classification of huminite iccp system 1994 abstract in the new classification iccp system 1994 the maceral group huminite has been revised from the previous classification iccp 1971 int handbook coal petr suppl to 2nd ed to accommodate the nomenclature to changes in the other maceral groups especially the changes in the vitrinite classification iccp 1998 the new vitrinite classification iccp system 1994 fuel 77 349 358 the vitrinite and huminite systems have been correlated so that down to the level of sub maceral groups the two systems can be used in parallel at the level of macerals and for finer classifications the analyst now has according to the nature of the coal and the purpose of the analysis a choice of using either of the two classification systems for huminite and vitrinite this is in accordance with the new iso coal classification that covers low rank coals as well and allows for the simultaneous use of the huminite and vitrinite nomenclature for low rank coals

the procedure used to develop a coal char classification commission iii combustion working group of the international committee for coal and organic petrology abstract this paper describes an assessment of char classification system by the combustion working group in commission iii of the international committee for coal and organic petrology iccp the work of the group culminated in the production of a char atlas after a final round robin exercise this round robin involved 21 analysts and was an electronic exercise using digitally captured images of individual char particles rather than actual char blocks a software program featuring 170 char images was specifically designed to allow operators to identify each char based on a classification system with 9 individual char types tenuisphere crassisphere tenuinetwork crassinetwork mixed porous mixed dense fusinoid solid and mineroid the program electronically recorded all decisions as well as the time taken for each decision to be made from 170 chars 128 chars were identified by a majority 70 and these chars were then compiled in a char atlas that is now available for download www nottingham ac uk eczehl charatlas as would be expected all analysts appeared to become more confident in identifying chars during the exercise taking less time per image but with no clear evidence of improvement without exception analysts took longer to make an incorrect decision

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

transporting capacity of overland flow on plane and on irregular beds in this paper the transporting capacity of thin flows in the laminar and transitional flow regime is studied experiments were carried out on irregular as well as on plane beds using two totally different set ups the results of these two types of experiment were convergent in both cases sediment concentration was clearly related to grain shear velocity and unit stream power expressed as the product of mean velocity and slope yang 1973 the data agreed with those of kramer and meyer 1969 for a sandy bed the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface for laminar and transitional flows both the unit stream power and the shear velocity are related in the same way to slope and unit discharge the unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow however before a sediment transport equation for thin flows can be developed more information is needed about the influence of the flow regime and grain size and density

small channels their experimental formation nature and significance the manner in which small channels are generated from plane beds beneath sheet flows has been experimentally elucidated on plane erodible sand beds the transition from thin supercritical sheet flows to the channelled condition was studied over ranges of discharge slope and temperature secondary flow of the second kind its action facilitated by steep vertical velocity gradients in the primary flows caused sheet flow instability along junctions between neighbouring secondary cells both either raised or lowered elements of the primary flow in the latter case fast surface water was lowered to the bed causing relatively intense local longitudinal scour dislodged grains were moved divergently to either side leaving straight central trenches development of positive feedback between cells and trenches led to rapid enlargement of the latter and concomitant growth of paired levees the resulting structures protochannels were themselves ephemeral developing two types of instability associated with secondary flow of the first kind firstly small deviations from bilateral symmetry were enhanced causing evolution into meandering channels secondly headcutting led to multiple tributary development and at resulting confluences the action of strong pairs of secondary cells led to the development of braiding channels because they are shortlived protochannels are but rarely seen in nature their seeding is markedly temperature sensitive reflecting their frictional origin the erosive power of shallow overland flow largely depends on flow energy concentration by secondary flow firstly into channels then within the channels themselves suppression of secondary flow as by intense raindrop bombardment can stabilize sheet flows in deeper water the effects of secondary flow appear relatively less dramatic however even if such motion is weak bedload divergence from attachment lines can favour entrainment locally and thus affect bed geometry analogy between our results and river behaviour appears close and on continental shelves where water must often flow as sheets structures resembling giant protochannels evidently persist

