Optimising for energy or robustness? Trade-offs for VM consolidation in virtualized datacenters under uncertainty

Reducing the energy consumption of virtualized datacenters and the Cloud is very important in order to lower CO\( _2 \) footprint and operational cost of a Cloud operator. However, there is a trade-off between energy consumption and perceived application performance. In order to save energy, Cloud operators want to consolidate as many Virtual Machines (VM) on the fewest possible physical servers, possibly involving overbooking of resources. However, that may involve SLA violations when many VMs run on peak load. Such consolidation is typically done using VM migration techniques, which stress the network. As a consequence, it is important to find the right balance between the energy consumption and the number of migrations to perform. Unfortunately, the resources that a VM requires are not precisely known in advance, which makes it very difficult to optimise the VM migration schedule. In this paper, we therefore propose a novel approach based on the theory of robust optimisation. We model the VM consolidation problem as a robust Mixed Integer Linear Program and allow to specify bounds for e.g. resource requirements of the VMs. We show that, by using our model, Cloud operators can effectively trade-off uncertainty of resource requirements with total energy consumption. Also, our model allows us to quantify the price of the robustness in terms of energy saving against resource requirement violations.     

Development of new chromatographic tools based on A2A adenosine receptor subtype for ligand characterization and screening by FAC-MS

A liquid chromatographic stationary phase containing immobilized membranes from cells expressing A_2A adenosine receptor (A_2AAR) is firstly described. Cellular membranes from CHO cells stably transfected with human A_2AAR vector (A_2A(+)) and from the same cell line transfected with the corresponding empty vector (A_2A(?)) were entrapped on immobilized artificial membrane (IAM) support and packed into 6.6 mm I.D. glass columns to create A_2A(+)-IAM and A_2A(?)-IAM stationary phases. Frontal chromatography experiments on both A_2A(+)-IAM and A_2A(?)-IAM columns demonstrated the presence of a low specific interaction with the receptor. However, immobilized A_2A retained its ability to specifically bind known ligands as demonstrated by the agreement of the calculated K _d values with two different chromatographic protocols in comparison to previously reported data. In order to maximize the specific interaction, the same cellular membranes were immobilized on the inner surface of a silica capillary (40 cm?×?100 μm I.D.) by non-covalent interactions using the avidin–biotin coupling system to create two open tubular columns A_2A(+)-OT and A_2A(?)-OT. The open tubular system was characterized by ranking experiments for affinity studies in mixture useful for the selection of new potential candidates.

Assessment of immobilized PGA orientation via the LC-MS analysis of tryptic digests of the wild type and its 3K-PGA mutant assists in the rational design of a high-performance biocatalyst

The mutant penicillin G acylase (PGA) 3K-PGA contains three additional Lys residues on the surface opposite the active site. This protein was designed to selectively drive its immobilization on aldehyde supports. We describe here a modified bottom-up proteomic method to assess the orientation of the immobilized wild-type and mutant proteins to verify our hypothesis of a driven immobilization induced by the mutations introduced. Tryptic digestion of the immobilized enzymes followed by liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis of released peptides was performed. This protocol generated peptides from the most accessible surface areas of the immobilized protein, thus not directly bound to the solid support, providing direct evidence of the areas involved in the linkage to the solid matrix. The results obtained suggest that 72 % of the wild-type PGA is immobilized on aldehyde agarose mainly through the Lys residues on the same side of the active site, whereas 3K-PGA reacted with the same support preferentially through the additional Lys residues introduced by mutation on the opposite side. This demonstrates that the active site of the 3K-PGA faces mostly (63 %) toward the reaction medium, resulting in significantly improved accessibility to the substrates. This finding is supported by the catalytic properties of the immobilized biocatalysts. The two immobilized preparations were tested in the synthesis of mandelyl-7-aminocephalosporanic acid (mandelyl-7-ACA) by N-acylation of the β-lactam nucleus (7-aminocephalosporanic acid) with mandelic acid methyl ester: upon immobilization, the synthetic properties of wild-type PGA strongly decreased, whereas those of 3K-PGA were unaffected. Furthermore, the activity of 3K-PGA was not influenced by the physicochemical nature of the support used for immobilization (glyoxyl agarose or aldehyde Sepabeads) unlike that of wild-type PGA, whose active site is close to the matrix. The results obtained from the analytical characterization correlate well with those obtained by investigation of the synthetic properties of the immobilized enzymes both in the synthesis of mandelyl-7-ACA and in the preparative synthesis of cefazolin. This work highlights the effect exerted by site-directed mutagenesis on the orientation of PGA upon immobilization on solid matrices and suggests how protein engineering tools can be exploited in a synergistic fashion to rationally develop efficient biocatalysts.

