One-step quantum phase gate in the ultrastrong coupling regime of circuit QED

In a previous publication (Phys Rev Lett 108: 120501, 2012), Romero et al. proposed an ultrastrong coupling circuit QED system that can implement a two-qubit quantum phase gate with four controlling pulses. Based on this architecture, we demonstrate that an ultrafast two-qubit phase gate can also be realized with only one oscillation and lower coupling strengths. In our operation scheme, two identical qubits evolve synchronously under a single pulse with a duration determined by a specific coupling strength. The phase gate can also be obtained periodically. The influences of parameter fluctuations are estimated. We demonstrate that the fidelities can be greater than 99% if the parameter fluctuations are controlled within 5%.     

Bell-state generation on remote superconducting qubits with dark photons

We present a scheme to generate the Bell state deterministically on remote transmon qubits coupled to different 1D superconducting resonators connected by a long superconducting transmission line. Using the coherent evolution of the entire system in the all-resonance regime, the transmission line need not to be populated with microwave photons which can robust against the long transmission line loss. This lets the scheme more applicable to the distributed quantum computing on superconducting quantum circuit. Besides, the influence from the small anharmonicity of the energy levels of the transmon qubits can be ignored safely.     

One-step approximations for detecting regime changes in the state space model with application to the influenza data

Kim and Nelson [1999. State Space Models with Regime Switching. MIT Press, Cambridge, MA] and others extended the framework of state space models involving independent regime changes to the Markov dependent case. The cost of dealing with state space models with Markov switching is high in computational effort because of the number of the possible paths through the chain. Thus it is necessary to make some approximations in order to obtain a computationally feasible algorithm for estimation. The approximations depend on modified smoothing and filtering recursions that can be easily incorporated into an EM algorithm for maximum likelihood estimation. To investigate the accuracy of approximations, we develop a new method to obtain more exact solutions, and then compare the two methods. We apply both methods to a simulated series. The result shows that employing the approximation-based algorithm not only provides accurate results but also leads to a significant reduction in the computational costs. We also apply the methods to an influenza mortality series, in which we develop a model that is general enough to include most structural models useful in monitoring changes of regime. The model proposed has the flexibility to deal with a wide range of problems involving possible regime shifts in pattern that may be seen to occur in many biological, medical and epidemiological studies.     

New regime of droplet generation in a T-shape microfluidic junction

We present an experimental study of a new regime of monodisperse micro-droplet generation that we named the balloon regime. A dispersion of oil in water in a T-junction microfluidic system was studied. Several microfluidic devices having different cross-sections of the continuous and the dispersed phases micro-channels were tested. This new regime appears only for low- dispersed phase velocity. The micro-droplet size is mainly related to the geometry of the T-junction micro-channels especially its width and depth, and independent of the continuous and dispersed phases velocities. In our experiments, the velocities of the continuous and the dispersed phases $\overline v_{\rm c}$ and $\overline v_{\rm d}$ respectively, have been varied in a wide range: $\overline v_{\rm c}$ from 0.5 to 500 mm/s, and $\overline v_{\rm d}$ from 0.01 to 30 mm/s. We show that the continuous phase only controls the micro-droplet density, while the dispersed phase linearly changes the frequency of the micro-droplet generation. Another particularity of the present regime, which differentiates it from all other known regimes, is that the micro-droplet retains its circular shape throughout its formation at the T junction, and undergoes no deformation due to the drag forces. We propose a mechanism to explain the formation of micro-droplets in this new regime.     

Suspended bimaterial microchannel resonators for thermal sensing of local heat generation in liquid

Suspended bimaterial microchannel resonator devices have been fabricated to measure the thermal behaviors of small biological molecules and individual cells in liquid. A resonant microbridge structure embeds this microfluidic channel in its interior. The fabrication process is based on the creation of buried channels in silicon-on-insulator wafers. For the bimaterial bridge structure layers of SiO₂ and SiN_x were used. This bimaterial resonant bridge with internal microfluidic channel could be employed as a very sensitive calorimeter, since the tensile stress generated by bimaterial effect in the heated bridge, produces a shift of resonant frequency. A laser beam was used to heat the center of the bridge resonator with the microchannel filled by water and the corresponding resonant frequency variations were evaluated. The measured sensitivity for the local heat at the center of the bridge is 8.6 ppm/μW in atmospheric condition.     

