Base de dados : MEDLINE
Pesquisa : E05.196.867.776 [Categoria DeCS]
Referências encontradas : 1571 [refinar]
Mostrando: 1 .. 10   no formato [Detalhado]

página 1 de 158 ir para página                         

  1 / 1571 MEDLINE  
              next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:29306092
[Au] Autor:Mohammad Modarresi S; Farhad Masoudi S
[Ad] Endereço:Department of Physics, K.N. Toosi University of Technology, P.O. Box 15875-4416, Tehran, Iran.
[Ti] Título:On the gamma spectrometry efficiency of reference materials and soil samples.
[So] Source:J Environ Radioact;183:54-58, 2018 Mar.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:The relative discrepancies between the gamma spectrometry efficiency of RGU, RGTh, RGK reference materials and some soil samples have been studied using a MCNP model of a real HPGe detector. It has been shown that, in a specified geometry, efficiencies differences depend on the sample elemental composition. The elemental compositions of RGU-1, RGTh-1 reference materials and a soil sample have been evaluated using X-Ray fluorescence (XRF) method and used in the MCNP simulation along with RGK-1 and six other soil samples with different elemental compositions to calculate their efficiencies in different gamma ray energies. To estimate the maximum relative efficiencies differences between soil samples and reference materials, five soil samples with higher attenuation properties were selected from a large data set of soils elemental compositions. The results show that the efficiency differences between soil samples and reference materials are almost ignorable for more than 100 KeV gamma energies. It strongly depends on the sample attenuation factor in the lower energies, so use of a self-attenuation correction is essential for radionuclide counting in low energies gamma rays. Results show about 8 percent discrepancy between RGU and two soil samples efficiencies in 63.2 KeV energy.
[Mh] Termos MeSH primário: Monitoramento de Radiação/métodos
Poluentes Radioativos do Solo/análise
Espectrometria gama
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Soil Pollutants, Radioactive)
[Em] Mês de entrada:1801
[Cu] Atualização por classe:180130
[Lr] Data última revisão:
180130
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:180107
[St] Status:MEDLINE


  2 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:29220714
[Au] Autor:Sálek O; Matolín M; Gryc L
[Ad] Endereço:Charles University, Faculty of Science, Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Czech Republic. Electronic address: ondrej.salek@natur.cuni.cz.
[Ti] Título:Mapping of radiation anomalies using UAV mini-airborne gamma-ray spectrometry.
[So] Source:J Environ Radioact;182:101-107, 2018 Feb.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:Localization of size-limited gamma-ray anomalies plays a fundamental role in uranium prospecting and environmental studies. Possibilities of a newly developed mini-airborne gamma-ray spectrometric equipment were tested on a uranium anomaly near the village of Trebsko, Czech Republic. The measurement equipment was based on a scintillation gamma-ray spectrometer specially developed for unmanned aerial vehicles (UAV) mounted on powerful hexacopter. The gamma-ray spectrometer has two 103 cm BGO scintillation detectors of relatively high sensitivity. The tested anomaly, which is 80 m by 40 m in size, was investigated by ground gamma-ray spectrometric measurement in a detail rectangular measurement grid. Average uranium concentration is 25 mg/kg eU attaining 700 mg/kg eU locally. The mini-airborne measurement across the anomaly was carried out on three 100 m long parallel profiles at eight flight altitudes from 5 to 40 m above the ground. The resulting 1 s 1024 channel gamma-ray spectra, recorded in counts per second (cps), were processed to concentration units of K, U and Th, while total count (TC) was reported in cps. Increased gamma ray intensity of the anomaly was indicated by mini-airborne measurement at all profiles and altitudes, including the highest altitude of 40 m, at which the recorded intensity is close to the natural radiation background. The reported instrument is able to record data with comparable quality as standard airborne survey, due to relative sensitive detector, lower flight altitude and relatively low flight speed of 1 m/s. The presented experiment brings new experience with using unmanned semi-autonomous aerial vehicles and the latest mini-airborne radiometric instrument. The experiment has demonstrated the instrument's ability to localize size-limited uranium anomalies.
[Mh] Termos MeSH primário: Poluentes Radioativos do Ar/análise
Monitoramento de Radiação/métodos
Espectrometria gama
[Mh] Termos MeSH secundário: Altitude
República Tcheca
Urânio/análise
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Air Pollutants, Radioactive); 4OC371KSTK (Uranium)
[Em] Mês de entrada:1712
[Cu] Atualização por classe:171228
[Lr] Data última revisão:
171228
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:171209
[St] Status:MEDLINE


