Approximation of slow attracting manifolds in chemical kinetics by trajectory-based optimization approaches.

Many common kinetic model reduction approaches are explicitly based on inherent multiple time scales and often assume and directly exploit a clear time scale separation into fast and slow reaction processes. They approximate the system dynamics with a dimension-reduced model after eliminating the fast modes by enslaving them to the slow ones. The corresponding restrictive assumption of full relaxation of fast modes often renders the resulting approximation of slow attracting manifolds inaccurate as a representation of the reduced model and makes the numerical solution of the nonlinear "reduction equations" particularly difficult in many cases where the gap in intrinsic time scales is not large enough. We demonstrate that trajectory optimization approaches can avoid such severe restrictions by computing numerical solutions that correspond to "maximally relaxed" dynamical modes in a suitable sense. We present a framework of trajectory-based optimization for model reduction in chemical kinetics and a general class of reduction criteria characterizing the relaxation of chemical forces along reaction trajectories. These criteria can be motivated geometrically exploiting ideas from differential geometry and fundamental physics and turn out to be highly successful in example applications. Within this framework, we provide results for the computational approximation of slow attracting low-dimensional manifolds in terms of families of optimal trajectories for a six-component hydrogen combustion mechanism.

[Presence of anti hepatitis E virus antibodies in swine: is it an animal reservoir for hepatitis E?]. / Presencia de anti-VHE en un estudio de cohorte de porcinos ¿reservorio animal de hepatitis E en Chile?

BACKGROUND: Swine hepatitis E virus (HEV) has a cross-reaction with human anti-HEV antibodies. Therefore, pigs could be an animal reservoir, rendering hepatitis E as a zoonosis. The spread of this infection among infected pigs across countries would be possible through trading. Previously, using an anti-human conjugate, we detected anti-HEV antobodies in adult pigs in Chile. AIM: To detect anti-HEV (ELISA) in a cohort of swine at different ages. MATERIAL AND METHODS: Two hundred pigs aged 42 to 360 days, divided in 20 groups of 10 animals were tested. Anti-HEV was detected by ELISA using anti-pig IgG horseradish peroxidase instead of anti-human conjugates. RESULTS: Anti-HEV were detected in one animal aged 90 days, two animals aged 120 days, one animal aged 260 days and 2 animals aged 360 days, five pregnant sows and two old hogs. This represents a total of 14 animals or 7% of the sample. CONCLUSIONS: There is a significant prevalence of anti-HEV in pigs from 90 days of birth, suggesting that these swine are a probable reservoir.

Presencia de anti-VHE en un estudio de cohorte de porcinos ¿reservorio animal de hepatitis E en Chile? / Presence of anti hepatitis E virus antibodies in swine

Background: Swine hepatitis E virus (HEV) has a cross-reaction with human anti-HEV antibodies. Therefore, pigs could be an animal reservoir, rendering hepatitis E as a zoonosis. The spread of this infection among infected pigs across countries would be possible through trading. Previously, using an anti-human conjugate, we detected anti-HEV antobodies in adult pigs in Chile. Aim: To detect anti-HEV (ELISA) in a cohort of swine at different ages. Material and Methods: Two hundred pigs aged 42 to 360 days, divided in 20 groups of 10 animals were tested. Anti-HEV was detected by ELISA using anti-pig IgG horseradish peroxidase instead of anti-human conjugates. Results: Anti-HEV were detected in one animal aged 90 days, two animals aged 120 days, one animal aged 260 days and 2 animals aged 360 days, five pregnant sows and two old hogs. This represents a total of 14 animals or 7 percent of the sample. Conclusions: There is a significant prevalence of anti-HEV in pigs from 90 days of birth, suggesting that these swine are aprobable reservoir.

Is stereotactic biopsy a reliable method to differentiate tumor from radiation necrosis?

We report a case of a 37-year-old female who suffered from seizures and underwent external beam radiotherapy due to a suspected low-grade astrocytoma in the left hemisphere. After 7 years free of seizures under antiepileptic treatment and no signs of change in the yearly performed control MRI, she developed a progressive right-sided hemiparesis. MRI now showed an enhancing lesion with space occupying perifocal edema in the entire left hemisphere. Stereotactic biopsy revealed only inflammation. Due to further progress of the neurological deficit an open biopsy was performed. Histological examination revealed a middle-graded astrocytoma and a radiation necrosis. This case demonstrates that radiation necrosis and tumor recurrence may develop concurrently and that it may be difficult to distinguish them by clinical or radiological methods.

