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Biomedical subjects

F Bert

Publications and source records attributed to F Bert.

At least 19 recordsLinked to original sources
PubMed2006

Unconventional dynamics in triangular Heisenberg antiferromagnet NaCrO2.

We report magnetization, specific heat, muon spin rotation, and Na NMR measurements on the S=3/2 rhombohedrally stacked Heisenberg antiferromagnet NaCrO2. This compound appears to be a good candidate for the study of isotropic triangular Heisenberg antiferromagnets with very weak interlayer coupling. While specific heat and magnetization measurements indicate the onset of a transition in the range Tc approximately 40-50 K, both muon spin rotation and NMR reveal a fluctuating crossover regime extending well below Tc, with a peak of relaxation rate T1(-1) around T approximately 25 K. This novel finding is discussed within the context of excitations in the triangular Heisenberg antiferromagnets.

Journal Article↗
PubMed2006

Direct evidence for a dynamical ground state in the highly frustrated Tb(2)Sn(2)O(7) pyrochlore.

mSR experiments have been performed on a powder sample of the "ordered spin ice" Tb(2)Sn(2)O(7) pyrochlore. At base temperature (T=35 mK), the muon relaxation is found to be of dynamical nature, which demonstrates that strong fluctuations persist below the ferromagnetic transition (T(C)=0.87 K). Hints of long-range ordering appear as oscillations of the muon polarization when an external field is applied and also as a hysteretic behavior below T(C). We propose that dynamics results from fluctuations of clusters of correlated spins with the ordered spin ice structure.

Journal Article↗
PubMed2005

Ground state of the kagomé-like S=1/2 antiferromagnet volborthite Cu3V2O7(OH)2 x 2H2O.

The volborthite compound is one of the very few realizations of S=1/2 quantum spins on a highly frustrated kagomé-like lattice. Low-T SQUID measurements reveal a broad magnetic transition below 2 K which is further confirmed by a peak in the 51V nuclear spin relaxation rate (1/T1) at 1.4 K +/- 0.2 K. Through 51V NMR, the ground state (GS) appears to be a mixture of different spin configurations, among which 20% corresponds to a well defined short-range order, possibly of the sqrt(3) x sqrt(3) type. While the freezing involves all the Cu2+ spins, only 40% of the copper moment is actually frozen which suggests that quantum fluctuations strongly renormalize the GS.

Journal Article↗
PubMed2005

Cascade of bulk magnetic phase transitions in NaxCoO2 as studied by muon spin rotation.

Using muon spin rotation, well-defined bulk approximately 100% magnetic phases in NaxCoO2 are revealed. A novel magnetic phase is detected for x=0.85 with the highest transition temperature ever observed for x>or=0.75. This stresses the diversity of x>or=0.75 magnetic phases and the link between magnetic and structural degrees of freedom. For the charge-ordered x=0.50 compound, a cascade of transitions is observed below 85 K. From a detailed analysis of our data, we conclude that the ordered moment varies continuously with temperature and suggest that the two secondary transitions at 48 and 29 K correspond to a moderate reorientation of antiferromagnetically coupled moments.

Journal Article↗
PubMed2005

ESTs from the fibre-bearing stem tissues of flax (Linum usitatissimum L.): expression analyses of sequences related to cell wall development.

In order to learn more about the diversity of genes expressed during flax fibre cell wall formation, expressed sequence tags (ESTs) were obtained from a cDNA library derived from the outer fibre-bearing tissues of flax (Linum usitatissimum) stems (cv Hermes) harvested at the mid-flowering stage. After elimination of vector and unreadable sequences, 927 ESTs were grouped into 67 clusters and 754 singletons. The flax ESTs have been submitted to the dbEST and GenBank databases with the accession numbers 25939634 - 25940560 (dbEST) and CV478070 - CV478996 (GenBank). Functional analysis allowed the grouping of ESTs into 13 functional categories and revealed that 62 % of ESTs were similar to known sequences, while 12.4 % of ESTs presented no similarity to any known sequences and 25.6 % of ESTs corresponded to proteins of unknown function. The most highly expressed transcripts belonged to four functional categories: protein maturation and metabolism (31 ESTs), signalling (22 ESTs), the cell wall (21 ESTs) and photosynthesis (19 ESTs). 4.4 % (41) of the total ESTs were potentially related to cell wall formation and maturation. The most highly expressed cell wall EST (15 ESTs) corresponded to a beta-xylosidase gene--potentially involved in cell wall remodelling during growth and development. Other cell wall-related ESTs corresponded to cellulose synthase, xyloglucan endotranglucosylase/hydrolase (XTH), beta-galactosidases, and peroxidases. The expression patterns of different cell wall-related ESTs were determined at different developmental stages in flax plants grown under different field conditions. The potential roles of gene products associated with cell wall related ESTs in fibre cell wall development is discussed.

