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Um paradigma orientado a análise de performance de redes de pacotes; A paradigm oriented to performance analysis of packet switched networks

Spohn, Marcelo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
65.93%
A crescente complexidade das redes de comunicação de dados tem como conseqüência direta tornar cada vez mais complexas as tarefas de projetar seu dimensionamento e evolução. Um passo preliminar vitalmente importante no projeto de uma rede é a coleta de dados relacionados ao uso esperado da rede. Os padrões de tráfego estimados são usados nos cálculos de dimensionamento dos recursos. Fortemente relacionada a estas atividades está a previsão da performance em termos de throughput da rede, tempos de resposta, probabilidade de congestionamento, entre outras. Uma análise de performance efetiva depende de se representar precisamente a configuração da rede e da carga de tráfego a ela submetida. Técnicas de modelagem analítica ou de simulação podem ser usadas para determinar a performance esperada do sistema. Neste trabalho a usada a técnica de simulação para modelar o tráfego da rede usando dados coletados em uma rede real por monitoração. Trabalhando-se com o modelo validado e possível ajustar a carga de tráfego para representar mudanças esperadas nos volumes de tráfego, e testar o efeito na performance de diferentes configurações de rede. Isso possibilita que os processos de planejamento e projeto sejam executados com confiança...

A Neural Circuit Covarying with Social Hierarchy in Macaques

Noonan, MaryAnn P.; Sallet, Jerome; Mars, Rogier B.; Neubert, Franz X.; O'Reilly, Jill X.; Andersson, Jesper L.; Mitchell, Anna S.; Bell, Andrew H.; Miller, Karla L.; Rushworth, Matthew F. S.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 02/09/2014 Português
Relevância na Pesquisa
25.69%
Despite widespread interest in social dominance, little is known of its neural correlates in primates. We hypothesized that social status in primates might be related to individual variation in subcortical brain regions implicated in other aspects of social and emotional behavior in other mammals. To examine this possibility we used magnetic resonance imaging (MRI), which affords the taking of quantitative measurements noninvasively, both of brain structure and of brain function, across many regions simultaneously. We carried out a series of tests of structural and functional MRI (fMRI) data in 25 group-living macaques. First, a deformation-based morphometric (DBM) approach was used to show that gray matter in the amygdala, brainstem in the vicinity of the raphe nucleus, and reticular formation, hypothalamus, and septum/striatum of the left hemisphere was correlated with social status. Second, similar correlations were found in the same areas in the other hemisphere. Third, similar correlations were found in a second data set acquired several months later from a subset of the same animals. Fourth, the strength of coupling between fMRI-measured activity in the same areas was correlated with social status. The network of subcortical areas...

Pulmonary Proteome and Protein Networks in Response to the Herbicide Paraquat in Rats

Cho, Il Kyu; Jeong, Mihye; You, Are-Sun; Park, Kyung Hun; Li, Qing X.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/2015 Português
Relevância na Pesquisa
35.7%
Paraquat (PQ) has been one of the most widely used herbicides in the world. PQ, when ingested, is toxic to humans and may cause acute respiratory distress syndrome. To investigate molecular perturbation in lung tissues caused by PQ, Sprague Dawley male rats were fed with PQ at a dose of 25 mg/kg body weight for 20 times in four weeks. The effects of PQ on cellular processes and biological pathways were investigated by analyzing proteome in the lung tissues in comparison with the control. Among the detected proteins, 321 and 254 proteins were over-represented and under-represented, respectively, in the PQ-exposed rat lung tissues in comparison with the no PQ control. All over- and under-represented proteins were subjected to Ingenuity Pathway Analysis to create 25 biological networks and 38 pathways of interacting protein clusters. Over-represented proteins were involved in the C-jun-amino-terminal kinase pathway, caveolae-mediated endocytosis signaling, cardiovascular-cancer-respiratory pathway, regulation of clathrin-mediated endocytosis, non-small cell lung cancer signaling, pulmonary hypertension, glutamate receptor, immune response and angiogenesis. Under-represented proteins occurred in the p53 signaling pathway, mitogen-activated protein kinase signaling pathway...

