bluuebunny/crossref_metadata_2025 huggingface dataset:
Isostatic postglacial rebound over Fennoscandia with a self-gravitating spherical visco-elastic Earth model
Authors: Le Meur E.
Published: September 2017

Accounting for isostasy in glaciological models has always been a necessity but these models mostly use very simple parameterizations (Le Meur and Huybrechts, 1996). The need for more realistic isostatic parameterizations rapidly became apparent, especially in the treatment of bedrock-sensitive issues such as the grounding-line migration (Huybrechts, 1990a, b). To this end, a rather sophisticated Earth model, avoiding most of the common assumptions, has been developed and is presented here. The two key groups of parameters, to which the model is most sensitive, are the Earth properties and the rheological law used for the mantle. The aim of this paper is first to justify the use of Maxwell rheology for the mantle and then to tune the most sensitive Earth parameter, namely the mantle viscosity, in order to match the numerous present-day uplift data over Fennoscandia. So, in the first instance, a short review of the different available rheologies is presented and discussed. The visco-elastic theory, as well as the mathematical background used in the present model, is also briefly sketched. Secondly, a glacial scenario over Fennoscandia served as an input for the model in a calibration test on the mantle-viscosity values. The degree of agreement of the model outputs with the present-day measurements gives a reference set of Green functions, to which one can reasonably refer when modelling the isostatic response over areas where such a control is not possible (Le Meur and Huybrechts, 1996). Finally, a closer look to the time-dependent surface displacements will confirm the ability for the model to reproduce correctly the main postglacial rebound characteristic features.
Sensitivity tests of coupled ice-sheet/ice-stream dynamics in the EISMINT experimental ice block
Authors: Marshall Shawn J. , Clarke Garry K. C.
Published: September 2017

A continuum mixture model of coupled ice-sheet/ice-stream dynamics has been developed within a conventional three-dimensional finite-difference model framework. The ice mass is areally divided into sheet-ice and stream-ice components. Dynamic evolution of each component is solved with coupling terms to describe mass exchange between flows. In this way, ice-stream fluxes can be incorporated in a rigorous dynamical model with only a doubling of computational cost. This paper presents simple model tests using the EISMINT experimental ice block, a 1500 km × 1500 km ice sheet which rests on a flat bed. Ice-stream behaviour is investigated for a range of coupling rules and activation scenarios. In simple tests presented here, we find that the viscous response time of source ice feeding the ice stream may be a factor limiting ice-stream vigour and longevity.
Geometric boundary conditions for modelling the velocity field of the Antarctic ice sheet
Authors: Bamber Jonathan L. , Huybrechts Philippe
Published: September 2017

This paper presents improved geometric boundary conditions (surface elevation and ice thickness) required as inputs to calculations of the surface-velocity field for the Antarctic ice sheet. A comparison of the two-dimensional horizontal velocity field obtained on the basis of conservation of mass (balance velocity) with the diagnostic velocity field calculated with an ice-sheet model (dynamic velocity) may yield information on shortcomings in the way the ice-sheet model describes the ice flow. Here, the surface-elevation grid is described in detail, as it has been generated specifically for such a study and represents a new standard in accuracy and resolution for calculating surface slopes. The digital-elevation model was generated on a 10 km grid size from over 20 000 000 height estimates obtained from eight 35 d repeat cycles of ERS-1 radar-altimeter data. For surface slopes less than 0.4°, the accuracy is better than 1.5 m. In areas of high surface slope (coastal and mountainous regions), the altimeter measurements have been supplemented with data taken from the Antarctic Digital Database. South of 81.5°, data from the SPRI folio map have been used. The ice-thickness grid was produced from a combination of a redigitization of the SPRI folio and the original radio-echo-sounding flight lines. For areas of grounded ice, the elevation of the bed was estimated from surface elevation and ice thickness. Significant differences (in excess of 25% of ice thickness) were obtained between an earlier digitization of the folio bed-elevation map and the data set derived here. Furthermore, a new value of 25.6 × 106 km3 was obtained for the total volume of the ice sheet and ice shelves, which is a reduction of 12% compared with the original estimate derived during the compilation of the SPRI folio. These differences will have an important influence on the results obtained by numerical ice-sheet models.
Polythermal three-dimensional modelling of the Greenland ice sheet with varied geothermal heat flux
Authors: Greve R. , Hutter K.
Published: September 2017

Computations over 50 000 years into steady state with Greve’s polythermal ice-sheet model and its numerical code are performed for the Greenland ice sheet with today’s climatological input (surface temperature and accumulation function) and three values of the geothermal heat flux: (42, 54.6, 29.4) mW m−2. It is shown that through the thermomechanical coupling the geometry as well as the thermal regime, in particular that close to the bed, respond surprisingly strongly to the basal thermal heat input. The most sensitive variable is the basal temperature field, but the maximum height of the summit also varies by more than ±100m. Furthermore, some intercomparison of the model outputs with the real ice sheet is carried out, showing that the model provides reasonable results for the ice-sheet geometry as well as for the englacial temperatures.
Variations in aerologically derived Arctic precipitation and snowfall
Authors: Serreze Mark C. , Rehder Mark C. , Barry Roger G. , Walsh John E. , Robinson David A.
Published: September 2017

