&DIGITAL-MICROFLUIDIC LAB-ON-A-CHIP (LoC) technology offers a platform for developing diagnostic applications with the advantages of portability, sample and reagent volume reduction, faster analysis, increased automation, low power consumption, compatibility with mass manufacturing, and high throughput. In addition to diagnostics, digital microfluidics is finding use in airborne chemical detection, DNA sequencing by synthesis, and tissue engineering. In this article, we review efforts to develop various LoC applications using electrowetting-based digital microfluidics. We describe these applications, their implementation, and associated design issues. The ''Related work'' sidebar gives a brief overview of microfluidics technology.

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We investigate theoretically the influence of the spin-orbit interaction of Rashba type on the magnetoresistance of a semiconducting ferromagnetic nanostructure with a laterally constrained domain wall. The domain wall is assumed sharp ͑on the scale of the Fermi wavelength of the charge carriers͒. It is shown that the magnetoresistance in such a case can be considerably large, which is in qualitative agreement with recent experimental observations. It is also shown that spin-orbit interaction may result in an increase of the magnetoresistance. The role of localization corrections is also briefly discussed.

Disorder in spin-orbit (SO) coupling is an important feature of real low-dimensional electron structures. We study spin relaxation due to such a disorder as well as resulting abilities of spin manipulation. The spin relaxation reveals quantum effects when the spatial scale of the randomness is smaller than the electron wavelength. Due to the disorder in SO coupling, a time-dependent external electric field generates a spatially random spin-dependent perturbation. The resulting electric dipole spin resonance in a two-dimensional electron gas leads to spin injection in a frequency range of the order of the Fermi energy. These effects can be important for possible applications in spintronics.PACS numbers: 72.25. Rb, 72.25.Hg Electron dynamics in low-dimensional semiconductor structures reveals features of a spin dependent transport that are interesting for fundamental and applied research 1 . One of the main ingredients necessary to generate spin dependent transport in nonmagnetic semiconductor systems is the SO interaction. Such an interaction offers a possibility of an efficient and fast spin manipulation with electric fields, which in turn allows to prepare a required spin state. 2,3,4,5,6,7,8 At the same time, spin relaxation and decoherence due to the SO coupling prevent long-distance spin propagation. Two models are widely used to describe the SO coupling in lowdimensional structures: the Rashba and the Dresselhaus ones. In both models, the SO field and the corresponding spin precession rate are approximately linear in the electron momentum. Random evolution in the momentum due to collisions with impurities, phonons, and other electrons results in randomness in the spin precession, and thus leads to spin relaxation. However, in reality both interactions have an intrinsic randomness due to system imperfections, including the fluctuations in the dopant ion density 9,10 or random bonds at the quantum well (QW) interface 11 . Even if the mean values of the Rashba and Dresselhaus fields vanish, their fluctuations remain and can cause interesting consequences, including memory effects 10 , spin Hall effect in the finite-size systems 12 , and spin-dependent localization. 13 There are at least four different two-dimensional (2D) systems, where the SO disorder plays an important or crucial role. First, the effect of random SO coupling can be responsible for the spin relaxation in Si/Ge QWs. 11,14 Second, the spin-dependent disorder influences 15 the spin helix pattern recently observed in the GaAs (001) QW with the balanced Rashba and Dresselhaus terms. 16 Third, the randomness causes relaxation of the spin component along the growth axis observed in Ref. [17] in GaAs (011) QW, investigated now for spintronics applications. 17,18 Fourth, the most recent example of the system with random SO coupling is graphene, where the randomness and spin relaxation appear due to the rippling of the layers 19 and due to the disorder and electronphonon coupling in the substrate. 20 In this paper we study the effects of randomness o...

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