Constructions for finite-state codes

A class of codes called finite-state (FS) codes is defined and investigated. These codes, which generalize both block and convolutional codes, are defined by their encoders, which are finite-state machines with parallel inputs and outputs. A family of upper bounds on the free distance of a given FS code is derived from known upper bounds on the minimum distance of block codes. A general construction for FS codes is then given, based on the idea of partitioning a given linear block into cosets of one of its subcodes, and it is shown that in many cases the FS codes constructed in this way have a d sub free which is as large as possible. These codes are found without the need for lengthy computer searches, and have potential applications for future deep-space coding systems. The issue of catastropic error propagation (CEP) for FS codes is also investigated

System Identification and Seismic Performance Evaluation of Earth Dams

A system identification technique is developed to provide dynamic properties of earth dams from their seismic records. The technique is utilized to assess the capabilities and limitation of analytical models in terms of dynamic nonlinear constitutive relationships as well as damping. The technique is based on the least square method using Gaussian hypothesis. Earth dams are modeled as a three-dimensional nonhomogeneous visco-elasto-plastic soil structure. The forward problem is solved using a Galerkin-Ritz formulation in which the solution is expanded using basis function, which is selected to be the eigenmodes. The spatial variation of the excitation is considered by using global shape functions defined on the boundary domain to interpolate the input motion on the dam boundaries using recorded motion at discrete locations. The constitutive model is used to accommodate the nonlinear path dependent behavior of the dam material as well as coupling between different constituent of the soil mixture. The model is implemented using Druker-Prager multi-yield surface model and linear Kelvin-Voigt model. Application to instrumented dams, in recent earthquake, showed significant match between the recorded response and the optimal estimated response

An Investigation of the dynamic characteristics of an earth dam

An investigation has been made to analyze observations of the effect of two earthquakes (with M L= 6. 3 and 4. 7) on Santa Felicia Dam, a rolled-fill embankment located in Southern California. The dam is 236.5 ft. high and 1,275 ft. long by 30 ft. wide at the crest. The purpose of the investigation is: (1) to study the nonlinear behavior of the dam during the two earthquakes, (2) to provide data on the in-plane dynamic shear moduli and damping factors for the materials of the dam during real earthquake conditions, and (3) to compare these properties with those previously available from laboratory investigations. From the recorded motions of the dam, amplification spectra were computed to indicate the natural frequencies of the dam and to estimate the relative contribution of different modes of vibrations. A comparison between these natural frequencies and those obtained by two elastic shear -beam models was made to obtain representative dam material properties. In addition, field wave-velocity measurements were carried out as a further check as well as to study the variation of shear wave velocity at various depths in the dam. The amplification spectra showed a predominant frequency of 1.45 Hz in the upstream/ downstream direction; in this direction the response was treated as that of a single-degree-of -freedom hysteretic structure. Three types of digital bandpass filtering of the crest and abutment records were used to enhance the hysteresis loops which show the relationship between the relative displacement of the crest with respect to the abutment and the absolute acceleration of the dam. A method is described which, using some of the existing elastic -response theories, enables the shear stresses and strains, and consequently the shear moduli, to be evaluated from the hysteresis loops. The equivalent viscous damping factors were calculated from the areas inside the hysteresis loops. The shear moduli and the damping factors were determined as functions of the induced strains in the dam. Finally, the shear moduli and damping factors obtained for the dam were compared with previously available laboratory data for sands and saturated clays

Full-scale experimental investigation of a modern earth dam

An extensive investigation has been made based on the results of full-scale dynamic tests performed on a modern earth dam, Santa Felicia Cam in Southern California. This dam was chosen for the experimental studies because it had been subjected to strong shaking during two earthquakes: the strong, 6.3 local Richter magnitude San Fernando earthquake of 1971, and a 1976 earthquake of magnitude 4.7. The records recovered from these two earthquakes provided usable information on the dynamic characteristics of the dam which was instrumented with motion sensors to yield data on the structural response as well as the input ground motion at the site. In the test programs, various types of dynamic excitations were used including mechanical vibration, ambient vibration, hydrodynamically generated forces, and the two strong seismic ground motions; thus, the imposed dynamic forces varied greatly in their time-history characteristics, spatial distributions, and intensities. For the forced vibration tests, the dam was excited into resonance in the upstream-downstream direction and in the longitudinal direction by a coupled pair of mechanical vibration generators (200 feet apart) capable of producing force up to 10,000 lbs. Symmetric and antisymmetric vibrations were separated by synchronizing the two shakers to run in-phase and 1800 out-of-phase, respectively, with the aid of control units. During the ambient vibration tests, the naturally occurring vibrations of the dam caused by strong wind and the spilling of the reservoir were measured. The test of dam response to hydrodynamic forces involved the use of pressure waves (to impinge upon the upstream face of the dam) originating from a controlled, submerged release of gas under pressure in the reservoir water. During the dynamic tests, three-dimensional measurements of the motions of approximately 25 stations along the crest and seven stations on the downstream slope were recorded and then analyzed in both time and frequency domains. Modes of vibrations and associated natural frequencies as well as damping ratios were determined in the frequency range from 0.0 to 6.0 Hz. The reliability of the existing analytical techniques for earth dams, which are restricted to horizontal shear deformation in the upstreamdownstream direction, was examined. Finally, in order to reveal any change in the dynamic properties of the dam, the dam's natural frequencies, mode shapes, dynamic shear moduli and damping factors (the latter two as functions of the induced strains) estimated from the measured responses to the two earthquakes were compared with those determined from the full-scale dynamic excitation tests

Placental pouch closure: a novel, safe and effective surgical procedure for conservative management of placenta accreta

Background: Placenta accreta spectrum (PAS) has become a global problem secondary to the high rate of cesarean delivery (CD). The current study presents an effective surgical procedure (placental pouch closure) for uterine preservation in patients with PAS. Methods: We applied this procedure in sixty cases at a tertiary university hospital between September 2017 and January 2019. We included women who were diagnosed as PAS based on preoperative ultrasound and Doppler evaluation, and who had the desire for uterine preservation. Results: The procedure was successful in almost all cases; the uterus was conserved 98.33 % of participants, with no associated severe maternal morbidities or mortality. In all cases, no additional surgical procedures were needed. The mean blood loss was 1263 ml, and the mean number of units of blood required for transfusion was 2.31 units. Conclusion: Identifying and meticulously closing the placental pouch is a novel surgical procedure for conservative management of PAS. In well-selected cases with the availability of facilities and expertise, the technique could have a place as a safe and effective surgical technique in women presenting with placenta accreta who desire uterine preservation. Trial registration number: NCT03241849. Registered on August 8, 201