  3 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28915436
[Au] Autor:Al-Shboul KF; Alali AE; Batayneh IM; Al-Khodire HY
[Ad] Endereço:Department of Nuclear Engineering, Jordan University of Science and Technology, Irbid 22110, Jordan. Electronic address: kfshboul@just.edu.jo.
[Ti] Título:Radiation hazards and lifetime risk assessment of tap water using liquid scintillation counting and high-resolution gamma spectrometry.
[So] Source:J Environ Radioact;178-179:245-252, 2017 Nov.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:In this work, two complementary techniques, viz. liquid scintillation counting and high-resolution gamma spectrometry are utilized to analyze radionuclides concentrations in tap water of Irbid governorate, Jordan, and study their correlation. Gross alpha and gross beta concentrations, in the tap water samples collected from the nine districts of Irbid governorate, ranged from <82 to 484 mBq/L with a mean of 295 mBq/L and from <216 to 984 mBq/L with a mean of 611 mBq/L, respectively. Furthermore, gamma spectrometry analysis, for the tap water samples, shows that the activity concentrations of Ra, Th, and K ranged between <19 and 302 mBq/L, 24 to 119 mBq/L, and <101 to 342 mBq/L, respectively. There was a weak or even no correlation among the identified natural radionuclides with no trace of artificial radioactivity. In addition, the results of both techniques show that storing tap water in drilled wells leads to higher levels of radioactivity concentrations beyond the international permissible limits. Furthermore, the average lifetime risk and annual effective dose received by age-grouped inhabitants due to direct and indirect tap water consumption are evaluated, where most of the received dose is attributed to Ra.
[Mh] Termos MeSH primário: Água Potável/química
Exposição à Radiação/estatística & dados numéricos
Monitoramento de Radiação
Poluição Radioativa da Água/estatística & dados numéricos
[Mh] Termos MeSH secundário: Seres Humanos
Jordânia
Dose de Radiação
Medição de Risco
Contagem de Cintilação
Espectrometria gama
Poluentes Radioativos da Água/análise
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Drinking Water); 0 (Water Pollutants, Radioactive)
[Em] Mês de entrada:1711
[Cu] Atualização por classe:171110
[Lr] Data última revisão:
171110
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170916
[St] Status:MEDLINE


  4 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28796752
[Au] Autor:Ji YY; Kim CJ; Lim KS; Lee W; Chang HS; Chung KH
[Ad] Endereço:*Environmental Radioactivity Assessment Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea; † SI Detection Co. Ltd., Daejeon 34051, Republic of Korea.
[Ti] Título:A New Approach for the Determination of Dose Rate and Radioactivity for Detected Gamma Nuclides Using an Environmental Radiation Monitor Based on an NaI(Tl) Detector.
[So] Source:Health Phys;113(4):304-314, 2017 Oct.
[Is] ISSN:1538-5159
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:To expand the application of dose rate spectroscopy to the environment, the method using an environmental radiation monitor (ERM) based on a 3' × 3' NaI(Tl) detector was used to perform real-time monitoring of the dose rate and radioactivity for detected gamma nuclides in the ground around an ERM. Full-energy absorption peaks in the energy spectrum for dose rate were first identified to calculate the individual dose rates of Bi, Ac, Tl, and K distributed in the ground through interference correction because of the finite energy resolution of the NaI(Tl) detector used in an ERM. The radioactivity of the four natural radionuclides was then calculated from the in situ calibration factor-that is, the dose rate per unit curie-of the used ERM for the geometry of the ground in infinite half-space, which was theoretically estimated by Monte Carlo simulation. By an intercomparison using a portable HPGe and samples taken from the ground around an ERM, this method to calculate the dose rate and radioactivity of four nuclides using an ERM was experimentally verified and finally applied to remotely monitor them in real-time in the area in which the ERM had been installed.
[Mh] Termos MeSH primário: Monitoramento Ambiental/métodos
Raios gama
Monitoramento de Radiação/métodos
[Mh] Termos MeSH secundário: Monitoramento Ambiental/instrumentação
Método de Monte Carlo
Dose de Radiação
Monitoramento de Radiação/instrumentação
Radioatividade
Radioisótopos/análise
Espectrometria gama/métodos
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Radioisotopes)
[Em] Mês de entrada:1709
[Cu] Atualização por classe:170915
[Lr] Data última revisão:
170915
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170811
[St] Status:MEDLINE
[do] DOI:10.1097/HP.0000000000000706


