Spin-current-mediated rapid magnon localisation and coalescence after ultrafast optical pumping of ferrimagnetic alloys

Sub-picosecond magnetisation manipulation via femtosecond optical pumping has attracted wide attention ever since its original discovery in 1996. However, the spatial evolution of the magnetisation is not yet well understood, in part due to the difficulty in experimentally probing such rapid dynamics. Here, we find evidence of a universal rapid magnetic order recovery in ferrimagnets with perpendicular magnetic anisotropy via nonlinear magnon processes. We identify magnon localisation and coalescence processes, whereby localised magnetic textures nucleate and subsequently interact and grow in accordance with a power law formalism. A hydrodynamic representation of the numerical simulations indicates that the appearance of noncollinear magnetisation via optical pumping establishes exchange-mediated spin currents with an equivalent 100% spin polarised charge current density of 107 A cm-2. Such large spin currents precipitate rapid recovery of magnetic order after optical pumping. The magnon processes discussed here provide new insights for the stabilization of desired meta-stable states.

Elimination of X-Ray Diffraction through Stimulated X-Ray Transmission

X-ray diffractive imaging with laterally coherent x-ray free-electron laser (XFEL) pulses is increasingly utilized to obtain ultrafast snapshots of matter. Here we report the amazing disappearance of single-shot charge and magnetic diffraction patterns recorded with resonantly tuned, narrow bandwidth XFEL pulses. Our experimental results reveal the exquisite sensitivity of single-shot charge and magnetic diffraction patterns of a magnetic film to the onset of field-induced stimulated elastic x-ray forward scattering. The loss in diffraction contrast, measured over 3 orders of magnitude in intensity, is in remarkable quantitative agreement with a recent theory that is extended to include diffraction.

Nanoscale spin reversal by non-local angular momentum transfer following ultrafast laser excitation in ferrimagnetic GdFeCo

Ultrafast laser techniques have revealed extraordinary spin dynamics in magnetic materials that equilibrium descriptions of magnetism cannot explain. Particularly important for future applications is understanding non-equilibrium spin dynamics following laser excitation on the nanoscale, yet the limited spatial resolution of optical laser techniques has impeded such nanoscale studies. Here we present ultrafast diffraction experiments with an X-ray laser that probes the nanoscale spin dynamics following optical laser excitation in the ferrimagnetic alloy GdFeCo, which exhibits macroscopic all-optical switching. Our study reveals that GdFeCo displays nanoscale chemical and magnetic inhomogeneities that affect the spin dynamics. In particular, we observe Gd spin reversal in Gd-rich nanoregions within the first picosecond driven by the non-local transfer of angular momentum from larger adjacent Fe-rich nanoregions. These results suggest that a magnetic material's microstructure can be engineered to control transient laser-excited spins, potentially allowing faster (~ 1 ps) spin reversal than in present technologies.

Clinical outcomes for early childhood caries: influence of aggressive dental surgery

PURPOSE

The objective of this study was to assess the relationship between the number of stainless steel crowns (SSCs) placed, number of surfaces at risk (SAR) post dental surgery, and the risk for relapse in patients treated for Early Childhood Caries (ECC).

METHODS

The study population consisted of 57 children treated for ECC under general anesthesia, ranging in age from 2.3 to 7.3 years old at the time of entry. Dental surgery utilized an aggressive approach: teeth that had necrotic pulps or were nonrestorable were extracted; decayed primary mandibular incisors that could not be treated by stripping were extracted; primary maxillary incisors with 3 or more carious surfaces were extracted; single-surface lesions of primary molars that did not compromise cusp integrity were restored with intracoronal amalgam restorations; primary maxillary, incisors and canines with smooth-surface lesions affecting 2 or less surfaces were treated with intracoronal composites; primary molars and canines requiring vital pulp therapy were restored with SSCs; primary molars with caries lesions affecting 2 or more surfaces (including smooth-surface, white-spot lesions) were restored with SSCs; primary canines with caries affecting 3 or more surfaces were restored with stainless steel crowns; topical fluoride was applied after all restorative therapy was completed. The cohort was examined for new caries lesions 6 months post dental surgery. Relapse was defined as the presence of new smooth-surface caries lesions as defined by Radike. Comparisons between relapse (R) and nonrelapse (NR) groups, with respect to the number of SSCs placed and the number of SAR, were performed using t tests and Wilcoxon tests. A 0.05 level of significance was employed in all statistical tests.

RESULTS

Twenty-one of the 57 (37%) patients relapsed. No statistically significant difference for the number of SSCs placed or SAR existed between the R group (SSCs: mean = 4.57, median = 4 +/- 2.18; SAR: mean = 39.76, median = 40 +/- 13.62) and NR group (SSCs: mean=5.44, median = 5.5 +/- 2.62; SAR: mean = 39.98, median = 39.5 +/- 15.19).

CONCLUSIONS

The risk for relapse in children treated for ECC is not associated with the number of SSCs placed or SAR; aggressive dental surgery for ECC does not result in acceptable clinical outcomes.

Identifying hearing impairment among older adults

A survey of older-young and younger-old adults (ages 45-64) was conducted to identify the existence of a hearing impairment as described by a self-administered hearing test. Seventy of 96 surveys were returned yielding a response rate of 73%. The results indicated that the younger age group (ages 45-54) scored lower on the hearing loss test than the older age group (ages 55-64), suggesting a greater degree of loss in older adults, and females scored lower suggesting a greater degree of hearing loss in males. Responses also revealed a positive correlation of .77% between the respondent's perception of ability to hear and a relative/friend's perception of the respondent's ability to hear.

Survey of recall systems in dental hygiene programs

A nationwide survey of the United States' 198 dental hygiene educational programs was conducted to determine the existence and type of clinical recall systems in the educational setting. Several factors contributing to recall systems were examined including program demographics, type and administration of the recall system, and patient acquisition and distribution. Responses were received from 177 educational programs, yielding a response rate of 89.4%. Approximately 85% of the programs responding utilize a recall system. Results indicate that the majority of programs do not employ a specific type of recall format. Preferred combinations of key individuals responsible for the administrative duties associated with the recall system include the clinic supervisor, students, and/or program secretary. Distribution of recall patients to students as needed, with variable intervals for recall, is promoted by the majority of respondents.

Residents' perception of their skill levels in the clinical management of adolescent health problems

Residents in six specialty training programs completed a 126-item questionnaire designed to assess their skill or confidence to manage adolescent health issues. The residency programs studied were family practice, internal medicine, pediatrics, emergency medicine, obstetrics/gynecology, and combined medicine/pediatrics. Although almost three-fourths of the residents were at least moderately interested in adolescent health care and 90% expected to care for adolescents, only 26% believed an adolescent rotation should be required during training. Residents generally considered themselves unskilled to manage adolescents in the areas of sexuality, handicapping conditions, and psychosocial problems. Significant differences in perceived skills were found among the specialty programs on 45% of the items presented. Resident training appears to be needed in the areas of adolescent growth and development, counseling, and sexuality.