A fast 2D image reconstruction algorithm from 1D data for the Gaia mission

A fast 2-dimensional image reconstruction method is presented, which takes as input 1-dimensional data acquired from scans across a central source in different orientations. The resultant reconstructed images do not show artefacts due to non-uniform coverage in the orientations of the scans across the central source, and are successful in avoiding a high background due to contamination of the flux from the central source across the reconstructed image. Due to the weighting scheme employed this method is also naturally robust to hot pixels. This method was developed specifically with Gaia data in mind, but should be useful in combining data with mismatched resolutions in different directions.Comment: accepted (18 pages, 13 figures) will appear in Experimental Astronom

From Hipparcos to Gaia

The measurement of the positions, distances, motions and luminosities of stars represents the foundations of modern astronomical knowledge. Launched at the end of the eighties, the ESA Hipparcos satellite was the first space mission dedicated to such measurements. Hipparcos improved position accuracies by a factor of 100 compared to typical ground-based results and provided astrometric and photometric multi-epoch observations of 118,000 stars over the entire sky. The impact of Hipparcos on astrophysics has been extremely valuable and diverse. Building on this important European success, the ESA Gaia cornerstone mission promises an even more impressive advance. Compared to Hipparcos, it will bring a gain of a factor 50 to 100 in position accuracy and of a factor of 10,000 in star number, collecting photometric, spectrophotometric and spectroscopic data for one billion celestial objects. During its 5-year flight, Gaia will measure objects repeatedly, up to a few hundred times, providing an unprecedented database to study the variability of all types of celestial objects. Gaia will bring outstanding contributions, directly or indirectly, to most fields of research in astrophysics, such as the study of our Galaxy and of its stellar constituents, the search for planets outside the solar system.Comment: 6 pages. New Horizons in Time Domain Astronomy Proceedings IAU Symposium No. 285, 2012, E. Griffin, B. Hanisch & R. Seaman, ed

Free energies in the presence of electric and magnetic fields

We discuss different free energies for materials in static electric and magnetic fields. We explain what the corresponding Hamiltonians are, and describe which choice gives rise to which result for the free energy change, dF, in the thermodynamic identity. We also discuss which Hamiltonian is the most appropriate for calculations using statistical mechanics, as well as the relationship between the various free energies and the "Landau function", which has to be minimized to determine the equilibrium polarization or magnetization, and is central to Landau's theory of second order phase transitions

Many-body Green's function theory for electron-phonon interactions: the Kadanoff-Baym approach to spectral properties of the Holstein dimer

We present a Kadanoff-Baym formalism to study time-dependent phenomena for systems of interacting electrons and phonons in the framework of many-body perturbation theory. The formalism takes correctly into account effects of the initial preparation of an equilibrium state, and allows for an explicit time-dependence of both the electronic and phononic degrees of freedom. The method is applied to investigate the charge neutral and non-neutral excitation spectra of a homogeneous, two-site, two-electron Holstein model. This is an extension of a previous study of the ground state properties in the Hartree (H), partially self-consistent Born (Gd) and fully self-consistent Born (GD) approximations published in Ref. [arXiv:1403.2968]. We show that choosing a homogeneous ground state solution leads to unstable dynamics for a sufficiently strong interaction, and that allowing a symmetry-broken state prevents this. The instability is caused by the bifurcation of the ground state and understood physically to be connected with the bipolaronic crossover of the exact system. This mean-field instability persists in the partially self-consistent Born approximation but is not found for the fully self-consistent Born approximation. By understanding the stability properties, we are able to study the linear response regime by calculating the density-density response function by time-propagation. This functions amounts to a solution of the Bethe-Salpeter equation with a sophisticated kernel. The results indicate that none of the approximations is able to describe the response function during or beyond the bipolaronic crossover for the parameters investigated. Overall, we provide an extensive discussion on when the approximations are valid, and how they fail to describe the studied exact properties of the chosen model system.Comment: 12 figure

