The Cosmic Twilight Polarimeter: a Model-Independent Approach to Constrain the Synchrotron Foreground Spectrum for Global 21-cm Cosmology

Detecting the cosmological sky-averaged (global) 21-cm spectrum as a function of observed frequency will provide a powerful tool to study the ionization and thermal history of intergalactic medium (IGM) in the high-redshift Universe (∼ 400 million years after the Big Bang). The biggest challenge in conventional ground-based total-power global 21-cm experiments is the removal of the Galactic and extragalactic synchrotron foreground (~ 10,000-100,000 K) to uncover the weak cosmological signal (∼ 10-100 mK) due to corruption on the spectral smoothness of foreground spectrum by instrumental effects. Although an absorption profile has been reported recently at 78 MHz in the sky-averaged spectrum by the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) experiment, it is necessary to confirm that the proposed observation is indeed the global 21-cm signal with an independent approach. In this thesis, we propose a new polarimetry-based observational approach that relies on the dynamic characteristics of the foreground emission at the circumpolar region to track and remove the foreground spectrum directly, without relying on any parametric foreground models as in conventional approaches. Due to asymmetry and the Earth's rotation, the projection of the anisotropic foreground sources onto a wide-view antenna pointing at the North Celestial Pole (NCP) can induce a net polarization which varies with time with a unique twice-diurnal periodicity. Different from the zenith-pointing global 21-cm experiments, by using this twice-diurnal signature, the Cosmic Twilight Polarimeter (CTP) is designed to measure and separate the varying foreground from the isotropic cosmological background simultaneously in the same observation. By combining preliminary results of the proof-of-concept instrument with numerical simulations, we present a detailed evaluation for this technique and its feasibility in conducting an independent global 21-cm measurement in the near future

Constraining a Model of the Radio Sky Below 6 MHz Using the Parker Solar Probe/FIELDS Instrument in Preparation for Upcoming Lunar-based Experiments

We present a Bayesian analysis of data from the FIELDS instrument on board the Parker Solar Probe (PSP) spacecraft with the aim of constraining low frequency ($\lesssim$ 6 MHz) sky in preparation for several upcoming lunar-based experiments. We utilize data recorded during PSP's ``coning roll'' maneuvers, in which the axis of the spacecraft is pointed 45$^{\circ}$ off of the Sun. The spacecraft then rotates about a line between the Sun and the spacecraft with a period of 24 minutes. We reduce the data into two formats: roll-averaged, in which the spectra are averaged over the roll, and phase-binned, in which the spectra are binned according to the phase of the roll. We construct a forward model of the FIELDS observations that includes numerical simulations of the antenna beam, an analytic emissivity function of the galaxy, and estimates of the absorption due to free electrons. Fitting 5 parameters, we find that the roll-averaged data can be fit well by this model and we obtain posterior parameter constraints that are in general agreement with previous estimates. The model is not, however, able to fit the phase-binned data well, likely due to limitations such as the lack of non-smooth emission structure at both small and large scales, enforced symmetry between the northern and southern galactic hemispheres, and large uncertainties in the free electron density. This suggests that significant improvement in the low frequency sky model is needed in order to fully and accurately represent the sky at frequencies below 6 MHz.Comment: 18 pages, 10 figures, 5 tables. Under review in the Astrophysical Journa

The Impact of Beam Variations on Power Spectrum Estimation for 21 cm Cosmology II: Mitigation of Foreground Systematics for HERA

One key challenge in detecting 21 cm cosmological signal at z > 6 is to separate the cosmological signal from foreground emission. This can be studied in a power spectrum space where the foreground is confined to low delay modes whereas the cosmological signal can spread out to high delay modes. When there is a calibration error, however, chromaticity of gain errors propagates to the power spectrum estimate and contaminates the modes for cosmological detection. The Hydrogen Epoch of Reionization Array (HERA) employs a high-precision calibration scheme using redundancy in measurements. In this study, we focus on the gain errors induced by nonredundancies arising from feed offset relative to the HERA's 14 meter parabolic dish element, and investigate how to mitigate the chromatic gain errors using three different methods: restricting baseline lengths for calibration, smoothing the antenna gains, and applying a temporal filter prior to calibration. With 2 cm/2 degree perturbations for translation/tilting motions, a level achievable under normal HERA operating conditions, the combination of the baseline cut and temporal filtering indicates that the spurious gain feature due to nonredundancies is significantly reduced, and the power spectrum recovers the clean foreground-free region. We found that the mitigation technique works even for large feed motions but in order to keep a stable calibration process, the feed positions need to be constrained to 2 cm for translation motions and 2 degree for tilting offset relative to the dish's vertex.Comment: Accepted for publication in Ap

Prevalence of systemic inflammatory response syndrome (SIRS) in hospitalized children: a point prevalence study

