TY - JOUR AB - The reaction between NiO and (0001)- and ([1\bar102])-oriented Al2O3 single crystals has been investigated on model experimental systems by using the ReflEXAFS technique. Depth-sensitive information is obtained by collecting data above and below the critical angle for total reflection. A systematic protocol for data analysis, based on the recently developed CARD code, was implemented, and a detailed description of the reactive systems was obtained. In particular, for ([1\bar102])-oriented Al2O3, the reaction with NiO is almost complete after heating for 6 h at 1273 K, and an almost uniform layer of spinel is found below a mixed (NiO + spinel) layer at the very upmost part of the sample. In the case of the (0001)-oriented Al2O3, for the same temperature and heating time, the reaction shows a lower advancement degree and a residual fraction of at least 30% NiO is detected in the ReflEXAFS spectra. AU - Costanzo, Tommaso AU - Benzi, Federico AU - Ghigna, Paolo AU - Pin, Sonia AU - Spinolo, Giorgio AU - d'Acapito, Francesco ID - 7455 IS - 2 JF - Journal of Synchrotron Radiation SN - 1600-5775 TI - Studying the surface reaction between NiO and Al2O3viatotal reflection EXAFS (ReflEXAFS) VL - 21 ER - TY - JOUR AU - Tan, Shutang AU - Xue, Hong-Wei ID - 7598 IS - 5 JF - Cell Reports SN - 2211-1247 TI - Casein kinase 1 regulates ethylene synthesis by phosphorylating and promoting the turnover of ACS5 VL - 9 ER - TY - CONF AB - Task allocation is a classic distributed problem in which a set of p potentially faulty processes must cooperate to perform a set of tasks. This paper considers a new dynamic version of the problem, in which tasks are injected adversarially during an asynchronous execution. We give the first asynchronous shared-memory algorithm for dynamic task allocation, and we prove that our solution is optimal within logarithmic factors. The main algorithmic idea is a randomized concurrent data structure called a dynamic to-do tree, which allows processes to pick new tasks to perform at random from the set of available tasks, and to insert tasks at random empty locations in the data structure. Our analysis shows that these properties avoid duplicating work unnecessarily. On the other hand, since the adversary controls the input as well the scheduling, it can induce executions where lots of processes contend for a few available tasks, which is inefficient. However, we prove that every algorithm has the same problem: given an arbitrary input, if OPT is the worst-case complexity of the optimal algorithm on that input, then the expected work complexity of our algorithm on the same input is O(OPT log3 m), where m is an upper bound on the number of tasks that are present in the system at any given time. AU - Alistarh, Dan-Adrian AU - Aspnes, James AU - Bender, Michael AU - Gelashvili, Rati AU - Gilbert, Seth ID - 768 TI - Dynamic task allocation in asynchronous shared memory ER - TY - JOUR AB - This article presents the first tight bounds on the time complexity of shared-memory renaming, a fundamental problem in distributed computing in which a set of processes need to pick distinct identifiers from a small namespace. We first prove an individual lower bound of ω(k) process steps for deterministic renaming into any namespace of size subexponential in k, where k is the number of participants. The bound is tight: it draws an exponential separation between deterministic and randomized solutions, and implies new tight bounds for deterministic concurrent fetch-and-increment counters, queues, and stacks. The proof is based on a new reduction from renaming to another fundamental problem in distributed computing: mutual exclusion. We complement this individual bound with a global lower bound of ω(klog(k/c)) on the total step complexity of renaming into a namespace of size ck, for any c = 1. This result applies to randomized algorithms against a strong adversary, and helps derive new global lower bounds for randomized approximate counter implementations, that are tight within logarithmic factors. On the algorithmic side, we give a protocol that transforms any sorting network into a randomized strong adaptive renaming algorithm, with expected cost equal to the depth of the sorting network. This gives a tight adaptive renaming algorithm with expected step complexity O(log k), where k is the contention in the current execution. This algorithm is the first to achieve sublinear time, and it is time-optimal as per our randomized lower bound. Finally, we use this renaming protocol to build monotone-consistent counters with logarithmic step complexity and linearizable fetch-and-increment registers with polylogarithmic