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Funding: This work is from the MELT project, a component of the International Thwaites Glacier Collaboration (ITGC). Support from the National Science Foundation (NSF, grant no. 1739003) and the Natural Environment Research Council (NERC, grant no. NE/S006656/1). Logistics provided by NSF U.S. Antarctic Program and NERC British Antarctic Survey. The ship-based CTD data were supported by the ITGC TARSAN project (NERC grant nos. NE/S006419/1 and NE/S006591/1; NSF grant no. 1929991). ITGC contribution no. ITGC 047. Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica1,2,3. Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland4, making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre2,3,5. The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat3,6, both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base7,8, resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates. Publisher PDF

Filchner-Ronne Ice Shelf (FRIS) is the world’s largest ice shelf by volume. It helps regulate Antarctica’s contribution to global sea level rise, and water mass transformations within the sub-ice-shelf cavity produce globally important dense water masses. Rates of ice shelf basal melting are relatively low, however, as the production of cold (-1.9°C) and dense High Salinity Shelf Water over the Weddell Sea continental shelf isolates the ice shelf from large-scale inflow of warm water. Nevertheless, a narrow inflow of relatively warm (-1.4°C) Modified Warm Deep Water (MWDW) that hugs the western flank of Berkner Bank is observed to reach Ronne Ice Front, although the processes governing its circulation and fate remain uncertain. Here we present the first observations taken within the ice shelf cavity along this warm water inflow using the Autosub Long Range autonomous underwater vehicle. We observe a core of MWDW with a south-westward velocity of 4 cm s-1 that reaches at least 18 km into the sub-ice cavity. The hydrographic properties are spatially heterogeneous, giving rise to temporal variability that is driven by tidal advection. The highest rates of turbulent dissipation are associated with the warmest MWDW, with the vertical eddy diffusivity reaching 10-4 m2 s-1 where the water column is fully turbulent. Mixing efficiency is close to the canonical value of 0.2. Modelling studies suggest MWDW may become the dominant water mass beneath FRIS in our changing climate, providing strong motivation to understand more fully the dynamics of this MWDW inflow.

Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment1–3. Because it is grounded below sea level4,5, Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean6,7. Recent ice-flow acceleration2,8 and retreat of the ice front8–10 and GL11,12 indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice–ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.

Juvenile social experience, such as social isolation, has profound effects on communicative behavior, including signal production and reception. In the current study, we explored responsiveness to the neuromodulator serotonin as a potential mechanistic link between early life social isolation and auditory processing. The serotonergic system is sensitive to social isolation in many brain regions including the inferior colliculus (IC), an auditory midbrain nucleus. We investigated the effects of social experience on serotonergic responsiveness by measuring cFos, an immediate early gene product, in the IC of female mice. Serotonin was manipulated pharmacologically by administering fenfluramine, pCPA, or saline to mice that had undergone an extreme dichotomy in social experience after weaning: being housed in social groups versus individually. These mice were exposed to a 60-min recording of vocalizations from an opposite-sex interaction and perfused. Using immunohistochemistry, we measured the density of cFos-positive (cFos+) nuclei in the major subdivisions of the IC. Housing condition, drug treatment, and IC subregion all had a significant effect on cFos+ density. The central IC showed the highest density of cFos+ cells and also the most pronounced effects of housing condition and drug treatment. In the central IC, cFos+ density was higher following fenfluramine treatment than saline, and lower following pCPA treatment than fenfluramine. Individually housed mice showed a higher cFos+ density than socially housed mice in both of the pharmacological treatment groups, but not in the saline group. Drug treatment but not housing condition had strong effects on the behaviors of grooming, digging, rearing, and movement. Once the effects of drug condition were controlled, there were no across-individual correlations between cFos+ densities and behaviors. These findings suggest that the responses of auditory neurons to neuromodulation by serotonin are influenced by early life experience.