observing the yield curve of compacted pack ice 1 a method for observing the yield curve of compacted pack ice is developed based on the characteristic analysis of the stress field within the pack ice the analysis shows that the slope of the yield curve is associated with the angle between intersecting linear kinematic features thus by measuring the intersection angles we can inversely estimate the yield curve applying this method to the observed angles generates a curved diamond yield curve which possesses almost all the advantages identified by the other methods however due to the limited data available more observations are favored to refine this yield curve

empirical relations for the sediment transport capacity of interrill flow experiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters such as effective stream power and shear velocity different sediments were used in order to study the effect of grain size the proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent the proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models

continuum sea ice rheology determined from subcontinuum mechanics 1 a method is presented to calculate the continuum scale sea ice stress as an imposed continuum scale strain rate is varied the continuum scale stress is calculated as the area average of the stresses within the floes and leads in a region the continuum element the continuum scale stress depends upon the imposed strain rate the subcontinuum scale material rheology of sea ice the chosen configuration of sea ice floes and leads and a prescribed rule for determining the motion of the floes in response to the continuum scale strain rate we calculated plastic yield curves and flow rules associated with subcontinuum scale material sea ice rheologies with elliptic linear and modified coulombic elliptic plastic yield curves and with square diamond and irregular convex polygon shaped floes for the case of a tiling of square floes only for particular orientations of the leads have the principal axes of strain rate and calculated continuum scale sea ice stress aligned and these have been investigated analytically the ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain rate principal axes and an isotropic continuum scale sea ice rheology we present a lemon shaped yield curve with normal flow rule derived from ensemble averages of sea ice stress suitable for direct inclusion into the current generation of sea ice models this continuum scale sea ice rheology directly relates the size strength of the continuum scale yield curve to the material compressive strength

the architecture of an anisotropic elastic plastic sea ice mechanics constitutive law the architecture for a new large scale anisotropic constitutive law intended for use in a sea ice dynamics model is presented here this architecture accounts directly for refrozen lead systems in the pack ice strength with an anisotropic failure surface and in the ice thickness distribution with an oriented thickness distribution the lower limit 5 km of the model resolution is controlled by the fracture spacing of old thicker ice and the maximum lead width the upper limit of the model resolution 100 km is controlled by curvature in the lead directions and variations in the lead width these in turn are controlled by the variations in internal ice stress due to driving forces winds and currents which set the time resolution this architecture features abrupt changes in the failure surface and the associated flow rule that cannot be averaged over a time step in addition the principal stress normal to a new lead must be zero as it opens this model has subscale simulations that allow for the inclusion of phenomena such as ridging rafting buckling and fracture on the behavior of the ice with this new ice constitutive law it is possible to test directly the ice failure strength plastic flow rule and ice thickness distribution the data most useful for this testing come from ice stress and position buoys together with synthetic aperture radar deformation data some data comparisons have already been made

the fracture of ice on scales large and small arctic leads and wing cracks from observations and calculations of crack patterns in ice it is suggested that a similar mechanism may account for cracking over a wide range of scales

a multithickness sea ice model accounting for sliding friction a multithickness sea ice model explicitly accounting for the ridging and sliding friction contributions to sea ice stress is developed both ridging and sliding contributions depend on the deformation type through functions adopted from the ukita and moritz kinematic model of floe interaction in contrast to most previous work the ice strength of a uniform ice sheet of constant ice thickness is taken to be proportional to the ice thickness raised to the 3 2 power as is revealed in discrete element simulations by hopkins the new multithickness sea ice model for sea ice stress has been implemented into the los alamos cice sea ice model code and is shown to improve agreement between model predictions and observed spatial distribution of sea ice thickness in the arctic

grains in motion a review abstract this review paper aims to present a practical integrated procedure for the prediction of sediment transport rates in both the continental and marine environment based on the settling velocity of particles such studies have important applications in diverse fields such as civil and coastal engineering sedimentology and environmental geology where they can assist in flood control and the prevention of contaminant dispersal by wind and water as well as the siltation of dams and harbours the formation of placer deposits including gold diamonds and other heavy minerals is also controlled by sediment transport processes so that these studies can form the basis for more efficient exploration programs the first part of the paper discusses some basic principles important in sediment transport followed by an overview of published methods to determine the settling velocity of differently shaped particles including natural grains the application of settling velocity to predict the entrainment threshold of sediments on plane horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed which finally leads to the determination of sediment transport rates over plane and rippled beds the validity of this approach to natural conditions is tested against published field data where possible other widely used methods are also critically discussed pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments

