Conventional or additive manufacturing for spare parts management: An extensive comparison for Poisson demand

Due to the main peculiarities of spare parts, i.e. intermittent demands, long procurement lead times and high downtime costs when the parts are not available on time, it is often difficult to find the optimal inventory level. Recently, Additive Manufacturing (AM) has emerged as a promising technique to improve spare parts inventory management thanks to a ‘print on demand’ approach. So far, however, the impact of AM on spare parts inventory management has been little considered, and it is not yet clear when the use of AM for spare parts inventory management would provide benefits over Conventional Manufacturing (CM) techniques. With this paper we thus aim to contribute to the field of AM spare parts inventory management by developing decision trees that can be of support to managers and practitioners. To this aim, we considered a Poisson-based inventory management system and we carried out a parametrical analysis considering different part sizes and complexity, backorder costs and part consumption. Moreover, we evaluated scenarios where the order-up-to level is limited to resemble applications with a limited storage capacity. For the first time, the analysis was not limited to just one AM and one CM technique, but several AM and CM techniques were considered, also combined with different post-process treatments, for a total of nine different sourcing alternatives. In addition, the economic and technical performance of the different sourcing options were obtained thanks to an interdisciplinary approach, where experts from production economics and material science were brought together

Influence of the air inlet configuration on the performances of a paraglider open airfoil

A finite volume flow solver was used to solve the Reynolds averaged Navier-Stokes equations for the 2D flow field on a paraglider open airfoil. The canopy was assumed to be smooth, rigid and impermeable. The parametric study performed concerns the position and the width of the air inlet at the leading edge. The range of values used covers the air inlet geometries from classical ram-air parafoil to sport paraglider airfoil, including transition toward the full closed baseline airfoil. Results are focused both on lift and drag coefficients for performance analysis and on the internal pressure coefficient which can be critical for a real flexible wing regarding the risk of collapse. Depending on the appearance of a separation bubble over the upper edge, two well separated behaviours can be observed. The first behaviour is more typical of ram-air parachutes and the second one corresponds to the design of performance paragliders. For paraglider configurations, it is shown that the aerodynamic coefficients of the open airfoil can be easily deduced from the pressure coefficients of the baseline airfoil without solving the internal flow

Enhancement of the Inelastic Nuclear Interaction Rate in Crystals via Antichanneling

The interaction rate of a charged particle beam with the atomic nuclei of a target varies significantly if the target has a crystalline structure. In particular, under specific orientations of the target with respect to the incident beam, the probability of inelastic interaction with nuclei can be enhanced with respect to the unaligned case. This effect, which can be named antichanneling, can be advantageously used in the cases where the interaction between beam and target has to be maximized. Here we propose to use antichanneling to increase the radioisotope production yield via cyclotron. A dedicated set of experimental measurements was carried out at the INFN Legnaro Laboratories with the AN2000 and CN accelerators to prove the existence of the antichanneling effect. The variation of the interaction yield at hundreds of keV to MeV energies was observed by means of sapphire and indium phosphide crystals, achieving an enhancement of the interaction rate up to 73% and 25%, respectively. Such a result may pave the way to the development of a novel type of nozzle for the existing cyclotrons, which can exploit crystalline materials as targets for radioisotope production, especially to enhance the production rate for expensive prime materials with minor upgrades of the current instrumentation

Synthesis of Large-Area Crystalline MoS2 by Sputter Deposition and Pulsed Laser Annealing

The wafer-scale synthesis of layered transitional metal dichalcogenides presenting good crystal quality and homogeneous coverage is a challenge for the development of next-generation electronic devices. This work explores a fairly unconventional growth method based on a two-step process consisting in sputter deposition of stochiometric MoS2 on Si/SiO2 substrates followed by nanosecond UV (248 nm) pulsed laser annealing. Large-scale 2H-MoS2 multi-layer films were successfully synthetized in a N2-rich atmosphere thanks to a fine-tuning of the laser annealing parameters by varying the number of laser pulses and their energy density. The identification of the optimal process led to the success in achieving a (002)-oriented nanocrystalline MoS2 film without performing post-sulfurization. It is noteworthy that the spatial and temporal confinement of laser annealing keeps the Si/SiO2 substrate temperature well below the back-end-of-line temperature limit of Si CMOS technology (770 K). The synthesis method described here can speed up the integration of large-area 2D materials with Si-based devices, paving the way for many important applications

