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Institute
- Fakultät II - Maschinenbau und Bioverfahrenstechnik (105) (remove)
The use of vibrational sum-frequency spectroscopy (VSFS) to study transferred graphene, produced by chemical vapour deposition, is presented. The VSF spectrum shows a clear CeH stretching mode at ~2924 cm⁻¹, which is attributed to residue of the polymer used for the transfer. This makes VSFS a powerful tool to identify adsorbates and contaminants affecting the properties of graphene.
We report velocity-dependent internal energy distributions of nitric oxide molecules, NO, scattered off graphene supported on gold to further explore the dynamics of the collision process between NO radicals and graphene. These experiments were performed by directing a molecular beam of NO onto graphene in a surface-velocity map imaging setup, which allowed us to record internal energy distributions of the NO radicals as a function of their velocity. We do not observe bond formation but (1) major contributions from direct inelastic scattering and (2) a smaller trapping–desorption component where some physisorbed NO molecules have residence times on the order of microseconds. This is in agreement with our classical molecular dynamics simulations which also observe a small proportion of two- and multi-bounce collisions events but likewise a small proportion of NO radicals trapped at the surface for the entire length of the molecular dynamics simulations (a few picoseconds). Despite a collision energy of 0.31 eV, which would be sufficient to populate NO(v = 1), we do not detect vibrationally excited nitric oxide.
Worldwide, seagrass meadows are under threat. Consequently, there is a strong need for seagrass restoration to guarantee the provision of related ecosystem services such as nutrient cycling, carbon sequestration and habitat provision. Seagrass often grows in vast meadows in which the presence of seagrass itself leads to a reduction of hydrodynamic energy. By modifying the environment, seagrass thus serves as foundation species and ecosystem engineer improving habitat quality for itself and other species as well as positively affecting its own fitness. On the downside, this positive feedback mechanism can render natural recovery of vanished and destroyed seagrass meadows impossible. An innovative approach to promote positive feedback mechanisms in seagrass restoration is to create an artificial seagrass (ASG) that mimics the facilitation function of natural seagrass. ASG could provide a window of opportunity with respect to suitable hydrodynamic and light conditions as well as sediment stabilization to allow natural seagrass to re-establish. Here, we give an overview of challenges and open questions for the application of ASG to promote seagrass restoration based on experimental studies and restoration trials and we propose a general approach for the design of an ASG produced from biodegradable materials. Considering positive feedback mechanisms is crucial to support restoration attempts. ASG provides promising benefits when habitat conditions are too harsh for seagrass meadows to re-establish themselves.
We have combined the velocity map imaging technique with time-of-flight measurements to study the surface photochemistry of KBr single crystals. This approach yields 3-dimensional velocity distributions of Br atoms resulting from 193 nm photodesorption. The velocity distributions indicate that at least two non-thermal mechanisms contribute to the photodesorption dynamics. Our experimental geometry also allows us to measure the Br(²P₃⁄₂):Br(²P₁⁄₂) branching ratio, which is found to be 24:1.
Complexes like iron (II)-triazoles exhibit spin crossover behavior at ambient temperature and are often considered for possible application. In previous studies, we implemented complexes of this type into polymer nanofibers and first polymer-based optical waveguide sensor systems. In our current study, we synthesized complexes of this type, implemented them into polymers and obtained composites through drop casting and doctor blading. We present that a certain combination of polymer and complex can lead to composites with high potential for optical devices. For this purpose, we used two different complexes [Fe(atrz)3](2 ns)2 and [Fe(atrz)3]Cl1.5(BF4)0.5 with different polymers for each composite. We show through transmission measurements and UV/VIS spectroscopy that the optical properties of these composite materials can reversibly change due to the spin crossover effect.