impact of a new anisotropic rheology on simulations of arctic sea ice 1 a new rheology that explicitly accounts for the subcontinuum anisotropy of the sea ice cover is implemented into the los alamos sea ice model this is in contrast to all models of sea ice included in global circulation models that use an isotropic rheology the model contains one new prognostic variable the local structure tensor which quantifies the degree of anisotropy of the sea ice and two parameters that set the time scale of the evolution of this tensor the anisotropic rheology provides a subcontinuum description of the mechanical behavior of sea ice and accounts for a continuum scale stress with large shear to compression ratio and tensile stress component results over the arctic of a stand alone version of the model are presented and anisotropic model sensitivity runs are compared with a reference elasto visco plastic simulation under realistic forcing sea ice quickly becomes highly anisotropic over large length scales as is observed from satellite imagery the influence of the new rheology on the state and dynamics of the sea ice cover is discussed our reference anisotropic run reveals that the new rheology leads to a substantial change of the spatial distribution of ice thickness and ice drift relative to the reference standard visco plastic isotropic run with ice thickness regionally increased by more than 1 m and ice speed reduced by up to 50

open water production in arctic sea ice satellite measurements and model parameterizations sequential synthetic aperture radar sar images from the ers 1 spacecraft were routinely used as input to the geophysical processor system at the alaska sar facility from 1992 through 1994 to produce sea ice displacement vectors on a 5 km grid we have combined some 5000 of these products consisting of nearly 700 000 displacement vectors into a set of 914 strips or mosaics of ice motion that span mostly 3 day intervals for each strip we compute the opening and closing of leads based on the change in area of the 5 km grid cells we also compute the area averaged deformation or strain invariants of the motion the small scale several kilometer lead activity can be parameterized fairly well in terms of the large scale several hundred kilometer strain invariants sea ice models implicitly contain such a parameterization through their constitutive equations the well known model of hibler 1979 that uses a viscous plastic rheology and an elliptical yield curve is in good agreement with our data the variance in the data about this theoretical relationship is less than that suggested by a random model of sea ice motion the data also indicate that shearing deformation contributes to the opening and closing of leads models with two categories or levels of ice thickness generally do not take shearing deformation into account in the evolution of the ice concentration nor do they redistribute ice as a result of ridging we show how to add these features to two level models however we argue that three level models consisting of open water thin ice and thick ice are much better suited to the proper treatment of open water production and we present such a model

entrainment threshold of natural grains in liquids determined empirically from dimensionless settling velocities and other measures of grain size abstract grain size plays a crucial role in sediment transport but different methods of size analysis do not yield comparable results particle diameters obtained by settling tube for example cannot be employed in equations based on sieve sizes although the majority of experiments on the initiation of sediment motion has been based on sieve data settling tube analysis is probably superior as both the settling rate and the entrainment threshold of grains are determined by the same factors of size shape and density in this paper empirical equations are provided which allow the determination of a non dimensional critical shear stress directly from the equivalent sedimentation diameter the equations apply to the entrainment of well sorted grains with a high sphericity on flat sediment beds and are valid for particles and liquids of different densities

calibration of manual measurements of rills using terrestrial laser scanning abstract this article reports the results of a field investigation aimed at comparing and verifying the agreement between two methods measuring rill morphological characteristics at the masse experimental area at first the data obtained both with a manual method profilometer and with a terrestrial laser scanner tls were compared the comparison showed that the manual measurements underestimate the width at the top of the cross sections and the length of the rill segments calibration curves were derived for these characteristics and were used to correct the manual data the comparison between the corrected total length and volume and between the morphological characteristics of the measured rills at masse showed that the power relationships available in the literature are valid also for the silty clay soil in masse

initiation of motion in overland flow this article reports the results of an experimental study concerning the initial movement of sediment in overland flow experiments were carried out in a small flume using water and quartz materials of various grain sizes the comparison of our experimental results with classic criteria showed that the shields curve and the criterion of yang can also be used for turbulent overland flow generally higher shear stresses are necessary to provoke bed instability under laminar flow conditions especially at higher shear velocity particle reynolds numbers a relative roughness effect also exists in laminar flow contrary to the observations by savat on fixed beds laminar flow does not show an uncommon selectivity when loose homogeneous beds are considered