Quantum Criticality in doped CePd_1-xRh_x Ferromagnet

Sereni, J. G.; Westerkamp, T.; Kuechler, R.; Caroca-Canales, N.; Gegenwart, P.; Geibel, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/02/2006 Português
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35.71%
CePd_1-xRh_x alloys exhibit a continuous evolution from ferromagnetism (T_C= 6.5 K) at x = 0 to a mixed valence (MV) state at x = 1. We have performed a detailed investigation on the suppression of the ferromagnetic (F) phase in this alloy using dc-(\chi_dc) and ac-susceptibility (\chi_ac), specific heat (C_m), resistivity (\rho) and thermal expansion (\beta) techniques. Our results show a continuous decrease of T_C (x) with negative curvature down to T_C = 3K at x*= 0.65, where a positive curvature takes over. Beyond x*, a cusp in cac is traced down to T_C* = 25 mK at x = 0.87, locating the critical concentration between x = 0.87 and 0.90. The quantum criticality of this region is recognized by the -log(T/T_0) dependence of C_m/T, which transforms into a T^-q (~0.5) one at x = 0.87. At high temperature, this system shows the onset of valence instability revealed by a deviation from Vegard's law (at x_V~0.75) and increasing hybridization effects on high temperature \chi_dc and \rho. Coincidentally, a Fermi liquid contribution to the specific heat arises from the MV component, which becomes dominant at the CeRh limit. In contrast to antiferromagnetic systems, no C_m/T flattening is observed for x > x_cr rather the mentioned power law divergence...

Size Dependence of Current-Voltage Properties in Coulomb Blockade Networks

Narumi, Takayuki; Suzuki, Masaru; Hidaka, Yoshiki; Kai, Shoichi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/09/2011 Português
Relevância na Pesquisa
35.69%
We theoretically investigate the current-voltage (I-V) property of two-dimensional Coulomb blockade (CB) arrays by conducting Monte Carlo simulations. The I-V property can be divided into three regions and we report the dependence of the aspect ratio delta (namely, the lateral size N_{y} over the longitudinal one N_{x}). We show that the average CB threshold obeys a power-law decay as a function of delta. Its exponent gamma corresponds to a sensitivity of the threshold depending on delta, and is inversely proportional to N_{x} (i.e., delta at fixed N_{y}). Further, the power-law exponent zeta, characterizing the nonlinearity of the I-V property in the intermediate region, logarithmically increases as delta increases. Our simulations describe the experimental result zeta=2.25 obtained by Parthasarathy et al. [Phys. Rev. Lett. 87 (2001) 186807]. In addition, the asymptotic I-V property of one-dimensional arrays obtained by Bascones et al. [Phys. Rev. B. 77 (2008) 245422] is applied to two-dimensional arrays. The asymptotic equation converges to the Ohm's law at the large voltage limit, and the combined tunneling-resistance is inversely proportional to delta. The extended asymptotic equation with the first-order perturbation well describes the experimental result obtained by Kurdak et al. [Phys. Rev. B 57 (1998) R6842]. Based on our asymptotic equation...

The structure of PX3 (X=Cl, Br, I) molecular liquids from X-ray diffraction, Molecular Dynamics simulations and Reverse Monte Carlo modeling

Pothoczki, Szilvia; Temleitner, László; Pusztai, László
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/02/2014 Português
Relevância na Pesquisa
35.64%
Synchrotron X-ray diffraction measurements have been conducted on liquid phosphorus trichloride, tribromide and triiodide. Molecular Dynamics simulations for these molecular liquids were performed with a dual purpose: (1) to establish whether existing intermolecular potential functions can provide a picture that is consistent with diffraction data; (2) to generate reliable starting configurations for subsequent Reverse Monte Carlo modelling. Structural models (i.e., sets of coordinates of thousands of atoms) that were fully consistent with experimental diffraction information, within errors, have been prepared by means of the Reverse Monte Carlo method. Comparison with reference systems, generated by hard sphere-like Monte Carlo simulations, was also carried out to demonstrate the extent to which simple space filling effects determine the structure of the liquids (and thus, also estimating the information content of measured data). Total scattering structure factors, partial radial distribution functions and orientational correlations as a function of distances between the molecular centres have been calculated from the models. In general, more or less antiparallel arrangements of the primary molecular axes that are found to be the most favourable orientation of two neighbouring molecules. In liquid PBr3 electrostatic interactions seem to play a more important role in determining intermolecular correlations than in the other two liquids; molecular arrangements in both PCl3 and PI3 are largely driven by steric effects.; Comment: 25 pages...

