Abstract. Workload placement on servers has been traditionally driven by mainly performance objectives. In this work, we investigate the design, implementation, and evaluation of a power-aware application placement controller in the context of an environment with heterogeneous virtualized server clusters. The placement component of the application management middleware takes into account the power and migration costs in addition to the performance benefit while placing the application containers on the physical servers. The contribution of this work is two-fold: first, we present multiple ways to capture the cost-aware application placement problem that may be applied to various settings. For each formulation, we provide details on the kind of information required to solve the problems, the model assumptions, and the practicality of the assumptions on real servers. In the second part of our study, we present the pMapper architecture and placement algorithms to solve one practical formulation of the problem: minimizing power subject to a fixed performance requirement. We present comprehensive theoretical and experimental evidence to establish the efficacy of pMapper.

Major breakthroughs have recently been reported that can help overcome two inherent drawbacks of NMR: the lack of sensitivity and the limited memory of longitudinal magnetization. Dynamic nuclear polarization (DNP) couples nuclear spins to the large reservoir of electrons, thus making it possible to detect dilute endogenous substances in magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). We have designed a method to preserve enhanced (''hyperpolarized'') magnetization by conversion into long-lived states (LLS). It is shown that these enhanced long-lived states can be generated for proton spins, which afford sensitive detection. Even in complex molecules such as peptides, long-lived proton states can be sustained effectively over time intervals on the order of tens of seconds, thus allowing hyperpolarized substrates to reach target areas and affording access to slow metabolic pathways. The natural abundance carbon-13 polarization has been enhanced ex situ by almost four orders of magnitude in the dipeptide Ala-Gly. The sample was transferred by the dissolution process to a high-resolution magnet where the carbon-13 polarization was converted into a long-lived state associated with a pair of protons. In Ala-Gly, the lifetime TLLS associated with the two nonequivalent H ␣ glycine protons, sustained by suitable radio-frequency irradiation, was found to be seven times longer than their spin-lattice relaxation time constant (TLLS/T1 ‫؍‬ 7). At desired intervals, small fractions of the populations of long-lived states were converted into observable magnetization. This opens the way to observing slow chemical reactions and slow transport phenomena such as diffusion by enhanced magnetic resonance.dynamic nuclear polarization ͉ dissolution process ͉ nuclear magnetic resonance ͉ magnetic resonance imaging ͉ metabolic pathways O ne of the many advantages of magnetic resonance (MR) compared with computed tomography (CT) and imaging methods based on radioactive tracers, such as positron emission tomography (PET) or single photon emission computed tomography (SPECT), lies in the ability of MR to determine both the spatial distribution of the substrates and their transformation through metabolic processes. Unfortunately, most applications of magnetic resonance imaging (MRI) techniques are limited to the detection of water, because other substances are not sufficiently abundant. Even with infusion of labeled substrates, chemical shift imaging (CSI) suffers from poor sensitivity. Thus, the potential to differentiate between molecules is often left unused. The sensitivity of magnetic resonance spectroscopy (MRS) and imaging (MRI) may be considerably improved by coupling the nuclear spins to electron spins via dynamic nuclear polarization (DNP) (1). By enhancing the nuclear polarization of selected endogenous substances, one cannot only image their spatial distribution without background signals, but also visualize their metabolic reaction products (2). The use of hyperpolarized substrates to follow metabol...

High Performance Computing applications and platforms have been typically designed without regard to power consumption. With increased awareness of energy cost, power management is now an issue even for compute-intensive server clusters. In this work, we investigate the use of power management techniques for high performance applications on modern power-efficient servers with virtualization support. We consider power management techniques such as dynamic consolidation and usage of dynamic power range enabled by low power states on servers.We identify application performance isolation and virtualization overhead with multiple virtual machines as the key bottlenecks for server consolidation. We perform a comprehensive experimental study to identify the scenarios where applications are isolated from each other. We also establish that the power consumed by HPC applications may be application dependent, non-linear and have a large dynamic range. We show that for HPC applications, working set size is a key parameter to take care of while placing applications on virtualized servers. We use the insights obtained from our experimental study to present a framework and methodology for power-aware application placement for HPC applications.