Data from a rawinsonde network are used to provide aerological estimates of monthly precipitation minus evaporation (P – E) averaged over the region north of 70° N. Using published climatological estimates of E, area-averaged P is obtained for each month and year as a residual. Using surface temperatures from the rawinsonde network, the fraction of precipitation falling as snow is then estimated. Over the 1974–91 study period, precipitation and snowfall (water equivalent) have annual means of 26.6 and 19.0 cm. respectively. Assuming a representative aged snowpack density of 330 kg m−3 yields a total snow depth of 57.5 cm. The mean annual cycles of both variables display an autumn maximum, but because of the temperature dependency, nearly all precipitation falls as rain during July and August. Composite analyses reveal that increased precipitation for all seasons and increased snowfall for winter and autumn are favored by a “winter-type” circulation pattern, characterized by stronger troughs over the Atlantic and Eurasian sectors of the Arctic, associated with increased cyclonic activity over the Arctic peripheral seas.
Simulations of the 1979–88 polar climates by global climate models
Authors: Chen Biao , Bromwich David H. , Hines Keith M. , Pan Xuguang
Published: September 2017

The simulation of the northern and southern polar climates for 1979–88 by 14 global climate models (GCMs), using the observed monthly averaged sea-surface temperatures and sea-ice extents as boundary conditions, is part of an international effort to determine the systematic errors of atmospheric models under realistic conditions, the so-called Atmospheric Model Intercomparison Project (AMIP), In this study, intercomparison of the models’ simulation of polar climate is discussed in terms of selected surface and vertically integrated monthly averaged quantities, such as sea-level pressure, cloudiness, precipitable water, precipitation and evaporation/sublimation. The results suggest that the accuracy of model-simulated climate features in high latitudes primarily depends on the horizontal resolution and the treatment of physical processes in the GCMs. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models and provides valuable information for model improvement.
The waxing and waning of the Northern Hemisphere ice sheets
Authors: Marsiat I.
Published: September 2017

Past modelling studies have shown that the energy balance of the ice-sheet surface is of primary importance in representing the 100 000 year glacial cycle. In particular, modelling of the net mass-balance function is an important part of coupled ice-sheet/climate models. We conduct a series of palaeoclimatic simulations with a vertically integrated ice-flow model coupled to the two-dimensional statistical-dynamical LLN (Louvain-la-Neuve) climate model. The models are coupled through a land-surface model which computes seasonal cycles of surface temperature and precipitation at the real altitude of the surface and evaluates the annual snow and/or ice-mass budget. The present-day climate of the Northern Hemisphere, the Greenland mass balance and the snowfield characteristics are quite well represented despite the relative simplicity of the model. Total ice-volume and sea-level variations during the last glacial cycle are well simulated. This suggests that the physical mechanisms included in the models are sufficient to explain the most striking features of the ice-age cycle. Introducing an improved and more detailed topography improves the simulation of the total ice volume but fails to correct inadequacies in the simulated ice distribution on the surface of the Earth.
Ice-sheet models as tools for palaeoclimatic analysis: the example of the European ice sheet through the last glacial cycle
Authors: Boulton G. S. , Hulton N. , Vautravers M.
Published: September 2017

A numerical model is used to simulate ice-sheet behaviour in Europe through the last glacial cycle. It is used in two modes: a forward mode, in which the model is driven by a proxy palaeoclimate record and the output compared with a geological reconstruction of ice-sheet fluctuation; and an inverse mode, in which we determine the climate function that would be required to simulate geologically reconstructed ice-sheet fluctuations.

From these simulations it is concluded that extra-glacial climates may be poor predictors of ice-sheet surface climates, and that climatic transitions during the glacial period may have been much more rapid and the intensity of warming during the early Holocene much greater than hitherto supposed. Stronger climate forcing is required to drive ice-sheet expansion when sliding occurs at the bed compared with a non-sliding bed. Sliding ice sheets grow more slowly and decay more rapidly than non-sliding ice sheets with the same climate forcing.
Recent increase in South Pole snow accumulation
Authors: Mosley-Thompson E. , Thompson L. G. , Paskievitch J. F. , Pourchet M. , Gow A. J. , Davis M.E. , Kleinman J.
Published: September 2017

This paper summarizes the 37 year history of net accumulation measurements at the geographic South Pole obtained by numerous investigators using a variety of techniques. These data lead to the conclusion that annual net snow accumulation has increased in the vicinity of South Pole Station (SPS) since 1955. The records were examined for evidence of a “station effect” and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station. Furthermore, the accumulation increase at the South Pole appears consistent with increases observed at other locations on the East Antarctic Plateau, and in the Peninsula region as well. These data suggest that the recent accumulation increase at SPS may be regionally extensive over the East Antarctic Plateau.
Ages and ablation and accumulation rates from 14C measurements on Antarctic ice
Authors: Roijen J.J. Van , der Borg K. van , De Jong A.F.M. , Oerlemans J.
Published: September 2017

