Critical slowing down near the multiferroic phase transition in MnWO4_4

By using broadband dielectric spectroscopy in the radiofrequency and microwave range we studied the magnetoelectric dynamics in the multiferroic chiral antiferromagnet MnWO$_4$. Above the multiferroic phase transition at $T_{N2} \approx 12.6$ K we observe a critical slowing down of the corresponding magnetoelectric fluctuations resembling the soft-mode behavior in canonical ferroelectrics. This electric field driven excitation carries much less spectral weight than ordinary phonon modes. Also the critical slowing down of this mode scales with an exponent larger than one which is expected for magnetic second order phase transition scenarios. Therefore the investigated dynamics have to be interpreted as the softening of an electrically active magnetic excitation, an electromagnon.Comment: 5 pages, 4 figures, appendi

Privacy Concerns and Personality Traits Influencing Online Behavior: A Structural Model

The concept of privacy has proven difficult to analyze because of its subjective nature and susceptibility to psychological and contextual influences. This study challenges the concept of privacy as a valid construct for addressing individuals' concerns regarding online disclosure of personal information, based on the premise that underlying behavioral traits offer a more reliable and temporally stable measure of privacy-oriented behavior than do snapshots of environmentally induced emotional states typically measured by opinion polls. This study investigated the relationship of personality characteristics associated with individuals' general privacy-related behavior to their online privacy behaviors and concerns. Two latent constructs, Functional Privacy Orientation and Online Privacy Orientation, were formulated. Functional Privacy Orientation is defined as a general measure of individuals' perception of control over their privacy. It was measured using the factors General Disclosiveness, Locus of Control, Generalized Trust, Risk Orientation, and Risk Propensity as indicator variables. Online Privacy Orientation is defined as a measure of individuals' perception of control over their privacy in an online environment. It was measured using the factors Willingness to Disclose Online, Level of Privacy Concern, Information Management Privacy Concerns, and Reported Online Disclosure as indicator variables. A survey questionnaire that included two new instruments to measure online disclosure and a willingness to disclose online was used to collect data from a sample of 274 adults. Indicator variables for each of the latent constructs, Functional Privacy Orientation and Online Privacy Orientation, were evaluated using corrected item-total correlations, factor analysis, and coefficient alpha. The measurement models and relationship between Functional Privacy Orientation and Online Privacy Orientation were assessed using exploratory factor analysis and structural equation modeling respectively. The structural model supported the hypothesis that Functional Privacy Orientation significantly influences Online Privacy Orientation. Theoretical, methodological, and practical implications and suggestions for analysis of privacy concerns and behavior are presented

Twentieth Century Geomorphic Changes of the Lower Green River in Canyonlands National Park, Utah: An Investigation of Timing, Magnitude and Process

Since the early 20th century, the Green River, the longest tributary of the Colorado River, has narrowed, decreasing available riparian and aquatic habitat. Initially, the widespread establishment of non-native tamarisk was considered to be the primary driver of channel narrowing. An alternative hypothesis postulated that changes in hydrology drove narrowing. Reductions in total streamflow and changes to flow regime occurred due to wide-spread water development, decreased snowmelt flood magnitude, and the increased cyclicity of wet and dry years. The two hypotheses agree on channel narrowing, but each influences modern river management differently. A tamarisk-driven model of narrowing implies that modern flow management doesn’t substantially affect channel change. Conversely, channel narrowing driven by changes in hydrology implies that present flow management decisions matter and continued adjustments to flow regime may result in future channel change. To understand the roles of decreasing total annual flow, declining annual peak flood magnitude, and changing vegetation communities on 20th century channel narrowing, we investigated channel narrowing along the lower Green River within Canyonlands National Park (CNP). Previous studies agree that the channel has narrowed, however, the rate, timing and magnitude of documented narrowing are only partially understood. Multiple lines of evidence were used to reconstruct the history of channel narrowing in the lower Green River. This study focuses on channel narrowing, but additionally investigated possible changes to channel depth, identified process, timing and magnitude of floodplain formation. Floodplain formation was described in the field using stratigraphy, sedimentology, and dendrogeomorphology exposed in a floodplain trench. Channel and floodplain surveys were conducted to determine possible changes in bed elevation. Additionally, existing aerial imagery, hydrologic data, and sediment transport data were analyzed. These techniques were applied to determine magnitude, timing and processes of channel narrowing at multiple spatial and temporal scales. The floodplain investigation identified a new period of channel narrowing by vertical accretion after high peak flow years of 1983 and 1984. Narrowing was initiated by vertical accretion in the active channel, deposited by moderate floods exceeded more than 50% of the time. Vertical accretion continued in the early 1990s, converting the active channel into a periodically inundated floodplain surface. Suspended-sediment deposition dominated deposits, resulting in the formation of natural levees and floodplain troughs in both inset floodplains. Rates of deposition were highly variable, ranging from 0.03-0.50 m/yr. The lower Green River within Canyonlands National Park has narrowed substantially since the late 1800s, resulting in a narrower channel. Changes to flood magnitude, rate and timing since 1900, driven by increased water storage and diversion in the Green River basin and declines in annual precipitation, were responsible for inset floodplain formation. Floodplains of the contemporary lower Green River in CNP began forming in the late 1930s and continued to form and vertically aggrade in the 20th century by inset floodplain formation. During this time period, peak flow and total runoff declined due to climatic changes and water development. Analysis of aerial imagery covering 61 kilometers (km) of the Green River in CNP shows that changes to the floodplain identified in the trench are representative of the entire study area. The establishment of non-native tamarisk (Tamarix spp.) did not drive channel narrowing, though dense stands stabilized banks and likely promoted sediment deposition. The lower Green River narrowed 12% from 1940-2014, with the majority of narrowing (10% of all narrowing) occurring from the 1980s to the present. Inset floodplain formation reflects changes to flood magnitude and timing resulting from water development and decreases in natural runoff. Findings suggest that long-term management of the riverine corridor within Canyonlands National Park will require a greater focus on upstream flow contributions and how those flows are currently managed. Recovery of endangered endemic native fishes, the Colorado pikeminnow (Ptychocheilus lucius), and the razorback sucker (Xyrauchen texanus), plays a primary role in determining current flow allocations. Collaboration with upstream stakeholders and managers is necessary to maximize elements of the flow regime that preserve channel width and limit channel narrowing

