Coupled atomistic spin-lattice simulations of ultrafast demagnetization in 3d ferromagnets

Despite decades of research, the role of the lattice and its coupling to the magnetisation during ultrafast demagnetisation processes is still not fully understood. Here we report on studies of both explicit and implicit lattice effects on laser induced ultrafast demagnetisation of bcc Fe and fcc Co. We do this using atomistic spin- and lattice dynamics simulations following a heat-conserving three-temperature model. We show that this type of Langevin-based simulation is able to reproduce observed trends of the ultrafast magnetization dynamics of fcc Co and bcc Fe. The parameters used in our models are all obtained from electronic structure theory, with the exception of the lattice dynamics damping term, where a range of parameters were investigated. It was found that while the explicit spin-lattice coupling in the studied systems does not impact the demagnetisation process notably, the lattice damping has a large influence on the details of the magnetization dynamics. The dynamics of Fe and Co following the absorption of a femtosecond laser pulse are compared with previous results for Ni and similarities and differences in the materials' behavior are analysed. For all elements investigated so far with this model, we obtain a linear relationship between the value of the maximally demagnetized state and the fluence of the laser pulse , which is in agreement with experiments. Moreover, we demonstrate that the demagnetization amplitude is largest for Ni and smallest for Co. This holds over a wide range of the reported electron-phonon couplings, and this demagnetization trend is in agreement with recent experiments.

A new African species of parasitic Dero (Annelida, Clitellata, Naididae) in the urinary tract of reed frogs

A new species of naidid oligochaete, Dero rwandae, detected in the bladder and the Wolffian ducts of reed frogs Hyperolius kivuensis from Rwanda, is described. Until now, D. bauchiensis was the only endoparasitic Dero known to infect African frogs infesting the eyes and Harderian glands. To the best of our knowledge, the finding of D. rwandae is the first record of an African Dero species infecting the urinary tract of anurans. In general morphology, the two African Dero parasites resemble each other, but differences in the features of ventral setae morphology exist. Parts of the mitochondrial 16S rRNA locus and the nuclear 18S and 28S rRNA loci were sequenced to assess the phylogenetic relationships to other Dero spp. Among those few species, that are barcoded so far, the closest relative of the new taxon is D. superterrenus, a free-living South American species. The species groups formerly termed subgenera Allodero, Aulophorus and Dero within the genus Dero do not represent distinct evolutionary lineages and the genus is paraphyletic including Branchiodrilus.

Development and Initial in Vivo Testing of a New Hydraulic Drive System (Paedipump) for Circulatory Support in Infants

The main limitation in the use of circulatory support in children is the lack of an adequate system with regard to size and pumping capacity Recently, two pneumatically driven ventricular support systems with low volume chambers for use in a pediatric population became available. We have developed a hydraulic drive system with an advantageous exact control of the stroke volume. The system enables two different modes of operation: the full-empty and the filled-empty modes. In both cases the ventricle is empty at the end of systole.

This new system was tested in experimental animals (6 pigs, body weight 9.5–14.0 kg) with normal and reduced left ventricular function (MAP<45 mmHg). A 25 ml ventricle (HIA-Medos) was implanted. The full-empty and the filled-empty mode used led to a significant load reduction, both in animals with normal and impaired cardiac function. Plasma lactate levels, pH-values and total body 0 2 consumption were in the normal range during circulatory support indicating adequate organ perfusion.

Results showed that sufficient ventricular support was achieved during all pumping modes due to the possibility of controlling and modifying the stroke volume of the hydraulically driven support system employed according to necessity. This is a promising feature for its future application in infants with congenital or acquired heart diseases.

An extraordinary endocytobiont in Acanthamoeba sp. isolated from a patient with keratitis

In the present article, the detection and the development of a parasitic endocytobiont within host amoebae (Acanthamoeba sp.) recently isolated from the contact lens and the inflamed eye of a patient with keratitis is presented. An otherwise healthy 55-year-old female patient presented with keratitis in her inflamed left eye. She was a contact lens wearer and had no history of a corneal trauma. Acanthamoebae as well as other smaller free-living amoebae could be detected from the fluid of the contact lens storage cases by culture methods. A successful therapy could be provided consequently. Two of these Acanthamoeba strains showed intracellular aggregating organisms. Within 2 to 3 days, the host amoebae ruptured, and numerous microorganisms were released. We succeeded in detecting the mechanism of infection and intrusion of this organisms by using light and electron microscopy. Infection with this endocytobiont is a suitable model for studying the host-parasite relations while the parasites use their hosts as so-called Trojan horses (see Barker, Lambert, Brown, Infect Immun 61:3503-3510, 1992).

