Low-resistivity Region Research Articles

Three-dimensional interpretation of magnetotelluric data at Fogo Volcano, Azores Islands

The resistivity structure of Fogo volcano and the seismically active Congro region of São Miguel Island has been determined by 3-D inversion from 44 magnetotelluric soundings to yield new insights into the internal architecture of this volcanic island. Following comprehensive testing of processing codes to yield optimum magnetotelluric responses from the collected time-series, a robust electrical resistivity model was obtained. Sensitivity analysis of various features from the inversion process was used to determine their reliability, and aid geological interpretation. The magnetotelluric data imaged, and provided new structural insights into the Ribeira Grande geothermal system on the northern flank of Fogo volcano, where a shallow low resistivity (1 - 5Ωm) region has strong correlation with borehole data, and is shown to be an excellent proxy for mapping temperature and clay alteration mineralogy. Beneath the central edifice of Fogo volcano and also throughout the Congro region, the geology is very resistive, however the new magnetotelluric observations do not yield any further constraints on the origin of the seismicity that poses threats to the local populations residing on this hazardous island.

A comparative study of using geophysical methods for imaging subsurface voids of various sizes and at different depths

Subsurface voids pose significant geohazards, underscoring the need for their timely detection in order to mitigate the associated hazard. We report on a field study aimed at the comparative assessment of electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and the multichannel analysis of surface waves (MASW) for void mapping in karstic regions. The field surveys were conducted at a site in central Texas, of typical karstic geomorphology, and involved the co-located deployment of ERT, SRT and MASW arrays. Post-surveying, boreholes were drilled at select locations for verification purposes. It is shown that MASW demonstrated limited ability to resolve voids due to its inherent theoretical limitations. In contrast, ERT revealed high-resistivity air-filled zones, and low-resistivity soil-filled regions, which aligned well with post-survey borehole logs, although deeper voids remained largely undetected. SRT clearly delineated voids through velocity reductions, but smoothing effects overestimated void velocities. Using ERT and SRT jointly provided improved void characterization compared to single-method-based interpretations, with ERT determining void type and SRT delineating boundaries. Despite the relative success of the joint ERT-SRT application, it is evident that without the corroboration provided by invasive testing, definitive void localization and characterization under arbitrary site conditions remains elusive.

Analysis of Grid Performance with Diversified Distributed Resources and Storage Integration: A Bilevel Approach with Network-Oriented PSO

The growing deployment of distributed resources significantly affects the distribution grid performance in most countries. The optimal sizing and placement of these resources have become increasingly crucial to mitigating grid issues and reducing costs. Particle Swarm Optimization (PSO) is widely used to address such problems but faces computational inefficiency due to its numerical convergence behavior. This limits its effectiveness, especially for power system problems, because the numerical distance between two nodes in power systems might be different from the actual electrical distance. In this paper, a scalable bilevel optimization problem with two novel algorithms enhances PSO’s computational efficiency. While the resistivity-driven algorithm strategically targets low-resistivity regions and guides PSO toward areas with lower losses, the connectivity-driven algorithm aligns solution spaces with the grid’s physical topology. It prioritizes actual physical neighbors during the search to prevent local optima traps. The tests of the algorithms on the IEEE 33-bus and the 69-bus and Norwegian networks show significant reductions in power losses (up to 74% for PV, wind, and storage) and improved voltage stability (a 21% reduction in mean voltage deviation index) with respect to the results of classical PSO. The proposed network-oriented PSO outperforms classical PSO by achieving a 2.84% reduction in the average fitness value for the IEEE 69-bus case with PV, wind, and storage deployment. The Norwegian case study affirms the effectiveness of the proposed approach in real-world applications through significant improvements in loss reduction and voltage stability.

