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Search Results: 1 - 10 of 189908 matches for " G. LAMPROPOULOS "
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Radio Access Selection in Integrated UMTS/WLAN Networks  [PDF]
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.29094
Abstract: Heterogeneous networks combine different access technologies. An important problem in such networks is the selection of the most suitable radio access network. To perform this task efficiently, a lot of information is required, such as signal strength, QoS, monetary cost, battery consumption, and user preferences. These are well known issues and a considerable effort has been made to tackle them using a number of solutions. These efforts improve the performance of vertical handover but also add considerable complexity. In this paper, we introduce an enhanced algorithm for radio access network selection, which is simple, flexible and applicable to future mobile systems. Its main characteristics are the distribution of the radio access selection process among the mobile terminal and the core network, the evaluation of mobile terminal connections separately and the primary role of user preferences in the final decision. The performance of the algorithm is evaluated through simulation results, which show that the algorithm provides a high rate of user satisfaction. It decreases the messages required for the vertical handovers in the whole network and it alleviates the core network from the processing of unnecessary requests.
On-chip SQUID measurements in the presence of high magnetic fields
L. Chen,W. Wernsdorfer,C. Lampropoulos,G. Christou,I. Chiorescu
Physics , 2010, DOI: 10.1088/0957-4484/21/40/405504
Abstract: We report a low temperature measurement technique and magnetization data of a quantum molecular spin, by implementing an on-chip SQUID technique. This technique enables the SQUID magnetometery in high magnetic fields, up to 7 Tesla. The main challenges and the calibration process are detailed. The measurement protocol is used to observe quantum tunneling jumps of the S=10 molecular magnet, Mn12-tBuAc. The effect of transverse field on the tunneling splitting for this molecular system is addressed as well.
Computational Modeling of an MRI Guided Drug Delivery System Based on Magnetic Nanoparticle Aggregations for the Navigation of Paramagnetic Nanocapsules
N. K. Lampropoulos,E. G. Karvelas,I. E. Sarris
Computer Science , 2015,
Abstract: A computational method for magnetically guided drug delivery is presented and the results are compared for the aggregation process of magnetic particles within a fluid environment. The model is developed for the simulation of the aggregation patterns of magnetic nanoparticles under the influence of MRI magnetic coils. A novel approach for the calculation of the drag coefficient of aggregates is presented. The comparison against experimental and numerical results from the literature is showed that the proposed method predicts well the aggregations in respect to their size and pattern dependance, on the concentration and the strength of the magnetic field, as well as their velocity when particles are driven through the fluid by magnetic gradients.
Automatic WSDL-guided Test Case Generation for PropEr Testing of Web Services
Leonidas Lampropoulos,Konstantinos Sagonas
Electronic Proceedings in Theoretical Computer Science , 2012, DOI: 10.4204/eptcs.98.3
Abstract: With web services already being key ingredients of modern web systems, automatic and easy-to-use but at the same time powerful and expressive testing frameworks for web services are increasingly important. Our work aims at fully automatic testing of web services: ideally the user only specifies properties that the web service is expected to satisfy, in the form of input-output relations, and the system handles all the rest. In this paper we present in detail the component which lies at the heart of this system: how the WSDL specification of a web service is used to automatically create test case generators that can be fed to PropEr, a property-based testing tool, to create structurally valid random test cases for its operations and check its responses. Although the process is fully automatic, our tool optionally allows the user to easily modify its output to either add semantic information to the generators or write properties that test for more involved functionality of the web services.
Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets
G. Redler,C. Lampropoulos,S. Datta,C. Koo,T. C. Stamatatos,N. E. Chakov,G. Christou,S. Hill
Physics , 2009, DOI: 10.1103/PhysRevB.80.094408
Abstract: High-frequency electron paramagnetic resonance (HFEPR) and AC susceptibility measurements are reported for a new high-symmetry Mn12 complex, [Mn12O12(O2CCH3)16(CH3OH)4].CH3OH. The results are compared with those of other high-symmetry spin S = 10 Mn12 single-molecule magnets (SMMs), including the original acetate, [Mn12(O2CCH3)16(H2O)4].2CH3CO2H.4H2O, and the [Mn12O12(O2CCH2Br)16(H2O)4].4CH2Cl2 & [Mn12O12(O2CCH2But)16(CH3OH)4].CH3OH complexes. These comparisons reveal important insights into the factors that influence the values of the effective barrier to magnetization reversal, Ueff, deduced on the basis of AC susceptibility measurements. In particular, we find that variations in Ueff can be correlated with the degree of disorder in a crystal which can be controlled by desolvating (drying) samples. This highlights the importance of careful sample handling when making measurements on SMM crystals containing volatile lattice solvents. The HFEPR data additionally provide important spectroscopic evidence suggesting that the relatively weak disorder induced by desolvation strongly influences the quantum tunneling interactions, and that it is under-barrier tunneling that is responsible for a consistent reduction in Ueff that is found upon drying samples. Meanwhile, the axial anisotropy deduced from HFEPR is found to be virtually identical for all four Mn12 complexes, with essentially no measurable reduction upon desolvation.
