High Degree Of Fragmentation Research Articles

A study of a pine bark humification process

A study of the biodegradation process of pine bark under natural and laboratory conditions was carried out. It was found that humification of bark under natural conditions with a high degree of fragmentation is characterised by a more favourable C:N. After 18 months of the composting process, there was a reduction in organic matter content to 56.0%. In the pine bark composted under natural conditions, the heavy metals Pb, Ni, Cd, and Cr were present in trace amounts, with concentrations many times below the level of allowable contaminants. The composting process of pine bark with urea and ammonia water, carried out under laboratory conditions, had a positive effect on lowering the C:N ratio, while significantly shortening the humification process.

Exploring data use in nonprofit organizations

Organizations around the world have increasingly employed data for a variety of purposes, and nonprofit organizations are no exception. This article reviews the use of data in nonprofit organizations, including the types of data collected and accessed, the motivations for data capture, and the barriers to systematic use of data. The literature shows that nonprofit organizations capture a variety of data, including public and financial data, performance measures, program evaluation data, and volunteer information. Organizations use these with diverse motivations such as program or organizational improvement, marketing, and accountability. Prominent barriers faced by organizations include challenges in identifying meaningful information, lack of technical ability, inability to prioritize data work, as well as external influences. The article highlights the challenges in synthesizing the available literature, with a high degree of fragmentation, including research from distinct intellectual traditions resulting in many disconnected constructs, measurements, and theories. Finally, the paper discusses challenges in the study of nonprofit data use and strives to provide guidance for future inquiry.

A social network analysis of interlocking directorates in the accommodation sector

PurposeBy adopting network analytic techniques, this paper aims to examine interlocking directorates among firms operating in the hospitality services sector in seven major Italian tourism destinations.Design/methodology/approachThe authors collected information for all the hotel corporations whose headquarters are located in the seven top Italian destinations: Florence, Milan, Naples, Rimini, Rome, Turin and Venice. Data come from the Analisi Informatizzata delle Aziende Italiane database by Bureau Van Dijk and were used to build a network where the nodes are board members (people) and corporations (hotels) and the links represent the membership of individuals in the boards. From this, with a one-mode projection, the authors obtain two networks: people and corporations. The overall networks’ structures are analysed by assessing their connectivity characteristics.FindingsThe findings indicate a relatively low number of interlocks that signals a high degree of fragmentation, showing that the interconnections (both within and between destinations) are scarce. This suggests that in absence of formalized cooperation arrangements, corporations might collaborate informally.Research limitations/implicationsThis work extends previous research on complexity in business settings, focusing specifically on service companies whose output depends on multiple interactions and helps clarifying coopetition practices of hospitality service firms. Policymaking perspectives are discussed as well as managerial viewpoints.Originality/valueNot many studies of the interlocking directorates in the hospitality domain exist. This paper uses network analysis for a better understanding of the cooperative practices and the formal social structures of the Italian hospitality industry and derives a series of implications important for both researchers and practitioners while also looking at potential future studies.

A novel numerical approach for rock slide blocking river based on the CEFDEM model: A case study from the Samaoding paleolandslide blocking river event

To better understand the dynamic process of rock avalanches blocking rivers, a novel numerical approach based on the coupled Eulerian-finite-discrete element method (CEFDEM) is proposed. The Samaoding paleolandslide blocking river event, which occurred at the upstream of the Jinsha River was used as a case study to further validate the new numerical approach. Field investigations, thermoluminescence dating, and geomorphological analysis were conducted to determine basic geological conditions and provide data for the numerical simulations. Then a calibrated 3D landslide blocking river simulation based on the CEFDEM was conducted. The landslide blocking river lasted for 70 s and landslide scale from the numerical simulation agrees well with the field investigation. The maximum overall feature speed of the entire sliding mass is 35 m/s, while part of the sliding mass can reach 69 m/s. Dynamic fragmentation of the rock slide is stratified such that the bottom of the sliding body has higher fragmentation degree than the top. The variation of kinetic energy, accumulated friction dissipation, and fracture energy of the sliding mass are also shown. The impulsive water wave is triggered immediately after sliding mass runs into river, and its maximum height is 132 m, while part of the wave can reach a speed of 64 m/s. The river water will be pushed by the subsequent sliding mass movement. A comparison of the CEFDEM model and particle flow code (PFC) model in landslide blocking river was conducted, and the advantages and limitations of CEFDEM model were discussed in detail.

