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J F Fernández

Publications and source records attributed to J F Fernández.

12 recordsLinked to original sources
PubMed2005

Interface double-exchange ferromagnetism in the Mn-Zn-O system: new class of biphase magnetism.

In this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn(3+) and Mn(4+) via a double-exchange mechanism. The presence of the ZnO around MnO(2) modifies the kinetics of MnO(2)-->Mn(2)O(3) reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.

Journal Article↗
PubMed2003

Long-range ferromagnetic dipolar ordering of high-spin molecular clusters.

We report the first example of a transition to long-range magnetic order in a purely dipolarly interacting molecular magnet. For the magnetic cluster compound Mn6O4Br4(Et2dbm)6, the anisotropy experienced by the total spin S = 12 of each cluster is so small that spin-lattice relaxation remains fast down to the lowest temperatures, thus enabling dipolar order to occur within experimental times at T(c) = 0.16 K. In high magnetic fields, the relaxation rate becomes drastically reduced and the interplay between nuclear- and electron-spin lattice relaxation is revealed.

Journal Article↗
PubMed2001

Tunnel window's imprint on dipolar field distributions.

We have performed Monte Carlo simulations of interacting dipoles that relax through quantum tunneling. We aim to mimic tunneling experiments on crystals of magnetic clusters, such as Fe(8), at very low temperatures. Accordingly, we allow spin flips only if the corresponding energy change is less than some 2 delta h(hf). Time evolutions of the dipolar field distribution P(t)(H) are studied. As in experiments, a "hole" develops in P(t)(H). The half-width W of incipient holes of weakly polarized systems are, under certain conditions, simply related to delta h(hf). For k(B)T less than approximately 0.5 delta h(hf) and delta h(hf) smaller than approximately 1/10 of the half-width of the dipolar field distributions of disordered systems, W approximately equal to 0.75 delta h(hf).

Journal Article↗
PubMed2000

Squamous metaplasia of sebaceous gland.

Squamous metaplasia in the skin has been reported in the eccrine ducts as eccrine squamous syringometaplasia (ESS). To our knowledge, squamous metaplasia of sebaceous gland (SMSG) has not been described in human skin. Twenty-two biopsy specimens from patients with pressure lesions after cardiac surgery with extracorporeal circulation were evaluated for the presence of SMSG. Squamous metaplasia of sebaceous gland was identified in five of the eight scalp biopsies and none of the buttock biopsies. The squamous metaplasia began in the germinative outer layer and advanced in a centripetal way. We believe that SMSG is an unspecific change of the sebaceous cells secondary to a chronic injury. Ischemia appears to play a mayor role, but other factors such as chronic trauma or toxicosis can not be ruled out.

Carcinoma, Squamous Cell↗
PubMed1999

Algorithm for normal random numbers.

We propose a simple algorithm for generating normally distributed pseudorandom numbers. The algorithm simulates N molecules that exchange energy among themselves following a simple stochastic rule. We prove that the system is ergodic, and that a Maxwell-like distribution that may be used as a source of normally distributed random deviates follows in the N-->infinity limit. The algorithm passes various performance tests, including Monte Carlo simulation of a finite two-dimensional Ising model using Wolff's algorithm. It only requires four simple lines of computer code, and is approximately ten times faster than the Box-Muller algorithm.

Journal Article↗
PubMed1990

Oral hairy leukoplakia: a histopathologic study of 32 cases.

Oral hairy leukoplakia (HL) was studied in 32 patients infected with the human immunodeficiency virus (HIV). Features most often found were parakeratosis of variable thickness, acanthosis, little or absent submucosal chronic inflammatory cell infiltrate, association with candidiasis in 71.8%, and intranuclear herpetic type inclusions in keratinocytes, associated with ballooned or ground-glass cytoplasm. The last feature was found in all biopsies and was most striking at the top of the stratum spinosum, just beneath the parakeratotic surface. We consider that intranuclear inclusions are the histologic hallmark of HL, which, together with other features described, make it possible to diagnose HL specifically by light microscopic examination. Ultrastructural studies were carried out in 20 cases. Viral particles of the human herpesvirus group were detected in 17 cases. Particles of papillomavirus (HPV) were not found in any of the specimens. Immunohistochemical studies were made in 26 cases using a rabbit antiserum to papillomavirus. Nuclear positivity was observed in 25 cases. Despite such apparently contradictory results, we think that a cross reaction may exist between the antiserum used against HPV and some antigens of the Epstein-Barr virus (EBV).

Acquired Immunodeficiency Syndrome↗
PubMed1988

Assessment of different selective agar media for enumeration and isolation of Listeria from dairy products.

Different selective agar media were compared for the recovery and isolation of five species of Listeria from raw milk and cheese. The selective media examined were Beerens medium, MacBride medium and that described by Dominguez et al. (1984) with 6 mg/l acriflavine, listeria selective agar medium (LSAM), and LSAM with 12 mg/l acriflavine (LSAM X 2A); a non-selective yeast glucose Lemco agar was included for comparison. When the difference between listeria and the natural microflora of raw milk and cheese was 10(2) cfu/ml, listeria could be isolated by direct plating on all media tested. When it was lower than 10(3)-10(4) cfu/ml, listeria were isolated by direct plating only on LSAM and LSAM X 2A. When the difference was greater than 10(4) cfu/ml, a previous enrichment was necessary to isolate them. LSAM and LSAM X 2A media performed better than the other media tested for isolating listeria by direct plating and improved their isolation from dairy products. This superior performance was evaluated by the ability of these media to support colony formation of different species of Listeria tested, the easy recognition of these colonies from those formed by other microorganisms and by their capacity to inhibit the natural microflora of these foods.

Agar↗
PubMedDate not supplied

[Hypnosis in odontology].

Explore the source record for details and available documents.

Evaluation Studies as Topic↗
PubMedDate not supplied

Effect of immunotherapy on the production of IgE regulatory soluble factors. The response of normal lymphocytes.

IgE synthesis is controlled not only by antigen-specific mechanism but also by other factors which selectively affect the IgE isotype. Several groups demonstrated that factors released by lymphocytes were involved in this regulation. Our previous investigations were also directed in this field. Immunotherapy improves clinical symptoms in allergic respiratory diseases and produces cellular and humoral changes that affect IgE production. So we decided to investigate if immunotherapy had any influence in the production of soluble factors. Bidirectional mixed cultures were performed with lymphocytes from healthy controls and allergic patients with different time periods of IT, and the supernatants obtained from chromatography were tested to determine their effect on IgE synthesis of normal lymphocytes. IT time periods exerted influence on the production of enhancing factors. Suppressor factors derived from allergic patients had no effect on IgE synthesis of normal lymphocytes.

B-Lymphocytes↗