High Harmonic Generation without Tunnel-Ionization

A new High Harmonic Generation (HHG) scheme, which doesn't rely on Tunnel-Ionization as the ionization mechanism but rather on Single-Photon Ionization, is theoretically proposed and numerically demonstrated. The scheme uses two driver fields: an extreme-ultraviolet driver which induces the ionization, and a circularly-polarized, co-rotating, two-color infrared driver carried at a fundamental frequency and its second harmonic which induces the recollision. Using Classical and time-dependent Schr\"odinger equation simulations of a model Argon atom, we show that in this scheme ionization is essentially decoupled from recollision. Releasing the process from being Tunneling-dependent reduces its degree of nonlinearity, which offers new capabilities in attosecond science, such as generation of High Harmonics from highly-charged ions, or from specific deep core electronic levels. It is shown that the emitted high harmonics involve the absorption of photons of one color of the infrared driver, and the emission of photons of the second color. This calls for future examination of the possible correlations between the emitted high harmonics

The Role of Macroprudential Policy for Financial Stability in East Asia’s Emerging Economies

This paper analyzes the role and scope of macroprudential policy in preventing financial instability in the context of East Asian economies. It analyzes the behavior of the housing market in a dynamic setting to identify some of the factors responsible for the volatility of housing markets and their susceptibility to boom-bust cycles, which it identifies as a key source of financial imbalances in these economies. It then discusses the causal nexus between price and financial stability and the roles and complementary nature of macroprudential and monetary policies in addressing aggregate risk in the financial system. The paper identifies currency and maturity mismatches, which contributed to the 1997 - 1998 Asian financial crisis, as ongoing concerns in these economies although the high levels of reserves in the region now act as a buffer

The Three-dimensional Structure of the Nitrogen Regulatory Protein IIANtr from Escherichia coli

The bacterial rpoN operon codes for σ54, which is the key σ factor that, under nitrogen starvation conditions, activates the transcription of genes needed to assimilate ammonia and glutamate. The rpoN operon contains several other open reading frames that are cotranscribed with σ54. The product of one of these, the 17.9 kDa protein IIANtr, is homologous to IIA proteins of the phosphoenolpyruvate:sugar phosphotransferase (PTS) system. IIANtr influences the transcription of σ54-dependent genes through an unknown mechanism and may thereby provide a regulatory link between carbon and nitrogen metabolism. Here we describe the 2.35 Å X-ray structure of Escherichia coli IIANtr. It is the first structure of a IIA enzyme from the fructose-mannitol family of the PTS. The enzyme displays a novel fold characterized by a central mixed parallel/anti-parallel β-sheet surrounded by six α-helices. The active site His73 is situated in a shallow depression on the protein surface.