bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computer-Based System for Fire Management in the Mountains of the Cape Province, South-Africa
Authors: Richardson DM , van Wilgen BW , Le Maitre DC , Higgins KB , Forsyth GG
Published: October 2005

This paper describes a Catchment Management System (CMS) that provides objective procedures for managing fire. Prescribed burning is carried out in the mountain catchments of the Cape Province, South Africa, to enhance water yield, to rejuvenate the indigenous shrubland vegetation, to reduce fire hazard and to control invasive alien plants. Fire is the only practical tool for achieving these aims in the mountainous terrain. Recent research has improved understanding of the response of these systems to fire, but managing fire to achieve goals is very difficult. The CMS comprises a central geographical information system for managing and processing spatial data, linked to personal computers with DBase IV data-bases and simple rule-based models for decision-making. Current applications are: prioritization of areas for burning, monitoring the success of fire management, mapping fire hazard for fire control planning, and the production of management summaries and statistics. This paper presents examples of these applications from three areas in the Cape Province with different management problems and priorities: the Kammanassie in the southern Cape, and the Kogelberg and Table Mountain areas in the western Cape.
Air Attack - Retardants, Rheology and Some New Options
Authors: Vandersall HL
Published: October 2005

The rheological properties of forest and brush land fire retardant solutions significantly affect their performance during and following aerial discharge and subsequent distribution within the fuel ladder. The degree of dispersion, the integrity of the retardant cloud, the magnitude of wind-induced drift, the continuity of coverage and retention on and penetration of the fuel complex are among diose performance related characteristics impacted. The viscous character of the solution during periods of extreme and relaxed shear and its elasticity are known to be important rheological properties. While applicable specifications and the technical literature document the importance of these factors, only the extremes (water-like and highly viscous and elastic fluids) have been available to the fire manager. A series of new fluid concentrate type retardants are now being evaluated jointly by the United States Forest Service and private industry. Upon simple dilution to use level concentration, these low viscosity fluids increase in viscosity and elasticity to one of three predetermined levels, i.e., low, medium or high as defined by the Federal Specifications. Selection of the proper rheology can, thus, be made by the fire manager dependent on the type and characteristics of the delivery platform, safe drop height relative to die terrain, atmospheric conditions, fuel characteristics and the management objective.
Internal-Combustion Engine Performance in the Fireground
Authors: Carter E , Milton B
Published: October 2005

The performance of internal combustion engines used in fire fighting equipment can be affected by the fireground ambient conditions. Both gasoline (SI) and diesel (CI) engines can suffer significant power losses due to high temperatures and reduced oxygen in the intake air caused by mixing with the products of combustion of a fire. This, and other engine problems associated with starting and operation under fireground conditions are examined in this paper.
Seed Production of Wiregrass in Central Florida Following Growing-Season Prescribed Burns
Authors: Outcalt KW
Published: October 2005

Wiregrass (Aristida stricta Michx.) is a major species in the long leaf pine (Pinus palustris Mill.) sandhills areas of central Florida, providing a major portion of the fuel for the recurring ground fires necessary to maintain the community. Growing season burning promotes flower and seed production. The objective of this study was to assess the seed production potential of wiregrass following prescribed burns from May through August. Four longleaf wiregrass sites were prescribed burned, one each in May, June, July, and August. Information on bunch size, bunch density, seed stalk density, seed density, and seed germination were collected. The four sites differed significantly in the density of wiregrass bunches, average bunch size, wiregrass cover and seed viability. The density of seed stalks was fairly consistent across sites. Viable seed production was lowest on the June burned site and highest on the July burned site. The study shows good quantities of seed are comparatively easy to produce with growing season bums.
Impacts of the 1988 Wildfires on the Water-Quality of Yellowstone and Lewis Lakes, Wyoming
Authors: Lathrop RG jr.
Published: October 2005

The objective of this paper is to examine whether the severity and great extent of the 1988 Yellow-stone fires impacted the water quality of two of Yellowstone's major lakes. Analysis of water quality records for Yellowstone and Lewis Lakes collected over a fifteen year period (1976-1991) have shown only a minimal shift in lake water quality following the fires. Though 25 percent of their watersheds were heavily burned, these lakes appear to be large enough to dilute increased inputs and have experienced few lasting effects from the 1988 fires. The relative importance of landwater interactions in affecting the water quality of Yellowstone's large lakes must be viewed in the context of a multitude of other factors, including changing atmospheric deposition and hydrothermal inputs.
A Synoptic Climatology for Forest-Fires in the NE US and Future Implications From GCM Simulations
Authors: Takle ES , Bramer DJ , Heilman WE , Thompson MR
Published: October 2005

