Aster repulsion drives short-ranged ordering in the Drosophila syncytial blastoderm

Biological systems are highly complex, yet notably ordered structures can emerge. During syncytial stage development of the Drosophila melanogaster embryo, nuclei synchronously divide for nine cycles within a single cell, after which most of the nuclei reach the cell cortex. The arrival of nuclei to the cortex occurs with remarkable positional order, which is important for subsequent cellularisation and morphological transformations. Yet, the mechanical principles underlying this lattice-like positional order of nuclei remain untested. Here, utilising quantification of nuclei position and division orientation together with embryo explants we show that short-ranged repulsive interactions between microtubule asters ensure the regular distribution and maintenance of nuclear positions in the embryo. Such ordered nuclear positioning still occurs with the loss of actin caps and even the loss of the nuclei themselves; the asters can self-organise with similar distribution to nuclei in the wild-type embryo. The explant assay enabled us to deduce the nature of the mechanical interaction between pairs of nuclei. We used this to predict how the nuclear division axis orientation changes upon nucleus removal from the embryo cortex, which we confirmed in vivo with laser ablation. Overall, we show that short-ranged microtubule-mediated repulsive interactions between asters are important for ordering in the early Drosophila embryo and minimising positional irregularity.

Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response S11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.

Enhanced Electrical Properties of Alkali-Doped ZnO Thin Films with Chemical Process

Doped ZnO are among the most attractive transparent conductive oxides for solar cells because they are relatively cheap, can be textured for light trapping, and readily produced for large-scale coatings. Here, we focus on the development of alternative Na and K-doped ZnO prepared by an easy low-cost spray pyrolysis method for conducting oxide application. To enhance the electrical properties of zinc oxide, alkali-doped Zn1−x MxO (x = 0.03) solid solutions were investigated. The resulting layers crystallize in a single hexagonal phase of wurtzite structure with preferred c-axis orientation along a (002) crystal plane. Dense, well attached to the substrate, homogeneous and highly transparent layers were obtained with great optical transmittance higher than 80%. The optical energy band gap of doped ZnO films increase from 3.27 to 3.29 eV by doping with Na and K, respectively. The electrical resistivity of the undoped ZnO could be decreased from 1.03 × 10−1 Ω.cm to 5.64 × 10−2 Ω.cm (K-doped) and 3.18 × 10−2 (Na-doped), respectively. Lastly, the carrier concentrations increased from 5.17 × 1017 (undoped ZnO) to 1 × 1018 (doped ZnO).

Microstructural control of ZnO films deposited by RF magnetron sputtering for ultrasound transducers

<p>The aim of this study was to develop a deposition process using RF magnetron sputtering for the production of zinc oxide (ZnO) thin films on glass substrates. These ZnO films were to be used as the active piezoelectric element in very high frequency ultrasound transducers (> 300 MHz). In order to achieve piezoelectric activity the films had to be oriented with the c-axis of the ZnO grains perpendicular to the substrate surface. At the same time, a moderately high, at least 1 m=hr (17 nm=min) deposition rate was required for the production of practical devices. Prior to a full investigation into the sputtering parameters, an initial evaluation of the HHV Auto500 RF magnetron sputter coater system was performed. Using the original chamber configuration it was not possible to deposit ZnO at the required deposition rates. A modification of the growth chamber to allow a reduced target-substrate distance was successful in producing ZnO films at the required deposition rates. A systematic study into the deposition parameters and their effect on the ZnO film quality and deposition rates was then performed and it was found that strong c-axis oriented films could be deposited only when depositing at rates below 15 nm=min at a low substrate temperature (< 50 C). Depositions above this rate resulted in the growth of polycrystalline films. A two-step deposition process was designed to preserve c-axis orientation at high deposition rates up to 28 nm=min. The ZnO films were found to be highly strained due to inherent stress from the sputtering process. The deposition pressure was identified as the most critical deposition parameter for stress control. It was found that deposition above a critical pressure of 1:2 x10-² mbar was essential to prevent mechanical failure of the films. Post growth annealing was investigated and determined to be a viable technique to relax stress and improve the crystalline quality of the films. Finally a four-step deposition process was proposed to facilitate the growth of c-axis oriented ZnO films at relatively high deposition rates whilst minimising film stress.</p>

Microstructural control of ZnO films deposited by RF magnetron sputtering for ultrasound transducers

<p>The aim of this study was to develop a deposition process using RF magnetron sputtering for the production of zinc oxide (ZnO) thin films on glass substrates. These ZnO films were to be used as the active piezoelectric element in very high frequency ultrasound transducers (> 300 MHz). In order to achieve piezoelectric activity the films had to be oriented with the c-axis of the ZnO grains perpendicular to the substrate surface. At the same time, a moderately high, at least 1 m=hr (17 nm=min) deposition rate was required for the production of practical devices. Prior to a full investigation into the sputtering parameters, an initial evaluation of the HHV Auto500 RF magnetron sputter coater system was performed. Using the original chamber configuration it was not possible to deposit ZnO at the required deposition rates. A modification of the growth chamber to allow a reduced target-substrate distance was successful in producing ZnO films at the required deposition rates. A systematic study into the deposition parameters and their effect on the ZnO film quality and deposition rates was then performed and it was found that strong c-axis oriented films could be deposited only when depositing at rates below 15 nm=min at a low substrate temperature (< 50 C). Depositions above this rate resulted in the growth of polycrystalline films. A two-step deposition process was designed to preserve c-axis orientation at high deposition rates up to 28 nm=min. The ZnO films were found to be highly strained due to inherent stress from the sputtering process. The deposition pressure was identified as the most critical deposition parameter for stress control. It was found that deposition above a critical pressure of 1:2 x10-² mbar was essential to prevent mechanical failure of the films. Post growth annealing was investigated and determined to be a viable technique to relax stress and improve the crystalline quality of the films. Finally a four-step deposition process was proposed to facilitate the growth of c-axis oriented ZnO films at relatively high deposition rates whilst minimising film stress.</p>

