Adjacent Fan Research Articles

Land-surface quantitative analysis for mapping and deciphering the construction processes of piedmont alluvial fans in the Anti-Lebanon Mountains

Land-surface quantitative analysis based on digital elevation model (DEM) has been applied for improving the geomorphological mapping of piedmont alluvial fans. Indeed, these fans are frequently along a mountain front, where a series of coalescing fans may eventually occur. The margins of adjacent fans are rather difficult to map, thus preventing accurate and meaningful quantification of fan morphometric properties such as fan area, length, and slope. These morphometric properties are essential for informing on the influence of climatic conditions and tectonic factors on the fan-building processes. Therefore, in this paper, we propose a quantitative digital mapping approach along a stretch of about 50 km in the southern front of the Anti-Lebanon Mountains. Here, the Geomorphological Map of Syria at 1:1,000,000 scale (1963) reported at least nine piedmont alluvial fans, but these were poorly characterized in terms of geomorphometric characteristics and construction processes. Adopting the 1-arcsec SRTMv3 DEM, we propose a four-step workflow to analyse the feeding catchments morphology and fan morphometry. In this manner, the identification and geomorphological mapping of coalescent piedmont fans as well as the recognition of the main construction process have been improved. The proposed approach can support geomorphological investigations of wide and inaccessible areas—especially where arid and semi-arid climate conditions prevail—as well as where socio-political issues may prevent effective field work.

Morphology and paleohydrology of intracrater alluvial fans north of Hellas Basin, Mars

Alluvial fans and sinuous ridges are both important records of the history of fluvial activity on Mars, and they often occur together. We present observations of alluvial fans, many of which exhibit inverted relief, in five craters in the region north of Hellas basin. The observed fans ranged in size from ~10 to 820 km2. We identified three primary fan surface morphology classes (chute, degraded, and Inverted) as well as many instances where the morphology transitions from proximal chutes (or, rarely, a cratered degraded surface) to distal ridges corresponding to increasing thermal inertia. Clear superposition relationships at contacts between adjacent fans are rarely observed, suggesting interfingered deposits and concurrent fan development across the region. Localized factors appear to influence fan development as there is no systematic trend in the azimuth range of fan location, size of fan or catchment, as well as the degree of crater filling. Water and sediment availability may be controlled by lithology differences and weather patterns. Many of the fans had a mismatch between catchment and fan volume, corresponding to significant amounts of erosion perhaps due to windblown stripping of fine sediment. However, several notable fans exhibited volumes greater than their corresponding catchments. This may reflect uncertainty in the accuracy of the estimated paleosurface, or it may indicate sediment contributions to the fan from outside the mapped catchment. Ridges, inferred to be the resistant remnants of fluvially transported deposits, were used to estimate flow magnitude in fan construction with computed discharges of 60–400 m3/s and corresponding supply rate runoff values ~1–20 mm/h. Acknowledging that width-derived discharge values may overestimate flow conditions due to the likelihood of amalgamated channel deposits, this quantification provides important climate constraints.The upper range of runoff values and discharge rates are quite high, and would require either intense rain storms to generate immediate runoff, or longer-term snow accumulation and subsequent melt-runoff, potentially enhanced by rain-on-snow events. Minimum continuous formation time scales of less than a century are computed, but are incompatible with fan morphology (e.g., superposition relationships, embedded craters) and mechanisms to sustain flows. More realistic lower-limit fan construction times, accounting for modeled precipitation rates from the literature, are tens to hundreds of thousands of years. Fans were active in multiple events spanning the Hesperian to Amazonian periods, requiring transient climate conditions to support the fan aggradation.