Cell Wall↗
PubMed2005

Brain abscess caused by Nocardia cyriacigeorgica in a patient with human immunodeficiency virus infection.

Nocardia cyriacigeorgica is a recently characterized species within the genus of Nocardia. We report a brain abscess, following a primary pulmonary colonization, due to this species in a human immunodeficiency virus-infected patient. This case confirms that isolation of Nocardia in sputum is associated with a high risk of disseminated infection in immunocompromised patients.

AIDS-Related Opportunistic Infections↗
PubMed2004

muSR study of the quantum dynamics in the frustrated S=3/2 kagomé bilayers.

We present muSR experiments in the S=3/2 kagomé bilayer compound Ba(2)Sn(2)ZnGa(10-7p)Cr(7p)O22 [BSZCGO(p)] and compare it to the isostructural SrCr(9p)Ga(12-9p)O19 [SCGO(p)], including for the latter new results for p > or =0.89. Quantum-dynamical low energy magnetic excitations are evidenced in this novel compound. We study the evolution of the muon relaxation rate with p, T, and field. A phenomenological model for the muon relaxation based on sporadic dynamics due to spin excitations in a singlet sea proposed by Uemura et al. is extended to all fields and T range. Its connection to the RVB picture is discussed, and we argue that such coherent states might mediate the interactions between "impurities" which induce the spin glass freezing.

Journal Article↗
PubMed2004

Spin anisotropy and slow dynamics in spin glasses.

We report on an extensive study of the influence of spin anisotropy on spin glass aging dynamics. New temperature cycle experiments allow us to compare quantitatively the memory effect in four Heisenberg spin glasses with various degrees of random anisotropy and one Ising spin glass. The sharpness of the memory effect appears to decrease continuously with the spin anisotropy. Besides, the spin glass coherence length is determined by magnetic field change experiments for the first time in the Ising sample. For three representative samples, from Heisenberg to Ising spin glasses, we can consistently account for both sets of experiments (temperature cycle and magnetic field change) using a single expression for the growth of the coherence length with time.

Journal Article↗
PubMed2004

Dose escalation study for defining the maximum tolerated dose of continuous oral trofosfamide in pretreated patients with metastatic lung cancer.

BACKGROUND: Trofosfamide is increasingly used in the treatment of patients with several types of malignancies. However, the optimal dose of trofosfamide for patients with advanced cancer has not been systematically investigated yet. The aim of this study was to define the maximum tolerated dose (MTD) of continuous oral trofosfamide. PATIENTS AND METHODS: 16 patients with advanced lung cancer (14 nonsmall cell lung cancer, 2 small cell lung cancer; 10 male, 6 female; median age 64 years (range 46-82); median Karnofsky status 70%; median number of organs involved 3 (range 1-6)) were enrolled. All patients were previously treated with chemotherapy (median 2x, range 1-6) and 8/16 (50%) with radiotherapy. Patients received trofosfamide p.o. administered in 3 doses per day for 3 weeks (1 cycle) using a 3-patient-cohort dose-escalation strategy. Toxicities were graded according to the WHO Criteria. RESULTS: Patients received a median of 2 cycles of trofosfamide (range 1-4) at 3 dose levels (90, 125, and 175 mg/m2). Grade 3 and 4 neutropenia, anemia, and thrombocytopenia were observed in 20, 13.3, and 6.6%, respectively. Dose-limiting toxicities during the first cycle were grade 3 muscle weakness and anorexia observed in 1/6 patients in cohort 1 (trofosfamide 90 mg/m2), grade 3 neutropenia in 1/6, and encephalopathy in 1/6 patients in cohort 3 (trofosfamide 175 mg/m2). Therefore, the dose level of 125 mg/m2 was defined as the MTD. CONCLUSION: Trofosfamide at 125 mg/m2 administered in 3 doses per day was well tolerated. This dose level is recommended for further clinical studies.

