Resonantly enhanced filamentation in gases

In this Letter, a low-loss Kerr-driven optical filament in Krypton gas is experimentally reported in the ultraviolet. The experimental findings are supported by ab initio quantum calculations describing the atomic optical response. Higher-order Kerr effect induced by three-photon resonant transitions is identified as the underlying physical mechanism responsible for the intensity stabilization during the filamentation process, while ionization plays only a minor role. This result goes beyond the commonly-admitted paradigm of filamentation, in which ionization is a necessary condition of the filament intensity clamping. At resonance, it is also experimentally demonstrated that the filament length is greatly extended because of a strong decrease of the optical losses

Business cycle volatility and country size: evidence for a sample of OECD countries

The main purpose of this paper is to investigate the relationship between business cycle volatility and country size using quarterly data for a sample of OECD countries over 1960-2000. The results suggest very strongly that the relationship between country size and business cycle volatility is negative and statistically significant. This finding is very robust, suggesting that country size does matter, at least for the severity of cyclical fluctuations

Orientation and Alignment Echoes

We present what is probably the simplest classical system featuring the echo phenomenon - a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation/alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of CO_2 molecules excited by a pair of femtosecond laser pulses

The ejection of triatomic molecular hydrogen ions H-3(+) produced by the interaction of benzene molecules with ultrafast laser pulses

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Sources of Output Fluctuations During the Interwar Period: Further Evidence on the Causes of the Great Depression

This paper decomposes output fluctuations during the 1913 to 1940 period into components resulting from aggregate supply and aggregate demand shocks. We estimates a number of different models, all of which yield qualitatively similar results. While identification is normally achieved by assuming that aggregate demand shocks have no long run real effects, we also estimate models that allow demand shocks to permanently affect output. Our findings support the following three conclusions: (i) there was a large negative aggregate demand shock in November 1929, immediately after the stock market crash; (ii) aggregate demand shocks are mainly responsible for the decline in output through mid to late 1931; (iii) beginning in mid 1931 there is an aggregate supply collapse that coincides with the onset on severe bank panics.

Fractional Echoes

We report the observation of fractional echoes in a double-pulse excited nonlinear system. Unlike standard echoes which appear periodically at delays which are integer multiple of the delay between the two exciting pulses, the fractional echoes appear at rational fractions of this delay. We discuss the mechanism leading to this phenomenon, and provide the first experimental demonstration of fractional echoes by measuring third harmonic generation in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses