The harp seal (Phoca groenlandica Erxleben) in Denmark, southern Scandinavia, during the Holocene     

OLE BENNIKE  PETER RASMUSSEN  KIM AARIS-SØRENSEN 《Boreas: An International Journal of Quaternary Research》2008,37(2):263-272

The harp seal ( Phoca groenlandica ) is a low-arctic species that is currently a rare visitor to Danish waters. However, bone remains from archaeological and geological deposits in Denmark and the Baltic Sea testify to a regular presence of harp seals in this region during the mid-Holocene. The paradox of the presence of a low-arctic seal species in southern Scandinavia during the mid-Holocene thermal maximum has been widely discussed. In order to improve the Holocene chronology for the presence of harp seal in Denmark, 24 bone remains of the species were radiocarbon dated. The oldest date is around 4100 cal. yr BC, indicating that the harp seal arrived several millennia after fully marine conditions were established in Danish waters. The majority of the dated specimens fall within two age groups, one centred around 3900 cal. yr BC (11 dates), the other around 2700 cal. yr BC (7 dates). It is argued that these two groups may reflect periods with suitable living conditions for the harp seal in Danish waters and that this is connected with an enhanced inflow of high-salinity North Sea water and higher biological productivity. Six dates show a scattered distribution between c . 1400 cal. yr BC and c . AD 1000, suggesting sporadic visits of the harp seal to Danish waters during the late Holocene.  相似文献   

Analysis of effects of operating parameters on rate of penetration in drilling process with air down-the-hole hammer     

HO Yinchol  PAK Kumdol  PENG Jianming  RI Jaemyong  KIM Yongnam  CHOE Cholho 《世界地质(英文版)》2021,24(1):64-70

Air down-the-hole(DTH)hammer drilling has long been recognized to have the potential of drilling faster than conventional rotary drill,especially in some hard rocks such as granite,sandstone,limestone,dolomite,etc.with the same weight on bit(WOB)and rotations per minute(RPM).So,it has been widely used in many drilling fields including mineral resource exploration drilling,oil and gas drilling and geothermal drilling.In order to reduce drilling cost by selecting optimal drilling parameters,rate of penetration(ROP)should be estimated accurately and the effects of different factors on ROP should be analyzed.In this research,ANN model with several multi-layer perception back propagation(BP)networks for predicting ROP of air DTH hammer drilling was developed using controllable parameters such as impact energy,impact frequency,WOB,RPM and bit operating time for the formations with a certain drillability index of rock.Several BP neural networks with the different neurons in hidden layers were developed and compared for selecting optimal architecture of ANN.The effects of the drilling parameters such as impact energy,impacting frequency,WOB,RPM and bit operating time on the ROP of air DTH hammer drilling were investigated by trained ANN.From the analyses,the optimum range of drilling parameters for providing high ROP were determined and analyzed for a formation with a certain drillability index of rock.The methodology proposed in this study can be used in many mathematical problems for optimization of drilling process with air DTH hammer.  相似文献   

Terrestrial ages of meteorites from the Nullarbor region,Australia, based on 14C and 14C–10Be measurements     

A. J. Timothy JULL  Lanny R. McHARGUE  Philip A. BLAND  Richard C. GREENWOOD  Alexander W. R. BEVAN  Kyeong J. KIM  Sarah E. LaMOTTA  Jeffrey A. JOHNSON 《Meteoritics & planetary science》2010,45(8):1271-1283

Abstract– We have investigated the terrestrial ages, or residence times, of 78 meteorites (representing 73 discrete falls) recovered in Western Australia, and one from South Australia, using both ¹⁴C measurements and also ¹⁴C/¹⁰Be. The samples studied included two ureilites, one CK and one EL chondrite. We have included ¹⁰Be measurements from 30 meteorites, including some meteorites for which the ¹⁴C terrestrial age was previously determined. We find that the ¹⁴C/¹⁰Be terrestrial ages are more precise than ¹⁴C alone, as we can correct for shielding effects. In general, the two different age determinations age by ¹⁴C–¹⁰Be are precise to 0.5–1 ka and ¹⁴C alone within 1–2 ka. However, measurement of the ¹⁴C age alone gives good agreement with the ¹⁴C–¹⁰Be for most samples. The study of the terrestrial ages of meteorites gives us useful information concerning the storage and weathering of meteorites and the study of fall times and terrestrial age. We have compared the terrestrial ages to weathering, degree of oxidation (estimated from Mössbauer studies) and Δ¹⁷O. In this study, we found that weathering is not well correlated with terrestrial age for Nullarbor meteorites. However, there is a good correlation between degree of oxidation and Δ¹⁷O. The implications for the study of terrestrial ages and weathering from other desert environments will be discussed.  相似文献   

