| 1. |
- Klionsky, Daniel J., et al.
(författare)
-
Guidelines for the use and interpretation of assays for monitoring autophagy
- 2012
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Ingår i: Autophagy. - : Informa UK Limited. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
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Forskningsöversikt (refereegranskat)abstract
- In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
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| 2. |
- Arndt, D. S., et al.
(författare)
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STATE OF THE CLIMATE IN 2017
- 2018
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 99:8, s. S1-S310
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Forskningsöversikt (refereegranskat)
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| 3. |
- Arndt, D. S., et al.
(författare)
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State of the Climate in 2016
- 2017
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 98:8, s. S1-S280
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Tidskriftsartikel (refereegranskat)abstract
- In 2016, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-continued to increase and reach new record highs. The 3.5 +/- 0.1 ppm rise in global annual mean carbon dioxide from 2015 to 2016 was the largest annual increase observed in the 58-year measurement record. The annual global average carbon dioxide concentration at Earth's surface surpassed 400 ppm (402.9 +/- 0.1 ppm) for the first time in the modern atmospheric measurement record and in ice core records dating back as far as 800000 years. One of the strongest El Nino events since at least 1950 dissipated in spring, and a weak La Nina evolved later in the year. Owing at least in part to the combination of El Nino conditions early in the year and a long-term upward trend, Earth's surface observed record warmth for a third consecutive year, albeit by a much slimmer margin than by which that record was set in 2015. Above Earth's surface, the annual lower troposphere temperature was record high according to all datasets analyzed, while the lower stratospheric temperature was record low according to most of the in situ and satellite datasets. Several countries, including Mexico and India, reported record high annual temperatures while many others observed near-record highs. A week-long heat wave at the end of April over the northern and eastern Indian peninsula, with temperatures surpassing 44 degrees C, contributed to a water crisis for 330 million people and to 300 fatalities. In the Arctic the 2016 land surface temperature was 2.0 degrees C above the 1981-2010 average, breaking the previous record of 2007, 2011, and 2015 by 0.8 degrees C, representing a 3.5 degrees C increase since the record began in 1900. The increasing temperatures have led to decreasing Arctic sea ice extent and thickness. On 24 March, the sea ice extent at the end of the growth season saw its lowest maximum in the 37-year satellite record, tying with 2015 at 7.2% below the 1981-2010 average. The September 2016 Arctic sea ice minimum extent tied with 2007 for the second lowest value on record, 33% lower than the 1981-2010 average. Arctic sea ice cover remains relatively young and thin, making it vulnerable to continued extensive melt. The mass of the Greenland Ice Sheet, which has the capacity to contribute similar to 7 m to sea level rise, reached a record low value. The onset of its surface melt was the second earliest, after 2012, in the 37-year satellite record. Sea surface temperature was record high at the global scale, surpassing the previous record of 2015 by about 0.01 degrees C. The global sea surface temperature trend for the 21st century-to-date of +0.162 degrees C decade(-1) is much higher than the longer term 1950-2016 trend of +0.100 degrees C decade(-1). Global annual mean sea level also reached a new record high, marking the sixth consecutive year of increase. Global annual ocean heat content saw a slight drop compared to the record high in 2015. Alpine glacier retreat continued around the globe, and preliminary data indicate that 2016 is the 37th consecutive year of negative annual mass balance. Across the Northern Hemisphere, snow cover for each month from February to June was among its four least extensive in the 47-year satellite record. Continuing a pattern below the surface, record high temperatures at 20-m depth were measured at all permafrost observatories on the North Slope of Alaska and at the Canadian observatory on northernmost Ellesmere Island. In the Antarctic, record low monthly surface pressures were broken at many stations, with the southern annular mode setting record high index values in March and June. Monthly high surface pressure records for August and November were set at several stations. During this period, record low daily and monthly sea ice extents were observed, with the November mean sea ice extent more than 5 standard deviations below the 1981-2010 average. These record low sea ice values contrast sharply with the record high values observed during 2012-14. Over the region, springtime Antarctic stratospheric ozone depletion was less severe relative to the 1991-2006 average, but ozone levels were still low compared to pre-1990 levels. Closer to the equator, 93 named tropical storms were observed during 2016, above the 1981-2010 average of 82, but fewer than the 101 storms recorded in 2015. Three basins-the North Atlantic, and eastern and western North Pacific-experienced above-normal activity in 2016. The Australian basin recorded its least active season since the beginning of the satellite era in 1970. Overall, four tropical cyclones reached the Saffir-Simpson category 5 intensity level. The strong El Nino at the beginning of the year that transitioned to a weak La Nina contributed to enhanced precipitation variability around the world. Wet conditions were observed throughout the year across southern South America, causing repeated heavy flooding in Argentina, Paraguay, and Uruguay. Wetter-than-usual conditions were also observed for eastern Europe and central Asia, alleviating the drought conditions of 2014 and 2015 in southern Russia. In the United States, California had its first wetter-than-average year since 2012, after being plagued by drought for several years. Even so, the area covered by drought in 2016 at the global scale was among the largest in the post-1950 record. For each month, at least 12% of land surfaces experienced severe drought conditions or worse, the longest such stretch in the record. In northeastern Brazil, drought conditions were observed for the fifth consecutive year, making this the longest drought on record in the region. Dry conditions were also observed in western Bolivia and Peru; it was Bolivia's worst drought in the past 25 years. In May, with abnormally warm and dry conditions already prevailing over western Canada for about a year, the human-induced Fort McMurray wildfire burned nearly 590000 hectares and became the costliest disaster in Canadian history, with $3 billion (U.S. dollars) in insured losses.
