DEM-CFD analysis of micromechanics for dry powder inhalers

Dry powder inhalers (DPIs) are widely used for the therapy of respiratory and pulmonary diseases. In this study, a coupled discrete element method and computational fluid dynamics (DEM-CFD) is employed to investigate the micromechanics of carrier-based DPIs. The effects of van der Waals forces and electrostatic forces on the mixing process, and the influences of air flow and particle-wall impact on the dispersion process are examined. For the mixing of carrier and active pharmaceutical ingredient (API) particles in a vibrating container, it is found that vibration conditions affect the mixing performance. While there is an optimal mixing condition to maximise the number of API particles attaching to the carrier (i.e. contact number) for van der Waals cases, the contact number decreases with increasing vibration velocity amplitude and frequency for electrostatic force cases. It is also revealed that van der Waals forces (short range) and electrostatic forces (long range) result in different mixing behaviours. For the air flow induced and impact induced dispersion, it is found that the dispersion performance improves with increasing air velocity, impact velocity and impact angle, and reduces with increasing work of adhesion. The dispersion performance can be approximated using the cumulative Weibull distribution function governed by the ratio of air drag force to adhesive force or the ratio of impact energy to adhesion energy

Microstructure and electric response of Li,Sn co-doped NiO ceramics

Phase composition, microstructure and electric response of Li0.05SnxNi0.95 – xO (x = 0, 0.025, 0.05, 0.1) ceramics were systematically investigated. Colossal dielectric permittivity (>5000) is observed in the frequency range of 102–105 Hz at room temperature which becomes highly frequency-independent with increasing temperature. Secondary Sn-rich phase is detected in the grain boundary regions and it has a remarkable influence on the dielectric properties. Impedance spectroscopy analysis demonstrates that the microstructure is electrically heterogeneous, consisting of semiconducting grain and insulating grain boundary. Defect dipoles or polyvalent cations induced at high temperature may activate an electron hopping process under electric field, resulting in the enhancements of grain conductivity and polarization effect. This behaviour should be considered as the origin of the observed dielectric response

Undoped Strained Ge Quantum Well with Ultrahigh Mobility Grown by Reduce Pressure Chemical Vapor Deposition

We fabricate an undoped Ge quantum well under 30 nm Ge0.8Si0.2 shallow barrier with reverse grading technology. The under barrier is deposited by Ge0.8Si0.2 followed by Ge0.9Si0.1 so that the variation of Ge content forms a sharp interface which can suppress the threading dislocation density penetrating into undoped Ge quantum well. And the Ge0.8Si0.2 barrier introduces enough in-plane parallel strain -0.41% in the Ge quantum well. The heterostructure field-effect transistors with a shallow buried channel get a high two-dimensional hole gas (2DHG) mobility over 2E6 cm2/Vs at a low percolation density of 2.51 E-11 cm2. We also discover a tunable fractional quantum Hall effect at high densities and high magnetic fields. This approach defines strained germanium as providing the material basis for tuning the spin-orbit coupling strength for fast and coherent quantum computation.Comment: 11 pages, 5 figure

