Optimization of a new liquid scintillation spectrometer for the measurement of environmental levels of 3H in water samples.

The activity concentration of 3H in water samples collected from places unaffected by nuclear activities or for human consumption can be very low. In these cases, determination procedures must achieve a Minimum Detectable Activity (MDA) low enough to ensure that 3H is accurately determined. In this paper, we present a method that uses a new Liquid Scintillation Spectrometer (LSC in what follows): the Quantulus GCT 6220. Furthermore, a new liquid scintillation cocktail, the ProSafe LT+, has been tested for 3H measurement, showing to be a good option for the determination of low levels of this radionuclide. The MDAs achieved are low enough to enable the measurement of very low levels of 3H in recent environmental water. The results obtained using a Quantulus GCT 6220 and Prosafe LT + are compared to those obtained with a Quantulus 1220 and Prosafe HC + as liquid scintillation cocktail.

Management of Patients with Suspected or Confirmed Antibiotic Allergy: Executive Summary of Guidelines from the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC), the Spanish Society of Allergy and Clinical Immunology (SEAIC), the Spanish Society of Hospital Pharmacy (SEFH) and the Spanish Society of Intensive Medicine and Coronary Care Units (SEMICYUC).

Suspected or confirmed antibiotic allergy is a frequent clinical circumstance that influences antimicrobial prescription and often leads to the avoidable use of less efficacious and/or more toxic or costly drugs than first-line antimicrobials. Optimizing antimicrobial therapy in patients with antibiotic allergy labels has become one of the priorities of antimicrobial stewardship programs in several countries. These guidelines aim to make recommendations for the systematic approach to patients with suspected or confirmed antibiotic allergy based on current evidence. An expert panel (11 members of various scientific societies) formulated questions about the management of patients with suspected or confirmed antibiotic allergy. A systematic literature review was performed by a medical librarian. The questions were distributed among panel members who selected the most relevant references, summarized the evidence, and formulated graded recommendations when possible. The answers to all the questions were finally reviewed by all panel members. A systematic approach to patients with suspected or confirmed antibiotic allergy was recommended to improve antibiotic selection and, consequently, clinical outcomes. A clinically oriented, 3-category risk-stratification strategy was recommended for patients with suspected antibiotic allergy. Complementary assessments should consider both clinical risk category and preferred antibiotic agent. Empirical therapy recommendations for the most relevant clinical syndromes in patients with suspected or confirmed ß-lactam allergy were formulated, as were recommendations on the implementation and monitoring of the impact of the guidelines. Antimicrobial stewardship programs and allergists should design and implement activities that facilitate the most appropriate use of antibiotics in these patients.

Management of Patients with Suspected or Confirmed Antibiotic Allergy: Executive Summary of Guidelines from the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC), the Spanish Society of Allergy and Clinical Immunology (SEAIC), the Spanish Society of Hospital Pharmacy (SEFH) and the Spanish Society of Intensive Medicine and Coronary Care Units (SEMICYUC)

Suspected or confirmed antibiotic allergy is a frequent clinical circumstance that influences antimicrobial prescription and often leads to the avoidable use of less efficacious and/or more toxic or costly drugs than first-line antimicrobials. Optimizing antimicrobial therapy in patients with antibiotic allergy labels has become one of the priorities of antimicrobial stewardship programs in several countries. These guidelines aim to make recommendations for the systematic approach to patients with suspected or confirmed antibiotic allergy based on current evidence. An expert panel (11 members of various scientific societies) formulated questions about the management of patients with suspected or confirmed antibiotic allergy. A systematic literature review was performed by a medical librarian. The questions were distributed among panel members who selected the most relevant references, summarized the evidence, and formulated graded recommendations when possible. The answers to all the questions were finally reviewed by all panel members. A systematic approach to patients with suspected or confirmed antibiotic allergy was recommended to improve antibiotic selection and, consequently, clinical outcomes. A clinically oriented, 3-category risk-stratification strategy was recommended for patients with suspected antibiotic allergy. Complementary assessments should consider both clinical risk category and preferred antibiotic agent. Empirical therapy recommendations for the most relevant clinical syndromes in patients with suspected or confirmed ß-lactam allergy were formulated, as were recommendations on the implementation and monitoring of the impact of the guidelines. Antimicrobial stewardship programs and allergists should design and implement activities that facilitate the most appropriate use of antibiotics in these patients (AU)