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| 4. |
- Gao, Hong, et al.
(författare)
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The landscape of tolerated genetic variation in humans and primates
- 2023
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6648
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Tidskriftsartikel (refereegranskat)abstract
- Personalized genome sequencing has revealed millions of genetic differences between individuals, but our understanding of their clinical relevance remains largely incomplete. To systematically decipher the effects of human genetic variants, we obtained whole-genome sequencing data for 809 individuals from 233 primate species and identified 4.3 million common protein-altering variants with orthologs in humans. We show that these variants can be inferred to have nondeleterious effects in humans based on their presence at high allele frequencies in other primate populations. We use this resource to classify 6% of all possible human protein-altering variants as likely benign and impute the pathogenicity of the remaining 94% of variants with deep learning, achieving state-of-the-art accuracy for diagnosing pathogenic variants in patients with genetic diseases.
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| 5. |
- Kuderna, Lukas F. K., et al.
(författare)
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A global catalog of whole-genome diversity from 233 primate species
- 2023
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6648, s. 906-913
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Tidskriftsartikel (refereegranskat)abstract
- The rich diversity of morphology and behavior displayed across primate species provides an informative context in which to study the impact of genomic diversity on fundamental biological processes. Analysis of that diversity provides insight into long-standing questions in evolutionary and conservation biology and is urgent given severe threats these species are facing. Here, we present high-coverage wholegenome data from 233 primate species representing 86% of genera and all 16 families. This dataset was used, together with fossil calibration, to create a nuclear DNA phylogeny and to reassess evolutionary divergence times among primate clades. We found within-species genetic diversity across families and geographic regions to be associated with climate and sociality, but not with extinction risk. Furthermore, mutation rates differ across species, potentially influenced by effective population sizes. Lastly, we identified extensive recurrence of missense mutations previously thought to be human specific. This study will open a wide range of research avenues for future primate genomic research.
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| 6. |
- Kuderna, Lukas F. K., et al.
(författare)
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Identification of constrained sequence elements across 239 primate genomes
- 2024
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 625:7996, s. 735-742
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Tidskriftsartikel (refereegranskat)abstract
- Noncoding DNA is central to our understanding of human gene regulation and complex diseases1,2, and measuring the evolutionary sequence constraint can establish the functional relevance of putative regulatory elements in the human genome3,4,5,6,7,8,9. Identifying the genomic elements that have become constrained specifically in primates has been hampered by the faster evolution of noncoding DNA compared to protein-coding DNA10, the relatively short timescales separating primate species11, and the previously limited availability of whole-genome sequences12. Here we construct a whole-genome alignment of 239 species, representing nearly half of all extant species in the primate order. Using this resource, we identified human regulatory elements that are under selective constraint across primates and other mammals at a 5% false discovery rate. We detected 111,318 DNase I hypersensitivity sites and 267,410 transcription factor binding sites that are constrained specifically in primates but not across other placental mammals and validate their cis-regulatory effects on gene expression. These regulatory elements are enriched for human genetic variants that affect gene expression and complex traits and diseases. Our results highlight the important role of recent evolution in regulatory sequence elements differentiating primates, including humans, from other placental mammals.
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| 7. |
- Blunden, Jessica, et al.
(författare)
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State of the Climate in 2012
- 2013
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 94:8, s. S1-S258
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Tidskriftsartikel (refereegranskat)abstract
- For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
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| 8. |
- Golchin, Arash, et al.