We studied surface-pressure patterns corresponding to reduced precipitation, high evaporation potential, and enhanced forest-fire danger for West Virginia, which experienced extensive forest-fire damage in November 1987. From five years of daily weather maps we identified eight weather patterns that describe distinctive flow situations throughout the year. Map patterns labeled extended-high, back-of-high, and pre-high were the most frequently occurring patterns that accompany forest fires in West Virginia and the nearby four-stare region. Of these, back-of-high accounted for a disproportionately large amount of fire-related damage. Examination of evaporation acid precipitation data showed that these three patterns and high-to-the-south patterns ail led to drying conditions and all other patterns led to moistening conditions. Surface-pressure fields generated by the Canadian Climate Centre global circulation model for simulations of the present (1xCO2) climate and 2xCO2 climate were studied to determine whether forest-fire potential would change under increased atmospheric CO2. The analysis showed a tendency for increased frequency of drying in the NE US, but the results were not statistically significant.
Long-Term Spatial Patterns Created by Fire: a Model Oriented Towards Boreal Forests
Authors: Ratz A
Published: October 2005

Fire is one of the most important factors structuring boreal forests. A spatial simulation model based on a cellular automata approach was built to obtain insights into the spatial pattern of successional stages. Two scenarios are compared: 1. constant flammability and 2. flammability increasing during succession. Spatial structure strongly depends on the specific form of age-dependent flammability. The fine structure of single fires generated by the model is analyzed by five different measures and is in agreement with empirical evidence.
Fire Propagation in Vertical Stick Arrays - the Effects of Wind
Authors: Beer T
Published: October 2005

A simple geometrical model of fire spread through arrays of vertically mounted fuel elements performs well in the absence of wind. The theory assumes that an adjacent fuel element ignites when the flame from the previous fuel element moves downward sufficiently that its temperature isotherm corresponding to the temperature of ignition intersects the top of the adjacent fuel element. This simple geometrical model is extended to incorporate the effects of wind, and its predictions are compared to wind tunnel observations of burning arrays. The model performs well at low wind speeds, but underestimates the wind speed at which the flame makes contact with adjacent fuel elements. The reason for this underestimate is likely to arise because of a weakness in one or more of the assumptions concerning, (1) the laminar nature of the flame, (2) the constancy of the flame height as the wind increases, or (3) the existence of a constant ignition temperature. The most significant finding is that this simple conceptual theory indicates that the rate of spread of a fire front as a result of wind is unlikely to be a simple function such as a power-law or an exponential, but is likely to be the solution to a set of differential equations that can be approximated by such simple functions over a portion of their range.
Mapping the Location of Wildfires in Alaskan Boreal Forests Using AVHRR Imagery
Authors: French NHF , Kasischke ES , Bourgeau-Chavez LL , Berry D
Published: October 2005

The results of a study using satellite imagery to map boreal forest fires in Alaska in 1990 and 1991 are presented. Composite AVHRR data detected more than 80% of fires greater than 2000 ha in size. Additionally, using a two season method, 78% of the area of all boreal forest fires in Alaska was mapped. This technique is considered to be an accurate way to detect forest fire scars and estimate area burned throughout the boreal forests, and could be very important in those regions where wildfire data are presently difficult or impossible to gather.
Modeling Ignition and Burning Rate of Large Woody Natural Fuels
Authors: Albini FA , Reinhardt ED
Published: October 2005

As part of the development of a model for predicting fuel loading reductions by and intensity histories of fires burning in large woody natural fuels, it was necessary to develop separate models for the processes of ignition and rate of burning of individual fuel elements. This paper describes the derivation of predictive equations for ignition delay time and burning rate (from diameter reduction rate) of large woody natural fuels in a fire environment. The method consists of deriving approximate functional forms using fuel component properties and a measurable ''fire environment temperature'' and then fitting these forms to data taken in laboratory fires using a large propane burner. The equations describe the calibration data with precision adequate for the purpose for which they were designed.
Response of Creeping Bluestem to Varying Month of Burn and Soil-Water Conditions
Authors: Kalmbacher R , Martin FG
Published: October 2005

Research was designed to determine if Schizachyrium scoparium var. polycladus responses vary with month of burn and soil water conditions during fire. Bluestem was grown in tanks with a 2 x 2 x 3 factorial of month (June or January), soil water (saturated or dry), and defoliation treatments (burn, clip, or none). Tiller density, rhizome mass, and total nonstructural carbohydrates were lower (P<0.05) during the 50 days after burning in June when dry soil (25mm depth) reached 90 degrees C and remained about 50 degrees C for 68 minutes postburn. Reproductive tiller density 94 days after June 1987 burn was not affected by water, but was lower in burn vs. other defoliation treatments. No treatment in January 1988 affected tiller density or rhizome mass in a 50 day postburn period. In September 1988, there were no effects due to month or water, but vegetative tiller density was lower in burn and clip vs. no defoliation, total tiller density was different among all treatments, and reproductive:vegetative tiller density (R:V) ratio was higher in burn vs. clip and no defoliation. In Florida, fire on hot, dry sandy soils in June may have short term negative effects, and fire at either season or soil water level may reduce total tiller density and increase R:V ratio in creeping bluestem for up to 476 days postburn.
Fire Behavior and Fire Effects on Eastern Redcedar in Hardwood Leaf-Litter Fires
Authors: Engle DM , Stritzke JF
Published: October 2005

