Truthful Multi-unit Procurements with Budgets

We study procurement games where each seller supplies multiple units of his item, with a cost per unit known only to him. The buyer can purchase any number of units from each seller, values different combinations of the items differently, and has a budget for his total payment. For a special class of procurement games, the {\em bounded knapsack} problem, we show that no universally truthful budget-feasible mechanism can approximate the optimal value of the buyer within $\ln n$, where $n$ is the total number of units of all items available. We then construct a polynomial-time mechanism that gives a $4(1+\ln n)$-approximation for procurement games with {\em concave additive valuations}, which include bounded knapsack as a special case. Our mechanism is thus optimal up to a constant factor. Moreover, for the bounded knapsack problem, given the well-known FPTAS, our results imply there is a provable gap between the optimization domain and the mechanism design domain. Finally, for procurement games with {\em sub-additive valuations}, we construct a universally truthful budget-feasible mechanism that gives an $O(\frac{\log^2 n}{\log \log n})$-approximation in polynomial time with a demand oracle.Comment: To appear at WINE 201

High-throughput measurement methodologies for developing nutrient-dense crops

With the development of nutrient-dense crops comes the need for analytical methodologies to enable rapid and accurate analysis of the micronutrients of interest. The analysis of provitamin A carotenoids (pVACs) and the minerals iron (Fe) and zinc (Zn) are the focus of this chapter with the considerations and commonly employed methods discussed. When analyzing samples there are various considerations to minimise analyte degradation (in the case of provitamin A) and reduce possible contamination from external sources (for Fe and Zn). Spectroscopic and chromatographic analyses are the most common analysis approaches utilised when screening for carotenoids. Spectroscopic analyses including near-infrared spectroscopy (NIRS) and iCheck are rapid and require minimal samples preparation and provide fast analysis times. The carotenoids present in the sample is dependent on the crop analyzed and resulting number and concentration of carotenoids present will impact the final decision on suitable analysis techniques. For example, in crops with high concentrations of non-pVACs, chromatographic analysis is necessary in order to accurately quantify the micronutrients. This process is able to accurately identify and quantify individual carotenoids, but requires extensive sample preparation and often long chromatographic separation analysis. When analyzing the minerals Fe and Zn, these same techniques are not suitable, but it is still important to ensure careful sample preparation to deliver accurate analytical results. Degradation of these micronutrients is not a concern, however, possible contamination from soil/ dust/ insects can lead to inaccurate results. Commonly employed analysis such as atomic absorption spectroscopy (AAS) and Inductively Coupled Plasma-Optical Emission Spectrometry ICP-OES or Inductively Coupled Plasma-Mass spectrometry (ICP-MS) require sample digestion prior to analysis and highly pure reagents and gases. These techniques are able to analyze multiple elements and have high accuracy and sensitivity but require specialised facilities and highly trained staff. The use of high-throughput analyses to complement these high-accuracy methods include colorimetric and X-ray flourescence (XRF) technologies. These approaches enable much higher throughput with simple sample preparation and enable screening for micronutrient concentration without the need for specialised facilities.Keywords: Screening, Analysis, Carotenoid, Provitamin A, Iron, Zinc, Micronutrient analysi

A selected ion flow tube study of the ion-molecule reactions of monochloroethene, trichloroethene and tetrachloroethene

Data for the rate coefficients and product cations of the reactions of a large number of atomic and small molecular cations with monochloroethene, trichloroethene and tetrachloroethene in a selected ion flow tube at 298 K are reported. The recombination energy of the ions range from 6.27 eV (H$_3$O$^+$) through to 21.56 eV (Ne$^+$). Collisional rate coefficients are calculated by modified average dipole orientation theory and compared with experimental values. Thermochemistry and mass balance predict the most feasible neutral products. Together with previously reported results for the three isomers of dichloroethene (J. Phys. Chem. A., 2006, 110, 5760), the fragment ion branching ratios have been compared with those from threshold photoelectron photoion coincidence spectroscopy over the photon energy range 9-22 eV to determine the importance or otherwise of long-range charge transfer. For ions with recombination energy in excess of the ionisation energy of the chloroethene, charge transfer is energetically allowed. The similarity of the branching ratios from the two experiments suggest that long-range charge transfer is dominant. For ions with recombination energy less than the ionisation energy, charge transfer is not allowed; chemical reaction can only occur following formation of an ion-molecule complex, where steric effects are more significant. The products that are now formed and their percentage yield is a complex interplay between the number and position of the chlorine atoms with respect to the C=C bond, where inductive and conjugation effects can be important

