948 resultados para 1 kyr running mean


Relevância:

100.00% 100.00%

Publicador:

Resumo:

The terrigenous sediment proportion of the deep sea sediments from off Northwest Africa has been studied in order to distinguish between the aeolian and the fluvial sediment supply. The present and fossil Saharan dust trajectories were recognized from the distribution patterns of the aeolian sediment. The following timeslices have been investigated: Present, 6,000, 12,000 and 18,000 y. B. P. Furthermore, the quantity of dust deposited off the Saharan coast has been estimated. For this purpose, 80 surface sediment samples and 34 sediment cores have been analysed. The stratigraphy of the cores has been achieved from oxygen isotopic curves, 14C-dating, foraminiferal transfer temperatures, and carbonate contents. Silt sized biogenic opal generally accounts for less than 2 % of the total insoluble sediment proportion. Only under productive upwelling waters and off river mouths, the opal proportion exceeds 2 % significantly. The modern terrigenous sediment from off the Saharan coast is generally characterized by intensely stained quartz grains. They indicate an origin from southern Saharan and Sahelian laterites, and a zonal aeolian transport in midtropospheric levels, between 1.5 an 5.5 km, by 'Harmattan' Winds. The dust particles follow large outbreaks of Saharan air across the African coast between 15° and 21° N. Their trajectories are centered at about 18° N and continue further into a clockwise gyre situated south of the Canary Islands. This course is indicated by a sickle-shaped tongue of coarser grain sizes in the deep-sea sediment. Such loess-sized terrigenous particles only settle within a zone extending to 700 km offshore. Fine silt and clay sized particles, with grain sizes smaller than 10- 15 µm, drift still further west and can be traced up to more than 4,000 km distance from their source areas. Additional terrigenous silt which is poor in stained quartz occurs within a narrow zone off the western Sahara between 20° and 27° N only. It depicts the present dust supply by the trade winds close to the surface. The dust load originates from the northwestern Sahara, the Atlas Mountains and coastal areas, which contain a particularly low amount of stained quartz. The distribution pattern of these pale quartz sediments reveals a SSW-dispersal of dust being consistent with the present trade wind direction from the NNE. In comparison to the sediments from off the Sahara and the deeper subtropical Atlantic, the sediments off river mouths, in particular off the Senegal river, are characterized by an additional input of fine grained terrigenous particles (< 6 µm). This is due to fluvial suspension load. The fluvial discharge leads to a relative excess of fine grained particles and is observed in a correlation diagram of the modal grain sizes of terrigenous silt with the proportion of fine fraction (< 6 µm). The aeolian sediment contribution by the Harmattan Winds strongly decreased during the Climatic Optimum at 6,000 y. B. P. The dust discharge of the trade winds is hardly detectable in the deep-sea sediments. This probably indicates a weakened atmospheric circulation. In contrast, the fluvial sediment supply reached a maximum, and can be traced to beyond Cape Blanc. Thus, the Saharan climate was more humid at 6,000 y B. P. A latitudinal shift of the Harmattan driven dust outbreaks cannot be observed. Also during the Glacial, 18,000 y. B. P., Harmattan dust transport crossed the African coast at latitudes of 15°-20° N. Its sediment load increased intensively, and markedly coarser grains spread further into the Atlantic Ocean. An expanded zone of pale-quart sediments indicates an enhanced dust supply by the trade winds blowing from the NE. No synglacial fluvial sediment contribution can be recognized between 12° and 30° N. This indicates a dry glacial climate and a strengthened stmospheric circulation over the Sahelian and Saharan region. The climatic transition pahes, at 12, 000 y. B. P., between the last Glacial and the Intergalcial, which is compareable to the Alerod in Europe, is characterized by an intermediate supply of terrigenous particles. The Harmattan dust transport wa weaker than during the Glacial. The northeasterly trade winds were still intensive. River supply reached a first postglacial maximum seaward of the Senegal river mouth. This indicates increasing humidity over the southern Sahara and a weaker atmospheric circulation as compared to the glacial. The accumulation rates of the terrigenous silt proportion (> 6 µm) decrcase exponentially with increasing distance from the Saharan coast. Those of the terrigenous fine fraction (< 6 µm) follow the same trend and show almost similar gradients. Accordingly, also the terrigenous fine fraction is believed to result predominantly from aeolian transport. In the Atlantic deep-sea sediments, the annual terrigenous sediment accumulation has fluctuated, from about 60 million tons p. a. during the Late Glacial (13,500-18,000 y. B. P, aeolian supply only) to about 33 million tons p. a. during the Holocene Climatic Optimum (6,000-9,000 y. B. P, mainly fluvial supply), when the river supply has reached a maximum, and to about 45 million tons p. a. during the last 4,000 years B. P. (fluvial supply only south of 18° N).