Treatment of stands of hardwoods in the cross timbers of the central United States with tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-dimethylurea) can significantly decrease canopy cover of hardwoods. However, at the rate used for hardwood control, tebuthiuron does not control eastern redcedar (Juniperus virginiana L.). Our objective was to determine the potential of using fires in the hardwood leaf litter, either before or after tebuthiuron, for controlling eastern redcedar. To do this, we compared fuelbed characteristics, fire behavior, and fire effects on eastern redcedar in naturally occurring hardwood leaf litter with those augmented by leaves dropped following a single application of tebuthiuron. Studies were conducted in 1988, 1989, and 1991 on a cross timbers site dominated by an overstory of post oak (Quercus stellata Wangenh.) and blackjack oak (Q. marilandica Muenchh.) and with eastern redcedar in the understory. Factors evaluated included herbicide treatment (tebuthiuron or no herbicide) and burning season (late summer or winter). Tebuthiuron at 2.2 kg a.i. Ha-1 was applied to plots (25 X 25 m) in March of the study years. In late summer, tebuthiuron-treated plots contained almost twice the 1-hr fuel loading as untreated plots. Fuel depth on untreated plots in late summer was about half that of other herbicide treatments and burning date combinations. Fuel loading on plots burned in winter was not affected by tebuthiuron treatment, and no differences in fuel consumption were detected among any treatments. Moisture content of 1-hr fuels on plots burned in winter was more than twice that of 1-hr fuels on plots burned in late summer. Fire intensity was low with all bums, and no differences in fire behavior were detected among any treatments. Crown scorch of 75% or greater on small eastern redcedar trees was considered a successful burn, and this resulted on all but the late summer-no tebuthiuron treatment. The natural log of fireline intensity explained about 47% (P<0.0006)) of the variation in fire success, and ambient air temperature explained an additional 19% (P<0.0468). Although tebuthiuron treatments effectively augmented leaf-litter fuel load by late-summer and provided a suitable fuelbed for burning, crown scorch and tree kill were not greatly improved by burning in late summer as compared to winter. We conclude that understory eastern redcedar can be controlled successfully by burning leaf-litter fuelbeds in either late fall or winter after natural leaf-fall from hardwood trees or in late summer, fall, or winter following a spring application of tebuthiuron for control of overstory hardwoods.
Fire Behaviour Modelling in Tasmanian Buttongrass Moorlands .II. Fire Behaviour
Authors: Marsden-Smedley JB , Catchpole WR
Published: October 2005

An experimental burning program was carried out in Tasmanian buttongrass moorlands to develop fire behaviour prediction models for improving fire management. A range of previously developed prediction models were examined, but none provided adequate fire behaviour predictions. Empirical models were then developed to predict rate of fire spread and flame height in flat terrain, using the variables site age, dead fuel moisture content and surface wind speed. The models should provide good predictions for low to moderate intensity fires and adequate predictions for high intensity wildfires.
Biomass Burning and Resulting Emissions in the Northern Territory, Australia
Authors: Beringer J , Packham D , Tapper N
Published: October 2005

The extent of biomass burning in the Northern Territory, Australia, during 1992 (a year of low fire activity) was estimated using NOAA-AVHRR satellite imagery and was subsequently used to calculate the emission of gaseous compounds from biomass burning for that year. A total of 73,729 km2 was determined to have been burnt, representing 5.5% of the total Northern Territory area. The extent of biomass burning in different vegetation units in the Northern Territory was also estimated with eucalypt communities comprising 72% of the total area burnt. An estimated 29.5 x 106 tonnes of biomass was consumed by burning, resulting in the production of an estimated : 1. 11.3 Tg C as carbon dioxide, 2. 1.02 Tg C as carbon monoxide, (3) 5.23 x 10-3 Tg C as total particulate matter, 4. 26.1 x 10-3 Tg N as nitrous oxides, 5. various other trace gases. The calculated release of CO2 in this study accounts for only 41% of the estimated Australian contribution to global emmissions from biomass burning, indicating that the Australian contribution may be overestimted.
Fire Growth in Grassland Fuels
Authors: Cheney NP , Gould JS
Published: October 2005

The development of grass fires originating from both point and line ignitions and burning in both open grasslands and woodlands with a grassy understorey was studied using 487 periods of fire spread and associated fuel, weather and fire-shape observations. The largest fires travelled more than 1000 m from the origin and the fastest 2-minute spread rate was over 2 m s-1. Given continuous fuel of uniform moisture content, the rate of forward spread was related to both the wind speed and the width of the head fire measured normal to the direction of fire travel. The head fire width required to achieve the potential quasi-steady rate of forward spread for the prevailing conditions increased with increasing wind speeds. These findings have important implications for relating small-scale field or laboratory measurements of fire spread to predictions of wildfire spread. The time taken to reach the potential quasi-steady rate of spread at any wind speed was highly variable. This time was strongly influenced by the frequency of changes in wind direction and the rate of development of a wide head fire.
The Role of Prescribed Burning in Regenerating Quercus Macrocarpa and Associated Woody Plants in Stringer Woodlands in the Black Hills, South Dakota
Authors: Sieg CH , Wright HA
Published: October 2005

