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This paper presents a systematic modeling methodology for microfluidic concentration gradient generators. The generator is decomposed into a system of microfluidic elements with relatively simple geometries. Parameterized models for such elements are analytically developed and hold for general sample concentration profiles and arbitrary flow ratios at the element inlet; hence, they are valid for concentration gradient generators that rely on either complete or partial mixing. The element models are then linked through an appropriate set of parameters embedded at the element interfaces. This yields a systematic, lumped-parameter representation of the entire generator in terms of a network of gradient-generation elements. The system model is verified by numerical analysis and experimental data and accurately captures the overall effects of network topologies, element sizes, flow rates and reservoir sample concentrations on the generation of sample concentration gradient. Finally, this modeling methodology is applied to propose a novel and compact microfluidic device that is able to create concentration gradients of complex shapes by juxtaposing simple constituent profiles along the channel width.

This article describes an approach for implementing a complete computer system ͑CPU, RAM, I/O, and nonvolatile mass memory͒ on a single integrated-circuit substrate ͑a chip͒-hence, the name ''single-chip computer.'' The approach presented combines advances in the field of microelectromechanical systems ͑MEMS͒ and micromagnetics with traditional low-cost very-large-scale integrated circuit style parallel lithographic manufacturing. The primary barrier to the creation of a computer on a chip is the incorporation of a high-capacity ͓many gigabytes ͑GB͔͒ re-writable nonvolatile memory ͑in today's terminology, a disk drive͒ into an integrated circuit ͑IC͒ manufacturing process. This article presents the following design example: a MEMS-based magnetic memory that can store over 2 GB of data in 2 cm 2 of die area and whose fabrication is compatible with a standard IC manufacturing process.

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We formulate an extended linear σ model of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) by virtue of chiral symmetry SUL(3) × SUR(3) and UA(1) symmetry. In the linear realization formalism, we study the mass spectra and components of the low-lying scalars and pseudo scalars in this model. The mass matrices for physical staes are obtained and the glueball candidates are examined. We find that the model can accommodate the mass spectra of low-lying states quite well. Our fits indicate that the most glueball like scalar should be 2 GeV or higher while the glueball pseudoscalar is η(1756). We also examine the parameter region where the lightest iso-scalar f0(600) can be the glueball and quarkonia dominant but find such a parameter region may be confronted with the problem of the unbounded vacuum from below.PACS numbers: I. INTRODUCTIONThe pseudoscalar, vector and axial-vector as well as tensor mesons of light quarks have been well-understood in the naive quark model in terms of the chiral symmetry. Despite of its success, the naive quark model can not explain the scalar meson sector, which have the same quantum numbers as the vacuum. There are about 19 states which are twice more than the expectedqq nonet as in vector and tensor sectors, while the mass and decay pattern of these low-lying scalars are different from the expectation of the naive quark model. To understand the nature of these scalars has been the focus of recent studies e.g. see Refs. [1][2][3][4] and references therein.Among the low-lying scalar mesons, the lightest scalar f 0 (600) or σ attracts a lot of interests. It is widely believed that f 0 (600) is like the Higgs boson which plays a crucial role in the spontaneous chiral symmetry breaking. Confirmation of existence of the elusive f 0 (600) from ππ scattering processes settles down a controversy last for more than a few decades [2,5]. The πK scattering [6] and analysis from D decay D + → K − π + π − [7] revealed that κ should also exist. BES II also found such a κ like structure in J/Ψ decays [8]. Combined with the well determined sharp resonances, i.e. isoscalar f 0 (980) and isotriplet a(980) from ππ and πη as well as KK scattering processes, now it is accepted in literature that these low-lying scalar mesons (say less than 1 GeV) can be cast into a chiral nonet. The next important issue is what is the nature of this nonet.There are a couple of viewpoints on the nature of this nonet. For example,the tetraquark model [9] can explain the mass hierarchy and decay pattern of this nonet quite successfully and is further supported from other experimental data, like the photon-photon collision data, which prefer the tetraquark interpretation for the lowest scalar meson nonet [10] (where it is demonstrated that f 0 (980) should be a tetraquark dominant state with great details). An alternative interpretation is that this nonet is bound state of the meson-meson molecule [11]. In any way, this nonet challenges a self-consistent interpretation in the naive quark mod...

This paper proposes novel microfluidic concentration gradient generator (CGG) devices that are capable of constructing complex profiles of chemical concentrations by laterally combining the constituent profiles (e.g., linear and bell-shaped) generated in simple Y- or psi-shaped mixers. While the majority of currently existing CGG devices are based on complete mixing of chemical species, our design harnesses partial diffusive mixing in multi-stream laminar flow, and hence, features simple network structures and enhanced device reliability. An iterative simulation approach that incorporates our previous system-level models of CGG networks is developed to locate best-matched combinations of geometrical and operating parameters (e.g., inlet flow rates and inlet sample concentrations) for the device design. Microfluidic CGG chips are fabricated and experimentally characterized using optimal layout and operating conditions selected by the design process. The experimental results not only serve as a benchmark for model verification but also establish the feasibility of concentration gradient generation based on partial mixing for a variety of microfluidic applications.

We investigate the chiral condensate and the dressed Polyakov loop or dual chiral condensate at finite temperature and density in two-flavor Nambu-Jona-Lasinio model. The dressed Polyakov loop is regarded as an equivalent order parameter of deconfinement phase transition in a confining theory. We find the behavior of dressed Polyakov loop in absence of any confinement mechanism is quite interesting, with only quark degrees of freedom present, it still shows an order parameter like behavior. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole (T, µ) plane. In the case of explicit chiral symmetry breaking, it is found that the transition temperature for chiral restoration T χ c is smaller than that of the dressed Polyakov loop T D c in the low baryon density region where the transition is a crossover. With the increase of current quark mass the difference between the two transition temperatures is found to be increasing. However, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. We give an explanation on the feature of T in the case of crossover, and expect this feature is general and can be extended to full QCD theory. Our result might indicate that in the case of crossover, there exists a small region where chiral symmetry is restored but the color degrees of freedom are still confined.