GPAW: open Python package for electronic-structure calculations

We review the GPAW open-source Python package for electronic structure calculations. GPAW is based on the projector-augmented wave method and can solve the self-consistent density functional theory (DFT) equations using three different wave-function representations, namely real-space grids, plane waves, and numerical atomic orbitals. The three representations are complementary and mutually independent and can be connected by transformations via the real-space grid. This multi-basis feature renders GPAW highly versatile and unique among similar codes. By virtue of its modular structure, the GPAW code constitutes an ideal platform for implementation of new features and methodologies. Moreover, it is well integrated with the Atomic Simulation Environment (ASE) providing a flexible and dynamic user interface. In addition to ground-state DFT calculations, GPAW supports many-body GW band structures, optical excitations from the Bethe-Salpeter Equation (BSE), variational calculations of excited states in molecules and solids via direct optimization, and real-time propagation of the Kohn-Sham equations within time-dependent DFT. A range of more advanced methods to describe magnetic excitations and non-collinear magnetism in solids are also now available. In addition, GPAW can calculate non-linear optical tensors of solids, charged crystal point defects, and much more. Recently, support of GPU acceleration has been achieved with minor modifications of the GPAW code thanks to the CuPy library. We end the review with an outlook describing some future plans for GPAW

Absence of evidence for the conservation outcomes of systematic conservation planning around the globe : A systematic map

Background Systematic conservation planning is a discipline concerned with the prioritisation of resources for biodiversity conservation and is often used in the design or assessment of terrestrial and marine protected area networks. Despite being an evidence-based discipline, to date there has been no comprehensive review of the outcomes of systematic conservation plans and assessments of the relative effectiveness of applications in different contexts. To address this fundamental gap in knowledge, our primary research question was: what is the extent, distribution and robustness of evidence on conservation outcomes of systematic conservation planning around the globe? Methods A systematic mapping exercise was undertaken using standardised search terms across 29 sources, including publication databases, online repositories and a wide range of grey literature sources. The review team screened articles recursively, first by title only, then abstract and finally by full-text, using inclusion criteria related to systematic conservation plans conducted at sub-global scales and reported on since 1983. We sought studies that reported outcomes relating to natural, human, social, financial or institutional outcomes and which employed robust evaluation study designs. The following information was extracted from included studies: bibliographic details, background information including location of study and broad objectives of the plan, study design, reported outcomes and context. Results Of the approximately 10,000 unique articles returned through our searches, 1209 were included for full-text screening and 43 studies reported outcomes of conservation planning interventions. However, only three studies involved the use of evaluation study designs which are suitably rigorous for inclusion, according to best-practice guidelines. The three included studies were undertaken in the Gulf of California (Mexico), Réunion Island, and The Nature Conservancy’s landholdings across the USA. The studies varied widely in context, purpose and outcomes. Study designs were non-experimental or qualitative, and involved use of spatial landholdings over time, stakeholder surveys and modelling of alternative planning scenarios. Conclusion Rigorous evaluations of systematic conservation plans are currently not published in academic journals or made publicly available elsewhere. Despite frequent claims relating to positive implications and outcomes of these planning activities, we show that evaluations are probably rarely conducted. This finding does not imply systematic conservation planning is not effective but highlights a significant gap in our understanding of how, when and why it may or may not be effective. Our results also corroborate claims that the literature on systematic conservation planning is dominated by methodological studies, rather than those that focus on implementation and outcomes, and support the case that this is a problematic imbalance in the literature. We emphasise the need for academics and practitioners to publish the outcomes of systematic conservation planning exercises and to consider employing robust evaluation methodologies when reporting project outcomes. Adequate reporting of outcomes will in turn enable transparency and accountability between institutions and funding bodies as well as improving the science and practice of conservation planning

Modelling load and vibrations due to iced turbine operation

Wind energy in icing and low-temperature climate has a huge growth potential, but rotor icing effects on turbine dynamics and lifetime are not well known and simulations with iced rotor are not required in current IEC 61400-1 turbine design standard. In this article, simulations with iced rotor are compared to measured mechanical loads. The dynamic behaviour of the wind turbine was simulated with FLEX5 aeroelastic code for Senvion MM92 2 MW wind turbine. Simulations with typical iced airfoil lift and drag coefficients, aerodynamic and mass imbalances for iced rotor were performed and compared to measured iced turbine loads. Resulting iced turbine simulation parameters can be used in defining new design load cases for cold climate turbines. The most representative simulation parameter combination was achieved with a symmetric aerodynamic penalty applied on all blades and an asymmetric rotor mass imbalance of 166 kg ice load on two blades and 83 kg ice load on one blade

Channel estimation algorithms for hybrid antenna arrays:performance and complexity

Abstract At the millimeter wave and higher frequency bands the radio channel can often be expressed as a linear combination of a small number of scattering clusters. Hence, the number of angles of arrivals with significant components is limited. Due to severe path losses, the receiver must be equipped with an antenna array capable of forming narrow beams. The channel estimation with narrow beams is challenging. Algorithms developed for sparse estimation problems can be utilized to overcome the problem. In this paper, the performance and computational complexity of channel estimation methods for millimeter and terahertz frequency bands are compared. The methods considered are based on Bayesian learning with the relevance vector machine, orthogonal matching pursuit and the least absolute shrinkage and selection operator optimization. The conventional least squares channel estimator is used as a reference method. The complexity of the least squares estimator is found to be the smallest. The estimation accuracy of the Bayesian learning based estimator is the best but with increased computational complexity

