Floor Depth Research Articles

Response of ground beetle (Carabidae) assemblages to logging history in northern hardwood–hemlock forests

We quantified differences in ground beetle (Coleoptera: Carabidae) communities in relation to forest management practices and historic forest cover changes in hardwood–hemlock forests of the north central United States. Beetles were sampled with pitfall traps in 1996 and 1997 and compared among three forest types: old-growth, and post-logging uneven- and even-aged forests. Non-metric multidimensional scaling ordination was used to assess compositional differences among forest types for 39 carabid species (43,483 individuals), which revealed distinct differences in beetle assemblages among forest types. Coarse woody debris, snag volume, gap area, understory vegetation and forest floor depth were significantly correlated with ordination axes suggesting that these variables are critical in structuring the beetle communities. Several of the species significantly associated with old-growth forests, like Carabus sylvosus, are known to favor forest habitats, whereas species commonly found in open habitats, such as Carabus nemoralis, had stronger affiliations with managed forests. Comparisons of northern hardwood–hemlock forest distribution from pre-Euroamerican settlement with current distributions reconstructed using the Forest Inventory and Analysis database indicate that old-growth habitat has declined to <1% of its original extent in this region. At the landscape level, these data suggest that the abundance of carabid species that prefer old-growth forest conditions has undergone broad-scale decline.

Spatial Distribution of Ammonium and Calcium in Optimally Fertilized Pine Plantation Soils

Commercial timber production is increasingly reliant on long‐term fertilization to maximize stand productivity, yet we do not understand the extent to which this practice homogenizes soil properties. The effects of 16 yr of optimal fertilization and optimal fertilization with irrigation (fertigation) on forest floor depth, pH, total organic carbon (TOC) and total nitrogen (TN) content, and concentrations of potentially plant available NH4+, Ca2+, Mg2+, and Al3+ in the fine root zone of monoculture loblolly pine (Pinus taeda L.) stands in North Carolina were examined. Generally, optimal fertilization significantly increased forest floor depth and the concentrations of potentially plant available NH4+, Ca2+, and Mg2+ No significant effects on TOC or TN were observed. However, differences were observed between optimally fertilized and fertigated treatments. Specifically, fertilization alone tended to retain more Ca2+ and Mg2+ in the root zone and to increase pH more than fertigation. Semivariogram analysis indicated optimal fertilization generally lead to a significant increase in the effective spatial autocorrelation ranges of NH4+ and Ca2+ at the end of the growing season, from approximately 25 m in controls to more than 100 m. However, optimally fertilized and fertigated plots differed in terms of their NH4+ and Ca2+ spatial autocorrelation ranges, with the ranges in fertigated plots being 1.5‐ to 2‐fold greater. A comparison of kriged maps of NH4+ and Ca2+ availability in fall 2000 and spring 2001 suggested that the spatial distribution of Ca2+, which has not been added to these soils for 6 yr, was stable, whereas the heterogeneity of NH4+ distribution increased post fertilization.

Effects of prescribed fires on first-year establishment of white oak ( Quercus alba L.) seedlings in the Upper Piedmont of South Carolina, USA

Effects of prescribed fires on the 1-year establishment of white oak seedlings were investigated on the Clemson Experimental Forest, South Carolina, USA. Three stands, each consisting of a burn and a control treatment of about 1 ha in size, were examined in the study. On each burn and control treatment, six to eight dominant white oak trees were randomly selected along the slope and four 2-m radius quadrats were set up around each selected tree. Prescribed fire increased seedling biomass but it did not affect seedling mortality and root to shoot ratio. Effects of prescribed fire on seedling density, forest floor depth, and understory light intensity depended on stands, where burning increased seedling density in stands 1 and 3 but not in stand 2. Burning also reduced forest floor depth and increased understory light intensity in stands 1 and 3 but not in stand 2. Regression analyses indicated that forest floor depth and understory light intensity were significantly related to seedling density and biomass, with thinner forest floor and higher light intensity favoring the establishment of new oak seedlings. We conclude that burning can benefit the establishment of new white oak seedlings as long as it significantly reduces forest floor depth and increases understory light intensity.

