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P Millet

Publications and source records attributed to P Millet.

At least 19 recordsLinked to original sources
PubMed2006

Frontal theta event-related synchronization: comparison of directed attention and working memory load effects.

Early studies showed that long-term encoding and retrieval of new information is associated with modulation of the theta rhythm. More recently, changes in theta power amplitude over frontal electrode sites were reported during working memory, yet their relative significance in regard to attentional and memory processes remains unclear. Event-related synchronisation responses in the 4-7.5 Hz theta EEG frequency band was studied in 12 normal subjects performing four different tasks: two working memory tasks in which load varied from one (1-back task) to two (2-back task) items, an oddball detection (attention) task and a passive fixation task. A phasic theta increase was observed following stimulus apparition on all electrode sites within each task, with longer culmination peak and maximal amplitude over frontal electrodes. Frontal theta event-related synchronization (ERS) was of higher amplitude in the 1-back, 2-back and detection tasks as compared to the passive fixation task. Additionally, the detection task elicited a larger frontal and central theta ERS than the 2-back task. By analyzing theta ERS characteristics in various experimental conditions, the present study reveals that early phasic theta response over frontal regions primarily reflects the activation of neural networks involved in allocation of attention related to target stimuli rather than working memory processes.

Adult↗
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↗
PubMed2004

Comparative in vitro-in vivo study of two quinine rectal gel formulations.

The main objective of this work was to develop and evaluate rectal quinine paediatric formulations to treat acute uncomplicated malaria attack in some African countries. Developed dosage forms must be able to assure a prolonged release in the rectum but not too much so as to avoid product expulsion by the child anus. Two quinine rectal gels, namely mucoadhesive (MA) gel and thermosensitive (TS) gel, containing 20 mg quinine base/g were developed and evaluated in vitro and in vivo in the rabbit. The MA and the TS gels contained hydroxypropyl methylcellulose 4000 (HPMC) and poloxamer 407, respectively. The calculated in vitro release exponent (n) values suggested that drug was released from both gels by non-Fickian diffusion. Both gels exhibit practically similar efficient of dissolution (ED%) which was not reflected in the plasma and, therefore, quinine bioavailability from MA gel was found to be higher than that obtained from TS gel and their AUC(0-infinity) were statistically different (P = 0.0006). The t(1/2) values of quinine were significantly higher for Hydrogels than for IV and rectal solutions. MRT values displayed by TS gel and MA gel were not statistically different but were about 3.8- and 1.3-fold, respectively, larger than those obtained for IV solution and rectal solution, respectively. These results confirm the sustained-release behaviour of both hydrogels in the rabbit. Tolerability study of hydrogels didn't show any damage on the rectal mucosa of the rabbit.

Administration, Rectal↗
PubMed2004

Direct determination of the magnetic ground state in the square lattice S = 1/2 antiferromagnet Li2VOSiO4.

Powder neutron diffraction and resonant x-ray scattering measurements from a single crystal have been performed to study the low-temperature state of the 2D frustrated, quantum-Heisenberg system Li2VOSiO4. Both techniques indicate a collinear antiferromagnetic ground state, with propagation vector k=(1 / 2 1 / 2 0), and magnetic moments in the a-b plane. Contrary to previous reports, the ordered moment at 1.44 K, m=0.63(3)micro(B), is very close to the value expected for the square lattice Heisenberg model ( approximately 0.6micro(B)). The magnetic order is three dimensional, with antiferromagnetic a-b layers stacked ferromagnetically along the c axis. Neither x-ray nor neutron diffraction shows evidence for a structural distortion between 1.6 and 10 K.

Journal Article↗
PubMed2004

Thermal residual stresses near the interface between plasma-sprayed hydroxyapatite coating and titanium substrate: finite element analysis and synchrotron radiation measurements.

