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Gearboxes of modern drivetrains, e.g., in wind turbines, can be exposed temporarily to low ambient temperatures during their manufacturing or during operation. During manufacturing or assembly, for example, very low temperatures sometimes occur during joining processes due to the cryogenic treatment of the components. In these cases, the temperature depends on the cooling medium used (typically dry ice or liquid nitrogen). Furthermore, depending on the application, gearboxes may be exposed to low ambient temperatures up to -60 °C when used in cold regions. The low temperatures can have an impact on the component properties and thus on the gear load carrying capacity. Therefore, the knowledge of these influences is very important regarding the design and dimensioning of gearboxes.

In gearboxes, rolling bearing power losses often make up a large amount of the total gearbox power losses. Therefore, an exact calculation of rolling bearing power losses is very important for resource and energy efficient gearbox design. The state of the art offers numerous friction calculation methods with different levels of detail to calculate power losses of rolling bearings. Bearing manufacturers like SKF and Schaeffler offer popular bearing-based/global calculation methods for standard rolling bearings. Contact-based/local calculation methods can consider a wider application field by generalization of tribological relations, which enables its application to e.g. hybrid bearings or non-standard bearings. The different methods may yield widely differing results. For its validation, measurement results are required. In this study, a broad comparison of calculation results with substantial measurement results is shown. Based on the validation a classification of the calculation methods is derived, which provides guidance for the design engineer to choose the appropriate method for the respective application. Contact-based/local calculation methods have the potential to predict friction in rolling bearings precisely.

In this paper a variant of eccentric drives will be described, which uses rolling elements instead of an eccentric gear. These rolling elements are constrained by a concentric carrier allowing for radial movement and are moved by an eccentric crank. They mesh with a gear geometry that translates their radial movement into tangential movement and constrains their position. Multiple offset eccentricities may be used with the same gear to reduce occurring forces. Such a drive may prove easier to manufacture than currently used eccentric drives, but the characteristics are not yet fully researched.

Im Rahmen dieser Veröffentlichung werden Ergebnisse experimenteller Untersuchungen an tauchgeschmierten Schneckengetrieben präsentiert. Ziel dieser Untersuchungen ist die experimentelle Bestimmung des Wärmestroms aus dem Zahnkontakt sowie die Evaliuerung der aktuell verwendeten rechnerischen Wärmestromaufteilung auf Basis der gemessenen Komponententemperaturen.

Due to increasing performance requirements and sometimes tribologically challenging operating conditions in gears (such as those found in wind turbines), alternative heat treatment processes to quenching and tempering or case hardening are becoming more and more important. Nitriding can significantly increase the load-carrying capacity of gears compared to the quenched and tempered initial state. The nitrided surface layer is characterized by a hard compound layer on the surface that is just a few micrometers thick and a diffusion zone that extends deeper into the material. The structure of the compound layer of iron and alloy element nitrides is primarily decisive for the wear behavior of nitrided components.

Gears made of polymers increasingly gain relevance in current research and industrial practice. Due to their advantages such as low density and the possibility of cost-efficient production in large quantities, more and more efforts are made to substitute steel gears with polymer wherever possible. However, the usage of polymer gears in current vehicle systems is still almost exclusively limited to applications with restricted power transmission, like actuators. To extend the field of application to power transmissions as well, in this study a transmission was developed for the usage in a small electric vehicle of the 7Le power class considering the application of polymer gears. Compared to the serial transmission, one of the gear stages was completely substituted with polymer gears. The load-carrying capacity of the newly designed hybrid polymer-steel transmission was investigated for functional verification on a specially developed test rig as well as inside a modified demonstrator vehicle under real-life conditions. Assuming usual operating conditions, the load-carrying capacity of the polymer gears appears suitable for the aimed application on the test rig as well as inside the demonstrator vehicle. Moreover, with increased power and under continuous sustained loading, high performance of the polymer stage as well as a stable temperature behavior can be observed. Under the given circumstances, polymer gears can be used as part of a powertrain in small electric vehicles.

Case hardening represents the most important heat treatment process to increase the load carrying capacity of gear components. Beside predominantly martensitic surface layers with low proportion of retained austenite, there were investigated material structures with differing properties in preceding research work.

