Effect of Pt impurities on the magnetocrystalline anisotropy of hcp Co: a first-principles study

In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we investigate the variation in the magnetocrystalline anisotropy energy (MAE) of hexagonal close-packed cobalt with the addition of platinum impurities. In particular, we perform calculations on a bulk cobalt system in which one of the atomic layers contains a fractional, substitutional platinum impurity. Our calculations show that at small concentrations of platinum the MAE is reduced, while at larger concentrations the MAE is enhanced. This change of the MAE can be attributed to an interplay between on-site Pt MAE contributions and induced MAE contributions on the Co sites. The latter ones are subject to pronounced, long-ranged Friedel-oscillations that can lead to significant size effects in the experimental determination of the MAE of nano-sized samples.Comment: 16 page

Two-divisibility of the coefficients of certain weakly holomorphic modular forms

We study a canonical basis for spaces of weakly holomorphic modular forms of weights 12, 16, 18, 20, 22, and 26 on the full modular group. We prove a relation between the Fourier coefficients of modular forms in this canonical basis and a generalized Ramanujan tau-function, and use this to prove that these Fourier coefficients are often highly divisible by 2.Comment: Corrected typos. To appear in the Ramanujan Journa

Effects of composition and chemical disorder on the magnetocrystalline anisotropy of Fe_{x}Pt_{1-x} alloys

We perform first principles calculations of the magnetocrystalline anisotropy energy (MAE) of the L1_{0}-like Fe_{x}Pt_{1-x} samples studied experimentally by Barmak and co-workers in [J. Appl. Phys. 98 (2005) 033904]. The variation of composition and long-range chemical order in the samples was studied in terms of the coherent potential approximation. In accordance with experimental observations, we find that, in the presence of long-range chemical disorder, Fe-rich samples exhibit a larger MAE than stoichiometric FePt. By considering the site- and species-resolved contributions to the MAE, we infer that the MAE is primarily a function of the degree of completeness of the nominal Fe layers in the L1_{0} FePt structure.Comment: 4 pages, 4 figure

Magnetic anisotropy of FePt: effect of lattice distortion and chemical disorder

We perform first principles calculations of the magnetocrystalline anisotropy energy in the five L10 FePt samples studied experimentally by Ding et al. [J. App. Phys. 97, 10H303 (2005)]. The effect of temperature-induced spin fluctuations is estimated by scaling the MAE down according to previous Langevin dynamics simulations. Including chemical disorder as given in experiment, the experimental correlation between MAE and lattice mismatch is qualitatively well reproduced. Moreover we determine the chemical order parameters that reproduce exactly the experimental MAE of each sample. We conclude that the MAE is determined by the chemical disorder rather than by lattice distortion.Comment: 5 pages, 3 figure

Validation of methods for monitoring of coastal and open sea areas with satellites and sensors on ships of opportunity

Årsliste 2003Final report to the Norwegian Research Council. The main objective of the project was to construct, install and test an automatic system for observations of temperature, salinity, chlorophyll fluorescence and turbidity from the cooling inlet aboard the ferry Color Festival (Oslo -Hirtshals). An automatic water sampler makes it possible to analyse other properties of the surface water, such as nutrients and organochlorides at selected positions. The potential of combined satellite and ship-sensor observations is illustrated as well as the use of the system for early warning of harmful algea. Examples are also given of the system's potential for low cost high frequency regular monitoring of the surface layer.Norwegian Research Counci