Excess ²¹⁰Po in the coastal atmosphere     

GUEBUEM KIM  NAJID HUSSAIN  THOMAS M. CHURCH 《Tellus. Series B, Chemical and physical meteorology》2000,52(1):74-80

Many researchers have reported the widespread occurrence of excess ²¹⁰ Po in the global atmosphere and suggested probable sources such as resuspension of top soils, stratospheric aerosols, sea spray of the surface micro‐layer, volcanic emission, and bio‐volatile ²¹⁰Po species from the productive ocean. We have observed excess ²¹⁰Po on aerosols in the coastal atmosphere of the Chesapeake and Delaware Bays. On‐board measurements in the Chesapeake Bay atmosphere show that the increase of this excess ²¹⁰Po is dependent upon wind speed. Simultaneously measured activity ratios of ⁷Be/²¹⁰Pb and ²¹⁰Pb/²²²Rn argue against either higher altitude air or continental soils as the source of this excess. We hypothesize that the excess ²¹⁰Po originates mainly from surface waters either by the sea‐spray of the surface microlayer, or more likely, by gas exchange. We conclude gas exchange as the mechanism since the polonium excess increases linearly with wind speed over a threshold of 3 m s⁻¹(mean) similar to other gases (i.e., CO₂, SF₆ , and DMS). In addition, higher ²¹⁰Po excess with lower ²²²Rn is observed in on‐shore marine air at Lewes, DE. This suggests sea‐air exchange of volatile Po along with other bio‐volatile species (i.e., DMS, DMSe, and MMHg) in the coastal productive ocean during high wind speeds.  相似文献   

Late Pleistocene remains of giant deer (Megaloceros giganteus Blumenbach) in Scandinavia: chronology and environment     

KIM AARIS-SØRENSEN  RONNIE LILJEGREN 《Boreas: An International Journal of Quaternary Research》2004,33(1):61-73

This article presents new data on the Late Pleistocene giant deer, Megaloceros giganteus (Blumenbach), describing its distribution in time and space, geographical and sexual variation and general biology. Twenty‐three south Scandinavian fossils found in situ in lacustrine sediments or redeposited in glaciofluvial material form the basis of this investigation. Fourteen C dates show that the giant deer inhabited southern Scandinavia in the ice‐free late Middle Weichselian from c. 40000 to 28000 BP (the Sandnes Interstadial) and again in the Late Weichselian from c. 12000 to 10700 BP (Older Dryas, Allerød and early Younger Dryas Chronozones), corresponding to a calibrated range from c. 14300 to 12400 cal. yr BP. Osteometric analyses show that the Scandinavian giant deer belonged to the upper size range of the lateglacial Irish population and that a marked sexual dimorphism existed, the males being 10–11% larger than the females. Investigations furthermore point at an antler cycle similar to that among extant northern cervids, and subsequently at a rutting season in autumn. The skeletal remains also prove the occurrence of twin delivery and the possibility of reaching an ontogenetic age of at least 23 years. During both occurrences the Scandinavian giant deer population was part of the northernmost distribution of the species in Europe and the palaeogeographical settings and palaeoenvironmental conditions of the two periods show striking similarities. Clearly, the giant deer were able to colonize and survive in a landscape dominated by grasses and sedges with scattered shrubs and dwarf shrubs. They came as close as 200–250 km to the ice front and their distribution included coastal areas along a cold sea with drifting icebergs. They were present in the area at least from March until November. However, the pure arctic conditions created during the early phase of the Younger Dryas event led to a new local extinction around 10700 ¹⁴C yr BP. This was the beginning of a total Eurasian extinction which, at least in Europe, was completed before the Pleistocene/Holocene transition.  相似文献   

Variability and Risk Analysis of Hong Kong Air Quality Based on Monsoon and El Nino Conditions     

