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K Brunner

Publications and source records attributed to K Brunner.

At least 19 recordsLinked to original sources
PubMed2006

Magnetization-switched metal-insulator transition in a (Ga,Mn)as tunnel device.

We observe the occurrence of an Efros-Shklovskii gap in (Ga,Mn)As based tunnel junctions. The occurrence of the gap is controlled by the extent of the hole wave function on the Mn acceptor atoms. Using k.p-type calculations we show that this extent depends crucially on the direction of the magnetization in the (Ga,Mn)As (which has two almost equivalent easy axes). This implies one can reversibly tune the system into the insulating or metallic state by changing the magnetization.

Journal Article↗
PubMed2006

NMR in the SPINE Structural Proteomics project.

This paper describes the developments, role and contributions of the NMR spectroscopy groups in the Structural Proteomics In Europe (SPINE) consortium. Focusing on the development of high-throughput (HTP) pipelines for NMR structure determinations of proteins, all aspects from sample preparation, data acquisition, data processing, data analysis to structure determination have been improved with respect to sensitivity, automation, speed, robustness and validation. Specific highlights are protonless (13)C-direct detection methods and inferential structure determinations (ISD). In addition to technological improvements, these methods have been applied to deliver over 60 NMR structures of proteins, among which are five that failed to crystallize. The inclusion of NMR spectroscopy in structural proteomics pipelines improves the success rate for protein structure determinations.

Algorithms↗
PubMed2006

Circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots.

We report circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots. The polarization conversion occurs under continuous wave excitation in the absence of any magnetic field. The effect originates from quantum interference of linearly and circularly polarized photon states, induced by the natural anisotropic shape of the self-assembled dots. The behavior can be qualitatively explained in terms of a pseudospin formalism.

Journal Article↗
PubMed2005

Effects of triplet exciton confinement induced by reduced conjugation length in polyspirobifluorene copolymers.

Using gated optical spectroscopy at low temperatures, a polyspirobifluorene has been compared with an alternating carbazole-spirobifluorene copolymer in which the backbone conjugation is interrupted due to meta coupling of the carbazole moieties. In the copolymer both singlet and triplet energy levels are blueshifted by 130 meV with respect to the homopolymer, resulting in an unaltered singlet-to-triplet splitting. Though the barrier for triplet exciton migration increases from 4.4 to 6.0 meV for the copolymer compared to the homopolymer, it still remained low enough to ensure efficient triplet diffusion at ambient temperature.

Journal Article↗
PubMed2005

Very large tunneling anisotropic magnetoresistance of a (Ga,Mn)As/GaAs/(Ga,Mn)As stack.

We report the discovery of a very large tunneling anisotropic magnetoresistance in an epitaxially grown (Ga,Mn)As/GaAs/(Ga,Mn)As structure. The key novel spintronics features of this effect are as follows: (i) both normal and inverted spin-valve-like signals; (ii) a large nonhysteretic magnetoresistance for magnetic fields perpendicular to the interfaces; (iii) magnetization orientations for extremal resistance are, in general, not aligned with the magnetic easy and hard axis; (iv) enormous amplification of the effect at low bias and temperatures.

Journal Article↗
PubMed2004

Tunneling anisotropic magnetoresistance: a spin-valve-like tunnel magnetoresistance using a single magnetic layer.

We introduce a new class of spintronic devices in which a spin-valve-like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normal-metal-insulator-ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction and the two-step magnetization reversal process in this material.

Journal Article↗
PubMed2003

Electroluminescent device with reversible switching between red and green emission.

Research on new materials for organic electroluminescence has recently focused strongly on phosphorescent emitters, with the aim of increasing the emission efficiency and stability. Here we report the fabrication of a simple electroluminescent device, based on a semiconducting polymer combined with a phosphorescent complex, that shows fully reversible voltage-dependent switching between green and red light emission. The active material is made of a polyphenylenevinylene (PPV) derivative molecularly doped with a homogeneously dispersed dinuclear ruthenium complex, which fulfils the dual roles of triplet emitter and electron transfer mediator. At forward bias (+4 V), the excited state of the ruthenium compound is populated, and the characteristic red emission of the complex is observed. On reversing the bias (-4 V), the lowest excited singlet state of the polymer host is populated, with subsequent emission of green light. The mechanism for the formation of the excited state of the PPV derivative involves the ruthenium dinuclear complex in a stepwise electron transfer process that finally leads to efficient charge recombination reaction on the polymer.

