Establishment of an endoscopic retrograde cholangiopancreatography (ERCP) program in rural Kenya: a review of patient and trainee outcomes.

BACKGROUND: Endoscopic retrograde cholangiopancreatography (ERCP) is a leading modality for treatment of biliary and pancreatic disease but is not widely available in sub-Saharan Africa. We aimed to assess the development and outcomes of an ERCP service in southwestern Kenya, including case volumes, success rates, infrastructure, and training. METHODS: We conducted a retrospective review of all ERCPs performed at Tenwek Hospital in Bomet, Kenya between January 1, 2011 and March 31, 2020. RESULTS: In total 277 ERCP procedures were attempted during the study period. The commonest indication was obstructive jaundice: 91 patients (32.9%) had malignancy and 85 (30.7%) had choledocholithiasis. Overall clinical success rate was 76.1% and was the highest in patients with biliary stones (81.2%) and lowest in those with tumors (73.5%) (p = 0.094). Procedure-related adverse events occurred in 11.9%, including post-ERCP pancreatitis in 3.6%, with a procedure-related mortality rate of 1.4%. Annual case volumes increased, and mean procedure duration decreased from 162 to 115 min (p = 0.0007) over time. A previously- rained endoscopist initially performed all cases; two staff endoscopists were trained in ERCP during the study period, performing 130 and 89 ERCPs during training, with clinical success rates of 84% and 74% during their subsequent independent practice. CONCLUSION: An ERCP service can be successfully developed at a rural African hospital, with acceptable success and adverse event rates. Biliary obstruction due to stones or tumors are the most common findings. While a previously trained endoscopist should initiate and champion the service, staff endoscopists can be successfully trained despite limited case volumes.

Undifferentiated carcinoma of pancreas: a rare entity with aggressive behavior and possible genetic link.

UNLABELLED: An aggressive undifferentiated carcinoma of pancreas is a rare tumor, especially with a strong personal and family history of malignant melanoma. Limited literature review and few case reports described a genetic association between distinct types of pancreatic cancer and malignant melanoma. CASE REPORT: We present an uncommon case of an aggressive undifferentiated carcinoma of the pancreas in a 50-year-old Caucasian female. Initially, she presented with intermittent epigastric postprandial pain and mild nausea. A computed tomography scan of the abdomen showed a 5 cm heterogenous pancreatic tail mass, which on biopsy was found to be a poorly differentiated non-small cell carcinoma. Past medical history included malignant melanoma, with extensive family history of pancreatic cancer and malignant melanoma. However, not genetically confirmed, a hereditary pancreatic linkage was highly suspected. A week later, repeat computed tomography demonstrated tremendous enlargement of the pancreatic tail mass. Within a few weeks, the patient developed aggressive metastasis in various organ systems, followed by multiple surgeries. An emergent first round of chemotherapy was started, followed by an intensive care unit stay, and she eventually died. CONCLUSION: Our case exposes the aggressive behavior of undifferentiated carcinoma of pancreas, along with possible hereditary link between pancreatic cancer and malignant melanoma.

Highly Efficient Photon Energy Conversion and Ultrasensitive Self-Powered Photodetection via a Monolithic p-3C-SiC Nanothin Film on p-Si/n-Si Double Junction.

The pursuit of increased efficiency of photoelectric energy conversion through optimized semiconductor structures remains highly competitive, with current results yet to align with broad expectations. In this study, we discover a significant enhancement in photocurrent performance of a p-3C-SiC nanothin film on p-Si/n-Si double junction (DJ) heterostructure that integrates p-3C-SiC/p-Si heterojunction and p-Si/n-Si homojunction. The vertical photocurrent (VPC) and vertical photoresponsivity exhibit a substantial enhancement in the DJ heterostructure, surpassing by a maximum of 43-fold compared to the p-3C-SiC/n-Si single junction (SJ) counterpart. The p-3C-SiC layer and n-Si substrate of the two heterostructures have similar material and geometrical properties. More importantly, the fabrication costs for the DJ and SJ heterostructure devices are comparable. Our results demonstrate a significant potential for using DJ devices in energy harvesters, micro/nano electromechanical systems, and sensing applications. This research may also lead to the creation of advanced optoelectronic devices using DJ structures, where employing various semiconductor materials to achieve exceptional performance through the application of the concept and theoretical model described in this work.