Effects of $^3$He Impurity on Solid $^4$He Studied by Compound Torsional Oscillator

Gumann, P.; Keiderling, M. C.; Ruffner, D.; Kojima, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/02/2011 Português
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25.73%
Frequency shifts and dissipations of a compound torsional oscillator induced by solid $^4$He samples containing $^3$He impurity concentrations ($x_3$ = 0.3, 3, 6, 12 and 25 in units of 10$^{-6}$) have been measured at two resonant mode frequencies ($f_1$ = 493 and $f_2$ = 1164 Hz) at temperatures ($T$) between 0.02 and 1.1 K. The fractional frequency shifts of the $f_1$ mode were much smaller than those of the $f_2$ mode. The observed frequency shifts continued to decrease as $T$ was increased above 0.3 K, and the conventional non-classical rotation inertia fraction was not well defined in all samples with $x_3 \geq$ 3 ppm. Temperatures where peaks in dissipation of the $f_2$ mode occurred were higher than those of the $f_1$ mode in all samples. The peak dissipation magnitudes of the $f_1$ mode was greater than those of the $f_2$ mode in all samples. The activation energy and the characteristic time ($\tau_0$) were extracted for each sample from an Arrhenius plot between mode frequencies and inverse peak temperatures. The average activation energy among all samples was 430 mK, and $\tau_0$ ranged from 2$\times 10^{-7}$ s to 5$\times 10^{-5}$ s in samples with $x_3$ = 0.3 to 25 ppm. The characteristic time increased in proportion to $x_3^{2/3}$. Observed temperature dependence of dissipation were consistent with those expected from a simple Debye relaxation model \emph{if} the dissipation peak magnitude was separately adjusted for each mode. Observed frequency shifts were greater than those expected from the model. The discrepancies between the observed and the model frequency shifts increased at the higher frequency mode.; Comment: 10 pages...

Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy x-ray diffraction

Petkov, V.; Billinge, S. J. L.; Shastri, S. D.; Himmel, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/07/2000 Português
Relevância na Pesquisa
35.71%
Structure factors for Cax/2AlxSi1-xO2 glasses (x=0,0.25,0.5,0.67) extended to a wave vector of magnitude Q= 40 1/A have been obtained by high-energy x-ray diffraction. For the first time, it is possible to resolve the contributions of Si-O, Al-O and Ca-O coordination polyhedra to the experimental atomic pair distribution functions (PDF). It has been found that both Si and Al are four-fold coordinated and so participate in a continuous tetrahedral network at low values of x. The number of network breaking defects in the form of non-bridging oxygens (NBO's) increases slowly with x until x=0.5 (NBO's ~ 10% at x=0.5). By x=0.67 the network breaking defects become significant as evidenced by the significant drop in the average coordination number of Si. By contrast, Al-O tetrahedra remain free of NBO's and fully integrated in the Al/Si-O network for all values of x. Calcium maintains a rather uniform coordination sphere of approximately 5 oxygen atoms for all values of x. The results suggest that not only Si/Al-O tetrahedra but Ca-O polyhedra, too, play a role in determining the glassy structure.

Collective Phenomena in the LiHo_xY_{1-x}F4 Quantum Ising Magnet: Recent Progress and Open Questions

Gingras, Michel J. P.; Henelius, Patrik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/03/2011 Português
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35.83%
In LiHo_xY_{1-x}F4, the magnetic Holmium Ho^{3+} ions behave as effective Ising spins that can point parallel or antiparallel to the crystalline c-axis. The predominant inter-Holmium interaction is dipolar, while the Y^{3+} ions are non-magnetic. The application of a magnetic field Bx transverse to the c-axis Ising direction leads to quantum spin-flip fluctuations, making this material a rare physical realization of the celebrated transverse field Ising model. The problems of classical and transverse-field-induced quantum phase transitions in LiHo_xY_{1-x}F_4 in the dipolar ferromagnetic (x=1), diluted ferromagnetic (0.25 <~ x < 1) and highly diluted x<~0.25 dipolar spin glass regimes have attracted much experimental and theoretical interest over the past twenty-five years. Two questions have received particular attention: (i) is there an {\it antiglass} (quantum disordered) phase at low Ho^{3+} concentration and (ii) what is the mechanism responsible for the fast Bx-induced destruction of the ferromagnetic (0.25 <~ x < 1) and spin glass (x <~ 0.25) phases? This paper reviews some of the recent theoretical and experimental progress in our understanding of the collective phenomena at play in LiHo_xY_{1-x}F4, in both zero and nonzero Bx.; Comment: 15 pages...