Throughout the range of Quercus macrocarpa, fire historically played an important role in maintaining Quercus stands. However, little is known about the role of fire in maintaining stringer Quercus stands on the western edge of its distribution. This research suggests that prescribed burning could be used to rejuvenate woody plants in Quercus woodlands. Relative to unburned areas, there were more (p < 0.1) Quercus, Fraxinus pennsylvanica and Acer negundo sprouts following spring burning. However, Quercus seedling density did not increase (p = 0.22) relative to unburned sites, and changes in the density of woody understory species in response to burning were erratic. Dormant season burning has some appeal from a fire control point of view and because carbohydrate reserves in woody plants are high during this time. However, if the objective is to regenerate woody plants and/or mimic historical fires, prescriptions should be set to achieve high intensities.
The Role of Soil Seed Bank in the Early Stages of Plant Recovery After Fire in a Pinus Pinaster Forest in SE Spain
Authors: Ferrandis P , Herranz JM , Martínez-Sánchez JJ
Published: October 2005

The implication of the viable soil seed bank in the early stages of the plant recovery after fire was studied in a recently burnt Mediterranean pine forest of Pinus pinaster. Seed number contained in soil samples taken inmediately after fire and emergent seedling number recorded in the field during the subsequent year were compared. Although the fire effect was important, available seed density in the soil after fire was relatively high (around 2,200 seeds/m2). A small group of species containing the main shrub species in the unburnt community predominated both in the viable seed bank and field germination after fire. However, these species showed low germination rates in the field, as opposed to species with the lowest presence in the seed bark. The predominance of woody obligate seeders in the seed bark after fire and the high specific correspondence between seed bank and germination in the field, emphasize the important role of the seed bank contained in the soil before fire in the postfire species establishment.
Simulation of Crown Fire Effects on Canopy Seed Bank in Lodgepole Pine
Authors: Despain DG , Clark DL , Reardon JJ
Published: October 2005

Analysis of video footage taken of crown fires during the 1988 fire season in Yellowstone National Park indicated that the most frequent length of time required to completely burn tree crowns was 15-20 seconds. Lodge-pole pine (Pinus contorta Laws.) seeds were tested for ability to germinate after exposing both serotinous and nonserotinous cones for 10 to 60 seconds in a flame front designed to simulate a crown fire. Heating enhanced germination of seeds from serotinous cones but not those from nonserotinous cones. Maximum germination rates for serotinous cone seeds ranged from 37 to 64 percent and occurred after 10-20 seconds exposure of cones to flames. Germination after 60 seconds exposure averaged 0.3 to 14 percent. Maximum germination of seeds from nonserotinous cones (about 80%) occurred with no exposure and after 10 seconds in the flames.
Aleppo Pine (Pinus Halepensis) Postfire Regeneration: the Role of Canopy and Soil Seed Banks
Authors: Daskalakou EN , Thanos CA
Published: October 2005

Pinus halepensis (Aleppo pine), is the dominant tree of a large fraction (26%) of the Greek coniferous forests; this species is an endemic pine of the Mediterranean Rim and well adapted to fire. Its regeneration is accomplished exclusively through seeds, thus its soil and canopy seed banks are of paramount importance for postfire resilience. Cone opening and seed dispersal were investigated in unburned forests of Attica (Greece) and it was found that Pinus halepensis trees maintain a significant percentage of the yearly cone crop (40-80%) closed, thus creating a persistent, canopy seed bank. Full viability of enclosed seeds was maintained for at least three years in canopy storage; moreover, preliminary results concerning the viability of seeds enclosed within the cones for four to more than 50 years showed a gradual reduction of both final percentage and rate of germination. Nevertheless, cones of up to 20 years of age contained a considerable fraction of germinable seeds. On the other hand, Aleppo pine forms only a short-lived (transient) soil seed bank; this bank was particularly abundant after a fire, as a result of the fire-induced cone opening. The germinable seed portion, although quite important prior to the start of the rainy season, was rapidly depleted, and at the end of the rainy season it was virtually absent in both burned and unburned forests. It is therefore concluded that postfire Aleppo pine seedling recruitment takes place almost exclusively during the first year after the fire and depends upon the germination of seeds in a transient soil bank which is produced by the postfire dispersal of pine seeds stored in the canopy seed bank.
Remote Sensing of Forest Fire Severity and Vegetation Recovery
Authors: White JD , Ryan KC , Key CC , Running SW
Published: October 2005