cost. AU - Alistarh, Dan-Adrian AU - Aspnes, James AU - Censor Hillel, Keren AU - Gilbert, Seth AU - Guerraoui, Rachid ID - 769 IS - 3 JF - Journal of the ACM TI - Tight bounds for asynchronous renaming VL - 61 ER - TY - CONF AB - Dynamic memory reclamation is arguably the biggest open problem in concurrent data structure design: All known solutions induce high overhead, or must be customized to the specific data structure by the programmer, or both. This paper presents StackTrack, the first concurrent memory reclamation scheme that can be applied automatically by a compiler, while maintaining efficiency. StackTrack eliminates most of the expensive bookkeeping required for memory reclamation by leveraging the power of hardware transactional memory (HTM) in a new way: it tracks thread variables dynamically, and in an atomic fashion. This effectively makes all memory references visible without having threads pay the overhead of writing out this information. Our empirical results show that this new approach matches or outperforms prior, non-automated, techniques. AU - Alistarh, Dan-Adrian AU - Eugster, Patrick AU - Herlihy, Maurice AU - Matveev, Alexander AU - Shavit, Nir ID - 770 TI - StackTrack: An automated transactional approach to concurrent memory reclamation ER - TY - CONF AB - We consider the following natural problem: n failure-prone servers, communicating synchronously through message passing, must assign themselves one-to-one to n distinct items. Existing literature suggests two possible approaches to this problem. First, model it as an instance of tight renaming in synchronous message-passing systems; for deterministic solutions, a tight bound of ©(logn) communication rounds is known. Second, model the scenario as an instance of randomized load-balancing, for which elegant sub-logarithmic solutions exist. However, careful examination reveals that known load-balancing schemes do not apply to our scenario, because they either do not tolerate faults or do not ensure one-to-one allocation. It is thus natural to ask if sublogarithmic solutions exist for this apparently simple but intriguing problem. In this paper, we combine the two approaches to provide a new randomized solution for tight renaming, which terminates in O (log log n) communication rounds with high probability, against a strong adaptive adversary. Our solution, called Balls-into-Leaves, combines the deterministic approach with a new randomized scheme to obtain perfectly balanced allocations. The algorithm arranges the items as leaves of a tree, and participants repeatedly perform random choices among the leaves. The algorithm exchanges information in each round to split the participants into progressively smaller groups whose random choices do not conflict. We then extend the algorithm to terminate early in O(log log) rounds w.h.p., where is the actual number of failures. These results imply an exponential separation between deterministic and randomized algorithms for the tight renaming problem in message-passing systems. AU - Alistarh, Dan-Adrian AU - Denysyuk, Oksana AU - Rodrígues, Luís AU - Shavit, Nir ID - 771 TI - Balls-into-Leaves: Sub-logarithmic renaming in synchronous message-passing systems ER - TY - CONF AB - Lock-free concurrent algorithms guarantee that some concurrent operation will always make progress in a finite number of steps. Yet programmers prefer to treat concurrent code as if it were wait-free, guaranteeing that all operations always make progress. Unfortunately, designing wait-free algorithms is generally a very complex task, and the resulting algorithms are not always efficient. While obtaining efficient wait-free algorithms has been a long-time goal for the theory community, most non-blocking commercial code is only lock-free. This paper suggests a simple solution to this problem. We show that, for a large class of lock-free algorithms, under scheduling conditions which approximate those found in commercial hardware architectures, lock-free algorithms behave as if they are wait-free. In other words, programmers can keep on designing simple lock-free algorithms instead of complex wait-free ones, and in practice, they will get wait-free progress. Our main contribution is a new way of analyzing a general class of lock-free algorithms under a stochastic scheduler. Our analysis relates the individual performance of processes with the global performance of the system using Markov chain lifting between a complex per-process chain and a simpler system progress chain. We show that lock-free algorithms are not only wait-free with probability 1, but that in fact a general subset of lock-free algorithms can be closely bounded