En la práctica clínica, un antecedente de alergia a los antibióticos, confirmada o sospechada, es frecuente y condiciona la selección de antibióticos, requiriendo con frecuencia el uso de fármacos menos eficaces, más tóxicos o más caros que los antibióticos de primera línea. La optimización del uso de antibióticos en pacientes con este antecedente es una de las prioridades de los programas de optimización de uso de antibióticos (PROA) en varios países. Estas guías pretenden formular recomendaciones para evaluar de una manera sistemática a estos pacientes mediante una aproximación basada en la evidencia. Un panel multidisciplinar constituido por alergólogos, infectólogos, farmacéuticos hospitalarios e intensivistas formularon una serie de preguntas sobre el manejo de estos pacientes; una documentalista realizó la revisión bibliográfica. Las preguntas se distribuyeron entre los miembros del grupo de trabajo, quienes seleccionaron las referencias más relevantes y formularon las correspondientes recomendaciones, que fueron revisadas y aprobadas por todos los miembros del grupo. Es necesaria una aproximación sistemática a los pacientes con antecedentes de alergia a antibióticos para optimizar la selección del tratamiento antibiótico y mejorar los resultados clínicos de estos pacientes cuando precisan antibioterapia. El presente documento recomienda una estrategia de estratificación clínica del riesgo en 3 categorías. La recomendación de realizar evaluaciones complementarias se basa en el riesgo clínico y el antibiótico de primera línea necesario. Además, se formulan recomendaciones de tratamiento antibiótico empírico para los principales síndromes infecciosos en pacientes con alergia confirmada o sospechada. Finalmente, se formulan recomendaciones sobre la implementación y monitorización del impacto de las recomendaciones de la guía (AU)

Effects of airborne ammonium and nitrate pollution strongly differ in peat bogs, but symbiotic nitrogen fixation remains unaffected.

Pristine bogs, peatlands in which vegetation is exclusively fed by rainwater (ombrotrophic), typically have a low atmospheric deposition of reactive nitrogen (N) (<0.5kgha-1y-1). An important additional N source is N2 fixation by symbiotic microorganisms (diazotrophs) in peat and mosses. Although the effects of increased total airborne N by anthropogenic emissions on bog vegetation are well documented, the important question remains how different N forms (ammonium, NH4+, versus nitrate, NO3-) affect N cycling, as their relative contribution to the total load strongly varies among regions globally. Here, we studied the effects of 11years of experimentally increased deposition (32 versus 8kgNha-1y-1) of either NH4+ or NO3- on N accumulation in three moss and one lichen species (Sphagnum capillifolium, S. papillosum, Pleurozium schreberi and Cladonia portentosa), N2 fixation rates of their symbionts, and potential N losses to peat soil and atmosphere, in a bog in Scotland. Increased input of both N forms led to 15-90% increase in N content for all moss species, without affecting their cover. The keystone species S. capillifolium showed 4 times higher N allocation into free amino acids, indicating N stress, but only in response to increased NH4+. In contrast, NO3- addition resulted in enhanced peat N mineralization linked to microbial NO3- reduction, increasing soil pH, N concentrations and N losses via denitrification. Unexpectedly, increased deposition from 8 to 32kgha-1y-1 in both N forms did not affect N2 fixation rates for any of the moss species and corresponded to an additional input of 5kgNha-1y-1 with a 100% S. capillifolium cover. Since both N forms clearly show differential effects on living Sphagnum and biogeochemical processes in the underlying peat, N form should be included in the assessment of the effects of N pollution on peatlands.

Evidence for differential effects of reduced and oxidised nitrogen deposition on vegetation independent of nitrogen load.

