756 research outputs found
Universal Wait-Free Memory Reclamation
In this paper, we present a universal memory reclamation scheme, Wait-Free
Eras (WFE), for deleted memory blocks in wait-free concurrent data structures.
WFE's key innovation is that it is completely wait-free. Although some prior
techniques provide similar guarantees for certain data structures, they lack
support for arbitrary wait-free data structures. Consequently, developers are
typically forced to marry their wait-free data structures with lock-free Hazard
Pointers or (potentially blocking) epoch-based memory reclamation. Since both
these schemes provide weaker progress guarantees, they essentially forfeit the
strong progress guarantee of wait-free data structures. Though making the
original Hazard Pointers scheme or epoch-based reclamation completely wait-free
seems infeasible, we achieved this goal with a more recent, (lock-free) Hazard
Eras scheme, which we extend to guarantee wait-freedom. As this extension is
non-trivial, we discuss all challenges pertaining to the construction of
universal wait-free memory reclamation.
WFE is implementable on ubiquitous x86_64 and AArch64 (ARM) architectures.
Its API is mostly compatible with Hazard Pointers, which allows easy
transitioning of existing data structures into WFE. Our experimental
evaluations show that WFE's performance is close to epoch-based reclamation and
almost matches the original Hazard Eras scheme, while providing the stronger
wait-free progress guarantee
Quantum dynamics of the avian compass
The ability of migratory birds to orient relative to the Earth's magnetic
field is believed to involve a coherent superposition of two spin states of a
radical electron pair. However, the mechanism by which this coherence can be
maintained in the face of strong interactions with the cellular environment has
remained unclear. This Letter addresses the problem of decoherence between two
electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei.
Dynamics of the radical pair density matrix are derived and shown to yield a
simple mechanism for sensing magnetic field orientation. Rates of dephasing and
decoherence are calculated ab initio and found to yield millisecond coherence
times, consistent with behavioral experiments
Workplace Bullying, Perceived Job Stressors, and Psychological Distress: Gender and Race Differences in the Stress Process
A large body of empirical research documents the adverse mental health consequences of workplace bullying. However, less is known about gender and race differences in the processes that link workplace bullying and poor mental health. In the current study, we use structural equation modeling of survey data from the 2010 Health and Retirement Study (N ¼ 2292) and draw on stress process theory to examine coworker support as a buffering mechanism against workplace bullying, and gender and race differences in the relationships between bullying and psychological distress. The results of the analysis indicate that coworker support serves as a protective buffer against workplace bullying, although the buffering effect is relatively small. We also find that the effects of workplace bullying more heavily impact women and persons of color. Specifically, women and African American individuals in our sample were less protected from the buffering mechanism of co-worker social support
The statistical properties of the city transport in Cuernavaca (Mexico) and Random matrix ensembles
We analyze statistical properties of the city bus transport in Cuernavaca
(Mexico) and show that the bus arrivals display probability distributions
conforming those given by the Unitary Ensemble of random matrices.Comment: 4 pages, 3 figure
Impact of Transcendental Meditation on Left Ventricular Mass in African American Adolescents
Background. An early sign of ventricular remodeling is increased left ventricular mass (LVM) which over time may lead to left ventricular hypertrophy, the strongest predictor of cardiovascular morbidity and mortality, other than advancing age. Methods. 62 (30 TM; 32 CTL) African American adolescents (age 16.2 ± 1.3 years) with high normal systolic BP were randomly assigned to either 4-month Transcendental Meditation (TM) or health education control groups. The echocardiographic-derived measure of LVM index (LVMI = LVM/ht2.7) was measured before and after the 4-month TM study and at 4-month followup. 2D-guided M-mode echocardiography using a Hewlett Packard 5500 echosonograph was used to determine LVMI. Results. The TM group exhibited a greater decrease in LVMI at 4-month followup compared to the CTL group (−2.6 versus +0.3 gm/ht2.7, P < 0.04). The TM group exhibited a lesser increase in BMI at 4-month follow-up compared to the CTL group (0.2 ± 1.6 versus 1.1 ± 1.4, P < 0.03). Conclusion. These findings indicate that among a group of prehypertensive African American adolescents, 4 months of TM compared to heath education resulted in a significant decrease in LVMI, and these changes were maintained at 4-month follow-up
Can Situational Action Theory Explain the Gender Gap in Adolescent Shoplifting? Results From Austria