Study of flow and heat transfer characteristics of heated asymmetrical concave surfaces under multi-piezoelectric fans actuation

A transient numerical simulation was carried out to investigate the convection heat transfer enhancement of heated asymmetrical concave surfaces using multi piezoelectric fans. And the numerical methodology has been validated through the comparison with the results of validation tests. The effects of the relative curvature (RK), dimensionless fan-to-fan pitch (P/WPF), vibration phase difference between adjacent piezoelectric fans (φ) and the dimensionless offset distance of multi-fans (Δy/APP) on flow and heat transfer performance were reported. RK was varied from 6 to 2. P/WPF was varied from 0.25 to 1.0. The value of φ was 0° and 180°. Δy/APP was varied from 0 to 1.0. The heat transfer of the heated surface was characterized by evaluating a time-averaged convection heat transfer coefficient over a complete vibration cycle of the multi-piezoelectric fans after the flow and thermal fields reached a quasi-steady state. In addition, transient and time-averaged flow fields were captured to study the underlying mechanism of the heat transfer enhancement. It was found that higher heat transfer coefficients were observed in stagnation zone with small P/WPF at smaller RK value of asymmetrical concave surfaces whereas the P/WPF is observed to affect the data only marginally at larger RK values. The influence of φ on the heat transfer coefficients was primarily reflected in the clearance region of adjacent fans, where operating in-phase could produce stronger flow in clearances than out-of-phase. Finally, it was also observed that proper adjustment of the fan position can reduce its equivalent relative curvature, resulting in improvement in the heat performance of the asymmetrical concave surface with large RK value.

Characterization of the thermal performance of multi piezoelectric fans for cooling a semi-cylindrical concave surface

Piezoelectric fan is widely used in the heat removal of high-temperature devices for its advantages of simple structure, low energy consumption, low noise, and good wind orientation. A theoretical and numerical study of characterizing the flow and heat transfer performances induced by single and multi-vibrating piezoelectric fans for cooling heated semi-cylindrical concave surface is conducted in this work. Two kinds of numerical models based on a dynamic meshing scheme and a user defined function describing the time-varying displacement of vibrating fans are employed to capture the instantaneous vortex structures and temperature contours on the semi-cylindrical concave surface. The influence mechanisms on heat removal performance of some vital factors, such as the dimensionless fan-to-fan pitch (P/W), vibrating phase difference and the dimensionless fan tip-to-concave surface distance (G/A) are analysed. The results prove that the evolution of the transient vortical structures around a single vibrating piezoelectric fan for cooling concave surface is almost the same as the case for cooling plane surface. The interaction of the streaming flow induced by multi fans is mainly concentrated in the clearance area between adjacent fans rather than the vibration envelopes. Moreover, the in-phase vibrating condition is more sensitive to the change of P/W and G/A than that of the out-of-phase. The simulations furnish a good reference for the design and optimization of multi piezoelectric fans.

Thermal Analysis of Radial Piezoelectric-Magnetic Fan (RPMF) for Electronics Cooling

Application of piezoelectric fan in electronic cooling system has been proven that it is more efficient than natural convection with least power consumption and has high potential to replace existing rotary fan for its simplicity and longer life. An integration of piezoelectric fan with magnet is to widen the cooling coverage area with similar power consumption and cost of running a single piezoelectric fan. By optimizing the repulsive magnetic force generated in between the magnets, the overall fans oscillate with significant average amplitude. The purpose of this paper is to investigate the performance of multiple piezoelectric-magnetic fan and its significance in reducing temperature while enhance the heat transfer. The parameters under investigation are the distance between magnets and fans orientation. In this study four magnetic fans were activated by a piezoelectric fan. It is found that at distance between magnets is 14 millimeters; the average amplitude is largest at highest resonant frequency. The multiple fans is better to be arranged in radial orientation for its ability to produce larger repulsive magnetic force to oscillate the adjacent fans. The distribution of repulsive magnetic force in radial orientation is five times better than array orientation. Therefore, radial piezoelectric-magnetic fan (RPMF) produces larger average amplitude of fans which is 111%. 30% of power consumption per unit coverage area is secured. RPMF generates average wind velocity of 0.4m/s compared to array orientation 0.17m/s.

