Glacial Lake Evolution (1962–2018) and Outburst Susceptibility of Gurudongmar Lake Complex in the Tista Basin, Sikkim Himalaya (India)

The Sikkim Himalayan glaciers and glacial lakes are affected by climate change like other parts of the Himalayas. As a result of this climate variability in the Sikkim Himalaya, a detailed study of the Gurudongmar lake complex (GLC) evolution and outburst susceptibility assessment is required. Glacial lake volume estimation and lake outburst susceptibility assessment were carried out to reveal different characteristics for all four lakes (GL-1, GL-2, GL-3, and GL-4) from the lake complex. Each of these lakes has a moderate to very high potential to outburst. As the dam of GL-1 provides no retention capacity, there is a very high potential of a combined effect with the sudden failure of the moraine-dams of GL-2 or GL-3 located upstream. Temporal analysis of GLC using optical remote sensing data and in-field investigations revealed a rapidly increasing total lake area by ~74 ± 3%, with an expansion rate of +0.03 ± 0.002 km2 a−1 between 1962 and 2018 due to climate change and ongoing glacier retreat. The overall lake area expansion rates are dependent on climate-driven factors, and constantly increasing average air temperature is responsible for the enlargement of the lake areas. Simultaneously, changes in GLC expansion velocity are driven by changes in the total amount of precipitation. The deficit in precipitation probably triggered the initial higher rate from 1962 to 1988 during the winter and spring seasons. The post-1990s positive anomaly in precipitation might have reduced the rate of the glacial lake area expansion considerably.

Discovery of a Wind-blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma

We report on CO and H i studies of the mixed-morphology supernova remnant (SNR) G346.6−0.2. We find a wind-blown bubble along the radio continuum shell with an expansion velocity of ∼10 km s−1, which was likely formed by strong stellar winds from the high-mass progenitor of the SNR. The radial velocities of the CO/H i bubbles at V LSR = −82 to −59 km s−1 are also consistent with those of shock-excited 1720 MHz OH masers. The molecular cloud in the northeastern shell shows a high kinetic temperature of ∼60 K, suggesting that shock heating occurred. The H i absorption studies imply that G346.6−0.2 is located on the farside of the Galactic center from us, and the kinematic distance of the SNR is derived to be 11.1 − 0.3 + 0.5 kpc. We find that the CO line intensity has no specific correlation with the electron temperature of recombining plasma, implying that the recombining plasma in G346.6−0.2 was likely produced by adiabatic cooling. With our estimates of the interstellar proton density of 280 cm−3 and gamma-ray luminosity <5.8 × 1034 erg s−1, the total energy of accelerated cosmic rays of W p < 9.3 × 1047 erg is obtained. A comparison of the age–W p relation to other SNRs suggests that most of the accelerated cosmic rays in G346.6−0.2 have escaped from the SNR shell.

Multiwavelength Observations of Sgr A*. I. 2019 July 18

We present and analyze ALMA submillimeter observations from a multiwavelength campaign of Sgr A* during 2019 July 18. In addition to the submillimeter, we utilize concurrent mid-infrared (mid-IR; Spitzer) and X-ray (Chandra) observations. The submillimeter emission lags less than δ t ≈ 30 minutes behind the mid-IR data. However, the entire submillimeter flare was not observed, raising the possibility that the time delay is a consequence of incomplete sampling of the light curve. The decay of the submillimeter emission is not consistent with synchrotron cooling. Therefore, we analyze these data adopting an adiabatically expanding synchrotron source that is initially optically thick or thin in the submillimeter, yielding time-delayed or synchronous flaring with the IR, respectively. The time-delayed model is consistent with a plasma blob of radius 0.8 R S (Schwarzschild radius), electron power-law index p = 3.5 (N(E) ∝ E −p ), equipartition magnetic field of B eq ≈ 90 Gauss, and expansion velocity v exp ≈ 0.004 c . The simultaneous emission is fit by a plasma blob of radius 2 R S, p = 2.5, B eq ≈ 27 Gauss, and v exp ≈ 0.014 c . Since the submillimeter time delay is not completely unambiguous, we cannot definitively conclude which model better represents the data. This observation presents the best evidence for a unified flaring mechanism between submillimeter and X-ray wavelengths and places significant constraints on the source size and magnetic field strength. We show that concurrent observations at lower frequencies would be able to determine if the flaring emission is initially optically thick or thin in the submillimeter.

