126 research outputs found
The 15 years of comet photometry: A comparative analysis of 80 comets
In 1976, a program of narrowband photometry of comets was initiated that has encompassed well over 400 nights of observations. To date, the program has provided detailed information on 80 comets, 11 of which were observed during multiple apparitions. The filters (initially isolating CN, C2, and continuum and later including C3, OH, and NH) as well as the detectors used for the observations were changed over time, and the parameters adopted in the reduction and modeling of the data have likewise evolved. Accordingly, we have re-reduced the entire database and have derived production rates using current values for scalelengths and fluorescence efficiencies. Having completed this task, the results for different comets can now be meaningfully compared. The general characteristics that are discussed include ranges in composition (molecular production rate ratios) and dustiness (gas production compared with Af(rho)). Additionally an analysis of trends on how the production rates vary with heliocentric distance and on pre- and post-perihelion asymmetries in the production rates of individual comets. Possible taxonomic groupings are also described
Machine Learning for Optical Scanning Probe Nanoscopy
The ability to perform nanometer-scale optical imaging and spectroscopy is
key to deciphering the low-energy effects in quantum materials, as well as
vibrational fingerprints in planetary and extraterrestrial particles, catalytic
substances, and aqueous biological samples. The scattering-type scanning
near-field optical microscopy (s-SNOM) technique has recently spread to many
research fields and enabled notable discoveries. In this brief perspective, we
show that the s-SNOM, together with scanning probe research in general, can
benefit in many ways from artificial intelligence (AI) and machine learning
(ML) algorithms. We show that, with the help of AI- and ML-enhanced data
acquisition and analysis, scanning probe optical nanoscopy is poised to become
more efficient, accurate, and intelligent
Magnetism and Structural Distortion in the La0.7Sr0.3MnO3 Metallic Ferromagnet
Neutron scattering studies on a single crystal of the highly-correlated
electron system, La1-xSrxMnO3 with x~0.3, have been carried out elucidating
both the spin and lattice dynamics of this metallic ferromagnet. We report a
large measured value of the spin wave stiffness constant, which directly shows
that the electron transfer energy of the d band is large. The spin dynamics,
including magnetic critical scattering, demonstrate that this material behaves
similar to other typical metallic ferromagnets such as Fe or Ni. The crystal
structure is rhombohedral, as previously reported, for all temperatures studied
(below ~425K). We have observed new superlattice peaks which show that the
primary rhombohedral lattice distortion arises from oxygen octahedra rotations
resulting in an R-3c structure. The superlattice reflection intensities which
are very sensitive to structural changes are independent of temperature
demonstrating that there is no primary lattice distortion anomaly at the
magnetic transition temperature, Tc = 378.1 K, however there is a lattice
contraction.Comment: Submitted to Phys. Rev. B. (03Aug95) Uuencoded gz-compressed .tar
file of Postscript text (12 pages) and 6 figures. Also available by WWW from
http://insti.physics.sunysb.edu/~mmartin/ under my list of publications or by
e-mail reques
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The alpha angle as a predictor of contralateral slipped capital femoral epiphysis
Purpose Contralateral hip involvement in slipped capital femoral epiphysis (SCFE) is common. Femoral head−neck asphericity, as measured by an elevated alpha angle, has not previously been assessed with respect to SCFE risk. Our aim was to assess the utility of the alpha angle in predicting contralateral SCFE. Methods: We retrospectively reviewed 168 patients (94 males) managed surgically for unilateral SCFE between 2001 and 2013 who had a minimum of 18 months follow-up. The alpha angle, the posterior sloping angle (PSA), and the modified Oxford score were recorded for every patient at the time of initial SCFE presentation. Follow-up clinical records and radiographs were assessed to determine the presence of absence of contralateral SCFE. Results: Forty-five patients (27 %) developed a contralateral SCFE. Patients who developed a contralateral SCFE had a significantly higher alpha angle (51° vs 45°, p 0.10) between patients who developed a contralateral SCFE and those who did not. Using a proposed alpha angle of 50.5° as a threshold for prophylactic fixation, 26 (58 %) of the 45 cases of contralateral SCFE in our study would have been prevented and 18 (15 %) of 123 patients would have undergone fixation unnecessarily. Conclusions: We found the alpha angle to positively correlate with contralateral SCFE risk. Patients with significantly elevated alpha angles may be at greater risk of contralateral SCFE and benefit from further investigation or prophylactic hip fixation
Patient-reported outcomes of periacetabular osteotomy from the prospective ANCHOR cohort study