Burned forested areas have patterns of varying burn severity as a consequence of various topographic, vegetation, and meteorological factors. These patterns are detected and mapped using satellite data. Other ecological information can be abstracted from satellite data regarding rates of recovery of vegetation foliage and variation of burn severity on different vegetation types. Middle infrared wavelengths are useful for burn severity mapping because the land cover changes associated with burning increase reflectance in this part of the electromagnetic spectrum. Simple stratification of Landsat Thematic Mapper data define varying classes of burn severity because of changes in canopy cover, biomass removal, and soil chemical composition. Reasonable maps of burn severity are produced when the class limits of burn severity reflectance are applied to the entire satellite data. Changes in satellite reflectance over multiple years reveal the dynamics of vegetation and fire severity as low burn areas have lower changes in reflectance relative to high burn areas. This results as a consequence of how much the site was altered due to the burn and how much space is available for vegetation recovery. Analysis of change in reflectance across steppe, riparian, and forested vegetation types indicate that fires potentially increase biomass in steppe areas, while riparian and forested areas are slower to regrow to pre-fire conditions. This satellite-based technology is useful for mapping severely burned areas by exploring the ecological manifestations before and after fire.
Extrapolation Problems in Modeling Fire Effects at Large Spatial Scales: a Review
Authors: Mckenzie D , Peterson DL , Alvarado E
Published: October 2005

Models of vegetation change in response to global warming need to incorporate the effects of disturbance at broad spatial scales. Process-based predictive models, whether for fire behavior or fire effects on vegetation, assume homogeneity of crucial inputs over the spatial scale to which they are applied. Landscape disturbance models predict final burning patterns, but either do not model mechanistic behavior and explicit spread rates, or require large amounts of data to initialize simulations and predict ecological effects. Empirical data on the ecological effects of fire are not generally available at these scales, and conclusions are often extrapolated upward from stand-level data. Three methods for extrapolating ecological effects of fire across spatial scales and the sources of error associated with each were identified: (1) extrapolating fire behavior models directly to larger spatial scales; (2) integrating fire behavior and fire effects models with successional models at the stand level, then extrapolating upward; and (3) aggregating model inputs to the scale of interest. Extreme fire events present a challenging problem for modelers, regardless of which extrapolation method is employed. No single approach to modeling fire effects is inherently superior; modeling objectives and the characteristics of specific systems will determine the best strategy for each situation.
A Review of Initial Attack Fire Crew Productivity and Effectiveness
Authors: Hirsch KG , Martell DL
Published: October 2005

Information regarding the productivity and effectiveness of initial attack fire crews is essential to a wide variety of forest fire management activities. This paper provides a selective review of crew productivity research conducted in Australia, Canada, and the United States and a cursory overview of how such information is used in computer-based fire management decision support systems. A description of several widely used rules-of-thumb that relate suppression effectiveness to fire intensity is presented as well as our understanding of how these guidelines may have evolved. This is followed by an example of some of the difficulties associated with transferring productivity and effectiveness information between fire management organizations and fire environments. The paper concludes with a discussion of strategies for investigating initial attack crew performance.
Reprogramming of tau alternative splicing by spliceosome-mediated RNA trans-splicing: Implications for tauopathies
Authors: Rodriguez-Martin Teresa , Garcia-Blanco Mariano A. , Mansfield S. Gary , Grover Andrew C. , Hutton Michael , Yu Qingming , Zhou Jianhua , Anderton Brian H. , Gallo Jean-Marc
Published: October 2005

Frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) is caused by mutations in the gene encoding the microtubule-associated protein, tau. Some FTDP-17 mutations affect exon 10 splicing. To correct aberrant exon 10 splicing while retaining endogenous transcriptional control, we evaluated the feasibility of using spliceosome-mediated RNA trans-splicing (SMaRT) to reprogram tau mRNA. We designed a pre-trans-splicing molecule containing human tau exons 10 to 13 and a binding domain complementary to the 3′ end of tau intron 9. A minigene comprising tau exons 9, 10, and 11 and minimal flanking intronic sequences was used as a target. RT-PCR analysis of SH-SY5Y cells or COS cells cotransfected with a minigene and a pre-trans-splicing molecule using primers to opposite sides of the predicted splice junction generated products containing exons 9 to 13. Sequencing of the chimeric products showed that an exact exon 9–exon 10 junction had been created, thus demonstrating that tau RNA can be reprogrammed by trans-splicing. Furthermore, by using the same paradigm with a minigene containing full-length intronic sequences, we show that cis-splicing exclusion of exon 10 can be by-passed by trans-splicing and that conversion of exon 10–tau RNA into exon 10+tau RNA could be achieved with ≈34% efficiency. Our results demonstrate that an alternatively spliced exon can be replaced by trans-splicing and open the way to novel therapeutic applications of SMaRT for tauopathies and other disorders linked to aberrant alternative splicing.
Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity
Authors: Christian Catherine A. , Mobley Jessica L. , Moenter Suzanne M.
Published: October 2005