Shallow ice cores from an Antarctic blue-ice area at Scharffenbergbotnen were l4C-analyzed using a dry-extraction technique and accelerator mass spectrometry. The in situ production was determined from the 14CO component and used to deduce the natural 14CO2 component. The ages were measured at 10 000 ± 3000 BP. The accumulation and ablation rates determined from the in situ production are 7–20 and 10 cm a−1. respectively, showing agreement with field observations. The derived ages and air-yield data show a nearby origin for the surface ice.
The climate sensitivity of Antarctic blue-ice areas
Authors: Bintanja Richard , Van Den Broeke Michiel R.
Published: September 2017

On time-scales of less than about 100 years, when the ice topography can be considered stationary, the extent of Antarctic blue-ice areas is governed mainly by the surface mass balance. In and near high-elevation blue-ice areas, ablation is due entirely to sublimation. An estimate of the mass-balance profile ranging from a blue-ice area to the adjacent snow surface is presented. By considering changes in sublimation induced by variations in local climate, the deviation from the mass-balance profile is evaluated. It is concluded that even for considerable changes in local climate these deviations remain relatively small and have only little effect on the extent of a blue-ice area. This can be attributed mainly to the steep mass-balance profile.
Recent warming as recorded in the Qinghai-Tibetan cryosphere
Authors: Yao Tandong , Thompson Lonnie G. , Jiao Keqin , Mosley-Thompson Ellen , Yang Zhihong
Published: September 2017

Oxygen-isotope ratios (δ18O) measured on ice cores on the Qinghai-Tibetan Plateau, China, increased by 1.2-2.2‰ from the 1960s to the 1990s. Measurements of the δ18O content of precipitation and the simultaneous air temperatures needed to compute the temperature increase corresponding to the increase in δ18O are currently made at the Delingha Meteorological Station, but the amount of data is not yet sufficient to obtain a reliable result.
Application of inventory data for estimating characteristics of and regional climate-change effects on mountain glaciers: a pilot study with the European Alps
Authors: Haeberli Wilfried , Hoelzle Martin
Published: September 2017

A parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate-change effects on mountain glaciers. For past and potential climate scenarios, glacier changes for assumed mass-balance changes are calculated as step functions between steady-state conditions for time intervals that approximately correspond to the characteristic dynamic response time (a few decades) of the glaciers. In order to test the procedure, a pilot study was carried out in the European Alps where detailed glacier inventories had been compiled around the mid-1970s. Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s; strongly negative mass balances are likely to have caused a loss of about 10–20% of this total volume during the decade 1980–90. Backward calculation of glacier-length changes using a mean annual mass balance of 0.25m w.e.a−1 since the end of the “Little Ice Age” around 1850 AD gives considerable scatter but satisfactory overall results as compared with long-term observations. The total loss of Alpine surface ice mass since 1850 can be estimated at about half the original value. An acceleration of this development, with annual mass losses of around 1 m a−1 or more as anticipated from IPCC scenario A for the coming century, could eliminate major parts of the presently existing Alpine ice volume within decades.
Recent changes of McCall Glacier, Alaska
Authors: Rabus Bernhard , Echelmeyer Keith , Trabant Dennis , Benson Carl
Published: September 2017

Detailed surveys of McCall Glacier in the Alaskan Arctic reveal changes from 1972 to 1993. The ice surface dropped everywhere, by amounts ranging from about 3 m in the highest cirques tq more than 42 m near the present terminus. The total volume loss was 3.5+ 0.2 x 10' m(, resulting in an average mass balance of 0.33 + 0.01 in a . l he terminus has retreated by about 285 m at a rale of 12_.5 ma \ Results from photogrammetry for an earlier period, 1958-71, were I.16x 10'm3 and 0.13 ma for volume change and mass balance, respectively; the mean terminus retreat rate was then 5.7 m a . The changes have to be seen in the context of McCall Glacier’s low mass-exchange rate; annual accumulation and ablation, averaged over the years 1969 72 were only +0.16 and 0.3 m a '. Cross-profiles in the ablation area, surveyed at intervals of a few years, show an increased drop rate since the late 1970s. 7 he volume-ehange data suggest a climate warming in the early 1970s. Enhanced thinning of the lower ablation region and accelerated terminus retreat seem to lag this climate change by not more than 10 years, This indicates a reaction time of McCall Glacier that is considerably shorter than its theoretic response time of about 50 70 years.
On the use of radiosondes to model glacier ablation
Authors: Conway H. , Rasmussen L. A. , Hayes P.
Published: September 2017

Data from twice-daily radiosonde flights are used to estimate spatial and temporal variations of air temperature, atmospheric transmissivity, wind speed and humidity at Blue Glacier, western Washington. U. S.A. Results indicate that the free-air conditions (interpolated in altitude and in time from radiosondes) provide a much better estimate of conditions on the glacier than do measurements from low-altitude stations. Data from the radiosondes are used to model the hourly exchange of mass and energy at the surface of Blue Glacier. In the absence of explicit information about clouds, temperature and humidity profiles from the radiosonde are used to estimate the atmospheric transmissivity needed for the calculation of short-wave radiation. Topographical influences (altitude, shading, slope angle and orientation) and surface albedo are parameterized explicitly to model the absorbed solar flux at specific sites on the glacier, Other energy fluxes (long-wave radiation, sensible-heat and latent-heat exchange) are estimated using established physical models. Hourly estimates of ablation are integrated to obtain the seasonal ablation. Modeled ablation and stake measurements made over 30 a at two sites on Blue Glacier agree within 16%, which is within the error associated with stake measurements of ablation.
Relation of glacier variations to climate changes in Iceland
Authors: Sigurdsson Oddur , Jónsson Trausti
Published: September 2017