Jong-Suk KIM  ZHOU Wen  Ho Nam CHEUNG  Chak Hang CHOW 《大气科学进展》2013,30(2):280-290

This study presents an exploratory analysis aimed at improving understanding of the variability of Hong Kong air quality associated with different climate conditions. Significantly negative correlations were found when Nino 3 led particulate matter ≤10 μm PM₁₀) and NO₂ by 2--3 months over the Hong Kong territory, while the other pollutants (e.g., O₃, SO₂) showed modest correlations. A significant decreasing trend in visibility was observed during the autumn and winter, which has potential implications for the air-quality degradation and the endangerment of human health in Hong Kong. In an El Nino summer, the visibility was relatively better, while visibility in other seasons was diminished. On the other hand, in La Nina events, significant changes occurred in visibility in winter and autumn. Air pollution indices were less sensitive to the South China Summer Monsoon (SCSM), but a relatively high correlation existed between the East Asian Winter Monsoon (EAWM) and air pollutants. Rainfall was lower during most of the strong EAWM years compared to the weak years. This result suggests that the pollutants that accumulate in Hong Kong are not easy to wash out, so concentrations remain at a higher level. Finally, based on the conditional Air Pollution Index (API) risk assessment, site-specific vulnerabilities were analyzed to facilitate the development of the air-quality warning systems in Hong Kong.  相似文献   

On the use of the Webb–Pearman–Leuning theory for closed-path eddy correlation measurements     

ANDREAS IBROM  EBBA DELLWIK  SØREN EJLING LARSEN  KIM PILEGAARD 《Tellus. Series B, Chemical and physical meteorology》2007,59(5):937-946

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Radon-222 in boundary layer and free tropospheric continental outflow events at three ACE-Asia sites     

WLODEK ZAHOROWSKI  SCOTT CHAMBERS  TAO WANG  CHANG-HEE KANG  ITSUSHI UNO  STEVEN POON  SUNG-NAM OH  SYLVESTER WERCZYNSKI  JIYOUNG KIM  ANN HENDERSON-SELLERS 《Tellus. Series B, Chemical and physical meteorology》2005,57(2):124-140

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Assessment of winter fluxes of CO₂ and CH₄ in boreal forest soils of central Alaska estimated by the profile method and the chamber method: a diagnosis of methane emission and implications for the regional carbon budget     

YONGWON KIM  MASAHITO UEYAMA  FUMIKO NAKAGAWA  URUMU TSUNOGAI  YOSHINOBU HARAZONO  NORIYUKI TANAKA 《Tellus. Series B, Chemical and physical meteorology》2007,59(2):223-233

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Correlation assessment and monitoring of the potential pollutants in the surface sediments of Pyeongchang River, Korea   总被引：1，自引：0，他引：1  

Md.Imran KABIR  Hosik LEE  Geonha KIM  Taesung JUN 《国际泥沙研究》2011,26(2):152-162

The study provides a baseline for the assessment of the organic and inorganic pollution specially, heavy metal contamination in the surface sediments of Pyeongchang River,South Korea.The assessment of the study areas was done with respect to metal pollution load,ecological risk and geoaccumulated risk.Based upon the used indices,a priority index(P_index) was used to rank the utmost contaminated sites.Though the concentrations of mercury in all sediments were below the guideline, the significant enriched contamination was observed by all applied indices.As expected,the values of pollution load index（PLI）,ecological risk index（RI） and geoaccumulation risk index(I_geo) demonstrated lower heavy metal contamination in upstream areas compared to the downstream. Admittedly,sediments were unpolluted to slightly-polluted according to PLI while high to extremely high ecological risks were observed in several sediment samples.Furthermore,all the samples were uncontaminated as per I_geo.After simplification of I_geo,the P_index,showed the utmost contaminated sediments with a value of 2.537.Notably,protective measures should be taken to the highly contaminated areas which are prioritized by P_index Admittedly,the maximum concentrations of total organic carbon,total nitrogen,inorganic nitrogen,total phosphorous,inorganic phosphorous,calcium, magnesium,sodium and potassium were significantly observed as 7.8×10⁴,3,185,36,1,032,3.7, 1,5163,2,881,669 and 4,076mg/kg accordingly.  相似文献