Space Efficient Algorithms for Breadth-Depth Search

Continuing the recent trend, in this article we design several space-efficient algorithms for two well-known graph search methods. Both these search methods share the same name {\it breadth-depth search} (henceforth {\sf BDS}), although they work entirely in different fashion. The classical implementation for these graph search methods takes $O(m+n)$ time and $O(n \lg n)$ bits of space in the standard word RAM model (with word size being $\Theta(\lg n)$ bits), where $m$ and $n$ denotes the number of edges and vertices of the input graph respectively. Our goal here is to beat the space bound of the classical implementations, and design $o(n \lg n)$ space algorithms for these search methods by paying little to no penalty in the running time. Note that our space bounds (i.e., with $o(n \lg n)$ bits of space) do not even allow us to explicitly store the required information to implement the classical algorithms, yet our algorithms visits and reports all the vertices of the input graph in correct order.Comment: 12 pages, This work will appear in FCT 201

If cooperation is likely punish mildly: Insights from economic experiments based on the snowdrift game

Punishment may deter antisocial behavior. Yet to punish is costly, and the costs often do not offset the gains that are due to elevated levels of cooperation. However, the effectiveness of punishment depends not only on how costly it is, but also on the circumstances defining the social dilemma. Using the snowdrift game as the basis, we have conducted a series of economic experiments to determine whether severe punishment is more effective than mild punishment. We have observed that severe punishment is not necessarily more effective, even if the cost of punishment is identical in both cases. The benefits of severe punishment become evident only under extremely adverse conditions, when to cooperate is highly improbable in the absence of sanctions. If cooperation is likely, mild punishment is not less effective and leads to higher average payoffs, and is thus the much preferred alternative. Presented results suggest that the positive effects of punishment stem not only from imposed fines, but may also have a psychological background. Small fines can do wonders in motivating us to chose cooperation over defection, but without the paralyzing effect that may be brought about by large fines. The later should be utilized only when absolutely necessary.Comment: 15 pages, 6 figures; accepted for publication in PLoS ON

Few-cycle pulses from a graphene mode-locked all-fiber laser

We combine a graphene mode-locked oscillator with an external compressor and achieve~29fs pulses with~52mW average power. This is a simple, low-cost, and robust setup, entirely fiber based, with no free-space optics, for applications requiring high temporal resolution

Influence of polarization on contact angle saturation during electrowetting

Electrowetting is widely used to manipulate liquids on a dielectric surface by changing the wettability of the solid-liquid interface using an externally applied electric field. While the contact angle can be adequately predicted at low fields using Lippmann's model, there is a large disagreement with experimental behavior at high fields, where the contact angle saturates. Previous attempts to explain this saturation effect (by considering a range of different mechanisms) have led to models that are applicable only to limited field ranges. Here, we use a model for the solid-liquid interfacial surface energy (based on a dipole-dipole interaction) to describe electrowetting and find that this explains the contact angle change at both low (continuous change) and high (saturation) fields. The model is compared with measured contact angle changes for both water and ethylene glycol liquids, with good agreement over the whole field range

The Effective Fragment Molecular Orbital Method for Fragments Connected by Covalent Bonds

We extend the effective fragment molecular orbital method (EFMO) into treating fragments connected by covalent bonds. The accuracy of EFMO is compared to FMO and conventional ab initio electronic structure methods for polypeptides including proteins. Errors in energy for RHF and MP2 are within 2 kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides similar to FMO but obtained two to five times faster. For proteins, the errors are also within a few kcal/mol of the FMO results. We developed both the RHF and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures had an RMSD of 0.40 and 0.44 {\AA} for RHF and MP2, respectively.Comment: Revised manuscrip

In-situ hybridization of an epoxy resin using polyurethane and MXene nanoplatelets for thermally stable nanocomposites with improved strength and toughness