Friction behavior is the key parameter for the design of automotive wet disk clutches. On the one hand, the Coefficient of Friction (CoF) level should be high to transmit torque efficiently. On the other hand, the clutch requires a positive slope of the CoF over sliding speed for good controllability, high comfort, and a low tendency to shudder. Clutches used in automatic or dual-clutch transmissions mostly use organic friction lining. These friction systems tend to have low CoF at low sliding speeds due to their high requirements regarding shifting comfort. Nevertheless, they show high values of CoF at high sliding speeds.

Highly stressed gears are usually manufactured from case hardening steels. The case hardening depth (CHD) has a significant influence on the tooth root load carrying capacity. For the materials 16MnCr5 and 20MnCr5, comprehensive investigations have been carried out in the past to determine the optimum case hardening depth up to size module mn= 10 mm on cylindrical spur gears. In certain applications, however, it may be necessary to select an increased CHD, e. g. to reduce the risk of tooth flank breakage. The question therefore arises as to what extent the available findings on the influence of the CHD on the tooth root load carrying capacity can also be transferred to materials of higher hardenability and larger sizes. For this purpose, several materials with different alloy systems and hardenabilities were examined under variation of the case hardening depth. In addition to extensive material characterization, pulsator tests were carried out to determine the tooth root load-carrying capacity on test gears of size mn= 12 mm. It is shown that the results obtained on MnCr steels up to size mn= 10 mm can in principle also be transferred to the variants investigated here.

The application of high-performance polymer gears in power transmissions is increasingly gaining focus in current research and industrial practice. The well-known advantages of thermoplastics such as cost-efficient production and low density compete with moderate strength and limited operating temperatures. However, the properties of thermoplastics can be used effectively to address the challenges of more efficient powertrains with higher power density, reduced fuel consumption, and reduced manufacturing costs. This work focuses on the implementation of high-performance polymer gears in the powertrain of a light electric vehicle. For demonstration purposes, a series transmission of a prototype of a light electric vehicle is modified and investigated considering the specific properties of polymers and steel materials. Due to its material properties, the high-performance polymer VESTAKEEP® 5000 G was used for the investigations. Different constructional modifications to the serial transmission as well as modifications of the micro geometry of the gears were applied to improve the load distribution and provide sufficient load carrying capacity to the polymer gears. Assuming usual driving cycles and lifetime, the calculations according to VDI 2736 [1] and RIKOR [2] indicate a sufficient load-carrying capacity for the polymer gears used inside. Under the given assumptions, the use of polymer gears in a powertrain of light electric vehicles appears to be possible.

Plastic gears and their numerous applications have become an integral part of industrial practice. In particular, the ability to produce large numbers of gears cost-effectively using injection molding techniques is making a significant contribution to growing market shares. Compared to conventional steel materials, however, the material properties of thermoplastics differ fundamentally. In particular, the high temperature dependence of the material properties and the lower strength pose challenges for designers. Against this background, theoretical and experimental studies on the operating and service life behavior of different thermoplastic materials have been conducted and evaluated. In addition to theoretical investigations on the tooth flank load carrying capacity, comprehensive measurements on temperature behavior were carried out and compared to common methods of temperature calculation for plastic gears. Experimental investigations on the tooth flank load capacity by means of back-to-back tests of different materials and their evaluation show the potential of thermoplastic materials for the application in power transmitting drivetrains. This contribution will give an overview of the performed research work and summarizes main results of these studies.

Due to their compactness and power density, planetary gearboxes are used for a wide range of high-performance applications in the automotive, aviation and marine sector. Aerospace applications in particular benefit from a full use of the load capacity potential to meet the requirements for lightweight construction and efficiency. Against this background, the load sharing between the individual planetary gears plays a decisive role. A uniform load sharing enables the design of the single tooth meshes without load increases and oversizing. However, due to manufacturing and assembly deviations, a perfect load sharing is technically not feasible. These load increases are taken into account in the standard calculation of the load capacity of planetary gearboxes by the mesh load factor Kγ. The load sharing in planetary gearboxes is influenced by a number of factors, such as the rigidity of shafts, housing and bearings, the number of planets, the quality of the gear wheels and the operating conditions. Detailed simulations or extensive experimental measurements are required to determine the exact load sharing. For new designs of planetary gearboxes, there are only simplified assumptions available, based on the number of planets and a rough estimation of the operating range. Especially additional dynamic forces, due to operation in high-speed ranges or near resonance frequencies, can lead to a considerable change of the dynamic load sharing compared to the static load sharing and cause an uncertainty in the design. Thus, in this paper the dynamic load sharing behaviour is investigated from 0 to 6800 rpm sun speed for different loads. Based on the experimental data recommendations for the design of planetary gearboxes under consideration of the operating conditions are derived.

