Dispersed Sources Research Articles

Residues of Persistent Organic Pollutants (POPs) in Agricultural Soils Adjacent to Historical Sources of Their Storage and Distribution-The Case Study of Azerbaijan.

The aim of this study was to identify and examine the levels of organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) in soil collected from the surroundings of historical pesticide storage facilities on former agricultural aerodromes, warehouses, and pesticide distribution sites located in the most important agricultural regions in Azerbaijan. The conducted research included determination of three groups of POPs (occurring together), in the natural soil environment influenced for many years by abiotic and biotic factors that could have caused their transformations or decomposition. In this study, soil samples were collected in 21 georeferenced points located in the administrative area of Bilasuvar, Saatly, Sabirabad, Salyan and Jalilabad districts of Azerbaijan. Soil chemical analysis involved determination of organochlorine compounds (OCP): hexachlorocyclohexanes (HCHs) (three isomers α-HCH, β-HCH and γ-HCH) and dichlorodiphenyltrichloroethanes (DDTs) (six congeners 2,4′DDT; 4,4′DDT; 2,4′DDE; 4,4′DDE; 2,4′DDE; and 4,4′DDE); polycyclic aromatic hydrocarbons (PAHs): 16 compounds from the United States Environmental Protection Agency US EPA list and, PCBs (seven congeners identified with the following IUPAC numbers: 28, 52, 101, 118, 138, 153, and 180). Our research showed that OCPs reached the highest concentration in the studied areas. The total concentrations of OCPs ranged from 0.01 to 21,888 mg∙kg−1 with significantly higher concentrations of Σ6DDTs (0.01 μg kg−1 to 21880 mg kg−1) compared to ΣHCH (0.14 ng kg−1 to 166.72 µg kg−1). The total concentrations of PCBs in the studied soils was varied from 0.02 to 147.30 μg·kg−1 but only PCB138 and PCB180 were detected in all analyzed samples. The concentrations of Σ16 PAHs were also strongly diversified throughout the sampling areas and ranged from 0.15 to 16,026 mg kg−1. The obtained results confirmed that the agricultural soils of Azerbaijan contained much lower (up to by three orders of magnitude) concentrations of PCBs and PAHs than DDT. It is supported by the fact that PCBs and PAHs were not directly used by agriculture sector and their content results from secondary sources, such as combustion and various industrial processes. Moreover, the high concentrations of PAHs in studied soils were associated with their location in direct neighborhood of the airport, as well as with accumulation of contaminants from dispersed sources and long range transport. The high concentrations of pesticides confirm that deposition of parent OCPs have occurred from obsolete pesticide landfills.

Persistent organic pollutants in wood fiber\u2013contaminated sediments from the Baltic Sea

PurposeMany coastal areas in the Baltic Sea are contaminated with wood fiber and pollutants from pulp and paper industries. These anthropogenic, organic-rich, sediments (fiberbanks) have not been characterized and knowledge about their role as secondary sources for dispersal of persistent organic pollutants (POPs) is limited. Hence, the aim of this study was to elucidate the fate of POPs and the relationships between sorption (KD and KTOC), sediment type, and compound hydrophobicity (KOW) in fiber-contaminated sediments.Materials and methodsPaired sediment and pore water samples (n = 24 sites) from three fiber-contaminated areas, located in the Ångermanälven river estuary in northern Sweden, were analyzed for POPs (viz. PCBs, DDT, and HCB) in sediment types representing different fiber content (i.e., fiberbanks, fiber-rich sediments, and natural less fiber impacted sediments). The freely dissolved concentration in sediment pore water was determined by sediment-polyoxymethylene (POM) partitioning. Instrumental analysis was performed using gas chromatography coupled to a triple quadrupole mass spectrometer (GC-MS/MS).Results and discussionHigher levels of total organic carbon (TOC) were found in the fiberbank sediment (range 8.6–37%) than in fiber-rich sediment (range 2.0–6.5%) and more natural sediment (range 2.0–2.9%). The sediment concentrations of POPs (dry weight basis) were also found to be significantly (p < 0.05) elevated in fiberbanks compared to the other sediment types. The fraction of DDD (48–66% of Σ6DDX) was larger in fiberbanks than in the other sediment types, likely due to anoxic conditions favoring reductive dechlorination of DDT. When sediment levels were normalized to TOC, HCB displayed similar levels across sediment type, suggesting a more diffuse source pattern than for PCB and DDT. Although significantly higher sorption (KD) of POPs was observed in fiberbanks, pore water levels were still elevated due to high bulk concentrations.ConclusionsThis study shows that fiberbanks are coastal hot spots for POPs in the Baltic Sea and that the levels are of ecotoxicological concern. Although the POPs are more strongly sorbed (KD) to this type of organic rich sediment, the high pore water concentrations in fiberbanks compared to the other sediment types investigated show that the risk of contaminant dispersal via pore water is elevated for fiberbanks.

