Dynamics of the molecular orientation field coupled to ions in two-dimensional ferroelectric liquid crystals

Molecular orientation fluctuations in ferroelectric smectic liquid crystals produce space charges, due to the divergence of the spontaneous polarization. These space charges interact with mobile ions, so that one must consider the coupled dynamics of the orientation and ionic degrees of freedom. Previous theory and light scattering experiments on thin free-standing films of ferroelectric liquid crystals have not included this coupling, possibly invalidating their quantitative conclusions. We consider the most important case of very slow ionic dynamics, compared to rapid orientational fluctuations, and focus on the use of a short electric field pulse to quench orientational fluctuations. We find that the resulting change in scattered light intensity must include a term due to the quasistatic ionic configuration, which has previously been ignored. In addition to developing the general theory, we present a simple model to demonstrate the role of this added term

Geographic concentration and firm survival

If localization economies are present, firms within denser industry concentrations should exhibit higher levels of performance than more isolated firms. Nevertheless, research in industrial organization that has focused on the influences on firm survival has largely ignored the potential effects from agglomeration. Recent studies in urban and regional economics suggests that agglomeration effects may be very localized. Analyses of industry concentration at the MSA or county-level may fail to detect important elements of intra-industry firm interaction that occur at the sub-MSA level. Using a highly detailed dataset on firm locations and characteristics for Texas, this paper analyses agglomeration effects on firm survival over geographic areas as small as a single mile radius. We find that greater firm density within very close proximity (within 1 mile) of firms in the same industry increases mortality rates while greater concentration over larger distances reduces mortality rates.Firm Survival, Agglomeration, Localization, and Knowledge Externalities

Research universities and regional high-tech firm start-ups and exit

If localized knowledge spillovers are present in the university setting, higher rates of both start-ups and/or survival than in the broader economy would be observed in areas that are geographically proximate to the university. Using a fully-disclosed Quarterly Census of Employment and Wages for Texas for the years 1999:3-2006:2, this paper analyzes start-ups and exit rates for high-tech firms in Texas. We find that there is evidence that the presence of a research institution will affect the likelihood of technology start-ups. However, results suggest that geographic proximity to knowledge centers does not reduce hazard rates.Entry and Survival, R & D, Regional, Urban, and Rural Analyses

Scaling behavior of explosive percolation on the square lattice

Clusters generated by the product-rule growth model of Achlioptas, D'Souza, and Spencer on a two-dimensional square lattice are shown to obey qualitatively different scaling behavior than standard (random growth) percolation. The threshold with unrestricted bond placement (allowing loops) is found precisely using several different criteria based upon both moments and wrapping probabilities, yielding p_c = 0.526565 +/- 0.000005, consistent with the recent result of Radicchi and Fortunato. The correlation-length exponent nu is found to be close to 1. The qualitative difference from regular percolation is shown dramatically in the behavior of the percolation probability P_(infinity) (size of largest cluster), the susceptibility, and of the second moment of finite clusters, where discontinuities appears at the threshold. The critical cluster-size distribution does not follow a consistent power-law for the range of system sizes we study L 2 for larger L.Comment: v2: Updated results in original version with new data; expanded discussion. v3: Resubmitted version. New figures, reference

Sea-level change and storm surges in the context of climate change

This paper reviews the latest research in New Zealand surrounding the issues of sea-level rise and extreme sea levels in the context of global warming and variability in the Pacific-wide El Nino– Southern Oscillation (ENSO). Past records of climate, sea level (excluding tides) and sea and air temperatures have shown that they are continuously fluctuating over various long-term timescales of years, decades and centuries. This has made it very difficult to determine whether the anthropogenic effects such as increased levels of “greenhouse” gases are having an accelerating effect on global sea levels or an increased incidence of extreme storms. Over the past century, global sea level has risen by 10–25 cm, and is in line with the rise in relative sea level at New Zealand’s main ports of +1.7 mm yr –1. What has become very clear is the need to better understand interannual (year-to-year) and decadal variability in sea-level, as these larger signals of the order of 5–15 cm in annual-mean sea level have a significant “flow-on” effect on the long-term trend in sea level. The paper describes sea level variability in northern New Zealand—both long- and short-term—involved in assessing the regional trends in sea level. The paper also discusses the relative contributions of tides, barometric pressure and wind set-up in causing extreme sea levels during storm surges. Some recent research also looked at a related question—Is there any sign of increased storminess, and hence storm surge, in northern New Zealand due to climate change? The paper concludes that, while no one can be completely sure how sea-level and the degree of storminess will respond in the near future, what is clear is that interannual and decadal variability in sea level is inextricably linked with Pacific-wide ENSO response and longer inter-decadal shifts in the Pacific climate regime, such as the latest shift in 1976

Classical integrability of chiral QCD2QCD_{2} and classical curves

In this letter, classical chiral $QCD_{2}$ is studied in the lightcone gauge $A_{-}=0$. The once integrated equation of motion for the current is shown to be of the Lax form, which demonstrates an infinite number of conserved quantities. Specializing to gauge group SU(2), we show that solutions to the classical equations of motion can be identified with a very large class of curves. We demonstrate this correspondence explicitly for two solutions. The classical fermionic fields associated with these currents are then obtained.Comment: Final version to appear in Mod. Phys. Lett. A. A reference and two footnotes added. 6 pages revte