In a previous publication, the influence of various process steps during the case-hardening process on the resulting material properties of two distinct batches of ultra-clean gear steels were investigated. The steel batches were case-hardened in the as-delivered condition. However, in the industrial practice it is common that pre-heat treatments are done, such as annealing to a ferritic-pearlitic microstructure, or quenching and tempering, as well as forging as a process if for example larger gears are needed. It is known that the whole heat treatment process route can affect the grain size negatively. Therefore, this publication presents investigations into the effects of preheat treatments on the grain size in the core region of ultra-clean gear steels after case-hardening. The aim is to receive a deeper understanding on how the whole process route influences the grain size in the core region of ultra-clean gear steels.

Power density demands for gearboxes are steadily increasing. Higher gear steel qualities can help to meet these demands. Steel manufacturer, as well as customers, usually examine the quality of gear steel batches. For this purpose, ultrasonic immersion testing is a fast and non-destructive evaluation method for the determination of the macroscopic degree of cleanliness. The evaluation follows certain standards and the common influence factors are usually well known. However, the state of knowledge shows that there are still many open questions. Some of these open questions can lead to differences between the results of different laboratories. In the framework of a research project, the macroscopic degree of cleanliness of ultra-clean gear steels had to be determined. However, first results showed significant differences between the results of the laboratories. For this reason, an interlaboratory test was initiated. The same samples were used for the characterizations at the different laboratories. The aim of the investigation was to determine the influencing factors that led to the different results. Based on the interlaboratory test, countermeasures should be defined to ensure a reliable determination of the macroscopic degree of cleanliness of (ultra-clean) gear steels and to ensure comparable results from different laboratories in the future.

Increasing the speed of the electric motor can significantly improve the power density of the powertrain of EVs (Electric Vehicles), resulting in a smaller size and thus weight and cost advantages. Achieving acceptable NVH behavior becomes more difficult at higher speeds, partly because the excitation frequencies of the gears cover a wider frequency range and therefore higher natural frequencies can also be directly excited. In the Speed4E joint research project, a high-speed electromechanical powertrain was developed, manufactured, and tested to investigate the main challenges on the NVH- and efficiency-behavior of high-speed powertrains. The high-speed design of the Speed4E drivetrain results in maximum electric motor speeds of up to 50,000 rpm, combined with a torque of up to 45 Nm at the transmission input shafts. This study presents the experimental results on the vibration behavior of the high-speed planetary gearbox, a comparison with the corresponding results of a highly efficient calculation method of the gearbox vibration excitation, and the theoretical background of the calculation method is presented. The results indicate the potential to improve the vibration behavior of high-speed drives in EVs and provide a deep understanding of the challenges associated with high speeds.

Fisheye failures due to non-metallic inclusions can lead to the reduced endurance fatigue limit of case-hardened, shot-peened gears. Various approaches for preventing crack initiation at non-metallic inclusions are conceivable. As one approach, steel manufacturers have invested much effort in the steelmaking process to produce ultra-clean gear steels. Such ultra-clean gear steels were investigated in a gear research project. For each steel batch, different measures were taken during steel production to avoid or bind off non-metallic inclusions in order to reduce or even suppress the harmful effect of the non-metallic inclusions. However, the influence of the measures taken on the chemical composition of non-metallic inclusions in such ultra-clean gear steels is not investigated in the gear industry in detail so far. Therefore, in the framework of this publication, the chemical composition of non-metallic inclusions in ultra-clean gear steels is investigated. Furthermore, a comparison of the chemical analysis with the crack-initiating inclusions from the experimental investigations is performed.

Surface hardening is an economical and technological alternative to case hardening, especially for larger gear sizes. Due to the high carburization depths required for case hardening with large component dimensions and technological limitations (e. g. furnace size), typical surface hardening processes such as flame or induction hardening show advantages here.