Dolichol: A Component of the Cellular Antioxidant Machinery

Dolichol, an end product of the mevalonate pathway, has been proposed a biomarker of aging, but its biological role, not to mention its catabolism, has not been fully understood. UV-B radiation was used to induce oxidative stress in isolated rat hepatocytes by the collagenase method. Effects on dolichol, phospholipids-bound polyunsaturated fatty acids (PL PUFA) and known lipid soluble antioxidants [coenzyme Q (CoQ) and α-tocopherol] were studied. The increase in oxidative stress was detected by a probe sensitive to reactive oxygen species (ROS). Peroxidation of lipids was assessed by measuring the release of thiobarbituric acid reactive substances (TBARS). Dolichol, CoQ and α-tocopherol were assessed by high-pressure liquid chromatography (HPLC), PL PUFA by gas-liquid chromatography (GC). UV-B radiation caused an immediate increase in ROS as well as lipid peroxidation and a simultaneous decrease in the levels of dolichol and lipid soluble antioxidants. Decrease in dolichol paralleled changes in CoQ levels and was smaller than that in α-tocopherol. The addition of mevinolin, a competitive inhibitor of the enzyme 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoAR), magnified the loss of dolichol and was associated with an increase in TBARS production. Changes in PL PUFA were minor. These findings highlight that oxidative stress has very early and similar effects on dolichol and lipid soluble antioxidants. Lower levels of dolichol are associated with enhanced peroxidation of lipids, which suggest that dolichol may have a protective role in the antioxidant machinery of cell membranes and perhaps be a key to understanding some adverse effects of statin therapy

