Ossmer, H.
Chluba, C.
Kauffmann-Weiss, S.
Quandt, E.
Kohl, M.
The global trend of miniaturization and concomitant increase of functionality in microelectronics, microoptics, and various other fields in microtechnology leads to an emerging demand for temperature control at small scales. In this realm, elastocaloric cooling is an interesting alternative to thermoelectrics due to the large latent heat and good down-scaling behavior. Here, we investigate the elastocaloric effect due to a stress-induced phase transformation in binary TiNi and quaternary TiNiCuCo films of 20 mu m thickness produced by DC magnetron sputtering. The mesoscale mechanical and thermal performance, as well as the fatigue behavior are studied by uniaxial tensile tests combined with infrared thermography and digital image correlation measurements. Binary films exhibit strong features of fatigue, involving a transition from Luders-like to homogeneous transformation behavior within three superelastic cycles. Quaternary films, in contrast, show stable Luders-like transformation without any signs of degradation. The elastocaloric temperature change under adiabatic conditions is -15 K and -12 K for TiNi and TiNiCuCo films, respectively. First-of-its-kind heat pump demonstrators are developed that make use of out-of-plane deflection of film bridges. Owing to their large surface-to-volume ratio, the demonstrators reveal rapid heat transfer. The TiNiCuCo-based devices, for instance, generate a temperature difference of 3.5 K within 13 s. The coefficients of performance of the demonstrators are about 3. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.
Gombert, A.
Graf, W.
Heinzel, A.
Joerger, R.
Kohl, M.
Weimar, U.
The optical constants of sputtered molybdenum layers and molybdenum/tin oxide cermets in the wavelength range 0.4-7 mum were determined by spectroscopic ellipsometry. The results were used for the evaluation of a suitable effective medium theory to describe cermets produced by a batch sputtering deposition system. In a following step, application of the effective medium theory to the refractive index of a cermet with low metal content allowed estimation of the optical constants of the embedded molybdenum particles
Speckmann, C.
Lehmberg, K.
Albert, M. H.
Damgaard, R. B.
Fritsch, M.
Gyrd-Hansen, M.
Rensing-Ehl, A.
Vraetz, T.
Grimbacher, B.
Salzer, U.
Fuchs, I.
Ufheil, H.
Belohradsky, B. H.
Hassan, A.
Cale, C. M.
Elawad, M.
Strahm, B.
Schibli, S.
Lauten, M.
Kohl, M.
Meerpohl, J. J.
Rodeck, B.
Kolb, R.
Eberl, W.
Soerensen, J.
von Bernuth, H.
Lorenz, M.
Schwarz, K.
zur Stadt, U.
Ehl, S.
X-linked inhibitor of apoptosis (XIAP) deficiency caused by mutations in BIRC4 was initially described in patients with X-linked lymphoproliferative syndrome (XLP) who had no mutations in SH2D1A. In the initial reports, EBV-associated hemophagocytic lymphohistiocytosis (HLH) was the predominant clinical phenotype. Among 25 symptomatic patients diagnosed with XIAP deficiency, we identified 17 patients who initially presented with manifestations other than HLH. These included Crohn-like bowel disease (n = 6), severe infectious mononucleosis (n = 4), isolated splenomegaly (n = 3), uveitis (n = 1), periodic fever (n = 1), fistulating skin abscesses (n = 1) and severe Giardia enteritis (n = 1). Subsequent manifestations included celiac-like disease, antibody deficiency, spienomegaly and partial HLH. Screening by flow cytometry identified 14 of 17 patients in our cohort. However, neither genotype nor protein expression nor results from cell death studies were clearly associated with the clinical phenotype. Only mutation analysis can reliably identify affected patients. XIAP deficiency must be considered in a wide range of clinical presentations. (C) 2013 Elsevier Inc. All rights reserved.
Ossmer, H.
Chluba, C.
Gueltig, M.
Quandt, E.
Kohl, M.
Strain and temperature profiles of magnetron-sputtered ferroelastic TiNi-based films of 20 mu m thickness are investigated during tensile load cycling with respect to strain, strain rate, and cycle number in order to assess their potential for elastocaloric cooling. Two different ferroelastic film specimens are considered, binary TiNi and quaternary TiNiCuCo films, which strongly differ regarding their phase transformation hysteresis and fatigue behavior. In situ digital image correlation and infrared thermography measurements reveal a correlated response of strain and temperature bands that is determined by mesoscale stress and temperature fields on the kinetics of phase transformation. In the case of binary TiNi films, this response is also strongly affected by cycling-induced fatigue causing vanishing band formation and decreasing elastocaloric effect size. In contrast, TiNiCuCo films show negligible fatigue and retain the local characteristics of the elastocaloric effect. Compared to TiNi films, they exhibit not only a reduced temperature change, but also a reduced work input for pseudoelastic cycling resulting in an improved material's coefficient of performance of 15.
