313 research outputs found
Electrical Noise From Phase Separation In Pr2/3Ca1/3MnO3 Single Crystal
Low frequency electrical noise measurements have been used to probe the
electronic state of the perovskite-type manganese oxide Pr2/3Ca1/3MnO3 versus
temperature and in the vicinity of the field-induced transition from the
insulating, charge-ordered state (I-CO) to the metallic, ferromagnetic state
(M-F). At high temperature we have observed a high level of the excess noise
with mainly a gaussian distribution of the resistance fluctuations, and the
associated power spectral density has a standard 1/f dependence. However, in
the hysteretic region, where the electrical resistance depends dramatically on
the sample history, we have observed a huge non-gaussian noise characterized by
two level fluctuator-like switching (TLS) in the time domain. We discuss the
origin of the noise in terms of percolative behavior of the conductivity. We
speculate that the dominant fluctuators are manganese clusters switching
between the M-F and the I-CO phases.Comment: RevTeX, 6 pages with 3 figure
Comparative study of 220 kV overhead transmission lines models subjected to lightning strike simulation by using electromagnetic and alternative transients program
Introduction. In high voltage networks intended for the transport of electrical energy, lightning can strike an electric line striking either a phase conductor, a pylon or a ground wire, causing significant overvoltage on the transmission lines classified as stresses the most dangerous for transformer stations and electro-energy systems in general. Modeling transmission lines becomes more complicated, if the frequency dependence of resistance and serial inductance due to the effect of lightning strike in the conductors and in the earth is considered. The difficulty increases the fact that the parameters of the line can be defined and calculated only in the frequency domain, while the simulation of transients is wanted to be in the time domain. Problem. Several models (J.R. Marti, Bergeron, nominal PI, Semlyen and Noda) exist for the modeling of transmission lines, the Electromagnetic Transients Program/Alternative Transient Program software (EMTP/ATPDraw) gives the possibility to choose between these models which is delicate due to the fact that we do not have experimental results to validate and justify the choice among the models available in the software. In this context, practical value: the overhead transport line OAT-El Hassi (220 kV) of the city of Sétif located in the north east of Algeria is used for the modeling of lightning strike by using the EMTP/ATPDraw software. Originality. A comparative study of the investigation of a lightning strike on an existing high voltage transmission line by different models of existing lines in the EMTP/ATPDraw software library of this software. Results. It was concluded that the choice of the model of the line is very important given the accuracy and quality of the curves of the voltage presented at the different calculation points. Вступ. У високовольтних мережах, призначених для передачі електроенергії, блискавка може вдарити по лінії електропередач, уразивши або фазний провід, опору, або заземлюючий провід, викликаючи значні перенапруги на лініях електропередач, визначені як загрози, найбільш небезпечні для трансформаторних підстанцій та електроенергетичних систем загалом. Моделювання ліній електропередач ускладнюється, якщо враховувати частотну залежність опору та послідовної індуктивності внаслідок дії удару блискавки у провідниках та землі. Складність підвищується тим, що параметри лінії можуть бути визначені і розраховані тільки в частотній області, в той час як моделювання перехідних процесів бажано проводити в часовій області. Проблема. Існує кілька моделей (J.R. Marti, Bergeron, номінальна П-подібна схема заміщення, Semlyen і Noda) для моделювання ліній електропередач, комп‘ютерна програма електромагнітних перехідних процесів/альтернативна програма перехідних процесів EMTP/ATPDraw дає можливість вибирати між цими моделями, що є «тонким питанням» через те, що ми не маємо експериментальних результатів для перевірки та обґрунтування вибору серед моделей, доступних у програмному забезпеченні. У цьому контексті, практична цінність: для моделювання удару блискавки за допомогою програмного забезпечення EMTP/ATPDraw використана повітряна лінія електропередачі ОАТ-Ель-Хассі (220 кВ) міста Сетіф, розташованого на північному сході Алжиру. Оригінальність. Порівняльне дослідження вивчення удару блискавки на існуючій високовольтній лінії електропередач за різними моделями існуючих ліній у бібліотеці програм EMTP/ATPDraw цього програмного забезпечення. Результати. Зроблено висновок, що вибір моделі лінії дуже важливий з урахуванням точності та якості кривих напруг, представлених у різних розрахункових точках.
Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3
Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a
macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been
observed at various temperatures ranging from 4K to 170K, well below the Curie
temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF)
vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the
TLF to gain insight into the microscopic electronic and magnetic state of this
manganite. At low temperature (below 30K) The TLF is well described by a
thermally activated two-level model. An estimate of the energy difference
between the two states is inferred. At higher temperature (between 60K and
170K) we observed critical effects of the temperature on the life-times of the
TLF. We discuss this peculiar temperature dependence in terms of a sharp change
in the free energy functional of the fluctuators. We attribute the origin of
the RTN to be a dynamic mixed-phase percolative conduction process, where
manganese clusters switch back and forth between two phases that differ in
their conductivity and magnetization.Comment: 15 pages, PDF only, Phys. Rev. Lett. (in press
Electronic control of the spin-wave damping in a magnetic insulator
It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, , in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of in a 5~m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of , in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.Comment: 6 pages 4 figure
Non-communicable disease comorbidities in KwaZulu-Natal Province, South Africa
Background. The prevalence of chronic non-communicable disease (NCD) comorbidity in low- to middle-income countries is increasing, yet evidence on the pattern, prevalence, awareness and treatment of NCD comorbidity is inadequate.Objectives. To investigate the prevalence, awareness, treatment and control of comorbid hypertension and diabetes, and the underlying risk factors in Mpumza, KwaZulu-Natal Province, South Africa (SA).Methods. Data were gathered by the SA Human Sciences Research Council from 587 participants in KwaZulu-Natal in 2015. Percentages were used to describe all the variables. Cross-tabulations and χ2 tests were used to describe variations in the prevalences of hypertension, diabetes and comorbidities according to sociodemographic and socioeconomic variables and lifestyle risk factors.Results. Approximately a third of the participants had hypertension (32%) and 9% had diabetes. The prevalence of comorbid hypertension and diabetes was 6%, and this was significantly higher among women, the aged, the obese, and the formerly married compared with their counterparts. Comorbidity awareness was high (86%). Although most of the participants with comorbidities were being treated with lifestyle changes, insulin and antihypertensive medication (74%), control of comorbidities was low (13%).Conclusions. The study reported a higher burden of comorbid hypertension and diabetes among vulnerable populations in Mpumza, SA, particularly women, the obese, and those with a low level of education. In addition, control of comorbidities was low. Developing appropriate interventions to improve control of comorbidities can reduce the risk of macrovascular and microvascular diseases in this population
Field-induced segregation of ferromagnetic nano-domains in PrSrMnO, detected by Mn NMR
The antiferromagnetic manganite PrSrMnO was investigated
at low temperature by means of magnetometry and Mn NMR. A field-induced
transition to a ferromagnetic state is detected by magnetization measurements
at a threshold field of a few tesla. NMR shows that the ferromagnetic phase
develops from zero field by the nucleation of microscopic ferromagnetic
domains, consisting of an inhomogeneous mixture of tilted and fully aligned
parts. At the threshold the NMR spectrum changes discontinuously into that of a
homogeneous, fully aligned, ferromagnetic state, suggesting a percolative
origin for the ferromagnetic transition.Comment: Latex 2.09 language. 4 pages, 3 figures, 23 references. Submitted to
physical Review
Protecting nickel with graphene spin-filtering membranes: A single layer is enough
We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.We acknowledge the Helmholtz-Zentrum-Berlin
Electron storage ring BESSY II for provision of synchrotron
radiation at the ISISS beamline and we thank the BESSY
staff for continuous support of our experiments. R.S.W.
acknowledges a Research Fellowship from St. John’s
College, Cambridge. S.H. acknowledges funding from ERC
grant InsituNANO (No. 279342) and EPSRC grant
GRAPHTED (EP/K016636/1). P.S. acknowledges the
Institut Universitaire de France for a junior fellowship. This
research was partially supported by the EU FP7 Work
Programme under Grant GRAFOL (No. 285275) and
Graphene Flagship (No. 604391).This is the final published version. It first appeared at http://scitation.aip.org/content/aip/journal/apl/107/1/10.1063/1.4923401
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