Frequency Modulation of Spin-Transfer Oscillators

Spin-polarized dc electric current flowing into a magnetic layer can induce precession of the magnetization at a frequency that depends on current. We show that addition of an ac current to this dc bias current results in a frequency modulated (FM) spectral output, generating sidebands spaced at the modulation frequency. The sideband amplitudes and shift of the center frequency with drive amplitude are in good agreement with a nonlinear FM model that takes into account the nonlinear frequency-current relation generally induced by spin transfer. Single-domain simulations show that ac current modulates the cone angle of the magnetization precession, in turn modulating the frequency via the demagnetizing field. These results are promising for communications and signal processing applications of spin-transfer oscillators.Comment: 13 pages, 3 Figure

Circularly polarized implantable antenna characterization for retinal prosthesis systems

We describe a miniaturized antenna design for retinal prosthesis applications that enhances data transfer between the implant and external camera. The circularly polarized and conformal 2.4–2.48 GHz microstrip patch antenna was simulated inside the vitreous humor and is intended for biomedical applications. Modified Hilbert and serpentine geometries were used for the proposed implant antenna design. Capacitive radiator loading offered miniaturized dimensions of 5.8 × 6.5 × 2 mm³ (width × height × thickness mm³). A truncated design enhanced the intrinsic circular polarization characteristics to >3 dB axial ratio. Polydimethylsiloxane substrate and superstrate materials were used to achieve an S11 value below –15 dB across the frequency range with biocompatible characteristics. The simulated peak gains for left-hand circular polarization and right-hand circular polarization at 2.45 GHz were –50 dBi and –60 dBi, respectively. These relatively small values were due to the high conductivity of the vitreous humor (s = 1.53 S/m), which imposed significant losses. Overall, the proposed antenna had an omnidirectional radiation pattern and +8.45 dBm input to meet the specific absorption rate regulation limit

Management of Gastric Motility Disorder

Gastric motility disorder or gastroparesis is an objective slowing of gastrointestinal emptying syndrome, in the absence of mechanical obstruction, with cardinal symptoms such as rapid feeling of fullness, fullness sensation after eating, nausea, vomiting, bloating, and upper abdominal pain. Patients with gastroparesis are at risk of weight loss, malnutrition, and lack of vitamins and minerals, as well as increasing morbidity and mortality. The prevalence and incidence data of gastroparesis do not describe the true reality, because of the complexity of diagnosis. Beside Diabetes mellitus, many other causes should also be considered. Several studies have shown that nausea, vomiting and fullness sensation in abdominal are the most associated symptoms with gastroparesis. A 4-hour solid phase gastric emptying scintigraphy is the diagnostic standard for the slowing of gastric emptying. Lowest effective dose metoclopramide starting with a dose of 3 x 5 mg is the first line for pharmacological therapy. For persistent or refractory gastroparesis with pharmacologic therapy, gastric electrical stimulation (GES) and surgical therapy may be considered. The management should involve relevant medical team by not forget to consider patient comfort

Coherent control of nanomagnet dynamics via ultrafast spin torque pulses

The magnetization orientation of a nanoscale ferromagnet can be manipulated using an electric current via the spin transfer effect. Time domain measurements of nanopillar devices at low temperatures have directly shown that magnetization dynamics and reversal occur coherently over a timescale of nanoseconds. By adjusting the shape of a spin torque waveform over a timescale comparable to the free precession period (100-400 ps), control of the magnetization dynamics in nanopillar devices should be possible. Here we report coherent control of the free layer magnetization in nanopillar devices using a pair of current pulses as narrow as 30 ps with adjustable amplitudes and delay. We show that the switching probability can be tuned over a broad range by timing the current pulses with the underlying free-precession orbits, and that the magnetization evolution remains coherent for more than 1 ns even at room temperature. Furthermore, we can selectively induce transitions along free-precession orbits and thereby manipulate the free magnetic moment motion. We expect this technique will be adopted for further elucidating the dynamics and dissipation processes in nanomagnets, and will provide an alternative for spin torque driven spintronic devices, such as resonantly pumping microwave oscillators, and ultimately, for efficient reversal of memory bits in magnetic random access memory (MRAM).Comment: 4 pages, 3 figures, submitted to Nature Physic

