Orbiting multi-beam microwave radiometer for soil moisture remote sensing

The effects of soil moisture and other factors on soil surface emissivity are reviewed and design concepts for a multibeam microwave radiometer with a 15 m antenna are described. Characteristic antenna gain and radiation patterns are shown and losses due to reflector roughness are estimated

Composite boson signature in the interference pattern of atomic dimer condensates

We predict the existence of high frequency modes in the interference pattern of two condensates made of fermionic-atom dimers. These modes, which result from fermion exchanges between condensates, constitute a striking signature of the dimer composite nature. From the 2-coboson spatial correlation function, that we derive analytically, and the Shiva diagrams that visualize many-body effects specific to composite bosons, we identify the physical origin of these high frequency modes and determine the conditions to see them experimentally by using bound fermionic-atom pairs trapped on optical lattice sites. The dimer granularity which appears in these modes comes from Pauli blocking that prevents two dimers to be located at the same lattice site.Comment: 10+7 pp, 3 figures. v2: version accepted for publication in New J. Phy

Markets in China and Europe on the Eve of the Industrial Revolution

Prevailing views suggest the Industrial Revolution began in Europe because markets had gradually become more efficient and by the 18th century the scope of economic activity was far larger than in other parts of the world. This paper compares the actual performance of markets in Europe and China, two regions of the world that were relatively advanced in the pre-industrial period, but would start to industrialize about 150 years apart. The analysis covers economies that account for about two-fifths of the world's population in the mid-18th century, and it considers some three centuries of data. Our findings suggest that relative levels of market function in China and Europe were similar prior to the Industrial Revolution. Higher efficiency in Europe is seen only in the nineteenth century when industrialization was already underway. Moreover, these improvements occurred in a dramatic and sudden fashion, further casting doubt on an evolutionary view of market development. Rather than being a key condition for subsequent growth, gains in efficiency appeared simultaneously with the turning point of modern growth. We discuss the implications of these findings for a number of explanations for long-run growth and the Industrial Revolution.

The Origins of Spatial Interaction

Geography shapes economic outcomes in a major way. This paper uses spatial empirical methods to detect and analyze trade patterns in a historical data set on Chinese rice prices. Our results suggest that spatial features were important for the expansion of interregional trade. Geography dictates, first, over what distances trade was possible in different regions, because the costs of ship transport were considerably below those for land transport. Spatial features also influence the direction in which a trading network is expanding. Moreover, our analysis captures the impact of new trade routes both within and outside the trading areas. We also discuss the long-run implications this might have.

Market Integration and Economic Development: A Long-run Comparison

How much of China's recent economic performance can be attributed to market-oriented reforms introduced in the last two decades? A long-run perspective may be important for understanding the process of economic development occurring today. This paper compares the integration of rice markets in China today and 270 years ago. In the 18th century, transport technology was non-mechanized, but markets were close to being free markets. We distinguish local harvest and weather from aggregate sources of price variation in a historical sample and in a similarly constructed contemporary sample. Findings indicate the degree of market integration in the 1720s is a very good predictor of per capita income in the 1990s. Moreover, the current pattern of interregional income in China is strongly linked to persistent geographic factors that were already apparent several centuries ago, well before the enactment of modern reform programs.

Cross-over from trion-hole to exciton-polaron in n-doped semiconductor quantum wells

We present a theoretical study of photo-absorption in n-doped two-dimensional (2D) and quasi-2D semiconductors that takes into account the interaction of the photocreated exciton with Fermi-sea (FS) electrons through (i) Pauli blocking, (ii) Coulomb screening, and (iii) excitation of FS electron-hole pairs---that we here restrict to one. The system we tackle is thus made of one exciton plus zero or one FS electron-hole pair. At low doping, the system ground state is predominantly made of a "trion-hole"---a trion (two opposite-spin electrons plus a valence hole) weakly bound to a FS hole---with a small exciton component. As the trion is poorly coupled to photon, the intensity of the lowest absorption peak is weak; it increases with doping, thanks to the growing exciton component, due to a larger coupling between 2-particle and 4-particle states. Under a further doping increase, the trion-hole complex is less bound because of Pauli blocking by FS electrons, and its energy increases. The lower peak then becomes predominantly due to an exciton dressed by FS electron-hole pairs, that is, an exciton-polaron. As a result, the absorption spectra of $n$-doped semiconductor quantum wells show two prominent peaks, the nature of the lowest peak turning from trion-hole to exciton-polaron under a doping increase. Our work also nails down the physical mechanism behind the increase with doping of the energy separation between the trion-hole peak and the exciton-polaron peak, even before the anti-crossing, as experimentally observed.Comment: 20 pages, 10 figure

Way to observe the implausible "trion-polariton"

Using the composite boson (coboson) many-body formalism, we determine under which conditions "trion-polariton" can exist. Dipolar attraction can bind an exciton and an electron into a trion having an energy well separated from the exciton energy. Yet, the existence of long-lived "trion-polariton" is a priori implausible not only because the photon-trion coupling, which scales as the inverse of the sample volume, is vanishingly small, but mostly because this coupling is intrinsically "weak". Here, we show that a moderately dense Fermi sea renders its observation possible: on the pro side, the Fermi sea overcomes the weak coupling by pinning the photon to its momentum through Pauli blocking, it also overcomes the dramatically poor photon-trion coupling by providing a volume-linear trion subspace to which the photon is coherently coupled. On the con side, the Fermi sea broadens the photon-trion resonance due to the fermionic nature of trions and electrons, it also weakens the trion binding by blocking electronic states relevant for trion formation. As a result, the proper way to observe this novel polariton is to use doped semiconductor having long-lived electronic states, highly-bound trion and Fermi energy as large as a fraction of the trion binding energy.Comment: 6 pages, 3 figure