A robust gonadotropin-releasing hormone (GnRH) surge is a prerequisite signal for the luteinizing hormone (LH) surge that triggers ovulation. In rodents, the GnRH surge is initiated by elevated estradiol and a diurnal switch in estrogen action from negative to positive feedback. The ability of constant estradiol treatment to induce daily LH surges was tested in adult mice that were ovariectomized (OVX) or OVX and treated with estradiol implants (OVX+E). LH in OVX mice showed no time-of-day difference. In contrast, OVX+E mice showed a large LH surge (8- to 124-fold relative to the a.m.) in p.m. samples on d 2–5 post-OVX+E. Targeted extracellular recordings were used to examine changes in firing activity of GnRH neurons in brain slices. There was no time-of-day difference in cells from OVX mice. In contrast, OVX+E cells recorded in the p.m. showed an increased mean firing rate and instantaneous firing frequency, which could increase GnRH release, and decreased duration of quiescence between bouts of firing, possibly reflecting increased pulse frequency, compared with cells recorded in the a.m. In the a.m., OVX+E cells showed changes in GnRH neuron firing reflecting negative feedback compared with OVX cells, whereas in the p.m., OVX+E cells exhibited changes suggesting positive feedback. These data indicate that differences in pattern and level of individual GnRH neuron firing may reflect the switch in estradiol action and underlie GnRH surge generation. The persistence of altered GnRH neuron activity in slices indicates that this approach can be used to study the neurobiological mechanisms of surge generation.
Visualization of retrovirus budding with correlated light and electron microscopy
Authors: Larson Daniel R. , Johnson Marc C. , Webb Watt W. , Vogt Volker M.
Published: October 2005

We have used correlated scanning EM (SEM) and multiphoton fluorescence microscopy to visualize budding of virus-like particles (VLPs) of Rous sarcoma virus (RSV) and HIV type 1 (HIV-1). When the Gag structural protein was expressed alone as a GFP fusion, most budding particles appeared morphologically aberrant, but normal assembly could be rescued by coexpression of untagged Gag protein. Imaging of live cells allowed budding to be seen in real time as the disappearance of fluorescent spots from the dorsal cell surface. The disappearance of very bright spots containing clusters of VLPs often occurred in a stepwise fashion. Even after imaging times >1 h, only a minority of the spots disappeared, suggesting that some might be budding-incompetent complexes. On individual cells, we enumerated both the fluorescent puncta and the budding structures visible by SEM and compared these numbers for WT Gag proteins and for Gag proteins that were blocked at the last step in budding by a late domain mutation. For the mutant HIV-1 and RSV proteins, almost all of the fluorescent spots corresponded to budding structures. For WT RSV, the dorsal side of cells showed 3-fold more fluorescent spots than budding structures, suggesting that formation of the polymerized Gag shell precedes bulging out of the membrane. For WT HIV-1, most fluorescent spots corresponded with budding structures, consistent with the slower budding rate of this virus. Combining these two types of microscopy will allow innovative approaches for elucidating the mechanism of retrovirus budding.
Intervening in the residential mobility process: Neighborhood outcomes for low-income populations
Authors: Clark William A. V.
Published: October 2005

Neighborhoods have become the focus of questions about how they affect the families that live within them. A current working assumption of some federal policies is that, with help, households can escape poverty neighborhoods and change their spatial context. How true is this, especially for low-income households, and does changing neighborhoods have measurable benefits? The study uses data from the Moving to Opportunity program, initiated by the Department of Housing and Urban Development, to test whether policy interventions by means of housing vouchers have aided moves away from low-poverty areas and into integrated residential settings. By examining the neighborhood demography of the initial and subsequent locations of the samples, it is possible to assess the success of the objectives of decreasing poverty and increasing integration. Although the program has shown some success in assisting households to live in lower-poverty neighborhoods, the findings here emphasize just how difficult it is to intervene in dynamic processes such as housing choice and mobility to create policy outcomes.
Assimilation and differences between the settlement patterns of individual immigrants and immigrant households
Authors: Ellis Mark , Wright Richard
Published: October 2005

Analyses of immigrant settlement patterns typically rely on counts of foreign-born individuals by neighborhood, metropolitan area, state, or region. As an alternative, this study classifies immigrants and their descendents into household types to shift attention from individuals to relationships between individuals. The study uses pooled current population survey data to identify seven household types, six of which have various degrees of immigrant or second-generation presence. The research compares distributions of first- and second-generation immigrants with different types of households that include first- and second-generation immigrants. Our analysis shows that the geography of immigration based on households differs considerably from geographies based on individuals. The spatial distribution and concentration of the foreign-stock population provides one picture of immigrant geographies, whereas the patterns of concentration by several different household types opens up the chance to tell other stories. More pointedly, we emphasize that the unit of analysis shapes assimilation research results and implies that this analytical choice cannot be thought of as independent from the politics of immigration.
Migration up and down the urban hierarchy and across the life course
Authors: Plane D. A. , Henrie C. J. , Perry M. J.
Published: October 2005