Study of one-neutron halo through (d, p) transfer reactions

In modern nuclear physics, a special group of nuclei located close to the drip line named halo nuclei has received tremendous attention due to their unique cluster structure. These nuclei exhibit large matter radii and are qualitatively described as a compact core surrounded by a diffuse halo which is formed by the loosely-bound valence nucleon(s). Their existence breaks down the consistent predictions by the classical shell model and challenges nuclear-structure calculations. To understand this exotic feature from first principles, lots of efforts have been undertaken by nuclear physicists during the past decades. One of the most successful probes to look into these questions is the (d,p) transfer which has been proved to be a very powerful tool to extract single-particle properties of nuclei and hence is ideal to study one-neutron halo nuclei. The main topic of this work is to improve the reliability of the nuclear-structure observables extracted from transfer reactions. In one of our works [Phys. Rev. C 98, 054602 (2018)], the experiment done by Schmitt et al. on the $^{10}$Be(d,p)$^{11}$Be transfer reaction at four beam energies [Phys. Rev. Lett. 108, 192701 (2012)] is reanalyzed. In order to probe only the halo of the nucleus which is represented by the asymptotic normalization coefficient (ANC), the beam energy and angular ranges at which such reaction is strictly peripheral have to be determined. These peripheral conditions are systematically identified by coupling a Halo effective field theory (EFT) description of the $^{11}$Be nucleus at leading order (LO) with the adiabatic distorted wave approximation (ADWA) to model the transfer. The results suggest that focussing on the transfer data collected with low beam energies and at forward scattering angles ensures the peripherality of the reaction and hence is the best way to reliably extract the ANC. The resulting values of ANC are (0.785 ± 0.030) fm$^{-1/2}$ for the ground state and (0.135 ± 0.005) fm$^{-1/2}$ for the first excited state. These values are in excellent agreement with the values predicted by ab initio calculations (0.786 fm$^{-1/2}$ for the ground state and 0.129 fm$^{-1/2}$ for the excited state) [Phys. Rev. Lett. 117, 242501 (2016)]. An alternative way to explore the sensitivity of transfer calculations to the short-range physics of the $^{10}$Be-n wave function using Halo EFT is offered by the supersymmetry (SuSy) method. With this method, the SuSy partner of the original wave function can be generated which shares the same asymptotic behavior but exhibits a very different internal part. Feeding those wave functions into the transfer calculations, the results confirm the above findings with respect to the peripherality of the $^{10}$Be(d,p) transfer. This method has then been extended to study another one-neutron halo nucleus: $^{15}$C which is important in nuclear astrophysics. Its ANC is extracted from the cross sections of the $^{14}$C(d,p) transfer measured by Mukhamedzhanov et al. [Phys. Rev. C, 84, 024616 (2011)]. The values obtained are (1.26 ± 0.02) fm$^{-1/2}$ and (0.056 ± 0.001) fm$^{-1/2}$ for the ground state and first excited state of $^{15}$C, respectively. Especially for the ground state case, again, a perfect agreement is reached between our result and the one predicted by Navrátil et al. (C$_{1/2+}$ = 1.282 fm$^{-1/2}$) in an ab initio calculation. Relying on the inferred ANC value, it enables us to fit an effective $^{14}$C-n interaction at NLO in Halo EFT, which has been used later in other reaction calculations, such as Coulomb breakup and radiative capture [Phys. Rev. C 100, 044615 (2019)]. We have also looked at the extension of this idea to resonant states. After an analogous analysis using a bin description, it is figured out that the resonant width plays a key role in determining the magnitude of the cross sections for such transfers. Its effect on resonance can be comparable to that of the ANC on bound states. But the associated uncertainty is larger than that in the case of bound state. In collaboration with Prof. Obertelli, we have studied the potential use of sub-Coulomb (d,p) transfer to investigate the possible presence of a halo structure in the excitation spectrum of medium to heavy nuclei. Based on the hypothetical case of $^{95}$Sr, the dependencies of the transfer calculation on several crucial parameters including Q-value, nuclear spin and beam energy have been tested to understand better how the halo feature could be revealed by measuring transfer cross sections. The feasibility of this idea requires an accurate theoretical prediction and sensitive detection systems. On the experimental side, efforts have been made to progress in the data analysis of the IS561A experiment on $^{9}$Li(d,p) transfer performed at HIE-ISOLDE, CERN. Thanks to the preprocessing of the acquired data done by Jesper Halkjær Jensen (Aarhus), the necessary information on the elastic scattering channel ($^{9}$Li + d) has been successfully collected and matches well with our theoretical calculation. Due to some practical problems happening during the measurement which would propagate to the analysis and result in a low statistics, the extraction of the (d,p) channel will require further detailed analyses. To make up for this, the available data measured by Jeppesen et al. [Phys. Lett. B, 642(5): 449 - 454, 2006] and Cavallaro et al. [Phys. Rev. Lett. 118, 012701 (2017)] are taken into account to check in those cases the validity of the chosen model which has already been used to study the resonance of $^{11}$Be. The outcome suggests that the method we use is a fast and efficient option to simulate the resonance during the transfer. For the non-resonant part, choosing the prior form of the transition matrix instead of the post one is better suited

Extraction of the ANC from the 10Be(d, p)11Be transfer reaction using the ADWA method

A halo nucleus is built from a core and at least one weakly bound neutron or proton. To understand this unique cluster structure, lots of efforts have been undertaken. During the past decades, the (d, p) reaction has been widely used in experiments and has become an important tool for extracting single-particle properties of nuclei. In this work, our goal is to obtain the Asymptotic Normalization Coefficient (ANC) of the halo nuclei 11Be using the ADWA method. We perform the analysis for the 10Be(d, p)11Be stripping reaction at Ed =21.4, 18, 15, and 12MeV for the ground state and first excited state of the composite nucleus 11Be. The experimental measurement was carried out at Oak Ridge National Laboratory by Schmitt et al. [1] The sensitivity of the calculations to the optical potential choice is also checked. Overall, the transfer process becomes more peripheral at lower energies and forward angles. Investigation in this area is the best way to extract a reliable ANC from the experimental data. For the ground state of 11Be, the ANC obtained using our method shows perfect agreement with the one obtained by Ab initio calculations (C Ab=0.786 fm-1/2) [2].SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Searching for halo nuclear excited states using sub-coulomb transfer reactions

Through this study we propose to use sub-Coulomb transfer to investigate the one-neutron halo phenomenon within nuclear excited states since this method could naturally guarantee the peripherality of the transfer. Zero-range ADWA calculations are performed with the final nucleus bound under different conditions. It can be observed that there is a clear enhancement of the interaction cross sections when the nucleus is loosely bound within an s orbital.SCOPUS: cp.pinfo:eu-repo/semantics/publishe