Competitive feedback in galaxy formation

It is now well established that many galaxies have nuclear star clusters (NCs) whose total masses correlate with the velocity dispersion (sigma) of the galaxy spheroid in a very similar way to the well--known supermassive black hole (SMBH) M - sigma relation. Previous theoretical work suggested that both correlations can be explained by a momentum feedback argument. Observations further show that most known NCs have masses < 10^8 Msun, while SMBHs frequently have masses > 10^8 Msun, which remained unexplained in previous work. We suggest here that this changeover reflects a competition between the SMBH and nuclear clusters in the feedback they produce. When one of the massive objects reaches its limiting M-sigma value, it drives the gas away and hence cuts off its own mass and also the mass of the ``competitor''. The latter is then underweight with respect to the expected M-sigma mass (abridged).Comment: To appear in MNRAS Letter

AGN outflows trigger starbursts in gas-rich galaxies

Recent well resolved numerical simulations of AGN feedback have shown that its effects on the host galaxy may be not only negative but also positive. In the late gas poor phase, AGN feedback blows the gas away and terminates star formation. However, in the gas-rich phase(s), AGN outflows trigger star formation by over-compressing cold dense gas and thus provide positive feedback on their hosts. In this paper we study this AGN-triggered starburst effect. We show that star formation rate in the burst increases until the star formation feedback counteracts locally the AGN outflow compression. Globally, this predicts a strong nearly linear statistical correlation between the AGN and starburst bolometric luminosities in disc galaxies, L_* \propto L_{AGN}^{5/6}. The correlation is statistical only because AGN activity may fluctuate on short time scales (as short as tens of years), and because AGN may turn off but its effects on the host may continue to last until the AGN-driven outflow leaves the host, which may be up to 10 times longer than the duration of the AGN activity. The coefficient in front of this relation depends on the clumpiness and morphology of the cold gas in the galaxy. A "maximum starburst" takes place in am azimuthally uniform gas disc, for which we derive an upper limit of L_* \sim 50 times larger than L_{AGN} for typical quasars. For more clumpy and/or compact cold gas distributions, the starburst luminosity decreases. We also suggest that similar AGN-triggerred starbursts are possible in hosts of all geometries, including during galaxy mergers, provided the AGN is activated. Finally, we note that due to the short duration of the AGN activity phase the accelerating influence of AGN on starbursts may be much more common than observations of simultaneous AGN and starbursts would suggest.Comment: 14 pages, 6 figures. Accepted for publication in MNRA

Linear transmitter design for MSAT terminals

One of the factors that will undoubtedly influence the choice of modulation format for mobile satellites, is the availability of cheap, power-efficient, linear amplifiers for mobile terminal equipment operating in the 1.5-1.7 GHz band. Transmitter linearity is not easily achieved at these frequencies, although high power (20W) class A/AB devices are becoming available. However, these components are expensive and require careful design to achieve a modest degree of linearity. In this paper an alternative approach to radio frequency (RF) power amplifier design for mobile satellite (MSAT) terminals using readily-available, power-efficient, and cheap class C devices in a feedback amplifier architecture is presented

Lubrication dynamics of a settling plate

If a flat, horizontal, plate settles onto a flat surface, it is known that the gap $h$ decreases with time $t$ as a power-law: $h\sim t^{-1/2}$. We consider what happens if the plate is not initially horizontal, and/or the centre of mass is not symmetrically positioned: does one edge contact the surface in finite time, or does the plate approach the horizontal without making contact? The dynamics of this system is analysed and shown to be remarkably complex.Comment: 22 pages, 9 figure

The Importance of C.S. Lewis to Faith-Based Theatre as Seen in The Silver Chair

The paper contains an adaptation of the book The Silver Chair by C. S. Lewis and details the purpose for why this particular story is important for the faith-based theatre community. There are a number of Christian themes that are evident in the story that are examined as well as the elements of the story that make it apt for adapting to a play format

Development and characterisation of a cytokine supplemented serum free medium formulation for bone marrow derived mesenchymal stromal cells

Eng D ThesisBackground: The discovery and subsequent characterisation of adult human-derived stem cells appears poised to help revolutionise the fields of regenerative medicine and tissue engineering, offering clinicians the opportunity to develop fully functional replacement tissues, alongside holding significant promise as next generation gene or protein delivery vehicles. Despite their apparent potential however, current stem cell-based therapeutics typically rely on delivering massive doses of cells to sites of injury in order to help ensure adequate cell survival in the highly detrimental microenvironments presented by damaged and degrading biological material. In order to produce the cell numbers required for these types of treatments, relatively modest donor cell populations are subjected to extended periods of in vitro expansion, within highly regulated GMP culture conditions. One crucially important aspect of this manufacturing framework is the requirement for xeno-free expansion systems, including the use of serum-free culture medium. Unfortunately, whilst a number of functional serum-free media formulations are commercially available at the present time, their proprietary nature makes them both highly expensive and wholly unsuitable for use in academic research. Aims: The goal of this project is to begin development of a characterised cytokinesupplemented serum-free medium formulation using a design of experiments-based methodology. Methods: Primary bone marrow-derived mesenchymal stromal cells (BM-MSCs) were isolated, characterised and used to screen a series of selected cytokines and growth supplements for their ability to successfully support cell proliferation and continued survival in the absence of serum. Cells cultured in the resultant serum-free formulation were then compared to those grown in conventional medium in regard to genetic, metabolic and morphological factors. In addition, the impact of batch-to-batch variability on BM-MSC growth and metabolic activity was assessed as a means of determining the potential impact of raw material variation on cell quality and any related manufacturing processes. Finally, a number of different extracellular matrix proteins were also screened for the purpose of mediating cell-surface interactions in serum-free conditions. ii Results: We successfully identified a cytokine supplemented medium preparation capable of supporting the proliferation of BM-MSCs during serum-free culture. Evaluation of cells expanded in this medium provided evidence of altered secretory and genetic characteristics leading to shifted therapeutic potential. Furthermore, the identification of a combination of different extracellular matrix proteins able to enhance cell adhesion in the absence of serum served to provide the beginnings of a complete serum-free formulation. In addition, FBS batch variability was shown to have significant effects on cell proliferation and gene expression, including a number of genetic markers linked to differentiation potential and lineage specificity. Conclusions: We offer a new serum-free medium formulation for use in the expansion of primary BM-MSCs, alongside providing evidence of the impact of raw material variability on the therapeutically relevant characteristics of these cells