Les Accidents Sur les Sites d’Orpaillage Traditionnel : Un Danger Pour la Vision au Niger

Nous avons colligé sur 18 mois 36 yeux ayant été victimes de traumatisme chez les orpailleurs clandestins du Niger. Les atteintes étaient bilatérales dans tous les cas mais volontiers asymétriques et touchent une ou plusieurs structures de l’œil et ses annexes, la présence des corps étrangers multiple était vus dans tous les yeux, nous avons retrouvé 9 cas d’éclatement du globe ayant nécessité une éviscération d’emblée. Il y avaient des lésions d’autres systèmes qui étaient dans 55% maxillo-faciales et dans 27% des fractures de membres. Le pronostic visuel était mauvais dans 94,43% des cas. Le manque d’infrastructures d’exploitation adéquates, la mauvaise manipulation des explosifs artisanaux sont à l’origine des accidents responsables de ces traumatismes. L’absence de structures de premiers soins, le manque de moyens de déplacement compliquent d’avantage les cas graves. Une formation substantielle en matière de santé et de sécurité est à envisager de même que des apprentissages pour aider les travailleurs à comprendre les dangers et les moyens de réduire les risques auxquels ils sont exposés.   Over 18 months, we collected 36 eyes that were victims of trauma among niger illegal gold panners. The lesions were bilateral in all cases but willingly asymmetrical and affect one or more structures of the eye and its adnnexias. The presence of multiple foreign bodies was seen in all eyes, we found 9 cases of bursting of the globe requiring immediate evisceration. Other systems were also affected in 55% maxillofacial and in 27% limb fractures. The visual prognosis was poor in 94.43% of the cases. The lack of adequate operating infrastructure and the improper handling of homemade explosives are at the origin of the accidents responsible for these traumas. The absence of first aid structures and the lack of means of transportation further complicate serious cases. Substantial health and safety training should be considered, as well as apprenticeship to help workers understand the dangers and how to reduce the risks to which they are exposed

Kinetics Study of the Formation of Pyrmidine Thione from the Reaction of 2,6-dibenzylidinecyclohexanone and its Derivatives with Thiourea

Kinetics of the addition of thiourea to 2,6-dibenzylidenecyclohexanone and its derivatives have been studied. The reaction is found as a pseudo-first order process which includes a nucleophilic attack by thiourea at the carbonyl group of the ketone system to produce the heterocyclic pyrimidine thione "thiopyrimidine" (Claisen route mechanism). The effect of the substituents at the para position of the 2,6-dibenzylidenecyclohexanone and its derivatives on the rate of reaction, at different temperatures, is studied. Arrhenius parameters, entropies, enthalpies and free energies of activations are estimated. A suitable mechanism, which is correspondent with the results and with Claisen routes mechanism, is suggested for this reaction

Syndrome D’aniridie Associé À La Dermatite Atopique: À Propos D’un Cas

Aniridia syndrome is a genetic anomaly affecting all ocular structures; it is transmitted by an autosomal dominant mode. In its isolated form aniridia is characterized by a hypoplasia of the iris frequently associated with other ocular anomalies. It the syndromic form it is associated to other systemic abnormalities. Authors are here reporting a case of aniridia associating: a corneal pannus, total aniridia, lens ectopia, and cataract found in a 14 years old girl. She also presented an atopic background with a positive family history of atopia. She is issued from a first degree consanguineous marriage. The management was multidisciplinary. In ophthalmology she underwent an intra-capsular extraction of the lens in both eyes with no intra-ocular lens implantation. Dermatological management was treatment of cuteanous lesions with emollients, corticoids and antihistamines drugs and ointments

Orbital Myositis with Sudden Visual Loss: A Case Study in Niamey, Niger

This paper focuses on presenting a case study of three cases of orbital myositis in one male and two female adult patients. All patients presented sudden loss of vision and proptosis at the initial stage. Ophthalmological examination outlined optic nerve atrophie. The diagnosis of all cases was confirmed with a CT scan which showed specific muscle inflammation. The treatment was successfully carried out using bolus doses of corticosteroids relayed with oral prednisolone for over 6 weeks. Six (6) months follow-up, however, did not show any relapse in all the cases