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The study was carried out on the main plots of a large grassland biodiversity experiment (the Jena Experiment). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. We tracked soil microbial basal respiration (BR; µlO2/g dry soil/h) and biomass carbon (Cmic; µgC/g dry soil) over a time period of 12 years (2003-2014) and examined the role of plant diversity and plant functional group composition for the spatial and temporal stability (calculated as mean/SD) of soil microbial properties (basal respiration and biomass) in bulk-soil. Our results highlight the importance of plant functional group composition for the spatial and temporal stability of soil microbial properties, and hence for microbially-driven ecosystem processes, such as decomposition and element cycling, in temperate semi-natural grassland.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The diagnosis of nutritional status is extremely re levant in clinical practice and population assessment, due to the association betwe en body fat and metabolic alterations. The aim of this study is to analyze th e prevalence of metabolic syndrome (MS) and its components in the pubertal stages of f emale students in Rio Grande do Norte state, Brazil, in accordance with Internation al Diabetes Federation criteria. This is a cross-sectional study with 449 students aged betw een 8 and 19 years, stratified into pubertal stages systematized by Marshal and Tanner (1969), as follows: 27.6% prepubertal, 44.3% pubertal and 28.1% postpubertal, with mean ages of 9.4±1.27, 12.4±2.23 and 15.1±1.88 years, respectively. Preval ences were analyzed using distribution of frequencies and their respective 95 % confidence intervals, while the chi- square test and odds ratio were applied to analyze the associations between variables. The general prevalence of MS was 3.3% (CI: 2% - 5%) , without occurrences in the prepubertal stage, observing that it emerges from t he pubertal stage onwards with a prevalence of 2.5% (CI 95% 0.1% - 5%), 1% (CI 95% 0.4% - 2.3%) of cases with overweight and 1.5% (CI 95% -0.1% - 3.2%) with obes e individuals, while in the postpubertal stage the prevalence is 7.9% (CI 95% 3 .2% - 12.6%), 0.8% (CI 95% -0.8% - 2.3%) normal weight cases, 4% (CI 95% 0.6% - 7.4% ) overweight and 3.1% (CI 0.1% - 6.2%) obese individuals. There was an association (p<0.02) between pubertal stages and MS ( x 2 =5.2), with an OR of 3.3 (CI: 1.2 - 5), showing tha t postpubertal adolescents are more prone to SM than pubertals, while the OR i n obese individuals was 2.1 (CI: 2– 2.2) compared to the overweight. Body mass index (B MI) ( x 2 = 29.4; p<0.001) and age range ( x 2 = 13.1; p<0.001) showed a significant linear assoc iation with MS. Of the adolescents with MS, those aged ten years or younge r exhibited higher %G. The most prevalent components in all the stages were altered waist circumference (27.2% [CI 23% - 31%]) and low HDL cholesterol (39.6% [CI 35% – 44%]), which, coupled with hypertension, displayed significant differences in the postpubertal stage in relation to the other stages. The results show that MS emerges from the pubertal stage onwards in proportion to excess childhood body fat, a fact tha t calls for prevention strategies using an educational approach, reducing the large demand on the National Health System. Keywords: Metabolic syndrome, pubertal stages, risk factors.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Aim : To evaluate and to standardize surface electromyography (sEMG) normalization procedures for respiratory muscles by comparing muscle activation during Maximal Voluntary Isometric Contraction (MVIC) and Maximal Respiratory Pressures (MIP, MEP and sniff test). Methods: Healthy subjects were evalua ted regarding demographics, spirometry and sEMG during the five maneuvers: sniff test, MIP , MEP and Maximal Voluntary Isometric C ontraction (MVIC) of RA, SCM and SC A . For electrode placement, skin was prepared with abrasion, followed by shaving in the foll owing regions for acquisition of el ectromyographic signals: (1) SC M: lower third of the distance between the mastoid process and t he sternoclavicular joint; (2) SC A : 5 cm to the right from the sternoclavicular joint and at this point, up to 2 cm; and (3 ) RA: the level of umbilicus, 4 cm to the right. In electromyographic variables analysis , the data normality was assessed by Shapiro - Wilk test. Comparisons among studied maneuvers were performed by Friedman Test and Dunn’s post - hoc for multiple comparisons a mong inspiratory maneuvers, and Mann Whitney test for expiratory maneuvers. Subgroups differences between genders were performed by