Practical Applications of Sources of Return Dispersion in Alternative Risk Premia

Practical Applications In Sources of Return Dispersion in Alternative Risk Premia from the Spring 2020 issue of The Journal of Alternative Investments, author David E. Kuenzi of AlphaSimplex Group identifies eight factors that drive differences in performance (i.e., return dispersion) among investment funds that use the same alternative risk premia (ARP) strategy. ARP strategies attempt to realize sustained returns that are not correlated with the underlying markets in which they invest. But even though each ARP strategy has a clear set of rules, there is significant return dispersion among different ARP funds that use the same strategy. The author says this happens because different fund managers implement the same strategy differently. He identifies eight specific drivers of such differences in implementation, and ranks them in order of importance. He then demonstrates that altering just two such factors can cause dramatic return dispersion. Kuenzi says the most important drivers of differences in strategy implementation—and therefore, of return dispersion—are investment firms’ different histories, philosophies, and core competencies. He recommends that investors learn about the history and culture of each firm to gain an understanding of how its fund managers are likely to implement any ARP strategy.

Optimizing an LED array for an infrared illumination source using the near field for venous pattern detection.

Accuracy in vein detection is important for intravenous applications such as venipuncture and other medical procedures. The near-infrared (NIR) imaging technique is used to visualize veins based on the difference of absorption of the infrared light by the oxyhemoglobin present in the blood and surrounding tissue. A problem commonly found during the visualization of veins is attributed to the source of light, saturation, low contrast, and dispersion, which are causes of inhomogeneous illumination. In this work, the design and implementation of a light source with LEDs in the range of 750-860 nm are presented. To obtain the design, a numerical simulation was made using the near-field diffraction theory to obtain homogeneous illumination at 40 cm of the sample, with a radial arrangement of three concentric LED rings. With the developed light source, an experimental scheme for the acquisition of vein patterns was implemented. Using a basic algorithm for the identification of intravenous patterns, a prototype was obtained that we believe can be used in intravenous applications and other medical procedures.

Metals and PFAS in stormwater and surface runoff in a semi-arid Canadian city subject to large variations in temperature among seasons.

Because compounds accumulate through dry periods and enter aquatic systems in just a few seasonal events such as snowmelt and summer storms, surface waters in semi-arid, cold regions, such as the Canadian Prairies, are particularly vulnerable to loading of contaminant from runoff events from surfaces. This study assessed concentrations of metals and selected trace organics entering a river via surface runoff from an urban region and how these semi-arid regions with large seasonal variations in temperature might differ from more temperate regions. Selected potentially harmful elements (PHEs) including, Mn with Cr, Cu, Zn, Ba and U all exceeded guideline discharge values set by the Canadian Council of the Ministers of the Environment (CCME) by as much as 16-fold. Variation among discharges during spring, summer and winter was observed. For example, across the whole city, an estimated 6kg of zinc was discharged in a spring storm, 36kg in a summer storm and 17tonnes in snowmelt. The mass of Zn discharged is similar to the annual loading estimated for Stockholm, Sweden, but in Saskatoon, Saskatchewan, Canada, the bulk of runoff was during snowmelt. The mean sum of poly- and per-fluoroalkyl substances (PFAS)in stormwater was 9.0ngL-1, which is consistent with concentrations observed in other Canadian cities (6.5-16ngL-1). These concentrations of PFAS are likely due to dispersed sources and orders of magnitude less than thresholds for toxicity to fish and aquatic invertebrates.

