Approximate theoretical performance evaluation for a diverging rocket

A simplified combustion model, which is motivated by available performance studies on the diverging rocket reactor, has been used as basis for an engine performance evaluation. Comparison with conventional rocket configurations shows that an upper performance limit for the diverging reactor is comparable with performance estimates for engines using an adiabatic work cycle. Development of the diverging reactor for engine applications may, however, offer some advantages for very hot, high-energy, propellant systems

Filtered screens and augmented Teichm\"uller space

We study a new bordification of the decorated Teichm\"uller space for a multiply punctured surface F by a space of filtered screens on the surface that arises from a natural elaboration of earlier work of McShane-Penner. We identify necessary and sufficient conditions for paths in this space of filtered screens to yield short curves having vanishing length in the underlying surface F. As a result, an appropriate quotient of this space of filtered screens on F yields a decorated augmented Teichm\"uller space which is shown to admit a CW decomposition that naturally projects to the augmented Teichm\"uller space by forgetting decorations and whose strata are indexed by a new object termed partially oriented stratum graphs.Comment: Final version to appear in Geometriae Dedicat

Enumeration of chord diagrams on many intervals and their non-orientable analogs

Two types of connected chord diagrams with chord endpoints lying in a collection of ordered and oriented real segments are considered here: the real segments may contain additional bivalent vertices in one model but not in the other. In the former case, we record in a generating function the number of fatgraph boundary cycles containing a fixed number of bivalent vertices while in the latter, we instead record the number of boundary cycles of each fixed length. Second order, non-linear, algebraic partial differential equations are derived which are satisfied by these generating functions in each case giving efficient enumerative schemes. Moreover, these generating functions provide multi-parameter families of solutions to the KP hierarchy. For each model, there is furthermore a non-orientable analog, and each such model likewise has its own associated differential equation. The enumerative problems we solve are interpreted in terms of certain polygon gluings. As specific applications, we discuss models of several interacting RNA molecules. We also study a matrix integral which computes numbers of chord diagrams in both orientable and non-orientable cases in the model with bivalent vertices, and the large-N limit is computed using techniques of free probability.Comment: 23 pages, 7 figures; revised and extended versio

Second messenger-activated calcium influx in rat peritoneal mast cells.

To study the regulation of calcium influx in non-excitable cells, membrane currents of rat peritoneal mast cells were recorded using the whole-cell patch-clamp technique. At the same time, intracellular calcium concentration ([Ca2+]i) was monitored via the fluorescent calcium-indicator dye Fura-2, which was loaded into cells by diffusion from the patch pipette. 2. Stimulation of mast cells with secretagogues, such as compound 48/80 or substance P, caused release of Ca2+ from internal stores. In addition, external agonists also induced influx of external calcium in 26% of the cells investigated. The agonist-stimulated Ca2+ influx was increased during membrane hyperpolarization and was associated with small whole-cell currents. 3. Likewise, internal application of inositol 1,4,5-trisphosphate (Ins1,4,5P3:0.5-10 microM) elevated [Ca2+]i due both to release of Ca2+ from internal stores and to influx of external calcium. The Ins1,4,5P3-induced influx was greater at more negative membrane potentials, suggesting that Ins1,4,5P3 opened a pathway through which calcium could enter at a rate governed by its electrochemical driving force. 4. Inositol 1,3,4,5-tetrakisphosphate (Ins1,3,4,5P4) did not induce Ca2+ influx by itself nor did it facilitate or enhance Ins1,4,5P3-induced Ca2+ entry. Calcium influx was also induced by inositol 2,4,5-trisphosphate. Since this inositol phosphate is a poor substrate for Ins1,4,5P3 3-kinase it seems unlikely that Ins1,3,4,5P4 plays a role in the regulation of the Ca2(+)-influx pathway in mast cells. 5. The Ins1,4,5P3-induced Ca2+ influx was associated with whole-cell currents of 1-2 pA or less, with no channel activity detectable in whole-cell recordings. The small size of the whole-cell current suggests either that the Ins1,4,5P3-dependent influx occurs via small-conductance channels that are highly calcium specific or that the influx is not via ion channels. 6. Agonist stimulation also activated large-conductance (ca 50 pS) cation channels, through which divalent cations could permeate; thus, these channels represent a second pathway for Ca2+ influx. The slow speed of activation of the channels by agonists, their activation by internal guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S), and the inhibition of agonist activation by internal guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S) all suggest that the 50 pS channels are regulated by a second messenger and/or a GTP-binding protein. The activity of the 50 pS channel in mast cells is not sensitive to either Ins1,4,5P3 or Ins1,3,4,5P4. Activity of the channel was inhibited by elevated [Ca2+]

Lectures on the Asymptotic Expansion of a Hermitian Matrix Integral

In these lectures three different methods of computing the asymptotic expansion of a Hermitian matrix integral is presented. The first one is a combinatorial method using Feynman diagrams. This leads us to the generating function of the reciprocal of the order of the automorphism group of a tiling of a Riemann surface. The second method is based on the classical analysis of orthogonal polynomials. A rigorous asymptotic method is established, and a special case of the matrix integral is computed in terms of the Riemann $\zeta$-function. The third method is derived from a formula for the $\tau$-function solution to the KP equations. This method leads us to a new class of solutions of the KP equations that are \emph{transcendental}, in the sense that they cannot be obtained by the celebrated Krichever construction and its generalizations based on algebraic geometry of vector bundles on Riemann surfaces. In each case a mathematically rigorous way of dealing with asymptotic series in an infinite number of variables is established

