Numerical Simulations of Mass Transfer in Close and Contact Binaries Using Bipolytropes

We present the first self-consistent, three dimensional study of hydrodynamic simulations of mass transfer in close and contact binary systems, with both stars represented as bipolytropes (composite polytopes). The project is motivated by the recent eruption of V1309 Scorpii which was proved to be the merger of a contact binary system. The final eruption is assumed to be the disruption of the core of the secondary inside the more massive star. The initial, equilibrium binary models are rotating synchronously in circular orbits and are obtained using the Bipolytropic Self Consistent Field (BSCF) technique, which is a modi cation of Hachisu\u27s Self Consistent Field (HSCF) method. Both stars have a fully resolved core and envelope structure where the difference in equation of state is represented by different polytropic indices and the difference in composition is represented as the ratio of the average molecular weights. The validity of the BSCF method is confirmed by constructing single, rapidly rotating stars and toroidal disks and comparing their properties with well established numerical as well as analytical results. We simulate mass transfer and mergers of bipolytropic binary systems using two fully three-dimensional grid-based Eulerian codes, Flow-ER and Octotiger, at two different resolutions. We discuss the suitability of both the codes to simulate bipolytropic stellar binaries faithfully. The simulations conducted using the Flow-ER code show certain numerical artifacts due to the limited resolving capacity of the implemented fixed cylindrical grid. We compare the results of these simulations with ones carried out using Octotiger with Adaptive Mesh Refinement (AMR) capabilities, where most of the limitations have been improved upon. The initial conditions for each simulation across the codes are chosen to match as closely as possible so that the simulations can be used as benchmarks. Although there are some key differences, the detailed comparison of the simulations suggests that there is remarkable agreement between the results obtained using the two codes. With the comparison across the resolutions, we found that both the hydrodynamic codes are convergent. This study enables us to confidently simulate mass transfer and merger scenarios of binary systems involving bipolytropic components

Outcome of comparative study of mini-laparoscopic cholecystectomy versus conventional laparoscopic cholecystectomy

Background: Laparoscopic cholecystectomy (LC) is considered the gold standard for cholecystectomy procedures. In recent years, many investigators have attempted to further improve the established technique of LC with the goal of minimising invasiveness of this procedure by reducing the number and size of the operating ports and instruments.Methods: This was a retrospective study done in a tertiary care hospital comparing the safety and efficacy of mini-laparoscopic cholecystectomy (MLC) with conventional laparoscopic cholecystectomy (CLC) done during the time period of June 2020 to January 2022 based on the variables like total operating time, post-operative pain, conversion rate to open procedure, duration of hospital stay and cosmetic results.Results: Out of 40 cases were collected and analysed, MLC has an advantage over CLC like postop pain on postop day 1 (p=0.016) and on postop day 3 (0.025) and postoperative scar (p<0.001). In aspects like duration of hospital stay (p=0.359) and operating time (p=0.805) MLC is equally comparable to CLC. CLC is proved to be better than MLC in one aspect- conversion to open cholecystectomy (p=0.042).Conclusions: Miniaturised instrumentation is an area of research which is studied for the past 3 decades. Although improved instrument durability and better optics are needed for widespread use of miniport techniques, this MLC approach can be routinely offered to many properly selected patients undergoing elective LC

Self-Sustaining Vortices in Protoplanetary Disks: Setting the Stage for Planetary System Formation

The core accretion scenario of planet formation assumes that planetesimals and planetary embryos are formed during the primordial, gaseous phases of the protoplanetary disk. However, how the dust particles overcome the traditional growth barriers is not well understood. The recently proposed viscous ring-instability may explain the concentric rings observed in protoplanetary disks by assuming that the dust grains can reduce the gas conductivity, which can weaken the magneto-rotational instability. We present an analysis of this model with the help of GPU-based numerical hydrodynamic simulations of coupled gas and dust in the thin-disk limit. During the evolution of the disk the dusty rings become Rossby unstable and break up into a cascade of small-scale vortices. The vortices form secularly stable dusty structures, which could be sites of planetesimal formation by the streaming instability as well as direct gravitational collapse. The phenomenon of self-sustaining vortices is consistent with observational constraints of exoplanets and sets a favorable environment for planetary system formation.Comment: 10 pages, accepted for publication in MNRA