Rainstorm statistics conditional on soil moisture index: Temporal and spatial characteristics

Soil moisture is the primary hydrological state variable that controls and it is controlled by land surface processes. Assessment of feedback mechanisms between land surface and the atmosphere must involve soil moisture. The Midwestern region of the United States is used as a case example in the preliminary investigations on the hypothesis that the structure and development of storm events are influenced by soil moisture conditions. In particular we deal with the antecedent soil moisture condition influence on storm precipitation amounts and interstorm durations. The analysis based on observations indicates that when the soil moisture is low, the ensuing interstorm duration and drying period is anomalously long. We also show that storm precipitation amounts are larger when the antecedent soil moisture is anomalously high. This finding supports the hypotheses that the Summer 1993 floods over Midwestern United States were partially forced by moist antecedent conditions.

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Sommario L'umidità del suolo è la variabile idrological di stato primaria che controlla ed è a sua volta controllata dai processi sulla superficie del terreno. La quantificazione dei meccanismi di retroazione fra superficie del terreno ed atmosfera deve comprendere l'umidità del suolo. La regione centro-occidentale degli Stati Uniti è usata come esempio in uno studio preliminare sull'ipotesi che la struttura e lo sviluppo di eventi di precipitazione siano influenzati dalle condizioni di umidità del suolo. In particolare, viene considerata l'influenza delle condizioni antecedenti di umidità del suolo sulle quantità di precipitazione e gli intervallamenti dei vari eventi. Le analisi basate sulle osservazioni indicano, che quando l'umidità del suolo è bassa, il periodo secco di attesa della pioggia successiva è più lungo del normale. Viene anche mostrato che le quantità di precipitazione sono maggiori quando l'umidità del suolo nel periodo antecedente è più alta del normale. Questo risultato supporta l'ipotesi secondo la quale le alluvioni dell' estate del 1993 negli Stati Uniti centro-occidentali furono parzialmente causate dalle condizioni antecedenti di umidità del suolo.

     

Assembly of nanozeolite monolayers on the gold substrates of piezoelectric sensors

Colloidal zeolites NaA (LTA structure type) and ZSM-5 (MFI-type) with crystal diameters of about 100 nm were synthesized as building blocks for the formation of microporous self-limiting monolayers on the piezo-active area (gold electrodes) of a quartz crystal microbalance (QCM). Two different coupling strategies were explored, concerning the modification of either the gold substrate or the external zeolite crystal surface with a bifunctional molecular interface. Diverse analytical methods were employed to fully characterize the materials (dynamic light scattering, X-ray diffraction, infrared and Raman spectroscopy, solid state 29Si NMR spectroscopy, N2 sorption) and to study the process of coupling the zeolite crystals to the gold surface (reflection-absorption IR spectroscopy, scanning electron microscopy). The molecularly selective sensing behavior of these zeolite-coated devices is demonstrated by measuring the full adsorption isotherms of n-butane and i-butane in the microporous films.     

Extraction of Lantana camara essential oil by supercritical carbon dioxide: influence of the grinding and biological activity

The aim of this study was to produce Lantana camara essential oil by SFE and to study the effect of matrix grinding on the yield and/or composition of the extract. Experiments were carried out on grinding matrices (G) and on not grinding matrices (NG). The extracts were analyzed by GC-MS. A comparison with the oil obtained by hydrodistillation is also given. Finally, the antibacterial and antifungal activity of the various extracts has been assayed.     