Innovative Methods for Germanium Doping

One of the main goals in the semiconductor research is the production of a shallow junctions conformal to the surface of a device. This request emerges from the increasing importance of nanostructured devices made by semiconductor materials like multi-gate transistors. The 3D geometry of these devices implies the capability to dope the semiconductor material in a nanostructured, non-planar geometry, which continues to be a difficult task. One of the most promising techniques for the deposition and diffusion of a well-defined amount of dopant is based on the use of self-limiting chemical deposition on semiconductor surfaces: that is the key points of the monolayer doping technique (MLD). This particular technique consists in adsorbing a monolayer of a molecular precursor by a self-limited surface adsorption interaction, which leads to an adsorbed mono- or multilayers formation. This layer(s) acts as a source of dopant for the substrate in-diffusion. This new technique allows to dope not only 3D nano-structured materials with an intrinsically conformal method, but also flat semiconductor surfaces by avoiding the ion implantation technique and the consequent damage of the crystal lattice. On the other hand, germanium is actually a very interesting semiconductor: small band-gap and high charge carrier mobilities have been recently making it more and more appealing in several application fields, from nano-electronics to photovoltaics, from optics to radiation detectors. This work is focused on the challenging n-type doping of Ge by using new doping methods based on the surface interaction between molecular precursors and germanium (001) surface. A complete study on phosphorus monolayer doping technique on germanium is presented, using surface molecular precursor, and also a new antimony self-limiting deposition via gas phase has been discovered and tested as a new technique to synthesized a surface monolayer that can be used as a source for Ge doping. The P and Sb ML sources are synthesised in a completely different way: the phosphorus precursors depositions is done via wet chemistry, using a reflux method or by using a dry procedure in a dry-box ambient both near 160°C, while the antimony monolayer is deposited via gas phase in a nitrogen flux at high temperature (about 600°C <T< 790°C). In both cases, the germanium oxide plays a crucial role: for P case, the oxide plays a fundamental role in the adsorption mechanism, while in the Sb case it contributes to oxidise the incoming antimony gas, playing a fundamental role in the monolayer formation. In both cases the new chemical bond generates between the precursor and the substrate is a Ge-O- based bond: Ge-O-P or Ge-O-Sb. The presence of the Ge-O- bond seems to be the cause of the high surface stability of monolayers, thus generating a lack in diffusion with standard thermal in-diffusion processes. Indeed, the presence of high stable chemical bonds act as a diffusion barrier, since P or Sb atoms release from the chemisorbed ML is possible only after a thermal bond disruption, as will be further discussed. A completely different scenario is presented with the use of pulsed laser melting technique (PLM): it has been used on monolayer molecular sources on Ge (001) and thanks to this out-of-equilibrium technique, the molecular precursor act as a doping source, being effective also for Ge doping. Phosphorus monolayers act as a source of dopant for PLM technique, releasing P and generating a doped layer. In the antimony oxide ML case, all the surface ML is available for diffusion (with no Sb loss), even if all the surface ML is in an initial oxidised state. The PLM technique promote its reduction and atomic Sb diffuse and doped the surface of Ge substrate. The creation of a fully active Sb layer with a surface concentration over 10^20 cm^-3 is the clearly demonstration of the feasibility of the use of Sb ML as a source of dopant.Uno dei principali obiettivi della ricerca nel campo dei semiconduttori è la produzione di giunzioni sottili conformi alla superficie. Questa richiesta emerge da un crescente uso di strutture di dimensioni nanometriche nei nuovi dispositivi a semiconduttore, le quali necessitano di nuovi metodi di drogaggio compatibili anche con geometrie non planari e adatte alla nano-scala. Una delle più promettenti tecniche che è stata proposta negli ultimi anni è chiamata “Monolayer Doping” (MLD). Proposta per la prima volta su silicio, essa si basa sul deposito di monostrati molecolari sulla superficie dei semiconduttori: la molecola depositata fungerà poi da sorgente di drogante superficiale, il quale diffonderà nel materiale a seguito di processi termici diffusivi. Grazie all’intrinseca natura conforme di questa tecnica, essa è compatibile con strutture tridimensionali anche alla nano-scala e grazie al suo basso costo, è adatta anche per il drogaggio su larga scala. Oggigiorno il germanio è ritornato ad essere un materiale semiconduttore in luce nel campo della ricerca scientifica per le sue ritrovate interessanti proprietà elettriche, come la mobilità dei portatori, la sua piccola band-gap e la scoperta della possibilità di promuovere transizioni dirette tramite l’uso di stress e alti drogaggi: grazie ad esse, nuove sue applicazioni nella nano-elettronica e nel termo-fotovoltaico, ma anche nella plasmonica e nei detector sono sempre più studiate nella letteratura scientifica. Questo lavoro si è focalizzato nello studio del drogaggio di tipo n del germanio, utilizzando la tecnica MLD: in particolare è stato studiato il comportamento e la reattività superficiale di questo semiconduttore con diversi precursori. Sono stati utilizzati tre diversi precursori del fosforo, appartenenti a tre famiglie di composti a base di P, fatti reagire o per via chimica in riflusso o tramite l’uso di una dry-box, mentre un nuovo fenomeno di adsorbimento autolimitante è stato scoperto e testato per il caso dell’antimonio, a partire da una sorgente gassosa. Alla luce di tutti gli studi è emerso che il comportamento dell’ossido di germanio gioca in tutti i casi un ruolo cruciale. Nei casi in studio, la formazione del legame P-O-Ge e Sb-O-Ge è alla base della formazione e della stabilità dei layer, ma determina anche il mancato rilascio della specie drogante. Infatti, le specie atomiche P e Sb debbono essere rilasciati dal layer e debbono diffondere nel semiconduttore sottostante come conseguenza del trattamento termico applicato. Un comportamento completamente diverso è stato rilevato tramite l’uso della tecnica “Pulsed Laser Melting” applicata ai monostrati molecolari sulla superficie di Ge. Tramite l’uso di impulsi laser nell’ultravioletto, tutti i precursori utilizzati hanno agito fungendo da sorgenti di drogante per il substrato. Nel caso dei vari precursori del fosforo, sono stati rilevati diversi comportamenti a seconda della tipologia del precursore, anche se in tutti i casi è sempre stata rilevata una diffusione del P e la formazione di una zona drogata superficialmente. Alla luce dei risultati diffusivi, per i precursori molecolari a base di fosforo trattamenti multi-impulso sono preferibili. Nel caso della sorgente di antimonio, tutto il monolayer è risultato disponibile alla diffusione già a seguito di un trattamento mono-impulso, sebbene la sorgente di partenza fosse un ossido stabile di antimonio. Le evidenze sperimentali suggeriscono che il laser abbia non solo un effetto sul riscaldamento della superficie del germanio, ma anche un effetto riducente. La creazione di giunzioni superficiali con concentrazioni di oltre 10^20 cm^-3 Sb, con il 100% di attivazione elettrica, è la chiara dimostrazione di come la tecnica PLM utilizzata ad esempio con una sorgente Sb ML sia un valido metodo di drogaggio per il Ge

