Two-orbital Systems with Crystal Field Splitting and Interorbital Hopping

The nondegenerate two-orbital Hubbard model is studied within the dynamic mean-field theory to reveal the influence of two important factors, i.e. crystal field splitting and interorbital hopping, on orbital selective Mott transition (OSMT) and realistic compound Ca$_{2-x}$Sr$_{x}$RuO$_{4}$. A distinctive feature of the optical conductivity of the two nondegenerate bands is found in OSMT phase, where the metallic character of the wide band is indicated by a nonzero Drude peak, while the insulating narrow band has its Drude peak drop to zero in the mean time. We also find that the OSMT regime expands profoundly with the increase of interorbital hopping integrals. On the contrary, it is shown that large and negative level splitting of the two orbitals diminishes the OSMT regime completely. Applying the present findings to compound Ca$_{2-x}$Sr$_{x}$RuO$_{4}$, we demonstrate that in the doping region from $x=0.2$ to 2.0, the negative level splitting is unfavorable to the OSMT phase.Comment: 7 pages with 5 figure

Development of electrochemical detection for capillary electrophoreses

The main purpose of this work was to develop reliable and sensitive electrochemical (EC) detection for capillary electrophoresis. To achieve this goal, electrochemical behavior of the electrolyte and analytes and the factors affecting the behavior were studied by on-line cyclic voltammetry (CV) to understand electrode response. The parameters investigated included adsorption of organic electrolytes, deposition of metal ions, and H\sp+ and O2 reactions. The results showed that the adsorption of organic compounds and deposition of some metals changed the electrode surface, which caused changes of electrochemical processing. The first EC approach studied was pulsed amperometric detection (PAD) with the potential frequency of 5 to 8 Hz at both Au and Pt 25 μm disk electrodes. To optimize PAD detection, pulse duration and applied potential were examined for both cathodic deposition and anodic stripping detection. Under the optimal conditions PAD can offer reliable detection for spiked and snow samples, with detection limits in the range of 2.010\sp{-7} to 2.010\sp{-5} mol/L, and the response factors were constant to within ±5% over the range of 50 μmol/L to 1000 μmol/L. To improve PAD detectability in CE, a number of experimental parameters were evaluated. These parameters included sample stacking, potential waveform shape and frequency, and signal analysis technique. Of these parameters, the use of a multiple-step pulse waveform gave a maximum S/N enhancement up to 10 fold, and the second harmonic response by means of Fourier transformation corrected baseline shifts. The next EC technique investigated was a fast-scan CV detection over sweep rates of 20 to 1,000 V/s at Au and Pt disk electrodes (25 and 10 μm). The results showed that maximum response was obtained at sweep rates of 100 to 200 V/s; however sweep rates of $>$400 V/s caused peak tailing. With this approach, co-migrating analytes could be identified and quantified. Response factors for metal ions over the range 1.010\sp{-7} to 1.010\sp{-5} mol/L were 15%, and detection limits were in the range of 510\sp{-9} mol/L to 410\sp{-8} mol/L, which are one to two order of magnitude better than results obtained previously with pulsed amperometric detection

Embedding Web-based Statistical Translation Models in Cross-Language Information Retrieval

Although more and more language pairs are covered by machine translation services, there are still many pairs that lack translation resources. Cross-language information retrieval (CLIR) is an application which needs translation functionality of a relatively low level of sophistication since current models for information retrieval (IR) are still based on a bag-of-words. The Web provides a vast resource for the automatic construction of parallel corpora which can be used to train statistical translation models automatically. The resulting translation models can be embedded in several ways in a retrieval model. In this paper, we will investigate the problem of automatically mining parallel texts from the Web and different ways of integrating the translation models within the retrieval process. Our experiments on standard test collections for CLIR show that the Web-based translation models can surpass commercial MT systems in CLIR tasks. These results open the perspective of constructing a fully automatic query translation device for CLIR at a very low cost.Comment: 37 page

Chip-Scale Microwave Photonic Signal Processing

The use of optical technology can provide unprecedented performance to the generation, distribution, and processing of microwave. Recently, on-chip microwave photonics (MWP) has gained significant interests for its numerous advantages, such as robustness, reconfigurability as well as reduction of size, weight, cost, and power consumption. In this chapter, we review our recent progress in ultracompact microwave photonic signal processing using silicon nanophotonic devices. Using the fabricated silicon waveguide, silicon microring resonators (MRRs) and silicon photonic crystal nanocavities, we demonstrate on-chip analog signal transmission, optically controlled tunable MWP filter, and ultra-high peak rejection notch MWP filter. The performance of analog links and the responses of MWP filters are evaluated in the experiment. In addition, microwave signal multiplication and modulation are also demonstrated based on a silicon Mach-Zehnder modulator in the experiment with favorable operation performance. The demonstrated on-chip analog links, MWP filters, microwave signal multiplication/modulation may help understand on-chip analog signaling and expand novel functionalities of MWP signal processing

M-ary Optical Computing

The era of cloud computing has fuelled the increasing demand on data centers for high-performance, high-speed data storage and computing. Digital signal processing may find applications in future cloud computing networks containing a large sum of data centers. Addition and subtraction are considered to be fundamental building blocks of digital signal processing which are ubiquitous in microprocessors for arithmetic operations. However, the processing speed is limited by the electronic bottleneck. It might be valuable to implement high-speed arithmetic operations of addition and subtraction in the optical domain. In this chapter, recent results of M-ary optical arithmetic operations for high base numbers are presented. By exploiting degenerate and nondegenerate four-wave mixing (FWM) in highly nonlinear fibers (HNLFs), graphene-assisted optical devices, and silicon waveguide devices, various types of two-/three-input high-speed quaternary/octal/decimal/hexadecimal optical computing operations have been demonstrated. Operation speed up to 50 Gbaud of this computing approach is experimentally examined. The demonstrated M-ary optical computing using high base numbers may facilitate advanced data management and superior network performance

Effects of interorbital hopping on orbital fluctuations and metal-insulator transitions: Extended linearized dynamical mean-field theory

We study the effects of interorbital hopping on orbital fluctuations and Mott-Hubbard metal-insulator transition (MIT) in the two-orbital Hubbard model within the extended linearized dynamical mean-field theory. By mapping the model onto an effective model with different bandwidths through the canonical transformation, we find that at half-filling, the increases of the interorbital Coulomb interaction $U^{\prime}$ and the Hund's coupling $J$ drive the MIT, and the critical $J_{c}$ for MIT increases with the lift of the inter-orbital hopping integral $t_{ab}$. Meanwhile at quarter filling and in the strong correlation regime, the system without $t_{ab}$ exhibits MIT with the decreasing of $J$, and favors the orbital liquid ground state. However, the system transits from metal to insulator with the increasing of t$_{ab}$, accompanied with the rising of the orbital order parameter. These results show the important role of the interorbital hopping in the orbital fluctuation and orbital ordering.Comment: 7 pages, 6 figure