Analysis of Landscape Characteristics and Influencing Factors of Residential Areas on the Qinghai-Tibet Plateau: A Case Study of Tibet, China.

The Qinghai-Tibet Plateau is the largest ecological barrier and one of the most vulnerable areas of the ecological environmental system. However, the increasing frequency of human activities in the Qinghai-Tibet Plateau has led to strong interference. Residential areas are the main places in which human activities are carried out and, as such, can effectively reflect the intensity of activities. Based on this, this research takes the Tibet Autonomous Region as the study area and analyzes the distribution characteristics of Tibetan residential areas using Zipf's law and various landscape indices, as well as discussing the influences of altitude, hydrology, ecological environment, and location on residential area distribution. The obtained results indicate the following: (1) The residential areas in Tibet basically conform to the rank-size principle. The residential areas in central and northwest Tibet are concentrated in size distribution, and the relatively large residential areas are prominent, while the residential areas in the eastern Hengduan mountain region are relatively balanced in size distribution. (2) The landscape index results demonstrate that the counties with an unbalanced distribution of residential areas are mainly concentrated in the northwest of Tibet, while the residential areas in the counties and regions where the administrative stations of each prefecture-level city (or region) are located tend to present a polarization phenomenon, with large patches. The area distribution of residential areas showed a "medium-high-low" pattern from southeast to northwest. The residential areas in eastern Tibet have a high degree of fragmentation and a low degree of aggregation, while the residential areas in northwest Tibet have a low degree of fragmentation and a relatively high degree of aggregation. (3) The residential areas in Tibet are most concentrated in the altitude range of 3000-5000 m above sea level and their water affinity and road-affinity are strong, with the distribution of residential areas within 500 m of roads and water networks accounting for more than one-quarter. The vegetation coverage in the residential areas is low, inconsistent with the surface vegetation coverage rate over the whole of Tibet.

Correlations between the hydrological regime and the morphodynamic processes in the Gilort river basin

This study highlights the relationship between the dynamics of the hydrological regime in a river basin and the morphodynamic potential that appears in the context of increasing frequency and intensity of current climatic phenomena. Climate change characterized by the high frequency and intensity of torrential rains and floods, especially in the last decade, with a maximum amplitude in the summer months (June-July), alternating with periods of drought have brought to a series of geomorphological changes in the Gilort river basin. These processes are amplified by the high degree of fragmentation of the relief, by the presence of springs that feed the hydrographic network and by the important rainfall contribution to the formation of river flows. In the high mountainous area of the basin, there are a series of debris flows that have been triggered in the last ten years, during torrential rains and exceptional floods, by major changes in the land cover and by the transport of materials in the drainage section. At the exit of the mountain, the longitudinal profile of the river changes radically with the decrease of the slope, so that most of the coarse alluvium is deposited in the riverbed in the sectors of the contact depressions at the foot of the mountain. At the contact between the mountains and the Subcarpathian Depression, due to a pronounced decrease of the riverbed slope, the phenomenon of bed aggradation occurs. In this study, all these geomorphological processes are explained from the perspective of hydrological and climatic influence combined with changes in land cover.

Analysis of the Impact of Landscape Patterns on Urban Heat Islands: A Case Study of Chengdu, China.