petrographic characteristics of lignite gasification chars abstract the article presents the petrographic characteristics of lignite subjected to fluidized bed gasification and the residues after the process the gasifying agents were air oxygen and carbon dioxide the petrographic composition of the lignite is dominated by huminite group with 81 7 vol share the inertinite group is 3 6 vol while the liptinite group amounts to 7 0 vol the mineral matter in the tested samples is 7 7 vol the gasification temperature was in the range of 850 950 c therefore the study focused mainly on the pyrolysis of coal the dominant particles in the residues after the gasification process include inertoid 35 5 vol and crassinetwork 31 6 vol the total amount of char with different kinds of pores arising as a result of degassing tenuisphere crassisphere tenuinetwork crassinetwork and mixed porous is 52 3 vol of all components the macerals from inertinite group do not change form during the gasification process the particles with thicker walls crassinetwork and intertoids represent approximately 70 vol are dominant such char composition is related to the chemical structure of coal during gasification process the macerals from liptinite group such as resinite release carboxyl groups increased porosity and swelling a similar phenomenon is observed in the case of textinite macerals of low porosity mainly ulminite do not substantially increase their porosity and take the inertoid form mineroids represent about 8 vol of char but the mineral matter is also associated with coal particles taking into account the efficiency of gasification process it should be noted that only a small percentage

critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires received 26 february 2004 revised 15 september 2004 accepted 5 november 2004 published 22 january 2005 1 increased erosion is a well known response after wildfire to predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles as this soil property is temperature dependent a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required in this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures 40 550 c for 1 hour results were obtained for four replicates of soils derived from three different types of parent material granitic bedrock sandstone and volcanic tuffs in general the relation between critical shear stress and temperature can be separated into three different temperature ranges 275 c which are similar to those for water repellency and temperature the critical shear stress was most variable 1 0 2 0 n m 2 for temperatures 2 0 n m 2 between 175 and 275 c and was essentially constant 0 5 0 8 n m 2 f or temperatures 275 c the changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire

a simulation model for unified interrill erosion and rill erosion on hillslopes a mathematical model was developed for simulating runoff generation and soil erosion on hillslopes the model is comprised of three modules one for overland flow one for soil infiltration and one for soil erosion including rill erosion and interrill erosion rainfall and slope characteristics affecting soil erosion on hillslopes were analysed the model results show that the slope length and gradient time distribution rainfall and distribution of rills have varying influence on soil erosion erosion rate increases nonlinearly with increase in the slope length a long slope length leads to more serious erosion the effect of the slope gradient on soil erosion can be both positive and negative thus there exists a critical slope gradient for soil erosion which is about 45 for the rate of erosion at the end of the slope and about 25 for the accumulated erosion copyright 2005 john wiley sons ltd

wave friction factor as related to the shields parameter for steady currents abstract the wave friction factor fw is an important dimensionless parameter used to estimate wave induced bed shear stress which together with current induced bed shear stress controls sediment transport in the marine and lacustrine environment however fw is either overestimated or underestimated by existing equations the matter is complicated by the fact that different equations must be used for hydrodynamically smooth or rough flows but the limit between these two boundary conditions is still poorly defined some equations also require estimated values for the nikuradse roughness length and the wave boundary layer thickness neither of which can be derived accurately it is therefore not surprising that fw values as calculated by existing equations differ by as much as a factor of 3 in the present paper fw is related to the shields parameter for unidirectional currents which not only facilitates the direct comparison and summation of bed shear stresses but also yields a more accurate equation valid for grains of different density in any fluid irrespective of the boundary condition

