The non-random walk of stock prices: The long-term correlation between signs and sizes

We investigate the random walk of prices by developing a simple model relating the properties of the signs and absolute values of individual price changes to the diffusion rate (volatility) of prices at longer time scales. We show that this benchmark model is unable to reproduce the diffusion properties of real prices. Specifically, we find that for one hour intervals this model consistently over-predicts the volatility of real price series by about 70%, and that this effect becomes stronger as the length of the intervals increases. By selectively shuffling some components of the data while preserving others we are able to show that this discrepancy is caused by a subtle but long-range non-contemporaneous correlation between the signs and sizes of individual returns. We conjecture that this is related to the long-memory of transaction signs and the need to enforce market efficiency.Comment: 9 pages, 5 figures, StatPhys2

Adapting the fire-grazing interaction to small pastures in a fragmented landscape for grassland bird conservation

In North America, the loss of habitat heterogeneity resulting from homogeneous livestock grazing is one factor contributing to steep population declines of many grassland bird species. Patch-burn grazing is a management technique that uses historic grassland disturbance as a model to create heterogeneous grassland composition and structure, providing for the diverse habitat requirements of grassland birds. Though this management technique has been used successfully in relatively extensive grasslands, its utility on smaller grassland patches is less clear. We examined the efficacy of patch-burn grazing to restore habitat heterogeneity and increase grassland bird diversity in relatively small pastures (15-32 ha) in a grassland landscape fragmented by cultivation and tree encroachment. In 2006, we established 12 experimental pastures in the Grand River Grasslands of southern Iowa and northern Missouri, with 4 pastures in each of three treatments: 1) patch-burn graze, with spatially discrete fires and free access by cattle (the fire-grazing interaction), 2) graze-and-burn, with free access by cattle and a single burn of the entire pasture every third year, and 3) burn-only, with a single burn of the entire pasture every third year and no grazing. Patch-burn grazing in the first phase of the project (2007-2009) did not generate habitat heterogeneity or significant differences in bird diversity. From 2010 to 2013, stocking rates were reduced to increase residual vegetation in unburned patches at the end of the grazing season to increase heterogeneity. Habitat heterogeneity in patch-burn graze pastures subsequently increased relative to other treatments. Concomitantly, diversity of obligate grassland birds also increased in patch-burn graze pastures and was greatest in 2012 and 2013. We conclude that the fire-grazing interaction can be used to restore habitat heterogeneity and increase grassland bird diversity, even in relatively small grassland patches embedded in a highly fragmented landscape. © 2016 The Society for Range Management. Published by Elsevier Inc.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Synthesis Paper: Assessment of Research on Rangeland Fire as a Management Practice

Rangelands are fire-dependent ecosystems severely altered through direct fire suppression and fuels management. The removal of fire is a dominant cause of ecological sites moving across thresholds with the majority of North American rangelands currently showingmoderate or high departure from reference conditions. Recognizing the need to restore fire on rangelands and incorporate prescribed fire into management plans, the Natural Resource Conservation Service initiated the Conservation Effects Assessment Project (CEAP) to evaluate the validity current practices through peer-reviewed scientific literature. We updated the CEAP review and broadened the discussion of prescribed fire as a global management practice. We reviewed and summarized prescribed fire literature available through Web of Science using search terms in the title. The majority of literature (40%) evaluated plant responses to fire with fire behavior and management (29%), wildlife and arthropods (12%), soils (11%), and air quality (4%) evaluated less frequently. Generally, fire effects on plants are neutral to positive and the majority of negative responses lasted less than 2 years. Similarly, soil responses were recovered within 2 yr after burning. However, most studies did not report how long treatments were in place (62%) or the size of experimental units (52%). The experimental literature supporting prescribed burning is in need of greater managerial relevance that can be obtained by directly addressing spatial scale, temporal scale, and interaction with other disturbances, including drought and grazing. Reliance on information from single fires applied on small plots tracked for a relatively short time interval greatly constrains inferences and application to ecosystem management and information should be applied with caution. Therefore, conservation purposes need to incorporate temporal dynamics to the extent that this information is available. The complex interaction of scientific knowledge, social concerns, and variable policies across regions are major limitations to the successful and critical restoration of fire regimes. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Woody Plant Encroachment Mitigated Differentially by Fire and Herbicide

Woodland expansion is a global phenomenon that, despite receiving substantial attention in recent years, remains poorly understood. Landscape change of this magnitude has several impacts perceived as negative on landscape processes, such as influencing fire regimes, habitat for wildlife, and hydrological processes. In southern Great Plains, Juniperus virginiana has been identified as a major contributor to woodland expansion. Adding to the perplexity of this phenomenon is its evidence on numerous landscape types on several continents, documented under varying climates. Our study aimed to quantify a direct treatment to reduce or slow down woodland expansion in an experimental rangeland in central Oklahoma, United States under three treatments: 1) herbicide, 2) fire with herbicide, and 3) control (no fire, no herbicide) within areas classified as “open grassland” in 1979. Thereafter, we identified these same areas in 2010 with remotely sensed imagery (Light Detection And Ranging) to quantify 1) total encroachment and 2) total encroachment by three size classes: a) small 1 − 2.5 m, b) intermediate 2.5 − 4.5 m and c) tall > 4.5 m. Overall, of the total area classified as grassland in 1979 (277.64 ha), 31% had been encroached by 2010. Encroachment was greatest in the control treatments, followed by herbicide-only treatment application and lowest in the fire and herbicide treatment with minor differences in mean plant height (4.11 m ± 0.28). Encroached areas were mostly dominated by tall individuals (45 ± 3.5%), followed by the intermediate-height class (31.53 ± 1.10%) and the least recorded in the smallest-height class (23.46 ± 2.29%), suggesting expansion occurred during the initial phases of treatment application. The costly practice of herbicide application did not provide a feasible solution to control further woodland expansion. However, when using herbicide with fire, woodland expansion was reduced, highlighting the effectiveness of early intervention by fire in reducing encroachment. This further supports landscape-scale studies highlighting the effect of fire to reduce woodland expansion.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

