Presence Of Dynamic Instability Research Articles

Exploring Jupiter's Polar Deformation Lengths with High-resolution Shallow Water Modeling

The polar regions of Jupiter host a myriad of dynamically interesting phenomena, including vortex configurations, folded-filamentary regions (FFRs), and chaotic flows. Juno observations have provided unprecedented views of the high latitudes, allowing for more constraints to be placed upon the troposphere and the overall atmospheric energy cycle. Moist convective events are believed to be the primary drivers of energetic storm behavior as observed on the planet. Here we introduce a novel single-layer shallow water model to investigate the effects of polar moist convective events at high resolution, the presence of dynamical instabilities over long timescales, and the emergence of FFRs at high latitudes. We use a flexible, highly parallelizable, finite difference hydrodynamic code to explore the parameter space set up by previous models. We study the long-term effects of deformation length (L d ), injected pulse size, and injected geopotential. We find that models with L d beyond 1500 km (planetary Burger number, Bu = 4.4 × 10−4) tend to homogenize their potential vorticity in the form of dominant stable polar cyclones, while lower-L d cases tend to show less stability with regard to Arnol’d-type flows. We also find that large turbulent forcing scales consistently lead to the formation of high-latitude FFRs. Our findings support the idea that moist convection occurring at high latitudes may be sufficient to produce the dynamical variety seen at the Jovian poles. Additionally, derived values of localized horizontal shear and L d may constrain FFR formation and evolution.

Case Series of Tubular Retractor Assisted Minimally Invasive Extraforaminal L5/S1 Microdiskectomy

We present the largest series of tubular assisted minimally invasive extraforaminal L5/S1 microdiskectomy and describe the operative nuances. An extraforaminal L5/S1 disk herniation poses a surgical challenge as a result of limited access from a high iliac crest, the sacral ala, and the large transverse process of L5 necessitating oblique working angles. This is a case series of 28 consecutive patients who underwent tubular retractor-assisted minimally invasive extraforaminal L5/S1 microdiskectomy between 2017 and 2020 for L5 radiculopathy. Preoperative variables include demographics (age, gender); imaging characteristics (presence of spondylolisthesis, grade and presence of dynamic instability); and patient-reported measures of pain and function. Postoperatively, any complications, pain, and function were documented at 1-day, 3-month, and 12-months follow-up. Statistical analysis involved descriptive analysis of measured variables. Patients (13 females and 15 males) had a median age of 62 years (range: 32-92). One patient demonstrated grade I spondylolisthesis with no dynamic instability. Twenty-six patients (93%) achieved complete pain resolution during the follow-up period. Two patients had persistent or recurrent radicular pain, 1 of whom resolved completely with a redo tubular retractor-assisted minimally invasive microdiskectomy. No other complications were noted during the postoperative follow-up. Tubular retractor-assisted minimally invasive extraforaminal L5/S1 microdiskectomy is an effective approach. Good surgical outcomes are achieved while avoiding the complications associated with more invasive options such as open surgery or fusion.

Can facet joint fluid on MRI and dynamic instability be a predictor of improvement in back pain following lumbar fusion for degenerative spondylolisthesis?

To investigate the relationship between lumbar facet fluid and dynamic instability in degenerative spondylolisthesis (DS), as well as the relationship between facet fluid and patient-reported outcomes following a posterior lumbar fusion. We analyzed consecutive patients with degenerative spondylolisthesis undergoing single level posterior lumbar fusion from December 2010 to January 2013 at a single academic institution. We investigated the relationship between fluid in the facet joint as measured on axial MRI and the presence of dynamic instability. We investigated the impact of facet fluid, Modic changes, and dynamic instability on patient-reported outcomes. There was a significant association between the amount of facet joint fluid and the presence of dynamic instability (p=0.03); as facet fluid increases, the probability of dynamic instability also increases. For every 1mm of facet fluid, there was a 41.6% increase (95% CI 1.8-97) in the odds of dynamic instability. A facet fluid amount less than 0.5mm gave a 90% probability that there was no dynamic instability. The presence of facet fluid and dynamic instability were associated with achieving minimal clinical important difference (MCID) in low back pain following lumbar fusion (p=0.04 and 0.05, respectively). Facet joint fluid is associated with the presence of dynamic instability in DS. The presence of facet fluid and dynamic instability may predict increased likelihood of achieving MCID for improvement in back pain following posterior lumbar fusion.

Resilience, Weather and Dynamic Adjustments in Agroecosystems: The Case of Wheat Yield in England

The paper presents an investigation of agroecosystem dynamics with an application to wheat yield data in England over the period 1885–2012. The analysis relies on a Threshold Quantile Autoregressive model. The model allows for lag effects to vary across quantiles of the distribution as well as with the values taken by the lagged variables. The analysis documents the dynamics and persistence of yield adjustments to shocks. The estimates indicate the presence of dynamic instability in the lower quantile of the distribution. The analysis shows that, after controlling for the role of technological trend, wheat yield exhibits resilience to adverse weather shocks.

