the reduced elasticity modulus and nanohardness scores. Scanning electron microscopy (SEM) was used to compare surface differences. Data were analyzed statistically using one-way ANOVA test and the significance was set at p < .05. The lowest roughness scores were observed in Z250, Estelite Bulk Fill, and HRi ENA in most of the test groups. Among conventional composites, Z250 group had the highest nanohardness and elasticity modulus scores. Among bulk-fill composites, Estelite Bulk Fill Flow had the lowest surface roughness after immersion in probiotic beverages and the highest nanohardness values. Reveal HD, as a bulk-fill group showed higher surface roughness and considerably lower nanohardness and elasticity modulus scores. Maximum height levels of samples were recorded. SEM images revealed voids and microcracks on the surfaces of test materials. Dentists may prefer Z250 as microhybrid and Estelite Bulk Fill Flow as bulk-fill composites for the restorations of patients who consume gut-friendly drinks regularly. When there are various types of materials, nanoindentation is a useful method for evaluating surface alterations and sensible comparisons.     

Improved mobility of the copper phthalocyanine thin-film transistor

Copper phthalocyanine (CuPc) organic thin-film transistor (OTFT) was fabricated by thermal evaporation deposition on p-SiO₂ dielectric layer. Organic thin-film transistors used in large display areas need the enhancement of transistor performances by increasing the I_on/I_off ratio and the mobility. The output and transfer characteristics of CuPc-OTFT having source/drain interdigitated-finger geometry were investigated. The mobility, I_on/I_off ratio and inverse sub-threshold slope for the CuPc-OTFT were found to be 5.32 × 10^?3 cm² V^?1 s^?1, 1.94 × 10⁴ and 2.5 V/decade, respectively. The interface state density of the transistor was found to be 3.73 × 10¹¹ eV^?1 cm^?2 using the conductance-frequency method. The CuPc film indicated a homogeneous surface having 3.878 nm small roughness values as observed by atomic force microscope (AFM) measurements. The obtained results indicate that we have improved a CuPc-OTFT transistor with high mobility without being of any substrate treatment.     

Estimation with the nested logit model: specifications and software particularities

The paper discusses the nested logit model for choices between a set of mutually exclusive alternatives (e.g. brand choice, strategy decisions, modes of transportation, etc.). Due to the ability of the nested logit model to allow and account for similarities between pairs of alternatives, the model has become very popular for the empirical analysis of choice decisions. However the fact that there are two different specifications of the nested logit model (with different outcomes) has not received adequate attention. The utility maximization nested logit (UMNL) model and the non-normalized nested logit (NNNL) model have different properties, influencing the estimation results in a different manner. This paper introduces distinct specifications of the nested logit model and indicates particularities arising from model estimation. The effects of using various software packages on the estimation results of a nested logit model are shown using simulated data sets for an artificial decision situation. Financial support by the German Research Foundation (DFG) through the research project #BO1952/1 and the SFB 649 “Economic Risk” is gratefully acknowledged. The authors would like to thank two anonymous reviewers for their helpful and constructive comments.     

Multi‐responsive microgel of a water‐soluble monomer via emulsion polymerization

Microgel of a water‐soluble monomer [2‐(N‐morpholino)ethyl methacrylate (MEMA)] was successfully prepared in aqueous media via emulsion polymerization by using a novel water‐soluble block copolymer as stabilizer. Characterization studies confirmed monodisperse spherical morphologies of microgels with a diameter of 280 nm at neutral pH. These microgels exhibited multi‐responsive behavior by responding solution pH, temperature, ionic strength, type of dispersing media, and magnetic particles. It swells well at low pH (<6.0) and at low temperature, but shrinks above pH 6.0, or even more shrinks with salt addition at neutral and basic conditions. In addition, the hydrodynamic diameter of PMEMA microgel was decreased gradually at basic and neutral pH when solution temperature was increased up to the lower critical solution temperature of PMEMA (LCST, 35°C), but microgel diameter did not change much above LCST. Multi‐responsive behavior of PMEMA microgel was investigated by using dynamic light scattering, UV‐Vis spectrophotometer and zeta potentiometer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42072.     

Hilbert–Huang Transform Based Approach for Measurement of Voltage Flicker Magnitude and Frequency

Voltage flicker is a non-stationary waveform for which direct spectral analysis is not appropriate. To overcome this difficulty, a Hilbert–Huang transform based technique is proposed here. Hilbert–Huang transform is a new signal processing method that can be used in the analysis of non-linear and non-stationary signals. In the suggested method, the recorded voltage signal is decomposed into Hilbert–Huang transform components, namely the empirical mode decomposition and intrinsic mode function components. These components are used in the calculation of the frequency and amplitude of voltage flicker. The clear success of empirical mode decomposition in depicting envelope variations of a sinusoidal waveform has been the main motivation for the adoption of Hilbert–Huang transform in flicker analysis. Simulations are performed over waveforms, including single- and multiple-flicker frequencies and flicker with harmonic, voltage sag, and voltage swell. The waveforms are selected as pure sinusoids, as well as harmonically rich voltage waveforms. Simulation results show that the proposed methodology constitutes a plausible way to analyze voltage flickers, making it an alternative to the available flicker analysis tools.     

Fidelity of soft nano-imprint lithographic replication of polymer masters fabricated by two-photon polymerization

Using modern laser fabrication techniques such as two-photon polymerisation (2PP), complex 3D and planar structures with the resolutions down to 100?nm can be achieved. Advantages of 2PP can be exploited by combining it with the nano-imprint lithography (NIL). We report on the fabrication of masters by 2PP and its replicas by the soft NIL technique using poly(dimethylsiloxane) (PDMS). With PDMS stamps, very reproducible replicas of the master can be created. The stamp surface quality can be better than that of the master due to hydrostatic pressure during the stamp fabrication. Putting the stamp under stress allows the fabrication of structures with controllable reduction of the structural dimensions in one direction compared to the original master. Experimental investigations of the shape transfer fidelity and surface roughness of the replicas are presented.