The effects of surface temperature on the gas-liquid interfacial reaction dynamics of O(³P)+squalane
(2005)
OH/OD product state distributions arising from the reaction of gas-phase O(³P) atoms at the surface of the liquid hydrocarbon squalane C₃₀H₆₂/C₃₀D₆₂ have been measured. The O(³P) atoms were generated by 355 nm laser photolysis of NO₂ at a low pressure above the continually refreshed liquid. It has been shown unambiguously that the hydroxyl radicals detected by laser-induced fluorescence originate from the squalane surface. The gas-phase OH/OD rotational populations are found to be partially sensitive to the liquid temperature, but do not adapt to it completely. In addition, rotational temperatures for OH/OD(v′=1) are consistently colder (by 34±5 K) than those for OH/OD(v′=0). This is reminiscent of, but less pronounced than, a similar effect in the well-studied homogeneous gas-phase reaction of O(³P) with smaller hydrocarbons. We conclude that the rotational distributions are composed of two different components. One originates from a direct abstraction mechanism with product characteristics similar to those in the gas phase. The other is a trapping-desorption process yielding a thermal, Boltzmann-like distribution close to the surface temperature. This conclusion is consistent with that reached previously from independent measurements of OH product velocity distributions in complementary molecular-beam scattering experiments. It is further supported by the temporal profiles of OH/OD laser-induced fluorescence signals as a function of distance from the surface observed in the current experiments. The vibrational branching ratios for (v′=1)/(v′=0) for OH and OD have been found to be (0.07±0.02) and (0.30±0.10), respectively. The detection of vibrationally excited hydroxyl radicals suggests that secondary and/or tertiary hydrogen atoms may be accessible to the attacking oxygen atoms.
Background: The topographical correlations between certain extracranial and intracranial osseous points of interest (POIs), and their age-related changes, are indispensable to know for a diagnostical or surgical access to intracranial structures; however, they are difficult to assess with conventional devices.
Materials and methods: In this pilot study, the 3-dimensional coordinates of extra-/intracranial POIs were determined, thus avoiding perspective distortions that used to be intrinsic problems in 2-dimensional morphometry. The data sets were then analysed by creating virtual triangles. The sizes, shapes, and positions of these triangles described the extent and the directions of the age-related shifts of the POIs. A selection of extracranial and intracranial POIs were marked on half skulls of four warmblood horses in two age groups (young: 6 weeks, n = 2; old: 14 and 17 years, n = 2). The x-, y-, and z-coordinates of these POIs were determined with a measurement arm (FaroArm Fusion, FARO Europe®). Direct distances between the POIs as well as their indirect distances on the x-, y-, and z-axis, and angles were calculated.
Results: The analysed virtual triangles revealed that some parts of the skull grew in size, but did not change in shape/relative proportions (proportional type of growth, as displayed by POI A and POI B at the Arcus zygomaticus). The same POIs (A and B) remained in a very stable relationship to their closest intracranial POI at the Basis cranii on the longitudinal axis, however, shifted markedly in the dorso-lateral direction. In contrast, a disproportional growth of other parts of the cranium was, for example, related to POI C at the Crista nuchae, which shifted strongly in the caudal direction with age. A topographically stable reference point (so-called anchor point) at the Basis cranii was difficult to determine.
Conclusions: Two candidates (one at the Synchondrosis intersphenoidalis, another one at the Synchondrosis sphenooccipitalis) were relatively stable in their positions. However, the epicentre of (neuro-)cranial growth could only be pinpointed to an area between them.
The authors describe the application of a combination of velocity map imaging and time-of-flight (TOF) techniques to obtain three-dimensional velocity distributions for surface photodesorption. They have established a systematic alignment procedure to achieve correct and reproducible experimental conditions. It includes four steps: (1) optimization of the velocity map imaging ion optics’ voltages to achieve optimum velocity map imaging conditions; (2) alignment of the surface normal with the symmetry axis (ion flight axis) of the ion optics; (3) determination of TOF distance between the surface and the ionizing laser beam; (4) alignment of the position of the ionizing laser beam with respect to the ion optics. They applied this set of alignment procedures and then measured Br(²P₃/₂) (Br) and Br(²P₁/₂) (Br∗) atoms photodesorbing from a single crystal of KBr after exposure to 193 nm light. They analyzed the velocity flux and energy flux distributions for motion normal to the surface. The Br∗ normal energy distribution shows two clearly resolved peaks at approximately 0.017 and 0.39 eV, respectively. The former is slightly faster than expected for thermal desorption at the surface temperature and the latter is hyperthermal. The Br normal energy distribution shows a single broad peak that is likely composed of two hyperthermal components. The capability that surface three-dimensional velocity map imaging provides for measuring state-specific velocity distributions in all three dimensions separately and simultaneously for the products of surface photodesorption or surface reactions holds great promise to contribute to our understanding of these processes.
