On 30 September 2012, a flux “dropout” occurred throughout Earth's outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA's Time History ...of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA's Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent of the dropout. THEMIS and the Van Allen Probes observed telltale signatures of loss due to magnetopause shadowing and subsequent outward radial transport, including similar loss of energetic ring current ions. However, Van Allen Probes observations suggest that another loss process played a role for multi‐MeV electrons at lower L shells (L* < ~4).
Key Points
Dropout events can encompass the entire outer radiation belt
Dropouts can result in >90% losses and be a hard reset on the system
Loss at L > ~4 is dominated by MP shadowing and outward transport
We present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular, we investigate the relationship between the tens and hundreds of ...keV seed electrons and >1 MeV core radiation belt electron population. Using a cross‐correlation analysis, we find that the seed and core populations are well correlated with a coefficient of ≈0.73 with a time lag of 10–15 h. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of hundreds of keV electrons is only one of several conditions required for MeV electron radiation belt acceleration.
Key Points
The seed population is strongly correlated with the core radiation belt population
The strongest correlation occurs at a 10–15 h time lag
The seed population is subject to a threshold limit
Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of ...energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave‐particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM‐H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.
Key Points
The radiation belts are inherently lossy
Substorms increase the likelihood of an increase in the radiation belts to 50%
The radiation belts have a memory of magnetospheric activity for up to 6 days
Gyroresonant wave‐particle interactions with very low frequency whistler mode chorus waves can accelerate subrelativistic seed electrons (hundreds of keV) to relativistic energies in the outer ...radiation belt during geomagnetic storms. In this study, we conduct a superposed epoch analysis of the chorus wave activity, the seed electron development, and the outer radiation belt electron response between L* = 2.5 and 5.5, for 25 coronal mass ejection and 35 corotating interaction region storms using Van Allen Probes observations. Electron data from the Magnetic Electron Ion Spectrometer and Relativistic Electron Proton Telescope instruments are used to monitor the storm‐phase development of the seed and relativistic electrons, and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science instrument are used to identify the chorus wave activity. Our results show a deeper (lower L*), stronger (higher flux), and earlier (epoch time) average seed electron enhancement and a resulting greater average radiation belt electron enhancement in coronal mass ejection storms compared to the corotating interaction region storms despite similar levels and lifetimes of average chorus wave activity for the two storm drivers. The earlier and deeper seed electron enhancement during the coronal mass ejection storms, likely driven by greater convection and substorm activity, provides a higher probability for local acceleration. These results emphasize the importance of the timing and the level of the seed electron enhancements in radiation belt dynamics.
Key Points
Van Allen Probes statistical study of seed electrons and chorus activity during CME and CIR storms
Seed electrons have a stronger, earlier, and deeper penetrating average enhancement during CME‐driven storms than CIR‐driven storms
A greater occurrence of radiation belt enhancements is observed during CME‐driven storms than CIR‐driven storms
The relation between radiation belt electrons and solar wind/magnetospheric processes is of particular interest due to both scientific and practical needs. Though many studies have focused on this ...topic, electron data from Van Allen Probes with wide L shell coverage and fine energy resolution, for the first time, enabled this statistical study on the relation between radiation belt electrons and solar wind parameters/geomagnetic indices as a function of first adiabatic invariant μ and L*. Good correlations between electron phase space density (PSD) and solar wind speed, southward IMF Bz, SYM‐H, and AL indices are found over wide μ and L* ranges, with higher correlation coefficients and shorter time lags for low‐μ electrons than high‐μ electrons; the anticorrelation between electron PSD and solar wind proton density is limited to high‐μ electrons at high L*. The solar wind dynamic pressure has dominantly positive correlation with low‐μ electrons and negative correlation with high‐μ electrons at different L*. In addition, electron PSD enhancements also correlate well with various solar wind/geomagnetic parameters, and for most parameters this correlation is even better than that of electron PSD while the time lag is also much shorter. Among all parameters investigated, AL index is shown to correlate the best with electron PSD enhancements, with correlation coefficients up to ~0.8 for low‐μ electrons (time lag ~ 0 day) and ~0.7 for high‐μ electrons (time lag ~ 1–2 days), suggesting the importance of seed and source populations provided by substorms in radiation belt electron PSD enhancements.