The urbanization process, such as population growth and the expansion of roads, railways, residential areas, and industrial areas, causes severe landscape fragmentation and changes in the surface temperature balance, resulting in the heat island effect. This study used Landsat data to study the impact of landscape patterns on urban heat islands (UHIs) and temporal-spatial change characteristics. In addition, spatial correlation analysis was employed to detect the relationships between land surface temperature (LST) and landscape patterns. The results showed that the impervious surfaces landscape area increased significantly, and the Woodland landscape area increased. However, the bare land, cropland, and water body area decreased. The cohesion of cropland and woodland landscape in the suburb decreased, and there was a high degree of fragmentation. The difference between the contributions of the central city and suburbs to the whole region is narrowing, and the expansion of urban heat islands is shifting from the central city to the suburbs. The percentage of landscape index (PLAND) and the patch cohesion index (COHESION) of woodland, water body, and cropland were negatively correlated with LST. Meanwhile, the PLAND and COHESION of impervious surface and bare land were positively correlated with LST, and the splitting index (SPLIT) was the opposite of the PLAND and COHESION. The fragmentation of impervious surfaces and bare land landscapes reduces the UHI effect. Based on these results, countermeasures to mitigate the heat island effect are proposed. These measures will play an essential role in improving urban ecology and the environmental quality of human settlements.

Spatial Patterns of Ceroxylon parvifrons (Engel) H.Wendl of the Montane Forests in Southern Ecuador

The species of the genus Ceroxylon have narrow geographical ranges, and subsequently, their populations are subjected to a high degree of fragmentation due to deforestation and land conversion. Ceroxylon parvifrons (Engel) H. Wendl is a representative floristic species of the Andean rainforest; however, little information related to its natural history, ecology, biology, and conservation status is available, making it difficult to assess its biological relationship with the environmental factors and the current status of their populations in natural environments. Here, we studied the spatial pattern of adults, rosettes, and seedlings of C. parvifrons in the montane rainforest and assessed the role of populations’ spatial structure and intraspecific interactions on plant performance. A total of 460 individuals were categorized according to their size, with 11 adults, 10 juveniles, 336 rosettes, and 103 seedlings being recorded. C. parvifrons showed that the population is expanding during the first two stages of the plant (seedling and rosette). After this, there is a significant decrease where the frequency of individuals of the juvenile and adult categories tend to disappear from the population. The L (r) function shows a robust clustering throughout the entire scale for seedlings, rosettes, and adult palms. Also, the Poisson cluster process describes a patchy distribution in which plant individuals are distributed in clumps (clusters). Thus, this approximation related to spatial patterns of C. parvifrons will provide an important step for the conservation of this species in tropical zones.

Untargeted region of interest selection for gas chromatography – mass spectrometry data using a pseudo F-ratio moving window

There are many challenges associated with analysing gas chromatography - mass spectrometry (GC–MS) data. Many of these challenges stem from the fact that electron ionization (EI) can make it difficult to recover molecular information due to the high degree of fragmentation with concomitant loss of molecular ion signal. With GC–MS data there are often many common fragment ions shared among closely-eluting peaks, necessitating sophisticated methods for analysis. Some of these methods are fully automated, but make some assumptions about the data which can introduce artifacts during the analysis. Chemometric methods such as Multivariate Curve Resolution (MCR), or Parallel Factor Analysis (PARAFAC/PARAFAC2) are particularly attractive, since they are flexible and make relatively few assumptions about the data - ideally resulting in fewer artifacts. These methods do require expert user intervention to determine the most relevant regions of interest and an appropriate number of components, k, for each region. Automated region of interest selection is needed to permit automated batch processing of chromatographic data with advanced signal deconvolution. Here, we propose a new method for automated, untargeted region of interest selection that accounts for the multivariate information present in GC–MS data to select regions of interest based on the ratio of the squared first, and second singular values from the Singular Value Decomposition (SVD) of a window that moves across the chromatogram. Assuming that the first singular value accounts largely for signal, and that the second singular value accounts largely for noise, it is possible to interpret the relationship between these two values as a probabilistic distribution of Fisher Ratios. The sensitivity of the algorithm was tested by investigating the concentration at which the algorithm can no longer pick out chromatographic regions known to contain signal. The algorithm achieved detection of features in a GC–MS chromatogram at concentrations below 10 pg on-column. The resultant probabilities can be interpreted as regions that contain features of interest.

