French-born settlers in the Lower Rio Grande Valley, 1821-1900 : immigration, influence, integration and identity

The thesis analyzes the French-born people who settled in the Lower Rio Grande Valley between 1821 and 1900. It focuses on four key elements which are inter-related: Immigration, influence, integration and identity. This study answers two complex questions: what was the influence exerted by the French-born settlers on the Lower Rio Grande Valley, and what was the influence of the area on their settlement, integration, and identity? Such an investigation aims to fill the gap in knowledge on the French and European presence in the 19th century Lower Rio Grande society, and to broaden our understanding of the immigration process in the North American borderlands. This thesis relies primarily on the Lower Rio Grande Valley Population Schedules which compile the data used to elaborate the U.S. censuses. Information drawn from these sources is gathered in sixteen tables which illuminate the different characteristics of the French-born population. The Population Schedules were complemented by narrative sources. This study demonstrates that, in spite of the fact that French-born settlers were few in the Lower Rio Grande Valley, their influence as a group and as individuals was determinant on the socio-economic and cultural evolutions of the area. They were also transformed by their immigration as they were compelled to adapt to the realities of this borderland area. Their re-settlements turned them into Valley immigrants whose identities became complex and inclusive

Arbuscular mycorrhizal fungi for the biocontrol of plant-parasitic nematodes: a review of the mechanisms involved

Arbuscular mycorrhizal fungi (AMF) are obligate root symbionts that can protect their host plant against biotic stress factors such as plant-parasitic nematode (PPN) infection. PPN consist of a wide range of species with different life styles that can cause major damage in many important crops worldwide. Various mechanisms have been proposed to play a role in the biocontrol effect of AMF against PPN. This review presents an overview of the different mechanisms that have been proposed, and discusses into more detail the plausibility of their involvement in the biocontrol against PPN specifically. The proposed mechanisms include enhanced plant tolerance, direct competition for nutrients and space, induced systemic resistance (ISR) and altered rhizosphere interactions. Recent studies have emphasized the importance of ISR in biocontrol and are increasingly placing rhizosphere effects on the foreground as well, both of which will be the focal point of this review. Though AMF are not yet widely used in conventional agriculture, recent data help to develop a better insight into the modes of action, which will eventually lead toward future field applications of AMF against PPN. The scientific community has entered an exciting era that provides the tools to actually unravel the underlying molecular mechanisms, making this a timely opportunity for a review of our current knowledge and the challenges ahead

Noninvasive Embedding of Single Co Atoms in Ge(111)2x1 Surfaces

We report on a combined scanning tunneling microscopy (STM) and density functional theory (DFT) based investigation of Co atoms on Ge(111)2x1 surfaces. When deposited on cold surfaces, individual Co atoms have a limited diffusivity on the atomically flat areas and apparently reside on top of the upper pi-bonded chain rows exclusively. Voltage-dependent STM imaging reveals a highly anisotropic electronic perturbation of the Ge surface surrounding these Co atoms and pronounced one-dimensional confinement along the pi-bonded chains. DFT calculations reveal that the individual Co atoms are in fact embedded in the Ge surface, where they occupy a quasi-stationary position within the big 7-member Ge ring in between the 3rd and 4th atomic Ge layer. The energy needed for the Co atoms to overcome the potential barrier for penetration in the Ge surface is provided by the kinetic energy resulting from the deposition process. DFT calculations further demonstrate that the embedded Co atoms form four covalent Co-Ge bonds, resulting in a Co4+ valence state and a 3d5 electronic configuration. Calculated STM images are in perfect agreement with the experimental atomic resolution STM images for the broad range of applied tunneling voltages.Comment: 19 pages, 15 figures, 3 table

Low-temperature scanning tunneling microscopy of ring-like surface electronic structures around Co islands on InAs(110) surfaces

We report on the experimental observation by scanning tunneling microscopy at low temperature of ring-like features that appear around Co metal clusters deposited on a clean (110) oriented surface of cleaved p-type InAs crystals. These features are visible in spectroscopic images within a certain range of negative tunneling bias voltages due to the presence of a negative differential conductance in the current-voltage dependence. A theoretical model is introduced, which takes into account non-equilibrium effects in the small tunneling junction area. In the framework of this model the appearance of the ring-like features is explained in terms of interference effects between electrons tunneling directly and indirectly (via a Co island) between the tip and the InAs surface.Comment: 8 pages, 4 figure

Spontaneous doping of two-dimensional NaCl films with Cr atoms: aggregation and electronic structure

Upon deposition of Cr atoms on ultrathin NaCl/Au(111) films they form substituting dopants either replacing Na or Cl ions, thereby changing the electronic properties of the film and in particular the work function