Enabling simultaneous cooling and data transmission in the terahertz band for board-to-board communications

Abstract A system enabling simultaneous cooling and board-to-board communications is proposed and analyzed. It is shown that hollow pipes used in computer cooling systems can be applied for communications with extreme data rates at distances up to tens of centimeters. This is done by using wireless communications in the terahertz frequency band, 0.1–10 THz. The experiments were performed in order to observe how straight and curved pipes of different diameters and lengths affect THz signals propagating inside the pipes. The measured pulses were recorded and used in numerical evaluation of bit error rate and throughput taking into account the effect of all possible combinations of N previous symbols. The numerical results show the dependency of the intersymbol interference on the delay profile of the channel and on the symbol period. The results demonstrate that even with simple on–off keying modulation the throughput reaches few terabits per second with qualitatively low bit error rates. This enables communications between rate-hungry electronics inside computers such as central and graphical processing units while simultaneously providing the cooling functionality

Adaptive wireless communications under competition and jamming in energy constrained networks

Abstract We propose a framed slotted Aloha-based adaptive method for robust communication between autonomous wireless nodes competing to access a channel under unknown network conditions such as adversarial disruptions. With energy as a scarce resource, we show that in order to disrupt communications, our method forces the reactive adversary to incur higher energy cost relative to a legitimate node. Consequently, the adversary depletes its energy resources and stops attacking the network. Using the proposed method, a transmitter node changes the number of selected time slots and the access probability in each selected time slot based on the number of unsuccessful transmissions of a data packet. On the receiver side, a receiver node changes the probability of listening in a time slot based on the number of unsuccessful communication attempts of a packet. We compare the proposed method with two other framed slotted Aloha-based methods in terms of average energy consumption and average time required to communicate a packet. For performance evaluation, we consider scenarios in which: (1) Multiple nodes compete to access a channel. (2) Nodes compete in the presence of adversarial attacks. (3) Nodes compete in the presence of channel errors and capture effect

Intelligent autonomous user discovery and link maintenance for mmWave and TeraHertz devices with directional antennas

Abstract Use of smart directional antennas in handheld devices to generate a narrow beam in different directions for mmWave/TeraHertz communications present significant challenges. Devices using such antennas may have to scan several different directions in three-dimensional (3D) space to discover another user or an access point, a process that can result in problematic delays. Moreover, small movements of a user/device in the form of rotation and/or displacement may cause the discovered link to be lost. This paper proposes adaptive link discovery algorithms for devices in both infrastructure/ad hoc networks and evaluates their performance in terms of time-to-discovery. We show that one of the two proposed methods provides guaranteed discovery. We use an inertial measurement unit sensor to help intelligently rediscover a lost/degraded link. We propose sensor assisted link prediction methods for low-latency rediscovery in 3D space. We evaluate the effectiveness of our prediction-based rediscovery methods by testing them with real datasets representing various user/device 3D rotation patterns. We show that the smoothing based rediscovery can reach the prediction accuracy to 100% when two antenna sectors are searched, and it reduces the time-to-rediscovery by up to Sx (S times) as compared to the time-to-discovery, where S is the number of antenna sectors

Last meter indoor terahertz wireless access:performance insights and implementation roadmap

Abstract The terahertz band, 0.1–10 THz, has sufficient resources not only to satisfy the 5G requirements of 10 Gb/s peak data rate but to enable a number of tempting rate-greedy applications. However, the terahertz band brings novel challenges, never addressed at lower frequencies. Among others, the scattering of terahertz waves from any object, including walls and furniture, and ultra-wideband highly directional links lead to fundamentally new propagation and interference structures. In this article, we review the recent progress in terahertz propagation modeling, and antenna and testbed designs, and propose a step-by-step roadmap for wireless terahertz Ethernet extension for indoor environments. As a side effect, the described concept provides a second life to the currently underutilized Ethernet infrastructure by using it as a universally available backbone. By applying real terahertz band propagation, reflection, and scattering measurements as well as ray-tracing simulations of a typical office, we analyze two representative scenarios at 300 GHz and 1.25 THz frequencies, illustrating that extremely high rates can be achieved with realistic system parameters at room scales

The impact of interference from the side lanes on mmWave/THz band V2V communication systems with directional antennas

Abstract Communications systems operating in the millimeter-wave (mmWave) and terahertz (THz) band have been recently suggested to enable high data-rate vehicle-to-vehicle (V2V) communications in 5G and beyond wireless networks. However, massive deployment of such systems may lead to significant interference, affecting the performance of information transmission. While the multipath interference caused by the signal reflections from the road has been extensively discussed in the literature, the interference caused by the vehicles on the side lanes has been insufficiently studied so far. In this paper, using a combination of measurement, simulation, and analytical methods, we comprehensively characterize the interference from the side lanes in two typical deployments including highway and urban road environments for millimeter-wave and low terahertz bands. Both the multipath interference and direct interference from the transmitting vehicles on the side lanes are taken into account. As a result of our study, we reveal that: the interference from the side lanes can be well approximated using two-dimensional stochastic models without any significant loss of accuracy; and even when highly directional antennas are used there are special spatial configurations, where the interference may greatly affect the performance of the communication systems. We lately apply the developed models to estimate the signal-to-interference ratio and link capacity of mmWave/THz band V2V communications