Glacier variations in Iceland have been recorded systematically since the 1930s at 27 different glacier termini. The advance/retreat records of non-surging glaciers show a clear relationship to climate. A change in the climate typically leads to a response at the snout within a time period of 10 years. The records of surge-type and mixed-type glaciers show variations that are unrelated to climate. However, the maximum extension of surge-type glaciers at the end of surges and the minimum extension just before a surge appear to be influenced by long-term climate changes. A strong warming in the 1920s was a turning-point in the climate of Iceland which led to a rapid retreat of most glaciers in the country in the 1930s. The summer temperature fell gradually after 1940, with a notable drop in the mid-1960s. Since about 1970, more than half of the glaciers in Iceland have been advancing. In the western part of the country, the recovery is about one-quarter of the ground lost and in the southern, central and northern parts it is about one-half. In southeastern Iceland, some of the glaciers have been stationary for about 30 years while others have advanced slightly. Glacier snow-budget index computed from meteorological data indicates that the timing of the turning-point around 1970 coincides with a minimum in the cumulative net glacier mass balance.
Satellite imagery, a base line for glacier variation study on James Ross Island, Antarctica
Authors: Skvarca Pedro , Rott Helmut , Nagler Thomas
Published: September 2017

Sequential visible and radar satellite imagery is used to document the fluctuations of 39 outlet glaciers on James Ross Island (JRI; 64° S, 58° W), Antarctic Peninsula. The monitoring time interval of 17.4 years extends from late 1975 until early 1993. The study is based on synergistic use of different sensors for monitoring glacier variations. The digitally enhanced Landsat TM images also allowed definition of boundaries between grounded and floating ice within Röhss Bay and detection of ice rumples, resulting in an improved measurement of the areal extent of JRI. In addition to glacier boundaries, the analyzed ERS-1 SAR images provide information on morphological properties of snow and ice. The satellite data show a general glacier retreat since 1975, resulting in clear decrease of overall glacier area on JRI. Of 39 glaciers measured, 33 glaciers retreated in the period 1975–93, 15 of which showed significant retreat in comparison to glacier size. This is in accordance with the pronounced atmospheric-warming trend recorded during the last two decades on the Antarctic Peninsula. The analysis of glacier areas on JRI thus provides a base line for detection of future changes.
Glacier Inventory in Chile: current status and recent glacier variations
Authors: Casassa Gino
Published: September 2017

The glacier inventory in Chile covers all the arid north of the country (18° to 33° S) and the central part down to the lake district (33° to 41° 30′ S) except for the Río Maule and Río Itata basins (35° to 37° S). The most glaciated region of Chile is Patagonia, characterized by a wet climate, but glacier data are lacking over vast areas of this region. A total area of 5515 km2 has been inventoried in Chile; this does not include Hielo Patagónico Sur (southern Patagonia ice field), by far the largest glaciated area in Chile with an area of 13000km2, part of which is in Argentina. Including the uninventoried giaciers of Maule, Itata and Patagonia, the total glaciated area in Chile is estimated to be 201715 km2.

Information on glacier variations in the north of Chile is very scarce. In the central and south-central parts, and especially in Patagonia where glacier variations have been most studied, there is ample evidence for general glacier retreat from a neoglacial maximum, although a few glacier advances have been reported. The generalized retreat might be a result of tropospheric warming observed in the second half of the 20th century.
Effects of the snow cover on Antarctic sea ice and potential modulation of its response to climate change
Authors: Eicken Hajo , Fischer Holger , Lemke Peter
Published: September 2017

Based on presented field data, it is shown that snow contributes roughly 8% to the total mass of ice in the Weddell Sea. Snow depth averages 0.16 m on first-year ice (average thickness 0.75 m) and 0.53 m on second-year ice (average thickness 1.70 m). Due to snow loading, sea ice is depressed below water level and flooded by sea water. As a result of flooding, snow ice forms through congelation of sea water and brine in a matrix of meteoric ice (i.e. snow). Sea-ice growth has been simulated with a one-dimensional model, treating the evolution of salinity, porosity and thermal properties of the ice. Simulations demonstrate that in the presence of a snow cover, ice growth is significantly reduced. Brine volumes increase by a factor of 1.5–2, affecting properties such as ice strength. Snow-ice formation depends on the evolution of freeboard and ice permeability. Effects of accumulation-rate changes have been assessed, for the Weddell Sea with a large-scale sea-ice model accounting for snow-ice formation. Results for different scenarios are presented and compared with field data and one-dimensional simulations. The role of snow in modulating the response of Antarctic sea ice to climate change is discussed.
Stability of Icebergs
Authors: Bass D. W.
Published: September 2017