Warmer and more persistent intrusions of Circumpolar Deep Water (CDW) onto the West Antarctic Peninsula are a key driver of the recent increase in ice shelf mass loss. The relatively warm and salty CDW is thought to be mixed up to the base of the ice shelves via shear‐driven turbulence where it has a high capacity to melt the ice. We analyze data from a year‐long mooring beneath George VI Ice Shelf at a location where double‐diffusive layering was observed. The turbulent dissipation rates do not vary with mean flow speed, suggesting shear‐driven mixing is not the driver of basal melt at this site. Instead, we predict the observed dissipation using a new method that links along‐isopycnal stirring of temperature anomalies with double‐diffusive convection. Our work suggests that along‐isopycnal temperature variance may be a stronger indicator of melt than flow speed within strongly stratified ice shelf‐ocean boundary layers.

The melt rate of Antarctic ice shelves is of key importance for rising sea levels and future climate scenarios. Recent observations beneath Larsen C Ice Shelf revealed an ocean boundary layer that was highly turbulent and raised questions on the effect of these rich flow dynamics on the ocean heat transfer and the ice shelf melt rate. Directly motivated by the field observations, we have conducted large-eddy simulations (LES) to further examine the ocean boundary layer beneath Larsen C Ice Shelf. The LES was initialized with uniform temperature and salinity (T–S) and included a realistic tidal cycle and a small basal slope. A new parameterization based on previous work was applied at the top boundary to model near-wall turbulence and basal melting. The resulting vertical T–S profiles, melt rate, and friction velocity matched well with the Larsen C Ice Shelf observations. The instantaneous melt rate varied strongly with the tidal cycle, with faster flow increasing the turbulence and mixing of heat toward the ice base. An Ekman layer formed beneath the ice base and, due to the strong vertical shear of the current, Ekman rolls appeared in the mixed layer and stratified region (depth ≈ 20–60 m). In an additional high-resolution simulation (conducted with a smaller domain) the Ekman rolls were associated with increased turbulent kinetic energy, but a relatively small vertical heat flux. Our results will help with interpreting field observations and parameterizing the ocean-driven basal melting of ice shelves.

Increased ocean‐driven basal melting beneath Antarctic ice shelves causes grounded ice to flow into the ocean at an accelerated rate, with consequences for global sea level. The turbulent transfer of heat through the ice shelf‐ocean boundary layer is critical in setting the basal melt rate, yet the processes controlling this transfer are poorly understood and inadequately represented in global climate models. This creates large uncertainties in predictions of future sea‐level rise. Using a hot‐water drilled access hole, two turbulence instrument clusters (TICs) were deployed 2.5 and 13.5 meters beneath Larsen C Ice Shelf in December 2011. Both instruments returned a year‐long record of turbulent velocity fluctuations, providing a unique opportunity to explore the turbulent processes within the ice shelf‐ocean boundary layer. Although the scaling between the turbulent kinetic energy (TKE) dissipation rate and mean flow speed varies with distance from the ice shelf base, at both TICs the TKE dissipation rate is balanced entirely by the rate of shear production. The freshwater released by basal melting plays no role in the TKE balance. When the upper TIC is within the log‐layer, we derive an under‐ice drag coefficient of 0.0022 and a roughness length of 0.44 mm, indicating that the ice base is smooth. Finally, we demonstrate that although the canonical three‐equation melt rate parameterization can accurately predict the melt rate for this example of smooth ice underlain by a cold, tidally‐forced boundary layer, the law of the wall assumption employed by the parameterization does not hold at low flow speeds.

The long-held belief that, in a compound nucleus (CN), fluctuations in transition strengths are drawn from a Porter-Thomas distribution (PTD), i.e., a χ2 distribution of one degree of freedom has been challenged by work done post-1990 at the Los Alamos Neutron Science Center and Oak Ridge Electron Linear Accelerator facilities. To date, the focus has been on data taken in the resolved resonance regime. I put forward arguments in support of the analysis of measurements of the total cross section in the unresolved but not strongly overlapping resonance regime.