Recognition of Landscape Key Areas in a Coal Mine Area of a Semi-Arid Steppe in China: A Case Study of Yimin Open-Pit Coal Mine

The ecological integrity and biodiversity of steppes were destroyed under the long-term and high-intensity development of open-pit coal mines in China, causing desertification, steppe degradation, landscape function defect, and so on. As a source of species maintenance and dispersal, an ecological source is a key area for preservation in order to restore the ecological security pattern of the larger landscape. The purpose of this study was to establish a landscape key area recognition model to identify the landscape key areas (LKA) surrounding an open pit coalmine located in semi-arid steppe. This study takes the Yimin open pit mining area as a case study. We assessed Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager (OLI) remote sensing images taken during the peak season of vegetation growth from July to August in 1999, 2006, 2011, and 2017. From these images, we identified the main landscape types and vegetation coverage grades in order to identify the ecological land. Next, we applied the three indices of Importance of Patch Connectivity, Habitat Quality, and Ecosystem Service Value to calculate the comprehensive results that identify ecological land. Finally, the ecological land quality results of different years are superimposed and averaged, and then Very Important Patch (VIMP), Important Patch (IMP), and General Patch (GEP) areas were used for LKA extraction. Our results showed LKA to cover 177.35 km2, accounting for 20.01% of the total study area. The landscape types identified as LKA are primarily grassland (47.37%), wetland (40.27%), and shrubland (11.88%), indicating that landscape type correlates strongly with its value as a landscape key area. The proposed landscape key area recognition model could enrich the foundations for ecological planning and ecological security pattern construction in order to support ecological protection and restoration in semi-arid steppe areas affected by coal mining.

HIV persists throughout deep tissues with repopulation from multiple anatomical sources.

BACKGROUNDUnderstanding HIV dynamics across the human body is important for cure efforts. This goal has been hampered by technical difficulties and the challenge of obtaining fresh tissues.METHODSThis observational study evaluated 6 individuals with HIV (n = 4 with viral suppression using antiretroviral [ART] therapy; n = 2 with rebound viremia after stopping ART), who provided serial blood samples before death and their bodies for rapid autopsy. HIV reservoirs were characterized by digital droplet PCR, single-genome amplification, and sequencing of full-length (FL) envelope HIV. Phylogeographic methods were used to reconstruct HIV spread, and generalized linear models were tested for viral factors associated with dispersal.RESULTSAcross participants, HIV DNA levels varied from approximately 0 to 659 copies/106 cells (IQR: 22.9-126.5). A total of 605 intact FL env sequences were recovered in antemortem blood cells and across 28 tissues (IQR: 5-9). Sequence analysis showed (a) the emergence of large, identical, intact HIV RNA populations in blood after cessation of therapy, which repopulated tissues throughout the body; (b) that multiple sites acted as hubs for HIV dissemination but that blood and lymphoid tissues were the main source; (c) that viral exchanges occurred within brain areas and across the blood-brain barrier; and (d) that migration was associated with low HIV divergence between sites and greater diversity at the recipient site.CONCLUSIONHIV reservoirs persisted in all deep tissues, and blood was the main source of dispersal. This may explain why eliminating HIV susceptibility in circulating T cells via bone marrow transplants allowed some individuals with HIV to experience therapy-free remission, even though deeper tissue reservoirs were not targeted.TRIAL REGISTRATIONNot applicable.FUNDINGNIH grants P01 AI31385, P30 AI036214, AI131971-01, AI120009AI036214, HD094646, AI027763, AI134295, and AI68636.

The origins of dengue and chikungunya viruses in Ecuador following increased migration from Venezuela and Colombia

BackgroundIn recent years, Ecuador and other South American countries have experienced an increase in arboviral diseases. A rise in dengue infections was followed by introductions of chikungunya and Zika, two viruses never before seen in many of these areas. Furthermore, the latest socioeconomic and political instability in Venezuela and the mass migration of its population into the neighboring countries has given rise to concerns of infectious disease spillover and escalation of arboviral spread in the region.ResultsWe performed phylogeographic analyses of dengue (DENV) and chikungunya (CHIKV) virus genomes sampled from a surveillance site in Ecuador in 2014–2015, along with genomes from the surrounding countries. Our results revealed at least two introductions of DENV, in 2011 and late 2013, that initially originated from Venezuela and/or Colombia. The introductions were subsequent to increases in the influx of Venezuelan and Colombian citizens into Ecuador, which in 2013 were 343% and 214% higher than in 2009, respectively. However, we show that Venezuela has historically been an important source of DENV dispersal in this region, even before the massive exodus of its population, suggesting already established paths of viral distribution. Like DENV, CHIKV was introduced into Ecuador at multiple time points in 2013–2014, but unlike DENV, these introductions were associated with the Caribbean. Our findings indicated no direct CHIKV connection between Ecuador, Colombia, and Venezuela as of 2015, suggesting that CHIKV was, at this point, not following the paths of DENV spread.ConclusionOur results reveal that Ecuador is vulnerable to arbovirus import from many geographic locations, emphasizing the need of continued surveillance and more diversified prevention strategies. Importantly, increase in human movement along established paths of viral dissemination, combined with regional outbreaks and epidemics, may facilitate viral spread and lead to novel virus introductions. Thus, strengthening infectious disease surveillance and control along migration routes and improving access to healthcare for the vulnerable populations is of utmost importance.