Nitrogen (N) deposition impacts natural and semi-natural ecosystems globally. The responses of vegetation to N deposition may, however, differ strongly between habitats and may be mediated by the form of N. Although much attention has been focused on the impact of total N deposition, the effects of reduced and oxidised N, independent of the total N deposition, have received less attention. In this paper, we present new analyses of national monitoring data in the UK to provide an extensive evaluation of whether there are differences in the effects of reduced and oxidised N deposition across eight habitat types (acid, calcareous and mesotrophic grasslands, upland and lowland heaths, bogs and mires, base-rich mires, woodlands). We analysed data from 6860 plots in the British Countryside Survey 2007 for effects of total N deposition and N form on species richness, Ellenberg N values and grass:forb ratio. Our results provide clear evidence that N deposition affects species richness in all habitats except base-rich mires, after factoring out correlated explanatory variables (climate and sulphur deposition). In addition, the form of N in deposition appears important for the biodiversity of grasslands and woodlands but not mires and heaths. Ellenberg N increased more in relation to NHx deposition than NOy deposition in all but one habitat type. Relationships between species richness and N form were habitat-specific: acid and mesotrophic grasslands appear more sensitive to NHx deposition while calcareous grasslands and woodlands appeared more responsive to NOy deposition. These relationships are likely driven by the preferences of the component plant species for oxidised or reduced forms of N, rather than by soil acidification.

Sphagnum mosses--masters of efficient N-uptake while avoiding intoxication.

Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N). N-uptake kinetics of these mosses are therefore expected to play a key role in differential N availability, plant competition, and carbon sequestration in Sphagnum peatlands. The interacting effects of rain N concentration and exposure time on moss N-uptake rates are, however, poorly understood. We investigated the effects of N-concentration (1, 5, 10, 50, 100, 500 µM), N-form ((15)N-ammonium or nitrate) and exposure time (0.5, 2, 72 h) on uptake kinetics for Sphagnum magellanicum from a pristine bog in Patagonia (Argentina) and from a Dutch bog exposed to decades of N-pollution. Uptake rates for ammonium were higher than for nitrate, and N-binding at adsorption sites was negligible. During the first 0.5 h, N-uptake followed saturation kinetics revealing a high affinity (Km 3.5-6.5 µM). Ammonium was taken up 8 times faster than nitrate, whereas over 72 hours this was only 2 times. Uptake rates decreased drastically with increasing exposure times, which implies that many short-term N-uptake experiments in literature may well have overestimated long-term uptake rates and ecosystem retention. Sphagnum from the polluted site (i.e. long-term N exposure) showed lower uptake rates than mosses from the pristine site, indicating an adaptive response. Sphagnum therefore appears to be highly efficient in using short N pulses (e.g. rainfall in pristine areas). This strategy has important ecological and evolutionary implications: at high N input rates, the risk of N-toxicity seems to be reduced by lower uptake rates of Sphagnum, at the expense of its long-term filter capacity and related competitive advantage over vascular plants. As shown by our conceptual model, interacting effects of N-deposition and climate change (changes in rainfall) will seriously alter the functioning of Sphagnum peatlands.

Inertia in an ombrotrophic bog ecosystem in response to 9 years' realistic perturbation by wet deposition of nitrogen, separated by form.

Wet deposition of nitrogen (N) occurs in oxidized (nitrate) and reduced (ammonium) forms. Whether one form drives vegetation change more than the other is widely debated, as field evidence has been lacking. We are manipulating N form in wet deposition to an ombrotrophic bog, Whim (Scottish Borders), and here report nine years of results. Ammonium and nitrate were provided in rainwater spray as NH4 Cl or NaNO3 at 8, 24 or 56 kg N ha(-1)  yr(-1) , plus a rainwater only control, via an automated system coupled to site meteorology. Detrimental N effects were observed in sensitive nonvascular plant species, with higher cumulative N loads leading to more damage at lower annual doses. Cover responses to N addition, both in relation to form and dose, were species specific and mostly dependent on N dose. Some species were generally indifferent to N form and dose, while others were dose sensitive. Calluna vulgaris showed a preference for higher N doses as ammonium N and Hypnum jutlandicum for nitrate N. However, after 9 years, the magnitude of change from wet deposited N on overall species cover is small, indicating only a slow decline in key species. Nitrogen treatment effects on soil N availability were likewise small and rarely correlated with species cover. Ammonium caused most N accumulation and damage to sensitive species at lower N loads, but toxic effects also occurred with nitrate. However, because different species respond differently to N form, setting of ecosystem level critical loads by N form is challenging. We recommend implementing the lowest value of the critical load range where communities include sensitive nonvascular plants and where ammonium dominates wet deposition chemistry. In the context of parallel assessment at the same site, N treatments for wet deposition showed overall much smaller effects than corresponding inputs of dry deposition as ammonia.

