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Objectives
To assess transient and residual stresses within the porcelain of veneered restorations (zirconia and metal) as a result of cooling rate and porcelain thickness.Methods
Porcelain-on-zirconia (PZ) and porcelain-fused-to-metal (PFM) crowns were fabricated with 1 or 2 mm of porcelain. Thermocouples were attached both internally and externally to the crowns to record transient temperatures. For fast cooling, the furnace was opened after the holding time and switched off. Slow cooling was accomplished by opening the furnace at 50 °C below the glass transition temperature (Tg) of the material. An axially symmetric FEA model simulated thermal stresses. Time-dependent temperature equations from thermocouple readings were set as boundary conditions. Framework materials and the porcelain below Tg were considered to behave elastically. Visco-elastic behavior was assumed for porcelain above the Tg modeling properties as dependent on cooling rate.Results
Differences in residual stress were found for fast and slow cooled PZ and PFM crowns. Significant transient stress waves were observed within the porcelain when fast cooling through Tg. They are believed to be related to non-uniform volumetric changes originated from thermal gradients. Results were confirmed by modeling and physical testing of crowns containing a defect.Significance
Residual stresses do not distinguish PZ from PFM. High magnitude transient stresses observed within the porcelain during fast cooling may explain clinical fractures involving internal defects. Stress waves may also originate internal micro-cracking which could grow under function. Therefore, slow cooling, especially for all-ceramic crowns with thick porcelain, is important to prevent thermal gradients and high-magnitude transient stresses. 相似文献146.
147.
Araujo Júnior E Guimarães Filho HA Saito M Pires AB Pontes AL Nardozza LM Moron AF 《Archives of gynecology and obstetrics》2007,275(2):141-144
Context
The cervical teratomas are rare, benign tumors, they are formed by the three embryonic layers, and they represent only 6%
of teratomas. The prognosis depends mainly on the size and location of the lesion, on the tumor growth rate, and on the level
of tracheal compression. Prenatal diagnosis is usually reached with the aid of a two-dimensional ultrasonography (2DUS) after
the 15th week of gestation, which shows a large heterogeneous mass in the cervical region, plus a polyhydramnios, on the Doppler
mode which also shows the vascularization of the tumor.
Case report
We report a case of cervical teratoma diagnosed on the 31st week of gestation with the aid of a 2DUS and color Doppler mode.
We focus on the main findings obtained with the three-dimensional ultrasonography in surface mode, and we highlight the importance
of this methodology for the indirect evaluation of the neonatal prognosis. 相似文献
148.
This review provides an update regarding newer options in hormonal contraception that include the progestin-releasing intrauterine system, the contraceptive patch and ring, the single rod progestin-releasing implant, extended and emergency oral contraception and recent advances in hormonal male contraception. These methods represent a major advancement in this field, allowing for the development of more acceptable, safety and effective birth control regimens. 相似文献
149.
Wilberg A. Moncada Arita Eduardo Smelin Perdomo Domínguez Astrid Yohaly Rivera Caballero Nelson A. EspinozaMoreno Mauricio E. Zavala Galeano Barbara R. DuPont Hctor M. RamosZaldívar 《Clinical Case Reports》2022,10(4)
Less than one percent of individuals with Down syndrome exhibit mosaicism, a biological phenomenon that describes an individual who has two or more genetically distinct cell lines. The percentage of mosaicism in different tissues can impact the presence of clinical findings and hinder cytogenetic diagnosis. We report a case of mosaicism for trisomy 21 diagnosed after multi‐tissue cytogenetic analysis of peripheral blood and buccal mucosa, associated with significant intellectual disability, dysmorphic facial features, congenital heart defects, macropenis, and imperforate anus. 相似文献
150.
Benjamin Lloyd Miller Gordon William Holtgrieve Mauricio Eduardo Arias Sophorn Uy Phen Chheng 《Proceedings of the National Academy of Sciences of the United States of America》2022,119(8)
Carbon dioxide (CO2) supersaturation in lakes and rivers worldwide is commonly attributed to terrestrial–aquatic transfers of organic and inorganic carbon (C) and subsequent, in situ aerobic respiration. Methane (CH4) production and oxidation also contribute CO2 to freshwaters, yet this remains largely unquantified. Flood pulse lakes and rivers in the tropics are hypothesized to receive large inputs of dissolved CO2 and CH4 from floodplains characterized by hypoxia and reducing conditions. We measured stable C isotopes of CO2 and CH4, aerobic respiration, and CH4 production and oxidation during two flood stages in Tonle Sap Lake (Cambodia) to determine whether dissolved CO2 in this tropical flood pulse ecosystem has a methanogenic origin. Mean CO2 supersaturation of 11,000 ± 9,000 atm could not be explained by aerobic respiration alone. 