Plasma-sprayed hydroxyapatite (HA) coatings on titanium alloy are often used in prosthetic implants. The metallic substrate gives the implant good mechanical strength which is combined with good biocompatibility and osteointegration of the ceramic coating. However, the interface between the HA coating and titanium alloy substrate is an area of critical weakness when compared with the interlamellar cohesive strength of the HA coating structure. Knowledge of the stresses in materials near the interface seems to be an important step in understanding why failure occurs. Synchrotron radiation, using Beamline BM16 at the European Synchrotron Radiation Facility (Grenoble, France), has been used to determine local stresses near the interface, down to 10 microm in resolution, between a plasma-sprayed HA coating and a titanium alloy substrate. This experimental determination of residual stresses is compared with the results found by a finite element analysis modeling the thermal effects of the plasma-spraying process. Residual stresses have been found in deposited ceramic near the interface due to a thermal properties mismatch of the materials. If the plane stress state is assumed, meaning the perpendicular component of residual stress is ignored (sigma(z) = 0), then the synchrotron residual stress measurements should be interpreted as mainly compressive in the ceramic coating. This is in contradiction with the coefficient of thermal expansion mismatch; therefore, the simplified plane stresses assumption seems to be inappropriate for the deposited morphology characterized by pores and a network of microcracks. The detailed finite element analysis model, taking into account the real morphology of the coating and the real three-dimensional stress field distribution, allowed the estimation of sigma(z), leading to a more accurate interpretation of synchrotron measurements, which is validated by the experimental results.

Algorithms↗
PubMed2004

Influence of fluorapatite minor additions on behavior of hydroxyapatite ceramics.

Fluorinated hydroxyapatite is known to be less soluble by body fluids, resulting in enhanced resistance to biodegradation in vivo conditions, as compared to the pure hydroxyapatite ceramics. The present work was aimed at the investigation of the effect of minor additions of ultrafine fluorapatite (up to 10 wt%) on the sintering behavior and mechanical properties of hydroxyapatite ceramics. In vitro testing for the osteoblast-like cells viability and proliferation was performed with the samples of varying fluorapatite content. It was found that the fluorapatite addition hinders the sintering shrinkage and lowers the strength, but does not generally affect negatively the viability of the cells.

Apatites↗
PubMed2003

Low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V3O7.

We report the results of measurements of the dc susceptibility and the 23Na-NMR response of Na2V3O7, a recently synthesized, nonmetallic low dimensional spin system. Our results indicate that, upon reducing the temperature to below 100 K, the V4+ moments are gradually quenched, leaving only one moment out of nine active. The NMR data reveal a phase transition at very low temperatures. With decreasing applied field H, the critical temperature shifts towards T=0 K, suggesting that Na2V3O7 may be regarded as an insulator reaching a quantum critical point at H=0.

Journal Article↗
PubMed2003

Relationship between entomological inoculation rate, Plasmodium falciparum prevalence rate, and incidence of malaria attack in rural Gabon.

To assess the relationships between variations of Plasmodium falciparum transmission and those of peripheral parasitaemia prevalence or malaria attack incidence rates in regions with limited fluctuations of transmission, we conducted a follow-up in two Gabonese populations. Entomological surveys were carried out from May 1995 to April 1996 in Dienga, and from May 1998 to April 1999 in Benguia. In Dienga, malaria transmission was seasonal, being not detected during two 3-month periods. Mean entomological inoculation rate (EIR) was 0.28 infective bite/person/night. In Benguia, malaria transmission was perennial with seasonal fluctuations, mean EIR being 0.76 infective bite/person/night. In Dienga, 301 schoolchildren were followed from October 1995 to March 1996. Clinical malaria attack was defined as fever associated with >5000 parasites/microl of blood. P. falciparum prevalence varied from 28 to 42%, and monthly malaria attack incidence from 30 to 169 per thousand. In Benguia, the entire population (122 persons) was followed from November 1998 to April 1999. Prevalence varied from 22 to 50%, and monthly malaria attack incidence from 52 to 179 per thousand. In each area, entomological variations were not related to parasite prevalence, but preceded malaria attack incidence with 1- or 2-month time lag, corresponding to the pre-patency period that differs in the two populations, possibly according to differences in immunity related to parasite transmission.

Adolescent↗
PubMed2003

Chloroquine efficacy in the treatment of uncomplicated malaria at three sentinel sites in northern Togo.