  5 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28771156
[Au] Autor:Karakaya MÇ; Dogru M; Karakaya N; Kuluöztürk F; Nalbantçilar MT
[Ad] Endereço:Selçuk University Engineering Faculty Geological Engineering Department, Konya 42079, Turkey E-mail: mcelik@selcuk.edu.tr.
[Ti] Título:Radioactivity and hydrochemical properties of certain thermal Turkish spa waters.
[So] Source:J Water Health;15(4):591-601, 2017 Aug.
[Is] ISSN:1477-8920
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:The study aims to determine the radioactivity levels of thermal waters which have been used seasonally or permanently in spas for therapeutic intentions. Samples were collected from spas in different regions of Turkey. Some radionuclides ( K, Th, Ra, Cs), gross alpha (GA) and gross beta (GB) activities, and physical and some chemical parameters were measured. Gamma radiation measurements for Ra, Th and K radionuclides were performed by using a high purity germanium (HPGe) detector. The results of the gamma spectrometry ranged from 1.385 to 11.025 Bql for Ra,
[Mh] Termos MeSH primário: Águas Minerais/análise
Radioisótopos/análise
Poluentes Radioativos da Água/análise
[Mh] Termos MeSH secundário: Banhos
Monitoramento Ambiental
Monitoramento de Radiação
Espectrometria gama
Turquia
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Mineral Waters); 0 (Radioisotopes); 0 (Water Pollutants, Radioactive)
[Em] Mês de entrada:1711
[Cu] Atualização por classe:171103
[Lr] Data última revisão:
171103
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170804
[St] Status:MEDLINE
[do] DOI:10.2166/wh.2017.263


  6 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28719852
[Au] Autor:Isaksson M; Fahlström M; Ossipova N; Rosén K
[Ad] Endereço:Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden. Electronic address: mats.isaksson@radfys.gu.se.
[Ti] Título:Rapid gamma spectrometric analysis of soil samples after radioactive fallout using a "conjugate view" technique.
[So] Source:J Environ Radioact;177:250-255, 2017 Oct.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:A method for fast determination of the activity in soil samples by measuring a fresh soil core sample from both ends with an HPGe-detector is proposed. The method was tested by simulations, as well as by measurements on spiked soil samples. Both simulations and measurements showed that the geometrical mean of the count rates when the sample is measured twice, with the bottom and the top end, respectively, facing the detector closely resembles the count rate from a measurement on a homogenized sample. Therefore, an efficiency calibration for homogenized samples could be used even if the activity is highly inhomogeneous in the soil core, as is the case with fresh fallout. It was also shown that by studying the ratio between the two measurements, a rough estimation of the extent of penetration of the radionuclide in the soil can be found. This will enhance the possibility to make rapid estimations of the soil inventory by field gamma spectrometry.
[Mh] Termos MeSH primário: Monitoramento de Radiação/métodos
Cinza Radioativa/análise
Poluentes Radioativos do Solo/análise
[Mh] Termos MeSH secundário: Calibragem
Espectrometria gama
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Radioactive Fallout); 0 (Soil Pollutants, Radioactive)
[Em] Mês de entrada:1709
[Cu] Atualização por classe:170908
[Lr] Data última revisão:
170908
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170719
[St] Status:MEDLINE