Investigation of Multiple Miniature Axial Fan Cooling Solutions and Thermal Modeling Approaches

This paper investigates the thermal and fluid dynamic characteristics due to multiple miniature axial fans with blade chord and span length scales less than 10 mm, impinging air onto finned surfaces. A coupled approach, utilizing both experimental and numerical techniques, has been devised to examine in detail the exit air flow interaction between cooling fans within an array. The findings demonstrate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan—heat sink unit operating standalone. Numerical simulations have provided an insight into the flow fields generated by adjacent fans and also the air flow interaction with fixed fan motor support structures downstream. A novel experimental approach utilizing infrared thermography has been developed to locally assess the validity of the numerical models. In particular, an assessment on implementing compact lumped parameter fans and fans modeled with full geometric detail is shown for two configurations that are impinging air onto finned and flat surfaces. Overall, the study provides an insight into fan cooled heat sinks incorporating multiple miniature axial fans and general recommendations for improving current numerical modeling approaches.

Thermal Performance Characteristics of Integrated Cooling Solutions Consisting of Multiple Miniature Fans

Thermal performance characteristics are assessed for multiple miniature axial fans of 24.6 mm diameter that provide impingement cooling on a finned surface. Combined experimental and numerical analyses indicate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan – heat sink unit operating standalone. However the level of thermal performance reductions, coupled with greater geometrical flexibility, makes the design approach a viable alternative to current single fan – heat sink units. Experimental measurements also suggest that for a fixed spacing, fan operating point is a sensitive criterion for ensuring optimal thermal performance over an equivalent single fan unit. Numerical simulations, modelled using experimental inputs, have provided an insight into the flow fields produced by the interaction between adjacent fans and the finned geometry. Fluid recirculation occurs beneath the fan hub of the centrally located fan in the array, with the adjacent fans on the periphery experiencing cross flow in the hub region. A novel experimental approach utilising infrared thermography has been developed to assess the validity of the numerical model. Indeed, the previously stated flow features were confirmed using this assessment, while limitations in the modelling assumptions have been outlined. Overall, the results provide recommendations in the design of fan cooled heat sinks utilising multiple axial fans for jet impingement and an understanding of the flow physics which occur within this compact cooling solution design.

Sound Attenuating Shield for an Electric Heater

A sound-abating flow disruptor quiets a PTAC refrigerant system by disturbing the airflow between an energized electric heater and an adjacent fan wheel. In some embodiments, the flow disruptor is a perforated metal plate that attenuates a whistle, which appears to be caused by vortex shedding in the confined area between the energized heater and the fan. In some cases, the heater comprises selectively energizable heating elements of various wattage. The heating elements closest to the fan wheel are the lower wattage ones to minimize the heat near the fan.

Computational study of forced air-convection in open-cathode polymer electrolyte fuel cell stacks

A mathematical model for a polymer electrolyte fuel cell (PEFC) stack with an open-cathode manifold, where a fan provides the oxidant as well as cooling, is derived and studied. In short, the model considers two-phase flow and conservation of mass, momentum, species and energy in the ambient and PEFC stack, as well as conservation of charge and a phenomenological membrane and agglomerate model for the PEFC stack. The fan is resolved as an interfacial condition with a polynomial expression for the static pressure increase over the fan as a function of the fan velocity. The results suggest that there is strong correlation between fan power rating, the height of cathode flow-field and stack performance. Further, the placement of the fan – either in blowing or suction mode – does not give rise to a discernable difference in stack performance for the flow-field considered (metal mesh). Finally, it is noted that the model can be extended to incorporate other types of flow-fields and, most importantly, be employed for design and optimization of forced air-convection open-cathode PEFC stacks and adjacent fans.

Controls on sediment evacuation from glacially modified and unmodified catchments in the eastern Sierra Nevada, California

AbstractThe degree of glacial modification in small catchments along the eastern Sierra Nevada, California, controls the timing and pattern of sediment flux to the adjacent fans. There is a close relationship between the depth of fan‐head incision and the pattern and degree of Late Pleistocene catchment erosion by valley glaciers; catchments with significant glacial activity are associated with deeply incised fan heads, whereas fans emerging from glacially unmodified catchments are unincised. We suggest that the depth of fan‐head incision is controlled by the potential for sediment storage during relatively dry ice‐free periods, which in turn is related to the downstream length of the glacially modified valley and creation of accommodation through valley floor slope lowering and glacial valley overdeepening and widening. Significant storage in glacially modified basins during ice‐free periods leads to sediment supply‐limited conditions at the fan head and causes deep incision. In contrast, a lack of sediment trapping allows quasi‐continuous sediment supply to the fan and prevents incision of the fan head. Sediment evacuation rates should thus show large variations in glacially modified basins, with major peaks during glacial and lows during interglacial or ice‐free periods, respectively. In contrast, sediment removal from glacially unmodified catchments in this type of setting should be free of this effect, and will be dominated instead by short‐term variations, modulated for example by changes in vegetation cover or storm frequency. This distinction may help improve our understanding of long‐term sediment yields as a measure of erosional efficiency. Copyright © 2008 John Wiley & Sons, Ltd.

