On conformally recurrent manifolds of dimension greater than 4

Conformally recurrent pseudo-Riemannian manifolds of dimension n>4 are investigated. The Weyl tensor is represented as a Kulkarni-Nomizu product. If the square of the Weyl tensor is nonzero, a covariantly constant symmetric tensor is constructed, that is quadratic in the Weyl tensor. Then, by Grycak's theorem, the explicit expression of the traceless part of the Ricci tensor is obtained, up to a scalar function. The Ricci tensor has at most two distinct eigenvalues, and the recurrence vector is an eigenvector. Lorentzian conformally recurrent manifolds are then considered. If the square of the Weyl tensor is nonzero, the manifold is decomposable. A null recurrence vector makes the Weyl tensor of algebraic type IId or higher in the Bel - Debever - Ortaggio classification, while a time-like recurrence vector makes the Weyl tensor purely electric.Comment: Title changed and typos corrected. 14 page

Weakly Z symmetric manifolds

We introduce a new kind of Riemannian manifold that includes weakly-, pseudo- and pseudo projective- Ricci symmetric manifolds. The manifold is defined through a generalization of the so called Z tensor; it is named "weakly Z symmetric" and denoted by (WZS)_n. If the Z tensor is singular we give conditions for the existence of a proper concircular vector. For non singular Z tensor, we study the closedness property of the associated covectors and give sufficient conditions for the existence of a proper concircular vector in the conformally harmonic case, and the general form of the Ricci tensor. For conformally flat (WZS)_n manifolds, we derive the local form of the metric tensor.Comment: 13 page

3D geomechanics in UGS projects. A comprehensive study in northern Italy.

The 3D geomechanical response to seasonal gas storage is investigated for a gas field managed by Stogit. The 1200-m deep reservoir is located in the Po basin, Italy, and a UGS program is under way since 1986 following a 5-year primary production life. The use of: i) a basin-scale geomechanical characterization of the Po basin, ii) a detailed knowledge of the subsurface geology made available by 3D seismic surveys, iii) almost 30-year measurements related to the gas field activities, and iv) an advanced PSInSAR analysis providing the vertical and horizontal West-East displacements of the ground surface above the field from 2003 to 2007, has allowed for the development, setup, and calibration of a representative 3D fluid-dynamical model and a transversally isotropic nonlinear geo-mechanical model. The latter successfully reproduces the largest vertical and horizontal seasonal land displacements, on the range of 8-10 mm and 6-8 mm, respectively, as observed above the reservoir. The model is then used to investigate the ground surface displacements in connection with UGS future programs where the maximum overpressure achieved in the field is planned to be raised to 107% pi and 120% pi, with pi the original in-situ pore pressure

Monitoring and modeling 3-D round movements induced by seasonal gas storage in deep reservoirs

Underground gas storage (UGS) in depleted hydrocarbon fields is a strategic practice to cope with the growing energy demand, and occurs in many places in Europe and North America. In response to summer gas injection and winter gas withdrawal the reservoir expands and contracts almost elastically, namely it \u201cbreathes\u201d, as a major consequence of the fluid pore pressure fluctuations. Depending on a number of factors, including the field burial depth, the difference between the largest and the smallest gas pore pressure, and the geomechanical properties of the injected formation and the overburden, the porous medium overlying the reservoir is subject to a three-dimensional deformation related to the cyclic motion of the land surface in both vertical and horizontal directions. We present a multidisciplinary methodology to evaluate the environmental impact of UGS from a geomechanical point of view in connection with the ground surface displacement that may cause some concern for the integrity of the existing engineered structures and infrastructures. Long-time records of injected/removed gas volume and fluid pore pressure, together with multiyear detection of vertical and horizontal west\u2013east displacement of the land surface above the field by an advanced PSInSARTM analysis have allowed calibration of a 3-D fluid-dynamic model and development of a 3-D transversally isotropic geomechanical model. The latter has been successfully implemented and used to reproduce the vertical and horizontal cyclical displacements, in the range 8\u201310 mm and 6\u20138 mm, respectively, measured between 2003 and 2007 above the \u201cLombardia\u201d gas reservoir, northern Italy, where since 1986 a UGS program has been under way by Stogit S.p.A. (Eni), following an initial 5-year field production life

Complications of endourological procedures and their treatment.

Endourological treatment for urinary stones and other obstructive urinary tract diseases is minimally invasive but in some cases it involves serious complications. This collection of cases describes some complications of endourological procedures and how they were treated. Case 1: A case of right ultrasound-guided percutaneous nephrostomy found to be misplaced in the inferior vena cava. The case was safely managed, but it showed that ultrasound guidance alone may be insufficient so it is recommended that percutaneous nephrostomy should be always placed under fluoroscopic control, either alone or in combination with ultrasound guidance. Case 2: A case of renal subcapsular hematoma occurring on retrograde intrarenal surgery at high perfusion pressure. The hematoma was drained under combined ultrasonic and radiological guidance. Post treatment recovery was uneventful. Large stone size, severe ipsilateral hydronephrosis, long operation time, higher hydrostatic pressure of the irrigating solution and low ureteral wall compliance are supposed to be risks factors associated with renal subcapsular formation. Management strategy should be tailored to patient's clinical conditions. In hemodynamically stable patients, large hematoma drainage is recommended to prevent further complications and favours early recovery. Case 3: A case of double J stent fracture discovered one month after the insertion to relieve obstruction from a 1 cm stone in the right proximal ureter. The distal fragment of the stent was removed by cystoscopy while the proximal fragment was removed by semirigid ureteroscopy in two sessions due to fever and extensive calcification. Case 4: A mini-invasive technique for transurethral replacement of completely encrusted urinary stents in female patients. This technique allows the interventional radiologist to replace obstructed urinary stents by avoiding more invasive and traumatic urological procedures with sedation