The first passage probability and control

First-passage probability used as measure of performance in stochastic control problem - dynamic programmin

Research in the development of an improved multiplier phototube Final report

Counting efficiency, noise factor measurement, dark noise, gain and counting rate, optical enhancemen

Chemical evolution in the environment of intermediate mass young stellar objects: NGC7129--FIRS2 and LkHα\alpha234

We have carried out a molecular survey of the Class 0 IM protostar NGC 7129 -- FIRS 2 (hereafter FIRS 2) and the Herbig Be star LkH$\alpha$ 234 with the aim of studying the chemical evolution of the envelopes of intermediate-mass (IM) young stellar objects (YSOs). Both objects have similar luminosities (~500 Lsun) and are located in the same molecular cloud which minimizes the chemical differences due to different stellar masses or initial cloud conditions. Moreover, since they are located at the same distance, we have the same spatial resolution in both objects. A total of 17 molecular species (including rarer isotopes) have been observed in both objects and the structure of their envelopes and outflows is determined with unprecedent detail. Our results show that the protostellar envelopes are dispersed and warmed up during the evolution to become a pre-main sequence star. In fact, the envelope mass decreases by a factor >5 from FIRS 2 to LkH$\alpha$234, while the kinetic temperature increases from ~13K to 28K. On the other hand, there is no molecular outflow associated with LkH$\alpha$234. The molecular outflow seems to stop before the star becomes visible. These physical changes strongly affect the chemistry of their envelopes. Based on our results in FIRS2 and LkH$\alpha$ 234, we propose some abundance ratios that can be used as chemical clocks for the envelopes of IM YSOs. The SiO/CS, CN/N2H+, HCN/N2H+, DCO+/HCO+ and D2CO/DCO+ ratios are good diagnostics of the protostellar evolutionary stage.Comment: 24 pages, 17 figure

Kinetics of the long-range spherical model

The kinetic spherical model with long-range interactions is studied after a quench to $T < T_c$ or to $T = T_c$. For the two-time response and correlation functions of the order-parameter as well as for composite fields such as the energy density, the ageing exponents and the corresponding scaling functions are derived. The results are compared to the predictions which follow from local scale-invariance.Comment: added "fluctuation-dissipation ratios"; fixed typo

DGSAT: Dwarf Galaxy Survey with Amateur Telescopes II. A catalogue of isolated nearby edge-on disk galaxies and the discovery of new low surface brightness systems

The connection between the bulge mass or bulge luminosity in disk galaxies and the number, spatial and phase space distribution of associated dwarf galaxies is a discriminator between cosmological simulations related to galaxy formation in cold dark matter and generalized gravity models. Here, a nearby sample of isolated Milky Way class edge-on galaxies is introduced, to facilitate observational campaigns to detect the associated families of dwarf galaxies at low surface brightness. Three galaxy pairs with at least one of the targets being edge-on are also introduced. About 60% of the catalogued isolated galaxies contain bulges of different size, while the remaining objects appear to be bulge-less. Deep images of NGC 3669 (small bulge, with NGC 3625 at the edge of the image) and NGC 7814 (prominent bulge), obtained with a 0.4-m aperture, are also presented, resulting in the discovery of two new dwarf galaxy candidates, NGC3669-DGSAT-3 and NGC7814-DGSAT-7. Eleven additional low surface brightness galaxies are identified, previously notified with low quality measurement flags in the Sloan Digital Sky Survey (SDSS). Integrated magnitudes, surface brightnesses, effective radii, Sersic indices, axis ratios, and projected distances to their putative major hosts are displayed. At least one of the galaxies, NGC3625-DGSAT-4, belongs with a surface brightness of approximately 26 mag per arcsec^2 and effective radius >1.5 kpc to the class of ultra-diffuse galaxies (UDGs). NGC3669-DGSAT-3, the galaxy with lowest surface brightness in our sample, may also be an UDG.Comment: 12 pages including 6 figures, 4 tables, a brief appendix, accepted for publication in Astronomy & Astrophysics (A&A). Paper slightly modified after A&A language editing, updating very few references and correcting a small typo at the start of the Appendi

Research in the development of an improved multiplier phototube

Parameters in analog /dc/ and digital /single electron pulse count/ modes of processing data from photomultiplier tube

Parts and materials application review for space systems

Parts and materials application review for project management of space systems engineerin

Scaling of the linear response in simple ageing systems without disorder

The time-dependent scaling of the thermoremanent and zero-field-cooled susceptiblities in ferromagnetic spin systems undergoing ageing after a quench to a temperature at or below criticality is studied. A recent debate on their interpretation is resolved by showing that for systems with a short-ranged equilibrium spin-spin correlator and above their roughening temperature, the field-cooled susceptibility $\chi_{\rm FC}(t)-\chi_0\sim t^{-A}$ where $\chi_0$ is related to the equilibrium magnetization and the exponent A is related to the time-dependent scaling of the interface width between ordered domains. The same effect also dominates the scaling of the zero-field-cooled susceptibility $\chi_{\rm ZFC}(t,s)$, but does not enter into the thermoremanent susceptibility $\rho_{\rm TRM}(t,s)$. However, there may be large finite-time corrections to the scaling of $\rho_{\rm TRM}(t,s)$ which are explicitly derived and may be needed in order to extract reliable ageing exponents. Consistency with the predictions of local scale invariance is confirmed in the Glauber-Ising and spherical models.Comment: Latex2e, 14 pages, with 6 figure

Ageing, dynamical scaling and its extensions in many-particle systems without detailed balance

Recent studies on the phenomenology of ageing in certain many-particle systems which are at a critical point of their non-equilibrium steady-states, are reviewed. Examples include the contact process, the parity-conserving branching-annihilating random walk, two exactly solvable particle-reaction models and kinetic growth models. While the generic scaling descriptions known from magnetic system can be taken over, some of the scaling relations between the ageing exponents are no longer valid. In particular, there is no obvious generalization of the universal limit fluctuation-dissipation ratio. The form of the scaling function of the two-time response function is compared with the prediction of the theory of local scale-invariance.Comment: Latex2e with IOP macros, 32 pages; extended discussion on contact process and new section on kinetic growth processe