Shear-induced detachment of biofilms from hollow fiber silicone membranes.

A suite of techniques was utilized to evaluate the correlation between biofilm physiology, fluid-induced shear stress, and detachment in hollow fiber membrane aerated bioreactors. Two monoculture species biofilms were grown on silicone fibers in a hollow fiber membrane aerated bioreactors (HfMBR) to assess detachment under laminar fluid flow conditions. Both physiology (biofilm thickness and roughness) and nutrient mass transport data indicated the presence of a steady state mature biofilm after 3 weeks of development. Surface shear stress proved to be an important parameter for predicting passive detachment for the two biofilms. The average shear stress at the surface of Nitrosomonas europaea biofilms (54.5 ± 3.2 mPa) was approximately 20% higher than for Pseudomonas aeruginosa biofilms (45.8 ± 7.7 mPa), resulting in higher biomass detachment. No significant difference in shear stress was measured between immature and mature biofilms of the same species. There was a significant difference in detached biomass for immature vs. mature biofilms in both species. However, there was no difference in detachment rate between the two species.

Dissolved organic carbon (DOC) concentrations in UK soils and the influence of soil, vegetation type and seasonality.

Given the lack of studies which measured dissolved organic carbon (DOC) over long periods, especially in non-forest habitat, the aim of this study was to expand the existing datasets with data of mainly non-forest sites that were representative of the major soil and habitat types in the UK. A further aim was to predict DOC concentrations from a number of biotic and abiotic explanatory variables such as rainfall, temperature, vegetation type and soil type in a multivariate way. Pore water was sampled using Rhizon or Prenart samplers at two to three week intervals for 1 year. DOC, pH, organic carbon, carbon/nitrogen (C:N) ratios of soils and slope were measured and data on vegetation, soil type, temperature and precipitation were obtained. The majority of the variation in DOC concentrations between the UK sites could be explained by simple empirical models that included annual precipitation, and soil C:N ratio with precipitation being negatively related to DOC concentrations and C:N ratio being positively related to DOC concentrations. Our study adds significantly to the data reporting DOC concentrations in soils, especially in grasslands, heathlands and moorlands. Broad climatic and site factors have been identified as key factors influencing DOC concentrations.

Hydrogen fluoride damage to vegetation from peri-urban brick kilns in Asia: a growing but unrecognised problem?

The rapid urbanisation of many cities in south and south-east Asia has increased the demand for bricks, which are typically supplied from brick kilns in peri-urban areas. We report visible foliar damage to mango, apricot and plum trees in the vicinity of traditional Bull's Trench brick kilns in Peshawar, Pakistan. Visible injury symptoms, hydrogen fluoride concentrations in air, and foliar fluoride concentrations were all greater in the vicinity of brick kilns than at more distant sites, indicating that fluoride emissions from brick kilns were the main cause of damage. Interviews with local farmers established the significant impact of this damage on their livelihoods. Since poorly regulated brick kilns are often found close to important peri-urban agricultural areas, we suggest that this may be a growing but unrecognised environmental problem in regions of Asia where emission control in brick kilns has not been improved.

Ecosystem responses to reduced and oxidised nitrogen inputs in European terrestrial habitats.

While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NH(x) and NO(y)) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NH(x):NO(y) ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH(4)(+) concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NH(x):NO(y) deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.

[Diverticular duodenal disease as incidental finding with computer tomography]. / La enfermedad diverticular duodenal como hallazgo incidental detectado por tomografía computarizada.