Effect of augmented visual feedback from a virtual reality simulation system on manual dexterity training

Little research has been published about the impact of simulation technology on the learning process of novel motor skills. Especially the role of augmented feedback (FB) on the quality of performance and the transfer of the acquired behaviour to a no-augmented FB condition require further investigation. Therefore, novice dental students were randomly assigned to one of three groups and given the task of drilling a geometrical class 1 cavity. The FB group trained under augmented visual FB conditions, provided by the virtual reality (VR) system (DentSim). The no-FB group practised under normal vision conditions, in the absence of augmented FB. A control group performed the test sessions without participating in any training programme. All preparations were evaluated by the VR grading system according to four traditional (outline shape, floor depth, floor smoothness and wall inclination), and two critical, criteria (pulp exposure and damage to adjacent teeth). Performance analyses revealed an overall trend towards significant improvement with training for the experimental groups. The FB group obtained the highest scores. It scored better for floor depth (P < 0.001), whilst the no-FB group was best for floor smoothness (P < 0.005). However, at the retention tests, the FB group demonstrated inferior performance in comparison with the no-FB group. The transfer test on a traditional unit revealed no significant differences between the training groups. Consequently, drilling experience on a VR system under the condition of frequently provided FB and lack of any tutorial input was considered to be not beneficial to learning. The present data are discussed in view of the guidance hypothesis of FB, which refers to the apprentice's dependence on FB.

Landscape influences on aluminium and dissolved organic carbon in streams draining the Hubbard Brook valley, New Hampshire, USA

Concentrations of both aluminium (Al) and dissolved organic carbon (DOC) in stream waters are likely to be regulated by factors that influence water flowpaths and residence times, and by the nature of the soil horizons through which waters flow. In order to investigate landscape-scale spatial patterns in streamwater Al and DOC, we sampled seven streams draining the Hubbard Brook valley in central New Hampshire. We observed considerable variation in stream chemistry both within and between headwater watersheds. Across the valley, concentrations of total monomeric aluminium (Alm) ranged from below detection limits (<0·7 µmol l−1) to 22·3 µmol l−1. In general, concentrations of Alm decreased as pH increased downslope. There was a strong relationship between organic monomeric aluminium (Alo) and DOC concentrations (R2 = 0·92). We observed the highest Alm concentrations in: (i) a watershed characterized by a steep narrow drainage basin and shallow soils and (ii) a watershed characterized by exceptionally deep forest floor soils and high concentrations of DOC. Forest floor depth and drainage area together explained much of the variation in ln Alm (R2 = 0·79; N = 45) and ln DOC (R2 = 0·87; N = 45). Linear regression models were moderately successful in predicting ln Alm and ln DOC in streams that were not included in model building. However, when back-transformed, predicted DOC concentrations were as much as 72% adrift from observed DOC concentrations and Alm concentrations were up to 51% off. This geographic approach to modelling Al and DOC is useful for general prediction, but for more detailed predictions, process-level biogeochemical models are required. Copyright © 2005 John Wiley & Sons, Ltd.

Diversity of filamentous fungi in organic layers of two forests in Zijin Mountain

