Electron g-Factor Anisotropy in Symmetric (110)-oriented GaAs Quantum Wells

We demonstrate by spin quantum beat spectroscopy that in undoped symmetric (110)-oriented GaAs/AlGaAs single quantum wells even a symmetric spatial envelope wavefunction gives rise to an asymmetric in-plane electron Land\'e-g-factor. The anisotropy is neither a direct consequence of the asymmetric in-plane Dresselhaus splitting nor of the asymmetric Zeeman splitting of the hole bands but is a pure higher order effect that exists as well for diamond type lattices. The measurements for various well widths are very well described within 14 x 14 band k.p theory and illustrate that the electron spin is an excellent meter variable to map out the internal -otherwise hidden- symmetries in two dimensional systems. Fourth order perturbation theory yields an analytical expression for the strength of the g-factor anisotropy, providing a qualitative understanding of the observed effects

Phonon-Assisted Tunneling of an Electron in a Strained Self-Assembled Quantum Dot Molecule

We calculate phonon-assisted relaxation rates in a self-assembled quantum dot molecule. The calculation is based on wave functions obtained within an envelope function approach, including strain effects. The single-phonon relaxation is shown to be efficient for separations between the dots around 10 nm when, in addition, the dots are brought close to resonance

Influence of velocity profile deformation on flow averaging tube flow coefficient

W pracy przedstawiono zasadę działania rurek uśredniających oraz stanowisko do ich wzorcowania. Zaprezentowano wyniki badań eksperymentalnych pomiaru strumienia powietrza przepływomierzami spiętrzającymi w strefie zaburzonego przepływu za pojedynczym kolanem. Określono profile prędkości w wybranych miejscach instalacji. Wyznaczono charakterystyki współczynnika przepływu K dla rurki o kształcie opływowym. Podano wartości współczynnika korekcyjnego umożliwiającego zmniejszenie niepewności pomiaru przepływu rurką uśredniającą. Wykazano, że lokalizacja przepływomierza poniżej 5D za kolanem powoduje istotny wzrost niepewności pomiaru.This paper presents experimental results of the air flow across an obstacle formed by a 90 degree segmented elbow. The internal diameter of the pipeline was D=152 mm, while the range of the mean velocities w = 10 30 m/s. The velocity profiles were determined (using Prandtl tube) both in the vertical and horizontal plane [12] in the relative distances L/D of the pipeline from 3 D to 20 D (Figs. 5 and 6). In the places of the established velocity profiles a streamlined flow averaging tube [7] was placed to determine the characteristics of the flow coefficient K (Figs. 8 and 9) as a function of the mean velocity (and Re number). The scope of this paper is also to present an automated test stand (equipped with a dedicated computer program - data acquisition) for calibrating flowmeters. The results of the experiments are given in the form of charts and compared. Analysis of the effect of changing the position of the averaging probe (vertical, horizontal) was conducted together with examination of the influence of the distance behind the obstacle (elbow) on the K-factor value. The realized experiment allowed shortening the distance between the obstacle and flowmeter installation place and informing about the correction factor value which can be used to minimise the uncertainty of the air flow rate measurement (Fig. 10). It was assumed that the horizontal plane is better for probe installation because of almost axi-symmetrical velocity profile and better repeatability of measurement points (K-factor changes by about 1%)

Phonon-Assisted Tunneling of an Electron in a Strained Self-Assembled Quantum Dot Molecule

We calculate phonon-assisted relaxation rates in a self-assembled quantum dot molecule. The calculation is based on wave functions obtained within an envelope function approach, including strain effects. The single-phonon relaxation is shown to be efficient for separations between the dots around 10 nm when, in addition, the dots are brought close to resonance