sorption of methane on lignite from polish deposits abstract coal samples from miocene lignite deposits ortholignite ece un 2002 in belchatow adamow konin and turow poland were analyzed to determine the relationships between coal properties and gas capacity investigations presented here addressed the occurrence of methane sorbet in lignite deposits within poland s largest penetrated lignite deposits e g belchatow adamow turow and konin lignite samples collected from surface mines were detritic coal with variable contents of xylites the highest level of xylites up to 25 vol was found in carbon samples taken from the belchatow deposit samples from other mines contained no more than 10 vol xylites petrographic compositions were dominated by huminite group macerals 73 88 vol with atrinite densinite and texto ulminite a porous form of ulminite inertinite groups were less important components 4 8 vol isotherms were determined for methane sorption at 298 k with test pressure ranges below 1 2 mpa at a pressure of 1 0 mpa the largest gas capacity of approximately 1 7 dm3 stp kg was found in the sample from belchatow this result may have been attributable to differences in the porosity of the samples the porosity of the sample from belchatow was twice as high as the porosities of the other coal samples this variation in porosity resulted from the lithologic and maceral composition of the coal sample that contained substantial quantities of porous textinite and texto ulminite the thermal sorption equation was used to determine the limiting values of isosteric enthalpy of sorption which suggested weak interactions between methane and the lignite matrix the residual gas capacity of the tested samples was also determined all samples exhibited a high residual methane bearing capacity which may not only cause methane to be released from coal at a pressure of 1 bar but also may pose a gas risk during mining operations

sea ice displacement from seasat synthetic aperture radar images obtained by a synthetic aperture radar on seasat have been used to measure sea ice displacements over a three day interval in october 1978 the position of a natural ice feature was measured on 5 october and again on october 8 the difference in these two positions is a displacement the displacement of many features was measured the tracked features lie roughly along a line and are quite dense about 2 km apart over a distance of 865 km the displacements are about 20 km displacement errors grow with distance from shore becoming as large as 3 km the graph of displacement versus distance has occasional discontinuities of several kilometers displacement discontinuities are accurate to 0 07 km along track and 3 of their magnitude across track

a sediment transport equation for interrill overland flow on rough surfaces a model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3 4 to 43 4 mm flow velocities from 0 09 to 0 65 m s 1 reynolds numbers from 5000 to 26 949 froude numbers from 0 23 to 2 93 bed slopes from 2 7 to 10 sediment diameters from 0 098 to 1 16 mm volumetric sediment concentrations from 0 002 to 0 304 roughness concentrations from 0 to 0 57 roughness diameters from 1 0 to 91 3 mm rainfall intensities from 0 to 159 mm h 1 flow densities from 1002 to 1501 kg m 3 and flow kinematic viscosities from 0 913 to 2 556 10 6 m2 s 1 stones cylinders and miniature ornamental trees are used as roughness elements given the diverse shapes sizes and concentrations of these elements the transport model is likely to apply to a wide range of ground surface morphologies using dimensional analysis a total load transport equation is developed for open channel flows and this equation is shown to apply to interrill flows both with and without rainfall the equation indicates that the dimensionless sediment transport rate is a function of and therefore can be predicted by the dimensionless shear stress its critical value c the resistance coefficient u u the inertial settling velocity of the sediment wi the roughness concentration cr and the roughness diameter dr the model has the form 1 where and testing reveals that the model gives good unbiased predictions of in flows with sediment concentrations less than 0 20 flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model copyright 2001 john wiley sons ltd

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

petrographic composition of polish lignite and its possible use in a fluidized bed gasification process abstract the main objectives of the study include the estimation of the proportion of lithotypes and macerals in lignite deposits and the determination of petrographic criteria for the assessment of quality and possible use of lignite in fluidized bed gasification process measures taken to meet the objectives included field research and laboratory studies the study included results from 293 samples of low rank coal from polish deposits the data used in the study included currently exploited abandoned and prospective lignite deposits lignite deposits were divided into seven regions a western b legnica c wielkopolska d konin e od belchatow f north and g radom polish lignite deposits include mainly humic coal with four basic lithotypes identified xylitic coal xylo detritic coal detro xylitic coal and detritic coal dominating lithotypes include detritic coal and xylo detritic coal fibrous xylites present only in minor amounts in polish lignite have a negative influence on coal gasification process grinding the highest content of fibrous xylites is observed in the konin region petrographic composition of coal was determined on the basis of maceral group and the sum of gelified macerals it has been found that the influence of macerals from the huminite group on fluidized bed gasification is significant the average content of this component in tested coal is 89 meanwhile average content of macerals from the liptinite group in polish coal is 8 while for macerals from the inertinite group it is 3 the content of mineral matter in lignite deposits is a highly variable parameter according to the proposed scheme in order to be suitable for fluidized bed gasification the maceral composition of the coal should contain at least 80 huminite while the sum of the macerals from the inertinite group and mineral matter should be less than 20 taking into account the whole region it should be noted that petrographic composition of lignite in almost all of the deposits allows its use in the process of fluidized bed gasification however limited usefulness in this process can be observed in some of the deposits containing bituminiferous lignite