远程教育环境中会话发起机制的研究

在基于多播的紧密控制的多媒体会议系统中,会话的发起经常采用发送会话公告信息的方法,但是在这样的会话发起框架中仍然存在一些问题,由于会话公告协议限制全局会话的公告报文带宽上限为4Mb／S,再加上多播信息的不可靠传送,客户端的会话目录工具经常需要等待10—20分钟才能得到特定会话的公告信息。讨论了远程教育环境中的会议发起机制以及与之紧密相关的会话目录服务,并在此基础上对上述的启动延迟问题进行了分析,提出了使用会话目录代理的方法未解决该问题。     

Analysis of compressional-wave influence on thickness-shear-mode resonators in liquids

The operation of a thickness-shear-mode (TSM) resonator contacting a finite liquid layer has been analysed to investigate the effect of compressional-wave generation. This effect is mainly related to the non-uniform shear velocity profile across the surface of a TSM device. Hydrophone measurements show two coils of longitudinal waves. Their influence on the TSM resonator response is studied with impedance analysis, varying the spacing between resonator and reflector as well as the reflecting conditions on the top side of the liquid layer. A characteristic response with a periodicity of λ/2 is observed when the spacing of the liquid cavity or the liquid layer thickness is changed. It indicates standing longitudinal waves in the cavity. Their influence can be modelled with an additional complex impedance in the motional arm of the Butterworth-van-Dyke equivalent circuit representing an own (compressional) transmission line.     

Scaled control in the QED regime

We develop many-server asymptotics in the Quality-and-Efficiency-Driven (QED) regime for models with admission control. The admission control, designed to reduce the incoming traffic in periods of congestion, scales with the size of the system. For a class of Markovian models with this scaled control, we identify the QED limits for two stationary performance measures. We also derive corrected QED approximations, generalizing earlier results for the Erlang B, C and A models. These results are useful for the dimensioning of large systems equipped with an active control policy. In particular, the corrected approximations can be leveraged to establish the optimality gaps related to square-root staffing and asymptotic dimensioning with admission control.     

Shortest multiple disconnected path for the analysis of entanglements in two- and three-dimensional polymeric systems

We present an algorithm which returns a shortest path and related number of entanglements for a given configuration of a polymeric system in 2 or 3 dimensions. Rubinstein and Helfand, and later Everaers et al. introduced a concept to extract primitive paths for dense polymeric melts made of linear chains (a multiple disconnected multibead ‘path’), where each primitive path is defined as a path connecting the (space-fixed) ends of a polymer under the constraint of non-interpenetration (excluded volume) between primitive paths of different chains, such that the multiple disconnected path fulfills a minimization criterion. The present algorithm uses geometrical operations and provides a—model independent—efficient approximate solution to this challenging problem. Primitive paths are treated as ‘infinitely’ thin (we further allow for finite thickness to model excluded volume), and tensionless lines rather than multibead chains, excluded volume is taken into account without a force law. The present implementation allows to construct a shortest multiple disconnected path (SP) for 2D systems (polymeric chain within spherical obstacles) and an optimal SP for 3D systems (collection of polymeric chains). The number of entanglements is then simply obtained from the SP as either the number of interior kinks, or from the average length of a line segment. Further, information about structure and potentially also the dynamics of entanglements is immediately available from the SP. We apply the method to study the ‘concentration’ dependence of the degree of entanglement in phantom chain systems.

