Practical Parallel Algorithms for Non-Monotone Submodular Maximization

Submodular maximization has found extensive applications in various domains within the field of artificial intelligence, including but not limited to machine learning, computer vision, and natural language processing. With the increasing size of datasets in these domains, there is a pressing need to develop efficient and parallelizable algorithms for submodular maximization. One measure of the parallelizability of a submodular maximization algorithm is its adaptive complexity, which indicates the number of sequential rounds where a polynomial number of queries to the objective function can be executed in parallel. In this paper, we study the problem of non-monotone submodular maximization subject to a knapsack constraint, and propose the first combinatorial algorithm achieving an $(8+\epsilon)$-approximation under $\mathcal{O}(\log n)$ adaptive complexity, which is \textit{optimal} up to a factor of $\mathcal{O}(\log\log n)$. Moreover, we also propose the first algorithm with both provable approximation ratio and sublinear adaptive complexity for the problem of non-monotone submodular maximization subject to a $k$-system constraint. As a by-product, we show that our two algorithms can also be applied to the special case of submodular maximization subject to a cardinality constraint, and achieve performance bounds comparable with those of state-of-the-art algorithms. Finally, the effectiveness of our approach is demonstrated by extensive experiments on real-world applications.Comment: Part of the contribution appears in AAAI-202

Single-nanowire spectrometers.

Spectrometers with ever-smaller footprints are sought after for a wide range of applications in which minimized size and weight are paramount, including emerging in situ characterization techniques. We report on an ultracompact microspectrometer design based on a single compositionally engineered nanowire. This platform is independent of the complex optical components or cavities that tend to constrain further miniaturization of current systems. We show that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along the length of the nanowire. Our devices are capable of accurate, visible-range monochromatic and broadband light reconstruction, as well as spectral imaging from centimeter-scale focal planes down to lensless, single-cell-scale in situ mapping.EPSRC (EP/M013812/1, EP/L016087/1), the Royal Commission for the Exhibition of 1851, CRUK Pioneer Award (C55962/A24669), , Business Finland (A-Photonics), Academy of Finland, ERC (834742), EU Horizon 2020 (820423), the Cambridge Trust, the Royal Society

A Novel Switchable Thermal Insulation Technology

Switchable thermal insulation, in the form of an opaque panel that alternates between thermally conductive and insulated states, can be an effective means of regulating the thermal environment by selectively transferring heat between the indoor and outdoor environments. Pioneering work has been undertaken by researchers to develop switchable insulation technologies intended for applications in the built environment, automotive, and aerospace, where conventional space heating and cooling technologies are either too bulky or too energy consuming to meet design requirements. Switchable insulation technologies are in their infancy and the emerging research on this topic is unstructured and fragmented across disparate application sectors and very few of the adaptive insulation concepts and technologies are actively being pursued by the buildings research community. The aim of this thesis is therefore to advance the understanding of switchable insulation for possible applications in the building envelope. We begin by reviewing and classifying the existing switchable insulation technologies systematically, with a particular focus on their working principles, theoretical performance and improvement opportunities. On the basis of qualitative and quantitative assessment of existing switchable insulation technologies, we design and fabricate a novel switchable insulation system, a multi-layer cellular structure, comprised of an alternating arrangement of snapping and support layers. The switchability, thermal performance, and the controllability of the proposed switchable insulation are examined analytically and numerically in further details, with a particular emphasis on the influence of microstructure design parameters and operational conditions on the overall performance

Joint Optimization of Trajectory and Discrete Reflection Coefficients for UAV-Aided Backscatter Communication System with NOMA

Backscatter communication is a promising technology for the Internet of Things (IoT) systems with low-energy consumption, in which the data transmission of the backscatter devices relies on reflecting the incident signal. However, limited by the low power characteristic of the reflected signal from backscatter devices, achieving efficient data collection for the widely distributed backscatter devices is a thorny problem. Considering that unmanned aerial vehicles (UAVs) have flexible deployment capability, employing UAVs in a backscatter communication network can achieve feasible data collection for backscatter devices. In this paper, we consider a UAV-aided backscatter system and introduce Non-orthogonal multiple access (NOMA) to enable the UAV to collect signals from multiple backscatter devices simultaneously. We formulate an optimization problem to maximize the communication throughput of the considered system by jointly designing the backscatter device matching, the trajectory of the UAV, and the reflection coefficients of the backscatter devices, which is a non-convex optimization problem and challenging to solve. Hence, we decouple the original problem into three sub-problems and propose an efficient iterative algorithm based on Block Coordinate Descent (BCD) to solve them. In detail, a game-based matching algorithm is designed to ensure the transmission needs of remote backscatter devices. The UAV trajectory and reflection coefficients of backscatter devices are optimized through the Successive Convex Approximation (SCA) algorithm and relaxation algorithm. By iterative optimization of the sub-problems, the original problem is solved. The simulation results show that the proposed scheme can obtain a significant throughput gain compared to benchmark schemes

Spatial evolution investigation and analysis of traditional dwellings in Dongzhu Island village of Jiaodong region