Feedback from γ Cassiopeiae: Large Expanding Cavity, Accelerating Cometary Globules, and Peculiar X-Ray Emission

We present wide-field multiwavelength observations of γ Cassiopeiae (or γ Cas for short) in order to study its feedback toward the interstellar environment. A large expanding cavity is discovered toward γ Cas in the neutral hydrogen (H i) images at a systemic velocity of about −10 km s−1. The measured dimension of the cavity is roughly 2.°0 × 1.°4 (or 6.0 pc × 4.2 pc at a distance of 168 pc), while the expansion velocity is ∼5.0 ± 0.5 km s−1. The CO observations reveal systematic velocity gradients in IC 63 (∼20 km s−1 pc−1) and IC 59 (∼30 km s−1 pc−1), two cometary globules illuminated by γ Cas, proving fast acceleration of the globules under stellar radiation pressure. The gas kinematics indicate that the cavity is opened by strong stellar wind, which has high potential to lead to the peculiar X-ray emission observed in γ Cas. Our result favors a new scenario that emphasizes the roles of stellar wind and binarity in the X-ray emission of the γ Cas stars.

On the Dynamics of Transient Plasmas Generated by Nanosecond Laser Ablation of Several Metals

The dynamics of transient plasma generated by UV ns-laser ablation of selected metals (Co, Cu, Ag, Bi) were investigated by the Langmuir Probe method in angle- and time-resolved modes. Multiple ionic and electronic structures were seen for all plasmas with some corresponding to anions or nanoparticle-dominated structures. The addition of an Ar atmosphere energetically confined the plasma and increased the charge density by several orders of magnitude. For pressure ranges exceeding 0.5 Pa fast ions were generated in the plasma as a result of Ar ionization and acceleration in the double layer defining the front of the plasma plume. Several correlations between the target nature plasma properties were attempted. The individual plasma structure expansion velocity increases with the melting point and decreases with the atomic mass while the corresponding charged particle densities decrease with the melting point, evidencing the relationship between the volatility of the sample and the overall abated mass.

Measurement of the expansion velocity of the plasma high-current vacuum arc discharge

In this work, we present experimental results on measuring the velocity of vacuum arc discharge plasma expansion. In the experiments, two designs of plasma guns were used. In the first version, the end of the arc discharge cathode was located below the plane of the anode, and the surface of the insulator separating them was parallel to the axis of symmetry of the plasma gun. In this design, the arc discharge plasma escapes the anode through a hole, the diameter of which coincides with the diameter of the cathode. In the second variant, the plane of the end face of the arc discharge cathode coincided with the plane of the anode, and the surface of the insulator separating them was located perpendicular to the axis of symmetry of the plasma gun. To obtain an image of plasma in the optical range, an FER-7 optical streak camera was used. Based on the results obtained, it can be concluded that the expansion velocity of the plasma of a high-current vacuum arc discharge does not depend on the design of the guns considered in this experiment.

Plasma channel dynamics in sub- and microsecond discharges in water

Simulation results of a fast electric discharge and a strong acoustic wave in the water is performed. A theoretical model of a high-current plasma channel is presented. The model accounts for the energy ratio between the input electric power and the plasma channel conductivity, and adiabatic expansion mechanism of this channel in water. It allows you to calculate the dynamics of the expansion of the channel and the generation of a radially diverging acoustic wave. The presented study makes it possible to estimate the probable parameters of the phenomenon: when electric energy is introduced into the channel, its expansion velocity reaches 1.9 km/s, electrons number density in the plasma is up to 2·1020 cm−3. In this case, a strong acoustic wave propagates with a sonic speed (~ 1500 m/s), and the pressure amplitude in the vicinity of the plasma channel can reach 200 MPa. The stability of the model in relation to variations in the initial task parameters has been analyzed. The calculated data for the acoustic wave are in good agreement with the measurements.