The effect of wafer thinning and thermal capacitance on chip temperature of SiC Schottky diodes during surge currents.

Due to superior material properties of SiC for high-voltage devices, SiC Schottky diodes are used in energy-conversion systems such as solar-cell inverters, battery chargers, and power modules for electric cars and unmanned aerial vehicles. The reliable operation of these systems requires the chip temperature of SiC Schottky diodes to be maintained within the limit set by the device package. This is especially crucial during surge-current events that dissipate heat within the device. As a thermal-management method, manufactures of commercial SiC Schottky diodes have introduced wafer thinning practices to reduce the thickness of the SiC chip and, consequently, to reduce its thermal resistance. However, this also leads to a reduction in the thermal capacitance. In this paper, we present experimental data and theoretical analysis to demonstrate that the reduced thermal capacitance has a much larger adverse effect in comparison to the beneficial reduction of the thermal resistance. An implication of the presented results is that, contrary to the adopted wafer thinning practices, SiC Schottky diodes fabricated without wafer thinning have superior surge-current capability.

Generation of a Charge Carrier Gradient in a 3C-SiC/Si Heterojunction with Asymmetric Configuration.

It is critical to investigate the charge carrier gradient generation in semiconductor junctions with an asymmetric configuration, which can open a new platform for developing lateral photovoltaic and self-powered devices. This paper reports the generation of a charge carrier gradient in a 3C-SiC/Si heterojunction with an asymmetric electrode configuration. 3C-SiC/Si heterojunction devices with different electrode widths were illuminated by laser beams (wavelengths of 405, 521, and 637 nm) and a halogen bulb. The charge carrier distribution along the heterojunction was investigated by measuring the lateral photovoltage generated when the laser spot scans across the 3C-SiC surface between the two electrodes. The highest lateral photovoltage generated is 130.58 mV, measured in the device with an electrode width ratio of 5 and under 637 nm wavelength and 1000 µW illumination. Interestingly, the lateral photovoltage was generated even under uniform illumination at zero bias, which is unusual for the lateral photovoltage, as it can only be generated when unevenly distributed photogenerated charge carriers exist. In addition, the working mechanism and uncovered behavior of the lateral photovoltaic effect are explained based on the generation and separation of electron-hole pairs under light illumination and charge carrier diffusion theory. The finding further elaborates the underlying physics of the lateral photovoltaic effect in nano-heterojunctions and explores its potential in developing optoelectronic sensors.

Description and Verification of the Fundamental Current Mechanisms in Silicon Carbide Schottky Barrier Diodes.

Attempts to model the current through Schottky barrier diodes using the two fundamental mechanisms of thermionic emission and tunnelling are adversely impacted by defects and second order effects. This has led to the publication of countless different models to account for these effects, including some with non-physical parameters. Recently, we have developed silicon carbide Schottky barrier diodes that do not suffer from second order effects, such as excessive leakage, carrier generation and recombination, and non-uniform barrier height. In this paper, we derive the foundational current equations to establish clear links between the fundamental current mechanisms and the governing parameters. Comparing these equations with measured current-voltage characteristics, we show that the fundamental equations for tunnelling and thermionic emission can accurately model 4H silicon carbide Schottky barrier diodes over a large temperature and voltage range. Based on the obtained results, we discuss implications and misconceptions regarding barrier inhomogeneity, barrier height measurement, and reverse-bias temperature dependencies.

3C-SiC/Si Heterostructure: An Excellent Platform for Position-Sensitive Detectors Based on Photovoltaic Effect.

