Single- and narrow-line photoluminescence in a boron nitride-supported MoSe2_2/graphene heterostructure

Heterostructures made from van der Waals materials provide a template to investigate proximity effects at atomically sharp heterointerfaces. In particular, near-field charge and energy transfer in heterostructures made from semiconducting transition metal dichalcogenides (TMD) have attracted interest to design model 2D "donor-acceptor" systems and new optoelectronic components. Here, using of Raman scattering and photoluminescence spectroscopies, we report a comprehensive characterization of a molybedenum diselenide (MoSe$_2$) monolayer deposited onto hexagonal boron nitride (hBN) and capped by mono- and bilayer graphene. Along with the atomically flat hBN susbstrate, a single graphene epilayer is sufficient to passivate the MoSe$_2$ layer and provides a homogenous environment without the need for an extra capping layer. As a result, we do not observe photo-induced doping in our heterostructure and the MoSe$_2$ excitonic linewidth gets as narrow as 1.6~meV, hence approaching the homogeneous limit. The semi-metallic graphene layer neutralizes the 2D semiconductor and enables picosecond non-radiative energy transfer that quenches radiative recombination from long-lived states. Hence, emission from the neutral band edge exciton largely dominates the photoluminescence spectrum of the MoSe$_2$/graphene heterostructure. Since this exciton has a picosecond radiative lifetime at low temperature, comparable with the energy transfer time, its low-temperature photoluminescence is only quenched by a factor of $3.3 \pm 1$ and $4.4 \pm 1$ in the presence of mono- and bilayer graphene, respectively. Finally, while our bare MoSe$_2$ on hBN exhibits negligible valley polarization at low temperature and under near-resonant excitation, we show that interfacing MoSe$_2$ with graphene yields a single-line emitter with degrees of valley polarization and coherence up to $\sim 15\,\%$.Comment: version 3, 5 figure

Does size matter? Study of performance of pseudo-ELISAs based on molecularly imprinted polymer nanoparticles prepared for analytes of different sizes

The aim of this work is to evaluate whether the size of the analyte used as template for the synthesis of molecularly imprinted polymer nanoparticles (nanoMIPs) can affect their performance in pseudo-enzyme linked immunosorbent assays (pseudo-ELISAs). Successful demonstration of a nanoMIPs-based pseudo-ELISA for vancomycin (1449.3 g mol) was demonstrated earlier. In the present investigation, the following analytes were selected: horseradish peroxidase (HRP, 44 kDa), cytochrome C (Cyt C, 12 kDa) biotin (244.31 g mol) and melamine (126.12 g mol). NanoMIPs with a similar composition for all analytes were synthesised by persulfate-initiated polymerisation in water. In addition, core-shell nanoMIPs coated with polyethylene glycol (PEG) and imprinted for melamine were produced in organics and tested. The polymerisation of the nanoparticles was done using a solid-phase approach with the correspondent template immobilised on glass beads. The performance of the nanoMIPs used as replacement for antibodies in direct pseudo-ELISA (for the enzymes) and competitive pseudo-ELISA for the smaller analytes was investigated. For the competitive mode we rely on competition for the binding to the nanoparticles between free analyte and corresponding analyte-HRP conjugate. The results revealed that the best performances were obtained for nanoMIPs synthesised in aqueous media for the larger analytes. In addition, this approach was successful for biotin but completely failed for the smallest template melamine. This problem was solved using nanoMIP prepared by UV polymerisation in an organic media with a PEG shell. This study demonstrates that the preparation of nanoMIP by solid-phase approach can produce material with high affinity and potential to replace antibodies in ELISA tests for both large and small analytes. This makes this technology versatile and applicable to practically any target analyte and diagnostic field

