Improvement of the accuracy of the quasigeoid model VIGAC2017

As mentioned in (Ha Minh Hoa, 2017), a national spatial reference system will be constructed based on a highly accurate national quasigeoid model with accuracy more than 4 cm. In Vietnam at the present stage there isn’t a detailed gravimetric measurement in mountainous regions and marine area. So with the purpose of improvement of accuracy of the national quasigeoid model VIGAC2017, we only can solve the task of fitting this model to national quasigeoid heights obtained from heights GPS/first, second orders levelling quasigeoid heights through least squares collocation.This scientific article will introduce a first research result for improvement of accuracy of the quasigeoid model VIGAC2017 on the base of it’s fitting to 194 national quasigeoid heights by the least squares collocation. Research results show that accuracy of the quasigeoid model VIGAC2017 will be obtained at level of ±0.058 m and increased to 20.69 %.ReferencesCressie N.A.C., 1993. Statistics for spatial data, John  Wiley Sons. New York, 900p.Ha Minh Hoa, et al.,  2012. Research scientific base for perfection of the height system in connection with construction of national dynamic reference system. General report of the science - technological teme of the Ministry of Natural Resources and Environment, Hanoi, 247p.Ha Minh Hoa (Editor), 2016. Research for determination of normal surfaces of sea levels (“zero” depth surface, mean sea surface, highest sea surface) by methods of geodesy, hydrography and geology with serving construction of buildings and planning of coastline in tendency of climate changes”. State techno - scientific theme with code KC.09.19/11-15 in period of 2011-2015, Vietnam Ministry of Science and Technology, Hanoi, 563p.       Huang J., Véronneau M., 2013. Contribution of the GRACE and GOCE models to a  geopotential - based geodetich vertical datum in Canada. Geophysical Research Abstracts, 15, EGU2013-10164.Iliffe J.C., Ziebart M., Cross P.A., Forsberg R., Strykowski G., Tscherning C.C., 2003. OSGM02: A New model for converting GPS-derived heights to local height datums in Great Britain and Ireland. Survey Review, 37(290), 276-293.Marcin Ligas, Marek Kulczycki, 2014. Kriging approch for local height transformations. J, Geodesy And Cartography, Polish Academy of Sciences, 63(1), 5-37, Doi: 10,2478/geocart-2014-0002.Metin Soycan, 2014. Improving EGM2008 by GPS and leveling data at local scale. BCG - Boletin de Ciências Geodésicas Sec, Artigos, Curitiba, 20(1), 3-18, on - lineversion, ISSN 1982-2170. Doi,org/10,1590/S1982-21702014000100001.Moritz H., 1980. Advanced Physical Geodesy. Herbert wichmann Verlag Karlsruhe, Abacus Press Tunbridge Wells Ken, 512p. Quasigeoid of the Federal Republic of Germany GCG2016. Federal Agency for Cartography and Geodesy, www,geodatenzentrum.de.Roman D.R., Wang Y.M., Saleh J., Li X., 2010. Geodesy, Geoids Vertical Datums: A Perspective from the U,S, National Geodetic Survey. FIG Congress 2010, Sydney, Australia, April 2010, 11-16.Schabenger O., Gotway C.A., 2005. Statistical methods for spatial data analysis. Chapman Hall/CRC, New York, ISBN 1-58488-322-7, 488p. Smirnov N.V., Belugin D.A., 1969. Probability theory and mathematical statistics in applying to geodesy. Moscow, Nedra, 379p.

Development of Recurrent Method with Rotation for Combined Adjustment of Terrestrial Geodetic and GNSS Networks in National Spatial Reference System

A construction of national spatial reference systems (NSRS) is promoted in many countries due to modern achievements of Global Navigation Satellite System (GNSS) methods and results of building of high accurate geoid/quasi-geoid models at centimeter level of accuracy. One of the most popular methods used for the construction of the NSRS is related to Helmert block adjustment method, by which we ought to solve techno-scientific task of a separate adjustment of GNSS network in International Terrestrial Reference Frame (ITRF) and next combination of a results of adjustment of the terrestrial geodetic and GNSS networks in the NSRS. In this chapter, we carry out a research on the usage of a recurrent adjustment method with Givens rotation for solving the abovementioned task on an account of its advantages of being effective for application of a technique of sparse matrix, outlier detection and very simple for solving the subsystem of observation equations, created based on the transformation of the results of the separate adjustment of the GNSS network from the ITRF into the NSRS. The experiment results of solving the abovementioned task for the GPS network in the North Vietnam had shown that the horizontal and vertical position accuracy of the GPS points in VN2000–3D had reached the few centimeter level

Estimating the geopotential value W0 of the local geoid based on data from local and global normal heights of GPS/leveling points in Vietnam