Surface atomic relaxation and magnetism on hydrogen-adsorbed Fe(110) surfaces from first principles
(2016)
We have computed adsorption energies, vibrational frequencies, surface relaxation and buckling for hydrogen adsorbed on a body-centred-cubic Fe(110) surface as a function of the degree of H coverage. This adsorption system is important in a variety of technological processes such as the hydrogen embrittlement in ferritic steels, which motivated this work, and the Haber–Bosch process. We employed spin-polarised density functional theory to optimise geometries of a six-layer Fe slab, followed by frozen mode finite displacement phonon calculations to compute Fe–H vibrational frequencies. We have found that the quasi-threefold (3f) site is the most stable adsorption site, with adsorption energies of ∼3.0 eV/H for all coverages studied. The long-bridge (lb) site, which is close in energy to the 3f site, is actually a transition state leading to the stable 3f site. The calculated harmonic vibrational frequencies collectively span from 730 to 1220 cm−1, for a range of coverages. The increased first-to-second layer spacing in the presence of adsorbed hydrogen, and the pronounced buckling observed in the Fe surface layer, may facilitate the diffusion of hydrogen atoms into the bulk, and therefore impact the early stages of hydrogen embrittlement in steels.
The ability to functionalize graphene with several methods, such as radical reactions, cycloadditions, hydrogenation, and oxidations, allows this material to be used in a large range of applications. In this framework, it is essential to be able to control the efficiency and stability of the functionalization process—this requires understanding how the graphene reactivity is affected by the environment, including the substrate. In this work we provide an insight on the substrate dependence of graphene reactivity towards hydrogenation by comparing three different substrates: silicon, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2). Although MoS2 and h-BN have flatter surfaces than silicon, we found that the H coverage of graphene on h-BN is about half of the H coverage on graphene on both silicon and MoS2. Therefore, graphene shows strongly reduced reactivity towards hydrogenation when placed on h-BN. The difference in hydrogenation reactivity between h-BN and MoS2 may indicate a stronger van der Waals force between graphene and h-BN, compared to MoS2, or may be related to the chemical properties of MoS2, which is a well-known catalyst for hydrogen evolution reactions.
A proven method to enhance the mechanical properties of additively manufactured plastic parts is the embedding of continuous fibers. Due to its great flexibility, continuous fiber-reinforced material extrusion allows fiber strands to be deposited along optimized paths. Nevertheless, the fibers have so far been embedded in the parts contour-based or on the basis of regular patterns. The outstanding strength and stiffness properties of the fibers in the longitudinal direction cannot be optimally utilized. Therefore, a method is proposed which allows to embed fibers along the principal stresses into the parts in a load-oriented manner. A G-code is generated from the calculated principal stress trajectories and the part geometry, which also takes into account the specific restrictions of the manufacturing technology used. A distinction is made between fiber paths and the matrix so that the average fiber volume content can be set in a defined way. To determine the mechanical properties, tensile and flexural tests are carried out on specimens consisting of carbon fiber-reinforced polyamide. In order to increase the influence of the principal stress-based fiber orientation, open-hole plates are used for the tensile tests, as this leads to variable stresses across the cross section. In addition, a digital image correlation system is used to determine the deformations during the mechanical tests. It was found that the peak load of the optimized open-hole plates was greater by a factor of 3 and the optimized flexural specimens by a factor of 1.9 than the comparison specimens with unidirectional fiber alignment.
Streptococcus dysgalactiae is among the most important pathogens causing bovine mastitis. Unfortunately, there is presently a lack of clear knowledge about the mode of transmission — contagious or environmental — of this pathogen. To obtain more information on this, knowledge of the genetic diversity of the isolated microorganisms at the farm level can be useful. To observe the strain variety in different herds of cattle, isolates of Strep. dysgalactiae were collected from clinical mastitis samples at different farms, and the strains were typed using the pulsed-field gel electrophoresis (PFGE) method. Overall, we performed strain typing on 93 isolates from 16 farms in Germany and used an index to describe the degree of contagiosity of Strep. dysgalactiae at each farm. This index (CI) represents the number of isolates divided by the number of strains found in mastitis milk of clinical cases within a period of 14 months. The results differed between the farms. In one farm, all six Strep. dysgalactiae cases that occurred during the study period were caused by a single strain (CI = 6), while in another farm the six cases that occurred were caused by five different strains (CI = 1.2). All other farms fell between these two extremes. This indicates that Strep. dysgalactiae infections can occur via several routes of transmission. At the farm level, strain comparisons are necessary to determine the routes of transmission. Two strains were able to survive on the farm for a minimum of 14 months.