Hepatitis aguda por virus A, E y no A-E en adultos chilenos a fines de los años 90 / Acute hepatitis caused by virus A, E and non A-E in chilean adults

Background: Sanitary and socioeconomic changes and the identification of new causative virus, have changed the epidemiology of hepatitis in Chile. Aim: To study the natural history of acute hepatitis caused by virus A, E and non A-E in Chilean adults. Patients and methods: A special study protocol was followed for patients with a clinical picture of acute hepatitis. Anti HAV IgM, anti HBc IgM, anti HEV IgG and IgM and Anti HCV antibodies were determined by ELISA. Results: Fifty nine patients (30 male), aged 15 to 58 years old were studied. Eighty nine percent had jaundice and 50 to 70 percent had malaise and abdominal pain. Virus A was positive in 80 percent, virus E in 7 percent. In 14 percent of patients, all viral markers were negative. The evolution was typical in 78 percent, biphasic in 14 percent and cholestatic in 5 percent. One patient had a prolonged and one a fulminant course. Mean ALT was 1148 U/l and mean total bilirubin was 5.5 mg/dl. Seventy three percent of cases occurred during early winter and spring and 27 percent during summer and early autumm. Conclusions: The main etiology of acute viral hepatitis in Chile is virus A and most cases occur during the rainy season. Clinical features of hepatitis non A-E are similar to enteral transmission forms

Estado actual de inmunidad para hepatitis por virus A en diversos grupos de adultos / Current state of hepatitis A virus immunity in adults

Background: As sanitary and economic conditions improve, the prevalence of antibodies to hepatitis A is now significantly lower. Aim: To evaluate the prevalence of hepatitis A virus antibodies in healthy Chilean adults. Material and methods: Antibodies to hepatitis A virus were measured, using a commercial ELISA assay, in 215 voluntary blood donors (163 male, aged 19 to 30 years old) and 295 medical students and health personnel (156 male, aged 19 to 39 years old), residing in Valdivia, Chile. Results: Antibodies against hepatitis A virus were found in 68,2 percent of the total sample (351/510). Ninety percent of flood donors and 54 percent of health personnel and students were positive (p <0.01). Age specific prevalence in blood donors 19 to 22, 23 to 29 and 27 to 30 years old was 81,0 percent, 95,2 percent and 95,6 percent respectively. Among the same age groups in medical students, the prevalence was 47,9 percent, 53,2 percent and 61,9 percent respectively (p <0.01). Conclusions: This study indicates a reduction in the prevalence of hepatitis A virus antibodies among adults in Valdivia (Chile). Differences detected between individuals are probably related to different socioeconomic levels. Medical students have an increased risk for hepatitis A infections than the general population

Multiple intracerebral metastases of a 17-year-old girl with previously diagnosed neurofibromatosis type I.

We report a case of a 17-year-old girl with multiple intracerebral tumors. Previously, a neurofibroma in the posterior mediastinum and neurofibromatosis had been diagnosed. She developed a spastic tetraparesis with a prominent hemiparesis of the right side within several weeks. On admission we found clinical signs of elevated intracranial pressure. Cranial CT and MRI scans showed multiple space-occupying intracerebral tumors, thought to be multiple meningeoma. The patient was referred to the neurosurgical department, where two of the intracerebral tumors were excised. The histological examination revealed metastases of a neurosarcoma.

Differences in anxiety between first-time and multiple-time inmates: a multicultural perspective.

The present study investigated differences in anxiety symptoms and associated features between 129 first-time and multiple-time male inmates from a large urban jail. Participants were assessed on three separate anxiety measures: the Structured Clinical Interview of DSM-III-R Disorders (SCID) anxiety disorders module, the State Trait Anxiety Inventory, and anxiety scales of the Personality Assessment Inventory (PAI). First-time inmates were found to have more symptom severity for Generalized Anxiety Disorder, especially symptoms related to scanning and vigilance. Both first-time and multiple-time inmates evidenced higher state than trait anxiety, although this pattern did not hold for African Americans. Contrary to previous research, few ethnic differences were found in this incarcerated sample.

Prevalencia de anticuerpos anti-hepatitis A en escolares en la década actual / Prevalence of antibodies against hepatitis A virus in chilean school age children

Background: As sanitary conditions of a population improve, hepatitis A virus infection occurs at higher ages,thus decreasing the prevalence of antibodies against the virus. In the eighties, the prevalence of antibodies among children was 97 percent and depended on the socioeconomic level. Aim: To assess the prevalence of antibodies against hepatitis A virus in school age children living in Valdivia. Subjects and methods: Two thousand three hundred thirty three school age children were studied. Total antibodies against hepatitis A virus were detected using an ELISA kit from Abbott. Children were stratified in age groups and school were classified as private, subsidized, municipal or foster homes. Results: Antibodies were positive in 65 percent of children (59 percent in children aged 6 to 8 years old, 66 percent in children aged 9 to 11 years and 69 percent in children aged 12 to 15 years. In private schools, the prevalence was 26 percent, in subsidized schools the figure was 54 percent, in municipal schools 73 percent and in foster homes 91 percent. Conclusions: The general prevalence of antibodies against hepatitis A virus is higher in low socioeconomic level children. There is a global decrease in the prevalence of these antibodies in the last years

