Mohamed Shaker Salem

Magnetic properties of cylindrical diameter modulated Ni80Fe20 nanowires: interaction and coercive fields

Magnetic properties of cylindrical Ni80Fe20 nanowires with modulated diameters are investigated theoretically as a function of their geometrical parameters and compared with those produced inside the pores of anodic alumina membranes by pulsed electrodeposition. We observe that the Ni80Fe20 nanowires with modulated diameters reverse their magnetization via the nucleation and propagation of a vortex domain wall. The system begins generating vortex domains in the nanowire ends and in the transition region between the two segments to minimize magnetostatic energy generated by surfaces perpendicular to the initial magnetization of the sample. Besides, we observed an increase of the coercivity for the sample with equal volumes in relation to the sample with equal lengths. Finally, the interaction field is stronger in the case of constant volume segments. These structures could be used to control the motions of magnetic domain walls. In this way, these nanowires with modulated diameters can be an alternative to store information or even perform logic functions.

Magnetic characterization of nickel-rich NiFe nanowires grown by pulsed electrodeposition

Nickel-rich NiFe nanowires with well-controlled diameters and compositions are fabricated in various porous alumina templates by using a pulsed electrochemical deposition technique. The average pore diameter of the templates is tuned either by coating the pore walls with thin silica layers using an atomic layer deposition (ALD) technique or by applying a chemical pore widening process. The composition of the alloy is controlled by varying the frequency of the deposition pulse. The coercivity of the nanowire array is influenced by its texture and the amount of iron content in the alloy. The effective field and the saturation magnetization are found to be reinforced with the decrease in Ni content. A distinct enhancement of the axial coercivity and squareness of permalloy, Ni80Fe20, nanowire array are obtained by decreasing the average nanowire diameter. The processes of magnetization reversal in Ni80Fe20 nanowire array are investigated. The temperature dependence of Ni80Fe20 nanowires coercivity is interpreted in accordance with magnetization fluctuation over a single energy barrier.

Mycobacterium avium subspecies paratuberculosis: an insidious problem for the ruminant industry

Mycobacterium avium subspecies paratuberculosis is considered as one of the most serious problems affecting the world’s ruminant industry due to its significant impact on the global economy and the controversial issue that it may be pathogenic for humans. M. avium subspecies paratuberculosis is the causative agent of Johne’s disease in animals and might be implicated in cases of human Crohn’s disease. We provide an insight into M. avium subspecies paratuberculosis from some bacteriological, clinical, and molecular epidemiological perspectives.

Impetigo herpetiformis during the puerperium triggered by secondary hypoparathyroidism: a case report

A 38-year-old multiparous woman with post thyroidectomy hypoparathyroidism developed pruritic erythematous patches with multiple pustules on its margins on her thighs and groin accompanied by fever few days after delivery by caesarean section. Impetigo herpetiformis was diagnosed based on the typical clinicopathological findings. The patient was treated with intravenous fluids, calcium, Calcitrol and corticosteroids. The correction of hypocalcaemia was accompanied with rapid improvement of her skin disease and general condition. Our case is the fourth case of impetigo herpetiformis initially presented during puerperium and the first case of puerperal impetigo herpetiformis that is precipitated by secondary hypoparathyroidism. The awareness of the possible occurrence of impetigo herpetiformis during the puerperium allows early diagnosis, treatment and prevention of maternal complications.

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm-5 μm) and diameter (25-45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.

Epidemiological studies on Johne's disease in ruminants and Crohn's disease in humans in Egypt

Abstract The correlation between Johne’s disease (JD) and Crohn’s disease (CD) in Egypt was investigated. A total of 371 human and 435 animal sera were collected from the same Egyptian governorates that had a known history of paratuberculosis infection and were subjected to screening for paratuberculosis using ELISA to assess the human/animal risk at a single time point. Five CD patients and five JD clinically infected dairy cattle were also included. Out of 435 animal serum samples, 196 (45.2%) were MAP-ELISA positive. Twenty three (6.1%) out of 371 human serum samples were MAP-ELISA positive, while 37 (9.9%) were positive for anti-Saccharomyces cerevisiae antibodies (ASCA) ELISAs. There was a very poor agreement between human MAP and ASCA ELISAs (0.036 by kappa statistics). The prevalence of MAP antibodies among humans is clearly lower than in animals. In conclusion there is an increase in Johne’s disease incidence in animals and a very weak relationship between MAP and Crohn’s disease in humans in Egypt.