Application of Multi-Near-Surface Geophysical Surveys for Geothermal Spring: A Case Study in Kon Tum Province, Vietnam

The occurrence of geothermal spring not only enhances human health, but also plays a crucial role in generating community’s revenue that boosts up the standard living of locals. An endeavor has been made to delineate the prospective areas of geothermal spring in Kon Tum province, Vietnam by the utilization of joint-geophysical techniques. The blended mode as mentioned is opted for its superiority in providing the rapidassesments of temperature in shallow temperature survey, comprehensive understanding the subsurface structure in electrical resistivity tomography in copporating with the validation in well log interpretation. The results found that the overlapping region of high temperature (35°C) region and low resistivity (200 Ωm) is observed in the east in the vicinity of Dlak Bla river, and it probably broadens to the west of the study area. The outcome of geophysical approaches strongly concur with the well log interpretation, revealing the presence of water-bearing zone encountered in fractured granite. The results also corroborated the existence of concealing fault F5 as a branch of the NE-SW fault F2 which is favorable for creating a route to form the geothermal spring. The output of this research could be considered as an intentive consultation for Kon Tum’s planners and makers on expanding the investigation and exploitation.

(Invited) Vertically Stacked Graphene Junction Diodes

Graphene is expected to be nanomaterial of the post-silicon era because of its numerous advantageous properties. The single crystal graphene thermally grown on SiC substrate is considered the most promising platform for future electric devices. Large area epitaxial graphene on SiC substrate has been successfully fabricated using high-temperature rapid thermal annealing [1]. In this study, we present vertically stacked graphene junction diodes fabricated using direct bonding technique [2–4]. Figure 1(a) shows the schematic of a stacked graphene junction diode. Two graphene layers on SiC are directly bonded to each other. Gold–coated contact pins are attached to the graphene surface to establish ohmic contact. The graphene samples and contact probes are fixed by acrylic molds. Strong nonlinear current–voltage (I-V) characteristics are observed for this simple device configuration, as shown in Fig. 1(b). In the low bias voltage (Vb) region, the resistance of the graphene diode is approximately 20 GΩ. The current abruptly increases when the bias voltage is increased to approximately 30 V. The two-terminal resistance at a high bias voltage (100 V) is approximately 21 kΩ. The vertically stacked graphene junction exhibits bidirectional thyristor-type characteristics with a high on-off ratio of approximately 106. The Fowler–Nordheim (F-N) tunneling phenomenon is observed in the sub-threshold region. The gap distance estimated from the F-N plot is approximately 6 nm, which can be attributed to the large off resistance. The Coulomb force generated by applying the bias voltage causes the two graphene layers to attract each other, resulting in an electrically conductive state. The junction voltage (Vj) of the device was measured using a four-terminal configuration. As shown in Fig. 1(c), negative resistance is observed in the low-resistance region. The effective internal resistance of the junction diode is reduced to approximately 450 Ω. The off resistance of the diodes is considerably modified by the initial distance between the graphene layers. However, the I-Vj characteristics in the negative resistance region are identical for each device. This result suggests that the cause of the negative resistance phenomena is closely related to the band structure of graphene. A vertically stacked graphene junction diode with a high on-off ratio was demonstrated. The main component of the diode comprised a pair of single-crystal graphene layers fabricated through direct bonding. The negative resistance of the graphene diode presents new possibilities for the application of functional devices, such as terahertz emitters.[1] T. Aritsuki, et al., Jpn. J. Appl. Phys. 55 (2016) 06GF03.[2] J. Du, eta al., Jpn. J. Appl. Phys. 58 (2019) SDDE01.[3] N. Murakami, et al., Jpn. J. Appl. Phys. 60 (2021) SCCD01.[4] M. Ohi, et al., Jpn. J. Appl. Phys. 62 (2023) to be published. Figure 1

Design of a lateral photoconductive semiconductor switch with a low resistivity region on semi-insulating GaN to enhance breakdown characteristics

