812 research outputs found
Carrier-induced ferromagnetism in p-Zn1-xMnxTe
We present a systematic study of the ferromagnetic transition induced by the
holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis
on the values of the Curie-Weiss temperature as a function of the carrier and
spin concentrations. The data are obtained from thorough analyses of the
results of magnetization, magnetoresistance and spin-dependent Hall effect
measurements. The experimental findings compare favorably, without adjustable
parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY)
model or its continuous-medium limit, that is, the Zener model, provided that
the presence of the competing antiferromagnetic spin-spin superexchange
interaction is taken into account, and the complex structure of the valence
band is properly incorporated into the calculation of the spin susceptibility
of the hole liquid. In general terms, the findings demonstrate how the
interplay between the ferromagnetic RKKY interaction, carrier localization, and
intrinsic antiferromagnetic superexchange affects the ordering temperature and
the saturation value of magnetization in magnetically and electrostatically
disordered systems.Comment: 14 pages, 10 figure
Influence of s,p-d and s-p exchange couplings on exciton splitting in (Zn,Mn)O
This work presents results of near-band gap magnetooptical studies on
(Zn,Mn)O epitaxial layers. We observe excitonic transitions in reflectivity and
photoluminescence, that shift towards higher energies when the Mn concentration
increases and split nonlinearly under the magnetic field. Excitonic shifts are
determined by the s,p-d exchange coupling to magnetic ions, by the
electron-hole s-p exchange, and the spin-orbit interactions. A quantitative
description of the magnetoreflectivity findings indicates that the free
excitons A and B are associated with the Gamma_7 and Gamma_9 valence bands,
respectively, the order reversed as compared to wurtzite GaN. Furthermore, our
results show that the magnitude of the giant exciton splittings, specific to
dilute magnetic semiconductors, is unusual: the magnetoreflectivity data is
described by an effective exchange energy N_0(beta-alpha)=+0.2+/-0.1 eV, what
points to small and positive N_0 beta. It is shown that both the increase of
the gap with x and the small positive value of the exchange energy N_0 beta
corroborate recent theory describing the exchange splitting of the valence band
in a non-perturbative way, suitable for the case of a strong p-d hybridization.Comment: 8 pages, 8 figure
Управління трудовим потенціалом при створенні інноваційної продукції
Super-resolution microscopy (SRM) bypasses the diffraction limit, a physical barrier that restricts the optical resolution to roughly 250 nm and was previously thought to be impenetrable. SRM techniques allow the visualization of subcellular organization with unprecedented detail, but also confront biologists with the challenge of selecting the best-suited approach for their particular research question. Here, we provide guidance on how to use SRM techniques advantageously for investigating cellular structures and dynamics to promote new discoveries
Granulocytic Sarcoma in a Nonleukemic Patient: Place of Radiotherapy and Systemic Therapies
Granulocytic sarcoma is a rare extramedullary tumour, which most often occurs in the course of an acute or chronic leukaemia or myeloproliferative disorders. Rarely it is found before peripheral blood or bone marrow evidence of leukemia is present. We report an unusual case of acute paraplegia at first presentation of a spinal epidural granulocytic sarcoma without any haematological disorder. Therapeutic strategies are discussed in the light of the literature
Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors
We suggest an approach to account for spatial (composition) and thermal
fluctuations in "disordered" magnetic models (e.g. Heisenberg, Ising) with
given spatial dependence of magnetic spin-spin interaction. Our approach is
based on introduction of fluctuating molecular field (rather than mean field)
acting between the spins. The distribution function of the above field is
derived self-consistently. In general case this function is not Gaussian,
latter asymptotics occurs only at sufficiently large spins (magnetic ions)
concentrations . Our approach permits to derive the equation for a
critical temperature of ferromagnetic phase transition with respect to
the above fluctuations. We apply our theory to the analysis of influence of
composition fluctuations on in diluted magnetic semiconductors (DMS) with
RKKY indirect spin-spin interaction.Comment: 6 pages, 2 figure
Initial Data for General Relativity with Toroidal Conformal Symmetry
A new class of time-symmetric solutions to the initial value constraints of
vacuum General Relativity is introduced. These data are globally regular,
asymptotically flat (with possibly several asymptotic ends) and in general have
no isometries, but a group of conformal isometries. After
decomposing the Lichnerowicz conformal factor in a double Fourier series on the
group orbits, the solutions are given in terms of a countable family of
uncoupled ODEs on the orbit space.Comment: REVTEX, 9 pages, ESI Preprint 12
Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors
The magnetic behavior of insulating doped diluted magnetic semiconductors
(DMS) is characterized by the interaction of large collective spins known as
bound magnetic polarons. Experimental measurements of the susceptibility of
these materials have suggested that the polaron-polaron interaction is
ferromagnetic, in contrast to the antiferromagnetic carrier-carrier
interactions that are characteristic of nonmagnetic semiconductors. To explain
this behavior, a model has been developed in which polarons interact via both
the standard direct carrier-carrier exchange interaction (due to virtual
carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due
to the interactions of polarons with magnetic ions in an interstitial region).
Using a variational procedure, the optimal values of the model parameters were
determined as a function of temperature. At temperatures of interest, the
parameters describing polaron-polaron interactions were found to be nearly
temperature-independent. For reasonable values of these constant parameters, we
find that indirect ferromagnetic interactions can dominate the direct
antiferromagnetic interactions and cause the polarons to align. This result
supports the experimental evidence for ferromagnetism in insulating doped DMS.Comment: 11 pages, 7 figure
Did Ebola emerge in West Africa by a policy-driven phase change in agroecology? Ebola's social context
SCOPUS: no.jinfo:eu-repo/semantics/publishe
A comparison of HIV outpatient care in primary and secondary healthcare-level settings in Zimbabwe.
SETTING: Decentralisation of HIV care to nurse-led primary care services is being implemented across low- and middle-income countries in sub-Saharan Africa. OBJECTIVE: To compare services offered to clients attending for HIV care at a physician-led and a nurse-led service in Harare, Zimbabwe. DESIGN: A cross-sectional study was performed at Harare Central Hospital (HCH) and Budiriro Primary Care Clinic (PCC) from June to August 2018. An interviewer-administered questionnaire was used to collect sociodemographics, HIV treatment and clinical history from clients attending for routine HIV care. The Mann-Whitney U-test was used to evaluate for differences between groups for continuous variables. For categorical variables, the χ2 test was used. RESULTS: The median age of the 404 participants recruited was 38 years (IQR 28-47); 69% were female. Viral suppression was comparable between sites (HCH, 70% vs. PCC, 80%; P = 0.07); however, screening for comorbidities such as cervical cancer screening (HCH, 61% vs. PCC, 41%; P = 0.001) and provision of referral services (HCH, 23% vs. PCC, 13%; P = 0.01) differed between sites. CONCLUSION: Efforts to improve service provision in primary care settings are needed to ensure equity for users of health services
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