Topological closed-string interpretation of Chern-Simons theory

The exact free energy of SU($N$) Chern-Simons theory at level $k$ is expanded in powers of $(N+k)^{-2}.$ This expansion keeps rank-level duality manifest, and simplifies as $k$ becomes large, keeping $N$ fixed (or vice versa)---this is the weak-coupling (strong-coupling) limit. With the standard normalization, the free energy on the three-sphere in this limit is shown to be the generating function of the Euler characteristics of the moduli spaces of surfaces of genus $g,$ providing a string interpretation for the perturbative expansion. A similar expansion is found for the three-torus, with differences that shed light on contributions from different spacetime topologies in string theory.Comment: 6 pages, iassns-hep-93-30 (title change, omitted refs. added, two sign errors corrected, no significant change

Eyes wide shut? UK consumer perceptions on aviation climate impacts and travel decisions to New Zealand

The purview of climate change concern has implicated air travel, as evidenced in a growing body of academic literature concerned with aviation CO2 emissions. This article assesses the relevance of climate change to long haul air travel decisions to New Zealand for United Kingdom consumers. Based on 15 semi-structured open-ended interviews conducted in Bournemouth, UK during June 2009, it was found that participants were unlikely to forgo potential travel decisions to New Zealand because of concern over air travel emissions. Underpinning the interviewees’ understandings and responses to air travel’s climate impact was a spectrum of awareness and attitudes to air travel and climate change. This spectrum ranged from individuals who were unaware of air travel’s climate impact to those who were beginning to consume air travel with a ‘carbon conscience’. Within this spectrum were some who were aware of the impact but not willing to change their travel behaviours at all. Rather than implicating long haul air travel, the empirical evidence instead exemplifies changing perceptions towards frequent short haul air travel and voices calls for both government and media in the UK to deliver more concrete messages on air travel’s climate impact

Radiative forcing of organic aerosol in the atmosphere and on snow: Effects of SOA and brown carbon

Organic aerosols (OA) play an important role in climate change. However, very few calculations of global OA radiative forcing include secondary organic aerosol (SOA) or the light‐absorbing part of OA (brown carbon). Here we use a global model to assess the radiative forcing associated with the change in primary organic aerosol (POA) and SOA between present‐day and preindustrial conditions in both the atmosphere and the land snow/sea ice. Anthropogenic emissions are shown to substantially influence the SOA formation rate, causing it to increase by 29 Tg/yr (93%) since preindustrial times. We examine the effects of varying the refractive indices, size distributions for POA and SOA, and brown carbon fraction in SOA. The increase of SOA exerts a direct forcing ranging from −0.12 to −0.31 W m −2 and a first indirect forcing in warm‐phase clouds ranging from −0.22 to −0.29 W m −2 , with the range due to different assumed SOA size distributions and refractive indices. The increase of POA since preindustrial times causes a direct forcing varying from −0.06 to −0.11 W m −2 , when strongly and weakly absorbing refractive indices for brown carbon are used. The change in the total OA exerts a direct forcing ranging from −0.14 to −0.40 W m −2 . The atmospheric absorption from brown carbon ranges from +0.22 to +0.57 W m −2 , which corresponds to 27%~70% of the black carbon (BC) absorption predicted in the model. The radiative forcing of OA deposited in land snow and sea ice ranges from +0.0011 to +0.0031 W m −2 or as large as 24% of the forcing caused by BC in snow and ice simulated by the model. Key Points A fully explicit SOA formation model is used to determine SOA radiative forcing The direct radiative forcing by brown carbon in SOA is estimated The radiative forcing of OA in snow/ice is estimated for the first timePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108060/1/jgrd51450.pd

Glassy Random Matrix Models

This paper discusses Random Matrix Models which exhibit the unusual phenomena of having multiple solutions at the same point in phase space. These matrix models have gaps in their spectrum or density of eigenvalues. The free energy and certain correlation functions of these models show differences for the different solutions. Here I present evidence for the presence of multiple solutions both analytically and numerically. As an example I discuss the double well matrix model with potential $V(M)= -{\mu \over 2}M^2+{g \over 4}M^4$ where $M$ is a random $N\times N$ matrix (the $M^4$ matrix model) as well as the Gaussian Penner model with $V(M)={\mu\over 2}M^2-t \ln M$. First I study what these multiple solutions are in the large $N$ limit using the recurrence coefficient of the orthogonal polynomials. Second I discuss these solutions at the non-perturbative level to bring out some differences between the multiple solutions. I also present the two-point density-density correlation functions which further characterizes these models in a new university class. A motivation for this work is that variants of these models have been conjectured to be models of certain structural glasses in the high temperature phase.Comment: 25 pages, Latex, 7 Figures, to appear in PR