A Hierarchical Spatio-Temporal Statistical Model Motivated by Glaciology

In this paper, we extend and analyze a Bayesian hierarchical spatio-temporal model for physical systems. A novelty is to model the discrepancy between the output of a computer simulator for a physical process and the actual process values with a multivariate random walk. For computational efficiency, linear algebra for bandwidth limited matrices is utilized, and first-order emulator inference allows for the fast emulation of a numerical partial differential equation (PDE) solver. A test scenario from a physical system motivated by glaciology is used to examine the speed and accuracy of the computational methods used, in addition to the viability of modeling assumptions. We conclude by discussing how the model and associated methodology can be applied in other physical contexts besides glaciology.Comment: Revision accepted for publication by the Journal of Agricultural, Biological, and Environmental Statistic

Puberty in Icelandic boys

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenIn a crosssectional study, 2751 healthy Icelandic boys aged 6-16 years, were examined for physical signs of puberty. The study was performed in 1983-1987 and was a part of a larger crosssectional growth study of 5526 Icelandic children all of whom were examined by the authors. Testicular volume of 4 ml (T 4) was considered the first sign of puberty in boys. The mean age of Icelandic boys reaching T 4 was 11.89 years (SD 1.08). The mean time interval between T 4 and T 12 was 2.21 years. The first signs of pubic hair growth, Tanner stage 2 (PH 2), were found at 12.74 years (SD 1.37). The mean time interval between PH 2 and PH 5 was 2.43 years. Even though comparison with studies from other countries is difficult because of different methods and different study design, we find that the timing and tempo of puberty in Icelandic boys is similar to what has been reported from other Nordic countries and countries in Western-Europe.Gerð var þverskurðarrannsókn á ytri kynþroskaeinkennum hjá 2751 heilbrigðum íslenskum dreng á aldrinum 6-16 ára. Rannsóknin var hluti af stærri rannsókn sem fór fram á árabilinu 1983-1987 en þar var meðal annars mæld hæð, bæði sitjandi og standandi, þyngd og húðfita. Alls tóku 5526 börn og unglingar þátt í rannsókninni, og var það meira en 95% af upprunalegum úrtakshópi. Fyrstu einkenni kynþroska drengja eru talin þegar eistu ná 4 ml rúmmáls (T 4). Meðalaldur íslenskra drengja við upphaf kynþroska var 11,89 ár, staðalfrávik (standard deviation) 1,08 ár. Tímalengd sem tekur eistun að vaxa úr 4 ml í 12 ml (T 4 -T 12) var 2,21 ár. Fyrsti vöxtur kynhára (PH 2) fannst að meðaltali við 12,74 ár, staðalfrávik 1,37 ár. Tímalengd milli PH 2 og PH 5, þegar fullum þroska kynhára var náð, var að meðaltali 2,43 ár. Niðurstöður benda til að kynþroski íslenskra pilta fylgi svipuðu ferli og hjá piltum á Norðurlöndum og meginlandi Vestur-Evrópu. Samanburður við erlendar rannsóknir er hins vegar að mörgu leyti erfiður vegna ólíkra rannsóknaraðferða

Height and weight of Icelandic children 6-20 years of age

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenIntroduction: Monitoring growth rate in children reflects the state of health and nutrition of the individual as well as the state of health of a nation. Until now little information has been available about the growth pattern of Icelandic children. We report here the results of a nationwide cross-sectional study of growth in Icelandic children aged 6-20 years. Material and methods: Height, standing and sitting and weight were measured in a total of 6500 schoolchildren, 3173 girls and 3327 boys. The measurements were performed 1983-1987. Children were randomly selected from The National Registry according to date of birth from both urban and rural areas of the whole country of Iceland. Stature was measured by a Harpenden stadiometer and the children were weighed in underwear only using a standardized scale. Results: The mean values and standard deviations for height, standing and sitting and weight are presented in tables. Growth charts for height weigt and sitting height are presented. No difference in height and weight was found between children from rural and urban areas. The results show that the growth of Icelandic children is in all age groups almost identical to the growth of Norwegian children. Compaired to other Nordic and WHO growth standards, Icelandic children are tall, especially during early pubertal development. Conclusions: Icelandic children are tall and the growth of Icelandic and Norwegian children follows the same pattern wich supports the theory that the two nations are closely related.Inngangur: Rannsóknir á vexti barna og unglinga gefa verðmætar upplýsingar um heilsufar, næringarástand og almenna velmegun, bæði einstaklinga og heilla þjóða. Óhætt er að fullyrða að vaxtarferill er einn besti mælikvarði sem völ er á til að fylgjast með almennu heilsufari og heilbrigði barna. Til þessa hafa ekki verið gerðar staðlaðar rannsóknir á vexti og þroska íslenskra barna. Hér eru birtar niðurstöður rannsóknar á hæð og þyngd íslenskra barna og unglinga á aldrinum 6-20 ára, en rannsóknin er hluti af stórri þverskurðarrannsókn á vexti, þroska og næringarástandi íslenskra ungmenna. Efniviður og aðferðir: Hæð, sethæð og þyngd var mæld hjá alls 6500 skólabörnum, 3173 stúlkum og 3327 piltum á árabilinu 1983-1987. Börnin voru valin samkvæmt fæðingardegi úr þjóðskrá, bæði af höfuðborgarsvæðinu og úr ýmsum grunn- og framhaldsskólum í öllum landsfjórðungum. Hæð barnanna var mæld sitjandi og standandi með Harpenden stadiometer og þau vegin léttklædd með löggiltri reisluvog. Niðurstöður: Meðalgildi og staðalfrávik fyrir hæð, sethæð og þyngd eru gefin upp í töflum. Birt eru vaxtarlínurit fyrir hæð, þyngd og sethæð. Ekki fannst marktækur munur á hæð eða þyngd barna í þéttbýli og dreifbýli. Rannsóknin leiddi í ljós að vöxtur íslenskra barna er á öllum aldursskeiðum nánast eins og vöxtur norskra barna. Samanborið við aðra norræna vaxtarstaðla, og staðla Alþjóðaheilbrigðisstofnunarinnar, eru íslensk börn hávaxin, einkum í byrjun kynþroskaskeiðs. Ályktanir: Íslensk börn eru hávaxin og vöxtur íslenskra barna fylgir nánast sama ferli og vöxtur norskra barna og samræmist það nánum skyldleika þjóðanna

