Molecular characterization of ‘Candidatus Phytoplasma mali’ strains in outbreaks of apple proliferation in north eastern Italy, Hungary, and Serbia

During 2005-2008 apple plants of different varieties showing proliferation symptoms were observed in diverse areas of north eastern Italy, Hungary and Serbia. PCR/RFLP analyses showed that all the samples were infected with ‘Candidatus Phytoplasma mali’. In the 16S plus spacer region two phytoplasma profiles (P-I and P-II) were distinguished. P-I profile was detected in reference strains AP, AT1, AT2, in samples from Serbia, and in the majority of samples from Trentino; the P-II profile was prevalent in samples from Veneto; both profiles were identified in samples from Hungary, in some cases together in single samples. The analyses of rpl22-s3 genes allow the identification, in all the samples showing a P-I profile, the presence of phytoplasmas belonging to rpX-A subgroup, while in the samples showing a P-II profile it was possible to distinguish the other three reported rpX subgroups. In the majority of samples from the Veneto region phytoplasmas belonging to rpX-D subgroup were identified, while rpX-B and rpX-C subgroups were identified only in a few samples from Trentino and Veneto regions, respectively. Further RFLP analyses on AP13/AP10 amplicons differentiate among strains belonging to the rpX-A subgroup: the samples from Serbia show AP profiles, while those from Trentino show AT-2 profiles. In the samples from Hungary the presence of AT1, AT2, and AP profiles was identified.Keywords: Apple, ‘Candidatus Phytoplasma mali’, phytoplasma strains, PCR/RFLP analyses, epidemiolog

The Geomechanics of CO2 Storage in Deep Sedimentary Formations

This paper provides a review of the geomechanics and modeling of geomechanics associated with geologic carbon storage (GCS), focusing on storage in deep sedimentary formations, in particular saline aquifers. The paper first introduces the concept of storage in deep sedimentary formations, the geomechanical processes and issues related with such an operation, and the relevant geomechanical modeling tools. This is followed by a more detailed review of geomechanical aspects, including reservoir stress-strain and microseismicity, well integrity, caprock sealing performance, and the potential for fault reactivation and notable (felt) seismic events. Geomechanical observations at current GCS field deployments, mainly at the In Salah CO2 storage project in Algeria, are also integrated into the review. The In Salah project, with its injection into a relatively thin, low-permeability sandstone is an excellent analogue to the saline aquifers that might be used for large scale GCS in parts of Northwest Europe, the U.S. Midwest, and China. Some of the lessons learned at In Salah related to geomechanics are discussed, including how monitoring of geomechanical responses is used for detecting subsurface geomechanical changes and tracking fluid movements, and how such monitoring and geomechanical analyses have led to preventative changes in the injection parameters. Recently, the importance of geomechanics has become more widely recognized among GCS stakeholders, especially with respect to the potential for triggering notable (felt) seismic events and how such events could impact the long-term integrity of a CO{sub 2} repository (as well as how it could impact the public perception of GCS). As described in the paper, to date, no notable seismic event has been reported from any of the current CO{sub 2} storage projects, although some unfelt microseismic activities have been detected by geophones. However, potential future commercial GCS operations from large power plants will require injection at a much larger scale. For such largescale injections, a staged, learn-as-you-go approach is recommended, involving a gradual increase of injection rates combined with continuous monitoring of geomechanical changes, as well as siting beneath a multiple layered overburden for multiple flow barrier protection, should an unexpected deep fault reactivation occur

