1,592 research outputs found
Ptychographic reconstruction of attosecond pulses
We demonstrate a new attosecond pulse reconstruction modality which uses an
algorithm that is derived from ptychography. In contrast to other methods,
energy and delay sampling are not correlated, and as a result, the number of
electron spectra to record is considerably smaller. Together with the robust
algorithm, this leads to a more precise and fast convergence of the
reconstruction.Comment: 12 pages, 7 figures, the MATLAB code for the method described in this
paper is freely available at
http://figshare.com/articles/attosecond_Extended_Ptychographyc_Iterative_Engine_ePIE_/160187
Chiral spin liquid and emergent anyons in a Kagome lattice Mott insulator
Topological phases in frustrated quantum spin systems have fascinated
researchers for decades. One of the earliest proposals for such a phase was the
chiral spin liquid put forward by Kalmeyer and Laughlin in 1987 as the bosonic
analogue of the fractional quantum Hall effect. Elusive for many years, recent
times have finally seen a number of models that realize this phase. However,
these models are somewhat artificial and unlikely to be found in realistic
materials. Here, we take an important step towards the goal of finding a chiral
spin liquid in nature by examining a physically motivated model for a Mott
insulator on the Kagome lattice with broken time-reversal symmetry. We first
provide a theoretical justification for the emergent chiral spin liquid phase
in terms of a network model perspective. We then present an unambiguous
numerical identification and characterization of the universal topological
properties of the phase, including ground state degeneracy, edge physics, and
anyonic bulk excitations, by using a variety of powerful numerical probes,
including the entanglement spectrum and modular transformations.Comment: 9 pages, 9 figures; partially supersedes arXiv:1303.696
Tunneling Time in Ultrafast Science is Real and Probabilistic
We compare the main competing theories of tunneling time against experimental
measurements using the attoclock in strong laser field ionization of helium
atoms. Refined attoclock measurements reveal a real and not instantaneous
tunneling delay time over a large intensity regime, using two different
experimental apparatus. Only two of the theoretical predictions are compatible
within our experimental error: the Larmor time, and the probability
distribution of tunneling times constructed using a Feynman Path Integral (FPI)
formulation. The latter better matches the observed qualitative change in
tunneling time over a wide intensity range, and predicts a broad tunneling time
distribution with a long tail. The implication of such a probability
distribution of tunneling times, as opposed to a distinct tunneling time,
challenges how valence electron dynamics are currently reconstructed in
attosecond science. It means that one must account for a significant
uncertainty as to when the hole dynamics begin to evolve.Comment: 11 pages, 4 figure
Daten in verteilten Systemen
Verteilte Systeme gewinnen zunehmend an Bedeutung für moderne
Anwendungen. Um sie geeignet unterstützen zu können, bedarf es
innovativer Mechanismen zur Fehlertoleranz, zur Integration von
Datenbanken und mobiler Teilnehmer sowie Basismechanismen zur
verteilten Einigung über Systementscheidungen. Diese Mechanismen
waren Gegenstand des Seminars "\u27Daten in verteilten Systemen"\u27, das
im Wintersemester 1994/95 am Institut für Telematik der Universität
Karlsruhe abgehalten wurde
High stability white light generation in water at multi-kilohertz repetition rate
Efficient supercontinuum (SC) generation featuring high spectral intensity
across a large bandwidth requires high peak powers of several megawatt from
pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition
rates, the SC generated in most materials is unstable due to thermal effects.
In this work, we leverage the superior dispersion properties of water to
maximize the spectral width of the SC, while avoiding stability issues due to
thermal loading by means of a constant laminar flow of the liquid. This flow is
controlled by a differential pressure scheme that allows to precisely adjust
the fluid velocity to an optimum value for maximum stability of the SC. This
approach is successfully implemented for repetition rates of 50 kHz and 100 kHz
and two different pump wavelengths in the visible (VIS) and near infrared (NIR)
spectral region with stability of the SC signal only limited by the driving
pulses. The resulting water SC spans more than one octave covering the VIS to
NIR range. Compared to established materials, such as yttrium aluminum garnet
(YAG) and sapphire, the spectral bandwidth is increased by 60 % and 40 %
respectively. Our scheme has the potential to be implemented with other liquids
such as bromine or carbon disulfide (CS2), which promise even wider broadening
and operation up to the mid-infrared
Improving MRO order processing by means of advanced technological diagnostics and data mining approaches
Production planning based on uncertain load information may lead to low schedule adherence or low capacity utilization. Thus, maintenance, repair and overhaul (MRO) service providers are striving to improve their business processes to achieve high logistics efficiency. To estimate repair expenditures and material demands as early as possible, different approaches may be pursued. In this paper, the advancement of technological diagnostics to enable condition assessment without prior disassembly and the use of data mining to generate reliable forecasts are discussed. Thereby, the potential for planning MRO order processing is focused using the example of aircraft engines and rail vehicle transformers
A minimally invasive multiple marker approach allows highly efficient detection of meningioma tumors
BACKGROUND: The development of effective frameworks that permit an accurate diagnosis of tumors, especially in their early stages, remains a grand challenge in the field of bioinformatics. Our approach uses statistical learning techniques applied to multiple antigen tumor antigen markers utilizing the immune system as a very sensitive marker of molecular pathological processes. For validation purposes we choose the intracranial meningioma tumors as model system since they occur very frequently, are mostly benign, and are genetically stable. RESULTS: A total of 183 blood samples from 93 meningioma patients (WHO stages I-III) and 90 healthy controls were screened for seroreactivity with a set of 57 meningioma-associated antigens. We tested several established statistical learning methods on the resulting reactivity patterns using 10-fold cross validation. The best performance was achieved by Naïve Bayes Classifiers. With this classification method, our framework, called Minimally Invasive Multiple Marker (MIMM) approach, yielded a specificity of 96.2%, a sensitivity of 84.5%, and an accuracy of 90.3%, the respective area under the ROC curve was 0.957. Detailed analysis revealed that prediction performs particularly well on low-grade (WHO I) tumors, consistent with our goal of early stage tumor detection. For these tumors the best classification result with a specificity of 97.5%, a sensitivity of 91.3%, an accuracy of 95.6%, and an area under the ROC curve of 0.971 was achieved using a set of 12 antigen markers only. This antigen set was detected by a subset selection method based on Mutual Information. Remarkably, our study proves that the inclusion of non-specific antigens, detected not only in tumor but also in normal sera, increases the performance significantly, since non-specific antigens contribute additional diagnostic information. CONCLUSION: Our approach offers the possibility to screen members of risk groups as a matter of routine such that tumors hopefully can be diagnosed immediately after their genesis. The early detection will finally result in a higher cure- and lower morbidity-rate
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