Effect of cast-iron disc thickness on the reliability of tribological data from pin-on-disc test: Case study of brake friction materials.

For braking system, rubbing between disc and brake pad generates heat, physical transformation on the contact, and activates many complex solicitations. Therefore, researchers used reduced scale testing to evaluate tribological and thermomechanical performance of friction composite. The pin-on-disc configuration of the tribometer is considered the better solution to reproduce these generated transformation and friction evolution. However, if the pin geometry is chospaden based on representative elementary volume (REV) approach, no research has investigated and justified the choice of the disc geometry and thickness. In this research work, an examination of the critical disc thickness is discussed, highlighting its substantial impact on the friction-wear behavior during brake application. For that, four disc thicknesses were tested, varying on thickness values (10, 15, 20, and 22 mm). Through this experiment, the friction coefficient evolution as function of braking numbers and sliding duration was studied while maintaining pressure and sliding velocity constant. Wear and temperature rise are identified for each disc thickness situation. A 3D thermal model is employed also to simulate the heat conduction and dissipation in brake system for various disc thickness. The temperature predictions are carried out using Ansys software. Experimental investigation presented the effect of the thickness on the friction stability, particularly at high temperature. Numerical results highlight the effect of reducing the thickness of the disc on the kinetic temperature rise through a rapid increase in disc temperature. The thickness modification used for the brake disc enhances the resulted thermal response and tribological brake pad performance, and consequently enhance the reliability of tribometer outcomes.

Genetic diversity of Pneumocystis jirovecii strains based on sequence variation of different DNA region.

Pneumocystis jirovecii is an important opportunistic pathogen that causes severe pneumonia in immunocompromised patients. The aim of the present study was to investigate the genetic diversity of P. jirovecii strains by direct sequencing and analysis of the Upstream Conserved Sequence (UCS) region, mitochondrial large-subunit (mtLSU) rRNA and dihydrofolate reductase (DHFR) genes. We identified the polymorphisms in P. jirovecii strains of 15 immunocompromised patients, as well as detecting a new tandem repeat of 5 nucleotides in UCS region. The following three different types of repeat unit were found: type a GCCCA; type b GCCCT; and type c GCCTT. In addition, we identified the repeat unit which consisted of 10 nucleotides and three different patterns of UCS repeats with 3 and 4 repeats, i.e., 1, 2, 3 (86.7%), 1, 2, 3, 3 (6.6%) and a new genotype 2, 2, 3, 3 (6.6%). The polymorphism in the mtLSUrRNA gene was seen primarily at position 85 where we detected three different genotypes. Genotype 3 and genotype 2 were the most abundant with frequencies of 53.3% and 40%, respectively. With regard to the DHFR gene, only two (20%) patients had nucleotide substitution in position 312. In conclusion, the multilocus analysis facilitated the typing of P. jirovecii strains and proved the important genetic biodiversity of this fungus.

Is there any change in the prevalence of intestinal and urinary parasitosis among "non-permanent resident" students in Tunisia ?

BACKGROUND: Intestinal parasitosis are cosmopolitan affections, often related to the fecal peril. However urinary bilharziosis is a disease eliminated in Tunisia. As part of monitoring the emergence and re-emergence of intestinal parasitosis and urinary bilharziasis, foreign students benefit from parasitological systematic monitoring stool and urine during their enrollment to the University. AIM: To study the prevalence of various intestinal parasitosis and urinary bilharziasis among non permanent resident students in Tunisia. METHODS: A retrospective survey was carried at the Laboratory of Parasitology- Mycology of Charles Nicolle Hospital of Tunis during the inscription period of 6 university years 2005-2010. 328 students profited from a parasitological examination of stool and urine. RESULTS: 144 students (43.9%) harbored intestinal parasites. More than one parasite was detected in 69 students (47.9%). Intestinal protozoa were the majority of identified parasites (96.9%). 9.7% of identified parasites were pathogenic. Three cases (0.91%) of urinary bilharziasis were diagnosed. CONCLUSION: The prevalence of intestinal and urinary parasitism among the "non-permanent residents" students in Tunisia has not changed. This justifies a systematic parasitologic monitoring for students coming from areas of high endemicity of parasitosis in order to avoid the introduction of these.

A rapid and easy method for the DNA extraction from Cryptococcus neoformans.

DNA isolation from C. neoformans is difficult due to a thick and resistant capsule. We have optimized a new and rapid DNA isolation method for Cryptococcus using a short urea treatment followed by a rapid method using a chelex resin suspension. This procedure is simpler than previously reported methods.

Two new media Pinus halepensis seed agar and blackberry agar for rapid identification of Cryptococcus neoformans.

Cryptococcus neoformans is an encapsulated yeast-like fungus that causes life-threatening infections, particularly in immunocompromised patients. The formation of brown pigment on many media described in the literature, such as that in Niger seed (Guizotia abyssinica) agar, has been used to identify C. neoformans. The present study compares melanin production by clinical and environmental isolates of C. neoformans and other medically important yeast on two new media, Pinus halepensis seed (PHS) agar and blackberry (BlaB) agar, and the classic medium Niger seed agar. Results obtained after the culture of 46 strains of C. neoformans, for 4, 24 and 48 h at 37 °C on these three media, showed that at 24 h, 100% of strains were pigmented on BlaB agar, 91.3% on PHS agar but only 34.8% on Niger seed agar. In conclusion, PHS and BlaB agar are two interesting new media for the rapid identification of C. neoformans isolates.

Epidemiology of dermatophytoses in Sfax, Tunisia.

The distribution of dermatophytes varies in different countries and geographical areas depending on several factors. To determine the frequency of aetiological agents and the clinical variants of dermatophytoses, we carried out a study between 1998 and 2007. Out of 25 432 subjects suspected to have superficial mycoses, 9960 (39.2%) were affected with dermatophytoses; 14957 positive samples were obtained. The mean age was 35.7 years (range: 21 days to 97 years). Sex ratio was 0.9. Our patients were from urban regions in 81.9% of cases. The most common type of infection was onychomycosis (30.3%), followed by tinea pedis (24.8%), intertrigo (21.7%), tinea corporis (11.4%) and tinea capitis (9.6%). Fifteen patients had generalised dermatophytosis. Hadida and Schousboe disease was diagnosed in one case with lethal evolution. The most isolated dermatophyte was Trichophyton rubrum (74.5%), followed by T. violaceum (7.9%), T. mentagrophytes (7.5%), Microsporum canis (3.8%), Epidermophyton floccosum (0.7%) and T. verrucosum (0.54%). Other species were occasionally isolated: T. schoenleinii, T. tonsurans, M. audouinii and M. ferrugineum. The prevalence of dermatophytoses remains high in our country (996 cases/year). Trichophyton rubrum is the predominant causal agent. However, zoophilic agents become more prevalent. Epidemiological surveys are an essential tool for developing strategies for infection control.