two dimensional deformation patterns in sea ice the mechanical behaviour for the geome trical properties of two dimensional def ormation has been investi gated the mohr formulation of failure which is based on the concept of slip at the plane of weakness is used in this study it is shown that alteration of the shear stress t n at the plane of weakn ess requires self similarity of features in deformation patt erns a general relationship between the angle of internal friction and the breaking angle of deformation patterns is derived using imagery data this relat ionship is used to find the angle of internal friction from selected sea ice deforma tion patterns the value obtained for this angle is is 0 20 for deform ation on a scale from 100 m to 100 km

dependence of sea ice yield curve shape on ice thickness in this note the authors discuss the contribution that frictional sliding of ice floes or floe aggregates past each other and pressure ridging make to the plastic yield curve of sea ice using results from a previous study that explicitly modeled the amount of sliding and ridging that occurs for a given global strain rate it is noted that the relative contribution of sliding and ridging to ice stress depends upon ice thickness the implication is that the shape and size of the plastic yield curve is dependent upon ice thickness the yield curve shape dependence is in addition to plastic hardening weakening that relates the size of the yield curve to ice thickness in most sea ice dynamics models the yield curve shape is taken to be independent of ice thickness the authors show that the change of the yield curve due to a change in the ice thickness can be taken into account by a weighted sum of two thickness independent rheologies describing ridging and sliding effects separately it would be straightforward to implement the thickness dependent yield curve shape described here into sea ice models used for global or regional ice prediction

the effect of spatial variability in overland flow on the downslope pattern of soil loss on a semiarid hillslope southern arizona summary in this study we investigate the relation between soil loss and slope length in an interrill portion of a gentle plan planar semiarid hillslope in southern arizona simulated rainfall experiments were conducted on an 18 m wide by 35 m long runoff plot the upper end of which coincided with the hillslope divide sediment loads were measured at two cross sections s1 and s2 located 12 5 and 21 m respectively downslope from the divide from these data section soil losses under equilibrium runoff conditions were computed average section soil loss was found to increase from the divide to s1 and to decrease from s1 to s2 to explain this downslope pattern of soil loss a simulation model was developed for soil detachment by raindrop impact and sediment removal by overland flow at a cross section input data for the model consist of overland flow depths and velocities measured at closely spaced points along a cross section the model was applied to three cross sections located at 3 3 12 5 and 21 m downslope from the divide and predicted a downslope pattern of soil loss similar to that observed the success of the model suggests that in the interrill portions of a wide range of gentle arid and semiarid hillslopes downslope patterns of soil loss are controlled in large part by downslope changes in across slope distributions of overland flow depth and velocity

chemical evolution of miocene wood example from the belchatow brown coal deposit central poland abstract miocene conifer wood samples from the belchatow brown coal deposit in poland were studied in order to discuss a range of chemical variations that occur as a result of biochemical coalification petrographic analysis ultimate analysis electron microprobe technique and ftir spectroscopy were used in this study our data show several progressive trends in functional groups distribution that take place during the wood transformation from group 1 to group 4 such as an overall increase in aromaticity an increase in lignin cellulose ratio and an increase in oxygen functionalities other observations include an increase in aliphatic stretching and bending functionalities from groups 1 to 3 followed by a decrease in the wood of group 4 appearance of aliphatic out of plane bands in group 3 and increase in group 4 an increase in ch2 ch3 in group 4 compared to the other groups and decrease in o h groups in group 4 compared to other groups these observations together with other chemical and petrological observations indicate that the progressive elimination of cellulose and modification of lignin are dominant processes of the wood transformation