Metabolic changes after surgical operations, with special reference to disturbances in protein, chloride, sodium and water metabolism after partial gastrectomy, and to the use of protein hydrolysates

(1) An investigation has been undertaken of certain post- operative metabolic disturbances in 59 surgical patients, and in 41 of these cases nitrogen balance studies were carried out. Control observations were also made on four healthy volunteers submitted to two types of food restriction, and on one patient who was not subjected to operation.(2) It was found that after gastrectomy in well- nourished subjects there was an increase in urinary nitrogen excretion which lasted for from five to eight days, the maximum loss of nitrogen being on the second to fifth days. During the same period the reduction in food intake combined with this increased excretion of nitrogen resulted in a period of negative nitrogen balance. Extension of the duration of this period of negative nitrogen balance beyond the minimum was related to protein and caloric intake or to complications, such as wound infection, broncho- pneumonia or superficial phlebitis.(3) In mal- nourished subjects there maybe no post -operative increase in urinary nitrogen excretion, or this may be much less severe than in well -nourished subjects.(4) The consumption of a high protein high calorie diet before operation has a variable effect on body weight: it is not, related in any consistent manner to nitrogen retention, and does not alter the response to operation in any significant way in well-nourished subjects. The catabolic phase is in no way diminished. An increase in the intake of calories after opera tion may accelerate the restoration of nitrogen equilibrium or positive balance. An increase in the protein intake without a proportionate increase in calories may lead to wastage of the protein. There is a physical limit to the quantity of food 'which may be eaten after gastrectomy, but this is much in excess of the diet which is usually provided.(5) The oral consumption of protein hydrolysate (such as pronutrin) was employed to increase the quantity of protein ingested. In the form at present available, such hydrolysates offer a compact means of administering protein if the patient can tolerate the smell and taste of the preparation.(6) Protein hydrolysates in the form of casydrol or amigen were administered by the intravenous route to 22 patients. In five of these detailed studies of the quantities of total nitrogen and the amino acid nitrogen excreted in the urine were made. The urinary amino acid nitrogen excretions during and after casydrol infusions were compared with those found in a control series of patients submitted to gastrectomy, and in a series of volunteers. About 60 per cent. of the amino acid nitrogen administered by the intravenous route as casydrol, and about 90 per cent. in the case of amigen, was apparently retained) in the body for metabolism. After gastrectomy, well- nourished subjects to whom casydrol or amigen was given by the intravenous route, excreted in addition to the increased quantity of nitrogen normally expected from protein catabolism, an amount of nitrogen about about equal to that administered as hydrolysate. In the remaining patients, no apparent benefit was obtained by the infusion of casydrol, except in one who was suffering from the effects of prolonged restriction of food consumption. Provided that a rate of 100 to 150 ml. per hour is not exceeded, casydrol does not cause nausea or other disturbances when administered by the intravenous route, and thrombosis and phlebitis are not more frequent than with 5 per cent, glucose solution alone. The few indications for the use of casydrol by the intravenous route which still appear to be justifiable on theoretical grounds, such as prolonged starvation or ulcerative colitis, require further examination by clinical trial.(7) Human plasma was administered to two patients as the sole source of protein. This method of supplying protein is condemned as unsound in conception and unsafe in practice.(8) After partial gastrectomy, the prevention of starvation throughout the post -operative period was achieved in three out of six patients in whom it was attempted by the administration of adequate quantities of protein and calories as milk mixture by jejunal tube or by mouth. There was still an increase in urinary nitrogen excretion, that is to say, the catabolic phase was not abolished. The negative nitrogen balance over the period of ten days after operation was, however, greatly reduced, being smaller than after any other procedure.(9) After partial gastrectomy there is usually some degree of haemodilution and increase in plasma volume indicated directly by measurement, and indirectly by reduction in haematocrit - 21 7 - haematocrit red blood corpuscles and haemoglobin concentration. There is often a reduction in plasma albumin concentration and a rise in plasma globulin concentration which may equal or exceed the change of albumin concentration. There are other and probably more important changes in the total quantities of these proteins in active circulation in the plasma. There is a contemporary shift of chloride from red blood corpuscles to plasma. There was no consistent change in plasma amino acid nitrogen, non -protein nitrogen or blood urea nitrogen concentra- tions even during or after hydrolysate infusions.(10) The observation of a reduction in urinary chloride excretion during the first six to eight days after major surgical operations led to further investigation and to a demonstration of a coincidence of reduction in urinary chloride excretion with the increased nitrogen excretion of the catabolic phase. Further investigation has revealed that following operation there is a retention in the body of chloride, sodium and water which is largely independent of the source or quantity of sodium and chloride, or the route by which they are made available.(11) There is no relationship between weight loss and nitrogen balance; this is probably due to changes in water and electrolyte balance masking the effects of nitrogen retention on loss of weight. After operation there appears to be a steady loss of body tissue which also for several days may be masked to some extent by water retention.(12) The possible clinical applications of these observations have been discussed and further hopeful lines of extension have been suggested