Mechanism of intrusion of a microspordian-like organism into the nucleus of host amoebae (Vannella sp.) isolated from a keratitis patient

Free-living amoebae (FLA) occur ubiquitously in many aquatic habitats and humid soils as well as in "artificial" water samples. In addition to their role as pathogens, FLA are known to serve as natural hosts and vehicles of transmission for various intracellular organisms. An otherwise healthy 24-year-old female patient presented with keratitis in her inflamed left eye. She was a contact lens wearer and had no history of corneal trauma. No acanthamoebae could be determined by culture methods. A Vannella strain (called VanAun0) isolated from corneal scrapings showed intracellular aggregating organisms. Within 1-2 days, the host amoebae ruptured, and numerous coccoid organisms (called Kaun1) were released. We succeeded in detecting the mechanisms of infection and intrusion of this eukaryotic organism, growing within the nucleus of the FLA, by light and electron microscopy. It could be shown that the spores at the cell membrane of strain KAun1 resemble Microsporidia and were taken up into the Amoeba by phagocytosis after adhesion of the spores and food cup formation (infective phase). The spores were transported into the cytoplasm of the vannellae in food vacuoles. Phase contrast microscopy revealed early stages of the parasites moving through the cytoplasm into the nucleus of the host amoeba. Electron microscopy showed the proliferation of polymorphic stages within the karyoplasm. The life cycle of these microsporidian-like organisms ended up with a sporogenic phase in which a terminal differentiation took place and numerous spores were released by rupture of the host cell wall. With the rupture of the host amoeba's cell membrane, the cycle started again from the beginning, the released infectious spores being ingested by other host amoebae. In particular, the morphology of the organelles made visible by electron microscopy finally allowed us to classify the endocytobionts as a microsporidan-like organism. Infection of Vannella sp. with the microsporidia-like organism strain KAun1 is a suitable model for studying the host-parasite relations of organisms using their hosts as so-called Trojan horses.

Telemicrobiology: a novel telemedical module for mission support in the field of infectious medicine

Infectious diseases are among the most common diseases suffered by soldiers while serving in missions away from their home countries. The diagnosis of theses diseases requires special procedures and expertise, both of which are provided by field microbiological laboratories. In order to support the diagnostic process by means of telemedicine, a modification of the standard telemedicine workstation, i.e. a telemicrobiology module with special equipment, camera and software, has been designed and validated. This module, currently in use in two operational theaters, has stood the test in routine practice. It enables the transmission of high-quality static images of microscopic specimens or overgrown nutrient media in a matter of seconds. The inclusion of experts into diagnostic analysis through the use of telemedicine improves diagnostic specificity by avoiding false positive results and, particularly in medical parasitology, allows a treatment-essential diagnosis without the dispatch of specimens to Germany. Telemicrobiology allows the control of the entire microbiology diagnostic process by expert workstation even with only a microbiological technician on site.

Rhythms, synchrony and electrical coupling in the Locus coeruleus

Electrical coupling of neurones is believed to promote synchronized activity. It may, however, also be a requirement for the maintenance of endogenous rhythmic activity in some systems. In en bloc isolated brainstem-spinal cord of the neonatal rat simultaneous whole cell recordings from pairs of LC neurones (n = 47 pairs) disclosed for the most part strongly synchronized activity which could take the form of tonic spiking or phasic bursts. Simultaneous whole cell recording from LC neurones and glia also revealed synchronized waves of depolarization in 7 of 17 pairs. This synchrony was partly due to respiratory-phased synaptic input and partly due to mechanisms, which were not dependent on chemical synapses. The gap junction uncoupler carbenoxolone suppressed non-synaptic rhythmic activity in LC neurones, but did not suppress either respiratory-phased synaptic input to these neurones or their excitatory response to increased CO(2). We give preliminary direct evidence for the existence of a current pathway between LC neurones, which is inhibited by carbenoxolone. Within the LC nucleus carbenoxolone-sensitive electrical coupling, which may involve neurone-glia as well as neurone-neurone interactions, may be required not just for synchronization, but also for the maintenance of rhythm.

