Federated Scheduling Admits No Constant Speedup Factors for Constrained-Deadline DAG Task Systems

In the federated scheduling approaches in multiprocessor systems, a task either 1) is restricted to execute sequentially on a single processor or 2) has exclusive access to the assigned processors. There have been several positive results to conduct good federated scheduling policies, which have constant speedup factors with respect to any optimal federated scheduling algorithm. This paper answers an open question: "For constrained-deadline task systems with directed acyclic graph (DAG) dependency structures, do federated scheduling policies have a constant speedup factor with respect to any optimal scheduling algorithm?" The answer is "No!" This paper presents an example, which demonstrates that any federated scheduling algorithm has a speedup factor of at least $\Omega(\min\{M, N\})$ with respect to any optimal scheduling algorithm, where $N$ is the number of tasks and $M$ is the number of processors.Comment: in Real-Time Systems Journal 201

Partitioned Multiprocessor Fixed-Priority Scheduling of Sporadic Real-Time Tasks

Partitioned multiprocessor scheduling has been widely accepted in academia and industry to statically assign and partition real-time tasks onto identical multiprocessor systems. This paper studies fixed-priority partitioned multiprocessor scheduling for sporadic real-time systems, in which deadline-monotonic scheduling is applied on each processor. Prior to this paper, the best known results are by Fisher, Baruah, and Baker with speedup factors $4-\frac{2}{M}$ and $3-\frac{1}{M}$ for arbitrary-deadline and constrained-deadline sporadic real-time task systems, respectively, where $M$ is the number of processors. We show that a greedy mapping strategy has a speedup factor $3-\frac{1}{M}$ when considering task systems with arbitrary deadlines. Such a factor holds for polynomial-time schedulability tests and exponential-time (exact) schedulability tests. Moreover, we also improve the speedup factor to $2.84306$ when considering constrained-deadline task systems. We also provide tight examples when the fitting strategy in the mapping stage is arbitrary and $M$ is sufficiently large. For both constrained- and arbitrary-deadline task systems, the analytical result surprisingly shows that using exact tests does not gain theoretical benefits (with respect to speedup factors) for an arbitrary fitting strategy.Comment: Extended version of ECRTS 201

Conductance fluctuation and shot noise in disordered graphene systems, a perturbation expansion approach

We report the investigation of conductance fluctuation and shot noise in disordered graphene systems with two kinds of disorder, Anderson type impurities and random dopants. To avoid the brute-force calculation which is time consuming and impractical at low doping concentration, we develop an expansion method based on the coherent potential approximation (CPA) to calculate the average of four Green's functions and the results are obtained by truncating the expansion up to 6th order in terms of "single-site-T-matrix". Since our expansion is with respect to "single-site-T-matrix" instead of disorder strength $W$, good result can be obtained at 6th order for finite $W$. We benchmark our results against brute-force method on disordered graphene systems as well as the two dimensional square lattice model systems for both Anderson disorder and the random doping. The results show that in the regime where the disorder strength $W$ is small or the doping concentration is low, our results agree well with the results obtained from the brute-force method. Specifically, for the graphene system with Anderson impurities, our results for conductance fluctuation show good agreement for $W$ up to $0.4t$, where $t$ is the hopping energy. While for average shot noise, the results are good for $W$ up to $0.2t$. When the graphene system is doped with low concentration 1%, the conductance fluctuation and shot noise agrees with brute-force results for large $W$ which is comparable to the hopping energy $t$. At large doping concentration 10%, good agreement can be reached for conductance fluctuation and shot noise for $W$ up to $0.4t$. We have also tested our formalism on square lattice with similar results. Our formalism can be easily combined with linear muffin-tin orbital first-principles transport calculations for light doping nano-scaled systems, making prediction on variability of nano-devices.Comment: 8 pages, 8 figure

Cylindrical-water-resonator-based ultra-broadband microwave absorber

A cylindrical-water-resonator-based absorber with ultra-broad operating band at microwave band is demonstrated theoretically and experimentally for the first time. By utilizing dielectric resonator (DR) mode and spoof surface plasmon polariton (SPP) mode of the cylindrical water resonators, the proposed absorber owns an absorptivity higher than 90% over almost the whole ultra-broad operating band from 5.58 GHz to 24.21 GHz, with a relative bandwidth as high as 125%. The angular tolerance and thermal stability of the proposed absorber are simulated and the results indicate the good performance of the absorber under wide incident angles and weakly dependent on water temperature. Low cost, ultra-broad operating band, good wide-angle characteristic and thermal stability make the absorber promising in the application of antenna measurement, steady technology and energy harvesting

