Height bias and scale effect induced by antenna gravitational deformations in geodetic VLBI data analysis

The impact of signal path variations (SPVs) caused by antenna gravitational deformations on geodetic very long baseline interferometry (VLBI) results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying these models in geodetic VLBI data analysis, estimates of the antenna reference point positions are shifted upward by 8.9 and 6.7 mm, respectively. The impact on other parameters is negligible. To simulate the impact of antenna gravitational deformations on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for other antennas according to their size. The effects of the simulations are changes in VLBI heights in the range [-3, 73] mm and a net scale increase of 0.3-0.8 ppb. The height bias is larger than random errors of VLBI position estimates, implying the possibility of significant scale distortions related to antenna gravitational deformations. This demonstrates the need to precisely measure gravitational deformations of other VLBI telescopes, to derive their precise SPV models and to apply them in routine geodetic data analysis

TERRESTRIAL SURVEYING APPLIED TO LARGE VLBI TELESCOPES AND ECCENTRICITY VECTORS MONITORING

Abstract: Large VLBI telescopes undergo gravitational deformations which affect both geodetic and astronomic observations as well as the real reference point (RP) position (i.e. the reference point which is directly linked to and determined by the physics of the VLBI observations). As a consequence, the accuracy of eccentricity vectors determined with high precision terrestrial observations strictly depends on the possibility of univocally defining the geodetic instrument\u2019s RP to be surveyed and estimated: technique dependent effects (e.g. gravitational and thermal deformations for VLBI, phase centre variations for GPS, etc) bias RP positions and weaken and perturb the information contained in the eccentricity. The impact on combined geodetic products is remarkable; a proper definition of space geodetic instruments\u2019 RP must therefore account for possible biases that modify its theoretical position. Whether the problem must be directly addressed by each technique-specific Service is still an open issue. Indirect approaches based on high precision terrestrial observations have proved to be additional, accurate and independent tools for determining and monitoring the eccentricities at co-location sites. Nevertheless, a deeper and rigorous investigation on RP location\u2019s variations is at least as important and it is nowadays fundamental for each space geodetic instrument. To this respect, we are presenting the investigations on VLBI telescope\u2019s RP position that were carried out at Medicina and Noto (Italy) on the 32 m antennas: trilateration, triangulation and laser scanning observations were applied and combined to monitor the gravitational deformations which affect the telescope\u2019s structure and to derive an elevation dependent correction function for radio signal path

A Multi-Objective Design Optimization Approach for the Preliminary Design of High Speed Low Pressure Turbine Disks for Green Engine Architectures

The so-called Green Engine architectures are deeply investigated by the scientific community with the aim of reducing fuel consumption and noise emissions by 50%, and pollutants by 80%, environmental targets established by the Advisory Council for Aeronautical Research in Europe to be achieved by 2020. Low pressure turbine improvements will be important to increase the efficiency of the two most innovative propulsive architectures, the Geared Turbofan and the Open Rotor Engine. The low pressure turbine is released from the fan and can rotate at higher speed values, implying a reduction in fuel consumption. Due to a higher rotational speed, low pressure turbine disks design needs careful considerations due to their higher stress level and reduced burst limit. This paper presents a multi-objective hybrid optimization methodology designed to study high speed low pressure turbine disks. The presented study falls within the preliminary design phase, thus a code based on finite differences was used to perform an optimization study of high speed low pressure turbine disks. The objective functions of the constrained multi-objective optimization were the minimization of the disks weight and the maximization of the burst speed, and a hybrid approach was pursued to better investigate the design space and find the optimum. Then a surrogate-model-based hybrid optimization was conducted to reduce computational time while ensuring the analysis accuracy. A trade-off of most common approximation strategies was conducted. Distributed computing was used involving three national research centers, and parallel computing was adopted to spread the calculation tasks on local workstations. Numeric and Finite-Element-Methodology-based validations followed. This study provides an innovative approach to design such critical components by reducing disks weight by 15% and computational time by 30% if compared to traditional design methodologies. Furthermore, a good match between optimal solutions was found, thus justifying a surrogate-model-based-approach that led to further gains in computational time

An Experimental Kalman Filter Approach to the International Terrestrial Reference Frame Realization

No abstract availabl

Temporal variations in ITRF station displacements analyzed with vector spherical harmonics