Innovative Methods for Germanium Doping

One of the main goals in the semiconductor research is the production of a shallow junctions conformal to the surface of a device. This request emerges from the increasing importance of nanostructured devices made by semiconductor materials like multi-gate transistors. The 3D geometry of these devices implies the capability to dope the semiconductor material in a nanostructured, non-planar geometry, which continues to be a difficult task. One of the most promising techniques for the deposition and diffusion of a well-defined amount of dopant is based on the use of self-limiting chemical deposition on semiconductor surfaces: that is the key points of the monolayer doping technique (MLD). This particular technique consists in adsorbing a monolayer of a molecular precursor by a self-limited surface adsorption interaction, which leads to an adsorbed mono- or multilayers formation. This layer(s) acts as a source of dopant for the substrate in-diffusion. This new technique allows to dope not only 3D nano-structured materials with an intrinsically conformal method, but also flat semiconductor surfaces by avoiding the ion implantation technique and the consequent damage of the crystal lattice. On the other hand, germanium is actually a very interesting semiconductor: small band-gap and high charge carrier mobilities have been recently making it more and more appealing in several application fields, from nano-electronics to photovoltaics, from optics to radiation detectors. This work is focused on the challenging n-type doping of Ge by using new doping methods based on the surface interaction between molecular precursors and germanium (001) surface. A complete study on phosphorus monolayer doping technique on germanium is presented, using surface molecular precursor, and also a new antimony self-limiting deposition via gas phase has been discovered and tested as a new technique to synthesized a surface monolayer that can be used as a source for Ge doping. The P and Sb ML sources are synthesised in a completely different way: the phosphorus precursors depositions is done via wet chemistry, using a reflux method or by using a dry procedure in a dry-box ambient both near 160°C, while the antimony monolayer is deposited via gas phase in a nitrogen flux at high temperature (about 600°C <T< 790°C). In both cases, the germanium oxide plays a crucial role: for P case, the oxide plays a fundamental role in the adsorption mechanism, while in the Sb case it contributes to oxidise the incoming antimony gas, playing a fundamental role in the monolayer formation. In both cases the new chemical bond generates between the precursor and the substrate is a Ge-O- based bond: Ge-O-P or Ge-O-Sb. The presence of the Ge-O- bond seems to be the cause of the high surface stability of monolayers, thus generating a lack in diffusion with standard thermal in-diffusion processes. Indeed, the presence of high stable chemical bonds act as a diffusion barrier, since P or Sb atoms release from the chemisorbed ML is possible only after a thermal bond disruption, as will be further discussed. A completely different scenario is presented with the use of pulsed laser melting technique (PLM): it has been used on monolayer molecular sources on Ge (001) and thanks to this out-of-equilibrium technique, the molecular precursor act as a doping source, being effective also for Ge doping. Phosphorus monolayers act as a source of dopant for PLM technique, releasing P and generating a doped layer. In the antimony oxide ML case, all the surface ML is available for diffusion (with no Sb loss), even if all the surface ML is in an initial oxidised state. The PLM technique promote its reduction and atomic Sb diffuse and doped the surface of Ge substrate. The creation of a fully active Sb layer with a surface concentration over 10^20 cm^-3 is the clearly demonstration of the feasibility of the use of Sb ML as a source of dopant