The effect of voids shape on hypervelocity cylindrical cavity expansion and shock waves formation in transversely isotropic porous materials

This paper investigates the steady-state dynamic radial expansion of a pressurized circular cylindrical cavity in an infinite porous medium modeled with the constitutive framework developed by Monchiet et al. (2008), which considers the material to display a periodic porous microstructure with spheroidal voids and matrix described by the orthotropic yield criterion of Hill (1948). For that purpose, we have extended the formulation of dos Santos et al. (2019) to consider oblate and prolate voids, which allows to assess the role of the initial voids shape on the elastoplastic-anisotropic fields that develop near the cavity. The theoretical development follows the cavity expansion formalism of Cohen and Durban (2013) and employs the artificial viscosity approach of Lew et al. (2001) to avoid singularities in the field variables due to the formation of plastic shock waves. The main outcome of this work is a relationship between the critical cavity expansion velocity for which plastic shocks emerge and the initial aspect ratio of the spheroidal voids. The results show that the formation of shocks is delayed for oblate voids, in comparison with spherical and prolate voids. These findings have been substantiated for different anisotropic behaviors and initial void volume fractions.

The Investigation of the Relation Between Expansion Strategy and Outcomes of Two-Stage Expander-Implant Breast Reconstruction

Numerous risk factors for the complications of two-stage, immediate implant-based breast reconstruction have been identified, although few studies have directly examined the impact of breast size and expansion protocols on the surgical outcomes of breast reconstruction. This study aimed to evaluate the impact of breast size, expansion velocity, and volume-related variables on postoperative complications of breast reconstruction. The cohort involved patients who underwent immediate breast expander reconstruction at a single center between 2017 and 2019. The breast size was classified into three categories according to the weight of the mastectomy specimen as small (< 300 g), medium (≥ 300 g, ≤ 500 g), or large (> 500 g). Multifactorial logistic regressions were used to assess the impact of variables, and receiver operating curve (ROC) analysis was used to determine the optimal cut-off value for predicting the complication event. Of the 174 breasts (168 patients), 51 (29.3%), 66 (37.9%), and 57 (32.6%) breasts were classified as small, medium, and large, respectively. The rate of infection (p = 0.014) and expander/implant failure (p = 0.007) significantly differed according to breast size, with the rate being the highest in large breasts. Multivariate logistic regression analysis showed that body mass index (odds ratio [OR]: 1.25, p = 0.003), nipple-sparing mastectomy (OR: 2.82, p = 0.036), sentinel biopsy (OR: 5.10, p = 0.016), final expansion volume (OR: 0.99, p = 0.022), and expansion velocity (OR: 0.703, p = 0.024) were significant independent predictors of any complication. In the ROC analysis, breast weight > 696 g could predict the possibility of revision surgery, with a sensitivity of 42.9% and specificity of 81.8%. The final expansion volume and expansion velocity have a significant negative relationship with overall complications in breast reconstruction. A standard expansion protocol needs to be established to ensure the success of two-stage breast reconstruction.

Flow directions of low-energy ions in and around the diamagnetic cavity of comet 67P

The flow direction of low-energy ions around comet 67P/Churyumov-Gerasimenko has previously been difficult to constrain due to the influence of the spacecraft potential. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) on Rosetta measured the distribution function of positive ions with energies down to just a few eV/q throughout the escort phase of the mission. Unfortunately, the substantial negative spacecraft potential distorted the directional information of the low-energy data. In this work, we present the flow directions of low-energy ions around comet 67P, corrected for the spacecraft potential using Particle-In-Cell simulation results. We focus on the region in and around the diamagnetic cavity, where low-energy ions are especially important for the dynamics. We separate between slightly accelerated “burst” features and a more constant “band” of low-energy ions visible in the data. The “bursts” are flowing radially outwards from the nucleus with an anti-sunward component while the “band” is predominantly streaming back towards the comet. This provides evidence of counter-streaming ions, which has implications for the overall expansion velocity of the ions. The backstreaming ions are present also at times when the diamagnetic cavity was not detected, indicating that the process accelerating the ions back towards the comet is not connected to the cavity boundary.