Plásmido de virulencia en yersinia enterocolítica 0-3 de origen murino / Virulence plasmid in yersinia enterocolitica 0-3 of murine origin

Background: Pathogenic strains of Yersinia enterocolitica harbor a virulence plasmid of 45-48 megadalton that can be detected using different techniques. Rodents are important reservoirs of Y enterocolitica. Aim: To investigate the carrier status of Y enterocolitica in murine rodents. Material and methods: Two hundred sixty one mice and rats were captured in rural and urban areas of Valdivia. Y enterocolitica was cultured from viscera and fecal homogenates. Virulence plasmids were detected using crystal violet binding. Results: Thirteen Y enterocolitica strains were isolated from 11 rodents. Ten strains belonged to the biotype 1 and three to the biotype 4, serotype O:3. The most frequently infected rodent species were R norvergicus (20 per cent), followed by A longipilis (11 per cent), A olivaceus (2 per cent) and O longicaudatus (2 per cent). Conclusions: Rodents, and specially the domestic rat, can be an important source of Y enterocolitica infection for human and susceptible animal species

The African polio vaccine-acquired immune deficiency syndrome connection.

Seroepidemiological, clinical and molecular findings suggest that the acquired immune deficiency syndrome virus human immunodeficiency virus-1 was introduced into the human species at the time (late 1950s) and in the geographic area (Zaire) in which millions of Africans were vaccinated with attenuated poliomyelitis virus strains that were produced in kidney tissue obtained from monkeys. Since monkeys not only harbor viruses that are remarkably similar to and genetically related to human immunodeficiency virus-1, but also served as tissue donors for the African polio vaccine, it is reasonable to suspect that a then non-detectable monkey virus with human-1-like properties was unknowingly co-cultured with the attenuated poliovirus virus and subsequently administered to the vaccinees. The possibility of such a polio vaccine-acquired immune deficiency syndrome connection is a reminder of the unpredictable danger of artifically crossing natural species-barriers in biomedical laboratories.

Prevalencia de anticuerpos del virus hepatitis E en donantes de bancos de sangre y otros grupos de población en la X región, Chile / Prevalence of hepatitis E virus antibodies in blood donors and other population groups at X region, Chile

Little is known about hepatitis E virus (HEV) prevalence in South American countries. AntiHEV was studied in 1,773 subjects from 1,360 blood donors of 3 cities in Chile, 72 in health care workers, 241 inmates in state jails and in 100 Araucarian indians. Anti-HEV was detected in 109 out of 1,360 (8.0 percent) total donors (6.3 percent, 6.1 percent and 18.8 percent from the cities of Valdivia, Osorno and Puerto Montt respectively); 9 out of 72 (12.5 percent) health care workers; 18 out of 241 (7.5 percent) inmates and 17 out of 100 (17 percent) Araucarian indians. Prevalence of anti-HEV was not related to age and sex. Hepatitis E is an endemic infection in some population groups of Southern Chile, associated to environmental pollution, crowding and low socioeconomic level

Virus hepatitis C: resultados de detección en algunos grupos de riesgo en la X región de Chile / Hepatitis C virus: results on detection in some risk groups in X region of Chile

The aim of this study was to determine the prevalence of hepatitis C virus antibodies in high rosk patients coming from Valdivia, Osorno and Puerto Montt. Fiftysix patients in hemodialysis, 51 renal grafts recipients, 42 cirrhotic and 14 patients with acute non A non B hepatitis were studied. Antibodies were detected with a second generation ELISA technique and positive cases were confirmed with RIBA. All hemodialysis patients and renal grafts recipients were negative for hepatitis C virus antibodies. In one non alcoholic patient with cirrhosis, a positive ALISA was confirmed with RIBA. Six patients with acute hepatitis had a positive ALISA tests but none was confirmed with RIBA. It is concluded that the prevalence of hepatitis C virus antibodies in this region of Chile is very low

Elevation of intracranial pressure in acute AIDS-related cryptococcal meningitis.