Ab Initio Calculations of the Magnetic Properties of Bimetallic Alloys

Magnetic recording technology is ubiquitous in the modern world and constitutes a corner stone of current research and development. Recent inventions such as heat-assisted magnetic recording and exchange-coupled media has focused magnetic recording research towards alloys exhibiting strong magnetocrystalline anisotropies. In this thesis, we investigate, from first principles using the screened Korringa-Kohn-Rostoker method, the effect of a range of compositional and microstructural defects and features upon the magnetocrystalline anisotropy energy (MAE) of FePt and CoPt alloys. We show that localised Pt alloying affects the MAE of bulk Co primarily through the Pt-induced effects on the Co sites. We demonstrate that stacking faults often reduce the Co MAE and that the effect of composite stacking faults upon the MAE is not necessarily additive, but synergistic. By varying the unit cell geometry and the compositional parameters of FePt, we show that the formation of complete Fe layers is, generally, the dominant factor in maintaining a large MAE. We investigate the magnetic properties (spin moments, magnetocrystalline anisotropy and magnetic exchange) across an Fe/FePt/Fe multi-layer and show that the effective exchange exhibits a strong reduction at the Fe/FePt interfaces and that the MAE of the whole multilayer system is very slightly reduced by the presence of the Fe/FePt interfaces. Across all systems, we observe that localised features such as stacking faults, interfaces and localised alloying incur relatively long-ranged spatial oscillations in the MAE, which may, in turn, cause significant finite-size effects on the nano-scale

Utilizing Chair Massage to Address One Woman’s Health in Rural Ghana West Africa: a Case Report

Background and Objectives: There is limited access to health care in rural Ghana and virtually no rehabilitative services available. This situation presents a unique opportunity to utilizechair massage in addressing women’s health in rural Ghana, particularly when it comes to muscle pain and fatigue from heavy labor. The objective of this case report is to determine the results of chair massage as a strategy to reduce neck, shoulder, and back pain, while increasing range of motion.Case Presentation: The patient is a 63-year old Ghanaian female, who was struck by a public transport van while carrying a 30–50 pound load on her head, two years prior. The accident resulted in a broken right humerus and soft tissue pain. A traditional medicine practitioner set the bone, however there was no post-accident rehabilitation available. At the time of referral, she presented complaints of shoulder, elbow, and wrist pain. In addition, she was unable to raise her right hand to hermouth for food intake.Results: The results of this case report include an increase in range of motion, as well as elimination of pain in the right shoulder, elbow, and hand. Visual assessments showed an approximate increase of ROM within the ranges of 45–65 degrees in the right arm, as well as 10–15 degrees in 4th and 5th fingers. There was also a decrease in muscle hypertonicity in the thoracic and cervical areas, and a profound increase in quality of life for the patient.Discussion: This case report illustrates how therapeutic chair massage was utilized to address a common health concern for one woman in rural Ghana. It also demonstrates that pre-existing musculoskeletal disorders and pain may be eliminated with massage intervention. Massage therapy may be important to ameliorating certain types of health problems in remote rural villages in low income countries

Phylogenetic diversity and temporal variation in the Spirochaeta populations from two Mediterranean microbial mats

Spirochetes represent one of the bacterial groups often observed in hydrogen- sulfide-rich layers from coastal microbial mats. However, relatively few spirochetes from these microbial mats have been described and characterized. We have used 16S rDNA phylogenetic analysis to investigate the spirochetal diversity of microbial mats from two different geographic locations in the western Mediterranean (Ebro Delta, Spain, and Camargue, France). Samples from each delta was monitored in the spring and winter over 1 to 2 year’s duration. In the sequence analysis of 332 clones derived from samples of both deltas, 42 novel phylotypes of not-yet-cultivated spirochetes belonging to the genus Spirochaeta were detected. None of the phylotypes were identified as known culturable species of Spirochaeta or previously identified phylotyepes cloned from other hypersaline microbial mat such as Guerrero Negro. Eight of the phylotypes were common to Ebro and Camargue mats, two of them, IF058 and LL066 are present both in spring and winter. Some phylotypes appeared to show seasonal variation, i.e. they were found only in the spring, but not in the winter. On the other hand, Ebro and Camargue phylotypes compared with phylotypes from Guerrero Negro grouped according to the vertical gradient of oxygen and sulfide in the mat. Some phylotypes, such as LH073, IE028, LH042 or LG013 are harbored in low H2S or H2S-O2 interface zone. In contrast, major phylotypes were detected presumably in deeper layers and they are likely to be strict anaerobes and high tolerance to H2S. The presence of spirochetes in different located microbial mats suggests that constitutes a very diverse and stable population involved in a well-integrated “symbiosis” (i.e., permanent physiological cooperation) with other guild-populations in the mats to maintain a coordinated functional and stable community