Focused Local Search for Random 3-Satisfiability

A local search algorithm solving an NP-complete optimisation problem can be viewed as a stochastic process moving in an 'energy landscape' towards eventually finding an optimal solution. For the random 3-satisfiability problem, the heuristic of focusing the local moves on the presently unsatisfiedclauses is known to be very effective: the time to solution has been observed to grow only linearly in the number of variables, for a given clauses-to-variables ratio $\alpha$ sufficiently far below the critical satisfiability threshold $\alpha_c \approx 4.27$. We present numerical results on the behaviour of three focused local search algorithms for this problem, considering in particular the characteristics of a focused variant of the simple Metropolis dynamics. We estimate the optimal value for the ``temperature'' parameter $\eta$ for this algorithm, such that its linear-time regime extends as close to $\alpha_c$ as possible. Similar parameter optimisation is performed also for the well-known WalkSAT algorithm and for the less studied, but very well performing Focused Record-to-Record Travel method. We observe that with an appropriate choice of parameters, the linear time regime for each of these algorithms seems to extend well into ratios $\alpha > 4.2$ -- much further than has so far been generally assumed. We discuss the statistics of solution times for the algorithms, relate their performance to the process of ``whitening'', and present some conjectures on the shape of their computational phase diagrams.Comment: 20 pages, lots of figure

Detection of a Fully-resolved Compton Shoulder of the Iron K-alpha Line in the Chandra X-ray Spectrum of GX 301-2

We report the detection of a fully-resolved, Compton-scattered emission line in the X-ray spectrum of the massive binary GX 301-2 obtained with the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory. The iron K-alpha fluorescence line complex observed in this system consists of an intense narrow component centered at an energy of E = 6.40 keV and a redward shoulder that extends down to ~6.24 keV, which corresponds to an energy shift of a Compton back-scattered iron K-alpha photon. From detailed Monte Carlo simulations and comparisons with the observed spectra, we are able to directly constrain the physical properties of the scattering medium, including the electron temperature and column density, as well as an estimate for the metal abundance.Comment: 13 pages, 4 figures, 1 table, accepted for publication in ApJ Lette

Ambiguous loss and incomplete abduction narratives in Kosovo

Ten mothers of men and boys who were abducted and listed as missing during the war in Kosovo in 1998/1999 were interviewed in Kosovo in the spring of 2012. Although the missing are presumed dead by the authorities, the mothers continue to live in a state of emotional ambiguity where a presumption of death is balanced with the hope of being reunited. In the absence of absolute proof, finding the remains of their loved ones becomes a major preoccupation. Using a social phenomenological approach, this study explored the social and political complexities existing within the life-world of these women. The findings suggest that they live in a continual state of psychological distress, and even when remains are returned, the unknown elements of the narrative of their abduction and murder only add to their distress and force many into self-imposed emotional exile away from community and close family

Report of the Working Group on `W Mass and QCD' (Phenomenology Workshop on LEP2 Physics, Oxford, April 1997)

The W Mass and QCD Working Group discussed a wide variety of topics relating to present and future measurements of M(W) at LEP2, including QCD backgrounds to W+W- production. Particular attention was focused on experimental issues concerning the direct reconstruction and threshold mass measurements, and on theoretical and experimental issues concerning the four jet final state. This report summarises the main conclusions.Comment: 43 pages LaTeX and 15 encapsulated postscript figures. Uses epsfig and ioplppt macros. Full Proceedings to be published in Journal of Physics

Photodissociation dynamics of methyl iodide probed using femtosecond extreme ultraviolet photoelectron spectroscopy

Femtosecond pump-probe photoelectron spectroscopy measurements using an extreme ultraviolet probe have been made on the photodissociation dynamics of UV (269 nm) excited CH3I. The UV excitation leads to population of the 3Q0 state which rapidly dissociates. The dissociation is manifested as shifts in the measured photoelectron kinetic energy that map the extending C-I bond. The increased energy available in the XUV probe relative to a UV probe means the dynamics are followed over the chemically important region as far as C-I bond lengths of approximately 4 Å