Program summary

Title of program:ZCatalogue number:ADVGProgram summary URL:http://cpc.cs.qub.ac.uk/summaries/ADVGProgram obtainable from: CPC Program Library, Queen's University of Belfast, N. IrelandComputer for which the program is designed and others on which it has been tested: Silicon Graphics (Irix), Sun (Solaris), PC (Linux)Operating systems or monitors under which the program has been tested: UNIX, LinuxProgram language used: USANSI Fortran 77 and Fortran 90Memory required to execute with typical data: 1 MByteNo. of lines in distributed program, including test data, etc.: 10 660No. of bytes in distributed program, including test data, etc.: 119 551Distribution formet:tar.gzNature of physical problem: The problem is to obtain primitive paths substantiating a shortest multiple disconnected path (SP) for a given polymer configuration (chains of particles, with or without additional single particles as obstacles for the 2D case). Primitive paths are here defined as in [M. Rubinstein, E. Helfand, J. Chem. Phys. 82 (1985) 2477; R. Everaers, S.K. Sukumaran, G.S. Grest, C. Svaneborg, A. Sivasubramanian, K. Kremer, Science 303 (2004) 823] as the shortest line (path) respecting ‘topological’ constraints (from neighboring polymers or point obstacles) between ends of polymers. There is a unique solution for the 2D case. For the 3D case it is unique if we construct a primitive path of a single chain embedded within fixed line obstacles [J.S.B. Mitchell, Geometric shortest paths and network optimization, in: J.-R. Sack, J. Urrutia (Eds.), Handbook of Computational Geometry, Elsevier, Amsterdam, 2000, pp. 633-701]. For a large 3D configuration made of several chains, short is meant to be the Euclidean shortest multiple disconnected path (SP) where primitive paths are constructed for all chains simultaneously. While the latter problem, in general, does not possess a unique solution, the algorithm must return a locally optimal solution, robust against minor displacements of the disconnected path and chain re-labeling. The problem is solved if the number of kinks (or entanglements Z), explicitly deduced from the SP, is quite insensitive to the exact conformation of the SP which allows to estimate Z with a small error.Efficient method of solution: Primitive paths are constructed from the given polymer configuration (a non-shortest multiple disconnected path, including obstacles, if present) by first replacing each polymer contour by a line with a number of ‘kinks’ (beads, nodes) and ‘segments’ (edges). To obtain primitive paths, defined to be uncrossable by any other objects (neighboring primitive paths, line or point obstacles), the algorithm minimizes the length of all primitive paths consecutively, until a final minimum Euclidean length of the SP is reached. Fast geometric operations rather than dynamical methods are used to minimize the contour lengths of the primitive paths. Neighbor lists are used to keep track of potentially intersecting segments of other chains. Periodic boundary conditions are employed. A finite small line thickness is used in order to make sure that entanglements are not ‘lost’ due to finite precision of representation of numbers.Restrictions on the complexity of the problem: For a single chain embedded within fixed line or point obstacles, the algorithm returns the exact SP. For more complex problems, the algorithm returns a locally optimal SP. Except for exotic, probably rare, configurations it turns out that different locally optimal SPs possess quite an identical number of nodes. In general, the problem constructing the SP is known to be NP-hard [J.S.B. Mitchell, Geometric shortest paths and network optimization, in: J.-R. Sack, J. Urrutia (Eds.), Handbook of Computational Geometry, Elsevier, Amsterdam, 2000, pp. 633-701], and we offer a solution which should suffice to analyze physical problems, and gives an estimate about the precision and uniqueness of the result (from a standard deviation by varying the parameter: cyclicswitch). The program is NOT restricted to handle systems for which segment lengths of the SP exceed half the box size.Typical running time: Typical running times are approximately two orders of magnitude shorter compared with the ones needed for a corresponding molecular dynamics approach, and scale mostly linearly with system size. We provide a benchmark table.     

Modelling of air damping effect on the performance of encapsulated MEMS resonators

Microsystem Technologies - The dynamic performance of a micro-resonator depends on its energy loss mechanism which is quantified by Q-factor (Quality factor). This paper presents numerical...     