Demands on modern gearboxes are constantly increasing, for example to comply with lightweight design goals or new CO2thresholds. Normally, to increase performance requires making gearboxes and powertrains more robust. However, this increases the weight of a standard gearbox. The two trends therefore seem contradictory. To satisfy both of these goals, gears in gearboxes can be shot-peened to introduce high compressive residual stresses and improve their bending fatigue strength. To determine a gear’s tooth root bending fatigue strength, experiments are conducted up to a defined number of load cycles in the high cycle fatigue range. However, investigations of shot-peened gears have revealed tooth root fracture damage initiated at non-metallic inclusions in and above the very high cycle fatigue range. This means that a further reduction in bending load carrying capacity has to be expected at higher load cycles, something which is not covered under current standard testing conditions. The question is whether there is a significant decrease in the bending load carrying capacity and, also, if pulsating tests conducted at higher load cycles—or even tests on the FZG back-to-back test rig—are necessary to determine a proper endurance fatigue limit for shot-peened gears. This paper examines these questions.

Ein noch nicht übliches Verfahrenzum Einsatzhärten von z. B. Zahnrädern ist das Carbonitrieren. In der Vergangenheit wurde das Carbonitrieren vorwiegend zur Steigerung der Härtbarkeit von unlegierten Stählen, aber nicht zur gezielten Steigerung der Zahnradtragfähigkeit eingesetzt. Im Rahmen umfassender experimenteller sowie theoretischer Arbeiten wurde daher der Einfluss des Carbonitrierens auf die Tragfähigkeit von Zahnrädern untersucht. Hierzu wurden Stirnräder aus drei unterschiedlichen Einsatzstählen mit unterschiedlichen Wärmebehandlungsparametern carbonitriert und anschließend in Zahnradlauf- und Pulsatorversuchen systematisch geprüft. Dabei wurden die unterschiedlichen Hauptschadensarten von Zahnrädern (Zahnfußbruch, Grübchen, Verschleiß, Grauflecken und Fressen) analysiert, die Ergebnisse in Korrelation mit den erzeugten Gefügezuständen und Werkstoffeigenschaften weitergehend bewertet und die Ergebnisse in den Stand des Wissens eingeordnet. Der Artikel gibt einen Überblick über die maßgebenden Ergebnisse der Zahnradtragfähigkeitsuntersuchungen. ▪

Härte und Korngröße von Zahnrädern aus hochreinen Zahnradstählen nach Einsatzhärtung und Kugelstrahlen wurden im Rahmen eines Forschungsprojekts untersucht, dessen Schwerpunkt auf der Bestimmung der Zahnfußtragfähigkeit von einsatzgehärteten, kugelgestrahlten Zahnrädern lag. Die häufigste Versagensart bei diesen hochfesten Zahnrädern ist der Zahnfußbruch, der durch eine Rissinitiierung unterhalb der Oberfläche an einem nicht-metallischen Einschluss verursacht wird (Bruchlinsenversagen, im Englischen: Fisheye failure). Neben solchen Einschlüssen sind auch die Härte und die Abschreckkorngröße dafür bekannt, dass sie einen erheblichen Einfluss auf die Tragfähigkeit eines Zahnrades haben. Um sicherzustellen, dass in diesem Forschungsprojekt ausschließlich der Einfluss von nicht-metallischen Einschlüssen untersucht wird, mussten mögliche Quereinflüsse ausgeschlossen, minimiert oder zumindest bekannt sein. Nach einem ungeeigneten Einsatzhärtungsprozess erreichen Zahnräder jedoch nicht die härtebezogenen Spezifikationen, oder Zahnräder aus Zahnradstählen mit hoher Feinkornstabilität können Mengen an gröberen Körnern enthalten. Daher wurden Einsatzhärtungsparameter abgeleitet und überprüft, ob sie zu den für einsatzgehärtete Zahnradstähle geforderten Korngrößen- und Härtespezifikationen nach ISO 6336 führen. Weiterhin wurde untersucht, wie sich ein reduzierter Aluminiumgehalt bei resultierenden höheren Reinheitsgrad, d. h. kompensiert durch eine Nioblegierung zur Erhaltung der Feinkornstabilität, auf die Korngröße nach dem Einsatzhärten auswirkt.