Morphology, kinematics and modelling of the elliptical planetary nebula Sa 2-21

The little studied PN, Sa 2-21 has been observed using the Manchester echelle spectrometer at the Anglo-Australian telescope. Narrow band, long-slit spectra were obtained at six positions over two perpendicular position angles in both the [N II] λ6584 A and [O III] λ5007 A emission lines. An [O III] halo has been detected for the first time. A morphological modelling program was used to help determine the geometry, structure and kinematics of this ellipsoidal PN. It is proposed that the structure includes a pair of mid-latitude rings of IN II] emission, not previously seen in elliptical PNe. Radial spokes of [O III] emission have been detected in the main nebular shell indicating the presence of dynamical instabilities.

Second-quantized Landau-Zener theory for dynamical instabilities

State engineering in nonlinear quantum dynamics sometimes may demand driving the system through a sequence of dynamically unstable intermediate states. This very general scenario is especially relevant to the dilute Bose-Einstein condensates, for which ambitious control schemes have been based on the powerful Gross-Pitaevskii mean-field theory. Since this theory breaks down on logarithmically short time scales in the presence of dynamical instabilities, an interval of instabilities introduces quantum corrections, which may possibly derail a control scheme. To provide a widely applicable theory for such quantum corrections, this paper solves a general problem of time-dependent quantum-mechanical dynamical instability, by modeling it as a second-quantized analog of a Landau-Zener avoided crossing: a ``twisted crossing.''

Polarization switch in a Zeeman laser in the presence of dynamical instabilities

The well-known switch of the polarization state of a Zeeman laser's emission into a single longitudinal mode as the cavity length is detuned is re-examined using a model that goes beyond third-order Lamb theory by retaining equations for the dynamics of the material variables for a J = 1 to J = 0 transition. For certain parameter values, the output of the laser as described by this model is predominantly two orthogonally polarized modes with different optical frequencies, as in third-order Lamb theories studied previously, but the more complicated field-material dynamics and near-threshold time-dependent solutions present in this model also give rise to more complicated pulsations and polarization dynamics as the cavity is detuned. Also as in third-order Lamb theories, in this model the preference (stability) for circularly or linearly polarized single mode emission depends on the ratio of the decay rates of the magnetic dipole and the electric quadrupole of the J = 1 level. For conditions in which the cross-saturation preference is for linearly polarized emission and there are weak linear anisotropies, the switching of the polarization state as the cavity is detuned has a range of overlap of the two polarization states (and corresponding time dependent dynamics) rather than the abrupt switching and hysteresis or polarization rotation more commonly found in simpler models. The detuning range for the overlap is sensitively dependent on the strength of the cross-saturation coupling. While there is similar exchange of relative dominance of two polarized modes when there is the combination of weak circular polarization anisotropies and cross-saturation preference for linearly polarized emission, the overlap region remains large, and it is relatively independent of the relaxation rate of the coherence between the upper levels. By comparing these results with experimental behavior found in a xenon laser which operates on a J = 3 → J = 2 transition we can estimate the effective parameters of the model suitable for describing certain features of this experimental situation, even though the xenon laser is known to have its preference for linearly polarized emission arise directly in the field-matter interaction rather than solely from relaxation rate differences as it does in the model considered here.

A Fixed-Lag Kalman Smoother for Retrospective Data Assimilation

Analyses incorporating future data, as well as current and past data, are termed retrospective analyses. In this paper, the fixed-lag Kalman smoother (FLKS) is proposed as a means of providing retrospective analysis capability in data assimilation. The FLKS is a direct generalization of the Kalman filter. It incorporates all data observed up to and including some fixed amount of time past each analysis time. A computationally efficient form of the FLKS is derived. A simple scalar examination of the FLKS demonstrates that incorporating future data improves analyses the most in the presence of dynamical instabilities, for accurate models and for accurate observations. An implementation of the FLKS for two-dimensional linear shallow-water model corroborates the scalar analysis. The numerical experiments also demonstrate the ability of the FLKS to propagate information upstream as well as downstream, thus improving analysis quality substantially in data voids.

Two interacting Seyfert 2 galaxies - VV 343 and III ZW 55

Spectroscopic results are presented for the nonisolated Seyfert 2 galaxies NGC 7674 and III Zw 55 and their respective companions. The values of the redshifts confirm that both active galaxies are members of physical groups. Signs of the presence of dynamical instabilities are found in both of the Seyfert galaxies. The extended emission in NGC 7674 and part of the far-IR fluxes of NGC 1410 are interpreted as being produced by hot, newly produced stars. Because of the significant differences in the level of activity in the two Seyfert objects, it is argued that even if gravitational interaction can trigger nuclear activity, the form in which it manifests itself largely depends on the particular properties of each object. 44 references.

Demand for international money 1962–1977

It has previously been shown that there is a well established pattern of substitution between external holdings of major currencies [ Chrystal (1977)]. The present paper extends the earlier results through a period of major perturbations in the international monetary system. Such substitutions continue to be well defined, though the present results indicate the presence of dynamic instability in the system as specified.