The tendency of icebergs to roll or heel over is well-known, and so the potential hazards and difficulties of towing unstable icebergs may be appreciated. It follows that there is a need for both accurate and approximate techniques for determining the stability of an iceberg.
Flow Around Icebergs
Authors: Foldvik A. , Gammelsrød T. , Gjessing Y.
Published: September 2017

During the Norwegian Antarctic Research Expedition 1978–79, two experiments were carried out to measure flow around icebergs. Drogues were equipped with surface markers constructed to drift with the flow at various levels down to 260 m. They were tracked by a helicopter and a Motorola positioning system. As expected, the surface-layer (0 to 20 m) flow was wind-induced, but even at greater depths a relative motion of a few cm/s between the water and the iceberg was measured. Such measurements are important for the determination of drag on icebergs, and for melting and erosion processes.
Some Satellite-Tracked Iceberg Drifts in the Antarctic
Authors: Vinje Torgny E.
Published: September 2017

The drift of eight tabular icebergs is discussed. In spite of large differences in the vertical dimension, the various icebergs seem to react in a similar manner to wind effects in areas covered with sea ice. Measurements indicate that it takes between one and five years for an iceberg to move into the westerlies from the coastal areas between about 50°E. and the Antarctic Peninsula. The drift of the icebergs reflects the integrated current effects in the upper 200-300 m, and may thus also give information about the transport of water masses.
Antarctic Iceberg Melt Rates Derived from Size Distributions and Movement Rates
Authors: Budd W. F. , Jacka T. H. , Morgan V. I.
Published: September 2017

The melt rates of Antarctic icebergs derived by Morgan and Budd (1978) were based primarily on the distribution of iceberg concentrations, data on iceberg size distribution being limited. Recently, more detailed data have been obtained, especially north of lat. 60°S which allow more precise calculations of the changes in size during drifting. On Australian National Antarctic Research Expedition (ANARE) voyages each summer since 1977, observations of icebergs have included photographs, number per unit area from ship’s radar, widths, heights, and shapes. These data have allowed separate calculations to be made for tabular icebergs which give a clearer indication of the contribution to average size changes of melting, breakage, and rollover. New data from satellite transponders placed on icebergs have provided more definite estimates of the average northward and then eastward drift rates of icebergs near 90°E. Combined with the new data on size more accurate melt rates have been derived. Detailed measurements with expendable bathy-thermographs (XBT) along the shipping routes have provided more definite data on water temperature which allow the melt rates to be studied as a function of temperature. Historical data on iceberg locations have been used to estimate the melt and decay rates of the icebergs at higher temperatures.
Remote Sensing of the Ross Ice Streams and Adjacent Ross Ice Shelf, Antarctica
Authors: Bentley C.R. , Shabtaie S. , Blankenship D.D. , Rooney S.T. , Schultz D.G. , Anandakrishnan S. , Alley R.B.
Published: September 2017

In the first few seasons of the Antarctic Siple Coast project, the University of Wisconsin has concentrated on radar and seismic studies. Highlights of the results to date include the delineation of ice streams A, B, and C and the ridges in between, determination of the surface elevations over the area, discovery of a much more advanced grounding line than previously recognized and recognition of a broad, flat, barely grounded “ice plain” just inside the grounding line. Complex zones between and adjoining some of the ice streams, characterized by an interspersal of undisturbed ice and crevassed patches, give the impression of being transformed from sheet flow into stream flow in a process of ice stream expansion. An indicated negative mass balance for ice stream B could be the result of this “activation” process. Ice stream C, currently stagnant, exhibits terraces and reversals of surface slope, associated with zones of strong, steady basal radar reflections. These features suggest that subglacial water has been trapped by reversals in the hydraulic pressure gradient.

Low seismic P-wave and S-wave velocities in a meters-thick layer immediately below the ice strongly indicate a saturated sediment of such high porosity (~40%) and low effective (differential) pressure (~50 kPa, or 0.5% of the glaciostatic pressure) that it must be too weak not to be deforming. We presume this deforming layer to be a dilated till. Its base exhibits ridges and troughs parallel to the flow direction that resemble glacial megaflutes. We believe that at our site on the upper part of ice stream B the ice stream moves principally by deforming its bed. Analysis of seismographic recordings of micro-earthquakes that occur at the glacier bed shows that the micro-earthquakes are both small in energy and infrequent. This implies that virtually none of the energy of ice stream motion is dissipated by brittle fracture at the bed. If our models are correct, the subgiacial deforming till becomes increasingly soft down-glacier, and/or the ice becomes decoupled from the till by intervening water, until on the “ice plain” basal drag is less important than longitudinal stresses in the dynamic balance. Our models also imply that the “ice plains” rest on “till deltas” that have been formed by the deposition of till carried along beneath the ice streams, and that the till deltas, and the grounding lines that bound them, are currently advancing in front of the active ice streams.
Microearthquakes Under and Alongside Ice Stream B, Antarctica. Detected By A New Passive Seismic Array
Authors: Blankenship D.D. , Anandakrishnan S. , Kempf J.L. , Bentley C.R.
Published: September 2017

