The variable source of the plasma sheet during a geomagnetic storm.

Both solar wind and ionospheric sources contribute to the magnetotail plasma sheet, but how their contribution changes during a geomagnetic storm is an open question. The source is critical because the plasma sheet properties control the enhancement and decay rate of the ring current, the main cause of the geomagnetic field perturbations that define a geomagnetic storm. Here we use the solar wind composition to track the source and show that the plasma sheet source changes from predominantly solar wind to predominantly ionospheric as a storm develops. Additionally, we find that the ionospheric plasma during the storm main phase is initially dominated by singly ionized hydrogen (H+), likely from the polar wind, a low energy outflow from the polar cap, and then transitions to the accelerated outflow from the dayside and nightside auroral regions, identified by singly ionized oxygen (O+). These results reveal how the access to the magnetotail of the different sources can change quickly, impacting the storm development.

Plasma Double Layers at the Boundary Between Venus and the Solar Wind.

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic-scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double-layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near-Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments.

Probing the energetic particle environment near the Sun.

NASA's Parker Solar Probe mission1 recently plunged through the inner heliosphere of the Sun to its perihelia, about 24 million kilometres from the Sun. Previous studies farther from the Sun (performed mostly at a distance of 1 astronomical unit) indicate that solar energetic particles are accelerated from a few kiloelectronvolts up to near-relativistic energies via at least two processes: 'impulsive' events, which are usually associated with magnetic reconnection in solar flares and are typically enriched in electrons, helium-3 and heavier ions2, and 'gradual' events3,4, which are typically associated with large coronal-mass-ejection-driven shocks and compressions moving through the corona and inner solar wind and are the dominant source of protons with energies between 1 and 10 megaelectronvolts. However, some events show aspects of both processes and the electron-proton ratio is not bimodally distributed, as would be expected if there were only two possible processes5. These processes have been very difficult to resolve from prior observations, owing to the various transport effects that affect the energetic particle population en route to more distant spacecraft6. Here we report observations of the near-Sun energetic particle radiation environment over the first two orbits of the probe. We find a variety of energetic particle events accelerated both locally and remotely including by corotating interaction regions, impulsive events driven by acceleration near the Sun, and an event related to a coronal mass ejection. We provide direct observations of the energetic particle radiation environment in the region just above the corona of the Sun and directly explore the physics of particle acceleration and transport.

Alfvénic velocity spikes and rotational flows in the near-Sun solar wind.

The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvénic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5-7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9-11, well within the distance at which stream interactions become important. We find that Alfvén waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second-considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12-14.

Majority of Solar Wind Intervals Support Ion-Driven Instabilities.

We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He^{2+} temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He^{2+} components on stability. Of 309 randomly selected spectra from the Wind spacecraft, 53.7% are unstable when the ion components are modeled as drifting bi-Maxwellians; only 4.5% of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates γ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively large He^{2+} drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified.

Revisiting the structure of low-Mach number, low-beta, quasi-perpendicular shocks.

A study of the structure of 145 low-Mach number (M ≤ 3), low-beta (ß ≤ 1), quasi-perpendicular interplanetary collisionless shock waves observed by the Wind spacecraft has provided strong evidence that these shocks have large-amplitude whistler precursors. The common occurrence and large amplitudes of the precursors raise doubts about the standard assumption that such shocks can be classified as laminar structures. This directly contradicts standard models. In 113 of the 145 shocks (~78%), we observe clear evidence of magnetosonic-whistler precursor fluctuations with frequencies ~0.1-7 Hz. We find no dependence on the upstream plasma beta, or any other shock parameter, for the presence or absence of precursors. The majority (~66%) of the precursors propagate at ≤45° with respect to the upstream average magnetic field and most (~87%) propagate ≥30° from the shock normal vector. Further, most (~79%) of the waves propagate at least 20° from the coplanarity plane. The peak-to-peak wave amplitudes (δB pk-pk) are large with a range of maximum values for the 113 precursors of ~0.4-13 nT with an average of ~2 nT. When we normalize the wave amplitudes to the upstream averaged magnetic field and the shock ramp amplitude, we find average values of ~40% and ~220%, respectively.

Collisional thermalization of hydrogen and helium in solar-wind plasma.