A study was conducted to evaluate the cultivable filamentous fungal diversity in organic layers (L, F, and H layers) and A1 layer of two main forest types,Pinus massoniana andLiguidambar formasana mixed forest andQuercus variabilis forest, in Zijin Mountain(32°5′ N, 118°48′ E), Nanjing, China. A total of 67 taxa comprising 56 Deuteromycetes, 3 Zygomycetes, 5 Ascomycetes and 3 unidentified fungi were recognized from samples from the forest floor of the two forest types. The most abundant group was Deuteromycetes. The dominant genera in both forests wereAlternaria sp.,Aspergillus sp.,Cladosporium sp.,Mucor sp.,Penicillium sp.,Rhizopus sp.,Gliocladium sp. andTrichoderma spp. The fungal diversity was higher in the mixed forest than that inQ. variabilis forest. For both forest types, the maximum fungal diversity was found in layer F and there existed significantly different in fungal diversity between layer F and layer L. In the mixed forest, richness of fungi isolated from needle litter (P. massoniana) was lower than that from leaf litter (L. formasana). The richness of fungi from needle litter increased with the increase of forest floor depth, but for leaf litter, the fungal diversity decreased with the depth of forest floor. The co-species of fungi from the two forest types, as well as from two kinds of litters in mixed forest, increased with the depth of the forest floor. The succession of fungi along with the process of decomposition was discussed here. The results also showed that litter quality was a critical factor affecting fungal diversity.

Toward reference conditions: wildfire effects on flora in an old-growth ponderosa pine forest

Remote ponderosa pine ( Pinus ponderosa) forests on the North Rim of Grand Canyon National Park, Arizona, USA provide valuable examples of reference conditions due to their relatively uninterrupted fire regimes, limited grazing history, and protection from logging. Wildfire is an important disturbance agent in upland forests of the Interior West, yet repeated measurements taken before and after lightning-ignited fires are rare. In 1999, a low-severity Wildland Fire Use fire burned 156 ha on Fire Point, a peninsula dominated by old-growth ponderosa pines, which had not burned for at least 76 years. We measured understory plant community and forest floor characteristics in 1998 (1 year before the fire) and 2001 (2 years after the fire) at this site and at nearby reference sites that did not burn in 1999 but have had continuing fire regimes throughout the past century. After the wildfire, the plant community at Fire Point shifted toward higher compositional similarity with the reference sites. Analysis of functional group composition indicated that this change was due primarily to an increase in annual and biennial forbs. Gayophytum diffusum, Polygonum douglasii, Chenopodium spp., Solidago spp., Elymus elymoides, Calochortus nuttallii, Hesperostipa comata, and Lotus spp. were indicative of forests influenced by recent fires. Species richness, plant cover, plant layer density and plant diversity were significantly lower at Fire Point than at the reference sites, possibly due to long-term fire exclusion, but the fire did not increase the rate of change in these variables after 2 years. Few exotic species were present at any site. Forest floor depths at Fire Point were reduced to depths similar to the reference sites, primarily due to consumption of the duff layer. There was a significant inverse relationship between the ratio of duff:litter and species richness. Compared to fire-excluded forests, old-growth ponderosa pine forests influenced by low-intensity surface fires generally have greater plant species richness (especially annual forbs) and lighter fuel loads. This study supports the continued application of the Wildland Fire Use strategy in old-growth montane forests to maintain and improve forest health by altering understory species composition and reducing fuel loads.

Environmental factors influencing skeletal grain sediment associations: a critical review of Miocene examples from the western Mediterranean

AbstractThe presence of foramol, rhodalgal and bryomol skeletal grain associations in ancient shallow‐marine limestones is commonly interpreted as evidence for non‐tropical palaeoclimate, despite temperature being only one of several factors influencing skeletal grain associations. Such interpretations neglect the multitude of factors other than temperature that influence carbonate‐producing biota. These include nutrients, water energy, water transparency, depth of the sea floor, salinity, oxygen, Ca2+ and CO2 concentrations, Mg/Ca ratio, alkalinity, substrate requirements, competitive displacement as well as biological and evolutionary trends. This uniformitarian approach also disregards the probability that conditions of present‐day biological systems may not be representative of past conditions of analogous systems. Here, the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western Mediterranean. These platforms are dominated by foramol, rhodalgal and bryomol associations of Miocene age in spite of having formed in tropical conditions. The platforms discussed are: (1) the Lower Tortonian ramp on Menorca, Balearic Islands; and (2) the Lower–Middle Miocene ramps of the central Apennines, Italy. Evidence for tropical conditions in the Mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera, by data from coeval continental basins and by global oxygen isotope data.

Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere II

We have extended our previous analysis of the effects of constant vs. variable, i.e., pressure and temperature dependent thermal conductivity (k) and constant thermal expansivity (α) on the thermal structure of the oceanic lithosphere. We apply our analysis to the actual data set including information on the geoid slope. The heat flow and ocean floor depth data constrain the thermal expansivity (α ≈ 3 × 10−5 1/°C). Including geoid slope data may loosely constrain both the thermal expansivity and the thermal conductivity. The probable value of thermal conductivity is ≈3 W/m/°C for the constant k case and ≈4 W/m/°C (at ambient conditions) for the variable k case. These a and k are generally consistent with laboratory data of appropriate lithospheric materials. Our analysis supports the plate model with thin lithosphere and high bottom temperature, such as GDH1 (95 km; 1450°C). Variable k case requires slightly thinner and higher temperature lithosphere (≈85 km and ≈1500°C) and gives a slightly better fit to the geoid slope data.

Controls on the release of dissolved organic carbon and nitrogen from a deciduous forest floor investigated by manipulations of aboveground litter inputs and water flux

Although dissolved organic matter (DOM) released from the forest floor plays a crucial role in transporting carbon and major nutrients through the soil profile, its formation and responses to changing litter inputs are only partially understood. To gain insights into the controlling mechanisms of DOM release from the forest floor, we investigated responses of the concentrations and fluxes of dissolved organic carbon (DOC) and nitrogen (DON) in forest floor leachates to manipulations of throughfall (TF) flow and aboveground litter inputs (litter removal, litter addition, and glucose addition) at a hardwood stand in Bavaria, Germany. Over the two-year study period, litter manipulations resulted in significant changes in C and N stocks of the uppermost organic horizon (Oi). DOC and DON losses via forest floor leaching represented 8 and 11% of annual litterfall C and N inputs at the control, respectively. The exclusion of aboveground litter inputs caused a slight decrease in DOC release from the Oi horizon but no change in the overall leaching losses of DOC and DON in forest floor leachates. In contrast, the addition of litter or glucose increased the release of DOC and DON either from the Oi or from the lower horizons (Oe + Oa). Net releases of DOC from the Oe + Oa horizons over the entire manipulation period were not related to changes in microbial activity (measured as rates of basal and substrate-induced respiration) but to the original forest floor depths prior to manipulation, pointing to the flux control by the size of source pools rather than a straightforward relationship between microbial activity and DOM production. In response to doubled TF fluxes, net increases in DOM fluxes occurred in the lower forest floor, indicating the presence of substantial pools of potentially soluble organic matter in the Oe + Oa horizons. In contrast to the general assumption of DOM as a leaching product from recent litter, our results suggest that DOM in forest floor leachates is derived from both newly added litter and older organic horizons through complex interactions between microbial production and consumption and hydrologic transport.

A Forest Nutrient Cycling and Biomass Model (ForNBM) based on year-round, monthly weather conditions: Part II: Calibration, verification, and application

The ForNBM was applied to the Nashwaak Experimental Watershed Project in central New Brunswick, Canada. The data represented a mixed hardwood site and included information about nutrient leaching, foliage and wood biomass, leaf fall, and ancillary information required for model initialization. Ancillary information included forest cover type, stand density, forest floor depth, soil rooting depth, soil texture, soil substrate type, initial amounts of biomass and N, S, Ca, Mg, and K content in foliage, wood, and roots, and mineral soil nutrient contents in soil solution, on ion-exchange sites, and in the soil. The authors were able to calibrate the model with existing data. The model simulated observed monthly leaching reasonably well. The r 2-values of model simulations compared with field observations of monthly leaching of NO 3 −_N, NH 4 +_N, Ca, Mg, and K were 0.78, 0.7, 0.78, 0.84, and 0.75, respectively. Modeled multi-year cumulative leaching of NO 3 −_N, NH 4 +_N, Ca, Mg, and K compared with actual values gave r 2-values close to one for all cases considered. The results also showed that soil nutrient leaching had increased approximately five-fold for NO 3 −_N, 80% for NH 4 +_N, 71% for K, 20% for Ca, and 14% for Mg during the 3 years following a stem-only harvest operation applied watershed-wide. However, the model simulation showed that increased nutrient leaching during the 11 years following the stem-only harvest was small compared with the amounts removed in the biomass during the harvest. Increased nutrient leaching following harvesting did not appear to impact site productivity over the long term.