To effectively prevent and control bovine mastitis, farmers and their advisors need to take infection pathways and durations into account. Still, studies exploring both aspects through molecular epidemiology with sampling of entire dairy cow herds over longer periods are scarce. Therefore, quarter foremilk samples were collected at 14-d intervals from all lactating dairy cows (n = 263) over 18 wk in one commercial dairy herd. Quarters were considered infected with Staphylococcus aureus, Streptococcus uberis, or Streptococcus dysgalactiae when ≥100 cfu/mL of the respective pathogen was detected, or with Staphylococcus epidermidis or Staphylococcus haemolyticus when ≥500 cfu/mL of the respective pathogen was detected. All isolates of the mentioned species underwent randomly amplified polymorphic DNA (RAPD)-PCR to explore strain diversity and to distinguish ongoing from new infections. Survival analysis was used to estimate infection durations. Five different strains of Staph. aureus were isolated, and the most prevalent strain caused more than 80% of all Staph. aureus infections (n = 46). In contrast, 46 Staph. epidermidis and 69 Staph. haemolyticus strains were isolated, and none of these caused infections in more than 2 different quarters. The 3 most dominant strains of Strep. dysgalactiae (7 strains) and Strep. uberis (18 strains) caused 81% of 33 and 49% of 37 infections in total, respectively. The estimated median infection duration for Staph. aureus was 80 d, and that for Staph. epidermidis and Staph. haemolyticus was 28 and 22 d, respectively. The probability of remaining infected with Strep. dysgalactiae or Strep. uberis for more than 84 and 70 d was 58.7 and 53.5%, respectively. Staphylococcus epidermidis and Staph. haemolyticus were not transmitted contagiously and the average infection durations were short, which brings into question whether antimicrobial treatment of intramammary infections with these organisms is justified. In contrast, infections with the other 3 pathogens lasted longer and largely originated from contagious transmission.
Staphylococcus aureus is recognized worldwide as one of the major agents of dairy cow intra-mammary infections. This microorganism can express a wide spectrum of pathogenic factors used to attach, colonize, invade and infect the host. The present study evaluated 120 isolates from eight different countries that were genotyped by RS-PCR and investigated for 26 different virulence factors to increase the knowledge on the circulating genetic lineages among the cow population with mastitis. New genotypes were observed for South African strains while for all the other countries new variants of existing genotypes were detected. For each country, a specific genotypic pattern was found. Among the virulence factors, fmtB, cna, clfA and leucocidins genes were the most frequent. The sea and sei genes were present in seven out of eight countries; seh showed high frequency in South American countries (Brazil, Colombia, Argentina), while sel was harboured especially in one Mediterranean country (Tunisia). The etb, seb and see genes were not detected in any of the isolates, while only two isolates were MRSA (Germany and Italy) confirming the low diffusion of methicillin resistance microorganism among bovine mastitis isolates. This work demonstrated the wide variety of S. aureus genotypes found in dairy cattle worldwide. This condition suggests that considering the region of interest might help to formulate strategies for reducing the infection spreading.
Compounds that exhibit the spin crossover effect are known to show a change of spin states through external stimuli. This reversible switching of spin states is accompanied by a change of the properties of the compound. Complexes, like iron (II)-triazole complexes, that exhibit this behavior at ambient temperature are often discussed for potential applications. In previous studies we synthesized iron (II)-triazole complexes and implemented them into electrospun nanofibers. We used Mössbauer spectroscopy in first studies to prove a successful implementation with maintaining spin crossover properties. Further studies from us showed that it is possible to use different electrospinning methods to either do a implementation or a deposition of the synthesized solid SCO material into or onto the polymer nanofibers. We now used a solvent in which both, the used iron (II)-triazole complex [Fe(atrz)3](2 ns)2 and three different polymers (Polyacrylonitrile, Polymethylmethacrylate and Polyvinylpyrrolidone), are soluble. This shall lead to a higher homogeneous distribution of the complex along the nanofibers. Mössbauer spectroscopy and other measurements are therefore in use to show a successful implementation without any significant changes to the complex.
