Excitation of airwaves by bubble bursting in suspensions : regime transitions and implications for basaltic volcanic eruptions

Basaltic magma becomes more viscous, solid-like (elastic), and non-Newtonian (shear-thinning, non-zero yield stress) as its crystal content increases. However, the rheological effects on bubble bursting and airwave excitation are poorly understood. Here we conduct laboratory experiments to investigate these effects by injecting a bubble of volume V into a refractive index-matched suspension consisting of non-Brownian particles (volumetric fraction $$\phi$$ ϕ ) and a Newtonian liquid. We show that depending on $$\phi$$ ϕ and V, airwaves with diverse waveforms are excited, covering a frequency band of $$f = {\mathcal {O}}(10-10^4)$$ f = O ( 10 - 10 4 ) Hz. In a suspension of $$\phi \le 0.3$$ ϕ ≤ 0.3 or in a suspension of $$\phi = 0.4$$ ϕ = 0.4 with a V smaller than critical, the bubble bursts after it forms a hemispherical cap at the surface and excites a high-frequency (HF) wave ($$f \sim 1-2 \times 10^4$$ f ∼ 1 - 2 × 10 4 Hz) with an irregular waveform, which likely originates from film vibration. However, in a suspension of $$\phi = 0.4$$ ϕ = 0.4 and with a V larger than critical, the bubble bursts as soon as it protrudes above the surface, and its aperture opens slowly, exciting Helmholtz resonance with $$f = {\mathcal {O}}(10^3)$$ f = O ( 10 3 ) Hz. Superimposed on the waveform are an HF wave component excited upon bursting and a low-frequency ($$f = {\mathcal {O}}(10)$$ f = O ( 10 ) Hz) air flow vented from the deflating bubble, which becomes dominant at a large V. We interpret this transition as a result of the bubble film of a solid-like $$\phi = 0.4$$ ϕ = 0.4 suspension, being stretched faster than the critical strain rate such that it bursts by brittle failure. When the Helmholtz resonance is excited by a bursting bubble in a suspension whose surface level is further below the conduit rim, an air column (length L) resonance is triggered. For L larger than critical, the air column resonance continues longer than the Helmholtz resonance because the decay rate of the former becomes less than that of the latter. The experiments suggest that a bubble bursting at basaltic volcanoes commonly excites HF wave by film vibration. The Helmholtz resonance is likely to be excited under a limited condition, but if detected, it may be used to track the change of magma rheology or bubble V, where the V can be estimated from its frequency and decay rate.