Shot-peened, case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix. Here, the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye. This failure type can lead to a reduced endurance fatigue limit of the gears. It is for this reason that, over the last decade, much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation. These ultra-clean gear steels were achieved by various measures in the steel production process. However, as a result, the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location. However, due to the inhomogeneity of ultra-clean steels, the question arose if the values derived according to the standards are still representative of ultra-clean steel batches. The results show that the standards can still be applied, but more effort must be applied. To determine the degree of cleanliness, six microsections are currently evaluated according to steel test specification (SEP) 1571, method K. It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels. In addition, it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.

In the framework of a research project, the tooth root bending strength of high-strength gears is investigated. The most common type of failure encountered with these shot-peened, case-hardened gears is tooth root breakage caused by a crack initiation below the surface at a non-metallic inclusion (fisheye failure). However, it is well known that case-hardening depth and quenching grain size can have a great influence on a gear’s load carrying capacity. To ensure that this research project solely investigates the influence of non-metallic inclusions, any cross-influences must be excluded or minimized, or at least known. However, in the case of such ultra-clean gear steels, no recommendations or investigations of the influence of case-hardening on material properties are currently available. Therefore, in the framework of this paper, extended investigations are conducted into the effects of different process steps during case-hardening on the resulting material properties of ultra-clean gear steels.

Globalization and international supply chains constantly challenge gear- and steel manufacturers. In the case of large gear units in particular, expensive alloy contents have a direct impact on the material price. Steels with lower alloy contents and therefore cheaper steels are therefore becoming the focus of attention in order to further improve competitiveness. This article therefore compares two materials with different alloying elements and contents and thus different hardenability behaviour. For this purpose, extensive material characterizations as well as pulsator tests were carried out on case-hardened large gears. The aim of these tests was to determine the tooth root load-bearing capacity of the two material variants. Finally, the results are compared, discussed and recommendations for industrial application are derived, taking into account the hardenability of large gears. ◼

This paper contains parts of the research project FVA 612 and investigates the correlation between low-temperature treatments of case-hardened gears made from the material 18CrNiMo7-6 and the resulting surface hardness, retained austenite content, and residual stress condition. These parameters were further investigated with regard to the tooth root bending strength obtained with pulsating test rigs. The tested gears were subjected to various low-temperature treatments including different temperature levels before or after tempering. Other investigated parameters were the application of a shot blasting treatment and the effect of low-temperature treatments on gears with increased retained austenite content after the carburizing process.

In recent years, the computational fluid dynamics method has developed into very useful tools for investigating the oil flow and the no-load losses in geared transmissions. It has neither restriction on the housing shape nor limitations on the lubrication configuration. For this work, a computational fluid dynamics method model based on the finite volume method of a single-stage, injection-lubricated gearbox was built. The influence of different parameters including the injection volume, oil viscosity, and gear speed on the oil supply and distribution were investigated. The results also include a comparison of the simulated no-load losses with empirical no-load loss equations. This work provides first results on computational fluid dynamics method investigations of injection-lubricated geared transmissions and a starting point for comprehensive validation and more complex modeling.

The tooth normal force is one of the main influencing factors for calculating the pitting load-carrying capacity of gears. In the current standards for cylindrical gears, it is calculated without regard to the friction force’s influence. This paper presents a simple local calculation approach for determining the friction force and driving direction’s influence on the tooth normal force of cylindrical gears on the whole tooth flank. Unlike previous models, without the need to set up a dynamic model of the gear mesh and having to solve differential equations numerically. For two exemplary spur and one helical gear set, the tooth normal forces are calculated considering the friction force and the driving direction’s influence and without regard to these effects. A comparison is carried out and the results are discussed thoroughly.

Future trends indicate that the demands on bevel and hypoid gears for higher power transmission and lower weight are continuously increasing. Beside typical fatigue failures such as pitting, tooth root breakage, and tooth flank fracture, spontaneous failures such as scuffing are often observed if the load-carrying capacity of the tribological system consisting of gears and lubricant is exceeded. This paper gives an overview of the newest findings on scuffing specifically on bevel and hypoid gears and discusses the hypoid-specific decisive influence parameters. Furthermore, the newly developed calculation method as well as its verification with test results and results from field application are presented.