Puberty in Icelandic girls

To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldIn a crosssectional study, 2775 healthy Icelandic girls, aged 6-16 years, were examined for physical signs of puberty. The study was performed in 1983-1987 and was a part of a larger crosssectional study of growth and development of 5526 Icelandic children all of whom were examined by the authors. Breast development stage 2 according to Tanner (B 2) was considered the first sign of puberty in girls. The mean age of Icelandic girls reaching B 2 was 10.84 years (SD 1.43). The mean time interval between B 2 and menarche was 2.42 years. The first signs of pubic hair growth, Tanner stage 2 (PH 2) were found at 11.46 years (SD 1.25). The mean time interval between PH 2 and PH 5 was 3.40 years. Comparison with studies from other countries is difficult because of different methods and different study designs, but the timing and tempo of puberty in Icelandic girls seems to be similar to what has been reported from other Nordic countries and countries in Western-Europe.Lýst er þverskurðarrannsókn (crosssectional) á kynþroska íslenskra stúlkna. Rannsóknin var hluti af stórri þverskurðarrannsókn á vexti og þroska íslenskra barna á aldrinum 6-16 ára. Í rannsókninni, sem fór fram á árunum 1983-1987, tók þátt alls 2751 drengur og 2775 stúlkur, eða samtals 5526 börn og unglingar. Allar mælingar og líkamsskoðun barnanna voru framkvæmdar af höfundum greinarinnar. Þroski brjósta og kynhára var stiggreindur samkvæmt aðferð Tanners (B 1-5 og PH 1-5). Til að kanna aldur við fyrstu tíðablæðingar (menarche) voru stúlkurnar spurðar hvort þær hefðu haft blæðingar. Svarið var skráð já eða nei. Meðalaldur stúlkna við upphaf brjóstaþroska (B 2) var 10,84 (staðalfrávik 1,43) ár og við fyrsta mælanlegan kynháravöxt (PH 2) 11,46 (staðalfrávik 1,25) ár. Meðalaldur stúlkna við fyrstu tíðablæðingar var 13,26 (staðalfrávik 1,15) ár. Þroski íslenskra stúlkna fylgir svipuðu ferli og lýst hefur verið á öðrum Norðurlöndum. Hins vegar virðist tímabilið 2,42 ár frá fyrstu einkennum kynþroska stúlkna (B 2) að fyrstu tíðablæðingum vera tiltölulega langt, borið saman við niðurstöður erlendra rannsókna

Geodetic mass balance record with rigorous uncertainty estimates deduced from aerial photographs and lidar data – Case study from Drangajökull ice cap, NW Iceland