Student's t test or Mann - Whitney test according to data normality. Results: 35 subjects participated in the study, b ut 5 we re excluded (BMI> 25 kg/ m²). Sample consisted of 30 subjects (1 5 women), mean age 27.3±7.43 years, BMI 22.2 ± 1.69 kg/m² and spirometric indices within normal limits. Specific MVIC for SCM, SCA and RA showed the highest RMS. When we grouped sample into gender we found no difference among RMS values for the studied SCM maneuvers, while for SCA, MVIC SCM / SCA was the one with the highest RMS and for RA, MVIC RA in men. Once considering women, MVIC SCM/SCA showed the highest RMS for SCM, SCA and MVIC RA showed t he highest value for RA. Conclusion: MVIC for SCM, SCA and RA muscles showed the highest RMS values. When comparing RMS between the studied groups, there was no significant difference between men and women.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The timing and nature of the penultimate deglaciation, also known as Termination II (T-II), is subject of controversial discussions due to the scarcity of precisely-dated palaeoclimate records. Here we present a new precisely-dated and highly-resolved multi-proxy stalagmite record covering T-II from the high alpine Schafsloch Cave in Switzerland, an area where climate is governed by the North Atlantic. The inception of stalagmite growth at 137.4 ± 1.4 kyr before present (BP) indicates the presence of drip water and cave air temperatures of above 0 °C, and is related to a climate-induced change in the thermal state (from cold-to warm-based) of the glacier above the cave. The cessation of stalagmite growth between 133.1 ± 0.7 and 131.9 ± 0.6 kyr BP is most likely related to distinct drop in temperature associated with Heinrich stadial 11. The resumption of stalagmite growth at 131.9 ± 0.6 kyr BP is accompanied by an abrupt increase in temperature and precipitation as indicated by distinct shifts in the oxygen and carbon isotopic composition as well as in trace element concentrations. The mid-point of T-II is around 131.8 ± 0.6 kyr BP in the Schafsloch Cave record is significantly earlier compared to the age of 129.1 ± 0.1 kyr BP in the Sanbao Cave record from China. The different ages between both records can be best explained by the competing effects of insolation and glacial boundary forcing on seasonality and snow cover extent in Eurasia.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Geochemical records are presented for five sediment cores from basins on the continental shelf of Mac. Robertson Land, East Antarctica. The cores contain 2-4 m thick sequences of hemipelagic, siliceous mud and ooze (SMO) deposited under seasonally open marine conditions. The inner and middle shelf SMO sequences are massive dark olive green material, whereas the outer shelf SMO sequences are dark olive material interspersed with light olive green layers ~1-10 cm thick. The biogenic material is dominated by marine diatoms including Fragilariopsis curta, Fragilariopsis cylindrus, and Chaetoceros spp. in the dark-colored SMO and Corethron criophilum in the light-colored layers. Radiocarbon dates suggest that the cores provide continuous accumulation records extending from < 1 kyr before present (B.P.) back as far as 4-15 kyr B.P., with estimated accumulation rates of 0.07-5 mm/yr. The three core records from the middle and outer shelf suggest six episodes of increased accumulation of biogenic material at ~5.5 kyr B.P. (all three cores), 1, 2, and 6.2 kyr B.P. (two of the three cores), and 3.8 and 10.8 kyr B.P. (one core), most of which coincide with Corethron layers. We interpret these features as the result of enhanced diatom production over the outer shelf, possibly related to climatic warm periods. The absence of such features in the inner shelf core records is thought to reflect a relatively constant level of seasonal diatom production in adjacent waters maintained by a coastal polynya.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The modern Aegean Sea is an important source of deep water for the eastern Mediterranean. Its contribution to deep water ventilation is known to fluctuate in response to climatic variation on a decadal timescale. This study uses marine micropalaeontological and stable isotope data to investigate longer-term variability during the late glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions, we identify the start of 'seasonal' stratification and highlight a lag in d18O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the d18O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in a stagnant basin for 1-1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its "stratified" sapropel mode, which is of the order of 450 years.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

