bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of NS5A and NS5B Resistance-Associated Substitutions from Genotype 1 Hepatitis C Virus Infected Patients in a Portuguese Cohort
Authors: Brandão Ruben , Marcelino Rute , Gonçalves Fátima , Diogo Isabel , Carvalho Ana , Cabanas Joaquim , Costa Inês , Brogueira Pedro , Ventura Fernando , Miranda Ana , Mansinho Kamal , Gomes Perpétua
Published: April 2018

This study is focused on the prevalent NS5 coding region resistance-associated substitutions (RASs) in DAA-naive genotype (GT)1 HCV-infected patients and their potential impact on success rates. Plasma RNA from 81 GT1 HCV-infected patients was extracted prior to an in-house nested RT-PCR of the NS5 coding region, which is followed by Sanger population sequencing. NS5A RASs were present in 28.4% (23/81) of all GT1-infected patients with 9.9% (8/81) having the Y93C/H mutation. NS5B RASs showed a prevalence of 14.8% (12/81) and were only detected in GT1b. Overall 38.3% (31/81) of all GT1 HCV-infected patients presented baseline RASs. The obtained data supports the usefulness of resistance testing prior to treatment since a statistically significant association was found between treatment failure and the baseline presence of specific NS5 RASs known as Y93C/H (p = 0.04).
Influence of Straw Amendment on Soil Physicochemical Properties and Crop Yield on a Consecutive Mollisol Slope in Northeastern China
Authors: Zhang Shaoliang , Wang Yao , Shen Qingsong
Published: April 2018

Straw amendment (SA) can be used to increase soil organic matter and decrease dioxide carbon emissions. However, the impact of SA on the crop yield is still subject to debate in different areas. In this study, soil temperature (ST), soil moisture (SM), soil bulk density, soil-available-nitrogen (AN), soil-available-phosphorus (AP), crop growth and yield were measured in SA and NSA (no straw amendment) at slope positions of a 130-m-long consecutive Mollisol slope during the maize (Zea mays) growth stages in the North Temperate Zone of China. Compared with NSA, the influence of SA on ST and SM was not consistent, while AN typically increased on the top slope. However, SA conventionally increased AP, increased daily ST and monthly ST (2.4–7.9%), and increased daily SM and monthly SM (2.1–12.5%) on the back slope. SA increased crop yield by 1–9.8% and 55.6–105.1% on the top and back slopes, respectively. At the bottom, SA conventionally decreased ST (0.20–1.48 °C in July and August), SM (3.5–29.6% from May to August), AN and AP, and decreased crop yield (4.1–30.6%). In conclusion, SA changed the equilibrium of ST and SM, influenced the dynamics of AN and AP on the consecutive slopes, and increased yield on both the top and back slopes but decreased yield at the bottom.
Évaluation de la transformation de la réduction d’impôt pour l’emploi de salariés à domicile en crédit d’impôt en 2007
Authors: Marbot Claire , Roy Delphine
Published: April 2018

Since 1991, users of in-home services have been eligible for a tax refund equal to50% of their spending on these services. The tax reductionwas turned into a tax credit in 2007, but only for economically active households. This condition greatly limited the impact of the policy change : in 2008, the tax credit covered 1.9% of the total € 7.8 bn annual expenditure, against 34% for the earlier tax reduction. We evaluate the impact of the reform using an exhaustive panel database of tax returns available for 2006-2008, and combining difference-in-differences andmatchingmethods. Our results suggest that the reform induced an additional 86,000 to 120,000 households to use declared in-home services.
Induced smectic phase in binary mixtures of twist-bend nematogens
Authors: Knežević Anamarija , Dokli Irena , Sapunar Marin , Šegota Suzana , Baumeister Ute , Lesac Andreja
Published: April 2018

The investigation of liquid crystal (LC) mixtures is of great interest in tailoring material properties for specific applications. The recent discovery of the twist-bend nematic phase (NTB) has sparked great interest in the scientific community, not only from a fundamental viewpoint, but also due to its potential for innovative applications. Here we report on the unexpected phase behaviour of a binary mixture of twist-bend nematogens. A binary phase diagram for mixtures of imino-linked cyanobiphenyl (CBI) dimer and imino-linked benzoyloxy-benzylidene (BB) dimer shows two distinct domains. While mixtures containing less than 35 mol % of BB possess a wide temperature range twist-bend nematic phase, the mixtures containing 55–80 mol % of BB exhibit a smectic phase despite that both pure compounds display a Iso–N–NTB–Cr phase sequence. The phase diagram shows that the addition of BB of up to 30 mol % significantly extends the temperature range of the NTB phase, maintaining the temperature range of the nematic phase. The periodicity, obtained by atomic force microscopy (AFM) imaging, is in the range of 6–7 nm. The induction of the smectic phase in the mixtures containing 55–80 mol % of BB was confirmed using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The origin of the intercalated smectic phase was unravelled by combined spectroscopic and computational methods and can be traced to conformational disorder of the terminal chains. These results show the importance of understanding the phase behaviour of binary mixtures, not only in targeting a wide temperature range but also in controlling the self-organizing processes.
ASSESSMENT OF MECHANICAL PROPERTIES OF HIGH STRENGTH CONCRETE (HSC) AFTER EXPOSURE TO HIGH TEMPERATURE
Authors: DRZYMAŁA Tomasz , JACKIEWICZ-REK Wioletta , GAŁAJ Jerzy , ŠUKYS Ritoldas
Published: April 2018