In situ observations of the solar wind frequently show the temperature of α particles (fully ionized helium) Tα to significantly differ from that of protons (ionized hydrogen) Tp. Many heating processes in the plasma act preferentially on α particles, even as collisions among ions act to gradually establish thermal equilibrium. Measurements from the Wind spacecraft's Faraday cups reveal that, at r=1.0 AU from the Sun, the observed values of the α-proton temperature ratio, θαp≡Tα/Tp, has a complex, bimodal distribution. This study applied a simple model for the radial evolution of θαp to these data to compute expected values of θαp at r=0.1 AU. These inferred θαp values have no trace of the bimodality seen in the θαp values measured at r=1.0 AU but are instead consistent with the actions of the known mechanisms for α-particle preferential heating. This result underscores the importance of collisional processes in the dynamics of the solar wind and suggests that similar mechanisms may lead to preferential α-particle heating in both slow and fast wind.

A simple delay-line 4-PPM demodulator with near-optimum performance.

We describe a simple 4-PPM demodulator that uses analog delay lines and simple 1-bit comparators to determine the least-significant bit and most-significant bit of the 4-PPM encoded data without additional digital signal processing. We show that with good optical filtering the comparator-based demodulator can theoretically operate with sensitivity only 0.23 dB from the optimum 4-ary receiver. We describe as an example of this approach the demodulator built for the Lunar Laser Communication Demonstration and show measured performance within 1.1 dB of the expected sensitivity. The technique is extendable to higher-order, and higher-symbol-rate orthogonal modulation formats.

Optical homodyne PSK demonstration of 1.5 photons per bit at 156 Mbps with rate-(1/2) turbo coding.

We report the first demonstration of a near quantum-limited optical homodyne PSK receiver combined with powerful forward-error-correction coding, achieving 1.5 photons/bit sensitivity, within 4.5 dB of the Shannon limit. Phase-locking was achieved at 1.55 microm using an analog dither-based optical phase-locked loop with an external phase modulator. Analysis for this configuration with arbitrary loop damping is given showing a performance advantage for the overdamped case.

High-sensitivity multi-channel single-interferometer DPSK receiver.

A high-sensitivity method of demodulating wavelength-division-multiplexed optical DPSK channels using a single interferometer is described and demonstrated. We show that this technique can operate within existing standards and achieve near-quantum-limited receiver performance. The resulting hardware simplification has potential to reduce the cost of deploying and scaling future wide-band optical-communication networks employing WDM-DPSK.

Recombinant human bone morphogenetic protein-2 enhances osteotomy healing in glucocorticoid-treated rabbits.

The objectives of this study were to evaluate the effect of chronic prednisolone treatment on osteotomy healing in rabbits and to determine whether recombinant human bone morphogenetic protein-2 (rhBMP-2) would enhance healing in the presence of chronic glucocorticoid therapy. Forty-nine skeletally mature, male rabbits were injected with either prednisolone (n = 26; 0.35 mg/kg per day, three times a week) or saline (n = 23). After a 6-week pretreatment period, bilateral ulnar osteotomies were created surgically. One osteotomy was treated with rhBMP-2 (0.2 mg/ml of rhBMP-2, 40 microg of rhBMP-2 total) delivered on an absorbable collage sponge (ACS), whereas the contralateral osteotomy remained untreated. Prednisolone or saline treatment was continued until the rabbits were killed either 6 weeks or 8 weeks after creation of the osteotomy. Osteotomy healing was evaluated by radiography, peripheral quantitative computed tomography (pQCT), torsional biomechanics, and undecalcified histology. Because we observed similar responses to both prednisolone and rhBMP-2/ACS treatment in the 6-week and 8-week cohorts, the results from these time points were combined. Serum osteocalcin and vertebral trabecular bone density were lower in the prednisolone-treated rabbits. Prednisolone treatment dramatically inhibited osteotomy healing. In the untreated ulnas, callus area and torsional strength were 25% and 55% less, respectively, in the prednisolone-treated rabbits than in the saline group (p < 0.001 for both). rhBMP-2/ACS enhanced healing in both the prednisolone- and the saline-treated groups, although the effect was larger in the prednisolone-treated rabbits. In the prednisolone-treated rabbits, callus area and torsional strength were 40% and 165% greater (p < 0.001 for both), respectively, in osteotomies treated with rhBMP-2/ACS compared with the contralateral, untreated osteotomies. Histological evaluation confirmed that osteotomy healing was inhibited by prednisolone and accelerated by rhBMP-2/ACS. In summary, a single application of rhBMP-2/ACS counteracted the inhibition of osteotomy healing caused by prednisolone exposure. These results suggest that rhBMP-2/ACS may be a useful treatment for enhancing fracture healing in patients who are undergoing chronic glucocorticoid therapy.

Evaluation of changes in trabecular bone architecture and mechanical properties of minipig vertebrae by three-dimensional magnetic resonance microimaging and finite element modeling.