OBJECTIVE: To evaluate the performance of a continuous quality improvement collaboration at Ridge Regional Hospital, Accra, Ghana, that aimed to halve maternal and neonatal deaths. METHODS: In a quasi-experimental, pre- and post-intervention analysis, system deficiencies were analyzed and 97 improvement activities were implemented from January 2007 to December 2011. Data were collected on outcomes and implementation rates of improvement activities. Severity-adjustment models were used to calculate counterfactual mortality ratios. Regression analysis was used to determine the association between improvement activities, staffing, and maternal mortality. RESULTS: Maternal mortality decreased by 22.4% between 2007 and 2011, from 496 to 385 per 100000 deliveries, despite a 50% increase in deliveries and five- and three-fold increases in the proportion of pregnancies complicated by obstetric hemorrhage and hypertensive disorders of pregnancy, respectively. Case fatality rates for obstetric hemorrhage and hypertensive disorders of pregnancy decreased from 14.8% to 1.6% and 3.1% to 1.1%, respectively. The mean implementation score was 68% for the 97 improvement processes. Overall, 43 maternal deaths were prevented by the intervention; however, risk severity-adjustment models indicated that an even greater number of deaths was averted. Mortality reduction was correlated with 26 continuous quality improvement activities, and with the number of anesthesia nurses and labor midwives. CONCLUSION: The implementation of quality improvement activities was closely correlated with improved maternal mortality.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Background: Fractured neck of femur is a common cause of hospital admission in the elderly and usually requires operative fixation. In a variety of clinical settings, preoperative glucocorticoid administration has improved analgesia and decreased opioid consumption. Our objective was to define the postoperative analgesic efficacy of single dose of dexamethasone administered preoperatively in patients undergoing operative fixation of fractured neck of femur. Methods: Institutional ethical approval was granted and written informed consent was obtained from each patient. Patients awaiting for surgery at Cork University Hospital were recruited between July 2009 and August 2012. Participating patients, scheduled for surgery were randomly allocated to one of two groups (Dexamethasone or Placebo). Patients in the dexamethasone group received a single dose of intravenous dexamethasone 0.1 mg kg -1 immediately preoperatively. Patients in the placebo group received the same volume of normal saline. Patients underwent operative fixation of fractured neck of femur using standardised spinal anaesthesia and surgical techniques. The primary outcome was pain scores at rest 6 h after the surgery. Results: Thirty seven patients were recruited and data from thirty patients were analysed. The groups were similar in terms of patient characteristics. Pain scores at rest 6 h after the surgery (the principal outcome) were lesser in the dexamethasone group compared with the placebo group [0.8(1.3) vs. 3.9(2.9), mean(SD) p = 0.0004]. Cumulative morphine consumption 24 h after the surgery was also lesser in the dexamethasone group [7.7(8.3) vs. 15.1(9.4), mean(SD) mg, p = 0.04]. Conclusions: A single dose of intravenous dexamethasone 0.1 mg kg -1 administered before operative fixation of fractured neck of femur improve significantly the early postoperative analgesia. Trial registration: ClinicalTrials.gov identifier: NCT01550146, date of registration: 07/03/2012

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Maerl community respiration, photosynthesis and calcification were measured seasonally in the Bay of Brest (France). The dynamics of oxygen, carbon and carbonate fluxes at the water-sediment interface were assessed using benthic chambers. Community respiration (CR) fluctuated in accordance with the seasonal changes in water temperature, from 1.5 mmol C m**-2 h**-1 in winter to 8.7 mmol C m**-2 h**-1 in summer. Mean gross community production (GCP) varied significantly among seasons, according to incident irradiance and temperature, from 3.4 mmol C m**-2 h**-1 in winter to 12.7 mmol C m-2 h-1 in summer. Mean annual Pmax for the P-E curve was estimated to 13.3 mmol C m-2 h-1. Carbonate precipitation only occurred during light incubations and varied seasonally from 0.7 mmol CaCO3 m-2 h-1 in winter to 4.2 mmol CaCO3 m-2 h-1 in summer. Mean annual Pmax was 3.2 mmol CaCO3 m-2 h-1. Annual CR was estimated to 407.4 g C m**-2 yr**-1, and GCP, to 240.9 g C m**-2 yr**-1. Maerl communities are, therefore, heterotrophic systems (GCP:CR = 0.6), and are a source of CO2 for surrounding environments. In addition, CO2 released by calcification averaged 39.2 g C m**-2 yr**-1. Maerl community annual carbonate production was estimated to 486.7 g CaCO3 m**-2 yr**-1; they are therefore one of the most important carbonate producers in shallow coastal waters.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