Innovative Methods for Germanium Doping

One of the main goals in the semiconductor research is the production of a shallow junctions conformal to the surface of a device. This request emerges from the increasing importance of nanostructured devices made by semiconductor materials like multi-gate transistors. The 3D geometry of these devices implies the capability to dope the semiconductor material in a nanostructured, non-planar geometry, which continues to be a difficult task. One of the most promising techniques for the deposition and diffusion of a well-defined amount of dopant is based on the use of self-limiting chemical deposition on semiconductor surfaces: that is the key points of the monolayer doping technique (MLD). This particular technique consists in adsorbing a monolayer of a molecular precursor by a self-limited surface adsorption interaction, which leads to an adsorbed mono- or multilayers formation. This layer(s) acts as a source of dopant for the substrate in-diffusion. This new technique allows to dope not only 3D nano-structured materials with an intrinsically conformal method, but also flat semiconductor surfaces by avoiding the ion implantation technique and the consequent damage of the crystal lattice. On the other hand, germanium is actually a very interesting semiconductor: small band-gap and high charge carrier mobilities have been recently making it more and more appealing in several application fields, from nano-electronics to photovoltaics, from optics to radiation detectors. This work is focused on the challenging n-type doping of Ge by using new doping methods based on the surface interaction between molecular precursors and germanium (001) surface. A complete study on phosphorus monolayer doping technique on germanium is presented, using surface molecular precursor, and also a new antimony self-limiting deposition via gas phase has been discovered and tested as a new technique to synthesized a surface monolayer that can be used as a source for Ge doping. The P and Sb ML sources are synthesised in a completely different way: the phosphorus precursors depositions is done via wet chemistry, using a reflux method or by using a dry procedure in a dry-box ambient both near 160°C, while the antimony monolayer is deposited via gas phase in a nitrogen flux at high temperature (about 600°C <T< 790°C). In both cases, the germanium oxide plays a crucial role: for P case, the oxide plays a fundamental role in the adsorption mechanism, while in the Sb case it contributes to oxidise the incoming antimony gas, playing a fundamental role in the monolayer formation. In both cases the new chemical bond generates between the precursor and the substrate is a Ge-O- based bond: Ge-O-P or Ge-O-Sb. The presence of the Ge-O- bond seems to be the cause of the high surface stability of monolayers, thus generating a lack in diffusion with standard thermal in-diffusion processes. Indeed, the presence of high stable chemical bonds act as a diffusion barrier, since P or Sb atoms release from the chemisorbed ML is possible only after a thermal bond disruption, as will be further discussed. A completely different scenario is presented with the use of pulsed laser melting technique (PLM): it has been used on monolayer molecular sources on Ge (001) and thanks to this out-of-equilibrium technique, the molecular precursor act as a doping source, being effective also for Ge doping. Phosphorus monolayers act as a source of dopant for PLM technique, releasing P and generating a doped layer. In the antimony oxide ML case, all the surface ML is available for diffusion (with no Sb loss), even if all the surface ML is in an initial oxidised state. The PLM technique promote its reduction and atomic Sb diffuse and doped the surface of Ge substrate. The creation of a fully active Sb layer with a surface concentration over 10^20 cm^-3 is the clearly demonstration of the feasibility of the use of Sb ML as a source of dopant

Conventional or additive manufacturing for spare parts management: An extensive comparison for Poisson demand

Due to the main peculiarities of spare parts, i.e. intermittent demands, long procurement lead times and high downtime costs when the parts are not available on time, it is often difficult to find the optimal inventory level. Recently, Additive Manufacturing (AM) has emerged as a promising technique to improve spare parts inventory management thanks to a ‘print on demand’ approach. So far, however, the impact of AM on spare parts inventory management has been little considered, and it is not yet clear when the use of AM for spare parts inventory management would provide benefits over Conventional Manufacturing (CM) techniques. With this paper we thus aim to contribute to the field of AM spare parts inventory management by developing decision trees that can be of support to managers and practitioners. To this aim, we considered a Poisson-based inventory management system and we carried out a parametrical analysis considering different part sizes and complexity, backorder costs and part consumption. Moreover, we evaluated scenarios where the order-up-to level is limited to resemble applications with a limited storage capacity. For the first time, the analysis was not limited to just one AM and one CM technique, but several AM and CM techniques were considered, also combined with different post-process treatments, for a total of nine different sourcing alternatives. In addition, the economic and technical performance of the different sourcing options were obtained thanks to an interdisciplinary approach, where experts from production economics and material science were brought together