The aim of this cross-sectional study was to investigate associated factors of the severity of clinical mastitis (CM). Milk samples of 249 cases of CM were microbiologically examined, of which 27.2% were mild, 38.5% moderate, and 34.3% severe mastitis. The samples were incubated aerobically and anaerobically to investigate the role of aerobic and anaerobic microorganisms. In addition, the pathogen shedding was quantitatively examined, and animal individual data, outside temperature and relative humidity, were collected to determine associated factors for the severity of CM. The pathogen isolated the most was Escherichia coli (35.2%), followed by Streptococcus spp. (16.4%). Non-aureus staphylococci (NaS) (15.4%) and other pathogens (e.g., Staphylococcus aureus, coryneforms) (15.4%) were the pathogens that were isolated the most for mild mastitis. Moderate mastitis was mostly caused by E. coli (38%). E. coli was also the most common pathogen in severe mastitis (50.6%), followed by Streptococcus spp. (16.4%), and Klebsiella spp. (10.3%). Obligate anaerobes (Clostridium spp.) were isolated in one case (0.4%) of moderate mastitis. The mortality rate (deceased or culled due to the mastitis in the following two weeks) was 34.5% for severe mastitis, 21.7% for moderate mastitis, and 4.4% for mild mastitis. The overall mortality rate of CM was 21.1%. The pathogen shedding (back logarithmized) was highest for severe mastitis (55,000 cfu/mL) and E. coli (91,200 cfu/mL). High pathogen shedding, low previous somatic cell count (SCC) before mastitis, high outside temperature, and high humidity were associated with severe courses of mastitis.
In this paper a new rotor position observer for permanent magnet synchronous machines (PMSM) based on an Extended-Kalman-Filter (EKF) is presented. With this method, just one single EKF is sufficent to evaluate the position information from electromotive force (EMF) and anisotropy. Thus, the PMSM can be controlled for the entire speed range without a position sensor and without the need to switch or synchronize between different observers. The approach covers online estimation of permanent magnetic field and mechanical load. The resulting EKF-based rotor position estimator is embedded in the existing cascaded control concept of the PMSM without need of additional angle trackers or signal filters. The experimental validation for the position sensorless control shows optimized dynamic behaviour.
To design cost-effective prevention strategies against mastitis in dairy cow farms, knowledge about infection pathways of causative pathogens is necessary. Therefore, we investigated the reservoirs of bacterial strains causing intramammary infections in one dairy cow herd. Quarter foremilk samples (n = 8056) and milking- and housing-related samples (n = 251; from drinking troughs, bedding material, walking areas, cow brushes, fly traps, milking liners, and milker gloves), were collected and examined using culture-based methods. Species were identified with MALDI-TOF MS, and selected Staphylococcus and Streptococcus spp. typed with randomly amplified polymorphic DNA-PCR. Staphylococci were isolated from all and streptococci from most investigated locations. However, only for Staphylococcus aureus, matching strain types (n = 2) were isolated from milk and milking-related samples (milking liners and milker gloves). Staphylococcus epidermidis and Staphylococcus haemolyticus showed a large genetic diversity without any matches of strain types from milk and other samples. Streptococcus uberis was the only Streptococcus spp. isolated from milk and milking- or housing-related samples. However, no matching strains were found. This study underlines the importance of measures preventing the spread of Staphylococcus aureus between quarters during milking.
Although Corynebacterium spp. can be regularly associated with subclinical and clinical mastitis cases in dairy cows, knowledge on their reservoirs in dairy farms is sparse. Therefore, samples were collected at 10 visits with 14 day intervals from bedding material (n = 50), drinking troughs (n = 20), different walking areas (n = 60), cow brushes (n = 8), fly traps (n = 4), the passage to pasture (n = 9) as well as milking liners (n = 80) and milker gloves (n = 20) in one dairy cow farm. Additionally, quarter foremilk samples from all lactating cows (approximately 200) were collected at each visit. All samples underwent microbiological examination and cultured isolates were identified using MALDI-TOF MS. Most Corynebacterium spp. that were cultivated from milk were also isolated from the housing environment and milking-related niches (C. amycolatum, C. confusum, C. stationis, C. variabile, C. xerosis) or from milking-related niches only (C. frankenforstense, C. pilosum, C. suicordis). C. bovis was not cultivated from any environmental niche, while being the dominant species in milk samples. This study demonstrates that many Corynebacterium spp. present in milk samples can also be isolated from the cows’ environment. For C. bovis, the most relevant Corynebacterium species with regard to intramammary infections, it indicates that environmental reservoirs are of little relevance.
During the transition from conventional towards purely electrical, sustainable mobility, transitional technologies play a major part in the task of increasing adaption rates and decreasing range anxiety. Developing new concepts to meet this challenge requires adaptive test benches, which can easily be modified e.g. when progressing from one stage of development to the next, but also meet certain sustainability demands themselves.
The system architecture presented in this paper is built around a service-oriented software layer, connecting a modular hardware layer for direct access to sensors and actuators to an extensible set of client tools. Providing flexibility, serviceability and ease of use, while maintaining a high level of reusability for its constituent components and providing features to reduce the required overall run time of the test benches, it can effectively decrease the CO2 emissions of the test bench while increasing its sustainability and efficiency.