  7 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28658059
[Au] Autor:Frank SJ; Kearfott KJ
[Ad] Endereço:*University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, MI 48109-2104.
[Ti] Título:Imaging of Gamma-ray Scatter from a Polymethyl-methacrylate Phantom Using a Compton Imaging Spectrometer.
[So] Source:Health Phys;113(2):135-142, 2017 Aug.
[Is] ISSN:1538-5159
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Commercially available gamma-ray imaging spectrometers have been introduced recently and are currently undergoing investigations for various applications in nuclear power plants, environmental management, and medical environments. A Compton imaging gamma-ray spectrometer uses an array of detectors or a single position-sensitive crystal to create planar images of radionuclide distributions. The typical software included with these devices creates images of specific radionuclides using only the counts under their known gamma emission photopeaks. This approach prevents the direct imaging of scattered radiation, which is of interest for many radiation protection applications. In this paper, a technique for imaging radiation scatter or portions of the scatter spectrum is implemented. This involves the creation of a virtual radionuclide in software with peaks placed throughout the backscatter continuum of interest and then imaging that virtual radionuclide in the post-processing software. This technique is used to image the Compton scatter successfully from a polymethyl-methacrylate (PMMA) phantom placed in a Cs irradiator beam. Measured scatter energies were found to be within 15% of the expected values, sufficient to predict scatter behavior and individually measure separate sources of scatter at different angles.
[Mh] Termos MeSH primário: Materiais Biomiméticos/química
Césio/análise
Raios gama
Imagens de Fantasmas
Polimetil Metacrilato/química
Espectrometria gama/instrumentação
[Mh] Termos MeSH secundário: Desenho de Equipamento
Análise de Falha de Equipamento
Seres Humanos
Dose de Radiação
Reprodutibilidade dos Testes
Sensibilidade e Especificidade
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
1KSV9V4Y4I (Cesium); 9011-14-7 (Polymethyl Methacrylate)
[Em] Mês de entrada:1708
[Cu] Atualização por classe:170818
[Lr] Data última revisão:
170818
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170629
[St] Status:MEDLINE
[do] DOI:10.1097/HP.0000000000000681


  8 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28570921
[Au] Autor:Druker E
[Ad] Endereço:6 Maple Meadows Lane, Maple, Ontario, L6A 2X6, Canada. Electronic address: eugene.druker@gmail.com.
[Ti] Título:Airborne gamma-ray spectrometry data processing using 1.5D inversion.
[So] Source:J Environ Radioact;177:13-23, 2017 Oct.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:Standard processing of Airborne Gamma-Ray Spectrometry data generally gives good results when the measurement conditions are almost constant within several footprint area sizes, with the possible exception of flight height variations in a small range. In practice, deviations, such as large or abrupt changes of flight height and/or rugged terrain are not so rare and lead to certain problems. This article proposes a different approach where the solutions of inverse problems are used for data processing. The approach is quite natural in the processing of field data measured along the flight lines: it explicitly takes into account 1.5D survey models and flight parameters - from topography to sources distribution on the surface. Also, it clearly demonstrates that the inverse problem of the Airborne Gamma-Ray Spectrometry does not have a unique solution. This feature can be used in accordance with the underlying geological problem since various formulations of inverse problems can lead to various geological solutions. The use of the approach is illustrated by several examples given for flight lines and survey areas. This approach can be particularly useful in situations where geological, geophysical and/or geographic survey conditions are far from the standard assumptions.
[Mh] Termos MeSH primário: Poluentes Radioativos do Ar/análise
Monitoramento de Radiação/métodos
Espectrometria gama
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Air Pollutants, Radioactive)
[Em] Mês de entrada:1709
[Cu] Atualização por classe:170908
[Lr] Data última revisão:
170908
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170602
[St] Status:MEDLINE