Sources of Return Dispersion in Alternative Risk Premia

The author qualitatively identifies eight sources of potential return dispersion across portfolios of risk premia strategies, including strategy inclusion, amount of systematic risk, instrument choices, parameter choices, instrument weighting mechanisms, data choices, execution timing/execution processes, and level of crowding in the strategies employed. The author then performs simulation analysis that shows that returns of simulated portfolios can be quite different from one another as a result of altering just a few of the sources of risk premia return dispersion. Although others have noted the return dispersion of risk premia providers, the author’s contribution is to provide an initial taxonomy of the drivers of this dispersion as well as an analysis that helps to make these ideas more concrete. <b>TOPICS:</b>Real assets/alternative investments/private equity, analysis of individual factors/risk premia, statistical methods, performance measurement <b>Key Findings</b> • Alternative risk premia (ARP) portfolios and indexes tend to perform very differently from one another, with low correlations and substantial return differentials, despite being similar in name and broad investment approach. This renders ARP funds difficult to compare, analyze, and benchmark. • The sources of return dispersion generally fall into eight categories. Analysis of ARP managers along these dimensions may be useful in determining how and why return streams of particular managers differ. This taxonomy may also be helpful in determining which ARP managers are most suitable for a given investor. • ARP strategy implementation matters, and there is no substitute for a more nuanced understanding of the potential offerings in the space.

ОПРЕДЕЛЕНИЕ МИНИМАЛЬНОЙ ВЫСОТЫ ИСТОЧНИКА ВЫБРОСОВ ИЗ КАМЕРЫ ПРИ СУШКЕ ДРЕВЕСИНЫ БУКА

The process of chamber drying of wood is accompanied by a prolonged exposure to wood of heat and moisture. As a result of this effect, the ligno-carbohydrate complex of wood decomposes with the release of various harmful substances, the most dangerous are furfural and formaldehyde. The amount of furfural and formaldehyde in the spent drying agent depends on the initial moisture content of the wood, duration and drying mode. The degree of environmental impact of harmful substances depends on the drying regime, the height of the release of the drying agent from the chamber, and environmental conditions. The low emission height of the spent drying agent with harmful substances leads to exceeding the maximum permissible concentration of harmful substances in the surface layer. Therefore, the aim of research is to reduce the concentration of furfural and formaldehyde in the surface layer. The studies were carried out on beech wood growing in the Krasnodar region. It was found that the maximum amount of furfural and formaldehyde is released from beech wood during drying by mild conditions. The largest amount of harmful substances is released from beech wood in the first stage, when free moisture is removed, regardless of the drying mode. It is possible to lower the value of near-ground concentration at the border of the sanitary zone by correctly choosing the height of the source of dispersion of harmful substances. The work determines the height of the source of emissions of harmful substances from the drying chamber, depending on the drying regime of beech wood and climatic environmental conditions. In the warm season and at dangerous wind speeds (less than 1 m / s), the height of the source of emission during drying of beech wood should be the greatest, in the cold - the smallest. Based on the studies performed, recommendations are given for the placement of exhaust pipes and their heights for drying chambers, taking into account the volume of simultaneously dried wood.

Research Progress of University Psychology Based on Big Data------discovery, challenges and opportunities

Big-Data, also known as mass data, refers to a large scale of data involved, which can not be intercepted, managed, processed and collated into information that can be interpreted by human beings in a reasonable time1. It is widely believed that big data only refers to that the scale of data is large. In fact, this is not the case. Big data needs to meet three characteristics: large capacity, fast speed, and rich types. Only when these three conditions are met concurrently can it be called big data2.The Outline for the Promotion of Big Data Development issued by the State Council in 2015 defines big data as follows: Big data is a collection of data characterized by large capacity, multiple types, fast access speed, and high application value. It is developing rapidly to be the new-generation information technology and service industry that collects, stores and correlates large amounts of data with dispersed sources and diverse formats, so as to discover new knowledge, create new value, and enhance new capabilities3.

