Characterizing alma for solar observation

ALMA (Atacama Large Millimeter/submillimeter Array) is an antenna array of 66 antennas located in northern Chile at 5000 meters altitude. It is the largest ground-based array operated at millimeter/submillimeter wavelengths. In this thesis, the advantages of using ALMA for solar observation are presented, together with the introduction of a campaign to commission ALMA for solar observations. Observation modes of the solar campaign are reviewed in Chapter 2. Methods for constructing images from single dish data as well as the procedure for processing interferometer data, including calibration and imaging, are given in Chapter 3. The CLEAN algorithm that is used for producing images is also discussed in this chapter. Examples of processed images, both for single dish and interferometer, are shown in Chapter 4. In the final Chapter 5, a discussion about what remains to be done to create the observing tool and define observing modes for future ALMA solar campaign is provided

Waves and oscillations in a sunspot: Observations and modeling of noaa ar 12470

Waves and oscillations are important solar phenomena not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. Among these phenomena, the one of the most interesting ones occurs in the sunspot umbra. In this area, continuously propagating magnetohydrodynamic (MHD) waves generated from below the photosphere create the famous 3-minute sunspot umbral oscillations that affect the line profile of spectral lines due to temperature, density, and velocity changes of the plasma in the region. In the past decades, numerous observations and models have been carried out about the nature of the 3-minute oscillation and its relation with the coronal heating problem, but the lack of direct observations of the temperature variation in the chromosphere has made it hard to answer these questions. The need for a better understanding of the fine structure of the 3-minute oscillation and its time evolution in sunspots has intensified with the development of better observing tools. Among modern observatories, the Atacama Large Millimeter/submillimeter Array (ALMA) opens up a new era of solar radio observation due to its high spatial and temporal resolution and image quality. When combined with other cutting-edge instruments, such as the Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO), the Atmospheric Imaging Assembly (AIA) on board the Solar DynamiCST Observatory, and Interface Region Imaging Spectrograph (IRIS), ALMA can provide unique electron temperature diagnostics that clarify the behavior of the solar chromosphere’s response to propagating waves. In this dissertation, a study is carried out about sunspot oscillations and wave propagation in NOAA active region 12470 using an approximately 1 hr long dataset acquired on 2015 December 17 by the instruments listed above. The discovery of 3-minute sunspot oscillations seen in the mm-wave band is reported for the first time. The 2 s cadence of ALMA images makes it possible to well resolve the typical 3-minute period sunspot oscillation in the chromosphere. Fourier analysis is applied to the ALMA 3 mm continuum and CST Hα data sets to obtain the power spectra as well as phase information of the oscillations. The properties of the wave propagation are analyzed by combining multiple wavelengths that probe physical parameters of the solar atmosphere at different heights. The chromospheric radiation is synthesized in 1-D using a radiation transfer code which uses the Solar Irradiance Physical Modeling (SRPM) as an input. A good correlation of the phase relationship between the observed and modeled oscillations of Hα and temperature fluctuations has been found and it is consistent with the result from a possible physical model for impulse-driven acoustic waves propagating in the gravitationally stratified medium. An asymmetry in the time profile of the temperature fluctuations discovered in the ALMA data is found to require a nonlinear wave solution, which is applied to several atmospheric models in an attempt to match the asymmetry and the absolute brightness temperature of the simulations to the observations. The asymmetry is successfully reproduced using the nonlinear wave scenario, although the absolute brightness of the simulated atmosphere remains lower than observed. These results demonstrate the capability of ALMA mm observations to provide new insight into what is needed for improving such atmospheric models in the future

Using internet search data to predict new HIV diagnoses in China: a modelling study.

ObjectivesInternet data are important sources of abundant information regarding HIV epidemics and risk factors. A number of case studies found an association between internet searches and outbreaks of infectious diseases, including HIV. In this research, we examined the feasibility of using search query data to predict the number of new HIV diagnoses in China.DesignWe identified a set of search queries that are associated with new HIV diagnoses in China. We developed statistical models (negative binomial generalised linear model and its Bayesian variants) to estimate the number of new HIV diagnoses by using data of search queries (Baidu) and official statistics (for the entire country and for Guangdong province) for 7 years (2010 to 2016).ResultsSearch query data were positively associated with the number of new HIV diagnoses in China and in Guangdong province. Experiments demonstrated that incorporating search query data could improve the prediction performance in nowcasting and forecasting tasks.ConclusionsBaidu data can be used to predict the number of new HIV diagnoses in China up to the province level. This study demonstrates the feasibility of using search query data to predict new HIV diagnoses. Results could potentially facilitate timely evidence-based decision making and complement conventional programmes for HIV prevention

Olfaction Contributes to Pelagic Navigation in a Coastal Shark.

How animals navigate the constantly moving and visually uniform pelagic realm, often along straight paths between distant sites, is an enduring mystery. The mechanisms enabling pelagic navigation in cartilaginous fishes are particularly understudied. We used shoreward navigation by leopard sharks (Triakis semifasciata) as a model system to test whether olfaction contributes to pelagic navigation. Leopard sharks were captured alongshore, transported 9 km offshore, released, and acoustically tracked for approximately 4 h each until the transmitter released. Eleven sharks were rendered anosmic (nares occluded with cotton wool soaked in petroleum jelly); fifteen were sham controls. Mean swimming depth was 28.7 m. On average, tracks of control sharks ended 62.6% closer to shore, following relatively straight paths that were significantly directed over spatial scales exceeding 1600 m. In contrast, tracks of anosmic sharks ended 37.2% closer to shore, following significantly more tortuous paths that approximated correlated random walks. These results held after swimming paths were adjusted for current drift. This is the first study to demonstrate experimentally that olfaction contributes to pelagic navigation in sharks, likely mediated by chemical gradients as has been hypothesized for birds. Given the similarities between the fluid three-dimensional chemical atmosphere and ocean, further research comparing swimming and flying animals may lead to a unifying paradigm explaining their extraordinary navigational abilities