Biomedical subjects

G Schmidt

Publications and source records attributed to G Schmidt.

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

Remanent zero field spin splitting of self-assembled quantum dots in a paramagnetic host.

We report on the observation of a finite spin splitting at zero magnetic field in resonant tunneling experiments on CdSe self-assembled quantum dots in a (Zn,Be,Mn)Se barrier. This is remarkable since bulk II-VI dilute magnetic semiconductors are paramagnets. Our experiment may be viewed as tunneling through a single magnetic polaron, where the carriers contained inside the dot act to mediate an effective ferromagnetic interaction between Mn ions in their vicinity. The effect is observable up to relatively high temperatures, which we tentatively ascribe to a feedback mechanism with the electrical current, previously predicted theoretically.

Journal Article↗

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↗

PubMed2006

Monitoring methods: SNAP.

The SNAP electroencephalogram (EEG) monitor, described as an interesting, innovative EEG tool that samples raw EEG signals and uses its own unique algorithm, analyses both high- (80-420 Hz) and low- (0-20 Hz) frequency components of the signal. This is termed the SNAP index, and it ranges from 100 (arbitrarily representing the fully awake state) to 0 to provide functional data points for patient management. The SNAP is the first commercial EEG-monitoring tool to use Personal Digital Assistant computer technology. The first version of SNAP index was introduced in 2002, and so far there has been little experience with the SNAP device reported in the literature. Compared with other EEG devices, there is no evidence that SNAP is superior to others in generating more specific information about 'depth of sedation'. Moreover, the influence of high-frequency electromyographic activity on the SNAP needs to be clarified.

Algorithms↗

PubMed2006

Endometrial safety, overall safety and tolerability of transdermal continuous combined hormone replacement therapy over 96 weeks: a randomized open-label study.

OBJECTIVES: To establish whether transdermal continuous hormone replacement therapy (HRT) with estrogen/progestogen provides adequate long-term endometrial protection in postmenopausal women over a period of 96 weeks. METHODS: This multicenter, randomized, open-label, parallel-group study evaluated the endometrial effects and overall safety and tolerability of a transdermal matrix patch delivering estradiol (E2) 50 microg/day and norethisterone acetate (NETA) 140 microg/day (Estalis; patches applied twice weekly without intermediate breaks) and a once-daily oral comparator (Kliogest; one tablet containing E2 2 mg/NETA 1 mg) in postmenopausal women. A total of 406 women with an intact uterus, aged 44-69 years, were randomized in the 48-week core phase of the study, and 239 continued into the 48-week extension phase. Subjects were randomized in the ratio 3 : 1 to transdermal or oral E2/NETA treatment. RESULTS: No cases of endometrial hyperplasia or endometrial cancer were reported with either treatment during the core or extension phase. Both treatments were generally well tolerated, with most adverse events (>90%) being mild to moderate, although minor differences in the tolerability profile were observed between treatments. CONCLUSIONS: Continuous combined transdermal HRT with E2/NETA shows no evidence of an increased endometrial hyperplasia or endometrial cancer risk over a 96-week period.

Administration, Cutaneous↗

PubMed2005

[Relationships between mental and cardiac diseases].

Affective and schizophrenic illnesses are associated with an elevated--in particular cardiovascular-related--risk of mortality. Patients with a cardiac disease who suffer from episodes of depression should be treated with selective serotonin reuptake inhibitors. Sertraline and citalopram have a low potential for interaction. Thioridazine, pimozid and ziprasidone are the substances that most commonly lead to lengthening of the QTc interval and thus to repolarization disorders. However, the results of studies carried out to date show that, in contrast to thioridazine and pimozid, ziprasidone has not so far been suspected of having an association with sudden heart death. Prior to starting treatment with tricyclic antidepressants or neuroleptics, a baseline ECG should be obtained. Follow-up ECG should be recorded and consideration given to possible drug interactions leading to cardiac arrhythmias, in particular when low-potency antipsychotics are used.

Controlled Clinical Trials as Topic↗

PubMed2005

Observation of giant magnetic linear dichroism in (Ga, Mn) As.

Giant magnetic linear dichroism (MLD) is observed in the ferromagnetic semiconductor Ga(0.98)Mn(0.02)As. The contribution to this effect induced by the spontaneous magnetization can be clearly identified by azimuthal dependencies. The spectral dependence of the effect in the range from 1.4 to 2.4 eV shows that the MLD induced by the spontaneous magnetization is strongly enhanced for excitations from the electronic states that are responsible for the ferromagnetism in this material. This spectral sensitivity and the size of the effect makes MLD a powerful tool for the study of (III, Mn)V alloys and similar novel ferromagnetic semiconductors.

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↗

PubMed2005

Direct percutaneous coronary intervention for NSTEMI in a patient with seropositive Wegener's granulomatosis.

