Integrity determination of RTK solutions in precision farming applications

Integrity of Real Time Kinematic (RTK) positioning solutions relates to the confidential level that can be placed in the information provided by the RTK system. It includes the ability of the RTK system to provide timely valid warnings to users when the system must not be used for the intended operation. For instance, in the controlled traffic farming (CTF) system that controls traffic separates wheel beds and root beds, RTK positioning error causes overlap and increases the amount of soil compaction. The RTK system’s integrity capacity can inform users when the actual positional errors of the RTK solutions have exceeded Horizontal Protection Levels (HPL) within a certain Time-To-Alert (TTA) at a given Integrity Risk (IR). The later is defined as the probability that the system claims its normal operational status while actually being in an abnormal status, e.g., the ambiguities being incorrectly fixed and positional errors having exceeded the HPL. The paper studies the required positioning performance (RPP) of GPS positioning system for PA applications such as a CTF system, according to literature review and survey conducted among a number of farming companies. The HPL and IR are derived from these RPP parameters. A RTK-specific rover autonomous integrity monitoring (RAIM) algorithm is developed to determine the system integrity according to real time outputs, such as residual square sum (RSS), HDOP values. A two-station baseline data set is analyzed to demonstrate the concept of RTK integrity and assess the RTK solution continuity, missed detection probability and false alarm probability.

Tip-induced C--H activation and oligomerization of thienoanthracenes

The tip of a scanning tunneling microscope (STM) can be used to dehydrogenate freely-diffusing tetrathienoanthracene (TTA) molecules on Cu(111), trapping the molecules into metal-coordinated oligomeric structures. The process proceeds at bias voltages above ∼3 V and produces organometallic structures identical to those resulting from the thermally-activated cross-coupling of a halogenated analogue. The process appears to be substrate dependent: no oligomerization was observed on Ag(111) or HOPG. This approach demonstrates the possibility of controlled synthesis and nanoscale patterning of 2D oligomer structures on selected surfaces.

Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics

Free charge generation in donor-acceptor (D-A) based organic photovoltaic diodes (OPV) progresses through formation of charge-transfer (CT) and charge-separated (CS) states and excitation decay to the triplet level is considered as a terminal loss. On the other hand a direct excitation decay to the triplet state is beneficial for multiexciton harvesting in singlet fission photovoltaics (SF-PV) and the formation of CT-state is considered as a limiting factor for multiple triplet harvesting. These two extremes when present in a D-A system are expected to provide important insights into the mechanism of free charge generation and spin-character of bimolecular recombination in OPVs. Herein, we present the complete cycle of events linked to spin conversion in the model OPV system of rubrene/C60. By tracking the spectral evolution of photocurrent generation at short-circuit and close to open-circuit conditions we are able to capture spectral changes to photocurrent that reveal the triplet character of CT-state. Furthermore, we unveil an energy up-conversion effect that sets in as a consequence of triplet population build-up where triplet-triplet annihilation (TTA) process effectively regenerates the singlet excitation. This detailed balance is shown to enable a rare event of photon emission just above the open-circuit voltage (VOC) in OPVs.