The breakdown characteristics of the semi-insulating lateral GaN photoconductive semiconductor switches (PCSS) with low resistivity region (LRR) structure were simulated. The design, which can reduce the peak electric field by adjusting the electric field distribution for PCSS, was first proposed. In comparison to conventional field plate and n-type doping below the electrode structures, the LRR structure robustly enhances the breakdown characteristics of PCSS while reducing the influence of on-state characteristics. The impact of different structural parameters on the breakdown voltage and on-state characteristics was investigated. In the case of a small size device with a 5 μm electrode gap, the LRR structure is able to decrease the peak electric field by 54 % at 400 kV/cm and increase breakdown voltage by 45 %. When the electrode gap is increased to 0.25 mm, under a bias voltage of 5 kV, the field plate structure can reduce the peak electric field by 35 %, but the LRR structure can reduce the peak electric field by 42 %. When applied a voltage of 2 kV, the PCSS with the LRR structure triggered by a laser pulse with a wavelength of 532 nm and an energy of 265 μJ has a minimum on-resistivity being less than 0.5 Ω cm and the resistivity ratio between the off and on states reaching up to 1 × 108.

Angular dependence of resistance and critical current of a Bi-2223 superconducting joint

Low resistance and high critical current are prerequisites for superconducting joints used in persistent-mode magnets. Herein, we use a joint resistance evaluation system, previously developed by us, to systematically evaluate the angular dependence of resistance and critical current of a Bi-2223 superconducting joint in a closed-loop sample. The current decay is measured by rotating the sample incrementally. The time dependence of the loop current is evaluated at 4 K, 0.15–0.28 T, and magnetic field angles ranging from 90° to 0, wherein 90° corresponds to the direction parallel to the tape surface. The results suggest that the resistance and critical current of the joint depend on the angle of the magnetic field. The evaluated critical current increases as the angle increases. The angular dependence of resistance can be divided into three regions: low-resistance, transition, and high-resistance regions. The low-resistance region exists at high angles close to 90°. In this region, the decay of the loop current is small, and the persistent current continues to flow. Furthermore, the joint resistance is less than 1.4 × 10−13 Ω. In the transition region, the joint resistance significantly increases by three orders of magnitude with sample rotation. This significant increase is attributed to an increase in the perpendicular component of the magnetic field, which decreases the critical current of the joint. At lower angles, the joint resistance remains high, ranging from 10−11 to 10−10 Ω. A significant decay in the loop current is observed in the high-resistance region. Based on these findings, we conclude that the design of a persistent-mode magnet must consider not only the magnitude but also the direction of the magnetic field applied to superconducting joints.

Nondestructive imaging of breakdown process in ferroelectric capacitors using in situ laser-based photoemission electron microscopy

HfO2-based ferroelectrics are one of the most actively developed functional materials for memory devices. However, in HfO2-based ferroelectric devices, dielectric breakdown is a main failure mechanism during repeated polarization switching. Elucidation of the breakdown process may broaden the scope of applications for the ferroelectric HfO2. Here, we report direct observations of a breakdown process in HfO2-based ferroelectric capacitors, by in situ laser-based photoemission electron microscopy. We have not only clearly visualized the hard dielectric breakdown (HDB) spot but also observed the regions responsible for the soft dielectric breakdown (SDB), which is a precursor phenomenon to HDB. It was found that the low-resistance region formed after SDB is wider than the conduction path formed after HDB. Furthermore, our spectromicroscopic analysis revealed that the photoelectron spectrum after SDB shows an enhancement in intensity without spectral-shape modulation, interpreted that the initially existed defects are increased. In the HDB spot, however, an additional shoulder structure was observed. These results provide spectroscopic evidence that the electronic states responsible for the conduction path after SDB are different from those after HDB. Through this work, we propose this microscopic approach as a versatile tool for studying buried materials as they are, accelerating the development of material engineering for advanced electronic devices.