BACKGROUND: Duodenal diverticular disease is a frequent condition but clinical diagnosis can be chalenging. Less than 10% of the cases are symptomatic and symptoms are vague. Only between 1% to 2% will require surgical treatment. OBJECTIVE: To establish the prevalence of duodenal diverticulum (Dd) in patients who underwent abdominal computed tomography (CT). METHODS: A retrospective review of all cases with Dd identified incidentally during abdominal CT scan was performed. Clinical data regarding type, location, differential diagnosis and complications were recorded. RESULTS: During the study period 12,704 abdominal CT scans were performed and 50 patients with Dd were identified (prevalence 0.46%). Thirty patients were women (60%) and the mean patient age was 69 years (range: 23 - 93 years). In thirteen patients the Dd were located in the second portion (26%) and 24 in the third portion of the duodenum (48%). Three Dd were detected in the papillary region, one of them (2%) was complicated with hemorrhage and required surgical treatment. CONCLUSIONS: Dd were detected in the 0.46% of the abdominal CT scans. Most of them were incidentally detected (94%). The prevalence of these lesions increases with age. Dd may mimic a cystic neoplasm in the head of the pancreas in 28% of cases and produce complications as bleeding in 2% of the cases.

Early diffuse demyelinating lesion in the cervical spinal cord predicts a worse prognosis in relapsing-remitting multiple sclerosis.

OBJECTIVE: To study the long-term outcome and persistence of two patterns of cervical spinal cord abnormality in early relapsing-remitting multiple sclerosis (RRMS). METHODS: RRMS patients with a spinal cord MRI performed during the first 3 years of the disease, a control MRI 5 years later and who have been followed up at least 10 years were included. Patients were grouped according the T2 spinal cord MRI into: (A) nodular pattern, if one or more focal lesions were present; and (B) diffuse pattern, defined as a poorly demarcated high signal area. The end point was defined as the time to reach an Expanded Disability Status Score (EDSS) of 4.0. RESULTS: Twenty-five patients were included; 12 in group A and 13 in group B. Three patients in group A and 9 in group B reached EDSS 4, in a mean time of 11 years in group A and 7 years in group B (log rank 10.3, p = 0.001). Multivariate Cox regression analysis assessing the risk of EDSS 4.0 including sex, age, number of relapses in the first 2 years, number of T2 brain lesions and spinal cord pattern showed higher risk for the diffuse pattern (hazard ratio 7.2, 95% confidence interval 1.4-36.4). Control MRI showed the persistence of the diffuse pattern in all patients, and the development of diffuse pattern in two patients with basal nodular lesions. CONCLUSIONS: The diffuse abnormality in cervical spinal cord at the beginning of the disease is persistent and predicts a worse prognosis in RRMS patients.

Development and validation of a computer program to design and calculate ROPS.

In Spain, there are more than 250,000 tractors built before 1980, when it became mandatory for all new tractors to be equipped with a rollover protective structure (ROPS). A similar situation is found in the European Union, but the situation is worse in the U.S. and in developing countries. Directive 2003/37/EEC establishes that tractors over 800 kg weight can be homologated by using the OECD standard code for the official testing of protective structures on agricultural and forestry tractors (static test), called Code 4. A ROPS attachable to the rear axle of different tractor models has been designed, and a computer program for the calculation of the ROPS design has been developed. The program, named ESTREMA, is available at: www.cfnavarra.es/insl. Using this program, it has been possible to design a ROPS for the Massey Ferguson model 178 tractor, one of the most common tractor models without a ROPS in Spain. After the tractor was equipped with the designed ROPS, it was tested at the Spanish Authorized Station for testing ROPS and passed the homologation test (OECD Code 4), the main results being a maximum distortion of 21.3 cm when the absorbed energy was 5437 N and the maximum force applied was 34 kN during loading from the side. The ROPS was improved, redesigned, and remounted on the tractor, the tractor was tested in a real overturn, and no part of the structure intruded on the driver's clearance zone during the test. In conclusion, the ESTREMA program worked correctly, and the designed ROPS was able to pass the authorized test and provide adequate protection to the operator during a real overturn.