The study objective was to analyze the three-dimensional (3D) trabecular architecture and mechanical properties in vertebral specimens of young and mature Sinclair minipigs to assess the relative contribution of architecture to bone strength. We used 3D magnetic resonance microimaging (MRmicroI) and direct image analysis to evaluate a set of standard structural measurements and new architectural descriptors of trabecular bone in biopsy specimens from L2, L3, and L4 vertebrae (n = 16 in each group) from young (mean age, 1.2 years) and mature (mean age, 4.8 years) minipigs. The measurements included bone volume/tissue volume (BV/TV), marrow star volume (Ma.St.V), connectivity density (ConnD), and two new parameters, percent platelike trabeculae (% plate) and percent bone in the load direction (% boneLD). The % plate, calculated from surface curvature, allowed the delineation of plates from rods. The % boneLD quantified the percentage of bone oriented along the long axis of the vertebral body. We showed that 3D MRmicroI can detect the subtle changes in trabecular architecture between the two age groups. ConnD, star volume, % plate, % boneLD, and BV/TV were found to be more effective than the model-based, derived indices (trabecular thickness [Tb.Th], trabecular separation [Tb.Sp], and trabecular number [Tb.N]) in differentiating the structural changes. BV/TV, % plate, and % boneLD significantly increased (p < 0.05) in all three vertebral sites of the mature minipigs. The significant decrease in ConnD and star volume in the mature vertebra was consistent with the concurrent increase of platelike trabecular bone (p < 0.05). Overall, ConnD, star volume, % plate, and % boneLD provided a coherent picture of the architectural changes between the two age groups. Apparent modulus and maximum stress were determined experimentally on biopsy specimens from L2 vertebrae (n = 16). When apparent modulus was predicted using 3D MRmicroI data sets as input for finite element modeling (FEM), the results were similar to the experimentally determined apparent modulus (p = 0.12). Both methods were then used to compare the young and the mature animals; the experimental and predicted apparent modulus were significantly higher for the mature group (p = 0.003 and 0.012, respectively). The experimental maximum stress in the vertebra of the mature animals was twice as high as that for the young animals (p = 0.006). Bone quantity (BV/TV or bone mineral content [BMC]) alone could explain approximately 74-85% of the total variability in stress and modulus. The inclusion of either ConnD or % boneLD with BV/TV in a multiple regression analysis significantly improved the predictability of maximum stress, indicating that architecture makes additional contributions to compressive strength in normal minipig vertebra.

The Quinlan case revisited: a history of the cultural politics of medicine and the law.

This article explores the cultural politics of medicine and the law through a historical examination of the case of Karen Ann Quinlan. In viewing the Quinlan case as, in part, an unanticipated consequence of the 1968 redefinition of death, this article implicates the importance of historical perspective and methodology in examining the nuances of the cultural negotiation of professional power. Using popular, legal, medical, and bioethics sources in historical context, it reveals how the legal process can nurture misconceptions about medical practice and the role of technology. It also sheds light on how the search for legal protection can motivate medical behavior. In so doing, it challenges the view that Quinlan was an important gain for patients' rights. Instead it views Quinlan's chief legacy as its offer to the medical profession of freedom from criminal prosecution when removing life support from patients in a chronically vegetative state.

The ferret as a small animal model with BMU-based remodeling for skeletal research.

UNLABELLED: The need exists for a small animal model with bone metabolic unit (BMU)-based remodeling to mimic the bone loss found in postmenopausal women. The purpose of this investigation was to evaluate the ferret as a potential model for skeletal research. Specifically, we determined whether the ferret: 1) exhibits evidence of BMU-remodeling, 2) has a skeletal response to parathyroid hormone (PTH) similar to other remodeling species, and 3) loses bone in response to reduced estrogen levels. METHODS: Using three sets of experiments, we determined the response of female ferrets to ovariectomy/light cycle manipulation or to administration of PTH. Scanning electron microscopy, light microscopy, determination of estrogen levels and/or single-photon absorptiometry (SPA) were used for evaluation. RESULTS: The ferret was found to exhibit BMU-based remodeling, and may therefore provide a small animal remodeling species for skeletal research. Ferrets reach skeletal maturity between four and seven months of age as evidenced by closure of the growth plate and maturation of trabecluae from thin rods to thick rods and plates. PTH treatment resulted in a marked increase in bone mass accompanied by the PTH-induced tunneling phenomenon known to occur in dogs and humans but not rats. The response to PTH supports the use of the ferret in studies of bone anabolic agents. Bone mass in the proximal tibia was significantly reduced when estrogen depletion was induced by either bilateral ovariectomy or short light/dark cycles (8 hour light, 16 hour dark). Maintenance of intact ferrets under short-light conditions mimiced ovariectomy in terms of serum estrogen levels, uterine weights, and tibial BMD.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in bone mineral density and bone-specific alkaline phosphatase in ovariectomized ewes.