Study on the cooling and drag reduction characteristics of multi-port injector array film cooling using gaseous hydrocarbon fuel as coolant

Supersonic film cooling utilizing gaseous hydrocarbon fuel is an effective method to meet the thermal protection and drag reduction requirements inside a scramjet engine. The film injection scheme for film cooling using gaseous hydrocarbon fuel is crucial in determining the thermal protection and drag reduction performance of the film with oxidative cracking reaction. In this paper, a numerical study is conducted to compare the thermal protection and drag reduction performance of gaseous hydrocarbon fuel film under the slot injector film cooling structure and the multi-port injector array film cooling structure. The results show that the multi-port injector array film cooling utilizing gaseous hydrocarbon fuel as a coolant improves both thermal protection and drag reduction performance compared to the slot injector film cooling structure. The chemical reaction of hydrocarbon fuel expands the cooling range and low resistance area of a single discrete hole. The reason is that the multi-port injector array film cooling intermittently interrupts the oxidation and heat release process of the hydrocarbon fuel in the boundary layer, resulting in higher cooling efficiency in the film cooling injection area. It also improves the spatial distribution of the hydrocarbon fuel film, allowing for effective utilization of the chemical heat sink of the hydrocarbon fuel, which improves the thermal protection performance and expands the effective cooling area. Furthermore, the enhanced mixing of the multi-port injector array film cooling in the film injection area improves drag reduction performance through combustion inside the boundary layer, resulting in a significant drag reduction of 36.6%. The multi-port injector array film cooling also effectively distributes the low skin-friction resistance region due to the low molecular viscosity after the secondary cooling flow injection. Moreover, under supersonic mainstream conditions, the mixing efficiency of the multi-port injector array film cooling structure and the slot injector film cooling structure both decreases, and the difference gradually decreases.

Visualization of resistance distribution and microstructure in locally degraded multilayered ceramic capacitor

This study characterizes low-resistance regions in a locally degraded multilayered ceramic capacitor (MLCC) using scanning spreading resistivity microscopy, scanning electron microscopy, and transmission electron microscopy. The MLCC consists of a core–shell structure that degrades before electrical breakdown in highly accelerated lifetime tests. Areas of local insulation degradation in the MLCC are revealed by Dy-containing solid solution grains. The characteristic grains within the low-resistance region show the resistance distribution. Degraded grains around the anode, which are assumed to strongly reflect the front-line insulation degradation, suggest that the shell and grain boundaries strongly repress insulation degradation. These results show that improved material uniformity and microstructure design are vital for achieving highly reliable MLCCs.

Field Effects in the Electrical Conductivity of Platinum/Diamond-Like Carbon/Platinum Capacitor Structures

The field dependences of the electrical conductivity of Pt/diamond-like carbon (DLC)/Pt structures based on thin layers of high-resistivity DLC are studied. It is shown that the nonohmic behavior of theconductance of structures is described by the Frenkel–Poole formula and is related to correlated distribution of charges under conditions of their percolation hopping transport between low-resistance DLC regions.

Tracking supercritical geothermal fluid distribution from continuous seismic monitoring

Continuous seismic monitoring could play a pivotal role in deep geothermal energy exploration. We monitored seismicity near geothermal production areas of the Kuju volcanic complex with a dense seismic network and automated event detection. Most events were shallow (less than 3 km below sea level) and distributed along a boundary between regions of high and low resistivity and S-wave velocity, interpreted as a lithological boundary or related fracture zone. Deeper events located on top of subvertical conductors may reflect fracturing associated with magmatic fluid intrusion. A correlation may exist between seismicity and heavy rainfall three days prior to increased pore pressure in pre-existing fractures. Our findings support the presence of supercritical geothermal fluids and demonstrate the importance of continuous seismic monitoring in supercritical geothermal energy exploration.