A Numerical Method for Generating Rapidly Rotating Bipolytropic Structures in Equilibrium

We demonstrate that rapidly rotating bipolytropic (composite polytropic) stars and toroidal disks can be obtained using Hachisu's self consistent field technique. The core and the envelope in such a structure can have different polytropic indices and also different average molecular weights. The models converge for high $T/|W|$ cases, where T is the kinetic energy and W is the gravitational energy of the system. The agreement between our numerical solutions with known analytical as well as previously calculated numerical results is excellent. We show that the uniform rotation lowers the maximum core mass fraction or the Sch$\ddot{\rm{o}}$nberg-Chandrasekhar limit for a bipolytropic sequence. We also discuss the applications of this method to magnetic braking in low mass stars with convective envelopes

Numerical Simulations of Mass Transfer in Binaries with Bipolytropic Components

We present the first self-consistent, three dimensional study of hydrodynamic simulations of mass transfer in binary systems with bipolytropic (composite polytropic) components. In certain systems, such as contact binaries or during the common envelope phase, the core-envelope structure of the stars plays an important role in binary interactions. In this paper, we compare mass transfer simulations of bipolytropic binary systems in order to test the suitability of our numerical tools for investigating the dynamical behaviour of such systems. The initial, equilibrium binary models possess a core-envelope structure and are obtained using the bipolytropic self-consistent field technique. We conduct mass transfer simulations using two independent, fully three-dimensional, Eulerian codes - Flow-ER and Octo-tiger. These hydrodynamic codes are compared across binary systems undergoing unstable as well as stable mass transfer, and the former at two resolutions. The initial conditions for each simulation and for each code are chosen to match closely so that the simulations can be used as benchmarks. Although there are some key differences, the detailed comparison of the simulations suggests that there is remarkable agreement between the results obtained using the two codes. This study puts our numerical tools on a secure footing, and enables us to reliably simulate specific mass transfer scenarios of binary systems involving components with a core-envelope structure

Outbursts in Global Protoplanetary Disk Simulations

While accreting through a circumstellar disk, young stellar objects are observed to undergo sudden and powerful accretion events known as FUor or EXor outbursts. Although such episodic accretion is considered to be an integral part of the star formation process, the triggers and mechanisms behind them remain uncertain. We conducted global numerical hydrodynamics simulations of protoplanetary disk formation and evolution in the thin-disk limit, assuming both magnetically layered and fully magnetorotational instability (MRI)-active disk structure. In this paper, we characterize the nature of the outbursts occurring in these simulations. The instability in the dead zone of a typical layered disk results in "MRI outbursts". We explore their progression and their dependence on the layered disk parameters as well as cloud core mass. The simulations of fully MRI-active disks showed an instability analogous to the classical thermal instability. This instability manifested at two temperatures--above approximately 1400 K and 3500 K--due to the steep dependence of Rosseland opacity on the temperature. The origin of these thermally unstable regions is related to the bump in opacity resulting from molecular absorption by water vapor and may be viewed as a novel mechanism behind some of the shorter duration accretion events. Although we demonstrated local thermal instability in the disk, more investigations are needed to confirm that a large-scale global instability will ensue. We conclude that the magnetic structure of a disk, its composition, as well as the stellar mass, can significantly affect the nature of episodic accretion in young stellar objects.Comment: 16 figure

Eruptive Behavior of Magnetically Layered Protoplanetary Disks in Low-metallicity Environments