Journal Article↗
PubMed2002

Identification of the N-acetyl-D-glucosamine-inducible element in the promoter of the Trichoderma atroviride nag1 gene encoding N-acetyl-glucosaminidase.

We have investigated the regulation by N-acetyl-glucosamine of the nag1 gene of the mycoparasitic biocontrol fungus Trichoderma atroviride (= T. harzianum P1), which encodes a 73-kDa N-acetyl-beta-D-glucosaminidase. The use of translational fusions revealed that a 290-bp fragment of the 5' regulatory region of nag1 is sufficient to confer inducibility on the Aspergillus niger goxA gene. The region between positions -150 and -290, upstream of the nag1 coding region, was investigated using in vivo methylation protection analysis and electrophoretic mobility shift assays (EMSAs). Two neighbouring regions that interacted with regulatory proteins were identified, and bases essential for these interactions were determined in vitro. These data reveal protein binding to a CCCCT element at -240, a CCAGN(13)CTGG motif at -284, and a CCAAT-box which is present in the spacer of the latter motif. Evidence for the binding of a Hap2/3/5 complex to this CCAAT motif is presented. Protein binding to all three motifs was constitutive, and no differences were observed between induced and non-induced cultures. Mutation of either the CCAGN(13)CTGG or the AGGGG motif resulted in loss of inducibility of nag1 expression by N-acetyl-D-glucosamine in vivo.

Acetylglucosamine↗
PubMed2001

Ultrafast dynamics of intersubband excitations in a quasi-two-dimensional hole gas.

We present the first study of ultrafast hole dynamics after resonant intersubband excitation in a quasi-two-dimensional semiconductor. p-type Si0.5Ge 0.5/Si multiple quantum wells are studied in pump-probe experiments with 150 fs midinfrared pulses. Intersubband scattering from the second heavy-hole back to the first heavy-hole subband occurs with a time constant of 250 fs, followed by intrasubband carrier heating within 1 ps. Such processes give rise to a strong reshaping of the intersubband absorption line, which is accounted for by calculations of the subband structure, optical spectra, and hole-phonon scattering rates.

Journal Article↗
PubMed2001

[Incidence, classification and therapy of isolated pelvic artery aneurysm].

INTRODUCTION: Isolated iliac artery aneurysms (IAA) are rare. The rupture risk, however, is high and the diagnosis can be difficult. The aim of this study was to report the frequency, morphology and outcome of these lesions. METHODS: Retrospective analysis of the medical data of all patients treated for IAA from 1990 to 1999. RESULTS: Fifty-nine consecutive patients, 55 (93%) male and 4 (7%) female, were included in the study. The median age was 68 (48-86) years. During the same time period, 741 consecutive patients with aortoiliac aneurysms were treated; thus the frequency of IAA was 8%. The median diameter of the IAA was 7 (3-12) cm. Most patients had at least one risk factor. IAA were unilateral in 40 (68%) or bilateral in 19 (32%) patients and affected the common iliac artery in 25 (19%), the internal iliac artery in 11 (19%) and simultaneously the common and internal iliac artery in 21 (36%) patients. Additional involvement of the external iliac artery was noted in 2 (3%) patients. Thirty-six (61%) patients with IAA underwent elective treatment while 23 (39%) patients had to be treated on an emergency basis. Endovascular stent grafts were inserted in 2 patients. Overall mortality was 10% (n = 6), 2.8% (n = 1) in asymptomatic and 22% (n = 5) in symptomatic or ruptured IAA. Overall morbidity in this study was 30%. The median follow-up of the patients was 36 (2-120) months. DISCUSSION: Surgical therapy in patients with asymptomatic IAA can be performed with a reasonable mortality. However, mortality and morbidity in patients with symptomatic or ruptured IAA remains high. Postoperative long-term results are excellent. The value of endovascular therapy for IAA has yet to be determined.

