979 resultados para History of science. Nature of science. Physics teaching. Optics


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This paper traces the history of the Library of the Montana State School of Mines from its inception in 1900 to 2006. The history includes sketches of the library directors over 106 years, and the library’s various campus locations and emerging collections and services.

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Millions of years of physiographic changes have conditioned us to the fact that our present drainage is a temporary feature. Rivers once flowing opposite to their present direction is not an unusual condition for physiographers to suggest.

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A 37 m deep ice core representing 1957–2009 and snow from 2009 to 2010 were collected on the Lomonosovfonna glacier, Svalbard (78.82° N; 17.43° E) and analyzed for 209 polychlorinated biphenyl (PCB) congeners using high-resolution mass spectrometry. Congener profiles in all samples showed the prevalence of tetra- and pentachlorobiphenyls, dominated in all samples by PCB-44, PCB-52, PCB-70 + PCB-74, PCB-87 + PCB-97, PCB-95, PCB-99, PCB-101, and PCB-110. The ∑PCB flux varied over time, but the peak flux, 19 pg cm–2 year–1 from 1957 to 1966, recurred in 1974–1983, 1998–2009, and 2009–2010. The minimum was 5.75 pg cm–2 year–1 in 1989–1998, following a 15 year decline. Peak ∑PCB fluxes here are lower than measured in the Canadian Arctic. The analysis of all 209 congeners revealed that PCB-11 (3,3′-dichlorobiphenyl) was present in all samples, representing 0.9–4.5% of ∑PCB. PCB-11 was not produced in a commercial PCB product, and its source to the Arctic has not been well-characterized; however, our results confirm that the sources to Lomonosovfonna have been active since 1957. The higher fluxes of ∑PCB correspond to periods when average 5 day air mass back trajectories have a frequency of 8–10% and reach 60° N or beyond over northern Europe and western Russia or the North Sea into the U.K

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The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600,000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serves to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by 40Ar/39Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflect rising lake-levels during the terminations; (ii) varved clayey silts reflect strong seasonality and an intralake oxic–anoxic boundary, for example, lake-level highstands during interglacials/interstadials; (iii) CaCO3-rich banded sediments are representative of a lowering of the oxic-anoxic boundary, for example, lake-level decreases during glacial inceptions; (iv) CaCO3-poor banded and mottled clayey silts reflect an oxic–anoxic boundary close to the sediment-water interface, for example, lake-level low-stands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicate the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka BP.

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William Osler (1849-1919): America’s Most Famous Physician (Robert E. Rakel) The Assassination of John F. Kennedy: A Neurosurgeon’s Eyewitness Account of the Medical Aspect of the Events of November 22, 1963 (Robert G. Grossman) Making Cancer History: Disease and Discovery at the University of Texas M.D. Anderson Cancer Center (James S. Olson) The History of Pathology as a Biological Science and Medical Specialty (L. Maximillian Buja) “Medicine in the Mid-19th Century America” (Student Essay Contest Winner) (David Hunter) The Achievements and Enduring Relevance of Rudolph Virchow (Nathan Grohmann) Medicine: Perspectives in History and Art (Robert E. Greenspan) What Every Physician Should Know: Lessons from the Past (Robert E. Greenspan) Medicine in Ancient Mesopotamia (Sajid Haque) The History of Texas Children’s Hospital (B. Lee Ligon) Visualizing Disease: Motion Pictures in the History of Medical Education (Kirsten Ostherr)