Symmetry-dependent dielectric screening of optical phonons in monolayer graphene

Quantised lattice vibrations (i.e., phonons) in solids are robust and unambiguous fingerprints of crystal structures and of their symmetry properties. In metals and semimetals, strong electron-phonon coupling may lead to so-called Kohn anomalies in the phonon dispersion, providing an image of the Fermi surface in a non-electronic observable. Kohn anomalies become prominent in low-dimensional systems, in particular in graphene, where they appear as sharp kinks in the in-plane optical phonon branches. However, in spite of intense research efforts on electron-phonon coupling in graphene and related van der Waals heterostructures, little is known regarding the links between the symmetry properties of optical phonons at and near Kohn anomalies and their sensitivity towards the local environment. Here, using inelastic light scattering (Raman) spectroscopy, we investigate a set of custom-designed graphene-based van der Waals heterostructures, wherein dielectric screening is finely controlled at the atomic layer level. We demonstrate experimentally and explain theoretically that, depending exclusively on their symmetry properties, the two main Raman modes of graphene react differently to the surrounding environment. While the Raman-active near-zone-edge optical phonons in graphene undergo changes in their frequencies due to the neighboring dielectric environment, the in-plane, zone-centre optical phonons are symmetry-protected from the influence of the latter. These results shed new light on the unique electron-phonon coupling properties in graphene and related systems and provide invaluable guidelines to characterise dielectric screening in van der Waals heterostructures and moir\'e superlattices.Comment: 22 pages, main manuscript with 3 figures, appendix with 5 figures, supplemental material with 6 figure

Modernization of the bucket wheel excavators SchRs 4600 mining unit

Przedstawiono poszczególne etapy modernizacji koła czerpakowego i czerpaków koparek SchRs 4600. Zaprezentowano kompletne podejście do procesu projektowania uwzględniające charakterystyki dynamiczne (modalne) maszyn o różnych postaciach geometrycznych, rzeczywiste warunki urabiania panujące na odkrywkach i wykorzystujące najnowocześniejsze narzędzia numeryczne do realizacji procesu konstruowania tego typu obiektów. Zaprezentowano koncepcje spełniające kryteria projektowe i wybrane rozwiązania konstrukcyjne nowego koła czerpakowego i czerpaków.The various stages of the bucket wheel and buckets of the SchRs 4600 excavator modernization are presented in the paper. The complete approach to the design process was taken into account. The following factors were considered in the projects: the dynamic characteristics (modal) of machines with different geometric positions as well as actual excavating conditions present in the open pits. Advanced numerical tools were also used in the process of designing such facilities. New selected concepts that meet the criteria and design solutions a new bucket wheel and buckets were presented

Analysis of the dynamics of the bucket wheel excavators type KWK

W artykule przedstawiono zestawienie z badań eksperymentalnych trzech wielonaczyniowych koparek kołowych typu KWK 1200, KWK 1500 oraz KWK 1500.1 pracujących w Kopalni Węgla Brunatnego „Turów”. Przeprowadzono porównanie poziomów drgań występujących podczas pracy maszyn i przeanalizowano je pod kątem różnic konstrukcyjnych, które mogą mieć wpływ na dynamikę przebadanych obiektów.In the paper the results of the experimental measurements of the vibrations level of the machines type KWK 1200, KWK 1500 and KWK 1500.1 are presented. All of the machines operate in the Polish lignite mine KWB “Turów”. The analysis of the accelerations were performed with relation to the superstructure construction differences which could influence to the structure dynamics

Wytyczne do projektowania maszyn górnictwa odkrywkowego oraz maszyn i urządzeń przeładunkowych

Opencast mining machines and material handling machines perform an important role in many branches of industry (e.g. mining and rock processing, power) all over the world. This fact caused that different standards were developed containing guidelines for the design of such facilities. The most important of them, which will be discussed in details in the presented article, are: the Australian Standard (AS), German Standard (DIN) and ISO Standard. The advantages and disadvantages of each of them will be discussed, and with all the consequences of using the chosen standard. The authors also present self-developed solutions and recommendations that go beyond the scope of the mentioned standards.Maszyny podstawowe górnictwa odkrywkowego oraz maszyny przeładunkowe pełnią istotne role w wielu gałęziach przemysłu ( górnictwo i przetwórstwo skalne, przemysł energetyczny, inne) na całym świecie. Fakt ten spowodował, iż powstały różne opracowania zawierające wytyczne do projektowania tego rodzaju obiektów. Najważniejsze z nich, które zostaną omówione szerzej w prezentowanym artykule, to norma australijska (AS), niemiecka (DIN) oraz norma ISO. Przedstawione zostaną wady i zalety poszczególnych z nich, a przede wszystkim to jakie konsekwencje pociąga za sobą stosowanie wybranej normy. Autorzy przedstawiają również samodzielnie opracowane rozwiązania i zalecenia wykraczające poza zakres wskazany w wymienionych normach