(författare)
-
Break-away friction of PTFE materials in lubricated conditions
- 2011
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 48, s. 54-62
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the tribological characteristics at initiation of sliding (break-away friction) of several polytetrafluoroethylene based materials. Four PTFE composites, pure PTFE, and white metal were tested in a reciprocating tribo-meter with the block on plate configuration against a steel counter-surface. Apparent contact pressure and oil temperature were varied from 1 to 8 MPa and 25 to 85 °C respectively. SEM investigations revealed wear patterns of the PTFE materials and the abrasive nature of hard fillers. Bronze filled, carbon filled, and pure PTFE were found to provide lower break-away friction and less variation over the course of testing and generally superior properties.
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| 9. |
- Golchin, Arash, et al.
(författare)
-
Break-away friction of PTFE materials in lubricated conditions
- 2010
-
Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
-
Konferensbidrag (refereegranskat)abstract
- This study investigates the tribological characteristics at the initiation of sliding (break-away friction) of several polytetrafluoroethylene (PTFE) based materials including virgin PTFE (PP), PTFE filled with 25% black glass (PG), PTFE filled with 40% Bronze (PB), PTFE filled with 25% Carbon (PC), and PTFE filled with 20% glass fibre and 5% Molybdenum disulphide (PM), as well as standard white-metal Babbitt (BA) in lubricated sliding contact with a steel counter-face. Experiments were carried out using a reciprocating tribo-meter in the block on plate configuration with the specific goal of determining the friction characteristics at break-away under varying conditions. Apparent contact pressures of 1 to 8 MPa were applied with oil temperature levels of 25° to 85°C. Bronze- and carbon-filled PTFE and virgin PTFE were found to provide generally lower break-away friction and less variation in break-away friction over the course of testing than the other tested materials. Break-away friction tests after an extended stop under loading found bronze- and carbon-filled PTFE and virgin PTFE to be minimally affected by the extended stop whereas Babbitt produced a significant increase in break-away friction in the first cycle after stopping. Break-away friction for the four tested materials after an extended stop returned to pre-stop values after 1 stroke.
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| 10. |
- Golchin, Arash, et al.
(författare)
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Tribological behaviour of polymeric materials in water-lubricated contacts
- 2013
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 227:8, s. 811-825
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Tidskriftsartikel (refereegranskat)abstract
- This study aims at investigating the tribological behaviour of several unfilled polymer materials sliding against 316L stainless steel in distilled water. The tests were carried out in a unidirectional pin-on-disc configuration with an initial apparent contact pressure of 5MPa at room temperature. The worn surfaces were examined using scanning electron microscopy and energy dispersive spectroscopy techniques and the wear mechanisms were discussed. These studies indicate the occurrence of tribocorrosion of stainless steel during sliding against polypropylene. It is inferred that the frictional behaviour of the polymers is determined by both their wettability and solubility in water, where generally an increased hydrophobicity and relative energy difference with regard to water results in lower friction. The results from friction and wear tests show overall superior tribological performance of ultrahigh molecular weight polyethylene compared with the other polymeric materials in water.
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| 11. |
- Golchin, Arash, et al.
(författare)
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Tribological behaviour of polymeric materials in water lubricated contacts
- 2012
-
Ingår i: 15th Nordic Symposium on Tribology - NordTrib 2012. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
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Konferensbidrag (refereegranskat)abstract
- The present study aims at investigating the tribological behaviour of several unfilled polymer materials sliding against 316L stainless steel in distilled water. The tests were carried out in a uni-directional pin-on-disc configuration with an initial apparent contact pressure of 5 MPa at room temperature. The worn surfaces were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques and the wear mechanisms were discussed. These studies indicate the occurrence of tribo-corrosion of stainless steel during sliding against polypropylene. The results from friction and wear tests show overall superior tribological performance of UHMWPE compared to the other polymeric materials in water.
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| 12. |
- Simmons, Gregory F., et al.
(författare)
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Dynamic characteristics of polymer faced tilting pad journal bearings
- 2014
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 74, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic characteristics of polymer faced tilting pad journal bearings are presented. Investigations are conducted using a single pad, load on pad configuration over a range of shaft speeds and loads. Two polyether ether ketone (PEEK) faced pads, one polytetrafluoroethylene (PTFE) faced pad and two entirely PEEK pads are investigated to determine the effect of varying mean bearing pressure and pivot characteristics as well as different material properties of the polymer layer. Experimental results indicate increased damping and decreased stiffness and slightly increased oil film temperature for entirely PEEK pads compared to pads with a PEEK lining and steel backing. Similar effects were observed by using a softer (PTFE) pad liner with a steel backing.
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| 13. |
- Simmons, Gregory F, et al.
(författare)
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Extending performance limits of turbine oils
- 2014
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 69, s. 52-60
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Tidskriftsartikel (refereegranskat)abstract
- New turbine oils providing both extremely high viscosity index (VI) and improved boundary/mixed lubrication performance are investigated. Comparisons are made in both laboratory scale testing using typical journal bearing sliding surfaces (steel and white metal) and full scale testing using a hydrodynamic journal bearing test machine. The results from these studies demonstrate the effectiveness of new, high VI, turbine oils for reducing friction at machine startup and improving performance during full film operation.
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| 14. |
- Simmons, Gregory F, et al.
(författare)
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Extending performance limits of turbine oils
- 2012
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Ingår i: 15th Nordic Symposium on Tribology - NordTrib 2012. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
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Konferensbidrag (refereegranskat)abstract
- New lubricants providing both extremely high viscosity index (VI) and improved boundary/mixed lubrication performanceare investigated. Comparisons are made in both laboratory scale testing using typical journal bearing slidingsurfaces (steel and white metal) and full scale testing using a hydrodynamic journal bearing test machine. The resultsfrom these studies demonstrate the effectiveness of new, high VI, turbine oils at reducing friction at machine startupand improving performance during steady state operation.
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| 15. |
- Simmons, Gregory F, et al.
(författare)
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Friction evaluation of elastomers in lubricated contact
- 2009
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Ingår i: Lubrication Science. - : Wiley. - 0954-0075 .- 1557-6833. ; 21:10, s. 427-440
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Tidskriftsartikel (refereegranskat)abstract
- Friction testing of elastomers in lubricated contact is discussed with a focus on developing experimental arrangements that can produce worthwhile results. Practical issues unique to elastomers are covered as well as their solutions, including contact mechanics, material response to loading, contact edges, oil absorption, cleaning and specimen geometry. A critique of reciprocating laboratory testing machines, including high-frequency short stroke and low-frequency long stroke friction and wear machines, is conducted for their usefulness, as is critical analysis of a wide variety of specimen configurations with the aim of helping the laboratory experimenter to overcome many of the pitfalls associated with testing of elastomers in lubricated conditions. Results from experiments using various testing arrangements are analysed, and it is found that the synthetic ester and mineral oil used produced similar results.
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| 16. |
- Simmons, Gregory F
(författare)
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Journal bearing design, lubrication and operation for enhanced performance
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing introduction of intermittent power sources combined with the de-regulation of electricity markets has led to increased instability in the electrical grid. This has led to increased start-up and shutdown of regulating power sources such as hydro-electric power plants and operation at non-ideal operating states both of which increase the wear and tear on machines. Likewise, the push for a less environmentally intrusive society has raised the importance of utilizing equipment with reduced impact on the natural surroundings.These challenges lead to a need to improve the robustness of existing and new equipment to guarantee their usefulness in a future with increased instability. While many components in hydropower systems require thorough investigation to improve their robustness, this work is focused on the guide/journal bearings which support the rotating portion of power generating machines.This work addresses the journal bearing problem through a multi scaled approach covering small and large scale laboratory experiments as well as investigations of a full scale machine.A journal bearing test machine was constructed to investigate a number of new synthetic lubricants and polymer bearing materials. These tests found that a significant reduction in power loss could be accomplished without significantly affecting the bearing's minimum film thickness by changing from a traditional mineral oil to a high viscosity index oil of much lower base viscosity grade. The high viscosity index lubricants were then improved to reduce start-up friction as well. Further studies were conducted in small scale to determine the optimum lubricant characteristics for the startup problem. This knowledge was used to develop new lubricants to test in the journal bearing test machine which showed great reductions in power loss in the bearing and pumping system as well as greatly reduced bearing operating temperature.Further experimental work led to the development of practical guidance for power plant operators contemplating a lubricant change. This technique focuses on the importance of maintaining equivalent viscosity in the minimum film thickness region after a lubricant change. Efficiency improvements can then be calculated by comparing the viscosity in the bulk of the bearing to that with the original lubricant.Experimental work with polymer bearing facing materials demonstrated the dramatic reductions in break away friction that these materials can provide. A number of polymer composite materials were investigated for their friction characteristics at the moment of the start of sliding, finding that PTFE based materials were far superior to traditional Babbitt metal. This work with polymer faced bearings was extended to testing in a tilting pad journal bearing test rig which allowed for identification of the dynamic characteristics resulting from changes in bearing pad material.Investigations in the full scale with the Porjus U9 unit provided valuable insight into the dynamics of a full scale machine as well as needed data for the improvement of multi-physics models of bearings. Insights from the Porjus U9 experiments clarify many of the design challenges for large journal bearings.The results from this work demonstrate that significant performance improvement of journal bearings is possible through the use of new lubricants, materials, and adjustments in operational methods.