Multivariate curve resolution of rapid-scan FTIR difference spectra of quinone photoreduction in bacterial photosynthetic membranes

Photosynthetic reaction centres and membranes are systems of particular interest and are often taken as models to investigate the molecular mechanisms of selected bioenergetic reactions. In this work, a multivariate curve resolution by alternating least squares procedure is detailed for resolution of time-resolved difference FTIR spectra probing the evolution of quinone reduction in photosynthetic membranes from Rhodobacter sphaeroides under photoexcitation. For this purpose, different data sets were acquired in the same time range and spectroscopic domain under slightly different experimental conditions. To enable resolution and provide meaningful results the different data sets were arranged in an augmented matrix. This strategy enabled recovery of three different species despite rank-deficiency conditions. It also results in better definition (identity and evolution) of the contributions. From the resolved spectra, the species have been attributed to: 1. the formation of ubiquinol, more precisely the disappearance of Q/appearance of QH₂; 2. conformational change of the protein in the surrounding biological medium; 3. oxidation of diaminodurene, a redox mediator. Because, moreover, results obtained from augmented data sets strategies enable quantitative and qualitative interpretation of concentration profiles, other effects, for example the consequence of repeated light excitation of the same sample, choice of illumination power, or the number of spectra accumulated could be compared and discussed.     

Butadiene–isoprene copolymerization with V(acac)3‐MAO. Crystalline and amorphous trans‐1,4 copolymers

Butadiene‐isoprene copolymerization with the system V(acac)₃‐MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans‐1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by ¹³C and ¹H NMR analysis. The thermal and X‐ray behaviors of the copolymers were also investigated and compared with results from solid‐state ¹³C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635–4646, 2007     

Fluoride as a probe for H-bonding interactions in the active site of heme proteins: the case of Thermobifida fusca hemoglobin

The structural and functional properties of the active site of the bacterial hemoglobin from Thermobifida fusca are largely determined by three polar amino acids: TrpG8, TyrCD1, and TyrB10. We have exploited the availability of a combinatorial set of mutants, in each of which these three amino acids have been singly, doubly, or triply replaced by a Phe residue, to perform a detailed study on H-bonding interactions between the protein and heme-bound fluoride. By appropriate choice of the excitation conditions, ν(Fe-F) stretching bands have been detected in the resonance Raman spectra. In the wild-type protein and one of the mutants, two ν(Fe-F) bands have been observed and assigned to the presence of two protein conformers where fluoride is singly or doubly H-bonded. Furthermore, by plotting the CT1 charge-transfer transition energy vs the ν(Fe-F) wavenumbers, an empirical correlation has been found. The data are well fitted by a straight line with a positive slope. The position along the correlation line can be considered as a novel, general spectroscopic indicator of the extent of H-bonding in the active site of heme proteins. In agreement with the spectroscopic results, we have observed that the rate of ligand dissociation in stopped-flow kinetic measurements progressively increases upon substitution of the H-bonding amino acids. Molecular dynamics simulations have been performed on the fluoride complexes of native and mutated forms, indicating the prevalent interactions at the active site. All the techniques yield evidence that TrpG8 and TyrCD1 can form strong H bonds with fluoride, whereas TyrB10 plays only a minor role in the stabilization of the ligand.     

Ru(x)Pt(y)Sn(z) cluster-derived nanoparticle catalysts: spectroscopic investigation into the nature of active multinuclear single sites

Cluster-derived Ru(x)Pt(y)Sn(z) nanoparticles are active catalysts in the hydrogenation of nitrobenzene. The nature of the active sites has been elucidated by FTIR spectroscopy using CO and NO as probe molecules. A new metal carbonyl cluster precursor, Pt(2)Ru(2)(SnBu(t)(3))(2)(CO)(9)(μ-H)(2), has been synthesized to obtain a Ru(2)Pt(2)Sn(2)/SiO(2) catalyst, that displayed remarkably high levels of conversion and selectivities compared to other bi-and monometallic analogues. Spectroscopic comparisons with Ru(5)PtSn/SiO(2) indicate that both the nature and the stoichiometry of the metals play a key role in modulating the catalytic activities and selectivities. A multinuclear single-site containing Pt centers, which facilitate the hydrogen activation, coupled with a highly reactive Ru site, possibly involved in the nitrobenzene activation, can be hypothesized. The oxophilicity of tin helps with the anchoring of the nanoparticles, aids the dispersion of the other metals, and can play an important role in influencing the selectivity to aniline.