Composition and diameter modulation of magnetic nanowire arrays fabricated by a novel approach

Straight magnetic nanowires composed of nickel and permalloy segments having different diameters are synthesized using a promising approach. This approach involves the controlled electrodeposition of each magnetic material into specially designed diameter-modulated porous alumina templates. Standard alumina templates are exposed to pore widening followed by a protective coating of the pore wall with ultrathin silica and further anodization. Micromagnetic simulations are employed to investigate the process of magnetization reversal in the fabricated nanowires when the magnetic materials exchange their places in the thick and thin segments. It is found that the magnetization reversal occurs by the propagation of transverse domain wall (DW) when the thick segment is composed of permalloy. However, the reversal process proceeds by the propagation of vortex DW when permalloy is located at the thin segment.

Fabrication and stabilization of silicon-based photonic crystals with tuned morphology for multi-band optical filtering

One-dimensional silicon-based photonic crystals are formed by the electrochemical anodization of silicon substrates in hydrofluoric acid-based solution using an appropriate current density profile. In order to create a multi-band optical filter, two fabrication approaches are compared and discussed. The first approach utilizes a current profile composed of a linear combination of sinusoidal current waveforms having different frequencies. The individual frequency of the waveform maps to a characteristic stop band in the reflectance spectrum. The stopbands of the optical filter created by the second approach, on the other hand, are controlled by stacking multiple porous silicon rugate multilayers having different fabrication conditions. The morphology of the resulting optical filters is tuned by controlling the electrolyte composition and the type of the silicon substrate. The reduction of sidelobes arising from the interference in the multilayers is observed by applying an index matching current profile to...

Genotyping of Mycobacterium avium field isolates based on repetitive elements

Abstract The economic and zoonotic importance of infections caused by Mycobacterium avium complex (MAC) strains in human, animals and birds are increasing. At present, few data are available about the genetic diversity of field isolates of M. avium subsp. hominissuis (MAH) and subspecies avium (MAA). The close relationship between human and swine isolates indicates a possible zoonotic role for such strains. In the present work 73 M. avium field strains isolated from feces and lymph nodes of diseased/slaughtered animals in Hesse State, Germany were investigated. Forty eight primers were used for the confirmation, differentiation and finally the genotyping of the isolates based on the presence of polymorphism of different repetitive loci. These include the Large Sequence Polymorphism (LSP), the Mycobacterial Interspersed Repetitive Units (MIRU) and Variable Number Tandem Repeats (VNTR). The genotyping of MAA (n = 27) and MAH (n = 16) isolates revealed 33 different genotypes (18 MAA, 14 MAH and 1 shared profile). The described methods show great potential for epidemiological mapping of M. avium subspecies.

Molecular characterization of Mycobacterium avium subsp. paratuberculosis field isolates recovered from dairy cattle in Germany

Abstract In the present work a total of 143 Mycobacterium avium subsp. paratuberculosis (Map) field isolates recovered from faeces of dairy cattle in Hessen State, Germany were investigated. Different Short Sequence Repeats (SSR), Mycobacterial Interspersed Repetitive Units (MIRU) and Variable Number Tandem Repeats (VNTR) were applied to classify these cattle-group field isolates into subgroups. When combining the results obtained from SSR sequencing together with the data obtained from other genotyping PCR techniques applied in the current study, 78 different Map profiles were detected. One profile dominates over the investigated field isolates. This profile was detected in 24 isolates (16.8%) with 11 G (SSR); amplicon size of 280 bp, 300 bp, 200 bp, 200 bp, 210 bp, 350 bp, 210 bp, 300 bp and 300 bp for the primer MIRU 2, MIRU 3, X3, Primer 3, Primer 7, Primer 25, Primer 47, 292 and VNTR 1658, respectively. One profile was represented by eight isolates. Two profiles were represented by six members each. The remaining isolates were subdivided into smaller groups (2 profiles each 4 isolates, 3 profiles each 3 isolates, 13 profiles as 2 isolates each and finally 56 profiles were represented by a single strain for each profile).