Past social experience affects the circuitry responsible for producing and interpreting current behaviors. The social behavior network (SBN) is a candidate neural ensemble to investigate the consequences of early-life social isolation. The SBN interprets and produces social behaviors, such as vocalizations, through coordinated patterns of activity (functional connectivity) between its multiple nuclei. However, the SBN is relatively unexplored with respect to murine vocal processing. The serotonergic system is sensitive to past experience and innervates many nodes of the SBN; therefore, we tested whether serotonin signaling interacts with social experience to affect patterns of immediate early gene (IEG; cFos) induction in the male SBN following playback of social vocalizations. Male mice were separated into either social housing of three mice per cage or into isolated housing at 18–24 d postnatal. After 28–30 d in housing treatment, mice were parsed into one of three drug treatment groups: control, fenfluramine (FEN; increases available serotonin), or pCPA (depletes available serotonin) and exposed to a 60-min playback of female broadband vocalizations (BBVs). FEN generally increased the number of cFos-immunoreactive (-ir) neurons within the SBN, but effects were more pronounced in socially isolated mice. Despite a generalized increase in cFos immunoreactivity, isolated mice had reduced functional connectivity, clustering, and modularity compared with socially reared mice. These results are analogous to observations of functional dysconnectivity in persons with psychopathologies and suggests that early-life social isolation modulates serotonergic regulation of social networks. Significance statement Social isolation and serotonergic signaling each modulate neural functions independently of each other. It is unknown whether these factors interact to affect activity at the level of individual nuclei, and/or functional networks. Using a vocal playback paradigm, we find that acutely increasing or systemically depleting available serotonin increased cFos immunoreactive neurons in the social behavior network (SBN) mice raised in social isolation compared to their socially reared counterparts. We show for the first time that mice raised in social isolation have reduced functional connectivity in the SBN relative to socially reared mice. Importantly, network perturbations were not resolved by drug treatment in isolated mice suggesting that social experience is necessary to facilitate functional relationships in the SBN.

Icefin performed the first long range robotic exploration of the grounding zone of Thwaites Glacier from January 9-12 2020. Icefin was part of the MELT project of the International Thwaites Glacier Collaboration deployed to the grounding zone of Thwaites Glacier, West Antarctica over the period December 2019-February 2020. MELT is an interdisciplinary project to explore rapid change across the grounding zone, and in particular basal melting. The subglacial cavity ~2km north of the grounding zone was accessed via hot water drilling on January 7-8, 2020. Icefin, a hybrid autonomous and remotely operated underwater vehicle designed for sub-ice and borehole operations, conducted over 15km of round-trip data collection under the ice along a section of the glacier from the grounding zone extending to a point 4 km oceanward. The vehicle collected data with ten different science sensors including cameras, sonars, conductivity/temperature and dissolved oxygen. Overall, the water column ranged from ~100m downstream that narrowed quickly to an average of 50m that spanned over 2km, to a long segment of ~30m thickness before quickly narrowing over 500m towards the grounding zone. The seafloor structures run roughly parallel to ice flow direction, consisting of furrows, ridges, and grooves in some cases mirrored by the ice structure. The Icefin dives revealed a diverse set of basal ice conditions, with complex geometry, including a range of terraced features, smooth ablated surfaces, crevassing, sediment rich layers of varying kinds, as well as interspersed clear, potentially accreted freshwater ice. The ocean directly beneath the ice varies spatially, from moderately well-mixed near the grounding zone to highly stratified within and below concavities in the ice downstream. Sediments along the sea floor range from fine grained downstream to course angular gravel near the grounding zone distributed between larger boulders. We observed rocky material in the ice that ranged from fine grained layers compressed within the ice to small angular particles volumetrically distributed within ice, to gravel and cobbles, as well as trapped boulders up to meter scale. In addition to the oceanographic, glaciological and sea floor conditions, we also catalogued communities of organisms along the seafloor and ice-ocean interface. We will report the highlights and initial conclusions from Icefin’s in situ data collection, and offer perspectives on change at the grounding zone.

