159 research outputs found
Influence of disorder on the structural phase transition and magnetic interactions in BaSrCrO
The spin dimer system is a
solid solution of the triplon Bose-Einstein condensation candidates
and . The magnetic intradimer
interaction constant in this spin system can be tuned by varying the Sr
content . Very interestingly, this variation of with is highly
nonlinear. In the present study, we show that this peculiar behavior of
can be only partly explained by the changes in the average crystal structure
alone. We report on neutron powder diffraction experiments to probe the
corresponding structural details. Performing extended H\"{u}ckel tight binding
calculations based on those structural details obtained at liquid helium
temperatures, we found that the change of the magnetic interaction constant can
be well reproduced by taking into account the presence of a structural
transition due to the Jahn-Teller active Cr-ions. This transition,
lifting the orbital degeneracy and thereby the magnetic frustration in the
system, is heavily influenced by disorder in the system arising from partially
exchanging Ba with Sr
Tuning the critical magnetic field of the triplon Bose-Einstein condensation in BaSrCrO
The structure and magnetic interactions of the triplon Bose-Einstein
condensation candidates BaCrO and SrCrO have been
studied thoroughly in the literature, but little is known about a possible
triplon condensation in the corresponding solid solution
BaSrCrO. We have prepared various members of this solid
solution and systematically examined their magnetic properties in high magnetic
fields up to 60 T and at low temperatures down to 340 mK, by means of pulsed
field and cantilever magnetometry. From these experiments for
, we find that the critical fields of
BaSrCrO decrease monotonically as a function of the Sr
content . This change is in good agreement with the earlier reported
variation of the magnetic interactions in these compounds
Structure and magnetic interactions in the solid solution Ba3-xSrxCr2O8
Solid solutions of the magnetic insulators Ba3Cr2O8 and Sr3Cr2O8
(Ba3-xSrxCr2O8) have been prepared in polycrystalline form for the first time.
Single crys- talline material was obtained using a mirror image floating zone
technique. X-ray diffraction data taken at room temperature indicate that the
space group of Ba3-xSrxCr2O8 remains unchanged for all values of x, while the
cell parameters depend on the chemical composition, as expected. Magnetization
data, measured from 300 K down to 2 K, suggests that the interaction constant
Jd within the Cr5+ dimers varies in a peculiar way as a function of x, starting
at Jd = 25K for x = 0, then first slightly dropping to Jd = 18K for x = 0.75,
before reaching Jd = 62K for x = 3
Condition monitoring of machines by tapping data from existing sensors and retrofitting simple energy measurement technology to existing machines
The average metal and mechanical engineering company must spend around two per cent of its annual turnover on electricity and natural gas, and companies are expecting
further price increases. As a result, the issue of energy saving is becoming more of a strategic factor than ever before. In order to save costs and ensure competitive
advantages, it is necessary to introduce precise energy-saving measures. The first steps taken by most mechanical engineering companies are to replace lighting, heating, and ventilation systems, improve compressed air generation and raise employee awareness. However, there is also a great potential for optimization in machines with their individual electrical drives, fans, and units. In this case, though, it is necessary to look at the machine and its processes as a whole rather than the individual electrical energy consumers. In most cases, however, there is a lack of suitable interfaces for analyzing the measured values from sensors (e.g. temperature, pressure sensors, etc.) and drives, which concludes that this potential is not fully exploited
Pupillometry examinations of the human eye with the eye diagnostic device PEP-2000 - first results
Pupillometry forms the diagnostic basis for numerous pathologies of the eye. For this reason, fast and accurate diagnostics in the field of ophthalmology are essential. Two examination techniques, full-field ERG and pupillometry were combined in a diagnostic device developed by ICM e.V. to reduce the examination process for both examiners and patients. In this paper, the device is examined for the quality of the pupillometry measurements. A study with 12 healthy subjects (3 f, 9 m, 36.33 ± 11.94 years) was conducted to evaluate the device. The results showed that the minimal pupil diameter is 40 % higher than the literature values. The main reason for the differences is the low light intensity of 15 cd/m2. However, the maximum pupil diameter is within the range of the researched values. The results of the pupillary reaction measurements show that the values obtained (amplitude, contraction time and peak time) are within the range of literature values. The latency time of 690 ms is 40 % too high. The reason for this could be the moderate pupil detection rate of 50-70 %. Nevertheless, plausible and comparable analysis values could be obtained with the eye diagnostic device PEP-2000. Further work will look at improving pupil detection rates
Full-field electroretinography examinations of the human eye with the eye diagnostic device PEP-2000 - first results