Insights into the differential fragmentation processes in rock avalanche emplacement from field investigation and experimental study

Fragmentation is a universal phenomenon associated with rock avalanches, resulting in an abundance of complex sedimentological structures. If studied in detail, these structures can provide insights into rock avalanche emplacement processes. Here, six typical avalanche cases are carefully analyzed in conjunction with an analogue experiment. Findings reveal the carapace facies is characterized by clast-supported structures composed of large blocks with sedimentological structures that include retained stratigraphic sequences, imbricate structures, and jigsaw structures. The body facies presents a high degree of fragmentation, with block-rich zones, fine matrix-rich zones, jigsaw structures, and inner shear zones. The basal facies displays the highest degree of fragmentation, however, it is mainly composed of millimeter grains with thin shear strips. Consistent with the field investigations, differential fragmentation is also observed in the analogue tests, with the vertical dimension of the carapace facies mainly fragmented along the lines of pre-existing structures; the body facies fragmented with an abundance of new fractures; and the basal facies fragmented into fine grains. Meanwhile, layer sequences preserved in longitudinal and vertical profiles are also observed in the analogue tests, indicating a low disturbance in the propagation. We, therefore, propose that a process characterized by a sparse state, dominated by collisions, minor disturbance, and pervasive dynamic fragmentation likely occurs in the carapace facies, with fragmentation mainly controlled by the breakage of pre-existing, fully-persistent structures. The body facies is mainly controlled by the fracturing of the weak, less-persistent structures, and the basal facies displays the highest degree of fragmentation with an abundance of new fractures. In the entire propagation, the avalanche mass displays low-disturbance laminar flow.

Urban Landscape Fragmentation as an Indicator of Urban Expansion Using Sentinel-2 Imageries

Rapid urbanization in some cities has led to the emergence of numerous subsidiary settlements around their primary cities. Due to this rapid urbanization and growth, there is a great demand for urban land, mostly for commercial, industrial, and residential uses. Urban green spaces and vegetation are at risk due to a large amount of urban land, as seen by a decline in connectivity and increased fragmentation, especially due to land conversion. However, the identification of the spatial and momentary variability in the clustering and fragmentation of vegetation patterns in urban settings has not made full use of local indicators of spatial distribution measurements, such as Baqubah, a city in Iraq. Since it is essential to measure the degree of fragmentation and evaluate urban expansion trajectories consistently, this study proposes a new approach to assessing the anticipated direction of urban extension, using the fragmentation indicator of built-up patterns in urban areas. Sentinel-2 data was used to map the fragmented urban centres and their future extent in the city at a single time point. The proposed method employs indices to capture the initial distribution of spatial patterns of vegetation cover and built-up areas. The main extracted land cover classes, landscape fragmentation performance, and surface density analysis were accomplished in ArcGIS. The results indicate that the entire built-up area in Baqubah has a high degree of fragmentation at 75%, and about 23% of the open space within the urban extent of the city. Two predicted trajectories of urban expansion were also revealed: one may follow the external road direction, while the other is multi-directional, commencing from the edges of the built-up area. The study concludes that the new method is useful for comprehending and assessing urban landscape fragmentation, as well as anticipating its path. This integrated approach to remote sensing and GIS can sufficiently and effectively determine priority urban regions for successful planning and management. In addition, our study's findings highlight the potential of the suggested strategy as a useful spatially explicit method for determining the spatial clustering and fragmentation of urban landscape patterns. Doi: 10.28991/CEJ-2022-08-09-04 Full Text: PDF