In Togo, chloroquine (CQ) remains the first-line drug for the treatment of uncomplicated, Plasmodium falciparum malaria. In the absence of recent data on the level of parasite resistance to antimalarial drugs, Togo's National Malaria Control Programme (NMCP) decided to assess the current efficacy of CQ in the treatment of uncomplicated, P. falciparum malaria at three sentinel sites in the north of the country. Between the September and November of 2001, the World Health Organization's standard 14-day protocol was used to investigate 153 malarious children aged 6-59 months old (46 from Sokode, 54 from Niamtougou and 53 from Dapaong). Of the subjects from Sokode, Niamtougou and Dapaong, early treatment failure was observed in 0%, 7% and 12%, late treatment failure in 0%, 11% and 17%, and overall parasitological failure in 0%, 45% [with a 95% confidence interval (CI) of 39%-51%] and 62% (CI=54%-70%), respectively. Even within northern Togo, there is clearly considerable geographical variation in the level of resistance to CQ. Before an efficient antimalarial-drug policy can be developed, there is an urgent need to develop and use the national surveillance system further, to collect relevant data on the efficacies of CQ and other antimalarial drugs, such as amodiaquine and sulfadoxine-pyrimethamine.

Animals↗
PubMed2002

Stress influence on interface in plasma-sprayed hydroxyapatite coatings on titanium alloy.

During clinical use of hydroxyapatite-coated implants, mechanical stresses are added to pre-existing residual stresses. The magnitude of these stresses affects the coating's performance. In this work we studied, by neutron diffraction and conventional X-ray diffraction methods, the macrostresses induced by a plasma-spraying process in the coating and at the interface. Neutron diffraction is one of the most suitable techniques for studying the strain distribution in a bulk material. X-ray diffraction was used to determine residual stress in the hydroxyapatite coating. Using a neutron diffraction method at the nearest point to the interface, we saw no real difference between the stress observed on coated and that on non-coated samples. With the X-ray diffraction method, it appeared that the stress level was compressive on every sample. The major advantage of the neutron diffraction method is that measurements can be made on a thick coating in a nondestructive way. The disadvantage is the large-gauge volume that we had to use because of the relatively low intensity of the neutron beam. Polishing is necessary for measurements inside the material when using the X-ray method. This destructive method may alter the stress field of the deposit.

Durapatite↗
PubMed2002

Very-low-frequency excitations in frustrated two-dimensional S = 1/2 Heisenberg antiferromagnets.

Muon spin resonance and 7Li NMR relaxation measurements in frustrated two-dimensional S = 1/2 Heisenberg antiferromagnets on a square lattice are presented. It is found that, in both Li2VOSiO4 and Li2VOGeO4, spin dynamics at frequencies orders of magnitude below the Heisenberg exchange frequency are present. These dynamics are associated with the motions of walls separating coexisting collinear domains with a magnetic wave vector rotated by 90 degrees.

Journal Article↗
PubMed2002

In vitro activities of ferrochloroquine against 55 Senegalese isolates of Plasmodium falciparum in comparison with those of standard antimalarial drugs.

The in vitro activities of ferrochloroquine, chloroquine, quinine, mefloquine, halofantrine, amodiaquine, artesunate, atovaquone, cycloguanil and pyrimethamine were evaluated against Plasmodium falciparum isolates from Senegal (Dielmo, Ndiop), using an isotopic micro-drug susceptibility test. The IC50 values for ferrochloroquine ranged from 0.55 to 28.2 nM and the geometric mean IC50 for the 55 isolates was 7.9 nM (95% CI, 6.5-9.7 nM). Ferrochloroquine was 35 times more active than chloroquine (35-fold greater against chloroquine-resistant isolates), quinine, mefloquine, amodiaquine, cycloguanil and pyrimethamine. Weak positive correlations were observed between the responses to ferrochloroquine and that to chloroquine, quinine, and amodiaquine, but not compulsorily predictive of cross-resistance. There was no significant correlation between the response to ferrochloroquine and that to mefloquine, halofantrine, artesunate, atovaquone, cycloguanil and pyrimethamine. Ferrochloroquine may be an important alternative drug for the treatment of chloroquine-resistant malaria.

Animals↗
PubMed2001

Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu(2)Te(2)O(5)Br(2).

Thermodynamic experiments as well as Raman scattering have been used to study the magnetic instabilities in the spin-tetrahedra systems Cu(2)Te(2)O(5)X(2), X = Cl and Br. While the phase transition observed in the Cl system at T(N) = 18.2 K is consistent with 3D antiferromagnetic ordering, the phase transition at T(o) = 11.4 K in the Br system has several unusual features. We propose an explanation in terms of weakly coupled tetrahedra with a singlet-triplet gap and low-lying singlets.