Influence of the phase damping for two-qubits system in the dispersive reservoir

An analytical solution of the master equation for two qubits-field system in the dispersive reservoir are investigated, the qubits are initially in werner states. Under the influence of the damping we investigate the quantum correlation in a two-qubit based on measurement-induced disturbance (MID). We compare MID and entanglement measured by negativity and illustrate their different characteristics. We find the effect of damping on MID is weaker than negativity. Negativity will experience a sudden transition but this will not happen for MID.     

Effect of geometry on droplet formation in the squeezing regime in a microfluidic T-junction

In the surface tension-dominated microchannel T-junction, droplets can be formed as a result of the mixing of two dissimilar, immiscible fluids. This article presents results for very low Capillary numbers and different flow rates of the continuous and dispersed phases. Through three-dimensional lattice Boltzmann-based simulations, the mechanism of the formation of “plugs” in the squeezing regime has been examined and the size of the droplets quantified. Results for Re_\textc << 1 Re_{\text{c}} \ll 1 show the dependence of flow rates of the two fluids on the length of the droplets formed, which is compared with existing experimental data. It is shown that the size of plugs formed decreases as the Capillary number increases in the squeezing regime. This article clearly shows that the geometry effect, i.e., the widths of the two channels and the depth of the assembly, plays an important role in the determination of the length of the plugs, a fact that was ignored in earlier experimental correlations.     

Propulsion of droplets on micro- and sub-micron ratchet surfaces in the Leidenfrost temperature regime

Spatially periodic systems with localized asymmetric surface structures (ratchets) can induce directed transport of matter (liquid/particles) in the absence of net force. Here, we show that propulsion for the directed motion of water droplets levitating on heated ratchet surfaces in the Leidenfrost (film boiling) regime is significantly enhanced as the ratchet period decreases down to micro- and sub-micrometers. At the temperature range slightly above the threshold temperature of droplet motion, sub-micron ratchets yield water droplet velocities reaching ~40 cm/s, a speed that has never been achieved with any chemical and topological gradient surfaces. This dramatic increase in the droplet velocity is attributed to an enhanced heat transfer through the local contacts between ratchet peaks and bottom of the droplet. A hydrophobic coating on the ratchet surfaces is found to further increase the droplet velocity and decrease the threshold temperature of the droplet motion. The results suggest that miniaturized ratchet surfaces can potentially be used in diverse applications requiring control over fluid transport and heat transfer such as two phase cooling systems for microprocessors and fuel injection for combustion technology and that for those applications the design of ratchet dimensions and surface chemistry are critically important.     

Parallel generation of architecture on the GPU

In this paper, we present a novel approach for the parallel evaluation of procedural shape grammars on the graphics processing unit (GPU). Unlike previous approaches that are either limited in the kind of shapes they allow, the amount of parallelism they can take advantage of, or both, our method supports state of the art procedural modeling including stochasticity and context‐sensitivity. To increase parallelism, we explicitly express independence in the grammar, reduce inter‐rule dependencies required for context‐sensitive evaluation, and introduce intra‐rule parallelism. Our rule scheduling scheme avoids unnecessary back and forth between CPU and GPU and reduces round trips to slow global memory by dynamically grouping rules in on‐chip shared memory. Our GPU shape grammar implementation is multiple orders of magnitude faster than the standard in CPU‐based rule evaluation, while offering equal expressive power. In comparison to the state of the art in GPU shape grammar derivation, our approach is nearly 50 times faster, while adding support for geometric context‐sensitivity.     