Currently, the determination of geopotential value W0 of local geoid that best fits local mean sea level at the Zero Tide Gauge Station is getting important in building the National Geoid-Based Vertical System. Ha Minh Hoa (2007) and Kotsakis et al. (2012) recommended a method, which estimates the geopotential value W0 of local geoid at the Zero Tide Gauge Station based on equations of relation between the local and global normal heights or between the local and global height anomalies at GPS/leveling points regularly located on the whole territory. The objective of this paper is to determine conditions for estimating the geopotential value W0 of local geoid at the Zero Tide Gauge Station accomplished for whole territory of Vietnam

All-optical flip flop based on a symmetric Mach-Zehnder switch with a feed-back loop and multiple forward set/reset signals

The paper proposed an improved performance for optical flip-flop using symmetric Mach-Zehnder interformeter with a feedback and multiple forward configurations. At the optimum operating condition for the optical flip-flop, high contrast ratio of 22 dB can be achieved. The findings in the paper will have an impact on the design of future optical flip-flop and other optical logic gates such as exclusive OR and NAND gates. A PhD research (Le-Minh) funded by the University Studentship, completed in 200

BER performance analysis of 100 and 200 Gbit/s all-optical OTDM node using symmetric Mach-Zehnder switches

New insight to the feasibility of all-optical ultra speed switching up to 200 Gb/s. The technique will reduce the dependency and bottleneck on the electronic-to-optical-to-electronic conversion. Current conversion speed is up to 40 Gb/s in laboratories. The novel clock extraction technique proposed shows the potential of an all-optical switch. The research results are directly relevant to the access technology where optical fibre and RF is competing to be the solution. The growing demands of bandwidth will exceed RF capability while the optical fibre will be the optimum solution. A PhD project (Le-Minh) funded by the University Studentship, completed in 2007

The linear span of projections in AH algebras and for inclusions of C*-algebras

A $C^*$-algebra is said to have the LP property if the linear span of projections is dense in a given algebra. In the first part of this paper, we show that an AH algebra $A = \underrightarrow{\lim}(A_i,\phi_i)$ has the LP property if and only if every real-valued continuous function on the spectrum of $A_i$ (as an element of $A_i$ via the non-unital embedding) belongs to the closure of the linear span of projections in $A$. As a consequence, a diagonal AH-algebra has the LP property if it has small eigenvalue variation. The second contribution of this paper is that for an inclusion of unital $C^*$-algebras $P \subset A$ with a finite Watatani Index, if a faithful conditional expectation $E\colon A \rightarrow P$ has the Rokhlin property in the sense of Osaka and Teruya, then $P$ has the LP property under the condition $A$ has the LP property. As an application, let $A$ be a simple unital $C^*$-algebra with the LP property, $G$ a finite group and $\alpha$ an action of $G$ onto $\mathrm{Aut}(A)$. If $\alpha$ has the Rokhlin property in the sense of Izumi, then the fixed point algebra $A^G$ and the crossed product algebra $A \rtimes_\alpha G$ have the LP property. We also point out that there is a symmetry on CAR algebra, which is constructed by Elliott, such that its fixed point algebra does not have the LP property.Comment: 24 page

All-optical router with PPM header processing in high speed photonic packet switching networks

Rapidly growing internet traffic volume is the major driving force behind the development of optically-transparent and ultra high-capacity photonic packet-switching networks. In such networks, the packet routing decision at each router is made by sequentially correlating an incoming packet header address with addresses in all entries of the router's look-up routing table. The routing task is achieved in the optical domain using all-optical logic gates and optical correlator technologies which have been predominantly replacing the existing low-speed electronic processing devices. Nevertheless when a network is expanded, a larger routing table is required thus exponentially increasing header processing time, which results in the increases in routing latency and complexity. This research aims to significantly reduce the size of the routing table and the number of optical devices required in a router by mapping both the packet header address and the look-up routing table entries into the pulse-position-modulation format, where more than one address could be located in a single entry of a new pulse-position routing table. By simply carrying out a single correlation of the packet header address with pulse- position routing table entries, the router can instantly obtain the routing decision, thus significantly reducing the processing time and neglecting the gain recovery time in existing optical logic gates. The structure of the pulse-position routing table also offers flexibility in the transmission mode including unicast, multicast or broadcast embedded in the optical (physical) layer. In the thesis, a new router based on the pulse-position¬modulation scheme will be introduced. Essential router modules including high on-off contrast-ratio clock extraction, pulse position routing table, header processing and optical switch are proposed and analysed. In addition, the thesis investigates and improves the switching window profile and residual crosstalk performance of the all- optical Mach-Zelmder switches as a building block for the implementation of the above router modules. A number of new variants of Mach-Zehnder-based switches are also introduced to enhance switching inter-output contrast ratio and reduce the complexity in multiple-channel OTDM demultiplexing