There has been a tendency to design ever slender building construction using high strength concrete in recent years. Application of HSC is also growing in tunnel construction. One of the most important challenges is to control explosive spalling of concrete and the method recommended by Eurocode 2 (EN 1992-1-2:2008/NA:2010P) is addition of polypropylene fibres to the mix. The purpose of the research described in this paper was to evaluate the changes of mechanical properties of HSC exposed to the effect of high temperature. The tests were carried out on three types of high strength concrete: air-entrained concrete, polypropylene fibre-reinforced concrete and reference concrete having constant water/cement ratio. The properties of hardened concrete including compressive strength, tensile splitting strength, flexural strength and E-modulus were studied. The latter tests were carried out on both on concrete cured at 20 °C and concrete subjected to high-temperature conditions at 300 °C, 450 °C and 600 °C. The results enabled us to evaluate the effect of high-temperature conditions on the properties of high-performance concrete and compare the effectiveness of the two methods designed to improve the high-temperature performance of the concrete: addition of polypropylene fibres and entrainment of air.
AN EXPERIMENTAL STUDY FOR QUALITY ASSURANCE OF FREE-FORM CONCRETE PANELS PRODUCED BY CNC MACHINE
Authors: LIM Jeeyoung , KIM Do Yeong , KIM Sunkuk
Published: April 2018

Various studies have been conducted to construct free-form buildings, but it still takes a lot of labor, cost, and time to assure the accuracy of designed shapes. In particular, molds for the production of free-form concrete panels (FCPs) are putting enormous burdens on productivity and cost. To produce FCPs economically, a computerized numeric control (CNC) machine that produces phase change material (PCM) molds for persistent use was developed in this study. The technology using CNC machine can produce precisely free-form molds and panels in a short time compared to the manual method. However, in order to commercialize this technology, it is necessary to verify the shape error of the FCPs. Therefore, the purpose of this paper is an experimental study for securing FCP quality produced by a CNC machine. The results of this study will be used to mass-produce uniform quality of FCPs without depending on the skill and workmanship of the labo.
Acoustic Disturbances in Galaxy Clusters
Authors: Zweibel Ellen G. , Mirnov Vladimir V. , Ruszkowski Mateusz , Reynolds Christopher S. , Yang H.-Y. Karen , Fabian Andrew C.
Published: April 2018

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is the dissipation of acoustic waves generated by active galactic nuclei. Fabian et al. showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self-limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semicollisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian et al. remains the most viable path to acoustic wave heating of galaxy cluster cores.
A Novel Approach to Resonant Absorption of the Fast Magnetohydrodynamic Eigenmodes of a Coronal Arcade
Authors: Hindman Bradley W. , Jain Rekha
Published: April 2018

The arched field lines forming coronal arcades are often observed to undulate as magnetohydrodynamic waves propagate both across and along the magnetic field. These waves are most likely a combination of resonantly coupled fast magnetoacoustic waves and Alfvén waves. The coupling results in resonant absorption of the fast waves, converting fast wave energy into Alfvén waves. The fast eigenmodes of the arcade have proven difficult to compute or derive analytically, largely because of the mathematical complexity that the coupling introduces. When a traditional spectral decomposition is employed, the discrete spectrum associated with the fast eigenmodes is often subsumed into the continuous Alfvén spectrum. Thus fast eigenmodes become collective modes or quasi-modes. Here we present a spectral decomposition that treats the eigenmodes as having real frequencies but complex wavenumbers. Using this procedure we derive dispersion relations, spatial damping rates, and eigenfunctions for the resonant, fast eigenmodes of the arcade. We demonstrate that resonant absorption introduces a fast mode that would not exist otherwise. This new mode is heavily damped by resonant absorption, travelling only a few wavelengths before losing most of its energy.
Radiation-mediated Shocks in Gamma-Ray Bursts: Pair Creation
Authors: Lundman Christoffer , Beloborodov Andrei M. , Vurm Indrek
Published: April 2018

Relativistic sub-photospheric shocks are a possible mechanism for producing prompt gamma-ray burst (GRB) emission. Such shocks are mediated by scattering of radiation. We introduce a time-dependent, special relativistic code which dynamically couples Monte Carlo radiative transfer to the flow hydrodynamics. The code also self-consistently follows electron–positron pair production in photon–photon collisions. We use the code to simulate shocks with properties relevant to GRBs. We focus on plane-parallel solutions, which are accurate deep below the photosphere. The shock generates a power-law photon spectrum through the first-order Fermi mechanism, extending upward from the typical upstream photon energy. Strong (high Mach number) shocks produce rising νF