Bucket wheel excavator dynamics optimization on the stage of preliminary project

Maszyny podstawowe górnictwa odkrywkowego należą do grupy maszyn roboczych poddawanych silnym obciążeniom dynamicznym, w dużej części o charakterze stochastycznym, na które nałożone są ciągłe pulsacje obciążeń, wynikające z procesu urabiania (w przypadku koparek kołowych lub łańcuchowych). Ponadto praca obiektów tego rodzaju ma wymiar całodobowy, a czas eksploatacji sięga nawet pięćdziesięciu lat. Odpowiednie dostosowanie charakterystyk dynamicznych obiektu przekłada się na jego wydłużoną i bezawaryjną pracę. Zaprezentowano proces badania charakterystyk dynamicznych wielonaczyniowej koparki kołowej na etapie projektu wstępnego. Wykazano wpływ modyfikacji strukturalnych na lokalne oraz globalne postacie drgań własnych. Przeprowadzenie symulacji na modelu numerycznym umożliwiło dostosowanie charakterystyk dynamicznych koparki optymalnie do przewidywanych warunków pracy. W rezultacie, zredukowane do minimum drgania, wynikające z charakterystyki samej maszyny, przełożą się na trwałość konstrukcji.Surface mining machinery belong to the group of heavy duty machines that are strongly exposed to the dynamic loads. Acting load derives from excavating system and its periodicity is directly related with the system characteristic. Machines operational time is round the clock and it lasts even till 50 years. Proper identification and tuning of the modal characteristics of the object, positively influence on the durability and failure-free operation. Presented results show investigations of the dynamic characteristics of bucket wheel excavator on the stage of preliminary project. The influence of the structure modification on the local and global eigenfrequency is shown. With the use of the numerical model simulation, performed for proper tuning of the modal characteristics, the structure was optimized. As a result, the reduced vibrations amplitude, will increase the durability of machine and its operational time

Evaluation of centrifugal fan impeller dynamic states in case of two different discrete models

Problem oceny stanów dynamicznych wirników wentylatorów jest możliwy do rozwiązania z wykorzystaniem metod numerycznych. W artykule przedstawiono porównanie wyników analizy modalnej metodą elementów skończonych, dwóch modeli wirnika wentylatora promieniowego: modelu powłokowego oraz objętościowego. Uzyskane wyniki wskazują, że poprawne przygotowanie modelu obliczeniowego skutkuje uzyskaniem analogicznych wyników w obu przypadkach.Preliminary evaluation of dynamic states in case of turbo machines is currently solved with use of numerical methods. In the article comparison of two models is presented. First model of impeller was discretized with use of shell elements and second with solid elements. For both models modal analysis was conducted. Thanks to received results comparison of both model was carried out. It should be stated that properly prepared models result in small differences in case of values of natural frequencies. On the other hand mode shapes can be transposed what was observed in case of third and fourth mode shapes

Technical condition assessment of surface mining machinery with the use of numerical and experimental methods

Na przykładzie badań koparki wieloczerpakowej SRs-2000 przedstawiono procedurę oceny stanu technicznego ustroju nośnego tej maszyny po wieloletniej eksploatacji z wykorzystaniem metod numerycznych i eksperymentalnych. Za pomocą MES z uwzględnieniem aktualnych norm, co do obciążeń, zidentyfikowano miejsca najbardziej wytężone. Metodami eksperymentalnymi zmierzono rzeczywiste oddziaływania dynamiczne podczas procesu urabiania węgla. Przedstawiono wybrane wyniki symulacji komputerowych i badań eksperymentalnych.Based on investigations of bucket wheel excavator SRs-2000, a procedure covering numerical and experimental methods for technical condition assessment of the superstructure of the machine, after many years of exploitation is presented. Using FEM with regard to loads obtained from current standards, areas indicating higher effort were identified. Experimental methods enabled to measure the actual dynamic loads during the process of coal excavation.Selected results of computer simulations and experimental studies are presented in the paper