in terms of the average number of steps required until an operation completes. To the best of our knowledge, this is the first attempt to analyze progress conditions, typically stated in relation to a worst case adversary, in a stochastic model capturing their expected asymptotic behavior. AU - Alistarh, Dan-Adrian AU - Censor Hillel, Keren AU - Shavit, Nir ID - 772 TI - Are lock-free concurrent algorithms practically wait-free? ER - TY - CONF AB - We describe a new randomized consensus protocol with expected message complexity O(n2log2n) when fewer than n/2 processes may fail by crashing. This is an almost-linear improvement over the best previously known protocol, and within logarithmic factors of a known Ω(n2) message lower bound. The protocol further ensures that no process sends more than O(n log3n) messages in expectation, which is again within logarithmic factors of optimal.We also present a generalization of the algorithm to an arbitrary number of failures t, which uses expected O(nt + t2log2t) total messages. Our protocol uses messages of size O(log n), and can therefore scale to large networks. We consider the problem of consensus in the challenging classic model. In this model, the adversary is adaptive; it can choose which processors crash at any point during the course of the algorithm. Further, communication is via asynchronous message passing: there is no known upper bound on the time to send a message from one processor to another, and all messages and coin flips are seen by the adversary. Our approach is to build a message-efficient, resilient mechanism for aggregating individual processor votes, implementing the message-passing equivalent of a weak shared coin. Roughly, in our protocol, a processor first announces its votes to small groups, then propagates them to increasingly larger groups as it generates more and more votes. To bound the number of messages that an individual process might have to send or receive, the protocol progressively increases the weight of generated votes. The main technical challenge is bounding the impact of votes that are still “in flight” (generated, but not fully propagated) on the final outcome of the shared coin, especially since such votes might have different weights. We achieve this by leveraging the structure of the algorithm, and a technical argument based on martingale concentration bounds. Overall, we show that it is possible to build an efficient message-passing implementation of a shared coin, and in the process (almost-optimally) solve the classic consensus problem in the asynchronous message-passing model. AU - Alistarh, Dan-Adrian AU - Aspnes, James AU - King, Valerie AU - Saia, Jared ED - Kuhn, Fabian ID - 773 TI - Communication-efficient randomized consensus VL - 8784 ER - TY - CONF AB - Lock-free concurrent algorithms guarantee that some concurrent operation will always make progress in a finite number of steps. Yet programmers would prefer to treat concurrent code as if it were wait-free, guaranteeing that all operations always make progress. Unfortunately, designing wait-free algorithms is in general a complex undertaking, and the resulting algorithms are not always efficient, so most non-blocking commercial code is only lock-free, and the design of efficient wait-free algorithms has been left to the academic community. In [2], we suggest a solution to this problem. We show that, for a large class of lock-free algorithms, under scheduling conditions which approximate those found in commercial hardware architectures, lock-free algorithms behave as if they are wait-free. In other words, programmers can keep on designing simple lock-free algorithms instead of complex wait-free ones, and in practice, they will get wait-free progress. Our main contribution is a new way of analyzing a general class of lock-free algorithms under a stochastic scheduler. Our analysis relates the individual performance of processes with the global performance of the system using Markov chain lifting between a complex per-process chain and a simpler system progress chain. We show that lock-free algorithms are not only wait-free with probability 1, but that in fact a broad subset of lock-free algorithms can be closely bounded in terms of the average number of steps required until an operation completes. AU - Alistarh, Dan-Adrian AU - Censor Hille, Keren AU - Shavit, Nir ID - 774 TI - Brief announcement: Are lock-free concurrent algorithms practically wait-free? ER - TY - CONF AB - The long-lived renaming problem appears in shared-memory systems where a set of threads need to register and deregister frequently from the computation, while concurrent operations scan the set of currently registered threads. Instances of this problem show up in concurrent implementations of transactional memory, flat combining, thread barriers, and memory reclamation schemes for lock-free data structures. In this paper, we analyze a randomized solution for long-lived renaming. The algorithmic technique we consider, called the Level Array, has previously been used for hashing and one-shot (single-use) renaming. Our main contribution is to prove that, in long-lived executions, where processes may register and deregister polynomially many times, the technique guarantees constant steps on average and O (log log n) steps with high probability for registering, unit cost for deregistering, and O (n) steps for collect queries, where n is an upper bound on the number of processes that may be active at any point in time. We also show that the algorithm has the surprising property that it is self-healing: under reasonable assumptions on the schedule, operations running while the data structure is in a degraded state implicitly help the data structure re-balance itself. This subtle mechanism obviates the need for expensive periodic rebuilding procedures. Our benchmarks validate this approach, showing that, for typical use parameters, the average number of steps a process takes to register is less than two and the worst-case number of steps is bounded by six, even in executions with billions of operations. We contrast this with other randomized implementations, whose worst-case behavior we show to be unreliable, and with deterministic implementations, whose cost is linear in n. AU - Alistarh, Dan-Adrian AU - Kopinsky, Justin AU - Matveev, Alexander AU - Shavit, Nir ID - 775 TI - The levelarray: A fast, practical long-lived renaming algorithm ER - TY - CHAP AB - Experimental studies have demonstrated that environmental variation can create genotype‐environment interactions (GEIs) in the traits involved in sexual selection. Understanding the genetic architecture of phenotype across environments will require statistical tests that can describe both changes in genetic variance and covariance across environments. This chapter outlines the theoretical framework for the processes of sexual selection in the wild, identifying key parameters in wild systems, and highlighting the potential effects of the environment. It describes the proposed approaches for the estimation of these key parameters in a quantitative genetic framework within naturally occurring pedigreed populations. The chapter provides a worked example for a range of analysis methods. It aims to provide an overview of the analytical methods that can be used to model GEIs for traits involved in sexual selection in naturally occurring pedigreed populations. AU - Robinson, Matthew Richard AU - Qvarnström, Anna ED - Hunt, John ED - Hosken, David ID - 7743 SN - 9780470671795 T2 - Genotype-by-Environment Interactions and Sexual Selection TI - Influence of the environment on the genetic architecture of traits involved in sexual selection within wild populations ER - TY - JOUR AU - Robinson, Matthew Richard AU - Wray, Naomi R. AU - Visscher, Peter M. ID - 7744 IS - 4 JF - Trends in Genetics SN - 0168-9525 TI - Explaining additional genetic variation in complex traits VL - 30 ER - TY - JOUR AB - We investigate the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions as a function of packing fraction. Certain properties of the vibrational density of states (vDOS) are shown to correlate with the density and structure of the samples (i.e., in sparsely versus densely packed samples). Specifically, a crossover from dense glassy to sparse gel-like states is suggested by an excess of phonon modes at low frequency and by a variation in the slope of the vDOS with frequency at low frequency. This change in phonon mode distribution is demonstrated to arise largely from localized vibrations that involve individual and/or small clusters of particles with few local bonds. Conventional order parameters and void statistics did not exhibit obvious gel-glass signatures as a function of volume fraction. These mode behaviors and accompanying structural insights offer a potentially new set of indicators for identification of glass-gel transitions and for assignment of gel-like versus glass-like character to a disordered solid material. AU - Lohr, Matthew A. AU - Still, Tim AU - Ganti, Raman AU - Gratale, Matthew D. AU - Davidson, Zoey S. AU - Aptowicz, Kevin B. AU - Goodrich, Carl Peter AU - Sussman, Daniel M. AU - Yodh, A. G. ID - 7768 IS - 6 JF - Physical Review E SN - 1539-3755 TI - Vibrational and structural signatures of the crossover between dense glassy and sparse gel-like