Prior to the AIDS-era, elevation of intracranial pressure was known to be a typical complication of cryptococcal meningitis associated with an increased risk of early death. In AIDS-patients, however, the prevalence and clinical significance of this complication are as yet unclear. We analysed clinical features and courses, CSF findings, serological results and neuroimaging scans in acute cryptococcal meningitis in eight patients with AIDS. Five showed symptoms and signs compatible with raised intracranial pressure, which was life-threatening in one and the most probable cause of death in another. Serial monitoring of intracranial pressure together with repeated CSF analysis revealed that severe intracranial pressure elevation in AIDS related cryptococcal meningitis can occur in spite of effective antimycotic treatment, does not depend on an increased CSF/serum osmolality ratio or CSF overproduction and can be associated with normal cranial computed tomography and magnetic resonance imaging findings. Our data support the hypothesis that CSF reabsorption failure plays the crucial role in the pathophysiological mechanism. External lumbar drainage may be of benefit in selected cases of acute AIDS related cryptococcal meningitis with persisting life threatening elevation in intracranial pressure and normal computed tomogram.

Pair-housing rather than single-housing for laboratory rhesus macaques.

A total of 378 adult and juvenile rhesus macaques of both sexes were transferred from single- to isosexual pair-housing arrangements. The incidence of serious injury resulting from partner incompatibility was 0.8% during the first year after pair formation. It was concluded that pair-housing offers a safe option to address the animals' social needs in compliance with federal rules and professional standards.

GABA binding sites: their density, their affinity to muscimol and their behaviour against neuroactive steroids in human gliomas of different degrees of malignancy.

The aim of the present investigation was to answer the question if there exists a relation between the equipment of human gliomas with GABA binding sites and the degree of malignancy of these tumours diagnostically characterized according to WHO classification. The following parameters were assessed: the density, the affinity and the sensitivity to the modulating steroids 3 alpha-hydroxy-5 alpha-pregnane-20-one (3 alpha OH-DHP) and 3 alpha,21 dihydroxy-5 alpha-pregnane-20-one (THDOC). Scatchard analysis and non linear computerization revealed that the occurrence of GABA sites was directly related to the degree of tumour malignancy: GABA sites were only detectable in lower malignant gliomas of WHO grade II but not in the very malignant glioblastomas. However, irrespective of the individual density to be detected all glioma GABA sites were sensitive to 3 alpha-hydroxy-5 alpha-pregnane-20-one (3 alpha OH-DHP) and 3 alpha,21 dihydroxy-5 alpha-pregnane-20-one (THDOC) without exception. The effects of THDOC were due to increases in the number of binding sites whereas in the presence of 3 alpha OH-DHP a decrease in affinity was noted, additionally. These findings support the view of a normal functional integrity of GABA receptors in gliomas.

[The scar tissue protective effect of free autologous fatty tissue transplants. An animal experiment on spinal surgery]. / Die narbenprotektive Wirkung freier autologer Fetttransplantate. Ein tierexperimenteller Beitrag zur Wirbelsäulenchirurgie.

All spinal operations can be followed by the formation of extensive epidural scar tissue. The development of fibrous adhesions around the nerve roots is known to be the main cause of recurrent symptoms after lumbar discectomy. In the past many materials have been used to prevent or to reduce postlaminectomy membrane, with very different results. They have to be implanted onto the dura at the end of the operation. Therefore, we carried out the following controlled experimental study in dogs to compare the materials that seemed to be most suitable. In 30 adult beagles three lumbar laminectomies were performed. For each level a different material was used--free autologous fat graft, cellulose mesh, gel foam, triamcinolone suspension. Animals were sacrificed after 7 days and 1, 3, and 6 months. The lumbar vertebral columns were prepared for further histological examination. We found that free autologous fat grafts reduce epidural scarring in a high percentage, especially after 3 and 6 months. Only in this group good or excellent results were found at all lumbar levels (n = 18). To compare the results with each other we used a newly developed classification scheme (I-IV). The consistency and extent of scar tissue, the kind of cellular infiltrations, and adhesions to the surrounding structures were estimated separately. Cellulose mesh yielded the worst results. We conclude that free autologous fat is superior to other materials, because of: (1) simple and uncomplicated operative handling, (2) good compatibility and (3) effective prevention of postlaminectomy membrane.

Spheroid control of malignant glioma cell lines after fractionated irradiation: relation to the surviving fractions at 2 Gy and colony forming efficiencies in a soft agar clonogenic assay.

Spheroid control doses (SCD50) were determined for ten human glioma lines after fractionated irradiation under oxic conditions. In addition, SF2 values and colony forming efficiencies (CFE) were measured in a soft agarose clonogenic assay. A significant relationship existed between the SCD50 values and the SF2-CFE data pairs (p = 0.01) but the SCD50 values were higher than expected from the SF2 and CFE values. This comparison shows the influence of environmental factors (different in both model systems) on reproductive tumour cell death after irradiation.