Although shoplifting is one of the crimes with the smallest gender gap among all offense types, most studies still conclude that males steal from shops more frequently than females. The roots of the gendered distribution of shoplifting have not yet been satisfactorily explained. This work investigates whether situational action theory (SAT) can account for males’ greater involvement in shoplifting compared to females and if the propensity–exposure interaction that is at the heart of the theory applies to both genders. Results from a large-scale student survey conducted in Austria suggest that SAT generalizes to both genders and that it is well suited to explain why males are more likely to shoplift than females.The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The research underlying this article was funded under grant no. SPA03–56 by the Sparkling Science Research Program of the Austrian Federal Ministry of Science and Research
The Effect of absorbing sites on the one-dimensional cellular automaton traffic flow with open boundaries
The effect of the absorbing sites with an absorbing rate , in both
one absorbing site (one way out) and two absorbing sites (two ways out) in a
road, on the traffic flow phase transition is investigated using numerical
simulations in the one-dimensional cellular automaton traffic flow model with
open boundaries using parallel dynamics.In the case of one way out, there exist
a critical position of the way out below which the current is
constant for and decreases when increasing
for . When the way out is located at a
position greater than , the current increases with for
and becomes constant for any value of
greater than . While, when the way out is located at any position
between and (), the current increases,
for , with and becomes constant for
and decreases with for
. In the later case the density undergoes two
successive first order transitions; from high density to maximal current phase
at and from intermediate density to the low one at
. In the case of two ways out located respectively
at the positions and , the two successive transitions occur
only when the distance - separating the two ways is smaller than
a critical distance . Phase diagrams in the (),
() and () planes are established. It is found
that the transitions between Free traffic, Congested traffic and maximal
current phase are first order
Temporal Modulation of the Control Parameter in Electroconvection in the Nematic Liquid Crystal I52
I report on the effects of a periodic modulation of the control parameter on
electroconvection in the nematic liquid crystal I52. Without modulation, the
primary bifurcation from the uniform state is a direct transition to a state of
spatiotemporal chaos. This state is the result of the interaction of four,
degenerate traveling modes: right and left zig and zag rolls. Periodic
modulations of the driving voltage at approximately twice the traveling
frequency are used. For a large enough modulation amplitude, standing waves
that consist of only zig or zag rolls are stabilized. The standing waves
exhibit regular behavior in space and time. Therefore, modulation of the
control parameter represents a method of eliminating spatiotemporal chaos. As
the modulation frequency is varied away from twice the traveling frequency,
standing waves that are a superposition of zig and zag rolls, i.e. standing
rectangles, are observed. These results are compared with existing predictions
based on coupled complex Ginzburg-Landau equations
Towards a Macroscopic Modelling of the Complexity in Traffic Flow
We present a macroscopic traffic flow model that extends existing fluid-like
models by an additional term containing the second derivative of the safe
velocity. Two qualitatively different shapes of the safe velocity are explored:
a conventional Fermi-type function and a function exhibiting a plateau at
intermediate densities. The suggested model shows an extremely rich dynamical
behaviour and shows many features found in real-world traffic data.Comment: submitted to Phys. Rev.
Life events and hemodynamic stress reactivity in the middle-aged and elderly
Recent versions of the reactivity hypothesis, which consider it to be the product of stress exposure and exaggerated haemodynamic reactions to stress that confers cardiovascular disease risk, assume that reactivity is independent of the experience of stressful life events. This assumption was tested in two substantial cohorts, one middle-aged and one elderly. Participants had to indicate from a list of major stressful life events up to six they had experienced in the previous two years. They were also asked to rate how disruptive and stressful they were, at the time of occurrence and now. Blood pressure and pulse rate were measured at rest and in response to acute mental stress. Those who rated the events as highly disruptive at the time of exposure and currently exhibited blunted systolic blood pressure reactions to acute stress. The present results suggest that acute stress reactivity may not be independent of stressful life events experience
- …