On the Hitting Times of Quantum Versus Random Walks

The hitting time of a classical random walk (Markov chain) is the time required to detect the presence of—or equivalently, to find—a marked state. The hitting time of a quantum walk is subtler to define; in particular, it is unknown whether the detection and finding problems have the same time complexity. In this paper we define new Monte Carlo type classical and quantum hitting times, and we prove several relationships among these and the already existing Las Vegas type definitions. In particular, we show that for some marked state the two types of hitting time are of the same order in both the classical and the quantum case. Then, we present new quantum algorithms for the detection and finding problems. The complexities of both algorithms are related to the new, potentially smaller, quantum hitting times. The detection algorithm is based on phase estimation and is particularly simple. The finding algorithm combines a similar phase estimation based procedure with ideas of Tulsi from his recent theorem (Tulsi A.: Phys. Rev. A 78:012310 2008) for the 2D grid. Extending his result, we show that we can find a unique marked element with constant probability and with the same complexity as detection for a large class of quantum walks—the quantum analogue of state-transitive reversible ergodic Markov chains. Further, we prove that for any reversible ergodic Markov chain P, the quantum hitting time of the quantum analogue of P has the same order as the square root of the classical hitting time of P. We also investigate the (im)possibility of achieving a gap greater than quadratic using an alternative quantum walk. In doing so, we define a notion of reversibility for a broad class of quantum walks and show how to derive from any such quantum walk a classical analogue. For the special case of quantum walks built on reflections, we show that the hitting time of the classical analogue is exactly the square of the quantum walk.     

Exploring Appropriation of Enterprise Wikis:

The purpose of this paper is to provide both application-oriented researchers and practitioners with detailed insights into conception, implementation, and utilization of intra-organizational wikis to support knowledge management and group work. Firstly, we report on three case studies and describe how wikis have been appropriated in the context of a concrete practice. Our study reveals that the wikis have been used as Knowledge Base, Encyclopedia and Support Base, respectively. We present the identified practices as a result of the wiki appropriation process and argue that due to their open and flexible nature these wikis have been appropriated according to the users’ needs. Our contribution helps to understand how platforms support working practices that have not been supported by groupware before, or at least not in the same way. Secondly, three detailed implementation reports uncover many aspects of wiki projects, e.g., different viewpoints of managers and users, an investigation of other sources containing business-relevant information, and perceived obstacles to wiki projects. In this context, our study generates a series of lessons learned for people who intend to implement wikis in their own organizations, including the awareness of usage potential, the need for additional managerial support, and clear communication strategies to promote wiki usage.     

Novel 3D manufacturing method combining microelectrial discharge machining and electrochemical polishing

This paper reports on the potential of microelectrical discharge machining (μEDM) as an innovative method for the fabrication of 3D microdevices. To demonstrate the wide capabilities of μEDM two different microsystems—a microfluidic device for the dispersion of nanoparticles and a star probe for microcoordinate metrology—are presented. To gain optimized process conditions as well as a high surface quality an adequate adaption of the single erosion parameters such as energy, pulse frequency and spark gap has to be carried out and is discussed below. Thus, a surface roughness of R_a?=?80?nm is achieved at the channel bottom. The fabricated stylus elements for the star probe have sphere diameters of 40–200?μm. For further surface quality enhancement a subsequent electrochemical polishing step is investigated. In case of the dispersion micromodule a combined process chain of μEDM-milling and electropolishing has reached a surface improvement above 70%.     

Cantilever probes for high speed AFM

Since the invention in 1986 atomic force microscopy (AFM) has become the most widely used scanning probe microscopy (Binnig et al. in Phys Rev Lett 56:930–933, 1986). The microscope images the interaction of forces like Van der Waals or Coulomb forces between a sample and the apex of a small tip integrated near the free end of a flexible cantilever. But as all other scanning probe techniques the AFM requires serial data acquisition and suffers therefore from a low temporal resolution. Enhancing the speed to video rate imaging makes high demands on scanner technology, control electronics and on the key feature the cantilever with integrated sharp stylus. For the cantilever probes, fundamental resonance frequencies in the MHz regime are envisaged while the force constant of a few nN/nm shall be maintained. We present different novel AFM probes with ultrashort cantilevers and integrated sharp tips for high speed AFM while focusing on widely dispersed applications and on aspects of mass fabrication.     