A new seismographic array with a band width of 500 Hz per channel and a dynamic range of 96 dB was developed for detecting natural events on glaciers. It was first deployed on ice stream B during the 1985–86 austral summer. The network consists of nine solar-powered seismographs, each monitoring three components of ground motion. Each of the seismographs is connected by up to 4 km of fiber-optic cable to a central node where seismic events are both detected and recorded. During 85 h of passive seismic monitoring on ice stream B, 25 microearthquakes were observed. Sixteen of these events were associated with shallow crevassing, mostly near the margins, although not within the zones of extreme shearing that bound the ice streams. Nine microearthquakes were associated with low-angle thrusting near the base of the ice stream. The principal initial result of these passive seismic studies is the demonstration that virtually none of the energy dissipated beneath ice stream B takes place through brittle fracture near the base. Nevertheless, fracture associated with microearthquakes may play a significant role in sub-glacial erosion.
Ground Data Inputs To Image Processing for Estimating Terrain Characteristics for Glacio-Hydrological Analysis
Authors: Clark M.J. , Gurnell A.M. , Hancock P.J.
Published: September 2017

Remote-sensing research in glacial and pro-glacial environments raises several methodological problems relating to the handling of ground and satellite radiometric data. An evaluation is undertaken of the use of ground radiometry to elucidate properties of relevant surface types in order to interpret satellite imagery. It identifies the influence that geometric correction and re-sampling have on the radiometric purity of the resulting data set. Methodological problems inherent in deriving catchment terrain characteristics are discussed with reference to currently glacierized and pro-glacial zones of south-western Switzerland.
Bio-based 3-hydroxypropionic Acid: A Review
Authors: Vidra Aladár , Németh Áron
Published: September 2017

3-hydroxypropionic acid is a commercially valuable, important platform chemical. It can serve as a precursor for several key compound, such as acrylic acid, 1,3-propanediol, methyl acrylate, acrylamide, ethyl 3-HP, malonic acid, propiolactone and acrylonitrile. Several microorganisms can produce through a range of metabolic pathways. It is indispensable for the commercial production of 3-HP to use cheap and abundant substrates and also to produce in highly efficient processes which could result high yield, titer and productivity. Because  of the fact, that natural microorganism do not perform these conditions, metabolic engineering and genetically engineered microorganism are widely used for research and production as well. Several metabolic pathways are introduced to utilize glucose or glycerol for 3-HP production. In this overview naturally producer microorganisms, synthetic biochemical pathways, results from the recent years and recovery of 3-HP are detailed.
SEROPREVALENCE OF TOXOPLASMOSIS IN WOMEN IN MYMENSINGH AND RANGPUR IN BANGLADESH: A HOSPITAL SURVEY
Authors: Margia U. H. , Begum N. , Hossain M. S. , Dey A. R. , Alam M. Z.
Published: September 2017

Toxoplasmosis is a great zoonotic threat that affects human species specially women. It has got major health significance because it causes abortion in pregnant women.  The aim of this study was to determine seroprevalence of toxoplasmosis in women in Mymensingh and Rangpur in Bangladesh and to identify possible risk factors associated with toxoplasmosis. In this study, 87 women of 15 to 45 years old were included. Among 87 women, 74.7% (n = 65) were seronegative and 25.3% were (n=22) seropositive for T. gondii IgG and IgM antibodies. However, seroprevalence was higher in women aged between 31-45years. Relationship between T. gondii antibody and pregnancy was found significant (p<0.05). This study also reveals that pregnant women are more susceptible to toxoplasmosis than non-pregnant women. Thusly, regular screening test for toxoplasmosis is necessary for pregnant women in Bangladesh.
An Inductive Discussion of the Interrelationships between Nursing Shortage, Horizontal Violence, Generational Diversity, and Healthy Work Environments
Authors: Armmer Francesca
Published: September 2017

The complex features of the nursing shortage, horizontal violence, generational diversity and healthy work environments have frequently been addressed within the context of their singular characteristics, challenges and potential solutions. Yet it is the interrelationships of these phenomena that holds solutions to the overarching challenges facing nurses and the nursing profession. Through an inductive approach, a preliminary discussion and related strategies to address the highlighted challenges have been proposed.
Indistinguishability Operators Applied to Task Allocation Problems in Multi-Agent Systems
Authors: Guerrero José , Miñana Juan-José , Valero Oscar , Oliver Gabriel
Published: September 2017

In this paper we show an application of indistinguishability operators to model response functions. Such functions are used in the mathematical modeling of the task allocation problem in multi-agent systems when the stimulus, perceived by the agent, to perform a task is assessed by means of the response threshold model. In particular, we propose this kind of operators to represent a response function when the stimulus only depends on the distance between the agent and a determined task, since we prove that two celebrated response functions used in the literature can be reproduced by appropriate indistinguishability operators when the stimulus only depends on the distance to each task that must be carried out. Despite the fact there is currently no systematic method to generate response functions, this paper provides, for the first time, a theoretical foundation to generate them and study their properties. To validate the theoretical results, the aforementioned indistinguishability operators have been used to simulate, with MATLAB, the allocation of a set of tasks in a multi-robot system with fuzzy Markov chains.
Supporting an Object-Oriented Approach to Unit Generator Development: The Csound Plugin Opcode Framework
Authors: Lazzarini Victor
Published: September 2017

