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LaIr3Ga2: A Superconductor Based on a Kagome Lattice of Ir
No full textIn solid-state materials, crystal structure is regarded as one of the major factors that determines the physical properties, including superconductivity. Materials based on Kagome lattices, especially those based on atoms with strong spin–orbit coupling, can host exotic quantum physics, displaying flat electronic bands, Dirac cones, and topologically nontrivial surface states. The existence of superconductivity in such systems is even more attractive. Here we report the discovery of superconductivity below 5.2 K in LaIr3Ga2─a previously unreported material based on stacked Kagome planes of Ir, an element known to display strong spin–orbit coupling. The superconductor is characterized experimentally, and calculations reveal that the electronic structure is significantly influenced by spin–orbit coupling. This material can thus be considered important for investigating the coupling between topological physics and superconductivity
A Constraint on Primordial B-modes from the First Flight of the Spider Balloon-borne Telescope
No full textWe present the first linear polarization measurements from the 2015 long-duration balloon flight of SPIDER, which is an experiment that is designed to map the polarization of the cosmic microwave background (CMB) on degree angular scales. The results from these measurements include maps and angular power spectra from observations of 4.8% of the sky at 95 and 150 GHz, along with the results of internal consistency tests on these data. While the polarized CMB anisotropy from primordial density perturbations is the dominant signal in this region of sky, Galactic dust emission is also detected with high significance. Galactic synchrotron emission is found to be negligible in the SPIDER bands. We employ two independent foreground-removal techniques to explore the sensitivity of the cosmological result to the assumptions made by each. The primary method uses a dust template derived from Planck data to subtract the Galactic dust signal. A second approach, which constitutes a joint analysis of SPIDER and Planck data in the harmonic domain, assumes a modified-blackbody model for the spectral energy distribution of the dust with no constraint on its spatial morphology. Using a likelihood that jointly samples the template amplitude and r parameter space, we derive 95% upper limits on the primordial tensor-to-scalar ratio from Feldman–Cousins and Bayesian constructions, finding r < 0.11 and r < 0.19, respectively. Roughly half the uncertainty in r derives from noise associated with the template subtraction. New data at 280 GHz from SPIDER’s second flight will complement the Planck polarization maps, providing powerful measurements of the polarized Galactic dust emission
Approximately Strategyproof Tournament Rules with Multiple Prizes
No full textWe consider the manipulability of tournament rules which take the results of (n2) pairwise matches and select a ranking over the teams. Prior work designs simple tournament rules such that no pair of teams can manipulate the outcome of their match to improve their probability of being ranked first by more than 1/3, and this is the best possible among any Condorcet-consistent tournament rule (which selects an undefeated team whenever one exists) [15,16]. We initiate the consideration of teams who may manipulate their match to improve their ranking (not necessarily to reach first).
Specifically, teams compete for a monetary prize, and the ith ranked team takes home in prize money (pi ≥ pi+1 for all i). In this language, prior work designs tournament rules such that no pair of teams can manipulate the outcome of their match to improve their (collective) expected prize money by more than 1/3, when the price vector is ⃭1,0,..., 0›. We design a simple tournament rule (that we call Nested Randomized King of the Hill) such that: a) no pair of teams can improve their collective expected prize money by more than 1/3 for any prize vector in [0,1]n, and b) no set of any teams can gain any prize money for the uniform prize vector with pi:=(n-i)/(n-1)
Can Rationalization Improve Robustness?
No full textA growing line of work has investigated the development of neural NLP models that can produce rationales–subsets of input that can explain their model predictions. In this paper, we ask whether such rationale models can provide robustness to adversarial attacks in addition to their interpretable nature. Since these models need to first generate rationales (“rationalizer”) before making predictions (“predictor”), they have the potential to ignore noise or adversarially added text by simply masking it out of the generated rationale. To this end, we systematically generate various types of ‘AddText’ attacks for both token and sentence-level rationalization tasks and perform an extensive empirical evaluation of state-of-the-art rationale models across five different tasks. Our experiments reveal that the rationale models promise to improve robustness over AddText attacks while they struggle in certain scenarios–when the rationalizer is sensitive to position bias or lexical choices of attack text. Further, leveraging human rationale as supervision does not always translate to better performance. Our study is a first step towards exploring the interplay between interpretability and robustness in the rationalize-then-predict framework
Circuits resilient to short-circuit errors
No full textGiven a Boolean circuit C, we wish to convert it to a circuit C′ that computes the same function as C even if some of its gates suffer from adversarial short circuit errors, i.e., their output is replaced by the value of one of their inputs. Can we design such a resilient circuit C′ whose size is roughly comparable to that of C? Prior work gave a positive answer for the special case where C is a formula.