Antarctic ice shelves restrain the flow of grounded ice into the ocean, and are thus an important control on Antarctica’s contribution to global sea level rise. West Antarctica represents the largest source of uncertainty in future sea level projections, and Thwaites Glacier has the potential to influence sea level more than any other outlet glacier in this region. The future behaviour of Thwaites Glacier is particular sensitive to basal melting in the grounding zone region. Basal melting is controlled by the turbulent transfer of heat through the ice shelf-ocean boundary layer. The physics of this boundary layer is poorly understood, however, and its inadequate representation in numerical models is hampering our ability to predict the future evolution of the Antarctic ice sheet. Using a hot-water drilled access hole, a turbulence instrument cluster was deployed in the grounding zone region of Thwaites Glacier in January 2020. By observing the momentum and scalar fluxes, these observations provide a unique opportunity to explore the important turbulent processes responsible for modulating the basal melt rate in this region. Ultimately, this observational effort will allow us to better constrain our parameterisations of the grounding zone region in large-scale numerical models, facilitating more accurate simulations of the Antarctic ice sheet in the changing climate.

Ocean‐driven basal melting of Amundsen Sea ice shelves has triggered acceleration, thinning, and grounding line retreat on many West Antarctic outlet glaciers. Here we present the first year‐long (2014) record of basal melt rate at sub‐weekly resolution from a location on the outer Pine Island Ice Shelf. Adjustment of the upper thermocline to local wind forced variability in the vertical Ekman velocity is the dominant control on basal melting at weekly to monthly timescales. Atmosphere–ice–ocean surface heat fluxes or changes in advection of modified Circumpolar Deep Water play no discernible role at these timescales. We propose that during other years, a deepening of the thermocline in Pine Island Bay driven by longer timescale processes may have suppressed the impact of local wind forcing on high‐frequency upper thermocline height variability and basal melting. This highlights the complex interplay between the different processes and their timescales that set the basal melt rate beneath Pine Island Ice Shelf.

A climatically-induced acceleration in ocean-driven melting of Antarctic ice shelves would have consequences for both the discharge of continental ice into the ocean and thus global sea level, and for the formation of Antarctic Bottom Water and the oceanic meridional overturning circulation. Using a novel gas-tight in-situ water sampler, noble gas samples have been collected from six locations beneath the Filchner Ice Shelf, the first such samples from beneath an Antarctic Ice shelf. Helium and neon are uniquely suited as tracers of glacial meltwater in the ocean. Basal meltwater fractions range from 3.6% near the ice shelf base to 0.5% near the sea floor, with distinct regional differences. We estimate an average basal melt rate for the Filchner-Ronne Ice Shelf of 177 ± 95 Gt/year, independently confirming previous results. We calculate that up to 2.7% of the meltwater has been refrozen, and we identify a local source of crustal helium.

We examine the autocorrelation function of the $^{235}\mathrm{U}(n,f)$ reaction with a view to quantify the presence of intermediate structure in the cross section. Fluctuations due to compound nucleus resonances on the eV energy scale are clearly visible up to $\ensuremath{\approx}100$ keV neutron energies. Structure on the one-keV energy scale is not present as a systematic feature of the correlation function, although it is present in the data covering the region around 20 keV.

The Filchner‐Ronne Ice Shelf, the ocean cavity beneath it, and the Weddell Sea that bounds it, form an important part of the global climate system by modulating ice discharge from the Antarctic Ice Sheet and producing cold dense water masses that feed the global thermohaline circulation. A prerequisite for modeling the ice sheet and oceanographic processes within the cavity is an accurate knowledge of the sub‐ice sheet bedrock elevation, but beneath the ice shelf where airborne radar cannot penetrate, bathymetric data are sparse. This paper presents new seismic point measurements of cavity geometry from a particularly poorly sampled region south of Berkner Island that connects the Filchner and Ronne ice shelves. An updated bathymetric grid formed by combining the new data with existing data sets reveals several new features. In particular, a sill running between Berkner Island and the mainland could alter ocean circulation within the cavity and change our understanding of paleo‐ice stream flow in the region. Also revealed are deep troughs near the grounding lines of Foundation and Support Force ice streams, which provide access for seawater with melting potential. Running an ocean tidal model with the new bathymetry reveals large differences in tidal current velocities, both within the new gridded region and further afield, potentially affecting sub‐ice shelf melt rates.