ν
spectra. We observe that in non-relativistic shocks the spectrum extends to

, where v is the speed difference between the upstream and downstream. In relativistic shocks the spectrum extends to energies

where its slope softens due to Klein–Nishina effects. Shocks with Lorentz factors γ > 1.5 are prolific producers of electron–positron pairs, yielding hundreds of pairs per proton. The main effect of pairs is to reduce the shock width by a factor of

. Most pairs annihilate far downstream of the shock, and the radiation spectrum relaxes to a Wien distribution, reaching equilibrium with the plasma at a temperature determined by the shock jump conditions and the photon number per proton. We discuss the implications of our results for observations of radiation generated by sub-photospheric shocks.
On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges
Authors: Nóbrega-Siverio D. , Moreno-Insertis F. , Martínez-Sykora J.
Published: April 2018

Surges are ubiquitous cool ejections in the solar atmosphere that often appear associated with transient phenomena like UV bursts or coronal jets. Recent observations from the Interface Region Imaging Spectrograph show that surges, although traditionally related to chromospheric lines, can exhibit enhanced emission in Si iv with brighter spectral profiles than for the average transition region (TR). In this paper, we explain why surges are natural sites to show enhanced emissivity in TR lines. We performed 2.5D radiative-MHD numerical experiments using the Bifrost code including the nonequilibrium (NEQ) ionization of silicon and oxygen. A surge is obtained as a by-product of magnetic flux emergence; the TR enveloping the emerged domain is strongly affected by NEQ effects: assuming statistical equilibrium would produce an absence of Si iv and O iv ions in most of the region. Studying the properties of the surge plasma emitting in the Si iv λ1402.77 and O iv λ1401.16 lines, we find that (a) the timescales for the optically thin losses and heat conduction are very short, leading to departures from statistical equilibrium, and (b) the surge emits in Si iv more and has an emissivity ratio of Si iv to O iv larger than a standard TR. Using synthetic spectra, we conclude the importance of line-of-sight effects: given the involved geometry of the surge, the line of sight can cut the emitting layer at small angles and/or cross it multiple times, causing prominent, spatially intermittent brightenings in both Si iv and O iv.
Quasi-periodic Pulsations in the Most Powerful Solar Flare of Cycle 24
Authors: Kolotkov Dmitrii Y. , Pugh Chloe E. , Broomhall Anne-Marie , Nakariakov Valery M.
Published: April 2018

Quasi-periodic pulsations (QPPs) are common in solar flares and are now regularly observed in stellar flares. We present the detection of two different types of QPP signals in the thermal emission light curves of the X9.3-class solar flare SOL2017-09-06T12:02, which is the most powerful flare of Cycle 24. The period of the shorter-period QPP drifts from about 12 to 25 s during the flare. The observed properties of this QPP are consistent with a sausage oscillation of a plasma loop in the flaring active region. The period of the longer-period QPP is about 4 to 5 minutes. Its properties are compatible with standing slow magnetoacoustic oscillations, which are often detected in coronal loops. For both QPP signals, other mechanisms such as repetitive reconnection cannot be ruled out, however. The studied solar flare has an energy in the realm of observed stellar flares, and the fact that there is evidence of a short-period QPP signal typical of solar flares along with a long-period QPP signal more typical of stellar flares suggests that the different ranges of QPP periods typically observed in solar and stellar flares is likely due to observational constraints, and that similar physical processes may be occurring in solar and stellar flares.
An Extreme-ultraviolet Wave Generating Upward Secondary Waves in a Streamer-like Solar Structure
Authors: Zheng Ruisheng , Chen Yao , Feng Shiwei , Wang Bing , Song Hongqiang
Published: April 2018

Extreme-ultraviolet (EUV) waves, spectacular horizontally propagating disturbances in the low solar corona, always trigger horizontal secondary waves (SWs) when they encounter the ambient coronal structure. We present the first example of upward SWs in a streamer-like structure after the passing of an EUV wave. This event occurred on 2017 June 1. The EUV wave happened during a typical solar eruption including a filament eruption, a coronal mass ejection (CME), and a C6.6 flare. The EUV wave was associated with quasi-periodic fast propagating (QFP) wave trains and a type II radio burst that represented the existence of a coronal shock. The EUV wave had a fast initial velocity of ∼1000 km s−1, comparable to high speeds of the shock and the QFP wave trains. Intriguingly, upward SWs rose slowly (∼80 km s−1) in the streamer-like structure after the sweeping of the EUV wave. The upward SWs seemed to originate from limb brightenings that were caused by the EUV wave. All of the results show that the EUV wave is a fast-mode magnetohydrodynamic (MHD) shock wave, likely triggered by the flare impulses. We suggest that part of the EUV wave was probably trapped in the closed magnetic fields of the streamer-like structure, and upward SWs possibly resulted from the release of slow-mode trapped waves. It is believed that the interplay of the strong compression of the coronal shock and the configuration of the streamer-like structure is crucial for the formation of upward SWs.
Amphibians of the Reserva Ecológica Michelin: a high diversity site in the lowland Atlantic Forest of southern Bahia, Brazil
Authors: Vinícius de Mira-Mendes Caio , Ruas Danilo Silva , Manoel de Oliveira Renan , Maria Castro Indira , Ribeiro Dias Iuri , Ernesto Baumgarten Julio , Acuña Juncá Flora , Solé Mirco
Published: April 2018