零电压零电流开关全桥PWM变换器的研究

文本通过分析全桥ZVZCS PWM变换器的工作原理,得出其与传统的全桥ZVZCS PWM变换器的不同之处,然后具体分析对于变化的负载电流,电路环流是如何自我调节以实现ZCS的,并给出了一些影响实现ZVZCS的关键元器件的参数设计公式。最后样机的试验波形证了本文的分析研究。     

Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications

Electronically controllable microvalves based on temperature sensitive hydrogels as actuators are described. A thermal-electronic interface was used for electronic control of the liquid flow. The hydrogel actuators were directly placed in a flow channel. They used the process medium as the swelling agent. Because of the direct placement into the channel the elastic properties of the hydrogel actuator were utilized to improve the pressure insensitivity, to achieve high particle tolerance and to avoid a leakage flow. The microvalves show an extremely simple structure. They can be fabricated using conventional micro technology within a few technical steps. The microvalves can also be miniaturized to a currently unrivalled extent of about 4 /spl mu/m/spl times/4 /spl mu/m/spl times/1/spl mu/m. Valves for "laboratory on chip" applications can already be obtained. The switching times of the electronically controllable microvalves based on hydrogels are 0.3 s to 10 s.     

Stability of discrete-time systems with quantized input and state measurements

This note focuses on linear discrete-time systems controlled using a quantized input computed from quantized measurements. Nominally stabilizing, but otherwise arbitrary, state feedback gains could result in limit cycling or nonzero equilibrium points. Although a single quantizer is a sector nonlinearity, the presence of a quantizer at each state measurement channel makes traditional absolute stability theory not applicable in a direct way. A global asymptotic stability condition is obtained by means of a result which allows us to apply discrete positive real theory to systems with a sector nonlinearity which is multiplicatively perturbed by a bounded function of the state. The stability result is readily applicable by evaluating the location of the polar plot of a system transfer function relative to a vertical line whose abcissa depends on the one-norm of the feedback gain. A graphical method is also described that can be used to determine the equilibrium points of the closed-loop system for any given feedback gain.     

Design of a Medical Non‐Linear Drilling Device: The Influence of Twist and Wear on the Fatigue Behaviour of NiTi Wires Subjected to Bending Rotation

This paper considers fundamental and experimental aspects associated with the engineering design of a medical, non‐linear drilling device which exploits shape memory pseudoelasticity of NiTi wires. For this application it is important that the NiTi wires have a good fatigue resistance. This is why the present authors have previously determined the influence of various parameters on cyclic life, crack growth and stress state of pseudoelastic wires subjected to bending rotation fatigue. The actual drilling device has to withstand twist in addition to bending rotation because the free rotation is constrained by friction between the drill head and the bone material. In addition, friction between the wire and a NiTi guiding tube results in wear and this may well promote fatigue crack nucleation. In this paper, we explain the function of the medical drill. We then report results on the effect of the additional parameters (1) twist and (2) wear on the fatigue life of thin pseudoelastic NiTi wires. We finally discuss the implications of our experimental results for the design process of the medical drilling device.     

Complementary Tasks to Measure Working Memory in Distinct Prefrontal Cortex Subregions in Rats.

Acquisition of odor-guided or visually-guided delayed win-shift behavior was evaluated in rats after lidocaine-induced inactivation within the agranular insular area of the prefrontal cortex (PFC) or the prelimbic area of the PFC. Additional sites and tasks were used to control for neuroanatomical and behavioral specificity of lidocaine inactivation of the agranular insular and prelimbic areas. Results showed that acquisition of the odor-guided delayed win-shift task was dependent on the agranular insular area, whereas acquisition of the visually-guided version was dependent on the prelimbic area. This dissociation suggests that the stimulus modality used is critical for revealing working memory functions of different PFC subregions. The described methods provide a complementary means to study working memory in PFC subregions using a radial-arm maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)