Automated Riverbed Sediment Classification Using Low-Cost Sidescan Sonar

The use of low-cost, low-profile, and highly portable sidescan sonar is on the ascendancy for imaging shallow riverine benthic sediments. A new automated, spatially explicit, and physically-based method for calculating lengthscales of bed texture elements in sidescan echograms (a 2D plot of acoustic intensity as a function of slant range and distance) is suggested. It uses spectral analysis based on the wavelet transform of short sequences of echograms. The recursive application of the transform over small overlapping windows of the echogram provides a robust measure of lengthscales of alternating patterns of strong and weak echoes. This textural lengthscale is not a direct measure of grain size. Rather, it is a statistical representation that integrates over many attributes of bed texture, of which grain size is the most important. The technique is a physically-based means to identify regions of texture within a sidescan echogram, and could provide a basis for objective, automated riverbed sediment classification. Results are evaluated using data from two contrasting riverbed environments: those of the Colorado River in Grand Canyon, Arizona, and the West Branch of the Penobscot River, Maine

Remote terminal system evaluation

An Earth Resources Data Processing System was developed to evaluate the system for training, technology transfer, and data processing. In addition to the five sites included in this project two other sites were connected to the system under separate agreements. The experience of these two sites is discussed. The results of the remote terminal project are documented in seven reports: one from each of the five project sites, Purdue University, and an overview report summarizing the other six reports

Riparian vegetation, Colorado River, and climate: Five decades of spatiotemporal dynamics in the Grand Canyon with river regulation

Documentation of the interacting effects of river regulation and climate on riparian vegetation has typically been limited to small segments of rivers or focused on individual plant species. We examine spatiotemporal variability in riparian vegetation for the Colorado River in Grand Canyon relative to river regulation and climate, over the five decades since completion of the upstream Glen Canyon Dam in 1963. Long-term changes along this highly modified, large segment of the river provide insights for management of similar riparian ecosystems around the world. We analyze vegetation extent based on maps and imagery from eight dates between 1965 and 2009, coupled with the instantaneous hydrograph for the entire period. Analysis confirms a net increase in vegetated area since completion of the dam. Magnitude and timing of such vegetation changes are river stage-dependent. Vegetation expansion is coincident with inundation frequency changes and is unlikely to occur for time periods when inundation frequency exceeds approximately 5%. Vegetation expansion at lower zones of the riparian area is greater during the periods with lower peak and higher base flows, while vegetation at higher zones couples with precipitation patterns and decreases during drought. Short pulses of high flow, such as the controlled floods of the Colorado River in 1996, 2004, and 2008, do not keep vegetation from expanding onto bare sand habitat. Management intended to promote resilience of riparian vegetation must contend with communities that are sensitive to the interacting effects of altered flood regimes and water availability from river and precipitation. å©2015. American Geophysical Union. All Rights Reserved

Geophysics

Contains research objectives and reports on three research projects