In this article, we begin by reviewing the concept of step migration that originated in E. G. Ravenstein's seminal papers “The Laws of Migration” (1885, 1889). As a result of the forces of the Industrial Revolution underway in 19th century Great Britain, migrants moved from farms to villages, from villages to towns, from towns to county seats, and thence to large cities. Throughout much of the industrialization era in the United States, net population movements similarly were upward within the urban hierarchy, and step migration today remains widespread throughout much of the still developing world. Our investigations of recent data and trends, however, suggest that the latest U.S. migration-pattern regime is a strongly contrasting one. Many of the major movements in the system of internal (or domestic) migration are flows down the urban hierarchy, although we note highly differentiated patterns for persons and households at specific stages of the life course. We make use of the newly defined metropolitan and micropolitan Core-Based Statistical Areas (CBSAs) and a seven-level size typology to tabulate origin-destination-specific migration flow data from both Census 2000 and IRS tax-return administrative records for the period 1995-2000. We discuss the causes for net movements being either upward or downward in the national urban hierarchy, including the effects of spatially focused immigration, and movement preferences at various ages, including migration in young adulthood associated with entering and leaving college and the military, as well as moves characteristic of the stages of family formation, childrearing, and retirement.
Mechanisms of classical crystal growth theory explain quartz and silicate dissolution behavior
Authors: Dove Patricia M. , Han Nizhou , De Yoreo James J.
Published: October 2005

The central control of mineral weathering rates on biogeochemical systems has motivated studies of dissolution for more than 50 years. A complete physical picture that explains widely observed variations in dissolution behavior is lacking, and some data show apparent serious inconsistencies that cannot be explained by the largely empirical kinetic “laws.” Here, we show that mineral dissolution can, in fact, be understood through the same mechanistic theory of nucleation developed for mineral growth. In principle, this theory should describe dissolution but has never been tested. By generalizing nucleation rate equations to include dissolution, we arrive at a model that predicts how quartz dissolution processes change with undersaturation from step retreat, to defect-driven and homogeneous etch pit formation. This finding reveals that the “salt effect,” recognized almost 100 years ago, arises from a crossover in dominant nucleation mechanism to greatly increase step density. The theory also explains the dissolution kinetics of major weathering aluminosilicates, kaolinite and K-feldspar. In doing so, it provides a sensible origin of discrepancies reported for the dependence of kaolinite dissolution and growth rates on saturation state by invoking a temperature-activated transition in the nucleation process. Although dissolution by nucleation processes was previously unknown for oxides or silicates, our mechanism-based findings are consistent with recent observations of dissolution (i.e., demineralization) in biological minerals. Nucleation theory may be the missing link to unifying mineral growth and dissolution into a mechanistic and quantitative framework across the continuum of driving force.
Confidentiality and spatially explicit data: Concerns and challenges
Authors: VanWey Leah K. , Rindfuss Ronald R. , Gutmann Myron P. , Entwisle Barbara , Balk Deborah L.
Published: October 2005

Recent theoretical, methodological, and technological advances in the spatial sciences create an opportunity for social scientists to address questions about the reciprocal relationship between context (spatial organization, environment, etc.) and individual behavior. This emerging research community has yet to adequately address the new threats to the confidentiality of respondent data in spatially explicit social survey or census data files, however. This paper presents four sometimes conflicting principles for the conduct of ethical and high-quality science using such data: protection of confidentiality, the social–spatial linkage, data sharing, and data preservation. The conflict among these four principles is particularly evident in the display of spatially explicit data through maps combined with the sharing of tabular data files. This paper reviews these two research activities and shows how current practices favor one of the principles over the others and do not satisfactorily resolve the conflict among them. Maps are indispensable for the display of results but also reveal information on the location of respondents and sampling clusters that can then be used in combination with shared data files to identify respondents. The current practice of sharing modified or incomplete data sets or using data enclaves is not ideal for either the advancement of science or the protection of confidentiality. Further basic research and open debate are needed to advance both understanding of and solutions to this dilemma.
Increase in toxicity of an invasive weed after reassociation with its coevolved herbivore
Authors: Zangerl Arthur R. , Berenbaum May R.
Published: October 2005

The ability of weeds to proliferate into nonindigenous habitats has been attributed to escape from their native natural enemies, allowing reallocation of resources from chemical defense into growth and reproduction. Many invasive weeds, however, eventually encounter their native, coevolved enemies in areas of introduction. Examination of herbarium specimens of an invasive phototoxic European weed,
Pastinaca sativa
, through 152 years reveals phytochemical shifts coincident in time with the accidental introduction of a major herbivore, the parsnip webworm,
Depressaria pastinacella
. Plants collected before the introduction of webworms in North America and during the earliest stages of establishment (1850–1889) are lower in toxic furanocoumarins than all plants subsequently collected in North America and lower than European plant samples collected before 1889. Thus, introduction of a major specialist herbivore can increase noxiousness of a species in its area of introduction, illuminating a potential consequence of classical biocontrol programs involving insect herbivores and poisonous weeds.
Altered cortical glutamatergic and GABAergic signal transmission with glial involvement in depression
Authors: Choudary P. V. , Molnar M. , Evans S. J. , Tomita H. , Li J.Z. , Vawter M. P. , Myers R. M. , Bunney W. E. , Akil H. , Watson S. J. , Jones E. G.
Published: October 2005