The seaweed cottage is a traditional residence in the Jiaodong (胶东) region that has existed for hundreds of years. During its development, its architectural form was evidently reconstructed and redeveloped. Based on historical documents, interviews, field investigations, and mapping, the author summarizes the village environment, overall layout, and architectural attributes of Dongchu Island Village (东褚岛村, DIV) to address the common needs of historical heritage protection. In order to examine in depth, the spatial evolution of the five stages in the past one hundred years, the Wangs’ grocery seaweed courtyard located on the southwest corner of Middle Street was selected as a typical research object. Analyzed as two clues, the village and dwelling, three key factors are identified as influencing spatial change: Characteristics of the time, economic industry, and personnel structure

Identification of Compound CB-2 as a Novel Late-Stage Autophagy Inhibitor Exhibits Inhibitory Potency against A549 Cells

Autophagy has been recognized as a stress tolerance mechanism that maintains cell viability, which contributes to tumor progression, dormancy, and treatment resistance. The inhibition of autophagy in cancer has the potential to improve the therapeutic efficacy. It is therefore of great significance to search for new autophagy inhibitors. In the present study, after screening a series of curcumin derivatives synthesized in our laboratory, (E)-3-((E)-4-chlorobenzylidene)-5-((5-methoxy-1H-indol-3-yl)methylene)-1-methylpiperidin-4-one (CB-2) was selected as a candidate for further study. We found that CB-2 increased the LC3B-II and SQSTM1 levels associated with the accumulation of autophagosomes in non-small cell lung cancer (NSCLC) A549 cells. The increased level of LC3B-II induced by CB-2 was neither eliminated when autophagy initiation was suppressed by wortmannin nor further increased when autophagosome degradation was inhibited by chloroquine (CQ). CB-2 enhanced the accumulation of LC3B-II under starvation conditions. Further studies revealed that CB-2 did not affect the levels of the key proteins involved in autophagy induction but significantly blocked the fusion of autophagosomes with lysosomes. High-dose CB-2 induced the apoptosis and necrosis of A549 cells, while a lower dose of CB-2 mainly impaired the migrative capacity of A549 cells, which only slightly induced cell apoptosis. CB-2 increased the levels of mitochondrial-derived reactive oxygen species (ROS) while decreasing the mitochondrial membrane potential (MMP). Scavenging ROS via N-acetylcysteine (NAC) reversed CB-2-induced autophagy inhibition and its inhibitory effect against A549 cells. In conclusion, CB-2 serves as a new late-stage autophagy inhibitor, which has a strong inhibitory potency against A549 cells

Miniaturized Spectrometers with a Tunable van der Waals Junction

Miniaturized computational spectrometers, which can obtain incident spectra using a combination of device spectral response and reconstruction algorithms, are essential for on-chip and implantable applications. Highly sensitive spectral measurement using a single detector allows the footprints of such spectrometers to be scaled down while achieving spectral resolution approaching that of benchtop systems. We report a high-performance computational spectrometer based on a single van der Waals junction with an electrically tunable transport-mediated spectral response. We achieve high peak wavelength accuracy (~0.36 nanometers), high spectral resolution (~3 nanometers), broad operation bandwidth (from ~405 to 845 nanometers), and proof-of-concept spectral imaging. Our approach provides a route toward ultraminiaturization and offers unprecedented performance in accuracy, resolution, and operation bandwidth for single-detector computational spectrometers.EP/T014601/

Data for: Single-nanowire spectrometers

Data for the plots in the main text. Instructions for some data sets are contained within the Excel file. Detailed description: One Microsoft Excel file containing data for each plot in the main manuscript figures, as labelled. Photoluminescent data (1A) is measured through 355 nm laser illumination of a typical CdSxSe1-x nanowire at 7 different locations as shown in the image in the main text; intensities for each location are normalized to their respective maximum intensity. Photocurrent measurements (1C) are made applying bias between two electrodes toward the CdSe-rich end of a typical nanowire photodetector array, under the labelled irradiances by 490 nm light. Time response (1D) is of the same unit as measured for the photocurrent data, under illumination by a blue LED, pulsed at a frequency of 50 Hz. Calibration data (1E) is supplied for each unit (labelled as R"i", where "i" is the unit index) of a typical nanowire spectrometer with 30 units, consisting of the photocurrent measured under illumination at different wavelengths from 490 to 630 nm (spaced in the case of this example at increments of 5 nm) by a tunable Xe arc lamp source. Note that for the nanowire devices presented in Figs. 2A-D, 3F and 4G, a narrower sample spacing of 3 nm was used in the calibration. Note also that calibration photocurrents have been normalised for the purpose of more clearly illustrating the spread of cut-off wavelengths across the set of units. Spectral datasets (2A-D, 3F, 4G) are, as labelled, either measured from a conventional spectrometer (Thorlabs, CCS100 compact spectrometer, 350-700 nm) or reconstructed by a 30-unit or 38-unit nanowire spectrometer as described in the text using the calibration data and photocurrents measured from each unit whilst under illumination by the unknown light signal. Data for 2A-D and 3F have been normalized so as to better compare the conventional and nanowire spectrometers. Both sets of mapping data (3D, 4F) show in effect a data cube with 3 dimensions (x, y, wavelength). The x-y planes measure 30 x 30 pixels, with pixel size 300 µm x 300 µm for 3D and 20 x 10 pixels with pixel size 20 µm x 20 µm for 4F. The pixels are indexed in a raster fashion, such that, for example, pixels 1 to 30 in 3D correspond to the first row in the spectral image, while 31 to 60 correspond to the second row, and so on