Experimental determination of velocity profile in a rectangular channel

Badania zrealizowane na potrzeby niniejszego artykułu miały na celu eksperymentalną ocenę wpływu typowego elementu armatury instalacyjnej oraz wartości turbulencji przepływu na wyznaczanie długość odcinka prostego pozwalającego na stabilizację strugi przepływającego płynu.The research reported in this article was concerned with experimental evaluation of the effect of installation of a typical element of armature and the level of flow turbulence on the length of the straight tube section needed for the development of fluid flow. In order to carry out the tests, an experimental setup was built, which main element consists of a steel channel through which ambient air is delivered inside the installation. The channel has a square cross-section and length of 160 mm. Along this channel, a system of three 30o elbows was installed and combined to form a single 90° segmented bend. With the purpose of assessing the flow disturbance at specified distances from the flow obstruction, it was necessary to determine the velocity profile of the fluid flow in the channel. This goal applied a measuring system comprising a Pitot tube connected to a linear module. This setup provided the measurements of the velocity along the entire section of the channel with the measurement space traversed with a step equal to 2mm

Method of liquid flow measurement using a modified PIV method

W pracy przedstawiono wyniki badań pomiaru prędkości ruchu cieczy. Prędkość określono na podstawie zdjęć fotograficznych z wizualizacji ruchu cieczy, w której znajdowały się znaczniki optyczne. Przedstawiona metoda umożliwia wyznaczenie prędkości ruchu cieczy z dokładnością do kilku procent wartości mierzonej.Phenomena related to the flow around different types of obstacles belong to one of the most difficult issues of fluid mechanics. Fluid flowing to the obstacle is disturbing what is associated with the formation of vortices. The frequency and intensity of vortices depend on flow and type of obstacle. The phenomenon is used in vortex flow meters. The paper present the test stand of flow visualization for vortex bluff bodies of vortex flowmeter. Very important parameter, which is necessary to designate in testing space is flow velocity. The paper proposes a method of measuring the velocity of liquid motion based on the image recorded during the visualization. The flow velocity was determined by the photographic images from the fluid flow visualization in which the tags were located. Pictures were taken with a camera with a long exposure time. The proposed method enables the determination of the fluid velocity to a certain percentage of the measured value. The uncertainty of this measurement significantly depends on the value of the measured velocity. In order to maintain the desired measurement accuracy, it is necessary to adjust the exposure time accordingly

Influence of typical flow disturbing elements on the flow rate in selected averaging Pitot tubes

Flowmeters with averaging Pitot tubes are becoming more and more common in the industrial practice. It is often the case in long straight sections of channels with large diameters that the conditions regarding the adequately long sections of pipelines before and behind a flowmeter cannot be fulfilled. This is associated with the occurrence of an additional measurement uncertainty with an unknown value. Most of the information regarding this issue can be found for the case of Venturi probes. The amount of data regarding the flow averaging Pitot tubes is also limited. Hence, the decision to undertake the proposed subject. The conducted research made it possible to state recommendations regarding the metrology of testing. The results indicate that it is not only the distance from the flow disturbing element that plays a role but it is also the plane in which the sensor is located that affects the uncertainty of measurements of the flow averaging Pitot tubes

Synthesis and catalytic behavior in olefin polymerization of bimetallic titanium(IV) silsesquioxane complex and its polymeric counterpart

Zsyntetyzowano, a następnie scharakteryzowano dwa tytanosilseskwioksany: nowy, nieznany dotąd z literatury, tetrachloroditytanosilseskwioksan (2) i jego polimeryczny odpowiednik (3). Zbadano właściwości katalityczne otrzymanych związków w polimeryzacji etylenu i 1-oktenu. Obydwa prekatalizatory, po aktywacji za pomocą Et2AlCl lub EtAlCl2, katalizują polimeryzację etylenu do polietylenu (PE) o małej masie molowej, która zmniejsza się zarówno ze wzrostem temperatury reakcji, jak i stosunku molowego Al:Ti. Kompleks (2) w połączeniu z metyloaluminoksanem lub związkami boru jest także aktywny w polimeryzacji 1-oktenu.The new compound, tetrachlorodititanasilsesquioxane (2) and its polymeric analogue (3) have been synthesized, characterized and used for the first time in ethylene and 1-octene polymerization. These precatalysts, activated by Et2AlCl and EtAlCl2, were found to be catalytically active in polymerization of ethylene. The resulting polyethylenes have rather low molecular weight, decreasing with an increase in both reaction temperature and molar ratio of Al:Ti. In the presence of methylaluminoxane or boron compounds, the complex (2) also promotes polymerization of 1-octene