An inventory of the amphibians of the Reserva Ecológica Michelin – REM in southern Bahia, Brazil is presented. Sixty-nine species were recorded during a ten-year sampling period. Amphibians were distributed in two orders (Gymnophiona and Anura), belonging to twelve families [Aromobatidae (1), Bufonidae (3), Centrolenidae (1), Craugastoridae (5), Eleutherodactylidae (3), Hemiphractidae (2), Hylidae (34), Phyllomedusidae (5) Leptodactylidae (7), Microhylidae (4), Odontophrynidae (3) and Caeciliidae (1)]. Fifty per cent of the reproductive modes known for Atlantic forest anurans were recorded. While no threatened species were found at REM, six species are classified as data deficient (DD) by the Brazilian Red List of threatened species and deserve additional attention.PhasmahylatimboandVitreoranaeurygnataare listed as endangered in Bahia according to the list of threatened species of the state. Despite a higher diversity of amphibians in the Atlantic forest having been reported for mountainous regions, our results revealed that amphibian richness for lowland forests is also high.
Données administratives et évaluation des politiques régionales
Authors: Ragazzi Elena , Sella Lisa
Published: April 2018

L’évaluation de l’impact des politiques du travail ou concernant le capital humain se base normalement sur des enquêtes menées directement auprès des individus ayant bénéficié des dispositifs d’aides. Pour estimer leur impact net il faut en plus observer des individus non traités mais très homogènes par rapport au groupe principal. Le coût élevé de réalisation des enquêtes empêche d’augmenter la taille des échantillons et il est alors difficile de pouvoir mener des comparaisons à un niveau local. L’accès à des bases de données (fiscales, administratives, de suivi) pourrait remédier à ces limites avec beaucoup d’avantages, mais la fiabilité de cette source est souvent surestimée. Dans cet article nous présentons un travail de validation d’une base de données très complexe qui enregistre les communications ( Cob ) qui sont prévues par la loi italienne quand il y a un changement de contrat de travail. Deux sources différentes pour l’évaluation de l’impact sont comparées et discutées : la base de données des Cob et une enquête plus classique. Classification JEL : C55, C81, P46 ; J08
Are probiotic treatments useful on fibromyalgia syndrome or chronic fatigue syndrome patients? A systematic review
Authors: Roman P. , Carrillo-Trabalón F. , Sánchez-Labraca N. , Cañadas F. , Estévez A.F. , Cardona D.
Published: April 2018

Evidence suggests that the gut microbiota might play an important role in fibromyalgia syndrome (FMS) and chronic fatigue syndrome (CFS). Our goal is to systematically review the reported effect of probiotic treatments in patients diagnosed with FMS or CFS. A systematic review was carried out using 14 databases (PubMed, Cochrane Library, Scopus, PsycINFO, and others) in February 2016 to search for randomised controlled trials (RCTs) and pilot studies of CFS or FMS patient, published in the last ten years (from 2006 to 2016). The Jadad scale was used to asseverate the quality of the clinical trials considered. Two studies (n=83) met the inclusion criteria, which were performed in CFS patients and both studies were considered as a ‘High range of quality score’. The administration of Lactobacillus casei strain Shirota in CFS patients, over the course of 8 weeks, reduced anxiety scores. Likewise, this probiotic changed the faecal composition following 8 weeks of treatment. Additionally, the treatment with Bifidobacterium infantis 35624 in CFS patients, during the same period, reduced inflammatory biomarkers. The evidence about the usefulness of probiotics in CFS and FMS patients remains limited. The studied strains of probiotics have demonstrated a significant effect on modulating the anxiety and inflammatory processes in CFS patients. However, more experimental research, focusing mainly on the symptoms of the pathologies studied, is needed.
Effect of agronomic practices and weather conditions on mycotoxins in maize: a case study of subsistence farming households in Zimbabwe
Authors: Ndemera M. , Landschoot S. , De Boevre M. , Nyanga L.K. , De Saeger S.
Published: April 2018

Maize is susceptible to many mycotoxigenic fungi and mycotoxins, being prone toFusarium spp. infection and subsequent mycotoxin contamination. Fumonisin B1 (FB1) is the predominant mycotoxin in Zimbabwean subsistence-grown maize and results of mycotoxin analyses indicated FB1 to be significantly higher compared to other mycotoxins. To fully elucidate maize agronomic practices influencing FB1 contamination of maize produced by Zimbabwean subsistence farming populations, an investigative field survey was conducted in the selected provinces of Mashonaland West and Manicaland. Agronomic data and associated climatic data were collected during the 2014/2015 agricultural season. A total of 158 maize samples were collected from households’ harvest, three months and six months post-harvest. Analysis and quantification of mycotoxin contamination in the maize samples was performed using a validated multi-mycotoxin analysis method with a scope of 23 mycotoxins. Maize was mainly contaminated by FB1. There was low mycotoxin co-occurrence in Zimbabwean maize, which was typically ofFusarium toxins. FB1 occurred in 23, 47 and 47% of samples at harvest, three and six months post-harvest, respectively. The corresponding means of positive samples were 609, 597 and 289 μg/kg, respectively. Regarding fumonisins, the choice of seed and fertiliser application were significant in modulating FB1 contamination. There was no significant difference in mean FB1 contamination during post-harvest maize storage. Daily temperatures were key factors influencing FB1 incidence and levels. High temperatures were associated with high FB1 contamination particularly at the flowering stage of maize. Rainfall was positively correlated with FB1 contamination. Good agricultural practices attributed to low FB1 contamination in maize pre-harvest. Post-harvest practices such as preserving seed integrity by preventing pest infestation using grain protection chemicals are important in achieving lower mycotoxin contamination and in particular, FB1, in maize grain.
Complex Big Data Analysis Based on Multi-granularity Generalized Functions
Authors: Xueya Zhang , Zhang Jianwei
Published: April 2018