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Unroofing of the Black Mountains, Death Valley, California, has resulted in the exposure of 1.7 Ga crystalline basement, late Precambrian amphibolite facies metasedimentary rocks, and a Tertiary magmatic complex. The Ar-40/Ar-39 cooling ages, obtained from samples collected across the entire length of the range (>55 km), combined with geobarometric results from synextensional intrusions, provide time-depth constraints on the Miocene intrusive history and extensional unroofing of the Black Mountains. Data from the southeastern Black Mountains and adjacent Greenwater Range suggest unroofing from shallow depths between 9 and 10 Ma. To the northwest in the crystalline core of the range, biotite plateau ages from approximately 13 to 6.8 Ma from rocks making up the Death Valley turtlebacks indicate a midcrustal residence (with temperatures >300-degrees-C) prior to extensional unroofing. Biotite Ar-40/Ar-39 ages from both Precambrian basement and Tertiary plutons reveal a diachronous cooling pattern of decreasing ages toward the northwest, subparallel to the regional extension direction. Diachronous cooling was accompanied by dike intrusion which also decreases in age toward the northwest. The cooling age pattern and geobarometric constraints in crystalline rocks of the Black Mountains suggest denudation of 10-15 km along a northwest directed detachment system, consistent with regional reconstructions of Tertiary extension and with unroofing of a northwest deepening crustal section. Mica cooling ages that deviate from the northwest younging trend are consistent with northwestward transport of rocks initially at shallower crustal levels onto deeper levels along splays of the detachment. The well-known Amargosa chaos and perhaps the Badwater turtleback are examples of this "splaying" process. Considering the current distance of the structurally deepest samples away from moderately to steeply east tilted Tertiary strata in the southeastern Black Mountains, these data indicate an average initial dip of the detachment system of the order of 20-degrees, similar to that determined for detachment faults in west central Arizona and southeastern California. Beginning with an initially listric geometry, a pattern of footwall unroofing accompanied by dike intrusion progress northwestward. This pattern may be explained by a model where migration of footwall flexures occur below a scoop-shaped banging wall block. One consequence of this model is that gently dipping ductile fabrics developed in the middle crust steepen in the upper crust during unloading. This process resolves the low initial dips obtained here with mapping which suggests transport of the upper plate on moderately to steeply dipping surfaces in the middle and upper crust.

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In the Mt. Olympos region of northeastern Greece, continental margin strata and basement rocks were subducted and metamorphosed under blueschist facies conditions, and thrust over carbonate platform strata during Alpine orogenesis. Subsequent exposure of the subducted basement rocks by normal faulting has allowed an integrated study of the timing of metamorphism, its relationship to deformation, and the thermal history of the subducted terrane. Alpine low-grade metamorphic assemblages occur at four structural levels. Three thrust sheets composed of Paleozoic granitic basement and Mesozoic metasedimentary cover were thrust over Mesozoic carbonate rocks and Eocene flysch; thrusting and metamorphism occurred first in the highest thrust sheets and progressed downward as units were imbricated from NE to SW. 40Ar/39Ar spectra from hornblende, white mica, and biotite samples indicate that the upper two units preserve evidence of four distinct thermal events: (1) 293–302 Ma crystallization of granites, with cooling from >550°C to <325°C by 284 Ma; (2) 98–100 Ma greenschist to blueschist-greenschist transition facies metamorphism (T∼350–500°C) and imbrication of continental thrust sheets; (3) 53–61 Ma blueschist facies metamorphism and deformation of the basement and continental margin units at T<350–400°C; (4) 36–40 Ma thrusting of blueschists over the carbonate platform, and metamorphism at T∼200–350°C. Only the Eocene and younger events affected the lower two structural packages. A fifth event, indicated by diffusive loss profiles in microcline spectra, reflects the beginning of uplift and cooling to T<100–150°C at 16–23 Ma, associated with normal faulting which continued until Quaternary time. Incomplete resetting of mica ages in all units constrains the temperature of metamorphism during continental subduction to T≤350°C, the closure temperature for Ar in muscovite. The diffusive loss profiles in micas and K-feldspars enable us to “see through” the younger events to older events in the high-T parts of the release spectra. Micas grown during earlier metamorphic events lost relatively small amounts of Ar during subsequent high pressure-low temperature metamorphism. Release spectra from phengites grown during Eocene metamorphism and deformation record the ages of the Ar-loss events. Alpine deformation in northern Greece occurred over a long time span (∼90 Ma), and involved subduction and episodic imbrication of continental basement before, during, and after the collision of the Apulian and Eurasian plates. Syn-subduction uplift and cooling probably combined with intermittently higher cooling rates during extensional events to preserve the blueschist facies mineral assemblages as they were exhumed from depths of >20 km. Extension in the Olympos region was synchronous with extension in the Mesohellenic trough and the Aegean back-arc, and concurrent with westward-progressing shortening in the external Hellenides.

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Ancient DNA from a Neolithic legging (1st half of the 3rd millennium BC) found at Lenk, Schnidejoch (2750 m a.sl.) in the Swiss Alps has demonstrated, that modern distribution of genetic variation does not reflect past spatio-temporal signatures. The legging was made from the skin of a domestic goat (Capra hircus), belonging to the caprine haplogroup B1, which is marginal in Europe today, but represents a third highly diverse goat haplogroup entering Europe already in the Neolithic. Population expansion of lineage B therefore happened more than 4500 years ago, but their members were at some point almost completely replaced by goats of today's common A and C haplogroups.