Realization of random-field dipolar Ising ferromagnetism in a molecular magnet
Bo Wen,P. Subedi,Lin Bo,Y. Yeshurun,M. P. Sarachik,A. D. Kent,C. Lampropoulos,G. Christou
Physics , 2009, DOI: 10.1103/PhysRevB.82.014406
Abstract: The longitudinal magnetic susceptibility of single crystals of the molecular magnet Mn$_{12}$-acetate obeys a Curie-Weiss law, indicating a transition to a ferromagnetic phase due to dipolar interactions. With increasing magnetic field applied transverse to the easy axis, the transition temperature decreases considerably more rapidly than predicted by mean field theory to a T=0 quantum critical point. Our results are consistent with an effective Hamiltonian for a random-field Ising ferromagnet in a transverse field, where the randomness is induced by an external field applied to Mn$_{12}$-acetate crystals that are known to have an intrinsic distribution of locally tilted magnetic easy axes.
Experimental determination of the Weiss temperature of Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH
Shiqi Li,Lin Bo,Bo Wen,M. P. Sarachik,P. Subedi,A. D. Kent,Y. Yeshurun,A. J. Millis,C. Lampropoulos,S. Mukherjee,G. Christou
Physics , 2010, DOI: 10.1103/PhysRevB.82.174405
Abstract: We report measurements of the susceptibility in the temperature range from $3.5$ K to $6.0$ K of a series of Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH samples in the shape of rectangular prisms of length $l_c$ and square cross-section of side $l_a$. The susceptibility obeys a Curie-Weiss Law, $\chi=C/(T-\theta)$, where $\theta$ varies systematically with sample aspect ratio. Using published demagnetization factors, we obtain $\theta$ for an infinitely long sample corresponding to intrinsic ordering temperatures $T_c \approx 0.85$ K and $\approx 0.74$ K for Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH, respectively. The difference in $T_c$ for two materials that have nearly identical unit cell volumes and lattice constant ratios suggests that, in addition to dipolar interactions, there is a non-dipolar (exchange) contribution to the Weiss temperature that differs in the two materials because of the difference in ligand molecules.
LEDDB: LOFAR Epoch of Reionization Diagnostic Database
O. Martinez-Rubi,V. K. Veligatla,A. G. de Bruyn,P. Lampropoulos,A. R. Offringa,V. Jelic,S. Yatawatta,L. V. E. Koopmans,S. Zaroubi
Physics , 2013,
Abstract: One of the key science projects of the Low-Frequency Array (LOFAR) is the detection of the cosmological signal coming from the Epoch of Reionization (EoR). Here we present the LOFAR EoR Diagnostic Database (LEDDB) that is used in the storage, management, processing and analysis of the LOFAR EoR observations. It stores referencing information of the observations and diagnostic parameters extracted from their calibration. This stored data is used to ease the pipeline processing, monitor the performance of the telescope and visualize the diagnostic parameters which facilitates the analysis of the several contamination effects on the signals. It is implemented with PostgreSQL and accessed through the psycopg2 python module. We have developed a very flexible query engine, which is used by a web user interface to access the database, and a very extensive set of tools for the visualization of the diagnostic parameters through all their multiple dimensions.
Geometric-phase interference in a Mn_{12} single-molecule magnet with four-fold rotational symmetry
S. T. Adams,E. H. da Silva Neto,S. Datta,J. F. Ware,C. Lampropoulos,G. Christou,Y. Myaesoedov,E. Zeldov,Jonathan R. Friedman
Physics , 2012, DOI: 10.1103/PhysRevLett.110.087205
Abstract: We study the magnetic relaxation rate Gamma of the single-molecule magnet Mn_{12}-tBuAc as a function of magnetic field component H_T transverse to the molecule's easy axis. When the spin is near a magnetic quantum tunneling resonance, we find that Gamma increases abruptly at certain values of H_T. These increases are observed just beyond values of H_T at which a geometric-phase interference effect suppresses tunneling between two excited energy levels. The effect is washed out by rotating H_T away from the spin's hard axis, thereby suppressing the interference effect. Detailed numerical calculations of Gamma using the known spin Hamiltonian accurately reproduce the observed behavior. These results are the first experimental evidence for geometric-phase interference in a single-molecule magnet with true four-fold symmetry.
Topical calcineurin inhibitors in systemic lupus erythematosus
Christos E Lampropoulos, David P D’Cruz
Therapeutics and Clinical Risk Management , 2010, DOI: http://dx.doi.org/10.2147/TCRM.S3193
Abstract: pical calcineurin inhibitors in systemic lupus erythematosus Review (3584) Total Article Views Authors: Christos E Lampropoulos, David P D’Cruz Published Date April 2010 Volume 2010:6 Pages 95 - 101 DOI: http://dx.doi.org/10.2147/TCRM.S3193 Christos E Lampropoulos, David P D’Cruz Lupus Research Unit, Rayne Institute, St. Thomas’ Hospital, London, UK Abstract: Cutaneous lupus erythematosus (CLE) encompasses a variety of lesions that may be refractory to systemic or topical agents. Discoid lupus erythematosus (DLE) and subacute cutaneous lupus erythematosus (SCLE) are the most common lesions in clinical practice. The topical calcineurin inhibitors, tacrolimus and pimecrolimus, have been used to treat resistant cutaneous lupus since 2002 and inhibit the proliferation and activation of T-cells and suppress immune-mediated cutaneous inflammation. This article reviews the mechanism of action, efficacy, adverse effects, and the recent concern about their possible carcinogenic effect. Although the total number of patients is small and there is only one relevant randomized controlled study, the data are encouraging. Many patients, previously resistant to systemic agents or topical steroids, improved after four weeks of treatment. DLE and SCLE lesions were less responsive, reflecting the chronicity of the lesions, although more than 50% of patients still showed improvement. Topical calcineurin inhibitors may be a safe and effective alternative to topical steroids for CLE although the only approved indication is for atopic dermatitis.
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