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71.
The literature describes two high performance concurrent stack algorithms based on combining funnels and elimination trees. Unfortunately, the funnels are linearizable but blocking, and the elimination trees are non-blocking but not linearizable. Neither is used in practice since they perform well only at exceptionally high loads. The literature also describes a simple lock-free linearizable stack algorithm that works at low loads but does not scale as the load increases. The question of designing a stack algorithm that is non-blocking, linearizable, and scales well throughout the concurrency range, has thus remained open. 相似文献
72.
Nir Gov 《Journal of Low Temperature Physics》2002,126(1-2):621-625
We propose a new model for the nature of the nucleation of solid from the superfluid phases of
4
He and
3
He. A fast solidification event in the superfluid results in a local release of pressure and a velocity field in the superfluid. This in turn facilitates the nucleation of vortex-loops. The kinetic energy gain of this process balances the surface tension, as the solid surface is quickly covered by many vortex-loops (hairy snow-ball). We show that this scenario gives good agreement with experiments on heterogeneous nucleation. 相似文献
73.
Breveruos Sheheade Miran Liber Mary Popov Yaron Berger Dinesh C. Khara Jürgen Jopp Eyal Nir 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(51)
Efficient fabrication of structurally and functionally diverse nanomolecular devices and machines by organizing separately prepared DNA origami building blocks into a larger structure is limited by origami attachment yields. A general method that enables attachment of origami building blocks using ‘sticky ends' at very high yields is demonstrated. Two different rectangular origami monomers are purified using agarose gel electrophoresis conducted in solute containing 100 × 10?3 m NaCl, a treatment that facilitates the dissociation of most of the incorrectly hybridized origami structures that form through blunt‐end interactions during the thermal annealing process and removes these structures as well as excess strands that otherwise interfere with the desired heterodimerization reaction. Heterodimerization yields of gel‐purified monomers are between 98.6% and 99.6%, considerably higher than that of monomers purified using the polyethylene glycol (PEG) method (88.7–96.7%). Depending on the number of PEG purification rounds, these results correspond to about 4‐ to 25‐fold reduction in the number of incorrect structures observed by atomic force microscopy. Furthermore, the analyses of the incorrect structures observed before and after the heterodimerization reactions and comparison of the purification methods provide valuable information on the reaction mechanisms that interfere with heterodimerization. 相似文献
74.
This paper presents an efficient preference-based ranking algorithm running in two stages. In the first stage, the algorithm learns a preference function defined over pairs, as in a standard binary classification problem. In the second stage, it makes use of that preference function to produce an accurate ranking, thereby reducing the learning problem of ranking to binary classification. This reduction is based on the familiar QuickSort and guarantees an expected pairwise misranking loss of at most twice that of the binary classifier derived in the first stage. Furthermore, in the important special case of bipartite ranking, the factor of two in loss is reduced to one. This improved bound also applies to the regret achieved by our ranking and that of the binary classifier obtained. Our algorithm is randomized, but we prove a lower bound for any deterministic reduction of ranking to binary classification showing that randomization is necessary to achieve our guarantees. This, and a recent result by Balcan et al., who show a regret bound of two for a deterministic algorithm in the bipartite case, suggest a trade-off between achieving low regret and determinism in this context. Our reduction also admits an improved running time guarantee with respect to that deterministic algorithm. In particular, the number of calls to the preference function in the reduction is improved from Ω(n 2) to O(nlog?n). In addition, when the top k ranked elements only are required (k?n), as in many applications in information extraction or search engine design, the time complexity of our algorithm can be further reduced to O(klog?k+n). Our algorithm is thus practical for realistic applications where the number of points to rank exceeds several thousand. 相似文献
75.
We present a scheme to convert self-stabilizing algorithms that use randomization during and following convergence to self-stabilizing algorithms that use randomization only during convergence. We thus reduce the number of random bits from an infinite number to an expected bounded number. The scheme is applicable to the cases in which there exits a local predicate for each node, such that global consistency is implied by the union of the local predicates. We demonstrate our scheme over the token circulation algorithm of Herman (Infor Process Lett 35:63–67, 1990) and the recent constant time Byzantine self-stabilizing clock synchronization algorithm by Ben-Or, Dolev and Hoch (Proceedings of the 27th Annual ACM SIGACT-SIGOPS symposium on principles of distributed computing, (PODC), 2008). The application of our scheme results in the first constant time Byzantine self-stabilizing clock synchronization algorithm that eventually stops using random bits. 相似文献
76.
Lorina Dascal Adi Ditkowski Nir A. Sochen 《Journal of Mathematical Imaging and Vision》2007,29(1):63-77
We analyze the discrete maximum principle for the Beltrami color flow. The Beltrami flow can display linear as well as nonlinear
behavior according to the values of a parameter β, which represents the ratio between spatial and color distances. In general, the standard schemes fail to satisfy the discrete
maximum principle. In this work we show that a nonnegative second order difference scheme can be built for this flow only
for small β, i.e. linear-like diffusion. Since this limitation is too severe, we construct a novel finite difference scheme, which is
not nonnegative and satisfies the discrete maximum principle for all values of β. Numerical results support the analysis.
