Short-Term (30-Day) Morbidity of Biliopancreatic Diversion Compared to Roux-en-Y Gastric Bypass as Revisional Procedures for Failed Vertical Banded Gastroplasty.

BACKGROUND: Silastic ring vertical gastroplasty (SRVG) and vertical banded gastroplasty (VBG) are associated with a high failure rate due to weight regain and complications at long-term follow-up. Consequently, surgical correction for such procedures is warranted. Controversy exists as to which surgical procedure is the ideal choice for such correction. Our aim is to compare short-term outcome of Roux-en-Y gastric bypass (RYGB) and biliopancreatic diversion (BPD) repair for failed VBG/SRVG bariatric procedures. METHODS: The medical records of patients with failed SRVG who underwent corrective procedures at our institute between 2004 and 2018 were retrospectively reviewed. Patients characteristics, surgical approaches, and intraoperative and post-operative complications were examined and compared. RESULTS: Sixty patients in total underwent a surgical corrective procedure for failed SRVG. Thirty-one patients underwent RYGB, and 29 patients underwent BPD. Major complications were seen more in the RYGB group (35% = 11) compared to the BPD (6.9% = 2). Even though anastomotic leak rates were not statistically significant (p = 0.053), an apparent tendency for such a complication was noted in the RYGB group. RYGB procedure had an increased 30-day complication rate (p = 0.055) compared to RYGB. Laparoscopic approach had statistically fewer complications than open approach. No mortality was observed in either group. CONCLUSION: Our study showed that BPD is a safe option with less complication rates than RYGB in the short-term period for surgical correction of failed VBG/SRVG procedures.

Broadening of the drumhead-mode spectrum due to in-plane thermal fluctuations of two-dimensional trapped ion crystals in a Penning trap.

Two-dimensional crystals of ions stored in Penning traps are a leading platform for quantum simulation and sensing experiments. For small amplitudes, the out-of-plane motion of such crystals can be described by a discrete set of normal modes called the drumhead modes, which can be used to implement a range of quantum information protocols. However, experimental observations of crystals with Doppler-cooled and even near-ground-state-cooled drumhead modes reveal an unresolved drumhead-mode spectrum. In this work, we establish in-plane thermal fluctuations in ion positions as a major contributor to the broadening of the drumhead-mode spectrum. In the process, we demonstrate how the confining magnetic field leads to unconventional in-plane normal modes, whose average potential and kinetic energies are not equal. This property, in turn, has implications for the sampling procedure required to choose the in-plane initial conditions for molecular-dynamics simulations. For current operating conditions of the NIST Penning trap, our study suggests that the two-dimensional crystals produced in this trap undergo in-plane potential-energy fluctuations of the order of 10mK. Our study therefore motivates the need for designing improved techniques to cool the in-plane degrees of freedom.

Parametric Instability Driven by Weakly Trapped Particles in Nonlinear Plasma Waves.

This Letter describes a new parametric instability mechanism caused by a distribution f_{T} of particles trapped in the potential wells of a wave train. The mechanism explains a nonlinear instability in Trivelpiece-Gould (TG) waves, and it could also be a destabilizing factor in a range of nearly collisionless nonlinear plasma waves. The theory is compared to particle in cell simulations of TG waves.

Neoclassical transport caused by collisionless scattering across an asymmetric separatrix.

Plasma loss due to apparatus asymmetries is a ubiquitous phenomenon in magnetic plasma confinement. When the plasma equilibrium has locally trapped particle populations partitioned by a separatrix from one another and from passing particles, the asymmetry transport is enhanced. The trapped and passing particle populations react differently to the asymmetries, leading to the standard 1/ν and sqrt[ν] transport regimes of superbanana orbit theory as particles collisionally scatter from one orbit type to another. However, when the separatrix is itself asymmetric, particles can collisionlessly transit from trapped to passing and back, leading to enhanced transport.

Chaotic transport and damping from θ-ruffled separatrices.

Variations in magnetic or electrostatic confinement fields give rise to trapping separatrices, and neoclassical transport theory analyzes effects from collision-induced separatrix crossings. Experiments on pure electron plasmas now quantitatively characterize a broad range of transport and wave damping effects due to "chaotic" separatrix crossings, which occur due to equilibrium plasma rotation across θ-ruffled separatrices, and due to wave-induced separatrix fluctuations.

Measurement of screening enhancement to nuclear reaction rates using a strongly magnetized and strongly correlated non-neutral plasma.

An analogy is uncovered between the nuclear reaction rate in a dense neutral plasma and the energy equipartition rate in a strongly magnetized non-neutral plasma. In strong magnetic fields, cyclotron energy, like nuclear energy, is released only through rare close collisions between charges. The probability of such collisions is enhanced by plasma screening effects, just as in nuclear reactions. Enhancements of up to 10(10) are measured in simulations of cyclotron energy equipartition and are compared to the theory of screened nuclear reactions.

Electronic and positronic guiding-center drift ions.

A novel type of guiding-center drift ion is described. These ions occur only in strong magnetic fields. They consist of a neutral atom to which either an electron or positron is weakly bound, at a sufficiently large radius that it may be described by ExB drift dynamics. Such ions may occur naturally in astrophysical plasmas and may have been formed in recent antihydrogen experiments, where their presence would provide proof that deeply bound H atoms are being created.