Relating starch structure in breakfast cereals and rice to their digestibility

Grain based food products are rich in the complex carbohydrate starch and represent a major source of dietary energy for the majority of the world’s population. These products play a significant role in digestive health, making them ideal targets for weight management and the prevention and management of obesity related illnesses such as type 2 diabetes and cardiovascular disease. Understanding the digestibility of grain products and improving their dietary quality is important for improving dietary management. However, the complex matrices of these products have resulted in poorly understood digestibility mechanisms. This project aims to characterise starch structure in grain foods to improve our understanding of their digestibility. In this work starches were employed as model samples with which to set up and optimise characterisation methods. Rice flour samples were then characterised. Rice has a relatively simple composition (90% starch) allowing for a less complex model with which to understand the relationship between starch structure and functional properties of starch such as digestibility. Breakfast cereals were also explored, allowing for an investigation into the characterisation of starch in a more complex sample matrix. Starch has multiple hierarchical structural levels on both the molecular and supramolecular level that need to be understood to comprehend the various models for starch digestibility. This has involved the mastering of a variety of techniques to characterise different structural levels of starch. Free solution capillary electrophoresis (CE) was employed in characterising the molecular of starch structure through the determination of amylose content and the investigation of heterogeneity of branching. The supramolecular structure of starch must also be characterised, with supramolecular arrangements introducing steric factors to digestibility. Both short- and long-range crystallinity were explored by a variety of techniques. Short-range order was investigated by Fourier-transform infrared (FTIR) spectroscopy, while long-range order was explored using X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). CE is a powerful separation technique that has been shown to be useful for the separation of amylose and amylopectin, the two macromolecular components of starch, by taking advantage of iodine binding and visible light detection. The amylose content of starch has been linked with digestive properties; therefore, accurate characterisation is an important step in understanding digestive properties. Separation approaches overcome the interference caused by overlapping absorbance bands in traditional approaches, allowing for a more accurate quantification. Previous applications of the CE method in the literature had employed non-ideal dissolution conditions, introducing inaccuracy into analysis. In this thesis the incorporation of improved dissolution conditions in the methodology was explored. A reduced sample concentration was found to be ideal, reducing aggregation. The use of anhydrous DMSO with the addition of a hydrogen bond disruptor, as well as high dissolution temperatures were also determined to be essential in obtaining a complete dissolution thus allowing for accurate characterisation. Using a new methodology developed by our research team, the heterogeneity of branching in starch was also explored by CE, assessing the broadness of resulting electrophoretic mobility distributions through the value of their dispersity. Results using this methodology indicated an extremely high degree of heterogeneity of branching in starch. Further optimisation of the separation method will allow the heterogeneity of amylose and amylopectin to be investigated independently. The determination of short-range order by FTIR spectroscopy is based on the ratio of infrared bands; however, the assignments of these bands are poorly understood. In this work, the improvement of spectral resolution, and the correlation of crystalline index values with published crystallinity values were explored. Transmission mode FTIR spectra measured at cryogenic temperatures yielded the best resolution of the peaks of interest with deconvolution also yielding slight improvements to spectral resolution. The influence of improved spectral resolution on the determined crystalline index was highly variable. Crystalline index values had a loose correlation with published crystallinity values in some cases; however, as a measure of crystallinity, this method was deemed to be suitable in cases where only an estimate is required. The determination of long-range order by XRD was also explored, investigating the influence of data processing and software packages in peak fitting approaches for crystallinity determinations. The different algorithms that the software packages employed impacted on the peak fitting, baseline fitting and resulting crystallinity determinations. SAXS has proven to be a valuable tool in the analysis of lamellar structures in starch. The relation between lamellar structure of maize starches and amylose content was explored. A decrease in the relative amount and size of semi-crystalline structure was observed with increasing amylose content. This trend is similar to those found in the literature in other plant starches. The same trend between varying amylose content and semi-crystalline structural features was also observed in rice flour for the first time. Degree of branching (as measured by another member of our research team) was also investigated in relation to other structural features. Degree of branching showed a trend with varying amylose content as well as a relationship with semi-crystalline structure. These relationships are expected to rely heavily on the amylose content itself and also on the branching structure of the amylases present. In conclusion, the starch structure is complex and every structural level influences digestive properties. A number of characterisation methods were explored in this work, aiming to develop a set of tools that may be used in understanding how starch structure at different levels relates to digestibility. Identifying the links between starch structure and digestibility creates opportunities for applications within the food industry to alter the digestion rates of foods and food ingredients. These relationships may then be used in more efficiently producing healthier food products to combat the issue of rising obesity rates and associated illnesses

