33 research outputs found
Wettbewerb im Linienluftverkehr: Erste Erfahrungen mit der Deregulierung in den USA
This paper presents an analysis of the structural changes the US-airline industry experienced since deregulation of that industry in 1978. The impact of concentration on competition and prices is evaluated for different segments of the market. Finally, conclusions for the ongoing process of liberalization of air transport in Europe are explored
Skew-orthogonal polynomials in the complex plane and their Bergman-like kernels
Non-Hermitian random matrices with symplectic symmetry provide examples for
Pfaffian point processes in the complex plane. These point processes are
characterised by a matrix valued kernel of skew-orthogonal polynomials. We
develop their theory in providing an explicit construction of skew-orthogonal
polynomials in terms of orthogonal polynomials that satisfy a three-term
recurrence relation, for general weight functions in the complex plane. New
examples for symplectic ensembles are provided, based on recent developments in
orthogonal polynomials on planar domains or curves in the complex plane.
Furthermore, Bergman-like kernels of skew-orthogonal Hermite and Laguerre
polynomials are derived, from which the conjectured universality of the
elliptic symplectic Ginibre ensemble and its chiral partner follow in the limit
of strong non-Hermiticity at the origin. A Christoffel perturbation of
skew-orthogonal polynomials as it appears in applications to quantum field
theory is provided.Comment: 33 pages; v2: uniqueness of odd polynomials clarified, minor
correction
Universality in the number variance and counting statistics of the real and symplectic Ginibre ensemble
In this article, we compute and compare the statistics of the number of
eigenvalues in a centred disc of radius in all three Ginibre ensembles. We
determine the mean and variance as functions of in the vicinity of the
origin, where the real and symplectic ensembles exhibit respectively an
additional attraction to or repulsion from the real axis, leading to different
results. In the large radius limit, all three ensembles coincide and display a
universal bulk behaviour of for the mean, and for the variance.
We present detailed conjectures for the bulk and edge scaling behaviours of the
real Ginibre ensemble, having real and complex eigenvalues. For the symplectic
ensemble we can go beyond the Gaussian case (corresponding to the Ginibre
ensemble) and prove the universality of the full counting statistics both in
the bulk and at the edge of the spectrum for rotationally invariant potentials,
extending a recent work which considered the mean and the variance. This
statistical behaviour coincides with the universality class of the complex
Ginibre ensemble, which has been shown to be associated with the ground state
of non-interacting fermions in a two-dimensional rotating harmonic trap. All
our analytical results and conjectures are corroborated by numerical
simulations.Comment: 47 pages, 6 figures; v2 48 pages, 6 figures, references and
associated text adde
Structural and magnetic properties of Co-Mn-Sb thin films
Thin Co-Mn-Sb films of different compositions were investigated and utilized
as electrodes in alumina based magnetic tunnel junctions with CoFe counter
electrode. The preparation conditions were optimized with respect to magnetic
and structural properties. The Co-Mn-Sb/Al-O interface was analyzed by X-ray
absorption spectroscopy and magnetic circular dichroism with particular focus
on the element-specific magnetic moments. Co-Mn-Sb crystallizes in different
complex cubic structures depending on its composition. The magnetic moments of
Co and Mn are ferromagnetically coupled in all cases. A tunnel magneto
resistance ratio of up to 24 % at 13K was found and indicates that Co-Mn-Sb is
not a ferromagnetic half-metal. These results are compared to recent works on
the structure and predictions of the electronic properties.Comment: 8 pages, 9 figure
Insights into ultrafast demagnetization in pseudo-gap half metals
Interest in femtosecond demagnetization experiments was sparked by Bigot's
discovery in 1995. These experiments unveil the elementary mechanisms coupling
the electrons' temperature to their spin order. Even though first quantitative
models describing ultrafast demagnetization have just been published within the
past year, new calculations also suggest alternative mechanisms.
Simultaneously, the application of fast demagnetization experiments has been
demonstrated to provide key insight into technologically important systems such
as high spin polarization metals, and consequently there is broad interest in
further understanding the physics of these phenomena. To gain new and relevant
insights, we perform ultrafast optical pump-probe experiments to characterize
the demagnetization processes of highly spin-polarized magnetic thin films on a
femtosecond time scale. Previous studies have suggested shifting the Fermi
energy into the center of the gap by tuning the number of electrons and thereby
to study its influence on spin-flip processes. Here we show that choosing
isoelectronic Heusler compounds (Co2MnSi, Co2MnGe and Co2FeAl) allows us to
vary the degree of spin polarization between 60% and 86%. We explain this
behavior by considering the robustness of the gap against structural disorder.
Moreover, we observe that Co-Fe-based pseudo gap materials, such as partially
ordered Co-Fe-Ge alloys and also the well-known Co-Fe-B alloys, can reach
similar values of the spin polarization. By using the unique features of these
metals we vary the number of possible spin-flip channels, which allows us to
pinpoint and control the half metals electronic structure and its influence
onto the elementary mechanisms of ultrafast demagnetization.Comment: 17 pages, 4 figures, plus Supplementary Informatio
Seebeck Effect in Magnetic Tunnel Junctions
Creating temperature gradients in magnetic nanostructures has resulted in a
new research direction, i.e., the combination of magneto- and thermoelectric
effects. Here, we demonstrate the observation of one important effect of this
class: the magneto-Seebeck effect. It is observed when a magnetic configuration
changes the charge based Seebeck coefficient. In particular, the Seebeck
coefficient changes during the transition from a parallel to an antiparallel
magnetic configuration in a tunnel junction. In that respect, it is the analog
to the tunneling magnetoresistance. The Seebeck coefficients in parallel and
antiparallel configuration are in the order of the voltages known from the
charge-Seebeck effect. The size and sign of the effect can be controlled by the
composition of the electrodes' atomic layers adjacent to the barrier and the
temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which
results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to
the parallel direction close to the predicted value of -12.1 {\mu}V/K.Comment: 16 pages, 7 figures, 2 table
Validation of a palliative care outcome measurement tool supplemented by neurological symptoms (HOPE+): Identification of palliative concerns of neurological patients
Background:
There is growing interest to integrate palliative care and its structures into the care of neurological patients. However, in Germany there is no comprehensive assessment tool capturing the symptoms of patients with advanced neurological diseases.
