Selection of TBM and geotechnical assessment of a microtunnel in a difficult geological environment: a case of a natural gas pipeline beneath an active landslide (Albania)

Bulletin of Engineering Geology and the Environment - This present paper presents an adopted methodology for Micro Tunnel Boring Machine (TBM) selection, based on the results of a...     

Adaptive disk scheduling with workload-dependent anticipation intervals

Anticipatory scheduling (AS) of I/O requests has become a viable choice for block-device schedulers in open-source OS-kernels as prior work has established its superiority over traditional disk-scheduling policies. An AS-scheduler selectively stalls the block-device right after servicing a request in hope that a new request for a nearby sector will be soon posted. Clearly, this decision may introduce delays if the anticipated I/O does not arrive on time. In this paper, we build on the success of the AS and propose an approach that minimizes the overhead of unsuccessful anticipations. Our suggested approach termed workload-dependent anticipation scheduling (WAS), determines the length of every anticipation period in an on-line fashion in order to reduce penalties by taking into account the evolving spatio-temporal characteristics of running processes as well as properties of the underlying computing system. We harvest the spatio-temporal features of individual processes and employ a system-wide process classification scheme that is re-calibrated on the fly. The resulting classification enables the disk scheduler to make informed decisions and vary the anticipation interval accordingly, on a per-process basis. We have implemented and incorporated WAS into the current Linux kernel. Through experimentation with a wide range of diverse workloads, we demonstrate WAS benefits and establish reduction of penalties over other AS-scheduler implementations.     

Stable Light‐Emitting Diodes Using Phase‐Pure Ruddlesden–Popper Layered Perovskites

State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Pb_nI_3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr^?1 cm^?2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm^?2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.     

Inorganic Halide Perovskitoid TlPbI3 for Ionizing Radiation Detection

Room temperature semiconductor detector (RTSD) materials for γ-ray and X-ray radiation are in great demand for the nonproliferation of nuclear materials as well as for biomedical imaging applications. Halide perovskites have attracted great attention as emerging and promising RTSD materials. In this contribution, the material synthesis, purification, crystal growth, crystal structure, photoluminescence properties, ionizing radiation detection performance, and electronic structure of the inorganic halide perovskitoid compound TlPbI₃ are reported on. This compound crystallizes in the ABX₃ non-perovskite crystal structure with a high density of d = 6.488 g·cm^–3, has a wide bandgap of 2.25 eV, and melts congruently at a low temperature of 360 °C without phase transitions, which allows for facile growth of high quality crystals with few thermally-activated defects. High-quality TlPbI₃ single crystals of centimeter-size are grown using the vertical Bridgman method using purified raw materials. A high electrical resistivity of ≈10¹² Ω·cm is readily obtainable, and detectors made of TlPbI₃ single crystals are highly photoresponsive to Ag K_α X-rays (22.4 keV), and detects 122 keV γ-rays from ⁵⁷Co radiation source. The electron mobility-lifetime product µ_eτ_e was estimated at 1.8 × 10^–5 cm²·V^–1. A high relative static dielectric constant of 35.0 indicates strong capability in screening carrier scattering and charged defects in TlPbI₃.     

Hybrid Organic–Inorganic Halide Post-Perovskite 3-Cyanopyridinium Lead Tribromide for Optoelectronic Applications

2D halide perovskite-like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to lasing. To date, the most studied families of such low-dimensional halide perovskite-like compounds are Ruddlesden–Popper, Dion–Jacobson, and other phases that can be derived from 3D halide perovskites by slicing along different crystallographic directions, which leads to the spatially isotropic corner-sharing connectivity type of metal-halide octahedra in the 2D layer plane. In this work, a new family of hybrid organic–inorganic 2D lead halides is introduced, by reporting the first example of the hybrid organic–inorganic post-perovskite 3-cyanopyridinium lead tribromide (3cp)PbBr₃. The post-perovskite structure has unique octahedra connectivity type in the layer plane: a typical “perovskite-like” corner-sharing connectivity pattern in one direction, and the rare edge-sharing connectivity pattern in the other. Such connectivity leads to significant anisotropy in the material properties within the inorganic layer plane. Moreover, the dense organic cation packing results in the formation of 1D fully organic bands in the electronic structure, offering the prospects of the involvement of the organic subsystem into material's optoelectronic properties. The (3cp)PbBr₃ clearly shows the 2D quantum size effect with a bandgap around 3.2 eV and typical broadband self-trapped excitonic photoluminescence at temperatures below 200 K.     