Journal Article↗
PubMed2001

Ferrocene-chloroquine analogues as antimalarial agents: in vitro activity of ferrochloroquine against 103 Gabonese isolates of Plasmodium falciparum.

The in vitro activities of ferrochloroquine, chloroquine, quinine, mefloquine, halofantrine, amodiaquine, primaquine, atovaquone and artesunate were evaluated against Plasmodium falciparum isolates from children with uncomplicated malaria from Libreville (Gabon), using an isotopic, micro, drug susceptibility test. The IC(50) values for ferrochloroquine were in the range 0.43-30.9 nM and the geometric mean IC(50) for the 103 isolates was 10.8 nM (95% CI 8.6-13.5 nM), while the geometric means for chloroquine, quinine, mefloquine, amodiaquine and primaquine were 370 nM, 341 nM, 8.3 nM, 18.1 nM and 7.6 microM, respectively. Ferrochloroquine was active against P. falciparum isolates, 95% of which showed in vitro resistance to chloroquine. Weak positive significant correlations were observed between the responses to ferrochloroquine and that to chloroquine, amodiaquine and quinine, but too low to suggest cross-resistance. There was no significant correlation between the response to ferrochloroquine and those to mefloquine, halofantrine, primaquine, atovaquone or artesunate. Ferrochloroquine may be an important alternative drug for the treatment of chloroquine-resistant malaria.

Animals↗
PubMed2001

[Allelic polymorphism of Plasmodium falciparum MSP-2 gene in blood samples from Gabonese children].

In this study we have undertaken the molecular analysis of the MSP-2 gene of R falciparum isolates collected from schoolchildren living in the village of Dienga (Gabon). Using conventional microscopy and the polymerase chain reaction, 61% of these children harboured parasites without any symptom of malaria (asymptomatic status). Children with a malaria episode were those with an axillary temperature > or = 37.5 degrees C and a parasitaemia > or =800 parasites/microl of blood. Comparisons of the allelic diversity and distribution of MSP-2 gene were carried out according to the clinical status at the time of sampling. Polymorphism of the MSP-2 gene was large in both clinical groups, both asymptomatic and symptomatic (11 identified alleles). The allele FC27/560bp (base pairs) was found significantly in clinical isolates. Prevalence of the 3D7 family was 68% and 44% in asymptomatic infections and clinical infections, respectively. Multiple P. falciparum genotypes were more predominant in clinical cases (2.96 clones/child with a malaria attack vs 2.01 clones/child with asymptomatic infections). We observed also a reduction of the complexity of infection beyond the age of 10 years. These results are discussed in regard to studies conducted in other areas in Africa.

Adolescent↗
PubMed2000

Li2VO(Si,Ge)O4, a prototype of a two-dimensional frustrated quantum heisenberg antiferromagnet

NMR and magnetization measurements in Li2VOSiO4 and Li2VOGeO4 are reported. The analysis of the susceptibility shows that both compounds are two-dimensional S = 1/2 Heisenberg antiferromagnets on a square lattice with a sizable frustration induced by the competition between the superexchange couplings J1 along the sides of the square and J2 along the diagonal. Li2VOSiO4 undergoes a low-temperature phase transition to a collinear order, as theoretically predicted for J2/J1>0.5. Just above the magnetic transition the degeneracy between the two collinear ground states is lifted by the onset of a structural distortion.

Journal Article↗
PubMed2000

LiVGe2O6, an anomalous quasi-1D, S = 1 system, as revealed by NMR

We report the results of 7Li nuclear magnetic resonance (NMR) studies of LiVGe2O6, a quasi-one-dimensional spin S = 1 model system, at low temperatures. Our data, including NMR spectra and the temperature dependence of the spin-lattice relaxation rate T-11, indicate that a first-order phase transition occurs at T(c) approximately 23 K. The NMR response of LiVGe2O6 below T(c) suggests that the ordered phase is antiferromagnetic and has unusual features. Possible reasons for this unexpected behavior are discussed.

Journal Article↗