To assess the contribution of soft-bottoms to the carbon cycle in coral reefs, the net community production (p) was measured in winter at 3 stations on La Saline inner reef flat (Reunion Island). Changes in pH and total alkalinity at different irradiances (I) were assessed using benthic chambers (0.2 m2) during a 1-h incubation. Mean grain size, the silt and clay load and chlorophyll a content of the sediments were analysed in each chamber. Daily community production (P), gross community production (Pg) and community respiration (R) were estimated from p-I curves and daily irradiance variations (PAR, 400-700 nm). Sediment characteristics and chlorophyll a contents did not differ between the three sites, except for the silt and clay fraction at one station. R being higher than Pg (84.88 ± 7.36 and -62.29 ± 3.34 mmolC m-2 d-1 respectively), P value reached 22.59 ± 5.66 mmolC m-2 d-1. The sediments were therefore heterotrophic with a mean Pg/R lower than 1 (0.74 ± 0.05) and appear to be a carbon source. Our data suggested the importance of the degradation process in the functioning of near-reef sediments.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The ability to project oneself into the future to pre-experience an event is referred to as episodic future thinking (Atance & O’Neill, 2001). Only a relatively small number of studies have attempted to measure this ability in pre-school aged children (Atance & Meltzoff, 2005; Busby & Suddendorf, 2005ab, 2010; Russell, Alexis, & Clayton, 2010).Perhaps the most successful method is that used by Russell et al (2010). In this task, 3- to 5-year-olds played a game of blow football on one end of a table. After this children were asked to select tools that would enable them to play the same game tomorrow from the opposite, unreachable, side of the table. Results indicated that only 5-year-olds were capable of selecting the right objects for future use more often than would be expected by chance. Above-chance performance was observed in this older group even though most children failed the task because there was a low probability of selecting the correct 2 objects from a choice of 6 by chance.This study aimed to identify the age at which children begin to consistently pass this type of task. Three different tasks were designed in which children played a game on one side of a table, and then were asked to choose a tool to play a similar game on the other side of the table the next day. For example, children used a toy fishing rod to catch magnetic fish on one side of the table; playing the same game from the other side of the table required a different type of fishing rod. At test, children chose between just 2 objects: the tool they had already used, which would not work on the other side, and a different tool that they had not used before but which was suitable for the other side of the table. Experiment 1: Forty-eight 4-year-olds (M = 53.6 months, SD = 2.9) took part. These children were assigned to one of two conditions: a control condition (present-self) where the key test questions were asked in the present tense and an experimental condition (future-self) where the questions were in the future tense. Surprisingly, the results showed that both groups of 4-year-olds selected the correct tool at above chance levels (Table 1 shows the mean number of correct answers out of three). However, the children could see the apparatus when they answered the test questions and so perhaps answered them correctly without imagining the future. Experiment 2: Twenty-four 4-year-olds (M = 53.7, SD = 3.1) participated. Pre-schoolers in this study experienced one condition: future-self looking-away. In this condition children were asked to turn their backs to the games when answering the test questions, which were in the future tense. Children again performed above chance levels on all three games.Contrary to the findings of Russell et al. (2010), our results suggest that episodic future thinking skills could be present in 4-year-olds, assuming that this is what is measured by the tasks. Table 1. Mean number of correct answers across the three games in Experiments 1 and 2Experimental Conditions (N=24 in each condition)Mean CorrectStandardDeviationStatistical SignificanceExp. 1 (present-self, look) – 2 items2.750.68p < 0.001Exp. 1 (future-self, look) – 2 items 2.790.42p < 0.001Exp. 2 (future-self, away) – 2 items 2.330.64p < 0.001Exp. 3 (future-self away) – 3 items1.210.98p = 0.157