Metallogenic Prediction of Magnetite in the Pandian Area at the Northwest Margin of Luxi Uplift, China: Constraints of Wide-Field Electromagnetic Data

The Pandian deposit is a newly discovered contact metasomatic skarn magnetite deposit found in the Cainozoic super-thick overburden on the northwest margin of Luxi Uplift (LXU). Presently, the horizontal scale of the deposit delineated by the potential field (gravity and magnetic method) has shown giant potential for ore deposits, and mapping the ore-controlling structures in the vertical scale becomes a primary task for metallogenic prediction. In our study, the wide-field electromagnetic method (WFEM), with a strong anti-noise ability in recording electromagnetic signals on the surface at multiple frequencies, is applied to characterize the deep conductivity distribution of the Pandian area. Based on the inversion results from two parallel WFEM profiles, which consist of 105 sites and previous geological and geophysical results, the 2D geoelectric models are established. The low-resistivity regions (with a typical range of 25~32 Ω·m) in the electrical models are proven to be ore bodies of Pandian deposit, which are developed along the contact zone between Yanshanian intrusive rocks and Paleozoic Ordovician strata. The scattered bodies (typically >32 Ω·m) in Ordovician limestone strata are probably caused by intrusive diorite pluton closely related to magnetite mineralization. Due to contact metasomatism, bedded limestone near magnetite was metamorphosed into marble and accompanied by low-resistivity skarn alteration, with resistivity much different from its high-resistivity protolith. The inverted geoelectrical models visually reflect the spatial distribution features of intrusive rocks and lithologic alteration/fracture zones.

New constraints on the structure and composition of the lithospheric mantle beneath the Slave craton, NW Canada from 3-D magnetotelluric data – Origin of the Central Slave Mantle Conductor and possible evidence for lithospheric scale fluid flow

Previously collected magnetotelluric data were used to produce an improved 3-D resistivity model of the lithosphere beneath the Slave craton. A region of low resistivity (<10 Ωm) at ∼100 km depth was imaged beneath the central Slave craton, and identified as the Central Slave Mantle Conductor (CSMC) reported in previous studies. Earlier studies interpreted the CSMC as graphite films but new analysis from laboratory experiments indicates that it is unlikely that graphite films are stable/continuous at this depth. Using recent laboratory experiments we review alternative conduction mechanisms for the CSMC including (a) metasomatic phlogopite, (b) grain boundary sulphides and (c) high density fluids including hydrous carbonatite melts or brines. None of these hypotheses are without flaws requiring either unreasonably high-volume fractions or have petrological challenges. However, brines are the preferred explanation as they (1) can explain geophysical observations, (2) are observed in fibrous diamonds coincident with the CSMC and (3) require small volume fractions (<1%). We hypothesize their emplacement was related to a Mesozoic subduction event. This implies that upper mantle conductors should not be used as an indicator of carbon concentration in the mantle to prospect for diamondiferous regions. Our resistivity model indicates a lithospheric thickness of 210 ± 10 km beneath the Slave craton, consistent with seismic and xenolith studies. A water content of 10–150 ppm at 100–170 km depth in the lithospheric mantle is inferred from resistivity, broadly agreeing with estimates from mantle xenoliths from the central Slave craton lithosphere. Below 170 km the bulk lithosphere is "dry" (<10 ppm), which may explain why the cratonic root has been resistant to erosion by the underlying asthenosphere. Low resistivity fingers extend to surface in multiple locations that may represent paleo-fluid flow pathways through the lithosphere, broadly resembling those observed beneath Olympic Dam, Australia.

Laminated indium-oxide/molybdenum-oxide nanocomposites for high-work-function electrodes in organic photovoltaics and capacitor devices