The design of concrete members for shear without stirrups has become a major issue worldwide especially for bridge decks as the shear capacity according to the 'new' regulations like the Eurocode often gives significant smaller values than the one predicted by former codes. Therefore nowadays stirrups are required in bridge decks. In addition the safety of existing structures mainly build without shear reinforcement has been brought into focus. The lack of the available design models will be demonstrated by comparing the results of various codes. The inaccuracy of the EC2 approach is checked by means of a shear database. Experimental as well as numerical studies revealed that the shear capacity of haunched beams is different from members with constant height. It is questionable whether this behavior is caused by the vertical component of the inclined compression chord V-cc.
Glanzer, G.
Sivaraman, T.
Buffalo, J.I.
Kohl, M.
Berger, H.
Electric vehicles (EVs) are new type of additional load on the power grid. The change of the load profile depends on the penetration level of EVs as well as on the used charging strategies. State-of-the-art charging strategies such as dumb charging and dual tariff charging are not the appropriate solutions for charging EVs. Both strategies causes peak demands which could induce violations of the power grid constrains. Hence; smart charging is necessary to reduce peak demands and to realise valley-filling. Furthermore smart charging in many cases is based on a novel smart power grid infrastructure. The major objectives of smart charging are the minimisation of the electricity costs of consumers and the cost-efficient update of the power grid infrastructure. In addition; all EVs have to be equipped with a bidirectional on-board charger which enables vehicle-to-grid (V2G) capability. This type of charger consists of a combined AC/DC rectifier and DC/AC inverter. The most efficient solution is to integrate the charger in the already existing propulsion machine inverter. The major objectives of an integrated on-board charger are the minimisations of manufacturing costs; maintenance costs and weight of the EV. In this paper several smart charging strategies as well as charger topologies are presented and assessed.
Muehlbrandt, S.
Melikyan, A.
Harter, T.
Koehnle, K.
Muslija, A.
Vincze, P.
Wolf, S.
Jakobs, P.
Fedoryshyn, Y.
Freude, W.
Leuthold, J.
Koos, C.
Kohl, M.
Silicon-plasmonics enables the fabrication of active photonic circuits in CMOS technology with unprecedented operation speed and integration density. Regarding applications in chip-level optical interconnects, fast and efficient plasmonic photodetectors with ultrasmall footprints are of special interest. A particularly promising approach to silicon-plasmonic photodetection is based on internal photoemission (IPE), which exploits intrinsic absorption in plasmonic waveguides at the metal-dielectric interface. However, while IPE plasmonic photodetectors have already been demonstrated, their performance is still far below that of conventional high-speed photodiodes. In this paper, we demonstrate a novel class of IPE devices with performance parameters comparable to those of state-of-the-art photodiodes while maintaining footprints below 1 mu m(2). The structures are based on asymmetric metal-semiconductor-metal waveguides with a width of less than 75 nm. We measure record-high sensitivities of up to 0.12 A/W at a wavelength of 1550 nm. The detectors exhibit opto-electronic bandwidths of at least 40 GHz. We demonstrate reception of on-off keying data at rates of 40 Gbit/s. (C) 2016 Optical Society of America
A free-energy function is constructed, which couples strain and magnetic moments in ferromagnetic shape memory alloys. The associated Gibbs function is used to calculate time-dependent transition probabilities between martensite variants in a magnetic field under applied stress. By keeping track of the variant fractions, the evolution of strain and magnetization is determined. The simulation model is built in a finite element program for structural analysis, in order to simulate magnetic field-dependent strain and magnetization characteristics of a test actuator. The influence of material parameters and sample geometry is discussed.
Simon, F.
Kelsey, J.
Kohl, M.
Majka, R.
Plesko, M.
Sakuma, T.
Smirnov, N.
Spinka, H.
Surrow, B.
Underwood, D.
Three Gas-Electron-Multiplier (GEM) tracking detectors with an active area of 10 cm x 10 cm and a two-dimensional, laser-etched orthogonal strip readout have been tested extensively in particle beams at the Meson Test Beam Facility at Fermilab. These detectors used GEM foils produced by Tech-Etch, Inc. They showed an efficiency in excess of 95% and spatial resolution better than 70 pm. The influence of the angle of incidence of particles on efficiency and spatial resolution was studied in detail. (C) 2008 Elsevier B.V. All rights reserved.
Ossmer, H.
Chluba, C.
Krevet, B.
Quandt, E.
Rohde, M.
Kohl, M.
The elastocaloric effect in magnetron-sputtered Ni50.4Ti49.6 films of 20 mu m thickness is studied by means of uniaxial tensile tests and infrared thermography. For the investigated films, the usable quantity of latent heat is about 7.2 J/g. When relieving the stress after tensile loading and subsequent temperature equalization at strain rates larger than d epsilon/dt = 0.2 s(-1), a maximum temperature change of Delta T = -16 K is observed as expected for adiabatic conditions. Compared to bulk specimens, the heat transfer times are reduced to about 850 ms due to the larger surface-to-volume ratio, which is attractive for rapid cooling.