attractive colloidal packings VL - 90 ER - TY - JOUR AB - In their Letter, Schreck, Bertrand, O'Hern and Shattuck [Phys. Rev. Lett. 107, 078301 (2011)] study nonlinearities in jammed particulate systems that arise when contacts are altered. They conclude that there is "no harmonic regime in the large system limit for all compressions" and "at jamming onset for any system size." Their argument rests on the claim that for finite-range repulsive potentials, of the form used in studies of jamming, the breaking or forming of a single contact is sufficient to destroy the linear regime. We dispute these conclusions and argue that linear response is both justified and essential for understanding the nature of the jammed solid. AU - Goodrich, Carl Peter AU - Liu, Andrea J. AU - Nagel, Sidney R. ID - 7771 IS - 4 JF - Physical Review Letters SN - 0031-9007 TI - Comment on “Repulsive contact interactions make jammed particulate systems inherently nonharmonic” VL - 112 ER - TY - JOUR AB - Particle tracking and displacement covariance matrix techniques are employed to investigate the phonon dispersion relations of two-dimensional colloidal glasses composed of soft, thermoresponsive microgel particles whose temperature-sensitive size permits in situ variation of particle packing fraction. Bulk, B, and shear, G, moduli of the colloidal glasses are extracted from the dispersion relations as a function of packing fraction, and variation of the ratio G/B with packing fraction is found to agree quantitatively with predictions for jammed packings of frictional soft particles. In addition, G and B individually agree with numerical predictions for frictional particles. This remarkable level of agreement enabled us to extract an energy scale for the interparticle interaction from the individual elastic constants and to derive an approximate estimate for the interparticle friction coefficient. AU - Still, Tim AU - Goodrich, Carl Peter AU - Chen, Ke AU - Yunker, Peter J. AU - Schoenholz, Samuel AU - Liu, Andrea J. AU - Yodh, A. G. ID - 7772 IS - 1 JF - Physical Review E SN - 1539-3755 TI - Phonon dispersion and elastic moduli of two-dimensional disordered colloidal packings of soft particles with frictional interactions VL - 89 ER - TY - JOUR AB - For more than a century, physicists have described real solids in terms of perturbations about perfect crystalline order1. Such an approach takes us only so far: a glass, another ubiquitous form of rigid matter, cannot be described in any meaningful sense as a defected crystal2. Is there an opposite extreme to a crystal—a solid with complete disorder—that forms an alternative starting point for understanding real materials? Here, we argue that the solid comprising particles with finite-ranged interactions at the jamming transition3,4,5 constitutes such a limit. It has been shown that the physics associated with this transition can be extended to interactions that are long ranged6. We demonstrate that jamming physics is not restricted to amorphous systems, but dominates the behaviour of solids with surprisingly high order. Just as the free-electron and tight-binding models represent two idealized cases from which to understand electronic structure1, we identify two extreme limits of mechanical behaviour. Thus, the physics of jamming can be set side by side with the physics of crystals to provide an organizing structure for understanding the mechanical properties of solids over the entire spectrum of disorder. AU - Goodrich, Carl Peter AU - Liu, Andrea J. AU - Nagel, Sidney R. ID - 7773 IS - 8 JF - Nature Physics SN - 1745-2473 TI - Solids between the mechanical extremes of order and disorder VL - 10 ER - TY - JOUR AB - Athermal packings of soft repulsive spheres exhibit a sharp jamming transition in the thermodynamic limit. Upon further compression, various structural and mechanical properties display clean power-law behavior over many decades in pressure. As with any phase transition, the rounding of such behavior in finite systems close to the transition plays an important role in understanding the nature of the transition itself. The situation for jamming is surprisingly rich: the assumption that jammed packings are isotropic is only strictly true in the large-size limit, and finite-size has a profound effect on the very meaning of jamming. Here, we provide a comprehensive numerical study of finite-size effects in sphere packings above the jamming transition, focusing on stability as well as the scaling of the contact number and the elastic response. AU - Goodrich, Carl Peter AU - Dagois-Bohy, Simon AU - Tighe, Brian P. AU - van Hecke, Martin AU - Liu, Andrea J. AU - Nagel, Sidney R. ID - 7769 