Density Fluctuations in Molten Lithium: Inelastic X-Ray Scattering Study

Scopigno, T.; Balucani, U.; Ruocco, G.; Sette, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.68%
New inelastic X-ray scattering experiments have been performed in liquid lithium at two different temperatures: T=475 K (slightly above the melting point) and 600 K. Taking advantage of the absence of any kinematical restriction and incoherent contribution, and pushing the instrumental resolution up to 1.5 meV, it was possible to perform an accurate investigation of the dynamic structure factor S(Q,E) in the wavevector range from 1 to 110 nm^-1. For Q smaller than Q_m=25 nm^-1, the position of the main peak of the static structure factor, a detailed analysis of the lineshapes shows that any picture of the relaxation mechanisms based on a simple viscoelastic model must be abandoned. All the spectral features can instead satisfactorily be accounted for by including both fast and slow relaxation processes. The physical origin of the slow relaxation is associated to the structural rearrangement, while the local nature of the fast one is extensively discussed. At larger Q values a gradual crossover from the strongly correlated to single particle dynamics occurs, with an important weight provided by quantum effects.; Comment: 25 pages, 12 PS figures

Long term aging of Selenide glasses: Evidence of sub-Tg endotherms and pre-Tg exotherms

Chen, Ping; Boolchand, P.; Georgiev, D. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
25.76%
Long term aging is studied on several families of chalcogenide glasses including the Ge-Se, As-Se, Ge-P-Se and Ge-As-Se systems. Special attention is given to the As-Se binary, a system that displays a rich variety of aging behavior intimately tied to sample synthesis conditions and the ambient environment in which samples are aged. Calorimetric (Modulated DSC) and Raman scattering experiments are undertaken. Our results show all samples display a sub-Tg endotherm below Tg in glassy networks possessing a mean coordination number r in the 2.25 < r < 2.45 range. Two sets of AsxSe1-x samples aged for 8 years were compared, set A consisted of slow cooled samples aged in the dark, and set B consisted of melt quenched samples aged at laboratory environment. Samples of set B in the As concentration range, 35% < x < 60%, display a pre-Tg exotherm, but the feature is not observed in samples of set A. The aging behavior of set A presumably represents intrinsic aging in these glasses, while that of set B is extrinsic due to presence of light. The reversibility window persists in both sets of samples but is less well defined in set B. These findings contrast with a recent study by Golovchak et al., which finds the onset of the reversibility window moved up to the stoichiometric composition (x = 40%). Here we show that the upshifted window is better understood as resulting due to demixing of As4Se4 and As4Se3 molecules from the backbone...

Interaction correction to the conductivity of two-dimensional electron gas in In$_x$Ga$_{1-x}$As/InP quantum well structure with strong spin-orbit coupling

Minkov, G. M.; Germanenko, A. V.; Rut, O. E.; Sherstobitov, A. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/11/2011 Português
Relevância na Pesquisa
35.61%
The electron-electron interaction quantum correction to the conductivity of the gated single quantum well InP/In$_{0.53}$Ga$_{0.47}$As heterostructures is investigated experimentally. The analysis of the temperature and magnetic field dependences of the conductivity tensor allows us to obtain reliably the diffusion part of the interaction correction for different values of spin relaxation rate, $1/\tau_s$. The surprising result is that the spin relaxation processes do not suppress the interaction correction in the triplet channel and, thus, do not enhance the correction in magnitude contrary to theoretical expectations even in the case of relatively fast spin relaxation, $1/T\tau_s\simeq (20-25)\gg 1$.; Comment: 7 pages, 6 figures