Abnormalities in
l
-glutamic acid (glutamate) and GABA signal transmission have been postulated to play a role in depression, but little is known about the underlying molecular determinants and neural mechanisms. Microarray analysis of specific areas of cerebral cortex from individuals who had suffered from major depressive disorder demonstrated significant down-regulation of SLC1A2 and SLC1A3, two key members of the glutamate/neutral amino acid transporter protein family, SLC1. Similarly, expression of
l
-glutamate-ammonia ligase, the enzyme that converts glutamate to nontoxic glutamine was significantly decreased. Together, these changes could elevate levels of extracellular glutamate considerably, which is potentially neurotoxic and can affect the efficiency of glutamate signaling. The astroglial distribution of the two glutamate transporters and
l
-glutamate-ammonia ligase strongly links glia to the pathophysiology of depression and challenges the conventional notion that depression is solely a neuronal disorder. The same cortical areas displayed concomitant up-regulation of several glutamate and GABA
A
receptor subunits, of which GABA
A
α1 and GABA
A
β3 showed selectivity for individuals who had died by suicide, indicating their potential utility as biomarkers of suicidality. These findings point to previously undiscovered molecular underpinnings of the pathophysiology of major depression and offer potentially new pharmacological targets for treating depression.
Large-scale translocation reversal within the thylakoid Tat system in vivo
Authors: Di Cola Alessandra , Robinson Colin
Published: October 2005

In vitro import assays have shown that the thylakoid twin-arginine translocase (Tat) system transports folded proteins in a unidirectional manner. Here, we expressed a natural substrate, pre-23K, and a 23K presequence–green fluorescent protein (GFP) chimera in vivo in tobacco protoplasts. Both are imported into chloroplasts, targeted to the thylakoids, and processed to the mature size by the lumen-facing processing peptidase. However, the vast majority of mature GFP and about half of the 23K are then returned to the stroma. Mutations in the twin-arginine motif block thylakoid targeting and maturation, confirming an involvement of the Tat apparatus. Mutation of the processing site yields membrane-associated intermediate-size protein in vivo, indicating a delayed reversal of translocation to the stroma and suggesting a longer lived interaction with the Tat machinery. We conclude that, in vivo, the Tat system can reject substrates at a late stage in translocation and on a very large scale, indicating the influence of factors that are absent in reconstitution assays.
Activation of GSK-3 and phosphorylation of CRMP2 in transgenic mice expressing APP intracellular domain
Authors: Ryan Kathleen A. , Pimplikar Sanjay W.
Published: October 2005

Amyloid precursor protein (APP), implicated in Alzheimer's disease, is a trans-membrane protein of undetermined function. APP is cleaved by γ-secretase that releases the APP intracellular domain (AICD) in the cytoplasm. In vitro studies have implicated AICD in cell signaling and transcriptional regulation, but its biologic relevance has been uncertain and its in vivo function has not been examined. To investigate its functional role, we generated AICD transgenic mice, and found that AICD causes significant biologic changes in vivo. AICD transgenic mice show activation of glycogen synthase kinase-3β (GSK-3β) and phosphorylation of CRMP2 protein, a GSK-3β substrate that plays a crucial role in Semaphorin3a-mediated axonal guidance. Our data suggest that AICD is biologically relevant, causes significant alterations in cell signaling, and may play a role in axonal elongation or pathfinding.
PIP2 Activates TRPV5 and Releases Its Inhibition by Intracellular Mg2+
Authors: Lee Jason , Cha Seung-Kuy , Sun Tie-Jun , Huang Chou-Long
Published: October 2005

The transient receptor potential type V5 channel (TRPV5) is a Ca2+-selective TRP channel important for epithelial Ca2+ transport. Intracellular Mg2+ causes a fast voltage-dependent block of the TRPV5 channel by binding to the selectivity filter. Here, we report that intracellular Mg2+ binding to the selectivity filter of TRPV5 also causes a slower reversible conformational change leading to channel closure. We further report that PIP2 activates TRPV5. Activation of TRPV5 by PIP2 is independent of Mg2+. Yet, PIP2 decreases sensitivity of the channel to the Mg2+-induced slow inhibition. Mutation of aspartate-542, a critical Mg2+-binding site in the selectivity filter, abolishes Mg2+-induced slow inhibition. PIP2 has no effects on Mg2+-induced voltage-dependent block. Thus, PIP2 prevents the Mg2+-induced conformational change without affecting Mg2+ binding to the selectivity filter. Hydrolysis of PIP2 via receptor activation of phospholipase C sensitizes TRPV5 to the Mg2+-induced slow inhibition. These results provide a novel mechanism for regulation of TRP channels by phospholipase C–activating hormones via alteration of the sensitivity to intracellular Mg2+.