Differential scanning calorimetry in a piston-cylinder apparatus: Design and calibration     

Robert P. Rapp  Alexandra Navrotsky 《Pure and Applied Geophysics》1993,141(2-4):615-629

We have designed and calibrated a piston-cylinder cell assembly suitable for conductingin situ measurements of enthalpies of phase transitions at elevated pressures by heat-flux differential scanning calorimetry (DSC). The high-pressure DSC detector consists of a Pt-Pt13%Rh thermopile wrapped around a frame of fired pyrophyllite. Four thermocouple junctions, arranged radially around the sample capsule, are connected in series, with four reference thermocouple junctions located 3–4 mm above the sample and embedded in thermally inert ceramic. A W-W25%Re control thermocouple is situated directly above the top of the sample; the whole detector assembly is enclosed in a 1.5 mm thick cylindrical ceramic sleeve located at the center of a 8–10 mm long hot-zone in the tapered graphite furnace. Using this detector design and cell assembly, we have observed the thermal signal associated with the fusion of Au at 0.5 and 1.2 GPa, and have calculated a calibration factor (K) for this detector based on the gold melting curve ofMirwald andKennedy (1979). Detector sensitivity decreases by a factor of four over this pressure-temperature interval. The reproducibility of the enthalpy of fusion of gold at 0.5 GPa suggests that detector geometry is reproducible from one experiment to the next, and thus confirms the viability of this particular detector design for quantitative DSC measurements. Subsequent experiments will assess the dependence of (K) on temperature and pressure by measuring the enthalpies of fusion of additional metals (e.g., Ag, Cu, Al, Ge) and salts (e.g., NaCl, CsCl).  相似文献   

Similar reproductive cycles and life-history traits in congeneric limid bivalves with different modes of nutrition     

Johanna Järnegren  Hans T. Rapp  & Craig M. Young 《Marine Ecology》2007,28(1):183-192

We have studied two congeneric limid bivalves, Acesta species novum and Acesta excavata (Bivalvia: Limidae), that live in similar physical conditions but use different food sources. Acesta sp. nov. live on the giant siboglinid tubeworm Lamellibrachia luymesi at cold seeps and feed on their eggs, a continuous food source that ultimately is derived from chemosynthesis, whereas A. excavata relies on planktonic food of photosynthetic origin, which varies seasonally. We hypothesized that these two species might show differences in the periodicity of reproduction; specifically, we predicted that A. sp. nov. would breed continuously and that A. excavata would demonstrate an annual reproductive cycle. Our hypothesis was refuted, as both species have a semi‐continuous reproductive cycle. Food quality, quantity or seasonality had no clear effect. Reproductive adults are functionally gonochoristic. Females broadcast buoyant eggs with an average size of 179 μm in A. sp. nov. and 160 μm in A. excavata. Both the size of the larval shell and the size of the spawned eggs are suggestive of pelagic lecithotrophic development. Both species also appear to be protandric hermaphrodites, changing from male to female at approximately 77 and 90 mm shell height, respectively, although not all individuals change sex. In the material investigated in this study there was a biased sex ratio favouring males.  相似文献   

A consideration of Hayford's best fitting ellipsoid data using the differential change equations of Vening Meinesz     

Richard H. Rapp 《Pure and Applied Geophysics》1963,54(1):1-5

Summary The relations of the defining parameters of a geodetic system to the deflections of the vertical in this system given byVening Meinesz have been used in the computation of a best fitting ellipsoid. The data was that used byHayford in the computation of the resulting International Ellipsoid. Assuming the undulation (N ₀) at Meades Ranch to be zero, the results are: a=6,378,194 m and l/f=299.9. This a is much nearer to modern values than that of the Internaitonal Ellipsoid. If a flattening of 1/298.24 is fixed andN ₀=+3m,a=6,378,164 m which differs by one meter from a recent determination given byKaula.  相似文献   

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site‡     

Josh Nichols  Dylan Mikesell  Kasper Van Wijk 《Geophysical Prospecting》2010,58(6):1011-1022

Seismic interferometry is a relatively new technique to estimate the Green's function between receivers. Spurious energy, not part of the true Green's function, is produced because assumptions are commonly violated when applying seismic interferometry to field data. Instead of attempting to suppress all spurious energy, we show how spurious energy associated with refractions contains information about the subsurface in field data collected at the Boise Hydrogeophysical Research Site. By forming a virtual shot record we suppress uncorrelated noise and produce a virtual refraction that intercepts zero offset at zero time. These two features make the virtual refraction easy to pick, providing an estimate of refractor velocity. To obtain the physical parameters of the layer above the refractor we analyse the cross‐correlation of wavefields recorded at two receivers for all sources. A stationary‐phase point associated with the correlation between the reflected wave and refracted wave from the interface identifies the critical offset. By combining information from the virtual shot record, the correlation gather and the real shot record we determine the seismic velocities of the unsaturated and saturated sands, as well as the variable relative depth to the water‐table. Finally, we discuss how this method can be extended to more complex geologic models.  相似文献   

Sub-inertial characteristics of the surface flow field over the shelf of the central Mid-Atlantic Bight     

Brian Dzwonkowski  Josh T. Kohut  Xiao-Hai Yan   《Continental Shelf Research》2009,29(15):1873-1886