A new method for the big data analysis - multi-granularity generalized functions data model (referred to as MGGF for short) is put forward. This method adopts the dynamic adaptive multi-granularity clustering technique, transforms the grid like "Hard partitioning" to the input data space by the generalized functions data model (referred to as GFDM for short) into the multi-granularity partitioning, and identifies the multi-granularity pattern class in the input data space. By defining the type of the mapping relationship between the multi-granularity model class and the decision-making category ftype:Ciâ†’y, and the concept of the Degree of Fulfillment (referred to as DoF (x)) of the input data to the classification rules of the various pattern classes, the corresponding MGGF model is established. Experimental test results of different data sets show that, compared with the GFDM method, the method proposed in this paper has better data summarization ability, stronger noise data processing ability and higher searching efficiency.
Modeling Distributed Real-time Elevator System by Three Model Checkers
Authors: Zhongsheng Qian , Xin Li , Xiaojin Wang
Published: April 2018

The characteristics of three popular model checking tools called SPIN, UPPAAL and NuSMV respectively, are compared and analyzed to determine which type of systems is propitious to be described. And a distributed elevator system model is built, whose related properties are verified and compared by these three model checking tools. To begin with, SPIN, UPPAAL and NuSMV, whose modeling language features are compared, are employed to construct an elevator system model respectively. Then, the three validation tools are used to verify several important properties of the elevator model, and the result is analyzed and their own characteristics are summarized. Finally, the experimental results show that SPIN and NuSMV are more suitable for verifying distributed systems while UPPAAL is better for verifying real-time systems.
Design of Smart home System Based on Basic Radio Frequency Wireless Sensor Network
Authors: Tian Fang , Long Xi , Liao Wendi
Published: April 2018

This paper attempts to integrate the wireless sensor network (WSN) into the smart home system. To this end, a smart home system was developed based on the basic radio frequency (RF) WSN. First, the author introduced the architecture, nodes and features of the WSN. Then, the design process of the smart home system was detailed. The hardware of the system consists of such three parts as the master control, wireless transceiver and sensor terminal; the software of the system includes the basic-RF WSN program and the master module STM32 programme. After that, the established system was applied to temperature collection and control. The results show that the collected temperature agreed well with the temperature measured by the thermometer. Finally, the temperature control effect of the system was successfully simulated with a potentiometer and an LED lamp. The research findings shed new light on the design of smart homes.
Movement Human Actions Recognition Based on Machine Learning
Authors: Xu Honghua , Li Li , Fang Ming , Zhang Fengrong
Published: April 2018

In this paper, the main technologies of foreground detection, feature description and extraction, movement behavior classification and recognition were introduced. Based on optical flow for movement objects detection, optical flow energy image was put forward for movement feature expression and region convolutional neural networks was adopt to choose features and decrease dimension. Then support vector machine classifier was trained and used to classify and recognize actions. After training and testing on public human actions database, the experiment result showed that the method could effectively distinguish human actions and significantly improved the recognition accuracy of human actions. And for the different situations of camera lens drawing near, pulling away or slight movement of camera, the solution had recognition effect as well. At last, this scheme was applied to intelligent video surveillance system, which was used to identify abnormal behavior and alarm. The abnormal behaviors of faint, smashing car, robbery and fighting were defined in the system. In running of the system, it obtained satisfactory recognition results.
Towards the Numerical Prediction of Galling Onset in Cold Forming
Authors: Filali Oussama , Dubois André , Dubar Laurent , Dubar Mirentxu
Published: April 2018