The circulation of the Arctic Ocean has traditionally been studied as a two-layer system, with a wind-driven anticyclonic gyre in the surface layer and a cyclonic boundary current in the Atlantic Water (AW) layer, primarily forced remotely through inflow and outflow to the basin. Here, an idealized numerical model is used to investigate the interplay between the dynamics of the two layers and to explore the response of the circulation in each of the layers to a change in the forcing in either layer. In the model, the intensity of the circulation in the surface and AW layers is primarily set by the ocean surface stress curl intensity and the inflow to the basin, respectively. Additionally, the surface layer circulation can strongly modulate the intensity of the intermediate layer by constraining the lateral extent of the AW current on the slope. In contrast, a change in the AW current strength has little effect on the surface layer circulation. The intensity of the circulation in the surface layer adjusts over a decade, on a time scale consistent with a balance between Ekman pumping and an eddy-induced volume flux toward the boundary, while the circulation in the AW layer adjusts quickly to any change of forcing (~1 month) through the propagation of boundary-trapped waves. As the two layers have different adjustment processes and time scales, and are subject to forcing that varies on all time scales, the interplay between the dynamics of the two layers is complex, and more simultaneous observations of the circulation within the two layers are required to fully understand it.

Recent satellite and hydrographic observations have shown that the rate of freshwater accumulation in the Beaufort Gyre of the Arctic Ocean has accelerated over the past decade. This acceleration has coincided with the dramatic decline observed in Arctic sea ice cover, which is expected to modify the efficiency of momentum transfer into the upper ocean. Here, a simple process model is used to investigate the dynamical response of the Beaufort Gyre to the changing efficiency of momentum transfer, and its link with the enhanced accumulation of freshwater. A linear relationship is found between the annual mean momentum flux and the amount of freshwater accumulated in the Beaufort Gyre. In the model, both the response time scale and the total quantity of freshwater accumulated are determined by a balance between Ekman pumping and an eddy-induced volume flux toward the boundary, highlighting the importance of eddies in the adjustment of the Arctic Ocean to a change in forcing. When the seasonal cycle in the efficiency of momentum transfer is modified (but the annual mean momentum flux is held constant), it has no effect on the accumulation of freshwater, although it does impact the timing and amplitude of the annual cycle in Beaufort Gyre freshwater content. This suggests that the decline in Arctic sea ice cover may have an impact on the magnitude and seasonality of the freshwater export into the North Atlantic.

It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant $\alpha$ over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both $\alpha$ and the average $m_q$ of the $u$ and $d$ current quark masses, and which makes explicit the dependence on mass number $A$ and atomic number $Z$. (Recent model independent results on hadronic $\sigma$-terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics (QCD) and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivity to changes in the pion mass $M_\pi$ of a single nucleon potential determined by an in-medium chiral perturbation theory ($\chi$PT) calculation which includes virtual $\mathrm{\Delta}$-excitations. Subject to some reasonable assumptions about low-energy constants (LECs), we confirm that the $m_q$-contribution to resonance shifts is enhanced by a factor of 10 or so relative to the $\alpha$-term and deduce that the Oklo data for Sm imply that $|m_q(\mathrm{Oklo})- m_q(\mathrm{now})| \lesssim 10^{-9}m_q(\mathrm{now})$., Comment: 11 pages, contribution to Light Cone 2014, Raleigh, North Carolina, USA (May 26-30), submitted to Few-Body Systems