Demands for higher performance have caused a need for improved component characteristics, e.g. through surface strengthening of gears and increased cleanliness of gear steels. Unfortunately, a resultant drawback is that cracks in such high-strength gears are more often initiated in the material matrix at nonmetallic inclusions and not at the surface. In standardized calculation methods, the degree of cleanliness of steels is not yet directly correlated to the tooth root load-carrying capacity. This paper considers the effects of nonmetallic inclusions in the steel matrix on the tooth root strength based on the theoretical approach of Murakami.

This paper contains data of the research project FVA 293 III by Schurer et al. and investigates the tooth root bending strength and the fatigue fracture characteristics of case-carburized and shot-peened gears of different sizes. The investigated carburized and shot-peened gears are made out of high-purity steel batches of the materials 20MnCr5 and 18CrNiMo7-6. Three different gear sizes with the normal modules mn= 1.5, 5, and 10 mm are examined in pulsator test rigs. Additionally, gear running tests in the FZG back-to-back gear test rigs for the gear size mn= 1.5 are performed.

Time series of groundwater head measurements serve as a primary source of information on groundwater systems. In different groundwater systems, and across several scales, we observe a multitude of patterns in groundwater time series, resulting from complex hydrogeological setups. Unlike in surface hydrology, there is no generalized classification to categorize and quantify the dynamics in groundwater time series. This leads to a lack of tools that could help us disentangle the information contained in groundwater time series in a systematic way. To approach such a classification, we present a principle for organization to qualitatively describe and to quantify groundwater dynamics in a nonredundant and data efficient way. We devise a descriptive typology of groundwater dynamics and assign quantitative measures, mathematically expressing these dynamics. Based on an extensive data set of daily groundwater hydrographs from central Europe, we analyze the relationship between indices and typology based on principal component analysis. The principal component analysis is also used to investigate and discuss redundancy, that is, indices expressing similar information content of hydrographs. Further, the indices' sensitivity to measurement interval and length of the overall observed period is investigated. Finally, a case study demonstrates the potential of the typology and index approach to link groundwater dynamics to the underlying hydrogeological process controls. The tools provided for characterization and quantification of groundwater dynamics should improve future efforts of groundwater classification and prediction in ungauged aquifers and other applications. Features of groundwater level time series are organized conceptuallyQuantitative indices are assigned to the conceptual organization to characterize patterns in time seriesIndex sensitivity analysis and demonstration of the potential for groundwater classification

The topic of this study was subject to the efficiency calculation of gearboxes. Additional analyses were performed with regard to an existing calculation approach, to improve the calculation of load-dependent gear losses by so far disregarded influences. On the one hand, the influence of the driving direction was investigated. During this, the driving and driven test gears considered showed high differences of the specific sliding at tooth root and tooth tip. On the other hand, the influence of the change of contact ratio under load was studied. Both influences showed considerable influence on the load-dependent gear losses. An equation for an optimized calculation of the load-dependent gear losses is given.

Precipitation‐based drought indices are most commonly used in drought monitoring and early warning systems whereas impacts of drought are often related to other domains of the hydrological cycle such as streamflow. Precipitation droughts do not always coincide with streamflow droughts, as the propagation from precipitation to streamflow is affected by climate, catchment properties, and human influences. For monitoring in ungauged catchments it is the question to what extent drought indices solely based on precipitation or other (more recently developed) meteorological drought indices that include evaporation or snowmelt, have a stronger correlation with streamflow, and whether this correlation is weaker in catchments where streamflow is altered by human influences. Results of a correlation exercise between various meteorological drought indices and streamflow showed that the strongest correlation was often found for meteorological drought indices that include evaporation (especially in drier climates) or snow processes (especially in colder climates). Most catchments with an indicated presence of human influences showed a maximum correlation between meteorological drought indices and streamflow that was comparable in strength to the same correlation for catchments with near‐natural flow. However, up to 15% of catchments with an indicated presence of human influences show weaker correlations. Drought indices derived from these influenced records with a weaker correlation do not necessarily correspond to reported drought impacts. In conclusion, knowing which meteorological drought index has the strongest correlation with streamflow in different climate zones has the potential of improving large‐scale drought monitoring and early warning systems in ungauged areas or regions that lack real‐time streamflow availability. Meteorological drought indices that include evaporation or snowmelt are often strongly correlated with streamflowSome of the streamflow records potentially affected by human influences have a weaker correlation with meteorological drought indicesDrought indices derived from records with a weaker correlation caused by human influences often do not correspond with reported drought impacts