Aluminum alloys are materials that have a strong tendency to galling when they are cold formed. Caused by a breakdown of the lubricant film between the part and the tool, galling can have dramatic consequences on the forming operation: scratches and cracks in the surface of the piece, clogging and deterioration of tools, etc. The present work studies the galling mechanisms of the aluminum alloy 6082 during its cold forming. Trials involving the Upsetting-Sliding Test (UST) are performed first. The UST is a test bench able to simulate in laboratory conditions the contact encountered at the part/tool interface of industrial processes. Trials are achieved under varying contact pressure and lubrication. UST results show that galling is strongly influenced by tool roughness and is not accompanied by a significant increase of friction. Three sets of finite element computation of the UST are then run to predict galling onset. Lubricant and adhesion forces are not modelled in this simplified approach: only the mechanical aspects are taken into account, the chemical ones are implicitly taken into account by coefficients of friction. The Lemaitre’s and the Xue’s damage models are compared. Results show that the Lemaitre model needs the tool roughness to be modeled to detect the galling onset. The Xue model is able to detect the occurrence of galling without modelling roughness. This result is due to the used of the Lode angle with enable the calculation of damage under low stress triaxiality.
The Galling Behavior of Advanced Coating Contacts with Aluminium Alloy during Sliding Wear
Authors: Hu Yi Ran , Gharbi Mohammad M. , Liang Vivian , Zheng Yang , Politis Denis J. , Wang Li Liang
Published: April 2018

This paper investigates the galling behaviour of a range of hard coatings applied to tooling surfaces during the sheet forming of an aluminium alloy workpiece. A total of three types of tooling materials were investigated, two of which were subject to PVD deposited coatings of AlCrN, CrN and DLC applied to the working surface. The third tooling material had undergone induction heating, plasma-nitriding and polishing. To evaluate the galling behaviour of the applied coatings, a tribological evaluation was conducted using a pin-on-disc test set-up at a constant load and varying temperature. The coated discs, replicating the tooling material, were tested against aluminium alloy pins AA6082 and AA7075 representing the workpiece material. This investigation indicated that the friction and galling behaviour of aluminium is highly dependent on temperature, and the use of two different aluminium pins had no significant effect. At room temperature, it was found that carbon-based coatings provide the lowest friction and the best protection against galling, whilst nitride-based treatments exhibit better performance at high temperature. Moreover, at elevated temperatures, coated tools exhibit superior anti-galling properties compared to uncoated tools.
Lubricant Influence on the Ejection and Roughness of In-Die Electro Sinter Forged Ti-Discs
Authors: Cannella Emanuele , Nielsen Chris Valentin
Published: April 2018

Electro Sinter Forging (ESF) is a new sintering process based on Joule heating by high electrical current flowing through compacted metal powder under mechanical pressure. The whole process takes about three seconds and is based on a closed-die setup, where the sample is sintered inside a die. A near-net shape component is therefore manufactured. One of the challenges associated with this process is the ejection of the sample after sintering. Due to powder compaction and axial loading during sintering, a radial pressure is generated at the die/sample interface. Consequently, the ejection can be difficult, and the final quality of the sintered component in terms of roughness and surface defects may be affected. In the present work, four different lubricants and non-lubricated conditions were tested to investigate the effects on the final part quality. The sintered sample is a disc made of commercially pure titanium powder. The force was measured while ejecting the samples by using a speed-controlled press. The surface roughness parameter Sa was measured by using a laser confocal microscope.
Investigation of Friction Conditions in Dry Metal Forming of Aluminum by Extended Conical Tube-Upsetting Tests
Authors: Teller Marco , Ross Ingo , Temmler André , Poprawe Reinhart , Prünte Stephan , Schneider Jochen M. , Hirt Gerhard
Published: April 2018

In cold forming of aluminum, various lubricants and coatings are typically used to reduce friction and wear, resulting in higher workpiece surface quality. The preparation of the workpiece surfaces and the cleaning of the products after the forming step generate a significant amount of environmentally hazardous residues. Therefore, current research focuses on the realization of dry metal forming processes. Instead of lubricants, modified tool surfaces can also optimize tribological conditions in the interaction zone of forming tool and workpiece. The applicability of these surfaces needs further examination before usage within an industrial manufacturing process. In this paper, different surface modifications are examined by using a conical tube-upsetting test setup that is based on the concept of the well-known ring-compression test. The conical tool surface homogenizes the relative displacement between tool and workpiece and suppresses the appearance of a neutral point. Conical tools from AISI H11 / DIN 1.2343 and AISI D2+ / DIN 1.2379+ are laser polished and functionalized with self-assembled monolayers. Friction conditions resulting from different surface modifications are analyzed and evaluated by the use of nomograms. Moreover, the applicability of different friction laws for dry metal forming of aluminum is investigated.
High Temperature Friction and Wear Testing for Closed-Die Steel and Aluminium Forgings
Authors: Buchmayr Bruno , Elser Jürgen
Published: April 2018

There are several testing methodologies to characterize the friction and wear behavior of coated or special heat treated dies and forging materials for closed-die forgings. In order to measure the friction coefficient, the wear rate, galling or fretting behavior or the effect of lubricants, three different testing types (ring compression testing, a self-made high temperature rotation tribometer and hot torsion friction) are described in detail. To meet the practical requirements, the influencing factors like temperature level, sliding speed, contact pressure and specific surface treatments or coatings have to be varied in proper ranges. The results may contribute to find better friction models for finite element analysis, and consequently to a better prediction of the material flow and other related parameters. By confocal microscopy and a full metallographic investigation, the microstructural changes near the interface are studied, which lead to a better understanding of the wear and degradation mechanisms involved. These findings may help to find out countermeasures for life time improvements of the forging dies.
Design of Progressive Die Sequence by Considering the Effect of Friction, Temperature and Contact Pressure
Authors: Üstünyagiz Esmeray , Altan Taylan
Published: April 2018