Administration, Oral↗
PubMed2003

Nosocomial and community-acquired spontaneous bacterial peritonitis: comparative microbiology and therapeutic implications.

In order to compare the microbiological characteristics of nosocomial and community-acquired episodes of bacterial peritonitis, 95 consecutive, spontaneous episodes were reviewed. Seventy of these episodes were bacteriologically documented. Fifty-three (55.8%) episodes were nosocomial and 42 (44.2%) were community acquired. A total of 78 pathogens were isolated, including 40 gram-positive cocci (34 streptococci, 6 Staphylococcus aureus), 35 gram-negative bacilli (including 23 Escherichia coli), 2 gram-positive bacilli and 1 yeast. Streptococci were found more frequently in community-acquired episodes (53.8%) than in nosocomial episodes (33.3%). Gram-negative bacilli were significantly more frequent in nosocomial episodes than in community-acquired episodes (56.4% vs. 33.3%, P<0.05). Nosocomial isolates were significantly more resistant to amoxicillin-clavulanic acid (48.7% vs. 18.4%, P<0.01) and cefotaxime (33.3% vs. 13.2%, P<0.05) than community-acquired isolates, but no difference was detected regarding resistance to ciprofloxacin. The results indicate that the empirical treatment of spontaneous bacterial peritonitis should differ for nosocomial and community-acquired cases.

Adult↗
PubMed2002

Tunneling state anisotropy in a single grain decagonal quasicrystal.

We present low-temperature measurements, between 20 mK and 20 K, of the sound velocity variations in a single grain of the decagonal quasicrystal Al-Ni-Co. We have used acoustic shear waves of frequency 70 MHz propagating in the quasicrystalline planes with two different polarizations: parallel and perpendicular to the quasicrystalline planes. Our results show the presence of tunneling states (TSs) with a strong difference of the phonon-TS coupling for the two polarizations, which reveals a strong anisotropy of distribution of the orientations of the TSs in the sample. This result gives direct evidence that TSs are generated by the quasicrystalline structure itself.

Journal Article↗
PubMed2001

Major mitochondrial DNA haplotype heterogeneity in highland and lowland Amerindian populations from Bolivia.

This study provides the frequencies of four mitochondrial DNA (mtDNA) haplogroups of 233 native South Amerindians in eight populations living in the Beni Department of Bolivia, including six populations not previously studied. Linguistically, these populations belong to the three principal South Amerindian language stocks, Andean, Equatorial-Tucanoan, and Ge-Pano-Carib. Frequency analyses under geographic, historic, linguistic, and genetic configurations using the theta statistic of Weir (Weir 1990) and analysis of molecular variance (AMOVA) show similar results. Results are also similar when phenetic cluster is used. Aymara belongs almost exclusively to haplogroup B, Quechua- and Moseten-speaking tribes belong to haplogroups A and B, but the first tribe presents high frequencies of haplogroup B. Yuracare, Trinitario, and Ignaciano exhibit high frequencies of A, B, and C haplogroups, and the Movima present a large proportion of haplogroup C. There is some correspondence between mtDNA haplogroup frequencies and language affiliation and historical connections, but less so with geographic aspects. The present study provides a context for understanding the relationship between different Amerindian populations living in a multiethnic area of Bolivia.

Analysis of Variance↗
PubMed2000

Population study of Aymara Amerindians for the PCR-DNA polymorphisms HUMTH01, HUMVWA31A, D3S1358, D8S1179, D18S51, D19S253, YNZ22 and HLA-DQalpha.