A novel ternary composite system has been developed by combining MXene nanoplatelets with pre-polyurethane (PU) and an epoxy (EP) resin through in-situ polymerization and solution blending. Our approach aims to enhance the strength and toughness of the EP matrix while maintaining its thermal stability. The strong compatibility between isocyanate-terminated PU and hydroxyl-terminated MXene with the resin was demonstrated through chemical grafting and hydrogen bonding processes. In this ternary composite, significant improvements were observed, including a 32 % increase in tensile strength, a 46.4 % increase in flexural strength, and a 13.4 % increase in fracture toughness, even at very low filler contents of 0.05 wt% for MXene and 1 wt% for PU. A thorough examination of the fractured surfaces revealed the underlying mechanisms responsible for the improved strength and toughness. These mechanisms involve a transition from a brittle to a ductile fracture mode, which can be attributed to the combined effects of thermoplastic toughness, strong chemical bonding between PU and EP, and crack-anchoring and bridging effects facilitated by MXene nanoplatelets. The results presented herein are relevant to a wide range of applications in aerospace, automotive, electronics and various other industries where durability and thermomechanical performance of materials are critical

A Lewis-Acid Monopolar Gate Dielectric for All-Inkjet-Printed Highly Bias-Stress Stable Organic Transistors

A Lewis-acid monopolar polymer with both hydrophobicity and lipophilicity is used as the gate dielectric for all-inkjet-printed organic thin-film transistors. The hydrophobicity of this polymer prevents water molecules from migrating and being trapped in the gate dielectric, while its lipophilicity allows good wetting by organic solvents for further deposition of other functional layers. These organic thin-film transistors demonstrate high bias-stress stability under both positive and negative bias in ambient air. This study unlocks the potential of all-inkjet-printed organic thin-film transistors for real-world low-cost large-area applications.The authors acknowledge the support of the China Scholarship Council, Kangqiao Xingang Photonics Co. Ltd. (RG74597) and the British Council/DST UKIERI (RG72045)

Anyonic interferometry and protected memories in atomic spin lattices

Strongly correlated quantum systems can exhibit exotic behavior called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and have been proposed as candidates for naturally fault-tolerant quantum computation. Despite these remarkable properties, anyons have never been observed in nature directly. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations.Comment: 14 pages, 6 figure

Multi-Timescale Perceptual History Resolves Visual Ambiguity

When visual input is inconclusive, does previous experience aid the visual system in attaining an accurate perceptual interpretation? Prolonged viewing of a visually ambiguous stimulus causes perception to alternate between conflicting interpretations. When viewed intermittently, however, ambiguous stimuli tend to evoke the same percept on many consecutive presentations. This perceptual stabilization has been suggested to reflect persistence of the most recent percept throughout the blank that separates two presentations. Here we show that the memory trace that causes stabilization reflects not just the latest percept, but perception during a much longer period. That is, the choice between competing percepts at stimulus reappearance is determined by an elaborate history of prior perception. Specifically, we demonstrate a seconds-long influence of the latest percept, as well as a more persistent influence based on the relative proportion of dominance during a preceding period of at least one minute. In case short-term perceptual history and long-term perceptual history are opposed (because perception has recently switched after prolonged stabilization), the long-term influence recovers after the effect of the latest percept has worn off, indicating independence between time scales. We accommodate these results by adding two positive adaptation terms, one with a short time constant and one with a long time constant, to a standard model of perceptual switching

Moisture transport by Atlantic tropical cyclones onto the North American continent

Tropical Cyclones (TCs) are an important source of freshwater for the North American continent. Many studies have tried to estimate this contribution by identifying TC-induced precipitation events, but few have explicitly diagnosed the moisture fluxes across continental boundaries. We design a set of attribution schemes to isolate the column-integrated moisture fluxes that are directly associated with TCs and to quantify the flux onto the North American Continent due to TCs. Averaged over the 2004–2012 hurricane seasons and integrated over the western, southern and eastern coasts of North America, the seven schemes attribute 7 to 18 % (mean 14 %) of total net onshore flux to Atlantic TCs. A reduced contribution of 10 % (range 9 to 11 %) was found for the 1980–2003 period, though only two schemes could be applied to this earlier period. Over the whole 1980–2012 period, a further 8 % (range 6 to 9 % from two schemes) was attributed to East Pacific TCs, resulting in a total TC contribution of 19 % (range 17 to 22 %) to the ocean-to-land moisture transport onto the North American continent between May and November. Analysis of the attribution uncertainties suggests that incorporating details of individual TC size and shape adds limited value to a fixed radius approach and TC positional errors in the ERA-Interim reanalysis do not affect the results significantly, but biases in peak wind speeds and TC sizes may lead to underestimates of moisture transport. The interannual variability does not appear to be strongly related to the El Nino-Southern Oscillation phenomenon