This article presents a new framework for unit generator development for Csound, supporting a full object-oriented programming approach. It introduces the concept of unit generators and opcodes, and its centrality with regards to music programming languages in general, and Csound in specific. The layout of an opcode from the perspective of the Csound C-language API is presented, with some outline code examples. This is followed by a discussion which places the unit generator within the object-oriented paradigm and the motivation for a full C++ programming support, which is provided by the Csound Plugin Opcode Framework (CPOF). The design of CPOF is then explored in detail, supported by several opcode examples. The article concludes by discussing two key applications of object-orientation and their respective instances in the Csound code base.
Effects of N Fertilizer Application on Soil N2O Emissions and CH4 Uptake: A Two-Year Study in an Apple Orchard in Eastern China
Authors: Xie Baohua , Gu Jiangxin , Yu Junbao , Han Guangxuan , Zheng Xunhua , Xu Yu , Lin Haitao
Published: September 2017

Land use changes from cropland to orchards in Eastern China have raised serious concerns about the regional nitrogen (N) cycle and greenhouse gas balance. We measured soil nitrous oxide (N2O) emissions and methane (CH4) uptake using manual static chambers in an apple orchard. The primary aims were to assess the effect of N fertilizer application on gas fluxes and quantify the site-specific N2O emission factor (EFd). Field experiments were arranged in a randomized block design with three N input rates (0, 800 and 2600/2000 kg N ha−1 year−1). We found that orchard soils were a negligible CH4 sink (−1.1 to −0.4 kg C ha−1 year−1). Annual N2O emissions responded positively to N input rates, ranging from 34.1 to 60.3 kg N ha−1 year−1. EFd ranged from 1.00% to 1.65% with a mean of 1.34%. The extremely large background emissions of N2O (34.1–34.3 kg N ha−1 year−1) most likely originated from nitrate accumulation in the soil profile because of historical overuse of N fertilizer. We conclude that (1) site-specific EFd is suitable for assessing regional direct N2O emissions from upland orchards; and (2) conventional fertilization regimes must be avoided, and reduced N input rates are recommended in the study region.
Investigating the Interaction of Cyclic RGD Peptidomimetics with αVβ6 Integrin by Biochemical and Molecular Docking Studies
Authors: Civera Monica , Arosio Daniela , Bonato Francesca , Manzoni Leonardo , Pignataro Luca , Zanella Simone , Gennari Cesare , Piarulli Umberto , Belvisi Laura
Published: September 2017

The interaction of a small library of cyclic RGD (Arg-Gly-Asp) peptidomimetics with αVβ6 integrin has been investigated by means of competitive solid phase binding assays to the isolated receptor and docking calculations in the crystal structure of the αVβ6 binding site. To this aim, a rigid receptor-flexible ligand docking protocol has been set up and then applied to predict the binding mode of the cyclic RGD peptidomimetics to αVβ6 integrin. Although the RGD interaction with αVβ6 recapitulates the RGD binding mode observed in αVβ3, differences between the integrin binding pockets can strongly affect the ligand binding ability. In general, the peptidomimetics exhibited IC50 values for integrin αVβ6 (i.e., the concentration of compound required for 50% inhibition of biotinylated fibronectin binding to isolated αVβ6 integrin) in the nanomolar range (77–345 nM), about 10–100 times higher than those for the related αVβ3 receptor, with a single notable ligand displaying a low nanomolar IC50 value (2.3 nM). Insights from the properties of the binding pocket combined with the analysis of the docking poses provided a rationale for ligand recognition and selectivity.
An Overview on Marine Sponge-Symbiotic Bacteria as Unexhausted Sources for Natural Product Discovery
Authors: Brinkmann Candice , Marker Amberlee , Kurtböke D.
Published: September 2017

Microbial symbiotic communities of marine macro-organisms carry functional metabolic profiles different to the ones found terrestrially and within surrounding marine environments. These symbiotic bacteria have increasingly been a focus of microbiologists working in marine environments due to a wide array of reported bioactive compounds of therapeutic importance resulting in various patent registrations. Revelations of symbiont-directed host specific functions and the true nature of host-symbiont interactions, combined with metagenomic advances detecting functional gene clusters, will inevitably open new avenues for identification and discovery of novel bioactive compounds of biotechnological value from marine resources. This review article provides an overview on bioactive marine symbiotic organisms with specific emphasis placed on the sponge-associated ones and invites the international scientific community to contribute towards establishment of in-depth information of the environmental parameters defining selection and acquisition of true symbionts by the host organisms.
Stock Selection for Portfolios Using Expected Utility-Entropy Decision Model
Authors: Yang Jiping , Feng Yijun , Qiu Wanhua
Published: September 2017