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| 17. |
- Simmons, Gregory F, et al.
(författare)
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Operational transients in the guide bearings of a 10 MW Kaplan turbine
- 2013
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Ingår i: International journal on hydropower and dams. - 1352-2523. ; 20:5, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- Experiments using a 10 MW Kaplan hydropower machine with a PowerFormerTM generator (the Porjus U9 research machine) are described. This machine has an extensive array of sensors to determine oil film thickness, pad tilting, pad load and oil temperature in all three guide bearings, as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all three guide bearings are examined during both steady-state and transient operation.
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| 18. |
- Simmons, Gregory F., et al.
(författare)
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Powerplant lubricant selection for improved efficiency and environmental impact reduction
- 2010
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Ingår i: Proceedings of the ASME 2010 International Mechanical Engineering Congress & Exposition, IMECE 2010.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Computational models were used to optimize bearing per-formance by adjusting a number of lubricant properties. Thiscomputational optimization showed that the most beneficialcharacteristics to hydrodynamic bearing operation were highviscosity index (VI) and high specific heat capacity. Four envi-ronmentally adapted synthetic lubricants were developed to pro-vide these characteristics including: ISO VG32 with 259 VI, ISOVG22 with 245 VI, ISO VG22 with 336 VI, and ISO VG15 with226 VI. A full scale bearing test machine was then operated withthese lubricants in addition to mineral based turbine oils, ISOVG68 with 103 VI and ISO VG32 with 105 VI, to determine theeffect on bearing performance and to validate the models. Thenew lubricants reduced bearing power loss by up to 20% and sig-nificantly reduced bearing temperatures with somewhat reducedfilm thickness. The machine was then operated to provide equiv-alent minimum viscosity with the new lubricants by varying inlettemperature, finding that changes in power loss were less sub-stantial with equivalent minimum viscosity.Comparison of simulated and experimental results led todevelopment of a simple, practical method to estimate benefitsand operational parameters for lubricants based on viscositygrade, viscosity index and a simplified description of the machine’s bearings. Other, less tangible, factors considered arebio-degradeability and impact of power loss reduction.
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| 19. |
- Simmons, Gregory F, et al.
(författare)
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Powerplant lubricant selection for improved efficiency and environmental impact reduction
- 2012
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Ingår i: Proceedings of the ASME International Mechanical Engineering Congress and Exposition. - New York : American Society of Mechanical Engineers. - 9780791844298 ; , s. 429-437
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Konferensbidrag (refereegranskat)abstract
- Computational models were used to optimize bearing performance by adjusting a number of lubricant properties. This computational optimization showed that the most beneficial characteristics to hydrodynamic bearing operation were high viscosity index (VI) and high specific heat capacity. Four environmentally adapted synthetic lubricants were developed to provide these characteristics including: ISO VG32 with 259 VI, ISO VG22 with 245 VI, ISO VG22 with 336 VI, and ISO VG15 with 226 VI. A full scale bearing test machine was then operated with these lubricants in addition to mineral based turbine oils, ISO VG68 with 103 VI and ISO VG32 with 105 VI, to determine the effect on bearing performance and to validate the models. The new lubricants reduced bearing power loss by up to 20% and significantly reduced bearing temperatures with somewhat reduced film thickness. The machine was then operated to provide equivalent minimum viscosity with the new lubricants by varying inlet temperature, finding that changes in power loss were less substantial with equivalent minimum viscosity. Comparison of simulated and experimental results led to development of a simple, practical method to estimate benefits and operational parameters for lubricants based on viscosity grade, viscosity index and a simplified description of the machine's bearings. Other, less tangible, factors considered are bio-degradeability and impact of power loss reduction
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| 20. |
- Simmons, Gregory F, et al.