Key Points
The correlation between radiation belt electrons and solar wind/geomagnetic parameters as a function of μ and L* has been unveiled
Various solar wind/geomagnetic parameters correlate better with the enhancements of electron phase space density (PSD) than electron PSD
Among all parameters investigated, AL index correlates the best with electron PSD enhancements, with correlation coefficients up to ~0.8
Goals of lower extremity microvascular reconstruction (LEMR) include the restoration of function, prevention of infection, and optimal cosmesis. Indications for LEMR include large defects that are ...not amenable to pedicled options, a large zone of injury, and large complex defects. The novice microsurgeon should first master a handful of free flaps to develop an armamentarium of options for addressing such defects. The scope of this review is to provide free flap options for LEMR in any of the thirds of the lower leg. After reading this article, the reader will understand variations, advantages, disadvantages, indications, and tips for raising each of these flaps.
Six most commonly used free flaps for LEMR are described in this paper, including the anterolateral thigh flap (ALT) and its variations, the radial forearm flap (RFFF), the lateral arm flap (LAF), the gracilis muscle flap, the rectus abdominis flap (RAF) and the latissimus dorsi flap and its variations. Indications, advantages, disadvantages and technique tips are discussed for each flap. Moreover, selection of the recipient vessels, preoperative management along with an algorithm are also provided.
The ALT flap is a workhorse in covering defects of the leg, foot, and ankle. It's the flap of choice at our institution, especially given the number of traumatic wounds seen as a result of motor vehicles, all-terrain vehicles (ATV), lawnmowers, and gunshot wounds (GSW). At times, the lower extremity zone of injury requires a distant donor site. The RAF can also provide coverage for large soft tissue defects but donor-site morbidity remains its main drawback. The LAF and RFFF provide two pliable options, one that provides pliable soft tissue with minimal donor site morbidity and another that provides a long pedicle. The free gracilis flap is an excellent choice for crossing the ankle joint. Lastly, the free latissimus dorsi is indicated for large defects of the lower extremity independently of the location.
Tissue blocks comprising muscle and bone from C5 to C7 segments were harvested at autopsy from 16 individuals ranging in age from 4 to 77 years. The prevertebral longus colli and postvertebral ...multifidus muscle pairs from one side in each individual were randomly selected for this study of muscle spindles.
To determine muscle spindle distribution, morphology, and density for the longus colli and multifidus in caudal segments of the human cervical spine, and to assess whether changes are evident from infancy to old age.
Age-related changes to the osteoligamentous framework of the cervical spine have been well documented. Postural modification accompanies these structural alterations, but there have been limited attempts to document whether muscle sustains a comparable level of morphologic alteration. Previous studies have examined muscle spindles in the neck muscles of various animal models and in a variety of isolated human muscles. However, most of these studies incurred bias through sampling and methodologic assumptions.
The longus colli and multifidus were resected between C5 and C7, and between left and right pairs selected randomly for spindle analysis. These vertebral segments were selected deliberately because they form the apex of the cervical lordosis and the site at which the greatest age-related modification occurs. The tissue was processed in paraffin, sectioned, and then stained by Masson's trichrome. Spindle characteristics were examined using light microscopy and analyzed by unbiased stereologic methods. A one-sample paired t test was used to ascertain whether the differences in spindle density between the two muscles were statistically significant.
The longus colli has a high density of muscle spindles, which appear clustered and concentrated anterolaterally, away from the vertebral body. The multifidus has a low density of muscle spindles, which are found predominantly as single units concentrated closely to the vertebral lamina. No change in spindle distribution, morphology, and density were observed with age.
