Boundary States for Supertubes in Flat Spacetime and Godel Universe

We construct boundary states for supertubes in the flat spacetime. The T-dual objects of supertubes are moving spiral D1-branes (D-helices). Since we can obtain these D-helices from the usual D1-branes via null deformation, we can construct the boundary states for these moving D-helices in the covariant formalism. Using these boundary states, we calculate the vacuum amplitude between two supertubes in the closed string channel and read the open string spectrum via the open closed duality. We find there are critical values of the energy for on-shell open strings on the supertubes due to the non-trivial stringy correction. We also consider supertubes in the type IIA Godel universe in order to use them as probes of closed timelike curves. This universe is the T-dual of the maximally supersymmetric type IIB PP-wave background. Since the null deformations of D-branes are also allowed in this PP-wave, we can construct the boundary states for supertubes in the type IIA Godel universe in the same way. We obtain the open string spectrum on the supertube from the vacuum amplitude between supertubes. As a consequence, we find that the tachyonic instability of open strings on the supertube, which is the signal of closed time like curves, disappears due to the stringy correction.Comment: 26 pages, 3 figures, v2: explanations added, references added, v3: explanations adde

Chain of refined perception in self-optimizing assembly of micro-optical systems

Today, the assembly of laser systems requires a large share of manual operations due to its complexity regarding the optimal alignment of optics. Although the feasibility of automated alignment of laser optics has been shown in research labs, the development effort for the automation of assembly does not meet economic requirements – especially for low-volume laser production. This paper presents a model-based and sensor-integrated assembly execution approach for flexible assembly cells consisting of a macro-positioner covering a large workspace and a compact micromanipulator with camera attached to the positioner. In order to make full use of available models from computer-aided design (CAD) and optical simulation, sensor systems at different levels of accuracy are used for matching perceived information with model data. This approach is named "chain of refined perception", and it allows for automated planning of complex assembly tasks along all major phases of assembly such as collision-free path planning, part feeding, and active and passive alignment. The focus of the paper is put on the in-process image-based metrology and information extraction used for identifying and calibrating local coordinate systems as well as the exploitation of that information for a part feeding process for micro-optics. Results will be presented regarding the processes of automated calibration of the robot camera as well as the local coordinate systems of part feeding area and robot base

Three Charge Supertubes in Type IIB Plane Wave Backgrounds

We deform the supersymmetric black ring of five dimensional supergravity coupled to N-1 vector multiplets to obtain an asymptotically Goedel supersymmetric black ring. For the U(1)^3 model we lift this solution to obtain a three charge D1-D5-P supertube which asymptotes to a 1/2 supersymmetric plane wave of Type IIB supergravity. Further, we also show how one may deform the asymptotically flat three charge supertube of type IIB, in the special case of vanishing KK dipole charge, to a three charge supertube which asymptotes to the maximally supersymmetric plane wave.Comment: 1+14 pages, JHEP

Employment Gains from Minimum-Wage Hikes under Perfect Competition: A Simple General-Equilibrium Analysis

Contrary to conventional wisdom, higher minimum wages may lead to greater levels of employment under perfect competition. We demonstrate this possibility in a simple generalequilibrium model with two goods produced by two factors and consumed by two representative households. Within our model, hiking a minimum wage redistributes income between heterogeneous consumers. This redistribution may create an excess demand for the laborintensive good, and hence increase employment to restore equilibrium, despite the fact that every firm becomes less labor intensive

Unemployment and Income-Distribution Effects of Economic Growth: A Minimum-Wage Analysis with Optimal Saving

Theoretically and numerically, we analyze the unemployment and income-distribution effects of economic growth, in a model with optimal saving (investment) and a minimum wage for unskilled labor. Within this three-factor model (including skilled labor), an exogenous rise in the growth rate increases unemployment if capital and unskilled labor are complements (versus substitutes), implying a trade-off between (faster) growth and (lower) unemployment. We also show how the growth rate affects the skill premium and factor shares of national income, providing little support for Piketty’s (2014) controversial thesis that capital’s share is higher when growth is slower

