Attosecond pulse shaping using partial phase matching

Peer ReviewedPostprint (published version

Direct Measurement of Hydrodynamic Cross Correlations between Two Particles in an External Potential

We report a direct measurement of the hydrodynamic interaction between two colloidal particles. Two micron-sized latex beads were held at varying distances in optical tweezers while their Brownian displacements were measured. In spite of the fact that fluid systems at low Reynolds number are generally considered to have no “memory,” the cross-correlation function of the bead positions shows a pronounced, time-delayed anticorrelation. We show that the anticorrelations can be understood in terms of the standard Oseen tensor hydrodynamic coupling

Is Crime Contagious?

We test the hypothesis that criminal behavior is “contagious” – or susceptible to what economists term “endogenous effects” – by examining the extent to which lower local-area crime rates decrease arrest rates among individuals. Using data from the Moving to Opportunity (MTO) randomized housing-mobility experiment, in operation since 1994 in five U.S. cities, we exploit the fact that the effect of treatment group assignment yields different types of neighborhood changes across the five demonstration sites and use treatment-site interactions to instrument for measures of post-randomization neighborhood crime rates as well as neighborhood poverty or racial segregation in analysis of individual arrest outcomes. We find no evidence that violence is contagious; neighborhood racial segregation appears to be the most important explanation for across-neighborhood variation in arrests for violent crimes. Our only evidence for contagion comes with less serious crimes. Some estimates suggest an effect for males, but these results are imprecise. We also find evidence that young males are more likely to engage in property crimes when violent crimes are relatively more prevalent within the community. These findings are consistent with a “resource swamping” model in which increases in the prevalence of more serious crimes dilutes the police resources available for deterring less serious crimes.endogenous effects, social multiplier, arrests, social experiment

Is Crime Contagious?

endogenous effects, social multiplier, arrests, social experiment

Coalescence of Liquid Drops

When two drops of radius $R$ touch, surface tension drives an initially singular motion which joins them into a bigger drop with smaller surface area. This motion is always viscously dominated at early times. We focus on the early-time behavior of the radius \rmn of the small bridge between the two drops. The flow is driven by a highly curved meniscus of length 2\pi \rmn and width \Delta\ll\rmn around the bridge, from which we conclude that the leading-order problem is asymptotically equivalent to its two-dimensional counterpart. An exact two-dimensional solution for the case of inviscid surroundings [Hopper, J. Fluid Mech. ${\bf 213}$, 349 (1990)] shows that \Delta \propto \rmn^3 and \rmn \sim (t\gamma/\pi\eta)\ln [t\gamma/(\eta R)]; and thus the same is true in three dimensions. The case of coalescence with an external viscous fluid is also studied in detail both analytically and numerically. A significantly different structure is found in which the outer fluid forms a toroidal bubble of radius \Delta \propto \rmn^{3/2} at the meniscus and \rmn \sim (t\gamma/4\pi\eta) \ln [t\gamma/(\eta R)]. This basic difference is due to the presence of the outer fluid viscosity, however small. With lengths scaled by $R$ a full description of the asymptotic flow for \rmn(t)\ll1 involves matching of lengthscales of order \rmn^2, \rmn^{3/2}, \rmn$, 1 and probably$\rmn^{7/4}$.Comment: 36 pages, including 9 figure

Chiral and deconfinement transitions in a magnetic background using the functional renormalization group with the Polyakov loop

We use the Polyakov loop coupled quark-meson model to approximate low energy QCD and present results for the chiral and deconfinement transitions in the presence of a constant magnetic background $B$ at finite temperature $T$ and baryon chemical potential $\mu_B$. We investigate effects of various gluoni potentials on the deconfinement transition with and without a fermionic backreaction at finite $B$. Additionally we investigate the effect of the Polyakov loop on the chiral phase transition, finding that magnetic catalysis at low $\mu_B$ is present, but weakened by the Polyakov loop.Comment: 17 pages and 8 figs. v2: added ref

Staggering and Synchronisation of Prices in a Low Inflation Environment: Evidence from German Food Stores

Only a few studies have analysed staggering and synchronisation in pricing behaviour of multi-product firms. These studies used low-frequency data in an environment of high rates of inflation. This paper investigates staggering and synchronisation of weekly prices for ten food products in 131 grocery stores in Germany over the period from May 1995 to December 2000 (296 weeks). Different forms of staggering and synchronisation (across-store synchronisation, within type-of-store synchronisation, within retailer synchronisation or across-product synchronisation) have been analysed. None of these forms of synchronisation is supported empirically however. In contrast, perfect staggering can only be rejected in very few cases indicating that fixed or firm specific menu costs are not major causes for price stickiness. --Food Retail Market,Germany,Pricing Behaviour,Menu Costs