Applications of Spectrally-Resolved Photoluminescence in Silicon Photovoltaics

In broad terms, this thesis is devoted to measuring and interpreting the photoluminescence spectra emitted from different structures in crystalline silicon wafers and solar cells. Based on the knowledge accumulated, it also establishes a variety of applications of photoluminescence spectroscopy in silicon photovoltaics. The thesis may be divided into 3 main categories: band-to-band luminescence from wafers, deep-level luminescence from defects and impurities, and composite luminescence from different structures and layers in solar cells. First, this thesis utilizes band-to-band photoluminescence spectra emitted from planar silicon wafers to determine the values of the band-to-band absorption coefficient and the radiative recombination coefficient as a function of temperature with high precision. Parameterizations of these two coefficients are established to allow convenient calculations. Based on the newly established temperature data, the impacts of surface geometries and excess carrier profiles on luminescence spectra emitted from various silicon wafers are investigated via both modeling and experiments as a function of temperature. The results suggest that, the accuracy of many photoluminescence-based techniques, established mainly at room temperature in the literature, can be further improved by performing the measurements at higher temperatures due to the increasing impacts of surface reflectivities and excess carrier profiles on luminescence spectra with rising temperatures. These applications highlight the significance of the established data of the two coefficients for spectral fitting techniques. Next, the thesis investigates the deep-level luminescence from defects and impurities distributed around sub-grain boundaries in multicrystalline silicon wafers. The thesis shows that, the dislocations at sub-grain boundaries and the defects and impurities trapped around the dislocations emit separate luminescence peaks at low temperatures. The luminescence intensity of the trapped defects and impurities is found to be altered significantly after phosphorus gettering, whereas the dislocation luminescence is not changed throughout different solar cell processing steps. Also, the trapped defects and impurities are found to be preferentially distributed on one side of the sub-grain boundaries due to the asymmetric distribution of their luminescence intensity across the sub-grain boundaries. In addition, the thesis also demonstrates that the damage induced by laser doping is related to dislocations, since its deep-level luminescence spectrum has similar properties to those emitted from dislocations in multicrystalline silicon wafers. The interface between the laser-doped and un-doped regions is found to contain more damage than the laser-doped regions. Furthermore, the thesis reports a new photoluminescence-based method to separate the luminescence signatures from different layers and structures in a single silicon substrate, courtesy of the well-resolved luminescence peaks at low temperatures from different layers. In particular, the technique is applied to characterize the doping level of both locally-diffused and laser-doped regions on various silicon solar cells and cell precursors, utilizing band-gap narrowing effects in heavily-doped silicon. The results show that, the interface between the laser-doped and un-doped regions is much more heavily-doped that the doped regions. In addition, the technique is also applied to evaluate and the parasitic absorption of different surface passivation films on finished solar cells, due to the correlation between the sub band-gap luminescence intensity from these passivation films and the optical absorption in the films. The technique is contactless and nondestructive, requires minimal sample preparation, and provides micron-scale spatial resolutions. Finally, the thesis combines the advantages of spectrally-resolved photoluminescence (PLS) and photoluminescence excitation spectroscopy (PLE) to develop a PLS-PLE-combined technique for characterizing wafers and solar cells. In particular, the entire photoluminescence spectrum from a silicon wafer or solar cell is captured and monitored while the excitation energy is varied. This technique allows us to quantitatively evaluate both the doping level and the junction depth of various diffused silicon wafers, the defects induced by the post-diffusion thermal treatment at different depths below the wafer surface, and the enhanced diffusion at grain boundaries and sub-grain boundaries in multicrystalline silicon wafers. The results show that, the enhanced diffusion happens at both grain boundaries and sub-grain boundaries

VFFINDER: A Graph-based Approach for Automated Silent Vulnerability-Fix Identification

The increasing reliance of software projects on third-party libraries has raised concerns about the security of these libraries due to hidden vulnerabilities. Managing these vulnerabilities is challenging due to the time gap between fixes and public disclosures. Moreover, a significant portion of open-source projects silently fix vulnerabilities without disclosure, impacting vulnerability management. Existing tools like OWASP heavily rely on public disclosures, hindering their effectiveness in detecting unknown vulnerabilities. To tackle this problem, automated identification of vulnerability-fixing commits has emerged. However, identifying silent vulnerability fixes remains challenging. This paper presents VFFINDER, a novel graph-based approach for automated silent vulnerability fix identification. VFFINDER captures structural changes using Abstract Syntax Trees (ASTs) and represents them in annotated ASTs. VFFINDER distinguishes vulnerability-fixing commits from non-fixing ones using attention-based graph neural network models to extract structural features. We conducted experiments to evaluate VFFINDER on a dataset of 36K+ fixing and non-fixing commits in 507 real-world C/C++ projects. Our results show that VFFINDER significantly improves the state-of-the-art methods by 39-83% in Precision, 19-148% in Recall, and 30-109% in F1. Especially, VFFINDER speeds up the silent fix identification process by up to 47% with the same review effort of 5% compared to the existing approaches.Comment: Accepted by IEEE KSE 202

