Linear Stochastic Fluid Networks: Rare-Event Simulation and Markov Modulation

We consider a linear stochastic fluid network under Markov modulation, with a focus on the probability that the joint storage level attains a value in a rare set at a given point in time. The main objective is to develop efficient importance sampling algorithms with provable performance guarantees. For linear stochastic fluid networks without modulation, we prove that the number of runs needed (so as to obtain an estimate with a given precision) increases polynomially (whereas the probability under consideration decays essentially exponentially); for networks operating in the slow modulation regime, our algorithm is asymptotically efficient. Our techniques are in the tradition of the rare-event simulation procedures that were developed for the sample-mean of i.i.d. one-dimensional light-tailed random variables, and intensively use the idea of exponential twisting. In passing, we also point out how to set up a recursion to evaluate the (transient and stationary) moments of the joint storage level in Markov-modulated linear stochastic fluid networks

Mechanical Properties of APbX3 (A=Cs or CH3NH3; X=I or Br) Perovskite Single Crystals

The remarkable optoelectronic, and especially photovoltaic performance of hybrid-organic-inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX3 (A = Cs, CH3NH3 and X = I, Br). The Youngs moduli are about 14, 19.5 and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3 and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss possible relevance of our results to suggested self-healing, ion diffusion and ease of manufacturing. Using our results, together with literature data on elastic moduli, we classified HOIPs amongst relevant materials groups, based on their elasto-mechanical properties.Comment: 20 pages (including 4 pages of Supporting Information after the references), 3 figures (+3 in the Supporting Information), 2 tables (+1 in the Supporting Information

How do electronic carriers cross Si-bound alkyl monolayers?

Electron transport through Si-C bound alkyl chains, sandwiched between n-Si and Hg, is characterized by two distinct types of barriers, each dominating in a different voltage range. At low voltage, current depends strongly on temperature but not on molecular length, suggesting transport by thermionic emission over a barrier in the Si. At higher voltage, the current decreases exponentially with molecular length, suggesting tunneling through the molecules. The tunnel barrier is estimated, from transport and photoemission data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

We compare the charge transport characteristics of heavy doped p- and n-Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p- and n-type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current

Mode-selective vibrational control of charge transport in ππ-conjugated molecular materials

The soft character of organic materials leads to strong coupling between molecular nuclear and electronic dynamics. This coupling opens the way to control charge transport in organic electronic devices by inducing molecular vibrational motions. However, despite encouraging theoretical predictions, experimental realization of such control has remained elusive. Here we demonstrate experimentally that photoconductivity in a model organic optoelectronic device can be controlled by the selective excitation of molecular vibrations. Using an ultrafast infrared laser source to create a coherent superposition of vibrational motions in a pentacene/C60 photoresistor, we observe that excitation of certain modes in the 1500-1700 cm$^{-1}$ region leads to photocurrent enhancement. Excited vibrations affect predominantly trapped carriers. The effect depends on the nature of the vibration and its mode-specific character can be well described by the vibrational modulation of intermolecular electronic couplings. Vibrational control thus presents a new tool for studying electron-phonon coupling and charge dynamics in (bio)molecular materials.This work was supported by the Netherlands Organization for Scientific Research (NWO) through the ‘Stichting voor Fundamenteel Onderzoek der Materie’ (FOM) research programme. A.A.B. also acknowledges a VENI grant from the NWO. A.A.B. is currently a Royal Society University Research Fellow. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 639750). R.L. acknowledges a Marie Curie IE Fellowship from the EU, held at the Weizmann Institute (FP7-PEOPLE-2011-IEF no. 29866). X.Y. thanks the Council for Higher Education (Israel) for a PBC programme postdoctoral research fellowship. V.C. thanks support from the Office of Naval Research and MURI Center on Advanced Molecular Photovoltaics, award No. N00014-14-1-0580. J.L.B. acknowledges support by competitive research funding from King Abdullah University of Science and Technology (KAUST) and by ONR Global, Grant N62909-15-1-2003. D.C. thanks the Israel Science Foundation Centre of Excellence program, the Grand Centre for Sensors and Security and the Schmidt Minerva Centre for Supramolecular Architecture for partial support. D.C. holds the Sylvia and Rowland Schaefer Chair in Energy Research.This is the final published version. It first appeared at http://dx.doi.org/10.1038/ncomms888

Trial-based cost-effectiveness analysis comparing surgical and endoscopic drainage in patients with obstructive chronic pancreatitis

Objective: Published evidence indicates that surgical drainage of the pancreatic duct was more effective than endoscopic drainage for patients with chronic pancreatitis. This analysis assessed the cost-effectiveness of surgical versus endoscopic drainage in obstructive chronic pancreatitis. Design: This trial-based cost-utility analysis (ISRCTN04572410) was conducted from a UK National Health Service (NHS) perspective and during a 79-month time horizon. During the trial the details of the diagnostic and therapeutic procedures, and pancreatic insufficiency were collected. The resource use was varied in the sensitivity analysis based on a review of the literature. The health outcome was the Quality-Adjusted Life Year (QALY), generated using EQ-5D data collected during the trial. There were no pancreas-related deaths in the trial. All-cause mortality from the trial was incorporated into the QALY estimates in the sensitivity analysis. Setting: Hospital. Participants: Patients with obstructive chronic pancreatitis. Primary and secondary outcome measures: Costs, QALYs and cost-effectiveness. Results: The result of the base-case analysis was that surgical drainage dominated endoscopic drainage, being both more effective and less costly. The sensitivity analysis varied mortality and resource use and showed that the surgical option remained dominant in all scenarios. The probability of cost-effectiveness for surgical drainage was 100% for the base case and 82% in the assessed most conservative case scenario. Conclusions: In obstructive chronic pancreatitis, surgical drainage is highly cost-effective compared with endoscopic drainage from a UK NHS perspective