It is argued that, for motion in a central force field, polar reciprocals of trajectories are an elegant alternative to hodographs. The principal advantage of polar reciprocals is that the transformation from a trajectory to its polar reciprocal is its own inverse. The form of polar reciprocals $k_*$ of Kepler problem orbits is established, and then the orbits $k$ themselves are shown to be conic sections using the fact that $k$ is the polar reciprocal of $k_*$. A geometrical construction is presented for the orbits of the Kepler problem starting from their polar reciprocals. No obscure knowledge of conics is required to demonstrate the validity of the method. Unlike a graphical procedure suggested by Feynman (and amended by Derbes), the algorithm based on polar reciprocals works without alteration for all three kinds of trajectories in the Kepler problem (elliptical, parabolic, and hyperbolic)., Comment: 11 pages, 5 figures, accepted for publication by American Journal of Physics

Background: A signature of many dynamical models of dark energy is that they admit variation in the fine structure constant $\ensuremath{\alpha}$ over cosmological time scales.Purpose: We reconsider the analysis of the sensitivity of neutron resonance energies ${E}_{i}$ to changes in $\ensuremath{\alpha}$ with a view to resolving uncertainties that plague earlier treatments.Methods: We point out that with more appropriate choices of nuclear parameters, the standard estimate (from Damour and Dyson) of the sensitivity for resonances in $\mathrm{Sm}$ is increased by a factor of 2.5. We go on to identify and compute excitation, Coulomb, and deformation corrections. To this end, we use deformed Fermi density distributions fitted to the output of Hartree-Fock (HF) + BCS calculations (with both the SLy4 and ${\mathrm{SkM}}^{*}$ Skyrme functionals), the energetics of the surface diffuseness of nuclei, and thermal properties of their deformation. We also invoke the eigenstate thermalization hypothesis, performing the requisite microcanonical averages with two phenomenological level densities which, via the leptodermous expansion of the level density parameter, include the effect of increased surface diffuseness. Theoretical uncertainties are assessed with the inter-model prescription of Dobaczewski et al. [J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014)].Results: The corrections diminish the revised $\mathrm{Sm}$ sensitivity but not by more than 25%. Subject to a weak and testable restriction on the change in ${m}_{q}/\mathrm{\ensuremath{\Lambda}}$ (relative to the change in $\ensuremath{\alpha})$ since the time when the Oklo reactors were active $({m}_{q}$ is the average of the $\text{u}$ and $\text{d}$ current quark masses, and $\mathrm{\ensuremath{\Lambda}}$ is the mass scale of quantum chromodynamics), we deduce that $|{\ensuremath{\alpha}}_{\text{Oklo}}\ensuremath{-}{\ensuremath{\alpha}}_{\text{now}}|l1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}{\ensuremath{\alpha}}_{\text{now}}$ (95% confidence level). The corresponding bound on the present-day time variation of $\ensuremath{\alpha}$ is tighter than the best limit to date from atomic clock experiments.Conclusions: The order of magnitude of our Oklo bound on changes in $\ensuremath{\alpha}$ is reliable. It is one order of magnitude lower than the Oklo-based bound most commonly adopted in earlier attempts to identify phenomenologically successful models of $\ensuremath{\alpha}$ variation.

We discuss a novel uniform semiclassical approximation for the bound state wave functions of simple conservative systems (of one degree of freedom) which sheds light on the success of semiclassical transformation theory in dealing with angle-action variables.

We observe that, within the effective generating function formalism for the implementation of canonical transformations within wave mechanics, non-trivial canonical transformations which leave invariant the form of the Hamilton function of the classical analogue of a quantum system manifest themselves in an integral equation for its stationary state eigenfunctions. We restrict ourselves to that subclass of these dynamical symmetries for which the corresponding effective generating functions are necessaarily free of quantum corrections. We demonstrate that infinite families of such transformations exist for a variety of familiar conservative systems of one degree of freedom. We show how the geometry of the canonical transformations and the symmetry of the effective generating function can be exploited to pin down the precise form of the integral equations for stationary state eigenfunctions. We recover several integral equations found in the literature on standard special functions of mathematical physics. We end with a brief discussion (relevant to string theory) of the generalization to scalar field theories in 1+1 dimensions.