Observations of surface velocity data from August 2002 to February 2004 were collected by a series of four long-range high-frequency (HF) radars along the coast of New Jersey. The shelf observations of the central Mid-Atlantic Bight (MAB) were compared to historical observations of surface flow characteristics in the area. The time-averaged spatial mean velocity of 4 cm/s in the down-shelf along-shelf direction and 3 cm/s in the offshore across-shelf direction compared very well to historical surface measurements in the study region. However, as the spatial resolution of the data set revealed, this simple measure masked significant spatial variations in the overall and seasonal mean flow structures. Three regions – the south bank of the Hudson Shelf Valley, the southern New Jersey inner shelf (LEO-15) region, and the region offshore of the Delaware Bay mouth (southwest corner) – had mean flows that favor offshore transport of surface water. In terms of temporal variability, maps of the principle axes showed that the across-shelf (minor) axis contribution was not insignificant in the surface layer ranging from 0.3 to 0.9 of along-shelf (major) axis and that there were seasonal differences in orientation and ellipticity. Analysis of the spatial changes in the temporal and spatial correlation scales over the shelf showed that shelf position, in addition to site separation, contributed to the differences in these properties. Furthermore, observations over the Hudson Shelf Valley region suggested that this was a region of transition in which the orientation of along- and across-shelf components begin to change.  相似文献   

A multivariate assessment of the coral ecosystem health of two embayments on the lee of the island of Hawai'i     

Parsons ML  Walsh WJ  Settlemier CJ  White DJ  Ballauer JM  Ayotte PM  Osada KM  Carman B 《Marine pollution bulletin》2008,56(6):1138-1149

Four coral-dominated coastal sites within two embayments (Kealakekua Bay and Honokōhau Bay) on the lee of the island of Hawai'i were studied to assess evidence of anthropogenic impacts in these relatively pristine locales. Nutrient-loading parameters were analyzed in relation to benthic composition data. Statistically, there were significant positive relationships between nitrate+nitrite, silicate, and ammonium with the abundance of macroalgae, coralline algae, and dead coral, and between delta(15)N and dead coral abundance. The north outside site of Kealakekua Bay and the south outside site of Honokōhau Bay appear to be most impacted by nutrient-loading factors in each bay, respectively. Comparisons with past nutrient data indicate that nutrient inputs have increased to the two bays, and that early impacts of these increased loadings are evident. It is predicted that at current nutrient-loading rates, the north sites of Kealakekua Bay and the south sites of Honokōhau Bay will exhibit evidence of further degradation in future years.  相似文献   

A formalized approach to analysis of geoarchaeological sediment samples: The location of the early punic Harbor at Carthage,Tunisia     

V. Vitali  J. A. Gifford  F. Djindjian  G. Rapp 《Geoarchaeology》1992,7(6):545-581

This article concerns, first, the development of an approach to data analysis of sedimentological, micro- and macrofaunal, and artifactual data obtained from analysis of geoarchaeological sediment core samples and, second, an algorithmic ordering of resulting sediment groups to arrive at a definitive stratigraphic sequence. Correspondence analysis (CA) was the principal data analysis technique applied, and the algorithmic ordering is one developed for discrete sampling sequences such as core transects. From a methodological standpoint, this approach allows an assessment of the usefulness of different types of analytical information pertaining to a paleoenvironmental reconstruction of a coastal archaeological site. In terms of the geoarchaeological problem that initiated the study, the results permit a possible reconstruction of the location and nature of the first Punic port at Carthage, Tunisia.  相似文献   

Optical dating of loessic hillslope sediments constrains timing of prehistoric rockfalls,Christchurch, New Zealand          下载免费PDF全文

Reza Sohbati  Josh Borella  Andrew Murray  Mark Quigley  Jan‐Pieter Buylaert 《第四纪科学杂志》2016,31(7):678-690

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Spatial gridding of daily maximum and minimum temperatures in Europe     

S. Kr?henmann  P. Bissolli  J. Rapp  B. Ahrens 《Meteorology and Atmospheric Physics》2011,114(3-4):151-161

We developed an operationally applicable land-only daily high-resolution (5?km?×?5?km) gridding method for station observations of minimum and maximum 2?m temperature (T _min/T _max) for Europe (WMO region VI). The method involves two major steps: (1) the generation of climatological T _min/T _max maps for each month of the year using block regression kriging, which considers the spatial variation explained by applied predictors; and (2) interpolation of transformed daily anomalies using block kriging, and combination of the resulting anomaly maps with climatological maps. To account for heterogeneous climatic conditions in the estimation of the statistical parameters, these steps were applied independently in overlapping climatic subregions, followed by an additional spatial merging step. Uncertainties in the gridded maps and the derived error maps were quantified: (a) by cross-validation; and (b) comparison with the T _min/T _max maps estimated in two regions having very dense temperature observation networks. The main advantages of the method are the high quality of the daily maps of T _min/T _max, the calculation of daily error maps and computational efficiency.  相似文献   

Response of a mid‐latitude cirque glacier to climate over the last two decades: Mangaehuehu Glacier,Mt Ruapehu     

Martin S. Brook  Josh F. Dean  Harry J. R. Keys 《地球表面变化过程与地形》2011,36(14):1973-1980

The recent loss of mountain glaciers in response to climate warming has been reported across a range of latitudes globally, but the processes involved are not always straightforward. In southern Pacific mid‐latitudes, twentieth‐century glacier fluctuations are thought to reflect the strength of westerly atmospheric circulation, which brings increased precipitation, leading to mass gains. We present a study of the response of Mangaehuehu Glacier, a cirque glacier on Mt Ruapehu, to climate over the last two decades. Glacier surface area fluctuated in size over this period, corresponding closely with mean end‐of‐summer snowlines in the Southern Alps. The key control on glacier extent appears to be ablation season temperature, itself controlled by regional atmospheric circulation, including El Niño‐Southern Oscillation, Interdecadal Pacific Oscillation (IPO), and to a lesser extent, Southern Annular Mode (SAM). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献