Pressure Raman Effects and Internal Stress in Network Glasses

Wang, Fei; Mamedov, Sergey; Boolchand, P.; Goodman, B.; Chandrasekhar, Meera
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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25.81%
Raman scattering from binary GexSe1-x glasses under hydrostatic pressure shows onset of a steady increase in the frequency of modes of corner-sharing GeSe4 tetrahedral units when the external pressure P exceeds a threshold value Pc. The threshold pressure Pc(x) decreases with x in the 0.15 < x < 0.20 range, nearly vanishes in the 0.20 < x < 0.25 range, and then increases in the 0.25 < x < 1/3 range. These Pc(x) trends closely track those in the non-reversing enthalpy, DeltaHnr(x), near glass transitions (Tgs), and in particular, both DeltaHnr(x) and Pc(x) vanish in the reversibility window (0.20 < x < 0.25). It is suggested that Pc provides a measure of stress at the Raman active units; and its vanishing in the reversibility window suggests that these units are part of an isostatically rigid backbone. Isostaticity also accounts for the non-aging behavior of glasses observed in the reversibility window.; Comment: 1 PDF file contains text and 3 figures

Neutron scattering experiments and simulations near the magnetic percolation threshold of Fe_x Zn_{1-x} F_2

Alvarez, G.; Aso, N.; Belanger, D. P.; Durand, A. M.; Martin-Mayor, V.; Motoya, K.; Muro, Y.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/07/2012 Português
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35.76%
The low temperature excitations in the anisotropic antiferromagnetic Fe_{1-x} Zn_x F_2 for x=0.25 and 0.31, at and just above the magnetic percolation threshold concentration x_p=0.25, were measured using inelastic neutron scattering. The excitations were simulated for x=0.31 using a localized, classical excitation model, which accounts well for the energies and relative intensities of the excitations observed in the scattering experiments.; Comment: 6 pages, 6 figures

Quasi-Long-Range Order in Random-Anisotropy Heisenberg Models

Fisch, Ronald
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/01/1998 Português
Relevância na Pesquisa
25.69%
Monte Carlo simulations have been used to study a discretized Heisenberg ferromagnet (FM) with random uniaxial single-site anisotropy on $L \times L \times L$ simple cubic lattices, for $L$ up to 64. The spin variable on each site is chosen from the twelve [110] directions. The random anisotropy has infinite strength and a random direction on a fraction $x$ of the sites of the lattice, and is zero on the remaining sites. In many respects the behavior of this model is qualitatively similar to that of the corresponding random-field model. Due to the discretization, for small $x$ at low temperature there is a [110] FM phase. For $x>0$ there is an intermediate quasi-long-range ordered (QLRO) phase between the paramagnet and the ferromagnet, which is characterized by a $|k|^{-3}$ divergence of the magnetic structure factor S$(k)$ for small $k$, but no true FM order. At the transition between the paramagnetic and QLRO phases S$(k)$ diverges like $|k|^{-2}$. The limit of stability of the QLRO phase is somewhat greater than $x=0.5$. For $x$ close to 1 the low temperature form of S$(k)$ can be fit by a Lorentzian, with a correlation length estimated to be $11 \pm 1$ at $x=1.0$ and $25 \pm 5$ at $x=0.75$.; Comment: 7 pages, 10 figures, gzipped

The metal-insulator transition in amorphous Si_{1-x}Ni_x: Evidence for Mott's minimum metallic conductivity

Mobius, A.; Frenzel, C.; Thielsch, R.; Rosenbaum, R.; Adkins, C. J.; Schreiber, M.; Bauer, H. -D.; Grotzschel, R.; Hoffmann, V.; Krieg, T.; Matz, N.; Vinzelberg, H.; Witcomb, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.69%
We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w = d ln sigma / d ln T, we observe that, for insulating samples, w(T) shows a minimum increasing at both low and high T. Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of w(T,x) leads to the conclusion that the transition in Si_{1-x}Ni_x is very likely discontinuous at zero temperature in agreement with Mott's original views.; Comment: RevTex-file: 25 pages, 17 Postscript figures, 1 GIF figure (original Ps file can be obtained on request). Published version. Changes of v2: Sec. VII completed by two paragraphs on nature of transition, several refs. added

Statistics of low energy excitations for the directed polymer in a $1+d$ random medium ($d=1,2,3$)

