Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS2_{2}

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS$_{2}$ encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1$^{st}$ and 2$^{nd}$ order phonon modes is unambiguously observed in a broad range of temperatures from 5 K to 320 K. The spectrum includes the Raman-active modes, $i.e.$ E$_\textrm{1g}^{2}$($\Gamma$) and A$_\textrm{1g}$($\Gamma$) along with their Davydov-split counterparts, $i.e.$ E$_\textrm{1u}$($\Gamma$) and B$_\textrm{1u}$($\Gamma$). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A$_{1g}$($\Gamma$) mode, which dominates the Raman scattering spectrum at $T$=5~K quenches with increasing temperature. Surprisingly, at room temperature the B$_\textrm{1u}$($\Gamma$) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A$_\textrm{1g}$($\Gamma$) counterpart.Comment: 7 pages, 3 figure

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe2_2

Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron-hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe$_2$ encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe$_2$ ML and BL allow us to determine $g$-factors of intralayer A and B excitons, as well as the $g$-factor of the interlayer exciton. We explain the dependence of $g$-factors on the number of layers and excitation state using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic $s$ states in the ML can be reproduced using the $\mathbf{k\cdot p}$ approach with the Rytova-Keldysh potential that describes the electron-hole interaction. In contrast, the analogous calculation for the BL case requires taking into account the out-of-plane dielectric response of the MoSe$_2$ BL.Comment: 10 pages, 4 figures, + S

Localisation-to-delocalisation transition of moir\'{e} excitons in WSe2_2/MoSe2_2 heterostructures

Moir\'{e} excitons (MXs) are electron-hole pairs localised by the periodic (moir\'{e}) potential forming in two-dimensional heterostructures (HSs). MXs can be exploited, $e.g.$, for creating nanoscale-ordered quantum emitters and achieving or probing strongly correlated electronic phases at relatively high temperatures. Here, we studied the exciton properties of a WSe$_2$/MoSe$_2$ HS from $T$=6 K to room temperature using time-resolved and continuous-wave micro-photoluminescence, also under magnetic field. The exciton dynamics and emission lineshape evolution with temperature show clear signatures that MXs de-trap from the moir\'{e} potential and turn into free interlayer excitons (IXs) at $T\gtrsim$120 K. The MX-to-IX transition is also apparent from the exciton magnetic moment reversing its sign when the moir\'{e} potential is not capable to localise excitons at elevated temperatures. Concomitantly, the exciton formation and decay times reduce drastically. Thus, our findings establish the conditions for a truly confined nature of the exciton states in a moir\'{e} superlattice with increasing temperature

Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

The temperature effect on the Raman scattering efficiency is investigated in ε-GaSe and γ-InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone. Two-dimensional (2D) van der Waals crystals have recently attracted considerable attention due to their unique electronic band structure and functionalities 1,2. The main focus of researchers has been on semiconducting transition metal dichalcogenides (S-TMDs), e.g. MoS 2 , WSe 2 , and MoTe 2 3,4. Currently, another much larger group of layered materials, i.e. semiconducting post-transition metal chalcogenides (S-PTMCs), e.g. SnS, GaS, InSe, and GaTe, has drawn the attention of the 2D community. Among these crystals, Se-based compounds of S-PTMCs, i.e. InSe and GaSe, demonstrate a tunability of their optical response from the near infrared to the visible spectrum with decreasing layer thickness down to monolayers 5-7. Raman scattering (RS) spectroscopy is a powerful and nondestructive tool to get useful information about material properties 8. The RS measurements provide an insight into their vibrational and electronic structures and are of particular importance in studies of layered materials 9. The flake thickness, strain, stability, charge transfer, stoichiometry, and stacking orders of the layers can be accessed by monitoring parameters of the observed pho-non modes 10-17. RS experiments can be performed under non-resonant and resonant excitation conditions: 18. The resonant excitation may lead to a significant enhancement of the RS intensity in S-TMD as well as the activation of otherwise inactive modes. This offers supplementary information on the coupling of particular phonons to electronic transitions of a specific symmetry 19-21. The crossover between the non-resonant and resonant conditions can be achieved not only by the variation of the excitation energy but also by the modulation of temperature as it was recently reported 22-24. In such an approach, it is the band structure that changes with temperature allowing for resonance with particular excitation energy. In this work, we present a comprehensive investigation of the effect of temperature on the Raman scattering in ε-GaSe and γ-InSe crystals. It has been found that the intensity of some phonon modes exhibits a strong variation as a function of temperature under excitation with specific energy due to the resonant conditions of RS. Moreover, a significant antiresonance behaviour accompanies the resonances at higher temperatures, which leads to the vanishing of the modes intensities. The observed effects are discussed in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone (BZ)

Analysis of the possibilities of manufacturing low-pressure valve blocks using 3D printing technology