FENOMENA SPORADIC E FREKUENSI 5.2 MHZ PADA KONDISI SOLAR MINIMUM TAHUN 2019

<p><em>High Frequency (HF) Communication is very dependent on the condition of the ionosphere which changes conditions over time. 2019 is a year with minimum solar conditions marked by a lack of solar cold spots. This condition can cause interference with the propagation path of radio waves in the ionosphere. In this research, a report on HF wave propagation observations is presented using a retrospective method to determine the sporadic E intensity at minimum solar conditions. Data retrieval is done by beacon / sounding system between radio stations by using a low power signal processing software that is Weak Signal Propagation Report (WSPR). Observations were made by building 2 radio stations in Surabaya (7.30S, 112.78E) as transmitter and radio stations in Jombang (7.61S, 112.31E) as receiver. Observations were carried out for one year from November 2018 until October 2019. During the observation process, a frequency of 5.2 MHz </em><em>is</em><em> used and the results showed that there were several days that described a favorable phenomenon for HF communication at close range (below 500 km), namely Sporadic E. During the observation it was obtained 8 times the Sporadic E phenomenon that is quite long with a time span of occurrence between 1 hour to 3 hours. Overall observations show that in May to August is the time when most Sporadic E phenomena occur. So from this </em><em>research,</em><em> it can be concluded that the sporadic E phenomenon can still occur when the sun enters the minimum solar conditions.</em></p><p><em><strong>Keywords</strong></em><em>: </em><em>HF, Solar Minimum, Ionospher, Sporadic E</em><strong><em> </em></strong></p><p><em>Komunikasi High Frequency (HF) sangat bergantung pada kondisi ionosfer yang mengalami perubahan kondisi dari waktu ke waktu. Tahun 2019 merupakan tahun dengan kondisi solar minimum yang ditandai dengan minimnya nilai titik dingin matahari. Kondisi ini dapat mengakibatkan gangguan pada jalur propagasi gelombang radio di lapisan ionosfer. Pada penelitian ini, disajikan laporan pengamatan propagasi gelombang HF menggunakan metode retrospektif untuk mengetahui intensitas sporadic E saat kondisi solar minimum. Pengambilan data dilakukan dengan sistem beacon / sounding antar stasiun radio dengan memanfaatkan software pengolahan sinyal daya rendah yaitu Weak Signal Propagation Report (WSPR). Pengamatan dilakukan dengan membangun 2 stasiun radio yang berada di Surabaya (7.30S, 112.78E) sebagai pemancar dan stasiun radio di Jombang (7.61S, 112.31E) sebagai penerima. Pengamatan dilakukan selama satu tahun dari bulan November 2018 sampai dengan bulan Oktober 2019. Pada proses pengamatan digunakan frekuensi 5.2 MHz dan hasilnya menunjukkan terdapat beberapa hari yang menggambarkan fenomena menguntungkan untuk komunikasi HF jarak dekat (dibawah 500 km) yaitu Sporadic E. Selama pengamatan telah didapatkan 8 kali fenomena Sporadic E yang cukup lama dengan rentang waktu kejadian antara 1 jam hingga 3 jam. Secara keseluruhan hasil pengamatan menunjukkan bahwa pada bulan Mei hingga bulan Agustus merupakan waktu paling banyak terjadinya fenomena Sporadic E. Sehingga dari penelitian ini dapat disimpulkan bahwa fenomena sporadic E masih bisa terjadi ketika matahari memasuki kondisi solar minimum.</em></p><p><em><strong>Kata kunci</strong></em><em>: </em><em>HF, Solar Minimum, Ionosfer, Sporadic E</em></p>

Influence of the breathing methods of the heated oxygen-helium mixture on the indicators of variability of the heart rhythm and functions of external respiration in military servers with chronic obstructive

The purpose of the research was to study the effectiveness of using heated oxygen-helium mixture in the medical rehabilitation of patients with chronic obstructive bronchitis. Material and methods. The study included 68 patients aged 32 to 56 years (43.7 4.1 years). The first group (n = 33) contained of practically healthy volunteers and the second group (n = 35) of patients with a verified diagnosis: chronic obstructive bronchitis, moderate to moderate degree of obstruction, the duration of the disease ranged from 2 to 16 years (5.4 1.4). In both groups, heated oxygen-helium mixture was used (the temperature of the mixture in the mask was 50С). Patients of the second group 30 minutes before inhalation of the heated oxygen-helium mixture used short or long-acting bronchodilators. The study was carried out before the start of therapy, after 5, 10 procedures. Estimated indicators of heart rate variability and respiratory function. Results and conclusion. The use of heated oxygen-helium mixture allowed to increase the activity of the parasympathetic department of the autonomic nervous system and reduce the tone of the sympathetic department, normalize the functioning of the bodys regulatory systems. The research data showed an increase in SDNN, RMSSD, a decrease in LF/HF wave power, and a decrease in the centralization index. After the 5th breathing procedure of the heated oxygen-helium mixture, the second group showed an increase in external respiration function by an average of 16%, and after a full course, by 20%, which indicates an improvement in pulmonary ventilation and a decrease in the degree of obstructive disorders. The use of heated oxygen-helium mixture is a promising method that does not give complications, can reduce the severity of obstructive syndrome, helps to restore the bodys adaptive systems, and can be used as one of the methods in the comprehensive rehabilitation of patients with chronic obstructive bronchitis.