Relating starch structure in rice to its digestibility

Rice is a globally important crop and a major staple for over two-thirds of the world’s population. Australian grown rice is renowned for its high and consistent quality and is the preferred choice in the domestic and many international rice markets. A long-established focus on quality in the Australian rice breeding program has led to a range of new varieties for different cuisines, for example sushi, long grain, medium grain and fragrant rice types. Development of new varieties takes up to 10 years from parental cross to a pure seed line that boasts sound agronomic, pest and disease resistance and the desired combination of quality traits. Selection techniques vary for each generation, and for each trait. This is a huge undertaking with upwards of 6500 breeding lines assessed for physical quality each year, and more than 3000 samples assessed for cooking qualities. As new consumer trends emerge, new market opportunities for rice are uncovered such as the recent shift toward more health-conscious consumer decisions. Development of more varieties with lower glycaemic index is one avenue to explore further. For this, additional, more well-understood tools are required to measure, predict and/or actively select for this trait at different stages of the breeding and quality program. Apparent amylose content is currently the only published link available with which researchers can predict the digestibility characteristics of a given rice sample. While the correlation between these attributes is good (r2 = 0.73), it is also indicative that there are other drivers at play. This is highlighted in instances where glycaemic index can vary by up to 20 points at a given apparent amylose content. There is a gap in the understanding of which levels of starch structure, if any, can account for the differences observed in digestibility where apparent amylose content is similar. To explore this, multiple levels of starch structure were assessed in different rice varieties using a combination of novel and well-established characterisation methods. The determination of factors of starch structure relevant to digestibility in this study was intended to better understand the drivers of digestibility in rice grains. And through this, attempt to provide new tools with which to assess samples likely to exhibit a higher or lower digestibility, thus allowing for better selectivity in breeding where certain digestibility characteristics are a grain quality goal. This was achieved through the characterisation of multiple features of starch structure which were found to provide valuable input to refining the understanding of rice digestibility

Significance of combined nutritional and morphological precaecal parameters for feed evaluations in non-ruminants