Ballistic aggregation on two-dimensional arrays of seeds with oblique incident flux: Growth model for amorphous Si on Si

Amorphous silicon (Si) structures on two-dimensional arrays of seeds on a Si substrate were experimentally prepared at near room temperature using a physical vapor deposition system with an $85\ifmmode^\circ\else\textdegree\fi{}$ oblique incident flux. In the stationary deposition case where the substrate is fixed at a position, the Si on the seeds form a ballistic inclined fanlike structure with an initial cone shape and the fan size $R$ grows with time in a power law form ${t}^{p}$, where $p\ensuremath{\sim}1$. We show that with a swing rotation where the substrate is rotated back-and-forth azimuthally, the fan size grows slower $(pl1)$ relative to that of the stationary deposition case and then saturates at a size depending on the swing angle. We proposed a modified ballistic deposition model considering the ballistic sticking, shadowing, surface diffusion, and substrate rotation in a three-dimensional Monte Carlo simulator. The evolution of the fanlike structures at different deposition times was simulated for both stationary deposition and swing rotation. The growth of the fan size $R$ with time $t$ in simulations was quantitatively analyzed and the exponents $p\ensuremath{\sim}1.0$ and $p\ensuremath{\sim}0.46$ were extracted for the stationary deposition and the swing rotation, respectively. For stationary deposition, the exponent 1 does not change significantly with the strength of surface diffusion. However, the fan-out angle decreases with the increased strength of surface diffusion. For swing rotation, the reduced exponent 0.46 at the initial stages of growth is primarily due to the self-shadowing of the fan itself under rotation. At the later stages of growth, the saturation of the fan size produces uniform rods and is due to the global shadowing from the adjacent fan structures. The morphology and the exponent obtained from our simulations are consistent with our experimental observations.

Timing and patterns of debris flow deposition on Shepherd and Symmes creek fans, Owens Valley, California, deduced from cosmogenic 10Be

Debris flow fans on the western side of Owens Valley, California, show differences in their depths of fan head incision and thus preserve significantly different surface records of sedimentation over glacial‐interglacial cycles. We mapped fan lobes on two fans (Symmes and Shepherd creeks) on the basis of the geometry of the deposits using field observations and high‐resolution airborne laser swath mapping data and established an absolute fan lobe chronology by using cosmogenic radionuclide exposure dating of large debris flow boulders. While both fans and their associated catchments were subject to similar tectonic and base level conditions, the Shepherd Creek catchment was significantly glaciated while that of Symmes Creek experienced only minor glaciation. Differences in the depth of fan head incision have led to cosmogenic surface age chronologies that differ in the length of the preserved depositional records. Symmes Creek fan preserves evidence of exclusively Holocene deposition with cosmogenic 10Be ages ranging from 8 to 3 ka. In contrast, the Shepherd Creek fan surface was formed by late Pleistocene and Holocene debris flow activity, with major deposition between 86–74, 33–15, and 11–3 ka. These age constraints on the depositional timing in Owens Valley show that debris flow deposition in Owens Valley occurred during both glacial and interglacial periods but may have been enhanced during marine isotope stages 4 and 2. The striking differences in the surface record of debris flow deposition on adjacent fans have implications for the use of fan surfaces as paleoenvironmental recorders and for the preservation of debris flow deposits in the stratigraphic record.