Husby in Glanshammar: cloisonné production, Viking Period silver deposition and memorialisation

Abstract This paper returns to Husby in Glanshammar, Sweden, where an important manorial settlement of the mid-to-late 1st millennium AD was excavated in the 1990s for a highway project. A recent intensive and comprehensive metal detector survey of the site’s surviving parts has secured additional finds that cast a new light on the manor and its afterlife. Fine copper alloy casting was amply demonstrated by the 1990s excavations. Now a die for the making of waffled gold foil has been added to this assemblage. Waffled foils formed part of gold-and-garnet cloisonné work, one of the most exclusive decorative techniques of the era. Hacksilver and coins from around AD 900 were found scattered over the old foundation of the torn-down mead-hall, apparently forming a first phase of memorialisation that continued from about AD 1100 onward with a small Christian cemetery next to the foundation. These single coins go back at least half a century before the start of silver hoarding in the region. The silver found at Husby shows clear signs of having been used as bullion in economic transactions, with a high degree of fragmentation and many test marks.

Diversity and Genetic Structure of Dicksonia navarrensis (Dicksoniaceae) Populations in the Mexican Sierra Madre Oriental

Background and Research Aims Dicksonia navarrensis is a species of tree fern at risk of extinction, distributed in the montane cloud forest (MCF) of the Americas from the central region of Mexico to Ecuador. In Mexico, populations of this species grow in primary vegetation of the MCF, in a matrix with a high degree of fragmentation and under threat of disappearance. Methods In the present study, the diversity and genetic structure of seven populations of D. navarrensis that are distributed in the cloud forest of the Sierra Madre Oriental were evaluated, with both standard laboratory and statistical analysis techniques, using 11 microsatellites developed for the genus Dicksonia. Results A total of 33 alleles were found. Genetic diversity differed between populations, and some presented low heterozygosity. Using assignment tests, three genetic groups were identified, associated with the geographical distribution of the populations; those from the north maintain connectivity with each other but diverge highly from the populations in the south, probably due to processes of isolation by distance (local environment), genetic drift, and natural selection. Conclusion The northernmost population, which is more isolated from the rest, has a broader genetic reservoir, which can be useful for maintaining the genetic diversity of the species. In the other populations, with less genetic diversity, the introduction of individuals and/or the dispersion of spores is important, to maintain and increase the genetic variability that they still possess, but which could disappear in a short time if their habitat continues to deteriorate at a high degree. Implications for Conservation The results obtained provide basic information that can be used in management and conservation plans, because the populations with the greatest genetic diversity and the possible processes that are influencing the genetic structure of the species were identified.

China’s Forest Eco-Bank Project: An Analysis Based on the Actor-Network Theory

The high degree of fragmentation and unsustainable exploitation patterns of forest resources have become prominent obstacles to the realisation of the economic and social value of China’s forest resources. China’s forest eco-bank (FEB) project was set up to achieve centralised utilisation of diffuse forest resources in an underdeveloped area. Analysing FEB projects is of great significance to countries with abundant forest resources aiming to benefit from the economic and ecological functions of such resources and achieve sustainable economic and social development. This study uses the actor-network theory framework to analyse cooperation among various actors in the implementation process of the FEB project in China. Our results indicate the following. First, the government was the principal actor playing a vital role in motivating the other parties and driving the project forward. Second, the diffuse nature of China’s forest resources is a major obstacle to their utilisation. The centralised integration of forest resources is a prerequisite for their effective utilisation. Finally, it is necessary to improve the balance of interests of the various actors to promote a more stable actor network and attract more actors to participate in the FEB project.