No abstract

Dynamic nuclear polarization (DNP) can enhance the nuclear polarization, that is the difference between the populations of the Zeeman levels j ai and j bi of spin I = 1/2, by up to four orders of magnitude with respect to their Boltzmann distribution at room temperature.[1] This enhancement arises from thermal mixing, which is brought about by microwave saturation of the EPR transitions of stable radicals that are mixed with the sample under investigation before freezing. In dissolution DNP, the sample is usually polarized at low temperatures and moderate magnetic fields (T = 1.2 K and B 0 = 3.35 or 5 T in our laboratory), [2] rapidly dissolved, [3] and heated to ambient temperature by a burst of water vapor.To minimize losses of nuclear spin polarization, the transfer from the polarizer to the NMR spectrometer or MRI magnet, including the settling of mechanical vibrations and convection currents, and, if required, the infusion into living organisms, must be completed within an interval T < T 1 . In our laboratory, the interval T has recently been lowered to 4.5 s. The radicals in the hyperpolarized solution lead to an increase of the longitudinal relaxation rate R 1 = 1/T 1 of the solute, thus limiting the timescales of the dynamic processes that can be monitored with hyperpolarized nuclei. A concomitant enhancement of the transverse relaxation rates R 2 = 1/T 2 leads to undesirable line-broadening. The relaxation rates R LLS = 1/T LLS of the populations of long-lived states (LLS) [4] and the decay rates R LLC = 1/T LLC of long-lived coherences (LLC) [5] are even more sensitive to the presence of free radicals than populations of eigenstates and single-quantum coherences. Free radicals can be toxic, and hyperpolarized solutions should not be infused into living organisms unless the radicals are removed.Herein, we demonstrate how N-oxide radicals that are widely used for DNP, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), can be reduced by scavengers like sodium ascorbate (vitamin C) during the dissolution process into 2,2,6,6-tetramethylpiperidine-1,4-diol (TEMPOL-H; Scheme 1), thus extending transverse and longitudinal relaxation times of solutes and slowing down the decay of their polarization during and after transfer. Scavenging free radicals with ascorbate merely leaves ascorbyl radicals, which rapidly disproportionate, [6] in contrast to scavenging with thiol-based (DTT) or phenolic (Vitamin E) antioxidants, so that no paramagnetic species are present in the sample after dissolution and reduction.Scheme 1. The reduction of TEMPOL by sodium ascorbate, leading to the formation of a delocalized sodium ascorbyl radical and diamagnetic TEMPOL-H.

Line broadening, which can arise from inhomogeneities or homogeneous relaxation effects that lead to finite lifetimes of quantum states, is the Achilles' heel of many forms of spectroscopy. We show that line broadening may be considerably reduced by exploiting long lifetimes associated with superpositions of quantum states with different symmetry, termed long-lived coherences. In proton NMR of arbitrary molecules (including proteins) in isotropic solution, the slow oscillatory decays of long-lived coherences can yield spectra with very high resolution. This improvement opens the way to high-field magnetic resonance of molecular assemblies that are almost an order of magnitude larger than could be hitherto studied. Coherences between states of different symmetry may be useful in other forms of spectroscopy to cancel unwanted line broadening effects.

We report the first observation of long-lived states (LLS) having lifetimes T(LLS) that exceed the corresponding spin-lattice relaxation times T(1) by more than a factor 6 in a protein. Slow diffusion coefficients characteristic of large biomolecules can be determined by combining LLS methods with moderate pulsed field gradients (PFGs) available on commercial probeheads, as the extension of spin memory reduces the strain on the duration and/or strength of the PFGs. No isotope labeling of the biomolecule is necessary.

Slow dynamic processes, such as folding or unfolding of proteins, can be witnessed by nuclear spins, provided that nonequilibrium populations of the energy levels can be sustained over time intervals that are on the order of the inverse of the rate constants of the dynamic processes. Large biomolecules have slow diffusion rates and may host exchange processes that involve high-energy barriers, such as concerted breaking and making of multiple hydrogen bonds, [1] or isomerisation in proline residues.[2]The lifetimes of the populations of ordinary Zeeman eigenstates, i.e., the well-known longitudinal relaxation times T 1 , are limited by various anisotropic interactions that are modulated by molecular tumbling. For spins with I = 1 = 2 , the dominant fluctuating interactions are dipole-dipole couplings and anisotropic chemical shifts. An obvious way to limit these magnetic interactions, and thereby extend the lifetimes of coherences, is to use spins with low gyromagnetic ratios ('heteronuclei'), [1] such as nitrogen-15. Methods have been developed to use heteronuclei in deuterated samples for resonance assignment, [3][4][5] opening the way for structural studies of paramagnetic proteins, [6] protein-protein interactions, [7] intrinsically disordered proteins, [8] slow diffusion, [9] protein dynamics, [10] and slow exchange. A more elegant approach is based on 'longlived states' (LLS), which in isolated two-spin systems are immune to relaxation mechanisms that are symmetric with respect to spin-exchange. [11,12] It was demonstrated that such states can be excited by appropriate pulse sequences and sustained either by a suitable radio-frequency (rf) irradiation or by moving the sample out of the static field. The populations of these states have relaxation time constants T LLS that can be much longer than T 1 . Ratios as large as T LLS /T 1 = 37 have been observed in partly deuterated saccharides. The longest lifetime recorded so far is T LLS = 1583 s = 26 min (T LLS /T 1 = 8), observed [13] in 15 N 2 O, using LLS involving 'heteronuclei'. The resulting longlived states offer very useful tools to follow slow exchange, [14] flow or diffusion. [15,16] Applications of long-lived states should become increasingly widespread provided they can be excited in systems featuring diverse spin patterns with more than two coupled spins. Alternatively, since the main (dipolar) interaction is silenced only for the pair of spins participating in the antisymmetric state, extended lifetimes can be obtained by substituting all remaining non-participating protons within a sphere of ca 5 by deuterons. [17] Significant progress has been made towards extending the range of applications of LLS. Long lifetimes have been obtained in symmetric molecules comprising four coupled spins. Thus, Pileio et al. measured ratios T LLS /T 1 = 8 in citric acid. [18] Pileio et al. [19] have also shown how the eigenvalues of the Liouvillian can be analysed to identify long-lived states by diagonalisation, also proposed by Gopalakrishnan et al. [20] This met...