The first operating period of machine elements is subject to a running-in phase. Thereby, stresses applied on the contacting surfaces are influenced by the running-in conditions including the lubricant used and can strongly affect the frictional behavior and load-carrying capacity of lubricated contacts after running-in. This study investigates the influences of operating conditions and lubricant additives on the running-in behavior of lubricated line contacts of discs and gears. Results show a strong influence of the lubricant additive on the coefficient of friction during running-in as well as on the surface roughness and surface condition after running-in. The specific boundary friction power, supplemented by considering load carrying capacity limits, has been introduced as a criterion for defining the running-in conditions of gears.

Durch Nitrierenkann die Beanspruchbarkeit von Zahnrädern, insbesondere die Flanken- und Zahnfußtragfähigkeit, signifikant gesteigert werden. Die Dauerfestigkeit und damit die Lebensdauer nitrierter Bauteile steigen mit zunehmender Nitriertiefe, wobei die benötigte Nitriertiefe abhängig von der Größe der Verzahnung ist. In der Praxis wird eine Nitrierhärtetiefe (NHD bzw. Nht) von etwa 0,6 mm als Grenzwert angesehen, sodass mit zunehmender Größe der Verzahnung überwiegend das Einsatzhärten Anwendung findet. Beim Tiefnitrieren werden Nitrierhärtetiefen von etwa 0,8-1,0 mm angestrebt, daher ist durch diese Behandlung eine deutliche Steigerung der Belastbarkeit der nitrierten Zahnräder bei mittlerer und größerer Verzahnung zu erwarten. Tiefnitrierte Zahnräder bieten aufgrund der höheren Nitrierhärtetiefe im Vergleich zu konventionell nitrierten Zahnrädern ein besseres Tragfähigkeitsverhalten und sind auch für den Einsatz im Trockenlauf und bei Mangelschmierung sowie bei Einsatztemperaturen oberhalb der Anlasstemperatur des Einsatzhärtens geeignet. Wegen der im Vergleich zum Einsatzhärten geringeren Behandlungstemperaturen zum Erreichen vergleichbarer Härtetiefen müssen beim Tiefnitrieren lange Behandlungsdauern in Kauf genommen werden. Mithilfe von Kurzversuchen zum Anlass- und Nitrierverhalten verschiedener Stähle wurden werkstoffabhängig Prozesse zur Erzeugung hoher Nitrierhärtetiefen entwickelt. Dabei wurde auf eine mehrstufige Prozessgestaltung gesetzt, um die Verbindungsschichtdicke und die Veränderung der Festigkeit durch Anlasseffekte zu kontrollieren.

Industrial robots with middle or high loads are currently driven by gearboxes with cycloidal shaped gear toothing. The Gear Research Center (FZG) of the Technische Universität München analyzed in a project founded by the Bayerische Forschungsstiftung, if it is possible to meet the high demands of mechanical drive trains with involute toothing. Prototypes of such a gearbox have been built and successfully tested.

ZnO2nanoparticles have been synthesized by an organometallic precursor method. The structure, structural stability, and magnetic and optical properties of ZnO2nanoparticles have been investigated by experiments and first-principles calculations. It is found that ZnO2nanoparticles decompose into ZnO at about 230 °C and is stable up to 36 GPa at ambient temperature. The cubic ZnO2phase has a bulk modulus of B0= 174 GPa at zero pressure. Nanocrystalline ZnO2material is an indirect semiconductor with an energy gap of about 4.5 eV and paramagnetic down to 5 K.

This article has been officially withdrawn from the journal.

Background We demonstrate a method that includes colocalization studies to analyze cell suspensions after isolation and to characterize 3-dimensional grafts consisting of cells and matrix in vitro and in vivo.Materials and methods Neonatal rat cardiomyocytes were labelled by CFDA-SE after harvest. Cells in the isolated cell suspension, the embodied cells in the seeded scaffolds were characterized measuring features such as viability and distribution of the cell types.Results Selective cell count revealed high yields of viable cardiomyocytes. After seeding cells in collagen matrix, viability of the cells decreased gradually in the time process in vitro. Histology of implanted bioartificial myocardial tissue detected viable cardiomyocytes within the graft.Conclusion Using colocalization histology we could label and track cells within the bioartificial myocardial tissue graft in vitro and post implant and assess viability and distribution.