相似文献
Nir A. Sochen (Corresponding author)Email: |
77.
This paper introduces solo-valency, a variation on the valency proof technique originated by Fischer, Lynch, and Paterson. The new technique focuses on critical
events that influence the responses of solo runs by individual operations, rather than on critical events that influence a
protocol’s single decision value. It allows us to derive lower bounds on the time to perform an operation for lock-free implementations of concurrent objects such as linearizable
queues, stacks, sets, hash tables, counters, approximate agreement, and more. Time is measured as the number of distinct base
objects accessed and the number of stalls caused by contention in accessing memory, incurred by a process as it performs a
single operation. We introduce the influence level metric that quantifies the extent to which the response of a solo execution of one process can be changed by other processes.
We then prove the existence of a relationship between the space complexity, latency, contention and influence level of all
lock-free object implementations. Our results are broad in that they hold for implementations that may use any collection of read-modify-write operations in addition to read and write, and in that they apply even if base objects have
unbounded size.
Part of this work was done while the first author was a graduate student in the Department of Computer Science, Tel-Aviv University.
This work was supported in part by a grant from Sun Microsystems. 相似文献
78.
We initiate a new line of investigation into online property-preserving data reconstruction. Consider a dataset which is assumed to satisfy various (known) structural properties; e.g., it may consist of sorted numbers, or points on a manifold, or vectors in a polyhedral cone, or codewords from an error-correcting code. Because of noise and errors, however, an (unknown) fraction of the data is deemed unsound, i.e., in violation with the expected structural properties. Can one still query into the dataset in an online fashion and be provided data that is always sound? In other words, can one design a filter which, when given a query to any item I in the dataset, returns a sound item J that, although not necessarily in the dataset, differs from I as infrequently as possible. No preprocessing should be allowed and queries should be answered online.We consider the case of a monotone function. Specifically, the dataset encodes a function f:{1,…,n}?? R that is at (unknown) distance ε from monotone, meaning that f can—and must—be modified at ε n places to become monotone.Our main result is a randomized filter that can answer any query in O(log?2 nlog? log?n) time while modifying the function f at only O(ε n) places. The amortized time over n function evaluations is O(log?n). The filter works as stated with probability arbitrarily close to 1. We provide an alternative filter with O(log?n) worst case query time and O(ε nlog?n) function modifications. For reconstructing d-dimensional monotone functions of the form f:{1,…,n} d ? ? R, we present a filter that takes (2 O(d)(log?n)4d?2log?log?n) time per query and modifies at most O(ε n d ) function values (for constant d). 相似文献
79.
Shape-Based Mutual Segmentation 总被引:1,自引:1,他引:0
Tammy Riklin-Raviv Nir Sochen Nahum Kiryati 《International Journal of Computer Vision》2008,79(3):231-245
We present a novel variational approach for simultaneous segmentation of two images of the same object taken from different viewpoints. Due to noise, clutter and occlusions, neither of the images contains
sufficient information for correct object-background partitioning. The evolving object contour in each image provides a dynamic
prior for the segmentation of the other object view. We call this process mutual segmentation. The foundation of the proposed method is a unified level-set framework for region and edge based segmentation, associated
with a shape similarity term. The suggested shape term incorporates the semantic knowledge gained in the segmentation process
of the image pair, accounting for excess or deficient parts in the estimated object shape. Transformations, including planar
projectivities, between the object views are accommodated by a registration process held concurrently with the segmentation.
The proposed segmentation algorithm is demonstrated on a variety of image pairs. The homography between each of the image
pairs is estimated and its accuracy is evaluated. 相似文献
80.
Patrice Godefroid Nir Piterman 《International Journal on Software Tools for Technology Transfer (STTT)》2011,13(6):571-584
Given a 3-valued abstraction of a program (possibly generated using static program analysis and predicate abstraction) and
a temporal logic formula, generalized model checking (GMC) checks whether there exists a concretization of that abstraction
that satisfies the formula. In this paper, we revisit generalized model checking for linear time (LTL) properties. First,
we show that LTL GMC is 2EXPTIME-complete in the size of the formula and polynomial in the model, where the degree of the
polynomial depends on the formula, instead of EXPTIME-complete and quadratic as previously believed. The standard definition
of GMC depends on a definition of concretization which is tailored for branching-time model checking. We then study a simpler
linear completeness preorder for relating program abstractions. We show that LTL GMC with this weaker preorder is only EXPSPACE-complete in the size of
the formula, and can be solved in linear time and logarithmic space in the size of the model. Finally, we identify classes
of formulas for which the model complexity of standard GMC is reduced. 相似文献