Lattice Boltzmann modeling of microchannel flows in the transition flow regime

Owing to its kinetic nature and distinctive computational features, the lattice Boltzmann method for simulating rarefied gas flows has attracted significant research interest in recent years. In this article, a lattice Boltzmann (LB) model is presented to study microchannel flows in the transition flow regime, which have gained much attention because of fundamental scientific issues and technological applications in various micro-electro-mechanical system (MEMS) devices. In the model, a Bosanquet-type effective viscosity is used to account for the rarefaction effect on gas viscosity. To match the introduced effective viscosity and to gain an accurate simulation, a modified second-order slip boundary condition with a new set of slip coefficients is proposed. Numerical investigations demonstrate that the results, including the velocity profile, the non-linear pressure distribution along the channel, and the mass flow rate, are in good agreement with the solution of the linearized Boltzmann equation, the direct simulation Monte Carlo (DSMC) results, and the experimental results over a broad range of Knudsen numbers. It is shown that taking the rarefaction effect on gas viscosity into consideration and employing an appropriate slip boundary condition can lead to a significant improvement in the modeling of rarefied gas flows with moderate Knudsen numbers in the transition flow regime.     

Study of the equation for the Abrikosov vortex pinning on a linear defect in a superconducting wafer

An equation for an Abrikosov vortex bound state on a linear defect in a superconducting thin film in the presence of transport current is studied. A theoretical analysis of the corresponding boundary problem has been carried out and an estimate of the density of the critical current resulting in the vortex string depinning is obtained. The shape of an elastic vortex string is calculated. The instability threshold of the vortex-bound state due to the increase in the current, which results in the vortex string depinning, is found using numerical modeling. The results agree qualitatively with the data of the experiments carried out on high-temperature superconductors.     

One-step maskless grayscale lithography for the fabrication of 3-dimensional structures in SU-8

We propose a novel and simplified method to fabricate complex 3-dimensional structures in SU-8 photoresist using maskless grayscale lithography. The proposed method uses a Digital Micro-mirror Device (DMD^®) to modulate the light intensity across a single SU-8 photoresist layer. Top and back-side exposure are implemented in the fabrication of original structures such as cantilevers, covered channels with embedded features and arrays of microneedles. The fabrication of similar structures in SU-8 with other techniques often requires complex physical masks or the patterning of several stacked layers. The effects of critical process parameters such as software mask design, exposure and developing conditions on the quality of 3-D structures are discussed. A number of applications using bridges, cantilevers and micromixers fabricated using this methodology are explored.     

Molecular modeling study on the effect of residues distant from the nucleotide-binding portion on RNA binding in Staphylococcus aureus Hfq

Hfq is an abundant RNA-binding bacterial protein that was first identified in E. coli as a required host factor for phage Qβ RNA replication. The pleiotrophic phenotype resulting from the deletion of Hfq predicates the importance of this protein. Two RNA-binding sites have been characterized: the proximal site which binds sRNA and mRNA and the distal site which binds poly(A) tails. Previous studies mainly focused on the key residues in the proximal site of the protein. A recent mutation study in E. coli Hfq showed that a distal residue Val43 is important for the protein function. Interestingly, when we analyzed the sequence and structure of Staphylococcus aureus Hfq using the CONSEQ server, the results elicited that more functional residues were located far from the nucleotide-binding portion (NBP). From the analysis seven individual residues Asp9, Leu12, Glu13, Lys16, Gln31, Gly34 and Asp40 were selected to investigate the conformational changes in Hfq–RNA complex due to point mutation effect of those residues using molecular dynamics simulations. Results showed a significant effect on Asn28 which is an already known highly conserved functionally important residue. Mutants D9A, E13A and K16A depicted effects on base stacking along with increase in RNA pore diameter, which is required for the threading of RNA through the pore for the post-translational modification. Further, the result of protein stability analysis by the CUPSAT server showed destabilizing effect in the most mutants. From this study we characterized a series of important residues located far from the NBP and provide some clues that those residues may affect sRNA binding in Hfq.     

基于FPGA的超导MRI的Bo涡流补偿算法

采用可以用FPGA实现的算法进行梯度电流预补偿的方法进行B0涡流的补偿.鉴于FP-GA具有高速并行处理和状态机无限循环的特点,设计了一种从开机到断电,1μs计算一次不间断的B0涡流补偿的模式.试验证明,该方法通用性好、速度快、体积小、成本低.