Yang and Qiu proposed and then recently improved an expected utility-entropy (EU-E) measure of risk and decision model. When segregation holds, Luce et al. derived an expected utility term, plus a constant multiplies the Shannon entropy as the representation of risky choices, further demonstrating the reasonability of the EU-E decision model. In this paper, we apply the EU-E decision model to selecting the set of stocks to be included in the portfolios. We first select 7 and 10 stocks from the 30 component stocks of Dow Jones Industrial Average index, and then derive and compare the efficient portfolios in the mean-variance framework. The conclusions imply that efficient portfolios composed of 7(10) stocks selected using the EU-E model with intermediate intervals of the tradeoff coefficients are more efficient than that composed of the sets of stocks selected using the expected utility model. Furthermore, the efficient portfolio of 7(10) stocks selected by the EU-E decision model have almost the same efficient frontier as that of the sample of all stocks. This suggests the necessity of incorporating both the expected utility and Shannon entropy together when taking risky decisions, further demonstrating the importance of Shannon entropy as the measure of uncertainty, as well as the applicability of the EU-E model as a decision-making model.
Partially Observable Markov Decision Process-Based Transmission Policy over Ka-Band Channels for Space Information Networks
Authors: Jiao Jian , Sui Xindong , Gu Shushi , Wu Shaohua , Zhang Qinyu
Published: September 2017

The Ka-band and higher Q/V band channels can provide an appealing capacity for the future deep-space communications and Space Information Networks (SIN), which are viewed as a primary solution to satisfy the increasing demands for high data rate services. However, Ka-band channel is much more sensitive to the weather conditions than the conventional communication channels. Moreover, due to the huge distance and long propagation delay in SINs, the transmitter can only obtain delayed Channel State Information (CSI) from feedback. In this paper, the noise temperature of time-varying rain attenuation at Ka-band channels is modeled to a two-state Gilbert–Elliot channel, to capture the channel capacity that randomly ranging from good to bad state. An optimal transmission scheme based on Partially Observable Markov Decision Processes (POMDP) is proposed, and the key thresholds for selecting the optimal transmission method in the SIN communications are derived. Simulation results show that our proposed scheme can effectively improve the throughput.
A Review of the Methane Hydrate Program in Japan
Authors: Oyama Ai , Masutani Stephen
Published: September 2017

In this paper, methane hydrate R&D in Japan was examined in the context of Japan’s evolving energy policies. Methane hydrates have been studied extensively in Japanese national R&D programs since 1993, with the goal of utilizing them as an energy resource. Currently, the Research Consortium for Methane Hydrate Resources in Japan (MH 21) is in the third phase of a project that began in early 2002. Based on publicly available reports and other publications, and presentations made at the ten International Workshops for Methane Hydrate Research and Development, we have attempted to provide a timeline and a succinct summary of the major technical accomplishments of MH 21 during project Phases 1, 2, and 3.
Stability Analysis and Trigger Control of LLC Resonant Converter for a Wide Operational Range
Authors: Fang Zhijian , Wang Junhua , Duan Shanxu , Shao Jianwei , Hu Guozheng
Published: September 2017

The gain of a LLC resonant converter can vary with the loads that can be used to improve the efficiency and power density for some special applications, where the maximum gain does not apply at the heaviest loads. However, nonlinear gain characteristics can make the converters unstable during a major disturbance. In this paper, the stability of an LLC resonant converter during a major disturbance is studied and a trigger control scheme is proposed to improve the converter’s stability by extending the converter’s operational range. Through in-depth analysis of the gain curve of the LLC resonant converter, we find that the switching frequency range is one of the key factors determining the system’s stability performance. The same result is also obtained from a mathematical point of view by utilizing the mixed potential function method. Then a trigger control method is proposed to make the LLC resonant converter stable even during a major disturbance, which can be used to extend the converter’s operational range. Finally, experimental results are given to verify the analysis and proposed control scheme.
Analysis of Voltage Variation in Silicon Carbide MOSFETs during Turn-On and Turn-Off
Authors: Li Hui , Liao Xinglin , Hu Yaogang , Huang Zhangjian , Wang Kun
Published: September 2017

Due to our limited knowledge about silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs), the theoretical analysis and change regularity in terms of the effects of temperature on their switching characteristics have not been fully characterized and understood. An analysis of variation in voltage (dVDS/dt) for SiC MOSFET during turn-on and turn-off has been performed theoretically and experimentally in this paper. Turn-off variation in voltage is not a strong function of temperature, whereas the turn-on variation in voltage has a monotonic relationship with temperature. The temperature dependence is a result of the competing effects between the positive temperature coefficient of the intrinsic carrier concentration and the negative temperature coefficient of the effective mobility of the electrons in SiC MOSFETs. The relationship between variation in voltage and supply voltage, load current, and gate resistance are also discussed. A temperature-based analytical model of dVDS/dt for SiC MOSFETs was derived in terms of internal parasitic capacitances during the charging and discharging processes at the voltage fall period during turn-on, and the rise period during turn-off. The calculation results were close to the experimental measurements. These results provide a potential junction temperature estimation approach for SiC MOSFETs. In SiC MOSFET-based practical applications, if the turn on dVDS/dt is sensed, the device temperature can be estimated from the relationship curve of turn on dVDS/dt versus temperature drawn in advance.