Full-field electroretinography (full-field ERG) forms the diagnostic basis for numerous pathologies of the eye. For this reason, fast and accurate diagnostics in the field of ophthalmology are essential. Two examination techniques, full-field ERG and pupillometry were combined in a diagnostic device developed by ICM e.V. to reduce the examination process for both examiners and patients. In this paper, the device is examined for the quality of the full-field ERG measurements. A feasibility study with 12 healthy subjects (3 f, 9 m, 36.33 ± 11.94 years) was conducted to evaluate the device. The results showed that the peak times for both light- and dark-adapted measurements were within the range of the researched literature values. However, the amplitudes were markedly lower in both measurements compared to the averaged literature values (dark-adapted about 8.5-fold and light-adapted about 5.5-fold) and are clearly outside the range of values researched. The main reason for this is the use of cup electrodes, which were placed on the skin of the lower eyelid. Nevertheless, plausible and comparable analysis values could be obtained with the eye diagnostic device PEP-2000. Further studies with wire electrodes will be performed
Zustandsüberwachung von Maschinen durch Datenabgriff an bestehender Sensorik und Nachrüstung einfacher Energiemesstechnik an Bestandsmaschinen
Metall- und Maschinenbauunternehmen müssen im Durchschnitt pro Jahr ca. zwei Prozent ihres Umsatzes für Strom und Erdgas ausgeben und die Unternehmer gehen
von weiteren Preissteigerungen aus. Damit rückt das Thema Energieeinsparung stärker denn je in den Fokus und wird zu einem strategischen Faktor. Um Kosten zu sparen und Wettbewerbsvorteile zu sichern, ist es notwendig, zielgenaue Energieeinsparmaßnahmen einzuleiten. Die ersten Maßnahmen, welche die meisten Maschinenbauunternehmen umsetzen, sind die Erneuerung der Beleuchtungs-, Heizungs- und Lüftungsanlage, die Verbesserung der Drucklufterzeugung sowie die thematische Sensibilisierung der Mitarbeiter. Aber auch in Maschinen mit ihren dazugehörigen elektrischen Antrieben, Lüftern und Aggregaten verbirgt sich eine große Menge an Optimierungspotenzial. Allerdings ist es hier notwendig nicht die Verbraucher im Einzelnen, sondern die Maschine und deren Prozesse im Ganzen zu betrachten. Meist fehlen hierfür aber geeignete Schnittstellen, um die Messwerte von Sensoren (bspw. Temperatur-, Drucksensoren, etc.) und Antrieben auslesen zu können, was dazu führt, dass diese Potenziale nicht ausgeschöpft werden
Towards analyzing the influence of measurement errors in magnetic resonance imaging of fluid flows : development of an interval-based iteration approach
Magnetic Resonance Imaging (MRI) provides an insight into opaque structures and does not only have a large number of applications in the field of medical examinations but also in the field of engineering. In technical applications, MRI enables a contactless measurement of the two- or threedimensional velocity field within minutes. However, various measurement methods would benefit from an acceleration of the measurement procedure. Compressed Sensing is a promising method to fit this need. A random undersampling of the sampled data points enables a significant reduction of acquisition time. As this method requires a nonlinear iterative reconstruction of unmeasured data to obtain the same data quality as for a conventional fully sampled measurement, it is essential to estimate the influence of uncertainty on the quantitative result. This paper investigates the implementation of interval arithmetic approaches with a focus on the applicability in the frame of compressed sensing techniques. These approaches are able to handle bounded uncertainty not only in the case of linear relationships between measured data and the computed outputs but also allow for solving the necessary optimality criteria for the fluid velocity reconstruction in an iterative manner under the assumption of set-valued measurement errors and bounded representations of noise
Chiral photoelectron angular distributions from ionization of achiral atomic and molecular species
We show that the combination of two achiral components - atomic or molecular
target plus a circularly polarized photon - can yield chirally structured
photoelectron angular distributions. For photoionization of CO, the angular
distribution of carbon K-shell photoelectrons is chiral when the molecular axis
is neither perpendicular nor (anti-)parallel to the light propagation axis. In
photo-double-ionization of He, the distribution of one electron is chiral, if
the other electron is oriented like the molecular axis in the former case and
if the electrons are distinguishable by their energy. In both scenarios, the
circularly polarized photon defines a plane with a sense of rotation and an
additional axis is defined by the CO molecule or one electron. This is
sufficient to establish an unambiguous coordinate frame of well-defined
handedness. To produce a chirally structured electron angular distribution,
such a coordinate frame is necessary, but not sufficient. We show that
additional electron-electron interaction or scattering processes are needed to
create the chiral angular distribution
Photo-enhanced magnetization in Fe-doped ZnO nanowires
An emerging branch of electronics, the optospintronics, would be highly boosted if the control of
magnetic order by light is implemented in magnetic semiconductors’ nanostructures being
compatible with the actual technology. Here, we show that the ferromagnetic magnetization of low
Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to
temperatures slightly below room temperature. This enhancement is related to the existence of an
oxygen vacancy VO in the neighborhood of an antiferromagnetic superexchange Fe3+-Fe3+ pair.
Under illumination, the VO is ionized to to V+O giving an electron to a closeFe3+ ion from the antiferromagnetic
pair. This light excited electron transition allows the transition of Fe3+ to Fe2+ forming
stable ferromagnetic double exchange pairs, increasing the total magnetization. The results presented
here indicate an efficient way to influence the magnetic properties of ZnO based nanostructures
by light illumination at high temperatures
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