3,475 research outputs found
Multispectral mapping of the lunar surface using groundbased telescopes
Images of the lunar surface were obtained at several wavelengths using a silicon vidicon imaging system and groundbased telescopes. These images were recorded and processed in digital form so that quantitative information is preserved. The photometric precision of the images is shown to be better than 1 percent. Ratio images calculated by dividing images obtained at two wavelengths (0.40/0.56 micrometer) and 0.95/0.56 micrometer are presented for about 50 percent of the lunar frontside. Spatial resolution is about 2 km at the sub-earth point. A complex of distinct units is evident in the images. Earlier work with the reflectance spectrum of lunar materials indicates that for the most part these units are compositionally distinct. Digital images of this precision are extremely useful to lunar geologists in disentangling the history of the lunar surface
Evidence for a dynamic phase transition in [Co/Pt]_3 magnetic multilayers
A dynamic phase transition (DPT) with respect to the period P of an applied
alternating magnetic field has been observed previously in numerical
simulations of magnetic systems. However, experimental evidence for this DPT
has thus far been limited to qualitative observations of hysteresis loop
collapse in studies of hysteresis loop area scaling. Here, we present
significantly stronger evidence for the experimental observation of this DPT,
in a [Co(4 A)/Pt(7 A)]_3-multilayer system with strong perpendicular
anisotropy. We applied an out-of-plane, time-varying (sawtooth) field to the
[Co/Pt]_3 multilayer, in the presence of a small additional constant field,
H_b. We then measured the resulting out-of-plane magnetization time series to
produce nonequilibrium phase diagrams (NEPDs) of the cycle-averaged
magnetization, Q, and its variance, Var(Q), as functions of P and H_b. The
experimental NEPDs are found to strongly resemble those calculated from
simulations of a kinetic Ising model under analagous conditions. The similarity
of the experimental and simulated NEPDs, in particular the presence of a
localized peak in the variance Var(Q) in the experimental results, constitutes
strong evidence for the presence of this DPT in our magnetic multilayer
samples. Technical challenges related to the hysteretic nature and response
time of the electromagnet used to generate the time-varying applied field
precluded us from extracting meaningful critical scaling exponents from the
current data. However, based on our results, we propose refinements to the
experimental procedure which could potentially enable the determination of
critical exponents in the future.Comment: substantial revision; 26 pages, 9 figures; to appear in Phys. Rev.
The Formation and Coarsening of the Concertina Pattern
The concertina is a magnetization pattern in elongated thin-film elements of
a soft material. It is a ubiquitous domain pattern that occurs in the process
of magnetization reversal in direction of the long axis of the small element.
Van den Berg argued that this pattern grows out of the flux closure domains as
the external field is reduced. Based on experimental observations and theory,
we argue that in sufficiently elongated thin-film elements, the concertina
pattern rather bifurcates from an oscillatory buckling mode. Using a reduced
model derived by asymptotic analysis and investigated by numerical simulation,
we quantitatively predict the average period of the concertina pattern and
qualitatively predict its hysteresis. In particular, we argue that the
experimentally observed coarsening of the concertina pattern is due to
secondary bifurcations related to an Eckhaus instability. We also link the
concertina pattern to the magnetization ripple and discuss the effect of a weak
(crystalline or induced) anisotropy
Suicide Screening in Primary Care: Use of an Electronic Screener to Assess Suicidality and Improve Provider Follow-Up for Adolescents
Purpose
The purpose of this study was to assess the feasibility of using an existing computer decision support system to screen adolescent patients for suicidality and provide follow-up guidance to clinicians in a primary care setting. Predictors of patient endorsement of suicidality and provider documentation of follow-up were examined.
Methods
A prospective cohort study was conducted to examine the implementation of a CDSS that screened adolescent patients for suicidality and provided follow-up recommendations to providers. The intervention was implemented for patients aged 12–20 years in two primary care clinics in Indianapolis, Indiana.
Results
The sample included 2,134 adolescent patients (51% female; 60% black; mean age = 14.6 years [standard deviation = 2.1]). Just over 6% of patients screened positive for suicidality. A positive endorsement of suicidality was more common among patients who were female, depressed, and seen by an adolescent−medicine board-certified provider as opposed to general pediatric provider. Providers documented follow-up action for 83% of patients who screened positive for suicidality. Documentation of follow-up action was correlated with clinic site and Hispanic race. The majority of patients who endorsed suicidality (71%) were deemed not actively suicidal after assessment by their provider.