03/01825 Low-enthalpy geothermal energy resources from groundwater in fluvioglacial gravels of buried valleys: Allen, A. and Milenic, D. Applied Energy, 2003, 74, (1–2), 9–19

Impact craters on the surface of Mars are degraded by erosion and infilling due to combinations of geological processes. These result in modifications of relative crater dimensions, including diameter increase and reduction of rim–floor depths. In principle, the longer a crater is exposed to geological processes, the more pronounced the modifications. Visualization and analysis of these effects are achieved by plotting the measured depths (M) of impact craters vs the corresponding theoretical depths (predicted: P) calculated from the crater diameters using depth/Diameter power laws. This type of diagram is referred to as MPD (measured depth vs predicted depth diagram). The advantage of using the MPD representation consists in the fact that the data plot along linear regressions, more easily interpreted than standard depth vs diameter diagrams.As an example of application of the method, the MPD was used to discriminate different generations of impact craters in Terra Sabaea into four groups: T0 (fresh craters), T1, T2 and T3 (from younger to older), all located on the most ancient geological unit in the area (Npld). Other units in the area are Hpl3 and Hr, impacted only by craters belonging to group T0, suggesting that these units are stratigraphically correlated. The data of 5 craters in superposition relationships with the eastern reaches of Evros Vallis, one of the major valley networks in the area, were plotted in the diagram and assigned each to a regression depending on the location of their data points in relation to the prediction bands of the regressions. The craters superposed to the valley all belonged to T0, indicating that Evros Vallis has the same relative age of units Hpl3 and Hr.A conceptual discussion of the results demonstrates that MPD statistics (a) are unaffected by the procedures used to acquire depths and diameters of impact craters and by the power laws used, and (b) can be interpreted irrespective of the sequence or combination of processes leading to modification of the crater morphometric data. These properties make the diagram a powerful statistical tool.

Distribution of moments in reinforced concrete slabs with continuous drop panels

Slabs with continuous drop panels between column lines facilitate formwork, make long spans possible in addition to increase punching shear resistance around supports and provide unobstructed spans with minimum structural floor depth resulting in lower floor-to-floor heights. The moment distribution in such slabs is different from that in conventional flat plates or slabs with drop panels systems. Dimensioning according to the current provisions in CSA A23.3-94 is problematic because the continuous drop panels are subject to moments exceeding the minimum values allowed by the Code for conventional slab systems. This analytical study presents the moment distribution in slabs with continuous drop panels in an attempt to provide more realistic transverse moment distribution factors.Key words: reinforced concrete, slab systems, slab design, drop panel, moment distribution.

Development of a protocol for monitoring status and trends in forest soil carbon at a national level

The national Forest Health Monitoring (FHM) program requires protocols for monitoring soil carbon contents. In a pilot study, 30 FHM plots loblolly/shortleaf ( Pinus taeda L./ Pinus echinata Mill.) pine forests across Georgia were sampled by horizon and by depth increments. For total soil carbon, approximately 40% of the variance was between plots, 40% between subplots and 20% within subplots. Results by depth differed from those obtained by horizon primarily due to the rapid changes in carbon content from the top to the bottom of the A horizon. Published soil survey information overestimated bulk densities for these forest sites. The measurement of forest floor depths as a substitute to sampling did not provide reliable estimates of forest floor carbon. Precision of replicate samples was approximately 10–30% for field duplicates and 5–10% for laboratory duplicates. Based on national indicator evaluation criteria, sampling by depth using bulk density core samplers has been recommended for national implementation. Additional procedures are needed when sampling organic soils or soils with a high percentage of large rock fragments.

Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere

The sensitivity of pressure‐ and temperature‐dependent thermal conductivity (k: W/m/K) and the thermal expansivity (α:1/K) on the thermal structure of the oceanic plate is investigated parametrically by comparing the ocean floor depth and heat flux calculated by one‐dimensional conduction model with those of GDH1, a theoretical thermal model of the oceanic lithosphere. We find that an optimum fit is obtained, when the value of thermal expansivity is ∼ 3 × 10−5, while those associated with the thermal conductivity have many possibilities. The estimates, which give an equally good fit to the GDH1 model, of the plate thickness D (km) and the temperature at the base of the plate Tm (°C) may be given by Tm ∼ 1450‐(k0−4.5) × 100‐(α−3.0 × 10−5) × 105×100, D ∼ 90 + (k0−4.5) × 20 ‐ (α−3.0 × 10−5) × 105 × 20 where k0 (W/m/K) is the lattice thermal conductivity at the ocean floor. A similar relation is obtained for constant thermal conductivity.

Post-Clearcutting Chronosequence in the B.C. Coastal Western Hemlock Zone

The depth, mass, and N-capital of the forest floor were measured in three plots in a 400-year-old forest of Pacific silver fir (Abies amabilis [Dougl.] Forbes), western hemlock (Tsuga heterophyl-la [Raf.] Sarg.) and western red cedar (Thuja plicata Donn) on Southern Vancouver Island, as well as in three plots in each of four neighboring unslashburned clearcuts ranging in ages from 3 to 26 years old. Forest floor depth, mass and N content did not differ significantly during the first three years following clearcutting but had dropped by 35% to 40% of pre-clearcut values by the sixth post-clearcutting year. Although values of these ecosystem characteristics gradually increased thereafter, they were still about 20% below pre-clearcut values by year 26. Re-measurements of the 3-year-old, 6-year-old and 10-year-old sites after two years, as well as of 6 independent neighboring sites, confirmed that each of the five intensively studied sites were representative members of the same chronosequence. Average mass loss of cellulose disks placed in the three younger clearcuts was two-to-four times greater than mass loss in the 26-year-old clearcut and 400-year-old forest sites, suggesting that the decrease in forest floor mass was not only attributable to lower rates of litter input but also to changes in litter decomposition rates. The average seasonal moisture content was higher in the 4-year-old clearcut than in the other sites, and the average daily air and soil temperatures were higher in the 10-year-old clearcut than in the old forest stand. The change in micro-climate was believed to be responsible for increasing decomposition rates in the younger three clearcuts. We conclude that forest floor N is quite dynamic during stand establishment.

Predicting Bathymetry from the Earth's Gravity Gradient Anomalies

Historically, prediction of ocean floor depth, or bathymetry, has been based on the isostatic modeling and linearized relationships between gravity anomalies and bathymetry. The need for isostatic modeling limits the application of the resulting bathymetry predictions as constraints in geophysical models. An alternative technique making use of the Earth's vertical gravity gradient for predicting bathymetry is explored in this paper. This technique is based on the fact that the observed gravity gradient anomalies result primarily from local mass concentrations on the ocean floor, and that mass compensation by the oceanic crust has an insignificant effect on the gravity gradients, and can be neglected. The resulting bathymetry prediction therefore is independent of isostatic modeling assumptions, allowing it to be used as a constraint on models of lithospheric compensation and for other geodetic and geophysical applications.