In this paper we describe how recent high-resolution digital elevation models (DEMs) can be used to extract glacier surface DEMs from old aerial photographs and to evaluate the uncertainty of the mass balance record derived from the DEMs. We present a case study for Drangajokull ice cap, NW Iceland. This ice cap covered an area of 144 km(2) when it was surveyed with airborne lidar in 2011. Aerial photographs spanning all or most of the ice cap are available from survey flights in 1946, 1960, 1975, 1985, 1994 and 2005. All ground control points used to constrain the orientation of the aerial photographs were obtained from the high-resolution lidar DEM. The lidar DEM was also used to estimate errors of the extracted photogrammetric DEMs in ice-and snow-free areas, at nunataks and outside the glacier margin. The derived errors of each DEM were used to constrain a spherical semivariogram model, which along with the derived errors in ice-and snow-free areas were used as inputs into 1000 sequential Gaussian simulations (SGSims). The simulations were used to estimate the possible bias in the entire glaciated part of the DEM and the 95% confidence level of this bias. This results in bias correction varying in magnitude between 0.03m (in 1975) and 1.66m (in 1946) and uncertainty values between +/- 0.21m (in 2005) and +/- 1.58m (in 1946). Error estimation methods based on more simple proxies would typically yield 2-4 times larger error estimates. The aerial photographs used were acquired between late June and early October. An additional seasonal bias correction was therefore estimated using a degree-day model to obtain the volume change between the start of 2 glaciological years (1 October). This correction was largest for the 1960 DEM, corresponding to an average elevation change of -3.5m or approx. three-quarters of the volume change between the 1960 and the 1975 DEMs. The total uncertainty of the derived mass balance record is dominated by uncertainty in the volume changes caused by uncertainties of the SGSim bias correction, the seasonal bias correction and the interpolation of glacier surface where data are lacking. The record shows a glacier-wide mass balance rate of (B) over dot = -0.26 +/- 0.04m w.e.a(-1) for the entire study period (1946-2011). We observe significant decadal variability including periods of mass gain, peaking in 1985-1994 with (B) over dot = -0.27 +/- 0.11m w.e.a(-1). There is a striking difference when (B) over dot is calculated separately for the western and eastern halves of Drangajokull, with a reduction of eastern part on average similar to 3 times faster than the western part. Our study emphasizes the need for applying rigorous geostatistical methods for obtaining uncertainty estimates of geodetic mass balance, the importance of seasonal corrections of DEMs from glaciers with high mass turnover and the risk of extrapolating mass balance record from one glacier to another even over short distances.This work was carried out within SVALI funded by the Nordic Top-level Research Initiative (TRI) and is SVALI publication number 70. It was also financially supported by alpS GmbH. This work is a contribution to the Rannis grant of excellence project, ANATILS. We thank the National Land Survey of Iceland and Loftmyndir ehf. for acquisition and scanning of the aerial photographs. This study used the recent lidar mapping of the glaciers in Iceland that was funded by the Icelandic Research Fund, the Landsvirkjun Research Fund, the Icelandic Road Administration, the Reykjavik Energy Environmental and Energy Research Fund, the Klima- og Luftgruppen (KoL) research fund of the Nordic Council of Ministers, the Vatnajokull National Park, the organization Friends of Vatnajokull, the National Land Survey of Iceland and the Icelandic Meteorological Office.Peer Reviewe

Modelling the 20th and 21st century evolution of Hoffellsjökull glacier, SE-Vatnajökull, Iceland

The Little Ice Age maximum extent of glaciers in Iceland was reached about 1890 AD and most glaciers in the country have retreated during the 20th century. A model for the surface mass balance and the flow of glaciers is used to reconstruct the 20th century retreat history of Hoffellsjökull, a south-flowing outlet glacier of the ice cap Vatnajökull, which is located close to the southeastern coast of Iceland. The bedrock topography was surveyed with radio-echo soundings in 2001. A wealth of data are available to force and constrain the model, e.g. surface elevation maps from ~1890, 1936, 1946, 1989, 2001, 2008 and 2010, mass balance observations conducted in 1936–1938 and after 2001, energy balance measurements after 2001, and glacier surface velocity derived by kinematic and differential GPS surveys and correlation of SPOT5 images. The approximately 20% volume loss of this glacier in the period 1895–2010 is realistically simulated with the model. After calibration of the model with past observations, it is used to simulate the future response of the glacier during the 21st century. The mass balance model was forced with an ensemble of temperature and precipitation scenarios derived from 10 global and 3 regional climate model simulations using the A1B emission scenario. If the average climate of 2000–2009 is maintained into the future, the volume of the glacier is projected to be reduced by 30% with respect to the present at the end of this century. If the climate warms, as suggested by most of the climate change scenarios, the model projects this glacier to almost disappear by the end of the 21st century. Runoff from the glacier is predicted to increase for the next 30–40 yr and decrease after that as a consequence of the diminishing ice-covered area

Theory of Thermoelectric Power in High-Tc Superconductors

We present a microscopic theory for the thermoelectric power (TEP) in high-Tc cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a square lattice Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-Tc cuprates, which have been a long-standing problem of high-Tc cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10. Figure 2 has been revise

Mg/Ti multilayers: structural, optical and hydrogen absorption properties

Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a "spinodal-like" microstructure with a small degree of chemical short-range order in the atoms distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities and characterize them both structurally and optically. Notwithstanding the large lattice parameter mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. Upon exposure to H2 gas a two-step hydrogenation process occurs, with the Ti layers forming the hydride before Mg. From in-situ measurements of the bilayer thickness L at different hydrogen pressures, we observe large out-of-plane expansions of the Mg and Ti layers upon hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. Upon unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces