17,161 research outputs found
Energy Saving In Data Centers
Globally CO2 emissions attributable to Information Technology are on par with those resulting from aviation. Recent growth in cloud service demand has elevated energy efficiency of data centers to a critical area within green computing. Cloud computing represents a backbone of IT services and recently there has been an increase in high-definition multimedia delivery, which has placed new burdens on energy resources. Hardware innovations together with energy-efficient techniques and algorithms are key to controlling power usage in an ever-expanding IT landscape. This special issue contains a number of contributions that show that data center energy efficiency should be addressed from diverse vantage points. © 2017 by the authors. Licensee MDPI, Basel, Switzerland
Tracing of Neuronal Connections in the Human Brain by Magnetic Resonance Imaging in vivo
Axon degeneration after disruption of fibre tracts in the mammalian nervous system is accompanied by myelin breakdown which leads to changes in its magnetic resonance properties. In two patients with pure motor strokes due to small ischaemic lesions restricted to the internal capsule, magnetic resonance imaging disclosed a narrow band of pathological signal increase descending band-like into the brain stem and ascending to the precentral gyrus, which corresponded to the well-known path of the pyramidal tract. The findings suggest that in man anterograde and possibly retrograde fibre degeneration can be traced in vivo by conventional magnetic resonance imaging techniques. Critical conditions are the presence of small, strategically located lesions, appropriate choice of imaging plane, and the interval between time of lesion and of imaging. This demonstration may open a new era for functional neuroanatomy of man
Monte-Carlo Approach to Calculating the Fragmentation Functions in NJL-Jet Model
Recent studies of the fragmentation functions using the Nambu--Jona-Lasinio
(NJL) - Jet model have been successful in describing the quark fragmentation
functions to pions and kaons. The NJL-Jet model employs the integral equation
approach to solve for the fragmentation functions in quark-cascade description
of the hadron emission process, where one assumes that the initial quark has
infinite momentum and emits an infinite number of hadrons. Here we introduce a
Monte Carlo (MC) simulation method to solve for the fragmentation functions,,
that allows us to relax the above mentioned approximations. We demonstrate that
the results of MC simulations closely reproduce the solutions of the integral
equations in the limit where a large number of hadrons are emitted in the quark
cascade. The MC approach provides a strong foundation for the further
development of the NJL-Jet model that might include many more hadronic emission
channels with decays of the possible produced resonances, as well as inclusion
of the transverse momentum dependence (TMD), all of which are of considerable
importance to the experimental studies of the transverse structure of hadrons.Comment: 5 pages, 3 figures, Proceedings of "TROPICAL QCD II Workshop
Collins Fragmentation Function within NJL-jet Model
The NJL-jet model is extended to accommodate hadronization of a transversely
polarized quark in order to explore the Collins effect within a multihadron
emission framework. This is accomplished by calculating the polarized quark
spin flip probabilities after a pseudoscalar hadron emission and the elementary
Collins functions. The model is used to calculate the number densities of the
hadrons produced in the polarized quark's decay chain. The full Collins
fragmentation function is extracted from the sine modulation of the polarized
number densities with respect to the polar angle between the initial quark's
spin and hadron's transverse momentum. Two cases are studied here. First, a toy
model for elementary Collins function is used to study the features of the
transversely polarized quark-jet model. Second, a full model calculation of
transverse momentum dependent pion and kaon Collins functions is presented. The
remarkable feature of our model is that the 1/2 moments of the favored Collins
fragmentation functions are positive and peak at large values of z but decrease
and oscillate at small values of z. The 1/2 moments of the unfavored Collins
functions have comparable magnitude and opposite sign to the favored functions,
vanish at large z and peak at small values of z. This feature is observed for
both the toy and full models and can be attributed to the quark-jet picture of
hadronization. Moreover, the transverse momentum dependencies of the model
Collins functions differ significantly from the Gaussian form widely used in
the empirical parametrizations. Finally, a naive interpretation of the
Schafer-Teryaev sum rule is proven not to hold in our model, where the
transverse momentum conservation is explicitly enforced. This is attributed to
the sizable average transverse momentum of the remnant quark that needs to be
accounted for to satisfy the transverse momentum sum-rule.Comment: 15 pages, 22 figures. v2 - minor changes/additions to conform to the
journal published versio
Energy Efficiency and Renewable Energy Management with Multi-State Power-Down Systems
A power-down system has an on-state, an off-state, and a finite or infinite number of intermediate states. In the off-state, the system uses no energy and in the on-state energy it is used fully. Intermediate states consume only some fraction of energy but switching back to the on-state comes at a cost. Previous work has mainly focused on asymptotic results for systems with a large number of states. In contrast, the authors study problems with a few states as well as systems with one continuous state. Such systems play a role in energy-efficiency for information technology but are especially important in the management of renewable energy. The authors analyze power-down problems in the framework of online competitive analysis as to obtain performance guarantees in the absence of reliable forecasting. In a discrete case, the authors give detailed results for the case of three and five states, which corresponds to a system with on-off states and three additional intermediate states “power save”, “suspend”, and “hibernate”. The authors use a novel balancing technique to obtain optimally competitive solutions. With this, the authors show that the overall best competitive ratio for three-state systems is 95 role= presentation style= box-sizing: border-box; max-height: none; display: inline; line-height: normal; text-align: left; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative; \u3e95 and the authors obtain optimal ratios for various five state systems. For the continuous case, the authors develop various strategies, namely linear, optimal-following, progressive and exponential. The authors show that the best competitive strategies are those that follow the offline schedule in an accelerated manner. Strategy “progressive” consistently produces competitive ratios significantly better than 2
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