1,680 research outputs found
Do food banks help? Food insecurity in the UK.
Belgium Herbarium image of Meise Botanic Garden
Thermoelectric properties of Co, Ir, and Os-Doped FeSi Alloys: Evidence for Strong Electron-Phonon Coupling
The effects of various transition metal dopants on the electrical and thermal
transport properties of Fe1-xMxSi alloys (M= Co, Ir, Os) are reported. The
maximum thermoelectric figure of merit ZTmax is improved from 0.007 at 60 K for
pure FeSi to ZT = 0.08 at 100 K for 4% Ir doping. A comparison of the thermal
conductivity data among Os, Ir and Co doped alloys indicates strong
electron-phonon coupling in this compound. Because of this interaction, the
common approximation of dividing the total thermal conductivity into
independent electronic and lattice components ({\kappa}Total =
{\kappa}electronic + {\kappa}lattice) fails for these alloys. The effects of
grain size on thermoelectric properties of Fe0.96Ir0.04Si alloys are also
reported. The thermal conductivity can be lowered by about 50% with little or
no effect on the electrical resistivity or Seebeck coefficient. This results in
ZTmax = 0.125 at 100 K, still about a factor of five too low for solid-state
refrigeration applications
Overcoming the barriers to implementing urban road user charging schemes
Urban road user charging offers the potential to achieve significant improvements in urban transport, but is notoriously difficult to implement. Cities need guidance on the range of factors to be considered in planning and implementing such schemes. This paper summarises the results of a 3 year programme which has collated evidence on the issues of most concern to cities. A state of the art report has provided evidence on 14 themes, ranging from objectives and design to implementation and evaluation. A set of 16 case studies has reviewed experience in design and implementation across Europe. The paper summarises their findings, provides references to more detailed information, presents the resulting policy recommendations to European, national and local government, and outlines the areas in which further research is needed
An efficient evolutionary algorithm for solving incrementally structured problems
Many real world problems have a structure where small problem instances are embedded within large problem instances, or where solution quality for large problem instances is loosely correlated to that of small problem instances. This structure can be exploited because smaller problem instances typically have smaller search spaces and are cheaper to evaluate. We present an evolutionary algorithm, INCREA, which is designed to incrementally solve a large, noisy, computationally expensive problem by deriving its initial population through recursively running itself on problem instances of smaller sizes. The INCREA algorithm also expands and shrinks its population each generation and cuts off work that doesn't appear to promise a fruitful result. For further efficiency, it addresses noisy solution quality efficiently by focusing on resolving it for small, potentially reusable solutions which have a much lower cost of evaluation. We compare INCREA to a general purpose evolutionary algorithm and find that in most cases INCREA arrives at the same solution in significantly less time.United States. Dept. of Energy (award DESC0005288
Hyperparameter Tuning in Bandit-Based Adaptive Operator Selection
EvoApplications 2012: EvoCOMNET, EvoCOMPLEX, EvoFIN, EvoGAMES, EvoHOT, EvoIASP, EvoNUM, EvoPAR, EvoRISK, EvoSTIM, and EvoSTOC, Málaga, Spain, April 11-13, 2012, ProceedingsWe are using bandit-based adaptive operator selection while autotuning parallel computer programs. The autotuning, which uses evolutionary algorithm-based stochastic sampling, takes place over an extended duration and occurs in situ as programs execute. The environment or context during tuning is either largely static in one scenario or dynamic in another. We rely upon adaptive operator selection to dynamically generate worthy test configurations of the program. In this paper, we study how the choice of hyperparameters, which control the trade-off between exploration and exploitation, affects the effectiveness of adaptive operator selection which in turn affects the performance of the autotuner. We show that while the optimal assignment of hyperparameters varies greatly between different benchmarks, there exists a single assignment, for a context, of hyperparameters that performs well regardless of the program being tuned
Physical properties of Ce3-xTe4 below room temperature
The physical properties of polycrystalline Ce3-xTe4 were investigated by
measurements of the thermoelectric properties, Hall coefficient, heat capacity,
and magnetization. The fully-filled, metallic x=0 compound displays a soft
ferromagnetic transition near 4K, and analysis of the corresponding heat
capacity anomaly suggests a doublet ground state for Ce^{3+}. The transition is
suppressed to below 2K in the insulating x=0.33 composition, revealing that
magnetic order in Ce3-xTe4 is driven by an RKKY-type interaction. The
thermoelectric properties trend with composition as expected from simple
electron counting, and the transport properties in Ce3Te4 are observed to be
similar to those in La3Te4. Trends in the low temperature thermal conductivity
data reveal that the phonons are efficiently scattered by electrons, while all
compositions examined have a lattice thermal conductivity near 1.2W/m/K at
200K.Comment: Submitted to Phys. Rev.
Di-μ-pivalato-κ3 O,O′:O′;κ3 O:O,O′-bisÂ[(methanol-κO)bisÂ(2,2,6,6-tetraÂmethylheptaÂne-3,5-dionato)praseoÂdymium(III)]
In the centrosymmetric dimeric title compound, [Pr2(C5H9O2)2(C11H19O2)4(CH3OH)2], the two praseodymium(III) atoms are eight-coordinate and are bridged by O atoms from the two pivalate anions. Each PrIII ion is further coordinated by two chelating 2,2,6,6-tetraÂmethyl-3,5-heptaÂnedionate (thd−) ligands and one methanol molÂecule. The distance between the two PrIII ions is 4.273 (5) Å. IntraÂmolecular hydrogen bonds exists between the methanol hyÂdroxy group on one PrIII atom and a chelating O atom of a thd− ligand coordinated to the symmetry-related PrIII atom
Revisiting Old Friends: Is CoDel Really Achieving What RED Cannot?
We use ns-2 simulations to compare RED's gentle mode to CoDel in terms of their ability to reduce the latency for various TCP variants. We use a common dumbbell topology with Pareto background traffic, and measure the packet delays and transmission time of a 10MB FTP transfer.
In our scenarios, we find that CoDel reduces the latency by 87%, but RED still manages to reduce it by 75%. However, the use of CoDel results in a transmission time 42% longer than when using RED. In light of its maturity, we therefore argue that RED could be considered as a good candidate to tackle Bufferbloat
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