Caroli formula in near-field heat transfer between parallel graphene sheets

In this work we conduct a close-up investigation into the nature of near-field heat transfer (NFHT) of two graphene sheets in parallel-plate geometry. We develop a fully microscopic and quantum approach using nonequilibrium Green's function (NEGF) method. A Caroli formula for heat flux is proposed and numerically verified. We show our near-field-to-black-body heat flux ratios generally exhibit $1/d^{\alpha}$ dependence, with an effective exponent $\alpha \approx 2.2$, at long distances exceeding 100 nm and up to one micron; in the opposite $d\rightarrow 0$ limit, the values converge to a range within an order of magnitude. Furthermore, from the numerical result, we find in addition to thermal wavelength, $\lambda_{th}$, a shorter distance scale $\sim$ 10 - 100 nm, comparable to the graphene thermal length ($\hbar v_{F}/k_{B} T$) or Fermi wavelength ($k_{F}^{-1}$), marks the transition point between the short- and long-distance transfer behaviors, within that point, relatively large variation of heat flux in response to doping level becomes a typical character. The emergence of such large variation is tied to relative NFHT contributions from the intra- and inter-band transitions. Beyond that point, scaling of thermal flux $\propto 1/d^{\alpha}$ can be generally observed.Comment: 7 page

Think Visually: Question Answering through Virtual Imagery

In this paper, we study the problem of geometric reasoning in the context of question-answering. We introduce Dynamic Spatial Memory Network (DSMN), a new deep network architecture designed for answering questions that admit latent visual representations. DSMN learns to generate and reason over such representations. Further, we propose two synthetic benchmarks, FloorPlanQA and ShapeIntersection, to evaluate the geometric reasoning capability of QA systems. Experimental results validate the effectiveness of our proposed DSMN for visual thinking tasks.Comment: Accepted in ACL 201

Optimized Signaling of Binary Correlated Sources over GMACs

This work focuses on the construction of optimized binary signaling schemes for two-sender uncoded transmission of correlated sources over non-orthogonal Gaussian multiple access channels. Specifically, signal constellations with binary pulse-amplitude-modulation are designed for two senders to optimize the overall system performance. Although the two senders transmit their own messages independently, it is observed that the correlation between message sources can be exploited to mitigate the interference present in the non-orthogonal multiple access channel. Based on a performance analysis under joint maximum-a-posteriori decoding, optimized constellations for various basic waveform correlations between the senders are derived. Numerical results further confirm the effectiveness of the proposed design.Comment: Technical Report; 22 pages, 9 figures, and 3 table

Capacity of Generalized Discrete-Memoryless Push-to-Talk Two-Way Channels

In this report, we generalize Shannon's push-to-talk two-way channel (PTT-TWC) by allowing reliable full-duplex transmission as well as noisy reception in the half-duplex (PTT) mode. Viewing a PTT-TWC as two state-dependent one-way channels, we introduce a channel symmetry property pertaining to the one-way channels. Shannon's TWC capacity inner bound is shown to be tight for the generalized model under this symmetry property. We also analytically derive the capacity region, which is shown to be the convex hull of (at most) 4 rate pairs. Examples that illustrate different shapes of the capacity region are given, and efficient transmission schemes are discussed via the examples.Comment: 10 pages, 5 figures, 5 tables, a typo corrected, presented at CWIT'1

Spin-Orientation Dependent Topological States in Two-Dimensional Antiferromagnetic NiTl2_2S4_4 Monolayers

The topological states of matters arising from the nontrivial magnetic configuration provide a better understanding of physical properties and functionalities of solid materials. Such studies benefit from the active control of spin orientation in any solid, which is yet known to rarely take place in the two-dimensional (2D) limit. Here we demonstrate by the first-principles calculations that spin-orientation dependent topological states can appear in the geometrically frustrated monolayer antiferromagnet. Different topological states including quantum anomalous Hall (QAH) effect and time-reversal-symmetry (TRS) broken quantum spin Hall (QSH) effect can be obtained by changing spin orientation in the NiTl2S4 monolayer. Remarkably, the dilated nc-AFM NiTl2S4 monolayer gives birth to the QAH effect with hitherto reported largest number of quantized conducting channels (Chern number C = -4) in 2D materials. Interestingly, under tunable chemical potential, the nc-AFM NiTl2S4 monolayer hosts a novel state supporting the coexistence of QAH and TRS broken QSH effects with a Chern number C = 3 and spin Chern number C_s = 1. This work manifests a promising concept and material realization toward topological spintronics in 2D antiferromagnets by manipulating its spin degree of freedom

Joint Source-Channel Coding for the Transmission of Correlated Sources over Two-Way Channels

A joint source-channel coding (JSCC) scheme based on hybrid digital/analog coding is proposed for the transmission of correlated sources over discrete-memoryless two-way channels (DM-TWCs). The scheme utilizes the correlation between the sources in generating channel inputs, thus enabling the users to coordinate their transmission to combat channel noise. The hybrid scheme also subsumes prior coding methods such as rate-one separate source-channel coding and uncoded schemes for two-way lossy transmission, as well as the correlation-preserving coding scheme for (almost) lossless transmission. Moreover, we derive a distortion outer bound for the source-channel system using a genie-aided argument. A complete JSSC theorem for a class of correlated sources and DM-TWCs whose capacity region cannot be enlarged via interactive adaptive coding is also established. Examples that illustrate the theorem are given.Comment: a spelling error correcte