(författare)
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Steady state and dynamic characteristics for guide bearings of a hydro-electric unit
- 2014
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 228:8, s. 836-848
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Tidskriftsartikel (refereegranskat)abstract
- Experiments are conducted using a 10-MW Kaplan hydropower machine which is outfitted with an extensive array of sensors to determine oil film thickness, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all journal bearings are compared to a commercial rotor dynamics model and results for the central journal bearing are compared to a multi-physics model to provide insight into the machine's steady state and dynamic characteristics and their variations during normal operation.
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| 21. |
- Simmons, Gregory F
(författare)
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Synthetic lubricants and polymer composites for large full film journal bearings
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid build-up of variable renewable power sources such as wind and solar are leading to increased instability in the electrical grid. Many methods of controlling this instability have been proposed but existing hydroelectric power plants in many cases already been enlisted to fill the regulating power needs of industry and the population. Filling this regulating power role necessitates that a machine changes load state more often and experiences an increase in starts and stops. Likewise, the push for a less environmentally intrusive society has raised the importance of utilizing equipment with reduced impact.This situation has created a host of opportunities to improve existing power plants and upgrade designs of new power plants to allow for reduced impact, better reliability, and increased efficiency. As one of the most critical and failure prone components of the power plant, the bearings hold great potential for improvements that together can reduce impact while increasing efficiency and reliability.To accomplish these opportunities, this work investigates the potential of new, environmentally adapted, lubricants to improve power plant efficiency. It then continues by developing guidelines for power plant operators when considering changing lubricants. Finally, the potential of polymer faced bearings to improve plant reliability at start up is investigated.A journal bearing test machine was constructed to investigate a number of new synthetic lubricants and polymer bearing materials. These tests found that a significant reduction in power loss could be accomplished without significantly affecting the bearing's minimum film thickness by changing from a traditional mineral oil based lubricant to a high viscosity index lubricant of much lower base viscosity grade.Further experimental work led to the development of practical guidance for power plant operators contemplating a lubricant change. This technique focuses on the importance of maintaining equivalent viscosity in the minimum film thickness region after a lubricant change. Efficiency improvements can then be calculated by comparing the viscosity in the bulk of the bearing to that with the original lubricant.Experimental work with polymer bearing facing materials demonstrated the dramatic reductions in break away friction that these materials can provide. A number of polymer composite materials were investigated for their friction characteristics at the moment of the start of sliding, finding that PTFE based materials were far superior to traditional Babbitt metal. The break away friction of PTFE materials was much lower than that of Babbitt and furthermore, the PTFE materials provided a much more stable friction than Babbitt through large variations in both pressure and oil bath temperature.Finally, experimental work with a full scale polymer faced bearing provided insight into the function of polymer faced bearings as well as valuable lessons in the further development of these bearings and their monitoring systems.
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- Simmons, Gregory F, et al.
(författare)
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Synthetic lubricants in hydrodynamic journal bearings : experimental results
- 2011
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 42:1, s. 109-115
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic lubricants and additives have seen many major improvements in recent years. However, very littleis known about the performance peculiarities of these new lubricants in actual machines. To fill this gap, anew full-scale hydro-dynamic journal bearing test rig has been constructed to evaluate the behavior ofconventional and new bearing designs, synthetic lubricants and variations in operating parameters. This testrig’s bearing has diameter 180 mm with measuring capabilities including continuous film thickness and filmpressure as well as temperature. The new machine was used to compare a number of synthetic lubricants tomineral based lubricants, finding that performance of the synthetic lubricants was superior to their mineralbased counterparts of much higher viscosity grade. These tests showed that high viscosity index (VI) syntheticlubricants had higher viscosity in the region of maximum pressure and lower viscosity elsewhere in the bearingthan similar mineral based lubricants. This reduction in viscosity in low pressure zones was found to producea measurable reduction in friction and power loss in the bearing system. This paper provides comparativeperformance results of several formulations of current and future turbine oils from measurements of losses,oil film thickness, and temperature under a range of operating parameters. Lubricants tested include ISOVG68 and VG32 mineral based turbine oils (VG68 and VG32), ISO VG32 synthetic ester based oil (SE32),two ISO VG22 synthetic ester based oils (SE22 and SV22), and ISO VG15 synthetic ester based oil (SE15).It was found that SE32 and VG68 provided similar performance at lower speeds while SV22 provided similarperformance to VG68 at the highest speed. Likewise, SE22 and SV22 provided similar performance toVG32 at low speeds while SE15 provided similar performance to VG32 at medium to higher speeds.Generally, the results demonstrate the potential for replacing mineral based lubricants with high performancesynthetic lubricants of significantly lower viscosity grade without sacrificing bearing safety.
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