Coupled-mode theory for stimulated Raman scattering in high-Q/Vm silicon photonic band gap defect cavity lasers

We demonstrate the dynamics of stimulated Raman scattering in designed high-Q/Vm silicon photonic band gap nanocavities through the coupled-mode theory framework towards optically-pumped silicon lasing. The interplay of other chi(3) effects such as two-photon absorption and optical Kerr, related free-carrier dynamics, thermal effects, as well as linear losses such as cavity radiation and linear material absorption are included and investigated numerically. Our results clarify the relative contributions and evolution of the mechanisms, and demonstrate the lasing and shutdown thresholds. Our studies illustrate the conditions for continuous-wave and pulsed highly-efficient Raman frequency conversion to be practically realized in monolithic silicon high-Q/Vm photonic band gap defect cavities.Comment: 40 pages, 11 figures, submitted to Physics Review

Influence of environmental and host factors on the temporal development of early life infant gut microbiome

The composition and dynamics of the early life gut microbiota plays a major role in establishing neonatal immunity and is suggested to have multiple impacts on the child’s long-term health. Meanwhile, the composition of the infant gut microbiome has been shown to be affected by the birth mode, infant health and diet. However, the characterization of the infant gut microbiome and its impact on the host’s health is still challenging as the contribution and importance of multiple co-factors on the early microbiome during infant growth is still poorly understood and characterized. The Health and Early-life microbiota (HELMi) is a cohort of more than 1000 healthy Finnish infants currently followed from birth to 4-5 years old. By now, the HELMi dataset comprises more than 400 whole genome shotgun metagenomes obtained from stool samples from 80 infants and parents, but also an in-depth characterization of the families’ lifestyle, environment, health and nutrition, allowing for a precise and cutting-edge characterization of the early gut microbiota. Based on the datasets from the HELMi, this project used Metaphlan3, Kraken and Braken to determine the best computational approach for the taxonomic profiling of the metagenomic reads. Then a PERMANOVA test was performed to evaluate and determine the factors significantly associated with the compositional microbiota variation within the infant gut metagenomes. This study first identified technical factors introducing bias in taxonomic profiling (e.g., DNA extraction batch), which served as confounders in the analysis of environmental and host variables. The investigation of these biological factors indicates that pre-natal and peri-natal variables such as the mode of delivery significantly impact the infant gut microbiota, while we did not identify any significant impact of breastfeeding habits and medication exposures in this study

Rapid, Robust, and Reliable Blind Deconvolution via Nonconvex Optimization

We study the question of reconstructing two signals $f$ and $g$ from their convolution $y = f\ast g$. This problem, known as {\em blind deconvolution}, pervades many areas of science and technology, including astronomy, medical imaging, optics, and wireless communications. A key challenge of this intricate non-convex optimization problem is that it might exhibit many local minima. We present an efficient numerical algorithm that is guaranteed to recover the exact solution, when the number of measurements is (up to log-factors) slightly larger than the information-theoretical minimum, and under reasonable conditions on $f$ and $g$. The proposed regularized gradient descent algorithm converges at a geometric rate and is provably robust in the presence of noise. To the best of our knowledge, our algorithm is the first blind deconvolution algorithm that is numerically efficient, robust against noise, and comes with rigorous recovery guarantees under certain subspace conditions. Moreover, numerical experiments do not only provide empirical verification of our theory, but they also demonstrate that our method yields excellent performance even in situations beyond our theoretical framework