A Spectral Mixture Analysis and Landscape Metrics Based Framework for Monitoring Spatiotemporal Forest Cover Changes: A Case Study in Mato Grosso, Brazil

An increasing amount of Brazilian rainforest is being lost or degraded for various reasons, both anthropogenic and natural, leading to a loss of biodiversity and further global consequences. Especially in the Brazilian state of Mato Grosso, soy production and large-scale cattle farms led to extensive losses of rainforest in recent years. We used a spectral mixture approach followed by a decision tree classification based on more than 30 years of Landsat data to quantify these losses. Research has shown that current methods for assessing forest degradation are lacking accuracy. Therefore, we generated classifications to determine land cover changes for each year, focusing on both cleared and degraded forest land. The analyses showed a decrease in forest area in Mato Grosso by 28.8% between 1986 and 2020. In order to measure changed forest structures for the selected period, fragmentation analyses based on diverse landscape metrics were carried out for the municipality of Colniza in Mato Grosso. It was found that forest areas experienced also a high degree of fragmentation over the study period, with an increase of 83.3% of the number of patches and a decrease of the mean patch area of 86.1% for the selected time period, resulting in altered habitats for flora and fauna.

The effect of excipient particle size on the reduction of compactibility after roller compaction

Developing a robust roller compaction process can be challenging, due to the diversity in process parameters and material properties of the components in a formulation. A major challenge in dry granulation is the reduction of tablet strength as a result of re-compaction of the materials. The aim of this study is to investigate the impact of excipient type and particle size distribution on tablet tensile strength after roller compaction. Lactose monohydrate, anhydrous lactose and microcrystalline cellulose with different particle sizes are roller compacted at varying specific compaction forces. Granules obtained are compressed into tablets to evaluate the reduction in tablet strength upon increasing the specific compaction force. The impact of particle size of the starting material is shown to be vastly different for the three types of excipients investigated, due to the differences in mechanical deformation mechanisms. The presence of rough surfaces and a high degree of fragmentation for anhydrous lactose appears to be beneficial for compaction and re-compaction process. Additionally, the particle size of anhydrous lactose hardly affects the tensile strength of tablets, which can be beneficial for the robustness of a roller compaction process.

Applying the Strategic Health Purchasing Progress Tracking Framework: Lessons from Nine African Countries

ABSTRACT The Strategic Purchasing Africa Resource Center (SPARC) developed a framework for tracking strategic purchasing that uses a functional and practical approach to describe, assess, and strengthen purchasing to facilitate policy dialogue within countries. This framework was applied in nine African countries to assess their progress on strategic purchasing. This paper summarizes overarching lessons from the experiences of the nine countries. In each country, researchers populated a Microsoft Excel–based matrix using data collected through document reviews and key informant interviews conducted between September 2019 and March 2021. The matrix documented governance arrangements; core purchasing functions (benefits specification, contracting arrangements, provider payment, and performance monitoring); external factors affecting purchasing; and results attributable to the implementation of these purchasing functions. SPARC and its partners synthesized information from the country assessments to draw lessons applicable to strategic purchasing in Africa. All nine countries have fragmented health financing systems, each with distinct purchasing arrangements. Countries have made some progress in specifying a benefit package that addresses the health needs of the most vulnerable groups and entering into selective contracts with mostly private providers that specify expectations and priorities. Progress on provider payment and performance monitoring has been limited. Overall, progress on strategic purchasing has been limited in most of the countries and has not led to large-scale health system improvements because of the persistence of out-of-pocket payments as the main source of health financing and the high degree of fragmentation, which limits purchasing power to allocate resources and incentivize providers to improve productivity and quality of care.