The SO2 oxidation catalyst solvent system Na2S2O7−K2S2O7 has been investigated by conductometric, calorimetric, and X-ray methods. The phase diagram has been constructed from the phase transition temperatures measured for totally 23 different compositions. The results agree well with previous thermal investigations. The phase diagram has been calculated from classical thermodynamics using all transition temperatures, the heat of liquid−liquid mixing obtained for 18 different compositions, and previously measured fundamental thermal data for liquid and solid Na2S2O7 and K2S2O7. The phase diagram exhibits two eutectics at XK2S2O7 equal to 0.4 (mp 615 K) and 0.6 (mp 613 K), respectively, and a maximum at XK2S2O7 = 0.5 (mp 619 K) corresponding to formation of the compound NaKS2O7. This was confirmed by XRD measurements and the crystal structure shown by Rietveld refinement to be triclinic, space group P-1, with a = 5.9050(1) Å, b = 7.2011(1) Å, c = 7.4190(1) Å, α = 101.707(1)°, β = 90.696(1)°, γ = 94.241(1)°, and Z = 2. The crystal structure of K2S2O7 was confirmed and the unknown structure of Na2S2O7 was similarly shown to be triclinic, space group P-1, with a = 6.8037(1) Å, b = 6.8265(1) Å, c = 6.7846(1) Å, α = 116.361(1)°, β = 95.959(1)°, γ = 84.194(1)°, and Z = 2. It could be excluded that the compound NaKS2O7 was a simple solid solution of the two compounds of the binary system. The measured conductivities in the liquid region of the 18 different compositions have been fitted to polynomials of the form k = A(X) + B(X)(T − Tm) + C(X)(T − Tm)², Tm = 693 K.

Review of the records of 678 children with acute injuries referred during an eight year period to this burn unit indicated that flame burns from a single ignition source (50%) outranked scalds (27%) or house fires (12%) as causes of injury. There was no temporal trend in the rank pattern. The majority of these single-source flame injuries were severe and involved ignition of the child's clothing. From 1969 through 1973, sleepwear was the clothing involved in 32% of the instances. Since that time and coincident with promulgation of strict federal and state standards for flammability of children's night clothing, a dramatic decline in the number of children referred with injuries of this type has taken place. It is probable that the single factor most important to the decline, in our experience with these injuries, is lower fabric flammability but, because our data may not be representative, corroboration is needed before one can exclude factors such as altered garment design, fire safety related practices at home, or changing patterns of hospital referral.

Experimental spinal cord trauma was produced in 3-month-old SS-1 minature pigs by dropping a 25 g weight from a height of 20 cm upon the exposed spinal cord. The histological lesion consisted of edema and hemorrhage. Phospholipid concentration and composition, cholesterol concentration and phospholipid fatty acid composition were determined in whole spinal cord 3 hours after injury, and in spinal cord myelin 5 hours after injury. Three hours after injury phospholipid and cholesterol concentration were decreased by about 14% in the whole spinal cord. Trauma had no effect on the phospholipid composition of whole spinal cord and myelin. Fatty acid composition of myelin also did not change after injury, and changed very slightly in the whole spinal cord. It is concluded that edema following spinal cord trauma is much more extensive than previously assumed. Furthermore, peroxidation of membrane lipid fatty acids does not appear to be a significant factor in spinal cord pathology 3 hours after injury.

HCG preparations from several commercial sources were tested for their ability to inhibit mitogen-induced lymphocyte blastogenesis. Proven biologically active preparations were found to vary widely in their ability to suppress PHA response, in their toxicity to lymphocytes, and in their anti-tryptic activity. Since high concentrations of a low toxicity, low trypsin inhibitor-containing preparation did not suppress blastogenesis, we conclude that previous reports of HCG being a potent inhibitor of CMI are erroneous and the effect observed by others probably due to contaminants of the HCG preparations used in their assay systems. Our findings cast doubt on the validity of the hypothesis that HCG is a potent inhibitor of CMI and therefore of importance in the role of maternal tolerance to the fetal allograft and in escape of HCG-secreting tumors from the host immune system.