<p>Abstract</p> <p>Background</p> <p>In accordance with the 1st International pediatric sepsis consensus conference, where sepsis was defined as SIRS associated with suspected or proven infection, we have identified the need to assess the prevalence of SIRS and sepsis in children with abnormal temperatures hospitalized in The Children's Clinical University Hospital in Latvia.</p> <p>Methods</p> <p>A descriptive prospective point prevalence study (using two time periods, each 24 h, randomly chosen) was conducted on all children (n = 943) treated in the hospital. All children with abnormal temperatures – fever or hypothermia (n = 92) – were included in the study. Questionnaires evaluating age-specific SIRS criteria were completed. The prevalence of SIRS was detected with 95% CI.</p> <p>Results</p> <p>Out of a total of 943 patients treated in the hospital, 10% (n = 92) had abnormal temperatures. In all these cases the abnormal temperature was a fever; hypothermia was not established in any patient. Of the children with fever, 72% (n = 66) had SIRS. Of the SIRS patients, 8% (n = 5) developed sepsis, 5% (n = 3) severe sepsis and 2% (n = 1) septic shock. Seventy-six percent (n = 50) of the SIRS patients had fever in combination with respiratory rate >2 SD above normal for age; 50% (n = 33) had fever with abnormal leukocyte count; 15% (n = 10) had fever with tachycardia >2 SD above normal for age. Most of the SIRS patients (39%, n = 25) were aged 2–5 years. Twenty-one percent (n = 14) of the children with SIRS and 50% (n = 2) of those with severe sepsis and septic shock had an underlying disease. In no case was SIRS and sepsis recognized by doctors and the diagnoses were not recorded on the patients' cards.</p> <p>Conclusion</p> <p>Our results would indicate a high risk for sepsis development in children with SIRS. Early SIRS diagnosis and awareness of risk of developing sepsis could change the medical approach to the patient in everyday clinical practice, eventually leading to early, goal-directed therapy for sepsis.</p

Determinants of export performance: Case of seafood firms in Viet Nam

Purpose : The purpose of this paper is to define and measure key factors regarding to export performance of seafood firms in Viet Nam. Methodology: This study has used qualitative and quantitative researches: (i) qualitative research has been carried out through focus group discussions with 10 chief executive officers of seafood firms, and (ii) quantitative research conducted through direct interviews with 305 seafood firms (chief executive officer or senior executive) in Mekong Delta region (Viet Nam). Result and conclusion: The results show that: (i) export performance is affected by export marketing strategy, characteristics and capabilities, industry characteristics, management characteristics, domestic market characteristics, and foreign market characteristics; (ii) export marketing strategy is affected by characteristics and capabilities, industry characteristics, management characteristics, domestic market characteristics, and foreign market characteristics. However, the research subject has certain limitations: (i) due to limited resources in conducting research, the sample size consisted of 305 seafood firms; (ii) this study conducted the sampling technique of using direct interview methods from respondents

Determinants of export performance: Case of seafood firms in Viet Nam

Purpose : The purpose of this paper is to define and measure key factors regarding to export performance of seafood firms in Viet Nam. Methodology: This study has used qualitative and quantitative researches: (i) qualitative research has been carried out through focus group discussions with 10 chief executive officers of seafood firms, and (ii) quantitative research conducted through direct interviews with 305 seafood firms (chief executive officer or senior executive) in Mekong Delta region (Viet Nam). Result and conclusion: The results show that: (i) export performance is affected by export marketing strategy, characteristics and capabilities, industry characteristics, management characteristics, domestic market characteristics, and foreign market characteristics; (ii) export marketing strategy is affected by characteristics and capabilities, industry characteristics, management characteristics, domestic market characteristics, and foreign market characteristics. However, the research subject has certain limitations: (i) due to limited resources in conducting research, the sample size consisted of 305 seafood firms; (ii) this study conducted the sampling technique of using direct interview methods from respondents

Advancing basalt fiber asphalt concrete design: A novel approach using gradient boosting and metaheuristic algorithms

Basalt Fiber Asphalt Concrete (BFAC) is an environmentally friendly and durable material with potential road, bridge, and infrastructure construction applications. This study investigates the application of Machine Learning (ML) models, specifically the classical Gradient Boosting (CGB) algorithm, in conjunction with metaheuristic algorithms, to predict the Marshall Stability (MS) and optimize the design of BFAC mixtures. The model is trained and tested on a comprehensive dataset of experimental samples, taking into account various input parameters, including basalt fiber (BF) properties, asphalt binder characteristics, and aggregate gradation. Hyperparameter tuning is employed to enhance the model's predictive performance using metaheuristic algorithms such as Particle Swarm Optimization (PSO), Hunger Games Search (HGS), and Bald Eagle Search (BES) and compared regarding the convergence and computational efficiency. The findings demonstrate that BES outperforms other algorithms, achieving the highest performance. The CGB-BES model is then applied to three optimization scenarios, focusing on maximizing the MS while minimizing BF and asphalt binder content. Post-processing and interpretation of the results reveal the importance of combining ML and materials engineering expertise. By highlighting the synergy between CGB-BES model and domain-specific knowledge, materials engineers can effectively optimize the mixtures and improve the design and performance of BFAC

Cancer Cell Coating Nanoparticles for Optimal Tumor-Specific Cytokine Delivery

© 2020 American Chemical Society. Although cytokine therapy is an attractive strategy to build a more robust immune response in tumors, cytokines have faced clinical failures due to toxicity. In particular, interleukin-12 has shown great clinical promise but was limited in translation because of systemic toxicity. In this study, we demonstrate an enhanced ability to reduce toxicity without affecting the efficacy of IL-12 therapy. We engineer the material properties of a NP to meet the enhanced demands for optimal cytokine delivery by using the layer-by-layer (LbL) approach. Importantly, using LbL, we demonstrate cell-level trafficking of NPs to preferentially localize to the cell's outer surface and act as a drug depot, which is required for optimal payload activity on neighboring cytokine membrane receptors. LbL-NPs showed efficacy against a tumor challenge in both colorectal and ovarian tumors at doses that were not tolerated when administered carrier-free