A protoplanetary disk typically forms a dead zone near its midplane at the distance of a few au from the central protostar. Accretion through such a magnetically layered disk can be intrinsically unstable and has been associated with episodic outbursts in young stellar objects. We present the first investigation into the effects of low metallicity environment on the structure of the dead zone as well as the resulting outbursting behavior of the protoplanetary disk. We conducted global numerical hydrodynamic simulations of protoplanetary disk formation and evolution in the thin-disk limit. The consequences of metallicity were considered via its effects on the gas and dust opacity of the disk, the thickness of the magnetically active surface layer, and the temperature of the prestellar cloud core. We show that the metal poor disks accumulate much more mass in the innermost regions, as compared to the solar metallicity counterparts. The duration of the outbursting phase also varies with metallicity - the low metallicity disks showed more powerful luminosity eruptions with a shorter burst phase, which was confined mostly to the early, embedded stages of the disk evolution. The lowest metallicity disks with the higher cloud core temperature showed the most significant differences. The occurrence of outbursts was relatively rare in the disks around low mass stars and this was especially true at lowest metallicities. We conclude that the metal content of the disk environment can have profound effects on both the disk structure and evolution in terms of episodic accretion.Comment: 24 pages, 11 figure

Self-sustaining vortices in protoplanetary discs: Setting the stage for planetary system formation

The core accretion scenario of planet formation assumes that planetesimals and planetary embryos are formed during the primordial, gaseous phases of the protoplanetary disc. However, how the dust particles overcome the traditional growth barriers is not well understood. The recently proposed viscous ring-instability may explain the concentric rings observed in protoplanetary discs by assuming that the dust grains can reduce the gas conductivity, which can weaken the magnetorotational instability. We present an analysis of this model with the help of GPU-based numerical hydrodynamic simulations of coupled gas and dust in the thin-disc limit. During the evolution of the disc the dusty rings become Rossby unstable and breakup into a cascade of small-scale vortices. The vortices form secularly stable dusty structures, which could be sites of planetesimal formation by the streaming instability as well as direct gravitational collapse. The phenomenon of self-sustaining vortices is consistent with observational constraints of exoplanets and sets a favourable environment for planetary system formation

Real-world evidence on the effectiveness and safety of gliclazide extended release treatment in Indian patients with type 2 diabetes undergoing Ramadan fast: an analysis from the global DIA-RAMADAN study

Context and Aim: Glycemic imbalance, especially hypoglycemia, is one of the greatest risks for patients with type 2 diabetes mellitus (T2DM) during Ramadan fasting. This paper outlines the efficacy and safety of gliclazide extended release (XR) in Indian patients with T2DM enrolled in the global DIA-RAMADAN study. Methods and Material: Adults (aged ≥18 years) with T2DM who chose to fast during Ramadan and received a gliclazide-based regimen once daily for 90 days before Ramadan were included in the study. Baseline and end-of-study visits were conducted 6–8 weeks before and 4–6 weeks after Ramadan, respectively. Primary outcome was the incidence of ≥1 symptomatic hypoglycemic event (HE). Changes in glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), and body weight were secondary outcomes. Results: Among 246 Indian patients enrolled in the study, most (78.9%, n=194) were at moderate/low risk as per the International Diabetes Federation and Diabetes and Ramadan guidelines. Most patients (69.1%) received gliclazide XR as monotherapy, and the rest received gliclazide XR with metformin or other antidiabetic therapy. Significant reductions in HbA1c (−0.5±0.8%, P&lt;0.001) and FPG (−21.8±59.4 mg/dL, P&lt;0.001) levels were observed but the slight reduction in body weight was not statistically significant (−0.3±3.7 kg, P=0.614) in patients post-Ramadan. Overall, no HE was reported in Indian patients with T2DM during Ramadan fasting. Conclusion: Overall, the effectiveness and safety of gliclazide XR in Indian patients was consistent with that observed in the global cohort. Gliclazide XR significantly reduced HbA1c with no incidence of hypoglycemic events in Indian patients with type 2 diabetes undergoing Ramadan fast, suggesting that gliclazide XR may be used without dose modification at Iftar to maintain optimal glycemic control during Ramadan