BACKGROUND: Current literature describing the periacetabular osteotomy (PAO) is mostly limited to retrospective case series. Larger, prospective cohort studies are needed to provide better clinical evidence regarding this procedure. The goals of the current study were to (1) report minimum 2-year patient-reported outcomes (pain, hip function, activity, overall health, and quality of life), (2) investigate preoperative clinical and disease characteristics as predictors of clinical outcomes, and (3) report the rate of early failures and reoperations in patients undergoing contemporary PAO surgery. METHODS: A large, prospective, multicenter cohort of PAO procedures was established, and outcomes at a minimum of 2 years were analyzed. A total of 391 hips were included for analysis (79% of the patients were female, and the average patient age was 25.4 years). Patient-reported outcomes, conversion to total hip replacement, reoperations, and major complications were documented. Variables with a p value of ≤0.10 in the univariate linear regressions were included in the multivariate linear regression. The backward stepwise selection method was used to determine the final risk factors of clinical outcomes. RESULTS: Clinical outcome analysis demonstrated major clinically important improvements in pain, function, quality of life, overall health, and activity level. Increasing age and a body mass index status of overweight or obese were predictive of improved results for certain outcome metrics. Male sex and mild acetabular dysplasia were predictive of lesser improvements in certain outcome measures. Three (0.8%) of the hips underwent early conversion to total hip arthroplasty, 12 (3%) required reoperation, and 26 (7%) experienced a major complication. CONCLUSIONS: This large, prospective cohort study demonstrated the clinical success of contemporary PAO surgery for the treatment of symptomatic acetabular dysplasia. Patient and disease characteristics demonstrated predictive value that should be considered in surgical decision-making. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence
Probing a Complex of Cytochromecand Cardiolipin by Magnetic Circular Dichroism Spectroscopy: Implications for the Initial Events in Apoptosis
Oxidation of cardiolipin (CL) by its complex with cytochrome c (cyt c) plays a crucial role in triggering apoptosis. Through a combination of magnetic circular dichroism spectroscopy and potentiometric titrations, we show that both the ferric and ferrous forms of the heme group of a CL:cyt c complex exist as multiple conformers at a physiologically relevant pH of 7.4. For the ferric state, these conformers are His/Lys- and His/OH–-ligated. The ferrous state is predominantly high-spin and, most likely, His/–. Interconversion of the ferric and ferrous conformers is described by a single midpoint potential of -80 ± 9 mV vs SHE. These results suggest that CL oxidation in mitochondria could occur by the reaction of molecular oxygen with the ferrous CL:cyt c complex in addition to the well-described reaction of peroxides with the ferric form
Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime mapping
Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid
of interacting electrons and holes. Interactions profoundly affect the charge
dynamics of graphene, which is encoded in the properties of its collective
modes: surface plasmon polaritons (SPPs). The group velocity and lifetime of
SPPs have a direct correspondence with the reactive and dissipative parts of
the tera-Hertz (THz) conductivity of the Dirac fluid. We succeeded in tracking
the propagation of SPPs over sub-micron distances at femto-second (fs) time
scales. Our experiments uncovered prominent departures from the predictions of
the conventional Fermi-liquid theory. The deviations are particularly strong
when the densities of electrons and holes are approximately equal. Our imaging
methodology can be used to probe the electromagnetics of quantum materials
other than graphene in order to provide fs-scale diagnostics under
near-equilibrium conditions
Graphene/-RuCl: An Emergent 2D Plasmonic Interface
Work function-mediated charge transfer in graphene/-RuCl
heterostructures has been proposed as a strategy for generating highly-doped 2D
interfaces. In this geometry, graphene should become sufficiently doped to host
surface and edge plasmon-polaritons (SPPs and EPPs, respectively).
Characterization of the SPP and EPP behavior as a function of frequency and
temperature can be used to simultaneously probe the magnitude of interlayer
charge transfer while extracting the optical response of the interfacial doped
-RuCl. We accomplish this using scanning near-field optical
microscopy (SNOM) in conjunction with first-principles DFT calculations. This
reveals massive interlayer charge transfer (2.7 10 cm)
and enhanced optical conductivity in -RuCl as a result of
significant electron doping. Our results provide a general strategy for
generating highly-doped plasmonic interfaces in the 2D limit in a scanning
probe-accessible geometry without need of an electrostatic gate.Comment: 22 pages, 5 figure
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