PT-Symmetry in Hartree–Fock Theory

<div> <div> <p>P T -symmetry — invariance with respect to combined space reflection P and time reversal T — provides a weaker condition than (Dirac) Hermiticity for ensuring a real energy spectrum of a general non-Hermitian Hamiltonian. PT -symmetric Hamiltonians therefore form an intermediate class between Hermitian and non-Hermitian Hamiltonians. In this work, we derive the conditions for PT-symmetry in the context of electronic structure theory, and specifically, within the Hartree–Fock (HF) approximation. We show that the HF orbitals are symmetric with respect to the P T operator if and only if the effective Fock Hamiltonian is PT -symmetric, and vice versa. By extension, if an optimal self-consistent solution is invariant under PT , then its eigenvalues and corresponding HF energy must be real. Moreover, we demonstrate how one can construct explicitly PT -symmetric Slater determinants by forming PT doublets (i.e. pairing each occupied orbital with its PT -transformed analogue), allowing PT -symmetry to be conserved throughout the self-consistent process. Finally, considering the H2 molecule as an illustrative example, we observe PT-symmetry in the HF energy landscape and find that the symmetry-broken unrestricted HF wave functions (i.e. diradical configurations) are P T -symmetric, while the symmetry-broken restricted HF wave functions (i.e. ionic configurations) break PT -symmetry.</p> </div> </div>

PT-Symmetry in Hartree–Fock Theory

<div> <div> <p>P T -symmetry — invariance with respect to combined space reflection P and time reversal T — provides a weaker condition than (Dirac) Hermiticity for ensuring a real energy spectrum of a general non-Hermitian Hamiltonian. PT -symmetric Hamiltonians therefore form an intermediate class between Hermitian and non-Hermitian Hamiltonians. In this work, we derive the conditions for PT-symmetry in the context of electronic structure theory, and specifically, within the Hartree–Fock (HF) approximation. We show that the HF orbitals are symmetric with respect to the P T operator if and only if the effective Fock Hamiltonian is PT -symmetric, and vice versa. By extension, if an optimal self-consistent solution is invariant under PT , then its eigenvalues and corresponding HF energy must be real. Moreover, we demonstrate how one can construct explicitly PT -symmetric Slater determinants by forming PT doublets (i.e. pairing each occupied orbital with its PT -transformed analogue), allowing PT -symmetry to be conserved throughout the self-consistent process. Finally, considering the H2 molecule as an illustrative example, we observe PT-symmetry in the HF energy landscape and find that the symmetry-broken unrestricted HF wave functions (i.e. diradical configurations) are P T -symmetric, while the symmetry-broken restricted HF wave functions (i.e. ionic configurations) break PT -symmetry.</p> </div> </div>

Electron correlation in Li + , He, H − and the critical nuclear charge system Z C : energies, densities and Coulomb holes

This paper presents high-accuracy correlation energies, intracule densities and Coulomb hole(s) for the lithium cation, helium, hydride ion and the system with the critical nuclear charge, Z C , for binding two electrons. The fully correlated (FC) wave function and the Hartree–Fock (HF) wave function are both determined using a Laguerre-based wave function. It is found that for the lithium cation and the helium atom a secondary Coulomb hole is present, in agreement with a previous literature finding, confirming a counterintuitive conclusion that electron correlation can act to bring distant electrons closer together. However, no evidence for a tertiary Coulomb hole is found. For the hydride anion and the system just prior to electron detachment only a single Coulomb hole is present and electron correlation decreases the probability of finding the electrons closer together at all radial distances. The emergence of a secondary Coulomb hole is investigated and found to occur between Z = 1.15 and Z = 1.20. The FC and HF energies and intracule densities (in atomic units) used to calculate the correlation energy and Coulomb hole, respectively, are accurate to at least the nano-scale for helium and the cation and at least the micro-scale for the anions.