A hierarchical perspective to woody plant encroachment for conservation of prairie-chickens

Encroachment of Great Plains grasslands by fire-sensitive woody plants is a large-scale, regional process that fragments grassland landscapes. Using prairie grouse (Tympanuchus spp.) of conservation concern,we apply hierarchy theory to demonstrate how regional processes constrain lower-level processes and reduce the success of local management. For example, fire and grazingmanagementmay be locally important to conservation, but the application of fire and grazing disturbances rarely cause irreversible fragmentation of grasslands in the Great Plains. These disturbance processes cause short-term alterations in vegetation conditions that can be positive or negative, but from a long-term perspective fire maintains large tracts of continuous rangelands by limiting woody plant encroachment. Conservation efforts for prairie grouse should be focused on landscape processes that contribute to landscape fragmentation, such as increased dominance of trees or conversion to other land uses. In fact, reliance on localmanagement (e.g.,maintaining vegetation structure) to alter prairie grouse vital rates is less important to grouse population persistence given contemporary landscape level changes. Changing grass height, litter depth, or increasing the cover of forbs may impact a fewremaining prairie-chickens, but itwill not create useable space at a scale relevant to the historic conditions that existed before land conversion and fire suppression.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

A hierarchical perspective to woody plant encroachment for conservation of prairie-chickens

Encroachment of Great Plains grasslands by fire-sensitive woody plants is a large-scale, regional process that fragments grassland landscapes. Using prairie grouse (Tympanuchus spp.) of conservation concern,we apply hierarchy theory to demonstrate how regional processes constrain lower-level processes and reduce the success of local management. For example, fire and grazingmanagementmay be locally important to conservation, but the application of fire and grazing disturbances rarely cause irreversible fragmentation of grasslands in the Great Plains. These disturbance processes cause short-term alterations in vegetation conditions that can be positive or negative, but from a long-term perspective fire maintains large tracts of continuous rangelands by limiting woody plant encroachment. Conservation efforts for prairie grouse should be focused on landscape processes that contribute to landscape fragmentation, such as increased dominance of trees or conversion to other land uses. In fact, reliance on localmanagement (e.g.,maintaining vegetation structure) to alter prairie grouse vital rates is less important to grouse population persistence given contemporary landscape level changes. Changing grass height, litter depth, or increasing the cover of forbs may impact a fewremaining prairie-chickens, but itwill not create useable space at a scale relevant to the historic conditions that existed before land conversion and fire suppression.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Nondestructive Estimation of Standing Crop and Fuel Moisture Content in Tallgrass Prairie

Accurate estimation of standing crop and herbaceous fuel moisture content (FMC) are important for grazing management and wildfire preparedness. Destructive sampling techniques have been used to accurately estimate standing crop and FMC, but those techniques are laborious and time consuming. Existing nondestructive methods for estimating standing crop in tallgrass prairie have limitations, and few studies have examined nondestructive estimation techniques for FMC in this environment. Therefore, our objective was to develop robust models for nondestructive estimation of standing crop and FMC in tallgrass prairie. We calibrated and validated stepwise multiple linear regression (SMLR) and artificial neural network (ANN) models for standing crop and FMC using data collected in tallgrass prairies near Stillwater, Oklahoma. Day of year (DOY), canopy height (CH), Normalized Difference Vegetation Index (NDVI), and percent reflectance in five wavelength bands were candidate input variables for the models. The study spanned two growing seasons and nine patches located within three pastures under patch burn management, and the resulting data set with > 3 000 observations was split randomly with 85% for model calibration and 15% withheld for validation. Standing crop ranged from 0 to 852 g m− 2, and FMC ranged from 0% to 204%. With DOY, CH, and NDVI as predictors, the SMLR model for standing crop produced a root mean squared error (RMSE) of 119 g m− 2 on the validation data, while the RMSE of the corresponding ANN model was 116 g m− 2. With the same predictors, the SMLR model for FMC produced an RMSE of 26.7% compared with 23.8% for the corresponding ANN model. Thus, the ANN models provided better prediction accuracy but at the cost of added computational complexity. Given the large variability in the underlying datasets, the models developed here may prove useful for nondestructive estimation of standing crop and FMC in other similar grassland environments. © 2018 Society for Range ManagementThe Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Understanding the context of network traffic alerts

For the protection of critical infrastructures against complex virus attacks, automated network traffic analysis and deep packet inspection are unavoidable. However, even with the use of network intrusion detection systems, the number of alerts is still too large to analyze manually. In addition, the discovery of domain-specific multi stage viruses (e.g., Advanced Persistent Threats) are typically not captured by a single alert. The result is that security experts are overloaded with low-level technical alerts where they must look for the presence of an APT. In this paper we propose an alert-oriented visual analytics approach for the exploration of network traffic content in multiple contexts. In our approach CoNTA (Contextual analysis of Network Traffic Alerts), experts are supported to discover threats in large alert collections through interactive exploration using selections and attributes of interest. Tight integration between machine learning and visualization enables experts to quickly drill down into the alert collection and report false alerts back to the intrusion detection system. Finally, we show the effectiveness of the approach by applying it on real world and artificial data sets