Progressive and transfer dies are used for forming of sheet metal parts in large quantities. For a given part, the design of progressive die sequence involves the selection of the number of forming stages as well as the determination of the punch and die dimensions at each stage. This design activity is largely experience-based and requires prototyping involving several trial and error operations. In some cases, empirical data and the experience based design procedure can be combined with Finite Element Method (FEM) based analysis to reduce time and cost. Often, when using FEM in progressive die design, friction and its effect upon temperatures is not adequately considered. However, at each forming station the plastic deformation and the tribological conditions influence the material flow as well as the temperatures and pressures at the tool/workpiece interface. The performance of the lubricant and coolant, used in progressive die forming, is affected significantly by interface pressure and temperatures. Therefore, a progressive process and die design methodology should include the consideration of metal flow as well as temperatures and pressures. Heat transfer coefficient, friction, plastic deformation, forming speed at each forming stage, time for part transfer from one stage to the next, and the ability of the used lubricant to cool the dies, have considerable effect upon a successful stamping. This paper describes a method for designing a progressive die sequence for forming axisymmetric sheet metal parts. The methodology for process sequence design combines experience based empirical data obtained through previous designs, design rules and numerical simulations including plastic deformation and friction. The initial experience-based design was refined using FEM and the thinning of the material in each successive drawing stage was calculated. The thermo-mechanical model was obtained using a constant friction coefficient along the tool/workpiece contact zone. Finally, the tool/workpiece interface temperature and the normal pressures were estimated in order that the lubricant can be selected based on these process conditions. The design predictions, made by using empirical data and FEM, were compared with experimental data.
On the Mechanism by which Chromium Improves Strip Surface Cleanliness in Steel Strip Cold Rolling
Authors: Montmitonnet Pierre , Bouadjadja Nassim , Luong Linh Phuong , Bertrandie Jean Jacques , Dietsch Hervé
Published: April 2018

“Detachable iron particles” or iron fines due to abrasive interactions in the roll bite between the roll surface and the strip are one of the major cleanliness defects. They may induce surface defects in particular on galvanizing lines. Chrome plating of rolls is generally recognized to result in a better strip surface cleanliness. In the present paper, the reasons for the success of chrome plating in this respect are investigated. An end-of-life industrial roll has been ground by parts under several conditions (Ra = 0.4 μm, 1.0 μm, 1.6 μm ± 0.1 μm), then cut into pieces for observation as well as for manufacturing tribological test tools (Plane Strain Compression Test, PSCT). Some of these pieces have been chrome-plated, the others not for comparison. Careful examination of just ground and chrome-plated roll has revealed that ground surface bears a number of rather aggressive features. Chrome plating covers them with a gentler pattern, although preserving the roughness in terms of Ra to maintain sufficient friction for correct mill operation. PSCT confirms that there is less wear debris on the strip when using Cr-plated tools.
Wear Prediction for Oscillating Gear Forming Processes Using Numerical Methods
Authors: Schmidt Wilhelm , Groche Peter
Published: April 2018

Oscillating forming processes offer outstanding opportunities for lightweight applications and economic advantages. Gears, especially splines, are industrially produced by oscillating ram movements. The oscillations enable the precise manufacturing of the gearing on the tubes. At the same time, they also enlarge the sliding distance in each stroke. Therefore, tool wear has to be considered carefully. Observations of oscillating gear forming processes reveal a startling phenomenon: Calibration regions of tools show the first wear marks during the manufacturing process, although the maximum contact stress is located in the forming area. According to Archard’s equation, the maximum wear is expected to be located in the area of maximum contact normal stress. In this paper wear prediction based on numerical simulations and a modified Archard ́s equation is presented. The implemented wear factor is of particular influence. Adequate values for this factor are derived from gear forming processes with tools made out of the steel 1.2379. Splines made of case hardening steel (16MnCrS5) can be produced with these tools, but wear is already evolving when laboratory lots are produced. Wear behavior and wear volume are recorded and used to determine the wear factor. The resulting values for wear factors in Archard’s equation indicate that changing contact and lubrication conditions during the pre-and the backstroke of oscillating processes have to be taken into account in wear modelling. This is achieved by a decomposition of the wear index into material and lubrication related factors. The extended model allows for a local wear forecast in processes with oscillating ram movements for which Archard’s classic wear model does not give plausible results.
Finite Element Modeling of Bond Formation in Cold Roll Bonding Processes
Authors: Khaledi Kavan , Wulfinghoff Stephan , Reese Stefanie
Published: April 2018