Monthus, Cecile; Garel, Thomas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/02/2006 Português
Relevância na Pesquisa
25.72%
We consider a directed polymer of length $L$ in a random medium of space dimension $d=1,2,3$. The statistics of low energy excitations as a function of their size $l$ is numerically evaluated. These excitations can be divided into bulk and boundary excitations, with respective densities $\rho^{bulk}_L(E=0,l)$ and $\rho^{boundary}_L(E=0,l)$. We find that both densities follow the scaling behavior $\rho^{bulk,boundary}_L(E=0,l) = L^{-1-\theta_d} R^{bulk,boundary}(x=l/L)$, where $\theta_d$ is the exponent governing the energy fluctuations at zero temperature (with the well-known exact value $\theta_1=1/3$ in one dimension). In the limit $x=l/L \to 0$, both scaling functions $R^{bulk}(x)$ and $R^{boundary}(x)$ behave as $R^{bulk,boundary}(x) \sim x^{-1-\theta_d}$, leading to the droplet power law $\rho^{bulk,boundary}_L(E=0,l)\sim l^{-1-\theta_d} $ in the regime $1 \ll l \ll L$. Beyond their common singularity near $x \to 0$, the two scaling functions $R^{bulk,boundary}(x)$ are very different : whereas $R^{bulk}(x)$ decays monotonically for $0

Single photon Mach-Zehnder interferometer for quantum networks based on the Single Photon Faraday Effect: principle and applications

Seigneur, H. P.; Leuenberger, Michael N.; Schoenfeld, W. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/10/2007 Português
Relevância na Pesquisa
25.7%
Combining the recent progress in semiconductor nanostructures along with the versatility of photonic crystals in confining and manipulating light, quantum networks allow for the prospect of an integrated and low power quantum technology. Within quantum networks, which consist of a system of waveguides and nanocavities with embedded quantum dots, it has been demonstrated in theory that many-qubit states stored in electron spins could be teleported from one quantum dot to another via a single photon using the Single Photon Faraday Effect. However, in addition to being able to transfer quantum information from one location to another, quantum networks need added functionality such as (1) controlling the flow of the quantum information and (2) performing specific operations on qubits that can be easily integrated. In this paper, we show how in principle a single photon Mach-Zehnder interferometer, which uses the concept of the single photon Faraday Effect to manipulate the geometrical phase of a single photon, can be operated both as a switch to control the flow of quantum information inside the quantum network and as various single qubit quantum gates to perform operations on a single photon. Our proposed Mach-Zehnder interferometer can be fully integrated as part of a quantum network on a chip. Given that the X gate...

Is Europe Evolving Toward an Integrated Research Area?

Chessa, Alessandro; Morescalchi, Andrea; Pammolli, Fabio; Penner, Orion; Petersen, Alexander M.; Riccaboni, Massimo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/02/2013 Português
Relevância na Pesquisa
25.69%
An integrated European Research Area (ERA) is a critical component for a more competitive and open European R&D system. However, the impact of EU-specific integration policies aimed at overcoming innovation barriers associated with national borders is not well understood. Here we analyze 2.4 x 10^6 patent applications filed with the European Patent Office (EPO) over the 25-year period 1986-2010 along with a sample of 2.6 x 10^5 records from the ISI Web of Science to quantitatively measure the role of borders in international R&D collaboration and mobility. From these data we construct five different networks for each year analyzed: (i) the patent co-inventor network, (ii) the publication co-author network, (iii) the co-applicant patent network, (iv) the patent citation network, and (v) the patent mobility network. We use methods from network science and econometrics to perform a comparative analysis across time and between EU and non-EU countries to determine the "treatment effect" resulting from EU integration policies. Using non-EU countries as a control set, we provide quantitative evidence that, despite decades of efforts to build a European Research Area, there has been little integration above global trends in patenting and publication. This analysis provides concrete evidence that Europe remains a collection of national innovation systems.; Comment: 24 pages...

An Investigation and Implementation of Recommendation X.25 on a Motorola M6800 Based Network

Nyerges, Louis
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
55.75%
A subset of the Recommendation X.25 protocol is implemented on a two node network. Each node accepts and translates data from the user in a sequential fashion into the appropriate protocol structure for transmission to another node. Each node has the capability of full duplex operation. The hardware is built around a Motorola M6800 microprocessor employing a minimum of 4096 words of random access memory and two asynchronous ports: one for communication with the user and the other for communication with the network. The software on each node contains the protocol programs and a multitasking monitor which is used to buffer the data bytes between the protocol software and the two communication ports. The multitasking monitor is also used to time slice among the seven tasks which implement the protocol structure. This paper illustrates in some detail the structure of Recommendation X.25. The subset of the packet types which are implemented is also examined. Finally, a scenario of the procedure for information exchange between one user and another is discussed in detail.