Nuclear quantum shape-phase transitions in odd-mass systems

Microscopic signatures of nuclear ground-state shape phase transitions in odd-mass Eu isotopes are explored starting from excitation spectra and collective wave functions obtained by diagonalization of a core-quasiparticle coupling Hamiltonian based on energy density functionals. As functions of the physical control parameter -- the number of nucleons -- theoretical low-energy spectra, two-neutron separation energies, charge isotope shifts, spectroscopic quadrupole moments, and $E2$ reduced transition matrix elements accurately reproduce available data, and exhibit more pronounced discontinuities at neutron number $N=90$, compared to the adjacent even-even Sm and Gd isotopes. The enhancement of the first-order quantum phase transition in odd-mass systems can be attributed to a shape polarization effect of the unpaired proton which, at the critical neutron number, starts predominantly coupling to Gd core nuclei that are characterized by larger quadrupole deformation and weaker proton pairing correlations compared to the corresponding Sm isotopes.Comment: 6 pages, 4 figure

Global analysis of quadrupole shape invariants based on covariant energy density functionals

Coexistence of different geometric shapes at low energies presents a universal structure phenomenon that occurs over the entire chart of nuclides. Studies of the shape coexistence are important for understanding the microscopic origin of collectivity and modifications of shell structure in exotic nuclei far from stability. The aim of this work is to provide a systematic analysis of characteristic signatures of coexisting nuclear shapes in different mass regions, using a global self-consistent theoretical method based on universal energy density functionals and the quadrupole collective model. The low-energy excitation spectrum and quadrupole shape invariants of the two lowest $0^{+}$ states of even-even nuclei are obtained as solutions of a five-dimensional collective Hamiltonian (5DCH) model, with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional PC-PK1, and a finite-range pairing interaction. The theoretical excitation energies of the states: $2^+_1$, $4^+_1$, $0^+_2$, $2^+_2$, $2^+_3$, as well as the $B(E2; 0^+_1\to 2^+_1)$ values, are in very good agreement with the corresponding experimental values for 621 even-even nuclei. Quadrupole shape invariants have been implemented to investigate shape coexistence, and the distribution of possible shape-coexisting nuclei is consistent with results obtained in recent theoretical studies and available data. The present analysis has shown that, when based on a universal and consistent microscopic framework of nuclear density functionals, shape invariants provide distinct indicators and reliable predictions for the occurrence of low-energy coexisting shapes. This method is particularly useful for studies of shape coexistence in regions far from stability where few data are available.Comment: 13 pages, 3 figures, accepted for publication in Phys. Rev.

Time To Live: Temporal Management of Large-Scale RFID Applications

In coming years, there will be billions of RFID tags living in the world tagging almost everything for tracking and identification purposes. This phenomenon will impose a new challenge not only to the network capacity but also to the scalability of event processing of RFID applications. Since most RFID applications are time sensitive, we propose a notion of Time To Live (TTL), representing the period of time that an RFID event can legally live in an RFID data management system, to manage various temporal event patterns. TTL is critical in the "Internet of Things" for handling a tremendous amount of partial event-tracking results. Also, TTL can be used to provide prompt responses to time-critical events so that the RFID data streams can be handled timely. We divide TTL into four categories according to the general event-handling patterns. Moreover, to extract event sequence from an unordered event stream correctly and handle TTL constrained event sequence effectively, we design a new data structure, namely Double Level Sequence Instance List (DLSIList), to record intermediate stages of event sequences. On the basis of this, an RFID data management system, namely Temporal Management System over RFID data streams (TMS-RFID), has been developed. This system can be constructed as a stand-alone middleware component to manage temporal event patterns. We demonstrate the effectiveness of TMS-RFID on extracting complex temporal event patterns through a detailed performance study using a range of high-speed data streams and various queries. The results show that TMS-RFID has a very high throughout, namely 170,000 - 870,000 events per second for different highly complex continuous queries. Moreover, the experiments also show that the main structure to record the intermediate stages in TMS-RFID does not increase exponentially with the number of events. These illustrate that TMS-RFID not only has a high processing speed, but also has a good scalability

Reconciling Protocol Mismatches of Web Services by Using Mediators

In the era of Global Services, Service Oriented Architecture (SOA) has been gaining momentum for building Web-based information systems. Service composition is one of the key objectives for adopting SOA. Unfortunately, Web services are not always exactly compatible and it is a non-trivial task to address the mismatches between them. To this end, an approach based on mediator patterns is proposed to develop mediators for reconciling protocol mismatches of partially compatible services and mediating them together. A heuristic technique is developed for identifying protocol mismatches and selecting appropriate patterns. The main steps of the reconciliation approach are presented.The work is partially supported by the MIT Sloan China Management Education Project

Compatibility checking of heterogeneous Web service policies using VDM++

Web service policies capture the capabilities and requirements of Web services from both functional and nonfunctional perspectives. Policies of a Web service govern and ensure the runtime consistency of the service, i.e., people or services interacting with this service are only allowed to perform legitimate actions. When composing Web services, policies of the participated Web services have to be compatible in order to make sensible compositions. Unfortunately, due to heterogeneity of policy specification languages, it is difficult to compare policies of different Web services directly. In this paper, we propose an approach for compatibility checking of Web service policies specified in difference languages. In particular, our approach applies the model-oriented specification from the Vienna Development Method (VDM++). An executable formal model of policy languages is represented in VDM++ and different policies are then translated to this VDM++ model for compatibility checking. Our approach has been validated by a prototype with different Web service policy languages such as WSPL and WS-Policy. © 2009 IEEE