Aim:
To validate a newly developed palliative care measurement tool based on an extension of the validated core documentation system Hospice and Palliative Care Evaluation considering additional neurological issues (HOPE+).
Design:
Prospective, observational study using HOPE+ and as external criteria, the Eastern Cooperative Oncology Group (ECOG) performance status and the 12 months “surprise” question (12-SQ) in a neurological population, and assessment for its construct validity and diagnostic accuracy.
Setting/participants:
All newly admitted patients to the Department of Neurorehabilitation, Dr. Becker Rhein-Sieg-Clinic aged 18–100 years (#DRKS00010947).
Results:
Data from 263 patients (63 ± 14 years of age) were analyzed. HOPE+ revealed a moderately correlated six-factor structure (r = –0.543–0.525). Correlation analysis to evaluate discriminant validity using ECOG as external criterion was high (rs(261) = 0.724, p < 0.001) and confirmed for severely affected patients by adding the 12-SQ (“No”-group: 48.00 ± 14.92 vs “Yes”-group: 18.67 ± 7.57, p < 0.009). Operating characteristics show satisfactory diagnostic accuracy (area under the curve: 0.746 ± 0.049, 95% confidence interval = 0.650–0.842).
Conclusion:
HOPE+ demonstrates promising psychometric properties. It helps to assess palliative care issues of patients in neurological settings and, in combination with the 12-SQ, conceivably conditions when to initiate the palliative care approach in a population underrepresented in palliative care structures so far
Congruence between NOTCH3 mutations and GOM in 131 CADASIL patients
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common hereditary subcortical vascular dementia. It is caused by mutations in NOTCH3 gene, which encodes a large transmembrane receptor Notch3. The key pathological finding is the accumulation of granular osmiophilic material (GOM), which contains extracellular domains of Notch3, on degenerating vascular smooth muscle cells (VSMCs). GOM has been considered specifically diagnostic for CADASIL, but the reports on the sensitivity of detecting GOM in patients’ skin biopsy have been contradictory. To solve this contradiction, we performed a retrospective investigation of 131 Finnish, Swedish and French CADASIL patients, who had been adequately examined for both NOTCH3 mutation and presence of GOM. The patients were examined according to the diagnostic practice in each country. NOTCH3 mutations were assessed by restriction enzyme analysis of specific mutations or by sequence analysis. Presence of GOM was examined by electron microscopy (EM) in skin biopsies. Biopsies of 26 mutation-negative relatives from CADASIL families served as the controls. GOM was detected in all 131 mutation positive patients. Altogether our patients had 34 different pathogenic mutations which included three novel point mutations (p.Cys67Ser, p.Cys251Tyr and p.Tyr1069Cys) and a novel duplication (p.Glu434_Leu436dup). The detection of GOM by EM in skin biopsies was a highly reliable diagnostic method: in this cohort the congruence between NOTCH3 mutations and presence of GOM was 100%. However, due to the retrospective nature of this study, exact figure for sensitivity cannot be determined, but it would require a prospective study to exclude possible selection bias. The identification of a pathogenic NOTCH3 mutation is an indisputable evidence for CADASIL, but demonstration of GOM provides a cost-effective guide for estimating how far one should proceed with the extensive search for a new or an uncommon mutations among the presently known over 170 different NOTCH3 gene defects. The diagnostic skin biopsy should include the border zone between deep dermis and upper subcutis, where small arterial vessels of correct size are located. Detection of GOM requires technically adequate biopsies and distinction of true GOM from fallacious deposits. If GOM is not found in the first vessel or biopsy, other vessels or additional biopsies should be examined
Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy: A Genetic Cause of Cerebral Small Vessel Disease
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a single-gene disorder of the cerebral small blood vessels caused by mutations in the Notch3 gene. The exact prevalence of this disorder was unknown currently, and the number of reported CADASIL families is steadily increasing as the clinical picture and diagnostic examinations are becoming more widely known. The main clinical manifestations are recurrent stroke, migraine, psychiatric symptoms, and progressive cognitive impairment. The clinical course of CADASIL is highly variable, even within families. The involvement of the anterior temporal lobe and the external capsule on brain magnetic resonance imaging was found to have high sensitivity and specificity in differentiating CADASIL from the much more common sporadic cerebral small-vessel disease (SVD). The pathologic hallmark of the disease is the presence of granular osmiophilic material in the walls of affected vessels. CADASIL is a prototype single-gene disorder that has evolved as a unique model for studying the mechanisms underlying cerebral SVD. At present, the incidence and prevalence of CADASIL seem to be underestimated due to limitations in clinical, neuroradiological, and genetic diagnoses of this disorder
Universal Scaling Limits of the Symplectic Elliptic Ginibre Ensemble
Ebke M. Universal Scaling Limits of the Symplectic Elliptic Ginibre Ensemble. Bielefeld: Universität Bielefeld; 2022.This thesis is concerned with eigenvalue statistics of non-Hermitian random matrices in the symplectic symmetry class. It contributes to the questions of how to compute the microscopic scaling limit and whether it is universal