Halide Perovskites: Poor Man's High‐Performance Semiconductors

Halide perovskites are a rapidly developing class of medium‐bandgap semiconductors which, to date, have been popularized on account of their remarkable success in solid‐state heterojunction solar cells raising the photovoltaic efficiency to 20% within the last 5 years. As the physical properties of the materials are being explored, it is becoming apparent that the photovoltaic performance of the halide perovskites is just but one aspect of the wealth of opportunities that these compounds offer as high‐performance semiconductors. From unique optical and electrical properties stemming from their characteristic electronic structure to highly efficient real‐life technological applications, halide perovskites constitute a brand new class of materials with exotic properties awaiting discovery. The nature of halide perovskites from the materials' viewpoint is discussed here, enlisting the most important classes of the compounds and describing their most exciting properties. The topics covered focus on the optical and electrical properties highlighting some of the milestone achievements reported to date but also addressing controversies in the vastly expanding halide perovskite literature.     

Collection trees for event-monitoring queries

In this paper we present algorithms for building and maintaining efficient collection trees that provide the conduit to disseminate data required for processing monitoring queries in a wireless sensor network. While prior techniques base their operation on the assumption that the sensor nodes that collect data relevant to a specified query need to include their measurements in the query result at every query epoch, in many event monitoring applications such an assumption is not valid. We introduce and formalize the notion of event monitoring queries and demonstrate that they can capture a large class of monitoring applications. We then show techniques which, using a small set of intuitive statistics, can compute collection trees that minimize important resources such as the number of messages exchanged among the nodes or the overall energy consumption. Our experiments demonstrate that our techniques can organize the data collection process while utilizing significantly lower resources than prior approaches.     

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Hybrid organic–inorganic perovskites such as methylammonium lead iodide have emerged as promising semiconductors for energy‐relevant applications. The interactions between charge carriers and lattice vibrations, giving rise to polarons, have been invoked to explain some of their extraordinary optoelectronic properties. Here, time‐resolved optical spectroscopy is performed, with off‐resonant pumping and electronic probing, to examine several representative lead iodide perovskites. The temporal oscillations of electronic bandgaps induced by coherent lattice vibrations are reported, which is attributed to antiphase octahedral rotations that dominate in the examined 3D and 2D hybrid perovskites. The off‐resonant pumping scheme permits a simplified observation of changes in the bandgap owing to the A_g vibrational mode, which is qualitatively different from vibrational modes of other symmetries and without increased complexity of photogenerated electronic charges. The work demonstrates a strong correlation between the lead–iodide octahedral framework and electronic transitions, and provides further insights into the manipulation of coherent optical phonons and related properties in hybrid perovskites on ultrafast timescales.     

Assessment of ground conditions with respect to mechanised tunnelling for the construction of the extension of the Athens Metro to the city of Piraeus

This paper refers to the proposed western extension of the Athens Metro to Piraeus city. The railway consists of a 9.45 m diameter, 8.2 km long tunnel and seven stations. Tunnelling works are expected to be undertaken within a variety of lithological formations ranging from very strong alpine limestones to recent soft littoral deposits. The tunnel alignment was divided into 12 areas with respect to the geological and geotechnical conditions that may be encountered during construction. In many of these zones, the geotechnical conditions together with the presence of sensitive surface and/or subsurface structures led to the selection of a closed-face TBM (Earth Pressure Balance Machine or Slurry Tunnel Boring Machine) as the appropriate tunnelling technique. The Piraeus extension is a project where in places both types of commonly used closed-face tunnelling machines will encounter ‘text book’ application areas, but not always. The applicability of each type of TBM is discussed using the available data obtained from an extensive site investigation.