Research on the development of transparent conductive oxides (TCOs) has been rapidly progressing. However, the limitations of the work function (WF), charge mobility, and surface roughness of TCOs hinder their widespread use in optoelectronic devices. In this study, we fabricated an atomic layer deposited (ALD)-transparent conductive electrode based on In2O3:MoOX nanolaminates with low resistivity (240 μΩ·cm) and high near-infrared region transmittance (∼90 %). The performance of In2O3:MoOX nanolaminates with high mobility (92.6 cm2/V·s) and WF (5.03 eV) was examined in organic photovoltaics (OPVs) and metal–insulator-metal (MIM) capacitors. In OPVs, the high WF of the proposed In2O3:MoOX nanolaminates simplifies the process by eradicating the requirement of the hole-transport layer (HTL). In this study, the In2O3:MoOX nanolaminates replaced PEDOT:PSS, a widely used HTL, thereby maintaining an efficiency greater than 90 % from its initial value after 500 h in a 1-sun environment. Further, in the MIM capacitor, the In2O3:MoOX nanolaminate-based capacitor demonstrated a high capacitance at high frequencies (1 MHz) and substantially low leakage current owing to its higher WF than those of conventional TiN-based capacitors. Thus, the diverse functionality of the proposed In2O3:MoOX nanolaminates demonstrated their excellent suitability for other optoelectronic devices.

Microstructure, dielectric response and impedance spectroscopy of SrCu3Ti4O12 ceramics prepared by a sol-gel technique

SrCu3Ti4O12 ultrafine powders and ceramics were successfully prepared using sol-gel and ceramic techniques. DTA/TG, XRD, HRTEM, SAED, SEM, and XPS were employed to characterize the samples' thermal decomposition, phase composition, microstructure, and element valence. During calcination, the dry precursors gradually decompose into oxides and recombine into SrCu3Ti4O12 polycrystalline above 620 °C. Simultaneously, the prepared ceramics sintered at 1025 °C for 8 h exhibited a colossal permittivity at room temperature (εr = 8.5 × 104, 1 kHz) and good temperature stability. XPS result confirms that Cu+/Cu2+ and Ti3+/Ti4+ coexist in ceramics, and Impedance analysis indicates a low-resistance region originating from inhomogeneity in the grain interiors. Finally, the relevance between defect formation and dielectric properties in SrCu3Ti4O12 materials is discussed.

Correlation of 2D Electrical Resistivity and Self-Potential Methods for the Assessment of the Integrity of Goronyo Dam NW Nigeria

Abstract In this research, combined 2D electrical resistivity and self-potential (SP) methods were employed to locate anomalous electrical conductivity around the Goronyo dam in order to determine the condition of the embankment of the earth dam. The data were taken with the reference to resistivity and SP values using Wenner configuration. The results obtained from these techniques shows that the area was underlain by four stratigraphic layers, namely; clayey sand, wet sandy clay, laterite and partially weathered basement complex rock as compared with the resistivities of common rocks and borehole lithology of the area. The low SP (&lt; 200 mV)/high resistivity zones in the overburden of profiles P1, P2 and P3 shows the presence of partially weathered basement complex rocks which was probably due to compactness and dryness around the dam. However, the zones of high SP (≥ 200 mV)/low apparent resistivity regions (z1 and z2) of profiles P1 (2 Ωm to 27 Ωm), P2 (3 Ωm to 25 Ωm) and P3 (3 Ωm to 14 Ωm) have revealed the weak zones associated with wet sandy soil. Results obtained from 2D electrical resistivity (z1) technique have correlated well with the results of SP sections (z2). These regions of weak zones occupied the x-distance along the profiles; P1/or S2 (120 m to 200 m and 250 m to 400 m), P2/or S2 (1 m to 156 m and 192 m to 400 m) and P3/or S3 (48 m to 400 m) with their corresponding depth y, ranging from 23 m to 30 m, 26 m to 30 m and 23 m to 30 m. Keywords: 2D Electrical Resistivity Tomography (ERT), Self-Potential (SP), Dam, Subsurface, Seepage, Condition

Giant dielectric response and nonlinear electrical behaviors of TiO2/CCTO composite ceramics with pomegranate-like microstructure

In this study, TiO2/CCTO composite ceramics with pomegranate-like grains were successfully prepared using a novel route. In addition, their microstructures, giant dielectric mechanisms, and nonlinear electrical behaviors were studied in detail. Analyses of the experimental results showed that the grains with a pomegranate-like microstructure had nano/micro-scale grain boundaries, which significantly increased the interfacial polarization at the grain and subgrain boundaries. Simultaneously, impedance analysis corroborated the existence of a low resistance region in the grain interiors. This resulted from the establishment of donor defects (TiCu..) through replacement of the Cu2+ positions with Ti4+ ions and the production of numerous weakly trapped electrons. The colossal permittivity (εr = 4.57 × 105 at 20 Hz, εr = 9.86 × 104 at 1 kHz) of TiO2/CCTO composite ceramics closely correlates to the charge accumulation on the hierarchical grain boundary barrier layers.