A case of a 49-year-old man who presented with symptoms of generalized classical Wegener's granulomatosis with the exceptional complication of acute non-ST-elevation myocardial infarction (NSTEMI) is reported. Coronary arteriography revealed an extensive arteritis with multi-local stenosis of the left anterior descending coronary artery. The culprit lesion was treated by stent implantation with success while immunosuppressive treatment with cyclophosphamide and prednisolone was continued. Using arteriography, 4 months later we found normal coronary arteries without manifestation of vasculitis. Within 8 months of medical treatment complete remission was achieved and therapy was changed to low-dose methotrexate once a week. Meanwhile medical treatment has been stopped entirely. The patient is in good clinical condition. This case indicates that the adverse event of coronary vasculitis in any patient suffering from primary or secondary vasculitis can occur. Clinically significant myocardial ischemia can occur and can even lead to myocardial infarction.

Angioplasty, Balloon, Coronary↗

PubMed2005

Determining ecoregions for environmental and GMO monitoring networks.

A representative environmental monitoring network at the regional scale cannot use raster-based or random sampling designs, but requires a stratified sampling procedure integrating different information layers, and it has to occur in ecologically differing homogeneous regions (ecoregions). These we have determined using a set of spatial strata with ecological variables which we analysed with classification and regression trees (CART). We present a framework for environmental monitoring, that covers different scales, and we transfer the framework to a potential GMO (genetically modified organisms) monitoring network. We use ecoregion and other environmental strata together with existing environmental monitoring networks to determine GMO monitoring sites more precisely.

Agriculture↗

PubMed2005

[Soft-tissue coverage of the hand using the posterior interosseous artery flap].

UNLABELLED: Significant trauma, severe bacterial infections and tumour resections of the hand are often complicated by primary or secondary soft-tissue defects. The Posterior Interosseous Artery Flap (PIA), described by Zancolli and Angrigiani in 1985 offers one possibility for soft-tissue coverage. In this abstract, we present the results of 35 patients who were treated with distally based PIA flap reconstructions during the years 1998 to 2003. 24 patients were available for one-year follow-up and beyond. RESULTS: Long-term follow-up demonstrates excellent colour and texture match with reliable soft-tissue coverage. Two of the 33 flaps were lost because of ischemic necrosis. The incidence of distal local ischemia was predictable when the flaps were extended to the level of the PIP joint or beyond. CONCLUSION: The PIA flap affords a very durable and aesthetic option for soft-tissue coverage of the dorsum of the hand. The flap donor site can usually be closed primarily with little to no morbidity. In comparison to other local and distally based flaps such as the radial forearm flap, major blood vessels are spared. In summary, the PIA flap should be considered as a reliable and judicious alternative to free microvascular transfer procedures for soft-tissue defects of the hand proximal to the level of the PIP joint.

Adolescent↗

PubMed2005

[Heart and brain -- the influence of psychiatric disorders and their therapy on the heart rate variability].

Psychiatric disorders are associated with autonomic dys-regulations. There is evidence that these dys-regulations are partly responsible for the increased mortality in patients with psychiatric disorders. The determination of the heart rate variability (HRV) is a method easily applicable and allows the assessment of the autonomic control of the heart rate regulation. A multitude of HRV parameters with different physiological meanings have been introduced, the most widely used parameters are presented and characterized in this paper. Many studies have shown a reduced HRV in patients with major depression. Most studies found a reduced parasympathetic activity. However some authors discuss an elevated sympathetic activity. The magnitude of HRV reduction correlates to the severity of the depression. In patients with coronary diseases, major depression is an independent risk factor of mortality. Antidepressive therapy with serotonin reuptake inhibitors has failed to improve the prognosis of this patients. Patients with panic disorders also have a reduced HRV due to an elevated sympathetic control and reduced vagal control. In schizophrenic patients a reduced HRV was found in long term electrocardiogram recordings, whereas short term recordings did not show a reduced HRV. Patients with Alzheimer's disease also have a reduced HRV, which is limited to the low frequency component. Therapy with cholinesterase inhibitors further influences HRV by reducing the high frequency component and might increase the risk for arrhythmias. HRV analysis and integration in the assessment and monitoring of psychiatric patients before and during therapy elucidate the role of autonomic disturbances in such diseases and may help to optimize treatment.

Alzheimer Disease↗

PubMed2005

[Peroneal nerve palsy caused by a recurrent proximal tibiofibular joint ganglion--a case report and review of the literature].