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Aflatoxin B1 (AFB1) is a secondary metabolite produced by the fungi Aspergillus flavus and is the most potent hepatocarcinogen known in mammals and has been classified by the International Agency of Research on Cancer as Group 1 carcinogen. Although dietary exposure to AFB1 has been extensively documented, there are still few studies dedicated to the problem of occupational exposure. Considering recent findings regarding AFB1 occupational exposure in poultry production, it was considered relevant to clarify if there is also exposure in poultry slaughterhouses. Occupational exposure assessment to AFB1 was done with a biomarker of internal dose that measures AFB1 in the serum by enzyme-linked immunosorbent assay. Thirty workers from a slaughterhouse were enrolled in this study. A control group (n = 30) was also considered in order to know AFB1 background levels for Portuguese population. Fourteen workers (47.0%) showed detectable levels of AFB1 with values from 1.06 to 4.03ng ml(-1), with a mean value of 1.73ng ml(-1). No AFB1 was detected in serum of individuals used as controls. Despite uncertainties regarding the exposure route that is contributing more to exposure (inhalation or dermal) is possible to state that exposure to AFB1 is occurring in the slaughterhouse studied. It seems that reducing AFB1 contamination in poultry production can have a positive result in this occupational setting.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Introduction. Primary cardiac tumors are uncommon in cardiac surgery. To investigate the clinical presentation, surgical results and long-term follow-up we retrospectively analyzed our experience in the treatment of primary cardiac tumors. Patients and methods. Ninety-one patients with primary cardiac tumors underwent surgery in our department in the last 20 years. Fifthy-one patients were female, the mean age was 62,2 years. Sixty-three had myxomas, 22 had papillary fibroelastoma, 4 had malignant neoformations and 2 had other benign tumors. Results. All myxomas, fibroelastomas and angiomyolipoma were radically removed. Only a palliative treatment was possible in malignant disease. In-hospital mortality was 1.2%. The mean follow-up time was 78.5 months. Three patients had recurrence of myxoma, all patients with malignant disease dead during the follow-up. Discussion. Primary benign cardiac tumors can be treated with low morbidity and mortality. The follow-up demonstrates that radical surgery is curative in case of benign tumors. The prognosis of malignant tumors is still poor. Palliative procedures have small impact on survival in these patients.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization rates inferred from these detections are in the range (1.7+-1.0)x10^-16 s^-1 < zeta_2 < (10.6+-6.8)x10^-16 s^-1 with a mean value of zeta_2=(3.3+-0.4)x10^-16 s^-1. Upper limits (3sigma) derived from non-detections of H3+ are as low as zeta_2 < 0.4x10^-16 s^-1. These low upper-limits, in combination with the wide range of inferred cosmic-ray ionization rates, indicate variations in zeta_2 between different diffuse cloud sight lines. Calculations of the cosmic-ray ionization rate from theoretical cosmic-ray spectra require a large flux of low-energy (MeV) particles to reproduce values inferred from observations. Given the relatively short range of low-energy cosmic rays --- those most efficient at ionization --- the proximity of a cloud to a site of particle acceleration may set its ionization rate. Variations in zeta_2 are thus likely due to variations in the cosmic-ray spectrum at low energies resulting from the effects of particle propagation. To test this theory, H3+ was observed in sight lines passing through diffuse molecular clouds known to be interacting with the supernova remnant IC 443, a probable site of particle acceleration. Where H3+ is detected, ionization rates of zeta_2=(20+-10)x10^-16 s^-1 are inferred, higher than for any other diffuse cloud. These results support both the concept that supernova remnants act as particle accelerators, and the hypothesis that propagation effects are responsible for causing spatial variations in the cosmic-ray spectrum and ionization rate. Future observations of H3+ near other supernova remnants and in sight lines where complementary ionization tracers (OH+, H2O+, H3O+) have been observed will further our understanding of the subject.