In this thesis the hypothesis is tested that the nutritional evaluation of dietary formulations in non-ruminants requires both functional-nutritional and functional-morphological parameters. The functional-nutritional parameters provide data on the outcome of the digestive process. Additionally, the functional-morphological parameters provide information about the effects of feed components on the small intestinal mucosa.Part I (chapters 2 - 4) considers the apparent digestibility as a functional-nutritional parameter for feed evaluation in pigs and roosters, whereas Part II (chapters 5 - 8) presents studies with functional-morphological parameters of the small intestinal mucosa of chickens, calves and piglets in relation to feed composition and additives.FUNCTIONAL-NUTRITIONAL PARAMETERS (PART I)The amount of protein and amino acids, which disappears in the large intestine of pigs, is not available for animal body maintenance and production (Zebrowska, et al ., 1978). Degradation of protein in the large intestines is mainly fermentative resulting in non-amino acid N end products, which are not available to the animal. This finding implies that precaecal digestion rather than whole tract digestion provides a more accurate parameter for the estimation of protein availability (Dierick et al., 1987). The in vivo determination of precaecal protein digestion relies on quantifying the ratio between the amount of the ingested protein to that which disappears proximal to the caecum. In digestibility experiments the diets and digesta, collected immediately after the ileum, are analysed on their protein contents. But digesta also contain undigested dietary protein of endogenous origin. Therefore, this ratio is determined as the apparent digestibility. Apparent digestibility is a quantitative parameter providing information on the digestive progress measured by nutrient disappearance at a defined site.Quantitative studies concerning the digestive processes in the small intestine require reproducible collection of digesta from the small intestine. Present procedures can be divided into techniques by which digesta are collected after sacrifying the animals and techniques based on a surgical intervention. Collection of digesta from animals after euthanasia is often used in experiments with broilers (Ravindran et al., 1999). This method, however, requires a large number of animals and for this reason is not commonly used in pigs. There are different surgical techniques described in literature for precaecal digesta collection. It is generally concluded that flexible (silicone) rubber is preferable to rigid materials. Regarding surgical techniques for intestinal studies in pigs, there is a consensus that simple T-shaped cannulae in the ileum and ileo-rectal anastomose (IRA) may not provide representative samples of digesta and/or may interfere with the animal's physiology (Köhler, 1992), whereas collection of digesta from re-entrant cannulae is considered to be hampered by technical difficulties (van Leeuwen et al ., 1987).In part I of the thesis surgical techniques and procedures for digesta collection in pigs and roosters are described and results of digestibility determinations are given.Chapter 1 describes a surgical procedure, which is called the Post Valve T-Caecum (PVTC) cannulation and is considered to be an alternative to the existing digesta collection methods. The prerequisites of this technique are that there is minimal hinder of the animal's physiology. Moreover, digesta samples should be representative, and the surgical technique acceptable in terms of animal welfare. The PVTC technique relies on partial caecectomy followed by placement of a wide flexible silicone T-cannula in the caecum. A considerable advantage of this technique is that the region of the intestine to be studied is not surgically treated. Gargallo and Zimmerman (1981) studied the possible effects of caecectomy on digestion in pigs. They observed small effects on overall digestibility of cellulose and nitrogen. Their final conclusion was that the absence of the caecum in pigs did not significantly alter digestive function. Darragh and Hodgkinson (2000) commented that the PVTC cannulation procedure appears to be the preferred method for the collection of ileal digesta.Chapter 2 describes digesta collection procedures and implications when using PVTC cannulated pigs. Collection of digesta after PVTC cannulation necessitates the use of an inert marker in the diets, to quantify the amounts of nutrients present in ileal digesta for determination of diet digestibility. Two experiments were conducted to evaluate chromic oxide (Cr 2 O 3 ) and HCl-insoluble ash as digestive markers by determining the apparent digestibility of dry matter (DM) and crude protein (CP). In addition, studies were performed of the effects of age (i.e. three different body weight (BW) classes) on apparent ileal DM and CP digestibilities. In experiment 1, barrows were fitted with PVTC cannulae to determine apparent ileal DM and CP digestibility of a wheat gluten/wheat bran ration and a soybean meal ration. Immediately after the morning feeding ileal digesta were collected on an hourly basis for a period of 12 hours. Subsequently, nitrogen (N) and marker contents were determined in these samples. The postprandial Cr/N ratio was more constant than the HCl-insoluble ash/N ratio. Therefore, chromic oxide is considered more suitable as a marker than HCl-insoluble ash when apparent digestibility of protein is the parameter to be studied. In experiment 2, apparent ileal DM and CP digestibilities were determined in 18 rations using twelve barrows fitted with PVTC cannulas (BW from 40 - 100 kg). The protein sources for these rations were derived from feedstuffs of different origin. Apparent precaecal digestibility differed significantly (P Chapter 3 examines precaecal digestion of protein and amino acids (AA) in roosters. Similar to pigs, undigested AA which reach the caeca are deaminated by the microflora and the end- products have no nutritional value (McNab, 1989). Moreover, Parsons (1986) observed a closer relationship between amino acid availability measured in chick growth assays, and digestibility determined in caecectomised rather than in intact birds. This means that, in poultry, digestion in the distal region of the intestines, more specifically the caeca, is mainly fermentative and that the AA synthesized in, or disappearing from the caeca, are not available for protein synthesis by the animal. Therefore, a procedure for ileostomy in adult roosters has been described with the use of flexible silicon cannulae. Apparent ileal digestibility coefficients for dry