Conclusions
Incorporating adolescent suicide screening and provider follow-up guidance into an existing computer decision support system in primary care is feasible and well utilized by providers. Female gender and depressive symptoms are consistently associated with suicidality among adolescents, although not all suicidal adolescents are depressed. Universal use of a multi-item suicide screener that assesses recency might more effectively identify suicidal adolescents
Acute ST-segment elevation myocardial infarction in a young patient with essential thrombocythemia: a case with long-term follow-up report
Essential thrombocythemia (ET) is a neoplastic proliferation of mature myeloid cells - in particular, megakaryocytes - leading to persistently elevated platelet count. Usual clinical presentation is related to an increase in the risk of hemorrhage and/or thrombosis. Management of ET consists of antiplatelet therapies - mainly aspirin and cytoreductive therapies. Coronary involvement in patients with ET is rare. The optimal treatment strategies for ET patients presenting with acute myocardial infarction remains unclear. Acute interventions like intracoronary thrombolytic therapy, angioplasty, and coronary-artery bypass grafting have been reported in such patients. However, several questions remain unanswered about the acute and long-term management of these patients. Herein, we report the case of a 47-year-old female who presented with acute myocardial infarction as the first clinical sign of ET, and also present the long-term follow-up of this patient
Contribution of Smoking to Excess Mortality in Harlem
The New York City neighborhood of Harlem has mortality rates that are among the highest in the United States. In absolute numbers, cardiovascular disease and cancer account for the overwhelming majority of deaths, especially among men, and these deaths occur at relatively young ages. The aim of this research was to examine self-reported smoking habits according to measures of socioeconomic status among Harlem men and women, in order to estimate the contribution of tobacco consumption to Harlem's remarkably high excess mortality. During 1992-1994, in-person interviews were conducted among 695 Harlem adults aged 18-65 years who were randomly selected from dwelling unit enumeration lists. The self-reported prevalence of current smoking was strikingly high among both men (48%) and women (41%), even among highly educated men (38%). The 21% of respondents without working telephones reported an even higher prevalence of current smoking (61%), indicating that national and state-based estimates which rely on telephone surveys may seriously underestimate the prevalence of smoking in poor urban communities. Among persons aged 35-64 years, the smoking attributable fractions for selected causes of death were larger in Harlem than in either New York City as a whole or the entire United States for both men and women. Tobacco consumption is likely to be one of several important mediators of the high numbers of premature deaths in Harlem. Am J Epidemiol 1998; 147: 250-
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
The relationship of offending style to psychological and social risk factors in a sample of adolescent males
Research has indicated that life-course persistent offenders typically vary their offending style, following a criminal career progression from co to solo offending. Few studies have investigated the offenders who contemporaneously mix their style of offending. A sample of 1047 male adolescent offenders from the Pathways to Desistance study was investigated over a seven-year period. Participants were identified as solo, co or contemporaneous mixed style (CMS) offenders for each wave of data and one-way between groups analysis of variance was conducted to examine variations between the different offending styles in terms of offending frequencies, exposure to violence, peer antisocial behaviour and influence, resistance to peer influence, impulse control, and psychopathy. CMS offenders were found to consistently report significantly higher rates of offending and present significantly higher negative risk factors and lower protective risk factors than solo and co offenders for the duration of the study. A Multinomial Logistic Regression was used to investigate predictors of offending style with CMS as the reference category. Higher levels of exposure to violence and peer antisocial behaviour and lower levels of impulse control predicted membership of the CMS group for the first part of the study when compared with co-offenders; and higher levels of exposure to violence and peer antisocial behaviour continued to predict CMS offending when compared to solo offenders until the end of the study
First mineralogical maps of 4 Vesta
Before Dawn arrived at 4 Vesta only very low spatial resolution (~50 km) albedo and color maps were available from HST data. Also ground-based color and spectroscopic data were utilized as a first attempt to map Vesta’s mineralogical diversity [1-4]. The VIR spectrometer [5] onboard Dawn has ac-quired hyperspectral data while the FC camera [6] ob-tained multi-color data of the Vestan surface at very high spatial resolutions, allowing us to map complex geologic, morphologic units and features. We here re-port about the results obtained from a preliminary global mineralogical map of Vesta, based on data from the Survey orbit. This map is part of an iterative map-ping effort; the map is refined with each improvement in resolution
The contamination of the surface of Vesta by impacts and the delivery of the dark material
The Dawn spacecraft observed the presence of dark material, which in turn
proved to be associated with OH and H-rich material, on the surface of Vesta.
The source of this dark material has been identified with the low albedo
asteroids, but it is still a matter of debate whether the delivery of the dark
material is associated with a few large impact events, to micrometeorites or to
the continuous, secular flux of impactors on Vesta. The continuous flux
scenario predicts that a significant fraction of the exogenous material
accreted by Vesta should be due to non-dark impactors likely analogous to
ordinary chondrites, which instead represent only a minor contaminant in the
HED meteorites. We explored the continuous flux scenario and its implications
for the composition of the vestan regolith, taking advantage of the data from
the Dawn mission and the HED meteorites. We used our model to show that the
stochastic events scenario and the micrometeoritic flux scenario are natural
consequences of the continuous flux scenario. We then used the model to
estimate the amounts of dark and hydroxylate materials delivered on Vesta since
the LHB and we showed how our results match well with the values estimated by
the Dawn mission. We used our model to assess the amount of Fe and siderophile
elements that the continuous flux of impactors would mix in the vestan
regolith: concerning the siderophile elements, we focused our attention on the
role of Ni. The results are in agreement with the data available on the Fe and
Ni content of the HED meteorites and can be used as a reference frame in future
studies of the data from the Dawn mission and of the HED meteorites. Our model
cannot yet provide an answer to the fate of the missing non-carbonaceous
contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the
journal ICARUS, "Dark and Bright Materials on Vesta" special issu
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