Semi‐idealized simulations of wintertime flows and pollutant transport in an Alpine valley. Part II: Passive tracer tracking

AbstractUnder wintertime quiescent conditions, thermally driven circulations represent one of the only sources of tracer dispersion over mountainous terrain. Those circulations can be unequally developed at a valley scale since they strongly depend on local morphological arrangement. At the same time, very heterogeneous pollutant distribution can be observed, as for instance in a French Alpine basin located in the Arve River valley. This complex basin regularly shows large variations in pollutant concentrations with certain sectors suffering from poor wintertime air quality. On the other hand, the surrounding tributary valleys appear to be less affected, suggesting that the basin local dynamics may participate in pollutant trapping. The present study intends to classify the pollutant transport mechanisms in terms of efficiency and to identify the most dynamically vulnerable atmospheric volumes regarding pollutant accumulation. This is achieved through a set of semi‐idealized high‐resolution numerical simulations reproducing a full diurnal cycle with passive tracers released continuously at a constant rate. The model is used as a laboratory in order to quantify the influence of several processes on transport mechanism efficiency. This approach underlines the high efficiency of vertical transport by anabatic winds while horizontal transport efficiency by up‐valley wind systems remains weak, leaving the surrounding tributary valleys almost unaffected by the basin pollution during daytime. At night, the efficiency of horizontal transport by the down‐valley wind systems depends on the tracer source location within the basin. In addition, the tracers emitted within the tributary valleys do not reach the basin bottom because of thermal stratification and local morphological arrangement but rather degrade the air quality of mid‐altitude villages lying along the basin sidewalls.

Polarization-dependent relative intensity noise of fiber supercontinuum sources

Detailed experimental polarization-dependent relative intensity noise (RIN) measurements of all-normal dispersion (ANDi) and conventional supercontinuum (SC) sources are presented. We show that the polarization-maintaining ANDi fiber suppresses polarization noise, is robust against pump polarization fluctua- tions, and allows ultra-low noise SC generation with RIN identi- cal to the pump laser (< 0.05%).

The use of wave power plants in water management for combating the greenhouse effect

Nowadays, the development of the greenhouse effect is caused not only by industrial facilities emissions into the atmosphere. The contribution of natural and anthropogenic sources of greenhouse gas emissions is becoming increasingly significant. For example, the amount of carbon dioxide produced by the decomposition of organic substances in the zones of degradation of permafrost increases every year. The contribution of the total emission of numerous dispersed sources of atmospheric pollution is also very significant. Traditional methods of control and limitation of greenhouse gas emissions in this case are irrevocable. The solution of the problem is possible only on the basis of the creation of controlled natural and technical systems. The task for the systems is to organize the flow of greenhouse gases from the atmosphere and carbon fixing in the stable components of the environment. The main area of this activity is the stimulation of bioproduction processes. This task is difficult to accomplish in the field of agricultural production. The main objective of the development of this industry is to meet the growing shortage of food products. Against the background of the threat of mass starvation in a number of regions of the world, the problem of the greenhouse effect loses its relevance.

Facilitated adaptation for conservation – Can gene editing save Hawaii's endangered birds from climate driven avian malaria?

Avian malaria has played a significant role in causing extinctions, population declines, and limiting the elevational distribution of Hawaiian honeycreepers. Most threatened and endangered honeycreepers only exist in high-elevation forests where the risk of malaria infection is limited. Because Culex mosquito vectors and avian malaria dynamics are strongly influenced by temperature and rainfall, future climate change is predicted to expand malaria infection to high-elevation forests and intensify malaria infection at lower elevations, likely resulting in future extinctions and loss of avian biodiversity in Hawaii. Novel, landscape-level mosquito control strategies are promising, but are logistically challenging and require costly long-term efforts. As an alternative or supplemental strategy, we evaluated the potential of releasing a gene-edited malaria-resistant honeycreeper (Iiwi, Drepanis coccinea) in Hawaiian rainforests; a strategy known as facilitated adaptation. While this approach also has significant technical challenges and costs, it may offer a more permanent solution to increasing malaria threats. If malaria-resistant honeycreepers can be developed, facilitated adaptation may provide a practical strategy for the reestablishment of abundant avian populations in Hawaiian forests. A successful strategy could be the release of malaria-resistant Iiwi in mid-elevation forests where development of a resistant population has the best chance of success. Establishment of a resistant Iiwi population could provide a source for dispersal and development of resistant populations in high-elevation forests and a permanent source of resistant individuals for translocation to other vulnerable areas.

