5,346 research outputs found
Innovative concepts for aerodynamic control of wind turbine rotors
New systems for the aerodynamic control of wind turbine rotors are being studied in various projects funded by the UK Department of Energy. Results from a current project, ongoing at the National Wind Turbine Test Centre (NWTC) in Scotland are presented. These systems show the promise of much cheaper and more affective active control of horizontal axis wind turbines than has been achieved with full span and partial span pitching systems
Bone marrow senescence and the microenvironment of hematological malignancies
Senescence is the irreversible arrest of cell proliferation that has now been shown to play an important role in both health and disease. With increasing age senescent cells accumulate throughout the body, including the bone marrow and this has been associated with a number of age-related pathologies including malignancies. It has been shown that the senescence associated secretory phenotype (SASP) creates a pro-tumoural environment that supports proliferation and survival of malignant cells. Understanding the role of senescent cells in tumor development better may help us to identify new treatment targets to impair tumor survival and reduce treatment resistance. In this review, we will specifically discuss the role of senescence in the aging bone marrow (BM) microenvironment. Many BM disorders are age-related diseases and highly dependent on the BM microenvironment. Despite advances in drug development the prognosis particularly for older patients remains poor and new treatment approaches are needed to improve outcomes for patients. In this review, we will focus on the relationship of senescence and hematological malignancies, how senescence promotes cancer development and how malignant cells induce senescence
Magnetic phase transitions in Ta/CoFeB/MgO multilayers
We study thin films and magnetic tunnel junction nanopillars based on
Ta/CoFeB/MgO multilayers by electrical transport and
magnetometry measurements. These measurements suggest that an ultrathin
magnetic oxide layer forms at the CoFeB/MgO interface. At
approximately 160 K, the oxide undergoes a phase transition from an insulating
antiferromagnet at low temperatures to a conductive weak ferromagnet at high
temperatures. This interfacial magnetic oxide is expected to have significant
impact on the magnetic properties of CoFeB-based multilayers used in spin
torque memories
The Inherent Structure Landscape Connection Between Liquids, Granular materials and the Jamming Phase Diagram
We provide a comprehensive picture of the jamming phase diagram by connecting
the athermal, granular ensemble of jammed states and the equilibrium fluid
through the inherent structure paradigm for a system hard discs confined to a
narrow channel. The J-line is shown to be divided into packings that are
thermodynamically accessible from the equilibrium fluid and inaccessible
packings. The J-point is found to occur at the transition between these two
sets of packings and is located at the maximum the inherent structure
distribution. A general thermodynamic argument suggests that the density of the
states at the configurational entropy maximum represents a lower bound on the
J-point density in hard sphere systems. Finally, we find that the granular and
fluid systems only occupy the same set of inherent structures, under the same
thermodynamic conditions, at two points, corresponding to zero and infinite
pressures, where they sample the J-point states and the most dense packing
respectively.Comment: 5 pages, 3 Figure
"Swarm relaxation": Equilibrating a large ensemble of computer simulations
It is common practice in molecular dynamics and Monte Carlo computer
simulations to run multiple, separately-initialized simulations in order to
improve the sampling of independent microstates. Here we examine the utility of
an extreme case of this strategy, in which we run a large ensemble of
independent simulations (a "swarm"), each of which is relaxed to equilibrium.
We show that if is of order , we can monitor the swarm's relaxation
to equilibrium, and confirm its attainment, within , where
is the equilibrium relaxation time. As soon as a swarm of this size
attains equilibrium, the ensemble of final microstates from each run is
sufficient for the evaluation of most equilibrium properties without further
sampling. This approach dramatically reduces the wall-clock time required,
compared to a single long simulation, by a factor of several hundred, at the
cost of an increase in the total computational effort by a small factor. It is
also well-suited to modern computing systems having thousands of processors,
and is a viable strategy for simulation studies that need to produce
high-precision results in a minimum of wall-clock time. We present results
obtained by applying this approach to several test cases.Comment: 12 pages. To appear in Eur. Phy. J. E, 201
Impact of generalized benefit functions on the evolution of cooperation in spatial public goods games with continuous strategies
Cooperation and defection may be considered as two extreme responses to a
social dilemma. Yet the reality is much less clear-cut. Between the two
extremes lies an interval of ambivalent choices, which may be captured
theoretically by means of continuous strategies defining the extent of the
contributions of each individual player to the common pool. If strategies are
chosen from the unit interval, where 0 corresponds to pure defection and 1
corresponds to the maximal contribution, the question is what is the
characteristic level of individual investments to the common pool that emerges
if the evolution is guided by different benefit functions. Here we consider the
steepness and the threshold as two parameters defining an array of generalized
benefit functions, and we show that in a structured population there exist
intermediate values of both at which the collective contributions are maximal.
However, as the cost-to-benefit ratio of cooperation increases the
characteristic threshold decreases, while the corresponding steepness
increases. Our observations remain valid if more complex sigmoid functions are
used, thus reenforcing the importance of carefully adjusted benefits for high
levels of public cooperation.Comment: 8 two-column pages, 8 figures; accepted for publication in Physical
Review
Correlation of Positive and Negative Reciprocity Fails to Confer an Evolutionary Advantage: Phase Transitions to Elementary Strategies
Economic experiments reveal that humans value cooperation and fairness. Punishing unfair behavior is therefore common, and according to the theory of strong reciprocity, it is also directly related to rewarding cooperative behavior. However, empirical data fail to confirm that positive and negative reciprocity are correlated. Inspired by this disagreement, we determine whether the combined application of reward and punishment is evolutionarily advantageous. We study a spatial public goods game, where in addition to the three elementary strategies of defection, rewarding, and punishment, a fourth strategy that combines the latter two competes for space. We find rich dynamical behavior that gives rise to intricate phase diagrams where continuous and discontinuous phase transitions occur in succession. Indirect territorial competition, spontaneous emergence of cyclic dominance, as well as divergent fluctuations of oscillations that terminate in an absorbing phase are observed. Yet, despite the high complexity of solutions, the combined strategy can survive only in very narrow and unrealistic parameter regions. Elementary strategies, either in pure or mixed phases, are much more common and likely to prevail. Our results highlight the importance of patterns and structure in human cooperation, which should be considered in future experiments
Magnetic Mineral Populations in Lower Oceanic Crustal Gabbros (Atlantis Bank, SW Indian Ridge): Implications for Marine Magnetic Anomalies
To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly \u3c1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank
Asymptotically optimal quantum channel reversal for qudit ensembles and multimode Gaussian states
We investigate the problem of optimally reversing the action of an arbitrary
quantum channel C which acts independently on each component of an ensemble of
n identically prepared d-dimensional quantum systems. In the limit of large
ensembles, we construct the optimal reversing channel R* which has to be
applied at the output ensemble state, to retrieve a smaller ensemble of m
systems prepared in the input state, with the highest possible rate m/n. The
solution is found by mapping the problem into the optimal reversal of Gaussian
channels on quantum-classical continuous variable systems, which is here solved
as well. Our general results can be readily applied to improve the
implementation of robust long-distance quantum communication. As an example, we
investigate the optimal reversal rate of phase flip channels acting on a
multi-qubit register.Comment: 17 pages, 3 figure
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