Using pebble lithology and roundness to interpret gravel provenance in piedmont fluvial systems of the Rocky Mountains, USA

Clast populations in piedmont fluvial systems are products of complex histories that complicate provenance interpretation. Although pebble counts of lithology are widely used, the information provided by a pebble count has been filtered by a potentially large number of processes and circumstances. Counts of pebble lithology and roundness together offer more power than lithology alone for the interpretation of provenance. In this study we analyze pebble counts of lithology and roundness in two contrasting fluvial systems of Pleistocene age to see how provenance varies with drainage size. The two systems are 1) a group of small high-gradient incised streams that formed alluvial fans and terraces and 2) a piedmont river that formed terraces in response to climate-driven cycles of aggradation and incision. We first analyze the data from these systems within their geographic and geologic context. After this is done, we employ contingency table analysis to complete the interpretation of pebble provenance. Small tributary streams that drain rugged mountains on both sides of the Santa Cruz River, southeast Arizona, deposited gravel in fan and terrace deposits of Pleistocene age. Volcanic, plutonic and, to a lesser extent, sedimentary rocks are the predominant pebble lithologies. Large contrasts in gravel lithology are evident among adjacent fans. Subangular to subrounded pebbles predominate. Contingency table analysis shows that hard volcanic rocks tend to remain angular and, even though transport distances have been short, soft tuff and sedimentary rocks tend to become rounded. The Wind River, a major piedmont stream in Wyoming, drains rugged mountains surrounding the northwest part of the Wind River basin. Under the influence of climate change and glaciation during the Pleistocene, the river deposited an extensive series of terrace gravels. In contrast to Santa Cruz tributary gravel, most of the Wind River gravel is relatively homogenous in lithology and is rounded to well-rounded. Detailed analysis reveals a multitude of sources in the headwaters and the basin itself, but lithologies from these sources are combined downstream. Well-rounded volcanic and recycled quartzite clasts were derived from the headwaters. Precambrian igneous and metamorphic clasts were brought down tributary valleys to the Wind River by glaciers, and sandstone was added where the river enters the Wind River structural basin.

Analysis of a spectrally unique deposit in the dissected Noachian terrain of Mars

We have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter‐toned fan‐shaped deposit in the dissected Noachian terrain of Mars using a combination of high spatial and spectral resolution remote sensing data sets. The spatial proximity of these two deposits and their dust‐free spectral character make these prime targets for (1) determining whether the dark‐toned deposit is derived from the fan‐shaped deposit and (2) constraining the nature and mineralogy of the fan‐shaped deposit. Stereo observations and derived digital elevation models of the of the fan‐shaped deposit show a set of three flows lobes. Calculations of the yield strength, based on morphometry of the lobes, indicate yield strengths consistent with those of other volcanic flows on Mars, although an aqueous origin cannot be discounted. The dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer. We find no obvious morphologic association between the dark deposit and adjacent fan. Multispectral imaging from the THEMIS VIS and IR instruments show that the two deposits have different spectral characteristics, probably caused by differences in their mineralogy rather than their physical properties. Finally, modeling of MGS/TES spectra of the combined deposits indicates a feldspar‐rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates, and possibly sulfates and clays. These results indicate that (1) there is no association between these deposits and (2) the combined deposits have a primarily igneous mineralogy, although some aqueous alteration may have occurred.

Slip rate on the Kunlun fault at Hongshui Gou, and recurrence time of great events comparable to the 14/11/2001, Mw∼7.9 Kokoxili earthquake

A field study of the surface rupture of the 14 November 2001, Mw∼7.9 Kokoxili (or Kunlun Shan) earthquake near Hongshui Gou (35.9° N, 92.2° E), a site with exceptional geomorphic offsets long identified on SPOT images, yields bounds on this earthquake return time and on the slip-rate along the Kusai Hu segment of the Kunlun Fault. Measurements of the sinistral coseismic and cumulative offsets of four distinct strath-terrace risers and of rill channels incised in the adjacent fan bajada, complemented by post-earthquake, metric-resolution satellite image restoration, are 3±0.5 m, 6±1 m, 31±2 m, 63±5 m, and 110±10 m. The smallest offset is unambiguously that of the 14/11/2001 earthquake. The 31 and 63 m riser offsets, which have thermoluminescence ages of 2885±285 and 5960±450 yr, respectively, imply an average slip rate of 10.0±1.5 mm/yr, almost identical to that found 200 km eastwards, in Xidatan, using 10Be cosmogenic dating of surface pebbles. The repetitive seismic slip (∼3 m) implies an average recurrence time of 300±50 yrs for earthquakes comparable to the 14/11/2001 event. This new data increases the body of evidence suggestive of local characteristic slip during large earthquakes and firmly corroborates the millennial eastward extrusion rate (1 cm/yr) of north-central Tibet relative to the Qaidam.