We study the general case and show that any Boolean circuit C of size s can be converted to a new circuit C′ of quasi-polynomial size sO(logs) that computes the same function as C even if a 1/51 fraction of the gates on any root-to-leaf path in C′ are short circuited. Moreover, if the original circuit C is a formula, the resilient circuit C′ is of near-linear size s1+є. The construction of our resilient circuits utilizes the connection between circuits and DAG-like communication protocols, originally introduced in the context of proof complexity
NiN-Passivated NiO Hole-Transport Layer Improves Halide Perovskite-Based Solar Cell
No full textThe interfaces between inorganic selective contacts and halide perovskites (HaPs) are possibly the greatest challenge for making stable and reproducible solar cells with these materials. NiOx, an attractive hole-transport layer as it fits the electronic structure of HaPs, is highly stable and can be produced at a low
cost. Furthermore, NiOx can be fabricated via scalable and controlled physical deposition methods such as RF sputtering to facilitate the quest for scalable, solvent-free, vacuum-deposited HaP-based solar cells (PSCs). However, the interface between NiOx and HaPs is still not well-controlled, which leads at times to a
lack of stability and Voc losses. Here, we use RF sputtering to fabricate NiOx and then cover it with a NiyN layer without breaking vacuum. The NiyN layer protects NiOx doubly during PSC production. Firstly, the NiyN layer protects NiOx from Ni3+ species being reduced to Ni2+ by Ar plasma, thus maintaining NiOx
conductivity. Secondly, it passivates the interface between NiOx and the HaPs, retaining PSC stability over time. This double effect improves PSC efficiency from an average of 16.5% with a 17.4% record cell to a 19% average with a 19.8% record cell and increases the device stability
QR Decomposition-Based Cyclic Prefixed Single-Carrier Transmissions for Cooperative Communications: Concepts and Research Landscape
No full textAs an alternative transmission scheme to orthogonal frequency division multiplexing (OFDM), cyclic prefixed single-carrier (CP-SC) transmissions have been widely adopted to overcome the shortcomings of OFDM. How to exploit the achievable full diversity in frequency selective fading channels is the key question in applying CP-SC-based transmissions. Thus, in this tutorial, we focus on recent research in the areas related to CP-SC transmissions for cooperative wireless systems. After explaining the basic concept and operation of CP-SC transmissions, we introduce various types of diversity that are achievable by CP-SC transmissions. To achieve these types of diversity, it is necessary to employ QR decomposition (QRD)-M-based data detection in the receiver. To verify the benefits of CP-SC transmissions in terms of diversity gain, we exemplify various wireless systems for relaying, spectrum sharing, physical layer security, and distributed cyclic delay diversity, and provide link-level simulations. Especially, as alternative metrics of reliability, which is one of the key features of 5G and beyond 5G (B5G) systems, we evaluate the average symbol error rate and outage probability. Finally, we discuss potential research directions involving CP-SC transmissions in emerging wireless communication systems
Private Key and Decoder Side Information for Secure and Private Source Coding
No full textWe extend the problem of secure source coding by considering a remote source whose noisy measurements are correlated random variables used for secure source reconstruction. The main additions to the problem are as follows: (1) all terminals noncausally observe a noisy measurement of the remote source; (2) a private key is available to all legitimate terminals; (3) the public communication link between the encoder and decoder is rate-limited; and (4) the secrecy leakage to the eavesdropper is measured with respect to the encoder input, whereas the privacy leakage is measured with respect to the remote source. Exact rate regions are characterized for a lossy source coding problem with a private key, remote source, and decoder side information under security, privacy, communication, and distortion constraints. By replacing the distortion constraint with a reliability constraint, we obtain the exact rate region for the lossless case as well. Furthermore, the lossy rate region for scalar discrete-time Gaussian sources and measurement channels is established. An achievable lossy rate region that can be numerically computed is also provided for binary-input multiple additive discrete-time Gaussian noise measurement channels
Entanglement-assisted concatenated quantum codes
No full textEntanglement-assisted concatenated quantum codes (EACQCs), constructed by concatenating two quantum codes, are proposed. These EACQCs show significant advantages over standard concatenated quantum codes (CQCs). First, we prove that, unlike standard CQCs, EACQCs can beat the nondegenerate Hamming bound for entanglement-assisted quantum error-correction codes (EAQECCs). Second, we construct families of EACQCs with parameters better than the best-known standard quantum error-correction codes (QECCs) and EAQECCs. Moreover, these EACQCs require very few Einstein–Podolsky–Rosen (EPR) pairs to begin with. Finally, it is shown that EACQCs make entanglement-assisted quantum communication possible, even if the ebits are noisy. Furthermore, EACQCs can outperform CQCs in entanglement fidelity over depolarizing channels if the ebits are less noisy than the qubits. We show that the error-probability threshold of EACQCs is larger than that of CQCs when the error rate of ebits is sufficiently lower than that of qubits. Specifically, we derive a high threshold of 47% when the error probability of the preshared entanglement is 1% to that of qubits
Secure Transmission Design for Cooperative NOMA in the Presence of Internal Eavesdropping
No full textThe application of successive interference cancellation (SIC) introduces critical security risks to cooperative non-orthogonal multiple access (NOMA) systems in the presence of untrustworthy network nodes, referred to as internal eavesdroppers. To address this potential security and reliability flaw, by assuming all users are untrusted, this letter investigates the effective secrecy throughput (EST) for a cooperative NOMA system, where a near user serves as an amplify-and-forward relay to help forward the information of a far user. Considering the inverse power allocation and SIC decoding order, a novel jamming strategy is proposed to enhance the security performance of the far user. Gauss-Chebyshev approximations of ESTs over Nakagami-m channels are derived. Asymptotic EST expressions are proposed to provide further insights. Numerical results demonstrate that the proposed jamming strategy and the inverse power allocation and SIC decoding order are both essential for achieving positive secrecy rates for both users