Aged↗
PubMed1998

Sensitivity of flavin fluorescence dynamics in neuronal nitric oxide synthase to cofactor-induced conformational changes and dimerization.

The fluorescence intensity of the two flavin prosthetic groups, FMN and FAD, in neuronal nitric oxide synthase (nNOS) was found to decay highly nonexponentially, being best described by four fluorescence lifetimes. This excited state heterogeneity is the result of multiple flavin quenching sites which are due to several flavin microenvironments created mainly by stacking with aromatic amino acids. Investigating nNOS in the absence of one or more of Ca2+/calmodulin, tetrahydrobiopterin, and heme revealed an influence of these cofactors on the microenvironments of the flavin prosthetic groups. Similar effects on the flavin rotational dynamics were found by analyzing the fluorescence anisotropy decay of the holo and of the different apo forms of nNOS. Since the tetrahydrobiopterin and the heme are located in the N-terminal oxygenase domain of nNOS, their effect on the flavins in the C-terminal reductase domain is explained by a folding back of the reductase domain onto the oxygenase domain. Thereby a domain-domain interface is created containing the FAD, FMN, heme, and tetrahydrobiopterin prosthetic groups which allows for efficient electron transfer during catalysis. The heme group, which is known to be essential for homodimerization of nNOS, was also found to be essential for the formation of the domain-domain interface.

Animals↗
PubMed1998

Augmented therapy of extensive Hodgkin's disease: radiation to known disease or prolongation of induction chemotherapy did not improve survival--results of a Cancer and Leukemia Group B study.

PURPOSE: This prospective randomized trial in extensive untreated Hodgkin's disease was undertaken to assess the potential benefit of augmented therapy (12 months chemotherapy or radiation to known disease) compared to standard 6 months chemotherapy. PATIENT AND METHODS: A total of 258 patients, mostly Stage IV, were randomized to four treatment regimens consisting of six cycles of CCNU, vinblastine, procarbazine, and prednisone (CVPP); 12 cycles of CVPP; six cycles of CVPP followed by 25 Gy radiotherapy; or three cycles CVPP, 25 Gy radiotherapy, and three cycles CVPP. RESULTS: Complete remissions were achieved in 65% of all patients. A 58% overall 5-year survival rate was obtained. Relapses in irradiated areas of known disease occurred in only 6% of responding patients. There was, however, no statistical difference in response frequency, disease-free survival, or overall survival among the four regimens. Elderly patients responded less frequently. CONCLUSION: While radiotherapy provided control of local (known) disease, no impact on overall survival was apparent. Likewise, doubling the duration of chemotherapy did not improve response or survival. Augmentation of therapy with either radiotherapy or more chemotherapy in this study was of no benefit compared to the standard 6 months of treatment.

Adult↗
PubMed1998

A neural network model for the emergence of grating cells.

A correlation-based learning (CBL) neural network model is proposed, which simulates the emergence of grating cells as well as some of their response characteristics to periodic pattern stimuli. These cells, found in areas V1 and V2 of the visual cortex of monkeys, respond vigorously and exclusively to bar gratings of a preferred orientation and periodicity. Their non-linear behaviour differentiates grating cells from other orientation-selective cells, which show linear spatial frequency filtering.

Animals↗
PubMed1998

Spectral analysis of electroencephalography changes after choking in judo (juji-jime).

PURPOSE: The present study was carried out to investigate possible electroencephalographic changes induced by choking in judo (shime-waza) by means of spectral analysis and brain mapping. METHODS: Power spectral changes in Electroencephalography (EEG) were recorded in six experienced judoka who underwent a choking trial with a "shime-waza choking" technique called juji-jime. RESULTS: A significant increase of global field power in the delta- and theta-range occurred, while physiological alpha-power decreased. These changes in the low-frequency range reached a statistically significant level within a time span up to 20 s after choking, which was performed at an average choking time of 8 s. In no case did choking provoke neuropsychological symptoms. Yet, spectral EEG-analysis revealed subclinical changes of brain function. CONCLUSIONS: Choking in judo may induce subclinical electroencephalographic perturbations. The extent and duration can be objectified by means of spectral analysis of EEG data, global field power computation, and brain-mapping representation.

Airway Obstruction↗