Groundwater Exploration Using Vertical Electrical Sounding And 2D Electrical Resistivity Tomography In Shale Formation: A Case Study Of Sabongida, Plateau State, North Central Nigeria

Sabongida is characterized by lots of abortive boreholes which are often shallow as a result of the complex nature of shale formation in the area and limited application of integrated geophysical techniques before drilling of boreholes. The presence of shale formation in the area makes it extremely difficult to drill productive boreholes, while the existing hand dug wells are always shallow due to the difficulty in digging deeper wells, this and other factors motivated the choice of the study location for the purpose of proffering solutions to solve the perennial water problem in the area. Twenty-two (22) vertical electric soundings data (VES) using Schlumberger array with the aid of Ohms mega resistivity meter were conducted with electrode spread of AB/2 = 215 m and eleven (11) 2D electrical resistivity tomography data (ERT) using ADMT – 600 S - X equipment were acquired. ERT was conducted using 20 m as the length of each profile with 300 m in 10 profile lines and 400 m as the depth of probing. The result of the VES interpretation shows three to five geo-electric layers while the geo-electric section revealed the aquifers to consist of sandstones with varying thicknesses. Two groundwater potential zones were delineated as shelly sandstones and clayey sand. The different color band indicates the different layers within the ground as the soil resistivity varies, blue indicates low resistivity values, green - yellow indicates moderate resistivity values while high resistivity values are brown - red. The results from the 2D images indicate the low resistivity regions, suggesting aquifer is within the depths of 150 to 300 m. Thus, the recommended depths for drilling of productive boreholes are 180 to 210 m and 270 to 300 m in Sabongida.

Antimicrobial Resistance Patterns and Bovine Sub-Clinical Mastitis Burden in Low and High Tick Acaricide Resistance Regions of Uganda

Mastitis, antimicrobial resistance and acaricide resistance pose significant threats to the development of the dairy industry in sub-Saharan Africa. This study aimed to determine the prevalence of antimicrobial resistance in bacteria isolated from CMT positive cows on farms located in high (HARA) and low (LARA) acaricide resistance challenge regions of Uganda. Among selected herds in both regions, subclinical mastitis (SCM) screening was performed using CMT. CMT positive samples were collected, cultured, bacteria isolated and antibiotic sensitivity tests conducted. Overall, the prevalence of SCM in cows was 71.5% and 27.7% for HARA and LARA respectively. A SCM herd prevalence of 66.3% and 28.2% was recorded for HARA and LARA respectively. Furthermore, 67.5% and 20.8% of the cows in the HARA and LARA groups, respectively, had three out of four udder quarters infected with SCM. Staphylococcus aureus (44.2%) and coagulase-negative Staphylococcus (CNS) (47.6%) were the most prevalent causative agents of SCM isolated from cows from HARA and LARA, respectively. Most isolates from both regions were highly resistant to penicillin (HARA, 84.3%; LARA, 95.6%) and colistin (HARA, 100%; LARA, 97.8%). Tetracycline (77.1%) and oxacillin (76.1%) resistance was high in isolates from HARA and LARA, respectively. Intermediate responses (neither susceptible nor resistant) to antibiotics were more common in isolates from HARA than in those from LARA. With this level of antibiotic resistance, there is a potential risk of failure to control mastitis in dairy cattle using antibiotics, especially in the HARA region, which may possibly jeopardize the growth of the dairy industry in Uganda.