PURPOSE/BACKGROUND: Compression of peripheral nerves is a well known complication of articular synovial cysts. The peroneal nerve is the most common site of intraneural ganglia (pseudocysts) originating from the proximal tibiofibular joint. The neurological deficit associated with these cysts is often severe due to delayed diagnostic and surgical treatment. Therefore, recurrence is very often seen and recovery is incomplete. MATERIAL AND METHODS: We report a case of a 60-year-old man with peroneal nerve palsy caused by recurrent proximal tibiofibular joint ganglion. RESULTS: Within the context of the current literature, clinical symptoms, diagnostics, differential diagnosis with regard to imaging methods, neurology, pathology and the broader spectrum of operative and non-operative treatment are discussed. The cyst was completely resected, but a recurrent cyst developed eight years later. At reoperation, a communication of the cyst with the tibiofibular joint was demonstrated. Despite complete resection of the cyst and ligation of the ganglion stem, a routine postoperative MRI disclosed a second recurrence of the cyst nine months later. On the last clinical examination, twelve years after onset of the symptoms, a complete paresis of the peroneal nerve was seen. CONCLUSION: This entity needs careful, prompt preoperative evaluation to avoid neurological damage. Surgical treatment includes microsurgical decompression and complete resection of the cyst and also ligation of the ganglion stem. Early diagnosis and treatment is required to ensure recovery.

Diagnosis, Differential↗

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↗

PubMed2004

The small GTPase Rac is involved in clustering of hippocampal neurons and fasciculation of their neurites.

In hippocampal neurons cultured from brains of newborn rats, the glutamate receptor agonist N-methyl-D-aspartate induced the clustering of neuronal perikarya and the fasciculation of neurites. In addition, N-methyl-D-aspartate activated the small GTPase Rac1. Other stimuli of Rac activity, such as the Rho kinase inhibitors Y-27632, H-1152, and H89, as well as the cytotoxic necrotizing factor-1 from Escherichia coli, also caused neuronal clustering and neurite bundling. In neurons transiently transfected with dominant negative Rac1N17 neither N-methyl-D-aspartate nor Y-27632 induced clustering and fasciculation. In addition, the PI3-kinase inhibitors wortmannin and LY-294002 prevented these effects, as did a dominant negative form of p110PI3-Kgamma. Time-lapse microscopy showed that lethal toxin from Clostridium sordellii, which inhibits Rac, and wortmannin blocked the neuronal migration induced by Y-27632. In contrast, only lethal toxin reversed the clustering and fasciculation induced by pre-treatment with Y-27632. This effect of the toxin may be due to inactivation of Ras, since FTI-277, which prevents the farnesylation of Ras and thereby inactivates the GTPase, also dissolved the preformed clusters. We suggest that active Rac and a PI3-kinase synergistically induce neuronal migration, whereas a Ras isoform is responsible for the lasting attachment of neurons necessary for clustering and neurite fasciculation.

Amides↗

PubMed2004

CNF and DNT.

The actin cytoskeleton of mammalian cells is involved in many processes that affect the growth and colonization of bacteria, such as migration of immune cells, phagocytosis by macrophages, secretion of cytokines, maintenance of epithelial barrier functions and others. With respect to these functions, it is not surprising that many bacterial protein toxins, which are important virulence factors and causative agents of human and/or animal diseases, target the actin cytoskeleton of the host. Some toxins target actin directly, such as the C2 toxin produced by Clostridium botulinum. Moreover, bacterial toxins target the cytoskeleton indirectly by modifying actin regulators such as the low-molecular-mass guanosine triphosphate (GTP)-binding proteins of the Rho family. Remarkably, toxins affect these GTPases in a bidirectional manner. Some toxins inhibit and some activate the GTPases. Here we review the Rho-activating toxins CNF1 and CNF2 (cytotoxic necrotizing factors) from Escherichia coli, the Yersinia CNF(Y) and the dermonecrotic toxin (DNT) from Bordetella species. We describe and compare their uptake into mammalian cells, mode of action, structure-function relationship, substrate specificity and role in diseases.

Amino Acid Sequence↗

PubMed2004

Shear-induced structure in polymer-clay nanocomposite solutions.

The equilibrium structure and shear response of model polymer-clay nanocomposite gels are measured using X-ray scattering, light scattering, optical microscopy, and rheometry. The suspensions form physical gels via the "bridging" of neighboring colloidal clay platelets by the polymer, with reversible adsorption of polymer segments onto the clay surface providing a short-range attractive force. As the flow disrupts this transient network, coupling between composition and stress leads to the formation of a macroscopic domain pattern, while the clay platelets orient with their surface normal parallel to the direction of vorticity. We discuss the shear-induced structure, steady-shear rheology, and oscillatory-shear response of these dynamic networks, and we offer a physical explanation for the mesoscale shear response. In contrast to flow-induced "banding" transitions, no stress plateau is observed in the region where macroscopic phase separation occurs. The observed platelet orientation is different from that reported for polymer-melt clay nanocomposites, which we attribute to effects associated with macroscopic phase separation under shear flow.

Journal Article↗

PubMed2004

Picosecond dynamics of the photoinduced spin polarization in epitaxial (Ga,Mn)as films.

Static and time-resolved magneto-optical spectra of the ferromagnetic semiconductor (Ga,Mn)As show that a pulsed photoexcitation with a fluence of 10 microJ/cm(2) is equivalent to the application of an external magnetic field of about 1 mT, which relaxes with a decay time of 30 ps. This relaxation is attributed to the spin relaxation of electrons in the conduction band and is found to be not affected by interactions with Mn ions.

Journal Article↗