A pseudo random-access synchronous meteorological satellite system

Communications satellite system uses pseudo-random time frequency multiplexing technique for extracting real-time meteorological data from great number of isolated weather stations /data collection platforms/ situated randomly throughout the world

Localized Dispersive States in Nonlinear Coupled Mode Equations for Light Propagation in Fiber Bragg Gratings.

Dispersion effects induce new instabilities and dynamics in the weakly nonlinear description of light propagation in fiber Bragg gratings. A new family of dispersive localized pulses that propagate with the group velocity is numerically found, and its stability is also analyzed. The unavoidable different asymptotic order of transport and dispersion effects plays a crucial role in the determination of these localized states. These results are also interesting from the point of view of general pattern formation since this asymptotic imbalance is a generic situation in any transport-dominated (i.e., nonzero group velocity) spatially extended system

Fragmentation And Evolution Of Molecular Clouds. III. The Effect Of Dust And Gas Energetics

Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas temperatures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles has properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates are, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high-density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate-mass objects form when improved thermal physics is included, but the resulting initial mass function (IMF) still has too few low-mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.NASA NAG5-10826, NAG5-13271Canada Research Chair programNSERCNSF AST-0607793, AST-1109116NASA GSRP Fellowship ProgramAstronom

Description of the inelastic collision of two solitary waves for the BBM equation

We prove that the collision of two solitary waves of the BBM equation is inelastic but almost elastic in the case where one solitary wave is small in the energy space. We show precise estimates of the nonzero residue due to the collision. Moreover, we give a precise description of the collision phenomenon (change of size of the solitary waves).Comment: submitted for publication. Corrected typo in Theorem 1.

Dynamics of a hyperbolic system that applies at the onset of the oscillatory instability

A real hyperbolic system is considered that applies near the onset of the oscillatory instability in large spatial domains. The validity of that system requires that some intermediate scales (large compared with the basic wavelength of the unstable modes but small compared with the size of the system) remain inhibited; that condition is analysed in some detail. The dynamics associated with the hyperbolic system is fully analysed to conclude that it is very simple if the coefficient of the cross-nonlinearity is such that , while the system exhibits increasing complexity (including period-doubling sequences, quasiperiodic transitions, crises) as the bifurcation parameter grows if ; if then the system behaves subcritically. Our results are seen to compare well, both qualitatively and quantitatively, with the experimentally obtained ones for the oscillatory instability of straight rolls in pure Rayleigh - Bénard convection

A homological model for Uqsl(2)U_q \mathfrak{sl}(2) Verma-modules and their braid representations

We extend Lawrence's representations of the braid groups to relative homology modules, and we show that they are free modules over a Laurent polynomials ring. We define homological operators and we show that they actually provide a representation for an integral version for $U_q \mathfrak{sl}(2)$. We suggest an isomorphism between a given basis of homological modules and the standard basis of tensor products of Verma modules, and we show it to preserve the integral ring of coefficients, the action of $U_q \mathfrak{sl}(2)$, the braid group representations and their grading. This recovers an integral version for Kohno's theorem relating absolute Lawrence representations with quantum braid representation on highest weight vectors. It is an extension of the latter theorem as we get rid of generic conditions on parameters, and as we recover the entire product of Verma-modules as a braid group and a $U_q \mathfrak{sl}(2)$-module

Stable self-similar blow-up dynamics for slightly L2L^2-supercritical generalized KdV equations

In this paper we consider the slightly $L^2$-supercritical gKdV equations $\partial_t u+(u_{xx}+u|u|^{p-1})_x=0$, with the nonlinearity $5<p<5+\varepsilon$ and $0<\varepsilon\ll 1$ . We will prove the existence and stability of a blow-up dynamic with self-similar blow-up rate in the energy space $H^1$ and give a specific description of the formation of the singularity near the blow-up time.Comment: 38 page

Non-semi-simple TQFT of the sphere with four punctures

In this work, we compute the representation of the mapping class group of the sphere with 4 punctures arising from the non-semi-simple TQFT [C. Blanchet, F. Costantino, N. Geer and B. Patureau, Non-semi-simple TQFTs, Reidemeister torsion and Kashaev’s invariants, Adv. Math.301 (2016) 1–78]. We show that it is faithful. Lastly, we compare quantum representations of punctured spheres in general with those of braid groups

The Spatial Distribution of the Galactic First Stars II: SPH Approach

We use cosmological, chemo-dynamical, smoothed particle hydrodynamical simulations of Milky-Way-analogue galaxies to find the expected present-day distributions of both metal-free stars that formed from primordial gas and the oldest star populations. We find that metal-free stars continue to form until z~4 in halos that are chemically isolated and located far away from the biggest progenitor of the final system. As a result, if the Population III initial mass function allows stars with low enough mass to survive until z=0 (< 0.8 Msol), they would be distributed throughout the Galactic halo. On the other hand, the oldest stars form in halos that collapsed close to the highest density peak of the final system, and at z=0 they are located preferentially in the central region of the Galaxy, i.e., in the bulge. According to our models, these trends are not sensitive to the merger histories of the disk galaxies or the implementation of supernova feedback. Furthermore, these full hydrodynamics results are consistent with our N-body results in Paper I, and lend further weight to the conclusion that surveys of low-metallicity stars in the Galactic halo can be used to directly constrain the properties of primordial stars. In particular, they suggest that the current lack of detections of metal-free stars implies that their lifetimes were shorter than a Hubble time, placing constraints on the metal-free initial mass function.Comment: Accepted by ApJ. Emulate ApJ styl

Money, output and real wages in a New Keynesian framework with heterogeneous labor and monopsonistic firms

Representative agent models do not match up well with three stylized facts of the business cycle: a money-output connection, countercyclical markups, and acyclical real wages. This thesis investigates whether a New Keynesian model which departs from the representative agent assumptions and models heterogeneity and imperfect competition in the labor market is more consistent with these stylized facts. One possible explanation of countercyclical markups and acyclical real wages is that labor markets are monopsonistic and monopsony power is weaker during expansions than in recessions, This would require that the elasticity of labor supply be procyclical. This is not possible if worker preferences are homothetic. An aggregate labor supply function for heterogeneous labor is constructed. Labor is indivisible, and workers are heterogeneous with respect to their nonlabor income endowments and preferences for risk. Nonlabor income is assumed to be distributed Lognormally. Workers\u27 optimizing choices in a take-it-or-leave it job market are determined by a reservation wage function which relates reservation wages to nonlabor income. Aggregate labor supply is a composite function of the Lognormal distribution of nonlabor income and the reservation wage function. The parameters of the aggregate labor supply function are affected by changes in the aggregate price level and the interest rate. An increase in the money supply increases aggregate labor supply. If workers have increasing relative risk aversion, an increase in money also increases the elasticity of labor supply. The magnitude of this increase depends upon the magnitudes of the interest- and wealth-elasticities of the aggregate money demand function. If firms are monopsonistic, the elasticity of the aggregate labor supply function will be procyclical with respect to monetary policy, and markups will be countercyclical. A calibrated version of the model indicates that the real wage would be weakly countercyclical, acyclical, or weakly procyclical, depending on the short-term elasticities of the price level and the interest rate with respect to changes in M2. The model implies a wealth-effects transmission channel from monetary policy to aggregate labor supply, employment and output, restoring a traditional Keynesian theme of a monetary theory of production