Lacustrine chalky carbonates: origin, physical properties and diagenesis (Palaeogene of the Madrid Basin, Spain)

The Palaeogene lacustrine chalky carbonates of the Madrid Basin are a peculiar type of very soft and friable carbonate facies with high porosity despite being covered by more than 800 m of sediment. Similar physical properties to those described in marine chalk reservoirs emphasize the interest in analysing and characterizing these carbonate facies within a lacustrine depositional system. Lithologically, they are calcitic and/or dolomitic poorly cemented carbonate muds with no significant amounts of skeletal debris. Clay minerals such as illite, smectite and palygorskite are present between the carbonate crystals. Palygorskite is the most common, covering the carbonate crystals and forming sheets between them. These lacustrine chalky carbonates were formed in the basinal areas of the lake as the result of inorganic carbonate precipitation and/or detrital sedimentation related to episodic reactivation of the adjacent fan systems. Their petrological, geochemical and physical properties indicate that few textural and compositional modifications occurred during diagenesis. Their main physical properties are a very low dry bulk and grain density (1.6–2.2 and 2.62 g/cm 3, respectively) and medium to high porosity (10–40%) due to micropores (<2 μm, 70%) and macropores (>2 μm, 30%). The convergence of lacustrine sedimentation dynamics (rapid sedimentation), the original mineralogy of these calcareous lacustrine muds (relatively stable low-magnesian calcite and dolomite), the early formation of the palygorskite cement of these muds, and the retention of Mg-enriched fluids in the pore system, were decisive in the partial inhibition of calcite cementation, compaction and recrystallization. The chalky carbonates are also intercalated between impermeable littoral carbonate facies that impeded fluid flow through their pore systems.

Late Weichselian iceberg, surface-melt and sediment production from the Eurasian Ice Sheet: results from numerical ice-sheet modelling

Results from a numerical ice-sheet model were matched with geological evidence detailing the extent and timing of the Late Weichselian ice sheet in the Eurasian Arctic, through simple adjustments in the model’s environmental inputs. The numerical model predicts the spatial and temporal variation in (1) subglacial sediment transport and deposition, (2) rates of iceberg calving and (3) rates of supraglacial melting over the past 30 000 yr. The ice sheet is characterised by a series of ice streams occupying bathymetric troughs in the Barents Sea and west of Norway, which act as sources for glacial sediment build-up and iceberg production. Our model indicates that significant volumes of sediment are deposited over the Bear Island fan (3000 km 3 in 12 000 yr), Franz Victoria Trough fan (500 km 3 in 8000 yr) and a series of smaller fans west of Norway (which combine to yield 4000 km 3 in 12 000 yr). The Norwegian Channel ice stream operated for only 4000 yr, during which time 400 km 3 of sediments were deposited on the adjacent fan. The ice sheet experienced two major periods of iceberg production where the rate of calving increased by ∼50% at about 15 000 and 12 500 yr ago. However, the time-dependent response of iceberg calving to sea-level rise for individual ice streams is shown to be more complicated than the generalised ice-sheet response. The marine portions of the ice sheet decayed after 15 000 yr ago, resulting in several embayments at the mouths of bathymetric troughs. A second pulse of enhanced iceberg calving at 12 500 yr ago caused further decay of the marine ice sheet and the ice margin retreated back to the shorelines of island archipelagos in the northern Barents Sea. Ice loss through surface melting was restricted mostly to the southern margin of the ice sheet.