A Minimum-Wage Model of Unemployment and Growth: The Case of a Backward-Bending Demand Curve for Labor

We add a minimum wage and hence involuntary unemployment to a conventional two-sector model of a perfectly competitive economy with optimal saving and endogenous growth. Our resulting model highlights the possible case of a backward-bending demand curve for labor, along which a hike in the minimum wage might increase total employment. This possibility provides theoretical support for some controversial empirical studies, which challenge the textbook prediction of an inverse relationship between employment and the minimum wage. Our model also implies that a minimum-wage hike has negative implications for both the growth rate and lifetime utilit

Yang-Mills Instantons Sitting on a Ricci-flat Worldspace of Double D4-brane

Thus far, there seem to be no complete criteria that can settle the issue as to what the correct generalization of the Dirac-Born-Infeld (DBI) action, describing the low-energy dynamics of the D-branes, to the non-abelian case would be. According to recent suggestions, one might pass the issue of worldvolume solitons from abelian to non-abelian setting by considering the stack of multiple, coincident D-branes and use it as a guideline to construct or censor the relevant non-abelian version of the DBI action. In this spirit, here we are interested in the explicit construction of SU(2) Yang-Mills (YM) instanton solutions in the background geometry of two coincident probe D4-brane worldspaces particularly when the metric of target spacetime in which the probe branes are embedded is given by the Ricci-flat, magnetic extremal 4-brane solution in type IIA supergravity theory with its worldspace metric being given by that of Taub-NUT and Eguchi-Hanson solutions, the two best-known gravitational instantons. And then we demonstrate that with this YM instanton- gravitational instanton configuration on the probe D4-brane worldvolume, the energy of the probe branes attains its minimum value and hence enjoys stable state provided one employs the Tseytlin's non-abelian DBI action for the description of multiple probe D-branes. In this way, we support the arguments in the literature in favor of Tseytlin's proposal for the non-abelian DBI action.Comment: 39 pages, Revtex, some more comments adde

Registering imagery to ICESat data for measuring elevation changes on Byrd Glacier, Antarctica

This is the published version, also available here: http://dx.doi.org/10.1029/2005GL024328.We present a new approach to derive control information from ICESat data that enables rigorous registration of aerial and satellite imagery. The technique, based on matching terrain features identified from ICESat measurements and aerial imagery, opens the door to transform results of previous studies to a global reference frame. We demonstrate the proposed methodology with historical aerial photographs to determine surface changes between 1979 and 2004 over Byrd Glacier. This is important because there is no satellite radar altimetry coverage south of 81.5° S, which limits mass balance knowledge of outlet glaciers draining the East Antarctic ice sheet through the southern Transantarctic Mountains. Our study indicates that the grounded part of Byrd Glacier is close to being in balance. However, we observe large thinning on the floating part of the glacier, probably induced by increased basal melting

Dyons in Nonabelian Born-Infeld Theory

We analyze a nonabelian extension of Born--Infeld action for the SU(2) group. In the class of spherically symmetric solutions we find that, besides the Gal'tsov--Kerner glueballs, only the analytic dyons have finite energy. The presented analytic and numerical investigation excludes the existence of pure magnetic monopoles of 't Hooft--Polyakov type.Comment: 12 pages, 3 figure

Gravitating dyons and dyonic black holes in Einstein-Born-Infeld-Higgs model

We find static spherically symmetric dyons in Einstein-Born-Infeld-Higgs model in 3+1 dimensions. The solutions share many features with the gravitating monopoles in the same model. In particular, they exist only up to some critical value of a parameter \a related to the strength of the gravitational interaction. We also study dyonic non-Abelian black holes. We analyse these solutions numerically.Comment: Minor modifications, few more references added. To appear in Phys. Lett.