W artykule zaprezentowano analizę możliwości wykorzystania druku 3D do wytwarzania niskociśnieniowych bloków zaworowych. Bloki te, stosowane są w szeregu układach hydraulicznych i służą do montażu różnego rodzaju elementów hydraulicznych w niskociśnieniowych gałęziach układów. W pierwszej części artykułu przedstawiono problematykę projektowania bloków zaworowych z wykorzystaniem programów Hydrosym i Hydroman oraz programu Creo Parametric 3.0. Następnie opisano technologie druku, które są wykorzystywane do drukowania elementów hydraulicznych z uwzględnieniem zakresu ich zastosowań. W drugiej części artykułu zaprezentowano przykładowy blok zaworowy niskociśnieniowy, który został specjalnie zaprojektowany i wydrukowany w technologii SLS. Zakres badań obejmował zarówno dokładność wymiarową wydrukowanych bloków jak i zbadanie ich własności wytrzymałościowych. Uzyskane wyniki badań pozwoliły na ocenę możliwości drukowania bloków za pomocą technologii druku SLS.The article presents an analysis of the possibility of using 3D printing to produce low- pressure valve blocks. These blocks are used in a number of hydraulic systems and are used to mount several types of hydraulic elements in low-pressure branches of systems. The first part of the article presents the issues of designing valve blocks using the Hydrosym and Hydroman programs and the Creo Parametric 3.0 program. Next, the printing technologies that are used to print hydraulic elements are described, considering the range of their applications. The second part of the article presents an example of a low-pressure valve block, which was specially designed and printed in SLS technology. The scope of research included both the dimensional accuracy of the printed blocks and the examination of their strength properties. The obtained research results allowed to assess the possibility of printing blocks using SLS printing technology.

International migration of Poles in the years 2004-2010.

Niniejsza praca poświęcona została zagranicznym migracjom zarobkowym, jej głównym motywom, przyczynom oraz skutkom. Przedstawia ruchy migracyjne Polaków w latach 2004-2010. Rozdział pierwszy opisuje podstawowe definicje, podziały migracji, a także jej skutki pozytywne oraz negatywne oraz kierunki dzisiejszych migracji na świecie. Rozdział drugi skupia się na trzech najważniejszych przyczynach migracji zarobkowych polskich obywateli: bezrobociu, wejściu do Unii Europejskiej oraz kryzysie światowym. Kolejny trzeci rozdział jest częścią analityczno-badawczą, gdzie weryfikacji poddane zostały dane statystyczne oraz dane z wywiadu i sformułowano istotne wnioski. Ostatni rozdział, czwarty, zawiera rekomendacje dla polityki migracyjnej stworzone na podstawie wniosków uzyskanych z rozdziału poprzedniego.This work has been devoted to profit-making international migration, its main themes, causes and effects. Shows the migration of Poles in the years 2004-2010.The first chapter describes the basic definitions, typologies of migration and its effects (positive and negative) and directions of migration in the world today. The second chapter focuses on three major causes of economic migration of Polish citizens: unemployment, accession to the European Union and the global crisis. Third chapter is a part of the analysis and research, where they were subjected to verification of statistical data and data from interviews and makes meaningful conclusions. The last chapter, the fourth, contains recommendations for immigration policy created on the basis of the conclusions derived from the previous chapter

Badania zaworu szybkoupustowego stojaka hydraulicznego z przepływem wewnętrznym dla upodatnienia obudowy hydraulicznej : praca doktorska /

Recenzenci pracy: Zenon Jędrzykiewicz, Kazimierz Stoiński.Praca doktorska. Akademia Górniczo-Hutnicza im. Stanisława Staszica (Kraków), 2011.Bibliogr. k. 121-125.Analiza stanu w zakresie badań upustowych zaworów hydraulicznych, rodzaje zabezpieczeń, regulacje prawne, rola, badania zaworów upustowych, informacje dotyczące zabezpieczeń stojaków hydraulicznych przed obciążeniami dynamicznymi, metody badań, opracowana metoda badań stojaków z zaworem upustowym, proponowane nowe rozwiązanie zaworu, konstrukcja zaworu upustowego, zasada pracy zaworu, jego lokalizacja, badania wstępne zaworu nowej konstrukcji, zakres pomiarowy, stanowisko pomiarowe, metodyka przeprowadzania pomiarów, dobór, nastawy pakietu sprężyn, dobór najlepszej nastawy zaworu, badania zasadnicze zaworu nowej konstrukcji, układ mechaniczny, hydrauliczny, pomiarowy, opracowana procedura badań stojaków z nowym rozwiązaniem zaworów, wielkości mierzone w badaniach, metodyka przeprowadzania pomiarów, wyniki pomiarów siłowników z zaworem, siłownika z zaworem nr 1, 2, 3, wpływ podstawowych parametrów hydraulicznych na ciśnienie otwarcia zaworu, wpływ ciśnienia, wysokości słupa cieczy pod tłokiem, ocena wyników pomiaró

Ageing process of hydraulic oil in single-bucket excavators in rock mining

The paper presents the problem of ageing processes of hydraulic oils when used in single-bucket excavators in mining of rock raw materials. Working parameters of these excavators are specific, particularly when a hydraulic hammer is mounted in place of the working bucket, therefore the course of the oil degradation process and the change times should be precisely determined as full functionality of hydraulic systems of excavators must be maintained and the wear of individual components of these systems should be reduced. Research on oil ageing processes has been carried out for excavators from various manufacturers that have operated in mines of rock raw materials of various raw material extraction quantities. The methodology adopted for testing the ageing processes of oils in excavators allowed to obtain a number of results that question the hitherto applied criteria for quality assessment of used oils in relation to the time of their actual use in hydraulic systems of excavators, as well as the time of change of such oils