Unravelling the patterns of alluvial fan development using mineral magnetic analysis: examples from the Sparta Basin, Lakonia, southern Greece

Mineral magnetic analysis of B-horizons of soils developing upon the surfaces of alluvial fans was undertaken in order to: (i) differentiate and rank discrete fan surfaces by order of formation; (ii) establish whether fan surfaces formed simultaneously in adjacent fan systems; and (iii) deduce probable patterns of fan development. The results of the analysis indicate that the greatest concentration of ferrimagnetic and anti-ferromagnetic minerals occurs within soils which have developed upon the proximal fan surfaces with a progressive reduction in magnetic minerals in soils associated with medial and distal surfaces. The build-up of magnetic minerals in the proximal fan soils suggests that these surfaces formed first followed by the medial and distal surfaces. With the exception of the Kalivia Sokas fan, the majority of depositional events responsible for fan surface formation occurred simultaneously, suggesting that adjacent fan systems share broadly similar depositional histories. Although the precise timing of depositional events is uncertain, it is probable that by the end of the late Pleistocene, small, largely undissected fans comprising two to three surfaces had formed. At the start of the Holocene, fan systems experienced significant fanhead incision. A net distal extension of the fan trench coupled with a progressive basinward shift of the locus of deposition during the middle and late Holocene resulted in formation of medial and distal fan surfaces. Changes in climate are deemed to be the major control of fanhead incision, fan trenching and fan surface formation. However, the likely effects of long-term tectonic activity and approximately five thousand years of human occupation upon fan development in the Sparta Basin remain unclear. Copyright © 2000 John Wiley & Sons, Ltd.

Random Orientation of Wood on Two Tiny Alluvial Fans (Tavaputs Plateau, NE Utah, U.S.A.)

ABSTRACT Abundant bits of wood scattered over the surfaces of two nearly identical, adjacent, tiny, steep, grassy, and smooth alluvial fans near Duchesne, Utah, allowed orientation measurements of 390 elongate and straight pieces that varied in size from twigs to tree trunks. On each fan, the pieces of wood are spread outward from the mouth of a small fan-head channel, but they showed effectively random orientations relative to fan slope, regardless of size. Almost all the wood lies loose and unburied on the two fan surfaces, and is thus free of associated sand and mud. Slopes uphill are similarly free of dead wood, although both scattered and tangled wood covers adjacent slope toes. One possible explanation is that a localized rain burst cleaned the upper slopes but failed to flush wood beyond slope toes wherever runoff was not concentrated. The lack of sediment can be explained if the ground was frozen and/or snow-covered at the time. If the wood was deposited by a sheetflood, then the results are significant to the small but ongoing controversy over whether running water should orient wood (1) transverse to flow (by rolling), (2) parallel to flow (by swiveling or sliding), (3) both, or (4) randomly. Alternatively, the wood may represent a snow or slush avalanche, in which case random orientations would not be surprising. In either case, the results provide a note of caution: because this study was prompted by seeing a variety of plausible preferred orientations in many small or local sets of waterlaid wood on other small fans and because randomness was (arguably) not evident on these two fans without extensive data collection, we have become mistrustful of inferring paleocurrents from small samples of fossil wood.

MINIMUM DISTANCE BETWEEN VENTILATION FANS IN ADJACENT WALLS OF TUNNEL VENTILATED BROILER HOUSES

Concerns in the poultry industry suggest a minimum distance (inlet to inlet) of up to 1.5 m (5 ft.) forpositioning large ventilation fans 90 to each other in adjacent walls. This minimum distance is based on a contention ofinterference resulting in a reduction of volumetric flow rate of one or both adjacent fans. Research was conducted todetermine what effect the proximity of adjacent inlets of 122-cm (48-in.) ventilation fans have on the volumetric flow ratesof each fan. Two 122-cm (48-in.) fans (one movable, one stationary) were placed in adjacent walls of a research broilerhouse. The volumetric flow of the stationary fan was determined as the movable fan was repositioned at regulardecreasing intervals from 1.8 to 0.3 m (6 ft. to 1 ft.) toward the stationary fan. Results showed a significant difference of2% in volumetric flow rate of the stationary fan when the other fan was moved to within a distance of 0.3 m (1 ft.). Nosignificant differences were observed at any other fan position.