The paper aims to present a finite element model for the bond strength evolution in cold roll bonding processes. To accomplish this, first, the micro-mechanisms taking place along the cold welded joint interfaces are explained. Then, based on the microscopic description of cold welding processes, a bonding interface model is employed to describe the bond formation between the rolled metallic layers. The obtained bond strength is calculated based on the governing parameters of the bonding such as the degree of plastic deformation and the surface cleanness. The numerical simulation given in this paper includes the modelling of joining during cold roll bonding followed by the debonding process in Double Cantilever Beam (DCB) peeling test. Finally, the effects of two important factors on the bond formation, i.e. (1) the degree of plastic deformation and (2) the surface cleanness, are numerically investigated.
Induction Pre-Heated Linear Friction Welding
Authors: Kelly Matthew R. , Schmid Steven R. , Adams Daniel C. , Fletcher Jeffrey
Published: April 2018

A two-level factorial design of experiments (DOE) approach is used to study the effect of four factors (average rubbing velocity, weld pressure, burn-off distance, and preheat temperature) on two response variables (weld strength and energy input) for the induction heating and linear friction welding of AISI 1020 steel. Weld strength, as analyzed though three-point bending, was insensitive to all four of the design factors. Pressure, upset, and velocity show statistically significant inverse, linear, and linear relationships with energy used, respectively. Pressure has the largest effect on energy used, followed by velocity and upset.
The Influence of Ultrasound Enhancement during Friction Stir Welding of Aluminum to Steel
Authors: Thomä Marco , Wagner Guntram , Straß Benjamin , Wolter Bernd , Benfer Sigrid , Fürbeth Wolfram
Published: April 2018

The innovative joining process of friction stir welding (FSW) offers a wide range of advantages for welding similar as well as dissimilar materials. Even for the field of poorly weldable material combinations like aluminum to steel with their strongly differing physical properties the method of FSW proved its capability for realizing dissimilar joints with tensile strengths up to more than 80 % of the aluminum base material. Trying to improve this value and other properties of the joints several approaches for hybrid friction stir welding processes were tested in the scientific community, whereas the ultrasound enhancement of FSW (USE-FSW) looked as one of the most promising reaching good results. To gain a deeper knowledge of the influence of the ultrasound on the friction stir welds different investigations were carried out in this paper. Therefore the method of USE-FSW was applied on two dissimilar aluminum/steel-joints with varying carbon content of the steel in this work. The material combinations AA6061/SAE1006 and AA6061/SAE1045 were welded successfully with and without additional power ultrasound. Afterwards a comparison between FSW-and USE-FSW-joints was carried out regarding the microstructure of the nugget and interface (IF) by light-microscopy as well as scanning electron microscopy. Furthermore the mechanical properties were characterized in a first step.
Numerical Analysis of the Scalability of Roller Clinching Processes
Authors: Hiller Maria , Vitzthum Simon , Hacker Martin , Benkert Tim , Volk Wolfram
Published: April 2018

Roller clinching combines the advantages of translational clinching with a continuous feed of the parts to be joined. Challenging tasks are the non-perpendicular impact and retraction of the tools leading to anisotropic joint properties. These effects are strongly influenced by scaling the setup. Reducing the size of roller clinching machines increases the impact angle of the tools on the sheets. This paper focuses on the kinematic description of the tool movement as well as the joint formation depending on different setup sizes. Process limits for different setups are investigated.
Parametric Study of Hybrid Metal-Composites Clinching Joints
Authors: Dean Aamir , Rolfes Raimund , Behrens Bernd-Arno , Hübner Sven , Chugreev Alexander , Grbic Nenad
Published: April 2018

In different innovative markets, such as electro mobility and flexible electronics, among others, the mechanical joining processes based on sheet metal forming technologies are gaining a significant relevance due to their low cost and ease of automation as compared to traditional joining techniques of riveting, bolting, fastening, welding, etc. In lightweight hybrid constructions, where a high production rate is required, clinching technology demonstrates a sustainable method to join hybrid metal-composite parts. However, the basic mechanisms of this hybrid joining process are not well studied at present and an accepted design theory in this area has not yet been established. The current contribution presents a parametric study of the hybrid clinching joining process. The Taguchi’s design of experiments method is used to investigate the effects of tools’ geometry on hybrid clinching joints’ quality characteristics, i.e. neck thickness, undercut and final bottom thickness. For this purpose, a 2D axisymmetric modelling approach was adopted for its simplicity. The study results are analyzed using the mean response and signal-to-noise ratio approaches. Accordingly, the relevant geometrical parameters of the tools with the highest influence on the accurate shaping of hybrid clinching joints are determined numerically.
Friction and Wear in Metal Forming: 25 Years at LAMIH UMR CNRS 8201
Authors: Dubar Laurent , Dubois André , Dubar Mirentxu
Published: April 2018

Since the beginning of the 90’s, research activities focused on friction and wear in metal forming have been developed at the LAMIH UMR CNRS 8201 in Valenciennes. Specific methodologies have been designed to optimize a given forming process (bulk forming process or sheet forming process). These methodologies involve prototype benches which have been built to reproduce contact conditions encountered in manufacturing plants by taking specimens and contactors from the real industrial workpieces and tools. The evaluation of the friction coefficient added to the fine analysis of the surfaces have helped us to better understand friction and wear during processes. These facilities have been settled by numerical simulation at meso and macro scales by means of finite element methods. So, this paper is the sum up of the output of these methodologies with a specific focus on wear and lubrication, at room and hot temperatures.