Factorised steady states for multi-species mass transfer models

A general class of mass transport models with Q species of conserved mass is considered. The models are defined on a lattice with parallel discrete time update rules. For one-dimensional, totally asymmetric dynamics we derive necessary and sufficient conditions on the mass transfer dynamics under which the steady state factorises. We generalise the model to mass transfer on arbitrary lattices and present sufficient conditions for factorisation. In both cases, explicit results for random sequential update and continuous time limits are given.Comment: 11 page

Criticality and Condensation in a Non-Conserving Zero Range Process

The Zero-Range Process, in which particles hop between sites on a lattice under conserving dynamics, is a prototypical model for studying real-space condensation. Within this model the system is critical only at the transition point. Here we consider a non-conserving Zero-Range Process which is shown to exhibit generic critical phases which exist in a range of creation and annihilation parameters. The model also exhibits phases characterised by mesocondensates each of which contains a subextensive number of particles. A detailed phase diagram, delineating the various phases, is derived.Comment: 15 pages, 4 figure, published versi

Condensation transitions in a model for a directed network with weighted links

An exactly solvable model for the rewiring dynamics of weighted, directed networks is introduced. Simulations indicate that the model exhibits two types of condensation: (i) a phase in which, for each node, a finite fraction of its total out-strength condenses onto a single link; (ii) a phase in which a finite fraction of the total weight in the system is directed into a single node. A virtue of the model is that its dynamics can be mapped onto those of a zero-range process with many species of interacting particles -- an exactly solvable model of particles hopping between the sites of a lattice. This mapping, which is described in detail, guides the analysis of the steady state of the network model and leads to theoretical predictions for the conditions under which the different types of condensation may be observed. A further advantage of the mapping is that, by exploiting what is known about exactly solvable generalisations of the zero-range process, one can infer a number of generalisations of the network model and dynamics which remain exactly solvable.Comment: 23 pages, 8 figure

An exactly solvable dissipative transport model

We introduce a class of one-dimensional lattice models in which a quantity, that may be thought of as an energy, is either transported from one site to a neighbouring one, or locally dissipated. Transport is controlled by a continuous bias parameter q, which allows us to study symmetric as well as asymmetric cases. We derive sufficient conditions for the factorization of the N-body stationary distribution and give an explicit solution for the latter, before briefly discussing physically relevant situations.Comment: 7 pages, 1 figure, submitted to J. Phys.

Cepheid Masses: FUSE Observations of S Mus

S Mus is the Cepheid with the hottest known companion. The large ultraviolet flux means that it is the only Cepheid companion for which the velocity amplitude could be measured with the echelle mode of the HST GHRS. Unfortunately, the high temperature is difficult to constrain at wavelengths longer than 1200 \AA because of the degeneracy between temperature and reddening. We have obtained a FUSE spectrum in order to improve the determination of the temperature of the companion. Two regions which are temperature sensitive near 16,000 K but relatively unaffected by H$_2$ absorption (940 \AA, and the Ly $\beta$ wings) have been identified. By comparing FUSE spectra of S Mus B with spectra of standard stars, we have determined a temperature of 17,000 $\pm$ 500 K. The resultant Cepheid mass is 6.0 $\pm$ 0.4 M$_\odot$. This mass is consistent with main sequence evolutionary tracks with a moderate amount of convective overshoot.Comment: accepted to Ap

Spontaneous Symmetry Breaking in a Non-Conserving Two-Species Driven Model

A two species particle model on an open chain with dynamics which is non-conserving in the bulk is introduced. The dynamical rules which define the model obey a symmetry between the two species. The model exhibits a rich behavior which includes spontaneous symmetry breaking and localized shocks. The phase diagram in several regions of parameter space is calculated within mean-field approximation, and compared with Monte-Carlo simulations. In the limit where fluctuations in the number of particles in the system are taken to zero, an exact solution is obtained. We present and analyze a physical picture which serves to explain the different phases of the model

GPS-aided gravimetry at 30 km altitude from a balloon-borne platform

A balloon-borne experiment, flown at 30 km altitude over New Mexico, was used to test dynamic differential Global Positioning System (GPS) tracking in support of gravimetry at high-altitudes. The experiment package contained a gravimeter (Vibrating String Accelerometer), a full complement of inertial instruments, a TI-4100 GPS receiver and a radar transponder. The flight was supported by two GPS receivers on the ground near the flight path. From the 8 hour flight, about a forty minute period was selected for analysis. Differential GPS phase measurements were used to estimate changes in position over the sample time interval, or average velocity. In addition to average velocity, differential positions and numerical averages of acceleration were obtained in three components. Gravitational acceleration was estimated by correcting for accelerations due to translational motion, ignoring all rotational effects

Induction of dark-adaptive retinomotor movement (cell elongation) in teleost retinal cones by cyclic adenosine 3,5-monophosphate.

In the teleost retina, the photoreceptors and retinal pigment epithelium (RPE) undergo extensive movements (called retinomotor movements) in response to changes in light conditions and to an endogenous circadian rhythm. Photoreceptor movements serve to reposition the light-receptive outer segments and are effected by changes in inner segment length. Melanin granule movements within the RPE cells provide a movable melanin screen for rod outer segments. In the dark (night), cones elongate, rods contract, and pigment granules aggregate to the base of the RPE cell; in the light (day), these movements are reversed. We report here that treatments that elevate cytoplasmic cyclic adenosine 3,5-monophosphate (cAMP) provoke retinomotor movements characteristic of nighttime dark adaptation, even in bright light at midday. To illustrate this response, we present a quantitative description of the effects of cyclic nucleotides on cone length in the green sunfish, Lepomis cyanellus. Cone elongation is induced when light-adapted retinas are exposed to exogenous cAMP analogues accompanied by phosphodiesterase (PDE) inhibitors (either by intraocular injection or in retinal organ culture). Cone movements is not affected by cyclic GMP analogies. Dose-response studies indicate that the extent, but not the rate, of cone elongation is proportional to the concentration of exogenous cAMP and analogue presented. As has been reported for other species, we find that levels of cAMP are significantly higher in dark- than in light-adapted green sunfish retinas. On the basis of these observations, we suggest that cAMP plays a role in the light and circadian regulation of teleost cone length

Variable geometry aft-fan for takeoff quieting or thrust augmentation of a turbojet engine

A concept is presented that combines the low-noise and high-thrust characteristics of a turbofan at takeoff, together with its high efficiency at subsonic flight speeds, with the high efficiency of a turbojet at supersonic cruise. It consists of a free turbine with tip fan mounted behind the turbine of a conventional turbojet engine. Fan air is supplied from blow-in doors or is ducted from the main engine inlet. At high flight speeds where fan augmentation is not desirable, the fan inlet is closed and the free turbine is stopped by adjustment of its variable-camber stators. Estimates of noise, cycle performance, and example configurations are presented for a typical supersonic transport application

Condensation Transitions in a One-Dimensional Zero-Range Process with a Single Defect Site

Condensation occurs in nonequilibrium steady states when a finite fraction of particles in the system occupies a single lattice site. We study condensation transitions in a one-dimensional zero-range process with a single defect site. The system is analysed in the grand canonical and canonical ensembles and the two are contrasted. Two distinct condensation mechanisms are found in the grand canonical ensemble. Discrepancies between the infinite and large but finite systems' particle current versus particle density diagrams are investigated and an explanation for how the finite current goes above a maximum value predicted for infinite systems is found in the canonical ensemble.Comment: 18 pages, 4 figures, revtex