Surveyor mission operations system. Space flight operations memorandum Surveyor 7

Surveyor Mission G flight operations from transit phase to second lunar da

D-Brane Boundary State Dynamics

We construct the open string boundary states corresponding to various time-dependent deformations of the D-brane and explore several ways in which they may be used to study stringy soliton collective coordinate quantum dynamics. Among other things, we find that D-strings have exact moduli corresponding to arbitrary chiral excitations of the basic soliton. These are presumably the duals of the BPS-saturated excitations of the fundamental Type IIB string. These first steps in a systematic study of the dynamics and interactions of Dirichlet-brane solitons give further evidence of the consistency of Polchinski's new approach to string soliton physics.Comment: 14 pages, harvmac; reference added, end of section 3 modifie

Exact Solution of a Boundary Conformal Field Theory

We study the conformal field theory of a free massless scalar field living on the half line with interactions introduced via a periodic potential at the boundary. An SU(2) current algebra underlies this system and the interacting boundary state is given by a global SU(2) rotation of the left-moving fields in the zero-potential (Neumann) boundary state. As the potential strength varies from zero to infinity, the boundary state interpolates between the Neumann and the Dirichlet values. The full S-matrix for scattering from the boundary, with arbitrary particle production, is explicitly computed. To maintain unitarity, it is necessary to attribute a hidden discrete ``soliton'' degree of freedom to the boundary. The same unitarity puzzle occurs in the Kondo problem, and we anticipate a similar solution.Comment: harvmac and epsf, 36 pages with 5 figures; v2: the version which appeared in NPB including a Note Added on the band structure of open string

Classical Dynamics of Macroscopic Strings

In recent work, Dabholkar {\it et al.} constructed static ``cosmic string" solutions of the low-energy supergravity equations of the heterotic string, and conjectured that these solitons are actually exterior solutions for infinitely long fundamental strings. In this paper we provide compelling dynamical evidence to support this conjecture by computing the dynamical force exerted by a solitonic string on an identical test-string limit, the Veneziano amplitude for the scattering of macroscopic winding states and the metric on moduli space for the scattering of two string solitons. All three methods yield trivial scattering in the low-energy limit.Comment: 16 page

Active Gel Model of Amoeboid Cell Motility

We develop a model of amoeboid cell motility based on active gel theory. Modeling the motile apparatus of a eukaryotic cell as a confined layer of finite length of poroelastic active gel permeated by a solvent, we first show that, due to active stress and gel turnover, an initially static and homogeneous layer can undergo a contractile-type instability to a polarized moving state in which the rear is enriched in gel polymer. This agrees qualitatively with motile cells containing an actomyosin-rich uropod at their rear. We find that the gel layer settles into a steadily moving, inhomogeneous state at long times, sustained by a balance between contractility and filament turnover. In addition, our model predicts an optimal value of the gel-susbstrate adhesion leading to maximum layer speed, in agreement with cell motility assays. The model may be relevant to motility of cells translocating in complex, confining environments that can be mimicked experimentally by cell migration through microchannels.Comment: To appear in New Journal of Physic

Charged Black Holes in Two-Dimensional String Theory

We discuss two dimensional string theories containing gauge fields introduced either via coupling to open strings, in which case we get a Born-Infeld type action, or via heterotic compactification. The solutions to the modified background field equations are charged black holes which exhibit interesting space-time geometries. We also compute their masses and charges.Comment: 39 page

Dirichlet Boundary State in Linear Dilaton Background

Dirichlet-branes have emerged as important objects in studying nonperturbative string theory. It is important to generalize these objects to more general backgrounds other than the usual flat background. The simplest case is the linear dilaton condensate. The usual Dirichlet boundary condition violates conformal invariance in such a background. We show that by switching on a certain boundary interaction, conformal invariance is restored. An immediate application of this result is to two dimensional string theory.Comment: 6 pages, harvmac, some remarks are modified and one reference is added, formulas remain the sam

A Comment on the Stability of String Monopoles

In recent work a multimonopole solution of heterotic string theory was obtained. The monopoles are noted to be stable, in contrast with analogous solutions of Einstein-Maxwell or Yang-Mills-dilaton theory. The existence of this and other classes of stable solitonic solutions in string theory thus provides a possible test for low-energy string theory as distinct from other gauge + gravity theories.Comment: 5 page

The Economic Crisis, Public Sector Pay, and the Income Distribution

An important aspect of the impact of the economic crisis is how pay in the public sector responds – in the face not only of the evolution of pay in the private sector, but also extreme pressure on public spending (of which pay is a very large proportion) as fiscal deficits soar. What are the effects on the income distribution of cutting public sector pay rates or alternative strategies to reduce the public sector pay bill, and how does these vary depending on the evolution of pay in the private sector? This paper investigates these issues using data and a tax-benefit simulation for Ireland, a country which faces a particularly severe fiscal crisis and where innovative measures have already been implemented to claw back pay from public sector workers in the guise of a "pensions levy", followed most recently by a significant cut in nominal pay rates. The SWITCH tax-benefit model first allows the distributional effects of these measures, which achieved a substantial reduction in the net public sector pay bill, to be teased out. The overall impact on the income distribution, set against alternative scenarios for pay in the private sector, is assessed. This provides empirical evidence relevant to policy choices in relation to a key aspect of household income over which governments have direct influence, while at the same time illustrating methodologically how a tax-benefit model can serve as the base for such investigation.public sector pay, income distribution, fiscal crisis