Protocolo combinado de fijación externa y arteriografía en fracturas de pelvis con inestabilidad hemodinámica asociada: estudio retrospectivo sobre 79 casos / A combined external fixation and arteriography protocol for pelvic fractures with associated hemodynamic instability: retrospective study of 79 cases

Objetivo. Las fracturas de pelvis se asocian con frecuencia a sangrado intrapélvico arterial y/o venoso, ocasionando una mortalidad elevada que varía entre el 10 y 50%. Existen numerosos protocolos de tratamiento publicados para el control temprano de la hemorragia, que coinciden en la necesidad de un abordaje decidido y multidisciplinario combinando distintas maniobras terapéuticas. El objetivo del presente estudio consiste en determinar la aplicabilidad y la evolución clínica y los resultados de la aplicación de un algoritmo diagnóstico terapéutico, en un grupo de 79 pacientes con fractura de pelvis e inestabilidad hemodinámica mantenida asociada. Material y método. Estudio retrospectivo sobre una serie de pacientes con fractura de pelvis e inestabilidad hemodinámica asociada ingresados en nuestro centro desde 1994 a 2004. Los criterios de inclusión fueron: pacientes con fractura de pelvis por mecanismo de alta energía e inestabilidad hemodinámica definida como tensión arterial sistólica < 90 mmHg al ingreso o necesidades transfusionales superiores a dos unidades de concentrado de hematíes durante las primeras 12 horas. Resultados. Se utilizó fijación externa en 45 pacientes (57%) y 48 pacientes (61%) fueron sometidos a arteriografía, encontrándose sangrado arterial activo intrapélvico en 44 casos (56%). Veintiún pacientes precisaron de arteriografía y fijación externa de manera secuencial. Se realizó laparotomía en 24 pacientes. La incidencia de complicaciones sistémicas fue alta y la mortalidad del 19%. La aplicación del algoritmo fue elevada, excepto para el grupo de pacientes que precisó laparotomía y tenía configuración de fractura en libro abierto. Dicho grupo presentó una mortalidad elevada. Conclusiones. La incidencia de lesiones arteriales comprobadas por arteriografía fue muy alta. El empleo de un protocolo combinado de fijación externa y arteriografía adaptado a las características asistenciales de cada centro permite controlar el sangrado intrapélvico en un número importante de casos. Las indicaciones de laparotomía deben restringirse al tratamiento del hemoperitoneo y de fracturas abiertas, y debe acompañarse siempre de fijación externa

Purpose. Frequently pelvic fractures are associated with arterial and/or venous intrapelvic bleeding, resulting in a high mortality rate ranging between 10 and 50%. Numerous treatment protocols have been published for the early control of hemorrhage. All of them agree on the need of a determined and multi-disciplinary approach that combines various therapeutic methods. The purpose of this study is to determine the applicability, clinical evolution and results of a therapeutic diagnostic algorithm used with a group of 79 patients with a pelvis fracture and a related hemodynamic instability. Materials and methods. This is a retrospective study of a series of patients with a pelvic fracture associated to hemodynamic instability, who were admitted to our hospital between 1994 and 2004. The inclusion criteria were as follows: patients with a high-energy pelvic fracture and hemodynamic instability. The criteria used to define hemodynamic instability were a systolic blood pressure < 90 mmHg on admission or transfusion needs higher than 2 units of red cell concentrate in the first 12 hours. Results. External fixation was used for 45 patients (57%). 48 patients (61%) were subjected to an arteriography, which revealed active arterial intrapelvic bleeding in 44 cases (56%). Twenty-one patients required an arterography plus external fixation, one after the other. twenty-four patients underwent a laparotomy. The incidence of systemic complications was high and mortality stood at 19%. The application of the algorithm was fairly widespread, except for patients requiring a laparotomy and presenting with an open-book type fracture. This group had a high mortality rate. Conclusions. The incidence of arteriography-validated arterial lesions was very high. The use of a combined external fixation and arteriography protocol, adapted to the specific health-care characteristics of each hospital makes it possible to check intrapelvic bleeding in quite a large number of cases. Indications for laparotomy should be restricted to the treatment of the hemoperitoneum and of open fractures, and should always be accompanied by some external fixation device

Effects of nitrogen enrichment on coastal dune grassland: a mesocosm study.