Reordering for the Iterative Solution of Hybrid Elastic Structures

The Finite Element Method (FEM) is widely used in civil engineering to analyze the behavior of complex structures where the coupling of different elements, such as beams, trusses, and shells, is often required. FEM leads to symmetric positive definite (SPD) matrices that, depending on the type of discretization, may prove quite unsuitable for the solution by the Preconditioned Conjugate Gradient (PCG) method. Preconditioning techniques based on the incomplete Cholesky decomposition may fail when far nodes are connected. In this case the native ordering of the nodal unknowns yields a large matrix bandwidth, and a poor quality preconditioner which is also very expensive to be calculated. Numerical experiments are planned and presented where the effect of reordering on the PCG performance for the solution of a realistic bridge structure is explored and discussed. The preconditioner used is a variant of the incomplete Cholesky factorization with variable fill-in. It is shown that some reordering specifically designed and implemented for direct elimination methods can be very helpful as they lead to both a faster PCG convergence and a cheaper preconditioner computation. A main disadvantage is the need for an appropriate degree of fill-in which turns out to be problem dependent and must be found empirically. On the other hand, direct solvers perform usually better than PCG and moreover do not require the selection of an user-specified parameter like the most appropriate degree of fill-in

A comparison of projective and direct solvers for finite elements in elastostatics

The Finite Element Method (FEM) is widely used in civil and mechanical engineering to simulate the behavior of complex structures and, more specifically, to predict stress and deformation fields of structural parts or mechanical bodies. In the former case, the coupling between different types of elements, such as beams, trusses, and shells, is often required, while in the latter fully 3D discretizations are typically used. For both, FEM leads to symmetric positive definite (SPD) matrices that, depending on the type of discretization and especially on the topology of the nodal connections, may be efficiently solved by either the Preconditioned Conjugate Gradient (PCG) or a direct solver such as the routine MA57 of the Harwell Software Library. Numerical experiments are shown and discussed where the effect of spatial discretization, different solution techniques, and a possible nodal reordering, is explored. The PCG preconditioner used is a variant of the incomplete Cholesky factorization with variable fill-in. It is shown that for structures with 1D or 2D connections, such as for example a bridge, MA57 performs usually better than PCG. In this case it is noted that some reorderings specifically designed and implemented for direct elimination methods can be very helpful for PCG as well as they yield a cheaper preconditioner and lead to a much faster PCG convergence. The main disadvantage is the need for an appropriate degree of fill-in for the preconditioner which turns out to be problem dependent and must be found empirically. However, in fully 3D problems, arising for example from the FE discretization of structural components or geomechanical structures, PCG outperforms MA57 while also requiring much less memory, and thus allowing for the use of much refined grids, if needed. With the aid of a large geomechanical problem it is shown that direct solvers may not be (even) used on serial computers due to their prohibitive computational cost with PCG the only viable alternative solver

Managed Versus Natural Recharge of Pre-Alpine Phreatic Aquifers

Managed aquifer recharge (MAR) is becoming a common practice worldwide. MAR is carried out in different environments from coastlands to highlands, in megalopolis, farmlands and pristine areas, and in arid and humid regions. Pre-Alpine aquifers represent an optimal target when MAR is aimed at storing large amounts of high-quality waters. In fact, pre-Alpine aquifers are generally characterized by high permeability and a thick unsaturated zone, with the catchments crossed by watercourses rich of high-quality water. Here, we focus the attention to a representative pre-Alpine aquifer system located in the Friuli region, northeastern Italy. A 1-year long MAR test was carried out through a ~700\ua0m2 infiltration basin recharged by water diverted from a nearby channel. The site was characterized from the hydrogeological viewpoint, and the MAR test was monitored through time-lapse hydrogeophysics, water level and piezometric records, and physicochemical water characterization. The data set was used to calibrate a local groundwater flow model, showing that MAR recharged the 50\ua0m deep phreatic aquifer with 1,000\ua0m3/day. Hydrogeologic data made available by previous studies were processed to develop a groundwater model of the regional aquifer that allowed for estimating the natural groundwater recharge of the phreatic system and, subsequently, evaluating the MAR effects in the context of the natural balance. If a single MAR site, like the tested one, plays a certain effect at a local scale only, the MAR implementation on several gravel pits and large-diameter wells scattered in the region could store several million cubic meters of water per year, significantly raising the water table and improving the groundwater quality