  9 / 1571 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28395154
[Au] Autor:Besic L; Muhovic I; Asic A; Kurtovic-Kozaric A
[Ad] Endereço:Department of Genetics and Bioengineering, International Burch University, Francuske revolucije bb, 71 000 Sarajevo, Bosnia and Herzegovina.
[Ti] Título:Meta-analysis of depleted uranium levels in the Balkan region.
[So] Source:J Environ Radioact;172:207-217, 2017 Jun.
[Is] ISSN:1879-1700
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:In recent years, contradicting data has been published on the connection between the presence of depleted uranium and an increased cancer incidence among military personnel deployed in the Balkans during the 1992-1999 wars. This has led to numerous research articles investigating possible depleted uranium contamination of the afflicted regions of the Balkan Peninsula, namely Bosnia & Herzegovina, Serbia, Kosovo and Montenegro. The aim of this study was to collect data from previously published reports investigating the levels of depleted uranium in the Balkans and to present the data in the form of a meta-analysis. This would provide a clear image of the extent of depleted uranium contamination after the Balkan conflict. In addition, we tested the hypothesis that there is a correlation between the levels of depleted uranium and the assumed depleted uranium-related health effects. Our results suggest that the majority of the examined sites contain natural uranium, while the area of Kosovo appears to be most heavily afflicted by depleted uranium pollution, followed by Bosnia & Herzegovina. Furthermore, the results indicate that it is not possible to make a valid correlation between the health effects and depleted uranium-contaminated areas. We therefore suggest a structured collaborative plan of action where long-term monitoring of the residents of depleted uranium-afflicted areas would be performed. In conclusion, while the possibility of depleted uranium toxicity in post-conflict regions appears to exist, there currently exists no definitive proof of such effects, due to insufficient studies of potentially afflicted populations, in addition to the lack of a common epidemiological approach in the reviewed literature.
[Mh] Termos MeSH primário: Monitoramento de Radiação
Poluentes Radioativos do Solo/análise
Urânio/análise
[Mh] Termos MeSH secundário: Península Balcânica
Bósnia e Herzegóvina
Kosovo
Montenegro
Sérvia
Espectrometria gama
Guerra
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Soil Pollutants, Radioactive); 4OC371KSTK (Uranium)
[Em] Mês de entrada:1706
[Cu] Atualização por classe:170602
[Lr] Data última revisão:
170602
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170411
[St] Status:MEDLINE


  10 / 1571 MEDLINE  
              first record previous record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:28342327
[Au] Autor:Araújo Dos Santos Júnior J; Dos Santos Amaral R; Simões Cezar Menezes R; Reinaldo Estevez Álvarez J; Marques do Nascimento Santos J; Herrero Fernández Z; Dias Bezerra J; Antônio da Silva A; Francys Rodrigues Damascena K; de Almeida Maciel Neto J
[Ad] Endereço:Grupo de Radioecologia (RAE), Brazil. Electronic address: jaraujo@ufpe.br.
[Ti] Título:Influence of terrestrial radionuclides on environmental gamma exposure in a uranium deposit in Paraíba, Brazil.
[So] Source:Ecotoxicol Environ Saf;141:154-159, 2017 Jul.
[Is] ISSN:1090-2414
[Cp] País de publicação:Netherlands
[La] Idioma:eng
[Ab] Resumo:One of the main natural uranium deposits in Brazil is located in the municipality of Espinharas, in the State of Paraíba. This area may present high levels of natural radioactivity due to the presence of these radionuclides. Since this is a populated area, there is need for a radioecological dosimetry assessment to investigate the possible risks to the population. Based on this problem, the objective of this study was to estimate the environmental effective dose outdoors in inhabited areas influenced by the uranium deposit, using the specific activities of equivalent uranium, equivalent thorium and K and conversion factors. The environmental assessment was carried using gamma spectroscopy in sixty-two points within the municipality, with a high-resolution gamma spectrometer with HPGe semiconductor detector and Be window. The results obtained ranged from 0.01 to 19.11 mSv y , with an average of 2.64 mSv y . These levels are, on average, 23 times higher than UNSCEAR reference levels and up to 273 times the reference value of the earth's crust for primordial radionuclides. Therefore, given the high radioactivity levels found, we conclude that there is need for further investigation to evaluate the levels of radioactivity in indoor environments, which will reflect more closely the risks of the local population.
[Mh] Termos MeSH primário: Radiação de Fundo
Raios gama
Monitoramento de Radiação/métodos
Radioisótopos/análise
Tório/análise
Urânio/análise
[Mh] Termos MeSH secundário: Brasil
Exposição Ambiental/análise
Seres Humanos
Radiometria
Poluentes Radioativos do Solo/análise
Espectrometria gama
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Radioisotopes); 0 (Soil Pollutants, Radioactive); 4OC371KSTK (Uranium); 60YU5MIG9W (Thorium)
[Em] Mês de entrada:1707
[Cu] Atualização por classe:170719
[Lr] Data última revisão:
170719
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170326
[St] Status:MEDLINE



página 1 de 158 ir para página                         
   


Refinar a pesquisa
  Base de dados : MEDLINE Formulário avançado   

    Pesquisar no campo  
1  
2
3
 
           



Search engine: iAH v2.6 powered by WWWISIS

BIREME/OPAS/OMS - Centro Latino-Americano e do Caribe de Informação em Ciências da Saúde