Mesocosms filled with dune sand were planted with graminoid (Calamagrostis epigejos, Carex arenaria) and herbaceous species (Carlina vulgaris, Galium verum). Strong effects of nitrogen addition on the vegetation were found within two to three years. The above-ground biomass of C. epigejos and C. arenaria increased at deposition rates between 10 and 80 kg N ha(-1) yr(-1). Both grasses were limited by N. In latter stages P limitation was suggested for C. arenaria. At high N-levels, C. epigejos dominated the vegetation within two years. C. vulgaris and G. verum declined drastically as a result of increased competition for light by the highly competitive grass C. epigejos. It is concluded that increased (ambient) N inputs are of major importance for the increased dominance of tall grasses in stable dune grasslands.

Decline of acid-sensitive plant species in heathland can be attributed to ammonium toxicity in combination with low pH.

The effects of increasing ammonium concentrations in combination with different pH levels were studied on five heathland plant species to determine whether their occurrence and decline could be attributed to ammonium toxicity and/or pH levels. Plants were grown in growth media amended with four different ammonium concentrations (10, 100, 500 and 1000 micromol l(-1)) and two pH levels resembling acidified (pH 3.5 or 4) and weakly buffered (pH 5 or 5.5) situations. Survival of Antennaria dioica and Succisa pratensis was reduced by low pH in combination with high ammonium concentrations. Biomass decreased with increased ammonium concentrations and decreasing pH levels. Internal pH of the plants decreased with increasing ammonium concentrations. Survival of Calluna vulgaris, Deschampsia flexuosa and Gentiana pneumonanthe was not affected by ammonium. Moreover, biomass increased with increasing ammonium concentrations. Biomass production of G. pneumonanthe reduced at low pH levels. A decline of acid-sensitive species in heathlands was attributed to ammonium toxicity effects in combination with a low pH.

Morphological bidirectional associative memories.

The theory of artificial neural networks has been successfully applied to a wide variety of pattern recognition problems. In this theory, the first step in computing the next state of a neuron or in performing the next layer neural network computation involves the linear operation of multiplying neural values by their synaptic strengths and adding the results. Thresholding usually follows the linear operation in order to provide for nonlinearity of the network. In this paper we discuss a novel class of artificial neural networks, called morphological neural networks, in which the operations of multiplication and addition are replaced by addition and maximum (or minimum), respectively. By taking the maximum (or minimum) of sums instead of the sum of products, morphological network computation is nonlinear before thresholding. As a consequence, the properties of morphological neural networks are drastically different from those of traditional neural network models. The main emphasis of the research presented here is on morphological bidirectional associative memories (MBAMs). In particular, we establish a mathematical theory for MBAMs and provide conditions that guarantee perfect bidirectional recall for corrupted patterns. Some examples that illustrate performance differences between the morphological model and the traditional semilinear model are also given.

[Gianturco-Grifka device in the percutaneous closure of patent ductus arteriosus]. / Dispositivo de Gianturco-Grifka en el cierre percutáneo del conducto arterioso permeable. Experiencia en 13 casos.

We present our early experience with the Gianturco-Grifka device for transcatheter closure of patent ductus arteriosus. Grifka occlusion was attempted in 13 patients (7 female, 6 male), median patient age was 6.5 years. Echocardiographic evaluation showed a mean ductal diameter of 5.47 +/- 1.09 mm, and the morphology was type C in 7 patients, type A in 5 and type E in 1 patient. The angiographic ductal morphology was 6 type A, 5 type C and 2 type E. Mean PDA diameter was 5.69 +/- 1.15 mm. Three patients had pulmonary hypertension. They were given supplemental oxygen (100%), decreasing their pulmonary pressures. A total of 13 devices were implanted, 5 of 7 mm and 8 of 9 mm. Twelve patients had complete ductal occlusion documented by aortic angiography (92%), one patient presented residual shunt (8%). Color echocardiography at 24 hrs documented complete occlusion in 12 cases. One device embolized to the descending aorta 2 hours after closure, and it was successfully retrieved in the catheterization lab. We conclude that the Gianturco-Grifka device is an appropriate alternative for transcatheter closure of the PDA. This technique can be performed in ductus arteriosus type C, D and E, with diameter < 9 mm. More clinical trials are needed to establish the long-term results of this technique.