Recovery from gastric mucus depletion in the intact guinea pig mucosa

BACKGROUND

In developed countries one-third of the population is infected with the gastric pathogen Helicobacter pylori. In the early stages of H. pylori-induced gastritis, typical symptoms include gastric erosions and mucus depletions. Artificial mucus depletion was generated, demonstrating both consequent irritation and recovery processes in the mucosa.

METHODS

The mucus depletion was examined by removing a small cylinder of mucus from the surface of the explanted guinea pig corpus mucosa, leaving the epithelial surface intact. pH microelectrodes were inserted into the mucosa in vitro, measuring the epicellular mucus pH, the pH(i) of the underlying epithelial cells and the pH inside the gastric glands during mucus regeneration. Using infrared microscopy, the same process of mucus layer renewal was followed in anaesthetized animals.

RESULTS

The depletion exposed the tissue surface to low luminal pH levels. At a luminal pH of 2.5, a decrease was observed in the crypt outlet pH and surface cell pH(i), while deeper cells were less affected. However, a subsequent neutralization in the deep gland lumen was found. During the repair process, a quarter of the mucus layer was regenerated within the first 5 min. This newly secreted mucus formed a structure similar to that before depletion. Within 45 min, pH(i) and tissue-near pH values had fully recovered.

CONCLUSION

Following mucus depletion, there is a decrease in surface cell pH(i) and crypt outlet pH values. The repair process is then characterized by extensive mucus secretion and local cessation of acid secretion.

[High dose rate brachytherapy: a potentially curative treatment for small invasive T1N0 endobronchial carcinoma and carcinoma in situ]

INTRODUCTION

High dose rate brachytherapy (HDR-BT) is an option for treatment of small invasive endobronchial carcinoma and carcinoma in situ. This retrospective study describes the results of 33 consecutive patients treated with curative intent and followed up for more than one year.

METHODS

Between July 1994 and October 1999, 35 tumours were treated with HDR-BT alone using a standard protocol delivering 6 fractions of 5 Gy delivered across 1cm from the catheters over 3 to 6 weeks. In 31 patients, surgical treatment was ruled out because of histology (in situ carcinoma), history of pneumonectomy or significant co-morbidity. Two patients were treated for positive resection margins following pneumonectomy. All the tumours were Tis or T1 N0.

RESULTS

The locations of tumours were: trachea - 2, main bronchus - 5, lobar - 20, and segmental - 8. Only one catheter was needed in 15 cases, 2 in 13 cases, 3 in 6 cases and 4 in 1 case. The median follow-up was 17 months (range, 5-53 months). The recurrence-free rate was 94.3% at 2 months and 86.2% at 6 months after the treatment. 15 patients (45.5%) developed local recurrence at a median time of 9 months. Three patients developed metastases. The 1-year and 2-year overall survival rate were 71.4% and 53.8% respectively and specific survival rates were 69.4% and 59%. One patient developed an acute pneumothorax, and late complications included 6 infections and 12 bronchial stenoses. There were no episodes of haemoptysis nor lethal complications.

CONCLUSIONS

With strict selection criteria, HDR-BT can be a curative treatment for early invasive or in situ endobronchial carcinoma without serious toxicity. It is therefore a good alternative treatment with curative intent for inoperable patients.

Synchronized rhythms in chemosensitive neurons of the locus coeruleus in the absence of chemical synaptic transmission

The activity of locus coeruleus (LC) neurons was examined in the en bloc isolated brainstem-spinal cord of the neonatal rat using paired whole cell or whole cell plus extracellular recording. In artificial cerebrospinal fluid (ACSF) LC neurons were synchronized by their respiratory innervation and in some neurons showing tonic or burst patterns of discharge these patterns of discharge could also be synchronized. Replacing ACSF with low Ca(2+)-high Mg(2+) generated synchronized rhythmic bursts which remained synchronized at high CO(2) (up to 20%). This rhythm was suppressed by TTX. Substitution of Ba(2+) for Ca(2+) in ACSF generated a synchronized rhythm which was TTX-insensitive. The frequency of this rhythm increased by 31+/-16% on raising CO(2) concentration from 2 to 10%. We conclude that the capacity of chemosensitive LC neurons to generate a synchronized rhythm depends on their electrical coupling, but not on chemical synaptic transmission.