matter (aDC DM), crude protein (aDC CP) and amino acids (aDC AA) were determined in diets formulated with maize/wheat gluten meal, wheat gluten meal, faba beans, lupins, soybean meal and casein as the main protein sources. These determinations were performed in ileostomised roosters fitted with silicon cannulae. In addition, aDC data determined using roosters (present study) were correlated with previously published aDC data of the same diets determined with pigs (van Leeuwen et al., 1996a, 1996b).The ileal aDC CP in roosters significantly (P Regarding methodological aspects the study showed comparable aDC CP and AA for soybean meal determined in the present experiment with the cannulated roosters and data from literature using adult caecectomised roosters. Secondly, the roosters provided with cannulae introduced after ileostomy can be used for periods up to a year after surgery.FUNCTIONAL-MORPHOLOGICAL PARAMETERS (PART II)The qualitative functional-morphological parameters of the small intestinal mucosa are examined in the chapters 5 - 8.Chapter 5 considers the morphology of the mucosal surface of the small intestine of broilers and the relationship with age, diet formulation, small intestinal microflora and growth performance. The villi of the small intestine were examined with a dissecting microscope and the surface was described using a morphological scoring scale. As illustrated by pictures, zigzag oriented ridges were observed in the broilers, which seem to be characteristic for poultry.The results showed that in clinically healthy broilers the shape and orientation of the small intestine villi were related to the age of the animal and the intestinal location. Effects of dietary composition and microflora are also demonstrated. Fermentable pectin as dietary component decreased the zigzag villus orientation and reduced performance. Addition of glutamin to a soybean diet limited the decrease of the zigzag villus-orientation caused by pectin and had a beneficial effect on performance. An oral challenge with a non-virulent Salmonella typhimurium increased the effects of dietary pectin on the small intestine morphology and performance.Chapter 6, contains a study of the functional-morphological effects of virginiamycin (VM), used as feed additive in piglets. The objective of this study was to determine the effects of VM on morphological parameters of the small intestinal mucosa, animal growth and feed conversion ratio (feed intake/weight gain) in piglets. The study comprised three trials: two experiments to study the morphological effects of VM on the small intestinal mucosa, whereas the third experiment was a performance study. Each experiment comprised a control group fed a diet without VM, and a VM group fed a diet containing 40 mg/kg VM. In the first experiment, the piglets were individually kept and an oral dose of K88 positive enterotoxigenic Escherichia (E.) coli (ETEC) was given as a sub-clinical challenge. The housing conditions in experiments 2 and 3 were according to practical standards. The results showed that the VM decreased feed conversion ratio and increased villus heights in conventionally kept piglets. Crypt depths were decreased in the individually kept piglets seven days after the ETEC challenge. Corpet (1999) and Anderson et al. (2000) reviewed the mode of action of antibiotics as feed additives and suggested that the antibiotics suppress bacterial activity and decomposition of bile salts resulting in a more slender villus structure. Increased villus heights indicated an increased mucosal surface and absorption capacity, which is in agreement with the improved precaecal nutrient digestibility of diets with VM, as observed by Decuypere et al . (1991). The difference in morphological response to the VM illustrated variation in the morphological characteristics between clinically healthy piglets.In chapter 7 the effect of the use of the combination of two bioactive proteins, lactoperoxidase- system (LP-s) and lactoferrin (LF), on a milk replacer diet were investigated. This study examined the severity of diarrhoea, morphology of the small intestinal mucosa and the microbiology of digesta and faeces in young weaned calves.Following weaning, the incidence of diarrhoea and mortality of calves is usually higher than that for unweaned calves (Reynolds et al ., 1981). In conventional calf production, antibiotics are added to the milk replacer to reduce gastrointestinal disorders caused by pathogenic bacteria in the gut. Recent legislation restricts the addition of antibiotics in diets for calves (EC, 1998) because of possible repercussions on human health (Van den Boogaard and Stobberingh, 1996).LP and LF are both specific protein constituents of colostrum. These naturally occurring proteins are probably at least partly inactivated during the processing of milk because of their thermo-instability, and the remaining levels are not constant. Moreover, in dairy milk replacers a significant part of the protein is of vegetable origin and therefore lacks LP and LF.The experiment with calves comprised the first two weeks post weaning. One group received a control diet and a second group a diet with LP-s/LF. Results showed that faecal consistency of the LP-s/LF group, as assessed by faecal consistency scores, was significantly improved compared to the control group. The numbers of E. coli in faeces were significantly lower and the villi in the distal jejunum more finger shaped and longer in those of the LP-s/LF group compared to the control group. These findings showed that the effects of LP-s/LF are mainly located in the distal region of the gastrointestinal tract. Reiter and Perraudin (1991) also showed positive effects of LP-s on live weight change in field trials. Still et al . (1989) studied the effects of a combination of LP-s and LF on the severity of diarrhoea in calves for a period 0 to 6 days after an experimental E. coli infection. They concluded that LP-s/LF had preventive and curing effects after the E. coli challenged infection. The results of the present experiment were in agreement with their observations.Chapter 8 considers the functional-morphological implications of condensed tannins in faba beans (Vicia faba L.). The nutritional value of faba beans is limited by the presence of these tannins (Marquardt et al., 1977). Jansman et al. (1993) studied the effects of tannins on the apparent faecal digestibility of a control diet, a diet containing hulls of white flowering, low-tannin faba beans, and a diet with hulls of coloured flowering, high-tannin faba beans. They concluded that whole tract crude protein digestibility of the high-tannin diet was significantly (P <strong