Aligned Nanorods of AlPO4-5 Within the Pores of Anodic Alumina

<p>Anodic aluminium oxide has been identified as a versatile porous template material having high pore density, (up to 1010 cm-2), controllable channel length and monodisperse pore diameter within the range 20-250 nm. A number of studies have demonstrated the concept of utilizing the porous structure for directing the growth of various nanostructures. An example of this is the growth of crystals of the aluminophosphate AlPO4-5 within the anodic nanochannels. The high aspect ratio of the template pores encourages growth of the crystals in the preferred c-axis orientation. We have produced membranes of this material and investigated the degree of crystal alignment using X-ray diffraction. The relative degree of preferred orientation is over 200 for a typical membrane. Field emission SEM micrographs clearly show the aligned crystals within the pores. The inclusion of luminescent guest molecules within the pores of the zeolite has also been achieved. This work describes the synthesis, characterization and potential application of these membranes.</p>

Aligned Nanorods of AlPO4-5 Within the Pores of Anodic Alumina

<p>Anodic aluminium oxide has been identified as a versatile porous template material having high pore density, (up to 1010 cm-2), controllable channel length and monodisperse pore diameter within the range 20-250 nm. A number of studies have demonstrated the concept of utilizing the porous structure for directing the growth of various nanostructures. An example of this is the growth of crystals of the aluminophosphate AlPO4-5 within the anodic nanochannels. The high aspect ratio of the template pores encourages growth of the crystals in the preferred c-axis orientation. We have produced membranes of this material and investigated the degree of crystal alignment using X-ray diffraction. The relative degree of preferred orientation is over 200 for a typical membrane. Field emission SEM micrographs clearly show the aligned crystals within the pores. The inclusion of luminescent guest molecules within the pores of the zeolite has also been achieved. This work describes the synthesis, characterization and potential application of these membranes.</p>

Revisiting left atrial volumetry by magnetic resonance imaging: the role of atrial shape and 3D angle between left ventricular and left atrial axis

Background Accurate measurement of left atrial (LA) volumes is needed in cardiac diagnostics and the follow up of heart and valvular diseases. Geometrical assumptions with 2D methods for LA volume estimation contribute to volume misestimation. In this study, we test agreement of 3D and 2D methods of LA volume detection and explore contribution of 3D LA axis orientation and LA shape in introducing error in 2D methods by cardiovascular magnetic resonance imaging. Methods 30 patients with prior first-ever ischemic stroke and no known heart disease, and 30 healthy controls were enrolled (age 18–49) in a substudy of a prospective case–control study. All study subjects underwent cardiac magnetic resonance imaging and were pooled for this methodological study. LA volumes were calculated by biplane area-length method from both conventional long axis (LAVAL-LV) and LA long axis-oriented images (LAVAL-LA) and were compared to 3D segmented LA volume (LAVSAX) to assess accuracy of volume detection. 3D orientation of LA long axis to left ventricular (LV) long axis and to four-chamber plane were determined, and LA 3D sphericity indices were calculated to assess sources of error in LA volume calculation. Shapiro–Wilk test, Bland–Altman analysis, intraclass and Pearson correlation, and Spearman’s rho were used for statistical analysis. Results Biases were − 9.9 mL (− 12.5 to − 7.2) for LAVAL-LV and 13.4 (10.0–16.9) for LAVAL-LA [mean difference to LAVSAX (95% confidence interval)]. End-diastolic LA long axis 3D deviation angle to LV long axis was 28.3 ± 6.2° [mean ± SD] and LA long axis 3D rotation angle to four-chamber plane 20.5 ± 18.0°. 3D orientation of LA axis or 3D sphericity were not correlated to error in LA volume calculation. Conclusions Calculated LA volume accuracy did not improve by using LA long axis-oriented images for volume calculation in comparison to conventional method. We present novel data on LA axis orientation and a novel metric of LA sphericity and conclude that these measures cannot be utilized to assess error in LA volume calculation. Trial registration Main study Searching for Explanations for Cryptogenic Stroke in the Young: Revealing the Etiology, Triggers, and Outcome (SECRETO; NCT01934725) has been registered previously.

Electromechanical Characteristics by a Vertical Flip of C70 Fullerene Prolate Spheroid in a Single-Electron Transistor: Hybrid Density Functional Methods

In this study, the B3LYP hybrid density functional theory was used to investigate the electromechanical characteristics of C70 fullerene with and without point charges to model the effect of the surface of the gate electrode in a C70 single-electron transistor (SET). To understand electron tunneling through C70 fullerene species in a single-C70 transistor, descriptors of geometrical atomic structures and frontier molecular orbitals were analyzed. The findings regarding the node planes of the lowest unoccupied molecular orbitals (LUMOs) of C70 and both the highest occupied molecular orbitals (HOMOs) and the LUMO of the C70 anion suggest that electron tunneling of pristine C70 prolate spheroidal fullerene could be better in the major axis orientation when facing the gate electrode than in the major (longer) axis orientation when facing the Au source and drain electrodes. In addition, we explored the effect on the geometrical atomic structure of C70 by a single-electron addition, in which the maximum change for the distance between two carbon sites of C70 is 0.02 Å.