IS - 2 JF - Physical Review E SN - 1539-3755 TI - Jamming in finite systems: Stability, anisotropy, fluctuations, and scaling VL - 90 ER - TY - JOUR AB - Packings of frictionless athermal particles that interact only when they overlap experience a jamming transition as a function of packing density. Such packings provide the foundation for the theory of jamming. This theory rests on the observation that, despite the multitude of disordered configurations, the mechanical response to linear order depends only on the distance to the transition. We investigate the validity and utility of such measurements that invoke the harmonic approximation and show that, despite particles coming in and out of contact, there is a well-defined linear regime in the thermodynamic limit. AU - Goodrich, Carl Peter AU - Liu, Andrea J. AU - Nagel, Sidney R. ID - 7770 IS - 2 JF - Physical Review E SN - 1539-3755 TI - Contact nonlinearities and linear response in jammed particulate packings VL - 90 ER - TY - JOUR AB - Most excitatory inputs in the mammalian brain are made on dendritic spines, rather than on dendritic shafts. Spines compartmentalize calcium, and this biochemical isolation can underlie input-specific synaptic plasticity, providing a raison d'etre for spines. However, recent results indicate that the spine can experience a membrane potential different from that in the parent dendrite, as though the spine neck electrically isolated the spine. Here we use two-photon calcium imaging of mouse neocortical pyramidal neurons to analyze the correlation between the morphologies of spines activated under minimal synaptic stimulation and the excitatory postsynaptic potentials they generate. We find that excitatory postsynaptic potential amplitudes are inversely correlated with spine neck lengths. Furthermore, a spike timing-dependent plasticity protocol, in which two-photon glutamate uncaging over a spine is paired with postsynaptic spikes, produces rapid shrinkage of the spine neck and concomitant increases in the amplitude of the evoked spine potentials. Using numerical simulations, we explore the parameter regimes for the spine neck resistance and synaptic conductance changes necessary to explain our observations. Our data, directly correlating synaptic and morphological plasticity, imply that long-necked spines have small or negligible somatic voltage contributions, but that, upon synaptic stimulation paired with postsynaptic activity, they can shorten their necks and increase synaptic efficacy, thus changing the input/output gain of pyramidal neurons. AU - Araya, R. AU - Vogels, Tim P AU - Yuste, R. ID - 8021 IS - 28 JF - Proceedings of the National Academy of Sciences SN - 0027-8424 TI - Activity-dependent dendritic spine neck changes are correlated with synaptic strength VL - 111 ER - TY - JOUR AB - Uniform random sparse network architectures are ubiquitous in computational neuroscience, but the implicit hypothesis that they are a good representation of real neuronal networks has been met with skepticism. Here we used two experimental data sets, a study of triplet connectivity statistics and a data set measuring neuronal responses to channelrhodopsin stimuli, to evaluate the fidelity of thousands of model networks. Network architectures comprised three neuron types (excitatory, fast spiking, and nonfast spiking inhibitory) and were created from a set of rules that govern the statistics of the resulting connection types. In a high-dimensional parameter scan, we varied the degree distributions (i.e., how many cells each neuron connects with) and the synaptic weight correlations of synapses from or onto the same neuron. These variations converted initially uniform random and homogeneously connected networks, in which every neuron sent and received equal numbers of synapses with equal synaptic strength distributions, to highly heterogeneous networks in which the number of synapses per neuron, as well as average synaptic strength of synapses from or to a neuron were variable. By evaluating the impact of each variable on the network structure and dynamics, and their similarity to the experimental data, we could falsify the uniform random sparse connectivity hypothesis for 7 of 36 connectivity parameters, but we also confirmed the hypothesis in 8 cases. Twenty-one parameters had no substantial impact on the results of the test protocols we used. AU - Tomm, Christian AU - Avermann, Michael AU - Petersen, Carl AU - Gerstner, Wulfram AU - Vogels, Tim P ID - 8023 IS - 8 JF - Journal of Neurophysiology SN - 0022-3077 TI - Connection-type-specific biases make uniform random network models consistent with cortical recordings VL - 112 ER -