The statistics of on-resonance measurements of the deformation effect cross section {sigma}{sub 02} in unpolarized neutron transmission through an aligned {sup 165}Ho target is discussed. Under the standard Porter-Thomas assumption about reduced partial width amplitudes, the sign of {sigma}{sub 02} is random at s-wave resonances with d-wave admixtures. Motivated by the observation of sign correlations in epithermal parity-violation studies, conditions under which a doorway state will give rise to {sigma}{sub 02}{close_quote}s of nonrandom sign are identified. Oblate shape isomers lying at excitation energies in the isolated resonance regime could meet these conditions. {copyright} {ital 1998} {ital The American Physical Society}

We introduce a Bayesian method for the analysis of epithermal neutron transmission data on space-time symmetries in which unique assignment of the prior is achieved by maximisation of the cross entropy and the imposition of a self-consistency criterion. Unlike the maximum likelihood method used in previous analyses of parity-violation data, our method is freed of an ad hoc cutoff parameter. Monte Carlo studies indicate that our self-consistent Bayesian analysis is superior to the maximum likelihood method when applied to the small data samples typical of symmetry studies.

Five to ten percent of patients with diabetes mellitus in the United States suffer from type 1 diabetes: approximately 1.5 million people. Type 1 diabetes occurs when there is no insulin production from the beta cells of the pancreas and has often been associated with younger patients and thin body habitus. Type 2 diabetes, often linked with obesity, is associated with impaired insulin secretion and insulin resistance. Although the therapeutic goal is to maintain strict glycemic control in both types, management of type 1 diabetes is of a dissimilar nature due to differences in pathophysiologic mechanisms and patient characteristics. Newer therapies are aimed at achieving better glycemic control with minimal compromise to lifestyle. Some of these treatment measures, such as insulin pump therapy, have been available for years but were not used frequently until the mid-1990s. The increased use of intensive insulin therapy became more readily acceptable after the Diabetes Control and Complications Trial showed a decrease in microvascular complications with better glycemic control (hemoglobin A1C value of 7% or less). Insulin pumps, along with meal timings and, to a certain extent, regulation of the amount of food consumed, have allowed diabetes patients a more flexible lifestyle. Newer insulins are structured to mimick the pharmacokinetics of the endogenous basal (peakless sustained activity) and bolus (short fast-acting) insulins. Development of continuous, noninvasive, glucose sensing devices may reduce the need for capillary blood glucose testing (needle pricks) and make diabetes management more patient friendly and effective.

We investigate the possibility that microscopic boson [ital g] factor estimates may require revision and consider the impact on 2[sub 1][sup +] [ital g] factors of the difference [epsilon][sub [ital v]] between the neutron and proton [ital d] boson energies found typically in microscopic evaluations of interacting boson model parameters. We recalculate microscopic estimates for both [ital d] and [ital g] boson [ital g] factors, this time using the similarity-transformed Dyson boson mapping approach. Modulo more pronounced variation at the beginning and end of shells, our results confirm previous estimates by other methods. Differences between [ital d] and [ital g] boson factors are too small for the inclusion of [ital g] bosons to have a significant effect on 2[sub 1][sup +] [ital g] factor predictions. Instead, we present qualitative and semiquantitative arguments in support of the contention that [ital microscopic] estimates of [epsilon][sub [ital v]] (taken in conjunction with our microscopic boson [ital g] factors) can, by and large, account for the systematics of 2[sub 1][sup +] [ital g] factors in the [ital Z]=50-to-82 and [ital N]=82-to-126 shells. Detailed calculations for [sup 148]Sm and [sup 154]Sm are consistent with this assertion provided the Majorana interaction strength [xi][sub 2] is negligible. more » Our detailed calculations suggest substantial [ital F]-spin admixtures in the 2[sub 1][sup +] states of [sup 148]Sm (at the 20% level or more) and the members of ground-state band of [sup 154]Sm (9% or so), and point to the existence of a mixed-symmetric [beta] bandhead in [sup 154]Sm at below 2 MeV. « less