Investigation of three different cooling treatments on dynamic mechanical properties and fragmentation characteristics of granite subjected to thermal cycling

Underground thermal engineering such as geothermal exploitation usually involves the response of impact loads due to the drilling operation and blasting load. This study investigated the dynamic mechanical properties and fragmentation characteristics of granite subjected to thermal cycling under natural cooling, water cooling, and liquid nitrogen cooling. Firstly, split Hopkinson pressure bar tests were performed on granite under three different cooling methods to study the dynamic mechanical parameters with thermal cycles. Subsequently, the damage factors were calculated to evaluate the damage on granite and the relationship between damage and stress. Finally, the granite fragments after impact were sieved, and the fractal dimension and average fragment size were introduced to analyze the fragmentation characteristics. The results demonstrate that the degradation of dynamic mechanical properties mainly occurs in the first four thermal cycles; with the increase of damage factor, the stress decreases linearly under the three cooling methods, and the damage caused by liquid nitrogen cooling to granite is the most significant, followed by water cooling. Fragments of granite change from axial splitting failure to a more complex composite failure mode. In addition, with the decrease of the average fragment size, the fractal dimension of the granite gradually increases, resulting in the higher fragmentation degree and the better uniformity of fragmentation.

Experimental assessment on the dynamic mechanical response of rocks under cyclic coupled compression-shear loading

Rock engineering structures are quite susceptible to cyclic coupled compression-shear loading. Accurately characterizing the dynamic compression-shear behaviors of rocks is thus crucial for the construction safety and disaster prevention of rock engineering. In this study, a convenient and reliable testing method is proposed to characterize the fatigue mechanical response of rocks under cyclic coupled compression-shear loading: an inclined specimen under cyclic uniaxial loading. With the specimen axis inclining the loading direction, a cyclic shear component is introduced into rocks when subjected to cyclic uniaxial compression. Our method has certain distinct merits in the specimen preparation and experimental operation since no undesired loading devices are required. To demonstrate this method, 21 cyclic loading tests are conducted on inclined sandstone specimens with different tilting angles (i.e., 0°, 3°, 6° and 10°) and under different loading frequencies (i.e., 0.5, 1, 2, and 3 Hz). Based on experimental results, the influence of the tilting angle and loading frequency on the dynamic properties of rocks is revealed and a fatigue life prediction function is proposed. With increasing tilting angle of rock specimens or decreasing loading frequency, rock specimens are featured by an increase of nominal hysteresis energy density, leading to higher damage variable and lower fatigue life. Quite different from the axial splitting failure of right cuboid specimens along the loading direction, all inclined rock specimens (i.e., 3°, 6° and 10°) exhibit a prominent shear-dominated failure accompanied by localized tensile damage, and the shear component becomes more remarkable as the tilting angle increases. In addition, with a higher tilting angle or under lower loading frequency, the cyclically failed specimen is characterized by a higher degree of fragmentation.

Differences in Petrophysical and Mechanical Properties Between Low- and Middle-Rank Coal Subjected to Liquid Nitrogen Cooling in Coalbed Methane Mining

Abstract Exploring the damage differences between different coal rank coal reservoirs subjected to liquid nitrogen cooling is of great significance to the rational development and efficient utilization of coalbed methane (CBM). For this purpose, the mechanical properties, acoustic emission (AE) characteristics, and energy evolution law of lignite and bituminous coal subjected to cooling treatment were investigated based on Brazilian splitting tests. Then, pore structure changes were analyzed to reveal the differences in microscopic damage between lignite and bituminous coal after a cooling treatment. The results showed that compared with bituminous coal, the pore structure of lignite coal changed more obviously, which manifested as follows: significant increases in porosity, pore diameters, and pore area and a larger transformation from micropores and transition pores to mesopores and macropores. After the cooling treatment, the thermal damage inside lignite and bituminous coal was 0.412 and 0.069, respectively. Thermal damage reduced the cohesive force between mineral particles, leading to the deterioration of the macroscopic physical and mechanical properties. Simultaneously, denser acoustic emission ringing counts and larger accumulated ringing counts were observed after cooling. Moreover, the random distribution of thermal damage enhanced the randomness of the macrocrack propagation direction, resulting in an increase in the crack path tortuosity. With more initial defects inside coal, a more obvious thermal damage degree and wider damage distribution will be induced by cooling treatment, leading to more complicated crack formation paths and a higher fragmentation degree, such as that of lignite coal.