The current study examined spindle characteristics for an intrinsic neck muscle pair whose coactivation contributes to segmental stability of the cervical spine. The distribution and morphology of muscle spindles differ between the longus colli and the multifidus. In addition, these muscles have significant differences in terms of mean spindle density. Spindle characteristics represent one of many factors that govern proprioceptive regulation in skeletal muscle, and in neck muscles, the central connectivity of these receptors remains undefined. Therefore, although there are anatomic differences between the neck flexor and extensor, the functional implications of these differences are not clear. It is also of interest that spindle characteristics remain unchanged in these intrinsic muscles whose underlying segments are subject to age-related osteoligamentous changes.
Summary Background Uncertainty exists about the best treatment for people with HIV-1 who have virological failure with first-line combination antiretroviral therapy of a non-nucleoside analogue ...(NNRTI) plus two nucleoside or nucleotide analogue reverse transcriptase inhibitors (NtRTI). We compared a second-line regimen combining two new classes of drug with a WHO-recommended regimen. Methods We did this 96-week, phase 3b/4, randomised, open-label non-inferiority trial at 37 sites worldwide. Adults with HIV-1 who had confirmed virological failure (plasma viral load >500 copies per mL) after 24 weeks or more of first-line treatment were randomly assigned (1:1) to receive ritonavir-boosted lopinavir plus two or three NtRTIs (control group) or ritonavir-boosted lopinavir plus raltegravir (raltegravir group). The randomisation sequence was computer generated with block randomisation (block size four). Neither participants nor investigators were masked to allocation. The primary endpoint was the proportion of participants with plasma viral load less than 200 copies per mL at 48 weeks in the modified intention-to-treat population, with a non-inferiority margin of 12%. This study is registered with ClinicalTrials.gov , number NCT00931463. Findings We enrolled 558 patients, of whom 541 (271 in the control group, 270 in the raltegravir group) were included in the primary analysis. At 48 weeks, 219 (81%) patients in the control group compared with 223 (83%) in the raltegravir group met the primary endpoint (difference 1·8%, 95% CI −4·7 to 8·3), fulfilling the criterion for non-inferiority. 993 adverse events occurred in 271 participants in the control group versus 895 in 270 participants in the raltegravir group, the most common being gastrointestinal. Interpretation The raltegravir regimen was no less efficacious than the standard of care and was safe and well tolerated. This simple NtRTI-free treatment strategy might extend the successful public health approach to management of HIV by providing simple, easy to administer, effective, safe, and tolerable second-line combination antiretroviral therapy. Funding University of New South Wales, Merck, AbbVie, the Foundation for AIDS Research.
To limit global warming below 2°C by 2100, we must drastically reduce greenhouse gas emissions and additionally remove ~100–900 Gt CO2 from the atmosphere (carbon dioxide removal, CDR) to compensate ...for unavoidable emissions. Seaweeds (marine macroalgae) naturally grow in coastal regions worldwide where they are crucial for primary production and carbon cycling. They are being considered as a biological method for CDR and for use in carbon trading schemes as offsets. To use seaweeds in carbon trading schemes requires verification that seaweed photosynthesis that fixes CO2 into organic carbon results in CDR, along with the safe and secure storage of the carbon removed from the atmosphere for more than 100 years (sequestration). There is much ongoing research into the magnitude of seaweed carbon storage pools (e.g., as living biomass and as particulate and dissolved organic carbon in sediments and the deep ocean), but these pools do not equate to CDR unless the amount of CO2 removed from the atmosphere as a result of seaweed primary production can be quantified and verified. The draw‐down of atmospheric CO2 into seawater is via air‐sea CO2 equilibrium, which operates on time scales of weeks to years depending upon the ecosystem considered. Here, we explain why quantifying air‐sea CO2 equilibrium and linking this process to seaweed carbon storage pools is the critical step needed to verify CDR by discrete seaweed beds and nearshore and open ocean aquaculture systems prior to their use in carbon trading.
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