13C depletion of dissolved CO2 relative to other sources of organic and inorganic C, together with corresponding 13C enrichment of CH4, suggested extensive CH4 oxidation. A stable isotope-mixing model shows that the oxidation of 13C depleted CH4 to CO2 contributes between 47 and 67% of dissolved CO2 in Tonle Sap Lake. 13C depletion of dissolved CO2 was correlated to independently measured rates of CH4 production and oxidation within the water column and underlying lake sediments. However, mass balance indicates that most of this CH4 production and oxidation occurs elsewhere, within inundated soils and other floodplain habitats. Seasonal inundation of floodplains is a common feature of tropical freshwaters, where high reported CO2 supersaturation and atmospheric emissions may be explained in part by coupled CH4 production and oxidation.Globally, most lakes and rivers are supersaturated with dissolved carbon dioxide (CO2) relative to the atmosphere, highlighting their outsized role in transferring and transforming terrestrial carbon (C) (1–3). Terrestrial–aquatic transfers of C can include CO2 dissolved in terrestrial ground and surface waters (3–6), dissolved inorganic carbon (DIC) from carbonate weathering (7, 8), or organic C from various sources that is subsequently respired in lakes and rivers (9, 10). Initially, oceanic export was thought to be the only fate for terrestrial–aquatic transfers of C, but a growing body of research on sediment burial of organic C and CO2 emissions from freshwaters prompted the “active pipe” revision to this initial set of assumptions (11). Although freshwaters are now recognized as focal points for transferring and transforming C on the landscape, most of this research has been conducted within temperate freshwaters (2, 11, 12). Few studies focus on the mechanisms of CO2 supersaturation in tropical lakes and rivers, with most conducted in just one watershed, the Amazon (4, 13–15).CO2 supersaturation within tropical freshwaters is likely influenced by their unique flood pulse hydrology. The canonical flood pulse concept hypothesizes that annual flooding of riparian land will lead to organic C mobilization and respiration (16). Partial pressures of CO2 (pCO2) have been measured in excess of 44,000 atm in the Amazon River (13), 16,000 atm in the Congo River (17), and 12,000 atm in the Lukulu River (17). Richey et al. (13), Borges et al. (18), and Zuidgeest et al. (17) have each shown that that riverine pCO2 scales with the amount of land flooded in these watersheds. Yet it was only recently that Abril and Borges (19) proposed the importance of flooded land to the “active pipe.” These authors differentiate uplands that unidirectionally drain water downhill (via ground and surface water) from floodplains that bidirectionally exchange water with lakes and rivers (19). They conceptualize how floodplains combine high hydrologic connectivity, high rates of primary production, and high rates of respiration to transfer relatively large amounts of C to tropical freshwaters (19).Methanogenesis inevitably results on floodplains after dissolved oxygen (O2) and other electron acceptors for anaerobic respiration such as iron and sulfate are consumed (16, 19). Horizontal gradients in dissolved O2 and reducing conditions have been observed extending from the center of lakes and rivers through their floodplains in the Mekong (20, 21), Congo (22), Pantanal (23), and Amazon watersheds (4). CH4 production and oxidation occur along such redox gradients (4, 16, 19, 23). CH4 is produced by acetate fermentation (Eq. 1) and carbonate reduction (Eq. 2) within freshwaters (24, 25). CH4 production coupled with aerobic oxidation results in CO2 (Eq. 3 and ref. 25), yet no studies have quantified the relative contribution of coupled CH4 production and oxidation to CO2 supersaturation within tropical freshwaters.[1][2][3]The relative contribution of coupled CH4 production and oxidation to CO2 supersaturation within tropical freshwaters can be traced with stable C isotopes of CO2 and CH4. Methanogenesis results in CH4 that is depleted in 13C (13C = −65 to −50‰ from acetate fermentation and −110 to −60‰ from carbonate reduction) compared to other potential sources of organic and inorganic C (13C = −37 to −7.7‰; see Materials and Methods) (24–26). The oxidation of this 13C-depleted CH4 results in 13C-depleted CO2 (24–26). At the same time, CH4 oxidation enriches the 13C/12C of residual CH4 as bacteria and archaea preferentially oxidize 12C-CH4 (25). This means that the 13C/12C of CO2 and CH4 can serve as powerful tools to determine the source of CO2 supersaturation within freshwaters.Tonle Sap Lake (TSL) is Southeast Asia’s largest lake and an understudied flood pulse ecosystem that supports a regionally important fishery (21, 22, 27). Each May through October, monsoonal rains and Himalayan snowmelt increase discharge in the Mekong River and cause one of its tributaries, the Tonle Sap River, to reverse course from southeast to northwest (21). During this course reversal, the Tonle Sap River floods TSL. The TSL flood pulse increases lake volume from 1.6 to 60 km3 and inundates 12,000 km2 of floodplain for 3 to 6 mo per year (21, 27). Holtgrieve et al. (22) have shown that aerobic respiration is consistently greater than primary production in TSL (i.e., net heterotrophy), with the expectation of consistent CO2 supersaturation. But, the partial pressures, C isotopic compositions, and ultimately the source of dissolved CO2 in TSL remain unquantified.To quantify CO2 supersaturation and its origins in TSL, we measured the partial pressures of CO2 and CH4 and compared their C isotopic composition to other potential sources of organic and inorganic C. We carried out these measurements in distinct lake environments during the high-water and falling-water stages of the flood pulse, hypothesizing that CH4 production and oxidation on the TSL floodplain would support CO2 supersaturation during the high-water stage. We found that coupled CH4 production and oxidation account for a nontrivial proportion of the total dissolved CO2 in all TSL environments and during both flood stages, showing that anaerobic degradation of organic C at aquatic–terrestrial transitions can support CO2 supersaturation within tropical freshwaters. 相似文献