Вдосконалення способів виконання захистів ліній зв’язку з підстанціями розосереджених джерел генерації

The article deals with the problems of using relay protection of power lines. Attention is paid to the peculiarities of the operation of protection under different modes of operation of these lines, namely: normal, post-accident and scheduled repair. The protection of two-sided power lines that connect individual local power plants to powerful electrical systems, including dispersed generation sources, local systems, and dispersed generation sources, must meet the general requirements of providing the required sensitivity, selectivity for various types of damage. Difficulties in providing the required sensitivity when using maximum current protections on such lines are associated with low levels of short-circuit currents from dispersed generation sources and local electrical systems. The features of the relay protection performance in redundant power supply of consumers using dispersed generation sources are given. The maximum operating current of the line consumed from the electrical system is 2 - 3 times the rated current, which is determined by the power of the generators of the dispersed sources of generation. In this case, the short-circuit currents from the low-power generators of the dispersed sources of generation are proportional to the maximum operating currents of the line. On double-sided power lines that connect local systems and dispersed power sources to a high-power electrical system, maximum current directional protection provides selectivity and are the main types of protection for such lines. Key words: power supply, relay protection, reclosers, sectionalizers, distributed sources of generation, short circuit, sectioning, selectivity

IMPROVING THE DYNAMICS OF AN INVERTER-BASED PV GENERATOR DURING LOAD DUMPS

In distribution power grids supplied by dispersed power sources, for example RES (Renewable Energy Sources), in the event of a load dump, unexpected transient states may appear. These states involve a dangerous increase in voltage or current. This situation may lead to the disconnection of these sources. To prevent this phenomenon, a non-linear anti-windup regulator with a conditional integrator has been proposed. This solution allows a significant improvement of the generator’s dynamic properties both at load dump and on return to full load.

Online Nuclear Emergency Response System (ONERS) for consequence assessment and decision support in the early phase of nuclear accidents - Simulations for postulated events and methodology validation

Online Nuclear Emergency Response System (ONERS) is a comprehensive Decision Support System developed using Open source WebGIS (Geographical Information System) technologies for management of Off-Site Nuclear Emergencies for Nuclear Power Plant sites of India. The system is based on numerical meteorological and dispersion models, weather data and source term estimation using environmental radiation monitors. It simulates the pattern of atmospheric dispersion, concentration, radioactivity fallout, and radiation dose profiles in various pathways around the affected site. The system projects the current and future radiological scenario along with geographical and demographic information and simulates the consequences of atmospheric releases on population by spatial analysis. It also computes counter measures using national regulatory guidelines for suggestion of protective actions to decision makers and first responders. This work presents the salient features of the ONERS, its monitoring network and utility. The methodology of dose projections is tested by performing simulations for a postulated accident and the effectiveness of the system for decision making during emergency scenarios is illustrated for a hypothetical scenario.

Firm dispersion and total factor productivity: Are Norwegian salmon producers less efficient over time?

The Norwegian salmon farming sector has experienced an increase in industry concentration for the last 20 years attributed to agglomeration externalities and scale economies; big firms increase their size and market share while small firms remain operating at the minimum level. However, small firms have higher profitability ratios than their bigger counterparts, a fact that contradicts economic theory as less efficient firms (and less profitable) will not grow and eventually will disappear. This paper quantifies the role of idiosyncratic demand and distortions on observed productivity differences across Norwegian salmon producers from 2001 to 2016. By using a data set that measures directly firm-level quantities, prices and sales, it is possible to break down the sources of total factor productivity dispersion on technical inefficiency and firm fundamentals. The understanding of total factor productivity (TFP) dispersion is useful as micro-productivity changes can point out aggregate productivity movements that matter on industrial and macroeconomic policies.

Self-consistent and squirt flow modelling of velocity dispersion and attenuation for effective-stress dependent experimental data

ABSTRACTWe evaluate acoustic scattering and Wave Induced Fluid Flow (WIFF) mechanisms as a source of velocity dispersion in experimental compressional P- and shear S- waves. The latter was carried out by implementing the Self Consistent (SC) approach and the Chapmańs squirt flow model over a data set consisting of frequency- and pressure dependent velocities obtained by Sothcott, McCann, and O'Hara (2000, The influence of two different pore fluids on the acoustic properties of reservoir sandstones at sonic and ultrasonic frequencies. 70th SEG Meeting, Expanded s, 1883–1886) on brine saturated Clashach sandstones. Modelled velocities are further used to estimate attenuation values for both P- and S- waves. Error estimation between experimental data and theoretical modelling suggest that WIFF is the main mechanism in defining dispersion and attenuation on the studied samples.