Single-crystalline silicon carbide (3C-SiC) on the Si substrate has drawn significant attention in recent years due to its low wafer cost and excellent mechanical, chemical, and optoelectronic properties. However, the applications of the structure have primarily been focused on piezoresistive and pressure sensors, bio-microelectromechanical system, and photonics. Herein, we report another promising application of the heterostructure as a laser spot position-sensitive detector (PSD) based on the lateral photovoltaic effect (LPE) under nonuniform optical illuminations at zero-bias conditions. The LPE shows a linear dependence on spot positions, and the sensitivity is found to be as high as 33 mV/mm under an illumination of 2.8 W/cm2 (635 nm). The structure also exhibits a linear dependence of the LPE over a large distance (7 mm) between two electrodes, which is crucial for PSDs as the region with a linear dependence of LPE is only usable for PSDs. The LPE at different spot positions and under different illumination conditions have been investigated and explained based on the energy-band analysis. The temperature dependence of the LPE and position sensitivity is also investigated. Furthermore, the two-dimensional mapping of the lateral photovoltages reveals the potential for utilizing the 3C-SiC/Si heterostructure to detect the laser spot position precisely on a plane.

Pushing the Limits of Piezoresistive Effect by Optomechanical Coupling in 3C-SiC/Si Heterostructure.

This letter reports a giant opto-piezoresistive effect in p-3C-SiC/p-Si heterostructure under visible-light illumination. The p-3C-SiC/p-Si heterostructure has been fabricated by growing a 390 nm p-type 3C-SiC on a p-type Si substrate using the low pressure chemical vapor deposition (LPCVD) technique. The gauge factor of the heterostructure was found to be 28 under a dark condition; however, it significantly increased to about -455 under illumination of 635 nm wavelength at 3.0 mW/cm2. This gauge factor is over 200 times higher than that of commercial metal strain gauge, 16 times higher than that of 3C-SiC thinfilm, and approximately 5 times larger than that of bulk Si. This enhancement of the gauge factor was attributed to the opto-mechanical coupling effect in p-3C-SiC/p-Si heterostructure. The opto-mechanical coupling effect is the amplified effect of the photoconductivity enhancement and strain-induced band structure modification in the p-type Si substrate. These findings enable extremely high sensitive and robust mechanical sensors, as well as optical sensors at low cost, as no complicated nanofabrication process is required.

Excellent Rectifying Properties of the n-3C-SiC/p-Si Heterojunction Subjected to High Temperature Annealing for Electronics, MEMS, and LED Applications.

This work examines the stability of epitaxial 3C-SiC/Si heterojunctions subjected to heat treatments between 1000 °C and 1300 °C. Because of the potential for silicon carbide in high temperature and harsh environment applications, and the economic advantages of growing the 3C-SiC polytype on large diameter silicon wafers, its stability after high temperature processing is an important consideration. Yet recently, this has been thrown into question by claims that the heterojunction suffers catastrophic degradation at temperatures above 1000 °C. Here we present results showing that the heterojunction maintains excellent diode characteristics following heat treatment up to 1100 °C and while some changes were observed between 1100 °C and 1300 °C, diodes maintained their rectifying characteristics, enabling compatibility with a large range of device fabrication. The parameters of as-grown diodes were J0 = 1 × 10-11 A/mm2, n = 1.02, and +/-2V rectification ratio of 9 × 106. Capacitance and thermal current-voltage analysis was used to characterize the excess current leakage mechanism. The change in diode characteristics depends on diode area, with larger areas (1 mm2) having reduced rectification ratio while smaller areas (0.04 mm2) maintained excellent characteristics of J0 = 2 × 10-10 A/mm2, n = 1.28, and +/-2V ratio of 3 × 106. This points to localized defect regions degrading after heat treatment rather than a fundamental issue of the heterojunction.

O2 plasma treated polyimide-based humidity sensors.

The effect of non-plasma and plasma treated polyimide-based humidity sensors is presented. Pure oxygen was used to etch polyimide in a plasma etcher. The sensor treated in a plasma exhibited higher sensitivity and faster response speed against moisture. The plasma treated sensor had 3.4 times the sensitivity and responded almost twice as fast as the non-plasma treated sensor. A further comparison of sensor outputs, sensitivity and response speed are presented. Chemical analysis of the polyimide surface was carried out by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (ATR-FTIR). XPS and ATR-FTIR showed the increase in carbonyl carbon bonds, C=O, after the plasma treatment. Geometrical modification was observed by atomic force microscopy (AFM). It showed considerable surface roughness after the plasma treatment. O2 plasma treatment improved the sensitivity, and reduced the hysteresis of the sensor due to the increase in C=O bonds in the polyimide.