In tests exploiting the unique sensitivity of a fully chaotic system like the compound nucleus, the possibility exists that unknown resonance parameters and interaction matrix elements taken on values which preclude the observation of a violation of time-reversal invariance independent of the strength of the time-reversal noninvariant interaction. A nontrivial constraint on time-reversal tests is implied, namely, that the observable has to be sampled a minimum number of times [ital M][sub min] where [ital M][sub min][gt]3. Several experiments purporting to be tests of time reversal do not satisfy this condition.

The physical content of a non-covariant quantum-field theoretic transport formalism for strong-field QED is addressed within an integral formulation of the evolution equations which highlights the relation to acoustic and Zitterbewegung modes of the field-free limit. Through the computation within this framework of the electric susceptibility of the vacuum at the one-loop level, it is established that the off-shell behaviour of the electron-positron field is correctly incorporated. The Zitterbewegung mode is seen to be solely responsible at the one-loop level for vacuum polarization. Implications for the full renormalisation of the theory are taken up.

The authors clarify the character of the semi-analytic 1/N-expansion method utilised in otherwise clumbersome studies with the sdg-variant of the interacting boson model. They draw attention to the dynamical foundations of the scheme. It is argued that, by respecting the conditions under which use of the asymptotic expansions involved is legitimate, it may be learned whether the dynamical assumptions made are appropriate or not. To this end, it is shown that an ad hoc [open quotes]gaussian[close quotes] approximation of previous applications can be avoided without any sacrifice of simplicity. The new asymptotic expansion of the fundamental overlap integral differs in every order beyond leading-order. Nevertheless, it is confirmed that, to the order of practical interest, the all-important variational functional for the groundstate-band coincides with that employed previously; the demonstration makes explicit the cancellation mechanism. To illustrate the practical advantages of the new scheme, the authors derive an expression for the gyromagnetic factors of the groundstate-band: it is freed of the deficiencies of the former 1/N-expansion method result. In general, claims that strong variations in an observable unaccounted for by the leading term can be described by higher-order terms are necessarily suspect. 11 refs.

We describe a search for the time reversal non-invariant five-fold correlation (s·Ixk)(I·k) in the scattering of 2 MeV polarized neutrons from an aligned165Ho target. Here s is the neutron spin,I is the target spin, andk is the neutron momentum vector. Differences in transmission were sought when s was reversed. The target was a single crystal of holmium, cryogenically aligned with a specially built dilution refrigerator. Rotating the target axis of alignment while cold permits the parity-even, five-fold correlation to be identified among other spin-dependent correlations in the forward elastic scattering amplitude. An analyzing power was found to be (1±6)×10−4, consistent with time reversal invariance.We obtain a bound of 5×10−3 for αT, the ratio of T-odd to T-even couplings in the effective nucleon-nucleon interaction.

The magnetic moments of excited members of the groundstate band of even-even medium-mass nuclei are considered within the framework of the sdg-version of IBM-2. A novel asymptotic realisation of the variation-after-(angular-momentum)-projection Hartree-Bose approximation is employed. The introduction of an explicit g-boson degree of freedom is found not to resolve the discrepancy between the values of the d-boson g -factors required phenomenologically and those expected microscopically. Further study of the microscopic underpinning of the g-boson and improved experimental data are required to clarify matters: a promising testing ground would appear to be the Hf-Pt nuclei. Neither the present asymptotic realisation nor its predecessor (the “1/ N -scheme”) are appropriate when strong variations of magnetic moments within a groundstate band are encountered.