Proposal of MIMO Ultra-Wide Band Antenna with Low Mutual Coupling

In this paper, a new ultra-wide band (UWB) MIMO antenna is proposed. A MIMO antenna set consists of two single ultra-wide band antennas. This simple and compact MIMO antenna, which is designed to work from 3.1 GHz to 10.6 GHz, has a broad bandwidth with the VSWR ≤ 2. In addition, MIMO antenna characteristics such as radiation pattern, maximal gain are thoroughly investigated

EmbryosFormer: Deformable Transformer and Collaborative Encoding-Decoding for Embryos Stage Development Classification

The timing of cell divisions in early embryos during the In-Vitro Fertilization (IVF) process is a key predictor of embryo viability. However, observing cell divisions in Time-Lapse Monitoring (TLM) is a time-consuming process and highly depends on experts. In this paper, we propose EmbryosFormer, a computational model to automatically detect and classify cell divisions from original time-lapse images. Our proposed network is designed as an encoder-decoder deformable transformer with collaborative heads. The transformer contracting path predicts per-image labels and is optimized by a classification head. The transformer expanding path models the temporal coherency between embryo images to ensure monotonic non-decreasing constraint and is optimized by a segmentation head. Both contracting and expanding paths are synergetically learned by a collaboration head. We have benchmarked our proposed EmbryosFormer on two datasets: a public dataset with mouse embryos with 8-cell stage and an in-house dataset with human embryos with 4-cell stage. Source code: https://github.com/UARK-AICV/Embryos.Comment: Accepted at WACV 202

Hemorrhagic Meningioma With Symptom of Convulsion: A Rare Presentation of Parietal Meningioma

Meningioma is the most common, extra-axial, non-glial intracranial tumor with an incidence of 2.3-5.5/100 000, accounting for 20%-30% of all primary brain tumor diagnoses in adults. Meningiomas associated with intratumoral hemorrhage are very rare occurring in 0.5%-2.4%. of individuals. Herein, we report a rare case of hemorrhagic meningioma with the symptom of convulsion. The case was a 68-year-old woman admitted to the hospital with severe headache and convulsions. Computed tomography revealed an increase in heterogeneous lesion measuring 4 × 3 × 2.5 cm at the right parietal lobe. Brain magnetic resonance imaging (MRI) showed a grossly stable homogeneously enhancing extra-axial mass measuring 43 × 33 × 28 mm, small calcified peripheral, intratumoral hemorrhage. Histopathology showed a multi-celled meningioma with bleeding areas (WHO grade I)

Effects of ENSO on Autumn Rainfall in Central Vietnam

28 years (1980–2007) of station and gridded reanalysis data were used to investigate the effects of El Niño/Southern Oscillation (ENSO) on autumn rainfall in the Extended Central Vietnam (ECV) region. Results show that, under El Niño conditions, autumn rainfall in Central Vietnam is reduced by about 10 to 30%. This reduction seems to be caused by a weakening of the North East monsoon circulation, which appears to be linked to an anomalous anticyclonic vortex and a positive sea level pressure anomaly over the East Sea. In addition, the disappearance of a secondary moisture source over the southern region of the East Sea also favors the reduction in rainfall over this region. Conversely, during La Niña, the total autumn rainfall in the ECV region increases by about 9 to 19%. The strengthening of the North East monsoon, with a cyclonic wind anomaly over the East Sea, helps to increase the moisture supply to the area by about 10 to 20%, resulting in enhanced rainfall in the ECV. It is also found that the La Niña conditions do not only cause an increase in rainfall, but also change the temporal distribution of the monthly rainfall over the region, with more rainfall in the latter months of the year

Le portail g-INFO pour surveiller la grippe Influenza A

Le portail g-INFO pour surveiller la grippe Influenza

Spondylolysis-induced Multilevel Lumbar Spondylolisthesis; Challenges in Lumbar Spine Surgery

Lumbar spondylolysis and multilevel lumbar spondylolysis account for 4.4-5.8% and 0.3% of the general population, and multilevel lumbar spondylolysis resulting in spondylolisthesis is even rarer. Herein, we report two cases of three-level lumbar spondylolisthesis because of spondylolysis: A 49-year-old woman was admitted to the hospital for dull lower back pain over the past 8 months, with exacerbating symptoms when standing and walking. Spasticity at lumbar region and radiculopathy at S1 nerve root was found on examination and a 63-year-old man was admitted to the hospital because of numbness and perianal sensory disturbances with difficulty urinating 2 weeks ago, the symptoms gradually increased to the time of examination. Both patients were diagnosed with multilevel lumbar spondylolisthesis because of spondylolysis and were indicated for posterior lumbar interbody fusion (PLIF). After surgery, both patients recovered well without any significant complications. The improved treatment results suggest the application of PLIF technique to treat spondylolysis-induced multilevel lumbar spondylolisthesis