Allele and genotype frequencies for eight DNA polymorphisms (HUMTH01, HUMVWA31A, D3S1358, D8S1179, D18S51, D19S253, YNZ22 and HLA-DQalpha) were determined in a population sample of Aymara Indians from Bolivia using PCR. No deviations of the observed allelic frequencies from Hardy-Weinberg equilibrium were found for all the systems studied. Significant differences in the allele frequencies were found between the Aymara and Quechua populations only for HUMVWA31A, which suggests a certain degree of genetic differentiation between the two populations.

Alleles↗
PubMed2000

Association between nasal carriage of Staphylococcus aureus and infection in liver transplant recipients.

We reviewed the records of 87 patients who underwent liver transplantation and who were screened by use of nasal swabs on the day before surgery. Twenty-four patients harbored methicillin-susceptible Staphylococcus aureus (MSSA), and 8 harbored methicillin-resistant S. aureus (MRSA). MSSA infection occurred in 3 (12.5%) of 24 MSSA carriers and in 2 (3.2%) of 63 noncarriers (nonsignificant). In contrast, MRSA infection occurred more frequently in MRSA carriers (7 [87.5%] of 8) than in MRSA noncarriers (8 [10.1%] of 79; P<.001). Nasal carriage of MRSA is associated with a very high risk of MRSA infection in liver transplant recipients.

Adolescent↗
PubMed1999

[Current microbiological problems. Antibiotic resistance and therapeutic problems raised by Pseudomonas aeruginosa].

RESISTANCE: Pseudomonas aeruginosa is characterized by its low intrinsic susceptibility to many antibiotics and its capacity to acquire additional resistance mechanisms to usually active drugs. Some beta-lactam resistance mechanisms are well known (penicillinase production, cephalosporinase overproduction) and others have been recently identified, such as active efflux systems, which confer coresistance to quinolones, and new beta-lactamases which are limited to a few countries (extended-spectrum beta-lactamases, imipenemase). Ceftazidime remains the most active beta-lactam agent. ACTIVE DRUGS: Among aminoglycosides, amikacin and isepamicin are the most frequently active drugs. The use of fluoroquinolones is limited by a high incidence of acquired resistance. The percentage of resistant strains is highly variable according to countries, hospitals and wards. CLINICAL PRACTICE: Therapy, usually based on a beta-lactam-aminoglycoside combination, will be empirical at first, according to local epidemiological factors, site of infection and previously administered antibiotics, then re-evaluated according to susceptibility results.

Cross Infection↗
PubMed1998

Multi-resistant Pseudomonas aeruginosa outbreak associated with contaminated tap water in a neurosurgery intensive care unit.

From July 1995 to November 1996, multi-resistant Pseudomonas aeruginosa O11 was isolated from 36 patients admitted to a neurosurgery intensive care unit. The strain was resistant to ticarcillin, ceftazidime, imipenem, gentamicin and ciprofloxacin, and susceptible to amikacin. Nine patients were colonized only; the remaining 27 patients had at least one infected site (17 urinary infections, 10 pneumonias and four with sinusitis). P. aeruginosa O11 with the same resistance pattern was isolated from tap water. The strain was also cultured from enteral nutrition solutions given to two infected patients. DNA macrorestriction analysis with XbaI established the similarity of the isolates from patients, tap water and solutions. The outbreak was controlled after reinforcement of isolation procedures for infected patients, changing the mode of enteral nutrition and replacement of all sinks in the unit. The sinks were presumably the main source of P. aeruginosa during this outbreak, via the hands of the nursing staff or nutrition solutions contaminated with tap water.

Adolescent↗
PubMed1998

Clinical significance of bacteremia involving the "Streptococcus milleri" group: 51 cases and review.

Fifty-one cases of bacteremia due to the "Streptococcus milleri" group were analyzed. Among these were 40 patients with underlying diseases, and associated local infections were present in 27 patients. The most frequent sites of infection were the thoracic cavity and the digestive and hepatobiliary tracts. A probable portal of entry related to mucosal-barrier trauma was identified for an additional 16 patients. The origin of bacteremia was unknown for the remaining eight patients. Abscess formation was evident for only six patients, and there were no cases of endocarditis. Multiple positive blood cultures and polymicrobial bacteremia were associated significantly with the presence of local sites of infection. The most common causative species were Streptococcus anginosus and Streptococcus constellatus. Two patients died of bacteremia.

Abscess↗