Central chemosensitivity of respiration: a brief overview

In this introductory article we make use of the work reviewed in detail by a number of contributors to this Special Issue (Respir. Physiol., 2001) to provide an outline of current approaches to identifying brainstem CO(2)/pH-chemosensitive neurones. The section headings which we have adopted are intended to reflect particular issues rather than experimental techniques, though some of these issues arise out of the choice of preparation and the advantages and limitations which follow from such a choice. We have also considered whether, in spite of the diversity in the kinds of neurones usually considered to be chemosensitive, there are any indications for shared or uniform features. Again, this is based on the material published together in this volume. Finally, and more speculatively, we suggest that the dendritic organization of chemosensitive neurones may play an important role in chemoreception, not simply as a means of sampling the stimulus but also as a way of compartmentalizing the effects of pH in relation to other aspects of a neurone's activity.

[Chemoprevention perspectives for bronchial cancer]

Lung cancer, with a high incidence and a 14% survival rate at 5 years is the leading cause of death in France. Because of past and present smoking habits in the French population and the lack of real expectations for significant therapeutic progress within a short or mid-term delay, the only reasonable way to try to limit the predictable hecatomb in the next 2 decades is to reduce exposure to the main risk factors (tobacco smoke, asbestos.), implement an early and effective (radiographic and/or endoscopic) screening system, and/or determine an active chemoprevention scheme. The principle of chemoprevention is based on the fundamental concept that since lung cancer develops through several stages, subjects exposed to risk factors could be given a compound or compounds counteracting the deleterious effect of carcinogenic substances on DNA and/or blocking the subsequent cascade of molecular events. Two families of products have been considered as potential chemoprevention agents: antioxidants (selenium, beta-caroten, vitamin E, and N-acetyl-cystein) and vitamin A and its analogs. Unfortunately, despite promising experimental data, large-scale clinical trials have not evidenced any protective effect of these compounds that have even been observed to produce opposing effects. To date, no chemopreventive substance can be reasonable proposed for subjects at risk. Due to the lack of proof of the efficacy of the different screening systems proposed, the only preventive action with proven efficacy is to limit exposure to risk factors. All health care givers must actively participate in the fight against active and passive smoking.

Inflammation in cystic fibrosis airways: relationship to increased bacterial adherence

It is unclear whether inflammation in the cystic fibrosis (CF) lung relates predominantly to bacterial infection, or occurs as a direct consequence of mutant cystic fibrosis transmembrane conductance regulator (CFTR) protein. Interleukin (IL)-8 secretion from CF and non-CF cell lines, and from CF and non-CF human primary nasal epithelial cells incubated with or without Pseudomonas aeruginosa, was measured. Activation of nuclear factor-kappaB (NF-kappaB) in unstimulated CF and non-CF nasal epithelial cells, cell lines and murine tissues was measured by gel-shift assays. No significant difference in basal IL-8 production or NF-kappaB activation was observed between CF and non-CF primary nasal cells. However, CF cells exhibited a significantly (p<0.01) increased IL-8 secretion following P. aeruginosa stimulation. Equalization of the increased P. aeruginosa adherence observed in CF cells, to non-CF levels, resulted in comparable IL-8 secretion. Further, IL-8 production did not differ with mutations which result in either correctly localized CFTR, or in partial/total mislocalization of this protein. Similar levels of NF-kappaB activation were observed in a number of organs of wildtype and CF mice. Finally, IL-8 secretion and NF-kappaB activity were not consistently increased in CF cell lines. Cos-7 cell transfection with plasmids expressing deltaF508 or G551D mutant CFTR protein resulted in increased activation of a p50-containing NF-kappaB complex, but IL-8 secretion was similar to wild-type cells. The authors conclude that the stimulus produced by Pseudomonas aeruginosa is the predominant inflammatory trigger in their models.