The ITRF2014 candidate solutions DTRF2014 and JTRF2014 provide time-dependent station coordinates accounting for irregular station motions. DTRF2014 by DGFI-TUM expands the secular coordinate model via non-tidal loading corrections caused by changes in the atmosphere and continental water storage. JTRF2014 by JPL follows a time series approach to TRF determination based on Kalman filtering, providing weekly updates to station coordinates. The process noise model of the Kalman filter is derived from non-tidal loading deformations. Global features in station displacements have been studied in the past by determining coefficients of spherical harmonics. So far, studies have mostly focused on individual coordinate components at a time. Typically, the vertical coordinate component is of most interest, since it most often contains the largest signals. In this work, we apply the concept of vector spherical harmonics (VSH) to study temporal variations in station displacements of DTRF2014 and JTRF2014. The advantage of VSH compared to scalar spherical harmonics is that all three coordinate components can be considered at the same time. We estimate VSH coefficients up to degree-2, which includes dipole and quadrupole deformations. Degree-1 deformations represent translations and rotations of the frame, while degree-2 terms contain, inter alia, information on the oblateness of the Earth. We use VSH to analyze station displacements of DTRF2014 and JTRF2014 individually and to conduct comparisons between the two frames. Furthermore, since the temporal variations in both DTRF2014 and JTRF2014 are linked to non-tidal loading deformations, our analysis of temporal variations in VSH coefficients allows for geophysical interpretation

Realization of time sequential estimation of terrestrial reference frame using square-root information filter and smoother

The JTRF2014 realization of terrestrial reference frame has adopted a weekly time series representation that can track dominant non-linear station motions including periodic and random variations. The realization is based on the Kalman filter and smoother algorithms whose time sequential nature would also be suitable for continuous updating of an existing frame as soon as new geodetic data become available. As a part of preparation for the next reference frame realization, we have been examining alternative filter and smoother algorithms based on the square-root information filter (SRIF), known generally for improved numerical accuracy of the covariance matrix represented by a square-root matrix. The new algorithms offer a number of other advantages over the conventional filter/smoother algorithms used in JTRF2014. Namely, the new approach allows us to (1) avoid using some fictitious covariance matrix to initialize the filter, (2) avoid the random-walk constraints for the Helmert parameter sequences, and (3) handle cross-temporal EOP data such as the week-long segments reported by the SLR and DORIS networks. We have also been enhancing the stochastic models of the station position motion to be used by the filter and smoother, including models for non-tidal deformation

Silencing of YY1 downregulates RIZ1 promoter in human osteosarcoma

RIZ1 isoform, but not RIZ2, is commonly silenced in many types of tumors. In osteosarcoma cells, RIZ1 protein is very abundant. The silencing of YY1 protein, a recent target gene in osteosarcoma cells, reduced the expression of RIZ1 protein. Here we show that RIZ1 overexpression is a transcriptional event documented by Western blot, RT-PCR, and promoter assays. YY1 protein binds and cooperates to positive regulation of the RIZ1 promoter and its presence reduced the dimethyl lysine 9 histone 3 by chromatin immunoprecipitation assays. These results indicate that overexpression of YY1 in osteosarcoma cells plays a key role in positive regulation of RIZ1. The coexpression of RIZ1/YY1 proteins suggests a tandem regulatory mechanism in human osteosarcoma cells and tissues

Molecular detection of epidermal growth factor receptor in colorectal cancer: does it still make sense? (Review)

AIM: The aim of the study was to detect and compare the epidermal growth factor receptor (EGFr) content using different methods, to establish whether the quantitative detection and functional study of EGFr in colorectal cancer, using methods other than immunohistochemistry (IHC), are appropriate. METHOD: Analysis of EGFr by IHC was performed in 230 colorectal cancer patients using monoclonal anti-EGFr. Total and activated EGFr (pY1068) contents were determined in 92 patients and real-time PCR, to determine the level of EGFr messenger RNA, was carried out in 60 patients. RESULTS: There was no association between EGFr IHC groups and the mean total EGFr levels measured using ELISA. CONCLUSION: The study shows that the results of different EGFr detection methods do not correlate with each other. Hence, the real role of EGFr in colorectal cancer remains unsettled. Clinically, the receptor itself does not seem to be important and it would be better to focus on EGFr signalling in downstream pathways