Soil quality standards and guidelines for forest sustainability in northwestern North America

Soil quality standards and guidelines of the USDA Forest Service were some of the first in the world to be developed to evaluate changes in forest soil productivity and sustainability after harvesting and site preparation. International and national development of criteria and indicators for maintenance of soil productivity make it imperative to have adequate threshold variables within the USDA Forest Service. In the Pacific Northwest, soils range from fine-textured Andisols to coarse-textured skeletal Inceptisols. Forest types encompass the highly productive coastal rain forest to marginally productive, dry, cold sites in the interior mountains. Constant values to detect detrimental disturbances within the soil quality guidelines are routinely applied across diverse soils and timber types and include diagnostic criteria for evaluating management-caused changes to soil productivity. Research information from short- or long-term research studies supporting the applicability of disturbance criteria is often lacking, or is available from a limited number of sites which have relatively narrow climatic and soil ranges. In this paper we calculated changes in soil carbon, nitrogen, erosion, and cation exchange capacity using threshold variables from the Regional USDA Forest Service Soil Guidelines to assess their applicability across diverse landscapes. Soils were selected from a climatic and elevational gradient in the Pacific Northwest. Application of selected USDA Forest Service standards indicate that blanket threshold variables applied over disparate soils do not adequately account for nutrient distribution within the profile or forest floor depth. These types of guidelines should be continually refined to reflect pre-disturbance conditions and site-specific information.

Fracture resistance of class II approximal slot restorations

Statement of Problem. Determination of the fracture resistance of various restorative materials in Class II approximal slot restorations has not been studied. Purpose. This study evaluated the effects of retention grooves and different restorative materials in Class II approximal slot restorations. To explore the possibilities for further research, the probable effects of preparation size and loading angle were investigated in a limited manner. Material and Methods. Ninety sound, caries-free human maxillary premolars were divided into 9 groups. The cavities were prepared either by hand or in a computer-controlled CNC machine with or without retention grooves. Four were restored with adhesive amalgam, another 4 with composite, and a single group with Compomer resin. The gingival floor depth was 1.5 mm. The specimens were loaded at an angle of 13.5 degrees to their longitudinal axes by using a computer-controlled material testing machine until failure occurred. For one specific preparation of adhesive amalgam, loading was applied at 0 and 30 degrees to determine the probable effects of the loading angle. For a specific composite, resin application, the effects of the change in gingival floor depth were analyzed by assigning the depth to 2.0 mm. Results. Composite and Compomer resin and composite exhibited better performance than amalgam. The existence of the retention grooves proved to be effective for adhesive amalgam restorations but did not have any advantageous effect in composite and Compomer restoration. Conclusion. For improved fracture resistance in small approximal restorations, the use of composite was the appropriate choice. Compomer also gave satisfactory results. Use of amalgam restoration should be accompanied with retention grooves and an adhesive system to improve its performance. (J Prosthet Dent 2000;84:297-302.)

Amino acid and hexosamine composition and flux of sinking particulate matter in the equatorial Pacific at 175°E longitude

Sinking matter collected by sediment traps, which were deployed in the equatorial Pacific Ocean at 175°E for about 11 months during 1992–1993, were analyzed for their flux and labile components in terms of amino acids and hexosamines. The samples provided a temporal resolution of 15 days and were collected from 1357 (shallow trap) and 4363 m (deep trap) depths where sea floor depth was 4880 m. Particle flux along with major components (carbonate, organic matter, biogenic opal and lithogenic material) and amino acid parameters showed distinct temporal variations, which were more pronounced in the shallow trap relative to deep trap. A coupling between the fluxes in the shallow and deep traps was more evident during the period of maximum particle flux, which seems to be connected with the short reappearance of non-El Niño conditions in equatorial Pacific during the 1991–1993 El Niño event. The biogeochemical indicators C/N, Asp/Bala, Glu/Gaba, Bala+Gaba mol%, THAA-C% and THAA-N% implied that the increase in sinking flux was associated with upwelling and enhanced surface production. Degradation of sinking particulate organic matter between the shallow and deep traps was also evident. Occasionally higher mass and major component fluxes in the deep trap relative to the shallow trap are attributed to contribution of resuspended particulates from sea floor (nepheloid layer) or to laterally advected particulates from nearby areas. Carbonate and opal composition of the sinking flux showed a predominance of calcareous plankton; however, Asp/Gly mol ratio and Ser+Thr mol% indicated enhanced occurrence of diatoms during the periods of higher flux.