Mixing cutoff for simple random walks on the Chung-Lu digraph

In this paper, we are interested in the mixing behaviour of simple random walks on inhomogeneous directed graphs. We focus our study on the Chung-Lu digraph, which is an inhomogeneous network that generalizes the Erd\H{o}s-R\'enyi digraph. In particular, under the Chung-Lu model, edges are included in the graph independently and according to given Bernoulli laws, so that the average degrees are fixed. To guarantee the a.s. existence of a unique reversible measure, which is implied by the strong connectivity of the graph, we assume that the average degree grows logarithmically in the size $n$ of the graph. In this weakly dense regime, we prove that the total variation distance to equilibrium displays a cutoff behaviour at the entropic time of order $\log(n)/\log\log(n)$. Moreover, we prove that on a precise window, the cutoff profile converges to the Gaussian tail function. This is qualitatively similar to what was proved in [6,7,8] for the directed configuration model, where degrees are deterministically fixed. In terms of statistical ensembles, our analysis provides an extension of these cutoff results from a hard to a soft-constrained model.Comment: 34 page

Integrated Imaging to Investigate Low-Flow Alarms of Left Ventricular Assist Devices

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Guest Editorial: Agile beyond software - In search of flexibility in a wide range of innovation projects and industries

The nine papers in this special section focus on new developments in agile software and reports on applications for its use. A key aspect for the extensive use of agile software is that it supports developers with coping with the growing uncertainty and turbulence in technological and market environments. Feedback and change are at the core of Agile for a dynamic, evolving, and organic, rather than static, predefined, and mechanistic development process advocated by waterfall management. To create timely, high-quality, cost-efficient, and innovative solutions, Agile developers organized in small, colocated, autonomous teams, build and test software in rapid iterative cycles, actively involving users to gather feedback, updating the project scope, and plan “on-the-fly,” using face-to-face communication as opposed to documentation. These papers contribute to the state-of-the-art of agile research by offering a rich, up-todate account of the dynamics occurring when expanding Agile into “not-just-software” contexts of the key challenges and perils related to the scaling and of the possible solutions to them

A simulation approach for predicting energy use during general milling operations

Manufacturing processes have a high impact on global energy consumption. Machine tool’s environmental impact is typically dominated by the energy absorbed during the use phase. Energy efficiency is progressively considered as an additional performance index in comparing alternative machines, process planning, and machining strategies. For this purpose, this paper proposes a simulation approach that estimates the energy used by a machine tool in producing a generic workpiece by general milling operations. The developed tool simulates the execution of a standard ISO part program, basing on an explicit geometric and mechanistic representation of the cutting process, coupled with an energy model of the machine tool reproducing the power consumption of spindle, axes, and auxiliary units. Energy models were identified by an experimental characterization procedure that can be easily adopted in industrial contexts. The simulator was validated comparing the estimated energy with measurements performed on different cutting tests, evaluating also its computational effort. Moreover, the simulator performances were compared to alternative energy evaluation methods proposed in the literature

Developing software beyond customer needs and plans: An exploratory study of its forms and individual-level drivers

Excessive software development is the tendency to develop new software above and beyond the requirements of the market and/or planned specifications. It is a widespread phenomenon involving both risks and flexibility advantages. As it represents a challenging dilemma for software developers, it is important to study its human origins. Drawing on the tripartite model of individual attitudes, this study investigates the influence of developers’s cognitive (intuitive and rational thinking styles), affective (emotional attachment) and behavioural (reliance on past experiences) traits on two forms of excess, beyond needs and beyond plans. Using survey data on 307 software developers, this study shows that different manifestations of excess are associated with distinct traits of software developers. Emotional attachment drives beyond needs excess. A positive (negative) association is found between relying on past experiences and beyond needs excess (beyond plans excess). An intuitive cognitive style fosters the inclusion of extra features in the new product scope, whereas a rational style might lead to developing one-size-fits-all software that targets the needs of a broad user base. These findings contribute to research on the development of digital new products and production technologies by offering a comprehensive yet fine-grained picture of excessive software development’s nature and drivers

Analysis of Vibration Damping in Machine Tools

AbstractThe dynamic behavior of a machine tool structure directly influences key metal cutting performance like being able to quickly remove hard workpiece material during roughing or minimize unwanted oscillations during high speed movements in finishing. While structure conception is still funded on designer experience and inventiveness, Finite Element models are very effective in analyzing the conceived structure, allowing its optimization, in term of stiffness increase and/or mass reduction.While today FE models provide a satisfying description of structure distributed stiffness and inertia, machine damping is usually not represented or is approximated as a uniform viscous damping, with no precise reference to the actual dissipation phenomena occurring in the structure. The corresponding incertitude in the estimation of the overall dynamic behavior often strongly limits the possibility of delivering accurate absolute estimations of machine performance. In order to overcome this limitation, this work aims at adding key energy dissipation mechanisms into numerical structural models: the velocity loop of the axis position controller, the frictional forces acting on the axis kinematic chain and guide ways and a distributed modal damping. Experimental tests have been performed on a machine tool axis equipped with tunable roller plus plain friction guide ways. The proposed model shows how different components and phenomena contribute into increasing machine performance, in term of material removal capacity. Given that the resulting models are essentially non-linear, appropriate methodologies are also suggested to integrate the proposed analysis into the usual machine development design cycle

COREC: Concurrent Non-Blocking Single-Queue Receive Driver for Low Latency Networking

Existing network stacks tackle performance and scalability aspects by relying on multiple receive queues. However, at software level, each queue is processed by a single thread, which prevents simultaneous work on the same queue and limits performance in terms of tail latency. To overcome this limitation, we introduce COREC, the first software implementation of a concurrent non-blocking single-queue receive driver. By sharing a single queue among multiple threads, workload distribution is improved, leading to a work-conserving policy for network stacks. On the technical side, instead of relying on traditional critical sections - which would sequentialize the operations by threads - COREC coordinates the threads that concurrently access the same receive queue in non-blocking manner via atomic machine instructions from the Read-Modify-Write (RMW) class. These instructions allow threads to access and update memory locations atomically, based on specific conditions, such as the matching of a target value selected by the thread. Also, they enable making any update globally visible in the memory hierarchy, bypassing interference on memory consistency caused by the CPU store buffers. Extensive evaluation results demonstrate that the possible additional reordering, which our approach may occasionally cause, is non-critical and has minimal impact on performance, even in the worst-case scenario of a single large TCP flow, with performance impairments accounting to at most 2-3 percent. Conversely, substantial latency gains are achieved when handling UDP traffic, real-world traffic mix, and multiple shorter TCP flows