An animal model of human osteoporosis which adequately meets many of the criteria needed to test new therapeutic agents is currently unavailable. The old ewe may serve this purpose, as changes in bone remodeling occur within 3 months, and a difference in bone mass has been indicated 6 months after ovariectomy. In the current study, we have measured longitudinal changes in bone mass and bone-specific alkaline phosphatase (BSAP) for six months in 7-9 year old ovariectomized (OVX) ewes. Thirty ewes were divided into three groups: sham-treated (n = 9), OVX (n = 12) and OVX with estrogen implants (OVXE, n = 9). Bone mineral density (BMD) was determined at 0, 3 and 6 months in the vertebrae (L4-L6/L5-L7), calcaneus (CAL) and distal radius (DR) using dual-energy X-ray absorptiometry (DEXA). Bone-Specific Alkaline Phosphatase (Tandem-R Ostase; Hybritech) was determined at monthly intervals. Body weight did not significantly change in any group during treatment compared to sham, although a trend of increasing body weight at 3 and 6 months was apparent in both OVX groups. Luteinizing hormone increased in all OVX ewes as a function of time as expected, demonstrating successful ovariectomies. Uterine weight was significantly increased (p < 0.01) in the OVXE animals compared to Sham and OVX groups. BMD did not change significantly during the 6-month treatment period in the CAL or DR. BMD in the vertebrae (L4-L6/L5-L7) was significantly lower in the OVX group compared to sham (p < 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Unbiased estimation of vertebral trabecular connectivity in calcium-restricted ovariectomized minipigs.

The topological changes in vertebral cancellous bone were estimated in vertebrae from calcium-restricted ovariectomized Sinclair S-1 minipigs, a recently described animal model of cancellous osteopenia. Connectivity was estimated using unbiased stereological principles in disector pairs of sections from the first lumbar vertebrae. Connectivity density was increased approximately twofold when compared with sham-operated minipigs fed a standard diet. These alterations in topology occurred coincident with a 25% increase in final resorption depth and a 150% increase in vertebral marrow star volume. Taken together, these changes suggest that in calcium-restricted ovariectomized minipigs, trabecular plates are transformed into rods by perforation. These changes in topology appear to be due, at least in part, to excessive resorptive cell function at the level of the bone remodeling unit. Conventional two-dimensional estimators of structural parameters of cancellous bone were not only less sensitive to these changes in topology but, in some cases, the estimates were directionally reversed.

Direct stereological estimation of three-dimensional connectivity in rat vertebrae: effect of estrogen, etidronate and risedronate following ovariectomy.

Newly developed unbiased stereological methods were employed to investigate the effects of estrogen deficiency on the three-dimensional connectivity of vertebral cancellous bone from ovariectomized (OVX) rats. The effects of two classes of antiresorptive agents, estrogen and bisphosphonates, on changes in connectivity in this animal model were also evaluated. Female rats were either sham-operated (sham-op) or surgically OVX at 90 days of age. OVX rats were administered either vehicle, estrogen (10 micrograms/kg 17-beta estradiol, 5 days/week subcutaneously [SC], etidronate disodium (5 mg/kg SC) or risedronate (5 micrograms/kg SC). The bisphosphonates were administered daily for 1 week followed by 3 weeks with no treatment. Treatment duration was 360 days. Systematic random sections, 30-microns thick, were prepared from methylmethacrylate-embedded decalcified second lumbar vertebrae. Total trabecular number and connectivity density were estimated using the ConnEulor principle. Vertebral cancellous bone volume was estimated on undecalcified sections from the first lumbar vertebrae. Connectivity density and cancellous bone volume were significantly reduced (approximately 25% and 40%, respectively) in the OVX group compared with the sham-op group. Estrogen treatment essentially maintained connectivity and cancellous bone volume at the level of the sham-op rats. Connectivity density and total trabecular number were significantly increased in the etidronate- and risedronate-treated rats compared with both the sham-op and OVX rats. These data demonstrate that reduction in the three-dimensional connectivity of vertebral cancellous bone is a long-term consequence of ovariectomy in the rat. This reduction in connectivity can be effectively prevented by the administration of antiresorptive agents such as estrogen, etidronate and risedronate.(ABSTRACT TRUNCATED AT 250 WORDS)